Mitochondrial dysfunction from malathion and chlorpyrifos exposure is associated with degeneration of GABAergic neurons in Caenorhabditis elegans

Toxicity resulting from off-target effects, beyond acetylcholine esterase inhibition, for the commonly used organophosphate (OP) insecticides chlorpyrifos (CPS) and malathion (MA) was investigated using Saccharomyces cerevisiae and Caenorhabditis elegans model systems. Mitochondrial damage and dysfunction were observed in yeast following exposure to CPS and MA, suggesting this organelle is a major target. In the C. elegans model, the mitochondrial unfolded protein response pathway showed the most robust induction from CPS and MA treatment among stress responses examined. GABAergic neurodegeneration was observed with CPS and MA exposure. Impaired movement observed in C. elegans exposed to CPS and MA may be the result of motor neuron damage. Our analysis suggests that stress from CPS and MA results in mitochondrial dysfunction, with GABAergic neurons sensitized to these effects. These findings may aid in the understanding of toxicity from CPS and MA from high concentration exposure leading to insecticide poisoning.     

Induction of chromosmal aberrations in the syrian hamster by insecticides tested in vivo

The insecticides demeton, dimetoat, dichlorovos, endosulfan, trichlorofon, carbaryl, lindane, methoxychlor, propoxur and malathion were examined for their ability to induce chromosomal aberrations in the bone marrow cells of the Syrian hamster (Mesocricetus auratus) treated in vivo. Mutagenicity of commercial preparations was examined at four doses: LD₅₀; 1/2, 1/5 and 1/10 LD₅₀. The positive control was an IP injection of cyclophosphamide to hamsters at a dose of 40 mg/kg body wt. Demeton, dichlorovos and endosulfan gave positive results. Malathion, dimethoate and the mixture of methoxychlor and propoxur were weakly clastogenic; at some doses these compounds induced statistically significant increases in the number of aberrations. Trichlorfon and the mixture of carbaryl and lindane were negative in this test.This work was supported by the Polish Academy of Sciences within the projet 09.7.3.4.3     

中华按蚊对杀虫剂敏感性调查

目的分析河南省疟疾媒介中华按蚊对DDT、氟氯氰菊酯、马拉硫磷和溴氰菊酯的敏感性,为制定疟疾媒介防制对策提供依据。方法2009年6月在河南省桐柏县、淮滨县和永城市3个县(市)现场分别捕获吸血后中华按蚊成蚊417、421和433只,采用WHO推荐的成蚊滤纸接触法进行检测,计算中华按蚊分别接触4%DDT(1.428g/m2),0.15%氟氯氰菊酯(0.0 534 g/m2),5%马拉硫磷(1.78 g/m2)和0.05%溴氰菊酯(0.0 178 g/m2)的半数击倒时间(KT50)和24 h后死亡率。根据死亡率判定抗性级别,死亡率98%～100%为敏感群体(S级),80%～97%为初步抗性群体(M级),80%以下为抗性群体(R级)。结果桐柏县、淮滨县和永城市3个县(市)中华按蚊接触DDT的KT50分别为206.13、877.04和826.81 min;接触氟氯氢菊酯的KT50分别为206.43、85.39和427.60 min;接触马拉硫磷的KT50分别为19.98、48.05和97.79 min;接触溴氰菊酯的KT50分别为1122.50、89.65和960 min。接触4%DDT 24 h死亡率分别为82.52%、57.41%和65.69%,抗性级别分别为M、R和R级;接触0.15%氟氯氰菊酯24 h死亡率分别为91.89%、85.00%和72.73%,抗性级别分别为M、M和R级;接触5%马拉硫磷24h死亡率分别为95.10%、95.37%和93.16%,抗性级别均为M级;接触0.05%溴氰菊酯24h死亡率分别为92.08%、77.14%和63.46%,抗性级别分别为M、R和R级。结论河南省中华按蚊对DDT、氟氯氰菊酯和溴氰菊酯已产生较强抗性,对马拉硫磷产生初步抗性。     

毛细管气相色谱法测定金银花中敌敌畏、甲基对硫磷和马拉硫磷的残留量

目的：建立测定金银花中敌敌畏、甲基对硫磷和马拉硫磷残留量的毛细管气相色谱分析方法。方法：样品以微波提取的方法进行处理。以FPD为检测器,色谱柱为HP-5石英毛细管柱（25m×0.32mm,0.17μm）,载气为高纯氮气,流速20ml/min;氢气流速45ml/min;空气流速450ml/min;程序升温：初始温度为120℃,最终温度为230℃,升温速率10℃/min。进样口温度250℃,检测器温度260℃。采用无分流进样方式。结果：敌敌畏、甲基对硫磷和马拉硫磷的测定浓度在0.25￣3.00μg/ml时,浓度与峰面积呈线性关系。当信噪比为2时,敌敌畏的最低检出量为0.3ng,甲基对硫磷的最低检出量为0.15ng,马拉硫磷的最低检出量为0.2ng。敌敌畏的平均回收率为88.7%,RSD为2.1%;甲基对硫磷平均回收率为89.7%,RSD为1.7%,马拉硫磷平均回收率为90.6%,RSD为1.1%。结论：该方法操作简便、准确、可靠,可用于金银花中敌敌畏、甲基对硫磷和马拉硫磷残留量的测定。     

Dimethylphosphorothioates

Five dimethylphosphorothioates were tested for their toxicity to rats, potentiation of malathion toxicity in rats, inhibition of carboxylesterase in vitro, and reaction with malathion in vitro. The compounds were: potassium salts of (CH₃S)₂P(O)O^–(I), (CH₃O)(CH₃S)P(O)S^–(II), (CH₃O)₂P(O)S^–(III), (CH₃O)₂P(S)S^–(IV), and (CH₃O)(CH₃S)P(O)O^–(V).The dimethylphosphorothioates are not toxic to rats (up to 1 g/kg, orally), they do not potentiate malathion toxicity in rats, and do not inhibit carboxylesterase activity in vitro (up to 1 mM concentrations). However, when the S-acid diesters (II, III, IV) are incubated with malathion for several days at room temperature or for several hours at 50° C they become methylated forming the trimethylphosphorothioates OSS-trimethyl phosphorodithioate, OOS-trimethyl phosphorothioate and OOS-trimethyl phosphorodithioate respectively, which potentiate malathion toxicity. Furthermore, these same acid diesters increase the rate of isomerization of malathion into OS-dimethyl-S-(1,2-dicarbethoxyethyl) phosphorodithioate (isomalathion) particularly, diester IV.The formation of the trimethylphosphorothioates and isomalathion from the interaction of the S-acid diesters with malathion was determined by thin layer chromatography (TLC), gas chromatography and mass spectrometry and could be detected by in vitro inhibition of carboxylesterase. TLC methods can detect 1 mg of the trimethylphosphorothioates and isomalathion per gram malathion.     

Paraoxonase 1 (PON1) modulates the toxicity of mixed organophosphorus compounds

A transgenic mouse model of the human hPON1_Q192R polymorphism was used to address the role of paraoxonase (PON1) in modulating toxicity associated with exposure to mixtures of organophosphorus (OP) compounds. Chlorpyrifos oxon (CPO), diazoxon (DZO), and paraoxon (PO) are potent inhibitors of carboxylesterases (CaE). We hypothesized that a prior exposure to these OPs would increase sensitivity to malaoxon (MO), a CaE substrate, and the degree of the effect would vary among PON1 genotypes if the OP was a physiologically significant PON1 substrate in vivo. CPO and DZO are detoxified by PON1. For CPO hydrolysis, hPON1_R192 has a higher catalytic efficiency than hPON1_Q192. For DZO hydrolysis, the two alloforms have nearly equal catalytic efficiencies. For PO hydrolysis, the catalytic efficiency of PON1 is too low to be physiologically relevant. When wild-type mice were exposed dermally to CPO, DZO, or PO followed 4-h later by increasing doses of MO, toxicity was increased compared to mice receiving MO alone, presumably due to CaE inhibition. Potentiation of MO toxicity by CPO and DZO was greater in PON1^−/− mice, which have greatly reduced capacity to detoxify CPO or DZO. Potentiation by CPO was more pronounced in hPON1_Q192 mice than in hPON1_R192 mice due to the decreased efficiency of hPON1_Q192 for detoxifying CPO. Potentiation by DZO was similar in hPON1_Q192 and hPON1_R192 mice, which are equally efficient at hydrolyzing DZO. Potentiation by PO was equivalent among all four genotypes. These results indicate that PON1 status can have a major influence on CaE-mediated detoxication of OP compounds.     

Role of HSP27 and reduced glutathione in modulating malathion-induced apoptosis of human peripheral blood mononuclear cells: Ameliorating effect of N-acetylcysteine and curcumin

Malathion exerts cholinergic effects at high doses. However, a consequence of low dose (non-cholinergic) exposure causes immunotoxicity and oxidative stress. Hence, this study was designed to find out (i) the cytotoxic and apoptotic effects of cholinergic and non-cholinergic doses of malathion using cultured peripheral blood mononuclear cells (PBMCs) and (ii) the role of GSH and HSP27 and (iii) protective effects of N-acetylcysteine (GSH inducer) and curcumin (HSP27 inducer). In low doses, malathion caused mild depletion of GSH, threefold increase in HSP27 level and a range bound cytotoxicity and apoptosis of PBMC. In contrast, cholinergic dose exposures caused severe GSH depletion and exhibited dose dependent cytotoxicity and necrosis without any significant effect on HSP27 levels. Curcumin increased the levels of HSP27 in PBMC only in presence of low doses and not at high doses of malathion. Both NAC and curcumin were able to prevent malathion-mediated apoptosis of PBMC effectively at non-cholinergic doses and at this concentration of malathion, HSP27 induction keeps apoptosis and GSH depletion under control. Also NAC and curcumin may act as potential therapeutic agents to prevent malathion-induced immunotoxicity.     

Comparison of the human skin grafted onto nude mouse model with in vivo and in vitro models in the prediction of percutaneous penetration of three lipophilic pesticides

The evaluation of the degree of percutaneous penetration of agrochemicals is a key part of risk assessment for operators. The availability of suitable and predictive experimental models is crucial, in particular in the case of lipophilic compounds which persist in the stratum corneum (SC). Regulatory models (rat in vivo, human and rat in vitro) and the innovative human skin grafted onto nude mice (HuSki) model were compared for their ability to predict the human skin absorption. Radiolabelled malathion, lindane and cypermethrin (4microg/cm(2)) were topically applied to each model. The % of applied dose absorbed and that present in skin and SC were evaluated at 24h. Additionally, the absorption profile of cypermethrin was evaluated in the in vivo rat and HuSki models for up to 11 days. We found that the human in vitro and HuSki models closely predicted the human skin absorption at 24h, while rat models overestimated the human skin absorption. Furthermore, our experiments with cypermethrin indicated that evaluation of % percutaneous absorption over extended periods of time was feasible with the HuSki model. In our studies the HuSki model overcame the limitations of the regulatory models and is promising to realistically refine the dermal absorption assessment of topically applied chemicals.     

Evidence of central influences on blood glucose level: malathion hyperglycemia.

To suppress the hyperglycemic effect of malathion in rats, a smaller amount of atropine was required when the drug was injected by intraventricular (i. vent.) than s.c. Pentobarbital, but not diazepam, blocked the hyperglycemic response. The results suggest that central accumulation of acetylcholine was the mediator of the response. Since hyperglycemia was not abolished by adrenalectomy and/or hypophysectomy, a hypothesis is presented to explain how central accumulation of acetylcholine might cause hyperglycemia.     

The acute oral toxicity of Malathion in relation to dietary protein

Summary The acute oral toxicity of Malathion Technical (95%) was determined in young, male albino rats which had been fed either laboratory chow (group I), a purified diet containing protein as casein in normal (26%) amounts (group II), or the same diet containing a deficient (3.5%) amount of casein (group III). The LD₅₀±S.E. was 1090±83 mg/kg body weight in group I, 1401±99 in II and 599±138 in III. The clinicopathologic syndrome of toxicity was essentially the same in all three groups. The clinical signs included ataxia, bradypnea, dacryorrhea, dyspnea, diarrhea, exophthalmos, hypothermia, hyporeflexia, listlessness, miosis pallor, retching movements, sialorrhea, teeth-chattering, thirst and tremors. Most deaths occurred at 1–15 hours, following respiratory failure. At autopsy there were found an acute enteritis, degenerative changes in the liver and kidneys, a stress reaction, and widespread capillary-venous vasodilatation, dehydration and loss of weight in body organs. In survivors there was generally a temporary anorexia, oligodipsia, loss of body weight, diuresis, glycosuria or proteinuria, aciduria or alkalinuria, abdominal tenderness, epistaxis, hemodacryorrhea, hind limb paralysis, prostration and thoracic rales lasting for a day or two. At 6 days survivors appeared normal and at 2 weeks and 1 month organ weights and water contents were within normal limits.This project was assisted by research grants from the World Health Organization and the Medical Research Council of Canada.