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Blood-Brain Barrier Tight Junction Disruption in Human Immunodeficiency Virus-1 Encephalitis
Abstract
The blood-brain barrier (BBB) plays a critical role in regulating cell trafficking through the central nervous system (CNS) due to several unique anatomical features, including the presence of interendothelial tight junctions that form impermeable seals between the cells. Previous studies have demonstrated BBB perturbations during human immunodeficiency virus encephalitis (HIVE); however, the basis of these permeability changes and its relationship to infiltration of human immunodeficiency virus type 1 (HIV-1)-infected monocytes, a critical event in the pathogenesis of the disease, remains unclear. In this study, we examined CNS tissue from HIV-1-seronegative patients and HIV-1-infected patients, both with and without encephalitis, for alterations in BBB integrity via immunohistochemical analysis of the tight junction membrane proteins, occludin and zonula occludens-1 (ZO-1). Significant tight junction disruption (P < 0.001), as demonstrated by fragmentation or absence of immunoreactivity for occludin and ZO-1, was observed within vessels from subcortical white matter, basal ganglia, and, to a lesser extent, cortical gray matter in patients who died with HIVE. These alterations were also associated with accumulation of activated, HIV-1-infected brain macrophages, fibrinogen leakage, and marked astrocytosis. In contrast, no significant changes (P > 0.05) were observed in cerebellar tissue from patients with HIVE compared to HIV-seronegative patients or HIV-1-infected patients without encephalitis. Our findings demonstrate that tight junction disruption is a key feature of HIVE that occurs in regions of histopathological alterations in association with perivascular accumulation of activated HIV-1-infected macrophages, serum protein extravasation, and marked astrocytosis. We propose that disruption of this key BBB structure serves as the main route of HIV-1-infected monocyte entry into the CNS.
... Autopsy evidence of brain endothelium injury and impaired BBB in HIV-infected patients has included enlarged microvessels and loss of hippocampal capillaries associated with degeneration of perivascular tissues [25], fragmentation and loss of microvessels TJ proteins, including claudin-5, occludin, ZO-1 and ZO-2 in several brain regions (frontal cortex, basal ganglia, subcortical white matter, and cortical gray matter) [26][27][28]. Brain tissues of HIV-infected humans has also showed significantly more capillary loss and decreased TJs in patients with HAND compared to HIV-infected subjects without HAND and seronegative controls subjects [20,23,[26][27][28][29]. ...
... Autopsy evidence of brain endothelium injury and impaired BBB in HIV-infected patients has included enlarged microvessels and loss of hippocampal capillaries associated with degeneration of perivascular tissues [25], fragmentation and loss of microvessels TJ proteins, including claudin-5, occludin, ZO-1 and ZO-2 in several brain regions (frontal cortex, basal ganglia, subcortical white matter, and cortical gray matter) [26][27][28]. Brain tissues of HIV-infected humans has also showed significantly more capillary loss and decreased TJs in patients with HAND compared to HIV-infected subjects without HAND and seronegative controls subjects [20,23,[26][27][28][29]. ...
Blood–brain barrier (BBB) injury and dysfunction following infection with the human immunodeficiency virus (HIV) enables viral entry into the brain, infection of resident brain cells, neuronal injury and subsequent neurodegeneration leading to HIV-associated neurocognitive disorders (HAND). Although combination antiretroviral therapy has significantly reduced the incidence and prevalence of acquired immunodeficiency syndrome and increased the life expectancy of people living with HIV, the prevalence of HAND remains high. With aging of people living with HIV associated with increased comorbidities, the prevalence of HIV-related central nervous system (CNS) complications is expected to remain high. Considering the principal role of the brain endothelium in HIV infection of the CNS and HAND, the purpose of this manuscript is to review the current literature on the pathobiology of the brain endothelium structural and functional dysregulation in HIV infection, including in the presence of HIV-1 and viral proteins (gp120, Tat, Nef, and Vpr). We summarize evidence from human and animal studies, in vitro studies, and associated mechanisms. We further summarize evidence of synergy or lack thereof between commonly abused substances (cocaine, methamphetamine, alcohol, tobacco, opioids, and cannabinoids) and HIV- or viral protein-induced BBB injury and dysfunction.
... In our experimental setting, we demonstrated that miR-142 significantly attenuated endothelial permeability triggered by the main agonist of TIM-1, namely, TIMD4 [51,52] ( Figure 5). Our data on endothelial leakage were further supported by the regulation of a major tight-junction protein, namely occludin [53][54][55][56], by miR-142 (Supplementary Figure S2). ...
... We established that TIM-1 is expressed in different types of endothelial cells and that miR-142 is able to significantly reduce its expression. One of the key findings of the Our data on endothelial leakage were further supported by the regulation of a major tight-junction protein, namely occludin [53][54][55][56], by miR-142 (Supplementary Figure S2). ...
T-cell immunoglobulin and mucin domain 1 (TIM-1) has been recently identified as one of the factors involved in the internalization of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in human cells, in addition to angiotensin-converting enzyme 2 (ACE2), trans-membrane serine protease 2 (TMPRSS2), neuropilin-1, and others. We hypothesized that specific microRNAs could target TIM-1, with potential implications for the management of patients suffering from coronavirus disease 2019 (COVID-19). By combining bioinformatic analyses and functional as-says, we identified miR-142 as a specific regulator of TIM-1 transcription. Since TIM-1 has been implicated in the regulation of endothelial function at the level of the blood-brain barrier (BBB) and its levels have been shown to be associated with stroke and cerebral ischemia-reperfusion injury, we validated miR-142 as a functional modulator of TIM-1 in human brain microvascular endothelial cells (hBMECs). Taken together, our results indicate that miR-142 targets TIM-1, representing a novel strategy against cerebrovascular disorders, as well as systemic complications of SARS-CoV-2 and other viral infections.
... The cold-injury model has been utilized extensively to study BBB breakdown, the initiating factor in vasogenic edema using tracers such as Evans blue [32] and horseradish peroxidase (HRP) [27,30] and also by the immunolocalization of extravasated circulating proteins such as serum proteins [27], fibrinogen [33], and fibronectin [8,29,30] through vessels into the surrounding brain. (a) A quantitative RT-PCR analysis of the total VEGFR-2 (red bars) and VEGFR-3 (green bars) mRNA relative to 18S of the control rats and cold-injured rats on days 0.5, 2, 4, and 6 post-lesion are shown. ...
... The cold-injury model has been utilized extensively to study BBB breakdown, the initiating factor in vasogenic edema using tracers such as Evans blue [32] and horseradish peroxidase (HRP) [27,30] and also by the immunolocalization of extravasated circulating proteins such as serum proteins [27], fibrinogen [33], and fibronectin [8,29,30] through vessels into the surrounding brain. Since all vessels within the lesion do not show BBB breakdown, immunofluorescence allows the identification of vessels leaking proteins while dual labeling allows the localization of a protein of interest in the endothelium of vessels leaking proteins in the same animal. ...
Alterations in the expression of the vascular endothelial growth factors (VEGF) A and B occur during blood–brain barrier (BBB) breakdown and angiogenesis following a brain injury. In this study, the temporal and spatial expression of VEGF-D and VEGF receptors-2 and -3 (VEGFR-2 and VEGFR-3, respectively) was determined at the mRNA and protein level in the rat cortical cold-injury model over a period of 0.5 to 6 days post-injury. In order to relate endothelial VEGF-D protein expression with BBB breakdown, dual labeling immunofluorescence was performed using antibodies to VEGF-D and to fibronectin, a marker of BBB breakdown. In control rats, VEGF-D signal was only observed in scattered perivascular macrophages in the cerebral cortex. The upregulation of VEGF-D mRNA expression was observed in the injury site between days 0.5 to 4, coinciding with the periods of BBB breakdown and angiogenesis. At the protein level, intracerebral vessels with BBB breakdown to fibronectin in the lesion on days 0.5 to 4 failed to show endothelial VEGF-D. Between days 0.5 to 6, increased VEGF-D immunoreactivity was noted in the endothelium of pial vessels overlying the lesion site, in neutrophils, macrophages, and free endothelial cells within the lesion. The upregulation of VEGFR-2 and -3 mRNA and protein expression was observed early post-injury on day 0.5. Although there was concurrent expression of VEGF-A, VEGF-B, and VEGF-D post-injury, differences in their spatial expression during BBB breakdown and angiogenesis suggest that they had specific and separate roles in these processes.
... HIV CNS entry occurs in the acute phase of infection and is near universal [15]. In times of high viral load, either through direct viral toxicity or due to the subsequent inflammatory response, the tight junctions of the BBB are disrupted [16][17][18][19]. The virus can cross the BBB directly and through infected monocytes and T cells-this establishes a reservoir of infection in microglia, perivascular macrophages and astrocytes [20,21]. ...
Neurocognitive impairment is an important cause of HIV-associated morbidity. The advent of antiretroviral therapy (ART) has shifted the spectrum of HIV-associated cognitive impairment from HIV-associated dementia to milder forms of cognitive impairment. Independent replication of HIV within the central nervous system in those on effective ART with peripheral suppression is a recognised phenomenon known as cerebrospinal fluid (CSF) HIV RNA escape. CSF HIV RNA escape is independently associated with neurocognitive impairment but has also been detected in asymptomatic persons with HIV. The current consensus for management of CSF HIV RNA escape is based on expert opinion rather than empirical evidence. The current evidence suggests having a low threshold to investigate for CSF HIV RNA escape and optimising ART based on resistance profiles. The use of central nervous system (CNS) penetration effectiveness scores is no longer recommended. The evidence for statins, SSRIs, minocycline, lithium and valproate is limited to small-scale studies. There are potential new developments in the form of nanoparticles, Janus Kinase inhibitors and latency reversal agents.
... Paracellular Barrier Properties in the Spheroids As ZO-1 is classically identified as a tight junction protein in the brain capillary endothelial cells 22) and its expression level correlated with the degree of BBB integrity through virusinduced encephalitis, 23) immunostaining of ZO-1 proteins in the multicellular spheroids was performed. On the spheroid surface (Fig. 3A), ZO-1-derived signals were detected. ...
The blood–brain barrier (BBB) is a dynamic interface controlling the compound translocation between the blood and the brain, thereby maintaining neural homeostasis. There is cumulative evidence that BBB impairment during diabetes mellitus (DM) takes part in the progression of cognitive dementia. As tight junction proteins and ATP-binding cassette (ABC) transporters regulate substance exchange between the circulating blood and brain, the expression and function of these molecules under DM should be fully clarified. To understand the alteration of ABC transporter function in the BBB under DM, in vitro multicellular rat BBB spheroids consisting of conditionally immortalized rat brain capillary endothelial cells, astrocytes, and pericytes were newly developed. Immunostaining and permeability analysis of paracellular transport markers suggested the construction of tight junctions on the surface of the BBB spheroids. Transport analyses using fluorescence substrates of P-glycoprotein (P-gp), the breast cancer resistance protein (BCRP), and multidrug resistance-associated protein 4 (MRP4) indicate the functional expression of these transporters in the spheroids. After treatment with advanced glycation end-products (AGEs), involved in various signals during DM, the mRNA expression of tight junction molecules and ABC transporters in the BBB spheroids was upregulated. Furthermore, the functional changes in P-gp and BCRP in the BBB spheroids exposed to AGEs were canceled by the inhibitors of the receptor for AGEs (RAGE). These results suggest that AGE-RAGE interaction upregulates P-gp and BCRP function in the BBB.
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... Endothelial cells are prone to dysfunction and death due to direct interaction with viral proteins and exposure to inflammatory cytokines released by infected cells (Andersson et al., 2001;Lee et al., 2004;Leibrand et al., 2017). Dysregulation of endothelial tight junction proteins such as claudin-5, occludin, and ZO-1 leads to increased BBB permeability and may facilitate infiltration of peripheral immune cells to the CNS (Boven et al., 2000;Chaudhuri et al., 2008;Dallasta et al., 1999;Eugenin et al., 2011). Decreased pericytes coverage of the endothelium and infected or dysregulated astrocytes have also been shown to contribute to barrier dysfunction in the HIV-infected brain (Piekna-Przybylska et al., 2019;Pla-Tenorio et al., 2023;Valdebenito et al., 2021). ...
Human immunodeficiency virus (HIV-1) remains a persistent global health crisis. Even while successfully virologically suppressed, people with HIV (PWH) experience a higher risk for inflammatory disorders such as HIV-associated neurocognitive disorder (HAND). Tobacco use puts PWH at higher risk for neurocognitive symptoms resulting from HIV-associated neuroinflammation. The NLR Family Pyrin Domain Containing 3 (NLRP3) inflammasome has been implicated as a driver of HIV-associated inflammation, including HAND. Nicotine, the psychoactive component of tobacco smoke, has also been shown to signal through the NLRP3 inflammasome and modulate inflammatory signaling in the CNS. Here, we explore the impacts of nicotine and tobacco on the complex neurobiology of HAND, including effects on cognition, inflammation, viral latency, and blood-brain barrier integrity. We outline nicotine’s role in the establishment of active and latent infection in the brain and posit the NLRP3 inflammasome as a common pathway by which HIV-1 and nicotine promote neuroinflammation in PWH.
... Clinical signs are most often a reflection of opportunistic infections, neoplasia and/or myelosuppression, as the disease progresses [28]. Like in HIV and simian immunodeficiency virus (SIV) infections, FIV is likely to enter the brain via the blood-brain and blood-cerebrospinal fluid (CSF) barriers [4,19,26], and thus understanding the mechanisms of interactions of virus and cells at both of these barriers is important in the quest to design therapies to prevent or modify central nervous system (CNS) infections. ...
... Occludin is abundant in brain endothelial cells and is not detected in non-neuronal endothelium (Hirase et al. 1997). It has been shown that disruption of the BBB in various pathological conditions is associated with changes in Occludin expression (Dallasta et al. 1999, Ohene-Nyako et al. 2021. Park et al. showed that Occludin expression decreased in mice with the maternal separation-induced depression model, while treadmill exercise and fluoxetine injection increased Occludin expression in mice (Park et al. 2020). ...
... A down-regulation of the TJ complex components, including claudin-5, was shown in vitro and in vivo, which leads to enhanced monocytes infiltration into the brain contributing to the neurocognitive impairments [48,49]. Interestingly, a brain autopsy revealed that the brain vasculature in WM is more compromised than in the GM, where expressions of the junctional proteins occludin and ZO-1 were more disrupted or even absent in the WM [50]. Heterogeneity in the brain vasculature could be involved in the manifestation of the differential pathologies in various brain regions [32]. ...
The blood–brain barrier (BBB) is part of a neurovascular structure located in the brain’s micro vessels, that is essential to maintain brain homeostasis, but prevents the brain uptake of most drugs. Because of its importance in neuro-pharmacotherapy, the BBB has been the subject of extensive research since its discovery over 100 years ago. Major advances in understanding the structure and function of the barrier have been made. Drugs are re-designed to cross the BBB. However, despite these efforts, overcoming the BBB efficiently to treat brain diseases safely remains challenging. The majority of BBB research studies focus on the BBB as a homogenous structure throughout the different brain regions. However, this simplification may lead to an inadequate understanding of the BBB function with significant therapeutic consequences. From this perspective, we analyzed the gene and protein expression profiles of the BBB in the micro vessels from the brains of mice that were isolated from two different brain regions, namely the cortex and the hippocampus. The expression profile of the inter-endothelial junctional protein (claudin-5), three ABC transporters (P-glycoprotein, Bcrp and Mrp-1), and three BBB receptors (lrp-1, TRF and GLUT-1) were analyzed. Our gene and protein analysis showed that the brain endothelium in the hippocampus exhibits different expression profiles compared to the brain cortex. Specifically, brain endothelial cells (BECs) of the hippocampus express higher gene levels of abcb1, abcg2, lrp1, and slc2a1 compared to the BECs of the cortex regions with a trend of increase for claudin-5, while BECs of the cortex express higher gene levels of abcc1 and trf compared to the hippocampus. At the protein levels, the P-gp expression was found to be significantly higher in the hippocampus compared to the cortex, while TRF was found to be up-regulated in the cortex. These data suggest that the structure and function of the BBB are not homogeneous, and imply that drugs are not delivered similarly among the different brain regions. Appreciation of the BBB heterogeneity by future research programs is thus critical for efficient drug delivery and the treatment of brain diseases.
... While it is clear in acute liver failure that vasogenic cerebral edema is important, this has not been consistently recognized in cirrhosisrelated type C HE. [8] In contrast to our findings in HE, other neuroinflammatory disease states, such as multiple sclerosis and HIV-1 infection, reveal permeability differences that preferentially affect white matter regions. [20,21] A recent study of gray matter volume in CHE using MRI has revealed both cortical and basal ganglia loss, which is more pronounced in CHE compared with NHE. [22] While the cause is unclear, it has been postulated to relate to chronic edema. ...
Background:
Using dynamic contrast-enhanced (DCE) MR perfusion and MR spectroscopy this study aimed to characterize the blood-brain barrier permeability and metabolite changes in patients with cirrhosis and without covert HE.
Methods:
Covert HE was defined using psychometric HE score (PHES). The participants were stratified into 3 groups: cirrhosis with covert HE (CHE) (PHES<-4); cirrhosis without HE (NHE) (PHES≥-4); and healthy controls (HC). Dynamic contrast-enhanced MRI and MRS were performed to assess KTRANS, a metric derivative of blood-brain barrier disruption, and metabolite parameters. Statistical analysis was performed using IBM SPSS (v25).
Results:
A total of 40 participants (mean age 63 y; male 71%) were recruited as follows: CHE (n=17); NHE (n=13); and HC (n=10). The KTRANS measurement in the frontoparietal cortex demonstrated increased blood-brain barrier permeability, where KTRANS was 0.01±0.02 versus 0.005±0.005 versus 0.004±0.002 in CHE, NHE, and HC patients, respectively (p = 0.032 comparing all 3 groups). Relative to HC with a value of 0.28, the parietal glutamine/creatine (Gln/Cr) ratio was significantly higher in both CHE 1.12 mmoL (p < 0.001); and NHE 0.49 (p = 0.04). Lower PHES scores correlated with higher glutamine/Cr (Gln/Cr) (r=-0.6; p < 0.001) and lower myo-inositol/Cr (mI/Cr) (r=0.6; p < 0.001) and lower choline/Cr (Cho/Cr) (r=0.47; p = 0.004).
Conclusion:
The dynamic contrast-enhanced MRI KTRANS measurement revealed increased blood-brain barrier permeability in the frontoparietal cortex. The MRS identified a specific metabolite signature with increased glutamine, reduced myo-inositol, and choline, which correlated with CHE in this region. The MRS changes were identifiable in the NHE cohort.
... Disruption of TJ is commonly observed in HIV-1-infected patients [45]. The HIV-1 and its proteins may act alone or in cooperation with host cytokines and chemokines to affect the integrity of the BBB [46]. ...
Paracoccidioidomycosis (PCM), a systemic mycosis caused by the fungus Paracoccidioides sp. is the most prevalent fungal infection among immunocompetent patients in Latin America. The estimated frequency of central nervous system (CNS) involvement among the human immunodeficiency virus (HIV)/PCM-positive population is 2.5%. We aimed to address the impact of neuroparacoccidioidomycosis (NPCM) and HIV/NPCM co-infection on the tight junctions (TJ) and adherens junction (AJ) proteins of the CNS.
Four CNS formalin-fixed paraffin-embedded (FFPE) tissue specimens were studied: NPCM, NPCM/HIV co-infection, HIV-positive without opportunistic CNS infection, and normal brain autopsy (negative control). Immunohistochemistry was used to analyze the endothelial cells and astrocytes expressions of TJ markers: claudins (CLDN)-1, -3, -5 and occludin; AJ markers: β-catenin and E-cadherin; and pericyte marker: alpha-smooth muscle actin in formalin-fixed paraffin-embedded CNS tissue specimens were analyzed using the immunoperoxidase assay.
CLDN-5 expression in the capillaries of the HIV/NPCM coinfected tissues (acute/subacute clinical form of PCM) was lower than that in the capillaries of the HIV or NPCM monoinfected (chronic clinical form of PCM) tissues.
A marked decrease in CLDN-5 expression and a compensatory increase in CLDN-1 expression in the NPCM/HIV co-infection tissue samples was observed. The authors suggest that Paracoccidioides sp. crosses the blood–brain barrier through paracellular pathway, owing to the alteration in the CLDN expression, or inside the macrophages (Trojan horse).
... Various neurological disorders, such as bacterial meningitis (18) and neurotropic virus infection, including human immunodeficiency virus (HIV) (19,20), Japanese encephalitis virus (JEV) (21,22), and West Nile virus (WNV) (23)(24)(25), can cause increased permeability of the BBB. In only a few cases, viral gene products are directly involved in BBB disruption; in the absence of such mechanisms, indirect effects of the virus on the immune system may be responsible for barrier disruption (16). ...
The ability to change BBB permeability was associated with the pathogenicity of RABV. BBB permeability was enhanced by infection with lab-attenuated RABV instead of wt RABV, allowing immune cells to infiltrate into the CNS.
... Disruption of TJ is commonly observed in HIV-1infected patients [47]. The HIV-1 and its proteins may act alone or in cooperation with host cytokines and chemokines to affect the integrity of the BBB [48]. ...
Paracoccidioidomycosis (PCM), a systemic mycosis caused by the fungus Paracoccidioides spp. is the most prevalent fungal infection among immunocompetent patients in Latin America. The estimated frequency of central nervous system (CNS) involvement among the human immunodeficiency virus (HIV)/PCM-positive population is 2.5%. We aimed to address the impact of neuroparacoccidioidomycosis (NPCM) and HIV/NPCM co-infection on the tight junctions (TJ) and adherens junction (AJ) proteins of the CNS. Four CNS formalin-fixed paraffin-embedded (FFPE) tissue specimens were studied: NPCM, NPCM/HIV co-infection, HIV-positive without opportunistic CNS infection, and normal brain autopsy (negative control). Immunohistochemistry was used to analyze the endothelial cells and astrocytes expressions of TJ markers: claudins (CLDN)-1, -3, -5 and occludin; AJ markers: β-catenin and E-cadherin; and pericyte marker: alpha-smooth muscle actin. FFPE CNS tissue specimens were analyzed using the immunoperoxidase assay. CLDN-5 expression in the capillaries of the HIV/NPCM coinfected tissues (mixed clinical form of PCM) was lower than that in the capillaries of the HIV or NPCM monoinfected (chronic clinical form of PCM) tissues. A marked decrease in CLDN-5 expression and a compensatory increase in CLDN-1 expression in the NPCM/HIV co-infection tissue samples was observed. The authors suggest that Paracoccidioides spp. crosses the blood–brain barrier through paracellular pathway, owing to the alteration in the CLDN expression, or inside the macrophages (Trojan horse).
... Some of the vital regulators of tight junctions' activities identified are cyclic adenosine monophosphate and astrocytes (Rubin et al., 1991;Hurst and Clark, 1998). In brain diseases and disorders, the BBB is highly disrupted, resulting into unregulated diffusion of molecules, leading to further brain damage (Dallasta et al., 1999;Algotsson and Winblad, 2007). Because the BBB prevents the entrance of materials basing on their size and solubility, most of the potential drugs fail to penetrate because they do not meet the required criteria (Pardridge, 2012). ...
Brain is by far the most complex organ in the body. It is involved in the regulation of cognitive, behavioral, and emotional activities. The organ is also a target for many diseases and disorders ranging from injuries to cancers and neurodegenerative diseases. Brain diseases are the main causes of disability and one of the leading causes of deaths. Several drugs that have shown potential in improving brain structure and functioning in animal models face many challenges including the delivery, specificity, and toxicity. For many years, researchers have been facing challenge of developing drugs that can cross the physical (blood-brain barrier), electrical, and chemical barriers of the brain and target the desired region with few adverse events. In recent years, nanotechnology emerged as an important technique for modifying and manipulating different objects at the molecular level to obtain desired features. The technique has proven to be useful in diagnosis as well as treatments of brain diseases and disorders by facilitating the delivery of drugs and improving their efficacy. As the subject is still hot, and new research findings are emerging, it is clear that nanotechnology could upgrade health care systems by providing easy and highly efficient diagnostic and treatment methods. In this review, we will focus on the application of nanotechnology in the diagnosis and treatment of brain diseases and disorders by illuminating the potential of nanoparticles.
... In HIV encephalitis, a complication of HIV associated with cognitive dysfunction, BBB integrity is lost. In this disease, this allows for accumulation of activated, HIV-infected macrophages and induction of reactive astrocytes, the mechanism behind this being significant loss of the TJ proteins occludin and ZO-1 (169). Systemic inflammatory pain rat models, including injection of formalin, carrageenan, and complete Freund's adjuvant (CFA) display increased BBB permeability. ...
The redox properties that make iron an essential nutrient also make iron an efficient pro-oxidant. Given this nascent cytotoxicity, iron homeostasis relies on a combination of iron transporters, chaperones, and redox buffers to manage the non-physiologic aqueous chemistry of this first-row transition metal. Although a mechanistic understanding of the link between brain iron accumulation (BIA) and neurodegenerative diseases is lacking, BIA is co-morbid with the majority of cognitive and motor function disorders. The most prevalent neurodegenerative disorders, including Alzheimer's Disease (AD), Parkinson's Disease (PD), Multiple System Atrophy (MSA), and Multiple Sclerosis (MS), often present with increased deposition of iron into the brain. In addition, ataxias that are linked to mutations in mitochondrial-localized proteins (Friedreich's Ataxia, Spinocerebellar Ataxias) result in mitochondrial iron accumulation and degradation of proton-coupled ATP production leading to neuronal degeneration. A comorbidity common in the elderly is a chronic systemic inflammation mediated by primary cytokines released by macrophages, and acute phase proteins (APPs) released subsequently from the liver. Abluminal inflammation in the brain is found downstream as a result of activation of astrocytes and microglia. Reasonably, the iron that accumulates in the brain comes from the cerebral vasculature via the microvascular capillary endothelial cells whose tight junctions represent the blood-brain barrier. A premise amenable to experimental interrogation is that inflammatory stress alters both the trans- and para-cellular flux of iron at this barrier resulting in a net accumulation of abluminal iron over time. This review will summarize the evidence that lends support to this premise; indicate the mechanisms that merit delineation; and highlight possible therapeutic interventions based on this model.
... Different reports have also evaluated the role of HIV in vivo. For instance, reduced expression of ZO-1, occludin, and claudins have been described in post-mortem samples from HIV-infected humans exhibiting encephalitis or dementia (Dallasta et al., 1999;Boven et al., 2000). Accordingly, pericytes in the BBB can also be infected by HIV in mice, and the expression of occludin by these cells modulates the transcription of HIV (Castro et al., 2016;Bertrand et al., 2019). ...
Reports regarding brain inflammation, known as encephalitis, have shown an increasing frequency during the past years. Encephalitis is a relevant concern to public health due to its high morbidity and mortality. Infectious or autoimmune diseases are the most common cause of encephalitis. The clinical symptoms of this pathology can vary depending on the brain zone affected, with mild ones such as fever, headache, confusion, and stiff neck, or severe ones, such as seizures, weakness, hallucinations, and coma, among others. Encephalitis can affect individuals of all ages, but it is frequently observed in pediatric and elderly populations, and the most common causes are viral infections. Several viral agents have been described to induce encephalitis, such as arboviruses, rhabdoviruses, enteroviruses, herpesviruses, retroviruses, orthomyxoviruses, orthopneumovirus, and coronaviruses, among others. Once a neurotropic virus reaches the brain parenchyma, the resident cells such as neurons, astrocytes, and microglia, can be infected, promoting the secretion of pro-inflammatory molecules and the subsequent immune cell infiltration that leads to brain damage. After resolving the viral infection, the local immune response can remain active, contributing to long-term neuropsychiatric disorders, neurocognitive impairment, and degenerative diseases. In this article, we will discuss how viruses can reach the brain, the impact of viral encephalitis on brain function, and we will focus especially on the neurocognitive sequelae reported even after viral clearance.
... Additionally, the presence of fragmented or reduced levels of TJs expression such as ZO-1 and OCLN was observed in the brains of deceased patients with HIV-1 encephalitis [247]. The extravasation of albumin and the overexpression of ICAM-1 and VCAM1 were also observed in the gp120 transgenic mice model of HIV. ...
The blood-brain barrier (BBB) is a fundamental component of the central nervous system (CNS). Its functional and structural integrity is vital to maintain the homeostasis of the brain microenvironment by controlling the passage of substances and regulating the trafficking of immune cells between the blood and the brain. The BBB is primarily composed of highly specialized microvascular endothelial cells. These cells' special features and physiological properties are acquired and maintained through the concerted effort of hemodynamic and cellular cues from the surrounding environment. This complex multicellular system, comprising endothelial cells, astrocytes, pericytes, and neurons, is known as the neurovascular unit (NVU). The BBB strictly controls the transport of nutrients and metabolites into brain parenchyma through a tightly regulated transport system while limiting the access of potentially harmful substances via efflux transcytosis and metabolic mechanisms. Not surprisingly, a disruption of the BBB has been associated with the onset and/or progression of major neurological disorders. Although the association between disease and BBB disruption is clear, its nature is not always evident, specifically with regard to whether an impaired BBB function results from the pathological condition or whether the BBB damage is the primary pathogenic factor prodromal to the onset of the disease. In either case, repairing the barrier could be a viable option for treating and/or reducing the effects of CNS disorders. In this review, we describe the fundamental structure and function of the BBB in both healthy and altered/diseased conditions. Additionally, we provide an overview of the potential therapeutic targets that could be leveraged to restore the integrity of the BBB concomitant to the treatment of these brain disorders.
... matter compared to those isolated from the cortex . Although ECs in the white matter seemingly form a tighter paracellular barrier, white matter vessels are reported to be more susceptible than gray matter vessels to junctional fragmentation and loss of occludin and ZO-1 in pathological conditions such as HIV-associated neurocognitive deficits (Dallasta et al., 1999). Consistently with these observations, several groups have reported that white matter vasculature is more susceptible to pathological hyperpermeability. ...
The neurovascular unit (NVU) of the brain is composed of multiple cell types that act synergistically to modify blood flow to locally match the energy demand of neural activity, as well as to maintain the integrity of the blood-brain barrier (BBB). It is becoming increasingly recognized that the functional specialization, as well as the cellular composition of the NVU varies spatially. This heterogeneity is encountered as variations in vascular and perivascular cells along the arteriole-capillary-venule axis, as well as through differences in NVU composition throughout anatomical regions of the brain. Given the wide variations in metabolic demands between brain regions, especially those of gray vs. white matter, the spatial heterogeneity of the NVU is critical to brain function. Here we review recent evidence demonstrating regional specialization of the NVU between brain regions, by focusing on the heterogeneity of its individual cellular components and briefly discussing novel approaches to investigate NVU diversity.
... The cytoplasmic proteins in the TJs include the zonula occludens (ZO) -1, -2, -3 (ZO-1, -2, -3), symplekin, 7H6, and cingulin e all playing a role as TJ organizers inside the cell [23,26,27]. It is important to mention that ZO-1 is the key protein of the TJs which provides the barrier integrity in the retina (Fig. 4.2) [28]. ...
The blood-retinal barrier (BRB) has evolutionarily adapted as a protective border for the cell structures found in this very important sensory organ responsible for vision. The inner BRB with its endothelium, pericytes, Müller glia cells, and astrocytes are the first barrier between the blood and the retina, controlling nutrients and metabolites supply, as well as preventing toxic molecules to enter the retinal space. The outer BRB with its retinal pigment epithelium and the Bruch’s membrane serve as additional barrier and at the same time a front line for the most intense phagocytosis and intra- and transcellular transport in the human body, as well as the place of nearly highest oxidative stress versus antioxidative and angiogenic versus antiangiogenic processes. The barrier molecules in physiology and disease are discussed in this chapter (zonula occludens (ZO)-1, occludin, collagens). Finally, a brief overview of the tissue engineering and three-dimensional organoids with implications for future artificial generation of tissue and barriers in the eye is given. Understanding the structural and molecular components of the BRB and their implications in physiology and disease, as well as tissue engineering can shed light on the current state-of-the-art in basic and applied ophthalmology research and novel developments in therapy.
... Clinical signs are most often a reflection of opportunistic infections, neoplasia and/or myelosuppression, as the disease progresses [28]. Like in HIV and simian immunodeficiency virus (SIV) infections, FIV is likely to enter the brain via the blood-brain and blood-cerebrospinal fluid (CSF) barriers [4,19,26], and thus understanding the mechanisms of interactions of virus and cells at both of these barriers is important in the quest to design therapies to prevent or modify central nervous system (CNS) infections. ...
... Some of the vital regulators of tight junctions' activities identified are cyclic adenosine monophosphate and astrocytes (Rubin et al., 1991;Hurst and Clark, 1998). In brain diseases and disorders, the BBB is highly disrupted, resulting into unregulated diffusion of molecules, leading to further brain damage (Dallasta et al., 1999;Algotsson and Winblad, 2007). Because the BBB prevents the entrance of materials basing on their size and solubility, most of the potential drugs fail to penetrate because they do not meet the required criteria (Pardridge, 2012). ...
Brain is by far the most complex organ in the body. It is involved in the regulation of cognitive, behavioral, and emotional activities. The organ is also a target for many diseases and disorders ranging from injuries to cancers and neurodegenerative diseases. Brain diseases are the main causes of disability and one of the leading causes of deaths. Several drugs that have shown potential in improving brain structure and functioning in animal models face many challenges including the delivery, specificity, and toxicity. For many years, researchers have been facing challenge of developing drugs that can cross the physical (blood–brain barrier), electrical, and chemical barriers of the brain and target the desired region with few adverse events. In recent years, nanotechnology emerged as an important technique for modifying and manipulating different objects at the molecular level to obtain desired features. The technique has proven to be useful in diagnosis as well as treatments of brain diseases and disorders by facilitating the delivery of drugs and improving their efficacy. As the subject is still hot, and new research findings are emerging, it is clear that nanotechnology could upgrade health care systems by providing easy and highly efficient diagnostic and treatment methods. In this review, we will focus on the application of nanotechnology in the diagnosis and treatment of brain diseases and disorders by illuminating the potential of nanoparticles.
... Previous research has shown that MMPs degrade TJ proteins and basement membrane proteins. Many hosts and viral factors contribute to the disruption of BBB integrity, such as HIV, which alternates the expression of occludin and ZO-1 with viral gp120 and CCL2 (Dallasta et al., 1999). MAV-1 infects ECs and directly affects TJ proteins (Gralinski et al., 2009). ...
Lab-attenuated rabies virus (RABV) is a highly cellular adaptation and less pathogenic than wild-type RABV. However, the molecular mechanisms that regulate the cellular adaptation and pathogenicity remain obscure. In this work, we isolated a wild-type RABV (CNIM1701) from a rabid bovine in northern China. The original CNIM1701 was lethal in adult mice and restricted replication in cell cultures. After 20 serial passages in the brains of suckling mice, the virus was renamed CNIM1701-P20, which was safe in adult mice and replicated well in cell cultures. In addition, sequence comparison analysis of the original CNIM1701 and CNIM1701-P20 identified 2 amino acid substitutions on G protein (Lys83 → Arg83 and Pro367 → Ser 367) related to pathogenesis and cellular adaptation. Using site-directed mutagenesis to exchange Lys83 with Arg83 and Pro367 with Ser 367 in the G protein of the RABV SAD strain, the pathogenicity of rSAD-K83R was significantly decreased. Our data indicate that the decreased pathogenicity of rSAD-K83R is due to increasing the expression of RABV-G, which also induced a higher level of apoptosis in infected cells. Furthermore, the K83 mutation induced high expression of MMP-2 and MMP-9 on DCs and promoted blood–brain barrier (BBB) permeability. These results demonstrate that the pathogenesis of RABV is partially dependent on G expression and BBB permeability, which may help in the design and development of highly safe, live-RABV vaccines.
... Inflammation and associated inflammatory factors mediate CNS damage and are driven by residual viral replication, persistently elevated levels of viral proteins despite systemic viral suppression, immune dysfunction and positive feedback loops [82]. With a focus on how neuroinflammation may impact therapeutic drug efficacy within the brain, neuroinflammation is known to alter the expression of tight junctions and compromise BBB integrity [84][85][86]. Additionally, inflammatory cytokines alter the expression and function of drug metabolizing enzymes and drug transport proteins, leading to alterations in plasma drug concentrations and target site concentrations, which may impact the efficacy of these drugs [87][88][89]. ...
Aggressive use of antiretroviral therapy has led to excellent viral suppression within the systemic circulation. However, despite these advances, HIV reservoirs still persist. The persistence of HIV within the brain can lead to the development of HIV-associated neurocognitive disorders (HAND). Although the causes of the development of neurocognitive disorders is likely multifactorial, the inability of antiretroviral therapy to achieve adequate concentrations within the brain is likely a major contributing factor. Information about antiretroviral drug exposure within the brain is limited. Clinically, drug concentrations within the cerebrospinal fluid (CSF) are used as markers for central nervous system (CNS) drug exposure. However, significant differences exist; CSF concentration is often a poor predictor of drug exposure within the brain. This article reviews the current information regarding antiretroviral exposure within the brain in humans as well as preclinical animals and discusses the impact of co-morbidities on antiretroviral efficacy within the brain. A more thorough understanding of antiretroviral penetration into the brain is an essential component to the development of better therapeutic strategies for neuroAIDS.
... Studies have shown serum protein leakage in the brains of HIV-associated dementia patients besides accumulation in subcortical neurons and glia [198]. Structural proteins of TJs, such as ZO-1 and occludin were absent or fragmented in brains of patients died from HIV-1 encephalitis where such changes was not observed in patients without encephalitis [199]. ...
The blood-brain barrier is playing a critical role in controlling the influx and efflux of biological substances essential for the brain's metabolic activity as well as neuronal function. Thus, the functional and structural integrity of the BBB is pivotal to maintain the homeostasis of the brain microenvironment. The different cells and structures contributing to developing this barrier are summarized along with the different functions that BBB plays at the brain-blood interface. We also explained the role of shear stress in maintaining BBB integrity. Furthermore, we elaborated on the clinical aspects that correlate between BBB disruption and different neurological and pathological conditions. Finally, we discussed several biomarkers that can help to assess the BBB permeability and integrity in-vitro or in-vivo and briefly explain their advantages and disadvantages.
... ATP-binding cassette transporters (ABC transporters) are a superfamily of proteins; the membrane proteins of this family are actively involved in the efflux of several proteins and lipid-soluble molecules. These transporters remove the potential neurotoxic molecules, thus, performing a vital neuroprotective role [30]. ABC transporters are actively involved in the efflux of Pglycoprotein, the multidrug resistance-associated proteins, MRPS (ABCB1 transporter), breast cancer resistance protein, BRCP (ABCG2 transporter) and cholesterol (ABCA1 & ABCG1 transporters) [31][32][33]. ...
Parkinson’s disease (PD) is one of the most prevalent and severe neurodegenerative disease affecting more than 6.1 million people globally. It is characterized by age-related progressive deterioration of neurological functions caused by neuronal damage or neuronal death. During PD the dopamine producing-cells in the substantia nigra region of the brain degenerate, which leads to symptoms like resting tremors and rigidity. Treatment of PD is very challenging due to the blood brain barrier, which restricts the drug from reaching the brain. Conventional drug delivery systems possess limited capacity to cross the blood barrier, leading to low bioavailability and high toxicity (due to off-site drug release). Therefore, it becomes necessary to accelerate the development of novel drug delivery systems including nanoparticles, microemulsions, matrix systems, solid dispersions, liposomes, and solid lipid nanoparticles for the treatment of PD. Exosomes are biological lipid bilayer membrane vesicles produced by nearly all mammalian cells. The characteristics of vesicles are unique to their cell of origin and are primarily involved in intracellular communication. Exosomes due to their nanoscale size could easily permeate across the central nervous system, which makes them ideal for targeting the neurons in the substantia nigra. Exosomes could be efficient drug carrier systems for brain targeting, which can increase the efficacy of the drug and minimize the side effects. The review aims at providing a broad updated view of exosomes and their application in the treatment of PD.
... BBB integrity and function are critical for maintaining CNS homeostasis, and mediating neuroimmune interactions with the periphery and drug delivery into the CNS. HIV and many individual HIV proteins can breakdown the BBB disrupting tight junction proteins (Dallasta et al. 1999;Boven et al. 2000;Andras et al. 2003;Mahajan et al. 2008;Banerjee et al. 2010;Gandhi et al. 2010;Xu et al. 2012;Patel et al. 2017) and decreasing transendothelial electrical resistance (TEER) (an in vitro measure of barrier integrity) (Mahajan et al. 2008;Gandhi et al. 2010;Mishra and Singh 2014;Patel et al. 2017), with resultant paracellular "leakage" of compounds/current between compromised barrier endothelial cells (Mahajan et al. 2008;Gandhi et al. 2010;Wen et al. 2011;McLane et al. 2014;Leibrand et al. 2017Leibrand et al. , 2019. Although opioids can also impair the BBB through alterations in tight junction proteins and/or increased paracellular flux (Baba et al. 1988;Mahajan et al. 2008;Wen et al. 2011;Leibrand et al. 2019), others have found that it is morphine withdrawal, not the continued exposure to morphine, that most greatly disrupts BBB integrity (Sharma and Ali 2006). ...
With the current national opioid crisis, it is critical to examine the mechanisms underlying pathophysiologic interactions between human immunodeficiency virus (HIV) and opioids in the central nervous system (CNS). Recent advances in experimental models, methodology, and our understanding of disease processes at the molecular and cellular levels reveal opioid-HIV interactions with increasing clarity. However, despite the substantial new insight, the unique impact of opioids on the severity, progression, and prognosis of neuroHIV and HIV-associated neurocognitive disorders (HAND) are not fully understood. In this review, we explore, in detail, what is currently known about mechanisms underlying opioid interactions with HIV, with emphasis on individual HIV-1-expressed gene products at the molecular, cellular and systems levels. Furthermore, we review preclinical and clinical studies with a focus on key considerations when addressing questions of whether opioid-HIV interactive pathogenesis results in unique structural or functional deficits not seen with either disease alone. These considerations include, understanding the combined consequences of HIV-1 genetic variants, host variants, and μ-opioid receptor (MOR) and HIV chemokine co-receptor interactions on the comorbidity. Lastly, we present topics that need to be considered in the future to better understand the unique contributions of opioids to the pathophysiology of neuroHIV.
Blood-brain barrier and the neurovascular unit. With HIV and opiate co-exposure (represented below the dotted line), there is breakdown of tight junction proteins and increased leakage of paracellular compounds into the brain. Despite this, opiate exposure selectively increases the expression of some efflux transporters, thereby restricting brain penetration of specific drugs.
... A series of diseases of the CNS, such as multiple sclerosis (Minagar and Alexander, 2003) or viral encephalitis (Dallasta et al., 1999) is caused by inflammatory processes in the brain of different origins. In connection with the inflammatory hypotheses of AD, altered permeability of the BBB or its disruption has been proposed to allow access to inflammation in the brain. ...
The vascular endothelium in the brain is an essential part of the blood-brain-barrier (BBB) because of its very tight structure to secure a functional and molecular separation of the brain from the rest of the body and to protect neurons from pathogens and toxins. Impaired transport of metabolites across the BBB due to its increasing dysfunction affects brain health and cognitive functioning, thus providing a starting point of neurodegenerative diseases. The term “cerebral metabolic syndrome” is proposed to highlight the importance of lifestyle factors in neurodegeneration and to describe the impact of increasing BBB dysfunction on neurodegeneration and dementia, especially in elderly patients. If untreated, the cerebral metabolic syndrome may evolve into dementia. Due to the high energy demand of the brain, impaired glucose transport across the BBB via glucose transporters as GLUT1 renders the brain increasingly susceptible to neurodegeneration. Apoptotic processes are further supported by the lack of essential metabolites of the phosphocholine synthesis. In Alzheimer’s disease (AD), inflammatory and infectious processes at the BBB increase the dysfunction and might be pace-making events. At this point, the potentially highly relevant role of the thrombocytic amyloid precursor protein (APP) in endothelial inflammation of the BBB is discussed. Chronic inflammatory processes of the BBB transmitted to an increasing number of brain areas might cause a lasting build-up of spreading, pore-forming β-amyloid fragments explaining the dramatic progression of the disease. In the view of the essential requirement of an early diagnosis to investigate and implement causal therapeutic strategies against dementia, brain imaging methods are of great importance. Therefore, status and opportunities in the field of diagnostic imaging of the living human brain will be portrayed, comprising diverse techniques such as positron emissions tomography (PET) and functional magnetic resonance imaging (fMRI) to uncover the patterns of atrophy, protein deposits, hypometabolism, and molecular as well as functional alterations in AD.
... The virus works by either entering the CNS via infected lymphocytes or monocytes and infects microglia and perivascular macrophages as a result releasing toxic substances such as chemokines, cytokines, viral proteins or acts directly infecting the BBB cells (Dallasta et al., 1999;Abbott et al., 2010). ...
Barriers are the hallmark of a healthy physiology, BBB being a tough nut to crack for most of the antigens and chemical substances. The presence of tight junctions plays a remarkable role in defending the brain from antigenic and pathogenic attacks. BBB constitutes a diverse assemblage of multiple physical and chemical barriers that judiciously restrict the flux of blood solutes into and out of the brain. Restrictions through the paracellular pathway and the tight junctions between intercellular clefts, together create well regulated metabolic and transport barricades, critical to brain pathophysiology. The brain being impermeable to many essential metabolites and nutrients regulates transportation via specialized transport systems across the endothelial abluminal and luminal membranes. The epithelial cells enveloping capillaries of the choroid plexus regulates the transport of complement, growth factors, hormones, microelements, peptides and trace elements into ventricles. Nerve terminals, microglia, and pericytes associated with the endothelium support barrier induction and function, ensuring an optimally stable ionic microenvironment that facilitates neurotransmission, orchestrated by multiple ion channels (Na+, K+ Mg2+, Ca2+, pH) and transporters. Brain pathology which can develop due to genetic mutations or secondary to other cerebrovascular, neurodegenerative diseases can cause aberration in the microvasculature of CNS which is the uniqueness of BBB. This can also alter BBB permeation and result in BBB breakdown and other neurodegenerative disorders such as Alzheimer’s disease, amyotrophic lateral sclerosis, Parkinson's disease, and multiple sclerosis. The concluding section outlines contemporary trends in drug discovery, focusing on molecular determinants of BBB permeation and novel drug-delivery systems, such as dendrimers, liposomes, nanoparticles, nanogels, etc.
... Given its distinctive anatomical features, it plays a crucial role in controlling the traffic through the CNS, having a variety of functions. Firstly, it preserves the internal brain environment, i.e. maintains the CSF and the interstitial fluid composition within extremely regulated limits, so that the neurons can fulfil their complex integrative roles [26,27]. This homeostasis of the CNS is achieved by a series of mechanisms, such as controlling the passage and efflux of nutrients and metabolites to and from the brain, restricting the transport of polar substances by passive diffusion from the systemic circulation to the brain and regulating the migration of immune cells [28]. ...
The central nervous system (CNS) is vulnerable to pathologic processes that lead to the development of neurodegenerative disorders like Alzheimer’s, Parkinson’s and Huntington’s diseases, Multiple sclerosis or Amyotrophic lateral sclerosis. These are chronic and progressive pathologies characterized by the loss of neurons and the formation of misfolded proteins. Additionally, neurodegenerative diseases are accompanied by a structural and functional dysfunction of the blood-brain barrier (BBB). Although serving as a protection for CNS, the existence of physiological barriers, especially the BBB, limits the access of several therapeutic agents to the brain, constituting a major hindrance in neurotherapeutics advancement. In this regard, nanotechnology-based approaches have arisen as a promising strategy to not only improve drug targeting to the brain, but also to increase bioavailability. Lipid nanocarriers such as liposomes, solid lipid nanoparticles (SLN), nanostructured lipid carriers (NLC), microemulsions and nanoemulsions, have already proven their potential for enhancing brain transport, crossing more easily into the CNS and allowing the administration of medicines that could benefit the treatment of neurological pathologies.
Given the socioeconomic impact of such conditions and the advent of nanotechnology that inevitably leads to more effective and superior therapeutics for their management, it is imperative to constantly update on the current knowledge of these topics. Herein, we provide insight on the BBB and the pathophysiology of the main neurodegenerative disorders. Moreover, this review seeks to highlight the several approaches that can be used to improve the delivery of therapeutic agents to the CNS, while also offering an extensive overview of the latest efforts regarding the use of lipid-based nanocarriers in the management of neurodegenerative diseases.
... IV infusion of MSCs has been demonstrated to restore BBB dysfunction in other experimental models, such as in cerebral small vessel disease, by promoting microvascular remodeling via the transforming growth factor-β and angiopoietin 1 signaling pathways (27). In the present study, the underlying signaling mechanism may involve mRNA expression of occludin, since disruption of BBB in many diseases is associated with changes in occludin expression (28)(29)(30). The increased occludin expression observed in the hippocampus of CLP + SAL mice is consistent with a previous study that showed increased occludin expression in human brains with Alzheimer's disease and vascular dementia compared with controls (31). ...
Objectives:
Survivors of sepsis are frequently left with significant cognitive and behavioral impairments. These complications derive from nonresolving inflammation that persists following hospital discharge. To date, no study has investigated the effects of mesenchymal stromal cell therapy on the blood-brain barrier, astrocyte activation, neuroinflammation, and cognitive and behavioral alterations in experimental sepsis.
Design:
Prospective, randomized, controlled experimental study.
Setting:
Government-affiliated research laboratory.
Subjects:
Male Swiss Webster mice (n = 309).
Interventions:
Sepsis was induced by cecal ligation and puncture; sham-operated animals were used as control. All animals received volume resuscitation (1 mL saline/mouse subcutaneously) and antibiotics (meropenem 10 mg/kg intraperitoneally at 6, 24, and 48 hours). Six hours after surgery, mice were treated with mesenchymal stromal cells IV (1 × 10 cells in 0.05 mL of saline/mouse) or saline (0.05 mL IV).
Measurements and main results:
At day 1, clinical score and plasma levels of inflammatory mediators were increased in cecal ligation and puncture mice. Mesenchymal stromal cells did not alter clinical score or survival rate, but reduced levels of systemic interleukin-1β, interleukin-6, and monocyte chemoattractant protein-1. At day 15, survivor mice completed a battery of cognitive and behavioral tasks. Cecal ligation and puncture mice exhibited spatial and aversive memory deficits and anxiety-like behavior. These effects may be related to increased blood-brain barrier permeability, with altered tight-junction messenger RNA expression, increased brain levels of inflammatory mediators, and astrogliosis (induced at day 3). Mesenchymal stromal cells mitigated these cognitive and behavioral alterations, as well as reduced blood-brain barrier dysfunction, astrocyte activation, and interleukin-1β, interleukin-6, tumor necrosis factor-α, and interleukin-10 levels in vivo. In cultured primary astrocytes stimulated with lipopolysaccharide, conditioned media from mesenchymal stromal cells reduced astrogliosis, interleukin-1β, and monocyte chemoattractant protein-1, suggesting a paracrine mechanism of action.
Conclusions:
In mice who survived experimental sepsis, mesenchymal stromal cell therapy protected blood-brain barrier integrity, reduced astrogliosis and neuroinflammation, as well as improved cognition and behavior.
... As a junctional adaptor protein, interacting with claudin-5 and ZO-1 controls adherens junctions and plays essential roles in the barrier formation (Tornavaca et al. 2015). The absence of ZO-1 on the BBB was observed in the encephalitis caused by human immunodeficiency virus type 1 (HIV-1) (Dallasta et al. 1999). ...
Enterovirus A71 (EV-A71) is the major cause of severe hand-foot-and-mouth diseases (HFMD), especially encephalitis and other nervous system diseases. EV-A71 capsid protein VP1 mediates virus attachment and is the important virulence factor in the EV-A71pathogenesis. In this study, we explored the roles of VP1 in the permeability of blood–brain barrier (BBB). Sera albumin, Evans blue, and dextran leaked into brain parenchyma of the 1-week-old C57BL/6J mice intracranially injected with VP1 recombinant protein. VP1 also increased the permeability of the brain endothelial cells monolayer, an in vitro BBB model. Tight junction protein claudin-5 was reduced in the brain tissues or brain endothelial cells treated with VP1. In contrast, VP1 increased the expression of virus receptor vimentin, which could be blocked with VP1 neutralization antibody. Vimentin expression in the VP1-treated brain endothelial cells was regulated by TGF-β/Smad-3 and NF-κB signal pathways. Moreover, vimentin over-expression was accompanied with compromised BBB. From these studies, we conclude that EV-A71 virus capsid protein VP1 disrupted BBB and increased virus receptor vimentin, which both may contribute to the virus entrance into brain and EV-A71 CNS infection.
... MAV-1 infects brain vascular endothelium in vivo [108] and dampens expression of TJ proteins in vitro [107]. Indeed, reduced expression of TJ and AJ proteins is a characteristic feature of BBB disruption by neurotropic viruses such as JEV, WNV, and human immunodeficiency virus type 1 (HIV-1) in vivo [104,109,110]. Viruses accomplish this either by downregulating transcription levels of TJ mRNA or promoting protein degradation [104,111]. ...
As the organ of highest metabolic demand, utilizing over 25% of total body glucose utilization via an enormous vasculature with one capillary every 73 μm, the brain evolves a barrier at the capillary and postcapillary venules to prevent toxicity during serum fluctuations in metabolites and hormones, to limit brain swelling during inflammation, and to prevent pathogen invasion. Understanding of neuroprotective barriers has since evolved to incorporate the neurovascular unit (NVU), the blood-cerebrospinal fluid (CSF) barrier, and the presence of CNS lymphatics that allow leukocyte egress. Identification of the cellular and molecular participants in BBB function at the NVU has allowed detailed analyses of mechanisms that contribute to BBB dysfunction in various disease states, which include both autoimmune and infectious etiologies. This chapter will introduce some of the cellular and molecular components that promote barrier function but may be manipulated by inflammatory mediators or pathogens during neuroinflammation or neuroinfectious diseases.
... Loss of BBB integrity has been described in a number of viral encephalitis animal models (HIV, Zika virus, Japanese encephalitis virus, La Crosse virus, and West Nile Virus) (3,40,54) and human cases of HIV-induced encephalitis (55,56). Here, we identified endothelial-IFN-␥ signaling as a contributor to BBB leakage. ...
In an experimental viral encephalitis mouse model in which mice are infected with reovirus, we show that IFN-γ induces blood-brain barrier leakage. We show that IFN-γ promotes Rho kinase activity, resulting in actin cytoskeletal contractions in the brain endothelium that lead to vascular junctional disorganization and cell-cell separations. These studies now provide insight into a previously unknown mechanism for how blood-brain barrier breakdown occurs in viral encephalitis and implicates IFN-γ-Rho kinase activity as major contributor to this phenomenon. By identifying this mechanism of blood-brain barrier breakdown, we now provide potential therapeutic targets in treating patients with viral causes of encephalitis with the hope of limiting damage to the central nervous system.
... HIV-derived cellular and viral toxins are known to alter the integrity of the BBB. Exposure to HIV alters tight junction expression (Dallasta et al. 1999;Boven et al. 2000;Persidsky et al. 2006;Chaudhuri et al. 2008b, a;Eugenin et al. 2011) and also increases transmigration of cells across the barrier (Saukkonen et al. 1997;Persidsky et al. 1999Persidsky et al. , 2000Eugenin 2006;Buckner et al. 2011;Eugenin et al. 2011;Williams et al. 2012;Coley et al. 2015). The HIV proteins Tat (transactivator of transcription) and/or gp120 (glycoprotein 120) decrease tight junction protein expression (Kanmogne et al. 2002(Kanmogne et al. , 2007Price et al. 2005;Shiu et al. 2007;Nakamuta et al. 2008;Louboutin et al. 2010;Louboutin and Strayer 2012), increase transmigration of monocytes (Weiss et al. 1999;Wu et al. 2000;Buckner et al. 2006, Williams et al. 2013, 2015, and increase barrier permeability to paracellular compounds (Andras et al. 2003;Andras et al. 2005;Pu et al. 2005Pu et al. , 2007Zhong et al. 2008;Banerjee et al. 2010;Gandhi et al. 2010;Xu et al. 2012;Leibrand et al. 2017). ...
Poor antiretroviral penetration may contribute to human immunodeficiency virus (HIV) persistence within the brain and to neurocognitive deficits in opiate abusers. To investigate this problem, HIV-1 Tat protein and morphine effects on blood–brain barrier (BBB) permeability and drug brain penetration were explored using a conditional HIV-1 Tat transgenic mouse model. Tat and morphine effects on the leakage of fluorescently labeled dextrans (10-, 40-, and 70-kDa) into the brain were assessed. To evaluate effects on antiretroviral brain penetration, Tat+ and Tat− mice received three antiretroviral drugs (dolutegravir, abacavir, and lamivudine) with or without concurrent morphine exposure. Antiretroviral and morphine brain and plasma concentrations were determined by LC-MS/MS. Morphine exposure, and, to a lesser extent, Tat, significantly increased tracer leakage from the vasculature into the brain. Despite enhanced BBB breakdown evidenced by increased tracer leakiness, morphine exposure led to significantly lower abacavir concentrations within the striatum and significantly less dolutegravir within the hippocampus and striatum (normalized to plasma). P-glycoprotein, an efflux transporter for which these drugs are substrates, expression and function were significantly increased in the brains of morphine-exposed mice compared to mice not exposed to morphine. These findings were consistent with lower antiretroviral concentrations in brain tissues examined. Lamivudine concentrations were unaffected by Tat or morphine exposure. Collectively, our investigations indicate that Tat and morphine differentially alter BBB integrity. Morphine decreased brain concentrations of specific antiretroviral drugs, perhaps via increased expression of the drug efflux transporter, P-glycoprotein.
... In particular, these cells appear to be associated with sites of TJ damage, revealed by the absence of ZO-1 [212]. Macrophage migration has similarly been associated with tight junction damage in HIV-1 encephalitis and HIV-1-associated dementia [212][213][214]. Monocytes and macrophages are believed to transition into microglia after entry into the brain [215] and unregulated microglial precursor infiltration through a damaged BBB could have serious consequences for the degenerative process. ...
Alzheimer's disease (AD) is the most prevalent form of dementia. Despite decades of research following several theoretical and clinical lines, all existing treatments for the disorder are purely symptomatic. AD research has traditionally been focused on neuronal and glial dysfunction. Although there is a wealth of evidence pointing to a significant vascular component in the disease, this angle has been relatively poorly explored. In this review, we consider the various aspects of vascular dysfunction in AD, which has a significant impact on brain metabolism and homeostasis and the clearance of β-amyloid and other toxic metabolites. This may potentially precede the onset of the hallmark pathophysiological and cognitive symptoms of the disease. Pathological changes in vessel haemodynamics, angiogenesis, vascular cell function, vascular coverage, blood-brain barrier permeability and immune cell migration may be related to amyloid toxicity, oxidative stress and apolipoprotein E (APOE) genotype. These vascular deficits may in turn contribute to parenchymal amyloid deposition, neurotoxicity, glial activation and metabolic dysfunction in multiple cell types. A vicious feedback cycle ensues, with progressively worsening neuronal and vascular pathology through the course of the disease. Thus, a better appreciation for the importance of vascular dysfunction in AD may open new avenues for research and therapy.
... Despite advances in antiretroviral therapy (ART), HIV-infected patients continue to suffer from HAND, which have been commonly linked to the breakdown of the BBB [17][18][19]. Previous studies clearly demonstrate the advantages of using a simian immunodeficiency virus (SIV) macaque model to imitate BBB breakdown in the brains of HIV-infected patients [20,21]. ...
Background:
Impairment of the blood-brain barrier (BBB) has been associated with cognitive decline in many CNS diseases, including HIV-associated neurocognitive disorders (HAND). Recent research suggests an important role for the Sonic hedgehog (Shh) signaling pathway in the maintenance of BBB integrity under both physiological and pathological conditions.
Methods:
In the present study, we sought to examine the expression of Shh and its downstream effectors in relation to brain pericytes and BBB integrity in HIV-infected humans and rhesus macaques infected with simian immunodeficiency virus (SIV), an animal model of HIV infection and CNS disease. Cortical brain tissues from uninfected (n = 4) and SIV-infected macaques with (SIVE, n = 6) or without encephalitis (SIVnoE, n = 4) were examined using multi-label, semi-quantitative immunofluorescence microscopy of Shh, netrin-1, tight junction protein zona occludens 1 (ZO1), glial fibrillary acidic protein, CD163, platelet-derived growth factor receptor b (PDGFRB), glucose transporter 1, fibrinogen, and SIV Gag p28.
Results:
While Shh presence in the brain persisted during HIV/SIV infection, both netrin-1 immunoreactivity and the size of PDGFRB+ pericytes, a cellular source of netrin-1, were increased around non-lesion-associated vessels in encephalitis compared to uninfected brain or brain without encephalitis, but were completely absent in encephalitic lesions. Hypertrophied pericytes were strongly localized in areas of fibrinogen extravasation and showed the presence of intracellular SIVp28 and HIVp24 by immunofluorescence in all SIV and HIV encephalitis cases examined, respectively.
Conclusions:
The lack of pericytes and netrin-1 in encephalitic lesions, in line with downregulation of ZO1 on the fenestrated endothelium, suggests that pericyte loss, despite the strong presence of Shh, contributes to HIV/SIV-induced BBB disruption and neuropathogenesis in HAND.
Background
HIV-associated neurocognitive disorders (HAND) still affects persons living with HIV (PLWH) and their pathogenesis isn’t completely understood. We aimed to explore the association between plasma and CSF markers of blood-brain barrier (BBB) impairment and HAND in untreated PLWH.
Design
Cross-sectional study.
Methods
We enrolled untreated PLWH, who underwent blood exams and lumbar puncture to measure inflammation (IL-15, TNF-α), BBB damage (zonulin and tight junction proteins, TJs: occludin, claudin-5) and endothelial adhesion molecules (VCAM-1, ICAM-1). A comprehensive neurocognitive battery was used to diagnose HAND (Frascati criteria).
Results
Twenty-one patients (21/78, 26,9%) patients presented HAND (100% ANI). HAND patients displayed more frequently non-CNS AIDS-defining conditions, lower nadir CD4+ T-cells and increased CD4+ T-cell exhaustion (lower CD4+CD127+ and CD4+CD45RA+ T cells percentages), in comparison to subjects without cognitive impairment. Furthermore, HAND was characterized by higher plasma inflammation (IL-15), but lower CSF levels of biomarkers of BBB impairment (zonulin and occludin). The association between BBB damage with HAND was confirmed by fitting a multivariable logistic regression. CSF/plasma endothelial adhesion molecules weren’t associated with HAND, but with a poor performance in different cognitive domains.
Conclusions
By showing heightened inflammation and BBB impairment, our study suggests loss of BBB integrity as a possible factor contributing to the development of HAND in untreated PLWH.
Nowadays, one of the major challenges in biomedical and biopharmaceutical field is designing novel and effective anti-amyloidogenic inhibitors for the treatment of various human pathophysiologies associated with protein aggregation. In this milieu, numerous small molecules, polyphenols, surfactants, nanoparticles, etc. have been extensively studied to explore their anti-amyloidogenic properties, and thus provide huge scope for them to appear as future therapeutic agents in the treatment of amyloidogenic disorders. Recently, inspired by the fascinating properties of polymers such as non-toxicity, excellent biocompatibility, tuneable architectures, controllable degradation rate, possibility of multiple interaction between amyloidogenic protein/peptide and polymer, and excellent in vivo stability, polymer-based therapeutic agents have been extensively explored in the field of protein misfolding and aggregation. This mini-review article emphasizes the recent advancements of polymeric materials in the field of protein aggregation for ameliorating neurodegenerative diseases. Finally, we conclude this mini-review by providing some viewpoints on future directions
The activities of HIV‐1 in the central nervous system (CNS) are responsible for a dysregulated neuroinflammatory response and the subsequent development of HIV‐associated neurocognitive disorders (HAND). The use of post‐mortem human brain tissue is pivotal for studying the neuroimmune mechanisms of CNS HIV infection. To date, numerous studies have investigated HIV‐1‐induced neuroinflammation in post‐mortem brain tissue. However, from the commonly investigated studies in this line of research, it is not clear which neuroinflammatory markers are consistently associated with HIV neurocognitive impairment (NCI) and neuropathology (i.e., HIV‐encephalitis, HIVE). Therefore, we conducted a systematic review of the association between neuroinflammation and NCI/HIVE from studies investigating post‐mortem brain tissue. Our aim was to synthesise the published data to date to provide commentary on the most noteworthy markers that are associated with NCI/HIVE. PubMed, Scopus, and Web of Science databases were searched using a search protocol designed specifically for this study. Sixty‐one studies were included that investigated the levels of inflammatory markers based on their gene and protein expression in association with NCI/HIVE. The findings revealed that the (1) transcript expressions of IL‐1β and TNF‐α were consistently associated with NCI/HIVE, whereas CCL2 and IL‐6 were commonly not associated with NCI/HIVE, (2) protein expressions of CD14, CD16, CD68, Iba‐1, IL‐1β and TNF‐α were consistently associated with NCI/HIVE, while CD45, GFAP, HLA‐DR, IL‐1 and IL‐6 were commonly not associated with NCI/HIVE, and (3) gene and protein expressions of CNS IL‐1β and TNF‐α were consistently associated with NCI/HIVE, while IL‐6 was consistently not associated with NCI/HIVE. These markers highlight the commonly investigated markers in this line of research and elucidates the neuroinflammatory mechanisms in the HIV‐1 brain that are involved in the pathophysiology of NCI/HIVE. These markers and related pathways should be investigated for the development of improved diagnostics, prognostics, and therapeutics of HAND.
Candidate drugs targeting the central nervous system (CNS) demonstrate extremely low clinical success rates, with more than 98% of potential treatments being discontinued due to poor blood–brain barrier (BBB) permeability. Neurological conditions were shown to be the second leading cause of death globally in 2016, with the number of people currently affected by neurological disorders increasing rapidly. This increasing trend, along with an inability to develop BBB permeating drugs, is presenting a major hurdle in the treatment of CNS‐related disorders, like dementia. To overcome this, it is necessary to understand the structure and function of the BBB, including the transport of molecules across its interface in both healthy and pathological conditions. The use of CNS drug carriers is rapidly gaining popularity in CNS research due to their ability to target BBB transport systems. Further research and development of drug delivery vehicles could provide essential information that can be used to develop novel treatments for neurological conditions. This review discusses the BBB and its transport systems and evaluates the potential of using nanoparticle‐based delivery systems as drug carriers for CNS disease with a focus on dementia.
Interactions between the immune and nervous systems are involved in many disease processes. Modulation of inflammation can provide an important opportunity to enhance regeneration within the central nervous system. This authoritative book defines the key cellular players in mounting an inflammatory response and highlights critical factors in the target organ that influence the nature of that response and its capacity either to damage or protect the brain. Several key clinical areas are highlighted – particularly autoimmune diseases of the nervous system including multiple sclerosis, as well as microbiological and traumatic challenges; the book therefore provides both a summary of the basic science background as well as practical, clinical-friendly guidelines to management. The book will be of interest to a wide range of physicians, including neurologists, neurosurgeons, neurorehabilitationists, infectious disease physicians, and clinical neuroscientists, as well as neuroscientists and immunologists.
The blood-brain barrier (BBB) is the principal regulator of transport of molecules and cells into and out of the central nervous system (CNS). It comprises endothelial cells, pericytes, immune cells, astrocytes, and basement membrane, collectively known as the neurovascular unit. The development of the barrier involves many complex pathways from all the progenitors of the neurovascular unit, but the timing of its formation is not entirely known. The coordinated activities of all the components of the neurovascular unit and other tissues ensure that materials required for growth and maintenance are allowed into the CNS while extraneous ones are excluded. This review summarizes current knowledge of the anatomy, development, and physiology of the BBB, and alterations that occur in disease conditions.
Initially, glial cells were believed to function as “glue or packaging” cells of the brain; however, the last two decades of research from basic and clinical scientists have duly recognized them as one of the most important cell types in the mammalian brain. It has been now well established that glial cells, and, in particular, astrocytes, play immensely important roles that enable neurons to function optimally. This chapter describes the historical aspects of research on astrocytes, their role during brain development and synaptogenesis and other physiological functions of the brain, and finally how they contribute to disease pathogenesis or CNS disorders.KeywordsAstrocytesBlood-brain barrierGlial cellsGFAP
Background:
Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the central nervous system. The exact pathogenesis behind the development of MS is unknown. This study aims to elucidate the role of fibrinogen in MS pathology and discuss candidacy as a biomarker for disease management.
Method:
The method applied is a systematic literature review on the bio-medical database PubMed.
Results:
This study found that even though the role of fibrinogen in disease development has been studied considerably, clinical application as a viable biomarker has not yet been achieved conclusively in human studies.
Conclusion:
Recent evidence points toward fibrinogen and its degradation products playing a possible role in the disease pathogenesis Further research is needed to convincingly evaluate fibrinogen as a practical biomarker for diagnostic use or for assessing disease severity.
Stlmmsr~ Human immunodeficiency virus (HIV) infection of brain macrophages and astroglial proliferation are central features of HIV-induced central nervous system (CNS) disorders. These observations suggest that glial cellular interactions participate in disease. In an experimental system to examine this process, we found that cocultures of HIV-infected monocytes and astroglia release high levels of cytokines and arachidonate metabolites leading to neuronotoxicity. HIV-l^D^-infected monocytes cocultured with human glia (astrocytoma, neuroglia, and primary human astrocytes) synthesized tumor necrosis factor (TNF-o 0 and interleukin 1B (IblB) as assayed by coupled reverse transcription-polymerase chain reaction, enzyme-linked immunosorbent assay, and biological activity. The cytokine induction was selective, cell specific, and associated with induction of arachidonic acid metabolites. TNF-B, Iblc~, IL-6, interferon c~ (IFN-c~), and IFN-'y were not produced. Leukotriene B4, leukotriene D4, lipoxin A4, and platelet-activating factor were detected in large amounts after high-performance liquid chromatography separation and correlated with cytokine activity. Specific inhibitors of the arachidonic cascade markedly diminished the cytokine response suggesting regulatory relationships between these factors. Cocultures of HIV-infected monocytes and neuroblastoma or endothelial cells, or HIV-infected monocyte fluids, sucrose gradient-concentrated viral particles, and paraformaldehyde-fixed or freeze-thawed HIV-infected monocytes placed onto astroglia failed to induce cytokines and neuronotoxins. This demonstrated that viable monocyte-astroglia interactions were required for the cell reactions. The addition of actinomycin D or cycloheximide to the HIV-infected monocytes before coculture reduced, >2.5-fold, the levels of TNF-o~. These results, taken together, suggest that the neuronotoxicity associated with HIV central nervous system disorders is mediated, in part, through cytokines and arachidonic acid metabolites, produced during cell-to-cell interactions between HIV-infected brain macrophages and astrocytes.
We wanted to establish an in vitro human model for AIDS-associated dementia and pursue the hypothesis that this disease process may be a result of soluble factors produced by HIV-infected macrophages. Human brain aggregates were prepared from nine different brain specimens, and were treated with supernatants from in vitro HIV-infected macrophages (SI), uninfected macrophages (SU), infected T cells, or macrophage-conditioned media from four AIDS patients. Seven of nine treated brains exposed to SI showed peripheral rarefaction after 1 wk of incubation that by ultrastructural analysis showed cytoplasmic vacuolation. Aggregates from two of three brain cultures treated with SI for 3 wk became smaller, an approximately 50% decrease in size. The degree of apparent toxicity in brains exposed to patient-derived macrophage supernatants paralleled the proportion of macrophages found to be expressing HIV p24. Ultrastructural abnormalities were not observed in brains treated with supernatants from HIV-infected T cells, uninfected macrophages, or LPS-activated macrophages. Levels of five neurotransmitter amino acids were decreased in comparison to the structural amino acid leucine. These findings suggest that HIV-infected macrophages, infected both in vitro as well as derived from AIDS patients' peripheral blood, produce factors that cause reproducible histochemical, ultrastructural, and functional abnormalities in human brain aggregates.
Depression or psychosis in a previously asymptomatic individual infected with the human immunodeficiency virus (HIV) may be psychogenic, related to brain involvement by the HIV or both. Although prognosis and treatment differ depending on etiology, computed tomography (CT) and magnetic resonance imaging (MRI) are usually unrevealing in early HIV encephalopathy and therefore cannot differentiate it from psychogenic conditions. Thirty of 32 patients (94%) with HIV encephalopathy had single-photon emission computed tomography (SPECT) findings that differed from the findings in 15 patients with non-HIV psychoses and 6 controls. SPECT showed multifocal cortical and subcortical areas of hypoperfusion. In 4 cases, cognitive improvement after 6-8 weeks of zidovudine (AZT) therapy was reflected in amelioration of SPECT findings. CT remained unchanged. SPECT may be a useful technique for the evaluation of HIV encephalopathy.
The presence and extent of encephalopathy were evaluated in 47 patients with AIDS or AIDS-related complex (ARC) by the use of MR imaging. Twenty-nine (62%) of the patients showed some form of white matter disease, exhibited as high signal intensity on T2-weighted images. Focal white matter lesions were seen in 23 (49%) of the patients, while a diffuse white matter process was observed in six patients (13%). Of the 29 patients who had white matter disease on MR scans, 17 (36%) had a suggestion of white matter involvement on an initial CT study. Meanwhile, 12 (26%) of the patients had a normal CT scan on the initial examination. MR findings showed predominant disease in the subinsular and peritrigonal white matter areas. Marked cerebral atrophy was observed in 17 (36%) of 47 patients, cerebellar atrophy in 18 (38%), and brainstem atrophy in seven patients (15%). Pathologic findings showed that toxoplasmosis was present in eight patients (17%), and primary CNS lymphoma was present in three patients (6%). Cryptococcal meningitis was noted in two (4%) of the patients at autopsy, and Mycobacterium tuberculosis was seen in one (2%) of the patients at autopsy. MR imaging has been shown to be a valuable technique for the detection of encephalopathy in AIDS patients.
Quantitative measurements of cerebral blood flow (CBF) by xenon-133 (133Xe) tomography, together with magnetic resonance imaging (MRI), electroencephalography (EEG), psychometric tests, and laboratory analyses were performed on 18 human immunodeficiency virus 1 (HIV-1) seropositive asymptomatic subjects. Abnormalities of cerebral perfusion were observed in 16 cases (88%). These abnormalities were particularly frequent in the frontal regions (77% of cases). MRI demonstrated leucoencephalopathy in only two cases. EEG showed only induced diffuse abnormalities in two cases. Psychometric tests showed restricted moderate disturbances in 55% of patients. These disturbances mostly concerned those sectors involved in cognitive functions and memorization. These results indicate that quantitative measurements of CBF by 133Xe-SPECT is capable of detecting abnormalities of cerebral perfusion at a very early stage (Phase II) of HIV-1 infection. These abnormalities are indications of disturbances resulting from unidentified metabolic or vascular lesions. This technique appears to be superior to MRI at this stage of the disease's development. It could provide objective information leading to earlier treatment, and prove useful in evaluating potential antiviral chemotherapy.
Dysfunction of the central nervous system (CNS) is a prominent feature of the acquired immune deficiency syndrome (AIDS). Many of these patients have a subacute encephalitis consistent with a viral infection of the CNS. We studied the brains of 12 AIDS patients using in situ hybridization to identify human immunodeficiency virus [HIV, referred to by others as human T-cell lymphotropic virus type III (HTLV-III), lymphadenopathy-associated virus (LAV), AIDS-associated retrovirus (ARV)] nucleic acid sequences and immunocytochemistry to identify viral and cellular proteins. Nine patients had significant HIV infection in the CNS. In all examined brains, the white matter was more severely involved than the grey matter. In most cases the infection was restricted to capillary endothelial cells, mononuclear inflammatory cells, and giant cells. In a single case with severe CNS involvement, a low-level infection was seen in some astrocytes and neurons. These results suggest that CNS dysfunction is due to indirect effects rather than neuronal or glial infection.
Infection with human immunodeficiency virus type 1 (HIV-1) is frequently complicated in its late stages by the AIDS dementia complex, a neurological syndrome characterized by abnormalities in cognition, motor performance, and behavior. This dementia is due partially or wholly to a direct effect of the virus on the brain rather than to opportunistic infection, but its pathogenesis is not well understood. Productive HIV-1 brain infection is detected only in a subset of patients and is confined largely or exclusively to macrophages, microglia, and derivative multinucleated cells that are formed by virus-induced cell fusion. Absence of cytolytic infection of neurons, oligodentrocytes, and astrocytes has focused attention on the possible role of indirect mechanisms of brain dysfunction related to either virus or cell-coded toxins. Delayed development of the AIDS dementia complex, despite both early exposure of the nervous system to HIV-1 and chronic leptomeningeal infection, indicates that although this virus is "neurotropic," it is relatively nonpathogenic for the brain in the absence of immunosuppression. Within the context of the permissive effect of immunosuppression, genetic changes in HIV-1 may underlie the neuropathological heterogeneity of the AIDS dementia complex and its relatively independent course in relation to the systemic manifestations of AIDS noted in some patients.
In summary, recent studies over the last ten years have concentrated on what the blood-brain barrier does rather than what it is. This focus has changed the concept of this important membrane from a passive, relatively immutable structure to a dynamic interface between blood and brain. Further understanding of the molecular cell physiology of the brain capillary endothelium will undoubtedly lead to new insights into both drug action at the BBB and drug delivery through this barrier.
A tight junction-enriched membrane fraction has been used as immunogen to generate a monoclonal antiserum specific for this intercellular junction. Hybridomas were screened for their ability to both react on an immunoblot and localize to the junctional complex region on frozen sections of unfixed mouse liver. A stable hybridoma line has been isolated that secretes an antibody (R26.4C) that localizes in thin section images of isolated mouse liver plasma membranes to the points of membrane contact at the tight junction. This antibody recognizes a polypeptide of approximately 225,000 D, detectable in whole liver homogenates as well as in the tight junction-enriched membrane fraction. R26.4C localizes to the junctional complex region of a number of other epithelia, including colon, kidney, and testis, and to arterial endothelium, as assayed by immunofluorescent staining of cryostat sections of whole tissue. This antibody also stains the junctional complex region in confluent monolayers of the Madin-Darby canine kidney epithelial cell line. Immunoblot analysis of Madin-Darby canine kidney cells demonstrates the presence of a polypeptide similar in molecular weight to that detected in liver, suggesting that this protein is potentially a ubiquitous component of all mammalian tight junctions. The 225-kD tight junction-associated polypeptide is termed "ZO-1."
Intercellular junctions are specialized regions of contact between the apposed plasma membranes of adjacent cells, and recent evidence suggests that they are essential for the development of multicellular organisms. They provide the structural means for groups of cells to interact in certain defined ways, and thereby enable them to create structures of higher order. This chapter reviews the morphological information on intercellular junctions derived from thin-sectioning, negative staining and freeze-cleave techniques, as well as from x-ray diffraction and biochemical investigations, and correlates the structural parameters with known or proposed physiological functions. The membrane structure of intercellular junctions is described. Membrane proteins can be divided into two groups: peripheral and integral. Peripheral membrane proteins are believed to be associated with the membrane surface, based on the observation that they are held to the membrane by rather weak noncovalent interactions, and are not strongly associated with membrane lipids. Only mild treatments, such as an increase in ionic strength of the medium or the addition of a chelating agent, are needed to dissociate them molecularly intact from the membrane. Furthermore, in the dissociated state they are relatively soluble in neutral aqueous buffers. In contrast, integral membrane proteins appear much more strongly bound to the lipid matrix, since they can be dissociated from the latter only by drastic treatments with chemicals such as detergents, protein denaturants, and organic solvents. The diversity in structure and function of intercellular junctions offers an exciting field for future research in which morphologists, physiologists, and biochemists should be able to make significant contributions to the knowledge of how individual cells interact to form structures of higher order.
Certain junctions between ependymal cells, between astrocytes, and between some electrically coupled neurons have heretofore been regarded as tight, pentalaminar occlusions of the intercellular cleft. These junctions are now redefined in terms of their configuration after treatment of brain tissue in uranyl acetate before dehydration. Instead of a median dense lamina, they are bisected by a median gap 20-30 A wide which is continuous with the rest of the interspace. The patency of these "gap junctions" is further demonstrated by the penetration of horseradish peroxidase or lanthanum into the median gap, the latter tracer delineating there a polygonal substructure. However, either tracer can circumvent gap junctions because they are plaque-shaped rather than complete, circumferential belts. Tight junctions, which retain a pentalaminar appearance after uranyl acetate block treatment, are restricted primarily to the endothelium of parenchymal capillaries and the epithelium of the choroid plexus. They form rows of extensive, overlapping occlusions of the interspace and are neither circumvented nor penetrated by peroxidase and lanthanum. These junctions are morphologically distinguishable from the "labile" pentalaminar appositions which appear or disappear according to the preparative method and which do not interfere with the intercellular movement of tracers. Therefore, the interspaces of the brain are generally patent, allowing intercellular movement of colloidal materials. Endothelial and epithelial tight junctions occlude the interspaces between blood and parenchyma or cerebral ventricles, thereby constituting a structural basis for the blood-brain and blood-cerebrospinal fluid barriers.
Horseradish peroxidase was administered to mice by intravenous injection, and its distribution in cerebral cortex studied with a recently available technique for localizing peroxidase with the electron microscope. Brains were fixed by either immersion or vascular perfusion 10-60 min after administration of various doses of peroxidase. Exogenous peroxidase was localized in the lumina of blood vessels and in some micropinocytotic vesicles within endothelial cells; none was found beyond the vascular endothelium. Micropinocytotic vesicles were few in number and did not appear to transport peroxidase while tight junctions between endothelial cells were probably responsible for preventing its intercellular passage. Our findings therefore localize, at a fine structural level, a "barrier" to the passage of peroxidase at the endothelium of vessels in the cerebral cortex. The significance of these findings is discussed, particularly with reference to a recent study in which similar techniques were applied to capillaries in heart and skeletal muscle.
Neuropathologic studies of AIDS patients have shown that brain capillary endothelial cells are a cellular target for human immunodeficiency virus (HIV) in vivo. We have established in vitro cultures of primary human brain capillary endothelial (HBCE) cells. Using this model system, we have shown a significant HIV infection of HBCE cells that is productive yet noncytopathic. The infection is mediated by a cellular interaction with gp120 that does not involve CD4 or galactosylceramide. HIV infection of HBCE cells may contribute to AIDS-associated neuropathology by disturbing the physiology of the endothelium and directly or indirectly facilitating dissemination of virus to the central nervous system.
As both astrocytes and cytokines modulate the permeability of cerebral endothelial cells, transgenic animal models which overexpress cytokines, such as interleukin-6 (IL-6), may provide insight into the neuropathological consequences of increased BBB permeability. In this study, a GFAP-IL6 transgenic mouse model and horseradish peroxidase (HRP) were used to investigate BBB permeability and associated neuropathologic changes. In the cerebellum of control mice, the BBB developed between postnatal days 7 and 14. In transgenic mice, the BBB never developed and extensive breakdown was evident in both high- and low-expressor animals by 1 month after birth. Vascular proliferation was apparent from birth in association with development and retention of normal cerebellar architecture until 3 and 6 months in high- and low-expressor animals, respectively. At these times, a leptomeningeal inflammatory infiltrate, vacuolated astrocytic foot processes and endothelial abnormalities were apparent in the cerebellum. At 6 months in high-expressor and 12 months in low-expressor animals, parenchymal inflammation, gliosis, spongiform change, axonal degeneration and macrophage accumulation were evident. The findings suggest that increased production of IL-6 can influence the development and physiologic function of the BBB as well as contribute to parenchymal central nervous system injury.
We measured serum and CSF 2-microglobulin (2M) levels in HIV-1 seropositive individuals with and without dementia to determine the frequency and diagnostic utility of elevation of CSF 2M. We compared 34 samples from 27 patients with HIV-1 dementia with 110 samples from 54 HIV-1 seropositive participants in the Multicenter AIDS Cohort Study, none of whom had progressive dementia. Neurosyphilis and CNS opportunistic pro-cesses were excluded in all subjects. We stratified the nondemented subjects by duration of HIV seropositivity and peripheral blood CD4 count. Compared with the nondemented group, demented subjects had significantly higher CSF total protein, IgG%, and CSF albumin/serum albumin ratios. A highly significant association was found between ele-vated CSF 2M and reduced CD4 count (p < 0.0001). No significant differences were noted between the demented and nondemented groups in CSF WBC count or in the frequency of CSF HIV-1 isolation. The mean CSF 2M was 1.9 mg/1 in the nondemented subjects compared with 4.2 mg/1 in those with dementia (p < 0.0001). We derived a cutoff of 3.8 mg/1 from the distribution of CSF 2M in the nondemented group. The determination of CSF 2M had a sensitivity of 44%, specificity of 90%, and a positive predictive value of 88% for diagnosis of HIV dementia when compared with non-demented subjects with CD4 counts <200. In those without dementia, there was a strong correlation between serum and CSF 2M (r = 0.50, p < 0.0001), but in demented subjects CSF 2M was elevated independently of serum levels, suggesting that CSF 2M is produced within the brain in HIV dementia. In the absence of CNS opportunistic process-es, elevated CSF 2M >3.8 mg/1 is a clinically useful marker for HIV dementia.
Patients with the acquired immunodeficiency syndrome (AIDS) are subject to a spectrum of central nervous system (CNS) disorders. Recent evidence implicates the human T-cell lymphotropic virus type III (HTLV-III) in the pathogenesis of some of these illnesses, although the cells infected by the virus have yet to be identified. Using in situ hybridization, we examined brain tissue from two patients with AIDS encephalopathy for the presence of HTLV-III RNA. In both cases, viral RNA was detected and concentrated in, though not limited to, the white matter. The CNS cells most frequently infected included macrophages, pleomorphic microglia, and multinucleated giant cells. Less frequently, cells morphologically consistent with astrocytes, oligodendroglia, and rarely neurons were also infected. The findings strengthen the association of HTLV-III with the pathogenesis of AIDS encephalopathy. In situ hybridization can be applied to routinely prepared biopsy tissue in the diagnosis of HTLV-III infection of the CNS.
(JAMA 1986;256:2360-2364)
As both astrocytes and cytokines modulate the permeability of cerebral endothelial cells, transgenic animal models which overexpress cytokines, such as interleukin-6 (IL-6), may provide insight into the neuropathological consequences of increased BBB permeability. In this study, a GFAP-IL6 transgenic mouse model and horseradish peroxidase (HRP) were used to investigate BBB permeability and associated neuropathologic changes. In the cerebellum of control mice, the BBB developed between postnatal days 7 and 14. In transgenic mice, the BBB never developed and extensive breakdown was evident in both high- and low-expressor animals by 1 month after blah. Vascular proliferation was apparent from birth in association with development and retention of normal cerebellar architecture until 3 and 6 months in high- and low-expressor animals, respectively. At these times, a leptomeningeal inflammatory infiltrate, vacuolated astrocytic foot processes and endothelial abnormalities were apparent in the cerebellum. At 6 months in high-expressor and 12 months in low-expressor animals, parenchymal inflammation, gliosis, spongiform change, axonal degeneration and macrophage accumulation were evident. The findings suggest that increased production of IL-6 can influence the development and physiologic function of the BBB as well as contribute to parenchymal central nervous system injury.
Discusses the neurologic, neuropsychological, and psychiatric aspects of central nervous system (CNS) illness associated with HIV infection. Proposed nomenclature for these CNS disorders is listed, along with the terms currently used for the same disorders. Clinical criteria for diagnosis in adolescents and adults are outlined. The major differences between clinical features of dementia complex associated with HIV-1 and HIV-1-associated minor cognitive/motor disorder are discussed. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
In human immunodeficiency virus 1 (HIV-1)-infected patients, a hypoperfusion is seen by SPECT analyses in different brain
regions but a specific pattern for the predominance of a specific brain region has not been found. The vessels of the cerebral
cortex of the frontal, temporal, parietal, and occipital lobes of acquired immunodeficiency syndrome (AIDS) brains and control
brains were analyzed by immunohistochemistry and lectin histochemistry. Immunohistochemistry was performed for collagen IV,
laminin (basal lamina), and factor VIII (endothelial cell) and lectin histochemistry [Ricinus communis agglutinin (RCA-I), Ulex europaeus agglutinin (UEA-I), wheatgerm agglutinin (WGA) and soybean agglutinin (SBA)] was used to study changes of glycoproteins in
the endothelial cell membrane. Vessels were counted in the gray and white matter, and their staining intensity for the different
antibodies and lectins was rated using a three-point scale. Immunoreactivity for collagen IV was reduced in AIDS brains, which
may be related to thinning of the basal lamina of cerebral vessels, as has previously been shown by electron microscopy. Lectin
histochemistry with SBA, UEA-I and WGA indicated loss of glycoproteins in the membrane of endothelial cells. The data from
the present study show morphological changes of the endothelial cells and of the basal lamina in the brain of individuals
with AIDS, and might represent the morphological sequelae of a disturbed blood-brain barrier, or may account for the hypoperfusion
seen in SPECT analyses.
Primary cultures of human embryonic neurons and astrocytes have been used to test the interactions between neural cells and either human immunodeficiency virus type 1 (HIV-1) or HIV-1-infected monocytes. After direct infection with HIV-1, neither morphological alteration of neurons and astrocytes nor signs of viral replication were observed. Similarly, cultured human neurons and astrocytes were resistant to incubation with the supernatant of HIV-1-infected U937 cells, a human monoblastoid cell line. In contrast, HIV-1-infected U937 monocytic cells adhered to neural cells and induced large plaques of necrosis surrounding them. This cytopathic effect began at the time of viral replication (day 16 after infection). Its intensity depended on that of viral replication, and its range was identical to the region of diffusion of viral antigens, as judged by immunocytochemistry. The cytopathic effect was not dependent on the release of free radicals. It could not be induced by cytokines or cytokine-stimulated U937 cells. It is likely that this cytopathic effect depends on the release of viral antigens either within the site of adherence itself or within close range of the astrocyte membrane.
We measured serum and CSF beta 2-microglobulin (beta 2M) levels in HIV-1 seropositive individuals with and without dementia to determine the frequency and diagnostic utility of elevation of CSF beta 2M. We compared 34 samples from 27 patients with HIV-1 dementia with 110 samples from 54 HIV-1 seropositive participants in the Multicenter AIDS Cohort Study, none of whom had progressive dementia. Neurosyphilis and CNS opportunistic processes were excluded in all subjects. We stratified the nondemented subjects by duration of HIV seropositivity and peripheral blood CD4 count. Compared with the nondemented group, demented subjects had significantly higher CSF total protein, IgG%, and CSF albumin/serum albumin ratios. A highly significant association was found between elevated CSF beta 2M and reduced CD4 count (p less than 0.0001). No significant differences were noted between the demented and nondemented groups in CSF WBC count or in the frequency of CSF HIV-1 isolation. The mean CSF beta 2M was 1.9 mg/l in the nondemented subjects compared with 4.2 mg/l in those with dementia (p less than 0.0001). We derived a cutoff of 3.8 mg/l from the distribution of CSF beta 2M in the nondemented group. The determination of CSF beta 2M had a sensitivity of 44%, specificity of 90%, and a positive predictive value of 88% for diagnosis of HIV dementia when compared with nondemented subjects with CD4 counts less than 200. In those without dementia, there was a strong correlation between serum and CSF beta 2M (r = 0.50, p less than 0.0001), but in demented subjects CSF beta 2M was elevated independently of serum levels, suggesting that CSF beta 2M is produced within the brain in HIV dementia. In the absence of CNS opportunistic processes, elevated CSF beta 2M greater than 3.8 mg/l is a clinically useful marker for HIV dementia.
Abnormalities in the blood-brain barrier (BBB) may be important in mediating some of the tissue damage that accompanies human immunodeficiency virus (HIV) infection of the brain, as well as in facilitating viral entry into the central nervous system. Accordingly, immunohistochemical detection of fibrinogen (FIB) and immunoglobulin G (IgG) was used as a marker of vascular permeability in formalin-fixed, paraffin-embedded brains of patients with acquired immunodeficiency syndrome (AIDS) who had HIV encephalitis (HIVE) (n = 17) and those who did not have HIVE (n = 16); nonimmunosuppressed patients served as control subjects (n = 22). The sex ratios and postmortem intervals were similar in all groups (p > 0.05), but the age of the two AIDS groups were younger than the control group (43.2 and 40.9 versus 62.5 yr; p < 0.05). The two AIDS groups had higher immunostaining for FIB and IgG than the control group (p < 0.001 and p < 0.0001, respectively) but did not differ from one another. Furthermore, the two AIDS groups had a significantly higher incidence of combined extravasation of both FIB and IgG, whereas the control group had a significantly higher incidence of negative staining for both proteins (p < 0.002). More than 95% of the microglial nodules of HIV were negative for serum proteins; however, all focal lesions with tissue necrosis, including lymphoma, opportunistic infections, and HIV (rarely), contained extravasated serum proteins.(ABSTRACT TRUNCATED AT 250 WORDS)
Neuropathology has defined novel HIV-specific diseases at tissue level: HIV encephalitis and HIV leukoencephalopathy. Both occur usually in the later stages of the AIDS infection and consistently demonstrate large amounts of HIV products. In contrast to this HIV-specific neuropathology, HIV-associated neuropathology features unspecific syndromes with disputed relation to HIV infection: myelin pallor, vacuolar myelopathy, vacuolar leukoencephalopathy, lymphocytic meningitis, and diffuse poliodystrophy. All types of neuropathology may contribute to clinical manifestation according to severity, extent, and distribution of lesions, but clinico-pathologic correlation may be poor in the individual case. Neuropathologic and other data suggest two major pathogenetic pathways of HIV-associated CNS damage: First, systemic and local increase of the virus load leads to HIV encephalitis or HIV leukoencephalopathy; this is corroborated by prominent HIV production within such lesions. Second, neuronotoxicity by HIV proteins or factors secreted from infected cells is supported by histological changes of diffuse poliodystrophy and by morphometric loss of frontocortical neurons.
Over a 2 year period, 124 neurologically normal HIV-1-infected patients had three successive cerebrospinal fluid (CSF) examinations approximately 1 year apart. Immunological status as measured by absolute CD4 counts in the blood identified two groups of patients over time: (a) a group with progressive CD4 decline (66 patients), and (b) a group with stable CD4 counts (58 patients). These two study groups provided us the opportunity to compare CSF changes (cells, protein, albumin index, IgG, IgG index, and IgG synthesis rate) in neurologically normal individuals with respect to immunological status over time. We found significantly increased intrathecal cellular response and IgG production over time independent of CD4 group. We conclude that any clinical study comparing CSF findings in neurologically symptomatic HIV-infected individuals must recognize and control for these CSF changes in neurologically asymptomatic patients.
Clinical and pathological evidence of subcortical central nervous system (CNS) damage is observed commonly in patients with human immunodeficiency virus (HIV) encephalitis. Whether other CNS regions are also affected has not been well studied. We report neocortical damage in patients with HIV encephalitis. Using quantitative techniques, we demonstrate statistically significant thinning of the neocortex, with a loss of large cortical neurons. Qualitative and quantitative assessments of neocortical neuropil reveal a loss of synaptic density and vacuolation of dendritic processes. Failure to demonstrate an association of these changes with the presence of HIV antigens suggests that neocortical damage may be an indirect effect of HIV infection of the CNS.
Continuous tight junctions between vascular endothelial cells, the principal anatomical basis for the blood-brain barrier, have been investigated functionally and morphologically but their molecular components have not been defined. This communication reports that the protein ZO-1, a specific constituent of epithelial tight junctions, is found in human and rat brain vasculature. ZO-1-positive immunocytochemical staining forms a tightly banded pattern outlining individual endothelial cells in blood vessels of the human cerebral cortex. Rat brain exhibits a similar staining of blood vessels as well as ZO-1-positive staining around individual epithelial cells of the choroid plexus. The antiserum used for immunocytochemistry recognizes a protein of about 200 kDa in rat brain microvessels by Western blot. These findings indicate that ZO-1 is located at the interendothelial junctions of brain vasculature, implicating its importance as a component of the blood-brain barrier.
Lesions of the central nervous system (CNS) in 23 patients with the acquired immunodeficiency syndrome (AIDS) were compared with control cases for the presence of serum protein by immunoperoxidase staining. A sensitive immunostaining kit in conjunction with rabbit antisera to human serum, albumin, immunoglobulins and complement component 3c was used to demonstrate specific immunoreactivity in paraffin-embedded sections. Most AIDS patients with CNS lesions had serum protein immunoreactivity in some neurons, glial cells (including astrocytes), gliomesenchymal cell nodules, vascular endothelial cells, inflammatory cells or microvascular walls. Cases with the most necrosis tended to have the least immunostaining. Immunoreactivity for IgG and fixed complement in anatomically intact or morphologically altered neural cells may indicate cellular lesions and potential cellular necrosis beyond the damage indicated by routine studies alone. Part of this immunoreactivity might represent a humoral autoimmune response.
Mononuclear phagocytes (microglia, macrophages, and macrophage-like giant cells) are the principal cellular targets for human
immunodeficiency virus-1 (HIV-1) in the central nervous system (CNS). Since HIV-1 does not directly infect neurons, the causes
for CNS dysfunction in acquired immunodeficiency syndrome (AIDS) remain uncertain. HIV-1-infected human monocytoid cells,
but not infected human lymphoid cells, released toxic agents that destroy chick and rat neurons in culture. These neurotoxins
were small, heat-stable, protease-resistant molecules that act by way of N-methyl-D-aspartate receptors. Macrophages and microglia
infected with HIV-1 may produce neurologic disease through chronic secretion of neurotoxic factors.
In order to determine if brain perfusion abnormalities, which are known in patients with acquiredimmunodeficiency syndrome dementia, occur in early stages of human immunodeficiency virus infection, technetium 99m hexamethyl-propyleneamine oxime-single-photon emission computed tomography studies were performed in 20 patients infected with human immunodeficiency virus who belonged to Walter Reed stages I through IV. None of these patients demonstrated signs of dementia or severe neurological dysfunction. Pathological patterns of hexamethyl-propyleneamine oxime uptake were seen in 14 patients, seven of whom had normal results during neurological examination. Only four patients had signs of cerebral atrophy on cranial computed tomographic scan. These data suggest that subtle changes in cerebral perfusion seem to arise early in the course of human immunodeficiency virus infection and may indicate human immunodeficiency virus encephalopathy before neurological symptoms or noticeable structural damage occurs.
The appearance on magnetic resonance (MR) and computed tomographic (CT) images of specific central nervous system disorders associated with acquired immunodeficiency syndrome in 12 cases was correlated with autopsy findings. There were three cases of human immunodeficiency virus (HIV) encephalopathy; three, primary lymphoma; three, toxoplasmosis; one, cryptococcosis; one, cytomegalovirus infection; and one, progressive multifocal leukoencephalopathy. MR imaging demonstrated the various cranial lesions more clearly than did CT. On the basis of MR imaging characteristics, HIV encephalopathy could be distinguished from other lesions, particularly progressive multifocal leukoencephalopathy. Basal ganglia were the most common sites of involvement in opportunistic infections and primary lymphoma. Reliable distinguishing features among lesions of the basal ganglia were not found, except for cryptococcal lesions, which had a unique appearance.
We studied the brains of three patients with acquired immune deficiency syndrome (AIDS), all of whom developed subacutely progressive dementia unassociated with opportunistic infection or neoplasm in the central nervous system. Computed tomographic (CT) scans of the head revealed cortical atrophy, ventricular dilation, and diffuse hypodensity of the centrum semiovale. On microscopic examination, the cerebral and cerebellar white matter in all cases showed diffuse and focal, angiocentric regions of myelin pallor, focal vacuolization, and extensive gliosis. Variable axonal loss and axonal spheroids were evident. The microvasculature showed striking changes, including mural thickening, increased cellularity, and enlargement and pleomorphism of endothelial cells with variable numbers of macrophages and multinucleated giant cells (MNGC), which often contained hemosiderin pigment. Human immunodeficiency virus type 1 (HIV-1) antigens were identified immunocytochemically within perivascular macrophages and MNGC and in some microglial cells. We suggest that the morphologic abnormalities of the microcirculation may be associated with an alteration of the blood-brain barrier. The increased vascular permeability could contribute to damage and loss of the white matter including both myelin and axons, and result in subcortical cerebral atrophy. The HIV-1 infected cells present in relation to the microvasculature may play a role in mediating the vascular injury.
Visna virus is the prototype of the lentivirus subfamily of retroviruses that cause slow infections of sheep and goats. These viruses persist and can be isolated from blood and cerebrospinal fluid for years despite neutralizing antibody. In the studies reported here we have used quantitative in situ hybridization to analyze infected leukocytes. We show that (1) monocytes harbor the visna genome; and (2) virus gene expression is as constrained in this cell as it is in glial and epithelial cells. These results are in accord with a Trojan Horse mechanism of virus dissemination in an immunologically responsive host.
In order to define the histopathological substrate of the dementia that frequently complicates the acquired immune deficiency syndrome (AIDS), we analyzed the neuropathological findings in 70 autopsied adult AIDS patients, 46 of whom had suffered clinically overt dementia. Less than 10% of the brains were histologically normal. Abnormalities were found predominantly in the white matter and in subcortical structures, with relative sparing of the cortex. Their frequency and severity generally correlated well with the degree and duration of clinical dementia. Most commonly noted was diffuse pallor in the white matter, which in the pathologically milder cases was accompanied by scanty perivascular infiltrates of lymphocytes and brown-pigmented macrophages, and in the most advanced cases by clusters of foamy macrophages and multinucleated cells associated with multifocal rarefaction of the white matter. However, in nearly one third of the demented cases the histopathological findings were remarkably bland in relation to the severity of clinical dysfunction. In addition, similar mild changes were noted in over one half of the nondemented patients, consistent with subclinical involvement. Vacuolar myelopathy was found in 23 patients and was generally more common and severe in patients with advanced brain pathology. Evidence of cytomegalovirus (CMV) infection was noted in nearly one quarter of the brains and was associated with a relative abundance of microglial nodules, but correlated neither with the major subcortical neuropathology nor with the clinical dementia, indicating that CMV infection likely represented a second, superimposed process. This study establishes the AIDS dementia complex as a distinct clinical and pathological entity and, together with accumulating virological evidence, suggests that it is caused by direct LAV/HTLV-III brain infection.
One of the common neurological complications in patients with the acquired immune deficiency syndrome (AIDS) is a subacute
encephalopathy with progressive dementia. By using the techniques of cocultivation for virus isolation, in situ hybridization,
immunocytochemistry, and transmission electron microscopy, the identity of an important cell type that supports replication
of the AIDS retrovirus in brain tissue was determined in two affected individuals. These cells were mononucleated and multinucleated
macrophages that actively synthesized viral RNA and produced progeny virions in the brains of the patients. Infected brain
macrophages may serve as a reservoir for virus and as a vehicle for viral dissemination in the infected host.
A review of the magnetic resonance (MR) images of 365 patients with acquired immunodeficiency syndrome (AIDS) revealed that 112 (31%) had signal abnormalities confined to the white matter. Four patterns were observed: (a) diffuse: widespread involvement of a large area; (b) patchy: localized involvement with ill-defined margins; (c) focal: well-defined areas of involvement; and (d) punctate: small foci less than 1 cm in diameter. Clinical or pathologic findings were available in 60 of the 112 patients and were correlated with the white matter patterns seen on MR images. The diffuse pattern correlated with AIDS dementia complex (ADC), which was the most common clinical diagnosis. Patchy or punctate lesions may be seen with ADC but are less common. Focal white matter lesions were not seen in patients with ADC but were seen in all six patients with progressive multifocal leukoencephalopathy, in both patients with lymphoma, and in one patient with toxoplasmosis. The authors conclude that white matter lesions are are common in AIDS and are often secondary to direct infection of the brain with human immunodeficiency virus, which causes the ADC and usually produces a diffuse white matter pattern. Biopsy is probably not indicated in these patients. Focal white matter lesions suggest a focal infection or tumor, and biopsy may be warranted.
The highly impermeable tight junctions between endothelial cells forming the capillaries and venules in the central nervous system (CNS) of higher vertebrates are thought to be responsible for the blood-brain barrier that impedes the passive diffusion of solutes from the blood into the extracellular space of the CNS. The ability of CNS endothelial cells to form a blood-brain barrier is not intrinsic to these cells but instead is induced by the CNS environment: Stewart and Wiley demonstrated that when avascular tissue from 3-day-old quail brain is transplanted into the coelomic cavity of chick embryos, the chick endothelial cells that vascularize the quail brain grafts form a competent blood-brain barrier; on the other hand, when avascular embryonic quail coelomic grafts are transplanted into embryonic chick brain, the chick endothelial cells that invade the mesenchymal tissue grafts form leaky capillaries and venules. It is, however, not known which cells in the CNS are responsible for inducing endothelial cells to form the tight junctions characteristic of the blood-brain barrier. Astrocytes are the most likely candidates since their processes form endfeet that collectively surround CNS microvessels. In this report we provide direct evidence that astrocytes are capable of inducing blood-brain barrier properties in non-neural endothelial cells in vivo.
Patients with the acquired immunodeficiency syndrome (AIDS) are subject to a spectrum of central nervous system (CNS) disorders. Recent evidence implicates the human T-cell lymphotropic virus type III (HTLV-III) in the pathogenesis of some of these illnesses, although, the cells infected by the virus have yet to be identified. Using in situ hybridization, we examined brain tissue from two patients with AIDS encephalopathy for the presence of HTLV-III RNA. In both cases, viral RNA was detected and concentrated in, though not limited to, the white matter. The CNS cells most frequently infected included macrophages, pleomorphic microglia, and multinucleated giant cells. Less frequently, cells morphologically consistent with astrocytes, oligodendroglia, and rarely neurons were also infected. The findings strengthen the association of HTLV-III with the pathogenesis of AIDS encephalopathy. In situ hybridization can be applied to routinely prepared biopsy tissue in the diagnosis of HTLV-III infection of the CNS.
Of 70 autopsied patients with the acquired immune deficiency syndrome (AIDS), 46 suffered progressive dementia that was frequently accompanied by motor and behavioral dysfunction. Impaired memory and concentration with psychomotor slowing represented the most common early presentation of this disorder, but in nearly one half of the patients either motor or behavioral changes predominated. Early motor deficits commonly included ataxia, leg weakness, tremor, and loss of fine-motor coordination, while behavioral disturbances were manifested most commonly as apathy or withdrawal, but occasionally as a frank organic psychosis. The course of the disease was steadily progressive in most patients, and at times was punctuated by an abrupt acceleration. However, in 20% of patients a more protracted indolent course was observed. In the most advanced stage of this disease, patients exhibited a stereotyped picture of severe dementia, mutism, incontinence, paraplegia, and in some cases, myoclonus. The high incidence and unique clinical presentation of this AIDS dementia complex is consistent with the emerging concept that this complication is due to direct brain infection by the retrovirus that causes AIDS.
The ultrastructural features that are critical to the efficient functioning of the blood-brain barrier (b-bb) were quantified in typical barrier vessels, i.e., cerebral gray and white matter capillaries, and compared with the same parameters in cerebral nonbarrier capillaries (area postrema), and in somatic capillaries, (muscle) of the mouse. The image analysis was done with the help of a simple, rapid system that required only a digitized bit pad and a microcomputer. We found that: (1) The number of pinocytotic vesicles that are thought to be associated with vascular permeability was three times higher in area postrema vessels and nearly seven times higher in muscle vessels than in barrier vessels. (2) A percentage of interendothelial junctions in nonbarrier capillaries displayed areas of separation that may represent interendothelial channels coursing from the luminal to the abluminal surface between areas of tight junctional complexes. Such areas were not observed in barrier capillaries under the normal conditions studied here, but have been seen by others under conditions in which the barrier has been breached. (3) A 39% decrease in wall thickness in barrier capillaries. (4) No differences in mitochondrial density or in area of associated pericytes among capillaries from any region. Therefore we have questioned both the universality of the apparently increased metabolic work capacity of barrier capillaries, and whether pericytes play any role in the barrier under normal conditions.
It has been postulated that the retrovirus HTLV-III/LAV thought to be the etiologic agent of AIDS also infects the central nervous system and directly causes AIDS encephalopathy. Electron microscopical studies performed on brain sections from three patients with AIDS complicated by progressive encephalopathy revealed structures morphologically consistent with HTLV-III/LAV retrovirus particles. The particles were located principally within multinucleated giant cells but were also present in astrocytes. Many particles were also noted in the extracellular space.
Osmotic opening of the blood-brain barrier had no effect on the structure of the interendothelial tight junctions located within approximately 9 micron 2 of brain capillary endothelial plasma membrane (junction-containing) examined in this study. These tight junctions restrict the passive diffusion between the blood and the brain and constitute the anatomic basis of the blood-brain barrier. Increased permeability of the blood-brain barrier in the cerebral cortex of the right hemisphere of rats, induced by an infusion of a hypertonic solution of arabinose and monitored with the protein tracer horseradish peroxidase (HRP), was evidenced by the extravasation of the tracer into the extracellular compartment of the brain. Freeze-fracture analysis of the capillaries from the same tissue revealed no alterations in the intramembrane components of the endothelial tight junctions. The junctions, which consist of 8-12 highly anastomosed parallel ridges situated on the PF fracture face of the endothelial plasmalemma, showed no loss of ridge continuity or intra-ridge connections, and were identical to zonulae occludentes from control capillaries. Consistent labeling of numerous vesiculo-tubular elements by HRP in the endothelia of experimental tissue and the three-dimensional nature of these elements observed in platinum replicas support the interpretation that these structures represent transendothelial conduits which are continuous with the luminal and abluminal surfaces of the endothelial cells. Absence of similar structures in control endothelia is taken as evidence that their presence in experimental tissues is a direct response to the osmotic insult. It was concluded, therefore, that during osmotic opening of the blood-brain barrier passage of HRP across the endothelium of brain capillaries is not by an inter-endothelial route due to disruption of tight junctions but rather by a transendothelial route due to amplified vesicular activity.
The pathogenesis of human immunodeficiency virus (HIV)-associated dementia is unclear, and the underlying pathological substrate has been a matter of debate. In a prospectively clinically characterized population of acquired immunodeficiency syndrome (AIDS) patients we investigated the relationship between the clinical syndrome of HIV-associated dementia and the presence and relative quantity of immunocytochemical markers for HIV-1 (gp41 antibody), and for macrophages and microglia (HAM-56 antibody). Sections from the basal ganglia and frontal lobes from the brains of 51 patients were studied, and the data were stratified for severity of dementia (16 nondemented, 12 mildly demented, 23 severely demented), rate of dementia progression, duration of AIDS, use of antiretrovirals, and several other demographic features. We found a highly significant correlation between the degree of macrophage staining and the severity of dementia but only a borderline correlation between the presence and amount of gp41-positive cells and dementia. Several nondemented patients showed abundant gp41 immunoreactivity, and some severely demented showed little to no gp41 immunoreactivity. Other correlations with the immunostaining data, including antiretroviral use, were not significant. We conclude that the presence of macrophages and microglia is a better correlate with HIV-associated dementia than is the presence and amount of HIV-infected cells in the brain. These data support the concept that the pathogenesis of HIV-associated dementia is likely due to indirect effects of HIV infection of the brain, possibly through the actions of macrophages and microglia.
Infection of the brain with human immunodeficiency virus 1 (HIV-1) often leads to the devastating loss of mental faculties. Surprisingly, HIV-1 elicits such brain dysfunction without significantly infecting neurons, astrocytes and oligodendroglia. The target for HIV-1 in the brain is the macrophage, which usually functions as a phagocytic, antigen-presenting and immune-regulatory cell. How can these cells produce such serious cognitive and motor brain impairments? Here, Hans Nottet and Howard Gendelman propose that HIV-1 penetrates the blood-brain barrier inside differentiating macrophages, which become immune activated once inside the brain, and secrete high levels of neurotoxins. Chronic, subclinical disease results by astrocyte regulation of macrophage effector functions. Ultimately, endogenous control mechanisms break down, leading to motor and mental impairments in some affected subjects.
We previously reported the expression of ZO-1 in cell types that do not form tight junctions. Here we compare the molecular environments of ZO-1 in epithelial cells, primary cultures of astrocytes and in the non-epithelial S180 sarcoma cell line. ZO-1 co-localizes with a subset of actin filaments in all cell types. In astrocytes, ZO-1 is found concentrated in discrete bands at points of cell-cell contact. Indirect immunofluorescent microscopy shows that these bands of ZO-1 co-localize with the adherens junction proteins vinculin and alpha-actinin, and with the antigen recognized by a pan-cadherin antibody. In contrast, ZO-1 in S180 cells, which exhibit limited cell-cell interactions, is diffusely distributed over the plasma membrane, with concentrations in lamellipodia where actin filaments accumulate. ZO-1 does not co-localize with vinculin at focal adhesions in this cell type. Analysis of ZO-1 immunoprecipitation profiles from different cell types, performed under conditions previously demonstrated to maintain interactions between ZO-1, ZO-2 and p130 from the MDCK epithelial cell line, show that the proteins which co-precipitate with ZO-1 vary with cell type. Precipitation of polypeptides at 165 kDa, potentially ZO-2, and 65 kDa occurs in both a mouse kidney tubule epithelial cell line and the non-epithelial S180 cells. No proteins specifically associate with ZO-1 immunoprecipitated from astrocytes. Spectrin, alpha-actinin, vinculin and cadherin are not detected in immunoblots of ZO-1 immunoprecipitates from any cell type.
HIV-1-associated dementia occurs in approximately one third of individuals infected with HIV-1, sometimes as the only presenting symptom (McArthur et al. 1994; for refinement of this number see Grant et al., this volume). It involves deficits in cognitive and higher motor functions. The dementia is linked to structural changes in neurons observed post mortem. The changes vary from dendritic dearborization to neuronal drop out (Masliah et al. 1992). Large pyramidal neurons especially vulnerable to as yet unknown pathogenic stimuli are located in the cerebral cortex. The cortex is the brain region known to control cognitive and motor functions. These functions are altered or deficient in AIDS patients. Thus, neuronal dysfunction is a likely direct cause of HIV-1-associated dementia. The precise cause and nature of neuronal dysfunction in AIDS are unknown. HIV-1-associated neuronal damage may be mediated by activation of one family of glutamate receptors (Lipton 1992). Glutamate is the major excitatory neurotransmitter in the brain. Glutamate receptor-mediated neuronal death—excitotoxicity—is implicated in the pathogenesis of several disorders affecting mental health such as Alzheimer’s dementia (Choi 1994).
The cause of acquired immunodeficiency syndrome (AIDS) dementia, which is a frequent late manifestation of human immunodeficiency virus (HIV) infection, is unknown but radiological and pathological studies have implicated alterations in subcortical white matter. To investigate the pathological basis of these white matter abnormalities, we performed an immunocytochemical and histological analysis of subcortical white matter from AIDS patients with and without dementia, from pre-AIDS patients (asymptomatic HIV-seropositive patients), and from HIV-seronegative control subjects. Reduced intensity of Luxol fast blue staining, designated "diffuse myelin pallor," was detected in 8 of 15 AIDS dementia patients, 3 of 13 AIDS nondemented patients, and none of the pre-AIDS patients (n = 2) or control subjects (n = 9). In contrast to Luxol fast blue staining, sections stained immunocytochemically for myelin proteins did not show decreased staining intensities in regions of diffuse myelin pallor. In addition, neither demyelinated axons nor active demyelination were detected in light and electron micrographs of subcortical white matter from brains of patients with AIDS dementia. An increase in the number of perivascular macrophages and hypertrophy of astrocytes and microglia occurred in brain sections from HIV-infected patients. These changes were not specific to dementia or regions of diffuse myelin pallor and they occurred in both gray and white matter. In contrast to the lack of myelin pathology in AIDS dementia brains, significant accumulations of serum proteins in white matter glia were detected in the brains of 12 of 12 patients with AIDS dementia and 6 of 12 AIDS patients without dementia. Serum protein-immunopositive cortical neurons were detected in the frontal cortex of 11 of 12 patients with AIDS dementia and 3 of 12 nondemented AIDS patients. Seronegative control subjects showed minimal serum protein immunoreactivity in both cortex and white matter. We conclude therefore that alterations in the blood-brain barrier and not demyelination contribute to the development of AIDS dementia.
We examined the ability of human immunodeficiency virus (HIV) type 1 (HIV-1) to infect in vitro, primary brain-derived human microvascular endothelial cells (HMEC) that constitute the blood-brain barrier (BBB). Immunofluorescence (IFA) and antigen capture assays failed to demonstrate p24 antigen from HIV inoculated endothelial cells and supernatants did not contain detectable levels of reverse transcriptase (RT). HIV could be rescued by cocultivation of infected HMEC with a susceptible T-lymphocyte line (CEM-SS), which were then shown to form syncytia and produce RT activity and p24 Ag (IFA, antigen captive assay). Polymerase chain reaction (PCR) was successfully used to amplify HIV-specific gag and env gene sequences from HMEC. CD4 expression was not identified on these cells by IFA. These results suggest that HIV infection of BBB endothelium occurs, but that viral replication is minimal. Infection of the BBB by HIV may give the virus a foothold in the CNS and suggests that the brain might be infected directly and may not be limited to just the passage of infected mononuclear cells.
Human immunodeficiency virus type 1 (HIV-1) sequences were generated from blood and from brain tissue obtained by stereotactic biopsy from six patients undergoing a diagnostic neurosurgical procedure. Proviral DNA was directly amplified by nested PCR, and 8 to 36 clones from each sample were sequenced. Phylogenetic analysis of intrapatient envelope V3-V5 region HIV-1 DNA sequence sets revealed that brain viral sequences were clustered relative to the blood viral sequences, suggestive of tissue-specific compartmentalization of the virus in four of the six cases. In the other two cases, the blood and brain virus sequences were intermingled in the phylogenetic analyses, suggesting trafficking of virus between the two tissues. Slide-based PCR-driven in situ hybridization of two of the patients' brain biopsy samples confirmed our interpretation of the intrapatient phylogenetic analyses. Interpatient V3 region brain-derived sequence distances were significantly less than blood-derived sequence distances. Relative to the tip of the loop, the set of brain-derived viral sequences had a tendency towards negative or neutral charge compared with the set of blood-derived viral sequences. Entropy calculations were used as a measure of the variability at each position in alignments of blood and brain viral sequences. A relatively conserved set of positions were found, with a significantly lower entropy in the brain-than in the blood-derived viral sequences. These sites constitute a brain "signature pattern," or a noncontiguous set of amino acids in the V3 region conserved in viral sequences derived from brain tissue. This brain-derived signature pattern was also well preserved among isolates previously characterized in vitro as macrophage tropic. Macrophage-monocyte tropism may be the biological constraint that results in the conservation of the viral brain signature pattern.