Sulfate conjugation by phenolsulfotransferases (PSTs) is an important process in the detoxification of xenobiotics and endogenous compounds. There are two forms of PSTs for the sulfation of small phenols (PST-P) and monoamines (PST-M). Phenolic acids are known to increase the activities of PST-P and PST-M. The purpose of this study is to investigate the synergistic effect of the combinations of phenolic acids on human PSTs activities. The combinations of p-hydroxybenzoic acid, gentisic acid, ferulic acid, gallic acid, and coumaric acid in a random order for their effects on PSTs activities were evaluated at concentrations of 2.5, 5.0, and 7.5 μM. The PST-M activity was significantly increased when gentisic acid was combined with each of the other phenolic acids. When p-hydroxybenzoic acid was combined with each of the other phenolic acids, a synergistic effect with respect to the promotion of PST-P activity was obtained. A potential synergistic effect for the PST-P activity was also found in the following combination: p-hydroxybenzoic acid + gallic acid + gentisic acid, p-hydroxybenzoic acid + gallic acid + m-coumaric acid, p-hydroxybenzoic acid + o-coumaric acid + p-coumaric acid, p-hydroxybenzoic acid + o-coumaric acid + m-coumaric acid, gallic acid + gentisic acid + p-coumaric acid, and gallic acid + o-coumaric acid + m-coumaric acid. Therefore, the activities of both forms of PSTs can be promoted by all of these combinations of phenolic acids. These results provide a better understanding regarding the effect of phenolic acids on human PSTs activities, as well as more information on the intake of antioxidant phenolic acids for human health.
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