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

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Abstract
L-TRYPTOPHAN may be used as a model endogenous molecule to study the binding characteristics of the plasma proteins of patients with connective-tissue diseases. A drug's ability to displace L-tryptophan from binding to human serum albumin may also represent a new in-vitro assay for screening drugs for potential anti-inflammatory activity. In patients with rheumatoid arthritis, ankylosing spondylitis, and psoriatic arthritis, antirheumatic drugs displace L-tryptophan from plasma proteins in vivo, whereas withdrawal of such therapy is associated with excessive binding of the amino-acid to plasma proteins. In children with Still's disease, virtually all plasma tryptophan exists in the protein-bound form, and protein-bound tryptophan is less easily displaced from Still's disease plasma than from healthy children's plasma by antirheumatic drugs in vitro. Results obtained with the novel in-vitro assay described indicate its greater sensitivity than the Mizushima test for screening antirheumatic agents.

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