Locomotor activity and tissue levels following acute administration of lambda- and gamma-cyhalothrin in rats

Lambda-cyhalothrin alters locomotion, mood and memory abilities in Swiss mice

Lambda-cyhalothrin (LCT) is a type II pyrethroid widely used in agriculture for plant protection against pests. However, pyrethroids represents a risk for rural female farmworkers, and few studies addressed LCT-behavioural alterations in mice. The present study evaluates the effect of LCT on behaviour of eight weeks aged female mice. Mice were divided into three groups including treated mice that received through gavage (i) 0.5 mg/kg bw and (ii) 2 mg/kg of LCT dissolved in corn oil, and (iii) the vehicle controls. Behavioural tests assess the locomotor activity using open field test, the anxiety by the dark-light box test, the learning memory with novel object recognition test, the memory retention by the elevated plus maze test, and the spatial working memory using the Y-maze test. Subacute treatment with low doses of LCT decreases total distance travelled, induces anxiogenic effect by reducing the time spent in the enlightened compartment, alters memory retention by increasing the latency time, and also affects learning memory by reducing the recognition index parameter. However, LCT does not significantly alter spatial working memory. In conclusion, LCT-treated female mice show an alteration in locomotor activity, mood state and memory abilities probably related to oxidative stress and altered neurotransmission.

Neurotoxicity induced by the pyrethroid lambda-cyhalothrin: Alterations in monoaminergic systems and dopaminergic and serotoninergic pathways in the rat brain

The effects of Type II pyrethroid lambda-cyhalothrin on dopamine (DA) and serotonin (5-HT) synthesis in rat brain regions (striatum, hippocampus, prefrontal cortex, hypothalamus and midbrain) were studied. Lambda-cyhalothrin (1, 4 and 8 mg/kg bw, oral gavage, 6 days) induced a decrease of DA, 5-HT and metabolites contents, in a brain regional- and dose-related manner. The major decreases in DA and 5-HT contents were observed in hippocampus and prefrontal cortex tissues. This research study also showed in hippocampus and prefrontal cortex, that lambda-cyhalothrin modified the mRNA levels of DA transporter gene (Dat1 up-regulation), 5-HT transporter gene (SERT down-regulation), DA receptor genes (Drd1and Drd2 down-regulation), 5-HT receptor genes (5-HT1A and 5-HT2A down-regulation/up-regulation), DA synthesis gene (TH down-regulation), 5-HT synthesis gene (TPH2 down-regulation), DA and 5-HT degradation genes (MAOA and MAOB up-regulation). These results reveal that lambda-cyhalothrin altered central nervous system (CNS) monoaminergic neurotransmitters. Lambda-cyhalothrin evoked a selective neurotoxic injury to dopaminergic and serotoninergic pathways. These findings may clarify on the pyrethroids-induced neurotoxicity mechanisms and could involve pyrethroids as environmental risk factors leading to the development of neurodegenerative diseases.

Physiologically Based Pharmacokinetic Modeling in Risk Assessment: Case Study With Pyrethroids

The assessment of potentially sensitive populations is an important application of risk assessment. To address the concern for age-related sensitivity to pyrethroid insecticides, life-stage physiologically based pharmacokinetic (PBPK) modeling supported by in vitro to in vivo extrapolation was conducted to predict age-dependent changes in target tissue exposure to 8 pyrethroids. The purpose of this age-dependent dosimetry was to calculate a Data-derived Extrapolation Factor (DDEF) to address age-related pharmacokinetic differences for pyrethroids in humans. We developed a generic human PBPK model for pyrethroids based on our previously published rat model that was developed with in vivo rat data. The results demonstrated that the age-related differences in internal exposure to pyrethroids in the brain are largely determined by the differences in metabolic capacity and in physiology for pyrethroids between children and adults. The most important conclusion from our research is that, given an identical external exposure, the internal (target tissue) concentration is equal or lower in children than in adults in response to the same level of exposure to a pyrethroid. Our results show that, based on the use of the life-stage PBPK models with 8 pyrethroids, DDEF values are essentially close to 1, resulting in a DDEF for age-related pharmacokinetic differences of 1. For risk assessment purposes, this indicates that no additional adjustment factor is necessary to account for age-related pharmacokinetic differences for these pyrethroids.

Fenvalerate triggers Parkinson-like symptom during zebrafish development through initiation of autophagy and p38 MAPK/mTOR signaling pathway

Fenvalerate (FEN), one of the most used synthetic pyrethroids, has the potential to interfere with human neural function. However, far too little attention was paid to the mechanism of FEN-induced neurotoxicity. Thus we exposed zebrafish to FEN from 4 to 120 h post fertilization (hpf), and analyzed the morphology and behavior of zebrafish. Our results showed that FEN decreased the survival rate of zebrafish, with increased malformation rates and abnormal behaviors. Furthermore, we found typical parkinson-like symptoms in FEN-exposed zebrafish with increases in parkinson's disease (PD), ubiquitin, and Lewy bodies-relevant genes. We also observed the loss of dopaminergic neurons in both FEN-exposed zebrafish and PC12 cells, which were all associated with PD-like symptoms. Besides, FEN activated autophagy by the enhanced expressions of p-mTOR, and LC3-II but the reduction of p62. Further, FEN initially activated p-p38 MAPK followed by p-mTOR, which triggered the transcription of genes responsible for autophagy process and prompted the Lewy bodies neuron generation leading to the PD-like symptoms. This process was inhibited by both 3-methyladenine (3-MA, an autophagy inhibitor) and SB203580 (a p38 MAPK selective inhibitor) in zebrafish and PC12 cells. These results suggest that FEN might cause parkinson-like symptom during zebrafish development through induction of autophagy and activation of p38 MAPK/mTOR signaling pathway. The study revealed the potential mechanism of FEN-induced neurotoxicity and should give new insights into a significant environmental risk factor of developing parkinson's disease.

Toxicokinetics of cis- and trans-Permethrin: Influence of Isomer, Maturation, and Sex

Permethrin exposure of children and adults is widespread in many populations, but knowledge of its relative toxicokinetics (TK) and health risks in immature age groups is lacking. Studies were conducted in rats to determine the influence of immaturity and sex (on plasma and target organ dosimetry of each of the insecticide’s 2 isomers, cis- and trans-permethrin [CIS and TRANS]). Postnatal day 15, 21, and 90 (adult), Sprague Dawley rats were orally administered a graduated series of doses of CIS and TRANS in corn oil. Serial sacrifices were conducted over 24 h to obtain plasma, brain, liver, skeletal muscle, and fat profiles of CIS and TRANS. Levels of TRANS decreased relatively rapidly, despite administration of relatively high doses. Concentrations of each isomer in plasma, brain, and other tissues monitored were inversely proportional to the animals’ age. The youngest pups exhibited 4-fold higher plasma and brain area under the curves than did adults. Little difference was observed in the TK of CIS or TRANS between adult male and female rats, other than higher initial plasma and liver CIS levels in females. Elevated exposure of the immature brain appears to be instrumental in increased susceptibility to the acute neurotoxicity of high-dose permethrin (Cantalamessa [1993]), but it remains to be established whether age-dependent TK is relevant to long-term, low-level risks.

Determination of offspring NOAEL for zeta-cypermethrin using internal exposure data from rat developmental neurotoxicity studies

Developmental neurotoxicity (DNT) studies via dietary method of administration have been conducted for zeta-cypermethrin, a pyrethroid insecticide. The objectives of the current study were to determine the toxicokinetics (TK) of zeta-cypermethrin in postnatal day (PND) 11, 21 and 90 rats after gavage doses and use the internal exposure data from the DNT and TK studies to calculate an offspring NOAEL in mg/kg/day during lactation. The DNT studies showed that zeta-cypermethrin is not a developmental neurotoxicant. The NOAEL for maternal and offspring was determined to be 125 ppm (9.0 and 21.4 mg/kg/day for dams during gestation and lactation, respectively), based on systemic toxicity of reductions in maternal body weight, body weight gains and food consumption and offspring body weight at 300 ppm (LOAEL). The TK data from the gavage study showed that dose normalized C_max and AUC is approximately 3-fold and 2-fold higher in PND 11 and 21 than those in PND 90 rats. By using the mean maternal/offspring plasma concentrations (535/245 ng/mL) during lactation day LD/PND 5-21 from the range-finding DNT studies, a conservative 3.1X relative TK factor (exposure ratio from the gavage study) and equation 3.1 × 535/21.4 = 245/x, the offspring NOAEL of 125 ppm was calculated to be 3.2 mg/kg/day during lactation. The offspring NOAEL based on internal exposure data from DNT studies and TK data after gavage doses is considered conservative for risk assessment for all human populations including infants and children for zeta-cypermethrin.

Non-target toxicity of novel insecticides

Humans have used insecticides since ancient times. The spectrum and potency of available insecticidal substances has greatly expanded since the industrial revolution, resulting in widespread use and unforeseen levels of synthetic chemicals in the environment. Concerns about the toxic effects of these new chemicals on non-target species became public soon after their appearance, which eventually led to the restrictions of use. At the same time, new, more environmentally-friendly insecticides have been developed, based on naturally occurring chemicals, such as pyrethroids (derivatives of pyrethrin), neonicotinoids (derivatives of nicotine), and insecticides based on the neem tree vegetable oil (Azadirachta indica), predominantly azadirachtin. Although these new substances are more selective toward pest insects, they can still target other organisms. Neonicotinoids, for example, have been implicated in the decline of the bee population worldwide. This review summarises recent literature published on non-target toxicity of neonicotinoids, pyrethroids, and neem-based insecticidal substances, with a special emphasis on neonicotinoid toxicity in honeybees. We also touch upon the effects of pesticide combinations and documented human exposure to these substances.