Age-related changes of proinsulin processing in diabetic and non-diabetic Japanese individuals

AimThe present study was carried out to examine whether the insulin secretory mechanism deteriorates during the aging process using the new intact proinsulin assay system in non-diabetic and diabetic individuals. MethodsA total of 172 participants were separated into four groups according to their age (<64years and >65years) and an association of type2 diabetes; that is, 46 older diabetics (mean age 74.56.2years, glycated hemoglobin [National Glycohemoglobin Standardization Program] 7.51.3%), 27 older non-diabetics (mean age 76.9 +/- 7.5years), 48 middle-aged diabetics (mean age 50.8 +/- 10.4, glycated hemoglobin 7.8 +/- 1.5%) and 51 middle aged non-diabetics (mean age 46.6 +/- 13.0years) participants were enrolled. ResultsThe proinsulin/insulin (PI/I) ratio of the diabetic group was higher than that of the non-diabetic group in the older group (0.19 +/- 0.12 vs 0.11 +/- 0.06, P =0.002). In the middle-aged groups, the PI/I ratio of the diabetic group was higher than that of the non-diabetic group (0.16 +/- 0.15 vs 0.09 +/- 0.09, P =0.003). Simple regression analysis showed that male sex (95% CI 0.02-0.01, P =0.004), age (95% CI 0.00-0.002, P =0.03), lower body mass index (95% CI -0.06 to 0.00, P =0.02) and the presence of diabetes mellitus (95% CI 0.04-0.012, P <0.0001) were significantly associated with the increase in the PI/I ratio. Multivariate regression analysis showed that male sex and age were the independent factors determining the increase in the PI/I ratio in the non-diabetic group. After adjusted for body mass index, the PI/I ratio correlated significantly with age only in the non-diabetic group (r =0.5, P =0.004). ConclusionsThe proinsulin processing system might deteriorate not only in diabetics, but also in non-diabetic Japanese individuals with age. Also, sex-related hormones can be protective for the proinsulin processing system. Geriatr Gerontol Int 2018; 18: 1046-1050.