Determination of OTNE-induced thyroid effects within an adverse outcome pathway (AOP) network.

Octahydro-tetramethyl-naphthalenyl-ethanone (OTNE) is a synthetic fragrance ingredient. OTNE was evaluated in repeated-dose toxicological studies. Target organs via oral and dermal routes were the liver and skin/liver, respectively. Effects were observed on the thyroid and thyroid hormones, suggesting hypothalamic-pituitary-thyroid axis perturbation. We investigated the molecular initiating event(s) (MIEs), key events (KEs), and adverse outcomes of OTNE-induced thyroid perturbation within an adverse outcome pathway (AOP). Data were generated using new approach methodologies (NAMs) on human, mouse, and/or rat receptors exploring MIEs using in vitro receptor ligand-binding assays for androstane receptor variant 3 (CAR), farnesoid X receptor (FXR), liver X receptor alpha (LXRα), peroxisome proliferator-activated receptors alpha, delta, and gamma (PPARα, δ, and γ), pregnane X receptor (PXR), and aryl hydrocarbon receptor (AhR). These data inform an AOP network where CAR, FXR, and PXR activation serve as MIEs with thyroid perturbation occurring as secondary effects. These data represent a robust evaluation using NAMs for mapping OTNE-induced thyroid effects and identifying activation of receptor-ligand binding as MIEs in lieu of additional in vivo experimentation. These data indicate the observed thyroid effects are secondary to liver effects and the thyroid effects, therefore, should not be the basis for assessing potential OTNE-induced human health hazards.

Human cell-based in vitro systems to assess respiratory toxicity: a case study using silanes.

Inhalation is a major route by which human exposure to substances can occur. Resources have therefore been dedicated to optimize human-relevant in vitro approaches that can accurately and efficiently predict the toxicity of inhaled chemicals for robust risk assessment and management. In this study-the IN vitro Systems to PredIct REspiratory toxicity Initiative-2 cell-based systems were used to predict the ability of chemicals to cause portal-of-entry effects on the human respiratory tract. A human bronchial epithelial cell line (BEAS-2B) and a reconstructed human tissue model (MucilAir, Epithelix) were exposed to triethoxysilane (TES) and trimethoxysilane (TMS) as vapor (mixed with N2 gas) at the air-liquid interface. Cell viability, cytotoxicity, and secretion of inflammatory markers were assessed in both cell systems and, for MucilAir tissues, morphology, barrier integrity, cilia beating frequency, and recovery after 7 days were also examined. The results show that both cell systems provide valuable information; the BEAS-2B cells were more sensitive in terms of cell viability and inflammatory markers, whereas MucilAir tissues allowed for the assessment of additional cellular effects and time points. As a proof of concept, the data were also used to calculate human equivalent concentrations. As expected, based on chemical properties and existing data, the silanes demonstrated toxicity in both systems with TMS being generally more toxic than TES. Overall, the results demonstrate that these in vitro test systems can provide valuable information relevant to predicting the likelihood of toxicity following inhalation exposure to chemicals in humans.

Use of new approach methodologies (NAMs) to meet regulatory requirements for the assessment of industrial chemicals and pesticides for effects on human health.

New approach methodologies (NAMs) are increasingly being used for regulatory decision making by agencies worldwide because of their potential to reliably and efficiently produce information that is fit for purpose while reducing animal use. This article summarizes the ability to use NAMs for the assessment of human health effects of industrial chemicals and pesticides within the United States, Canada, and European Union regulatory frameworks. While all regulations include some flexibility to allow for the use of NAMs, the implementation of this flexibility varies across product type and regulatory scheme. This article provides an overview of various agencies' guidelines and strategic plans on the use of NAMs, and specific examples of the successful application of NAMs to meet regulatory requirements. It also summarizes intra- and inter-agency collaborations that strengthen scientific, regulatory, and public confidence in NAMs, thereby fostering their global use as reliable and relevant tools for toxicological evaluations. Ultimately, understanding the current regulatory landscape helps inform the scientific community on the steps needed to further advance timely uptake of approaches that best protect human health and the environment.

Use of new approach methodologies (NAMs) to meet regulatory requirements for the assessment of tobacco and other nicotine-containing products.

Regulatory frameworks on tobacco and other nicotine-containing products (TNCP) continue to evolve as novel products emerge, including electronic nicotine delivery systems (e.g., electronic cigarettes or vaping products), heated tobacco products, or certain smokeless products (e.g., nicotine pouches). This article focuses on selected regulations for TNCPs that do not make health claims, and on the opportunities to use new approach methodologies (NAMs) to meet regulatory requirements for toxicological information. The manuscript presents a brief overview of regulations and examples of feedback from regulatory agencies whilst highlighting NAMs that have been successfully applied, or could be used, in a regulatory setting, either as stand-alone methods or as part of a weight-of-evidence approach to address selected endpoints. The authors highlight the need for agencies and stakeholders to collaborate and communicate on the development and application of NAMs to address specific regulatory toxicological endpoints. Collaboration across sectors and geographies will facilitate harmonized use of robust testing approaches to evaluate TNCPs without animal testing.

Comparative and cumulative quantitative risk assessments on a novel heated tobacco product versus the 3R4F reference cigarette.

Novel tobacco products that heat rather than burn tobacco (heated tobacco products or HTPs) have been shown to produce lower levels of harmful and potentially harmful constituents than conventional combusted cigarettes. The present study uses a quantitative risk assessment approach to compare non-cancer and cancer risk estimates for emissions generated by an HTP with smoke from a reference cigarette (3R4F). Fifty-four analytes were evaluated from the HTP aerosol and the 3R4F cigarette smoke. Emissions were generated using the ISO and the Health Canada Intense smoking regimes. The measured values were extrapolated to define a conservative exposure assumption for per day use and lifetime use based on an estimated maximum usage level of 400 puffs per day i.e., approximately 8 HTP tobacco capsules or 40 combustible cigarettes. Non-cancer and cancer risk estimates were calculated using these exposure assumptions for individual and per health outcome domains based on toxicological reference values derived by regulatory and/or public health agencies. The results of this assessment showed a reduction of non-cancer and cancer risk estimates by more than 90 % for the HTP versus the 3R4F cigarette, regardless of the smoking regime.

Natural inhibitors of poly(ADP-ribose) polymerase-1.

Poly(ADP-ribose) polymerases (PARPs) are enzymes that catalyze the transfer of ADP-ribose units from ß-nicotinamide adenine dinucleotide (NAD(+)) to acceptor proteins. PARP-1 is responsible for more than 90 % of protein poly-ADP-ribosylation in the brain and may play a role as a molecular switch for cell survival and death. The functional roles of PARP-1 are largely mediated by its activation after binding to damaged DNA. Upon binding, PARP-1 activity increases rapidly and cleaves NAD(+) into ADP-ribose and nicotinamide. Increased activity of PARP-1 can promote DNA repair and its interaction with several transcription factors, whereas hyperactivation of PARP-1 can result in poly(ADP-ribose) accumulation and depletion of NAD(+) and ATP which may lead to caspase independent apoptotic or necrotic cell death, respectively. Excessive PARP-1 activity has been implicated in the pathogenesis of numerous clinical conditions such as stroke, myocardial infarction, inflammation, diabetes, and neurodegenerative disorders. Therefore, it is not surprising that the search for PARP-1 inhibitors with specific therapeutic uses (e.g., brain ischemia, cancer) has been an active area of research. Beyond medicinal uses, naturally occurring PARP-1 inhibitors may also offer a unique preventative means at attenuating chronic inflammatory diseases through dietary supplementation. This possibility has prompted research for specific, naturally occurring inhibitors of PARP-1. Though fewer investigations focus on identifying endogenous inhibitors/modulators of PARP-1 activity in vivo, these activities are very important for better understanding the complex regulation of this enzyme and the potential long-term benefits of supplementation with PARP-1 inhibitors. With this in mind, the focus of this article will be on providing a state-of-the-science review on endogenous and naturally occurring compounds that inhibit PARP-1.

Inhibition of poly(ADP-ribose) polymerase-1 attenuates the toxicity of carbon tetrachloride.

Carbon tetrachloride (CCl(4)) is routinely used as a model compound for eliciting centrilobular hepatotoxicity. It can be bioactivated to the trichloromethyl radical, which causes extensive lipid peroxidation and ultimately cell death by necrosis. Overactivation of poly(ADP-ribose) polymerase-1 (PARP-1) can rapidly reduce the levels of ß-nicotinamide adenine dinucleotide and adenosine triphosphate and ultimately promote necrosis. The aim of this study was to determine whether inhibition of PARP-1 could decrease CCl(4)-induced hepatotoxicity, as measured by degree of poly(ADP-ribosyl)ation, serum levels of lactate dehydrogenase (LDH), lipid peroxidation, and oxidative DNA damage. For this purpose, male ICR mice were administered intraperitoneally a hepatotoxic dose of CCl(4) with or without 6(5H)-phenanthridinone, a potent inhibitor of PARP-1. Animals treated with CCl(4) exhibited extensive poly(ADP-ribosyl)ation in centrilobular hepatocytes, elevated serum levels of LDH, and increased lipid peroxidation. In contrast, animals treated concomitantly with CCl(4) and 6(5H)-phenanthridinone showed significantly lower levels of poly(ADP-ribosyl)ation, serum LDH, and lipid peroxidation. No changes were observed in the levels of oxidative DNA damage regardless of treatment. These results demonstrated that the hepatotoxicity of CCl(4) is dependent on the overactivation of PARP-1 and that inhibition of this enzyme attenuates the hepatotoxicity of CCl(4).

An oral developmental neurotoxicity study of decabromodiphenyl ether (DecaBDE) in rats.

BACKGROUND: Decabromodiphenyl ether (DecaBDE; CASRN 1163-19-5) is a flame retardant used in a variety of manufactured products. A single oral dose of 20.1 mg/kg administered to mice on postnatal day 3 has been reported to alter motor activity at 2, 4, and 6 months of age. METHODS: To further evaluate these results, a developmental neurotoxicity study was conducted in the most commonly used species for studies of this type, the rat, according to international validated testing guidelines and Good Laboratory Practice Standards. DecaBDE was administered orally via gavage in corn oil to dams from gestation day 6 to weaning at doses of 0, 1, 10, 100, or 1,000 mg/kg/day. Standard measures of growth, development, and neurological endpoints were evaluated in the offspring. Motor activity was assessed at 2 months of age. Additional motor activity assessments were conducted at 4 and 6 months of age. Neuropathology and morphometry evaluations of the offspring were performed at weaning and adulthood. RESULTS: No treatment-related neurobehavioral changes were observed in detailed clinical observations, startle response, or learning and memory tests. No test substance-related changes were noted in motor activity assessments performed at 2, 4, or 6 months of age. Finally, no treatment-related neuropathological or morphometric alterations were found. CONCLUSIONS: Under the conditions of this study, the no-observed-adverse-effect level for developmental neurotoxicity of DecaBDE was 1,000 mg/kg/day, the highest dose tested.

Computational assessment of the environmental fate, bioaccumulation, and toxicity potential of brominated benzylpolystyrene.

Brominated benzylpolystyrene (BrBPS) is a fire safety polymer, which imparts flame retardancy in a variety of styrenic polymers and resins. In this study, the individual components of BrBPS were evaluated using a novel screening process to inform various endpoints relevant for assessing risks to the environment and human health. For this purpose, representative components were created using the B3LYP density functional method to generate the energetically optimal bromine substitution patterns of the parent molecules toluene, ethylbenzene, and cumene. Representative low energy conformations of the components were identified by using repetitive short bursts of Molecular Dynamics, followed by Molecular Mechanics minimization. The resulting structures were energy minimized at the quantum mechanical Becke-Perdew GGA density functional level. Thereafter, octanol:water partition coefficients, maximum molecular lengths, average maximum diameters, and cross-sectional diameters were calculated to inform parameters on environmental fate, bioaccumulation, and mammalian and ecological toxicity. The relevance of these data for informing risk assessment is discussed.

Effects of dose, administration route, and/or vehicle on decabromodiphenyl ether concentrations in plasma of maternal, fetal, and neonatal rats and in milk of maternal rats.

The effects of route and vehicle on blood and milk levels of decabromodiphenyl ether (DecaBDE; CASRN 1163-19-5) were investigated in the rat to assist in the design and conduct of a developmental neurotoxicity study. Blood plasma and/or milk concentrations were determined in dams, fetuses, and/or nursing pups after repeated DecaBDE administration by gavage throughout gestation or gestation and lactation using corn oil (CO) or soyaphospholipon/Lutrol F 127-water (SPL) as the vehicle. The impact of vehicle on plasma levels was also investigated in pups derived from naive dams after a single postnatal dose. This study reports for the first time fetal and neonatal plasma concentrations concurrent with those of maternal plasma and/or milk. Higher concentrations of DecaBDE were achieved in plasma and in milk with CO than with SPL. Furthermore, pups derived from dams treated with only SPL were lower in body weight, compared with those from dams treated with either CO, CO and DecaBDE, or SPL and DecaBDE. The study further shows that exposure to DecaBDE is relatively consistent across the dose range of 100 to 1000 mg/(kg · day) when administered in CO.

Prenatal developmental toxicity of decabromodiphenyl ethane in the rat and rabbit.

BACKGROUND: The potential embryotoxic and teratogenic effects of decabromodiphenyl ethane (DBDPEthane; CASRN 84852-53-9) were evaluated in prenatal developmental studies using rats and rabbits and performed in accordance with international guidelines and Good Laboratory Practice standards. Preliminary dose-range-finding studies were conducted, which indicated doses up to 1,250 mg/kg-day were well tolerated by both rats and rabbits. METHODS: For the developmental studies, animals were administered DBDPEthane via gavage at dosage levels of 0, 125, 400, or 1,250 mg/kg-day from gestation day (GD) 6 through 15 for rats and GDs 6 through 18 for rabbits. All female rats and rabbits were sacrificed on GD 20 or GD 29, respectively, and subjected to cesarean section. Fetuses were individually weighed, sexed, and examined for external, visceral and skeletal abnormalities. RESULTS: No treatment-related mortality, abortions, or clinical signs of toxicity were observed during the study. Body weights, body weight gain, and food consumption were not affected by treatment. No significant internal abnormalities were observed in either species on necropsy. Cesarean section parameters were comparable between control and treated groups. No treatment-induced malformations or developmental variations occurred. CONCLUSIONS: Based on these results, no evidence of maternal toxicity, developmental toxicity, or teratogenicity was observed in rats or rabbits treated with DBDPEthane at dosage levels up to 1,250 mg/kg-day.