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References (16)

Title : Human carboxylesterases: an update on CES1, CES2 and CES3 - Sanghani_2009_Protein.Pept.Lett_16_1207
Author(s) : Sanghani SP , Sanghani PC , Schiel MA , Bosron WF
Ref : Protein Pept Lett , 16 :1207 , 2009
Abstract : Carboxylesterases belong to Phase I group of drug metabolizing enzymes. They hydrolyze a variety of drug esters, amides, carbamates and similar structures. There are five 'carboxylesterase' genes listed in the Human Genome Organization database. In this review, we will focus on the CES1, CES2 and CES3 genes and their protein products that have been partially characterized. Several variants of these three CESs result from alternate splicing, single nucleotide polymorphisms and multiple copy variants. The three CESs, are largely localized to tissues that are major sites of drug metabolism like the mucosa of the gastrointestinal tract, lungs and liver but, they differ in tissue-specific expression. The amino acid alignment of the three CESs reveals important conserved catalytic and structural residues. There are interesting insertions and deletions that may affect enzymatic function as determined by homology modeling of CES3 using the CES1 three-dimensional structure. A comparison of the substrate specificity of CES1 versus CES2 reveals broad but distinct substrate preferences. There is little information on the substrate specificity of CES3 but it seems to have a lower catalytic efficiency than the other two CESs for selected substrates.
ESTHER : Sanghani_2009_Protein.Pept.Lett_16_1207
PubMedSearch : Sanghani_2009_Protein.Pept.Lett_16_1207
PubMedID: 19508181
Gene_locus related to this paper: human-CES1 , human-CES2 , human-CES3

Title : Expression of carboxylesterase and lipase genes in rat liver cell-types - Mello_2008_Biochem.Biophys.Res.Commun_374_460
Author(s) : Mello T , Nakatsuka A , Fears S , Davis W , Tsukamoto H , Bosron WF , Sanghani SP
Ref : Biochemical & Biophysical Research Communications , 374 :460 , 2008
Abstract : Approximately 80% of the body vitamin A is stored in liver stellate cells with in the lipid droplets as retinyl esters. In low vitamin A status or after liver injury, stellate cells are depleted of the stored retinyl esters by their hydrolysis to retinol. However, the identity of retinyl ester hydrolase(s) expressed in stellate cells is unknown. The expression of carboxylesterase and lipase genes in purified liver cell-types was investigated by real-time PCR. We found that six carboxylesterase and hepatic lipase genes were expressed in hepatocytes. Adipose triglyceride lipase was expressed in Kupffer cells, stellate cells and endothelial cells. Lipoprotein lipase expression was detected in Kupffer cells and stellate cells. As a function of stellate cell activation, expression of adipose triglyceride lipase decreased by twofold and lipoprotein lipase increased by 32-fold suggesting that it may play a role in retinol ester hydrolysis during stellate cell activation.
ESTHER : Mello_2008_Biochem.Biophys.Res.Commun_374_460
PubMedSearch : Mello_2008_Biochem.Biophys.Res.Commun_374_460
PubMedID: 18639528

Title : Expression and characterization of a human carboxylesterase 2 splice variant - Schiel_2007_J.Pharmacol.Exp.Ther_323_94
Author(s) : Schiel MA , Green SL , Davis WI , Sanghani PC , Bosron WF , Sanghani SP
Ref : Journal of Pharmacology & Experimental Therapeutics , 323 :94 , 2007
Abstract : CPT-11 [7-ethyl-10-[4-(1-piperidino)-1-piperidino] carbonyloxycamptothecin or Irinotecan] is a carbamate prodrug that is activated in vivo by carboxylesterase (CES)-2 to SN-38 (7-ethyl-10-hydroxycamptothecin), a potent topoisomerase I inhibitor. There is high interindividual variation when CPT-11 is used in the treatment of colorectal cancer. Several splice variants of CES2 are reported in the expressed sequence tag database. Real-time polymerase chain reaction was used to determine the abundance of the CES2 and splice variant of human carboxylesterase 2 (CES2Delta(458-473)) transcripts in 10 paired samples of human tumor and normal colon tissue. The results showed that the CES2Delta(458-473) transcript accounts for an average of 6% of total CES2 transcripts in colon tissue, and there is large interindividual variation in CES2 expression in both tumor and normal colon samples. The carboxylesterase activity of the colon samples was determined by 4-methylumbelliferyl acetate hydrolysis assays and nondenaturing polyacrylamide gel electrophoresis followed by activity staining. Significant, positive correlations were found between CES2 expression levels and both measures of carboxylesterase activity. We cloned and expressed the CES2Delta(458-473) protein in Sf9 insect cells. The purification profiles and preliminary characterization of the CES2Delta(458-473) protein indicated that the expressed protein is folded and glycosylated like CES2. However, in vitro assays show that the CES2Delta(458-473) protein lacks 4-methylumbelliferyl acetate and irinotecan hydrolase activities. In conclusion, we found that the CES2Delta(458-473) protein is an inactive splice variant of CES2 and that its transcript is spliced at a relatively constant rate in tumor and normal colon tissue.
ESTHER : Schiel_2007_J.Pharmacol.Exp.Ther_323_94
PubMedSearch : Schiel_2007_J.Pharmacol.Exp.Ther_323_94
PubMedID: 17636009

Title : Hydrolysis of capecitabine to 5'-deoxy-5-fluorocytidine by human carboxylesterases and inhibition by loperamide - Quinney_2005_J.Pharmacol.Exp.Ther_313_1011
Author(s) : Quinney SK , Sanghani SP , Davis WI , Hurley TD , Sun Z , Murry DJ , Bosron WF
Ref : Journal of Pharmacology & Experimental Therapeutics , 313 :1011 , 2005
Abstract : Capecitabine is an oral prodrug of 5-fluorouracil that is indicated for the treatment of breast and colorectal cancers. A three-step in vivo-targeted activation process requiring carboxylesterases, cytidine deaminase, and thymidine phosphorylase converts capecitabine to 5-fluorouracil. Carboxylesterases hydrolyze capecitabine's carbamate side chain to form 5'-deoxy-5-fluorocytidine (5'-DFCR). This study examines the steady-state kinetics of recombinant human carboxylesterase isozymes carboxylesterase (CES) 1A1, CES2, and CES3 for hydrolysis of capecitabine with a liquid chromatography/mass spectroscopy assay. Additionally, a spectrophotometric screening assay was utilized to identify drugs that may inhibit carboxylesterase activation of capecitabine. CES1A1 and CES2 hydrolyze capecitabine to a similar extent, with catalytic efficiencies of 14.7 and 12.9 min(-1) mM(-1), respectively. Little catalytic activity is detected for CES3 with capecitabine. Northern blot analysis indicates that relative expression in intestinal tissue is CES2 > CES1A1 > CES3. Hence, intestinal activation of capecitabine may contribute to its efficacy in colon cancer and toxic diarrhea associated with the agent. Loperamide is a strong inhibitor of CES2, with a K(i) of 1.5 muM, but it only weakly inhibits CES1A1 (IC(50) = 0.44 mM). Inhibition of CES2 in the gastrointestinal tract by loperamide may reduce local formation of 5'-DFCR. Both CES1A1 and CES2 are responsible for the activation of capecitabine, whereas CES3 plays little role in 5'-DFCR formation.
ESTHER : Quinney_2005_J.Pharmacol.Exp.Ther_313_1011
PubMedSearch : Quinney_2005_J.Pharmacol.Exp.Ther_313_1011
PubMedID: 15687373
Gene_locus related to this paper: human-CES1 , human-CES2 , human-CES3

Title : Methylphenidate is stereoselectively hydrolyzed by human carboxylesterase CES1A1 - Sun_2004_J.Pharmacol.Exp.Ther_310_469
Author(s) : Sun Z , Murry DJ , Sanghani SP , Davis WI , Kedishvili NY , Zou Q , Hurley TD , Bosron WF
Ref : Journal of Pharmacology & Experimental Therapeutics , 310 :469 , 2004
Abstract : Methylphenidate is an important stimulant prescribed to treat attention-deficit hyperactivity disorder. It has two chiral centers, but most current commercial formulations consist of the racemic mixture of the threo pair of methylphenidate isomers (d-, l-threo-methylphenidate). The d-isomer is the pharmacologically active component. Numerous studies reported that oral administration of the methylphenidate racemate undergoes first-pass, stereoselective clearance in humans with l-methylphenidate being eliminated faster than d-methylphenidate. Accordingly, the kinetics of hydrolysis of individual enantiomers by purified native and recombinant human liver carboxylesterases CES1A1 and CES2 and a colon isoenzyme CES3 were examined with a liquid chromatography/mass spectrometry assay. The expression of CES1A1, CES2, and CES3 in Sf9 cells and the methods for purification of the three isoenzymes are reported. CES1A1 has a high catalytic efficiency for both d- and l-enantiomers of methylphenidate. No catalytic activity was detected with CES2 and CES3 for either enantiomer. The catalytic efficiency of CES1A1 for l-methylphenidate (k(cat)/K(m) = 7.7 mM(-1) min(-1)) is greater than that of d-methylphenidate (k(cat)/K(m) = 1.3-2.1 mM(-1) min(-1)). Hence, the catalytic efficiency of CES1A1 for methylphenidate enantiomers agrees with stereoselective clearance of methylphenidate reported in human subjects. Both enantiomers of methylphenidate can be fit into the three-dimensional model of CES1A1 to form productive complexes in the active site. We conclude that CES1A1 is the major enzyme responsible for the first-pass, stereoselective metabolism of methylphenidate.
ESTHER : Sun_2004_J.Pharmacol.Exp.Ther_310_469
PubMedSearch : Sun_2004_J.Pharmacol.Exp.Ther_310_469
PubMedID: 15082749

Title : Hydrolysis of irinotecan and its oxidative metabolites, 7-ethyl-10-[4-N-(5-aminopentanoic acid)-1-piperidino] carbonyloxycamptothecin and 7-ethyl-10-[4-(1-piperidino)-1-amino]-carbonyloxycamptothecin, by human carboxylesterases CES1A1, CES2, and a newly expressed carboxylesterase isoenzyme, CES3 - Sanghani_2004_Drug.Metab.Dispos_32_505
Author(s) : Sanghani SP , Quinney SK , Fredenburg TB , Davis WI , Murry DJ , Bosron WF
Ref : Drug Metabolism & Disposition: The Biological Fate of Chemicals , 32 :505 , 2004
Abstract : Carboxylesterases metabolize ester, thioester, carbamate, and amide compounds to more soluble acid, alcohol, and amine products. They belong to a multigene family with about 50% sequence identity between classes. CES1A1 and CES2 are the most studied human isoenzymes from class 1 and 2, respectively. In this study, we report the cloning and expression of a new human isoenzyme, CES3, that belongs to class 3. The purified recombinant CES3 protein has carboxylesterase activity. Carboxylesterases metabolize the carbamate prodrug 7-ethyl-10-[4-(1-piperidino)-1-piperidino] carbonyloxycamptothecin (CPT-11; irinotecan) to its active metabolite 7-ethyl-10-hydroxycamptothecin (SN-38), a potent topoisomerase I inhibitor. CYP3A4 oxidizes CPT-11 to two major oxidative metabolites, 7-ethyl-10-[4-N-(5-aminopentanoic acid)-1-piperidino] carbonyloxycamptothecin (APC) and 7-ethyl-10-[4-(1-piperidino)-1-amino]-carbonyloxycamptothecin (NPC). In this study, we investigate whether these oxidative metabolites, NPC and APC, can be metabolized to SN-38 by purified human carboxylesterases, CES1A1, CES2, and CES3. We find that CPT-11, APC, and NPC can all be metabolized by carboxylesterases to SN-38. CES2 has the highest catalytic activity of 0.012 min(-1) microM(-1) among the three carboxylesterases studied for hydrolysis of CPT-11. NPC was an equally good substrate of CES2 in comparison to CPT-11, with a catalytic efficiency of 0.005 min(-1) microM(-1). APC was a very poor substrate for all three isoenzymes, exhibiting a catalytic activity of 0.015 x 10(-3) min(-1) microM(-1) for CES2. Catalytic efficiency of CES3 for CPT-11 hydrolysis was 20- to 2000-fold less than that of CES1A1 and CES2. The relative activity of the three isoenzymes was CES2 > CES1A1 >> CES3, for all three substrates.
ESTHER : Sanghani_2004_Drug.Metab.Dispos_32_505
PubMedSearch : Sanghani_2004_Drug.Metab.Dispos_32_505
PubMedID: 15100172
Gene_locus related to this paper: human-CES2 , human-CES3

Title : Carboxylesterases expressed in human colon tumor tissue and their role in CPT-11 hydrolysis - Sanghani_2003_Clin.Cancer.Res_9_4983
Author(s) : Sanghani SP , Quinney SK , Fredenburg TB , Sun Z , Davis WI , Murry DJ , Cummings OW , Seitz DE , Bosron WF
Ref : Clin Cancer Research , 9 :4983 , 2003
Abstract : PURPOSE: The purpose is to develop new analytical methods to study the expression profile of CPT-11 carboxylesterases and topoisomerase I in colon tumor samples and understand the impact of their expression on CPT-11 metabolism in chemotherapy. EXPERIMENTAL DESIGN: We investigated 24 colon tumors for expression of carboxylesterases CES1A1, CES2, CES3, hBr-3, and topoisomerase I genes by real-time PCR and correlated the gene expression with activity assays. The relative abundance of the carboxylesterase isoenzymes and topoisomerase I genes was determined by real-time PCR. Activity assays performed on colon tumor extracts included CPT-11 hydrolase, 4-methylumbelliferyl acetate hydrolase, and topoisomerase I activity assays. Additionally, nondenaturing activity gel electrophoresis with activity staining showed the distribution of carboxylesterases. RESULTS: We detect the expression of CES1A1, CES2, and CES3 carboxylesterase genes in human colon tumors. We were unable to detect the hBr-3 (also called hCE-3) in human liver, colon, or brain. We find large interindividual variation, >/=150-fold, for both CES1A1 and CES3 genes, 23-fold for CES2, and 66-fold for topoisomerase I. Only CES2 gene expression correlated with the carboxylesterase activity assays (P < 0.01) with CPT-11 and 4-methylumbelliferyl acetate as substrates. Nondenaturing activity gel electrophoresis showed that CES2 was the most predominant activity. Topoisomerase I gene expression significantly correlated with topoisomerase I activity (P < 0.01) in the colon tumors, but interindividual variation was very high. CONCLUSIONS: We conclude that CES2 is the most abundant carboxylesterase in colon tumors that is responsible for CPT-11 hydrolysis. This pilot study reinforces the hypothesis that there is a large interindividual variation in expression of carboxylesterases that may contribute to variation in therapeutic outcome and/or toxicity of CPT-11 therapy for colon cancer.
ESTHER : Sanghani_2003_Clin.Cancer.Res_9_4983
PubMedSearch : Sanghani_2003_Clin.Cancer.Res_9_4983
PubMedID: 14581373
Gene_locus related to this paper: human-CES3

Title : Identification of microsomal rat liver carboxylesterases and their activity with retinyl palmitate - Sanghani_2002_Eur.J.Biochem_269_4387
Author(s) : Sanghani SP , Davis WI , Dumaual NG , Mahrenholz A , Bosron WF
Ref : European Journal of Biochemistry , 269 :4387 , 2002
Abstract : Retinyl esters are a major endogenous storage source of vitamin A in vertebrates and their hydrolysis to retinol is a key step in the regulation of the supply of retinoids to all tissues. Some members of nonspecific carboxylesterase family (EC 3.1.1.1) have been shown to hydrolyze retinyl esters. However, the number of different isoenzymes that are expressed in the liver and their retinyl palmitate hydrolase activity is not known. Six different carboxylesterases were identified and purified from rat liver microsomal extracts. Each isoenzyme was identified by mass spectrometry of its tryptic peptides. In addition to previously characterized rat liver carboxylesterases ES10, ES4, ES3, the protein products for two cloned genes, AB010635 and D50580 (GenBank accession numbers), were also identified. The sixth isoenzyme was a novel carboxylesterase and its complete cDNA was cloned and sequenced (AY034877). Three isoenzymes, ES10, ES4 and ES3, account for more than 95% of rat liver microsomal carboxylesterase activity. They obey Michaelis-Menten kinetics for hydrolysis of retinyl palmitate with Km values of about 1 micro m and specific activities between 3 and 8 nmol.min-1.mg-1 protein. D50580 and AY034877 also hydrolyzed retinyl palmitate. Gene-specific oligonucleotide probing of multiple-tissue Northern blot indicates differential expression in various tissues. Multiple genes are highly expressed in liver and small intestine, important tissues for retinoid metabolism. The level of expression of any one of the six different carboxylesterase isoenzymes will regulate the metabolism of retinyl palmitate in specific rat cells and tissues.
ESTHER : Sanghani_2002_Eur.J.Biochem_269_4387
PubMedSearch : Sanghani_2002_Eur.J.Biochem_269_4387
PubMedID: 12230550
Gene_locus related to this paper: ratno-Ces1d , ratno-LOC246252 , ratno-pbcxe

Title : Current progress on esterases: from molecular structure to function - Satoh_2002_Drug.Metab.Dispos_30_488
Author(s) : Satoh T , Taylor P , Bosron WF , Sanghani SP , Hosokawa M , La Du BN
Ref : Drug Metabolism & Disposition: The Biological Fate of Chemicals , 30 :488 , 2002
Abstract : This article reports on a symposium sponsored by the American Society for Pharmacology and Experimental Therapeutics and held at the April 2001 Experimental Biology meeting. Current developments in molecular-based studies into the structure and function of cholinesterases, carboxylesterases, and paraoxonases are described. This article covers mechanisms of regulation of gene expression of the various esterases by developmental factors and xenobiotics, as well as the interplay between physiological and chemical regulation of enzyme activity.
ESTHER : Satoh_2002_Drug.Metab.Dispos_30_488
PubMedSearch : Satoh_2002_Drug.Metab.Dispos_30_488
PubMedID: 11950776

Title : Lessons from a bacterial cocaine esterase -
Author(s) : Bosron WF , Hurley TD
Ref : Nat Struct Biol , 9 :4 , 2002
PubMedID: 11753424

Title : Binding and hydrolysis of meperidine by human liver carboxylesterase hCE-1 - Zhang_1999_J.Pharmacol.Exp.Ther_290_314
Author(s) : Zhang J , Burnell JC , Dumaual N , Bosron WF
Ref : Journal of Pharmacology & Experimental Therapeutics , 290 :314 , 1999
Abstract : Human liver carboxylesterases catalyze the hydrolysis of apolar drug or xenobiotic esters into more soluble acid and alcohol products for elimination. Two carboxylesterases, hCE-1 and hCE-2, have been purified and characterized with respect to their role in cocaine and heroin hydrolysis. The binding of meperidine (Demerol) and propoxyphene (Darvon) was examined in a competitive binding, spectrophotometric assay. The hCE-1 and hCE-2 bound both drugs, with Ki values in the 0.4- to 1.3-mM range. Meperidine was hydrolyzed to meperidinic acid and ethanol by hCE-1 but not hCE-2. The Km of hCE-1 for meperidine was 1.9 mM and the kcat (catalytic rate constant) was 0.67 min-1. Hydrolysis of meperidine by hCE-1 was consistent with its specificity for hydrolysis of esters containing simple aliphatic alcohol substituents. Hence, hCE-1 in human liver microsomes may play an important role in meperidine elimination. Propoxyphene was not hydrolyzed by hCE-1 or hCE-2. This observation is consistent with the absence of a major hydrolytic pathway for propoxyphene metabolism in humans.
ESTHER : Zhang_1999_J.Pharmacol.Exp.Ther_290_314
PubMedSearch : Zhang_1999_J.Pharmacol.Exp.Ther_290_314
PubMedID: 10381793

Title : Human liver carboxylesterase hCE-1: binding specificity for cocaine, heroin, and their metabolites and analogs - Brzezinski_1997_Drug.Metab.Dispos_25_1089
Author(s) : Brzezinski MR , Spink BJ , Dean RA , Berkman CE , Cashman JR , Bosron WF
Ref : Drug Metabolism & Disposition: The Biological Fate of Chemicals , 25 :1089 , 1997
Abstract : Purified human liver carboxylesterase (hCE-1) catalyzes the hydrolysis of cocaine to form benzoylecgonine, the deacetylation of heroin to form 6-acetylmorphine, and the ethanol-dependent transesterification of cocaine to form cocaethylene. In this study, the binding affinities of cocaine, cocaine metabolites and analogs, heroin, morphine, and 6-acetylmorphine for hCE-1 were evaluated by measuring their kinetic inhibition constants with 4-methylumbelliferyl acetate in a rapid spectrophotometric assay. The naturally occurring (R)-(-)-cocaine isomer displayed the highest affinity of all cocaine and heroin analogs or metabolites. The pseudo- or allopseudococaine isomers of cocaine exhibited lower affinity indicating that binding to the enzyme is stereoselective. The methyl ester, benzoyl, and N-methyl groups of cocaine play important roles in binding because removal of these groups increased K(i) values substantially. Compounds containing a variety of hydrophobic substitutions at the benzoyl group of cocaine bound to the enzyme with high affinity. The high K(i) value obtained for cocaethylene relative to cocaine is consistent with weaker binding to the esterase and a longer elimination half-life reported for the metabolite. The spectrophotometric competitive inhibition assay used here represents an effective method to identify drug or environmental esters metabolized by carboxylesterases like hCE-1.
ESTHER : Brzezinski_1997_Drug.Metab.Dispos_25_1089
PubMedSearch : Brzezinski_1997_Drug.Metab.Dispos_25_1089
PubMedID: 9311626

Title : Human liver cocaine carboxylesterases -
Author(s) : Bosron WF , Dean RA , Brzezinski MR , Pindel EV
Ref : NIDA Res Monogr , 173 :27 , 1997
PubMedID: 9260181

Title : Purification and cloning of a broad substrate specificity human liver carboxylesterase that catalyzes the hydrolysis of cocaine and heroin - Pindel_1997_J.Biol.Chem_272_14769
Author(s) : Pindel EV , Kedishvili NY , Abraham TL , Brzezinski MR , Zhang J , Dean RA , Bosron WF
Ref : Journal of Biological Chemistry , 272 :14769 , 1997
Abstract : A human liver carboxylesterase (hCE-2) that catalyzes the hydrolysis of the benzoyl group of cocaine and the acetyl groups of 4-methylumbelliferyl acetate, heroin, and 6-monoacetylmorphine was purified from human liver. The purified enzyme exhibited a single band on SDS-polyacrylamide gel electrophoresis with a subunit mass of approximately 60 kDa. The native enzyme was monomeric. The isoelectric point of hCE-2 was approximately 4.9. Treatment with endoglycosidase H caused an increase in electrophoretic mobility indicating that the liver carboxylesterase was a glycoprotein of the high mannose type. The complete cDNA nucleotide sequence was determined. The authenticity of the cDNA was confirmed by a perfect sequence match of 78 amino acids derived from the hCE-2 purified from human liver. The mature 533-amino acid enzyme encoded by this cDNA shared highest sequence identity with the rabbit liver carboxylesterase form 2 (73%) and the hamster liver carboxylesterase AT51p (67%). Carboxylesterases with high sequence identity to hCE-2 have not been reported in mouse and rat liver. hCE-2 exhibited different drug ester substrate specificity from the human liver carboxylesterase called hCE-1, which hydrolyzes the methyl ester of cocaine. hCE-2 had higher catalytic efficiencies for hydrolysis of 4-methylumbelliferyl acetate, heroin, and 6-monoacetylmorphine and greater inhibition by eserine than hCE-1. hCE-2 may play an important role in the degradation of cocaine and heroin in human tissues.
ESTHER : Pindel_1997_J.Biol.Chem_272_14769
PubMedSearch : Pindel_1997_J.Biol.Chem_272_14769
PubMedID: 9169443
Gene_locus related to this paper: human-CES1 , human-CES2

Title : Metabolism of cocaine and heroin is catalyzed by the same human liver carboxylesterases - Kamendulis_1996_J.Pharmacol.Exp.Ther_279_713
Author(s) : Kamendulis LM , Brzezinski MR , Pindel EV , Bosron WF , Dean RA
Ref : Journal of Pharmacology & Experimental Therapeutics , 279 :713 , 1996
Abstract : Concomitant i.v. use of cocaine and heroin ("speedballing") is prevalent among drug-abusing populations. Heroin is rapidly metabolized by sequential deacetylation of two separate ester bonds to yield 6-monoacetylmorphine and morphine. Hydrolysis of heroin to 6-monoacetylmorphine is catalyzed by pseudocholinesterase. The pathway for hydrolysis of 6-monoacetylmorphine to morphine in vivo has yet to be established. Pseudocholinesterase and two human liver carboxylesterases [human liver carboxylesterase form 1 (hCE-1) and human liver carboxylesterase form 2 (hCE-2)] catalyze the rapid hydrolysis of ester linkages in cocaine. This investigation examined the relative catalytic efficiencies of hCE-1, hCE-2 and pseudocholinesterase for heroin metabolism and compared them with cocaine hydrolysis. Enzymatic formation of 6-monoacetylmorphine and morphine was determined by reverse-phase high-performance liquid chromatography. All three enzymes rapidly catalyzed hydrolysis of heroin to 6-monoacetylmorphine (hCE-1 kcat = 439 min-1, hCE-2 kcat = 2186 min-1 and pseudocholinesterase kcat = 13 min-1). The catalytic efficiency, under first-order conditions, for hCE-2-catalyzed formation of 6-monoacetylmorphine (314 min-1 mM-1) was much greater than that for either hCE-1 or pseudocholinesterase (69 and 4 min-1 mM-1, respectively). Similarly, the catalytic efficiency for hydrolysis of 6-monoacetylmorphine to morphine by hCE-2 (22 min-1 mM-1) was substantially greater than that for hCE-1 (0.024 min-1 mM-1). Cocaine competitively inhibited hCE-1-, hCE-2- and pseudocholinesterase-catalyzed hydrolysis of heroin to 6-monoacetylmorphine (Ki = 530, 460 and 130 microM, respectively) and 6-monoacetylmorphine hydrolysis to morphine (Ki = 710, 220 and 830 microM, respectively). These data demonstrate that metabolism of cocaine and heroin in humans is mediated by common metabolic pathways. The role of hepatic hCE-2 is particularly important for the hydrolysis of heroin to 6-monoacetylmorphine and of 6-monoacetylmorphine to morphine.
ESTHER : Kamendulis_1996_J.Pharmacol.Exp.Ther_279_713
PubMedSearch : Kamendulis_1996_J.Pharmacol.Exp.Ther_279_713
PubMedID: 8930175

Title : Purification and characterization of a human liver cocaine carboxylesterase that catalyzes the production of benzoylecgonine and the formation of cocaethylene from alcohol and cocaine - Brzezinski_1994_Biochem.Pharmacol_48_1747
Author(s) : Brzezinski MR , Abraham TL , Stone CL , Dean RA , Bosron WF
Ref : Biochemical Pharmacology , 48 :1747 , 1994
Abstract : The psychomotor stimulant cocaine is inactivated primarily by hydrolysis to benzoylecgonine, the major urinary metabolite of the drug. A non-specific carboxylesterase was purified from human liver that catalyzes the hydrolysis of the methyl ester group of cocaine to form benzoylecgonine. In the presence of ethanol, the enzyme also catalyzes the transesterification of cocaine producing the pharmacologically active metabolite cocaethylene (benzoylecgonine ethyl ester). The carboxylesterase obeys simple Michaelis-Menten kinetics with Km values of 116 microM for cocaine and 43 mM for ethanol. The enzymatic activity suggests that it may play an important role in regulating the detoxication of cocaine and in the formation of the active metabolite cocaethylene. Additionally, the enzyme catalyzes the formation of ethyloleate from oleic acid and ethanol. The carboxylesterase was purified from autopsy liver by gel filtration, chromatofocusing, ion-exchange, and hydrophobic interaction chromatography to purity by SDS-PAGE and agarose gel isoelectric focusing. The subunit molecular weight was determined to be 59,000 and the native molecular weight was estimated to be 170,000 from a calibrated gel filtration column, suggesting that the active enzyme is a trimer. The isoelectric point was approximately 5.8. Digestion of carbohydrate residues on the protein with an acetylglucosaminidase plus binding to several lectins indicates that the enzyme is glycosylated. The esterase was cleaved with two proteases, and the amino acid sequences from fourteen peptides were used to search GenBank. Two identical matches were found corresponding to carboxylesterase cDNAs from human liver and lung.
ESTHER : Brzezinski_1994_Biochem.Pharmacol_48_1747
PubMedSearch : Brzezinski_1994_Biochem.Pharmacol_48_1747
PubMedID: 7980644
Gene_locus related to this paper: human-CES1