Acetaldehyde selectively stimulates collagen production in cultured rat liver fat-storing cells but not in hepatocytes

Fibrosin: A novel lymphokine in alcohol-induced fibrosis

In this study, we examined the role of fibrogenic cytokines in alcohol-induced fibrosis. In particular, we examined the production of a novel fibrogenic cytokine, fibrosin, among others, by fibroblasts in response to ethanol in vitro; we also studied the production of fibrosin in an animal model of alcohol-induced liver injury. This model system utilizes the intragastric feeding rat model in which rats are fed different dietary fats and ethanol or dextrose. Our study showed that physiologic concentrations of ethanol directly induced proliferation of fibroblasts in vitro and also stimulated the production of cytokines. In particular, fibrosin, the novel fibrogenic cytokine, was produced. Other cytokines such as TGFbeta, IL-6, and TNFalpha were also induced. Also, exposure of fibroblasts to interleukin-1beta, interleukin-6, and tumor necrosis factor alpha induced production of fibrosin. In the fish oil-ethanol-fed rats which showed fibrotic lesions in the liver, fibrosin mRNA as well as protein was expressed. Fibrosin was not detected in control rats not exhibiting fibrosis. These studies show that ethanol can directly stimulate fibroblast proliferation and production of fibrogenic cytokines. It is likely that fibrosin, which may be derived from inflammatory cells, contributes to alcohol-induced hepatic fibrosis in vivo.

Prevention and treatment of liver fibrosis based on pathogenesis

Multiple agents have been proposed for the prevention and treatment of fibrosis. S-adenosylmethionine was reported to oppose CCl4-induced fibrosis in the rat, to attenuate the consequences of the ethanol-induced oxidative stress, and to decrease mortality in cirrhotics. Anti-inflammatory medications and agents that interfere with collagen synthesis, such as inhibitors of prolyl-4-hydroxylase and antioxidants, are also being tested. In nonhuman primates, polyenylphosphatidylcholine (PPC), extracted from soybeans, protected against alcohol-induced fibrosis and cirrhosis and prevented the associated hepatic phosphatidylcholine (PC) depletion by increasing 18:2 containing PC species; it also attenuated the transformation of stellate cells into collagen-producing transitional cells. Furthermore, it increased collagen breakdown, as shown in cultured stellate cells enriched with PPC or pure dilinoleoyl PC, the main PC species present in the extract. Because PPC and dilinoleoyl PC promote the breakdown of collagen, there is reasonable hope that this treatment may be useful for the management of fibrosis of alcoholic, as well as nonalcoholic, etiologies and that it may affect not only the progression of the disease, but may also reverse pre-existing fibrosis, as demonstrated for CCl4-induced cirrhosis in the rat and as presently tested in an ongoing clinical trial.

Acetaldehyde-mediated collagen regulation in hepatic stellate cells

Alcohol-induced liver cirrhosis is one of the major causes of death worldwide. Strong evidence has established that ethanol's first metabolite, acetaldehyde, is highly fibrogenic and enhances the deposition of many extracellular matrix components by hepatic stellate cells. This article reviews our current knowledge of the molecular mechanisms whereby acetaldehyde induces these activities, with particular emphasis on those related to the upregulation of type I collagen.

Role of Rho small GTP binding protein in the regulation of actin cytoskeleton in hepatic stellate cells

BACKGROUND/AIMS

In the fibrotic response to liver injury, hepatic stellate cells are activated, leading to the myofibroblastic cell shape, with actin cytoskeletal reorganization and increased extracellular matrix production. The reorganization of actin cytoskeleton suggests that the small GTP binding protein Rho might modulate the process of this myofibroblastic change. The aim of this study was to investigate the role of Rho in the phenotypic changes of hepatic stellate cells.

METHODS

The phenotypic changes were investigated by the overexpression of Rho regulator, Rho GDI or dominant negative mutant of Rho in mouse hepatic stellate cell line, GRX cells. In activated rat hepatic stellate cells, the effects of microinjection of Botulinus toxin C3, which is the specific inhibitor for Rho, were analyzed. Furthermore, the effect of C3 on the type I collagen accumulation in hepatic stellate cells was investigated.

RESULTS

Overexpression of Rho GDI or the dominant negative mutant of Rho caused the shrinkage cell shape and suppressed stress fiber formation. Microinjection of toxin C3 caused a markedly distorted cell shape and the disappearance of stress fibers in rat stellate cells. In addition, C3 strongly suppressed collagen accumulation in activated stellate cells.

CONCLUSIONS

These results suggest that Rho regulates the actin cytoskeletal reorganization, and may be implicated in the collagen accumulation in activated stellate cells. These findings provide evidence for the role of Rho in the myofibroblastic phenotype in hepatic stellate cells.

Regulation of hepatic transport systems involved in bile secretion during liver regeneration in rats

We investigated the expression of hepatic transport systems involved in bile secretion during liver regeneration after partial hepatectomy (PH) in rats. Initial studies showed maximal BrdU incorporation 24 hours after PH. Therefore, transporter expression and bile secretion were analyzed in detail at this time. The mRNA levels of the multidrug resistance genes mdr1a and mrp1 slightly increased, whereas mdr1b mRNA levels showed an extensive increase after PH. The mRNA levels of the conjugate transporter, mrp2, decreased slightly, whereas mrp2 protein levels did not change. Bilirubin secretion did not change, but the biliary glutathione secretion markedly decreased and the hepatic GSH content increased. The messenger RNA levels of the bile salt uptake transporters ntcp, oatp1, and oatp2 and the bile salt exporter, bsep/spgp, all decreased with ntcp showing the most prominent decrease. Protein levels of ntcp dramatically decreased whereas oatp2 only slightly decreased. Oatp1 protein expression slightly increased and bsep/spgp protein levels did not change. Decreased levels of bile salt uptake systems were associated with a 10-fold increase in the plasma bile salt concentration, yet, bile flow and bile salt secretion were increased when expressed per gram liver and unaffected when expressed on the basis of body weight. In conclusion, during the initial phase of rat liver regeneration ntcp is down-regulated whereas other transporter proteins involved in bile secretion are only slightly affected. Despite increased serum bile salt levels the remnant liver is not cholestatic: bile flow is maintained by uptake of bile salts probably via oatp isoforms and their secretion via bsep/spgp.

Alcohol, vitamin A, and beta-carotene: adverse interactions, including hepatotoxicity and carcinogenicity

Isozymes of alcohol and other dehydrogenases convert ethanol and retinol to their corresponding aldehydes in vitro. In addition, new pathways of retinol metabolism have been described in hepatic microsomes that involve, in part, cytochrome P450s, which can also metabolize various drugs. In view of these overlapping metabolic pathways, it is not surprising that multiple interactions between retinol, ethanol, and other drugs occur. Accordingly, prolonged use of alcohol, drugs, or both, results not only in decreased dietary intake of retinoids and carotenoids, but also accelerates the breakdown of retinol through cross-induction of degradative enzymes. There is also competition between ethanol and retinoic acid precursors. Depletion ensues, with associated hepatic and extrahepatic pathology, including carcinogenesis and contribution to fetal defects. Correction of deficiency through vitamin A supplementation has been advocated. It is, however, complicated by the intrinsic hepatotoxicity of retinol, which is potentiated by concomitant alcohol consumption. By contrast, beta-carotene, a precursor of vitamin A, was considered innocuous until recently, when it was found to also interact with ethanol, which interferes with its conversion to retinol. Furthermore, the combination of beta-carotene with ethanol results in hepatotoxicity. Moreover, in smokers who also consume alcohol, beta-carotene supplementation promotes pulmonary cancer and, possibly, cardiovascular complications. Experimentally, beta-carotene toxicity was exacerbated when administered as part of beadlets. Thus ethanol, while promoting a deficiency of vitamin A also enhances its toxicity as well as that of beta-carotene. This narrowing of the therapeutic window for retinol and beta-carotene must be taken into account when formulating treatments aimed at correcting vitamin A deficiency, especially in drinking populations.

Hepatic lipid peroxidation in hereditary hemochromatosis and alcoholic liver injury

Studies in experimental animals have indicated that enhanced lipid peroxidation may play a role in the hepatic injury produced by iron overload or by excessive alcohol consumption. The aim of this study was to compare the formation of lipid peroxidation-derived aldehydes in the liver of patients with hereditary hemochromatosis (HH) and alcohol abuse. Liver biopsy specimens from 10 nondrinking patients with HH were evaluated. These patients were classified as having HH based on hepatic iron index or human leukocyte antigen identity with a known proband. All patients were homozygous for the Cys282Tyr mutation. In addition, 8 patients with alcoholic liver disease were examined, 2 of whom also had hemochromatosis. For comparison, 17 patients with liver diseases unrelated to iron overload or alcohol abuse were studied. Liver biopsy specimens were immunostained for protein adducts with malondialdehyde and 4-hydroxynonenal. Both malondialdehyde- and 4-hydroxynonenal-protein adducts were found from liver specimens of patients with HH and alcohol abuse in more abundant amounts than from patients in a control group. In alcoholics the adducts were primarily in zone 3, whereas in hemochromatosis staining had an acinar zone 1 predominance, which followed the localization of iron. The most abundant amounts of protein adducts were noted in patients with alcohol abuse plus iron overload. The data support the concept that both chronic alcohol use and iron overload induce hepatic lipid peroxidation. Through formation of reactive aldehydic products, excessive alcohol consumption and iron overload may have additive hepatotoxic effects.

Dilinoleoylphosphatidylcholine decreases hepatic stellate cell activation

The prevention of cirrhosis in alcohol-fed baboons by the administration of a soybean extract-43% to 50% of which was dilinoleoyl-phosphatidylcholine (DLPC) and 24% of which was 1,palmitoyl 2,linoleoyl-phosphatidylcholine (PLPC)-was associated with a significant reduction in the number of stellate cells transformed to myofibroblast-like cells. To study whether these two major phospholipids affect the similar transformation that occurs by culturing stellate cells on uncoated plastic, we assessed their effects on proliferation (by (methyl-3H)-thymidine incorporation into DNA), expression of alpha-smooth muscle actin and type I procollagen (by densitometry of Western blots), and collagen synthesis (by incorporation of tritiated proline into collagenase-digestible proteins). These manifestations of stellate cell activation were decreased by 10 micromol/L DLPC but not by 10 micromol/L PLPC when compared with controls incubated either with 17 mmol/L ethanol (used as solvent for the phospholipids) or without addition. These agents did not affect cell viability, contamination with other cells, or the capacity of stellate cells to synthesize protein. Thus DLPC specifically decreases the in vitro activation of stellate cells, as judged by the decreases in proliferative activity, alpha-smooth muscle actin and procollagen I expressions, and collagen synthesis, whereas PLPC did not show such effects. alpha-Procollagen (type I) mRNA was not affected by DLPC, suggesting a post-translational effect. The reduction in the activation of hepatic stellate cells by DLPC may be responsible for, or at least contribute to, the prevention of fibrosis by the polyenylphosphatidylcholine mixture administered in vivo.

Expression of inducible nitric oxide synthase in endotoxemic rat hepatocytes is dependent on the cellular glutathione status

The inducible nitric oxide synthase (iNOS) promoter contains nuclear factor kappaB (NF-kappaB) binding sites. NF-kappaB activation is determined, in part, by the intracellular redox status. The aim of this study was to determine the importance of the cellular glutathione status in relation to NF-kappaB activation and iNOS expression in hepatocytes in vivo and in vitro. For in vivo experiments, rats were injected with endotoxin and sacrificed 6 hours later. Glutathione was depleted by diethylmaleate. For in vitro experiments, cultured hepatocytes from untreated rats were exposed to a cytokine mixture. Glutathione levels were depleted by diethylmaleate and restored by N-acetylcysteine. iNOS expression was assessed by Western blot, reverse transcription polymerase chain reaction, nitric oxide (NO) metabolites, and immunohistochemistry. NF-kappaB binding was assessed by electrophoretic mobility shift assay. Endotoxin-induced iNOS expression in rat liver was prominent in hepatocytes, Kupffer cells, and inflammatory cells, in particular neutrophils. Glutathione depletion prevented iNOS induction in hepatocytes, but not in inflammatory cells. iNOS protein levels were in accordance with iNOS messenger RNA and NO metabolites in plasma. Glutathione depletion did not affect neutrophil infiltration. Cytokines strongly induced iNOS in cultured hepatocytes. Induction was prevented by glutathione depletion and could be restored by addition of N-acetylcysteine. NF-kappaB binding correlated with iNOS induction. In conclusion, in this study we show that iNOS induction in hepatocytes in vivo and in vitro is dependent on the intracellular glutathione status and correlates with NF-kappaB binding. Glutathione-depletion has no effect on the expression of iNOS in inflammatory cells, nor on neutrophil infiltration.

Chronic alcohol intake interferes with retinoid metabolism and signaling

Chronic and excessive ethanol consumption is associated with cellular proliferation, fibrosis, cirrhosis, and cancer of the liver. The critical event in early alcohol-induced hepatic injury is an alcohol-induced activation (cell proliferation and increased fibrogenesis) of hepatic stellate cells. However, the mechanisms by which alcohol causes proliferative activation in hepatic stellate cells have not been identified. An important characteristic of alcohol-induced injury is impaired vitamin A nutritional status. The demonstration that retinoic acid is the most physiologically active derivative of vitamin A and the discovery of retinoic acid receptors provide a mechanistic basis for understanding the actions of vitamin A and alcohol on hepatic cell proliferation. Recent studies have demonstrated that chronic alcohol intake can reduce hepatic retinoic acid concentrations, diminish retinoid signaling, and enhance activator protein-1 (AP-1 (c-Jun and c-Fos)) expression in rat liver. These are the possible biochemical and molecular mechanisms whereby ethanol ingestion results in hepatic stellate cell proliferative activation and hepatic fibrogenesis.

Identification of two repressor elements in the mouse alpha 2(I) collagen promoter

We recently identified three areas of Sp1 binding located between -568 and -453 of the 5' flanking region of the murine alpha2(I) collagen promoter which are necessary for optimal activity. We now identify two additional regions of Sp1 binding located at -371 to -351 (region 4) and at -690 to -613 (region 5), which when mutated increased promoter activity in transfected rat hepatic stellate cells indicating they contain negative regulatory elements. AP-2 bound to region 4 while YY1 bound most strongly to region 5. AP-2 decreased Sp1 binding to region 4 and had a dual effect on Sp1 binding to region 5 decreasing and increasing Sp1 binding at low and high concentrations of AP-2, respectively. YY1 enhanced Sp1 binding to both regions. AP-2 inhibited or enhanced the stimulatory effect of a transfected Sp1 expression vector on the alpha2(I) collagen promoter in Drosophila cells at low or high AP-2 expression, respectively. YY1 enhanced or inhibited the activation of the promoter by low or high Sp1 expression, respectively. This study identifies two negative regulatory elements in the murine alpha2(I) collagen promoter and shows that AP-2 and YY1 interact with Sp1 at these sites and can inhibit the activating action of Sp1.

Liver fibrosis

Knowledge on the development and progression of liver fibrosis has grown exponentially in the past decade. At present, liver fibrogenesis is referred to as a dynamic process involving complex cellular and molecular mechanisms, resulting from the chronic activation of the tissue repair mechanisms that follows reiterated liver tissue injury. The identification and characterization of the cell types and of the different mediators involved in this process has allowed a "re-visitation" of several issues related to liver cirrhosis and its immediate consequences. Among these, evaluation of the relationships occurring between fibrogenesis and portal hypertension, cholestasis and the development of hepatocellular carcinoma, represent some of the hottest areas of research in this field of hepatology. The elucidation of many of the cellular and molecular mechanisms responsible for the progression of liver fibrosis has provided a sound basis for the development of pharmacological strategies able to modulate this important pathophysiological process.

Long- and short-term D-alpha-tocopherol supplementation inhibits liver collagen alpha1(I) gene expression

We analyzed the role of oxidative stress on liver collagen gene expression in vivo. Long- and short-term supplementation with the lipophilic antioxidant D-alpha-tocopherol (40 IU/day for 8 wk or 450 IU for 48 h) to normal C57BL/6 mice selectively decreased liver collagen mRNA by approximately 70 and approximately 60%, respectively. In transgenic mice, the -0.44 kb of the promoter and the first intron of the human collagen alpha1(I) gene were sufficient to confer responsiveness to D-alpha-tocopherol. Inhibition of collagen alpha1(I) transactivation in primary cultures of quiescent stellate cells from these transgenic animals by D-alpha-tocopherol required only -0.44 kb of the 5' regulatory region. This regulation resembled that of the intact animal following D-alpha-tocopherol treatment and indicates that D-alpha-tocopherol may act directly on stellate cells. Transfection of stellate cells with collagen-LUC chimeric genes allowed localization of an "antioxidant"-responsive element to the -0.22 kb of the 5' region excluding the first intron. These findings suggest that oxidative stress, independently of confounding variables such as tissue necrosis, inflammation, cell activation, or cell proliferation, modulates in vivo collagen gene expression.

Up-regulation of the multidrug resistance genes, Mrp1 and Mdr1b, and down-regulation of the organic anion transporter, Mrp2, and the bile salt transporter, Spgp, in endotoxemic rat liver

Endotoxin-induced cholestasis is mainly caused by an impaired canalicular secretion. Mrp2, the canalicular multispecific organic anion transporter, is strongly down-regulated in this situation, and canalicular bile salt secretion is also reduced. We hypothesized that other adenosine triphosphate-binding cassette (ABC) transporters may compensate for the decreased transport activity to protect the cell from cytokine-induced oxidative damage. Therefore, we examined the expression of ABC-transport proteins in membrane fractions of whole liver and of isolated hepatocytes of endotoxin-treated rats and performed reverse-transcriptase polymerase chain reaction (RT-PCR) on mRNA isolated from these livers. In addition, the localization of these transporters was examined using confocal scanning laser microscopy. By 6 hours after endotoxin administration, we found a clear increase of mrp1 mRNA and protein, whereas mrp2 mRNA and protein were decreased. This was confirmed in isolated hepatocytes. In addition, mdr1b mRNA was strongly increased, whereas mdr1a and mdr2 mRNA did not change significantly. Both the mRNA and protein levels of the sister of P-glycoprotein (spgp), the recently cloned bile salt transporter, decreased. After endotoxin treatment, the normally sharply delineated canalicular staining of mrp2 and spgp had changed to a fuzzy pattern, suggesting localization in a subapical compartment. We conclude that endotoxin-induced cholestasis is caused by decreased mrp2 and spgp levels, as well as an abnormal localization of these proteins. The simultaneous up-regulation of mrp1 and mdr1b may confer resistance to hepatocytes against cytokine-induced metabolic stress.

No significant expression of CYP2E1 in rat liver stellate cells

The putative role of the ethanol-inducible cytochrome P450(CYP)2E1 in stimulating collagen synthesis by rat liver stellate cells was studied. Analysis of carefully isolated stellate cells revealed that their content of immunoreactive CYP2E1 protein and of CYP2E1 mRNA, as determined by reverse transcription, polymerase chain reaction (RT-PCR), was very low, i.e. only 0-4% of that in hepatocytes. We conclude that it is improbable that such low expression of CYP2E1 in stellate cells would have functional importance.

Alcohol and lipids

Alcoholic fatty liver and hyperlipemia result from the interaction of ethanol and its oxidation products with hepatic lipid metabolism. An early target of ethanol toxicity is mitochondrial fatty acid oxidation. Acetaldehyde and reactive oxygen species have been incriminated in the pathogenesis of the mitochondrial injury. Microsomal changes offset deleterious accumulation of fatty acids, leading to enhanced formation of triacylglycerols, which are partly secreted into the plasma and partly accumulate in the liver. However, this compensatory mechanism fades with progression of the liver injury, whereas the production of toxic metabolites increases, exacerbating the lesions and promoting fibrogenesis. The early presence of these changes confers to the fatty liver a worse prognosis than previously thought. Alcoholic hyperlipemia results primarily from increased hepatic secretion of very-low-density lipoprotein and secondarily from impairment in the removal of triacylglycerol-rich lipoproteins from the plasma. Hyperlipemia tends to disappear because of enhanced lipolytic activity and aggravation of the liver injury. With moderate alcohol consumption, the increase in high-density lipoprotein becomes the predominant feature. Its mechanism is multifactorial (increased hepatic secretion and increased extrahepatic formation as well as decreased removal) and explains part of the enhanced cholesterol transport from tissues to bile. These changes contribute to, but do not fully account for, the effects on atherosclerosis and/or coronary heart disease attributed to moderate drinking.

Further characterization of a new in vitro angiogenesis model under serum free culture conditions; suppression of endothelial cell differentiation by serum

We studied the regulation of the extracellular matrix in the recently established murine vascular endothelial cell clones, F-2 or F-2C. F-2 cells constitutively show a cobblestone growth pattern under serum supplemented culture conditions, whereas F-2C cells undergo spontaneous histodifferentiation to form tubular structures in chemically defined media. We reported that the tubulogenesis induced by F-2C might relate to the heavy deposition of a 'basement membrane analog' as a subendothelial matrix (SEM). We further characterized the regulation of extracellular matrix (ECM) metabolism in these cell clones, in terms of gelatinase expression, ECM degradation and the effects of serum. F-2C cells in culture medium containing 1% serum did not undergo tubulogenesis but presented cobblestone growth. Zymography analysis showed that both F-2 and F-2C cells express two gelatinase (72 and 92 kDa). However, F-2 cells mainly expressed the former and faintly the latter, whereas F-2C mainly expressed the latter. Proteolysis studies showed that the spent media conditioned by F-2C cells partially cleaved type IV collagen and completely degraded type V collagen. The cleavage of type V collagen was suppressed by the addition of serum, whereas that of type IV collagen was not. The proteolysis of laminin and fibronectin by the conditioned medium was not observed. Serum-supplemented F-2 or F-2C cultures markedly suppressed SEM deposition. These results indicated that F-2C cells under serum free culture conditions not only present a simple and useful in vitro model with which to study the dynamic processes of proteolysis and ECM metabolism during the sequential phases of angiogenesis, but is also useful for analyzing the serum effects on angiogenesis (AG).

Signal transduction in hepatic stellate cells

Hepatic stellate cells (HSC) are presently regarded as one of the key cell types involved in the progression of liver fibrosis and in the related pathophysiological and clinical complications. Following acute or chronic liver tissue damage, HSC undergo a process of activation towards a phenotype characterised by increased proliferation, motility, contractility and synthesis of extracellular matrix (ECM) components. Several factors have been shown to play a key role in the promotion of the full-blown picture of activated HSC. These include extensive changes in the composition and organisation of the ECM, the secretion of several growth factors, cytokines, chemokines, products of oxidative stress and other soluble factors. It is evident that each cellular response to extracellular stimuli must be framed in a scenario where different forces modulate one another and result in a prevalent biological effect. Along these lines, the identification and characterisation of intracellular signalling pathways activated by different stimuli in HSC represent a mandatory step. In this review article we have made an attempt to summarise recent acquisitions to our knowledge of the involvement of different intracellular signalling pathways in key aspects of HSC biology.

Human hepatic stellate cells express class I alcohol dehydrogenase and aldehyde dehydrogenase but not cytochrome P4502E1

BACKGROUND/AIMS

Alcohol dehydrogenase, cytochrome P4502E1 (CYP2E1), and aldehyde dehydrogenase are known to play an important role in alcohol metabolism in the liver. Although the ethanol oxidation pathways are mainly localized in hepatocytes, we examine whether human hepatic stellate cells might also metabolize ethanol and acetaldehyde.

METHODS

Hepatic stellate cells were isolated from normal human livers and exposed in vitro to 50 mmol/l ethanol or 85 micromol/l acetaldehyde for different periods of time. Alcohol dehydrogenase/aldehyde dehydrogenase activity and CYP2E1 protein expression were measured in hepatic stellate cells. Moreover, alcohol dehydrogenase and aldehyde dehydrogenase mRNA expression were evaluated in hepatic stellate cells.

RESULTS

Exposure of hepatic stellate cells to ethanol for 24 h resulted in a 5-fold increase in cell alcohol dehydrogenase activity. The effect of ethanol on alcohol dehydrogenase activity was paralleled by a significant increase in the alcohol dehydrogenase mRNA expression in hepatic stellate cells. Acetaldehyde significantly increased the activity of high affinity aldehyde dehydrogenase in hepatic stellate cells, whereas ethanol was devoid of any effect. Acetaldehyde also induced high affinity aldehyde dehydrogenase mRNA expression in hepatic stellate cells. CYP2E1 was not expressed in hepatic stellate cells either in basal condition or after ethanol/acetaldehyde exposure.

CONCLUSIONS

This study shows that human hepatic stellate cells have the capacity to metabolize both ethanol and acetaldehyde through a class I alcohol dehydrogenase- and an aldehyde dehydrogenase-oxidizing pathway. Conversely, no detectable levels of CYP2E1-associated proteins are expressed in these cells.

Metabolism of ethanol and some associated adverse effects on the liver and the stomach

Current knowledge of alcohol oxidation and its effects on hepatic metabolism and its toxicity are summarized. This includes an evaluation of the relationship of the level of consumption to its interaction with nutrients (especially retinoids, carotenoids, and folate) and the development of various stages of liver disease. Ethanol metabolism in the stomach and its link to pathology and Helicobacter pylori is reviewed. Promising therapeutic approaches evolving from newly gained insight in the pathogenesis of medical complications of alcoholism are outlined. At present, the established approach for the prevention and treatment of alcoholism are outlined. At present, the established approach for the prevention and treatment of alcoholic liver injury is to control alcohol abuse, with the judicial application of selective antioxidant therapy, instituted at early stages, prior to the social or medical disintegration of the patient, and associated with antiinflammatory agents at the acute phase of alcoholic hepatitis. In addition, effective antifibrotic therapy may soon become available.

Cytotoxic effect of 7alpha-hydroxy-4-cholesten-3-one on HepG2 cells: hypothetical role of acetaldehyde-modified delta4-3-ketosteroid-5beta-reductase (the 37-kd-liver protein) in the pathogenesis of alcoholic liver injury in the rat

We recently identified delta4-3-ketosteroid-5beta-reductase as the 37 kd liver protein which is highly susceptible to acetaldehyde modification in rats continuously fed alcohol. The 5beta-reductase is a key enzyme involved in bile acid synthesis. We report here that the ability to degrade 7alpha-hydroxy-4-cholesten-3-one (HCO) was lower in the liver cytosol of alcohol-fed rats than in control animals, suggesting an inhibition of the 5beta-reductase enzyme activity by acetaldehyde modification. We also showed that HCO exhibited a time- and concentration-dependent cytotoxicity to HepG2 cells. HCO cytotoxicity was noticeable at a concentration of 2.5 microg/mL. When 10 microg/mL of HCO was added to confluent cell monolayers, 57% and 37% of cells remained viable after 24 and 48 hours of treatment. The decrease in cell viability was accompanied by an increased lactic dehydrogenase activity in the culture medium. DNA extracted from HCO-treated cells showed no evidence of DNA fragmentation when analyzed by agarose gel electrophoresis. Staining with propidium iodide showed no nuclear condensation in cells. Thus, cell death by HCO treatment was caused by necrosis and not by apoptosis. Various agents, including, serum proteins, hormones, bile acids, antioxidants, Ca++-chelators, Fe++-chelator, CYP450 inhibitor, adenylate cyclase inhibitor, protease inhibitors, and nitric oxide synthase inhibitor, did not protect against HCO cytotoxicity. We speculate that HCO concentrations may be elevated around the pericentral area in the liver after chronic alcohol ingestion, causing local cell necrosis. The release of cellular contents and protein-acetaldehyde adducts (PAAs) may activate nonparenchymal cells and provoke autoimmune reaction. Thus, the formation of the 37 kd-PAA may play an important role in the initiation of alcoholic liver injury.

Ethanol induces the expression of alpha 1(I) procollagen mRNA in a co-culture system containing a liver stellate cell-line and freshly isolated hepatocytes

To study the fibrogenic action of ethanol in vitro we used a co-culture system of freshly isolated hepatocytes and a liver stellate cell line (CFSC-2G) developed in our laboratory. Our results show that in this co-culture system ethanol induces the expression of alpha 1(I) procollagen mRNA in a dose- and time-dependent manner. This effect of ethanol was due to its metabolism by alcohol dehydrogenase since 4-methylpyrazole prevented the ethanol-mediated increase in alpha 1(I) procollagen mRNA. Ethanol was more efficient than acetaldehyde in inducing alpha 1(I) procollagen mRNA expression and its effect was protein synthesis-independent. Transfection of either hepatocytes or liver stellate cells with a reporter gene, chloramphenicol acetyl transferase (CAT), driven by 3700 bp of the mouse alpha 1(I) procollagen promoter demonstrated that only LSC expressed significant CAT activity and that this activity was enhanced by ethanol. Overall, our results suggest that this co-culture system is a useful model to study alcohol-induced fibrogenesis in vitro and that mechanisms other than acetaldehyde formation may also play an important role in alcohol-induced fibrogenesis.

Collagen synthesis by liver stellate cells is released from its normal feedback regulation by acetaldehyde-induced modification of the carboxyl-terminal propeptide of procollagen

Acetaldehyde stimulates collagen synthesis in stellate cells and forms adducts with procollagen in the liver of alcoholics. To assess the possibility that modification of the carboxyl-terminal propeptide by acetaldehyde affects its capacity to exert a feedback inhibition of collagen synthesis after splitting from procollagen, the propeptide was prepared by gel filtration of the bacterial collagenase digests of procollagen type I (obtained from 10(9) calvaria fibroblasts of newborn rats) and reacted with either 250 mM acetaldehyde and 100 mM CNBH3 or with 170 microM acetaldehyde without reducing agents, to mimick in vivo conditions. The unmodified propeptide produced a concentration-dependent inhibition of collagen synthesis by Ito cells. By contrast, the acetaldehyde-modified propeptide produced a lesser inhibition of procollagen synthesis in the cells, associated with a greater accumulation of collagen in the media. The incubation with 170 microM acetaldehyde and, to a lesser extent, 50 mM ethanol produced collagenase-digestible adducts in stellate cells. Thus, the formation of acetaldehyde adducts with the carboxyl-terminal propeptide of procollagen may account, at least in part, for the stimulatory effect of acetaldehyde on collagen synthesis by stellate cells and may lead to collagen accumulation through a decrease of the normal feedback regulation of collagen synthesis by the propeptide.

Establishment and characterization of a novel in vitro angiogenesis model using a microvascular endothelial cell line, F-2C, cultured in chemically defined medium

The behavior of vascular endothelial cells (EC) is an important factor in the processes involved in angiogenesis, but the regulatory mechanisms of angiogenesis, especially underlying the tubulogenesis by EC are not yet clear. Although a number of in vitro experimental models of tubulogenesis have been developed by use of cultured EC, most of those models are too complex to be easily handled and further, the culture media are usually supplemented with serum, creating problems in interpretation of experimental results. To generate a simple in vitro angiogenesis study model under serum-free culture conditions, we adapted a murine microvascular endothelial cell line, F-2, to a chemically defined medium, Cos Medium 001, and successfully established a subline of F-2, designated F-2C, which revealed a unique growth pattern. In Cos Medium 001, F-2C proliferates in a cobblestone pattern at an early growth stage, but, at a late growth stage, spontaneously differentiates to form three-dimensional honeycomblike tubular structures without the supplementation of any specific factors. The cell aggregation activity of F-2C in the presence of Ca2+ was much greater than that of F-2. The amount of subendothelial matrix deposited by F-2C was significantly higher than that by F-2, and increased prominently after the F-2C cells reached the differentiating stage of tubulogenesis. These findings indicate that F-2C is a new EC line in which tubulogenesis is spontaneously induced by the marked deposition of basement membrane analog to the subendothelial matrix and by the enhancement of presumable cadherin activity. We suggest that this cell line, F-2C, represents a simple and useful in vitro angiogenesis model.

Effect of acetaldehyde on Sp1 binding and activation of the mouse alpha 2(I) collagen promoter

Acetaldehyde activates the mouse alpha 2(I) collagen promoter and this effect is mediated in part by increased binding of nuclear factor I (NF-I). Additional mechanisms may exist since deletions in the promoter upstream to the NF-I binding site prevented enhancement by acetaldehyde. Three adjacent areas of binding by nuclear proteins from activated hepatic stellate cells were identified at -568 to -554 (region 1), -542 to -518 (region 2), and -473 to -453 (region 3) of the promoter using DNase I protection analyses. Multiple DNA-protein complexes were formed in electrophoretic mobility shift assays with oligonucleotide probes specifying the three regions. Sp1 and NF-1 bound to all three regions, while Sp3 bound to region 2. Acetaldehyde decreased nuclear protein binding to all three regions. Mutations of regions 1, 2, and 3 reduced basal activity of the promoter and inhibited acetaldehyde stimulation in transfected stellate cells. Acetaldehyde inhibited the stimulatory effect of the Sp1 vector pPacSp1 on the promoter in transfected Drosophila cells. In conclusion, three regions of Sp1 binding were identified and are required for optimal activity of the alpha 2(I) collagen promoter. Sp1 is required for basal activity of the alpha 2(I) collagen promoter; however, the enhancing effect of acetaldehyde on the promoter is not mediated by Sp1.

The hepatic stellate (Ito) cell: its role in human liver disease

The hepatic stellate (Ito) cell lies within the space of Disse and has a variety of functions. Stellate cells store vitamin A in characteristic lipid droplets. In the normal human liver, the cells can be identified by the presence of these lipid droplets; in addition, many stellate cells in the normal liver express alpha-smooth muscle actin. In acute liver injury, there is an expansion of the stellate cell population with increased alpha-smooth muscle actin expression; stellate cells appear to play a role in extracellular matrix remodelling after recovery from injury. In chronic liver injury, the stellate cell differentiates into a myofibroblast-like cell with marked expression of alpha-smooth muscle actin and occasional expression of desmin. Myofibroblast-like cells have a high fibrogenic capacity in the chronically diseased liver and are also involved in matrix degradation. In vitamin A intoxication, hypertrophy and proliferation of the stellate and myofibroblast-like cells may lead to non-cirrhotic portal hypertension, fibrosis and cirrhosis. In liver tumours, myofibroblast-like cells are involved in the capsule formation around the tumour and in the production of extracellular matrix within it. The transition of stellate cells into myofibroblast-like cells is regulated by an intricate network of intercellular communication between stellate cells and activated Kupffer cells, damaged hepatocytes, platelets, endothelial and inflammatory cells, involving cytokines and nonpeptide mediators such as reactive oxygen species, eicosanoids and acetaldehyde. The findings suggest that the stellate cell plays an active role in a number of human liver diseases, with a particular reactivity pattern in fibrotic liver disorders.

The formation and measurement of DNA neuroadduction in alcoholism. Case report

We present a case report of an intoxicated alcoholic driver who sustained fatal motor vehicle injuries. We subsequently quantified ethanol-derived acetaldehyde (ACE) DNA products in his brain, which may represent a major contributor to clinical alcoholic use and complications. Further, ACE DNA neuroadducts may indicate chronic exposure to alcohol, as demonstrated by 32P-prelabeled DNA and two-dimensional thin-layer chromatography. ACE and other unknown neuroadducts were evident in the histologically normal frontal, parietal, and caudate lobes. DNA neuroadduct formation was extensive and similar in three separate brain regions with normal histology. Contributing neuroadduction by chronic drug abuse is also possible, though the deceased's terminal acute blood screens for recent drug abuse were negative. The mechanism of alcohol neurotoxicity remains unknown, but biochemical nonenzymatic changes of DNA at the nucleic acid level (adduct formation) can alter gene function and stability. DNA neuroadduct detection may represent an important determinant in quantifying neurotoxicity from drug abuse or alcoholism in the absence of history, the presence of negative blood, tissue, and urine assays for recent drug and alcohol use, and the absence of neuropathology.

Medical considerations for dental care of patients with alcohol-related liver disease

More than 7 percent of all adults in the United States have met diagnostic criteria for alcohol abuse and alcohol dependence. Many of these people and even occasional users of alcohol may exhibit medical complexities, particularly liver disease, that can adversely affect provision of routine dental care. This article highlights some of the important clinical topics associated with alcoholic liver disease as it relates to dental care and provides guidelines on treatment of affected people.

Detection of activity in the conditioned medium of ethanol-treated HepG2 cells which stimulates collagen synthesis in IMR-90 cells

Hepatic fibrosis often occurs in alcoholic liver diseases without accompanying tissue necrosis or inflammation. However, the precise mechanism of this fibrosis has not been fully clarified. In the present study, using the hepatoblastoma cell line HepG2 as a model for hepatocytes, we identified a factor that stimulates collagen synthesis of fibroblasts in a conditioned medium of HepG2 cells after treatment with ethanol. Type 1 procollagen peptide (PIC) in a culture of human fibroblast IMR-90 markedly increased after incubation with the conditioned medium of ethanol-treated HepG2 cells. The stimulating activity on the production of PIC by IMR-90 remained after the dialysis and evaporation of the conditioned medium of HepG2 cells, indicating this factor was not as volatile from low molecular substances such as acetaldehyde, acetate, or lactate. The activity of this factor diminished with heat or trypsin treatment. A gel chromatographic analysis disclosed that the molecular weight of this factor was approximately 8000 Da. These results suggest that a polypeptide factor secreted from HepG2 cells by treatment with ethanol stimulates collagen synthesis of fibroblasts.

Activation of hepatic stellate cells by TGF alpha and collagen type I is mediated by oxidative stress through c-myb expression

Excessive production of collagen type I is a major contributor to hepatic fibrosis. Activated (myofibroblastic), but not quiescent, hepatic stellate cells (lipocytes) have a high level of collagen type I and alpha-smooth muscle actin expression. Therefore, stellate cell activation is a critical step in hepatic fibrosis. Here we show that quiescent stellate cells were activated by the generation of free radicals with ascorbate/FeSO4 and by malondialdehyde, a product of lipid peroxidation. In addition, stellate cell activation by collagen type I matrix and TGF alpha was blocked by antioxidants, such as d-alpha-tocopherol and butylated hydroxytoluene. Moreover, oxidative stress, TGF alpha and collagen type I markedly stimulated stellate cell entry into S-phase, NFkB activity, and c-myb expression, which were prevented by antioxidants. c-myb antisense oligonucleotide blocked the activation and proliferation of stellate cells induced by TGF alpha. Nuclear extracts from activated, but not from quiescent, stellate cells formed a complex with the critical promoter E box of the alpha-smooth muscle actin gene, which was disrupted by c-myb and NFkB65 antibodies, and competed by c-myb and NFkB cognate DNA. c-Myb expression was also stimulated in activated stellate cells in carbon tetrachloride-induced hepatic injury and fibrogenesis. This study indicates that oxidative stress plays an essential role, through the induction of c-myb and NFkB, on stellate cell activation.

In vitro comparison of the effects of ethanol and acetaldehyde on dorsal root ganglion neurons

Results of previous experiments designed to investigate the role of acetaldehyde, the primary metabolite of ethanol, have been contradictory. Experiments have provided evidence that supports and refutes the idea that acetaldehyde is responsible for the teratogenic effects observed in fetal alcohol syndrome. In the present study, cell culture techniques were used to examine the effects of acetaldehyde, both independently and in conjunction with ethanol. The purpose was to determine whether acetaldehyde had any effect on survival and process outgrowth of dorsal root ganglion (DRG) neurons cultured in vitro. This study revealed that acetaldehyde was as toxic to DRG survival as is ethanol, but had a lesser effect on neurite outgrowth than ethanol. Also, acetaldehyde and ethanol do not act synergistically to damage neurons in culture. The results indicate that, although acetaldehyde is probably not solely responsible for ethanol neurotoxicity, it does exhibit a secondary toxicity that could be the subject of future studies.

Novel insights into the biology and physiology of the Ito cell

Ito cells, perisinusoidal mesenchymal elements with possible pericytic functions within the liver, recently have been shown to play multiple physiological and pathophysiological roles. In particular, several in vivo and in vitro studies have clearly indicated that Ito cells play a relevant role in the progression of liver fibrogenesis. More recently, attention has been focussed on the mechanisms leading to Ito cell activation, proliferation and synthesis of extracellular matrix components. Among other soluble factors potentially involved in these processes, transforming growth factor-beta 1 and platelet-derived growth factor have been shown to act in a paracrine, and possibly autocrine, fashion on Ito cells, thus perpetuating their activated state. Finally, other studies have shown that Ito cells could play an active role in chronic liver tissue inflammation by promoting chemotaxis of infiltrating inflammatory cells.

Increased expression of matrix metalloproteinase-II in experimental liver fibrosis in rats

Matrix metalloproteinase-II (MMP-II, 72-kd type IV collagenase, or gelatinase) is one of the gene families of zinc enzymes capable of degrading extracellular matrix molecules, and specifically of degrading type IV and V collagens, gelatin, fibronectin, and elastin. In this study, we used both the liver fibrosis model and the reversibility model of experimental cirrhosis to clarify how MMP-II participates in liver fibrosis of rats. To produce fibrosis model, rats received subcutaneous injections of CCl4 twice weekly for 7, 9, or 14 weeks. For the reversibility model, rats were treated with CCl4 three times a week for 8 weeks and killed at 3, 7, 14, 28, or 42 days after discontinuation of treatment. MMP-II gene expression was studied by Northern hybridization technique, and gelatinase activity of MMP-II was examined by zymography using gelatin substrate. At the same time, an immunohistochemical study using anti-type IV collagen antibody was carried out. In liver fibrosis model, nodule formation was established at 14 weeks. Immunodeposit of type IV collagen was increased in wide fibrous septa and was clearly observed along sinusoidal wall. Gene expression of MMP-II increased up to 7 to 12 times compared with that of controls, with the expression rate being maximum at an intermediate stage of fibrosis. Zymography showed the expressions of both 65-kd latent MMP-II, which is confirmed to be activated by adding p-aminophenylmercuric acetate, and 62-kd active MMP-II during fibrosis. The expression of both forms increased 13 to 28 times as the fibrosis progressed.(ABSTRACT TRUNCATED AT 250 WORDS)

Degradation of matrix proteins in liver fibrosis

Hepatic fibrosis occurs as a consequence of net accumulation of matrix proteins (particularly collagen types I and III) in liver. Current concepts of the pathogenesis of liver fibrosis place major emphasis on the activation of hepatic lipocytes (fat-storing or Ito cells) to a myofibroblast-like phenotype with a consequent increase in their synthesis of matrix proteins. While this is an important factor, there is increasing evidence to indicate that liver fibrosis is a dynamic pathologic process in which altered matrix degradation may also play a significant role. Extracellular degradation of matrix proteins is regulated by a family of enzymes called the matrix metalloproteinases, which is subdivided into three groups; collagenases which degrade interstitial collagens (types I, II and III), type IV collagenases/gelatinases which degrade basement membrane (type IV) collagen and gelatins and stromelysins which degrade a broad range of substrates including proteoglycans, laminin, gelatins and fibronectin. The extracellular activity of these enzymes is regulated by several mechanisms which include alterations in gene transcription and proenzyme synthesis, cleavage of secreted proenzymes to active forms, and specific inhibition of activated forms by tissue inhibitor(s) of metalloproteinases (TIMPs). In liver, current evidence indicates that activated hepatic lipocytes and Kupffer cells play a central role in synthesis of matrix metalloproteinases. Under defined conditions they synthesize interstitial collagenase, 72 kDa and 95 kDa type IV collagenase/gelatinase and possibly stromelysin. Moreover, lipocytes also contribute to regulation of the extracellular activity of these enzymes by secretion of TIMP-1 and alpha 2-macroglobulin.(ABSTRACT TRUNCATED AT 250 WORDS)

Collagen-acetaldehyde adducts in alcoholic and nonalcoholic liver diseases

Alcoholic and, to a lesser extent, nonalcoholic patients with liver disease have serum antibodies to acetaldehyde-protein adducts produced in vitro. These antibodies presumably reflect the presence of adducts in the liver, but the protein that triggers this immune response has not been identified. To study this, we measured the reactivity of cytosolic proteins to rabbit IgG developed against a P-450 2E1-acetaldehyde adduct, isolated from alcohol-fed rats, that recognizes acetaldehyde-modified epitopes in proteins. Adducts were determined on Western blots by scanning densitometry of antibody-linked alkaline phosphatase activity in 4 normal livers and in needle biopsy specimens from subjects with liver disease, 17 alcoholic and 14 nonalcoholic. In all livers, except for a normal one, we found a reactive protein of at least 200 kD, similar to the collagen-acetaldehyde adduct we reported to be markedly increased in rats with experimentally induced cirrhosis. The immunostaining intensity in the alcoholic patients with liver disease was eightfold (p < 0.01) and that in nonalcoholic patients with liver disease was fourfold, greater (p < 0.02) than the weak staining in normal livers; it correlated with the degree of inflammation and serum AST or gamma-glutamyl transpeptidase activities. The adduct was reproduced on incubation of normal cytosolic proteins with 2.5 mmol/L acetaldehyde, whereas higher concentrations yielded many additional adducts; the adduct also reacted with IgG antibody to rat collagen type I and disappeared after digestion with collagenase, suggesting that the target protein is a form of collagen.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetaldehyde exposure causes growth inhibition in a Chinese hamster ovary cell line that expresses alcohol dehydrogenase

Chronic ethanol exposure causes many pathophysiological changes in cellular function due to ethanol itself and/or the effects of its metabolism (i.e., generation of acetaldehyde and redox equivalents). However, the role of each of these effects remains controversial. To address these questions, we have developed a cell line that expresses alcohol dehydrogenase. This cell line permits separate examination of the effects of ethanol and its metabolite acetaldehyde on cell function. An expression vector for the mouse liver alcohol dehydrogenase was constructed and transfected into Chinese hamster ovary cells. Cells expressing alcohol dehydrogenase were identified by screening with allyl alcohol, which is metabolized by alcohol dehydrogenase to the toxic aldehyde acrolein. A number of cell lines were identified that expressed alcohol dehydrogenase. A-10 cells were selected for further study because of their high sensitivity to allyl alcohol, suggesting a high level of alcohol dehydrogenase expression. These cells expressed a mRNA that hybridizes with the alcohol dehydrogenase cDNA and had an alcohol dehydrogenase activity comparable to murine liver. When cultures of these cells were exposed to ethanol, acetaldehyde was detected in both the medium and cells. The acetaldehyde concentration in the medium remained constant for at least 1 week in culture and was a function of the added ethanol concentration. Chronic exposure of A-10 cells to ethanol resulted in a dose-dependent reduction in the number of cells that accumulated over 7 days. Ethanol-treated cells remained viable, and growth inhibition was reversible. Growth inhibition was blocked by the alcohol dehydrogenase inhibitor 4-methylpyrazole, suggesting that acetaldehyde and not ethanol was responsible for growth inhibition in these cells.

Acetaldehyde-induced stimulation of collagen synthesis and gene expression is dependent on conditions of cell culture: studies with rat lipocytes and fibroblasts

Acetaldehyde has been proposed as a mediator of fibrogenesis in alcoholic liver disease, based in part on its ability to stimulate collagen synthesis by hepatic lipocytes in late primary or passaged culture. In this study, we examined the effect of acetaldehyde on rat lipocytes and fibroblasts at various stages of culture, in an effort to determine whether culture-related events influence responsiveness to this compound. Lipocytes from normal rat liver were studied in primary culture at 3 and 7 days after plating; fibroblasts were studied in subculture, at subconfluent and confluent densities. Both cell types were incubated with 100 microM acetaldehyde for 24 hr followed by measurement of collagen synthesis and type I collagen gene expression. Acetaldehyde had no effect on lipocytes at either 3 or 7 days in primary culture. The inability of acetaldehyde to stimulate collagen synthesis in primary culture was not attributable to toxicity, because cell morphology and total protein synthesis were identical in both treated and untreated cultures. Fibroblasts exhibited a variable response to acetaldehyde that was dependent on cell density: subconfluent cells contained similar amounts of type I collagen mRNA in both the presence and absence of acetaldehyde, whereas confluent cells exhibited a 2- to 3-fold increase in collagen mRNA levels upon acetaldehyde exposure. To determine whether quiescent lipocytes would respond to acetaldehyde in a culture system that mimics the hepatic environment in vivo, lipocytes were plated in coculture with hepatocytes on a basement membrane gel and incubated with 20 mM ethanol for 72 hr. Direct communication between these two cell types did not provoke lipocyte activation, even in the setting of ethanol oxidation.(ABSTRACT TRUNCATED AT 250 WORDS)

Alcohol and the liver: 1994 update

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

Acetaldehyde activates the promoter of the mouse alpha 2(I) collagen gene

The mechanism whereby ethanol ingestion results in hepatic fibrosis remains unknown. Acetaldehyde has been shown to increase alpha 1(I) collagen gene transcription in human fibroblasts and in rat myofibroblastlike cells (Ito cells) in culture. In this study, the effect of acetaldehyde was determined on the activation of the alpha 2(I) collagen promoter. A plasmid containing the mouse alpha 2(I) collagen promoter region (-2000 to 54), fused to the coding sequence of the reporter gene chloramphenicol acetyl transferase and similar plasmid constructs containing deletions in the collagen promoter, were transfected into NIH 3T3 fibroblasts in culture. Acetaldehyde (200 mumol/L) and transforming growth factor-beta 1 (5 ng/ml) activated the wild type promoter. The combination of acetaldehyde and transforming growth factor-beta 1 did not result in a greater effect than either alone. Acetaldehyde inhibited, whereas transforming growth factor-beta 1 did not activate, the promoter, with a -352 to -104 deletion. By contrast, acetaldehyde had no effect, whereas transforming growth factor-beta 1 resulted in a small decrease in the activity of the promoter, with a -501 to -352 deletion. This study shows that acetaldehyde and transforming growth factor-beta 1 independently activate the mouse alpha 2(I) collagen promoter and that this activation is mediated by the same proximal region of the promoter.

Mechanisms of ethanol-drug-nutrition interactions

Mechanisms of the toxicologic manifestations of ethanol abuse are reviewed. Hepatotoxicity of ethanol results from alcohol dehydrogenase-mediated excessive hepatic generation of nicotinamide adenine dinucleotide and acetaldehyde. It is now recognized that acetaldehyde is also produced by an accessory (but inducible) pathway, the microsomal ethanol-oxidizing system, which involves a specific cytochrome P450. It generates oxygen radicals and activates many xenobiotics to toxic metabolites, thereby explaining the increased vulnerability of heavy drinkers to industrial solvents, anesthetics, commonly used drugs, over-the-counter medications and carcinogens. The contribution of gastric alcohol dehydrogenase to the first pass metabolism of ethanol and alcohol-drug interactions is now recognized. Alcohol also alters the degradation of key nutrients, thereby promoting deficiencies as well as toxic interactions with vitamin A and beta-carotene. Conversely, nutritional deficits may affect the toxicity of ethanol and acetaldehyde, as illustrated by the depletion in glutathione, ameliorated by S-adenosyl-L-methionine. Other supernutrients include polyenylphosphatidylcholine, shown to correct the alcohol-induced hepatic phosphatidylcholine depletion and to prevent alcoholic cirrhosis in non-human primates. Thus, a better understanding of the pathology induced by ethanol has now generated improved prospects for therapy.

Acetaldehyde regulates the gene expression of matrix-metalloproteinase-1 and -2 in human fat-storing cells

Altered degradation of extracellular matrix has been implicated in the pathogenesis of hepatic fibrosis. We studied the effect of acetaldehyde (AcCHO) on gene expression of matrix-metalloproteinase (MMP)-1 (fibroblast type- interstitial collagenase) and MMP-2 (72 kDa gelatinase-type IV collagenase) in comparison with the AcCHO effect on collagen type I and IV synthesis in cultures of fat-storing cells (FSC) isolated from normal human livers. Cultured human FSC expressed single mRNA transcripts (2.7 and 3.2 kb) specific for MMP-1 and MMP-2, respectively. AcCHO inhibited MMP-1 mRNA levels, whereas it stimulated collagen type I mRNA and protein expression. Opposite AcCHO effects were evident on MMP-2 mRNA and collagen IV synthesis, being MMP-2 up-regulated and collagen IV down-regulated. These data suggest that regulation of MMP-1 and MMP-2 genes by AcCHO may contribute to disruption of the normal basement membrane and its replacement with fibrillar collagens in the early stages of alcoholic liver fibrosis.

Phosphatidylcholine protects against fibrosis and cirrhosis in the baboon

BACKGROUND/AIMS

Polyunsaturated soybean lecithin (55%-60% phosphatidylcholine [PC]) protects against fibrosis in alcohol-fed baboons. The present study was undertaken to determine whether PC is the active agent.

METHODS

Virtually pure PC (equivalent to that contained in the lecithin) was administered for up to 6.5 years with or without alcohol, and the results were compared with those of unsupplemented groups.

RESULTS

Control livers remained normal, whereas 10 of 12 baboons fed alcohol without PC developed septal fibrosis or cirrhosis with transformation of 81% +/- 3% of the hepatic lipocytes to collagen-producing transitional cells. By contrast, none of the eight animals fed alcohol with PC developed septal fibrosis or cirrhosis, and only 48% +/- 9% of their lipocytes were transformed, indicating that PC was indeed the protective compound. Ethanol feeding also resulted in decreased liver phospholipids and PC, and both were corrected by the supplementation. Furthermore, PC stimulated collagenase activity in cultured lipocytes. This PC consisted of several species, mainly dilinoleoylphosphatidylcholine (40%-52%) and palmitoyl-linoleoylphosphatidylcholine (23%-24%). Only dilinoleoylphosphatidylcholine duplicated the effect of the PC on collagenase. Other species of PC, phosphatidylethanolamine, free fatty acids, or choline were without effect.

CONCLUSIONS

PC prevents alcohol-induced fibrosis and cirrhosis in nonhuman primates, and dilinoleoylphosphatidylcholine appears to be the active species, possibly by promoting collagen breakdown.