Role of secreted protein acidic and rich in cysteine (SPARC) in patients with diabetic nephropathy

Background A protein called “secreted protein acidic and rich in cysteine” (SPARC) may be important in the progression of diabetic nephropathy. Recent animal studies have shown a possible correlation between SPARC levels and diabetes-related kidney growth. Methods We measured serum levels of SPARC in patients with diabetic nephropathy and compared them to the severity of glomerular lesions as determined by renal biopsy. A total of 50 non-insulin-dependent diabetic patients were divided into 2 groups; patients with endstage diabetic nephropathy (ESDN, n=10) or without ESDN (DM, n=40). Renal biopsies were performed in all patients without ESDN. Serum levels of SPARC were measured by enzyme-linked immunosorbent assay (ELISA) in the 50 patients with diabetes, in 10 healthy controls, and in 10 patients with immunoglobulin (Ig) A nephropathy. Values for serum creatinine, creatinine clearance, β₂-microglobulin, and hemoglobin A_1C also were obtained. Results The mean serum SPARC levels (ng/mL) were 29±12, 41±21, 43±20, and 85±28, for healthy controls, IgA nephropathy, DM, and ESDN patients, respectively. Serum SPARC levels showed a significant increase with an increase in severity of glomerular diffuse lesions. Serum levels of SPARC were significantly higher in the DM group than in controls, and significantly higher in the ESDN group than in the control, IgA nephropathy and DM groups. Conclusion The findings suggest that SPARC may contribute to the progression of diabetic nephropathy.