Impact of MPO-ANCA mediated oxidative imbalance on renal vasculitis.

Glomerulonephritis is a severe complication of microscopic polyangiitis (MPA), a small-vessel vasculitis associated with anti-myeloperoxidase antibodies (MPO-ANCA). We previously showed the pathogenic effects of MPO-ANCA that activate MPO to trigger an oxidative burst mainly through HOCl production, contributing to endothelial injury and lung fibrosis. The aim of this study was to investigate the relationship between MPO-induced oxidative stress, anti-oxidant defenses and renal histological lesions in MPA patients. We therefore analyzed histological data from a prospective cohort of ANCA-associated glomerulonephritis. Serum-mediated HOCl production, advanced oxidation protein products (AOPP), and thiol concentration in sera were determined. From 38 patients included, histological classification noted 50% focal glomerulonephritis, 15.8% crescentic-glomerulonephritis, and 34.2% mixed-glomerulonephritis. MPA patients' sera displayed higher HOCl production by MPO (p<0.001), higher AOPP (p<0.001) and thiol (p<0.01) levels, compared with healthy subjects. The presence of cellular crescents was associated with higher serum-mediated HOCl production (p=0.049) and lower thiol levels (p=0.022) at disease onset. Higher thiol concentrations were associated with focal glomerulonephritis (p=0.042), less interstitial fibrosis (p=0.039) and hyalinosis (p=0.066). In remission, HOCl production was decreased (p<0.01), and thiol concentration remained high (p=0.39). Our findings suggest that HOCl production by activated MPO could contribute to the very early stage of glomerulonephritis, whereas thiol may exert a protective effect against the development of renal vasculitis and glomerulosclerosis. This study highlights the importance of oxidative defenses to counteract the process of MPO-ANCA associated glomerulonephritis.