Hidenori Hirukawa

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.

Protective effects of SGLT2 inhibitor luseogliflozin on pancreatic β-cells in obese type 2 diabetic db/db mice

It is well known that Sodium-Glucose Co-transporter 2 (SGLT2) inhibitors, new hypoglycemic agents, improve glycemic control by increasing urine glucose excretion, but it remained unclear how they exert protective effects on pancreatic β-cells. In this study, we examined the effects of SGLT2 inhibitor luseogliflozin on β-cell function and mass using obese type 2 diabetic db/db mice. Ten-week-old male diabetic db/db mice were treated with luseogliflozin 0.0025% or 0.01% in chow (Luse 0.0025% or Luse 0.01%) or vehicle (control) for 4 weeks. Urinary glucose excretion was increased in Luse groups (0.0025% and 0.01%) compared to control mice 3 days after the intervention. Fasting blood glucose levels were significantly lower in mice treated with Luse compared to control mice. Fasting serum insulin concentrations were significantly higher in mice treated with Luse compared to control mice. Triglyceride levels tended to be lower in Luse groups compared to control mice. In immunohistochemical study using pancreas tissues, β-cell mass was larger in Luse groups compared to control group which was due to the increase of β-cell proliferation and decrease of β-cell apoptosis. Furthermore, in gene analysis using isolated islets, insulin 1, insulin 2, MafA, PDX-1 and GLUT2 gene expression levels were significantly higher in Luse groups compared to control group. In contrast, expression levels of fibrosis-related gene such as TGFβ, fibronectin, collagen I and collagen III were significantly lower in Luse groups. In conclusion, SGLT2 inhibitor luseogliflozin ameliorates glycemic control and thus exerts protective effects on pancreatic β-cell mass and function.

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.

Association of GA/HbA1c ratio and cognitive impairment in subjects with type 2 diabetes mellitus

AIMS The aim of this study was to search for factors influencing cognitive impairment and to clarify the association between the fluctuation of blood glucose levels and cognitive impairment in elderly Japanese subjects with type 2 diabetes. METHODS We recruited 88 relatively elderly subjects (≥65years old) with type 2 diabetes who were hospitalized in Kawasaki Medical School from January 2014 to December 2015. We evaluated the fluctuation of blood glucose levels with glycoalbumin (GA)/hemoglobin A1c (HbA1c) ratio, and estimated cognitive impairment with Hasegawa dementia scale-revised (HDS-R) score and mini mental state examination (MMSE) score. RESULTS Multivariate analyses showed that GA/HbA1c ratio and urinary albumin excretion, but not hypoglycemia, were independent determinant factors for cognitive impairment in elderly Japanese subjects with type 2 diabetes. CONCLUSIONS The fluctuation of blood glucose levels per se is closely associated with cognitive impairment in elderly subjects with type 2 diabetes even when hypoglycemia is not accompanied. Since it is very easy to calculate GA/HbA1c ratio, we should check this ratio so that we can reduce the fluctuation of blood glucose levels especially in elderly subjects with type 2 diabetes.

Influence of atherosclerosis‐related risk factors on serum high‐sensitivity C‐reactive protein levels in patients with type 2 diabetes: Comparison of their influence in obese and non‐obese patients

Increased levels of high‐sensitivity C‐reactive protein (hs‐CRP) likely leads to the development of atherosclerosis. Therefore, it is very important to know which factors largely influence hs‐CRP levels. In the present study, we examined the influence of various atherosclerosis‐related factors on hs‐CRP levels in patients with type 2 diabetes.

Promising Diabetes Therapy Based on the Molecular Mechanism for Glucose Toxicity: Usefulness of SGLT2 Inhibitors as well as Incretin-Related Drugs.

Pancreatic β-cell dysfunction and insulin resistance are the main characteristics of type 2 diabetes. Chronic exposure of β-cells to hyperglycemia leads to the deterioration of β-cell function. Such phenomena are well known as pancreatic β-cell glucose toxicity. MafA, a strong transactivator of insulin gene, is particularly important for the maintenance of mature β-cell function, but its expression level is significantly reduced under diabetic conditions which is likely associated with β-cell failure. Reduction of incretin receptor expression level in β-cells in diabetes is also likely associated with β-cell failure. On the other hand, incretin-related drugs and sodium-glucose co-transporter 2 (SGLT2) inhibitors are promising diabetes therapy based on the mechanism for pancreatic β-cell glucose toxicity. Indeed, it was shown that incretin-related drugs exerted protective effects on β-cells through the augmentation of IRS-2 expression especially in the presence of pioglitazone. It was also shown that incretin-related drug and/or pioglitazone exerted more protective effects on β-cells at the early stage of diabetes compared to the advanced stage. SGLT2 inhibitors, new hypoglycemic agents, also exert beneficial effects for the protection of pancreatic β-cells as well as for the reduction of insulin resistance in various insulin target tissues. Taken together, it is important to select appropriate therapy based on the molecular mechanism for glucose toxicity.

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.

Clinical effects of liraglutide are possibly influenced by hypertriglyceridemia and remaining pancreatic β-cell function in subjects with type 2 diabetes mellitus.

We searched for factors influencing the clinical effects of GLP-1 analogue liraglutide in subjects with type 2 diabetes. Multivariate analyses showed that hypertriglyceridemia and baseline HbA1c levels were independent predictors for the efficacy of liraglutide and that CPR index was an independent predictor for the durability of liraglutide.

Durability of protective effect of dulaglutide on pancreatic β-cells in diabetic mice: GLP-1 receptor expression is not reduced despite long-term dulaglutide exposure

AIMS It is well-known that chronic exposure to large amounts of ligand leads to downregulation of its receptor. It is not known, however, whether a GLP-1R agonist downregulates its receptor. For this reason, our study examined whether GLP-1R expression is reduced after long-term exposure to dulaglutide (Dula) in non-diabetic and diabetic mice. METHODS Seven-week-old male db/db and db/m mice were given either Dula (0.6mg/kg×2/week) or a control vehicle (CTL) for 17 weeks. Various metabolic parameters, such as glucose-stimulated insulin secretion (GSIS), insulin and TG content in islets, were evaluated after the intervention. β-cell-related gene expression was also analyzed by real-time RT-PCR. RESULTS In db/m mice, GLP-1R expression in β-cells did not decrease, not even after long-term administration of Dula, compared with control mice, while GLP-1R expression in 24-week-old db/db mice treated with Dula was augmented, rather than downregulated, compared with 24-week-old CTL db/db mice. This was probably due to improved glycaemic control. In db/db mice treated with Dula, food intake and blood glucose levels were significantly decreased up to 24 weeks of age compared with CTL db/db mice, and their expression levels of various β-cell-related genes, insulin content and GSIS were also enhanced. In contrast, oxidative and endoplasmic reticulum stress, inflammation, fibrosis and apoptosis were suppressed with Dula treatment. CONCLUSION Dula exerts beneficial effects on glycaemic control and has long-lasting protective effects on pancreatic β-cells. GLP-1R expression levels were not reduced at all in non-diabetic as well as diabetic mice despite long-term dulaglutide exposure.