Quantitative Evaluation of the Contribution of Each Aldo-Keto Reductase and Short-Chain Dehydrogenase/Reductase Isoform to Reduction Reactions of Compounds Containing a Ketone Group in the Human Liver

Abstract

Enzymes of the aldo-keto reductase (AKR) and short-chain dehydrogenase/reductase superfamilies are involved in the reduction of compounds containing a ketone group. In most cases, multiple isoforms appear to be involved in the reduction of a compound, and the enzyme(s) that are responsible for the reaction in the human liver have not been elucidated.The purpose of this study was to quantitatively evaluate the contribution of each isoform to reduction reactions in the human liver. Recombinant cytosolic isoforms were constructed, i.e., AKR1C1, AKR1C2, AKR1C3, AKR1C4, and carbonyl reductase 1 (CBR1), and a microsomal isoform, 11β-hydroxysteroid dehydrogenase type 1 (HSD11B1), and their contributions to the reduction of 10 compounds were examined by extrapolating the relative expression of each reductase protein in human liver preparations to recombinant systems quantified by liquid chromatography-mass spectrometry (MS)/MS. The reductase activities for acetohexamide, doxorubicin, haloperidol, loxoprofen, naloxone, oxcarbazepine, and pentoxifylline were predominantly catalyzed by cytosolic isoforms, and the sum of the contributions of individual cytosolic reductases was almost 100%. Interestingly, AKR1C3 showed the highest contribution to acetohexamide and loxoprofen reduction, although previous studies have revealed that CBR1 mainly metabolizes them. The reductase activities of bupropion, ketoprofen, and tolperisone were catalyzed by microsomal isoform(s), and the contributions of HSD11B1 were calculated to be 41%, 32%, and 104%, respectively. To our knowledge, this is the first study to quantitatively evaluate the contribution of each reductase to the reduction of drugs in the human liver.

Quantitative Analysis of mRNA and Protein Expression Levels of Aldo-Keto Reductase and Short-Chain Dehydrogenase/Reductase Isoforms in the Human Intestine

“…CBR1 catalyzes the reduction reaction of several drugs, such as loxoprofen and haloperidol (Ohara et al, 1995;Kudo and Ishizaki, 1999). Recently, we found that the contributions of CBR1, AKR1C3, and AKR1C4 to loxoprofen reduction in human liver cytosol were 31%, 54%, and 34%, respectively (Ichida et al, 2023a). When we evaluated CBR1 and AKR1C3 protein levels by immunoblotting, their levels were higher in the intestine than in the liver.…”

“…In support of this, loxoprofen reductase activity in human intestinal cytosol was 4.5-fold higher than that in human liver cytosol (151 ± 2.1 pmol/min/mg protein vs 35.8 ± 1.4 pmol/min/mg protein) at a substrate concentration of 5 µM (Suzuki et al, in preparation). It has been reported that the CL int value of the reduction reaction for haloperidol, which is a substrate specific for CBR1 (Ichida et al, 2023a), in the human intestinal cytosol (0.016 mL/min/mg protein) is 2.7-fold higher than that in the human liver cytosol (0.006 mL/min/mg protein) (Nishimuta et al, 2013). Thus, the reduction reaction of CBR1 substrates would occur substantially in the intestine in addition to the liver.…”

“…3C). In the liver, drugs such as bupropion, ketoprofen, and tolperisone are efficiently reduced by HSD11B1 (Ichida et al, 2023a). Another microsomal drug-metabolizing reductase, This article has not been copyedited and formatted.…”

“…We previously investigated the hepatic mRNA expression levels of AKR and SDR isoforms and found that AKR1C1, AKR1C2, AKR1C3, CBR1, and HSD11B1 each accounting for more than 10% of the sum of all AKR and SDR levels (Amai et al, 2020). By evaluating the contribution of each isoform to the reduction of various drugs in the liver, we have shown that most of the reactions in the liver are explained by the above 5 isoforms as well as AKR1C4 (Ichida et al, 2023a), although there are some cases in which the less abundant isoforms contribute significantly to the reduction reaction of drugs. Thus, the determination of the isoforms highly expressed in target organs would be useful for understanding drug metabolism.…”

In Vitro Evaluation of the Reductase Activities of HumanAKR1C3Allelic Variants

“…Among them, 12 isoforms, AKR1A1, 1B1, 1B10, 1B15, 1C1, 1C2, 1C3, 1C4, 1D1, 1E2, 7A2, and 7A3, have been reported to be involved in the reduction reaction of xenobiotics (Fukami et al, 2022). The human SDR family consists of 75 isoforms (Persson and Kallberg, 2013), and 7 isoforms, carbonyl reductase (CBR) 1, 3, 4, 11β-hydroxysteroid dehydrogenase type 1 (HSD11B1), 17β-hydroxysteroid dehydrogenase type 12 (HSD17B12), dehydrogenase/reductase member (DHRS) 4, and dicarbonyl/ L -xylulose reductase (DCXR), have been suggested to be involved in the reduction reaction of xenobiotics (Matsunaga et al, 2006, Ichida et al, 2023a. Among these members, AKR1C1, AKR1C2, AKR1C3, AKR1C4, CBR1, and HSD11B1 are highly expressed in the liver and contribute to the reduction reaction of clinically used drugs (Barski et al, 2008;Amai et al, 2020) with overlapping substrate specificities (Ichida et al, 2023a).…”