Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: 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)

We present evidence of a link between low-density lipoprotein (LDL) receptor binding and activation of a platelet G-coupled protein. LDL stimulation induced cytosolic [Ca2+]i mobilization, increase in inositol 1,4,5-triphosphate (IP3) formation and a rapid cytosol-to-membrane translocation of protein kinase C (PKC) enzymatic activity. Pertussis toxin inhibited all the stimulatory effects, whereas cholera toxin had no effect. Using ligand-binding assays, we demonstrated that exposing platelet LDL receptors to high concentrations of LDL (1.5 g/l) caused a rapid down-regulation and desensitization, as shown by the reduction in the Bmax, intracellular [Ca2+]i mobilization and IP3 formation to 65, 73 and 63%, respectively. The inhibitory effects were reversible and dose and time dependent. Furthermore, VLDL (0.2 g/l) and IDL (0.07 g/l) induced similar desensitization effects. However, HDL3 (up to 1.5 g/l), chylomicrons (up to 0.5 g/l) and cyclohexandione-modified LDL (which does not bind to platelets) had no significant effects. Protein kinase C inhibitors (150 nmol/l staurosporine, 100 micromol/l H-7, and 10 nmol/l bisindolylmaleimide) inhibited desensitization to 71%, on average. Sequestration blocking agents (0.30 g/l, concanavalin A) had no significant effect if phosphorylation was operative. However, there was a complete blockade with the concurrent inhibition of both pathways. In contrast, cAMP-dependent protein kinase inhibitors (PKI, 1 micromol/l) or beta2-adrenergic receptor kinase inhibitors (100 nmol/l, heparin), had no effect. Overall results indicate that LDL binds to a pertussis sensitive G-protein coupled receptor and that high levels of lipoproteins down-regulate the number of receptors and desensitize its mediated response by a mechanism that involves PKC-phosphorylation and sequestration of binding sites. This new regulatory mechanism may have implications for the thrombogenicity in hyperlipidemia and for effects of lipid lowering therapy.
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PMID:Low-density lipoprotein (LDL) binds to a G-protein coupled receptor in human platelets. Evidence that the proaggregatory effect induced by LDL is modulated by down-regulation of binding sites and desensitization of its mediated signaling. 1122 31

The insulin resistance syndrome is characterized by several risk factors for cardiovascular disease. Chronic chemical activation of AMP-activated protein kinase by the adenosine analog 5-aminoimidazole-4-carboxamide-1-beta -D-ribofuranoside (AICAR) has been shown to augment insulin action, upregulate mitochondrial enzymes in skeletal muscles, and decrease the content of intra-abdominal fat. Furthermore, acute AICAR exposure has been found to reduce sterol and fatty acid synthesis in rat hepatocytes incubated in vitro as well as suppress endogenous glucose production in rats under euglycemic clamp conditions. To investigate whether chronic AICAR administration, in addition to the beneficial effects on insulin sensitivity, is capable of improving other phenotypes associated with the insulin resistance syndrome, obese Zucker (fa/fa) rats (n = 6) exhibiting insulin resistance, hyperlipidemia, and hypertension were subcutaneously injected with AICAR (0.5 mg/g body wt) daily for 7 weeks. Obese control rats were either pair-fed (PF) (n = 6) or ad libitum-fed (AL) (n = 6). Lean Zucker rats (fa/-) (n = 8) served as a reference group. AICAR administration significantly reduced plasma triglyceride levels (P < 0.01 for AICAR vs. AL, and P = 0.05 for AICAR vs. PF) and free fatty acids (P < 0.01 for AICAR vs. AL, and P < 0.05 for AICAR vs. PF) and increased HDL cholesterol levels (P < 0.01 for AICAR vs. AL and PF). AICAR treatment also lowered systolic blood pressure by 14.6 +/- 4.3 mmHg (P < 0.05), and AICAR-treated animals exhibited a tendency toward decreased intra-abdominal fat content. Furthermore, AICAR administration normalized the oral glucose tolerance test and decreased fasting concentrations of glucose and insulin close to the level of the lean animals. Finally, in line with previous findings, AICAR treatment was also found to enhance GLUT4 protein expression and to increase maximally insulin-stimulated glucose transport in primarily white fast-twitch muscles. Our data provide strong evidence that long-term administration of AICAR improves glucose tolerance, improves the lipid profile, and reduces systolic blood pressure in an insulin-resistant animal model. The present study gives additional support to the hypothesis that AMPK activation might be a potential future pharmacological strategy for treating the insulin resistance syndrome.
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PMID:Long-term AICAR administration reduces metabolic disturbances and lowers blood pressure in rats displaying features of the insulin resistance syndrome. 1208 50

Obesity, a state of increased adipose tissue mass, is a major cause for type 2 diabetes, hyperlipidemia, and hypertension, resulting in clustering of risk factors for atherosclerosis. Heterozygous PPARgamma knockout mice and KKA(y) mice administered with a PPARgamma antagonist were protected from high-fat diet-induced adipocyte hypertrophy and insulin resistance. Moderate reduction of PPARgamma activity prevented adipocyte hypertrophy, thereby diminution of TNFalpha, resistin, and FFA and upregulation of adiponectin and leptin. These alterations led to reduction of tissue TG content in muscle/liver, thereby ameliorating insulin resistance. Insulin resistance in the lipoatrophic mice and KKA(y) mice were ameliorated by replenishment of adiponectin. Moreover, adiponectin transgenic mice ameliorated insulin resistance and diabetes, but not the obesity of ob/ob mice. Furthermore, targeted disruption of the adiponectin gene caused moderate insulin resistance and glucose intolerance. In muscle, adiponectin activated AMP kinase and PPARgamma pathways, thereby increasing beta-oxidation of lipids, leading to decreased TG content, which ameliorated muscle insulin resistance. In the liver, adiponectin also activated AMPK, thereby downregulating PEPCK and G6Pase, leading to decreased glucose output from the liver. In conclusion, PPARgamma plays a central role in the regulation of adipocyte hypertrophy and insulin sensitivity. The upregulation of the adiponectin pathway by PPARgamma may play a role in the increased insulin sensitivity of heterozygous PPARgamma knockout mice, and activation of adiponectin pathway may provide novel therapeutic strategies for obesity-linked disorders such as type 2 diabetes and metabolic syndrome.
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PMID:[The mechanisms by which PPARgamma and adiponectin regulate glucose and lipid metabolism]. 1450 Nov 64

Diabetes mellitus (DM) causes the development of a specific cardiomyopathy that results from the metabolic derangements present in DM and manifests as cardiac contractile dysfunction. Although myocardial dysfunction in Type 1 DM has been associated with defects in the function and regulation of the sarcoplasmic reticulum (SR), very little is known about SR function in Type 2 DM. Accordingly, this study examined whether abnormalities in cardiac contractile performance and SR function occur in the prestage of Type 2 DM (i.e., during insulin resistance). Sucrose feeding was used to induce whole body insulin resistance, whereas cardiac contractile performance was assessed by echocardiography and SR function was measured by SR calcium (Ca(2+)) uptake. Sucrose-fed rats exhibited hyperinsulinemia, hyperglycemia, and hyperlipidemia relative to control rats. Serial echocardiographic assessments in the sucrose-fed rats revealed early abnormalities in diastolic function followed by late systolic dysfunction and concurrent alterations in myocardial structure. The hearts of the 10-wk sucrose-fed rats showed depressed SR function demonstrated by a significant reduction in SR Ca(2+) uptake. The decline in SR Ca(2+) uptake was associated with a significant decrease in the cAMP-dependent protein kinase and Ca(2+)/calmodulin-dependent protein kinase II-mediated phosphorylation of phospholamban. The results show that abnormalities in cardiac contractile performance and SR function occur at an insulin-resistant stage before the manifestation of overt Type 2 DM.
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PMID:Alterations in cardiac contractile performance and sarcoplasmic reticulum function in sucrose-fed rats is associated with insulin resistance. 1697 23

Resveratrol may protect against metabolic disease through activating SIRT1 deacetylase. Because we have recently defined AMPK activation as a key mechanism for the beneficial effects of polyphenols on hepatic lipid accumulation, hyperlipidemia, and atherosclerosis in type 1 diabetic mice, we hypothesize that polyphenol-activated SIRT1 acts upstream of AMPK signaling and hepatocellular lipid metabolism. Here we show that polyphenols, including resveratrol and the synthetic polyphenol S17834, increase SIRT1 deacetylase activity, LKB1 phosphorylation at Ser(428), and AMPK activity. Polyphenols substantially prevent the impairment in phosphorylation of AMPK and its downstream target, ACC (acetyl-CoA carboxylase), elevation in expression of FAS (fatty acid synthase), and lipid accumulation in human HepG2 hepatocytes exposed to high glucose. These effects of polyphenols are largely abolished by pharmacological and genetic inhibition of SIRT1, suggesting that the stimulation of AMPK and lipid-lowering effect of polyphenols depend on SIRT1 activity. Furthermore, adenoviral overexpression of SIRT1 stimulates the basal AMPK signaling in HepG2 cells and in the mouse liver. AMPK activation by SIRT1 also protects against FAS induction and lipid accumulation caused by high glucose. Moreover, LKB1, but not CaMKKbeta, is required for activation of AMPK by polyphenols and SIRT1. These findings suggest that SIRT1 functions as a novel upstream regulator for LKB1/AMPK signaling and plays an essential role in the regulation of hepatocyte lipid metabolism. Targeting SIRT1/LKB1/AMPK signaling by polyphenols may have potential therapeutic implications for dyslipidemia and accelerated atherosclerosis in diabetes and age-related diseases.
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PMID:SIRT1 regulates hepatocyte lipid metabolism through activating AMP-activated protein kinase. 1848 75

AMPK (AMP-activated protein kinase) has been suggested to be a central player regulating FA (fatty acid) metabolism through its ability to regulate ACC (acetyl-CoA carboxylase) activity. Nevertheless, its involvement in insulin resistance- and TD2 (Type 2 diabetes)-associated dyslipidaemia remains enigmatic. In the present study, we employed the Psammomys obesus gerbil, a well-established model of insulin resistance and TD2, in order to appreciate the contribution of the AMPK/ACC pathway to the abnormal hepatic lipid synthesis and increased lipid accumulation in the liver. Our investigation provided evidence that the development of insulin resistance/diabetic state in P. obesus is accompanied by (i) body weight gain and hyperlipidaemia; (ii) elevations of hepatic ACC-Ser79 phosphorylation and ACC protein levels; (iii) a rise in the gene expression of cytosolic ACC1 concomitant with invariable mitochondrial ACC2; (iv) an increase in hepatic AMPKalpha-Thr172 phosphorylation and protein expression without any modification in the calculated ratio of phospho-AMPKalpha to total AMPKalpha; (v) a stimulation in ACC activity despite increased AMPKalpha phosphorylation and protein expression; and (vi) a trend of increase in mRNA levels of key lipogenic enzymes [SCD-1 (stearoyl-CoA desaturase-1), mGPAT (mitochondrial isoform of glycerol-3-phosphate acyltransferase) and FAS (FA synthase)] and transcription factors [SREBP-1 (sterol-regulatory-element-binding protein-1) and ChREBP (carbohydrate responsive element-binding protein)]. Altogether, our findings suggest that up-regulation of the AMPK pathway seems to be a natural response in order to reduce lipid metabolism abnormalities, thus supporting the role of AMPK as a promising target for the treatment of TD2-associated dyslipidaemia.
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PMID:Increased hepatic lipogenesis in insulin resistance and Type 2 diabetes is associated with AMPK signalling pathway up-regulation in Psammomys obesus. 1884 11

AMPK is an evolutionarily conserved fuel-sensing enzyme that is activated in shortage of energy and suppressed in its surfeit. AMPK activation stimulates fatty acid oxidation, enhances insulin sensitivity, alleviates hyperglycemia and hyperlipidemia, and inhibits proinflammatory changes. Thus, AMPK is a well-received therapeutic target for metabolic syndrome and Type 2 diabetes. Recent studies indicate that AMPK plays a role in linking metabolic syndrome and cancer. AMPK is an essential mediator of the tumor suppressor LKB1 and could be suppressed in cancer cells containing loss-of-function mutations of LKB1 or containing active mutations of B-Raf, or in cancers associated with metabolic syndrome. The activation of AMPK reprograms cellular metabolism and enforces metabolic checkpoints by acting on mTORC1, p53, fatty acid synthase and other molecules for regulating cell growth and metabolism. In keeping with in vitro studies, recent epidemiological studies indicate that the incidence of cancer is reduced in Type 2 diabetes treated with metformin, an AMPK activator. Thus, AMPK is emerging as an interesting metabolic tumor suppressor and a promising target for cancer prevention and therapy.
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PMID:AMPK as a metabolic tumor suppressor: control of metabolism and cell growth. 2022 1

Deficiency of adiponectin (APN), an adipocyte-derived vascular protective molecule, contributes to diabetic vascular injury. The current study determined whether obesity/hyperlipidemia may alter the vascular response to APN, and investigated the involved mechanisms and pathologic significance. Adult male Sprague-Dawley rats were fed a regular or high-fat diet (HF) for 4-16 weeks. Circulating APN levels, aortic pAMPK/AMPK, peNOS/eNOS, and APN receptor expression levels were determined. Compared to time-matched animals fed control diet, plasma APN levels in HF-diet animals were significantly increased at 8 weeks, and rapidly declined thereafter. Despite unchanged or elevated circulating APN levels, phosphorylated AMPK and eNOS in vascular tissue were significantly reduced at all observed time points. Recombinant full-length APN (rAPN)-induced AMPK/eNOS phosphorylation and vasodilatation were significantly reduced in 16-week obese/hyperlipidemic aortic segments. Vascular APN receptor 1 (AdipoR1) and receptor 2 (AdipoR2) expression were significantly reduced 16 weeks after HF-diet. Pre-incubation of rAPN with obese/hyperlipidemic plasma, but not with normal plasma, significantly reduced its AMPK and eNOS activation effect, and blunted its protective effect against TNFalpha-induced HUVEC apoptosis. This study demonstrated for the first time that obesity/hyperlipidemia reduces vascular responsiveness to APN. Modification/inactivation of APN by unidentified factors present in obese/hyperlipidemic plasma, decreased vascular AdipoR1/R2 expression, and reduced circulating APN levels contribute to reduced vascular responsiveness to APN at different stages of the obese condition. Reduced APN bioactivity allows unmitigated TNFalpha pro-apoptotic and pro-inflammatory actions, contributing to vascular injury in obesity/hyperlipidemia.
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PMID:Reduced vascular responsiveness to adiponectin in hyperlipidemic rats--mechanisms and significance. 2030 76

Adiponectin (Ad) is an insulin-sensitizing adipokine known to stimulate fatty acid (FA) oxidation in skeletal muscle. Skeletal muscle can become resistant to Ad very rapidly, after only 3 days of high saturated fat feeding in rats. Whether the same occurs following a high polyunsaturated fat diet is unknown. Obesity, insulin resistance, and hyperlipidemia are recognized as low-grade inflammatory diseases; therefore, we hypothesized that high-fat feeding induces inflammation, which interferes with Ad action at skeletal muscle. To this end, rats were placed into one of three dietary groups, control (CON, 10% kcal from fat), high saturated (SAT), or high polyunsaturated (PUFA) fat (60% kcal from fat) for 3 days to determine whether Ad resistance develops. Half of the animals from each group were further supplemented with aspirin, a common anti-inflammatory drug. Ad stimulated FA metabolism, Ad signaling intermediates [AdipoR1, APPL1, LKB1, AMPK, and acetyl-CoA carboxylase (ACC)], and inflammatory proteins [Toll-like receptor (TLR4), IKK alpha/beta, IkappaB alpha, NF-kappaB, suppressor of cytokine signaling-3 (SOCS3), and JNK] were measured in soleus muscle. Three days of SAT feeding induced Ad resistance in soleus muscle, assessed as an inability of Ad to phosphorylate ACC and increase FA oxidation. In PUFA-fed animals, Ad-stimulated FA oxidation and ACC phosphorylation to the same degree as CON animals (FA oxidation: +35%, +41%; pACC +29%, +19%; CON, PUFA, P < 0.05). However, neither SAT nor PUFA feeding for 3 days induced skeletal muscle inflammation. Surprisingly, aspirin prevented Ad-stimulated increases in FA oxidation. In conclusion, FA type is critical in the development of Ad resistance, but this does not appear to be mediated by inflammation.
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PMID:Skeletal muscle inflammation is not responsible for the rapid impairment in adiponectin response with high-fat feeding in rats. 2055 37

AMPK has emerged as a critical mechanism for salutary effects of polyphenols on lipid metabolic disorders in type 1 and type 2 diabetes. Here we demonstrate that AMPK interacts with and directly phosphorylates sterol regulatory element binding proteins (SREBP-1c and -2). Ser372 phosphorylation of SREBP-1c by AMPK is necessary for inhibition of proteolytic processing and transcriptional activity of SREBP-1c in response to polyphenols and metformin. AMPK stimulates Ser372 phosphorylation, suppresses SREBP-1c cleavage and nuclear translocation, and represses SREBP-1c target gene expression in hepatocytes exposed to high glucose, leading to reduced lipogenesis and lipid accumulation. Hepatic activation of AMPK by the synthetic polyphenol S17834 protects against hepatic steatosis, hyperlipidemia, and accelerated atherosclerosis in diet-induced insulin-resistant LDL receptor-deficient mice in part through phosphorylation of SREBP-1c Ser372 and suppression of SREBP-1c- and -2-dependent lipogenesis. AMPK-dependent phosphorylation of SREBP may offer therapeutic strategies to combat insulin resistance, dyslipidemia, and atherosclerosis.
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PMID:AMPK phosphorylates and inhibits SREBP activity to attenuate hepatic steatosis and atherosclerosis in diet-induced insulin-resistant mice. 2145 23


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