Characterization of the action of S 21403 (mitiglinide) on insulin secretion and biosynthesis in normal and diabetic beta-cells

Characteristics of repaglinide effects on insulin secretion

The dynamics of insulin secretion stimulated by repaglinide, a glinide, and the combinatorial effects of repaglinide and incretin were investigated. At 4.4 mM glucose, repaglinide induced insulin secretion with a gradually increasing first phase, showing different dynamics from that induced by glimepiride, a sulfonylurea. In the presence of glucagon-like peptide-1 (GLP-1), insulin secretion by repaglinide was augmented significantly but to lesser extent and showed different dynamics from that by glimepiride. At 4.4 mM glucose, the intracellular Ca²⁺ level was gradually increased by repaglinide alone or repaglinide plus GLP-1, which differs from the Ca²⁺ dynamics by glimepiride alone or glimepiride plus GLP-1, suggesting that the difference in Ca²⁺ dynamics contributes to the difference in the dynamics of insulin secretion. At a higher concentration (8.8 mM) of glucose, the dynamics of insulin secretion stimulated by repaglinide was similar to that by glimepiride. Combination of repaglinide and GLP-1 significantly augmented insulin secretion, the amount of which was comparable to that by the combination of glimepiride and GLP-1. The Ca²⁺ dynamics was similar for repaglinide and glimepiride at 8.8 mM glucose. Our data indicate that repaglinide has characteristic properties in its effects on the dynamics of insulin secretion and intracellular Ca²⁺ and that the combination of repaglinide and GLP-1 stimulates insulin secretion more effectively than the combination of glimepiride and GLP-1 at a high concentration of glucose, providing a basis for its use in clinical settings.

Effects of mitiglinide, a short-acting insulin secretagogue, on daily glycemic variability and oxidative stress markers in Japanese patients with type 2 diabetes mellitus

BACKGROUND AND OBJECTIVE

The objective of this study was to clarify the effects of mitiglinide on daily glycemic variability and oxidative stress markers in outpatients with type 2 diabetes mellitus that is insufficiently controlled by diet and/or non-insulin secretagogues.

METHODS

We enrolled 24 patients with type 2 diabetes whose glycemic control had been suboptimal [i.e. glycosylated hemoglobin (HbA(1c)) ≥ 6.9 %]. The patients were treated with mitiglinide 10 mg three times daily for 16 weeks. If their glycemic control was not improved at week 8, the dose of mitiglinide was increased to 20 mg three times daily. Daily glycemic variability was assessed by 7-point self-monitoring of blood glucose for 2 days, and standard deviation (SD), M value, and mean of daily differences(MODD) were calculated. Oxidative stress was assessed by oxidized low-density lipoprotein, pentosidine,urinary 8-iso-prostaglandin F2 alpha, and urinary 8-hydroxydeoxy guanosine.

RESULTS

After 16 weeks of mitiglinide treatment, the HbA(1c) level was significantly decreased (mean ± SD,7.4 ± 0.7 to 6.8 ± 0.5 %, P < 0.0001). Postprandial glucose excursion and glycemic variability were also significantly improved after mitiglinide treatment (all P < 0.05). The reductions in SD, M value, and MODD were 17, 50,and 48 %, respectively. There was a significant positive correlation between the change in HbA(1c) and change in SD during the study (r = 0.454, P = 0.03). There were no significant changes in oxidative stress markers.

CONCLUSIONS

The present study supports the notion that mitiglinide improves postprandial glucose excursion and HbA(1c) level in patients with type 2 diabetes. In addition,we demonstrated that mitiglinide also effectively improves daily glycemic variability. The effect of mitiglinide on oxidative stress needs further investigation.

Comparison of the hypoglycemic effect of sitagliptin versus the combination of mitiglinide and voglibose in drug-naïve Japanese patients with type 2 diabetes

OBJECTIVE

The postprandial glucose (PPG) level is reduced by α-GIs, glinides and DPP4Is through different pharmacological actions. The aim of this study was to compare the effect of sitagliptin (S) versus that of the combination of mitiglinide and voglibose (M+V) on markers of glycemic control.

RESEARCH DESIGN AND METHODS

A randomized cross-over trial was performed in 20 patients with drug-naïve type 2 diabetes. The patients were randomized to receive S (50 mg/day) or M+V (1 tablet 3 times daily). Treatment was continued for 8 weeks, after which they were switched to the other regimen and treated for another 8 weeks. At baseline, after the first regimen, and after the second regimen, a meal test was performed.

MAIN OUTCOME MEASURES

The markers of glycemic control were examined.

RESULTS

Reduction of glucose excursion was significantly greater with M+V than with S. HbA1c did not change with either regimen. However, 1,5-anhydroglucitol showed a significant increase from baseline with both regimens (7.9 ± 4.3 μg/ml at baseline vs. 10.6 ± 5.5 with S, p < 0.05 and 15.1 ± 6.2 with M+V, p < 0.01). Compared with baseline, glycoalbumin was significantly reduced by M+V, but not S (19.6 ± 2.9% at baseline vs. 17.3 ± 3.8% with M+V, p < 0.05).

CONCLUSION

M+V achieved better control of PPG excursion than S.

Pharmacogenomic analysis of ATP-sensitive potassium channels coexpressing the common type 2 diabetes risk variants E23K and S1369A. Pharmacogenet Genomics. 2012;22:206-214. [PMID: 22209866 DOI: 10.1097/fpc.0b013e32835001e7]

OBJECTIVES

The common ATP-sensitive potassium (KATP) channel variants E23K and S1369A, found in the KCNJ11 and ABCC8 genes, respectively, form a haplotype that is associated with an increased risk for type 2 diabetes. Our previous studies showed that KATP channel inhibition by the A-site sulfonylurea gliclazide was increased in the K23/A1369 haplotype. Therefore, we studied the pharmacogenomics of seven clinically used sulfonylureas and glinides to determine their structure-activity relationships in KATP channels containing either the E23/S1369 nonrisk or K23/A1369 risk haplotypes.

RESEARCH DESIGN AND METHODS

The patch-clamp technique was used to determine sulfonylurea and glinide inhibition of recombinant human KATP channels containing either the E23/S1369 or the K23/A1369 haplotype.

RESULTS

KATP channels containing the K23/A1369 risk haplotype were significantly less sensitive to inhibition by tolbutamide, chlorpropamide, and glimepiride (IC50 values for K23/A1369 vs. E23/S1369=1.15 vs. 0.71 μmol/l; 4.19 vs. 3.04 μmol/l; 4.38 vs. 2.41 nmol/l, respectively). In contrast, KATP channels containing the K23/A1369 haplotype were significantly more sensitive to inhibition by mitiglinide (IC50=9.73 vs. 28.19 nmol/l for K23/A1369 vs. E23/S1369) and gliclazide. Nateglinide, glipizide, and glibenclamide showed similar inhibitory profiles in KATP channels containing either haplotype.

CONCLUSION

Our results demonstrate that the ring-fused pyrrole moiety in several A-site drugs likely underlies the observed inhibitory potency of these drugs on KATP channels containing the K23/A1369 risk haplotype. It may therefore be possible to tailor existing therapy or design novel drugs that display an increased efficacy in type 2 diabetes patients homozygous for these common KATP channel haplotypes.

Postprandial hyperglycemia and endothelial function in type 2 diabetes: focus on mitiglinide

The risk of cardiovascular complication in a diabetes patient is similar to that in a nondiabetic patient with a history of myocardial infarction. Although intensive control of glycemia achieved by conventional antidiabetic agents decreases microvascular complications such as retinopathy and nephropathy, no marked effect has been reported on macrovascular complications or all-cause mortality. Evidence from VADT, ACCORD, and ADVANCE would suggest that glycemic control has little effect on macrovascular outcomes. Moreover, in the case of ACCORD, intensive glycemic control may be associated with an increased risk of mortality. There is sufficient evidence that suggests that postprandial hyperglycemia may be an independent risk factor for cardiovascular disease in diabetes patients. However, there are no prospective clinical trials supporting the recommendation that lowering postprandial blood glucose leads to lower risk of cardiovascular outcomes. Mitiglinide is a short-acting insulinotropic agent used in type 2 diabetes treatment. It has a rapid stimulatory effect on insulin secretion and reduces postprandial plasma glucose level in patients with type 2 diabetes. Because of its short action time, it is unlikely to exert adverse effects related to hypoglycemia early in the morning and between meals. Mitiglinide reduces excess oxidative stress and inflammation, plays a cardioprotective role, and improves postprandial metabolic disorders. Moreover, mitiglinide add-on therapy with pioglitazone favorably affects the vascular endothelial function in type 2 diabetes patients. These data suggest that mitiglinide plays a potentially beneficial role in the improvement of postprandial hyperglycemia in type 2 diabetes patients and can be used to prevent cardiovascular diseases. Although the results of long-term, randomized, placebo-controlled trials for determining the cardiovascular effects of mitiglinide on clinical outcomes are awaited, this review is aimed at summarizing substantial insights into this topic.

The GK rat: a prototype for the study of non-overweight type 2 diabetes

Type 2 diabetes mellitus (T2D) arises when the endocrine pancreas fails to secrete sufficient insulin to cope with the metabolic demand because of β-cell secretory dysfunction and/or decreased β-cell mass. Defining the nature of the pancreatic islet defects present in T2D has been difficult, in part because human islets are inaccessible for direct study. This review is aimed to illustrate to what extent the Goto Kakizaki rat, one of the best characterized animal models of spontaneous T2D, has proved to be a valuable tool offering sufficient commonalities to study this aspect. A comprehensive compendium of the multiple functional GK abnormalities so far identified is proposed in this perspective, together with their time-course and interactions. A special focus is given toward the pathogenesis of defective β-cell number and function in the GK model. It is proposed that the development of T2D in the GK model results from the complex interaction of multiple events: (1) several susceptibility loci containing genes responsible for some diabetic traits; (2) gestational metabolic impairment inducing an epigenetic programming of the offspring pancreas and the major insulin target tissues; and (3) environmentally induced loss of β-cell differentiation due to chronic exposure to hyperglycemia/hyperlipidemia, inflammation, and oxidative stress.

Islet structure and function in the GK rat

Type 2 diabetes mellitus (T2D) arises when the endocrine pancreas fails to secrete sufficient insulin to cope with the metabolic demand because of beta-cell secretory dysfunction and/or decreased beta-cell mass. Defining the nature of the pancreatic islet defects present in T2D has been difficult, in part because human islets are inaccessible for direct study. This review is aimed to illustrate to what extent the Goto-Kakizaki rat, one of the best characterized animal models of spontaneous T2D, has proved to be a valuable tool offering sufficient commonalities to study this aspect. A comprehensive compendium of the multiple functional GK islet abnormalities so far identified is proposed in this perspective. The pathogenesis of defective beta-cell number and function in the GK model is also discussed. It is proposed that the development of T2D in the GK model results from the complex interaction of multiple events: (i) several susceptibility loci containing genes responsible for some diabetic traits (distinct loci encoding impairment of beta-cell metabolism and insulin exocytosis, but no quantitative trait locus for decreased beta-cell mass); (ii) gestational metabolic impairment inducing an epigenetic programming of the offspring pancreas (decreased beta-cell neogenesis and proliferation) transmitted over generations; and (iii) loss of beta-cell differentiation related to chronic exposure to hyperglycaemia/hyperlipidaemia, islet inflammation, islet oxidative stress, islet fibrosis and perturbed islet vasculature.