Characterization of microvascular basal lamina damage and blood-brain barrier dysfunction following subarachnoid hemorrhage in rats

Role of microglia after subarachnoid hemorrhage

Subarachnoid hemorrhage is a devastating sequela of aneurysm rupture. Because it disproportionately affects younger patients, the population impact of hemorrhagic stroke from subarachnoid hemorrhage is substantial. Secondary brain injury is a significant contributor to morbidity after subarachnoid hemorrhage. Initial hemorrhage causes intracranial pressure elevations, disrupted cerebral perfusion pressure, global ischemia, and systemic dysfunction. These initial events are followed by two characterized timespans of secondary brain injury: the early brain injury period and the delayed cerebral ischemia period. The identification of varying microglial phenotypes across phases of secondary brain injury paired with the functions of microglia during each phase provides a basis for microglia serving a critical role in both promoting and attenuating subarachnoid hemorrhage-induced morbidity. The duality of microglial effects on outcomes following SAH is highlighted by the pleiotropic features of these cells. Here, we provide an overview of the key role of microglia in subarachnoid hemorrhage-induced secondary brain injury as both cytotoxic and restorative effectors. We first describe the ontogeny of microglial populations that respond to subarachnoid hemorrhage. We then correlate the phenotypic development of secondary brain injury after subarachnoid hemorrhage to microglial functions, synthesizing experimental data in this area.

Pathophysiology, Management, and Therapeutics in Subarachnoid Hemorrhage and Delayed Cerebral Ischemia: An Overview

Subarachnoid hemorrhage (SAH) is a type of hemorrhagic stroke resulting from the rupture of an arterial vessel within the brain. Unlike other stroke types, SAH affects both young adults (mid-40s) and the geriatric population. Patients with SAH often experience significant neurological deficits, leading to a substantial societal burden in terms of lost potential years of life. This review provides a comprehensive overview of SAH, examining its development across different stages (early, intermediate, and late) and highlighting the pathophysiological and pathohistological processes specific to each phase. The clinical management of SAH is also explored, focusing on tailored treatments and interventions to address the unique pathological changes that occur during each stage. Additionally, the paper reviews current treatment modalities and pharmacological interventions based on the evolving guidelines provided by the American Heart Association (AHA). Recent advances in our understanding of SAH will facilitate clinicians' improved management of SAH to reduce the incidence of delayed cerebral ischemia in patients.

Early Brain Injury After Subarachnoid Hemorrhage: Incidence and Mechanisms

Aneurysmal subarachnoid hemorrhage is a devastating condition causing significant morbidity and mortality. While outcomes from subarachnoid hemorrhage have improved in recent years, there continues to be significant interest in identifying therapeutic targets for this disease. In particular, there has been a shift in emphasis toward secondary brain injury that develops in the first 72 hours after subarachnoid hemorrhage. This time period of interest is referred to as the early brain injury period and comprises processes including microcirculatory dysfunction, blood-brain-barrier breakdown, neuroinflammation, cerebral edema, oxidative cascades, and neuronal death. Advances in our understanding of the mechanisms defining the early brain injury period have been accompanied by improved imaging and nonimaging biomarkers for identifying early brain injury, leading to the recognition of an elevated clinical incidence of early brain injury compared with prior estimates. With the frequency, impact, and mechanisms of early brain injury better defined, there is a need to review the literature in this area to guide preclinical and clinical study.

The protective effect of low-dose minocycline on brain microvascular ultrastructure in a rodent model of subarachnoid hemorrhage

The multifaceted nature of subarachnoid hemorrhage (SAH) pathogenesis is poorly understood. To date, no pharmacological agent has been found to be efficacious for the prevention of brain injury when used for acute SAH intervention. This study was undertaken to evaluate the beneficial effects of low-dose neuroprotective agent minocycline on brain microvascular ultrastructures that have not been studied in detail. We studied SAH brain injury using an in vivo prechiasmatic subarachnoid hemorrhage rodent model. We analyzed the qualitative and quantitative ultrastructural morphology of capillaries and surrounding neuropil in the rodent brains with SAH and/or minocycline administration. Here, we report that low-dose minocycline (1 mg/kg) displayed protective effects on capillaries and surrounding cells from significant SAH-induced changes. Ultrastructural morphology analysis revealed also that minocycline stopped endothelial cells from abnormal production of vacuoles and vesicles that compromise blood-brain barrier (BBB) transcellular transport. The reported ultrastructural abnormalities as well as neuroprotective effects of minocycline during SAH were not directly mediated by inhibition of MMP-2, MMP-9, or EMMPRIN. However, SAH brain tissue treated with minocycline was protected from development of other morphological features associated with oxidative stress and the presence of immune cells in the perivascular space. These data advance the knowledge on the effect of SAH on brain tissue ultrastructure in an SAH rodent model and the neuroprotective effect of minocycline when administered in low doses.

Hypoxia-induced upregulation of matrix metalloproteinase 9 increases basement membrane degradation by downregulating collagen type IV alpha 1 chain

Hypoxia can cause basement membrane (BM) degradation in tissues. Matrix metalloproteinase 9 (MMP-9) is involved in various human cancers as well as BM degradation by downregulating type IV collagen (COL4). This study investigated the role of MMP-9 in hypoxia-mediated BM degradation in rat bone marrow based on its regulation of collagen type IV alpha 1 chain (COL4A1). Eighty male rats were randomly divided into four groups based on exposure to hypoxic conditions at a simulated altitude of 7,000 m, control (normoxia) and 3, 7, and 10 days of hypoxia exposure. BM degradation in bone marrow was determined by transmission electron microscopy. MMP-9 levels were assessed by western blot and real-time PCR, and COL4A1 levels were assessed by western blot and immunohistochemistry. Microvessels BMs in bone marrow exposed to acute hypoxia were observed by electron microscopy. MMP-9 expression increased, COL4A1 protein expression decreased, and BM degradation occurred in the 10-, 7-, and 3-day hypoxia groups compared with that in the control group (all P < 0.05). Hypoxia increased MMP-9 levels, which in turn downregulated COL4A1, thereby increasing BM degradation. MMP-9 upregulation significantly promoted BM degradation and COL4A1 downregulation. Our results suggest that MMP-9 is related to acute hypoxia-induced BM degradation in bone marrow by regulating COL4A1.

The blood-brain barrier and the neurovascular unit in subarachnoid hemorrhage: molecular events and potential treatments

The response of the blood-brain barrier (BBB) following a stroke, including subarachnoid hemorrhage (SAH), has been studied extensively. The main components of this reaction are endothelial cells, pericytes, and astrocytes that affect microglia, neurons, and vascular smooth muscle cells. SAH induces alterations in individual BBB cells, leading to brain homeostasis disruption. Recent experiments have uncovered many pathophysiological cascades affecting the BBB following SAH. Targeting some of these pathways is important for restoring brain function following SAH. BBB injury occurs immediately after SAH and has long-lasting consequences, but most changes in the pathophysiological cascades occur in the first few days following SAH. These changes determine the development of early brain injury as well as delayed cerebral ischemia. SAH-induced neuroprotection also plays an important role and weakens the negative impact of SAH. Supporting some of these beneficial cascades while attenuating the major pathophysiological pathways might be decisive in inhibiting the negative impact of bleeding in the subarachnoid space. In this review, we attempt a comprehensive overview of the current knowledge on the molecular and cellular changes in the BBB following SAH and their possible modulation by various drugs and substances.

The Role of the Glycocalyx in the Pathophysiology of Subarachnoid Hemorrhage-Induced Delayed Cerebral Ischemia

The glycocalyx is an important constituent of blood vessels located between the bloodstream and the endothelium. It plays a pivotal role in intercellular interactions in neuroinflammation, reduction of vascular oxidative stress, and provides a barrier regulating vascular permeability. In the brain, the glycocalyx is closely related to functions of the blood-brain barrier and neurovascular unit, both responsible for adequate neurovascular responses to potential threats to cerebral homeostasis. An aneurysmal subarachnoid hemorrhage (aSAH) occurs following rupture of an intracranial aneurysm and leads to immediate brain damage (early brain injury). In some cases, this can result in secondary brain damage, also known as delayed cerebral ischemia (DCI). DCI is a life-threatening condition that affects up to 30% of all aSAH patients. As such, it is associated with substantial societal and healthcare-related costs. Causes of DCI are multifactorial and thought to involve neuroinflammation, oxidative stress, neuroinflammation, thrombosis, and neurovascular uncoupling. To date, prediction of DCI is limited, and preventive and effective treatment strategies of DCI are scarce. There is increasing evidence that the glycocalyx is disrupted following an aSAH, and that glycocalyx disruption could precipitate or aggravate DCI. This review explores the potential role of the glycocalyx in the pathophysiological mechanisms contributing to DCI following aSAH. Understanding the role of the glycocalyx in DCI could advance the development of improved methods to predict DCI or identify patients at risk for DCI. This knowledge may also alter the methods and timing of preventive and treatment strategies of DCI. To this end, we review the potential and limitations of methods currently used to evaluate the glycocalyx, and strategies to restore or prevent glycocalyx shedding.

Neurofilament light predicts neurological outcome after subarachnoid haemorrhage

To improve outcome prediction following subarachnoid haemorrhage (SAH), we sought a biomarker integrating early brain injury and multiple secondary pathological processes in a prospective study of 42 non-traumatic SAH patients and 19 control individuals. Neurofilament light (NF-L) was elevated in CSF and serum following SAH. CSF and serum NF-L on Days 1–3 post-SAH strongly predicted modified Rankin score at 6 months, independent of World Federation of Neurosurgical Societies (WFNS) score. NF-L from Day 4 onwards also had a profound impact on outcome. To link NF-L to a SAH-specific pathological process, we investigated NF-L’s relationship with extracellular haemoglobin. Most CSF haemoglobin was not complexed with haptoglobin, yet was able to be bound by exogenous haptoglobin i.e. haemoglobin was scavengeable. CSF scavengeable haemoglobin was strongly predictive of subsequent CSF NF-L. Next, we investigated NF-L efflux from the brain after SAH. Serum and CSF NF-L correlated positively. The serum/CSF NF-L ratio was lower in SAH versus control subjects, in keeping with glymphatic efflux dysfunction after SAH. CSF/serum albumin ratio was increased following SAH versus controls. The serum/CSF NF-L ratio correlated negatively with the CSF/serum albumin ratio, indicating that transfer of the two proteins across the blood–brain interface is dissociated. In summary, NF-L is a strong predictive marker for SAH clinical outcome, adding value to the WFNS score, and is a promising surrogate end point in clinical trials.

Physiological and Pathological Factors Affecting Drug Delivery to the Brain by Nanoparticles

The prevalence of neurological/neurodegenerative diseases, such as Alzheimer's disease is known to be increasing due to an aging population and is anticipated to further grow in the decades ahead. The treatment of brain diseases is challenging partly due to the inaccessibility of therapeutic agents to the brain. An increasingly important observation is that the physiology of the brain alters during many brain diseases, and aging adds even more to the complexity of the disease. There is a notion that the permeability of the blood-brain barrier (BBB) increases with aging or disease, however, the body has a defense mechanism that still retains the separation of the brain from harmful chemicals in the blood. This makes drug delivery to the diseased brain, even more challenging and complex task. Here, the physiological changes to the diseased brain and aged brain are covered in the context of drug delivery to the brain using nanoparticles. Also, recent and novel approaches are discussed for the delivery of therapeutic agents to the diseased brain using nanoparticle based or magnetic resonance imaging guided systems. Furthermore, the complement activation, toxicity, and immunogenicity of brain targeting nanoparticles as well as novel in vitro BBB models are discussed.

Blood-brain barrier permeability imaging as a predictor for delayed cerebral ischaemia following subarachnoid haemorrhage. A narrative review

BACKGROUND

Aneurysmal subarachnoid haemorrhage is associated with significant morbidity and mortality due to the myriad of complications contributing to early brain injury and delayed cerebral ischaemia. There is increasing interest in the exploration of the association between blood-brain barrier integrity and risks of delayed cerebral ischaemia and poor outcomes. Despite recent advances in cerebral imaging, radiographic imaging of blood-brain barrier disruption, as a biomarker for outcome prediction, has not been adopted in clinical practice.

METHODS

We performed a narrative review by searching for articles describing molecular changes or radiological identification of changes in BBB permeability following subarachnoid haemorrhage (SAH) on MEDLINE. Preclinical studies were analysed if reported structural changes and clinical studies were included if they investigated for radiological markers of BBB disruption and its correlation with delayed cerebral ischaemia.

RESULTS

There is ample preclinical evidence to suggest that there are structural changes in BBB permeability following SAH. The available clinical literature has demonstrated correlations between permeability imaging and outcomes following aneurysmal subarachnoid haemorrhage (aSAH).

CONCLUSION

Radiological biomarkers offer a potential non-invasive prognostication tool and may also allow early identifications of patients who may be at risk of DCI.

Inhibition of miR-103-3p Preserves Neurovascular Integrity Through Caveolin-1 in Experimental Subarachnoid Hemorrhage

Caveolin-1 (Cav-1) is a constitutive structural protein of caveolae in the plasma membrane. It plays an important role in maintaining blood brain barrier (BBB) integrity. In this study, we identified that miR-103-3p, a hypoxia-responsive miRNA, could interact with Cav-1. In endothelial cells, miR-103-3p mimic diminished the expression of Cav-1 and tight junction proteins, which were rescued by the inhibition of miR-103-3p. We found a substantial increase of miR-103-3p and decease of Cav-1 in the rat subarachnoid hemorrhage (SAH) model. Pre-SAH intracerebroventricularly injection of miR-103-3p antagomir relieved Cav-1 loss, sequentially reduced BBB permeability and improved neurological function. Finally, we demonstrated that the salutary effects of miR-103-3p antagomir were abolished in Cav-1 knock-out mice, suggesting that Cav-1 was required for the miR-103-3p inhibition-induced neurovascular protection. Taken together, our findings suggest that the inhibition of miR-103-3p could exert neuroprotective effects through preservation of Cav-1 and BBB integrity, making miR-103-3p a novel therapeutic target for SAH.

Biologic Effect of Hydrogen Sulfide and Its Role in Traumatic Brain Injury

Ever since endogenous hydrogen sulfide (H₂S) was found in mammals in 1989, accumulated evidence has demonstrated that H₂S functions as a novel neurological gasotransmitter in brain tissues and may play a key role in traumatic brain injury. It has been proved that H₂S has an antioxidant, anti-inflammatory, and antiapoptosis function in the neuron system and functions as a neuroprotective factor against secondary brain injury. In addition, H₂S has other biologic effects such as regulating the intracellular concentration of Ca²⁺, facilitating hippocampal long-term potentiation (LTP), and activating ATP-sensitive K channels. Due to the toxic nature of H₂S when exceeding the physiological dose in the human body, only a small amount of H₂S-related therapies was applied to clinical treatment. Therefore, it has huge therapeutic potential and has great hope for recovering patients with traumatic brain injury.

The Updated Role of the Blood Brain Barrier in Subarachnoid Hemorrhage: From Basic and Clinical Studies

Subarachnoid hemorrhage (SAH) is a type of hemorrhagic stroke associated with high mortality and morbidity. The blood-brain-barrier (BBB) is a structure consisting primarily of cerebral microvascular endothelial cells, end feet of astrocytes, extracellular matrix, and pericytes. Post-SAH pathophysiology included early brain injury and delayed cerebral ischemia. BBB disruption was a critical mechanism of early brain injury and was associated with other pathophysiological events. These pathophysiological events may propel the development of secondary brain injury, known as delayed cerebral ischemia. Imaging advancements to measure BBB after SAH primarily focused on exploring innovative methods to predict clinical outcome, delayed cerebral ischemia, and delayed infarction related to delayed cerebral ischemia in acute periods. These predictions are based on detecting abnormal changes in BBB permeability. The parameters of BBB permeability are described by changes in computed tomography (CT) perfusion and magnetic resonance imaging (MRI). K_ep seems to be a stable and sensitive indicator in CT perfusion, whereas K^trans is a reliable parameter for dynamic contrast-enhanced MRI. Future prediction models that utilize both the volume of BBB disruption and stable parameters of BBB may be a promising direction to develop practical clinical tools. These tools could provide greater accuracy in predicting clinical outcome and risk of deterioration. Therapeutic interventional exploration targeting BBB disruption is also promising, considering the extended duration of post-SAH BBB disruption.

Neurobehavioral Deficits After Subarachnoid Hemorrhage in Mice: Sensitivity Analysis and Development of a New Composite Score

Background

Because of the failure of numerous clinical trials, various recommendations have been made to improve the usefulness of preclinical studies. Specifically, the STAIR (Stroke Therapy Academic Industry Roundtable) recommendations highlighted functional outcome as a critical measure. Recent reviews of experimental subarachnoid hemorrhage (SAH) studies have brought to light the numerous neurobehavioral scoring systems that are used in preclinical SAH studies. To gain insight into the utility of these scoring systems, as well as to identify a scoring system that best captures the deficits caused by SAH in mice, we designed the current study.

Methods and Results

Adult male C57BL/6J mice were used. One cohort of mice was randomly allocated to either sham or SAH and had functional testing performed on days 1 to 3 post‐SAH using the modified Bederson Score, Katz Score, Garcia Neuroscore, and Parra Neuroscore, as well as 21 individual subtests. A new composite neuroscore was developed using the 8 most diagnostically accurate subtests. To validate the use of the developed composite neuroscore, another cohort of mice was randomly assigned to either the sham or SAH group and neurobehavior was evaluated on days 1 to 3, 5, and 7 after injury. Receiver operating characteristic curves were used to analyze the diagnostic accuracy of each scoring system, as well as the subtests. Of the 4 published scoring systems, the Parra Neuroscore was diagnostically accurate for SAH injury in mice versus the modified Bederson and Katz Scores, but not the Garcia Neuroscore. However, the newly developed composite neuroscore was found to be statistically more diagnostically accurate than even the Parra Neuroscore.

Conclusions

The findings of this study promote use of the newly developed composite neuroscore for experimental SAH studies in mice.

Loss of mural cell-derived laminin aggravates hemorrhagic brain injury

BACKGROUND

Mural cells synthesize and deposit laminin to the basement membrane. To investigate the function of mural cell-derived laminin, we generated a mutant mouse line lacking mural cell-derived laminin (termed PKO). In a previous study, we showed that the PKO mice were grossly normal under homeostatic condition, but developed blood-brain barrier (BBB) breakdown with advanced age (> 8 months), suggesting that these mutants are intrinsically weak. Based on these findings, we hypothesized that PKO mice have exacerbated injuries in pathological conditions.

METHODS

Using collagenase-induced intracerebral hemorrhage (ICH) as an injury model, we examined various stroke outcomes, including hematoma volume, neurological function, neuronal death, BBB integrity, paracellular/transcellular transport, inflammatory cell infiltration, and brain water content, in PKO mice and their wildtype littermates at young age (6-8 weeks). In addition, transmission electron microscopy (TEM) analysis and an in vitro ICH model were used to investigate the underlying molecular mechanisms.

RESULTS

Compared to age-matched wildtype littermates, PKO mice display aggravated stroke outcomes, including larger hematoma size, worse neurological function, increased neuronal cell death, enhanced BBB permeability, increased transcytosis, and elevated inflammatory cell infiltration. These mutants also exhibit high baseline brain water content independent of aquaporin-4 (AQP4). In addition, mural cell-derived laminin significantly reduced caveolin-1 without affecting tight junction proteins in the in vitro ICH model.

CONCLUSIONS

These results suggest that mural cell-derived laminin attenuates BBB damage in ICH via decreasing caveolin-1 and thus transcytosis, regulates brain water homeostasis, and plays a beneficial role in ICH.

Materials for blood brain barrier modeling in vitro

Brain homeostasis relies on the selective permeability property of the blood brain barrier (BBB). The BBB is formed by a continuous endothelium that regulates exchange between the blood stream and the brain. This physiological barrier also creates a challenge for the treatment of neurological diseases as it prevents most blood circulating drugs from entering into the brain. In vitro cell models aim to reproduce BBB functionality and predict the passage of active compounds through the barrier. In such systems, brain microvascular endothelial cells (BMECs) are cultured in contact with various biomaterial substrates. However, BMEC interactions with these biomaterials and their impact on BBB functions are poorly described in the literature. Here we review the most common materials used to culture BMECs and discuss their potential impact on BBB integrity in vitro. We investigate the biophysical properties of these biomaterials including stiffness, porosity and material degradability. We highlight a range of synthetic and natural materials and present three categories of cell culture dimensions: cell monolayers covering non-degradable materials (2D), cell monolayers covering degradable materials (2.5D) and vascularized systems developing into degradable materials (3D).

Early blood-brain barrier dysfunction predicts neurological outcome following aneurysmal subarachnoid hemorrhage

BACKGROUND

Disease progression and delayed neurological complications are common after aneurysmal subarachnoid hemorrhage (aSAH). We explored the potential of quantitative blood-brain barrier (BBB) imaging to predict disease progression and neurological outcome.

METHODS

Data were collected as part of the Co-Operative Studies of Brain Injury Depolarizations (COSBID). We analyzed retrospectively, blinded and semi-automatically magnetic resonance images from 124 aSAH patients scanned at 4 time points (24-48 h, 6-8 days, 12-15 days and 6-12 months) after the initial hemorrhage. Volume of brain with apparent pathology and/or BBB dysfunction (BBBD), subarachnoid space and lateral ventricles were measured. Neurological status on admission was assessed using the World Federation of Neurosurgical Societies and Rosen-Macdonald scores. Outcome at ≥6 months was assessed using the extended Glasgow outcome scale and disease course (progressive or non-progressive based on imaging-detected loss of normal brain tissue in consecutive scans). Logistic regression was used to define biomarkers that best predict outcomes. Receiver operating characteristic analysis was performed to assess accuracy of outcome prediction models.

FINDINGS

In the present cohort, 63% of patients had progressive and 37% non-progressive disease course. Progressive course was associated with worse outcome at ≥6 months (sensitivity of 98% and specificity of 97%). Brain volume with BBBD was significantly larger in patients with progressive course already 24-48 h after admission (2.23 (1.23-3.17) folds, median with 95%CI), and persisted at all time points. The highest probability of a BBB-disrupted voxel to become pathological was found at a distance of ≤1 cm from the brain with apparent pathology (0·284 (0·122-0·594), p < 0·001, median with 95%CI). A multivariate logistic regression model revealed power for BBBD in combination with RMS at 24-48 h in predicting outcome (ROC area under the curve = 0·829, p < 0·001).

INTERPRETATION

We suggest that early identification of BBBD may serve as a key predictive biomarker for neurological outcome in aSAH. FUND: Dr. Dreier was supported by grants from the Deutsche Forschungsgemeinschaft (DFG) (DFG DR 323/5-1 and DFG DR 323/10-1), the Bundesministerium für Bildung und Forschung (BMBF) Center for Stroke Research Berlin 01 EO 0801 and FP7 no 602150 CENTER-TBI. Dr. Friedman was supported by grants from Israel Science Foundation and Canada Institute for Health Research (CIHR). Dr. Friedman was supported by grants from European Union's Seventh Framework Program (FP7/2007-2013; grant #602102).

Laminins and their receptors in the CNS

Laminin, an extracellular matrix protein, is widely expressed in the central nervous system (CNS). By interacting with integrin and non-integrin receptors, laminin exerts a large variety of important functions in the CNS in both physiological and pathological conditions. Due to the existence of many laminin isoforms and their differential expression in various cell types in the CNS, the exact functions of each individual laminin molecule in CNS development and homeostasis remain largely unclear. In this review, we first briefly introduce the structure and biochemistry of laminins and their receptors. Next, the dynamic expression of laminins and their receptors in the CNS during both development and in adulthood is summarized in a cell-type-specific manner, which allows appreciation of their functional redundancy/compensation. Furthermore, we discuss the biological functions of laminins and their receptors in CNS development, blood-brain barrier (BBB) maintenance, neurodegeneration, stroke, and neuroinflammation. Last, key challenges and potential future research directions are summarized and discussed. Our goals are to provide a synthetic review to stimulate future studies and promote the formation of new ideas/hypotheses and new lines of research in this field.

Basement membrane and stroke

Located at the interface of the circulation system and the CNS, the basement membrane (BM) is well positioned to regulate blood-brain barrier (BBB) integrity. Given the important roles of BBB in the development and progression of various neurological disorders, the BM has been hypothesized to contribute to the pathogenesis of these diseases. After stroke, a cerebrovascular disease caused by rupture (hemorrhagic) or occlusion (ischemic) of cerebral blood vessels, the BM undergoes constant remodeling to modulate disease progression. Although an association between BM dissolution and stroke is observed, how each individual BM component changes after stroke and how these components contribute to stroke pathogenesis are mostly unclear. In this review, I first briefly introduce the composition of the BM in the brain. Next, the functions of the BM and its major components in BBB maintenance under homeostatic conditions are summarized. Furthermore, the roles of the BM and its major components in the pathogenesis of hemorrhagic and ischemic stroke are discussed. Last, unsolved questions and potential future directions are described. This review aims to provide a comprehensive reference for future studies, stimulate the formation of new ideas, and promote the generation of new genetic tools in the field of BM/stroke research.

The Contractile Apparatus Is Essential for the Integrity of the Blood-Brain Barrier After Experimental Subarachnoid Hemorrhage

Development of vasogenic brain edema is a key event contributing to mortality after subarachnoid hemorrhage (SAH). The precise underlying mechanisms at the neurovascular level that lead to disruption of the blood-brain barrier (BBB) are still unknown. Activation of myosin light chain kinases (MLCK) may result in change of endothelial cell shape and opening of the intercellular gap with subsequent vascular leakage. Male C57Bl6 mice were subjected to endovascular perforation. Brain water content was determined by wet-dry ratio and BBB integrity by Evans-Blue extravasation. The specific MLCK inhibitor ML-7 was administered to the mice to determine the role of the contractile apparatus of the neurovascular unit in determining brain water content, BBB integrity, neurofunctional outcome, brain damage, and survival at 7 days after SAH. Inhibition of MLCK significantly reduced BBB permeability (Evans Blue extravasation − 28%) and significantly decreased edema formation in comparison with controls (− 2%). MLCK-treated mice showed reduced intracranial pressure (− 53%), improved neurological outcome at 24 h and 48 h after SAH, and reduced 7-day mortality. Tight junction proteins claudin-5 and zonula occludens-1 levels were not influenced by ML-7 at 24 h after insult. The effect of ML-7 on pMLC was confirmed in brain endothelial cell culture (bEnd.3 cells) subjected to 4-h oxygen-glucose deprivation. The present study indicates that MLCK contributes to blood-brain barrier dysfunction after SAH by a mechanism that does not involve modulation of tight junction protein levels, but via activation of the contractile apparatus of the endothelial cell skeleton. This underlying mechanism may be a promising target for the treatment of SAH.

Brain endothelial cell junctions after cerebral hemorrhage: Changes, mechanisms and therapeutic targets

Vascular disruption is the underlying cause of cerebral hemorrhage, including intracerebral, subarachnoid and intraventricular hemorrhage. The disease etiology also involves cerebral hemorrhage-induced blood-brain barrier (BBB) disruption, which contributes an important component to brain injury after the initial cerebral hemorrhage. BBB loss drives vasogenic edema, allows leukocyte extravasation and may lead to the entry of potentially neurotoxic and vasoactive compounds into brain. This review summarizes current information on changes in brain endothelial junction proteins in response to cerebral hemorrhage (and clot-related factors), the mechanisms underlying junction modification and potential therapeutic targets to limit BBB disruption and, potentially, hemorrhage occurrence. It also addresses advances in the tools that are now available for assessing changes in junctions after cerebral hemorrhage and the potential importance of such junction changes. Recent studies suggest post-translational modification, conformational change and intracellular trafficking of junctional proteins may alter barrier properties. Understanding how cerebral hemorrhage alters BBB properties beyond changes in tight junction protein loss may provide important therapeutic insights to prevent BBB dysfunction and restore normal function.

Dexmedetomidine attenuated early brain injury in rats with subarachnoid haemorrhage by suppressing the inflammatory response: The TLR4/NF-κB pathway and the NLRP3 inflammasome may be involved in the mechanism

Early brain injury (EBI) plays a pivotal role in the prognosis of patients with subarachnoid haemorrhage (SAH). Dexmedetomidine (DEX), a highly selective α₂ receptor agonist, is reported to exert multiple protective effects in many neurological diseases. This study was designed to investigate whether DEX had neuroprotective functions in EBI after SAH, and to explore the possible mechanisms. The SAH model was established by an endovascular perforation in adult male Sprague-Dawley (SD) rats. DEX (25 µg/kg) or vehicle was administered intraperitoneally 2 h after SAH. Neurological deficits, brain oedema, inflammation, BBB damage, and cell apoptosis at 24 h after SAH were evaluated. Additionally, the expression of components of the Toll-like receptor 4 (TLR4)/nuclear factor-κB (NF-κB) pathway, and the nucleotide-binding oligomerization domain-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome were also assessed. We demonstrated that DEX treatment improved neurological scores, alleviated brain oedema, reduced the permeability of the blood-brain barrier (BBB), and up-regulated the expression of tight junction proteins. DEX treatment could reduce the neutrophil infiltration, microglial activation, and pro-inflammatory factor release. In addition, DEX alleviated cell apoptosis at 24 h after SAH. Notably, DEX could also suppress the activation of the TLR4/NF-κB pathway and the NLRP3 inflammasome. These findings suggested that treatment with DEX after SAH attenuated SAH-induced EBI, partially through the suppression of the TLR4/NF-κB pathway and the NLRP3 inflammasome.

An In Vivo Assessment of Blood-Brain Barrier Disruption in a Rat Model of Ischemic Stroke

Ischemic stroke leads to vasogenic cerebral edema and subsequent primary brain injury, which is mediated through destruction of the blood-brain barrier (BBB). Rats with induced ischemic stroke were established and used as in vivo models to investigate the functional integrity of the BBB. Spectrophotometric detection of Evans blue (EB) in the brain samples with ischemic injury could provide reliable justification for the research and development of novel therapeutic modalities. This method generates reproducible results, and is applicable in any laboratory without a need for special equipment. Here, we present a visualized and technical guideline on the detection of the extravasation of EB following induction of ischemic stroke in rats.

Cell-free DNA as a biomarker in stroke: Current status, problems and perspectives

There is currently no proposed stroke biomarker with consistent application in clinical practice. A number of studies have examined cell-free DNA (cfDNA), which circulates in biological fluids during stroke, as a potential biomarker of this disease. The data available suggest that dynamically-determined levels of blood cfDNA may provide new prognostic information for assessment of stroke severity and outcome. However, such an approach has its own difficulties and limitations. This review covers the potential role of cfDNA as a biomarker in stroke, and includes evidence from both animal models and clinical studies, protocols used to analyze cfDNA, and hypotheses on the origin of cfDNA.

Nanoagonist-mediated endothelial tight junction opening: A strategy for safely increasing brain drug delivery in mice

Even though opening endothelial tight junctions is an efficient way to up-regulate brain drug delivery, the extravasation of blood-borne components from the compromised tight junctions can result in adverse consequences such as edema and neuronal injuries. In this work, we developed a nanoagonist that temporarily opened tight junctions by signaling adenosine 2A receptor, a type of G protein-coupled receptor expressed on brain capillary endothelial cells. Magnetic resonance imaging demonstrated remarkable blood-brain barrier permeability enhancements and significantly increased brain uptakes of both small molecular and macromolecular paramagnetic agents after nanoagonist administration. Gamma ray imaging and transmission electron microscope observed tight junction opening followed by spontaneous recovery after nanoagonist treatment. Immunofluorescence staining showed the unspoiled basal membrane, pericytes and astrocyte endfeet that enwrapped the vascular endothelium. Importantly, edema, apoptosis and neuronal injuries observed after hypertonic agent mediated tight junction-opening were not observed after nanoagonist intervention. The uncompromised neurovascular units may prevent the leakage of blood-borne constituents into brain parenchyma and accelerate tight junction recovery. Considering blood-brain barrier impermeability is a major obstacle in the treatment of central nervous system diseases, nanoagonist-mediated tight junction opening provides a promising strategy to enhance brain drug delivery with minimized adverse effects.

Effects of deferoxamine on blood-brain barrier disruption after subarachnoid hemorrhage

Blood brain barrier (BBB) disruption is a key mechanism of subarachnoid hemorrhage (SAH)-induced brain injury. This study examined the mechanism of iron-induced BBB disruption after SAH and investigated the potential therapeutic effect of iron chelation on SAH. Male adult Sprague-Dawley rats had an endovascular perforation of left internal carotid artery bifurcation or sham operation. The rats were treated with deferoxamine (DFX) or vehicle (100mg/kg) for a maximum of 7 days. Brain edema, BBB leakage, behavioral and cognitive impairment were examined. In SAH rat, the peak time of brain edema and BBB impairment in the cortex was at day 3 after SAH. SAH resulted in a significant increase in ferritin expression in the cortex. The ferritin positive cells were colocalized with endothelial cells, pericytes, astrocytes, microglia and neurons. Compared with vehicle, DFX caused less ferritin upregulation, brain water content, BBB impairment, behavioral and cognitive deficits in SAH rats. The results suggest iron overload could be a therapeutic target for SAH induced BBB damage.

Cortical microcirculatory disturbance in the super acute phase of subarachnoid hemorrhage - In vivo analysis using two-photon laser scanning microscopy

OBJECTIVE

Subarachnoid hemorrhage (SAH) causes cerebral ischemia and drastically worsens the clinical status at onset. However, the arterial flow is surprisingly well maintained on the cerebral surface. We investigated cortical microcirculatory changes in the super acute phase of SAH using two-photon laser scanning microscopy (TPLSM).

METHODS

SAH was induced at the skull base in 10 mice using a prone endovascular perforation model. Before SAH, and 1, 2, 5, 10, 20, 30 and 60min after SAH, the cortical microcirculation was observed with TPLSM through a cranial window. Diameters of penetrating and precapillary arterioles were measured and red blood cell (RBC) velocities in precapillary arterioles were analyzed using a line-scan method after administration of Q-dot 655 nanocrystals.

RESULTS

One minute after SAH, RBC velocity and flow in precapillary arterioles drastically decreased to <20% of the pre-SAH values, while penetrating and precapillary arterioles dilated significantly. Subsequently, the arterioles either dilated or constricted inconsistently for 60min with continual decreases in RBC velocity and flow in the arterioles, suggesting neurovascular dysfunction.

CONCLUSION

SAH caused sudden worsening of the cortical arteriolar velocity and flow at onset. The neurovascular unit cannot function sufficiently to maintain cortical microcirculatory flow in the super acute phase of SAH.

Leukocyte plugging and cortical capillary flow after subarachnoid hemorrhage

BACKGROUND

It is believed that increased intracranial pressure immediately after subarachnoid hemorrhage (SAH) causes extensive brain ischemia and results in worsening clinical status. Arterial flow to the cerebral surfaces is clinically well maintained during clipping surgery regardless of the severity of the World Federation of Neurological Societies grade after SAH. To explore what kinds of changes occur in the cortical microcirculation, not at the cerebral surface, we examined cortical microcirculation after SAH using two-photon laser scanning microscopy (TPLSM).

METHODS

SAH was induced in mice with an endovascular perforation model. Following continuous injection of rhodamine 6G, velocities of labeled platelets and leukocytes and unlabeled red blood cells (RBCs) were measured in the cortical capillaries 60 min after SAH with a line-scan method using TPLSM, and the data were compared to a sham group and P-selectin monoclonal antibody-treated group.

RESULTS

Velocities of leukocytes, platelets, and RBCs in capillaries decreased significantly 60 min after SAH. Rolling and adherent leukocytes suddenly prevented other blood cells from flowing in the capillaries. Flowing blood cells also decreased significantly in each capillary after SAH. This no-reflow phenomenon induced by plugging leukocytes was often observed in the SAH group but not in the sham group. The decreased velocities of blood cells were reversed by pretreatment with the monoclonal antibody of P-selection, an adhesion molecule expressed on the surfaces of both endothelial cells and platelets.

CONCLUSIONS

SAH caused sudden worsening of cortical microcirculation at the onset. Leukocyte plugging in capillaries is one of the reasons why cortical microcirculation is aggravated after SAH.

Hydrogen sulfide attenuates brain edema in early brain injury after subarachnoid hemorrhage in rats: Possible involvement of MMP-9 induced blood-brain barrier disruption and AQP4 expression

AIMS

This study investigated the effect of H2S on brain edema formation and the possible underlying mechanisms in early brain injury (EBI) of SAH using the endovascular perforation model.

METHODS

96 male rats were randomly divided into four groups: sham group, SAH+vehicle group, SAH+low-dosage NaHS group, and SAH+high-dosage NaHS group. Brain samples were used for brain water content and blood-brain barrier (BBB) leakage measurement, gelatin zymography, Western blot and immunohistochemistry.

RESULTS

H2S markedly attenuated brain edema formation and apoptotic cell death, improved neurological dysfunction in the acute stage of SAH. The possible mechanisms of H2S's effect on brain edema formation were through preventing BBB disruption and reducing APQ4 expression on astrocytes. In detail, H2S prevented BBB disruption by inhibiting MMP-9 induced tight junction proteins (TJPs) degradation. H2S down-regulated AQP4 expression on astrocytes by suppressing glial cell activation and pro-inflammatory cytokines secretion.

CONCLUSION

Taken together, this study showed that H2S attenuated brain edema formation partially by inhibiting the degradation of TJPs via reducing MMP-9 expression/activity and suppressing AQP4 expression via alleviating glia activation and pro-inflammatory cytokines secretion.

The TNF-α/NF-κB signaling pathway has a key role in methamphetamine-induced blood-brain barrier dysfunction

Methamphetamine (METH) is a psychostimulant that causes neurologic and psychiatric abnormalities. Recent studies have suggested that its neurotoxicity may also result from its ability to compromise the blood-brain barrier (BBB). Herein, we show that METH rapidly increased the vesicular transport across endothelial cells (ECs), followed by an increase of paracellular transport. Moreover, METH triggered the release of tumor necrosis factor-alpha (TNF-α), and the blockade of this cytokine or the inhibition of nuclear factor-kappa B (NF-κB) pathway prevented endothelial dysfunction. Since astrocytes have a crucial role in modulating BBB function, we further showed that conditioned medium obtained from astrocytes previously exposed to METH had a negative impact on barrier properties also via TNF-α/NF-κB pathway. Animal studies corroborated the in vitro results. Overall, we show that METH directly interferes with EC properties or indirectly via astrocytes through the release of TNF-α and subsequent activation of NF-κB pathway culminating in barrier dysfunction.

Upregulation of tissue inhibitor of metalloproteinase-1 contributes to restoration of the extracellular matrix in the rabbit basilar artery during cerebral vasospasm after subarachnoid hemorrhage

Vascular remodeling caused by extracellular matrix (ECM) metabolism contributes to the development of cerebral vasospasm after subarachnoid hemorrhage (SAH). The balance between tissue inhibitor of metalloproteinases (TIMPs) and matrix metalloproteinases (MMPs) plays an important role in ECM remodeling. We investigated the mechanism of vascular remodeling following cerebral vasospasm in a rabbit double hemorrhage model. Rabbit basilar arteries were harvested on days 3, 5, and 7 after initial hemorrhage. TIMP-1, TIMP-2, MMP-2, and MMP-9 mRNA and protein expression were investigated with microarray analysis, quantitative real-time PCR, immunoblot analysis, and enzyme-linked immunosorbent assay (ELISA). The expression and localization of TIMP-1, TIMP-2, MMP-2, MMP-9, elastin, fibronectin, laminin, and collagens I, III, and IV were investigated with immuohistochemical staining. After SAH, TIMP-1 mRNA and protein expression were significantly increased on day 3 and then decreased to the control level on days 5 and 7. MMP-9 protein expression was significantly increased on day 7. TIMP-2 and MMP-2 mRNA and protein expression were significantly increased on day 7. Elastin, fibronectin, laminin, and collagens I, III, and IV protein expression was decreased on day 3 and then restored to control levels on day 7. Upregulation of TIMP-1 during the early phase of cerebral vasospasm may contribute to the recovery of the ECM during the late phase of cerebral vasospasm, resulting in a protective role of TIMP-1 from cerebral vasospasm. Moreover, the increase in arterial compliance by the decrease in ECM during the early phase of cerebral vasospasm may facilitate vasoconstriction of the cerebral artery.

Aneurysmal subarachnoid hemorrhage: pathobiology, current treatment and future directions

Aneurysmal subarachnoid hemorrhage is the most devastating form of stroke. Many pathological mechanisms ensue after cerebral aneurysm rupture, including hydrocephalus, apoptosis of endothelial cells and neurons, cerebral edema, loss of blood-brain barrier, abnormal cerebral autoregulation, microthrombosis, cortical spreading depolarization and macrovascular vasospasm. Although studied extensively through experimental and clinical trials, current treatment guidelines to prevent delayed cerebral ischemia is limited to oral nimodipine, maintenance of euvolemia, induction of hypertension if ischemic signs occur and endovascular therapy for patients with continued ischemia after induced hypertension. Future investigations will involve agents targeting vasodilation, anticoagulation, inhibition of apoptosis pathways, free radical neutralization, suppression of cortical spreading depolarization and attenuation of inflammation.

The pathophysiology and treatment of delayed cerebral ischaemia following subarachnoid haemorrhage

Cerebral vasospasm has traditionally been regarded as an important cause of delayed cerebral ischaemia (DCI) which occurs after aneurysmal subarachnoid haemorrhage, and often leads to cerebral infarction and poor neurological outcome. However, data from recent studies argue against a pure focus on vasospasm as the cause of delayed ischaemic complications. Findings that marked reduction in the incidence of vasospasm does not translate to a reduction in DCI, or better outcomes has intensified research into other possible mechanisms which may promote ischaemic complications. Early brain injury and cell death, blood-brain barrier disruption and initiation of an inflammatory cascade, microvascular spasm, microthrombosis, cortical spreading depolarisations and failure of cerebral autoregulation, have all been implicated in the pathophysiology of DCI. This review summarises the current knowledge about the mechanisms underlying the development of DCI. Furthermore, it aims to describe and categorise the known pharmacological treatment options with respect to the presumed mechanism of action and its role in DCI.

Rat endovascular perforation model

Experimental animal models of aneurysmal subarachnoid hemorrhage (SAH) have provided a wealth of information on the mechanisms of brain injury. The rat endovascular perforation (EVP) model replicates the early pathophysiology of SAH and hence is frequently used to study early brain injury following SAH. This paper presents a brief review of historical development of the EVP model and details the technique used to create SAH and considerations necessary to overcome technical challenges.

Agile delivery of protein therapeutics to CNS

A variety of therapeutic proteins have shown potential to treat central nervous system (CNS) disorders. Challenge to deliver these protein molecules to the brain is well known. Proteins administered through parenteral routes are often excluded from the brain because of their poor bioavailability and the existence of the blood-brain barrier (BBB). Barriers also exist to proteins administered through non-parenteral routes that bypass the BBB. Several strategies have shown promise in delivering proteins to the brain. This review, first, describes the physiology and pathology of the BBB that underscore the rationale and needs of each strategy to be applied. Second, major classes of protein therapeutics along with some key factors that affect their delivery outcomes are presented. Third, different routes of protein administration (parenteral, central intracerebroventricular and intraparenchymal, intranasal and intrathecal) are discussed along with key barriers to CNS delivery associated with each route. Finally, current delivery strategies involving chemical modification of proteins and use of particle-based carriers are overviewed using examples from literature and our own work. Whereas most of these studies are in the early stage, some provide proof of mechanism of increased protein delivery to the brain in relevant models of CNS diseases, while in few cases proof of concept had been attained in clinical studies. This review will be useful to broad audience of students, academicians and industry professionals who consider critical issues of protein delivery to the brain and aim developing and studying effective brain delivery systems for protein therapeutics.

Role of oxidized LDL and lectin-like oxidized LDL receptor-1 in cerebral vasospasm after subarachnoid hemorrhage

OBJECT

Cerebral vasospasm after subarachnoid hemorrhage (SAH) is a serious complication. Free radicals derived from subarachnoid clotting are recognized to play an important role. Oxidized low-density lipoprotein (ox-LDL) and lectin-like oxidized LDL receptor-1 (LOX-1) have been shown to be related to the pathogenesis of atherosclerosis and may increase in cerebral arteries after SAH, due to the action of free radicals derived from a subarachnoid clot. These molecules may also affect the pathogenesis of vasospasm, generating intracellular reactive oxygen species and downregulating the expression of endothelial NO synthase (eNOS). If so, apple polyphenol might be effective in the prevention of vasospasm due to an abundant content of procyanidins, which exhibit strong radical scavenging effects, and the ability to suppress ox-LDL and LOX-1. The purposes of this study were to investigate changes in levels of ox-LDL and LOX-1 after SAH and whether administering apple polyphenol can modify cerebral vasospasm.

METHODS

Forty Japanese white rabbits were assigned randomly to 4 groups: an SAH group (n = 10); a shamoperation group (n = 10), which underwent intracisternal saline injection; a low-dose polyphenol group (n = 10) with SAH and oral administration of apple polyphenol at 10 mg/kg per day from Day 0 to Day 3; and a high-dose polyphenol group (n = 10) with SAH and oral administration of apple polyphenol at 50 mg/kg per day. At Day 4, the basilar artery and brain was excised from each rabbit. The degree of cerebral vasospasm was evaluated by measuring the cross-sectional area of each basilar artery, and the expression of ox-LDL, LOX-1, and eNOS was examined for each basilar artery by immunohistochemical staining and reverse transcriptase polymerase chain reaction. In addition, neuronal apoptosis in the cerebral cortex was evaluated by TUNEL.

RESULTS

Compared with the sham group, the expression of ox-LDL and LOX-1 in the basilar arterial wall was significantly increased in the SAH group, the expression of eNOS was significantly decreased, and the cross-sectional area of basilar artery was significantly decreased. Compared with the SAH group, the cross-sectional area of basilar artery was increased in the polyphenol groups, together with the decreased expression of ox-LDL and LOX-1 and the increased expression of eNOS. In the high-dose polyphenol group, those changes were statistically significant compared with the SAH group. In the low-dose polyphenol group, those changes were smaller than in the high-dose polyphenol group. No apoptosis and no changes were seen in the cerebral cortex in all groups.

CONCLUSIONS

This is the first study suggesting that ox-LDL and LOX-1 increase due to SAH and that they may play a role in the pathogenesis of vasospasm. It is assumed that procyanidins in apple polyphenol may inhibit a vicious cycle of ox-LDL, LOX-1, and ROS in a dose-dependent manner. Apple polyphenol is a candidate for preventive treatment of cerebral vasospasm.

Physical exercise training and neurovascular unit in ischemic stroke

Physical exercise could exert a neuroprotective effect in both clinical studies and animal experiments. A series of related studies have indicated that physical exercise could reduce infarct volume, alleviate neurological deficits, decrease blood-brain barrier dysfunction, promote angiogenesis in cerebral vascular system and increase the survival rate after ischemic stroke. In this review, we summarized the protective effects of physical exercise on neurovascular unit (NVU), including neurons, astrocytes, pericytes and the extracellular matrix. Furthermore, it was demonstrated that exercise training could decrease the blood-brain barrier dysfunction and promote angiogenesis in cerebral vascular system. An awareness of the exercise intervention benefits pre- and post stroke may lead more stroke patients and people with high-risk factors to accept exercise therapy for the prevention and treatment of stroke.

Controversies and evolving new mechanisms in subarachnoid hemorrhage

Despite decades of study, subarachnoid hemorrhage (SAH) continues to be a serious and significant health problem in the United States and worldwide. The mechanisms contributing to brain injury after SAH remain unclear. Traditionally, most in vivo research has heavily emphasized the basic mechanisms of SAH over the pathophysiological or morphological changes of delayed cerebral vasospasm after SAH. Unfortunately, the results of clinical trials based on this premise have mostly been disappointing, implicating some other pathophysiological factors, independent of vasospasm, as contributors to poor clinical outcomes. Delayed cerebral vasospasm is no longer the only culprit. In this review, we summarize recent data from both experimental and clinical studies of SAH and discuss the vast array of physiological dysfunctions following SAH that ultimately lead to cell death. Based on the progress in neurobiological understanding of SAH, the terms "early brain injury" and "delayed brain injury" are used according to the temporal progression of SAH-induced brain injury. Additionally, a new concept of the vasculo-neuronal-glia triad model for SAH study is highlighted and presents the challenges and opportunities of this model for future SAH applications.

Cell-specific blood-brain barrier regulation in health and disease: a focus on hypoxia

The blood-brain barrier (BBB) is a complex vascular structure consisting of microvascular endothelial cells that line the vessel wall, astrocyte end-feet, pericytes, as well as the basal lamina. BBB cells act in concert to maintain the characteristic impermeable and low paracellular flux of the brain vascular network, thus ensuring a homeostatic neuronal environment. Alterations in BBB stability that occur during injury have dire consequences on disease progression and it is clear that BBB cell-specific responses, positive or negative, must make a significant contribution to injury outcome. Reduced oxygenation, or hypoxia, is a characteristic of many brain diseases that significantly increases barrier permeability. Recent data suggest that hypoxia-inducible factor (HIF-1), the master regulator of the hypoxic response, probably mediates many hypoxic effects either directly or indirectly via its target genes. This review discusses current knowledge of physiological cell-specific regulation of barrier function, their responses to hypoxia as well as consequences of hypoxic- and HIF-1-mediated mechanisms on barrier integrity during select brain diseases. In the final sections, the potential of current advances in targeting HIF-1 as a therapeutic strategy will be overviewed.

The role of the microcirculation in delayed cerebral ischemia and chronic degenerative changes after subarachnoid hemorrhage

The mortality after aneurysmal subarachnoid hemorrhage (SAH) is 50%, and most survivors suffer severe functional and cognitive deficits. Half of SAH patients deteriorate 5 to 14 days after the initial bleeding, so-called delayed cerebral ischemia (DCI). Although often attributed to vasospasms, DCI may develop in the absence of angiographic vasospasms, and therapeutic reversal of angiographic vasospasms fails to improve patient outcome. The etiology of chronic neurodegenerative changes after SAH remains poorly understood. Brain oxygenation depends on both cerebral blood flow (CBF) and its microscopic distribution, the so-called capillary transit time heterogeneity (CTH). In theory, increased CTH can therefore lead to tissue hypoxia in the absence of severe CBF reductions, whereas reductions in CBF, paradoxically, improve brain oxygenation if CTH is critically elevated. We review potential sources of elevated CTH after SAH. Pericyte constrictions in relation to the initial ischemic episode and subsequent oxidative stress, nitric oxide depletion during the pericapillary clearance of oxyhemoglobin, vasogenic edema, leukocytosis, and astrocytic endfeet swelling are identified as potential sources of elevated CTH, and hence of metabolic derangement, after SAH. Irreversible changes in capillary morphology and function are predicted to contribute to long-term relative tissue hypoxia, inflammation, and neurodegeneration. We discuss diagnostic and therapeutic implications of these predictions.

Plasma taurine as a predictor of poor outcome in patients with mild neurological deficits after aneurysmal subarachnoid hemorrhage

Object

The object of this study was to determine the relationship between plasma taurine and subarachnoid hemorrhage (SAH) outcome.

Methods

Forty patients with SAH and mild neurological deficits were included in this prospective, blinded cohort study. Plasma taurine levels were measured using high-performance liquid chromatography on admission and were correlated with patient outcomes at discharge.

Results

Twenty-five percent of the patients ultimately had a poor outcome. Plasma taurine concentrations at admission were increased (2-fold) in SAH patients with a favorable outcome and were further increased (6-fold) in those who had a poor outcome. Increased taurine levels identified patients who would be discharged with a poor outcome, with sensitivity and specificity values of approximately 80% and 100%, respectively, and positive and negative predictive values of approximately 90%. Delayed cerebral vasospasm showed an OR of 27.9 (95% CI 1.090–714.9) for a poor outcome, whereas an increased taurine concentration had an OR of 105 for a poor outcome (95% CI 8.3–1328.0, p < 0.001).

Conclusions

Increased plasma taurine concentrations on admission predict a poor outcome in SAH.

Pathophysiological Role of Global Cerebral Ischemia following Subarachnoid Hemorrhage: The Current Experimental Evidence

Subarachnoid hemorrhage (SAH) is the subtype of stroke with one of the highest mortality rates and the least well-understood pathophysiologies. One of the very early events which may occur after SAH is a significant decrease of cerebral perfusion pressure (CPP) caused by the excessive increase of intracranial pressure during the initial bleeding. A severely decreased CPP results in global cerebral ischemia, an event also occurring after cardiac arrest. The aim of the current paper is to review the pathophysiological events occurring in experimental models of SAH and global cerebral ischemia and to evaluate the contribution and the importance of global cerebral ischemia for the pathophysiology of SAH.

Early brain injury: a common mechanism in subarachnoid hemorrhage and global cerebral ischemia

Early brain injury (EBI) has become an area of extreme interest in the recent years and seems to be a common denominator in the pathophysiology of global transient ischemia and subarachnoid hemorrhage (SAH). In this paper, we highlight the importance of cerebral hypoperfusion and other mechanisms that occur in tandem in both pathologies and underline their possible roles in triggering brain injury after hemorrhagic or ischemic strokes.

Intraocular hemorrhage causes retinal vascular dysfunction via plasma kallikrein

PURPOSE

Retinal hemorrhages occur in a variety of sight-threatening conditions including ocular trauma, high altitude retinopathy, and chronic diseases such as diabetic and hypertensive retinopathies. The goal of this study is to investigate the effects of blood in the vitreous on retinal vascular function in rats.

METHODS

Intravitreal injections of autologous blood, plasma kallikrein (PK), bradykinin, and collagenase were performed in Sprague-Dawley and Long-Evans rats. Retinal vascular permeability was measured using vitreous fluorophotometry and Evans blue dye permeation. Leukostasis was measured by fluorescein isothiocyanate-coupled concanavalin A lectin and acridine orange labeling. Retinal hemorrhage was examined on retinal flatmounts. Primary cultures of bovine retinal pericytes were cultured in the presence of 25 nM PK for 24 hours. The pericyte-conditioned medium was collected and the collagen proteome was analyzed by tandem mass spectrometry.

RESULTS

Intravitreal injection of autologous blood induced retinal vascular permeability and retinal leukostasis, and these responses were ameliorated by PK inhibition. Intravitreal injections of exogenous PK induced retinal vascular permeability, leukostasis, and retinal hemorrhage. Proteomic analyses showed that PK increased collagen degradation in pericyte-conditioned medium and purified type IV collagen. Intravitreal injection of collagenase mimicked PK's effect on retinal hemorrhage.

CONCLUSIONS

Intraocular hemorrhage increases retinal vascular permeability and leukostasis, and these responses are mediated, in part, via PK. Intravitreal injections of either PK or collagenase, but not bradykinin, induce retinal hemorrhage in rats. PK exerts collagenase-like activity that may contribute to blood-retinal barrier dysfunction.

Vulnerability of the developing brain to hypoxic-ischemic damage: contribution of the cerebral vasculature to injury and repair?

As clinicians attempt to understand the underlying reasons for the vulnerability of different regions of the developing brain to injury, it is apparent that little is known as to how hypoxia-ischemia may affect the cerebrovasculature in the developing infant. Most of the research investigating the pathogenesis of perinatal brain injury following hypoxia-ischemia has focused on excitotoxicity, oxidative stress and an inflammatory response, with the response of the developing cerebrovasculature receiving less attention. This is surprising as the presentation of devastating and permanent injury such as germinal matrix-intraventricular haemorrhage (GM-IVH) and perinatal stroke are of vascular origin, and the origin of periventricular leukomalacia (PVL) may also arise from poor perfusion of the white matter. This highlights that cerebrovasculature injury following hypoxia could primarily be responsible for the injury seen in the brain of many infants diagnosed with hypoxic-ischemic encephalopathy (HIE). Interestingly the highly dynamic nature of the cerebral blood vessels in the fetus, and the fluctuations of cerebral blood flow and metabolic demand that occur following hypoxia suggest that the response of blood vessels could explain both regional protection and vulnerability in the developing brain. However, research into how blood vessels respond following hypoxia-ischemia have mostly been conducted in adult models of ischemia or stroke, further highlighting the need to investigate how the developing cerebrovasculature responds and the possible contribution to perinatal brain injury following hypoxia. This review discusses the current concepts on the pathogenesis of perinatal brain injury, the development of the fetal cerebrovasculature and the blood brain barrier (BBB), and key mediators involved with the response of cerebral blood vessels to hypoxia.