AB0027 XANTHINE OXIDOREDUCTASE: ENZYME PROFILE OF PLASMA AND LYMPHOCYTES IN RHEUMATOID ARTHRITIS

Abstract

BackgroundDisorders of acquired and adaptive immunity play an important role in the rheumatoid arthritis (RA) pathogenesis. Important changes can nevertheless be detected at the metabolic level in the immune cells along with immune disorders. The imbalance between generation and neutralization of the free radicals during oxidative stress may cause damage of both cellular structures and components of extracellular matrix. One of principal free radical generators is xanthine oxidoreductase (XOR), the prooxidant enzyme complex which could be active either in its oxidase or dehydrogenase form. The study of plasma and lymphocytic xanthine oxidase (XO) and xanthine dehydrogenase (XDG) activities is of emerging interest because of their putative role in initiation and chronization of RA.ObjectivesEvaluation the relationship between RA activity and XO and XDG activities using both plasma and lysed lymphocyte samples.MethodsThe research was carried out in agreement with the WMA Declaration of Helsinki principles after the local ethical board approval. RA diagnosis was verified using ACR/EULAR criteria (2010). RA activity was measured using the Disease Activity Score of 28 joints (DAS28). Blood lymphocytes were isolated by means of density gradient centrifugation in lymphosep (JCN Biomedicals), 1.077-1.079 g/ml. XO (ЕС 1.17.3.2) and XDG (ЕС 1.17.1.4) activities in plasma and lysed lymphocytes were measured using spectrophotometric techniques and expressed as nmol/ml/min [1]. Data are presented as median and quartiles (Me (Q25; Q75). Differences were considered significant when p<0.05.Results77 RA patients (57 women and 20 men) were enrolled in the study. Mean age of patients was 45 (37; 49) years, mean RA duration was 8 (6; 10) years. 16 (21%) RA patients had low disease activity, 49 (63%) patients moderate, and 12 (16%) patients had high one. 30 (19 women and 16 men) healthy persons comprised the control group. Reference ranges for plasma XO and XDG activities were 2.60–3.96 nmol/min/ml and 4.49–5.93 nmol/min/ml, respectively. Reference ranges for XO and XDG activities in lysed lymphocytes were 14.11-31.33 nmol/min/ml and 18.62-39.64 nmol/min/ml, respectively. Plasma enzymatic pattern in RA patients was characterized by increase in XO activity (p<0.001) and a somewhat decrease in XDG activity (p=0.059). Lymphocytic enzymatic pattern in RA patients was characterized by decreased activity of both enzymes (p<0.001 for both cases). Plasma XO activity was increased and lymphocytic XO activity was decreased in all the grades of RA activity. XO activity reached its highest changes at maximum disease activity. Plasma XDG activity was increased in low disease activity (р<0.001), while patients with moderate or high disease activities were characterized by decreased activity of this enzyme (р=0.008). Lymphocytic XDG activity was decreased in all the grades of disease activity (р<0.001). XDG activity reached its highest changes at maximum disease activity. Activities of XO and XDG in lymphocytes negatively correlated with RA activity. Activities of XO in plasma positively correlated with RA activity, while XDG activity negatively correlated with RA activity.ConclusionPlasmatic and lymphocytic enzymatic patterns in RA patients were characterized by multidirectional changes of XO and XDG activities. Multiple correlations were found between RA activity and enzyme activities in both studied compartments. These changes in oxidant enzyme activities may point at involvement of free radical oxidation in the RA pathogenesis. Free radical generation triggers metabolic cascades that lead to cell damage, premature death, promote endothelial dysfunction, extracellular neutrophil trap formation, support chronic inflammation and joint destruction, and other organs and systems under oxidative stress.