Stereoselectivity in the oxidation of bufuralol, a chiral substrate, by human cytochrome P450s

Abstract

Bufuralol (BF), a nonselective beta-adrenoceptor blocking agent, has a chiral center in its molecule, yielding the enantiomers 1'R-BF and 1'S-BF. beta-Adrenoceptor blocking potency is much higher in 1'S-BF than in 1'R-BF. One of the metabolic pathways of BF is 1"-hydroxylation of an ethyl group attached at the aromatic 7-position forming a carbinol metabolite (1"-hydroxybufuralol, 1"-OH-BF), and further oxidation (or dehydrogenation) produces a ketone metabolite (1-oxobufuralol, 1"-Oxo-BF). Both 1"-OH-BF and 1"-Oxo-BF are known to have beta-adrenoceptor blocking activities comparable to or higher than those of the parent drug. The 1"-hydroxylation introduces another chiral center into the BF molecule and four 1"-OH-BF diastereomers are formed from BF racemate in mammals, including humans, making elucidation of the metabolic profiles complicated. HPLC methods employing derivatization, reversed phase, or chiral columns have been developed to efficiently separate the four 1"-OH-BF diastereomers formed from BF enantiomers or racemate. Accumulated in vitro experimental results revealed that 1'R-BF is a much more preferential substrate than 1'S-BR for BF 1"-hydroxylation in human liver microsomes. Kinetic studies using recombinant human cytochrome P450 (CYP) enzymes indicate that CYP2D6 serves as a major BF 1"-hydroxylase and that CYP1A2 and CYP2C19 also contribute to BF 1"-hydroxylation in human livers. This mini-review summarizes the knowledge reported so far on the pharmacology of BF and its metabolites and the profiles of BF metabolism, especially focusing on the stereoselectivity in the oxidation of BF mainly in human livers and recombinant CYP enzymes.

Highly Efficient Differentiation of Functional Hepatocytes From Human Induced Pluripotent Stem Cells

“…(ϩ/Ϫ)-Bufuralol is a nonselective ␤-adrenoceptor blocking agent; its major metabolic pathways in humans are oxidation and glucuronidation [16,17], and our recent study showed that there are seven major metabolic pathways in vitro [6]. Predictive multiple reaction monitoring (MRM) is the most sensitive approach in metabolite identification [18,19].…”

Predictions of Cytochrome P450-Mediated Drug-Drug Interactions Using Cryopreserved Human Hepatocytes: Comparison of Plasma and Protein-Free Media Incubation Conditions

“…(R)-Bufuralol was selected rather than racemic bufuralol because CYP2D6 displays substrate enantioselectivity for (R)-bufuralol over (S)-bufuralol (Dayer et al, 1987;Narimatsu et al, 2003;Masuda et al, 2005). CYP2D6 is responsible for 95% of racemic bufuralol 1Ј-hydroxylation clearance, whereas CYP2C19 is responsible for 5% and CYP1A2 has a small contribution (Ͻ1%) (Mankowski, 1999).…”

Cytochrome P450 bio-affinity detection coupled to gradient HPLC: On-line screening of affinities to cytochrome P4501A2 and 2D6

“…Moreover, different stereoisomers of a ligand may inhibit isoenzymes in different ways, which in turn may lead to varying pharmacokinetic and drug-drug interactions characteristics of the two stereoisomers [37]. Methylenedioxy-alkylamphetamine (MDMA, also known as XTC), for instance is a known chiral substrate for CYP2D6 and also are the chiral analogs methylenedioxy-ethylamphetamine (MDEA) and methylenedioxy-amphetamine (MDA), which are high affinity CYP2D6 substrates [38].…”