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 ingested 1 mg (2852 nmol) of chlorpyrifos. Blood samples were taken over 24 hours and total void volumes of urine were collected over 100 hours. Four weeks later 28.59 mg (81567 nmol) of chlorpyrifos was administered dermally to each volunteer for 8 hours. Unabsorbed chlorpyrifos was washed from the skin and retained for subsequent measurement. The same blood and urine sampling regime was followed as for the oral administration. Plasma and erythrocyte cholinesterase concentrations were determined for each blood sample. The concentration of two urinary metabolites of chlorpyrifos, diethylphosphate and diethyl-thiophosphate was determined for each urine sample. ... Most of the oral dose (mean (range) 93% (55-115%)) and 1% of the applied dermal dose was recovered as urinary metabolites. About half (53%) of the dermal dose was recovered from the skin surface. The absorption rate through the skin, as measured by urinary metabolites was 456 ng/sq cm/hr. ...
Male volunteers received chlorpyrifos as an oral dose of 0.5 mg/kg bw and 1 month later a dermal dose of 5 mg/kg bw. The time to the maximal concentration of TCP in blood was 0.5 hr after oral dosing and 22 hr after dermal treatment. The elimination half-time, irrespective of the route of administration, was 27 hr. The percentage of the administered dose recovered from the urine was 70% after oral dosing and 1.3% after dermal administration.
In persons poisoned with chlorpyrifos formulations, chlorpyrifos was detected in serum samples only and at lower concentration than the diethylphosphorus metabolites, which were excreted mainly in urine.
By 72 hr after a single oral dose of 19 mg/kg bw [(14)C]ring-labelled chlorpyrifos was given by intubation to male Sprague-Dawley rats, 83-87% had been eliminated, mainly in the urine (68-70%), feces (14-15%), and expired air (0.15-0.39%). The residues found at this time represented about 1.7% of the total dose, and the concentration, while highest in fat, was < 1 ppm in any tissue.
For more Absorption, Distribution and Excretion (Complete) data for CHLORPYRIFOS (21 total), please visit the HSDB record page.

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Metabolism / Metabolites
Metabolism of Dursban in fish was studied in a tank ... After exposure to Dursban, the fish were sacrificed and the fish and some water examined by paper chromatography. In addition to oxygen analog (ii) of Dursban, the monoethyl analog (iii) of Dursban and its oxygen analog (iv), 3,5,6-trichloro-2-pyridyl phosphate (v), and 3,5,6-trichloro-2-pyridinol (vi) were also found. In the fish tissues themselves, compounds ii, iv, v, vi were found.
Two goats were fed [(14)C]ring labeled (positions 2 and 6) chlorpyrifos twice daily in capsules for 10 days at concentrations equivalent to 15-19 ppm in the feed. The majority (80%) of the radiolabel was recovered in urine, with smaller amounts in feces (3.6%), gut (0.9%), tissues (0.8%), and milk (0.1%). The major urinary metabolite (> 75% of the residual radiolabel) was the beta-glucuronide conjugate of TCP, with smaller amounts of unconjugated TCP. The major residue in fat was chlorpyrifos (0.12 ppm), while TCP was the major residue in liver and kidney. A similar pattern of elimination was seen in a study in which lactating goats were fed [(14)C]ring labeled chlorpyrifos twice daily by capsule; little radiolabel (0.05-0.14%), mainly associated with chlorpyrifos, was recovered in milk.
Chlorpyrifos (CPF) is a commonly used diethylphosphorothionate organophosphorus (OP) insecticide. Diethylphosphate (DEP), diethylthiophosphate (DETP) and 3,5,6-trichloro-2-pyridinol (TCPy) are products of metabolism and of environmental degradation of CPF and are routinely measured in urine as biomarkers of exposure. However, because these same chemicals can result from metabolism or by biodegradation, monitoring total urinary metabolite levels may be reflective of not only an individual's contact with the parent pesticide, but also exposure with the metabolites, which are present in the environment. The objective of the current study was to compare the pharmacokinetics of orally administered DEP, DETP and TCPy with their kinetics following oral dosing with the parent insecticide CPF in the rat. Groups of rats were orally administered CPF, DEP, TCPy or DETP at doses of 140 umol/kg body weight, and the time-courses of the metabolites were evaluated in blood and urine. Following oral administration, all three metabolites were well absorbed with peak blood concentrations being attained between 1 and 3 hr post-dosing. In the case of DEP and TCPy virtually all the administered dose was recovered in the urine by 72 hr post-dosing, suggesting negligible, if any, metabolism; whereas with DETP, approximately 50% of the orally administered dose was recovered in the urine. The CPF oral dose was likewise rapidly absorbed and metabolized to DEP, TCPy and DETP, with the distribution of metabolites in the urine followed the order: TCPy (22+/-3 umol)>DETP (14+/-2 umol)>DEP (1.4+/-0.7 umol). Based upon the total amount of TCPy detected in the urine a minimum of 63% of the oral CPF dose was absorbed. These studies support the hypotheses that DEP, DETP and TCPy present in the environment can be readily absorbed and eliminated in the urine of rats and potentially humans.
Non-invasive biomonitoring approaches are being developed using reliable portable analytical systems to quantify dosimetry utilizing readily obtainable body fluids, such as saliva. In the current study, rats were given single oral gavage doses (1, 10, or 50 mg/kg) of the insecticide chlorpyrifos (CPF). Saliva and blood were then collected from groups of animals (4/time-point) at 3, 6, and 12 hr post-dosing, and were analyzed for the CPF metabolite trichloropyridinol (TCP). Trichloropyridinol was detected in both blood and saliva at all doses and the TCP concentration in blood exceeded saliva, although the kinetics in blood and saliva were comparable. A physiologically based pharmacokinetic and pharmacodynamic (PBPK/PD) model for CPF incorporated a compartment model to describe the time-course of TCP in blood and saliva. The model adequately simulated the experimental results over the dose ranges evaluated. A rapid and sensitive sequential injection (SI) electrochemical immunoassay was developed to monitor TCP, and the reported detection limit for TCP was 6 ng/L (in water). ...
For more Metabolism/Metabolites (Complete) data for CHLORPYRIFOS (23 total), please visit the HSDB record page.
Chlorpyrifos has known human metabolites that include 3,5,6-Trichloro-2-pyridinol, Diethyl phosphorothioate, and Chlorpyrifos-oxon.
Metabolism of organophosphates occurs principally by oxidation, by hydrolysis via esterases and by reaction with glutathione. Demethylation and glucuronidation may also occur. Oxidation of organophosphorus pesticides may result in moderately toxic products. In general, phosphorothioates are not directly toxic but require oxidative metabolism to the proximal toxin. The glutathione transferase reactions produce products that are, in most cases, of low toxicity. Paraoxonase (PON1) is a key enzyme in the metabolism of organophosphates. PON1 can inactivate some organophosphates through hydrolysis. PON1 hydrolyzes the active metabolites in several organophosphates insecticides as well as, nerve agents such as soman, sarin, and VX. The presence of PON1 polymorphisms causes there to be different enzyme levels and catalytic efficiency of this esterase, which in turn suggests that different individuals may be more susceptible to the toxic effect of organophosphate exposure.

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Biological Half-Life
A dose of 50 mg/kg bw [(36)Cl] chlorpyrifos given orally to male Wistar rats by intubation ...The concentrations of residue were highest in liver and kidney 4 hr after dosing, but the half-life in these tissues was < 20 hr. The longest half-time, 62 hr, was recorded in fat.
In persons poisoned with chlorpyrifos formulations, chlorpyrifos was detected in serum samples only and at lower concentration than the diethylphosphorus metabolites, which were excreted mainly in urine. The urinary diethylphosphorus metabolites were excreted by first-order kinetics, with an average elimination half-life of 6.1 + or - 2.2 hr in the fastest phase and 80 + or - 26 hr in the slowest.
... Five volunteers ingested 1 mg (2852 nmol) of chlorpyrifos. Blood samples were taken over 24 hours and total void volumes of urine were collected over 100 hours. Four weeks later 28.59 mg (81567 nmol) of chlorpyrifos was administered dermally to each volunteer for 8 hours. ... The apparent elimination half-life of urinary dialkylphosphates after the oral dose was 15.5 hours and after the dermal dose it was 30 hours. ...
Urinary ... biological half-life of chlorpyrifos (O, O-diethyl-O-3,5,6-trichloro-2-pyridinyl phosphorothioate) ... /was/ investigated. Male Wistar rats weighing 200 g were intraperitoneally injected with chlorpyrifos at a level of 0.2 mmol/kg body weight. Both chlorpyrifos and 3,5,6-trichloro-2-pyridinol (TCP) levels in blood showed maximum values at 5 hr post-injection, and then decreased rapidly. Biological half-lives of the blood chlorpyrifos and TCP were estimated to 8.15 and 24.66 hr, respectively. ...
For more Biological Half-Life (Complete) data for CHLORPYRIFOS (6 total), please visit the HSDB record page.

Toxicity Summary
IDENTIFICATION AND USE: Chlorpyrifos (CPF) is a colorless to white crystalline solid with a mild mercaptan odor. CPF is an organophosphate insecticide, acaricide, and miticide used to control foliage and soil-borne insect pests on a variety of food and feed crops. It is registered for use in the U.S. but approved pesticide uses may change periodically and so federal, state and local authorities must be consulted for currently approved uses. HUMAN EXPOSURE AND TOXICITY: CPF can cause cholinesterase inhibition in humans leading to an overstimulated nervous system causing nausea, dizziness, confusion, and respiratory paralysis and death at very high exposures. Significant changes in plasma cholinesterase inhibition were seen in repeated doses of 0.1 mg/kg of CPF but not in single doses. Organophosphate poisoning may mimic acute complications in pregnancy, such as eclampsia and seizures. Poisoning during pregnancy may result in serious adverse effects for both mother and the fetus or neonate. Prompt diagnosis and treatment including general supportive measures and use of specific pharmacological agents such as atropine and oximes are necessary to avoid adverse outcomes. ANIMAL STUDIES: CPF affects cardiac cholinesterase (ChE) activity and muscarinic receptor binding in neonatal and adult rats. Dose- and time-related changes in body weight and cholinergic signs of toxicity (involuntary movements) were noted in both age groups. With 1x LD(10), relatively similar maximal reductions in ChE activity and muscarinic receptor binding were noted, but receptor binding reductions appeared earlier in adults and were more prolonged in neonates. Studies were performed in dogs to find out whether exposure limits that protect brain acetylcholinesterase (AChE) will protect peripheral tissue AChE after exposure to CPF. The results show that red blood cells AChE is more sensitive than brain or peripheral tissue AChE to inhibition by CPF, and that protection of brain AChE would protect peripheral tissue AChE. Fetal or neonatal exposure to CPF or related organophosphate pesticides leads to abnormalities of brain cell development, synaptic function, and behavior. Studies in rats indicate profound effects on serotonin (5HT) systems that originate during CPF exposure and that are still present at 2 months posttreatment in the young adult. Findings at 5 months of age replicate those seen in young adulthood and strongly suggest that the effects of neonatal CPF exposure on 5HT systems are permanent. Developmental exposure to CPF alters cell signaling both in the brain and in peripheral tissues, affecting the responses to a variety of neurotransmitters and hormones. When tested in adulthood, CPF-exposed male animals displayed elevations in plasma cholesterol and triglycerides, without underlying alterations in nonesterified free fatty acids and glycerol. Similarly, in the postprandial state, male rats showed hyperinsulinemia in the face of normal circulating glucose levels but demonstrated appropriate reduction of circulating insulin concentrations after fasting. Apparently subtoxic neonatal chlorpyrifos exposure, devoid of effects on viability or growth, produce a metabolic pattern for plasma lipids and insulin that resembles the major adult risk factors for atherosclerosis and type 2 diabetes mellitus. CPF was evaluated for clastogenic potential using rat lymphocytes treated for 4 hours with concentrations of up to 5000 mg/mL with and without metabolic activation. No increase in chromosomal aberrations was detected. ECOTOXICITY STUDIES: Intoxication in the bobwhite was characterized by reduced food consumption and diarrhea in 48 hr, followed by lethargy, wing droop, muscular incoordination, tremors and tetany immediately preceding death. There was a significant correlation between ChE activity and total food consumption. A major spillage of the insecticide Dursban (500 L) occurred along the River Roding, Essex, UK on 2 Apr 1985. Within 30 to 40 hr, Dursban had entered tidal reaches of the river, 26 km downstream from the spillage point. 90% of the previous biomass of fish (4740 kg) and all aquatic arthropods were killed over a 23 km stretch of the River Roding. Mollusks and annelids, which are relatively tolerant of chlorpyrifos, survived.
Chlorpyrifos is a cholinesterase or acetylcholinesterase (AChE) inhibitor. A cholinesterase inhibitor (or 'anticholinesterase') suppresses the action of acetylcholinesterase. Because of its essential function, chemicals that interfere with the action of acetylcholinesterase are potent neurotoxins, causing excessive salivation and eye-watering in low doses, followed by muscle spasms and ultimately death. Nerve gases and many substances used in insecticides have been shown to act by binding a serine in the active site of acetylcholine esterase, inhibiting the enzyme completely. Acetylcholine esterase breaks down the neurotransmitter acetylcholine, which is released at nerve and muscle junctions, in order to allow the muscle or organ to relax. The result of acetylcholine esterase inhibition is that acetylcholine builds up and continues to act so that any nerve impulses are continually transmitted and muscle contractions do not stop. Among the most common acetylcholinesterase inhibitors are phosphorus-based compounds, which are designed to bind to the active site of the enzyme. The structural requirements are a phosphorus atom bearing two lipophilic groups, a leaving group (such as a halide or thiocyanate), and a terminal oxygen.

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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 over 4 hours (Inhalation, Rat) (T42)

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Interactions
Chlorpyrifos (CPF) is one of the most widely used organophosphorous insecticides in agriculture with its attendant adverse health outcomes. This study aimed at evaluating the effect of subchronic oral CPF administration on hematological and serum biochemical indices, and the possible ameliorating effect of vitamin C on the indices in mice. Thirty mice divided into 3 groups of 10 mice each were used for this study. Mice in group I (control) were dosed with vegetable oil, while those in group II were given CPF (21.3 mg/kg~ 1/5(th) LD50) only. Mice in group III were pretreated with vitamin C (100 mg/kg) prior to dosing with CPF 30 min later (Vitamin C + CPF-treated group). This regime was given to each group of mice three times a week for a period of ten weeks. During the study period, mice were examined for signs of toxicity, and weight of each mouse was measured every week. At the end of the study period, blood samples were collected from the mice and analyzed for packed cell volume (PCV), total red blood cell (RBC), white blood cell (WBC) and total protein (TP). Serum obtained from the blood was analyzed for Na(+, K+ and Cl-), urea, creatinine, alanine aminotransferase (ALT), aspartate aminotransferase (AST), and alkaline phosphatase (ALP). The results showed that mice in the vitamin C + CPF-treated group exhibited milder signs of toxicity and significant increase in weight gain (p<0.01) compared to the CPF-treated group. No significant increase in weight in the CPF-treated group was observed compared to the control. There was a significant increase in PCV, RBC, Hb, TP and creatinine, but a significant decrease was obtained in WBC, ALT and AST in the CPF-treated group compared to the control. All the parameters with the exception of WBC, ALT and AST (which increased significantly), were significantly decreased in the vitamin C + CPF-treated group compared to CPF-treated group. ALP was significantly elevated in the CPF-treated group compared to both the control and vitamin C + CPF-treated group. No significant changes in urea and the measured electrolytes in all three groups, except a significant decrease in the concentration of Na(+) was observed in the CPF-treated group compared to the control. The study demonstrated that pretreatment of CPF-administered mice with vitamin C significantly altered some important hematological and serum biochemical parameters, revealing the protective action of the vitamin against some organ damage induced by CPF.
... Interestingly, clinical evidence suggests that exposure to organophosphates might be linked to increased ethanol sensitivity and reduced voluntary consumption of ethanol-containing beverages in humans. ... Present study specifically evaluated neurobiological and behavioral responses to ethanol in Wistar rats that were previously exposed to the pesticide organophosphate chlorpyrifos (CPF). In agreement with clinical data, animals pretreated with a single injection of CPF showed long-lasting ethanol avoidance that was not secondary to altered gustatory processing or enhancement of the aversive properties of ethanol. Furthermore, CPF pretreatment increased ethanol-induced sedation without altering blood ethanol levels. An immunocytochemical assay revealed reduced c-fos expression in the Edinger-Westphal nucleus following CPF treatment, a critical brain area that has been implicated in ethanol intake and sedation. /It was hypothesized/ ... that CPF might modulate cellular mechanisms (decreased intracellular cAMP signaling, alpha-7-nicotinic receptors, and/or cerebral acetylcholinesterase inhibition) in neuronal pathways critically involved in neurobiological responses to ethanol.
... The effects of developmental exposure to terbutaline, a beta2-adrenergic receptor agonist used to arrest preterm labor, and chlorpyrifos, a widely used organophosphate pesticide, on serotonin (5HT) systems /were examined/. Treatments were chosen to parallel periods typical of human developmental exposures, terbutaline (10 mg/kg) on postnatal days (PN) 2-5 and chlorpyrifos (5 mg/kg) on PN11-14, with assessments conducted in juvenile and adolescent stages (PN21, PN30 and PN45), comparing each agent alone as well as sequential administration of both. By itself, terbutaline produced persistent 5HT presynaptic hyperactivity as evidenced by increased 5HT turnover in brain regions containing 5HT terminal zones; this effect was similar to that seen in earlier studies with chlorpyrifos administration during the same early postnatal period. Later administration of chlorpyrifos (PN11-14) produced a transient increase in 5HT turnover during the juvenile stage, and the sequential exposure paradigm, terbutaline followed by chlorpyrifos, showed a corresponding increase in effect over either agent alone. ... the interaction between terbutaline and chlorpyrifos suggests that tocolytic therapy may alter the subsequent susceptibility to common environmental toxicants.
Addition of ascorbic acid to the diet (0.5%) enhanced the acute toxicity of leptophos, chlorpyrifos and diazinon and protected a number of the monitored serum enzymes from being decreased except for leptophos.
For more Interactions (Complete) data for CHLORPYRIFOS (15 total), please visit the HSDB record page.

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Non-Human Toxicity Values
LD50 albino Rats males oral 151 mg/kg /purity 99%/
LD50 Rock Doves (domestic pigeons) oral 26.9 mg/kg (95% confidence limit 19.0-38 mg/kg) /purity 94.5%/
LD50 domestic goats females oral 500-1000 mg/kg /purity 94.5%/
LD50 Rabbit dermal, Himalayan (male & femle) 1233 mg/kg bw
For more Non-Human Toxicity Values (Complete) data for CHLORPYRIFOS (23 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 an insecticide that is a white crystal-like solid with a strong odor. It does not mix well with water, so it is usually mixed with oily liquids before it is applied to crops or animals. It may also be applied to crops in a capsule form. Chlorpyrifos has been widely used in homes and on farms. In the home, it is used to control cockroaches, fleas, and termites; it is also used in some pet flea and tick collars. On the farm, it is used to control ticks on cattle and as a spray to control crop pests.
Chlorpyrifos can cause developmental toxicity according to an independent committee of scientific and health experts.
Chlorpyrifos is a white crystalline or irregularly flaked solid. It has a very faint mercaptan-type odor. It is not soluble in water. It can cause slight irritation to the eye and skin.
Chlorpyrifos is an organic thiophosphate that is O,O-diethyl hydrogen phosphorothioate in which the hydrogen of the hydroxy group has been replaced by a 3,5,6-trichloropyridin-2-yl group. It has a role as an EC 3.1.1.7 (acetylcholinesterase) inhibitor, an agrochemical, an EC 3.1.1.8 (cholinesterase) inhibitor, an environmental contaminant, a xenobiotic, an acaricide and an insecticide. It is an organic thiophosphate and a chloropyridine.
Chlorpyrifos is a synthetic organophosphate acetylcholinesterase inhibitor, reproduction toxicant, and neurotoxicant that is used as a pesticide. It is characterized as a highly toxic colorless, white, or light brown crystalline solid with a mild rotten egg odor, and exposure occurs by inhalation, ingestion, or contact.
Chlorpyrifos (IUPAC name: O,O-diethyl O-3,5,6-trichloropyridin-2-yl phosphorothioate) is a crystalline organophosphate insecticide. It was introduced in 1965 by Dow Chemical Company and is known by many trade names (see table), including Dursban and Lorsban. It acts on the nervous system of insects by inhibiting acetylcholinesterase. Chlorpyrifos is moderately toxic to humans, and exposure has been linked to neurological effects, persistent developmental disorders, and autoimmune disorders. Exposure during pregnancy retards the mental development of children, and most use in homes has been banned since 2001 in the U.S. In agriculture, it remains one of the most widely used organophosphate insecticides, according to the United States Environmental Protection Agency (EPA).
An organothiophosphate cholinesterase inhibitor that is used as an insecticide and as an acaricide.

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Mechanism of Action
The toxicity of chlorpyrifos is probably the result of metabolic conversion to its oxygen analog, chlorpyrifos-oxon, and its subsequent inhibition of various enzymes (eg, cholinesterases, carboxylases, acetylcholinesterases, and mitochondrial oxidative phosphorylases).
The organophosphorus insecticides have been known for many years to cause cholinergic crisis in humans as a result of the inhibition of the critical enzyme acetylcholinesterase. The interactions of the activated, toxic insecticide metabolites (termed oxons) with acetylcholinesterase have been studied extensively for decades. However, more recent studies have suggested that the interactions of certain anticholinesterase organophosphates with acetylcholinesterase are more complex than previously thought since their inhibitory capacity has been noted to change as a function of inhibitor concentration. In the present report, chlorpyrifos oxon (O,O-diethyl O-(3,5,6-trichloro-2-pyridyl) phosphate) was incubated with human recombinant acetylcholinesterase in the presence of p-nitrophenyl acetate in order to better characterize kinetically the interactions of this oxon with enzyme. Determination of the dissociation constant, K(d), and the phophorylation rate constant, k(2), for chlorpyrifos oxon with a range of oxon and p-nitrophenyl acetate concentrations revealed that K(d), but not k(2), changed as a function of oxon concentration. Changes in p-nitrophenyl acetate concentrations did not alter these same kinetic parameters. The inhibitory capacity of chlorpyrifos oxon, as measured by k(i) (k(2)/K(d)), was also affected as a result of the concentration-dependent alterations in binding affinity. These results suggest that the concentration-dependent interactions of chlorpyrifos oxon with acetylcholinesterase resulted from a different mechanism than the concentration-dependent interactions of acetylthiocholine. In the latter case, substrate bound to the peripheral anionic site of acetylcholinesterase has been shown to reduce enzyme activity by blocking the release of the product thiocholine from the active site gorge. With chlorpyrifos oxon, the rate of release of 3,5,6-trichloro-2-pyridinol is irrelevant since the active site is not available to interact with other oxon molecules after phosphorylation of Ser-203 has occurred.
... Mechanisms contributing to the adverse effects of chlorpyrifos (CPF) on DNA synthesis, cell number and size, and cell signaling mediated by adenylyl cyclase (AC) in PC12 cells, a neuronotypic cell line that recapitulates the essential features of developing mammalian neurons /were concluded/ . ... In undifferentiated cells, cholinergic receptor antagonists had little or no protective effect against the antimitotic actions of CPF; however, when nerve growth factor was used to evoke differentiation, the antagonists showed partial protection against deficits in cell loss and alteration in cell size elicited by CPF, but were ineffective in preventing the deterioration of AC signaling. Nicotine, which stimulates nicotinic acetylcholine receptors but also possesses a mixture of prooxidant/antioxidant activity, had adverse effects by itself but also protected undifferentiated cells from the actions of CPF and had mixed additive/protective effects on cell number in differentiating cells. The antioxidant vitamin E also protected both undifferentiated and differentiating cells from many of the adverse effects of CPF but worsened the impact on AC signaling. Theophylline, which prevents the breakdown of cyclic AMP, was the only agent that restored AC signaling to normal or supranormal levels but did so at further cost to cell replication. ... /It was concluded that the/ results show definitive contributions of cholinergic hyperstimulation, oxidative stress, and interference with AC signaling in the developmental neurotoxicity of CPF and point to the potential use of this information to design treatments to ameliorate these adverse effects.
Organophosphorus derivatives act by combining with and inactivating the enzyme acetylcholinesterase (AChE). ... The inactivation of cholinesterase by cholinesterase inhibitor pesticides allows the accumulation of large amounts of acetylcholine, with resultant widespread effects that may be ... separated into 4 categories: (1) Potentiation of postganglionic parasympathetic activity. ... (2) Persistent depolarization of skeletal muscle ... (3) Initial stimulation following depression of cells of central nervous system ... (4) Variable ganglionic stimulation or blockade ... /Cholinesterase inhibitor pesticides/
For more Mechanism of Action (Complete) data for CHLORPYRIFOS (6 total), 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.)