beta-Oxidation in human alcoholic and non-alcoholic hepatic steatosis

1. The CoA and carnitine ester intermediates of mitochondrial beta-oxidation have not previously been quantified in liver disease, although there is some evidence that beta-oxidation is inhibited in alcoholic fatty liver. Mitochondria were isolated from needle liver biopsies from normal subjects, from patients with alcoholic fatty liver and patients with fatty liver of other aetiologies, incubated with 60 mumol/l [U-14C]hexadecanoate and the resultant CoA and carnitine esters were measured. 2. Although there was no significant difference in beta-oxidation flux between the patient groups, there was a significant rise in the proportion of 3-hydroxyacyl-CoA and 2-enoyl-CoA esters in patients with alcoholic fatty liver compared with normal subjects, and in patients with non-alcoholic fatty liver, suggesting an inhibition at the level of 3-hydroxyacyl-CoA dehydrogenase activity. 3. In alcoholic patients this difference could not be accounted for on the basis of the measured activity of short and long-chain 3-hydroxyacyl-CoA dehydrogenases, and it is suggested that either an inhibition of complex I activity or diminished amounts of ubiquinone are likely to be responsible for the observed accumulation of CoA and carnitine esters, which may contribute to the accumulation of triacylglycerols in alcoholic steatosis. In fatty liver of other aetiologies, short- and long-chain 3-hydroxyacyl-CoA dehydrogenase activities were decreased.

Activity and subcellular distribution of phosphatidate phosphohydrolase (EC 3.1.3.4) in alcoholic liver disease

A micromethod was developed to assay the hepatic activity and subcellular distribution of phosphatidate phosphohydrolase (PAH, EC 3.1.3.4), an important regulatory enzyme in triacylglycerol synthesis, in human needle biopsy specimens. In normal liver PAH is predominantly cytosolic in distribution, but on treatment with oleic acid it shifts to the membranous compartments of the cell, its physiologically active site. The hepatic specific activity of PAH was similar in controls and patients with fatty liver but significantly more of the enzyme was associated with the membranous compartments in patients with severe alcoholic fatty liver. These observations may explain the enhanced rates of triacylglycerol synthesis observed in these patients and may be implicated in the pathogenesis of alcoholic fatty liver.

Association between restriction fragment length polymorphism of the human cytochrome P450IIE1 gene and susceptibility to alcoholic liver cirrhosis

OBJECTIVES

Cytochrome P450IIE1 (P450IIE1) is involved in ethanol metabolism and in the metabolic activation of carcinogenic nitrosoamines. The purpose of our investigation was to determine whether P450IIE1 restriction fragment length polymorphisms (RFLP) were associated with the development of alcoholic cirrhosis in Japanese alcoholics.

METHODS

We determined the human P450IIE1 RFLP with the restriction endonucleases, RsaI and PstI, using the polymerase chain reaction (PCR) on lymphocytes from 82 male Japanese alcoholics. Twenty patients had alcoholic fatty liver or nonspecific reaction (nonfibrotic group), and 62 had severe hepatic fibrosis or liver cirrhosis (fibrotic group).

RESULTS

PCR-RFLP revealed three P450IIE1 genotypes, namely, heterozygotes [type B (c1/c2)] and two homozygotes [types A (c1/c1) and C (c2/c2)]. Homozygotes (c1/c1) were significantly more prevalent in the fibrotic group than in the nonfibrotic group (p < 0.05).

CONCLUSIONS

This result suggests that susceptibility to alcoholic liver cirrhosis may be associated with the RsaI and PstI polymorphism of the P450IIE1 gene.

The activity of the metabolic form of hepatic phosphatidate phosphohydrolase correlates with the severity of alcoholic fatty liver in human beings

Increased esterification of fatty acids to triglyceride is common to most of the mechanisms proposed to explain the causation of alcoholic fatty liver. However, it is unclear whether this is caused by increased substrate supply or whether direct stimulation of the enzymes of the esterification pathway occurs after excessive alcohol intake. The rate-limiting step in triglyceride synthesis is catalyzed by the enzyme phosphatidate phosphohydrolase, which is present in the cytosol and microsomes and is sensitive to inhibition by N-ethylmaleimide. This enzyme is physically distinct from a second form of phosphatidate phosphohydrolase that is located predominantly in the plasma membrane, is insensitive to N-ethylmaleimide inhibition and has a putative role in cell-signaling. We have investigated whether the activity of the N-ethylmaleimide-sensitive ("metabolic") form of phosphatidate phosphohydrolase is increased in patients with alcoholic liver disease and whether any increased activity correlates with the severity of steatosis. N-ethylmaleimide-sensitive and -insensitive phosphatidate phosphohydrolase activities were measured in needle liver biopsy specimens from 42 alcoholic patients and 6 patients with primary biliary cirrhosis and in wedge biopsy specimens from 6 normal patients undergoing routine cholecystectomy. Steatosis was "scored" on coded slides from 0 to 3. N-ethylmaleimide-sensitive activity was higher in alcoholic biopsy specimens scoring 3 (3.25 +/- 0.4 units/mg protein, n = 10) than in those scoring either 0 (1.21 +/- 0.2, n = 14) or 1 to 2 (1.58 +/- 0.2, n = 18), and it was also higher than in biopsy specimens from normal and primary biliary cirrhosis patients (1.65 +/- 0.3, n = 12; p < 0.0001, analysis of variance).(ABSTRACT TRUNCATED AT 250 WORDS)

Beta-hexosaminidase activity in alcoholic fatty liver and in CCl4-induced liver fibrosis of the rat

beta-Hexosaminidase (Hex) activity was previously found to be increased in the sera of patients with liver cirrhosis, cholestasis and acute alcohol intoxication, as well as in rats with CCl4-induced liver cirrhosis. We studied this enzymatic activity in the sera and liver tissue of rats with alcoholic fatty liver due to prolonged alcohol intake and CCl4-induced liver fibrosis in association with moderate alterations in liver function tests. Serum and liver Hex activity did not show any significant change in both experimental models. These data suggest that Hex is not an alcohol-induced enzyme, and that severe, but not moderate, liver damage can determine the increase in this lysosomal enzymatic activity.

Angiotensin-converting enzyme activity in experimental alcoholic fatty liver of the rat

Angiotensin-converting enzyme (ACE) activity was found increased in serum of patients with chronic alcoholism. We studied this enzymatic activity in serum and liver tissue of rats with alcoholic fatty liver due to prolonged intake of ethanol with a liquid diet, according to De Carli and Lieber. Serum and liver ACE activity did not show any significant increase in rats with alcoholic fatty liver when compared with controls, whereas gamma-glutamyltransferase activity exhibited a striking enhancement in serum and liver. Our data suggest that ACE is not an alcohol-induced enzyme in the experimental rat model.

Inducing efficacy of ethanol on hepatic drug metabolizing enzymes in patients

In liver biopsy material of eighty-nine patients with suspected liver disease the drug-metabolizing function was investigated. The capacity of the liver to oxidatively metabolize drugs was assessed by determination of cytochrome P-450 dependent monooxygenase activity in vitro. The biotransformational function of these microsomal enzymes was tested with compounds representing the activity of oxidative drug metabolism (7-ethoxycoumarin, p-nitroanisol and cytochrome c). From the eight-nine patients sixty-one had various liver diseases not related to ethanol and twenty-eight abused ethanol. When both groups were matched for age, sex, smoking, treatment with sedatives, drugs and degree of liver damage the alcoholic group had significantly higher activities of 7-ethoxycoumarin O-deethylase (EOD: 76.9 +/- 31.1 pmol min-1 mg-1 protein, mean +/- SD) than the non-alcoholic liver disease group (42.7 +/- 14.1). The inducing effect of ethanol was most striking on the EOD activity, less for the O-demethylation of p-nitroanisol (PNA) and not present for the NADPH-cytochrome c reductase. The induced patients were analysed in detail to find out which factors were responsible for the observed scatter of enzyme activities within the alcoholic group. Alcoholics with fatty liver (n = 7) had the highest EOD activities (108.9 +/- 25.0), patients with alcoholic hepatitis (n = 10) had significantly less activity (66.0 +/- 1.9) than the former group. However, alcoholics without liver damage (n = 6) had activities not significantly different (46.0 +/- 15.8) from controls (39.4 +/- 9.1). These subgroups among the alcoholics were comparable in terms of sex, age, smoking and drinking habits.(ABSTRACT TRUNCATED AT 250 WORDS)

Ascorbic acid chronic alcohol consumption in the guinea pig

Protection against the toxic effects of chronic alcohol consumption was observed in male guinea pigs maintained on a high-ascorbic-acid diet (vitamin C-deficient chow plus 2.0 mg ascorbic acid/ml drinking water) as compared to animals on a low-ascorbic-acid diet (vitamin C-deficient chow and from 0.025 to 0.050 mg ascorbic acid/ml drinking water). Alcohol was orally administered to the guinea pigs at a dose of 2.5 g/kg for up to 14 weeks. Levels of serum aspartate aminotransferase and serum alanine aminotransferase were significantly elevated in animals on the low-ascorbic-acid diet that received alcohol, 120 and 250%, respectively. In contrast, in animals on the high-ascorbic-acid diet that received alcohol, levels of alanine aminotransferase were not significantly elevated and levels of aspartate aminotransferase were elevated 50%. In addition, some of the animals on the low-ascorbic-acid diet that received alcohol for 12 to 14 weeks developed hepatic steatosis and necrosis, whereas none of the animals on the high-ascorbic-acid diet that received alcohol for the same length of time manifested these changes.

[Hepatic GOT and GPT activities in patients with various liver diseases--especially alcoholic liver disease]

GOT and GPT activities were measured in percutaneous needle biopsy specimens of human liver tissue from 98 cases including normal subjects and patients with various liver diseases. Hepatic GOT activity was markedly decreased in liver tissue of patients with nonalcoholic liver cirrhosis. Hepatic GPT activity was markedly decreased in liver tissue of patients with alcoholic liver cirrhosis. The GOT/GPT ratio in liver tissue was increased in patients with alcoholic liver cirrhosis (5.32 +/- 2.03) and alcoholic liver disease (4.78 +/- 2.43). The increased SGOT/SGPT ratio in patients with alcoholic liver disease is due to primarily to the increased LGOT/LGPT ratio.

Activities and subcellular distributions of hepatic lipases in control subjects and in patients with alcoholic fatty liver

Human hepatic lipase activities were studied in needle biopsy specimens by fluorogenic and radioisotopic assay methods. Using analytical subcellular fractionation by sucrose density gradient centrifugation a lysosomal acid lipase, with pH optimum of 4.0, and an endoplasmic reticulum alkaline lipase, with pH optimum of 8.5, were demonstrated with the fluorogenic assay. The apparent Km of the acid lipase was 17 mumol/l by the fluorogenic method and 23 mmol/l by the radioisotopic method. The values for alkaline lipase were 94 mumol/l and 1.4 mmol/l respectively. Assay of these activities in biopsies from 16 control subjects and 42 chronic alcoholics showed increasing activity with increasing hepatic fatty infiltration when the fluorogenic assay was used: no differences were demonstrated with radioisotopic assay. These results suggest that depressed lipolysis due to a relative deficiency of triglyceride lipase is not a causal factor in triglyceride accumulation in chronic alcoholic fatty liver.

Severe and progressive steatosis and focal necrosis in rat liver induced by continuous intragastric infusion of ethanol and low fat diet

Blood alcohol levels (BAL) were maintained at high levels (overall mean +/- S.D. achieved in 14 alcoholic rats was 216.0 +/- 120.1 mg%) in male Wistar rats for 15 to 85 days by continuous intragastric infusion of ethanol and nutritionally defined low fat liquid diet. The ethanol intake was progressively increased from 32% of total calories up to 41.4% in order to maintain high BAL. Pair-fed animals received isocaloric glucose solution and the liquid diet. Despite the low level of dietary fat (4.9% of total calories), histopathological evaluation of the liver revealed severe and progressive fatty infiltration in the alcoholic rats. In addition, following 30 days of intoxication, one third of the animals showed focal necrosis with mononuclear cell infiltration in centrilobular areas of the livers. This was correlated with the markedly elevated levels of SGOT and SGPT in these animals. Pair-fed controls showed no abnormality in the morphology of liver or blood chemistry. Chemical quantitation of liver triglycerides confirmed the histological observation, with triglyceride levels of 61.51 +/- 16.45 and 89.61 +/- 5.94 mg per gm at 30 and 85 days, respectively. Most importantly, the degree of steatosis was tightly and significantly correlated with the mean BAL achieved (r = 0.80, p less than 0.001). These data represent the first confirmation of the hypothesis that continuously high BAL correlate with the severity of alcohol-induced liver pathology.

Comparative diagnosis of alcoholic liver diseases by multivariate and histological analysis

Sixty-seven cases of alcoholic liver disease were histologically classified into 4 groups: alcoholic liver cirrhosis (ALC), alcoholic hepatitis (AH), alcoholic liver fibrosis (ALF) and alcoholic fatty liver (AFL). They were statistically reclassified by the likelihood method using age, total alcohol intake, hepatomegaly and 12 liver function tests. A score table for likely diagnosis was constructed from the incidences of each range. The cases were re-evaluated using the score table, with an overall correct diagnosis rate of 73%. The best combination of 5 parameters included the indocyanine green plasma disappearance rate, total alcohol intake, cholesterol, choline esterase and glutamic oxaloacetic transaminase/glutamic pyruvic transaminase ratio. A correct diagnosis rate of 75% was attained using these 5 parameters, and 94% of patients were correctly diagnosed by the first or the second likelihood diagnosis. Differential diagnosis of alcoholic liver diseases was easily and confidently obtained with the likelihood score table.

[Metabolic aspects of alcoholic liver damage: 1984/5 update. 1. Epidemiology and alcohol metabolism]

In western industrialized countries ethanol is an important etiologic factor in the development of cirrhosis of the liver. Metabolic, immunologic and physico-chemical alterations of the hepatocyte due to ethanol are involved in the pathogenesis of alcoholic liver disease. However, the mechanisms by which ethanol damages the liver are far from clear. During the last two decades, the effect of ethanol on multiple biochemical pathways of the hepatocyte has been investigated intensively. The present paper is focusing on the metabolic aspects of alcoholic liver disease. In the first part of the review, special emphasis has been led on the metabolites of ethanol oxidation, while in the second part microsomal enzyme induction due to alcohol has been discussed. More than 90% of ethanol metabolism takes place in the liver via cytoplasmic alcoholdehydrogenase (ADH) and via a microsomal ethanol oxidizing system (MEOS). The products of these reactions are reduced nicotinadenine dinucleotide phosphate (NADH), acetaldehyde and acetate. NADH alters the redox state of the liver cell favouring all reductive processes. This shift in metabolic pathways results in hyperlactacidaemia, lactacidosis, ketosis and hyperuricaemia. Disturbances of the carbohydrate metabolism may lead either to hypo- or hyperglycaemia. The altered redox state also influences the metabolic pathways of lipid metabolism leading to lipid accumulation within the hepatocyte which can be morphologically observed as alcoholic fatty liver. In addition, porphyrin and collagen metabolism is also affected by the increased NADH/NAD+ ratio. On the other hand, acetaldehyde damages the microtubular system and the mitochondria. Acetaldehyde may also be responsible for the increased lipidperoxidation after chronic ethanol ingestion.

Alcohol-induced mitochondrial changes in the liver

The chronic ingestion of ethanol results in liver-cell damage, and characteristic features of this injury are the marked alterations in both the functions and morphology of the mitochondria. Morphologically, the changes observed in human alcoholics and experimental animals appear similar. Bizarrely shaped mitochondria and megamitochondria are detected at the fatty liver stage and persist as the disease progresses. As yet, however, no correlation has been found between the severity of these morphological changes and the development of cirrhosis. Analysis of the mitochondrial membranes indicates that ethanol consumption produces changes in both the protein and lipid composition of the membrane. Profound decreases in the components of the respiratory chain have been detected, and these changes are associated with marked depressions in the activity of NAD+-linked dehydrogenases, cytochrome oxidase, and the ATP synthetase complex. On the other hand, no consistent pattern has emerged as to the effect of chronic ethanol consumption on the composition of the membrane phospholipids. Many of the changes appear to be dependent on the sex of the animal, the dietary status, and the duration of ethanol intake, and are suggestive of changes in fatty acid desaturase activity. Mitochondria isolated from ethanol-fed rats displayed impaired respiration and a lowered steady-state rate of ATP synthesis. Whether or not these functional changes are directly related to alterations in the physical properties of the membranes remains to be resolved. This marked depression of respiratory functions in isolated mitochondria was not reflected by a significant decrease in O2 consumption by the livers of ethanol-fed animals.

Aldehyde dehydrogenase (E.C. 1.2.1.3) in chronic alcoholic liver diseases

Acetaldehyde dehydrogenase (ALDH) activity in liver biopsy specimens was considerably reduced in alcoholic cirrhosis (n = 5), elevated in alcoholic fatty liver (n = 11)--probably due to enzyme induction--only slightly elevated in alcoholic hepatitis (n = 6), but unaffected in non-alcoholic liver diseases (n = 23) in comparison with specimens obtained from patients with minimal liver lesions. We will argue as a working hypothesis that alcoholics with induced ALDH activity will mainly develop fatty liver, whereas reduced hepatic ALDH appears to be a reason for elevated acetaldehyde levels followed by additional liver injury and progression at least for alcoholic cirrhosis.

Hepatic gamma-glutamyltransferase activity in alcoholic fatty liver: comparison with other liver enzymes in man and rats

Compared with controls, patients with alcoholic fatty liver showed a significant increase of gamma-glutamyltransferase activity both in the liver and serum, whereas alkaline phosphatase activity was raised only in the liver but not in the serum. The activities of other enzymes such as aspartate aminotransferase, alanine aminotransferase and glutamate dehydrogenase remained virtually unchanged in the liver of patients with alcoholic fatty liver but were strikingly enhanced in the serum. The hepatic and serum alterations of enzymic activities observed in patients with alcoholic fatty liver could be reproduced in the rat model of alcoholic fatty liver only for gamma-glutamyltransferase but not for the other enzymes tested, substantiating evidence that the animal model may serve as an appropriate tool for studying interactions between alcohol and gamma-glutamyltransferase. The present experiments also indicate that the primary cause for increased serum gamma-glutamyltransferase activities associated with prolonged alcohol consumption is hepatic enzyme induction rather than liver cell injury.

Hepatic ADH and ALDH isoenzymes in different racial groups and in chronic alcoholism

A method has been developed for simultaneous analysis of alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) isoenzymes in small (2.5 mg) liver biopsy cores by starch gel electrophoresis. All the currently recognized hepatic isoenzymes coded by ADH1, ADH2, ADH3 and ADH4 can be detected as can the five ALDH isoenzymes. Using this technique we have investigated the isoenzyme composition of liver samples from English and Chinese subjects and a group of chronic alcoholics. Pronounced racial differences in frequency of ADH2 and ALDH phenotypes were found--only 2 (4%) of English controls had the "atypical" ADH2 variant whereas this was present in 42 (84%) of Chinese subjects, and whereas all the English subjects had the rapidly migrating mitochondrial isoenzyme of ALDH, this was absent in 27 (54%) of Chinese. No differences in ADH or ALDH phenotype were seen in the chronic alcoholics, all of whom were of English origin, compared with the English controls, but there was a reduction in overall ALDH activity and particularly in the mitochondrial isoenzyme in those with cirrhosis. The reduction in ALDH activity is probably acquired; by limiting acetaldehyde oxidation it could be responsible for the rapid deterioration in liver function in patients who continue drinking excessively.

Biochemical mode of action of a hepatoprotective drug: observations on (+)-catechin

(+)-Catechin inhibits the hepatic lipid accumulation resulting from chronic ethanol ingestion in the rat. Experiments have been carried out to determine the mechanisms underlying this effect. Ethanol was administered (2.0 g/kg intraperitoneally) to Wistar rats and 90 min later 1 microCi [U-14C] palmitic acid injected intraperitoneally. Animals were sacrificed 10 min after injection of palmitate and the liver freeze-clamped. Ethanol caused a 250% increase in the hepatic lactate:pyruvate (L:P) ratio and a 100% increase in the amount of [U-14C] palmitate incorporated into the hepatic lipids when compared with controls. Pretreatment of animals with (+)-catechin (200 mg/kg orally) at 24 and 0 hr before ethanol caused significant reductions in the L:P ratio and amount of radioactivity incorporated into hepatic lipids, when compared with animals receiving ethanol alone. (+)-Catechin also stimulated 14CO2 production from [1-14C] palmitate by liver slices taken from rats 90 min after ethanol administration. Thus, (+)-catechin appears to mediate its effect on fat accumulation partly by correcting the ethanol-induced alterations in hepatic redox state as there is no evidence of the drug inhibiting ethanol metabolism.