UMLS:C0015695 - FACTA Search

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Query: UMLS:C0015695 (fatty liver)
13,941 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Peroxisomes contain a classical L-hydroxy-specific peroxisome proliferator-inducible beta-oxidation system and also a second noninducible D-hydroxy-specific beta-oxidation system. We previously generated mice lacking fatty acyl-CoA oxidase (AOX), the first enzyme of the L-hydroxy-specific classical beta-oxidation system; these AOX-/- mice exhibited sustained activation of peroxisome proliferator-activated receptor alpha (PPARalpha), resulting in profound spontaneous peroxisome proliferation in liver cells. These observations implied that AOX is responsible for the metabolic degradation of PPARalpha ligands. In this study, the function of enoyl-CoA hydratase/L-3-hydroxyacyl-CoA dehydrogenase (L-PBE), the second enzyme of this peroxisomal beta-oxidation system, was investigated by disrupting its gene. Mutant mice (L-PBE-/-) were viable and fertile and exhibited no detectable gross phenotypic defects. L-PBE-/- mice showed no hepatic steatosis and manifested no spontaneous peroxisome proliferation, unlike that encountered in livers of mice deficient in AOX. These results indicate that disruption of classical peroxisomal fatty acid beta-oxidation system distal to AOX step does not interfere with the inactivation of endogenous ligands of PPARalpha, further confirming that the AOX gene is indispensable for the physiological regulation of this receptor. The absence of appreciable changes in lipid metabolism also indicates that enoyl-CoAs, generated in the classical system in L-PBE-/- mice are diverted to D-hydroxy-specific system for metabolism by D-PBE. When challenged with a peroxisome proliferator, L-PBE-/- mice showed increases in the levels of hepatic mRNAs and proteins that are regulated by PPARalpha except for appreciable blunting of peroxisome proliferative response as compared with that observed in hepatocytes of wild type mice similarly treated. This blunting of peroxisome proliferative response is attributed to the absence of L-PBE protein in L-PBE-/- mouse liver, because all other proteins are induced essentially to the same extent in both wild type and L-PBE-/- mice.
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PMID:Absence of spontaneous peroxisome proliferation in enoyl-CoA Hydratase/L-3-hydroxyacyl-CoA dehydrogenase-deficient mouse liver. Further support for the role of fatty acyl CoA oxidase in PPARalpha ligand metabolism. 1033 79

We hypothesized that the lipid-activated transcription factor, the peroxisome proliferator-activated receptor alpha (PPARalpha), plays a pivotal role in the cellular metabolic response to fasting. Short-term starvation caused hepatic steatosis, myocardial lipid accumulation, and hypoglycemia, with an inadequate ketogenic response in adult mice lacking PPARalpha (PPARalpha-/-), a phenotype that bears remarkable similarity to that of humans with genetic defects in mitochondrial fatty acid oxidation enzymes. In PPARalpha+/+ mice, fasting induced the hepatic and cardiac expression of PPARalpha target genes encoding key mitochondrial (medium-chain acyl-CoA dehydrogenase, carnitine palmitoyltransferase I) and extramitochondrial (acyl-CoA oxidase, cytochrome P450 4A3) enzymes. In striking contrast, the hepatic and cardiac expression of most PPARalpha target genes was not induced by fasting in PPARalpha-/- mice. These results define a critical role for PPARalpha in a transcriptional regulatory response to fasting and identify the PPARalpha-/- mouse as a potentially useful murine model of inborn and acquired abnormalities of human fatty acid utilization.
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PMID:A critical role for the peroxisome proliferator-activated receptor alpha (PPARalpha) in the cellular fasting response: the PPARalpha-null mouse as a model of fatty acid oxidation disorders. 1037 39

Fasting causes lipolysis in adipose tissue leading to the release of large quantities of free fatty acids into circulation that reach the liver where they are metabolized to generate ketone bodies to serve as fuels for other tissues. Since fatty acid-metabolizing enzymes in the liver are transcriptionally regulated by peroxisome proliferator-activated receptor alpha (PPARalpha), we investigated the role of PPARalpha in the induction of these enzymes in response to fasting and their relationship to the development of hepatic steatosis in mice deficient in PPARalpha (PPARalpha(-/-)), peroxisomal fatty acyl-CoA oxidase (AOX(-/-)), and in both PPARalpha and AOX (double knock-out (DKO)). Fasting for 48-72 h caused profound impairment of fatty acid oxidation in both PPARalpha(-/-) and DKO mice, and DKO mice revealed a greater degree of hepatic steatosis when compared with PPARalpha(-/-) mice. The absence of PPARalpha in both PPARalpha(-/-) and DKO mice impairs the induction of mitochondrial beta-oxidation in liver following fasting which contributes to hypoketonemia and hepatic steatosis. Pronounced steatosis in DKO mouse livers is due to the added deficiency of peroxisomal beta-oxidation system in these animals due to the absence of AOX. In mice deficient in AOX alone, the sustained hyperactivation of PPARalpha and up-regulation of mitochondrial beta-oxidation and microsomal omega-oxidation systems as well as the regenerative nature of a majority of hepatocytes containing numerous spontaneously proliferated peroxisomes, which appear refractory to store triglycerides, blunt the steatotic response to fasting. Starvation for 72 h caused a decrease in PPARalpha hepatic mRNA levels in wild type mice, with no perceptible compensatory increases in PPARgamma and PPARdelta mRNA levels. PPARgamma and PPARdelta hepatic mRNA levels were lower in fed PPARalpha(-/-) and DKO mice when compared with wild type mice, and fasting caused a slight increase only in PPARgamma levels and a decrease in PPARdelta levels. Fasting did not change the PPAR isoform levels in AOX(-/-) mouse liver. These observations point to the critical importance of PPARalpha in the transcriptional regulatory responses to fasting and in determining the severity of hepatic steatosis.
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PMID:Defect in peroxisome proliferator-activated receptor alpha-inducible fatty acid oxidation determines the severity of hepatic steatosis in response to fasting. 1084 2

Fatty acid beta-oxidation occurs in both mitochondria and peroxisomes. Mitochondria catalyze the beta-oxidation of the bulk of short-, medium-, and long-chain fatty acids derived from diet, and this pathway constitutes the major process by which fatty acids are oxidized to generate energy. Peroxisomes are involved, preferentially, in the beta-oxidation chain shortening of very long chain fatty acids (VLCFAs) and in the process produce H2O2. Long-chain fatty acids and VLCFAs are also metabolized by the cytochrome P450 CYP4A omega-oxidation system to toxic dicarboxylic acids (DCAs) that serve as substrates for peroxisomal beta-oxidation, and this process also leads to the production of superoxide and H2O2. The genes encoding peroxisomal, microsomal, and certain mitochondrial fatty acid metabolizing enzymes in liver are transcriptionally regulated by peroxisome proliferator-activated receptor alpha (PPAR alpha). Deficiencies of the enzymes of peroxisomal beta-oxidation have been recognized as important causes of disease. Evidence from mice deficient in PPAR alpha (PPAR alpha-/-), deficient in peroxisomal fatty acyl-CoA oxidase (AOX-/-), the first enzyme of the classical beta-oxidation system, and deficient in both PPAR alpha and AOX (PPAR alpha-/-AOX-/-) points to the critical importance of PPAR alpha-inducible peroxisomal and microsomal oxidation systems that metabolize LCFAs and VLCFAs in the pathogenesis of nonalcoholic microvesicular hepatic steatosis and steatohepatitis. These and other mouse models should provide greater understanding of the molecular mechanism responsible for hepatic steatosis and steatohepatitis. Deficiency of AOX disrupts the oxidation of VLCFAs, DCAs, and other substrates leading to extensive microvesicular steatosis and steatohepatitis. Loss of this enzyme also causes sustained hyperactivation of PPAR alpha, leading to transcriptional up-regulation of PPAR alpha-regulated genes, indicating that unmetabolized substrates of AOX function as ligands of PPAR alpha. beta-Oxidation is the major process by which fatty acids are oxidized to generate energy, especially when glucose availability is low during periods of starvation. Mice deficient in PPAR alpha and those nullizygous for both PPAR alpha and AOX show a minimal steatotic phenotype under fed conditions but manifest an exaggerated steatotic response to fasting, indicating that defects in PPAR alpha-inducible fatty acid oxidation determine the severity of fatty liver phenotype to conditions reflecting energy-related stress.
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PMID:Peroxisomal beta-oxidation and steatohepatitis. 1129 96

beta-Oxidation occurs in both mitochondria and peroxisomes. Mitochondria catalyze the beta-oxidation of the bulk of short-, medium-, and long-chain fatty acids derived from diet, and this pathway constitutes the major process by which fatty acids are oxidized to generate energy. Peroxisomes are involved in the beta-oxidation chain shortening of long-chain and very-long-chain fatty acyl-coenzyme (CoAs), long-chain dicarboxylyl-CoAs, the CoA esters of eicosanoids, 2-methyl-branched fatty acyl-CoAs, and the CoA esters of the bile acid intermediates di- and trihydroxycoprostanoic acids, and in the process they generate H2O2. Long-chain and very-long-chain fatty acids (VLCFAs) are also metabolized by the cytochrome P450 CYP4A omega-oxidation system to dicarboxylic acids that serve as substrates for peroxisomal beta-oxidation. The peroxisomal beta-oxidation system consists of (a) a classical peroxisome proliferator-inducible pathway capable of catalyzing straight-chain acyl-CoAs by fatty acyl-CoA oxidase, L-bifunctional protein, and thiolase, and (b) a second noninducible pathway catalyzing the oxidation of 2-methyl-branched fatty acyl-CoAs by branched-chain acyl-CoA oxidase (pristanoyl-CoA oxidase/trihydroxycoprostanoyl-CoA oxidase), D-bifunctional protein, and sterol carrier protein (SCP)x. The genes encoding the classical beta-oxidation pathway in liver are transcriptionally regulated by peroxisome proliferator-activated receptor alpha (PPAR alpha). Evidence derived from mice deficient in PPAR alpha, peroxisomal fatty acyl-CoA oxidase, and some of the other enzymes of the two peroxisomal beta-oxidation pathways points to the critical importance of PPAR alpha and of the classical peroxisomal fatty acyl-CoA oxidase in energy metabolism, and in the development of hepatic steatosis, steatohepatitis, and liver cancer.
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PMID:Peroxisomal beta-oxidation and peroxisome proliferator-activated receptor alpha: an adaptive metabolic system. 1137 35

Proper function of the peroxisome proliferator-activated receptor alpha (PPARalpha) is essential for the regulation of hepatic fatty acid metabolism. Fatty acid levels are increased in liver during the metabolism of ethanol and should activate PPARalpha. However, recent in vitro data showed that ethanol metabolism inhibited the function of PPARalpha. We now report that ethanol feeding impairs fatty acid catabolism in the liver in part via blocking PPARalpha-mediated responses in C57BL/6J mice. Ethanol feeding decreased PPARalpha/retinoid X receptor alpha binding in electrophoretic mobility shift assay of liver nuclear extracts. mRNAs for PPAR-regulated genes were reduced (long chain and medium chain acyl-CoA dehydrogenases) or failed to be induced (acyl-CoA oxidase, liver carnitine palmitoyl-CoA transferase, very long chain acyl-CoA synthetase, very long chain acyl-CoA dehydrogenase) in livers of the ethanol-fed animals, and ethanol feeding did not increase the rate of fatty acid beta-oxidation. Wy14,643, a PPARalpha agonist, restored the DNA binding activity of PPARalpha/retinoid X receptor alpha, induced mRNA levels of PPARalpha target genes, stimulated the rate of fatty acid beta-oxidation, and prevented fatty liver in ethanol-fed animals. Impairment of PPARalpha function during ethanol consumption contributes to the development of alcoholic fatty liver, which can be overcome by Wy14,643.
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PMID:Peroxisome proliferator-activated receptor alpha (PPARalpha) agonist treatment reverses PPARalpha dysfunction and abnormalities in hepatic lipid metabolism in ethanol-fed mice. 1279 98

Liver fatty acid binding protein (L-FABP) has been proposed to limit the availability of long-chain fatty acids (LCFA) for oxidation and for peroxisome proliferator-activated receptor alpha (PPAR-alpha), a fatty acid binding transcription factor that determines the capacity of hepatic fatty acid oxidation. Here, we used L-FABP null mice to test this hypothesis. Under fasting conditions, this mutation reduced beta-hydroxybutyrate (BHB) plasma levels as well as BHB release and palmitic acid oxidation by isolated hepatocytes. However, the capacity for ketogenesis was not reduced: BHB plasma levels were restored by octanoate injection; BHB production and palmitic acid oxidation were normal in liver homogenates; and hepatic expression of key PPAR-alpha target (MCAD, mitochondrial HMG CoA synthase, ACO, CYP4A3) and other (CPT1, LCAD) genes of mitochondrial and extramitochondrial LCFA oxidation and ketogenesis remained at wild-type levels. During standard diet, mitochondrial HMG CoA synthase mRNA was selectively reduced in L-FABP null liver. These results suggest that under fasting conditions, hepatic L-FABP contributes to hepatic LCFA oxidation and ketogenesis by a nontranscriptional mechanism, whereas L-FABP can activate ketogenic gene expression in fed mice. Thus, the mechanisms whereby L-FABP affects fatty acid oxidation may vary with physiological condition.
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PMID:Liver fatty acid binding protein is required for high rates of hepatic fatty acid oxidation but not for the action of PPARalpha in fasting mice. 1465 98

Pathogenesis of steatohepatitis, a common liver disease, remains controversial. It is proposed that fatty liver with a second hit capable of inducing necroinflammation results in nonalcoholic steatohepatitis. Long chain and very long chain fatty acids are considered important in induction of steatohepatitis. Peroxisome proliferator-activated receptor alpha (PPARalpha) plays an important role in beta-oxidation of long chain and very long chain fatty acids and mitogenic effect caused by peroxisome proliferators in the liver. To determine the role of PPARalpha in the pathogenesis of steatohepatitis and compensatory liver cell hyperplasia, we have used PPARalpha null mice and methionine and choline deficient nutritional model. Male and female PPARalpha null mice and wild type mice were fed methionine and choline deficient diet (MCDD) or normal chow for 4 weeks. Livers were analyzed morphologically for steatosis, steatohepatitis and hepatocyte proliferation (PCNA labeling) and biochemically for triglyceride levels. In addition, serum alanine transaminase, aspartate transaminase and triglyceride levels were measured. In MCDD fed PPARalpha null mice there was severe steatohepatitis and very high liver triglyceride levels compared to wild type mice. Serum aspartate transaminase levels were also significantly higher in MCDD fed PPARalpha null mice compared to wild type mice. The severity of steatohepatitis in MCDD fed male and female PPARalpha null mice was greater compared to wild type mice fed the same diet. The PCNA labeling index was similar in PPARalpha null mice and wild type mice fed MCDD, and significantly higher in both the groups compared to the mice fed control diet. These findings indicate that defective fatty acid oxidation aggravates steatohepatitis caused by methionine and choline deficiency and further establishes the role of long chain and very long chain fatty acids in the pathogenesis of steatohepatitis. In addition, the results of this study also indicate that there is no difference between males and females in the severity of steatohepatitis induced by MCDD and lack of PPARalpha does not affect compensatory hyperplasia in the liver.
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PMID:Lack of peroxisome proliferator-activated receptor alpha in mice enhances methionine and choline deficient diet-induced steatohepatitis. 1551 75

Persistent infection of hepatitis C virus (HCV) can lead to a high risk for hepatocellular carcinoma(HCC). HCV core protein plays important roles in HCV-induced hepatocarcinogenesis, because its expression in mice causes hepatic steatosis and HCC without accompanying hepatitis. However, its precise mechanisms remain unclear. We investigated whether the HCV core protein alters the expression of the factors associated with hepatic steatosis and HCC in vivo. By Western immunoblot and Northern blot analyses, expression of the proteins including fatty acid-metabolizing enzymes and cell cycle regulators, which are induced by the activation of peroxisome proliferator-activated receptor alpha (PPARalpha), significantly increased in HCV core protein transgenic mice. This result suggests the possibility that PPARalpha activation might contribute to HCV core protein-mediated hepatocarcinogenesis.
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PMID:[Possible mechanisms of hepatitis C virus-related hepatocarcinogenesis]. 1555

Alcoholic liver disease is a major cause of illness and death in the United States. In the initial stages of the disease, fat accumulation in hepatocytes leads to the development of fatty liver (steatosis), which is a reversible condition. If alcohol consumption is continued, steatosis may progress to hepatitis and fibrosis, which may lead to liver cirrhosis. Alcoholic fatty liver has long been considered benign; however, increasing evidence supports the idea that it is a pathologic condition. Blunting of the accumulation of fat within the liver during alcohol consumption may block or delay the progression of fatty liver to hepatitis and fibrosis. To achieve this goal, it is important to understand the underlying biochemical and molecular mechanisms by which chronic alcohol consumption leads to fat accumulation in the liver and fatty liver progresses to hepatitis and fibrosis. In addition to alcohol consumption, dietary fatty acids and obesity have been shown to affect the degree of fat accumulation within the liver. Again, it is important to know how these factors modulate the progression of alcoholic liver disease. The National Institute on Alcohol Abuse and Alcoholism and the Office of Dietary Supplements, National Institutes of Health, sponsored a symposium on "Role of Fatty Liver, Dietary Fatty Acid Supplements, and Obesity in the Progression of Alcoholic Liver Disease" in Bethesda, Maryland, USA, October 2003. The following is a summary of the symposium. Alcoholic fatty liver is a pathologic condition that may predispose the liver to further injury (hepatitis and fibrosis) by cytochrome P450 2E1 induction, free radical generation, lipid peroxidation, nuclear factor-kappa B activation, and increased transcription of proinflammatory mediators, including tumor necrosis factor-alpha. Increased acetaldehyde production and lipopolysaccharide-induced Kupffer cell activation may further exacerbate liver injury. Acetaldehyde may promote hepatic fat accumulation by impairing the ability of peroxisome proliferator-activated receptor alpha to bind DNA, and by increasing the synthesis of sterol regulatory binding protein-1. Unsaturated fatty acids (corn oil, fish oil) exacerbate alcoholic liver injury by accentuating oxidative stress, whereas saturated fatty acids are protective. Polyenylphosphatidylcholine may prevent liver injury by down-regulating cytochrome P450 2E1 activity, attenuating oxidative stress, reducing the number of activated hepatic stellate cells, and up-regulating collagenase activity. Nonalcoholic steatohepatitis may develop through several mechanisms, such as oxidative stress, mitochondrial dysfunction and associated impaired fat metabolism, dysregulated cytokine metabolism, insulin resistance, and altered methionine/S-adenosylmethionine/homocysteine metabolism. Obesity (adipose tissue) may contribute to the development of alcoholic liver disease by generating free radicals, increasing tumor necrosis factor-alpha production, inducing insulin resistance, and producing fibrogenic agents, such as angiotensin II, norepinephrine, neuropeptide Y, and leptin. Finally, alcoholic fatty liver transplant failure may be linked to oxidative stress. In vitro treatment of fatty livers with interleukin-6 may render allografts safer for clinical transplantation.
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PMID:Role of fatty liver, dietary fatty acid supplements, and obesity in the progression of alcoholic liver disease: introduction and summary of the symposium. 1567 Jun 59

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