Identification of Xanthomicrol as a Major Metabolite of 5-demethyltangeretin in Mouse Gastrointestinal Tract and Its Inhibitory Effects on Colon Cancer Cells

Biotransformation may greatly affect the biological properties of dietary compounds. The metabolites generated in the body by the biotransformation may have different bioactivities in comparison with the ingested parent compounds. Polymethoxyflavones (PMFs) are natural bioactive flavonoids almost exclusively present in citrus fruits. 5-demethyltangeretin (5DT) is a unique PMF that has been demonstrated with potent chemopreventive effects on various human cancer cells. In this study, we determined the metabolic fate of 5DT in mice and the bioactivities of its major metabolite. We found that 5DT underwent extensive biotransformation in 5DT-fed mice, and demethylated and hydroxylated metabolites were produced via phase I metabolism, while glucuronide and sulfate conjugates were generated via phase II metabolism. In particular, 4′ position on the B-ring of 5DT was the primary site for demethylation (formation of xanthomicrol, XAN), 3′ position on the B-ring was the primary site for hydroxylation, and 5 position on the A-ring was the primary site for methylation. Importantly, it is observed that the colonic level of XAN was much higher than that of 5DT. Therefore, next, we investigated the chemopreventive effects of XAN on HCT116 human colon cancer cells. It was found that XAN significantly inhibited the growth of HCT116 cells by inducing cell cycle arrest and cellular apoptosis and modulated multiple key signaling pathways associated with colon cancer in an anti-carcinogenic direction. For example, XAN treatment upregulated p53, and p21 and downregulated cyclin D and CDK4 level, compared to untreated control cells. In conclusion, this study identified major metabolites of 5DT in the gastrointestinal tract, and demonstrated the suppressive effects of its primary colonic metabolite —XAN— on colon cancer in vitro. NIH, USDA-NIFA.