OBJECTIVES--To develop and apply an immunochemical approach to the study of drug-plasma protein conjugates derived from the anti-arthritic drug D-penicillamine (DP). METHODS--An antiserum with specificity for protein-conjugated DP was raised in a rabbit. Plasma samples from patients receiving DP or from incubations of isolated normal plasma with DP were analysed for DP-derived conjugates by Western blotting using the anti-drug antibody. RESULTS--A single DP-positive protein band was detected in plasma samples from 15/16 patients with rheumatoid arthritis receiving DP but in none of 20 patients of similar disease status who had not taken DP. The positive band appeared in patients' plasma during the course of treatment with DP. It was seen under nonreducing but not reducing conditions indicating that the drug is disulphide linked to the protein. The drug-modified protein migrated to a position intermediate between the trailing edge of albumin and the leading edge of transferrin (both non-reduced) suggesting a molecular weight of between 66 and 77 kDa. Incubations of normal human plasma, but not purified albumin or transferrin, with low concentrations of DP generated the same distinct band plus several less intense DP-positive bands. CONCLUSIONS--Drug-plasma protein conjugates derived from DP in vivo and in vitro can be detected immunochemically by the Western blot method. Theories of DP immunotoxicity have implicated antigenicity of the drug, but this is the first immunochemical demonstration of a potential DP-derived antigen in human plasma. The method we describe may have application to studies of the relationship between DP antigenicity and toxicity.
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