Extravascular Blood Augments Myogenic Constriction of Cerebral Arterioles: Implications for Hemorrhage-Induced Vasospasm

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.

An Update on Antioxidative Stress Therapy Research for Early Brain Injury After Subarachnoid Hemorrhage

The main reasons for disability and death in aneurysmal subarachnoid hemorrhage (aSAH) may be early brain injury (EBI) and delayed cerebral ischemia (DCI). Despite studies reporting and progressing when DCI is well-treated clinically, the prognosis is not well-improved. According to the present situation, we regard EBI as the main target of future studies, and one of the key phenotype-oxidative stresses may be called for attention in EBI after laboratory subarachnoid hemorrhage (SAH). We summarized the research progress and updated the literature that has been published about the relationship between experimental and clinical SAH-induced EBI and oxidative stress (OS) in PubMed from January 2016 to June 2021. Many signaling pathways are related to the mechanism of OS in EBI after SAH. Several antioxidative stress drugs were studied and showed a protective response against EBI after SAH. The systematical study of antioxidative stress in EBI after laboratory and clinical SAH may supply us with new therapies about SAH.

Regulation of cerebral blood flow in humans: physiology and clinical implications of autoregulation

Brain function critically depends on a close matching between metabolic demands, appropriate delivery of oxygen and nutrients, and removal of cellular waste. This matching requires continuous regulation of cerebral blood flow (CBF), which can be categorized into four broad topics: 1) autoregulation, which describes the response of the cerebrovasculature to changes in perfusion pressure; 2) vascular reactivity to vasoactive stimuli [including carbon dioxide (CO2)]; 3) neurovascular coupling (NVC), i.e., the CBF response to local changes in neural activity (often standardized cognitive stimuli in humans); and 4) endothelium-dependent responses. This review focuses primarily on autoregulation and its clinical implications. To place autoregulation in a more precise context, and to better understand integrated approaches in the cerebral circulation, we also briefly address reactivity to CO2 and NVC. In addition to our focus on effects of perfusion pressure (or blood pressure), we describe the impact of select stimuli on regulation of CBF (i.e., arterial blood gases, cerebral metabolism, neural mechanisms, and specific vascular cells), the interrelationships between these stimuli, and implications for regulation of CBF at the level of large arteries and the microcirculation. We review clinical implications of autoregulation in aging, hypertension, stroke, mild cognitive impairment, anesthesia, and dementias. Finally, we discuss autoregulation in the context of common daily physiological challenges, including changes in posture (e.g., orthostatic hypotension, syncope) and physical activity.

Cerebral Autoregulation in Subarachnoid Hemorrhage

Subarachnoid hemorrhage (SAH) is a devastating stroke subtype with a high rate of mortality and morbidity. The poor clinical outcome can be attributed to the biphasic course of the disease: even if the patient survives the initial bleeding emergency, delayed cerebral ischemia (DCI) frequently follows within 2 weeks time and levies additional serious brain injury. Current therapeutic interventions do not specifically target the microvascular dysfunction underlying the ischemic event and as a consequence, provide only modest improvement in clinical outcome. SAH perturbs an extensive number of microvascular processes, including the “automated” control of cerebral perfusion, termed “cerebral autoregulation.” Recent evidence suggests that disrupted cerebral autoregulation is an important aspect of SAH-induced brain injury. This review presents the key clinical aspects of cerebral autoregulation and its disruption in SAH: it provides a mechanistic overview of cerebral autoregulation, describes current clinical methods for measuring autoregulation in SAH patients and reviews current and emerging therapeutic options for SAH patients. Recent advancements should fuel optimism that microvascular dysfunction and cerebral autoregulation can be rectified in SAH patients.

Systemic exosomal miR-193b-3p delivery attenuates neuroinflammation in early brain injury after subarachnoid hemorrhage in mice

Background

Inflammation is a potential crucial factor in the pathogenesis of subarachnoid hemorrhage (SAH). Circulating microRNAs (miRNAs) are involved in the regulation of diverse aspects of neuronal dysfunction. The therapeutic potential of miRNAs has been demonstrated in several CNS disorders and is thought to involve modulation of neuroinflammation. Here, we found that peripherally injected modified exosomes (Exos) delivered miRNAs to the brains of mice with SAH and that the potential mechanism was regulated by regulation of neuroinflammation.

Methods

Next-generation sequencing (NGS) and qRT-PCR were used to define the global miRNA profile of plasma exosomes in aSAH patients and healthy controls. We peripherally injected RVG/Exos/miR-193b-3p to achieve delivery of miR-193b-3p to the brain of mice with SAH. The effects of miR-193b-3p on SAH were assayed using a neurological score, brain water content, blood-brain barrier (BBB) injury, and Fluoro-Jade C (FJC) staining. Western blotting analysis, enzyme-linked immunosorbent assay (ELISA), and qRT-PCR were used to measure various proteins and mRNA levels.

Results

NGS and qRT-PCR revealed that four circulating exosomal miRNAs were differentially expressed. RVG/Exos exhibited improved targeting to the brains of SAH mice. MiR-193b-3p suppressed the expression and activity of HDAC3, upregulating the acetylation of NF-κB p65. Finally, miR-193b-3p treatment mitigated the neurological behavioral impairment, brain edema, BBB injury, and neurodegeneration induced by SAH, and reduced inflammatory cytokine expression in the brains of mice after SAH.

Conclusions

Exos/miR-193b-3p treatment attenuated the inflammatory response by acetylation of the NF-κB p65 via suppressed expression and activity of HDAC3. These effects alleviated neurobehavioral impairments and neuroinflammation following SAH.

Antioxidant Melatonin: Potential Functions in Improving Cerebral Autoregulation After Subarachnoid Hemorrhage

Subarachnoid hemorrhage (SAH) is a subtype of stroke with high mortality and morbidity. Impaired cerebral autoregulation following SAH has been reported owing to effects on sympathetic control, endothelial function, myogenic response, and cerebral metabolism. Impaired cerebral autoregulation is associated with early brain injury, cerebral vasospasm/delayed cerebral ischemia, and SAH prognosis. However, few drugs have been reported to improve cerebral autoregulation after SAH. Melatonin is a powerful antioxidant that is effective (easily crosses the blood brain barrier) and safe (tolerated in large doses without toxicity). Theoretically, melatonin may impact the control mechanisms of cerebral autoregulation via antioxidative effects, protection of endothelial cell integrity, suppression of sympathetic nerve activity, increase in nitric oxide bioavailability, mediation of the myogenic response, and amelioration of hypoxemia. Furthermore, melatonin may have a comprehensive effect on cerebral autoregulation. This review discusses the potential effects of melatonin on cerebral autoregulation following SAH, in terms of the association between pharmacological activities and the mechanisms of cerebral autoregulation.