title: Effect of Cytochrome b5 Content on the Activity of Polymorphic CYP1A2, 2B6, and 2E1 in Human Liver Microsomes.
abstract: Human cytochrome b5 (Cyt b5) plays important roles in cytochrome P450 (CYP)-mediated drug metabolism. However, the expression level of Cyt b5 in normal human liver remains largely unknown. The effect of Cyt b5 on overall CYP activity in human liver microsomes (HLM) has rarely been reported and the relationship between Cyt b5 and the activity of polymorphic CYP has not been systematically investigated. In this study, we found that the median value of Cyt b5 protein was 270.01 pmol/mg from 123 HLM samples, and 12- and 19-fold individual variation was observed in Cyt b5 mRNA and protein levels, respectively. Gender and smoking clearly influenced Cyt b5 content. In addition, we found that Cyt b5 protein levels significantly correlated with the overall activity of CYP1A2, 2B6, and 2E1 in HLM. However, when the CYP activities were sorted by single nucleotide polymorphisms (SNP), the effect of Cyt b5 protein on the kinetic parameters varied greatly. There were significant correlations between Cyt b5 content and Vmax and CLint of CYP1A2 wild-types (3860GG, 2159GG, and 5347CC) as well as homozygous mutants (163AA and 3113GG). In contrast to Vmax and CLint, the Km of CYP2B6 516GG and 785AA genotypes was inversely associated with Cyt b5 content. Correlations between Cyt b5 content and Vmax and CLint of CYP2E1 -1293GG, -1293GC, 7632TT, 7632TA, -333TT, and -352AA genotypes were also observed. In conclusion, Cyt b5 expression levels varied considerably in the Chinese cohort from this study. Cyt b5 had significant impact on the overall activity of CYP1A2, 2B6, and 2E1 in HLM and the effects of Cyt b5 protein on polymorphic CYP1A2, 2B6, and 2E1 activity were SNP-dependent. These findings suggest that Cyt b5 plays an important role in CYP-mediated activities in HLM and may possibly be a contributing factor for the individual variation observed in CYP enzyme activities.
authors.affiliation: Institute of Clinical Pharmacology, Zhengzhou University, Zhengzhou, China.
authors.forename: Haifeng
authors.initials: H
authors.lastname: Zhang
authors.affiliation: Institute of Clinical Pharmacology, Zhengzhou University, Zhengzhou, China.
authors.forename: Na
authors.initials: N
authors.lastname: Gao
authors.affiliation: Institute of Clinical Pharmacology, Zhengzhou University, Zhengzhou, China.
authors.forename: Tingting
authors.initials: T
authors.lastname: Liu
authors.affiliation: Institute of Clinical Pharmacology, Zhengzhou University, Zhengzhou, China.
authors.forename: Yan
authors.initials: Y
authors.lastname: Fang
authors.affiliation: Institute of Clinical Pharmacology, Zhengzhou University, Zhengzhou, China.
authors.forename: Bing
authors.initials: B
authors.lastname: Qi
authors.affiliation: Institute of Clinical Pharmacology, Zhengzhou University, Zhengzhou, China.
authors.forename: Qiang
authors.initials: Q
authors.lastname: Wen
authors.affiliation: Institute of Clinical Pharmacology, Zhengzhou University, Zhengzhou, China.
authors.forename: Jun
authors.initials: J
authors.lastname: Zhou
authors.affiliation: Institute of Clinical Pharmacology, Zhengzhou University, Zhengzhou, China.
authors.forename: Linjing
authors.initials: L
authors.lastname: Jia
authors.affiliation: Institute of Clinical Pharmacology, Zhengzhou University, Zhengzhou, China.
authors.forename: Hailing
authors.initials: H
authors.lastname: Qiao
mesh_terms: D000328:Adult; D000368:Aged; D002681:China; D015331:Cohort Studies; D019388:Cytochrome P-450 CYP1A2 / Q000378:metabolism*; D065702:Cytochrome P-450 CYP2B6 / Q000378:metabolism*; D019392:Cytochrome P-450 CYP2E1 / Q000378:metabolism*; D015786:Cytochromes b5 / Q000235:genetics / Q000378:metabolism*; D005260:Female; D005838:Genotype; D006801:Humans; D007700:Kinetics; D008297:Male; D008862:Microsomes, Liver / Q000378:metabolism*; D008875:Middle Aged; D020641:Polymorphism, Single Nucleotide; D012333:RNA, Messenger / Q000378:metabolism; D012737:Sex Factors; D012907:Smoking
chemical_list: D012333:RNA, Messenger; D015786:Cytochromes b5; D019392:Cytochrome P-450 CYP2E1; C504573:CYP1A2 protein, human; D019388:Cytochrome P-450 CYP1A2; D065702:Cytochrome P-450 CYP2B6