Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0015695 (fatty liver)
 13,941 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Oxidation of ethanol via alcohol dehydrogenase (ADH) explains various metabolic effects of ethanol but does not account for the tolerance. This fact, as well as the discovery of the proliferation of the smooth endoplasmic reticulum (SER) after chronic alcohol consumption, suggested the existence of an additional pathway which was then described by Lieber and DeCarli, namely the microsomal ethanol oxidizing system (MEOS), involving cytochrome P450. The existence of this system was initially challenged but the effect of ethanol on liver microsomes was confirmed by Remmer and his group. After chronic ethanol consumption, the activity of the MEOS increases, with an associated rise in cytochrome P450, especially CYP2E1, most conclusively shown in alcohol dehydrogenase negative deer mice. There is also cross-induction of the metabolism of other drugs, resulting in drug tolerance. Furthermore, the conversion of hepatotoxic agents to toxic metabolites increases, which explains the enhanced susceptibility of alcoholics to the adverse effects of various xenobiotics, including industrial solvents. CYP2E1 also activates some commonly used drugs (such as acetaminophen) to their toxic metabolites, and promotes carcinogenesis. In addition, catabolism of retinol is accelerated resulting in its depletion. Contrasting with the stimulating effects of chronic consumption, acute ethanol intake inhibits the metabolism of other drugs. Moreover, metabolism by CYP2E1 results in a significant release of free radicals which, in turn, diminishes reduced glutathione (GSH) and other defense systems against oxidative stress which plays a major pathogenic role in alcoholic liver disease. CYP1A2 and CYP3A4, two other perivenular P450s, also sustain the metabolism of ethanol, thereby contributing to MEOS activity and possibly liver injury. CYP2E1 has also a physiologic role which comprises gluconeogenesis from ketones, oxidation of fatty acids, and detoxification of xenobiotics other than ethanol. Excess of these physiological substrates (such as seen in obesity and diabetes) also leads to CYP2E1 induction and nonalcoholic fatty liver disease (NAFLD), which includes nonalcoholic fatty liver and nonalcoholic steatohepatitis (NASH), with pathological lesions similar to those observed in alcoholic steatohepatitis. Increases of CYP2E1 and its mRNA prevail in the perivenular zone, the area of maximal liver damage. CYP2E1 up-regulation was also demonstrated in obese patients as well as in rat models of obesity and NASH. Furthermore, NASH is increasingly recognized as a precursor to more severe liver disease, sometimes evolving into "cryptogenic" cirrhosis. The prevalence of NAFLD averages 20% and that of NASH 2% to 3% in the general population, making these conditions the most common liver diseases in the United States. Considering the pathogenic role that up-regulation of CYP2E1 also plays in alcoholic liver disease (vide supra), it is apparent that a major therapeutic challenge is now to find a way to control this toxic process. CYP2E1 inhibitors oppose alcohol-induced liver damage, but heretofore available compounds are too toxic for clinical use. Recently, however, polyenylphosphatidylcholine (PPC), an innocuous mixture of polyunsaturated phosphatidylcholines extracted from soybeans (and its active component dilinoleoylphosphatidylcholine), were discovered to decrease CYP2E1 activity. PPC also opposes hepatic oxidative stress and fibrosis. It is now being tested clinically.
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PMID:The discovery of the microsomal ethanol oxidizing system and its physiologic and pathologic role. 1555 33

Nonalcoholic fatty liver disease (NAFLD) is the preferred term to describe the spectrum of liver damage ranging from hepatic steatosis to steatohepatitis, liver fibrosis, and cirrhosis, and it is emerging as the most common liver disease in industrialized countries. Thus, the discovery of food components that would ameliorate NAFLD is of interest. Conjugated linoleic acid (CLA), a mixture of positional and geometric isomers of linoleic acid, has attracted considerable attention because of its potentially beneficial biological effects both in vitro and in vivo. We tested whether dietary CLA protects Zucker (fa/fa) rats from hepatic injury. After 8 wk of feeding, hepatomegaly, hepatic triglyceride (TG) accumulation, and elevated hepatic injury markers in plasma were markedly alleviated in CLA-fed Zucker rats compared with linoleic acid-fed (control) rats. These effects were attributed in part to the enhanced hepatic activities of carnitine palmitoyltransferase, a key enzyme of fatty acid beta-oxidation, and microsomal TG transfer protein, an important factor for lipoprotein secretion due to the CLA diet. We previously reported that the severe hyperinsulinemia in control Zucker rats was attenuated in CLA-fed rats due to an enhanced level of plasma adiponectin, which improves insulin sensitivity. In the present study, the adiponectin concentration was increased and the mRNA expression of tumor necrosis factor-alpha, an inflammatory cytokine, was markedly suppressed in the liver of CLA-fed Zucker rats. We speculate that the enhanced level of liver adiponectin may prevent the development and progression of NAFLD in CLA-fed Zucker rats.
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PMID:Dietary conjugated linoleic acid alleviates nonalcoholic fatty liver disease in Zucker (fa/fa) rats. 1562 25

NADPH-cytochrome P450 reductase (CPR) is an essential component for the function of many enzymes, including microsomal cytochrome P450 (P450) monooxygenases and heme oxygenases. In liver-Cpr-null (with liver-specific Cpr deletion) and Cpr-low (with reduced CPR expression in all organs examined) mouse models, a reduced serum cholesterol level and an induction of hepatic P450s were observed, whereas hepatomegaly and fatty liver were only observed in the liver-Cpr-null model. Our goal was to identify hepatic gene expression changes related to these phenotypes. Cpr-lox mice (with a floxed Cpr gene and normal CPR expression) were used as the control. Through microarray analysis, we identified many genes that were differentially expressed among the three groups of mice. We also recognized the 12 gene ontology terms that contained the most significantly changed gene expression in at least one of the two mouse models. We further uncovered potential mechanisms, such as an increased activation of constitutive androstane receptor and a decreased activation of peroxisomal proliferator-activated receptor-alpha by precursors of cholesterol biosynthesis, that underlie common changes (e.g. induction of multiple P450s and suppression of genes for fatty acid metabolism) in response to CPR loss in the two mouse models. Additionally, we observed model-specific gene expression changes, such as the induction of a fatty-acid translocase (Cd36 antigen) and the suppression of carnitine O-palmitoyltransferase 1 (Cpt1a) and acyl-CoA synthetase long chain family member 1 (Acsl1), that are potentially responsible for the severe hepatic lipidosis and an altered fatty acid profile observed in liver-Cpr-null mice.
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PMID:Hepatic gene expression changes in mouse models with liver-specific deletion or global suppression of the NADPH-cytochrome P450 reductase gene. Mechanistic implications for the regulation of microsomal cytochrome P450 and the fatty liver phenotype. 1600 52

Fifty years ago the dogma prevailed that alcohol was not toxic to the liver and that alcoholic liver disease was exclusively a consequence of nutritional deficiencies. We showed, however, that liver pathology developed even in the absence of malnutrition. This toxicity of alcohol was linked to its metabolism via alcohol dehydrogenase which converts nicotinamide adenine dinucleotide (NAD) to nicotinamide adenine dinucleotide-reduced form (NADH) which contributes to hyperuricemia, hypoglycemia and hepatic steatosis by inhibiting lipid oxidation and promoting lipogenesis. We also discovered a new pathway of ethanol metabolism, the microsomal ethanol oxidizing system (MEOS). The activity of its main enzyme, cytochrome P4502E1 (CYP2E1), and its gene are increased by chronic consumption, resulting in metabolic tolerance to ethanol. CYP2E1 also detoxifies many drugs but occasionally toxic and even carcinogenic metabolites are produced. This activity is also associated with the generation of free radicals with resulting lipid peroxidation and membrane damage as well as depletion of mitochondrial reduced glutathione (GSH) and its ultimate precursor, namely methionine activated to S-adenosylmethionine (SAMe). Its repletion restores liver functions. Administration of polyenylphosphatidylcholine (PPC), a mixture of unsaturated phosphatidylcholines (PC) extracted from soybeans, restores the structure of the membranes and the function of the corresponding enzymes. Ethanol impairs the conversion of beta-carotene to vitamin A and depletes hepatic vitamin A and, when it is given together with vitamin A or beta-carotene, hepatotoxicity is potentiated. Our present therapeutic approach is to reduce excess alcohol consumption by the Brief Intervention technique found to be very successful. We correct hepatic SAMe depletion and supplementation with PPC has some favorable effects on parameters of liver damage which continue to be evaluated. Similarly dilinoleoylphosphatidylcholine (DLPC), PPC's main component, also partially opposes the increase in CYP2E1 by ethanol. Hence, therapy with SAMe +DLPC is now being considered.
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PMID:Pathogenesis and treatment of alcoholic liver disease: progress over the last 50 years. 1636 67

Adipose differentiation-related protein (ADFP; also known as ADRP or adipophilin), is a lipid droplet (LD) protein found in most cells and tissues. ADFP expression is strongly induced in cells with increased lipid load. We have inactivated the Adfp gene in mice to better understand its role in lipid accumulation. The Adfp-deficient mice have unaltered adipose differentiation or lipolysis in vitro or in vivo. Importantly, they display a 60% reduction in hepatic triglyceride (TG) and are resistant to diet-induced fatty liver. To determine the mechanism for the reduced hepatic TG content, we measured hepatic lipogenesis, very-low-density lipoprotein (VLDL) secretion, and lipid uptake and utilization, all of which parameters were shown to be similar between mutant and wild-type mice. The finding of similar VLDL output in the presence of a reduction in total TG in the Adfp-deficient liver is explained by the retention of TG in the microsomes where VLDL is assembled. Given that lipid droplets are thought to form from the outer leaflet of the microsomal membrane, the reduction of TG in the cytosol with concomitant accumulation of TG in the microsome of Adfp-/- cells suggests that ADFP may facilitate the formation of new LDs. In the absence of ADFP, impairment of LD formation is associated with the accumulation of microsomal TG but a reduction in TG in other subcellular compartments.
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PMID:Protection against fatty liver but normal adipogenesis in mice lacking adipose differentiation-related protein. 1642 58

Familial hypobetalipoproteinemia (FHBL) due to truncation-specifying mutations of apolipoprotein B (apoB), which impair hepatic lipid export in very low-density lipoprotein (VLDL) particles, is associated with fatty liver. In an FHBL-like mouse with the apoB38.9 mutation, fatty liver develops despite reduced hepatic fatty acid synthesis. However, hepatic cholesterol contents in apoB38.9 mice are normal. We found that cholesterogenic enzymes (3-hydroxy-3-methylglutaryl-coenzyme A reductase, sterol-C5-desaturase, and 7-dehydrocholesterol reductase) were consistently downregulated in two separate expression-profiling experiments using a total of 19 mice (n = 7 each for apob(+/+) and apob(+/38.9), and n = 5 for apob(38.9/38.9)) and Affymetrix Mu74Av2 GeneChip microarrays. Results were confirmed by real-time PCR. Cholesterol synthesis rates in cultured hepatocytes were reduced by 35% and 25% in apob(38.9/38.9) and apob(+/38.9), respectively, vs. apob(+/+). Hepatic triglycerides and lipid peroxides, the latter measured by thiobarbituric acid-reactive substances (TBARS) assay, were significantly elevated in apob(+/38.9) (117%) and apob(38.9/38.9) (132%) vs. apob(+/+) (100%), as were mRNA expression of the microsomal lipid peroxidizing enzymes Cyp4A10 and Cyp4A14. Hepatic lipid peroxide levels were positively correlated with triglyceride contents (r = 0.601, P = 0.0065). Thus the fatty liver due to a VLDL secretion defect is associated with insufficient adaptation to triglyceride accumulation and with increased lipid peroxidation. In contrast, apoB38.9 mice effectively maintain cholesterol homeostasis in the liver, at least in part, by reducing hepatic cholesterol synthesis.
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PMID:A targeted apoB38.9 mutation in mice is associated with reduced hepatic cholesterol synthesis and enhanced lipid peroxidation. 1645 90

The protective effect of a 30 kDa glycoprotein (GF-AS) isolated from the stem bark of Acanthopanax senticosus against acute and chronic alcohol-induced hepatotoxicity were studied. N-terminal amino acid sequence of GF-AS showed NH(2)-Val-Ala-Tyr-Pro-Trp-Ala-Gly-Phe-Ala-Leu-Ser-Leu-Glx-Pro-Pro-Ala-Gly-Tyr-. GF-AS significantly increases the activities of alcohol-metabolizing enzymes, including alcohol dehydrogenase, microsomal ethanol metabolizing system, and acetaldehyde dehydrogenase in rats acutely treated with alcohol, resulting in decreased plasma alcohol levels. GF-AS also increases the activities of antioxidant enzymes and glutathione level. Markers of liver injury induced by alcohol: elevated serum levels of aspartate aminotransferase, alanine aminotransferase, triglyceride and cholesterol, are reduced by GF-AS in both acutely and chronically treated rats. The activities of lipogenic enzymes including malic enzyme, glucose-6-phosphate dehydrogenase, and 6-phosphoglucuronic acid dehydrogenase in chronic alcohol-treated rats are significantly decreased by GF-AS. Furthemore, GF-AS improves histological change in fatty liver and hepatic lesions induced by alcohol. Collectively, GF-AS may alleviate alcohol-induced hepatotoxicity through increasing ethanol and lipid metabolism, as well as antioxidant defense systems in livers injured by acute- and chronic-alcohol treatment.
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PMID:Glycoprotein isolated from Acanthopanax senticosus protects against hepatotoxicity induced by acute and chronic alcohol treatment. 1646 37

Fatty liver disease (FLD), whether it is alcoholic FLD (AFLD) or nonalcoholic FLD (NAFLD), encompasses a morphological spectrum consisting of hepatic steatosis (fatty liver) and steatohepatitis. FLD has the inherent propensity to progress toward the development of cirrhosis and hepatocellular carcinoma. It is generally difficult to distinguish AFLD from NAFLD on morphological grounds alone despite the distinctions implied by these etiological designations. The indistinguishable spectrum of histological features of both AFLD and NAFLD suggests a possible convergence of pathogenetic mechanisms at some critical juncture that enables the progression of steatohepatitis toward cirrhosis and liver cancer. From a pathogenetic perspective, FLD may be considered a single disease with multiple etiologies. Excess energy consumption and reduced energy combustion appear to be critical events that culminate in lipid storage in the liver. Energy combustion in the liver is controlled by peroxisome proliferator-activated receptor (PPAR)-alpha-regulated mitochondrial and peroxisomal fatty acid beta-oxidation systems and the microsomal omega-oxidation system. PPAR-alpha, a receptor for peroxisome proliferators, functions as a sensor for fatty acids (lipid sensor), and ineffective PPAR-alpha sensing can lead to reduced energy burning resulting in hepatic steatosis and steatohepatitis. Delineation of the pathogenetic aspects of FLD is necessary for developing novel therapeutic strategies for this disease.
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PMID:Lipid metabolism and liver inflammation. II. Fatty liver disease and fatty acid oxidation. 1660 29

Hepatic steatosis may develop as a consequence of several dysfunctions. An increased circulating non-esterified fatty acid (NEFA) pool seems to be a major determinant in the pathogenesis of non-alcoholic fatty liver disease. Increased activation of the transcription factor sterol-regulatory-element-binding protein-1c, which promotes fatty acid synthesis, also contributes to hepatic fat accumulation. Increased hepatic fat oxidation with hepatic steatosis may be triggered by increased hepatic fat concentrations through the action of hepatic peroxisomes mediated by peroxisome proliferator-activated receptor alpha. Finally, inhibition in very low density lipoprotein secretion may also result in hepatic steatosis. This appears to be mainly controlled by the esterification of NEFAs into triacylglycerols by diacyglycerol acyltransferase-1 and -2 and the microsomal transfer protein. Physical exercise would interfere with the development of hepatic steatosis by stimulating lipid oxidation and inhibiting lipid synthesis in liver through the activation of the AMP-activated protein kinase pathway.
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PMID:Regulation of fat metabolism in the liver: link to non-alcoholic hepatic steatosis and impact of physical exercise. 1664 40

Nonalcoholic fatty liver disease (NAFLD) is a frequent and potentially progressive chronic liver disease that occurs in subjects who do not abuse alcohol. NAFLD is often associated with obesity, metabolic syndrome and insulin resistance and its more aggressive form, nonalcoholic steatohepatitis (NASH) is a major cause of cryptogenic cirrhosis. NAFLD/NASH are commonly detected because of elevated serum aminotransferase levels, ultrasonographic fatty liver and, at liver histology, steatosis, inflammation, and occasionally fibrosis that may progress to cirrhosis. No established treatment exists for this potentially serious disorder. Current management of NAFLD/NASH is largely conservative and includes diet regimen, aerobic exercise, and interventions towards the associated metabolic abnormalities. The main concern is therefore to decrease liver steatosis and its progression toward steatohepatitis and fibrosis, and the risk of "cryptogenic" cirrhosis. Among the most promising medications, weight reducing drugs, insulin sensitizers and lipid-lowering agents, antioxidants, bile salts, co-factors increasing the mitochondrial transport of fatty acids are being considered. Among them, thiazolidinediones are the most promising drug family that act by activating PPARgamma nuclear receptors and by regulating both microsomal and peroxisomal lipid oxidative pathways. Pharmacological treatment of obesity and probiotics should be considered as potential therapeutic options. In this review, after summarizing the general background on fatty liver, the most current and attractive pharmacological approaches to the problem of NAFLD/NASH are discussed.
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PMID:Current pharmacological treatment of nonalcoholic fatty liver. 1707 35


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