Islet β-cell Function And It's Relation To Amylin And Melatonin In Newly Diagnosed Elderly Diabetic Patients

Objective The present study was to explore the relationship between isletβ-cell function and the serum levels of amylin and melatonin by observing the feature of isletβ-cell function and measuring the serum levels of amylin and melatonin in newly diagnosed elderly diabetic patients, furtherly to explore the possible mechanism of senile diabetes.Methods 70 newly diagnosed subjects with type 2 diabetes were divided into elderly-onset diabetes group (EOD, aged 60 to 94) and adult-onset diabetes group (AOD, aged 25 to 59 years), oral glucose tolerance test (OGTT) was detected and the area under the curve of glucose (AUCg),the area under the curve of insulin (AUCi),the function of pancreatic beta-cell(HOMA-β),the ratio of the increment of insulin to that of serum glucose of the initial 30 minutes(△I30/△G30) and the homeostasis model assessment of insulin resistance (HOMA-IR) after OGTT was calculated. The levels of serum amylin and melatonin of all patients were determined with ELISA, compared with that of 30 healthy aged subjects(elderly healthy control group, EHC). For all of the subjects, fasting serum triglycerid (TG),total cholesterol(TC),high density lipoprotein cholesterol (HDL-C),low density lipoprotein cholesterol (LDL-C) and blood pressure were measured and body mass index (BMI), waist/hip ratio(WHR) were calculated.Results 1. Compared with AOD group, EOD group had lower value of HOMA-β[(58.20±24.89) vs (81.20±40.80), P＜0.01] and△I30/△G30[(2.62±0.43) vs (3.37±0.58), P＜0.01], but had higher values of OGTT 2 h serum glucose[(15.17±3.03) vs (13.59±2.76) mmol/L, P＜0.05], serum insulin[(73.34±43.39) vs (64.22±29.75) uIU/ml, P＜0.05] and HOMA-IR[(4.20±1.67) vs (3.49±1.83), P＜0.05], though the values of AUCg and AUCi were higher in EOD group than that in AOD group, no significant difference was found.2. The serum amylin level in EOD group was obviously higher than that in AOD group[(21.57±15.88) vs (19.8±13.18) ng/L, P＜0.05] and EHC group[(21.57±15.88) vs (17.82±12.15) ng/L, P＜0.01].There wasn't obvious difference between AOD group and EHC group on serum amylin level(P＞0.05).The serum melatonin level in EOD group was obviously lower than that in AOD group[(6.56±1.32) vs (8.17±1.23) pg/ml, P＜0.05] and EHC group[(6.56±1.32) vs (7.65±1.39) pg/ml, P＜0.01]; There wasn't obvious difference between AOD group and EHC group on serum melatonin level(P＞0.05).3. The correlation analysis results showed that:serum amylin level had positive correlation with HOMA-IR(r= 0.498, P= 0.016), fasting serum insulin(r= 0.517, P= 0.031), AUCi(r= 0.516, P= 0.021) and had negative correlation with HAMA-β(r=-0.461, P= 0.003). The serum amylin had no significant correlation with AUCg, FBG, blood lipids,△I30/△G30, WHR and BMI(P＞0.05).4. The level of serum melatonin had positive correlation with HAMA-β(r= 0.403, P= 0.016) and HDL-C(r= 0.416, P= 0.018) and had negative correlation with HOMA-IR(r=-0.549, P= 0.019), AUCi(r=-0.521, P= 0.014), WHR(r=-0.514, P = 0.023), fasting blood glucose(r=-0.345, P= 0.032) and LDL-C(r=-0.479, P= 0.012), the serum melatonin had no significant correlation with AUCg,△I30/△G30 and BMI(P＞0.05).Conclusion 1. Newly diagnosed elderly diabetic patients have obviousβ-cell deterioration and impaired early-phase insulin secretion, at the same time have a certain degree of insulin resistance and delayed peak of insulin release, suggesting that isletβ-cell dysfunction is the main reason of glucose metabolism disorder in elderly diabetic patients.2. Compared with the healthy elderly, the elderly-onset diabetic patients had significantly higher level of amylin and lower level of melatonin, suggesting that the increased serum amylin and decreased serum melatonin may be related to the pathogenesis of senile diabetes.3. The serum amylin level had significant negative correlation relationship with islets beta-cell function and had positive correlation relationship with obesity and insulin resistance, it is one of useful markers which estimate the function of pancreaticβ-cells.4. The serum melatonin level had positive correlation with pancreatic beta-cell function and had negative correlation relationship with blood lipids and insulin resistance index, speculating that it may become a new index of evaluation of isletβ-cell function.