Development of physiologically-based toxicokinetic-toxicodynamic (PBTK-TD) model for 4-nonylphenol (4-NP) reflecting physiological changes according to age in males: Application as a new risk assessment tool with a focus on toxicodynamics

Human risk assessment through development and application of a physiologically based toxicokinetic model for 4-tert-octylphenol

4-tert-octylphenol (4-tert-OP) is an ecologically hazardous substance, and exposure to it in the environment has been consistently reported in the past. Despite the hazards and widespread exposure to 4-tert-OP, tools for scientific assessment of 4-tert-OP exposure risk level in humans are lacking. The main purpose of this study was to develop a physiologically-based-toxicokinetic (PBTK) model for 4-tert-OP and to perform quantitative risk assessment of 4-tert-OP in various population groups using the established model. Based on the results of toxicokinetic experiments on male rats, the PBTK model for 4-tert-OP was established and verified, and this was converted to a model for humans through interspecies extrapolation. Based on the previously reported no-observed-adverse-effect-levels for rats, it was possible to estimate the 4-tert-OP reference dose in humans through reverse dosimetry using the model. Biomonitoring data derived from various population groups were applied to the human PBTK model to calculate external exposures and margin of safety for 4-tert-OP for each population group. The PBTK model established in this study adequately explained the toxicokinetic experimental values at acceptable levels and was able to quantitatively predict the 4-tert-OP exposure level in the testes related to male reproductive toxicity. In addition, the degree of external exposure to 4-tert-OP could be scientifically estimated based on biomonitoring values derived from various biological matrices. The reference doses for systemic and reproductive toxicity caused by 4-tert-OP in male humans were calculated to be 0.16 and 1.12 mg/kg/day, respectively. The mean external exposure to 4-tert-OP in each population group estimated based on plasma and urine biomonitoring data was 0.04-66.24 mg/kg/day, showing very large exposure diversity between groups. Exposure risks to 4-tert-OP in populations ranged from safe to risky, suggesting the need for continued monitoring and risk management of 4-tert-OP worldwide. This study provides valuable scientific insight regarding the 4-tert-OP human risk assessment.

Bioaccumulation and in vivo tracking of radiolabeled 4-nonylphenol in mice

4-Nonylphenol (4NP) is concerning due to its growing presence and endocrine-disrupting nature, raising concerns about its impact on health. In this study 124I-labeled 4NP was synthesized for in vivo tracing. Positron emission tomography imaging and biodistribution studies showed significant accumulation in various tissues after oral or intraperitoneal administration, emphasizing its intricate distribution and potential long-term effects, crucial for future risk assessments.

Sex differences in 4-tert-octylphenol toxicokinetics: Exploration of sex as an effective covariate through an in vivo modeling approach

4-tert-octylphenol (4-tert-OP) is a potentially harmful substance, which is found widely in the environment. Nevertheless, information on the in vivo toxicokinetics of 4-tert-OP is lacking, and quantitative risk assessment studies are urgently needed. Therefore, we aimed to quantitatively identify differences in the toxicokinetics of 4-tert-OP and its distribution among tissues between sexes. To this end, following exposure of male and female rats to 10 or 50 mg/kg 4-tert-OP orally and 4 or 8 mg/kg 4-tert-OP intravenously, we conducted a quantitative analysis of samples using ultra-high performance liquid chromatography-tandem mass spectrometry. The results revealed that the 4-tert-OP plasma concentration profiles differed between sexes; however, systemic absorption of 4-tert-OP through the gastrointestinal tract occurred within 0.5 h of exposure in both sexes. Although small, the excretion percentage of 4-tert-OP in urine and feces was lower in males than females (0.06-0.08% vs. 0.82-1.11% of exposure). Significant sex differences were also confirmed in the tissue distribution patterns of 4-tert-OP, and overall, the average tissue distribution in males was lower than that in females. The distribution of 4-tert-OP to liver, adipose, spleen, kidney, brain, and lung in both sexes was predominant. A covariate exploration modeling approach revealed that sex explained the differences in 4-tert-OP toxicokinetics between sexes. These significant differences in the toxicokinetics and tissue distribution of 4-tert-OP between sexes will be important for the scientific precision human risk assessment of 4-tert-OP.

Exploring Differences in Pharmacometrics of Rabeprazole between Genders via Population Pharmacokinetic-Pharmacodynamic Modeling

Rabeprazole is a proton pump inhibitor that inhibits gastric acid production and increases gastric pH; it is widely used clinically as a treatment option for gastritis and gastric ulcers. However, information on the inter-individual variability of rabeprazole pharmacometrics, which is a key element in establishing its scientific clinical use, is still lacking. Particularly, the differences in pharmacokinetics between genders and the degree of variation in pharmacodynamics have not been clearly identified. Thus, the main purpose of this study was to explore any differences in rabeprazole pharmacokinetics between genders and to quantitatively predict and compare the effects of any differences in pharmacokinetics between genders on known pharmacodynamics using population pharmacokinetic-pharmacodynamic modeling. To compare pharmacokinetics and modeling data between genders, bioequivalence results were used simultaneously on healthy Korean men and women using the physiological and biochemical parameters derived from each individual. Pharmacodynamic modeling was performed based on the data of previously reported gastric pH changes in response to rabeprazole plasma concentrations, which was co-linked to the central compartmental bioavailable concentration in the population pharmacokinetic model. There was no significant difference in the level of rabeprazole exposure and elimination of plasma between genders following oral administration of 10 mg enteric-coated rabeprazole tablets; however, there was a clear delay in absorption in women compared to men. Additionally, a comparison of pharmacokinetic parameters normalized to body weight between genders showed that the maximum plasma concentrations were significantly higher in women than in men, again suggesting gender differences in rabeprazole absorption. The population pharmacokinetic profiles for rabeprazole were described using a three-sequential multi-absorption with lag time (Tlag) two-compartment model, whereas body surface area and gender were explored as effective covariates for absorption rate constant and Tlag, respectively. The effect of increased gastric pH due to plasma exposure to rabeprazole was explained using the Sigmoid Emax model, with the baseline as a direct response. The significantly longer rabeprazole Tlag in females delayed the onset of an effect by an average of 1.58 times (2.02-3.20 h), yet the overall and maximum effects did not cause a significant difference within 15%. In the relative comparison of the overall efficacy of rabeprazole enteric-coated tablet administration between genders, it was predicted based on the model that males would have higher efficacy. This study will be very useful in broadening the perspective of interpreting drug diversity between individuals and narrowing the gap in knowledge related to scientific precision medicine by presenting new information on gender differences in rabeprazole pharmacometrics that had not been previously identified.

Inter-individual exposure variability interpretation through reflection of biological age algorithm in physiologically based toxicokinetic model: Application to human risk assessment of di-isobutyl-phthalate

Age-related changes and interindividual variability in the degree of exposure to hazardous substances in the environment are pertinent factors to be considered in human risk assessment. Existing risk assessments remain in a one-size-fits-all approach, often without due consideration of inter-individual toxicokinetic variability factors, such as age. The purpose of this study was to advance from the existing risk assessment of hazardous substances based on toxicokinetics to a precise human risk assessment by additionally considering the effects of physiologic and metabolic fluctuations and interindividual variability in age. Qualitative age-associated physiologic and metabolic changes in humans, obtained through a meta-analysis, were quantitatively modeled to produce the final biological age algorithm (BAA). The developed BAAs (for males) were extended and applied to the reported testicular reproductive toxicity-focused di-isobutyl-phthalate (DiBP)-mono-isobutyl-phthalate (MiBP) physiologically based toxicokinetic (PBTK) model in males. The advanced PBTK model combined with the BAA was applied to the human risk assessment based on MiBP biomonitoring data. As a result, the specialized DiBP external exposure values for each age could be estimated. Additionally, by applying the Monte Carlo simulation, the distribution of internal exposure diversity among individuals according to the same external exposure dose could be estimated. The contributions of physiologic and metabolic factors to the age-dependent toxicokinetic changes were approximately 93.41-99.99 and 0.01-6.59%, respectively. In addition, the relative contribution of metabolic factors was major in infants and continued to decrease as age increased (up to about age 30 years). This study provides a step-by-step platform that can be widely applied to overcome the limitations of existing toxicokinetic models that still require interindividual pharmacokinetic variability explanations. This will be important for the rationalization and explanation of inter-individual variability in the pharmacokinetics of many substances.

In vitro to in vivo extrapolation for predicting human equivalent dose of phenolic endocrine disrupting chemicals: PBTK model development, biological pathways, outcomes and performance

In vitro to in vivo (IVIVE) leverages in vitro high-throughput biological responses to predict the corresponding in vivo exposures and further estimate the human safe dose. However, for phenolic endocrine disrupting chemicals (EDCs) linked with complicated biological pathways and adverse outcomes (AO), such as bisphenol A (BPA) and 4-nonylphenol (4-NP), plausible estimation of human equivalent doses (HED) by IVIVE approaches considering various biological pathways and endpoints is still challenging. To explore the capabilities and limitations of IVIVE, this study conducted physiologically based toxicokinetic (PBTK)-IVIVE approaches to derive pathway-specific HEDs using BPA and 4-NP as examples. In vitro HEDs of BPA and 4-NP varied in different adverse outcomes, pathways, and testing endpoints and ranged from 0.0013 to 1.0986 mg/kg bw/day and 0.0551 to 1.7483 mg/kg bw/day, respectively. In vitro HEDs associated with reproductive AOs initiated by PPARα activation and ER agonism were the most sensitive. Model verification suggested the potential of using effective in vitro data to determine reasonable approximation of in vivo HEDs for the same AO (fold differences of most AOs ranged in 0.14-2.74 and better predictions for apical endpoints). Furthermore, system-specific parameters of cardiac output and its fraction, body weight, as well as chemical-specific parameters of partition coefficient and liver metabolic were most sensitive for the PBTK simulations. The results indicated that the application of fit for-purpose PBTK-IVIVE approach could provide credible pathway-specific HEDs and contribute to high throughput prioritization of chemicals in a more realistic scenario.

Nicotinamide mononucleotide (NMN) ameliorated Nonylphenol-induced learning and memory impairment in rats via the central 5-HT system and the NAD+/SIRT1/MAO-A pathway

Nonylphenol (NP) exposure can trigger neurotoxicity and cause learning and memory impairment. Nicotinamide mononucleotide (NMN) has a therapeutic effect on neurodegenerative diseases, but the role of NMN on NP-induced learning and memory impairment is not known. Here, we examined the mitigative effect of NMN on the impaired learning and memory ability of rats exposed to NP. The NP impaired learning and memory in rats, while the low-dose intervention with NMN significantly prolonged the step-through latency of the PAT and improved the NAMPT and NMNAT1 content in brain tissue. At the same time, the NMN intervention also increased the content of 5-HTR_1A, 5-HTR₄, and 5-HTR₆ related to learning and memory in the hippocampus. In line with this, we found that the NMN intervention activated the SIRT1/MAO-A pathway in brain tissue. NMN intervention, especially at 125 mg/kg doses, may improve rats' NP-induced learning and memory impairment via the central 5-HT system and the NAD⁺/SIRT1/MAO-A pathway in the brain.