Human esterases, inhibitors

Pancreatic cholesterol esterase (3.1.1.3.) aids in transporting cholesterol to the enterocyte. By utilizing a selective and potent cholesterol esterase inhibitor 6-chloro-3-(l-ethyl-2-cyclohexyl)-2-pyrone, the absorption of cholesterol in hamsters could be reduced [71]. Wadkins et al. [72] synthesized novel sulfonamide derivatives, which demonstrated greater than 200-fold selectivity for human intestinal carboxylesterase compared with the human liver carboxylesterase hCEl, and none of them was an inhibitor of human acetylcholinesterase or butyrylcholinester-ase. Maybe these agents can serve as lead compounds for the development of effective, selective carboxylesterase inhibitors for clinical applications. Also the potent P-gp inhibitor verapamil [73] as well as S,S,S-tributylphosphortrithionate (DEF) [74] may exhibit carboxylesterase inhibitory properties. Various other inhibitors of human esterases are listed in Table 5.6. 

Cocaine metabolism and disposition following acute ethanol administration were studied in the rat to determine if the in vitro effects of ethanol on cocaine methyl esterase and ethyl transferase activities had significance in vivo (Zachman et al. 1993). The rat was used as it possesses both ethyl transferase and methyl esterase activities, is frequently employed for behavioral and toxicity studies of cocaine, and the size provides sufficient tissue for anal 4 ical work. This study was designed to address three questions. First, do significant concentrations of cocaethylene form and accumulate in tissues with controlled coadministrations of cocaine and alcohol Second, does ethanol administration significantly diminish the hydrolysis of cocaine to benzoylecgonine and methanol, as occurs in vitro when cocaine and ethanol are coincubated with purified human liver carboxylesterase (Brzezinski et al. 1994 Dean et al. 1991) Third, does ethanol inhibition of cocaine methyl ester hydrolysis increase the N-oxidative metabolism of cocaine, as noted when rodents are pretreated with nonspecific esterase inhibitors (Thompson etal. 1979) ... 

KIO. Kalow, W., and Davies, R. O., The activity of various esterase inhibitors towards atypical human serum cholinesterase. Biochem. Pharmacol. 1, 183-192 (1958). 

This assay is relatively simple and well suited to HTS, but it can t really distinguish between a P-gp inhibitor and a substrate, and compounds that are esterase inhibitors may give false negatives. A study at Hoffmann-La Roche compared results of this assay for cells transfected with human MDRl and the equivalent proteins in mouse, called mdrla and mdrlb, and found some important differences between them, a reminder once again that results obtained for one species won t necessarily apply to another. " ... 

XII Hageman factor The first factor in the intrinsic pathway. A/, 74000 (bovine), 76000 (human). Single chain glycoprotein. Activated by plasmin, kallikrein and XII,. Inhibited by antithrombin III (inhibition accelerated by heparin). Cl esterase inhibitor and lima bean trypsin inhibitor. Activation of XII initiated by contact with abnormal surfaces. 

Dorresteijn MJ, Visser T, Cox LA, Bouw MP, Pillay J, Koenderman AH, Strengers PF, Leenen LP, van der Hoeven JG, Koenderman L, Pickkers P. Cl-esterase inhibitor attenuates the inflammatory response during human endotoxemia. Crit Care Med 2010 38(11) 2139-45. 

Individuals with hereditary angioneurotic oedema lack serum CT-esterase inhibitor, the inhibitor of the activated first component of hemolytic complement. During an acute episode of this disorder circulating CT-esterase, which is a permeability-increasing factor in human skin, is markedly increased [57, 97, 140, 142, 219, 332]. It is unlikely that a similar mechanism is involved in the anaphylactoid reaction in rats as reactivity is not an absolute phenomenon [32-34, 274]. The final inflammatory mediator(s) of the reaction is, therefore, available for release in both reactor and non-reactor rats. This implies that the trigger mechanism or some intermediary step in the reaction is different in the two types of rat. 

Despite cases of transmission of hepatitis C associated with intravenous immunoglobulin in the 1990s, no cases of transmission of hepatitis, HIV, or Creutzfeldt-Jakob disease have since been reported with immunoglobulins [6 J. Before 1996, PCCs (prothrombin complex concentrates) were associated with minimal risk of transmission of infective agents [7 ]. There are no documented cases of viral transmission in patients with von Willebrand disease or hemophilia A treated with Haemate P/Humate P in over 25 years of clinical experience in Europe and more than 17 years in the USA [ ]. In the IMPACT-1 and IMPACT-2 trial in 124 patients there were no cases of HIV, hepatitis, or human B19 virus conversion. Furthermore, no cases of viral transmission have been reported during 30 years of post-marketing surveillance of Cl-esterase inhibitor concentrate [9, 10 ]. 

Keating GM. Human Cl-esterase inhibitor concentrate (Berinert). BioDrugs 2009 23 (6) 399 06. 

Craig TJ, Levy RJ, Wasserman RL, Bewtra AK, Hurewitz D, Obtulowicz K, Reshef A, Ritchie B, Moldovan D, Shirov T, Grivcheva-Panovska V, Kiessling PC, Keinecke HO, Bernstein JA. Efficacy of human Cl esterase inhibitor concentrate compared with placebo in acute hereditary angioedema attacks. J Allergy Clin Immunol 2009 124(4) 801-8. 

Riedl MA, Hurewitz DS, Levy R, Busse PJ, Fitts D, Kalfus 1. Nanofiltered Cl esterase inhibitor (human) for the treatment of acute attacks of hereditary angioedema an open-label trial. Ann allergy, asthma Immimol official Publ Am CoU Allergy, Asthma, Immunol January 2012 108(l) 49-53. 

Studies of the carcinogenicity of PG in a human leukemia cell line have suggested that gallic acid plays an important role in this effect since it is more easily oxidized than PG [11]. However, when rat hepatocytes were incubated with the esterase inhibitor diazinon, the cytotoxic effects of PG were enhanced. These results suggest that the hepatotoxicity of PG was not mediated by its metabolites [3]. 

Y. Kurono, N. Ohta, T. Yotsuyanagj, K. Ikeda, Effects of Drug Binding on the Esterase-Like Activity of Human Serum Albumin. III. Evaluation of the Two Active Sites by Using Clofibric Acid as an Inhibitor , Chem. Pharm. Bull. 1981, 29, 2345 - 2350. 

For example, the hydrolysis of phenyl acetate (7.15) by carboxylesterase isozymes was investigated over a broad pH range, allowing many insights into their catalytic mechanisms [30] (see Chapt. 3). This substrate was also used together with various inhibitors to characterize esterases in human and rat tissues [31], Thus, the approximate values of Km (in pM) and Vmax (in pmol min 1 (g tissue)-1) in human tissues were 300 and 60 in liver micro-somes, 200 and 40 in liver cytosol, and 1500 and 250 in plasma, respective-... 

The resolution of racemic FTC butyrate (34) was required for the synthesis of the antiviral drug emtricitabine (Emtriva) (Scheme 7.15) a nucleoside reverse transcriptase inhibitor targeted for treatment of human immunodeficiency virus (HIV) and hepatitis infections [35]. The racemic FTC butyrate ester (34) was treated with immobilized cholesterol esterase, which cleaved the required isomer to the corresponding alcohol (-) 35 with 91% and 52% conversion [36]. The product was isolated as the hydrochloride salt to give 31% yield (98% ) from the 8 kg demonstration. The esterase was immobilized by precipitation onto an accurel polypropylene support using acetone followed by cross linking with glutaralde-... 

Esterase activity is important in both the detoxication of organophosphates and the toxicity caused by them. Thus brain acetylcholinesterase is inhibited by organophosphates such as paraoxon and malaoxon, their oxidized metabolites (see above). This leads to toxic effects. Malathion, a widely used insecticide, is metabolized mostly by carboxylesterase in mammals, and this is a route of detoxication. However, an isomer, isomalathion, formed from malathion when solutions are inappropriately stored, is a potent inhibitor of the carboxylesterase. The consequence is that such contaminated malathion becomes highly toxic to humans because detoxication is inhibited and oxidation becomes important. This led to the poisoning of 2800 workers in Pakistan and the death of 5 (see chap. 5 for metabolism and chap. 7 for more details). 

Figure 9.17. Organophosphate inhibitors of acetylcholinesterase. a The catalytic mechanism, shown here for diiso-propylfluorophosphate(DFP).b Stmcturesof soman and tabun. Like DFP, these were developed during world war II as nerve gases , c Stractures of the insecticides parathion and malathion, and of paraoxon, which is the achve metabolite of parathion. (Malathion likewise requires conversion to malaoxon.) The arrow above the malathione stmcture indicates the esterase cleavage sites in its leaving group esterase cleavage occurs in human plasma and renders the molecule non-toxic.

The wide use of cholinesterase inhibitors in various spheres of human activities and the risk of acute and chronic intoxications associated with this process prompted investigation of the role of acetylcholinesterase (AChE) and nonspecific esterases in the immunotropic effects of these chemicals. They irreversibly bind to AChE that normally catalyzes the hydrolysis of acetylcholine (ACh) at the... 

In the presence of human serum albumin, the H spectrum of acetyl-salicyclic acid is specifically shifted and broadened [119]. The interpretation of changes in T, and T2 require several theoretical assumptions. These have been discussed in detail [120] for JV-acetylsulphanilamide and acetate binding to the active site of carbonic anhydrase. It was concluded that the acetyl groups of these inhibitors have a motion additional to that of the enzyme. It can be shown by NMR that acetate binds to two sites on the enzyme, only one of which is inhibitory to esterase activity (methyls are 4.3 and 4.8 A from the metal in the Mn substituted enzyme [121]). Strict care must be taken to avoid paramagnetic impurities when NMR relaxation enhancement by diamagnetic macromolecules is being studied. A preparation of carbonic anhydrase, for example, can contain 0.24 paramagnetic Cu atoms per Zn atom [122]. 

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