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

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.

Acute and chronic effects of the organophosphate malathion on the pancreatic α and β cell viability, cell structure, and voltage-gated K+ currents

Studies indicate that the pesticide malathion may have a role in diabetes. Herein, we determined the effects of different concentrations of malathion on survival, ultrastructure, and electrophysiologic islet cell parameters. Acutely, high concentrations of malathion (0.5 or 1 mM) increased cell death in rat islet cells, while low concentrations (0.1 mM) caused signs of cell damage in pancreatic α and β cells. Exposure of RINm5F cells to malathion for 24 or 48 h confirmed the reduction in β-cell viability at lower concentrations (0.001-100 µM). Chronic exposure of mouse pancreatic α and β cells to 3 nM of malathion led to increased voltage-gated K⁺ (K_v) currents in α-cells. Our findings show a time and concentration dependency for the malathion effect on the reduction of islet cell viability and indicate that pancreatic α cells are more sensitive to malathion effects on K_v currents and cell death.

Mechanisms of organophosphorus pesticide toxicity in the context of airway hyperreactivity and asthma

Numerous epidemiologic studies have identified an association between occupational exposures to organophosphorus pesticides (OPs) and asthma or asthmatic symptoms in adults. Emerging epidemiologic data suggest that environmentally relevant levels of OPs may also be linked to respiratory dysfunction in the general population and that in utero and/or early life exposures to environmental OPs may increase risk for childhood asthma. In support of a causal link between OPs and asthma, experimental evidence demonstrates that occupationally and environmentally relevant OP exposures induce bronchospasm and airway hyperreactivity in preclinical models. Mechanistic studies have identified blockade of autoinhibitory M2 muscarinic receptors on parasympathetic nerves that innervate airway smooth muscle as one mechanism by which OPs induce airway hyperreactivity, but significant questions remain regarding the mechanism(s) by which OPs cause neuronal M2 receptor dysfunction and, more generally, how OPs cause persistent asthma, especially after developmental exposures. The goals of this review are to 1) summarize current understanding of OPs in asthma; 2) discuss mechanisms of OP neurotoxicity and immunotoxicity that warrant consideration in the context of OP-induced airway hyperreactivity and asthma, specifically, inflammatory responses, oxidative stress, neural plasticity, and neurogenic inflammation; and 3) identify critical data gaps that need to be addressed in order to better protect adults and children against the harmful respiratory effects of low-level OP exposures.

A review of experimental evidence linking neurotoxic organophosphorus compounds and inflammation

Organophosphorus (OP) nerve agents and pesticides inhibit acetylcholinesterase (AChE), and this is thought to be a primary mechanism mediating the neurotoxicity of these compounds. However, a number of observations suggest that mechanisms other than or in addition to AChE inhibition contribute to OP neurotoxicity. There is significant experimental evidence that acute OP intoxication elicits a robust inflammatory response, and emerging evidence suggests that chronic repeated low-level OP exposure also upregulates inflammatory mediators. A critical question that is just beginning to be addressed experimentally is the pathophysiologic relevance of inflammation in either acute or chronic OP intoxication. The goal of this article is to provide a brief review of the current status of our knowledge linking inflammation to OP intoxication, and to discuss the implications of these findings in the context of therapeutic and diagnostic approaches to OP neurotoxicity.

Organophosphorus pesticides decrease M2 muscarinic receptor function in guinea pig airway nerves via indirect mechanisms

Background

Epidemiological studies link organophosphorus pesticide (OP) exposures to asthma, and we have shown that the OPs chlorpyrifos, diazinon and parathion cause airway hyperreactivity in guinea pigs 24 hr after a single subcutaneous injection. OP-induced airway hyperreactivity involves M2 muscarinic receptor dysfunction on airway nerves independent of acetylcholinesterase (AChE) inhibition, but how OPs inhibit neuronal M2 receptors in airways is not known. In the central nervous system, OPs interact directly with neurons to alter muscarinic receptor function or expression; therefore, in this study we tested whether the OP parathion or its oxon metabolite, paraoxon, might decrease M2 receptor function on peripheral neurons via similar direct mechanisms.

Methodology/Principal Findings

Intravenous administration of paraoxon, but not parathion, caused acute frequency-dependent potentiation of vagally-induced bronchoconstriction and increased electrical field stimulation (EFS)-induced contractions in isolated trachea independent of AChE inhibition. However, paraoxon had no effect on vagally-induced bradycardia in intact guinea pigs or EFS-induced contractions in isolated ileum, suggesting mechanisms other than pharmacologic antagonism of M2 receptors. Paraoxon did not alter M2 receptor expression in cultured cells at the mRNA or protein level as determined by quantitative RT-PCR and radio-ligand binding assays, respectively. Additionally, a biotin-labeled fluorophosphonate, which was used as a probe to identify molecular targets phosphorylated by OPs, did not phosphorylate proteins in guinea pig cardiac membranes that were recognized by M2 receptor antibodies.

Conclusions/Significance

These data indicate that neither direct pharmacologic antagonism nor downregulated expression of M2 receptors contributes to OP inhibition of M2 function in airway nerves, adding to the growing evidence of non-cholinergic mechanisms of OP neurotoxicity.

Ragweed pollen-mediated IgE-independent release of biogenic amines from mast cells via induction of mitochondrial dysfunction

Normal functions of mitochondria are required for physiological dynamics of cells, while their dysfunction contributes to development of various disorders including those of immune system. Here we demonstrate that exposure of mast cells to ragweed pollen extract increases production of H(2)O(2) via mitochondrial respiratory complex III. These mitochondrial ROS (mtROS) enhance secretion of histamine and serotonin from mast cells, but not enzymes such as beta-hexosaminidase, independently from FcvarepsilonRI-generated stimuli. The release of biogenic amines is associated with inhibition of secretory granules' H(+)-ATPase activity, activation of PKC-delta and microtubule-dependent motility, and it is independent from intracellular free Ca(2+) levels. To asses differences from IgE-mediated mast cell degranulation we show that mtROS decrease antigen-triggered beta-hexosaminidase release, while they are synergistic with antigen-induced IL-4 production in sensitized cells. Taken together, these data indicate that mitochondrial dysfunction can act independently from adaptive immunity, as well as augments Th2-type responses. Pharmacological maintenance of physiological mitochondrial function could have clinical benefits in prevention and treatment of allergic diseases.

Antigen sensitization influences organophosphorus pesticide-induced airway hyperreactivity

BACKGROUND

Recent epidemiologic studies have identified organophosphorus pesticides (OPs) as environmental factors potentially contributing to the increase in asthma prevalence over the last 25 years. In support of this hypothesis, we have demonstrated that environmentally relevant concentrations of OPs induce airway hyperreactivity in guinea pigs.

OBJECTIVES

Sensitization to allergen is a significant contributing factor in asthma, and we have shown that sensitization changes virus-induced airway hyperreactivity from an eosinophil-independent mechanism to one mediated by eosinophils. Here, we determine whether sensitization similarly influences OP-induced airway hyperreactivity.

METHODS

Nonsensitized and ovalbumin-sensitized guinea pigs were injected subcutaneously with the OP parathion (0.001-1.0 mg/kg). Twenty-four hours later, animals were anesthetized and ventilated, and bronchoconstriction was measured in response to either vagal stimulation or intravenous acetylcholine. Inflammatory cells and acetylcholinesterase activity were assessed in tissues collected immediately after physiologic measurements.

RESULTS

Ovalbumin sensitization decreased the threshold dose for parathion-induced airway hyperreactivity and exacerbated parathion effects on vagally induced bronchoconstriction. Pretreatment with antibody to interleukin (IL)-5 prevented parathion-induced hyperreactivity in sensitized but not in nonsensitized guinea pigs. Parathion did not increase the number of eosinophils in airways or the number of eosinophils associated with airway nerves nor did it alter eosinophil activation as assessed by major basic protein deposition.

CONCLUSIONS

Antigen sensitization increases vulnerability to parathion-induced airway hyperreactivity and changes the mechanism to one that is dependent on IL-5. Because sensitization to allergens is characteristic of 50% of the general population and 80% of asthmatics (including children), these findings have significant implications for OP risk assessment, intervention, and treatment strategies.

Increased T-lymphocyte dependent antibody production in female SJL/J mice following exposure to commercial grade malathion

The organophosphate pesticide, malathion, was evaluated for effects on immune function in female SJL/J mice. Commercial grade malathion was dissolved in corn oil and administered at doses of 0.018-180 mg/kg to mice via oral gavage on alternate days for 28 days. Exposure to malathion did not alter brain acetylcholinesterase activity, body weight gain, organ/body weight ratios or food and water consumption during the treatment period. Malathion enhanced the primary IgM antibody response to sheep red blood cells (SRBCs) by approximately 150% (P<0.02) at all doses tested when the response was expressed per 10(6) viable spleen cells and per spleen. B-lymphocyte blastogenesis induced by lipopolysaccharide (LPS, P=0.10) was not affected by malathion exposure. T-lymphocyte blastogenesis induced by concanavalin A (ConA, P=0.23) and phytohemagglutinin (PHA-P, P=0.24) also was unaffected by treatment with malathion. Malathion had no effect on splenic macrophage phagocytosis (P>0.11). These results indicate that repeated oral administration of commercial-grade malathion increased antibody production following immunization with a T-lymphocyte dependent antigen at doses as low as 0.018 mg/kg, which is below the human allowable daily intake (0.02 mg/kg). These changes occurred in the absence of B- or T-lymphocyte hyper responsiveness or alterations in macrophage phagocytosis. Immune system alterations at a sub-clinical level following exposure to a commercial formulation of malathion may have an important impact on human and animal health risk assessment. Therefore, further investigation into the mechanisms responsible for the increased antibody production is warranted.

Mucosal injury and eicosanoid kinetics during hyperventilation-induced bronchoconstriction

Bronchoalveolar lavage (BAL) of canine peripheral airways was performed at various times after hyperventilation, and BAL fluid (BALF) cell and mediator data were used to evaluate two hypotheses: 1) hyperventilation-induced mucosal injury stimulates mediator production, and 2) mucosal damage is correlated with the magnitude of hyperventilation-induced bronchoconstriction. We found that epithelial cells increased in BALF immediately after a 2- and a 5-min dry air challenge (DAC). Prostaglandins D(2) and F(2alpha) and thromboxane B(2) were unchanged immediately after a 2-min DAC but were significantly increased after a 5-min DAC. Leukotriene C(4), D(4), and E(4) did not increase until 5 min after DAC. Hyperventilation with warm moist air did not alter BALF cells or mediators and caused less airway obstruction that occurred earlier than DAC. BALF epithelial cells were correlated with mediator release, and mediator release and epithelial cells were correlated with hyperventilation-induced bronchoconstriction. These observations are consistent with the hypothesis that hyperventilation-induced mucosal damage initiates peripheral airway constriction via the release of biochemical mediators.

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).