Alcohol and the Cardiovascular System
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Alcohol and the Cardiovascular System Molecular Mechanisms for Beneficial and Harmful Action SAM ZAKHARI, PH.D. Alcohol can be beneficial or harmful to the cardiovascular system, depending on the amount consumed and the characteristics of the consumer. Of the numerous cellular and molecular mechanisms that are thought to explain the beneficial effects of moderate drinking, this article discusses four, involving (1) high density lipoproteins, (2) cellular signaling, (3) platelet function in blood clot formation, and (4) stimulation of blood clot dissolution. Although light-to-moderate drinking can protect against coronary artery disease, heavy alcohol consumption can damage the cardiovascular system, resulting in maladies such as heart muscle disorders, irregular heart rhythms, high blood pressure, and strokes. This article summarizes representative epidemiological and animal studies on these cardiovascular consequences of chronic heavy alcohol consumption and reviews mechanisms that have been suggested to explain alcohol’s effects. KEY WORDS: chronic AODE (alcohol and other drug effects); molecular interaction; biochemical mechanism; lipoproteins; platelets; blood coagulation; moderate AOD use; heavy AOD use; therapeutic drug effect; AODR (alcohol and other drug related) disorder; alcoholic cardiomyopathy; cardiac arrhythmia; hypertensive disorder; stroke; literature review; cell signaling lcoholic beverages have been sumed. This chronic heavy drinking1 is used—and abused—since the 1The term “heavy drinking” is not used consistently in a significant factor in the development the alcohol literature; therefore, this article generally dawn of history. Although most 2 A of alcohol dependence, or alcoholism, refers to “heavy drinking” and “heavy drinkers” based people who choose to drink can limit their and is associated with serious adverse on the terms used in the reference cited. intake to a level that produces no harm to health consequences, including nega- 2The terms “alcoholism” and “alcoholic” as used in their health or to society, about 34 percent tive effects on the cardiovascular sys- this article are summary terms for the diagnoses of of the population drinks approximately 62 tem, such as heart muscle disorders alcohol abuse and alcohol dependence. percent of all alcoholic beverages con- (i.e., cardiomyopathy), heartbeat rhythm 3In this article, the term “moderate drinking” generally irregularities (i.e., arrhythmias), high refers to the consumption of one or two drinks per SAM ZAKHARI, PH.D., is chief of the blood pressure (i.e., hypertension), and day. Moderate drinking cannot be achieved by simply strokes. averaging the number of drinks consumed, however. Biomedical Research Branch at the For example, consuming seven drinks on a Saturday 3 National Institute on Alcohol Abuse In contrast, moderate drinking has night will not have the same effects as consuming one and Alcoholism, Bethesda, Maryland. been known since ancient times to drink each day of the week. VOL. 21, NO. 1, 1997 21 promote conviviality and decrease arterial plaque formation, but the formed mainly in the liver and enter the tension, anxiety, and self-conscious- underlying mechanisms by which blood circulation to transport choles- ness; the possible physical health alcohol influences the several interde- terol and triglycerides to peripheral benefits of moderate drinking were pendent events leading to atheroscle- tissues throughout the body. In the cap- noted long ago as well.4 In modern rosis (see, for example, Foegh and illaries within fatty tissues and muscles, times, numerous epidemiological Virmani 1993) are not totally clear. In an enzyme known as lipoprotein lipase studies associate moderate alcohol addition, it should be noted that some (LPL) breaks down triglycerides in consumption with protective health of these mechanisms work after re- both chylomicrons and VLDL to sub- benefits (see table), including a lower peated or chronic alcohol consump- stances used in metabolism and energy risk of coronary artery disease (CAD) tion (such as the effect on lipoproteins), storage (i.e., fatty acids and glycerol). (see, for example, Boffetta and but some start to act after a single As LPL breaks down VLDL mole- Garfinkel 1990). In the United States, drink (such as the effect on blood cules, LDL particles are formed. LDL where CAD accounts for about platelets) as described below. This particles contain large concentrations 450,000 deaths every year, some peo- article reviews findings on the follow- of cholesterol and phospholipids. ple advocate moderate drinking to ing factors that have received research Some cholesterol is released to body reduce the risk of death from CAD. attention: tissues, where it plays an important Moderate drinking is not risk free, role in maintaining cell membranes however (see, for example, Criqui • Blood concentrations of high den- and synthesizing steroids such as sex 1996), and careful analysis of the sity and low density lipoproteins hormones, corticosteroids, bile acids, tradeoffs between its benefits and risks • Cellular signaling and vitamin D. LDL cholesterol not should be considered on an individual delivered to tissues (about 60 percent) basis and across the life span (Dufour • Blood clot formation by cells may be recaptured by special LDL 1996; Zakhari and Wassef 1996). known as platelets receptors in the liver. If LDL mole- This article first focuses on ad- • Blood clot dissolution through cules are not recaptured by the liver vances from biochemical research that enzyme action. (e.g., because of a hereditary deficien- have improved our understanding of cy of LDL receptors), blood levels of alcohol’s beneficial effects on the cholesterol rise. Because accumulated cardiovascular system. Building on Alcohol’s Effects on High Density and Low Density Lipoprotein Levels cholesterol forms a major component this foundation, the article next exam- of the characteristic fatty plaques that ines several specific consequences of Major plasma lipids (i.e., the fatlike build up along artery walls in athero- long-term heavy alcohol consumption substances cholesterol and triglycer- genesis, high cholesterol levels often on the cardiovascular system. ides) circulate as macromolecular are associated with CAD. complexes of fat molecules and pro- Clinical studies have shown, how- BIOCHEMICAL STUDIES teins (i.e., lipoproteins). Of the several ever, that every 1-percent reduction in different types of lipoproteins present plasma cholesterol levels decreases the Biochemical studies designed to ad- in the body, two are known to have risk for CAD by 2 percent. HDL plays a dress the mechanisms of alcohol’s particular relevance to the formation key role in reducing cholesterol levels. effects on CAD risk have focused on of arterial plaque deposits: high densi- Free cholesterol released from cells factors that promote or protect against ty and low density lipoproteins. In the initially is incorporated into HDL by an the abnormal narrowing of coronary simplest terms, high levels of high enzyme called lecithin-cholesterol acyl arteries and the formation of fatty density lipoproteins (HDL) and low transferase (LCAT), which changes the plaque deposits (i.e., atherogenesis),5 levels of low density lipoproteins cholesterol to cholesteryl esters. To which leads to degenerative changes (LDL) are desirable. Current recom- remove cholesterol from the circulation, in the arterial walls and eventually to mendations advocate plasma HDL the cholesteryl esters then are trans- “hardening of the arteries” (i.e., ath- levels of at least 35 milligrams per ported to LDL by cholesteryl ester erosclerosis). Research using a geneti- deciliter (mg/dL) and LDL levels of transfer protein (CETP) for recapture cally defined inbred strain of mice less than 160 mg/dL in adults. Ideally, by the LDL receptors in the liver. In confirmed that alcohol can reduce the LDL:HDL ratio should be be- addition, a newly discovered species of tween 2.5:1 and 4.5:1. HDL called pre-high density lipopro- 4For example, Psalm 104:14–15 mentions “wine that Chylomicrons and very low density tein binds with free cholesterol in a gladdens the heart of man” as one of the fruits brought lipoproteins (VLDL) are two other ma- process known as reverse cholesterol forth from the earth as a result of God’s handiwork, and in I Timothy 5:23, Paul advises Timothy: “Stop jor classes of lipoproteins in the body. transport, in which excess cholesterol is drinking only water, and use a little wine because of Chylomicrons, the largest lipoprotein removed from body tissues, transported your stomach and your frequent illnesses.” particles, carry triglycerides consumed to the liver, and excreted in bile. 5 For a definition of this and other technical terms, see in food from the intestine to the blood, Biochemical studies examining the glossary, pp. 93–96 whereas the smaller VLDL particles are alcohol’s effects on HDL are rooted in 22 ALCOHOL HEALTH & RESEARCH WORLD Alcohol and the Cardiovascular System epidemiological studies that show an inverse relationship between plasma Effects of Moderate and Heavy Drinking . HDL cholesterol levels and CAD. Beneficial Effects of Moderate Drinking Harmful Effects of Heavy Drinking Further epidemiological studies show an association between alcohol con- Reduction of plaque deposits in arteries Increased risk for heart muscle disease sumption and increased plasma HDL (i.e., atherosclerosis) (i.e., alcoholic cardiomyopathy) 6 levels. A study by Linn and col- Protection