Metabolism of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) by human CYP1B1 genetic variants

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Abstract

Human cytochrome P450 1B1 (CYP1B1) plays a critical role in the metabolic activation of a variety of procarcinogens, including 2-amino-1-methyl-6- phenylimidazo[4,5-b]pyridine (PhIP). The existence of human CYP1B1 missense genetic variants has been demonstrated, but their activities in metabolizing PhIP are unknown. In this study, we expressed 15 naturally occurring CYP1B1 variants (with either single or multiple amino acid substitutions) and determined their activity changes in metabolizing PhIP to its two major metabolites, 2-hydroxyamino-PhIP and 4′-hydroxy-PhIP. Although the PhIP-metabolizing activities of four variants (Ala119Ser, Pro 379Leu, Ala443Gly, Arg48Gly/Leu 432Val) were comparable with that of the expressed wild-type CYP1B1, five variants (Trp57Cys, Gly61Glu, Arg48Gly/ Ala119Ser, Arg48Gly/Ala119Ser/Leu 432Val, Arg48Gly/Ala119Ser/ Leu 432Val/Ala443Gly) exhibited more than 2-fold decrease in activity and a reduction in the catalytic efficiency (Vmax/K m) for both N- and 4-hydroxylation of PhIP. Six variants (Gly 365Trp, Glu387Lys, Arg390His, Pro 437Leu, Asn453Ser, Arg469Trp) showed little activity in PhIP metabolism, but the molecular mechanisms involved are apparently different. The microsomal CYP1B1 protein level was significantly decreased for the Trp365, Lys387, and His390 variants and was not detectable for the Ser453 variant. In contrast, there was no difference between the Trp469 variant and the wild-type in the microsomal CYP1B1 protein level and P450 content but the Trp 469 variant totally lost its metabolic activity toward PhIP. The Leu437 variant also had a substantial amount of CYP1B1 protein in the microsomes, but there was a lack of detectable P450 peak and activity. Our results should be useful in selecting appropriate CYP1B1 variants as cancer susceptibility biomarkers for human population studies related to PhIP exposure.

Original languageEnglish (US)
Pages (from-to)745-752
Number of pages8
JournalDrug Metabolism and Disposition
Volume36
Issue number4
DOIs
StatePublished - Apr 1 2008

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Cytochrome P-450 Enzyme System
2-amino-1-methyl-6-phenylimidazo(4,5-b)pyridine
Proteins
Amino Acid Substitution
Hydroxylation
Tumor Biomarkers
Microsomes

All Science Journal Classification (ASJC) codes

  • Pharmacology
  • Pharmaceutical Science

Cite this

@article{b8689e0e95f3469cb24a17cd9be660c2,
title = "Metabolism of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) by human CYP1B1 genetic variants",
abstract = "Human cytochrome P450 1B1 (CYP1B1) plays a critical role in the metabolic activation of a variety of procarcinogens, including 2-amino-1-methyl-6- phenylimidazo[4,5-b]pyridine (PhIP). The existence of human CYP1B1 missense genetic variants has been demonstrated, but their activities in metabolizing PhIP are unknown. In this study, we expressed 15 naturally occurring CYP1B1 variants (with either single or multiple amino acid substitutions) and determined their activity changes in metabolizing PhIP to its two major metabolites, 2-hydroxyamino-PhIP and 4′-hydroxy-PhIP. Although the PhIP-metabolizing activities of four variants (Ala119Ser, Pro 379Leu, Ala443Gly, Arg48Gly/Leu 432Val) were comparable with that of the expressed wild-type CYP1B1, five variants (Trp57Cys, Gly61Glu, Arg48Gly/ Ala119Ser, Arg48Gly/Ala119Ser/Leu 432Val, Arg48Gly/Ala119Ser/ Leu 432Val/Ala443Gly) exhibited more than 2-fold decrease in activity and a reduction in the catalytic efficiency (Vmax/K m) for both N- and 4-hydroxylation of PhIP. Six variants (Gly 365Trp, Glu387Lys, Arg390His, Pro 437Leu, Asn453Ser, Arg469Trp) showed little activity in PhIP metabolism, but the molecular mechanisms involved are apparently different. The microsomal CYP1B1 protein level was significantly decreased for the Trp365, Lys387, and His390 variants and was not detectable for the Ser453 variant. In contrast, there was no difference between the Trp469 variant and the wild-type in the microsomal CYP1B1 protein level and P450 content but the Trp 469 variant totally lost its metabolic activity toward PhIP. The Leu437 variant also had a substantial amount of CYP1B1 protein in the microsomes, but there was a lack of detectable P450 peak and activity. Our results should be useful in selecting appropriate CYP1B1 variants as cancer susceptibility biomarkers for human population studies related to PhIP exposure.",
author = "White, {Lori A.} and Hong, {Jun Yan}",
year = "2008",
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doi = "https://doi.org/10.1124/dmd.107.016824",
language = "English (US)",
volume = "36",
pages = "745--752",
journal = "Drug Metabolism and Disposition",
issn = "0090-9556",
publisher = "American Society for Pharmacology and Experimental Therapeutics",
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T1 - Metabolism of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) by human CYP1B1 genetic variants

AU - White, Lori A.

AU - Hong, Jun Yan

PY - 2008/4/1

Y1 - 2008/4/1

N2 - Human cytochrome P450 1B1 (CYP1B1) plays a critical role in the metabolic activation of a variety of procarcinogens, including 2-amino-1-methyl-6- phenylimidazo[4,5-b]pyridine (PhIP). The existence of human CYP1B1 missense genetic variants has been demonstrated, but their activities in metabolizing PhIP are unknown. In this study, we expressed 15 naturally occurring CYP1B1 variants (with either single or multiple amino acid substitutions) and determined their activity changes in metabolizing PhIP to its two major metabolites, 2-hydroxyamino-PhIP and 4′-hydroxy-PhIP. Although the PhIP-metabolizing activities of four variants (Ala119Ser, Pro 379Leu, Ala443Gly, Arg48Gly/Leu 432Val) were comparable with that of the expressed wild-type CYP1B1, five variants (Trp57Cys, Gly61Glu, Arg48Gly/ Ala119Ser, Arg48Gly/Ala119Ser/Leu 432Val, Arg48Gly/Ala119Ser/ Leu 432Val/Ala443Gly) exhibited more than 2-fold decrease in activity and a reduction in the catalytic efficiency (Vmax/K m) for both N- and 4-hydroxylation of PhIP. Six variants (Gly 365Trp, Glu387Lys, Arg390His, Pro 437Leu, Asn453Ser, Arg469Trp) showed little activity in PhIP metabolism, but the molecular mechanisms involved are apparently different. The microsomal CYP1B1 protein level was significantly decreased for the Trp365, Lys387, and His390 variants and was not detectable for the Ser453 variant. In contrast, there was no difference between the Trp469 variant and the wild-type in the microsomal CYP1B1 protein level and P450 content but the Trp 469 variant totally lost its metabolic activity toward PhIP. The Leu437 variant also had a substantial amount of CYP1B1 protein in the microsomes, but there was a lack of detectable P450 peak and activity. Our results should be useful in selecting appropriate CYP1B1 variants as cancer susceptibility biomarkers for human population studies related to PhIP exposure.

AB - Human cytochrome P450 1B1 (CYP1B1) plays a critical role in the metabolic activation of a variety of procarcinogens, including 2-amino-1-methyl-6- phenylimidazo[4,5-b]pyridine (PhIP). The existence of human CYP1B1 missense genetic variants has been demonstrated, but their activities in metabolizing PhIP are unknown. In this study, we expressed 15 naturally occurring CYP1B1 variants (with either single or multiple amino acid substitutions) and determined their activity changes in metabolizing PhIP to its two major metabolites, 2-hydroxyamino-PhIP and 4′-hydroxy-PhIP. Although the PhIP-metabolizing activities of four variants (Ala119Ser, Pro 379Leu, Ala443Gly, Arg48Gly/Leu 432Val) were comparable with that of the expressed wild-type CYP1B1, five variants (Trp57Cys, Gly61Glu, Arg48Gly/ Ala119Ser, Arg48Gly/Ala119Ser/Leu 432Val, Arg48Gly/Ala119Ser/ Leu 432Val/Ala443Gly) exhibited more than 2-fold decrease in activity and a reduction in the catalytic efficiency (Vmax/K m) for both N- and 4-hydroxylation of PhIP. Six variants (Gly 365Trp, Glu387Lys, Arg390His, Pro 437Leu, Asn453Ser, Arg469Trp) showed little activity in PhIP metabolism, but the molecular mechanisms involved are apparently different. The microsomal CYP1B1 protein level was significantly decreased for the Trp365, Lys387, and His390 variants and was not detectable for the Ser453 variant. In contrast, there was no difference between the Trp469 variant and the wild-type in the microsomal CYP1B1 protein level and P450 content but the Trp 469 variant totally lost its metabolic activity toward PhIP. The Leu437 variant also had a substantial amount of CYP1B1 protein in the microsomes, but there was a lack of detectable P450 peak and activity. Our results should be useful in selecting appropriate CYP1B1 variants as cancer susceptibility biomarkers for human population studies related to PhIP exposure.

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U2 - https://doi.org/10.1124/dmd.107.016824

DO - https://doi.org/10.1124/dmd.107.016824

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VL - 36

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JO - Drug Metabolism and Disposition

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