A specific structural alteration in the heparan sulphate of human glomerular basement membrane in diabetes

Aims/hypothesis. Heparan sulphate proteoglycan is an important component of the glomerular anionic filtration barrier and its reduced amount in diabet es contributes to glomerular dysfunction. The objective of this study was t o determine if there is also an alteration in the sulphation pattern of the diabetic heparan sulphate chains. Methods. The heparan sulphate in the glomerular basement membrane/mesangial matrix from human diabetic and nondiabetic kidneys obtained at autopsy was fragmented by a hydrazine/nitrous acid procedure and after radiolabelling with NaB[H-3](4). the disaccharide products were chromatographically resolv ed and quantified. Results. Six sulphated disaccharides were identified in both the diabetic a nd nondiabetic samples and the molar distribution of these was similar, wit h the notable exception of the iduronic acid-2-O-sulphate alpha 1 --> 4gluc osamine-3-O-sulphate species which occurred in the diabetic glomeruli in le ss than half the amount as in the nondiabetic samples (9.0% compared to 18. 7% of total sulphated disaccharides, p < 0.005). Conclusion/interpretation. 3-O-sulphated glucosamine is a rare constituent of heparan sulphate occurring usually in a glucuronic acid beta 1 --> 4gluc osamine-3-O-sulphate(+/- 6-O-sulphate) sequence within the antithrombin-bin ding domain. In the glomerular basement membrane where the 3-O-sulphated gl ucosamine is present in substantial amounts, however, it occurs exclusively in an iduronic acid-containing sequence. It is likely that the recently di scovered 3-O-sulphotransferase variant which specifically acts on the iduro nic acid alpha 1 --> 4glucosamine sequence is decreased in human diabetes a nd moreover that this unusual disaccharide could be a component of a specif ic heparan sulphate domain which interacts with bioactive proteins.