1,009 research outputs found

    Using neurophotonic tools to access the effects of repeated blood-brain-barrier opening with focused ultrasound

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    The blood-brain barrier (BBB) is a critical protective structure that tightly controls which molecules can pass from the bloodstream into the brain parenchyma. Focused ultrasound (FUS) is an emerging technology that allows the possibility of a non-invasive and controlled opening of the BBB for the delivery of therapeutics that would not otherwise reach the brain. However, the secondary effects of repeated BBB disruption are not fully understood. In this study, we used mesoscopic and microscopic imaging to track neuronal and vascular activity following repeated FUS-BBB opening in mice. We used genetically encoded calcium indicators (GECI) to measure neuronal activity and used reflectance light to estimate changes in oxy-, deoxyand total hemoglobin levels. The hemodynamic response function was calculated to evaluate the alteration of neurovascular coupling. This study provided a better understanding of the relationship between repeated FUS-BBB opening and the alteration of neurovascular coupling in an animal model

    Using Computed Tomography Perfusion to Evaluate the Blood-Brain-Barrier and Blood-Tumor-Barrier Response following Focused Ultrasound Sonication with Microbubble Administration

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    The blood-brain-barrier (BBB) is the single most limiting factor in the delivery of neurotherapeutics into the brain. Focused ultrasound sonication combined with intravenous microbubble administration (FUSwMB) is a novel technique that can transiently disrupt the BBB, with minimal vascular or tissue damage, allowing for localized drug delivery over the targeted region. The goals of this thesis are to: 1) use computed tomography (CT) perfusion to measure the permeability surface area product (PS) following USwMB in normal rabbits with an intact BBB, and 2) to evaluate the blood-tumor-barrier (BTB) PS response following FUSwMB in a C6 rat glioma model

    Using focused ultrasound to modulate microglial structure and function

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    Transcranial focused ultrasound (FUS) has the unique ability to target regions of the brain with high spatial precision, in a minimally invasive manner. Neuromodulation studies have shown that FUS can excite or inhibit neuronal activity, demonstrating its tremendous potential to improve the outcome of neurological diseases. Recent evidence has also shed light on the emerging promise that FUS has, with and without the use of intravenously injected microbubbles, in modulating the blood-brain barrier and the immune cells of the brain. As the resident immune cells of the central nervous system, microglia are at the forefront of the brain’s maintenance and immune defense. Notably, microglia are highly dynamic and continuously survey the brain parenchyma by extending and retracting their processes. This surveillance activity aids microglia in performing key physiological functions required for brain activity and plasticity. In response to stressors, microglia rapidly alter their cellular and molecular profile to help facilitate a return to homeostasis. While the underlying mechanisms by which both FUS and FUS + microbubbles modify microglial structure and function remain largely unknown, several studies in adult mice have reported changes in the expression of the microglia/macrophage marker ionized calcium binding adaptor molecule 1, and in their phagocytosis, notably of protein aggregates, such as amyloid beta. In this review, we discuss the demonstrated and putative biological effects of FUS and FUS + microbubbles in modulating microglial activities, with an emphasis on the key cellular and molecular changes observed in vitro and in vivo across models of brain health and disease. Understanding how this innovative technology can modulate microglia paves the way for future therapeutic strategies aimed to promote beneficial physiological microglial roles, and prevent or treat maladaptive responses

    Biomolecular Ultrasound and Sonogenetics

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    Visualizing and modulating molecular and cellular processes occurring deep within living organisms is fundamental to our study of basic biology and disease. Currently, the most sophisticated tools available to dynamically monitor and control cellular events rely on light-responsive proteins, which are difficult to use outside of optically transparent model systems, cultured cells, or surgically accessed regions owing to strong scattering of light by biological tissue. In contrast, ultrasound is a widely used medical imaging and therapeutic modality that enables the observation and perturbation of internal anatomy and physiology but has historically had limited ability to monitor and control specific cellular processes. Recent advances are beginning to address this limitation through the development of biomolecular tools that allow ultrasound to connect directly to cellular functions such as gene expression. Driven by the discovery and engineering of new contrast agents, reporter genes, and bioswitches, the nascent field of biomolecular ultrasound carries a wave of exciting opportunities

    Simvastatin Blocks Blood-Brain Barrier Disruptions Induced by Elevated Cholesterol Both In Vivo and In Vitro

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    Background. Hypercholesterolemia and disruptions of the blood brain barrier (BBB) have been implicated as underlying mechanisms in the pathogenesis of Alzheimer's disease (AD). Simvastatin therapy may be of benefit in treating AD; however, its mechanism has not been yet fully understood. Objective. To explore whether simvastatin could block disruption of BBB induced by cholesterol both in vivo and in vitro. Methods. New Zealand rabbits were fed cholesterol-enriched diet with or without simvastatin. Total cholesterol of serum and brain was measured. BBB dysfunction was evaluated. To further test the results in vivo, rat brain microvascular endothelial cells (RBMECs) were stimulated with cholesterol in the presence/absence of simvastatin in vitro. BBB disruption was evaluated. Results. Simvastatin blocked cholesterol-rich diet induced leakage of Evan's blue dye. Cholesterol content in the serum was affected by simvastatin, but not brain cholesterol. Simvastatin blocked high-cholesterol medium-induced decrease in TEER and increase in transendothelial FITC-labeled BSA Passage in RBMECs. Conclusions. The present study firstly shows that simvastatin improves disturbed BBB function both in vivo and in vitro. Our data provide that simvastatin may be useful for attenuating disturbed BBB mediated by hypercholesterolemia

    Challenges for molecular neuroimaging with MRI

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    Magnetic resonance (MRI)-based molecular imaging methods are beginning to have impact in neuroscience. A growing number of molecular imaging agents have been synthesized and tested in vitro, but so far relatively few have been validated in the brains of live animals. Here, we discuss key challenges associated with expanding the repertoire of successful molecular neuroimaging approaches. The difficulty of delivering agents past the blood-brain barrier (BBB) is a particular obstacle to molecular imaging in the central nervous system. We review established and emerging techniques for trans-BBB delivery, including intracranial infusion, BBB disruption, and transporter-related methods. Improving the sensitivity with which MRI-based molecular agents can be detected is a second major challenge. Better sensitivity would in turn reduce the requirements for delivery and alleviate potential side effects. We discuss recent efforts to enhance relaxivity of conventional longitudinal relaxation time (T1) and transverse relaxation time (T2) MRI contrast agents, as well as strategies that involve amplifying molecular signals or reducing endogenous background influences. With ongoing refinement of imaging approaches and brain delivery methods, MRI-based techniques for molecular-level neuroscientific investigation will fall increasingly within reach.Raymond and Beverley Sackler FoundationNational Institutes of Health (U.S.) (R01-DA28299)National Institutes of Health (U.S.) (DP2-OD2441

    Ultrasound-driven microbubble dynamics in microvessels

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    Ultrasound and microbubble induced blood-brain barrier opening has shown success in clinical trials as a promising method to deliver drugs to the brain. Shelled gas bubbles, a few micrometres in diameter, are administered intravenously, and distribute throughout the cardiovascular system. When ultrasound is applied to the brain, the microbubbles expand and contract within the vasculature, temporarily disrupting the blood-brain barrier, and allowing drugs to pass through. While this technique has been shown to be effective at delivering drugs, its mechanisms remain relatively poorly understood. Better understanding how microbubbles interact with tissues could enable refinement of therapies. This thesis investigates the fundamental physical interactions between microbubbles and soft tissues using two distinct but related experimental platforms that utilise high-speed microscopy. Firstly, microbubbles within soft tissue-mimicking hydrogel channels are observed during exposure to typical therapeutic ultrasound pulses. The primary radiation force is shown to be significant, and can cause bubbles to deform the soft gels by several micrometres. Microbubbles are also investigated in brain tissue, using acute cortical slices from the brains of juvenile rats, transcardially perfused post-mortem with a concentrated solution of SonoVue®. This technique is shown to be an effective method of observing microbubbles using optical microscopy within the microvasculature of live brain tissue. Radial oscillations of bubbles within brain microvessels can deform surrounding tissue at both microsecond and millisecond time scales. Extravasation of microbubbles due to the primary radiation force can occur during typical ultrasound pulses, and is common at higher ultrasound pressures (mechanical index of 0.6 and above). These results demonstrate the significance of both radial oscillations and the primary radiation force as ways in which microbubbles can physically impact their surroundings. Additionally, acute brain slices are shown to be a valuable tool to investigate microbubble behaviours and mechanisms of drug delivery in a physiologically relevant environment.Open Acces

    The Dual Role of Hypoxia-Inducible Factor-1 in Ischemic Stroke: Neuroprotection and Blood-Brain Barrier Disruption

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    Stroke is a major cause of death and the leading cause of long-term disability in industrialized countries. Ischemic stroke-induced brain injury results from the interaction of complex pathophysiological processes, including energy failure, calcium overload, excitotoxicity, oxidative stress, disruption of blood-brain barrier (BBB) and inflammation. Despite the wealth of knowledge regarding the cellular and molecular mechanisms underlying neuronal death after stroke, research for several decades has failed to develop an effective and safe neuroprotective treatment. One complicating factor in the development of neuroprotective strategies is the dual nature of many of the processes that occur in the brain during stroke. Hypoxia-inducible factor 1 (HIF-1) is a master regulator of cellular and tissue adaption to hypoxia. It plays both protective and detrimental roles in ischemic stroke by inducing a wide array of target genes involved in angiogenesis, erythropoiesis, cell survival/death, and energy metabolism. The dual face of HIF-1 in the pathophysiology of cerebral ischemia is postulated to partially depend on thedifferent functions of its target proteins in specific type of brain cells. In the current studies, we hypothesize that neuronal HIF-1 accumulation is protective whereas endothelial HIF-1 induction is implicated in BBB disruption. We first evaluated HIF-1's role in the antioxidant N-acetylcysteine (NAC)-mediated neuroprotection in a transient cerebral ischemia animal model. The study demonstrated that pre-treatment of NAC increased the neuronal expression of HIF-1α, the regulatable subunit of HIF-1, and its target proteins erythropoietin (EPO) and glucose transporter (GLUT)-3 in the ischemic brain of rodents subjected to 90 min middle cerebral artery occlusion (MCAO) and 24 h reperfusion. Suppressing HIF-1 activity by pharmacological inhibitorsor by specific knock-out neuronal HIF-1α abolished NAC's neuroprotective effects. Furthermore, we observed that NAC increased HIF-1α stability through enhancingits interaction with heat-shock protein 90 (Hsp90) in ischemic brains. Increased BBB permeability and associated cerebral edema formation are potentially lethal complications of ischemic stroke. Accumulating evidence has shown that admission hyperglycemia in conjunction with ischemia/reperfusion causes exacerbated cerebrovascular endothelial cell dysfunction and increased BBB permeability, which leads to augmented brain edema and hemorrhagic transformation in ischemic stroke.The hypothesis of the second part of this dissertation is that endothelial HIF-1 is implicated in hyperglycemia-exacerbated BBB disruption after ischemia. Both in vitro and in vivo studies were undertaken to investigate the effect of hyperglycemia on (1) HIF-1α and its target genes expression; (2) ischemia-induced BBB permeability change; and (3) the effect of HIF-1α inhibition on BBB permeability after ischemia. The in vitrostudy showed that high glucose enhanced HIF-1αand its downstream factors expression in the endothelial cell culture after oxygen glucose deprivation (OGD)/reoxygenation. This was correlated withan increased paracellular permeability as well as diminished expression and disrupted continuity of tight junction (TJ) proteins. Suppressing HIF-1 activity by HIF-1α inhibitors ameliorated the alterations in paracellular permeability and expression and distribution pattern of TJ proteins induced by high glucose exposure. In in vivo studies, diabetic mice subjected to 90 min MCAOfollowed by reperfusiondemonstrated higher expression of HIF-1α and its target gene vascular endothelial growth factor (VEGF) in the ischemic brain microvessels than non-diabetic control mice. Diabetic mice also showed exacerbated BBB damage and TJ disruption, increased infarct volume, and worsened neurological deficits. SuppressingHIF-1 activity by specific knock-out endothelial HIF-1α ameliorated BBB leakage and brain infarction in diabetic animals. Taken together, these present studies provide new information concerning HIF-1's function in experimental models of acute ischemic stroke. Neuronal HIF-1α is an important mediator of antioxidant NAC's neuroprotective effect in ischemic stroke, whereas endothelial HIF-1α is involved in hyperglycemia-induced BBB breakdown after cerebral ischemia. The results suggest that developing therapeutic strategies by targeting HIF-1 needs to consider its multifunctional roles and differential effects on different cell types

    Targeting Fibronectin to Overcome Remyelination Failure in Multiple Sclerosis:The Need for Brain- and Lesion-Targeted Drug Delivery

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    Multiple sclerosis (MS) is a neuroinflammatory and neurodegenerative disease with unknown etiology that can be characterized by the presence of demyelinated lesions. Prevailing treatment protocols in MS rely on the modulation of the inflammatory process but do not impact disease progression. Remyelination is an essential factor for both axonal survival and functional neurological recovery but is often insufficient. The extracellular matrix protein fibronectin contributes to the inhibitory environment created in MS lesions and likely plays a causative role in remyelination failure. The presence of the blood-brain barrier (BBB) hinders the delivery of remyelination therapeutics to lesions. Therefore, therapeutic interventions to normalize the pathogenic MS lesion environment need to be able to cross the BBB. In this review, we outline the multifaceted roles of fibronectin in MS pathogenesis and discuss promising therapeutic targets and agents to overcome fibronectin-mediated inhibition of remyelination. In addition, to pave the way for clinical use, we reflect on opportunities to deliver MS therapeutics to lesions through the utilization of nanomedicine and discuss strategies to deliver fibronectin-directed therapeutics across the BBB. The use of well-designed nanocarriers with appropriate surface functionalization to cross the BBB and target the lesion sites is recommended
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