Genomic structure and transcriptional regulation of the rat, mouse, and human carboxylesterase genes

In vitro demonstration of antedrug mechanism of a pharmacokinetic booster to improve CYP3A4 substrates by CYP3A4-mediated metabolism inhibition

We previously reported novel benzyl-ether derivatives with an imidazole ring and a hydroxyl group (A-01) or carboxyl group (B-01) and esters (2 esters of A-01, and 7 esters of B-01) as pharmacokinetics (PK) boosters. This study demonstrates how these ester compounds embody the concept of a safe pharmacokinetic booster, with potent and transient inhibition of CYP3A4-mediated drug metabolism. As a model CYP3A4 substrate and CYP3A4 enzyme, midazolam (MDZ) and rat liver microsomes were used. A-01 inhibited MDZ metabolism significantly, while B-01 induced only slight inhibition. Although rat liver microsomes hydrolyzed the ester compounds over time, several ester compounds strongly inhibited MDZ metabolism. Due to the significant activity of A-01, A-01 esters affected MDZ metabolism, irrespective of hydrolysis state. Time-dependent inhibition evaluation indicated that the B-01 ester inhibition is not mechanism-based, as hydrolysis eliminated MDZ metabolism inhibition. We report that the B-01 esters significantly inhibit CYP3A4-mediated drug metabolism, and upon hydrolysis this property is eliminated. In conclusion, B-01 ester compounds may be safe PK boosters with antedrug characteristics.

Pharmacogenetic study of CES1 gene and enalapril efficacy

Enalapril is an orally administered angiotensin-converting enzyme inhibitor which is widely prescribed to treat hypertension, chronic kidney disease, and heart failure. It is an ester prodrug that needs to be activated by carboxylesterase 1 (CES1). CES1 is a hepatic hydrolase that in vivo biotransforms enalapril to its active form enalaprilat in order to produce its desired pharmacological impact. Several single nucleotide polymorphisms in CES1 gene are reported to alter the catalytic activity of CES1 enzyme and influence enalapril metabolism. G143E, L40T, G142E, G147C, Y170D, and R171C can completely block the enalapril metabolism. Some polymorphisms like Q169P, E220G, and D269fs do not completely block the CES1 function; however, they reduce the catalytic activity of CES1 enzyme. The prevalence of these polymorphisms is not the same among all populations which necessitate to consider the genetic panel of respective population before prescribing enalapril. These genetic variations are also responsible for interindividual variability of CES1 enzyme activity which ultimately affects the pharmacokinetics and pharmacodynamics of enalapril. The current review summarizes the CES1 polymorphisms which influence the enalapril metabolism and efficacy. The structure of CES1 catalytic domain and important amino acids impacting the catalytic activity of CES1 enzyme are also discussed. This review also highlights the importance of pharmacogenomics in personalized medicine.

Human Carboxylesterase 1A Plays a Predominant Role in Hydrolysis of the Anti-Dyslipidemia Agent Fenofibrate in Humans

Fenofibrate, a marketed peroxisome proliferator-activated receptor-α (PPARα) agonist, has been widely used for treating severe hypertriglyceridemia and mixed dyslipidemia. As a canonical prodrug, fenofibrate can be rapidly hydrolyzed to release the active metabolite (fenofibric acid) in vivo, but the crucial enzyme(s) responsible for fenofibrate hydrolysis and the related hydrolytic kinetics have not been well-investigated. This study aimed to assign the key organs and crucial enzymes involved in fenofibrate hydrolysis in humans, as well as reveal the impact of fenofibrate hydrolysis on its non-PPAR-mediated biologic activities. Our results demonstrated that fenofibrate could be rapidly hydrolyzed in the preparations from both human liver and lung to release fenofibric acid. Reaction phenotyping assays coupling with chemical inhibition assays showed that human carboxylesterase 1A (hCES1A) played a predominant role in fenofibrate hydrolysis in human liver and lung, while human carboxylesterase 2A (hCES2A) and human monoacylglycerol esterase (hMAGL) contributed to a very lesser extent. Kinetic analyses showed that fenofibrate could be rapidly hydrolyzed by hCES1A in human liver preparations, while the inherent clearance of hCES1A-catalyzed fenofibrate hydrolysis is much higher (>200-fold) than than that of hCES2A or hMAGL. Biologic assays demonstrated that both fenofibrate and fenofibric acid showed very closed Nrf2 agonist effects, but fenofibrate hydrolysis strongly weakens its inhibitory effects against both hCES2A and hNtoum. Collectively, our findings reveal that the liver is the major organ and hCES1A is the predominant enzyme-catalyzing fenofibrate hydrolysis in humans, while fenofibrate hydrolysis significantly reduces inhibitory effects of fenofibrate against serine hydrolases. SIGNIFICANCE STATEMENT: Fenofibrate can be completely converted to fenofibric acid in humans and subsequently exert its pharmacological effects, but the hydrolytic pathways of fenofibrate in humans have not been well-investigated. This study reported that the liver was the predominant organ and human carboxylesterase 1A was the crucial enzyme involved in fenofibrate hydrolysis in humans.

Discovery of novel carboxylesterase 2 inhibitors for the treatment of delayed diarrhea and ulcerative colitis

Human carboxylesterase 2 (hCES2) is an enzyme that metabolizes irinotecan to SN-38, a toxic metabolite considered a significant source of side effects (lethal delayed diarrhea). The hCES2 inhibitors could block the hydrolysis of irinotecan in the intestine and thus reduce the exposure of intestinal SN-38, which may alleviate irinotecan-associated diarrhea. However, existing hCES2 inhibitors (except loperamide) are not used in clinical applications due to lack of validity or acceptable safety. Therefore, developing more effective and safer drugs for treating delayed diarrhea is urgently needed. This study identified a lead compound 1 with a novel scaffold by high-throughput screening in our in-house library. After a comprehensive structure-activity relationship study, the optimal compound 24 was discovered as an efficient and highly selective hCES2 inhibitor (hCES2: IC50 = 6.72 μM; hCES1: IC50 > 100 μM). Further enzyme kinetics study indicated that compound 24 is a reversible inhibitor of hCES2 with competitive inhibition mode (Ki = 6.28 μM). The cell experiments showed that compound 24 could reduce the level of hCES2 in living cells (IC50 = 6.54 μM). The modeling study suggested that compound 24 fitted very well with the binding pocket of hCES2 by forming multiple interactions. Notably, compound 24 can effectively treat irinotecan-induced delayed diarrhea and DSS-induced ulcerative colitis, and its safety has also been verified in subtoxic studies. Based on the overall pharmacological and preliminary safety profiles, compound 24 is worthy of further evaluation as a novel agent for irinotecan-induced delayed diarrhea.

Metabolic Activation of Pesticide Isoprocarb Mediated by CYP3A4 and the Possible Correlation with Its Cytotoxicity

Isoprocarb (IPC), one of the most important carbamate pesticides, is used to control pests, such as rice planthoppers in crops. Studies have found that IPC induced hepatotoxicity in poultry chicken. However, the mechanisms of IPC-induced hepatotoxicity are unclear. The objectives of this study were to characterize reactive metabolites of IPC in vitro and in vivo, to identify cytochrome P450 enzymes for metabolic activation, and to define a possible correlation between the metabolic activation and cytotoxicity of IPC. In GSH- or NAC-supplemented microsomal incubations, one GSH conjugate (M6) and two NAC conjugates (M7 and M8) were detected after exposure to IPC. The corresponding GSH conjugate and NAC conjugates were found in the liver homogenates and urine of mice after IPC administration. IPC was found to be metabolized to a quinone intermediate reactive to GSH in vitro and in vivo. IPC was found to induce marked cytotoxicity in cultured mouse primary hepatocytes. Ketoconazole, a selective CYP3A4/5 enzyme inhibitor, attenuated the susceptibility of hepatocytes to IPC cytotoxicity.

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.

Association between CES1 rs2244613 and the pharmacokinetics and safety of dabigatran: Meta-analysis and quantitative trait loci analysis

Objective

To date, the influence of the carboxylesterase 1 (CES1) rs2244613 genotype on the pharmacokinetics (PKs) and safety of dabigatran remains controversial. Hence, a systematic review was performed to study the association between CES1 rs2244613 genotype and the PKs and safety of dabigatran and CES1 relative expression.

Methods

In addition to the three English databases (Web of Science, PubMed, and Embase), two Chinese databases (CNKI and Wanfang) were thoroughly revised. The mean differences (MD) and corresponding 95% confidence intervals (CI) were applied to evaluate the differences in PKs between the CES1 rs2244613 genotype. Odds ratio (OR) was used to study the risk for bleeding events between the CES1 rs2244613 genotypes. Subsequent expression quantitative trait loci (eQTL) analyses were performed to evaluate genotype-specific expressions in human tissues.

Results

Ten studies (n = 2,777) were included. CES1 rs2244613 G allele carriers exhibited significantly lower dabigatran trough concentrations compared to T allele carriers (MD: −8.00 ng/mL; 95% CI: −15.08 to −0.92; p = 0.03). The risk for bleeding events was significantly lower in carriers of the G allele compared to T allele carriers (OR: 0.65; 95% CI: 0.44–0.96; p = 0.03). Subsequent eQTL analysis showed significant genome-wide expressions in two human tissues, whole blood (p = 5.1 × 10^–10) and liver (p = 6.2 × 10^–43).

Conclusion

Our meta-analysis indicated a definite relation between the CES1 rs2244613 genotype and tolerability variations or pharmacokinetic fluctuations. The carriers of T allele showed higher dabigatran concentrations; therefore, they would benefit from a dose reduction.

Systematic review registration

[https://inplasy.com/inplasy-2022-6-0027/], identifier [NPLASY202260027].

Directionally Modified Fluorophores for Super-Resolution Imaging of Target Enzymes: A Case Study with Carboxylesterases

In the need for improving the labeling quality of super-resolution imaging, multifarious fluorescent labeling strategies have sprang up. Among them, a small molecule inhibitor-probe (SMI-probe) shows its advancement in fine mapping due to its smaller size and its specific binding to a specific site. Herein, we report a novel protocol of mechanism-guided directional modification of fluorophores into fluorescent inhibitors for enzyme targeting, which could half the size of the SMI-probe. To confirm the feasibility of the strategy, carboxylesterase (hCE) inhibitors are designed and developed. Among the constructed molecule candidates, NIC-4 inhibited both isoforms of hCE1 and hCE2, with IC₅₀ values of 4.56 and 4.11 μM. The CE-targeting specificity of NIC-4 was confirmed by colocalizing with an immunofluorescent probe in fixed-cell confocal imaging. Moreover, NIC-4 was used in live-cell super-resolution microscopy, which indicates dotlike structures instead of the larger staining with the immunofluorescent probe. Moreover, it enables the real-time tracking of dynamic flow of carboxylesterases in live cells.

Human risk assessment of di-isobutyl phthalate through the application of a developed physiologically based pharmacokinetic model of di-isobutyl phthalate and its major metabolite mono-isobutyl phthalate

Di-isobutyl phthalate (DiBP) is a substance used in the production of objects frequently used in human life. Mono-isobutyl phthalate (MiBP), a major in vivo metabolite of DiBP, is a biomarker for DiBP exposure assessment. Therefore, risk assessment studies on DiBP and MiBP, which have not yet been reported in detail, are needed. The aim of this study was to develop and evaluate a physiologically based pharmacokinetic (PBPK) model for DiBP and MiBP in rats and extend this to human risk assessment based on human exposure. Pharmacokinetic studies were performed in male rats following the administration of 5-100 mg/kg DiBP, and these results were used for the development and validation of the PBPK model. In addition, the previous pharmacokinetic results in female rats following DiBP administration and the pharmacokinetic results in both males and females according to multiple exposures to DiBP were used to develop and validate the PBPK model. The metabolism of DiBP to MiBP in the body was very significant and rapid, and the biodistribution of MiBP was broad and major. Furthermore, the amount of MiBP in the body showed a correlation with DiBP exposure, and from this, a PBPK model was developed to evaluate the external exposure of DiBP from the internal exposure of MiBP. The predicted rat plasma, urine, fecal, and tissue concentrations using the developed PBPK model fitted well with the observed values. The established PBPK model for rats was extrapolated to a human PBPK model of DiBP and MiBP based on human physiological parameters and allometric scaling. The reference dose of 0.512 mg/kg/day of DiBP and external doses of 6.14-280.90 μg/kg/day DiBP for human risk assessment were estimated using Korean biomonitoring values. Valuable insight and approaches to assessing human health risks associated with DiBP exposure were provided by this study.

Recent Progress in Fluorescent Sensors for Drug-Induced Liver Injury Assessment

Drug-induced liver injury (DILI) is a persistent concern in drug discovery and clinical medicine. The current clinical methods to assay DILI by analyzing the enzymes in serum are still not optimal. Recent studies showed that fluorescent sensors would be efficient tools for detecting the concentration and distribution of DILI indicators with high sensitivity and specificity, in real-time, in situ, and with low damage to biosamples, as well as diagnosing DILI. This review focuses on the assessment of DILI, introduces the current mechanisms of DILI, and summarizes the design strategies of fluorescent sensors for DILI indicators, including ions, small molecules, and related enzymes. Some challenges for developing DILI diagnostic fluorescent sensors are put forward. We believe that these design strategies and challenges to evaluate DILI will inspire chemists and give them opportunities to further develop other fluorescent sensors for accurate diagnoses and therapies for other diseases.

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.

Downregulation of Keap1 Confers Features of a Fasted Metabolic State

Transcription factor nuclear factor erythroid 2 p45-related factor 2 (Nrf2) and its main negative regulator, Kelch-like ECH-associated protein 1 (Keap1), are at the interface between redox and intermediary metabolism, allowing adaptation and survival under conditions of oxidative, inflammatory, and metabolic stress. Nrf2 is the principal determinant of redox homeostasis, and contributes to mitochondrial function and integrity and cellular bioenergetics. Using proteomics and lipidomics, we show that genetic downregulation of Keap1 in mice, and the consequent Nrf2 activation to pharmacologically relevant levels, leads to upregulation of carboxylesterase 1 (Ces1) and acyl-CoA oxidase 2 (Acox2), decreases triglyceride levels, and alters the lipidome. This is accompanied by downregulation of hepatic ATP-citrate lyase (Acly) and decreased levels of acetyl-CoA, a trigger for autophagy. These findings suggest that downregulation of Keap1 confers features of a fasted metabolic state, which is an important consideration in the drug development of Keap1-targeting pharmacologic Nrf2 activators.

Construction and application of a high-content analysis for identifying human carboxylesterase 2 inhibitors in living cell system

Human carboxylesterase 2 (hCE2), one of the most principal drug-metabolizing enzymes, catalyzes the hydrolysis of a variety of endogenous esters, anticancer agents, and environmental toxicants. The significant roles of hCE2 in both endobiotic and xenobiotic metabolism sparked great interest in the discovery and development of efficacious and selective inhibitors. However, the safe and effective inhibitors of hCE2 are scarce, due to the lack of efficient screening and evaluation systems for complex biological systems. To offer a solution to this problem, a high-content analysis (HCA)-based cell imaging and multiparametric assay method was constructed for evaluating the inhibitory effect and safety of hCE2 inhibitors in living cell system. In this study, we first established a cell imaging-based method for identifying hCE2 inhibitors at the living cell level with hCE2 fluorescent probe NCEN. Meanwhile, two nuclear probes, Hoechst 33342 and PI, were integrated to evaluate the potential cytotoxicity of compounds simultaneously. Then, the accuracy of the HCA-based method was verified by the LC-FD-based method with a positive inhibitor BNPP, and the results showed that the HCA-based method exhibited excellent precision, robustness, and reliability. Finally, the newly established HCA-based multiparametric assay panel was successfully applied to re-evaluate a series of reported hCE2 inhibitors in living cells. In summary, the HCA-based multiparametric method could serve as an efficient tool for the accuracy measurement inhibitory effect and cytotoxicity of compounds against hCE2 in living cell system. Graphical abstract.

Skin Metabolism: Relevance of Skin Enzymes for Rational Drug Design

Transdermal therapeutic systems (TTS) have numerous pharmacological benefits. Drug release, for example, is independent of whether a patient is in a fed or a fasted state, and lower doses can be given as gastrointestinal and hepatic first-pass metabolism is avoided. In addition, inter- and intrapatient variability is minimized as the release of the drug is mainly controlled by the system. This makes TTS interesting as alternative systems to the most common dosage form of oral tablets. The difficulty with the dermal administration route is transporting the drug through the skin, since the skin is an efficient barrier against foreign bodies. Various strategies have been reported in the literature of how drug penetration can be improved. Most of them, however, focus on overcoming the stratum corneum as the first (mechanical) skin barrier. However, penetration is much more complex, and the skin's barrier function does not only depend on the stratum corneum; what has been underestimated is the second (biological) skin barrier formed of enzymes. Compared to the stratum corneum, very little is known about these enzymes, e.g., which enzymes are present in the skin and where exactly they are localized. Hence, very few strategies can be found for how to bypass or even use the skin enzyme barrier for TTS development. This review article provides an overview of the skin enzymes considered to be relevant for the biotransformation of dermally applied drugs. Also, we discuss the use of dermal prodrugs and soft drugs and give the stereoselectivity of skin metabolism careful consideration. Finally, we provide suggestions on how to make use of the current knowledge about skin enzymes for rational TTS design.

Potential Pharmacokinetic Herb-Drug Interactions: Have we Overlooked the Importance of Human Carboxylesterases 1 and 2?

Background:

Herbal products have grown steadily across the globe and have increasingly been incorporated into western medicine for healthcare aims, thereby causing potential pharmacokinetic Herb-drug Interactions (HDIs) through the inhibition or induction of drug-metabolizing enzymes and transporters. Human Carboxylesterases 1 (CES1) and 2 (CES2) metabolize endogenous and exogenous chemicals including many important therapeutic medications. The growing number of CES substrate drugs also underscores the importance of the enzymes. Herein, we summarized those potential inhibitors and inducers coming from herbal constituents toward CES1 and CES2. We also reviewed the reported HDI studies focusing on herbal products and therapeutic agents metabolized by CES1 or CES2.

Methods:

We searched in PubMed for manuscript published in English after Jan 1, 2000 combining terms “carboxylesterase 1”, “carboxylesterase 2”, “inhibitor”, “inducer”, “herb-drug interaction”, “inhibitory”, and “herbal supplement”. We also searched specific websites including FDA and EMA. The data of screened papers were analyzed and summarized.

Results:

The results showed that more than 50 natural inhibitors of CES1 or CES2, including phenolic chemicals, triterpenoids, and tanshinones were found from herbs, whereas only few inducers of CES1 and CES2 were reported. Systemic exposure to some commonly used drugs including oseltamivir, irinotecan, and clopidogrel were changed when they were co-administered with herb products such as goldenseal, black cohosh, ginger, St. John’s Wort, curcumin, and some Chinese compound formula in animals.

Conclusion:

Nonclinical and clinical studies on HDIs are warranted in the future to provide safety information toward better clinical outcomes for the combination of herbal products and conventional drugs.

Synthesis and evaluation of haloperidol ester prodrugs metabolically activated by human carboxylesterase

Two types of haloperidol prodrugs in which a chemical modification was carried out on the hydroxyl group or carbonyl group were synthesized, and their metabolic activation abilities were evaluated in a human liver microsome (HLM) solution, a human small intestine microsome (HIM) solution and solutions of human recombinant carboxylesterases (hCESs). The metabolic activation rates of alcohol ester prodrugs in HLM solution were similar to those in hCES2 solution, and haloperidol pentanoate and haloperidol hexanoate showed high metabolic activation rates in the synthesized alcohol ester prodrugs. In addition, haloperidol acetate and haloperidol 2-methylbutanoate were hydrolyzed as slowly as haloperidol decanoate. The results suggested that haloperidol prodrugs with a small chain or a branched chain are useful as prodrugs for sustained release. The metabolic activation rate of the enol ester prodrug in HLM solution was similar to that in hCES1 solution, and the enol ester prodrug was found to behave differently from alcohol ester prodrugs, which were metabolically activated by hCES2.

Development of an oxidative stress in vitro assay in zebrafish (Danio rerio) cell lines

The nuclear factor erythroid 2-related factor 2 (Nrf2) is a key regulator of cellular defense against oxidative stress and correlated with classical toxicological endpoints. In vitro methods using fish cell lines for the assessment of aquatic toxicity are needed for mechanistic studies and as an alternative to in vivo. We describe an in vitro assay to study oxidative stress using zebrafish cell lines. Transfection efficiency of twelve commercially available transfection reagents were tested in the zebrafish cell lines ZFL, ZF4, and Pac2. The most efficient reagent for each cell line was selected for further experiments. Cells were transiently transfected with an Nrf2-responsive luciferase plasmid. The assay was tested using the oxidative stress inducing chemicals tertbutylhydroquinone, hydrogen peroxide, and sulforaphane. Of the transfected cell lines, ZF4 and ZFL showed higher sensitivity. The latter were used to study potential oxidative stress induced by pesticides (diazinon, deltamethrin, atrazine, metazachlor, terbutylazine, diuron). Besides known inducers, Nrf2 activity was also significantly induced by diazinon, deltametrin, diuron, and metazachlor. Activation of Nrf2 by metazachlor is a novel finding. The described assay could be a valuable tool for research in toxicology to study the stress response of both pure chemicals and environmental water samples.

Carboxylesterase 1 genes: systematic review and evaluation of existing genotyping procedures

The carboxylesterase 1 gene (CES1) encodes a hydrolase that metabolizes commonly used drugs. The CES1-related pseudogene, carboxylesterase 1 pseudogene 1 (CES1P1), has been implicated in gene exchange with CES1 and in the formation of hybrid genes including the carboxylesterase 1A2 gene (CES1A2). Hence, the CES1 region is complex. Using in silico PCR and alignment, we assessed the specificity of PCR-assisted procedures for genotyping CES1, CES1A2 and CES1P1 in studies identified in PubMed. We identified 33 such studies and excluded those that were not the first to use a procedure or lacked sequence information. After this 17 studies remained. Ten of these used haplotype-specific amplification, restriction enzyme treatment or amplicon sequencing, and included five that were predicted to lack specificity. All procedures for genotyping of single nucleotide polymorphisms in eight studies lacked specificity. One of these studies also used amplicon sequencing, thus being present in the group above. Some primers and their intended targets were mismatched. We provide experimental evidence that one of the procedures lacked specificity. Additionally, a complex pattern of segmental duplications in the CES1 region was revealed. In conclusion, many procedures for CES1, CES1A2 and CES1P1 genotyping appear to lack specificity. Knowledge about the segmental duplications may improve the typing of these genes.

Identification of carboxylesterase genes associated with pyrethroid resistance in the malaria vector Anopheles sinensis (Diptera: Culicidae)

BACKGROUND

Carboxylesterases (CCEs) are one of three large detoxification enzyme families. Some CCEs are active on synthetic insecticides with ester structures. Anopheles sinensis is an important malaria vector in eastern Asia. This study identified and characterized the CCE genes in the A. sinensis genome and determined CCE genes associated with pyrethroid resistance using RNA sequencing (RNA-seq) and quantitative reverse transcription - polymerase chain reaction (qRT-PCR), in A. sinensis from Anhui, Chongqing, and Yunnan in China.

RESULTS

Fifty-seven putative CCEs were identified and placed into three classes, 12 subfamilies and 14 clades through phylogenetic and homology analyses. Exon sizes ranged from 31 to 4317 bp, with 49 CCEs having two to five exons and eight having six to 11 exons. A total of 183 introns were recognized with sizes ranging from 31 to 4317 bp. The 57 CCEs were located on 14 scaffolds, with 70% located on four scaffolds. The alpha-esterase subfamily was significantly expanded compared with that of Anopheles gambiae. In a pyrethroid-resistant strain, RNA-seq detected five upregulated CCE genes and qRT-PCR detected 12 upregulated CCE genes. The α-esterase 10 (AsAe10) and acetylcholinesterase 1 (AsAce1) genes were the main CCE genes associated with pyrethroid resistance.

CONCLUSION

This information will be useful for further study of the CCE gene family and pyrethroid resistance mechanisms mediated by CCEs. © 2017 Society of Chemical Industry.

Recent progresses in small-molecule enzymatic fluorescent probes for cancer imaging

An overview of recent advances in small-molecule enzymatic fluorescent probes for cancer imaging, including design strategies and cancer imaging applications.

Anti-Tumor Activity and Immunotherapeutic Potential of a Bisphosphonate Prodrug

Bisphosphonates have benefits in breast cancer and multiple myeloma patients and have been used with adoptive immunotherapy with γδ T cells expressing Vγ2 Vδ2 TCRs. Although treatment with γδ T cells is safe, it has shown limited efficacy. Present bisphosphonates stimulate γδ T cells but were designed to inhibit bone resorption rather than treating cancer and have limited oral absorption, tumor cell entry, and cause bone side effects. The development of phosphate and phosphonate nucleotide prodrugs has led to important drugs for hepatitis C and HIV. Using a similar approach, we synthesized bisphosphonate prodrugs and found that they efficiently limit tumor cell growth. Pivoxil bisphosphonate esters enter cells where esterases convert them to their active acids. The bisphosphonate esters stimulated γδ T cells to secrete TNF-α in response to a variety of tumor cells more efficiently than their corresponding acids. The most active compound, tetrakis-pivaloyloxymethyl 2-(thiazole-2-ylamino)ethylidene-1,1- bisphosphonate (7), specifically expanded γδ T cells and stimulated them to secrete interferon-γ and kill tumor cells. In preclinical studies, combination therapy with compound 7 and γδ T cells prolonged survival of mice inoculated with either human bladder cancer or fibrosarcoma cells. Therefore, bisphosphonate prodrugs could enhance the effectiveness of adoptive cancer immunotherapy with γδ T cells.

Comparative metabolism of DDAO benzoate in liver microsomes from various species

DDAB (6,8-dichloro-9,9-dimethyl-7-oxo-7,9-dihydroacridin-2-yl benzoate) is a newly developed near-infrared fluorescent probe for human carboxylesterase 2 (hCE2), exhibiting high specificity and good reactivity for real-time monitoring the enzymatic activities of hCE2 in complex biological systems. In order to explore the applicability of DDAB in commonly used animal species, the interspecies difference in DDAB hydrolysis was carefully investigated by using liver microsomes from human and five experimental animals including mouse, rat, dog, minipig and monkey. Metabolite profiling demonstrated that DDAB hydrolysis could be catalyzed by all tested liver microsomes from different animals but displayed significant difference in the reaction rate. Chemical inhibition assays demonstrated that carboxylesterases (CEs) were the major enzymes involved in DDAB hydrolysis in all tested liver microsomes, indicating that DDAB was a selective substrate of CEs in a variety of mammals. However, the differential effects of loperamide (LPA, a specific inhibitor against hCE2) on DDAB hydrolysis among various species were observed. The apparent kinetic parameters and the maximum intrinsic clearances (CL_max) for DDAB hydrolysis in liver microsomes from different animals were determined, and the order of CL_max values for the formation of DDAO was CyLM>MLM≈PLM>RLM>HLM≈DLM. These findings were helpful for the rational use of DDAB as an imaging tool for CE2 in different mammals, as well as for translational researches on the function of mammalian CEs and CE2-associated drug-drug interactions.

Cardiac drug-drug interaction between HCV-NS5B pronucleotide inhibitors and amiodarone is determined by their specific diastereochemistry

Severe bradycardia/bradyarrhythmia following coadministration of the HCV-NS5B prodrug sofosbuvir with amiodarone was recently reported. Our previous preclinical in vivo experiments demonstrated that only certain HCV-NS5B prodrugs elicit bradycardia when combined with amiodarone. In this study, we evaluate the impact of HCV-NS5B prodrug phosphoramidate diastereochemistry (D-/L-alanine, R-/S-phosphoryl) in vitro and in vivo. Co-applied with amiodarone, L-ala,S_P prodrugs increased beating rate and decreased beat amplitude in human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs), but D-ala,R_P produgs, including MK-3682, did not. Stereochemical selectivity on emerging bradycardia was confirmed in vivo. Diastereomer pairs entered cells equally well, and there was no difference in intracellular accumulation of L-ala,S_P metabolites ± amiodarone, but no D-ala,R_P metabolites were detected. Cathepsin A (CatA) inhibitors attenuated L-ala,S_P prodrug metabolite formation, yet exacerbated L-ala,S_P + amiodarone effects, implicating the prodrugs in these effects. Experiments indicate that pharmacological effects and metabolic conversion to UTP analog are L-ala,S_P prodrug-dependent in cardiomyocytes.

Prognostic impact of carboxylesterase 1 gene variants in patients with congestive heart failure treated with angiotensin-converting enzyme inhibitors

OBJECTIVE

Most angiotensin-converting enzyme inhibitors (ACEIs) are prodrugs activated by carboxylesterase 1 (CES1). We investigated the prognostic importance of CES1 gene (CES1) copy number variation and the rs3815583 single-nucleotide polymorphism in CES1 among ACEI-treated patients with congestive heart failure (CHF).

METHODS

Danish patients with chronic CHF enrolled in the previously reported Echocardiography and Heart Outcome Study were categorized according to their CES1 variants and followed up for up to 10 years. Risk for cardiovascular death and all-cause death was modeled by Cox proportional hazard analyses.

RESULTS

A total of 491 ACEI-treated patients were included in the analyses. After a mean follow-up of 5.5 years, we found no difference in the risk for cardiovascular death and all-cause death between patients having three [hazard ratios (HRs) 1.06 (95% confidence interval (CI) 0.77-1.45) and 1.16 (95% CI 0.88-1.52)] or four [HRs 0.88 (95% CI 0.39-2.01) and 1.37 (95% CI 0.74-2.54)] CES1 copies and those with two copies, respectively. Similarly, no difference in the risk for cardiovascular and all-cause death was found for patients heterozygous [HRs 0.91 (95% CI 0.70-1.19) and 0.88 (95% CI 0.69-1.12)] or homozygous [HRs 0.58 (95% CI 0.30-1.15) and 0.82 (95% CI 0.48-1.39)] for the rs3815583 minor allele versus patients homozygous for the major allele. The active promoter of CES1A2 and the rs71647871 single-nucleotide polymorphism minor allele were detected at very low frequencies.

CONCLUSION

This study did not support the use of CES1 copy number variation or rs3815583 as a predictor of fatal outcomes in ACEI-treated patients with CHF.

A Two-Photon Ratiometric Fluorescent Probe for Imaging Carboxylesterase 2 in Living Cells and Tissues

In this study, a two-photon ratiometric fluorescent probe NCEN has been designed and developed for highly selective and sensitive sensing of human carboxylesterase 2 (hCE2) based on the catalytic properties and substrate preference of hCE2. Upon addition of hCE2, the probe could be readily hydrolyzed to release 4-amino-1,8-naphthalimide (NAH), which brings remarkable red-shift in fluorescence (90 nm) spectrum. The newly developed probe exhibits good specificity, ultrahigh sensitivity, and has been successfully applied to determine the real activities of hCE2 in complex biological samples such as cell and tissue preparations. NCEN has also been used for two-photon imaging of intracellular hCE2 in living cells as well as in deep-tissues for the first time, and the results showed that the probe exhibited high ratiometric imaging resolution and deep-tissue imaging depth. All these findings suggested that this probe holds great promise for applications in bioimaging of endogenous hCE2 in living cells and in exploring the biological functions of hCE2 in complex biological systems.

Individualization of treatments with drugs metabolized by CES1: combining genetics and metabolomics

CES1 is involved in the hydrolysis of ester group-containing xenobiotic and endobiotic compounds including several essential and commonly used drugs. The individual variation in the efficacy and tolerability of many drugs metabolized by CES1 is considerable. Hence, there is a large interest in individualizing the treatment with these drugs. The present review addresses the issue of individualized treatment with drugs metabolized by CES1. It describes the composition of the gene encoding CES1, reports variants of this gene with focus upon those with a potential effect on drug metabolism and provides an overview of the protein structure of this enzyme bringing notice to mechanisms involved in the regulation of enzyme activity. Subsequently, the review highlights drugs metabolized by CES1 and argues that individual differences in the pharmacokinetics of these drugs play an important role in determining drug response and tolerability suggesting prospects for individualized drug therapies. Our review also discusses endogenous substrates of CES1 and assesses the potential of using metabolomic profiling of blood to identify proxies for the hepatic activity of CES1 that predict the rate of drug metabolism. Finally, the combination of genetics and metabolomics to obtain an accurate prediction of the individual response to CES1-dependent drugs is discussed.

CES1A -816C as a genetic marker to predict greater platelet clopidogrel response in patients with percutaneous coronary intervention

This study was designed to determine whether CES1A -816A/C polymorphism could be associated with altered clopidogrel response. Recruited patients were pretreated with 300 mg clopidogrel loading dose before undergoing percutaneous coronary intervention for stenting and genotyped with CYP2C19 *2, *3, or *17, and CES1A -816A/C, respectively. Adenosine diphosphate-induced maximum platelet aggregation (MPA) was determined on day 3 after initiation of daily clopidogrel maintenance doses. The clinical primary end point was the 1-year incidence of definite stent thrombosis (ST). Multivariable linear regression revealed that the CES1A -816A/C polymorphism was independently associated with MPA measures with an absolute β value of 6.76. Of 617 patients, a subcohort of 249 patients not carrying CYP2C19 *2, *3, or *17 were categorized into 3 groups based on the -816A/C genotype. The median MPA value was lower in 125 carriers of the -816C variant than in 124 noncarriers (21.5% vs. 31.7%, P = 0.001). The 1-year definite ST occurred in 7 patients in that subcohort, and only 1 ST case was one of carriers of the -816 A/A that was associated with higher MPA values. The CES1A -816C would be used to predict greater platelet response to clopidogrel than the CES1A -816A in percutaneous coronary intervention-treated patients not carrying CYP2C19 variants.

The catalytic mechanism of carboxylesterases: a computational study

The catalytic mechanism of carboxylesterases (CEs, EC 3.1.1.1) is explored by computational means. CEs hydrolyze ester, amide, and carbamate bonds found in xenobiotics and endobiotics. They can also perform transesterification, a reaction important, for instance, in cholesterol homeostasis. The catalytic mechanisms with three different substrates (ester, thioester, and amide) have been established at the M06-2X/6-311++G**//B3LYP/6-31G* level of theory. It was found that the reactions proceed through a mechanism involving four steps instead of two as is generally proposed: (i) nucleophilic attack of serine to the substrate, forming the first tetrahedral intermediate, (ii) formation of the acyl-enzyme complex concomitant with the release of the alcohol product, (iii) nucleophilic attack of a water or alcohol molecule forming the second tetrahedral intermediate, and (iv) the release of the second product of the reaction. The results agree very well with the available experimental data and show that the hydrolytic and the transesterification reactions are competitive processes when the substrate is an ester. In all the other studied substrates (thioester or amide), the hydrolytic and transesterification process are less favorable and some of them might not even take place under in vivo conditions.

In vitro evaluation of the inhibitory potential of pharmaceutical excipients on human carboxylesterase 1A and 2

Two major forms of human carboxylesterase (CES), CES1A and CES2, dominate the pharmacokinetics of most prodrugs such as imidapril and irinotecan (CPT-11). Excipients, largely used as insert vehicles in formulation, have been recently reported to affect drug enzyme activity. The influence of excipients on the activity of CES remains undefined. In this study, the inhibitory effects of 25 excipients on the activities of CES1A1 and CES2 were evaluated. Imidapril and CPT-11 were used as substrates and cultured with liver microsomes in vitro. Imidapril hydrolase activities of recombinant CES1A1 and human liver microsomes (HLM) were strongly inhibited by sodium lauryl sulphate (SLS) and polyoxyl 40 hydrogenated castor oil (RH40) [Inhibition constant (Ki) = 0.04 ± 0.01 μg/ml and 0.20 ± 0.09 μg/ml for CES1A1, and 0.12 ± 0.03 μg/ml and 0.76 ± 0.33 μg/ml, respectively, for HLM]. The enzyme hydrolase activity of recombinant CES2 was substantially inhibited by Tween 20 and polyoxyl 35 castor oil (EL35) (K(i) = 0.93 ± 0.36 μg/ml and 4.4 ± 1.24 μg/ml, respectively). Thus, these results demonstrate that surfactants such as SLS, RH40, Tween 20 and EL35 may attenuate the CES activity; such inhibition should be taken into consideration during drug administration.

OATP1A/1B transporters affect irinotecan and SN-38 pharmacokinetics and carboxylesterase expression in knockout and humanized transgenic mice

Organic anion-transporting polypeptides (OATP) mediate the hepatic uptake of many drugs, thus codetermining their clearance. Impaired hepatic clearance due to low-activity polymorphisms in human OATP1B1 may increase systemic exposure to SN-38, the active and toxic metabolite of the anticancer prodrug irinotecan. We investigated the pharmacokinetics and toxicity of irinotecan and SN-38 in Oatp1a/1b-null mice: Plasma exposure of irinotecan and SN-38 was increased 2 to 3-fold after irinotecan dosing (10 mg/kg, i.v.) compared with wild-type mice. Also, liver-to-plasma ratios were significantly reduced, suggesting impaired hepatic uptake of both compounds. After 6 daily doses of irinotecan, Oatp1a/1b-null mice suffered from increased toxicity. However, Oatp1a/1b-null mice had increased levels of carboxylesterase (Ces) enzymes, which caused higher conversion of irinotecan to SN-38 in plasma, potentially complicating pharmacokinetic analyses. Ces inhibitors blocked this increased conversion. Interestingly, liver-specific humanized OATP1B1 and OATP1B3 transgenic mice had normalized hepatic expression of Ces1 genes. While irinotecan liver-to-plasma ratios in these humanized mice were similar to those in Oatp1a/1b-null mice, SN-38 liver-to-plasma ratios returned to wild-type levels, suggesting that human OATP1B proteins mediate SN-38, but not irinotecan uptake in vivo. Upon direct administration of SN-38 (1 mg/kg, i.v.), Oatp1a/1b-null mice had increased SN-38 plasma levels, lower liver concentrations, and decreased cumulative biliary excretion of SN-38. Mouse Oatp1a/1b transporters have a role in the plasma clearance of irinotecan and SN-38, whereas human OATP1B transporters may only affect SN-38 disposition. Oatp1a/1b-null mice have increased expression and activity of Ces1 enzymes, whereas humanized mice provide a rescue of this phenotype.

RNA-sequencing quantification of hepatic ontogeny of phase-I enzymes in mice

Phase-I drug metabolizing enzymes catalyze reactions of hydrolysis, reduction, and oxidation of drugs and play a critical role in drug metabolism. However, the functions of most phase-I enzymes are not mature at birth, which markedly affects drug metabolism in newborns. Therefore, characterization of the expression profiles of phase-I enzymes and the underlying regulatory mechanisms during liver maturation is needed for better estimation of using drugs in pediatric patients. The mouse is an animal model widely used for studying the mechanisms in the regulation of developmental expression of phase-I genes. Therefore, we applied RNA sequencing to provide a "true quantification" of the mRNA expression of phase-I genes in the mouse liver during development. Liver samples of male C57BL/6 mice at 12 different ages from prenatal to adulthood were used for defining the ontogenic mRNA profiles of phase-I families, including hydrolysis: carboxylesterase (Ces), paraoxonase (Pon), and epoxide hydrolase (Ephx); reduction: aldo-keto reductase (Akr), quinone oxidoreductase (Nqo), and dihydropyrimidine dehydrogenase (Dpyd); and oxidation: alcohol dehydrogenase (Adh), aldehyde dehydrogenase (Aldh), flavin monooxygenases (Fmo), molybdenum hydroxylase (Aox and Xdh), cytochrome P450 (P450), and cytochrome P450 oxidoreductase (Por). Two rapidly increasing stages of total phase-I gene expression after birth reflect functional transition of the liver during development. Diverse expression patterns were identified, and some large gene families contained the mRNA of genes that are enriched at different stages of development. Our study reveals the mRNA abundance of phase-I genes in the mouse liver during development and provides a valuable foundation for mechanistic studies in the future.

Investigating the effects of a hydrolytically stable hapten and a Th1 adjuvant on heroin vaccine performance

We challenged the performance of our previous heroin vaccine with a similar vaccine containing a more hydrolytically stable hapten analogue and a Th1 adjuvant (CpG ODN). Our results indicate that the elements of our previous vaccine are essential for its anti-heroin potency, i.e., a chemically labile hapten and an exclusively Th2 humoral response elicited by alum. Such design elements are critical for producing next-generation heroin vaccines.

Bovine Carboxylesterases: Evidence for Two CES1 and Five Families of CES Genes on Chromosome 18

Predicted bovine carboxylesterase (CES) protein and gene sequences were derived from bovine (Bos taurus) genomic sequence data. Two bovine CES1 genes (CES1.1 and CES1.2) were located on chromosome 18 encoding amino acid sequences that were 81% identical. Two forms of CES1.2 were also observed apparently caused by an indel polymorphism encoded at the C-terminus end. Two CES gene clusters were observed on chromosome 18: CES5-CES1.1-CES1.2 and CES2-CES3-CES6. Bovine CES1, CES2, CES3, CES5 and CES6 shared 39-45% identity with each other, but showed 71-76% identity with each of the five corresponding human CES family members. Phylogeny studies indicated that bovine CES genes originated from five ancestral gene duplication events which predated the eutherian mammalian common ancestor. In addition, a subsequent CES1 gene duplication event is proposed during mammalian evolution prior to the appearance of the Bovidae common ancestor ~ 20 MY ago.

Mammalian carboxylesterase 5: comparative biochemistry and genomics

Carboxylesterase 5 (CES5) (also called cauxin or CES7) is one of at least five mammalian CES gene families encoding enzymes of broad substrate specificity and catalysing hydrolytic and transesterification reactions. In silico methods were used to predict the amino acid sequences, secondary structures and gene locations for CES5 genes and gene products. Amino acid sequence alignments of mammalian CES5 enzymes enabled identification of key CES sequences previously reported for human CES1, as well as other sequences that are specific to the CES5 gene family, which were consistent with being monomeric in subunit structure and available for secretion into body fluids. Predicted secondary structures for mammalian CES5 demonstrated significant conservation with human CES1 as well as distinctive mammalian CES5 like structures. Mammalian CES5 genes are located in tandem with the CES1 gene(s), are transcribed on the reverse strand and contained 13 exons. CES5 has been previously reported in high concentrations in the urine (cauxin) of adult male cats, and within a protein complex of mammalian male epididymal fluids. Roles for CES5 may include regulating urinary levels of male cat pheromones; catalysing lipid transfer reactions within mammalian male reproductive fluids; and protecting neural tissue from drugs and xenobiotics.

Carboxylesterases are uniquely expressed among tissues and regulated by nuclear hormone receptors in the mouse

Carboxylesterases (CES) are a well recognized, yet incompletely characterized family of proteins that catalyze neutral lipid hydrolysis. Some CES have well-defined roles in xenobiotic clearance, pharmacologic prodrug activation, and narcotic detoxification. In addition, emerging evidence suggests other CES may have roles in lipid metabolism. Humans have six CES genes, whereas mice have 20 Ces genes grouped into five isoenzyme classes. Perhaps due to the high sequence similarity shared by the mouse Ces genes, the tissue-specific distribution of expression for these enzymes has not been fully addressed. Therefore, we performed studies to provide a comprehensive tissue distribution analysis of mouse Ces mRNAs. These data demonstrated that while the mouse Ces family 1 is highly expressed in liver and family 2 in intestine, many Ces genes have a wide and unique tissue distribution defined by relative mRNA levels. Furthermore, evaluating Ces gene expression in response to pharmacologic activation of lipid- and xenobiotic-sensing nuclear hormone receptors showed differential regulation. Finally, specific shifts in Ces gene expression were seen in peritoneal macrophages following lipopolysaccharide treatment and in a steatotic liver model induced by high-fat feeding, two model systems relevant to disease. Overall these data show that each mouse Ces gene has its own distinctive tissue expression pattern and suggest that some CES may have tissue-specific roles in lipid metabolism and xenobiotic clearance.

A discriminative analytical method for detection of CES1A1 and CES1A2/CES1A3 genetic variants

Human carboxylesterase 1 (hCES1), encoded by the CES1 gene, is the predominant hepatic hydrolase responsible for the metabolism of many therapeutic agents, toxins, and endogenous substances. Genetic variants of CES1 can affect hCES1 function and expression and ultimately influence clinical response to drugs serving as hCES1 substrates. The CES1 gene consists of three isoforms including the functional CES1A1 and CES1A2 genes and the nonfunctional pseudogene CES1A3. Natural variants of these isoforms exert differing impacts on hCES1 function. However, the existing CES1 genotyping methods are incapable of determining whether these variants belong to CES1A1, CES1A2, or CES1A3 because of the high similarity among these three genes, as a consequence they are unable to discriminate between heterozygotes and homozygotes. We report the development of a novel long-range PCR-based, discriminative genotyping assay capable of specifically detecting the variants among CES1A1, CES1A2, and CES1A3 genes. The comparison of the genotyping results between this novel assay and those previously reported methods highlighted the necessity of applying the discriminative genotyping assay in pharmacogenetic studies involving CES1 gene.

Pharmacologic considerations for oseltamivir disposition: focus on the neonate and young infant

Across much of the world, pandemic H1N1 infection has produced a significant healthcare crisis, reflected in significant morbidity and mortality. Statistics reveal that infection-associated deaths among individuals without pre-existing conditions (e.g. immunosuppression) are clustered in pregnant women and young infants. In developing countries where the availability of influenzae vaccine is limited, the only currently available pharmacologic counter-measure for H1N1 disease is oseltamivir, a neuraminidase inhibitor with excellent in vitro activity against the virus. This drug is available in oral solid and liquid formulations, has excellent peroral bioavailability in adults, and generally has a very favorable safety profile. Many observational studies indicate that oseltamivir treatment is associated with symptomatic improvement in pediatric patients with H1N1 infection and, therefore, is considered to represent a viable therapeutic option for use in children. However, the disposition of the ethyl ester prodrug and its active metabolite has not been well characterized in infants and children. Presently, data are available from only two published investigations and preliminary summary information from a recent presentation of an ongoing study. Given that recent in vitro data support the importance of a target exposure-response profile for the active metabolite of oseltamivir and that many processes known to modulate drug disposition have a developmental basis, understanding the potential impact of age on oseltamivir disposition becomes crucial in the development of age-appropriate dosing regimens for the drug. In this review, the impact of ontogeny on processes that are important in regulating the absorption, distribution, metabolism, and excretion of oseltamivir and its active metabolite are considered. Data from both animal and human investigations are presented in the context of defining how development might influence the dose-exposure relationship and, most importantly, the significant variability associated with it. In addition, the available pediatric pharmacokinetic data for oseltamivir and its active metabolite are summarized and current 'information gaps' deserving of future study are presented.

Characterisation of the carboxylesterase enzyme cauxin in the seminal fluid of the cat

The carboxylesterase cauxin is a major urinary protein in cats that is also found in seminal fluid (SF). This study investigated cauxin in feline SF including biochemical features, concentration, distribution and gene expression in epididymal tissue, and its reaction with acylglycerol substrates. Monomeric, dimeric, and/or multimeric forms of cauxin carrying N-glycosylations were detected on Western blots of feline SF but most were monomeric. Cauxin concentrations were markedly lower in SF (0.042±0.020 mg/mL) than in urine (∼0.5 mg/mL) and cauxin gene expression was 60-fold lower in the epididymis than in the kidney. Immunohistochemical examination localised cauxin within the stereocilia and cytoplasm of epithelial cells lining the caput and corpus epididymis. Cauxin-positive spermatozoa were detected in the lumen of the cauda epididymis but not in the cytoplasm of the epithelial cell lining. Using an in vitro assay, cauxin hydrolysed saturated 1-mono- but not di- and tri-acylglycerols. The results suggest that cauxin secreted from the caput and corpus epididymis acts as an esterase on lipid within feline SF.

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

Mammalian carboxylesterase (CES or Ces) genes encode enzymes that participate in xenobiotic, drug, and lipid metabolism in the body and are members of at least five gene families. Tandem duplications have added more genes for some families, particularly for mouse and rat genomes, which has caused confusion in naming rodent Ces genes. This article describes a new nomenclature system for human, mouse, and rat carboxylesterase genes that identifies homolog gene families and allocates a unique name for each gene. The guidelines of human, mouse, and rat gene nomenclature committees were followed and "CES" (human) and "Ces" (mouse and rat) root symbols were used followed by the family number (e.g., human CES1). Where multiple genes were identified for a family or where a clash occurred with an existing gene name, a letter was added (e.g., human CES4A; mouse and rat Ces1a) that reflected gene relatedness among rodent species (e.g., mouse and rat Ces1a). Pseudogenes were named by adding "P" and a number to the human gene name (e.g., human CES1P1) or by using a new letter followed by ps for mouse and rat Ces pseudogenes (e.g., Ces2d-ps). Gene transcript isoforms were named by adding the GenBank accession ID to the gene symbol (e.g., human CES1_AB119995 or mouse Ces1e_BC019208). This nomenclature improves our understanding of human, mouse, and rat CES/Ces gene families and facilitates research into the structure, function, and evolution of these gene families. It also serves as a model for naming CES genes from other mammalian species.

Mammalian carboxylesterase 3: comparative genomics and proteomics

At least five families of mammalian carboxylesterases (CES) catalyse the hydrolysis or transesterification of a wide range of drugs and xenobiotics and may also participate in fatty acyl and cholesterol ester metabolism. In this study, in silico methods were used to predict the amino acid sequences, secondary and tertiary structures, and gene locations for CES3 genes and encoded proteins using data from several mammalian genome projects. Mammalian CES3 genes were located within a CES gene cluster with CES2 and CES6 genes, usually containing 13 exons transcribed on the positive DNA strand. Evidence is reported for duplicated CES3 genes for the chimp and mouse genomes. Mammalian CES3 protein subunits shared 58-97% sequence identity and exhibited sequence alignments and identities for key CES amino acid residues as well as extensive conservation of predicted secondary and tertiary structures with those previously reported for human CES1. The human genome project has previously reported CES3 mRNA isoform expression in several tissues, particularly in colon, trachea and in brain. Predicted human CES3 isoproteins were apparently derived from exon shuffling and are likely to be secreted extracellularly or retained within the cytoplasm. Mouse CES3-like transcripts were localized in specific regions of the mouse brain, including the cerebellum, and may play a role in the detoxification of drugs and xenobiotics in neural tissues and other tissues of the body. Phylogenetic analyses demonstrated the relationships and potential evolutionary origins of the mammalian CES3 family of genes which were related to but distinct from other mammalian CES gene families.