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Abstract

2-Mercaptomethyl-4-(4-methylphenyl)-4-oxobutanoic acid (KE-758), which is the active metabolite of 2-acetylthiomethyl-4-(4-methylphenyl)-4-oxobutanoic acid (KE-298), is a novel sulphydryl anti-rheumatic drug. In this study we analyzed the effect of KE-758 on the proliferation of murine lymphocytes, and on the production of nitric oxide (NO) by RAW264.7 murine macrophage cells. We compared its effect with other sulphydryl drugs such as d-penicillamine, bucillamine and auranofin. The proliferation of lymphocytes was measured by 3H-thymidine incorporation assay. Nitrite was measured using Griess Reagent. In the absence of copper ions, KE-758, d-penicillamine and bucillamine rarely affected the proliferation of concanavarin A (ConA) activated murine splenocytes. However, in the presence of copper, pharmacological concentrations of KE-758 but not d-penicillamine and bucillamine suppressed the proliferation of murine splenocytes through a hydrogen peroxide-dependent mechanism. Auranofin markedly suppressed the proliferation regardless of the presence of copper ions by reducing the cellular viability. Furthermore, only KE-758 markedly suppressed the proliferation of phorbol myristate acetate (PMA) plus ionomycin activated murine whole blood lymphocytes (WBL) even in the absence of exogenous copper ions by a hydrogen peroxide-independent mechanism. Meanwhile, lipopolysaccharide (LPS) or LPS plus interferon-gamma (IFN-γ) induced NO production by RAW264.7 cells were suppressed by KE-758 and auranofin but not by d-penicillamine and bucillamine. In conclusion, KE-758 is a novel immunosuppressive drug, which inhibits both lymphocyte and macrophage functions and its unique anti-rheumatic profile is distinct from that of d-penicillamine, bucillamine and auranofin.