Nonenzymatic glycosylation of proteins and protease activities in granulation tissues in experimental diabetes

Serum proteins and hemoglobins show increased nonenzymatic glycosylation in diabetes mellitus. The measure of glycosylated proteins, particularly hemoglobin, is considered to be a preferred indicator in the control of diabetes. In a study of diabetes and inflammation, we assessed the extent of nonenzymatic glycosylation of proteins of granulation tissue from diabetic rats. Five, seven, and ten days after carrageenan injection, the granuloma proteins were extracted. Nonenzymatic glycosylation was measured in soluble and insoluble granuloma proteins by thiobarbituric acid assay. Protease activities and free amino groups were assayed in soluble extracts. Nonenzymatic glycosylation in soluble proteins of both groups reached a maximum on the seventh day. However, nonenzymatic glycosylation in soluble proteins of the diabetic granulomas was significantly greater than the controls on days five and seven. During the days after granuloma induction, nonenzymatic glycosylation in the insoluble granuloma tissue proteins gradually decreased without any significant differences between controls and diabetics. Significant decreases in the free amino groups in soluble proteins of the diabetic tissues were noted. Greater activities of cathepsins B and D were noted in diabetic tissues over controls. These observations suggest that, in addition to increased proteolysis, increased nonenzymatic glycosylation of tissue proteins could be associated with the impaired process of wound healing in diabetics.