Objectives In this study serum antioxidant and oxygen derived free radical status of patients with ankylosing spondylitis (AS) has been investigated and compared with age and sex matched healthy controls.

Methods Thirty patients fulfilling the New York criteria for AS and age and sex matched 16 healthy control subjects were included in the study. Patients who were smoking, under the treatment of DMARDs or any other drugs (except NSAIDs informally used by the patients) excluded.

Catalase (CAT) (EC 1.11.1.6) activity was measured by the determination of rate constant of hydrogen peroxide decomposition. Total (Cu-Zn and Mn) SOD (EC 1.15.1.1) activity was determined by the method based on the inhibition of NBT reduction by the xanthine-xanthine oxidase system. Malandialdehyde (MDA) levels determination was based on the coupling of MDA with thiobarbituric acid (TBA) at +95 ºC. XO (EC 1.2.3.2) activity was measured spectrophotometrically by the formation of uric acid from xanthine through the increase in absorbency at 293 nm. Nitrite (NO2-) and nitrate (NO3-) were estimated as an index of NO production. Quantitation of nitrate and nitrite was based on the Griess reaction, in which a chromophore with a strong absorbency at 540 nm is formed by reaction of nitrite with a mixture of naphthlethylenediamine and sulphanilamide.

Results Patients had significantly higher MDA and CAT activity with respect to controls. CAT activity of patients correlated significantly with CRP and ESR levels.

Conclusion Our results indicate that MDA and CAT activity increase in patients with AS, and CAT activity may be related to disease activity.