Identification of colonic metabolites of 5‐hydroxylnobiletin and their roles in colon cancer inhibition

Abstract

Previously, we reported that oral administration of 5‐ hydroxylnobiletin (5HN, a citrus flavonoid) potently inhibited colon carcinogenesis in mice. To further understand the molecular mechanism involved, we investigated colonic metabolism of 5HN in mice after oral administration for 16 weeks. Utilizing HPLC, UV spectroscopy, 1H and 13C NMR, and mass spectroscopy, we identified 8 metabolites of 5HN in the colon. They are mono‐, di‐, or tri‐demethylated derivatives of 5HN. We synthesized 3 major metabolites i.e. 5,3′‐didemethylnobiletin (M1), 5,4′‐ didemethylnobiletin (M2), and 5,3′,4′‐tridemethylnobiletin (M3), and compared their bioactivities with those of 5HN. All 3 metabolites showed stronger anti‐proliferative and pro‐apoptotic effects on colon cancer cells than 5HN, especially M1 was more than 50‐fold stronger than 5HN. M1 showed similar antiinflammatory effects as 5HN in lipopolysaccharide‐stimulated macrophages, while M2 was 3‐fold more potent in anti‐inflammation than 5HN. Moreover, M1 showed more than 10‐fold stronger anti‐angiogenic activities than 5HN in a capillary tube formation assay of human umbilical vein endothelial cells. In conclusion, our results demonstrated that colonic metabolites of 5HN had potent activities in inhibiting cancer cell growth, suppressing inflammation, and decreasing angiogenesis, which may contribute significantly to colon cancer inhibition.Grant Funding Source: NIH, AICR and USDA