Mechanism for selective perivenular hepatotoxicity of ethanol

Induction of hepatic 11beta-hydroxysteroid dehydrogenase type 1 in patients with alcoholic liver disease

BACKGROUND AND AIM

The alcohol-induced pseudo-Cushing's syndrome is an important differential diagnosis of hypercortisolism that is poorly understood. Two isozymes of 11beta-hydroxysteroid dehydrogenase (11beta-HSD) interconvert hormonally active cortisol (F) and inactive cortisone (E). Previously we have shown higher urinary F:E metabolite ratios (a reflection of global 11beta-HSD activity) in patients with alcoholic liver disease (ALD) compared to patients with chronic liver disease (CLD) of other aetiologies, suggesting that the phenotype of alcoholic pseudo-Cushing's may relate to altered metabolism of F.

SUBJECTS AND METHODS

We performed selective venous sampling of the hepatic, renal and peripheral veins measuring F and E concentrations (using in-house radioimmunoassay) in 20 patients with histologically confirmed ALD and 19 patients with CLD. Six patients who also had selective venous sampling for investigation of suspected hyperaldosteronism were used as 'normal' controls.

RESULTS

There was a significant difference in the hepatic F gradient (mean +/- SEM) between groups, indicating increased F production in the liver in patients with ALD (34.5 +/- 21.7 nmol/l) compared to those with CLD (-21.0 +/- 18.5 nmol/l) (P < 0.05) and normals (-19.7 +/- 17.2 nmol/l) (P < 0.05). 11beta-HSD1 mRNA expression was increased fivefold in the ALD group compared with normal controls (P < 0.01).

CONCLUSIONS

These results indicate significant induction of HSD11B1 gene expression and activity in patients with ALD during short- and long-term abstinence from alcohol. The mechanism is unknown but might be explained on the basis of alcohol-induced changes in intracellular redox potential or as a protective mechanism to limit liver inflammation and injury. Selective 11beta-HSD1 inhibitors may offer a novel therapeutic approach to treat alcoholic pseudo-Cushing's.

Ethanol acutely stimulates islet blood flow, amplifies insulin secretion, and induces hypoglycemia via nitric oxide and vagally mediated mechanisms

Hypoglycemia induced by alcohol ingestion is a well-known problem in diabetic patients. However, the mechanisms underlying this phenomenon have largely remained elusive. Because insulin secretion in vivo can be rapidly tuned by changes in pancreatic microcirculation, we evaluated the influence of acute alcohol administration on pancreatic islet blood flow (IBF), and dynamic changes in insulin secretion and glycemia in the rat. Ethanol (10%) or saline was iv injected as a bolus into Wistar rats, yielding serum ethanol concentrations of approximately 8 mmol/liter. Measurements of pancreatic blood flow (PBF) were performed by a microsphere technique in combination with a freeze-thawing technique after 10-min injection. Ethanol preferentially and significantly increased pancreatic IBF approximately 4-fold, whereas not influencing whole PBF. The alcohol also augmented late-phase insulin secretion and induced late hypoglycemia upon ip glucose tolerance tests. The nitric oxide synthase inhibitor N-w-nitro-L-arginine methyl ester and atropine prevented the increased pancreatic IBF, enhanced insulin secretion, and hypoglycemia evoked by ethanol. Thus, our findings demonstrate that ethanol acutely exerts substantial influences on pancreatic microcirculation by evoking a massive redistribution of PBF from the exocrine into the endocrine part via mechanisms mediated by nitric oxide and vagal stimuli, augmenting late-phase insulin secretion, and thereby evoking hypoglycemia. This effect may in part underlie the well-known hypoglycemic properties of alcohol in diabetic patients or in alcoholics with hepatic failure.

Metabolism of alcohol

Most tissues of the body contain enzymes capable of ethanol oxidation or nonoxidative metabolism, but significant activity occurs only in the liver and, to a lesser extent, in the stomach. Hence, medical consequences are predominant in these organs. In the liver, ethanol oxidation generates an excess of reducing equivalents, primarily as NADH, causing hepatotoxicity. An additional system, containing cytochromes P-450 inducible by chronic alcohol feeding, was demonstrated in liver microsomes and found to be a major cause of hepatotoxicity.

Peroxisome proliferator-activated receptor alpha (PPARalpha) agonist treatment reverses PPARalpha dysfunction and abnormalities in hepatic lipid metabolism in ethanol-fed mice

Proper function of the peroxisome proliferator-activated receptor alpha (PPARalpha) is essential for the regulation of hepatic fatty acid metabolism. Fatty acid levels are increased in liver during the metabolism of ethanol and should activate PPARalpha. However, recent in vitro data showed that ethanol metabolism inhibited the function of PPARalpha. We now report that ethanol feeding impairs fatty acid catabolism in the liver in part via blocking PPARalpha-mediated responses in C57BL/6J mice. Ethanol feeding decreased PPARalpha/retinoid X receptor alpha binding in electrophoretic mobility shift assay of liver nuclear extracts. mRNAs for PPAR-regulated genes were reduced (long chain and medium chain acyl-CoA dehydrogenases) or failed to be induced (acyl-CoA oxidase, liver carnitine palmitoyl-CoA transferase, very long chain acyl-CoA synthetase, very long chain acyl-CoA dehydrogenase) in livers of the ethanol-fed animals, and ethanol feeding did not increase the rate of fatty acid beta-oxidation. Wy14,643, a PPARalpha agonist, restored the DNA binding activity of PPARalpha/retinoid X receptor alpha, induced mRNA levels of PPARalpha target genes, stimulated the rate of fatty acid beta-oxidation, and prevented fatty liver in ethanol-fed animals. Impairment of PPARalpha function during ethanol consumption contributes to the development of alcoholic fatty liver, which can be overcome by Wy14,643.

Mediation by nitric oxide of the stimulatory effects of ethanol on blood flow

The contribution of nitric oxide (NO) to the hemodynamic effects associated with alcohol oxidation was assessed in rats given either ethanol or water by gastric tube, with and without pre-treatment with either the NO synthase inhibitor N(omega)-monomethyl-L-arginine (L-NMMA; 15 mg/Kg i.p.) or the alcohol dehydrogenase inhibitor 4-methylpyrazole (4-MP; 82 mg/Kg i.p.). Alcohol increased plasma NO (measured with chemiluminescence) by 63%. This was prevented by either L-NMMA or 4-MP. Cardiac output and regional blood flows were determined with 57Cobalt-labeled microspheres. Alcohol markedly enhanced portal blood flow (130 +/- 6 ml/min/Kg vs. 62 +/- 4, in controls; p < 0.01) with no changes in the hepatic, splenic or pancreatic arterial blood flows, indicating that the vasodilatation is mainly mesenteric. In addition, it quadrupled the coronary blood flow, doubled the renal flow and increased cardiac output by 38%, with no significant changes in pulmonary, cerebral or testicular flows. All the stimulatory effects of ethanol on flow, as well as the rise in NO levels, were prevented by L-NMMA, incriminating NO as the mediator of the hemodynamic effects of ethanol oxidation, acting probably via acetate and adenosine.

Alcoholic liver disease: new insights in pathogenesis lead to new treatments

Much progress has been made in the understanding of the pathogenesis of alcoholic liver disease, resulting in improvement of prevention and therapy, with promising prospects for even more effective treatments. The most successful approaches that one can expect to evolve are those that deal with the fundamental cellular disturbances resulting from excessive alcohol consumption. Two pathologic concepts are emerging as particularly useful therapeutically. Whereas it continues to be important to replenish nutritional deficiencies, when present, it is crucial to recognize that because of the alcohol-induced disease process, some of the nutritional requirements change. This is exemplified by methionine, which normally is one of the essential amino acids for humans, but needs to be activated to S-adenosylmethionine (SAMe), a process impaired by the disease. Thus, SAMe rather than methionine is the compound that must be supplemented in the presence of significant liver disease. Indeed, SAMe was found to attenuate mitochondrial lesions in baboons, replenish glutathione, and significantly reduce mortality in patients with Child A or B cirrhosis. Similarly, polyenylphosphatidylcholine (PPC) corrects the ethanol-induced hepatic phospholipid depletion as well as the decreased phosphatidylethanolamine methyltransferase activity and opposes oxidative stress. It also deactivates hepatic stellate cells, whereas its dilinoleoyl species (DLPC) increases collagenase activity, resulting in prevention of ethanol-induced septal fibrosis and cirrhosis in the baboon. Clinical trials with PPC are ongoing in patients with alcoholic liver disease. Furthermore, enzymes useful for detoxification, such as CYP2E1, when excessively induced, become harmful and should be downregulated. PPC is one of the substances with anti-CYP2E1 properties that is now emerging. Another important aspect is the association of alcoholic liver disease with hepatitis C: a quarter of all patients with alcoholic liver disease also have markers of HCV infection, with an even higher incidence in some urban areas but, at present, no specific therapy is available since interferon is contraindicated in that population. However, in addition to antiviral medications, agents that oppose oxidative stress and fibrosis should also be tested for hepatitis C treatment since these two processes contribute much to the pathology and mortality associated with the virus. In addition to antioxidants (such as PPC, silymarin, alpha-tocopherol and selenium), anti-inflammatory medications (corticosteroids, colchicine, anticytokines) are also being tested as antifibrotics. Transplantation is now accepted treatment in alcoholics who have brought their alcoholism under control and who benefit from adequate social support but organ availability is still the major limiting factor and should be expanded more aggressively. Finally, abstinence from excessive drinking is always indicated; it is difficult to achieve but agents that oppose alcohol craving are becoming available and they should be used more extensively.

Role of the cellular redox state in modulating acute ethanol toxicity in isolated hepatocytes

OBJECTIVES

To propose a mechanism for ethanol induced hepatocytotoxicity.

DESIGN AND METHODS

Hepatocytotoxicity was determined at various concentrations of oxygen and agents involved in NADH metabolism.

RESULTS

At 1% O2, hepatocytes were nearly 8-fold more susceptible to ethanol than at 95% O2 (carbogen). Cytotoxicity at 1% O2 was enhanced in the presence of glycolytic substrates that generate NADH (e.g., sorbitol or xylitol), and prevented by glycolytic substrates that reoxidise NADH (e.g., fructose or dihydroxyacetone). Susceptibility to ethanol correlated with the cytosolic redox state (lactate; pyruvate ratio). Cytotoxicity also correlated with reactive oxygen species (ROS) formation. Cytotoxicity was averted by ROS scavengers or the ferric chelator desferoxamine but was increased by hydroxylamine, a catalase inhibitor, or by prior glutathione depletion. Ethanol induced cytotoxicity was also decreased by inhibitors of alcohol/aldehyde dehydrogenases or CYP2E1, an alcohol inducible cytochrome P450.

CONCLUSIONS

A cytotoxic mechanism was proposed where the sustained increase in NADH levels, resulting from ethanol metabolism, maintains CYP2E1 in a more reduced state that increases ROS formation.

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.

Serum activities of classes I and II alcohol dehydrogenases in toxic liver damage

The activities of classes I and II alcohol dehydrogenase isoenzymes were determined in the sera of patients with toxic hepatitis using class-specific fluorogenic substrates. The activities of total alcohol dehydrogenase and enzymes indicative of liver damage were also measured. We found a statistically significant increase of class I alcohol dehydrogenase isoenzymes. The increase in class I (two-fold) was similar to the increase of alkaline phosphatase. In a correlated study, we observed a good correlation of the activity of class II isoenzymes with alanine aminotransferase. The total alcohol dehydrogenase activity was enhanced and correlated with lactate dehydrogenase. These results demonstrated that the alcohol dehydrogenase and class I isoenzymes are indicatory enzymes of liver cell damage, and may be diagnostically useful in toxic hepatitis.

Role of oxidative stress and antioxidant therapy in alcoholic and nonalcoholic liver diseases

The main pathway for the hepatic oxidation of ethanol to acetaldehyde proceeds via ADH and is associated with the reduction of NAD to NADH; the latter produces a striking redox change with various associated metabolic disorders. NADH also inhibits xanthine dehydrogenase activity, resulting in a shift of purine oxidation to xanthine oxidase, thereby promoting the generation of oxygen-free radical species. NADH also supports microsomal oxidations, including that of ethanol, in part via transhydrogenation to NADPH. In addition to the classic alcohol dehydrogenase pathway, ethanol can also be reduced by an accessory but inducible microsomal ethanoloxidizing system. This induction is associated with proliferation of the endoplasmic reticulum, both in experimental animals and in humans, and is accompanied by increased oxidation of NADPH with resulting H2O2 generation. There is also a concomitant 4- to 10-fold induction of cytochrome P4502E1 (2E1) both in rats and in humans, with hepatic perivenular preponderance. This 2E1 induction contributes to the well-known lipid peroxidation associated with alcoholic liver injury, as demonstrated by increased rates of superoxide radical production and lipid peroxidation correlating with the amount of 2E1 in liver microsomal preparations and the inhibition of lipid peroxidation in liver microsomes by antibodies against 2E1 in control and ethanol-fed rats. Indeed, 2E1 is rather "leaky" and its operation results in a significant release of free radicals. In addition, induction of this microsomal system results in enhanced acetaldehyde production, which in turn impairs defense systems against oxidative stress. For instance, it decreases GSH by various mechanisms, including binding to cysteine or by provoking its leakage out of the mitochondria and of the cell. Hepatic GSH depletion after chronic alcohol consumption was shown both in experimental animals and in humans. Alcohol-induced increased GSH turnover was demonstrated indirectly by a rise in alpha-amino-n-butyric acid in rats and baboons and in volunteers given alcohol. The ultimate precursor of cysteine (one of the three amino acids of GSH) is methionine. Methionine, however, must be first activated to S-adenosylmethionine by an enzyme which is depressed by alcoholic liver disease. This block can be bypassed by SAMe administration which restores hepatic SAMe levels and attenuates parameters of ethanol-induced liver injury significantly such as the increase in circulating transaminases, mitochondrial lesions, and leakage of mitochondrial enzymes (e.g., glutamic dehydrogenase) into the bloodstream. SAMe also contributes to the methylation of phosphatidylethanolamine to phosphatidylcholine. The methyltransferase involved is strikingly depressed by alcohol consumption, but this can be corrected, and hepatic phosphatidylcholine levels restored, by the administration of a mixture of polyunsaturated phospholipids (polyenylphosphatidylcholine). In addition, PPC provided total protection against alcohol-induced septal fibrosis and cirrhosis in the baboon and it abolished an associated twofold rise in hepatic F2-isoprostanes, a product of lipid peroxidation. A similar effect was observed in rats given CCl4. Thus, PPC prevented CCl4- and alcohol-induced lipid peroxidation in rats and baboons, respectively, while it attenuated the associated liver injury. Similar studies are ongoing in humans.

Liver cell necrosis: cellular mechanisms and clinical implications

Based on our current understanding, we have developed a provisional model for hepatocyte necrosis that may be applicable to cell necrosis in general (Figure 6). Damage to mitochondria appears to be a key early event in the progression to necrosis. At least two pathways may be involved. In the first, inhibition of oxidative phosphorylation in the absence of the MMPT leads to ATP depletion, ion dysregulation, and enhanced degradative hydrolase activity. If oxygen is present, toxic oxygen species may be generated and lipid peroxidation can occur. Subsequent cytoskeleton and plasma membrane damage result in plasma membrane bleb formation. These steps are reversible if the insult to the cell is removed. However, if injury continues, bleb rupture and cell lysis occur. In the second pathway, mitochondrial damage results in an MMPT. This step is irreversible and leads to cell death by as yet uncertain mechanisms. It is important to note that MMPT may occur secondary to changes in the first pathway (e.g. oxidative stress, increased Cai2+, and ATP depletion) and that all the "downstream events" occurring in the first pathway may result from MMPT (e.g., ATP depletion, ion dysregulation, or hydrolase activation). Proof of this model's applicability to cell necrosis in general awaits further validation. In this review, we have attempted to highlight the advances in our understanding of the cellular mechanisms of necrotic injury. Recent advances in this understanding have allowed scientists and clinicians a better comprehension of liver pathophysiology. This knowledge has provided new avenues of therapy and played a key role in the practice of hepatology as evidenced by advances in organ preservation. Understanding the early reversible events leading to cellular and subcellular damage will be key to prevention and treatment of liver disease. Hopefully, disease and injury specific preventive or pharmacological strategies can be developed based on this expanding data base.

Hepatic and metabolic effects of ethanol: pathogenesis and prevention

Mechanisms of the hepatotoxicity of ethanol are reviewed, including effects resulting from alcohol dehydrogenase (ADH) mediated excessive hepatic generation of NADH and acetaldehyde. Gastric ADH explains first-pass metabolism by ethanol; its activity is low in alcoholics and in females and is decreased by some commonly used drugs. In addition to ADH, ethanol can be oxidized by liver microsomes: studies over the last 25 years have culiminated in the molecular elucidation of the ethanol-inducible cytochrome P-450 (2E1) which causes metabolic tolerance to ethanol and to various commonly used medications, enhanced degradation of testosterone and vitamin A (with vitamin A depletion) and selective hepatic perivenular toxicity. The latter results from free radical generation and activation of various xenobiotics, causing increased vulnerability of the heavy drinker to the toxicity of industrial solvents, anaesthetic agents, commonly prescribed drugs, over-the-counter analgesics, chemical carcinogens and even nutritional factors such as vitamin A and beta-carotene. Furthermore, induction of the microsomal pathway contributes to increased acetaldehyde generation which promotes GSH depletion and lipid peroxidation and other toxic effects. Nutritional deficits may affect the toxicity of ethanol and acetaldehyde, as illustrated by the depletion in glutathione, ameliorated by S-adenosyl-L-methionine. Other 'supernutrients' include polyenylphosphatidylcholine, shown to correct the alcohol-induced hepatic phosphatidylcholine depletion and to prevent alcoholic cirrhosis in non-human primates.

Alcohol and the liver: 1994 update

This article reviews current concepts on the pathogenesis and treatment of alcoholic liver disease. It has been known that the hepatotoxicity of ethanol results from alcohol dehydrogenase-mediated excessive generation of hepatic nicotinamide adenine dinucleotide, reduced form, and acetaldehyde. It is now recognized that acetaldehyde is also produced by an accessory (but inducible) microsomal pathway that additionally generates oxygen radicals and activates many xenobiotics to toxic metabolites, thereby explaining the increased vulnerability of heavy drinkers to industrial solvents, anesthetics, commonly used drugs, over-the-counter medications, and carcinogens. The contribution of gastric alcohol dehydrogenase to the first-pass metabolism of ethanol and alcohol-drug interactions is discussed. Roles for hepatitis C, cytokines, sex, genetics, and age are now emerging. Alcohol also alters the degradation of key nutrients, thereby promoting deficiencies as well as toxic interactions with vitamin A and beta carotene. Conversely, nutritional deficits may affect the toxicity of ethanol and acetaldehyde, as illustrated by the depletion in glutathione, ameliorated by S-adenosyl-L-methionine. Other "supernutrients" include polyunsaturated lecithin, shown to correct the alcohol-induced hepatic phosphatidylcholine depletion and to prevent alcoholic cirrhosis in nonhuman primates. Thus, a better understanding of the pathology induced by ethanol is now generating improved prospects for therapy.

Long-term ethanol feeding selectively impairs the attachment of rat perivenous hepatocytes to extracellular matrix substrates

BACKGROUND/AIMS

We have previously shown that long-term ethanol consumption by rats results in a profound decrease in hepatocyte attachment to various extracellular matrix substrates. The present study investigated whether differences in attachment exist between cells isolated from either the periportal or perivenous regions of the liver.

METHODS

Rats received long-term ethanol, and hepatocytes were selectively isolated by the digitonin-collagenase perfusion method. The ability of periportal and perivenous cells isolated from ethanol-fed and pair-fed control rats to attach to plates coated with either laminin, fibronectin, or type I collagen was then assayed.

RESULTS

With all substrates, the attachment of perivenous hepatocytes isolated from ethanol-fed animals was significantly impaired. Time-course studies showed that although the rate of attachment of perivenous cells from ethanol-fed animals was only slightly reduced, a dramatic decrease in absolute attachment was observed. Furthermore, the perivenous cells isolated from ethanol-fed animals detached more readily from the substrate-coated plates than the corresponding periportal cells or either periportal or perivenous cells from pair-fed controls.

CONCLUSIONS

Long-term ethanol consumption impairs hepatocyte-extracellular matrix interactions more severely in the perivenous region of the liver. This finding could be relevant to the pathological changes observed in alcoholic liver injury.

Aetiology and pathogenesis of alcoholic liver disease

Until the 1960s, liver disease of the alcoholic patient was attributed exclusively to dietary deficiencies. Since then, however, our understanding of the impact of alcoholism on nutritional status has undergone a progressive evolution. Alcohol, because of its high energy content, was at first perceived to act exclusively as 'empty calories' displacing other nutrients in the diet, and causing primary malnutrition through decreased intake of essential nutrients. With improvement in the overall nutrition of the population, the role of primary malnutrition waned and secondary malnutrition was emphasized as a result of a better understanding of maldigestion and malabsorption caused by chronic alcohol consumption and various diseases associated with chronic alcoholism. At the same time, the concept of the direct toxicity of alcohol came to the forefront as an explanation for the widespread cellular injury. Some of the hepatotoxicity was found to result from the metabolic disturbances associated with the oxidation of ethanol via the liver alcohol dehydrogenase (ADH) pathway and the redox changes produced by the generated NADH, 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 contributes to the exacerbation of the ethanol-induced lesions in zone 3. 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 P450IIE1 (CYP2E1) which contributes not only to ethanol metabolism and tolerance, but also to the selective hepatic perivenular toxicity of various xenobiotics. Their activation by CYP2E1 now provides an understanding for the increased susceptibility of the heavy drinker to the toxicity of industrial solvents, anaesthetic 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 hepatotoxicity. Furthermore, induction of the microsomal pathway contributes to increased acetaldehyde generation, with formation of protein adducts, resulting in antibody production, enzyme inactivation and decreased DNA repair; it is also associated with a striking impairment of the capacity of the liver to utilize oxygen. Moreover, acetaldehyde promotes glutathione depletion, free-radical mediated toxicity and lipid peroxidation. In addition, acetaldehyde affects hepatic collagen synthesis: both in vivo and in vitro (in cultured myofibroblasts and lipocytes), ethanol and its metabolite acetaldehyde were found to increase collagen accumulation and mRNA levels for collagen. This new understanding of the pathogenesis of alcoholic liver disease may eventually improve therapy with drugs and nutrients.

The effects of ethanol concentration on glycero-3-phosphate accumulation in the perfused rat liver. A reassessment of ethanol-induced inhibition of glycolysis using 31P-NMR spectroscopy and HPLC

The dose-dependent effect of ethanol on the hepatic metabolism of the perfused rat liver has been investigated by (a) 31P-NMR spectroscopy for the follow-up of intracellular phosphorylated metabolites and (b) HPLC for compounds released in the effluents. Perfusion of livers from fed rats with ethanol induced an increase in the level of sn-glycerol 3-phosphate and net accumulations of 3.30 +/- 0.33 and 0.69 +/- 0.15 mumol x g-1 wet liver were reached after 20 min, for 70 mM and 0.5 mM ethanol, respectively. sn-Glycerol-3-phosphate accumulation was fully detected by 31P NMR as indicated by comparing quantitations based on NMR and biochemical assays. Ethanol administration up to a concentration of 10 mM induced a dose-dependent decrease in the release of lactate + pyruvate by the liver. Lactate release decreased from 1129 +/- 39 to 674 +/- 84 nmol x min-1 x g-1, while pyruvate decreased from 230 +/- 9 to 6.2 +/- 0.4 nmol x min-1 x g-1, after 20 min of perfusion with 10 mM ethanol. Nevertheless, the flux through 6-phosphofructo-1-kinase, as measured by both the accumulation of sn-glycerol 3-phosphate and release of lactate + pyruvate, was not affected in the early phase of ethanol oxidation. Finally, data obtained from oxygen consumption, the release of acetate and the accumulation of sn-glycerol 3-phosphate do not support the involvement of the microsomal ethanol-oxidizing system in the catalysis of ethanol oxidation, even at high doses of alcohol.

Biochemistry of alcoholic liver disease

The biochemistry of alcohol liver disease as it relates to clinical medicine and experimental alcohol liver disease is presented. Clinical features are emphasized in the diagnosis of alcohol liver disease, particularly as it relates to staging the disease and predictors of prognosis. Currently, it is true that the biochemical diagnosis of alcohol liver disease is at best very limited in terms of the sensitivity tests and specificity of the test. It is particularly difficult to detect alcohol liver disease biochemically in the early stages when steatohepatitis is not severe. Consequently, 50% of the patients have already developed cirrhosis at the time they are diagnosed clinically. In this review indicators of malnutrition are emphasized because they have the strongest implications regarding survival during the acute hospitalization stage of the disease. They are also the best indicators of response to therapy during the recovery phase. With respect to experimental work on the pathogenesis of alcohol liver disease, it appears that necrosis is due to the inability to increase blood flow to compensate for increased oxygen utilization. The hypothesis that mitochondrial damage is the cause of liver cell damage is regarded as less important in the pathogenesis of necrosis. The shift in the redox state during alcohol metabolism accounts for the fatty change noted in the central lobular area of the liver in animals fed alcohol. Apparently, there is strong experimental evidence that highly reactive intermediates are important in the pathogenesis of liver damage due to the induction of the isozyme cytochrome P450 IIE1 by alcohol ingestion. This mechanism is enhanced by a diet high in polyunsaturated fatty acids.

Intraacinar profiles of alcohol dehydrogenase and aldehyde dehydrogenase activities in human liver

The intraacinar activity profiles of alcohol dehydrogenase and the aldehyde dehydrogenases (I, I plus II, and total) were determined, using liver biopsy samples from eight male and eight female patients. Microchemical assays were performed in microdissected tissue samples from the whole length of the sinusoid. Alcohol dehydrogenase activity in men less than 53 years of age showed a maximum in the intermediate zone, whereas in women less than 50 years of age an increase in the gradient toward the perivenous zone was observed. Furthermore, alcohol dehydrogenase activity in the livers of women was significantly higher than in men. After the age of 53 in men and 50 in women, the sex specificity of the distribution profiles was no longer apparent. The intraacinar profiles of aldehyde dehydrogenase isoenzymes showed only minor variations in the different groups; they were not statistically significant. This is also true for low-Michaelis constant (Km) aldehyde dehydrogenase, which is most important for acetaldehyde oxidation in vivo. Thus, of the variations in zonal heterogeneity of ethanol-degrading enzymes, it is mainly the activity of alcohol dehydrogenase that may contribute to the sex- and age-related susceptibility of liver parenchyma.

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)

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.

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)

Plasma carnitine levels in liver cirrhosis: relationship with nutritional status and liver damage

The plasma level of carnitine, a co-factor involved in many metabolic reactions, is high in alcoholic liver cirrhosis, due to an increased amount of esterified carnitine. To determine if this alteration is linked to alcoholic liver disease or to liver cirrhosis per se. total carnitine, free carnitine, total esterified carnitine, short chain acylcarnitine and long chain acylcarnitine were measured in 41 patients suffering from liver cirrhosis of different aetiology and severity. In 19 of these patients, acetylcarnitine was also measured. Moreover, multivariate analysis was performed to assess the association of carnitine plasma levels with nutritional and liver disease indices. Of the nutritional indices (creatinine/height ratio, mid upper arm muscle circumference and triceps skinfold) only triceps skinfold appeared to be weakly correlated with carnitine (with long chain acylcarnitine). Significantly high levels of acetylcarnitine, short chain acylcarnitine, total esterified carnitine and total carnitine were found in cirrhotics independently of the aetiology of cirrhosis, even though a trend towards higher levels of acetylcarnitine was evident in heavy drinkers. Direct correlations of gamma-glutamyltransferase with acetylcarnitine, acetylcarnitine/free carnitine, short chain acylcarnitine/free carnitine and total esterified carnitine/free carnitine were found. Carnitine plasma levels did not differ in the three Pugh-Child's classes; however, a trend towards higher levels of acetylcarnitine was found in Pugh-Child's class C. In conclusion, the high levels of acetylcarnitine, short chain acylcarnitine, total esterified carnitine and total carnitine found in cirrhosis were linked to liver disease. Alcohol abuse seemed only to be an exacerbating factor.

Histochemical and immunohistochemical evidence for hepatic zone 3 distribution of alcohol dehydrogenase in rats

The distribution of alcohol dehydrogenase in the hepatic acinus was examined by both histochemical and immunohistochemical approaches. The immunohistochemical method using anti-alcohol dehydrogenase antibody indicated zone 3 predominance of this enzyme in the hepatic acinus, whereas a conventional histochemical method showed slight zone 1 predominance. However, when the histochemical technique was improved by using 2% glutaraldehyde instead of formalin for fixation and by adding phenazine methosulfate (0.33 mmol/L) to the staining incubation mixture, this method also supported zone 3 predominance of alcohol dehydrogenase. Evidence for zone 3 distribution of alcohol dehydrogenase may be of value in elucidating the mechanism of zone 3 liver damage by alcohol.

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.

Ethanol-induced iron mobilization: role of acetaldehyde-aldehyde oxidase generated superoxide

Superoxide radicals, a species known to mobilize ferritin iron, and their interaction with catalytic iron have been implicated in the pathogenesis of alcohol-induced liver injury. The mechanism(s) by which ethanol metabolism generates free radicals and mobilizes catalytic iron, however, is not fully defined. In this investigation the role of hepatic aldehyde oxidase in the mobilization of catalytic iron from ferritin was studied in vitro. Iron mobilization due to the metabolism of ethanol to acetaldehyde by alcohol dehydrogenase was increased 100% by the addition of aldehyde oxidase. Iron release was favored by low pH and low oxygen concentration. Mobilization of iron due to acetaldehyde metabolism by aldehyde oxidase was completely inhibited by superoxide dismutase but not by catalase suggesting that superoxide radicals mediate mobilization. Acetaldehyde-aldehyde oxidase mediated reduction of ferritin iron was facilitated by incubation with menadione, an electron acceptor for aldehyde oxidase. Mobilization of ferritin iron due to the metabolism of acetaldehyde by aldehyde oxidase may be a fundamental mechanism of alcohol-induced liver injury.

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.

Effect of ethanol on splanchnic hemodynamics in awake and unrestrained rats with portal hypertension

Alcoholic liver disease is frequently accompanied by portal hypertension. We have previously shown that alcohol intake in awake, unrestrained rats is followed by an increase in portal tributary blood flow. In this study, the effect of ethanol on splanchnic hemodynamics in rats with portal hypertension was analyzed. Portal hypertension was induced by partial ligation of the portal vein. This procedure resulted in an increase in portal tributary and hepatic arterial blood flows compared to sham-operated animals. Ethanol (2 gm per kg, oral) increased portal tributary blood flow in both sham-operated and portal vein-ligated rats (sham + water = 37.6 +/- 1.4; sham + ethanol = 63.1 +/- 1.9; p less than 0.01; partial portal vein stenosis + water = 53.2 +/- 3.3; partial portal vein stenosis + ethanol = 69.5 +/- 2.2 ml.kg-1.min-1; p less than 0.01). In sham-operated rats, hepatic artery blood flow was unchanged following ethanol (sham + water = 6.6 +/- 0.7; sham + ethanol = 7.1 +/- 1.0 ml.kg-1.min-1), whereas in portal vein-ligated rats, flow was increased (partial portal vein stenosis + water = 13.7 +/- 1.4; partial portal vein stenosis + ethanol = 19.8 +/- 1.1 ml.kg-1.min-1; p less than 0.025). The adenosine receptor blocker 8-phenyltheophylline suppressed only the ethanol-induced increase in both portal tributary and hepatic artery blood flows in portal vein-ligated rats. The increases in hepatic artery and portal tributary blood flows observed in portal vein-ligated rats without ethanol were not influenced by 8-phenyltheophylline.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of propylthiouracil and methimazole on splanchnic hemodynamics in awake and unrestrained rats

The treatment of alcoholic liver disease with propylthiouracil is based on its effect of suppressing the ethanol-induced increase in hepatic oxygen consumption. It has been postulated that liver necrosis ensues when the increase in oxygen demand by the liver exceeds oxygen delivery to this organ. Data are now presented which show that propylthiouracil also increases portal blood flow in awake, unrestrained rats. Liver blood flow was determined using the labeled microsphere technique in rats at various intervals (0.25, 0.5, 1.0, 3.0, 6.0 and 24 hr) after oral propylthiouracil (50 mg per kg). Administration of propylthiouracil (dose range: 6.25 to 100.0 mg per kg) produced a dose-dependent increase in portal blood flow when given either orally or intraarterially. Maximal flows were obtained with 50 mg per kg (controls = 37.8 +/- 1.5, oral propylthiouracil = 50.7 +/- 2.2 ml.kg-1.min-1). This increase in portal blood flow was accompanied by a decrease in preportal vascular resistance (controls = 2.61 +/- 0.16; propylthiouracil, 50 mg per kg = 1.79 +/- 0.09 mmHg per ml.kg-1.min-1). These effects were correlated with the plasma concentrations of propylthiouracil (r = 0.67, n = 68, p less than or equal to 0.001). The effect of oral propylthiouracil (50 mg per kg) on portal blood flow started at 0.5 hr and lasted for 6 hr after administration, whereas total liver blood flow was increased for 3 hr. Oral propylthiouracil (50 mg per kg) for 5 days resulted in a 53% increase in thyroid weight, an 85% reduction in 125I thyroid uptake and a 74% decrease in serum thyroxine concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Biochemical basis for alcohol-induced liver injury

Chronic ethanol ingestion leads to hepatocellular injury and alcoholic liver disease (ALD) only if multiple factors combine to favor centrilobular hepatocellular hypoxia. It is hypothesized that these factors include a shift in the redox state, the induction of the microsomal ethanol oxidizing system (MEOS), a high blood alcohol level (BAL), a high polyunsaturated fat diet and episodic decreased O2 supply to the liver. The shift in the redox state favors a low cellular pH, decreased fatty acid oxidation and increased triglyceride formation. The increased MEOS activity increases O2 consumption and portal-central O2 gradient as well as favors acetaldehyde toxic effects including retention of hepatic lipids and export proteins causing cell swelling. The resultant increase in the concentration of acetaldehyde and lactate may stimulate fibrosis as they stimulate collagen synthesis in vitro. The resultant fatty liver narrows the sinusoids slowing sinusoid blood flow. The combination of events reduces available O2 leading to decreased levels of ATP and cellular pH making the liver vulnerable to episodes of systemic hypoxia. The role of membrane changes are reviewed, i.e., 1) membrane fluidity as related to changes in the species of phospholipids, 2) mitochondrial function as related to the changes in the lipid environment of the electron transport chain, and 3) linoleic acid-prostaglandin metabolism. Acute ethanol in vitro has been shown to affect liver cell metabolism regulation by triggering and increasing protein phosphorylation through the Ca2+-phospholipase C pathway. A high fat diet enhances the liver injury caused by chronic ethanol ingestion.

Lipid peroxidation, iron mobilization and radical generation induced by alcohol

Increasing evidence points to a major role for free radicals in the pathogenesis of alcohol-induced liver injury. In vitro, free radicals may be generated during ethanol metabolism by the further metabolism of acetaldehyde by molybdenum-dependent oxidases such as xanthine oxidase. Ferritin iron mobilized by such free radicals may serve as catalytic iron. Increased stores of ferritin iron and induction of microsomal P-450 reductase activity are mechanisms by which chronic alcohol feeding may potentiate the acute effects of alcohol.

Preferential distribution of apoptotic bodies in acinar zone 3 of normal human and rat liver

The aim of the present investigation was to study the number and acinar distribution of apoptotic bodies in normal liver as an approach to a better understanding of cell kinetics in the hepatic parenchyma. The material included 20 normal human needle liver biopsies and 20 normal male Sprague-Dawley rats. For each liver sample, the following parameters were measured: number of apoptotic bodies in the lobule, topographical localization, and distance from terminal hepatic veins (THV), i.e., the row of hepatocytes concerned, H1 being the closest to the THV. The results were strikingly similar in human and in animal material, showing that apoptotic bodies are rare in the normal liver and, when present, are always observed in zone 3, next to the THV. In fact, the first two rows of hepatocytes (H1 and H2) contained 80% of the apoptotic bodies in human liver, and 95% in rat liver. These data show that apoptotic bodies are not randomly dispersed in normal liver tissue but show a preferential acinar distribution. In addition, the vast majority of apoptotic bodies are located in the row of liver cells immediately adjacent to the THV. If apoptosis is indeed an expression of physiological cell renewal or 'programmed cell death', these findings support the concept of an aging gradient of liver cells, with zone 3 containing older hepatocytes.

A quantitative evaluation of apoptotic bodies in rat liver

The aim of the present study was to determine if data on the number and acinar distribution of apoptotic bodies (AB) in normal liver could help in the understanding of cell kinetics in the liver, and the mechanism of early ethanol-induced liver damage. Normal male Sprague-Dawley rats were studied. They had free access to Purina chow and drinking water. Ethanol-treated rats received the drug at increasing concentration in drinking water for 5 weeks. The following parameters were measured: number of AB in the lobule, topographical localization, distance from terminal hepatic veins (THV), i.e. row of hepatocytes concerned, H1 being the closest to the THV. The results show that AB are rare in the normal liver and are always observed in zone 3, next to the THV. Of 149 THV examined, 56 showed one associated AB, exceptionally two. 74% of the AB were confined to the first row of hepatocytes (H1), 21% to H2, 4% to H3, and 1% to H4. In ethanol-treated rats the mean number of AB was 2 or 3 for each THV. 42% were found in H1, 32% in H2, 15% in H3, 7% in H4, and 4% in H5. The data show that AB are not randomly dispersed in normal liver but show a preferential acinar distribution. In addition, most AB are located in the row of liver cells immediately adjacent to the THV. If apoptosis is indeed an expression of physiological cell renewal, these findings support the concept that zone 3 contains older hepatocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

Liver hypermetabolism during alcohol withdrawal in humans. Role of sympathetic overactivity

Catecholamines, which are elevated during alcohol withdrawal, can alter hepatic blood flow and increase hepatic oxygen consumption. We hypothesized that, in the withdrawal state, hepatic oxygen consumption and delivery could be altered in relation to an increased sympathetic activity. Thirteen chronic alcoholics were studied 34-72 h after withdrawal and 10 days later (control period) using conventional hemodynamic methods. As compared with the control period, splanchnic oxygen uptake was elevated at withdrawal (74.5 +/- 27.1 vs. 59.2 +/- 16.8 ml/min, p less than 0.025) and its variation was correlated with that of plasma epinephrine (r = 0.70, p less than 0.01). The hepatic venous oxygen content was reduced at withdrawal (113 +/- 22 vs. 126 +/- 21 ml/L, p less than 0.025) and correlated inversely with plasma norepinephrine levels (r = 0.56, p less than 0.01). We conclude that, during alcohol withdrawal in humans, hepatic energy expenditure may be elevated in relation to epinephrine secretion and that sympathetic overactivity may hinder the adaptive response in hepatic blood flow. The wide range in sympathetic nervous response to alcohol withdrawal could explain some differences in individual susceptibility to liver damage caused by alcohol.

Subcellular changes and apoptosis induced by ethanol in rat liver

The livers of rats given ethanol for 5 weeks showed marked structural alterations of hepatocytes of acinar zone 3 including mitochondrial pleomorphism, increased smooth endoplasmic reticulum and deposition of small (less than 0.5 micron) lipid droplets. In addition, apoptotic bodies involving altered parenchymal cells were frequently observed, together with prominent mononuclear infiltrates adjacent to the terminal hepatic veins. It is suggested that 'age' of liver cells may play a role in the preferential perivenular localization of early ethanol-induced liver damage.

Lipid peroxidation as a mechanism of alcoholic liver injury: role of iron mobilization and microsomal induction

Lipid peroxidation has been invoked as a mechanism of alcoholic liver injury but its role has been controversial and the mechanism by which it occurs is unclear. Catalytic iron is known to play an important role in cellular injury and is produced during mobilization of ferritin iron. In vivo administration of a large acute dose of ethanol (5 g/kg) which produces hepatic lipid peroxidation in chow-fed rats resulted in mobilization of non-heme iron. The generation of NADH from alcohol metabolism via ADH or superoxide from acetaldehyde-xanthine oxidase mobilized iron from horse spleen ferritin in vitro. Chronic feeding of alcohol as 36% of energy for 6 weeks does not itself produce peroxidation in the rat but potentiates acute effects of ethanol. It produced microsomal induction which enhanced iron-stimulated lipid peroxidation and increased hepatic non-heme iron. Carbon monoxide increased rather than decreased accumulation of microsomal peroxidation products in vitro suggesting that cytochrome P-450 reductase mediates peroxidation but cytochrome P-450 may metabolize products. Incubation at lowered oxygen tensions equivalent to those observed in the perivenular zone (pO2 = 24 mmHg) enhanced in vitro iron mobilization but decreased peroxidation. Lipid peroxidation and its stimulation by iron mobilization and microsomal induction may be an important contributory mechanism of alcohol-induced liver injury.

Hepatic metabolism during acute ethanol administration: a phosphorus-31 nuclear magnetic resonance study on the perfused rat liver under normoxic or hypoxic conditions

The effect of ethanol metabolism on the energetic parameters and intracellular pH of the isolated perfused rat liver from fed rats was studied by phosphorus-31 nuclear magnetic resonance spectroscopy. This technique allowed us to analyze nondestructively and in real time the role of low oxygen tension on the possible injurious effect of ethanol on the liver cells. A quantitative analysis of nuclear magnetic resonance data recorded on a perfused rat liver within a 30 mm diameter probe has been performed at 80.9 MHz. Under normoxic and normothermic conditions, the levels of phosphorylated metabolites detected by nuclear magnetic resonance were 2.8, 0.3 and 2 mumoles per gm liver wet weight for ATP, ADP and inorganic orthophosphate, respectively. The cytosolic pH was 7.25 +/- 0.05. During a period of 4 min of hypoxia induced by reducing the perfusion flow rate to 25% of its initial value (i.e., from 12 ml to 3 ml per min per 100 gm body weight), the level of ATP dropped to 2.2 mumoles per gm liver wet weight. Concomitantly, ADP and inorganic orthophosphate increased to 0.6 and 3.3 mumoles per gm liver wet weight. Cytosolic pH fell to 7.02 +/- 0.05. Perfusion of the liver with a Krebs medium containing 70 mM (0.4%) ethanol induced a sharp decrease in intracellular inorganic orthophosphate to reach 1.3 mumole per gm liver wet weight and after a lag time of 4 to 6 min, a decrease in ATP level (2.15 mumoles per gm liver wet weight). A large increase in phosphomonoesters (mainly sn-glycerol 3-phosphate) up to 6 mumoles per gm liver wet weight was also observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Ethanol-induced increase in portal hepatic blood flow: interference by anesthetic agents

While a number of studies show that acute oral administration of ethanol results in increases in liver blood flow, a large body of evidence has also been presented in which such an effect is not observed. To shed light on this discrepancy, we have studied in rats, a number of variables that might modulate or inhibit the effect of ethanol. These included the use of three anesthetic agents studied at two different times after anesthetic administration and the effect of animal age, gender, batches and seasonal variation. Portal blood flows were determined by the radiolabeled microsphere method in 12 separate experiments in awake rats. Ethanol given at doses ranging from 0.5 to 4.0 gm per kg consistently increased portal vein blood flow by approximately 50% (42.2 +/- 3.5 to 63.4 +/- 6.5 ml per min per kg). The interexperiment variation was 2.4 to 3.0%, showing remarkable consistency, typical of an all-or-none effect at the doses employed. On the other hand, the ethanol-induced increase in portal blood flow was completely suppressed by ketamine (75 mg per kg), thiopental (50 mg per kg) and fentanyl (15 micrograms per kg) when given 15 min prior to blood flow determinations. This suppression was dependent on the dose and duration of anesthesia. These anesthetic agents had no effect on basal hepatic arterial or portal blood flows. Ethanol or the anesthetics were without effects on hepatic artery blood flow. Neither gender, weight (150 to 350 gm) nor animal batch had effect on the response to ethanol. Similarly, there was no effect of seasonal variation.(ABSTRACT TRUNCATED AT 250 WORDS)