SELECTIVE PROTEINURIA IN DIABETIC NEPHROPATHY IN THE RAT IS ASSOCIATED WITH A RELATIVE DECREASE IN GLOMERULAR-BASEMENT-MEMBRANE HEPARAN-SULFATE

In the present study we investigated whether glomerular hyperfiltratio n and albuminuria in streptozotocin-induced diabetic nephropathy in ma le Wistar-Munich rats are associated with changes in the heparan sulph ate content of the glomerular basement membrane. Rats with a diabetes mellitus duration of 8 months, treated with low doses of insulin, show ed a significant increase in glomerular filtration rate (p<0.01) and e ffective renal plasma flow (p < 0.05), without alterations in filtrati on fraction or mean arterial blood pressure. Diabetic rats developed p rogressive albuminuria (at 7 months, diabetic rats (D): 42+/-13 vs con trol rats (C): 0.5+/-0.2 mg/24 h, p<0.002) and a decrease of the selec tivity index (clearance IgG/clearance albumin) of the proteinuria (at 7 months, D: 0.20+/-0.04 vs C: 0.39+/-0.17, p<0.05), suggesting loss o f glomerular basement membrane charge. Light- and electron microscopy demonstrated a moderate increase of mesangial matrix and thickening of the glomerular basement membrane in the diabetic rats. Immunohistoche mically an increase of laminin, collagen III and IV staining was obser ved in the mesangium and in the glomerular basement membrane, without alterations in glomerular basement membrane staining of heparan sulpha te proteoglycan core protein or heparan sulphate. Glomerular basement membrane heparan sulphate content, quantitated in individual glomerula r extracts by a new inhibition ELISA using a specific anti-glomerular basement membrane heparan sulphate monoclonal antibody (JM403), was no t altered (median (range) D: 314 (152-941) vs C: 262 (244-467) ng hepa ran sulphate/mg glomerulus). However, the amount of glomerular 4-hydro xyproline, as a measure for collagen content, was significantly increa sed (D: 1665 (712-2014) vs C: 672 (515-1208) ng/mg glomerulus, p<0.01) . Consequently, a significant decrease of the heparan sulphate/4-hydro xyproline ratio (D: 0.21 (0.14-1.16) vs C: 0.39 (0.30-0.47), p<0.05) w as found. In summary, we demonstrate that in streptozotocin-diabetic r ats glomerular hyperfiltration and a progressive, selective proteinuri a are associated with a relative decrease of glomerular basement membr ane heparan sulphate. Functionally, a diminished heparan sulphate-asso ciated charge density within the glomerular basement membrane might ex plain the selective proteinuria in the diabetic rats.