Tryptophan Metabolism in the Synovial Fluid in Rheumatoid Arthritis and Osteoarthritis

Abstract

Tryptophan and its intermediate metabolites in the synovial fluid were studied in order to know a specificity of the tryptophan metabolism in rheumatoid arthritis and osteoarthritis. A metabolic map was made, and the pathways of tryptophan breakdown in both diseases were compared. It was found that tryptophan in rheumatoid arthritis was metabolized mainly to anthranilic acid through kynurenine, whereas in osteoarthritis the pathway of kynurenic acid and nicotinic acid was characteristic.
Tryptophan in the blood and the synovial fluid, and intermediate tryptophan metabolites in the synovial fluid were determined for the purpose of examining the specificity of tyrptophan metabolism in joint diseases.
1) The fluorescent spots in the concentrate of the synovial fluid, namely anthranilic acid, xanthurenic acid and 3-hydroxykynurenine derivative and kynurenine, were found in both diseases.
2) The tryptophan content in the synovial fluid in rheumatoid arthritis was found to be higher than that of osteoarthritis, but no change was found in the blood of joint diseases.
3) No relation was found between the tryptophan content in the blood and theexistence of joint hydrops in both diseases and also among the tryptophan content in blood and synovial fluid and stages in rheumatoid arthritis.
4) The closest correlation was found between the tryptophan content in the synovial fluid and the erythrocyte sedimentation rate in rheumatoid arthritis.
5 Among the tryptophan intermediates in synovial fluid, kynurenine and anthranilic acids were higher in rheumatoid arthritis than those in osteoarthritis, but kynurenic acid and nicotinic acid contents in rheumatoid arthritis were found to be about half those in osteoarthritis. No difference was found in xanthurenic acid content between the two diseases.