Objective: We assessed the serum glucagon-like peptide-1 (GLP-1) levels for Chinese adults with pre-diabetes (PD) and newly-diagnosed diabetes mellitus (NDDM) during oral glucose tolerance test (OGTT). The relationships between total GLP-1 level and islet β cell function, insulin resistance (IR) and insulin sensitivity (IS) were also investigated.Methods: A 75g glucose OGTT was given to 531 subjects. Based on the results, they were divided into groups of normal glucose tolerance (NGT), isolated impaired fasting glucose (IFG), isolated impaired glucose tolerance (IGT), IFG combined IGT (IFG+IGT) and NDDM. Total GLP-1 levels were measured at 0- and 2-hour during OGTT. Homeostasis model assessment of β cell function (HOMA-β), HOMA of insulin resistance (HOMA-IR), Gutt and Matsuda indexes were calculated. The relationships between GLP-1 level and β cell function, IR and IS were analyzed.Results: The levels of total fasting GLP-1 (FGLP-1), 2h GLP-1 (2hGLP-1) and 2hGLP-1 increments (∆GLP-1) following OGTT reduced significantly in IFG+IGT and NDDM groups (P<0.005). HOMA-β , HOMA-IR, Gutt and Matsuda indexes demonstrated various patterns among NGT, isolated IFG, isolated IGT, IFG+IGT and NDDM groups (P<0.05). Spearman rank correlation analysis and multivariable linear regression model suggested that some levels of correlation between GLP-1 levels, ∆GLP-1 and β cell function, IR (P<0.05).Conclusions: The total GLP-1 levels and its response to glucose load decreased significantly in IFG+IGT group, compared to isolated IFG or IGT group. They were even similar to that of NDDM group. Moreover, there were observable correlations between impaired GLP-1 secretion and β cell function, IR and IS.

This study aims at synthesizing novel di-morpholine 1,3,5-triazine derivatives as antidiabetic agent via inhibition of dipeptidyl peptidase-4 (DPP-4). The molecules were developed via sequential nucleophilic reaction to afford target derivatives 5(a–f) and subsequently tested for inhibitory potency against DPP iso-enzymes, such as DPP-4, DPP-8, and DPP-9. The in vitro inhibition assay suggested that these derivatives prominently and selectively inhibit DPP-4 over ­DPP-8 and DPP-9. These molecules also showed no presence of cardiotoxicity, as confirmed by no activity against human Ether-à-go-go related gene channel. The study disclosed compound 5c as the most potent inhibitor of DPP-4 with IC₅₀ of 1.10 nmol/L as compared to the standard. Compound 5c was further evaluated for oral glucose tolerance test (OGTT) and antidiabetic activity in ICR mice and Wistar rats, respectively. In OGTT, compound 5c showed dose-dependent ­improvement of glucose tolerance with a maximum at 30 mg/kg. It also showed reduction in area under the curve from 0 to 120 min, similar to alogliptin (standard). In Wistar rats, compound 5c causes reduction in the blood glucose level, total cholesterol, triglyceride, low density lipoprotein (LDL) and very LDL level as compared to the diabetic control group, whereas the level of high-density lipoprotein was found to be increased. Compound 5c causes improvement in antioxidant defense mechanism, as confirmed via improving superoxide dismutase, catalase, glutathione peroxidase and reducing the malondialdehyde level as compared to normal control group rats.

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