Phosphocalcic metabolism and its potential association with biomarkers of kidney disease in dogs with spontaneous hyperadrenocorticism.

The pathogenesis of increased serum phosphate concentration and proteinuria in dogs with spontaneous hyperadrenocorticism (HAC) is unclear. A potential link between proteinuria and calcium/phosphate metabolism has never been studied in dogs with HAC. The aims of the study were: (1) To evaluate calcium/phosphate metabolism in dogs with spontaneous HAC and compare to healthy dogs as well as to dogs with non-HAC illness; (2) to look for associations between markers of calcium/phosphate metabolism and biomarkers of kidney disease in dogs with HAC. Fifty-four dogs were included in the study, classified as HAC (n=27), non-HAC disease (n=17), and healthy (n=10). Serum calcium, phosphate, 25(OH)Vitamin D, 1,25(OH)2Vitamin D, plasma intact parathyroid hormone concentration (iPTH), FGF23, and urinary fractional excretion of calcium and phosphate were evaluated in all dogs at diagnosis and compared between each group. The correlation between these variables and urine protein-to-creatinine ratio (UPC) and urinary N-acetylglucosaminidase-to-creatinine ratio (uNAG/C) was evaluated in the HAC group. Medians [range] of serum phosphate concentration, urinary fractional excretion of calcium (FE(Ca)), and iPTH were significantly higher in dogs with HAC than in dogs with non-HAC illness (P<0.01) and healthy dogs (P<0.01). Increased 1,25(OH)2Vitamin D/25(OH)Vitamin D was also observed (P<0.001). In HAC group, UPC was significantly negatively correlated with 25(OH)Vitamin D (r(s): -0.54; P<0.01). Urinary NAG/C was significantly positively correlated with serum phosphate (r(s): 0.46; P=0.019). Increased serum phosphate, urinary excretion of calcium, and hyperparathyroidism were observed in dogs with HAC. Vitamin D metabolism may be shifted towards increased 1-alpha hydroxylation.

In vivo infectivity of liver extracts after resolution of hepadnaviral infection following therapy associating DNA vaccine and cytokine genes.

DNA-based vaccination appears of promise for chronic hepatitis B immunotherapy, although there is an urgent need to increase its efficacy. In this preclinical study, we evaluated the therapeutic benefit of cytokine (IL-2, IFN-γ) genes co-delivery with DNA vaccine targeting hepadnaviral proteins in the chronic duck hepatitis B virus (DHBV) infection model. Then, we investigated the persistence of replication-competent virus in the livers of apparently resolved animals. DHBV carriers received four injections of plasmids encoding DHBV envelope and core alone or co-delivered with duck IL-2 (DuIL-2) or duck IFN-γ (DuIFN-γ) plasmids. After long-term (8 months) follow-up, viral covalently closed circular (ccc) DNA was analysed in duck necropsy liver samples. Liver homogenates were also tested for in vivo infectivity in neonatal ducklings. Co-delivery of DuIFN-γ resulted in significantly lower mean viremia starting from week 21. Viral cccDNA was undetectable by conventional methods in the livers of 25% and 57% of animals co-immunized with DuIL-2 and DuIFN-γ, respectively. Interestingly, inoculation of liver homogenates from 7 such apparently resolved animals, exhibiting cccDNA undetectable in Southern blotting and DHBV expression undetectable or restricted to few hepatocytes, revealed that three liver homogenates transmitted high-titre viremia (3-5×10(10) vge/mL) to naïve animals. In conclusion, our results indicate that IFN-γ gene co-delivery considerably enhances immunotherapeutic efficacy of DNA vaccine targeting hepadnaviral proteins. Importantly, we also showed that livers exhibiting only minute amounts of hepadnaviral cccDNA could induce extremely high-titre infection, highlighting the caution that should be taken in occult hepatitis B patients to prevent HBV transmission in liver transplantation context.

Natural variability and response interpretation of fecundity, vertebrate-like sex-steroid levels and energy status in the New Zealand mudsnail Potamopyrgus antipodarum (Gray).

Potamopyrgus antipodarum is a promising test organism that is often used in ecotoxicology, both in laboratory and field exposures. As no data are available on the physiological variation range of its life-traits and the biomarkers it uses, we studied the variation of fecundity, steroid levels and energy reserves over the course of a year in a field population. The reproductive cycle was described and showed seasonal activity during summer and autumn. Steroid levels (17ß-estradiol and testosterone) varied significantly during the year and were correlated with the reproductive cycle, which suggested a potential role for sex-steroids in P. antipodarum reproduction. Energy status also showed seasonal variations. Triglycerides (TG) seemed to be the main energy lipid, whereas cholesterol appeared to be mostly used as a structural lipid. Proteins were also involved in the reproductive cycle, but only when TG were not sufficient to support the reproductive strain, similar to cholesterol. Glycogen seemed to be used as an early reserve. Threshold values under which no reproduction occurred were defined in starved snails. We proposed a range of variation in the measured parameters, allowing for a better understanding and interpretation of their levels during laboratory or in situ exposures. The data suggest that the variability of fecundity in snails has not been fully appreciated in literature.

Delimiting species boundaries within Dermanyssus Dugès, 1834 (Acari:Dermanyssidae) using a total evidence approach.

The genus Dermanyssus is currently composed of 24 hematophagous mite species and includes the Poultry Red Mite, Dermanyssus gallinae, a serious pest in poultry houses. Morphologically, Dermanyssus species fall into two groups corresponding to Moss'gallinae-group and to hirsutus-group+Microdermanyssus. Species of the gallinae-group exhibit high levels of morphological variability, and are nearly impossible to distinguish. Species of the second group display consistent characters and host associations and are easily distinguishable. Species of the gallinae-group tend to be the major problems in poultry houses and it is unknown whether D. gallinae is the only pest, or if there are numerous cryptic species present in the system. Twenty species of Dermanyssus were tested phylogenetically based on 46 morphological characters. A subset of species, mainly of the gallinae-group, represented each by several populations, was sequenced for two mitochondrial and one nuclear gene regions. This allowed testing their specific status and their interrelationships based and on morphological and molecular characters. The molecular data was analysed separately and in combination with morphological characters. As expected, morphology did a poor job resolving relationships. Molecular data proved more informative. The resulting phylogenetic hypotheses brought some information about interrelationships among species of the gallinae-group showing a split into two main clades. The invasion of human managed environments seems to occur only in taxa within one of the two clades. The host spectrum seems to get enlarged in more derived taxa in the same clade. A delineation of six species within the gallinae-group is provided. Additionally, a key for morphological identification of these species is provided. D. gallinae appears to be the only pest in poultry houses, but is composed of several different and more or less strongly isolated lineages. A new species found from the black swift is described.

Molecular phylogenetic assessment of host range in five Dermanyssus species.

Given that 14 out of the 25 currently described species of Dermanyssus Dugès, 1834, are morphologically very close to each another, misidentifications may occur and are suspected in at least some records. One of these 14 species is the red fowl mite, D. gallinae (De Geer, 1778), a blood parasite of wild birds, but also a pest in the poultry industry. Using molecular phylogenetic tools we aimed to answer two questions concerning host specificity and synanthropicity: (1) is D. gallinae the only species infesting European layer farms?, and (2) can populations of D. gallinae move from wild to domestic birds and vice versa? Mitochondrial cytochrome oxidase I gene sequences were obtained from 73 Dermanyssus populations collected from nests of wild European birds and from poultry farms and these were analyzed using maximum parsimony and Bayesian inference. Mapping of the observed host range on the obtained topology and correlation with behavioural observations revealed that (1) host range is strongly dependent on some ecological parameters (e.g. nest hygiene, exposure to pesticides and predators), that (2) out of five species under test, synanthropic populations were found only in lineages of D. gallinae, and that (3) at least some haplotypes found in wild birds were very close to those found in association with domestic birds.

Stereoselective S-oxygenation of an aryl-trifluoromethyl sulfoxide to the corresponding sulfone by rat liver cytochromes P450.

Toltrazuril sulfoxide (TZR.SO) is the metabolite of the antiparasitic drug toltrazuril (TZR; 1-methyl-3-[3-methyl-4-[4-[trifluoromethyl]thio]phenoxy]phenyl- 1,3,5-triazine-2,4,6(1H,3H,5H)-trione). The results of the present paper demonstrate that TZR.SO was metabolized by rat liver microsomes to the corresponding sulfone (TZR.SO2). The reaction was mediated almost exclusively by different cytochromes P450, the most active being cytochromes P450 3A. TZR.SO exists as a racemic mixture; when each enantiomer was incubated separately in the presence of untreated rat liver microsomes, a 7.3-fold difference in the rate of S-oxygenation was found, indicating a marked substrate enantioselectivity for the reaction.

Possible involvement of multiple cytochrome P450S in fentanyl and sufentanil metabolism as opposed to alfentanil.

Fentanyl, sufentanil, and alfentanil are commonly used as opioid analgesics. Alfentanil clearance has previously been shown to exhibit an important interindividual variability, which was not observed for fentanyl or sufentanil. Differences in pharmacokinetic parameters of alfentanil have previously been associated with the wide distribution of CYP3A4, the only known hepatic cytochrome P450 monooxygenase (CYP) involved in the conversion of alfentanil to noralfentanil. Little is known about the involvement of CYP enzymes in the oxidative metabolism of fentanyl and sufentanil. Microsomes prepared from different human liver samples were compared for their abilities to metabolize fentanyl, sufentanil and alfentanil, and it was found that disappearance of the three substrates was well correlated with immunoreactive CYP3A4 contents but not with other CYPs, including CYP1A2, CYP2A6, CYP2C8, CYP2C9, CYP2D6 and CYP2E1. Specific known inhibitors of CYP enzymes gave similar results, whereas the use of recombinant human CYP enzymes expressed in yeast provided information about the possible involvement of other CYPs than CYP3A4 in the biotransformation of fentanyl and sufentanil. The possible in vivo interaction of fentanyl and sufentanil with other drugs catalyzed by CYP3A4 is also discussed.

Field evidence of secondary poisoning of foxes (Vulpes vulpes) and buzzards (Buteo buteo) by bromadiolone, a 4-year survey.

This paper presents the result of a 4 year survey in France (1991-1994) based on the activity of a wildlife disease surveillance network (SAGIR). The purpose of this study was to evaluate the detrimental effects of anticoagulant (Ac) rodenticides in non-target wild animals. Ac poisoning accounted for a very limited number of the identified causes of death (1-3%) in most species. Predators (mainly foxes and buzzards) were potentially exposed to anticoagulant compounds (especially bromadiolone) via contaminated prey in some instances. The liver concentrations of bromadiolone residues were elevated and species-specific diagnostic values were determined. These values were quite similar to those reported in the literature when secondary anticoagulant poisoning was experimentally assessed.

Anticoagulant poisoning in animals: a simple new high-performance thin-layer chromatographic (HPTLC) method for the simultaneous determination of eight anticoagulant rodenticides in liver samples.

The purpose of this study was to develop and evaluate a technique for the analysis of anticoagulant rodenticides in serum and liver samples using a new high-performance thin-layer chromatographic apparatus. Detection limits were estimated at 0.2 micrograms/g in liver extracts for eight different substances. Overall, this technique was repeatable and reproducible. The percent recovery was greater than 87% for each substance. Liver and serum samples of animals known to be exposed to one anticoagulant and showing clinical signs of poisoning were analyzed. Concentrations measured varied between 0.2 and 3 micrograms/g (liver extracts). Only blood samples from one dog could be analyzed. The concentration was 150 ng/mL the first day after admission and 140 ng/mL the following day. Analyses are technically easily and rapidly performed, and they are inexpensive. Therefore, this technique could be a valuable alternative to current high-performance liquid chromatographic methods.

Caged mudsnail Potamopyrgus antipodarum (Gray) as an integrated field biomonitoring tool: exposure assessment and reprotoxic effects of water column contamination.

This study highlights the usefulness of gastropods for water quality monitoring. Gastropods were caged upstream and downstream of an effluent discharge. Exposure was assessed by measurement of organic contaminants in water. Contamination of the Potamopyrgus antipodarum mudsnail was also measured using innovative techniques at the end of the 42 days of exposure. Biological effects were measured at the individual level (growth, reproduction) and subindividual level (energy reserves, vitellin-like proteins, steroid levels, expression of genes involved in estrogen signaling pathways), thus providing a better understanding of reprotoxic effects. The effluent was mainly contaminated by pharmaceutical compounds, as was the mudsnail. The highest concentrations were measured for oxazepam and were higher than 2 mg/kg downstream of the effluent discharge. Alkylphenols, bisphenol A, and vertebrate-like sex-steroid hormones were also bioaccumulated by the mudsnail downstream of the effluent. The combined use of water and snail contamination provided a complete exposure assessment. Exposure was further linked to biological effects. The mudsnail was shown to be a better adapted species for in situ exposures than Valvata piscinalis. Reproduction was sharply decreased after 6 weeks of exposure in the mudsnail. Feeding issues were excluded, confirming the toxic origin. These effects were related to estrogen signaling pathways using genomic analysis. Genes coding for proteins involved in nongenomic signaling pathways were inhibited, and those of genomic pathway repressors were induced. These results suggest that the chemical contamination due to the effluent discharge altered steroid control of reproduction and blocked the transition between oocyte and unshelled embryo, resulting in a drastic decrease of embryo production, while survival was not affected.

Organic solvents impair life-traits and biomarkers in the New Zealand mudsnail Potamopyrgus antipodarum (Gray) at concentrations below OECD recommendations.

Potamopyrgus antipodarum is a gastropod mollusk proposed for use in the development of reproduction tests within the Organization for Economic Cooperation and Development (OECD). Numerous chemicals, including endocrine disrupters, are relatively water-insoluble, and water-miscible solvents are currently used for testing them. OECD recommends a maximum concentration of 100 µll(-1). As several studies highlighted effects of lower concentrations of solvents, this study assessed the effects of 20 µll(-1) acetone, ethanol, methanol and dimethylsulfoxide (DMSO) on juvenile and adult snails during 42 days. Ethanol decreased juvenile growth, while acetone increased the rate of embryonic development. All solvents increased estradiol-like levels in adult snails. DMSO only increased mRNA expression of vitellogenin-like gene, while acetone, ethanol and methanol decreased mRNA expression of three nuclear receptor (estrogen receptor-like, ecdysone-induced protein and chicken ovalbumin upstream promoter transcription factor) genes as well as of genes encoding proteins involved in genomic (prohibitin-2) and non-genomic (striatin) pathways of estrogens activity in vertebrates. This study highlights the confounding effects of low concentrations of solvents and recommends avoiding their use. Where solvent use is inevitable, their concentrations and type should be investigated for suitability for the measured endpoints prior to use in chemical testing strategies.

Is exposure temperature a confounding factor for the assessment of reproductive parameters of New Zealand mudsnails Potamopyrgus antipodarum (Gray)?

Potamopyrgus antipodarum is a promising test organism often used in ecotoxicology testing, both in laboratory and in field exposure experiments. It has been recommended for use in the development of an OECD reproduction test. However, exposure temperature is important to take into account when assessing reproduction and related biomarkers, because it can act as a confounding factor inducing variability in physiological values. The effect of three environmentally realistic exposure temperatures (8, 16 and 24°C) was examined with respect to the number of neonates born, the number of embryos in the brood pouch and the duration of embryonic development. We also measured additional markers likely to be related to the modulation of reproductive performance, such as vertebrate-like sex steroid, energy status and vitellin-like proteins. Exposure temperature had a significant effect on reproduction in P. antipodarum, on both the duration of embryonic development and the quantity of embryos and neonates. The consequences of these observations must not be neglected when using this species in laboratory and field experiments. This study determined suitable temperatures for field experiments and a mean duration for embryonic development independent of temperature. In addition to steroid levels, energy status and Vn-like protein levels were only slightly modified by exposure temperature between 8 and 24°C. Thus, they can be easily implemented and their variations related to anthropogenic factors during field exposure of mudsnails.

Comprehensive biological effects of a complex field poly-metallic pollution gradient on the New Zealand mudsnail Potamopyrgus antipodarum (Gray).

The Lot River is known to be contaminated by metals, mainly cadmium and zinc, due to a former Zn ore treatment plant in the watershed of the Riou-Mort, a tributary of the Lot River. Many studies have been performed to characterize contamination, but few have assessed its consequences on the biological responses of organisms along the gradient. We exposed adult and juvenile New Zealand freshwater mudsnails Potamopyrgus antipodarum at several sites along the gradient of metal contamination for 28 days. Biological responses were monitored at different levels: individual (survival, growth and fecundity), tissue and biochemical (energy status and vertebrate-like sex steroid levels) to better understand the toxicity mechanisms involved. Accumulation of Cd and Zn was high during exposure. Most of the biological effects observed could be linked to this contamination and were concentration-dependent. Histological lesions of the digestive gland were observed, with hypertrophy of calcium cells and vacuolization of digestive cells. Such effects are likely to explain the decrease of energy status (triglycerides and proteins), juvenile growth and adult fecundity observed at the most polluted site. However the magnitude of the fall in fecundity cannot be attributed only to these tissular effects, indicating another mode of action of Cd or possible confounding factors. Steroid accumulation in snails indicated only organic pollution. Histopathological effects proved the most sensitive endpoint to metal (Cd and Zn) contamination.

Development, validation and comparison of LC-MS/MS and RIA methods for quantification of vertebrates-like sex-steroids in prosobranch molluscs.

The role of vertebrate-like sex-steroids (testosterone, T, progesterone, P, and 17beta-estradiol, E2) in molluscs is still debated, but they could represent potential biomarkers of endocrine disruption. A radioimmunoassay (RIA) and a liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) methods have been developed and compared to measure their levels in a gastropod snail Potamopyrgus antipodarum. Both methods showed a good reproducibility despite the complex matrix and the very low levels of vertebrate-like sex-steroids. Only T and P were detected using the LC-MS/MS method, while the RIA method reached lower detection limits and enabled the detection of all three steroids. Results indicated that T and P were mainly present as unconjugated forms. Both methods were compared in the analysis of snails exposed to waste water treatment plant effluents and led to the same conclusions concerning the modulation of steroids levels. Moreover, they both were in agreement concerning T measurements. On the other hand, LC-MS/MS appeared to be more suitable when analyzing P levels due to a low sensitivity of the RIA method. As E2 was not measured using the LC-MS/MS method because of a higher detection limit compared to the other steroids, the results obtained with the RIA method should be interpreted with caution. LC-MS/MS remains the gold standard for sex-steroid determinations, however a relevant and alternative method based on RIA was developed, requiring fewer organisms. RIA seems a promising method as a screening tool for experimental use, allowing comparison of sex-steroid levels in the mudsnail both in laboratory and in field experiments.

Sensitivity of New Zealand mudsnail Potamopyrgus antipodarum (Gray) to a specific aromatase inhibitor.

The freshwater prosobranch Potamopyrgus antipodarum (Molluska, Hydrobiidea, Smith 1889) has been proposed as a suitable species to assess the impact of endocrine disrupting compounds (EDC) in aquatic ecosystems. Steroid hormone biosynthesis pathway is potentially an important target for EDC, and vertebrate-like sex steroids seem to play a functional role in the control of mollusk reproduction. To assess the response and the sensitivity of P. antipodarum to disrupters of the steroid hormone biosynthesis pathway, we have experienced the action of a specific vertebrate aromatase inhibitor, fadrozole, acting on 17beta-estradiol synthesis in two separate 28 and 42d exposures. Fadrozole had effects consistent with the expected mechanism of action. A decrease of the reproduction parameters (such as on the number of neonates and number of embryos in the brood pouch) in a dose-dependant manner was observed. The steroids levels were also impaired with the ratio 17beta-estradiol/testosterone decreased by half in exposed snails. This shift of the steroids balance was accompanied by some alteration in the gonads histology and immunohistochemistry in fadrozole-exposed snails. This study highlights the value role of P. antipodarum as a test species for assessing EDC effects in aquatic wildlife.

Effects of fluoxetine on the reproduction of two prosobranch mollusks: Potamopyrgus antipodarum and Valvata piscinalis.

Fluoxetine is a widely used antidepressant, frequently found in aquatic ecosystems. We investigated its effects on two freshwater prosobranch gastropods: Valvata piscinalis (European valve snail) and Potamopyrgus antipodarum (New Zealand mudsnail), which have different reproductive modes. The fecundity of V. piscinalis (cumulate number of eggs at day 42) was not affected with an NOEC of 100 mvg/L nominal concentration (69 microg/L measured concentration). The mudsnail P. antipodarum responded in a biphasic dose-effect curve at low concentrations. The cumulate number of neonates at day 42 had an LOEC of 100 microg/L (69 microg/L) and an NOEC of 33.3 microg/L (13 microg/L), whereas the embryos in the brood pouch at day 42 only showed an LOEC of 3.7 microg/L (1 microg/L). We also observed histological effects in P. antipodarum (gonadal thickness). Among the sexual steroids we measured only testosterone which varied, independent of reproduction. Moreover the use of two closely related species highlights the interspecific variability.

Effect of cytochrome P-450 1A induction on enantioselective metabolism and pharmacokinetics of an aryltrifluoromethyl sulfide in the rat.

The pharmacokinetics of the antiparasitic drug toltrazuril (1-methyl-3-[3-methyl-4-[4-[trifluoromethyl]thio]phenoxy]phenyl- 1,3,5-triazine-2,4,6(1H,3H,5H)-trione) were studied in the rat following pretreatment with 3-methylcholanthrene, an inducer of rat liver cytochrome P-450 1A. The induction markedly modified the pharmacokinetics of the compound, leading to a decrease in the AUC value for toltrazuril sulfoxide. The results were explained on the basis of previous results from our laboratory relating to the product enantioselectivity of the formation of the sulfoxide and the substrate enantioselectivity of the subsequent formation of the sulfone.

Thioesterification of 2-arylpropionic acids by recombinant acyl-coenzyme A synthetases (ACS1 and ACS2).

2-Arylpropionic acids are a class of frequently used nonsteroidal anti-inflammatory drugs exhibiting a potent inhibition of cyclooxygenase isoforms supported by the (+)S-enantiomer alone. Nevertheless, some of these compounds in the (-)R configuration may undergo extensive inversion of configuration to their antipode. The key molecular basis for this mechanism invokes the stereoselective formation of the coenzyme A (CoA) thioester of the 2-arylpropionic acid by long-chain acyl-CoA synthetases (ACSs). In this report, rat recombinant ACS1 and ACS2 enzymes, constitutively highly expressed in adult rat liver and brain, respectively, have been overproduced in Escherichia coli strains and purified to homogeneity to investigate the involvement of these enzymes in the thioesterification of fenoprofen and ibuprofen. Recombinant ACS1 efficiently catalyzed both nonsteroidal anti-inflammatory drugs with Michaelis-Menten parameters of K(M) = 1686 +/- 93 microM, V(max) = 353 +/- 45 nmol/min/mg protein for (-)R-ibuprofen and K(M) = 103 +/- 12 microM, V(max) = 267 +/- 10 nmol/min/mg protein for (-)R-fenoprofen, and exhibited a marked stereoselectivity in favor of the (-)R-enantiomer. Recombinant ACS2, a closely related sequence with ACS1, exhibited a lower enzymatic efficacy from 7- to 130-fold for (-)R-ibuprofen and (-)R-fenoprofen, respectively. On the basis of these findings and considering the level of tissue expression of the different long-chain ACSs, ACS1 appears to be the major enzyme involved in the first step of the chiral inversion of 2-arylpropionic acids. Nevertheless, the participation of other ACS isoforms of minor quantitative importance could not be excluded in the thioesterification of xenobiotics.

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.

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).