[Show abstract][Hide abstract] ABSTRACT: Cell death is one of the pathophysiological hallmarks after stroke. Markers to image cell death pathways in vivo are highly desirable. We previously showed that fluorescently labeled Annexin A5 (AnxA5), which binds specifically to phosphatidylserine (PS) on dead/dying cells, can be used in experimental stroke for monitoring cell death with optical imaging. Here we investigated whether dual-labeled AnxA5 (technetium and fluorescence label) can be used for single-photon emission computed tomography (SPECT) of cell death in the same model. C57Bl6/N mice were subjected to 60-minute middle cerebral artery occlusion (MCAO) and underwent SPECT imaging at 24, 48, and 72 hours afterwards. They were injected intravenously with either PS-binding AnxA5 or the nonfunctional AnxA5 (negative control), labeled with 99mTc and Alexa Fluor 568, respectively. After SPECT imaging, brain sections were cut for autoradiography and fluorescence microscopy. Ethanol-induced cell death in the femur muscle was used as positive control. We detected dual-labeled AnxA5 in the model of ethanol-induced cell death in the femur muscle, but not after MCAO at any time point, either with SPECT or with ex vivo autoradiography or fluorescence microscopy. Dual-labeled AnxA5 appears to be unsuited for visualizing death of brain cells in this MCAO model.Journal of Cerebral Blood Flow & Metabolism advance online publication, 2 July 2014; doi:10.1038/jcbfm.2014.115.
[Show abstract][Hide abstract] ABSTRACT: Neuronal damage shortly after onset or after brief episodes of cerebral ischemia has remained difficult to assess with clinical and preclinical imaging techniques as well as with microscopical methods. We here show, in rodent models of middle cerebral artery occlusion (MCAO), that neuronal damage in acute focal cerebral ischemia can be mapped with single-cell resolution using thallium autometallography (TlAMG), a histochemical technique for the detection of the K(+)-probe thallium (Tl(+)) in the brain. We intravenously injected rats and mice with thallium diethyldithiocarbamate (TlDDC), a lipophilic chelate complex that releases Tl(+) after crossing the blood-brain barrier. We found, within the territories of the affected arteries, areas of markedly reduced neuronal Tl(+) uptake in all animals at all time points studied ranging from 15 minutes to 24 hours after MCAO. In large lesions at early time points, areas with neuronal and astrocytic Tl(+) uptake below thresholds of detection were surrounded by putative penumbral zones with preserved but diminished Tl(+) uptake. At 24 hours, the areas of reduced Tl(+)uptake matched with areas delineated by established markers of neuronal damage. The results suggest the use of (201)TlDDC for preclinical and clinical single-photon emission computed tomography (SPECT) imaging of hyperacute alterations in brain K(+) metabolism and prediction of tissue viability in cerebral ischemia.Journal of Cerebral Blood Flow & Metabolism advance online publication, 16 October 2013; doi:10.1038/jcbfm.2013.177.
Journal of cerebral blood flow and metabolism: official journal of the International Society of Cerebral Blood Flow and Metabolism 10/2013; · 5.46 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Non-invasive optical imaging techniques, such as fluorescence imaging (FI) or bioluminescence imaging (BLI) have emerged as important tools in biomedical research. As demonstrated in different animal disease models, they enable visualization of physiological and pathophysiological processes at the cellular and molecular level in vivo with high specificity. Optical techniques are easy to use, fast, and affordable. Furthermore, they are characterized by their high sensitivity. In FI, very low amounts of the imaging agent (nano- to femtomol or even less) can be detected. Due to the absorption and scattering of light in tissue, optical techniques exhibit a comparably low spatial resolution in the millimeter range and a depth limit of a few centimeters. However, non-invasive imaging of biological processes in small animals and in outer or inner surfaces as well as during surgery even in humans is feasible. Currently two agents for fluorescence imaging are clinically approved, namely indocyanine green (ICG) and 5-aminolevulinic acid (5-ALA). In the past years, a number of new optical imaging agents for FI and reporter systems for BLI have been developed and successfully tested in animal models. Some of the FI agents might promise the application in clinical oncology. In this chapter, we describe the basic principles of non-invasive optical imaging techniques, give examples for the visualization of biological processes in animal models of cancer, and discuss potential clinical applications in oncology.
Recent results in cancer research. Fortschritte der Krebsforschung. Progrès dans les recherches sur le cancer 01/2013; 187:221-46.
[Show abstract][Hide abstract] ABSTRACT: Inflammation is a pathophysiological hallmark of many diseases of the brain. Specific imaging of cells and molecules that contribute to cerebral inflammation is therefore highly desirable, both for research and in clinical application. The 18 kDa translocator protein (TSPO) has been established as a suitable target for the detection of activated microglia/macrophages. A number of novel TSPO ligands have been developed recently. Here, we evaluated the high affinity TSPO ligand DPA-714 as a marker of brain inflammation in two independent animal models. For the first time, the specificity of radiolabeled DPA-714 for activated microglia/macrophages was studied in a rat model of epilepsy (induced using Kainic acid) and in a mouse model of stroke (transient middle cerebral artery occlusion, tMCAO) using high-resolution autoradiography and immunohistochemistry. Additionally, cold-compound blocking experiments were performed and changes in blood-brain barrier (BBB) permeability were determined. Target-to-background ratios of 2 and 3 were achieved in lesioned vs. unaffected brain tissue in the epilepsy and tMCAO models, respectively. In both models, ligand uptake into the lesion corresponded well with the extent of Ox42- or Iba1-immunoreactive activated microglia/macrophages. In the epilepsy model, ligand uptake was almost completely blocked by pre-injection of DPA-714 and FEDAA1106, another high-affinity TSPO ligand. Ligand uptake was independent of the degree of BBB opening and lesion size in the stroke model. We provide further strong evidence that DPA-714 is a specific ligand to image activated microglia/macrophages in experimental models of brain inflammation.
PLoS ONE 01/2013; 8(8):e69529. · 3.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The blood–brain barrier (BBB) is a highly complex structure, which separates the extracellular fluid of the central nervous system (CNS) from the blood of CNS vessels. A wide range of neurologic conditions, including stroke, epilepsy, Alzheimer’s disease, and brain tumors, are associated with perturbations of the BBB that contribute to their pathology. The common consequence of a BBB dysfunction is increased permeability, leading to extravasation of plasma constituents and vasogenic brain edema. The BBB impairment can persist for long periods, being involved in secondary inflammation and neuronal dysfunction, thus contributing to disease pathogenesis. Therefore, reliable imaging of the BBB impairment is of major importance in both clinical management of brain diseases and in experimental research. From landmark studies by Ehrlich and Goldman, the use of dyes (probes) has played a critical role in understanding BBB functions. In recent years methodologic advances in morphologic and functional brain imaging have provided insight into cellular and molecular interactions underlying BBB dysfunction in animal disease models. These imaging techniques, which range from in situ staining to noninvasive in vivo imaging, have different spatial resolution, sensitivity, and capacity for quantitative and kinetic measures of the BBB impairment. Despite significant advances, the translation of these techniques into clinical applications remains slow. This review outlines key recent advances in imaging techniques that have contributed to the understanding of BBB dysfunction in disease and discusses major obstacles and opportunities to advance these techniques into the clinical realm.
[Show abstract][Hide abstract] ABSTRACT: Regional cerebral blood flow (rCBF) is a useful surrogate marker of neuronal activity and a parameter of primary interest in the diagnosis of many diseases. The increasing use of mouse models spawns the demand for in vivo measurement of rCBF in the mouse. Small animal SPECT provides excellent spatial resolution at adequate sensitivity and is therefore a promising tool for imaging the mouse brain. This study evaluates the feasibility of mouse brain perfusion SPECT and assesses the regional pattern of normal Tc-99m-HMPAO uptake and the impact of age and gender. Whole-brain kinetics was compared between Tc-99m-HMPAO and Tc-99m-ECD using rapid dynamic planar scans in 10 mice. Assessment of the regional uptake pattern was restricted to the more suitable tracer, HMPAO. Two HMPAO SPECTs were performed in 18 juvenile mice aged 7.5±1.5weeks, and in the same animals at young adulthood, 19.1±4.0weeks (nanoSPECT/CTplus, general purpose mouse apertures: 1.2kcps/MBq, 0.7mm FWHM). The 3-D MRI Digital Atlas Database of an adult C57BL/6J mouse brain was used for region-of-interest (ROI) analysis. SPECT images were stereotactically normalized using SPM8 and a custom made, left-right symmetric HMPAO template in atlas space. For testing lateral asymmetry, each SPECT was left-right flipped prior to stereotactical normalization. Flipped and unflipped SPECTs were compared by paired testing. Peak brain uptake was similar for ECD and HMPAO: 1.8±0.2 and 2.1±0.6 %ID (p=0.357). Washout after the peak was much faster for ECD than for HMPAO: 24±7min vs. 4.6±1.7h (p=0.001). The general linear model for repeated measures with gender as an intersubject factor revealed an increase in relative HMPAO uptake with age in the neocortex (p=0.018) and the hippocampus (p=0.012). A decrease was detected in the midbrain (p=0.025). Lateral asymmetry, with HMPAO uptake larger in the left hemisphere, was detected primarily in the neocortex, both at juvenile age (asymmetry index AI=2.7±1.7%, p=0.000) and at young adult age (AI=2.4±1.7%, p=0.000). Gender had no effect on asymmetry. Voxel-wise testing confirmed the ROI-based findings. In conclusion, high-resolution HMPAO SPECT is a promising technique for measuring rCBF in preclinical research. It indicates lateral asymmetry of rCBF in the mouse brain as well as age-related changes during late maturation. ECD is not suitable as tracer for brain SPECT in the mouse because of its fast clearance from tissue indicating an interspecies difference in esterase activity between mice and humans.
[Show abstract][Hide abstract] ABSTRACT: Noninvasive fluorescence imaging (NFI) is a powerful tool to study physiology and pathophysiology in animal disease models. NFI has been successfully applied in a number of animal disease models including cancer, arthritis, and stroke. Furthermore, several applications in humans have been described. NFI is widely available in research laboratories because it has a number of advantages. It uses non-ionizing radiation and requires comparably simple and inexpensive instrumentation which is easy to handle. Fluorochromes can be detected with high sensitivity, and image acquisition time is relatively short. Furthermore, a plethora of fluorescent imaging agents is available including unspecific, target-specific, and activatable imaging probes. With these probes biological processes such as inflammation, cell death, or enzyme activity and many others can be visualized in living animals. This review offers an overview of current approaches in the NFI of stroke pathophysiology in animal models of cerebral ischemia. First, the instrumentation and the different types of imaging agents for NFI are described. Second, a short introduction to animal models of stroke is provided. Third, examples for NFI in animal models of stroke are given. Finally, the use of NFI in human stroke is critically discussed.
Current Medicinal Chemistry 08/2012; · 3.72 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: One of the hallmarks of stroke pathophysiology is the widespread death of many different types of brain cells. As our understanding of the complex disease that is stroke has grown, it is now generally accepted that various different mechanisms can result in cell damage and eventual death. A plethora of techniques is available to identify various pathological features of cell death in stroke; each has its own drawbacks and pitfalls, and most are unable to distinguish between different types of cell death, which partially explains the widespread misuse of many terms. The purpose of this review is to summarize the standard histopathological and immunohistochemical techniques used to identify various pathological features of stroke. We then discuss how these methods should be properly interpreted on the basis of what they are showing, as well as advantages and disadvantages that require consideration. As there is much interest in the visualization of stroke using noninvasive imaging strategies, we also specifically discuss how these techniques can be interpreted within the context of cell death.
Journal of cerebral blood flow and metabolism: official journal of the International Society of Cerebral Blood Flow and Metabolism 11/2011; 32(2):213-31. · 5.46 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: To monitor stroke-induced brain damage and assess neuroprotective therapies, specific imaging of cell death after cerebral ischemia in a noninvasive manner is highly desirable. Annexin A5 has been suggested as a marker for imaging cell death under various disease conditions including stroke. In this study, C57BL6/N mice received middle cerebral artery occlusion (MCAO) and were injected intravenously with either active or inactive Cy5.5-annexin A5 48 hours after reperfusion. Some mice also received propidium iodide (PI), a cell integrity marker. Only in mice receiving active Cy5.5-annexin A5 were fluorescence intensities significantly higher over the hemisphere ipsilateral to MCAO than on the contralateral side. This was detected noninvasively and ex vivo 4 and 8 hours after injection. The majority of cells positive for fluorescent annexin A5 were also positive for PI and fragmented DNA as detected by terminal deoxynucleotidyl transferase-mediated 2'-deoxyuridine 5'-triphosphate-biotin nick end labeling (TUNEL) staining. This study demonstrates the high specificity of annexin A5 for visualization of cell death in a mouse model of stroke. To our knowledge, this is the first study to compare the distribution of injected active and inactive annexin A5, PI, and TUNEL staining. It provides important information on the experimental and potential clinical applications of annexin A5-based imaging agents in stroke.
Journal of cerebral blood flow and metabolism: official journal of the International Society of Cerebral Blood Flow and Metabolism 01/2011; 31(5):1311-20. · 5.46 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Non-invasive imaging technologies play a substantial role in the evaluation of physiological and pathophysiological processes.
They are indispensable in biomedical research and in the clinic. In the past decade, designated small animal imaging scanners
have become available for almost all imaging modalities used in clinical routine. These include nuclear imaging techniques
such as positron emission tomography (PET) or single photon emission computed tomography (SPECT), magnetic resonance imaging
(MRI), X-ray computed tomography (CT), and ultrasound (US). Among the imaging modalities used for small animal imaging, optical
techniques such as fluorescence imaging (FI) and biolumnescence imaging (BLI) are becoming increasingly important. In this
chapter, we describe the basic principles of optical imaging and the application of the techniques for the non-invasive visualization
of biological processes in animal disease models, with special emphasis on small animal models of stroke.
Key wordsBioluminescence imaging-Brain-Cerebral ischemia-Fluorescence imaging-Molecular imaging-Small animal imaging-Stroke
[Show abstract][Hide abstract] ABSTRACT: Non-invasive near-infrared fluorescence (NIRF) imaging is a powerful tool to study pathophysiology in a wide variety of animal disease models including brain diseases. However, especially in NIRF imaging of the brain or other deeper laying target sites, background fluorescence emitted from the scalp or superficial blood vessels can impede the detection of fluorescence in deeper tissue. Here, we introduce an effective method to reduce the impact of fluorescence from superficial layers. The approach uses excitation light at two different wavelengths generating two images with different depth sensitivities followed by an adapted subtraction algorithm. This technique leads to significant enhancement of the contrast and the detectability of fluorochromes located in deep tissue layers in tissue simulating phantoms and murine models with stroke.
[Show abstract][Hide abstract] ABSTRACT: Impairment of the blood-brain barrier (BBB) after cerebral ischemia leads to extravasation of plasma constituents into the brain parenchyma. We describe a novel method using non-invasive near-infrared fluorescence (NIRF) imaging and bovine serum albumin labeled with a NIRF dye (NIRF-BSA) to detect BBB impairment after middle cerebral artery occlusion (MCAO) in mice. We first explored the time course of BBB impairment after transient MCAO using Evans blue (EB), which binds to plasma albumin in vivo. An initial BBB impairment was observed at 4-8h and a second impairment at 12-16h after reperfusion. No EB extravasation was detected at 8-12h. Non-invasive NIRF imaging with NIRF-BSA confirmed biphasic BBB impairment. Upon co-injection of NIRF-BSA with EB we found a strong correlation between the detected NIRF signal and the amount of extravasated EB (r=0.857, P=0.00178). When MCAO mice received NIRF-BSA together with gadolinium-diethylene triamine penta-acetic acid (Gd-DTPA), T1-weighted images showed Gd-DTPA enhancement at all times while NIRF imaging showed biphasic BBB impairment. In conclusion, NIRF-BSA is a suitable marker of plasma albumin extravasation in the mouse brain. Non-invasive NIRF imaging with NIRF-BSA is a useful tool to study BBB integrity in preclinical models of central nervous system pathology.
Journal of neuroscience methods 06/2009; 180(1):126-32. · 2.30 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Matrix metalloproteinases (MMPs) have been implicated in the pathophysiology of cerebral ischemia. In this study, we explored whether MMP activity can be visualized by noninvasive near-infrared fluorescence (NIRF) imaging using an MMP-activatable probe in a mouse model of stroke. C57Bl6 mice were subjected to transient middle cerebral artery occlusion (MCAO) or sham operation. Noninvasive NIRF imaging was performed 24 h after probe injection, and target-to-background ratios (TBRs) between the two hemispheres were determined. TBRs were significantly higher in MCAO mice injected with the MMP-activatable probe than in sham-operated mice and in MCAO mice that were injected with the nonactivatable probe as controls. Treatment with an MMP inhibitor resulted in significantly lower TBRs and lesion volumes compared to injection of vehicle. To test the contribution of MMP-9 to the fluorescence signal, MMP9-deficient (MMP9(-/-)) mice and wild-type controls were subjected to MCAO of different durations to attain comparable lesion volumes. TBRs were significantly lower in MMP9(-/-) mice, suggesting a substantial contribution of MMP-9 activity to the signal. Our study shows that MMP activity after cerebral ischemia can be imaged noninvasively with NIRF using an MMP-activatable probe, which might be a useful tool to study MMP activity in the pathophysiology of the disease.
Journal of cerebral blood flow and metabolism: official journal of the International Society of Cerebral Blood Flow and Metabolism 05/2009; 29(7):1284-92. · 5.46 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Inflammation is crucially involved in many diseases of the CNS. Immune cells may attack the CNS, as in multiple sclerosis, and therefore be responsible for primary damage. Immune cells may also be activated by injury to the CNS, as for example in stroke or brain trauma, secondarily enhancing lesion growth. In general, CNS inflammation involves a complex interplay of pro- and anti-inflammatory cells and molecules. The blood-brain barrier loses its integrity, plasma proteins leak into the CNS parenchyma, followed by invasion of blood-borne immune cells, and activation of resident microglial cells and astrocytes. However, inflammation not only exacerbates CNS disease, it is also indispensable in containment and resolution of tissue damage, as well as repair and regeneration. The time course and the contribution of inflammatory processes to the pathophysiology of the disease depend on several factors including the type of injury and the time point after injury, and can exhibit a high individual variability. Imaging technologies that enable specific visualization of these inflammatory processes non-invasively are therefore highly desirable. They provide powerful tools to further evaluate the contribution of specific processes to the pathophysiology of CNS disease. Moreover, these technologies may be valuable in detecting and assessing disease progression, in stratifying patients for therapy, and in monitoring therapy. Among the existing non-invasive imaging methods to visualize neuroinflammation in the CNS, we here review the current status of nuclear and optical imaging techniques, with particular emphasis on the sensitivity, specificity, as well as the limitations of these approaches.
[Show abstract][Hide abstract] ABSTRACT: Brain inflammation is a hallmark of stroke, where it has been implicated in tissue damage as well as in repair. Imaging technologies that specifically visualize these processes are highly desirable. In this study, we explored whether the inflammatory receptor CD40 can be noninvasively and specifically visualized in mice after cerebral ischemia using a fluorescent monoclonal antibody, which we labeled with the near-infrared fluorescence dye Cy5.5 (Cy5.5-CD40MAb).
Wild-type and CD40-deficient mice were subjected to transient middle cerebral artery occlusion. Mice were either intravenously injected with Cy5.5-CD40MAb or control Cy5.5-IgGMAb. Noninvasive and ex vivo near-infrared fluorescence imaging was performed after injection of the compounds. Probe distribution and specificity was further assessed with single-plane illumination microscopy, immunohistochemistry, and confocal microscopy.
Significantly higher fluorescence intensities over the stroke-affected hemisphere, compared to the contralateral side, were only detected noninvasively in wild-type mice that received Cy5.5-CD40MAb, but not in CD40-deficient mice injected with Cy5.5-CD40MAb or in wild-type mice that were injected with Cy5.5-IgGMAb. Ex vivo near-infrared fluorescence showed an intense fluorescence within the ischemic territory only in wild-type mice injected with Cy5.5-CD40MAb. In the brains of these mice, single-plane illumination microscopy demonstrated vascular and parenchymal distribution, and confocal microscopy revealed a partial colocalization of parenchymal fluorescence from the injected Cy5.5-CD40MAb with activated microglia and blood-derived cells in the ischemic region.
The study demonstrates that a CD40-targeted fluorescent antibody enables specific noninvasive detection of the inflammatory receptor CD40 after cerebral ischemia using optical techniques.
[Show abstract][Hide abstract] ABSTRACT: In vivo molecular fluorescence tomography of brain disease mouse models has two very specific demands on the optical setup: the use of pigmented furry mice does not allow for a purely noncontact setup, and a high spatial accuracy is required on the dorsal side of the animal due to the location of the brain. We present an optimized setup and tomographic scheme that meet these criteria through a combined CW reflectance-transmittance fiber illumination approach and a charge-coupled device contactless detection scheme. To consider the anatomy of the mouse head and take short source detector separations into account, the forward problem was evaluated by a Monte Carlo simulation input with a magnetic resonance image of the animal. We present an evaluation of reconstruction performance of the setup under three different condition. (i) Using a simulated dataset, with well-defined optical properties and low noise, the reconstructed position accuracy is below 0.5 mm. (ii) Using experimental data on a cylindrical tissue-simulating phantom with well-defined optical properties, a spatial accuracy of about 1 mm was found. (iii) Finally, on an animal model with a fluorescent inclusion in the brain, the target position was reconstructed with an accuracy of 1.6 mm.
Journal of Biomedical Optics 08/2008; 13(4):041311. · 2.88 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Light in the near-infrared (NIR) region between 700-900 nm can penetrate deep into living tissue, thereby offering a unique opportunity to use near-infrared fluorescence (NIRF) imaging techniques to detect and visualize fluorescent probes in-vivo. In the past few years, many novel NIR fluorescent probes have been designed, synthesized and studied in a variety of disease conditions. Recent research has focused primarily on the class of cyanines dyes as non-specific agents and as part of specific NIR fluorescent probes. The publications reviewed herein discuss the characteristics of cyanine dyes and their conjugates and present examples for the application of these probes for imaging vascular pathophysiology.
Archiv für Kreislaufforschung 04/2008; 103(2):144-51. · 5.90 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Pathophysiological processes in the vascular system are the major cause of mortality and disease. Atherosclerosis, an inflammatory process in arterial walls, can lead to formation of plaques, whose rupture can lead to thrombus formation, obstruction of vessels (thrombosis), reduction of the blood flow (ischemia), cell death in the tissue fed by the occluded vessel, and depending on the affected vessel, to myocardial infarction or stroke. Imaging techniques enabling visualization of the biological processes involved in this scenario are therefore highly desirable. In recent years, a number of reporter agents and reporter systems have been developed to visualize these processes using different imaging modalities including nuclear imaging techniques, such as positron emission tomography or single photon emission computed tomography, magnetic resonance imaging, and ultrasound. This article comprises a brief overview of optical imaging techniques, such as fluorescence imaging and bioluminescence imaging for the visualization of vascular pathophysiology.
Archiv für Kreislaufforschung 04/2008; 103(2):182-90. · 5.90 Impact Factor