Involvement of superoxide in malaoxon-induced toxicity in primary cultures of cortical neurons

Abstract

Organophosphorus compounds (OP) represent a class of insecticides that are used most globally. The neurotoxic effects are attributed mainly to acetylcholinesterase (AChE) enzyme inhibition, which is responsible for cholinergic manifestations in individuals acutely exposed to OP. However, AChE inhibition alone cannot account for the wide range of symptoms that were reported following OP exposures. In agreement with this, evidence shows that non-cholinergic events may be mechanistically linked to OP-induced neurotoxicity. The aim of this study was to investigate the potential occurrence of oxidative stress as a critical step in the toxicity induced by the OP malaoxon(MAL) using primary cultures of mouse cortical neurons, as well as to distinguish MAL-induced oxidative stress and cell toxicity from an action on AChE blockade. Primary cultures of mouse cortical neurons were treated with MAL (0.01; 0.1; 1; 10; or 100 µM) at varying time points (1, 3, 6, 24, 48, or 144 hr) and the following biochemical parameters determined including cell viability, AChE activity, and superoxide production. MAL significantly reduced cell viability in a concentration- and time-dependent manner. Of note, 1 µM MAL significantly inhibited (approximately 75%) AChE activity after 48 hr incubation. Pralidoxime (PRAL) (600 µM), a classical AChE reactivator, significantly protected against MAL-induced AChE blockade; however, PRAL did not affect MAL-mediated fall in cellular viability, indicating that AChE inhibition is not necessarily correlated with insecticide-induced decrease in cell survival. MAL-induced diminished cell viability was preceded by a significant increase in superoxide anion production. The antioxidant agent ascorbic acid (AA) (200 µM), which significantly protected against MAL-induced superoxide anion production, did not alter MAL-induced AChE inhibition and significantly prevented insecticide-mediated fall in cell survival. Data show that increased superoxide anion production is an event that precedes MAL-induced cell toxicity in primary cultures of mouse cortical neurons. Based on the preventative effects of AA against MAL-mediated superoxide anion production and reduced cell viability, evidence indicates that oxidative stress represents an important step mediating MAL-induced toxicity in neurons and that AChE inhibition is not necessarily correlated with lowered cell survival noted in insecticide-exposed cells.

Organophosphate toxicity: updates of malathion potential toxic effects in mammals and potential treatments

“…DMPT dimethyltiophosphate, MMA malathion (malaoxon)-monocarboxylic acid, MDA malathion (malaoxon)-dicaroxylic acid significantly counteracted the decrease of cell viability with no effect on AChE activity. This provides evidence of the role of oxidative stress in MAL-induced toxicity (Rieger et al 2017).…”

“…They found that MAL-induced decreased cell viability was directly correlated with a significant increase in superoxide anion production and that the use of an antioxidant significantly protected against MAL-induced cytotoxic effects and proceeded with the decrease in superoxide anion level; however, it did not affect MAL-induced AChE inhibition. Thus, they provided a good evidence of the significant role of oxidative stress in MAL-induced neurotoxicity (Rieger et al 2017).…”

“…Santos et al (2012) proposed a potential link between AChE activity and oxidative stress in experimental models of neurotoxicity (Santos et al 2012). However, Rieger et al (2017) proved experimentally that MAL-induced oxidative stress in cortical cell culture does not involve AChE inhibition. They found that MAL-induced decreased cell viability was directly correlated with a significant increase in superoxide anion production and that the use of an antioxidant significantly protected against MAL-induced cytotoxic effects and proceeded with the decrease in superoxide anion level; however, it did not affect MAL-induced AChE inhibition.…”

An Antenna-Abundant Glutathione S-Transferase BdGSTd8 Participates in Detoxification of Two Organophosphorus Insecticides in Bactrocera dorsalis (Hendel)

“…5 Among these, organophosphorus is the most widely used insecticide class in the world because it possesses high specific toxicity to insects and low toxicity to mammals. 7 With this insecticide, it causes cell apoptosis via lipid peroxidation while also inhibiting the activity of acetylcholinesterase, which is the key enzyme used to degrade acetylcholine in nerve signal transmission. 7 Additionally, neonicotinoid is another important class of insecticide that targets nicotinic acetylcholine receptors.…”

“…7 With this insecticide, it causes cell apoptosis via lipid peroxidation while also inhibiting the activity of acetylcholinesterase, which is the key enzyme used to degrade acetylcholine in nerve signal transmission. 7 Additionally, neonicotinoid is another important class of insecticide that targets nicotinic acetylcholine receptors. 8 In comparison, pyrethroid and macrolides disturb voltage-gated chloride channels and the γ-aminobutyric acid receptor (GABAR) that block the transmission of nerve signals.…”