Pharmacokinetic-pharmacodynamic cutoff values for benzylpenicillin in horses to support the establishment of clinical breakpoints for benzylpenicillin antimicrobial susceptibility testing in horses

Introduction

The aim of this international project was to establish a species-specific Clinical Breakpoint for interpretation of Antimicrobial Susceptibility Testing of benzylpenicillin (BP) in horses.

Methods

A population pharmacokinetic model of BP disposition was developed to compute PK/PD cutoff values of BP for different formulations that are commonly used in equine medicine around the world (France, Sweden, USA and Japan). Investigated substances were potassium BP, sodium BP, procaine BP, a combination of procaine BP and benzathine BP and penethamate, a prodrug of BP. Data were collected from 40 horses that provided 63 rich profiles of BP corresponding to a total of 1022 individual BP plasma concentrations.

Results

A 3-compartment disposition model was selected. For each of these formulations, the PK/PD cutoff was estimated for different dosage regimens using Monte Carlo simulations. The fAUC/MIC or fT>MIC were calculated with a free BP fraction set at 0.4. For fAUC/MIC, a target value of 72 h (for a 72h treatment) was considered. For fT>MIC, efficacy was assumed when free plasma concentrations were above the explored MIC (0.0625-2 mg/L) for 30 or 40 % of the dosing interval. For continuous infusion, a fT>MIC of 90 % was considered. It was shown that a PK/PD cutoff of 0.25 mg/L can be achieved in 90 % of horses with routine regimen (typically 22,000 IU/kg or 12.4 mg/kg per day) with IM procaine BP once a day (France, Japan, Sweden but not USA1) and with IM sodium BP at 14.07 mg/kg, twice a day or IV sodium BP infusion of 12.4 mg/kg per day. In contrast, penethamate and the combination of procaine BP and benzathine BP were unable to achieve this PK/PD cutoff not even an MIC of 0.125 mg/L.

Discussion

The PK/PD cutoff of 0.25 mg/L is one dilution lower than the clinical breakpoint released by the CLSI (0.5 mg/ L). From our simulations, the CLSI clinical breakpoint can be achieved with IM procaine BP twice a day at 22,000 IU i.e. 12.4 mg/kg.

Doxycycline serum protein binding in pigs reveals a relatively high free fraction

Doxycycline is an antibiotic widely used in pig farming. As with all antibiotics, only the free concentrations are considered to be bacteriologically active. Historically, the free fraction (fu) in pig plasma has been estimated at 7%, which, given the effective dosage regime used in pigs, leads to free plasma concentrations of doxycycline largely lower than the minimum inhibitory concentrations of the target pathogens. This apparent inconsistency led us to reassess plasma protein binding of doxycycline in pigs. Using an equilibrium dialysis method, the extent of doxycycline binding was measured individually in 26 pigs for total doxycycline concentration ranging from 10 to 1000 μmol/L. Analysis of the data using a non-linear mixed-effects model demonstrated linearity of plasma protein binding with a mean fu value of 31% and a relatively low inter-subject variability of approximately 10%. This new data showing that the free fraction is four times greater than what could have been anticipated from historical data is discussed in particular for the calculation of the PK/PD cut-offs, which are used to establish the clinical breakpoints for antimicrobial susceptibility testing.

Contribution of Reliable Chromatographic Data in QSAR for Modelling Bisphenol Transport across the Human Placenta Barrier

Regulatory measures and public concerns regarding bisphenol A (BPA) have led to its replacement by structural analogues, such as BPAF, BPAP, BPB, BPF, BPP, BPS, and BPZ. However, these alternatives are under surveillance for potential endocrine disruption, particularly during the critical period of fetal development. Despite their structural analogies, these BPs differ greatly in their placental transport efficiency. For predicting the fetal exposure of this important class of emerging contaminants, quantitative structure-activity relationship (QSAR) studies were developed to model and predict the placental clearance indices (CI). The most usual input parameters were molecular descriptors obtained by modelling, but for bisphenols (BPs) with structural similarities or heteroatoms such as sulfur, these descriptors do not contrast greatly. This study evaluated and compared the capacity of QSAR models based either on molecular or chromatographic descriptors or a combination of both to predict the placental passage of BPs. These chromatographic descriptors include both the retention mechanism and the peak shape on columns that reflect specific molecular interactions between solute and stationary and mobile phases and are characteristic of the molecular structure of BPs. The chromatographic peak shape such as the asymmetry and tailing factors had more influence on predicting the placental passage than the usual retention parameters. Furthermore, the QSAR model, having the best prediction capacity, was obtained with the chromatographic descriptors alone and met the criteria of internal and cross validation. These QSAR models are crucial for predicting the fetal exposure of this important class of emerging contaminants.

Comparison of toxicokinetic properties of eleven analogues of Bisphenol A in pig after intravenous and oral administrations

Due to the restrictions of its use, Bisphenol A (BPA) has been replaced by many structurally related bisphenols (BPs) in consumer products. The endocrine disrupting potential similar to that of BPA has been described for several bisphenols, there is therefore an urgent need of toxicokinetic (TK) data for these emerging BPs in order to evaluate if their internal exposure could increase the risk of endocrine disruption. We investigated TK behaviors of eleven BPA substitutes (BPS, BPAF, BPB, BPF, BPM, BPZ, 3-3BPA, BP4-4, BPAP, BPP, and BPFL) by intravenous and oral administrations of mixtures of them to piglets and serial collection of blood over 72 h and urine over 24 h, to evaluate their disposition. Data were analyzed using nonlinear mixed-effects modeling and a comparison was made with TK predicted by the generic model HTTK package. The low urinary excretion of some BPs, in particular BPM, BPP and BPFL, is an important aspect to consider in predicting human exposure based on urine biomonitoring. Despite their structural similarities, for the same oral dose, all BPA analogues investigated showed a higher systemic exposure (area under the plasma concentration-time curve (AUC) of the unconjugated Bisphenol) than BPA (2 to 4 fold for 3-3BPA, BPAF, BPB and BPZ, 7-20 fold for BP4-4, BPAP, BPP, BPFL, BPF and BPM and 150 fold for BPS) due mainly to a considerable variation of oral bioavailability (proportion of BP administered by oral route that attains the systemic circulation unchanged). Given similarities in the digestive tract between pigs and humans, our TK data suggest that replacing BPA with some of its alternatives, particularly BPS, will likely lead to higher internal exposure to potential endocrine disruptive compounds. These findings are crucial for evaluating the risk of human exposure to these emerging BPs.

Combining sequential extraction and 3D fluorescence to investigate the behavior of antibiotic and polycyclic aromatic hydrocarbons during solar drying of sewage sludge

Solar drying and liming are commonly used for sludge treatment, but little is known about their efficiency on antibiotics and Polycyclic Aromatic Hydrocarbons (PAHs) removal. This study aimed to investigate the removal of antibiotics and PAHs during solar drying of Limed Sludge (LS) and Non-Limed Sludge (NLS). Thus, organic matter fractionation and 3D fluorescence were used to assess the accessibility and the complexity of organic matter. 2 experiments have been conducted using LS and NLS for 45 days of drying in a pilot scale tunnel. Physicochemical results indicated significant decrease of water content (90%) for both sludge samples within 15 days of drying. For both treatments, the removal of total organic carbon and total nitrogen was low and similar for both treatments. Through this study, it has been confirmed that liming and drying contributed to a strong modification of the organic matter quality with an increase of its accessibility. On the other hand, drying alone increased the less accessible compartments, while the presence of lime affected the interconnexion between the organic matter pools. 3D fluorescence confirmed the obtained results and indicated that LS leads to obtaining more simple molecules in the most accessible compartments, while NLS leads to obtaining more complex molecules in the less accessible compartments. In addition, solar radiations and leaching may contribute to the significant removal (p < 0.01) of roxithromycin, benzo(a)anthracene, chrysene, benzo[k]fluoranthene, benzo[a]pyrene, and benzo(g, h, i) perylene in the presence of lime. Furthermore, the evolution of organic matter pools in terms of accessibility and complexity may drive the bioavailability of these pollutants, leading to their significant removal.

Comparison of the materno-fetal transfer of fifteen structurally related bisphenol analogues using an ex vivo human placental perfusion model

Regulatory measures and public concerns regarding bisphenol A (BPA) have led to its replacement by a variety of alternatives in consumer products. Due to their structural similarity to BPA, these alternatives are under surveillance, however, for potential endocrine disruption. Understanding the materno-fetal transfer of these BPA-related alternatives across the placenta is therefore crucial to assess prenatal exposure risks. The objective of the study was to assess and compare the placental transfer of a set of 15 selected bisphenols (BPs) (BP 4-4, BPA, BPAF, BPAP, 3-3 BPA, BPB, BPBP, BPC, BPE, BPF, BPFL, BPM, BPP, BPS and BPZ) using the ex vivo human placental perfusion model. The UHPLC-MS/MS method for simultaneous quantification of these BPs in perfusion media, within a concentration range of 0.003-5 μM, was able to measure placenta transfer rates as low as 0.6%-4%. Despite their structural similarities, these BPs differed greatly in placental transport efficiency. The placental transfer rates of BP4-4, BPAP, BPE, BPF, 3-3BPA, BPB, BPA were similar to that of antipyrine, indicating that their main transport mechanism was passive diffusion. By contrast, the placental transfer rates of BPFL and BPS were very limited, and intermediate for BPBP, BPZ, BPC, BPM, BPP and BPAF, suggesting weak diffusional permeability and/or that their passage might involve efflux transport. These placental transfer data will be particularly useful for predicting the fetal exposure of this important class of emerging contaminants.

A new LC/MS method for specific determination of human systemic exposure to bisphenol A, F and S through their metabolites: Application to cord blood samples

Due to restriction of the use of BPA, several structural analogues such as BPS and BPF have been proposed for its replacement in many consumer products. This has increased the prevalence of BPS and BPF in urine from tested cohorts. However, these substitutes have similar endocrine disrupting properties to BPA, particularly on reproductive and metabolic functions, which suggests that fetal exposure to these analogues could be of concern for human health. Bisphenols (BPs) are mainly metabolized to glucuronides (BP-Gs), which are considered as inactive but provide a relevant marker of fetal exposure during pregnancy. In most instances, these metabolites are indirectly quantified after hydrolysis and measurement of the corresponding native BPs, which may lead to bias due to spurious BPs contamination during blood collection and/or analyses. We have developed a new method for direct quantification of BP-Gs, which has the advantage of not being affected by errors related to the presence of BPs. First, BP-Gs were extracted from plasma by anion exchange solid phase extraction. They were then labelled with dansyl chloride, using experimentally-optimized incubation conditions, after which the dansyl derivatives were injected into an on-line SPE-UHPLC/MS/MS system. The performance of the method, in terms of sensitivity, precision and accuracy, was evaluated in plasma over a concentration range of 0.05-5 ng/mL. The intra- and inter-day CV% precision were lower than 20% with accuracies ranging from 93% to 115%. The limit of quantification was set at 0.05 ng/mL. The method was then applied to measure BP-Gs in forty-four cord plasma samples. Although no BPF-G was found, BPA-G and BPS-G was determined in almost half of the cord plasma samples with concentration ranges nd-0.089 ng/mL and nd-0.586 ng/mL, respectively.

Basal Ti level in the human placenta and meconium and evidence of a materno-foetal transfer of food-grade TiO2 nanoparticles in an ex vivo placental perfusion model

Background

Titanium dioxide (TiO₂) is broadly used in common consumer goods, including as a food additive (E171 in Europe) for colouring and opacifying properties. The E171 additive contains TiO₂ nanoparticles (NPs), part of them being absorbed in the intestine and accumulated in several systemic organs. Exposure to TiO₂-NPs in rodents during pregnancy resulted in alteration of placental functions and a materno-foetal transfer of NPs, both with toxic effects on the foetus. However, no human data are available for pregnant women exposed to food-grade TiO₂-NPs and their potential transfer to the foetus. In this study, human placentae collected at term from normal pregnancies and meconium (the first stool of newborns) from unpaired mothers/children were analysed using inductively coupled plasma mass spectrometry (ICP-MS) and scanning transmission electron microscopy (STEM) coupled to energy-dispersive X-ray (EDX) spectroscopy for their titanium (Ti) contents and for analysis of TiO₂ particle deposition, respectively. Using an ex vivo placenta perfusion model, we also assessed the transplacental passage of food-grade TiO₂ particles.

Results

By ICP-MS analysis, we evidenced the presence of Ti in all placentae (basal level ranging from 0.01 to 0.48 mg/kg of tissue) and in 50% of the meconium samples (0.02–1.50 mg/kg), suggesting a materno-foetal passage of Ti. STEM-EDX observation of the placental tissues confirmed the presence of TiO₂-NPs in addition to iron (Fe), tin (Sn), aluminium (Al) and silicon (Si) as mixed or isolated particle deposits. TiO₂ particles, as well as Si, Al, Fe and zinc (Zn) particles were also recovered in the meconium. In placenta perfusion experiments, confocal imaging and SEM-EDX analysis of foetal exudate confirmed a low transfer of food-grade TiO₂ particles to the foetal side, which was barely quantifiable by ICP-MS. Diameter measurements showed that 70 to 100% of the TiO₂ particles recovered in the foetal exudate were nanosized.

Conclusions

Altogether, these results show a materno-foetal transfer of TiO₂ particles during pregnancy, with food-grade TiO₂ as a potential source for foetal exposure to NPs. These data emphasize the need for risk assessment of chronic exposure to TiO₂-NPs during pregnancy.

Levers to Improve Antibiotic Treatment of Lambs via Drinking Water in Sheep Fattening Houses: The Example of the Sulfadimethoxine/Trimethoprim Combination

To limit the spread of bacterial diseases in sheep fattening houses, antibiotics are often administered collectively. Collective treatments can be delivered by drinking water but data on the drug’s solubility in water or on plasma exposure of the animals are lacking. We first assessed the solubility of products containing sulfadimethoxine (SDM), associated or not with trimethoprim (TMP), in different waters. We then compared in lambs the SDM and TMP pharmacokinetic profiles after individual intravenous (IV) and oral administrations of SDM-TMP in experimental settings (n = 8) and after a collective treatment by drinking water with SDM-TMP or SDM alone in a sheep fattening house (n = 100 for each treatment). The individual water consumption during the collective treatments was also monitored to characterize the ingestion variability. We showed that TMP had a short terminal half-life and very low oral bioavailability, demonstrating that it would be unable to potentiate SDM by oral route. Conversely, SDM had a long terminal half-life of 18 h and excellent oral bioavailability. However, delivery by drinking water resulted in a very high interindividual variability of SDM plasma concentrations, meaning that although disease spread could be controlled at the group level, some individuals would inevitably be under- or over-exposed to the antibiotic.

Bisphenol S Impaired Human Granulosa Cell Steroidogenesis in Vitro

Bisphenol S (BPS) is a structural analog of the endocrine disruptor bisphenol A (BPA); it is the main BPA replacement in the plastics industry. Previous studies have shown that BPA and BPS exhibit similar effects on reproduction in fish and rodent species. BPS reportedly alters steroidogenesis in bovine granulosa cells. Luteinised granulosa cells collected from 59 women who were undergoing an in vitro fertilization procedure were cultured for 48 h in the presence or absence of BPS (10 nM, 100 nM, 1 µM, 10 µM or 50 µM). BPS exposure was investigated by assessing follicular fluids from these 59 women for their BPS content. Culture medium, cells, total messenger RNA (mRNA) and total protein extracted from the luteinised granulosa cells were examined for oestradiol and progesterone secretion, cellular proliferation, viability, gene expression, steroidogenic enzyme expression and cell signaling. BPS was measured in follicular fluids using mass spectrometry. Exposure of granulosa cells to 10 or 50 µM BPS for 48 h induced a 16% (p = 0.0059) and 64% (p < 0.0001) decrease, respectively, in progesterone secretion; 50 µM BPS decreased oestradiol secretion by 46% (p < 0.0001). Ten µM BPS also tended to reduce CYP11A1 protein expression by 37% (p = 0.0947) without affecting HSD3B1 and CYP19A1 expression. Fifty µM BPS increased ERRγ expression. Environmental levels of BPS (nanomolar range) did not induce changes in steroidogenesis in human granulosa cells. The effects of BPS were observed after only 48 h of BPS exposure. These acute effects might be similar to chronic effects of physiological BPS levels.

Toxicokinetics of bisphenol S in rats for predicting human bisphenol S clearance from allometric scaling

Previous data obtained in piglets suggested that despite structural analogy with Bisphenol A (BPA), Bisphenol S (BPS) elimination may proceed more slowly, resulting in a much higher systemic exposure to unconjugated BPS than to BPA. Interspecies allometric scaling was applied to predict the toxicokinetic (TK) parameters of BPS, namely plasma clearance in humans from values obtained in animals, and thus contribute to assessment of the human internal exposure to BPS. Allometric scaling was performed using mean BPS plasma clearance values measured in rats after intravenous administration of 5 mg BPS /kg body weight (BW) and those previously obtained in piglets and sheep using identical IV BPS dosing and analytical procedures. The BPS plasma clearance, evaluated at 0.92 L/kg.h in rats, was proportional to species body weight, enabling the prediction of human BPS plasma clearance by extrapolating to a BW of 70 kg. The estimated BPS plasma clearance in humans was thus 0.92 L/min (0.79 L/kg.h), i.e. about two times lower than the previously estimated BPA clearance (1.79 L/min). By increasing systemic exposure to the active moiety of an environmental estrogenic chemical, this less efficient clearance of BPS in humans, as compared with BPA, might worsen the harmful consequences of replacing BPA by BPS.

Oral Systemic Bioavailability of Bisphenol A and Bisphenol S in Pigs

BACKGROUND

Given its hormonal activity, bisphenol S (BPS) as a substitute for bisphenol A (BPA) could actually increase the risk of endocrine disruption if its toxicokinetic (TK) properties, namely its oral availability and systemic persistency, were higher than those of BPA.

OBJECTIVES

The TK behavior of BPA and BPS was investigated by administering the two compounds by intravenous and oral routes in piglet, a known valid model for investigating oral TK.

METHODS

Experiments were conducted in piglets to evaluate the kinetics of BPA, BPS, and their glucuronoconjugated metabolites in plasma and urine after intravenous administration of BPA, BPS, and BPS glucuronide (BPSG) and gavage administration of BPA and BPS. A population semiphysiologically based TK model describing the disposition of BPA and BPS and their glucuronides was built from these data to estimate the key TK parameters that drive the internal exposure to active compounds.

RESULTS

The data indicated that almost all the BPS oral dose was absorbed and transported into the liver where only 41% of BPS was glucuronidated, leading to a systemic bioavailability of 57.4%. In contrast, only 77% of the oral dose of BPA was absorbed and underwent an extensive first-pass glucuronidation either in the gut (44%) or in the liver (53%), thus accounting for the low systemic bioavailability of BPA (0.50%). Due to the higher systemic availability of BPS, in comparison with BPA, and its lower plasma clearance (3.5 times lower), the oral BPS systemic exposure was on average about 250 times higher than for BPA for an equal oral molar dose of the two compounds.

CONCLUSION

Given the similar digestive tracts of pigs and humans, our results suggest that replacing BPA with BPS will likely lead to increased internal exposure to an endocrine-active compound that would be of concern for human health. https://doi.org/10.1289/EHP4599.

Is bisphenol S a safer alternative to bisphenol A in terms of potential fetal exposure ? Placental transfer across the perfused human placenta

The aim of our study was to evaluate the bidirectional transfer of Bisphenol S (BPS) and its main metabolite, BPS Glucuronide (BPSG), using the model of perfused human placenta and to compare the obtained values with those of Bisphenol A (BPA) and BPA Glucuronide. Fourteen placentas at term were perfused in an open dual circuit with deuterated BPS (1 and 5 μM) and non-labelled BPSG (2.5 μM) and a freely diffusing marker antipyrine (800 ng/ml) in the presence of albumin (25 mg/ml). In a second experiment, the potential role of P-glycoprotein in the active efflux of BPS across the placental barrier was studied using the well-established P-glycoprotein inhibitor, PSC833 (2 and 4 μM). Placental transfer of BPS was much lower than that of BPA in both directions. The placental clearance index of BPS in the materno-fetal direction was three times lower than in the opposite direction, strongly suggesting some active efflux transport. However, our results show that P-glycoprotein is not involved in limiting the materno-fetal transfer of BPS. Placental transfer of BPSG in the fetal compartment was almost non-existent indicating that, in the fetal compartment, BPSG originates mainly from feto-placental metabolism. The feto-maternal clearance index for BPSG was 20-fold higher than the materno-fetal index. We conclude that the blood-placental barrier is much more efficient in limiting fetal exposure to BPS than to BPA, indicating that the placenta has a crucial role in protecting the human fetus from BPS exposure.

Quantification of Lipids: Model, Reality, and Compromise

Lipids are key molecules in various biological processes, thus their quantification is a crucial point in a lot of studies and should be taken into account in lipidomics development. This family is complex and presents a very large diversity of structures, so analyzing and quantifying all this diversity is a real challenge. In this review, the different techniques to analyze lipids will be presented: from nuclear magnetic resonance (NMR) to mass spectrometry (with and without chromatography) including universal detectors. First of all, the state of the art of quantification, with the definitions of terms and protocol standardization, will be presented with quantitative lipidomics in mind, and then technical considerations and limitations of analytical chemistry's tools, such as NMR, mass spectrometry and universal detectors, will be discussed, particularly in terms of absolute quantification.

A pressurized liquid extraction approach followed by standard addition method and UPLC-MS/MS for a fast multiclass determination of antibiotics in a complex matrix

In this work a fast analytical method for the determination of macrolides, tetracyclines and fluoroquinolones in a compost originating from a mixture of sewage sludge, palm waste and grass was developed by ultra-high performance liquid chromatography coupled to mass spectrometry (U-HPLC/MS). Antibiotics were extracted from compost by using the accelerated solvent extraction (ASE). The chromatographic separation was carried out on a T3 Cortecs C18 column using a mobile phase gradient mixture of water acidified with 1% of formic acid and acetonitrile. Recoveries of 24-30%, 53-93%, 33-57%, 69-135% and 100-171% were obtained for roxithromycin (ROX), chlortetracycline (CTC), oxytetracycline (OTC), enrofloxacin (ENR) and ciprofloxacin (CIP), respectively. As the most part of antibiotics showed significant matrix effect (ME), the method was validated using the standard addition method (SAM) to correct the observed ME. Instrumental variation, of LC/MS system, showed that 93.75% of the relative standard deviation (RSD %) are below 15%, although the organic load of extracts. This analytical method was applied to assess the fate of antibiotics during composting. Two composting experiments were conducted separately after spiking sludge at 2 different concentrations levels. The resulting elimination rates were of 52-76, 69-100, 100 and 24-50% for ROX, CTC, OTC and CIP, respectively. These results suggest that composting process contributes to the removal of residuals concentrations of macrolides and tetracyclines while the fluoroquinolones persist in the final compost product.

Bisphenol S instead of Bisphenol A: Toxicokinetic investigations in the ovine materno-feto-placental unit

Bisphenol S (BPS) is widely used as a substitute for Bisphenol A in consumer products. Despite its potential endocrine-disrupting effects and widespread exposure, toxicokinetic data, particularly during the critical period of pregnancy, are not available for BPS. The objectives of our study were to evaluate the mechanisms determining fetal exposure to BPS and to BPS glucuronide (BPSG) and to compare them with those prevailing for BPA. The disposition of BPS and BPSG was evaluated in the materno-fetal unit of the catheterized pregnant ewe model, following intravenous administrations of BPS and BPSG to mothers and their fetuses. In a second experiment, the rate of BPS accumulation in the fetal compartment was determined under steady-state conditions after repeated intravenous BPS administrations to the mother. In the maternal compartment, BPS was mainly metabolized into BPSG and totally eliminated in urine. Only 0.40% of the maternal dose was transferred to the fetus. However, once in the fetal compartment, 26% of the fetal dose was rapidly eliminated through placental transfer, while 46% of BPS was metabolized into BPSG which remained trapped in the fetal compartment. Thus, the elimination of BPSG from the fetal compartment required its back-conversion into bioactive BPS, leading to an 87% enhancement of the fetal BPS exposure. Our findings demonstrate that, despite the low materno-fetal placental transfer of BPS, this substitute for BPA is able to accumulate in the fetal compartment after repeated maternal exposure, leading to chronic fetal exposure to BPS in a range of concentrations similar to those of BPA.

Differential Activity of the Combination of Vancomycin and Amikacin on Planktonic vs. Biofilm-Growing Staphylococcus aureus Bacteria in a Hollow Fiber Infection Model

Combining currently available antibiotics to optimize their use is a promising strategy to reduce treatment failures against biofilm-associated infections. Nevertheless, most assays of such combinations have been performed in vitro on planktonic bacteria exposed to constant concentrations of antibiotics over only 24 h and the synergistic effects obtained under these conditions do not necessarily predict the behavior of chronic clinical infections associated with biofilms. To improve the predictivity of in vitro combination assays for bacterial biofilms, we first adapted a previously described Hollow-fiber (HF) infection model by allowing a Staphylococcus aureus biofilm to form before drug exposure. We then mimicked different concentration profiles of amikacin and vancomycin, similar to the free plasma concentration profiles that would be observed in patients treated daily over 5 days. We assessed the ability of the two drugs, alone or in combination, to reduce planktonic and biofilm-embedded bacterial populations, and to prevent the selection of resistance within these populations. Although neither amikacin nor vancomycin exhibited any bactericidal activity on S. aureus in monotherapy, the combination had a synergistic effect and significantly reduced the planktonic bacterial population by -3.0 to -6.0 log₁₀ CFU/mL. In parallel, no obvious advantage of the combination, as compared to amikacin alone, was demonstrated on biofilm-embedded bacteria for which the addition of vancomycin to amikacin only conferred a further maximum reduction of 0.3 log₁₀ CFU/mL. No resistance to vancomycin was ever found whereas a few bacteria less-susceptible to amikacin were systematically detected before treatment. These resistant bacteria, which were rapidly amplified by exposure to amikacin alone, could be maintained at a low level in the biofilm population and even suppressed in the planktonic population by adding vancomycin. In conclusion, by adapting the HF model, we were able to demonstrate the different bactericidal activities of the vancomycin and amikacin combination on planktonic and biofilm-embedded bacterial populations, suggesting that, for biofilm-associated infections, the efficacy of this combination would not be much greater than with amikacin monotherapy. However, adding vancomycin could reduce possible resistance to amikacin and provide a relevant strategy to prevent the selection of antibiotic-resistant bacteria during treatments.

Prediction of human prenatal exposure to bisphenol A and bisphenol A glucuronide from an ovine semi-physiological toxicokinetic model

Bisphenol A (BPA) risk assessment is hampered by the difficulty of determining the extent of internal exposure in the human fetus and uncertainties regarding BPA toxicokinetics (TK) in the maternal-fetal unit. A feto-maternal TK model describing BPA and BPA glucuronide (BPAG) disposition in sheep was humanized, using human TK data obtained after d6-BPA administration on a cookie, to predict BPA and BPAG kinetics in the human mother-fetus unit. Validation of the model predictions included the assessed dose proportionality of BPA and BPAG disposition and the similarity between the simulated and measured time courses of BPA and BPAG in fetal rhesus monkeys after BPA maternal dosing. The model predicted fluctuations in fetal BPA concentrations associated with typical maternal exposure to BPA through the diet, with similar trough (0.011 ng/L vs 0.014 ng/L) and lower peak BPA concentrations (0.023 ng/L vs 0.14 ng/L) in fetal than in maternal plasma. BPAG concentrations in fetal plasma were predicted to increase over time to reach a steady value (29 ng/L) reflecting the cumulative BPA dose received by the fetus. Model-predicted BPAG concentrations in fetal plasma are consistent with reported levels in human cord blood that may be considered as relevant markers of the BPA dose entering blood throughout fetal life.

Evidence for bisphenol A-induced disruption of maternal thyroid homeostasis in the pregnant ewe at low level representative of human exposure

Many uncertainties remain regarding the potential of bisphenol A (BPA) as a thyroid disruptor in mammals and the relevance of experimental data to humans. The relevance of the exposure schemes used in experimental in vivo studies is also a major source of uncertainty when analysing the risk of BPA exposure for human health. In this context, the goals of our study, conducted in an ovine model relevant to human gestation and thyroid physiologies, were to: 1) determine the equivalence of subcutaneous and dietary exposures and 2) determine if environmentally relevant doses of BPA can alter gestational and newborn thyroid functions. The difference between the two routes of exposure was mainly related to the overall BPA exposure and much less to the peak serum concentrations. Interestingly, BPA-GLUC (the main metabolite of BPA) internal exposure via both routes was almost identical. The decrease in thyroid hormones concentration overtime was more accentuated in ewes treated with BPA, particularly with the medium dose (50 μg/(kg.d); SC) for which the maximum BPA concentrations were predicted to be within the 1-10 ng/mL range i.e. very similar to the highest blood concentrations reported in humans. The balance between TT4 and rT3 varied differently between the vehicle and the medium dose group. The mechanisms underlying those modifications of maternal thyroid homeostasis remain to be determined. Our study did not evidence significant modification of TSH secretion or binding to serum proteins but might suggest an effect at the level of deiodinases.

In vitro Degradation of Antimicrobials during Use of Broth Microdilution Method Can Increase the Measured Minimal Inhibitory and Minimal Bactericidal Concentrations

The antibacterial activity of some antimicrobials may be under-estimated during in vitro microbiological susceptibility tests, due to their instability under such conditions. The in vitro degradation of seven widely used antimicrobials (amoxicillin, cephalexin monohydrate, cefotaxime sodium salt, ciprofloxacin, erythromycin hydrate, clarithromycin, and doxycycline hyclate) and its effect on MIC and MBC determinations was studied using the broth microdilution method, considered as the gold standard for MIC determinations. In vitro concentrations of antimicrobials, over a 24 h incubation period in the medium tested without bacteria, decreased from 33% for ciprofloxacin to 69% for clarithromycin. For cephalexin, cefotaxime, clarithromycin, and doxycycline which were the most degraded drugs, MIC and MBC values for one strain of E. coli and one strain of S. aureus were compared using the standard method or after ad-hoc drug complementation aiming at maintaining constant drug concentration. Abiotic degradation during the standard method was associated with a significant increase of the MIC (2 antibiotics) and MBC (3 antibiotics). However, the observed discrepancy (less than one twofold dilution), even for the most degraded drug for which the concentration at 24 h was reduced by two thirds, suggests that this would only be clinically significant in special cases such as slow-growing bacteria.

Bisphenol A in culture media and plastic consumables used for ART

STUDY QUESTION

Do the embryo culture media and plastic materials used during assisted reproductive technology (ART) laboratory procedures expose embryos to bisphenol A (BPA)?

SUMMARY ANSWER

BPA was not detected in embryo culture media or protein supplements at concentrations above those encountered in normal patient serum and follicular fluids.

WHAT IS KNOWN ALREADY

BPA is strongly suspected of altering the epigenome during mammalian development. Medical devices have been shown to be a source of BPA exposure in adult and neonatal intensive care units.

STUDY DESIGN, SIZE, DURATION

An analytical study of ART culture media and plastic labware products was performed under conditions close to routine practice and if BPA was detected, tests were carried out under more stringent conditions.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Two single-step embryo culture media, two sequential media and three different protein supplements [a purified human serum albumin (HSA), a synthetic serum substitute, and a recombinant HSA] were tested for BPA. Thirty-three different plastic consumables, used from oocyte collection through to embryo transfer, were tested for their ability to leach BPA into their surrounding environment.BPA concentrations were measured according to a previously described liquid chromatography/mass spectrometry method. This method is linear over the calibration range from 0.5 to 100 ng/ml using a linear model weighted by 1/X² and validated in terms of selectivity, linearity, repeatability, reproducibility and limit of quantification (0.5 ng/ml).

MAIN RESULTS AND THE ROLE OF CHANCE

Neither the culture media nor the protein supplements were shown to contain detectable levels of BPA. None of the plastic materials leached BPA into the surrounding medium at levels higher than the upper limit detected previously in serum and follicular fluids in women (about 2 ng/ml). However, the plastic of the three tested strippers used for oocyte denudation/embryo handling did contain BPA. Two of these strippers are made with polycarbonate, a plastic whose synthesis is known to require BPA.

LIMITATIONS, REASONS FOR CAUTION

This study is limited to the ART media and materials tested here and using a BPA assay with a limit of quantification at 0.5 ng/ml. A minimum volume was required for testing, and one type of plastic labware could not be tested in conditions identical to those in routine use.

WIDER IMPLICATIONS OF THE FINDINGS

Although we demonstrated that some plastic materials used in ART contain BPA, under routine conditions none appear capable of leaching BPA at levels higher than those from maternal internal exposure. However, BPA is strongly suspected of altering the epigenome. Since important epigenetic modifications occur in the early embryonic stage, it is questionable whether plastics that contain BPA, polycarbonate in particular, should be used in the manufacture of plastic consumables for ART procedures.

STUDY FUNDING/COMPETING INTERESTS

This work was supported by a grant from the Agence de Biomédecine (AOR 2012) and by a grant from the French Ministry of Health (Clinical Research Hospital Program 2012; no.12-018-0560). The authors declared no competing interest.

Bisphenol A glucuronide deconjugation is a determining factor of fetal exposure to bisphenol A

Previous studies in experimental animals have shown that maternal exposure to bisphenol A (BPA) during late pregnancy leads to high plasma concentrations of BPA glucuronide (BPAG) in fetus compared to mother due to the inability of BPAG to cross the placental barrier. A recent in vitro study has reported that BPAG can exert adipogenic effect underlining the need for characterization of the fetal disposition of BPAG. Experiments were conducted in chronically catheterized fetal sheep to determine the contribution of BPAG hydrolysis to BPA to the elimination of BPAG from the fetal compartment and its resulting effect on the overall fetal exposure to free BPA. Serial sampling of fetal arterial blood, amniotic fluid, maternal venous blood and urine was performed following separate single doses of BPA and BPAG administered intravenously to eight fetal/maternal pairs after cesarean section, and repeated BPAG doses given to two fetal sheep. On average 67% of the BPA entering the fetal circulation was rapidly eliminated through fetal to maternal clearance, with a very short half-life (20 min), while the remaining fraction (24%) was glucuronoconjugated. BPA conjugation-deconjugation cycling was responsible for a 43% increase of the overall fetal exposure to free BPA. A very specific pattern of fetal exposure to free BPA was observed due to its highly increased persistence with a hydrolysis-dependent plasma terminal free BPA half-life of several tens of hours. These findings suggest that although the high fetal to maternal clearance of free BPA protects the fetus from transient increases in free BPA plasma concentrations associated with maternal BPA intake, low but sustained basal free BPA concentrations are maintained in the fetus through BPA conjugation-deconjugation cycling. The potential health implications of these low but sustained basal concentrations of free BPA in fetal plasma should be addressed especially when considering time-dependent effects.

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.

Bisphenol A disposition in the sheep maternal-placental-fetal unit: mechanisms determining fetal internal exposure

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.

Maternal and fetal exposure to bisphenol a is associated with alterations of thyroid function in pregnant ewes and their newborn lambs

The putative thyroid-disrupting properties of bisphenol A (BPA) highlight the need for an evaluation of fetal exposure and its consequence on the mother/newborn thyroid functions in models relevant to human. The goals of this study were to characterize in sheep a relevant model for human pregnancy and thyroid physiology, the internal exposures of the fetuses and their mothers to BPA and its main metabolite BPA-glucuronide (Gluc), and to determine to what extent it might be associated with thyroid disruption. Ewes were treated with BPA [5 mg/(kg · d) sc] or vehicle from d 28 until the end of pregnancy. Unconjugated BPA did not appear to accumulate in pregnant ewes, and its concentration was similar in the newborns and their mothers (0.13 ± 0.02 and 0.18 ± 0.03 nmol/ml in cord and maternal blood, respectively). In amniotic fluid and cord blood, BPA-Gluc concentrations were about 1300-fold higher than those of BPA. Total T(4) concentrations were decreased in BPA-treated pregnant ewes and in the cord and the jugular blood of their newborns (30% decrease). A similar difference was observed for free T(4) plasma concentrations in the jugular blood of the newborns. Our results show in a long-gestation species with a similar regulatory scheme of thyroid function as humans that BPA in utero exposure can be associated with hypothyroidism in the newborns. If such an effect were to be confirmed for a more relevant exposure scheme to BPA, this would constitute a major issue for BPA risk assessment.

Assessment of the genotoxicity of quinolone and fluoroquinolones contaminated soil with the Vicia faba micronucleus test

The genotoxicity of quinolone and fluroquinolones was assessed using the micronucleus (MN) test on Vicia faba roots by direct contact exposure to a solid matrix. Plants were exposed to quinolones (nalidixic acid) and fluoroquinolones (ciprofloxacin and enrofloxacin) alone or mixed with artificially contaminated soils. Four different concentrations of each of these antibiotics were tested (0.01, 0.1, 1 and 10 mg/Kg) for nalidixic acid and (0.005, 0.05, 0.5 and 5 mg/Kg) for ciprofloxacin and enrofloxacin. These antibiotics were also used in mixture. Exposure of Vicia faba plants to each antibiotic at the highest two concentrations showed significant MN induction. The lowest two concentrations had no significant genotoxic effect. The mixture of the three compounds induced a significant MN induction whatever the mixture tested, from 0.02 to 20 mg/Kg. The results indicated that a similar genotoxic effect was obtained with the mixture at 0.2 mg/Kg in comparison with each molecule alone at 5-10 mg/Kg. Data revealed a clear synergism of these molecules on Vicia faba genotoxicity.

Paw inflammation model in dogs for preclinical pharmacokinetic/pharmacodynamic investigations of nonsteroidal anti-inflammatory drugs

The goal of the present study was to develop and validate a new canine model of inflammation. The motivation was to make available a scientifically appropriate and ethically acceptable model to conduct pharmacokinetic/pharmacodynamic investigations for testing nonsteroidal anti-inflammatory drugs in dogs. A kaolin-induce paw inflammation model previously developed in cats was adapted to the dog. The paw inflammation developed within a few hours, reached maximum values 24 h and up to 3 days after kaolin administration, and then progressively resolved over 2 months. Five end points of clinical interest (body temperature, creeping time under a tunnel, paw withdrawal latency to a standardized thermal stimulus, lameness score, and vertical force developed during walking on a force plate) were measured regularly over the next 24 h and beyond to characterize the time development of the inflammation either in control conditions (placebo period) or after the administration of meloxicam (test period) according to a crossover design. Pharmacodynamic data were modeled using an indirect response pharmacokinetic/pharmacodynamic model. This model described three effects of meloxicam, namely, classic anti-inflammatory, analgesic, and antipyretic effects. The mean plasma meloxicam IC(50) values were 210 ng/ml for the antipyretic effect, 390 ng/ml for the analgesic effect, and 546 ng/ml for the vertical force exerted by the paw on the ground as measured by force plates. These in vivo IC(50) values require approximately 80 (antipyretic effect) to 90% (all other effects) cyclooxygenase-2 inhibition as calculated ex vivo whole-blood assay data.

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).

Quantification of fipronil and its metabolite fipronil sulfone in rat plasma over a wide range of concentrations by LC/UV/MS

Fipronil is an insecticide extensively used to treat pets, which has been identified as a potential thyroid disruptor in the rat. In this species, fipronil is mainly metabolized to fipronil sulfone and plasma concentrations of fipronil sulfone can be at least 20-fold higher than those of fipronil. Investigations of fipronil and fipronil sulfone exposure in blood remain sparse because of the lack of convenient and suitable analytical methods. We have developed and validated an LC/UV/MS/MS method to quantify both fipronil and fipronil sulfone within a wide range of concentrations in rat plasma. The double detection UV and MS coupled on-line enabled the concentrations to be measured over a 3 Log range (2.5-2500 ng/mL). The volume of sample required for the extraction by solid phase extraction was reduced to 75 microL with a recovery higher than 70%. The two-detection method agreement, evaluated with a Bland-Altman plot, was good for concentrations between 50 and 150 ng/mL. The method was applied to monitor plasma concentrations following a commonly used dosage regimen for the toxicological evaluation of fipronil in rats.