Dose-response relationships of the protective and antiprotective effects of acute ethanol exposure in isolated rabbit hearts

Moderate ethanol ingestion and cardiovascular protection: from epidemiologic associations to cellular mechanisms

While ethanol intake at high levels (3-4 or more drinks), either in acute (occasional binge drinking) or chronic (daily) settings, increases the risk for myocardial infarction and stroke, an inverse relationship between regular consumption of alcoholic beverages at light to moderate levels (1-2 drinks per day) and cardiovascular risk has been consistently noted in a large number of epidemiologic studies. Although initially attributed to polyphenolic antioxidants in red wine, subsequent work has established that the ethanol component contributes to the beneficial effects associated with moderate intake of alcoholic beverages regardless of type (red versus white wine, beer, spirits). Concerns have been raised with regard to interpretation of epidemiologic evidence for this association including heterogeneity of the reference groups examined in many studies, different lifestyles of moderate drinkers versus abstainers, and favorable risk profiles in moderate drinkers. However, better controlled epidemiologic studies and especially work conducted in animal models and cell culture systems have substantiated this association and clearly established a cause and effect relationship between alcohol consumption and reductions in tissue injury induced by ischemia/reperfusion (I/R), respectively. The aims of this review are to summarize the epidemiologic evidence supporting the effectiveness of ethanol ingestion in reducing the likelihood of adverse cardiovascular events such as myocardial infarction and ischemic stroke, even in patients with co-existing risk factors, to discuss the ideal quantities, drinking patterns, and types of alcoholic beverages that confer protective effects in the cardiovascular system, and to review the findings of recent experimental studies directed at uncovering the mechanisms that underlie the cardiovascular protective effects of antecedent ethanol ingestion. Mechanistic interrogation of the signaling pathways invoked by antecedent ethanol ingestion may point the way towards development of new therapeutic approaches that mimic the powerful protective effects of socially relevant alcohol intake to limit I/R injury, but minimize the negative psychosocial impact and pathologic outcomes that also accompany consumption of ethanol.

Time-dependent and ethanol-induced cardiac protection from ischemia mediated by mitochondrial translocation of varepsilonPKC and activation of aldehyde dehydrogenase 2

The cardioprotective effects of moderate alcohol consumption have been well documented in animal models and in humans. Protection afforded against ischemia and reperfusion injury (I/R) proceeds through an ischemic preconditioning-like mechanism involving the activation of epsilon protein kinase C (varepsilonPKC) and is dependent on the time and duration of ethanol treatment. However, the substrates of varepsilonPKC and the molecular mechanisms by which the enzyme protects the heart from oxidative damage induced by I/R are not fully described. Using an open-chest model of acute myocardial infarction in vivo, we find that intraperitoneal injection of ethanol (0.5 g/kg) 60 min prior to (but not 15 min prior to) a 30-minute transient ligation of the left anterior descending coronary artery reduced I/R-mediated injury by 57% (measured as a decrease of creatine phosphokinase release into the blood). Only under cardioprotective conditions, ethanol treatment resulted in the translocation of varepsilonPKC to cardiac mitochondria, where the enzyme bound aldehyde dehydrogenase-2 (ALDH2). ALDH2 is an intra-mitochondrial enzyme involved in the detoxification of toxic aldehydes such as 4-hydroxy-2-nonenal (4-HNE) and 4-HNE mediates oxidative damage, at least in part, by covalently modifying and inactivating proteins (by forming 4-HNE adducts). In hearts subjected to I/R after ethanol treatment, the levels of 4-HNE protein adducts were lower and JNK1/2 and ERK1/2 activities were diminished relative to the hearts from rats subjected to I/R in the absence of ethanol. Together, this work provides an insight into the mitochondrial-dependent basis of ethanol-induced and varepsilonPKC-mediated protection from cardiac ischemia, in vivo.

Protective and anti-protective effects of acute ethanol exposure in myocardial ischemia/reperfusion

Epidemiological data suggest that a cardioprotective effect of acute alcohol exposure exists in humans. Recent studies in animal models indicate that transient alcohol exposure can indeed reduce myocardial infarct size and exert a preconditioning-like protective effect akin to ischemic preconditioning (IPC). Moreover, the mechanism of alcohol-induced cardioprotection in part resembles the signaling cascade triggered by ischemic preconditioning, with adenosine receptors, PKC, protein tyrosine kinases, and mitochondrial K(ATP) channels all being implicated as key components. However, it was also seen, at least in the rabbit, that if alcohol were present during the ischemic insult, it could block its own protection. The primary protective effect of alcohol use is probably in the chronic setting where alcohol exposure causes a second window type of protection that persists for many days thereafter. Regular moderate drinking should keep the heart in a second window state indefinitely.

The protective and anti-protective effects of ethanol in a myocardial infarct model

Recent data indicate that acute alcohol exposure can have a preconditioning-like protective effect on the heart. We investigated the effect of ethanol exposure shortly before regional ischemia in an infarct model. Both in the open-chest rabbit and in the isolated rabbit heart, exposure of the heart to ethanol significantly reduced infarct size, but only if the alcohol were washed out or sufficiently metabolized before the onset of ischemia. If ethanol were still present during ischemia, it could not only prevent its own protective effect, but also abolish protection induced by ischemic preconditioning or the mitochondrial K(ATP) channel activator diazoxide. In the in vitro model, we tested for possible mediators of ethanol-induced protection and made comparisons to the signaling cascade of ischemic preconditioning. Neither adenosine receptor blockade with 8-(p-sulfophenyl) theophylline, scavenging of free radicals with N-2-mercaptopropionyl glycine, nor closure of K(ATP) channels with glibenclamide affected ethanol's protective effect. However, either a PKC inhibitor or a protein tyrosine kinase inhibitor could completely block ethanol-induced infarct size reduction. Both the protective and anti-protective effects of ethanol had a threshold of about 5 mM. Thus, ethanol-induced protection is mediated by protein kinase C and at least one protein tyrosine kinase, but, in contrast to ischemic preconditioning, is not triggered by either adenosine receptors, free radicals, or K(ATP) channels. Ethanol can only exert its protective effect if it is removed before the onset of ischemia. If still present during ischemia, ethanol has the opposite effect, and inhibits preconditioning by an as yet unidentified mechanism.