Immunotoxicity of organophosphorus compounds. Modulation of cell-mediated immune responses by inhibition of monocyte accessory functions

Phenotypic and Functional Outcomes in Macrophages Exposed to an Environmentally Relevant Mixture of Organophosphate Esters in Vitro

BACKGROUND

Organophosphate esters (OPEs) are flame retardants and plasticizers used in consumer products. OPEs are found ubiquitously throughout the environment with high concentrations in indoor house dust. Exposure to individual OPEs is associated with immune dysfunction, particularly in macrophages. However, OPEs exist as complex mixtures and the effects of environmentally relevant mixtures on the immune system have not been investigated.

OBJECTIVES

The objectives of this study were to evaluate the toxicity of an environmentally relevant mixture of OPEs that models Canadian house dust on macrophages using phenotypic and functional assessments in vitro.

METHODS

High-content live-cell fluorescent imaging for phenotypic biomarkers of toxicity in THP-1 macrophages treated with the OPE mixture was undertaken. We used confocal microscopy and cholesterol analysis to validate and expand on the observed OPE-induced lipid phenotype. Then, we used flow cytometry and live-cell imaging to conduct functional tests and uncover mechanisms of OPE-induced phagocytic suppression. Finally, we validated our THP-1 findings in human primary peripheral blood mononuclear cells (hPBMC) derived macrophages.

RESULTS

Exposure to non-cytotoxic dilutions of the OPE mixture resulted in higher oxidative stress and disrupted lysosome and lipid homeostasis in THP-1 and primary macrophages. We further observed that phagocytosis of apoptotic cells in THP-1 and primary macrophages was lower in OPE-exposed cells vs. controls. In THP-1 macrophages, phagocytosis of both Gram-positive and Gram-negative bacteria was also lower in OPE-exposed cells vs. controls. Additionally, the OPE mixture altered the expression of phagocytic receptors linked to the recognition of phosphatidylserine and pathogen-associated molecular patterns.

DISCUSSION

The results of this in vitro study suggested that exposure to an environmentally relevant mixture of OPEs resulted in higher lipid retention in macrophages and poor efferocytic response. These effects could translate to enhanced foam cell generation resulting in higher cardiovascular mortality. Furthermore, bacterial phagocytosis was lower in OPE-exposed macrophages in an in vitro setting, which may indicate the potential for reduced bacterial clearance in models of infections. Taken together, our data provide strong evidence that mixtures of OPEs can influence the biology of macrophages and offer new mechanistic insights into the impact of OPE mixtures on the immune system. https://doi.org/10.1289/EHP13869.

Organophosphate-Pesticide-Mediated Immune Response Modulation in Invertebrates and Vertebrates

Organophosphate pesticides (OPs) have greatly facilitated food production worldwide, and their use is not limited to agriculture and the control of pests and disease vectors. However, these substances can directly affect the immune response of non-target organisms. In this sense, exposure to OPs can have negative effects on innate and adaptive immunity, promoting deregulation in humoral and cellular processes such as phagocytosis, cytokine expression, antibody production, cell proliferation, and differentiation, which are crucial mechanisms for host defense against external agents. This review focuses on the scientific evidence of exposure to OPs and their toxic effects on the immune system of non-target organisms (invertebrates and vertebrates) from a descriptive perspective of the immuno-toxic mechanisms associated with susceptibility to the development of bacterial, viral, and fungal infectious diseases. During the exhaustive review, we found that there is an important gap in the study of non-target organisms, examples of which are echinoderms and chondrichthyans. It is therefore important to increase the number of studies on other species directly or indirectly affected by Ops, to assess the degree of impact at the individual level and how this affects higher levels, such as populations and ecosystems.

Infants' diminished response to DTaP vaccine is associated with exposure to organophosphate esters

Organophosphate esters (OPEs) are commonly applied as flame retardants and plasticizers. Toxicological studies suggest exposure effects on immune endpoints, raising concerns as infants' OPE exposures are elevated compared to older children and adults due to hand-to-mouth behavior and breastfeeding. Here, we sought to evaluate the immune responsiveness of infants to a neoantigen (e.g., a newly encountered antigen) in the presence of OPE exposures. As a proxy for immune responsiveness, children were given three doses of the Diphtheria, Tetanus, and Pertussis (DTaP) vaccine as recommended, and diphtheria and tetanus antibodies were evaluated in serum samples collected when children were 12 months old (n = 84). Titers were compared, based on maximum sample overlap, to measurements of OPE metabolites in spot urine samples collected before vaccination (age 2 months, n = 73) and at the time of antibody assessment (12 months of age, n = 46). Metabolites of two chlorinated OPEs were significantly associated with diminished antibodies for diphtheria and tetanus. A metabolite of tris (1,3-dichloroisopropyl)phosphate (TDCIPP) measured at 2 months was associated with decreased diphtheria antibodies (-0.07 IU/mL per log₁₀ increase in metabolite). One metabolite of tris(2-chloroisopropyl)phosphate (TCIPP) measured at 12 months was associated with decreased tetanus antibodies (-0.57 IU/mL per log₁₀ increase in metabolite). These results provide some preliminary insights for OPE exposure impacts on vaccine responses in early life and may have important implications for immune health through childhood and adulthood.

A review on organophosphate flame retardants in the environment: Occurrence, accumulation, metabolism and toxicity

Organophosphate flame retardants (OPFRs), as a substitute for brominated flame retardants (BFRs), are widely used in industrial production and life. The presence of OPFRs in the environment has an adverse effect on the ecological environment system. This review provides comprehensive data for the occurrence of OPFRs and their diester metabolites (OP diesters) in wastewater treatment plants, surface water, drinking water, sediment, soil, air and dust in the environment. In particular, the accumulation and metabolism of OPFRs in organisms and the types of metabolites and metabolic pathways are discussed for animals and plants. In addition, the toxicity of OP triesters and OP diesters in organisms is discussed. Although research on OPFRs has gradually increased in recent years, there are still many gaps to be filled, especially for metabolic and toxicity mechanisms that need in-depth study. This review also highlights the shortcomings of current research and provides suggestions for a basis for future research on OPFRs.

Immunotoxic role of organophosphates: An unseen risk escalating SARS-CoV-2 pathogenicity

Consistent gathering of immunotoxic substances on earth is a serious global issue affecting people under pathogenic stress. Organophosphates are among such hazardous compounds that are ubiquitous in nature. They fuel oxidative stress to impair antiviral immune response in living entities. Aside, organophosphates promote cytokine burst and pyroptosis in broncho-alveolar chambers leading to severe respiratory ailments. At present, we witness COVID-19 outbreak caused by SARS-CoV-2. Infection triggers cytokine storm coupled with inflammatory manifestations and pulmonary disorders in patients. Since organophosphate-exposure promotes necroinflammation and respiratory troubles hence during current pandemic situation, additional exposure to such chemicals can exacerbate inflammatory outcome and pulmonary maladies in patients, or pre-exposure to organophosphates might turn-out to be a risk factor for compromised immunity. Fortunately, antioxidants alleviate organophosphate-induced immunosuppression and hence under co-exposure circumstances, dietary intake of antioxidants would be beneficial to boost immunity against SARS-CoV-2 infection.

Regioselective phosphinylation of coumarins under green LED irradiation and its mechanism

A regioselective and efficient approach to 3-phosphinylated coumarins was developed via the active P-centered radical generated by energy transfer and electron transfer processes under green LED irradiation.

Of Pesticides and Men: a California Story of Genes and Environment in Parkinson's Disease

At the start of the postgenomics era, most Parkinson's disease (PD) etiology cannot be explained by our knowledge of genetic or environmental factors alone. For more than a decade, we have explored gene-environment (GxE) interactions possibly responsible for the heterogeneity of genetic as well as environmental results across populations. We developed three pesticide exposure measures (ambient due to agricultural applications, home and garden use, and occupational use) in a large population-based case-control study of incident PD in central California. Specifically, we assessed interactions with genes responsible for pesticide metabolism (PON1); transport across the blood-brain barrier (ABCB1); pesticides interfering with or depending on dopamine transporter activity (DAT/SLC6A3) and dopamine metabolism (ALDH2); impacting mitochondrial function via oxidative/nitrosative stress (NOS1) or proteasome inhibition (SKP1); and contributing to immune dysregulation (HLA-DR). These studies established some specificity for pesticides' neurodegenerative actions, contributed biologic plausibility to epidemiologic findings, and identified genetically susceptible populations.

Ligand Activity of Group 15 Compounds Possessing Triphenyl Substituent for the RXR and PPARγ Nuclear Receptors

We investigated the ability of group 15 compounds with a triphenyl substituent to bind to and activate human retinoic X receptor (RXR) and peroxisome proliferator-activated receptor (PPAR) γ and their ability to activate the receptor. Triphenylphosphine oxide (TPPO) transcriptionally activated both RXR and PPARγ. Triphenylbismuth (TPBi) transcriptionally activated PPARγ but not RXR. However, TPBi significantly inhibited RXR transcriptional activity induced by 9-cis retinoic acid (9cRA) and PPARγ transcriptional activity induced by rosiglitazone (Rosi). Triphenylarsine (TPAs) also significantly inhibited the 9cRA- and Rosi-induced transcriptional activity of both receptors, whereas TPAs alone had no effect on the transcriptional activity of RXR and PPARγ. Consistent with these results, TPAs and TPBi blocked the binding of [³H]9cRA to RXR and of [³H]Rosi to PPARγ in a competitive manner. However, contrary to the results of the reporter gene assay, TPPO did not compete with [³H]9cRA and [³H]Rosi for binding to RXR and PPARγ, respectively. Our findings indicate that 1) TPPO is a transcriptional activator-but not a ligand-of RXR and PPARγ; 2) TPBi is an antagonist of RXR and a partial agonist of PPARγ; and 3) TPAs is a dual antagonist of RXR and PPARγ. These results suggest that TPPO, TPAs, and TPBi are potential endocrine disrupters of the PPARγ-RXR signaling pathway.

Immunotoxicity Evaluation of Resorcinol Bis-Diphenylphosphate (Fyrolflex RDP) in B6C3F1 Mice

RDP was administered daily to groups of female B6C3F1 mice by oral gavage for 28 days at dose levels of 500, 1500, or 5000 mg/kg/day body weight (BW). Control animals were sham dosed. Animals were euthanized 1 day following final exposure or following a 60-day recovery period. End point observations included necropsy and histopathology, spleen and thymus weights and cellularity, peritoneal cell numbers and differential cell analysis, splenic natural killer (NK) cell activity, lymphocyte blastogenesis, antibody-forming cell (AFC) response, peritoneal macrophage phagocytic activity, and host susceptibility to Listeria monocytogenes infection. In-life observations included weekly clinical examinations and body weights. No adverse clinical signs were noted and the only significant finding was an increase in body weight in high dose mice on week 4 as compared to sham controls. Small changes in body weight gain were seen in all dose groups as compared to sham controls after completion of dosing on weeks 5 and 6 and in mid-dose mice on weeks 7 and 12. No significant differences were found in spleen and thymus weights or in cellularity. No changes were found in peritoneal cell numbers or cell types, peritoneal macrophage phagocytic activity, or host susceptibility to infection. Likewise, splenic NK cell activity, lymphocyte blastogenesis, and AFC function were also unaffected. No histopathologic changes were observed. All animals that received positive-control substances demonstrated a significant effect in the respective tests. In conclusion, a standardized and validated battery of immune function tests demonstrated no immunotoxicity following daily oral exposure to up to 5000 mg/kg BW of RDP for 28 days.

A comprehensive review of pesticides and the immune dysregulation: mechanisms, evidence and consequences

Nowadays, in many communities, there is a growing concern about possible adverse effects of pesticides on human health. Reports indicate that during environmental or occupational exposure, pesticides can exert some intense adverse effects on human health through transient or permanent alteration of the immune system. There is evidence on the relation between pesticide-induced immune alteration and prevalence of diseases associated with alterations of the immune response. In the present study, direct immunotoxicity, endocrine disruption and antigenicity have been introduced as the main mechanisms working with pesticides-induced immune dysregulation. Moreover, the evidence on the relationship between pesticide exposure, dysregulation of the immune system and predisposition to different types of psychiatric disorders, cancers, allergies, autoimmune and infectious diseases are criticized.

Common Genetic Variant Association with Altered HLA Expression, Synergy with Pyrethroid Exposure, and Risk for Parkinson's Disease: An Observational and Case-Control Study

Background:

The common noncoding single-nucleotide polymorphism (SNP) rs3129882 in HLA-DRA is associated with risk for idiopathic Parkinson’s disease (PD). The location of the SNP in the major histocompatibility complex class II (MHC-II) locus implicates regulation of antigen presentation as a potential mechanism by which immune responses link genetic susceptibility to environmental factors in conferring lifetime risk for PD.

Aims:

The aim of this study was to determine the effect of this SNP on the MHC-II locus and its synergy with pesticide exposure.

Methods:

For immunophenotyping, blood cells from 81 subjects were analyzed by quantitative reverse transcription-PCR and flow cytometry. A case–control study was performed on a separate cohort of 962 subjects to determine association of pesticide exposure and the SNP with risk of PD.

Results:

Homozygosity for G at this SNP was associated with heightened baseline expression and inducibility of MHC class II molecules in B cells and monocytes from peripheral blood of healthy controls and PD patients. In addition, exposure to a commonly used class of insecticide, pyrethroids, synergized with the risk conferred by this SNP (odds ratio=2.48, P=0.007), thereby identifying a novel gene–environment interaction that promotes risk for PD via alterations in immune responses.

Conclusions:

In sum, these novel findings suggest that the MHC-II locus may increase susceptibility to PD through presentation of pathogenic, immunodominant antigens and/or a shift toward a more pro-inflammatory CD4+ T-cell response in response to specific environmental exposures, such as pyrethroid exposure through genetic or epigenetic mechanisms that modulate MHC-II gene expression.

Pesticide induced immunotoxicity in humans: a comprehensive review of the existing evidence

The immune system can be the target of many chemicals, with potentially severe adverse effects on the host's health. In Western countries pesticides, together with new and modified patterns of exposure to chemicals, have been implicated in the increasing prevalence of diseases associated with alterations of the immune response, such as hypersensitivity reactions, certain autoimmune diseases and cancers. Xenobiotics may initiate, facilitate or exacerbate pathological immune processes, resulting in immunotoxicity by induction of mutations in genes coding for immunoregulatory factors, modifying immune tolerance and activation pathways. The purpose of this article is to update the evidence of pesticide immunotoxicity. Even if experimental data as well as sporadic human studies indicate that some pesticides can affect the immune system, overall, existing epidemiological studies are inadequate to raise conclusions on the immunotoxic risk associated to pesticide exposure. The available studies on the effects of pesticides on human immune system have several limitations including poor indication on exposure levels, multiple chemical exposures, heterogeneity of the approach, and difficulty in giving a prognostic significance to the slight changes often observed. Further studies are necessary, and they should be preferably carried out through comparison of pre and post-exposure findings in the same group of subjects with a matched control group. Attempt should be made to define the prognostic significance of slight changes often observed. Animal and in vitro studies are also important and necessary to scientifically support epidemiological evidences on pesticide-induced immunotoxicity.

Triphenylphosphine oxide is a potent and selective inhibitor of the transient receptor potential melastatin-5 ion channel

Transient receptor potential melastatin-5 (TRPM5) is a calcium-gated monovalent cation channel expressed in highly specialized cells of the taste bud and gastrointestinal tract, as well as in pancreatic β-cells. Well established as a critical signaling protein for G protein-coupled receptor-mediated taste pathways, TRPM5 also has recently been implicated as a regulator of incretin and insulin secretion. To date, no inhibitors of practical use have been described that could facilitate investigation of TRPM5 functions in taste or secretion of metabolic hormones. Using recombinant TRPM5-expressing cells in a fluorescence imaging plate reader-based membrane potential assay, we identified triphenylphosphine oxide (TPPO) as a selective and potent inhibitor of TRPM5. TPPO inhibited both human (IC₅₀ = 12 μM) and murine TRPM5 (IC₅₀ = 30 μM) heterologously expressed in HEK293 cells, but had no effect (up to 100 μM) on the membrane potential responses of TRPA1, TRPV1, or TRPM4b. TPPO also inhibited a calcium-gated TRPM5-dependent conductance in taste cells isolated from the tongues of transgenic TRPM5(+/)⁻ mice. In contrast, TPP had no effect on TRPM5 responses, indicating a strict requirement of the oxygen atom for activity. Sixteen additional TPPO derivatives also inhibited TRPM5 but none more potently than TPPO. Structure-activity relationship of tested compounds was used for molecular modeling-based analysis to clarify the positive and negative structural contributions to the potency of TPPO and its derivatives. TPPO is the most potent TRPM5 inhibitor described to date and is the first demonstrated to exhibit selectivity over other channels.

Effects of pesticide exposure on the human immune system

Epidemiological evidence from Western countries indicates that the prevalence of diseases associated with alterations in the immune response, such as asthma, certain autoimmune diseases and cancer, are increasing to such an extent that it cannot be attributed to improved diagnostics alone. There is some concern that this trend could be, at least, partially attributable to new or modified patterns of exposures to chemicals, including pesticides. The purpose of this article is to review the evidence on pesticide immunotoxicity in humans. Overall, the available data are inadequate to draw firm conclusions on the immunotoxic risk associated with pesticide exposure. The available studies on the effects of pesticides on the human immune system have several limitations, including limited data on exposure levels, heterogeneity of the applied methods, and difficulties in assessing the prognostic significance of observed slight changes and in the interpretation of the reported findings. Further studies are needed and preferably as prospective studies, comparing pre- and post-exposure data in the same group of subjects and including an appropriate non-exposed control group. More knowledge is required regarding the prognostic significance of the small changes observed.

The Alteration of Immune Reactions in Inbred BALB/cMice Following Low-Level Sarin Inhalation Exposure

To study the influence of low-level sarin inhalation exposure on immune functions, inbred BALB/c mice were exposed to low concentrations of sarin for 60 min in the inhalation chamber. The evaluation of immune functions was carried out using phenotyping of CD3 (T lymphocytes), CD4 (helper T lymphocytes), CD8 (cytotoxic T lymphocytes), and CD19 cells (B lymphocytes) in the lungs, blood, and spleen, lymphoproliferation of spleen cells stimulated in vitro by various mitogens (concanavalin A, lipopolysaccharides), phagocyte activity of peritoneal and alveolar macrophages, production of N-oxides by peritoneal macrophages, and the measurement of the natural killer cell activity at 1 wk following sarin exposure. The results were compared to the values obtained from control mice exposed to pure air instead of sarin. The results indicate that low doses of sarin are able to alter the reaction of immune system at one week following exposure to sarin. While the numbers of CD3 cells in the lungs, blood, and spleen were slightly decreased, an increase in CD19 cells was observed, especially in the lungs and blood. The reduced proportion of T lymphocytes is caused by decay of CD4-positive T cells. Lymphoproliferation was significantly decreased regardless of the mitogen and sarin concentration used. The production of N-oxides by peritoneal macrophages was stimulated after exposure to the highest dose of sarin, whereas their ability to phagocytize the microbes was increased after exposure to the lowest dose of sarin. The natural killer cell activity was significantly higher in the case of inhalation exposure of mice to the highest level of sarin. Thus, not only organophosphorus insecticides but also nerve agents such as sarin are able to alter immune functions even at a dose that does not cause clinically manifested disruption of cholinergic nervous system in the case of inhalation exposure. Nevertheless, the alteration of immune functions following the inhalation exposure to a symptomatic concentration of sarin seems to be more pronounced.

Diazinon immunotoxicity in mice: modulation of cytokines level and their gene expression

Diazinon is one of the organophosphate pesticides of wide spectrum insect-killing power. Diazinon extensive application as an effective pesticide was associated with direct or indirect modulation of major and vital immune mechanisms. This study addressed the effect of diazinon toxicity on cytokines that are involved in the regulation of innate, cellular and humoral immune responses. Mice intoxicated with 50 mg/kg (1/5 LD50) body weight for 30 days indicated gradual decrease in the level of interleukin-2 (IL-2), interleukin-4 (IL-4), interleukin-10 (IL-10), interleukin-12 (IL-12) and interferon-gamma (IFN-gamma) in the splenocytes cultures that were pulsed with phytohaemagglutinin (PHA). Sever suppression of these cytokines was confirmed by the RT-PCR. The level of IL-10 in CD4(+), CD8(+), and B cells indicated significant increase, whereas INF-gamma level was significantly decreased in B cells only. On the molecular level, the INF-gamma mRNA synthesis was significantly increased in all cells subpopulation, whereas, IL-2 mRNA synthesis was only increased in CD4(+). It was shown that diazinon immunotoxicity in mice capable of modulating the major cytokines involved in the regulation of the immune responses. In certain stage of diazinon toxicity, Th2 type responses appeared dominant. Diazinon could accelerate the INF- gamma and IL-2 mRNA synthesis but their translation might be impaired.

Determination of triphenylphosphine oxide in active pharmaceutical ingredients by hollow-fiber liquid-phase microextraction followed by reversed-phase liquid chromatography

A versatile procedure has been developed and validated for the determination of triphenylphosphine oxide (TPPO) at low levels in various active pharmaceutical ingredients (APIs). This procedure incorporates the use of the novel hollow-fiber liquid-phase microextraction (LPME) for the measurement of this potential process-related impurity in aqueous solutions of APIs. A small volume (40 microL) of 1-octanol contained within a hollow polypropylene fiber is used for the extraction of TPPO from low pH aqueous API solutions. More than a 100-fold increase in the TPPO concentration is obtained without additional evaporation of the extract. Experimental parameters of the extraction procedure were investigated to optimize extraction efficiency and minimize sample matrix interference. Using HPLC/UV as the end analysis technique, the procedure was validated for TPPO in the concentration range of 3-16 microg/L with an API present at 1500 mg/L. The versatility of the method was demonstrated by applying the procedure to the analysis of APIs with different molecular structures. This simple LPME procedure is inexpensive and offers appropriate sensitivity for the intended use while providing several advantages over other analysis methods for pharmaceutical samples.

Integrative assessment of multiple pesticides as risk factors for non-Hodgkin's lymphoma among men

BACKGROUND

An increased rate of non-Hodgkin's lymphoma (NHL) has been repeatedly observed among farmers, but identification of specific exposures that explain this observation has proven difficult.

METHODS

During the 1980s, the National Cancer Institute conducted three case-control studies of NHL in the midwestern United States. These pooled data were used to examine pesticide exposures in farming as risk factors for NHL in men. The large sample size (n = 3417) allowed analysis of 47 pesticides simultaneously, controlling for potential confounding by other pesticides in the model, and adjusting the estimates based on a prespecified variance to make them more stable.

RESULTS

Reported use of several individual pesticides was associated with increased NHL incidence, including organophosphate insecticides coumaphos, diazinon, and fonofos, insecticides chlordane, dieldrin, and copper acetoarsenite, and herbicides atrazine, glyphosate, and sodium chlorate. A subanalysis of these "potentially carcinogenic" pesticides suggested a positive trend of risk with exposure to increasing numbers.

CONCLUSION

Consideration of multiple exposures is important in accurately estimating specific effects and in evaluating realistic exposure scenarios.

Low-level sarin-induced alteration of immune system reaction in inbred BALB/c mice

To study the influence of low-level sarin inhalation exposure on immune functions, inbred BALB/c mice were exposed to low concentrations of sarin for 60 min in the inhalation chamber. Two concentrations of sarin were chosen-asymptomatic concentration (LEVEL 1) and non-convulsive symptomatic concentration (LEVEL 2). The evaluation of immune functions was carried out using phenotyping of CD3 (T-lymphocytes), CD4 (helper T-lymphocytes), CD8 (cytotoxic T-lymphocytes) and CD19 cells (B-lymphocytes) in the lungs, blood and spleen, lymphoproliferation of spleen cells stimulated in vitro by various mitogens (concanavalin A, lipopolysaccharides), phagocyte activity of peritoneal and alveolar macrophages, production of N-oxides by peritoneal macrophages and the measurement of the natural killer cell activity at 1 week following sarin exposure. The results were compared to the values obtained from control mice exposed to pure air instead of sarin. The results indicate that not only symptomatic but also asymptomatic dose of sarin is able to alter the reaction of immune system at 1 week following exposure to sarin. While the number of CD3 cells in the lungs was slightly decreased, an increase in CD19 cells was observed especially in the lungs and blood. The reduced proportion of T-lymphocytes is caused by decay of CD4 positive T-cells. Lymphoproliferation was significantly decreased regardless of the mitogen and sarin concentration used. The production of N-oxides by peritoneal macrophages was stimulated after exposure to LEVEL 2 of sarin whereas their ability to phagocyte the microbes was increased after exposure to LEVEL 1. The natural killer cell activity was significantly higher in the case of inhalation exposure of mice to LEVEL 2 of sarin. Thus, not only organophosphorus insecticides but also nerve agents such as sarin are able to alter immune functions even at a dose that does not cause clinically manifested intoxication following the inhalation exposure. Nevertheless, the alteration of immune functions following the inhalation exposure to a symptomatic concentration of sarin seems to be more pronounced.

Familiality of monocyte esterase deficiency in patients on continuous ambulatory peritoneal dialysis

The purpose of this study was to determine whether or not peripheral blood monocyte esterase deficiency occurring in patients on CAPD was a familial characteristic. The peripheral blood monocyte esterase status of 74 patients on CAPD was determined by a naphthyl acetate esterase staining of cytospin preparations of their mononuclear cells following separation over ficoll. The peripheral blood of first degree relatives and spouses of monocyte esterase deficiency patients was similarly investigated for the deficiency. Three patients bad monocyte esterase deficiency and familiality of the defect was demonstrated in two of their families. The third family was incompletely investigated because of lack of consent. The monocyte esterase deficiency demonstrated in this cohort of patients did not result from their renal failure but was a familial characteristic.

Renal failure and esterase-negative monocytes

Monocyte esterase deficiency (MED) has been found to be linked with autoimmune (1,2) and lymphoproliferative (2,3) disease. The incidence of MED where > 85% of peripheral blood monocytes are consistently negative in the cytochemical stain for monocyte esterase activity, was shown to be significantly raised in patients with renal failure (3.8%) as compared to the incidence in normal blood donors (0.8%) in a survey performed at the Belfast City Hospital in 1987 (2). The overall occurrence of any proportion of esterase-negative monocytes (ENMs) in patients with renal disease has not been previously studied. The aims of this study were to document this occurrence, and by examining the clinical and biochemical parameters associated with ENMs to identify possible reasons for their occurrence. The original survey data were reexamined and further information previously unreported regarding the occurrence of ENMs was extracted from the renal patient cohort data. Clinical and biochemical data were obtained from the hospital notes of the renal patients and associations sought between these parameters and the occurrence of ENMs. ENMs occurred in a significantly higher proportion (31%) of the renal patients than in the normal population (8%; p < 0.001 chi-sq.) or any other hospital population. A highly significant association between rising serum phosphate levels and increasing proportions of ENMs was identified (p < .001) and this association proved to be independent of serum creatinine levels and renal dialysis status. There is a marked increase in occurrence of esterase-negative monocytes in patients with renal failure. This increase was not caused by the degree of renal failure as reflected by serum creatinine levels, nor by renal transplantation or immunosuppressive therapy. A significant association between rising serum phosphate and increasing proportion of esterase-negative monocytes was identified. This new information, when considered with the previously described experimental and epidemiology evidence for malfunction of esterase negative monocytes, identifies a phenomenon which may contribute to the immunological difficulties of patients with chronic renal failure.

Clinical immunotoxicity of pesticides

Because of the wide use of pesticides for domestic and industrial purposes, the evaluation of their immunotoxic effects is of major concern for public health. Despite the large amount of experimental data describing pesticide-induced immunosuppression, evidence that pesticides may severely impair immune functions in humans is lacking or scarce. Contact hypersensitivity is a well-identified immunotoxic effect of pesticides but remains a rare complaint in pesticide-exposed workers. By contrast, immunologically mediated systemic reactions have been described only as debatable case reports. The association between autoimmune diseases and pesticide exposure has more recently been suggested. Despite the lack of convincing human data, a potential risk for the immune system should not be excluded, especially during chronic exposure to pesticides or in otherwise (immuno) compromised patients (malnutrition, children, old patients). Epidemiological studies including markers of exposure and the assessment of immune competence in exposed individuals, or registries of sentinel diseases related to immunosuppression (e.g., non-Hodgkin's lymphoma, opportunistic infections) or autoimmunity (e.g. lupus erythematosus, rheumatoid arthritis), are warranted.

Organophosphates and monocyte esterase deficiency

AIMS

To examine the possibility that monocyte esterase deficiency (MED) could be caused by exposure to organophosphates.

METHODS

Pseudocholinesterase, paraoxonase and arylesterase activities were measured in the serum and acetylcholinesterase activity was measured in the red cells of a group of monocyte esterase deficient subjects and compared with the enzyme activities of a control group of monocyte esterase positive subjects.

RESULTS

No significant difference was found between the enzyme activities of the monocyte esterase deficient group and the control group for any of the esterases investigated.

CONCLUSION

Current or recent exposure to organophosphorus is not the cause of MED.

Structural requirements for the inhibition of human monocyte carboxylesterase by organophosphorus compounds

Human blood monocyte carboxylesterase (CBE) is inhibited by a variety of organophosphorus compounds including arylphosphates and arylphosphites and some alkylphosphites. Triphenyl phosphate and triphenyl phosphite with Ki values of 8 x 10(-9) M and 4.8 x 10(-8) M, respectively, are the most potent inhibitors of this enzyme evaluated by this study. The arylphosphates vary in their capacity to inhibit carboxylesterase activity. Diphenyl phosphate with its strong negative charge is not a potent inhibitor (Ki = 1 x 10(-4) M), whereas if its negative charge is neutralized, as in diphenyl methyl phosphate, its capacity to inhibit carboxylesterase is significantly increased. Compounds with increased bulk, such as trinaphthyl phosphate, only inhibit the enzyme at concentrations of 10(-5) M or greater. Arylphosphites have inhibitory capacities similar to the arylphosphates. Alkylphosphites (tributyl phosphite/triethyl phosphite) inhibit carboxylesterase activity, whereas alkylphosphates (tributyl phosphate/triethyl phosphate) have no inhibitory effect. Arylphosphines and arylphosphine oxides do not inhibit carboxylesterase activity. This study demonstrates that organophosphates and organophosphites are relatively effective inhibitors of human monocyte CBE activity with the exception of the alkylphosphates which have no inhibitory activity. We conclude that molecular bulk and charge have a significant role in determining the potency of organophosphorus inhibitors of monocyte CBE. The observed variations in the degree of esterase inhibition by organophosphorus compounds as well as the differences in the pathological expression of neuropathic disorders associated with such chemicals suggest that different esterase enzymes derived from the family of esterase genes may mediate the different neuropathies observed with organophosphorus exposures. Such data also provide the rationale for the kinetic analyses of esterases and the design of non-toxic organophosphorus compounds with low or no monocyte CBE inhibitory capacity to reduce the potential of these commonly used chemicals for human toxicity.