Analysis of chlorpyrifos exposure and human health: expert panel report

This report summarizes the deliberations of an eight-member panel of scientists convened by Dow AgroSciences in cooperation with the U.S. Environmental Protection Agency (EPA). The panel was charged with evaluating the scientific literature on the health effects potentially associated with exposure to the insecticide chlorpyrifos. Specifically, the panel was asked to (1) evaluate human experience data available and address the adequacy of the available current literature; (2) develop a list of recommendations for epidemiology studies, including appropriate endpoints and study populations, and strengths and weaknesses of each approach; and (3) draft a report to summarize its recommendations. The panel assessed the quality of the existing epidemiologic literature on chlorpyrifos and specific outcomes such as neuropathy (including organophosphate induced delayed neurotoxicity), behavior (cognition and affect), immunologic, and multiple complaints (also referred to as multiple chemical sensitivities). The majority of panel members (five members) agreed that the literature reviewed provided little or no scientific evidence that chlorpyrifos exposure causes harm to human health other than its known cholinergic effects associated with acute poisoning. Those panel members voting in the minority (three members) agreed that the studies reviewed provided inadequate evidence to preclude the possibility of adverse effects to human health from chlorpyrifos exposure at levels associated with its manufacture or professional application. Those voting in the minority suggested further investigation of cohort(s) of workers engaged in either the manufacture or the professional application of chlorpyrifos, or both. Compared to the general population, these groups have relatively high levels of exposure to chlorpyrifos. The primary health outcomes recommended for study were cognitive and affective disorders, with consideration of the assessment of peripheral neuropathy also suggested for at least a subset of the cohort.     

Analysis of chlorpyrifos exposure and human health: expert panel report

This report summarizes the deliberations of an eight-member panel of scientists convened by Dow AgroSciences in cooperation with the U.S. Environmental Protection Agency (EPA). The panel was charged with evaluating the scientific literature on the health effects potentially associated with exposure to the insecticide chlorpyrifos. Specifically, the panel was asked to (1) evaluate human experience data available and address the adequacy of the available current literature; (2) develop a list of recommendations for epidemiology studies, including appropriate endpoints and study populations, and strengths and weaknesses of each approach; and (3) draft a report to summarize its recommendations. The panel assessed the quality of the existing epidemiologic literature on chlorpyrifos and specific outcomes such as neuropathy (including organophosphate induced delayed neurotoxicity), behavior (cognition and affect), immunologic, and multiple complaints (also referred to as multiple chemical sensitivities). The majority of panel members (five members) agreed that the literature reviewed provided little or no scientific evidence that chlorpyrifos exposure causes harm to human health other than its known cholinergic effects associated with acute poisoning. Those panel members voting in the minority (three members) agreed that the studies reviewed provided inadequate evidence to preclude the possibility of adverse effects to human health from chlorpyrifos exposure at levels associated with its manufacture or professional application. Those voting in the minority suggested further investigation of cohort(s) of workers engaged in either the manufacture or the professional application of chlorpyrifos, or both. Compared to the general population, these groups have relatively high levels of exposure to chlorpyrifos. The primary health outcomes recommended for study were cognitive and affective disorders, with consideration of the assessment of peripheral neuropathy also suggested for at least a subset of the cohort.     

Comparative neurochemical effects of repeated methyl parathion or chlorpyrifos exposures in neonatal and adult rats.

Several studies have reported higher sensitivity based on lethality in young animals compared to adults following acute exposure to organophosphorus insecticides (OPs). We propose that age-related differences in sensitivity to OPs may differ qualitatively and quantitatively with different OPs and varying exposure conditions (e. g., high vs. low dose, acute vs. repeated). To test this hypothesis, we treated neonatal (7 days of age) and adult (90 days of age) rats with either methyl parathion (MPS) or chlorpyrifos (CPF) daily for 14 days and measured neurochemical endpoints {cholinesterase (ChE) inhibition, total muscarinic receptor ([(3)H]quinuclidinyl benzilate, QNB) and muscarinic M2 subtype-preferential ([(3)H]AF-DX 384) binding} in frontal cortex and striatum at timepoints both during (1 day after the 7(th) and 14(th) dose) and after (8 days after the 14(th) dose) exposures. Repeated CPF exposures were associated with relatively similar degrees of ChE inhibition between the age groups during dosing but more extensive inhibition was noted in adults after termination of exposures. Relatively similar changes in muscarinic receptor binding were also noted between age groups following CPF exposures. Moreover, the degree of muscarinic receptor binding reduction relative to ChE inhibition appeared similar in both age groups following CPF exposures. In contrast, ChE activity and muscarinic receptor binding were generally more reduced in neonatal relative to adult brain regions following repeated MPS exposures. Furthermore, the relationship between the degree of ChE inhibition and the reduction in cortical muscarinic receptor binding appeared different between the age groups, i.e., more extensive reduction was noted in neonates compared to adults with a given level of ChE inhibition. We conclude that OP-selective differences in in vivo ChE sensitivity, differential rates of enzyme recovery following inhibition, and age-dependent differences in muscarinic receptor adaptations can all influence the nature of age-related susceptibility to OPs.     

Neuroanatomical targets of the organophosphate chlorpyrifos by c-fos immunolabeling.

Chlorpyrifos (CPF) is an organophosphate widely used as an insecticide in agriculture which elicits short- and long-term neurobehavioral deficits after acute administration. Because little is known about the specific brain areas targeted by CPF, investigating for the location of its neuroanatomical targets could help to describe the brain systems involved in the neurobehavioral toxicity developed in CPF-exposed organisms. To meet this objective, in the present study we evaluated CPF-induced c-fos expression. In addition, locomotor behavior and cerebral cholinesterase level were evaluated. We found two main sets of results. First, no significant c-fos expression was found in cholinoceptive regions in CPF-treated rats 2 h or 24 h post-administration, despite the fact that 41% and 62% acetylcholinesterase inhibition, respectively, were present in brain homogenates. These results are consistent with previous reports showing CPF-induced activation of adaptive neural mechanisms re-establishing cholinergic tone. Second, 24 h post-intoxication CPF elicited c-fos expression in cytokine-related areas. Cytokines have been involved in anxiety-like responses and psychiatric stress syndromes. Taking into account that CPF triggers the synthesis of peripheral cytokines, the present data stress the need to further clarify functional relations between organophosphate-triggered peripheral cytokines and emotional disturbances reported in intoxicated organisms.     

An evaluation of the inhibition of human butyrylcholinesterase and acetylcholinesterase by the organophosphate chlorpyrifos oxon

Acetylcholinesterase (EC 3.1.1.7) and butyrylcholinesterase (EC 3.1.1.8) are enzymes that belong to the superfamily of α/β-hydrolase fold proteins. While they share many characteristics, they also possess many important differences. For example, whereas they have about 54% amino acid sequence identity, the active site gorge of acetylcholinesterase is considerably smaller than that of butyrylcholinesterase. Moreover, both have been shown to display simple and complex kinetic mechanisms, depending on the particular substrate examined, the substrate concentration, and incubation conditions. In the current study, incubation of butyrylthiocholine in a concentration range of 0.005–3.0 mM, with 317 pM human butyrylcholinesterase in vitro, resulted in rates of production of thiocholine that were accurately described by simple Michaelis–Menten kinetics, with a K_m of 0.10 mM. Similarly, the inhibition of butyrylcholinesterase in vitro by the organophosphate chlorpyrifos oxon was described by simple Michaelis–Menten kinetics, with a k_i of 3048 nM⁻¹ h⁻¹, and a K_D of 2.02 nM. In contrast to inhibition of butyrylcholinesterase, inhibition of human acetylcholinesterase by chlorpyrifos oxon in vitro followed concentration-dependent inhibition kinetics, with the k_i increasing as the inhibitor concentration decreased. Chlorpyrifos oxon concentrations of 10 and 0.3 nM gave k_is of 1.2 and 19.3 nM⁻¹ h⁻¹, respectively. Although the mechanism of concentration-dependent inhibition kinetics is not known, the much smaller, more restrictive active site gorge of acetylcholinesterase almost certainly plays a role. Similarly, the much larger active site gorge of butyrylcholinesterase likely contributes to its much greater reactivity towards chlorpyrifos oxon, compared to acetylcholinesterase.     

Comparative cholinergic neurotoxicity of oral chlorpyrifos exposures in preweanling and adult rats.

Chlorpyrifos (CPF) is a common organophosphorus (OP) pesticide. Previous studies have demonstrated that neonatal rats are more sensitive than adults to the acute toxicity of high dosages of CPF. The present study examined lethality and age-related differences in neurochemical indicators and functional signs of neurotoxicity following a broad range of acute and repeated oral CPF exposures. There was about a 9-fold difference in sensitivity to the acute-dose lethality of chlorpyrifos among neonatal (7 days-of-age) and adult (90 days-of-age) rats (LD(10): neonates = 15 mg/kg; adults = 136 mg/kg), while juvenile rats (21 days-of-age) exhibited intermediate sensitivity (LD(10) = 47 mg/kg). Neonatal and adult rats (n = 5-7/treatment/age group/time point) were given CPF (0, 0.15, 0.45, 0. 75, 1.5, 4.5, 7.5, or 15 mg/kg/day) for 14 days and sacrificed 4 h after either the first or 14th dose for neurochemical measurements (cholinesterase activity in frontal cortex, plasma and RBC, and muscarinic ([(3)H]QNB) and nicotinic ([(3)H]epibatidine) receptor binding in frontal cortex. No overt signs of functional toxicity (involuntary movements, SLUD signs) were noted in either age group by 4 h after the first dose. With repeated CPF exposures, however, signs of cholinergic toxicity were noted in both age groups at the higher dose levels [no observed effect levels (NOELs): neonate = 4.5 mg/kg/day; adult = 7.5 mg/kg/day]. Similar degrees of ChE inhibition were noted in neonatal brain and blood fractions following acute exposure, but substantial ChE inhibition was only noted in adult plasma and RBC 4 h after the first treatment. Following repeated CPF exposures, similar degrees of ChE inhibition were again noted in tissues from immature animals, but a wide range of sensitivity to inhibition was noted in adult tissues. NOELs based on ChE inhibition for adults were about 1->/=10-fold higher than in neonates with acute exposure but only 0.2-2 times higher with repeated dosing. Moreover, dose-related inhibition of brain ChE was similar between age groups, and similar reductions in both QNB and epibatidine binding were noted between the age groups after repeated dosing, even though by the end of the dosing period young animals (juveniles) were still about 3 times more sensitive than adults, based on acute lethality. We conclude that while immature animals can be markedly more sensitive to lethal effects of high doses of CPF, lesser or no age-related differences are apparent, based on non-lethal endpoints, in particular with repeated exposures.     

Acute and sublethal effects of organophosphate insecticide chlorpyrifos on freshwater fish Oreochromis niloticus

Chlorpyrifos is a widely used organosphosphate insecticide in India. Residue of the insecticide is frequently detected in trace to moderate concentration in food grains and in surface water of different freshwater ecosystems of the country. In this study, 96?h LC₅₀ of the technical grade (94% a.i.) and commercial formulation (20% EC) of chlorpyrifos to freshwater fish Oreochromis niloticus were determined as 90.0 and 42.0?µg/L based on 2?h actual concentration of chlorpyrifos in water. About 96?h exposure to sublethal concentrations (0, 12.0 and 25.0?μg/L) of the commercial formulation (20% EC) of chlorpyrifos reduced the level of hepatic glycogen, activities of alkaline phosphatase, acetylcholinesterase, and catalase in liver and elevated the level of plasma glucose and activities of hepatic acid phosphatase, aspartate aminotransferase, and alanine aminotransferase in O. niloticus. About 28-day exposure to these sub-lethal concentrations caused anemia in fish, while 90 days exposure reduced growth of the fish and carcass concentration of crude protein and crude lipid as compared to control. It was concluded from this study that commercial formulation of chlorpyrifos (20% EC) was highly toxic to O. niloticus. Exposure to sub-lethal concentrations of the insecticide could induce oxidative stress and anemia resulting in reduced growth of the fish.     

In vitro rat hepatic and intestinal metabolism of the organophosphate pesticides chlorpyrifos and diazinon.

Chlorpyrifos (CPF) and diazinon (DZN) are thionophosphorus organophosphate (OP) insecticides; their toxicity is mediated through CYP metabolism to CPF-oxon and DZN-oxon, respectively. Conversely, CYPs also detoxify these OPs to trichloropyridinol (TCP) and 2-isopropyl-4-methyl-6-hydroxypyrimidine (IMHP), respectively. In addition, A-esterase (PON1) metabolism of CPF- and DZN-oxon also forms TCP and IMHP. This study evaluated the role intestinal and hepatic metabolism may play in both the activation and detoxification of CPF and DZN in Sprague-Dawley rats. Similar CYP- and PON1-mediated metabolic profiles were demonstrated in microsomes from liver or isolated intestinal enterocytes. The metabolic efficiency was estimated by calculating the psuedo-1st order rate constant from the metabolic constants by dividing Vmax/Km. In enterocyte microsomes, the CYP metabolic efficiency for metabolism to the oxon metabolites was approximately 28-fold greater for CPF than DZN. Compared on a per nmol P450 basis, the Vmax for CPF in enterocytes was approximately 2-3 times higher than in liver microsomes for the production of CPF-oxon and TCP. The Michaelis-Menten rate constant (Km) for the metabolism of CPF to CPF-oxon was comparable in liver and enterocyte microsomes; however, the enterocyte Km for TCP production was higher (indicating a lower affinity). The smaller volume of intestine, lower amount of CYP, and higher Km for TCP in the enterocyte microsomes, resulted in a lower catalytic efficiency (2 and 62 times) than in liver for oxon and TCP. PON1-mediated metabolism of CPF- and DZN-oxon was also demonstrated in liver and enterocyte microsomes. Although PON1 affinity for the substrates was comparable in hepatic and enterocytic microsomes, the Vmax were 48- to 275-fold higher, in the liver. These results suggest that intestinal metabolism may impact the metabolism of CPF and DZN, especially following low-dose oral exposures.     

Reconstructing human exposures using biomarkers and other "clues"

Biomonitoring is the process by which biomarkers are measured in human tissues and specimens to evaluate exposures. Given the growing number of population-based biomonitoring surveys, there is now an escalated interest in using biomarker data to reconstruct exposures for supporting risk assessment and risk management. While detection of biomarkers is de facto evidence of exposure and absorption, biomarker data cannot be used to reconstruct exposure unless other information is available to establish the external exposure-biomarker concentration relationship. In this review, the process of using biomarker data and other information to reconstruct human exposures is examined. Information that is essential to the exposure reconstruction process includes (1) the type of biomarker based on its origin (e.g., endogenous vs. exogenous), (2) the purpose/design of the biomonitoring study (e.g., occupational monitoring), (3) exposure information (including product/chemical use scenarios and reasons for expected contact, the physicochemical properties of the chemical and nature of the residues, and likely exposure scenarios), and (4) an understanding of the biological system and mechanisms of clearance. This review also presents the use of exposure modeling, pharmacokinetic modeling, and molecular modeling to assist in integrating these various types of information.     

The effect of stress on the acute neurotoxicity of the organophosphate insecticide chlorpyrifos

A study was conducted to determine if multiple exposures to several stress paradigms might affect the anticholinesterase effect of subsequently administered organophosphate insecticide chlorpyrifos. Male Sprague-Dawley rats were subject to daily periods of restraint, swimming, a combination of the two, or neither of the two (controls) (n=8/group) for 5 days per week over a six-week period. The most profound stress, as measured by reduced body weight gain and elevated levels of plasma corticosterone, was swimming. On day 39 of the study, shortly after the daily stress episode, one half of the rats in each group was dosed with 60 mg/kg chlorpyrifos subcutaneously. This had no effect on subsequent levels of plasma corticosterone. There were no stress-related differences in the degree of chlorpyrifos-induced inhibition of brain acetylcholinesterase in animals sacrificed on day 43.     

Effect of the organophosphate insecticide chlorpyrifos exposure on oxidative stress and quality of Salmo coruhensis spermatozoa

The use of pesticides has been increasing along with increasing farming activities and has caused deleterious environmental impacts. Non-target organisms in particular, including fish, are affected by pesticides. In this work, the impacts of Chlorpyrifos (CPF) on sperm oxidative stress markers and sperm motility were investigated in vitro. CPF concentrations were 0?μg/L (control), 5?μg/L, 10?μg/L and 15?μg/L. Lipid peroxidation [malondialdehyde (MDA)], nonenzymatic antioxidants [glutathione (GSH)] and enzymatic [superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and catalase (CAT)] activities in sperm cells were examined for the determination of oxidative stress status. Our findings showed that motility and survival of sperm cells significantly decreased with exposure to Chlorpyrifos. Biochemical assays revealed that CAT activity and levels of MDA and, GSH increased in spermatozoa based on CPF concentration while activity of GSH-Px and SOD decreased. Consequently, spermatozoa were highly sensitive to CPF exposure. It can be deduced that CPF has the potential to disrupt sperm quality and to cause to oxidative stress in sperm cells of S. coruhensis.     

A Physiologically based pharmacokinetic and pharmacodynamic (PBPK/PD) model for the organophosphate insecticide chlorpyrifos in rats and humans.

A PBPK/PD model was developed for the organophosphate insecticide chlorpyrifos (CPF) (O,O-diethyl-O-[3,5,6-trichloro-2-pyridyl]-phosphorothioate), and the major metabolites CPF-oxon and 3,5,6-trichloro-2-pyridinol (TCP) in rats and humans. This model integrates target tissue dosimetry and dynamic response (i.e., esterase inhibition) describing uptake, metabolism, and disposition of CPF, CPF-oxon, and TCP and the associated cholinesterase (ChE) inhibition kinetics in blood and tissues following acute and chronic oral and dermal exposure. To facilitate model development, single oral-dose pharmacokinetic studies were conducted in rats (0.5-100 mg/kg) and humans (0.5-2 mg/kg), and the kinetics of CPF, CPF-oxon, and TCP were determined, as well as the extent of blood (plasma/RBC) and brain (rats only) ChE inhibition. In blood, the concentration of analytes followed the order TCP > CPF > CPF-oxon; in humans CPF-oxon was not quantifiable. Simulations were compared against experimental data and previously published studies in rats and humans. The model was utilized to quantitatively compare dosimetry and dynamic response between rats and humans over a range of CPF doses. The time course of CPF and TCP in both species was linear over the dose range evaluated, and the model reasonably simulated the dose-dependent inhibition of plasma ChE, RBC acetylcholinesterase (AChE), and brain (rat only) AChE. Model simulations suggest that rats exhibit greater metabolism of CPF to CPF-oxon than humans do, and that the depletion of nontarget B-esterase is associated with a nonlinear, dose-dependent increase in CPF-oxon blood and brain concentration. This CPF PBPK/PD model quantitatively estimates target tissue dosimetry and AChE inhibition and is a strong framework for further organophosphate (OP) model development and for refining a biologically based risk assessment for exposure to CPF under a variety of scenarios.     

Determination of the reference dose for chlorpyrifos: proceedings of an expert panel.

Chlorpyrifos is an extensively used organophosphate insecticide with numerous agricultural crop and urban pest control uses. Dow AgroSciences, one of the manufacturers of chlorpyrifos, convened a panel of toxicology and medical experts to consider the available scientific literature (both published papers and unpublished reports from Dow AgroSciences) on chlorpyrifos with respect to determining the acute and chronic toxicological reference doses (RfD) for chlorpyrifos. The most sensitive effect observed in the body of animal and human studies on chlorpyrifos is the inhibition of the various cholinesterases. In animal studies chlorpyrifos is not carcinogenic, teratogenic, or mutagenic. Reproductive toxicity studies indicate some effects on postnatal survival, but these effects were seen at doses higher than maternal toxic dose levels. There are no clinical signs of cholinergic toxicity below 70% inhibition of brain cholinesterase. Cognitive or behavioral defects are not observed until substantial brain cholinesterase inhibition occurs. There are no indications that chlorpyrifos caused delayed neurotoxicity at dose levels below twice the oral LD50. The panel members stated that plasma cholinesterase was an inappropriate endpoint for the RfD. They recommended that brain, erythrocyte cholinesterase depression and clinical signs were appropriate as endpoints for the RfD. Plasma cholinesterase should be used only as an indicator of exposure. After a thorough review of the experimental animal literature, it was determined that the chlorpyrifos repeated-exposure RfD based on application of a 100-fold uncertainty factor on the no observed adverse effects level (NOAEL) for brain cholinesterase inhibition or on a 10-fold uncertainty factor on the NOAEL for erythrocyte cholinesterase inhibition is 0.01 mg/kg/d. Based on the human volunteer studies, which indicate a repeated-dose NOAEL of 0.1 mg/kg/d for erythrocyte cholinesterase inhibition, and then using a 10-fold uncertainty factor, the RfD is again 0.01 mg/kg/d. In this human volunteer study on d 9 (last day) of administration, 1 individual in the 0.1 mg/kg/day dose group was removed from the study due to a "cold" (runny nose, blurred vision, and a feeling of faintness). He was asymptomatic 12 h later. To some degree this diagnosis is supported by the hematology, since lymphocyte counts were reduced and neutrophil counts were increased markedly, indicating a possible inflammatory reaction on d 8 of dosing, clearing by posttreatment d 5. In the absence of any indication of erythrocyte cholinesterase inhibition and with plasma cholinesterase inhibition being greater in two of the four other individuals treated at the same dose level, these signs and symptoms are unlikely to have been induced by cholinesterase inhibition. The panel concluded that the symptoms this individual displayed were not an appropriate endpoint for the RfD. The single-exposure reference dose can be based on the human data. No erythrocyte cholinesterase inhibition or clinical signs of toxicity were observed after a single oral dose of 0.5 mg/kg. Utilizing a 10-fold uncertainty factor, the single-dose RfD is 0.05 mg/kg.     

Dose-related inhibition of brain and plasma cholinesterase in neonatal and adult rats following sublethal organophosphate exposures.

Developing mammals are markedly more sensitive to acute toxicity from exposure to a variety of organophosphorus (OP) pesticides. The present study examined dose-related inhibition of both brain and plasma cholinesterase activity in neonatal and adult rats exposed to sublethal doses of one of three common OP pesticides, methyl parathion, parathion and chlorpyrifos. Effective dose 50 (i.e., ED50 or dose which would inhibit 50% of the cholinesterase activity) values were determined and then correlated with an indicator of acute toxicity, the maximal tolerated dose (MTD). It was found that ED50 estimates for both brain and plasma cholinesterase correlated highly (r = 0.932-0.992) with previously derived MTD values. In no case was there a significant difference between in vivo brain and plasma cholinesterase inhibition across doses in neonatal rats was high (r = 0.962-0.975) but lower in adults (r = 0.700-0.943). The results suggest that in vivo inhibitory potency of the three OPs towards either brain or plasma ChE activity is highly correlated with sensitivity to acute toxicity in both neonatal and adult rats. Additionally, under defined experimental conditions, plasma ChE inhibition may be a useful quantitative index for the degree of brain cholinesterase inhibition following OP exposures.     

Effects of acute and repeated oral exposure to the organophosphate insecticide chlorpyrifos on open-field activity in chicks

The effects of the organophosphate insecticide chlorpyrifos on 5min open-field activity were examined in a 7-15 days old chick model. Chlorpyrifos was acutely administered taking into account cholinesterase inhibition and determination of the acute (24h) median lethal dose (LD50). The oral LD50 value of chlorpyrifos in chicks was 18.14mg/kg, with cholinergic toxicosis observed on intoxicated chicks. Chlorpyrifos at the dose rates of 5,10 and 20mg/kg orally produced within 2h signs of cholinergic toxicosis in the chicks and significantly inhibited plasma (40-70%), whole brain (43-69%) and liver (31-46%) cholinesterase activities in a dose-dependent manner. Chlorpyrifos at 2 and 4mg/kg, orally did not produce overt signs of cholinergic toxicosis, but decreased (30, 60 and 90min after dosing) the general locomotor activity of the chicks as seen by a significant increase in the latency to move from the central square of the open-field arena, decreases in the numbers of lines crossed and vocalization score. Repeated daily chlorpyrifos treatments (2 and 4mg/kg, orally) for seven consecutive days also caused hypoactivity in chicks in the open-field behavioral paradigm. Only the high dose of chlorpyrifos (4mg/kg, orally) given repeatedly for 7 days caused significant cholinesterase inhibition in the whole brain (37%) and the liver (22%). In conclusion, chlorpyrifos at single or short-term repeated doses-induced behavioral changes in 7-15 days old chicks, in a model that could be used for further neurobehavioral studies involving subtle effects of organophosphates on chicks.     

Effect of organophosphate intoxication on human serum paraoxonase

Recently, interindividual variations in serum paraoxonase (PON1) activity and the differences in its metabolic activity towards different organophosphates (OPs) caused by the coding region polymorphisms L55M and Q192R have been found to be important risk factors in susceptibility to OP poisoning. In this study, we investigated the effect of PON1 on the outcome of acute OP intoxication and the effect of acute OP intoxication on PON1. Twenty-eight OP-poisoned patients and 66 healthy volunteers were studied. Patients were evaluated for the clinical manifestations of OP intoxication as well as PON1 activity, PON1 mass and PON1 polymorphisms. Butyrylcholine-esterase (BChE) activity was 50% lower (2,276 +/- 738 U/L versus 5,037 +/- 1,553 U/L, P<0.01) while PON1 activity was 30% lower [114.2 +/- 67.4 nmol/mL/min versus 152.9 +/- 78.9 nmol/mL/ min, P<0.05) in patients than in controls. We observed that the PON1 and BChE activities of eight of the original subjects returned to normal levels when they were reinvestigated six months after exposure. The frequency of the PON192Q allele was significantly higher in patients than controls (85.7% versus 59.7%, chi2=6.745, P=0.034). QQ/ MM individuals had the lowest activity towards paraoxon, while RR/LL individuals had the highest activity. Our data indicate that interindividual differences in PON1 activity and the PON1-55 and -192 polymorphisms are important risk factors in susceptibility to acute OP poisoning; therefore, identifying an individual's PON1 alloenzymes may play an important role in the treatment of patients suffering from OP intoxication.     

有机磷农药中毒机理研究进展

有机磷化合物做为农用杀虫剂开发应用已半个多世纪,由于其品种繁多,杀虫效果好,在有机合成农药中占有极重要地位。但随之带来的人畜中毒,促进了对其中毒防治的不断深入研究,从而较清楚地揭示了有机磷进入体内,通过神经末稍的胆碱酯酶磷酰化使其失活,造成乙酰胆碱大量蓄积在胆硷能神经与效应器接点,发生毒蕈硷样与烟硷样效应及中枢神经系统症状。又根据此中毒机理,结合实践订出有机磷中毒诊断标准,并研制了解毒剂,提出一整套中毒抢救措施,挽救了无数的生命。但随着科技手段的不断更新,研究仍在继续深入。文献较集中于以下三个方向的研究。1　…     

Effects of the organophosphate insecticides phosmet and chlorpyrifos on trophoblast JEG-3 cell death,proliferation and inflammatory molecule production

Epidemiological data have associated environmental organophosphate insecticide (OP) exposure during pregnancy with fetal growth deficits. To better understand OP injury that may adversely affect pregnancy, we used the JEG-3 choriocarcinoma cell line, which provide a recognized in vitro model to study placental function. The effects of the OP phosmet (Pm) and chlorpyrifos (Cp) on JEG-3 cells viability, proliferation, cell cycle and inflammatory molecule production were evaluated. Both insecticides affected cellular viability in a concentration- and time-dependent manner, inducing apoptosis and decreasing [³H]-thymidine incorporation. However, only Pm reduced DNA synthesis independently of cellular death and decreased the cell percentage at the S-phase. Unlike apoptosis, TNFα production varied with the concentration tested, suggesting that other TNFα independent mechanisms might trigger cell death. No induction of the inflammatory molecule nitric oxide was detected. The mRNA levels of pro-inflammatory IL-6, IL-17 and the anti-inflammatory IL-13 cytokines were differentially modulated. These findings show that Pm and Cp generate a specific toxicity signature, altering cell viability and inducing an inflammatory cytokine profile, suggesting that trophoblasts may represent a possible target for OP adverse effects.