Disposition of fipronil in rats

Transfer and risk assessment of fipronil in laying hen tissues and eggs

Fipronil is a persistent insecticide known to transfer into hen eggs from exposure from animal drinking water and feed, but some questions remain regarding its transfer behavior and distribution characteristics. Therefore, the dynamic metabolism, residue distribution and transfer factor (TF) of fipronil were investigated in 11 edible tissues of laying hens and eggs over 21 days. After a continuous low-dose drinking water exposure scenario, the sum of fipronil and all its metabolites (defined as fipronilT) quickly transferred to each edible tissue and gradually increased with exposure time. FipronilT residue in eggs first appeared at 3 days and then gradually increased. After a single high-dose feed exposure scenario, fipronilT residue in edible tissues first appeared after 2 h, quickly peaked at 1 day, and then gradually decreased. In eggs, fipronilT residue first appeared at 2 days, peaked 6-7 days and then gradually decreased. The TF values followed the order of the skin (0.30-0.73) > egg yolk (0.30-0.71) > bottom (0.21-0.59) after drinking water exposure, and the order of the skin (1.01-1.59) > bottom (0.75-1.1) > egg yolk (0.58-1.10) for feed exposure. Fipronil sulfone, a more toxic compound, was the predominant metabolite with higher levels distributed in the skin and bottom for both exposure pathways. FipronilT was distributed in egg yolks rather than in albumen owing to its lipophilicity, and the ratio of egg yolk to albumen may potentially reflect the time of exposure. The distinction is that the residues after feed exposure were much higher than that after drinking water exposure in edible tissues and eggs. The study highlights the residual characteristics of two exposure pathways, which would contribute to the tracing of contamination sources and risk assessment.

Comparative toxicological evaluation of carvacrol, acetylcarvacrol anda fipronil-based pesticide in human blood cells

Plant-derived chemicals are promising substances to control arthropod pests, although synthetic ones are still the most frequently used. Thus, comparative toxicological studies are needed to determine if natural substances are safe alternatives to replace the use of synthetic chemicals. This study aimed to compare the toxicity of carvacrol (natural origin), acetylcarvacrol (semi-synthetic) and a fipronil-based pesticide (synthetic). We assessed the effects of these chemicals on hemolytic activity, erythrocytes morphology and leucocyte viability using whole blood from human subjects. Additionally, DNA damage was evaluated through comet and DNA fragmentation assays. Fipronil and carvacrol caused hemolysis at concentrations ranging from 0.5 to 2.0%, whereas acetylcarvacrol did not cause hemolysis at 0.5 and 0.75%. Fipronil and carvacrol caused severe alterations in erythrocytes' morphology at 2%, such as ghost erythrocytes, elliptocyte-like shape and rouleau-like shape, presenting only 3.3 and 8.3% normal cells, respectively, at this concentration. However, 73.3% erythrocytes incubated with 2% acetylcarvacrol exhibited normal morphology. Fipronil considerably reduced leucocytes viability, decreasing it to 78% at 2%. Carvacrol and acetylcarvacrol showed no differences in leucocyte viability for 0.5 to 1.0%, but a decrease was observed for 2% carvacrol. The comet assay showed similar DNA damage for fipronil and carvacrol, but it was significantly lower for 1 and 2% acetylcarvacrol. Incubation with genomic DNA showed that only fipronil caused fragmentation of this molecule. Thus, we conclude that carvacrol and fipronil can present similar toxicity at higher concentrations. However, acetylation of carvacrol significantly reduced its toxicity to human blood cells compared with the other chemicals.

Temperature-Dependent Bioaccumulation, Metabolism, and Hepatotoxicity of Flufiprole in Lizards (Eremias argus)

As a phenylpyrazole insecticide, flufiprole is an important substitute for fipronil in the agricultural field of China. However, its bioaccumulation and metabolism in terrestrial organisms especially in the lizards living in the agricultural area have rarely been investigated. As an ectothermic animal, lizards are also sensitive to temperature changes. Considering global warming, this study measured bioaccumulation, metabolism, and hepatotoxicity of flufiprole in the Chinese native lizard (Eremias argus) under different temperature stresses. Lizards exposed to flufiprole-contaminated soil adsorbed flufiprole through the skin and flufiprole was preferred to accumulate in lizard liver and brain. The oxidation product fipronil sulfone was the main metabolite of flufiprole in both lizard liver and human liver microsomes, which were mainly metabolized by lizard CYP3A19 or human CYP3A4. The fipronil sulfone concentration increased with increased temperature in lizard tissues. In addition, more serious oxidative damage was shown under higher temperature as the glutathione (GSH), malondialdehyde (MDA), and 8-hydroxy-2'-deoxyguanosine (8-OHdG) levels in lizards increased with increased temperature after flufiprole exposure. Flufiprole exposure also induced lizard liver lesions, and these lesions became more serious in the higher-temperature groups. This study provided new insights into the risk assessment of flufiprole in lizards under global warming.

To flea or not to flea: survey of UK companion animal ectoparasiticide usage and activities affecting pathways to the environment

Due to the convenience and efficacy of modern ectoparasiticides, routine prophylactic use has become commonplace for dogs and cats. However, the environmental consequences of this large-scale use are not well-understood, and multiple potential pathways for ectoparasiticides to the environment exist. Of particular concern is the potential for topically applied ectoparasiticides to pass to waterways, both down-the-drain via wastewater treatment plants and directly through swimming. In this online cross-sectional survey of 1,009 UK cat and dog owners, we investigated ectoparasiticide usage and the frequency of activities that are likely to result in transfer of the active substance to the environment, with a focus on pathways to waterways. A total of 603 dog owners and 406 cat owners completed the survey. Amongst dog and cat owners, 86.1% and 91.1% had administered an ectoparasiticide treatment to their pet in the preceding 12 months. Imidacloprid was the most frequently administered ectoparasiticide in both cats and dogs, followed by fluralaner in dogs and fipronil in cats. Eighty-four percent of owners who applied topical ectoparasiticides to their dog said they were aware of product warnings regarding swimming and bathing after application. Spot-on treated dogs were reported to swim significantly less frequently than non spot-on treated dogs (p = 0.007); however, 36.2% were reported to swim at least monthly. Similarly, significant differences were found in bathing frequency between spot-on treated and non spot-on treated dogs, with treated dogs less likely to be bathed at frequent (weekly) intervals, however 54.6% were reported to be bathed at least monthly. Washing of bedding was unaffected by ectoparasiticide treatment, and 87.8% of dog owners and 69.1% of cat-owners reported washing their pet's bedding at least every 3 months, suggesting that residue washoff from bedding may be occurring for most topically treated animals. Results suggest that transfer of ectoparasiticides to the environment is likely to occur for many of the millions of animals treated annually in the UK, with imidacloprid spot-on treated dogs estimated to swim, be bathed and have their bedding washed over 3.3 million, 5 million and 6.3 million times per year, respectively.

Metabolism of an insecticide fipronil by soil fungus Cunninghamella elegans ATCC36112

In this study, the metabolic pathway of the phenylpyrazole insecticide fipronil in Cunninghamella elegans (C. elegans) was investigated. Approximately 92% of fipronil was removed within 5 days, and seven metabolites were accumulated simultaneously. The structures of the metabolites were completely or tentatively identified by GC-MS and ¹H, ¹³C NMR. To determine the oxidative enzymes involved in metabolism, piperonyl butoxide (PB) and methimazole (MZ) were used, and the kinetic responses of fipronil and its metabolites were determined. PB strongly inhibited fipronil metabolism, while MZ weakly inhibited its metabolism. The results suggest that cytochrome P450 (CYP) and flavin-dependent monooxygenase (FMO) may participate in fipronil metabolism. Integrated metabolic pathways can be inferred from the control and inhibitor experiments. Several novel products from the fungal transformation of fipronil were identified, and similarities between C. elegans transformation and mammalian metabolism of fipronil were compared. Therefore, these results will help to gain insight into the fungal degradation of fipronil and potential applications in fipronil bioremediation. At present, microbial degradation of fipronil is the most promising approach and maintains environmental sustainability. In addition, the ability of C. elegans to mimic mammalian metabolism will assist in illustrating the metabolic fate of fipronil in mammalian hepatocytes and assess its toxicity and potential adverse effects.

Toxicological effects of fipronil on laying hens and its residue elimination in eggs

Eighty 24-week-old laying hens were divided into eight groups, seven given a single oral dose per chicken with 7 dosing levels from 13.6 to 137 mg/kg body weight (bw) and one serving as sham control. The hens were observed for 28 days for clinical abnormalities, egg yield, and body weight. Egg samples from groups of low-to-medium doses were analyzed for residues of fipronil and its metabolites by LC-MS/MS. Blood and organ samples from hens of the group receiving 63.3 mg/kg bw were collected for hematochemical and histopathological analysis. We found that the median lethal dose (LD₅₀) of fipronil was 74 mg/kg bw for laying hens. No death occurred, and there were no obvious changes in body weight and egg production in the hens receiving doses at or below 20 mg/kg bw. In the hens that survived exposure to the dose at 63.3 mg/kg bw, there was significant reduction in body weight and egg yield; histopathological changes in the liver and kidney; and increased levels of creatine, urea, glutamate oxaloacetate transferase, and glutamate pyruvic transaminase. Fipronil-sulfone was the residual marker in eggs with significantly higher concentrations and longer withdrawal periods than its maternal compound. We conclude that fipronil is efficiently transformed into fipronil-sulfone in the body with subsequent excretion into eggs. More attention should be paid to the potential food safety risk of fipronil-sulfone because of its persistence in eggs.

Pet dogs transfer veterinary medicines to the environment

Worldwide, the number of pet dogs increases yearly, and as a result so does the use of veterinary medicines for flea and tick control. We investigated the potential transfer of veterinary flea products from dogs to the environment in a 'proof of principle' experiment. For this purpose, samples of hair, urine, and water after swimming were investigated. Nine dogs were recruited for this study, eight of which had been recently treated with an ectoparasiticide product. Hair and urine samples were tested for afoxalaner, fluralaner, fipronil and imidacloprid. Interestingly, contamination with ectoparasiticides was frequently demonstrated in samples from dogs untreated with these particular substances, suggesting widespread secondary transfer. In addition, hair retrieved from a bird's nest contained fipronil, fluralaner and imidacloprid, indicating a potential pathway for the exposure of juvenile birds. Three of the dogs also participated in a swimming experiment. One had been treated with oral fluralaner, whilst the remaining two had received other compounds not included in our study. However, in all three dogs, both fluralaner and imidacloprid were detected in hair samples. Fluralaner concentrations in the swimming water exceeded Dutch water quality standards, indicating a potential risk to the aquatic environment. Imidacloprid levels increased after each swimming dog, but did not breach Dutch water quality standard levels. These findings all call for improvements in the current risk assessment and management for veterinary medicines, by including companion animals and their exposure pathways into ecosystems.

Fipronil and its metabolites in chicken feather: residue analysis, depletion study, and application analysis of pollution sources in laying hens

A method based on a multi-mechanism impurity adsorption and ultra-performance liquid chromatography-tandem mass spectrometry was established to detect fipronil and four of its metabolites in chicken feathers. This method was successfully applied to the depletion study of fipronil in feathers of laying hens. Fipronil and two metabolites were found in feathers during treatment. Fipronil concentrations in feathers increased during medication and then regularly decreased during withdrawal, and they were still detected on the 14th day after withdrawal. High residue concentrations were also present in feathers on day 23 of the experimental period. Pollution sources of fipronil can be inferred on the basis of the residue ratio of fipronil metabolites from different pollution modes. Result shows that feathers were an effective matrix for residue monitoring and risk analysis of fipronil in animals and the environment.

Ameliorative effects of the phytochemicals in dates (Phoenix dactylifera) against the toxicological changes induced by fipronil in male albino rats

Scientific evidence has shown that fipronil induces oxidative stress and genotoxicity. Our study aimed to evaluate the potential oxidation in redox parameters and DNA, as well as determine the protective effect of date extract of increasing resistance to cellular damage. 30 Male albino rats were divided into six groups ( n = 5): 1) control group; 2) treatment group with date extract (1 g/kg B.W.); 3) treatment group with 1/20 LD50 of fipronil; 4) treatment group with 1/40 LD50 of fipronil; 5) treatment group with 1/20 LD50 of fipronil + 1 g/kg date extract; and 6) treatment group with 1/40 LD50 of fipronil + 1 g/kg dates extract. Date extract showed a high content of phenolic compounds and antioxidant properties. Fipronil increased 8-hydroxy-2-deoxyguanosine levels and lipid peroxidation by malondialdehyde but decreased the total antioxidant capacity in plasma. Moreover, glutathione, catalase, and superoxide dismutase levels in the liver and kidney decreased, along with histopathological abnormalities. Additionally, tail moment parameters of liver DNA and micronucleus frequencies in the bone marrow increased. This study showed that fipronil-induced various health hazards in vivo, whereas date extract alleviated the said toxicological effects. However, date extract failed to reduce genotoxicity.

Fipronil and fipronil sulfone in chicken: From in vitro experiments to in vivo PBK model predictions

In 2017 a large-scale fipronil contamination in eggs occurred in several European countries. Fipronil and its metabolites have the potential to be transferred into the eggs of laying hens, thereby entering the human food chain. Here, first the metabolism of fipronil was measured in vitro using chicken liver S9. The results show that fipronil is mainly metabolised into fipronil sulfone and the clearance obtained in vitro was extrapolated to in vivo liver clearance. In a second step a physiologically based kinetic model was developed with a focus on fipronil and its major sulfone metabolite and the model outcome was compared to available in vivo data in eggs from the literature. The experimentally obtained clearance was used as model input to evaluate whether such an in vitro-based model can be used in an early phase of a contamination incident to predict the time-concentration curves. Overall, all model predictions were within a 10-fold difference and the estimated elimination half-life for fipronil equivalents was 14 days. In vitro experiments are definitely recommended compared to in vivo studies, since they provide a fast first insight into the behaviour of a chemical in an organism.

Fipronil and its metabolites in human seminal plasma from Shijiazhuang, north China

Fipronil (FP) is an emerging insecticide which could induce reproductive toxicity in male rats at very low dosage, but the occurrence of FP and its transformation products (FPs) in human seminal plasma and their impacts on human semen quality have not been documented. In this study, FPs including FP, fipronil desulfinyl (FP-DES), fipronil sulfone (FP-SFO), fipronil amide (FP-AM), and fipronil sulfide (FP-SFI), were measured in seminal plasma samples (n = 200), which were collected from Shijiazhuang, north China. The cumulative concentration of FPs (ΣFPs), in the seminal plasma samples ranged from 0.003 to 0.180 ng/mL (median: 0.043 ng/mL). FP-SFO was the major target analyte (median: 0.040 ng/mL), accounting for approximately 42.3-100.0% of the ΣFPs. Significantly higher exposure levels of FPs were found in the overweight or obese group (≥25 kg/m²) vs. the normal BMI group (18.5-25 kg/m²) (ΣFPs: 0.047 vs. 0.033 ng/mL), never smoking group vs. current smoking group (ΣFPs: 0.057 vs. 0.037 ng/mL), and low sexual frequency group (<1 time/week) vs. high sexual frequency group (≥3 times/week) (ΣFPs: 0.048 vs. 0.030 ng/mL). No significant association between FPs and impaired semen quality parameter was found in this study. This is the first time to report FPs' occurrence in human seminal plasma and variations in their concentrations among people with different demographic and behavioral characteristics. Further studies on adverse effects of exposure to FPs on reproductive function are needed.

Chiral resolution of the insecticide fipronil enantiomers and the simultaneous determination of its major transformation products by high-performance liquid chromatography interfaced with mass spectrometry

A high-performance liquid chromatography-mass spectrometry (HPLC-MS) method was developed using a chiral column based on amylose tris(3-chloro-5-methylphenylcarbamate) for analysis of fipronil (a popular insecticidal nerve agent) and the related transformation products. The optimized method reached the goal of the simultaneous and complete separation of the multiple fiproles in a single run, including the chiral separation of fipronil enantiomers, fipronil metabolites, and photoproducts. The efficacy of such a method was demonstrated by its application in analyzing a series of fipronil samples exposed to sunlight conditions. In general terms, our study provided experimental approaches and an efficient analytical tool for monitoring the environmental fate of fipronil as well as its multitransformation products upon its applications either in agricultural or any other areas.

Tracking the environmental fate of fipronil and three of its metabolites in garlic based on sampling rate-corrected in vivo solid phase microextraction combined with gas chromatography-mass spectrometry

In this study, a sampling rate-corrected in vivo solid-phase microextraction-gas chromatography-mass spectrometry method (SR-in vivo SPME-GC-MS) was constructed to simultaneously detect fipronil and three of its metabolites in garlic, and their environmental behavior was long-term monitored in in vivo mode. All of three fipronil metabolites were more difficult to degrade than the parent pesticide. The final degradation rates of the metabolites in garlic were in the range of 4.4%-25.1%, much lower than that of the parent (78.6%-85.8%). While their total residues amount was about 3 times as high as fipronil, exceeding the maximum residue limits regulated by China and the European Union. The steady-state concentrations of fipronil and its metabolites in garlic were positively correlated with the pesticide stress dose. In short, the established in vivo tracking method is efficient and convenient. The features of simple operation, fast analysis, acceptable sensitivity, non-harmful or non-lethal to plants, available repeated and long-term monitoring of the same organism make it attractive for in vivo tracking assay, it is of great significance for the guidance of rational use of fipronil and protection of food safety.

Cu(II)-Mediated aerobic oxidative synthesis of 2-sulfonylated chromeno[4,3-c]pyrazol-4(2H)-ones

Herein, a concise and facial synthesis of 2-sulfonylated chromeno [4,3-c]pyrazol-4(2H)-ones and 2,5-dihydro-4H-pyrazolo[4,3-c]quinolin-4-ones via a Cu(II)-promoted aerobic oxidative cascade C–C/C–N bonds formations was described. The protocol has advantages of atom economy,...

Insecticide fipronil and its transformation products in human blood and urine: Assessment of human exposure in general population of China

Fipronil (FP) is widely used as a highly effective insecticide worldwide, thereby raising concern about environmental contamination and risk for human health. However, data on the occurrence of FP and its transformation products (FPs) in human blood and urine are limited. In this study, 39 pairs of serum, plasma, blood cells (BCs), and urine samples were collected from adults in Wuhan, central China (2020), in order to characterize the concentration profiles of FPs in different matrices. FPs were also determined in serum samples (n = 226, including 57, 56, 56, and 57 samples for Wuhan, Huangshi, Nanjing, and Zhenjiang, respectively) collected from four cities of China (2015) to characterize the exposure levels of FPs among the general population and potential spatial variations. Fipronil sulfone (FP-SFO) was 100% detectable in blood samples, and it was the predominant metabolite (accounting for 86-95% of the cumulative concentrations of FPs [ΣFPs]), with the median concentrations (ng/mL) of 0.17, 0.16, and 0.03 in serum (range: 0.07-1.53), plasma (range: 0.06-1.41), and BCs (range: 0.01-0.24), respectively. The compositional profiles of FPs in serum, plasma, and BCs were similar; very strong positive correlations were observed between different blood matrices for FP-SFO (r = 0.94-0.97, p < 0.01) but not between blood and urine. The median ΣFPs (ng/mL) in the serum (0.20; range: 0.09-1.56) and the plasma samples (0.19; range: 0.09-1.43) was higher than that in BCs samples (0.04; range: 0.01-0.24). In the urine samples, only the major metabolite FP-SFO was detectable in approximately 10% of the samples. Additionally, the highest median ΣFPs (ng/mL) in the serum samples was found in Nanjing (0.56; range: 0.13-1.88), followed by Wuhan (0.34; range: 0.06-1.02), Huangshi (0.10; range: 0.03-0.60), and Zhenjiang (0.08; range: 0.02-0.42). The level of ΣFPs seemed to increase with city sizes and urbanization scale, though further studies are needed to confirm the variations with larger sample size. The estimated daily intake of ΣFPs based on the median concentration of samples from Nanjing (18.5 ng/kg-bw/d) was higher than that of Wuhan (11.3), Huangshi (3.40), and Zhenjiang (2.80). Dietary intake should be the major exposure route for the general population, while water or indoor dust accounted for <1% of the ΣFPs intake. This pilot study provided the first data on the profiles of FPs in paired human serum, plasma, BCs, and urine samples, and potential spatial variations of ΣFPs in China. FP-SFO and FP desulfinyl should be considered among priority substances worthy to be bio-monitored in China due to its moderated persistence and ubiquitous occurrence in human blood.

Fipronil induced oxidative stress in neural tissue of albino rat with subsequent apoptosis and tissue reactivity

Fipronil (FIP) insecticide is extensively used in agriculture, public health and veterinary medicine. Although it is considered as a neurotoxin to insects (target organisms) and exhibits neurological signs upon vertebrates (non-target organisms) exposure, slight is known about its potential neurotoxic effects and its molecular mechanisms on vertebrates. The current study is designed to assess oxidative stress as a molecular mechanism of FIP neurotoxicity subordinated with apoptosis and neural tissue reactivity. Ten adult male albino rats received 10 mg/kg body weight fipronil technical grade by oral gavage daily for 45 days (subacute exposure). Brain neural tissue regions (hippocampus, cerebellum and caudate putamen) were processed to examine oxidative stress induced cellular macromolecular alterations as MDA, PCC and DNA fragmentation. Besides, TNF-α and Bcl-2 gene expression and immunoreactivity for caspase-3 (active form), iNOS and GFAP were evaluated. Also, histopathological assessment was conducted. We found that FIP significantly raised MDA, PCC and DNA fragmentation (p ≤ 0.05). Also, it significantly upregulated TNF-α and non-significantly down-regulated Bcl-2 gene expression (p ≤ 0.05). Further, significant increased immunoreactivity to GFAP, iNOS and caspase-3 (active form) in these brain neural tissue regions in FIP treated group was noticed (p ≤ 0.05). Histopathological findings, including alterations in the histological architecture and neuronal degeneration, were also observed in these brain regions of FIP treated group. In conclusion, we suggest the ability of FIP to induce oxidative stress mediated macromolecular alterations, leading to apoptosis and tissue reaction in these brain regions which showed variable susceptibility to FIP toxic effects.

Boswellia serrata suppress fipronil-induced neuronal necrosis and neurobehavioral alterations via promoted inhibition of oxidative/inflammatory/apoptotic pathways

Boswellic acid (BA) is a pentacyclic terpenoid derived from the gum-resin of Boswellia serrate. It is known for its strong antioxidant, anti-inflammatory, and anticancer properties. It has improved spatial learning and provides neuroprotection against trimethyltin-induced memory impairment. The aim of this study is to evaluate the possible neuroprotective activity of B. serrata extract (BSE) containing BA against fipronil (FPN)-induced neurobehavioral toxicity in Wister male albino rats. Sixty male rats were allocated equally into six groups. The first group served as control; the second and third groups received BSE at two different oral doses (250 or 500 mg/kg body weight [BW], respectively). The fourth group was orally intoxicated with FPN (20 mg/kg BW), whereas the fifth and sixth groups served as preventive groups and co-treated with FPN (20 mg/kg BW) and BSE (250 or 500 mg/kg BW, respectively). The experiment was conducted over 8 weeks period. Results revealed that co-treatment with BSE led to significant (p > 0.05) dose-dependent reduction in malondialdehyde (MDA), nitric oxide (NO), interleukin-6 (IL6), tumor necrosis factors-alpha (TNF-α), nuclear factor Kappa-B (NF-κB), Cyclooxegenase-2 (COX-2), prostaglandin E2 (PGE2), serotonin, and acetylcholine (ACh). Conversely, significant (p > 0.05) up regulation of catalase (CAT), glutathione peroxidase (GSH-Px), gamma-aminobutyric acid (GABA), and acetylcholine esterase (AChE) has reported in BSE-co-treated groups. In addition, significant (p > 0.05) promotion in neurobehaviours, histopathologic imaging of the cerebral, cerebellar, and hippocampal regions, and immunohistochemical expression of caspase-3 and glial fibrillary acidic protein (GFAP) were also reported in the BSE-treated groups in a dose-dependent manner. In conclusion, BSE (500 mg/kg BW) is a natural, promising neuroprotective agent that can mitigate FPN-induced neurobehavioral toxicity via the suppression of oxidative, inflammatory, and apoptotic pathways and relieve neuronal necrosis and astrogliosis.

A comprehensive review of environmental fate and degradation of fipronil and its toxic metabolites

The use of pesticides to increase crop production has become one of the inevitable components of modern agriculture. Fipronil, a phenylpyrazoles insecticide, is one of the most widely used, systemic, broad-spectrum insecticides. Owing to its unique mode of action and selective toxicity, it was once regarded as safer alternatives to more toxic and persistent organochlorine insecticides. However, with the increased use, many studies have reported the toxicity of fipronil and its metabolites in various non-target organisms during the last two decades. Currently, it is regarded as one of the most persistent and lipophilic insecticides in the market. In the environment, fipronil can undergo oxidation, reduction, hydrolysis, or photolysis to form fipronil sulfone, fipronil sulfide, fipronil amide, or fipronil desulfinyl respectively. These metabolites except fipronil amide are more or less toxic and persistent than fipronil and have been reported from diverse environmental samples. Recently many studies have focused on the degradation and removal of fipronil residues from the environment. However, a comprehensive review summarizing and combining these recent findings is lacking. In the present review, we evaluate, summarize, and combine important findings from recent degradation studies of fipronil and its metabolites. An attempt has been made to elucidate the possible mechanism and pathways of degradation of fipronil and its toxic metabolites.

Oral pharmacokinetic profile of fipronil and efficacy against flea and tick in dogs

Fipronil (FIP) is an ectoparasiticide of the phenylpyrazole class, used in veterinary medicine in topical form. Supported by evidence of uncontrolled human exposure to FIP and environmental damage caused by commercially available formulations, its use by oral administration has become promising. The effectiveness of FIP against the flea Ctenocephalides felis felis and the tick Rhipicephalus sanguineus and its pharmacokinetics and main active metabolite, fipronil sulfone (SULF) were evaluated after single oral administration of tablets in three different doses (2, 4, and 6 mg/kg) in dogs. Through the plasma concentration curves, it was possible to observe that the FIP showed rapid absorption and metabolization and slow elimination. The values of C_max (β = 0.7653) and AUC_{0- t} (β = 0.3209) did not increase proportionally with increasing dose. At 48 h after treatment, doses of 4 mg/kg (AUC_{0- t}  = 442.39 ± 137.35 µg/ml*h) and 6 mg/kg (AUC_{0- t}  = 421.32 ± 102.84 µg/ml*h) provided 100% and 99% efficacy against fleas, and 95% and 98% against ticks, respectively. The estimated EC₉₀ of FIP +SULF was 1.30 µg/ml against C. felis felis and 2.16 µg/ml against R. sanguineus. The correlation between the FIP pharmacokinetic and efficacy data demonstrated its potential for oral administration in the form of tablets for the control of ectoparasites in dogs, as a safer alternative for animals, humans, and the environment, aligned with the One Health concept.

Neurotoxic Effect of Fipronil in Male Wistar Rats: Ameliorative Effect of L-Arginine and L-Carnitine

Simple Summary

Insecticides are widely used in agricultural and household environments. They induce wide range of deleterious effects. Fipronil is one of the most widely used phenylpyrazoles insecticides. The neurotoxic effect of such insecticide was tested in the present study with special emphasis on cognitive deficit as well as testing the possible ameliorative impacts of L-arginine and L-carnitine. The study proposed fipronil-induced cognitive deficit as a reflection to oxidative stress and neuro-inflammation. Moreover, L-arginine and L-carnitine exerted ameliorative influence on fipronil induced oxidative stress and neuro-inflammation. Therefore, L-arginine and L-carnitine can be considered as prospective candidates for mitigation of pesticide induced neurotoxicity especially in people with high-risk exposure to pesticide.

Abstract

The ameliorative effect of L-arginine (LA) and L-carnitine (LC) against fipronil (FPN)-induced neurotoxicity was explored. In this case, 36 adult male rats were randomly divided into six groups: group I received distilled water, group II received 500 mg/kg LA, group III received 100 mg/kg LC, group IV received 4.85 mg/kg FPN, group V received 4.85 mg/kg FPN and 500 mg/kg LA and group VI received 4.85 mg/kg FPN and 100 mg/kg LC for 6 weeks. Cognitive performance was assessed using Barnes maze (BM). Serum corticosterone, brain total antioxidant capacity (TAC), malondialdehyde (MDA) and dopamine were measured. Histopathology and immunohistochemistry of ionized calcium-binding adaptor (Iba-1), doublecortin (DCX) and serotonin (S-2A) receptors were performed. Fipronil induced noticeable deterioration in spatial learning and memory performance. In addition, FPN significantly (p < 0.05) diminished brain antioxidant defense system and dopamine coincide with elevated serum corticosterone level. Histopathological examination revealed degenerative and necrotic changes. Furthermore, Iba-1 and DCX were significantly expressed in cortex and hippocampus whereas S-2A receptors were significantly lowered in FPN group. However, administration of LA or LC alleviated FPN-induced deteriorations. In conclusion, LA and LC could be prospective candidates for mitigation of FPN-induced neurotoxicity via their antioxidant, anti-inflammatory and neuropotentiating effects.

Transition Metal-Free De Novo Synthesis of Sulfonated Pyrazoles from Sulfonyl Hydrazides, 1,3-Diketones, and Sodium Sulfinates at Room Temperature

A transition metal-free method for de novo construction of diverse sulfonated pyrazoles from readily available sulfonyl hydrazides, 1,3-diketones, and sodium sulfinates was established under mild conditions. Pyrazoles bearing two different sulfonyl groups were obtained in one step. The method features a diversity of substituents of the pyrazole products and a remarkably simple work-up.

Mitochondrial and transcriptome responses in rat dopaminergic neuronal cells following exposure to the insecticide fipronil

The phenylpyrazole fipronil is an insecticide that inhibits γ -amino-butyric acid (GABA) ionotropic receptors in the central nervous system. Experimental evidence suggests that fipronil acts as a neurotoxin and it is implicated in neurodegenerative diseases; however, the mechanisms of neurotoxicity are not fully elucidated. The objective of this study was to quantify mechanisms of fipronil-induced neurotoxicity in dopamine cells. Rat primary immortalized mesencephalic dopaminergic cells (N27) were treated with fipronil (0.25 up to 500 μM depending on the assay). We measured endpoints related to mitochondrial bioenergetics, mitophagy, mitochondrial membrane potential, and ATP production in addition to discerning transcriptome responses to the pesticide. Fipronil reduced cell viability at 500 μM after 24 h exposure and caspase 3/7 activity was significant increased after 6 and 12 h by 250 and 500 μM fipronil. Subsequent endpoints were thus assessed at concentrations that were below cytotoxicity. We measured oxidative respiration of N27 cells following a 24 h exposure to one dose of either 0.25, 2.5, 25, or 50 μM fipronil. Oxygen consumption rates (OCR) were not different between vehicle-control and 0.25 or 2.5 μM fipronil treatments, but there was a ∼40-60 % reduction in basal respiration, as well as reduced oligomycin-induced ATP production at 50 μM. The reduction in OCR is hypothesized to be related to lower mitochondrial mass due to mitophagy. Mitochondrial membrane potential was also sensitive to fipronil, and it was compromised at concentrations of 2.5 μM and above. To further elucidate the mechanisms linked to neurotoxicity, we conducted transcriptomics in dopamine cells following treatment with 25 μM fipronil. Fipronil suppressed transcriptional networks associated with mitochondria (damage, depolarization, permeability, and fission), consistent with its effects on mitochondrial membrane potential. Altered gene networks also included those related to Alzheimer disease, inflammatory disease, nerve fiber degeneration, and neurofibrillary tangles. This study clarifies molecular targets of fipronil-induced neurotoxicity and supports, through multiple lines of evidence, that fipronil acts as a mitochondrial toxicant in dopamine cells. This is relevant to neurodegenerative diseases like Parkinson's disease as exposure to fipronil is associated with the progressive loss of nigrostriatal dopaminergic neurons in rodents.

Developmental Neurotoxicity of Fipronil and Rotenone on a Human Neuronal In Vitro Test System

Pesticide exposure during in utero and early postnatal development can cause a wide range of neurological defects. However, relatively few insecticides have been recognized as developmental neurotoxicants, so far. Recently, discovery of the insecticide, fipronil, in chicken eggs has raised public concern. The status of fipronil as a potential developmental neurotoxicant is still under debate. Whereas several in vivo and in vitro studies suggest specific toxicity, other in vitro studies could not confirm this concern. Here, we tested fipronil and its main metabolic product, fipronil sulfone both at concentrations between 1.98 and 62.5 µM, alongside with the established developmental neurotoxicant, rotenone (0.004-10 µM) in vitro on the human neuronal precursor cell line NT2. We found that rotenone impaired all three tested DNT endpoints, neurite outgrowth, neuronal differentiation, and precursor cell migration in a dose-dependent manner and clearly separable from general cytotoxicity in the nanomolar range. Fipronil and fipronil sulfone specifically inhibited cell migration and neuronal differentiation, but not neurite outgrowth in the micromolar range. The rho-kinase inhibitor Y-27632 counteracted inhibition of migration for all three compounds (EC50 between 12 and 50 µM). The antioxidant, n-acetyl cysteine, could ameliorate the inhibitory effects of fipronil on all three tested endpoints (EC 50 between 84 and 164 µM), indicating the involvement of oxidative stress. Fipronil sulfone had a stronger effect than fipronil, confirming the importance to test metabolic products alongside original pesticides. We conclude that in vitro fipronil and fipronil sulfone display specific developmental neurotoxicity on developing human model neurons.

Oral and topical extra-label administration of fipronil to laying hens: Assessment of the egg residue patterns

This experimental work reproduces the fipronil extra-label administration performed by producers in laying hens. The scientific goal was to characterize the residual concentrations in eggs from treated hens and suggest the withdrawal periods that should be respected to avoid risk for consumers. Thirty-four laying hens were allocated into two groups: Group A was treated with fipronil in feed, two single doses of 1 mg kg^-1  day^-1 ; Group B was administered a single dose of 1 mg kg^-1 by the topical route. Fipronil egg residues were quantified by HPLC-MS/MS. Fipronil and its sulphone metabolite (fipronil-SO₂ ) were measured in egg after both treatments. The highest egg residual profile was always for fipronil-SO₂ . Mean maximum egg concentrations (C_max ) of 228.5 ± 79.8 ng/g (fipronil) and 1,849 ± 867 ng/g (fipronil-SO₂ ) were found after fipronil administration in feed. The lowest residual levels were quantified after the topical treatment with C_max of 27.1 ± 4.9 and 163 ± 26 ng/g for fipronil and fipronil-SO₂ . Mean fipronil marker residues and established MRLs allowed calculating the withdrawal periods, the shortest being 74 days after topical administration. Such a long withdrawal period is difficult to meet in egg production systems. Thus, the extra-label use of fipronil in laying hens should not be recommended under any circumstances.

An update of the Worldwide Integrated Assessment (WIA) on systemic insecticides. Part 1: new molecules, metabolism, fate, and transport

With the exponential number of published data on neonicotinoids and fipronil during the last decade, an updated review of literature has been conducted in three parts. The present part focuses on gaps of knowledge that have been addressed after publication of the Worldwide Integrated Assessment (WIA) on systemic insecticides in 2015. More specifically, new data on the mode of action and metabolism of neonicotinoids and fipronil, and their toxicity to invertebrates and vertebrates, were obtained. We included the newly detected synergistic effects and/or interactions of these systemic insecticides with other insecticides, fungicides, herbicides, adjuvants, honeybee viruses, and parasites of honeybees. New studies have also investigated the contamination of all environmental compartments (air and dust, soil, water, sediments, and plants) as well as bees and apicultural products, food and beverages, and the exposure of invertebrates and vertebrates to such contaminants. Finally, we review new publications on remediation of neonicotinoids and fipronil, especially in water systems. Conclusions of the previous WIA in 2015 are reinforced; neonicotinoids and fipronil represent a major threat worldwide for biodiversity, ecosystems, and all the services the latter provide.

A facile, sensitive and rapid sensing platform based on CoZnO for detection of fipronil; an environmental toxin

A sensitive detection of extremely toxic phenylpyrazole insecticide, 'Fipronil' is presented. Currently, the advancement of approaches for the detection of insecticides at low concentrations with less time is important for environmental safety assurance. Considering this fact, an effort has been made to develop an electrospun CoZnO nanofiber (NF) based label-free electrochemical system for the detection of fipronil. The CoZnO NF were characterized using different techniques including field emission scanning electron microscopy (FE-SEM), Energy Dispersive X-Ray Analysis (EDX), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and Raman Spectroscopy. Based on the experimental results, the proposed platform displayed a linear response for fipronil in the attogram/mL range despite the multiple interfering agents. The sensitivity of the device was found to be 3.99 Kῼ (g/ml)^-1 cm^-2. Limit of detection (LOD) and limit of quantification (LOQ) were calculated and found to be 112 ag mL^-1 and 340 ag mL^-1 respectively. Further, this proposed sensor will be implemented in the fields for the rapid and proficient detection of the real samples.

Multi-organ characterisation of B-esterases in the European sea bass (Dicentrarchus labrax): Effects of the insecticide fipronil at two temperatures

In fish, the study of cholinesterases (ChEs) and carboxylesterases (CEs), apart from their involvement in neural activity and xenobiotic metabolism, respectively, requires to be further explored. The European sea bass (Dicentrarchus labrax) was the fish model used to characterise B-esterases in several matrices and organs, as well as to assess the impacts of the insecticide fipronil at two temperatures: the natural temperature at the time of sampling (13 °C) and at 16 °C (based on climate change-related predictions for the Mediterranean region). Fipronil exerts harmful effects in non-target species; however, some countries are reluctant to implement regulations without additional evidence on their toxicity. A comprehensive study was performed in fish pre-acclimated to the two targeted temperatures for 15 days. B-esterases were evaluated in multiple samples after 7 and 14 day exposures to fipronil in feed (dose of 10 mg/kg) and after a 7-day depurative period. Based on hydrolysis rates, results showed that CEs were measurable in all matrices while ChEs were more abundant in muscle and, particularly, acetylcholinesterase (AChE) in the brain. A + 3 °C increase in temperature had little influence on B-esterase activity; however, fipronil caused a significant increase in brain AChE (1.5-fold) and CE (3-fold) activities. Other matrices and organs also experienced alterations in their B-esterase activities that could compromise their physiological functions.

Preclinical Transplacental Transfer and Pharmacokinetics of Fipronil in Rats

Fipronil, a widely used insecticide and pesticide, with its toxic metabolite fipronil sulfone was detected in fipronil-contaminated eggs as a result of inappropriate use. However, little is known about whether fipronil and fipronil sulfone transfer into fetus through the blood-placenta barrier. Our objectives were to investigate the transplacental transfer and the pharmacokinetics of fipronil and fipronil sulfone in rats. Male and female (with 13 days of gestation) Sprague-Dawley rats were used in pharmacokinetics and transplacental transfer experiments, respectively. Biologic samples were collected at each time point after fipronil intravenous or oral administration. To monitor fipronil and fipronil sulfone in the plasma, placenta, amniotic fluid, and fetus, a validated liquid chromatography tandem mass spectrometry method was developed. After fipronil administration in male rats, the oral bioavailability decreased, whereas the biotransformation increased as the dose increased, revealing an enhancement of first-pass effect and a fast metabolism in vivo. The results of fipronil transplacental transfer in pregnant rats demonstrated that the concentration of fipronil and fipronil sulfone varied in the following order, respectively: placenta > plasma > fetus > amniotic fluid and plasma > placenta > fetus > amniotic fluid. This is the first direct evidence that fipronil and fipronil sulfone cross the blood placental barriers and enter the fetus. The amount of fipronil distributed to the fetus was greater than that of fipronil sulfone in the short term, but by contrast, pharmacokinetic data showed that the latter stayed longer in the body. These findings provide constructive information for public health alarm. SIGNIFICANCE STATEMENT: Fipronil and fipronil sulfone interfere with the GABAergic system. Fipronil can cause thyroid dysfunction, which may affect brain growth and nerve development. Although we knew that fipronil and fipronil sulfone could enter eggs, there was no direct evidence that they would enter fetuses. This research provided evidence on the pharmacokinetics and transplacental transfer of fipronil and fipronil sulfone, confirming our hypothesis.

Long-Term Fipronil Treatment Induces Hyperactivity in Female Mice

Fipronil is an insecticide widely used for veterinary and agricultural purposes. While its insecticidal properties mostly rely on its high affinity antagonistic activity on insect γ aminobutyric acid (GABA) receptors, fipronil and its main metabolite fipronil sulfone nevertheless display non-negligible affinity for mammalian GABAA receptor. As several environmental toxicants have been shown to raise the risk of developing various neurodegenerative disorders, the aim of this study was to evaluate whether long-term low dose administration of fipronil could lead to cognitive deficiencies. Our results indicate that long-term fipronil treatment leads to behavioral perturbations in mice, indicating an accumulative effect of sustained exposure to low dose of fipronil. Although no memory impairment was observed during the course of our study, we noticed a significant hyperlocomotion behavior after 43 weeks of weekly fipronil administration, which is consistent with its direct effect on the GABAergic system.

Implication of human drug transporters to toxicokinetics and toxicity of pesticides

Human membrane drug transporters are recognized as major actors of pharmacokinetics. Pesticides also interact with human drug transporters, which may have consequences for pesticide toxicokinetics and toxicity. The present review summarizes key findings about this topic. In vitro assays have demonstrated that some pesticides, belonging to various chemical classes, modulate drug transporter activity, regulate transporter expression and/or are substrates, thus bringing the proof of concept for pesticide-transporter relationships. The expected low human concentration of pesticides in response to environmental exposure constitutes a key-parameter to be kept in mind for judging the in vivo relevance of such pesticide-transporter interactions and their consequences for human health. Existing data about interactions of pesticides with drug transporters remain, however, rather sparse; more extensive and systematic characterization of pesticide-transporter relationships, through the use of high throughput in vitro assays and/or in silico methods, is, therefore, required. In addition, consideration of transporter polymorphisms, pesticide mixture effects and physiological and pathological factors governing drug transporter expression may help to better define the in vivo relevance of pesticide-transporter interactions in terms of toxicokinetics and toxicity for humans. © 2019 Society of Chemical Industry.

Transcriptomic modifications of the thyroid gland upon exposure to phytosanitary-grade fipronil: Evidence for the activation of compensatory pathways

Fipronil is a phenylpyrazole insecticide used for the control of a variety of pest for domestic, veterinary and agricultural uses. Fipronil exposure is associated to thyroid disruption in the rat. It increases thyroid hormone (TH) hepatic clearance. The effect on thyroxine (T4) clearance is about four fold higher than the effect on T4 plasma concentrations suggesting that the thyroid gland might develop compensatory mechanisms. The aim of this study was to document the potential effects of fipronil treatment on the thyroid transcriptome together with its effects on TSH and TH blood levels under well characterized internal exposure to fipronil and its main metabolite fipronil sulfone. Fipronil (3 mg/kg/d by gavage for 14 days) clearance increased while its half-life decreased (about 10 fold) throughout treatment. Fipronil treatment in adult female rats significantly decreased total T4 and free triiodothyronine (T3) concentrations. Key genes related to thyroid hormone synthesis and/or cellular dynamic were modulated by fipronil exposure. RT-PCR confirmed that thyroglobulin gene expression was upregulated. A trend toward higher Na/I symporter expression was also noted, while sulfotransferase 1a1 gene expression was down-regulated. The expression of genes potentially involved in thyroid cell dynamic were upregulated (e.g. prostaglandin synthase 1, amphiregulin and Rhoa). Our results indicate that both pathways of TH synthesis and thyroid cell dynamics are transcriptional targets of fipronil and/or its main sulfone metabolite. The underlying mechanisms remain to be elucidated.

Fipronil Tablets: Development and Pharmacokinetic Profile in Beagle Dogs

Increased human-pet interactions have led to concerns related to the prevention and treatment of ectoparasite infestations. Fipronil (FIP) is a widely used ectoparasiticide in veterinary medicine available for topical administration; however, its use may cause damage to the owners and the environment. The aim of the study was to develop immediate-release tablets of FIP, as well as to determine its pharmacokinetic properties after oral administration in beagle dogs. The prepared FIP tablets were evaluated for pre-compression (angle of repose, speed flow, and Carr's index) and post-compression (weight variation, friability, thickness, hardness, disintegration time, and dissolution rate) parameters. Orally administered FIP at a dose of 2 mg/kg was rapidly absorbed with C_máx of 3.13 ± 1.39 μg/mL at 1.83 ± 0.40 h post treatment (P.T.) and metabolized with 1.27 ± 1.04 μg/mL at 2.33 ± 0.82 h P.T. for fipronil sulfone (SULF) (the primary metabolite). The elimination of FIP and SULF occurred slowly and had maintained quantifiable plasma levels in the blood for up to 28 days P.T. The goal of the study is aligned with the concept of One Health, which aims to collaboratively achieve the best health for people, animals, and the environment. Therefore, the use of FIP tablets for the control of ectoparasites in dogs may be a safer alternative for owners and the environment.

A first approach using micellar electrokinetic capillary chromatography for the determination of fipronil and fipronil-sulfone in eggs

Fipronil is an insecticide that is not approved in the European Union in food. In 2017, fipronil was involved in a European health alert due to its presence in fresh hen eggs because of an illicit use in poultry farms, so reliable methods are needed to determine fipronil and its main metabolites in these matrixes. In this work, we report the first approach to the study of fipronil and two metabolites, fipronil-sulfone and fipronil-sulfide by CE. MEKC mode was employed using a solution of 50 mM ammonium perfluorooctanoate pH 9.0 with 10% (v/v) methanol as background electrolyte. The proposed method was combined with a simple sample treatment based on salting-out assisted LLE (SALLE) using acetonitrile as extraction solvent and ammonium sulfate as salt. The SALLE-MEKC-UV method allowed the simultaneous quantification of fipronil and fipronil-sulfone. Validation parameters yielded satisfactory results, with precision, expressed as relative SD, below 14% and recoveries higher than 83%. Limits of detection were 90 µg/kg for fipronil and 150 µg/kg for fipronil-sulfone, so in terms of sensitivity further studies of sample treatments allowing extra preconcentration or the use of more sensitive detection, such as MS, would be needed.

Garlic and allopurinol attenuate hepatic apoptosis induced by fipronil in male albino rats

Fipronil (FPN) can induce oxidative tissue damage and may be contemplated as an apoptosis inducer. Our aim is to investigate the possible hepatoprotective roles of garlic or allopurinol (ALP) against fipronil subacute toxicity. Thirty-six mature male albino rats were randomly divided into six groups; the first group was saved as control (C), the 2nd (G) was orally intubated with 500 mg/kg aqueous garlic extract, and the 3rd (A) received 150 mg/L allopurinol in their drinking water. The 4th group (F) was administered 13.277 mg/kg fipronil by gavage, while the 5th (G + F) and 6th (A + F) groups received the same doses of garlic and allopurinol, respectively two hours before fipronil intoxication. Our results revealed that FPN significantly increased the hepatic malondialdehyde, protein carbonyl levels, and the enzymatic activities of superoxide dismutase, catalase, glutathione peroxidase, and xanthine oxidase, but it decreased glutathione-S-transferase compared to the control group. Moreover, FPN exhibited significant up-regulation in the hepatic pro-apoptotic (Bax) and caspase-3 genes expression, down-regulation in the anti-apoptotic (Bcl-2) mRNA gene expression and induced DNA fragmentation. Surprisingly, garlic or allopurinol co-treatment ameliorated the hepatic lipid peroxidation, antioxidants disruption, and apoptosis induced by FPN. In conclusion, garlic and allopurinol relieved the oxidative injury and reduced the fipronil-induced apoptosis probably by improving the tissue antioxidant defense system.

Induction of Amyloid-β42 Production by Fipronil and Other Pyrazole Insecticides

Generation of amyloid-β peptides (Aβs) by proteolytic cleavage of the amyloid-β protein precursor (AβPP), especially increased production of Aβ42/Aβ43 over Aβ40, and their aggregation as oligomers and plaques, represent a characteristic feature of Alzheimer's disease (AD). In familial AD (FAD), altered Aβ production originates from specific mutations of AβPP or presenilins 1/2 (PS1/PS2), the catalytic subunits of γ-secretase. In sporadic AD, the origin of altered production of Aβs remains unknown. We hypothesize that the 'human chemical exposome' contains products able to favor the production of Aβ42/Aβ43 over Aβ40 and shorter Aβs. To detect such products, we screened a library of 3500 + compounds in a cell-based assay for enhanced Aβ42/Aβ43 production. Nine pyrazole insecticides were found to induce a β- and γ-secretase-dependent, 3-10-fold increase in the production of extracellular Aβ42 in various cell lines and neurons differentiated from induced pluripotent stem cells derived from healthy and FAD patients. Immunoprecipitation/mass spectrometry analyses showed increased production of Aβs cleaved at positions 42/43, and reduced production of peptides cleaved at positions 38 and shorter. Strongly supporting a direct effect on γ-secretase activity, pyrazoles shifted the cleavage pattern of another γ-secretase substrate, alcadeinα, and shifted the cleavage of AβPP by highly purified γ-secretase toward Aβ42/Aβ43. Focusing on fipronil, we showed that some of its metabolites, in particular the persistent fipronil sulfone, also favor the production of Aβ42/Aβ43 in both cell-based and cell-free systems. Fipronil administered orally to mice and rats is known to be metabolized rapidly, mostly to fipronil sulfone, which stably accumulates in adipose tissue and brain. In conclusion, several widely used pyrazole insecticides enhance the production of toxic, aggregation prone Aβ42/Aβ43 peptides, suggesting the possible existence of environmental "Alzheimerogens" which may contribute to the initiation and propagation of the amyloidogenic process in sporadic AD.

Distribution of fipronil in humans, and adverse health outcomes of in utero fipronil sulfone exposure in newborns

Fipronil is a highly effective insecticide with extensive usages; however, its distribution and toxic/health effects in the human population after chronic exposure have not yet been clearly identified. Our objectives were to determine the levels of serum fipronil and fipronil sulfone, a primary fipronil metabolite, in a general and sensitive human population using a birth cohort of parent-infant triads in Korea. We further investigated whether in utero exposure to fipronil and fipronil sulfone can affect health outcomes in newborn infants. Blood and umbilical cord blood from 169 participants, 59 mother-neonate pairs and 51 matching biological fathers, were collected; serum fipronil and fipronil sulfone (both blood and cord blood) and serum thyroid hormones (cord blood) were measured. Demographic, physiological, behavioral, clinical, and socioeconomic data for each participant were collected via a one-on-one interview and a questionnaire survey. Fipronil sulfone was detected in the serum of mothers, fathers, and infantile cord blood, while fipronil itself was not. Maternal fipronil sulfone levels were correlated to those of matched biological fathers and newborn infants. Adjusted analyses identified significant associations between parental fipronil sulfone levels and household income. Infantile fipronil sulfone levels were significantly associated with both maternal and paternal levels as well as maternal pre-pregnant BMI. Furthermore, infantile fipronil sulfone levels were inversely associated with cord blood T3 and free T3 levels as well as 5-min Apgar scores of newborn infants. Serum fipronil sulfone was detected in a specific population of mother-neonate pairs and their matched biological fathers in a manner suggestive of regular exposure to fipronil among urban residents. The findings also suggest that serum fipronil sulfone placentally transfers to the fetus and affects infantile adverse health outcomes. This is a first of its kind study; therefore, future studies are warranted.

Quantitative Detection of Fipronil and Fipronil-Sulfone in Sera of Black-Tailed Prairie Dogs and Rats after Oral Exposure to Fipronil by Camel Single-Domain Antibody-Based Immunoassays

The insecticide fipronil can be metabolized to its sulfone in mammalian species. Two camel single-domain antibodies (VHHs) F1 and F6, selective to fipronil and fipronil-sulfone, respectively, were generated and used to develop enzyme linked immunosorbent assays (ELISAs) for the detection of the two compounds in the sera of black-tailed prairie dogs and rats. The limits of detection of fipronil and fipronil-sulfone in the rodent sera by the corresponding ELISAs were 10 and 30 ng mL-1, and the linear ranges were 30-1000 and 75-2200 ng mL-1. ELISAs showed a good recovery for fipronil and fipronil-sulfone cospiked in the control sera of the black-tailed prairie dogs (90-109%) and rats (93-106%). The VHH-based ELISAs detected fipronil and fipronil-sulfone in the sera of the rodents that received a repeated oral administration of fipronil. The average concentration of fipronil-sulfone was approximately 3.2-fold higher than fipronil in the prairie dog sera (1.15 vs 0.36 μg mL-1) and rat sera (1.77 vs 0.53 μg mL-1). ELISAs agreed well with a liquid chromatography-mass spectrometry method for the quantification of both fipronil and fipronil-sulfone in real serum samples. Fipronil-sulfone was identified as the predominant metabolite of fipronil in the black-tailed prairie dog and rat sera.

The effect of biochar on the mitigation of the chiral insecticide fipronil and its metabolites burden on loach (Misgurnus.anguillicaudatus)

In this work, the enantioselective toxicity, enrichment, and distribution of fipronil and its main metabolites (fipronil sulfone, fipronil sulfide, and fipronil desulfinyl) in loach (Misgurnus anguillicaudatus) were studied. The influence of maize-straw derived biochar on acute toxicity and bioaccumulation of contaminants were also investigated. The three main metabolites were more toxic to loach than parent fipronil. Meanwhile, loach exhibited more sensitive to S-enantiomer. The alleviated toxic response of loach was observed in the presence of biochar during 72-h acute toxicity test. Fipronil was readily metabolized to sulfone and sulfide with enantioselectivity in loach liver, and it was also found R-fipronil could transform into S-fipronil. The metabolites profile indicated that oxidation processes was the most predominant pathway in loach. Bioaccumulation factors showed the metabolites could be enriched in loach and they were relatively persistent. The bioaccessibility of fipronil and its metabolite decreased significantly when biochar was applied to the ecosystem. The present study provided basic data and outlines of enantioselective toxicity, biotransformation and metabolism of chiral pesticide fipronil and its main derivatives along with biochar in loach-water ecosystem, and further provide an alternative approach for field remediation to mitigate environmental adverse effects of fipronil.

Fipronil causes toxicity in mouse preimplantation embryos

In this study the possible toxicity of phenylpyrazole fipronil, the related commercial product FIPRON spot-on as well as FIPRON spot-on secondary ingredients on the developmental capacities and quality of mouse preimplantation embryos was evaluated. During in vitro tests, isolated two-cell stage embryos were cultured in media with addition of the listed chemicals until blastocyst formation. Stereomicroscopic evaluation of in vitro produced embryos showed that fipronil at 1 μM and higher concentration negatively affected embryonic development. Fluorescence staining revealed that the obtained blastocysts displayed lower numbers of blastomeres at 10 μM concentrations and elevated incidence of cell death from 1 μM concentration. The presence of FIPRON spot-on at a concentration equivalent to 10 μM of fipronil caused massive degeneration of all embryos. Secondary ingredients (butylhydroxyanisolum, butylhydroxytoluenum) at corresponding concentrations negatively impacted the development and quality of preimplantation embryos as well. During in vivo tests (daily oral administration of fipronil during the preimplantation period) in embryos collected from treated mouse females, significantly elevated incidence of cell death was observed even at the acute reference dose. Fipronil impaired the development and quality of mouse preimplantation embryos in both in vitro and in vivo tests. Embryotoxicity of the commercial product FIPRON spot-on was potentiated by the presence of secondary ingredients.

Fluorescent-fipronil: Design and synthesis of a stable conjugate

Fipronil is a phenyl pyrazole molecule widely used across the world as both insecticide and veterinary drug. The main goal of this work was to synthesize a fluorescently labeled fipronil derivative for cellular imaging without affecting its intrinsic properties. We selected fluorescein as fluorescent probe and we investigated different strategies for stable chemical ligation between both entities, such as thiourea and direct peptide bond. While thiourea bond displayed low stability, direct peptide bond was difficult to achieve due to problems of steric hindrance. The best result was obtained by conjugation using click chemistry, which allowed to obtain fipronil stably labeled with the fluorescent probe.

Development and validation of an ultra performance liquid chromatography Q-Exactive Orbitrap mass spectrometry for the determination of fipronil and its metabolites in tea and chrysanthemum

A fast, sensitive and reliable method for the determination of fipronil and its metabolites in tea and chrysanthemum was developed using a modified QuEChERS technique and an ultra performance liquid chromatography Q-Exactive Orbitrap mass spectrometry. The mixture of adsorbents containing primary secondary amine (PSA), octadecylsilane (C₁₈) and carbon nanotubes (CNTs), was used as QuEChERS adsorbents. The use of mass resolution at 70000 full width at half maximum (FWHM) and narrow mass windows at 5 ppm achieved high selectivity and repeatability. Satisfactory linearity with correlative coefficient (R²) higher than 0.996 was achieved for all compounds. Recoveries at three levels (2, 10 and 50 μg kg^-1) ranged from 86% to 112%, while the intra- and inter-day accuracies were less than 15%. Limits of quantification for fipronil and its metabolites were 2 μg kg^-1, which fulfils the requirement of maximum residue limits formulated by European Union and Japan.

Hydroxy-fipronil is a new urinary biomarker of exposure to fipronil

Occupational medical surveillance is highly desirable in manufacturing facilities where exposure to chemicals is significant. The insecticide fipronil is generally considered safe for humans but with increasing use, exposure to fipronil is of concern. Identification of urinary metabolites of fipronil may allow development of affordable, cheap and rapid procedures for human exposure evaluation. In this study we developed a fast and easy approach for synthesis of hydroxy-fipronil, a potential urinary metabolite of fipronil. This standard was used to develop a sensitive analytical LC-MS/MS method with a limit of quantification (LOQ) of 0.4ng/mL. Fipronil sulfone, a known metabolite, and hydroxy-fipronil were quantified in urine samples from rats treated with a fipronil containing diet. Fipronil sulfone concentration centered around 20ng/mL, while the concentration of hydroxy-fipronil was dose-dependent ranging in 10-10,000ng/mL and thus being a more sensitive marker of fipronil exposure. A fipronil immunoassay with cross-reactivity to hydroxy-fipronil showed a good correlation in signal intensity with LC-MS data. It was also used to demonstrate the applicability of the method for sample screening in the evaluation of exposure levels.

Involvement of vimentin in neurite outgrowth damage induced by fipronil in SH-SY5Y cells

Fipronil, a phenylpyrazole insecticide, is more selective in its potency towards insects than humans and is thus commonly used. In this study, we demonstrated that exposure to fipronil may pose a human health risk. We observed in vitro the shortening of neurite outgrowths of SH-SY5Y neuroblastoma cells upon treatment with fipronil, even at a non-cytotoxic concentration. Fipronil induced apoptosis involving caspase-6, which is an apoptotic effector highly implicated in neurodegenerative diseases. Moreover, at a concentration that did not induce apoptosis, mitochondrial dysfunction and autophagic vacuole formation were detected. Interestingly using proteomics, we identified vimentin to be dramatically expressed by SH-SY5Y cells as a response to fipronil treatment. Not only did the expression of total vimentin increase, different isoforms were observed, indicating alterations in post-translational modifications. Vimentin was localized at the neurite outgrowth, possibly to repair the damage in cellular structure. However at high concentrations of fipronil, vimentin was found in less defined fibrils, in bridge-like formation, and dense surrounding vacuoles. In all, our results indicate that vimentin plays an important role in fipronil-induced neurotoxicity in SH-SY5Y cells.