Véronique Gayrard

Comparison of pharmacokinetic profiles of doramectin and ivermectin pour-on formulations in cattle.

The plasma pharmacokinetics of doramectin and invermectin after topical administration (500 microg kg(-1)) were compared over a 50-day period in 24 young beef cattle. Observed maximum concentration (Cmax) and time to maximum concentration (Tmax) were determined directly from plasma concentrations for each animal. The area under the plasma concentration-time curve (AUC) and mean residence time (MRT) were calculated as indices of drug exposure and persistence. The Cmax of doramectin (12.2+/-4.8 ng ml(-1)) and ivermectin (12.2+/-6.0 ng ml(-1)) and Tmax of doramectin (4.3+/-1.6 days) and ivermectin (3.4+/-0.8 days) were not significantly different (p > 0.05). In contrast, the AUC of doramectin (168.0+/-41.7 ng day ml(-1)) was significantly greater than that of ivermectin (115.5+/-43.0 ng day ml(-1)). Furthermore, the range of AUC values calculated for ivermectin was wider than that obtained for doramectin, extending from 51.3 to 182.3 ng day ml(-1) for ivermectin versus 104.3-228.7 ng day ml(-1) for doramectin. The MRT was significantly greater for doramectin (12.8+/-1.9 days) than for ivermectin (8.4+/-1.5 days). It was concluded that a 500 microg kg(-1) pour-on administration of doramectin and ivermectin led to an overall exposure as reflected by the mean AUC, that was 45% higher for doramectin compared to ivermectin and that the relative inter-individual variability was less for doramectin than for ivermectin. Possible therapeutic consequences of these differences between doramectin and ivermectin pour-on formulations are discussed.

Interspecies variations of corticosteroid-binding globulin parameters

In mammalian plasma, cortisol binds to a specific alpha 1-glycoprotein: corticosteroid-binding globulin (CBG). In this study, we measured the protein binding of cortisol by equilibrium dialysis in seven species in which plasma cortisol concentrations varied from 0.02 to 0.05 (ewe, dog, cow) to 0.1 to 0.6 (horse, human, cynomolgus monkey) to reach 1.6 microM (squirrel monkey). No binding of cortisol to CBG was discernible in plasma from squirrel monkey. In all other species examined, we showed that the CBG maximal capacity (Bmax) was 3 (1.7 to 5.2) times more than the plasma cortisol levels, with cow, dog, ewe exhibiting the lowest and cynomolgus monkey exhibiting the highest values. We also noted the existence of a linear relationship between Bmax and the corresponding dissociation constant (Kd), Bmax being systematically 10 (8.5 to 11.8) times more than Kd. The low binding affinity of cortisol assigned to albumin did not differ between species. The free (6 to 14%), CBG-bound (67 to 87%), and albumin-bound (7 to 19%) cortisol fractions calculated from the estimated binding parameters and measured plasma cortisol concentrations were similar within species, except for squirrel monkey, in which half of the cortisol was albumin bound, and the other half remained protein free. Our most appealing finding was that in most species, as much as 68% of plasma CBG remained free of cortisol under physiologic conditions. These results are discussed with respect to the theories concerning the role of CBG in plasma transport and the local delivery of cortisol and free CBG as a proper hormone.

High Bioavailability of Bisphenol A from Sublingual Exposure

Background: Bisphenol A (BPA) risk assessment is currently hindered by the rejection of reported higher-than-expected plasma BPA concentrations in humans after oral ingestion. These are deemed incompatible with the almost complete hepatic first-pass metabolism of BPA into its inactive glucurono-conjugated form, BPA glucuronide (BPAG). Objectives: Using dogs as a valid model, we compared plasma concentrations of BPA over a 24-hr period after intravenous, orogastric, and sublingual administration in order to establish the absolute bioavailability of BPA administered sublingually and to compare it with oral bioavailability. Methods: Six dogs were sublingually administered BPA at 0.05 mg/kg and 5 mg/kg. We compared the time course of plasma BPA concentrations with that obtained in the same dogs after intravenous administration of the same BPA doses and after a 20-mg/kg BPA dose administrated by orogastric gavage. Results: The data indicated that the systemic bioavailability of BPA deposited sublingually was high (70–90%) and that BPA transmucosal absorption from the oral cavity led to much higher BPA internal exposure than obtained for BPA absorption from the gastrointestinal tract. The concentration ratio of BPAG to BPA in plasma was approximately 100-fold lower following sublingual administration than after orogastric dosing, distinguishing the two pathways of absorption. Conclusions: Our findings demonstrate that BPA can be efficiently and very rapidly absorbed through the oral mucosa after sublingual exposure. This efficient systemic entry route of BPA may lead to far higher BPA internal exposures than known for BPA absorption from the gastrointestinal tract.

Fipronil-induced disruption of thyroid function in rats is mediated by increased total and free thyroxine clearances concomitantly to increased activity of hepatic enzymes

Fipronil is a widely used phytosanitary product and insecticide for pets. In the rat, fipronil can disrupt thyroid function by decreasing plasma concentrations of total thyroxine (T4) likely through increased T4 clearance. However, the mechanism of fipronil action on thyroid function remains unclear. The goals of the present study were to evaluate the effects of fipronil on thyroid hormone (TH) concentrations and elimination in the rat under well characterized plasma exposure to fipronil and its main metabolite fipronil sulfone. In thyroid-intact female rats, fipronil treatment (3 mg/(kg day) per os for 14 days) decreased both total and free TH plasma concentrations concomitantly to increased thyroid stimulating hormone plasma concentrations. A T4-free euthyroid-like model consisting of thyroidectomized rats treated with tri-iodothyronine (12 microg/(kg day), sc) was developed to evaluate both total and free T4 clearances. In this model, fipronil treatment induced a twofold increase in total and free T4 clearances. The same fipronil treatment increased antipyrine clearance in thyroid-intact rats suggesting an increase in the activity of cytochrome P450 enzymes. Finally, this treatment was also associated with an increase in hepatic microsomal 4-nitrophenol UDP-glucuronosyltransferase activity involved in T4 glucuronidation. Thus, fipronil-induced thyroid disruption results from an increased rate of T4 elimination likely mediated by increased hepatic enzyme activity. Plasma concentrations of fipronil sulfone were at least 20-fold higher than those of fipronil. This highlights the need to further investigate the contribution of fipronil sulfone to the fipronil-induced thyroid disruption.

A possible pharmacological explanation for quinacrine failure to treat prion diseases: pharmacokinetic investigations in a ovine model of scrapie

1 Quinacrine was reported to have a marked in vitro antiprion action in mouse neuroblastoma cells. On compassionate grounds, quinacrine was administered to Creutzfeldt–Jakob disease patients, despite the absence of preclinical in vivo studies to evaluate efficacy. Quinacrine failed to provide therapeutic benefit. The aim of the study was to investigate possible pharmacokinetic and/or pharmacodynamic explanations for the discrepancy between the proven action of quinacrine in vitro and its lack of clinical efficacy. 2 We conducted in vitro experiments reproducing the culture conditions in which antiprion effects had been previously observed and recalculated the EC50 by determining the actual extracellular (120 nM) and intracellular (6713 nM) quinacrine neuroblastoma concentrations with the reported quinacrine EC50 (300 nM). 3 A randomized clinical trial in scrapie‐affected ewes confirmed the absence of therapeutic benefit of quinacrine. The in vivo quinacrine exposure was evaluated in a pharmacokinetic investigation in healthy ewes. Cerebrospinal fluid concentrations (<10.6 and 55 nM after administration of therapeutic and toxic quinacrine doses, respectively) were much lower than the quinacrine extracellular neuroblastoma concentrations corresponding to the reported EC50. The total brain tissue concentrations (3556 nM) obtained after a repeated therapeutic dosage regimen were within the range of the intracellular neuroblastoma quinacrine concentrations. 4 In conclusion, in order to avoid in vivo trials for which failure can be predicted, the measurement in vitro of the antiprion EC50 in both intra‐ and extracellular biophases should be determined. It can then be established if these in vitro antiprion concentrations are achievable in vivo.

Efferent projections from the retrochiasmatic area to the median eminence and to the pars nervosa of the hypophysis with special reference to the A15 dopaminergic cell group in the sheep.

Anterograde tracers, viz. Phaseolus vulgaris leucoagglutinin and fluorescein dextran, were used in conjunction with tyrosine hydroxylase immunohisto-chemistry to study the projections of the A15 dopaminergic cell group towards the median eminence and pituitary in sheep. After injection of the tracers in the retrochiasmatic area, which contains the cell group A15, fibres containing anterograde tracer were observed in the internal zone of the median eminence and in the pars nervosa of the pituitary. Numerous tyrosine hydroxylase immunoreactive fibers were present in the external zone of the median eminence and in the pars intermedia and the pars nervosa of the pituitary, with characteristic patterns of organisation in each area. Most tyrosine hydroxylase-immunoreactive fibres containing fluorescein dextran were located in the pars nervosa, whereas only a few were observed in the internal zone of the median eminence. It was concluded that at least part of the dopaminergic innervation of the pars nervosa originated from the A15 group. These results provide morphological evidence for (1) the role of dopaminergic neurons of the A15 cell group in the seasonal control of prolactin secretion via the release of dopamine in the pars nervosa, and (2) putative physiological interactions between dopamine and the secretion of neurohypophysial hormones in sheep.

Bisphenol A Disposition in the Sheep Maternal-Placental-Fetal Unit: Mechanisms Determining Fetal Internal Exposure

ABSTRACT The widespread human exposure to bisphenol A (BPA), a xenoestrogen interfering with developmental processes, raises the question of the mechanisms determining fetal exposure to BPA. A physiological model was developed in ewes to determine whether the pregnancy-associated physiological changes and the metabolic specificities of the fetal-placental unit can influence BPA toxicokinetics (TK) and fetal exposure to BPA. In a first longitudinal study, BPA was infused (2 mg/[kg·day] i.v. for 1 day) into ewes before breeding, at early and late stages of gestation, and after lambing. In a second study, BPA and BPA-glucuronide (BPA-G) were infused intravenously into pregnant ewes or into fetuses at 4 mo of gestation. BPA and its metabolites were assayed in maternal and fetal plasma and amniotic fluid sampled at steady state and after the end of the infusion. The pregnancy status did not modify the TK parameters of BPA and of BPA-G. Five percent of the BPA dose infused into the pregnant ewe was transferred across the placenta to the fetus. The fetal-placental unit was very efficient in metabolizing BPA into conjugated compounds; those metabolites remained trapped in the fetal-placental compartment, leading to a high fetal exposure to BPA conjugates. Taking into account a body weight adjustment, the ovine fetus in late pregnancy is exposed to a BPA dose similar to that of its mother. In contrast to its mother, the fetus exhibits much higher and sustained exposure to BPA metabolites without evidence of their hydrolysis.

Environmental pollutants, a possible etiology for premature ovarian insufficiency: a narrative review of animal and human data

BackgroundBecause only 25% of cases of premature ovarian insufficiency (POI) have a known etiology, the aim of this review was to summarize the associations and mechanisms of the impact of the environment on this pathology.Main body of the abstractEligible studies were selected from an electronic literature search from the PUBMED database from January 2000 to February 2016 and associated references in published studies. Search terms included ovary, follicle, oocyte, endocrine disruptor, environmental exposure, occupational exposure, environmental contaminant, pesticide, polyaromatic hydrocarbon, polychlorinated biphenyl PCB, phenol, bisphenol, flame retardant, phthalate, dioxin, phytoestrogen, tobacco, smoke, cigarette, cosmetic, xenobiotic. The literature search was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. We have included the human and animal studies corresponding to the terms and published in English. We have excluded articles that included results that did not concern ovarian pathology and those focused on ovarian cancer, polycystic ovary syndrome, endometriosis or precocious puberty. We have also excluded genetic, auto-immune or iatrogenic causes from our analysis. Finally, we have excluded animal data that does not concern mammals and studies based on results from in vitro culture. Data have been grouped according to the studied pollutants in order to synthetize their impact on follicular development and follicular atresia and the molecular pathways involved.Ninety-seven studies appeared to be eligible and were included in the present study, even though few directly address POI. Phthalates, bisphenol A, pesticides and tobacco were the most reported substances having a negative impact on ovarian function with an increased follicular depletion leading to an earlier age of menopause onset. These effects were found when exposure occured at different times throughout the lifetime from the prenatal to the adult period, possibly due to different mechanisms. The main mechanism seemed to be an increase in atresia of pre-antral follicles.ConclusionEnvironmental pollutants are probably a cause of POI. Health officials and the general public must be aware of this environmental effect in order to implement individual and global preventive actions.

Conjugation and Deconjugation Reactions within the Fetoplacental Compartment in a Sheep Model: A Key Factor Determining Bisphenol A Fetal Exposure

The widespread human exposure to bisphenol A (BPA), an endocrine disruptor targeting developmental processes, underlines the need to better understand the mechanisms of fetal exposure. Animal studies have shown that at a late stage of pregnancy BPA is efficiently conjugated by the fetoplacental unit, mainly into BPA-glucuronide (BPA-G), which remains trapped within the fetoplacental unit. Fetal exposure to BPA-G might in turn contribute to in situ exposure to bioactive BPA, following its deconjugation into parent BPA at the level of fetal sensitive tissues. The objectives of our study were 1) to characterize the BPA glucurono- and sulfoconjugation capabilities of the ovine fetal liver at different developmental stages, 2) to compare hepatic conjugation activities in human and sheep, and 3) to evaluate the extent of BPA conjugation and deconjugation processes in placenta and fetal gonads. At an early stage of pregnancy, and despite functional sulfoconjugation activity, ovine fetuses expressed low hepatic BPA conjugation capabilities, suggesting that this stage of development represents a critical window in terms of BPA exposure. Conversely, the late ovine fetus expressed an efficient detoxification system that metabolized BPA into BPA-G. Hepatic glucuronidation activities were quantitatively similar in adult sheep and humans. In placenta, BPA conjugation and BPA-G deconjugation activities were relatively balanced, whereas BPA-G hydrolysis was systematically higher than BPA conjugation in gonads. The possible reactivation of BPA-G into BPA could contribute to an increased exposure of fetal sensitive tissues to bioactive BPA in situ.

Estrogenicity of Bisphenol A: A Concentration-Effect Relationship on Luteinizing Hormone Secretion in a Sensitive Model of Prepubertal Lamb

The model of the prepubertal ovariectomized lamb was selected as a sensitive model to characterize the estrogenic effects of bisphenol A (BPA) on the hypothalamo-pituitary axis (HPA). In a first experiment, the disrupting effect of BPA and of 17-beta estradiol (E2), administered as a constant 54-h iv infusion, on luteinizing hormone (LH) pulsatility was quantified. The results showed that the inhibitory effect of BPA and E2 on LH secretion appeared to follow a dual mechanism: a rapid (about 1 h) suppressive effect for high exposure and an effect observed with a period of latency (about 48 h) probably of genomic origin and observed for lower E2 and BPA levels. For E2, the disrupting dose was 0.14 microg/(kg x d), corresponding to a plasma concentration of 2 pg/ml; for BPA, the lowest observed disrupting plasma concentration was 38 ng/ml, a value only 10-fold higher than the human plasma concentration routinely reported in biomonitoring surveys. In a second experiment, we showed that after 7 weeks of BPA treatment, there was no BPA accumulation and no evidence of an alteration in the HPA responsiveness to BPA. Finally, our results showed that directly considering plasma concentrations, the ratio of the BPA disrupting plasma concentration in lambs over the observed human plasma concentration is only 10, whereas if the dose is considered, it could be concluded that the BPA disrupting dose in lamb is conservatively 50-fold higher than the currently recommended Tolerable Daily Intake of 50 microg/(kg x d).