2-Arylpropionic acid derivatives are probably the most frequently cited drugs exhibiting the phenomenon that is best known as chiral inversion. One enantiomer of drug is converted into its antipode either in the presence of a solvent or more often in inner environment of an organism. Mechanistic studies of the metabolic chiral inversion were carried out for several drugs from NSAIDs, and a model of this inversion was suggested and subsequently confirmed. The chiral inversion of NSAIDs has been intensively studied in the context of the pharmacological and toxicological consequences. However, the group of NSAIDs is not the sole group of drugs in which the inversion phenomenon can be observed. There exist several other drugs that also display chiral inversion of one or even both of their enantiomers. These drugs belong to different pharmacotherapeutic groups as monoamine oxidase inhibitors, antiepileptic drugs, drugs used in the treatment of hyperlipoproteinemia or drugs that are effective in the treatment of leprosy. Moreover, some chiral or prochiral drugs are metabolized to give chiral metabolites that undergo chira l inversion too, which can have direct impact on pharmacological properties or toxicity of the drug. As the process of chiral inversion is affected by several factors, so the intensity of chiral inversion of individual substances and at different conditions can differ considerably. Interspecies differences and types of tissue are reported to be the main factors that were recognized to play the key role in the process of chiral inversion. Some of more recent studies have revealed that several other factors, such as the route of administration or interaction with other xenobiotics, can influence the enantiomeric conversion, too. Chiral inversion does not seem to be a phenomenon connected with only several drugs from some unique group of 2- arylpropionic acid derivatives: it is also observed in drugs with rather different chemical structures and is much more frequent than it can be realized.

Members of the aldo-keto reductase (AKR) superfamily have a broad substrate specificity in catalyzing the reduction of carbonyl group-containing xenobiotics. In the present investigation, a member of the aldose reductase subfamily, AKR1B10, was purified from human liver cytosol. This is the first time AKR1B10 has been purified in its native form. AKR1B10 showed a molecular mass of 35 kDa upon gel filtration and SDS-polyacrylamide gel electrophoresis. Kinetic parameters for the NADPH-dependent reduction of the antiemetic 5-HT₃ receptor antagonist dolasetron, the antitumor drugs daunorubicin and oracin, and the carcinogen 4-methylnitrosamino-1-(3-pyridyl)-1-butanone (NNK) to the corresponding alcohols have been determined by HPLC. K_m values ranged between 0.06 mM for dolasetron and 1.1 mM for daunorubicin. Enzymatic efficiencies calculated as k_cat/K_m were more than 100 mM^–1 min^–1 for dolasetron and 1.3, 0.43, and 0.47 mM^–1 min^–1 for daunorubicin, oracin, and NNK, respectively. Thus, AKR1B10 is one of the most significant reductases in the activation of dolasetron. In addition to its reducing activity, AKR1B10 catalyzed the NADP⁺-dependent oxidation of the secondary alcohol (S)-1-indanol to 1-indanone with high enzymatic efficiency (k_cat/K_m = 112 mM^–1 min^–1). The gene encoding AKR1B10 was cloned from a human liver cDNA library and the recombinant enzyme was purified. Kinetic studies revealed lower activity of the recombinant compared with the native form. Immunoblot studies indicated large interindividual variations in the expression of AKR1B10 in human liver. Since carbonyl reduction of xenobiotics often leads to their inactivation, AKR1B10 may play a role in the occurrence of chemoresistance of tumors toward carbonyl group-bearing cytostatic drugs.

The understanding of drug biotransformation is an important medical topic. The oxidative pathways that involve CYPs have been extensively studied in drug metabolism in contrast to the reductive pathways. This review focuses on drugs that have been reported to be reduced at the carbonyl group in vivo. Although the carbonyl reduction of these drugs is well known, our understanding of the carbonyl reducing enzymes (CRE) that perform these reactions is limited. We have summarized the published data in order to thoroughly describe the reductive metabolism of the selected drugs and to demonstrate the role of carbonyl reduction in the context of their overall metabolism. The number of drugs recognized as substrates for CREs has increased considerably in recent years. Moreover, the importance of carbonyl reduction in the overall metabolism of these drugs is often surprisingly high. Because only limited information is available about the CREs responsible for these reactions, additional research is needed to improve our understanding of the metabolism of drugs undergoing carbonyl reduction. Carbonyl reduction should be investigated during drug development because it can either positively or negatively influence drug efficacy.