Depression Of Cholinesterase Activity Research Articles

Sarin Exposures in A Cohort of British Military Participants in Human Experimental Research at Porton Down 1945-1987.

The effects of exposure to chemical warfare agents in humans are topical. Porton Down is the UK's centre for research on chemical warfare where, since WWI, a programme of experiments involving ~30000 participants drawn from the UK armed services has been undertaken. Our aim is to report on exposures to nerve agents, particularly sarin, using detailed exposure data not explored in a previous analysis. In this paper, we have used existing data on exposures to servicemen who attended the human volunteer programme at Porton Down to examine exposures to nerve agents in general and to sarin in particular. Six principal nerve agents were tested on humans between 1945 and 1987. Of all 4299 nerve agent tests recorded, 3511 (82%) were with sarin, most commonly in an exposure chamber, with inhalation being the commonest exposure route (85%). Biological response to sarin exposure was expressed as percentage change in cholinesterase activity and, less commonly, change in pupil size. For red blood cell cholinesterase, median inhibition for inhalation tests was 41% (interquartile range 28-51%), with a maximum of 87%. For dermal exposures the maximum inhibition recorded was 99%. There was a clear association between increasing exposure to sarin and depression of cholinesterase activity but the strength and direction of the association varied by exposure route and the presence of chemical or physical protection. Pupil size decreased with increased exposure but this relationship was less clear when modifiers, such as atropine drops, were present. These results, drawn from high quality experimental data, offer a unique insight into the effects of these chemical agents on humans.

Impacts of the herbicide butachlor on the larvae of a paddy field breeding frog (Fejervarya limnocharis) in subtropical Taiwan

Butachlor is the most commonly used herbicide on paddy fields in Taiwan and throughout Southeast Asia. Since paddy fields provide habitat for pond breeding amphibians, we examined growth, development, time to metamorphosis, and survival of alpine cricket frog tadpoles (Fejervarya limnocharis) exposed to environmentally realistic concentrations of butachlor. We documented negative impacts of butachlor on survival, development, and time to metamorphosis, but not on tadpole growth. The 96 h LC(50) for tadpoles was 0.87 mg/l, much lower than the 4.8 mg/l recommended dosage for application to paddy fields. Even given the rapid breakdown of butachlor, tadpoles would be exposed to concentrations in excess of their 96 h LC(50) for an estimated 126 h. We also documented DNA damage (genotoxicity) in tadpoles exposed to butachlor at concentrations an order of magnitude less than the 4.8 mg/l recommended application rate. We did not find that butachlor depressed cholinesterase activity of tadpoles, unlike most organophosphorus insecticides. We conclude that butachlor is likely to have widespread negative impacts on amphibians occupying paddy fields with traditional herbicide application.

Exposures Recorded for Participants in the UK Chemical Warfare Agent Human Research Programme, 1941–1989

This study describes exposures to military veterans who participated between 1941 and 1989 in British research at Porton Down on the effects of exposure to chemical warfare agents and to defences against those agents. The study is part of a programme of epidemiological research initiated in response to service veterans' concerns about possible long-term health effects of their participation. All entries in 97 books held in the Porton Down historical experimental archive covering the years 1939-1989 were reviewed. For tests between April 1941 and December 1989, data were abstracted on chemicals used, with additional detail abstracted for tests involving vesicants and nerve agents. For tests recorded during 1939-1941, similar data were abstracted for a representative sample of tests. Historical data were abstracted for 17 303 veterans included in the cohort study of 18,276 servicemen who took part in tests at Porton Down between 1941 and 1989. The median number of days per veteran on which tests were carried out was 2 days. The median difference between the last and first day of testing was 4 days. A large number of chemicals were tested over this period (n = 492). The type of chemical tested varied over time. Exposures were often modified by respirator use or use of protective clothing or protective equipment. It was possible to assign a quantitative measure of cumulative exposure to 73% of veterans exposed to the vesicant sulphur mustard--3491 (34%) of exposed veterans had cumulative exposures > or =10.63 mg and for 70% of veterans exposed to the nerve agent sarin--658 (29%) of exposed veterans had cumulative exposures > or =15.0 mg min m(-3). Ninety-three per cent of veterans exposed to sulphur mustard were classified to a semi-quantitative scale of dermal effect--3771 (37%) had a vesicle or necrosed area, and 69% of veterans exposed to sarin could be categorized by change in blood cholinesterase activity--1033 (31%) had a depression in cholinesterase activity of > or =30%. The experimental archive at Porton Down has proved to be a rich source of data on tests conducted between 1941 and 1989. It has been possible to categorize most veterans according to date of test, chemical group, chemical, type of protection and, for certain chemicals, level of exposure and/or degree of acute toxicity. These categorizations have been used to assign veterans to exposure groups for epidemiological analysis.

Organophosphate and carbamate insecticides in agricultural waters and cholinesterase (ChE) inhibition in common carp (Cyprinus carpio).

Cholinesterase (ChE) activity was used as a biomarker for assessing exposure of common carp (Cyprinus carpio) to organophosphate and carbamate insecticides from irrigated agricultural waters. Carp were collected from a lake (Royal Lake) that receives most of its water from irrigation return flows and from a reference lake (Billy Clapp Lake) outside of the irrigation system. Results indicated that the mean whole-brain ChE activity of carp from Royal Lake (3.47 micromol/min/g tissue) was 34.2% less than that of carp from Billy Clapp Lake (5.27 micromol/min/g tissue) (p = 0.003). The depressed ChE activity in brain tissue of Royal Lake carp was in response to ChE-inhibiting insecticides detected in water samples in the weeks prior to tissue sampling; the most frequently detected insecticides included chlorpyrifos, azinphos-methyl, carbaryl, and ethoprop. Neither sex nor size appears to be a covariable in the analysis; ChE activity was not correlated with fish length or weight in either lake and there was no significant difference in ChE activity between the two sexes within each lake. Although organophosphate and carbamate insecticides can break down rapidly in the environment, this study suggests that in agricultural regions where insecticides are applied for extended periods of the year, nontarget aquatic biota may be exposed to high levels of ChE-inhibiting insecticides for a period of several months.

The impacts of molluscicide pellets on spring and autumn populations of wood mice Apodemus sylvaticus

Methiocarb is a carbamate molluscicide widely used in pelleted form. Wood mice Apodemus sylvaticus are commonly found in arable fields and will eat methiocarb pellets. Two previous field studies on the impacts on arable wood mice of broadcasting methiocarb pellets produced contrasting results, the number of mice being temporarily reduced in one but not the other. The season of application is also likely to influence the degree of impact on populations but the previous trials were both in autumn. The aim of the present study was to determine the effects on wood mice of broadcast applications of methiocarb in both autumn and spring and to determine whether depression of brain and serum cholinesterase (ChE) activity, a biomarker of exposure, could be detected in mice alive on treated fields after application. In trials carried out in October 1994 and April 1995, there were decreases in the number of wood mice on arable fields following pesticide application. The October decline (78%) was greater than that in April (33%), even though the activity of the mice appeared to be more heavily centred on the hedgerows, where pellets were not applied, in the autumn. Despite the reductions in numbers, no depression of ChE activity was detected in mice captured alive after application, suggesting that either exposed animals were not captured or that reactivation of ChE activity was rapid. This study confirmed that broadcast application of methiocarb can reduce wood mouse populations on arable fields. It also demonstrated that such effects can occur irrespective of season and that measurement of ChE activity in mice trapped after application may fail to indicate that exposure of the population has occurred.

Regional cholinesterase activity in white-throated sparrow brain is differentially affected by acephate (orthene®)

Effects of a 14-day dietary exposure to an organophosphorus pesticide, acephate (acetylphosphoramidothioic acid O,S-dimethyl ester), were determined on cholinesterase activity in three regions (basal ganglia, hippocampus, and hypothalamus) of the white-throated sparrow, Zonotrichia albicollis, brain. All three regions experienced depressed cholinesterase activity between 0.5–2 ppm acephate. The regions exhibited cholinesterase recovery at 2–16 ppm acephate; however, cholinesterase activity dropped and showed no recovery at higher dietary levels (>16 ppm acephate). Evidence indicates that the recovery is initiated by the magnitude of depression, not the duration. In general, as acephate concentration increased, differences in ChE activity among brain regions decreased. Three terms are introduced to describe ChE response to acephate exposure: 1) ChE resistance threshold, 2) ChE compensation threshold, and 3) ChE depression threshold. It is hypothesized that adverse effects to birds in the field may occur at pesticide exposure levels customarily considered negligible.

Postulated Interaction Between Hydroxychloroquine and Cholinesterase Enzyme Activity:

Serum and red blood cell (RBC) cholinesterase activity testing has been mandatory in the State of California for agricultural pesticide applicators since 1989. The case of a worker with depressed cholinesterase activity levels is presented. When he started taking hydroxychloroquine for systemic lupus erythematosus his serum cholinesterase activity levels decreased and remained decreased while RBC activity levels remained unchanged. Sources of organophosphate exposure were ruled out and other possible causes of cholinesterase depression were excluded. The author postulates that hydroxychloroquine was responsible for the depression of serum cholinesterase activity levels.While this finding has no impact on those taking the drug, it does alert physicians managing a monitoring program to be aware of causes of cholinesterase activity depression other than organophosphate poisoning.

Biological monitoring of workers occupationally exposed to organophosphorus pesticides

AbstractThis paper describes the development and use of a biological monitoring method for assessing exposure to organophosphorus pesticides. The method is used to determine the concentration of six dialkyl phosphates and phosphoro‐thioates (dimethyl phosphate, diethyl phosphate, O,O‐dimethyl phosphorothioate, O,O‐diethyl phosphorothioate, O,O‐dimethyl phosphorodithioate and O,O‐diethyl phosphorodithioate) in urine. The method involves the azeotropic distillation of urine, derivatisation of the residue with pentafluorobenzylbromide followed by high resolution gas chromatography with flame photometric detection.The technique has been applied to the analysis of over 400 urine samples obtained from 140 workers with potential occupational exposure to organophosphorus pesticides during various agricultural activities, sheep dipping or pesticide formulation. Wherever possible, blood samples were taken for measurement of red blood cell and plasma cholinesterase activity. The results show that in over 300 instances where blood samples were also obtained, urinary dialkyl phosphate metabolites could be detected even though there was no depression of red cell or plasma cholinesterase activity. Formulation workers had higher urinary metabolite levels (expressed as nmoles metabolite per mmole creatinine) than any of the other groups studied and were the only group where a significant reduction in cholinesterase activity was also seen.The results discussed here show that the method for the analysis of urinary dialkyl phosphate metabolites described is useful for monitoring occupational exposure to organophosphorus pesticides and is capable of detecting low levels of exposure not detectable by depression of cholinesterase activity.

Effects of methyl parathion on red-winged blackbird (Agelaius Phoeniceus) incubation behavior and nesting success

Free-living female red-winged blackbirds (Agelaius phoeniceus) were captured on their nests and given oral doses of 0, 2.37 or 4.21 mg/kg methyl parathion in a propylene glycol carrier during incubation. Birds were released immediately after dosing and observed for 5 h to document behavioral effects, amount of time spent off the nest after dosing and time spent incubating. Each nest was monitored until nestlings fledged or until all nestlings died or disappeared. For each nest, the time of abandonment, hatching success and fledging success were determined. In addition, prefledging weights were obtained for all nestlings in nests at 8 d after hatch. Although methyl parathion caused ataxia, lacrimation and lethargy and significantly depressed cholinesterase activity (>35%) at 4.21 mg/kg, there were no apparent adverse effects on reproduction. Females receiving 4.21 mg/kg methyl parathion were able to return to their nests, resume incubation, successfully hatch their clutch and rear their young. Nestlings of poisoned females did not have significantly different body weights at 8 d compared to controls, indicating that methyl parathion did not disrupt the females' ability to forage and deliver adequate food to nestlings. Band returns from the following year indicated that treatment birds returned and nested in nearly the same proportion as did controls and other red-winged blackbirds occupying the ponds. There was no indication that a single oral dose of methyl parathion (2.37 or 4.21 mg/kg) decreased over-winter survival.

Case histories of wild birds killed intentionally with famphur in Georgia and West Virginia.

Five incidences of bird mortality in Georgia and West Virginia (USA) involving migratory waterfowl, cranes, raptors, corvids and songbirds were investigated during the first 6 mo of 1988. Gross and histopathologic examinations revealed no evidence of infectious or other diseases. However, severe depression of cholinesterase activity was evident in brains of birds found dead, suggesting gross exposure to an organophosphorus (OP) or carbamate pesticide. All of the gastrointestinal tract contents chemically analyzed contained famphur, an OP insecticide used as a pour-on treatment against lice and grubs on livestock, ranging from 5 to 1,480 ppm (wet weight). Grain scattered at two of the mortality sites contained 4,240 and 8,500 ppm famphur. Gastrointestinal tracts of most of the dead birds contained mainly corn and some wheat. This is the first report to document the use of famphur as an intentional means of killing wildlife thought to be depredating crops.

Cholinesterase activity depression among California agricultural pesticide applicators.

Cholinesterase activity measurements for 542 California agricultural pesticide applicators under medical supervision during the first 9 months of 1985 were analyzed. Twenty-six workers, 4.8% of the sample, had cholinesterase values at or below the California threshold values for removal from continued exposure to cholinesterase-inhibiting pesticides (60% of baseline for red blood cell cholinesterase and 50% of baseline for plasma cholinesterase activity). Eight of these 26 workers, 31.5%, had pesticide-related illnesses. Pesticides most frequently associated with cholinesterase depressions exceeding California threshold values included mevinphos (Phosdrin), oxydemeton methyl (Metasystox-R), methomyl (Lannate), and acephate (Orthene); these pesticides included organophosphates in toxicity categories I and II and one carbamate in toxicity category I.

Effects of inhaled cholinesterase inhibitors on bronchial tonus and on plasma and erythrocyte acetylcholine estarase activity in rats

Young adult male and female Wistar rats were inhalationally exposed head-only for 1 or 4 h to different anticholinesterase aerosols. The compounds tested were dichlorvos, fenamiphos, methamidophos, parathion, a pyrimidine thiophosphate and the carbamate propoxur. These compounds are direct or indirect inhibitors of cholinesterase activity. Immediately after termination of exposure to the compounds, the rats were anesthetized with barbiturate and subjected to pulmonary function tests. An acetylcholine provocation test was performed to correlate the effect of the cholinesterase inhibition and lung resistance. The results basically revealed that by inhalation exposure bronchoconstriction in the absence of acetylcholine provocation did not occur at toxicologically significant doses of the pesticides. An increase in lung resistance was observed only after provocation. However, measurements of plasma cholinesterase activity proved to be more sensitive than the provocation test. With regard to their diagnostic value, the results of the reported study may be summarized as follows (beginning with the most sensitive parameter): plasma cholinesterase activity depression ⩾ acetylcholine-induced bronchoconstriction ⩾ cholinergic symptoms > erythrocyte cholinesterase activity depression > pulmonary resistance without acetylcholine provocation.

Toxicity of methyl parathion to bats: Mortality and coordination loss

AbstractThe 24‐h oral LD50 of methyl parathion (phosphorothioic acid O, O‐dimethyl O‐(4‐nitrophenyl) ester) to little brown bats (Myotis lucifugus) (372 mg/kg) was 8.5 times the LD50 for mice (Mus musculus) (44 mg/kg). However, orally dosed mice either died or appeared behaviorally normal after 2 to 3 h, whereas many dosed bats, although alive at 24 h, could not right themselves when placed on their backs. The oral dose estimated to cause this loss of coordination in 50% of a sample of big brown bats (Eptesicus fuscus) was one‐third or less the LD50 of this species. Cholinesterase activity depression in brains of little brown bats was similar whether dosage was oral or dermal. With death as the criterion, bats proved relatively insensitive to methyl parathion in 24‐h tests, but considerations of the chemical's potential to cause coordination loss, leading to capture and death by predators, coupled with bats' naturally low reproductive rates, suggest possible injury to exposed bat populations.

Occupational exposure control by simultaneous determination of N-methylcarbamates and organophosphorus pesticide residues in human urine.

On-column transesterification with methanol was applied for the gas chromatographic determination of N-methylcarbamates extracted from human urine. Transesterification conversion efficiencies of N-methylcarbamates dioxacarb, carbofuran and OMS-22, calculated from the amount of the on-column produced O-methyl-N-methylcarbamate (DMC), were 96, 77 and 76% with detection limits of 8, 10 and 10 ng, respectively. In the investigated concentration range of 0.2-3 micrograms/ml of urine the extraction efficiencies with methylene chloride were independent of the initial concentration of N-methylcarbamate added to urine samples of non-exposed persons. The recoveries and rel. S.D. were 74 +/- 11, 64 +/- 8 and 79 +/- 12% for dioxacarb, carbofuran and OMS-22, respectively. The procedure was applied for the gas chromatographic determination of carbofuran and its metabolites containing the N-methylcarbamic group extracted from urine samples of occupationally exposed persons in a pesticide formulating plant. The level of extracted N-methylcarbamates and the concentration of degradation products of organophosphorus pesticides detected in the urine of the same persons were correlated with the blood and plasma cholinesterase activities. Although the determination of DMC includes only a smaller part of the excreted N-methylcarbamate, a simultaneous determination of both carbamates and organophosphorus residues made it possible to distinguish the cause of depression in cholinesterase activity, indicating early and specifically the exposure to a particular group of agents hazardous to health.

Chronic toxicity of metrifonate.

From chronic toxicity studies with metrifonate (identical with trichlorfon) on different animal species, the following conclusion can be reached: 1. There is no conclusive evidence that trichlorfon has a carcinogenic effect. 2. There is no indication that trichlorfon has a significant cumulative toxic effect. 3. There is no confirmation that trichlorfon has a specific effect on liver, blood and haematopoietic organs. 4. The toxicological profile of trichlorfon in the chronic toxicity study consists, on the one hand, in a depression of cholinesterase activity whereby the different animal species differed in their sensitivity. In rats, cholinesterase activity was depressed in serum at dietary levels of 500 p.p.m. and above and also in erythrocytes at a dietary concentration of 1000 p.p.m. In dogs, cholinesterase activity was depressed in serum and erythrocytes at a dietary level of only 200 p.p.m. The Rhesus monkey seemingly is very sensitive because erythrocyte cholinesterase activity is possibly reduced at a daily dose of 0.2 mg/kg per os. On the other hand, induction of an inhibition of spermatogenesis in rats and dogs at a high dose level is discussed, an effect which seemingly is morphologically detectable but nonetheless seems not to affect function as animal experiments have demonstrated.

Clinical pharmacology of dichlorvos.

Polyvinyl resin formulation pellets (V-3 and V-12) containing dichlorvos were administered to male volunteers in single doses up to 32 mg/kg and repeated doses up to 16 mg/kg/day for up to three weeks. The cholinesterase activity depressions following single doses were dose related. Following multiple doses, the plasma cholinesterase activity was maximally depressed at all dose levels and the RBC cholinesterase activity depression was dose related.

Depression of cholinesterase activity by ethylestrenol in organophosphorus-poisoned and normal rats

The twice-daily oral administration of ethylestrenol to nonpoisoned rats depressed cholinesterase activity in the brain, stomach, and diaphragm. In rats chronically poisoned with disulfoton, ethylestrenol reduced the rate of return of cholinesterase activity in the stomach and diaphragm but not in the brain. Ethylestrenol also decreased the rate of weight gain of both poisoned and nonpoisoned animals.

Effects of acute and chronic dieldrin administration on liver and plasma esterases of the rat

The administration of a single oral dose of dieldrin, 40 mg/kg, or the feeding of a diet containing 50 ppm of dieldrin for up to 8 weeks to male and female rats produced changes in plasma and liver esterases that were dependent on the type of esterase, the duration of exposure, and the sex of the animal. Two hours after oral administration of dieldrin, plasma carboxylesterase activity declined in males but not in females; hepatic microsomal carboxylesterase activity was also slightly lower in dieldrin-treated males, but not females. Forty-eight and 120 hr after dieldrin administration, hepatic microsomal carboxylesterase activity was elevated in rats of both sexes. After 8 weeks of dieldrin feeding (50 ppm), both plasma and microsomal carboxylesterase activities were significantly elevated in males and females. In most instances, elevations in the activities of hepatic microsomal esterases were due to dieldrin-induced increases in microsomal protein content and not to increased esterase specific activity. Electrophoresis of solubilized microsomal membranes from control and dieldrin-treated animals revealed no sex differences or major dieldrin-induced alterations on esterase isozyme patterns. Plasma cholinesterase activity was significantly reduced in females fed 50 ppm of dieldrin in the diet for 8 weeks. Since the level of activity of this enzyme is regulated in part by estrogen, depression of cholinesterase activity may result from an increased rate of steroid metabolism in dieldrin-treated female rats. Plasma cholinesterase activity of male rats was unaffected by either acute or chronic dieldrin administration.

Studies of the acute and long-term oral toxicity of chlorpyrifos ( O,O-diethyl- O-(3,5,6-trichloro-2-pyridyl) phosphorothioate)

The acute and long-term toxicity of orally administered chlorpyrifos ( O,O-diethyl- O-(3,5,6-trichloro-2-pyridyl) phosphorothioate), a broad-spectrum insecticide, has been determined. No sex or strain differences in acute oral toxicity were detected using two strains of rat, and LD 50 values determined in several tests ranged from 118 to 245 mg/kg. LD 50 values (in mg/kg) for other species were approximately 2000 for rabbits, 504 for guinea-pigs and 32 for leghorn chicks. Rats and dogs were maintained on diets providing doses of 0·0, 0·01, 0·03, 0·1, 1·0 or 3·0 mg chlorpyrifos/kg/day. In dogs, ChE activity in plasma was depressed by the 3·0, 1·0 and 0·1 mg/kg/day doses, and receiving 3·0 or 1·0 mg/kg/day. ChE activity of the brain of rats was depressed by a dose of 3·0 mg/kg/day. In dogs, ChE activity in plasma was depressed by the 3·0, 1·0 and 0·1 mg/kg/day doses, and that in red cells by the 3·0 and 1·0 mg/kg/day doses. Brain ChE was slightly depressed in dogs receiving the highest dose. In the long-term study, no clinical evidence of induction of cholinergic activity was observed in either species at any time. Depression of ChE activity was readily reversible when the control diets were substituted for diets containing chlorpyrifos. No significant effects related to treatment were observed in rats or dogs receiving any dose of chlorpyrifos, using the following criteria:mortality, body weights, food intake, haematological studies, urine analyses, clinical chemistry studies, organ weights and organ to body weight ratios, tumour incidence and gross and histopathological examination of tissues. It was concluded that 0·1 and 0·03 mg chlorpyrifos/kg/day fed in the diet for 2 yr produced no significant toxicological effect in rats and dogs, respectively. Even in animals receiving 3·0 mg/kg/day, no effects were observed other than a reversible depression of cholinesterase activity.

Consummatory behavior during tolerance to and withdrawal from chronic depression of cholinesterase activity

Two experiments were conducted, using rats, to study behavioral tolerance development to chronically lowered levels of cholinesterase (ChE) activity induced by intramuscular injection of diisopropyl fluorophosphate (DFP) and effects on behavior of withdrawal from the treatment. Three parameters of consummatory behavior were measured: food intake, water intake and laps. Results showed that food intake and laps were affected in similar manners both during tolerance development and during withdrawal: an initial decrease in performance recovered to pre-DFP baseline levels within the first seven days of treatment and continued at these levels during the 30-day test period following withdrawal from DFP. By contrast the parameter, water intake, required 13 days for full tolerance to develop and reacted to withdrawal of DFP, first, by some 25 days of drinking at pre-treatment baseline levels and, later, by an extended period of suprabaseline performance significantly greater in magnitude than that of control animals. Hypotheses about peripheral and central mechanisms underlying these behavioral effects are discussed in the light of present empirical data.