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

Metabolism of ethanol and associated hepatotoxicity

Over the last three decades, direct hepatotoxic effects of ethanol were established, some of which were linked to redox changes produced by NADH generated via the alcohol dehydrogenase (ADH) pathway and shown to affect the metabolism of lipids, carbohydrates, proteins, and purines. It was also determined that ethanol can be oxidized by a microsomal ethanol oxidizing system (MEOS) involving a specific cytochrome P-450; this newly discovered ethanol-inducible cytochrome P-450 (P-450 IIEi) contributes to ethanol metabolism, tolerance, energy wastage (with associated weight loss), and the selective hepatic perivenular toxicity of various xenobiotics. Their activation by P-450IIEi now provides an understanding of the increased susceptibility of the heavy drinker to the toxicity of industrial solvents, anaesthetic agents, commonly prescribed drugs, over-the-counter analgesics, and chemical carcinogens. P-450 induction also explains depletion (and toxicity) of nutritional factors such as vitamin A. As a consequence, treatment with vitamin A and other nutritional factors is beneficial, but must take into account a narrowed therapeutic window in alcoholics who have increased needs for nutrients and also display an enhanced susceptibility to some of their adverse effects. Acetaldehyde (the metabolite produced from ethanol by either ADH or MEOS) impairs hepatic oxygen utilization and forms protein adducts, resulting in antibody production, enzyme inactivation, and decreased DNA repair. It also stimulates collagen production by the vitamin A storing cells (lipocytes) and myofibroblasts, and causes glutathione depletion. Supplementation with S-adenosyl-L-methionine partly corrects the depletion and associated mitochondrial injury, whereas administration of polyunsaturated lecithin opposes the fibrosis. Thus, at the cellular level, the classic dichotomy between the nutritional and toxic effects of ethanol has now been bridged. The understanding of how the ensuing injury eventually results in irreversible scarring or cirrhosis may provide us with improved modalities for treatment and prevention.

Cellular fibronectin stimulates hepatocytes to produce factors that promote alcohol-induced liver injury

AIM

To examine the consequences of cellular fibronectin (cFn) accumulation during alcohol-induced injury, and investigate whether increased cFn could have an effect on hepatocytes (HCs) by producing factors that could contribute to alcohol-induced liver injury.

METHODS

HCs were isolated from rats fed a control or ethanol liquid diet for four to six weeks. Exogenous cFn (up to 7.5 μg/mL) was added to cells cultured for 20 h, and viability (lactate dehydrogenase,LDH), apoptosis (caspase activity) and secretion of proinflammatory cytokines (tumor necrosis factor alpha, TNF-α and interleukin 6 IL-6), matrix metalloproteinases (MMPs) and their inhibitors (tissue inhibitors of metalloproteinases, TIMPs) was determined. Degradation of iodinated cFn was determined over a 3 h time period in the preparations.

RESULTS

cFn degradation is impaired in HCs isolated from ethanol-fed animals, leading to its accumulation in the matrix. Addition of exogenous cFn did not affect viability of HCs from control or ethanol-fed animals, and apoptosis was affected only at the higher concentration. Secretion of MMPs, TIMPs, TNF-α and IL-6, however, was increased by exogenously added cFn, with HCs from ethanol-fed animals showing increased susceptibility compared to the controls.

CONCLUSION

These results suggest that the elevated amounts of cFn observed in alcoholic liver injury can stimulate hepatocytes to produce factors which promote further tissue damage.

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.

Impact of asialoglycoprotein receptor deficiency on the development of liver injury

The asialoglycoprotein (ASGP) receptor is a well-characterized hepatic receptor that is recycled via the common cellular process of receptor-mediated endocytosis (RME). The RME process plays an integral part in the proper trafficking and routing of receptors and ligands in the healthy cell. Thus, the mis-sorting or altered transport of proteins during RME is thought to play a role in several diseases associated with hepatocyte and liver dysfunction. Previously, we examined in detail alterations that occur in hepatocellular RME and associated receptor functions as a result of one particular liver injury, alcoholic liver disease (ALD). The studies revealed profound ethanol-mediated impairments to the ASGP receptor and the RME process, indicating the importance of this receptor and the maintenance of proper endocytic events in normal tissue. To further clarify these observations, studies were performed utilizing knockout mice (lacking a functional ASGP receptor) to which were administered several liver toxicants. In addition to alcohol, we examined the effects following administration of anti-Fas (CD95) antibody, carbon tetrachloride (CCl(4)) and lipopolysaccharide (LPS)/galactosamine. The results of these studies demonstrated that the knockout mice sustained enhanced liver injury in response to all of the treatments, as shown by increased indices of liver damage, such as enhancement of serum enzyme levels, histopathological scores, as well as hepatocellular death. Overall, the work completed to date suggests a possible link between hepatic receptors and liver injury. In particular, adequate function and content of the ASGP receptor may provide protection against various toxin-mediated liver diseases.

Effect of ethanol on pro-apoptotic mechanisms in polarized hepatic cells

Chronic ethanol consumption is associated with serious and potentially fatal alcohol-related liver injuries such as hepatomegaly, alcoholic hepatitis and cirrhosis. Moreover, it has been documented that the clinical progression of alcohol-induced liver damage may be associated with an increase in hepatocellular death that involves apoptotic mechanisms. Although much information has been learned about the clinical manifestations associated with alcohol-related diseases, the search continues for a better understanding of the molecular and/or cellular mechanisms by which ethanol exerts its deleterious effects such as the induction of pro-apoptotic mechanisms and related cell damaging events. As part of the effort to enhance our understanding of those particular cellular pathways and mechanisms associated with ethanol toxicity, researchers over the years have utilized a variety of model systems. Recently, work has come forth demonstrating the utility of a hybrid cell line (WIF-B) as a cell culture model system for the study of alcohol-associated alterations in hepatocellular mechanisms. Success with such emerging model systems could aid in the development of potential therapeutic treatments for the prevention of alcohol-induced apoptotic cell death that may ultimately serve as a significant target in delaying the onset and/or progression of clinical symptoms of alcohol-mediated liver disease. This review article summarizes the current understanding of ethanol-mediated modifications in cell survival and thus the promotion of pro-apoptotic events with emphasis on analyses made in various experimental model systems, particularly the more recently characterized WIF-B cell system.

Ethanol-induced apoptosis in polarized hepatic cells possibly through regulation of the Fas pathway

BACKGROUND

It has been noted that alcohol-related liver diseases can be associated with an increase in apoptotic hepatocellular death. Moreover, the promotion of hepatocyte apoptosis may be linked to signals emanating from death receptors, particularly Fas [CD95/apoptosis-inducing protein 1 (APO-1)]. In the present study, we utilized an in vitro hepatic culture model [hybrid of human fibroblast (WI 38) and rat hepatoma (Fao) cells, WIF-B cells] to study potential contributing mechanisms involved in hepatocellular apoptosis following ethanol administration.

METHODS

WIF-B cultures (differentiated hepatic cells that efficiently metabolize alcohol) were treated with or without ethanol and specific inhibitors of alcohol metabolism and cysteine protease activity, followed by morphological and biochemical examination of proapoptotic parameters.

RESULTS

The results of this work demonstrated that ethanol administration leads to an increase (45%-60%) in caspase-3 activity and that the induction of apoptosis was found to be linked to the metabolism of alcohol. Additionally, increases were observed in the activity of upstream initiator caspases (caspase-2 and caspase-8) that are directly related to membrane signaling events of death receptors such as Fas. Moreover, it was determined that the activation of caspase-3 could be blocked by the presence of a specific caspase-8 inhibitor, again linking death receptor-associated proteases to downstream effector caspase activity in alcohol-related death. Finally, ethanol administration was found to result in an increase in the amount of Fas protein present in the membrane fraction of the cell. The increase in membrane Fas protein indicates ligand-independent membrane targeting of Fas in the alcohol-treated cells that could potentially be a key signaling event in the induction of the proapoptotic caspase cascade.

CONCLUSIONS

The data presented here indicate that alcohol metabolism induces apoptosis in WIF-B cells that occurs, in part, by mechanisms involving signals emanating from death receptors.

Inhibition of system A amino acid transport activity by ethanol in BeWo choriocarcinoma cells

OBJECTIVE

Our purpose was to investigate the influence of ethanol on system A amino acid transporter in BeWo cells.

STUDY DESIGN

BeWo cells were cultured in the absence or presence of ethanol. The function of system A was monitored by the transport of alpha-(methylamino)isobutyric acid. Messenger RNA levels for system A were assessed by Northern analysis.

RESULTS

Treatment of BeWo cells with ethanol reduced the activity of system A. The effect was dose and treatment time dependent. The decrease in system A activity was 38% +/- 3% at 0.75% ethanol with a 16-hour treatment time. The activities of several other transporters tested were not affected. The effect on system A activity was associated with a decrease in the maximal velocity of the transport system without affecting the substrate affinity. Ethanol did not alter the messenger RNA levels for system A.

CONCLUSION

Exposure of BeWo cells to ethanol significantly reduces the function of system A. This finding has potential implications that may be relevant to the pathogenesis of the fetal alcohol syndrome.

Chronic ethanol administration decreases the ligand binding properties and the cellular content of the mannose 6-phosphate/insulin-like growth factor II receptor in rat hepatocytes

We have shown previously that chronic ethanol administration impairs the maturation of lysosomal enzymes in rat hepatocytes. The mannose 6-phosphate/insulin-like growth factor II receptor (M6P/IGF-IIR) is a protein that facilitates the transport of lysosomal enzymes into the lysosome. Therefore, we examined whether ethanol consumption altered the ligand binding properties and the cellular content of M6P/IGF-IIR. Rats were pair-fed liquid diets containing either ethanol (36% of calories) or isocaloric maltose-dextrin for either 1 week or 5-7 weeks. Hepatocytes prepared from these animals were examined for receptor-ligand binding and receptor content. One week of ethanol feeding had no significant effect on ligand [radioiodinated pentamannose phosphate conjugated to bovine serum albumin ((125)I-PMP-BSA)] binding to hepatocytes, but cells from rats fed ethanol for 5-7 weeks bound less (125)I-PMP-BSA than pair-fed controls. Scatchard plot analysis revealed that the number of (125)I-PMP-BSA binding sites in hepatocytes from ethanol-fed rats was 49% lower than that of controls. (125)I-PMP-BSA binding by perivenular (PV) and periportal (PP) hepatocytes from ethanol-fed rats was, respectively, 40 and 48% lower than their controls, but there was no significant difference between these two types of hepatocytes. Ligand blot analysis using (125)I-insulin-like growth factor II ((125)I-IGF-II) also showed that the receptor in lysates of hepatocytes from ethanol-fed rats bound 26-27% less ligand than controls. Similarly, immunoblot analysis of cell lysates from ethanol-fed rats revealed 62% lower levels of immunoreactive M6P/IGF-IIR than controls. Feeding rats a low carbohydrate-ethanol diet did not exacerbate the reduction in M6P/IGF-IIR-ligand binding nor did it reduce the levels of immunoreactive receptor. Our findings indicate that chronic ethanol consumption lowers M6P/IGF-IIR activity and content in hepatocytes. This reduction may account, in part, for the impaired processing and delivery of acid hydrolases to lysosomes previously observed in ethanol-fed rats.

A subtoxic interactive toxicity study of ethanol and chromium in male Wistar rats

The purpose of this study was to evaluate the interactive toxicity of ethanol with potassium dichromate (K2Cr2O7-chromium). Young, male Wistar rats (100-120 g) were divided into four groups of five or six animals each and were dosed, through water, with 10% ethanol (vol./vol.) or 25 ppm chromium or were dosed with a combination of ethanol+chromium at the same concentrations for a period of 22 weeks ad libitum and were maintained on normal diet. Control animals were maintained on a normal diet and water for the same period. The serum succinate dehydrogenase and liver total triglyceride levels were significantly reduced in the three treated groups. The serum alkaline phosphatase levels were significantly reduced in ethanol-treated rats, and there was no significant change in the acid phosphatase activity. Serum aspartate and alanine aminotransferase levels in the three treated groups were significantly increased. The liver glycogen significantly decreased in both the ethanol-treated and the chromium-treated rats. There was a significant increase in liver total cholesterol levels in chromium-treated rats. Total glutathione levels were significantly decreased in the livers of ethanol-treated and ethanol+chromium-treated rats. To further substantiate these findings, a histological examination of the liver and kidneys was undertaken. The livers of alcohol-treated animals showed altered hepatic architecture in the centrilobular and periportal areas, with increased sinusoidal space (space of Disse), vacuolation, and necrosis of hepatocytes. Similar changes were observed in a histological examination of the livers of chromium-treated rats, except that the damage to the hepatocytes was more confined to the periportal area. Moreover, histological examination of the livers of ethanol+chromium-treated rats revealed uniform damage in the centrilobular and periportal areas, as was observed in the groups treated either with ethanol or chromium. The histological examination of the kidneys in the three treated groups revealed significant damage to the renal tubules and Bowman's capsule, which showed vacuolation and degeneration of the basement membrane. These findings correlate well with the serum enzyme levels found in the treated groups. It is evident from this study that chronic ethanol consumption sensitizes the liver to the toxic action of agents such as chromium. It leads to impairment of the biochemical functions in the liver, and it causes liver and kidney damage. Long-term simultaneous exposure to ethanol and chromium may cause severe health problems in people who are alcoholics and work in chrome-plating and leather-tanning industries.

Effects of ethanol on receptor-mediated endocytosis in the liver

Ethanol administration impairs multiple aspects in the process of receptor-mediated endocytosis (RME) in the liver. Studies from our laboratory over the last 10 years have carefully examined RME by the hepatocyte-specific asialoglycoprotein receptor (ASGP-R). We have identified a time course for ethanol-induced defects in RME and established that many of the impairments occur initially in the centrilobular region of the liver and as early as one week after ethanol administration. Impaired intravesicular acidification in ethanol-fed animals has been identified, and these defects in acidification could alter multiple protein trafficking pathways including RME. In addition to altered acidification, altered receptor function (including receptor inactivation) could also contribute to impaired trafficking. Current studies in our laboratory are aimed at an examination of posttranslational modifications in the receptor (acylation and phosphorylation) that are known to affect its function. A role for the ASGP-R in the process of alcoholic apoptosis is also being examined because proper functioning of the ASGP-R is thought to be important in clearance of apoptotic cells.

Chronic ethanol consumption impairs receptor-mediated endocytosis of formaldehyde-treated albumin by isolated rat liver endothelial cells

Receptor-mediated endocytosis (RME) by a scavenger receptor on sinusoidal liver endothelial cells (LECs) for formaldehyde-treated bovine serum albumin (f-Alb) has previously been shown to be impaired following chronic ethanol consumption. These studies were initially performed by in situ perfusion, making it difficult to determine the point in the process at which RME is affected. Therefore, it was the purpose of this study to use isolated LECs to begin elucidating at what point in the process chronic ethanol consumption affects RME. Initial studies showed that degradation at the single-cell level were similarly decreased at levels that had been observed for in situ studies, suggesting that the ethanol effects can be repeated using isolated LECs, making them useful for in vitro studies. Binding studies with 125I-formaldehyde-treated bovine serum albumin (125I-f-Alb) demonstrated there was a slight, but significantly different, decrease in binding by LECs from ethanol-fed rats when compared with pair-fed or chow-fed rats. However, the affinity of these receptors was not different between these groups. In contrast, a defect in the initial stages of receptor-ligand internalization was indicated as less surface-bound ligand was internalized and subsequently degraded in cells from the ethanol-treated animals as compared with controls. Additionally, once the data were adjusted for the amount of ligand internalized, the degradation of the internalized ligand was only slightly impaired. These results indicate that chronic ethanol feeding impairs the process of RME by the liver; the major cause of this impairment appears to be caused by a decreased ability of these cells to internalize all of the surface-bound ligand, with a minimal defect in postinternalization events.

Tumor necrosis factor-alpha internalization and degradation by isolated hepatocytes of rats exposed to ethanol

Internalization and degradation of human recombinant [125I]TNF-alpha was studied in hepatocytes isolated from rats exposed to ethanol (EtOH) either acutely (i.p. injection, 2.2 g kg(-1) b.wt.) or chronically (14-16 weeks of EtOH feeding in liquid diet). Both acute and chronic EtOH exposure diminished cytokine binding to the cell-surface receptors. In the acute group, EtOH increased internalization of the cytokine, accelerated its disappearance from the cell surface, and markedly reduced its conversion into acid-soluble 125I-containing compounds. In the chronic group, EtOH did not markedly affect these parameters. Internalization and degradation of the cytokine in the chronic group was much lower than in the acute group. It is concluded that EtOH interferes not only with the cytokine binding to the cell-surface receptors, as demonstrated in previous studies, but also with postbinding events, such as internalization and intracellular degradation of TNF-alpha. Possible mechanisms of action of EtOH are discussed.

Inhibition of gap junction intercellular communications of cultured rat hepatocytes by ethanol: role of ethanol metabolism

BACKGROUND/AIMS

In a previous study, we reported that in cultured rat hepatocytes, ethanol inhibits intercellular communication which is known to play a central role in the regulation of cell growth and differentiation. This work was designed to find out if ethanol exerts a direct action on cell membranes, comparable to other long-chain (C6-C9) alcohols, or an indirect action.

METHODS

Intercellular communication was measured on short-term cultured rat hepatocytes by the fluorescent Lucifer-Yellow CH transfer method. Intracellular pH was measured by spectrofluorimetry and membrane expression of connexin 32 by indirect immunofluorescence.

RESULTS

Under our conditions, ethanol (20 mM) inhibited intercellular communication of hepatocytes to the same extent as did octanol and 1 mM. Immunofluorescence semi-quantitative studies of connexin 32 suggested that the observed inhibition was not related to a decrease in the number of gap junction plaques. In contrast with those of octanol, the inhibitory effects of ethanol appeared to be indirect because the inhibition of ethanol metabolism by 4-methyl pyrazole abolished its effects on intercellular communication, while 4-methyl pyrazole did not influence the effects of octanol. Acetaldehyde, the main metabolite of ethanol was without effect on gap junctions.

CONCLUSIONS

This suggests that the inhibition of intercellular communication induced by ethanol may be included among the consequences of intermediary cell metabolism disturbances indirectly due to ethanol oxidation. This may be one of the mechanisms by which ethanol metabolism exerts a hepatotoxic possibly carcinogenic action.

Serum carbohydrate-deficient transferrin: mechanism of increase after chronic alcohol intake

Carbohydrate-deficient transferrin (CDT) is now considered to be the most sensitive and specific biological marker of alcohol abuse. However, the mechanism by which chronic alcohol consumption causes an elevation of CDT levels in serum is still not understood. Therefore, we fed eight pairs of male rats a nutritionally adequate liquid diet containing either alcohol (36% of energy) or isocaloric dextrose (control) for 4 weeks, after which blood and liver samples were obtained. Serum CDT content in alcohol-treated rats increased by 45% (P < .05) in ethanol-fed animals compared with their corresponding controls. In contrast, in rats fed ethanol, the activities of sialyltransferase (ST), galactosyltransferase (GT), and N-acetylglucosamine transferase (N-AGT), which are glycosyltransferases involved in transferrin carbohydrate side chain synthesis, were diminished by 24% and 40% (P < .05), 23% and 51% (P < .05, .001), and 20% and 26% (P < .05) in total liver homogenates and Golgi fraction (GF) 1, respectively, when expressed as units/100 g body weight. These enzymes were also significantly less active in hepatic GFs 2 and 3. The depression of the transferase activities in ethanol-fed rats appeared to be due, at least in part, to enzyme inactivation by acetaldehyde, whereas ethanol itself was without effect. Similar results were obtained in humans: five alcohol abusers were found to exhibit a 23% decrease in hepatic sialyltransferase and a 41% increase in sialidase activities, respectively, when compared with three nondrinking subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Impairment of glucagon-induced hepatic system A activity by short-term ethanol administration in the rat

BACKGROUND/AIMS

System A is a membrane-bound, hormonally regulated carrier of amino acids that is induced by liver regeneration and impaired by ethanol. The mechanism of ethanol inhibition of system A is unknown; this study examines the effects of ethanol on the subcellular expression of system A activity following hormonal induction.

METHODS

Following hormonal treatment and short-term ethanol administration to rats, isolated liver Golgi and plasma membrane vesicles were examined for system A transport, and the kinetic parameters were determined.

RESULTS

Four hours after ethanol administration, the initial rate of system A activity was depressed 30% +/- 9% and 19% +/- 7% into Golgi and plasma membrane vesicles, respectively. The affinity constant of 2-(methylamino)-isobutyric acid uptake was unchanged between control and ethanol-treated vesicles, regardless of their subcellular origin. However, the maximal velocity of system A transport decreased from 1030 to 850 pmol.mg-1 protein.10 s-1 in Golgi vesicles and from 740 to 355 pmol.mg-1 protein.10 s-1 in plasma membrane vesicles.

CONCLUSIONS

Ethanol impairs hormonally induced system A activity in Golgi as well as in the plasma membrane vesicles. Ethanol potentially reduces glucagon induction of system A activity through an impairment of carrier biosynthesis or expression.

Time course of ethanol-induced impairment in fluid-phase endocytosis in isolated rat hepatocytes

The time-course effects of long-term ethanol administration on fluid-phase endocytosis were studied in isolated rat hepatocytes. Rats were pair-fed an ethanol-supplemented liquid diet or an isocaloric control diet for 3 days, 1 wk, 2 wk or 5 wk. Hepatocytes were isolated and incubated at 37 degrees C with various concentrations of the fluid-phase marker Lucifer yellow. Net internalization of the marker dye was determined. After as little as 1 wk, ethanol-fed rats demonstrated marked decreases in the net internalization of dye compared with pair-fed controls; these changes persisted throughout 5 wk of feeding. Because net internalization is the balance between uptake into the cells vs. efflux from the cells, these components were examined individually. Early uptake was not significantly decreased by ethanol feeding; however, efflux of preloaded Lucifer yellow from cells from the ethanol-fed animals was markedly faster than efflux from pair-fed controls. This increased efflux was more prominent in the longer preload time (90 min) compared with a shorter preload time (15 min), indicating an alteration in dye distribution among various intracellular pools. These ethanol-induced changes in fluid-phase endocytosis were apparent for 1 wk through 5 wk of feeding and were similar for all Lucifer yellow concentrations examined. These results indicate that the decreased net internalization of Lucifer yellow through fluid-phase endocytosis is mainly a result of an ethanol-induced increase in efflux possibly caused by altered intracellular trafficking rather than by reduction in uptake.

Effects of ethanol on intercellular communications and polarization of hepatocytes in short-term culture

The formation of intracellular lumina with apical differentiation is observed in several cancerous epithelial cell lines including human hepatocarcinoma. This disorder of cell polarization can be induced by the inhibition of cell-cell communication, a known factor of carcinogenesis. This work was designed to study the effects of ethanol on the differentiation of hepatocytes in short-term culture. Isolated hepatocytes were plated on plastic culture dishes that were 35 mm in diameter (10(6) cells/dish). Three hours after plating, the hepatocytes were incubated in the presence of 20 mmol/L ethanol for 1 hr. Treated cells were compared with controls using morphometric methods after conventional treatment for ultramicroscopy and by measuring cellular dye coupling by the fluorescent Lucifer Yellow CH transfer method. Bile canaliculi formation decreased in alcohol-treated cells (6.5% vs. 9.9%, 2p less than 0.05), whereas intracellular lumina incidence increased (3.1% vs. 0.5%, 2p less than 0.01). In parallel, the dye-coupling capacity decreased significantly when hepatocytes were treated with alcohol (2p less than 0.01). This work shows that short-term ethanol treatment induces significant disturbances of cell polarization and inhibits the reestablishment of cell-cell communication in cultured hepatocytes. These disorders could, at least in part, explain the carcinogenic effects of ethanol.

Effect of chronic ethanol treatment on the gamma-aminobutyric acid-mediated enhancement of [3H]flunitrazepam binding in rat cortex and hippocampus

The mechanism by which ethanol affects the gamma-aminobutyric acid (GABA)/benzodiazepine complex is not clear. It is known that ethanol enhances the Cl- influx mediated by the GABAA receptor complex, and although chronic ethanol administration does not change the KD or Bmax for [3H]flunitrazepam binding, some reports have suggested that it could modify the modulation of benzodiazepine binding produced by GABA. In the present work, we studied the effect of chronic ethanol treatment on the modulation by GABA of [3H]flunitrazepam binding, using light microscopic autoradiography. This technique allows the measurement of densities of benzodiazepine receptors in different brain areas, the visual cortex and hippocampus, which appear to constitute the anatomical support for the behavioral and physiological responses affected by ethanol. We found enhancement of benzodiazepine binding by GABA at concentrations of greater than 10(-6) M for the various cortical and hippocampal areas studied from both control and ethanol-treated animals; this enhancement peaked at 10(-4) M GABA but decreased at 10(-3) M GABA. We found a clear effect of ethanol treatment on the modulatory properties of GABAA receptor, in both cortex and hippocampus, although only in cortex were the differences statistically significant between control and ethanol-treated animals.

The effects of chronic ethanol administration on the rates of internalization of various ligands during hepatic endocytosis

The purpose of the present study was to further characterize the ethanol-induced impairments in hepatic endocytosis. Specifically, we examined the effects of ethanol treatment on receptor-ligand internalization via the coated and noncoated pit pathways. Insulin, epidermal growth factor (EGF) and asialoorosomucoid (ASOR) were used as model ligands to study internalization by isolated hepatocytes. ASOR and EGF are thought to be internalized strictly in coated pit regions of the cell membrane, while insulin may be internalized in both coated and uncoated membrane regions. Ethanol administration for 5-7 weeks decreased internalization of ASOR and EGF while internalization of insulin was unchanged during a single round of endocytosis of surface-bound ligand. Similarly, a more quantitative measure of endocytosis, the endocytic rate constant, was decreased for EGF and ASOR but not for insulin in livers of experimental rats. When endocytosis of Lucifer yellow, a fluorescent dye known to be internalized in the cell by fluid-phase endocytosis was examined, the initial rates of dye uptake were not significantly altered by alcohol administration. These results indicate that ethanol may selectively impair internalization occurring by coated pits while it has a minimal effect on initial uptake of molecules which are internalized by noncoated membrane regions.

Nutritional and developmental regulation of glycosylation processes in digestive organs

We review the nutritional and developmental variations of the glycosylation processes in digestive organs, since glycoproteins play a prominent part as mucins or digestive enzymes in these tissues. The biosynthesis of the glycannic chains is demonstrated to be largely sensitive to various exogenous (such as nutritional) or endogenous (such as developmental) factors. Although the metabolic regulation by dietary variations appears as rather complex, according to the variety of experimental conditions and the diversity of the organs studied, available data demonstrate that this regulation does exist, depending on the quantity or sometimes the quality of the major or minor components of the diet, which induce significant variations in the glycosylation processes. The synthesis of the internal core of N-glycans is essentially regulated by diet-induced variations of the phosphoryl-dolichol level, whereas the modulation of the biosynthesis of the external part of N-glycans or the biosynthesis of O-glycans is controlled by diet-induced variations in the systems transferring fucose, galactose, sialic acid or hexosamines. Modifications in intestinal glycosylation during post-natal development in the rat control the quality of the glycannic chains of mucins and brush-border enzymes. The post-natal maturation of the intestinal rat tissue is characterized by a shift from sialylation to fucosylation, depending on coordinate changes in glycosyltransferase activities, in sugar-nucleotide breakdown or synthesis or in the activity of regulatory proteins. These activities are largely sensitive to dietary manipulations at weaning and to hormonal stimulations before weaning. However, glucocorticoid hormones do not appear as the triggering signal for the induction of these changes.

Alcohol, liver, and nutrition

Until two decades ago, dietary deficiencies were considered to be the major reason why alcoholics developed liver disease. As the overall nutrition of the population improved, more emphasis was placed on secondary malnutrition. Direct hepatotoxic effects of ethanol were also established, some of which were linked to redox changes produced by reduced nicotinamide adenine dinucleotide (NADH) generated via the alcohol dehydrogenase (ADH) pathway. It was also determined that ethanol can be oxidized by a microsomal ethanol oxidizing system (MEOS) involving cytochrome P-450: the newly discovered ethanol-inducible cytochrome P-450 (P-450IIE1) contributes to ethanol metabolism, tolerance, energy wastage (with associated weight loss), and the selective hepatic perivenular toxicity of various xenobiotics. P-450 induction also explains depletion (and enhanced toxicity) of nutritional factors such as vitamin A. Even at the early fatty-liver stage, alcoholics commonly have a very low hepatic concentration of vitamin A. Ethanol administration in animals was found to depress hepatic levels of vitamin A, even when administered with diets containing large amounts of the vitamin, reflecting, in part, accelerated microsomal degradation through newly discovered microsomal pathways of retinol metabolism, inducible by either ethanol or drug administration. The hepatic depletion of vitamin A was strikingly exacerbated when ethanol and other drugs were given together, mimicking a common clinical occurrence. Hepatic retinoid depletion was found to be associated with lysosomal lesions and decreased detoxification of chemical carcinogens. To alleviate these adverse effects, as well as to correct problems of night blindness and sexual inadequacies, the alcoholic patient should be provided with vitamin A supplementation. Such therapy, however, is complicated by the fact that in excessive amounts vitamin A is hepatotoxic, an effect exacerbated by long-term ethanol consumption. This results in striking morphologic and functional alterations of the mitochondria with leakage of mitochondrial enzymes, hepatic necrosis, and fibrosis. Thus, treatment with vitamin A and other nutritional factors (such as proteins) is beneficial but must take into account a narrowed therapeutic window in alcoholics who have increased needs for such nutrients, but also display an enhanced susceptibility to their adverse effects. Massive doses of choline also exerted some toxic effects and failed to prevent the development of alcoholic cirrhosis. Acetaldehyde (the metabolite produced from ethanol by either ADH or MEOS) impairs hepatic oxygen utilization and forms protein adducts, resulting in antibody production, enzyme inactivation, and decreased DNA repair. It also enhances pyridoxine and perhaps folate degradation and stimulates collagen production by the vitamin A storing cells (lipocytes) and myofibroblasts.(ABSTRACT TRUNCATED AT 400 WORDS)

Hepatic, metabolic and toxic effects of ethanol: 1991 update

Until two decades ago, dietary deficiencies were considered to be the only reason for alcoholics to develop liver disease. As the overall nutrition of the population improved, more emphasis was placed on secondary malnutrition and direct hepatotoxic effects of ethanol were established. Ethanol is hepatotoxic through redox changes produced by the NADH generated in its oxidation via the alcohol dehydrogenase pathway, which in turn affects the metabolism of lipids, carbohydrates, proteins, and purines. Ethanol is also oxidized in liver microsomes by an ethanol-inducible cytochrome P-450 (P-450IIE1) that contributes to ethanol metabolism and tolerance, and activates xenobiotics to toxic radicals thereby explaining increased vulnerability of the heavy drinker to industrial solvents, anesthetic agents, commonly prescribed drugs, over-the-counter analgesics, chemical carcinogens, and even nutritional factors such as vitamin A. In addition, ethanol depresses hepatic levels of vitamin A, even when administered with diets containing large amounts of the vitamin, reflecting, in part, accelerated microsomal degradation through newly discovered microsomal pathways of retinol metabolism, inducible by either ethanol or drug administration. The hepatic depletion of vitamin A is strikingly exacerbated when ethanol and other drugs were given together, mimicking a common clinical occurrence. Microsomal induction also results in increased production of acetaldehyde. Acetaldehyde, in turn, causes injury through the formation of protein adducts, resulting in antibody production, enzyme inactivation, decreased DNA repair, and alterations in microtubules, plasma membranes and mitochondria with a striking impairment of oxygen utilization. Acetaldehyde also causes glutathione depletion and lipid peroxidation, and stimulates hepatic collagen production by the vitamin A storing cells (lipocytes) and myofibroblasts.(ABSTRACT TRUNCATED AT 250 WORDS)

Chronic ethanol administration impairs receptor-mediated endocytosis of epidermal growth factor by rat hepatocytes

The effects of chronic ethanol administration on the receptor-mediated endocytosis of epidermal growth factor were studied in isolated rat hepatocytes. In initial experiments, it was demonstrated that significantly less ligand was bound by hepatocytes isolated from rats fed an ethanol liquid diet for 5 to 7 wk than by cells isolated from chow-fed or pair-fed controls. Reduced binding was shown to be primarily caused by a decreased number of surface receptors rather than by changes in receptor affinity. When hepatocytes were incubated at 37 degrees C in the presence of a large saturating concentration of epidermal growth factor (80 nmol/L), intracellular levels of the ligand were significantly lower in cells from the ethanol-fed animals. However, no effect on degradation of the ligand was observed under those conditions. A defect in the initial stages of receptor-ligand internalization was also indicated because less surface-bound ligand was internalized and subsequently degraded in cells from the ethanol-treated rats. When the endocytosis of a lower, more physiological concentration of the growth factor (0.5 nmol/L) was studied, both the uptake of ligand and its degradation were markedly impaired in hepatocytes from the ethanol-fed animals. These results indicate that chronic ethanol administration impairs the receptor-mediated endocytosis of epidermal growth factor by the liver. The major impairment appears to be a reduction of cell surface receptors; however, other steps of the endocytotic pathway also appear to be affected. These altered steps include defective receptor-ligand internalization and changes in intracellular processing of the ligand leading to decreased degradation.

Effect of chronic ethanol administration on the uptake and degradation of asialoglycoproteins by the perfused rat liver

We have shown previously reduced binding, internalization, degradation and receptor-ligand dissociation during receptor-mediated endocytosis (RME) of 125I-asialoorosomucoid (ASOR) by hepatocytes isolated from rats fed ethanol for 4-6 weeks. In the present study, we investigated the effect of ethanol feeding on RME by using the intact perfused liver as a model. Male, Sprague-Dawley rats were fed a liquid diet containing either ethanol (36% of calories) or isocaloric carbohydrate. Receptor-mediated endocytosis of 125I-ASOR was then examined over a time course of perfusion. In all cases, clearance of the labeled glycoprotein was followed by a slower but steady appearance of acid-soluble products in the medium. Ethanol-fed animals had a significantly (P less than 0.01) slower rate of clearance of the labeled ligand from the circulating perfusate than did control animals. Impairment of ASOR surface binding and degradation in ethanol-fed animals was also demonstrated in this model. When we examined the subcellular distribution of labeled ligand after various times of perfusion, we found that in control livers, a shift of radiolabeled ligand from the subcellular fractions containing endosomes and plasma membranes to fractions containing lysosomes occurred, while significantly less ligand was shifted to the lysosomes of ethanol-treated rats. These results show that ethanol administration inhibits RME of ASOR in the isolated perfused liver model, thus confirming our earlier reported defects in isolated hepatocytes. In addition, transport of ligand along the intracellular RME pathway was also shown to be altered by ethanol treatment as indicated by the impaired movement of ASOR from the endosomal to the lysosomal compartment.

Effect of chronic ethanol administration on total asialoglycoprotein receptor content and intracellular processing of asialoorosomucoid in isolated rat hepatocytes

Chronic ethanol administration markedly impairs the process of receptor-mediated endocytosis (RME) of a representative asialoglycoprotein, asialoorosomucoid (ASOR), by the liver (Casey et al. (1987) J. Biol. Chem. 262, 2704-2710). Decreased surface binding was the major defect reported in our initial study, along with impaired internalization and degradation of 125I-ASOR in chronically-fed ethanol animals. In this study, we further characterized these impairments by examining the content of intracellular receptors and by investigating ligand processing directed by these intracellular receptors. Ethanol administration for 5-7 weeks decreased intracellular ASOR receptor content by 40%, a result which was confirmed by using both a ligand-binding assay and an antibody-binding assay. In addition to a decreased number of intracellular receptors, an impairment in intracellular processing of receptor-ligand complexes was identified. In ethanol-fed animals, dissociation of receptor-ligand complexes was decreased during steady-state conditions of endocytosis at 37 degrees C. Impaired receptor-ligand dissociation did not alter the fate of the ligand which was to undergo diacytosis (ligand recycling), but did appear to impair degradation of intracellular ligand. These results indicate that chronic ethanol administration decreases ligand binding due to a decreased number of receptors and impairs intracellular processing of ASOR in hepatocytes.

Mechanism of ethanol induced hepatic injury

Ethanol is hepatotoxic through redox changes produced by the NADH generated in its oxidation via the alcohol dehydrogenase pathway, which in turn affects the metabolism of lipids, carbohydrates, proteins and purines. Ethanol is also oxidized in liver microsomes by an ethanol-inducible cytochrome P-450 (P-450IIE1) which contributes to ethanol metabolism and tolerance, and activates xenobiotics to toxic radicals thereby explaining increased vulnerability of the heavy drinker to industrial solvents, anesthetic agents, commonly prescribed drugs, over-the-counter analgesics, chemical carcinogens and even nutritional factors such as vitamin A. Induction also results in energy wastage and increased production of acetaldehyde. Acetaldehyde, in turn, causes injury through the formation of protein adducts, resulting in antibody production, enzyme inactivation, decreased DNA repair, and alterations in microtubules, plasma membranes and mitochondria with a striking impairment of oxygen utilization. Acetaldehyde also causes glutathione depletion and lipid peroxidation, and stimulates hepatic collagen synthesis, thereby promoting fibrosis.

Effect of acute and chronic ethanol administration on rat liver alpha 2,6-sialyltransferase activity responsible for sialylation of serum transferrin

The effect of a single administration and a 6-week treatment with ethanol on rat liver sialyltransferase activity towards asialoglycoproteins and N-acetyllactosamine (Gal beta 1,4GlcNAc) was studied. Since only the alpha 2,6-sialyltransferase is involved in the in vivo sialylation of transferrin, Gal beta 1,4GlcNAc was chosen as an acceptor and alpha 2,6-sialyl-N-acetyllactosamine was separated from the corresponding alpha 2,3-sialyl isomer present in the sialyltransferase reaction mixture by high-performance liquid chromatography. After a single ethanol administration there was a low (about 20%) but significant (p less than 0.005) reduction of sialyltransferase activity towards asialotransferrin as well as a reduced alpha 2,6-sialyltransferase activity towards N-acetyllactosamine. An opposite result was found in the chronically ethanol-treated rats: in these animals either the total or alpha 2,6-sialyltransferase activity was slightly higher than in control animals. Blood ethanol concentration was significantly high (3.3 +/- 1.2 mg/ml) only in the acute-treated animals, suggesting that the accumulation in the body of ethanol and/or its metabolites induces a reduction of liver alpha 2,6-sialyltransferase activity responsible for the transferrin sialylation. Current results are consistent with the finding (Stibler H, Hultcrantz R: Alcohol Clin Exp Res 11:468-473, 1987) that an enhanced level of hyposialylated transferrin isoforms is a marker of present but not previous alcohol abuse.

Ethanol-induced impairments in receptor-mediated endocytosis of asialoorosomucoid in isolated rat hepatocytes: time course of impairments and recovery after ethanol withdrawal

Chronic ethanol administration markedly impairs the process of receptor-mediated endocytosis (RME) of a representative asialoglycoprotein, asialoorosomucoid (ASOR), by the liver. In this study, we further characterized these impairments by identifying the time of onset for ethanol-induced changes in RME as well as establishing the time course for recovery to normal endocytotic values after ethanol withdrawal. Ethanol administration for 3 days did not alter any aspect of endocytosis examined in this study. After feeding ethanol to rats for 7 days, however, significant decreases in amounts of ligand bound, internalized, and degraded were apparent. These impairments persisted throughout the 5-week feeding study although the effects were somewhat attenuated with more prolonged ethanol feeding. In addition, an accumulation of intracellular receptors was observed in ethanol-fed animals relative to controls after 7 days of ethanol feeding. In all cases, recovery of endocytotic values to control levels was partially completed after 2 to 3 days of refeeding control diet and was fully completed after 7 days of refeeding. These results indicate that ethanol feeding for as little as 7 days profoundly impairs the process of RME by the liver. These impairments can be reversed after refeeding control diet for 7 days.

Effect of the chronic ethanol action on the activity of the general amino-acid permease from Saccharomyces cerevisiae var. ellipsoideus

The presence of ethanol and cycloheximide during growth were found to inhibit the function of the general amino-acid permease of Saccharomyces cerevisiae var. ellipsoideus. Contrary to cycloheximide, the effect of ethanol upon growth in alcohol-free medium was reversible. The effect of both inhibitors could be explained in terms of reduction of the number of active carrier molecules located in the plasma membrane.

Carbohydrate-deficient transferrin (CDT) in serum in women with early alcohol addiction

Carbohydrate-deficient transferrin (CDT) in serum was determined by micro anion exchange chromatography and a transferrin radioimmune assay in 58 consecutive women treated for early alcohol dependence compared, with 62 healthy females with an alcohol consumption of 0-15 g of ethanol/day. The upper normal CDT level was 74 mg/l. CDT was elevated above this value in 83% of the alcoholic women with an intake of 60 g of ethanol/day or more for at least 7 days within the preceding two weeks. CDT values were significantly positively correlated with daily alcohol consumption but not with GT, ASAT, ALAT or MCV. During abstinence CDT level declined exponentially with a half-life of 14 +/- 3 days. The results indicated that CDT may be as sensitive and specific a marker in women with early alcohol addiction as in previously studied male alcoholics. The amount of alcohol consumed appeared to be more important than sex or liver function. Determination of CDT may thus offer a means for early objective diagnosis and adequate treatment also of women in early stages of alcoholism.

Specific modulation by ethanol of the protein synthesis pattern in the C2 rat hepatoma cell line

The effect of ethanol on protein synthesis in the C2 rat hepatoma cell line was analyzed by two-dimensional gel electrophoresis after the labeling with [35S]methionine of cells that were untreated or had been treated with 180 mM ethanol. In this cell line, this concentration of ethanol is known to induce gamma-glutamyl transpeptidase, a marker of alcoholism in man (Barouki et al., Hepatology 1983; 3: 323-329). In the present work we demonstrate that ethanol, besides causing a slight decrease in overall protein synthesis (less than 25%), primarily regulates the expression of two unique proteins among 1500 labeled products that were analyzed: one of these was induced and did not correspond to gamma-glutamyl transpeptidase, and one was repressed after 20 h of ethanol treatment. We conclude that the set of hepatic proteins altered by ethanol is likely to be very limited in number, which reflects the specificity of alcohol action on protein synthesis in the C2 cell line.

Carbohydrate-deficient transferrin in serum in patients with liver diseases

Carbohydrate-deficient transferrin (CDT) in serum was analyzed by isocratic microanion exchange chromatography at pH 5.65 followed by a transferrin radioimmunoassay in 102 patients with biopsy-verified liver diseases. CDT values were normal in all of the 87 nonalcohol-abusing patients irrespective of type or degree of liver disease. Thirteen of the 15 alcoholic patients (87%) with current abuse showed elevated CDT values while in abstaining alcoholics with remaining liver disease the values were normal. No correlations were found between CDT level and volume density of liver fibrosis or steatosis or values of a number of clinicochemical liver tests. The only significant correlation demonstrated was between CDT concentration and the level of present daily alcohol consumption in the alcoholic patients. These results indicate that CDT can be used as a marker of present but not previous alcohol abuse, even in patients with various liver diseases.

Glycolysis in the mouse uterus during the early post-implantation stages of pregnancy and the effects of acute doses of ethanol

The objective of this study was to assess the possibility that, in mice, alcohol interferes with uterine glycolysis to influence indirectly embryonal development. Glycolysis was found to be a major metabolic process in the mouse uterus and its pattern of activity changed during post-implantation pregnancy between days 5 and 9. This was evidenced by changes in glycolytic enzymes and intermediates, and in the capacity of endometrial preparations to consume oxygen and produce lactate during incubation in vitro. The intraperitoneal administration of ethanol at 3.0 and 6.0 gm/kg body weight, but not at 1.5 gm/kg body weight, on day 9 of pregnancy modified glycolysis in the uterus after 2 hours, resulting in significant changes in the rates of accumulation of glucose, glucose-6-phosphate, fructose-6-phosphate, fructose-1,6-diphosphate, and citrate. These effects were not mediated by changes in redox state, since the ratio of lactate to pyruvate remained unchanged after injection of ethanol. Citrate was considered to be a major factor involved both in the regulation of uterine glycolysis and in the ethanol-induced alterations in the levels of hexose phosphates. The elevated levels of uterine glucose registered after treatment with ethanol were related to an acceleration of glycogen degradation in the liver and not in the uterine endometrium. The results suggest that part of the adverse action that these doses of ethanol exert on embryonal development stems from indirect effects that involve uterine functions relating to the nurture of the conceptus via glycolysis.

Micro anion exchange chromatography of carbohydrate-deficient transferrin in serum in relation to alcohol consumption (Swedish Patent 8400587-5)

A new simplified and rapid method for detection and quantitation of "carbohydrate-deficient transferrin" in serum is described. The method is based on isocratic anion exchange chromatography of isotransferrins in disposable microcolumns followed by a double antibody transferrin radioimmune assay. This technique, which separates all transferrin components isoelectric above pH 5.65, showed a very good reproducibility and accuracy with a coefficient of variation between 5 and 9%. 77 alcoholic patients could be clearly separated from 80 healthy "normal consumers" and 33 total abstainers with a specificity of 100% and a sensitivity of 91%. The values were significantly correlated to the amount of alcohol consumed during the latest month, and declined in abstaining alcoholics with a mean biological half-life of 17 days. Elevated levels occasionally appeared in healthy individuals after daily consumption of 60 g of ethanol during a 10-day period. In a sample of 187 patients with nonalcohol-related conditions only 2% false-positive values were found. This method is suggested as a potential tool for detecting and monitoring alcohol abuse.

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.

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.