Acute Exposure to Permethrin Modulates Behavioral Functions, Redox, and Bioenergetics Parameters and Induces DNA Damage and Cell Death in Larval Zebrafish

Neurotoxic pesticides change respiratory parameters in early gill-breathing, but not in skin-breathing life-stages of zebrafish (Danio rerio)

Neurotoxic compounds can interfere with active gill ventilation in fish, which might lead to premature death in adult fish, but not in skin-breathing embryos of zebrafish, since these exclusively rely on passive diffusion across the skin. Regarding lethality, this respiratory failure syndrome (RFS) has been discussed as one of the main reasons for the higher sensitivity of adult fish in the acute fish toxicity test (AFT), if compared to embryos in the fish embryo toxicity test (FET). To further elucidate the relationship between the onset of gill respiration and death by a neurotoxic mode of action, a comparative study into oxygen consumption (MO2), breathing frequency (fv) and amplitude (fampl) was performed with 4 d old skin-breathing and 12 d old early gill-breathing zebrafish. Neurotoxic model substances with an LC50 FET/AFT ratio of > 10 were used: chlorpyrifos, permethrin, aldicarb, ziram, and fluoxetine. Exposure to hypoxia served as a positive control, whereas aniline was tested as an example of a narcotic substance interfering non-specifically with gill membranes. In 12 d old larvae, all substances caused an increase in MO2, fv and partly fampl, whereas effects were minor in 4 d old embryos. An increase of fv in 4 d old embryos following exposure to chlorpyrifos, aldicarb and hypoxia could not be correlated with an increased MO2 and might be attributed either to (1) to the successfully postponed decrease of arterial partial pressure of oxygen (PO2) through support of skin respiration by increased fv, (2) to an unspecific stimulation of the sphincter muscles at the base of the gill filaments, or (3) to the establishment of oxygen sensing for later stages. In gill-breathing 12 d old zebrafish, a concentration-dependent increase of fv was detected for aniline and chlorpyrifos, whereas for aldicarb, fluoxetine and permethrin, a decline of fv at higher substance concentrations was measured, most likely due to the onset of paralysis and/or fatigue of the gill filament sphincter muscles. Since alterations of fv serve to postpone the decrease in arterial PO2 and MO2 increased with decreasing fv, the respiratory failure syndrome could clearly be demonstrated in 12 d old zebrafish larvae. Passive respiration across the skin in zebrafish embryos could thus be confirmed as a probable reason for the lower sensitivity of early life-stages to neurotoxicants. Integration of respiratory markers into existing testing protocols with non-protected developmental stages such as embryos might help to not underestimate the toxicity of early life-stages of fish.

Permissible concentration of mancozeb in Brazilian drinking water elicits oxidative stress and bioenergetic impairments in embryonic zebrafish

Mancozeb (MZ) is widely used as a fungicide in Brazil due to its effectiveness in combating fungal infections in plantations. However, its toxicity to non-target organisms, including aquatic organisms, has been reported in the literature. Recently, Brazilian legislation was updated to allow a concentration of 8 μg/L of MZ in drinking water (Ordinance GM/MS nº 888, of May 4, 2021). However, the safety of this concentration for aquatic organisms has not yet been put to the test. To address this gap, we conducted a study using zebrafish (Danio rerio) embryos at 4 hpf exposed to MZ at the concentration allowed by law, as well as slightly higher sublethal concentrations (24, 72, and 180 μg/L), alongside a control group. We evaluated various morphophysiological markers of toxicity, including survival, spontaneous movements, heart rate, hatching rate, body axis distortion, total body length, total yolk sac area, and total eye area. Additionally, we measured biochemical biomarkers such as reactive oxygen species (ROS) levels, lipid peroxidation, non-protein thiols (NPSH), and mitochondrial bioenergetic parameters. Our results showed that the concentration of 8 μg/L, currently permitted in drinking water according to Brazilian legislation, increased ROS production levels and caused alterations in mitochondrial physiology. Among the markers assessed, mitochondrial bioenergetic function appeared to be the most sensitive indicator of MZ embryotoxicity, as a decrease in complex I activity was observed at concentrations of 8 and 180 μg/L. Furthermore, concentrations higher than 8 μg/L impaired morphophysiological markers. Based on these findings, we can infer that the concentration of MZ allowed in drinking water by Brazilian environmental legislation is not safe for aquatic organisms. Our study provides evidence that this fungicide is a potent embryotoxic agent, highlighting the potential risks associated with its exposure.

Oxytocin protective effects on zebrafish larvae models of autism-like spectrum disorder

Objectives

Autism is a complicated neurodevelopmental disorder characterized by social interaction deficiencies, hyperactivity, anxiety, communication disorders, and a limited range of interests. The zebrafish (Danio rerio) is a social vertebrate used as a biomedical research model to understand social behavior mechanisms.

Materials and Methods

After spawning, the eggs were exposed to sodium valproate for 48 hr, after which the eggs were divided into eight groups. Except for the positive and control groups, there were six treatment groups based on oxytocin concentration (25, 50, and 100 μM) and time point (24 and 48 hr). Treatment was performed on days 6 and 7, examined by labeling oxytocin with fluorescein-5-isothiocyanate (FITC) and imaging with confocal microscopy and the expression levels of potential genes associated with the qPCR technique. Behavioral studies, including light-dark background preference test, shoaling behavior, mirror test, and social preference, were performed on 10, 11, 12, and 13 days post fertilization (dpf), respectively.

Results

The results showed that the most significant effect of oxytocin was at the concentration of 50 μM and the time point of 48 hr. Increased expression of shank3a, shank3b, and oxytocin receptor genes was also significant at this oxytocin concentration. Light-dark background preference results showed that oxytocin in the concentration of 50 µM significantly increased the number of crosses between dark and light areas compared with valproic acid (positive group). Also, oxytocin showed an increase in the frequency and time of contact between the two larvae. We showed a decrease in the distance in the larval group and an increase in time spent at a distance of one centimeter from the mirror.

Conclusion

Our findings showed that the increased gene expression of shank3a, shank3b, and oxytocin receptors improved autistic behavior. Based on this study some indications showed that oxytocin administration in the larval stage could significantly improve the autism-like spectrum.

Permethrin inhibits tube formation and viability of endothelial cells

BACKGROUND

Exposure to environmental chemicals has been linked with endothelial dysfunction, which is a leading cause of human diseases, including atherosclerosis. Permethrin is a frequently used synthetic pyrethroid insecticide for which longer exposure may cause toxicity in several types of tissues and the development of metabolic diseases, including atherosclerosis, obesity and diabetes. The present study was designed to evaluate the potential adverse effect of permethrin on the function and activity of human endothelial cells.

RESULTS

Permethrin was found to repress migration and tube formation by human umbilical vein endothelial cells (HUVECs) in a dose-dependent manner, as well as to significantly repress their viability after 24 and 48 h of treatment. Furthermore, increased reactive oxygen species (ROS) production was observed in cells treated with permethrin, and the permethrin-induced repression of cell viability was ROS-dependent. Permethrin did not influence apoptosis, necrosis or mitochondrial membrane potential in HUVECs.

CONCLUSION

The results of the present study suggest that permethrin represses angiogenesis and viability through ROS-dependent and cell growth-, apoptosis- and necrosis-independent means. © 2022 Society of Chemical Industry.

A Common Feature of Pesticides: Oxidative Stress-The Role of Oxidative Stress in Pesticide-Induced Toxicity

Pesticides are important chemicals or biological agents that deter or kill pests. The use of pesticides has continued to increase as it is still considered the most effective method to reduce pests and increase crop growth. However, pesticides have other consequences, including potential toxicity to humans and wildlife. Pesticides have been associated with increased risk of cardiovascular disease, cancer, and birth defects. Labels on pesticides also suggest limiting exposure to these hazardous chemicals. Based on experimental evidence, various types of pesticides all seem to have a common effect, the induction of oxidative stress in different cell types and animal models. Pesticide-induced oxidative stress is caused by both reactive oxygen species (ROS) and reactive nitrogen species (RNS), which are associated with several diseases including cancer, inflammation, and cardiovascular and neurodegenerative diseases. ROS and RNS can activate at least five independent signaling pathways including mitochondrial-induced apoptosis. Limited in vitro studies also suggest that exogenous antioxidants can reduce or prevent the deleterious effects of pesticides.

Exposure to Sub-Lethal Doses of Permethrin Is Associated with Neurotoxicity: Changes in Bioenergetics, Redox Markers, Neuroinflammation and Morphology

Permethrin (PERM) is a member of the class I family of synthetic pyrethroids. Human use has shown that it affects different systems, with wide health dysfunctions. Our aim was to determine bioenergetics, neuroinflammation and morphology changes, as redox markers after subacute exposure to PERM in rats. We used MDA determination, protein carbonyl assay, mitochondrial O₂ consumption, expression of pro-inflammatory cytokines and a deep histopathological analysis of the hippocampus. PERM (150 mg/kg and 300 mg/kg body weight/day, o.v.) increased lipoperoxidation and carbonylated proteins in a dose-dependent manner in the brain regions. The activities of antioxidant enzymes glutathione peroxidase, reductase, S-transferase, catalase, and superoxide dismutase showed an increase in all the different brain areas, with dose-dependent effects in the cerebellum. Cytokine profiles (IL-1β, IL-6 and TNF-α) increased in a dose-dependent manner in different brain tissues. Exposure to 150 mg/kg of permethrin induced degenerated and/or dead neurons in the rat hippocampus and induced mitochondrial uncoupling and reduction of oxidative phosphorylation and significantly decreased the respiratory parameters state 3-associated respiration in complex I and II. PERM exposure at low doses induces reactive oxygen species production and imbalance in the enzymatic antioxidant system, increases gene expression of pro-inflammatory interleukins, and could lead to cell damage mediated by mitochondrial functional impairment.

How does sublethal permethrin effect non-target aquatic organisms?

Permethrin is belonged to pyrethroids that are one of the substances developed as an alternative to pesticides. Permethrin, which is used especially in agriculture, can bioaccumulate in the water and sediment when mixed into aquatic ecosystems. For this reason, it is necessary to investigate the effect of this substance on aquatic organisms other than the target organism. The aim of this study was the determination of acute and sublethal effects as antioxidant enzyme levels on different organs and hemolymph biochemistry of the non-target aquatic organism, narrow-clawed crayfish (Astacus leptodactylus), after exposure to permethrin, one of the synthetic pyrethroid pesticides, contaminating aquatic ecosystems due to its increase usage. The invertebrate model organism, the narrow-clawed crayfish, was selected for its bioindicator role in food webs as planktivorous grazers epibenthic scavengers and good alternative models in ecotoxicology studies with the importance in conservation of freshwater ecosystems. The 96-h LC₅₀ value of permethrin to experimental species was estimated as 0.903 μg/L (95% CI = 0.5042-2.2734 μg/L) with probit analysis method. The sublethal concentration of the permethrin was determined by 1/10 of 96-h LC₅₀ values as 0.09 μg/L. There were two control (negative and acetone) groups in the experiment. The sampling of hemolymph and the tissues (gills, hepatopancreas, and muscle) were done 48 h and 96 h after exposure of the permethrin. The total hemocyte counts significantly increased in the 96-h exposed group of permethrin (p<0.05). Among the hemolymph biochemical parameters, the hemolymph potassium and chloride values increased statistically (p<0.05). Malondialdehyde levels (MDA) of gills and muscle were significantly increased, whereas the MDA level of the hepatopancreas was significantly decreased at the end of the experiment (p<0.05). Hyperplasia in the lamella was recorded in gills, while the degenerations of the hepatopancreas tissues were observed. According to obtained results, permethrin was extremely toxic as acutely to narrow-clawed crayfish and also effected at sublethal concentrations.

The insecticide permethrin induces transgenerational behavioral changes linked to transcriptomic and epigenetic alterations in zebrafish (Danio rerio)

The pyrethroid insecticide permethrin is widely used for agricultural and domestic purposes. Previous data indicated that it acts as a developmental neurotoxicant and can induce transgenerational effects in non-target organisms. However, associated underlying mechanisms remain unclear. The aim of this study was to investigate permethrin-related transgenerational effects in the zebrafish model, and to identify possible molecular mechanisms underlying inheritance. Zebrafish (F0) were exposed to permethrin during early-life (2 h post-fertilization up to 28 days). The F1 and F2 offspring generations were obtained by pairing exposed F0 males and females, and were bred unexposed. Locomotor and anxiety behavior were investigated, together with transcriptomic and epigenomic (DNA methylation) changes in brains. Permethrin exposed F0 fish were hypoactive at adulthood, while males from the F1 and F2 generations showed a specific decrease in anxiety-like behavior. In F0, transcriptomic data showed enrichment in pathways related to glutamatergic synapse activity, which may partly underlie the behavioral effects. In F1 and F2 males, dysregulation of similar pathways was observed, including a subset of differentially methylated regions that were inherited from the F0 to the F2 generation and indicated stable dysregulation of glutamatergic signaling. Altogether, the present results provide novel evidence on the transgenerational neurotoxic effects of permethrin, as well as mechanistic insight: a transient exposure induces persistent transcriptional and DNA methylation changes that may translate into transgenerational alteration of glutamatergic signaling and, thus, into behavioral alterations.

Salinity Changes the Dynamics of Pyrethroid Toxicity in Terms of Behavioral Effects on Newly Hatched Delta Smelt Larvae

Salinity can interact with organic compounds and modulate their toxicity. Studies have shown that the fraction of pyrethroid insecticides in the aqueous phase increases with increasing salinity, potentially increasing the risk of exposure for aquatic organisms at higher salinities. In the San Francisco Bay Delta (SFBD) estuary, pyrethroid concentrations increase during the rainy season, coinciding with the spawning season of Delta Smelt (Hypomesus transpacificus), an endangered, endemic fish. Furthermore, salinity intrusion in the SFBD is exacerbated by global climate change, which may change the dynamics of pyrethroid toxicity on aquatic animals. Therefore, examining the effect of salinity on the sublethal toxicity of pyrethroids is essential for risk assessments, especially during the early life stages of estuarine fishes. To address this, we investigated behavioral effects of permethrin and bifenthrin at three environmentally relevant concentrations across a salinity gradient (0.5, 2 and 6 PSU) on Delta Smelt yolk-sac larvae. Our results suggest that environmentally relevant concentrations of pyrethroids can perturb Delta Smelt larvae behavior even at the lowest concentrations (<1 ng/L) and that salinity can change the dynamic of pyrethroid toxicity in terms of behavioral effects, especially for bifenthrin, where salinity was positively correlated with anti-thigmotaxis at each concentration.

Behavioral and biochemical consequences of Danio rerio larvae exposure to polylactic acid bioplastic

The literature has largely shown the toxicity of petroleum-based PLA biomicroplastics (PLABioMPs) and encouraged the production of alternative materials to replace their use, such as biopolymers. However, knowledge concerning the effects of biopolymers on aquatic organisms remains under development. The hypothesis that the acute exposure (five days) to polylactic acid (PLA) biopolymers may lead to behavioral and biochemical changes and to their accumulation in Danio rerio larvae was tested. Based on the results, PLA biomicroplastics (PLA BioMPs) at concentration of 3 and 9 mg/L decreased swimming distance and speed of larvae in the open field test. This outcome suggests effects on animals' locomotor and exploration activities. Larvae's longer immobility time and greater permanence in the peripheral zone of the apparatus is indicative of anxiety-like behavior caused by the exposure to PLA BioMPs. Zebrafish larvae accumulated PLA BioMPs and their acetylcholinesterase activity was inhibited by their presence, which reinforces the accumulative potential of biopolymers and their direct or indirect role as anxiogenic agents, even at sublethal concentrations. The decreased activity of acetylcholinesterase reinforces the neurotoxic action in groups exposed to PLA BioMPs. The current study has confirmed the initial hypothesis and is an insight about the toxicity of these biopolymers in D. rerio larvae, since it deepens the discussion about the environmental risk of these substances in freshwater ecosystems.

Behavioral changes occur earlier than redox alterations in developing zebrafish exposed to Mancozeb

As agriculture expands to provide food and wellbeing to the world's growing population, there is a simultaneous increasing concern about the use of agrochemicals, which can harm non-target organisms, mainly in the aquatic environment. The fungicide Mancozeb (MZ) has been used on a large-scale and is a potent inducer of oxidative stress. Therefore, there is an urgent need for the development of more sensitive biomarkers designed to earlier biomonitoring of this compound. Here we tested the hypothesis that behavioral changes induced by sublethal MZ concentrations would occur first as compared to biochemical oxidative stress markers. Embryos at 4 h post-fertilization (hpf) were exposed to Mancozeb at 5, 10 and 20 μg/L. Controls were kept in embryo water only. Behavioral and biochemical parameters were evaluated at 24, 28, 72, and 168 hpf after MZ exposure. The results showed that MZ significantly altered spontaneous movement, escape responses, swimming capacity, and exploratory behavior at all exposure times. However, changes in ROS steady-stead levels and the activity of antioxidant enzymes were observable only at 72 and 168 hpf. In conclusion, behavioral changes occurred earlier than biochemical alterations in zebrafish embryos exposed to MZ, highlighting the potential of behavioral biomarkers as sensitive tools for biomonitoring programs.

Effectiveness of melatonin to restore fish brain activity in face of permethrin induced toxicity

Present study demonstrates permethrin induced oxidative damage in fish brain and explores effectiveness of melatonin to ameliorate brain function. Adult female Notopterus notopterus were exposed to nominal permethrin concentrations at 1/20th (0.34 μg/l) and 1/10th (0.68 μg/l) of LC₅₀ for 15 days. The measured permethrin concentrations using gas chromatography (GC-ECD) were 0.28 μg/l and 0.57 μg/l, respectively. Some fish were sacrificed to collect brain tissue after 15 days of exposure. Remaining fish from both groups were administered exogenous melatonin (50 μg/kg, 100 μg/kg body weight) for 7 days and brain tissues were collected. Brain enzymes, ntioxidant factors, HSP70, HSP90, nuclear factor-kappa binding (NFkB), melatonin receptor (MT1R) proteins were measured. Permethrin treatment significantly (P < 0.05) decreased the levels of glutathione and brain enzymes. Malondialdehyde (MDA), xanthine oxidase (XO), HSPs increased at each concentration of permethrin. However, superoxide dismutase, glutathione s-transferase levels increased at low permethrin concentration followed by sharp decrease at higher concentration. Expression of NFkB and MT1R increased significantly (P < 0.05). Melatonin administration reinstated activity of brain enzymes, reduced MDA, XO levels and modulated HSPs. Melatonin also increased expression of NFkB and MT1R. Exogenous melatonin improves oxidative status in permethrin stressed fish brain. Melatonin modulates expression of HSPs that enables brain to become stress tolerant and survive by initiating NFkB translocation. Melatonin could act through melatonin receptor protein to induce synthesis of antioxidant proteins. Therefore the study successfully evaluates the potential of melatonin application for better culture and management of fish against pesticide toxicity.