Stereospecific Metabolism ofR- andS-Warfarin by Human Hepatic Cytosolic Reductases

Abstract

Coumadin (rac-warfarin) is the most commonly used anticoagulant in the world; however, its clinical use is often challenging because of its narrow therapeutic range and interindividual variations in response. A critical contributor to the uncertainty is variability in warfarin metabolism, which includes mostly oxidative but also reductive pathways. Reduction of each warfarin enantiomer yields two warfarin alcohol isomers, and the corresponding four alcohols retain varying levels of anticoagulant activity. Studies on the kinetics of warfarin reduction have often lacked resolution of parent-drug enantiomers and have suffered from coelution of pairs of alcohol metabolites; thus, those studies have not established the importance of individual stereospecific reductive pathways. We report the first steady-state analysis of - and-warfarin reduction in vitro by pooled human liver cytosol. As determined by authentic standards, the major metabolites were 9R,11S-warfarin alcohol for -warfarin and 9S,11S-warfarin alcohol for-warfarin. -warfarin ( 150 pmol/mg per minute, 0.67 mM) was reduced more efficiently than-warfarin ( 27 pmol/mg per minute, 1.7 mM). Based on inhibitor phenotyping, carbonyl reductase-1 dominated-and -warfarin reduction, followed by aldo-keto reductase-1C3 and then other members of that family. Overall, the carbonyl at position 11 undergoes stereospecific reduction by multiple enzymes to form the alcohol for both drug enantiomers, yet -warfarin undergoes reduction preferentially. This knowledge will aid in assessing the relative importance of reductive pathways for- and -warfarin and factors influencing levels of pharmacologically active parent drugs and metabolites, thus impacting patient dose responses.

Evaluation of pharmacokinetics of warfarin from validated pharmacokinetic-pharmacodynamic model

“…L/hour; and elimination half-life of 35 hours [2]. Warfarin is a racemic mixture of S-and R-warfarin posing challenges in measurements [3]. Pharmacokinetic-pharmacodynamic (PK-PD) relationship of warfarin has been well elucidated and therapeutic drug monitoring is carried out by PT-INR measurement [4].…”

Discovery of Novel Reductive Elimination Pathway for 10-Hydroxywarfarin

“…Historically, studies carried out with rac -warfarin yielded partially resolvable isomers called alcohol 1 (minor metabolite) and alcohol 2 (major metabolite) ( Alshogran, et al, 2014 ; Malátkova, et al, 2016 ). Our previous study further assessed the role of chirality in warfarin reductive reactions with authentic standards for all isomers ( Barnette, et al, 2017 ). We determined that alcohol 1 consisted of two co-eluted alcohol isomers sharing common chiral orientations ( 9R-11R -hydroxywarfarin and 9S-11S -hydroxywarfarin), whereas alcohol 2 was the combination of alcohols with mixed chiral centers ( 9R-11S -hydroxywarfarin and 9S-11R -hydroxywarfarin).…”

“…We determined that alcohol 1 consisted of two co-eluted alcohol isomers sharing common chiral orientations ( 9R-11R -hydroxywarfarin and 9S-11S -hydroxywarfarin), whereas alcohol 2 was the combination of alcohols with mixed chiral centers ( 9R-11S -hydroxywarfarin and 9S-11R -hydroxywarfarin). Nevertheless, R -warfarin was more efficiently metabolized than S -warfarin and both reactions resulted mainly in formation of the S alcohol by CBR1 and AKR1C3 ( Malátkova, et al, 2016 ; Barnette, et al, 2017 ). Consequently, rac -warfarin reactions mainly yielded 9S-11S -hydroxywarfarin (alcohol 1, minor metabolite), and 9R-11S -hydroxywarfarin (alcohol 2, major metabolite).…”

“…The model does not consider chirality but does yield a useful, scalable output for ranking the likelihood of reactions like reductions to occur. For experimental studies, we leveraged our previous methodologies ( Barnette, et al, 2017 ) for characterizing R- and S-warfarin reduction by human liver cytosolic fractions to assess this metabolic pathway for 6-, 7-, 8-, 10-, and 4′-hydroxywarfarins. Isomeric mixtures were necessary for these studies given the lack of commercial availability of the individual isomers.…”

Levosalbutamol as alternative to drugs on the basis of racemic salbutamol: Review of the results of pre-clinical research

“…Аминокислоты, за исключением глицина, характеризуются хиральными свойствами, в связи с чем активные сайты связывания в составе протеинов являются асимметричными, а значит, помимо комлементарности, важным условием эффективного взаимодействия с лигандом, обладающим хиральными свойствами, является пространственная конфигурация его энантиомеров. Последняя, в свою очередь, определяет существенные различия аффинитета связывания R-и S-энантиомеров хиральных лекарственных субстанций (Burke and Henderson, 2002;Kubinyi, 2003) и лежит в основе феномена энантиоселективности их фармакокинетики или фармакодинамики (Barnette et al, 2017;Kuchay and Mithal, 2017;Noguchi et al, 2017;Välitalo et al, 2017). Удаление из лекарственного препарата энантиомера, лишенного фармакологической активности или обладающего неоптимальными фармакодинамическими или фармакокинетическими свойствами, может ассоциироваться с повышением клинической эффективности лекарственных средств, в том числе ранее одобренных для клинического применения, минимизировать фармакодинамическую и фармакокинетическую вариабельность ответов на лечение и, возможно, снизить вероятность развития нежелатель-ных событий, ассоциированных с фармакотерапией рацематами.…”