Role of nitric oxide synthases in early blood-brain barrier disruption following transient focal cerebral ischemia

H2S prevents the disruption of the blood-brain barrier in rats with prenatal hyperhomocysteinemia

Elevation of the homocysteine concentration in the plasma called hyperhomocysteinemia (hHCY) during pregnancy causes a number of pre- and postnatal developmental disorders. The aim of our study was to analyze the effects of H2S donors -NaHS and N-acetylcysteine (NAC) on blood-brain barrier (BBB) permeability in rats with prenatal hHCY. In rats with mild hHCY BBB permeability assessed by Evans Blue extravasation in brain increased markedly throughout life. Administration of NaHS or NAC during pregnancy attenuated hHCY-associated damage and increased endogenous concentrations of sulfides in brain tissues. Acute application of dl-homocysteine thiolactone induced BBB leakage, which was prevented by the NMDA receptor antagonist MK-801 or H2S donors. Rats with hHCY demonstrated high levels of NO metabolite - nitrites and proinflammatory cytokines (IL-1β, TNF-α, IL-6) in brain. Lactate dehydrogenase (LDH) activity in the serum was higher in rats with hHCY. Mitochondrial complex-I activity was lower in brain of hHCY rats. NaHS treatment during pregnancy restored levels of proinflammatory cytokines, nitrites and activity of the respiratory chain complex in brain as well as the LDH activity in serum. Our data suggest that H2S has neuroprotective effects against prenatal hHCY-associated BBB disturbance providing a potential strategy for the prevention of developmental impairments in newborns.

Anti-Neuroinflammatory Effects of Arecae pericarpium on LPS-Stimulated BV2 Cells

Arecae pericarpium (AP), the fruit peel of the betel palm, is a traditional Oriental herbal medicine. AP is used to treat various diseases and conditions, such as ascites, edema, and urinary retention, in traditional Korean medicine. Recent studies have demonstrated its anti-obesity and antibacterial effects; however, its anti-neuroinflammatory effects have not yet been reported. Therefore, we investigated the anti-neuroinflammatory effects of AP on lipopolysaccharide (LPS)-stimulated mouse microglia in this study. To determine the anti-neuroinflammatory effects of AP on BV2 microglial cells, we examined the production of nitric oxide (NO) using Griess assay and assessed the mRNA expression levels of inflammatory mediators, such as inducible NO synthase (iNOS) and cyclooxygenase (COX)-2, and pro-inflammatory cytokines, such as interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α, using a real-time reverse transcription-polymerase chain reaction. Furthermore, we determined the levels of mitogen-activated protein kinases and IκBα via Western blotting to understand the regulating mechanisms of AP. AP treatment decreased NO production in LPS-stimulated BV2 cells. Additionally, AP suppressed the expression of iNOS and COX-2 and the production of pro-inflammatory cytokines. AP also inhibited the activation of p38 and nuclear factor-kappa B (NF-κB) in LPS-stimulated BV2 cells. Therefore, AP exerts anti-neuroinflammatory effects via inactivation of the p38 and NF-κB pathways.

PSD-95 inhibitor Tat-NR2B9c (NA-1) protects the integrity of the blood-brain barrier after transient middle artery occlusion in rats by downregulating matrix metalloprotease-9 and upregulating endothelial nitric oxide synthase

BACKGROUND

Protection against ischemic stroke may be most effective when multiple components of the neurovascular unit are protected, yet current treatments target mainly neurons. Here we explored whether the PSD-95 inhibitor Tat-NR2B9c (NA-1) can protect not only neurons but also the blood-brain barrier.

METHODS

Adult male Sprague-Dawley rats were randomly divided into three groups, which were subjected to either sham surgery or transient cerebral ischemia-reperfusion, after which some animals were treated with Tat-NR2B9c. The therapeutic efficacy of Tat-NR2B9c was assessed in terms of the degree of neurological deficit and cerebral infarction, integrity of the blood-brain barrier, cerebral water content, as well as expression of PSD-95, nitric oxide synthase, and matrix metalloprotease-9.

RESULTS

Tat-NR2B9c (NA-1) ameliorated neurofunctional deficit, reduced cerebral infarction, mitigated blood-brain barrier injury and improved its integrity following ischemia-reperfusion, leading to less cerebral edema. These improvements were associated with upregulation of tight junction proteins in the blood-brain barrier. At the same time, Tat-NR2B9c (NA-1) downregulated neuronal nitric oxide synthase and matrix metalloprotease-9, while reversing the ischemia-induced downregulation of endothelial nitric oxide synthase in brain. We report here the first evidence that PSD-95 is expressed in vascular endothelial cells in the brain.

CONCLUSION

Our experiments in a rat model of transient occlusion of the middle cerebral artery suggest that Tat-NR2B9c (NA-1) can mitigate ischemic injury to the blood-brain barrier, and that it may do so by downregulating matrix metalloprotease-9 and upregulating endothelial nitric oxide synthase.

Argininosuccinate lyase deficiency causes blood-brain barrier disruption via nitric oxide-mediated dysregulation of claudin expression

Nitric oxide (NO) is a critical signaling molecule that has been implicated in the pathogenesis of neurocognitive diseases. Both excessive and insufficient NO production have been linked to pathology. Previously, we have shown that argininosuccinate lyase deficiency (ASLD) is a novel model system to investigate cell-autonomous, nitric oxide synthase-dependent NO deficiency. Humans with ASLD are at increased risk for developing hyperammonemia due to a block in ureagenesis. However, natural history studies have shown that individuals with ASLD have multisystem disease including neurocognitive deficits that can be independent of ammonia. Here, using ASLD as a model of NO deficiency, we investigated the effects of NO on brain endothelial cells in vitro and the blood-brain barrier (BBB) in vivo. Knockdown of ASL in human brain microvascular endothelial cells (HBMECs) led to decreased transendothelial electrical resistance, indicative of increased cell permeability. Mechanistically, treatment with an NO donor or inhibition of Claudin-1 improved barrier integrity in ASL-deficient HBMECs. Furthermore, in vivo assessment of a hypomorphic mouse model of ASLD showed increased BBB leakage, which was partially rescued by NO supplementation. Our results suggest that ASL-mediated NO synthesis is required for proper maintenance of brain microvascular endothelial cell functions as well as BBB integrity.

Microglia and the Blood-Brain Barrier: An External Player in Acute and Chronic Neuroinflammatory Conditions

Microglia are the resident immune cells of the central nervous system that guarantee immune surveillance and exert also a modulating role on neuronal synaptic development and function. Upon injury, microglia get activated and modify their morphology acquiring an ameboid phenotype and pro- or anti-inflammatory features. The active role of microglia in blood-brain barrier (BBB) function and their interaction with different cellular components of the BBB-endothelial cells, astrocytes and pericytes-are described. Here, we report the specific crosstalk of microglia with all the BBB cell types focusing in particular on the involvement of microglia in the modulation of BBB function in neuroinflammatory conditions that occur in conjunction with an acute event, such as a stroke, or in a slow neurodegenerative disease, such as Alzheimer's disease. The potential of microglia to exert a dual role, either protective or detrimental, depending on disease stages and environmental conditioning factors is also discussed.

Nitric Oxide/Nitric Oxide Synthase System in the Pathogenesis of Neurodegenerative Disorders-An Overview

Nitric oxide, a ubiquitous molecule found throughout the natural world, is a key molecule implicated in many central and benefic molecular pathways and has a well-established role in the function of the central nervous system, as numerous studies have previously shown. Dysregulation of its metabolism, mainly the upregulation of nitric oxide production, has been proposed as a trigger and/or aggravator for many neurological affections. Increasing evidence supports the implication of this molecule in prevalent neurodegenerative diseases, such as Parkinson's disease, Alzheimer's disease, or amyotrophic lateral sclerosis. The mechanisms proposed for its neurotoxicity mainly center around the increased quantities of nitric oxide that are produced in the brain, their cause, and, most importantly, the pathological metabolic cascades created. These cascades lead to the formation of neuronal toxic substances that impair the neurons' function and structure on multiple levels. The purpose of this review is to present the main causes of increased pathological production, as well as the most important pathophysiological mechanisms triggered by nitric oxide, mechanisms that could help explain a part of the complex picture of neurodegenerative diseases and help develop targeted therapies.

Leonurine Reduces Oxidative Stress and Provides Neuroprotection against Ischemic Injury via Modulating Oxidative and NO/NOS Pathway

Leonurine (Leo) has been found to have neuroprotective effects against cerebral ischemic injury. However, the exact molecular mechanism underlying its neuroprotective ability remains unclear. The aim of the present study was to investigate whether Leo could provide protection through the nitric oxide (NO)/nitric oxide synthase (NOS) pathway. We firstly explored the effects of NO/NOS signaling on oxidative stress and apoptosis in in vivo and in vitro models of cerebral ischemia. Further, we evaluated the protective effects of Leo against oxygen and glucose deprivation (OGD)-induced oxidative stress and apoptosis in PC12 cells. We found that the rats showed anxiety-like behavior, and the morphology and number of neurons were changed in a model of photochemically induced cerebral ischemia. Both in vivo and in vitro results show that the activity of superoxide dismutase (SOD) and glutathione (GSH) contents were decreased after ischemia, and reactive oxygen species (ROS) and malondialdehyde (MDA) levels were increased, indicating that cerebral ischemia induced oxidative stress and neuronal damage. Moreover, the contents of NO, total NOS, constitutive NOS (cNOS) and inducible NOS (iNOS) were increased after ischemia in rat and PC12 cells. Treatment with L-nitroarginine methyl ester (L-NAME), a nonselective NOS inhibitor, could reverse the change in NO/NOS expression and abolish these detrimental effects of ischemia. Leo treatment decreased ROS and MDA levels and increased the activity of SOD and GSH contents in PC12 cells exposed to OGD. Furthermore, Leo reduced NO/NOS production and cell apoptosis, decreased Bax expression and increased Bcl-2 levels in OGD-treated PC12 cells. All the data suggest that Leo protected against oxidative stress and neuronal apoptosis in cerebral ischemia by inhibiting the NO/NOS system. Our findings indicate that Leo could be a potential agent for the intervention of ischemic stroke and highlighted the NO/NOS-mediated oxidative stress signaling.

Role of Glial Cell-Derived Oxidative Stress in Blood-Brain Barrier Damage after Acute Ischemic Stroke

The integrity of the blood-brain barrier (BBB) is mainly maintained by endothelial cells and basement membrane and could be regulated by pericytes, neurons, and glial cells including astrocytes, microglia, oligodendrocytes (OLs), and oligodendrocyte progenitor cells (OPCs). BBB damage is the main pathological basis of hemorrhage transformation (HT) and vasogenic edema after stroke. In addition, BBB damage-induced HT and vasogenic edema will aggravate the secondary brain tissue damage. Of note, after reperfusion, oxidative stress-initiated cascade plays a critical role in the BBB damage after acute ischemic stroke (AIS). Although endothelial cells are the target of oxidative stress, the role of glial cell-derived oxidative stress in BBB damage after AIS also should receive more attention. In the current review, we first introduce the physiology and pathophysiology of the BBB, then we summarize the possible mechanisms related to BBB damage after AIS. We aim to characterize the role of glial cell-derived oxidative stress in BBB damage after AIS and discuss the role of oxidative stress in astrocytes, microglia cells and oligodendrocytes in after AIS, respectively.

Enhancing S-nitrosoglutathione reductase decreases S-nitrosylation of Drp1 and reduces neuronal apoptosis in experimental subarachnoid hemorrhage both in vivo and in vitro

Subarachnoid hemorrhage (SAH) is a hemorrhagic stroke with a high mortality and disability rate. Nitric oxide (NO) can promote blood supply through vasodilation, leading to protein S-nitrosylation. However, the function of S-nitrosylation in neurons after SAH remains unclear. Excessive NO in the pathological state is converted into S-nitrosoglutathione (GSNO) and stored in cells, which leads to high S-nitrosylation of intracellular proteins and causes nitrosative stress. S-nitrosoglutathione reductase (GSNOR) promotes GSNO degradation and protects cells from excessive S-nitrosylation. We conducted an in vivo rat carotid puncture model and an in vitro neuron hemoglobin intervention. The results showed that SAH induction increased NO, GSNO, neuron protein S-nitrosylation, and neuronal apoptosis, while decreasing the level and activity of GSNOR. GSNOR overexpression by lentivirus decreased GSNO but had little effect on NO. GSNOR overexpression also improved short- and long-term neurobehavioral outcomes in rats and alleviated nitrosative stress. Furthermore, GSNOR reduced neuronal apoptosis and played a neuroprotective role by alleviating Drp1 S-nitrosylation, reducing mitochondrial division. Thus, the regulation of GSNOR in early brain injury and neuronal denitrosylation may play an important role in neuroprotection.

Reactive Astrocytes in Central Nervous System Injury: Subgroup and Potential Therapy

Traumatic central nervous system (CNS) injury, which includes both traumatic brain injury (TBI) and spinal cord injury (SCI), is associated with irreversible loss of neurological function and high medical care costs. Currently, no effective treatment exists to improve the prognosis of patients. Astrocytes comprise the largest population of glial cells in the CNS and, with the advancements in the field of neurology, are increasingly recognized as having key functions in both the brain and the spinal cord. When stimulated by disease or injury, astrocytes become activated and undergo a series of changes, including alterations in gene expression, hypertrophy, the loss of inherent functions, and the acquisition of new ones. Studies have shown that astrocytes are highly heterogeneous with respect to their gene expression profiles, and this heterogeneity accounts for their observed context-dependent phenotypic diversity. In the inured CNS, activated astrocytes play a dual role both as regulators of neuroinflammation and in scar formation. Identifying the subpopulations of reactive astrocytes that exert beneficial or harmful effects will aid in deciphering the pathological mechanisms underlying CNS injuries and ultimately provide a theoretical basis for the development of effective strategies for the treatment of associated conditions. Following CNS injury, as the disease progresses, astrocyte phenotypes undergo continuous changes. Although current research methods do not allow a comprehensive and accurate classification of astrocyte subpopulations in complex pathological contexts, they can nonetheless aid in understanding the roles of astrocytes in disease. In this review, after a brief introduction to the pathology of CNS injury, we summarize current knowledge regarding astrocyte activation following CNS injury, including: (a) the regulatory factors involved in this process; (b) the functions of different astrocyte subgroups based on the existing classification of astrocytes; and (c) attempts at astrocyte-targeted therapy.

Chronic Low-Dose Alcohol Consumption Promotes Cerebral Angiogenesis in Mice

Chronic alcohol consumption dose-dependently affects the incidence and prognosis of ischemic stroke. We determined the influence of chronic alcohol consumption on cerebral angiogenesis under physiological conditions and following ischemic stroke. In in vitro studies, acute exposure to low-concentration ethanol significantly increased angiogenic capability and upregulated vascular endothelial growth factor A (VEGF-A) and vascular endothelial growth factor receptor 2 (VEGFR2) in C57BL/6J mouse brain microvascular endothelial cells (MBMVECs). The increased angiogenic capability was abolished in the presence of a VEGFR2 inhibitor. In addition, the increased angiogenic capability and upregulated VEGF-A and VEGFR2 remained in chronically low-concentration ethanol-exposed MBMVECs. In in vivo studies, 8-week gavage feeding with low-dose ethanol significantly increased vessel density and vessel branches and upregulated VEGF-A and VEGFR2 in the cerebral cortex under physiological conditions. Furthermore, vessel density, vessel branches, and expression of VEGF-A and VEGFR2 in the peri-infarct cortex were significantly greater in low-dose ethanol-fed mice at 72 h of reperfusion. Although low-dose ethanol did not alter cerebral vasoreactivity and regional cerebral blood flow (rCBF) either before or during ischemia, it significantly augmented post-ischemic hyperemia during reperfusion. In contrast, exposure to high-concentration ethanol and 8-week gavage feeding with high-dose ethanol only had a mild inhibitory effect on angiogenic capability and cerebral angiogenesis, respectively. We conclude that heavy alcohol consumption may not dramatically alter cerebral angiogenesis, whereas light alcohol consumption significantly promotes cerebral angiogenesis.

Activation and Role of Astrocytes in Ischemic Stroke

Ischemic stroke refers to the disorder of blood supply of local brain tissue caused by various reasons. It has high morbidity and mortality worldwide. Astrocytes are the most abundant glial cells in the central nervous system (CNS). They are responsible for the homeostasis, nutrition, and protection of the CNS and play an essential role in many nervous system diseases’ physiological and pathological processes. After stroke injury, astrocytes are activated and play a protective role through the heterogeneous and gradual changes of their gene expression, morphology, proliferation, and function, that is, reactive astrocytes. However, the position of reactive astrocytes has always been a controversial topic. Many studies have shown that reactive astrocytes are a double-edged sword with both beneficial and harmful effects. It is worth noting that their different spatial and temporal expression determines astrocytes’ various functions. Here, we comprehensively review the different roles and mechanisms of astrocytes after ischemic stroke. In addition, the intracellular mechanism of astrocyte activation has also been involved. More importantly, due to the complex cascade reaction and action mechanism after ischemic stroke, the role of astrocytes is still difficult to define. Still, there is no doubt that astrocytes are one of the critical factors mediating the deterioration or improvement of ischemic stroke.

Nitric Oxide-Dependent Mechanisms Underlying MK-801- or Scopolamine-Induced Memory Dysfunction in Animals: Mechanistic Studies

MK-801, an NMDA receptor antagonist, and scopolamine, a cholinergic receptor blocker, are widely used as tool compounds to induce learning and memory deficits in animal models to study schizophrenia or Alzheimer-type dementia (AD), respectively. Memory impairments are observed after either acute or chronic administration of either compound. The present experiments were performed to study the nitric oxide (NO)-related mechanisms underlying memory dysfunction induced by acute or chronic (14 days) administration of MK-801 (0.3 mg/kg, i.p.) or scopolamine (1 mg/kg, i.p.). The levels of L-arginine and its derivatives, L-citrulline, L-glutamate, L-glutamine and L-ornithine, were measured. The expression of constitutive nitric oxide synthases (cNOS), dimethylaminohydrolase (DDAH1) and protein arginine N-methyltransferases (PMRTs) 1 and 5 was evaluated, and the impact of the studied tool compounds on cGMP production and NMDA receptors was measured. The studies were performed in both the cortex and hippocampus of mice. S-nitrosylation of selected proteins, such as GLT-1, APP and tau, was also investigated. Our results indicate that the availability of L-arginine decreased after chronic administration of MK-801 or scopolamine, as both the amino acid itself as well as its level in proportion to its derivatives (SDMA and NMMA) were decreased. Additionally, among all three methylamines, SDMA was the most abundant in the brain (~70%). Administration of either compound impaired eNOS-derived NO production, increasing the monomer levels, and had no significant impact on nNOS. Both compounds elevated DDAH1 expression, and slight decreases in PMRT1 and PMRT5 in the cortex after scopolamine (acute) and MK-801 (chronic) administration were observed in the PFC, respectively. Administration of MK-801 induced a decrease in the cGMP level in the hippocampus, accompanied by decreased NMDA expression, while increased cGMP production and decreased NMDA receptor expression were observed after scopolamine administration. Chronic MK-801 and scopolamine administration affected S-nitrosylation of GLT-1 transport protein. Our results indicate that the analyzed tool compounds used in pharmacological models of schizophrenia or AD induce changes in NO-related pathways in the brain structures involved in cognition. To some extent, the changes resemble those observed in human samples.

Nitric Oxide-Dependent Pathways as Critical Factors in the Consequences and Recovery after Brain Ischemic Hypoxia

Brain ischemia is one of the leading causes of disability and mortality worldwide. Nitric oxide (NO^•), a molecule that is involved in the regulation of proper blood flow, vasodilation, neuronal and glial activity constitutes the crucial factor that contributes to the development of pathological changes after stroke. One of the early consequences of a sudden interruption in the cerebral blood flow is the massive production of reactive oxygen and nitrogen species (ROS/RNS) in neurons due to NO^• synthase uncoupling, which leads to neurotoxicity. Progression of apoptotic or necrotic neuronal damage activates reactive astrocytes and attracts microglia or lymphocytes to migrate to place of inflammation. Those inflammatory cells start to produce large amounts of inflammatory proteins, including pathological, inducible form of NOS (iNOS), which generates nitrosative stress that further contributes to brain tissue damage, forming vicious circle of detrimental processes in the late stage of ischemia. S-nitrosylation, hypoxia-inducible factor 1α (HIF-1α) and HIF-1α-dependent genes activated in reactive astrocytes play essential roles in this process. The review summarizes the roles of NO^•-dependent pathways in the early and late aftermath of stroke and treatments based on the stimulation or inhibition of particular NO^• synthases and the stabilization of HIF-1α activity.

Blood-Brain Barrier and Neurodegenerative Diseases-Modeling with iPSC-Derived Brain Cells

The blood-brain barrier (BBB) regulates the delivery of oxygen and important nutrients to the brain through active and passive transport and prevents neurotoxins from entering the brain. It also has a clearance function and removes carbon dioxide and toxic metabolites from the central nervous system (CNS). Several drugs are unable to cross the BBB and enter the CNS, adding complexity to drug screens targeting brain disorders. A well-functioning BBB is essential for maintaining healthy brain tissue, and a malfunction of the BBB, linked to its permeability, results in toxins and immune cells entering the CNS. This impairment is associated with a variety of neurological diseases, including Alzheimer's disease and Parkinson's disease. Here, we summarize current knowledge about the BBB in neurodegenerative diseases. Furthermore, we focus on recent progress of using human-induced pluripotent stem cell (iPSC)-derived models to study the BBB. We review the potential of novel stem cell-based platforms in modeling the BBB and address advances and key challenges of using stem cell technology in modeling the human BBB. Finally, we highlight future directions in this area.

Interaction between Aβ and Tau in the Pathogenesis of Alzheimer's Disease

Extracellular neuritic plaques composed of amyloid‑β (Aβ) protein and intracellular neurofibrillary tangles containing phosphorylated tau protein are the two hallmark proteins of Alzheimer's disease (AD), and the separate neurotoxicity of these proteins in AD has been extensively studied. However, interventions that target Aβ or tau individually have not yielded substantial breakthroughs. The interest in the interactions between Aβ and tau in AD is increasing, but related drug investigations are in their infancy. This review discusses how Aβ accelerates tau phosphorylation and the possible mechanisms and pathways by which tau mediates Aβ toxicity. This review also describes the possible synergistic effects between Aβ and tau on microglial cells and astrocytes. Studies suggest that the coexistence of Aβ plaques and phosphorylated tau is related to the mechanism by which Aβ facilitates the propagation of tau aggregation in neuritic plaques. The interactions between Aβ and tau mediate cognitive dysfunction in patients with AD. In summary, this review summarizes recent data on the interplay between Aβ and tau to promote a better understanding of the roles of these proteins in the pathological process of AD and provide new insights into interventions against AD.

Memantine protects blood-brain barrier integrity and attenuates neurological deficits through inhibiting nitric oxide synthase ser1412 phosphorylation in intracerebral hemorrhage rats: involvement of peroxynitrite-related matrix metalloproteinase-9/NLRP3 inflammasome activation

Memantine has demonstrated beneficial effects on several types of brain insults via therapeutic mechanisms mainly related to its activity as a receptor antagonist of N-methyl-d-aspartate. However, the influences of memantine on intracerebral hemorrhage (ICH) remain obscure. This research probed into the neurovascular protective mechanisms of memantine after ICH and its impacts on neuronal nitric oxide synthase (nNOS) ser1412 phosphorylation. ICH model was established by employing intrastriatal collagenase injection in rats. After modeling, rats were then allocated randomly into sham-operated (sham), vehicle-treated (ICH+V), and memantine-administrated (ICH+M) groups. Memantine (20 mg/kg/day) was intraperitoneally administered 30 min after ICH and thenceforth once daily. Rats were dedicated at 0.25, 6, 12, 24 h, 3 and 7 d post-ICH for measurement of corresponding indexes. Behavioral changes, brain edema, levels of nNOS ser1412 phosphorylation, peroxynitrite, matrix metalloproteinase (MMP)-9, NLRP3, IL-1β and numbers of dying neurons, as well as the cellular localization of gelatinolytic activity, were detected among the groups. Memantine improved the neurologic deficits and mitigated brain water content, levels of MMP-9, NLRP3, IL-1β and dying neurons. Additionally, treatment with memantine also reduced nNOS ser1412 phosphorylation and peroxynitrite formation compared with the ICH+V group at 24 h after ICH. In situ zymography simultaneously revealed that gelatinase activity was primarily colocalized with vessel walls and neurons. We concluded that memantine ameliorated blood-brain barrier disruption and neurologic dysfunction in an ICH rat model. The underlying mechanism might involve repression of nNOS ser1412 phosphorylation, as well as peroxynitrite-related MMP-9 and NLRP3 inflammasome activation.

Dual roles of astrocytes in plasticity and reconstruction after traumatic brain injury

Traumatic brain injury (TBI) is one of the leading causes of fatality and disability worldwide. Despite its high prevalence, effective treatment strategies for TBI are limited. Traumatic brain injury induces structural and functional alterations of astrocytes, the most abundant cell type in the brain. As a way of coping with the trauma, astrocytes respond in diverse mechanisms that result in reactive astrogliosis. Astrocytes are involved in the physiopathologic mechanisms of TBI in an extensive and sophisticated manner. Notably, astrocytes have dual roles in TBI, and some astrocyte-derived factors have double and opposite properties. Thus, the suppression or promotion of reactive astrogliosis does not have a substantial curative effect. In contrast, selective stimulation of the beneficial astrocyte-derived molecules and simultaneous attenuation of the deleterious factors based on the spatiotemporal-environment can provide a promising astrocyte-targeting therapeutic strategy. In the current review, we describe for the first time the specific dual roles of astrocytes in neuronal plasticity and reconstruction, including neurogenesis, synaptogenesis, angiogenesis, repair of the blood-brain barrier, and glial scar formation after TBI. We have also classified astrocyte-derived factors depending on their neuroprotective and neurotoxic roles to design more appropriate targeted therapies.

Anti-inflammatory Effects of Traditional Chinese Medicines on Preclinical in vivo Models of Brain Ischemia-Reperfusion-Injury: Prospects for Neuroprotective Drug Discovery and Therapy

Acquired brain ischemia-and reperfusion-injury (IRI), including both Ischemic stroke (IS) and Traumatic Brain injury (TBI), is one of the most common causes of disability and death in adults and represents a major burden in both western and developing countries worldwide. China’s clinical neurological therapeutic experience in the use of traditional Chinese medicines (TCMs), including TCM-derived active compounds, Chinese herbs, TCM formulations and decoction, in brain IRI diseases indicated a trend of significant improvement in patients’ neurological deficits, calling for blind, placebo-controlled and randomized clinical trials with careful meta-analysis evaluation. There are many TCMs in use for brain IRI therapy in China with significant therapeutic effects in preclinical studies using different brain IRI-animal. The basic hypothesis in this field claims that in order to avoid the toxicity and side effects of the complex TCM formulas, individual isolated and identified compounds that exhibited neuroprotective properties could be used as lead compounds for the development of novel drugs. China’s efforts in promoting TCMs have contributed to an explosive growth of the preclinical research dedicated to the isolation and identification of TCM-derived neuroprotective lead compounds. Tanshinone, is a typical example of TCM-derived lead compounds conferring neuroprotection toward IRI in animals with brain middle cerebral artery occlusion (MCAO) or TBI models. Recent reports show the significance of the inflammatory response accompanying brain IRI. This response appears to contribute to both primary and secondary ischemic pathology, and therefore anti-inflammatory strategies have become popular by targeting pro-inflammatory and anti-inflammatory cytokines, other inflammatory mediators, reactive oxygen species, nitric oxide, and several transcriptional factors. Here, we review recent selected studies and discuss further considerations for critical reevaluation of the neuroprotection hypothesis of TCMs in IRI therapy. Moreover, we will emphasize several TCM’s mechanisms of action and attempt to address the most promising compounds and the obstacles to be overcome before they will enter the clinic for IRI therapy. We hope that this review will further help in investigations of neuroprotective effects of novel molecular entities isolated from Chinese herbal medicines and will stimulate performance of clinical trials of Chinese herbal medicine-derived drugs in IRI patients.

Dual Roles of Astrocyte-Derived Factors in Regulation of Blood-Brain Barrier Function after Brain Damage

The blood-brain barrier (BBB) is a major functional barrier in the central nervous system (CNS), and inhibits the extravasation of intravascular contents and transports various essential nutrients between the blood and the brain. After brain damage by traumatic brain injury, cerebral ischemia and several other CNS disorders, the functions of the BBB are disrupted, resulting in severe secondary damage including brain edema and inflammatory injury. Therefore, BBB protection and recovery are considered novel therapeutic strategies for reducing brain damage. Emerging evidence suggests key roles of astrocyte-derived factors in BBB disruption and recovery after brain damage. The astrocyte-derived vascular permeability factors include vascular endothelial growth factors, matrix metalloproteinases, nitric oxide, glutamate and endothelin-1, which enhance BBB permeability leading to BBB disruption. By contrast, the astrocyte-derived protective factors include angiopoietin-1, sonic hedgehog, glial-derived neurotrophic factor, retinoic acid and insulin-like growth factor-1 and apolipoprotein E which attenuate BBB permeability resulting in recovery of BBB function. In this review, the roles of these astrocyte-derived factors in BBB function are summarized, and their significance as therapeutic targets for BBB protection and recovery after brain damage are discussed.

Nano-liposomes of lycopene reduces ischemic brain damage in rodents by regulating iron metabolism

In order to discover new drug delivery approaches and to understand the mechanism of iron overload in cerebral ischemia/reperfusion (I/R), we aimed to investigate the effects of lycopene (LYC) in the form of nano-liposomes (L-LYC) on iron-regulating proteins and ischemic brain injury. We found that L-LYC significantly increased the LYC content in serum and the brain. Adult male Sprague-Dawley rats treated with L-LYC for 14 days were subjected to 60 min of ischemia and 7 days of reperfusion. The effects of L-LYC were evaluated by infarction volume, neurological score, neuronal apoptosis, and markers for oxidative stress. Levels of iron-regulating protein such as hepcidin and ferroportin (FPN1) were examined. L-LYC reduced cerebral infarction and improved neurobehavior of the rats more efficiently than "naked" LYC. L-LYC reduced protein levels of oxidases (e.g. nitric oxide synthase and NOX2), increased the level of Bcl-2, lowered caspase-3, and suppressed apoptosis through inhibiting MAPK-JNK. Furthermore, L-LYC suppressed hepcidin-mediated decrease in FPN1, a sole iron exporter, and normalized the levels of iron. We further demonstrated that the effect of L-LYC on hepcidin expression might result from its ability to attenuate the release of the inflammatory factor interleukin 6. The results demonstrated that nano-liposomal encapsulation significantly improved LYC efficacy in providing neuronal protection against I/R injury. The data also revealed a novel mechanism of L-LYC's neuroprotection by regulating iron metabolism in an ischemic brain.

Development of a reactive oxygen species-sensitive nitric oxide synthase inhibitor for the treatment of ischemic stroke

Ischemic stroke is caused by a blockage of cerebral blood flow resulting in neuronal and glial hypoxia leading to inflammatory and reactive oxygen species (ROS)-mediated cell death. Nitric oxide (NO) formed by NO synthase (NOS) is known to be protective in ischemic stroke, however NOS has been shown to 'uncouple' under oxidative conditions to instead produce ROS. Nitrones are antioxidant molecules that are shown to trap ROS to then decompose and release NO. In this study, the nitrone 5 was designed such that its decomposition product is a NOS inhibitor, 6, effectively leading to NOS inhibition specifically at the site of ROS production. The ability of 5 to spin-trap radicals and decompose to 6 was observed using EPR and LC-MS/MS. The pro-drug concept was tested in vitro by measuring cell viability and 6 formation in SH-SY5Y cells subjected to oxygen glucose deprivation (OGD). 5 was found to be more efficacious and more potent than PBN, and was able to increase phospho-Akt while reducing nitrotyrosine and cleaved caspase-3 levels. 6 treatment, but not 5, was found to decrease NO production in LPS-stimulated microglia. Doppler flowmetry on anesthetized mice showed increased cerebral blood flow upon intravenous administration of 1mg/kg of 5, but a return to baseline upon administration of 10mg/kg, likely due to its dual nature of antioxidant/NO-donor and NOS-inhibition. Mice treated with 5 after permanent ischemia exhibited a >30% reduction in infarct volume, and higher formation of 6 in ischemic tissue resulting in region specific effects limited to the infarct area.

Neuroprotective effect of total flavonoids from Ilex pubescens against focal cerebral ischemia/reperfusion injury in rats

Ilex pubescens is commonly used in traditional Chinese medicine to treat cardiovascular and cerebrovascular diseases, such as coronary artery disease and stroke. However, the underlying mechanisms remain to be fully elucidated. The aim of the present study was to investigate the effects of Ilex pubescens total flavonoids (IPTF) on neuroprotection and the potential mechanisms in a rat model of focal cerebral ischemia/reperfusion (I/R) injury. Rats were pretreated with intragastric administration of IPTF at doses of 200 and 100 mg/kg for 5 days; middle cerebral artery occlusion surgery was then performed to induce cerebral I/R injury. Neurological deficits were determined using the 5‑point neurological function score evaluation system, brain infarct sizes were determined by 2,3,5‑triphenyltetrazolium chloride staining and alterations in brain histology were determined by hematoxylin and eosin staining. The neurological deficit score, the infarcted area and the brain tissue pathological injury were significantly reduced when the rats were pretreated with IPTF. In addition, inflammatory mediators and neurotrophic factors in the brain were investigated. IPTF pretreatment decreased the activities of total nitric oxide synthase (TNOS), induced NOS (iNOS) and constitutive NOS (cNOS), and the levels of nitric oxide (NO), interleukin‑1β (IL‑1β) and tumor necrosis factor‑α (TNF‑α), however, it increased the levels of IL‑10 in brain tissues. Furthermore, pretreatment with IPTF also increased the protein expressions of brain‑derived neurotrophic factor, glial cell‑derived neurotrophic factor and vascular endothelial growth factor, when compared with the model group. In conclusion, the results of the present study demonstrated that IPTF has a neuroprotective effect against focal cerebral I/R injury in rats. The mechanism may be associated with the decreased production of certain proinflammatory cytokines including NO, IL‑1β, TNF‑α, TNOS, iNOS and cNOS, the increased production of the anti‑inflammatory cytokine IL‑10 and the increased secretion of neurotrophic factors.

Connexin Channels at the Glio-Vascular Interface: Gatekeepers of the Brain

Neuronal survival, electrical signaling and synaptic activity require a well-balanced micro-environment in the central nervous system. This is achieved by the blood-brain barrier (BBB), an endothelial barrier situated in the brain capillaries, that controls near-to-all passage in and out of the brain. The endothelial barrier function is highly dependent on signaling interactions with surrounding glial, neuronal and vascular cells, together forming the neuro-glio-vascular unit. Within this functional unit, connexin (Cx) channels are of utmost importance for intercellular communication between the different cellular compartments. Connexins are best known as the building blocks of gap junction (GJ) channels that enable direct cell-cell transfer of metabolic, biochemical and electric signals. In addition, beyond their role in direct intercellular communication, Cxs also form unapposed, non-junctional hemichannels in the plasma membrane that allow the passage of several paracrine messengers, complementing direct GJ communication. Within the NGVU, Cxs are expressed in vascular endothelial cells, including those that form the BBB, and are eminent in astrocytes, especially at their endfoot processes that wrap around cerebral vessels. However, despite the density of Cx channels at this so-called gliovascular interface, it remains unclear as to how Cx-based signaling between astrocytes and BBB endothelial cells may converge control over BBB permeability in health and disease. In this review we describe available evidence that supports a role for astroglial as well as endothelial Cxs in the regulation of BBB permeability during development as well as in disease states.

One-Compound-Multi-Target: Combination Prospect of Natural Compounds with Thrombolytic Therapy in Acute Ischemic Stroke

Tissue plasminogen activator (t-PA) is the only FDA-approved drug for acute ischemic stroke treatment, but its clinical use is limited due to the narrow therapeutic time window and severe adverse effects, including hemorrhagic transformation (HT) and neurotoxicity. One of the potential resolutions is to use adjunct therapies to reduce the side effects and extend t-PA's therapeutic time window. However, therapies modulating single target seem not to be satisfied, and a multitarget strategy is warranted to resolve such complex disease. Recently, large amount of efforts have been made to explore the active compounds from herbal supplements to treat ischemic stroke. Some natural compounds revealed both neuro- and bloodbrain- barrier (BBB)-protective effects by concurrently targeting multiple cellular signaling pathways in cerebral ischemia-reperfusion injury. Thus, those compounds are potential to be one-drug-multi-target agents as combined therapy with t-PA for ischemic stroke. In this review article, we summarize current progress about molecular targets involving in t-PA-mediated HT and neurotoxicity in ischemic brain injury. Based on these targets, we select 23 promising compounds from currently available literature with the bioactivities simultaneously targeting several important molecular targets. We propose that those compounds merit further investigation as combined therapy with t-PA. Finally, we discuss the potential drawbacks of the natural compounds' studies and raise several important issues to be addressed in the future for the development of natural compound as an adjunct therapy.

Sex-dichotomous effects of NOS1AP promoter DNA methylation on intracranial aneurysm and brain arteriovenous malformation

The goal of this study was to investigate the contribution of NOS1AP-promoter DNA methylation to the risk of intracranial aneurysm (IA) and brain arteriovenous malformation (BAVM) in a Han Chinese population. A total of 48 patients with IAs, 22 patients with BAVMs, and 26 control individuals were enrolled in the study. DNA methylation was tested using bisulfite pyrosequencing technology. We detected significantly higher DNA methylation levels in BAVM patients than in IA patients based on the multiple testing correction (CpG4-5 methylation: 5.86±1.04% vs. 4.37±2.64%, P=0.006). In women, CpG4-5 methylation levels were much lower in IA patients (3.64±1.97%) than in BAVM patients (6.11±1.20%, P<0.0001). However, in men, CpG1-3 methylation levels were much higher in the controls (6.92±0.78%) than in BAVM patients (5.99±0.70%, P=0.008). Additionally, there was a gender-based difference in CpG1 methylation within the controls (men vs. women: 5.75±0.50% vs. 4.99±0.53%, P=0.003) and BAVM patients (men vs. women: 4.70±0.74% vs. 5.50±0.87%, P=0.026). A subgroup analysis revealed significantly higher CpG3 methylation in patients who smoked than in those who did not (P=0.041). Our results suggested that gender modulated the interaction between NOS1AP promoter DNA methylation in IA and BAVM patients. Our results also confirmed that regular tobacco smoking was associated with increased NOS1AP methylation in humans. Additional studies with larger sample sizes are required to replicate and extend these findings.

Modulation of Hyperosmotic and Immune-Induced Disruption of the Blood-Brain Barrier by the Nitric Oxide System

OBJECTIVES

The role of nitric oxide (NO) in modulating the blood-brain barrier (BBB) is not entirely clear. We examined the effect of different NO synthase (NOS) inhibitors and NO donors on the permeability of the BBB in animals with normally functioning brain blood vessels, following disruption by hyperosmotic mannitol and during immune inflammation.

METHODS

We administered L-NAME, aminoguanidine, S-methyl-thiocitrulline (SMT) and 7-indazole (NOS inhibitors) and NOR-4 (an NO donor) into the cerebral ventricle of rats. Disruption of the BBB was induced by intracarotid injection of mannitol (25%). Experimental autoimmune encephalomyelitis (EAE) was induced by brain homogenate. The extent of disruption was evaluated by Evans blue (2%) dye extravasation.

RESULTS

L-NAME (a nonspecific NOS inhibitor) and SMT (a neuronal and endothelial NOS inhibitor) increased mannitol-induced disruption of BBB. This effect was inhibited by NO donors. In animals with a normally functioning BBB, none of these inhibitors or NO donors caused a change in the permeability. 7-indazole (a specific neuronal NOS inhibitor) and aminoguanidine (an inducible NOS inhibitor) had no facilitatory effect on BBB permeability, either alone or in combination with hyperosmotic mannitol. Administration of L-NAME and SMT to rats with EAE significantly aggravated the clinical outcome. In contrast, the administration of NOR-4 diminished clinical signs of EAE.

CONCLUSION

The NOS system does not play a role in BBB permeability in naïve animals. Only endothelial NOS takes part in the facilitation of BBB compromised by mannitol and EAE. Extrinsic NO decreases this facilitatory effect.

Markers for blood-brain barrier integrity: how appropriate is Evans blue in the twenty-first century and what are the alternatives?

In recent years there has been a resurgence of interest in brain barriers and various roles their intrinsic mechanisms may play in neurological disorders. Such studies require suitable models and markers to demonstrate integrity and functional changes at the interfaces between blood, brain, and cerebrospinal fluid. Studies of brain barrier mechanisms and measurements of plasma volume using dyes have a long-standing history, dating back to the late nineteenth-century. Their use in blood-brain barrier studies continues in spite of their known serious limitations in in vivo applications. These were well known when first introduced, but seem to have been forgotten since. Understanding these limitations is important because Evans blue is still the most commonly used marker of brain barrier integrity and those using it seem oblivious to problems arising from its in vivo application. The introduction of HRP in the mid twentieth-century was an important advance because its reaction product can be visualized at the electron microscopical level, but it also has limitations. Advantages and disadvantages of these markers will be discussed together with a critical evaluation of alternative approaches. There is no single marker suitable for all purposes. A combination of different sized, visualizable dextrans and radiolabeled molecules currently seems to be the most appropriate approach for qualitative and quantitative assessment of barrier integrity.

The Zinc Ion Chelating Agent TPEN Attenuates Neuronal Death/apoptosis Caused by Hypoxia/ischemia Via Mediating the Pathophysiological Cascade Including Excitotoxicity, Oxidative Stress, and Inflammation

AIMS

We aim to determine the significant effect of TPEN, a Zn(2+) chelator, in mediating the pathophysiological cascade in neuron death/apoptosis induced by hypoxia/ischemia.

METHODS

We conducted both in vivo and in vitro experiments in this study. PC12 cells were used to establish hypoxia/ischemia model by applying oxygen-glucose deprivation (OGD). SHR-SP rats were used to establish an acute ischemic model by electrocoagulating middle cerebral artery occlusion. The effect of TPEN on neuron death/apoptosis was evaluated. In addition, the relative biomarks of excitotoxicity, oxidative stress, and inflammation reactions in hypoxia/ischemia PC12 cell model as well as in SHR-SP rat hypoxia/ischemia model were also assessed.

RESULTS

TPEN significantly attenuates the neurological deficit, reduced the cerebral infarction area and the ratio of apoptotic neurons, and increased the expression of GluR2 in the rat hypoxia/ischemia brain. TPEN also increased blood SOD activity, decreased blood NOS activity and blood MDA and IL-6 contents in rats under hypoxia/ischemia. In addition, TPEN significantly inhibited the death and apoptosis of cells and attenuated the alteration of GluR2 and NR2 expression caused by OGD or OGD plus high Zn(2+) treatments.

CONCLUSIONS

Zn(2+) is involved in neural cell apoptosis and/or death caused by hypoxia/ischemia via mediating excitotoxicity, oxidative stress, and inflammation.

Endothelial NOS activation induces the blood-brain barrier disruption via ER stress following status epilepticus

The blood-brain barrier (BBB) maintains the unique brain microenvironment, which is separated from the systemic circulating system. Since the endoplasmic reticulum (ER) is an important cell organelle that is responsible for protein synthesis, the correct folding and sorting of proteins contributing to cell survivals, ER stress is a potential cause of cell damage in various diseases. Therefore, it would be worthy to explore the the relationship between the ER stress and BBB disruption during vasogenic edema formation induced by epileptogenic insults. In the present study, we investigated the roles of ER stress in vasogenic edema and its related events in rat epilepsy models provoked by pilocarpine-induced status epilepticus (SE). SE-induced eNOS activation induces BBB breakdown via up-regulation of GRP78 expression and dysfunction of SMI-71 (an endothelial BBB marker) in the piriform cortex (PC). In addition, caveolin-1 peptide (an eNOS inhibitor) effectively attenuated GRP78 expression and down-regulation of SMI-71. Taken together, our findings suggest that eNOS-mediated ER stress may participate in SE-induced vasogenic edema formation. Therefore, the modulation of ER stress may be a considerable strategy for therapy in impairments of endothelial cell function.

Neuronal self-injury mediated by IL-1β and MMP-9 in a cerebral palsy model of severe neonatal encephalopathy induced by immune activation plus hypoxia-ischemia

BACKGROUND

Inflammation due to remote pathogen exposure combined to hypoxia/ischemia (HI) is one of the most common causes of neonatal encephalopathy affecting at-term or near-term human newborn, which will consequently develop cerebral palsy. Within term-equivalent rat brains exposed to systemic lipopolysaccharide (LPS) plus HI, it was previously showed that neurons produce IL-1β earlier than do glial cells, and that blocking IL-1 was neuroprotective. To further define the mechanisms whereby IL-1 exerts its neurotoxic effect, we hypothesize that IL-1β plays a pivotal role in a direct and/or indirect mechanistic loop of neuronal self-injury through matrix metalloproteinase (MMP)-9.

METHODS

An established preclinical rat model of LPS+HI-induced neonatal encephalopathy was used. In situ hybridization, ELISA, and immunolabeling techniques were employed. Selective blocking compounds allowed addressing the respective roles of IL-1 and MMP-9.

RESULTS

In LPS+HI-exposed forebrains, neuronal IL-1β was first detected in infarcted neocortical and striatal areas and later in glial cells of the adjacent white matter. Neuronal IL-1β played a key role: (i) in the early post-HI exacerbation of neuroinflammation and (ii) in generating both core and penumbral infarcted cerebral areas. Systemically administered IL-1 receptor antagonist (IL-1Ra) reached the brain and bound to the neocortical and deep gray neuronal membranes. Then, IL-1Ra down-regulated IL-1β mRNA and MMP-9 neuronal synthesis. Immediately post-HI, neuronal IL-1β up-regulated cytokine-induced neutrophil chemoattractant (CINC-1), monocyte chemoattractant protein-1 (MCP-1), and inducible nitric oxide synthase. MMP-9 would disrupt the blood-brain barrier, which, combined to CINC-1 up-regulation, would play a role in polymorphonuclear cell (PMN) infiltration into the LPS+HI-exposed brain. IL-1β blockade prevented PMN infiltration and oriented the phenotype of macrophagic/microglial cells towards anti-inflammatory and neurotrophic M2 profile. IL-1β increased the expression of activated caspase-3 and of receptor-interacting-protein (RIP)-3 within infarcted forebrain area. Such apoptotic and necroptotic pathway activations were prevented by IL-1Ra, as well as ensuing cerebral palsy-like brain damage and motor impairment.

CONCLUSIONS

This work uncovered a new paradigm of neuronal self-injury orchestrated by neuronal synthesis of IL-1β and MMP-9. In addition, it reinforced the translational neuroprotective potential of IL-1 blockers to alleviate human perinatal brain injuries.

Glycolysis-mediated control of blood-brain barrier development and function

The blood-brain barrier (BBB) consists of differentiated cells integrating in one ensemble to control transport processes between the central nervous system (CNS) and peripheral blood. Molecular organization of BBB affects the extracellular content and cell metabolism in the CNS. Developmental aspects of BBB attract much attention in recent years, and barriergenesis is currently recognized as a very important and complex mechanism of CNS development and maturation. Metabolic control of angiogenesis/barriergenesis may be provided by glucose utilization within the neurovascular unit (NVU). The role of glycolysis in the brain has been reconsidered recently, and it is recognized now not only as a process active in hypoxic conditions, but also as a mechanism affecting signal transduction, synaptic activity, and brain development. There is growing evidence that glycolysis-derived metabolites, particularly, lactate, affect barriergenesis and functioning of BBB. In the brain, lactate produced in astrocytes or endothelial cells can be transported to the extracellular space via monocarboxylate transporters (MCTs), and may act on the adjoining cells via specific lactate receptors. Astrocytes are one of the major sources of lactate production in the brain and significantly contribute to the regulation of BBB development and functioning. Active glycolysis in astrocytes is required for effective support of neuronal activity and angiogenesis, while endothelial cells regulate bioavailability of lactate for brain cells adjusting its bidirectional transport through the BBB. In this article, we review the current knowledge with regard to energy production in endothelial and astroglial cells within the NVU. In addition, we describe lactate-driven mechanisms and action of alternative products of glucose metabolism affecting BBB structural and functional integrity in developing and mature brain.

Role of hydrogen sulfide in early blood-brain barrier disruption following transient focal cerebral ischemia

We determined the role of endogenous hydrogen sulfide (H₂S) in cerebral vasodilation/hyperemia and early BBB disruption following ischemic stroke. A cranial window was prepared over the left frontal, parietal and temporal cortex in mice. Transient focal cerebral Ischemia was induced by directly ligating the middle cerebral artery (MCA) for two hours. Regional vascular response and cerebral blood flow (CBF) during ischemia and reperfusion were measured in real time. Early BBB disruption was assessed by Evans Blue (EB) and sodium fluorescein (Na-F) extravasation at 3 hours of reperfusion. Topical treatment with DL-propargylglycine (PAG, an inhibitor for cystathionine γ-lyase (CSE)) and aspartate (ASP, inhibitor for cysteine aminotransferase/3-mercaptopyruvate sulfurtransferase (CAT/3-MST)), but not O-(Carboxymethyl)hydroxylamine hemihydrochloride (CHH, an inhibitor for cystathionine β-synthase (CBS)), abolished postischemic cerebral vasodilation/hyperemia and prevented EB and Na-F extravasation. CSE knockout (CSE^-/-) reduced postischemic cerebral vasodilation/hyperemia but only inhibited Na-F extravasation. An upregulated CBS was found in cerebral cortex of CSE^-/- mice. Topical treatment with CHH didn’t further alter postischemic cerebral vasodilation/hyperemia, but prevented EB extravasation in CSE^-/- mice. In addition, L-cysteine-induced hydrogen sulfide (H₂S) production similarly increased in ischemic side cerebral cortex of control and CSE^-/- mice. Our findings suggest that endogenous production of H₂S by CSE and CAT/3-MST during reperfusion may be involved in postischemic cerebral vasodilation/hyperemia and play an important role in early BBB disruption following transient focal cerebral ischemia.

Relaxin peptide hormones are protective during the early stages of ischemic stroke in male rats

The pregnancy hormone relaxin protects tissue from ischemic damage. The ability of relaxin-3, a relaxin paralog, to do so has not been explored. The cerebral expression levels of these peptides and their receptors make them logical targets for study in the ischemic brain. We assessed relaxin peptide-mediated protection, relative relaxin family peptide receptor (RXFP) involvement, and protective mechanisms. Sprague-Dawley rats receiving permanent (pMCAO) or transient middle cerebral artery occlusions (tMCAO) were treated with relaxin peptides, and brains were collected for infarct analysis. Activation of the endothelial nitric oxide synthase pathway was evaluated as a potential protective mechanism. Primary cortical rat astrocytes were exposed to oxygen glucose deprivation and treated with relaxin peptides, and viability was examined. Receptor involvement was explored using RXFP3 antagonist or agonist treatment and real-time PCR. Relaxin and relaxin-3 reduced infarct size after pMCAO. Both peptides activated endothelial nitric oxide synthase. Because relaxin-3 has not previously been associated with this pathway and displays promiscuous RXFP binding, we explored the receptor contribution. Expression of rxfp1 was greater than that of rxfp3 in rat brain, although peptide binding at either receptor resulted in similar overall protection after pMCAO. Only RXFP3 activation reduced infarct size after tMCAO. In astrocytes, rxfp3 gene expression was greater than that of rxfp1. Selective activation of RXFP3 maintained astrocyte viability after oxygen glucose deprivation. Relaxin peptides are protective during the early stages of ischemic stroke. Differential responses among treatments and models suggest that RXFP1 and RXFP3 initiate different protective mechanisms. This preliminary work is a pivotal first step in identifying the clinical implications of relaxin peptides in ischemic stroke.

Middle cerebral artery remodeling following transient brain ischemia is linked to early postischemic hyperemia: a target of uric acid treatment

Ischemia impairs blood supply to the brain, and reperfusion is important to restore cerebral blood flow (CBF) and rescue neurons from cell death. However, reperfusion can induce CBF values exceeding the basal values before ischemia. This hyperemic effect has been associated with a worse ischemic brain damage, albeit the mechanisms that contribute to infarct expansion are not clear. In this study, we investigated the influence of early postischemic hyperemia on brain damage and middle cerebral artery (MCA) properties and the effect of treatment with the endogenous antioxidant uric acid (UA). The MCA was occluded for 90 min followed by 24 h reperfusion in adult male Sprague-Dawley rats. Cortical CBF increases at reperfusion beyond 20% of basal values were taken as indicative of hyperemia. UA (16 mg/kg) or vehicle (Locke's buffer) was administered intravenously 135 min after MCA occlusion. Hyperemic compared with nonhyperemic rats showed MCA wall thickening (sham: 22.4 ± 0.8 μm; nonhyperemic: 23.1 ± 1.2 μm; hyperemic: 27.8 ± 0.9 at 60 mmHg; P < 0.001, hyperemic vs. sham) involving adventitial cell proliferation, increased oxidative stress, and interleukin-18, and more severe brain damage. Thus MCA remodeling after ischemia-reperfusion takes place under vascular oxidative and inflammatory stress conditions linked to hyperemia. UA administration attenuated MCA wall thickening, induced passive lumen expansion, and reduced brain damage in hyperemic rats, although it did not increase brain UA concentration. We conclude that hyperemia at reperfusion following brain ischemia induces vascular damage that can be attenuated by administration of the endogenous antioxidant UA.