A biochemical basis for alcoholism and alcohol-induced damage including the fetal alcohol syndrome and cirrhosis: interference with essential fatty acid and prostaglandin metabolism

Biochemical interactions of ethanol with the arachidonic acid cascade

A rapidly increasing scientific literature now supports the possibility of an alcohol-prostaglandin interaction. This chapter reviews evidence for both direct and indirect biochemical interactions between ethanol and the metabolism of arachidonic acid and several related compounds. Much of the present data is based on pharmacological manipulation of prostaglandin (PG) levels by potent nonsteroid anti-inflammatory agents such as indomethacin. Indomethacin markedly alters the behavioral response to ethanol, particularly in the mouse model. These data suggest that PGs are involved in the behavioral response to acute ethanol exposure in the mouse. In other animal models, alcohol has been reported to alter blood platelet metabolism of arachidonic acid, to suppress the enzymatic degradation of PGs, and to alter the response of the adenyl cyclase system to several hormones including PGs of the "E" series. In humans, both the stimulation and inhibition of PG synthesis is reported to aid the treatment of various aspects of alcoholism. Further, PGs are reported to protect against alcohol-induced fatty liver, and both PGs and arachidonic acid protect the gastric mucosa against ethanol-induced lesions. Certainly the residual consequences of acute, excessive ethanol consumption are commonly treated with a prostaglandin synthesis inhibitor. The material in this chapter is an attempt to review the data and to discuss the molecular mechanism underlying these observations.

Synthesis of prostaglandins and leukotrienes. Effects of ethanol

Prostaglandins, thromboxane, and leukotrienes are metabolites of arachidonic acid that have a variety of physiological effects at low concentrations. Effects include smooth muscle contraction, platelet aggregation, platelet disaggregation, bronchoconstriction, increased capillary permeability, cardiac dysfunction, and polymorphonuclear leukocyte accumulation. Although their formation does not appear to be essential for life, these eicosanoid activities are wide ranging and have important roles in normal physiology as well as pathophysiology. At the center of eicosanoid biosynthesis lies the plasma cell membrane which serves as the arachidonic acid reservoir. It has been widely appreciated that ethanol exerts effects on the lipid bilayer, and it is not surprising that a growing body of evidence supports the concept that important interactions between ethanol and eicosanoid biosynthesis can occur. Furthermore, at various steps leading to ultimate prostaglandin, thromboxane and leukotriene production, reactive intermediates such as radicals are involved whose lifetime in the biological milieu can be profoundly modulated by ethanol.

Breakdown of P.G.E. 1 synthesis is responsible for the acquired immunodeficiency syndrome

This hypothesis suggests that repeated viral infections disrupt the biosynthesis of P.G.E. 1 and nullify a major system by which t lymphocytes are regulated. It is hypothesized that a breakdown of P.G.E. 1 synthesis is responsible for the acquired immunodeficiency syndrome and the frequently associated Kaposi's sarcoma. A means of restoring P.G.E. 1 synthesis and reversing the immunodeficiency is proposed.

Maternal glucose injections do not alter the suppression of fetal breathing following maternal ethanol ingestion

In order to determine whether intravenous injections of glucose could reverse the effects of maternal ingestion of ethanol (0.25 gm/kg), glucose (25 gm intravenously) or an equal volume of saline solution was administered to eight pregnant women at 37 to 40 weeks' gestation after ingestion of ethanol. Fetal breathing movements were abolished within 30 minutes after ingestion of ethanol and were not increased by maternal intravenous injections of glucose. Maternal heart rate was increased by ethanol. The disposition of ethanol in maternal blood was not altered by injection of glucose, and fetal gross body movements were not influenced by maternal ingestion of ethanol or by injections of glucose after ethanol.

Ethanol consumption and serum lipid profiles in Sinclair(S-1) miniature swine

Ethanol consumption was correlated with changes in acyl group profiles of phosphatidylcholine and triacylglycerols in serum of Sinclair(S-1) miniature boars. Serum triacylglycerols in the control pigs were high in linoleate (18:2) (48%) and low in stearate (18:0 (3%). Upon feeding with 10% (w/v) ethanol ad lib for two weeks, the proportion of 18:2 in serum triacylglycerols decreased to 12-15% with a concomitant increase in 16:0, 18:0 and 18:1. Similar, but less extensive, acyl group changes were observed in the serum phosphatidylcholine. In addition, there was a decrease in the proportion of 20:3(n-6), but a biphasic change was shown in 20:4(n-6) with respect to ethanol consumption. In general, the high ethanol consumers (7.0 g/kg/day) indicated a more rapid rate of acyl group change than the low consumers (3.8 g/kg/day). Upon withdrawal of ethanol, acyl groups of triacylglycerols rapidly returned towards the control values, whereas only small changes were observed for the recovery in phospholipids. In this situation, the low-consumer group indicated a more rapid recovery than the high-consumer group. Results indicate that with the swine model, serum lipid changes can be a useful parameter for correlating biological changes upon ethanol consumption.

Prostaglandins in alcohol intolerance and hangover

The effects of alcohol on the formation of prostaglandins (PGs) and the blockade of some actions of alcohol by PG-inhibitors suggest that PGs may be involved in the action of ethyl alcohol. Regulation of lipid peroxidation and synthesis and release of precursor fatty acids may affect the overall formation of PGs. The effect of alcohol may be qualitative for several reasons: (i) the possible preferred formation of 1-series of PGs would mean an important qualitative change in PG-impact in some tissues; (ii) inhibition of PG-metabolism in the lung might affect mostly the plasma levels of PGE; (iii) a selective blockade of certain PG-effects and a potentiation of some others gives rise to qualitative changes in the actions of PGs. PGs may be involved in several acute or short-term reactions caused by alcohol. Chlorpropamide-alcohol flush, alcohol intolerance and hangover are effectively alleviated by a prophylactic use of PG-inhibitors. Speculatively PGs might also be involved in migraine attacks provoked by alcohol and in antabuse in reaction. The roles of PGs in the regulation of vascular tone, water and electrolyte balance as well as in certain secretory and metabolic processes may be important in the generation of alcohol related reactions.

Ethanol ingestion and polyunsaturated fatty acids: effects on the acyl-CoA desaturases

The ingestion of ethanol results in altered compositions of the polyenoic fatty acids in a variety of liver and brain membranes. A possible cause for these alterations in hepatic endoplasmic reticulum membranes has been studied by measuring the delta 9, delta 6, and delta 5 acyl-CoA desaturase activities in hepatic microsomes from chronically or acutely treated rats. Chronically, ethanol decreased all three enzyme activities with the following order of sensitivity: delta 6 (65%), delta 9 (54%), and delta 5 (46%). The short-term study indicated that all three desaturase activities were affected after 1 day of ethanol feeding. NADPH- and NADH-cytochrome c reductase activities were found to be reduced in chronically treated rats, and the NADH-cytochrome c reductase was decreased in the acutely treated. However, these reduced enzyme activities could not account for the decrease in desaturase activities due to the very marked differences between the specific activities of these enzymes compared to the desaturase. Thus, we conclude that changes in membrane polyenoic fatty acid composition can be result of ethanol-induced decreases in the terminal desaturase enzymes.

Hangover headache and prostaglandins: prophylactic treatment with tolfenamic acid

Tolfenamic acid (TA), a potent inhibitor of prostaglandin (PG) biosynthesis and action, was tested prophylactically against hangover symptoms in 30 healthy volunteers in a double-blind cross-over study. One capsule of TA (200 mg) or placebo was taken before starting to drink alcohol and another before going to bed. The hangover symptoms were evaluated in the morning. TA was found significantly better than placebo in the subjective evaluation of drug efficacy (p less than 0.001) and in reducing the reported hangover symptoms in general (p less than 0.01). In the TA group, significantly lower symptom scores were obtained for headache (p less than 0.01), and for nausea, vomiting, irritation, tremor, thirst and dryness of mouth (all p less than 0.05). In a separate study with eight participants, plasma levels of PGs were followed during ingestion of alcohol with or without TA. The plasma concentrations of PGE2 and TXB2 (a metabolite of thromboxane A2) were lower in the TA group during alcohol ingestion, while PGF2 alpha and 6-keto-PGF1 alpha (a metabolite of prostacyclin) were unaffected. TXB2 correlated with blood alcohol levels in a U-shaped manner.

Effect of maternal ethanol ingestion on fetal breathing movements, gross body movements, and heart rate at 37 to 40 weeks' gestational age

The effect of maternal ingestion of ethanol (0.25 gm/kg) on fetal breathing movements, gross fetal body movements, and fetal heart rate was studied in 11 healthy pregnant women at 37 to 40 weeks' gestation. Fetal breathing movements were almost abolished within 30 minutes of the alcoholic drink and remained significantly decreased for 3 hours. The incidence of gross fetal body movements before or after ethanol was not different from that on the control day, and the fetal heart rate was not changed after maternal ingestion of ethanol.

Ethanol, essential fatty acids and prostaglandins

In the body the essential fatty acid (EFA) linoleic acid (18:2, omega-6) is desaturated and chain elongated to form homo-gamma-linoleic acid (20:3, omega-6) and arachidonic acid (20:4, omega-6). Apart from their structural function in cell membranes, the EFAs serve as precursors to the prostaglandins and related substances. The prostaglandins can, in general terms, be described as a defensive regulatory system of importance for cardiovascular, gastrointestinal and urogenital function. Acute intake of ethanol gives facial flushing, inhibition of platelet aggregation and elevation of tissue c-AMP. These effects are consistent with release of vasodilatory and antiaggregating PGs. In epidemiological studies, moderate ethanol intake offers some protection against coronary heart disease. Chronic intake high doses of ethanol is associated with damage to, e.g., liver, heart, brain, immunoregulation and various hormonal systems. Decreased tissue levels of 18:2, 20:4 and PGs have been observed both in animals and man. The conversion of 18:2 to 20:4 is inhibited by chronic ethanol exposure. It is suggested that ethanol depletes the PG precursor pool by a dual mechanism of releasing precursor acids and by inhibiting their synthesis. This would lead to a functional EFA-deficiency, manifested by a hypoactive PG system.

Effects of ethanol on thermoregulation

Clinical reports of accidental hypothermia in alcohol intoxicated individuals exposed to low ambient temperature ( Paton , 1983) have generally been borne out by experimental studies in healthy volunteers. Small doses of ethanol, given to human subjects at normal ambient temperature (Ta), have very little effect on body temperature but a combination of large dose, low Ta and vasodilatation provoked by strenuous exercise, causes a sharp fall in rectal temperature. In experimental animals, the use of relatively larger doses of alcohol and more extreme temperatures, both above and below the thermoneutral zone, has shown that the effect of ethanol is essentially poikilothermic, i.e. an impairment of adaptation to both heat and cold. This effect has been studied in greater detail, in relation to each of the basic thermoregulatory processes. Though small doses of alcohol may increase the metabolic rate under some circumstances, the most common effect at low Ta is inhibition of shivering and therefore reduction of thermogenesis. At the same time it tends to cause increased heat loss by cutaneous vasodilatation. This makes for a greater feeling of comfort in the cold exposed subjects but increases in rate of fall of core temperature. The combination of decreased thermogenesis and increased heat loss, despite falling body temperature, is suggestive of a lowering of the set-point of the thermoregulatory control mechanisms. Consistent with this is a slight increase in ventilatory heat loss after low doses of ethanol but larger doses cause respiratory depression, so that heat loss through the lungs is minor. However, at high Ta ethanol caused hyperthermia in experimental animals and shows enhanced lethality, so that impairment of thermoregulatory effector mechanisms seems to be at least as important as change in set-point. Studies of the effects of ethanol on electrophysiological activity of single neurons in the pre-optic area and anterior hypothalamus (POAH), biochemical activities of neuronal membranes, hypothalamic blood flow, conventional neurotransmitters, amino acid putative neurotransmitters, neuropeptides, prostaglandins and inorganic ions have all failed so far to yield a clear comprehensive picture of the mechanisms by which ethanol affects thermoregulation. In each case, contradictory evidence has been obtained concerning the consequences of ethanol administration, whether by oral, intraperitoneal, intravenous, intracerebroventricular, or direct local (POAH) route.(ABSTRACT TRUNCATED AT 400 WORDS)

Malondialdehyde production by erythrocytes from alcoholic and non-alcoholic subjects

A survey of the capacity of erythrocyte suspensions to handle a standard hydrogen peroxide oxidative load was made in a population of white male hospitalized alcoholics and non-hospitalized, non-alcoholic subjects. As measured by malondialdehyde (MDA) production, the capacity to handle this oxidation load was decreased in a significant percentage of individuals with a positive family history of alcoholism and who have experienced problems with alcohol sufficient to produce cytopathological changes and to require hospitalization.

Loss of delta-6-desaturase activity as a key factor in aging

Aging is characterized by a wide variety of defects, particularly in the cardiovascular and immune systems. Cyclic AMP levels fall, especially in lymphocytes. Delta-6-desaturase (D6D) levels have been found to fall rapidly in the testes and more slowly in the liver in aging rats. D6D is an enzyme which converts cis-linoleic acid to gamma-linolenic acid (GLA). Other factors which inhibit D6D activity are diabetes, alcohol and radiation, all of which may be associated with accelerated aging. In meat eaters or omnivores which can acquire arachidonic acid from food, the main consequences of D6D loss will be deficiencies of GLA, dihomogamma-linolenic acid (DGLA) and prostaglandin (PG) E1. PGE1 activates T lymphocytes, inhibits smooth muscle proliferation and thrombosis, is important in gonadal function and raises cyclic AMP levels in many tissues. It is a good candidate for a key factor lost in aging. Moderate food restriction, the only manoeuvre which consistently slows aging in homoiotherms, raises D6D activity by 300%. Other factors important in regulating D6D and the conversion of GLA to PGE1 are zinc, pyridoxine, ascorbic acid, the pineal hormone, melatonin, and possibly vitamin B3. GLA administration to humans has been found to lower blood pressure and cholesterol, and to cause clinical improvement in patients with Sjogren's syndrome, scleroderma and alcoholism. These diseases are associated with some features of accelerated aging. The proposition that D6D loss is not only a marker of aging but a cause of some of its major manifestations is amenable to experimental test even in humans. The blocked enzyme can be by-passed by giving GLA directly.