Preference for O-demethylation reactions in the oxidation of 2′-, 3′-, and 4′-methoxyflavones by human cytochrome P450 enzymes

Abstract

1. 2′-, 3′-, and 4′-Methoxyflavones (MeFs) were incubated with nine forms of recombinant human cytochrome P450 (P450 or CYP) enzymes in the presence of an NADPH-generating system and the products formed were analyzed with LC-MS/MS methods.

2. CYP1B1.1 and 1B1.3 were highly active in demethylating 4′MeF to form 4′-hydroxyflavone (rate of 5.0 nmol/min/nmol P450) and further to 3′,4′-dihydroxyflavone (rates of 2.1 and 0.66 nmol/min/nmol P450, respectively). 3′MeF was found to be oxidized by P450s to m/z 239 (M-14) products (presumably 3′-hydroxyflavone) and then to 3′,4′-dihydroxyflavone. P450s also catalyzed oxidation of 2′MeF to m/z 239 (M-14) and m/z 255 (M-14, M-14 + 16) products, presumably mono- and di-hydroxylated products, respectively.

3. At least two types of ring oxidation products having m/z 269 fragments were formed, although at slower rates than the formation of mono- and di-hydroxylated products, on incubation of these MeFs with P450s; one type was products oxidized at the C-ring, having m/z 121 fragments, and the other one was the products oxidized at the A-ring (having m/z 137 fragments).

4. Molecular docking analysis indicated the preference of interaction of O-methoxy moiety of methoxyflavones in the active site of CYP1A2.

5. These results suggest that 2′-, 3′-, and 4′-methoxyflavones are principally demethylated by human P450s to form mono- and di-hydroxyflavones and that direct oxidation occurs in these MeFs to form mono-hydroxylated products, oxidized at the A- or B-ring of MeF.

Keywords:

• Methoxyflavones
• O-demethylation
• oxidation
• human
• cytochrome P450
• CYP1B1
• CYP1A2

Disclosure statement

The authors declare no conflict of interest associated with this manuscript. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.

Additional information

Funding

This study was supported in part by JSPS KAKENHI [16K21710] (to H. N), [15K07770] (to S. T.), [17K08630] (to J. K.), [JP18K0600] (to M. K.), [17K08426] (to N. M.), and [17K08425] (to H. Y.), National Research Foundation of Korea [NRF-2019R1A2C1004722] (to D. K.), and United States Public Health Service grant [R01 GM118122] (to F. P. G.).