Improving the NQO1-inducing activities of phenolic acids from radix Salvia miltiorrhiza: a methylation strategy

NAD(P)H: quinone oxidoreductase1 (NQO1) is an important detoxification enzyme that can protect mammalian cells against toxic quinones and reduce the risk of tumorigenesis. In this study, it was found that salvianolic acid B (SaB), lithospermic acid (LA), and rosmarinic acid (RA), three main hydrophilic constituents in Danshen, conjugated with glutathione (GSH) easily in vitro but exhibited no NQO1-inducing activities in Hepa 1c1c7 cells, which might attribute to their poor absorptions. After a simple methylation strategy that aimed at improving the liposolubility, both the NQO1-inducing activities and the absorptions in cells of the phenolic acids improved obviously, without losing the GSH-conjugating abilities. The concentration to double the specific activity of NQ01 values of methylated products of lithospermic acid and rosmarinic acid were 17.86 ± 2.34 μg/mL and 11.97 ± 0.60 μg/mL, respectively. The findings indicated that methylation is an effective strategy to improve the NQO1-inducing activities of phenolic acids in Danshen.