Autoxidative quinone formation in vitro and metabolite formation in vivo from tea polyphenol (-)-epigallocatechin-3-gallate: studied by real-time mass spectrometry combined with tandem mass ion mapping.

(-)-Epigallocatechin-3- gallate (EGCG), the most abundant and biologically active compound in tea, has been proposed to have beneficial health effects, including prevention of cancer and heart disease. Based mainly on studies in cell-line systems, in which EGCG is not stable, different mechanisms of action of EGCG have been proposed. It has been proposed also that oxidation of EGCG and its production of reactive oxygen species are responsible for biological activities such as receptor inactivation and telomerase inhibition. It is unclear, however, whether this phenomenon occurs in vivo. In the present study, the stability of EGCG and product formation in Tris-HCl buffer was investigated using real- time mass spectrometry combined with tandem mass ion mapping. With real-time mass data acquisition, we demonstrate for the first time the formation of EGCG quinone, EGCG dimer quinone, and other related compounds. The structural information of the major appearing ions was provided by tandem mass analysis of each ion. A mechanism for the autoxidation of EGCG based on the structural information of these ions was proposed. None of these oxidation products were observed in the plasma samples of mice after treatment with 50 mg/kg EGCG, i.p. daily for 3 days. Instead, the methylated and conjugated metabolites of EGCG were observed. Therefore the roles of EGCG autoxidation in the biological activities of this compound in vivo remain to be investigated further.