NITRIC-OXIDE (NO)-RELEASING PATHWAY OF FK409 IN THE PRESENCE OF SULFHYDRYL-BEARING COMPOUNDS

Purpose. We have recently reported that degradation of FK409 with gene ration of NO is spontaneous and is accelerated in the presence of sulf hydryl-bearing compounds, such as L-cysteine (Cys) and glutathione (GS H). The purpose of the present study is to investigate the NO-releasin g pathway of FK409 in the presence of sulfhydryl-bearing compounds. Me thods, The degradation process of FK409 in the presence of Cys or GSH was investigated by means of H-1-nuclear magnetic resonance (NMR) spec troscopy and high-performance liquid chromatography (HPLC). Results. T he degradation of FK409 in the presence of Cys was dependent on concen tration of Cys, and showed pH-dependency, accelerating with an increas e in pH. The H-1-NMR spectra of FK409 with Cys suggested that time-dep endent elimination of the hydrogen atom at the a-position of the nitro moiety (5-position) was accelerated by Cys in weakly alkaline solutio n. Cys and GSH were transformed readily, concomitant with FX409 degrad ation, to give their oxidized forms and probably S-nitrosothiols. Conc lusion. The effect of sulfhydryl-bearing compounds on FK409 degradatio n is due to the acceleration of deprotonation of the hydrogen atom at the 5-position by thiolate anion as well as hydroxyl ion. Sulfhydryl-b earing compounds reacted with the released NO resulting in formation o f disulfides via intermediate S-nitrosothiols.