Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.1.1.7 (acetylcholinesterase)
 28,390 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Evidence based on thermal lability and enzyme inhibition data suggests that the sulfoxidation of methiocarb (an N-methylcarbamate insecticide) by rat liver microsomes is catalyzed by flavin-containing monooxygenase(s) (FMO) and by cytochrome(s) P450 (P450). In control rats, the relative proportion is ca. 50% P450:50% FMO. Stereoselective formation of methiocarb sulfoxide from the corresponding sulfide has also been examined to compare the enantioselectivity of the two different enzyme systems. Only the FMO-dependent sulfoxidation presents a high stereoselectivity with an enantiomeric excess of 88% in favor of the (A)-enantiomer. Pretreatment of rats with different P450 inducers such as phenobarbital, 3-methylcholanthrene, dexamethasone, and pyrazole did not affect, or decreased, the rate of methiocarb sulfoxidation. Stereoselectivity of the reaction was modified, mainly because of changes in the relative involvement of FMO and P450 in sulfoxidase activity in pretreated animals. The acetylcholinesterase inhibition properties of methiocarb and its main metabolites were also investigated. Racemic methiocarb sulfoxide was slightly less inhibitory (Ki = 0.216 microM-1.min-1) than methiocarb, but a 10-fold difference was observed between the bimolecular rate constants found for the two sulfoxides produced (0.054 and 0.502 microM-1.min-1 for the (A) and (B) enantiomers, respectively).
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PMID:Stereoselective sulfoxidation of the pesticide methiocarb by flavin-containing monooxygenase and cytochrome P450-dependent monooxygenases of rat liver microsomes. Anticholinesterase activity of the two sulfoxide enantiomers. 856 32

In an attempt to understand underlying mechanism(s) of salinity-induced aldicarb toxicity in Japanese medaka (Oryzias latipes), aldicarb uptake, biotransformation, and its effect on acetylcholinesterase (AChE) were examined. Salinity had no effect on aldicarb uptake. However, gill microsomal flavin-containing monooxygenase (FMO) activity and a 57-kDa FMO1-like protein increased as the salinity was raised from 0.15 to 2.0%. Sulfoxidation of 14C-aldicarb by liver and gill microsomal incubations showed ninefold and 1.8-fold increases, respectively, as the salinity was raised from 0.15 to 2.0%. Formation of aldicarb sulfoxide was not affected by incubation with carbon monoxide, indicating that cytochrome P450 (CYP450) was not a primary pathway in the formation of the sulfoxide. Muscle AChE activity showed no significant relationship with salinity, although the IC50 of aldicarb to muscle AChE differed significantly between 6.21 +/- 1. 253 and 2.97 +/- 0.597 microM for 0.15 and 2.0% salinity, respectively. Aldicarb sulfoxide was 40 times more potent than aldicarb in inhibiting muscle AChE in Japanese medaka. Based on these results, we conclude that salinity-induced enhancement of aldicarb toxicity to Japanese medaka might be partly attributed to the upregulation of FMO(s), which, in turn, increase the biotransformation of aldicarb to aldicarb sulfoxide, which is a more potent inhibitor of AChE than aldicarb. In addition, salinity also seems to potentiate the anticholinesterase activity of aldicarb (the parent) through an unknown mechanism.
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PMID:Potential mechanisms of the enhancement of aldicarb toxicity to Japanese medaka, Oryzias latipes, at high salinity. 977 13

Fluctuations in several environmental variables, such as salinity, can influence the interactions between organisms and pollutants in aquatic organisms, and, therefore, affect the toxicity of xenobiotics. In this study, after 2 species of fish, rainbow trout (Oncorhynchus mykiss) and hybrid striped bass (Morone saxatilis x chrysops) were acclimated to 4 salinity regimens of 1.5, 7, 14, and 21 ppt for 1 week and then exposed to 0.5 mg/l aldicarb. Mortality, brain, and muscle cholinesterase levels were measured after 96 h. Rates of (14)C-aldicarb sulfoxide formation were determined in kidney (trout only), liver, and gill microsomes from each species acclimated to the 4 salinity regimens. Salinity significantly enhanced aldicarb toxicity, cholinesterase inhibition, and (14)C-aldicarb sulfoxide formation in rainbow trout but not in striped bass. In vitro incubations with (14)C-aldicarb and the cytochrome P450 (CYP) inhibitor, N-benzylimidazole, did not significantly alter aldicarb sulfoxide formation in tissue microsomes from either species of fish, indicating CYP did not contribute to aldicarb sulfoxidation. Salinity increased flavin-containing monooxygenase (FMO) mRNA expression and catalytic activities in microsomes of liver, gill, and kidney of rainbow trout, which was consistent with the salinity-induced enhancement of aldicarb toxicity. Salinity did not alter FMO mRNA expression and catalytic activities in striped bass, which was also consistent with the lack of an effect of salinity on aldicarb toxicity in this species. These results suggest that salinity-mediated enhancement of aldicarb toxicity is species-dependent, and at least partially due to the salinity-related upregulation of FMOs, which, in turn, increases the bioactivation of aldicarb to aldicarb sulfoxide, which is a more potent inhibitor of cholinesterase than aldicarb.
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PMID:Effects of salinity on aldicarb toxicity in juvenile rainbow trout (Oncorhynchus mykiss) and striped bass (Morone saxatilis x chrysops). 1171 2

Previous studies in our laboratory indicated gender differences in salinity-enhanced acute toxicity of aldicarb in Japanese medaka with females being more susceptible. In the current study, the effects of the sex steroids, 17beta estradiol (E2) and testosterone (T) on aldicarb toxicity was examined. Adult Japanese medaka were separated by sex and exposed to 100 microg/l E2 or T for 6 days followed by exposure to the 96-h LC50 (0.5 mg/l) of aldicarb. The toxicity of aldicarb to adult males was significantly lowered by E2 and T whereby the mortality percentage was reduced to 23.3 +/- 5.8% and 3.3 +/- 5.8%, respectively, compared to the fish not receiving steroids (46.7 +/- 5.8% mortality). In females, T caused significant reduction in aldicarb toxicity to 16.7 +/- 5.8%, while E2 significantly enhanced the toxicity to 96.7 +/- 5.8% mortality. Since the flavin-containing monooxygenase (FMO) enzyme system had been shown to play a critical role in aldicarb toxicity, the effect of E2 and T on FMO expression was examined. Gill FMO activity showed a direct correlation with the overall toxicity of aldicarb in both male and female medaka. Expression of FMO1-like protein was significantly reduced by T in male livers and gills, and T did not affect the expression of FMOs in female tissues. In contrast, E2 significantly reduced FMO1-like protein expression in male gills and female livers, as well as FMO3 expression in both male and female livers, but significantly increased gill FMO1 expression in females. Since aldicarb acts by inhibiting the enzyme cholinesterase (ChE), the effect of sex hormones on the activity of this enzyme was also examined. In both male and female medaka, T counteracted the inhibitory effect of aldicarb on muscle ChE. In male fish, E2 had similar effects but did not seem to counteract the ChE inhibition in females. In conclusion, E2 and T modulation of aldicarb toxicity in Japanese medaka seems to be mediated via alteration of gill FMO and ChE actitivies.
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PMID:Effect of 17beta-estradiol and testosterone on the expression of flavin-containing monooxygenase and the toxicity of aldicarb to Japanese medaka, Oryzias latipes. 1215 34

The flavin-containing monooxygenase gene family (FMO1-6) in humans encodes five functional isoforms that catalyze the monooxygenation of numerous N-, P- and S-containing drugs and toxicants. A previous single nucleotide polymorphism (SNP) analysis of FMO1 in African-Americans identified seven novel SNPs. To determine the functional relevance of the coding FMO1 variants (H97Q, I303V, I303T, R502X), they were heterologously expressed using a baculovirus system. Catalytic efficiency and stereoselectivity of N- and S-oxygenation was determined in the FMO1 variants using several substrates. The I303V variant showed catalytic constants equal to wild-type FMO1 for methimazole and methyl p-tolyl sulfide. Catalytic efficiency (V(max)/K(m)) of methyl p-tolyl sulfide oxidation by R502X was unaltered. In contrast, methimazole oxidation by R502X was not detected. Both H97Q and I303T had elevated catalytic efficiency with regards to methyl p-tolyl sulfide (162% and 212%, respectively), but slightly reduced efficiency with regards to methimazole (81% and 78%). All the variants demonstrated the same stereoselectivity for methyl p-tolyl sulfide oxidation as wild-type FMO1. FMO1 also metabolized the commonly used insecticide fenthion to its (+)-sulfoxide, with relatively high catalytic efficiency. FMO3 metabolized fenthion to its sulfoxide at a lower catalytic efficiency than FMO1 (27%) and with less stereoselectivity (74% (+)-sulfoxide). Racemic fenthion sulfoxide was a weaker inhibitor of acetylcholinesterase than its parent compound (IC(50) 0.26 and 0.015 mM, respectively). The (+)- and (-)-sulfoxides were equally potent inhibitors of acetylcholinesterase. These data indicate that all the currently known FMO1 variants are catalytically active, but alterations in kinetic parameters were observed.
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PMID:Evaluation of xenobiotic N- and S-oxidation by variant flavin-containing monooxygenase 1 (FMO1) enzymes. 1497 51

Phorate and disulfoton are organophosphate insecticides containing three oxidizable sulfurs, including a thioether. Previous studies have shown that only the thioether is oxygenated by flavin-containing monooxygenase (FMO) and the sole product is the sulfoxide with no oxygenation to the sulfone. The major FMO in lung of most mammals, including non-human primates, is FMO2. The FMO2*2 allele, found in all Caucasians and Asians genotyped to date, codes for a truncated, non-functional, protein (FMO2.2A). Twenty-six percent of individuals of African descent and 5% of Hispanics have the FMO2*1 allele, coding for full-length, functional protein (FMO2.1). We have here demonstrated that the thioether-containing organophosphate insecticides, phorate and disulfoton, are substrates for expressed human FMO2.1 with Km of 57 and 32 microM, respectively. LC/MS confirmed the addition of oxygen and formation of a single polar metabolite for each chemical. MS/MS analysis confirmed the metabolites to be the respective sulfoxides. Co-incubations with glutathione did not reduce yield, suggesting they are not highly electrophilic. As the sulfoxide of phorate is a markedly less effective acetylcholinesterase inhibitor than the cytochrome P450 metabolites (oxon, oxon sulfoxide or oxon sulfone), humans possessing the FMO2*1 allele may be more resistant to organophosphate-mediated toxicity when pulmonary metabolism is an important route of exposure or disposition.
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PMID:S-oxygenation of the thioether organophosphate insecticides phorate and disulfoton by human lung flavin-containing monooxygenase 2. 1529 58

Earlier reports have demonstrated that recombinant flavin-containing monooxygenase 1 (FMO1) catalyzes the oxidation of the organophosphate pesticide fenthion to (+)-fenthion sulfoxide in a stereoselective fashion. In order to elucidate the absolute configuration of the sulfoxide metabolite produced, we established an efficient synthesis of both enantiomers of fenthion sulfoxide, which were transformed into chiral fenoxon sulfoxides using a two-step protocol. The use of chiral oxidants, namely, N-(phenylsulfonyl)(3,3-dichlorocamphoryl) oxaziridines, afforded enantioenriched fenthion sulfoxides with high ee (>82%) from the parent sulfide. Single recrystallizations afforded chiral fenthion sulfoxides with >99% ee, measured by chiral HPLC analysis. The absolute configuration of the (+)-sulfoxide generated from fenthion metabolism by FMO1 was determined to be (R)-(+)-fenthion sulfoxide, confirmed by X-ray crystallographic analysis of the (S)-(-)-antipode. Inhibition of human recombinant (hrAChE) and electric eel (eeAChE) acetylcholinesterase were assayed with fenthion, fenoxon, and the racemates and enantiomers of fenthion sulfoxide and fenoxon sulfoxide. Results revealed stereoselective inhibition with (R)-(+)-fenoxon sulfoxide when compared with that of (S)-(-)-fenoxon sulfoxide (IC50 of 6.9 and 6.5 microM vs 230 and 111 microM in hrAChE and eeAChE, respectively). Fenthion sulfoxide (R or S enantiomers) did not present anti-AChE properties. Although the stereoselective sulfoxidation of fenthion to (R)-(+)-fenthion sulfoxide by FMO represents a detoxification pathway, the results of this study support the notion that subsequent oxidative desulfuration of (R)-(+)-fenthion sulfoxide (in vivo) may represent a critical bioactivation pathway, resulting in the production of (R)-(+)-fenoxon sulfoxide, a potent AChE inhibitor.
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PMID:Synthesis of fenthion sulfoxide and fenoxon sulfoxide enantiomers: effect of sulfur chirality on acetylcholinesterase activity. 1725 27