Apoptosis, blood-brain barrier, and subarachnoid hemorrhage

Remodeling of the Neurovascular Unit Following Cerebral Ischemia and Hemorrhage

Formulated as a group effort of the stroke community, the transforming concept of the neurovascular unit (NVU) depicts the structural and functional relationship between brain cells and the vascular structure. Composed of both neural and vascular elements, the NVU forms the blood-brain barrier that regulates cerebral blood flow to meet the oxygen demand of the brain in normal physiology and maintain brain homeostasis. Conversely, the dysregulation and dysfunction of the NVU is an essential pathological feature that underlies neurological disorders spanning from chronic neurodegeneration to acute cerebrovascular events such as ischemic stroke and cerebral hemorrhage, which were the focus of this review. We also discussed how common vascular risk factors of stroke predispose the NVU to pathological changes. We synthesized existing literature and first provided an overview of the basic structure and function of NVU, followed by knowledge of how these components remodel in response to ischemic stroke and brain hemorrhage. A greater understanding of the NVU dysfunction and remodeling will enable the design of targeted therapies and provide a valuable foundation for relevant research in this area.

Early metabolic impairment as a contributor to neurodegenerative disease: Mechanisms and potential pharmacological intervention

The metabolic syndrome comprises a family of clinical and laboratory findings, including insulin resistance, hyperglycemia, hypertriglyceridemia, low high-density lipoprotein cholesterol levels, and hypertension, in addition to central obesity. The syndrome confers a high risk of cardiovascular mortality. Indeed, metabolic dysfunction has been shown to cause a direct insult to smooth muscle and endothelial components of the vasculature, which leads to vascular dysfunction and hyperreactivity. This, in turn, causes cerebral vasoconstriction and hypoperfusion, eventually contributing to cognitive deficits. Moreover, the metabolic syndrome disrupts key homeostatic processes in the brain, including apoptosis, autophagy, and neurogenesis. Impairment of such processes in the context of metabolic dysfunction has been implicated in the pathogenesis of neurodegenerative diseases, including Alzheimer, Parkinson, and Huntington diseases. The aim of this review is to elucidate the role that the metabolic syndrome plays in the pathogenesis of the latter disorders, with a focus on the role of perivascular adipose inflammation in the peripheral-to-central transduction of the inflammatory insult. This review delineates common signaling pathways that contribute to these pathologies. Moreover, the role of therapeutic agents aimed at treating the metabolic syndrome, as well as their risk factors that interfere with the aforementioned pathways, are discussed as potential interventions for neurodegenerative diseases.

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.

Neutrophil Extracellular Traps may be a Potential Target for Treating Early Brain Injury in Subarachnoid Hemorrhage

Neuroinflammation is closely associated with poor prognosis in patients with subarachnoid hemorrhage (SAH). The purpose of this study was to investigate the role of neutrophil extracellular traps (NETs), which are important regulators of sterile inflammation, in SAH. In this study, markers of NET formation, quantified by the level of citrullinated histone H3 (CitH3), were significantly increased after SAH and correlated with SAH severity. CitH3 peaked at 12 h in peripheral blood and at 24 h in the brain. Administration of the peptidyl arginine deiminase 4 (PAD4) selective antagonist GSK484 substantially attenuated SAH-induced brain edema and neuronal injury. Moreover, the benefit of NET inhibition was also confirmed by DNAse I treatment and neutrophil depletion. Mechanistically, NETs markedly exacerbated microglial inflammation in vitro. NET formation aggravated neuroinflammation by promoting microglial activation and increased the levels of TNF-α, IL-1β, and IL-6, while inhibiting NETs demonstrated anti-inflammatory effects by decreasing the levels of these proinflammatory factors. Moreover, neurogenic pulmonary edema (NPE), a severe nonneurological complication after SAH, is associated with a high level of NET formation. However, GSK484 effectively inhibited the formation of NETs in the lungs of NPE mice, thereby preventing the diffusion of neutrophilic infiltration and attenuating the swelling of the alveolar interstitium. In conclusion, NETs promoted neuroinflammation after SAH, while pharmacological inhibition of PAD4-NETs could reduce the inflammatory damage caused by SAH. These results supported the idea that NETs might be potential therapeutic targets for SAH.

Netrin-1 alleviates subarachnoid haemorrhage-induced brain injury via the PPARγ/NF-KB signalling pathway

Netrin‐1 (NTN‐1) is a novel drug to alleviate early brain injury following subarachnoid haemorrhage (SAH). However the molecular mechanism of NTN‐1‐mediated protection against early brain injury following SAH remains largely elusive. This study aims to evaluate the effects and mechanisms of NTN‐1 in protecting SAH‐induced early brain injury. The endovascular perforation SAH model was constructed using male C57BL/6J mice, and recombinant NTN‐1 was administrated intravenously. Mortality rates, SAH grade, brain water content, neurological score and neuronal apoptosis were evaluated. The expression of PPARγ, Bcl‐2, Bax and nuclear factor‐kappa B (NF‐κB) were detected by Western blot. Small interfering RNA specific to NTN‐1 receptor, UNC5B, and a selective PPARγ antagonist, bisphenol A diglycidyl ether (BADGE), were applied in combination with NTN‐1. The results suggested that NTN‐1 improved the neurological deficits, reduced the brain water content and alleviated neuronal apoptosis. In addition, NTN‐1 enhanced PPARγ and Bcl‐2 expression and decreased the levels of Bax and NF‐κB. However, the neuroprotection of NTN‐1 was abolished by UNC5B and BADGE. In conclusion, our results demonstrated that NTN‐1 attenuates early brain injury following SAH via the UNC5B PPARγ/NF‐κB signalling pathway.

Advances in the understanding of delayed cerebral ischaemia after aneurysmal subarachnoid haemorrhage

Delayed cerebral ischaemia has been described as the single most important cause of morbidity and mortality in patients who survive the initial aneurysmal subarachnoid haemorrhage. Our understanding of the pathophysiology of delayed cerebral ischaemia is meagre at best and the calcium channel blocker nimodipine remains the only intervention to consistently improve functional outcome after aneurysmal subarachnoid haemorrhage. There is substantial evidence to support cerebral vessel narrowing as a causative factor in delayed cerebral ischaemia, but contemporary research demonstrating improvements in vessel narrowing has failed to show improved functional outcomes. This has encouraged researchers to investigate other potential causes of delayed cerebral ischaemia, such as early brain injury, microthrombosis, and cortical spreading depolarisation. Adherence to a common definition of delayed cerebral ischaemia is needed in order to allow easier assessment of studies using multiple different terms. Furthermore, improved recognition of delayed cerebral ischaemia would not only allow for faster treatment but also better assessment of interventions. Finally, understanding nimodipine's mechanism of action may allow us to develop similar agents with improved efficacy.

Early CT perfusion changes and blood-brain barrier permeability after aneurysmal subarachnoid hemorrhage

INTRODUCTION

Early brain injury (EBI) can occur within 72 h of aneurysmal subarachnoid hemorrhage (aSAH). The objective of this study was to determine if there are differences in early CTP parameters (<72 h) with respect to delayed cerebral ischemia (DCI), cerebral infarction, and functional outcome.

METHODS

We performed a prospective cohort study of aSAH patients admitted to a single tertiary care center. MTT, CBF and blood-brain barrier permeability (PS) were quantified with CTP within 72 h of aneurysm rupture. Primary outcomes were functional outcome by the Modified Rankin Scale (mRS) at 3 months and cerebral infarction. Secondary outcome was the development of DCI. Differences between early CTP parameters were determined with respect to primary and secondary outcomes.

RESULTS

Fifty aSAH patients were included in the final analysis. MTT was significantly higher in patients who developed DCI (6.7 ± 1.2 vs 5.9 ± 1.0; p = 0.03) and cerebral infarction (7.0 ± 1.2 vs 5.9 ± 0.9; p = 0.007); however, no difference in MTT was found between patients with and without a poor outcome (mRS > 2). Early CBF and PS did not differ with respect to functional outcome, DCI, and cerebral infarction.

CONCLUSIONS

Elevated MTT within 72 h of aneurysm rupture is associated with DCI and cerebral infarction but not with long-term functional outcome. Blood-brain barrier permeability, as assessed by CT perfusion, was not associated with DCI or worse outcome in this cohort.

Imatinib preserves blood-brain barrier integrity following experimental subarachnoid hemorrhage in rats

Blood-brain barrier (BBB) disruption and consequent edema formation contribute to the development of early brain injury following subarachnoid hemorrhage (SAH). Various cerebrovascular insults result in increased platelet-derived growth factor receptor (PDGFR)-α stimulation, which has been linked to BBB breakdown and edema formation. This study examines whether imatinib, a PDGFR inhibitor, can preserve BBB integrity in a rat endovascular perforation SAH model. Imatinib (40 or 120 mg/kg) or a vehicle was administered intraperitoneally at 1 hr after SAH induction. BBB leakage, brain edema, and neurological deficits were evaluated. Total and phosphorylated protein expressions of PDGFR-α, c-Src, c-Jun N-terminal kinase (JNK), and c-Jun were measured, and enzymatic activities of matrix metalloproteinase (MMP)-2 and MMP-9 were determined in the injured brain. Imatinib treatment significantly ameliorated BBB leakage and edema formation 24 hr after SAH, which was paralleled by improved neurological functions. Decreased brain expressions of phosphorylated PDGFR-α, c-Src, JNK, and c-Jun as well as reduced MMP-9 activities were found in treated animals. PDGFR-α inhibition preserved BBB integrity following experimental SAH; however, the protective mechanisms remain to be elucidated. Targeting PDGFR-α signaling might be advantageous to ameliorate early brain injury following SAH.

To look beyond vasospasm in aneurysmal subarachnoid haemorrhage

Delayed cerebral vasospasm has classically been considered the most important and treatable cause of mortality and morbidity in patients with aneurysmal subarachnoid hemorrhage (aSAH). Secondary ischemia (or delayed ischemic neurological deficit, DIND) has been shown to be the leading determinant of poor clinical outcome in patients with aSAH surviving the early phase and cerebral vasospasm has been attributed to being primarily responsible. Recently, various clinical trials aimed at treating vasospasm have produced disappointing results. DIND seems to have a multifactorial etiology and vasospasm may simply represent one contributing factor and not the major determinant. Increasing evidence shows that a series of early secondary cerebral insults may occur following aneurysm rupture (the so-called early brain injury). This further aggravates the initial insult and actually determines the functional outcome. A better understanding of these mechanisms and their prevention in the very early phase is needed to improve the prognosis. The aim of this review is to summarize the existing literature on this topic and so to illustrate how the presence of cerebral vasospasm may not necessarily be a prerequisite for DIND development. The various factors determining DIND that worsen functional outcome and prognosis are then discussed.

Interference of apoptosis in the pathophysiology of subarachnoid hemorrhage

Programmed cell death is crucial for the correct development of the organism and the clearance of harmful cells like tumor cells or autoreactive immune cells. Apoptosis is initiated by the activation of cell death receptors and in most cases it is associated with the activation of the cysteine proteases, which lead to apoptotic cell death. Cells shrink, chromatin clumps and forms a large, sharply demarcated, crescent-shaped or round mass; the nucleus condenses, apoptotic bodies are formed and eventually dead cells are engulfed by a neighboring cell or cleared by phagocytosis. The authors have summarized the most important data concerning apoptosis in subarachnoid hemorrhage that have been issued in the medical literature in the last 20 years.

Neuroprotective effects of anti-tumor necrosis factor-alpha antibody on apoptosis following subarachnoid hemorrhage in a rat model

Recent studies have emphasized the importance of apoptosis in subarachnoid hemorrhage (SAH) and the subsequent early brain injury. However, the apoptotic pathways induced by SAH in different brain regions are not fully understood. We investigated gene expression levels of classical apoptosis-related molecules (caspase-3, bax, and bcl-2) following SAH in the hippocampus of male Wistar rats. Temporally specific changes were found in caspase-3 and bax messenger RNA only. Interestingly, we found increased expression of bax, but not caspase-3, in the prefrontal cortex, which indicates different molecular mechanisms of apoptosis in distinct brain regions. Most important, changes in expression were reversed by functional blockade of tumor necrosis factor-alpha, which has a critical role in brain injury. In addition, we found that apoptosis induced by SAH may be associated with a relative elevation of pro-brain derived neurotrophic factor.

The importance of early brain injury after subarachnoid hemorrhage

Aneurysmal subarachnoid hemorrhage (aSAH) is a medical emergency that accounts for 5% of all stroke cases. Individuals affected are typically in the prime of their lives (mean age 50 years). Approximately 12% of patients die before receiving medical attention, 33% within 48 h and 50% within 30 days of aSAH. Of the survivors 50% suffer from permanent disability with an estimated lifetime cost more than double that of an ischemic stroke. Traditionally, spasm that develops in large cerebral arteries 3-7 days after aneurysm rupture is considered the most important determinant of brain injury and outcome after aSAH. However, recent studies show that prevention of delayed vasospasm does not improve outcome in aSAH patients. This finding has finally brought in focus the influence of early brain injury on outcome of aSAH. A substantial amount of evidence indicates that brain injury begins at the aneurysm rupture, evolves with time and plays an important role in patients' outcome. In this manuscript we review early brain injury after aSAH. Due to the early nature, most of the information on this injury comes from animals and few only from autopsy of patients who died within days after aSAH. Consequently, we began with a review of animal models of early brain injury, next we review the mechanisms of brain injury according to the sequence of their temporal appearance and finally we discuss the failure of clinical translation of therapies successful in animal models of aSAH.

Apoptotic mechanisms for neuronal cells in early brain injury after subarachnoid hemorrhage

OBJECTS

The major causes of death and disability in subarachnoid hemorrhage (SAH) may be early brain injury (EBI) and cerebral vasospasm. Although cerebral vasospasm has been studied and treated by a lot of drugs, the outcome is not improved even if vasospasm is reversed. Based on these data, EBI is considered a primary target for future research, and apoptosis may be involved in EBI after experimental SAH.

METHODS

We reviewed the published literature about the relationship between SAH induced EBI and apoptosis in PubMed.

RESULT

Most available information can be obtained from the endovascular filament perforation animal model. After onset of SAH, intracranial pressure is increased and then cerebral blood flow is reduced. Many factors are involved in the mechanism of apoptotic cell death in EBI after SAH. In the neuronal cells, both intrinsic and extrinsic pathways of apoptosis can occur. Some antiapoptotic drugs were studied and demonstrated a protective effect against EBI after SAH. However, apoptosis in EBI after SAH has been little studied and further studies will provide us more beneficial findings.

CONCLUSIONS

The study of apoptosis in EBI after experimental SAH may give us new therapies for SAH.

Glibenclamide reduces inflammation, vasogenic edema, and caspase-3 activation after subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) causes secondary brain injury due to vasospasm and inflammation. Here, we studied a rat model of mild-to-moderate SAH intended to minimize ischemia/hypoxia to examine the role of sulfonylurea receptor 1 (SUR1) in the inflammatory response induced by SAH. mRNA for Abcc8, which encodes SUR1, and SUR1 protein were abundantly upregulated in cortex adjacent to SAH, where tumor-necrosis factor-alpha (TNFalpha) and nuclear factor (NF)kappaB signaling were prominent. In vitro experiments confirmed that Abcc8 transcription is stimulated by TNFalpha. To investigate the functional consequences of SUR1 expression after SAH, we studied the effect of the potent, selective SUR1 inhibitor, glibenclamide. We examined barrier permeability (immunoglobulin G, IgG extravasation), and its correlate, the localization of the tight junction protein, zona occludens 1 (ZO-1). SAH caused a large increase in barrier permeability and disrupted the normal junctional localization of ZO-1, with glibenclamide significantly reducing both effects. In addition, SAH caused large increases in markers of inflammation, including TNFalpha and NFkappaB, and markers of cell injury or cell death, including IgG endocytosis and caspase-3 activation, with glibenclamide significantly reducing these effects. We conclude that block of SUR1 by glibenclamide may ameliorate several pathologic effects associated with inflammation that lead to cortical dysfunction after SAH.

Atorvastatin ameliorates cerebral vasospasm and early brain injury after subarachnoid hemorrhage and inhibits caspase-dependent apoptosis pathway

Backgroud

Cerebral vasospasm (CVS) and early brain injury remain major causes of morbidity and mortality after aneurysmal subarachnoid hemorrhage (SAH). Hydroxymethylglutaryl coenzyme A reductase inhibitors, also known as statins, has the neuroprotective effects and ameliorating CVS after SAH. This study was designed to explore apoptosis inhibiting effects of atorvastatin and its potential apoptotic signal pathway after SAH.

Results

Preserving blood-brain-barrier permeability, decreasing brain edema, increasing neurological scores and ameliorating cerebral vasospasm were obtained after prophylactic use of atorvastatin. TUNEL-positive cells were reduced markedly both in basilar artery and in brain cortex by atorvastatin. Apoptosis-related proteins P53, AIF and Cytochrome C were up-regulated after SAH, while they were not affected by atorvastatin. In addition, up-regulation of caspase-3 and caspase-8 after SAH was decreased by atorvastatin treatment both in mRNA and in protein levels.

Conclusion

The neuroprotective effects of atorvastatin after SAH may be related to its inhibition of caspase-dependent proapoptotic pathway based on the present results.