Towards translating in vitro measures of thyroid hormone system disruption to in vivo responses in the pregnant rat via a biologically based dose response (BBDR) model.

Despite the number of in vitro assays that have been recently developed to identify chemicals that interfere with the hypothalamic-pituitary-thyroid axis (HPT), the translation of those in vitro results into in vivo responses (in vitro to in vivo extrapolation, IVIVE) has received limited attention from the modeling community. To help advance this field a steady state biologically based dose response (BBDR) model for the HPT axis was constructed for the pregnant rat on gestation day (GD) 20. The BBDR HPT axis model predicts plasma levels of thyroid stimulating hormone (TSH) and the thyroid hormones, thyroxine (T4) and triiodothyronine (T3). Thyroid hormones are important for normal growth and development of the fetus. Perchlorate, a potent inhibitor of thyroidal uptake of iodide by the sodium iodide symporter (NIS) protein, was used as a case study for the BBDR HPT axis model. The inhibitory blocking of the NIS by perchlorate was associated with dose-dependent steady state decreases in thyroid hormone production in the thyroid gland. The BBDR HPT axis model predictions for TSH, T3, and T4 plasma concentrations in pregnant Sprague Dawley (SD) rats were within 2-fold of observations for drinking water perchlorate exposures ranging from 10 to 30,000 µg/kg/d. In Long Evans (LE) pregnant rats, for both control and perchlorate drinking water exposures, ranging from 85 to 82,000 µg/kg/d, plasma thyroid hormone and TSH concentrations were predicted within 2 to 3.4- fold of observations. This BBDR HPT axis model provides a successful IVIVE template for thyroid hormone disruption in pregnant rats.

Toxicokinetics of praseodymium and cerium administered as chloride salts in Sprague-Dawley rats: impacts of the dose and of co-exposure with additional rare earth elements.

We conducted a rat exposure study to assess the impacts of dose and co-exposure with other rare earth elements (REEs) on the toxicokinetics of praseodymium (Pr) and cerium (Ce). We first determined the kinetic profiles of elemental Pr and Ce in blood, urine and feces along with tissue levels at sacrifice on the seventh day following intravenous injection of PrCl3 or CeCl3 at 0.3 or 1 mg/kg bw (of the chloride salts) in adult male Sprague-Dawley rats (n = 5 per group). In blood, Pr and Ce half-lives for the initial phase (t1/2α) increased with increasing doses, while their half-lives for the terminal phase (t1/2ß) were similar at both doses. In urine, a minor excretion route, no significant effect of the dose on the cumulative excretion was apparent. In feces, a major excretion route, the fraction of the Pr dose recovered was significantly lower at the 1 mg/kg bw dose compared to the 0.3 mg/kg bw dose, while no significant dose effect was apparent for Ce. In the liver and spleen, which are the main sites of REEs accumulation, there was a significant effect of the dose only for Ce retention in the spleen (i.e., increased retention of Ce in spleen at higher dose). Results were compared with those of a previous toxicokinetic study with a similar design but an exposure to a quaternary mixture of CeCl3, PrCl3, NdCl3 and YCl3, each administered at 0.3 mg/kg bw or 1 mg/kg bw. A mixture effect was apparent for the initial elimination phase (t1/2α) of Pr and Ce from blood and for the fecal excretion of Ce at the 1 mg/kg bw. In urine and liver, there was no evident overall mixture effect; in the spleen, there was a higher retention of Pr and Ce in rats exposed to the mixture at the 0.3 mg/kg bw, but not at the 1 mg/kg bw dose. Overall, this study showed that the dose and mixture exposure are two important factors to consider as determinants of the toxicokinetics of REEs.

Comprehensive interpretation of in vitro micronucleus test results for 292 chemicals: from hazard identification to risk assessment application.

Risk assessments are increasingly reliant on information from in vitro assays. The in vitro micronucleus test (MNvit) is a genotoxicity test that detects chromosomal abnormalities, including chromosome breakage (clastogenicity) and/or whole chromosome loss (aneugenicity). In this study, MNvit datasets for 292 chemicals, generated by the US EPA's ToxCast program, were evaluated using a decision tree-based pipeline for hazard identification. Chemicals were tested with 19 concentrations (n = 1) up to 200 µM, in the presence and absence of Aroclor 1254-induced rat liver S9. To identify clastogenic chemicals, %MN values at each concentration were compared to a distribution of batch-specific solvent controls; this was followed by cytotoxicity assessment and benchmark concentration (BMC) analyses. The approach classified 157 substances as positives, 25 as negatives, and 110 as inconclusive. Using the approach described in Bryce et al. (Environ Mol Mutagen 52:280-286, 2011), we identified 15 (5%) aneugens. IVIVE (in vitro to in vivo extrapolation) was employed to convert BMCs into administered equivalent doses (AEDs). Where possible, AEDs were compared to points of departure (PODs) for traditional genotoxicity endpoints; AEDs were generally lower than PODs based on in vivo endpoints. To facilitate interpretation of in vitro MN assay concentration-response data for risk assessment, exposure estimates were utilized to calculate bioactivity exposure ratio (BER) values. BERs for 50 clastogens and two aneugens had AEDs that approached exposure estimates (i.e., BER < 100); these chemicals might be considered priorities for additional testing. This work provides a framework for the use of high-throughput in vitro genotoxicity testing for priority setting and chemical risk assessment.

Estimation of toluene exposure in air from BMA (S-benzylmercapturic acid) urinary measures using a reverse dosimetry approach based on physiologically pharmacokinetic modeling.

This study aimed to use a reverse dosimetry PBPK modeling approach to estimate toluene atmospheric exposure from urinary measurements of S-benzylmercapturic acid (BMA) in a small group of individuals and to evaluate the uncertainty associated to urinary spot-sampling compared to 24-h collected urine samples. Each exposure assessment technique was developed namely to estimate toluene air exposure from BMA measurements in 24-h urine samples (24-h-BMA) and from distributions of daily urinary BMA spot measurements (DUBSM). Model physiological parameters were described based upon age, weight, size and sex. Monte Carlo simulations with the PBPK model allowed converting DUBSM distribution (and 24-h-BMA) into toluene air levels. For the approach relying on DUBSM distribution, the ratio between the 95% probability of predicted toluene concentration and its 50% probability in each individual varied between 1.2 and 1.4, while that based on 24-h-BMA varied between 1.0 and 1.1. This suggests more variability in estimated exposure from spot measurements. Thus, estimating toluene exposure based on DUBSM distribution generated about 20% more uncertainty. Toluene levels estimated (0.0078-0.0138 ppm) are well below Health Canada's maximum chronic air guidelines. PBPK modeling and reverse dosimetry may be combined to interpret urinary metabolites data of VOCs and assess related uncertainties.

Derivation of Biomonitoring Equivalents for aluminium for the interpretation of population-level biomonitoring data.

Aluminium is widely used in many consumer products, however the primary source of aluminium exposure to the Canadian general population is through food. Aluminium can cause neurotoxicity and reproductive toxicity at elevated exposure levels. Health-based exposure guidance values have been established for oral exposure to aluminium, including a Minimal Risk Level (MRL) by the Agency for Toxic Substances and Disease Registry (ATSDR), a Provincial Tolerable Weekly Intake (PTWI) by the Joint FAO/WHO Expert Committee on Food Additives (JECFA) and a Tolerable Weekly Intake (TWI) by the European Food Safety Authority (EFSA). Aluminium concentration in blood and urine can be used as a tool for exposure characterization in a population. A pharmacokinetic (PK) model was developed based on human dosing data to derive blood Biomonitoring Equivalents (BEs), whereas a mass balance approach was used to derive urine BEs for the above guidance values. The BEs for blood for daily intake consistent with the MRL, PTWI and TWI were 18, 16 and 8 µg/L, respectively. BEs for urine for the same guidance values were 137, 123 and 57 µg/L, respectively. The derived BEs may be useful in interpreting population-level biomonitoring data in a health risk context and thereby screening and prioritizing substances for human health risk assessment and risk management.

Derivation of biomonitoring equivalents (BE values) for bismuth.

Bismuth (Bi) is a natural element present in the environmental media. Bismuth has been used medicinally for centuries, specifically for the treatment of gastrointestinal (GI) disorders. Although bismuth toxicity is rare in humans, an outbreak of bismuth-induced neurotoxicity was reported in France and Australia in the mid-1970s. The primary source of bismuth exposure in the general population is via food. US FDA (2019) estimated recommended daily intake (RDI) for bismuth as 848 mg bismuth/day (12.1 mg Bi/kg-d assuming a body weight of 70 kg) for GI tract disorders. Exposures to bismuth can be quantified by measuring concentrations in blood and urine. Biomonitoring equivalents (BEs) were derived based on US FDA's RDI as a tool for interpretation of population-level biomonitoring data. A regression between steady state plasma concentrations and oral intakes was used to derive plasma BEs. A whole blood: plasma partitioning coefficient of 0.6 was used to convert plasma BE into whole blood BE. A mass balance equation with a urinary excretion fraction of 0.0003 was used to derive urinary BE. The BE values associated with US FDA's RDI for plasma, whole blood and urine were 8.0, 4.8 and 0.18 µg/L, respectively. These BE values together with bismuth biomonitoring data may be used in screening and prioritization of health risk assessment of bismuth in the general population.

Development of Biomonitoring Equivalents for chlordane and toxaphene with application to the general Canadian population.

Biomonitoring Equivalents (BEs) were developed for chlordane and toxaphene using one-compartment pharmacokinetic models and compared with biomonitoring data from the Canadian Health Measures Survey, Cycle 1 (2007-2009). A secondary objective was to examine the toxicities of the components of technical chlordane in a HEPG2 cell culture experiment. Oral reference doses were identified from national and international regulatory agencies and sources. Pharmacokinetic parameters were obtained from experimental data in rodent models. A set of BEs have been derived for the main chlordane isomers, cis-chlordane, trans-chlordane, cis-nonachlor, and trans-nonachlor, and the chlordane metabolite, oxychlordane. BEs were also derived for the main toxaphene isomers found in biota, Parlar No. 26, 50 and 62. Among the general Canadian population, no exceedances of chlordane or toxaphene BEs were observed. Based on the LC50 from the in vitro study, trans-nonachlor was the most toxic, and the trans-isomers were more toxic than the cis-isomers. The derived BE values can be used as screening guidelines to assess the risk of biomonitoring data in human populations. The results of an in vitro experiment suggest that trans-nonachlor is more toxic than technical chlordane and, therefore, the BE for this compound may need to be further lowered.

Reverse dosimetry modeling of toluene exposure concentrations based on biomonitoring levels from the Canadian health measures survey.

Biomonitoring might provide useful estimates of population exposure to environmental chemicals. However, data uncertainties stemming from interindividual variability are common in large population biomonitoring surveys. Physiologically based pharmacokinetic (PBPK) models might be used to account for age- and gender-related variability in internal dose. The objective of this study was to reconstruct air concentrations consistent with blood toluene measures reported in the third Canadian Health Measures Survey using reverse dosimetry PBPK modeling techniques. Population distributions of model's physiological parameters were described based upon age, weight, and size for four subpopulations (12-19, 20-39, 40-59, and 60-79 years old). Monte Carlo simulations applied to PBPK modeling allowed converting the distributions of venous blood measures of toluene obtained from CHMS into related air levels. Based upon blood levels observed at the 50th, 90th and 95th percentiles, corresponding air toluene concentrations were estimated for teenagers aged 12-19 years as being, respectively, 0.009, 0.04 and 0.06 ppm. Similarly, values were computed for adults aged 20-39 years (0.007, 0.036, and 0.06 ppm), 40-59 years (0.007, 0.036 and 0.06 ppm) and 60-79 years (0.006, 0.022 and 0.04 ppm). These estimations are well below Health Canada's maximum recommended chronic air guidelines for toluene. In conclusion, PBPK modeling and reverse dosimetry may be combined to help interpret biomonitoring data for chemical exposure in large population surveys and estimate the associated toxicological health risk.

Biomonitoring Equivalents for interpretation of urinary iodine.

Iodine is an essential nutrient whose deficiency or excess exposure can cause adverse health effects. The primary sources of iodine exposure in the general population are iodized salt, dairy products, bread and sea food. Urinary iodine concentrations (UIC) have been measured by Canadian Health Measures Survey (CHMS) and US National Health and Nutrition Examination Survey (NHANES). The Institute of Medicine (IOM), the US Agency for Toxic Substances and Disease Registry (ATSDR) and World Health Organization (WHO) have established exposure guidance values for nutrition (IOM Estimated Average Requirement (EAR), Recommended Dietary Allowance (RDA), WHO Recommended Nutrient Intake (RNI)) and toxicity (IOM Tolerable Upper Intake Level (UL); ATSDR Minimal Risk Level (MRL), WHO International Programme on Chemical Safety (IPCS) Tolerable Daily Intake (TDI)). Using a urinary excretion fraction of 0.9, Biomonitoring Equivalents (BE) for the EAR, RDA, UL and MRL were derived for adults (60, 100, 730 and 450 µg/L, respectively) and children (50, 80, 580 and 360 µg/L, respectively). The population median UIC values from NHANES and CHMS for adults (140-181, 122-126 µg/L, respectively) and children (232, 189 µg/L, respectively) were above the criteria for assessing iodine nutrition, indicating that US and Canadian populations are likely to have adequate population iodine nutrition. The median UIC from NHANES and CHMS do not exceed BE values derived from exposure guidance values for toxicity.

Screening-level Biomonitoring Equivalents for tiered interpretation of urinary 3-phenoxybenzoic acid (3-PBA) in a risk assessment context.

3-Phenoxybenzoic acid (3-PBA) is a common metabolite of several pyrethroid pesticides of differing potency and also occurs as a residue in foods resulting from environmental degradation of parent pyrethroid compounds. Thus, 3-PBA in urine is not a specific biomarker of exposure to a particular pyrethroid. However, an approach derived from the use of Biomonitoring Equivalents (BEs) can be used to estimate a conservative initial screening value for a tiered assessment of population data on 3-PBA in urine. A conservative generic urinary excretion fraction for 3-PBA was estimated from data for five pyrethroid compounds with human data. Estimated steady-state urinary 3-PBA concentrations associated with reference doses and acceptable daily intakes for each of the nine compounds ranged from 1.7 µg/L for cyhalothrin and deltamethrin to 520 µg/L for permethrin. The lower value can be used as a highly conservative Tier 1 screening value for assessment of population urinary 3-PBA data. A second tier screening value of 87 µg/L was derived based on weighting by relative exposure estimates for the different pyrethroid compounds, to be applied as part of the data evaluation process if biomonitoring data exceed the Tier 1 value. These BE values are most appropriately used to evaluate the central tendency of population biomarker concentration data in a risk assessment context. The provisional BEs were compared to available national biomonitoring data from the US and Canada.

Recommended approaches in the application of toxicogenomics to derive points of departure for chemical risk assessment.

There is increasing interest in the use of quantitative transcriptomic data to determine benchmark dose (BMD) and estimate a point of departure (POD) for human health risk assessment. Although studies have shown that transcriptional PODs correlate with those derived from apical endpoint changes, there is no consensus on the process used to derive a transcriptional POD. Specifically, the subsets of informative genes that produce BMDs that best approximate the doses at which adverse apical effects occur have not been defined. To determine the best way to select predictive groups of genes, we used published microarray data from dose-response studies on six chemicals in rats exposed orally for 5, 14, 28, and 90 days. We evaluated eight approaches for selecting genes for POD derivation and three previously proposed approaches (the lowest pathway BMD, and the mean and median BMD of all genes). The relationship between transcriptional BMDs derived using these 11 approaches and PODs derived from apical data that might be used in chemical risk assessment was examined. Transcriptional BMD values for all 11 approaches were remarkably aligned with corresponding apical PODs, with the vast majority of toxicogenomics PODs being within tenfold of those derived from apical endpoints. We identified at least four approaches that produce BMDs that are effective estimates of apical PODs across multiple sampling time points. Our results support that a variety of approaches can be used to derive reproducible transcriptional PODs that are consistent with PODs produced from traditional methods for chemical risk assessment.

Evaluation and modeling of the impact of coexposures to VOC mixtures on urinary biomarkers.

CONTEXT: Urinary biomarkers are widely used among biomonitoring studies because of their ease of collection and nonintrusiveness. Chloroform and TEX (i.e., toluene, ethylbenzene, and m-xylene) are chemicals that are often found together because of common use. Although interactions occurring among TEX are well-known, no information exists on possible kinetic interactions between these chemicals and chloroform at the level of parent compound or urinary biomarkers. OBJECTIVE: The objective of this study was therefore to study the possible interactions between these compounds in human volunteers with special emphasis on the potential impact on urinary biomarkers. MATERIALS AND METHODS: Five male volunteers were exposed by inhalation for 6 h to single, binary, and quaternary mixtures that included chloroform. Exhaled air and blood samples were collected and analyzed for parent compound concentrations. Urinary biomarkers (o-cresol, mandelic, and m-methylhippuric acids) were quantified in urine samples. Published PBPK model for chloroform was used, and a Vmax of 3.4 mg/h/kg was optimized to provide a better fit with blood data. Adapted PBPK models from our previous study were used for parent compounds and urinary biomarkers for TEX. RESULTS: Binary exposures with chloroform resulted in no significant interactions. Experimental data for quaternary mixture exposures were well predicted by PBPK models using published description of competitive inhibition among TEX components. However, no significant interactions were observed at levels used in this study. CONCLUSION: PBPK models for urinary biomarkers proved to be a good tool in quantifying exposure to VOC.

Biomonitoring Equivalents for molybdenum.

Molybdenum is an essential trace element for mammalian, plant, and other animal systems. The Institute of Medicine (IOM) has established an Estimated Average Requirement (EAR) to assure sufficient molybdenum intakes for human populations; however excessive exposures can cause toxicity. As a result, several agencies have established exposure guidance values to protect against molybdenum toxicity, including a Reference Dose (RfD), Tolerable Daily Intake (TDI) and a Tolerable Upper Intake Level (UL). Biomonitoring for molybdenum in blood or urine in the general population is being conducted by the Canadian Health Measures Survey (CHMS) and the U.S. National Health and Nutrition Examination Survey (NHANES). Using pharmacokinetic data from controlled human dosing studies, Biomonitoring Equivalents (BEs) were calculated for molybdenum in plasma, whole blood, and urine associated with exposure guidance values set to protect against both nutritional deficits and toxicity. The BEEAR values in plasma, whole blood and urine are 0.5, 0.45 and 22 µg/L, respectively. The BEs associated with toxicity range from 0.9 to 31 µg/L in plasma, 0.8-28 µg/L in whole blood and 200-7500 µg/L in urine. These values can be used to interpret molybdenum biomonitoring data from a nutritional and toxicity perspective.

Biomonitoring Equivalents for selenium.

Selenium is an essential nutrient for human health with a narrow range between essentiality and toxicity. Selenium is incorporated into several proteins that perform important functions in the body. With insufficient selenium intake, the most notable effect is Keshan disease, an endemic cardiomyopathy in children. Conversely, excessive selenium intake can result in selenosis, manifested as brittle nails and hair and gastro-intestinal disorders. As such, guidance values have been established to protect against both insufficient and excessive selenium exposures. Dietary Reference Intakes (DRIs) have been established as standard reference values for nutritional adequacy in North America. To protect against selenosis resulting from exposure to excessive amounts of selenium, several government and non-governmental agencies have established a range of guidance values. Exposure to selenium is primarily through the diet, but monitoring selenium intake is difficult. Biomonitoring is a useful means of assessing and monitoring selenium status for both insufficient and excessive exposures. However, to be able to interpret selenium biomonitoring data, levels associated with both DRIs and toxicity guidance values are required. Biomonitoring Equivalents (BEs) were developed for selenium in whole blood, plasma and urine. The BEs associated with assuring adequate selenium intake (Estimated Average Requirements - EAR) are 100, 80 and 10µg/L in whole blood, plasma and urine, respectively. The BEs associated with protection against selenosis range from 400 to 480µg/L in whole blood, 180-230µg/L in plasma, and 90-110µg/L in urine. These BE values can be used by both regulatory agencies and public health officials to interpret selenium biomonitoring data in a health risk context.

Integrating gene expression and splicing dynamics across dose-response oxidative modulators.

Toxicological risk assessment increasingly utilizes transcriptomics to derive point of departure (POD) and modes of action (MOA) for chemicals. One essential biological process that allows a single gene to generate several different RNA isoforms is called alternative splicing. To comprehensively assess the role of splicing dysregulation in toxicological evaluation and elucidate its potential as a complementary endpoint, we performed RNA-seq on A549 cells treated with five oxidative stress modulators across a wide dose range. Differential gene expression (DGE) showed limited pathway enrichment except at high concentrations. However, alternative splicing analysis revealed variable intron retention events affecting diverse pathways for all chemicals in the absence of significant expression changes. For instance, diazinon elicited negligible gene expression changes but progressive increase in the number of intron retention events, suggesting splicing alterations precede expression responses. Benchmark dose modeling of intron retention data highlighted relevant pathways overlooked by expression analysis. Systematic integration of splicing datasets should be a useful addition to the toxicogenomic toolkit. Combining both modalities paint a more complete picture of transcriptomic dose-responses. Overall, evaluating intron retention dynamics afforded by toxicogenomics may provide biomarkers that can enhance chemical risk assessment and regulatory decision making. This work highlights splicing-aware toxicogenomics as a possible additional tool for examining cellular responses.

Toxicokinetics of rare earth element oxides administered intravenously to rats.

Rare earth elements (REEs) are increasingly used in a wide range of applications. However, their toxicokinetic behaviors in animals and humans are not yet fully documented, hindering health risk assessments. We used a rat experimental model to provide novel data on the toxicokinetics of the insoluble oxide forms of praseodymium (Pr), neodymium (Nd), cerium (Ce) and yttrium (Y) administered intravenously. Detailed blood, urinary and fecal time courses were documented through serial sampling over 21 days in male Sprague-Dawley rats exposed to a mixture of these REE oxides administered at two different doses (0.3 or 1 mg kg-1 bw of each REE oxide commercially sold as bulk µm-sized particles). Tissue REE levels at the time of sacrifice were also measured. Significant effects of the dose on REE time courses in blood and on cumulative urinary and fecal excretion rates were observed for all four REE oxides assessed, as lower cumulative excretion rates were noted at the higher REE dose. In the liver, the main accumulation organ, the fraction of the administered REE dose remaining in the tissue at necropsy was similar at both doses. Toxicokinetic data for the REE oxides were compared to similar data for their chloride salts (also administered intravenously in a mixture, at 0.3 and 1 mg kg-1 bw of each REE chloride) obtained from a previous study. Compared to their chloride counterparts, faster elimination of REE oxides from the blood was observed in the first hours post-dosing. Furthermore, higher mean residence time (MRT) values as well as slower cumulative urinary and fecal excretion were determined for the REE oxides. Also, while liver REE retention was similar for both REE forms, the fractions of the administered REEs recovered in the spleen and lungs were noticeably higher for the REE oxides, at both dose levels. This study highlights the importance of both the dose and form of the administered REEs on their toxicokinetic profiles. Results indicate that chronic exposure and increased doses of REEs may favor bioaccumulation in the body, in particular for insoluble oxide forms of REEs, which are eliminated more slowly from the body.

Mining toxicogenomic data for dose-responsive pathways: implications in advancing next-generation risk assessment.

Introduction: While targeted investigation of key toxicity pathways has been instrumental for biomarker discovery, unbiased and holistic analysis of transcriptomic data provides a complementary systems-level perspective. However, in a systematic context, this approach has yet to receive comprehensive and methodical implementation. Methods: Here, we took an integrated bioinformatic approach by re-analyzing publicly available MCF7 cell TempO-seq data for 44 ToxCast chemicals using an alternative pipeline to demonstrate the power of this approach. The original study has focused on analyzing the gene signature approach and comparing them to in vitro biological pathway altering concentrations determined from ToxCast HTS assays. Our workflow, in comparison, involves sequential differential expression, gene set enrichment, benchmark dose modeling, and identification of commonly perturbed pathways by network visualization. Results: Using this approach, we identified dose-responsive molecular changes, biological pathways, and points of departure in an untargeted manner. Critically, benchmark dose modeling based on pathways recapitulated points of departure for apical endpoints, while also revealing additional perturbed mechanisms missed by single endpoint analyses. Discussion: This systems-toxicology approach provides multifaceted insights into the complex effects of chemical exposures. Our work highlights the importance of unbiased data-driven techniques, alongside targeted methods, for comprehensively evaluating molecular initiating events, dose-response relationships, and toxicity pathways. Overall, integrating omics assays with robust bioinformatics holds promise for improving chemical risk assessment and advancing new approach methodologies (NAMs).

Animal-free assessment of developmental toxicity: Combining PBPK modeling with the ReproTracker assay.

in vitro screening platforms to assess teratogenic potential of compounds are emerging rapidly. ReproTracker is a human induced pluripotent stem cells (hiPSCs)-based biomarker assay that is shown to identify the teratogenicity potential of new pharmaceuticals and chemicals reliably. In its current state, the assay is limited to identifying the potential teratogenic effects and does not immediately quantify a clinical dose relevant to the exposure of chemicals or drugs observable in mothers or fetuses. The goal of this study was to evaluate whether the ReproTracker assay can be extrapolated in vivo and quantitatively predict developmental toxicity exposure levels of two known human teratogens, thalidomide, and carbamazepine. Here, we utilized Physiologically Based Pharmacokinetic (PBPK) modeling to describe the pharmacokinetic behavior of these compounds and conducted an in vitro to in vivo extrapolation (IVIVE) approach to predict human equivalent effect doses (HEDs) that correspond with in vitro concentrations potentially associated with adverse outcomes in ReproTracker. The HEDs derived from the ReproTracker concentration predicted to cause developmental toxicity were close to the reported teratogenic human clinical doses and the HED derived from the rat or rabbit developmental toxicity study. The ReproTracker derived-HED revealed to be sensitive and protective of humans. Overall, this pilot study demonstrated the importance of integrating PBPK model in extrapolating and assessing developmental toxicity in vitro. The combination of these tools demonstrated that they could improve the safety assessment of drugs and chemicals without animal testing.

Insights into ultrasound-promoted degradation of naphthenic acid compounds in oil sands process affected water. Part II: In silico quantum screening of hydroxyl radical initiated and propagated degradation of benzoic acid.

In Part I, we outlined the importance of sustainable sonochemical treatment to intensify oil sands process affected water (OSPW) treatment empirically and hypothesized degradation pathways. Herein, we elucidate the formation of intermediate products with well-defined molecular level solutions. Proposed mechanisms describe hydroxylation, decarboxylation and bond scission which drive the degradation of intermediates towards mineralization. This comprehensive first study on in silico screening of sonochemical degradation investigates quantum methods using density functional theory to explain the postulated degradation mechanisms through a theoretical radical attack approach, based on condensed Fukui reactivity indicators. A nudged elasticity band (NEB) approach is applied to find a minimum energy path (MEP), allowing the determination of intermediate products and energy barriers associated with naphthenic acid degradation. This approach provides structures and energies of the breakdown compounds formed along the reaction pathway enabling the determination of molecular reaction kinetics. In continuation of Part 1, the focus of this study is to evaluate sonochemically-induced hydroxyl radical (OH•) reactions of benzoic acid using density functional theory. Hydroxylation and decarboxylation mechanisms of the model naphthenic acid compound and its intermediates were simulated to determine the prospective pathway to ideal mineralization. DFT was applied to calculate interaction energies, Mulliken charges, Hirshfeld population analysis, dipole moments, frontier orbitals, and polarizability. Electronic properties and frontier orbital trends were also compared to computational work by Riahi et al.[1] to confirm the transition states by Nudged Elastic Band Transition State theory (NEB-TS). In combination with Hirshfeld Population analysis, Fukui indices suggest a more linear degradation pathway narrowed down from earlier experimental work by Singla et al.[2]. The linear free energy relationship for the newly suggested computational benzoic acid degradation can be determined by lnkTST/W=-1.677ΔG-15.41 with a R2 of 0.9997 according to classic transition state theory and Wigner tunneling. This computational method can be used to explore possible degradation pathways of other NAs and bridges molecular-to-macroscale sonochemical degradation of NA's through a manifestation of molecular solutions.