Oxidation of 1-chloropyrene by human CYP1 family and CYP2A subfamily cytochrome P450 enzymes: catalytic roles of two CYP1B1 and five CYP2A13 allelic variants

Abstract

Chloropyrene, one of the major chlorinated polycyclic aromatic hydrocarbon contaminants, was incubated with human cytochrome P450 (P450 or CYP) enzymes including CYP1A1, 1A2, 1B1, 2A6, 2A13, 2B6, 2C9, 2D6, 2E1, 3A4, and 3A5. Catalytic differences in 1-chloropyrene oxidation by polymorphic two CYP1B1 and five CYP2A13 allelic variants were also examined.CYP1A1 oxidized 1-chloropyrene at the 6- and 8-positions more actively than at the 3-position, while both CYP1B1.1 and 1B1.3 preferentially catalyzed 6-hydroxylation.Five CYP2A13 allelic variants oxidized 8-hydroxylation much more than 6- and 3-hydroxylation, and the variant CYP2A13.3 was found to slowly catalyze these reactions with a lower kcat value than other CYP2A13.1 variants.CYP2A6 catalyzed 1-chloropyrene 6-hydroxylation at a higher rate than the CYP2A13 enzymes, but the rate was lower than the CYP1A1 and 1B1 variants. Other human P450 enzymes had low activities towards 1-chloropyrene.Molecular docking analysis suggested differences in the interaction of 1-chloropyrene with active sites of CYP1 and 2A enzymes. In addition, a naturally occuring Thr134 insertion in CYP2A13.3 was found to affect the orientation of Asn297 in the I-helix in interacting with 1-chloropyrene (and also 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, NNK) and caused changes in the active site of CYP2A13.3 as compared with CYP2A13.1.

Site-specific oxidation of flavanone and flavone by cytochrome P450 2A6 in human liver microsomes

“…We used CYP2A6.1 and 2A6.35 variants and CYP2A13.1 and 2A13.3 variants to determine if there are differences in catalytic specificities in the oxidation of flavanone and flavone. The results showed that activities of CYP2A6.1 and 2A13.1 were always higher than those of the respective CYP2A6.35 and CYP2A13.3 variants, supporting previous results for lower activities of these variants with other substrates examined (Han et al, 2012; Shimada et al, 2018; Hosono et al, 2017; Kumondai et al, 2018; Kim et al, 2018). HPLC profiles of flavanone product formation in human liver microsomes were basically similar to those by CYP2A6.1, except when liver sample HH2 was used (Figures 2 and 3).…”

“…2´-, 3´-, and 4´-Hydroxyflavanone (2´OHFva, 3´OHFva, and 4´OHFva) were purchased from Tokyo Kasei Co. (Tokyo). Other chemicals and reagents used in this study were obtained from the sources described previously or were of the highest quality commercially available (Shimada et al, 2018; Kakimoto et al, 2018).…”

“…In this study, we examined oxidation of flavanone and flavone by liver microsomes of four human samples, one of which (sample HH2), was defective in coumarin 7-hydroxylation activity and was thus assigned as a poor metabolizer of CYP2A6. We also determined catalytic differences in the ability of CYP2A6.1 and 2A6.35 and CYP2A13.1 and 2A13.3 to oxidize flavanone and flavone; our previous studies have shown catalytic differences due to variations in humans (Shimada et al, 2018; Kakimoto et al, 2018). Other human P450 enzymes, including CYP1A2 and 2B6, were used to determine abilities to oxidize these flavonoids.…”

The clinical value and potential molecular mechanism of the downregulation of MAOA in hepatocellular carcinoma tissues

“…We found downregulated DEGs that positively correlated with MAOA , especially CYP1A1 , CYP1A2 , CYP2A , CYP2E1 , CYP3A4 , GST , HSD11B1 , NAT , NAT2 , and UGT , were significantly aggregated in the chemical carcinogenesis pathway. Interestingly, CYP1A1 , CYP1A2 , CYP2A , CYP2E1 , and CYP3A4 all belong to genes that encode the essential enzymes of the cytochrome P450 system and participate in the metabolism and biological transformation of chemicals 44‐47 . Among these genes, CYP3A4 , which is highlighted in the KEGG pathway, played an important role in the carcinogenesis process of HCC by promoting the transformation from aflatoxin B1 to AFB1‐exo‐8,9‐epoxide, consistent with Bonomo et al 48 There is a consensus that AFB1, 49 the most powerful carcinogen to date, works as a trigger in the carcinogenesis of the liver.…”

New Perspectives of CYP1B1 Inhibitors in the Light of Molecular Studies

“…CYP1B1 variants are also investigated with regard to the metabolism of environmental pollutants [2]. Both allelic variants CYP1B1.1 and 1B1.3 preferentially oxidized 1-chloropyrene, a chlorinated polycyclic hydrocarbon, at the 6-position, while CYP1A1 catalyzed hydroxylation at the 6-and 8-positions more actively than that at the 3-position [107]. The orientation of 1-chloropyrene in the CYP1B1 binding site (3PM0) was determined with position 6 directed to the heme in the distance of 5.71 Å.…”