Blood Acetylcholinesterase Inhibition Research Articles

SAT-133 BLOOD ACETYLCHOLINESTERASE ACTIVITY AND COMPARATIVE eGFR IN RURAL FARMERS WITH LOW, INTERMEDIATE, AND HIGH EXPOSURE TO ORGANOPHOSPHOROUS CONTAINING AGROCHEMICALS

Organophosphorous containing agrochemicals (OCAs) are commonly used by farmers to prevent destruction of farm products by pests and weeds. Their role as risk factors of kidney disease is currently being evaluated. Blood acetylcholinesterase inhibition is a recognized marker of exposure to organophosphorous containing chemicals. We conducted a study to determine the proportion of rural farmers who use these agents, their blood acetylcholinesterase activities and comparative estimated glomerular filtration rate (eGFR) in those with low, intermediate, and high exposure. A cross-sectional study of nine rural farming communities in Southwestern Nigeria. Degree of exposure was categorized using the following criteria: (a) Years of active farming - Low (0-10 years) and High (> 10 years), (b) Use of protective garment - Low (Yes), High (No). A score of low for both parameters was categorized as low exposure, a score of low and high in both parameters was graded as intermediate exposure, while a score of high in both parameters was graded as high exposure. All participants were evaluated for kidney function using CKD-EPI equation to calculate the eGFR. Blood acetylcholinesterase activity was evaluated by the modified Ellman’s method. Five hundred and seventy two farmers participated in the study. Two hundred and twenty five (39.3%) were males while 347 (60.7%) were females. Mean age of participants was 52 ± 17.5 (range 18 – 100) years. Years of active farming ranged from 0.5 to 80 years, with a median of 25 years. Blood acetylcholinesterase activity ranged from 0 – 20.1 (mean 3.5 ± 3.5) µmol/min/mL in all participants. Four hundred participants (69.9%) stated that they used organophosphate containing agrochemicals. Exposure was low in 32 (8%), intermediate in 161 (40.6%), and high in 200 (50%) of these participants. Blood acetylcholinesterase activities / eGFR levels in low, intermediate, and high exposures are shown in the table. Statistically, blood acetylcholinesterase activities were similar in those with high compared to those with low exposure (P = 0.338). However, eGFR was significantly lower in those with high compared to those with low exposure (P = 000). Use of organophosphate containing agrochemicals was high in the rural farmers examined. There was a decline in eGFR with higher exposure. However, blood acetylcholinesterase activity levels did not appear to differ significantly among the different groups of exposure studied. There is a need for a prospective study to determine the normal range of blood acetylcholinesterase levels in unexposed individuals to define the minimum duration of exposure to organophosphate agrochemicals neccessary for significant surpression of blood of acetylcholinesterase levels in the rural farmers.

Longitudinal assessment of occupational exposures to the organophosphorous insecticides chlorpyrifos and profenofos in Egyptian cotton field workers.

Chlorpyrifos (CPF) and profenofos (PFF) are organophosphorus (OP) insecticides that are applied seasonally in Egypt to cotton fields. Urinary trichloro-2-pyridinol (TCPy), a specific CPF metabolite, and 4-bromo-2-chlorophenol (BCP), a specific PFF metabolite, are biomarkers of exposure, while inhibition of blood butyrylcholinesterase (BChE) and acetylcholinesterase (AChE) activities are effect biomarkers that may be associated with neurotoxicity. Urinary TCPy and BCP and blood BChE and AChE activities were measured in 37 adult Egyptian Ministry of Agriculture workers during and after 9-17 consecutive days of CPF application followed by an application of PFF (9-11 days), and a second CPF application (5 days) in 2008. During the OP applications, urinary TCPy and BCP levels were significantly higher than baseline levels, remained elevated following the application periods, and were associated with an exposure related inhibition of blood BChE and AChE. Analysis of blood AChE levels before and after the PFF application period suggests that individual workers with peak BCP levels greater than 1000 μg/g creatinine exhibited further inhibition of blood AChE with PFF application, demonstrating that PFF exposure had a negative impact on AChE activity in this highly exposed worker population. While large interindividual differences in exposure were observed throughout this longitudinal study (peak urinary BCP and peak TCPy levels for individuals ranging from 13.4 to 8052 and 16.4 to 30,107 μg/g creatinine, respectively), these urinary biomarkers were highly correlated within workers (r=0.75, p<0.001). This suggests that the relative exposures to CPF and PFF were highly correlated for a given worker. The variable exposures between job classification and work site suggest that job title and work location should not be used as the sole basis for categorizing OP exposures when assessing neurobehavioral and other health outcomes in Egyptian cotton field workers. Together, these findings will be important in educating the Egyptian insecticide application workers in order to encourage the development and implementation of work practices and personal protective equipment to reduce their exposure to CPF and PFF.

Incorporating Low-dose Epidemiology Data in a Chlorpyrifos Risk Assessment.

USEPA assessed whether epidemiology data suggest that fetal or early-life chlorpyrifos exposure causes neurodevelopmental effects and, if so, whether they occur at exposures below those causing the current most sensitive endpoint, 10% inhibition of blood acetylcholinesterase (AChE). We previously conducted a hypothesis-based weight-of-evidence analysis and found that a proposed causal association between chlorpyrifos exposure and neurodevelopmental effects in the absence of AChE inhibition does not have a substantial basis in existing animal or in vitro studies, and there is no plausible basis for invoking such effects in humans at their far lower exposure levels. The epidemiology studies fail to show consistent patterns; the few associations are likely attributable to alternative explanations. Human data are inappropriate for a dose-response assessment because biomarkers were only measured at one time point, may reflect exposure to other pesticides, and many values are at or below limits of quantification. When considered with pharmacokinetic data, however, these biomarkers provide information on exposure levels relative to those in experimental studies and indicate a margin of exposure of at least 1,000. Because animal data take into account the most sensitive lifestages, the use of AChE inhibition as a regulatory endpoint is protective of adverse effects in sensitive populations.

Incorporating Low-Dose Epidemiology Data in a Chlorpyrifos Risk Assessment

USEPA assessed whether epidemiology data suggest that fetal or early-life chlorpyrifos exposure causes neurodevelopmental effects and, if so, whether they occur at exposures below those causing the current most sensitive endpoint, 10% inhibition of blood acetyl-cholinesterase (AChE). We previously conducted a hypothesis-based weight-of-evidence analysis and found that a proposed causal association between chlorpyrifos exposure and neurodevelopmental effects in the absence of AChE inhibition does not have a substantial basis in existing animal or in vitro studies, and there is no plausible basis for invoking such effects in humans at their far lower exposure levels. The epidemiology studies fail to show consistent patterns; the few associations are likely attributable to alternative explanations. Human data are inappropriate for a dose-response assessment because biomarkers were only measured at one time point, may reflect exposure to other pesticides, and many values are at or below limits of quantification. When considered with pharmacokinetic data, however, these biomarkers provide information on exposure levels relative to those in experimental studies and indicate a margin of exposure of at least 1,000. Because animal data take into account the most sensitive lifestages, the use of AChE inhibition as a regulatory endpoint is protective of adverse effects in sensitive populations.

Therapeutic effects of multi-dose activated charcoal on the acute dichlorvos poisoning in rats

Objective To assess the therapeutic effects of activated charcoal on the acute dichlorvos poisoning in rats. Method Thirty male clean grade Wistar rats were randomly (random number) divided into three groups: control group (group A, n = 10), single dose activated charcoal group (group B, n = 10) and multi-dose activated charcoal (group C, n=10). The rats of group A were suffered from 35 mg/kg dichlorvos exposure by oral without activated charcoal and senna. The rats of group B received 35 mg/kg dichlorvos exposure by oral with 175 mg/kg activated charcoal given immediately after dichlorvos exposure and 35 mg/kg senna given half an hour later. In the group C, 35 mg/kg dichlorvos was given to rats by oral with 175 mg/kg activated charcoal given immediately after dichlorvos exposure and 35 mg/kg senna given half an hour later and then every four hours. Blood samples were collected from the carotid artery at different intervals after exposure. DDVP concentration and total blood acetyl-cholinesterase activity were detected. Differences in serum DDVP concentration, Cmax, AUC (0→∞ ), MRT and acetylcholinesterase among three groups were calculated by using ANOVA. Results Serum DDVP levels in single dose group and in multi-dose group were significantly different from those in control group (P 0.05). Another four hours later, no differences in acetylcholinesterase were found a-mong three groups (P > 0.05). Conclusions The peak concentrations of dichlorvos in blood are lower in group B and group C, and the blood acetylcholinesterase inhibition is quelled by activated charcoal. Therefore, the effects of multi - dose of activated charcoal is better than that of single dose of activated charcoal. Key words: Dichlorvos; Activated carbon; Organophosphate poisoning; Oral intaken; LC-MS; Rat; Toxicoki-netics; Statistical moment model

Effect of seven newly synthesized and currently available oxime cholinesterase reactivators on cyclosarin-intoxicated rats.

Seven new oxime-based acetylcholinesterase reactivators were compared with three currently available ones (obidoxime, trimedoxime, HI-6) for their ability to lessen cholinesterase inhibition in blood and brain of cyclosarin-treated rats. Oximes were given at doses of 5% their LD50 along with 21 mg/kg atropine five min before the LD50 of cyclosarin (120 ug/kg) was administered. Blood and brain samples were collected 30 minutes later. The greatest difference between acetylcholinesterase inhibition in blood of cyclosarin-treated rats was found after administration of HI-6 (40%), compared to 22% for trimedoxime and 6% for obidoxime. Only two of the seven newly synthesized oximes had any effect (K203 at 7%, K156 at 5%). Effective oximes against cyclosarin-inhibited plasma butyrylcholinesterase were HI-6 (42%), trimedoxime (11%), and K156 (4%). The oximes were less effective in brain than in blood, with reactivation values for HI-6 30% against acetylcholinesterase and 10% against butyrylcholinesterase. Values for newly synthesized oximes were less than 10% for K206, K269 and K203.

Blood and Bronchoalveolar Lavage Fluid Acetylcholinesterase Levels Following Microinstillation Inhalation Exposure to Sarin in Guinea Pigs

We determined acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibition in the bronchoalveolar lavage fluid (BALF) following inhalation exposure to chemical threat nerve agent (CTNA) sarin. Age- and weight-matched male guinea pigs were exposed to five different doses of sarin (169.3, 338.7, 508, 677.4, and 846.5 mg/m3) using a microinstillation inhalation exposure technique for 4 min. The technique involves aerosolization of the agent in the trachea using a microcatheter with a center hole that delivers the agent and multiple peripheral holes that pumps air to aerosolize the agent at the tip. Animals exposed to higher doses of sarin occasionally developed seizures and succumbed to death within 15 min after exposure. The LCt50 for sarin using the microinstillation technique was determined to be close to 677.4 mg/m3. Ear blood AChE activity showed a dose-dependent inhibition at 15 min postexposure. The inhibition of blood AChE remained constant over 35 and 55 min after sarin exposure indicating that there was no lung depot effect. Cardiac blood AChE and butyrylcholinesterase (BChE) activity in surviving animals euthanized at 24 h postexposure showed a dose-dependent inhibition with an inhibition of 60% at 677.4 and 846.5 mg/m3 sarin exposure. AChE and BChE activity in bronchoalveolar lavage fluid (BALF) showed a slight increase at 338.7 to 677.4 mg/m3 sarin exposure but a marginal inhibition at 169.3 mg/m3. In contrast, the AChE protein levels determined by immunoblotting showed an increase at 169.3 mg/m3 in the BALF. The BALF protein level, a biomarker of lung injury, was increased maximally at 338.7 mg/m3 and that increase was dropped with an increase in the dose of sarin. The BALF protein levels correlated with the AChE and BChE activity. These data suggest that sarin microinstillation inhalation exposure results in respiratory toxicity and lung injury characterized by changes in lavage AChE, BChE, and protein levels.

Subchronic physostigmine pretreatment in marmosets: absence of side effects and effectiveness against soman poisoning with negligible postintoxication incapacitation.

Subchronic pretreatment with physostigmine (PHY) (0.0125 mg/kg/h) leading to a blood acetylcholinesterase inhibition of about 30% caused no side effects when applied to marmoset monkeys. This was evident on behavioral parameters and on EEG and cortical visual evoked response. Furthermore, this treatment regime, followed by atropine as postintoxication therapy, protected the marmosets against lethality after a 2 x LD50 dose of soman with negligible postintoxication incapacitation. These findings suggest that a symptom-free pretreatment with subchronic PHY could protect man sufficiently against severe soman intoxication.

Importance of cholinolytic drug selection for the efficacy of HI-6 against soman in rats

The influence of cholinolytic drugs (atropine, benactyzine, biperiden) on the efficacy of the oxime HI-6 (1-[[[(4-aminocarbonyl)pyridinio]methoxy]methyl]-2-[(hydroxyimino)methyl]pyridinium dichloride monohydrate) on soman-induced anticholinesterase and stressogenic effects was studied in rats. Soman-induced acetylcholinesterase inhibition in blood and diaphragm and the stressogenic effects of soman, i.e. an increase in plasma corticosterone level and liver tyrosine aminotransferase activity, were more significantly diminished by HI-6 in combination with benactyzine or biperiden in comparison with HI-6 plus atropine. These findings support a hypothesis that benactyzine as well as biperiden can increase the efficacy of the oxime HI-6 in comparison with atropine. They demonstrate the importance of cholinolytic drug selection in the treatment of soman poisoning in rats.

The effect of ondansetron on pyridostigmine-induced blood acetylcholinesterase inhibition in the guinea pig.

The purpose of this study was to assess the compatibility, in terms of red blood cell acetylcholinesterase (AChE) inhibition, of ondansetron (OND; a 5-hydroxytryptamine subtype-3 receptor antagonist) with the organophosphorus pretreatment compound pyridostigmine (PYR) after simultaneous oral (p.o.) administration to guinea pigs. The time-course of PYR-induced (0.94 mg/kg, p.o.) AChE inhibition was determined in the absence and presence of OND. Ondansetron (10, 20 and 30 mg/kg; p.o.) did not modify AChE inhibition, whereas concurrent administration of PYR with OND (10 or 20 mg/kg; p.o.) produced significantly greater decreases in AChE activity than PYR alone. The decreases in AChE activity for PYR plus OND, 10 and 20 mg/kg, (between 30 -240 min) were 12.3 +/- 2.8% and 16.1 +/- 2.3% (mean +/- SD) respectively relative to PYR alone. The slope for recovery of AChE activity (120 - 240 min) was 0.0914 for PYR alone; recovery rates (slopes) for PYR plus OND, 10 and 20 mg/kg, were 0.0796 and 0.0433 respectively. Additionally, altered PYR-induced AChE activity profiles were ameliorated when PYR and OND (20 mg/kg) were administered 150 min apart. Since the results of this study provided evidence that the oral administration of OND alone did not inhibit AChE, the changes in PYR-induced AChE activity by the simultaneous administration of OND suggest mechanisms other than a direct action on the enzyme. The significance of these findings is that the increased AChE inhibition resulting from simultaneous oral administration of both component could result in undesirable cholinergic toxicities and subsequent perform decrements.

Study of muscular effects of short-term pyridostigmine treatment in resting and exercising rats.

1. Pyridostigmine (PYR) pretreatment is used by the military to obtain 20-30% whole blood acetylcholinesterase (AChE) inhibition in order to enhance the effectiveness of the standard therapeutic regimen for poisoning by an organophosphate anticholinesterase agent. The present study was undertaken to investigate in a rat model the potential muscle damage produced by this pretreatment when given alone or combined with physical exercise. 2. Grip strength and biochemical measurements, i.e. serum creatine phosphokinase (CPK) activity and creatine urinary excretion rate, together with histological studies, were performed in resting animals during a period of 14 days of PYR administration in a dose producing 20-30% whole blood acetylcholinesterase inhibition. No evidence was found of a deleterious effect of this treatment on the skeletal muscle. 3. In contrast, following physical exercise, the same treatment significantly exacerbated the biochemical changes reflecting a loss of integrity in skeletal muscles, namely, increased CPK and urinary creatine excretion rate. The significance of this observation remains to be clarified.

Active avoidance behavior in guinea pigs: Effects of physostigmine and scopolamine

Behavioral training of guinea pigs by conventional methods, such as used for rats and mice, appears difficult. Hence, only a few behavioral experiments with guinea pigs have been described in the literature. An active avoidance technique in an automated two-way shuttlebox is described using sound as a conditioned (CS) and a tactile stimulus (a stream of air ruffling their fur) as an unconditioned (UCS) stimulus. Acquisition is fairly rapid and reproducible. Doses of physostigmine that caused moderate blood acetylcholinesterase inhibition induced dose-dependent performance decrements. These decrements were counteracted by a sign-free dose of scopolamine.

Evaluation of the efficacy of two carbamates, physostigmine and pyridostigmine, when used in conjunction for protection against organophosphate exposure

Recent studies have shown that pretreatment with either pyridostigmine (PYR) or physostigmine (PHY) followed by atropineoxime therapy is very effective in reducing the lethality of nerve agents. The therapeutic efficacy of a PHY and PYR combination pretreatment was evaluated in guinea pigs challenged with two LD50s of soman. Endpoints measured were percentage of acetylcholinesterase inhibition induced by the pretreatment and survival up to 24 hr postchallenge. Response surface methodology was employed to describe the relationship between each endpoint and the pretreatment combination. Although both carbamates contributed to blood acetylcholinesterase inhibition, PHY alone protected as well as the optimal dose of the combination.

Pyridostigmine-induced inhibition of blood acetylcholinesterase (AChE) and resulting effects on manual ocular tracking performance in the trained baboon

A method was developed to determine the effects of pyridostigmine on sensory-motor control in baboons trained to perform visuo-oculo-manual tracking tasks. The performance was evaluated in terms of accuracy, maximum smooth pursuit velocity, and gain. Administration of pyridostigmine (0.4-0.7 mg/kg intramuscularly) induced a dose-related decrease in smooth pursuit performance which appeared 10 to 30 min after injection and lasted about 1 h. If the animal was allowed to track the target with its hand or to move the target itself, the smooth pursuit performance increased significantly, returning to near normal values. The movement of the hand was not altered. The effect of intramuscular injections of pyridostigmine (0.5 mg/kg) was studied on blood acetylcholinesterase activity in alert baboons. Maximum inhibition of about 60% of baseline activity was observed 10 min after pyridostigmine injection. Subsequently the activity slowly tended to return to control level. Three hours after drug administration, acetylcholinesterase activity inhibition was still 34.1% of control value. In the baboon, the time-course of acetylcholinesterase activity recovery after injection is similar to that recorded in human. The similarity of the time-course of blood acetylcholinesterase activity and changes in smooth pursuit performance suggests a causal relationship between the two factors. A further experiment showed that pyridostigmine administered per os at a dose normally used as a prophylactic against organophosphates does not significantly alter sensorimotor performance as evaluated at the oculomanual tracking system level. When compared to the literature, our results suggest that the baboon can be used as a human experimental analog for pharmacological studies such as the action of acetylcholinesterase inhibitors.

Relationship between reversible acetylcholinesterase inhibition and efficacy against soman lethality

Carbamate pretreatment (45% inhibition, reversible), combined with therapy, protected rats from soman-induced lethality [The Pharmacologist 23 , 224 (1981)]. The present study was done to see if less than 45% inhibition protects and to see if reversible acetylcholinesterase (AChE) inhibition and efficacy against soman lethality are correlated. At 30 min pre-soman, guinea pigs and rats received (im) either pyridostigmine (Py) or physostigmine (Ph) to inhibit whole blood AChE from 10 to 70%; at 1 min post-soman (sc), they received (im) atropine (16 mg/kg)/2-PAMC1 (50 mg/kg) and mecamylamine (0.8 mg/kg)/atropine (16 mg/kg), respectively. Protective ratios (PRs) were computed and they ranged from 3.1 to 7.7 for guinea pigs and from 1.8 to 2.4 for rats. In guinea pigs the PRs for Py + therapy were roughly similar to those of Ph + therapy. In both species at 30 min after im injection of Py and Ph, a linear relationship was found between percentage of whole blood AChE inhibition and In dosage of carbamate. Positive correlation (p<0.05) was found between the degree of reversible AChE inhibition by pretreatment, coupled with therapy, and efficacy against soman lethality. The present data indicate that inhibition levels as low as 10% may provide some protection.

Determination of blood acetylcholinesterase inhibition caused by reversible inhibitors in vivo

A method for measuring acetylcholinesterase inhibition in blood from animals treated with reversible anticholinesterases is described. Its applicability is shown by results obtained with the reversible, competitive inhibitor, edrophonium.

Inhibition of acetylcholinesterase in rat brain subcellular fractions following O-isopropyl methylphosphonofluoridate intoxication

Acetylcholinesterase inhibition in blood and subcellular fractions of the medulla oblongata of the rat brain was studied following O-isopropyl methylphosphonofluoridate intoxication. Total acetylcholinesterase inhibition at time of death was found only in microsomal and crude mitochondrial fractions (probably in nerve ending particles).