Slow accumulation of acetylcholinesterase in rat brain during enzyme inhibition by repeated dosing with chlorpyrifos

Anxiolytic activity of paraoxon is associated with alterations in rat brain glutamatergic system

Exposure to organophosphate (OP) compounds leads to behavioral alterations. To determine whether paraoxon has effects on anxiety, anxiety-like behaviors were assessed in paraoxon-exposed rats. Protein expression of glutamate transporters has also been measured in hippocampus and prefrontal cortex. Three doses of paraoxon (0.3, 0.7, or 1 mg/kg) or corn oil (vehicle) were intraperitoneally injected to adult male rats. At 14 or 28 days after exposure, behavioral tests were done using elevated plus-maze (EPM) or open field tests. Thereafter, animals were sacrificed and both hippocampi and prefrontal cortices were extracted for cholinesterase assay and western blotting. Animals treated with convulsive doses of paraoxon (0.7 and 1 mg/kg) showed an increase in percentage of time spent in open arms and percentage of open arm entries in the EPM. In the open field test, an increase in the time spent in central area was observed in rats treated with the same doses of paraoxon. These effects of paraoxon were independent of any changes in locomotor activity. There was an increase in both astrocytic glutamate transporter proteins (GLAST and GLT-1) in the hippocampus of animals treated with 0.7 and 1 mg/kg of paraoxon. In the prefrontal cortex, protein levels of the GLAST and GLT-1 increased in 0.7 and decreased in 1 mg/kg groups. Only a significant decrease in EAAC1 protein was observed in the prefrontal cortex at 14 days following exposure to 1 mg/kg of paraoxon. Collectively, this study showed that exposure to convulsive doses of paraoxon induced anxiolytic-like behaviors in both behavioral tests. This effect may be attributed to alterations of glutamate transporter proteins in the rat hippocampus and prefrontal cortex.

Possibility of Acetylcholinesterase Overexpression in Alzheimer Disease Patients after Therapy with Acetylcholinesterase Inhibitors

Acetylcholinesterase is an enzyme responsible for termination of excitatory transmission at cholinergic synapses by the hydrolyzing of a neurotransmitter acetylcholine. Nowadays, other functions of acetylcholinesterase in the organism are considered, for example its role in regulation of apoptosis. Cholinergic nervous system as well as acetylcholinesterase activity is closely related to pathogenesis of Alzheimer disease. The mostly used therapy of Alzheimer disease is based on enhancing cholinergic function using inhibitors of acetylcholinesterase like rivastigmine, donepezil or galantamine. These drugs can influence not only the acetylcholinesterase activity but also other processes in treated organism. The paper is aimed mainly on possibility of increased expression and protein level of acetylcholinesterase caused by the therapy with acetylcholinesterase inhibitors.

Strain dependent effects of conditioned fear in adult C57Bl/6 and Balb/C mice following postnatal exposure to chlorpyrifos: relation to expression of brain acetylcholinesterase mRNA

Following reports of emotional psychopathology in children and adults exposed to organophosphates, the effects of postnatal chlorpyrifos (CPF) on fear-conditioning and depression-like behaviors were tested in adult mice. Concomitant changes in expression of mRNA for synaptic and soluble splice variants of acetylcholinesterase (AChE) were examined in mouse pups and adults of the Balb/C and C57Bl/6 (B6) strains, which differ in their behavioral and hormonal stress response. Mice were injected subcutaneously with 1 mg/kg CPF on postnatal days 4–10 and tested as adults for conditioned fear, sucrose preference, and forced swim. Acetylcholinesterase activity was assessed in the brains of pups on the first and last day of treatment. Expression of soluble and synaptic AChE mRNA was assessed in brains of treated pups and fear-conditioned adults using real-time PCR. Adult Balb/C mice exposed postnatally to CPF showed exacerbated fear-conditioning and impaired active avoidance. Adult B6 mice exposed postnatally to CPF showed a more specific fear response to tones and less freezing in the inter-tone intervals, in contrast to the vehicle-pretreated mice. Chlorpyrifos also attenuated sweet preference and enhanced climbing in the forced swim test. Chlorpyrifos-treated mice had increased expression of both synaptic and readthrough AChE transcripts in the hippocampus of Balb/C mice and decreased expression in the amygdala following fear-conditioning. In conclusion, postnatal CPF had long-term effects on fear and depression, as well as on expression of AChE mRNA. These changes may be related to alteration in the interaction between hippocampus and amygdala in regulating negative emotions.

Effects of melatonin on changes in cognitive performances and brain malondialdehyde concentration induced by sub-chronic co-administration of chlorpyrifos and cypermethrin in male Wister rats

OBJECTIVE

To evaluate the ameliorative effect of melatonin on sub-chronic chlorpyrifos (CPF) and cypermethrin (CYP)-evoked cognitive changes in male Wistar rats.

METHODS

Fifty adult male Wistar rats, divided into five groups of ten rats each, were used for the study. Groups 1 and II were given distilled water and soya oil (2 mL/kg) respectively. Group III was administered with melatonin at 0.5 mg/kg only. Group IV was administered with CPF [7.96 mg/kg (1/10th LD50)] and CYP [29.6 mg/kg (1/10th LD50)], and Group V was administered with CPF [7.96 mg/kg (1/10th LD50)] and CYP [29.6 mg/kg (1/10th LD50)] 30 min after melatonin (0.5 mg/kg). The regimens were administered by gavage once daily for 12 weeks. Thereafter, cognitive performances were determined and the brain was evaluated for malonaldehyde concentration.

RESULTS

CPF and CYP induced cognitive deficits and increased brain malonaldehyde concentration, which were all ameliorated by melatonin.

CONCLUSION

Cognitive deficits elicited by CPF and CYP was mitigated by melatonin due to its antioxidant property.

Effects of chemical and thermal stress on acetylcholinesterase activity in the brain of the bank vole, Myodes glareolus

One of the most important issues in ecotoxicology is better understanding the effects of interactions between chemical pollutants and physical environmental factors on animals. To fill this knowledge gap, changes in the activity of acetylcholinesterase (AChE) in the brain samples of bank voles Myodes (Clethrionomys) glareolus due to temperature effects, and two chemical stressors were studied in a full factorial laboratory experiment (27 treatments). The experiment was divided into three phases: acclimatisation (3 days), intoxication (42 days) and elimination (21 days). During the intoxication phase, animals were orally exposed to different concentrations of either nickel (0, 300 or 800 mg Ni/kg food), chlorpyrifos (CPF) (0, 50 or 350 mg CPF/kg food) or a mixture of both chemicals. During the acclimatisation and elimination phases, the bank voles were given uncontaminated food. The experiment was conducted at three different temperatures (10, 20 or 30 °C), and a 12 h:12 h light:dark regime. The animals were sacrificed at 0, 5, 10, 20, 42, 49 and 63 days after the beginning of the intoxication, and brain samples were obtained for chemical analysis. The nickel accumulation in the brain depended on the level of nickel exposure and on interactions between the temperature and other factors. Nickel exhibited no effect on AChE activity. In contrast, AChE was drastically inhibited by chlorpyrifos and low temperature, but interactions between all factors significantly influenced the enzyme activity during the elimination phase of the experiment. High mortality was observed in the groups exposed to high concentrations of nickel and chlorpyrifos.

Induction of plasma acetylcholinesterase activity and apoptosis in mice treated with the organophosphorus toxicant, tri-o-cresyl phosphate

Organophosphorus compounds (OP) inhibit acetylcholinesterase (AChE) activity and cause cultured cells to undergo apoptosis. Live mice treated with OP have reduced AChE activity, but after a short recovery period, their AChE activity rebounds to levels that exceed baseline by more than 2-fold. To date no information is available on whether abnormally high AChE activity is characteristic of apoptosis in animals. Our goal was to determine whether induction of AChE activity is associated with apoptosis in live mice. For this purpose we treated mice with 1500 mg kg−1tri-o-cresyl phosphate. On day one after treatment their plasma AChE activity was inhibited by 50%. On day 4, plasma AChE activity rebounded to a level 2.2-fold higher than pretreatment activity and remained elevated for about two months. On day 4, AChE activity in the lung was 1.5-fold higher than in controls. Cells in lung sections that were positive in the apoptosis TUNEL assay, stained heavily for AChE activity. In conclusion, AChE activity and apoptosis are induced in mice treated with tri-o-cresyl phosphate. Unusually high AChE activity may be a marker of exposure to apoptosis-inducing substances.

Differential acetylcholinesterase inhibition of chlorpyrifos, diazinon and parathion in larval zebrafish

Zebrafish are increasingly used for developmental neurotoxicity testing because early embryonic events are easy to visualize, exposures are done without affecting the mother and the rapid development of zebrafish allows for high throughput testing. We used zebrafish to examine how exposures to three different organophosphorus pesticides (chlorpyrifos, diazinon and parathion) over the first five days of embryonic and larval development of zebrafish affected their survival, acetylcholinesterase (AChE) activity and behavior. We show that at non-lethal, equimolar concentrations, chlorpyrifos (CPF) is more effective at equimolar concentrations than diazinon (DZN) and parathion (PA) in producing AChE inhibition. As concentrations of DZN and PA are raised, lethality occurs before they can produce the degree of AChE inhibition observed with CPF at 300 nM. Because of its availability outside the mother at the time of fertilization, zebrafish provides a complementary model for studying the neurotoxicity of very early developmental exposures.

Revisiting the Role of Acetylcholinesterase in Alzheimer's Disease: Cross-Talk with P-tau and β-Amyloid

A common feature in the Alzheimer’s disease (AD) brain is the presence of acetylcholinesterase (AChE) which is commonly associated with β-amyloid plaques and neurofibrillary tangles (NFT). Although our understanding of the relationship between AChE and the pathological features of AD is incomplete, increasing evidence suggests that both β-amyloid protein (Aβ) and abnormally hyperphosphorylated tau (P-tau) can influence AChE expression. We also review recent findings which suggest the possible role of AChE in the development of a vicious cycle of Aβ and P-tau dysregulation and discuss the limited and temporary effect of therapeutic intervention with AChE inhibitors.

Induction of plasma acetylcholinesterase activity in mice challenged with organophosphorus poisons

The restoration of plasma acetylcholinesterase activity in mice following inhibition by organophosphorus pesticides and nerve agents has been attributed to synthesis of new enzyme. It is generally assumed that activity levels return to normal, are stable and do not exceed the normal level. We have observed over the past 10 years that recovery of acetylcholinesterase activity levels in mice treated with organophosphorus agents (OP) exceeds pretreatment levels and remains elevated for up to 2 months. The most dramatic case was in mice treated with tri-cresyl phosphate and tri-ortho-cresyl phosphate, where plasma acetylcholinesterase activity rebounded to a level 250% higher than the pretreatment activity. The present report summarizes our observations on plasma acetylcholinesterase activity in mice treated with chlorpyrifos, chlorpyrifos oxon, diazinon, tri-ortho-cresyl phosphate, tri-cresyl phosphate, tabun thiocholine, parathion, dichlorvos, and diisopropylfluorophosphate. We have developed a hypothesis to explain the excess acetylcholinesterase activity, based on published observations. We hypothesize that acetylcholinesterase activity is induced when cells undergo apoptosis and that consequently there is a rise in the level of plasma acetylcholinesterase.

Pharmacokinetics and pharmacodynamics of chlorpyrifos in adult male Long-Evans rats following repeated subcutaneous exposure to chlorpyrifos

Chlorpyrifos (CPF) is a commonly used organophosphorus pesticide. Several pharmacokinetic and pharmacodynamic studies have been conducted in rats in which CPF was administered as a single bolus dose. However, there is limited data regarding the pharmacokinetics and pharmacodynamics following daily exposure. Since occupational exposures often consist of repeated, daily exposures, there is a need to evaluate the pharmacokinetics and pharmacodynamics of CPF under exposure conditions which more accurately reflect real world human exposures. In this study, the pharmacokinetics and pharmacodynamics of CPF were assessed in male Long-Evans rats exposed daily to CPF (0, 3 or 10mg/kg/day, s.c. in peanut oil) over a 10 day study period. Throughout the study, multiple pharmacokinetic (urinary TCPy levels and tissue CPF and metabolite levels) and pharmacodynamic (blood and brain AChE activity) determinants were measured. Average blood AChE activity on day 10 was 54% and 33% of baseline among animals in the 3 and 10mg/kg/day CPF treatment groups, respectively, while average brain AChE activity was 67% and 28% of baseline. Comparable dose-response relationships between brain AChE inhibition and blood AChE inhibition, suggests that blood AChE activity is a valid biomarker of brain AChE activity. The pharmacokinetic and pharmacodynamic measures collected in this study were also used to optimize a rat physiologically based pharmacokinetic/pharmacodynamic (PBPK/PD) model for multiple s.c. exposures to CPF based on a previously published rat PBPK/PD model for CPF following a single bolus injection. This optimized model will be useful for determining pharmacokinetic and pharmacodynamic responses over a wide range of doses and durations of exposure, which will improve extrapolation of results between rats and humans.

Changes in acetylcholinesterase expression are associated with altered presenilin-1 levels

We have previously identified presenilin-1 (PS1), the active component of the γ-secretase complex, as an interacting protein of the amyloid-associated enzyme acetylcholinesterase (AChE). In this study, we have explored the consequences of AChE-PS1 interactions. Treatment of SH-SY5Y cells with the AChE-inhibitor tacrine decreased PS1 levels, in parallel with increase in the secretion of amyloid precursor protein APPα, whereas the cholinergic agonist carbachol had no effect on PS1. AChE knockdown with siRNA also decreased PS1 levels, while AChE overexpression exerted opposing effect. AChE-deficient also had decreased PS1. Mice administered with tacrine or donepezil displayed lower levels of brain PS1. However, sustained AChE inhibition failed to exert long-term effect on PS1. This limited duration of response may be due to AChE upregulation caused by chronic inhibition. Finally, we exposed SH-SY5Y cells to β-amyloid (Aβ)42 which triggered elevation of both AChE and PS1 levels. The Aβ42-induced PS1 increase was abolished by siRNA AChE pretreatment, suggesting that AChE may participate in the pathological feedback loop between PS1 and Aβ. Our results provide insight into AChE-amyloid interrelationships.

Brain cholinergic impairment in liver failure

The cholinergic system is involved in specific behavioural responses and cognitive processes. Here, we examined potential alterations in the brain levels of key cholinergic enzymes in cirrhotic patients and animal models with liver failure. An increase (∼30%) in the activity of the acetylcholine-hydrolyzing enzyme, acetylcholinesterase (AChE) is observed in the brain cortex from patients deceased from hepatic coma, while the activity of the acetylcholine-synthesizing enzyme, choline acetyltransferase, remains unaffected. In agreement with the human data, AChE activity in brain cortical extracts of bile duct ligated (BDL) rats was increased (∼20%) compared to controls. A hyperammonemic diet did not result in any further increase of AChE levels in the BDL model, and no change was observed in hyperammonemic diet rats without liver disease. Portacaval shunted rats which display increased levels of cerebral ammonia did not show any brain cholinergic abnormalities, confirming that high ammonia levels do not play a role in brain AChE changes. A selective increase of tetrameric AChE, the major AChE species involved in hydrolysis of acetylcholine in the brain, was detected in both cirrhotic humans and BDL rats. Histological examination of BDL and non-ligated rat brains shows that the subcellular localization of both AChE and choline acetyltransferase, and thus the accessibility to their substrates, appears unaltered by the pathological condition. The BDL-induced increase in AChE activity was not parallelled by an increase in mRNA levels. Increased AChE in BDL cirrhotic rats leads to a pronounced decrease (∼50–60%) in the levels of acetylcholine. Finally, we demonstrate that the AChE inhibitor rivastigmine is able to improve memory deficits in BDL rats. One week treatment with rivastigmine (0.6 mg/kg; once a day, orally, for a week) resulted in a 25% of inhibition in the enzymatic activity of AChE with no change in protein composition, as assessed by sucrose density gradient fractionation and western blotting analysis. In conclusion, this study is the first direct evidence of a cholinergic imbalance in the brain as a consequence of liver failure and points to the possible role of the cholinergic system in the pathogenesis of hepatic encephalopathy.

Association between acetylcholinesterase and beta-amyloid peptide in Alzheimer's cerebrospinal fluid

The altered expression of acetylcholinesterase (AChE) in the brains of patients with Alzheimer's disease (AD) has raised much interest of late. Despite an overall decrease in the AD brain, the activity of AChE increases around beta-amyloid plaques and indeed, the beta-amyloid peptide (Abeta) can influence AChE levels. Such evidence stimulated our interest in the possibility that the levels of AChE and amyloid might vary together in AD. We previously found that the different AChE forms present in both the brain and in the cerebrospinal fluid (CSF) of AD patients varied in conjunction with abnormal glycosylation. Thus, the alterations in glycosylation are correlated with the accumulation of a minor subspecies of AChE monomers. We also recently analysed whether long-term exposure to the cholinesterase inhibitor (ChE-I) donepezil influences the AChE species found in AD CSF. The marked increase in CSF-AChE activity in AD patients following long-term treatment with donepezil was not paralleled by a rise in this subset of light variants. Hence, the correlation with the levels of CSF-Abeta is unique to these AChE species in patients receiving such treatment. The aim of this report is to review the links between AChE and beta-amyloid, and to discuss the significance of the responses of the distinct AChE species to ChE-I during the treatment of AD.

A monoclonal antibody against synaptic AChE: a useful tool for detecting apoptotic cells

The classical function of acetylcholinesterase (AChE) is to terminate synaptic transmission at cholinergic synapses by rapidly hydrolyzing the neurotransmitter acetylcholine (ACh). Non-classical functions of AChE involve accelerating the assembly of Abeta peptide into amyloid fibrils and participating in haematopoiesis and neurite growth. Although numerous antibodies have been raised against AChE, many researchers have questioned their reliability to identify the AChE in situ, especially with the regard to its non-classical roles. Researchers attended the Ninth International Meeting on Cholinesterase raised this question by showing different Western blot patterns of AChE detected by different Abs. Producing more effective and reliable Abs for measuring AChE in vivo or in situ has become an important issue in many scientific fields. In this paper, we introduce a monoclonal antibody raised against synaptic AChE that we identified by Western blot assays, immunofluorescent staining and immunoprecipitation of AChE, and mass spectrometry. Our results strongly demonstrate the specificity of our monoclonal antibody to recognize synaptic AChE; hence our antibody can be used as an effective tool to study the various functions of AChE. Since the apoptosis-related AChE was its synaptic form, our antibody can be used as a tool to detect apoptotic cells.

Cerebrospinal fluid acetylcholinesterase changes after treatment with donepezil in patients with Alzheimer's disease

We analyzed whether donepezil differently influences acetylcholinesterase (AChE) variants from cerebrospinal fluid (CSF) in patients with Alzheimer's disease (AD) after long-term treatment. Overall CSF-AChE activity in AD patients before treatment was not different from controls, but the ratio between the major tetrameric form, G(4), and the smaller G(1) and G(2) species was significantly lower. AChE levels at study outset were found to correlate positively with beta-amyloid (1-42) (Abeta42). When patients were re-examined after 12 months treatment with donepezil, there was a remarkable increase in both the G(4) and the lighter species of CSF AChE. As compared with placebo, donepezil caused decreases in the percentage of AChE that failed to bind to the lectin concanavalin A and the antibody AE1. These non-binding species comprised primarily a small subset of G(1) and G(2) forms. In treated patients, these light variants were the only subset of CSF AChE that correlated with CSF-Abeta42 levels. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis showed that a 77-kDa band, attributed in part to inactive AChE, was lower in AD patients than in controls. Unlike enzyme activity, the intensity of this band did not increase after donepezil treatment. The varying responses of different AChE species to ChE-I treatment suggest different modes of regulation, which may have therapeutic implications.

Effects of huperzine A on secretion of nerve growth factor in cultured rat cortical astrocytes and neurite outgrowth in rat PC12 cells

AIM

To study the effects of huperzine A (HupA) on neuritogenic activity and the expression of nerve growth factor (NGF).

METHODS

After being treated with 10 micromol/L HupA, neurite outgrowth of PC12 cells was observed and counted under phase-contrast microscopy. Mitogenic activity was assayed by [3H]thymidine incorporation. Cell cytotoxicity was evaluated by lactate dehydrogenase (LDH) release. AChE activity, mRNA and protein expression were measured by the Ellman method, RT-PCR, and Western blot, respectively. NGF mRNA and protein levels were determined by RT-PCR and ELISA assays.

RESULTS

Treatment of PC12 cells with 10 micromol/L HupA for 48 h markedly increased the number of neurite-bearing cells, but caused no significant alteration in cell viability or other signs of cytotoxicity. In addition to inhibiting AChE activity, 10 micromol/L HupA also increased the mRNA and protein levels of this enzyme. In addition, following 2 h exposure of the astrocytes to 10 micromol/L HupA, there was a significant up-regulation of mRNA for NGF and P75 low-affinity NGF receptor. The protein level of NGF was also increased after 24 h treatment with HupA.

CONCLUSION

Our findings demonstrate for the first time that HupA has a direct or indirect neurotrophic activity, which might be beneficial in treatment of neurodegenerative disorders such as Alzheimer disease.

Dietary modulation of parathion-induced neurotoxicity in adult and juvenile rats

Previous studies indicated that dietary glucose (15% in drinking water) could markedly exacerbate the toxicity of parathion in adult rats. The present study evaluated the effect of consumption of the commonly used sweetener, high fructose corn syrup (HFCS), on parathion toxicity in adult and juvenile rats. Animals were given free access to either water or 15% HFCS in drinking water for a total of 10 days and challenged with parathion (6 or 18 mg/kg, s.c., for juveniles or adults, respectively) on the 4th day. Signs of cholinergic toxicity, body weight and chow/fluid intake were recorded daily. Acetylcholinesterase (AChE) activity and immunoreactivity (AChE-IR) in frontal cortex and diaphragm were measured at 2, 4, and 7 days after parathion. As HFCS was associated with significant reduction in chow intake, adult rats were also pair-fed to evaluate the effect of similar reduced chow intake alone on parathion toxicity. The results indicated that the cholinergic toxicity of parathion was significantly increased by HFCS feeding in both age groups. The excess sugar consumption, however, did not significantly affect parathion-induced AChE inhibition in either tissue or either age group. Enzyme immunoreactivity in frontal cortex was generally not affected in either age group while diaphragm AChE-IR was significantly reduced by parathion and HFCS alone in adult animals at 2 and 4 days timepoints, and more so by the combination of sugar feeding and parathion exposure in both age groups. Food restriction alone did not exacerbate parathion toxicity. While the mechanism(s) remains unclear, we conclude that voluntary consumption of the common sweetener HFCS can markedly amplify parathion acute toxicity in both juvenile and adult rats.

Mechanisms of organophosphate insecticide-induced airway hyperreactivity

It has been suggested that pesticide exposure may be a contributing factor underlying the increased incidence of asthma in the United States and other industrialized nations. To test this hypothesis, airway hyperreactivity was measured in guinea pigs exposed to chlorpyrifos, a widely used organophosphate pesticide. Electrical stimulation of the vagus nerves caused frequency-dependent bronchoconstriction that was significantly potentiated in animals 24 h or 7 days after a single subcutaneous injection of either 390 mg/kg or 70 mg/kg of chlorpyrifos, respectively. Mechanisms by which chlorpyrifos may cause airway hyperreactivity include inhibition of acetylcholinesterase (AChE) or dysfunction of M3 muscarinic receptors on airway smooth muscle or of autoinhibitory M2 muscarinic receptors on parasympathetic nerves in the lung. AChE activity in the lung was significantly inhibited 24 h after treatment with 390 mg/kg of chlorpyrifos, but not 7 days after injection of 70 mg/kg of chlorpyrifos. Acute exposure to eserine (250 microg/ml) also significantly inhibited lung AChE but did not potentiate vagally induced bronchoconstriction. Neuronal M2 receptor function was tested using the M2 agonist pilocarpine, which inhibits vagally induced bronchoconstriction in control animals. In chlorpyrifos-treated animals, pilocarpine dose-response curves were shifted significantly to the right, demonstrating decreased responsiveness of neuronal M2 receptors. In contrast, chlorpyrifos treatment did not alter methacholine-induced bronchoconstriction, suggesting that chlorpyrifos does not alter M3 muscarinic receptor function on airway smooth muscle. These data demonstrate that organophosphate insecticides can cause airway hyperreactivity in the absence of AChE inhibition by decreasing neuronal M2 receptor function.

Induction of acetylcholinesterase expression during apoptosis in various cell types

Acetylcholinesterase (AChE) plays a key role in terminating neurotransmission at cholinergic synapses. AChE is also found in tissues devoid of cholinergic responses, indicating potential functions beyond neurotransmission. It has been suggested that AChE may participate in development, differentiation, and pathogenic processes such as Alzheimer's disease and tumorigenesis. We examined AChE expression in a number of cell lines upon induction of apoptosis by various stimuli. AChE is induced in all apoptotic cells examined as determined by cytochemical staining, immunological analysis, affinity chromatography purification, and molecular cloning. The AChE protein was found in the cytoplasm at the initiation of apoptosis and then in the nucleus or apoptotic bodies upon commitment to cell death. Sequence analysis revealed that AChE expressed in apoptotic cells is identical to the synapse type AChE. Pharmacological inhibitors of AChE prevented apoptosis. Furthermore, blocking the expression of AChE with antisense inhibited apoptosis. Therefore, our studies demonstrate that AChE is potentially a marker and a regulator of apoptosis.

Appraisal of risks from nonoccupational exposure to chlorpyrifos

The toxicological database for chlorpyrifos indicates that humans are not more sensitive than laboratory animals to the toxic effects. Although an oral dose of 1 mg/kg-day resulted in measurable levels of chlorpyrifos in the blood, daily dosing at this level from 9 days to 2 years did not affect brain acetylcholinesterase activity (AChE) in laboratory animals. Developmental toxicity did not occur at doses below maternal toxicity. Most nonoccupational illnesses resulting from entry into areas treated with chlorpyrifos likely stem from odor, rather than the ability of the organophosphate to inhibit AChE. Based on biological monitoring studies, chronic aggregate nonoccupational exposures to chlorpyrifos ranged from 0.0002 mg/kg-day (adults) to 0.0005 mg/kg-day (infants and small children)-1 order of magnitude less than exposures estimated by standard procedures. Other biological monitoring data indicated that cumulative exposure to all organophosphate pesticides ranged from 0.0003 mg/kg-day (adults) to 0.003 mg/kg-day (children). Considering all these factors, the risks of aggregate, nonoccupational exposure to chlorpyrifos have been overstated by more than a 1000-fold.

The effect of continuous pyridostigmine administration on functional (A12) acetylcholinesterase activity in guinea-pig muscles

Pyridostigmine which causes a reversible inhibition of acetylcholinesterase (AChE), was administered continuously for 6 days to guinea-pigs, via a subcutaneously implanted osmotic pump. This produced 40-50% inhibition of red cell acetylcholinesterase (AChE). Controls were animals treated with saline via pumps, and untreated animals. The activities of the functional A12 molecular form of AChE were compared in diaphragm, extensor digitorum longus (EDL) and soleus muscles in the three animal groups at 6 days. The pumps were removed at 6 days and the A12 AChE activities were determined at various times thereafter As the enzyme separation procedure was lengthy, drug-induced inhibition was no longer present when the enzyme activity was measured. At 6 days, the activity was significantly higher in EDL (over 50% higher) and soleus (over two-fold higher) in pyridostigmine-treated animals than saline-treated animals. In the diaphragm, the activities in pyridostigmine and saline-treated animals were similar but both were significantly (over two-fold) higher than in untreated animals. At 1 day after pump removal (day 7) the activity had declined in all three muscles of the pyridostigmine-treated animals and in the diaphragm of saline-treated animals. Thereafter, in the diaphragm (but not the EDL or soleus) in pyridostigmine-treated animals, there were marked variations in the enzyme activity up to day 20. In saline-treated animals there was a marked transient increase in activity at day 13 in all muscles. The results indicate that the homeostatic control offunctional AChE had been affected in both the pyridostigmine and saline treatment groups.

Cognitive function and cholinergic neurochemistry in weanling rats exposed to chlorpyrifos

Previous studies have shown that moderate to high levels of chlorpyrifos (CPF) alter cognitive function in adult and immature rats. In the present study, we tested the hypothesis that lower-level exposure to CPF before or immediately after weaning causes deficits in cognitive function. A total of 78 Long-Evans rats were injected subcutaneously with 0, 0.3 or 7.0 mg/kg CPF every 4 days before or after weaning and were tested with the Morris swim task from postnatal day 24 through 28. Exposure to CPF before weaning did not cause signs of overt cholinergic intoxication or impaired growth nor did the exposures cause significant inhibition of regional brain cholinesterase (ChE) activity or reduction in muscarinic receptors 24 h after the last injection. However, spatial learning was impaired after 5 days of training in the group of weanling rats administered 7.0 mg/kg CPF. Rats administered 0.3 or 7.0 mg/kg CPF after weaning were also impaired in the task, without significant changes in brain ChE activity. These data indicate that low-level exposure to CPF caused deficits in cognitive function in weanling rats, and these effects did not appear to be mediated by the inhibition of brain ChE. It is suggested that the alteration of cognitive function in juvenile rats is an important functional correlate of the cellular and molecular effects of CPF in the immature brain. The mechanisms for CPF-induced cognitive dysfunction are unknown.

Chronic, low-level exposure to the cholinesterase inhibitor DFP. I. Time course of neurochemical changes in the rat pontomesencephalic tegmentum

Rats were repeatedly administered with a low dose of diisopropylfluorosphosphate (DFP; 0.2 mg/kg/day, SC, for 9 or 21 days), an irreversible cholinesterase (ChE) inhibitor. Control rats received a daily injection of oil vehicle. Neurochemical changes occurring in the pontomesencephalic tegmentum (PMT), a brain stem region critically involved in behavioral state control, were evaluated at various times of treatment and after DFP withdrawal. First, enzyme assay revealed a profile of ChE inhibition in the whole PMT which looked like that observed in the striatum; both the inhibition and recovery proceeded more slowly than they did in the plasma. Second, quantitative histochemistry indicated that ChE activity in the mesopontine cholinergic nuclei and the pontine reticular formation progressively decreased across the first days of DFP exposure, to reach an asymptotic level of inhibition after 6 days (74-82% inhibition). The inhibition was less pronounced in the locus coeruleus (49%). Third, [3H]QNB autoradiography showed that muscarinic receptor density was unchanged in any of the PMT areas selected. These results are discussed regarding the question of regional variation in susceptibility to anti-ChE agents. To what extent behavioral state alterations occur concomitantly with ChE activity changes is assessed in the companion article.

Differential recovery of acetylcholinesterase in guinea pig muscle and brain regions after soman treatment

1. In brain areas of untreated guinea-pigs the highest activity of acetylcholinesterase was seen in the striatum and cerebellum, followed by the midbrain, medulla-pons and cortex, and the lowest in the hippocampus. The activity in diaphragm was seven-fold lower than in the hippocampus. 2. At 1 h after soman (27 micrograms/kg) administration the activity of the enzyme was dramatically reduced in all tissues studied. In muscle the three major molecular forms (A12, G4 and G1) showed a similar degree of inhibition and a similar rate of recovery and the activity had returned to normal by 7 days. 3. In the brain soman inhibited the G4 form more than the G1 form. The hippocampus, cortex and midbrain showed the greatest reductions in enzyme activity. At 7 days the activity in the cortex, medulla pons and striatum had recovered but in the hippocampus, midbrain and cerebellum it was still inhibited. 4. Thus the effects of soman administration varied in severity and time course in the different tissues studied. However the enzyme activity was still reduced in all tissues at 24 h when the overt signs of poisoning had disappeared.

Effect of repeated treatment with pyridostigmine on acetylcholinesterase in mouse muscles

1. Pyridostigmine bromide was administered subcutaneously (0.4 mumoles/kg) in mice twice a day for 3 weeks. The activities of the predominant (G1, G4 and A12) molecular forms of acetylcholinesterase were determined in diaphragm, extensor digitorum longus (EDL) and soleus muscles. 2. After the treatment the G4 and A12 forms were reduced in diaphragm, but increased in EDL and soleus. One week later all forms were elevated in all three muscles. At 2 weeks the activity had returned to normal in diaphragm but not in EDL and soleus. 3. A single dose of pyridostigmine was administered in mice which had been pretreated for 3 weeks and left untreated for 2 weeks, and in control mice. 4. In the controls there was no significant effect on the enzyme activities in diaphragm up to 5 days, but there were decreases in EDL, and increases in soleus. In the pretreated group all three forms were increased in diaphragm, especially the A12 form. In soleus and EDL there was a prolonged decrease in all forms, although in the soleus the A12 activity remained above normal. 5. Repeated treatment with pyridostigmine caused delayed changes in functional acetylcholinesterase. Furthermore the treatment had altered the sensitivity of the muscles to the drug.

Effects of pyridostigmine on acetylcholinesterase in different muscles of the mouse

1. Pyridostigmine bromide was administered subcutaneously in mice, in a dose of 4.0 or 2.0 mu moles/kg, and the activity of the predominant (G1, G4 and A12) molecular forms of acetylcholinesterase were examined in diaphragm, extensor digitorum longus (EDL), and soleus muscles at 3 h, 6 h, 24 h and 5 days. 2. In diaphragm, no effect was apparent after the low dose, but after the high dose there was a reduction in activity of the functional A12 form at 24 h, followed by an increase which had overshot the control level at 5 days. 3. In the fast EDL, after the low dose, all three molecular forms were decreased at 3 h but had returned to normal by 6 h. This effect was not apparent after the high dose. 4. In the slow soleus the low dose caused a significant increase in total enzyme activity at 5 days, but the high dose caused significant increases in all molecular forms at 3 hours. 5. Thus pyridostigmine had delayed effects on the levels of acetylcholinesterase. The three muscles displayed different sensitivities to the drug, but the changes were consistent with initial inhibition of the activity leading to down-regulation of the enzyme followed by up-regulation, which could overshoot the normal levels.