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)

The mechanisms by which ethanol consumption causes accumulation of hepatic triacylglycerols are complex. AMP-activated protein kinase (AMPK) plays a central role in the regulation of lipid metabolism. Therefore, in the present study we investigated whether AMPK may have a role in the development of ethanol-induced fatty liver. Hepatocytes isolated from rats fed with an ethanol-containing liquid diet showed higher rates of fatty acid and triacylglycerol syntheses, but a decreased rate of fatty acid oxidation, concomitant to a lower activity of carnitine palmitoyltransferase I. Hepatocytes from both ethanol-fed and pair-fed control rats were incubated with 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR), an AMPK activator in intact cells. In both hepatocyte preparations AICAR strongly inhibited the activity of acetyl-CoA carboxylase in parallel to fatty acid synthesis, but cells from ethanol-fed rats showed significantly lower sensitivity to inhibition by AICAR. Moreover, AICAR strongly decreased triacylglycerol synthesis and increased fatty acid oxidation in control hepatocytes, but these effects were markedly attenuated in hepatocytes from ethanol-fed rats. In parallel, AMPK in liver of ethanol-fed rats showed a decreased specific activity and a lower sensitivity to changes in the AMP/ATP ratio, compared to the enzyme of control rats. These effects are consistent with the impairment of AMPK-mediated regulation of fatty acid metabolism after ethanol consumption, that will facilitate triacylglycerol accumulation. Taken together, these findings suggest that a decreased AMPK activity may have an important role in the development of alcoholic fatty liver.
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PMID:Ethanol consumption impairs regulation of fatty acid metabolism by decreasing the activity of AMP-activated protein kinase in rat liver. 1799 5

Exercise training is commonly prescribed for treatment of nonalcoholic fatty liver disease (NAFLD). We sought to determine whether exercise training prevents the development of NAFLD in Otsuka Long-Evans Tokushima Fatty (OLETF) rats and to elucidate the molecular mechanisms underlying the effects of exercise on hepatic steatosis. Four-week-old OLETF rats were randomly assigned to either a sedentary control group (Sed) or a group given access to voluntary running wheels for 16 wk (Ex). Wheels were locked 2 days before euthanasia in the Ex animals, and both groups were euthanized at 20 wk old. Voluntary wheel running attenuated weight gain and reduced serum glucose, insulin, free fatty acids, and triglycerides in Ex animals compared with Sed (P < 0.001). Ex animals exhibited significantly reduced hepatic triglyceride levels and displayed fewer lipid droplets (Oil Red O staining) and reduced lipid droplet size compared with Sed. Wheel running increased by threefold the percent of palmitate oxidized completely to CO(2) in the Ex animals but did not alter AMP-activated protein kinase-alpha (AMPKalpha) or AMPK phosphorylation status. However, fatty acid synthase and acetyl-coenzyme A carboxylase (ACC) content were significantly reduced (approximately 70 and approximately 35%, respectively), and ACC phosphorylation and cytochrome c content were significantly elevated (approximately 35 and approximately 30%, respectively) in the Ex animals. These results unequivocally demonstrate that daily physical activity attenuates hepatic steatosis and NAFLD in an obese rodent model and suggest that this effect is likely mediated, in part, through enhancement of hepatic fatty acid oxidation and reductions in key protein intermediates of fatty acid synthesis.
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PMID:Daily exercise increases hepatic fatty acid oxidation and prevents steatosis in Otsuka Long-Evans Tokushima Fatty rats. 1817 72

The adenine monophosphate (AMP) activated protein kinase (AMPK), is a heterotrimeric complex that is activated by an increase in the AMP/ATP ratio, and is considered to be a cellular energy sensor that contributes to regulate energy balance and caloric intake. AMPK is activated by LKB1 hinase and it can phophorylate several enzymes involved in anabolism to prevent further ATP consumption, and induces some catabolic enzymes to increase ATP generation. Furthermore, AMPK regulates the expression of genes involved in lipogenesis and mitochondrial biogenesis, among others. AMPK is distributed in most organs including, liver, skeletal muscle, heart and hypothalamus; and even in adipose cells. In addition, AMPK is activated in the hypothalamus stimulating appetite due to energy depletion. AMPK also participates in glycolysis regulation, glucose uptake, lipid oxidation, fatty acid synthesis, cholesterol synthesis and gluconeogenesis, and it has been considered as a possible target enzyme in the treatment of some diseases such as obesity, type 2 diabetes and hepatic steatosis. This review provides a general overview of AMPK structure, its activators and its function in the organism.
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PMID:[AMPK as a cellular energy sensor and its function in the organism]. 1840 38

Excess carbohydrate intake leads to fat accumulation and insulin resistance. Glucose and insulin coordinately regulate de novo lipogenesis from glucose in the liver, and insulin activates several transcription factors including SREBP1c and LXR, while those activated by glucose remain unknown. Recently, a carbohydrate response element binding protein (ChREBP), which binds to the carbohydrate response element (ChoRE) in the promoter of rat liver type pyruvate kinase (LPK), has been identified. The target genes of ChREBP are involved in glycolysis, lipogenesis, and gluconeogenesis. Although the regulation of ChREBP remains unknown in detail, the transactivity of ChREBP is partly regulated by a phosphorylation/dephosphorylation mechanism. During fasting, protein kinase A and AMP-activated protein kinase phosphorylate ChREBP and inactivate its transactivity. During feeding, xylulose-5-phosphate in the hexose monophosphate pathway activates protein phosphatase 2A, which dephosphorylates ChREBP and activates its transactivity. ChREBP controls 50% of hepatic lipogenesis by regulating glycolytic and lipogenic gene expression. In ChREBP (-/-) mice, liver triglyceride content is decreased and liver glycogen content is increased compared to wild-type mice. These results indicate that ChREBP can regulate metabolic gene expression to convert excess carbohydrate into triglyceride rather than glycogen. Furthermore, complete inhibition of ChREBP in ob/ob mice reduces the effects of the metabolic syndrome such as obesity, fatty liver, and glucose intolerance. Thus, further clarification of the physiological role of ChREBP may be useful in developing treatments for the metabolic syndrome.
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PMID:ChREBP: a glucose-activated transcription factor involved in the development of metabolic syndrome. 1849 Aug 33

Alcoholic fatty liver is a potentially pathologic condition which can progress to steatohepatitis, fibrosis, and cirrhosis if alcohol consumption is continued. Alcohol exposure may induce fatty liver by increasing NADH/NAD(+) ratio, increasing sterol regulatory element-binding protein-1 (SREBP-1) activity, decreasing peroxisome proliferator-activated receptor-alpha (PPAR-alpha) activity, and increasing complement C3 hepatic levels. Alcohol may increase SREBP-1 activity by decreasing the activities of AMP-activated protein kinase and sirtuin-1. Tumor necrosis factor-alpha (TNF-alpha) produced in response to alcohol exposure may cause fatty liver by up-regulating SREBP-1 activity, whereas betaine and pioglitazone may attenuate fatty liver by down-regulating SREBP-1 activity. PPAR-alpha agonists have potentials to attenuate alcoholic fatty liver. Adiponectin and interleukin-6 may attenuate alcoholic fatty liver by up-regulating PPAR-alpha and insulin signaling pathways while down-regulating SREBP-1 activity and suppressing TNF-alpha production. Recent studies show that paracrine activation of hepatic cannabinoid receptor 1 by hepatic stellate cell-derived endocannabinoids also contributes to the development of alcoholic fatty liver. Furthermore, oxidative modifications and inactivation of the enzymes involved in the mitochondrial and/or peroxisomal beta-oxidation of fatty acids could contribute to fat accumulation in the liver.
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PMID:Molecular mechanisms of alcoholic fatty liver. 1903 84

AMP-activated protein kinase (AMPK) plays an important role in regulating whole body energy homeostasis. Recently, it has been demonstrated that berberine (BBR) exerts antiobesity and antidiabetic effects in obese and diabetic rodent models through the activation of AMPK in peripheral tissues. Here we show that BBR improves lipid dysregulation and fatty liver in obese mice through central and peripheral actions. In obese db/db and ob/ob mice, BBR treatment reduced liver weight, hepatic and plasma triglyceride, and cholesterol contents. In the liver and muscle of db/db mice, BBR promoted AMPK activity and fatty acid oxidation and changed expression of genes involved in lipid metabolism. Additionally, intracerebroventricular administration of BBR decreased the level of malonyl-CoA and stimulated the expression of fatty acid oxidation genes in skeletal muscle. Together, these data suggest that BBR would improve fatty liver in obese subjects, which is probably mediated not only by peripheral AMPK activation but also by neural signaling from the central nervous system.
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PMID:Berberine improves lipid dysregulation in obesity by controlling central and peripheral AMPK activity. 1917 54

Omega-3-polyunsaturated fatty acids (omega-3-PUFAs) have well-documented protective effects that are attributed not only to eicosanoid inhibition but also to the formation of novel biologically active lipid mediators (i.e., resolvins and protectins). In this study, we examined their effects on ob/ob mice, an obesity model of insulin resistance and fatty liver disease. Dietary intake of omega-3-PUFAs had insulin-sensitizing actions in adipose tissue and liver and improved insulin tolerance in obese mice. Genes involved in insulin sensitivity (PPARgamma), glucose transport (GLUT-2/GLUT-4), and insulin receptor signaling (IRS-1/IRS-2) were up-regulated by omega-3-PUFAs. Moreover, omega-3-PUFAs increased adiponectin, an anti-inflammatory and insulin-sensitizing adipokine, and induced AMPK phosphorylation, a fuel-sensing enzyme and a gatekeeper of the energy balance. Concomitantly, hepatic steatosis was alleviated by omega-3-PUFAs. A lipidomic analysis with liquid chromatography/mass spectrometry/mass spectrometry revealed that omega-3-PUFAs inhibited the formation of omega-6-PUFA-derived eicosanoids, while triggering the formation of omega-3-PUFA-derived resolvins and protectins. Moreover, representative members of these lipid mediators, namely resolvin E1 and protectin D1, mimicked the insulin-sensitizing and antisteatotic effects of omega-3-PUFAs and induced adiponectin expression to a similar extent that of rosiglitazone, a member of the thiazolidinedione family of antidiabetic drugs. Taken together, these findings uncover beneficial actions of omega-3-PUFAs and their bioactive lipid autacoids in preventing obesity-induced insulin resistance and hepatic steatosis.
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PMID:Obesity-induced insulin resistance and hepatic steatosis are alleviated by omega-3 fatty acids: a role for resolvins and protectins. 1921 25

Elevated blood triacylglycerol (TG) is a significant contributing factor to the current epidemic of obesity-related health disorders, including type-2 diabetes, nonalcoholic fatty liver disease, and cardiovascular disease. The observation that mice lacking the enzyme sn-glycerol-3-phosphate acyltransferase are protected from insulin resistance suggests the possibility that the regulation of TG synthesis be a target for therapy. Five-week-old Zucker Diabetic Fatty (ZDF) rats were fed a diet containing (R)-alpha-lipoic acid (LA, approximately 200mg/kg body weight per day) for 5 weeks. LA offset the rise in blood and liver TG by inhibiting liver lipogenic gene expression (e.g. sn-glycerol-3-phosphate acyltransferase-1 and diacylglycerol O-acyltransferase-2), lowering hepatic TG secretion, and stimulating clearance of TG-rich lipoproteins. LA-induced TG lowering was not due to the anorectic properties of LA, as pair-fed rats developed hypertriglyceridemia. Livers from LA-treated rats exhibited elevated glycogen content, suggesting dietary carbohydrates were stored as glycogen rather than becoming lipogenic substrate. Although AMP-activated protein kinase (AMPK) reportedly mediates the metabolic effects of LA in rodents, no change in AMPK activity was observed, suggesting LA acted independently of this kinase. The hepatic expression of peroxisome proliferator activated receptor alpha (PPARalpha) target genes involved in fatty acid beta-oxidation was either unchanged or decreased with LA, indicating a different mode of action than for fibrate drugs. Given its strong safety record, LA may have potential clinical applications for the treatment or prevention of hypertriglyceridemia and diabetic dyslipidemia.
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PMID:Lipoic acid improves hypertriglyceridemia by stimulating triacylglycerol clearance and downregulating liver triacylglycerol secretion. 1923 11

Previous studies have shown that administration of fibroblast growth factor-19 (FGF-19) reverses diabetes, hepatic steatosis, hyperlipidemia, and adipose accretion in animal models of obesity. To investigate the mechanism for this effect, we determined whether FGF-19 modulated hepatic fatty acid synthesis, a key process controlling glucose tolerance and triacylglycerol accumulation in liver, blood, and adipose tissue. Incubating primary hepatocyte cultures with recombinant FGF-19 suppressed the ability of insulin to stimulate fatty acid synthesis. This effect was associated with a reduction in the expression of lipogenic enzymes. FGF-19 also suppressed the insulin-induced expression of sterol regulatory element-binding protein-1c (SREBP-1c), a key transcriptional activator of lipogenic genes. FGF-19 inhibition of lipogenic enzyme expression was not mediated by alterations in the activity of the insulin signal transduction pathway or changes in the activity of ERK, p38 MAPK, and AMP-activated protein kinase (AMPK). In contrast, FGF-19 increased the activity of STAT3, an inhibitor of SREBP-1c expression and decreased the expression of peroxisome proliferator-activated receptor-gamma coactivator-1beta (PGC-1beta), an activator of SREBP-1c activity. FGF-19 also increased the expression of small heterodimer partner (SHP), a transcriptional repressor that inhibits lipogenic enzyme expression via a SREBP-1c-independent mechanism. Inhibition of SREBP-1c activity by changes in STAT3 and PGC-1beta activity and inhibition of gene transcription by an elevation in SHP expression can explain the inhibition of lipogenesis caused by FGF-19. In summary, the inhibitory effect of FGF-19 on insulin activation of hepatic fatty acid synthesis constitutes a mechanism that would explain the beneficial effect of FGF-19 on metabolic syndrome.
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PMID:Fibroblast growth factor-19, a novel factor that inhibits hepatic fatty acid synthesis. 1923 43

The liver of dairy cows is involved in signaling the current hepatic metabolic state to the brain via metabolites and nerval afferents to control and adjust feed intake. Feed deprivation may result in mobilization of body reserves favoring hepatic steatosis. While the overall metabolic changes are well characterized, specific regulatory mechanisms are not readily understood. To identify molecular events associated with metabolic adaptation and the control of energy homeostasis, liver specimens from six ad libitum-fed and six feed-deprived cows were analyzed for selected metabolites, for the activation of AMP kinase, and for regulatory/regulated proteins using two-dimensional gel electrophoresis and MALDI-TOF-MS. Feed deprivation increased total liver fat and the calcium content, as well as augmented AMPK phosphorylation, while it decreased the contents of protein, glucose, glycogen, and cholesterol when expressed as a percentage of dry matter. Among 34 differentially expressed proteins identified, we found downregulation of proteins associated with fatty acid oxidation, glycolysis, electron transfer, protein degradation, and antigen processing, as well as cytoskeletal rearrangement. Proteins upregulated after feed deprivation included enzymes of the urea cycle, fatty acid or cholesterol transport proteins, an inhibitor of glycolysis, and previously unknown changes in calcium signaling network. Direct correlation was found between expression of glycolytic enzymes and glucose/glycogen content, whereas inverse correlation exists between expression of beta-oxidative enzymes and total liver fat content. In conclusion, the regulatory response of identified proteins may help to explain development and consequences of hepatic lipidosis but also offers novel candidates potentially involved in signaling for maintaining energy homeostasis.
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PMID:Proteome analysis of fatty liver in feed-deprived dairy cows reveals interaction of fuel sensing, calcium, fatty acid, and glycogen metabolism. 1924 Mar


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