The extent of renal fibrosis in chronic kidney disease (CKD) is the best predictor for progression of most renal diseases. To date, no established biomarkers of renal fibrosis exist.

We measured circulating and urinary-specific matrix metalloproteinase (MMP)-generated collagen type I and III degradation fragments (C1M and C3M) and an N-terminal propeptide of collagen III (Pro-C3), as markers of collagen type III production, in three rat models of CKD and fibrosis: renal mass reduction (5/6 nephrectomy), progressive glomerulonephritis (chronic anti-Thy1.1 nephritis) and adenine crystal-induced nephropathy. Healthy rats served as controls.

In all three models, the animals developed significant CKD and renal fibrosis. Compared with healthy rats, serum C1M and C3M significantly increased in rats with 5/6 nephrectomy and adenine nephropathy (2- to 3-fold), but not with chronic anti-Thy1.1 nephritis. Urinary C1M and C3M levels increased 9- to 100-fold in all three models compared with controls. Urinary degradation markers correlated closely with renal deposition of collagen type I and type III. Pro-C3 was significantly increased only in the urine of 5/6 nephrectomy rats.

In particular, urinary markers of MMP-driven collagen degradation, rather than collagen production markers, may represent a novel, specific and non-invasive diagnostic approach to assess kidney fibrosis.