Unstabilized DNA breaks in lymphocytes of patients with different subsets of systemic sclerosis

The clastogenic effects on DNA, proven by the presence of micronuclei (MN) and the protective cellular mechanisms normally used to stabilize DNA breaks were investigated in three subsets of patients with systemic sclerosis (SSc). The frequency of MN found in cultures of peripheral lymphocytes in patients with anticentromere and antitopoisomerase I antibodies was significantly higher than that in the control group. The group with anticentromere antibody showed a significantly higher frequency of MN than did the subjects with antitopoisomerase antibody (4.22% versus 2.34%, P < 0.001). Patients with anti-RNA polymerase III, instead, had a low prevalence of typical micronucleated cells (0.98%), not significantly different from that of the healthy controls (0.82%). Moreover, when MN was characterized for the presence or absence of DNA fragments with free 3'-OH ends by digoxigenin-dUTP (DIG-dUTP) using terminal deoxynucleotidil transferase, its frequency was found to be increased in the groups with anticentromere and antitopoisomerase I antibodies with respect to that in the controls. The increase was significantly higher in the lymphocytes of the patients with anticentromere than in those with antitopoisomerase I antibody (35% versus 20.08%, P < 0.001). Nonetheless, the prevalence of unstable DNA fragments in patients with anti-RNA polymerase III antibody was low (2.05%) and not significantly different from that of the control group (1.18%). Our results indicate that there is a clastogenic effect on DNA and an interference in the protective cellular mechanisms normally stabilizing DNA breaks only in some subsets of SSc patients.