Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0020473 (hyperlipidemia)
 15,891 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Melatonin, which is synthesized in the pineal gland and other tissues, has a variety of physiological, immunological, and biochemical functions. It is a direct scavenger of free radicals and has indirect antioxidant effects due to its stimulation of the expression and activity of antioxidative enzymes such as glutathione peroxidase, superoxide dismutase and catalase, and NO synthase, in mammalian cells. Melatonin also reduces serum lipid levels in mammalian species, and helps to prevent oxidative stress in diabetic subjects. Long-term melatonin administration to diabetic rats reduced their hyperlipidemia and hyperinsulinemia, and restored their altered ratios of polyunsaturated fatty acid in serum and tissues. It was recently reported that melatonin enhanced insulin-receptor kinase and IRS-1 phosphorylation, suggesting the potential existence of signaling pathway cross-talk between melatonin and insulin. Because TNF-alpha has been shown to impair insulin action by suppressing insulin receptor-tyrosine kinase activity and its IRS-1 tyrosine phosphorylation in peripheral tissues such as skeletal muscle cells, it was speculated that melatonin might counteract TNF-alpha-associated insulin resistance in type 2 diabetes. This review will focus on the physiological and metabolic effects of melatonin and highlight its potential use for the treatment of cholesterol/lipid and carbohydrate disorders.
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PMID:Metabolic effects of melatonin on oxidative stress and diabetes mellitus. 1621 26

Resistin and resistin-like molecules (RELMs) are a family of proteins reportedly related to insulin resistance and inflammation. Because the serum concentration and intestinal expression level of RELMbeta were elevated in insulin-resistant rodent models, in this study we investigated the effect of RELMbeta on insulin signaling and metabolism using transgenic mice and primary cultured hepatocytes. First, transgenic mice with hepatic RELMbeta overexpression were shown to exhibit significant hyperglycemia, hyperlipidemia, fatty liver, and pancreatic islet enlargement when fed a high fat diet. Hyperinsulinemic glucose clamp showed a decreased glucose infusion rate due to increased hepatic glucose production. In addition, the expression levels of IRS-1 and IRS-2 proteins as well as the degrees of insulin-induced phosphatidylinositol 3-kinase and Akt activations were attenuated in RELMbeta transgenic mice. Similar down-regulations of IRS-1 and IRS-2 proteins were observed in primary cultured hepatocytes chronically treated (for 24 h) with RELMbeta, suggesting the insulin resistance-inducing effect of RELMbeta to be direct. Furthermore, it was shown that RELMbeta acutely and markedly activates ERK and p38, while weakly activating JNK, in primary cultured hepatocytes. This increased basal p38 phosphorylation level was also observed in the livers of RELMbeta transgenic mice. In conclusion, RELMbeta, a gut-derived hormone, impairs insulin signaling probably via the activations of classic MAPKs, and increased expression of RELMbeta may be involved in the pathogenesis of glucose intolerance and hyperlipidemia in some insulin-resistant models. Thus, RELMbeta is a potentially useful marker for assessing insulin resistance and may also be a target for future novel anti-diabetic agents.
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PMID:Resistin-like molecule beta activates MAPKs, suppresses insulin signaling in hepatocytes, and induces diabetes, hyperlipidemia, and fatty liver in transgenic mice on a high fat diet. 1624 41

Elevations in free fatty acids (FFAs) impair glucose uptake in skeletal muscle. However, there is no information pertaining to the effect of elevated circulating lipids on either basal protein synthesis or the anabolic effects of leucine and insulin-like growth factor I (IGF-I). In chronically catheterized conscious rats, the short-term elevation of plasma FFAs by the 5-h infusion of heparin plus Intralipid decreased muscle protein synthesis by approximately 25% under basal conditions. Lipid infusion was associated with a redistribution of eukaryotic initiation factor (eIF)4E from the active eIF4E.eIF4G complex to the inactive eIF4E.4E-BP1 complex. This shift was associated with a decreased phosphorylation of eIF4G but not 4E-BP1. Lipid infusion did not significantly alter either the total amount or phosphorylation state of mTOR, TSC2, S6K1, or the ribosomal protein S6 under basal conditions. In control rats, oral leucine increased muscle protein synthesis. This anabolic response was not impaired by lipid infusion, and no defects in signal transduction pathways regulating translation initiation were detected. In separate rats that received a bolus injection of IGF-I, lipid infusion attenuated the normal redistribution of eIF4E from the active to inactive complex and largely prevented the increased phosphorylation of 4E-BP1, eIF4G, S6K1, and S6. This IGF-I resistance was associated with enhanced Ser(307) phosphorylation of insulin receptor substrate-1 (IRS-1). These data indicate that the short-term elevation of plasma FFAs impairs basal protein synthesis in muscle by altering eIF4E availability, and this defect may be related to impaired phosphorylation of eIF4G, not 4E-BP1. Moreover, hyperlipidemia impairs IGF-I action but does not produce leucine resistance in skeletal muscle.
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PMID:Elevated plasma free fatty acids decrease basal protein synthesis, but not the anabolic effect of leucine, in skeletal muscle. 1668 54

Diabetic conditions are associated with hyperglycemia and hyperlipidemia, but the role of saturated fatty acids (SFA) vs. unsaturated fatty acids (UFA) in activation of T-lymphocytes and human aortic endothelial cells (HAEC) is not known. We investigated in vitro effects of various concentrations of SFA (palmitate) and UFA (oleic, linoleic, linolenic, and arachidonic) acids in activation of these cells. These cells in presence of palmitate, but not UFA, exhibited time, and concentration-dependent emergence of insulin receptors, GLUT 4 expression, generation of ROS, cytokines, lipid peroxidation, and IRS-1. We conclude that both T-lymphocytes and HAEC share common characteristics in exhibiting activation of these cells to palmitate, but not to UFA, by developing insulin receptors and becoming insulin responsive tissues, a hitherto unknown response to palmitate. We hypothesize that these events may serve as protective defense mechanisms against acute effects of glucotoxicity and lipotoxicity in these cells.
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PMID:Palmitic acid-induced activation of human T-lymphocytes and aortic endothelial cells with production of insulin receptors, reactive oxygen species, cytokines, and lipid peroxidation. 1678 68

Inappropriate adaptation of beta-cell mass is a primary cause of the development of diabetic hyperglycemia. However, the mechanisms underlying regulation of the beta-cell mass in response to insulin resistance or in the development of type 2 diabetes remain unclear. We determined the insulin signaling in the beta-cells and the adaptation of the beta-cell mass in response to the progression of insulin resistance in OLETF rats. By 25 weeks of age, at the onset of diabetes, compared to control LETO rats, OLETF rats developed obesity (Body weight: LETO vs OLETF = 474.0+/-9.5 vs 581.3+/-21.8 g, P < 0.001, n=6), hyperlipidemia (Cholesterol: LETO vs OLETF = 1.67+/-0.07 vs 2.19+/-0.20 mM, P < 0.05, n=6; triglyceride: LETO vs OLETF = 0.36+/-0.05 vs 1.36+/-0.12 mM, P < 0.001, n=6), and impaired glucose tolerance (AUC: LETO vs OLETF = 10.3+/-3.4 vs 29.6+/-7.8 mM, P < 0.001, n=6). Insulin sensitivities as assessed by the insulin sensitivity index (ISI) and the homeostasis model assessment (HOMA) indicated that OLETF rats developed severe insulin resistance. The measurement of plasma insulin levels by ELISA demonstrated, at the onset of diabetes, that fasting insulin levels were increased by 1.2-fold, and 2 hr postprandial insulin levels were increased by 3-fold (P < 0.05, n=6) in OLETF rats compared to age-matched LETO mates which is suggestive of hyperinsulinemia. Immunostaining detected a significant reduction in the insulin receptor substrate 1 (IRS1) (by 54%, P < 0.001) and IRS2 (by 55%, P < 0.001) in the beta-cells of the OLETF rats. Interestingly, while the beta-cell mass was found to be increased (by 2.2-fold; P < 0.001), the beta-cell insulin content as determined by immunostaining was significantly reduced by 32% (P < 0.001) in the OLETF rats when compared to the controls. Our findings suggest that despite increasing beta-cell mass the impaired beta-cell insulin signaling and reduced beta-cell insulin content may contribute to the onset of overt diabetes in OLETF rats.
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PMID:Increased beta-cell apoptosis and impaired insulin signaling pathway contributes to the onset of diabetes in OLETF rats. 1845 52

We have shown previously that a maternal junk food diet during pregnancy and lactation plays a role in predisposing offspring to obesity. Here we show that rat offspring born to mothers fed the same junk food diet rich in fat, sugar and salt develop exacerbated adiposity accompanied by raised circulating glucose, insulin, triglyceride and/or cholesterol by the end of adolescence (10 weeks postpartum) compared with offspring also given free access to junk food from weaning but whose mothers were exclusively fed a balanced chow diet in pregnancy and lactation. Results also showed that offspring from mothers fed the junk food diet in pregnancy and lactation, and which were then switched to a balanced chow diet from weaning, exhibited increased perirenal fat pad mass relative to body weight and adipocyte hypertrophy compared with offspring which were never exposed to the junk food diet. This study shows that the increased adiposity was more enhanced in female than male offspring and gene expression analyses showed raised insulin-like growth factor-1 (IGF-1), insulin receptor substrate (IRS)-1, vascular endothelial growth factor (VEGF)-A, peroxisome proliferator-activated receptor-gamma (PPARgamma), leptin, adiponectin, adipsin, lipoprotein lipase (LPL), Glut 1, Glut 3, but not Glut 4 mRNA expression in females fed the junk food diet throughout the study compared with females never given access to junk food. Changes in gene expression were not as marked in male offspring with only IRS-1, VEGF-A, Glut 4 and LPL being up-regulated in those fed the junk food diet throughout the study compared with males never given access to junk food. This study therefore shows that a maternal junk food diet promotes adiposity in offspring and the earlier onset of hyperglycemia, hyperinsulinemia and/or hyperlipidemia. Male and female offspring also display a different metabolic, cellular and molecular response to junk-food-diet-induced adiposity.
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PMID:Offspring from mothers fed a 'junk food' diet in pregnancy and lactation exhibit exacerbated adiposity that is more pronounced in females. 1846 62

A number of patients with hyperlipidemia are prescribed 3-hydroxy-3-methylglutaryl-CoA reductase inhibitors that are concomitantly used along with the treatment of diabetes mellitus. The effects of atorvastatin and pravastatin on insulin-induced glucose uptake and the related signal transduction in 3T3L1 adipocytes were studied. 3T3L1 fibroblasts were differentiated into adipocytes, pretreated with atorvastatin or pravastatin, and then exposed to insulin. Glucose uptake and the amount of insulin signal proteins were measured. Atorvastatin significantly decreased insulin-stimulated 2-deoxyglucose uptake in 3T3L1 adipocytes associated with the prevention of translocation of GLUT4 into the plasma membrane. The amounts of Rab4 and RhoA that required lipid modification with farnesyl or geranylgeranyl pyrophosphate, in the membrane fraction were decreased by atorvastatin. Insulin-induced tyrosine phosphorylation of IRS-1 and serine/threonine phosphorylation of Akt were reduced by atorvastatin. Pravastatin did not modify these insulin-induced changes in the signal transduction. Inhibitors of the RhoA/Rho kinase system, C3 and Y27632, as well as atorvastatin reduced insulin-induced changes in signal transduction. Atorvastatin and pravastatin did not affect messenger RNA expression, protein level, and tyrosine phosphorylation of insulin receptors. In conclusion, hydrophobic atorvastatin decreases the glucose uptake by 3T3L1 adipocytes since it can enter the cell and prevents lipid modification of some proteins that are involved in the insulin signal transduction process.
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PMID:Effects of atorvastatin and pravastatin on signal transduction related to glucose uptake in 3T3L1 adipocytes. 1846

Clinical, epidemiological, and biochemical studies have highlighted the role of obesity-induced insulin resistance in various metabolic diseases. However, the underlying molecular mechanisms remain to be established. In the present study, we show that palmitate-induced serine phosphorylation of phosphoinositide-dependent protein kinase-1 (PDK1) negatively regulates insulin signaling. PDK1-mediated Akt phosphorylation at Thr308 in the activation loop is reduced in C2C12 myotubes treated with palmitate or overexpressing protein kinase C theta (PKCtheta), a kinase that has been implicated in hyperlipidemia-induced insulin resistance. Palmitate treatment also inhibited platelet-derived growth factor-stimulated Akt phosphorylation, suggesting that the inhibition could occur at a site independent of IRS1/2. The inhibitory effect of palmitate on PDK1 and Akt was diminished in PKCtheta-deficient mouse embryonic fibroblasts (MEFs) by treating C2C12 myotubes with PKCtheta pseudosubstrates. In vivo labeling studies revealed that PDK1 undergoes palmitate-induced phosphorylation at two novel sites, Ser504 and Ser532. Replacing Ser504/532 with alanine disrupted PKCtheta-catalyzed PDK1 phosphorylation in vitro and palmitate-induced PDK1 phosphorylation in cells. PDK1-deficient MEFs transiently expressing PDK1S504A/S532A but not PDK1S504E/S532D showed increased basal and insulin-stimulated Akt phosphorylation at Thr308 when compared with MEFs expressing wild-type PDK1. Taken together, our results identify PDK1 as a novel target in free fatty acid-induced insulin resistance and PKCtheta as the kinase mediating the negative regulation.
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PMID:Protein kinase C theta (PKCtheta)-dependent phosphorylation of PDK1 at Ser504 and Ser532 contributes to palmitate-induced insulin resistance. 1904 61

Obesity is frequently associated with systemic insulin resistance, glucose intolerance, and hyperlipidemia. Impaired insulin action in muscle and paradoxical diet/insulin-dependent overproduction of hepatic lipids are important components of obesity, but their pathogenesis and inter-relationships between muscle and liver are uncertain. We studied two murine obesity models, moderate high-fat-feeding and heterozygous muscle-specific PKC-lambda knockout, in both of which insulin activation of atypical protein kinase C (aPKC) is impaired in muscle, but conserved in liver. In both models, activation of hepatic sterol receptor element binding protein-1c (SREBP-1c) and NFkappaB (nuclear factor-kappa B), major regulators of hepatic lipid synthesis and systemic insulin resistance, was chronically increased in the fed state. In support of a critical mediatory role of aPKC, in both models, inhibition of hepatic aPKC by adenovirally mediated expression of kinase-inactive aPKC markedly diminished diet/insulin-dependent activation of hepatic SREBP-1c and NFkappaB, and concomitantly improved hepatosteatosis, hypertriglyceridemia, hyperinsulinemia, and hyperglycemia. Moreover, in high-fat-fed mice, impaired insulin signaling to IRS-1-dependent phosphatidylinositol 3-kinase, PKB/Akt and aPKC in muscle and hyperinsulinemia were largely reversed. In obesity, conserved hepatic aPKC-dependent activation of SREBP-1c and NFkappaB contributes importantly to the development of hepatic lipogenesis, hyperlipidemia, and systemic insulin resistance. Accordingly, hepatic aPKC is a potential target for treating obesity-associated abnormalities.
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PMID:The critical role of atypical protein kinase C in activating hepatic SREBP-1c and NFkappaB in obesity. 1920 34

Obesity, type 2 diabetes mellitus (T2DM), and non-alcoholic steatohepatitis (NASH) are associated with cognitive impairment, brain insulin resistance, and neurodegeneration. Recent studies linked these effects to increased pro-ceramide gene expression in liver and increased ceramide levels in serum. Since ceramides are neurotoxic and cause insulin resistance, we directly examined the role of ceramides as mediators of impaired signaling and central nervous system function using an in vivo model. Long Evans rat pups were administered C2Cer:N-acetylsphinganine or its inactive dihydroceramide analog (C2DCer) by i.p. injection. Rats were subjected to rotarod and Morris water maze tests of motor and cognitive function, and livers and brains were examined for histopathology and integrity of insulin/IGF signaling. C2Cer treatment caused hyperglycemia, hyperlipidemia, and mild steatohepatitis, reduced brain lipid content, and increased ceramide levels in liver, brain, and serum. Quantitative RT-PCR analysis revealed significant alterations in expression of several genes needed for insulin and IGF-I signaling, and multiplex ELISAs demonstrated inhibition of signaling through the insulin or IGF-1 receptors, IRS-1, and Akt in both liver and brain. Ultimately, the toxic ceramides generated in peripheral sources such as liver or adipose tissue caused sustained impairments in neuro-cognitive function and insulin/IGF signaling needed for neuronal survival, plasticity, and myelin maintenance in the brain. These findings support our hypothesis that a liver/peripheral tissue-brain axis of neurodegeneration, effectuated by increased toxic lipid/ceramide production and transport across the blood-brain barrier, could mediate cognitive impairment in T2DM and NASH.
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PMID:Ceramide-mediated insulin resistance and impairment of cognitive-motor functions. 2069 50


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