Cleaved Form of Osteopontin in Urine as a Clinical Marker of Lupus Nephritis.

We assessed the utility of two forms of osteopontin (OPN), OPN full and its cleaved form (OPN N-half), in plasma and urine as markers of disease activity in lupus nephritis (LN). Samples were collected from patients with systemic lupus erythematosus (SLE) (LN: N = 29, non-LN: N = 27), IgA nephropathy (IgAN) (N = 14), minimal change nephrotic syndrome (MCNS) (N = 5), diabetic nephropathy (DN) (N = 14) and healthy volunteers (HC) (N = 17). While there was no significant difference in urine OPN full concentration between groups, urine OPN N-half concentration was significantly higher in patients with LN than HC (p < 0.05). Moreover, urine OPN N-half was higher in LN patients with overt proteinuria (urine protein/creatinine ratio: P/C > 0.5) than LN patients with minimal proteinuria (P/C < 0.5, p < 0.0001), and also higher than in DN patients with overt proteinuria (P/C > 0.5, p < 0.01). Urine thrombin activity correlated with urine OPN N-half concentration (p < 0.0001), but not with urine OPN full concentration. These results suggest that urine OPN N-half concentration reflects renal inflammation. Thus, urine OPN N-half may be a novel disease activity marker for LN.
Competing Interests: This work was supported by grants from the Center for Innovation in Immunoregulative Technology and Therapeutics, Graduate School of Medicine, Kyoto University, Kyoto, Japan. The Center was founded by a special coordination of the Ministry of Education, Culture, Sports, Science and Technology of Japan and Astellas Pharma Inc. Takuma Oku, Chiyomi Sasaki, and Yoshitaka Hirayama are employees of Astellas Pharma Inc. This does not alter our adherence to PLOS ONE policies on sharing data and materials.