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Query: UMLS:C0028754 (obesity)
 124,988 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Obese Zucker rats were dosed orally for one week with fenofibrate (100 mg/kg). Liver weights of treated rats as expressed as percent of body weight were slightly increased, while protein, DNA and lipid contents were unaffected per g of liver or increased when expressed in whole liver. Compared with the control animals, activities of fatty acid oxidase, of the peroxisomal fatty acid-oxidizing system and of catalase were markedly increased by fenofibrate both per g of liver and per total liver, while urate oxidase activity was unchanged when expressed per g of liver. The activity of monoamine oxidase and that of cytochrome c oxidase used as marker enzymes for mitochondria were increased only when expressed per total liver. However, fenofibrate treatment induced a pronounced increase in the activities of mitochondrial palmitoyl-CoA dehydrogenase and carnitine acyltransferases, particularly carnitine acetyltransferase. Fenofibrate also caused a significant increase of carnitine content in liver and hepatic mitochondria. The greatest observed increases were in free carnitine and in the rate of carnitine-dependent oleate oxidation, which might be favoured in vivo by a lesser sensitivity of CPT-I to a malonyl-CoA inhibitory effect. The present results suggest that fenofibrate treatment induces increased hepatic mitochondrial beta-oxidation in obese Zucker rats.
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PMID:Effects of fenofibrate treatment on fatty acid oxidation in liver mitochondria of obese Zucker rats. 366 37

This study was designed to examine whether n-3 and n-6 polyunsaturated fatty acids at a very low dietary level (about 0.2%) would alter liver activities in respect to fatty acid oxidation. Obese Zucker rats were used because of their low level of fatty acid oxidation, which would make increases easier to detect. Zucker rats were fed diets containing different oil mixtures (5%, w/w) with the same ratio of n-6/n-3 fatty acids supplied either as fish oil or arachidonic acid concentrate. Decreased hepatic triacylglycerol levels were observed only with the diet containing fish oil. In mitochondrial outer membranes, which support carnitine palmitoyltransferase I activity, cholesterol content was similar for all diets, while the percentage of 22:6n-3 and 20:4n-6 in phospholipids was enhanced about by 6 and 3% with the diets containing fish oil and arachidonic acid, respectively. With the fish oil diet, the only difference found in activities related to fatty acid oxidation was the lower sensitivity of carnitine palmitoyltransferase I to malonyl-CoA inhibition. With the diet containing arachidonic acid, peroxisomal fatty acid oxidation and carnitine palmitoyltransferase I activity were markedly depressed. Compared with the control diet, the diets enriched in fish oil and in arachidonic acid gave rise to a higher specific activity of aryl-ester hydrolase in microsomal fractions. We suggest that slight changes in composition of n-3 or n-6 polyunsaturated fatty acids in mitochondrial outer membranes may alter carnitine palmitoyltransferase I activity.
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PMID:Effect of dietary n-3 and n-6 polyunsaturated fatty acids on lipid-metabolizing enzymes in obese rat liver. 796 69

Insulin resistance is present in liver and muscle of subjects with type 2 diabetes and obesity. Recent studies suggest that such insulin resistance could be related to abnormalities in lipid-mediated signal transduction; however, the nature of these abnormalities is unclear. To examine this question further, tissue levels of diacylglycerol (DAG), malonyl-CoA, and triglyceride (TG) were determined in liver and soleus muscle of obese insulin-resistant KKAy mice and lean C57 BL control mice. In addition, the effects of treatment with pioglitazone, an antidiabetic agent that acts by increasing insulin sensitivity in muscle, liver, and other tissues, were assessed. The KKAy mice were hyperglycemic (407 vs. 138 mg/dl), hypertriglyceridemic (337 vs. 109 mg/dl), hyperinsulinemic (631 vs. 15 mU/ml), and weighed more (42 vs. 35 g) than the control mice. They also had 1.5- to 2.0-fold higher levels of malonyl-CoA in both liver and muscle, higher DAG (twofold) and TG (1.3-fold) levels in muscle, and higher TG (threefold), but not DAG, levels. Treatment of the KKAy mice with pioglitazone for 4 days decreased plasma glucose, TGs, and insulin by approximately 50% and restored hepatic and muscle malonyl-CoA levels to control values. In contrast, pioglitazone increased hepatic and muscle DAG levels two- or threefold. It has no effect on muscle or hepatic TG content, and it slightly increased hepatic TGs in the control group. The results indicate that abnormalities in tissue lipids occur in both liver and muscle of the KKAy mouse and that they are differentially altered when insulin sensitivity is enhanced by treatment with pioglitazone.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Lipid abnormalities in tissues of the KKAy mouse: effects of pioglitazone on malonyl-CoA and diacylglycerol. 804 19

Widely held theories of the pathogenesis of obesity-associated NIDDM have implicated apparently incompatible events as seminal: 1) insulin resistance in muscle, 2) abnormal secretion of insulin, and 3) increases in intra-abdominal fat. Altered circulating or tissue lipids are characteristic features of obesity and NIDDM. The etiology of these defects is not known. In this perspective, we propose that the same metabolic events, elevated malonyl-CoA and long-chain acyl-CoA (LC-CoA), in various tissues mediate, in part, the pleiotropic alterations characteristic of obesity and NIDDM. We review the evidence in support of the emerging concept that malonyl-CoA and LC-CoA act as metabolic coupling factors in beta-cell signal transduction, linking fuel metabolism to insulin secretion. We suggest that acetyl-CoA carboxylase, which synthesizes malonyl-CoA, a "signal of plenty," and carnitine palmitoyl transferase 1, which is regulated by it, may perform as fuel sensors in the beta-cell, integrating the concentrations of all circulating fuel stimuli in the beta-cell as well as in muscle, liver, and adipose tissue. The target effectors of LC-CoA may include protein kinase C sub-types, complex lipid formation, genes encoding metabolic enzymes or transduction factors, and protein acylation. We support the concept that only under conditions in which both glucose and lipids are plentiful will the metabolic abnormality, which may be termed glucolipoxia, become apparent. If our hypothesis is correct that common signaling abnormalities in the metabolism of malonyl-CoA and LC-CoA contribute to altered insulin release and sensitivity, it offers a novel explanation for the presence of variable combinations of these defects in individuals with differing genetic backgrounds and for the fact that it has been difficult to determine whether one or the other is the primary event.
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PMID:Are the beta-cell signaling molecules malonyl-CoA and cystolic long-chain acyl-CoA implicated in multiple tissue defects of obesity and NIDDM? 859 30

It is widely held that although obesity and type 2 diabetes are polygenic in origin, the primary defect causing both conditions is insulin resistance, which in turn gives rise to a constellation of other abnormalities, including hyperinsulinemia, dyslipidemia, glucose intolerance, and (in the genetically predisposed) frank hyperglycemia. Explored here is an alternative, albeit speculative, scenario in which hyperinsulinemia and insulin resistance arise either simultaneously or sequentially from some preexisting defect within the leptin signaling pathway. In either case, a central component of the model is that the breakdown of glucose homeostasis that is characteristic of the condition of obesity with type 2 diabetes is secondary to disturbances in lipid dynamics. The possibility is raised that abnormally high concentrations of malonyl-CoA in liver and skeletal muscle suppress the activity of mitochondrial carnitine palmitoyltransferase I and thus fatty acid oxidation in both sites. It is suggested that the buildup of fat within the muscle cell (caused in part by excessive delivery of VLDLs from the liver) interferes with glucose transport or metabolism or both, producing insulin resistance. Elevated circulating concentrations of fatty acids are also implicated in the etiology of type 2 diabetes by virtue of 1) their powerful acute insulinotropic effect, 2) their ability to exacerbate insulin resistance in muscle, and 3) their long-term detrimental action on pancreatic beta-cell function.
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PMID:Glucose-fatty acid interactions in health and disease. 949 60

In obesity several mechanisms contribute to produce insulin resistance. Elevation of plasma FFA increases the concentration of cytoplasmic long-chain-CoA (LC-CoA) and mitochondrial acetyl-CoA. The latter inhibits pyruvate dehydrogenase (PDH) and, therefore, glucose oxidation. LC-CoA exerts an array of effects, some mediated by peroxisome proliferator-activated receptors, including modulation of gene expression of enzymes of glycolipid metabolism, thus inhibiting glucose utilization and potentiating FFA oxidation. Enhanced availability of glucose plus insulin forces glucose utilization (activation of PDH and glycogen synthase) and leads to increased production of malonyl-CoA (via citrate), which inhibits carnitine palmitoyl transferase 1 and therefore FFA beta-oxidation. In obesity there is often enhanced availability of both FFA and glucose plus insulin. The latter, by increasing malonyl-CoA, may limit FFA beta-oxidation. This, however, leads to further increases in LC-CoA, which worsens insulin resistance. All these mechanisms occur through both short-term and long-term effects. Therefore, when insulin sensitivity is measured with the hyperinsulinemic clamp, which artificially suppresses FFA levels, the FFA short-term effects are lost. More physiological methods are those utilizing OGTT data, allowing calculation of an Insulin Sensitivity Index for glycemia, or ISI(gly), through the formula: 2/((INSp x GLYp)+1), where INSp and GLYp are the measured insulin and glycemic areas expressed by taking mean normal value as 1. The corresponding Insulin Resistance Index, or IRI(gly), can be obtained through the formula: 2/((1/(INSp x GLYp))+1). Substitution of glycemic (GLYp) with FFA (FFAp) values allows the calculation of indices of insulin sensitivity and resistance for FFA, i.e., ISI(ffa) and IRI(ffa).
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PMID:Insulin resistance in obesity: metabolic mechanisms and measurement methods. 978 4

Malonyl-CoA is an allosteric inhibitor of carnitine palmitoyltransferase (CPT) I, the enzyme that controls the transfer of long-chain fatty acyl (LCFA)-CoAs into the mitochondria where they are oxidized. In rat skeletal muscle, the formation of malonyl-CoA is regulated acutely (in minutes) by changes in the activity of the beta-isoform of acetyl-CoA carboxylase (ACCbeta). This can occur by at least two mechanisms: one involving cytosolic citrate, an allosteric activator of ACCbeta and a precursor of its substrate cytosolic acetyl-CoA, and the other involving changes in ACCbeta phosphorylation. Increases in cytosolic citrate leading to an increase in the concentration of malonyl-CoA occur when muscle is presented with insulin and glucose, or when it is made inactive by denervation, in keeping with a diminished need for fatty acid oxidation in these situations. Conversely, during exercise, when the need of the muscle cell for fatty acid oxidation is increased, decreases in the ATP/AMP and/or creatine phosphate-to-creatine ratios activate an isoform of an AMP-activated protein kinase (AMPK), which phosphorylates ACCbeta and inhibits both its basal activity and activation by citrate. The central role of cytosolic citrate links this malonyl-CoA regulatory mechanism to the glucose-fatty acid cycle concept of Randle et al. (P. J. Randle, P. B. Garland. C. N. Hales, and E. A. Newsholme. Lancet 1: 785-789, 1963) and to a mechanism by which glucose might autoregulate its own use. A similar citrate-mediated malonyl-CoA regulatory mechanism appears to exist in other tissues, including the pancreatic beta-cell, the heart, and probably the central nervous system. It is our hypothesis that by altering the cytosolic concentrations of LCFA-CoA and diacylglycerol, and secondarily the activity of one or more protein kinase C isoforms, changes in malonyl-CoA provide a link between fuel metabolism and signal transduction in these cells. It is also our hypothesis that dysregulation of the malonyl-CoA regulatory mechanism, if it leads to sustained increases in the concentrations of malonyl-CoA and cytosolic LCFA-CoA, could play a key role in the pathogenesis of insulin resistance in muscle. That it may contribute to abnormalities associated with the insulin resistance syndrome in other tissues and the development of obesity has also been suggested. Studies are clearly needed to test these hypotheses and to explore the notion that exercise and some pharmacological agents that increase insulin sensitivity act via effects on malonyl-CoA and/or cytosolic LCFA-CoA.
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PMID:Malonyl-CoA, fuel sensing, and insulin resistance. 988 45

C75, a known inhibitor of fatty acid synthase is postulated to cause significant weight loss through decreased hypothalamic neuropeptide Y (NPY) production. Peripherally, C75, an alpha-methylene-gamma-butyrolactone, reduces adipose tissue and fatty liver, despite high levels of malonyl-CoA. To investigate this paradox, we studied the effect of C75 on fatty acid oxidation and energy production in diet-induced obese (DIO) mice and cellular models. Whole-animal calorimetry showed that C75-treated DIO mice had a 50% greater weight loss, and a 32.9% increased production of energy because of fatty acid oxidation, compared with paired-fed controls. Etomoxir, an inhibitor of carnitine O-palmitoyltransferase-1 (CPT-1), reversed the increased energy expenditure in DIO mice by inhibiting fatty acid oxidation. C75 treatment of rodent adipocytes and hepatocytes and human breast cancer cells increased fatty acid oxidation and ATP levels by increasing CPT-1 activity, even in the presence of elevated concentrations of malonyl-CoA. Studies in human cancer cells showed that C75 competed with malonyl-CoA, as measured by CPT-1 activity assays. Thus, C75 acts both centrally to reduce food intake and peripherally to increase fatty acid oxidation, leading to rapid and profound weight loss, loss of adipose mass, and resolution of fatty liver. The pharmacological stimulation of CPT-1 activity is a novel finding. The dual action of the C75 class of compounds as fatty acid synthase inhibitors and CPT-1 agonists has therapeutic implications in the treatment of obesity and type II diabetes.
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PMID:C75 increases peripheral energy utilization and fatty acid oxidation in diet-induced obesity. 1209 27

Malonyl-CoA, generated by acetyl-CoA carboxylases ACC1 and ACC2, is a key metabolite in the control of fatty acid synthesis and oxidation in response to dietary changes. ACC2 is associated to the mitochondria, and Acc2-/- mice have a normal lifespan and higher fatty acid oxidation rate and accumulate less fat. Mutant mice fed high-fat/high-carbohydrate diets weighed less than their WT cohorts, accumulated less fat, and maintained normal levels of insulin and glucose, whereas the WT mice became type-2 diabetic with hyperglycemic and hyperinsulinemic status. Fatty acid oxidation rates in the soleus muscle and in hepatocytes of Acc2-/- mice were significantly higher than those of WT cohorts and were not affected by the addition of insulin. mRNA levels of uncoupling proteins (UCPs) were significantly higher in adipose, heart (UCP2), and muscle (UCP3) tissues of mutant mice compared with those of the WT. The increase in the UCP levels along with increased fatty acid oxidation may play an essential role in the regulation of energy expenditure. Lowering intracellular fatty acid accumulation in the mutant relative to that of the WT mice may thus impact glucose transport by higher GLUT4 activity and insulin sensitivity. These results suggest that ACC2 plays an essential role in controlling fatty acid oxidation and is a potential target in therapy against obesity and related diseases.
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PMID:Acetyl-CoA carboxylase 2 mutant mice are protected against obesity and diabetes induced by high-fat/high-carbohydrate diets. 1292 Jan 82

Increases in glucose or fatty acids affect metabolism via changes in long-chain acyl-CoA formation and chronically elevated fatty acids increase total cellular CoA. Understanding the response of pancreatic beta cells to increased amounts of fuel and the role that altered insulin secretion plays in the development and maintenance of obesity and Type 2 diabetes is important. Data indicate that the activated form of fatty acids acts as an effector molecule in stimulus-secretion coupling. Glucose increases cytosolic long-chain acyl-CoA because it increases the "switch" compound malonyl-CoA that blocks mitochondrial beta-oxidation, thus implementing a shift from fatty acid to glucose oxidation. We present arguments in support of the following: (i) A source of fatty acid either exogenous or endogenous (derived by lipolysis of triglyceride) is necessary to support normal insulin secretion; (ii) a rapid increase of fatty acids potentiates glucose-stimulated secretion by increasing fatty acyl-CoA or complex lipid concentrations that act distally by modulating key enzymes such as protein kinase C or the exocytotic machinery; (iii) a chronic increase of fatty acids enhances basal secretion by the same mechanism, but promotes obesity and a diminished response to stimulatory glucose; (iv) agents which raise cAMP act as incretins, at least in part, by stimulating lipolysis via beta-cell hormone-sensitive lipase activation. Furthermore, increased triglyceride stores can give higher rates of lipolysis and thus influence both basal and stimulated insulin secretion. These points highlight the important roles of NEFA, LC-CoA, and their esterified derivatives in affecting insulin secretion in both normal and pathological states.
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PMID:Fatty acid metabolism and insulin secretion in pancreatic beta cells. 1368 Jan 27


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