Abstract
Vascular pathophysiological changes after haemorrhagic stroke, such as phenotypic modulation of the cerebral arteries and cerebral vasospasms, are associated with delayed cerebral ischemia (DCI) and poor outcome. The only currently approved drug treatment shown to reduce the risk of DCI and improve neurologic outcome after aneurysmal subarachnoid haemorrhage (SAH) is nimodipine, a dihydropyridine L-type voltage-gated Ca2+ channel blocker. MEK1/2 mediated transcriptional upregulation of contractile receptors, including endothelin-1 (ET-1) receptors, has previously been shown to be a factor in the pathology of SAH. The aim of the study was to compare intrathecal and subcutaneous treatment regimens of nimodipine and intrathecal treatment regimens of U0126, a MEK1/2 inhibitor, in a single injection experimental rat SAH model with post 48 h endpoints consisting of wire myography of cerebral arteries, flow cytometry of cerebral arterial tissue and behavioural evaluation. Following ET-1 concentration-response curves, U0126 exposed arteries had a significantly lower ET-1max than vehicle arteries. Arteries from both the intrathecal- and subcutaneous nimodipine treated animals had significantly higher ET-1max contractions than the U0126 arteries. Furthermore, Ca2+ concentration response curves (precontracted with ET-1 and in the presence of nimodipine) showed that nimodipine treatment could result in larger nimodipine insensitive contractions compared to U0126. Flow cytometry showed decreased protein expression of the ETB receptor in U0126 treated cerebral vascular smooth muscle cells compared to vehicle. Only U0126 treatment lowered ET-1max contractions and ETB receptor levels, as well as decreased the contractions involving nimodipine-insensitive Ca2+ channels, when compared to both intrathecal and subcutaneous nimodipine treatment. This indicate that targeting gene expression might be a better strategy than blocking specific receptors or ion channels in future treatments of SAH.
Highlights
Aneurysmal subarachnoid haemorrhage (SAH), is a type of haemorrhagic stroke responsible for around 5% of stroke incidents, but with an approx. 50% short term mortality rate and with remaining survivors having reduced quality of life due to cognitive impairments [1, 2]
An important mechanism associated with this delayed brain injury is delayed cerebral ischemia (DCI), which consists of various pathophysiological changes; including inflammation [4], oedema [5], blood-brain barrier disruption and vascular phenotypic changes associated with remodelling and narrowing of the cerebral arteries, often referred to as delayed cerebral vasospasm (CVS) [3, 6]
In this study we conclude that the most desirable treatment regimen for vascular phenotypic modulation and outcome following experimental SAH, is three administrations (6 h, 12 h and 24 h) of high (10 μM, 0.064 mg/kg) dose U0126
Summary
Aneurysmal subarachnoid haemorrhage (SAH), is a type of haemorrhagic stroke responsible for around 5% of stroke incidents, but with an approx. 50% short term mortality rate and with remaining survivors having reduced quality of life due to cognitive impairments [1, 2]. SAH has a multiphase course; consisting of an early phase with a rapid leakage of blood into the subarachnoid space causing a rise in intracranial pressure (ICP) and a drop in cerebral blood flow (CBF), depriving the brain of oxygen and glucose, causing cerebral ischemia and brain damage, sometimes referred to as early brain injury [3]. An important mechanism associated with this delayed brain injury is delayed cerebral ischemia (DCI), which consists of various pathophysiological changes; including inflammation [4], oedema [5], blood-brain barrier disruption and vascular phenotypic changes associated with remodelling and narrowing of the cerebral arteries, often referred to as delayed cerebral vasospasm (CVS) [3, 6]. Several experimental treatments with e.g. endothelin receptor antagonists have been used to relieve CVS and delayed cerebral ischemia, but with poor results on functional outcomes, including the specific endothelin receptor A (ETA) and B (ETB) antagonist clazosentan [11,12,13]
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