NITRIC-OXIDE AS S-NITROSOPROTEINS IN RHEUMATOID-ARTHRITIS

Objective. Nitric oxide (NO) is a free radical involved in inflammatio n and immune reactions. The presence of NO is usually assessed by assa ying its degradation products, nitrite and nitrate. NO binds to thiol- containing proteins to form S-nitrosoproteins (SNP). The aim of this s tudy was to investigate the presence of S-NP, together with nitrite an d nitrate, in patients with rheumatoid arthritis (RA). Methods. Forty patients with RA were studied and compared with 24 patients with osteo arthritis (OA) and 21 control subjects. Fourteen patients were treated with 3 consecutive pulses of methylprednisolone for flares of RA. Nit rite was measured by the Griess reaction, and nitrate by a spectrophot ometric assay using nitrate reductase, Spectrofluorometry coupled with the inner filter effect was used for the measurement of S-NP. Results . S-NP was detected in all RA samples, both in serum and synovial flui d (SF). Serum and articular S-NP concentrations were correlated (P < 0 .03). In RA, nitrite and S-NP levels were higher in SF than in serum; higher SF levels of the 3 compounds were observed in RA than in OA. S- NP levels in RA patients decreased significantly (P < 0.03) after puls e methylprednisolone treatment, in parallel with the clinical improvem ent. Conclusion. S-NP, a biologically active form of NO, was consisten tly present in RA,with higher concentrations within the arthritic join t, S-NP assays should be added to nitrite and nitrate assays for the e valuation of NO metabolism. S-NP could be a stable storage form of act ive NO in RA, and its measurement could be useful in evaluating pharma cologic interventions that modulate NO generation.