Cysteine-Conjugated Metabolite of Ginger Component [6]-Shogaol Serves as a Carrier of [6]-Shogaol in Cancer Cells and in Mice

Shogaols, a series of major constituents in dried ginger (Zingiber officinale), show high anticancer potencies. Previously, we reported that a major metabolite resulting from the mercapturic acid pathway, S-cysteinyl-[6]-shogaol (M2), showed comparable growth inhibitory effects toward cancer cells to [6]shogaol (6S). Here, we probe the mechanism by which M2 exerts its bioactivity. We utilized a series of chemical stability tests in conjunction with bioassays to show that thiol-conjugates display chemopreventative potency by acting as carriers of active ginger component 6S. M2 chemical degradation to 6S was observed in an environment most resembling physiological conditions, with a pH of 7.4 at 37 degrees C. The metabolic profiles of M2 in cancer cells HCT-116 and H-1299 resembled those of 6S, indicating that its biotransformation route was initiated by deconjugation. Further, the presence of excess glutathione significantly delayed 6S and M2 metabolism and counteracted cell death induced by 6S and M2, suggesting that increasing available free thiols exogenously both promoted the formation of 5-glutathionyl-[6]-shogaol (M13) and inhibited the production of free 6S from M2 deconjugation, resulting in delayed 6S cell entry and bioactivity. Given the chemopreventative properties of M2 and our observations in vitro, we investigated its metabolism in mice. M2 and 6S showed similar metabolic profiles in mouse urine and fecal samples. Six new thiol-conjugated metabolites (M16-M21), together with previously reported ones; were identified by LC/MS. In particular, the increase of 5-N-acetylcystenyl-[6]-shogaol (MS) and its 3'-demethylated product (M16) abundance in mouse feces after treatment with M2 indicates that in addition to acting as a carrier of 6S, M2 is also directly acetylated to MS, which is further demethylated to M16 in vivo. In conclusion, the cysteine-conjugated metabolite of [6]-shogaol M2 exerts its bioactivity by acting as a carrier of 6S in both cancer cells and in mice.