Insulin degrading enzyme activity and insulin binding of erythrocytes in normal subjects and Type 2 (non-insulin-dependent) diabetic patients.

Specific insulin degrading enzyme activity of erythrocytes was determined in relation to erythrocyte insulin binding in 16 healthy subjects, 14 Type 1 (insulin-dependent) and various groups of Type 2 (non-insulin-dependent) diabetic patients (n = 39). Degrading activity was increased in Type 2 diabetic patients on sulphonylureas, as well as in a subgroup with good metabolic control (p less than 0.001) and in patients with secondary failure to oral therapy (p less than 0.02); degrading activity returned to normal in the latter patients after 1 week of insulin treatment. Highest degrading activity was found in insulin-treated, yet insulin-insensitive patients (daily insulin dose greater than 80 U). Degrading activity was significantly correlated in healthy subjects both with circulating insulin concentrations and maximal specific insulin binding. In contrast, in Type 2 diabetic subjects, degrading activity was inversely correlated with serum insulin with no apparent association with maximal specific insulin binding except in those patients given 1 week of insulin treatment. High erythrocyte insulin degrading enzyme activity might be a common feature in the insulin-insensitive Type 2 diabetic patient and might occur subsequent to some aspect of insulin deficiency at the tissue level.