Mechanisms of statin treatment in cerebral vasospasm

Interleukin-6: Important Mediator of Vasospasm Following Subarachnoid Hemorrhage

The correlation of neuroinflammation with the development of cerebral vasospasm following subarachnoid hemorrhage has been well documented in the literature; both clinical and preclinical. The exact mechanisms by which this process occurs, however, are poorly elucidated. Recent evidence indicates that interleukin-6 is not only an important prognostic biomarker for subarachnoid hemorrhage and subsequent vasospasm development but also an integral component in the progression of injury following initial insult. In this review, we briefly highlight other pathways under investigation and focus heavily on what has been discovered regarding the role of interleukin 6 and cerebral vasospasm following subarachnoid hemorrhage. A proposed mechanistic pathway is highlighted in written and graphical format. A discussion regarding the human correlative findings and initial pre-clinical mechanistic studies is addressed. Finally, in the future investigation section, innovative developments and a clear description of areas warranting further scientific inquiry are emphasized. This review will catalyze continued discovery in this area of emerging significance and aid in the quest for effective vasospasm treatment where limited clinical therapeutics currently exist.

Vasospasm in cerebral inflammation

All forms of cerebral inflammation as found in bacterial meningitis, cerebral malaria, brain injury, and subarachnoid haemorrhage have been associated with vasospasm of cerebral arteries and arterioles. Vasospasm has been associated with permanent neurological deficits and death in subarachnoid haemorrhage and bacterial meningitis. Increased levels of interleukin-1 may be involved in vasospasm through calcium dependent and independent activation of the myosin light chain kinase and release of the vasoconstrictor endothelin-1. Another key factor in the pathogenesis of cerebral arterial vasospasm may be the reduced bioavailability of the vasodilator nitric oxide. Therapeutic trials in vasospasm related to inflammation in subarachnoid haemorrhage in humans showed a reduction of vasospasm through calcium antagonists, endothelin receptor antagonists, statins, and plasminogen activators. Combination of therapeutic modalities addressing calcium dependent and independent vasospasm, the underlying inflammation, and depletion of nitric oxide simultaneously merit further study in all conditions with cerebral inflammation in double blind randomised placebo controlled trials. Auxiliary treatment with these agents may be able to reduce ischemic brain injury associated with neurological deficits and increased mortality.

Inflammation, cerebral vasospasm, and evolving theories of delayed cerebral ischemia

Cerebral vasospasm (CVS) is a potentially lethal complication of aneurysmal subarachnoid hemorrhage (aSAH). Recently, the symptomatic presentation of CVS has been termed delayed cerebral ischemia (DCI), occurring as early as 3-4 days after the sentinel bleed. For the past 5-6 decades, scientific research has promulgated the theory that cerebral vasospasm plays a primary role in the pathology of DCI and subsequently delayed ischemic neurological decline (DIND). Approximately 70% of patients develop CVS after aSAH with 50% long-term morbidity rates. The exact etiology of CVS is unknown; however, a well-described theory involves an antecedent inflammatory cascade with alterations of intracellular calcium dynamics and nitric oxide fluxes, though the intricacies of this inflammatory theory are currently unknown. Consequently, there have been few advances in the clinical treatment of this patient cohort, and morbidity remains high. Identification of intermediaries in the inflammatory cascade can provide insight into newer clinical interventions in the prevention and management of cerebral vasospasm and will hopefully prevent neurological decline. In this review, we discuss current theories implicating the inflammatory cascade in the development of CVS and potential treatment targets.

Suppression of the Rho/Rho-kinase pathway and prevention of cerebral vasospasm by combination treatment with statin and fasudil after subarachnoid hemorrhage in rabbit

The Rho/Rho-kinase pathway is considered important in the pathogenesis of sustained smooth muscle cell contraction during cerebral vasospasm after aneurysmal subarachnoid hemorrhage (SAH). The aims of this study were to investigate whether combination treatment, with pitavastatin as an inhibitor of RhoA and fasudil as an inhibitor of Rho-kinase, prevents the cerebral vasospasm. SAH was simulated using the double-hemorrhage rabbit model, and pitavastatin, or fasudil, or both (combination treatment) were administrated. The basilar artery (BA) cross-sectional area only in the combination treatment group was statistically larger than in the SAH group (p < 0.05). BA Rho-kinase, as measured by ELISA, was statistically reduced only in the combination treatment group compared with the SAH group (p < 0.05). In the other two treatment groups, pitavastatin or fasudil treatment group showed larger BA cross-sectional areas and lower value for BA Rho-kinase, but there were no statistically significant differences compared with the SAH group. The expression of endothelial nitric oxide synthase (eNOS), evaluated by immunohistochemistry in the pitavastatin group and the combination group, was higher than in the SAH group. Results indicate that combination treatment could extensively prevent cerebral vasospasm due to the synergic effect of combining pitavastatin and fasudil on the Rho/Rho-kinase pathway and on eNOS.

Simvastatin induces neuroprotection in 6-OHDA-lesioned PC12 via the PI3K/AKT/caspase 3 pathway and anti-inflammatory responses

BACKGROUND

In addition to their original applications for lowering cholesterol, statins display multiple neuroprotective effects. Inflammatory reactions and the PI3K/AKT/caspase 3 pathway are strongly implicated in dopaminergic neuronal death in Parkinson's disease (PD). This study aims to investigate how simvastatin affects 6-hydroxydopamine-lesioned PC12 via regulating PI3K/AKT/caspase 3 and modulating inflammatory mediators.

METHODS

6-hydroxydopamine-treated PC12 cells were used to investigate the neuroprotection of simvastatin, its association with the PI3K/AKT/caspase 3 pathway, and antiinflammatory responses. Dopamine transporters (DAT) and tyrosine hydroxylase (TH) were examined in 6-hydroxydopamine-treated PC12 after simvastatin treatment.

RESULTS

Simvastatin-mediated neuroprotection was associated with a robust reduction in the upregulation induced by 6-OHDA of inflammatory mediators including IL-6, COX2, and TNF-α. The downregulated DAT and TH levels in 6-OHDA-lesioned PC12 were restored after simvastatin treatment. Simvastatin reversed 6-OHDA-induced downregulation of PI3K/Akt phosphorylation and attenuated 6-OHDA-induced upregulation of caspase 3 in PC12. Furthermore, the PI3K inhibitor LY294002 pronouncedly abolished the simvastatin-mediated attenuation in caspase 3.

CONCLUSIONS

Our results demonstrate that simvastatin provides robust neuroprotection against dopaminergic neurodegeneration, partially via antiinflammatory mechanisms and the PI3K/Akt/caspase 3 pathway. These findings contribute to a better understanding of the critical roles of simvastatin in treating PD and might elucidate the molecular mechanisms of simvastatin effects in PD.

Role of calcitonin gene-related peptide in cerebral vasospasm, and as a therapeutic approach to subarachnoid hemorrhage

Calcitonin gene-related peptide (CGRP) is one of the most potent microvascular vasodilators identified to date. Vascular relaxation and vasodilation is mediated via activation of the CGRP receptor. This atypical receptor is made up of a G protein-coupled receptor called calcitonin receptor-like receptor (CLR), a single transmembrane protein called receptor activity-modifying protein (RAMP), and an additional protein that is required for Ga(s) coupling, known as receptor component protein (RCP). Several mechanisms involved in CGRP-mediated relaxation have been identified. These include nitric oxide (NO)-dependent endothelium-dependent mechanisms or cAMP-mediated endothelium-independent pathways; the latter being more common. Subarachnoid hemorrhage (SAH) is associated with cerebral vasoconstriction that occurs several days after the hemorrhage and is often fatal. The vasospasm occurs in 30-40% of patients and is the major cause of death from this condition. The vasoconstriction is associated with a decrease in CGRP levels in nerves and an increase in CGRP levels in draining blood, suggesting that CGRP is released from nerves to oppose the vasoconstriction. This evidence has led to the concept that exogenous CGRP may be beneficial in a condition that has proven hard to treat. The present article reviews: (a) the pathophysiology of delayed ischemic neurologic deficit after SAH (b) the basics of the CGRP receptor structure, signal transduction, and vasodilatation mechanisms and (c) the studies that have been conducted so far using CGRP in both animals and humans with SAH.