Inhibition of glycoprotein secretion by ethanol and acetaldehyde in rat liver slices

Exposure of precision-cut rat liver slices to ethanol accelerates fibrogenesis

Ethanol metabolism in the liver induces oxidative stress and altered cytokine production preceding myofibroblast activation and fibrogenic responses. The purpose of this study was to determine how ethanol affects the fibrogenic response in precision-cut liver slices (PCLS). PCLS were obtained from chow-fed male Wistar rats (200-300 g) and were cultured up to 96 h in medium, 25 mM ethanol, or 25 mM ethanol and 0.5 mM 4-methylpyrazole (4-MP), an inhibitor of ethanol metabolism. Slices from every time point (24, 48, 72, and 96 h) were examined for glutathione (GSH) levels, lipid peroxidation [thiobarbituric acid-reactive substance (TBARS) assay], cytokine production (ELISA and RT-PCR), and myofibroblast activation [immunoblotting and immunohistochemistry for smooth muscle actin (SMA) and collagen]. Treatment of PCLS with 25 mM ethanol induced significant oxidative stress within 24 h, including depletion of cellular GSH and increased lipid peroxidation compared with controls (P < 0.05). Ethanol treatment also elicited a significant and sustained increase in interleukin-6 (IL-6) production (P < 0.05). Importantly, ethanol treatment accelerates a fibrogenic response after 48 h, represented by significant increases in SMA and collagen 1alpha(I) production (P < 0.05). These ethanol-induced effects were prevented by the addition of 4-MP. Ethanol metabolism induces oxidative stress (GSH depletion and increased lipid peroxidation) and sustained IL-6 expression in rat PCLS. These phenomena precede and coincide with myofibroblast activation, which occurs within 48 h of treatment. These results indicate the PCLS can be used as in vitro model for studying multicellular interactions during the early stages of ethanol-induced liver injury and fibrogenesis.

Alcohol consumption impairs hepatic protein trafficking: mechanisms and consequences

Alcoholic liver disease is a major biomedical health concern in the United States. Despite considerable research efforts aimed at understanding the progression of the disease, the specific mechanisms leading to alcohol-induced damage remain elusive. Numerous proteins are known to have alcohol-induced alterations in their dynamics. Defining these defects in protein trafficking is an active area of research. In general, two trafficking pathways are affected: transport of newly synthesized secretory or membrane glycoproteins from the Golgi to the basolateral membrane and clathrin-mediated endocytosis from the sinusoidal surface. Both impaired secretion and internalization require ethanol metabolism and are likely mediated by acetaldehyde. Although the mechanisms by which ethanol exposure impairs protein trafficking are not fully understood, recent work implicates alcohol-induced modifications on tubulin or components of the clathrin machinery as potential mediators. Furthermore, the physiological ramifications of impaired protein trafficking are not fully understood. In this review, we will list and discuss the proteins whose trafficking patterns are known to be impaired by ethanol exposure. We will then describe what is known about the possible mechanisms leading to impaired protein trafficking and how disrupted protein trafficking alters liver function and may explain clinical features of the alcoholic patient.

An in vitro method of alcoholic liver injury using precision-cut liver slices from rats

Alcohol abuse results in liver injury, but investigations into the mechanism(s) for this injury have been hampered by the lack of appropriate in vitro culture models in which to conduct in depth and specific studies. In order to overcome these shortcomings, we have developed the use of precision-cut liver slices (PCLS) as an in vitro culture model in which to investigate how ethanol causes alcohol-induced liver injury. In these studies, it was shown that the PCLS retained excellent viability as determined by lactate dehydrogenase and adenosine triphosphate (ATP) levels over a 96-h period of incubation. More importantly, the major enzymes of ethanol detoxification; alcohol dehydrogenase, aldehyde dehydrogenase, and cytochrome P4502E1, remained active and PCLS readily metabolized ethanol and produced acetaldehyde. Within 24 h and continuing up to 96h the PCLS developed fatty livers and demonstrated an increase in the redox state. These PCLS secreted albumin, and albumin secretion was decreased by ethanol treatment. All of these impairments were reversed following the addition of 4-methylpyrazole, which is an inhibitor of ethanol metabolism. Therefore, this model system appears to mimic the ethanol-induced changes in the liver that have been previously reported in human and animal studies, and may be a useful model for the study of alcoholic liver disease.

WIF-B cells as a model for alcohol-induced hepatocyte injury

A potential in vitro model for studying the mechanisms of alcohol-induced hepatocyte injury is the WIF-B cell line. It has many hepatocyte-like features, including a differentiated, polarized phenotype resulting in formation of bile canaliculi. The aim of this study was to examine the effects of ethanol treatment on this cell line. WIF-B cells were cultured up to 96 h in the absence or presence of 25 mM ethanol and subsequently were analyzed for ethanol-induced physiological and morphological changes. Initial studies revealed WIF-B cells exhibited alcohol dehydrogenase (ADH) activity, expressed cytochrome p4502E1 (CYP2E1), and efficiently metabolized ethanol in culture. This cell line also produced the ethanol metabolite acetaldehyde and exhibited low K(m) aldehyde dehydrogenase (ALDH) activity, comparable to hepatocytes. Ethanol treatment of the WIF-B cells for 48 h led to significant increases in the lactate/pyruvate redox ratio and cellular triglyceride levels. Ethanol treatment also significantly altered WIF-B morphology, decreasing the number of bile canaliculi, increasing the number of cells exhibiting finger-like projections, and increasing cell diameter. The ethanol-induced changes occurring in this cell line were negated by addition of the ADH inhibitor, 4-methylpyrazole (4-MP), indicating the effects were due to ethanol metabolism. In summary, the WIF-B cell line metabolizes ethanol and exhibits many ethanol-induced changes similar to those found in hepatocytes. Because of these similarities, WIF-B cells appear to be a suitable model for studying ethanol-induced hepatocyte injury.

Quantification of acetaldehyde released by lung cancer cells in vitro using selected ion flow tube mass spectrometry

The production of volatile compounds from cancer cell lines in vitro has been investigated using selected ion flow tube mass spectrometry (SIFT-MS). This technique enables on-line quantitative analyses of the headspace above cell/medium cultures. This paper reports the discovery that acetaldehyde is released by the lung cancer cell lines SK-MES and CALU-1. The concentration of acetaldehyde in the headspace of the medium/cell culture was measured after 16 h incubation at 37 degrees C and found to be proportional to the number of cancer cells in the medium (typically 10(8)). From these data, the acetaldehyde production rates of the SK-MES cells and the CALU-1 cells in vitro are determined to be 1 x 10(6) and 1.5-3 x 10(6) molecules/cell/min, respectively. The potential value of this new technique in cell biology and in industrial cell biotechnology is discussed.

Relationship between acetaldehyde levels and cell survival in ethanol-metabolizing hepatoma cells

We have created a number of recombinant Hep G2 cell lines, designated VA cells, that constitutively express alcohol dehydrogenase. Oxidation of ethanol by the VA cells results in the production and accumulation of acetaldehyde, and a dramatic increase in the nicotinamide adenine dinucleotide, reduced (NADH)/nicotinamide adenine dinucleotide (NAD(+)) ratio (redox-state). It is believed that production of acetaldehyde, and the increase in the redox-state of hepatocytes, are responsible for many of the dysfunctions associated with alcoholic liver disease. When the VA cells were cultured in the presence of ethanol, we observed a dramatic reduction in cell accumulation. This reduction was more pronounced in cells that metabolized ethanol more efficiently. Inhibition of alcohol dehydrogenase activity abolished this reduction, demonstrating that ethanol oxidation was required for this dysfunction. Subsequent investigations indicated that this ethanol oxidation-mediated reduction in cell accumulation was the result of both cytotoxicity and impaired DNA synthesis. To dissociate the increase in the cellular redox-state from acetaldehyde production, VA cells were cultured in the presence of isopropanol. The oxidation of isopropanol results in similar redox changes, but the metabolic by-product of isopropanol oxidation is acetone. The metabolism of isopropanol by VA cells resulted in very little reduction in cell number. Furthermore, treatment of ethanol-metabolizing VA cells with the aldehyde dehydrogenase inhibitor, cyanamide, increased the levels of acetaldehyde and resulted in an additional reduction in cell number. In conclusion, these studies indicated that exposure to acetaldehyde caused cytotoxicity, as well as the ethanol oxidation-mediated reduction in cell number.

Sialic acid: new potential marker of alcohol abuse

BACKGROUND

A number of laboratory markers are suggested for the detection and monitoring of alcohol abuse. However, there is still a need to find better indicators of alcohol abuse. Sialic acid (SA) is the name for a series of acyl-derivatives of neuraminic acids that occur as nonreducing terminal residues of glycoproteins or glycolipids in biological fluids and cell membranes. In this study, we investigated the diagnostic value of SA as a marker of alcohol abuse.

METHODS

Sera from social drinkers (n = 38) and alcoholics (n = 77) were analyzed for sialic acid by a colorimetric assay and for carbohydrate-deficient transferrin (CDT) by a radioimmunoassay method. Mean corpuscular volume (MCV), gamma-glutamyltransferase (GGT), aspartate aminotransferase (ASAT), and alanine aminotransferase (ALAT) were determined by using routine methods.

RESULTS

The sialic acid levels of both female and male subjects were significantly (p < 0.001) increased among alcoholic subjects when compared with social drinkers. SA levels were decreased after 3 weeks of treatment. The sensitivity and specificity for SA, respectively, were 57.7 and 95.5 for women and 47.8 and 81.3 for men. The respective values for CDT were 57.7 and 95.5 for women and 78.3 and 100.0 for men; for GGT, 60.0 and 95.5 for women and 60.9 and 87.5 for men; for MCV, 52.4 and 95.5 for women and 47.8 and 100.0 for men; for ASAT, 53.8 and 95.5 for women and 43.5 and 100.0 for men; and for ALAT, 38.5 and 90.9 for women and 39.1 and 87.5 for men. Among women, SA and GGT, and among men CDT, showed the largest area under receiver operation curve.

CONCLUSION

This study indicated that sialic acid levels were elevated by high alcohol consumption and reduced during abstinence, especially among women. Thus, sialic acid seems to be an interesting marker that needs further evaluation as a diagnostic tool for alcohol abuse.

Ethanol-induced retention of nascent proteins in rat hepatocytes is accompanied by altered distribution of the small GTP-binding protein rab2

Chronic ethanol consumption induces hepatocellular retention of nascent proteins leading to hepatomegaly. While the molecular mechanisms behind this impairment are undefined, it has been predicted that protein retention results from a disruption of vesicle-mediated secretory processes. Small GTP-binding proteins (rab proteins) have recently been implicated in the regulation of vesicular trafficking in eukaryotic cells. Our objectives were to identify intracellular sites of ethanol-induced protein retention and to determine whether the distribution of secretory rab proteins was altered by ethanol. Transport of hepatic proteins along the secretory pathway in livers from control and ethanol-fed rats was analyzed using subcellular fractionation and immunoprecipitation in the context of in vivo pulse-chase experiments. We show that pre-Golgi and Golgi compartments, as well as secretory vesicles, are sites of ethanol-induced retention of nascent soluble and transmembrane secretory proteins. These results are supported by immunofluorescence localization of hepatic proteins on liver sections. Further, immunoblot analyses of hepatic subcellular fractions from ethanol-damaged livers indicate a dramatic reduction in the association of rab2 with a Golgi compartment as compared with controls. In contrast, rab6 and alpha-mannosidase II, Golgi marker proteins, appear unchanged. These studies provide a detailed analysis of the intracellular site of ethanol-induced protein retention in the hepatocyte and lend novel insight into a potential mechanism behind this impairment. The effects of ethanol exposure on rab proteins and Golgi function are discussed.

Feeding patterns of rats chronically ingesting an ethanol-containing liquid diet

We compared the feeding patterns of rats ingesting a 36% ethanol-containing liquid diet for 30 days with those of rats pair-fed an isocaloric liquid control diet or provided control diet or ground rat chow ad libitum. Ethanol-fed rats consumed fewer calories per day and gained less body weight than rats fed control diets ad libitum. Daily caloric intakes were approximately 50% lower during the first 10 days and 20% thereafter. Lower intakes in ethanol-fed rats occurred through a decrease in mean meal size rather than number of meals per day, although meals were more evenly distributed diurnally. Pair-fed rats ingested most of their food in one or two meals within a few hours of presentation. In a related experiment, a 4-hr duodenal infusion of ethanol at a rate comparable to that of ethanol ingestion resulted in plasma ethanol levels of 28 +/- 4 mM and suppressed 5-hr intake by approximately 40% by increasing the mean postmeal interval and satiety ratio. These results suggest that the suppressive effect of ethanol ingestion on food intake may be mediated in part by a post-gastric mechanism of ethanol action.

In vivo hepatic 31P magnetic resonance spectroscopy in chronic alcohol abusers

BACKGROUND/AIMS

In vivo hepatic 31P magnetic resonance spectroscopy (MRS) can provide information on hepatic energy metabolism, phospholipid substrates, and hepatocyte lipid bilayers. The aim of this study was to ascertain the effects of alcohol ingestion on hepatic 31P spectral variables.

METHODS

Twenty-six chronic alcohol abusers underwent hepatic 31P MRS 6-12 hours after their last alcoholic drink; studies were repeated in 17 individuals following abstinence from alcohol. The reference population comprised 16 healthy volunteers. Ratios of phosphomonoesters (PME), inorganic phosphate, and phosphodiesters (PDE) relative to beta-adenosine triphosphate (ATP) were measured.

RESULTS

In patients with minimal liver injury, recent drinking was associated with a significant elevation in the mean PDE/ATP ratio (P < 0.0001) and an increase in mean PME/ATP, which was not significant; abstinence was associated with reductions in both metabolite ratios. In patients with alcoholic cirrhosis, recent drinking was associated with an elevation in mean PME/ATP (P < 0.05) and an increase in mean PDE/ATP, which was not significant; abstinence was associated with no significant change in PME/ATP but with a reduction in PDE/ATP.

CONCLUSIONS

In the absence of significant liver injury, chronic alcohol abuse is associated with the elevation of PME/ATP, possibly reflecting changes in hepatic redox potential, and of PDE/ATP, most likely reflecting the induction of hepatocyte endoplasmic reticulum. In the presence of cirrhosis, these changes are attenuated and modified.

Correlations between serum proteins modified by acetaldehyde and biochemical variables in heavy drinkers

A strong and highly significant correlation was observed between serum aspartate transaminase (AST) activity and an index of the cytotoxic activity associated with serum proteins modified by acetaldehyde in a group of 24 heavy drinkers. A weaker but significant correlation (R = 0.564, p = 0.008) was found between total serum creatine kinase activity and this index of serum cytotoxicity. As it is likely that the concentration of circulating modified protein was largely determined by the quantity of free acetaldehyde generated in the liver and that the AST activity was mainly derived from damaged hepatocytes, the data indicate a correlation between hepatic acetaldehyde generation and hepatocyte damage. This correlation may indicate either that increased quantities of acetaldehyde are released by damaged hepatocytes or that acetaldehyde is hepatotoxic in vivo. As only the creatine kinase isoenzyme present in skeletal muscle (CK-MM) was demonstrable in the serum in all but one of our patients, the data also suggest that circulating modified serum proteins may be toxic towards skeletal muscle cells.

Role of acetaldehyde in the ethanol-induced impairment of hepatic glycoprotein secretion in the rat in vivo

Ethanol administration inhibits hepatic protein and glycoprotein secretion. Previous studies have shown that the metabolism of ethanol is required for this effect. Experiments were designed to determine whether acetaldehyde, the first metabolite of ethanol oxidation, mediated the ethanol-induced secretory defect in rats with normal and stimulated (inflammation-induced) rates of hepatic protein secretion. This study used cyanamide, an aldehyde dehydrogenase inhibitor, to correlate enhanced acetaldehyde levels with an increased ethanol-induced inhibition of hepatic protein secretion. Inflammation was induced by turpentine 24 hr prior to cyanamide (5 mg per kg body weight) or saline pretreatment. Nonfasted rats were intragastrically gavaged with ethanol (4 to 6 gm per kg body weight) or isocaloric glucose 1 hr following pretreatment. [3H]Fucose and/or [14C]leucine were injected intravenously 2 hr following intubation. With elevated levels of acetaldehyde, the ethanol-induced impairment of secretion of labeled proteins and their parallel retention in the liver were markedly potentiated. During inflammation, this inhibition of secretion by ethanol was maintained and further increased with cyanamide pretreatment. These results indicate that the ethanol-induced impairment of hepatic glycoprotein secretion is mediated by acetaldehyde in both normal and inflammation-stimulated animals.

The role of the hepatocellular redox state in the hepatic triglyceride accumulation following acute ethanol administration

The role of the increased hepatocellular redox-state [( NADH]/[NAD+] ratio) as a mechanism underlying hepatic triglyceride deposition after acute ethanol dosing has been investigated in the rat. Following a single dose of ethanol (2 g/kg i.p.) in fasted rats, increases were observed at 1.5 hr in the hepatic [lactate]/[pyruvate] (133%), [3-hydroxybutyrate]/[acetoacetate] (69%) ratios, and the liver triglyceride concentration (129%). At the same time point, ethanol increased radioactivity incorporated into hepatic total lipid and triglyceride, after an injection of [U-14C] palmitic acid, by 76% and 158% respectively. Treatment of animals with Naloxone hydrochloride (2 mg/kg i.p.) at 1.0 hr and 2.5 hr after ethanol abolished these ethanol-mediated redox-state changes, without inhibiting ethanol oxidation or affecting hepatic acetaldehyde levels. This, however, did not prevent completely the triglyceride accumulation in the liver or reverse the enhanced uptake of radio-labelled palmitate caused by ethanol. Administration of sorbitol (3.5 g/kg i.p.) caused 109%, 57% and 200% increases in the hepatic [lactate]/[pyruvate], [3-hydroxybutyrate]/[acetoacetate] ratios and glycerol-3-phosphate concentrations respectively. However, the hepatic triglyceride concentration and the incorporation of [U-14C] palmitic acid into hepatic lipids were not influenced by this treatment. In vitro studies in which rat liver slices were incubated with [1-14C] palmitic acid also indicated that the altered [NADH]/[NAD+] ratio was not responsible for the decreased rate of fatty acid oxidation seen after ethanol administration or after the addition of ethanol to the incubation medium. In conclusion, these experiments indicate that increases in the hepatic [NADH]/[NAD+] ratio resulting from ethanol oxidation may not be directly implicated in the altered hepatic fatty acid utilisation and triglyceride deposition observed after acute ethanol administration in rats.

Biliary excretion of gamma-glutamyltransferase. Selective enhancement by acute ethanol administration

To study the acute effect of ethanol on various constituents of the bile, female Wistar rats received by intravenous administration 0.9% NaCl solution either alone or containing in addition ethanol (0.1 ml ethanol 96% hr-1 100 g body weight-1). Compared to saline-treated controls there was a significant enhancement of biliary gamma-glutamyltransferase excretion after ethanol infusion for 5 hr by 166% (22.1 +/- 2.8 microU/min/100 g body weight vs. 58.2 +/- 13.7; P less than 0.0125), whereas no changes or only marginal alterations have been observed for bile flow and the biliary excretion of total bile acids and alkaline phosphatase. The selective enhancement of biliary gamma-glutamyltransferase excretion by ethanol can be ascribed to an increased solubilization of the membrane-bound enzyme originating from the bile canaliculi of the hepatocytes and/or the epithelial cells of the bile ducts. Since the biliary excretion of total bile acids remained unchanged by ethanol, the observed selective solubilization of gamma-glutamyltransferase may occur by a mechanism primarily not involving total bile acids and could be linked to a direct effect of ethanol on physico-chemical properties such as an increased fluidity of liver plasma membranes.

Impaired acetaldehyde metabolism in patients with non-alcoholic liver disorders

In order to determine the specificity of abnormalities of alcohol metabolism in patients with alcoholic liver disease, blood acetaldehyde concentrations after oral ethanol challenge and the activities of alcohol metabolising enzymes in liver biopsy samples have been determined in patients with alcoholic liver disease and a wide variety of non-alcoholic liver disorders. Significant decreases in hepatic cytosolic aldehyde dehydrogenase activity were associated with significant increases in acetaldehyde concentrations after ethanol in both patient groups compared with control subjects. There was a significant correlation between hepatic cytosolic aldehyde dehydrogenase and mean blood acetaldehyde concentration 30-180 min after ethanol ingestion (y = 17.4-0.45x; r = -0.56; p less than 0.01) confirming the importance of this enzyme in controlling blood acetaldehyde concentrations. These findings suggest that disturbances in alcohol metabolism in patients with alcoholic liver disease are the consequence of liver damage rather than a specific abnormality predisposing to alcohol induced liver injury.

Acetaldehyde causes a prolongation of the doubling time and an increase in the modal volume of cells in culture

The effects of culturing four human cell lines--Raji, MOLT-4, WI-L2, and K562--in the presence of 10-360 microM acetaldehyde for 3-18 days have been investigated. Concentrations of 45-360 microM caused a prolongation of the cell doubling time, and those of 90-360 microM caused an increase in the modal cell volume and in the protein content per cell. The results indicate that relatively low concentrations of acetaldehyde cause an impairment of cell proliferation and an abnormality of cell growth in vitro and support the possibility that ethanol-derived acetaldehyde may be responsible for some aspects of tissue damage in chronic alcoholics, including the increase in the mean cell volume of erythrocytes. Three of the four cell lines studied showed a reduction and the fourth showed no change in modal cell volume after culture with 100 mM ethanol, suggesting that the macrocytosis of red cells induced by chronic alcoholism is not caused via some direct effect of ethanol on the erythron.

Ethanol-induced alterations of plasma membrane assembly in the liver

The effects of acute ethanol administration on the assembly of glycoproteins into the hepatic plasma membrane were studied in the rat. When [14C]fucose and N-acetyl[3H]mannosamine, a sialic acid precursor, were injected following an acute dose of ethanol, the incorporation of these precursors into the total pool of membrane glycoproteins was minimally affected. This finding indicated that ethanol treatment did not appreciably alter the glycosylation of proteins in the Golgi apparatus. However, the assembly of labeled fucoproteins and sialoproteins into the plasma membrane was markedly inhibited in the ethanol-treated animals. This inhibition of plasmalemmal glycoprotein assembly was accompanied by a corresponding accumulation of labeled glycoproteins in the cytosolic fraction of the hepatocyte. The content of labeled glycoproteins in the Golgi complex was not significantly altered by ethanol treatment. These results indicate that ethanol administration impairs the late stages of hepatic plasma membrane assembly and further suggest that ethanol administration interferes with the flow of membrane components from the Golgi apparatus to the surface membrane.

Acetaldehyde inhibition of protein synthesis in isolated rat pancreatic acini

Exposure of isolated dispersed pancreatic acini to increasing concentrations of ethanol (5 to 500 mM) or acetaldehyde (0.5 to 100 mM) produced a progressive inhibition of [3H]leucine incorporation into both "cellular" (those remaining in the cell) and "secretory" (those released into the medium) proteins. Whereas 500 mM ethanol caused 90-95% inhibition in the synthesis of "cellular" and "secretory" proteins, the concentration of acetaldehyde needed to produce a similar inhibition was found to be 50 mM. All subsequent experiments were performed with 12.5 mM acetaldehyde, a concentration that consistently inhibited acinar protein synthesis by about 50%. The acetaldehyde-mediated inhibition of acinar protein synthesis was partially normalized when this metabolite was removed after 30 min during a 90-min incubation period. In the presence of acetaldehyde, the secretion of 3H-pulse-labeled proteins, but not amylase, trypsinogen, or chymotrypsinogen, was greatly depressed. Acetaldehyde also caused a marked reduction in [3H]uridine incorporation into acinar RNA. The entry of [3H]uridine, [3H]leucine, and [3H]aminoisobutyric acid into isolated acini was found to be slightly (15-25%) decreased by acetaldehyde. It is concluded that acetaldehyde exerts a direct toxic effect on isolated dispersed pancreatic acini as evidenced by diminution of both protein and RNA synthesis and decreased secretion of the newly synthesized proteins. This inhibitory effect of acetaldehyde could be partially reversed.

Covalent binding of acetaldehyde selectively inhibits the catalytic activity of lysine-dependent enzymes

Hepatic ethanol metabolism generates the reactive intermediate, acetaldehyde, which binds to proteins. The binding of acetaldehyde to purified enzymes was determined in order to ascertain whether such binding altered their catalytic functions. [14C]Acetaldehyde was incubated with alcohol dehydrogenase, glucose-6-phosphate dehydrogenase, lactate dehydrogenase and RNase A, each at 37 degrees C (pH 7.4). In some reactions, sodium cyanoborohydride was included for stabilization of Schiff bases, formed as a result of the reaction between acetaldehyde and the amino groups of the enzymes. Portions of each reaction mixture were removed for determination of stable and total (stable plus borohydride-reducible) adducts. Alcohol dehydrogenase and lactate dehydrogenase were not inhibited by adduct formation. Glucose-6-phosphate dehydrogenase and RNase, the activities of which depend on a lysine residue at their catalytic sites, were inhibited in a dose- and time-dependent manner. The degree of inhibition directly correlated with total adduct formation. Phosphate, known to inhibit binding to the active site lysine of RNase, prevented the inhibition of catalytic activity caused by adduct formation. These findings indicate that the binding of acetaldehyde to lysine at the catalytic site can inhibit enzyme activity.

Subcellular location of secretory proteins retained in the liver during the ethanol-induced inhibition of hepatic protein secretion in the rat

Ethanol administration inhibits the secretion of proteins by the liver, resulting in their hepatocellular retention. Experiments were designed in this study to determine the subcellular location of the retained secretory proteins. Ethanol was administered acutely to nonfasted rats by gastric intubation, whereas control animals received an isocaloric dose of glucose. Two hours after intubation, when maximum blood ethanol levels (45 mM) were observed, [3H]leucine and [14C]fucose were injected simultaneously into the dorsal vein of the penis. The labelling of secretory proteins was determined in the liver and plasma at various time periods after label injection. Ethanol treatment decreased the secretion of both leucine- and fucose-labeled proteins into the plasma. This inhibition of secretion was accompanied by a corresponding increase in the hepatic retention of both leucine- and fucose-labeled immunoprecipitable secretory proteins. At the time of maximum inhibition of secretion, leucine labeled secretory proteins located in the Golgi apparatus represented about 50% of the accumulated secretory proteins in the livers of the ethanol-treated rats, whereas the remainder was essentially equally divided among the rough and smooth endoplasmic reticulum and cytosol. Because fucose is incorporated into secretory proteins almost exclusively in the Golgi complex, fucose-labeled proteins accumulated in the livers of the ethanol-treated rats mainly in the Golgi apparatus, with the remainder located in the cytosol. These results show that ethanol administration causes an impaired movement of secretory proteins along the secretory pathway, and that secretory proteins accumulate mainly, but not exclusively, in the Golgi apparatus.

The effect of methylene blue on the hepatocellular redox state and liver lipid content during chronic ethanol feeding in the rat

Feeding of ethanol in a liquid diet to male Wistar rats caused decreases in the hepatic cytosolic and mitochondrial [NAD+]/[NADH] ratios. This redox-state change was attenuated after 16 days of feeding ethanol as 36% of the total energy intake. Supplementation of the ethanol-containing liquid diet with Methylene Blue largely prevented the ethanol-induced redox state changes, but did not significantly decrease the severity of the hepatic lipid accumulation that resulted from ethanol ingestion. Methylene Blue did not affect body-weight gain, ethanol intake or serum ethanol concentrations in ethanol-fed rats, nor did the compound influence the hepatic redox state or liver lipid content of appropriate pair-fed control animals. These findings suggest that the altered hepatic redox state that results from ethanol oxidation is not primarily responsible for the production of fatty liver after long-term ethanol feeding in the rat.

Ethanol intoxication stimulates lipolysis in isolated Golgi complex secretory vesicle fraction from rat liver

Ethanol (0.6 g/100 g) was administered orally to rats by means of an intragastric tube. This caused an accumulation of secretory vesicles laden with VLDL particles which were seen 90 min after administration and later disappeared. Lysosomes and Golgi complex secretory vesicle (GCSV) fractions were isolated. The proteolytic and lipolytic activities of these fractions were measured in order to assess their possible role in the elimination of the initially retained secretory material. There was no change in proteolysis neither in lysosomes or in the GCSV-fraction from ethanol-intoxicated rats when measured by the release of degradation products during incubation. Similarly, the activities of acid hydrolases were unaffected by acute ethanol intoxication. On the other hand, lipolysis increased by some 50-100% in the GCSV fraction, whereas the lysosomes displayed unchanged lipolytic levels compared with controls. Ultrastructurally, the GCSV-fraction from ethanol-intoxicated rat livers showed signs of disintegrated VLDL particles. It is concluded that acute ethanol intoxication causes an increase in lipolysis but not in proteolysis in the operationally defined GCSV fraction. Since triacylglycerol lipase activities did not change in the GCSV fraction, increased amounts of substrate seem to cause the enhanced lipolysis observed.

Impaired plasma membrane glycoprotein assembly in the liver following acute ethanol administration

The in vivo effects of acute ethanol administration on hepatic plasma membrane assembly were studied in the rat. When [14C]fucose and [3H]N-acetylmannosamine, a sialic acid precursor, were injected following an acute dose of ethanol, minimal effects on fucose and a slight reduction of sialic acid incorporation into the total pool of hepatic membrane glycoproteins were observed. However, the assembly of labeled fucoproteins and sialoproteins into the plasma membrane was markedly inhibited in the ethanol-treated animals. These results indicate that ethanol administration impairs the late stages of membrane assembly which include the transport of glycoproteins from the Golgi complex to the plasma membrane and/or the insertion of glycoproteins into the membrane.

Transferrin glycans: a possible link between alcoholism and hepatic siderosis

The hepatic uptake of 59Fe from diferric rat and rabbit asialotransferrins and from human transferrin lacking two sialyl residues was investigated in rats in experiments lasting for 1 hr. The 59Fe attached to either of these preparations disappeared from the plasma more rapidly than the 59Fe introduced with the unmodified respective parent proteins. Most of the 59Fe activity that had disappeared from the circulation could be recovered with the liver. Studies with double-labeled (125I, 59Fe) preparations showed that the enhanced 59Fe clearance was not associated with increased catabolism of the modified transferrins. Prolonged, heavy alcohol consumption, as shown by others, results in the appearance of sialic acid-deficient transferrin (two residues missing) in human serum. We suggest that the increased capacity of transferrin deficient in sialic acid to selectively deposit iron in the hepatocyte may be of significance for the development of the hepatic siderosis observed in alcoholism.

Effect of ethanol and chlorpromazine on transhepatic transport and biliary secretion of horseradish peroxidase

In order to demonstrate the effect to the acute administration of ethanol and chlorpromazine (CPZ) on bile flow and transhepatic transport of horseradish peroxidase (HRP) into bile, male rats were administered either 5 gm per kg ethanol intragastrically (E-rats) or 3 mg per kg CPZ intraperitoneally (CPZ rats). Control rats (C-rats) received saline. Two hours after ethanol feeding or 90 min after CPZ injection HRP was injected into the portal vein, and bile samples were collected at 10-min intervals for 2 hr. Tissue samples were removed at 1, 10, 60, and 120 min to study HRP transport using electron microscopic cytochemical localization. Bile flow was reduced (p less than 0.001) both in E- and CPZ-rats compared to C-rats. In E-rats HRP secretion was significantly decreased at 30 and 40 min post-HRP injection (p less than 0.05) and the peak rate of HRP secretion was delayed by 10 min compared to C-rats. Uptake and transhepatic transport of HRP were similar to controls. These results suggest that bile secretion and flow were impaired by ethanol. CPZ inhibited secretion of HRP significantly (p less than 0.001) during the first hr after HRP injection and by 25% after 2 hr. In CPZ rats studied cytochemically HRP reaction product decreased in the cytoplasm of hepatocytes 10 min after HRP injection (p less than 0.01). These findings suggest that acute CPZ administration caused an inhibition of the uptake of HRP as well as secretion and bile flow.

Ethanol and the pancreas

The acute and chronic effects of ethanol on pancreatic structure and function are discussed. Acute necrotizing, acute edematous, acute relapsing, chronic relapsing, and painless pancreatitis have an established association with ethanol abuse. The management of these disorders is outlined.

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.

Evidence for a direct inhibitory effect of ethanol upon gonadotropin secretion at the pituitary level

Mixed rat pituitary cells harvested from pituitaries obtained from adult male rats were maintained in tissue culture for periods up to 240 hr. Viability determined by trypan blue exclusion at the end of each experiment was greater than 90%. Basal secretory rats of luteinizing hormone (LH) into the culture medium were determined before and after the addition of ethanol (30 mg/100 ml) to the incubation medium. Ethanol-reduced (p less than .01) LH secretion of treated cultures were compared to control cultures. Based upon this preliminary in vitro study with rat tissue and on prior studies performed in man and animals, we suggest that ethanol inhibits LH secretion at the pituitary level.

Acetaldehyde adducts with proteins: binding of [14C]acetaldehyde to serum albumin

Acetaldehyde, the immediate oxidation product of ethanol metabolism, was assessed for its ability to bind covalently to a purified protein in solution. Bovine serum albumin (BSA) was used as the model protein incubated in the presence of 0.2 mM [14C]acetaldehyde at pH 7.4 and at 37 degrees C. Acetaldehyde formed both stable and unstable adducts with serum albumin. Unstable adducts were identified following stabilization with the reducing agent sodium borohydride. We examined both types of binding using trichloroacetic acid precipitation, gel filtration, and dialysis as means to separate bound from free acetaldehyde. All three methods of analysis gave comparable results except that the number of stable acetaldehyde adducts with albumin were significantly lower following separation by dialysis. The effects of L-cysteine, L-lysine, and reduced glutathione were assessed for their abilities as competitive reagents to decrease binding of [14C]acetaldehyde to BSA. Addition of cysteine caused a rather dramatic concentration-dependent reduction in [14C]acetaldehyde binding to BSA when compared to that caused by lysine which displayed a relatively mild effect on covalent binding. The presence of glutathione caused a concentration-dependent decrease in protein-bound radioactivity that was stronger than that by lysine but not as effective as cysteine. The ability of each reagent to reverse the formation of preformed acetaldehyde adducts with BSA was also examined. Only L-cysteine effectively decreased the number of unstable acetaldehyde adducts with BSA while stable binding of acetaldehyde remained essentially unaffected by any of the three reagents. These results indicate that acetaldehyde can covalently bind to protein and form unstable as well as stable adducts.

Effect of ethanol on the synthesis and secretion of hepatic secretory glycoproteins and albumin

The effects of ethanol on the synthesis and secretion of serum glycoproteins and albumin, a nonglycosylated protein, were studied in rat liver slices. Serum glycoproteins and albumin were determined by immunoprecipitation from either the incubation medium or from the washed slices. When ethanol (10 mM) was present in the incubation medium, [14C]glucosamine incorporation in secretory glycoproteins was decreased. This inhibitory effect was, however, much greater in the secretory proteins released into the medium than in those retained in the liver slices. Similar inhibitions by ethanol were also observed when leucine or valine were used as a label for either total export proteins or albumin. Since ethanol impaired protein synthesis, and inhibitor of protein synthesis, cycloheximide, was used so that both the control and ethanol-treated slices had identical pools of protein acceptors available for glycosylation. When cycloheximide alone was added to the slices, glucosamine radioactivity of secretory glycoproteins was equally reduced in both the medium and the liver. When cycloheximide and ethanol were both present, decreased appearance of glucosamine-labeled proteins in the medium was observed when compared to the slices containing cycloheximide alone; however, radioactivity of secretory glycoproteins retained in the liver was elevated. Ethanol also decreased the appearance of fucose-labeled glycoproteins in the medium without altering fucose incorporation into the total pool of secretory glycoproteins. The effects of ethanol on hepatic protein secretion independent of its effect on synthesis were further determined by prelabeling proteins with either [14C]leucine or [14C]fucose. Ethanol impaired the secretion of these prelabeled proteins into the medium. The results of this study show that ethanol impairs both the synthesis and secretion of secretory glycoproteins and albumin.

Inhibition of protein degradation in regenerating rat liver by ethanol treatment

The effect of ethanol on the activity of ornithine decarboxylase (ODC), tyrosine aminotransferase (TAT), alanine aminotransferase (ALAT) and lactate dehydrogenase (LD), as well as on protein concentration, was studied in regenerating rat liver after partial hepatectomy. It was found that administration of an ethanol-containing liquid diet for 5 days after partial hepatectomy caused a significant accumulation of proteins in the liver. The activities of ODC and TAT were stimulated by ethanol treatment in the beginning of the regeneration. In control livers, partial hepatectomy decreased the activity of ALAT, but ethanol prevented this decrease. No differences in the activity of LD was found between ethanol and control groups after partial hepatectomy. When the half-lives of ODC and TAT were measured 24 hr after partial hepatectomy by using cycloheximide, it appeared that ethanol caused a significant stabilization of both enzymes. It is concluded that ethanol caused inhibition of degradation of ODC and TAT and it is suggested that this could be a general phenomenon, and could markedly contribute to the pathological accumulation of proteins in the liver after chronic ethanol consumption.