Relationship between exposure, body burden and target tissue concentration after oral administration of a low-dose mixture of pyrethroid insecticides in young adult rats

Critical review and analysis of literature on low dose exposure to chemical mixtures in mammalian in vivo systems

Anthropogenic chemicals are ubiquitous throughout the environment. Consequentially, humans are exposed to hundreds of anthropogenic chemicals daily. Current chemical risk assessments are primarily based on testing individual chemicals in rodents at doses that are orders of magnitude higher than that of human exposure. The potential risk from exposure to mixtures of chemicals is calculated using mathematical models of mixture toxicity based on these analyses. These calculations, however, do not account for synergistic or antagonistic interactions between co-exposed chemicals. While proven examples of chemical synergy in mixtures at low doses are rare, there is increasing evidence that, through non-conformance to current mixture toxicity models, suggests synergy. This review examined the published studies that have investigated exposure to mixtures of chemicals at low doses in mammalian in vivo systems. Only seven identified studies were sufficient in design to directly examine the appropriateness of current mixture toxicity models, of which three showed responses significantly greater than additivity model predictions. While the remaining identified studies were unable to provide evidence of synergistic toxicity, it became apparent that many results of such studies were not always explicable by current mixture toxicity models. Additionally, two data gaps were identified. Firstly, there is a lack of studies where individual chemical components of a complex mixture (>10 components) are tested in parallel to the chemical mixture. Secondly, there is a lack of dose-response data for mixtures of chemicals at low doses. Such data is essential to address the appropriateness and validity of future chemical mixture toxicity models.

Use of subcutaneous transponders to monitor body temperature in laboratory rats

Implantable radiofrequency transponders may be adequate for the characterization of hazardous chemicals targeting body temperature control in experimental animals when colonic probes and automated monitoring systems based on intraperitoneal transmitters are not available, installable or applicable for any reason. In this work, we summarize a series of experiments showing the implantation protocol and utility of rice-grain size transponders to monitor subcutaneous temperature (T_sc) after exposure to pharmacological or toxicological treatments targeting body temperature control in laboratory rats. In addition, to explore the responsiveness of this thermometric system, the influence of physiological activity on T_sc readings was examined by monitoring T_sc after a motor exercise in a RotaRod system. Moreover, we characterized the effects of acute oral administration of the pyrethroid insecticide permethrin (PRM) in corn oil (1 mL/kg) on T_sc. PRM has been previously reported to cause dose-related increases in core temperature after administering oral doses ≥75 mg/kg, with peak effects at 2-4 h in adult rats. We monitored T_sc at 30 min intervals over a 4 h period after exposure to PRM (40-160 mg/kg). PRM caused a moderate increase in T_sc starting at ~3.5 h. Overall, T_sc assays showed minimal animal stress (if any) and rapid animal recovery from transponder implantation, simplicity to collect data, convenient testing room space requirements, and a competitive global cost per animal examined. However, various experimental factors may greatly influence the variability within and between individuals, some of which can be controlled by carefully setting up experimental conditions.

Acute and chronic toxicity of deltamethrin, permethrin, and dihaloacetylated heterocyclic pyrethroids in mice

BACKGROUND

Pyrethroids, a class of insecticides, that act on the nervous system of insects. Frequent consumption of foods with pyrethroid residues increase the risk of developmental and neurological diseases in humans. Assessing the toxicity of novel synthetic pyrethroids to mammals is also critical to the development of agrochemicals.

RESULTS

Using mice as models, the acute and chronic toxicity of deltamethrin, permethrin, dihaloacetylated pyrethroids to mammals was researched by gavage administration. Acute toxicity assessment displayed that the median lethal dose (LD₅₀ ) of deltamethrin, permethrin and dihaloacetylated heterocyclic pyrethroids DCA-O, DCA-01, and DCA-11 tested were greater than 500 mg/kg of weight. Furthermore, chronic toxicity assessment demonstrated that deltamethrin, permethrin caused epidermal damage near the genitals, while dihaloacetylated heterocyclic pyrethroids DCA-O, DCA-01, and DCA-11 showed no relevant symptoms. However, both the acute and chronic toxicity assessment suggested that pyrethroids exposure induced mice loss weight. Additionally, the elevated plus maze (EPM) test showed that pyrethroids caused anxiety-like behaviors and no motor defects in Kunming mice. Beside, during the sucrose preference test (SPT), 60-day pyrethroids exposure increased excitatory behaviors in mice. However, the neurochemical studies displayed that pyrethroids exposure increased the total amount of glutamate (Gln), glutamine (Glu) and γ-aminobutyric acid (GABA) in the mice's blood.

CONCLUSION

Pyrethroids exposure induced weight loss in mice, although the acute oral toxicity of deltamethrin, permethrin and dihaloacetylated heterocyclic pyrethroids DCA-O, DCA-01, and DCA-11 was low. However, regarding chronic toxicity, deltamethrin, permethrin and dihaloacetylated heterocyclic pyrethroids DCA-O, DCA-01, and DCA-11 induced anxiety-like behaviors, excitatory behaviors, Gln-Glu-GABA circulatory dysfunction in blood. Particularly, deltamethrin, though permethrin also had reproductive toxicity. © 2020 Society of Chemical Industry.

Induced alteration of rat erythrocyte membrane with effect of pyrethroid based compounds

The effects of tetramethrin and prallethrin exposure on plasma total proteins, free amino acids, albumins, urea, urea nitrogen, uric acid, creatinine were tested. Serum SGOT, SGPT and lipid profile, antioxidants super oxide dismutase (SOD), catalase, GSH, G-Px, phospholipids, cholesterol, C/P ratio in membranes of erythrocyte and membrane fluidity were analyzed. The reason of the study were analyzed to examine the possessions of mosquito repellent pyrethroid (MRP) based compounds tetramethrin and prallethrin exposure on plasma profile, antioxidant status of erythrocyte membrane, membrane fluidity in male Wistar rats. We tested chronically for three months exposure every day (continuously for 8-10 h per day by inhalation) of tetramethrin and prallethrin markedly available (MRP) repellents treated on male Wistar rats. Our results confirmed that tetrarmethrin and prallethrin treatment effect of plasma profile alterations, and lipid homeostasis mechanism in Red Blood cells (RBCs). Tetramethrin and prallethrin treatment significantly increased in erythrocyte membrane phospholipids and decreased levels of cholesterol with no change of protein content, increased C/P ration levels. Inhalation of tetramethrin and prallethrin stimulate plasma biophysical and biochemical modify SGOT, SGPT, erythrocyte membrane cholesterol and phospholipid levels, individual phospholipids and membrane fluidity of exposure rats compared to controls.

Synthesis, insecticidal activity, resistance, photodegradation and toxicity of pyrethroids (A review)

Pyrethroids are a class of highly effective, broad-spectrum, less toxic, biodegradable synthetic pesticides. However, despite the extremely wide application of pyrethroids, there are many problems, such as insecticide resistance, lethal/sub-lethal toxicity to mammals, aquatic organisms or other beneficial organisms. The objectives of this review were to cover the main structures, synthesis, steroisomers, mechanisms of action, anti-mosquito activities, resistance, photodegradation and toxicities of pyrethroids. That was to provide a reference for synthesizing or screening novel pyrethroids with low insecticide resistance and low toxicity to beneficial organisms, evaluating the environmental pollution of pyrethroids and its metabolites. Besides, pyrethroids are mainly used for the control of vectors such as insects, and the non-target organisms are mammals, aquatic organisms etc. While maintaining the insecticidal activity is important, its toxic effects on non-target organisms should be also considered. Pyrethroid resistance is present not only in insect mosquitoes but also in environmental microorganisms, which results in anti-pyrethroids resistance (APR) strains. Besides, photodegradation product dibenzofurans is harmful to mammals and environment. Additionally, pyrethroid metabolites may have higher hormonal interference than the parents. Particularly, delivery of pyrethroids in nanoform can reduce the discharge of more toxic substances (such as organic solvents, etc.) to the environment.

Camel milk rescues neurotoxic impairments induced by fenpropathrin via regulating oxidative stress, apoptotic, and inflammatory events in the brain of rats

This study explored the camel milk (CM) efficacy to ameliorate the fenpropathrin (FNP) induced neurotoxic impacts in rats. Six groups were orally administered physiological saline, corn oil, CM (2ml/rat/day), FNP (15 mg/kg bw daily for 60 days), CM/FNP (protective) or FNP + CM (therapeutic). Sensorimotor functions, memory, exploratory, and locomotor activities were assessed. The levels of dopamine (DOPA) neurotransmitter, acetylcholinesterase (AChE) enzyme, oxidative stress, and inflammatory markers were determined. Brain histopathology and apoptotic markers immunohistochemical detection were performed. The results revealed that FNP exposure resulted in deficit sensorimotor functions, impaired memory, and less exploration. DOPA and AChE Levels were significantly reduced. FNP exposure increased nitric oxide, malondialdehyde, myeloperoxidase, Caspase-3, and tumor necrosis factor-alpha levels but interleukin 10, total antioxidant capacity, and Bcl-2 levels were declined. Also, FNP exposure induced obvious encephalopathy. Additionally, neurodegenerative changes were seen in the hippocampi of FNP-treated rats. FNP Exposure induced a significant decrease of Bcl-2 immunolabelling but Caspase-3 immunoexpression was increased in cerebral cortices and hippocampus tissues. CM significantly counteracted the FNP injurious impacts, especially when used as a prophylactic routine than a therapeutic one. Conclusively, these findings confirmed that CM could be a biologically effective protective agent against FNP induced neurobehavioral aberrations and neurotoxic impacts.

Relationship Between the Dose Administered, Target Tissue Dose, and Toxicity Level After Acute Oral Exposure to Bifenthrin and Tefluthrin in Young Adult Rats

Most pyrethroid insecticides (PYRs) share a similar primary target site in mammals. However, the potency estimates of the lethal and sublethal effects of these compounds differ up to 103-fold. The aim of this study was to evaluate the relationship between the dose administered, the target tissue dose, and the effect of 2 highly toxic PYRs, tefluthrin (TEF; 0.1-9 mg/kg) and bifenthrin (BIF; 0.5-12 mg/kg), by using the oral route, a corn oil vehicle (1 ml/kg) and subcutaneous temperature (Tsc) monitoring assays in adult rats. The Tsc was determined at 30-min intervals for 5 h (TEF) or 4.5 h (BIF) after dosing. Rats were sacrificed at 6 h after dosing, and BIF and TEF concentrations were determined in blood (Bd), liver (Lv), and cerebellum (Cb) by using a GC-ECD system. The minimal effective dose of BIF (3 mg/kg) affecting Tsc was similar to that found in prior studies using other testing paradigms. Regarding TEF, a very steep relationship between the dose administered and toxicity was observed, with a near-threshold to low-effective range for Tsc at 0.1-6 mg/kg, and a near lethal syndrome at ≥ 7.5 mg/kg. At 6-7.5 mg/kg TEF, the Cb/Bd and Cb/Lv concentration ratios were both > 1. Conversely, for BIF, the Cb concentration was barely over the Bd concentration and the Cb/Lv concentration ratio remained < 1. Our results and previous findings call for more comprehensive consideration to establish the relevance of the distribution into target tissues and the tissue dosimetry for health risks through the exposure to PYRs in humans.