Acute disturbance of calcium homeostasis in PC12 cells as a novel mechanism of action for (sub)micromolar concentrations of organophosphate insecticides

• Published in: Neurotoxicology (Park Forest South) Vol. 43; pp. 110 - 116
• Main Authors: Meijer, Marieke, Hamers, Timo, Westerink, Remco H.S.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Amsterdam Elsevier B.V 01.07.2014; Elsevier
• Subjects: Acetylcholinesterase - metabolism; Animals; Biological and medical sciences; Calcium - metabolism; Carbaryl; Dose-Response Relationship, Drug; Evoked Potentials - drug effects; Fura-2 - analogs & derivatives; Homeostasis - drug effects; In vitro neurotoxicology; Insecticides - pharmacology; Medical sciences; Organophosphates; Organophosphates - pharmacology; PC12 Cells; Pesticide mixture toxicity; Pesticides, fertilizers and other agrochemicals toxicology; Rats; Single-cell fluorescent calcium imaging; Toxicology; Voltage-gated calcium channels; Pesticide mixture toxicity; Voltage-gated calcium channels; Single-cell fluorescent calcium imaging; Carbaryl; In vitro neurotoxicology; Organophosphates; Insecticide; Rat; Calcium; Toxicity; Homeostasis; Inorganic element; Mixture; Mechanism of action; Cell; Nervous system diseases; Acute; Pesticides; Rodentia; Concentration; In vitro; Trade agreement; Vertebrata; Cell line; Mammalia; Neuron; Carbaryl (pesticide); Medical imagery; Organophosphorus compounds; General agreement on trade in services; Carbamate
• ISSN: 0161-813X; 1872-9711
• DOI: 10.1016/j.neuro.2014.01.008

•OPs concentration-dependently inhibit the depolarization-evoked increase in calcium.•Parent compounds are more potent in disturbing calcium than their -oxon metabolites.•Parent compounds more effectively inhibit VGCCs than AChE activity.•The carbamate carbaryl did not disturb intracellular calcium homeostasis.•OPs show complex mixture effects on the depolarization-evoked increase in calcium. Organophosphates (OPs) and carbamates are widely used insecticides that exert their neurotoxicity via inhibition of acetylcholine esterase (AChE) and subsequent overexcitation. OPs can induce additional neurotoxic effects at concentrations below those for inhibition of AChE, indicating other mechanisms of action are also involved. Since tight regulation of the intracellular calcium concentration ([Ca2+]i) is essential for proper neuronal development and function, effects of one carbamate (carbaryl) and two OPs (chlorpyrifos, parathion-ethyl) as well as their -oxon metabolites on [Ca2+]i were investigated. Effects of acute (20min) exposure to (mixtures of) insecticides on basal and depolarization-evoked [Ca2+]i were measured in fura-2-loaded PC12 cells using single-cell fluorescence microscopy. Acute exposure to chlorpyrifos and its metabolite chlorpyrifos-oxon (10μM) induced a modest increase in basal [Ca2+]i. More importantly, the tested OPs concentration-dependently inhibited depolarization-evoked [Ca2+]i. Chlorpyrifos already induced a ∼30% inhibition at 0.1μM and a 100% inhibition at 10μM (IC50=0.43μM), whereas parathion-ethyl inhibited the depolarization-evoked [Ca2+]i increase with ∼70% at 10μM. Interestingly, -oxon metabolites were more potent inhibitors of AChE, but were less potent inhibitors of depolarization-evoked [Ca2+]i compared to their parent compound (chlorpyrifos-oxon) or were even without effect (paraoxon-ethyl and -methyl). Similarly, acute exposure to carbaryl had no effect on [Ca2+]i. Exposure to mixtures of chlorpyrifos with its oxon-analog or with parathion-ethyl did not increase the degree of inhibition, indicating additivity does not apply. These data demonstrate that concentration-dependent inhibition of depolarization-evoked [Ca2+]i is a novel mechanism of action of (sub)micromolar concentrations of OPs that could partly underlie OP-induced neurotoxicity.