Stereoselective bioaccumulation of chiral anticoagulant rodenticides in the liver of predatory and scavenging raptors.

Second-generation anticoagulant rodenticides (SGARs) are persistent chiral pesticides used to control rodent populations. Raptors are protected species and may be exposed through the ingestion of rodents contaminated with SGARs. Commercial formulations of SGARs are a mixture of four stereoisomers (E1, E2, E3, E4): the cis- and trans-diastereoisomers are each a racemic mixture of two enantiomers. In this study, the residue levels of all SGARs (bromadiolone, difenacoum, brodifacoum, difethialone, flocoumafen) were evaluated in the liver of 529 raptor carcasses. All species (n = 18) and 75 % of individuals (n = 396) were SGAR positive and 29 % (n = 154) had summed hepatic concentrations above 100 ng/g ww. Concentrations were higher for predators with facultative scavenging behaviors than for predators and obligate scavengers. Bromadiolone, brodifacoum and difenacoum had equivalent hepatic prevalence (between 48.9 and 49.9 %), and difethialone was detected less frequently (31.7 %). Concentrations and enantiomeric fractions of the four stereoisomers of all SGARs are described in to demonstrate the biological enantioselectivity of these chiral pesticides in the food chain. A difference was observed between the proportions of SGARs diastereoisomers and stereoisomers in the liver of all raptor species and in commercial baits. The enantioselective bioaccumulation of E1-trans-bromadiolone, E3-cis-brodifacoum, E1-cis-difenacoum and E3-cis-difethialone was characterized and represented 96.8 % of total SGARs hepatic residues. While hepatic concentrations were heterogeneous, the proportions of stereoisomers and diastereoisomers were homogeneous with no inter-individual or inter-species differences (only E1-trans-bromadiolone is present in hepatic residues). However, proportions of brodifacoum stereoisomers and diastereoisomers were more scattered, probably due to their slower elimination. This could provide an opportunity to date the exposure of individuals to brodifacoum. We highlight the need to consider each SGAR as four molecular entities (four stereoisomers) rather than one. These findings suggest new commercial formulations with the less persistent stereoisomers could reduce secondary exposure of non-target species.

Structural investigation of vitamin K epoxide reductase domain-containing protein in Leptospira species: a potential target for the development of new leptospirosis treatments as an alternative to antibiotics.

Leptospirosis is a worldwide zoonosis caused by the motile bacterium Leptospira. This disease can cause hemorrhagic symptoms, multi-visceral and renal failures, resulting in one million cases and approximately 60,000 deaths each year. The motility of Leptospira is highly involved in its virulence and is ensured by the presence of two flagella in the periplasm. Several proteins that require the formation of disulfide bridges are essential for flagellar function. In Leptospira, these redox reactions are catalysed by the vitamin K epoxide reductase domain-containing protein (VKORdcp). The aim of the present work was to study the conservation of VKORdcp among Leptospira species and its interactions with putative substrates and inhibitor. Our results evidenced the presence of ten amino acids specific to either pathogenic or saprophytic species. Furthermore, structural studies revealed a higher affinity of the enzyme for vitamin K1 quinone, compared to ubiquinone. Finally, characterisation of the binding of a potential inhibitor revealed the involvement of some VKORdcp amino acids that have not been present in the human enzyme, in particular the polar residue D114. Our study thus paves the way for the future development of Leptospira VKORdcp inhibitors, capable of blocking bacterial motility. Such molecules could therefore offer a promising therapeutic alternative to antibiotics, especially in the event of the emergence of antibiotic-resistant strains.Communicated by Ramaswamy H. Sarma.

Exposure and resistance to anticoagulant rodenticides in invasive and endemic Chadian urban rodent species to develop a rational management strategy.

Rodent management involves the use of anticoagulant rodenticides (ARs). This use has resulted in the selection of numerous resistance alleles in the Vkorc1 gene, encoding the target enzyme of ARs. In Africa, although rodents are a major problem as a consequence of their transport and transmission of zoonotic pathogens, and damage to crops, the use of ARs and the spread of resistance alleles are poorly documented. We attempted to address both issues in Chad which is one of the largest countries in Africa. Owing to its location at the crossroads of central and northern Africa, Chad is representative of many African countries. METHODS: Using a sampling of nearly 300 rodents composed of invasive and endemic rodents collected in six of Chad's largest cities, exposure to ARs was analyzed by their quantification in the liver; the spread of AR resistance alleles was analyzed by Vkorc1 sequencing. RESULTS: We demonstrate the use of both ARs generations in Chadian cities and report the total sequencing of the Vkorc1 for 44 Mastomys natalensis with detection of two different haplotypes, the sequencing of the Vkorc1 for two other endemic rodent species, M. kollmannspergeri and Arvicanthis niloticus, and finally the detection of three new missense mutations - V29E, V69E and D127V - in R. rattus, potentially associated with resistance to ARs. DISCUSSION: These results should argue for the implementation of a reasoned management of rodent populations in Africa to avoid the spread of ARs resistance alleles. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Design of a structure-activity relationship model of vitamin K epoxide reductase (VKORC1) inhibitors combining chemical synthesis of new compounds, enzymatic assays and molecular modelling.

Vitamin K antagonists (VKAs) anticoagulants have been used since the 1950s as medicines and rodenticides. These molecules are mainly 4-hydroxycoumarin derivatives and act by inhibiting the vitamin K epoxide reductase (VKORC1), an endoplasmic reticulum membrane resident enzyme. However, many VKORC1 mutations have been reported over the last decade, inducing VKAs resistances and thus treatments failures. Although studies have reported experimental and computational investigations of VKAs based on VKORC1 structural homology models, the development of new effective anticoagulants has been quite complex due to the lack of structural data and reliable structure-activity relationships. However, the recent publication of VKORC1 crystal structure provides new information for further studies. Based on these findings, we combined chemical synthesis, enzymatic assays and molecular modelling methods to design a structure-activity relationship (SAR) model. Our results proved that the lipophilicity, the membrane permeability of inhibitors and their affinity towards human VKORC1 enzyme are the main characteristics for potent anticoagulants. Our SAR model managed to rank compounds according to their ability to inhibit the human VKORC1. Such a tool might constitute an alternative to evaluate new molecules potency before their chemical synthesis and biological assessment and might assist the development of new VKAs.

Sexual discrimination and attraction through scents in the water vole, Arvicola terrestris.

In mammals, especially rodents, social behaviours, such as parenting, territoriality or mate attraction, are largely based on olfactory communication through chemosignals. These behaviours are mediated by species-specific chemosignals, including small organic molecules and proteins that are secreted in the urine or in various fluids from exocrine glands. Chemosignal detection is mainly ensured by olfactory neurons in two specific sensory organs, the vomeronasal organ (VNO) and the main olfactory epithelium (MOE). This study aimed to characterise the olfactory communication in the fossorial ecotype of the water voles, Arvicola terrestris. We first measured the olfactory investigation of urine and lateral scent gland secretions from conspecifics. Our results showed that water voles can discriminate the sex of conspecifics based on the smell of urine, and that urinary male odour is attractive for female voles. Then, we demonstrated the ability of the VNO and MOE to detect volatile organic compounds (VOCs) found in water vole secretions using live-cell calcium imaging in dissociated cells. Finally, we evaluated the attractiveness of two mixtures of VOCs from urine or lateral scent glands in the field during a cyclical outbreak of vole populations.

Identification of Pathogenic Leptospira kirschneri Serogroup Grippotyphosa in Water Voles (Arvicola terrestris) from Ruminant Pastures in Puy-de-Dôme, Central France.

Rodents are the primary reservoirs for pathogenic Leptospira species, which cause leptospirosis. Among the key potential carriers are water voles, whose population outbreaks can consequently pose a major threat to human and animal health. We studied the prevalence, prominence, and epidemiology of pathogenic Leptospira species in water voles in central France. First, 46 voles were captured, and DNA was extracted from kidney, lung, liver, blood, and urine and tested for the presence of Leptospira using three molecular methods: PCR, O-antigen typing, and variable number tandem repeat (VNTR) typing. We also attempted to culture leptospires from kidney and urine samples. In addition, we investigated leptospiral antibodies in serum samples from 60 sheep using microscopic agglutination testing. These animals co-occurred with the voles, so we sought to assess their degree of exposure and involvement in pathogen dynamics. The overall prevalence of infection was 76.1% (CI95% [61.2%, 87.4%]). The only strain found was L. kirschneri serogroup Grippotyphosa and a similar VNTR profile was acquired. Leptospires were successfully cultured from kidney and urine samples for four voles. Three sheep had low antibody titers against the Leptospira serogroup Grippotyphosa. Taken together, our results suggest the exclusive carriage of L. kirschneri serogroup Grippotyphosa among water voles in central France. Nevertheless, their ability to act as reservoir hosts that transmit the pathogen to co-occurring livestock remains unclear and merits further research.

Splice variants of protein disulfide isomerase - identification, distribution and functional characterization in the rat.

BACKGROUND: Protein Disulfide Isomerase (PDI) enzyme is an emerging therapeutic target in oncology and hematology. Although PDI reductase activity has been studied with isolated fragments of the protein, natural structural variations affecting reductase activity have not been addressed. METHODS: In this study, we discovered four coding splice variants of the Pdi pre-mRNA in rats. In vitro Michaelis constants and apparent maximum steady-state rate constants after purification and distribution in different rat tissues were determined. RESULTS: The consensus sequence was found to be the most expressed splice variant while the second most expressed variant represents 15 to 35% of total Pdi mRNA. The third variant shows a quasi-null expression profile and the fourth was not quantifiable. The consensus sequence splice variant and the second splice variant are widely expressed (transcription level) in the liver and even more present in males. Measurements of the reductase activity of recombinant PDI indicate that the consensus sequence and third splice variant are fully active variants. The second most expressed variant, differing by a lack of signal peptide, was found active but less than the consensus sequence. GENERAL SIGNIFICANCE: Our work emphasizes the importance of taking splice variants into account when studying PDI-like proteins to understand the full biological functionalities of PDI.

Interest of the faecal and plasma matrix for monitoring the exposure of wildlife or domestic animals to anticoagulant rodenticides.

Anticoagulant rodenticides (ARs), particularly second-generation compounds (SGAR), are known to be a potential threat to unintended species due to their tissue persistence. The liver is the storage tissue of ARs and is a matrix of choice in diagnosing exposure and intoxication of non-target fauna. However, it is only available on dead animals. Blood and faeces can be used on living animals. These two biological matrices were compared in terms of their relevance to exposure to ARs. In addressing this question, we compared the faecal, plasma and liver concentrations of bromadiolone, one of the SGAR frequently implicated in wildlife exposure. We studied this comparison at the individual level and at the population level, considering three influencing factors: dose, sex and time. Our findings demonstrate that faecal analyses are more valuable than plasma analyses for monitoring AR exposure of domestic and wild animals, even if faecal concentrations cannot be correlated with liver concentrations.

Investigation of anticoagulant rodenticide resistance induced by Vkorc1 mutations in rodents in Lebanon.

Anticoagulant rodenticides (AR) remain the most effective chemical substances used to control rodents in order to limit their agricultural and public health damage in both rural and urban environments. The emergence of genetically based resistance to AR worldwide has threatened effective rodent control. This study gives a first overview of the distribution and frequency of single nucleotide polymorphism in the vitamin K epoxide reductase subcomponent 1 (Vkorc1) gene in rodents in Lebanon. In the Mus genus, we detected two missense mutations Leu128Ser and Tyr139Cys, that confer resistance to anticoagulant rodenticides in house mice and a new missense mutation Ala72Val in the Mus macedonicus species, not previously described. In the Rattus genus, we found one missense mutation Leu90Ile in the roof rat and one missense mutation Ser149Ile in the Norway rat. This is the first study to demonstrate potential resistance to AR in Lebanese rodents and therefore it provides data to pest control practitioners to choose the most suitable AR to control rodents in order to keep their efficacy.

Asymptomatic Anticoagulant Rodenticide Exposure in Dogs and Cats-A French and Belgian Rural and Urban Areas Study.

Anticoagulant rodenticides (ARs) are important tools for controlling rodent pests, but they also pose a health threat to non-target species. ARs are one of the most common causes of pet poisoning. However, exposure of domestic animals to subclinical doses of ARs is poorly documented. To study the random exposure of dogs and cats to ARs, feces from animals showing no clinical signs of rodenticide poisoning were collected from a network of French and Belgian veterinarians. We analyzed fresh feces from 304 dogs and 289 cats by liquid chromatography-tandem mass spectrometry. This study showed a limited prevalence of AR exposure in dogs and cats of 2.6 and 4.5% respectively. In both species, access to the outdoors is a risk factor for ARs exposure. In contrast, the sex of the animals did not affect the ARs exposure status. The observation of the ratio of cis and trans isomers suggested primary exposure in dogs, but also in some cats. While primary exposure in dogs appears to be related to the use of ARs as plant protection products, primary exposure in cats may be malicious, as warfarin, an anticoagulant formerly used as a rodenticide and now used only in humans, was found in 4 of 13 exposed cats. Secondary exposure may also occur in cats.Our study showed reduced exposure in dogs and cats, compared to wildlife, which often has high exposure, especially in areas where rodent control is important.

Distribution of non-synonymous Vkorc1 mutations in roof rats (Rattus rattus) in France and in Spain - consequences for management.

Rodent control is mainly done using anticoagulant rodenticides leading to the death of rodents through internal bleeding by targeting the VKORC1 protein. However, mutations in VKORC1 can lead to resistance to anticoagulant rodenticides that can cause treatment failure in the field. This study provides the first insight into the distribution, frequency and characterization of Vkorc1 mutations in roof rats (Rattus rattus) in France and in three administrative areas of Spain. The roof rat is present in France while it was thought to have almost disappeared with the expansion of the brown rat. Nevertheless, it has been found mainly in maritime areas. 151 roof rats out of 219 tested presented at least one missense mutation in the coding sequences of Vkorc1 gene (i.e. 69.0% of the rat). Nine Vkorc1 genotypes were detected (Y25F, A26P, R40G, S57F, W59C, W59R, H68N, Y25F/K152T and Y25F/W59R. Biochemical characterization of the consequences of these different genotypes proved that these various genotypes did not induce severe resistance to anticoagulant rodenticides. Even if many mutations of the Vkorc1 gene are present in roof rat populations in France, their management may be based in a first approach, considering the low levels of resistance induced, on the use of first-generation anticoagulants less dangerous for wildlife. The use of second-generation may be considered when treatment failure is observed or when bait consumption is limited.

Overexpression of protein disulfide isomerase enhances vitamin K epoxide reductase activity.

Vitamin K epoxide reductase (VKOR) activity is catalyzed by the VKORC1 enzyme. It is a target of vitamin K antagonists (VKA). Numerous mutations of VKORC1 have been reported and are suspected to confer resistance to VKA and (or) affect its velocity. Nevertheless, the results of these studies have been conflicting, and the functional characterization of these mutations in the cell system is complex because of the interweaving of VKOR activity in the vitamin K cycle. In this study, a new cellular approach was implemented to evaluate the vitamin K cycle in HEK293 cells. This global approach was based on the vitamin K quinone/vitamin K epoxide (K/KO) balance. In the presence of VKA or when VKORC1 and VKORC1L1 were knocked out, the K/KO balance decreased significantly due to the accumulation of vitamin KO. In contrast, when VKORC1 was overexpressed, the balance remained unchanged, demonstrating the limitation of VKOR activity. This limitation was shown to be due to insufficient expression of the activation partner of VKORC1, as overexpression of protein disulfide isomerase (PDI) overcomes this limitation. This study is the first to demonstrate the functional interaction between VKORC1 and PDI.

Comparative pharmacokinetics of difethialone stereoisomers in male and female rats and mice: development of an intra- and inter-species model to predict the suitable formulation mix.

The ecotoxicity of anticoagulants used for rodent pests' management is a major concern, particularly with second generation anticoagulants, which are more persistent in the body of rodents and therefore more likely to cause secondary exposure in their predators. One of the solutions envisaged to mitigate this risk is to use stereoisomers of these anticoagulants, each of which has particular pharmacokinetics. However, the few studies published to date have considered only one species and one sex. Here, we study the pharmacokinetics of the 4 stereoisomers of 3.4 mg/kg of difethialone in rats (Rattus norvegicus) and 3 mg/kg in mice (Mus musculus) in both sexes and propose a model to choose the optimal stereoisomer efficacy/ecotoxicity mixture for the management of all these animals. Our results show that while the most persistent stereoisomer (E3-cis) is common to both species and sexes, the pharmacokinetics of the other stereoisomers show marked differences between sexes and species. Thus, the area under curve (AUC) of E4-trans in male rats is four times lower than in females or mice, making it a priori unusable in male rats. Conversely, our modeling seems to show that the E1-trans stereoisomer seems to offer the best compromise AUC persistence. In conclusion, we highlight that studies on anticoagulants must necessarily integrate research on the effect of gender and species both on efficacy and with regard to the ecotoxicity of these molecules.

Exposure of predatory and scavenging birds to anticoagulant rodenticides in France: Exploration of data from French surveillance programs.

Wild raptors are widely used to assess exposure to different environmental contaminants, including anticoagulant rodenticides (ARs). ARs are used on a global scale for rodent control, and act by disruption of the vitamin K cycle that results in haemorrhage usually accompanied by death within days. Some ARs are highly persistent and bioaccumulative, which can cause significant exposure of non-target species. We characterized AR exposure in a heterogeneous sample of dead raptors collected over 12 years (2008-2019) in south-eastern France. Residue analysis of 156 liver samples through LC-MS/MS revealed that 50% (78/156) were positive for ARs, with 13.5% (21/156) having summed second-generation AR (SGAR) concentrations >100 ng/g ww. While SGARs were commonly detected (97.4% of positive samples), first-generation ARs were rarely found (7.7% of positive samples). ARs were more frequently detected and at greater concentration in predators (prevalence: 82.5%) than in scavengers (38.8%). Exposure to multiple ARs was common (64.1% of positive samples). While chlorophacinone exposure decreased over time, an increasing exposure trend was observed for the SGAR brodifacoum, suggesting that public policies may not be efficient at mitigating risk of exposure for non-target species. Haemorrhage was observed in 88 birds, but AR toxicosis was suspected in only 2 of these individuals, and no difference in frequency of haemorrhage was apparent in birds displaying summed SGAR levels above or below 100 ng/g ww. As for other contaminants, 17.2% of liver samples (11/64) exhibited Pb levels compatible with sub-clinical poisoning (>6 µg/g dw), with 6.3% (4/64) above the threshold for severe/lethal poisoning (>30 µg/g dw). Nine individuals with Pb levels >6 µg/g dw also had AR residues, demonstrating exposure to multiple contaminants. Broad toxicological screening for other contaminants was positive for 18 of 126 individuals, with carbofuran and mevinphos exposure being the suspected cause of death of 17 birds. Our findings demonstrate lower but still substantial AR exposure of scavenging birds compared to predatory birds, and also illustrate the complexity of diagnosing AR toxicosis through forensic investigations.

Photoperiod is involved in the regulation of seasonal breeding in male water voles (Arvicola terrestris).

Mammals living at temperate latitudes typically display annual cyclicity in their reproductive activity: births are synchronized when environmental conditions are most favorable. In a majority of these species, day length is the main proximate factor used to anticipate seasonal changes and to adapt physiology. The brain integrates this photoperiodic signal through key hypothalamic structures, which regulate the reproductive axis. In this context, our study aimed to characterize regulations that occur along the hypothalamo-pituitary-gonadal (HPG) axis in male fossorial water voles (Arvicola terrestris, also known as Arvicola amphibius) throughout the year and to further probe the implication of photoperiod in these seasonal regulations. Our monthly field monitoring showed dramatic seasonal changes in the morphology and activity of reproductive organs, as well as in the androgen-dependent lateral scent glands. Moreover, our data uncovered seasonal variations at the hypothalamic level. During the breeding season, kisspeptin expression in the arcuate nucleus (ARC) decreases, while RFRP3 expression in the dorsomedial hypothalamic nucleus (DMH) increases. Our follow-up laboratory study revealed activation of the reproductive axis and confirmed a decrease in kisspeptin expression in males exposed to a long photoperiod (summer condition) compared with those maintained under a short photoperiod (winter condition) that retain all features reminiscent of sexual inhibition. Altogether, our study characterizes neuroendocrine and anatomical markers of seasonal reproductive rhythmicity in male water voles and further suggests that these seasonal changes are strongly impacted by photoperiod.

Field study reveals morphological and neuroendocrine correlates of seasonal breeding in female water voles, Arvicola terrestris.

Seasonally breeding mammals display timely physiological switches between reproductive activity and sexual rest, which ensure synchronisation of births at the most favourable time of the year. These switches correlate with seasonal changes along the hypothalamo-pituitary-gonadal axis, but they are primarily orchestrated at the hypothalamic level through environmental control of KISS1-dependent GnRH release. Our field study shows that births of fossorial water voles, Arvicola terrestris, are concentrated between March and October, which indicates the existence of an annual reproductive cycle in this species. Monthly field monitoring for over a year further reveals dramatic seasonal changes in the morphology of the ovary, uterus and lateral scent glands, which correlate with the reproductive status. Finally, we demonstrate seasonal variation in kisspeptin expression within the hypothalamic arcuate nucleus. Altogether, this study demonstrates a marked rhythm of seasonal breeding in the water vole and we speculate that this is governed by seasonal changes in photoperiod.

Seasonal diet-based resistance to anticoagulant rodenticides in the fossorial water vole (Arvicola amphibius).

Anticoagulant rodenticides (AR) resistance has been defined as "a major loss of efficacy due to the presence of a strain of rodent with a heritable and commensurately reduced sensitivity to the anticoagulant". The mechanism that supports this resistance has been identified as based on mutations in the Vkorc1 gene leading to severe resistance in rats and mice. This study evaluates the validity of this definition in the fossorial water vole and explores the possibility of a non-genetic diet-based resistance in a strict herbivorous rodent species. Genetic support was explored by sequencing the Vkorc1 gene and the diet-based resistance was explored by the dosing of vitamins K in liver of voles according to seasons. From a sample of 300 voles, only 2 coding mutations, G71R and S149I, were detected in the Vkorc1 gene in the heterozygous state with low allele frequencies (0.5-1%). These mutations did not modify the sensitivity to AR, suggesting an absence of genetic Vkorc1-based resistance in the water vole. On the contrary, vitamin K1 was shown to be 5 times more abundant in the liver of the water vole compared to rats. This liver concentration was shown to seasonally vary, with a trough in late winter and a peak in late spring/early summer related to the growth profile of grass. This increase in concentration might be responsible for the increased resistance of water voles to AR. This study highlights a non-genetic, diet-related resistance mechanism in rodents to AR. This diet-based resistance might explain the different evolution of the Vkorc1 gene in the fossorial water vole compared to rats and mice.

Monitoring the hepatic residues of cis- and trans-diastereoisomers of second generation anticoagulant rodenticides reveals a different bioaccumulation of diastereoisomers in the food chain of the Réunion harrier (Circus maillardi).

The Réunion harrier is an endangered raptor and endemic species to the Réunion Island. Second generation anticoagulant rodenticides (SGARs) are widely used pesticides on the island in order to control rodent populations. The latter are responsible for the transmission of leptospirosis to humans, the damage of sugarcane crops, and the decline of endemic endangered birds. SGARs are very persistent chiral pesticides and consequent secondary exposure or poisoning of the Réunion harrier has been observed (73% of prevalence in a group of 58 harriers). Commercial formulations of SGARs are a mixture of trans- and cis-diastereoisomers. Both diastereoisomers of all SGARs have been shown to inhibit coagulation function with the same potency. On the other hand, they have been shown to have a significant difference in terms of tissue-persistence. This difference has led to residue levels in rats with a significantly lower proportion of one of the isomers compared to the bait composition. In this study, residue levels of the diastereoisomers of all SGARs were evaluated in the livers of 58 harrier carcasses. The respective concentrations and proportions of cis- and trans- diastereoisomers of all SGARs are presented. cis-Brodifacoum and trans-bromadiolone had the highest concentrations (up to 438 and 573 ng/g ww respectively), while trans-brodifacoum was less than 46 ng/g and cis-bromadiolone was barely detected. cis-Difenacoum showed the highest prevalence and the highest concentration was 82 ng/g ww, while trans-difenacoum was never detected. This study demonstrated that only cis-brodifacoum and trans-bromadiolone (and cis-difethialone, but with a low prevalence) had hepatic concentrations above a toxic threshold. The cis- and trans-diastereoisomers of SGARs had differential bioaccumulation in the food chain of the Réunion harrier compared to commercial baits. This suggests that a change of the proportions of SGARs diastereoisomers in baits could reduce the risk of secondary poisoning of predators, but maintain primary toxicity.

Water vole management - Could anticoagulant rodenticides stereochemistry mitigate the ecotoxicity issues associated to their use?

Cyclic water vole population explosions can be controlled in some European countries with anticoagulant rodenticides leading sometimes to wildlife poisonings due to the toxin's tissue persistence. Here, we analyzed the pharmacokinetics of rodenticide residues in voles and we explored potential ways of improving the mass application of these agents based on the concept of stereoisomers. We demonstrated the dramatic persistence of bromadiolone in vole tissues with a hepatic half-life of about 10-30 days, while the tissue persistence of chlorophacinone is rather short with a hepatic half-life of about one day. The dramatic persistence of bromadiolone is due to the trans-isomer group (the major compound in bromadiolone), while the cis-isomer group has a short half-life. Because of resistance to chlorophacinone, the cis-bromadiolone isomers may constitute an excellent compromise between efficacy and ecotoxicological risk to control voles. A mathematical model is proposed to favor the development of baits mixed with cis-isomer groups.

Differences in teratogenicity of some vitamin K antagonist substances used as human therapeutic or rodenticide are due to major differences in their fate after an oral administration.

All vitamin K antagonist active substances used as rodenticides were reclassified in 2016 by the European authorities as active substances "toxic for reproduction", using a "read-across" alternative method based on warfarin, a human vitamin K antagonist drug. Recent study suggested that all vitamin K antagonist active substances are not all teratogenic. Using a neonatal exposure protocol, warfarin evokes skeletal deformities in rats, while bromadiolone, a widely used second-generation anticoagulant rodenticide, failed to cause such effects. Herein, using a rat model we investigated the mechanisms that may explain teratogenicity differences between warfarin and bromadiolone, despite their similar vitamin K antagonist mechanism of action. This study also included coumatetralyl, a first-generation active substance rodenticide. Pharmacokinetic studies were conducted in rats to evaluate a potential difference in the transfer of vitamin K antagonists from mother to fetus. The data clearly demonstrate that warfarin is highly transferred from the mother to the fetus during gestation or lactation. In contrast, bromadiolone transfer from dam to the fetus is modest (5% compared to warfarin). This difference appears to be associated to almost complete uptake of bromadiolone by mother's liver, resulting in very low exposure in plasma and eventually in other peripheric tissues. This study suggests that the pharmacokinetic properties of vitamin K antagonists are not identical and could challenge the classification of such active substances as "toxic for reproduction".