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Query: UMLS:C0011849 (diabetes)
 277,896 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

When mammals fast, glucose homeostasis is achieved by triggering expression of gluconeogenic genes in response to glucagon and glucocorticoids. The pathways act synergistically to induce gluconeogenesis (glucose synthesis), although the underlying mechanism has not been determined. Here we show that mice carrying a targeted disruption of the cyclic AMP (cAMP) response element binding (CREB) protein gene, or overexpressing a dominant-negative CREB inhibitor, exhibit fasting hypoglycaemia [corrected] and reduced expression of gluconeogenic enzymes. CREB was found to induce expression of the gluconeogenic programme through the nuclear receptor coactivator PGC-1, which is shown here to be a direct target for CREB regulation in vivo. Overexpression of PGC-1 in CREB-deficient mice restored glucose homeostasis and rescued expression of gluconeogenic genes. In transient assays, PGC-1 potentiated glucocorticoid induction of the gene for phosphoenolpyruvate carboxykinase (PEPCK), the rate-limiting enzyme in gluconeogenesis. PGC-1 promotes cooperativity between cyclic AMP and glucocorticoid signalling pathways during hepatic gluconeogenesis. Fasting hyperglycaemia is strongly correlated with type II diabetes, so our results suggest that the activation of PGC-1 by CREB in liver contributes importantly to the pathogenesis of this disease.
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PMID:CREB regulates hepatic gluconeogenesis through the coactivator PGC-1. 1155 65

In vitro, the transcription factor sterol regulatory element binding protein-1c (SREBP-1c) mimics the positive effects of insulin on hepatic genes involved in glucose utilization, such as glucokinase (GK) and enzymes of the lipogenic pathway, suggesting that it is a key factor in the control of hepatic glucose metabolism. Decreased glucose utilization and increased glucose production by the liver play an important role in the development of the hyperglycemia in diabetic states. We thus reasoned that if SREBP-1c is indeed a mediator of hepatic insulin action, a hepatic targeted overexpression of SREBP-1c should greatly improve glucose homeostasis in diabetic mice. This was achieved by injecting streptozotocin-induced diabetic mice with a recombinant adenovirus containing the cDNA of the mature, transcriptionally active form of SREBP-1c. We show here that overexpressing SREBP-1c specifically in the liver of diabetic mice induces GK and lipogenic enzyme gene expression and represses the expression of phosphoenolpyruvate carboxykinase, a key enzyme of the gluconeogenic pathway. This in turn increases glycogen and triglyceride hepatic content and leads to a marked decrease in hyperglycemia in diabetic mice. We conclude that SREBP-1c has a major role in vivo in the long-term control of glucose homeostasis by insulin.
Diabetes 2001 Nov
PMID:Adenovirus-mediated overexpression of sterol regulatory element binding protein-1c mimics insulin effects on hepatic gene expression and glucose homeostasis in diabetic mice. 1167 17

Type 2 diabetes is characterized by the inability of insulin to suppress glucose production in the liver and kidney. Insulin inhibits glucose production by indirect and direct mechanisms. The latter result in transcriptional suppression of key gluconeogenetic and glycogenolytic enzymes, phosphoenolpyruvate carboxykinase (Pepck) and glucose-6-phosphatase (G6p). The transcription factors required for this effect are incompletely characterized. We report that in glucogenetic kidney epithelial cells, Pepck and G6p expression are induced by dexamethasone (dex) and cAMP, but fail to be inhibited by insulin. The inability to respond to insulin is associated with reduced expression of the forkhead transcription factor Foxo1, a substrate of the Akt kinase that is inhibited by insulin through phosphorylation. Transduction of kidney cells with recombinant adenovirus encoding Foxo1 results in insulin inhibition of dex/cAMP-induced G6p expression. Moreover, expression of dominant negative Foxo1 mutant results in partial inhibition of dex/cAMP-induced G6p and Pepck expression in primary cultures of mouse hepatocyes and kidney LLC-PK1-FBPase(+) cells. These findings are consistent with the possibility that Foxo1 is involved in insulin regulation of glucose production by mediating the ability of insulin to decrease the glucocorticoid/cAMP response of G6p.
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PMID:The forkhead transcription factor Foxo1 (Fkhr) confers insulin sensitivity onto glucose-6-phosphatase expression. 1169 81

The effect of tramadol on the plasma glucose level of streptozotocin (STZ)-induced diabetic rats was investigated. A dose-dependent lowering of plasma glucose was seen in the fasting STZ-induced diabetic rats 30 min after intravenous injection of tramadol. This effect of tramadol was abolished by pretreatment with naloxone or naloxonazine at doses sufficient to block opioid mu-receptors. However, response to tramadol was not changed in STZ-induced diabetic rats receiving p-chlorophenylalanine at a dose sufficient to deplete endogenous 5-hydroxytrptamine (5-HT). Therefore, mediation of 5-HT in this action of tramadol is ruled out. In isolated soleus muscle, tramadol enhanced the uptake of radioactive glucose in a concentration-dependent manner. The stimulatory effects of tramadol on glycogen synthesis were also seen in hepatocytes isolated from STZ-induced diabetic rats. The blockade of these actions by naloxone and naloxonazine indicated the mediation of opioid mu-receptors. The mRNA and protein levels of the subtype 4 form of glucose transporter in soleus muscle were increased after repeated treatments for 4 days with tramadol in STZ-induced diabetic rats. Moreover, similar repeated treatments with tramadol reversed the elevated mRNA and protein levels of phosphoenolpyruvate carboxykinase in the liver of STZ-induced diabetic rats. These results suggest that activation of opioid mu-receptors by tramadol can increase the utilization of glucose and/or decrease hepatic gluconeogenesis to lower plasma glucose in diabetic rats lacking insulin.
Diabetes 2001 Dec
PMID:Plasma glucose-lowering effect of tramadol in streptozotocin-induced diabetic rats. 1172 65

Regulation of the turnover of triglycerides in adipose tissue requires the continuous provision of 3-glycerophosphate, which may be supplied by the metabolism of glucose or by glyceroneogenesis, the de novo synthesis of 3-glycerophosphate from sources other than hexoses or glycerol. The importance of glyceroneogenesis in adipose tissue was assessed in mice by specifically eliminating the expression of the cytosolic form of phosphoenolpyruvate carboxykinase (PEPCK-C), an enzyme that plays a pivotal role in the pathway. To accomplish this, we mutated the binding site for the peroxisome proliferator-activated receptor gamma (PPAR gamma) called the peroxisome proliferator-activated receptor element (PPARE), in the 5' flanking region of the PEPCK-C gene in the mouse by homologous recombination. The mutation abolished expression of the gene in white adipose tissue and considerably reduced its expression in brown adipose tissue, whereas the level of PEPCK-C mRNA in liver and kidney remained normal. Epididymal white adipose tissue from these mice had a reduced triglyceride deposition, with 25% of the animals displaying lipodystrophy. There was also a greatly reduced level of lipid accumulation in brown adipose tissue. A strong correlation between the hepatic content of triglycerides and the size of the epididymal fat pad in PPARE(-/-) mice suggests that hepatic triglyceride synthesis predominantly utilizes free fatty acids derived from the adipose tissue. Unlike other models, PPARE(-/-) mice with lipodystrophy did not exhibit the lipodystrophy-associated features of diabetes and displayed only moderate hyperglycemia. These studies establish the importance of the PPARE site for PEPCK-C gene expression in adipose tissue and the role of PEPCK-C in the regulation of glyceroneogenesis, a pathway critical for maintaining the deposition of triglycerides in adipose tissue.
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PMID:A mutation in the peroxisome proliferator-activated receptor gamma-binding site in the gene for the cytosolic form of phosphoenolpyruvate carboxykinase reduces adipose tissue size and fat content in mice. 1179 50

Prohormone convertase 2 (PC2) plays an essential role in the processing of proglucagon to mature active glucagon in pancreatic alpha-cells (J Biol Chem 276:27197-27202, 2001). Mice lacking PC2 demonstrate multiple defects, including chronic mild hypoglycemia and dramatic hyperplasia of the pancreatic alpha-cells. To define the contribution of mature glucagon deficiency to the hypoglycemia and alpha-cell hyperplasia, we have attempted to correct the defects by delivery of exogenous glucagon by micro-osmotic pumps. Intraperitoneal delivery of 0.5 microg glucagon/h in PC2(-/-) mice resulted in the normalization of blood glucose concentrations. Islet remodeling through the loss of hyperplastic alpha-cells was evident by day 11 after pump implantation; by 25 days postimplantation, PC2(-/-) islets were indistinguishable from wild-type islets. These rapid changes were brought about by induction of apoptosis in the alpha-cell population. Morphological normalization of islets was also accompanied by marked downregulation of endogenous preproglucagon gene expression, but with little or no change in the level of preproinsulin gene expression. Exogenous glucagon delivery also normalized hepatic expression of the gluconeogenic enzyme PEPCK. These results demonstrate that the lack of mature glucagon in PC2(-/-) mice is responsible for the aberrant blood glucose levels, islet morphology, and gene expression, and they confirm the role of glucagon as a tonic insulin antagonist in regulating glycemia.
Diabetes 2002 Feb
PMID:Glucagon replacement via micro-osmotic pump corrects hypoglycemia and alpha-cell hyperplasia in prohormone convertase 2 knockout mice. 1181 47

We report crystal structures of the human enzyme phosphoenolpyruvate carboxykinase (PEPCK) with and without bound substrates. These structures are the first to be determined for a GTP-dependent PEPCK, and provide the first view of a novel GTP-binding site unique to the GTP-dependent PEPCK family. Three phenylalanine residues form the walls of the guanine-binding pocket on the enzyme's surface and, most surprisingly, one of the phenylalanine side-chains contributes to the enzyme's specificity for GTP. PEPCK catalyzes the rate-limiting step in the metabolic pathway that produces glucose from lactate and other precursors derived from the citric acid cycle. Because the gluconeogenic pathway contributes to the fasting hyperglycemia of type II diabetes, inhibitors of PEPCK may be useful in the treatment of diabetes.
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PMID:Crystal structure of human cytosolic phosphoenolpyruvate carboxykinase reveals a new GTP-binding site. 1185 36

Adipose tissue glyceroneogenesis generates glycerol 3-phosphate, which could be used for fatty acid esterification during starvation. To determine whether increased glyceroneogenesis leads to increased fat mass and to explore the role of obesity in the development of insulin resistance, we overexpressed PEPCK, a regulatory enzyme of glyceroneogenesis in adipose tissue. Transgenic mice showed a chronic increase in PEPCK activity, which led to increased glyceroneogenesis, re-esterification of free fatty acids (FFAs), increased adipocyte size and fat mass, and higher body weight. In spite of increased fat mass, transgenic mice showed decreased circulating FFAs and normal leptin levels. Moreover, glucose tolerance and whole-body insulin sensitivity were preserved. Skeletal muscle basal and insulin-stimulated glucose uptake and glycogen content were not affected, suggesting that skeletal muscle insulin sensitivity is normal in transgenic obese mice. Our results indicate the key role of PEPCK in the control of FFA re-esterification in adipose tissue and, thus, the contribution of glyceroneogenesis to fat accumulation. Moreover, they suggest that higher fat mass without increased circulating FFAs does not lead to insulin resistance or type 2 diabetes in these mice.
Diabetes 2002 Mar
PMID:Increased fatty acid re-esterification by PEPCK overexpression in adipose tissue leads to obesity without insulin resistance. 1187 59

Herbs have been used for medicinal purposes, including the treatment of diabetes, for centuries. Plants containing flavonoids are used to treat diabetes in Indian medicine and the green tea flavonoid, epigallocatechin gallate (EGCG), is reported to have glucose-lowering effects in animals. We show here that the regulation of hepatic glucose production is decreased by EGCG. Furthermore, like insulin, EGCG increases tyrosine phosphorylation of the insulin receptor and insulin receptor substrate-1 (IRS-1), and it reduces phosphoenolpyruvate carboxykinase gene expression in a phosphoinositide 3-kinase-dependent manner. EGCG also mimics insulin by increasing phosphoinositide 3-kinase, mitogen-activated protein kinase, and p70(s6k) activity. EGCG differs from insulin, however, in that it affects several insulin-activated kinases with slower kinetics. Furthermore, EGCG regulates genes that encode gluconeogenic enzymes and protein-tyrosine phosphorylation by modulating the redox state of the cell. These results demonstrate that changes in the redox state may have beneficial effects for the treatment of diabetes and suggest a potential role for EGCG, or derivatives, as an antidiabetic agent.
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PMID:Epigallocatechin gallate, a constituent of green tea, represses hepatic glucose production. 1211 6

The effects of benfluorex and two of its metabolites (S 422-1 and S 1475-1) on fatty acid and glucose metabolic fluxes and specific gene expression were studied in hepatocytes isolated from 24-h fasted rats. Both benfluorex and S 422-1 (0.1 or 1 mmol/l) reduced beta-oxidation rates and ketogenesis, whereas S 1475-1 had no effect. At the same concentration, benfluorex and S 422-1 were more efficient in reducing gluconeogenesis from lactate/pyruvate than S 1475-1. Benfluorex inhibited gluconeogenesis at the level of pyruvate carboxylase (45% fall in acetyl-CoA concentration) and of glyceraldehyde-3-phosphate dehydrogenase (decrease in ATP/ADP and NAD(+)/NADH ratios). Accordingly, neither benfluorex nor S 422-1 inhibited gluconeogenesis from dihydroxyacetone, but both stimulated gluconeogenesis from glycerol. In hepatocytes cultured in the presence of benfluorex or S 422-1 (10 or 100 micromol/l), the expression of genes encoding enzymes of fatty acid oxidation (carnitine palmitoyltransferase [CPT] I), ketogenesis (hydroxymethylglutaryl-CoA synthase), and gluconeogenesis (glucose-6-phosphatase, PEPCK) was decreased, whereas mRNAs encoding glucokinase and pyruvate kinase were increased. By contrast, Glut-2, acyl-CoA synthetase, and CPT II gene expression was not affected by benfluorex or S 422-1. In conclusion, this work suggests that benfluorex mainly via S 422-1 reduces gluconeogenesis by affecting gene expression and metabolic status of hepatocytes.
Diabetes 2002 Aug
PMID:Effects of benfluorex on fatty acid and glucose metabolism in isolated rat hepatocytes: from metabolic fluxes to gene expression. 1214 46


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