RAD51 and systemic sclerosis: The pretreatment with sildenafil reduced significantly the recruitment of RAD51 in the presence of low doses of H2O2 (50 μM) only in SSc Hfbs (50 μM H2O2 vs. 50 μM H2O2 + S: 66.3 ± 5.3 vs. 46.1 ± 4.3, p < 0.01), whereas no differences were observed in healthy Hfbs, where the level of RAD51 remained quite similar to that without sildenafil (p > 0.05) (Figure 2A).