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

Jing Fen Han, Xiao Yang He, Jason S. Herrington, Lori White, Jun Feng Zhang, Jun-Yan Hong

Research output: Contribution to journalArticle

7 Citations (Scopus)

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 (Ala 119 Ser, Pro 379 Leu, Ala 443 Gly, Arg 48 Gly/Leu 432 Val) were comparable with that of the expressed wild-type CYP1B1, five variants (Trp 57 Cys, Gly 61 Glu, Arg 48 Gly/ Ala 119 Ser, Arg 48 Gly/Ala 119 Ser/Leu 432 Val, Arg 48 Gly/Ala 119 Ser/ Leu 432 Val/Ala 443 Gly) exhibited more than 2-fold decrease in activity and a reduction in the catalytic efficiency (V max /K m ) for both N- and 4-hydroxylation of PhIP. Six variants (Gly 365 Trp, Glu 387 Lys, Arg 390 His, Pro 437 Leu, Asn 453 Ser, Arg 469 Trp) showed little activity in PhIP metabolism, but the molecular mechanisms involved are apparently different. The microsomal CYP1B1 protein level was significantly decreased for the Trp 365 , Lys 387 , and His 390 variants and was not detectable for the Ser 453 variant. In contrast, there was no difference between the Trp 469 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 Leu 437 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

Han, Jing Fen ; He, Xiao Yang ; Herrington, Jason S. ; White, Lori ; Zhang, Jun Feng ; Hong, Jun-Yan. / Metabolism of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) by human CYP1B1 genetic variants. In: Drug Metabolism and Disposition. 2008 ; Vol. 36, No. 4. pp. 745-752.
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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 (Ala 119 Ser, Pro 379 Leu, Ala 443 Gly, Arg 48 Gly/Leu 432 Val) were comparable with that of the expressed wild-type CYP1B1, five variants (Trp 57 Cys, Gly 61 Glu, Arg 48 Gly/ Ala 119 Ser, Arg 48 Gly/Ala 119 Ser/Leu 432 Val, Arg 48 Gly/Ala 119 Ser/ Leu 432 Val/Ala 443 Gly) exhibited more than 2-fold decrease in activity and a reduction in the catalytic efficiency (V max /K m ) for both N- and 4-hydroxylation of PhIP. Six variants (Gly 365 Trp, Glu 387 Lys, Arg 390 His, Pro 437 Leu, Asn 453 Ser, Arg 469 Trp) showed little activity in PhIP metabolism, but the molecular mechanisms involved are apparently different. The microsomal CYP1B1 protein level was significantly decreased for the Trp 365 , Lys 387 , and His 390 variants and was not detectable for the Ser 453 variant. In contrast, there was no difference between the Trp 469 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 Leu 437 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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Metabolism of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) by human CYP1B1 genetic variants. / Han, Jing Fen; He, Xiao Yang; Herrington, Jason S.; White, Lori; Zhang, Jun Feng; Hong, Jun-Yan.

In: Drug Metabolism and Disposition, Vol. 36, No. 4, 01.04.2008, p. 745-752.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Metabolism of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) by human CYP1B1 genetic variants

AU - Han, Jing Fen

AU - He, Xiao Yang

AU - Herrington, Jason S.

AU - White, Lori

AU - Zhang, Jun Feng

AU - Hong, Jun-Yan

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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 (Ala 119 Ser, Pro 379 Leu, Ala 443 Gly, Arg 48 Gly/Leu 432 Val) were comparable with that of the expressed wild-type CYP1B1, five variants (Trp 57 Cys, Gly 61 Glu, Arg 48 Gly/ Ala 119 Ser, Arg 48 Gly/Ala 119 Ser/Leu 432 Val, Arg 48 Gly/Ala 119 Ser/ Leu 432 Val/Ala 443 Gly) exhibited more than 2-fold decrease in activity and a reduction in the catalytic efficiency (V max /K m ) for both N- and 4-hydroxylation of PhIP. Six variants (Gly 365 Trp, Glu 387 Lys, Arg 390 His, Pro 437 Leu, Asn 453 Ser, Arg 469 Trp) showed little activity in PhIP metabolism, but the molecular mechanisms involved are apparently different. The microsomal CYP1B1 protein level was significantly decreased for the Trp 365 , Lys 387 , and His 390 variants and was not detectable for the Ser 453 variant. In contrast, there was no difference between the Trp 469 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 Leu 437 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 (Ala 119 Ser, Pro 379 Leu, Ala 443 Gly, Arg 48 Gly/Leu 432 Val) were comparable with that of the expressed wild-type CYP1B1, five variants (Trp 57 Cys, Gly 61 Glu, Arg 48 Gly/ Ala 119 Ser, Arg 48 Gly/Ala 119 Ser/Leu 432 Val, Arg 48 Gly/Ala 119 Ser/ Leu 432 Val/Ala 443 Gly) exhibited more than 2-fold decrease in activity and a reduction in the catalytic efficiency (V max /K m ) for both N- and 4-hydroxylation of PhIP. Six variants (Gly 365 Trp, Glu 387 Lys, Arg 390 His, Pro 437 Leu, Asn 453 Ser, Arg 469 Trp) showed little activity in PhIP metabolism, but the molecular mechanisms involved are apparently different. The microsomal CYP1B1 protein level was significantly decreased for the Trp 365 , Lys 387 , and His 390 variants and was not detectable for the Ser 453 variant. In contrast, there was no difference between the Trp 469 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 Leu 437 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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