Urinary and serum type III collagen: markers of renal fibrosis

Background. The progression of chronic renal failure is characterized by the progressive fibrosis of the kidneys. Such fibrosis reflects the increased deposition of collagens (I, III, and IV) as well as fibronectin within scarred kidneys. In this study, we determined whether changes in renal extracellular matrix (ECM) components are reflected by parallel changes in their circulating or urinary levels. Patients and methods. We studied 40 patients with a range of subacute and chronic nephropathies who underwent a renal biopsy. At the time of the biopsy, their serum and urinary levels of collagens III (amino terminal peptide of procollagen III; PIIINP) and IV, as well as fibronectin were measured. Clinical, biochemical and histological parameters were correlated. Multiple regression analysis was applied to determine the predictive value of circulating and urinary ECM components for the severity of renal fibrosis. Results. We noted an increase in circulating and urinary levels of collagens III and IV but not fibronectin in patients with nephropathies compared to healthy volunteers. Increased immunoreactivity for these ECM components was also detected in kidney biopsies when compared to normal kidneys. A strong positive correlation was detected between circulating and urinary procollagen III (PIIINP) and the severity of renal interstitial fibrosis (serum PIIINP: r=0.49, P<0.01; urine PIIINP: r=0.51, P<0.01). Conclusion. We conclude that the measurements of urinary collagen III (PIIINP), and to a lesser extent serum collagen III (PIIINP), are useful indicators of the extent of renal fibrosis. This may have diagnostic implications and may prove useful for the monitoring of disease progression.