Dietary Cholesterol Protects Against Alcohol‐Induced Cerebral Artery Constriction

Abstract

Background Binge drinking represents the major form of excessive alcohol (EtOH) consumption in the US. Episodic (such as binge) drinking results in blood alcohol levels (BAL) of 18–80 mM, and leads to alcohol-induced cerebral artery constriction (AICAC). AICAC was shown to arise from EtOH-induced inhibition of large-conductance, calcium/voltage-gated potassium (BK) channels in the vascular smooth muscle. Factors that modulate BK channel-mediated AICAC remain largely unknown. Methods Male Sprague-Dawley rats were placed on high-cholesterol (2% of cholesterol) diet for 18–23 weeks. Their littermates were placed on control iso-caloric diet. AICAC was evaluated both in vivo and in vitro, by means of pial arteriole diameter monitoring through a closed cranial window and diameter measurements of isolated, pressurized cerebral arteries. Cholesterol level in the cerebral artery tissue was manipulated by methyl-β-cyclodextrin to reverse dietary-induced accumulation of cholesterol. BK channel surface presence on the plasma membrane of cerebral artery myocytes was evaluated by immunofluorescence staining. BK channel function in pressurized cerebral artery was assessed using selective BK channel blocker paxilline. Results Within 5 minutes of 50 mM EtOH injection into carotid artery in vivo, arteriole diameter decreased by 20% in control group. Pial arteriole constriction was significantly reduced in rats on high-cholesterol diet, resulting in only 10% reduction of diameter. BAL in both groups, however, remained the same. Significant reduction of AICAC in group on high-cholesterol diet compared to control was also observed after middle cerebral artery dissection and in vitro pressurization at 60 mmHg, this reduction remaining after endothelium removal. Cholesterol level in de-endothelialized cerebral arteries was significantly increased in rats on high-cholesterol diet. Removal of excessive cholesterol content restored AICAC to the level, observed in cerebral arteries of rats on normal diet. Immunofluorescence staining of BK channel- forming and accessory, smooth muscle-specific β1 subunit in freshly isolated cerebral artery myocyte showed that high-cholesterol diet did not down-regulate surface presence of BK protein. However, paxilline-induced cerebral artery constriction was diminished in arteries from rats on high-cholesterol diet. Conclusions Our data indicate that dietary cholesterol protects against AICAC. This protection is caused by cholesterol buildup in the arterial tissue and diminished function (but not surface presence) of EtOH target – BK channel.

Endothelial Nitric Oxide Mediates Caffeine Antagonism of Alcohol-Induced Cerebral Artery Constriction

“…First, our current results confirm previous studies by our group and others (Zhang et al, 1993;Liu et al, 2004;Bukiya et al, 2014) reporting that intoxicating levels of ethanol (10-100 mM) constrict rat middle cerebral arteries, an effect that does not depend on an intact endothelium (Figs. 4A).…”

“…To determine the impact of caffeine-ethanol coadministration on Caffeine Protection against Alcohol-Induced Vasoconstriction cerebral artery diameter, we used intravital microscopy in a closed cranial window on anesthetized adult rats. As reported in animal models and humans (Altura and Altura, 1984;Reynolds et al, 2003;Bukiya et al, 2014), infusion of 50 mM ethanol into the carotid artery caused cerebral arteriole constriction (Fig. 1A, top panels), which quickly disappeared upon washout of the artery with ethanol-free PSS (Fig.…”

“…After determining that the caffeine-ethanol functional antagonism on cerebral vessels occurred at the cerebral artery itself, and considering that vascular actions of caffeine that are independent of neuroendocrine mediation may be either endotheliumdependent or directly targeted at the vascular smooth muscle (Echeverri et al, 2010), we next addressed whether caffeine antagonism of ethanol-induced cerebral artery constriction required the presence of a functional endothelium. Thus, some segments from a given artery were de-endothelized by mechanical means, the presence/absence of a functional endothelium being pharmacologically verified (Liu et al, 2004;Bukiya et al, 2009Bukiya et al, , 2014. Both ethanol (50 mM) and caffeine (10 mM) were able to constrict de-endothelialized cerebral arteries when these agents were applied separately.…”

“…Then, drug action in intact versus de-endothelialized arteries was explored to narrow the primary target(s) involved in the caffeine-ethanol interaction. Thus, rat middle cerebral arteries were dissected out and pressurized in vitro at 60 mm Hg to develop and maintain myogenic tone (Liu et al, 2004;Bukiya et al, 2014).…”

“…Cerebrovascular ischemia may result from impaired vasodilatation and/or enhanced constriction of cerebral arteries. Using a rat model that mimics human cerebral artery reactivity, we showed that ethanol (10-100 mM) constricted middle cerebral arteries both in vivo and in vitro (Liu et al, 2004;Bukiya et al, 2009Bukiya et al, , 2014.…”