Recommended nomenclature for five mammalian carboxylesterase gene families: human, mouse, and rat genes and proteins

Compared Inhibitory Activities of Tamoxifen and Avenanthramide B on Liver Esterase and Correlation Based on the Superimposed Structure Between Porcine and Human Liver Esterase

Exposure to tamoxifen can exert effects on the human liver, and esterases process prodrugs such as antibiotics and convert them to less toxic metabolites. In this study, the porcine liver esterase (PLE)-inhibitory activity of tamoxifen has been investigated. PLE showed inhibition of a PLE isoenzyme (PLE5). In addition, avenanthramides, which have a similar structure to that of tamoxifen, have been used to determine the PLE-inhibitory effect. Among the avenanthramide derivatives, avenanthramide B has been shown to inhibit PLE. Avenanthramide B interacts with Lys284 of PLE, whereas avenanthramide A and C counteract with Lys284. Avenanthramide B has shown a similar inhibitory effect to that of tamoxifen. Given that avenanthramide B can modulate the action of PLE, it can be used in pharmaceutical and industrial applications for modulating the effects of PLE. Based on superimposed structures between PLE and human liver esterase, the impact of tamoxifen use in humans is discussed. In addition, this study can serve as a fundamental basis for future investigations regarding the potential risk of tamoxifen and other drugs. Thus, this study presents an insight into the comparison of structurally similar tamoxifen and avenanthramides on liver esterases, which can have implications for the pharmaceutical and agricultural industries.

Intestinal human carboxylesterase 2 (CES2) expression rescues drug metabolism and most metabolic syndrome phenotypes in global Ces2 cluster knockout mice

Carboxylesterase 2 (CES2) is expressed mainly in liver and intestine, but most abundantly in intestine. It hydrolyzes carboxylester, thioester, and amide bonds in many exogenous and endogenous compounds, including lipids. CES2 therefore not only plays an important role in the metabolism of many (pro-)drugs, toxins and pesticides, directly influencing pharmacology and toxicology in humans, but it is also involved in energy homeostasis, affecting lipid and glucose metabolism. In this study we investigated the pharmacological and physiological functions of CES2. We constructed Ces2 cluster knockout mice lacking all eight Ces2 genes (Ces2-/- strain) as well as humanized hepatic or intestinal CES2 transgenic strains in this Ces2-/- background. We showed that oral availability and tissue disposition of capecitabine were drastically increased in Ces2-/- mice, and tissue-specifically decreased by intestinal and hepatic human CES2 (hCES2) activity. The metabolism of the chemotherapeutic agent vinorelbine was strongly reduced in Ces2-/- mice, but only marginally rescued by hCES2 expression. On the other hand, Ces2-/- mice exhibited fatty liver, adipositis, hypercholesterolemia and diminished glucose tolerance and insulin sensitivity, but without body mass changes. Paradoxically, hepatic hCES2 expression rescued these metabolic phenotypes but increased liver size, adipose tissue mass and overall body weight, suggesting a "healthy" obesity phenotype. In contrast, intestinal hCES2 expression efficiently rescued all phenotypes, and even improved some parameters, including body weight, relative to the wild-type baseline values. Our results suggest that the induction of intestinal hCES2 may combat most, if not all, of the adverse effects of metabolic syndrome. These CES2 mouse models will provide powerful preclinical tools to enhance drug development, increase physiological insights, and explore potential solutions for metabolic syndrome-associated disorders.

Carboxylesterase 1 directs the metabolic profile of dendritic cells to a reduced inflammatory phenotype

The metabolic profile of dendritic cells (DCs) shapes their phenotype and functions. The carboxylesterase 1 (CES1) enzyme is highly expressed in mononuclear myeloid cells; however, its exact role in DCs is elusive. We used a CES1 inhibitor (WWL113) and genetic overexpression to explore the role of CES1 in DC differentiation in inflammatory models. CES1 expression was analyzed during CD14+ monocytes differentiation to DCs (MoDCs) using quantitative polymerase chain reaction. A CES1 inhibitor (WWL113) was applied during MoDC differentiation. Surface markers, secreted cytokines, lactic acid production, and phagocytic and T cell polarization capacity were analyzed. The transcriptomic and metabolic profiles were assessed with RNA sequencing and mass spectrometry, respectively. Cellular respiration was assessed using seahorse respirometry. Transgenic mice were used to assess the effect of CES1 overexpression in DCs in inflammatory models. CES1 expression peaked early during MoDC differentiation. Pharmacological inhibition of CES1 led to higher expression of CD209, CD86 and MHCII. WWL113 treated MoDCs secreted higher quantities of interleukin (IL)-6, IL-8, tumor necrosis factor, and IL-10 and demonstrated stronger phagocytic ability and a higher capacity to polarize T helper 17 differentiation in an autologous DC-T cell coculture model. Transcriptomic profiling revealed enrichment of multiple inflammatory and metabolic pathways. Functional metabolic analysis showed impaired maximal mitochondrial respiration capacity, increased lactate production, and decreased intracellular amino acids and tricarboxylic acid cycle intermediates. Transgenic human CES1 overexpression in murine DCs generated a less inflammatory phenotype and increased resistance to T cell-mediated colitis. In conclusion, CES1 inhibition directs DC differentiation toward a more inflammatory phenotype that shows a stronger phagocytic capacity and supports T helper 17 skewing. This is associated with a disrupted mitochondrial respiration and amino acid depletion.

In vitro pharmacokinetic behavior in lung of harringtonine, an antagonist of SARS-CoV-2 associated proteins: New insights of inhalation therapy for COVID-19

BACKGROUND

Recent studies have shown that harringtonine (HT) could specifically bind with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike (S) protein and host cell transmembrane serine protease 2 (TMPRSS2) to block membrane fusion, which is an effective antagonist for SARS-CoV-2.

PURPOSE

Our study focused on in-depth exploration of in vitro pharmacokinetic characteristics of HT in lung.

METHODS

HPLC-fluorescence detection method was used to detect changes of HT content. Incubation systems of lung microsomes for phase I metabolism and UGT incubation systems for phase II metabolism were performed to elucidate metabolites and metabolic mechanisms of HT, and then the metabolic enzyme phenotypes for HT were clarified by chemical inhibition method and recombinant enzyme method. Through metabolomics, we comprehensively evaluated the physiological dynamic changes in SD rat and human lung microsomes, and revealed the relationship between metabolomics and pharmacological activity of HT.

RESULTS

HPLC-fluorescence detection method showed strong specificity, high accuracy, and good stability for rapid quantification of HT. We confirmed that HT mainly underwent phase I metabolism, and the metabolites of HT in different species were all identified as 4'-demethyl HT, with metabolic pathway being hydrolysis reaction. CYP1A2 and CYP2E1 participated in HT metabolism, but as HT metabolism was not NADPH dependent, the esterase HCES1 in lung also played a role. The main KEGG pathways in SD rat and human lung microsomes were cortisol synthesis and secretion, steroid hormone biosynthesis and linoleic acid metabolism, respectively. The downregulated key biomarkers of 11-deoxycortisol, 21-deoxycortisol and 9(10)-EpOME suggested that HT could prevent immunosuppression and interfere with infection and replication of SARS-CoV-2.

CONCLUSION

HT was mainly metabolized into 4'-demethyl HT through phase I reactions, which was mediated by CYP1A2, CYP2E1, and HCES1. The downregulation of 11-deoxycortisol, 21-deoxycortisol and 9(10)-EpOME were key ways of HT against SARS-CoV-2. Our study was of great significance for development and clinical application of HT in the treatment of COVID-19.

Role of carboxylesterase and arylacetamide deacetylase in drug metabolism, physiology, and pathology

Carboxylesterases (CES1 and CES2) and arylacetamide deacetylase (AADAC), which are expressed primarily in the liver and/or gastrointestinal tract, hydrolyze drugs containing ester and amide bonds in their chemical structure. These enzymes often catalyze the conversion of prodrugs, including the COVID-19 drugs remdesivir and molnupiravir, to their pharmacologically active forms. Information on the substrate specificity and inhibitory properties of these enzymes, which would be useful for drug development and toxicity avoidance, has accumulated. Recently,in vitroandin vivostudies have shown that these enzymes are involved not only in drug hydrolysis but also in lipid metabolism. CES1 and CES2 are capable of hydrolyzing triacylglycerol, and the deletion of their orthologous genes in mice has been associated with impaired lipid metabolism and hepatic steatosis. Adeno-associated virus-mediated human CES overexpression decreases hepatic triacylglycerol levels and increases fatty acid oxidation in mice. It has also been shown that overexpression of CES enzymes or AADAC in cultured cells suppresses the intracellular accumulation of triacylglycerol. Recent reports indicate that AADAC can be up- or downregulated in tumors of various organs, and its varied expression is associated with poor prognosis in patients with cancer. Thus, CES and AADAC not only determine drug efficacy and toxicity but are also involved in pathophysiology. This review summarizes recent findings on the roles of CES and AADAC in drug metabolism, physiology, and pathology.

Comparative Analysis of Differentially Expressed Genes in Chondrocytes from Rats Exposed to Low Selenium and T-2 Toxin

The aim of this study was to construct rat models of environmental risk factors for Kashin-Beck disease (KBD) with low selenium and T-2 toxin levels and to screen the differentially expressed genes (DEGs) between the rat models exposed to environmental risk factors. The Se-deficient (SD) group and T-2 toxin exposure (T-2) group were constructed. Knee joint samples were stained with hematoxylin-eosin, and cartilage tissue damage was observed. Illumina high-throughput sequencing technology was used to detect the gene expression profiles of the rat models in each group. Gene Ontology (GO) functional enrichment analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) signaling pathway enrichment analysis were performed and five differential gene expression results were verified by quantitative real-time polymerase chain reaction (qRT‒PCR). A total of 124 DEGs were identified from the SD group, including 56 upregulated genes and 68 downregulated genes. A total of 135 DEGs were identified in the T-2 group, including 68 upregulated genes and 67 downregulated genes. The DEGs were significantly enriched in 4 KEGG pathways in the SD group and 9 KEGG pathways in the T-2 group. The expression levels of Dbp, Pc, Selenow, Rpl30, and Mt2A were consistent with the results of transcriptome sequencing by qRT‒PCR. The results of this study confirmed that there were some differences in DEGs between the SD group and the T-2 group and provided new evidence for further exploration of the etiology and pathogenesis of KBD.

PBPK Modelling for Drugs Cleared by Non-CYP Enzymes: State-of-the-Art and Future Perspectives

Physiologically-based pharmacokinetic (PBPK) modeling has become the established method for predicting human pharmacokinetics (PK) and drug-drug interactions (DDI). The number of drugs cleared by non-CYP enzyme metabolism has increased steadily and to date, there is no consolidated overview of PBPK modeling for drugs cleared by non-CYP enzymes. This review aims to describe the state-of-the-art for PBPK modeling for drugs cleared via non-CYP enzymes, to identify successful strategies, to describe gaps and to provide suggestion to overcome them. To this end, we conducted a detailed literature search and found 58 articles published before the 1st of January 2023 containing 95 examples of clinical PBPK models for 62 non-CYP enzyme substrates. Reviewed articles covered the drug clearance by uridine 5'-diphospho-glucuronosyltransferases (UGTs), aldehyde oxidase (AO), flavin-containing monooxygenases (FMOs), sulfotransferases (SULTs) and carboxylesterases (CES), with UGT2B7, UGT1A9, CES1, FMO3 and AO being the enzymes most frequently involved. In vitro-in vivo extrapolation (IVIVE) of intrinsic clearance and the bottom-up PBPK modeling involving non-CYP enzymes remains challenging. We observed that the middle-out modeling approach was applied in 80% of the cases, with metabolism parameters optimized in 73% of the models. Our review could not identify a standardized approach used for model optimization based on clinical data, with manual optimization employed most frequently. Successful development of models for UGT2B7, UGT1A9, CES1, and FMO3 substrates provides a foundation for other drugs metabolized by these enzymes and guides the way forward in creating PBPK models for other enzymes in these families. Significance Statement Our review charts the rise of PBPK modeling for drugs cleared by non-CYP enzymes. Analyzing 58 articles and 62 non-CYP enzyme substrates, we found that UGTs, AO, FMOs, SULTs, and CES were the main enzyme families involved and that UGT2B7, UGT1A9, CES1, FMO3 and AO are the individual enzymes with the strongest PBPK modeling precedents. Approaches established for these enzymes can now be extended to additional substrates and to drugs metabolized by enzymes that are similarly well characterized.

Natural deletion of mouse carboxylesterases Ces1c/d/e impacts drug metabolism and metabolic syndrome development

Mammalian carboxylesterase 1 enzymes can hydrolyze many xenobiotic chemicals and endogenous lipids. We here identified and characterized a mouse strain (FVB/NKI) in which three of the eight Ces1 genes were spontaneously deleted, removing Ces1c and Ces1e partly, and Ces1d entirely. We studied the impact of this Ces1c/d/e deficiency on drug and lipid metabolism and homeostasis. Ces1c/d/e-/- mice showed strongly impaired conversion of the anticancer prodrug irinotecan to its active metabolite SN-38 in plasma, spleen and lung. Plasma hydrolysis of the oral anticancer prodrug capecitabine to 5-DFCR was also profoundly reduced in Ces1c/d/e-/- mice. Our findings resolved previously unexplained FVB/NKI pharmacokinetic anomalies. On a medium-fat diet, Ces1c/d/e-/- female mice exhibited moderately higher body weight, mild inflammation in gonadal white adipose tissue (gWAT), and increased lipid load in brown adipose tissue (BAT). Ces1c/d/e-/- males showed more pronounced inflammation in gWAT and an increased lipid load in BAT. On a 5-week high-fat diet exposure, Ces1c/d/e deficiency predisposed to developing obesity, enlarged and fatty liver, glucose intolerance and insulin resistance, with severe inflammation in gWAT and increased lipid load in BAT. Hepatic proteomics analysis revealed that the acute phase response, involved in the dynamic cycle of immunometabolism, was activated in these Ces1c/d/e-/- mice. This may contribute to the obesity-related chronic inflammation and adverse metabolic disease in this strain. While Ces1c/d/e deficiency clearly exacerbated metabolic syndrome development, long-term (18-week) high-fat diet exposure overwhelmed many, albeit not all, observed phenotypic differences.

Development of a next-generation endogenous OCT4 inducer and its anti-aging effect in vivo

The identification of small molecules capable of replacing transcription factors has been a longstanding challenge in the generation of human chemically induced pluripotent stem cells (iPSCs). Recent studies have shown that ectopic expression of OCT4, one of the master pluripotency regulators, compromised the developmental potential of resulting iPSCs, This highlights the importance of finding endogenous OCT4 inducers for the generation of clinical-grade human iPSCs. Through a cell-based high throughput screen, we have discovered several new OCT4-inducing compounds (O4Is). In this work, we prepared metabolically stable analogues, including O4I4, which activate endogenous OCT4 and associated signaling pathways in various cell lines. By combining these with a transcription factor cocktail consisting of SOX2, KLF4, MYC, and LIN28 (referred to as "CSKML") we achieved to reprogram human fibroblasts into a stable and authentic pluripotent state without the need for exogenous OCT4. In Caenorhabditis elegans and Drosophila, O4I4 extends lifespan, suggesting the potential application of OCT4-inducing compounds in regenerative medicine and rejuvenation therapy.

Hydrolysis of dibutyl phthalate and di(2-ethylhexyl) phthalate in human liver, small intestine, kidney, and lung: An in vitro analysis using organ subcellular fractions and recombinant carboxylesterases

Phthalates are widely used plasticizers that are primarily and rapidly metabolized to monoester phthalates in mammals. In the present study, the hydrolysis of dibutyl phthalate (DBP) and di(2-ethylhexyl) phthalate (DEHP) in the human liver, small intestine, kidney, and lung was examined by the catalytic, kinetic, and inhibition analyses using organ microsomal and cytosolic fractions and recombinant carboxylesterases (CESs). The V_max (y-intercept) values based on the Eadie-Hofstee plots of DBP hydrolysis were liver > small intestine > kidney > lung in microsomes, and liver > small intestine > lung > kidney in cytosol, respectively. The CL_int values (x-intercept) were small intestine > liver > kidney > lung in both microsomes and cytosol. The V_max and CL_int or CL_max values of DEHP hydrolysis were small intestine > liver > kidney > lung in both microsomes and cytosol. Bis(4-nitrophenyl) phosphate (BNPP) effectively inhibited the activities of DBP and DEHP hydrolysis in the microsomes and cytosol of liver, small intestine, kidney, and lung. Although physostigmine also potently inhibited DBP and DEHP hydrolysis activities in both the microsomes and cytosol of the small intestine and kidney, the inhibitory effects in the liver and lung were weak. In recombinant CESs, the V_max values of DBP hydrolysis were CES1 (CES1b, CES1c) > CES2, whereas the CL_max values were CES2 > CES1 (CES1b, CES1c). On the other hand, the V_max and CL_max values of DEHP hydrolysis were CES2 > CES1 (CES1b, CES1c). These results suggest an extensive organ-dependence of DBP and DEHP hydrolysis due to CES expression, and that CESs are responsible for the metabolic activation of phthalates.

Carboxylesterase 1 family knockout alters drug disposition and lipid metabolism

The mammalian carboxylesterase 1 (Ces1/CES1) family comprises several enzymes that hydrolyze many xenobiotic chemicals and endogenous lipids. To investigate the pharmacological and physiological roles of Ces1/CES1, we generated Ces1 cluster knockout (Ces1 ^-/- ) mice, and a hepatic human CES1 transgenic model in the Ces1 ^-/- background (TgCES1). Ces1 ^-/- mice displayed profoundly decreased conversion of the anticancer prodrug irinotecan to SN-38 in plasma and tissues. TgCES1 mice exhibited enhanced metabolism of irinotecan to SN-38 in liver and kidney. Ces1 and hCES1 activity increased irinotecan toxicity, likely by enhancing the formation of pharmacodynamically active SN-38. Ces1 ^-/- mice also showed markedly increased capecitabine plasma exposure, which was moderately decreased in TgCES1 mice. Ces1 ^-/- mice were overweight with increased adipose tissue, white adipose tissue inflammation (in males), a higher lipid load in brown adipose tissue, and impaired blood glucose tolerance (in males). These phenotypes were mostly reversed in TgCES1 mice. TgCES1 mice displayed increased triglyceride secretion from liver to plasma, together with higher triglyceride levels in the male liver. These results indicate that the carboxylesterase 1 family plays essential roles in drug and lipid metabolism and detoxification. Ces1 ^-/- and TgCES1 mice will provide excellent tools for further study of the in vivo functions of Ces1/CES1 enzymes.

Interfering with lipid metabolism through targeting CES1 sensitizes hepatocellular carcinoma for chemotherapy

Hepatocellular carcinoma (HCC) is the most common lethal form of liver cancer. Apart from surgical removal and transplantation, other treatments have not yet been well established for patients with HCC. In this study, we found that carboxylesterase 1 (CES1) is expressed at various levels in HCC. We further revealed that blockage of CES1 by pharmacological and genetical approaches leads to altered lipid profiles that are directly linked to impaired mitochondrial function. Mechanistically, lipidomic analyses indicated that lipid signaling molecules, including polyunsaturated fatty acids (PUFAs), which activate PPARα/γ, were dramatically reduced upon CES1 inhibition. As a result, the expression of SCD, a PPARα/γ target gene involved in tumor progression and chemoresistance, was significantly downregulated. Clinical analysis demonstrated a strong correlation between the protein levels of CES1 and SCD in HCC. Interference with lipid signaling by targeting the CES1-PPARα/γ-SCD axis sensitized HCC cells to cisplatin treatment. As a result, the growth of HCC xenograft tumors in NU/J mice was potently slowed by coadministration of cisplatin and CES1 inhibition. Our results, thus, suggest that CES1 is a promising therapeutic target for HCC treatment.

NUDT7 regulates total hepatic CoA levels and the composition of the intestinal bile acid pool in male mice fed a Western diet

Nudix hydrolase 7 (NUDT7) is an enzyme that hydrolyzes CoA species, is highly expressed in the liver, and resides in the peroxisomes. Peroxisomes are organelles where the preferential oxidation of dicarboxylic fatty acids occurs and where the hepatic synthesis of the primary bile acids cholic acid and chenodeoxycholic acid is completed. We previously showed that liver-specific overexpression of NUDT7 affects peroxisomal lipid metabolism but does not prevent the increase in total liver CoA levels that occurs during fasting. We generated Nudt7^-/- mice to further characterize the role that peroxisomal (acyl-)CoA degradation plays in the modulation of the size and composition of the acyl-CoA pool and in the regulation of hepatic lipid metabolism. Here, we show that deletion of Nudt7 alters the composition of the hepatic acyl-CoA pool in mice fed a low-fat diet, but only in males fed a Western diet does the lack of NUDT7 activity increase total liver CoA levels. This effect is driven by the male-specific accumulation of medium-chain dicarboxylic acyl-CoAs, which are produced from the β-oxidation of dicarboxylic fatty acids. We also show that, under conditions of elevated synthesis of chenodeoxycholic acid derivatives, Nudt7 deletion promotes the production of tauromuricholic acid, decreasing the hydrophobicity index of the intestinal bile acid pool and increasing fecal cholesterol excretion in male mice. These findings reveal that NUDT7-mediated hydrolysis of acyl-CoA pathway intermediates in liver peroxisomes contributes to the regulation of dicarboxylic fatty acid metabolism and the composition of the bile acid pool.

The Crystal Structure of Mouse Ces2c, a Potential Ortholog of Human CES2, Shows Structural Similarities in Substrate Regulation and Product Release to Human CES1

Members of the carboxylesterase 2 (Ces2/CES2) family have been studied intensively with respect to their hydrolytic function on (pro)drugs, whereas their physiological role in lipid and energy metabolism has been realized only within the last few years. Humans have one CES2 gene which is highly expressed in liver, intestine, and kidney. Interestingly, eight homologous Ces2 (Ces2a to Ces2h) genes exist in mice and the individual roles of the corresponding proteins are incompletely understood. Mouse Ces2c (mCes2c) is suggested as potential ortholog of human CES2. Therefore, we aimed at its structural and biophysical characterization. Here, we present the first crystal structure of mCes2c to 2.12 Å resolution. The overall structure of mCes2c resembles that of the human CES1 (hCES1). The core domain adopts an α/β hydrolase-fold with S230, E347, and H459 forming a catalytic triad. Access to the active site is restricted by the cap, the flexible lid, and the regulatory domain. The conserved gate (M417) and switch (F418) residues might have a function in product release similar as suggested for hCES1. Biophysical characterization confirms that mCes2c is a monomer in solution. Thus, this study broadens our understanding of the mammalian carboxylesterase family and assists in delineating the similarities and differences of the different family members.

Carboxylesterase 1d Inactivation Augments Lung Inflammation in Mice

Carboxylesterases are members of the serine hydrolase superfamily and metabolize drugs, pesticides, and lipids. Previous research showed that inhibition of carboxylesterase 1 (CES1) in human macrophages altered the immunomodulatory effects of lipid mediators called prostaglandin glyceryl esters, which are produced by cyclooxygenase-catalyzed oxygenation of the endocannabinoid 2-arachidonoylglycerol (2-AG). Ces1d - the mouse ortholog of human CES1 - is the most abundant Ces isoform in murine lung tissues and alveolar macrophages and a major target of organophosphate poisons. Monoacylglycerol lipase (Magl) is also expressed in murine lung and is the main enzyme responsible for 2-AG catabolism. Several metabolic benefits are observed in Ces1d-/- mice fed a high-fat diet; thus, we wondered whether pharmacological and genetic inactivation of Ces1d in vivo might also ameliorate the acute inflammatory response to lipopolysaccharide (LPS). C57BL/6 mice were treated with WWL229 (Ces1d inhibitor) or JZL184 (Magl inhibitor), followed 30 min later by either LPS or saline. Wild-type (WT) and Ces1d-/- mice were also administered LPS to determine the effect of Ces1d knockout. Mice were sacrificed at 6 and 24 h, and cytokines were assessed in serum, lung, liver, and adipose tissues. Lipid mediators were quantified in lung tissues, while activity-based protein profiling and enzyme assays determined the extent of lung serine hydrolase inactivation by the inhibitors. WWL229 was shown to augment LPS-induced lung inflammation in a female-specific manner, as measured by enhanced neutrophil infiltration and Il1b mRNA. The marked Ces inhibition in female lung by 4 h after drug treatment might explain this sex difference, although the degree of Ces inhibition in female and male lungs was similar at 6 h. In addition, induction of lung Il6 mRNA and prostaglandin E2 by LPS was more pronounced in Ces1d-/- mice than in WT mice. Thus, WWL229 inhibited lung Ces1d activity and augmented the female lung innate immune response, an effect observed in part in Ces1d-/- mice and Ces1d/CES1-deficient murine and human macrophages. In contrast, JZL184 attenuated LPS-induced Il1b and Il6 mRNA levels in female lung, suggesting that Ces1d and Magl have opposing effects. Mapping the immunomodulatory molecules/pathways that are regulated by Ces1d in the context of lung inflammation will require further research.

Ethanol and its Nonoxidative Metabolites Promote Acute Liver Injury by Inducing ER Stress, Adipocyte Death, and Lipolysis

BACKGROUND & AIMS

Binge drinking in patients with metabolic syndrome accelerates the development of alcohol-associated liver disease. However, the underlying mechanisms remain elusive. We investigated if oxidative and nonoxidative alcohol metabolism pathways, diet-induced obesity, and adipose tissues influenced the development of acute liver injury in a single ethanol binge model.

METHODS

A single ethanol binge was administered to chow-fed or high-fat diet (HFD)-fed wild-type and genetically modified mice.

RESULTS

Oral administration of a single dose of ethanol induced acute liver injury and hepatic endoplasmic reticulum (ER) stress in chow- or HFD-fed mice. Disruption of the Adh1 gene increased blood ethanol concentration and exacerbated acute ethanol-induced ER stress and liver injury in both chow-fed and HFD-fed mice, while disruption of the Aldh2 gene did not affect such hepatic injury despite high blood acetaldehyde levels. Mechanistic studies showed that alcohol, not acetaldehyde, promoted hepatic ER stress, fatty acid synthesis, and increased adipocyte death and lipolysis, contributing to acute liver injury. Increased serum fatty acid ethyl esters (FAEEs), which are formed by an enzyme-mediated esterification of ethanol with fatty acids, were detected in mice after ethanol gavage, with higher levels in Adh1 knockout mice than in wild-type mice. Deletion of the Ces1d gene in mice markedly reduced the acute ethanol-induced increase of blood FAEE levels with a slight but significant reduction of serum aminotransferase levels.

CONCLUSIONS

Ethanol and its nonoxidative metabolites, FAEEs, not acetaldehyde, promoted acute alcohol-induced liver injury by inducing ER stress, adipocyte death, and lipolysis.

Going deeper into the toxicokinetics of synthetic cannabinoids: in vitro contribution of human carboxylesterases

Synthetic cannabinoids (SC) are new psychoactive substances known to cause intoxications and fatalities. One reason may be the limited data available concerning the toxicokinetics of SC, but toxicity mechanisms are insufficiently understood so far. Human carboxylesterases (hCES) are widely known to play a crucial role in the catalytic hydrolysis of drugs (of abuse). The aim of this study was to investigate the in vitro contribution of hCES to the metabolism of the 13 SC 3,5-AB-5F-FUPPYCA, AB-5F-P7AICA, A-CHMINACA, DMBA-CHMINACA, MBA-CHMINACA, MDMB-4F-BINACA, MDMB-4en-PINACA, MDMB-FUBICA, MDMB-5F-PICA, MMB-CHMICA, MMB-4en-PICA, MMB-FUBINACA, and MPhP-5F-PICA. The SC were incubated with recombinant hCES1b, hCES1c, or hCES2 and analyzed by liquid chromatography-ion trap mass spectrometry to assess amide or ester hydrolysis in an initial activity screening. Enzyme kinetic studies were performed if sufficient hydrolysis was observed. No hydrolysis of the amide linker was observed using those experimental conditions. Except for MDMB-5F-PICA, ester hydrolysis was always detected if an ester group was present in the head group. In general, SC with a terminal ester bearing a small alcohol part and a larger acyl part showed higher affinity to hCES1 isozymes. Due to the low hydrolysis rates, enzyme kinetics could not be modeled for the SC with a tert-leucine-derived moiety, but hydrolysis reactions of MPhP-5F-PICA and of those containing a valine-derived moiety followed classic Michaelis-Menten kinetics. In conclusion, drug-drug/drug-food interactions or hCES polymorphisms may prolong the half-life of SC and the current results help to estimate the risk of toxicity in the future after combining them with activity and clinical data.

Deciphering the species differences in CES1A-mediated hydrolytic metabolism by using a bioluminescence substrate

Carboxylesterases 1A (CES1A) is a key enzyme responsible for the hydrolytic metabolism of a great deal of endogenous and exogenous substrates bearing ester- or amide-bond(s). This study aimed to decipher the species difference in CES1A-mediated hydrolytic metabolism by using a newly developed bioluminescence CES1A sensor (termed NLMe) as the probe substrate, while the liver microsomes from six different mammalian species (human, cynomolgus monkey, dog, minipig, rat and mouse) were used as the enzyme sources. Metabolite profiling demonstrated that all tested liver microsomes from various species could catalyze NLMe hydrolysis, but significant difference in hydrolytic rate was observed. Kinetic plots of NLMe hydrolysis in liver microsomes from different species showed that the inherent clearance rates (C_lint) of NLMe in human liver microsomes (HLM), cynomolgus monkey liver microsomes (CyLM), and pig liver microsome (PLM) were comparable, while the C_lint values of NLMe in dog liver microsomes (DLM), mouse liver microsomes (MLM), and rat liver microsomes (RLM) were relatively small. Moreover, chemical inhibition assays showed that NLMe hydrolysis in all tested liver microsomes could be competently inhibited by BNPP (a potent broad-spectrum inhibitor of CES), but CUA (a selective inhibitor of human CES1A) only inhibited NLMe hydrolysis in human liver microsomes and dog liver microsomes. In summary, the species differences in CES1A-catalyzed NLMe hydrolysis were carefully investigated from the views of the similarities in metabolite profile, hydrolytic kinetics and inhibitor response. All these findings provide new insights into the species differences in CES1A-mediated hydrolytic metabolism and suggest that it is necessary for the pharmacologists to choose appropriate animal models to replace humans for evaluating the in vivo effects of CES1A inhibitors.

Emerging role of carboxylesterases in nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is increasingly recognized as a global public health problem. Carboxylesterases (CESs), as potential influencing factors of NAFLD, are very important to improve clinical outcomes. This review aims to deeply understand the role of CESs in the progression of NAFLD and proposes that CESs can be used as potential targets for NAFLD treatment. We first introduced CESs and analyzed the relationship between CESs and hepatic lipid metabolism and inflammation. Then, we further reviewed the regulation of nuclear receptors on CESs, including PXR, CAR, PPARα, HNF4α and FXR, which may influence the progression of NAFLD. Finally, we evaluated the advantages and disadvantages of existing NAFLD animal models and summarized the application of CES-related animal models in NAFLD research. In general, this review provides an overview of the relationship between CESs and NAFLD and discusses the role and potential value of CESs in the treatment and prevention of NAFLD.

The COVID-19 Oral Drug Molnupiravir Is a CES2 Substrate: Potential Drug-Drug Interactions and Impact of CES2 Genetic Polymorphism In Vitro

Molnupiravir is one of the two coronavirus disease 2019 (COVID-19) oral drugs that were recently granted the emergency use authorization by the Food and Drug Administration (FDA). Molnupiravir is an ester and requires hydrolysis to exert antiviral activity. Carboxylesterases constitute a class of hydrolases with high catalytic efficiency. Humans express two major carboxylesterases (CES1 and CES2) that differ in substrate specificity. Based on the structural characteristics of molnupiravir, this study was performed to test the hypothesis that molnupiravir is preferably hydrolyzed by CES2. Several complementary approaches were used to test this hypothesis. As many as 24 individual human liver samples were tested and the hydrolysis of molnupiravir was significantly correlated with the level of CES2 but not CES1. Microsomes from the intestine, kidney, and liver, but not lung, all rapidly hydrolyzed molnupiravir and the magnitude of hydrolysis was related closely to the level of CES2 expression among these organs. Importantly, recombinant CES2 but not CES1 hydrolyzed molnupiravir, collectively establishing that molnupiravir is a CES2-selective substrate. In addition, several CES2 polymorphic variants (e.g., R180H) differed from the wild-type CES2 in the hydrolysis of molnupiravir. Molecular docking revealed that wild-type CES2 and its variant R180H used different sets of amino acids to interact with molnupiravir. Furthermore, molnupiravir hydrolysis was significantly inhibited by remdesivir, the first COVID-19 drug granted the full approval by the FDA. The results presented raise the possibility that CES2 expression and genetic variation may impact therapeutic efficacy in clinical situations and warrants further investigation. SIGNIFICANCE STATEMENT: COVID-19 remains a global health crisis, and molnupiravir is one of the two recently approved oral COVID-19 therapeutics. In this study, we have shown that molnupiravir is hydrolytically activated by CES2, a major hydrolase whose activity is impacted by genetic polymorphic variants, disease mediators, and many potentially coadministered medicines. These results presented raise the possibility that CES2 expression and genetic variation may impact therapeutic efficacy in clinical situations and warrants further investigation.

Inhibition of Radix Scutellariae flavones on carboxylesterase mediated activations of prodrugs

AIMS

Carboxylesterase (CES) plays an essential role in the hydrolysis of ester prodrugs. Our study explored the inhibitions of Radix Scutellariae flavones, including baicalein (B), baicalin (BG), wogonin (W), wogonoside (WG), oroxylin A (OXA) and oroxylin A-7-O-glucuronide (OAG), on CES-mediated hydrolysis of seven prodrugs (capecitabine, clopidogrel, mycophenolate mofetil, dabigatran etexilate, acetylsalicylic acid, prasugrel and irinotecan).

MAIN METHODS

In vitro screenings were developed by incubating the flavones with prodrugs in rat plasma, intestine S9 and liver S9. Docking simulations were conducted using AMDock v1.5.2. In vivo evaluations were performed in rats co-administered with the selected flavone and prodrug via oral gavage/intravenous administration for five consecutive days.

KEY FINDINGS

The in vitro investigation showed that B and OXA demonstrated strongest inhibitions on the hydrolysis of irinotecan followed by dabigatran in rat plasma, intestine S9 and liver S9. Consistent results showed in the molecular docking analyses. Additionally, in rats receiving irinotecan, B/OXA intravenous and oral pre-treatments both led to reduction trends on the active metabolite SN-38 formation in plasma. Besides, significant decreases of SN-38/irinotecan plasma concentration ratios were found in the B/OXA oral pre-treatment group with quicker and stronger inhibition potential in OXA pre-treatment than that from B pre-treatment. OXA oral pre-treatment was also found to be able to significantly inhibit intestinal CES2 activities at 0.5 h and 5 h after irinotecan administration.

SIGNIFICANCE

Our current findings for the first time alert on potential CES-mediated HDIs between RS flavones and prodrugs, which provide a constructive information referring to rational drug combinations in clinical practice.

A New Anesthetic, Remimazolam, Is Useful in the Management of Anesthesia in Patients with Liver Cirrhosis

Background

Management of general anesthesia in patients with liver cirrhosis is challenging because it is difficult to maintain the circulation and concentration of anesthetics within a safe range. Unlike many other anesthetics, which are metabolized by cytochrome P450 enzymes, remimazolam is metabolized by carboxylesterase. In a liver cirrhosis model, cytochrome P450 activity is suppressed by approximately 30%; however, carboxylesterase activity is maintained at approximately 60%. Also, remimazolam is less likely to inhibit circulation. A 77-year-old woman was scheduled to undergo laparoscopic cholecystectomy. The patient was diagnosed with Child-Pugh B liver cirrhosis due to type C viral hepatitis. General anesthesia with remimazolam stabilized the intraoperative circulation and resulted in rapid postoperative awakening.

Conclusion

We report a case in which a patient with Child-Pugh B cirrhosis was safely managed under general anesthesia using remimazolam during laparoscopic cholecystectomy.

Carbonate-Based Fluorescent Chemical Tool for Uncovering Carboxylesterase 1 (CES1) Activity Variations in Live Cells

Carboxylesterase 1 (CES1) plays a key role in the metabolism of endogenous biomolecules and xenobiotics including a variety of pharmaceuticals. Despite the established importance of CES1 in drug metabolism, methods to study factors that can vary CES1 activity are limited with only a few suitable for use in live cells. Herein, we report the development of FCP1, a new CES1 specific fluorescent probe with a unique carbonate substrate constructed from commercially available reagents. We show that FCP-1 can specifically report on endogenous CES1 activity with a robust fluorescence response in live HepG2 cells through studies with inhibitors and genetic knockdowns. Subsequently, we deployed FCP-1 to develop a live cell fluorescence microscopy-based approach to identify activity differences between CES1 isoforms. To the best of our knowledge, this is the first application of a fluorescent probe to measure the activity of CES1 sequence variants in live cells.

Screening and Conjoint Analysis of Key lncRNAs for Milk Fat Metabolism in Dairy Cows

Long noncoding RNAs (lncRNAs) play an important regulatory role in various biological processes as a key regulatory factor. However, the complete expression profile of lncRNAs in dairy cows and its function in milk fat synthesis are unknown. In this study, RNA sequencing (RNA-seq) was used to research the whole genome expression of lncRNAs and mRNA transcripts in high and low milk fat percentage (MFP) bovine mammary epithelial cells (BMECs), and joint analysis was carried out. We identified a total of 47 differentially expressed genes (DEGs) and 38 differentially expressed lncRNAs (DELs, Padj <0.05), enrichment analysis screened out 11 candidate DEGs that may regulate milk fat metabolism. Downregulated differential gene ENPP2 (The expression level in BMECs of high milk fat dairy cows was lower than that of low milk fat cows) and upregulated differential gene BCAT1 are more likely to participate in the milk fat metabolism, and its function needs further experiments verification. The enrichment analysis of target genes predicted by DELs identified 7 cis (co-localization) and 10 trans (co-expression) candidate target genes related to milk lipid metabolism, corresponding to a total of 18 DELs. Among them, the targeting relationship between long intervening/intergenic noncoding RNA (lincRNA) TCONS_00082721 and FABP4 is worthy of attention. One hundred and fifty-six competing endogenous RNAs (ceRNAs) interaction regulation networks related to milk fat metabolism were constructed based on the expression information of DELs, differential microRNAs (miRNAs), and lipid metabolism-related target genes. The regulatory network centered on miR-145 will be the focus of subsequent experimental research. The ceRNAs regulatory network related to TCONS_00082721 and TCONS_00172817 are more likely to be involved in milk fat synthesis. These results will provide new ways to understand the complex biology of dairy cow milk fat synthesis and provide valuable information for breed improvement of Chinese Holstein cow.

Lipolysis: cellular mechanisms for lipid mobilization from fat stores

The perception that intracellular lipolysis is a straightforward process that releases fatty acids from fat stores in adipose tissue to generate energy has experienced major revisions over the last two decades. The discovery of new lipolytic enzymes and coregulators, the demonstration that lipophagy and lysosomal lipolysis contribute to the degradation of cellular lipid stores and the characterization of numerous factors and signalling pathways that regulate lipid hydrolysis on transcriptional and post-transcriptional levels have revolutionized our understanding of lipolysis. In this review, we focus on the mechanisms that facilitate intracellular fatty-acid mobilization, drawing on canonical and noncanonical enzymatic pathways. We summarize how intracellular lipolysis affects lipid-mediated signalling, metabolic regulation and energy homeostasis in multiple organs. Finally, we examine how these processes affect pathogenesis and how lipolysis may be targeted to potentially prevent or treat various diseases.

Construction and Characterization of CRISPR/Cas9 Knockout Rat Model of Carboxylesterase 2a Gene

Carboxylesterase (CES) 2, an important metabolic enzyme, plays a critical role in drug biotransformation and lipid metabolism. Although CES2 is very important, few animal models have been generated to study its properties and functions. Rat Ces2 is similar to human CES2A-CES3A-CES4A gene cluster, with highly similar gene structure, function, and substrate. In this report, CRISPR-associated protein-9 (CRISPR/Cas9) technology was first used to knock out rat Ces2a, which is a main subtype of Ces2 mostly distributed in the liver and intestine. This model showed the absence of CES2A protein expression in the liver. Further pharmacokinetic studies of diltiazem, a typical substrate of CES2A, confirmed the loss of function of CES2A both in vivo and in vitro. At the same time, the expression of CES2C and CES2J protein in the liver decreased significantly. The body and liver weight of Ces2a knockout rats also increased, but the food intake did not change. Moreover, the deficiency of Ces2a led to obesity, insulin resistance, and liver fat accumulation, which are consistent with the symptoms of nonalcoholic fatty liver disease (NAFLD). Therefore, this rat model is not only a powerful tool to study drug metabolism mediated by CES2 but also a good disease model to study NAFLD. SIGNIFICANCE STATEMENT: Human carboxylesterase (CES) 2 plays a key role in the first-pass hydrolysis metabolism of most oral prodrugs as well as lipid metabolism. In this study, CRISPR/Cas9 technology was used to knock out Ces2a gene in rats for the first time. This model can be used not only in the study of drug metabolism and pharmacokinetics but also as a disease model of nonalcoholic fatty liver disease (NAFLD) and other metabolic disorders.

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. Expected final online publication date for the Annual Review of Pharmacology and Toxicology, Volume 62 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Human carboxylesterases and fluorescent probes to image their activity in live cells

Human carboxylesterases (CESs) are serine hydrolases that are responsible for the phase I metabolism of an assortment of ester, amide, thioester, carbonate, and carbamate containing drugs. CES activity is known to be influenced by a variety of factors including single nucleotide polymorphisms, alternative splicing, and drug-drug interactions. These different factors contribute to interindividual variability of CES activity which has been demonstrated to influence clinical outcomes among people treated with CES-substrate therapeutics. Detailed exploration of the factors that influence CES activity is emerging as an important area of research. The use of fluorescent probes with live cell imaging techniques can selectively visualize the real-time activity of CESs and have the potential to be useful tools to help reveal the impacts of CES activity variations on human health. This review summarizes the properties of the five known human CESs including factors reported to or that could potentially influence their activity before discussing the design aspects and use considerations of CES fluorescent probes in general in addition to highlighting several well-characterized probes.

Carboxylesterase inhibitors from clinically available medicines and their impact on drug metabolism

Mammalian carboxylesterases (CES), the key members of the serine hydrolase superfamily, hydrolyze a wide range of endogenous substances and xenobiotics bearing ester or amide bond(s). In humans, most of identified CES are segregated into the CES1A and CES2A subfamilies. Strong inhibition on human CES (including hCES1A and hCES2A) may modulate pharmacokinetic profiles of CES-substrate drugs, thereby changing the pharmacological and toxicological responses of these drugs. This review covered recent advances in discovery of hCES inhibitors from clinically available medications, as well as their impact on CES-associated drug metabolism. Three comprehensive lists of hCES inhibitors deriving from clinically available medications including therapeutic drugs, pharmaceutical excipients and herbal medicines, alongside with their inhibition potentials and inhibition parameters, are summarized. Furthermore, the potential risks of hCES inhibitors to trigger drug/herb-drug interactions (DDIs/HDIs) and future concerns in this field are highlighted. Potent hCES inhibitors may trigger clinically relevant DDIs/HDIs, especially when these inhibitors are co-administrated with CES substrate-drugs with very narrow therapeutic windows. All data and knowledge presented here provide key information for the clinicians to assess the risks of clinically available hCES inhibitors on drug metabolism. In future, more practical and highly specific substrates for hCES1A/hCES2A should be developed and used for studies on CES-mediated DDIs/HDIs both in vitro and in vivo.

Ciclesonide activates glucocorticoid signaling in neonatal rat lung but does not trigger adverse effects in the cortex and cerebellum

Synthetic glucocorticoids (sGCs) such as dexamethasone (DEX), while used to mitigate inflammation and disease progression in premature infants with severe bronchopulmonary dysplasia (BPD), are also associated with significant adverse neurologic effects such as reductions in myelination and abnormalities in neuroanatomical development. Ciclesonide (CIC) is a sGC prodrug approved for asthma treatment that exhibits limited systemic side effects. Carboxylesterases enriched in the lower airways convert CIC to the glucocorticoid receptor (GR) agonist des-CIC. We therefore examined whether CIC would likewise activate GR in neonatal lung but have limited adverse extra-pulmonary effects, particularly in the developing brain. Neonatal rats were administered subcutaneous injections of CIC, DEX or vehicle from postnatal days 1-5 (PND1-PND5). Systemic effects linked to DEX exposure, including reduced body and brain weight, were not observed in CIC treated neonates. Furthermore, CIC did not trigger the long-lasting reduction in myelin basic protein expression in the cerebral cortex nor cerebellar size caused by neonatal DEX exposure. Conversely, DEX and CIC were both effective at inducing the expression of select GR target genes in neonatal lung, including those implicated in lung-protective and anti-inflammatory effects. Thus, CIC is a promising, novel candidate drug to treat or prevent BPD in neonates given its activation of GR in neonatal lung and limited adverse neurodevelopmental effects. Furthermore, since sGCs such as DEX administered to pregnant women in pre-term labor can adversely affect fetal brain development, the neurological-sparing properties of CIC, make it an attractive alternative for DEX to treat pregnant women severely ill with respiratory illness, such as with asthma exacerbations or COVID-19 infections.

Hydrolase activities of cynomolgus monkey liver microsomes and recombinant CES1, CES2, and AADAC

The cynomolgus monkey is a nonhuman primate that is often used for pharmacokinetic and toxicokinetic studies of new chemical entities. Species differences in drug metabolism are obstacles for the extrapolation of animal data to humans. This study aimed to characterize hydrolase activities for typical compounds by cynomolgus monkey liver microsomes and recombinant monkey carboxylesterases (CES1 and CES2) and arylacetamide deacetylase (AADAC) compared with the activities in humans. To estimate the contribution of each hydrolase, the ratios of the expression level of each hydrolase in the liver microsomes and recombinant systems were used. For almost all of the tested human CES1 substrates, hydrolase activities in cynomolgus monkey liver microsomes tended to be lower than those in human liver microsomes, and recombinant cynomolgus monkey CES1 showed catalytic activity, but not for all substrates. For human CES2 substrates, hydrolase activities in cynomolgus monkey liver were higher than those in human liver microsomes, and recombinant monkey CES2 was responsible for their hydrolysis. Among human AADAC substrates, phenacetin was mainly hydrolyzed by monkey AADAC, whereas indiplon and ketoconazole were hydrolyzed by AADAC and other unknown enzymes. Flutamide was hydrolyzed by monkey CES2, not by AADAC. Rifamycins were hardly hydrolyzed in monkey liver microsomes. In conclusion, this study characterized the hydrolase activities of cynomolgus monkeys compared with those in humans. The findings would be helpful for pharmacokinetic or toxicokinetic studies of new chemical entities whose main metabolic pathway is hydrolysis.

Pig Liver Esterases Hydrolyze Endocannabinoids and Promote Inflammatory Response

Endocannabinoids are endogenous ligands of cannabinoid receptors and activation of these receptors has strong physiological and pathological significance. Structurally, endocannabinoids are esters (e.g., 2-arachidonoylglycerol, 2-AG) or amides (e.g., N-arachidonoylethanolamine, AEA). Hydrolysis of these compounds yields arachidonic acid (AA), a major precursor of proinflammatory mediators such as prostaglandin E₂. Carboxylesterases are known to hydrolyze esters and amides with high efficiency. CES1, a human carboxylesterase, has been shown to hydrolyze 2-AG, and shares a high sequence identity with pig carboxylesterases: PLE1 and PLE6 (pig liver esterase). The present study was designed to test the hypothesis that PLE1 and PLE6 hydrolyze endocannabinoids and promote inflammatory response. Consistent with the hypothesis, purified PLE1 and PLE6 efficaciously hydrolyzed 2-AG and AEA. PLE6 was 40-fold and 3-fold as active as PLE1 towards 2-AG and AEA, respectively. In addition, both PLE1 and PLE6 were highly sensitive to bis(4-nitrophenyl) phosphate (BNPP), an aryl phosphodiester known to predominately inhibit carboxylesterases. Based on the study with BNPP, PLEs contributed to the hydrolysis of 2-AG by 53.4 to 88.4% among various organs and cells. Critically, exogenous addition or transfection of PLE6 increased the expression and secretion of proinflammatory cytokines in response to the immunostimulant lipopolysaccharide (LPS). This increase was recapitulated in cocultured alveolar macrophages and PLE6 transfected cells in transwells. Finally, BNPP reduced inflammation trigged by LPS accompanied by reduced formation of AA and proinflammatory mediators. These findings define an innovative connection: PLE-endocannabinoid-inflammation. This mechanistic connection signifies critical roles of carboxylesterases in pathophysiological processes related to the metabolism of endocannabinoids.

Effects of Chlorpyrifos on Serine Hydrolase Activities, Lipid Mediators, and Immune Responses in Lungs of Neonatal and Adult Mice

Chlorpyrifos (CPF) is an organophosphate (OP) pesticide that causes acute toxicity by inhibiting acetylcholinesterase (AChE) in the nervous system. However, endocannabinoid (eCB) metabolizing enzymes in brain of neonatal rats are more sensitive than AChE to inhibition by CPF, leading to increased levels of eCBs. Because eCBs are immunomodulatory molecules, we investigated the association between eCB metabolism, lipid mediators, and immune function in adult and neonatal mice exposed to CPF. We focused on lung effects because epidemiologic studies have linked pesticide exposures to respiratory diseases. CPF was hypothesized to disrupt lung eCB metabolism and alter lung immune responses to lipopolysaccharide (LPS), and these effects would be more pronounced in neonatal mice due to an immature immune system. We first assessed the biochemical effects of CPF in adult mice (≥8 weeks old) and neonatal mice after administering CPF (2.5 mg/kg, oral) or vehicle for 7 days. Tissues were harvested 4 h after the last CPF treatment and lung microsomes from both age groups demonstrated CPF-dependent inhibition of carboxylesterases (Ces), a family of xenobiotic and lipid metabolizing enzymes, whereas AChE activity was inhibited in adult lungs only. Activity-based protein profiling (ABPP)-mass spectrometry of lung microsomes identified 31 and 32 individual serine hydrolases in neonatal lung and adult lung, respectively. Of these, Ces1c/Ces1d/Ces1b isoforms were partially inactivated by CPF in neonatal lung, whereas Ces1c/Ces1b and Ces1c/BChE were partially inactivated in adult female and male lungs, respectively, suggesting age- and sex-related differences in their sensitivity to CPF. Monoacylglycerol lipase (MAGL) and fatty acid amide hydrolase (FAAH) activities in lung were unaffected by CPF. When LPS (1.25 mg/kg, i.p.) was administered following the 7-day CPF dosing period, little to no differences in lung immune responses (cytokines and immunophenotyping) were noted between the CPF and vehicle groups. However, a CPF-dependent increase in the amounts of dendritic cells and certain lipid mediators in female lung following LPS challenge was observed. Experiments in neonatal and adult Ces1d^-/- mice yielded similar results as wild type mice (WT) following CPF treatment, except that CPF augmented LPS-induced Tnfa mRNA in adult Ces1d^-/- mouse lungs. This effect was associated with decreased expression of Ces1c mRNA in Ces1d^-/- mice versus WT mice in the setting of LPS exposure. We conclude that CPF exposure inactivates several Ces isoforms in mouse lung and, during an inflammatory response, increases certain lipid mediators in a female-dependent manner. However, it did not cause widespread altered lung immune effects in response to an LPS challenge.

Novel potent bifunctional carboxylesterase inhibitors based on a polyfluoroalkyl-2-imino-1,3-dione scaffold

An expanded series of alkyl 2-arylhydrazinylidene-3-oxo-3-polyfluoroalkylpropionates (HOPs) 3 was obtained via Cu(OAc)₂-catalyzed azo coupling. All were nanomolar inhibitors of carboxylesterase (CES), while moderate or weak inhibitors of acetylcholinesterase and butyrylcholinesterase. Steady-state kinetics studies showed that HOPs 3 are mixed type inhibitors of the three esterases. Molecular docking studies demonstrated that two functional groups in the structure of HOPs, trifluoromethyl ketone (TFK) and ester groups, bind to the CES active site suggesting subsequent reactions: formation of a tetrahedral adduct, and a slow hydrolysis reaction. The results of molecular modeling allowed us to explain some structure-activity relationships of CES inhibition by HOPs 3: their selectivity toward CES in comparison with cholinesterases and the high selectivity of pentafluoroethyl-substituted HOP 3p to hCES1 compared to hCES2. All compounds were predicted to have good intestinal absorption and blood-brain barrier permeability, low cardiac toxicity, good lipophilicity and aqueous solubility, and reasonable overall drug-likeness. HOPs with a TFK group and electron-donor substituents in the arylhydrazone moiety were potent antioxidants. All compounds possessed low cytotoxicity and low acute toxicity. Overall, a new promising type of bifunctional CES inhibitors has been found that are able to interact with the active site of the enzyme with the participation of two functional groups. The results indicate that HOPs have the potential to be good candidates as human CES inhibitors for biomedicinal applications.

Carboxylesterase Activities and Protein Expression in Rabbit and Pig Ocular Tissues

Hydrolytic reactions constitute an important pathway of drug metabolism and a significant route of prodrug activation. Many ophthalmic drugs and prodrugs contain ester groups that greatly enhance their permeation across several hydrophobic barriers in the eye before the drugs are either metabolized or released, respectively, via hydrolysis. Thus, the development of ophthalmic drug therapy requires the thorough profiling of substrate specificities, activities, and expression levels of ocular esterases. However, such information is scant in the literature, especially for preclinical species often used in ophthalmology such as rabbits and pigs. Therefore, our aim was to generate systematic information on the activity and expression of carboxylesterases (CESs) and arylacetamide deacetylase (AADAC) in seven ocular tissue homogenates from these two species. The hydrolytic activities were measured using a generic esterase substrate (4-nitrophenyl acetate) and, in the absence of validated substrates for rabbit and pig enzymes, with selective substrates established for human CES1, CES2, and AADAC (d-luciferin methyl ester, fluorescein diacetate, procaine, and phenacetin). Kinetics and inhibition studies were conducted using these substrates and, again due to a lack of validated rabbit and pig CES inhibitors, with known inhibitors for the human enzymes. Protein expression levels were measured using quantitative targeted proteomics. Rabbit ocular tissues showed significant variability in the expression of CES1 (higher in cornea, lower in conjunctiva) and CES2 (higher in conjunctiva, lower in cornea) and a poor correlation of CES expression with hydrolytic activities. In contrast, pig tissues appear to express only CES1, and CES3 and AADAC seem to be either low or absent, respectively, in both species. The current study revealed remarkable species and tissue differences in ocular hydrolytic enzymes that can be taken into account in the design of esterase-dependent prodrugs and drug conjugates, the evaluation of ocular effects of systemic drugs, and in translational and toxicity studies.

Clock gene Bmal1 controls diurnal rhythms in expression and activity of intestinal carboxylesterase 1

OBJECTIVES

We aimed to characterize diurnal rhythms in CES1 expression and activity in mouse intestine, and to investigate a potential role of the core clock gene Bmal1 in generating diurnal rhythms.

METHODS

The regulatory effects of intestinal Bmal1 on diurnal CES1 expression were assessed using intestine-specific Bmal1 knockout (Bmal1iKO) mice and colon cancer cells. The relative mRNA and protein levels were determined by qPCR and Western blotting, respectively. Metabolic activity of CES1 in vitro and in vivo were determined by microsomal assays and pharmacokinetic studies, respectively. Transcriptional gene regulation was investigated using luciferase reporter assay.

KEY FINDINGS

Total CES1 protein varied significantly according to time of the day in wild-type (Bmal1fl/fl) mice, peaking at ZT6. Of detectable Ces1 genes, Ces1d mRNA displayed a robust diurnal rhythm with a peak level at ZT6, whereas mRNAs of Ces1e, 1f and 1g showed no rhythms in wild-type mice. Loss of intestinal Bmal1 reduced the levels of total CES1 protein and Ces1d mRNA, and blunted their diurnal rhythms in mice. In vitro microsomal assays indicated that intestinal metabolism of mycophenolate mofetil (MMF, a known CES1 substrate) was more extensive at ZT6 than at ZT18. ZT6 dosing of MMF to wild-type mice generated a higher systemic exposure of mycophenolic acid (the active metabolite of MMF) as compared with ZT18 dosing. Intestinal ablation of Bmal1 down-regulated CES1 metabolism at ZT6, and abolished its time-dependency both in vitro and in vivo. Furthermore, Ces1d/CES1 rhythmicity and positive regulation of Ces1d/CES1 by BMAL1 were confirmed in CT26 and Caco-2 cells. Mechanistically, BMAL1 trans-activated Ces1d/CES1 probably via binding to the E-box elements in the gene promoters.

CONCLUSIONS

Bmal1 controls diurnal rhythms in expression and activity of intestinal CES1. Our findings have implications for understanding the crosstalk between circadian clock and xenobiotic metabolism in the intestine.

Hepatocyte-specific expression of human carboxylesterase 2 attenuates nonalcoholic steatohepatitis in mice

Human carboxylesterase 2 (CES2) has triacylglycerol hydrolase (TGH) activities and plays an important role in lipolysis. In this study, we aim to determine the role of human CES2 in the progression or reversal of steatohepatitis in diet-induced or genetically obese mice. High-fat/high-cholesterol/high-fructose (HFCF) diet-fed C57BL/6 mice or db/db mice were intravenously injected with an adeno-associated virus expressing human CES2 under the control of an albumin promoter. Human CES2 protected against HFCF diet-induced nonalcoholic fatty liver disease (NAFLD) in C57BL/6J mice and reversed steatohepatitis in db/db mice. Human CES2 also improved glucose tolerance and insulin sensitivity. Mechanistically, human CES2 reduced hepatic triglyceride (T) and free fatty acid (FFA) levels by inducing lipolysis and fatty acid oxidation and inhibiting lipogenesis via suppression of sterol regulatory element-binding protein 1. Furthermore, human CES2 overexpression improved mitochondrial respiration and glycolytic function, and inhibited gluconeogenesis, lipid peroxidation, apoptosis, and inflammation. Our data suggest that hepatocyte-specific expression of human CES2 prevents and reverses steatohepatitis. Targeting hepatic CES2 may be an attractive strategy for treatment of NAFLD.NEW & NOTEWORTHY Human CES2 attenuates high-fat/cholesterol/fructose diet-induced steatohepatitis and reverses steatohepatitis in db/db mice. Mechanistically, human CES2 induces lipolysis, fatty acid and glucose oxidation, and inhibits hepatic glucose production, inflammation, lipid oxidation, and apoptosis. Our data suggest that human CES2 may be targeted for treatment of non-alcoholic steatohepatitis (NASH).

Kinetic analysis of an enzymatic hydrolysis of p-nitrophenyl acetate with carboxylesterase by pressure-assisted capillary electrophoresis/dynamic frontal analysis

An enzymatic hydrolysis of p-nitrophenyl acetate with carboxylesterase was analyzed by capillary electrophoresis/dynamic frontal analysis (CE/DFA). A plateau signal was expected with the anionic product of p-nitrophenol by the CE/DFA applying in-capillary reaction and the continuous CE resolution of the product from the substrate zone. However, the plateau height was not sufficient, and/or the plateau signal fluctuated and drifted. Therefore, a pressure assist was utilized in the CE/DFA to detect the product zone fast and to average the fluctuated plateau signal by mixing in a laminar flow. The plateau signal became relatively flat and its height was developed by the pressure-assisted capillary electrophoresis/dynamic frontal analysis (pCE/DFA). The plateau height was used for the Michaelis-Menten analysis, and a Michaelis-Menten constant was determined as KM = 0.83 mmol L-1. An enzyme inhibition was also examined with bis(p-nitrophenyl) phosphate by adding it in the separation buffer. The height of the plateau signal decreased by the inhibition, and a 50% inhibitory concentration was determined as IC50 = 0.79 μmol L-1. The values of KM and IC50 obtained in this study agreed well with the reported values. Since the proposed pCE/DFA includes electrophoretic migration of the substrate zone in a capillary, it is also noticed that the deactivation of the enzyme by ethanol on the preparation of the substrate solution can be avoided, as well as the exclusion of the inhibition by the product.

Natural Products as Modulators of CES1 Activity

Carboxylesterase (CES) 1 is the predominant esterase expressed in the human liver and is capable of catalyzing the hydrolysis of a wide range of therapeutic agents, toxins, and endogenous compounds. Accumulating studies have demonstrated associations between the expression and activity of CES1 and the pharmacokinetics and/or pharmacodynamics of CES1 substrate medications (e.g., methylphenidate, clopidogrel, oseltamivir). Therefore, any perturbation of CES1 by coingested xenobiotics could potentially compromise treatment. Natural products are known to alter drug disposition by modulating cytochrome P450 and UDP-glucuronosyltransferase enzymes, but this issue is less thoroughly explored with CES1. We report the results of a systematic literature search and discuss natural products as potential modulators of CES1 activity. The majority of research reports reviewed were in vitro investigations that require further confirmation through clinical study. Cannabis products (Δ ⁹-tetrahydrocannabinol, cannabidiol, cannabinol); supplements from various plant sources containing naringenin, quercetin, luteolin, oleanolic acid, and asiatic acid; and certain traditional medicines (danshen and zhizhuwan) appear to pose the highest inhibition potential. In addition, ursolic acid, gambogic acid, and glycyrrhetic acid, if delivered intravenously, may attain high enough systemic concentrations to significantly inhibit CES1. The provision of a translational interpretation of in vitro assessments of natural product actions and interactions is limited by the dearth of basic pharmacokinetic data of the natural compounds exhibiting potent in vitro influences on CES1 activity. This is a major impediment to assigning even potential clinical significance. The modulatory effects on CES1 expression after chronic exposure to natural products warrants further investigation. SIGNIFICANCE STATEMENT: Modulation of CES1 activity by natural products may alter the course of treatment and clinical outcome. In this review, we have summarized the natural products that can potentially interact with CES1 substrate medications. We have also noted the limitations of existing reports and outlined challenges and future directions in this field.

Inhibitory effects of organophosphate esters on carboxylesterase activity of rat liver microsomes

We investigated the inhibitory effects of 13 organophosphate esters (OPEs) and hydrolytic metabolites on the carboxylesterase activity of rat liver microsomes in vitro in order to examine whether there might be a potential impact on human health, and to elucidate the structure activity relationship. Among the test compounds, 2-ethylhexyl diphenyl phosphate (EDPhP) was the most potent inhibitor of carboxylesterase activity, as measured in terms of 4-nitrophenol acetate hydrolase activity, followed by tri-m-cresyl phosphate (TmCP), cresyl diphenyl phosphate (CDPhP) and triphenyl phosphate (TPhP). The IC₅₀ values were as follows: EDPhP (IC₅₀: 0.03 μM) > TmCP (0.4 μM) > CDPhP (0.8 μM) > TPhP (14 μM) > tris(1,3-dichloro-2-propyl) phosphate (17 μM) > tris(2-ethylhexyl) phosphate (77 μM) > tri-n-propyl phosphate (84 μM) > tris(2-chloroethyl) phosphate (104 μM) > tris(2-butoxyethyl) phosphate (124 μM) > tri-n-butyl phosphate (230 μM). The IC₅₀ value of EDPhP was three orders of magnitude lower than that of bis(4-nitrophenyl) phosphate, which is widely used as an inhibitor of carboxylesterase. Trimethyl phosphate, triethyl phosphate and tris(2-chloroisopropyl) phosphate slightly inhibited the carboxylesterase activity; their IC₅₀ values were above 300 μM. Lineweaver-Burk plots indicated that the inhibition by several OPEs was non-competitive. Diphenyl and monophenyl phosphates, which are metabolites of TPhP, showed weaker inhibitory effects than that of TPhP.

Genetic Analysis Reveals a Significant Contribution of CES1 to Prostate Cancer Progression in Taiwanese Men

The genes that influence prostate cancer progression remain largely unknown. Since the carboxylesterase gene family plays a crucial role in xenobiotic metabolism and lipid/cholesterol homeostasis, we hypothesize that genetic variants in carboxylesterase genes may influence clinical outcomes for prostate cancer patients. A total of 478 (36 genotyped and 442 imputed) single nucleotide polymorphisms (SNPs) in five genes of the carboxylesterase family were assessed in terms of their associations with biochemical recurrence (BCR)-free survival in 643 Taiwanese patients with prostate cancer who underwent radical prostatectomy. The strongest association signal was shown in CES1 (P = 9.64×10^-4 for genotyped SNP rs8192935 and P = 8.96 × 10^-5 for imputed SNP rs8192950). After multiple test correction and adjustment for clinical covariates, CES1 rs8192935 (P = 9.67 × 10^-4) and rs8192950 (P = 9.34 × 10^-5) remained significant. These SNPs were correlated with CES1 expression levels, which in turn were associated with prostate cancer aggressiveness. Furthermore, our meta-analysis, including eight studies, indicated that a high CES1 expression predicted better outcomes among prostate cancer patients (hazard ratio 0.82, 95% confidence interval 0.70-0.97, P = 0.02). In conclusion, our findings suggest that CES1 rs8192935 and rs8192950 are associated with BCR and that CES1 plays a tumor suppressive role in prostate cancer.

[Evaluation of the Oral Absorption of Ester-type Prodrugs]

The first-pass hydrolysis of oral ester-type prodrugs in the liver and intestine is mediated mainly by hCE1 and hCE2 of the respective predominant carboxylesterase (CES) isozymes. In order to provide high blood concentrations of the parent drugs, it is preferable that prodrugs are absorbed as an intact ester in the intestine, then rapidly converted to active parent drugs by hCE1 in the liver. In the present study, we designed a prodrug of fexofenadine (FXD) as a model parent drug that is resistant to hCE2 but hydrolyzed by hCE1, utilizing the differences in catalytic characteristics of hCE1 and hCE2. In order to precisely predict the intestinal absorption of an FXD prodrug candidate, we developed a novel high-throughput system by modifying Caco-2 cells. Further, we evaluated species differences and aging effects in the intestinal and hepatic hydrolysis of prodrugs to improve the estimation of in vivo first-pass hydrolysis of ester-type prodrugs. Consequently, it was possible to design a hepatotropic prodrug utilizing the differences in tissue distribution and substrate specificity of CESs. In addition, we successfully established three useful in vitro systems for predicting the intestinal absorption of hCE1 substrate using Caco-2 cells. However, some factors involved in estimating the bioavailability of prodrugs in human, such as changes in recognition of drug transporters by esterification, and species differences of the first-pass hydrolysis, should be comprehensively considered in prodrug development.

Hepatocyte-Specific Expression of Human Carboxylesterase 1 Attenuates Diet-Induced Steatohepatitis and Hyperlipidemia in Mice

Rodents have at least five carboxylesterase 1 (Ces1) genes, whereas there is only one CES1 gene in humans, raising the question as to whether human CES1 and mouse Ces1 genes share the same functions. In this study, we investigate the role of human CES1 in the development of steatohepatitis or dyslipidemia in C57BL/6 mice. Hepatocyte-specific expression of human CES1 prevented Western diet or alcohol-induced steatohepatitis and hyperlipidemia. Mechanistically, human CES1 induced lipolysis and fatty acid oxidation, leading to a reduction in hepatic triglyceride and free fatty acid levels. Human CES1 also reduced hepatic-free cholesterol levels and induced low-density lipoprotein receptor. In addition, human CES1 induced hepatic lipoprotein lipase and apolipoprotein C-II expression. Conclusion: Hepatocyte-specific overexpression of human CES1 attenuates diet-induced steatohepatitis and hyperlipidemia.

KEA-1010, a ketamine ester analogue, retains analgesic and sedative potency but is devoid of Psychomimetic effects

Background

Ketamine, a widely used anaesthetic and analgesic agent, is known to improve the analgesic efficacy of opioids and to attenuate central sensitisation and opioid-induced hyperalgesia. Clinical use is, however, curtailed by unwanted psychomimetic effects thought to be mediated by N-methyl-D-aspartate (NMDA) receptor antagonism. KEA-1010, a ketamine ester-analogue designed for rapid offset of hypnosis through hydrolysis mediated break-down, has been shown to result in short duration sedation yet prolonged attenuation of nociceptive responses in animal models. Here we report on behavioural effects following KEA-1010 administration to rodents.

Methods

KEA-1010 was compared with racemic ketamine in its ability to produce loss of righting reflex following intravenous injection in rats. Analgesic activity was assessed in thermal tail flick latency (TFL) and paw incision models when injected acutely and when co-administered with fentanyl. Tail flick analgesic assessment was further undertaken in morphine tolerant rats. Behavioural aberration was assessed following intravenous injection in rats undergoing TFL assessment and in auditory pre-pulse inhibition models.

Results

KEA-1010 demonstrated an ED₅₀ similar to ketamine for loss of righting reflex following bolus intravenous injection (KEA-1010 11.4 mg/kg [95% CI 10.6 to 12.3]; ketamine (racemic) 9.6 mg/kg [95% CI 8.5–10.9]). Duration of hypnosis was four-fold shorter in KEA-1010 treated animals. KEA-1010 prolonged thermal tail flick responses comparably with ketamine when administered de novo, and augmented morphine-induced prolongation of tail flick when administered acutely. The analgesic effect of KEA-1010 on thermal tail flick was preserved in opioid tolerant rats. KEA-1010 resulted in increased paw-withdrawal thresholds in a rat paw incision model, similar in magnitude yet more persistent than that seen with fentanyl injection, and additive when co-administered with fentanyl. In contrast to ketamine, behavioural aberration following KEA-1010 injection was largely absent and no pre-pulse inhibition to acoustic startle was observed following KEA-1010 administration in rats.

Conclusions

KEA-1010 provides antinociceptive efficacy in acute thermal and mechanical pain models that augments standard opioid analgesia and is preserved in opioid tolerant rodents. The NMDA channel affinity and psychomimetic signature of the parent compound ketamine is largely absent for KEA-1010.

Adipocyte abundances of CES1, CRYAB, ENO1 and GANAB are modified in-vitro by glucose restriction and are associated with cellular remodelling during weight regain

Long-term weight loss maintenance is a problem of overweight and obesity. Changes of gene expression during weight loss (WL) by calorie restriction (CR) are linked to the risk of weight regain (WR). However, detailed information on genes/proteins involved in the mechanism is still lacking. Therefore, we developed an in-vitro model system for glucose restriction (GR) and refeeding (RF) to uncover proteome differences between GR with RF vs normal feeding, of which we explored the relation with WR after WL. Human Simpson-Golabi-Behmel Syndrome cells were subjected to changing levels of glucose to mimic the condition of CR and RF. Proteome profiling was performed by liquid chromatography tandem mass spectrometry. This in-vitro model revealed 44 proteins differentially expressed after GR and RF versus feeding including proteins of the focal adhesions. Four proteins showed a persistent up- or down-regulation: liver carboxylesterase (CES1), mitochondrial superoxide dismutase [Mn] (SOD2), alpha-crystallin B-chain (CRYAB), alpha-enolase (ENO1). In-vivo weight loss-induced RNA expression changes linked CES1, CRYAB and ENO1 to WR. Moreover, of these 44 proteins, CES1 and glucosidase II alpha subunit (GANAB) during follow up correlated with WR. Correlation clustering of in-vivo protein expression data indicated an interaction of these proteins with structural components of the focal adhesions and cytoplasmic filaments in the adipocytes.

DNA methylation profiling to explore colorectal tumor differences according to menopausal hormone therapy use in women

Aim: Use of menopausal hormone therapy (MHT) has been associated with a reduced risk for colorectal cancer, but mechanisms underlying this relationship are not well understood. In the colon, MHT appears to act through estrogen receptor β (ERβ) which may influence DNA methylation by binding to DNA. Using genome-wide methylation profiling data, we aimed to identify genes that may be differentially methylated according to MHT use. Materials & methods: DNA methylation was measured using Illumina HumanMethylation450k arrays in two independent tumor sample sets of colorectal cancer patients. Differential methylation was determined using R/limma. Results: In the discovery analysis, two CpG sites showed differential DNA methylation according to MHT use, both were not replicated. In stratified analyses, 342 CpG sites were associated with current MHT use only in ERβ-positive tumors. Conclusion: The suggestive findings of differential methylation according to current MHT use in ERβ-positive tumors warrant further investigation.

Interspecies variation of clopidogrel hydrolysis in liver microsomes from various mammals

Clopidogrel, a clinically used antiplatelet agent, can be readily hydrolyzed by human carboxylesterase 1A (CES1A) to release an inactive metabolite clopidogrel carboxylic acid (CCA). In this study, clopidogrel was used as a tool substrate to investigate the interspecies variation of clopidogrel hydrolysis in hepatic microsomes from various mammals including human and six laboratory animals (such as mouse, rat, rabbit, beagle dog, minipig and cynomolgus monkey). The results demonstrated that clopidogrel could be hydrolyzed into CCA by all tested hepatic microsomes from human or other mammals, but the hydrolytic rates greatly varied among species. Inhibition assays demonstrated that BNPP (an inactivator of mammalian CES) strongly inactivated clopidogrel hydrolytic activity in all tested hepatic microsomes, suggested that mammalian CES were major contributor(s) responsible for clopidogrel hydrolysis in hepatic preparations from all above-mentioned species. By contrast, the response of a reversible inhibitor of human CES1A on clopidogrel hydrolysis in these liver preparations varied significantly among different species. Moreover, the enzymatic kinetics and the apparent kinetic parameters of clopidogrel hydrolysis in hepatic microsomes from various animal species were evaluated and compared to each other. These findings provide crucial information for deeply understanding the differences in catalytic behaviors of mammalian CES, which will be very helpful for choosing suitable laboratory animal(s) for whole tests of CES1A substrate-drugs.