Since the insulin receptor substrate-1 (IRS-1) is the major substrate of the insulin receptor tyrosine kinase and has been shown to activate phosphatidylinositol (PI) 3-kinase and promote GLUT4 translocation, the IRS-1 gene is a potential candidate for development of non-insulin-dependent diabetes mellitus (NIDDM). In this study, we have identified IRS-1 gene polymorphisms, evaluated their frequencies in Japanese subjects, and analysed the contribution of these polymorphisms to the development of NIDDM. The entire coding region of the IRS-1 gene of 94 subjects (47 NIDDM and 47 control subjects) was screened by polymerase chain reaction-single stranded conformation polymorphism (PCR-SSCP) analysis. Seven SSCP polymorphisms were identified. These corresponded to two previously identified polymorphisms [Gly971 --> Arg (GGG --> AGG) and Ala804 (GCA --> GCG)] as well as five novel polymorphisms [Pro190 --> Arg (CCC --> CGC), Met209 --> Thr (ATG --> ACG), Ser809 --> Phe (TCT --> TTT), Leu142 (CTT --> CTC), and Gly625 (GGC --> GGT)]. Although the prevalence of each of these polymorphisms was not statistically different between NIDDM and control subjects, the prevalence of the four IRS-1 polymorphisms with an amino acid substitution together was significantly higher in NIDDM than in control subjects (23.4 vs 8.5%, p < 0.05), and two substitutions (Met 209 --> Thr and Ser809 --> Phe) were found only in NIDDM patients. Equilibrium glucose infusion rates during a euglycaemic clamp in NIDDM and control subjects with the IRS-1 polymorphisms decreased by 29.5 and 22.0%, respectively on the average when compared to those in comparable groups without polymorphisms, although they were not statistically significant. Thus, IRS-1 polymorphisms may contribute in part to the insulin resistance and development of NIDDM in Japanese subjects; however, they do not account for the major part of the decrease in insulin-stimulated glucose uptake which is observed in subjects with clinically apparent NIDDM.

Aims/IntroductionThe aim of the present prospective observational study was to assess long‐term efficacy and safety of insulin degludec as a part of a basal–bolus therapy for Japanese patients with type 1 or type 2 diabetes in routine clinical practice.Materials and MethodsIn the present study, 93 type 1 diabetes patients and 135 type 2 diabetes patients treated with insulin glargine or detemir were switched from their basal insulin to insulin degludec. The primary end‐points were the changes in glycated hemoglobin (HbA1c) from baseline at 3, 6 and 12 months. The secondary end‐points were changes in body mass index, insulin dose, frequency of hypoglycemia and adverse events.ResultsHbA1c levels from baseline were significantly reduced at 3, 6, and 12 months by 0.4, 0.4 and 0.3% in type 1 diabetes patients, respectively, and by 0.5, 0.5 and 0.3% in type 2 diabetes patients, respectively. Body mass index in type 1 diabetes patients increased significantly (P < 0.05), whereas that in type 2 diabetes patients did not change. Basal insulin dose decreased significantly at 3 months after switching (P < 0.05), and returned baseline dose at 12 months in type 1 diabetes and type 2 diabetes patients. The frequency of both total and nocturnal hypoglycemia decreased significantly in type 1 diabetes and type 2 diabetes patients (P < 0.05). The result of multiple regression analysis showed that baseline HbA1c was a significant independent variable of the percentage change in HbA1c with switching.ConclusionIn both type 1 diabetes and type 2 diabetes patients, switching from insulin glargine or insulin detemir to insulin degludec led to improvement of glycemic control with a significant reduction of hypoglycemia.

Insulin receptor substrate-1 (IRS-1) is one of the major substrates of insulin receptor tyrosine kinase and mediates various insulin signals downstream. In this study, we have examined the impact of three natural IRS-1 mutations identified in NIDDM patients (G971R, P170R, and M209T) on insulin signaling. G971R is located near src homology 2 protein binding sites, and P170R and M209T are located in the phosphotyrosine binding domain of IRS-1. 32D-IR cells, stably overexpressing human insulin receptor, were transfected with wild-type human IRS-1 cDNA (WT) or three mutant IRS-1 cDNAs and analyzed. All the cell lines expressing mutant IRS-1 showed a significant reduction in [3H]thymidine incorporation compared with WT. Upon insulin stimulation, cells expressing G971R showed a 39% decrease (P < 0.005) in phosphatidylinositol 3-kinase (PI 3-kinase) activity, a 43% decrease (P < 0.01) in binding of the 85-kDa regulatory subunit of PI 3-kinase, and a 22% decrease (P < 0.05) in mitogen-activated protein kinase activity compared with those expressing WT. Cells expressing P170R and M209T showed slight but significant decreases in PI 3-kinase activity (17 and 14%, respectively; both P < 0.05) and in binding of p85 (22 and 16%, respectively; both P < 0.05) and a greater decrease in mitogen-activated protein kinase activity (41 and 43%, respectively; both P < 0.005) compared with WT. After insulin stimulation, cells expressing P170R and M209T showed significant decreases in IRS-1 phosphorylation (37 and 42%, respectively; both P < 0.05) and in IRS-1 binding to the insulin receptor (48 and 53%, respectively; P < 0.01) compared with WT. G971R showed no changes in IRS-1 phosphorylation and in IRS-1 binding to the insulin receptor compared with WT. These data suggest that the impaired mitogenic response of P170R and M209T was mainly due to reduced binding to the insulin receptor, whereas the impaired response of G971R was mainly due to reduced association with PI 3-kinase p85.

To examine the efficacy and safety of once-daily insulin degludec/insulin aspart (IDegAsp) or once-daily secondgeneration basal insulin analogs (insulin degludec and insulin glargine 300 units/mL) in insulin-naïve Japanese adults with type 2 diabetes in routine clinical practice. A 12-week multicenter, open-label, randomized, pilot study was performed in 52 subjects with type 2 diabetes treated with oral antidiabetic drugs (OADs). Subjects were randomized to once-daily IDegAsp (n = 26) or basal insulin (n = 26). The primary endpoint was percent change in HbA1c from baseline to week 12. Furthermore, it was analyzed post hoc in subgroups stratified by baseline HbA1c. During a follow-up period, percent change in HbA1c was not significantly different between the two groups (p = 0.161). Daily insulin doses and frequency of overall hypoglycemia were also similar in the two groups. In post hoc analyses, once-daily basal insulin was more effective than IDegAsp in subjects with HbA1c more than or equal to 8.5% (p < 0.05); however, in subjects with HbA1c less than 8.5%, once-daily IDegAsp showed a significant improvement in percent change in HbA1c at week 12, compared with basal insulin (p < 0.01). Although there was no apparent difference in the HbA1c-lowering effects between two groups, when compared in subjects with HbA1c less than 8.5%, once-daily IDegAsp showed a significant effect in comparison with once-daily basal insulin. These findings suggest that the baseline HbA1c level might provide the important information for choosing IDegAsp or basal insulin in patients insufficiently controlled with OADs. This trial was registered with UMIN (no. UMIN000035431).

Insulin receptor substrate 1 (IRS-1) is one of the major substrates of insulin receptor tyrosine kinase and mediates multiple insulin signals downstream. We have previously shown that the levels of IRS-1 mRNA varied in different tissues. To elucidate the molecular mechanisms of the tissue specific regulation of IRS-1, we have studied the cis-acting elements and transacting factors in CHO and HepG2 cells. Using the chloramphenicol acetyltransferase (CAT) assay with the various deletion mutants of the IRS-1 promoter-CAT fusion plasmids, several regions responsible for positive or negative regulation in each cell line were identified. A region from -1645 to -1585 bp, which regulated expression negatively in CHO cells and positively in HepG2 cells, was further analyzed. Within this region a fragment from -1645 to -1605 bp upregulated the IRS-1 promoter only in HepG2 cells, whereas a fragment from -1605 to -1585 bp downregulated only in CHO cells. In the gel mobility shift assay, several nuclear proteins that bind to these fragments were detected, and among them, two nuclear proteins that bind to a potential E box (nucleotide [nt] -1635 to -1630) and two nuclear proteins that bind to a potential C/EBP binding site (nt -1599 to -1591) were identified in HepG2 and CHO cells, respectively. CAT assays using promoters mutated at the E box or at the C/EBP binding site revealed that these sequences were responsible for cell-specific regulation of the IRS-1 gene. We therefore concluded that the two nuclear proteins that bind to the E box regulate IRS-1 gene expression positively in HepG2 cells and the two nuclear proteins that bind to the C/EBP binding site regulate it negatively in CHO cells.