Non-P450 Drug-Metabolizing Enzymes: Contribution to Drug Disposition, Toxicity, and Development.

Most clinically used drugs are metabolized in the body via oxidation, reduction, or hydrolysis reactions, which are considered phase I reactions. Cytochrome P450 (P450) enzymes, which primarily catalyze oxidation reactions, contribute to the metabolism of over 50% of clinically used drugs. In the last few decades, the function and regulation of P450s have been extensively studied, whereas the characterization of non-P450 phase I enzymes is still incomplete. Recent studies suggest that approximately 30% of drug metabolism is carried out by non-P450 enzymes. This review summarizes current knowledge of non-P450 phase I enzymes, focusing on their roles in controlling drug efficacy and adverse reactions as an important aspect of drug development.

Cytochrome P450 and UDP-glucuronosyltransferase expressions, activities, and induction abilities in 3D-cultured human renal proximal tubule epithelial cells.

The role of the kidney as an excretory organ for exogenous and endogenous compounds is well recognized, but there is a wealth of data demonstrating that the kidney has significant metabolizing capacity for a variety of exogenous and endogenous compounds that in some cases surpass the liver. The induction of drug-metabolizing enzymes by some chemicals can cause drug-drug interactions and intraindividual variability in drug clearance. In this study, we evaluated the expression and induction of cytochrome P450 (P450) and UDP-glucuronosyltransferase (UGT) isoforms in 3D-cultured primary human renal proximal tubule epithelial cells (RPTEC) to elucidate their utility as models of renal drug metabolism. CYP2B6, CYP2E1, CYP3A4, CYP3A5, and all detected UGTs (UGT1A1, UGT1A4, UGT1A6, UGT1A9, and UGT2B7) mRNA levels in 3D-RPTEC were significantly higher than those in 2D-RPTEC and HK-2 cells and were close to the levels in the human kidney cortex. CYP1B1 and CYP2J2 mRNA levels in 3D-RPTEC were comparable to those in 2D-RPTEC, HK-2 cells, and the human kidney cortex. Midazolam 1'-hydroxylation, trifluoperazine N-glucuronidation, serotonin O-glucuronidation, propofol O-glucuronidation, and morphine 3-glucuronidation in the 3D-RPTEC were significantly higher than the 2D-RPTEC and comparable to those in the HepaRG cells, although bupropion, ebastine, and calcitriol hydroxylations were not different between the 2D- and 3D-RPTEC. Treatment with ligands of the aryl hydrocarbon receptor and farnesoid X receptor induced CYP1A1 and UGT2B4 expression, respectively, in 3D-RPTEC compared to 2D-RPTEC. We provided information on the expression, activity, and induction abilities of P450s and UGTs in 3D-RPTEC as an in vitro human renal metabolism model. Significance Statement This study demonstrated that the expression of P450s and UGTs in 3D-RPTEC was higher than those in 2D-RPTEC and HK-2 cells. The results were comparable to that in the human kidney cortex. 3D-RPTEC are useful for evaluating the induction of kidney P450s, UGTs, and human renal drug metabolism in cellulo.

Prediction of combination effect of quinidine on the pharmacokinetics of tipepidine using a physiologically based pharmacokinetic model.

Tipepidine, an antitussive drug, has been reported to have central pharmacological effects and can be expected to be safely repositioned as treatment for psychiatric disorders. Since tipepidine requires three doses per day, development of a once-daily medication would be highly beneficial. Previously, we reported that combination use with quinidine, a CYP2D6 inhibitor, prolongs the half-life of tipepidine in chimeric mice with humanised liver.In this study, to predict this combination effect in humans, a physiologically based pharmacokinetic (PBPK) model was developed, and quantitative simulation was conducted. The simulation results indicated that concomitant administration of tipepidine with quinidine increased the predicted Cmax, AUC, and t1/2 of tipepidine in the Japanese population by 3.4-, 6.6-, and 2.4-fold, respectively.Furthermore, to compare with another approach that aims to prolong the half-life, the PK profile of tipepidine administered in hypothetical extended-release form was simulated. Extended-release form was predicted to be more influenced by CYP2D6 genotype than combination with quinidine, and the predicted plasma exposure was markedly increased in poor metabolizers, potentially leading to adverse effects.In conclusion, quantitative simulation using the PBPK model suggests the feasibility of the safe repositioning of tipepidine as a once-daily medication in combination with quinidine.

Evaluation of Drug-Drug Interactions via Inhibition of Hydrolases by Orlistat, an Anti-Obesity Drug.

Drug-drug interactions (DDI) have a significant impact on drug efficacy and safety. It has been reported that orlistat, an anti-obesity drug, inhibits the hydrolysis of p-nitrophenol acetate, a common substrate of the major drug-metabolizing hydrolases, carboxylesterase (CES) 1, CES2, and arylacetamide deacetylase (AADAC), in vitro. The aim of this study was to examine whether orlistat affects the pharmacokinetics of drug(s) metabolized by hydrolases in vivo after evaluating its inhibitory potencies against CES1, CES2, and AADAC in vitro. Orlistat potently inhibited the hydrolysis of acebutolol, a specific substrate of CES2, in a non-competitive manner (inhibition constant, K i = 2.95 ± 0.16 nM), whereas it slightly inhibited the hydrolysis of temocapril and eslicarbazepine acetate, specific substrates of CES1 and AADAC, respectively (IC50 >100 nM). The in vivo DDI potential was elucidated using mice, in which orlistat showed strong inhibition against acebutolol hydrolase activities in the liver and intestinal microsomes, similar to humans. The area under the curve (AUC) of acebutolol was increased by 43%, whereas the AUC of acetolol, a hydrolyzed metabolite of acebutolol, was decreased by 47% by co-administration of orlistat. The ratio of the K i value to the maximum unbound plasma concentration of orlistat (<0.012) is lower than the risk criteria for DDI in the liver defined by the US Food and Drug Administration guideline (>0.02), whereas the ratio of the K i value to the estimated intestinal luminal concentration (3.3 × 105) is considerably higher than the risk criteria in the intestine (>10). Therefore, this suggests that orlistat causes DDI by inhibiting hydrolases in the intestine. SIGNIFICANCE STATEMENT: This study demonstrated that orlistat, an anti-obesity drug, causes drug-drug interactions in vivo by potently inhibiting carboxylesterase 2 in the intestine. This is the first evidence that inhibition of hydrolases causes drug-drug interactions.

In Vitro Evaluation of the Reductase Activities of Human AKR1C3 Allelic Variants.

Aldo-keto reductase 1C3 (AKR1C3) plays a role in the detoxification and activation of clinical drugs by catalyzing reduction reactions. There are approximately 400 single-nucleotide polymorphisms (SNPs) in the AKR1C3 gene, but their impact on the enzyme activity is still unclear. This study aimed to clarify the effects of SNPs of AKR1C3 with more than 0.5% global minor allele frequency on the reductase activities for its typical substrates. Recombinant AKR1C3 wild-type and R66Q, E77G, C145Y, P180S, or R258C variants were constructed using insect Sf21 cells, and reductase activities for acetohexamide, doxorubicin, and loxoprofen by recombinant AKR1C3s were measured by liquid chromatography-tandem mass spectrometry. Among the variants tested, the C145Y variant showed remarkably low (6%-14% of wild type) intrinsic clearances of reductase activities for all three drugs. Reductase activities of these three drugs were measured using 34 individual Japanese liver cytosols, revealing that heterozygotes of the SNP g.55101G>A tended to show lower reductase activities for three drugs than homozygotes of the wild type. Furthermore, genotyping of the SNP g.55101G>A causing C145Y in 96 Caucasians, 166 African Americans, 192 Koreans, and 183 Japanese individuals was performed by polymerase chain reaction-restriction fragment length polymorphism. This allelic variant was specifically detected in Asians, with allele frequencies of 6.8% and 3.6% in Koreans and Japanese, respectively. To conclude, an AKR1C3 allele with the SNP g.55101G>A causing C145Y would be one of the causal factors for interindividual variabilities in the efficacy and toxicity of drugs reduced by AKR1C3. SIGNIFICANCE STATEMENT: This is the first study to clarify that the AKR1C3 allele with the SNP g.55101G>A causing C145Y results in a decrease in reductase activity. Since the allele was specifically observed in Asians, the allele would be a factor causing an interindividual variability in sensitivity of drug efficacy or toxicity of drugs reduced by AKR1C3 in Asians.

NEAT1_2 and DAZAP1, Paraspeckle Components, Interact with PXR to Negatively Regulate CYP3A4 Induction.

Human pregnane X receptor (PXR) is a major nuclear receptor that upregulates the expression of drug-metabolizing enzymes such as CYP3A4. In our recent study, it was revealed that PXR interacts with DAZ-associated protein 1 (DAZAP1), which is an essential component of the paraspeckle, a membraneless nuclear body, and the interaction was disassociated by rifampicin, a ligand of PXR. The purpose of this study was to clarify the roles of paraspeckles in PXR-mediated transcriptional regulation. Immunoprecipitation assays using PXR-overexpressing HepG2 (ShP51) cells revealed that PXR interacts with not only DAZAP1 but also NEAT1_2, a long noncoding RNA included in the paraspeckle, and that the interaction between PXR and NEAT1_2 was disassociated by rifampicin. These results suggest that PXR is trapped in paraspeckles and that the activation of PXR by its ligands facilitates its disassociation from paraspeckles. Induction of CYP3A4 by rifampicin was significantly enhanced by the knockdown of NEAT1_2 or DAZAP1 in ShP51 cells and their parental HepG2 cells. A luciferase assay using a plasmid containing the PXR response elements of CYP3A4 revealed that the increased CYP3A4 induction by siNEAT1_2 or siDAZAP1 was due to the increased transactivation by PXR. These results suggest that paraspeckles play a role in trapping nuclear PXR in the absence of the ligand to negatively regulate transactivation of its downstream gene. Collectively, this is the first study to demonstrate that the paraspeckle components NEAT1_2 and DAZAP1 negatively regulate CYP3A4 induction by PXR. SIGNIFICANCE STATEMENT: This study revealed that PXR interacts with paraspeckle components NEAT1_2 and DAZAP1 to suppress CYP3A4 induction by PXR, and the interaction is dissociated by PXR ligands. This finding provides a novel concept that paraspeckles formed by liquid-liquid phase separation potentially affect drug metabolism via negative regulation of PXR function.

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

Enzymes catalyzing the reduction reaction of xenobiotics are mainly members of the aldo-keto reductase (AKR) and short-chain dehydrogenase/reductase (SDR) superfamilies. The intestine, together with the liver, is responsible for first-pass effects and is an organ that determines the bioavailability of orally administered drugs. In this study, we evaluated the mRNA and protein expression levels of 12 AKR isoforms (AKR1A1, AKR1B1, AKR1B10, AKR1B15, AKR1C1, AKR1C2, AKR1C3, AKR1C4, AKR1D1, AKR1E2, AKR7A2, and AKR7A3) and 7 SDR isoforms (CBR1, CBR3, CBR4, DCXR, DHRS4, HSD11B1, and HSD17B12) in each region of the human intestine using next-generation sequencing and data-independent acquisition proteomics. At both the mRNA and protein levels, most AKR isoforms were highly expressed in the upper regions of the intestine, namely the duodenum and jejunum, and then declined toward the rectum. Among the members in the SDR superfamily, CBR1 and DHRS4 were highly expressed in the upper regions, whereas the expression levels of the other isoforms were almost uniform in all regions. Significant positive correlations between mRNA and protein levels were observed in AKR1A1, AKR1B1, AKR1B10, AKR1C3, AKR7A2, AKR7A3, CBR1, and CBR3. The mRNA level of AKR1B10 was highest, followed by AKR7A3 and CBR1, each accounting for more than 10% of the sum of all AKR and SDR levels in the small intestine. This expression profile in the human intestine was greatly different from that in the human liver, where AKR1C isoforms are predominantly expressed. SIGNIFICANCE STATEMENT: In this study comprehensively determined the mRNA and protein expression profiles of aldo-keto reductase (AKR) and short-chain dehydrogenase/reductase isoforms involved in xenobiotic metabolism in the human intestine and found that most of them are highly expressed in the upper region, where AKR1B10, AKR7A3, and CBR1 are predominantly expressed. Since the intestine is significantly involved in the metabolism of orally administered drugs, the information provided here is valuable for pharmacokinetic studies in drug development.

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.

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, 11ß-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. 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. SIGNIFICANCE STATEMENT: To our knowledge, this is the first study to determine the contribution of aldo-keto reductase (AKR)-1C1, AKR1C2, AKR1C3, AKR1C4, carbonyl reductase 1, and 11ß-hydroxysteroid dehydrogenase type 1 to drug reductions in the human liver by utilizing the relative expression factor approach. This study found that AKR1C3 contributes to the reduction of compounds at higher-than-expected rates.

Development and Validation of a Proteomic Correlation Profiling Technique to Detect and Identify Enzymes Involved in Metabolism of Drugs of Concern.

To predict the variation of pharmacological or toxicological effect caused by pharmacokinetic variance, it is important to be able to detect previously unknown and unsuspected enzymes involved in drug metabolism. We investigated the use of proteomic correlation profiling (PCP) as a technique to identify the enzymes involved in metabolism of drugs of concern. By evaluating the metabolic activities of each enzyme (including isoforms of cytochrome P450, uridine 5' diphospho-glucuronosyltransferase, and hydrolases, plus aldehyde oxidase and carbonyl reductase) on their typical substrates using a panel of human liver samples, we were able to show the validity of PCP for this purpose. R or Rs and P values were calculated for the association between the protein abundance profile of each protein and the metabolic rate profile of each typical substrate. For the 18 enzymatic activities examined, 13 of the enzymes reported to be responsible for the reactions had correlation coefficients higher than 0.7 and were ranked first to third. For the remaining five activities, the responsible enzymes had correlation coefficients lower than 0.7 and lower rankings. The reasons for this were diverse, including confounding resulting from low protein abundance ratios, artificially high correlations of other enzymes due to limited sample numbers, the presence of inactive enzyme forms, and genetic polymorphisms. Overall, PCP was able to identify the majority of responsible drug-metabolizing enzymes across several enzyme classes (oxidoreductase, transferase, hydrolase); use of this methodology could allow more timely and accurate identification of unknown drug-metabolizing enzymes. SIGNIFICANCE STATEMENT: Proteomic correlation profiling using samples from individual human donors was proven to be a useful methodology for the identification of enzymes responsible for drug-metabolism. This methodology could accelerate the identification of unknown drug-metabolizing enzymes in the future.

Characterization of Enzymes Involved in Nintedanib Metabolism in Humans.

Nintedanib, which is used to treat idiopathic pulmonary fibrosis and non-small cell lung cancer, is metabolized to a pharmacologically inactive carboxylate derivative, BIBF1202, via hydrolysis and subsequently by glucuronidation to BIBF1202 acyl-glucuronide (BIBF1202-G). Since BIBF1202-G contains an ester bond, it can be hydrolytically cleaved to BIBF1202. In this study, we sought to characterize these metabolic reactions in the human liver and intestine. Nintedanib hydrolysis was detected in human liver microsomes (HLMs) (Clearance [CL int]: 102.8 ± 18.9 µL/min per mg protein) but not in small intestinal preparations. CES1 was suggested to be responsible for nintedanib hydrolysis according to experiments using recombinant hydrolases and hydrolase inhibitors as well as proteomic correlation analysis using 25 individual HLM. BIBF1202 glucuronidation in HLM (3.6 ± 0.3 µL/min per mg protein) was higher than that in human intestinal microsomes (1.5 ± 0.06 µL/min per mg protein). UGT1A1 and gastrointestinal UGT1A7, UGT1A8, and UGT1A10 were able to mediate BIBF1202 glucuronidation. The impact of UGT1A1 on glucuronidation was supported by the finding that liver microsomes from subjects homozygous for the UGT1A1*28 allele showed significantly lower activity than those from subjects carrying the wild-type UGT1A1 allele. Interestingly, BIBF1202-G was converted to BIBF1202 in HLS9 at 70-fold higher rates than the rates of BIBF1202 glucuronidation. An inhibition study and proteomic correlation analysis suggested that ß-glucuronidase is responsible for hepatic BIBF1202-G deglucuronidation. In conclusion, the major metabolic reactions of nintedanib in the human liver and intestine were quantitatively and thoroughly elucidated. This information could be helpful to understand the inter- and intraindividual variability in the efficacy of nintedanib. SIGNIFICANCE STATEMENT: To our knowledge, this is the first study to characterize the enzymes responsible for each step of nintedanib metabolism in the human body. This study found that ß-glucuronidase may contribute to BIBF1202-G deglucuronidation.

Identification of HSD17B12 as an enzyme catalyzing drug reduction reactions through investigation of nabumetone metabolism.

Nabumetone, a nonsteroidal anti-inflammatory prodrug, is converted to a pharmacologically active metabolite, 6-methoxy-2-naphthylacetic acid (6-MNA); however, it is 11-fold more efficiently converted to 4-(6-methoxy-2-naphthyl)butan-2-ol (MNBO) via a reduction reaction in human hepatocytes. The goal of this study was to identify the enzyme(s) responsible for MNBO formation from nabumetone in the human liver. MNBO formation by human liver microsomes (HLM) was 5.7-fold higher than in the liver cytosol. In a panel of 24 individual HLM samples with quantitative proteomics data, the 17ß-hydroxysteroid dehydrogenase 12 (HSD17B12) protein level had the high correlation coefficient (r = 0.80, P < 0.001) among 4457 proteins quantified in microsomal fractions during MNBO formation. Recombinant HSD17B12 expressed in HEK293T cells exhibited prominent nabumetone reductase activity, and the contribution of HSD17B12 to the activity in the HLM was calculated as almost 100%. MNBO formation in HepG2 and Huh7 cells was significantly decreased by the knockdown of HSD17B12. We also examined the role of HSD17B12 in drug metabolism and found that recombinant HSD17B12 catalyzed the reduction reactions of pentoxifylline and S-warfarin, suggesting that HSD17B12 prefers compounds containing a methyl ketone group on the alkyl chain. In conclusion, our study demonstrated that HSD17B12 is responsible for the formation of MNBO from nabumetone. Together with the evidence for pentoxifylline and S-warfarin reduction, this is the first study to report that HSD17B12, which is known to metabolize endogenous compounds, such as estrone and 3-ketoacyl-CoA, plays a role as a drug-metabolizing enzyme.

Activation of Inflammation by MCF-7 Cells-Derived Small Extracellular Vesicles (sEV): Comparison of Three Different Isolation Methods of sEV.

PURPOSE: Small extracellular vesicles (sEV) containing proteins and RNAs play important roles as intercellular signal mediators. A critical issue is that there are multiple methods to prepare sEV fractions. The purpose of this study was to examine whether cancer cell-derived sEV fractions prepared by different isolation methods show similar responses for the induction of inflammatory cytokines in macrophages. METHODS: sEV fractions from the conditioned medium of MCF-7 cells were prepared by ultracentrifugation (UC), the MagCapture Exosome Isolation Kit PS (PS), or the ExoQuick-TC kit (EQ). The mRNA levels of inflammatory cytokines in differentiated THP-1 cells treated with the sEV fractions were evaluated. RESULTS: The yields of sEV fractions obtained from 1 mL conditioned medium by UC, PS, or EQ were 3.2×108 particles (0.27 µg protein), 12.8×108 particles (0.87 µg protein) and 23.5 ×108 particles (4.50 µg protein), respectively. The average particle sizes in the UC, PS, and EQ fractions were 184.8 ± 1.8 nm, 157.8 ± 1.3 nm and 165.8 ± 1.1 nm, respectively. CD9 and CD81, markers of sEV, were most highly detected in the PS fraction, followed by the EQ and UC fractions. These results suggest that PS gave sEV with relatively high purity, and many protein contaminants appear to be included in the EQ fraction. The mRNA levels of inflammatory cytokines in THP-1 macrophages were most prominently increased by treatment with the UC fraction, followed by the EQ and PS fractions, suggesting that contaminants rather than sEV may largely induce an inflammatory response. CONCLUSION: The isolation method affects the evaluation of sEV function.

In vitro deacetylation of N-acetylserotonin by arylacetamide deacetylase.

Arylacetamide deacetylase (AADAC) is a deacetylation enzyme present in the mammalian liver, gastrointestinal tract, and brain. During our search for mammalian enzymes capable of metabolizing N-acetylserotonin (NAS), AADAC was identified as having the ability to convert NAS to serotonin. Both human and rodent recombinant AADAC proteins can deacetylate NAS in vitro, although the human AADAC shows markedly higher activity compared with rodent enzyme. The AADAC-mediated deacetylation reaction can be potently inhibited by eserine in vitro. In addition to NAS, recombinant hAADAC can deacetylate melatonin (to form 5-methoxytryptamine) and N-acetyltryptamine (NAT) (to form tryptamine). In addition to the in vitro deacetylation of NAS by the recombinant AADAC proteins, liver (mouse and human) and brain (human) extracts were able to deacetylate NAS; these activities were sensitive to eserine. Taken together, these results demonstrate a new role for AADAC and suggest a novel pathway for the AADAC-mediated metabolism of pineal indoles in mammals.

Estimation of contribution of CYP2D6 to tipepidine metabolism in humans and prolongation of the half-life of tipepidine by combination use with a CYP2D6 inhibitor in chimeric mice with humanised liver.

Recently, it has been reported that tipepidine has various central pharmacological effects and can be expected to be safely repositioned as a treatment for psychiatric disorders. Since tipepidine has a very short half-life and requires three doses per day, the development of a once-daily medication would be highly beneficial to improve adherence and quality of life in patients with chronic psychiatric disorders. The aim of this study was to identify the enzymes involved in tipepidine metabolism and to verify that combination use with an enzyme inhibitor prolongs the half-life of tipepidine.Metabolism studies using recombinant human cytochrome P450 (P450, CYP) isoforms and inhibition studies using various selective P450 inhibitors and human liver microsomes revealed that CYP2D6 is the main enzyme catalysing tipepidine metabolism, with a metabolic contribution ratio of 85.4%.Furthermore, a pharmacokinetic study using chimeric mice with humanised liver showed that oral coadministration of a CYP2D6 inhibitor, quinidine, increased the Cmax, AUC0-t, and t1/2 of tipepidine by 1.5-, 3.2-, and 3.0-fold, respectively.These results indicated that coadministration of a CYP2D6 inhibitor is effective in increasing plasma exposure and prolonging the half-life of tipepidine and is useful for repositioning tipepidine as a treatment for psychiatric disorders.

Methionine Sulfoxide Reductase A in Human and Mouse Tissues is Responsible for Sulindac Activation, Making a Larger Contribution than the Gut Microbiota.

Sulindac is a nonsteroidal anti-inflammatory prodrug that is converted to its pharmacologically active metabolite, sulindac sulfide, via a reduction reaction. It is widely accepted that the gut microbiota is responsible for sulindac activation; however, sulindac-induced gastrointestinal injury, which is caused by irritation of the gastrointestinal tract by its active metabolite, is uncommon. Therefore, it is surmised that sulindac is converted to its active metabolite in tissues after absorption. In this study, we sought to identify the enzyme(s) responsible for sulindac activation in tissues and to compare its/their contribution to the gut microbiota. Sulindac is enzymatically reduced in human intestinal, liver, and renal cytosols. Since sulindac is known to be reduced by methionine sulfoxide reductase (Msr) in Escherichia coli, we investigated whether the human ortholog MSRA catalyzes the sulindac reduction reaction. We found that recombinant human MSRA shows sulindac reductase activity with a similar Michaelis constant value as tissue cytosols. In addition, it was revealed that cytosolic factor(s) efficiently enhanced MSRA activity. By using the relative expression factor, the contribution of MSRA to the sulindac reductase activities in each tissue cytosol was calculated to be almost 100%. In mice, depletion of the gut microbiota by administration of antibiotics resulted in a 31% decrease in the area under the curve ratio of sulindac sulfide to sulindac, indicating that the contribution of tissue MsrA to sulindac activation is expected to be 69% in the body. In conclusion, we demonstrated that MSRA expressed in tissues is involved in sulindac activation, making a larger contribution than the gut microbiota. SIGNIFICANCE STATEMENT: Methionine sulfoxide reductase A is responsible for the activation of sulindac, a nonsteroidal anti-inflammatory prodrug, to sulindac sulfide, an active form, in human tissues. Methionine sulfoxide reductase A expressed in tissues activates sulindac with a higher contribution than gut microbiota in body.

Role of Human Arylacetamide Deacetylase (AADAC) on Hydrolysis of Eslicarbazepine Acetate and Effects of AADAC Genetic Polymorphisms on Hydrolase Activity.

Human arylacetamide deacetylase (AADAC) plays a role in the detoxification or activation of drugs and is sometimes involved in the incidence of toxicity by catalyzing hydrolysis reactions. AADAC prefers compounds with relatively small acyl groups, such as acetyl groups. Eslicarbazepine acetate, an antiepileptic drug, is a prodrug rapidly hydrolyzed to eslicarbazepine. We sought to clarify whether AADAC might be responsible for the hydrolysis of eslicarbazepine acetate. Eslicarbazepine acetate was efficiently hydrolyzed by human intestinal and liver microsomes and recombinant human AADAC. The hydrolase activities in human intestinal and liver microsomes were inhibited by epigallocatechin gallate, a specific inhibitor of AADAC, by 82% and 88% of the control, respectively. The hydrolase activities in liver microsomes from 25 human livers were significantly correlated (r = 0.87, P < 0.001) with AADAC protein levels, suggesting that the enzyme AADAC is responsible for the hydrolysis of eslicarbazepine acetate. The effects of genetic polymorphisms of AADAC on eslicarbazepine acetate hydrolysis were examined by using the constructed recombinant AADAC variants with T74A, V172I, R248S, V281I, N366K, or X400Q. AADAC variants with R248S or X400Q showed lower activity than wild type (5% or 21%, respectively), whereas those with V172I showed higher activity than wild type (174%). Similar tendencies were observed in the other four substrates of AADAC; that is, p-nitrophenyl acetate, ketoconazole, phenacetin, and rifampicin. Collectively, we found that eslicarbazepine acetate is specifically and efficiently hydrolyzed by human AADAC, and several AADAC polymorphic alleles would be a factor affecting the enzyme activity and drug response. SIGNIFICANCE STATEMENT: This is the first study to clarify that arylacetamide deacetylase (AADAC) is responsible for the activation of eslicarbazepine acetate, an antiepileptic prodrug, to eslicarbazepine, an active form, in the human liver and intestines. In addition, we found that several AADAC polymorphic alleles would be a factor affecting the enzyme activity and drug response.

Differences in Hydrolase Activities in the Liver and Small Intestine between Marmosets and Humans.

For drug development, species differences in drug-metabolism reactions present obstacles for predicting pharmacokinetics in humans. We characterized the species differences in hydrolases among humans and mice, rats, dogs, and cynomolgus monkeys. In this study, to expand the series of such studies, we attempted to characterize marmoset hydrolases. We measured hydrolase activities for 24 compounds using marmoset liver and intestinal microsomes, as well as recombinant marmoset carboxylesterase (CES) 1, CES2, and arylacetamide deacetylase (AADAC). The contributions of CES1, CES2, and AADAC to hydrolysis in marmoset liver microsomes were estimated by correcting the activities by using the ratios of hydrolase protein levels in the liver microsomes and those in recombinant systems. For six out of eight human CES1 substrates, the activities in marmoset liver microsomes were lower than those in human liver microsomes. For two human CES2 substrates and three out of seven human AADAC substrates, the activities in marmoset liver microsomes were higher than those in human liver microsomes. Notably, among the three rifamycins, only rifabutin was hydrolyzed by marmoset tissue microsomes and recombinant AADAC. The activities for all substrates in marmoset intestinal microsomes tended to be lower than those in liver microsomes, which suggests that the first-pass effects of the CES and AADAC substrates are due to hepatic hydrolysis. In most cases, the sums of the values of the contributions of CES1, CES2, and AADAC were below 100%, which indicated the involvement of other hydrolases in marmosets. In conclusion, we clarified the substrate preferences of hydrolases in marmosets. SIGNIFICANCE STATEMENT: This study confirmed that there are large differences in hydrolase activities between humans and marmosets by characterizing marmoset hydrolase activities for compounds that are substrates of human CES1, CES2, or arylacetamide deacetylase. The data obtained in this study may be useful for considering whether marmosets are appropriate for examining the pharmacokinetics and efficacies of new chemical entities in preclinical studies.

Pirfenidone 5-hydroxylation is mainly catalysed by CYP1A2 and partly catalysed by CYP2C19 and CYP2D6 in the human liver.

Pirfenidone is a first-line drug for the treatment of idiopathic pulmonary fibrosis. The primary metabolic pathways of pirfenidone in humans are 5-hydroxylation and subsequent oxidation to 5-carboxylpirfenidone. The aims of this study were to determine the cytochrome P450 isoforms responsible for pirfenidone 5-hydroxylation and to evaluate their contributions in human liver microsomes (HLM).Among the recombinant P450 isoforms, CYP1A2, CYP2D6, CYP2C19, CYP2A6, and CYP2B6 were shown to catalyse the 5-hydroxylation of pirfenidone. Pirfenidone 5-hydroxylase activity by HLM was inhibited by α-naphthoflavone (by 45%), 8-methoxypsolaren (by 84%), tranylcypromine (by 53%), and quinidine (by 15%), which are CYP1A2, CYP1A2/CYP2A6/CYP2C19, CYP2A6/CYP2C19, and CYP2D6 inhibitors, respectively.In 17 individual HLM donors, pirfenidone 5-hydroxylase activity was significantly correlated with phenacetin O-deethylase (r = 0.89, P < 0.001) and S-mephenytoin 4'-hydroxylase activities (r = 0.51, P < 0.05), which are CYP1A2 and CYP2C19 marker activities, respectively.By using the relative activity factors, the contributions of CYP1A2, CYP2C19, and CYP2D6 to pirfenidone 5-hydroxylation in the human liver were 72.8%, 11.8%, and 8.9%, respectively.In conclusion, we clearly demonstrated the predominant P450 involved in pirfenidone 5-hydroxylation in the human liver is CYP1A2, with CYP2C19 and CYP2D6 playing a minor role.

Adenosine Deaminases Acting on RNA Downregulate the Expression of Constitutive Androstane Receptor in the Human Liver-Derived Cells by Attenuating Splicing.

Adenosine deaminases acting on RNA (ADARs) enzymes-catalyzing adenosine-to-inosine RNA editing possibly modulates gene expression and function. In this study, we investigated whether ADARs regulate the expression of human constitutive androstane receptor (CAR), which controls the expression of various drug-metabolizing enzymes. CAR mRNA and protein levels in human hepatocellular carcinoma-derived HepG2 cells were increased by knockdown of ADAR1 and slightly increased by ADAR2, indicating that ADARs negatively regulate CAR expression. Increased luciferase activity of a reporter plasmid containing the CYP3A4 promoter region by phenobarbital was augmented by transfection of siRNA for ADAR1 (siADAR1) but not by siADAR2. In addition, the knockdown of ADAR1 resulted in the enhanced induction of CYP2B6 and CYP3A4 mRNA by 6-(4-chlorophenyl)imidazo[2,1-b][1,3]thiazole-5-carbaldehyde O-(3,4-dichlorobenzyl)oxime and phenobarbital, respectively. These results suggest that ADAR1-mediated downregulation of CAR affects its downstream cytochrome P450 expression. When the transcription was inhibited by α-amanitin, the degradation of CAR mRNA was attenuated by knockdown of ADAR1, suggesting that the increase in CAR mRNA level by ADAR1 knockdown is a post-transcriptional event. Finally, we found that ADAR1 knockdown promotes the splicing of CAR as a mechanism of the increased expression of CAR by ADAR1 knockdown. In conclusion, this study revealed that ADAR1 plays a role in modulating xenobiotic metabolism potency via regulation of CAR. SIGNIFICANCE STATEMENT: This study revealed that adenosine deaminase acting on RNA 1 (ADAR1) and ADAR2, which catalyze adenosine-to-inosine RNA editing, downregulate the expression of constitutive androstane receptor (CAR) in human liver-derived cells by attenuating splicing. The downregulation of CAR by ADARs affected its downstream cytochrome P450 expression. ADARs would play a role in modulating xenobiotic metabolism potency via regulation of CAR.

RNA Editing Enzymes Modulate the Expression of Hepatic CYP2B6, CYP2C8, and Other Cytochrome P450 Isoforms.

A-to-I RNA editing, the most frequent type of RNA editing in mammals, is catalyzed by adenosine deaminase acting on RNA (ADAR) enzymes. Recently, we found that there is a large interindividual variation in the expression of ADAR1 protein in the human livers. In this study, we investigated the possibility that A-to-I RNA editing may modulate the expression of cytochrome P450 (P450), causing interindividual variations in drug metabolism potencies. We found that knockdown of ADAR1 or ADAR2 in HepaRG cells resulted in the decreased expression of CYP2B6 and CYP2C8 mRNA and protein. Knockdown of ADARs significantly decreased the stability of CYP2B6 mRNA but not CYP2C8 mRNA. Luciferase assays revealed that the 3'-untranslated region of CYP2B6 and the promoter region of CYP2C8 would be involved in the decrease in their expression by the knockdown of ADARs. We found that the decreased expression of the hepatocyte nuclear factor 4α (HNF4α) protein by the knockdown of ADARs was one of the reasons for the decreased transactivity of CYP2C8. The mRNA levels of other P450 isoforms, such as CYP2A6, 2C9, 2C19, 2D6, and 2E1, which are known to be regulated by HNF4α, were also decreased by ADAR1 or ADAR2 knockdown. Exceptionally, the CYP3A4 mRNA level was significantly increased by ADAR1 knockdown, suggesting the possibility that the change could be due to the change in the expression or function of other regulatory factors. In conclusion, this study revealed that the RNA editing enzymes ADAR1 and ADAR2 are novel regulatory factors of P450-mediated drug metabolism in the human liver.