Low doses of imidacloprid induce disruption of intercellular adhesion and initiate proinflammatory changes in Caco-2 cells

Comparative evaluation of neonicotinoids and their metabolites-induced oxidative stress in carp primary leukocytes and CLC cells

Neonicotinoids (NEOs) have been designed to act selectively on insect nicotinic acetylcholine receptors (nAChRs). However, nAChRs are also expressed in vertebrate immune cells, so NEOs may interfere with the immune system in exposed non-target animals. The present study shows that NEOs: imidacloprid and thiacloprid, and their main metabolites: desnitro-imidacloprid and thiacloprid amide, at sub-micromolar concentrations ranging from 2.25 to 20 μM, affect the immune cells of fish. This was found both in primary cultures of leukocytes isolated from the carp head kidney and in the continuous adherent carp monocyte/macrophage cell line. Moreover, the results revealed that the studied pesticides and metabolites generate oxidative stress in carp immune cells and that this is one of the most important mechanisms of neonicotinoid immunotoxicity. Significant increases were observed in the formation of ROS and malondialdehyde (MDA). The antioxidant status alteration was linked with decrease in antioxidant enzyme activity: superoxide dismutase (SOD), catalase (CAT), and non-enzymatic antioxidant glutathione (GSH). Importantly, the metabolites: desnitro-imidacloprid and thiacloprid amide showed significantly higher cytotoxicity towards fish leukocytes than their parent compounds, imidacloprid and thiacloprid, which emphasizes the importance of including intermediate metabolites in toxicology studies.

Molecular Physicochemical Properties of Selected Pesticides as Predictive Factors for Oxidative Stress and Apoptosis-Dependent Cell Death in Caco-2 and HepG2 Cells

In this work, three pesticides of different physicochemical properties: glyphosate (GLY, herbicide), imidacloprid (IMD, insecticide), and imazalil (IMZ, fungicide), were selected to assess their cytotoxicity against Caco-2 and HepG2 cells. Cell viability was assessed by the Alamar Blue assay, after 24 and 48 h exposure to different concentrations, and IC50 values were calculated. The mechanisms underlying toxicity, namely cellular reactive oxygen species (ROS), glutathione (GSH) content, lipid peroxidation, loss of mitochondrial membrane potential (MMP), and apoptosis/necrosis induction were assessed by flow cytometry. Cytotoxic profiles were further correlated with the molecular physicochemical parameters of pesticides, namely: water solubility, partition coefficient in an n-octanol/water (Log Pow) system, topological polar surface area (TPSA), the number of hydrogen-bonds (donor/acceptor), and rotatable bonds. In vitro outputs resulted in the following toxicity level: IMZ (Caco-2: IC50 = 253.5 ± 3.37 μM, and HepG2: IC50 = 94 ± 12 μM) > IMD (Caco-2: IC50 > 1 mM and HepG2: IC50 = 624 ± 24 μM) > GLY (IC50 >>1 mM, both cell lines), after 24 h treatment, being toxicity time-dependent (lower IC50 values at 48 h). Toxicity is explained by oxidative stress, as IMZ induced a higher intracellular ROS increase and lipid peroxidation, followed by IMD, while GLY did not change these markers. However, the three pesticides induced loss of MMP in HepG2 cells while in Caco-2 cells only IMZ produced significant MMP loss. Increased ROS and loss of MMP promoted apoptosis in Caco-2 cells subjected to IMZ, and in HepG2 cells exposed to IMD and IMZ, as assessed by Annexin-V/PI. The toxicity profile of pesticides is directly correlated with their Log Pow, as affinity for the lipophilic environment favours interaction with cell membranes governs, and is inversely correlated with their TPSA; however, membrane permeation is favoured by lower TPSA. IMZ presents the best molecular properties for membrane interaction and cell permeation, i.e., higher Log Pow, lower TPSA and lower hydrogen-bond (H-bond) donor/acceptor correlating with its higher toxicity. In conclusion, molecular physicochemical factors such as Log Pow, TPSA, and H-bond are likely to be directly correlated with pesticide-induced toxicity, thus they are key factors to potentially predict the toxicity of other compounds.

In Vitro Assessment of Pesticides Toxicity and Data Correlation with Pesticides Physicochemical Properties for Prediction of Toxicity in Gastrointestinal and Skin Contact Exposure

In this work, three pesticides of different physicochemical properties, namely, glyphosate (herbicide), imidacloprid (insecticide) and imazalil (fungicide), were selected to assess their cytotoxicity against distinct cell models (Caco-2, HepG2, A431, HaCaT, SK-MEL-5 and RAW 264.7 cells) to mimic gastrointestinal and skin exposure with potential systemic effect. Cells were subjected to different concentrations of selected pesticides for 24 h or 48 h. Cell viability was assessed by Alamar Blue assay, morphological changes by bright-field microscopy and the IC50 values were calculated. Cytotoxic profiles were analysed using the physico-chemical parameters of the pesticides, namely: molecular weight, water solubility, the partition coefficient in the n-octanol/water (Log Pow) system, the topological polar surface area (TPSA), and number of hydrogen-bonds (donor/acceptor) and rotatable bonds. Results showed that glyphosate did not reduce cell viability (up to 1 mM), imidacloprid induced moderate toxicity (IC50 > 1 mM for Caco-2 cells while IC50 = 305.9 ± 22.4 μM for RAW 264.7 cells) and imazalil was highly cytotoxic (IC50 > 253.5 ± 3.37 for Caco-2 cells while IC50 = 31.3 ± 2.7 μM for RAW 264.7 cells) after 24 h exposure. Toxicity was time-dependent as IC50 values at 48 h exposure were lower, and decrease in cell viability was accompanied by changes in cell morphology. Pesticides toxicity was found to be directly proportional with their Log Pow, indicating that the affinity to a lipophilic environment such as the cell membranes governs their toxicity. Toxicity is inverse to pesticides TPSA, but lower TPSA favours membrane permeation. The lower toxicity against Caco-2 cells was attributed to the physiology and metabolism of cell barriers equipped with various ABC transporters. In conclusion, physicochemical factors such as Log Pow, TPSA and H-bond are likely to be directly correlated with pesticide-induced toxicity, thus being key factors to potentially predict the toxicity of other compounds.

Low Doses of Imidacloprid Induce Oxidative Stress and Neural Cell Disruption in Earthworm <i>Eisenia fetida</i>

Imidacloprid is a widely used pesticide that belongs to the class of neonicotinoids. There is a piece of rising evidence that neonicotinoids exert cytotoxic effects in non-target organisms including vertebrate species such as mammals. Nevertheless, dose-limiting toxicity and molecular mechanisms of neonicotinoids' deleterious effects are still poorly understood. In accord to imidacloprid fate in the environment, the most of used pesticide is absorbed in the soil. Therefore, earthworms, which are prevailing soil organisms, could be considered as a target of neonicotinoids toxicity. The earthworm’s simple nervous system is a prospective model for neurotoxicological studies. We exposed earthworms to imidacloprid in a paper contact test with a doses range of 0.1‑0.4 µg/cm2 for 14 days. In the present work, we studied the imidacloprid effect on oxidative stress generation and neuronal marker neuron-specific enolase (NSE) expression. The exposure to imidacloprid induced a dose-dependent decrease in NSE. Both reactive oxygen species production and lipid peroxidation level were upregulated as well. Observed NSE decline suggests imidacloprid-caused disturbance in earthworm neuron cells. Obtained data have shown that relatively low doses of imidacloprid are potent to induce cytotoxicity in neurons. Furthermore, neurotoxicity could be recognized as one of an individual scenario of the general imidacloprid toxicity. Thus, presented results suggest the cytotoxicity of imidacloprid low doses in non-target organisms and hypothesize that NSE downregulation could be estimated as a biomarker of neonicotinoid cytotoxicity in a nervous system of non-insect species.

Low Doses of Imidacloprid Induce Oxidative Stress and Neural Cell Disruption in Earthworm <i>Eisenia fetida</i>

Imidacloprid is a widely used pesticide that belongs to the class of neonicotinoids. There is a piece of rising evidence that neonicotinoids exert cytotoxic effects in non-target organisms including vertebrate species such as mammals. Nevertheless, dose-limiting toxicity and molecular mechanisms of neonicotinoids' deleterious effects are still poorly understood. In accord to imidacloprid fate in the environment, the most of used pesticide is absorbed in the soil. Therefore, earthworms, which are prevailing soil organisms, could be considered as a target of neonicotinoids toxicity. The earthworm’s simple nervous system is a prospective model for neurotoxicological studies. We exposed earthworms to imidacloprid in a paper contact test with a doses range of 0.1‑0.4 µg/cm2 for 14 days. In the present work, we studied the imidacloprid effect on oxidative stress generation and neuronal marker neuron-specific enolase (NSE) expression. The exposure to imidacloprid induced a dose-dependent decrease in NSE. Both reactive oxygen species production and lipid peroxidation level were upregulated as well. Observed NSE decline suggests imidacloprid-caused disturbance in earthworm neuron cells. Obtained data have shown that relatively low doses of imidacloprid are potent to induce cytotoxicity in neurons. Furthermore, neurotoxicity could be recognized as one of an individual scenario of the general imidacloprid toxicity. Thus, presented results suggest the cytotoxicity of imidacloprid low doses in non-target organisms and hypothesize that NSE downregulation could be estimated as a biomarker of neonicotinoid cytotoxicity in a nervous system of non-insect species.