Influence of High‐Polyphenol Sorghum on Benzo[a]pyrene‐Metabolizing Enzymes

Colorectal cancer ranks among the top five most common types of cancer in the United States. Lifestyle, diet, and environmental factors are correlated to the increased risk of colon cancer. One of those environmental factors is the polycyclic aromatic hydrocarbon (PAHs) Benzo[a]pyrene (BaP), formed by the incomplete combustion of organic material. Human exposure to BaP occurs through air pollution, tobacco smoke, engine exhaust, and the consumption of BaP‐exposed foods. BaP crosses cellular membranes, and it becomes metabolically activated by Phase I enzymes, primarily cytochrome P450s (CYPs) and Epoxide Hydrolase, and subsequently has the potential to bind to DNA. The binding of BaP to DNA may result in adverse genotypic alterations, which may result in tumorigenesis. On the other hand, cellular Phase II enzymes play a role in the inactivation of BaP and its metabolites, which can facilitate the excretion of these molecules. Polyphenols, a group of plant micronutrients known for their antioxidant and anti‐inflammatory properties, have been suggested to contribute to the prevention of colon cancer. Extracts from two types of Sorghum bicolor were provided by the USDA ARS Kansas. Preliminary studies in our lab suggest that polyphenol‐rich varietals of the grain Sorghum affect pathways in carcinogenesis. Specifically, mRNA expression of UDP‐glucuronosyl transferase (UGT) 1A1, a Phase II PAH‐bioinactivating enzyme, is significantly increased in high‐polyphenol sorghum treated HCT116 cells. Therefore, we propose to investigate the impact of high‐polyphenol sorghum on BaP‐exposed colon cancer cells, assessing the expression and activity of Phase I and Phase II enzymes in particular. Our hypothesis is that compared to controls, high polyphenol sorghum extracts will decrease expression and activity of Phase I, and increase expression and activity of Phase II enzymes in BaP‐treated colon cancer cells. Human colorectal cancer HCT116 cells were incubated with either 0, 1, 2, or 5 µM BaP alone, Sorghum extracts alone, or in the presence of high‐polyphenol sorghum and Benzo[a] pyrene for up to 48 hours. RNA was extracted and reverse‐transcribed to cDNA. mRNA expression of carcinogen activating and inactivating enzymes was measured using qPCR. BaP alone increased mRNA expression of CYP1A1 as expected. Our high polyphenol Sorghum extract dramatically decreased mRNA expression of the Phase I enzyme CYP1B1, but also moderately increased mRNA expression of Epoxide Hydrolase. We plan to complete assessment of the expression and catalytic activity of Phase I and Phase II enzymes in the presence of high‐polyphenol sorghum and Benzo[a] pyrene. Our initial results suggest that high‐polyphenol Sorghum may be able to shift the balance of Phase I and Phase II enzymes in BaP‐exposed cells, and thus provide an avenue of a dietary approach to support chemoprevention.