G I Liou

Georgia Regents University, Augusta, Georgia, United States

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Publications (91)367.66 Total impact

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    ABSTRACT: Adenosine provides anti-inflammatory effects in cardiovascular disease via the activation of adenosine A2A receptors; however, the physiological effect of adenosine could be limited due to its phosphorylation by adenosine kinase. We hypothesized that inhibition of adenosine kinase exacerbates extracellular adenosine levels to reduce renal inflammation and injury in streptozotocin-induced diabetes. Diabetes was induced in male C57BL/6 mice by daily injection of streptozotocin (50mg/kg/day, i.p. for 5 days). Control and diabetic mice were then treated with the adenosine kinase inhibitor ABT702 (1.5mg/kg, i.p two times a week for 8 weeks, n=7-8/group) or the vehicle (5% DMSO). ABT702 treatment reduced blood glucose level in diabetic mice (∼ 20%; p<0.05). ABT702 also reduced albuminuria and markers of glomerular injury, nephrinuria and podocalyxin excretion levels, in diabetic mice. Renal NADPH oxidase activity and urinary thiobarbituric acid reactive substances (TBARS) excretion, indices of oxidative stress, were also elevated in diabetic mice and ABT702 significantly reduced these changes. ABT702 increased renal endothelial nitric oxide synthase expression (eNOS) and nitrate/nitrite excretion levels in diabetic mice. In addition, the diabetic mice displayed an increase in renal macrophage infiltration, in association with increased renal NFκB activation. Importantly, treatment with ABT702 significantly reduced all these inflammatory parameters (P<0.05). Furthermore, ABT702 decreased glomerular permeability and inflammation and restored the decrease in glomerular occludin expression in vitro in high glucose treated human glomerular endothelial cells. Collectively, the results suggest that the reno-protective effects of ABT702 could be attributed to the reduction in renal inflammation and oxidative stress in diabetic mice.
    Pharmacological research : the official journal of the Italian Pharmacological Society. 05/2014;
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    ABSTRACT: Purpose. To evaluate the effects of the sigma 1 receptor (σR1) agonist, (+)-pentazocine, on lipopolysaccharide(LPS)-induced inflammatory changes in retinal microglia cells. Methods. Retinal microglia cells were isolated from Sprague-Dawley (SD) rat pups. Cells were treated with LPS with or without (+)-pentazocine and with or without the σR1 antagonist, BD1063. Morphological changes were assayed. Cell viability was assessed using MTT assay. Supernatant levels of tumor necrosis factor alpha (TNF-α), interleukin 10, (IL-10), monocyte chemoattractant protein-1 (MCP-1), and nitric oxide (NO) were determined. Reactive oxygen species (ROS) formation was assayed, and levels of mitogen-activated protein kinases (MAPKs) were analyzed using Western blot. Results. σR1 protein was expressed in retinal microglia. Incubation with LPS and/or (+)-pentazocine did not alter cell viability or σR1 protein levels. Incubation with LPS for 24 hours induced a marked change in microglial morphology and a significant increase in secreted levels of TNF-α, IL-10, MCP-1, and NO. Pre-treatment with (+)-pentazocine inhibited the LPS-induced morphological changes. Release of TNF-α, IL-10, MCP-1, and NO was reduced with (+)-pentazocine. Intracellular ROS formation was suppressed with (+)-pentazocine. Phosphorylation of extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) was reduced in the presence of (+)-pentazocine. The σR1 antagonist, BD1063, blocked the (+)-pentazocine-mediated inhibition of LPS-induced morphological changes. In addition, BD1063 treatment blocked (+)-pentazocine-mediated suppression of LPS-induced TNF-α, IL-10, MCP-1, NO, and intracellular ROS release. Conclusions. Treatment with (+)-pentazocine suppresses inflammatory responses of retinal microglia and inhibits LPS-induced activation of ERK/JNK MAPK. In neurodegenerative disease, (+)-pentazocine may exert neuroprotective effects through manipulation of microglia.
    Investigative ophthalmology & visual science 05/2014; · 3.43 Impact Factor
  • Pharmacological Research. 01/2014;
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    ABSTRACT: Interphotoreceptor retinoid-binding protein (IRBP) secreted by photoreceptors plays a pivotal role in photoreceptor survival with an unknown mechanism. A mutation in the human IRBP has been linked to retinitis pigmentosa, a progressive retinal degenerative disease. Mice lacking IRBP display severe early and progressive photoreceptor degeneration. However, the signaling pathway(s) leading to photoreceptor death in IRBP-deficient mice remains poorly understood. Here, we show that amounts of tumor necrosis factor-α (TNF-α) in the interphotoreceptor matrix and retinas of Irbp(-/-) mice were increased more than 10-fold and fivefold, respectively, compared with those in wild-type mice. Moreover, TNF-α receptor 1, an important membrane death receptor that mediates both programmed apoptosis and necrosis, was also significantly increased in Irbp(-/-) retina, and was colocalized with peanut agglutinin to the Irbp(-/-) cone outer segments. Although these death signaling proteins were increased, the caspase-dependent and independent apoptotic pathways were mildly activated in the Irbp(-/-) retinas, suggesting that other cell death mechanism(s) also contributes to the extensive photoreceptor degeneration in Irbp(-/-) retina. We found that receptor interacting protein 1 and 3 (RIP1 and RIP3) kinases, the intracellular key mediators of TNF-induced cellular necrosis, were elevated at least threefold in the Irbp(-/-) retinas. Moreover, pharmacological inhibition of RIP1 kinase significantly prevented cone and rod photoreceptor degeneration in Irbp(-/-) mice. These results reveal that RIP kinase-mediated necrosis strongly contributes to cone and rod degeneration in Irbp(-/-) mice, implicating the TNF-RIP pathway as a potential therapeutic target to prevent or delay photoreceptor degeneration in patients with retinitis pigmentosa caused by IRBP mutation.
    Journal of Neuroscience 10/2013; 33(44):17458-68. · 6.91 Impact Factor
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    ABSTRACT: In traumatic optic neuropathy (TON), apoptosis of retinal ganglion cells is closely related to the local production of reactive oxygen species and inflammatory mediators from activated microglial cells. Adenosine receptor A2A (A2AAR) has been shown to possess anti-inflammatory properties that have not been studied in TON. In the present study, we examined the role of A2AAR in retinal complications associated with TON. Initial studies in wild-type mice revealed that treatment with the A2AAR agonist resulted in marked decreases in the TON-induced microglial activation, retinal cell death and releases of reactive oxygen species and pro-inflammatory cytokines TNF-α and IL-6. To further assess the role of A2AAR in TON, we studied the effects of A2AAR ablation on the TON-induced retinal abnormalities. A2AAR-/- mice with TON showed a significantly higher mRNA level of TNF-α, Iba1-1 in retinal tissue, and ICAM-1 expression in retinal sections compared with wild-type mice with TON. To explore a potential mechanism by which A2AAR-signaling regulates inflammation in TON, we performed additional studies using hypoxia- or LPS-treated microglial cells as an in vitro model for TON. Activation of A2AAR attenuates hypoxia or LPS-induced TNF-α release and significantly repressed the inflammatory signaling, ERK in the activated microglia. Collectively, this work provides pharmacological and genetic evidence for A2AAR signaling as a control point of cell death in TON and suggests that the retinal protective effect of A2AAR is mediated by attenuating the inflammatory response that occurs in microglia via interaction with MAPKinase pathway.
    Journal of neuroimmunology 09/2013; · 2.84 Impact Factor
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    ABSTRACT: A number of studies have revealed that Type I diabetes (T1D) is associated with bone loss and an increased risk of fractures. T1D induces oxidative stress in various tissues and organs. Vitamin C plays an important role in the attenuation of oxidative stress; however, little is known about the effect of T1D induced oxidative stress on the regulation of vitamin C transporter in bone and bone marrow cells. To investigate this, T1D was induced in mice by multiple low dose injections of streptozotocin. We have demonstrated that endogenous antioxidants, glutathione peroxidase (GPx) and superoxide dismutase (SOD) are down-regulated in the bone and bone marrow of T1D. The vitamin C transporter isoform SVCT2, the only known transporter expressed in bone and bone marrow stromal cells (BMSCs), is negatively regulated in the bone and bone marrow of T1D. The μCT imaging of the bone showed significantly lower bone quality in the 8week T1D mouse. The in-vitro study in BMSCS showed that the knockdown of SVCT2 transporter decreases ascorbic acid (AA) uptake, and increases oxidative stress. The significant reversing effect of antioxidant vitamin C is only possible in control cells, not in knockdown cells. This study suggested that T1D induces oxidative stress and decreases SVCT2 expression in the bone and bone marrow environment. Furthermore, this study confirms that T1D increases bone resorption, decreases bone formation and changes the microstructure of bones. This study has provided evidence that the regulation of the SVCT2 transporter plays an important role not only in T1D osteoporosis but also in other oxidative stress-related musculoskeletal complications.
    Experimental and Molecular Pathology 08/2013; · 2.13 Impact Factor
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    ABSTRACT: AIMS: This study was undertaken to determine the effect of an adenosine kinase inhibitor (AKI) in diabetic retinopathy (DR). We have shown previously that adenosine signaling via A2A receptors (A2AAR) is involved in retinal protection from diabetes-induced inflammation. Here we demonstrate that AKI-enhanced adenosine signaling provides protection from DR in mice. MAIN METHODS: We targeted AK, the key enzyme in adenosine metabolism, using a treatment regime with the selective AKI, ABT-702 (1.5mg/kg intraperitoneally twice a week) commencing at the beginning of streptozotocin-induced diabetes at the age of eight weeks. This treatment, previously demonstrated to increase free adenosine levels in vivo, was maintained until the age of 16weeks. Retinal inflammation was evaluated using Western blot, Real-Time PCR and immuno-staining analyses. Role of A2AAR signaling in the anti-inflammation effect of ABT-702 was analyzed in Amadori-glycated-albumin (AGA)-treated microglial cells. KEY FINDINGS: At 16weeks, when diabetic mice exhibit significant signs of retinal inflammation including up-regulation of oxidative/nitrosative stress, A2AAR, ENT1, Iba1, TNF-α, ICAM1, retinal cell death, and down-regulation of AK, the ABT-702 treated group showed lower signs of inflammation compared to control animals receiving the vehicle. The involvement of adenosine signaling in the anti-inflammation effect of ABT-702 was supported by the TNF-α release blocking effect of A2AAR antagonist in AGA-treated microglial cells. SIGNIFICANCE: These results suggest a role for AK in regulating adenosine receptor signaling in the retina. Inhibition of AK potentially amplifies the therapeutic effects of site- and event-specific accumulation of extracellular adenosine, which is of highly translational impact.
    Life sciences 06/2013; · 2.56 Impact Factor
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    ABSTRACT: The early activation of microglia that induces retinal inflammation in DR may serve as a target for therapeutic intervention of DR. Our demonstration that retinal inflammation is attenuated via adenosine receptor A2AAR supports the hypothesis that a mechanism to maintain extracellular concentrations of adenosine important in normal physiology is impaired in DR. Extracellular concentrations of adenosine are regulated by the interplay of equiliberative nucleoside transporter (ENT)s with enzymes of adenosine metabolism including adenosine deaminase-1 (ADA1), adenosine kinase (AK) and CD73. In the vertebrates but not rodents, a macrophage-associated ADA2 is identified. The role of ADA2 is, therefore, understudied as the sequencing probes or antibodies to mouse ADA2 are not available. We identified increased ADA2 expression and activity in human and porcine retinas with diabetes, and in Amadori glycated albumin (AGA)- or hyperglycemia-treated porcine and human microglia. In rodent as well as porcine cells, modulation of TNF-α release is mediated by A2AAR. Quantitative analysis of normal and diabetic porcine retinas reveals that while the expression levels of ADA2, A2AAR, ENT1, TNF-α and MMP9 are increased, the levels of AK are reduced during inflammation as an endogenous protective mechanism. To determine the role of ADA2, we found that AGA induces ADA2 expression, ADA2 activity and TNF-α release, and that TNF-α release is blocked by ADA2-neutralizing antibody or ADA2 siRNA, but not by scrambled siRNA. These results suggest that retinal inflammation in DR is mediated by ADA2, and that the anti-inflammatory activity of A2AAR signaling is impaired in diabetes due to increased ADA2 activity.
    Biochemical and Biophysical Research Communications 05/2013; · 2.41 Impact Factor
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    ABSTRACT: Amyloid β peptides (Aβ) have been implicated in the pathogenesis of age-related macular degeneration (ARMD) and glaucoma. In this study, retinas of mice overexpressing Aβ (Tg) were compared to those of wild-type mice (Wt) and analyzed for oxidative stress parameters. We observed a progressive decrease in all retinal cell layers, which was significantly greater in Tg mice at 14 months and culminated in loss of the outer retina at 18 months of age. We also observed higher levels of reactive oxygen species, glial fibrillary acidic protein, and hydroperoxide in Tg versus Wt mice (14 months). These effects were associated with phosphorylation/activation of the apoptosis signal kinase 1 and the p38 mitogen-activated kinase. Western blotting analysis revealed progressive increases in the levels of thioredoxin 1 and thioredoxin inhibitory protein in Tg compared to Wt mice. No changes were observed in the levels of thioredoxin reductase 1 (TrxR1); however, measurements of TrxR1 activity showed a 42.7±8% reduction in Tg mice versus Wt at 14 months of age. Our data suggest that Aβ-mediated retinal neurotoxicity involves impairment of the thioredoxin system and enhanced oxidative stress, potentially implicating this mechanism in the pathogenesis of ARMD and glaucoma.
    Free Radical Biology & Medicine 04/2012; 53(3):577-88. · 5.27 Impact Factor
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    ABSTRACT: Tyrosine kinase inhibition is known to reduce diabetes-induced end-organ damage but the mechanisms remain elusive. We hypothesized that inhibition of tyrosine kinase reduces renal inflammation and injury in streptozotocin-induced diabetes. Male C57BL/6 mice were given daily injections of streptozotocin (45mg/kg/day, i.p. for 5days); control animals received the vehicle (citrate buffer). Thereafter, streptozotocin-treated mice were treated with genistein (10mg/kg, i.p three times a week for 10weeks, n=8-10/group) or the vehicle (5% DMSO). The streptozotocin-treated mice displayed significant elevation in blood glucose level and decrease in plasma insulin level compared to their vehicle-treated controls. Treatment with genistein reduced blood glucose level (~15%; p<0.05) without a significant effect on plasma insulin level; however, blood glucose remained significantly higher than the control group. The development of diabetes was associated with significant increases in total protein, albumin, nephrin and collagen excretions compared to their controls. In addition, the diabetic mice displayed increased urinary MCP-1 excretion in association with increased renal ICAM-1 expression and apoptotic cells. Furthermore, renal gp91 expression levels and urinary Thio-Barbituric Acid Reactive Substances (TBARs) excretion, indices of oxidative stress, were also elevated in diabetic mice. These changes were associated with increased renal phospho-tyrosine expression and renal phospho-ERK/ERK ratio. Importantly, treatment with genistein reduced all these parameters towards control values. Collectively, the results suggest that the reno-protective effect of genistein likely relates to reduced renal inflammation, oxidative stress and apoptosis in diabetic mice.
    Vascular Pharmacology 07/2011; 55(5-6):149-56. · 3.21 Impact Factor
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    ABSTRACT: Because interphotoreceptor retinoid-binding protein (IRBP) is expressed before being needed in its presumptive role in the visual cycle, we tested whether it controls eye growth during development. The eyes of congenic IRBP knockout (KO) and C57BL/6J wild-type (WT) mice ranging in age from postnatal day (P)2 to P440 were compared by histology, laser micrometry, cycloplegic photorefractions, and partial coherence interferometry. The size and weight of IRBP KO mouse eyes were greater than those of the WT mouse, even before eye-opening. Excessive ocular enlargement started between P7 and P10, with KO retinal arc lengths becoming greater compared with WT from P10 through P30 (18%; P < 0.01). The outer nuclear layer (ONL) of KO retinas became 20% thinner between P12 to P25, and progressed to 38% thinner at P30. At P30, there were 30% fewer cones per vertical section in KO than in WT retinas. Bromodeoxyuridine (BrdU) labeling indicated the same number of retinal cells were born in KO and WT mice. A spike in apoptosis was observed in KO outer nuclear layer at P25. These changes in size were accompanied by a large decrease in hyperopic refractive error, which reached -4.56 ± 0.70 diopters (D) versus +9.98 ± 0.993 D (mean ± SD) in WT, by postnatal day 60 (P60). CONCLUSIONS; In addition to its role in the visual cycle, IRBP is needed for normal eye development. How IRBP mediates ocular development is unknown.
    Investigative ophthalmology & visual science 06/2011; 52(8):5804-11. · 3.43 Impact Factor
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    ABSTRACT: In diabetic retinopathy (DR), abnormalities in vascular and neuronal function are closely related to the local production of inflammatory mediators whose potential source is microglia. Adenosine and its receptors have been shown to possess anti-inflammatory properties that have only recently been studied in DR. Here, we review recent studies that determined the roles of adenosine and its associated proteins, including equilibrative nucleoside transporters, adenosine receptors, and underlying signaling pathways in retinal complications associated with diabetes.
    Journal of ocular biology, diseases, and informatics 06/2011; 4(1-2):19-24.
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    Shahid Husain, Gregory I Liou, Craig E Crosson
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    ABSTRACT: The detrimental role of TNF-α in ischemia-induced tissue damage is known. The authors study examined whether opioid receptor activation alters TNF-α levels in the postischemic retina. Retinal ischemia was induced by raising the intraocular pressure above systolic blood pressure (155-160 mm Hg) for 45 minutes. Rats were pretreated with the opioid receptor agonist morphine (1 mg/kg; intraperitoneally) before injury. Selected animals were pretreated with the opioid antagonist naloxone (3 mg/kg; intraperitoneally). Human optic nerve head (ONH) astrocytes and rat microglial cells were treated with morphine (0.1-1 μM) for 24 hours and then treated with 10 μg/mL or 30 ng/mL lipopolysaccharide (LPS), respectively. TNF-α was measured by ELISA. Opioid receptor subtypes in astrocytes and microglia were determined by Western blot analysis. There was a time-dependent increase in TNF-α production; the maximum production occurred at 4 hours after ischemia and localized to the inner retinal regions. Ischemia-induced TNF-α production was significantly inhibited by morphine. In astrocytes and microglia, LPS triggered a robust increase in the release of TNF-α, which was significantly inhibited (P < 0.05) by morphine. Naloxone reversed the morphine-induced suppression of TNF-α production in vivo and in vitro. Both ONH astrocytes and microglial cells expressed δ-, κ-, and μ-opioid receptor subtypes. These data provide evidence that the production of TNF-α after ischemia/reperfusion injury is an early event and that opioid receptor activation reduces the production of TNF-α. Immunohistochemistry data and in vitro studies provide evidence that ONH astrocytes and microglial cells are the primary sources for the TNF-α production under ischemic/inflammatory conditions. Activation of one or more opioid receptors can reduce ischemic/reperfusion injury by the suppression of TNF-α production.
    Investigative ophthalmology & visual science 02/2011; 52(5):2577-83. · 3.43 Impact Factor
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    ABSTRACT: OBJECTIVE—During diabetes, retinal microglial cells are acti-vated to release inammatory cytokines that initiate neuronal loss and blood–retinal barrier breakdown seen in diabetic reti-nopathy (DR). The mechanism by which diabetes activates microglia to release those inammatory mediators is unclear and was therefore elucidated. RESEARCH DESIGN AND METHODS—Microglia activation was characterized in streptozocin-injected rats and in isolated microglial cells using immunouorescence, enzyme-linked immu-nosorbent assay, RT-PCR, and Western blot analyses. RESULTS—In 8-week diabetic retina, phospho-extracellular signal–related kinase (ERK) and P38 mitogen-activated protein kinases were localized in microglia, but not in Mueller cells or astrocytes. At the same time, Amadori-glycated albumin (AGA)-like epitopes were featured in the regions of microglia distribu-tion, implicating a pathogenic effect on microglial activation. To test this, diabetic rats were treated intravitreally with A717, a specic AGA-neutralizing antibody, or murine IgG. Relative to nondiabetic rats, diabetic rats (IgG-treated) manifested 3.9-and 7.9-fold increases in Iba-1 and tumor necrosis factor (TNF)-a mRNAs, respectively. Treatment of diabetic rats with A717 sig-nicantly attenuated overexpression of these mRNAs. Intravitreal injection of AGA per se in normal rats resulted in increases of Iba-1 expression and TNF-a release. Guided by these results, a cultured retinal microglia model was developed to study micro-glial response after AGA treatment and the mechanistic basis behind this response. The results showed that formation of re-active oxygen species and subsequent activation of ERK and P38, but not Jun NH2-terminal kinase, are molecular events underpin-ning retinal microglial TNF-a release during AGA treatment. CONCLUSIONS—These results provide new insights in un-derstanding the pathogenesis of early DR, showing that the accumulated AGA within the diabetic retina elicits the microglial activation and secretion of TNF-a. Thus, intervention trials with agents that neutralize AGA effects may emerge as a new thera-peutic approach to modulate early pathologic pathways long be-fore the occurrence of vision loss among patients with diabetes.
    Diabetes 01/2011; 60:1122-1133. · 7.90 Impact Factor
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    ABSTRACT: In diabetic retinopathy (DR), abnormalities in vascular and neuronal function are closely related to the local production of inflammatory mediators whose potential source is microglia. A(₂A) adenosine receptor (A(₂A)AR) has been shown to possess anti-inflammatory properties that have not been studied in DR. Here, we evaluate the role of A(₂A)AR and its underlying signaling in retinal complications associated with diabetes. Initial studies in wild-type mice revealed that the treatment with the A(₂A)AR agonist resulted in marked decreases in hyperglycemia-induced retinal cell death and tumor necrosis factor (TNF)-α release. To further assess the role of A(₂A)AR in DR, we studied the effects of A(₂A)AR ablation on diabetes-induced retinal abnormalities. Diabetic A(₂A)AR(-/-) mice had significantly more terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling-positive cells, TNF-α release, and intercellular adhesion molecule-1 expression compared with diabetic wild-type mice. To explore a potential mechanism by which A(₂A)AR signaling regulates inflammation in DR, we performed additional studies using microglial cells treated with Amadori-glycated albumin, a risk factor in diabetic disorders. The results showed that activation of A(₂A)AR attenuated Amadori-glycated albumin-induced TNF-α release in a cAMP/exchange protein directly activated by cAMP-dependent mechanism and significantly repressed the inflammatory cascade, C-Raf/extracellular signal-regulated kinase (ERK), in activated microglia. Collectively, this work provides pharmacological and genetic evidence for A(₂A)AR signaling as a control point of cell death in DR and suggests that the retinal protective effect of A(2A)AR is mediated by abrogating the inflammatory response that occurs in microglia via interaction with C-Raf/ERK pathway.
    American Journal Of Pathology 01/2011; 178(5):2136-2145. · 4.60 Impact Factor
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    Gregory I Liou
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    ABSTRACT: Diabetic retinopathy is a leading cause of blindness among working-age adults. Despite many years of research, treatment options for diabetic retinopathy remain limited and with adverse effects. Discovery of new molecular entities with adequate clinical activity for diabetic retinopathy remains one of the key research priorities in ophthalmology. This review is focused on the therapeutic effects of cannabidiol (CBD), a non-psychoactive native cannabinoid, as an emerging and novel therapeutic modality in ophthalmology based on systematic studies in animal models of inflammatory retinal diseases including diabetic retinopathy - a retinal disease associated with vascular-neuroinflammation. Special emphasis is placed on novel mechanisms which may shed light on the pharmacological activity associated with CBD preclinically. These include a self-defence system against inflammation and neurodegeneration mediated by inhibition of equilibrative nucleoside transporter and activation of adenosine receptor by treatment with CBD.
    World journal of diabetes. 03/2010; 1(1):12-8.
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    ABSTRACT: We have previously shown that non-psychotropic cannabidiol (CBD) protects retinal neurons in diabetic rats by inhibiting reactive oxygen species and blocking tyrosine nitration. Tyrosine nitration may inhibit glutamine synthetase (GS), causing glutamate accumulation and leading to further neuronal cell death. We propose to test the hypothesis that diabetes-induced glutamate accumulation in the retina is associated with tyrosine nitration of GS and that CBD treatment inhibits this process. Sprague Dawley rats were made diabetic by streptozotocin injection and received either vehicle or CBD (10 mg/kg/2 days). After eight weeks, retinal cell death, Müller cell activation, GS tyrosine nitration, and GS activity were determined. Diabetes causes significant increases in retinal oxidative and nitrative stress compared with controls. These effects were associated with Müller cell activation and dysfunction as well as with impaired GS activity and tyrosine nitration of GS. Cannabidiol treatment reversed these effects. Retinal neuronal death was indicated by numerous terminal deoxynucleotidyl transferase dUTP nick end-labeling (TUNEL)-labeled cells in diabetic rats compared with untreated controls or CBD-treated rats. These results suggest that diabetes-induced tyrosine nitration impairs GS activity and that CBD preserves GS activity and retinal neurons by blocking tyrosine nitration.
    Molecular vision 01/2010; 16:1487-95. · 1.99 Impact Factor
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    ABSTRACT: Diabetic retinopathy (DR) is associated with microglial activation and increased levels of inflammatory cytokines. Genistein, a tyrosine kinase inhibitor, has been shown to possess anti-inflammatory potential that so far untested in animal models of diabetes. The aims of this study are to evaluate the efficacy of genistein for alleviation of diabetes-induced retinal inflammation and also to gain insight into the molecular mechanisms involved therein by analyzing the effect of genistein on concomitant microglia activation in the diabetic retina and in isolated cells. Streptozotocin (STZ)-induced diabetic Sprague Dawley rats were used. After diabetes was established for two weeks a single intravitreal injection of genistein or vehicle was performed. Forty-eight hours later, rats were killed, their retinal and vitreal samples were processed for Quantitative Real Time-PCR (qRT-PCR) and Enzyme-linked immunosorbent assay (ELISA) analyses, respectively. For the in vitro study, isolated microglial cells from retinas of newborn rats were used. mRNA as well as protein levels for tumor necrosis factor α (TNF-α), a robust marker of inflammation, were increased in the retina early in the course of diabetes. Moreover, diabetes resulted in elevation of ionized calcium binding adaptor molecule-1 (Iba1) mRNA, known to be upregulated in activated microglia. These effects of diabetes in retina were all reduced by intervention treatment with genistein. Using an in vitro bioassay, we demonstrated the release of TNF-α from microglia activated by glycated albumin, a risk factor for diabetic disorders. This inflammatory signal involves the activation of tyrosine kinase and its subsequent events, ERK and P38 MAPKs. Genistein represses the release of TNF-α and significantly inhibits ERK and P38 phosphorylation in activated microglial cells by acting as a tyrosine kinase inhibitor. These findings show genistein to be effective in dampening diabetes-induced retinal inflammation by interfering with inflammatory signaling (ERK and P38 MAPKs) that occurs in activated microglia. This beneficial effect of genistein may represent a new intervention therapy to modulate early pathological pathways long before the occurrence of vision loss among diabetics.
    Molecular vision 01/2010; 16:2033-42. · 1.99 Impact Factor
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    ABSTRACT: The production of proinflammatory cytokines has been shown to play a critical role in a variety of retinal vascular diseases. Angiotensin II and VEGF have been implicated in the initiation of vascular inflammation and retinal vascular disease. However, detailed mechanisms of this process and interactions between inflammatory agonists and angiotensin II in promoting retinopathy are poorly understood. The present study was an investigation of the role of interleukin (IL)-6 in angiotensin II-induced retinopathy. Rats and IL-6-deficient and wild-type mice were treated with angiotensin II or IL-6, and their retinas were analyzed for leukocyte adhesion or for the expression and localization of VEGF or IL-6. Leukocyte adhesion was assayed by concanavalin A labeling. Vascular density was determined by morphometric analysis. NADPH oxidase activity was assayed by dihydroethidium imaging of superoxide. Intravitreal injection of angiotensin II caused increases in IL-6 mRNA and protein and in leukocyte adhesion to the retinal vessels. IL-6 protein was localized to CD11b-positive microglia and macrophage-like cells. Angiotensin II treatment stimulated increases in retinal levels of VEGF expression and NADPH oxidase activity, which were associated with increased surface area and remodeling of the retinal vessels. These effects were blocked by knocking out IL-6. Intravitreal IL-6 directly induced leukocyte adhesion in both wild-type and IL-6-deficient mice. The results indicate that IL-6 expression is essential for angiotensin II-induced increases in retinal VEGF expression, leukostasis, and vascular remodeling. The data suggest a critical role for IL-6 in mediating angiotensin II-induced retinal vascular inflammation and remodeling.
    Investigative ophthalmology & visual science 10/2009; 51(3):1709-18. · 3.43 Impact Factor
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    ABSTRACT: 11-cis-retinal is the light-sensitive component in rod and cone photoreceptors, and its isomerization to all-trans retinal in the presence of light initiates the visual response. For photoreceptors to function normally, all-trans retinal must be converted back into 11-cis-retinal through a series of enzymatic steps known as the visual cycle. The interphotoreceptor retinoid-binding protein (IRBP) is a proposed retinoid transporter in the visual cycle, but rods in Irbp(-/-) mice have a normal visual cycle. While rods are primarily responsible for dim light vision, the ability of cones to function in constant light is essential to human vision and may be facilitated by cone-specific visual cycle pathways. We analyzed the cones in Irbp(-/-) mice to determine whether IRBP has a cone-specific visual cycle function. Cone electroretinogram (ERG) responses were reduced in Irbp(-/-) mice, but similar responses from Irbp(-/-) mice at all ages suggest that degeneration does not underlie cone dysfunction. Furthermore, cone densities and opsin levels in Irbp(-/-) mice were similar to C57BL/6 (wild-type) mice, and both cone opsins were properly localized to the cone outer segments. To test for retinoid deficiency in Irbp(-/-) mice, ERGs were analyzed before and after intraperitoneal injections of 9-cis-retinal. Treatment with 9-cis-retinal produced a significant recovery of the cone response in Irbp(-/-) mice and shows that retinoid deficiency underlies cone dysfunction. These data indicate that IRBP is essential to normal cone function and demonstrate that differences exist in the visual cycle of rods and cones.
    Journal of Neuroscience 05/2009; 29(14):4616-21. · 6.91 Impact Factor

Publication Stats

2k Citations
367.66 Total Impact Points

Institutions

  • 2014
    • Georgia Regents University
      • Department of Ophthalmology
      Augusta, Georgia, United States
  • 2013–2014
    • Mansoura University
      • Department of Ophthalmology
      El-Manṣûra, Ad Daqahlīyah, Egypt
    • King Abdulaziz University
      Djidda, Makkah, Saudi Arabia
  • 2010
    • University of Georgia
      Атина, Georgia, United States
  • 2000–2010
    • Medical College of Georgia
      Атина, Georgia, United States
    • University of Illinois at Chicago
      • Department of Ophthalmology and Visual Sciences (Chicago)
      Chicago, IL, United States
  • 1991–2010
    • Georgia Health Sciences University
      • • Department of Ophthalmology
      • • Vascular Biology Center
      • • College of Dental Medicine
      • • Department of Pharmacology & Toxicology
      Augusta, GA, United States
  • 2008
    • Medical College of Wisconsin
      Milwaukee, Wisconsin, United States
  • 2003–2008
    • National Institutes of Health
      • Laboratory of Immunology
      Bethesda, MD, United States
  • 2006
    • National Eye Institute
      Maryland, United States
  • 1998
    • Saint Louis University
      Saint Louis, Michigan, United States
  • 1982–1993
    • Baylor College of Medicine
      • • Department of Ophthalmology
      • • Cullen Eye Institute
      Houston, TX, United States
  • 1986
    • Howard Hughes Medical Institute
      Maryland, United States