Nano- and microplastic PBK modeling in the context of human exposure and risk assessment

Insufficient data on nano- and microplastics (NMP) hinder robust evaluation of their potential health risks. Methodological disparities and the absence of established toxicity thresholds impede the comparability and practical application of research findings. The diverse attributes of NMP, such as variations in sizes, shapes, and compositions, complicate human health risk assessment. Although probability density functions (PDFs) show promise in capturing this diversity, their integration into risk assessment frameworks is limited. Physiologically based kinetic (PBK) models offer a potential solution to bridge the gap between external exposure and internal dosimetry for risk evaluation. However, the heterogeneity of NMP poses challenges for accurate biodistribution modeling. A literature review, encompassing both experimental and modeling studies, was conducted to examine biodistribution studies of monodisperse micro- and nanoparticles. The literature search in PubMed and Scopus databases yielded 39 studies that met the inclusion criteria. Evaluation criteria were adapted from previous Quality Assurance and Quality Control (QA-QC) studies, best practice guidelines from WHO (2010), OECD guidance (2021), and additional criteria specific to NMP risk assessment. Subsequently, a conceptual framework for a comprehensive NMP-PBK model was developed, addressing the multidimensionality of NMP particles. Parameters for an NMP-PBK model are presented. QA-QC evaluations revealed that most experimental studies scored relatively well (>0) in particle characterizations and environmental settings but fell short in criteria application for biodistribution modeling. The evaluation of modeling studies revealed that information regarding the model type and allometric scaling requires improvement. Three potential applications of PDFs in PBK modeling of NMP are identified: capturing the multidimensionality of the NMP continuum, quantifying the probabilistic definition of external exposure, and calculating the bio-accessibility fraction of NMP in the human body. A framework for an NMP-PBK model is proposed, integrating PDFs to enhance the assessment of NMP's impact on human health.

ADME characterization and PBK model development of 3 highly protein-bound UV filters through topical application

Estimating human exposure in the safety assessment of chemicals is crucial. Physiologically based kinetic (PBK) models which combine information on exposure, physiology, and chemical properties, describing the absorption, distribution, metabolism, and excretion (ADME) processes of a chemical, can be used to calculate internal exposure metrics such as maximum concentration and area under the concentration-time curve in plasma or tissues of a test chemical in next-generation risk assessment. This article demonstrates the development of PBK models for 3 UV filters, specifically octyl methoxycinnamate, octocrylene, and 4-methylbenzylidene camphor. The models were parameterized entirely based on data obtained from in vitro and/or in silico methods in a bottom-up modeling approach and then validated based on human dermal pharmacokinetic (PK) data. The 3 UV filters are "difficult to test" in in vitro test systems due to high lipophilicity, high binding affinity for proteins, and nonspecific binding, for example, toward plastic. This research work presents critical considerations in ADME data generation, interpretation, and parameterization to assure valid PBK model development to increase confidence in using PBK modeling to help make safety decisions in the absence of human PK data. The developed PBK models of the 3 chemicals successfully simulated the plasma concentration profiles of clinical PK data following dermal application, indicating the reliability of the ADME data generated and the parameters determined. The study also provides insights and lessons learned for characterizing ADME and developing PBK models for highly lipophilic and protein-bound chemicals in the future.

Modeling of clearance, retention, and translocation of inhaled gold nanoparticles in rats

Objective: The increasing exposure to gold nanoparticles (AuNPs), due to their wide range of applications, has led to the need for thorough understanding of their biodistribution, following exposure. The objective of this paper is to develop a PBK model in order to study the clearance, retention and translocation of inhaled gold nanoparticles in rats, providing a basis for the understanding of the absorption, distribution, metabolism and elimination (ADME) mechanisms of AuNPs in various organs.Materials and methods: A rat PBK computational model was developed, connected to a detailed respiratory model, including the olfactory, tracheobronchial, and alveolar regions. This model was coupled with a Multiple Path Particle Dosimetry (MPPD) model to appropriately simulate the exposure to AuNPs. Three existing in vivo experimental datasets from scientific literature for the biodistribution of inhaled AuNPs for different AuNP sizes and exposure scenarios were utilized for model calibration and validation.Results and Discussion: The model was calibrated using two individual datasets for nose only inhaled and intratracheally instilled AuNPs, while an independent dataset for nose only inhaled AuNPs was used as external validation. The overall fitting over the three datasets was proved acceptable as shown by the relevant statistical metrics. The influence of several physiological parameters is also studied via a sensitivity analysis, providing useful insights into the mechanisms of NP pharmacokinetics. The key aspects of the inhaled AuNPs biodistribution are discussed, revealing the key mechanisms for the AuNPs absorption routes, the AuNP uptake by secondary organs and the influence of the AuNP size on the translocation from the lungs to blood circulation.Conclusions: The model results together with the model sensitivity analysis clarified the key mechanisms for the inhaled AuNPs biodistribution to secondary organs. It was observed that nose-only inhaled AuNPs of smaller size can enter the blood circulation through secondary routes, such as absorption through the gastrointestinal (GI) lumen, showing that such translocations should not be underestimated in biodistribution modelling. Finally, the computational framework presented in this study can be used as a basis for a more wide investigation of inhaled nanoparticles biodistribution, including interspecies extrapolation of the resulting PBK model for the inhalation and subsequent biodistribution of AuNPs in humans.

An integrative approach to define chemical exposure threshold limits for endangered sea turtles

Environmental contaminants pose serious health threats to marine megafauna species, yet methods defining exposure threshold limits are lacking. Here, a three-pillar chemical risk assessment framework is presented based on (1) species- and chemical-specific lifetime bioaccumulation modelling, (2) non-destructive in vitro and in vivo toxicity threshold assessment, and (3) chemical risk quantification. We used the effects of cadmium (Cd) in green sea turtles (Chelonia mydas) as a proof of concept to evaluate the quantitative mechanistic modelling approach. A physiologically-based kinetic (PBK) model simulated Cd tissue concentrations (liver, kidney, muscle, fat, brain, scute, and 'rest of the body') in C.mydas. The validated PBK model then translated species-specific in vitro results to in vivo effects. The results showed that the resilience of C.mydas towards Cd kidney toxicity is age-dependent and differs with changing physiology and feeding ecology. Using the model in reverse mode, a steady-state exposure threshold of 0.1 µg/g dry weight Cd in forage was derived and compared to real-world exposure scenarios. Three out of the four globally distinct C.mydas populations assessed are exposed to Cd levels above this threshold limit. This approach can be adapted to other marine species and chemicals to prioritize measures for managing potentially harmful chemical exposures.

Monocrotaline-induced liver toxicity in rat predicted by a combined in vitro physiologically based kinetic modeling approach

The aim of the present study was to use an in vitro–in silico approach to predict the in vivo acute liver toxicity of monocrotaline and to characterize the influence of its metabolism on its relative toxic potency compared to lasiocarpine and riddelliine. In the absence of data on acute liver toxicity of monocrotaline upon oral exposure, the predicted dose–response curve for acute liver toxicity in rats and the resulting benchmark dose lower and upper confidence limits for 10% effect (BMDL₁₀ and BMDU₁₀) were compared to data obtained in studies with intraperitoneal or subcutaneous dosing regimens. This indicated the predicted BMDL₁₀ value to be in line with the no-observed-adverse-effect levels (NOAELs) derived from availabe in vivo studies. The predicted BMDL₁₀–BMDU₁₀ of 1.1–4.9 mg/kg bw/day also matched the oral dose range of 1–3 mg PA/kg bw/day at which adverse effects in human are reported. A comparison to the oral toxicity of the related pyrrolizidine alkaloids (PAs) lasiocarpine and riddelliine revealed that, although in the rat hepatocytes monocrotaline was less toxic than lasiocarpine and riddelliine, due to its relatively inefficient clearance, its in vivo acute liver toxicity was predicted to be comparable. It is concluded that the combined in vitro-PBK modeling approach can provide insight in monocrotaline-induced acute liver toxicity in rats, thereby filling existing gaps in the database on PA toxicity. Furthermore, the results reveal that the kinetic and metabolic properties of PAs can vary substantially and should be taken into account when considering differences in relative potency between different PAs.

Physiologically based kinetic modeling of hesperidin metabolism and its use to predict in vivo effective doses in humans

SCOPE

To develop a physiologically based kinetic (PBK) model that describes the absorption, distribution, metabolism, and excretion of hesperidin in humans, enabling the translation of in vitro concentration-response curves to in vivo dose-response curves.

METHODS AND RESULTS

The PBK model for hesperidin in humans was developed based on in vitro metabolic parameters. Hesperidin was predicted to mainly occur in the systemic circulation as different monoglucuronides. The plasma concentrations of hesperidin aglycone (hesperetin) was predicted to be <0.02 mg/L at an oral dose of 50 mg/kg bw. The developed PBK model allowed conversion of in vitro concentration-response curves for different effects to in vivo dose-response curves. The BMD₀₅ (benchmark dose for 5% response) values for protein kinase A inhibition ranged between 135 and 529 mg/kg bw hesperidin, and for inhibition of endothelial cell migration and prostaglandin E₂ and nitric oxide production ranged between 2.19 and 44 mg/kg bw hesperidin. These values are in line with reported human data showing in vivo effects by hesperidin and show that these effects may occur at Western dietary and supplementary intake of hesperidin.

CONCLUSIONS

The developed PBK model adequately predicts absorption, distribution, metabolism, and excretion of hesperidin in humans and allows to evaluate the human in vivo situation without the need for human intervention studies.