Human amylin, a major constituent of pancreatic amyloid deposits, may be a pathogenetic factor for noninsulin-dependent diabetes mellitus (NIDDM). We demonstrated that the human amylin S20G gene mutation (S20G) was associated with a history of early onset, more severe type of NIDDM, linking the amylin gene to this disease. Also, we demonstrated that expression of human wild-type (WT) amylin in COS-1 cells leads to intracellular amyloidogenesis and induction of apoptosis, suggesting a possible mechanism for disease induction. Therefore we compared the abilities of S20G and WT amylin to induce apoptosis in transfected COS-1 cells and form amyloid in vitro. We transfected the rat (RAT), mutated human (MUT), WT, and S20G amylin genes into COS-1 cells and measured apoptosis using fluorescent-activated cell sorting analysis at 48, 72, and 96 hours. At 96 hours apoptosis increased significantly (P < 0.01) in cells transfected with WT and S20G over RAT or MUT (WT, 19%; S20G, 25%; RAT, 13%; and MUT, 12%) and the difference between WT and S20G was significant (P < 0.05). Synthetic WT and S20G monomeric peptides were used to generate amyloid fibrils in vitro as measured by the thioflavin T binding assay. The S20G amylin formed approximately twofold more amyloid at a rate approximately threefold higher than WT. Electron micrography indicated that the in vitro amyloid generated by WT and S20G amylins were morphologically indistinguishable. The results suggest that increased cytotoxicity by S20G is because of increased amyloidogenicity, which may be a causative factor in the early development of NIDDM, possibly through loss of ss cell mass.

Fasting plasma islet amyloid polypeptide concentrations and their responses to an oral glucose load were determined in non-diabetic control subjects and patients with abnormal glucose tolerance in relation to the responses of insulin or C-peptide. Plasma islet amyloid polypeptide was measured by radioimmunoassay. In the non-diabetic control subjects, fasting plasma islet amyloid polypeptide was 6.4 +/- 0.5 fmol/ml (mean +/- SEM) and was about 1/7 less in molar basis than in insulin. The fasting islet amyloid polypeptide level rose in obese patients and fell in patients with Type 1 (insulin-dependent) diabetes mellitus. In non-obese patients with impaired glucose tolerance and Type 2 (non-insulin-dependent) diabetic patients without insulin therapy, the level was equal to that of the control subjects, but a low concentration of islet amyloid polypeptide relative to insulin or C-peptide was observed in the non-obese Type 2 diabetic group. The patterns of plasma islet amyloid polypeptide responses after oral glucose were similar to those of insulin or C-peptide. However, compared to non-obese patients, a hyper-response of islet amyloid polypeptide relative to C-peptide was noted in obese patients who had a hyper-response of insulin relative to C-peptide. This study suggests that basal hypo-secretion of islet amyloid polypeptide relative to insulin exists in non-obese Type 2 diabetes and that circulating islet amyloid polypeptide may act physiologically with insulin to modulate the glucose metabolism.

Common uncoupling protein 2 (UCP2) promoter polymorphism ؊866G/A is reported to be associated with its expression in adipose tissue and the risk of obesity in Caucasians. On the other hand, several studies suggested that UCP2 expression in ␤-cells is an important determinant of insulin secretion. In the Japanese population, morbid obesity is very rare, and insulin secretion capacity is relatively low as compared with Caucasians. Because UCP2 would link to insulin secretion and obesity, it might explain this ethnic difference. Here, we report that the UCP2 promoter with the A allele showed higher promoter activity in the INS-1 ␤-cell line. The frequency of the A allele is higher in our Japanese study than that in Caucasians. Type 2 diabetic patients with the A allele need insulin therapy earlier and showed higher frequency of insulin treatment. Moreover glucose-induced early insulin secretion is significantly lower in patients with the A allele. However, there was no difference in allele frequency between obese and lean type 2 diabetic patients. In conclusion, UCP2 promoter polymorphism ؊866G/A does not affect obesity in Japanese type 2 diabetic patients but affects its transcription in ␤-cells and modulates glucose-induced insulin secretion and eventually insulin requirement in Japanese type 2 diabetic patients. Higher A allele frequency in the Japanese population might partly explain the ethnic difference of insulin secretion capacity. Diabetes 53:482-485, 2004 T he major defects in type 2 diabetes are those in insulin secretion and insulin sensitivity (1). Obesity is obviously an important factor for insulin sensitivity or resistance. Morbidly obese subjects are very rare in the Japanese population, and mean BMI in Japanese type 2 diabetic patients is also smaller than that in Caucasians (2). On the other hand, insulin secretion capacity is reported to be lower in Japanese (3,4). These ethnic differences may be explained by differences in genetic background associated with both obesity and insulin secretion. Uncoupling protein 2 (UCP2) is a subtype of the UCP family that mediates mitochondrial proton leak (5). Thus, higher expression of UCP2 might lead to the consumption of excess energy and a lessening of obesity. However, higher expression of UCP2 in ␤-cells would lead to a decrease in ATP production and a defect in insulin secretion. Several lines of evidence, including knockout mice, have also indicated an important role of UCP2 in insulin secretion (6 -9). Because UCP2 is related to both obesity and insulin secretion, it will be a strong candidate gene for type 2 diabetes. UCP2 promoter polymorphism Ϫ866G/A has been reported to associate with its expression in adipose tissue and obesity in Caucasians (10). Therefore, we have investigated the promoter activity of each allele of UCP2 in an INS-1 ␤-cell line and the relationship between this polymorphism and clinical profiles of Japanese type 2 diabetic patients. RESEARCH DESIGN AND METHODSA total of 413 type 2 diabetic patients and 172 nondiabetic control s...