Stereoselective Bupropion Hydroxylation by Cytochrome P450 CYP2B6 and Cytochrome P450 Oxidoreductase Genetic Variants

Abstract

Bioactivation of the antidepressant and smoking cessation drug bupropion is catalyzed predominantly by cytochrome P4502B6 (CYP2B6). The metabolite hydroxybupropion derived from t-butylhydroxylation is considered to contribute to the antidepressant and smoking-cessation effects of the parent drug.Bupropion hydroxylation is the canonical in vitro and in vivo probe for CYP2B6 activity. P450 also requires obligate partnership with P450 oxidoreductase (POR). Human CYP2B6 and POR genes are highly polymorphic. Some CYP2B6 variants affect bupropion disposition. This investigation evaluated the influence of several human CYP2B6 and POR genetic variants on stereoselective bupropion metabolism, using an insect cell coexpression system containing CYP2B6, POR and cytochrome b 5 .Based on intrinsic clearances, relative activities for S,S-hydroxybupropion formation were in the order CYP2B6.4>CYP2B6.1>CYP2B6.17>CYP2B6.5>CYP2B6.6≈CYP2B6.26≈CYP2B6.19>CYP2B6.7> CYP2B6.9>>CYP2B6.16 and CYP2B6.18; relative activities for R,R-hydroxybupropion formation were in the order CYP2B6.17>CYP2B6.4>CYP2B6.1>CYP2B6.5≈CYP2B6.19≈CYP2B6.26>CYP2B6.6> CYP2B6.7≈ CYP2B6.9>>CYP2B6.16 and CYP2B6.18. Bupropion hydroxylation was not influenced by POR variants. CYP2B6-catalyzed bupropion hydroxylation is stereoselective. Though V max and K m varied widely among CYP2B6 variants, stereoselectivity was preserved, reflected by similar Cl int (S,Shydroxybupropion)/Cl int (R,R-hydroxybupropion) ratios (1.8 to 2.9), except CYP2B6.17, which was less enantioselective. Established concordance between human bupropion hydroxylation in vitro and in vivo, together with these new results, suggests additional CYP2B6 variants may influence human bupropion disposition.

A Computational Understanding of Inter-Individual Variability in CYP2D6 Activity to Investigate the Impact of Missense Mutations on Ochratoxin A Metabolism

“…In this case, an altered production of 4-OH-OTA compared to other OTA metabolites might have consequences on OTA’s TK and TD, and this would require further investigation. Broadly speaking, TK consequences associated with these specific CYP2D6 alleles have been extensively reported from the literature for a wide range of probe substrates, and consequences on TD have also been demonstrated, particularly for pharmaceuticals [ 6 , 9 , 27 , 28 , 29 ].…”

CYP2B6 allelic variants and non-genetic factors influence CYP2B6 enzyme function

“…The CYP2B6*4 allele contributed to increased activity in efavirenz 8-hydroxylation and to reduced plasma concentration of efavirenz in HIV-infected patients 15 , 18 ; however, dose modification was not required for efficient efavirenz therapy 23 . Intrinsic clearance of both bupropion enantiomers was minimally increased by CYP2B6*4 , whereas pharmacokinetic studies demonstrated significantly high bupropion clearance in vivo and consequently high hydroxy-bupropion exposure in CYP2B6*4 carrier subjects 17 , 61 , 66 . Interestingly, CYP2B6*4 displayed lower cyclophosphamide 4-hydroxylation activity in vitro than CYP2B6*1 18 , 63 ; however, CYP2B6*1/*4 genotype appeared to have no impact on 4-hydroxy-cyclophosphamide formation in vivo comparing to CYP2B6*1/*1 64 .…”

Methadone pharmacogenetics in vitro and in vivo: Metabolism by CYP2B6 polymorphic variants and genetic variability in paediatric disposition

“…41 In wild-type CYP2B6.1, the lysine262 side chain is not able to form similar hydrogen bonds with the neighbouring residues. This may account for the differences in methadone 27 artemether, 45 and selegiline, 46 but not bupropion, 44 ketamine, 26 nicotine, 43 cyclophosphamide 47,48 and ifosfamide. 49,50 CYP2B6 variant activity for methadone appears most similar to that for efavirenz among the various CYP2B6 substrates evaluated.…”