Interference of ethanol in hepatic cellular metabolism

Effect of ethanol on lipid metabolism

Hepatic lipid metabolism is a series of complex processes that control influx and efflux of not only hepatic lipid pools, but also organismal pools. Lipid homeostasis is usually tightly controlled by expression, substrate supply, oxidation and secretion that keep hepatic lipid pools relatively constant. However, perturbations of any of these processes can lead to lipid accumulation in the liver. Although it is thought that these responses are hepatic arms of the 'thrifty genome', they are maladaptive in the context of chronic fatty liver diseases. Ethanol is likely unique among toxins, in that it perturbs almost all aspects of hepatic lipid metabolism. This complex response is due in part to the large metabolic demand placed on the organ by alcohol metabolism, but also appears to involve more nuanced changes in expression and substrate supply. The net effect is that steatosis is a rapid response to alcohol abuse. Although transient steatosis is largely an inert pathology, the chronicity of alcohol-related liver disease seems to require steatosis. Better and more specific understanding of the mechanisms by which alcohol causes steatosis may therefore translate into targeted therapies to treat alcohol-related liver disease and/or prevent its progression.

Oral epithelial response to experimental chronic alcohol ingestion in hamsters

The purpose of this study was to assess the effect of alcohol on oral epithelium by quantifying epithelial compartment thicknesses after chronic alcohol ingestion with the use of a computerized planimetry system. A 10% solution of absolute alcohol in water was given as the sole source of drinking fluid to young adult Syrian hamsters over a period of 9 months. Quantitative histologic analysis showed significant atrophy of the posterior lateral tongue epithelium. The epithelium of the dorsal tongue showed an increase in the thickness percentage of keratin. No significant change was found in the ventral aspect of the tongue epithelium. It was concluded that such alcohol-related atrophy may render the lateral margins of the posterior tongue more susceptible to carcinogenesis.

The effects of prenatal tertiary butanol administration in CBA/J and C57BL/6J mice

Pregnant mice of the CBA/J and C57BL/6J strains were given either tertiary butanol (10.5 mmoles/kg, p.o.) or an equivalent volume of tap water twice daily from day 6 through day 18 of gestation. Examination on day 18 revealed significantly more resorptions per litter in the t-butanol-treated animals but no interstrain difference. Tertiary butanol did not significantly affect the body weight of the survivors nor produce significant abnormalities in either strain. Subsequent blood concentration profiles in female C57BL/6J mice indicated that the treatment regimen produced blood levels equivalent to teratogenic ethanol treatment. Mice receiving 3 days of t-butanol treatment did not eliminate the drug more rapidly than control animals, indicating that tolerance was not a factor in the treatment regimen. Since t-butanol shares membrane disordering effects with ethanol but is not metabolized by the same pathway, a role for acetaldehyde or the process of ethanol metabolism is suggested in ethanol teratogenicity.

Effects of acetaldehyde on human red cell metabolism: evidence for the formation of enzyme inhibitors

Since red cells transport and metabolize acetaldehyde in vivo, the effects of acetaldehyde on human red cell enzyme activities were studied. Incubation of intact red cells or undiluted red cell lysates at 37 degrees C for 4 h with 1-10 mmol/l acetaldehyde decreased only GOT, GPT and aldolase activities among the 26 enzymes tested. No inhibition occurred at 4 degrees C or when acetaldehyde was incubated with dilute hemolysates. Incubation of lysates with other reducing substrates or with acetate inhibited aldolase but not GOT or GPT. Preincubation of lysates with cyanate or fluoride markedly decreased acetaldehyde-mediated transaminase inhibition but not aldolase inhibition. Addition of pyridoxal phosphate, the vitamin B6 transaminase coenzyme, to GOT and GPT assay mixes did not reverse acetaldehyde-mediated transaminase inhibition. These findings suggest that acetaldehyde-mediated aldolase inhibition results from oxidation of acetaldehyde while transaminase inhibition results from nonoxidative acetaldehyde metabolism. When 100-200 mumol/l acetaldehyde is added to lysates at 2-h intervals and when lysates are incubated with ethanol, alcohol dehydrogenase and an NAD-regenerating system, enzyme inhibition occurs at acetaldehyde levels approaching those seen in vivo. Thus, the role of acetaldehyde-mediated enzyme inhibition in the toxicity of alcohol abuse warrants further study.

Pharmacokinetics of ethanol in pigtailed macaques: intersubject variability and effect of subchronic administration

The pharmacokinetics of IV ethanol (0.6 g/kg) were examined in 11 male colony-bred pigtailed macaques (Macaca nemestrina) aged 3 to 13 years. The animals were either chaired during blood sampling (4 hr) or connected to a tether system that allowed injections and blood sampling while the animal moved freely about its cage. In all instances, ethanol pharmacokinetics could be described by a single Michaelis-Menten function; inclusion of a parallel first-order rate constant to account for non-alcohol dehydrogenase elimination of ethanol did not improve the fit. Volume of distribution was 0.802 +/- 0.054 L/kg (mean +/- SD), Km (the apparent in vivo Michaelis constant) was 0.063 +/- 0.022 micrograms/ml, and Vmax was 0.199 +/- 0.039 g/kg/hr. The pharmacokinetic parameter values of chaired and tethered monkeys did not differ. Three of the tethered monkeys received 3 g/kg of ethanol daily for two weeks by IV infusion (subchronic administration). Ethanol pharmacokinetics, determined on five occasions before and five occasions after subchronic ethanol administration, showed that the treatment did not alter the volume of distribution or Km in any of the three monkeys. The value of Vmax increased approximately 23% in one of the three monkeys that received subchronic ethanol; this increase may have been due to a single, inadvertent administration of a 4.5-g/kg dose over a 20-min period. Vmax did not change in the other two monkeys.

The effect of chronic ethanol administration on lipogenesis in liver and adipose tissue in the rat

Rates of lipogenesis de novo have been studied in liver and epididymal fat pads of male rats chronically treated with ethanol. A solution of ethanol (150 ml/l) was administered as the only drinking fluid for 3 months with a standard solid diet; both food and drink were available ad lib. Lipogenesis in vivo was measured by the incorporation of tritiated water into lipid fractions: non-saponifiable lipid and fatty acids. Non-saponifiable lipid, both in liver and in adipose tissue, was unaffected by ethanol treatment. However, fatty acid synthesis de novo was significantly enhanced in both liver and adipose tissue, by 150 and 300% respectively. Plasma triacylglycerol and non-esterified fatty acid levels were unchanged and plasma glucose concentration slightly increased by ethanol administration. The rate of lipogenesis increased when insulin: glucagon increased twofold due to the effect of ethanol.

Alcohol-mediated effects on the level of cytochrome P-450 and heme biosynthesis in cultured rat hepatocytes

Interaction of alcohol and drugs in the liver appears to involve common microsomal oxidative enzymes which utilize cytochrome P-450. Since alcohol augments the toxicity of a variety of drugs, the regulation of the P-450 hemoprotein, a primary component in hepatic drug metabolizing systems, may play a vital role in this phenomenon. We utilize an adult rat liver culture system as a model to explore the action of levels of alcohol below that which is necessary to produce intoxication in humans. The addition of 16 mM ethanol (70 mg/dl) to these hepatocytes results in a 49.5% decrease in cytochrome P-450 activity after 24 h, and a 3-fold increase in the activity of delta-aminolevulinate synthase, the rate-limiting enzyme in hepatic heme biosynthesis. Furthermore, ethanol treatment also causes a transient decrease in the level of intracellular heme. However, the diminished level of total heme does not appear to act as a repressor for delta-aminolevulinate synthase, since it occurs after the initial stimulation of the enzyme by ethanol.

Failure of ethanol to induce dominant lethal mutations in Wistar male rats

2 groups of Wistar male rats (6-7 weeks old) were given ethanol, 15% in drinking water, for 5 days. The level of ethanol was gradually raised to 20 and 30% resp. Both groups received ethanol between 15 and 20% or 15 and 30% continuously during 35 days. Another group was given 30% ethanol for a period of 4 days before mating started. In addition to a control group, which received no treatment, a positive control group of rats exposed to 200 R X-rays, was used. After the treatments, individual males were paired with virgin Wistar females (10-12 weeks) at weekly intervals, and 8 sequential pairings were undertaken. Females were examined for uterine contents and corpora lutea, 10-11 days after their separation from the males. The females mated with irradiated males showed a high incidence of dead implantations and reduction of live implantations. No significant differences in the number of dead, live and total implantations at pre- and/or post-implantation levels were observed among the control and the ethanolic groups, showing that ethanol did not induce any dominant lethal mutations in these Wistar male rats. In the light of studies on alcoholics and other recent data, a need to investigate, independently, the potential mutagenic effects of ethanol and alcoholic beverages is discussed.

The fetal alcohol syndrome in mice: maternal variables

CBA, C3H, and C57 female mice maintained on a diet of 20 percent ethanol-derived calories prior to and throughout gestation were mated in a diallele cross. Prenatal death, malformations, and fetal weights were directly related to maternal blood alcohol levels, indicating a maternal effect. Fetal abnormalities and maternal blood alcohol levels varied with maternal strain (CBA > C3H > C57) and were inversely related to maternal alcohol dehydrogenase activity. Microsomal ethanol oxidizing systems induction was directly associated with increased fetal abnormalities, being greatest in CBA females. These results indicate that liability for the pattern of malformation observed in this syndrome is dependent on maternal blood alcohol levels, which are determined by the rate of maternal alcohol metabolism as well as the amount of maternal alcohol consumption.

Paired helical filaments in rat spinal ganglia following chronic alcohol administration: an electron microscopic investigation

Young Wistar rats were given a 15% (v/v) ethanol solution ad libitum for at least 6 months, spinal ganglia (C6-7 and L1-2) in some of the experimental animals showed paired helical filaments. These curvilinear profiles consisted of 10 nm filaments with the twist every 35nm. There was also an increase in granular material and in nematosomes. Whether these features may be caused by an impaired cerebral protein biosynthesis is discussed.

Acute effect of ethanol on membranes of the endoplasmic reticulum and on protein synthesis in rat liver

The acute effect of ethanol on the membranes of hepatic endoplasmic reticulum, on the in vitro protein-synthetic activities of hepatic free and membrane-bound polyribosomes and on the plasma proteins of rats fasted overnight was investigated. Ethanol (0.75 g/100 g body weight) was tube-fed as a 50% (v/v) solution in saline 3 hr before sacrifice. Hepatic endoplasmic reticulum membranes from control and ethanol-treated rats were compared using the following techniques: (1) lactoperoxidase-catalyzed radioiodination of proteins and sodium dodecylsulfate-polyacrylamide gel electrophoresis, and (2) measurement of 14C-choline incorporation into membranes. Hepatic microsomal membranes from ethanol-treated rats incorporated in vitro les 125I into total proteins (as well as into the 55,000 molecular weight proteins) and incorporated in vivo less 14C-choline into microsomal membranes than membranes of control rats. Ethanol administration inhibited in vivo incorporation of 14C-leucine or 14C-phenylalanine into liver protein and plasma albumin and globulin. The data also indicate that an acute dose of ethanol reduced the in vitro protein-synthetic activity of hepatic membrane-bound polyribosomes, while free polyribosomes were relatively unaffected.

Effect of thiourea on microsomal oxidation of alcohols and associated microsomal functions

Thiourea and diethylthiourea, two compounds which react with hydroxyl radicals, inhibited NADPH-dependent microsomal oxidation of ethanol and 1-butanol. Inhibition by both compounds was more effective in the presence of the catalase inhibitor, azide. Inhibition by thiourea was noncompetitive with respect to ethanol in the absence of azide but was competitive in the presence of azide. Urea, a compound which does not react with hydroxyl radicals or H2O2, was without effect. Thiourea had no effect on NADH- and NADH-cytochrome c reductase, NADPH oxidase, and NADH- and NADPH-dependent oxygen uptake. Thiourea inhibited the activities of aniline hydroxylase and aminopyrine demethylase. Thiourea, but no other hydroxyl radical scavengers, e.g., dimethyl sulfoxide, mannitol, and benzoate, reacted directly with H202 and decreased H2O2 accumulation in the presence of azide. Therefore the actions of thiourea are complex because it can react with both hydroxyl radicals and H2O2. Differences between the actions of thiourea and those previously reported for dimethyl sulfoxide, mannitol, and benzoate, e.g., effects on drug metabolism, effectiveness of inhibition in the absence of azide, or kinetics of the inhibition, probably reflect the fact that thiourea reacts directly with H2O2 whereas the other agents do not. The current results remain consistent with the concept that microsomal oxidation of alcohols involves interactions of the alcohols with hydroxyl radicals generated from microsomal electron transfer.

The fetal alcohol syndrome in mice: an animal model

CBA and C3H female mice were maintained on liquid diets--Metrecal plus ethanol--containing 15-35% ethanol-derived calories. These diets, which resulted in alcohol blood levels of 73-398 mg/100 ml blood in nonpregnant females, were the sole sustenance for the females for at least 30 days before and throughout gestation. Females were killed on day 18 of gestation and offspring examined for skeletal and soft tissue anomalies. Prenatal death and maldevelopment increased with the level of alcohol intake. Deficient occiput ossification, neural anomalies, and low fetal weight occurred with low ethanol diets, and cardiac and eye-lid dysmorphology with higher ethanol diets. This pattern of malformations, which exhibited both a dose-response effect and strain differences in susceptibility, indicated that chronic maternal alcoholism is embryolethal and teratogenic in mice.

Alcohol and liver disease

It has recently been shown that alcohol may produce liver damage even in the presence of adequate nutrition. Absolute intake, regardless of the type of alcoholic beverage consumed, appears to be the important determinant of whether liver damage will occur. The spectrum of liver injury produced by alcohol includes fatty liver, hepatitis, and cirrhosis. Liver biopsy is necessary for confirmation and to determine prognosis. Therapy includes abstinence, supportive care and nutritional replacement.

The metabolic basis of alcohol's toxicity

The mechanisms by which excess alcohol directly damages the liver cells have been elucidated by studies in the baboon, which have shown that inability of the liver's enzyme systems to cope with hydrogen and fat overloads is far more significant in the progression to cirrhosis than any indirect effects of malnutrition. With the appearance of mitochondrial deformation, the process may have reached the stage of irreversibility.

Electron microscopic study of alcoholic liver disease with special attention to the changes of mesenchymal cells of the liver

The authors investigated electron microscopically the biopsy material of 48 chronic alcoholic liver patients. On the basis of clinical and histological criteria 5 stages were differentiated: fatty liver, fatty liver with increased mesenchymal activity, acute alcoholic hepatitis, chronic alcoholic hepatitis, alcoholic cirrhosis. In each group changes of liver cell organelles and mesenchymal cells were compared. In this investigation it was demonstrated that liver cell damage--except for acute alcoholic hepatitis was not parallel with the severity of the clinical picture. On the contrary, the proliveration of mesenchymal cells, signs of its secretory activity and fibre forming, were in correlation with the progression of liver disease. The authors suggest that an intermediate stage must be taken into account between acute alcoholic hepatitis and alcoholic cirrhosis: the chronic progressive alcoholic hepatitis. It reminds morphologically to a great extent of the active chronic hepatitis and it is characterized not by severity of the injury of liver cell organelles, but by great proliferation of mesenchymal cells and lymphoid infiltration.