PLASMA L-TRYPTOPHAN CONCENTRATIONS IN CHRONIC RHEUMATIC DISEASES AND THE EFFECTS OF SOME ANTIRHEUMATIC DRUGS ON THE BINDING OF THE AMINO-ACID TO PLASMA PROTEINS IN VIVO AND IN VITRO

L-TRYPTOPHAN may be used as a model endogenous molecule to studythe binding characteristics of the plasma proteins of patientswith connective-tissue diseases. A drug's ability to displaceL-tryptophan from binding to human serum albumin may also representa new in-vitro assay for screening drugs for potential anti-inflammatoryactivity. In patients with rheumatoid arthritis, ankylosingspondylitis, and psoriatic arthritis, antirheumatic drugs displaceL-tryptophan from plasma proteins in vivo, whereas withdrawalof such therapy is associated with excessive binding of theamino-acid to plasma proteins. In children with Still's disease,virtually all plasma tryptophan exists in the protein-boundform, and protein-bound tryptophan is less easily displacedfrom Still's disease plasma than from healthy children's plasmaby antirheumatic drugs in vitro. Results obtained with the novelin-vitro assay described indicate its greater sensitivity thanthe Mizushima test for screening antirheumatic agents. ^*Based on a paper presented at a combined meeting of the BritishAssociation for Rheumatology and Rehabilitation with the RoyalSociety of Medicine, Section of Rheumatology and Rehabilitation,Cardiff, September 1973.