Evaluation of glycated insulin in diabetic animals using immunocytochemistry and radioimmunoassay

Glycated insulin was evaluated in plasma and biological tissues of diabetic animal models by immuno. cytochemistry (ICC) and a novel radioimmunoassay. Glycated insulin circulated at 0.10 +/-0.04 ng/ml and 2.20 +/-0.14 ng/ml i n lean and diabetic obese (ob/ob) mice, corresponding to 12.5 and 9.8% tota l plasma insulin, respectively. The concentration of glycated insulin was e levated 22-fold in obese mice compared to controls (P<0.001). In the pancre as, glycated insulin was 48<plus/minus>10 and 83 +/-4 ng/g wt (P<0.05) in l ean and obese mice, respectively, representing approximately 2% total insul in in the diabetic pancreas (4.60<plus/minus>0.17 mug/g wt). ICC revealed f luorescent positively stained cells in pancreatic islets from hydrocortison e (HC)treated diabetic rats. Fasting of HC-treated rats, resulted in 3-fold and 15-fold reductions in plasma glycated insulin (P<0.01) and insulin (P< 0.001), respectively. Following a 30 min feeding period in these insulin re sistant rats, plasma glucose, insulin, and glycated insulin increased (P<0. 001) rapidly with 1.4-, 1.6-, and 2.9-fold elevations, respectively. Inject ion of HC-treated rats with insulin (50 U/kg) resulted in a rapid 33% decre ase of plasma glucose (P<0.001) and a marked 4-fold increase in plasma insu lin (P<0.01), whereas glycated insulin concentrations remained unchanged. S ince glycation of insulin impairs biological activity, physiologically regu lated secretion of glycated insulin into the circulation in diabetic animal models suggests a role in the pathogenesis of diabetes. (C) 2001 Academic Press.