Fatty Liver, Alcoholic :: etiology
Chronic alcohol exposure stimulates adipose tissue lipolysis in mice: role of reverse triglyceride transport in the pathogenesis of alcoholic steatosis.
Wei Zhong, Yantao Zhao, Yunan Tang, Xiaoli Wei, Xue Shi, Wenlong Sun, Xiuhua Sun, Xinmin Yin, Xinguo Sun, Seongho Kim, Craig J McClain, Xiang Zhang, Zhanxiang Zhou
Department of Nutrition, University of North Carolina at Greensboro, Greensboro, North Carolina 28081, USA.
Alcohol consumption induces liver steatosis; therefore, this study investigated the possible role of adipose tissue dysfunction in the pathogenesis of alcoholic steatosis. Mice were pair-fed an alcohol or control liquid diet for 8 weeks to evaluate the alcohol effects on lipid metabolism at the adipose tissue-liver axis. Chronic alcohol exposure reduced adipose tissue mass and adipocyte size. Fatty acid release from adipose tissue explants was significantly increased in alcohol-fed mice in association with the activation of adipose triglyceride lipase and hormone-sensitive lipase. Alcohol exposure induced insulin intolerance and inactivated adipose protein phosphatase 1 in association with the up-regulation of phosphatase and tensin homolog (PTEN) and suppressor of cytokine signaling 3 (SOCS3). Alcohol exposure up-regulated fatty acid transport proteins and caused lipid accumulation in the liver. To define the mechanistic link between adipose triglyceride loss and hepatic triglyceride gain, mice were first administered heavy water for 5 weeks to label adipose triglycerides with deuterium, and then pair-fed alcohol or control diet for 2 weeks. Deposition of deuterium-labeled adipose triglycerides in the liver was analyzed using Fourier transform ion cyclotron mass spectrometry. Alcohol exposure increased more than a dozen deuterium-labeled triglyceride molecules in the liver by up to 6.3-fold. These data demonstrate for the first time that adipose triglycerides due to alcohol-induced hyperlipolysis are reverse transported and deposited in the liver.
Most cited papers:
Alcohol promotes accumulation of fat in the liver mainly by substitution of ethanol for fatty acids as the major hepatic fuel. The degree of lipid accumulation depends on the supply of dietary fat. Progressive alteration of the mitochondria, which occurs during chronic alcohol consumption, decreases fatty acid oxidation by interfering with citric acid cycle activity. This block is partially compensated for by increased ketone body production, which results in ketonemia. Thus, mitochondrial damage perpetuates fatty acid accumulation even in the absence of ethanol oxidation. Alcohol facilitates esterification of the accumulated fatty acids to triglycerides, phospholipids, and cholesterol esters, all of which accumulate in the liver. The accumulated lipids are disposed of in part as serum lipoprotein, resulting in moderate hyperlipemia. In some individuals with pre-existing alterations of lipid metabolism, small ethanol dose may provoke marked hyperlipemia which responds to alcohol withdrawal. Inhibition of the catabolism of cholesterol to bile salt may contribute to the hepatic accumulation and hypercholesterolemia. The capacity of lipoprotein production and hyperlipemia development increases during chronic alcohol consumption, probably as a result of the concomitant hypertrophy of the endoplasmic reticulum and Golgi apparatus. However, this compensation is relatively inefficient in ridding the liver of fat. This inefficiency may be linked to alterations of hepatic microtubules induced by ethanol or its metabolites, which interfere with the export of protein from liver to serum, promoting hepatic accumulation of proteins as well as fat. As liver injury aggravates, hyperlipemia wanes and liver steatosis is exaggerated. Derangements of serum lipids similar to those found in other types of liver disease also become apparent. The changes in serum lipids may be a sensitive indicator of the progression of liver damage in the alcoholic.
Bronx Veterans Affairs Medical Center, Bronx, NY 10468, USA. firstname.lastname@example.org
Liver disease in the alcoholic is due not only to malnutrition but also to ethanol's hepatotoxicity linked to its metabolism by means of the alcohol dehydrogenase and cytochrome P450 2E1 (CYP2E1) pathways and the resulting production of toxic acetaldehyde. In addition, alcohol dehydrogenase-mediated ethanol metabolism generates the reduced form of nicotinamide adenine dinucleotide (NADH), which promotes steatosis by stimulating the synthesis of fatty acids and opposing their oxidation. Steatosis is also promoted by excess dietary lipids and can be attenuated by their replacement with medium-chain triglycerides. Through reduction of pyruvate, elevated NADH also increases lactate, which stimulates collagen synthesis in myofibroblasts. Furthermore, CYP2E1 activity is inducible by its substrates, not only ethanol but also fatty acids. Their excess and metabolism by means of this pathway generate release of free radicals, which cause oxidative stress, with peroxidation of lipids and membrane damage, including altered enzyme activities. Products of lipid peroxidation such as 4-hydroxynonenal stimulate collagen generation and fibrosis, which are further increased through diminished feedback inhibition of collagen synthesis because acetaldehyde forms adducts with the carboxyl-terminal propeptide of procollagen in hepatic stellate cells. Acetaldehyde is also toxic to the mitochondria, and it aggravates their oxidative stress by binding to reduced glutathione and promoting its leakage. Oxidative stress and associated cellular injury promote inflammation, which is aggravated by increased production of the proinflammatory cytokine tumor necrosis factor-alpha in the Kupffer cells. These are activated by induction of their CYP2E1 as well as by endotoxin. The endotoxin-stimulated tumor necrosis factor-alpha release is decreased by dilinoleoylphosphatidylcholine, the active phosphatidylcholine (PC) species of polyenylphosphatidylcholine (PPC). Moreover, defense mechanisms provided by peroxisome proliferator-activated receptor alpha and omega fatty acid oxidation are readily overwhelmed, particularly in female rats and also in women who have low hepatic induction of fatty acid-binding protein (L-FABPc). Accordingly, the intracellular concentration of free fatty acids may become high enough to injure membranes, thereby contributing to necrosis, inflammation, and progression to fibrosis and cirrhosis. Eventually, hepatic S-adenosylmethionine and PCs become depleted in the alcoholic, with impairment of their multiple cellular functions, which can be restored by PC replenishment. Thus, prevention and therapy opposing the development of steatosis and its progression to more severe injury can be achieved by a multifactorial approach: control of alcohol consumption, avoidance of obesity and of excess dietary long-chain fatty acids, or their replacement with medium-chain fatty acids, and replenishment of S-adenosylmethionine and PCs by using PPC. Progress in the understanding of the pathogenesis of alcoholic fatty liver and its progression to inflammation and fibrosis has resulted in prospects for their better prevention and treatment.
Possible mechanisms whereby alcohol abuse and alcohol-related diseases may promote the development of cancer are analyzed. The mechanisms discussed include:(a) contact-related local effects on the upper gastrointestinal tract;(b) the presence of low levels of carcinogens in alcoholic beverages;(c) induction of microsomal enzymes involved in carcinogen metabolism;(d) various types of cellular injury produced by ethanol and its metabolites and their relationship to cancer, particularly in the liver;(e) the nutritional disturbances frequently associated with alcohol abuse. The relationship between alcohol-induced cirrhosis and hepatocellular carcinoma is also discussed, and case histories of patients seen at the Bronx Veterans Administration Medical Center with hepatocellular carcinoma in the absence of cirrhosis are reviewed. Data are presented demonstrating the induction, by chronic ethanol consumption, of microsomal enzymes which convert procarcinogens to carcinogens. These data were derived from experiments in which the ability of microsomes isolated from liver, intestine, and lung tissues of ethanol-fed and control rats to activate several test carcinogens was examined in the Ames Salmonella-mutagenicity test. The hypothesis is presented that ethanol-mediated induction of enzyme systems which activate procarcinogens to carcinogens in various tissues contributes to the enhanced incidence of cancer in the alcoholic.
Division of Gastroenterology and Internal Medicine, Mayo Clinic, Rochester, Minnesota 55905, USA.
Patients with nonalcoholic steatohepatitis (NASH) may develop progressive liver dysfunction necessitating liver transplantation (OLT). We report the incidence of recurrent disease and outcome in patients undergoing OLT for NASH. Patients transplanted for NASH were identified according to pretransplant and explant liver histology. Patients with significant alcohol consumption were excluded. Medical records were reviewed to extract pre- and posttransplant data, including sequential body weight, biochemistry, and graft histology. Of 622 liver explants, eight patients had features consistent with NASH. All patients were female with a median age of 58. Seven patients were diagnosed with NASH preoperatively, including three who had undergone jejunoileal bypass. One patient was diagnosed as cryptogenic cirrhosis. At a median of 15 months following OLT, all of the eight patients were alive with no graft failure. Six patients developed persistent fatty infiltration in their graft, three of whom had accompanying hepatocellular degeneration, consistent with a diagnosis of recurrent NASH. In two patients, transition from mild steatosis to steatohepatitis and early fibrosis was observed over one to two years. The patients who did not develop recurrent steatosis had significant weight loss following transplantation, although the length of follow-up was relatively short. Patients undergoing OLT for NASH may develop recurrent steatosis shortly after transplantation, with possible progression to steatohepatitis and fibrosis. Although longer follow-up is necessary to determine the eventual prognosis related to the recurrent fat and fibrosis in the graft, patients with endstage liver disease due to NASH should be considered good candidates for OLT.
Department of Pharmacology and Biological Chemistry, Mount Sinai School of Medicine, New York, New York 10029, USA.
Fatty livers of obese fa/fa rats are vulnerable to injury when challenged by insults such as endotoxin, ischemia-reperfusion or acute ethanol treatment. The objective of this study was to evaluate whether a high-fat diet can act as a "second hit" and cause progression to liver injury in obese fa/fa rats compared with lean Fa/? rats. Accordingly, obese fa/fa rats and their lean littermates were fed a diet low in fat (12% of total calories) or a diet with 60% calories as lard for 8 weeks. Hyperglycemia and steatohepatitis occurred in the fa/fa rats fed the high-fat diet. This was accompanied by liver injury as assessed by alanine aminotransferase, hematoxilin and eosin staining, increased TNFalpha and stellate cell-derived TGFbeta, collagen deposition, and up-regulation of alpha-smooth muscle actin. Active MMP13 decreased in fa/fa rats independently of the diet, and TIMP1 expression increased with the high-fat diet, especially in fa/fa rats. Although UCP2 expression was higher in fa/fa rats regardless of the diet, minor changes in ATP levels were observed. Oxidative stress occurred in the fa/fa rats fed the high-fat diet as lipid peroxidation and protein carbonyls were elevated, while glutathione and antioxidant enzymes were very low. Expression and activity of cytochrome P450 2E1 and xanthine oxidase activity were down-regulated in fa/fa compared with Fa/? rats, and no effect was seen by the high-fat diet. However, NADPH oxidase activity increased 2.5-fold in fa/fa rats fed with the high-fat diet. In summary, a high-fat diet induces liver injury in fa/fa rats leading to periportal fibrosis. A role for oxidative stress is suggested via increased NADPH oxidase activity, lipid peroxidation, protein carbonyl formation, and low antioxidant defense.
The role of endotoxin in the pathogenesis of progressive liver disease is receiving increasing attention, but remains controversial. Similarly, although alcoholic hepatitis is now recognized as the transitional link between alcoholic fatty liver and advanced alcoholic liver disease, the aetiology of liver cell necrosis in alcoholic hepatitis is not known. Rats fed a nutritionally adequate liquid alcohol diet according to the formula of Lieber and DeCarli developed fatty livers. Littermates fed an identical diet and challenged with small IV doses (1 microgram/g body weight) of E. coli lipopolysaccharide endotoxin (LPS) developed focal necrotizing hepatitis. Control littermates fed an identical calorie balanced but alcohol free diet and challenged with identical doses of LPS did not develop any liver lesions. The hepatocyte necrosis with associated inflammatory changes induced by LPS in fatty livers has some features of early human alcoholic hepatitis and suggests that progressive alcohol induced damage may be multifactorial in origin.
National Public Health Institute, Alcohol Research Center, Helsinki, Finland.
Male Wistar rats were administered a modified, but nutritionally adequate, ethanol liquid diet with a low content of carbohydrate (5.5% of energy). The high daily intake of ethanol (mean 12.9 g/kg body wt) resulted in consistently sustained elevation of diurnal blood ethanol levels (mean 40.3 +/- 14.9mmol/l, corresponding to 180mg/dl). Marked micro- and macrovesicular panlobular steatosis, occasional inflammatory foci and a threefold elevation of serum alanine aminotransferase activity developed in 6 weeks. In livers from rats on regular 11% carbohydrate diet, lesions beyond periportally located steatosis were rare. These observations suggest that oral administration of a low-carbohydrate liquid ethanol diet may provide an affordable alternative to the technically demanding intragastric feeding model for experimental studies of alcoholic liver disease.
Multiple hepatic mitochondrial DNA deletions suggest premature oxidative aging in alcoholic patients.
INSERM Unité 24 and Centre de Recherche de Physiopathologie Hépatique(Association Claude Bernard), Hôpital Beaujon, Clichy, France.
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.
Inactivation of oxidized and S-nitrosylated mitochondrial proteins in alcoholic fatty liver of rats.
Kwan-Hoon Moon, Brian L Hood, Bong-Jo Kim, James P Hardwick, Thomas P Conrads, Timothy D Veenstra, Byoung J Song
Laboratory of Membrane Biochemistry and Biophysics, National Institute on Alcohol Abuse and Alcoholism, Bethesda, MD, USA.
Increased oxidative/nitrosative stress is a major contributing factor to alcohol-mediated mitochondrial dysfunction. However, which mitochondrial proteins are oxidatively modified under alcohol-induced oxidative/nitrosative stress is poorly understood. The aim of this study was to systematically investigate oxidized and/or S-nitrosylated mitochondrial proteins and to use a biotin-N-maleimide probe to evaluate their inactivation in alcoholic fatty livers of rats. Binge or chronic alcohol exposure significantly elevated nitric oxide, inducible nitric oxide synthase, and ethanol-inducible CYP2E1. The biotin-N-maleimide-labeled oxidized and/or S-nitrosylated mitochondrial proteins from pair-fed controls or alcohol-fed rat livers were subsequently purified with streptavidin-agarose. The overall patterns of oxidized and/or S-nitrosylated proteins resolved by 2-dimensional polyacrylamide gel electrophoresis were very similar in the chronic and binge alcohol treatment groups. Seventy-nine proteins that displayed differential spot intensities from those of control rats were identified by mass spectrometry. These include mitochondrial aldehyde dehydrogenase 2 (ALDH2), ATP synthase, acyl-CoA dehydrogenase, 3-ketoacyl-CoA thiolase, and many proteins involved in chaperone activity, mitochondrial electron transfer, and ion transport. The activity of 3-ketoacyl-CoA thiolase involved in mitochondrial beta-oxidation of fatty acids was significantly inhibited in alcohol-exposed rat livers, consistent with hepatic fat accumulation, as determined by biochemical and histological analyses. Measurement of activity and immunoblot results showed that ALDH2 and ATP synthase were also inhibited through oxidative modification of their cysteine or tyrosine residues in alcoholic fatty livers of rats. In conclusion, our results help to explain the underlying mechanism for mitochondrial dysfunction and increased susceptibility to alcohol-mediated liver damage.