Morphine metabolism revisited. II. Isolation and chemical characterization of a glutathionylmorphine adduct from rat liver microsomal preparations.

Incubation of tritium-labeled morphine and cold glutathione (GSH) or cold morphine and tritiated GSH with liver microsomal preparations obtained from phenobarbital-treated rats led to the identification by high performance liquid chromatography (HPLC) of a glutathionylmorphine adduct. Liquid secondary ion mass spectral analysis established the molecular weight of the metabolite to be 590 which corresponds to the mass of a mono-GSH-morphine adduct. High resolution (360 and 500 MHz) 1H-NMR experiments have led to the tentative assignment of the structure of this metabolite as 10-alpha-S-glutathionylmorphine. Based on both in vivo and in vitro data, the formation of this product appears to be mediated by cytochrome P-450 and to involve a reactive intermediate that may be responsible for the observed covalent binding of radiolabeled morphine to proteins and, at least in part, for the morphine-induced depletion of GSH in the rat.