LncRNA KCNQ1OT1 ameliorates the liver injury induced by acetaminophen through the regulation of miR-122-5p/CES2 axis.

Long noncoding RNAs (lncRNAs) have been shown to be implicated in acetaminophen (APAP)-induced liver injury (AILI). We applied this study to investigate the role and functional mechanism of KCNQ1 overlapping transcript 1 (KCNQ1OT1) in AILI. The AILI model was established by APAP treatment in mice. The liver injury was preliminarily evaluated by ALT and AST activities via the detection kits. The quantitative real-time polymerase chain reaction (qRT-PCR) was exploited for detecting the expression of KCNQ1OT1, microRNA-122-5p (miR-122-5p), and carboxylesterase 2 (CES2). Protein levels were analyzed via Western blot. 3-(4, 5-dimethylthiazol-2-y1)-2, 5-diphenyl tetrazolium bromide (MTT) assay, and flow cytometry were separately applied to determine cell proliferation and apoptosis rate. Inflammation was assessed by enzyme-linked immunosorbent assay (ELISA). Dual-luciferase reporter assay was implemented to testify the intergenic combination. The function of KCNQ1OT1 in vivo was explored through KCNQ1OT1 knockdown in mice. APAP triggered the downregulation of KCNQ1OT1 and CES2 in mice serums. KCNQ1OT1 upregulation could relieve the AILI in HepaRG cells, which were abrogated by CES2 downregulation. KCNQ1OT1 served as a sponge of miR-122-5p and miR-122-5p directly targeted CES2. KCNQ1OT1 overexpression abated the AILI through the miR-122-5p/CES2 axis in HepaRG cells in vitro and mice in vivo. The collective results clarified that KCNQ1OT1 weakened the AILI in vitro and in vivo by the miR-122-5p/CES2 axis, providing an explicit molecular mechanism and selectable therapeutic strategy of AILI.

Ketamine as adjunct to midazolam treatment following soman-induced status epilepticus reduces seizure severity, epileptogenesis, and brain pathology in plasma carboxylesterase knockout mice.

Delayed treatment of cholinergic seizure results in benzodiazepine-refractory status epilepticus (SE) that is thought, at least in part, to result from maladaptive trafficking of N-methyl-d-aspartate (NMDA) and gamma-aminobutyric acid type A (GABAA) receptors, the effects of which may be ameliorated by combination therapy with the NMDA receptor antagonist ketamine. Our objective was to establish whether ketamine and midazolam dual therapy would improve outcome over midazolam monotherapy following soman (GD) exposure when evaluated in a mouse model that, similar to humans, lacks plasma carboxylesterase, greatly reducing endogenous scavenging of GD. In the current study, continuous cortical electroencephalographic activity was evaluated in male and female plasma carboxylesterase knockout mice exposed to a seizure-inducing dose of GD and treated with midazolam or with midazolam and ketamine combination at 40 min after seizure onset. Ketamine and midazolam combination reduced GD-induced lethality, seizure severity, and the number of mice that developed spontaneous recurrent seizure (SRS) compared with midazolam monotherapy. In addition, ketamine-midazolam combination treatment reduced GD-induced neuronal degeneration and microgliosis. These results support that combination of antiepileptic drug therapies aimed at correcting the maladaptive GABAA and NMDA receptor trafficking reduces the detrimental effects of GD exposure. Ketamine may be a beneficial adjunct to midazolam in reducing the epileptogenesis and neuroanatomical damage that follows nerve agent exposure and pharmacoresistant SE.

Purification of a chymotrypsin-like enzyme present on adult Schistosoma mansoni worms from infected mice and its characterization as a host carboxylesterase.

A serine protease-like enzyme found in detergent extracts of Schistosoma mansoni adult worms perfused from infected mice has been purified from mouse blood and further characterized. The enzyme is approximately 85 kDa and hydrolyses N-acetyl-DL-phenylalanine ß-naphthyl-ester, a chromogenic substrate for chymotrypsin-like enzymes. The enzyme from S. mansoni worms appears to be antigenically and enzymatically similar to a molecule that is present in normal mouse blood and so is seemingly host-derived. The enzyme was partially purified by depleting normal mouse serum of albumin using sodium chloride and cold ethanol, followed by repeated rounds of purification by one-dimensional sodium dodecyl sulphate polyacrylamide gel electrophoresis. The purified material was subjected to tandem mass spectrometry and its derived peptides found to belong to mouse carboxylesterase 1C. Its ability to hydrolyse α- or ß-naphthyl acetates, which are general esterase substrates, has been confirmed. A similar carboxylesterase was purified and characterized from rat blood. Additional evidence to support identification of the enzyme as a carboxylesterase has been provided. Possible roles of the enzyme in the mouse host-parasite relationship could be to ease the passage of worms through the host's blood vessels and/or in immune evasion.

Hormone-dependence of sarin lethality in rats: Sex differences and stage of the estrous cycle.

Chemical warfare nerve agents (CWNAs) are highly toxic compounds that cause a cascade of symptoms and death, if exposed casualties are left untreated. Numerous rodent models have investigated the toxicity and mechanisms of toxicity of CWNAs, but most are limited to male subjects. Given the profound physiological effects of circulating gonadal hormones in female rodents, it is possible that the daily cyclical fluctuations of these hormones affect females' sensitivity to the lethal effects of CWNAs, and previous reports that included female subjects did not control for the stage of the hormonal cycle. The aim of the current study was to determine the 24-hour median lethal dose (LD50) of the CWNA sarin in male, ovariectomized (OVEX) female, and female rats during different stages of the estrous cycle (diestrus, proestrus, and estrus). Additionally, baseline activity levels of plasma acetylcholinesterase, butyrylcholinesterase, and carboxylesterase were measured to determine differences among the groups. Results indicated that females in proestrus had a significantly higher LD50 of sarin compared to OVEX and estrous females. Although some sex differences were observed in the activity levels of plasma esterases, they were not consistent and likely not large enough to significantly affect the LD50s. These results suggest that hormonal cyclicity can influence the outcome of CWNA-related studies using female rodents, and that this variability can be minimized by controlling for the stage of the cycle. Additional research is necessary to determine the precise mechanism of the observed differences because it is unlikely to be solely explained by plasma esterase activity.

P-glycoprotein, CYP3A, and Plasma Carboxylesterase Determine Brain Disposition and Oral Availability of the Novel Taxane Cabazitaxel (Jevtana) in Mice.

We aimed to clarify the roles of the multidrug-detoxifying proteins ABCB1, ABCG2, ABCC2, and CYP3A in oral availability and brain accumulation of cabazitaxel, a taxane developed for improved therapy of docetaxel-resistant prostate cancer. Cabazitaxel pharmacokinetics were studied in Abcb1a/1b, Abcg2, Abcc2, Cyp3a, and combination knockout mice. We found that human ABCB1, but not ABCG2, transported cabazitaxel in vitro. Upon oral cabazitaxel administration, total plasma levels were greatly increased due to binding to plasma carboxylesterase Ces1c, which is highly upregulated in several knockout strains. Ces1c inhibition and in vivo hepatic Ces1c knockdown reversed these effects. Correcting for Ces1c effects, Abcb1a/1b, Abcg2, and Abcc2 did not restrict cabazitaxel oral availability, whereas Abcb1a/1b, but not Abcg2, dramatically reduced cabazitaxel brain accumulation (>10-fold). Coadministration of the ABCB1 inhibitor elacridar completely reversed this brain accumulation effect. After correction for Ces1c effects, Cyp3a knockout mice demonstrated a strong (six-fold) increase in cabazitaxel oral availability, which was completely reversed by transgenic human CYP3A4 in intestine and liver. Cabazitaxel markedly inhibited mouse Ces1c, but human CES1 and CES2 only weakly. Ces1c upregulation can thus complicate preclinical cabazitaxel studies. In summary, ABCB1 limits cabazitaxel brain accumulation and therefore potentially therapeutic efficacy against (micro)metastases or primary tumors positioned wholly or partly behind a functional blood-brain barrier. This can be reversed with elacridar coadministration, and similar effects may apply to ABCB1-expressing tumors. CYP3A4 profoundly reduces the oral availability of cabazitaxel. This may potentially be greatly improved by coadministering ritonavir or other CYP3A inhibitors, suggesting the option of patient-friendly oral cabazitaxel therapy.

A human life-stage physiologically based pharmacokinetic and pharmacodynamic model for chlorpyrifos: development and validation.

Sensitivity to some chemicals in animals and humans are known to vary with age. Age-related changes in sensitivity to chlorpyrifos have been reported in animal models. A life-stage physiologically based pharmacokinetic and pharmacodynamic (PBPK/PD) model was developed to predict disposition of chlorpyrifos and its metabolites, chlorpyrifos-oxon (the ultimate toxicant) and 3,5,6-trichloro-2-pyridinol (TCPy), as well as B-esterase inhibition by chlorpyrifos-oxon in humans. In this model, previously measured age-dependent metabolism of chlorpyrifos and chlorpyrifos-oxon were integrated into age-related descriptions of human anatomy and physiology. The life-stage PBPK/PD model was calibrated and tested against controlled adult human exposure studies. Simulations suggest age-dependent pharmacokinetics and response may exist. At oral doses ⩾0.6mg/kg of chlorpyrifos (100- to 1000-fold higher than environmental exposure levels), 6months old children are predicted to have higher levels of chlorpyrifos-oxon in blood and higher levels of red blood cell cholinesterase inhibition compared to adults from equivalent doses. At lower doses more relevant to environmental exposures, simulations predict that adults will have slightly higher levels of chlorpyrifos-oxon in blood and greater cholinesterase inhibition. This model provides a computational framework for age-comparative simulations that can be utilized to predict chlorpyrifos disposition and biological response over various postnatal life stages.

Mouse serum paraoxonase-1 lactonase activity is specific for medium-chain length fatty acid lactones.

Recent studies suggest that paraoxonase-1 (PON1), complexed with high-density lipoproteins, is the major lactonase in the circulation. Using 5-hydroxy eicosatetraenoate δ-lactone (5-HETEL) as the substrate, we observed lactonase activity in serum from Pon1-/- mice. However, 6-12 carbon fatty acid γ- and δ-lactones were not hydrolyzed in serum from Pon1-/- mice. Serum from both wild-type and Pon1-/- mice contained a lactonase activity towards 5-HETEL and 3-oxo-dodecanoyl-homoserine lactone that was resistant to inactivation by EDTA. This lactonase activity was sensitive to the serine esterase inhibitor phenyl methyl sulfonyl fluoride and co-eluted with carboxylesterase activity by size-exclusion chromatography. Analysis of serum from the Es1e mouse strain, which has a deficiency in the carboxylesterase, ES-1, proved that this activity was due to ES-1. PON1 activity predominated at early time points (30 s), whereas both PON1 and ES-1 contributed equally at later time points (15 min). When both PON1 and ES-1 were inhibited, 5-HETEL was stable in mouse serum. Thus, while long-chain fatty acid lactones are substrates for PON1, they can be hydrolyzed by ES-1 at neutral pH. In contrast, medium-chain length fatty acid lactones are stable in mouse serum in the absence of PON1, suggesting that PON1 plays a specific role in the metabolism of these compounds.

Prolonged toxic effects after cocaine challenge in butyrylcholinesterase/plasma carboxylesterase double knockout mice: a model for butyrylcholinesterase-deficient humans.

Death and toxicity after cocaine use do not correlate with cocaine blood levels. One explanation for this observation is that cocaine abusers may posses one or more of the 58 possible known mutations in the butyrylcholinesterase gene (BCHE). Butyrylcholinesterase (BChE) serves as the primary cocaine hydrolase producing a nontoxic product ecgonine methyl ester. A reduction in endogenous levels of BChE may result in increased metabolism by hepatic carboxylesterase to produce norcocaine, a toxic product. Humans have carboxylesterase in tissues but not in plasma, whereas wild-type mice have significant amounts of carboxylesterase in tissues and plasma. Knockout mice with no plasma carboxylesterase were created to eliminate the contribution of plasma carboxylesterase in cocaine hydrolysis, thereby simulating human enzyme levels. This study tested the hypothesis that reductions in BChE such as those in humans with BChE mutations contribute to increased toxicity after cocaine use. Carboxylesterase and BChE double knockout mice, models for humans with BChE deficiency, were challenged with a nonlethal dose of 100 mg/kg (-)-cocaine. Carboxylesterase/BChE double knockout mice demonstrated toxic signs significantly longer than did wild-type and carboxylesterase knockout mice. The carboxylesterase/BChE-deficient mice took approximately 2.5 times as long to recover from cocaine toxicities, including the following: hypothermia, hyperactivity, stereotypical behavior, ocular effects, and dorsiflexion of the tail. The carboxylesterase/BChE double knockout mouse model demonstrates the importance of endogenous BChE for protection against cocaine toxicity and provides an in vivo system for studying drug sensitivity of humans who carry a BChE mutation.

B-esterase activities and blood cell morphology in the frog Leptodactylus chaquensis (Amphibia: Leptodactylidae) on rice agroecosystems from Santa Fe Province (Argentina).

Activity of B-esterases (BChE: butyrylcholinesterase and CbE: carboxylesterase using two model substrates: α-naphthyl acetate and 4-nitrophenyl valerate) in a native frog, Leptodactylus chaquensis from rice fields (RF1: methamidophos and RF2: cypermethrin and endosulfan sprayed by aircraft) and non-contaminated area (pristine forest) was measured. The ability of pyridine-2-aldoxime methochloride (2-PAM) to reactivate BChE levels was also explored. In addition, changes in blood cell morphology and parasite infection were determined. Mean values of plasma BChE activities were lower in samples from the two rice fields than in those from the reference site. CbE (4-nitrophenyl valerate) levels varied in the three sites studied, being highest in RF1. Frog plasma from RF1 showed positive reactivation of BChE activity after incubation with 2-PAM. Blood parameters of frogs from RF2 revealed morphological alterations (anisochromasia and immature erythrocytes frequency). Moreover, a major infection of protozoan Trypanosoma sp. in individuals from the two rice fields was detected. We suggest that integrated use of several biomarkers (BChE and CBEs, chemical reactivation of plasma with 2-PAM, and blood cell parameters) may be a promising procedure for use in biomonitoring programmes to diagnose pesticide exposure of wild populations of this frog and other native anuran species in Argentina.

Comparative analysis of esterase activities of human, mouse, and rat blood.

Acetylcholinesterase, butyrylcholinesterase, carboxylesterase, and paraoxonase activities in human, mouse, and rat blood were measured. The proportions of these enzymes activities differed significantly. In humans, the most significant were cholinesterase activities, while in rats and mice the contribution of carboxylesterase activity was the greatest. High arylesterase activity of paraoxonase was observed in all cases. Species-specific differences should be taken into consideration when carrying out preclinical trials on rodents for optimization of the pharmacokinetic characteristics of drugs containing complex ester groups.

In vitro age-related differences in rats to organophosphates.

The mechanism of toxic action for organophosphates (OPs) is the persistent inhibition of acetylcholinesterase (AChE) resulting in accumulation of acetylcholine and subsequent hyperstimulation of the nervous system. Organophosphates display a wide range of acute toxicities. Differences in the OP's chemistries results in differences in the compound's metabolism and toxicity. Acute toxicities of OPs appear to be principally dependent on compound specific efficiencies of detoxication, and less dependent upon efficiencies of bioactivation and sensitivity of AChE. Serine esterases, such as carboxylesterase (CaE) and butyrylcholinesterase (BChE), play a prominent role in OP detoxication. Organophosphates can stoichiometrically inhibit these enzymes, removing OPs from circulation thus providing protection for the target enzyme, AChE. This in vitro study investigated age-related sensitivity of AChE, BChE and CaE to twelve structurally different OPs in rat tissues. Sensitivity of esterases to these OPs was assessed by inhibitory concentration 50s (IC50s). The OPs displayed a wide range of inhibitory potency toward AChE with IC50s in the low nM-µM range with no differences among ages; however, the CaE IC50s generally increased with age reflecting greater protection in adults. These results suggest age-related differences in acute toxicities of OPs in mammals are primarily a result of their detoxication capacities.

The intestinal lymph fistula model--a novel approach to study ghrelin secretion.

The orexigenic hormone ghrelin is secreted from the stomach and has been implicated in the regulation of energy and glucose homeostasis. We hypothesized that ghrelin, like other gastrointestinal (GI) hormones, is present in intestinal lymph, and sampling this compartment would provide advantages for studying ghrelin secretion in rodents. Blood and lymph were sampled from catheters in the jugular vein and mesenteric lymph duct before and after intraduodenal (ID) administration of isocaloric Ensure, dextrin, or Liposyn meals or an equal volume of saline in conscious Sprague-Dawley rats. Total ghrelin levels were measured using an established radioimmunoassay. Acyl and des-acyl ghrelin were measured using two-site ELISA. Fasting ghrelin levels in lymph were significantly higher than in plasma (means +/- SE: 3,307.9 +/- 272.9 vs. 2,127.1 +/- 115.0 pg/ml, P = 0.004). Postingestive acyl and des-acyl ghrelin levels were also significantly higher, whereas the ratio of acyl:des-acyl ghrelin was similar in lymph and plasma (0.91 +/- 0.28 vs. 1.20 +/- 0.36, P = 0.76). The principle enzymes responsible for deacylation of ghrelin were lower in lymph than in plasma. Following ID Ensure, maximum ghrelin suppression occurred at 2 h in lymph compared with at 1 h in plasma. The return of suppressed ghrelin levels to baseline was also delayed in lymph. Similarly, dextrin also induced significant suppression of ghrelin (two-way ANOVA: P = 0.02), whereas Liposyn did not (P = 0.32). On the basis of these findings, it appears that intestinal lymph, which includes drainage from the interstitium of the GI mucosa, is enriched in ghrelin. Despite reduced deacylating activity in lymph, there is not a disproportionate amount of acyl ghrelin in this pool. The postprandial dynamics of ghrelin are slower in lymph than plasma, but the magnitude of change is greater. Assessing ghrelin levels in the lymph may be advantageous for studying its secretion and concentrations in the gastric mucosa.

[Chronic occupational bronchitis in workers of coal extracting enterprises in Kouzbass: role of endogenous factors].

The authors studied distribution of biochemical markers for HP, GC, EsD, AcP genes, polymorphism of GSTT1 (GST-theta 1), GSTM1 (GST-mu 1), locus WNTR of NOS3 gene (alleles A/B) in chronic dust bronchitis patients and in apparently healthy individuals. Genotypes EsD 1-2 and AcP bb individuals were proved to be most prone to the disease. Endogenous resistent factors for chronic dust bronchitis are genotypes GC 1-1, EsD 1-1, AcP bc.

Characterization of an equine macrophage cell line: application to studies of EIAV infection.

EIAV is a monocyte/macrophage tropic virus. To date, even though EIAV has been under investigation for numerous years, very few details have been elucidated about EIAV/macrophage interactions. This is largely due to the absence of an equine macrophage cell line that would support viral replication. Herein we describe the spontaneous immortalization and generation of a clonal equine macrophage-like (EML) cell line with the functional and immunophenotype characteristics of differentiated equine monocyte derived macrophage(s) (eMDM(s)). These cells possess strong non-specific esterase (NSE) activity, are able to phagocytose fluorescent bioparticles, and produce nitrites in response to LPS. The EML-3C cell line expresses the EIAV receptor for cellular entry (ELR1) and supports replication of the virulent EIAV(PV) biological clone. Thus, EML-3C cells provide a useful cell line possessing equine macrophage related properties for the growth and study of EIAV infection as well as of other equine macrophage tropic viruses.

Decreased serum levels of carboxylesterase-2 in patients with ovarian cancer.

AIMS AND BACKGROUND: Carboxylesterase-2 has been identified as the key enzyme in the metabolic activation ofirinotecan, a topoisomerase I inhibitor commonly used in the treatment of many solid tumors. Previous studies have shown that carboxylesterase-2 is down-regulated in colorectal cancer following progression of the disease. However, very limited information is available on carboxylesterase-2 expression in ovarian cancer. The aim of the present study was to detect the serum level and the tissue expression of carboxylesterase-2 in human ovarian cancer patients at different stages of the disease. METHODS: Carboxylesterase-2 levels in the serum of ovarian cancer patients were investigated by western blot and ELISA and in the tumor mass of ovarian cancer patients by western blot. RESULTS: Both the serum carboxylesterase-2 level and the expression of carboxylesterase-2 in tumor tissues were significantly different among patients at different stages of the disease (n = 40). No positive correlation was found between the serum carboxylesterase-2 level and the cancer antigen 125 level (n = 40). Serum carboxylesterase-2 is more sensitive than cancer antigen 125 in detecting the early stage patient with ovarian cancer. CONCLUSIONS: Our results indicate that serum carboxylesterase-2 level might be a potential marker in the diagnosis of the early stage ovarian cancer.

An age-dependent physiologically based pharmacokinetic/pharmacodynamic model for the organophosphorus insecticide chlorpyrifos in the preweanling rat.

Juvenile rats are more susceptible than adults to the acute toxicity of organophosphorus insecticides like chlorpyrifos (CPF). Age- and dose-dependent differences in metabolism may be responsible. Of importance are CYP450 activation and detoxification of CPF to chlorpyrifos-oxon (CPF-oxon) and trichloropyridinol (TCP), as well as B-esterase (B-est) and PON-1 (A-esterase) detoxification of CPF-oxon to TCP. In the current study, a physiologically based pharmacokinetic/pharmacodynamic (PBPK/PD) model incorporating age-dependent changes in CYP450, PON-1, and tissue B-est levels for rats was developed. In this model, age was used as a dependent function to estimate body weight which was then used to allometrically scale both metabolism and tissue cholinesterase (ChE) levels. In addition, age-dependent changes in brain, liver, and fat volumes and brain blood flow were obtained from the literature and used in the simulations. Model simulations suggest that preweanling rats are particularly sensitive to CPF toxicity, with levels of CPF-oxon in blood and brain disproportionately increasing, relative to the response in adult rats. This age-dependent nonlinear increase in CPF-oxon concentration may potentially result from both the depletion of nontarget B-est and a lower PON-1 metabolic capacity in younger animals. The PBPK/PD model behaves consistently with the general understanding of CPF toxicity, pharmacokinetics, and tissue ChE inhibition in neonatal and adult rats. Hence, this model represents an important starting point for developing a computational model to assess the neurotoxic potential of environmentally relevant organophosphate exposures in infants and children.

In Vitro-In Vivo Extrapolation of Intestinal Availability for Carboxylesterase Substrates Using Portal Vein-Cannulated Monkey.

Prediction of intestinal availability (FaFg) of carboxylesterase (CES) substrates is of critical importance in designing oral prodrugs with optimal properties, projecting human pharmacokinetics and dose, and estimating drug-drug interaction potentials. A set of ester prodrugs were evaluated using in vitro permeability (parallel artificial membrane permeability assay and Madin-Darby canine kidney cell line-low efflux) and intestinal stability (intestine S9) assays, as well as in vivo portal vein-cannulated cynomolgus monkey. In vitro-in vivo extrapolation (IVIVE) of FaFg was developed with a number of modeling approaches, including a full physiologically based pharmacokinetic (PBPK) model as well as a simplified competitive-rate analytical solution. Both methods converged as in the PBPK simulations enterocyte blood flow behaved as a sink, a key assumption in the competitive-rate analysis. For this specific compound set, the straightforward analytical solution therefore can be used to generate in vivo predictions. Strong IVIVE of FaFg was observed for cynomolgus monkey with R2 of 0.71-0.93. The results suggested in vitro assays can be used to predict in vivo FaFg for CES substrates with high confidence.

Tissue-infiltrating plasma cells are an important source of carboxylesterase 2 contributing to the therapeutic efficacy of prodrugs.

Carboxylesterase 2 (CES-2) is instrumental for conversion of ester-containing prodrugs in cancer treatment. CES-2 expression was analyzed by immunohistochemistry in colorectal cancer (CRC) compared to colonic inflammation as well as in liver and peripheral blood. In CRC, tumor grades showed no correlation with levels of CES-2 expression, which was heterogeneous within these tumors. Cellular infiltrates in the immediate tumor vicinity expressed high levels of CES-2. Thus, tissue adjacent to the tumor was a substantial source of CES-2 with high expression in plasma cells. CES-2(high) plasma cells were abundantly found in the colon of patients with inflammatory bowel disease. CES-2 expression is strong in hepatocytes of normal livers, while CES-2 expression in peripheral blood mononuclear cells of healthy donors was overall low at protein and mRNA levels. In summary, the conversion of ester-containing prodrugs by CES-2 is mainly to occur in the periphery, during liver passage and in the colon after enterohepatic recirculation. We here demonstrated plasma cells as strong producers of CES-2. Further studies should elucidate the role of CES-2(+) plasma cells in intestinal inflammation and cancer.

Butyrylcholinesterase, paraoxonase, and albumin esterase, but not carboxylesterase, are present in human plasma.

The goal of this work was to identify the esterases in human plasma and to clarify common misconceptions. The method for identifying esterases was nondenaturing gradient gel electrophoresis stained for esterase activity. We report that human plasma contains four esterases: butyrylcholinesterase (EC 3.1.1.8), paraoxonase (EC 3.1.8.1), acetylcholinesterase (EC 3.1.1.7), and albumin. Butyrylcholinesterase (BChE), paraoxonase (PON1), and albumin are in high enough concentrations to contribute significantly to ester hydrolysis. However, only trace amounts of acetylcholinesterase (AChE) are present. Monomeric AChE is seen in wild-type as well as in silent BChE plasma. Albumin has esterase activity with alpha- and beta-naphthylacetate as well as with p-nitrophenyl acetate. Misconception #1 is that human plasma contains carboxylesterase. We demonstrate that human plasma contains no carboxylesterase (EC 3.1.1.1), in contrast to mouse, rat, rabbit, horse, cat, and tiger that have high amounts of plasma carboxylesterase. Misconception #2 is that lab animals have BChE but no AChE in their plasma. We demonstrate that mice, unlike humans, have substantial amounts of soluble AChE as well as BChE in their plasma. Plasma from AChE and BChE knockout mice allowed identification of AChE and BChE bands without the use of inhibitors. Human BChE is irreversibly inhibited by diisopropylfluorophosphate, echothiophate, and paraoxon, but mouse BChE spontaneously reactivates. Since human plasma contains no carboxylesterase, only BChE, PON1, and albumin esterases need to be considered when evaluating hydrolysis of an ester drug in human plasma.

Efficacy of trimedoxime in mice poisoned with dichlorvos, heptenophos or monocrotophos.

The aim of the study was to examine antidotal potency of trimedoxime in mice poisoned with three direct dimethoxy-substituted organophosphorus inhibitors. In order to assess the protective efficacy of trimedoxime against dichlorvos, heptenophos or monocrotophos, median effective doses and efficacy half-times were calculated. Trimedoxime (24 mg/kg intravenously) was injected 5 min. before 1.3 LD50 intravenously of poisons. Activities of brain, diaphragmal and erythrocyte acetylcholinesterase, as well as of plasma carboxylesterases were determined at different time intervals (10, 40 and 60 min.) after administration of the antidotes. Protective effect of trimedoxime decreased according to the following order: monocrotophos > heptenophos > dichlorvos. Administration of the oxime produced a significant reactivation of central and peripheral acetylcholinesterase inhibited with dichlorvos and heptenophos, with the exception of erythrocyte acetylcholinesterase inhibited by heptenophos. Surprisingly, trimedoxime did not induce reactivation of monocrotophos-inhibited acetylcholinesterase in any of the tissues tested. These organophosphorus compounds produced a significant inhibition of plasma carboxylesterase activity, while administration of trimedoxime led to regeneration of the enzyme activity. The same dose of trimedoxime assured survival of experimental animals poisoned by all three organophosphorus compounds, although the biochemical findings were quite different.