Molecular docking analysis of acetylcholinesterase corroborates the protective effect of pralidoxime against chlorpyrifos-induced behavioral and neurochemical impairments in Nauphoeta cinerea

Theoretical insights into the HO●-induced oxidation of chlorpyrifos pesticide: Mechanism, kinetics, ecotoxicity, and cholinesterase inhibition of degradants

The oxidation of the common pesticide chlorpyrifos (CPF) initiated by HO● radical and the risks of its degradation products were studied in the gaseous and aqueous phases via computational approaches. Oxidation mechanisms were investigated, including H-, Cl-, CH3- abstraction, HO●-addition, and single electron transfer. In both phases, HO●-addition at the C of the pyridyl ring is the most energetically favorable and spontaneous reaction, followed by H-abstraction reactions at methylene groups (i.e., at H19/H21 in the gas phase and H22/H28 in water). In contrast, other abstractions and electron transfer reactions are unfavorable. However, regarding the kinetics, the significant contribution to the oxidation of CPF is made from H-abstraction channels, mostly at the hydrogens of the methylene groups. CPF can be decomposed in a short time (5-8 h) in the gas phase, and it is more persistent in natural water with a lifetime between 24 days and 66 years, depending on the temperature and HO● concentration. Subsequent oxidation of the essential radical products with other oxidizing reagents, i.e., HO●, NO2●, NO●, and 3O2, gave primary neutral products P1-P15. Acute and chronic toxicity calculations estimate very toxic levels for CPF and two degradation products, P7w and P12w, in aquatic systems. The neurotoxicity of these products was investigated by docking and molecular dynamics. P7w and P12w show the most significant binding scores with acetylcholinesterases, while P8w and P13w are with butyrylcholinesterase enzyme. Finally, molecular dynamics illustrate stable interactions between CPF degradants and cholinesterase enzyme over a 100 ns time frame and determine P7w as the riskiest degradant to the neural developmental system.

Utility of cockroach as a model organism in the assessment of toxicological impacts of environmental pollutants

Environmental pollution is a global concern because of its associated risks to human health and ecosystem. The bio-monitoring of environmental health has attracted much attention in recent years and efforts to minimize environmental contamination as well as to delineate toxicological mechanisms related to toxic exposure are essential to improve the health conditions of both humans and animals. This review aims to substantiate the need and advantages in utilizing cockroaches as a complementary, non-mammalian model to further understand the noxious impact of environmental contaminants on humans and animals. We discuss recent advances in neurotoxicology, immunotoxicology, reproductive and developmental toxicology, environmental forensic entomotoxicology, and environmental toxicology that corroborate the utility of the cockroach (Periplaneta americana, Blaptica dubia, Blattella germanica and Nauphoeta cinerea) in addressing toxicological mechanisms as well as a sensor of environmental pollution. Indeed, recent improvements in behavioural assessment and the detection of potential biomarkers allow for the recognition of phenotypic alterations in cockroaches following exposure to toxic chemicals namely saxitoxin, methylmercury, polychlorinated biphenyls, electromagnetic fields, pharmaceuticals, polycyclic aromatic hydrocarbon, chemical warfare agents and nanoparticles. The review provides a state-of-the-art update on the current utility of cockroach models in various aspects of toxicology as well as discusses the potential limitations and future perspectives.

Pesticidal efficacy, mode of action and safety limits profile of essential oils based nanoformulation against Callosobruchus chinensis and Aspergillus flavus

The study explores the pesticidal efficacy, mode of action, and safety limit profile of essential oils-based formulation using the combination of Myristica fragrans (M), Bunium persicum (B), and Zanthoxylum alatum (Z) (1:1:1 v/v/v) and their nanoformulation (Ne-MBZ) against the Callosobruchus chinensis, Aspergillus flavus and aflatoxin B₁ production. Linalool, γ-terpinene, and cuminaldehyde were identified as the major compounds of the formulation (MBZ) by Gas chromatography-mass spectrometry (GC-MS). Nanoencapsulation of developed formulation (Ne-MBZ) was prepared using chitosan and characterized by scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), and Fourier transform infrared spectroscopy (FTIR). The pesticidal efficacy of nanoformulation (Ne-MBZ) against C. chinensis IC₅₀ (0.14 μl/ml), A. flavus (0.8 μl/ml) and AFB₁ (0.8 μl/ml) was significantly higher in both in-vitro and in-situ conditions than the sum of their individual revealing a notable synergistic effect. Besides, the detailed mode of pesticidal action and safety limit profile were explored using biochemical, in-silico and ADMET (absorption, distribution, metabolism, excretion, and toxicity) approaches.

High level of methylmercury exposure causes persisted toxicity in Nauphoeta cinerea

Methylmercury (MeHg⁺) is a neurotoxicant abundantly present in the environment. The long-term effects of MeHg⁺ have been investigated in rodents, yet data on the long-term or persisted toxicity of MeHg⁺ in invertebrates is scanty. Here, we examined the acute, intermediate, and chronic effects upon dietary administration of MeHg⁺ in nymphs of Nauphoeta cinerea. Besides, the potential reversibility of the toxic effects of MeHg⁺ after a detoxification period was evaluated. Nymphs were exposed to diets containing 0 (control), 2.5, 25, and 100 μg MeHg⁺/g of diet for 10, 30, and 90 days. Additional groups of nymphs were fed with the same dose of MeHg⁺ for 30 days and then were subjected to a detoxification period for 60 days. The nymphs exposed to 100 μg MeHg⁺/g succumbed to a high mortality rate, along with multiple biochemical (increase of reactive oxygen species production and glutathione S-transferase activity, as well as decrease in the acetylcholinesterase activity) and behavioral alterations. We observed delayed mortality rate and behavioral alterations in nymphs exposed to 100 μg MeHg⁺/g for 30 days and subsequently subjected to 60 days of detoxification. However, the biochemical alterations did not persist throughout the detoxification period. In conclusion, our results established the persistent toxic effect of MeHg⁺ even after a prolonged detoxification period and evidenced the use of N. cinerea as an alternative model to study the toxicity of MeHg⁺.

Molecular docking and in vitro evaluation of a new hybrid molecule (JM-20) on cholinesterase activity from different sources

The main function of AChE is the hydrolysis of the neurotransmitter acetylcholine (ACh) at the neuromuscular and in cholinergic brain synapses. In some pathologies, loss of cholinergic neurons may be associated with a deficiency of ACh in specific brain areas. Consequently, the study of new safe drugs that inhibit AChE is important, because they can increase ACh levels in the synaptic cleft without adverse effects. Here, we evaluated the effects of JM-20 (a benzodiazepine-dihydropyridine hybrid molecule) on cholinesterase (ChE) activities from distinct sources (AChE from Electrophorus electricus (EeAChE), human erythrocyte membranes (HsAChE (ghost)), total erythrocyte (HsAChE (erythrocyte)) and BChE from plasma (HsBChE) and purified enzyme from the horse (EcBChE)). Kinetic parameters were determined in the presence of 0.05-1.6 mM of substrate concentration. The interactions ChEs with JM-20 were performed using molecular docking simulations. JM-20 inhibited all tested AChE but not BChE. The IC₅₀ values were 123 nM ± 0.2 (EeAChE), 158 nM ± 0.1 (ghost HsAChE), and 172 nM ± 0.2 (erythrocytic HsAChE). JM-20 caused a mixed type of inhibition (it altered K_m and V_max of AChE). The molecular docking indicated the binding poses and the most plausible active isomer of JM-20. Besides giving important data for future drug design, our results help us understand the mode of action of JM-20 as a specific inhibitor of AChE enzymes.

Staphylococcus aureus-induced sepsis in the lobster cockroach Nauphoeta cinerea

Invertebrates have been instrumental in understanding the mechanisms involved in infectious diseases, considering the idea to replace, reduce and refine the use of mammals as well as to understand the basic principles of immune response in insect. We evaluated the consequences of Staphylococcus aureus-induced sepsis in the last instar nymphs of Nauphoeta cinerea injected with different concentrations of bacteria preserved in two culture media. Infected groups had a decrease in hemolymph metabolites (glucose, amino acids, total proteins, and cholesterol), in contrast to the proteins in the fat body. Higher concentrations of S. aureus caused permanent morphological alterations in adults, decrease in food consumption, increase in isolation, and increase in CFU until death of the cockroaches. Survival and protection of nymphs against a repeated and stronger challenge with the same bacteria varied according to the medium they were conserved. N. cinerea proves to be a suitable and promising model for studies related to bacterial infections.