Low-level exposures to organophosphorus esters and peripheral nerve function

Prevalence of pesticide related occupational diseases among Indonesian vegetable farmers - A collaborative work

Objective

This study was done to understand the prevalence of various occupational diseases including dry eyes, nail dystrophy, and neuropathy related to pesticide exposure in Indonesian local vegetable farmers.

Methods

The data were collected through questionnaires and physical examination involving dermatology, neurology, and ophthalmology domains at Ngablak District, Magelang, Central Java directed to local vegetable farmers. Ocular Surface Disease Index (OSDI) questionnaire and the Schirmer test were used. Analysis was done using descriptive statistics using the Statistical Package for the Social Sciences (SPSS 21.0) and presented in tables.

Results

Inadequate spraying equipment and improper storage of pesticides were found. Out of 105 farmers, 41.9 % experienced occupational skin diseases (OSD). Definite cognitive impairments were found in 3.4 % of subjects but probable in 28.3 % of subjects. Neuropathies were found in 61.7 % of subjects, and dry-eyes syndrome were found in 28.78 % of subjects.

Conclusion

There was a high prevalence of peripheral neuropathy and tremor, dry eyes syndrome in one-third of the population, and the most common skin problem was nail discoloration, with a low incidence of contact dermatitis.

Benomyl, a benzimidazole fungicide, induces oxidative stress and apoptosis in neural cells

Fungicides are used in the agricultural sector against the harmful action of fungi, however they are potential toxic agents for the environment and the living organisms. Benomyl is a widely encountered benzimidazole fungicide that exerts its toxicity via inhibiting microtubule formation in the nervous system and the male reproductive and endocrine systems, whilst it is a known teratogen. Since toxic effects of benomyl and its molecular mechanisms are not fully understood, we aimed to detect its neurotoxic potential via evaluating cytotoxicity, oxidative stress and apoptosis in SH-SY5Y cell line. The cells were incubated with benomyl in a concentration range between 1 and 6 μM for 24 h. Our results indicated a concentration-dependent enhancement of reactive oxygen species measured through flow cytometry and DNA damage evaluated via the comet assay. Additionally, it induced apoptosis in all tested concentrations. According to the findings of the present study, benomyl is a xenobiotic, which it appears to exert its toxic action via a redox-related mechanism that, finally, induces cell apoptosis and death. We believe that this study will offer further insight in the toxicity mechanism of benomyl, although further studies are recommended in order to elucidate these mechanisms in the molecular level.

HINDLIMB PARALYSIS SYNDROME IN WILD CARNABY'S COCKATOOS (CALYPTORHYNCHUS LATIROSTRIS): A NEW THREAT FOR AN ENDANGERED SPECIES

Carnaby's Cockatoos (Calyptorhynchus latirostris) are in decline in SW Western Australia from several processes, including habitat loss and fragmentation. However, in recent years, a disease syndrome has also emerged as a significant population threat. Emerging diseases in wildlife have the potential for catastrophic effects on population numbers, especially if a species is experiencing existing pressure from other threatening processes. This article describes an investigation into a hindlimb paralysis syndrome that has occurred in the summer and autumn since 2012 in 84 wild Carnaby's Cockatoos. Recovery from the syndrome has been demonstrated in 21 of 33 cases when supportive therapy was applied. Although a definitive diagnosis has not been obtained, the hypothesized etiology is an organophosphate-induced delayed-onset neuropathy. The syndrome may indicate that interaction between the cockatoos and inland agricultural practices are affecting this migratory species in ways that are, so far, poorly understood.

DEET potentiates the development and persistence of anticholinesterase dependent chronic pain signs in a rat model of Gulf War Illness pain

Exposure to DEET (N,N-diethyl-meta-toluamide) may have influenced the pattern of symptoms observed in soldiers with GWI (Gulf War Illness; Haley and Kurt, 1997). We examined how the addition of DEET (400mg/kg; 50% topical) to an exposure protocol of permethrin (2.6mg/kg; topical), chlorpyrifos (CP; 120mg/kg), and pyridostigmine bromide (PB;13mg/kg) altered the emergence and pattern of pain signs in an animal model of GWI pain (Nutter et al., 2015). Rats underwent behavioral testing before, during and after a 4week exposure: 1) hindlimb pressure withdrawal threshold; 2) ambulation (movement distance and rate); and 3) resting duration. Additional studies were conducted to assess the influence of acute DEET (10-100μM) on muscle and vascular nociceptor K_v7, K_DR, Na_v1.8 and Na_v1.9. We report that a 50% concentration of DEET enhanced the development and persistence of pain-signs. Rats exposed to all 4 compounds exhibited ambulation deficits that appeared 5-12weeks post-exposure and persisted through weeks 21-24. Rats exposed to only three agents (CP or PB excluded), did not fully develop ambulation deficits. When PB was excluded, rats also developed rest duration pain signs, in addition to ambulation deficits. There was no evidence that physiological doses of DEET acutely modified nociceptor K_v7, K_DR, Na_v1.8 or Na_v1.9 activities. Nevertheless, DEET augmented protocols decreased the conductance of K_v7 expressed in vascular nociceptors harvested from chronically exposed rats. We concluded that DEET enhanced the development and persistence of pain behaviors, but the anticholinesterases CP and PB played a determinant role.

Biosensors Incorporating Bimetallic Nanoparticles

This article presents a review of electrochemical bio-sensing for target analytes based on the use of electrocatalytic bimetallic nanoparticles (NPs), which can improve both the sensitivity and selectivity of biosensors. The review moves quickly from an introduction to the field of bio-sensing, to the importance of biosensors in today's society, the nature of the electrochemical methods employed and the attendant problems encountered. The role of electrocatalysts is introduced with reference to the three generations of biosensors. The contributions made by previous workers using bimetallic constructs, grouped by target analyte, are then examined in detail; following which, the synthesis and characterization of the catalytic particles is examined prior to a summary of the current state of endeavor. Finally, some perspectives for the future of bimetallic NPs in biosensors are given.

Evaluating suspected work-related neurologic disorders (clinical diagnosis)

The clinical diagnosis of work-related neurologic disorders is essentially one of exclusion because symptoms and signs are often nonspecific. The clinical reasoning requires a three-step approach: (1) establish the characteristics of the presenting disease; (2) ascertain that observed clinical features are consistent with those caused by the suspected agent(s); and (3) assess occupational exposures. A detailed history is of paramount importance in evaluating patients with suspected work-related neurologic disorders as it is in other clinical contexts, especially because in some circumstances it may represent the only criterion to establish causality. Thus, besides characterization of neurologic symptoms, including their location, quality, timecourse, and possible other associated symptoms, the work environment of the patient should be understood in full detail. In this respect, when a neurotoxin is suspected, then the history collection can be guided by the knowledge of the likely syndromes it produces. Similarly, physical examination should be directed to the target of toxicity/entrapment based on information from the work history. Although specific sites and elements of the nervous system may be affected depending on the offending agent, most neurotoxic disorders are characterized by generalized rather than focal neurologic abnormalities. Laboratory toxicologic tests have limited application for the etiologic diagnosis of neurotoxic disorders, except in cases of acute poisoning and in patients exposed to neurotoxic chemicals with prolonged half-life. In most cases examination takes place after the end of exposure, when the offending chemical is no longer detectable in body fluids. Electrophysiologic studies, in particular evoked potentials, electromyography, and conduction velocities, are important to confirm the organic basis of symptoms, particularly to detect subclinical or early neurologic involvement and to reduce the number of disorders to be considered in the differential diagnoses. In general, imaging studies with computed tomography and magnetic resonance are of limited utility in the evaluation of suspected neurotoxic disorders, except for helping to exclude other causes of the patient's clinical state. Improved conditions and safer practices in the workplace have led to a gradual shift in application of neuropsychologic evaluation from the assessment of severe neurotoxic damage to the evaluation of mild subclinical disturbances, and these tests are nowadays extensively used in screening workers exposed to neurotoxicants. Tools used in the screening of large groups of workers exposed to neurotoxicants may differ from those used in the clinic. Whereas some are obviously impractical, such as physical examination, others, such as, for instance, toxicologic tests, are used for biologic monitoring of exposure to ascertain compliance with occupational exposure limits.

Long- and short-term health effects of pesticide exposure: a cohort study from China

Pesticides are extensively used by farmers in China. However, the effects of pesticides on farmers’ health have not yet been systematically studied. This study evaluated the effects of pesticides exposure on hematological and neurological indicators over 3 years and 10 days respectively. A cohort of 246 farmers was randomly selected from 3 provinces (Guangdong, Jiangxi, and Hebei) in China. Two rounds of health investigations, including blood tests and neurological examinations, were conducted by medical doctors before and after the crop season in 2012. The data on pesticide use in 2009–2011 were collected retrospectively via face-to-face interviews and the 2012 data were collected from personal records maintained by participants prospectively. Ordinary least square (OLS), Probit, and fixed effect models were used to evaluate the relationship between pesticides exposure frequency and the health indicators. Long-term pesticide exposure was found to be associated with increased abnormality of nerve conductions, especially in sensory nerves. It also affected a wide spectrum of health indicators based on blood tests and decreased the tibial nerve compound muscle action potential amplitudes. Short-term health effects included alterations in complete blood count, hepatic and renal functions, and nerve conduction velocities and amplitudes. However, these effects could not be detected after 3 days following pesticide exposure. Overall, our results demonstrate that pesticide exposure adversely affects blood cells, the liver, and the peripheral nervous system. Future studies are needed to elucidate the specific effects of each pesticide and the mechanisms of these effects.

Organophosphorus and carbamate insecticide poisoning

Both organophosphorus (OP) and carbamate insecticides inhibit acetylcholinesterase (AChE), which results in accumulation of acetylcholine (ACh) at autonomic and some central synapses and at autonomic postganglionic and neuromuscular junctions. As a consequence, ACh binds to, and stimulates, muscarinic and nicotinic receptors, thereby producing characteristic features. With OP insecticides (but not carbamates), "aging" may also occur by partial dealkylation of the serine group at the active site of AChE; recovery of AChE activity requires synthesis of new enzyme in the liver. Relapse after apparent resolution of cholinergic symptoms has been reported with OP insecticides and is termed the intermediate syndrome. This involves the onset of muscle paralysis affecting particularly upper-limb muscles, neck flexors, and cranial nerves some 24-96 hours after OP exposure and is often associated with the development of respiratory failure. OP-induced delayed neuropathy results from phosphorylation and subsequent aging of at least 70% of neuropathy target esterase. Cramping muscle pain in the lower limbs, distal numbness, and paresthesiae are followed by progressive weakness, depression of deep tendon reflexes in the lower limbs and, in severe cases, in the upper limbs. The therapeutic combination of oxime, atropine, and diazepam is well established experimentally in the treatment of OP pesticide poisoning. However, there has been controversy as to whether oximes improve morbidity and mortality in human poisoning. The explanation may be that the solvents in many formulations are primarily responsible for the high morbidity and mortality; oximes would not be expected to reduce toxicity in these circumstances. even if given in appropriate dose.

Clinical description of toxic neuropathies

Toxic neuropathy, although rare, is an important consideration in the setting of a known or suspected toxic exposure in the workplace or other environment. This chapter discusses the clinical and electrodiagnostic evaluation of peripheral neuropathies, highlighting findings that direct further workup and may point to specific toxins as etiology. The difficulty of establishing causality of a toxin in relation to peripheral neuropathy is discussed; guidelines for establishing causality are presented. Examples of common industrial toxins are listed, including their typical industrial uses and their mechanisms of action in producing neuropathy. Characteristic clinical presentations of specific toxic neuropathies are highlighted with selected case studies.

Neurological effects of pesticide use among farmers in China

The intensive use of pesticides has attracted great attention from the Chinese government. However, current regulations have had limited influence on their safe use. Although the acute neurologic effects of pesticides have been well documented, little is known about their cumulative effects. Knowledge of the impact of pesticides on health may convince farmers to minimize their use. We conducted a cross-sectional study in three provinces of China to evaluate the relationship between pesticide exposure and neurological dysfunction. Crop farmers were divided into two groups depending on their level of pesticide exposure. A total of 236 participants were assessed by questionnaire and neurological examination for symptoms and signs of neuropathy. Characteristics of neurologic dysfunction following cumulative low-level exposure were assessed with logistic regression analysis. Farmers exposed to high-level pesticide use had greater risk of developing sensations of numbness or prickling (odds ratio (OR) 2.62, 95% confidence interval (CI): 1.08–6.36). After adjusting for recent exposure, the risk of numbness or prickling symptoms (OR 2.55, 95% CI: 1.04–6.25) remained statistically significant. Loss of muscle strength and decreased deep tendon reflexes had OR > 2, however, this did not reach statistical significance. These findings suggest that overuse of pesticides increased risk of neurologic dysfunction among farmers, with somatosensory small fibers most likely affected. Measures that are more efficient should be taken to curb excessive use of pesticides.

Health symptoms related to pesticide exposure and agricultural tasks among rice farmers from Northern Thailand

PURPOSE

The objective of this cross-sectional study was to investigate health symptoms related to occupational pesticide exposure and agricultural tasks in rice farmers.

METHODS

Data on demographic variables and health symptoms associated with pesticide exposure were collected from 182 rice farmers (exposed subjects) and 122 non-farmers (controlled group) using interviews and measuring whole blood acetylcholinesterase (AChE) activity during August and October 2012.

RESULTS

Rice farmers had a significantly lower median AChE activity than the controls (9,594 vs. 10,530 U/L, respectively) and a significantly higher prevalence of difficulty in breathing and chest pain [odds ratio (OR) 2.8, P < 0.01 and OR 2.5, P < 0.05, respectively]. The prevalence of dry throat and cramp was associated with those farmers who sprayed and mixed pesticides (OR 2.5 and 2.6 for dry throat, OR 2.5 and 2.9 for cramp, respectively; P < 0.01). The prevalence of numbness and diarrhea was associated with those farmers who scattered seed (OR 2.2, P < 0.01 and OR 3.6, P < 0.05, respectively). The prevalence of numbness and increasing anxiety was also associated with those farmers who harvested crops (OR 3.6, P < 0.01 and OR 3.0, P < 0.05, respectively).

CONCLUSIONS

Our findings suggest that occupational pesticide exposure and agricultural tasks in the paddy field may be associated with the increasing prevalence of respiratory tract and muscle symptoms. This possibility warrants further investigation in more detail.

A systematic review on the nerve–muscle electrophysiology in human organophosphorus pesticide exposure

This article presents a systematic review of the recent literature on the scientific support of electromyography (EMG) and nerve conduction velocity (NCV) in diagnosing the exposure and toxicity of organophosphorus pesticides (OP). Specifically, this review focused on changes in EMG, NCV, occurrence of intermediate syndrome (IMS), and OP-induced delayed polyneuropathy (OPIDN) in human. All relevant bibliographic databases were searched for human studies using the key words “OP poisoning”, “electromyography”, “nerve conduction study,” and “muscles disorders”. IMS usually occurs after an acute cholinergic crisis, while OPIDN occurs after both acute and chronic exposures. Collection of these studies supports that IMS is a neuromuscular junction disorder and can be recorded upon the onset of respiratory failure. Due to heterogeneity of reports on outcomes of interest such as motor NCV and EMG amplitude in acute cases and inability to achieve precise estimation of effect in chronic cases meta-analysis was not helpful to this review. The OPIDN after both acute and low-level prolonged exposures develops peripheral neuropathy without preceding cholinergic toxicity and the progress of changes in EMG and NCV is parallel with the development of IMS and OPIDN. Persistent inhibition of acetylcholinesterase (AChE) is responsible for muscle weakness, but this is not the only factor involved in the incidence of this weakness in IMS or OPIDN suggestive of AChE assay not useful as an index of nerve and muscle impairment. Although several mechanisms for induction of this neurodegenerative disorder have been proposed as were reviewed for this article, among them oxidative stress and resulting apoptosis can be emphasized. Nevertheless, there is little synchronized evidence on subclinical electrophysiological findings that limit us to reach a strong conclusion on the diagnostic or prognostic use of EMG and NCV for acute and occupational exposures to OPs.

Peripheral nervous system function and organophosphate pesticide use among licensed pesticide applicators in the Agricultural Health Study

BACKGROUND

Evidence is limited that long-term human exposure to organophosphate (OP) pesticides, without poisoning, is associated with adverse peripheral nervous system (PNS) function.

OBJECTIVE

We investigated associations between OP pesticide use and PNS function by administering PNS tests to 701 male pesticide applicators in the Agricultural Health Study (AHS).

METHODS

Participants completed a neurological physical examination (NPx) and electrophysiological tests as well as tests of hand strength, sway speed, and vibrotactile threshold. Self-reported information on lifetime use of 16 OP pesticides was obtained from AHS interviews and a study questionnaire. Associations between pesticide use and measures of PNS function were estimated with linear and logistic regression controlling for age and outcome-specific covariates.

RESULTS

Significantly increased odds ratios (ORs) were observed for associations between ever use of 10 of the 16 OP pesticides and one or more of six NPx outcomes. Most notably, abnormal toe proprioception was significantly associated with ever use of 6 OP pesticides, with ORs ranging from 2.03 to 3.06; monotonic increases in strength of association with increasing use was observed for 3 of the 6 pesticides. Mostly null associations were observed between OP pesticide use and electrophysiological tests, hand strength, sway speed, and vibrotactile threshold.

CONCLUSIONS

This study provides some evidence that long-term exposure to OP pesticides is associated with signs of impaired PNS function among pesticide applicators.

Clinical Toxicology of Insecticides

Some insects compete for our food, some damage construction materials and some are important disease vectors in humans and animals. Hence, it is not surprising that chemicals (insecticides) have been developed that kill insects and other arthropods. More recently introduced insecticides, such as the neonicotinoids, have been produced with the intent that humans and animals will not be harmed by their appropriate use. This chapter reviews the clinical features and management of exposure to organophosphorus (OP) and carbamate insecticides, neonicotinoids, phosphides and pyrethroids. In the developing world where the ambient temperature is often high and personal protection equipment often not worn, poisoning particularly from OP and carbamate insecticides is common in an occupational setting, though more severe cases are due to deliberate ingestion of these pesticides. Both of these insecticides produce the cholinergic syndrome. The neonicotinoids, a major new class of insecticide, were introduced on the basis that they were highly specific for subtypes of nicotinic receptors that occur only in insect tissues. However, deliberate ingestion of substantial amounts of a neonicotinoid has resulted in features similar to those found in nicotine (and OP and carbamate) poisoning, though the solvent in some formulations may have contributed to their toxicity. Phosphides interact with moisture in air (or with water or acid) to liberate phosphine, which is the active pesticide. Inhalation of phosphine, however, is a much less frequent cause of human poisoning than ingestion of a metal phosphide, though the toxicity by the oral route is also due to phosphine liberated by contact of the phosphide with gut fluids. It is then absorbed through the alimentary mucosa and distributed to tissues where it depresses mitochondrial respiration by inhibiting cytochrome c oxidase and other enzymes. Dermal exposure to pyrethroids may result in paraesthesiae, but systemic toxicity usually only occurs after ingestion, when irritation of the gastrointestinal tract and CNS toxicity, predominantly coma and convulsions, result.

Neurobehavioral function and organophosphate insecticide use among pesticide applicators in the Agricultural Health Study

Although persistent decrements in cognitive function have been observed among persons who have recovered from clinically overt organophosphate (OP) pesticide poisoning, little is known about the cognitive effects of chronic OP exposures that do not result in acute poisoning. To examine associations between long-term pesticide use and neurobehavioral (NB) function, NB tests were administered to licensed pesticide applicators enrolled in the Agricultural Health Study (AHS) in Iowa and North Carolina. Between 2006 and 2008, 701 male participants completed nine NB tests to assess memory, motor speed and coordination, sustained attention, verbal learning and visual scanning and processing. Data on ever-use and lifetime days of use of 16 OP pesticides were obtained from AHS interviews conducted before testing between 1993 and 2007 and during the NB visit. The mean age of participants was 61 years (SD=12). Associations between pesticide use and NB test performance were estimated with linear regression controlling for age and outcome-specific covariates. NB test performance was associated with lifetime days of use of some pesticides. Ethoprop was significantly associated with reduced performance on a test of motor speed and visual scanning. Malathion was significantly associated with poor performance on a test of visual scanning and processing. Conversely, we observed significantly better test performance for five OP pesticides. Specifically, chlorpyrifos, coumaphos, parathion, phorate, and tetrachlorvinphos were associated with better verbal learning and memory; coumaphos was associated with better performance on a test of motor speed and visual scanning; and parathion was associated with better performance on a test of sustained attention. Several associations varied by state. Overall, we found no consistent evidence of an association between OP pesticide use and adverse NB test performance among this older sample of pesticide applicators. Potential reasons for these mostly null results include a true absence of effect as well as possible selective participation by healthier applicators.

Degradation of organophosphorus pesticide induced by oxygen plasma: effects of operating parameters and reaction mechanisms

The degradation effectiveness and degradation mechanism of representative organophosphorus (OP) pesticide during oxygen plasma treatment have been studied. The identification and quantitative determination of OP pesticide, the degradation mechanisms for OP pesticide destruction, its destruction intermediates, and by-products were performed using gas chromatography/mass spectrometry (GC/MS). Plausible mechanisms of the degradation are discussed. Experimental results indicate that oxygen plasma treatment has noticeable effects on OP pesticide with satisfactory degradation efficiency, which mainly depends on related operating parameters including plasma treatment time, discharge power, distance from the center of the induction coil, and concentrations of OP pesticide. It was found that OP pesticide was degraded into less-toxic compounds, and free radical reaction and addition reaction were to be the dominated the degradation mechanisms for OP pesticides treated by oxygen plasma. Therefore, our results suggest that oxygen plasma is suitable for degradation of OP pesticide.

Analytical approaches to investigate protein-pesticide adducts

Organophosphorus pesticides primarily elicit toxicity via their common covalent adduction of acetylcholinesterase (AChE), but pesticide binding to additional sensitive secondary targets may also compromise health. We have utilised tritiated-diisopropylfluorophosphate ((3)H-DFP) binding to quantify the levels of active immune and brain tissue serine hydrolases, and visualise them using autoradiography after protein separation by one-dimensional and two-dimensional techniques. Preincubation of protein extracts with pesticide in vitro or dosing of rats with pesticide in vivo was followed by (3)H-DFP radiolabelling. Pesticide targets were identified by a reduction in (3)H-DFP radiolabelling relative to controls, and characterised by their tissue presence, molecular weight, and isoelectric point. Conventional column chromatography was employed to enrich pesticide targets to enable their further characterisation, and/or identification by mass spectrometry. The major in vivo pesticide targets characterised were 66 kDa, serum albumin, and 60 kDa, likely carboxylesterase 1, both of which displayed differential pesticide binding character under conditions producing approximately 30% tissue AChE inhibition. The characterisation and identification of sensitive pesticide secondary targets will enable an evaluation of their potential contribution to the ill health that may arise from chronic low-dose pesticide exposures. Additionally, secondary targets may provide useful biomonitors and/or bioscavengers of pesticide exposures.

Intermediate Syndrome after Organophosphate Intoxication in Patient with End-Stage Renal Disease

A 42-year-old woman with a 24-year history of systemic lupus erythematous and lupus nephritis for 8 years who had been receiving regular hemodialysis for 4 years for nonoligoric end-stage renal disease (ESRD) ingested about 100 mL of 40.8% chlorpyrifos in a suicide attempt. On admission to our emergency department, she was drowsy. Gastric lavage, activated charcoal, pralidoxime (PAM), and atropine were administered 4 h later. Her consciousness level improved gradually with treatment, which included hemodialysis. However, on the second hospital day, intermittent fever to 38.4 degrees C, sore throat, and trismus were noted. About 45 h after chlorpyrifos ingestion, the patient developed profound motor paralysis followed by respiratory arrest, consistent with the diagnosis of intermediate syndrome (IMS), even with adequate atropine and PAM. Chorealike involuntary movements of her upper limbs were noticed on the fifth day. Intermittent tonic-clonic seizures, each attack lasting for 3 to 5 min, appeared on the 13th day, which responded well to intravenous diazepam and phenytoin. She was discharged on the 18th day. This case suggests that patients with ESRD suffering chlorpyrifos intoxication are at risk of IMS. Prompt endotracheal intubation, intensive care, and hemodialysis are necessary for life support.

Albumin binding as a potential biomarker of exposure to moderately low levels of organophosphorus pesticides

We have evaluated the potential of plasma albumin to provide a sensitive biomarker of exposure to commonly used organophosphorus pesticides in order to complement the widely used measure of acetylcholinesterase (AChE) inhibition. Rat or human plasma albumin binding by tritiated-diisopropylfluorophosphate (³H-DFP) was quantified by retention of albumin on glass microfibre filters. Preincubation with unlabelled pesticide in vitro or dosing of F344 rats with pesticide in vivo resulted in a reduction in subsequent albumin radiolabelling with ³H-DFP, the decrease in which was used to quantify pesticide binding. At pesticide exposures producing approximately 30% inhibition of AChE, rat plasma albumin binding in vitro by azamethiphos (oxon), chlorfenvinphos (oxon), chlorpyrifos-oxon, diazinon-oxon and malaoxon was reduced from controls by 9±1%, 67±2%, 56±2%, 54±2% and 8±1%, respectively. After 1 h of incubation with 19 µM ³H-DFP alone, the level of binding to rat or human plasma albumins reached 0.011 or 0.039 moles of DFP per mole of albumin, respectively. This level of binding could be further increased by raising the concentration of ³H-DFP, increasing the ³H-DFP incubation time, or by substitution of commercial albumins for native albumin. Pesticide binding to albumin was presumed covalent since it survived 24 h dialysis. After dosing rats with pirimiphos-methyl (dimethoxy) or chlorfenvinphos (oxon) (diethoxy) pesticides, the resultant albumin binding were still significant 7 days after dosing. As in vitro, dosing of rats with malathion did not result in significant albumin binding in vivo. Our results suggest albumin may be a useful additional biomonitor for moderately low-level exposures to several widely used pesticides, and that this binding differs markedly between pesticides.

Effects of oral tetrachlorvinphos fly control (Equitrol®) administration in horses: Physiological and behavioural findings

Highly reactive horses may pose risks to humans involved in equestrian activities. Among the factors that may affect horses' reactivity to external stimuli are pesticides used for fly control in equine facilities. The organophosphorus (OP) insecticide tetrachlorvinphos (TCVP) is used as a feed-through larvicide to prevent completion of the fly larval life cycle in horse manure. TCVP exerts its effect by inhibiting the enzyme cholinesterase (ChE) leading to the accumulation of the neurotransmitter acetylcholine (AChE) in synapses of the central and peripheral nervous systems. The aim of the present study was to investigate alterations of whole-blood ChE levels associated with feeding a commercially available product (Equitrol, Farnam Companies, Inc.) to horses for fly control. A second aim was to report neurological, physiological and behavioural findings in addition to profiles of selected immune markers (IFN-gamma, IL-12p40 and COX-2) and serum thyroid hormones during and after a 30-day treatment period of TCVP feeding. The results indicated significant decreases in whole-blood ChE activity and concomitant behavioural alterations, manifested as increased reactivity and decreased controllability in treated horses. No changes were detected in physiological or neurological parameters, immune markers or thyroid hormones in treated (n=6) or control (n=4) horses during the course of the study.

Current issues in organophosphate toxicology

Organophosphates (OPs) are one of the main classes of insecticides, in use since the mid 1940s. OPs can exert significant adverse effects in non-target species including humans. Because of the phosphorylation of acetylcholinesterase, they exert primarily a cholinergic toxicity, however, some can also cause a delayed polyneuropathy. Currently debated and investigated issues in the toxicology of OPs are presented in this review. These include: 1) possible long-term effects of chronic low-level exposures; 2) genetic susceptibility to OP toxicity; 3) developmental toxicity and neurotoxicity; 4) common mechanism of action; 5) mechanisms of delayed neurotoxicity; and 6) possible additional OP targets. Continuing and recent debates, and molecular advances in these areas, and their contributions to our understanding of the toxicology of OPs are discussed.

Purification and characterization of neuropathy target esterase (NTE) from rat brain

Neuropathy target esterase (NTE) is an integral membrane protein in vertebrate neurons and a member of a novel family of putative serine hydrolases. Neuropathic organophosphates react covalently with the active site serine residue of NTE, causing degeneration of long axons in spinal cord and peripheral nerves which becomes clinically evident 1-3 weeks after exposure to OPs, hence termed as organophosphate induced delayed neuropathy. The present study reports the isolation and characterization of NTE protein from rat brain. Rat brain microsomes were solubilized with phospholipase A2 and they were fractionated by gel filtration chromatography in S-300 column. The sample was eluted in buffer containing polyoxyethylene W1 detergent, which yielded an active fraction of 200 kDa. The most enriched NTE active fraction was further purified by 3-9'-mercaptononylthio-1,1,1-trifluoropropan-2-one bound to sepharose CL4B. The SDS-PAGE confirmed the 155-kDa protein as the most likely candidate for NTE. Database searching of rat N-terminal protein revealed homology with variety of polypeptides from different organisms and suggested that NTE protein has function beyond the nervous system and mediates a biochemical reaction highly conserved through evolution.

Veterinary pharmacovigilance. Part 4. Adverse reactions in humans to veterinary medicinal products

Although seemingly rare, adverse reactions to veterinary products do occur. These may arise from inadvertent exposure during use or as a result of occupational accidents. They are often mild in nature and include adverse effects such as minor skin reactions. However, more serious reactions may occur, and they are not restricted to the effects of the veterinary medicines themselves. For example, high-pressure injection injuries may occur as a result of accidents occurring during animal vaccination operations. This paper reviews some of these events, mentions where appropriate the regulatory actions taken, and describes some of the measures used to minimise such effects in the future, and serves to bring the issues discussed here to the attention of pharmacologists, pharmacoepidemiologists and others who train those who use veterinary medicinal products.

Organophosphate-Induced Delayed Polyneuropathy

Organophosphate-induced delayed polyneuropathy (OPIDP) is a rare toxicity resulting from exposure to certain organophosphorus (OP) esters. It is characterised by distal degeneration of some axons of both the peripheral and central nervous systems occurring 1-4 weeks after single or short-term exposures. Cramping muscle pain in the lower limbs, distal numbness and paraesthesiae occur, followed by progressive weakness, depression of deep tendon reflexes in the lower limbs and, in severe cases, in the upper limbs. Signs include high-stepping gait associated with bilateral foot drop and, in severe cases, quadriplegia with foot and wrist drop as well as pyramidal signs. In time, there might be significant recovery of the peripheral nerve function but, depending on the degree of pyramidal involvement, spastic ataxia may be a permanent outcome of severe OPIDP. Human and experimental data indicate that recovery is usually complete in the young. At onset, the electrophysiological changes include reduced amplitude of the compound muscle potential, increased distal latencies and normal or slightly reduced nerve conduction velocities. The progression of the disease, usually over a few days, may lead to non-excitability of the nerve with electromyographical signs of denervation. Nerve biopsies have been performed in a few cases and showed axonal degeneration with secondary demyelination. Neuropathy target esterase (NTE) is thought to be the target of OPIDP initiation. The ratio of inhibitory powers for acetylcholinesterase and NTE represents the crucial guideline for the aetiological attribution of OP-induced peripheral neuropathy. In fact, pre-marketing toxicity testing in animals selects OP insecticides with cholinergic toxicity potential much higher than that to result in OPIDP. Therefore, OPIDP may develop only after very large exposures to insecticides, causing severe cholinergic toxicity. However, this was not the case with certain triaryl phosphates that were not used as insecticides but as hydraulic fluids, lubricants and plasticisers and do not result in cholinergic toxicity. Several thousand cases of OPIDP as a result of exposure to tri-ortho-cresyl phosphate have been reported, whereas the number of cases of OPIDP as a result of OP insecticide poisoning is much lower. In this article, we mainly discuss OP pesticide poisoning, particularly when caused by chlorpyrifos, dichlorvos, isofenphos, methamidophos, mipafox, trichlorfon, trichlornat, phosphamidon/mevinphos and by certain carbamates. We also discuss case reports where neuropathies were not convincingly attributed to fenthion, malathion, omethoate/dimethoate, parathion and merphos. Finally, several observational studies on long-term, low-level exposures to OPs that sometimes reported mild, inconsistent and unexplained changes of unclear significance in peripheral nerves are briefly discussed.

The effects of occupational exposure to chlorpyrifos on the peripheral nervous system: a prospective cohort study

AIMS

To determine whether chronic occupational exposure to chlorpyrifos at levels associated with various aspects of manufacturing produced a clinically evident or subclinical peripheral neuropathy.

METHODS

Clinical and quantitative nerve conduction study (NCS) examinations were performed on two occasions on chlorpyrifos manufacturing workers who had measurable chlorpyrifos exposure and a referent group. Baseline evaluations were performed on 53 of 66 eligible chlorpyrifos subjects and on 60 of 74 eligible referent subjects; one-year evaluations were completed on 111 of the 113 subjects evaluated at baseline.

RESULTS

Chlorpyrifos and referent groups differed significantly in measures of 3,5,6 trichloro-2-pyridinol excretion and plasma butyrylcholinesterase (BuChE) activity, indicating substantially higher exposures among chlorpyrifos subjects. Few subjects had clinically important neurological symptoms or signs. NCS results were comparable to control values, and there were no significant group differences in NCS results at baseline, one year, or change over one year. No chlorpyrifos subject fulfilled conventional criteria for confirmed peripheral neuropathy at baseline or one-year examinations. The odds ratios for developing any diagnosable level of peripheral neuropathy among the chlorpyrifos subjects was not increased at baseline or at one year compared to referents at baseline. Mixed regression models used to evaluate subclinical group-by-time interactions showed numerous significant NCS differences attributable to near-nerve temperature differences among all subjects between the baseline and one-year examinations, but only a few disparate effects related to group.

CONCLUSIONS

Chronic chlorpyrifos exposure during the manufacturing process sufficient to produce biological effects on BuChE activity was not associated with clinically evident or subclinical peripheral neuropathy at baseline or with measurable deterioration among chlorpyrifos subjects compared to referents after one year of additional exposure.

Absence of sensory neuropathy among workers with occupational exposure to chlorpyrifos

Several studies have reported the occurrence of sensory neuropathy with exposure to chlorpyrifos and other organophosphorus insecticides, at levels not associated with overt toxicity. We evaluated 113 chemical workers, including 53 of 66 (80%) eligible chlorpyrifos workers and 60 of 74 (81%) randomly selected referent workers, to identify evidence of sensory neuropathy or subclinical neuropathy. Compared to referents, chlorpyrifos subjects had significantly longer duration of work in chlorpyrifos-exposed areas (9.72 vs. 0.01 years; P < 0.0001), greater cumulative chlorpyrifos exposure (64.16 vs. 0.69 mg/m(3). day; P < 0.0001), higher urine 3,5,6-trichloro-2-pyridinol (TCP) excretion (108.6 vs. 4.3 microg/g creatinine; P < 0.0001), and lower plasma butyrylcholinesterase (BuChE) activity (7281 vs. 8176 mU/ml; P = 0.003). Despite exposures among chlorpyrifos subjects to levels at which well-described physiological effects on B-esterases exist, the frequency of symptoms or signs of neuropathy did not differ significantly between groups, and the only 2 subjects fulfilling criteria for confirmed neuropathy were both in the referent group. Mean nerve conduction study results were comparable to established control values and did not differ significantly between groups. We found no evidence of sensory neuropathy or isolated peripheral abnormalities among subjects with long-term chlorpyrifos exposure at levels known to be associated with the manufacturing process.

Polymorphisms of paraoxonase (PON1) and their significance in clinical toxicology of organophosphates

Paraoxonase (PON1) is an HDL-associated enzyme capable of hydrolyzing multiple substrates, including several organophosphorous insecticides and nerve agents, oxidized lipids, and a number of drugs or pro-drugs. Several polymorphisms in the paraoxonase (PON1) gene have been described, which have been shown to affect either the catalytic efficiency of hydrolysis or the expression level of PON1. This review discusses the relevance of these polymorphisms for modulating sensitivity to organophosphorous compounds. Animal studies characterizing the PON1 polymorphisms have demonstrated the relevance of PON1 in modulating OP toxicity and have indicated the importance of an individual's PON1 status (i.e., genotype and phenotype taken together) rather than genotyping alone. Nevertheless, direct confirmation in humans of the relevance of PON1 status in conferring susceptibility to OP toxicity is still elusive. Recent studies examining the involvement of PON1 status in determining OP susceptibility of Gulf War veterans, sheep dippers, and individuals poisoned with chemical warfare agents represent a step in the right direction, but more studies are needed, with better documentation of both the level of exposure and the consequences of exposure.

Loss of neuropathy target esterase in mice links organophosphate exposure to hyperactivity

Neuropathy target esterase (NTE) is involved in neural development and is the target for neurodegeneration induced by selected organophosphorus pesticides and chemical warfare agents. We generated mice with disruptions in Nte, the gene encoding NTE. Nte(-/-) mice die after embryonic day 8, and Nte(+/-) mice have lower activity of Nte in the brain and higher mortality when exposed to the Nte-inhibiting compound ethyl octylphosphonofluoridate (EOPF) than do wild-type mice. Nte(+/-) and wild-type mice treated with 1 mg per kg of body weight of EOPF have elevated motor activity, showing that even minor reduction of Nte activity leads to hyperactivity. These studies show that genetic or chemical reduction of Nte activity results in a neurological phenotype of hyperactivity in mammals and indicate that EOPF toxicity occurs directly through inhibition of Nte without the requirement for Nte gain of function or aging.