Oxidation of 3 '-methoxyflavone, 4 '-methoxyflavone, and 3 ',4 '-dimethoxyflavone and their derivatives having 5,7-dihydroxyl moieties by human cytochromes P450 1B1 and 2A13

1. Oxidation of 3'-methoxyflavone, 4'-methoxyflavone, and 3',4'-dimethoxyflavone and their derivatives containing 5,7-dihydroxyl groups by human cytochrome P450 (P450 or CYP) 1B1 and 2A13 was determined using LC-MS/MS systems. 2. 3'-Methoxyflavone and 4'-methoxyflavone were mainly O-demethylated to form 3'-hydroxyflavone and 4'-hydroxyflavone, respectively, and then 3',4'-dihydroxyflavone at higher rates with CYP1B1 than with CYP2A13. 4'-Methoxy-5,7-dihydroxyflavone (acacetin) was found to be demethylated by CYP1B1 arid 2A13 to form 4',5,7-trihydroxyflavone (apigenin) at rates of 0.098(-1) arid 0.42 min(-1), respectively. 3'-Methoxy-5,7-dihydroxyflavone was also demethylated by both P450s, with CYP2A13 being more active. 3. 3',4'-Dimethoxyflavone was a good substrate for CYP1B1 but not for CYP2A13 and was found to be mainly O-demethylated to form 3',4'-dihydroxyflavone (at a rate of 4.2min(-1)) and also several ring-oxygenated products having m/z 299 fragments. Molecular docking analysis supported the proper orientation for formation of these products by CYP1B1. 4. Our present results showed that 3'- and 4'-methoxyflavone can be oxidised to their 0-demethylated products and, to a lesser extent, to ring oxidation products by both P450s 1B1 and 2A13 and that 3',4'-dimethoxyflavone is a good substrate for CYP1 B1 in forming both 0-demethylated and ring-oxidation products. Introduction of a 57diOHF moiety into these methoxylated flavonoids caused decreased in oxidation by CYP1B1 and 2A13.