Biochemical and morphological alterations of baboon hepatic mitochondria after chronic ethanol consumption

Soybean polyenylphosphatidylcholine (PPC) is beneficial in liver and extrahepatic tissue injury: An update in experimental research

Polyenylphosphatidylcholine (PPC) is a purified polyunsaturated phosphatidylcholine extract of soybeans. This article updates PPC's beneficial effects on various forms of liver cell injury and other tissues in experimental research. PPC downregulates hepatocyte CYP2E1 expression and associated hepatotoxicity, as well as attenuates oxidative stress, apoptosis, lipoprotein oxidation and steatosis in alcoholic and nonalcoholic liver injury. PPC inhibits pro-inflammatory cytokine production, while stimulating anti-inflammatory cytokine secretion in ethanol or lipopolysaccharide-stimulated Kupffer cells/macrophages. It promotes M2-type macrophage polarization and metabolic reprogramming of glucose and lipid metabolism. PPC mitigates steatosis in NAFLD through inhibiting polarization of pro-inflammatory M1-type Kupffer cells, alleviating metabolic inflammation, remodeling hepatic lipid metabolism, correcting imbalances between lipogenesis and lipolysis and enhancing lipoprotein secretion from hepatocytes. PPC is antifibrotic by preventing progression of alcoholic hepatic fibrosis in baboons and also prevents CCl4-induced fibrosis in rats. PPC supplementation replenishes the phosphatidylcholine content of damaged cell membranes, resulting in increased membrane fluidity and functioning. Phosphatidylcholine repletion prevents increased membrane curvature of the endoplasmic reticulum and Golgi and decreases sterol regulatory element binding protein-1-mediated lipogenesis, reducing steatosis. PPC remodels gut microbiota and affects hepatic lipid metabolism via the gut-hepatic-axis and also alleviates brain inflammatory responses and cognitive impairment via the gut-brain-axis. Additionally, PPC protects extrahepatic tissues from injury caused by various toxic compounds by reducing oxidative stress, inflammation, and membrane damage. It also stimulates liver regeneration, enhances sensitivity of cancer cells to radiotherapy/chemotherapy, and inhibits experimental hepatocarcinogenesis. PPC's beneficial effects justify it as a supportive treatment of liver disease.

Succinate as a signaling molecule in the mediation of liver diseases

Succinate, one of the intermediates of the tricarboxylic acid (TCA) cycle, plays an essential role in the metabolism of mitochondria and the production of energy, and is considered as a signaling molecule in metabolism as well as in initiation and progression of hepatic diseases. Of note, succinate activates a downstream signaling pathway through GPR91, and elicits a variety of intracellular responses, such as succinylation, production of reactive oxygen species (ROS), stabilization of hypoxia-inducible factor-1α (HIF-1α), and significant impact in cellular metabolism because of the pivotal role in the TCA cycle. Therefore, it is intriguing to deeply elucidate signaling mechanisms of succinate in hepatic fibrosis, metabolic reprogramming in inflammatory or immune responses, as well as carcinogenesis. This manuscript intends to review current understanding of succinate in mediating metabolism, inflammatory and immunologic reactions in liver diseases in order to establish molecular basis for the development of therapeutic strategies.

Mitochondrial respiratory chain activity is associated with severity, corticosteroid response and prognosis of alcoholic hepatitis

BACKGROUND AND AIMS

Little is known about the extent of mitochondrial respiratory chain (MRC) activity dysfunction in patients with alcoholic hepatitis (AH). We aimed to assess the hepatic MRC activity in AH patients and its potential impact on the severity and prognosis of this life-threatening liver disease.

METHODS

MRC complexes were measured in liver biopsies of 98 AH patients (non-severe, 17; severe, 81) and in 12 histologically normal livers (NL). Severity was assessed according to Maddrey's Index and MELD score. Corticosteroid response rate and cumulative mortality were also evaluated.

RESULTS

The activity of the five MRC complexes was markedly decreased in the liver of AH patients compared with that of NL subjects, being significantly lower in patients with severe AH than in those with non-severe AH. There was a negative correlation between the activity of all MRC complexes and the severity of AH. Interestingly, only complex I and III activities showed a significant positive correlation with the corticosteroid response rate and a significant negative correlation with the mortality rate at all-time points studied. In a multivariate regression analysis, besides the MELD score and the corticosteroid response rate, complex I activity was significantly associated with 3-month mortality (OR = 6.03; p = 0.034) and complex III activity with 6-month mortality (OR = 4.70; p = 0.041) in AH patients.

CONCLUSION

Our results indicate that MRC activity is markedly decreased in the liver of AH patients, and, particularly, the impairment of MRC complexes I and III activity appears to have a significant impact on the clinical outcomes of patients with AH.

Cellular Bioenergetics: Experimental Evidence for Alcohol-induced Adaptations

At-risk alcohol use is associated with multisystemic effects and end-organ injury, and significantly contributes to global health burden. Several alcohol-mediated mechanisms have been identified, with bioenergetic maladaptation gaining credence as an underlying pathophysiological mechanism contributing to cellular injury. This evidence-based review focuses on the current knowledge of alcohol-induced bioenergetic adaptations in metabolically active tissues: liver, cardiac and skeletal muscle, pancreas, and brain. Alcohol metabolism itself significantly interferes with bioenergetic pathways in tissues, particularly the liver. Alcohol decreases states of respiration in the electron transport chain, and activity and expression of respiratory complexes, with a net effect to decrease ATP content. In addition, alcohol dysregulates major metabolic pathways, including glycolysis, the tricarboxylic acid cycle, and fatty acid oxidation. These bioenergetic alterations are influenced by alcohol-mediated changes in mitochondrial morphology, biogenesis, and dynamics. The review highlights similarities and differences in bioenergetic adaptations according to tissue type, pattern of (acute vs. chronic) alcohol use, and energy substrate availability. The compromised bioenergetics synergizes with other critical pathophysiological mechanisms, including increased oxidative stress and accelerates cellular dysfunction, promoting senescence, programmed cell death, and end-organ injury.

Advancements in the Alcohol-Associated Liver Disease Model

Alcohol-associated liver disease (ALD) is an intricate disease that results in a broad spectrum of liver damage. The presentation of ALD can include simple steatosis, steatohepatitis, liver fibrosis, cirrhosis, and even hepatocellular carcinoma (HCC). Effective prevention and treatment strategies are urgently required for ALD patients. In previous decades, numerous rodent models were established to investigate the mechanisms of alcohol-associated liver disease and explore therapeutic targets. This review provides a summary of the latest developments in rodent models, including those that involve EtOH administration, which will help us to understand the characteristics and causes of ALD at different stages. In addition, we discuss the pathogenesis of ALD and summarize the existing in vitro models. We analyse the pros and cons of these models and their translational relevance and summarize the insights that have been gained regarding the mechanisms of alcoholic liver injury.

Succinate causes α-SMA production through GPR91 activation in hepatic stellate cells

Succinate acts as an extracellular signaling molecule as well as an intermediate in the citric acid cycle. It binds to and activates its specific G protein-coupled receptor 91 (GPR91). GPR91 is present in hepatic stellate cells (HSCs), but its role in hepatic fibrogenesis remains unclear. Cultured HSCs treated with succinate showed increased protein expression of GPR91 and α-smooth muscle actin (α-SMA), markers of fibrogenic response. Succinate also increased mRNA expression of α-SMA, transforming growth factor β (TGF-β), and collagen type I. Transfection of siRNA against GPR91 abrogated succinate-induced increases in α-SMA expression. Malonate, an inhibitor of succinate dehydrogenase (SDH), increased succinate levels in cultured HSCs and increased GPR91 and α-SMA expression. Feeding mice a methionine- and choline-deficient (MCD) diet is a widely used technique to create an animal model of nonalcoholic steatohepatitis (NASH). HSCs cultured in MCD media showed significantly decreased SDH activity and increased succinate concentration and GPR91 and α-SMA expression. Similarly, palmitate treatment significantly decreased SDH activity and increased GPR91 and α-SMA expression. Finally, C57BL6/J mice fed the MCD diet had elevated succinate levels in their plasma. The MCD diet also decreased SDH activity, increased succinate concentration, and increased GPR91 and α-SMA expression in isolated HSCs. Collectively, our results show that succinate plays an important role in HSC activation through GPR91 induction, and suggest that succinate and GPR91 may represent new therapeutic targets for modulating hepatic fibrosis.

MnSOD overexpression prevents liver mitochondrial DNA depletion after an alcohol binge but worsens this effect after prolonged alcohol consumption in mice

Both acute and chronic alcohol consumption increase reactive oxygen species (ROS) formation and lipid peroxidation, whose products damage hepatic mitochondrial DNA (mtDNA). To test whether manganese superoxide dismutase (MnSOD) overexpression modulates acute and chronic alcohol-induced mtDNA lesions, transgenic MnSOD-overexpressing (TgMnSOD(+++)) mice and wild-type (WT) mice were treated by alcohol, either chronically (7 weeks in drinking water) or acutely (single intragastric dose of 5 g/kg). Acute alcohol administration increased mitochondrial ROS formation, decreased mitochondrial glutathione, depleted and damaged mtDNA, durably increased inducible nitric oxide synthase (NOS) expression, plasma nitrites/nitrates and the nitration of tyrosine residues in complex V proteins and decreased complex V activity in WT mice. These effects were prevented in TgMnSOD(+++) mice. In acutely alcoholized WT mice, mtDNA depletion was prevented by tempol, a superoxide scavenger, L-NAME and 1400W, two NOS inhibitors, or uric acid, a peroxynitrite scavenger. In contrast, chronic alcohol consumption decreased cytosolic glutathione and increased hepatic iron, lipid peroxidation products and respiratory complex I protein carbonyls only in ethanol-treated TgMnSOD(+++) mice but not in WT mice. In chronic ethanol-fed TgMnSOD(+++) mice, but not WT mice, mtDNA was damaged and depleted, and the iron chelator, deferoxamine (DFO), prevented this effect. In conclusion, MnSOD overexpression prevents mtDNA depletion after an acute alcohol binge but aggravates this effect after prolonged alcohol consumption, which selectively triggers iron accumulation in TgMnSOD(+++) mice but not in WT mice. In the model of acute alcohol binge, the protective effects of MnSOD, tempol, NOS inhibitors and uric acid suggested a role of the superoxide anion reacting with NO to form mtDNA-damaging peroxynitrite. In the model of prolonged ethanol consumption, the protective effects of DFO suggested the role of iron reacting with hydrogen peroxide to form mtDNA-damaging hydroxyl radical.

IGFR-I expression and structural analysis of the hard palatine mucosa in an ethanol-drinking rat strain (UChA and UChB)

The study analyzed the effects of chronic alcohol ingestion on the ultrastructure of the lining epithelium of the hard palatine mucosa of rats UChA and UChB (lines with voluntary alcohol consumption) in order to contribute to the understanding of the consequences of alcohol abuse for the morphology of the digestive system. Thirty female adult animals aged 120 days were divided into three experimental groups. (1) Ten UChA rats (genetically low ethanol consumer) with voluntary intake of 10% v/v (5.45 g/kg/day) ethanol solution and water. (2) Ten UChB (genetically high ethanol consumer) rats with voluntary intake of 10% v/v (7.16 g/kg/day) ethanol solution and water. (3) Ten Wistar rats with voluntary ad libitum water intake (control group). Both groups received Nuvital pellets ad libitum. The IGFR-I expression was intense in both experimental groups. The epithelial cells of the alcoholic rats UChA and UChB showed many alterations such as the presence of lipid droplets, altered nuclei, nuclei in corneum layer and disrupted mitochondria. It was concluded that ethanol intake induces ultrastructural lesions in the hard palatine mucosa.

Analysis of the liver mitochondrial proteome in response to ethanol and S-adenosylmethionine treatments: novel molecular targets of disease and hepatoprotection

S-adenosylmethionine (SAM) minimizes alcohol hepatotoxicity; however, the molecular mechanisms responsible for SAM hepatoprotection remain unknown. Herein, we use proteomics to determine whether the hepatoprotective action of SAM against early-stage alcoholic liver disease is linked to alterations in the mitochondrial proteome. For this, male rats were fed control or ethanol-containing liquid diets +/- SAM and liver mitochondria were prepared for proteomic analysis. Two-dimensional isoelectric focusing (2D IEF/SDS-PAGE) and blue native gel electrophoresis (BN-PAGE) were used to determine changes in matrix and oxidative phosphorylation (OxPhos) proteins, respectively. SAM coadministration minimized alcohol-dependent inflammation and preserved mitochondrial respiration. SAM supplementation preserved liver SAM levels in ethanol-fed rats; however, mitochondrial SAM levels were increased by ethanol and SAM treatments. With use of 2D IEF/SDS-PAGE, 30 proteins showed significant changes in abundance in response to ethanol, SAM, or both. Classes of proteins affected by ethanol and SAM treatments were chaperones, beta oxidation proteins, sulfur metabolism proteins, and dehydrogenase enzymes involved in methionine, glycine, and choline metabolism. BN-PAGE revealed novel changes in the levels of 19 OxPhos proteins in response to ethanol, SAM, or both. Ethanol- and SAM-dependent alterations in the proteome were not linked to corresponding changes in gene expression. In conclusion, ethanol and SAM treatment led to multiple changes in the liver mitochondrial proteome. The protective effects of SAM against alcohol toxicity are mediated, in part, through maintenance of proteins involved in key mitochondrial energy conserving and biosynthetic pathways. This study demonstrates that SAM may be a promising candidate for treatment of alcoholic liver disease.

Interactions of ethanol drinking withn-3 fatty acids in rats: potential consequences for the cardiovascular system

Moderate ethanol drinking (ED) andn-3 fatty acids have both been associated with low cardiac mortality. However, there are few data evaluating the interactions of ED withn-3. We recently reported that moderate ED results in increasedn-3 in cardiac patients. The main aim of the present study was, through a well-controlled experimental model, to confirm that chronic ED actually results in increasedn-3. Secondary aims were to examine the effects of chronic ED on cardiac mitochondria, cardiac function and experimental myocardial infarction. We studied the fatty acid profiles of plasma, cell membranes and cardiac mitochondria phospholipids in a rat model of chronic ED. In plasma and cell membranes, ED actually resulted in highern-3 (P = 0·005). In mitochondria phospholipids of ED rats,n-3 were also increased (P < 0·05) but quite modestly. Cardiac mitochondrial function and left ventricular function were not significantly different in ED and control rats, while infarct size after 30 min ischaemia and reperfusion was smaller (P < 0·0001) in ED rats. This is the first animal study confirming interaction of alcohol drinking withn-3. We found no harmful effect of chronic ED on the heart in that model but a significant cardioprotection. Further studies are warranted to investigate the mechanisms by which moderate ED alters the metabolism ofn-3 and whethern-3 are the mediators of the ED-induced cardioprotection.

Evaluation of the ethanol intake on the Calomys callosus seminal vesicle structure

The effects of chronic alcohol ingestion on the structure of the glandular epithelium of the seminal vesicle of the rodent Calomys callosus were analyzed in 24 adult animals aged 3 months divided into three experimental groups. The control group received a solid diet and tap water, the alcoholic group received the same solid diet and ethanol P.A. diluted 20% in water (v/v) for 4 months. The abstinent group received the same liquid diet of the alcoholic one for the same period and after that the alcoholic diet was changed by water for a period of 3 months. After treatment, all animals were anesthetized, weighed and sacrificed. At the end of treatment, mean body weight did not differ between animal groups. The glandular epithelial cells of the alcoholic and abstinent groups showed atrophy and ultrastructural alterations such as the presence of altered nuclei, intense dilatation of the cisterns of the granular endoplasmic reticulum, intense digestive vacuoles and lipid droplets. Ethanol ingestion provokes marked lesions on the epithelium of the seminal vesicle probably interfering on the glandular secretion.

Alcohol-induced oxidative stress

Alcohol-induced oxidative stress is linked to the metabolism of ethanol involving both microsomal and mitochondrial systems. Ethanol metabolism is directly involved in the production of reactive oxygen species (ROS) and reactive nitrogen species (RNS). These form an environment favourable to oxidative stress. Ethanol treatment results in the depletion of GSH levels and decreases antioxidant activity. It elevates malondialdehyde (MDA), hydroxyethyl radical (HER), and hydroxynonenal (HNE) protein adducts. These cause the modification of all biological structures and consequently result in serious malfunction of cells and tissues.

Ethanol self-administration and alterations in the livers of the cynomolgus monkey, Macaca fascicularis

BACKGROUND

Most of the studies of alcoholic liver disease use models in which animals undergo involuntary administration of high amounts of ethanol and consume diets that are often high in polyunsaturated fatty acids. The objectives of this study were (1) to evaluate whether cynomolgus monkeys (Macaca fascicularis) drinking ethanol voluntarily and consuming a diet with moderate amounts of lipid would demonstrate any indices of alcoholic liver disease past the fatty liver stage and (2) to determine whether these alterations were accompanied by oxidative stress.

METHODS

Six adult male and 6 adult female cynomolgus monkeys were allowed to consume ethanol voluntarily for 18 to 19 months. Additional monkeys were maintained on the same consumption protocol, but were not provided with ethanol. During the course of the study, liver biopsy samples were monitored for lipid deposition and inflammation, serum for levels of liver enzymes, and urine for concentrations of the isoprostane (IsoP) metabolite, 2,3-dinor-5,6-dihydro-15-F(2t)-IsoP, a biomarker for oxidative stress. Liver mitochondria were monitored for respiratory control and liver for concentrations of neutral lipids, adenine nucleotides, esterified F(2) isoprostanes, oxidized proteins, 4-hydroxynonenal (HNE)-protein adducts, and protein levels of cytochrome P-450 2E1 and 3A4.

RESULTS

Ethanol consumption ranged from 0.9 to 4.05 g/kg/d over the period of the study. Serum levels of aspartate amino transferase were elevated in heavy-consuming animals compared with those in ethanol-naïve or moderate drinkers. Many of the ethanol consumers developed fatty liver and most showed loci of inflammation. Both hepatic energy charge and phosphorylation potential were decreased and NADH-linked respiration was slightly, but significantly depressed in coupled mitochondria as a result of heavy ethanol consumption. The urinary concentrations of 2,3-dinor-5,6-dihydro-15-F(2t)-IsoP increased as high as 33-fold over that observed in ethanol-abstinent animals. Liver cytochrome P-450 2E1 concentrations increased in ethanol consumers, but there were no ethanol-elicited increases in hepatic concentrations of the esterified F(2) isoprostanes, oxidized proteins, or HNE-protein adducts.

CONCLUSION

Our studies show that cynomolgus monkeys undergoing voluntary ethanol consumption for 1.5 years exhibit many of the features observed in the early stages of human alcoholic liver disease. Ethanol-elicited fatty liver, inflammation, and elevated serum aspartate amino transferase were evident with a diet that contained modest amounts of polyunsaturated lipids. The dramatic increases in urinary IsoP demonstrated that the animals were being subjected to significant oxidative stress that correlated with their level of ethanol consumption.

Hepatic phospholipids in alcoholic liver disease assessed by proton-decoupled 31P magnetic resonance spectroscopy

BACKGROUND/AIMS

Alteration of the phospholipid composition of hepatic biomembranes may be one mechanism of alcoholic liver disease (ALD). We applied proton-decoupled (31)P magnetic resonance spectroscopic imaging ({(1)H}-(31)P MRSI) to 40 patients with ALD and to 13 healthy controls to confirm that metabolic alterations in hepatic phospholipid intermediates could be detected non-invasively.

METHODS

All patients underwent liver biopsy. Specimens were scored in non-cirrhosis [fatty liver (n=3), alcoholic hepatitis (n=2), fibrosis (n=4), alcoholic hepatitis plus fibrosis (n=16)], and cirrhosis (n=15). {(1)H}-(31)P spectra were collected on a clinical 1.5-Tesla MR system and were evaluated by calculating signal intensity ratios of hepatic phosphomonoester (PME), phosphodiester (PDE), phosphoethanolamine (PE), phosphocholine (PC), glycerophosphorylethanolamine (GPE), and glycerophosphorylcholine (GPC) resonances.

RESULTS

The signal intensity ratio GPE/GPC was significantly elevated in cirrhotic (1.19+/-0.22; P=0.002) and non-cirrhotic ALD patients (1.01+/-0.13; P=0.006) compared to healthy controls (0.68+/-0.04), while PE/PC and PME/PDE were significantly elevated in cirrhotic ALD patients compared to controls (1.68+/-0.60 vs. 0.97+/-0.31; P=0.02, and 0.38+/-0.02 vs. 0.25+/-0.01; P=0.002, respectively) and non-cirrhotic patients.

CONCLUSIONS

The data support that {(1)H}-(31)P MRSI appears to distinguish cirrhotic from non-cirrhotic ALD patients and confirms changes in hepatic phospholipid metabolism observed in an animal model.

The effects of moderate ethanol consumption on the liver of the monkey, Macaca fascicularis

BACKGROUND

Although evidence has accumulated for the cardioprotective effects of moderate ethanol consumption, little is known about the effects on the liver of consuming the equivalent of two drinks per day. The objective of this study was to determine the effects of moderate ethanol administration on the hepatic content of enzymes involved in ethanol oxidation, on hepatic lipid accumulation, and on serum markers of liver function/damage in the monkey, Macaca fascicularis.

METHODS

Ovariectomized, adult monkeys were maintained for 34 months on an atherogenic diet containing cholesterol 1.21 mg/kJ. They were trained to drink ethanol plus vehicle at a dose of 0.5 g/kg body weight, which was administered 5 days a week for 2 years. Blood was collected for ethanol concentrations (1 hr after ethanol administration) and was also assayed for gamma-glutamyltransferase, alanine aminotransferase (ALT), and alkaline phosphatase (ALP) activities. Liver obtained at necropsy was analyzed for triglyceride and cholesterol contents and for alcohol dehydrogenase, cytochrome P450 2E1, and cytochrome P450 3A4 by Western blots.

RESULTS

The blood ethanol concentrations measured 1 hr after ethanol administration were relatively constant over the 2-year dosing period. Hepatic levels of alcohol dehydrogenase and the cytochrome P450s were not significantly different between ethanol-consuming animals and control animals. Ethanol-associated increases in liver triglyceride were not significant due to high variability in hepatic lipid content in both the controls and ethanol consumers. However, covariance analyses using pretreatment concentrations of plasma cholesterol and apolipoprotein A-I suggested that the ethanol-related increase in hepatic free cholesterol was significant. Relative to controls, alcohol consumers had higher levels of serum ALT and a transient increase in ALP at 5 months.

CONCLUSIONS

The observations made in this study on primates administered an atherogenic diet suggest that moderate ethanol ingestion has modest effects on the liver, including slightly increased ALT and ALP values. However, additional studies will be required to verify that this level of consumption is hepatotoxic when ingested over extended periods. This is still a concern because some human studies suggest that levels of ethanol considered to be cardioprotective cause liver injury when consumed over a lifetime.

Advances in nonhuman primate alcohol abuse and alcoholism research

Advances in our understanding of the biological basis of alcohol abuse and alcoholism and the development of prevention and therapeutic intervention require appropriate animal models. Nonhuman primates are important to the study of complex biomedical disease processes. Genetic, anatomical, physiological, and behavioral similarities to humans offer unique opportunities for translational research along with the advantage of a degree of experimental control that is not possible in human studies. The purpose of this review is to outline the approaches taken with nonhuman primates as subjects in alcohol research and to highlight our current understanding of data on organismal variables that can be uniquely studied in these complex organisms. We review literature on alcohol self-administration to provide an integrative framework for discussion of progress in 2 important areas of research. Designs that incorporate self-administration provide a context for studying excessive alcohol consumption, including the organismal and environmental factors that influence risk for heavy drinking. We then review the use of monkeys to identify aspects of adverse biomedical consequences that follow excessive alcohol consumption. One of the primary conclusions to be drawn from this review is that nonhuman primates are a central part of the translational bridge in alcohol research, providing powerful and unique opportunities for experimental work that can address the biomedical complexities of alcohol abuse and alcoholism.

Pathogenesis of alcoholic hepatic steatosis

Chronic alcohol misuse is the most common cause of hepatic steatosis. The accumulation of lipid is reversible with abstinence, but some workers have suggested that the severity of hepatic steatosis predicts the progression with time to alcoholic cirrhosis. Triacylglycerol is the major accumulating lipid and subcellular fractionation and electron microscopy studies have shown accumulation of lipid droplets within the golgi fraction. This is consistent with the reports in both experimental animals and man of reduced hepatic secretion of very low density lipoprotein triacylglycerol which may be secondary to acetaldehyde-induced disruption of the cytoskeletal elements. In addition, hepatic production of triacylglycerol increases, but most studies in animal models suggest that increased triacylglycerol synthesis becomes less important as hepatic lipid accumulates.

Dilinoleoylphosphatidylcholine is responsible for the beneficial effects of polyenylphosphatidylcholine on ethanol-induced mitochondrial injury in rats

Chronic ethanol consumption depletes phosphatidylcholines (PC) in membranes and hepatic mitochondria are an early target of this toxicity. Our previous studies showed that soybean-derived polyenylphosphatidylcholine (PPC), attenuated mitochondrial liver injury. Since dilinoleoylphosphatidylcholine (DLPC) is the major component of PPC, we assessed whether it is responsible for the protection of PPC. Forty-two male rats were fed the following liquid diets for 8 weeks: Control; Control with DLPC (1.5 g/1000 Calories (Cal); Alcohol (36% of Cal); Alcohol with DLPC (1.5 g/1000 Cal) and Alcohol with PPC (3 g/1000 Cal). As expected, ethanol feeding diminished the capacity of hepatic mitochondria to oxidize glutamate and palmitoyl-1-carnitine, and also decreased the activity of mitochondrial cytochrome oxidase. These effects were equally prevented by either PPC or DLPC. In conclusion, DLPC fully reproduced PPC's protective action and may be effective in the prevention or delay of more severe liver damage.

Alcoholic liver injury: pathogenesis and therapy in 2001

Much progress has been made in the understanding of the pathogenesis of alcoholic liver disease, resulting in improvement of prevention and promising prospects for even more effective treatments. It continues to be important to replenish nutritional deficiencies when present but it is crucial to recognize that, because of the alcohol-induced disease process, some of the nutritional requirements change. For instance, methionine, one of the essential amino acids for humans, must be activated to SAMe but, in severe liver disease, the activity of the corresponding enzyme is depressed. Therefore, the resulting deficiencies and associated pathology can be attenuated by the administration of SAMe, but not by methionine. Similarly, phosphatidylethanolamine methyltransferase (PEMT) activity, which is important for hepatic phosphatidylcholine (PC) synthesis, is also depressed in alcoholic liver disease, therefore calling for administration of the products of the reaction. It might also be beneficial to add other compounds to such therapeutic regiment. Since free radical generation by the ethanol-induced CYP2E1 plays a key role in the oxidative stress, inhibitors of this enzyme have great promise. Several have been investigated experimentally and PPC is particularly interesting because of its innocuity. In view of the striking negative interaction between alcoholic liver injury and hepatitis C, an antiviral agent is eagerly awaited that, unlike Interferon, is not contraindicated in the alcoholic. Anti-inflammatory agents are also required. In addition to down-regulators of cytokines and end toxic are being considered. Finally, since excess drinking is the crux of the issue, anticraving agents should be incorporated in any contemplated therapeutic cocktail, in view of the recent promising results obtained with some of these agents such as naltrexone and acamprosate.

Hepatic, metabolic, and nutritional disorders of alcoholism: from pathogenesis to therapy

Much progress has been made in the understanding of the pathogenesis of alcoholic liver disease, resulting in an improvement in treatment. Nutritional deficiencies should be corrected when present but, because of the alcohol-induced disease process, some of the nutritional requirements change. For instance, methionine, one of the essential amino acids for humans, must be activated to S-adenosylmethionine (SAMe), but, in severe liver disease, the activity of the corresponding enzyme is depressed. Therefore, the resulting deficiencies and associated pathology can be attenuated by the administration of SAMe, but not by methionine. Similarly, phosphatidylethanolamine methyltransferase (PEMT) activity, which is important for hepatic phosphatidylcholine (PC) synthesis, is also depressed in alcoholic liver disease, therefore calling for the administration of the products of the reaction. Inasmuch as free radical generation by the ethanol-induced CYP2E1 plays a key role in the oxidative stress, inhibitors of this enzyme have great promise and PPC, which is presently being evaluated clinically, is particularly interesting because of its innocuity. In view of the striking negative interaction between alcoholic liver injury and hepatitis C, an antiviral agent is eagerly awaited that, unlike Interferon, is not contraindicated in the alcoholic. Antiinflamatory agents may also be useful. In addition to steroids, down-regulators of cytokines and endotoxin are being considered. Finally, anticraving agents such as naltrexone or acamprosate should be incorporated into any contemplated therapeutic cocktail.

Alcoholic liver disease: new insights in pathogenesis lead to new treatments

Much progress has been made in the understanding of the pathogenesis of alcoholic liver disease, resulting in improvement of prevention and therapy, with promising prospects for even more effective treatments. The most successful approaches that one can expect to evolve are those that deal with the fundamental cellular disturbances resulting from excessive alcohol consumption. Two pathologic concepts are emerging as particularly useful therapeutically. Whereas it continues to be important to replenish nutritional deficiencies, when present, it is crucial to recognize that because of the alcohol-induced disease process, some of the nutritional requirements change. This is exemplified by methionine, which normally is one of the essential amino acids for humans, but needs to be activated to S-adenosylmethionine (SAMe), a process impaired by the disease. Thus, SAMe rather than methionine is the compound that must be supplemented in the presence of significant liver disease. Indeed, SAMe was found to attenuate mitochondrial lesions in baboons, replenish glutathione, and significantly reduce mortality in patients with Child A or B cirrhosis. Similarly, polyenylphosphatidylcholine (PPC) corrects the ethanol-induced hepatic phospholipid depletion as well as the decreased phosphatidylethanolamine methyltransferase activity and opposes oxidative stress. It also deactivates hepatic stellate cells, whereas its dilinoleoyl species (DLPC) increases collagenase activity, resulting in prevention of ethanol-induced septal fibrosis and cirrhosis in the baboon. Clinical trials with PPC are ongoing in patients with alcoholic liver disease. Furthermore, enzymes useful for detoxification, such as CYP2E1, when excessively induced, become harmful and should be downregulated. PPC is one of the substances with anti-CYP2E1 properties that is now emerging. Another important aspect is the association of alcoholic liver disease with hepatitis C: a quarter of all patients with alcoholic liver disease also have markers of HCV infection, with an even higher incidence in some urban areas but, at present, no specific therapy is available since interferon is contraindicated in that population. However, in addition to antiviral medications, agents that oppose oxidative stress and fibrosis should also be tested for hepatitis C treatment since these two processes contribute much to the pathology and mortality associated with the virus. In addition to antioxidants (such as PPC, silymarin, alpha-tocopherol and selenium), anti-inflammatory medications (corticosteroids, colchicine, anticytokines) are also being tested as antifibrotics. Transplantation is now accepted treatment in alcoholics who have brought their alcoholism under control and who benefit from adequate social support but organ availability is still the major limiting factor and should be expanded more aggressively. Finally, abstinence from excessive drinking is always indicated; it is difficult to achieve but agents that oppose alcohol craving are becoming available and they should be used more extensively.

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.

Cytotoxicity of short-chain alcohols

Ethanol and other short-chain alcohols elicit a number of cellular responses that are potentially cytotoxic and, to some extent, independent of cell type. Aberrations in phospholipid and fatty acid metabolism, changes in the cellular redox state, disruptions of the energy state, and increased production of reactive oxygen metabolites have been implicated in cellular damage resulting from acute or chronic exposure to short-chain alcohols. Resulting disruptions of intracellular signaling cascades through interference with the synthesis of phosphatidic acid, decreases in phosphorylation potential and lipid peroxidation are mechanisms by which solvent alcohols can affect the rate of cell proliferation and, consequently, cell number. Nonoxidative metabolism of short-chain alcohols, including phospholipase D-mediated synthesis of alcohol phospholipids, and the synthesis of fatty acid alcohol esters are additional mechanisms by which alcohols can affect membrane structure and compromise cell function.

Ursodeoxycholate protects against ethanol-induced liver mitochondrial injury

The purpose of this work was to examine whether ursodeoxycholate (UDC), a hydrophilic bile salt, could reduce mitochondrial liver injury from chronic ethanol consumption in rats. Animals were pair-fed liquid diets containing 36% of calories as ethanol or isocaloric carbohydrates. They were randomly assigned into 4 groups of 7 rats each and received a specific treatment for 5 weeks: control diet, ethanol diet, control diet + UDC, and ethanol diet + UDC. Respiratory rates of isolated liver mitochondria were measured using a Clark oxygen electrode with sodium succinate as substrate. Mitochondria from rats chronically fed ethanol demonstrated an impaired ability to produce energy. At the fatty liver stage, the ADP-stimulated respiration (V3) was depressed by 33%, the respiratory control ratio (RC) by 25% and the P/O ratio by 15%. In ethanol-fed rats supplemented with UDC, both the rate and efficiency of ATP synthesis via the oxidative phosphorylation were improved: V3 was increased by 35%, P/O by 8%. All the respiratory parameters were similar in control group and control + UDC group. On the other hand, the number and size of mitochondria were assessed by electron microscopy and computer-assisted quantitative analysis. The number of mitochondria from ethanol-treated rats was decreased by 29%, and they were enlarged by 74%. Both parameters were normalized to control values by UDC treatment. These studies demonstrate that UDC has a protective effect against ethanol-induced mitochondrial injury by improving ATP synthesis and preserving liver mitochondrial morphology. These UDC positive effects may contribute to the observed decrease in fat accumulation and may delay the progression of alcoholic injury to more advanced stages.

Acute and chronic ethanol increases reactive oxygen species generation and decreases viability in fresh, isolated rat hepatocytes

Although reactive oxygen species (ROS) have been implicated in the etiology of alcohol-induced liver disease, neither their relative contribution to cell death nor the cellular mechanisms mediating their formation are known. The purpose of this study was to test the hypothesis that acute and chronic ethanol exposure enhances the mitochondrial generation of ROS in fresh, isolated hepatocytes. Acute ethanol exposure stimulated ROS production, increased the cellular NADH/NAD+ ratio, and decreased hepatocyte viability slightly, which was prevented by pretreatment with 4-methylpyrazole (4-MP), an inhibitor of alcohol dehydrogenase. Similarly, xylitol, an NADH-generating compound, enhanced hepatocyte ROS production and decreased viability. Incubation with pyruvate, an NADH-oxidizing compound, and cyanamide, an inhibitor of aldehyde dehydrogenase, significantly decreased ROS levels in acute ethanol-treated hepatocytes. Chronic ethanol consumption produced a sixfold increase in hepatocyte ROS production compared with levels measured in controls. Hepatocytes from ethanol-fed rats were less viable compared with controls, e.g., viability was 68% +/- 2% (ethanol) versus 83% +/- 1% (control) after 60 minutes of incubation. Antimycin A increased ROS production and decreased cell viability; however, the toxic effect of antimycin A was more pronounced in ethanol-fed hepatocytes. These results suggest that acute and chronic ethanol exposure exacerbates mitochondrial ROS production, contributing to cell death.

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.

Multiple hepatic mitochondrial DNA deletions suggest premature oxidative aging in alcoholic patients

BACKGROUND/AIMS

A 4977-base pair deletion has been detected in the hepatic mitochondrial DNA of alcoholic patients with microvesicular steatosis, a lesion ascribed to impaired mitochondrial beta-oxidation. However, only a single deletion had been looked for in this previous study, and it could not be determined whether the deletion was preexisting or acquired. Alcohol abuse increases the formation of reactive oxygen species in hepatic mitochondria. If this effect accelerates the oxidative aging of mitochondrial DNA, several other mutations would be expected.

METHODS

The mtDNA region extending from nucleotide 8167 to nucleotide 14246 was screened for the presence of large mitochondrial DNA deletions in 58 alcoholic patients and 67 age-matched non-alcoholic controls. Hepatic DNA was subjected to polymerase chain reactions that amplified non-deleted and deleted mitochondrial DNA, respectively, and the boundaries of the mitochondrial DNA deletions were sequenced.

RESULTS

Only 3% of the non-alcoholic controls carried a mitochondrial DNA deletion, whereas 24% of all alcoholic patients and 85% of the 13 alcoholic patients with microvesicular steatosis exhibited either single or multiple 4977, 5385, 5039 and 5556-base pair mitochondrial DNA deletions. No deletion(s) were observed, however, in 13 patients with microvesicular steatosis due to other causes.

CONCLUSIONS

Diverse mitochondrial DNA rearrangements are observed in alcoholic patients with microvesicular steatosis. We suggest that alcohol abuse leads to premature oxidative aging of mitochondrial DNA. Hypothetically, oxidative damage to mitochondrial constituents (DNA, proteins and lipids) may favor microvesicular fat deposition.

Hepatic mitochondrial and lysosomal alterations in acute experimental pancreatitis with ethanolic coetiology in rats

In order to assess the cumulative effects of antecedent acute ethanol intake and acute pancreatitis on the liver, the mitochondrial respiratory functions and lysosomal membrane integrity of the liver were evaluated in taurocholate pancreatitis (AP) in rats, induced 6 hr after intragastric ethanol 40% (5 g/kg body wt). The oxygen consumption rate, RCR (respiratory control ratio), and ADP/O ratio were measured according to Estabrook. Fractional free activity of lysosomal hydrolases was assayed. RCR with glutamate + malate was most decreased at 12 hr of AP with partial improvement after 18 hr. The ADP/O ratio dropped maximally after 18 hr of AP. The fragility of lysosomal membranes increased significantly at 18 hr of AP. The antecedent ethanol intake abolished the partial restoration of RCR after 18 hr; however, it did not affect the ADP/O ratio or the integrity of lysosomal membranes impaired in AP at this time. In conclusion, the antecedent acute ethanol abuse could aggravate the liver mitochondrial deterioration, but not the lysosomal membrane labilization seen in AP.

Effect of ethanol consumption on adult rat liver mitochondrial populations analyzed by flow cytometry

In the present study, the effects of administering ethanol to adult male rats on the distribution of the low fluorescence population (LFP) and high fluorescence population (HFP), and the rhodamine-123 fluorescence intensity of these groups of mitochondria are analyzed by flow cytometry. Our results show that ethanol administration to adult male rats induces a redistribution of the HFP and LFP mitochondrial populations leading to an increase of the less functional HFP mitochondria. In addition, ethanol induced an increase in the mean intensity of green fluorescence of the HFP that is probably related to an increased number of rhodamine-123 binding sites per mitochondria resulting from mitochondria enlargement.

Liver cell necrosis: cellular mechanisms and clinical implications

Based on our current understanding, we have developed a provisional model for hepatocyte necrosis that may be applicable to cell necrosis in general (Figure 6). Damage to mitochondria appears to be a key early event in the progression to necrosis. At least two pathways may be involved. In the first, inhibition of oxidative phosphorylation in the absence of the MMPT leads to ATP depletion, ion dysregulation, and enhanced degradative hydrolase activity. If oxygen is present, toxic oxygen species may be generated and lipid peroxidation can occur. Subsequent cytoskeleton and plasma membrane damage result in plasma membrane bleb formation. These steps are reversible if the insult to the cell is removed. However, if injury continues, bleb rupture and cell lysis occur. In the second pathway, mitochondrial damage results in an MMPT. This step is irreversible and leads to cell death by as yet uncertain mechanisms. It is important to note that MMPT may occur secondary to changes in the first pathway (e.g. oxidative stress, increased Cai2+, and ATP depletion) and that all the "downstream events" occurring in the first pathway may result from MMPT (e.g., ATP depletion, ion dysregulation, or hydrolase activation). Proof of this model's applicability to cell necrosis in general awaits further validation. In this review, we have attempted to highlight the advances in our understanding of the cellular mechanisms of necrotic injury. Recent advances in this understanding have allowed scientists and clinicians a better comprehension of liver pathophysiology. This knowledge has provided new avenues of therapy and played a key role in the practice of hepatology as evidenced by advances in organ preservation. Understanding the early reversible events leading to cellular and subcellular damage will be key to prevention and treatment of liver disease. Hopefully, disease and injury specific preventive or pharmacological strategies can be developed based on this expanding data base.

Hepatic mitochondrial DNA deletion in alcoholics: association with microvesicular steatosis

BACKGROUND/AIMS

Alcohol abuse may lead to microvesicular steatosis, a lesion ascribed to impaired mitochondrial function. Because alcohol abuse leads to reactive oxygen species in the hepatic mitochondria, it may damage mitochondrial DNA. The aim of this study was to look for the presence of the "common" 4977-base pair deletion in the hepatic mitochondrial DNA of alcoholic patients and age-matched, nonalcoholic controls.

METHODS

Hepatic DNA was subjected to two polymerase chain reactions that amplified non-deleted and deleted mitochondrial DNA, respectively.

RESULTS

The deletion was found in 6 of 10 alcoholics with microvesicular steatosis, 2 of 17 alcoholic patients with macrovacuolar steatosis, but in none of 12 patients with acute alcoholic hepatitis, 11 patients with alcoholic cirrhosis, or 62 nonalcoholic patients of comparable ages with various other liver diseases or normal liver histology. In all patients with the deletion, restriction fragments of deleted mitochondrial DNA co-migrated with those of reference Pearson bone marrow-pancreas syndrome patients with the common mitochondrial DNA deletion.

CONCLUSIONS

The common deletion is frequent in the hepatic DNA of alcoholic patients with microvesicular steatosis. Alcohol-induced mitochondrial DNA damage may contribute to the occurrence of this lesion in some alcoholics.

Inhibition of mitochondrial beta-oxidation as a mechanism of hepatotoxicity

Severe and prolonged impairment of mitochondrial beta-oxidation leads to microvesicular steatosis, and, in severe forms, to liver failure, coma and death. Impairment of mitochondrial beta-oxidation may be either genetic or acquired, and different causes may add their effects to inhibit beta-oxidation severely and trigger the syndrome. Drugs and some endogenous compounds can sequester coenzyme A and/or inhibit mitochondrial beta-oxidation enzymes (aspirin, valproic acid, tetracyclines, several 2-arylpropionate anti-inflammatory drugs, amineptine and tianeptine); they may inhibit both mitochondrial beta-oxidation and oxidative phosphorylation (endogenous bile acids, amiodarone, perhexiline and diethylaminoethoxyhexestrol), or they may impair mitochondrial DNA transcription (interferon-alpha), or decrease mitochondrial DNA replication (dideoxynucleoside analogues), while other compounds (ethanol, female sex hormones) act through a combination of different mechanisms. Any investigational molecule should be screened for such effects.

Bone mass improves in alcoholics after 2 years of abstinence

To evaluate the effect of abstinence on bone mass and bone mineral metabolism in chronic alcoholics, a 2 year longitudinal follow-up study was carried out in a group of 30 chronic alcoholic males who started a rehabilitation program. Lumbar and femoral bone mineral density (BMD) and serum levels of osteocalcin and 25-hydroxyvitamin D were measured at entry and after 1 and 2 years in all patients. Circulating cortisol and parathyroid hormone were measured in 14 and 6 patients, respectively, at entry and every year. Testosterone was measured in 18 patients at entry and after 1 year. At entry, lumbar BMD was significantly lower in alcoholics (1.06 +/- 0.03 g/cm2) than in age-matched healthy men (1.22 +/- 0.03 g/cm2; p < 0.001). Circulating osteocalcin and vitamin D levels were also significantly lower in alcoholics than in controls. Lumbar and femoral neck BMD increased in alcoholics after 2 years of abstinence (lumbar BMD, mean +/- SEM, 1.06 +/- 0.03 to 1.10 +/- 0.04 g/cm2, p < 0.05; femoral BMD, 0.82 +/- 0.02 to 0.84 +/- 0.02 g/cm2; p < 0.02). Moreover, lumbar BMD increased in alcoholics (2.9 +/- 1.4%) and decreased in controls (-1.1 +/- 0.2%; p < 0.02). Femoral BMD also increased in alcoholics (2.8 +/- 1.0%) but the expected mean decrease of -0.92% was found in healthy age-matched males. Baseline low osteocalcin levels (5.1 +/- 0.6 ng/ml) increased after 1 year (8.6 +/- 0.5 ng/ml, p < 0.001) and 2 years of abstinence (9.5 +/- 0.7 ng/ml, p < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Hepatic and metabolic effects of ethanol: pathogenesis and prevention

Mechanisms of the hepatotoxicity of ethanol are reviewed, including effects resulting from alcohol dehydrogenase (ADH) mediated excessive hepatic generation of NADH and acetaldehyde. Gastric ADH explains first-pass metabolism by ethanol; its activity is low in alcoholics and in females and is decreased by some commonly used drugs. In addition to ADH, ethanol can be oxidized by liver microsomes: studies over the last 25 years have culiminated in the molecular elucidation of the ethanol-inducible cytochrome P-450 (2E1) which causes metabolic tolerance to ethanol and to various commonly used medications, enhanced degradation of testosterone and vitamin A (with vitamin A depletion) and selective hepatic perivenular toxicity. The latter results from free radical generation and activation of various xenobiotics, causing increased vulnerability of the heavy drinker to the toxicity of industrial solvents, anaesthetic agents, commonly prescribed drugs, over-the-counter analgesics, chemical carcinogens and even nutritional factors such as vitamin A and beta-carotene. Furthermore, induction of the microsomal pathway contributes to increased acetaldehyde generation which promotes GSH depletion and lipid peroxidation and other toxic effects. 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.

Mitochondrial function reflected by the decarboxylation of [13C]ketoisocaproate is impaired in alcoholics

Mitochondria of patients with alcoholic liver disease exhibit structural abnormalities, and mitochondria isolated from animals exposed to ethanol are functionally deficient when studied in vitro. To assess possible functional consequences of these ethanol-associated alterations in vivo, we measured mitochondrial function in alcoholics noninvasively with a breath test. A mitochondrial function, the decarboxylation of ketoisocaproate (KICA), was assessed by measuring the exhalation of 13CO2 following the administration of 1 mg/kg 2-keto[1-13C]isocaproic acid, the decarboxylation of which occurs in mitochondria. The results of the KICA breath test in 12 alcoholic subjects were compared with the results in healthy controls and patients with nonalcoholic liver disease. The peak exhalation of 13CO2 and the fraction of the administered dose decarboxylated in 120 min were both significantly lower in alcoholics than in healthy controls and patients with nonalcoholic liver disease. In alcoholics, KICA decarboxylation was impaired in the presence of normal quantitative liver function tests such as the aminopyrine breath test and galactose elimination capacity, indicating that KICA decarboxylation does not simply reflect a decreased functional hepatic mass. The enrichment of circulating KICA with [13C]KICA was similar in alcoholics and controls, indicating that a decreased bioavailability or an increased dilution of labeled KICA cannot account for the decreased exhalation of 13CO2. It is concluded that mitochondrial function as reflected by KICA decarboxylation is impaired in chronic alcoholics. The functional impairment is specific for ethanol abuse and not a reflection of decreased global hepatic function. KICA decarboxylation could thus be useful as a marker for excessive ethanol consumption.

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.

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.

Alterations in mitochondrial function and morphology in chronic liver disease: pathogenesis and potential for therapeutic intervention

Studies assessing mitochondrial function and structure in livers from humans or experimental animals with chronic liver disease, including liver cirrhosis, revealed a variety of alterations in comparison with normal subjects or control animals. Depending on the etiology of chronic liver disease, the function of the electron transport chain and/or ATP synthesis was found to be impaired, leading to decreased oxidative metabolism of various substrates and to impaired recovery of the hepatic energy state after a metabolic insult. Changes in mitochondrial structure include megamitochondria with reduced cristae, dilatation of mitochondrial cristae and crystalloid inclusions in the mitochondrial matrix. The most important strategies to maintain an adequate mitochondrial function per liver are mitochondrial proliferation and increases in the activity of critical enzymes or in the content of cofactors per mitochondrion. Possibilities to assess hepatic mitochondrial function and to treat mitochondrial dysfunction in patients with chronic liver disease are discussed.

Aetiology and pathogenesis of alcoholic liver disease

Until the 1960s, liver disease of the alcoholic patient was attributed exclusively to dietary deficiencies. Since then, however, our understanding of the impact of alcoholism on nutritional status has undergone a progressive evolution. Alcohol, because of its high energy content, was at first perceived to act exclusively as 'empty calories' displacing other nutrients in the diet, and causing primary malnutrition through decreased intake of essential nutrients. With improvement in the overall nutrition of the population, the role of primary malnutrition waned and secondary malnutrition was emphasized as a result of a better understanding of maldigestion and malabsorption caused by chronic alcohol consumption and various diseases associated with chronic alcoholism. At the same time, the concept of the direct toxicity of alcohol came to the forefront as an explanation for the widespread cellular injury. Some of the hepatotoxicity was found to result from the metabolic disturbances associated with the oxidation of ethanol via the liver alcohol dehydrogenase (ADH) pathway and the redox changes produced by the generated NADH, which in turn affects the metabolism of lipids, carbohydrates, proteins and purines. Exaggeration of the redox change by the relative hypoxia which prevails physiologically in the perivenular zone contributes to the exacerbation of the ethanol-induced lesions in zone 3. In addition to ADH, ethanol can be oxidized by liver microsomes: studies over the last twenty years have culminated in the molecular elucidation of the ethanol-inducible cytochrome P450IIE1 (CYP2E1) which contributes not only to ethanol metabolism and tolerance, but also to the selective hepatic perivenular toxicity of various xenobiotics. Their activation by CYP2E1 now provides an understanding for the increased susceptibility of the heavy drinker to the toxicity of industrial solvents, anaesthetic agents, commonly prescribed drugs, 'over the counter' analgesics, chemical carcinogens and even nutritional factors such as vitamin A. Ethanol causes not only vitamin A depletion but it also enhances its hepatotoxicity. Furthermore, induction of the microsomal pathway contributes to increased acetaldehyde generation, with formation of protein adducts, resulting in antibody production, enzyme inactivation and decreased DNA repair; it is also associated with a striking impairment of the capacity of the liver to utilize oxygen. Moreover, acetaldehyde promotes glutathione depletion, free-radical mediated toxicity and lipid peroxidation. In addition, acetaldehyde affects hepatic collagen synthesis: both in vivo and in vitro (in cultured myofibroblasts and lipocytes), ethanol and its metabolite acetaldehyde were found to increase collagen accumulation and mRNA levels for collagen. This new understanding of the pathogenesis of alcoholic liver disease may eventually improve therapy with drugs and nutrients.