Toxicological Sciences最新文献

An extensive battery of 17 in vitro assays has been developed for assessing developmental neurotoxicity (DNT), with the aim of replacing or supplementing traditional in vivo guideline studies for risk assessment, as these mechanistic assays provide advantages over costly, lengthy, in vivo studies. However, one major challenge in employing in vitro assays is the translation of in vitro bioactive concentrations into in vivo doses that can be compared with human exposures. This study describes an in vitro to in vivo extrapolation (IVIVE) approach to derive human-relevant administered equivalent doses based on chemical partitioning into DNT target organs during the critical period of brain development. We used data from chemicals previously found to elicit bioactivity in a subset (seven of 17) of the in vitro DNT battery assays conducted at the U.S. Environmental Protection Agency. Three physiologically based pharmacokinetic modeling platforms were evaluated for their suitability for this DNT-IVIVE approach. Chemical predictions for administrated equivalent doses were compared against in vivo effect levels, where available, and found to be within three-fold for 78% of chemicals. To provide metrics for risk assessment considerations, administered equivalent doses were compared to predicted human exposures. Overall, this DNT-IVIVE approach was found to be relatively transferable among modeling platforms, albeit with varying limitations and considerations that should be taken into account for specific contexts of use.

Per- and polyfluoroalkyl substances are a class of synthetic chemicals detected ubiquitously in the environment, humans, and wildlife. Perfluorooctanesulfonic acid (PFOS) is one prevalent chemical previously shown to cause adverse effects on nervous system function across in vivo and in vitro models, including dark-phase hyperactivity in larval zebrafish. The objective of this study was to evaluate the role of gamma-aminobutyric acid receptors (GABARs), GABAAR and GABABR, as mediators of dark-phase hyperactivity in PFOS-exposed larval zebrafish. Zebrafish were acutely exposed to 7.87 to 120 μM PFOS, 0.68 to 12.4 μM picrotoxin (GABAAR antagonist), 0.77 to 14.05 μM propofol (GABAAR-positive allosteric modulator), 4.4 to 80 μM saclofen (GABABR antagonist), 0.43 to 7.87 μM CGP13501 (GABABR-positive allosteric modulator), or the solvent control 0.4% dimethyl sulfoxide 60 min before behavior assessment at 5 days post fertilization. Co-exposures to positive allosteric modulators and PFOS were performed. Acute exposure to PFOS caused transient dark-phase hyperactivity. Concentration-dependent dark-phase hypoactivity was observed following acute propofol or CGP13501 exposure, in contrast to the concentration-dependent hyperactivity caused by acute picrotoxin exposure. Saclofen exposure provoked a modest reduction in dark-phase motor activity at the highest concentration tested. PFOS-induced hyperactivity was rescued to baseline activity by co-exposure to propofol or CGP13501. To assess relevance across species, electrophysiological measurements were performed in cultured mouse cortical neurons and BrainSpheres derived from human-induced pluripotent stem cells. PFOS exposure reduced GABAAR-mediated currents in mouse neurons. GABAAR- and GABABR-dependent units in BrainSphere-derived neural networks exhibited increased spiking activity following PFOS exposure. This study demonstrates that PFOS antagonizes GABARs in zebrafish, mouse, and human experimental systems. Taken together, this study supports the concept that early life-stage zebrafish can be used to rapidly identify causative mechanisms, conserved across taxa, by which xenobiotic agents alter neuroactivity.

Animal studies are commonly used in drug development and in chemical and environmental toxicology to predict human toxicity, but their reliability, particularly in the central nervous system (CNS), is limited. For example, animal models often fail to predict drug-induced seizures, leading to unforeseen convulsions in clinical trials. Evaluating environmental compounds, such as pesticides, also poses challenges due to time and resource constraints, resulting in compounds remaining untested. To address these limitations, a government-industry collaboration identified 27 biological target families linked to seizure mechanisms by combining key events from adverse outcome pathways (AOPs) with drug discovery data. Over a hundred in vitro assay endpoints were identified, covering 26 of the target families, including neurotransmitter receptors, transporters, and voltage-gated calcium channels. A review of reference compounds identified 196 seizure-inducing and 34 seizure-negative chemicals, with 80% being tested in the in vitro assays. However, some target familes were more data-poor than others, highlighting significant data gaps. This proof-of-concept study demonstrates how mechanistic seizure liability can be assessed using an AOP framework and in vitro data. It underscores the need for expanded screening panels to include additional seizure-relevant targets. By integrating mechanistic insights into early drug development and environmental risk assessment, this approach enhances compound prioritization, complements animal studies, and optimizes resource use. Ultimately, this strategy refines CNS safety evaluation in drug development, improves public health protection to neurotoxicants, and bridges knowledge gaps.

The emergence of synthetic nicotine analogs in "tobacco-free" products, such as 6-methylnicotine (6MN; aka Metatine) in SPREE BAR, presents new regulatory and public health challenges. Alarmingly, little is known about the metabolism of 6MN, its potential biomarkers of exposure, or its toxicity. In this study, we systematically characterized oxidized metabolites of 6MN in the urine of mice exposed to 6MN (via intraperitoneal or inhalation route) using liquid chromatography-high resolution mass spectrometry. Similarly, human urine samples were analyzed for 6MN metabolites after use of the SPREE BAR (Blue Razz Ice) product. Nine 6MN metabolites were identified in mouse urine, and each metabolite corresponded with a known nicotine metabolite, albeit with increased mass (i.e. m/z + 14 Da). Although 6MN and nicotine share oxidative routes, the metabolism of 6MN was dominated via N-oxidation (likely FMO3-mediated) rather than C-oxidation (likely CYP2A6-dependent) pathways, whereas nicotine metabolism is vice versa. Six 6MN metabolites were detected in human urine after SPREE BAR use, demonstrating strong cross-species metabolic concordance. Among these 6MN human metabolites, 6-methylcotinine, 6-methyl-3'-hydroxycotinine, and 6-methylcotinine-N-oxide emerged as potential urinary biomarkers of exposure due to their prevalence. Importantly, 6MN, yet not an equimolar dose of nicotine, induced acute neurotoxic effects in mice, highlighting distinct toxicological risks of 6MN compared with nicotine. This research revealed a distinct metabolic profile of 6MN and established a framework for biomonitoring of 6MN exposure. Together, these findings advanced our understanding of the metabolism of synthetic nicotine analogs and emphasized the importance of compound-specific profiling to support regulatory oversight of emerging nicotine-like products.

Plastic microparticles, a form of microparticles commonly referred to as microplastics (MP), have been the focus of increasing interest for understanding potential human and ecological impacts, including the development of health-based benchmark values. This systematic review critically evaluates 24 mammalian studies reporting reproductive and developmental outcomes, a disproportionately focused research area, with a particular focus on methodological rigor and risk of bias. Fit-for-purpose aspects of selection, performance, and attrition bias were integrated into the critical appraisal to better understand the potential bias studies may have across these domains. All studies received a tier III rating based on the National Toxicology Program's Office of Health Assessment and Translation framework, indicating a high risk of bias and insufficient reliability for risk assessment. Key issues identified across the body of evidence include poor exposure characterization, inadequate outcome assessment, lack of validated test guidelines, and failure to account for critical reproductive parameters such as estrous cycle monitoring and sperm analysis standards. Additionally, discrepancies in the particle characterization and homogeneity of the test material limit comparability and reproducibility across studies. This work highlights the current limitations in the body of evidence in terms of internal and construct validity, which preclude any conclusions on MP-related reproductive toxicity, and details a path forward for investigators to consider in future research.

The toxicologic impacts on the normative function of the chemosensory system and the loss of its contribution to organism protection and homeostasis remain an underrepresented area of interest in the published literature. The impact of chemical constituents in electronic nicotine delivery system e-liquids or aerosols on the chemosensory system is even less known, as are the effects on product selection and use behavior-and this may be an overlooked impact on the public health. This review is a snapshot of the current state of the science and opportunities for improving and increasing the volume of publications in chemosensory toxicology on the potential impacts of tobacco products. The proposed solutions rely on the determination of the scientific community to take advantage of an unexplored field of opportunity. Active research engagement and use of an integrative, risk-driven planning framework to address harmonization and data gaps in neurosensory research programs would support harmonization, improve scientific visibility in the published literature, and recruit additional investigators to this research community.

Chemosensory systems detect and discriminate a wide variety of molecules to monitor internal and external chemical environments. They initiate olfactory, gustatory, and chemesthetic sensations; influence human brain cognition and emotion; and guide a wide variety of behaviors essential for survival, including protective reactions, such as avoidance of contaminated foods and potential toxicants. Electronic nicotine delivery systems (ENDS) aerosolize e-liquids for inhaled consumption that typically contain flavorants, propylene glycol, vegetable glycerin, and nicotine. E-liquid aerosols also contain toxicants, such as formaldehyde, acetaldehyde, acrolein, and heavy metals. Chemosensory evaluation of ENDS aerosol plays an essential role in the assessment of whether a product will attract new users of all ages, as well as determining their likely use patterns, perceptions of product harm, satisfaction, and product selection. Nicotine and individual flavorant constituents stimulate multiple sensory receptor systems in complex patterns, initiating distinctive sensory perceptions depending on the chemical properties and quantity in the aerosol. There are limited data on chemosensory evaluation of ENDS aerosols and their influence on ENDS use and protective biologic mechanisms. This two-part manuscript provides an overview of (i) the physiology of the olfactory, gustatory, and chemesthetic chemosensory systems, their detection mechanisms, and their role in protective defenses; and (ii) the in vitro, in vivo, and in silico computer-based methodology available to evaluate ENDS irritants and toxicants, their impact on chemosensory pathways, the current state of the science related to e-liquid and ENDS aerosols, and challenges for future studies and scientific innovation.

Microphysiological systems (MPS) contain multiple cell types in three dimensions and often incorporate fluidic shear forces. There is interest in MPS for disease and efficacy modeling, safety and disposition studies. Animal cell-based MPS are needed to provide confidence in the translation of data from human cell-based MPS. We developed rat and dog quad-culture liver MPS incorporating primary hepatocytes, sinusoidal endothelial, Kupffer, and stellate cells. Using cryopreserved primary cells, we established a protocol for co-culturing cells under physiological flow conditions. Cells were evaluated for viability, morphology, and function (e.g. albumin production, cytochrome P450, and flavin-containing monooxygenase [FMO] activity). Optimized culture conditions maintained high-quality rat and dog liver chips for up to 7 days. Model performance was evaluated with ABT-288, a histamine-3 receptor antagonist that caused elevated serum transaminases in dogs but not rats. This finding was partially attributed to the high levels of FMO-mediated N-oxide metabolites produced in the dog. Key findings in our study were (i) dog chips showed much higher FMO-mediated N-oxidation compared with rat, and (2) dog chips exhibited modestly higher sensitivity to ABT-288 toxicity endpoints (albumin, alanine transaminase, and lactate dehydrogenase) compared with rat. Species differences in N-oxidation were not observed in rat and dog liver microsomes or 2D hepatocyte monocultures, suggesting that properties of the quad-culture MPS were necessary to model higher FMO activity observed in dogs in vivo. The data suggest that this preclinical species liver chip model provides novel understanding of in vitro to in vivo translation of ABT-288 dog liver toxicity.

Acute exposure to ozone (O3) causes pulmonary inflammation and injury in humans and animal models. In rodents, acute O3-induced inflammation and injury can be mitigated by pre-exposure to relatively low concentrations of O3, a phenomenon referred to as tolerance. Although tolerance was first described long ago, the underlying mechanisms are not known. We hypothesized that alveolar macrophages (AMs) play a key role in tolerance to O3 based on prior studies with other exposures. To enable our studies, we first generated a mouse model in which female C57BL6/NJ mice were pre-exposed to filtered air or 0.8 ppm O3 for 4 days (4 h/day), then challenged with 2 ppm O3 (3 h) 2 days later, and phenotyped for airway inflammation and injury 6 or 24 h thereafter. As expected, pre-exposure to O3 resulted in significantly reduced airway inflammation and injury 24 h following O3 challenge. Tolerance was associated with regenerative hyperplasia in the terminal bronchioles and changes in the frequency of proliferating alveolar type 2 cells. O3 pre-exposure altered the expression of ∼1,500 genes in AMs, most notably downregulation of Toll-like receptor and proinflammatory cytokine signaling pathways, suggesting AMs had become hypo-responsive. Depletion of tolerized AMs prior to acute O3 challenge did not, however, alter inflammation and injury. Additionally, adoptive transfer of tolerized AM to naïve recipient mice failed to alter responses to acute O3 challenge. In total, our results argue against an important role for AMs in tolerance to ozone and suggest that other cell types are involved.

C12 alkyl benzoate is present in the commercial emollient cosmetic ingredient C12-15 alkyl benzoate (Finsolv TN). Finsolv TN is a mixture of linear and branched esters of benzoic acid and aliphatic alcohols where linear C12 alkyl benzoate is a representative homolog with the shortest alkyl C-chain and lowest molecular weight. A preliminary non-GLP in vitro skin penetration study which monitored dermal bioavailability of all C12-15 alkyl benzoate constituents using GC-MS was carried out which demonstrated C12 alkyl benzoate could be considered a worst-case representative constituent to determine dermal absorption of the overall substance. Subsequently, [14C]-C12 alkyl benzoate was mixed into Finsolv TN, and applied, neat (10 µl/cm2), to dermatomed human skin mounted in a flow-through diffusion cell system. Receptor fluid was collected up to 24 h postdose and the skin was decontaminated at 8 h postdose. The absorbed dose, dermal delivery, potentially absorbable dose and dermally absorbed value of [14C]-C12 alkyl benzoate were 0.41%, 0.97%, 2.20%, and 2.97%, respectively. Metabolism during absorption was assessed in skin from the same donors, with no C12 alkyl benzoate detected in the receptor fluid, although the primary metabolite, [14C]-benzoic acid (>93%), was detected. A phenyl acetate esterase assay confirmed the presence of esterase activity in the donor skins used. Therefore, this study confirmed that dermal exposure of C12-15 alkyl benzoate (Finsolv TN) results in an absorbed dose of 2.97% completely metabolized to benzoic acid and aliphatic alcohol(s) in human skin. These findings indicate that a more in-depth investigation and assessment of toxicokinetic behavior (specifically for occupational exposures via the skin) provide opportunities to develop exposure-led strategies to avoid unnecessary animal testing allowing registrants to fulfill obligations to adhere to the "last resort" principle under REACH.