Increased susceptibility of hepatic mitochondria to the toxicity of acetaldehyde after chronic ethanol consumption

Metabolism of ethanol and associated hepatotoxicity

Over the last three decades, direct hepatotoxic effects of ethanol were established, some of which were linked to redox changes produced by NADH generated via the alcohol dehydrogenase (ADH) pathway and shown to affect the metabolism of lipids, carbohydrates, proteins, and purines. It was also determined that ethanol can be oxidized by a microsomal ethanol oxidizing system (MEOS) involving a specific cytochrome P-450; this newly discovered ethanol-inducible cytochrome P-450 (P-450 IIEi) contributes to ethanol metabolism, tolerance, energy wastage (with associated weight loss), and the selective hepatic perivenular toxicity of various xenobiotics. Their activation by P-450IIEi now provides an understanding of the increased susceptibility of the heavy drinker to the toxicity of industrial solvents, anaesthetic agents, commonly prescribed drugs, over-the-counter analgesics, and chemical carcinogens. P-450 induction also explains depletion (and toxicity) of nutritional factors such as vitamin A. As a consequence, treatment with vitamin A and other nutritional factors is beneficial, but must take into account a narrowed therapeutic window in alcoholics who have increased needs for nutrients and also display an enhanced susceptibility to some of their adverse effects. Acetaldehyde (the metabolite produced from ethanol by either ADH or MEOS) impairs hepatic oxygen utilization and forms protein adducts, resulting in antibody production, enzyme inactivation, and decreased DNA repair. It also stimulates collagen production by the vitamin A storing cells (lipocytes) and myofibroblasts, and causes glutathione depletion. Supplementation with S-adenosyl-L-methionine partly corrects the depletion and associated mitochondrial injury, whereas administration of polyunsaturated lecithin opposes the fibrosis. Thus, at the cellular level, the classic dichotomy between the nutritional and toxic effects of ethanol has now been bridged. The understanding of how the ensuing injury eventually results in irreversible scarring or cirrhosis may provide us with improved modalities for treatment and prevention.

Acyclovir-induced nephrotoxicity: the role of the acyclovir aldehyde metabolite

For decades, acyclovir-induced nephrotoxicity was believed to be secondary to crystalluria. Clinical evidence of nephrotoxicity in the absence of crystalluria suggests that acyclovir induces direct insult to renal tubular cells. We postulated that acyclovir is metabolized by the alcohol dehydrogenase (ADH) enzyme to acyclovir aldehyde, which is metabolized by the aldehyde dehydrognase 2 (ALDH2) enzyme to 9-carboxymethoxymethylguanine (CMMG). We hypothesized that acyclovir aldehyde plays a role in acyclovir-induced nephrotoxicity. Human renal proximal tubular (HK-2) cells were used as our in vitro model. Western blot and enzymes activities assays were performed to determine whether the HK-2 cells express ADH and ALDH2 isozymes, respectively. Cytotoxicity (measured as a function of cell viability) assays were conducted to determine (1) whether the acyclovir aldehyde plays a role in acyclovir-induced nephrotoxicity and (2) whether CMMG induces cell death. A colorimetric assay was performed to determine whether acyclovir was metabolized to an aldehyde in vitro. Our results illustrated that (1) HK-2 cells express ADH and ALDH2 isozymes, (2) 4-methylpyrazole rendered significant protection against cell death, (3) CMMG does not induce cell death, and (4) acyclovir was metabolized to an aldehyde in tubular cells. These data indicate that acyclovir aldehyde is produced in HK-2 cells and that inhibition of its production by 4-methylpyrazole offers significant protection from cell death in vitro, suggesting that acyclovir aldehyde may cause the direct renal tubular insult associated with acyclovir.

Naringenin modulates circulatory lipid peroxidation, anti-oxidant status and hepatic alcohol metabolizing enzymes in rats with ethanol induced liver injury

We have investigated the modulatory efficacy of naringenin on circulatory lipid peroxidation and anti-oxidant status, hepatic alcohol metabolizing enzymes in rats with ethanol induced hepatotoxicity. Rats were divided into four groups: groups 1 and 2 received isocaloric glucose and 0.5% carboxymethyl cellulose; groups 3 and 4 received 20% ethanol equivalent to 6 g/kg body weight everyday for the total experimental period of 60 days. In addition, groups 2 and 4 were given naringenin (50 mg/kg) everyday for the last 30 days of the experiment. The results showed significantly elevated levels/activities of bilirubin, alkaline phosphatase (ALP), lactate dehydrogenase (LDH), thiobarbituric acid reactive substances (TBARS), lipid hydroperoxides (LOOH), conjugated dienes (CD) and phase I enzymes, and significantly lowered the activities of alcohol dehydrogenase (ADH), aldehyde dehydrogenase (ALDH), superoxide dismutase (SOD), catalase (CAT) and phase II enzymes in ethanol-fed rats as compared to those of the control. Supplementation with naringenin for the last 30 days of the experiment to ethanol-fed rats, significantly decreased the levels/activities of bilirubin, ALP, LDH, TBARS, LOOH, CD and phase I enzymes, and significantly elevated the activities of ADH, ALDH, SOD, CAT and phase II enzymes as compared to control rats. These findings suggest that naringenin can effectively modulate the hepatic alcohol metabolizing enzymes in rats with ethanol induced liver injury.

Taurine enhances the metabolism and detoxification of ethanol and prevents hepatic fibrosis in rats treated with iron and alcohol

The study examines the effects of taurine on the metabolism and detoxification of ethanol in liver fibrosis induced by simultaneous administration of iron carbonyl (0.5%, w/w) and ethanol (6g/(kgday)). Ethanol and iron administration caused liver damage and fibrosis as evidenced by liver histology and biochemical profile in plasma. Over accumulation of iron and a loss in taurine in hepatic tissue was observed in fibrotic animals. The activities of alcohol dehydrogenase and aldehyde dehydrogenase were significantly reduced in these rats compared to control. Adaptive induction of activities of Cytochrome P4502E1 (CYP2E1) and aniline hydroxylase accompanied by the reduction in glutathione-S-transferase, DT-diaphorase and glyoxalases I and II was observed. Taurine administration (2% in drinking water) ameliorated the effects of ethanol and iron. Hepatic damage and fibrosis were reduced in taurine-supplemented rats. Thus taurine has the potential for the treatment of alcoholic liver fibrosis.

Effect of the inducer of interleukin-6 (ME3738) on rat liver treated with ethanol

BACKGROUND

Recently, ME3738, a derivative of soyasapogenol B, was developed as an inducer of interleukin (IL)-6. It has been demonstrated that ME3738 is stimulate to produce IL-6 and that it protects against concanavalin A-induced liver failure. It has also been reported that IL-6 prevents alcoholic fatty liver in mice. These results suggest that ME3738 may prevent alcoholic liver injury. In the present study, we investigated whether ME3738 prevents fatty liver in ethanol-fed rats.

METHODS

Twenty-four male rats were fed with liquid diets containing ethanol or carbohydrates for 8 weeks. Liquid diets were prepared with or without ME3738 (0.8 mg/mL). Liver sections were stained for histology and IL-6 expression. Fatty changes of liver were classified into 4 grades: 0, 1+, 2+, and 3+. Plasma levels of aspartate aminotransferase (AST), alanine aminotransferase (ALT), gamma-glutamyl transpeptidase (GGT), triglyceride, total cholesterol, and IL-6 were measured, as was hepatic ATP content.

RESULTS

The extent of fatty degeneration in ethanol-fed rats was significantly greater (p=0.023) than that in controls. Fatty changes in rats fed ethanol containing ME3738 decreased, but were not significantly different from those in rats fed ethanol. Immunohistochemical staining of IL-6 was observed in perivenular hepatocytes of all rats, with its intensity becoming stronger in the order of controls, controls containing ME3738, ethanol, and ethanol-containing ME3738-fed rats. Plasma levels of AST and ALT in rats fed ethanol were significantly higher than those in controls. In rats fed ethanol-containing ME3738, these levels decreased to those of control-fed rats, but were not significantly different from those in rats fed ethanol. Plasma IL-6 was not detected in any rats. Hepatic ATP content in rats fed ethanol was significantly (p<0.05) lower than that in control-fed rats; however, in rats fed ethanol-containing ME3738, it increased to that in control-fed rats.

CONCLUSIONS

Oral administration of ME3738, inducer of IL-6 may prevent the development of fatty liver caused by chronic ethanol consumption.

Megamitochondria formation - physiology and pathology

Mitochondria undergo structural changes simultaneously with their functional changes in both physiological and pathological conditions. These structural changes of mitochondria are classified into two categories: simple swelling and the formation of megamitochondria (MG). Data have been accumulated to indicate that free radicals play a crucial role in the mechanism of the MG formation induced by various experimental conditions which are apparently various. These include ethanol-, chloramphenicol- and hydrazine-induced MG formation. Involvement of free radicals in the mechanism of MG formation is showed by the fact that MG formation is successfully suppressed by free radical scavengers such as alpha-tocopherol, coenzyme Q(10), and 4-OH-TEMPO. Detailed mechanisms and pathophysiological meanings of MG formation still remain to be investigated. However, a body of evidence strongly suggests that enormous changes in physicochemical and biochemical properties of the mitochondrial membranes during MG formation take place and these changes are favorable for membrane fusion. A recent report showed that continous exposure of cells with MG to free radicals induces apoptosis, finding which suggests that MG formation is an adaptative process to unfavorable environments at the level of intracellular organelles. Mitochondria try to decrease intracellular reactive oxygen species (ROS) levels by decreasing the consume of oxygen via MG formation. If mitochondria succeed to suppress intracellular ROS levels, MG return to normal both structurally and functionally, and they restore the ability to actively synthesize ATP. If cells are additionally exposed to excess amounts of free radicals, MG become swollen, membrane potential of mitochondria (DeltaPsim) decreases, cytochrome c is released from mitochondria, leading to activation of caspases and apoptosis is induced.

The role of acetaldehyde in pregnancy outcome after prenatal alcohol exposure

It is not known why some heavy-drinking women give birth to children with alcohol-related birth defects (ARBD) whereas others do not. The objective of this study was to determine whether the frequency of elevated maternal blood acetaldehyde levels among alcoholics is in the range of ARBD among alcoholic women. MEDLINE was searched from 1980 to 2000 using the key words acetaldehyde, pharmacokinetics, and alcoholism for controlled trials reporting blood or breath acetaldehyde levels in alcoholics and nonalcoholics. Separately, using the key words fetal alcohol syndrome, epidemiology, prevalence, incidence, and frequency, articles were identified reporting ARBD incidences among the offspring of heavy drinkers. Of 23 articles reporting acetaldehyde levels in alcoholics, four met the inclusion criteria. Forty-three studies reported on the rate of ARBD in heavy drinkers, and 14 were accepted. Thirty-four percent of heavy drinkers had a child with ARBD, and 43% of chronic alcoholics had high acetaldehyde levels. The similar frequencies of high acetaldehyde levels among alcoholics and the rates of ARBD among alcoholic women provide epidemiologic support to the hypothesis that acetaldehyde may play a major role in the cause of ARBD.

Energy expenditure in chronic alcohol abuse

BACKGROUND

In healthy subjects, alcohol decreases lipid oxidation favouring fat deposition. However, individuals who chronically abuse alcohol are not obese. To investigate this paradox, we measured energy expenditure (EE) and fuel utilization in chronic alcohol abusers in relation to their drinking behaviour.

METHODS

Resting and postprandial EE and nonprotein respiratory quotient (NPRQ) were measured using indirect calorimetry, in 36 alcohol abusers [mean (+/- SE) age 42 +/- 2 years; weight 67 +/- 2 kg; 21 with steatosis, eight with hepatitis; seven with cirrhosis] and in 36 gender-, age- and weight-matched healthy controls. Alcoholic patients were re-evaluated either after 14 days (n = 14) or on days 2, 4, 6, 8, 14 and 42 (n = 6) after abstinence.

RESULTS

When alcoholics were compared to healthy controls, mean energy intake was greater, 15 +/- 1 MJ day-1 (38 +/- 2% from alcohol) cf. 9 +/- 1 MJ day-1 (P < 0.001), resting EE increased, 82 +/- 2 cf. 65 +/- 2 W (P < 0.001) and NPRQ decreased, 0.75 +/- 0.02 cf. 0.82 +/- 0.01 (P < 0.001). The postprandial increases in EE and NPRQ were of similar magnitude in both groups. Abstinence from alcohol for 14 days was accompanied by reduced energy intake, 16 +/- 1 cf. 11 +/- 1 MJ day-1 (P < 0.005) and decreased resting EE, 84 +/- 5 cf. 73 +/- 4 W (P < 0.05). The decrease in resting EE consistently occurred 4 days after abstinence from alcohol.

CONCLUSIONS

Chronic alcohol abuse is associated with energy wasting and inhibition of adipose tissue accumulation. This may explain why alcoholics are not obese despite high total energy intakes.

Ex vivo and in vivo investigations of picroliv from Picrorhiza kurroa in an alcohol intoxication model in rats

Picroliv, the active constituent isolated from the plant Picrorhiza kurroa, was evaluated as a hepatoprotective agent against ethanol-induced hepatic injury in rats. Alcohol feeding (3.75 g/kg x45 days) produced 20-114% alteration in selected serum (AST, ALT and ALP) and liver markers (lipid, glycogen and protein). Further, it reduced the viability (44-48%) of isolated hepatocytes (ex vivo) as assessed by Trypan blue exclusion and rate of oxygen uptake. Its effect was also seen on specific alcohol-metabolizing enzymes (aldehyde dehydrogenase, 41%; acetaldehyde dehydrogenase, 52%) in rat hepatocytes. The levels of these enzymes were found to be reduced in the cells following alcohol intoxication. Ethyl alcohol also produced cholestasis (41-53%), as indicated by reduction in bile volume, bile salts and bile acids. Picroliv treatment (3-12 mg/kg p.o. x45 days) restored the altered parameters in a dose-dependent manner (36-100%).

Alcohol and lipids

Alcoholic fatty liver and hyperlipemia result from the interaction of ethanol and its oxidation products with hepatic lipid metabolism. An early target of ethanol toxicity is mitochondrial fatty acid oxidation. Acetaldehyde and reactive oxygen species have been incriminated in the pathogenesis of the mitochondrial injury. Microsomal changes offset deleterious accumulation of fatty acids, leading to enhanced formation of triacylglycerols, which are partly secreted into the plasma and partly accumulate in the liver. However, this compensatory mechanism fades with progression of the liver injury, whereas the production of toxic metabolites increases, exacerbating the lesions and promoting fibrogenesis. The early presence of these changes confers to the fatty liver a worse prognosis than previously thought. Alcoholic hyperlipemia results primarily from increased hepatic secretion of very-low-density lipoprotein and secondarily from impairment in the removal of triacylglycerol-rich lipoproteins from the plasma. Hyperlipemia tends to disappear because of enhanced lipolytic activity and aggravation of the liver injury. With moderate alcohol consumption, the increase in high-density lipoprotein becomes the predominant feature. Its mechanism is multifactorial (increased hepatic secretion and increased extrahepatic formation as well as decreased removal) and explains part of the enhanced cholesterol transport from tissues to bile. These changes contribute to, but do not fully account for, the effects on atherosclerosis and/or coronary heart disease attributed to moderate drinking.

Polyenylphosphatidylcholine attenuates alcohol-induced fatty liver and hyperlipemia in rats

Chronic administration of a soybean-derived polyenylphosphatidylcholine (PPC) extract prevents the development of cirrhosis in alcohol-fed baboons. To assess whether this phospholipid also affects earlier changes induced by alcohol consumption (such as fatty liver and hyperlipemia), 28 male rat littermates were pair-fed liquid diets containing 36% of energy either as ethanol or as additional carbohydrate for 21 d, and killed 90 min after intragastric administration of the corresponding diets. Half of the rats were given PPC (3 g/l), whereas the other half received the same amount of linoleate (as safflower oil) and choline (as bitartrate salt). PPC did not affect diet or alcohol consumption [15.4 +/- 0.5 G/(kg.d)], but the ethanol-induced hepatomegaly and the hepatic accumulation of lipids (principally triglycerides and cholesterol esters) and proteins were about half those in rats not given PPC. The ethanol-induced postprandial hyperlipemia was lower with PPC than without, despite an enhanced fat absorption and no difference in the level of plasma free fatty acids. The attenuation of fatty liver and hyperlipemia was associated with correction of the ethanol-induced inhibition of mitochondrial oxidation of palmitoyl-1-carnitine and the depression of cytochrome oxidase activity, as well as the increases in activity of serum glutamate dehydrogenase and aminotransferases. Thus, PPC attenuates early manifestations of alcohol toxicity, at least in part, by improving mitochondrial injury. These beneficial effects of PPC at the initial stages of alcoholic liver injury may prevent or delay the progression to more advanced forms of alcoholic liver disease.

Chronic ethanol feeding increases apoptosis and cell proliferation in rat liver

The present study was conducted to evaluate if the increased rate of apoptosis previously reported in the liver of ethanol-treated rats was accompanied by increased cell renewal. A quantitative analysis of apoptosis was performed in rats fed an ethanol-containing liquid diet for 5 weeks. S-phase cells were demonstrated by immunohistochemistry, using the Bromodeoxyuridine/anti-Bromodeoxyuridine method. In ethanol-fed rats apoptosis was five times greater than in pair-fed controls. Bromodeoxyuridine-labelled hepatocytes increased from 0.07 +/- 0.009% in controls to 0.17 +/- 0.013% (p < 0.001) and Bromodeoxyuridine-labelled lipocytes (desmin-positive sinusoidal cells) increased from 3.43 +/- 0.28% to 6.60 +/- 1.04% (p < 0.001). The lobular distribution of labelled cells was modified with a shift towards the perivenular areas. The results of this study suggest that the replacement of liver cells lost by ethanol-induced apoptosis is not impaired in intact (non-operated) animals. The impaired regeneration following partial hepatectomy reported in ethanol-fed rats is possibly due to differences in the extent of parenchymal loss, to altered relationships between hepatocytes and blood supply and to the modalities of regeneration involved.

Alcohol, liver, and nutrition

Until two decades ago, dietary deficiencies were considered to be the major reason why alcoholics developed liver disease. As the overall nutrition of the population improved, more emphasis was placed on secondary malnutrition. Direct hepatotoxic effects of ethanol were also established, some of which were linked to redox changes produced by reduced nicotinamide adenine dinucleotide (NADH) generated via the alcohol dehydrogenase (ADH) pathway. It was also determined that ethanol can be oxidized by a microsomal ethanol oxidizing system (MEOS) involving cytochrome P-450: the newly discovered ethanol-inducible cytochrome P-450 (P-450IIE1) contributes to ethanol metabolism, tolerance, energy wastage (with associated weight loss), and the selective hepatic perivenular toxicity of various xenobiotics. P-450 induction also explains depletion (and enhanced toxicity) of nutritional factors such as vitamin A. Even at the early fatty-liver stage, alcoholics commonly have a very low hepatic concentration of vitamin A. Ethanol administration in animals was found to depress hepatic levels of vitamin A, even when administered with diets containing large amounts of the vitamin, reflecting, in part, accelerated microsomal degradation through newly discovered microsomal pathways of retinol metabolism, inducible by either ethanol or drug administration. The hepatic depletion of vitamin A was strikingly exacerbated when ethanol and other drugs were given together, mimicking a common clinical occurrence. Hepatic retinoid depletion was found to be associated with lysosomal lesions and decreased detoxification of chemical carcinogens. To alleviate these adverse effects, as well as to correct problems of night blindness and sexual inadequacies, the alcoholic patient should be provided with vitamin A supplementation. Such therapy, however, is complicated by the fact that in excessive amounts vitamin A is hepatotoxic, an effect exacerbated by long-term ethanol consumption. This results in striking morphologic and functional alterations of the mitochondria with leakage of mitochondrial enzymes, hepatic necrosis, and fibrosis. Thus, treatment with vitamin A and other nutritional factors (such as proteins) is beneficial but must take into account a narrowed therapeutic window in alcoholics who have increased needs for such nutrients, but also display an enhanced susceptibility to their adverse effects. Massive doses of choline also exerted some toxic effects and failed to prevent the development of alcoholic cirrhosis. Acetaldehyde (the metabolite produced from ethanol by either ADH or MEOS) impairs hepatic oxygen utilization and forms protein adducts, resulting in antibody production, enzyme inactivation, and decreased DNA repair. It also enhances pyridoxine and perhaps folate degradation and stimulates collagen production by the vitamin A storing cells (lipocytes) and myofibroblasts.(ABSTRACT TRUNCATED AT 400 WORDS)

Hepatic, metabolic and toxic effects of ethanol: 1991 update

Until two decades ago, dietary deficiencies were considered to be the only reason for alcoholics to develop liver disease. As the overall nutrition of the population improved, more emphasis was placed on secondary malnutrition and direct hepatotoxic effects of ethanol were established. Ethanol is hepatotoxic through redox changes produced by the NADH generated in its oxidation via the alcohol dehydrogenase pathway, which in turn affects the metabolism of lipids, carbohydrates, proteins, and purines. Ethanol is also oxidized in liver microsomes by an ethanol-inducible cytochrome P-450 (P-450IIE1) that contributes to ethanol metabolism and tolerance, and activates xenobiotics to toxic radicals thereby explaining increased vulnerability of the heavy drinker to industrial solvents, anesthetic agents, commonly prescribed drugs, over-the-counter analgesics, chemical carcinogens, and even nutritional factors such as vitamin A. In addition, ethanol depresses hepatic levels of vitamin A, even when administered with diets containing large amounts of the vitamin, reflecting, in part, accelerated microsomal degradation through newly discovered microsomal pathways of retinol metabolism, inducible by either ethanol or drug administration. The hepatic depletion of vitamin A is strikingly exacerbated when ethanol and other drugs were given together, mimicking a common clinical occurrence. Microsomal induction also results in increased production of acetaldehyde. Acetaldehyde, in turn, causes injury through the formation of protein adducts, resulting in antibody production, enzyme inactivation, decreased DNA repair, and alterations in microtubules, plasma membranes and mitochondria with a striking impairment of oxygen utilization. Acetaldehyde also causes glutathione depletion and lipid peroxidation, and stimulates hepatic collagen production by the vitamin A storing cells (lipocytes) and myofibroblasts.(ABSTRACT TRUNCATED AT 250 WORDS)

Formation of a 37 kilodalton liver protein-acetaldehyde adduct in vivo and in liver cell culture during chronic alcohol exposure

With the use of antibodies that can recognize acetaldehyde adducts and the application of various immunological techniques, several protein-AAs have now been shown to form in vivo during chronic alcohol ingestion. These protein-AAs include the 37-kDa liver protein-AA, the CytP450IIE1-AA, hemoglobin-AA, two serum protein-AAs with molecular weights of 50 kDa and 103 kDa, and collagen type I protein-AA in liver. If acetaldehyde is the agent responsible for alcoholic liver injury, acetaldehyde toxicity in chronic alcohol ingestion must be linked to the ability of acetaldehyde to form adducts with proteins and perhaps other macromolecules. This is at least one mechanism of acetaldehyde-mediated liver injury. For proteins that serve critical functions, acetaldehyde adduct formation may alter their functions and thereby produce organ damage. Acetaldehyde adduct formation can also elicit humoral or cytotoxic immune responses and these responses may also lead to organ injury.

Effects of alkyl alcohols and related chemicals on rat liver structure and function. II. Some biochemical properties of ethanol-, propanol- and butanol-treated rat liver mitochondria

Functional changes of mitochondria in the liver obtained from rats given 32% ethanol, 32% propanol and 6.9% butanol in drinking water for up to 3 months were investigated. Animals were also fed a liquid diet containing ethanol for comparison. Results obtained were as follows: 1) Animals given ethanol in drinking water consumed twice as much ethanol daily as those fed a liquid diet containing ethanol, while ultrastructural changes of hepatic mitochondria were essentially the same between the former and the latter animals: the co-existence of megamitochondria and small mitochondria with poorly developed cristae. 2) Effects of alkyl alcohols tested on the respiratory rates and coupling efficiency of mitochondria were variable, depending on the kind of alkyl alcohols, the duration of experiments and oxidizable substrates used. 3) There was essentially no difference between the heavy and the light mitochondrial fractions obtained from alkyl alcohol-treated rat livers in terms of respiratory rates and coupling efficiencies. 4) Decreases in the content of cytochrome aa3 and the activity of activity of cytochrome oxidase, and increases in MEOS activity were most distinct in ethanol-treated rat livers. A possible role of chronic relative oxygen deficiency inside the hepatocyte caused by the metabolization of alkyl alcohols is discussed in order to interpret such peculiar ultrastructural changes of mitochondria.

The effect of the prostaglandin analogue-misoprostol on rat liver mitochondria after chronic alcohol feeding

Rats fed ethanol (36% of total calories in a nutritionally adequate liquid diet) for 5 weeks develop functional alterations of hepatic mitochondria and steatosis of the liver. At the fatty liver stage, ADP-stimulated respiration of mitochondria was depressed in ethanol fed rats by 30% (p less than 0.001) with glutamate + malate and by 23% (p less than 0.001) with succinate as substrates. A similar decrease was noted in the respiratory control ratio (RCR) (34% and 29%, respectively). The total lipid content of the liver increased 2.6 fold (p less than 0.001). Mitochondrial dysfunction could be prevented, in part, by the treatment with a synthetic derivative of prostaglandin E1, misoprostol, at a mean daily dose of 80 micrograms/kg of body weight. The RCR with glutamate + malate as substrates was improved by 36% (p less than 0.05). We conclude that misoprostol attenuates several functional alterations in liver mitochondria during alcohol feeding.

Mechanism of ethanol induced hepatic injury

Ethanol is hepatotoxic through redox changes produced by the NADH generated in its oxidation via the alcohol dehydrogenase pathway, which in turn affects the metabolism of lipids, carbohydrates, proteins and purines. Ethanol is also oxidized in liver microsomes by an ethanol-inducible cytochrome P-450 (P-450IIE1) which contributes to ethanol metabolism and tolerance, and activates xenobiotics to toxic radicals thereby explaining increased vulnerability of the heavy drinker to industrial solvents, anesthetic agents, commonly prescribed drugs, over-the-counter analgesics, chemical carcinogens and even nutritional factors such as vitamin A. Induction also results in energy wastage and increased production of acetaldehyde. Acetaldehyde, in turn, causes injury through the formation of protein adducts, resulting in antibody production, enzyme inactivation, decreased DNA repair, and alterations in microtubules, plasma membranes and mitochondria with a striking impairment of oxygen utilization. Acetaldehyde also causes glutathione depletion and lipid peroxidation, and stimulates hepatic collagen synthesis, thereby promoting fibrosis.

High levels of acetaldehyde in nonalcoholic liver injury after threonine or ethanol administration

Acetaldehyde, a product of ethanol oxidation which forms adducts with proteins, has been incriminated in the pathogenesis of alcoholic liver injury. High serum antibody titers against acetaldehyde-protein adducts have been found not only in alcoholics but also in patients with nonalcoholic liver disease, suggesting a contribution of acetaldehyde derived from sources other than exogenous ethanol. To investigate the effect of liver injury on the removal and the production of acetaldehyde, we produced fibrosis and cirrhosis (by chronic administration of carbon tetrachloride) and fatty liver (with very small doses of dimethylnitrosamine) in rats. Endogenous blood acetaldehyde levels increased by 38% in rats with severe liver injury (p less than 0.005), but not significantly in rats with fatty liver. However, an i.v. load of threonine (a physiological source of acetaldehyde), in amounts equivalent to the daily intake of this amino acid, increased blood and hepatic acetaldehyde levels in the rats with both types of liver injury more than in controls. Threonine dehydrogenase and dehydratase activities, involved in the major pathways for threonine degradation in mitochondria and cytosol, respectively, were markedly decreased in rats with liver injury with a resulting increase in hepatic threonine concentration. Moreover, the threonine aldolase activity, which splits threonine into glycine and acetaldehyde, remained unaffected or even slightly increased. Liver injury was also associated with impaired mitochondrial functions, including a 10 to 23% decrease in acetaldehyde oxidation (depending upon the severity of the lesions). As a consequence, administration of ethanol (an exogenous source of acetaldehyde) resulted in striking elevations in the levels of acetaldehyde in carbon tetrachloride-treated rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Human aldehyde dehydrogenases: their role in alcoholism

This article surveys the state of our knowledge concerning the biochemical and genetic variations in aldehyde dehydrogenases (ALDHs) in humans and their role in alcohol sensitivity, alcohol drinking habits, and alcoholism. Variations in acetaldehyde metabolism via genetically determined polymorphisms in ALDH enzymes seem to play an important role in individual and racial differences in acute and chronic effects of alcohol drinking as well as towards vulnerability to organ damage after chronic alcohol abuse. Alcohol sensitivity and associated discomfort symptoms accompanying alcohol ingestion may be determinantal for the significantly low incidence of alcoholism among Japanese, Chinese and other Orientals of Mongoloid origin. An abnormal ALDH isozyme has been found to be widely prevalent among individuals of Mongoloid race, and is mainly responsible for the acute sensitivity to alcohol commonly observed in this race. Persons sensitive to alcohol by virtue of their genetically controlled ALDH isozyme deficiency may be discouraged from drinking large amounts of alcohol in their daily life due to the initial adverse reaction experienced after drinking alcohol, and thus are protected against alcoholism.

Inhibition of rat liver transaminases by low levels of acetaldehyde and the pharmacologic effects of B6 vitamers

To better define the significance and mechanism of acetaldehyde-mediated transaminase inhibition, acetaldehyde metabolism was studied in rat liver homogenates and cytosols. When either preparation was incubated at 37 degrees with 1.5 mM acetaldehyde for 4 hr, acetaldehyde levels fell rapidly in the first 30 min and little inhibition of aspartate aminotransferase (GOT) or alanine aminotransferase (GPT) resulted. In contrast, incubation with 50 mM ethanol also resulted in a peak acetaldehyde level of 1.0 to 1.5 mM by 2 hr, but this level was then maintained for the next 2 hr and transaminases were inhibited by 20-35%. Sequential addition of low dose (125-250 microM) pulses of acetaldehyde to rat liver preparations resulted in a progressive decrease in the rate of acetaldehyde disappearance. When the pulsing schedule was adjusted accordingly to maintain acetaldehyde levels between 50 and 250 microM for 8 hr, transaminases were again inhibited by 20-40%. Finally, addition of 1-5 mM pyridoxal and pyridoxal 5'-phosphate, aldehydic B6 vitamers, to cytosols 2-4 hr after pulsing with acetaldehyde was begun, almost completely prevented further transaminase inhibition. In contrast, the non-aldehydic B6 vitamers, pyridoxine, pyridoxamine and pyridoxamine 5'-phosphate, did not affect acetaldehyde-mediated transaminase inhibition. These findings suggest that (1) prolonged exposure to low levels of acetaldehyde impairs acetaldehyde metabolism in rat liver homogenates and cytosols; (2) acetaldehyde toxicity may be more dependent on sustained exposure to acetaldehyde than on the peak level of acetaldehyde attained; and (3) aldehydic B6 vitamers can modify on-going acetaldehyde-mediated transaminase inhibition.

Impaired oxygen utilization. A new mechanism for the hepatotoxicity of ethanol in sub-human primates

The role of oxygenation in the pathogenesis of alcoholic liver injury was investigated in six baboons fed alcohol chronically and in six pair-fed controls. All animals fed alcohol developed fatty liver with, in addition, fibrosis in three. No evidence for hypoxia was found, both in the basal state and after ethanol at moderate (30 mM) or high (55 mM) levels, as shown by unchanged or even increased hepatic venous partial pressure of O2 and O2 saturation of hemoglobin in the tissue. In controls, ethanol administration resulted in enhanced O2 consumption (offset by a commitant increase in splanchnic blood flow), whereas in alcohol fed animals, there was no increase. At the moderate ethanol dose, the flow-independent O2 extraction, measured by reflectance spectroscopy on the liver surface, tended to increase in control animals only, whereas a significant decrease was observed after the high ethanol dose in the alcohol-treated baboons. This was associated with a marked shift in the mitochondrial redox level in the alcohol-fed (but not in control) baboons, with striking rises in splanchnic output of glutamic dehydrogenase and acetaldehyde, reflecting mitochondrial injury. Increased acetaldehyde, in turn, may aggravate the mitochondrial damage and exacerbate defective O2 utilization. Thus impaired O2 consumption rather than lack of O2 supply characterizes liver injury produced by high ethanol levels in baboons fed alcohol chronically.

Effects of ethanol feeding on the activity and regulation of hepatic carnitine palmitoyltransferase I

The effects of ethanol administration on activity and regulation of carnitine palmitoyltransferase I (CPT-I) were studied in hepatocytes isolated from rats fed a liquid, high-fat diet containing 36% of total calories as ethanol or an isocaloric amount of sucrose. Cells were isolated at several time points in the course of a 5-week experimental period. Ethanol consumption markedly decreased CPT-I activity and increased enzyme sensitivity to inhibition by exogenously added malonyl-CoA. Changes in enzyme activity occurred sooner than those in enzyme sensitivity. Fatty acid oxidation to CO2 and ketone bodies was depressed in hepatocytes from ethanol-fed animals during the first part of the treatment. At the end of the 35-day period, there were no longer differences in the rate of ketogenesis between the two groups. At that time, however, the rate of CO2 formation was still impaired in the ethanol-fed animals. Furthermore, addition of ethanol or acetaldehyde to the incubation medium strongly depressed CPT-I activity and rates of fatty acid oxidation in hepatocytes from ethanol-treated rats, whereas these effects were much less pronounced in cells from control animals. The response of CPT-I activity to insulin, glucagon, vasopressin, and phorbol ester was blunted in cells derived from ethanol-fed rats. These changes in the regulation of CPT-I activity corresponded with those observed in the rate of fatty acid oxidation. It is concluded that CPT-I may play a role in the generation of the ethanol-induced fatty liver.

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.

Intralobular distribution of rat liver aldehyde dehydrogenase and alcohol dehydrogenase

1. The activity of liver microsomal high Km-ALDH and mitochondrial low Km-ALDH, which may be primarily responsible for the oxidation of acetaldehyde after ethanol administration was found to be predominantly distributed in the centrilobular area. 2. The activities of other ALDH isozymes in mitochondrial and soluble fractions were evenly distributed in periportal and perivenous regions. 3. The activity of ADH which is involved in production of acetaldehyde was predominantly located in the periportal area. 4. From these results it seems unlikely that a concentration of acetaldehyde after ethanol ingestion is higher in perivenous hepatocytes than in periportal ones. Additional data would be needed to understand fully the mechanism by which ethanol induces predominantly centrilobular liver injury.

Human liver aldehyde dehydrogenase: subcellular distribution in alcoholics and nonalcoholics

Activity assay and isoelectric focusing analysis of human biopsy and autopsy liver specimens showed the existence of two major aldehyde dehydrogenases (ALDH I, ALDH II). Subcellular distribution of these isozymes was determined in autopsy livers from alcoholics and nonalcoholics. Nearly 70% of the total ALDH activity was recovered in the cytosol which contained both the major isozymes. Densitometric evaluation of isozyme bands showed that about 65% of the cytosolic enzyme activity was due to ALDH II and the rest due to ALDH I isozyme. Only about 5% of the total ALDH activity was found in the mitochondrial fraction (70% ALDH I and 30% ALDH II). Significantly reduced total and specific ALDH activities were noted in all the subcellular fractions from cirrhotic liver specimens. Apparently, ALDH I isozyme from cytosol and mitochondria is primarily responsible for the oxidation of small amounts of acetaldehyde normally found in the blood of nonalcoholics after drinking moderate amounts of alcohol. However, in alcoholics who exhibit higher blood acetaldehyde concentrations after drinking alcohol, ALDH II isozyme may be of greater physiological significance.

International Commission for Protection against Environmental Mutagens and Carcinogens. ICPEMC Working Paper No. 15/5. Acute aldehyde syndrome and chronic aldehydism

Different types of alcohol dehydrogenase and of aldehyde dehydrogenase lead to different blood acetaldehyde levels. With respect to acetaldehyde levels in human blood 3 types can be distinguished: (1) the normal range, (2) the acute aldehyde syndrome, and (3) the chronic aldehydism. Acetaldehyde is electrophilic and reacts with nucleophilic groups of various macromolecules including DNA. Acetyldehyde inhibits synthetic and metabolic pathways, it interferes with the polymerization of tubulin and stimulates collagen synthesis. By depletion of cellular glutathione levels, acetaldehyde leads to lipid peroxidation and to the formation of malonaldehyde. There are indications that acetaldehyde may play a role in positively reinforcing mood changes induced by alcohol in humans.

Studies on the mechanism of acetaldehyde-mediated inhibition of rat liver transaminases

Incubation of mitochondria-depleted rat liver homogenates with 5 mmol/l acetaldehyde at 37 degrees C for 1 h inhibited both aspartate and alanine aminotransferases by 30%. Inhibition was prevented by decreasing temperature to 4 degrees C or by preincubating homogenates with cyanate but was unaffected by cyanamide and methylpyrazole which block acetaldehyde oxidation and reduction respectively. Cyanate-sensitive acetaldehyde-mediated inhibition of purified porcine heart transaminases was also demonstrated in the presence of rat liver homogenate but not in Tris/sucrose medium. Moreover, porcine transaminases were inhibited by trichloroacetic acid extracts of rat liver homogenates previously incubated with acetaldehyde but not by extracts of homogenates incubated with both acetaldehyde and cyanate. These findings suggest that acetaldehyde-mediated transaminase inhibition requires further non-oxidative metabolism of acetaldehyde. Since transaminase activities were not restored by addition of pyridoxal 5'-phosphate to the assay systems, acetaldehyde-induced transaminase inhibition does not appear to be mediated by displacement or depletion of this B6 coenzyme.

Evidence for the generation of transaminase inhibitor(s) during ethanol metabolism by rat liver homogenates: a potential mechanism for alcohol toxicity

Since ethanol consumption decreases hepatic aminotransferase activities in vivo, mechanisms of ethanol-mediated transaminase inhibition were explored in vitro using mitochondria-depleted rat liver homogenates. When homogenates were incubated at 37 degrees with 50 mM ethanol for 1 hr, alanine aminotransferase decreased by 20%, while aspartate aminotransferase was unchanged. After 2 hr, aspartate aminotransferase decreased by 20% and by 3 hr, alanine and aspartate aminotransferases were decreased by 31 and 23%, respectively. Levels of acetaldehyde generated during ethanol oxidation were 525 +/- 47 microM at 1 hr, 855 +/- 14 microM at 2 hr, and 1293 +/- 140 microM at 3 hr. Although inhibition of alcohol oxidation with methylpyrazole or cyanide markedly decreased ethanol-mediated transaminase inhibition, neither incubation with acetate nor generation of reducing equivalents by oxidation of lactate, malate, xylitol, or sorbitol altered the activity of either enzyme. However, semicarbazide, an aldehyde scavenger, prevented inhibition of both aminotransferases by ethanol. Moreover, incubation with 5 mM acetaldehyde for 1 hr inhibited alanine and aspartate aminotransferases by 36 and 26%, respectively. Cyanamide, an aldehyde dehydrogenase inhibitor, had little effect on ethanol-mediated transaminase inhibition. Thus, metabolism of ethanol by rat liver homogenates produces transaminase inhibition similar to that described in vivo and this effect requires acetaldehyde generation but not acetaldehyde oxidation. Since addition of pyridoxal 5'-phosphate to assay mixes did not reverse ethanol effects, aminotransferase inhibition does not result from displacement of vitamin B6 coenzymes.

Serum mitochondrial aspartate aminotransferase as a marker of chronic alcoholism: diagnostic value and interpretation in a liver unit

Serum mitochondrial aspartate aminotransferase activity was measured using an immunochemical method in 251 subjects, of whom 140 were chronic alcoholics. The alcoholic patients included 37 with normal liver routine tests (Group I), 61 with noncirrhotic alcoholic liver disease (Group II) and 42 with cirrhosis (Group III), of whom 21 had been abstainers for at least 2 months. All of the remaining 111 subjects were nonalcoholic: 61 had various types of liver disease (Group IV) and 50 were healthy controls. A second assay of serum mitochondrial aspartate aminotransferase activity was performed in 76 alcoholics after a period of abstinence of about 7 days. In addition, serial mitochondrial aspartate aminotransferase determinations were performed in four nonalcoholic volunteers prior to, during and following an alcohol bout. Mean mitochondrial aspartate aminotransferase and mitochondrial aspartate aminotransferase/total aspartate aminotransferase ratio were significantly increased in the alcoholics whatever their liver status, with a sensitivity of the ratio of 81, 85 and 66% for Group I, Group II and the 21 drinkers of Group III, respectively. Only 1 of the 21 cirrhotic abstainers had an increased ratio. Among the 61 nonalcoholic patients with liver disease, 11 had an increased mitochondrial aspartate aminotransferase/total aspartate aminotransferase ratio, specificity of which was 82%. After drinking had been stopped for about 1 week, mitochondrial aspartate aminotransferase decreased by more than 50% and therefore appears as a reliable tool to assess abstinence. In the four cases of alcohol bouts, no significant modifications in mitochondrial aspartate aminotransferase serum values were observed, thus suggesting that mitochondrial aspartate aminotransferase is indeed a marker of chronic, but not of acute, alcohol intake.

Canine liver aldehyde dehydrogenases: distribution, isolation, and partial characterization

Canine liver aldehyde dehydrogenases (ALDH) (aldehyde:NAD oxidoreductase; EC 1.2.1.3) are analogous to enzymes identified in human and other mammalian liver tissue in regard to subcellular localization, affinity for substrates, inhibition by disulfiram, and effects of magnesium ions on enzyme activity. Aldehyde dehydrogenase activity is distributed in the mitochondrial, microsomal, and cytosolic fractions of the cell. Four isoenzymes designated ALDH IA, IB, IIA, and IIB have been isolated from canine liver via ammonium sulfate fractionation, ion-exchange chromatography, and affinity chromatography. Based on cell fractionation followed by enzyme isolation, ALDH IA and IB appear to be extramitochondrial whereas ALDH IIA and IIB appear to be mitochondrial in origin. ALDH IA has a high Km for acetaldehyde (3 mM) and propionaldehyde (4 mM). ALDH IB and IIA have Km values for acetaldehyde and propionaldehyde in the range of 4-60 microM. ALDH IIB has the lowest Km of the four isoenzymes for acetaldehyde and propionaldehyde (1-3 microM). All four isoenzymes have Km values for NAD in the range of 4-70 microM. ALDH IB and IIA are sensitive to inhibition by disulfiram whereas ALDH IA and IIB are resistant. Magnesium ions inhibit ALDH IA, IB, and IIA whereas ALDH IIB activity is stimulated approximately 2-fold. Magnesium ions do not affect molecular weight estimates of the isoenzymes as determined by gel filtration chromatography.

Effects of high hepatic acetaldehyde level following simultaneous administration of ethanol and cyanamide on liver function in rats

Extremely high concentrations of hepatic acetaldehyde were induced in rats by the intragastric administration of ethanol and cyanamide, an aldehyde dehydrogenase inhibitor; and these high levels were maintained for 4 weeks. Liver function tests, including mitochondrial ornithine carbamoyltransferase (OCT) and GOT activities, were within normal limits, and no increase in either hepatic triglyceride or collagen contents was observed. These results suggest that hepatotoxic effects of ethanol are not derived from the high acetaldehyde levels in the liver.

Ethanol feeding can produce secondary alterations in aldehyde dehydrogenase isozymes

Depressed hepatic aldehyde dehydrogenase (ALDH) activity levels have been observed in alcoholics, but whether the deficit is primary or secondary in nature remains controversial. In this study, we examined liver ALDH in rodent (rat) and primate (baboon) animal models pair-fed nutritionally adequate ethanol or isocaloric carbohydrate containing liquid diets. Both species show qualitative changes in ALDH isozymes after ethanol consumption. The changes include alterations in isozyme patterns seen upon electrofocusing and decreased responsiveness to the ALDH inhibitor, disulfiram. The subcellular locus of most of the changes is cytosolic in the baboon and mitochondrial in the rat. Study of partially purified (enriched) baboon cytosolic ALDH confirmed changes seen in the original cytosols and kinetic characterization of the enriched enzyme revealed a 9-fold higher Km for acetaldehyde in ALDH from an ethanol treated animal. We note that qualitative and quantitative changes secondary to ethanol treatment in the primate model closely parallel those described in human alcoholics.

A report of unusually high blood ethanol and acetaldehyde levels in two surviving patients

Two men with unusually high blood acetaldehyde levels of 750 and 2410 micrograms/dl presented only mild symptomatology. Their blood ethanol levels, 730 and 1121 mg/dl, were also extraordinarily high. However, liver function tests demonstrated no abnormalities.

Blood acetaldehyde concentration gradient between hepatic and antecubital venous blood in ethanol-intoxicated alcoholics and controls

After ethanol (0.8 g kg-1 body weight orally) significant concentrations of acetaldehyde (2-20 mumol 1(-1] were found in hepatic venous blood of moderately intoxicated non-alcoholic male Caucasians in spite of the absence of detectable levels (less than 2 mumol 1(-1] in simultaneously taken antecubital blood. In thirteen chronic alcoholics the elevation of blood acetaldehyde was more constant in the hepatic than in the peripheral vein. Fructose infusion caused a marked elevation of acetaldehyde both in the hepatic and peripheral vein of four controls, but not of four alcoholics, who eliminated ethanol about 50% faster than controls. The rate of disappearance of acetaldehyde from sampled and in vitro incubated hepatic venous blood was similar to that observed after addition of acetaldehyde in vitro to ethanol-free control blood (2 nmol ml-1 min-1 at 20 mumol 1(-1) acetaldehyde; Km about 30 mumol 1(-1]. Uptake of acetaldehyde in blood was calculated to explain maximally 30-40% of the concentration gradient between central and peripheral blood.

Ethanol and lipids

The interaction of ethanol with lipid metabolism is complex. When ethanol is present, it becomes a preferred fuel for the liver and displaces fat as a source of energy. This favors fat accumulation. In addition, the altered redox state secondary to the oxidation of ethanol promotes lipogenesis, for instance, through enhanced formation of acylglycerols. The depressed oxidative capacity of the mitochondria injured by chronic alcohol feeding also contributes to the development of the fatty liver. Accumulation of fat acts as a stimulus for the secretion of lipoproteins and the development of hyperlipemia. Hyperlipemia may also be facilitated by the proliferation of the endoplasmic reticulum after chronic ethanol consumption and the associated increase of enzymes involved in the production of triglycerides and lipoproteins. The propensity to enhance lipoprotein secretion is offset, at least in part, by a decrease in microtubules and an impairment of the secretory capacity of the liver. The level of blood lipids depends on the balance between these two opposite changes: At the early stage of alcohol abuse, when liver damage is still small, hyperlipemia will prevail, whereas the opposite occurs with severe liver injury. When hyperlipemia occurs, it involves all lipoprotein classes, including high density lipoprotein (HDL). The latter have been suggested to be responsible for the lower incidence of coronary complications of moderate drinkers compared to teetotalers, but in fact, the subtype of HDL involved (HDL3) differs from the HDL2 subtype associated with protection.

Metabolism and metabolic effects of alcohol

The author provides an excellent overview of the three major pathways for the metabolism of ethanol. Many of the toxic effects of ethanol can be attributed to two specific products, hydrogen and acetaldehyde, and these effects are explored in detail.

Subcellular localization of acetaldehyde dehydrogenase in human liver

The subcellular distribution of aldehyde dehydrogenase activity was determined in human liver biopsies by analytical sucrose density-gradient centrifugation. There was bimodal distribution of activity corresponding to mitochondrial and cytosolic localizations. At pH 9.6 cytosolic aldehyde dehydrogenase had a lower apparent Kappm for NAD (0.03 mmol l-1), than the mitochondrial enzyme (Kappm NAD = 1.1 mmol l-1). Also, the pH optimum for cytosolic aldehyde dehydrogenase activity (pH 7.5) was lower than that for the mitochondrial enzyme activity (pH 9.0), and the cytosolic enzyme activity was more sensitive to inhibition by disulfiram in vitro. Disulfiram (40 mumol l-1) caused a 70% reduction in cytosolic aldehyde dehydrogenase activity, but only a 30% reduction in mitochondrial enzyme activity after 10 min incubation. The liver cytosol may therefore be the major site of acetaldehyde oxidation in vivo in man.

Determinants of blood acetaldehyde level during ethanol oxidation in chronic alcoholics

We analyzed the blood alcohol and acetaldehyde concentrations in nine alcoholics and four healthy nonalcoholic controls during and after an intravenous infusion of a high and a low dose of alcohol. In the alcoholics, the mean rates of plasma ethanol disappearance were significantly higher than in nonalcoholic controls. In the control subjects, the blood acetaldehyde levels were, in general, below the detection limit (less than 0.5 microM), but in sharp contrast to this, an elevated blood acetaldehyde during ethanol infusion was found in 6/9 alcoholics. Peak blood acetaldehyde values were higher after the high than the low dose of alcohol. Fructose infusion significantly enhanced the rate of plasma ethanol disappearance both in controls and in alcoholics, and this was usually associated with a significant elevation of blood acetaldehyde level. The maximal specific activities (expressed as milliunits/mg og protein) of alcohol, lactate, and aldehyde dehydrogenases in liver were significantly lower in alcoholics than in controls. Even more importantly, the peak blood acetaldehyde correlated negatively with the activity of hepatic "low-Km" aldehyde dehydrogenase. Our results suggest that the main reason for blood acetaldehyde elevation seen in these chronic alcoholics is their impaired capacity to metabolize acetaldehyde. This may be further accentuated by the increased rate of ethanol oxidation.

Determination of aspartate aminotransferase isoenzymes in hepatic diseases--preliminary findings

The study sought to establish a relationship between the AST isoenzyme levels in serum and degree of hepatic damage, by using a new and simple immunochemical method for the differential determination of the isoenzymes. Sixty-nine patients with various hepatic diseases were studied. During hepatic damage, cytoplasmic isoenzyme (s-AST) is found in greater quantities than mitochondrial isoenzyme (m-AST), but the m-AST level increases to a greater extent in acute liver diseases. However, m-AST in alcoholic hepatitis is higher than expected from the total AST (t-AST) values. The ratio of m-AST to t-AST seems to discriminate alcoholic hepatitis from other liver diseases.