Detection of xanthine oxidase in human plasma

Xanthine oxidase is a highly versatile enzyme which is widely distributed among various species. Though the presence of the enzyme in serum is not yet established, high antibody titre of this enzyme has been reported. Xanthine oxidase is thought to be the principal source of free radical generation via degradation of nucleotides to the end product, uric acid. The aim of this study was to detect xanthine oxidase activity in human plasma and report any significant relationships found between its activity and variables such as race, age and sex for the sample size studied. Forty six normal healthy individuals (14 males and 32 females) were studied. The enzyme activity was measured by a spectrophotometric method whereby the reduction of ferricytochrome c by free radicals was calculated and expressed as nmol O2 production/ml/min. Results obtained showed that there was a positive relationship between xanthine oxidase activity with age (r = 0.415, p < 0.05) and weight (r = 0.369, p < 0.05) in the normal individual. For the age group 30-39 yrs (n = 11), a higher enzyme activity was observed in males (2.71 +/- 1.44) as compared to females (2.34 +/- 1.23) but it was not significant (p = 0.53). For racial distribution, the Malays [M] have a higher enzyme activity (2.65 +/- 0.86, N = 32) than their Indian [I] (2.27 +/- 0.58; N = 7) and Chinese counterparts [C] (1.44 +/- 1.22; N = 7) but this was also not statistically significant (M vs I: p = 0.39; M vs C: p = 0.07; I vs C: p = 0.16). In conclusion this study showed that there is a measurable amount of xanthine oxidase activity in the human plasma.