Hypoxanthine, xanthine, and urate in synovial fluid from patients with inflammatory arthritides

As nucleotide catabolism increases during tissue injury the appearance of purine metabolites in inflamed synovial fluid might be of value in understanding the joint damage in inflammatory arthritides. In this study, therefore, synovial and plasma concentrations of hypoxanthine, xanthine, and urate in 16 patients with rheumatoid arthritis (three with psoriatic arthropathy) were analysed. It was found that their plasma concentrations of hypoxanthine were greater than those of a reference group of healthy subjects. The synovial fluid concentrations of hypoxanthine, xanthine, and urate were higher than corresponding concentrations in plasma. Positive correlations were found between the respective plasma and synovial fluid values of xanthine and urate. These findings indicate a local enhanced purine metabolism in inflamed joint tissue and diffusion of oxypurines from joint cavity to plasma. No relation was found between measured metabolites and disease duration, radiological joint findings, or synovial fluid cells. Except for a weak correlation between plasma urate and serum haptoglobin, measured purine metabolites were not related to laboratory measures of systemic inflammation.