Effect of vegetables on human phenolsulfotransferases in relation to their antioxidant activity and total phenolics

Epidemiology studies have shown that consumption of fruits and vegetables is associated with the prevention of chronic diseases such as cancer and cardiovascular disease. Induction of cellular phase II detoxifying enzymes is associated with cancer preventive potential. Phenolsulfotransferases (PSTs) are traditionally known as phase II drug-metabolizing or detoxifying enzymes that facilitate the removal of drugs and other xenobiotic compounds. Phenolic acids are known to increase the activities of PSTs. In the present study, human HepG2 cells were used as model to investigate the influence of twenty vegetables on human PST activity and to evaluate the relationships to their antioxidant activity and total phenolics content. The result showed that PST-P activity was significantly (p < 0.01) induced by asparagus, broccoli, cauliflower, celery and eggplant, whereas PST-M activity was induced by asparagus, broccoli, carrot, eggplant and potato at a concentration of 100 microg/ml. The vegetable extracts that induced both forms of PSTs activities were found to have higher antioxidant capacities and total phenolic content in the oxygen radical absorbance capacity (ORAC) and Folin-Ciocalteu assay. The major polyphenols in broccoli, the most potential inducer in both forms of PSTs activities, was antioxidant phenolic acids. HPLC retention times and standard spiked indicated the presence of gallic acid, p-hydroxybenzoic acid, p-coumaric acid, gentisic acid and ferulic acid in broccoli. The overall effect of vegetables tested on the activity of PST-P was well correlated to their ORAC value and total phenolics content (r= 0.82, p < 0.05 and r = 0.78, p < 0.05). These results imply that vegetables have a capability of inducing PST activity, and the PST induction may be possibly ascribed to antioxidant phenolic acids in vegetable extracts.