VITAMIN E DELTA-TOCOTRIENOL AND METABOLITE: MODULATION OF GUT MICROBIOTA AND CHEMOPREVENTION OF COLORECTAL CANCER
Colorectal cancer is one of the leading causes of cancer deaths in the United States and multiple modifiable factors contribute to colorectal carcinogenesis. Gut microbiota are believed to play key roles in colon cancer development. Dietary factors may modulate gut microbiota composition, which may potentially have impact on carcinogenesis. Thus, it is reasonable to develop dietary interventions to effectively prevent colorectal cancer development through alteration of gut microbiota. In this thesis, the first objective is to evaluate the effect of vitamin E forms and metabolites, i.e., δ-tocotrienol (δTE), γ-tocotrienol (γTE) and δTE-13’-COOH (δTE-13’), respectively, on gut microbiota in mice. Healthy male balb/c mice were supplemented with a δTE/γTE mixture or δTE-13’ by gavage for two weeks, while control mice received soybean oil. We isolated DNAs from fecal samples and used 16S rRNA gene sequencing to evaluate the impact of these compounds on gut microbiota compositions. Further, we also examined the effect on short chain fatty acids (SCFAs). We observed that supplementation of δTE-13’ increased microbial richness using the Faith index. On the other hand, supplementation did not separate the microbial communities from the control group. But, these compounds managed to alter the relative abundances of several taxa that might present chemopreventive activities against colon cancer. Specifically, Desulfovibrio, a sulfur-reducing bacterium, was decreased after δTE/γTE supplementation. Eubacterium coprostanoligenes group, a group of microbes that can reduce circulating cholesterol, was increased after δTE/γTE supplementation. In addition, several members from the Lachnospiraceae family were elevated under δTE/γTE and δTE-13’ supplementation, and these microbes are known to produce SCFAs and maintain colonic health. However, the measurement of SCFAs showed that supplementation of δTE/γTE and δTE-13’ did not change SCFAs compared with controls. In the second project, I investigated anti-proliferative effects of combining δTE or δTE-13’ with sodium butyrate (NaBu) on human colorectal carcinoma HCT116 cells. Our data showed promising additive effects against cell growth. Collectively, these results indicate that δTE/γTE and δTE-13’ can modulate gut microbiota under healthy conditions, which provides insights into potential chemopreventive activities of these vitamin E forms. Our cell-based studies also showed additive anticancer effects of combining δTE or δTE-13’ with NaBu, which provides rationale to further develop combination of butyrate producers with vitamin E forms for cancer prevention.