Enrique Baraona

Pathogenesis of alcohol-induced accumulation of protein in the liver.

Alcohol feeding to rats produced hepatomegaly, associated with enlargement of the hepatocytes. The increase in liver dry weight was accounted for not only by fat but also by protein accumulation, primarily in microsomes and cytosol, with a selective increase in export proteins: concentrations of both immunoreactive albumin and transferrin were augmented in liver microsomes and cytosol of ethanol-fed rats. To investigate the mechanism of this protein accumulation, [14C]leucine was injected intravenously and its incorporation into both liver and serum proteins was measured after various time intervals. Rates of synthesis and export were assessed from protein labeling and specific activities of leucyl-tRNA. Synthesis of liver protein and proalbumin were enhanced by chronic ethanol feeding, but this was not associated with a corresponding rise in serum albumin output. Actually, there was a significant retention of the label in liver albumin and transferrin with delayed appearance in the serum of ethanol-fed rats. This indicated that, regardless of the changes in synthesis, the export of protein from the liver into the plasma was impaired. This alteration in export was associated with a decreased amount of polymerized tubulin in the liver of ethanol-treated animals. Thus, both enhanced protein synthesis and defective export contribute to the ethanol-induced accumulation of liver protein, and the decrease in liver microtubules represents a possible site for impairment of protein export.

Small Intestinal Damage and Changes in Cell Population Produced by Ethanol Ingestion in the Rat

Abstract Acute intragastric administration of ethanol in concentrations similar to those of common alcoholic beverages produced hemorrhagic erosions of the small intestinal villi in rats. The lesions were most obvious proximally and were concentration-dependent. Moderate lesions produced by a low ethanol concentration (5 g per 100 ml) were associated with decreased activities of jejunal lactase ( − 25%, P P P P P P P P P P 3 H-thymidine into deoxyribonucleic acid (+60%, P

Effects of chronic ethanol feeding on serum lipoprotein metabolism in the rat

In rats, chronic ethanol feeding was found to enhance the postprandial hyperlipemia and to increase the incorporation of dietary palmitic acid-(3)H and intravenously injected L-lysine-(14)C into serum lipoproteins. The main increases of total amount, labeling, and specific activity of lipid and protein occurred in the d < 1.019 lipoprotein fraction. Fat absorption and the clearance of injected chylomicrons were not affected by ethanol feeding. Blocking of lipoprotein and chylomicron removal with Triton did not prevent the action of ethanol on serum lipids, indicating that the ethanol effect is not likely due to defective removal of lipids from the circulation. Ethanol enhanced the incorporation of chylomicron fatty acids into newly synthetized very low density lipoproteins, as shown by an increased reappearance of the fatty acid label into the lipids of this fraction after injection of palmitate-(14)C/glycerol-(3)H doubly labeled chylomicrons. These results indicate that alcoholic hyperlipemia is due, at least in part, to an increase in newly synthetized lipoproteins. The hyperlipemia produced by ethanol was accompanied by hepatic steatosis. The simultaneous production of fatty liver and hyperlipemia makes it unlikely that defective lipoprotein synthesis or secretion is a primary mechanism for the pathogenesis of the alcoholic fatty liver.

Effects of Cimetidine on Gastric Alcohol Dehydrogenase Activity and Blood Ethanol Levels

Chronic use of cimetidine and alcohol are commonly associated, but studies on their interactions are the subject of controversy. To investigate this question, a small ethanol dose (0.15 g/kg body wt) was randomly administered on 2 consecutive days either orally or intravenously to 6 normal volunteers, before and after 1 wk of oral administration of 400 mg of cimetidine twice daily. Although cimetidine did not change the areas under the curve of blood ethanol concentrations after intravenous administration, those after oral alcohol intake were twice as large with cimetidine than without. Similar effects were reproduced in rats after intravenous administration of cimetidine (50 mg/kg body wt). In vitro, cimetidine was a noncompetitive inhibitor of gastric alcohol dehydrogenase activity at concentrations as low as 0.01 mM, 100-fold lower than those needed to inhibit the hepatic dehydrogenase. These results indicate that gastric alcohol dehydrogenase activity governs, in part, the systemic bioavailability of ethanol. Consequently, systemic effects of alcohol may be exacerbated in patients receiving cimetidine.

Role of intestinal bacterial overgrowth in ethanol production and metabolism in rats

To investigate the role of intestinal bacterial overgrowth on the production and metabolism of ethanol, rats with a jejunal self-filling diverticulum (blind-loop) were compared to controls with a self-emptying diverticulum. Both endogenous ethanol and acetaldehyde were found in the blind-loop contents. Intragastric administration of sucrose produced a marked increase in acetaldehyde and acetate in the portal venous blood, with only a modest elevation of ethanol. Blind-loop contents readily oxidized ethanol to acetaldehyde in a concentration-dependent manner and more actively under aerobic than anaerobic conditions. This oxidation was inhibited by antibiotics and was reproduced with isolated microorganisms. Intragastric administration of ethanol to rats with blind-loops markedly increased acetaldehyde and acetate concentrations in the portal vein and, to a lesser extent, in the systemic blood, compared with the controls. By contrast, both portal and systemic blood ethanol concentrations were lower in the rats with a blind-loop compared with controls, even though the amounts of ethanol retained in the digestive tract were similar. A dose of ethanol about twice as large as in controls was required to produce similar systemic blood levels. Both in rats with a blind-loop and in the controls, the areas under the curve of blood ethanol concentrations were smaller after intragastric than after intravenous ethanol administration (1 g ethanol/kg body wt). This difference was exaggerated in the rats with a blind-loop. Thus, a considerable amount of ethanol is oxidized in the gastrointestinal lumen of rats with a blind-loop. The resulting high concentrations of acetaldehyde, both in the intestinal lumen and the portal blood, may have deleterious effects on the gastrointestinal mucosa and the liver.

First pass metabolism of ethanol: An important determinant of blood levels after alcohol consumption

Alcohol consumption by rats fed ethanol-containing liquid diets is considerably greater than the measured rate of ethanol elimination from the blood, suggesting that a significant fraction of the alcohol ingested does not enter the systemic circulation. To assess the possibility of a first pass metabolism of ethanol, we compared the areas under the blood ethanol concentration curves after administration of various doses through various routes in alcohol-fed and control rats. In both groups, blood ethanol concentrations were significantly lower after intragastric than after intraportal or intravenous (femoral) administrations and, to a lesser extent, than after an intraduodenal dose. By contrast, the rise in blood acetate, a product of ethanol oxidation, was faster after intragastric administration. Moreover, absorption of the ethanol dose was virtually complete at the time of ethanol disappearance from the blood. The fraction of the dose that did not enter the systemic circulation was proportionally greater with the smaller doses. These results indicate that there is a significant first pass metabolism of ethanol which takes place in the gastrointestinal tract and particularly in the stomach, where alcohol dehydrogenase (ADH) activity is the highest. Chronic alcohol administration decreased ADH activity (probably secondary to gastric mucosal injury) and also decreased the magnitude of the first pass metabolism. The amount of ethanol ingested which does not enter the systemic circulation accounts for the apparent dissociation between alcohol consumption, blood ethanol levels and rate of blood ethanol elimination in alcohol-fed animals.

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.

Lack of alcohol dehydrogenase isoenzyme activities in the stomach of Japanese subjects

Alcohol dehydrogenase (ADH) isoenzymes different from those of the liver were shown to be present in the human gastric mucosa. Two ADH activity bands present in the gastric mucosa of surgical specimens from all 7 black and 11 white Americans studied were absent in 14 and barely detectable in 3 of 21 Japanese subjects evaluated. Similar ethnic differences pertained to both genders and were independent of the gastric pathology. The mobility of these bands on starch gel electrophoresis corresponded to those recently reported and named mu-ADH or sigma-ADH. The absence of these bands was associated with a 70% decreased capacity to reduce m-nitrobenzaldehyde, a preferred substrate for sigma-ADH, suggesting that the bands missing from the Japanese stomachs comprise this isoenzyme.

Increased hepatic oxygenation following ethanol administration in the baboon.

Summary The effects of ethanol on hepatic oxygenation were measured by hepatic vein catheterization in the baboon. Chronic alcohol administration resulted in slightly lower oxygen tension in the hepatic vein, but not ischemia, when measured after an overnight fast when alcohol was no longer present in the blood. Intravenous alcohol administration resulted in an increase in hepatic vein oxygen tension regardless of prior exposure to alcohol or the presence of liver disease. The increased oxygen tension after alcohol was associated with a marked increase in hepatic blood flow. These data in conjunction with the observation of progressive liver injury in the alcohol-fed animals support the concept that alcoholic liver injury can develop despite unimpaired hepatic oxygenation.

Pathogenesis of Postprandial Hyperlipemia in Rats Fed Ethanol-Containing Diets

To study the mechanism of the increase in serum lipoproteins which occurs in rats fed alcohol chronically, and especially to assess the role of the intestine, the effects of acute and chronic ethanol administration on lymph and plasma lipids were compared in rats with and without intestinal lymph fistulae. In rats not previously given alcohol, the administration of one dose of a diet containing ethanol (3 g/kg) produced a significant increase in lymph flow, lipid output, and incorporation of dietary fat into lymph lipids when compared with the effects of a control diet containing isocaloric carbohydrate. However, no hyperlipemia developed after ethanol. By contrast, previous feeding of ethanol for several weeks modified the acute effects of ethanol on both lymph and serum lipids. Compared with control animals pair-fed with isocaloric carbohydrate-containing diets, rats which had been fed a diet with 36% of total calories as ethanol for 3-4 wk developed postprandial hyperlipemia when given a single dose of the ethanol-containing or even the ethanol-free diet. This was associated with an increased incorporation of labeled dietary fat and of intravenously injected [(3)H]lysine into plasma lipoproteins of d < 1.006. However, postprandial lymph flow and lipid output were not higher in rats fed alcohol chronically than in their pair-fed controls. Moreover, when rats with lymph fistulae were given intravenous (i.v.) infusions of lymph lipids (to substitute for the diverted intestinal lymph), the ethanol-fed animals still developed hyperlipemia. Incorporation of i.v. lysine into d < 1.006 plasma lipoproteins also remained significantly increased. Thus, under these conditions, alcoholic hyperlipemia does not result from changes in intestinal lymph lipids. Two main factors appear to be involved; the acute effects of ethanol on hepatic lipid metabolism and the development of an increased capacity for lipoprotein synthesis during chronic ethanol feeding. The latter most likely occurs in the liver and it is postulated that it is linked to the associated changes in the hepatic endoplasmic reticulum.