AChE/acetylcholinesterase

The production of hazardous character oxyketone (CPO), which has opposing affinity for the active site of serine inhibitory enzymes (like AChE), is regulated by toxic acid through desulfurization [2]. Characteristics of toxicity (3.9-250 μM; 24-72 h) on serine that inhibits the enzymes' active site (like AChE). The toxicity features (7.5-480 μM; 18 h) cause nuclear condensation, raise the activity of caspase 3/7 (60 μM; 2, 4 h), and increase the number of central stars. The progenitor cells of oligodendrocytes are cytotoxic [3]. H2DCF-DA intensity is increased by cellular heme oxygenase-1 mRNA expression (30, 60, 120 μM; 24 h) [3].

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The metabolism of chlorpyrifos (CPS) and chlorpyrifos oxon (CPO) by human hepatocytes and human liver S9 fractions was investigated using LC-MS/MS. Cytochrome P450 (CYP)-dependent and phase II-related products were determined following incubation with CPS and CPO. CYP-related products, 3,5,6-trichloro-2-pyridinol (TCP), diethyl thiophosphate, and dealkylated CPS, were found following CPS treatment and dealkylated CPO following CPO treatment. Diethyl phosphate was not identified because of its high polarity and lack of retention with the chromatographic conditions employed. Phase II-related conjugates, including O- and S-glucuronides as well as 11 GSH-derived metabolites, were identified in CPS-treated human hepatocytes, although the O-sulfate of TCP conjugate was found only when human liver S9 fractions were used as the enzyme source. O-Glucuronide of TCP was also identified in CPO-treated hepatocytes. CPS and CPO were identified using HPLC-UV after CPS metabolism by the human liver S9 fraction. However, CPO was not found following treatment of human hepatocytes with either CPS or CPO. These results suggest that human liver plays an important role in detoxification, rather than activation, of CPS. [2]

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There are increasing concerns regarding the relative safety of chlorpyrifos (CPF) to various facets of the environment. Although published works suggest that CPF is relatively safe in adult animals, recent evidence indicates that juveniles, both animals and humans, may be more sensitive to CPF toxicity than adults. In young animals, CPF is neurotoxic and mechanistically interferes with cellular replication and cellular differentiation, which culminates in the alteration of synaptic neurotransmission in neurons. However, the effects of CPF on glial cells are not fully elucidated. Here we report that chlorpyrifos is toxic to oligodendrocyte progenitors. In addition, CPF produced dose-dependent increases in 2',7'-dichlorodihydrofluorescein diacetate (H(2)DCF-DA) and dihydroethidium (DHE) fluorescence intensities relative to the vehicle control. Moreover, CPF toxicity is associated with nuclear condensation and elevation of caspase 3/7 activity and Heme oxygenase-1 mRNA expression. Pan-caspase inhibitor QVDOPh and cholinergic receptor antagonists' atropine and mecamylamine failed to protect oligodendrocyte progenitors from CPF-induced injury. Finally, glutathione (GSH) depletion enhanced CPF-induced toxicity whereas nitric oxide synthetase inhibitor L-NAME partially protected progenitors and the non-specific antioxidant vitamin E (alpha-tocopherol) completely spared cells from injury. Collectively, this data suggests that CPF induced toxicity is independent of cholinergic stimulation and is most likely caused by the induction of oxidative stress [3].

The lethal dose (LD< sub>50) for 50% of the sample is 97-276 mg/kg, and the toxicity characteristics are moderate acute injury toxicity and po; singleose[2]. 1 mg/kg and 5 mg/kg as 1 mL/kg; subcutaneous injection; once daily for 3 days) to manage pregnancy tracking on days 9–12 of pregnancy, which could cause adverse effects and abnormal behavior in the offspring [4].

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The widely used organophosphate insecticide, Chlorpyrifos (CPF), elicits neurobehavioral abnormalities after apparently subtoxic neonatal exposures. In the current study, we administered 1 or 5 mg/kg/day of CPF to pregnant rats on gestational days 9-12, the embryonic phase spanning formation and closure of the neural tube. Although there were no effects on growth or viability, offspring showed behavioral abnormalities when tested in adolescence and adulthood. In the CPF-exposed groups, locomotor hyperactivity was noted in early T-maze trials, and in the elevated plus-maze; alterations in the rate of habituation were also identified. Learning and memory were adversely affected, as assessed using the 16-arm radial maze. Although all CPF-exposed animals eventually learned the task, reference and working memory were impaired in the early training sessions. After training, rats in the CPF group did not show the characteristic amnestic effect of scopolamine, a muscarinic acetylcholine antagonist, suggesting that, unlike the situation in the control group, muscarinic pathways were not used to solve the maze. These results indicate that apparently subtoxic CPF exposure during neurulation adversely affects brain development, leading to behavioral anomalies that selectively include impairment of cholinergic circuits used in learning and memory. The resemblance of these findings to those of late gestational or neonatal CPF exposure indicates a prolonged window of vulnerability of brain development to CPF.

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CPF/Chlorpyrifos treatment in rodents at low noncholinergic doses during neurodevelopment showed behavioral effects, including locomotor activity, neuromotor function (NMF), cognition, anxiety, social behavior, and maternal care. Zebrafish and C. elegans, which are transparent during development, allow for detailed analysis of specific systems; further, they exhibit neurotoxic effects closely emulating those observed in mammalian pathways. Qualitative results showed concordance among rodents, zebrafish and C. elegans for adverse effects on locomotor activity, NMF, and AChE inhibition. Male rodents had greater sensitivity for effects on locomotor activity than females and exposure during the gestation day 10-14 window showed consistent increases in locomotor activity at low CPF doses (≤1.0 mg kg-1 day-1 ). Zebrafish had cognitive and anxiety deficits after CPF treatment at low doses and young adult C. elegans had reproductive dysfunction associated NMF and disruption of the serotonergic pathway. Quantitative data for all three species showed neurobehavioral effects after exposure to CPF doses approximately 2-10-fold below the threshold for AChE inhibition. Conclusions: Taken together, these findings provided a weight-of-evidence for low-dose CPF neurotoxicity and noncholinergic mechanisms. Variability in laboratories, exposure methods, tests, sex, and animal species/strain might have contributed to the inconsistent results. The detrimental CPF effects during early development are relevant to human populations [1].

Cell Viability Assay [3]
Cell Types: Oligodendrocyte CG-4 Cell
Tested Concentrations: 3.9, 7.8, 15.6, 31.25, 62.5, 125 and 250 μM
Incubation Duration: 24, 48 and 72 hrs (hours)
Experimental Results: More than 62.5 μM Significant Inhibit cell viability.

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Immunofluorescence [3]
Cell Types: Oligodendrocyte CG-4 Cell
Tested Concentrations: 0, 30, 60, 120 μM
Incubation Duration: 24 hrs (hours)
Experimental Results: Nuclear pyknosis and elevation in a dose-dependent manner.

Timed-pregnant Sprague–Dawley rats were housed in breeding cages with a 12-h light–dark cycle and with free access to food and water. Chlorpyrifos/CPF was dissolved in dimethylsulfoxide to provide rapid and complete absorption and was injected subcutaneously in a volume of 1 ml/kg body weight; control animals received vehicle injections on the same schedule. Animals were randomly assigned to receive 0, 1, or 5 mg/kg daily on GD 9–12; these doses lie below the threshold for fetal growth impairment or effects on fetal viability. On the day after birth, pups were randomized within treatment groups and redistributed to the nursing dams with a litter size of 10, so as to maintain standardized nutrition. Randomization was repeated at intervals of several days, and in addition, dams were rotated among litters to distribute any maternal caretaking differences randomly across litters and treatment groups. These animals were part of a much larger cohort. The description of toxicity (i.e. litter size, neonatal mortality, pup weight as well as neurochemical effects) were described by Qiao et al. Animals were weaned on PN 21 and their light–dark cycle was reversed (lights on at 1800) for the remainder of the study.

Absorption, Distribution and Excretion
Five volunteers were given 1 mg (2852 nanomoles) of chlorpyrifos orally. Blood samples were collected within 24 hours, and total urine samples were collected within 100 hours. Four weeks later, each volunteer was given 28.59 mg (81567 nanomoles) of chlorpyrifos percutaneously over 8 hours. Unabsorbed chlorpyrifos was washed off the skin and retained for subsequent assays. Blood and urine collection protocols were the same as for oral administration. Plasma and erythrocyte cholinesterase concentrations were measured in each blood sample. Concentrations of two urinary metabolites of chlorpyrifos—diethyl phosphate and diethyl thiophosphate—were measured in each urine sample. The majority of the oral dose (mean (range) 93% (55–115%)) and 1% of the percutaneous dose were recovered as urinary metabolites. Approximately half (53%) of the percutaneous dose was recovered from the skin surface. The skin absorption rate, as measured by urinary metabolites, was 456 ng/cm²/hr. Male volunteers were given 0.5 mg/kg body weight of chlorpyrifos orally, followed by a 5 mg/kg body weight transdermal administration one month later. Peak plasma concentrations were reached 0.5 hours after oral administration and 22 hours after transdermal administration. The elimination half-life was 27 hours regardless of the route of administration. 70% of the administered dose was recovered in urine after oral administration and 1.3% after transdermal administration. In chlorpyrifos poisoning, chlorpyrifos was detected only in serum samples at concentrations lower than those of diethylphosphine metabolites, which are primarily excreted in urine. In male Sprague-Dawley rats, 83-87% of the drug was excreted 72 hours after a single oral administration of 19 mg/kg body weight of [(14)C] ring-labeled chlorpyrifos via cannulation, primarily via urine (68-70%), feces (14-15%), and exhaled air (0.15-0.39%). The detected residual amount at this time was approximately 1.7% of the total dose, with the highest concentration in fat, but concentrations in any tissue below 1 ppm. For more complete data on the absorption, distribution, and excretion of chlorpyrifos (21 species in total), please visit the HSDB record page. Metabolites/Metabolites were studied in aquariums… Fish exposed to chlorpyrifos were euthanized, and the fish bodies and selected water samples were analyzed by paper chromatography. In addition to the oxygen analogue (ii) of chlorpyrifos, monoethyl analogue (iii) and its oxygen analogue (iv), 3,5,6-trichloro-2-pyridyl phosphate (v), and 3,5,6-trichloro-2-pyridinol (vi) were also found. Compounds ii, iv, v, and vi were found in fish tissues. Two goats were administered [(14)C]-ring labeled (positions 2 and 6) chlorpyrifos capsules twice daily for 10 days, resulting in chlorpyrifos concentrations in their feed equivalent to 15–19 ppm. Most (80%) of the radiolabeled chlorpyrifos was recovered in urine, with smaller amounts present in feces (3.6%), intestines (0.9%), tissues (0.8%), and milk (0.1%). The major metabolite in urine (>75% of residual radiolabeled chlorpyrifos) was a β-glucuronide conjugate of TCP, with a smaller amount of unconjugated TCP. The major residue in fat was chlorpyrifos (0.12 ppm), while the major residue in the liver and kidneys was TCP. A similar elimination pattern was observed in lactating goats administered [(14)C]-ring labeled chlorpyrifos capsules twice daily; small amounts of radiolabeled chlorpyrifos (0.05–0.14%), primarily associated with chlorpyrifos, were detected in milk. Chlorpyrifos (CPF) is a commonly used diethyl thiophosphate (OP) insecticide. Diethyl phosphate (DEP), diethyl thiophosphate (DETP), and 3,5,6-trichloro-2-pyridinol (TCPy) are metabolites and environmental degradation products of chlorpyrifos, and are usually detected in urine as exposure biomarkers. However, since these chemicals can originate from both metabolism and biodegradation, monitoring the total level of metabolites in urine may reflect not only an individual's exposure to the parent pesticide but also their exposure to metabolites present in the environment. This study aimed to compare the pharmacokinetics of oral administration of DEP, DETP, and TCPy in rats with that of oral administration of the parent insecticide chlorpyrifos. Rats were divided into groups and orally administered chlorpyrifos (CPF), diethylpyridinol (DEP), trichloropyridinol (TCPy), or diethylpyridinol (DETP) at a dose of 140 μmol/kg body weight, respectively, and the changes in metabolite concentrations in blood and urine were assessed. Following oral administration, all three metabolites were well absorbed, with peak plasma concentrations reached 1 to 3 hours post-administration. Almost all doses of DEP and TCPy were excreted in the urine within 72 hours, indicating minimal metabolism (if any metabolism occurred, it was negligible); approximately 50% of the dose of DETP was excreted in the urine. The oral dose of CPF was also rapidly absorbed and metabolized into DEP, TCPy, and DETP, with the following urinary distribution order: TCPy (22±3 μmol) > DETP (14±2 μmol) > DEP (1.4±0.7 μmol). Based on the total amount of TCPy detected in the urine, at least 63% of the oral dose of chlorpyrifos was absorbed. These studies support the hypothesis that environmentally present DEP, DETP, and TCPy are readily absorbed by rats (and possibly humans) and excreted in the urine. Methods for non-invasive biomonitoring using reliable portable analytical systems are currently being developed to perform dose quantification analysis using readily available bodily fluids such as saliva. In this study, rats were administered a single dose (1, 10, or 50 mg/kg) of the insecticide chlorpyrifos (CPF) via gavage. Subsequently, saliva and blood samples were collected from each group of animals (n=4 at each time point) at 3, 6, and 12 hours post-administration, and the levels of the CPF metabolite trichloropyridinol (TCP) were analyzed. Trichloropyridinol (TCP) was detected in both blood and saliva at all doses, with higher concentrations in blood than in saliva, despite similar pharmacokinetic characteristics in both. A physiologically based chlorpyrifos (CPF) pharmacokinetic/pharmacodynamic (PBPK/PD) model was developed using a compartmental model to describe the time progression of TCP in blood and saliva. This model successfully simulated the experimental results within the evaluated dose range. We developed a rapid and sensitive sequential injection (SI) electrochemical immunoassay to monitor TCP, with a detection limit of 6 ng/L in water. ...
For more complete data on the metabolism/metabolites of chlorpyrifos (23 metabolites in total), please visit the HSDB record page.
Known human metabolites of chlorpyrifos include 3,5,6-trichloro-2-pyridinol, diethyl thiophosphate, and chlorpyrifos oxyphosphate.
Organophosphate metabolism mainly occurs through oxidation, esterase hydrolysis, and reactions with glutathione. Demethylation and glucuronidation may also occur. Oxidation of organophosphate pesticides can produce moderately toxic products. Generally, thiophosphates themselves are not directly toxic and require oxidative metabolism to be converted into proximal toxins. Products produced by glutathione transferase reactions are generally less toxic. Paraoxyphosphokinase (PON1) is a key enzyme in organophosphate metabolism. PON1 can inactivate some organophosphates through hydrolysis. PON1 hydrolyzes active metabolites in many organophosphate insecticides and nerve agents (such as soman, sarin, and VX). The presence of PON1 polymorphism leads to differences in the enzyme activity and catalytic efficiency of this esterase, which in turn suggests that different individuals may be more susceptible to the toxic effects of organophosphate exposure.

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Biological Half-Life
Administered via intubation to male Wistar rats 50 mg/kg body weight of [(36)Cl] chlorpyrifos…Four hours after administration, the highest residual concentrations were observed in the liver and kidneys, but the half-life in these tissues was less than 20 hours.The longest half-life was 62 hours, recorded in adipose tissue.
In patients poisoned by chlorpyrifos preparations, chlorpyrifos was detected only in serum samples, and at concentrations lower than those of diethylphosphine metabolites, which are primarily excreted in the urine. Urinary diethylphosphine metabolites were excreted according to first-order kinetics, with a mean elimination half-life of 6.1 ± 2.2 hours in the fastest phase and 80 ± 26 hours in the slowest phase. Five volunteers ingested 1 mg (2852 nanomoles) of chlorpyrifos. Blood samples were collected within 24 hours, and total urine volume was collected within 100 hours. Four weeks later, each volunteer was given 28.59 mg (81567 nanomoles) of chlorpyrifos percutaneously over 8 hours. The apparent elimination half-life of dialkyl phosphate in urine was 15.5 hours after oral administration and 30 hours after percutaneous administration. The urinary biological half-life of chlorpyrifos (O,O-diethyl-O-3,5,6-trichloro-2-pyridinyl thiophosphate) was investigated. Male Wistar rats weighing 200 g were intraperitoneally injected with 0.2 mmol/kg body weight of chlorpyrifos. Five hours after injection, the concentrations of both chlorpyrifos and 3,5,6-trichloro-2-pyridinol (TCP) in the blood reached peak values and then rapidly declined. The estimated biological half-lives of chlorpyrifos and TCP in blood are 8.15 hours and 24.66 hours, respectively. ...
For more complete data on the biological half-lives of chlorpyrifos (6 species in total), please visit the HSDB record page.

Toxicity Summary
Identification and Uses: Chlorpyrifos (CPF) is a colorless to white crystalline solid with a slight thiol odor. Chlorpyrifos is an organophosphate insecticide, acaricide, and miticide used to control foliar and soil pests on a variety of food and feed crops. It is registered for use in the United States, but approved pesticide uses may change periodically, so it is essential to consult federal, state, and local authorities for currently approved uses. Human Exposure and Toxicity: Chlorpyrifos can inhibit cholinesterase activity in humans, leading to excessive excitation of the nervous system, causing nausea, dizziness, confusion, respiratory paralysis, and even death at high concentrations. Repeated administration of 0.1 mg/kg chlorpyrifos resulted in significant changes in plasma cholinesterase inhibition, but this was not observed with a single dose. Symptoms of organophosphate poisoning may be similar to acute complications of pregnancy, such as eclampsia and seizures. Poisoning during pregnancy can have serious adverse effects on the mother, fetus, or newborn. Timely diagnosis and treatment are essential, including general supportive therapy and the use of specific drugs such as atropine and oximes, to avoid adverse consequences. Animal studies: Chlorpyrifos (CPF) affects cardiac cholinesterase (ChE) activity and muscarinic receptor binding in newborn and adult rats. Dose- and time-related weight changes and cholinergic toxicity symptoms (involuntary movements) were observed in both age groups. At 1x LD10, the maximum reduction in ChE activity and muscarinic receptor binding was relatively similar, but the reduction in receptor binding occurred earlier in adult rats and lasted longer in newborn rats. Studies in dogs were conducted to determine whether the exposure limit protecting brain acetylcholinesterase (AChE) also protects peripheral tissue AChE after exposure to chlorpyrifos. Results showed that erythrocyte acetylcholinesterase (AChE) was more susceptible to inhibition by chlorpyrifos (CPF) than brain or peripheral tissue AChE, and protection of brain tissue AChE also protected peripheral tissue AChE. Fetal or neonatal exposure to chlorpyrifos or related organophosphorus pesticides can lead to abnormalities in brain cell development, synaptic function, and behavior. Rat studies have shown that the serotonin (5-HT) system produced during chlorpyrifos exposure is significantly affected, and this effect persists for up to two months after treatment in adult rats. Results from studies in 5-month-old rats are consistent with those in adult rats and strongly suggest that the effects of neonatal chlorpyrifos exposure on the 5-HT system are permanent. Exposure to chlorpyrifos during developmental periods alters cellular signaling in brain and peripheral tissues, affecting responses to multiple neurotransmitters and hormones. Adult males tested showed elevated plasma cholesterol and triglyceride levels, but no significant changes in non-esterified free fatty acids and glycerol levels. Similarly, male rats exhibited hyperinsulinemia in a postprandial state with normal circulating glucose levels, but their circulating insulin concentrations decreased appropriately after fasting. Neonatal exposure to subtoxic doses of chlorpyrifos did not affect survival or growth but produced plasma lipid and insulin metabolic patterns similar to those of major risk factors for atherosclerosis and type 2 diabetes in adults. The chromosome breakage potential of chlorpyrifos was assessed by treating rat lymphocytes at concentrations up to 5000 mg/mL for 4 hours, with or without metabolic activation. No increase in chromosomal aberrations was detected. Ecotoxicity studies: Quail poisoning was characterized by reduced food intake and diarrhea within 48 hours, followed by lethargy, drooping wings, muscle incoordination, tremors, and rigidity, ultimately leading to death. A significant correlation was found between cholinesterase activity and total food intake. On April 2, 1985, a serious chlorpyrifos (500 liters) spill occurred on the River Rodin in Essex, England. Within 30 to 40 hours, chlorpyrifos had entered a tidal section of the river 26 km downstream. Within a 23 km stretch of the River Rodin, 90% of the fish biomass (4740 kg) and all aquatic arthropods died. Molluscs and annelids, which were relatively tolerant to chlorpyrifos, survived. Chlorpyrifos is a cholinesterase or acetylcholinesterase (AChE) inhibitor. Cholinesterase inhibitors (or "anticholinesterases") inhibit the activity of acetylcholinesterase. Because acetylcholinesterase plays a crucial role, chemicals that interfere with its activity are potent neurotoxins; even low doses can cause excessive salivation and lacrimation, followed by muscle spasms and ultimately death. Neurotoxins and substances in many pesticides have been shown to exert their effects by binding to serine residues at the active site of acetylcholinesterase, thus completely inhibiting the enzyme's activity. Acetylcholinesterase breaks down the neurotransmitter acetylcholine, which is released at the neuromuscular junction, causing muscle or organ relaxation. Inhibition of acetylcholinesterase results in the accumulation and sustained action of acetylcholine, leading to continuous nerve impulse transmission and unstoppable muscle contractions. The most common acetylcholinesterase inhibitors are phosphorus-containing compounds designed to bind to the enzyme's active site. Their structure requires one phosphorus atom linked to two lipophilic groups, a leaving group (such as a halide or thiocyanate), and a terminal oxygen atom.

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Toxicity Data
LD50: 102 mg/kg (oral, rat) (T42)
LD50: 1233 mg/kg (dermal, rabbit) (T42)
LD50: 192 mg/kg (intraperitoneal, mouse) (T14)
LC50: 560 mg/m3 (4 hours) (inhalation, rat) (T42)

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Interactions
Chlorpyrifos (CPF) is one of the most widely used organophosphate pesticides in agriculture, and it carries corresponding health hazards. This study aimed to evaluate the effects of subchronic oral administration of chlorpyrifos (CPF) on hematological and serum biochemical parameters in mice, and the potential ameliorative effect of vitamin C on these parameters. Thirty mice were randomly assigned to three groups of ten each. Mice in Group I (control group) were given vegetable oil, mice in Group II were given only chlorpyrifos (21.3 mg/kg, approximately 1/5 LD50), and mice in Group III were given vitamin C (100 mg/kg) 30 minutes before administration of chlorpyrifos (vitamin C + chlorpyrifos treatment group). Mice in each group were administered the drugs three times a week for 10 weeks. During the study, toxicity was observed weekly, and the body weight of each mouse was measured. At the end of the study, blood samples were collected from mice to analyze hematocrit (PCV), total red blood cell count (RBC), total white blood cell count (WBC), and total protein (TP). Serum was separated, and the levels of sodium (Na⁺), potassium (K⁺), chloride (Cl⁻), urea, creatinine, alanine aminotransferase (ALT), aspartate aminotransferase (AST), and alkaline phosphatase (ALP) were analyzed. The results showed that mice treated with vitamin C + chlorpyrifos had milder toxic symptoms and significantly increased body weight compared with the chlorpyrifos-only group (p<0.01). Compared with the control group, mice treated with chlorpyrifos alone did not show a significant increase in body weight. Compared with the control group, mice treated with chlorpyrifos alone had significantly higher levels of PCV, RBC, hemoglobin (Hb), TP, and creatinine, while WBC, ALT, and AST levels were significantly lower. Except for significantly elevated white blood cell count (WBC), alanine aminotransferase (ALT), and aspartate aminotransferase (AST), all parameters in the vitamin C + chlorpyrifos (CPF) treatment group were significantly lower than those in the chlorpyrifos-only group. Compared with the control and vitamin C + CPF treatment groups, the alkaline phosphatase (ALP) level in the chlorpyrifos-only group was significantly higher. Except for a significantly lower sodium ion (Na⁺) concentration in the chlorpyrifos-treated group compared to the control group, there were no significant changes in urea and measured electrolytes in all three groups. This study demonstrates that vitamin C pretreatment of mice with chlorpyrifos significantly alters several important hematological and serum biochemical parameters, revealing a protective effect of vitamin C against chlorpyrifos-induced organ damage. Interestingly, clinical evidence suggests that exposure to organophosphates may be associated with increased ethanol sensitivity and reduced voluntary consumption of alcoholic beverages in humans. This study specifically evaluated the neurobiological and behavioral responses to ethanol in Wistar rats previously exposed to the organophosphate insecticide chlorpyrifos (CPF). Consistent with clinical data, animals pretreated with a single injection of CPF exhibited persistent ethanol avoidance behavior, which was not secondary to altered taste processing or enhanced ethanol aversion. Furthermore, CPF pretreatment enhanced ethanol-induced sedation but did not alter blood ethanol levels. Immunocytochemical analysis revealed decreased c-fos expression in the Edinger-Westphal nucleus (a brain region closely associated with ethanol intake and sedation) after CPF treatment. It is hypothesized that chlorpyrifos (CPF) may modulate cellular mechanisms in neuronal pathways closely related to the neurobiological response to ethanol (reducing intracellular cAMP signaling, α7-nicotine receptors, and/or inhibiting brain acetylcholinesterase). ...The effects of developmental exposure to terbutaline (a β2-adrenergic receptor agonist used to prevent preterm birth) and chlorpyrifos (a widely used organophosphorus pesticide) on the serotonin (5-HT) system were investigated. Treatment regimens were chosen to correspond to typical exposure phases in human development: terbutaline (10 mg/kg) was administered on days 2–5 postnatally (PN2–5), and chlorpyrifos (5 mg/kg) on days 11–14 postnatally (PN11–14), with evaluations conducted during juvenile and adolescence (PN21, PN30, and PN45) to compare the effects of each drug alone and sequential administration of the two drugs. Terbutaline alone resulted in sustained presynaptic hyperactivity of serotonin (5-HT), manifested as increased 5-HT turnover in brain regions containing 5-HT terminals; this effect is similar to that observed in earlier studies with administration of chlorpyrifos in the same early postnatal period. Administration of chlorpyrifos on days 11–14 postnatally (PN11–14) resulted in a transient increase in juvenile 5-HT turnover, with sequential dosing of terbutaline followed by chlorpyrifos showing a stronger effect than either drug alone. The interaction between terbutaline and chlorpyrifos suggests that treatment with tocolytics may alter subsequent susceptibility to common environmental toxins. Dietary supplementation with ascorbic acid (0.5%) enhanced the acute toxicity of raptophos, chlorpyrifos, and diazinon, and protected several monitoring serum enzymes except raptophos from decreases. For more complete data on interactions with chlorpyrifos (15 species in total), please visit the HSDB record page.

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Non-human toxicity values
Male albino rat oral LD50: 151 mg/kg / purity 99%/
Dog (rock pigeon) oral LD50: 26.9 mg/kg (95% confidence interval 19.0-38 mg/kg) / purity 94.5%/
Female domestic goat oral LD50: 500-1000 mg/kg / purity 94.5%/
Himalaya rabbit (male and female) skin 1233 mg/kg body weight
For more complete non-human toxicity data for chlorpyrifos (23 in total), please visit the HSDB record page.

[1]. Silva MH. Effects of low-dose chlorpyrifos on neurobehavior and potential mechanisms: A review of studies in rodents, zebrafish, and Caenorhabditis elegans. Birth Defects Res. 2020 Apr 1;112(6):445-479.

[2]. Metabolism of chlorpyrifos and chlorpyrifos oxon by human hepatocytes. J Biochem Mol Toxicol. 2006;20(6):279-91.

[3]. Chlorpyrifos induces oxidative stress in oligodendrocyte progenitor cells. Toxicology. 2009 May 2;259(1-2):1-9.

[4]. Behavioral alterations in adolescent and adult rats caused by a brief subtoxic exposure to chlorpyrifos during neurulation. Neurotoxicol Teratol. 2004 Jan-Feb;26(1):95-101.

Chlorpyrifos is a white, crystalline solid insecticide with a strong odor. It is poorly soluble in water and is usually mixed with an oily liquid before application to crops or animals. It can also be applied to crops in capsule form. Chlorpyrifos was once widely used in homes and farms. In homes, it was used to control cockroaches, fleas, and termites; some pet flea and tick collars also contain chlorpyrifos. On farms, it was used to control ticks on cattle and as a spray to control crop pests. According to an independent committee of scientific and health experts, chlorpyrifos may cause developmental toxicity. Chlorpyrifos is a white crystalline or irregularly flaky solid. It has a very faint thiol odor. It is insoluble in water. It may cause mild irritation to the eyes and skin. Chlorpyrifos is an organothiophosphate, chemically named O,O-diethylhydrothiophosphate, in which the hydrogen atom on the hydroxyl group is replaced by a 3,5,6-trichloropyridin-2-yl group. It is an EC 3.1.1.7 (acetylcholinesterase) inhibitor, agricultural chemical, EC 3.1.1.8 (cholinesterase) inhibitor, environmental pollutant, exogenous substance, acaricide, and insecticide. It is an organothiophosphate and chloropyridine compound. Chlorpyrifos is a synthetic organophosphate acetylcholinesterase inhibitor, reproductive toxin, and neurotoxin used as an insecticide. It is a highly toxic colorless, white, or light brown crystalline solid with a slight rotten egg odor and can be poisoned through inhalation, ingestion, or contact. Chlorpyrifos (IUPAC name: O,O-diethylO-3,5,6-trichloropyridin-2-ylthiophosphate) is a crystalline organophosphate insecticide. It was introduced by Dow Chemical Company in 1965 and has many trade names (see table), including Dursban and Lorsban. It acts on the insect nervous system by inhibiting acetylcholinesterase. Chlorpyrifos is moderately toxic to humans, and exposure has been associated with neurological disorders, persistent developmental delays, and autoimmune diseases. Exposure to chlorpyrifos during pregnancy can impair intellectual development in children, and its use in households has been banned in the United States since 2001. According to the U.S. Environmental Protection Agency (EPA), chlorpyrifos remains one of the most widely used organophosphate pesticides in agriculture. Chlorpyrifos is an organothiophosphoric acid cholinesterase inhibitor and is used as both an insecticide and acaricide. Mechanism of Action: The toxicity of chlorpyrifos is likely due to its metabolism into the oxygen analog chlorpyrifos-oxyphosphate, which subsequently inhibits several enzymes, such as cholinesterase, carboxylase, acetylcholinesterase, and mitochondrial oxidative phosphorylase. For many years, it has been known that organophosphate pesticides inhibit the key enzyme acetylcholinesterase, leading to cholinergic crises in humans. The interaction between activated toxic pesticide metabolites (called oxoforms) and acetylcholinesterase has been extensively studied for decades. However, recent studies have shown that the interaction between certain anticholinesterase organophosphates and acetylcholinesterase is more complex than previously thought, as their inhibitory capacity varies with inhibitor concentration. In this report, we incubated chlorpyrifos oxophosphate (O,O-diethylO-(3,5,6-trichloro-2-pyridyl)phosphate) with recombinant human acetylcholinesterase in the presence of p-nitrophenylacetate to better characterize the interaction between the oxophosphate and the enzyme from a kinetic perspective. The dissociation constant K_d and phosphorylation rate constant k₂ of the chlorpyrifos oxophosphate were measured at different oxophosphate and p-nitrophenylacetate concentrations. The results showed that K_d varied with oxophosphate concentration, while k₂ remained unaffected. Changes in p-nitrophenylacetate concentration did not alter these kinetic parameters. The inhibitory capacity of chlorpyrifos oxoform (measured by k_i(k₂/K_d)) was also affected by concentration-dependent binding affinity changes. These results indicate that the concentration-dependent interaction mechanism between chlorpyrifos oxoform and acetylcholinesterase differs from that of acetylthiocholine. In the latter, the substrate binds to the peripheral anionic site of acetylcholinesterase, thereby reducing enzyme activity by blocking the release of the product thiocholine from the active site. For chlorpyrifos oxophosphoric acid, the release rate of 3,5,6-trichloro-2-pyridinol is irrelevant because its active site cannot interact with other oxophosphoric acid molecules after Ser-203 phosphorylation. …This study summarizes the mechanisms by which chlorpyrifos (CPF) adversely affects DNA synthesis, cell number and size, and adenylate cyclase (AC)-mediated cell signaling in PC12 cells (a neuron-like cell line that mimics the basic characteristics of mammalian developing neurons). …In undifferentiated cells, cholinergic receptor antagonists offer little protection against the antimitotic effects of chlorpyrifos (CPF); however, when differentiation is induced by nerve growth factor, the antagonists show partial protection against CPF-induced cell loss and changes in cell size, but fail to prevent the deterioration of acetylcholine (AC) signaling. Nicotine stimulates nicotinic acetylcholine receptors but also possesses pro-oxidative/antioxidant activity; it produces adverse effects itself but also protects undifferentiated cells from the effects of CPF and has a mixed additive/protective effect on the number of differentiated cells. The antioxidant vitamin E also protects both undifferentiated and differentiated cells from many of the adverse effects of CPF, but exacerbates the effects on acetylcholine (AC) signaling. Theophylline inhibits the breakdown of cyclic adenosine monophosphate (cAMP) and is the only drug that can restore AC signaling to normal or supernormal levels, but further impairs cell replication. …/Conclusion/The results indicate that cholinergic overstimulation, oxidative stress, and interference with AC signaling play a decisive role in the developmental neurotoxicity of CPF, and suggest that this information can be used to design treatment regimens to mitigate these adverse effects.
The mechanism of action of organophosphate derivatives is to bind to and inactivate acetylcholinesterase (AChE). Cholinesterase inhibitor pesticides produce a wide range of effects by inactivating cholinesterase, leading to the accumulation of large amounts of acetylcholine. These effects can be classified into four categories: (1) enhanced postganglionic parasympathetic activity; (2) sustained depolarization of skeletal muscle; (3) initial stimulation following central nervous system cell inhibition; and (4) varying degrees of ganglion stimulation or blockade. /Cholinesterase Inhibitor Pesticides/
For more complete data on the mechanisms of action of chlorpyrifos (6 types), please visit the HSDB record page.

C9H11CL3NO3PS

350.57

348.926

C, 30.83; H, 3.16; Cl, 30.34; N, 4.00; O, 13.69; P, 8.84; S, 9.14

2921-88-2

Chlorpyrifos-d10;285138-81-0

2730

White to off-white solid powder

1.5±0.1 g/cm3

375.9±52.0 °C at 760 mmHg

42-44°C

181.1±30.7 °C

0.0±0.8 mmHg at 25°C

1.566

4.77

0

5

6

18

303

0

CCOP(=S)(OCC)OC1=C(C=C(C(=N1)Cl)Cl)Cl

SBPBAQFWLVIOKP-UHFFFAOYSA-N

InChI=1S/C9H11Cl3NO3PS/c1-3-14-17(18,15-4-2)16-9-7(11)5-6(10)8(12)13-9/h5H,3-4H2,1-2H3

diethoxy-sulfanylidene-(3,5,6-trichloropyridin-2-yl)oxy-λ5-phosphane

Chlorpyrifos; Stipend; chlorpyrifos; 2921-88-2; Dursban; Chlorpyriphos; Lorsban; Trichlorpyrphos; Coroban; Brodan; Suscon; Spannit

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Note: Please store this product in a sealed and protected environment, avoid exposure to moisture.

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

H2O : ~100 mg/mL (~285.23 mM)
DMSO : ~50 mg/mL (~142.62 mM)

Solubility in Formulation 1: ≥ 6.25 mg/mL (17.83 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 62.5 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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Solubility in Formulation 2: 2.5 mg/mL (7.13 mM) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), suspension solution; with ultrasonication.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly.
Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.

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Solubility in Formulation 3: ≥ 2.5 mg/mL (7.13 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

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 (Please use freshly prepared in vivo formulations for optimal results.)