Prospective investigation of the oxidative DNA damage and lipid peroxidation levels in patients with rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic and inflammatory autoimmune disease that is involving the joints. Current clinical approaches aim to alleviate the symptoms, although the pathogenesis of RA yet to be known. Reactive oxygen species formed both endogenously and exogenously. By attacking cellular macromolecules, they lead to the formation of oxidatively damaged end products which are related to many diseases. This study aims to investigate the changes in DNA nucleoside damage and lipid peroxidation levels in patients with RA after six months of treatment, along with the comparison of healthy controls and patients with RA. We also aim to prospectively examine the relationship between the Disease Activity Score (DAS28 score), Health Assessment Questionnaire (HAQ) score, C-Reactive protein (CRP) and erythrocyte sedimentation rate (ESH) levels and oxidative macromolecule damage levels at the end of the six-month treatment period. 69 RA patients and 31 healthy controls were included in the study. As the main indicators of oxidative DNA damage 8-hydroxy-deoxyguanosine (8-OH-dG), R and S forms of 8,5'-cyclo-2'-deoxyadenosine (R-cdA and S-cdA); and for the evaluation of lipid peroxidation, 8-isoprostane which is one of the end products of peroxidation was investigated. The liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was used to determine nucleoside damage, and the Enzyme immunoassay (ELISA) method was used to determine the level of lipid peroxidation. As a result of our study, 8-OH-dG, R-cdA, and 8-isoprostane levels of the patients found significantly higher than the healthy controls (p=0.003; p=0.005; p<0.001, respectively). After six months of treatment, a significant decrease was observed in the 8-OH-dG, R-cdA, and S-cdA levels of the patients (p=0.001; p=0.040; p<0.001, respectively); in contrary, the level of 8-isoprostane found higher after treatment than before treatment (p=0.010). DAS 28 and HAQ scores, CRP, and ESR levels of the patients were found significantly lower after treatment than before treatment (p<0.001; p=0.002; p=0.017; p=0.001, respectively). The patients grouped according to the change in disease severity after six months of treatment, a decrease in DAS 28 score along with 8-OH-dG and S-cdA levels was observed after treatment than before, in patients who were in flare-up period at the time of diagnosis and went in remission after treatment (p<0.001; p=0.003; p=0,005, respectively). No correlation was found between clinical parameters and oxidative damage levels except ESR measured at diagnosis and S-cdA measured at diagnosis (r=0.307; p=0.011). This is the first study in the literature that compares three different DNA damage parameters and lipid peroxidation product levels simultaneously before and after the treatment applied to the patients, besides the comparison of healthy controls and patients with RA. In addition, it has been shown that the applied treatment process suppresses oxidative DNA damage and induces lipid damage. In this respect, our study reveals that oxidative DNA and lipid damage formation respond to the RA treatment process with different mechanisms and in opposition to each other. We believe that the findings obtained within the scope of our study will shed light on the differential diagnosis of RA, its clinical course, and the evaluation of the response to treatment.