Biochemical composition of glomerular basement membrane in streptozotocin diabetic rats

Alterations of biochemical compositon were studied in glomerular basement membrane (GBM) which were isolated from control and streptozotocine diabetic rats of 1-6 months duration. Streptozotocine (STZ) diabetic rats were induced by intravenous injection of STZ 65 mg/ kg body weight, and exhibited marked hyperglycemia and glucosuria. Preparation of GBM was obtained by sonication of isolated glomeruli using various stainless sieves. After extraction of non-collagen protein with 8M urea, the extent of glycosylation in GBM collagen was determined with a specific colorimetric reaction that detects carbohydrate in ketoamine linkage with protein. (1) Six months after the onset of diabetes, ultrastructural studies revealed that GBM of diabetic rats was about 1.4-fold thicker than that of control rats. (2) After 1, 3 and 6 months, no significant difference was observed in the content of hydroxyproline between control and diabetic GBM. But the GBM of diabetic rats contained less hydroxylysine and glycine, and more lysine, aspartic acid, threonine, half-cystine and tyrosine than in control rast. The ratio of hydroxylysine to lysine was decreased in diabetic rats. These findings indicated that there was no significant changes of the collagenous protein content of diabetic GBM, but decrease of hydroxylation of lysine in diabetic state. (3) There was no constant changes of carbohydrate composition in diabetic GBM- However in the 6 months of diabetes, there was significant increase of fucose, mannose and galactosamine. This suggested that there was increase of heteropolysaccharide unit which linked to non-collagenous protein. (4) Glucosyl-galactosyl-hydroxylysine, disaccharide unit linked to collagen, was decreased in diabetic GBM of 3 and 6 months. (5) There was no changes in the degree of non-enzymatic glycosylation of diabetic GBM collagen. These biohemical changes of diabetic GBM suggested that in diabetic state there were some alterations in molecular packing of GBM, and this may play an important role in the appearance of proteinuria.