Involvement of low adiponectin levels in impaired glucose tolerance.

To investigate the association between serum adiponectin levels and 2-hour post-75-g oral glucose load glycemia, we conducted 75-g oral glucose tolerance tests in 50 subjects who had been diagnosed as having impaired glucose tolerance (IGT) within the prior 3 years. When adjusted for age, body mass index, and sex, serum adiponectin levels in the IGT and diabetes mellitus groups were significantly lower than those in the normal glucose tolerance and impaired fasting glucose groups (P < .0001). To determine which variables had significant impacts on 2-hour post-oral glucose glycemia, we performed multiple regression analyses. In stepwise analysis, serum adiponectin levels showed the highest F value (F = 6.43), suggesting the adiponectin level to be an independent predictor of 2-hour post-oral glucose glycemia. Thus, our clinical data suggest the involvement of low adiponectin levels in IGT and diabetes mellitus. To further assess this possibility, we prepared mice fed a high-fat diet for 2 months as an IGT model. Afterward, we compared the 2-hour postglucose glycemia in the IGT mice overexpressing recombinant adiponectin with that in control IGT mice. Mice overexpressing adiponectin showed significantly blunted 2-hour postglucose glycemia (5.66 +/- 0.39 mmol/L) as compared with control mice (8.52 +/- 0.67 mmol/L), whereas fasting glycemia was not significantly altered by adiponectin overexpression. Taken together, our results reveal the plasma glucose level in response to a glucose load to be negatively associated with serum adiponectin levels, suggesting low adiponectin levels to be one of the predictors of abnormal glucose homeostasis in IGT.

Identification of a novel WFS1 mutation (AFF344-345ins) in Japanese patients with Wolfram syndrome.

Wolfram syndrome (WFS) is an autosomal recessive disorder characterized by early onset diabetes mellitus, progressive optic atrophy, sensorineural deafness and diabetes insipidus. Affected individuals may also have renal tract abnormalities as well as neurogical and psychiatric syndromes. WFS1 encoding a transmembrane protein was identified as the gene responsible for WFS. We report herein a Japanese family, of which two members had this syndrome. In the WFS1 gene of these patients, we identified a novel mutation, a nine nucleotide insertion (AFF344-345ins). In addition, one of these patients had preclinical hypopituitarism, which is an unusual feature of WFS. As only the two family members homozygous for the mutation showed WFS, these data support the notion that this mutation is the cause of WFS.

Functional VEGF C-634G polymorphism is associated with development of diabetic macular edema and correlated with macular retinal thickness in type 2 diabetes.

Since vascular endothelial growth factor (VEGF) has a strong effect on induction of vascular permeability, VEGF is an attractive candidate gene for development of diabetic macular edema (ME). Among the 378 patients with type 2 diabetes studied, 203 patients had no retinopathy, 93 had non-proliferative diabetic retinopathy (NPDR), and 82 had proliferative diabetic retinopathy (PDR). ME was present in 16 patients with NPDR and 47 patients with PDR. We genotyped three VEGF polymorphisms: C-2,578A, G-1,154A, and C-634G. Genotype and allele distribution of C-634G, but not C-2,578A or G-1,154A, were significantly different between patients with and without diabetic retinopathy. Logistic regression analysis revealed that the C-634G genotype was a risk factor for DR (p = 0.002), and furthermore for ME (p = 0.047), independently from severity of DR, with the -634C allele increasing the risk. Macular thickness measured by optical coherence tomography was correlated with the C-634G genotype, with the trend increasing with the presence of more -634C alleles (p = 0.006). Stepwise regression analysis showed that duration of diabetes and presence of the C-634G genotype were independent predictors of macular thickness. In addition, basic transcriptional activity levels associated with the -634C allele were greater compared to those seen with the -634G allele in human glioma and lymphoblastic T-lymphocyte cells. These results demonstrate that the VEGF C-634G polymorphism is a genetic risk factor for ME as well as DR.

Efficacy of glimepiride in Japanese type 2 diabetic subjects.

We investigated the efficacy of glimepiride, a third-generation sulfonylurea (SU), in Japanese type 2 diabetic patients in whom glycemic control had been inadequate with a conventional SU, gliclazide or glibenclamide. A total of 172 Japanese type 2 diabetic patients (HbA1C > or = 7.0%), maintained on a conventional SU, were randomly assigned to the 3rd SU group (SU treatments switched to glimepiride) or the 2nd SU group (treatments not changed). The conventional SU was switched to the indicated doses of glimepiride (gliclazide 40 mg = glimepiride 1 mg, glibenclamide 2.5 mg = glimepiride 2 mg). After 6 months, glycemic control (HbA1C and fasting plasma glucose) had not changed significantly in either the 2nd or the 3rd SU group. The homeostasis assessment model of insulin resistance (HOMA-IR) in the 3rd SU group was decreased by more than 10% (p = 0.015), whereas no change was observed in the 2nd SU group. The triglyceride level was decreased by approximately 10% in the 3rd SU group, not a significant change (p = 0.080). Patients who had been treated with only SU, or treated with SU for a short time (less than 5 years), and who were also obese (BMI > or = 25) or had a high HOMA-IR (HOMA-IR > or = 3), showed significantly reduced insulin resistance. According to logistic regression analysis, high BMI ( > or = 25) was the only variable predicting that glimepiride would more effectively improve HbA1C than conventional SU treatment. In conclusion, switching conventional SUs to glimepiride reduced insulin resistance without improving glycemic control. A notable finding of this study is that glimepiride was more beneficial in obese than in non-obese Japanese type 2 diabetic patients.

Glimepiride enhances intrinsic peroxisome proliferator-activated receptor-gamma activity in 3T3-L1 adipocytes.

Glimepiride, a third-generation sulfonylurea (SU), exerts its effects mainly by stimulating insulin secretion but has also been shown to have pleiotropic effects. Recent clinical studies showed glimepiride to enhance insulin sensitivity. In the present study, to clarify the mechanism by which insulin resistance is improved, we investigated the effects of glimepiride on AMP-activated protein kinase (AMPK) and peroxisome proliferator-activated receptor-gamma (PPAR gamma) activity, using cultured adipocytes and muscle cells. When we treated fully differentiated 3T3-L1 adipocytes with 1 microM glimepiride, endogenous PPAR gamma transcriptional activity was significantly elevated, while AICAR-induced phosphorylation of AMPK was not affected in differentiated C2C12 myoblasts. The maximum PPAR gamma activity enhancing effect of glimepiride is approximately 20% that of 1 microM pioglitazone. In contrast, this mild PPAR gamma-stimulatory effect was not observed under the same conditions with a 2nd generation SU, glibenclamide. Furthermore, with glimepiride treatment, transcriptional levels of aP2, the adipogenic marker gene, were increased 2.4- and 3.7-fold in 3T3-L1 adipocytes and fibroblasts, respectively. Analysis of triglyceride contents revealed glimepiride to promote differentiation of 3T3-L1 adipocytes. These results indicate that glimepiride has the potential to induce PPAR gamma activity, thereby improving insulin resistance.

Regulation of adiponectin receptor gene expression in diabetic mice.

Adiponectin is an adipocyte-derived factor that plays pivotal roles in lipid and glucose metabolism in muscle and liver. The following two adiponectin receptor types were recently identified: AdipoR1 is abundantly expressed in muscle, whereas AdipoR2 is predominantly expressed in the liver. To clarify the regulation of adiponectin receptor gene expression in diabetic states, we examined mRNA levels of AdipoR1 in the muscles of diabetic animals by Northern blotting. The level of AdipoR1 mRNA was increased approximately 2.5-fold in muscle of streptozotocin (STZ) diabetic mice, but the normal level was restored by insulin administration, indicating that insulin has an inhibitory effect on AdipoR1 expression. To confirm this inhibitory effect of insulin, we performed in vitro experiments using C2C12 skeletal muscle cells. Insulin treatment for 24 h decreased AdipoR1 expression by approximately 60% in C2C12 cells. In addition, this effect was mediated by the phosphatidylinositol 3-kinase-dependent pathway rather than the mitogen-activated protein kinase pathway. AdipoR1 expression in insulin-resistant diabetic mice was also investigated. AdipoR1 expression was decreased by 36% in type 2 diabetic obese db/db mice compared with lean mice. In contrast, hepatic AdipoR2 expression was not significantly changed in either STZ mice or genetically obese mice. Our results indicate that regulation of AdipoR1, but not that of AdipoR2, may be involved in glucose and lipid metabolism in diabetic states.

Endothelial nitric oxide synthase gene is associated with diabetic macular edema in type 2 diabetes.

OBJECTIVE: We examined the endothelial nitric oxide (eNOS) gene polymorphisms to assess its possible association with diabetic retinopathy and macular edema. RESEARCH DESIGN AND METHODS: A total of 226 patients with type 2 diabetes and 186 healthy subjects were studied. Type 2 diabetic patients consisted of 110 patients without retinopathy, 46 patients with nonproliferative diabetic retinopathy, and 71 patients with proliferative diabetic retinopathy. Diabetic macular edema was present in 48 patients. Three polymorphisms of the eNOS gene were determined: T-786C in the promoter region, 27-bp repeat in intron 4, and Glu298Asp in exon 7. RESULTS: Close linkage disequilibrium was observed between the T-786C polymorphism and the 27-bp repeat, as has been previously reported, but Glu298Asp was not in linkage disequilibrium with the other two polymorphisms. The eNOS gene polymorphisms were not significantly associated with the presence of retinopathy or with retinopathy severity or type 2 diabetes itself. However, by both association study and multiple logistic regression analysis, the T-786C and 27-bp repeat polymorphisms were significantly associated with a risk of developing macular edema with the -786C allele and the "a" allele increasing the risk. CONCLUSIONS: The present study suggests that the eNOS gene is a novel genetic risk factor for diabetic macular edema. The eNOS gene polymorphisms may contribute to the development of macular edema by impairing basal eNOS expression and resulting in the breakdown of the blood-retina barrier.

ANGPTL3 is increased in both insulin-deficient and -resistant diabetic states.

Angiopoietin-like protein 3 (ANGPTL3) is secreted by the liver and was recently postulated to be an important hormone regulating serum triglyceride levels. In the present study, in order to clarify the regulation of ANGPTL3 gene expression in diabetic states, we examined mRNA and protein levels of ANGPTL3 in the livers of diabetic animals. The level of ANGPTL3 mRNA was increased approximately 2.2-fold in the livers of streptozotocin (STZ) diabetic mice, and this effect was reversed by administration of insulin. Furthermore, the level of ANGPTL3 mRNA was increased more than 3.0-fold in type 2 diabetic obese mice, db/db mice, as compared with age matched lean littermates. The hepatic level of ANGPTL3 protein was also increased in these diabetic mice to an extent similar to that of ANGPTL3 mRNA. Thus, the expression of ANGPTL3 was enhanced in both insulin-deficient and -resistant diabetic states. These results strongly suggest ANGPTL3 to play an important role in hyperlipidemia in diabetes.