Evaluation of anticancer activities of phenolic compounds in blueberries and muscadine grapes
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Research has shown that diets rich in phenolic compounds may be associated with lower risk of several chronic diseases including cancer. This study systematically evaluated the bioactivities of phenolic compounds in blueberries and muscadine grapes, and assessed their potential cell growth inhibition and apoptosis induction effects using two colon cancer cell lines (HT-29 and Caco-2), and one liver cancer cell line (HepG2). In addition, the absorption of blueberry anthocyanin extracts was evaluated using Caco-2 human intestinal cell monolayers. Polyphenols in three blueberry cultivars (Briteblue, Tifblue and Powderblue), and four cultivars of muscadine (Carlos, Ison, Noble, and Supreme) were extracted and freeze dried. The extracts were further separated into phenolic acids, tannins, flavonols, and anthocyanins using a HLB cartridge and LH20 column. In both blueberries and muscadine grapes, some individual phenolic acids and flavonoids were identified by HPLC with more than 90% purity in anthocyanin fractions. The dried extracts and fractions were added to the cell culture medium to test for cell growth inhibition and induction of apoptosis. Polyphenols from both blueberries and muscadine grapes had significant inhibitory effects on cancer cell growth. The phenolic acid fraction showed relatively lower bioactivities with 50% inhibition at 0.5-3 µg/mL. The intermediate bioactivities were observed in the flavonol and tannin fractions. The greatest inhibitory effect among all four fractions was from the anthocyanin fractions in the three cell lines. Cell growth was significantly inhibited more than 50% by the anthocyanin fractions at concentrations of 15-300 µg/mL. Anthocyanin fractions from blueberries and muscadine grapes also resulted in significant increase in DNA fragmentation, indicating the induction of apoptosis. The results of the transport/absorption study showed that anthocyanins from blueberries could be transported through the Caco-2 cell monolayers although the transport/absorption efficiency was relatively low compared to other aglycone polyphenols. Delphinidin-glucopyranoside (Dp-glc) showed the lowest transport/absorption efficiency, and malvidin-glucopyranoside showed the highest transport/absorption efficiency. Our result indicates that more free hydroxyl groups and less OCH3 group can decrease the bioavailability of anthocyanins. In addition, the results showed that glucose-based anthocyanins might have higher bioavailability than galactose-based anthocyanins. These findings suggest that blueberries and muscadine grapes intake may reduce cancer risk.