Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0011849 (diabetes)
 277,896 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Pyruvate dehydrogenase kinase (PDK) catalyzes phosphorylation and inactivation of the pyruvate dehydrogenase complex (PDC). Two isoforms of this mitochondrial kinase (PDK2 and PDK4) are induced in a tissue-specific manner in response to starvation and diabetes. Inactivation of PDC by increased PDK activity promotes gluconeogenesis by conserving three-carbon substrates. This helps maintain glucose levels during starvation, but is detrimental in diabetes. Factors that regulate PDK2 and PDK4 expression were examined in Morris hepatoma 7800 C1 cells. The peroxisome proliferator-activated receptor-alpha (PPAR-alpha) agonist WY-14,643 and the glucocorticoid dexamethasone increased PDK4 mRNA levels. Neither compound affected the half-life of the PDK4 message, suggesting that both increase gene transcription. Fatty acids caused an increase in the PDK4 message comparable to that induced by WY-14,643. Insulin prevented and reversed the stimulatory effects of dexamethasone on PDK4 gene expression, but was less effective against the stimulatory effects of WY-14,643 and fatty acids. Insulin also decreased the abundance of the PDK2 message. The findings suggest that decreased levels of insulin and increased levels of fatty acids and glucocorticoids promote PDK4 gene expression in starvation and diabetes. The decreased level of insulin is likely responsible for the increase in PDK2 mRNA level in starvation and diabetes.
Diabetes 2002 Feb
PMID:Regulation of pyruvate dehydrogenase kinase expression by peroxisome proliferator-activated receptor-alpha ligands, glucocorticoids, and insulin. 1181 33

The peroxisome proliferator-activated receptors (PPARs) are a group of three nuclear receptor isoforms, PPAR gamma, PPAR alpha, and PPAR delta, encoded by different genes. PPARs are ligand-regulated transcription factors that control gene expression by binding to specific response elements (PPREs) within promoters. PPARs bind as heterodimers with a retinoid X receptor and, upon binding agonist, interact with cofactors such that the rate of transcription initiation is increased. The PPARs play a critical physiological role as lipid sensors and regulators of lipid metabolism. Fatty acids and eicosanoids have been identified as natural ligands for the PPARs. More potent synthetic PPAR ligands, including the fibrates and thiazolidinediones, have proven effective in the treatment of dyslipidemia and diabetes. Use of such ligands has allowed researchers to unveil many potential roles for the PPARs in pathological states including atherosclerosis, inflammation, cancer, infertility, and demyelination. Here, we present the current state of knowledge regarding the molecular mechanisms of PPAR action and the involvement of the PPARs in the etiology and treatment of several chronic diseases.
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PMID:The mechanisms of action of PPARs. 1181 83

We have previously reported that omental (OM) preadipocytes respond less well to the prodifferentiating effects of thiazolidinediones than do preadipocytes from subcutaneous (SC) depots. This finding is consistent with in vivo alterations in fat distribution that occur in humans treated with thiazolidinediones. To explore these site-related differences further, we used real-time RT-PCR to quantify the specific mRNAs encoding peroxisome proliferator-activated receptor (PPAR) gamma1 and gamma2 and found that both isoforms were more highly expressed in SC than in OM preadipocytes. After 10 days of thiazolidinedione treatment, preadipocytes from both depots showed a small and comparable increase in expression of PPARgamma1 mRNA (1.7 +/- 0.2-fold [P = 0.007]) and 1.3 +/- 0.1-fold [P = 0.008] increase for SC and OM, respectively). There was a much larger increase in PPARgamma2 expression, which was significantly greater in SC compared with OM preadipocytes (11.1 +/- 2.8-fold [P = 0.0003] and 5.5 +/- 1.7-fold [P = 0.0003], respectively; P = 0.014 for SC versus OM). To establish whether the refractoriness of OM preadipocytes to differentiation was unique to activators of the PPARgamma pathway, we examined the effects of the retinoid X receptor (RXR) ligand LG100268. As assessed by glycerol-3-phosphate dehydrogenase activity, LG100268 had a greater effect on the differentiation of SC compared with OM preadipocytes when examined alone (SC = 5.7 +/- 1.7-fold vs. OM = 1.9 +/- 0.6-fold; P < 0.05) or in combination with rosiglitazone (SC = 27.0 +/- 7.5 vs. OM = 10.6 +/- 3.6-fold; P < 0.05). Consistent with this, RXRalpha mRNA levels were also higher in SC than in OM preadipocytes. In summary, the previously reported insensitivity of OM preadipocytes to the differentiating effects of thiazolidinediones may relate to their lower basal levels of PPARgamma1 and gamma2 mRNA and their diminished capacity to upregulate PPARgamma2 expression in response to ligand. That omentally derived cells also show reduced responsiveness to the prodifferentiating actions of an RXR ligand and a lower expression of RXRalpha in the undifferentiated state suggests that they may have a more generalized resistance to differentiation.
Diabetes 2002 Mar
PMID:Regional differences in the response of human pre-adipocytes to PPARgamma and RXRalpha agonists. 1187 72

To elucidate the mechanisms by which troglitazone, which is a direct ligand for peroxisome proliferator-activated receptor (PPAR) gamma, ameliorates insulin resistance, we have demonstrated that PPAR gamma is expressed in a pancreatic beta cell line, INS-1, using reverse transcription-polymerase chain reaction (RT-PCR). We incubated the cells with 5 micromol/l troglitazone and 1 mmol/l of each major free fatty acid (FFA; palmitic acid, oleic acid, and linoleic acid), alone or in combination, for 48 h. After that, we evaluated glucose-stimulated insulin secretion (GSIS) and 25 mmol/l KCl-induced insulin secretion in the presence of diazoxide, which clamps membrane potential. Our results showed: (1) treatment with troglitazone for 48 h caused enhancement of GSIS, although troglitazone significantly suppressed cell viability assessed by MTT assay. (2) In cells co-treated with troglitazone and FFA, troglitazone ameliorated lipotoxicity due to FFA. (3) In the presence of 300 micromol/l diazoxide and 25 mmol/l KCl, troglitazone did not affect the recovery of GSIS in INS-1 cells. These results suggest that insulin secretion from the rat insulinoma cell line, INS-1, is modulated by troglitazone, acting somewhere in the ATP-sensitive K(+) channel pathway, possibly through PPAR gamma.
Diabetes Res Clin Pract 2002 May
PMID:Troglitazone ameliorates lipotoxicity in the beta cell line INS-1 expressing PPAR gamma. 1189 Oct 15

In an effort to understand the role of key eicosanoid-forming enzymes in the activation of peroxisome proliferator-activated receptor (PPAR), this study was designed to evaluate the possible contributions of cytosolic phospholipase A(2) (cPLA(2)) and group IIA secretory phospholipase A(2) (sPLA(2)) in the regulation of PPAR-mediated gene transcription in a human hepatoma cell line (HepG2). The HepG2 cells express both PPAR-alpha and -gamma but not PPAR-beta. Overexpression of cPLA(2), but not group IIA sPLA(2) in the HepG2 cells, caused a significantly increased PPAR-alpha/gamma-mediated reporter activity. Antisense inhibition of cPLA(2) resulted in a significantly decreased PPAR-alpha/gamma activity. The PPAR-alpha/gamma-induced gene transcription in the HepG2 cells was inhibited by the cPLA(2) inhibitors methyl arachidonyl fluorophosphonate and arachidonyltrifluoromethyl ketone, but not by the sPLA(2) inhibitor LY311727. The expression of PPAR-alpha-mediated endogenous gene apolipoprotein A-II was increased in cells with overexpression of cPLA(2), decreased in cells with antisense inhibition of cPLA(2), but unaltered in cells with overexpression of group IIA sPLA(2). The above results demonstrated an important role of cPLA(2), but not group IIA sPLA(2) in the control of PPAR activation. The cPLA(2)-mediated PPAR activation was likely mediated by arachidonic acid and prostaglandin E(2). This study reveals a novel intracellular function of cPLA(2) in PPAR activation in HepG2 cells. The cPLA(2) thus may represent a potential therapeutic target for the control of PPAR-related liver and metabolic disorders such as obesity, lipid metabolic disorders, diabetes mellitus, and atherosclerosis.
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PMID:85-kDa cPLA(2) plays a critical role in PPAR-mediated gene transcription in human hepatoma cells. 1189 17

In humans, skeletal muscle is a major site of peroxisome proliferator-activated receptor-alpha (PPAR-alpha) expression, but its function in this tissue is unclear. We investigated the role of hPPAR-alpha in regulating muscle lipid utilization by studying the effects of a highly selective PPAR-alpha agonist, GW7647, on [(14)C]oleate metabolism and gene expression in primary human skeletal muscle cells. Robust induction of PPAR-alpha protein expression occurred during muscle cell differentiation and corresponded with differentiation-dependent increases in oleate oxidation. In mature myotubes, 48-h treatment with 10-1,000 nmol/l GW7647 increased oleate oxidation dose-dependently, up to threefold. Additionally, GW7647 decreased oleate esterification into myotube triacylglycerol (TAG), up to 45%. This effect was not abolished by etomoxir, a potent inhibitor of beta-oxidation, indicating that PPAR-alpha-mediated TAG depletion does not depend on reciprocal changes in fatty acid catabolism. Consistent with its metabolic actions, GW7647 induced mRNA expression of mitochondrial enzymes that promote fatty acid catabolism; carnitine palmityltransferase 1 and malonyl-CoA decarboxylase increased approximately 2-fold, whereas pyruvate dehydrogenase kinase 4 increased 45-fold. Expression of several genes that regulate glycerolipid synthesis was not changed by GW7647 treatment, implicating involvement of other targets to explain the TAG-depleting effect of the compound. These results demonstrate a role for hPPAR-alpha in regulating muscle lipid homeostasis.
Diabetes 2002 Apr
PMID:Peroxisome proliferator-activated receptor-alpha regulates fatty acid utilization in primary human skeletal muscle cells. 1191 5

Thiazolidinediones (TZDs) are a new class of compounds that improve insulin sensitivity in type 2 diabetic patients as well as in rodent models of this disease. These compounds act as ligands for a member of the nuclear hormone receptor superfamily, peroxisome proliferator-activated receptor-gamma (PPAR-gamma), which is highly expressed in adipose tissue and, moreover, has been shown to play an important role in adipocyte differentiation. The strong correlation between the antidiabetic activity of TZDs and their ability to activate PPAR-gamma suggests that PPAR-gamma, through downstream-regulated genes, mediates the effects of TZDs. In this report, we present the isolation and characterization of 81 genes, encoding proteins of known function, differentially expressed during TZD-stimulated differentiation of 3T3-L1 cells. By the use of different reverse- Northern blot techniques, the differential expression of 50 of these genes could be verified, and 21 genes were specifically regulated by a potent TZD during the course of adipocyte differentiation, whereas no effect of a PPAR-gamma antagonist could be observed in mature adipocytes. The differential expression of a large fraction of the isolated genes was also shown to occur in white adipose tissue of ob/ob mice treated with rosiglitazone; combined, our results suggest that an important effect of rosiglitazone in adipose tissue is based on activation of PPAR-gamma in preexisting preadipocytes found among the mature adipocytes, resulting in subsequent adipocyte differentiation.
Diabetes 2002 Apr
PMID:Novel genes regulated by the insulin sensitizer rosiglitazone during adipocyte differentiation. 1191 24

Delta-6 Desaturase, one of the rate-limiting enzymes, catalyzes the conversion of linoleic acid (C18:2 omega6) into gamma-linolenic acid (C18:3 omega6), arachidonic acid (C20:4 omega6), and further metabolites. Recently, it has been shown that human Delta-6 desaturase is expressed not only in liver but in a variety of human tissues, including muscle. Skeletal muscle is a major site of insulin action, and insulin sensitivity may be related to the fatty acid composition of muscle lipids. We examined the effects of troglitazone on the regulation of Delta-6 desaturase gene expression in human muscle cell cultures obtained from muscle biopsies (n = 15). Delta-6 Desaturase mRNA and peroxisome proliferator-activated receptor gamma2 (PPARgamma2) mRNA were quantified by two-step RT-PCR, and the activity of the Delta-6 desaturase enzyme was estimated by gas chromatographic analysis of the omega 6-C18:3/C18:2 fatty acids ratio. In cells treated with 11.5 micromol troglitazone for 4 days, PPARgamma2 mRNA levels were significantly increased (301.0 +/- 51.5%, P < 0.05) and Delta-6 desaturase mRNA levels were significantly decreased (41.7 +/- 5.9%, P < 0.0005) compared with the untreated controls. In accordance with the decrease of Delta-6 desaturase mRNA, there was a significant decrease in the omega6-C18:3/C18:2 ratio down to 47.4 +/- 7.5% in cholesterol esters, 54.2 +/- 7.4% in phospholipids, 56.7 +/- 6.5% in nonesterified fatty acids, and 67.7 +/- 5.9% in triglycerides. The troglitazone-induced decrease in Delta-6 desaturase mRNA is associated with a change in the unsaturated fatty acid composition of the muscle cells. These results add new aspects to the known thiazolidinedione effects on lipid metabolism.
Diabetes 2002 Apr
PMID:Troglitazone downregulates delta-6 desaturase gene expression in human skeletal muscle cell cultures. 1191 26

Troglitazone, rosiglitazone and pioglitazone are members of the thiazolidinedione (TZD) class - antidiabetic agents that have proven efficacy in the treatment of patients with type 2 diabetes. All three agents are believed to mediate their effects via activation of the gamma isoform of the peroxisome proliferator-activated receptor (PPAR gamma). Despite this common mechanism of action, they all have unique chemical structures and receptor-binding affinities, and consequently, in addition to the class effects (probably mediated through PPAR gamma), each TZD has a unique safety profile. Side effects have been categorized as unique to individual TZDs, or common to the class of drug. Of the unique effects, the best characterized is hepatotoxicity, which has been associated specifically with troglitazone to date. Studies with rosiglitazone and pioglitazone indicate that hepatotoxicity is not a class effect. Further differences in the safety profiles of these agents arise because the oxidative metabolism for each agent occurs by distinct cytochrome pathways: troglitazone and pioglitazone involve CYP 3A4 and CYP 2C8 whereas rosiglitazone is principally metabolized by CYP 2C8. CYP 3A4 is involved in the metabolism of over 150 drugs, hence the potential for drug interactions with troglitazone and pioglitazone is much greater than with rosiglitazone. Class effects include edema, slight reductions in hemoglobin and hematocrit (due to hemodilution), weight gain and alterations in plasma lipid profiles. This article considers safety data obtained from both clinical trials and clinical practice as a means of differentiating among troglitazone, rosiglitazone and pioglitazone.
Diabetes Metab Res Rev
PMID:Differentiating members of the thiazolidinedione class: a focus on safety. 1192 35

The thiazolidinediones (TZDs) or 'glitazones' are a new class of oral antidiabetic drugs that improve metabolic control in patients with type 2 diabetes through the improvement of insulin sensitivity. TZDs exert their antidiabetic effects through a mechanism that involves activation of the gamma isoform of the peroxisome proliferator-activated receptor (PPAR gamma), a nuclear receptor. TZD-induced activation of PPAR gamma alters the transcription of several genes involved in glucose and lipid metabolism and energy balance, including those that code for lipoprotein lipase, fatty acid transporter protein, adipocyte fatty acid binding protein, fatty acyl-CoA synthase, malic enzyme, glucokinase and the GLUT4 glucose transporter. TZDs reduce insulin resistance in adipose tissue, muscle and the liver. However, PPAR gamma is predominantly expressed in adipose tissue. It is possible that the effect of TZDs on insulin resistance in muscle and liver is promoted via endocrine signalling from adipocytes. Potential signalling factors include free fatty acids (FFA) (well-known mediators of insulin resistance linked to obesity) or adipocyte-derived tumour necrosis factor-alpha (TNF-alpha), which is overexpressed in obesity and insulin resistance. Although there are still many unknowns about the mechanism of action of TZDs in type 2 diabetes, it is clear that these agents have the potential to benefit the full 'insulin resistance syndrome' associated with the disease. Therefore, TZDs may also have potential benefits on the secondary complications of type 2 diabetes, such as cardiovascular disease.
Diabetes Metab Res Rev
PMID:The mode of action of thiazolidinediones. 1192 33


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