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 immunocytochemistry (ICC) and a novel radioimmunoassay. Glycated insulin circulated at 0.10 +/- 0.04 ng/ml and 2.20 +/- 0.14 ng/ml in lean and diabetic obese (ob/ob) mice, corresponding to 12.5 and 9.8% total plasma insulin, respectively. The concentration of glycated insulin was elevated 22-fold in obese mice compared to controls (P < 0.001). In the pancreas, glycated insulin was 48 +/- 10 and 83 +/- 4 ng/g wt (P < 0.05) in lean and obese mice, respectively, representing approximately 2% total insulin in the diabetic pancreas (4.60 +/- 0.17 microg/g wt). ICC revealed fluorescent positively stained cells in pancreatic islets from hydrocortisone (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 resistant rats, plasma glucose, insulin, and glycated insulin increased (P < 0.001) rapidly with 1.4-, 1.6-, and 2.9-fold elevations, respectively. Injection of HC-treated rats with insulin (50 U/kg) resulted in a rapid 33% decrease of plasma glucose (P < 0.001) and a marked 4-fold increase in plasma insulin (P < 0.01), whereas glycated insulin concentrations remained unchanged. Since glycation of insulin impairs biological activity, physiologically regulated secretion of glycated insulin into the circulation in diabetic animal models suggests a role in the pathogenesis of diabetes.
McKillop
A M
AM
School of Biomedical Sciences, University of Ulster, Cromore Road, Coleraine, BT52 1SA, Northern Ireland. am.mckillop@ulst.ac.uk
Mooney
M H
MH
Harriott
P
P
Flatt
P R
PR
O'Harte
F P
FP
D000818:Animals; D003920:Diabetes Mellitus / Q000378:metabolism*; D004435:Eating; D005947:Glucose; D006031:Glycosylation; D006854:Hydrocortisone / Q000494:pharmacology; D007150:Immunohistochemistry / Q000379:methods*; D007328:Insulin / Q000032:analysis* / Q000737:chemistry / Q000276:immunology; D008297:Male; D051379:Mice; D008820:Mice, Obese; D010179:Pancreas / Q000737:chemistry / Q000187:drug effects; D011863:Radioimmunoassay / Q000379:methods*; D051381:Rats; D017208:Rats, Wistar
D007328:Insulin; D005947:Glucose; D006854:Hydrocortisone