How the sialylation level of serum N-acetyl-beta-D-glucosaminidase A form in Type 1 diabetes mellitus influences their activity?

Abstract

It was verified that the serum N-acetyl-beta-D-glucosaminidase (NAG) activity is elevated in diabetes, but there are no reports about changes in the sialic acid (SA) content in the carbohydrate parts of the NAG A form and its influence on the total changes in NAG activity in type 1 diabetes mellitus patients with and without secondary complications. The NAG A form was isolated from the serum of 81 insulin-dependent diabetes mellitus (IDDM) patients with and without secondary complications (retinopathy, polyneuropathy and nephropathy) and 25 healthy persons, and purified and characterised. The content of alpha-2,6-bound SA, the isoenzyme patterns of the purified A form, and the total NAG and A form activities were determined. In all diabetic groups, the sialylation levels of the A form were 2-3.5 times lower compared to control, while their acidities (fractions with pI 4.25-5.1) increased, particularly with progression of secondary complications. Total serum NAG activities and percentages of A form were significantly higher (P lt 0.001) in all diabetic groups and negatively correlated with the alpha-2,6-bound SA content of the A form. In addition, they decreased as secondary diabetic complications became more complex. The observed changes could be the consequence of structural changes in the A form due to significant increases in its acidity, i.e., negative charge, which originated from groups other than SA.