The toxicological properties of impurities in malathion

Learning perturbation-inducible cell states from observability analysis of transcriptome dynamics

A major challenge in biotechnology and biomanufacturing is the identification of a set of biomarkers for perturbations and metabolites of interest. Here, we develop a data-driven, transcriptome-wide approach to rank perturbation-inducible genes from time-series RNA sequencing data for the discovery of analyte-responsive promoters. This provides a set of biomarkers that act as a proxy for the transcriptional state referred to as cell state. We construct low-dimensional models of gene expression dynamics and rank genes by their ability to capture the perturbation-specific cell state using a novel observability analysis. Using this ranking, we extract 15 analyte-responsive promoters for the organophosphate malathion in the underutilized host organism Pseudomonas fluorescens SBW25. We develop synthetic genetic reporters from each analyte-responsive promoter and characterize their response to malathion. Furthermore, we enhance malathion reporting through the aggregation of the response of individual reporters with a synthetic consortium approach, and we exemplify the library's ability to be useful outside the lab by detecting malathion in the environment. The engineered host cell, a living malathion sensor, can be optimized for use in environmental diagnostics while the developed machine learning tool can be applied to discover perturbation-inducible gene expression systems in the compendium of host organisms.

Ginseng® Alleviates Malathion-Induced Hepatorenal Injury through Modulation of the Biochemical, Antioxidant, Anti-Apoptotic, and Anti-Inflammatory Markers in Male Rats

This study aims to see if Ginseng^® can reduce the hepatorenal damage caused by malathion. Four groups of forty male Wistar albino rats were alienated. Group 1 was a control group that got orally supplied corn oil (vehicle). Group 2 was intoxicated by malathion dissolved in corn oil orally at 135 mg/kg/day. Group 3 orally received both malathion + Panax Ginseng^® (300 mg/kg/day). Group 4 was orally given Panax Ginseng^® at a 300 mg/kg/day dose. Treatments were administered daily and continued for up to 30 consecutive days. Malathion's toxic effect on both hepatic and renal tissues was revealed by a considerable loss in body weight and biochemically by a marked increase in liver enzymes, LDH, ACP, cholesterol, and functional renal markers with a marked decrease in serum TP, albumin, and TG levels with decreased AchE and Paraoxonase activity. Additionally, malondialdehydes, nitric oxide (nitrite), 8-hydroxy-2-deoxyguanosine, and TNFα with a significant drop in the antioxidant activities were reported in the malathion group. Malathion upregulated the inflammatory cytokines and apoptotic genes, while Nrf2, Bcl2, and HO-1 were downregulated. Ginseng^® and malathion co-treatment reduced malathion's harmful effects by restoring metabolic indicators, enhancing antioxidant pursuit, lowering the inflammatory reaction, and alleviating pathological alterations. So, Ginseng^® may have protective effects against hepatic and renal malathion-induced toxicity on biochemical, antioxidant, molecular, and cell levels.

Gestational Exposure to Common Endocrine Disrupting Chemicals and Their Impact on Neurodevelopment and Behavior

Endocrine disrupting chemicals are common in our environment and act on hormone systems and signaling pathways to alter physiological homeostasis. Gestational exposure can disrupt developmental programs, permanently altering tissues with impacts lasting into adulthood. The brain is a critical target for developmental endocrine disruption, resulting in altered neuroendocrine control of hormonal signaling, altered neurotransmitter control of nervous system function, and fundamental changes in behaviors such as learning, memory, and social interactions. Human cohort studies reveal correlations between maternal/fetal exposure to endocrine disruptors and incidence of neurodevelopmental disorders. Here, we summarize the major literature findings of endocrine disruption of neurodevelopment and concomitant changes in behavior by four major endocrine disruptor classes:bisphenol A, polychlorinated biphenyls, organophosphates, and polybrominated diphenyl ethers. We specifically review studies of gestational and/or lactational exposure to understand the effects of early life exposure to these compounds and summarize animal studies that help explain human correlative data.

Experimental measurements for the effect of dilution procedure in blood esterases as animals biomarker for exposure to OP compounds

Organophosphate compounds can bind to carboxylesterase, which may lower the concentration of organophosphate pesticides at the target site enzyme, cholinesterase. It is unclear from the literature whether it is the carboxylesterase affinity for the organophosphate and/or the number of carboxylesterase molecules that is the dominant factor in determining the protective potential of carboxylesterase. The fundamental dilutions and kinetic effects of esterase enzyme are still poorly understood. This study aims to confirm and extend our current knowledge about the effects of dilutions on esterases activities in the blood for birds with respect to protecting the enzyme from organophosphate inhibition. There was significantly higher esterases activities in dilution 1 : 10 in the all blood samples from quail, duck, and chick compared to other dilutions (1 : 5, 1 : 15, 1 : 20, and 1 : 25) in all cases. Furthermore, our results also pointed to the importance of estimating different dilutions effects prior to using in birds as biomarker tools of environmental exposure. Concentration-inhibition curves were determined for the inhibitor in the presence of dilutions 1 : 5, 1 : 10, plus 1 : 15 (to stimulate carboxylesterase). Point estimates (concentrations calculated to produce 20, 50, and 80% inhibition) were compared across conditions and served as a measure of esterase-mediated detoxification. Results with well-known inhibitors (malathion) were in agreement with the literature, serving to support the use of this assay. Among the thiol-esters dilution 1 : 5 was observed to have the highest specificity constant (k_cat/K_m), and the K_m and k_cat values were 176 μM and 16,765 s⁻¹, respectively, for S-phenyl thioacetate ester, while detected in dilution 1 : 15 was the lowest specificity constant (k_cat/K_m), and the K_m and k_cat values were 943 μM and 1154 s⁻¹, respectively, for acetylthiocholine iodide ester.

Toxic effects of pesticide mixtures at a molecular level: their relevance to human health

Pesticides almost always occur in mixtures with other ones. The toxicological effects of low-dose pesticide mixtures on the human health are largely unknown, although there are growing concerns about their safety. The combined toxicological effects of two or more components of a pesticide mixture can take one of three forms: independent, dose addition or interaction. Not all mixtures of pesticides with similar chemical structures produce additive effects; thus, if they act on multiple sites their mixtures may produce different toxic effects. The additive approach also fails when evaluating mixtures that involve a secondary chemical that changes the toxicokinetics of the pesticide as a result of its increased activation or decreased detoxification, which is followed by an enhanced or reduced toxicity, respectively. This review addresses a number of toxicological interactions of pesticide mixtures at a molecular level. Examples of such interactions include the postulated mechanisms for the potentiation of pyrethroid, carbaryl and triazine herbicides toxicity by organophosphates; how the toxicity of some organophosphates can be potentiated by other organophosphates or by previous exposure to organochlorines; the synergism between pyrethroid and carbamate compounds and the antagonism between triazine herbicides and prochloraz. Particular interactions are also addressed, such as those of pesticides acting as endocrine disruptors, the cumulative toxicity of organophosphates and organochlorines resulting in estrogenic effects and the promotion of organophosphate-induced delayed polyneuropathy.

Malignant transformation of rat kidney induced by environmental substances and estrogen

The use of organophosphorous insecticides in agricultural environments and in urban settings has increased significantly. The aim of the present study was to analyze morphological alterations induced by malathion and 17β-estradiol (estrogen) in rat kidney tissues. There were four groups of animals: control, malathion, estrogen and combination of both substances. The animals were injected for five days and sacrificed 30, 124 and 240 days after treatments. Kidney tissues were analyzed for histomorphological and immunocytochemical alterations. Morphometric analysis indicated that malathion plus estrogen-treated animals showed a significantly (p < 0.05) higher grade of glomerular hypertrophy, signs of tubular damage, atypical proliferation in cortical and hilium zone than malathion or estrogen alone-treated and control animals after 240 days. Results indicated that MFG, ER-α, ER-β, PgR, CYP1A1, Neu/ErbB2, PCNA, vimentin and Thrombospondin 1 (THB) protein expression was increased in convoluted tubules of animals treated with combination of malathion and estrogen after 240 days of 5 day treatment. Malignant proliferation was observed in the hilium zone. In summary, the combination of malathion and estrogen induced pathological lesions in glomeruli, convoluted tubules, atypical cell proliferation and malignant proliferation in hilium zone and immunocytochemical alterations in comparison to control animals or animals treated with either substance alone. It can be concluded that an increased risk of kidney malignant transformation can be induced by exposure to environmental and endogenous substances.

Cytogenetic evaluation of malathion-induced toxicity in Sprague-Dawley rats

Malathion is a well known pesticide and is commonly used in many agricultural and non-agricultural settings. Its toxicity has been attributed primarily to the accumulation of acetylcholine (Ach) at nerve junctions, due to the inhibition of acetylcholinesterase (AChE), and consequently overstimulation of the nicotinic and muscarinic receptors. However, the genotoxicity of malathion has not been adequately studied; published studies suggest a weak interaction with the genetic material. In the present study, we investigated the genotoxic potential of malathion in bone marrow cells and peripheral blood obtained from Sprague-Dawley rats using chromosomal aberrations (CAs), mitotic index (MI), and DNA damage as toxicological endpoints. Four groups of four male rats, each weighing approximately 60 ± 2g, were injected intraperitoneally (i.p.) once a day for five days with doses of 2.5, 5, 10, and 20mg/kg body weight (BW) of malathion dissolved in 1% DMSO. The control group was made up of four animals injected with 1% DMSO. All the animals were sacrificed 24h after the fifth day treatment. Chromosome preparations were obtained from bone marrow cells following standard protocols. DNA damage in peripheral blood leukocytes was determined using alkaline single-cell gel electrophoresis (comet assay). Malathion exposure significantly increased the number of structural chromosomal aberrations (CAs) and the percentages of DNA damage, and decreased the mitotic index (MI) in treated groups when compared with the control group. Our results demonstrate that malathion has a clastogenic/genotoxic potential as measured by the bone marrow CA and comet assay in Sprague-Dawley rats.

Dermal absorption of a dilute aqueous solution of malathion

Malathion is an organophosphate pesticide commonly used on field crops, fruit trees, livestock, agriculture, and for mosquito and medfly control. Aerial applications can result in solubilized malathion in swimming pools and other recreational waters that may come into contact with human skin. To evaluate the human skin absorption of malathion for the assessment of risk associated with human exposures to aqueous solutions, human volunteers were selected and exposed to aqueous solutions of malathion. Participants submerged their arms and hands in twenty liters of dilute malathion solution in either a stagnant or stirred state. The "disappearance method" was applied by measuring malathion concentrations in the water before and after human exposure for various periods of time. No measurable skin absorption was detected in 42% of the participants; the remaining 58% of participants measured minimal absorbed doses of malathion. Analyzing these results through the Hazard Index model for recreational swimmer and bather exposure levels typically measured in contaminated swimming pools and surface waters after bait application indicated that these exposures are an order of magnitude less than a minimal dose known to result in a measurable change in acetylcholinesterase activity. It is concluded that exposure to aqueous malathion in recreational waters following aerial bait applications is not appreciably absorbed, does not result in an effective dose, and therefore is not a public health hazard.

Physiological and histopathological investigations on the effects of alpha-lipoic acid in rats exposed to malathion

The present study was designed to evaluate the influence of α-lipoic acid treatment in rats exposed to malathion. Forty adult male rats were used in this study and distributed into four groups. Animals of group 1 were untreated and served as control. Rats of group 2 were orally given malathion at a dose level of 100 mg/kg body weight (BW) for a period of one month. Experimental animals of group 3 were orally given α-lipoic acid at a dose level of 20 mg/kg BW and after 3 hours exposed to malathion at the same dose given to group 2. Rats of group 4 were supplemented with α-lipoic acid at the same dose given to group 3. The activities of serum glutamic oxaloacetic acid transaminase (GOT), glutamic pyruvic acid transaminase (GPT), alkaline phosphatase (ALP), and acid phosphatase (ACP), and the values of creatinine, urea, and uric acid were statistically increased, while the values of total protein and total albumin were significantly decreased in rats exposed to malathion. Moreover, administration of malathion for one month resulted in damage of liver and kidney structures. Administration of α-lipoic acid before malathion exposure to rat can prevent severe alterations of hematobiochemical parameters and disruptions of liver and kidney structures. In conclusion, this study obviously demonstrated that pretreatment with α-lipoic acid significantly attenuated the physiological and histopathological alterations induced by malathion. Also, the present study identifies new areas of research for development of better therapeutic agents for liver, kidney, and other organs' dysfunctions and diseases.

Paradox findings may challenge orthodox reasoning in acute organophosphate poisoning

It is generally accepted that inhibition of acetylcholinesterase (AChE) is the most important acute toxic action of organophosphorus compounds, leading to accumulation of acetylcholine followed by a dysfunction of cholinergic signaling. However, the degree of AChE inhibition is not uniformly correlated with cholinergic dysfunction, probably because the excess of essential AChE varies among tissues. Moreover, the cholinergic system shows remarkable plasticity, allowing modulations to compensate for dysfunctions of the canonical pathway. A prominent example is the living (-/-) AChE knockout mouse. Clinical experience indicates that precipitous inhibition of AChE leads to more severe poisoning than more protracted yet finally complete inhibition. The former situation is seen in parathion, the latter in oxydemeton methyl poisoning. At first glance, this dichotomy is surprising since parathion is a pro-poison and has to be activated to the oxon, while the latter is still the ultimate inhibitor. Also oxime therapy in organophosphorus poisoning apparently gives perplexing results: Oximes are usually able to reactivate diethylphosphorylated AChE, but the efficiency may be occasionally markedly smaller than expected from kinetic data. Dimethylphosphorylated AChE is in general less amenable to oxime therapy, which largely fails in some cases of dimethoate poisoning where aging was much faster than expected from a dimethylphosphorylated enzyme. Similarly, poisoning by profenofos, an O,S-dialkyl phosphate, leads to a rapidly aged enzyme. Most surprisingly, these patients were usually well on admission, yet their erythrocyte AChE was completely inhibited. Analysis of the kinetic constants of the most important reaction pathways, determination of the reactant concentrations in vivo and comparison with computer simulations may reveal unexpected toxic reactions. Pertinent examples will be presented and the potentially underlying phenomena discussed.

Levels of metrifonate and dichlorvos in plasma and erythrocytes during treatment of schistosomiasis with Bilarcil

A method for the simultaneous quantitation of metrifonate (0,0-dimethyl-(1-hydroxy-2,2,2-trichloroethyl)-phosphonate) and dichlorvos (2,2-dichlorovinyl dimethyl phosphate, DDVP) in human blood has been worked out. It is based upon multiple labelling of the compounds with deuterium and gas phase analysis using the mass spectrometer as a selective detector. The amount of DDVP in plasma is about 1% of the amount of metrifonate. In erythrocytes the corresponding amount of DDVP is 0.5% or less of metrifonate. Both compounds reach peak levels in blood within two hours after oral dosing and are detectable for at least eight hours. Cholinesterase activity in plasma reaches zero levels within 15 min. and remains inhibited for more than eight hours. Red blood cell cholinesterase is inhibited only 60-80%. According to kinetic calculations, clearance of metrifonate occurs primarily via dichlorvos. If dichlorvos is the only active component, which in all likelihood it is, it's slow release may be important in the schistosomicidal effect. Clinical data in seven metrifonate treated patients revealed that mild vertigo subsiding in a few hours was the most common side effect.

Cumulative risk assessment of pesticide residues in food

There is increasing need to address the potential risks of combined exposures to multiple residues from pesticides in the diet. The available evidence suggests that the main concern is from dose addition of those compounds that act by the same mode of action. The possibility of synergy needs to be addressed on a case-by-case basis, where there is a biologically plausible hypothesis that it may occur at the levels of residues occurring in the diet. Cumulative risk assessment is a resource-intense activity and hence a tiered approach to both toxicological evaluation and intake estimation is recommended, and the European Food Safety Authority (EFSA) has recently published such a proposal. Where assessments have already been undertaken by some other authority, full advantage should be taken of these, subject of course to considerations of quality and relevance. Inclusion of compounds in a cumulative assessment group (CAG) should be based on defined criteria, which allow for refinement in a tiered approach. These criteria should include chemical structure, mechanism of pesticidal action, target organ and toxic mode of action. A number of methods are available for cumulating toxicity. These are all inter-related, but some are mathematically more complex than others. The most useful methods, in increasing levels of complexity and refinement, are the hazard index, the reference point index, the Relative Potency Factor method and physiologically based toxicokinetic modelling, although this last method would only be considered should a highly refined assessment be necessary. Four possible exposure scenarios are of relevance for cumulative risk assessment, acute and chronic exposure in the context of maximum residue level (MRL)-setting, and in relation to exposures from the actual use patterns, respectively. Each can be addressed either deterministically or probabilistically. Strategies for dealing with residues below the limit of detection, limit of quantification or limit of reporting need to be agreed. A number of probabilistic models are available, but some of there are geographically constrained due to the underlying datasets used in their construction. Guidance on probabilistic modelling needs to be finalised. Cumulative risk assessments have been performed in a number of countries, on organophosphate insecticides alone (USA) or together with carbamates (UK, DK, NL), triazines, chloroacetanilides, carbamates alone (USA), and all pesticides (DE). All identifiable assumptions and uncertainties should be tabulated and evaluated, at least qualitatively. Those likely to have a major impact on the outcome of the assessment should be examined quantitatively. In cumulative risk assessment, it is necessary, as in other risk assessments, for risk managers to consider what level of risk would be considered "acceptable", for example what percentile of the population should be below the reference value. Criteria for prioritising CAGs for cumulative risk assessment include frequency of detection in monitoring programmes, high usage, high exposure relative to the reference value, large number of compounds (e.g. five or more) in a group.

Management of acute organophosphorus pesticide poisoning

Organophosphorus pesticide self-poisoning is an important clinical problem in rural regions of the developing world, and kills an estimated 200,000 people every year. Unintentional poisoning kills far fewer people but is a problem in places where highly toxic organophosphorus pesticides are available. Medical management is difficult, with case fatality generally more than 15%. We describe the limited evidence that can guide therapy and the factors that should be considered when designing further clinical studies. 50 years after first use, we still do not know how the core treatments--atropine, oximes, and diazepam--should best be given. Important constraints in the collection of useful data have included the late recognition of great variability in activity and action of the individual pesticides, and the care needed cholinesterase assays for results to be comparable between studies. However, consensus suggests that early resuscitation with atropine, oxygen, respiratory support, and fluids is needed to improve oxygen delivery to tissues. The role of oximes is not completely clear; they might benefit only patients poisoned by specific pesticides or patients with moderate poisoning. Small studies suggest benefit from new treatments such as magnesium sulphate, but much larger trials are needed. Gastric lavage could have a role but should only be undertaken once the patient is stable. Randomised controlled trials are underway in rural Asia to assess the effectiveness of these therapies. However, some organophosphorus pesticides might prove very difficult to treat with current therapies, such that bans on particular pesticides could be the only method to substantially reduce the case fatality after poisoning. Improved medical management of organophosphorus poisoning should result in a reduction in worldwide deaths from suicide.

Roles of neuropeptides in O,O,S-trimethylphosphorothioate (OOS-TMP)-induced anorexia in mice

O,O,S-Trimethylphosphorothioate (OOS-TMP), an impurity present in various organophosphorus insecticides, has previously been shown to induce hypophagia. The major goal of this study was to investigate its mechanism of action. Both intracerebroventricular (i.c.v.) and intraperitoneal (i.p.) injection transiently induced hypophagia at a dose of 5mg/kg within 6h, without causing lung injury. Hypophagia was accompanied by up-regulation of corticotropin releasing factor (CRF) (2.92+/-0.45 vs. 1.7+/-0.5, at 2h after i.c.v., 3.40+/-1.38 vs. 1.76+/-0.41 at 6h after i.p., P<0.05) in the hypothalamus. After i.c.v. injection, hypophagia recovered by 6h after dosing. At doses higher than 5mg/kg, i.c.v. injection induced continuous hypophagia from 20min to 72h after dosing, accompanied by hypothermia and lung injury. OOS-TMP was considered to induce hypophagia through enhancing expression of CRF.

Therapy for head lice based on life cycle, resistance, and safety considerations

The timing of head lice maturation most favorable to their survival in the presence of anti-lice agents is the maximum time as an ovum (12 days) and the shortest possible time of maturing from newly hatched nymph to egg-laying adult (8.5 days). Pediculicides that are not reliably ovicidal (pyrethroids and lindane) require 2 to 3 treatment cycles to eradicate lice. Ovicidal therapies (malathion) require 1 to 2 treatments. Treatment with an agent to which there is genetic resistance is unproductive. In the United States, lice have become increasingly resistant to pyrethroids and lindane but not to malathion. Treatment with malathion has favorable efficacy and safety profiles and enables the immediate, safe return to school. Nit combing can be performed adjunctively. No-nit policies should be rendered obsolete.

Malathion detoxification by human hepatic carboxylesterases and its inhibition by isomalathion and other pesticides

The organophosphorothioate (OPT) pesticide malathion (MAL) in mammals is readily hydrolyzed by mammalian carboxylesterases (CE). The reaction competes with the CYP-catalyzed formation of malaoxon (MOX), the toxic metabolite. Alterations or individual variations in CE activity may result in increased MOX formation, enhancing MAL toxicity. We have characterized the human hepatic CE activity in a panel of 18 human liver microsomes as well as the inhibitory effect of IsoMAL, a major impurity of MAL commercial formulations, parathion (PAR), chlorpyrifos (CPF), and chlorpyrifos-oxon (CPFO). CE activity showed a low level of variation among individuals (4-fold). The reaction consists of two different phases, differing in their affinity for mal (k(m1)=0.25-0.69 microm; K(m2)=10.3-26.8 microM). The relatively low K(m1) values confirmed that human CE efficiently detoxify MAL. IsoMAL was shown to be a potent noncompetitive inhibitor of MAL detoxification (K(i)=0.6 microM), with a higher inhibitory potency than CPF and PAR (K(i)=7.5 microM and 50 microM, respectively). These two latter compounds very likely act as mixed inhibitors. CPFO showed the highest inhibitory potency toward CE-mediated detoxification, being characterized by a K(i)=22 nM. The present results provide useful information for a better understanding of possible interactions between different OPTs and for assessing the potential cumulative risk for exposure to OPT mixtures.

MALATHION BIOACTIVATION IN THE HUMAN LIVER: THE CONTRIBUTION OF DIFFERENT CYTOCHROME P450 ISOFORMS

Among organophosphorothioate (OPT) pesticides, malathion is considered relatively safe for use in mammals. Its rapid degradation by carboxylesterases competes with the cytochrome P450 (P450)-catalyzed formation of malaoxon, the toxic metabolite. However, impurities in commercial formulations are potent inhibitors of carboxylesterase, allowing a dramatic increase in malaoxon formation. Malathion desulfuration has been characterized in human liver microsomes (HLMs) with a method based on acetylcholinesterase inhibition that is able to detect nanomolar levels of oxon. The active P450 isoforms have been identified by means of a multifaceted strategy, including the use of cDNA-expressed human P450s and correlation, immunoinhibition, and chemical inhibition studies in a panel of phenotyped HLMs. HLMs catalyzed malaoxon formation with a high level of variability (>200-fold). One or two components (K(mapp1) = 53-67 microM; K(mapp2) = 427-1721 microM) were evidenced, depending on the relative specific P450 content. Results from different approaches indicated that, at low malathion concentration, malaoxon formation is catalyzed by CYP1A2 and, to a lesser extent, 2B6, whereas the role of 3A4 is relevant only at high malathion levels. These results are in line with those found with chlorpyrifos, diazinon, azynphos-methyl, and parathion, characterized by the presence of an aromatic ring in the molecule. Since malathion has linear chains as substituents at the thioether sulfur, it can be hypothesized that, independently from the chemical structure, OPTs are bioactivated by the same P450s. These results also suggest that CYP1A2 and 2B6 can be considered as possible metabolic biomarkers of susceptibility to OPT-induced toxic effects at actual human exposure levels.

Selective enrichment of sulfides, thiols and methylthiophosphates from water samples on metal-loaded cation-exchange materials for gas chromatographic analysis

The suitability of using metal-loaded sorbents for solid-phase extraction to enrich organic sulfur compounds from water samples was studied. To test the retention behavior of a number of sulfides, thiols and methylthiophosphates, a cation-exchanger was loaded with various metal ions. The elution behavior of sulfur compounds was investigated with different solvents. A combination of Pb2+-modified cation-exchanger as sorbent and CS2 (1%, v/v) in toluene proved to be the most suitable approach for the given problem. Using GC with a pulsed flame photometric detector yielded detection limits of between 0.6 and 2.9 microg/l. The results showed good reproducibility with relative standard deviations of 2-11%.

Identification of butyrylcholinesterase adducts after inhibition with isomalathion using mass spectrometry: difference in mechanism between (1R)- and (1S)-stereoisomers

Previous kinetic studies found that butyrylcholinesterase (BChE) inhibited by (1R)-isomalathions readily reactivated, while enzyme inactivated by (1S)-isomers did not. This study tested the hypothesis that (1R)- and (1S)-isomers inhibit BChE by different mechanisms, yielding distinct adducts identifiable by peptide mass mapping with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Equine BChE (EBChE) was inhibited to <10% of control activity with each isomer of isomalathion and the reference compound isoparathion methyl. Control and treated enzyme was digested with trypsin, and peptides were fractionated with HPLC. Separated and unseparated peptides were analyzed with MALDI-TOF-MS. Identity of an organophosphorus peptide adduct was confirmed by fragmentation using postsource decay analysis. EBChE inhibited by (1R)-isomalathions or (S)-isoparathion methyl readily reactivated after oxime treatment with 30-40% activity recovered. Enzyme inactivated by (1S)-isomalathions or (R)-isoparathion methyl recovered <2% and <5% activity, respectively, after oxime treatment. MALDI-TOF-MS analysis revealed that inhibition of EBChE by (1R)-isomalathions and (R)- or (S)-isoparathion methyl yielded O,S-dimethyl phosphate adducts. Enzyme inactivated by (1S)-isomalathions produced only O-methyl phosphate adduct. EBChE modified by (1R)-isomalathions or either enantiomer of isoparathion methyl yielded an O-methyl phosphate adduct as well. The results indicate that EBChE inhibition by (1R)-isomalathions proceeds with loss of diethyl thiosuccinate, but inactivation by (1S)-isomers occurs with loss of thiomethyl as the primary leaving group followed by rapid expulsion of diethyl thiosuccinate to yield an aged enzyme. Furthermore, the data suggest that aging of the O,S-dimethyl phosphate adduct occurs via an S(N)2 process with loss of thiomethyl.

Biological Monitoring of Pesticide Exposure: a review. Introduction

Pesticides are used worldwide in agriculture, industry, public health and for domestic applications: as a consequence, a great part of the population may be exposed to these compounds. In spite of this extensive use, knowledge on the health risks associated with prolonged exposure is rather poor, and major uncertainties still exist. Epidemiological observations in man have so far produced little conclusive information, mainly because of weaknesses in exposure assessment. Therefore, information on the type and levels of exposure is fundamental in order to better understand and characterize risk to human health. Exposure assessment can be carried out via measurement of environmental concentrations, as well as via determination of the chemical or its metabolites in body tissues (biological monitoring). Besides indices of internal dose, biological monitoring also includes measurements of early effects attributable to interaction between the chemical agent and the human body. Biological monitoring has the advantage, over environmental monitoring, of determining the dose actually absorbed via any possible route: differences in absorption can be taken into account. whether they are due to biological variability or to use of protective equipment. When, in some cases, a combination of occupational and non-occupational exposure occurs, this also can be taken into consideration by biological monitoring. Few reference documents have been published on biological monitoring of pesticides. For this reason, the Office of Occupational Health of the World Health Organization gave ICPS a mandate to prepare a monograph specifically addressed to reviewing methods for biological monitoring of pesticide exposure. This review is based on more than 300 studies published over the period 1980-1999. For the most representative chemical classes, the available biological exposure indices are reported. Both indices of internal dose and. when available, of early effects are discussed. The reported tests were used to monitor exposure of pesticide applicators in agriculture and public health, manufacturing and formulating workers. subjects poisoned after accidental exposure or attempted suicide, volunteers involved in pharmacokinetic studies, as well as sub-groups of the general population exposed to environmentally persistent pesticides. Single chapters deal with organophosphorus insecticides, carbamate pesticides, dithiocarbamates, phenoxyacids, quaternary ammonium compounds. coumarin rodenticides, synthetic pyrethroids, organochlorine pesticides, chlorotriazines, and pentachlorophenol.

Kinetic evidence for different mechanisms of acetylcholinesterase inhibition by (1R)- and (1S)-stereoisomers of isomalathion

Inhibition of acetylcholinesterase (AChE) by isomalathion has been assumed to proceed by expulsion of diethyl thiosuccinyl to produce O, S-dimethyl phosphorylated AChE. If this assumption is correct, AChE inhibited by (1R)- or (1S)-isomalathions should reactivate at the same rate as AChE inhibited by configurationally equivalent (S)- or (R)-isoparathion methyl, respectively, which are expected to inhibit AChE by loss of 4-nitrophenoxyl to yield O,S-dimethyl phosphorylated AChEs. Previous work has shown that rat brain AChE inhibited by (1R)-isomalathions reactivates at the same rate as the enzyme inhibited by (S)-isoparathion methyl. However, although rat brain AChE inhibited by (R)-isoparathion methyl reactivates at a measurable rate, the enzyme inhibited by (1S)-isomalathions is intractable to reactivation. This surprising finding suggests the hypothesis that (1R)- and (1S)-stereoisomers of isomalathion inhibit AChE by different mechanisms, yielding enzymatic species distinguishable by their postinhibitory kinetics. The present study was carried out to test this hypothesis by comparing kinetic constants of reactivation (k+3) and aging (k+4) of hen brain AChE and bovine erythrocyte AChE inhibited by the four stereoisomers of isomalathion and the two stereoisomers of isoparathion methyl. Both AChEs inhibited by either (1R,3R)- or (1R,3S)-isomalathion had comparable corresponding k+3 values (spontaneous and oxime-mediated) to those of AChEs inhibited with (S)-isoparathion methyl. However, spontaneous and oxime-mediated k+3 values comparable to those of (R)-isoparathion methyl could not be obtained for AChEs inhibited by (1S,3R)- and (1S,3S)-isomalathion. Comparison of k+4 values for hen brain AChE inhibited by each stereoisomer of isomalathion and isoparathion methyl corroborated that only the (1S)-isomalathions failed to produce the expected O,S-dimethyl phosphoryl-conjugated enzymes. The results for (1R)-isomalathions suggest that the mechanism of inhibition of AChE by these isomers is the expected one involving diethyl thiosuccinyl as the primary leaving group. In contrast, the results for (1S)-isomalathions are consistent with an alternative mechanism of inhibition by these isomers implicating loss of thiomethyl as the primary leaving group.

Effect of acute administration of malathion by oral and dermal routes on serum histamine levels

Previous studies have shown that acute, oral administration of malathion increased the generation of a humoral immune response, stimulated macrophage function and caused mast cell degranulation and histamine release. In this study, the effect of acute administration of various doses of malathion via oral and dermal routes to mice and rats on serum levels of histamine was evaluated. Oral administration of malathion to mice led to an increase in the level of serum histamine 4 and 8 h after administration. At 4 h after administration, the peak in serum histamine levels was observed at a dose of 10 mg/kg malathion. At 8 h, a maximal effect was observed at a dose of 700 mg/kg and the response was more prolonged than at lower doses. At 12 and 24 h after administration, the level of histamine in the serum of treated mice was comparable to controls. A similar pattern was observed in rats. However, the time point at which histamine levels returned to control was 8 rather than 12 h. After application of malathion to the skin of mice or rats in dimethyl sulphoxide (DMSO), the level of histamine in the blood was also increased. As before, the peak increase was observed at 4 h after administration and the level had returned to control levels within 8 h (slight increase at 8 h in rats) after application. However, after dermal application the maximal levels of histamine in the serum were noted at the highest doses of malathion. The no effect levels for histamine in the blood after malathion administration to these two species by these two routes are as follows: (1) Mice, oral in corn oil, 0.1 mg/kg; (2) Rats, oral in corn oil, 0.1 mg/kg; (3) Mice, dermal in DMSO, 2 mg/kg; (4) Rats, dermal in DMSO--not determined (2 mg/kg low effect level).

Effects of malathion metabolites on degranulation of and mediator release by human and rat basophilic cells

In the present study, the effects of malathion and malathion derivatives on histamine and beta-hexosaminidase release by RBL-1 cells, rat peritoneal mast cells (RPMC), and human peripheral blood basophils (HPBB) and cutaneous mast calls were examined. One hour of incubation of RBL-1 cells with all organophosphate compounds tested, except for malathion and malathion monoacid, led to an increase in histamine release. beta-Hexosaminidase, an enzyme released by basophilic cells and a biochemical marker of degranulation, was not released from RBL-1 cells after 1 h of exposure to organophosphate compounds. Within 4 h, all compounds tested increased the release of histamine and beta-hexosaminidase. Longer exposures led to a decrease in the concentration of the compound that was required to cause mediator release. Exposure of RPMC to organophosphate compounds, with the exception of malathion monoacid and malathion (30 min) or malathion monoacid (1 h), led to the release of histamine, but not beta-hexosaminidase. Incubation of HPBB with malaoxon (51.4 +/- 2.8% total histamine released), malathion diacid (25.7 +/- 2.9%), beta-malathion monoacid (31.4 +/- 2.8%), and isomalathion (57.1 +/- 17.1%) for 1 h led to the release of histamine. Only malaoxon and isomalathion caused beta-hexosaminidase release from HPBB after a 1-h incubation. Incubation of cutaneous mast cells with malaoxon and beta-monoacid for 4 h led to increased release of histamine and beta-hexosaminidase at levels comparable to compound 48/80. These data suggest that malathion metabolites can cause rapid release of histamine from basophilic cells from a variety of origins and species. With prolonged incubation, malathion itself caused the release of mast-cell mediators, suggesting that the cells may be capable of metabolizing malathion. These data also indicate a disparity between the release kinetics of two different mast-cell mediators contained in granules by organophosphates, and that there are different mechanisms of mediator release.

Contributions of inflammatory mast cell mediators to alterations in macrophage function after malathion administration

Recent studies using mast cell-defined mice showed that the presence of mast cells was necessary for the increase in macrophage function observed after oral administration of malathion and reconstitution with bone marrow-derived mast cells restored the ability of malathion to increase macrophage function. In addition, the release of mast cell mediators (blocked by cromolyn) and histamine (action blocked by pyrilamine) was shown to be involved in the action of malathion on macrophage function. In the present study, the contribution of inflammatory mediators (i.e. arachidonic acid metabolites and tumor necrosis factor [TNF]) which may be generated by mast cells after oral administration of malathion, was examined. Controls in this study included the effects of the agent to be examined on: (1) resident peritoneal macrophages; and (2) macrophages elicited with pristane, and agent shown previously to stimulate macrophage function in the absence of mast cells. Intraperitoneal administration of indomethacin, and inhibitor of cycloxygenase, or neutralizing antibody to TNF 30 h before and 4 h after oral malathion blocked the ability of malathion to increase macrophage function, as measured by the generation of respiratory burst activity and the production of cathepsin D. On the other hand, administration of these agents to mice injected intraperitoneally with pristane did not affect the observed increase in cathepsin D production. Respiratory burst function after elicitation with pristane was slightly decreased (indomethacin) or not affected (antibody to TNF). The effect of intraperitoneal administration of nordihydroguaiaretic acid (NDGA), and inhibitor of both cycloxygenase and lipoxygenase, was also examined. Intraperitoneal administration of NDGA partially blocked the effects of oral administration of malathion on peritoneal macrophage function, but did not affect the function of resident pristane-elicited peritoneal macrophages. These data suggest that inflammatory mediators (potentially released from mast cells upon stimulation) contribute to the elevation in macrophage function observed after oral malathion administration.

A direct involvement of the central nervous system in hypophagia and inhibition of respiratory rate in rats after treatment with O,O,S-trimethyl phosphorothioate

O,O,S-Trimethyl phosphorothioate (OOS-TMP) is known to induce unique symptoms, which are characterized by hypophagia, progressive weight loss, and hypothermia. To determine whether there is the possibility of a causal relationship between these toxic symptoms and a direct action of OOS-TMP on the central nervous system, we investigated the development of these symptoms in Fischer 344 female rats after oral or intracerebral treatment with OOS-TMP. Oral administration of OOS-TMP at 20 mg/kg induced marked hypophagia, progressive weight loss and hypothermia. Moreover, inhibition of respiratory rate was observed immediately after treatment. It lasts during the entire experimental period. Profound hypothermia below 34 degrees C was observed more frequently in the rats, which became hypercapnic (PaCO2 > or = 50 mmHg). In contrast, administration of OOS-TMP at 20 mg/kg (as much as the oral dose) into the cerebral lateral ventricle succeeded in inducing hypophagia, progressive weight loss and lowered respiratory rates. On the other hand, by this route of administration, OOS-TMP at 20 mg/kg failed to induce hypothermia, hypercapnia and lung injury. The present results suggest that hypophagia and inhibitions of respiratory rate are attributable to the direct action of OOS-TMP on the central nervous system, while other symptoms are associated with lung injury.

Toxic interactions among environmental pollutants: corroborating laboratory observations with human experience

Combined exposures to multiple chemicals may result in interactions leading to a significant increase or decrease in the overall toxicity of the mixture compared to the summation of the toxicity of the components. A large number of chemical interactions have been described in animal studies by administering high doses of chemicals by routes and scenarios often different from anticipated human exposures. Though limited, there is some evidence for the occurrence of several supra-additive (the combined effects are greater than the simple summation of the individual effects) and infra-additive (the combined effects are smaller than the simple summation of the individual effects) chemical interactions in humans. For example, toxicokinetic interactions between several solvents have been found to occur in the workplace, whereas those involving pesticides have been reported less frequently, especially during accidental exposures. Toxic interactions involving nutritionally important metals and metalloids appear to occur more frequently, since several of them have an important role in a variety of physiological and biochemical processes. On the contrary, there is not much evidence to confirm the occurrence of toxic interactions among the commonly encountered inorganic gaseous pollutants in humans. Overall, the majority of chemical interactions observed in animal studies have neither been investigated in humans nor been extrapolated to humans based on appropriate mechanistic considerations. Future research efforts in the chemical interactions arena should address these issues by focusing on the development of mechanistically and biologically based models that allow predictions of the extent of interactions likely to be observed in humans.

Unusual manifestations after malathion poisoning

We report a case of organophosphate poisoning with a commercial preparation of malathion (deliberate ingestion of Malathane Garden Spray: malathion 15% in isopropyl alcohol) in which the initial cholinergic crisis was followed by cardiac, pulmonary, neurological and renal manifestations. They occurred when erythrocyte and plasma cholinesterases were reactivating. A chemical analysis of the pesticide preparation revealed, apart from malathion itself, the presence of isopropylmalathion and O,O,S-trimethylphosphorothioate. Although pure malathion is regarded as one of the safest organophosphate insecticides, this observation underlines the possibility of severe complications after exposure to a preparation which has been stored for a long period of time.

O,O,S-Trimethyl phosphorothioate induces hypothermia in Fischer 344 rats in a manner dependent on both doses and housing temperatures

We explored the effects of O,O,S-trimethyl phosphorothioate (OOS-TMP) on body temperatures in Fischer 344 female rats. The 7-day LD50 p.o. for Fischer 344 female rats was found to be 11.8 mg/kg. OOS-TMP induced long-lasting (more than 48 h) and extensive hypothermia at doses > or = 14 mg/kg at a typical laboratory temperature (22 degrees C) while it produced typical symptoms at 10 mg/kg without hypothermia. In contrast, pair-fed (to 20 mg/kg rats) rats (n = 4) did not become hypothermic, negating any role of hypophagia in OOS-TMP associated hypothermia. We next investigated the effects of housing temperatures on toxicities at a LD50 dose (12 mg/kg). At 30 degrees C (n = 11) and 22 degrees C (n = 13), rats did not have hypothermic bouts but at 15 degrees C, eight out of ten rats had. Evidence that changes of housing temperatures neither modified clinical symptoms nor changed mortality rates discards a possibility of hypothermia being involved in delayed toxicity. A novel result of the present study suggests that thermoregulation may be heavily impaired by a special class of organophosphorus compounds.

HI-6 in man: efficacy of the oxime in poisoning by organophosphorus insecticides

The efficacy of the oxime HI-6 was studied as a treatment for organophosphorus poisoning. HI-6 was given four times daily as a single intramuscular injection of 500 mg accompanied by atropine and diazepam therapy. Oxime treatment was started on admission and continued for a minimum of 48 h and a maximum of 7 d. HI-6 rapidly reactivated human blood acetylcholinesterase inhibited by dimethoxy organophosphorus compounds, while the dimethoxy-inhibited enzyme was mainly resistant to the treatment by HI-6. Although both HI-6 and pralidoxime chloride reactivated the red blood cell cholinesterase in quinalphos-poisoned subjects, the return of enzyme activities was more rapid following the use of HI-6. The general improvement of poisoned patients, which was sometimes more rapid than the rise of acetylcholinesterase activity, pointed to direct pharmacological effects of HI-6. No undesirable side-effects were noted in patients when HI-6 plasma concentrations were maintained at levels far above the 'therapeutic' concentration for up to 7 d.

Alterations in xenobiotic metabolizing enzymes in brain and liver of rats coexposed to endosulfan and malathion

The effects of endosulfan (3 mg kg-1 body wt., i.p.) and malathion (30 mg kg-1 body wt.) and their coexposure on rat hepatic and brain xenobiotic metabolizing enzymes were investigated. Endosulfan was found to induce aminopyrine-n-demethylase (81%) and aniline hydroxylase (59%) activities significantly in liver and to a lesser extent in brain. Malathion treatment induced malathion carboxylesterase activity in both liver (50%) and brain (22%), significantly depleted liver glutathione (35%) content with stimulation of glutathione-S-transferase (50%) and inhibited the activity of mixed-function oxidases. In the coexposed animals, malathion's inhibitory influence on mixed-function oxidases and endosulfan's inhibitory effect on malathion carboxylesterase were found to dominate, while endosulfan potentiated the activity of glutathione-S-transferase significantly in liver (69%) and brain. A similar trend of alteration in coexposed brain was found, but to a lesser extent. A significant inhibition in brain acetylcholine esterase activity (42%) in the coexposed animals suggests that endosulfan may potentiate the toxicity of malathion by interfering with glutathione and carboxylesterase routes of malathion detoxification.

Structure and pulmonary toxicity relationship on O,O-dimethyl S-alkyl phosphorothioate esters

The structure-pulmonary toxicity relationship was investigated using three different O,O,S-trimethylphosphorothioate (OOS-TMP) analogues, which is known to induce a typical mortality pattern (delayed death) and pulmonary injury; O,O-dimethyl S-ethyl (OOS-DMEP), O,O-dimethyl S-propyl (OOS-DMPP), and O,O-dimethyl S-butyl (OOS-DMBP) phosphorothioates. The mortality pattern in rats dosed with OOS-DMEP was similar to the "delayed death" pattern: the LD50s in rats for OOS-DMEP decreased dramatically from more than 200 mg/kg within 24 hr to 41.1 (males) or 13.8 (females) mg/kg 7 days after treatment while the LD50s in rats for OOS-DMPP and OOS-DMBP did not. Histopathological examinations revealed that OOS-DMEP induced pulmonary oedema and bleeding at a dose of 1/2 LD50 by 72 hr after dosing while the other two compounds did not. Thus, it was concluded that OOS-DMEP induces pulmonary injury, thereby eliciting the "delayed death" mortality pattern.

Protection against chemical-induced lung injury by inhibition of pulmonary cytochrome P-450

Protection afforded by trialkyl phosphorothionates against the lung injury caused by trialkyl phosphorothiolates probably results from the inhibition by the P = S moiety of the thionates, of one or more pulmonary cytochrome P-450 isozymes. The aromatic hydrocarbons p-xylene and pseudocumene also protect against this injury and inhibit some P-450 isozymes, but by a different mechanism. OOS-Trimethylphosphorothionate and p-xylene were compared as protective agents against the effect of OOS-trimethylphosphorothiolate and two other lung toxins ipomeanol and 1-nitronaphthalene that are known to be activated by cytochrome P-450. The effects of these protective compounds, in vivo, on pulmonary cytochrome P-450 activity were also determined. Both compounds inhibited pentoxyresorufin O-deethylase activity, but not ethoxyresorufin O-deethylase. The phosphorothionate was most effective against lung injury caused by the phosphorothiolates and 1-nitronaphthalene, whereas p-xylene was much more effective against ipomeanol. beta-Naphthoflavone, which induces pulmonary ethoxyresorufin O-deethylase activity, did not protect against phosphorothiolate or 1-nitronaphthalene injury, and it was only marginally effective in decreasing the toxicity of ipomeanol.

Inhibition of serum cholinesterase by trialkylphosphorothiolates

The kinetics of inhibition of horse serum cholinesterase (EC 3.1.1.8) by six trialkylphosphorothiolates was studies (25 degrees C, pH 7.4). The compounds were : OOS-trimethylphosphorothiolate (OOS-Me), OSS-trimethylphosphorodithiolate (OSS-Me), SSS-trimethylphosphorotrithiolate (SSS-Me) and their corresponding ethyl analogues (OOS-Et, OSS-Et, SSS-Et). The second order rate constants of inhibition ranged from 7.2 to 2128 mol-1 1 min-1, of inhibition ranged from 7.2 to 2128 mol-1 1 min-1, and the enzyme/inhibitor dissociation constants from 0.079 to 1.5 mM. The ethyl esters were better inhibitors than their methyl analogues and the OSS-compounds were better inhibitors than the OOS- or SSS-compounds. The same structure-activity relationship is known to hold for the reaction of the compounds with acetylcholinesterase (EC 3.1.1.7).

A pneumotoxin, O,O,S-trimethyl phosphorothioate, induces hemorheological alteration in rats

O,O,S-trimethyl phosphorothioate (OOS-TMP), an impurity present in widely used organophosphorus insecticides, has been shown to induce lung injury after oral administration. To date, very little is known about the hemorheological changes which may occur during the inflammation of lung caused by OOS-TMP. The present study has demonstrated that oral administration of OOS-TMP (10 mg/kg, 20 mg/kg) to rats produced an increase in whole blood apparent viscosity at 24, 48 and 72 h following the treatment in rats. Concomitantly, the plasma fibrinogen level and red blood cell (RBC) aggregation were increased at 24 and 48 h. There was no change in RBC filterability. Thus, OOS-TMP, a pneumotoxin, was capable of causing a systemic hemorheological alteration, probably via increase in fibrinogen content, an acute-phase protein, in rats.

Immature alveolar/blood barrier and low disaturated phosphatidylcholine in fetal lung after intrauterine exposure to O,O,S-trimethylphosphorothioate

Intrauterine exposure to the potent lung toxicant OOS-TMP was found to result in neonatal lethality attributed to immature lungs (Koizumi et al. 1988). The present study was initiated to investigate biological/pathological profiles of such pulmonary immaturity. OOS-TMP was given p.o. to five pregnant female Sprague-Dawley rats on gestation day (G) 19 at 2.5, 7 or 20 mg/kg. Control (N = 6) or pair-fed dams (N = 5: pair-fed to 20 mg/kg dams) received 2 ml/kg corn oil. On G 22, fetuses were delivered by Cesarean section. The biochemical maturity of lungs was assessed by glycogen content and production of disaturated phosphatidylcholine (DSPC), a major component of pulmonary surfactant. Mean DSPC content was significantly lower in fetuses from dams dosed at 7 or 20 mg/kg while mean glycogen concentration, in contrast, was 3- to 6-fold higher in those fetuses than fetuses from control or pair-fed dams. Pathological examination revealed that in fetuses delivered from dams dosed at 7 mg/kg or 20 mg/kg, glycogen-rich cuboidal epithelial cells completely covered the terminal air space and alveolar/blood barriers stayed at the poorly developed stage. The stage of the pulmonary development in those fetuses was similar to those in fetuses on G19. Therefore it was concluded that intrauterine exposure to OOS-TMP delayed pulmonary development, thereby causing respiratory failure after birth.

Morphogenesis of O,O,S-trimethyl phosphorothioate-induced pulmonary injury in mice

The purpose of this study was to establish and characterize an experimental model in mice that examined the pulmonary effects of O,O,S-trimethyl phosphorothioate (OOS-TMP), a contaminant present in commercially important organophosphorus insecticides. Characterization of the model will allow the delineation of comparative effects between species and its possible extrapolation to man, and provide an additional experimental animal species satisfactory for mechanistic-oriented studies on OOS-TMP and related compounds. The morphogenesis of pulmonary injury induced by OOS-TMP was studied in mice by light and transmission electron microscopy. Weanling female C57BL/Ka mice received OOS-TMP dissolved in corn oil by intraperitoneal injection and were studied at intervals from 6 to 168 hr after treatment. Morphologic changes were observed in Clara cells only at the initial time period examined. Injury of pulmonary parenchymal cell populations, including the endothelium and type I alveolar epithelium, occurred after morphologic changes indicative of severe cell injury and necrosis in Clara cells. Endothelial cell injury was accompanied by significant increases in wet lung weight and percentage lung water content. Type I alveolar epithelial cell injury and loss resulted in a bare basal lamina, followed by attenuation, hypertrophy, and hyperplasia of type II alveolar epithelial cells. The results of this study document the successful establishment of a mouse experimental model of OOS-TMP-induced pulmonary toxicity. It is concluded that the Clara cell was the initial and most severely affected pulmonary cell population in mice receiving OOS-TMP. The administration of OOS-TMP in mice also results in marked morphologic alterations in the pulmonary parenchyma that were accompanied by significant changes in lung weight and composition.

Pulmonary endothelial and alveolar epithelial lesions induced by O,O,S-trimethyl phosphorothioate in rats

The morphogenesis of pulmonary injury induced by an impurity present in a commercially important organophosphorus insecticide, O,O,S-trimethyl phosphorothioate (OOS-TMP), was studied by combined light and transmission electron microscopy. Weanling female WAG/Rij rats received OOS-TMP dissolved in corn oil by gavage and were studied at intervals from 6 to 168 h after treatment. Sequestration of neutrophils was initially observed at 12 h after treatment and was accompanied by interstitial oedema. Plasmalemma alterations in endothelium lining capillaries and small arteries and veins were observed from 12 to 120 h after treatment and were accompanied by endothelial cell detachment and separation from the basal lamina. Abundant aggregates of fibrin were sequentially observed in intravascular, interstitial, and alveolar spaces. Platelet aggregation and degranulation were occasionally observed in capillaries as early as 12 h after treatment, and frequently observed in capillaries and small vessels from 24 to 96 h after treatment. Significant increases in wet lung weight and lung water content occurred at the same time that morphologic changes were observed in pulmonary endothelium. Alterations in type I alveolar epithelial cells were initially observed at 24 h after treatment. Cell swelling, fragmentation, and necrosis were observed in both type I and type II cells and resulted in a bare basal lamina. Marked attenuation, hypertrophy, and proliferation of type II epithelial cells followed alveolar epithelial cell injury and loss. Minimal changes were observed in non-ciliated bronchiolar epithelial (Clara) cells; predominant changes included the loss of surface microvilli and apical cytoplasmic bulge. The results of this study indicate that the endothelium and alveolar epithelium are the predominant cell types in the rat lung injured following OOS-TMP administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of acute administration of O,O,S-trimethyl phosphorothioate on the respiratory burst and phagocytic activity of splenic and peritoneal leukocytes

An impurity in malathion, O,O,S-trimethyl phosphorothioate (OOS-TMP), was previously shown to be immunosuppressive. The immune cell type which induced immune suppression caused by OOS-TMP at 24 hrs after administration was found to be splenic macrophages. Further characterization of macrophages from OOS-TMP treated mice indicated that OOS-TMP led to macrophage differentiation. In this study, these initial studies were continued and extended to examine the effects of OOS-TMP on splenic and peritoneal macrophages at various times following exposure. Administration of OOS-TMP increased the size heterogeneity of cell volume, phagocytic capability and respiratory burst activity of splenic and peritoneal macrophages. However, by day 7 splenic and peritoneal macrophages from treated animals had size frequency histograms, phagocytic capability and respiratory burst activity similar to control. These data would suggest that macrophages not previously exposed to OOS-TMP migrated to the spleen and peritoneum of treated animals. This migration may allow the restoration of the ability of splenocytes from treated animals to generate an immune response. Alternatively, these data may indicate that 7 days following exposure to OOS-TMP, the differentiative state of the splenic and peritoneal macrophages of treated mice had decayed and hence these cells had regained resident characteristics.

Neonatal death and lung injury in rats caused by intrauterine exposure to O,O,S-trimethylphosphorothioate

O,O,S-Trimethyl phosphorothioate (OOS-TMP) is an impurity present in a number of widely used organophosphorus insecticides and has been recognized as a potent lung toxicant. OOS-TMP was given p.o. to pregnant rats on gestation day (G) 20 at 0.5, 2.5, 10 and 40 mg/kg. Control dams or pair-fed dams (pair-fed to 40 mg/kg) received 2 ml/kg corn oil. Neonates from treated dams died within 72 h after delivery in a dose-related manner: 100% at 40 mg/kg, 86% at 10 mg/kg, 15% at 2.5 mg/kg, 1% at 0.5 mg/kg, with 3% in controls and 2% in neonates from pair-fed dams. Neonates from treated (40 or 10 mg/kg) and control dams were cross-fostered. The cross-fostering did not affect mortality of neonates from either dosed dams or from control dams. Disposition of OOS-TMP was studied by using [3H]-OOS-TMP at 0.5, 2.5 and 10 mg/kg. Concentrations of OOS-TMP equivalent in fetal lung were about one half of those in mothers at all doses. In another set of experiments, dams (five dams for each dose) were dosed on G 20 with OOS-TMP p.o. at 0, 0.5, 2.5, 10, and 40 mg/kg or pair-fed (pair-fed to 40 mg/kg) and the fetuses were delivered by cesarean section (C-section) on G 23. In neonates from dams dosed with 10 and 40 mg/kg, cyanosis occurred within 4 h after C-section. Histopathological examination revealed dose-related proliferation of type II pneumocytes in dams and proliferation of interstitial cells and delayed septal/capillary development in neonates.(ABSTRACT TRUNCATED AT 250 WORDS)

Pulmonary hydroxyproline content and production following treatment of mice with O,S,S-trimethyl phosphorodithioate

The systemic administration of O,S,S-trimethyl phosphorodithioate (OSS), a contaminant of various organophosphorus insecticides, induces delayed damage to rat and mouse lung tissue. The lesion, particularly in the rat, closely resembles that produced by butylated hydroxytoluene (BHT) in mice. Although the time course of cell damage and repair has been studied in both species, it is not clear whether excess collagen, indicative of fibrosis, is deposited. Changes in pulmonary hydroxyproline content and synthesis, indices of collagen metabolism, were analysed in mice treated with 45 mg/kg OSS. A significant increase in total lung hydroxyproline was evident 21 days after treatment compared to both pair-fed and ad libitum controls. This increase was not augmented by subsequent treatment with 35 mg/kg 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) or exposure to 70% oxygen for 7 days. The rate at which lung tissue synthesized hydroxyproline was increased 7-14 days after treatment with OSS. These data demonstrate that treatment of mice with OSS results in changes indicative of pulmonary fibrosis. However, in contrast to some other lung-toxic chemicals, this lesion was not enhanced by subsequent treatment with BCNU or hyperoxia.

The interaction between phosphorothionate insecticides, pneumotoxic trialkyl phosphorothiolates and effects on lung 7-ethoxycoumarin O-deethylase activity

A number of phosphorothionate (P = S) insecticides, including bromophos and fenitrothion, prevent trialkyl phosphorothiolate (P = O)-induced lung toxicity and the resulting increase in lung weight normally observed at 3 days in the rat. Measurement of 7-ethoxycoumarin O-deethylase (7-EC) activity after both phosphorothionate and phosphorothiolate dosing revealed differing patterns of loss of enzyme activity. Depletion of 7-EC activity by phosphorothionates was maximal between 2 and 10 h after dosing, with recovery between 24 and 72 h. Phosphorothiolates, however, appear to cause two phases of loss of 7-EC activity, an initial fall of approximately 30% observed at 2 h and a secondary fall, maximal on day 3, with loss of 97% of activity, apparently associated with the pathological changes in the lung. It is suggested that oxidative metabolism of phosphorothionates known to occur at the P = S moiety, with suicidal loss of P-450, may then prevent oxidative activation of an S-methyl on the phosphorothiolates, the most likely site for production of a reactive intermediate capable of damaging the lung. Lung 7-EC in rat is sensitive to concentrations of the phosphorothionates bromophos and fenitrothion at 5-25 times less than those causing loss of liver 7-EC activity and at doses 125-600 times less than their LD50s. If repeated in man this may have implications for personnel occupationally exposed to these compounds.

Induction of the hepatic microsomal cytochrome P-450 system by trialkyl phosphorothioates in rats

Single i.p. doses of O,O,O-triethyl phosphorothioate [OOO-Et(S)], one of the suicide substrates for cytochrome P-450, caused a rapid increase of NADPH-cytochrome c reductase activity in rat liver microsomes. The increase was dose dependent but did not coincide with the recovery from the inhibition of drug-metabolizing activities. There was no change of Km value of the reductase in the induced state. The co-administration of cycloheximide repressed the stimulatory effect of OOO-Et(S), suggesting that a de novo synthesis of enzyme protein may be responsible for the increase in activity. Of four homologous tri-n-alkyl esters tested, the triethyl compound was the most effective at 24 and 48 hr after administration. Triethyl phosphate, the oxygen analog of OOO-Et(S), also caused an increase of the reductase activity, but carbon disulfide had no influence on this activity. Although O,O,S-triethyl phosphorodithioate [OOS-Et(S)] and its n-alkyl homologs also caused the inhibition of drug-metabolizing activities and the increase of the reductase activity, the recovery and the stimulation of enzyme activity were different from that of O,O,O-tri-n-aklyl phosphorothioates.