LAUSR

Background: Increased endogenous DNA damage poses a serious threat to cell health, since it may lead to mutagenesis, genomic instability and cellular apoptosis. DNA damage accumulation in immune cells occurs in patients with chronic inflammatory diseases, however; little is known on the types and prevalence of endogenous DNA damage in patients with Rheumatoid arthritis (RA). Objectives: To study DNA damage response and repair network in patients with active RA and to test the hypothesis that anti-rheumatic treatment influences this network. Methods: Peripheral blood mononuclear cells were isolated from 15 patients with active RA and 65 apparently healthy controls; 8 patients were re-examined after 12-week treatment. Endogenous DNA damage was determined using alkaline comet assay. Specific markers for single-strand DNA breaks (SSBs; RPA32) and double-strand DNA breaks (DSBs; γH2Ax, 53BP1) were measured using western-blot. Formation of DNA damage was assessed by oxidative stress and abasic DNA sites measurements. Chromatin organization and the two subpathways of the fundamental nucleotide excision repair mechanism, namely, transcription-coupled repair (TCR) and global genome repair (GGR), were assessed along the N-ras gene. Results: A 3-fold increase of endogenous DNA damage levels (Olive Tail Moment reflecting both SSBs and DSBs) was evident in active RA [mean±SD; 12.8±7.5 versus 4.5±2.4, p<0.001), as well as induction of RPA32, γH2Ax and 53BP1, higher oxidative stress levels and increased abasic sites, compared to controls. While TCR capacity was preserved, GGR capacity was deficient in all active RA patients. Moreover, a more condensed chromatin structure was found in active RA compared to controls. Following treatment, chromatin structure loosened, GGR capacity was restored, oxidative stress and abasic sites decreased and levels of endogenous DNA damage reached control values in all patients. Conclusion: Deregulated chromatin organization, deficient DNA repair capacity and augmented formation of DNA damage contribute to the accumulation of endogenous DNA damage in patients with active RA and are reversible after treatment. Additional studies to better understand the negative impact of DNA endogenous damage accumulation may create new therapeutic opportunities for patients with RA. Disclosure of Interests: None declared