Kazuhito Tawaramoto

Molecular mechanism by which pioglitazone preserves pancreatic β-cells in obese diabetic mice: evidence for acute and chronic actions as a PPARγ agonist

Pioglitazone preserves pancreatic β-cell morphology and function in diabetic animal models. In this study, we investigated the molecular mechanisms by which pioglitazone protects β-cells in diabetic db/db mice. In addition to the morphological analysis of the islets, gene expression profiles of the pancreatic islet were analyzed using laser capture microdissection and were compared with real-time RT-PCR of db/db and nondiabetic m/m mice treated with or without pioglitazone for 2 wk or 2 days. Pioglitazone treatment (2 wk) ameliorated dysmetabolism, increased islet insulin content, restored glucose-stimulated insulin secretion, and preserved β-cell mass in db/db mice but had no significant effects in m/m mice. Pioglitazone upregulated genes that promote cell differentiation/proliferation in diabetic and nondiabetic mice. In db/db mice, pioglitazone downregulated the apoptosis-promoting caspase-activated DNase gene and upregulated anti-apoptosis-related genes. The above-mentioned effects of pioglitazone treatment were also observed after 2 days of treatment. By contrast, the oxidative stress-promoting NADPH oxidase gene was downregulated, and antioxidative stress-related genes were upregulated, in db/db mice treated with pioglitazone for 2 wk, rather than 2 days. Morphometric results for proliferative cell number antigen and 4-hydroxy-2-noneal modified protein were consistent with the results of gene expression analysis. The present results strongly suggest that pioglitazone preserves β-cell mass in diabetic mice mostly by two ways; directly, by acceleration of cell differentiation/proliferation and suppression of apoptosis (acute effect); and indirectly, by deceleration of oxidative stress because of amelioration of the underlying metabolic disorder (chronic effect).

Vildagliptin preserves the mass and function of pancreatic β cells via the developmental regulation and suppression of oxidative and endoplasmic reticulum stress in a mouse model of diabetes

We investigated the molecular mechanisms by which vildagliptin preserved pancreatic β cell mass and function.

Protective effects of pioglitazone and/or liraglutide on pancreatic β-cells in db/db mice: Comparison of their effects between in an early and advanced stage of diabetes.

The aim was to compare the protective effects of pioglitazone (PIO) and/or liraglutide (LIRA) on β-cells with the progression of diabetes. Male db/db mice were treated with PIO and/or LIRA for 2 weeks in an early and advanced stage. In an early stage insulin biosynthesis and secretion were markedly increased by PIO and LIRA which was not observed in an advanced stage. In concomitant with such phenomena, expression levels of various β-cell-related factors were up-regulated by PIO and LIRA only in an early stage. Furthermore, β-cell mass was also increased by the treatment only in an early stage. Although there was no difference in apoptosis ratio between the two stages, β-cell proliferation was augmented by the treatment only in an early stage. In conclusion, protective effects of pioglitazone and/or liraglutide on β-cells were more powerful in an early stage of diabetes compared to an advanced stage.

Effects of sulfonylurea drugs on adiponectin production from 3T3-L1 adipocytes: Implication of different mechanism from pioglitazone

Adiponectin is a fat-derived cytokine with anti-diabetic and anti-atherogenic properties. In this study, effects of sulfonylureas (SUs) on adiponectin production and the action mechanism were evaluated using 3T3-L1 adipocytes. The cells were incubated with glimepiride, glibenclamide, gliclazide, pioglitazone, metformin and the medium only as the control. In the control, the adiponectin level evaluated as the production rate per 24 h was not changed, while pioglitazone significantly increased the adiponectin level. SUs also increased the adiponectin level, but metformin failed to show any increase in adiponectin production. SUs induced adiponectin gene expression as well as pioglitazone. Pioglitazone significantly increased adipogenesis, but glimepiride did not. The aP2 gene expression was increased by pioglitazone, but not by glimepiride. Forskolin, a protein kinase A stimulator, reduced the adiponectin production stimulated by glimepiride but not by pioglitazone. These observations strongly suggest that SUs stimulate the adiponectin production through a different mechanism from pioglitazone, namely an interaction with protein kinase A activity. The significance of the extrapancreatic action of SUs observed in this study should be further evaluated in the clinical field.

Low bilirubin levels are an independent risk factor for diabetic retinopathy and nephropathy in Japanese patients with type 2 diabetes.

Diabetes & Metabolism - In Press.Proof corrected by the author Available online since lundi 8 juin 2015

Ice Cube Tray–Shaped Insulin Lipoatrophy Throughout the Abdomen in a Subject With Type 2 Diabetes

A 71-year-old woman with type 2 diabetes was referred to our hospital because of severe lipoatrophy throughout the whole abdomen induced by insulin therapy. The patient was diagnosed with type 2 diabetes when she was 63 years old and was treated with diet therapy only. When she was 69, her glycemic control became poor and insulin therapy was introduced (before breakfast, 20 units biphasic insulin Novolin 30R). Just after treatment began, she noticed that her abdomen gradually became atrophic, but she left it as it was. HbA1c levels were ∼8–9% (64–75 mmol/mol). She was treated only with biphasic insulin, and other antidiabetes agents were not used. Since her understanding about diabetes was poor, it was possible that she forgot to rotate the insulin injection site. When she was 71 years old, her glycemic control became …

Self-inducible secretion of glucagon-like peptide-1 (GLP-1) that allows MIN6 cells to maintain insulin secretion and insure cell survival.

Based on the hypothesis that MIN6 cells could produce glucagon-like peptide-1 (GLP-1) to maintain cell survival, we analyzed the effects of GLP-1 receptor agonist, exendin-4 (Ex4), and antagonist, exendin-(9-39) (Ex9) on cell function and cell differentiation. MIN6 cells expressed proglucagon mRNAs and produced GLP-1, which was accelerated by Ex4 and suppressed by Ex9. Moreover, Ex4 further enhanced glucose-stimulated GLP-1 secretion, suggesting autocrine loop-contributed amplification of the GLP-1 signal. Ex4 up-regulated cell differentiation- and cell function-related CREBBP, Pdx-1, Pax6, proglucagon, and PC1/3 gene expressions. The confocal laser scanning images revealed that GLP-1 positive cells were dominant in the early stage of cells, but positive for insulin were more prominent in the mature stage of cells. Ex4 accelerated cell viability, while Ex9 and anti-GLP-1 receptor antibody enhanced cell apoptosis. MIN6 cells possess a mechanism of GLP-1 signal amplification in an autocrine fashion, by which the cells maintained insulin production and cell survival.

Dietary restriction preserves the mass and function of pancreatic β cells via cell kinetic regulation and suppression of oxidative/ER stress in diabetic mice.

To assess the molecular mechanisms by which dietary restriction preserves the β-cell mass and function in diabetic db/db mice. Male db/db mice were divided into two groups with or without diet restriction. Daily food intake of db/db mice was adjusted to that of the control db/m mice, which was determined in advance. A dietary restriction was implemented for 6 weeks from 6 weeks of age. Islet morphology, β-cell function and gene expression profiles specific for pancreatic islet cells were compared. Food intake in db/m mice was 50% of that in db/db mice. Impaired glucose tolerance and insulin sensitivity were significantly ameliorated in db/db mice with dietary restriction. The pancreatic β-cell mass was greater in mice with dietary restriction than that in mice without intervention. The dietary restriction significantly increased cyclin D gene expression and down-regulated CAD gene expression at 12 weeks compared with untreated db/db mice. Antiapoptotic bcl-2 gene expression was significantly increased, whereas genes related to oxidative stress, ER stress and inflammatory processes, such as NADPH oxidase, CHOP10 and TNF, were markedly down-regulated in mice with dietary restriction. Dietary restriction preserved the pancreatic β-cell function and β-cell mass in diabetic db/db mice, suggesting that alimentary therapy prevented β-cell loss by suppressing cellular apoptosis and antioxidative stress in the pancreatic β cells.

Ablation of 3-Phosphoinositide-Dependent Protein Kinase 1 (PDK1) in Vascular Endothelial Cells Enhances Insulin Sensitivity by Reducing Visceral Fat and Suppressing Angiogenesis

The phosphatidylinositol 3-kinase signaling pathway in vascular endothelial cells is important for systemic angiogenesis and glucose metabolism. In this study, we addressed the precise role of the 3-phosphoinositide-dependent protein kinase 1 (PDK1)-regulated signaling network in endothelial cells in vivo, using vascular endothelial PDK1 knockout (VEPDK1KO) mice. Surprisingly, VEPDK1KO mice manifested enhanced glucose tolerance and whole-body insulin sensitivity due to suppression of their hepatic glucose production with no change in either peripheral glucose disposal or even impaired vascular endothelial function at 6 months of age. When mice were fed a standard diet at 6 months of age and a high-fat diet at 3 months of age, hypertrophy of epididymal adipose tissues was inhibited, adiponectin mRNA was significantly increased, and mRNA of MCP1, leptin, and TNFα was decreased in the white adipose tissue of VEPDK1KO mice in comparison with controls. Consequently, both the circulating adiponectin levels and the activity of hepatic AMP-activated protein kinase were significantly increased, subsequently enhancing whole-body insulin sensitivity and energy expenditure with increased hepatic fatty acid oxidation in VEPDK1KO mice. These results provide the first in vivo evidence that lowered angiogenesis through the deletion of PDK1 signaling not only interferes with the growth of adipose tissue but also induces increased energy expenditure due to amelioration of the adipocytokine profile. This demonstrates an unexpected role of PDK1 signaling in endothelial cells on the maintenance of proper glucose homeostasis through the regulation of adipocyte development.

Concomitant use of miglitol and mitiglinide as initial combination therapy in type 2 diabetes mellitus.

AIM To evaluate the efficacy of miglitol and mitiglinide alone or in combination on the metabolic profile and incretin secretion in Japanese type 2 diabetes patients. METHODS Patients on diet and exercise with or without metformin, were randomized to receive either miglitol, mitiglinide, or a combination, three times daily for 12 weeks. RESULTS At 12 weeks, HbA1c decreased significantly (p<0.001) and 1,5-AG increased significantly (p<0.001) in all three groups, with the greatest change seen with combination therapy. Effective improvement of postprandial hyperglycemia was demonstrated by a meal-loading test in all three interventions but serum insulin concentration was not increased by miglitol. In a subset of patients without prior metformin administration, faster and better glycemic control was achieved with the initial combination. After meal loading, serum total GLP-1 significantly increased only with miglitol monotherapy (p<0.05) and serum total GIP significantly decreased (p<0.01) in the arms employing miglitol after 12 weeks. CONCLUSION Miglitol/mitiglinide combination is more potent than monotherapy in improving glycemic control through the reduction of postprandial glucose excursion and the simultaneous sparing of additional insulin secretion. A marked difference in the effects of miglitol and mitiglinide on incretin secretion was also demonstrated.