Studies on metabolic tolerance to alcohol, hepatomegaly and alcoholic liver disease

An Adolescent Porcine Model of Voluntary Alcohol Consumption Exhibits Binge Drinking and Motor Deficits in a Two Bottle Choice Test

AIMS

Alcohol is the most commonly abused substance leading to significant economic and medical burdens. Pigs are an attractive model for studying alcohol abuse disorder due to the comparable alcohol metabolism and consumption behavior, which are in stark contrast to rodent models. This study investigates the usage of a porcine model for voluntary binge drinking (BD) and a detailed analysis of gait changes due to motor function deficits during alcohol intoxication.

METHODS

Adolescent pigs were trained to drink increasing concentration (0-8%) of alcohol mixed in a 0.2% saccharin solution for 1 h in a two bottle choice test for 2 weeks. The training period was followed by a 3-week alcohol testing period, where animals were given free access to 8% alcohol in 0.2% saccharin solution and 0.2% saccharin water solution. Blood alcohol levels were tested and gait analysis was performed pre-alcohol consumption, last day of training, and Day 5 of each testing period.

RESULTS

Pigs voluntarily consumed alcohol to intoxication at all timepoints with blood alcohol concentration (BAL) ≥80 mg/dl. Spatiotemporal gait parameters including velocity, cadence, cycle time, swing time, stance time, step time, and stride length were perturbed as a result of intoxication. The stratification of the gait data based on BAL revealed that the gait parameters were affected in a dose-dependent manner.

CONCLUSION

This novel adolescent BD porcine model with inherent anatomical and physiological similarities to humans display similar consumption and intoxication behavior that is likely to yield results that are translatable to human patients.

Cellular network modeling and single cell gene expression analysis reveals novel hepatic stellate cell phenotypes controlling liver regeneration dynamics

Background

Recent results from single cell gene and protein regulation studies are starting to uncover the previously underappreciated fact that individual cells within a population exhibit high variability in the expression of mRNA and proteins (i.e., molecular variability). By combining cellular network modeling, and high-throughput gene expression measurements in single cells, we seek to reconcile the high molecular variability in single cells with the relatively low variability in tissue-scale gene and protein expression and the highly coordinated functional responses of tissues to physiological challenges. In this study, we focus on relating the dynamic changes in distributions of hepatic stellate cell (HSC) functional phenotypes to the tightly regulated physiological response of liver regeneration.

Results

We develop a mathematical model describing contributions of HSC functional phenotype populations to liver regeneration and test model predictions through isolation and transcriptional characterization of single HSCs. We identify and characterize four HSC transcriptional states contributing to liver regeneration, two of which are described for the first time in this work. We show that HSC state populations change in vivo in response to acute challenges (in this case, 70% partial hepatectomy) and chronic challenges (chronic ethanol consumption). Our results indicate that HSCs influence the dynamics of liver regeneration through steady-state tissue preconditioning prior to an acute insult and through dynamic control of cell state balances. Furthermore, our modeling approach provides a framework to understand how balances among cell states influence tissue dynamics.

Conclusions

Taken together, our combined modeling and experimental studies reveal novel HSC transcriptional states and indicate that baseline differences in HSC phenotypes as well as a dynamic balance of transitions between these phenotypes control liver regeneration responses.

Electronic supplementary material

The online version of this article (10.1186/s12918-018-0605-7) contains supplementary material, which is available to authorized users.

Oxidation of ethanol in the rat brain and effects associated with chronic ethanol exposure

It has been reported that chronic and acute alcohol exposure decreases cerebral glucose metabolism and increases acetate oxidation. However, it remains unknown how much ethanol the living brain can oxidize directly and whether such a process would be affected by alcohol exposure. The questions have implications for reward, oxidative damage, and long-term adaptation to drinking. One group of adult male Sprague-Dawley rats was treated with ethanol vapor and the other given room air. After 3 wk the rats received i.v. [2-(13)C]ethanol and [1, 2-(13)C2]acetate for 2 h, and then the brain was fixed, removed, and divided into neocortex and subcortical tissues for measurement of (13)C isotopic labeling of glutamate and glutamine by magnetic resonance spectroscopy. Ethanol oxidation was seen to occur both in the cortex and the subcortex. In ethanol-naïve rats, cortical oxidation of ethanol occurred at rates of 0.017 ± 0.002 µmol/min/g in astroglia and 0.014 ± 0.003 µmol/min/g in neurons, and chronic alcohol exposure increased the astroglial ethanol oxidation to 0.028 ± 0.002 µmol/min/g (P = 0.001) with an insignificant effect on neuronal ethanol oxidation. Compared with published rates of overall oxidative metabolism in astroglia and neurons, ethanol provided 12.3 ± 1.4% of cortical astroglial oxidation in ethanol-naïve rats and 20.2 ± 1.5% in ethanol-treated rats. For cortical astroglia and neurons combined, the ethanol oxidation for naïve and treated rats was 3.2 ± 0.3% and 3.8 ± 0.2% of total oxidation, respectively. (13)C labeling from subcortical oxidation of ethanol was similar to that seen in cortex but was not affected by chronic ethanol exposure.

Identification of factors contributing to hepatomegaly in severely burned children

Hepatomegaly is a common postmortem observation in severely burned children, with the liver often tripling in size when compared with normal livers for age, weight, and sex. Lesions identified at autopsy include deposition of large and small fat droplets in the hepatocyte, congestion, centrilobular necrosis, and cholestasis. The present study was designed to identify the primary causes of hepatomegaly in severely burned children postmortem. For this purpose, 41 autopsies were reviewed and, when available, blood and tissue samples were studied. Histopathologic findings showed that large intrahepatocytic fat droplets within hepatocytes and cholestasis were important contributors to hepatomegaly. Liver density and wet/dry weight ratios significantly decreased with increasing liver size. Hepatocyte volume increased with increasing liver size (P < 0.001) as did total fat content (P < 0.001). The liver enzymes, alanine aminotransferase and aspartate aminotransferase, remained normal except within 5 to 10 days of injury and 5 to 10 days of death. Triglycerides made up 4% to 70% of the total fat, with the percentage of triglycerides increasing with the severity of hepatomegaly. Saturated fatty acids represented about 85% of the total fatty acids in normal-sized livers, whereas in the largest livers (400% of predicted), only 25% of the fatty acids were saturated. This study provides evidence that 85% to 90% of the hepatomegaly observed in severely burned children postmortem is associated with hepatocyte enlargement, which includes up to 19% intracellular fat. Increases in extracellular protein, intracellular glycogen, and fluid accumulation may make a minor contribution to postburn hepatomegaly.

Opposing effects of chronic alcohol consumption on hepatic gluconeogenesis for female versus male rats

BACKGROUND

The impact of chronic alcohol consumption on hepatic gluconeogenesis (HGN) between males and females is unknown. To determine the effects of chronic alcohol consumption (8 weeks) on HGN, the isolated liver perfusion technique was used on 24-hr-fasted male and female Wistar rats.

METHODS

After surgical isolation, livers were perfused (single pass) for 30 min with Krebs-Henseleit bicarbonate buffer and fresh bovine erythrocytes with no added substrate (washout period). After the washout period, livers were perfused with lactate (10 mM) and [U-14C]lactate (15,000 dpm/ml) using the recirculation method.

RESULTS

There was no significant difference in HGN between males and females fed the control diet. In contrast, the females chronically fed the ethanol diet (FE) had significantly lower HGN rates (2.73 +/- 0.37 micromol/min x g liver protein(-1)), whereas males fed the ethanol diet (ME) had significantly higher HGN rates (4.99 +/- 0.45 micromol/min x g liver protein(-1)) than controls (3.83 +/- 0.34 micromol/min x g liver protein(-1)). Concomitant decreases were also observed for both 14C-lactate incorporation into 14C-glucose and rates of lactate uptake for FE, while corresponding increases were observed for 14C-lactate incorporation into 14C-glucose for ME. The livers from ME were able to convert a greater percentage of the lactate into glucose, resulting in the elevation in gluconeogenic capacity.

CONCLUSION

Chronic alcohol consumption lowers the hepatic gluconeogenic capacity from lactate in females and elevates HGN in males.

Liver alcohol dehydrogenase activity and ethanol levels during chronic ethanol intake in pregnant rats and their offspring

The effects of chronic alcohol intake on the ethanol levels in body fluids (blood, amniotic fluid, and fetal intragastric content), hepatic alcohol dehydrogenase (ADH) activity, isoenzyme distribution, and hepatic zinc levels were studied in pregnant rats at term (19 and 21 days), in their offspring at fetal, perinatal, and weaned stages, and in adult virgin rats. Three experimental groups were studied: 1) the alcohol group received ethanol in drinking water (from 10% to 25% over 2 months), 2) the fibre diet group was undernourished on a hypocaloric diet, to assess the effects of malnutrition associated with chronic alcohol intake, and 3) the control group received no alcohol and normal diet. A gradient of increasing ethanol concentrations was found in fetal blood, amniotic fluid, and fetal intragastric contents with respect to maternal blood. A decrease in ADH activity was found in alcohol-consuming pregnant rats compared to controls. This was related neither to liver ADH isoenzyme distribution nor to changes in hepatic zinc levels. Chronic alcohol consumption in pregnant rats produced high ethanol accumulation in fetal fluids and changes in the liver ADH activity depending on the physiological situation (pregnancy, development, virgin state).

Decreased tolerance to ethanol-induced hypothermia in long-term castrate male rats

A potential role for central stores of vasopressin in the development of tolerance was studied in the long-term castrate rat. Vasopressin stores in the septal region are known to be dramatically depressed following long-term castration. Sprague-Dawley male rat littermates were castrated at 26 days of age or given a sham surgery. Experiments began when animals reached 130 days of age. Tolerance to the hypothermic effects of ethanol occurred in intact but not castrate animals over the course of six daily IP injections of 3.0 g/kg ethanol. Both groups exhibited tolerance to the length of time needed to return to baseline temperature over the 6 days of ethanol injections. Tolerance to this effect of ethanol was still evident in intact animals but not castrates following another injection of ethanol 1 week later. No tolerance developed to the rebound hyperthermia that occurred in both groups. Blood ethanol levels did not differ significantly between castrate and intact littermates administered a single dose of ethanol. Overall, these results support the hypothesis that endogenous vasopressin is involved in the development of some aspects of tolerance to ethanol.

The effect of alcohol-induced hepatomegaly on portal hypertension in cirrhotic rats

Male Sprague-Dawley rats with CCl4-induced cirrhosis (confirmed by increased collagen content and light microscopy) were fed either ethanol (Group A, n = 9) or isocaloric carbohydrate diet (Group B, n = 8) for 4 weeks. Histologic and hemodynamic measurements were obtained in the awake state before (time 1) and after the 4 weeks of diet (time 2). Portal-systemic shunts were evaluated using radiolabelled microspheres. Liver weight was increased in Group A (16.5 +/- 0.5 vs. 14.2 +/- 0.5 g, mean +/- SE, p less than 0.005) as was the ratio of liver weight over total body weight (3.41 +/- 0.05 vs. 2.86 +/- 0.09%, p less than 0.0001, +19.2%). Hepatocytes surface area was increased in the ethanol group (357 +/- 9 vs. 294 +/- 7 microns 2, p less than 0.0001). In Group B, only 9 +/- 2% of hepatocytes had steatosis as opposed to 69 +/- 3% of centronodular and 34 +/- 3% of perinodular hepatocytes in Group A (p less than 0.001). Portal pressure remained stable in both groups (time 1 (A) 16.9 +/- 0.8, (B) 15.8 +/- 1.1 mmHg, n.s.; time 2 (A) 15.9 +/- 0.7, (B) 15.8 +/- 0.6 mmHg, n.s.). Portal-systemic shunts did not change with time or diet (time 1 (A) 10.6 +/- 3.7%, (B) 4.1 +/- 2.1%, n.s.; time 2 (A) 13.4 +/- 5.9%, (B) 10.8 +/- 4.3%, n.s.).(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiolipins and biomembrane function

Evidence is discussed for roles of cardiolipins in oxidative phosphorylation mechanisms that regulate State 4 respiration by returning ejected protons across and over bacterial and mitochondrial membrane phospholipids, and that regulate State 3 respiration through the relative contributions of proteins that transport protons, electrons and/or metabolites. The barrier properties of phospholipid bilayers support and regulate the slow proton leak that is the basis for State 4 respiration. Proton permeability is in the range 10(-3)-10(-4) cm s-1 in mitochondria and in protein-free membranes formed from extracted mitochondrial phospholipids or from stable synthetic phosphatidylcholines or phosphatidylethanolamines. The roles of cardiolipins in proton conductance in model phospholipid membrane systems need to be assessed in view of new findings by Hübner et al. [313]: saturated cardiolipins form bilayers whilst natural highly unsaturated cardiolipins form nonlamellar phases. Mitochondrial cardiolipins apparently participate in bilayers formed by phosphatidylcholines and phosphatidylethanolamines. It is not yet clear if cardiolipins themselves conduct protons back across the membrane according to their degree of fatty acyl saturation, and/or modulate proton conductance by phosphatidylcholines and phosphatidylethanolamines. Mitochondrial cardiolipins, especially those with high 18:2 acyl contents, strongly bind many carrier and enzyme proteins that are involved in oxidative phosphorylation, some of which contribute to regulation of State 3 respiration. The role of cardiolipins in biomembrane protein function has been examined by measuring retained phospholipids and phospholipid binding in purified proteins, and by reconstituting delipidated proteins. The reconstitution criterion for the significance of cardiolipin-protein interactions has been catalytical activity; proton-pumping and multiprotein interactions have yet to be correlated. Some proteins, e.g., cytochrome c oxidase are catalytically active when dimyristoylphosphatidylcholine replaces retained cardiolipins. Cardiolipin-protein interactions orient membrane proteins, matrix proteins, and on the outerface receptors, enzymes, and some leader peptides for import; activate enzymes or keep them inactive unless the inner membrane is disrupted; and modulate formation of nonbilayer HII-phases. The capacity of the proton-exchanging uncoupling protein to accelerate thermogenic respiration in brown adipose tissue mitochondria of cold-adapted animals is not apparently affected by the increased cardiolipin unsaturation; this protein seems to take over the protonophoric role of cardiolipins in other mitochondria. Many in vivo influences that affect proton leakage and carrier rates selectively alter cardiolipins in amount per mitochondrial phospholipids, in fatty acyl composition and perhaps in sidedness; other mitochondrial membrane phospholipids respond less or not at all.(ABSTRACT TRUNCATED AT 400 WORDS)

The rat liver microcirculation in alcohol-induced hepatomegaly

It has been suggested that hepatocyte enlargement can lead to compression of the extracellular space (sinusoidal and interstitial) and induce portal hypertension. However, this hypothesis has never been tested by measuring the vascular and extravascular spaces in the intact liver. The aim of the present study was to investigate the effects of chronic alcohol intake on the hepatic microcirculation using Goresky's multiple-indicator dilution technique in the isolated perfused rat liver. Female rat littermates were pair-fed either ethanol (n = 7) or an isocaloric carbohydrate diet (n = 7) for 21 days. As expected, chronic alcohol intake produced a significant increase in liver/body weight ratio (+32%, p less than 0.01) and hepatocyte size (+45%, p less than 0.001), which was accompanied by a marked increase in the cellular water space (control: 3.3 +/- 0.6 ml; ethanol-fed: 4.9 +/- 0.9 ml; p less than 0.001). When expressing data per total liver, the sinusoidal space was similar in the two groups (control: 1.87 +/- 0.2; ethanol-fed: 1.95 +/- 0.2 ml; not significant), whereas the interstitial space was increased in alcohol rats compared to controls (albumin space +58%, p less than 0.01; sucrose space +51%, p less than 0.01). In alcoholic rats, the sinusoidal space was probably stretched, with an overall reduced transversal diameter, as suggested by the reduced values found when data were expressed per gm of liver weight. However, despite this finding and the enlargement of the liver and hepatocytes observed in alcoholic rats, similar values were obtained between the two groups for the portal perfusion pressure and thus the intrahepatic vascular resistance.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition by ethanol of rat liver plasma membrane (Na+,K+)ATPase: protective effect of S-adenosyl-L-methionine, L-methionine, and N-acetylcysteine

(Na+,K+)ATPase activity of rat liver plasma membranes was evaluated in female rats feeding an ethanol containing diet for 46 days (total ethanol ingested, 59.7 g/100 g body wt). Determinations were performed at the end of ethanol treatment or at various times after stopping treatment. (Na+,K+)ATPase and 5'-nucleotidase activities exhibited a 8- and 1.4-fold decrease, respectively, at the end of ethanol ingestion. In contrast no modifications of Mg2+-ATPase activity were observed. There also occurred, in ethanol-treated rats, release of sorbitol dehydrogenase into the blood, fat accumulation in liver cells, and decrease in reduced glutathione (GSH) liver content. A decrease in (Na+,K+)ATPase activity was also found in plasma membranes isolated from hepatocyte suspensions after a 2-hr incubation with 50 mM ethanol or 1 mM acetaldehyde (ACA), in conditions that caused a great fall in hepatocyte GSH content but did not cause cell death. After the cessation of ethanol administration, there occurred a progressive recovery of (Na+,K+)ATPase activity, GSH and triacylglycerol content, and release of sorbitol dehydrogenase. These parameters reached control values 12 hr after ethanol withdrawal. S-Adenosyl-L-methionine (SAM), L-methionine, and N-acetylcysteine (NAC), given to rats during ethanol treatment, prevented the decrease in (Na+,K+)ATPase activity and GSH content. They also reduced steatosis and liver necrosis. The efficiency of these compounds decreased in this order: SAM, methionine, NAC. SAM accelerated the recovery of all parameters studied after ethanol withdrawal, and also protected (Na+,K+)ATPase activity and GSH content of isolated hepatocytes from the deleterious effect of ethanol. These SAM effects were prevented by 1-chloro-2,4-dinitro-benzene, a compound which depletes cell GSH. Treatment of isolated hepatocytes with [35S]SAM led to the synthesis of labeled GSH. The total amount and specific activity of labeled GSH underwent a significant increase, in the presence of 2 mM ethanol or 0.5 mM ACA, which indicates a marked stimulation of GSH synthesis by ethanol and ACA. These data indicate that ethanol intoxication may inhibit (Na+,K+)ATPase activity; an effect that does not seem to depend on cell necrosis. SAM, methionine, and NAC exert various degrees of protection toward ethanol-induced cell injury, which are related to the efficiency of these compounds in maintaining a high GSH pool.

Control of alcohol addiction by SKV therapy--its action on water, food intake, brain function and cell membrane composition

Alcohol being easily permeable through cell membrane causes toxic damage to many tissues. Rats drinking aqueous ethanol (25% v/v) for 120 days and 240 days showed an initial rise in body weight. The reduced rate in weight gain in chronic alcoholism is associated with a fall in food intake. Ethanol ingesting animals showed slow response to stimuli and increase in blood ethanol and serum GGTP levels. Liver plasma membrane, kidney brush-border membrane and pancreatic plasma membrane from alcoholic rats showed significant alterations in cholesterol/phospholipid molar ratio and membrane ATPases. Water retention with the enlargement of liver and kidney associated with increased fluid consumption are also seen during alcoholism. SKV by breaking alcohol dependence reduces drinking, lowers blood ethanol level and fluid intake without developing withdrawal symptoms. Restriction of ethanol intake by SKV therapy resulted in the reversal of organ enlargement and membrane composition in alcoholics.

Effects of aging and testosterone administration on liver alcohol dehydrogenase activity in male Fischer 344 rats

The activity of alcohol dehydrogenase was measured in liver cytosolic fractions of male Fischer 344 rats at ages representing young adulthood, middle age, and old age. The activities were 1.7 +/- 0.1, 2.3 +/- 0.1, and 2.6 +/- 0.2 mumol/min/g liver in rats aged 4-5, 14-15, and 24-25 months, respectively. Hepatic alcohol dehydrogenase activity in female rats (3.4 +/- 0.2 mumol/min/g liver) was the same in young as in old rats. Castration increased alcohol dehydrogenase activity in young males to levels found in females, and testosterone administration reversed the effect. However, neither physiological nor pharmacological doses of the hormone restored the elevated enzyme activities of old male rats to levels found in young male rats.

International Commission for Protection against Environmental Mutagens and Carcinogens. ICPEMC Working Paper No. 15/2. Metabolism and metabolic effects of ethanol, including interaction with drugs, carcinogens and nutrition

Different pathways of alcohol metabolism, the alcohol dehydrogenase pathway, the microsomal ethanol-oxidizing system and the catalase pathway are discussed. Alcohol consumption leads to accelerated ethanol metabolism by different mechanisms including an increased microsomal function. Microsomal induction leads to interactions of ethanol with drugs, hepatotoxic agents, steroids, vitamins and to an increased activation of mutagens/carcinogens. A number of ethanol-related complications may be explained by the production of its first metabolite, acetaldehyde, such as alterations of mitochondria, increased lipid peroxidation and microtubular alterations with its adverse effects on various cellular activities, including disturbances of cell division. Nutritional factors in alcoholics such as malnutrition are discussed especially with respect to its possible relation to cancer.

Hepatocyte and nuclear areas in alcoholic liver cirrhosis: their relationship with the size of the nodules and the degree of fibrosis

The aim of the study in alcoholic cirrhotic patients was to determine if a relationship exists between the areas of hepatocytes and their nuclei and the area of the nodules to which these cells belong as well as the thickness of the fibrous tracts which delimit these nodules. It was found that hepatocyte and nuclear areas were enlarged the smaller the nodules and the thicker the surrounding fibrous tracts. Considering that oxygen supply in liver cirrhosis decreases with increasing fibrosis, our results permit the hypothesis that a low oxygen supply causes an increase not only in liver cell size but also in nuclear size, which is an index of nuclear activity.

Inhibition of intracellular protein degradation by ethanol in perfused rat liver

Ethanol (50 mM) inhibited proteolysis in the perfused rat liver during stringent amino acid deprivation and also in the presence of normal and 10 times normal concentrations of plasma amino acids. The concentration-response curve of ethanol reached a plateau after 5 mM in both the presence and the absence of normal plasma amino acids, suggesting inhibition by oxidation products of ethanol. Intracellular glutamine, tyrosine and proline increased in concentration with ethanol, but the increases were too small to explain the observed inhibition of proteolysis. The uptake of 125I-asialofetuin was slightly decreased and the output of ammonia increased in the presence of ethanol. These, together with a significant suppression of basal proteolysis in the presence of amino acids, suggest that lysosomal function was directly affected. Electron-microscopic examination of lysosomal components showed that the aggregate volume of autophagosomes (initial vacuoles) were significantly smaller in livers perfused with ethanol than in controls. However, the equivalent volume of autolysosomes (degradative vacuoles) was the same in both groups. According to these results, ethanol inhibits protein degradation in the liver by two discrete mechanisms: one decreasing the formation of autophagic vacuoles and the other involving lysosomotropic inhibition, possibly via ammonia.

Biochemical basis of alcoholism: statements and hypotheses of present research

Experimental results and theoretical considerations on the biology of alcoholism are devoted to the following topics: genetically determined differences in metabolic tolerance; participation of the alternative alcohol metabolizing systems in chronic alcohol intake; genetically determined differences in functional tolerance of the CNS to the hypnotic effect of alcohol; cross tolerance between alcohol and centrally active drugs; dissociation of tolerance and cross tolerance from physical dependence; permanent effect of uncontrolled drinking behavior induced by alkaloid metabolites in the CNS; genetically determined alterations in the function of opiate receptors; and genetic predisposition to addiction due to innate endorphin deficiency. For the purpose of introducing the most important research teams and their main work, statements from selected publications of individual groups have been classified as to subject matter and summarized. Although the number for summary-quotations had to be restricted, the criterion for selection was the relevance to the etiology of alcoholism rather than consequences of alcohol drinking.

Effect of age on metabolic tolerance and hepatomegaly following chronic ethanol administration

Chronic consumption of ethanol often results in an increased rate of ethanol metabolism (metabolic tolerance) and in hepatomegaly. However, the extent of these changes is highly variable. We have found that these two phenomena are greatly influenced by age. We studied the effect of age on the development of metabolic tolerance and hepatomegaly and on the increase in hepatic oxygen consumption produced by chronic ethanol administration. The latter has been proposed to contribute to metabolic tolerance to ethanol. Ethanol was administered to female Sprague-Dawley rats with different initial ages (4, 6, 8, 11, and 17 weeks) for a 4-week period in a high-fat liquid diet. Control animals were pair-fed an isocaloric liquid diet in which ethanol was replaced with carbohydrate. Metabolic tolerance and hepatomegaly following chronic ethanol consumption were markedly dependent on the initial age of the animal, with young animals showing the largest increases. Although showing a similar general trend with age, the degree of metabolic tolerance was not linked proportionally with the degree of hepatomegaly. Perfused livers from young rats fed chronically with ethanol showed increases in ethanol metabolism and oxygen consumption, whereas no increase were observed in those from older animals. These findings support the hypothesis that an elevated rate of hepatic oxygen consumption contributes to metabolic tolerance. Total hepatic alcohol dehydrogenase activity was not increased by chronic ethanol consumption in any age group, demonstrating that an increase in the levels of this enzyme is not obligatory for metabolic tolerance.(ABSTRACT TRUNCATED AT 250 WORDS)

The inhibitory effect of testosterone on the development of metabolic tolerance to ethanol

We have investigated the mechanism(s) of metabolic tolerance to ethanol in a rat strain (spontaneously hypertensive or SH) in which liver alcohol dehydrogenase (ADH) levels are very low due to a marked inhibitory effect of testosterone on ADH. Chronic ethanol administration resulted in marked increases in the rate of ethanol metabolism and in ADH activity (+65 to 90%). Oxygen consumption measured in the perfused livers of the ethanol-fed rats was also elevated (+40%). The administration of 6-n-propyl-2-thiouracil (PTU), which was previously found to reduce hepatic oxygen consumption and to increase ADH activity, resulted in no change in the rate of ethanol metabolism in the ethanol-fed rats and an increase in the sucrose-fed controls, suggesting that increased ADH activity is more important for the development of metabolic tolerance to ethanol, in the male SH rat, than increased oxygen consumption. The activity of the microsomal ethanol-oxidizing system (MEOS) in vitro was induced by chronic ethanol treatment (+95%), but it may only account for a small part (32%) of the increase in ethanol metabolism in vivo. Serum testosterone concentrations were lower in the ethanol-fed rats at peak blood ethanol levels, relative to those found in controls. Concurrent chronic administration of ethanol and testosterone abolished about one-third of the absolute increases in ethanol metabolism and in ADH activity in the ethanol-fed rats. In conclusion, most of the metabolic tolerance to ethanol, in the male SH rat, appears to occur mainly due to a testosterone-independent increase in ADH activity and to a lesser degree to an increase in ADH activity produced by a reduction in testosterone levels in the ethanol-fed rats.

Hypermetabolic state and hypoxic liver damage

The concept of a hypermetabolic state to explain metabolic tolerance to ethanol grew from the recognition that the rate of alcohol metabolism is, in general, limited by the rate at which mitochondria can reoxidize reducing equivalents and thus by the rate at which oxygen can be consumed by the liver. This relationship appears to be most important in conditions in which the alcohol dehydrogenase (ADH)/QO2 ratio is high and is not in conflict with observations suggesting that ADH can, under certain conditions, constitute a rate-determining step for ethanol metabolism in rodents. Liver preparations from animals fed alcohol chronically, in which an increase in ethanol metabolism is shown, consume oxygen at higher rates. This effect, concerning which there is discrepancy among investigators, depends on the type of preparation. Thyroid hormones play a permissive role in the development of the hypermetabolic state, while increased circulating levels of these hormones are not required. Antithyroid drugs inhibit both metabolic tolerance in vivo and the hypermetabolic state. While the hypermetabolic state requires an increased ATP utilization in the form of an adenosine triphosphatase, or an inhibition of ATP synthesis, the different mechanisms proposed for such an effect do not quantitatively account for the increases in oxygen consumption. In humans and animals chronically exposed to ethanol, but withdrawn, oxygen tensions in blood leaving the liver are significantly reduced. In some situations, low oxygen tensions in zone 3 of the hepatic acinus can reach critical hypoxic levels and may lead to cell necrosis. Studies in which the effectiveness of propylthiouracil is tested in human alcoholic hepatitis are discussed.

Effect of ethanol on hepatic secretory proteins

Both acute and chronic ethanol administration inhibit the secretion of albumin and glycoproteins from the liver. Impairment of posttranslational steps of the secretory process are mainly involved in this secretory defect, although in some instances altered synthesis of the protein moiety may be a factor. Decreased secretion following ethanol administration results in the intrahepatic retention of export proteins. The secretory defect is a consequence of the metabolism of ethanol and is likely mediated via acetaldehyde, although more conclusive proof is still required. The manner by which acetaldehyde impairs the secretory process is unknown, but may be related to its high reactivity with hepatocellular proteins. The specific posttranslational steps or processes involved in the secretory defect are still unclear; however, it appears that the final steps of secretion (post-Golgi events) may be the primary site of impairment. Impaired secretion of proteins from the liver could contribute to altered levels of plasma proteins and hepatomegaly as well as to the liver injury observed in the alcoholic.

Time interval between sequential exposures to ethanol is critical for the development of neural tolerance or sensitivity

DBA/2 and SW mice were injected sequentially with 4 g/kg body weight of ethanol five times at 24-, 48- and 72-h intervals, and the sleeping time induced by each exposure was recorded. DBA/2 mice given ethanol at 24-h and 48-h intervals developed tolerance, i.e., slept less than previously untreated animals, whereas SW mice slept longer, i.e., developed an increased neural sensitivity to ethanol. Injection of ethanol at 72-h intervals did not change the duration of sleep in either mouse strain. These data show the importance of timing of sequential ethanol injections for the induction of both tolerance and increased neural sensitivity.

Rat liver alcohol dehydrogenase. II. Quantitative enzyme-linked immunoadsorbent assay

Monospecific rabbit antibodies against purified Fischer-344 rat liver alcohol dehydrogenase were produced and used to develop an enzyme-linked immunoadsorbent assay for alcohol dehydrogenase. The assay is based upon the competitive inhibition of specific antibody binding to antigen (alcohol dehydrogenase adsorbed onto plastic microtiter plates) by soluble alcohol dehydrogenase (contained in unknown sample extracts or in known standard solutions). The amount of bound antibody is determined following incubation with peroxidase-linked second antibody (goat anti-rabbit IgG antibody-peroxidase conjugate) by colorimetric measurements of peroxidase activity at 490 nm in the presence of O-phenylenediamine. The assay is highly sensitive (it detects 10-1000 ng alcohol dehydrogenase/50 microliter) and it offers a precise (interexperimental variations in samples were less than 10%), rapid (6-8 h), and specific method for measurements of alcohol dehydrogenase in tissue homogenates or cultured hepatocytes. The assay was used to study changes in alcohol dehydrogenase levels during the growth cycle of cultured hepatocytes over a 2-week period and in rat liver homogenates after starving the animals for 72 h. In cultured hepatocytes, alcohol dehydrogenase activity and immunoassayable enzyme levels decreased coordinately during lag and early log phase, from 13.2 +/- 1.2 to 5.0 +/- 1.0 micrograms enzyme/mg protein, respectively. In mid-log phase, the enzyme levels were very low (1.3 +/- 0.4 micrograms enzyme/mg protein). During stationary phase, the levels (5.7 +/- 0.6 micrograms enzyme/mg protein) increased to 35% of the levels of freshly isolated hepatocytes (15.6 +/- 1.4 micrograms enzyme/mg protein). In starved animals, the enzyme levels decreased from 7.56 +/- 0.55 to 2.97 +/- 0.27 mg enzyme/liver. These changes also coincided with decreases in activity from 8.84 +/- 0.35 to 6.56 +/- 0.68 microM/min/liver.

Effects of ethanol and acetaldehyde on hepatic plasma membrane ATPases

To elucidate possible causes of the hepatocyte swelling and necrosis found in alcoholic liver disease, the effects of ethanol and acetaldehyde on the activities of two hepatic plasma membrane ATPases--(Na+K+) ATPase and Mg2+ ATPase--were investigated. The activity of another plasma membrane-bound enzyme, 5' nucleotidase, was also determined to assess the specificity of these effects. Over concentrations ranging from 8 to 90 mM ethanol did not cause significant inhibition of any of the three enzymes. At 120 mM ethanol (Na+K+) ATPase activity was inhibited by 20% (P less than 0.01) and at higher concentrations there was progressive inhibition of all three enzymes that was non-competitive in type. Acetaldehyde produced non-competitive inhibition of (Na+K+) ATPase and Mg2+ ATPase at concentrations of 6 and 56 mM respectively and 5' nucleotidase activity was also inhibited at these concentrations. We conclude that ethanol and acetaldehyde inhibit (Na+K+) ATPase and Mg2+ ATPase activities as part of a generalised effect on the liver plasma membrane. Because the inhibitory concentrations of both substances are higher than are usually found in alcoholic subjects or in experimental animals after alcohol feeding, it seems unlikely that direct suppression of ATPase activity by ethanol or acetaldehyde is responsible for the morphological abnormalities of alcohol-induced liver disease. It could, however, be implicated in the development of hepatocellular necrosis in severe ethanol poisoning.

On the characteristics of alcohol-induced liver enlargement and its possible hemodynamic consequences

Chronic consumption of alcohol leads to an increase in liver weight, primarily due to an increase in hepatocyte volume. About 50-60% of such an increase is due to an increase in intracellular water. Accumulation of intracellular K+ osmotically accounts for about one half of the increase in intracellular water, while an increase in soluble proteins plays only a minor role in such an increase in cell volume. The increase in intracellular water is accompanied by a relative reduction in water in the extracellular space, probably due to compression of the extracellular volume by the enlarged hepatocytes. It is suggested that such an increase in hepatocyte size, with an attending reduction of the extracellular volume, results in an increased resistance to blood flow through the liver and thus in an increase in portal pressure. In alcoholics, portal and intrahepatic pressure correlate with cell size both in cirrhotics (r = 0.79) and in non-cirrhotics (r = 0.74), thus suggesting that cell enlargement plays a major role in the production of portal hypertension in the alcoholic.

Zonal redox changes as a cause of selective perivenular hepatotoxicity of alcohol

Alcohol-induced lesions predominate in perivenular zones of the liver. To test the hypothesis that ethanol aggravates hypoxia in this zone by stimulating oxygen consumption, we measured hepatic venous pO2 after ethanol-administration to both alcohol-fed baboons (with perivenular lesions) and their controls, and found no changes: the stimulation of oxygen consumption was fully offset by a parallel increase in blood flow. Despite the lack of hypoxia, ethanol increased lactate/pyruvate (L/P) 15-fold in hepatic venous blood and only 3-fold in liver tissue. Addition of lactate to increase arterial L/P several-fold produced no changes in the hepatic venous ratio, indicating that the equilibrium between this ratio and the cytosolic redox state was reached in one passage through the liver. Thus, the higher L/P in hepatic venous blood most likely reflects an enhanced redox shift in perivenular zones. In isolated hepatocytes, a pO2 comparable to that normally prevailing in perivenular zones mimicked the exaggeration of the ethanol-induced redox shift and aggravated inhibition of protein synthesis. We therefore propose an alternate mechanism for the selective perivenular injury; namely, that the low pO2 normally prevailing at this site aggravates the redox-linked toxicity of ethanol.

Sex-dependency of hepatic alcohol metabolizing enzymes

In mature female rats the administration of testosterone led to a striking reduction of hepatic alcohol dehydrogenase activity, whereas the hepatic microsomal ethanol oxidizing system as well as catalase were both increased in activity under these experimental conditions. Conversely, estradiol left the activities of all hepatic alcohol metabolizing enzymes virtually unchanged. Ovariectomy also had little if any influence on the activity levels of the enzymes. There was a clear difference between the sexes in the hepatic alcohol metabolizing enzymes with higher enzymic activities of the microsomal ethanol oxidizing system and catalase in male than in female rats, whereas the opposite constellation was found for alcohol dehydrogenase activity. These data therefore indicate the sex-dependent nature of alcohol dehydrogenase, the hepatic microsomal ethanol oxidizing system and catalase activities in rat liver.

Control of alcohol tolerance by reinforcement in nonalcoholics

The development of tolerance to alcohol was examined in two experiments with nonalcoholic drinkers. In both experiments, male undergraduates received pretraining on a pursuit rotor task and were then randomly assigned to either alcohol or placebo conditions. In the first experiment, monetary and performance feedback reinforcement for pursuit rotor performance were provided to both groups over four drinking sessions. In the second experiment, two final drinking sessions were added where no reinforcement was provided to either the alcohol or placebo subjects, and an additional alcohol group received no reinforcement throughout the six drinking sessions. Tolerance to the impairing effects of alcohol on pursuit rotor performance developed only for the reinforced alcohol subjects; withdrawal of reinforcement from tolerant subjects resulted in a return of impaired performance, i.e. tolerance was extinguished. Impairment remained consistently high in the non-reinforced alcohol subjects throughout all six drinking sessions. The results provide support for the learning hypothesis of behavioural tolerance by demonstrating that its acquisition and extinction may be controlled by reinforcement.

Does cellular tolerance develop to the lethal effect of ethanol in the rat?

Rats were kept intoxicated by forced intragastric administration of a liquid diet containing ethanol for 4 days or 3 weeks. Control animals were pair-fed with the same liquid diet containing starch instead of ethanol. After withdrawal the animals pretreated for 3 weeks showed tolerance to the lethal effect of ethanol as indicated by significantly prolonged survival and higher cerebrospinal fluid ethanol level at death after an oral test dose of 15 g/kg. The tolerance disappeared within a week. Metabolic tolerance, although present, did not prolong the survival of the animals, and the results suggest involvement of cellular tolerance in the central nervous system.

Experimental fibrogenesis: enhancement by chronic ethanol administration

The authors have presented a new, simple, and reproducible model of fibrogenesis and have shown that chronic alcohol treatment clearly stimulates the production of fibrous tissue in this model.