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Biomedical subjects

C S Lieber

Publications and source records attributed to C S Lieber.

At least 163 records · Page 9Linked to original sources
PubMed1991

Contribution of exogenous ethanol and endogenous substrates to acetaldehyde-adduct formation in liver injury.

Acetaldehyde was found to be transported in the blood mainly bound reversibly to 2 components of the red blood cells (RBC): a) hemoglobin, which provides binding of a high affinity, but low capacity, and b) a non-protein component (presumably cysteine), which has a lower affinity but a higher capacity. In alcoholics, the main increase in RBC-acetaldehyde binding occurred in the protein-free fraction, in association with a marked increase in RBC-cysteine. Elevated RBC-acetaldehyde persisted for at least 2 weeks after alcohol withdrawal in 83% of the blood samples from alcoholics. Even in the absence of alcohol consumption, liver injury increased acetaldehyde from sources other than ethanol. This was associated with high serum antibody titers against acetaldehyde adducts. In an animal model of non-alcoholic liver cirrhosis, a target protein for the formation of acetaldehyde adducts appears to be procollagen type I.

Acetaldehyde↗
PubMed1991

Biochemical mechanisms of alcohol-induced hepatic injury.

Three decades of research in ethanol metabolism have established that alcohol is hepatotoxic not only because of secondary malnutrition but also through metabolic disturbances associated with the oxidation of ethanol. Some of these alterations are due to redox changes produced by the NADH generated via the alcohol dehydrogenase (ADH) pathway which in turn affects the metabolism of lipids, carbohydrates, proteins and purines. Exaggeration of the redox change by the relative hypoxia which prevails physiologically in the perivenular zone explains the exacerbation of the ethanol-induced lesions in zone III. In addition to ADH, ethanol can be oxidized by liver microsomes: studies over the last twenty years have culminated in the molecular elucidation of the ethanol-inducible cytochrome P450 (P450IIE1) which contributes not only to ethanol metabolism and tolerance, but also to the toxicity of various xenobiotics. Their activation by P450IIE1 now provides an understanding for the increased susceptibility of the heavy drinker to the toxicity of industrial solvents, anesthetic agents, commonly prescribed drugs, over-the-counter analgesics, chemical carcinogens and even nutritional factors such as vitamin A. Ethanol causes not only vitamin A depletion but it also enhances its hepatoxicity. Furthermore, induction of the microsomal pathway results in increased acetaldehyde production. Acetaldehyde, in turn, causes injury through the formation of protein adducts, resulting in antibody production, enzyme inactivation, decreased DNA repair, and is associated with a striking impairment of the capacity of the liver to utilize oxygen. Acetaldehyde also promotes glutathione depletion, free-radical mediated toxicity, lipid peroxidation and hepatic collagen synthesis. This new understanding may eventually improve drug and nutritional therapy.

Acetaldehyde↗
PubMed1991

Alcohol and fibrogenesis.

In addition to fibrosis in response to necrosis and inflammation, alcohol may promote fibrogenesis directly, resulting in pericellular, perisinusoidal and perivenular fibrosis, in association with increased collagen mRNA. Acetaldehyde (produced in increased amounts because of the selective induction of cytochrome P450IIE1) stimulates collagen formation from either myofibroblasts, Ito cells or fibroblasts. One postulated mechanism is adduct formation of acetaldehyde with intracellular proteins, possibly stabilized by the NADH generated upon ethanol oxidation. The latter also increases lactate which might inhibit proline oxidase activity and increase available proline. During the initial stage of alcohol consumption, collagenase activity is increased, in keeping with enhanced collagen production. In later stages, however, there is a secondary decrease of collagenase activity; its deficiency relative to synthesis may also promote collagen deposition. In the early stage of alcohol induced fibrosis, collagens type I and type III accumulate, whereas later, type I predominates. Both can be formed in vitro by Ito cells, but cultured hepatocytes produce mainly type III. Immunohistochemical techniques revealed the deposition of type III procollagen in the extrahepatic collagen fibrils. Its degradation, as well as its enhanced synthesis, contribute to the appearance of procollagen III peptides in the blood. Their measurement by Fab fragments of the antibody is useful to assess the degree of fibrosis and to detect perivenular fibrosis, a precirrhotic lesion. In the baboon model, polyunsaturated lecithin was found to be effective in opposing alcohol-induced fibrosis.

Alcoholism↗
PubMed1991

Induction of cytochrome P450IIE1 in the obese overfed rat.

Cytochrome P450IIE1 (IIE1) is a microsomal xenobiotic-activating enzyme that is inducible not only by various chemical agents but also by fasting and diabetes. Using a rat model that mimics human obesity, we have found that hepatic IIE1 levels are also increased by this common clinical disorder. Liver microsomes from rats made obese by feeding with an energy-dense diet displayed elevated aggregate P450 content (+28%) and enhanced catalytic activities associated with IIE1, including low-Km N-nitrosodimethylamine demethylation (+66%), aniline hydroxylation (+52%), p-nitrophenol hydroxylation (+170%), and acetaminophen-cysteine conjugate formation (+28%). In contrast, obesity had no significant effect on cytochrome b5 content, P450 reductase activity, benzphetamine demethylation, or erythromycin demethylation, with the latter two reactions being linked with rat IIC11 and IIIA1, respectively. The enhancement of IIE1-dependent drug-metabolizing activities noted in liver microsomes from obese rats was paralleled by a similar increase (111%) in hepatic IIE1 protein content in these animals, as assessed on immunoblots developed with anti-hamster IIE1 IgG. Anti-IIE1-inhibitable rates of microsomal p-nitrophenol metabolism, a reaction highly correlated with IIE1 content (r = 0.88, p less than 0.01), were over 3-fold higher in obese rats than in nonobese controls, providing additional evidence for the obesity-related increase of hepatic IIE1. The induction of IIE1 by the pathophysiological condition of obesity may provide a biochemical basis for the increased incidence of occult liver disease and certain cancers noted in obese individuals.

Acetaminophen↗
PubMed1991

Acetaldehyde increases procollagen type I and fibronectin gene transcription in cultured rat fat-storing cells through a protein synthesis-dependent mechanism.

We previously reported that acetaldehyde increases the production of type I collagen in cultured rat fat-storing cells. We studied the regulation of this effect by determining the expression of procollagen type I, fibronectin and transforming growth factor-beta 1 messenger RNAs in passage 1 and 2 cultures of fat-storing cells exposed to acetaldehyde for up to 24 hr. By 6 hr, acetaldehyde increased the steady-state levels of alpha 1 procollagen type I messenger RNA 3.2-fold and of fibronectin messenger RNA 2.8-fold above control values. At 24 hr, messenger RNA levels remained elevated. In contrast, transforming growth factor-beta 1 messenger RNA steady-state levels remained unaltered by 6 hr, but increased 1.5-fold by 24 hr. Cycloheximide (0.3 mmol/L) completely inhibited the acetaldehyde effect when added at zero time but was less effective when added at 15 min. The effect of acetaldehyde was not modified when cells were cultured in the presence of the acetaldehyde dehydrogenase inhibitor cyanamide (100 mumol/L). Fat-storing cells were also cultured in the presence of lactate (5, 15 and 25 mmol/L) for 6 hr. At none of these concentrations was any effect seen on either alpha 1(I) procollagen or fibronectin messenger RNAs. In the presence of methylene blue, a scavenger of reducing equivalents, the effect of acetaldehyde on alpha 1(I) procollagen and fibronectin gene expression was totally inhibited. Transcription run-on assay showed that acetaldehyde increased both procollagen type I and fibronectin transcriptional activity threefold and 2.5-fold, respectively. We conclude that acetaldehyde increases alpha 1(I) procollagen and fibronectin gene expression through enhanced transcription by a mechanism dependent on newly synthesized proteins.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetaldehyde↗
PubMed1990

Acetaldehyde-collagen adducts in CCl4-induced liver injury in rats.

Circulating AC levels as well as antibodies against AC-protein adducts are increased in non-alcoholic liver injury. To identify the adducts, we used rats with CCl4-induced cirrhosis. Liver subcellular fractions were analyzed by immunochemical staining of protein slot blots and of electrophoretically separated proteins, transferred to nitrocellulose, using AC-protein adduct-specific antibodies. One reactive protein of about 200 kD was detected in the liver soluble fraction and in the cytosol of isolated hepatocytes and, to a lesser extent in the liver microsomes of CCl4-treated rats; in control animals, this reactivity was much weaker. The immunopositive AC adduct co-migrated with the beta 1,2 dimer of rat collagen type I; it was sensitive to digestion by a highly purified collagenase and also reacted with anti-rat collagen type I-specific IgG. In addition, comparison of peptides of the CNBr-digested, immunoprecipitated AC adduct with those of rat collagen type I revealed a high degree of similarity. Thus, AC adduct formation occurs in liver injury of non-alcoholic origin, and a target protein appears to be related to collagen type I, most likely the procollagen precursor.

Acetaldehyde↗
PubMed1990

Aspirin increases blood alcohol concentrations in humans after ingestion of ethanol.

Gastric first-pass metabolism of ethanol is an important determinant of blood alcohol concentrations. We studied five healthy volunteers after ingestion of ethanol (0.3 g/kg of body weight) and found that blood alcohol concentrations in the fed state (ie, 1 hour after a standard breakfast) were significantly higher when the subjects received 1 g of aspirin 1 hour before ingestion of ethanol than without the drug. In vitro, aspirin clearly decreased the activity of gastric alcohol dehydrogenase in human subjects and in rat models, but not that of hepatic alcohol dehydrogenase in rats. Furthermore, blood alcohol concentrations in rats were unaffected by ingestion of aspirin when ethanol was infused intravenously. Thus, aspirin may increase the bioavailability of ingested ethanol in humans, possibly by reducing ethanol oxidation by gastric alcohol dehydrogenase.

Adult↗
PubMed1990

High blood alcohol levels in women. The role of decreased gastric alcohol dehydrogenase activity and first-pass metabolism.

After consuming comparable amounts of ethanol, women have higher blood ethanol concentrations than men, even with allowance for differences in size, and are more susceptible to alcoholic liver disease. Recently, we documented significant "first-pass metabolism" of ethanol due to its oxidation by gastric tissue. We report a study of the possible contribution of this metabolism to the sex-related difference in blood alcohol concentrations in 20 men and 23 women. Six in each group were alcoholics. The first-pass metabolism was determined on the basis of the difference in areas under the curves of blood alcohol concentrations after intravenous and oral administration of ethanol (0.3 g per kilogram of body weight). Alcohol dehydrogenase activity was also measured in endoscopic gastric biopsies. In nonalcoholic subjects, the first-pass metabolism and gastric alcohol dehydrogenase activity of the women were 23 and 59 percent, respectively, of those in the men, and there was a significant correlation (rs = 0.659) between first-pass metabolism and gastric mucosal alcohol dehydrogenase activity. In the alcoholic men, the first-pass metabolism and gastric alcohol dehydrogenase activity were about half those in the nonalcoholic men; in the alcoholic women, the gastric mucosal alcohol dehydrogenase activity was even lower than in the alcoholic men, and first-pass metabolism was virtually abolished. We conclude that the increased bioavailability of ethanol resulting from decreased gastric oxidation of ethanol may contribute to the enhanced vulnerability of women to acute and chronic complications of alcoholism.

Adult↗
PubMed1990

S-adenosyl-L-methionine attenuates alcohol-induced liver injury in the baboon.

Chronic ethanol consumption by baboons (50% of energy from a liquid diet) for 18 to 36 mo resulted in significant depletion of hepatic S-adenosyl-L-methionine concentration: 74.6 +/- 2.4 nmol/gm vs. 108.9 +/- 8.2 nmol/gm liver in controls (p less than 0.005). The depletion was corrected with S-adenosyl-L-methionine (0.4 mg/kcal) administration (102.1 +/- 15.4 nmol/gm after S-adenosyl-L-methionine-ethanol, with 121.4 +/- 11.9 nmol/gm in controls). Ethanol also induced a depletion of glutathione (2.63 +/- 0.13 mumol/gm after ethanol vs. 4.87 +/- 0.36 mumol/gm in controls) that was attenuated by S-adenosyl-L-methionine (3.89 +/- 0.51 mumol/gm in S-adenosyl-L-methionine-methanol vs. 5.22 +/- 0.53 mumol/gm in S-adenosyl-L-methionine controls). There was a significant correlation between hepatic S-adenosyl-L-methionine and glutathione level (r = 0.497; p less than 0.01). After the baboons received ethanol, we observed the expected increase in circulating levels of the mitochondrial enzyme glutamic dehydrogenase: 95.1 +/- 21.4 IU/L vs. 13.4 +/- 1.8 IU/L; p less than 0.001, whereas in a corresponding group of animals given S-adenosyl-L-methionine with ethanol, the values were only 30.3 +/- 7.1 IU/L (vs. 9.6 +/- 0.7 IU/L in the S-adenosyl-L-methionine controls). This attenuation by S-adenosyl-L-methionine of the ethanol-induced increase in plasma glutamic dehydrogenase (p less than 0.005) was associated with a decrease in the number of giant mitochondria (assessed in percutaneous liver biopsy specimens), with a corresponding change in the activity of succinate dehydrogenase, a mitochondrial marker enzyme.(ABSTRACT TRUNCATED AT 250 WORDS)

Alanine Transaminase↗
PubMed1990

Acetaldehyde selectively stimulates collagen production in cultured rat liver fat-storing cells but not in hepatocytes.

Hepatocytes and fat-storing cells have been implicated in the production of collagen, under both normal and pathological conditions. In this study, short-term primary cultures of rat hepatocytes, maintained in a serum-free, hormonally defined medium without dexamethasone and cultured on a fibronectin-collagen type IV substratum, were used. Primary and passage 1 and 2 cultures of fat-storing cells maintained on tissue culture plastic were also studied. Hepatocytes produced significant amounts of collagen type III, but formation of collagen type I was not detectable. Laminin and collagen type IV production were very low. Hepatocytes maintained their ability to metabolize ethanol (at levels comparable to those observed at 2 hr) for at least 48 hr after plating and this metabolism was inhibited 86% to 95% by 4-methylpyrazole (1 mmol/L). Neither ethanol (50 mmol/L) nor acetaldehyde (175 mumol/L, initial concentration) had any effect on the production of collagen type III or laminin. Fat-storing cells (95% to 100% desmin-positive) produced significant amounts of both type I and type III collagen. Production of collagen type IV and laminin was very low. Metabolism of ethanol by these cultures was not detected. Addition of ethanol had no effect on collagen or laminin production in fat-storing cells. In contrast, acetaldehyde significantly increased the production of collagen type I, but did not alter the production of collagen type III, IV or laminin. Incorporation of 3H-proline into total protein was not affected by addition of ethanol or acetaldehyde to fat-storing cells or hepatocytes. Exposure of fat-storing cells to ethanol or acetaldehyde did not change 3H-collagen degrading activity in the media.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetaldehyde↗
PubMed1990

Attenuation of alcohol-induced hepatic fibrosis by polyunsaturated lecithin.

Characteristic features of alcoholic liver injury include fibrosis and striking membrane alterations, with associated phospholipid changes. To offset some of these abnormalities, a 10-yr study was conducted in baboons: 12 animals (eight females, four males) were fed a liquid diet supplemented with polyunsaturated lecithin (4.1 mg/kcal) for up to 8 yr, with either ethanol (50% of total energy) or isocaloric carbohydrate. They were compared with another group of 18 baboons fed an equivalent amount of the same diet (with or without ethanol), but devoid of lecithin. In the two groups, comparable increases in lipids developed in the ethanol-fed animals, but striking differences in the degree of fibrosis were seen. Whereas at least septal fibrosis (with cirrhosis in two) and transformation of their lipocytes into transitional cells developed in seven of the nine baboons fed the regular diet with ethanol, septal fibrosis did not develop in any animals fed lecithin (p less than 0.005). They did not progress beyond the stage of perivenular fibrosis (sometimes associated with pericellular and perisinusoidal fibrosis) and had a significantly lesser activation of lipocytes to transitional cells. Furthermore, when three of these animals were taken off lecithin, but continued on the same amount of the ethanol-containing diet, they rapidly (within 18 to 21 mo) progressed to cirrhosis, accompanied by an increased transformation of their lipocytes to transitional cells. These results indicate that some component of lecithin exerts a protective action against the fibrogenic effects of ethanol. Because we had previously found that choline, in amounts present in lecithin, has no comparable action, the polyunsaturated phospholipids themselves might be responsible for the protective effect.

Animals↗
PubMed1990

Immunohistochemical detection of proliferating lipocytes in regenerating rat liver.

For the detection of proliferating lipocytes in regenerating liver, partially hepatectomized rats were injected intraperitoneally with 5-bromo-2'-deoxyuridine (BrdUrd, 50 mg/kg body weight) and killed 1 h later. Acetone-fixed frozen liver sections were used for the simultaneous detection of cytoplasmic desmin and BrdUrd-labelled nuclei of lipocytes using double immunohistochemical procedures. The best results were obtained with the sequences: rabbit anti-desmin----biotinylated anti-rabbit IgG----avidin-biotin-peroxidase complex----3,3'-diaminobenzidine tetrahydrochloride, followed by DNA denaturation----mouse anti-BrdUrd----anti-mouse IgG----peroxidase-anti-peroxidase complex----4-chloro-1-naphthol. With this method, cytoplasmic desmin was stained a brown colour, which sharply contrasted with the blue-stained BrdUrd-labelled nuclei. Unlabelled nuclei appeared green after counterstaining with methyl green. No cross-reaction between immunoreagents of desmin and BrdUrd stainings was observed. The labelling index of lipocytes peaked (25.7 per cent) 48 h after partial hepatectomy, whereas it was 3.7 per cent in normal rat liver.

Animals↗
PubMed1990

Immunohistochemical localization of ethanol-inducible P450IIE1 in the rat alimentary tract.

To determine whether P450IIE1, a microsomal P450 enzyme inducible by ethanol in the liver, is also present and inducible in the alimentary tract, corresponding frozen tissue sections were prepared from rats pair-fed liquid diets containing 36% of total calories as either ethanol or carbohydrate (control) for 3 weeks. Immunohistochemical staining was performed using the peroxidase-antiperoxidase method after tissue sections were reacted with antibody against human P450IIE1. In control animals, immunoreactive P450IIE1 was detected only in duodenal and jejunal villous cells. After ethanol treatment, the content of P450IIE1 increased in duodenal and jejunal villi, and the enzyme was now also found in squamous epithelial cells of the cheek mucosa, tongue, esophagus, and forestomach, and in surface epithelium of the proximal colon. P450IIE1 was neither expressed nor induced by alcohol in the epithelium of stomach fundic and antral mucosa, ileum, distal colon, and rectum. When considered together with the xenobiotic activation properties of P450IIE1, these results may partly explain why alcohol abuse is a risk factor for cellular damage or cancer or both in those alimentary tract tissues in which P450IIE1 is inducible by chronic ethanol intake.

Animals↗
PubMed1990

Interactive effects of dietary protein and ethanol on rat pancreas. Protein synthesis and enzyme secretion.

Nutritional factors, especially the protein and fat content of the diet, may alter the likelihood of pancreatic injury after a number of insults, including chronic ethanol intake. This issue was studied experimentally by match-feeding rats liquid diets of varying protein content with and without ethanol. Protein synthesis and enzyme secretion were investigated, because these parameters are believed to increase the capacity for pancreatic autodigestion. Protein synthesis was assessed by determining the incorporation of tritiated phenylalanine into trichloroacetic acid precipitated protein 10 minutes after IP injection and then corrected for the size of the precursor pool. Enzyme secretion was studied using pancreatic acini, which were prepared using clostripain-poor collagenase. Chronic ethanol feeding stimulated protein synthesis and lipase secretion and content in rats receiving adequate amounts of protein. These stimulatory effects of ethanol were markedly attenuated in rats administered protein poor diets. Protein deficiency per se significantly decreased the weight, protein, and enzyme content of the rat pancreas as well as increased the percentage release of lipase from acini. Although extrapolation from animal studies may be tenuous, the present findings may explain the link between nutrition and the occurrence of alcoholic pancreatitis.

Animals↗
PubMed1990

Role of xanthine oxidase in ethanol-induced lipid peroxidation in rats.

To investigate a possible role of free radical production by xanthine oxidase in the pathogenesis of ethanol-induced hepatic lipid peroxidation, chow-fed rats were given ethanol (5 g/kg) and placed at 32 degrees C for 6 h, which resulted in increased hepatic malondialdehyde levels. Pretreatment with allopurinol in amounts that effectively inhibited xanthine metabolism also significantly decreased ethanol-induced lipid peroxidation, suggesting participation of free radicals produced by xanthine oxidase in the peroxidative process. Both acetaldehyde and purine can serve as substrates for xanthine oxidase. Pretreatment with cyanamide increased hepatic acetaldehyde levels 5-fold, yet this was associated with a decrease in lipid peroxidation, indicating that acetaldehyde is not the xanthine oxidase substrate involved. By contrast, ethanol increased hepatic contents of hypoxanthine and xanthine and enhanced urinary output of allantoin (a final product of xanthine metabolism), incriminating increased metabolism of purines. Ethanol administration also enhanced hepatic nicotinamide adenine dinucleotide (reduced form). A corresponding rise of nicotinamide adenine dinucleotide (reduced form) in vitro inhibited xanthine dehydrogenase activity by 60%-76%. Increased purine degradation, possibly associated with a shift from the dehydrogenase to the xanthine oxidase pathway (secondary to nicotinamide adenine dinucleotide [reduced form]-mediated inhibition of xanthine dehydrogenase activity) is proposed as a possible mechanism for ethanol-stimulated free radical production. Because allopurinol attenuates the associated lipid peroxidation, this agent might be considered for possible therapeutic use in alcohol-induced liver damage.

Allopurinol↗