Simultaneous determination of diethyl phthalate and its major metabolite, monoethyl phthalate, in rat plasma, urine, and various tissues collected from a toxicokinetic study by ultrahigh performance liquid chromatography-tandem mass spectrometry

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.

Adverse cardiovascular effects of long-term exposure to diethyl phthalate in the rat aorta

Phthalates are classified as priority environmental pollutants, since they are ubiquitous in the environment, have endocrine disrupting properties and can contribute to impaired health. Used primarily in personal care products and excipients for pharmaceuticals, diethyl phthalate (DEP) is a short-chain alkyl phthalate that has been linked to decreased blood pressure, glucose tolerance, and increased gestational weight gain in humans, while in animals it has been associated with atherosclerosis and metabolic syndrome. Although all these findings are related to risk factors or cardiovascular diseases, DEP's vascular impacts still need to be clarified. Thus, performing ex vivo and in vitro experiments, we aimed to understand the vascular DEP effects in rat. To evaluate the vascular contractility of rat aorta exposed to different doses of DEP (0.001-1000 μM), an organs bath was used; and resorting to a cell line of the rat aorta vascular smooth muscle, electrophysiology experiments were performed to analyse the effects of a rapid (within minutes with no genomic effects) and a long-term (24 h with genomic effects) exposure of DEP on the L-type Ca2+ current (ICa,L), and the expression of several genes related with the vascular function. For the first time, vascular electrophysiological properties of an EDC were analysed after a long-term genomic exposure. The results show a hormetic response of DEP, inducing a Ca2+ current inhibition of the rat aorta, which may be responsible for impaired cardiovascular electrical health. Thus, these findings contribute to a greater scientific knowledge about DEP's effects in the cardiovascular system, specifically its implications in the development of electrical disturbances like arrhythmias and its possible mechanisms.

Phthalates, physical activity, and diet, which are the most strongly associated with obesity? A case-control study of Chinese children

PURPOSE

Phthalate esters have been a research hotspot recently owing to potential obesogenic activity, but conflicting results have been reported. This case-control study was designed to investigate whether there was an association between phthalate metabolites and childhood obesity in China.

METHODS

A total of 240 pairs of obese/overweight children and age- (±3 months) and gender-matched controls were recruited. Nine phthalate metabolites were analyzed in the first morning urine sample. Physical activity and dietary intake were recorded using validated questionnaires.

RESULTS

In monofactor analysis, the levels of monomethyl phthalate (MMP) and monobutyl phthalate (MnBP) in controls were significantly higher than those of overweight/obese children (p < 0.05). Moderate physical activity (p = 0.004), consumption of vegetables, fruits, and tonic were significantly higher in controls (all p < 0.05), and consumption of fried food, western fast food, carbonated drinks, and juice were higher in cases (all p < 0.05). After adjusting for physical activity and dietary intake, neither MMP [OR = 0.825, (95% CI: 0.559-1.217)] nor MnBP [(OR = 0.808, 95% CI: 0.556-1.176)], were significantly associated with obesity. In all models, moderate physical activity was negatively associated and high glucose high fat dietary patterns were positively associated with the risk of childhood obesity (p < 0.01).

CONCLUSION

Diet and physical activity, but not phthalate metabolites were associated with childhood obesity. Further studies are needed to verify our findings. The trial was registered at clinicaltrials.gov as NCT05622513.

Stereoselective Toxicokinetic and Distribution Study on the Hexaconazole Enantiomers in Mice

Hexaconazole (Hex) has been widely used in agricultural products, and its residues may pose a potential risk to human health. However, the metabolic behavior of Hex enantiomers in mammal organisms is still unknown, which is important for evaluating the differences in their toxicity. In this study, the distribution of S-(+)- and R-(-)-Hex in mice was detected by an ultra-high performance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS), and the mechanism differences in the toxicokinetic behavior were analyzed by molecular docking. Good linearities, accuracies, and precisions were achieved for S-(+)- and R-(-)-Hex, with recoveries of 88.7~104.2% and RSDs less than 9.45% in nine tissues of mice. This established method was then used to detect the toxicokinetic of Hex enantiomers in mice after oral administration within 96 h. The results showed that the half-lives of S-(+)- and R-(-)-Hex were 3.07 and 3.71 h in plasma. Hex was mainly accumulated in the liver, followed by the kidneys, brain, lungs, spleen, and heart. The enantiomeric fraction (EF) values of Hex enantiomers in most of the samples were below 1, indicating that S-(+)-Hex decreased faster than its antipode. The molecular docking showed that the binding of S-(+)-Hex with P450arom was much more stable than R-(-)-Hex, which verified the fact that S-(+)-Hex was prefer to decrease in most of the tissues. The results of this study could be helpful for further evaluating the potential toxic risk of Hex enantiomers and for the development and usage of its pure monomer.

Toxicokinetic studies of di-isobutyl phthalate focusing on the exploration of gender differences in rats

Due to the use of di-isobutyl-phthalate (DiBP) in the production of soft-polyvinyl chloride articles, it is currently a hazardous substance prevalent in human daily life. However, reports on DiBP's toxicokinetics are still very scarce. And no studies have been reported on gender differences in DiBP toxicokinetics. Therefore, this study was conducted in accordance with these research needs. DiBP of 100 mg/kg has been exposed to male and female rats single or multiple times. DiBP and its major metabolite, mono-isobutyl-phthalate (MiBP), were quantified from various biological samples obtained from rats administered with DiBP. Based on these results, several toxicokinetic parameters were estimated. Toxicokinetic results between genders were compared, and from this, existence and extent of gender differences in DiBP's toxicokinetics were explored. Investigation of presence and extent of subacute toxicity in male and female rats following multiple exposures to DiBP were also conducted. This study provided comprehensive information on DiBP toxicity and gender differences that have not been reported in detail. Results of these studies imply that subacute toxicity in liver, kidney, lung, and testis of rats at 100 mg/kg of DiBP is modest and that there is little difference in toxicokinetics between genders. And in both male and female rats, the metabolism of DiBP (to MiBP) was significant, and excretion of MiBP into urine was a major indicator of DiBP exposure.

Toxicokinetics of di-isodecyl phthalate and its major metabolites in rats through the application of a developed and validated UHPLC-ESI-MS/MS method

Di-isodecyl phthalate (DiDP) is a high-molecular-weight phthalate that is mainly used as a plasticizer for plastics. Therefore, exposure to DiDP in the environment has become common with the increasing use of plastics around the world. Environmental regulations and scientific risk management for DiDP, which can be associated with endocrine disruption and various metabolic diseases, are urgently needed. The purpose of this study was to provide useful reference material for future human DiDP risk assessments by conducting toxicokinetic studies on DiDP. Rats were given 100 mg/kg of DiDP orally or intravenously, and plasma, urine, feces, and various tissues were sampled at preset times. DiDP and its major metabolites mono-isodecyl-phthalate (MiDP), mono-hydroxy-isodecyl-phthalate (MHiDP), mono-carboxy-isononyl-phthalate (MCiNP), and mono-oxo-isodecyl-phthalate (MOiDP) were simultaneously quantified from collected biological samples through the application of a newly developed and verified ultrahigh-performance liquid chromatography-electrospray ionization-tandem mass spectrometer (UHPLC-ESI-MS/MS) method. Based on the quantitative results for each analyte, toxicokinetic analyses were performed. DiDP was rapidly and extensively metabolized to MiDP, MHiDP, MCiNP, and MOiDP. The major metabolite excreted in the urine was MCiNP, suggesting that it could be a useful biomarker. The conjugated forms of DiDP and its metabolites have been significantly quantified in the plasma, urine, and feces. DiDP and its major metabolites were also distributed in various tissues in significant quantities. The toxicokinetic properties of DiDP, which have not been clearly reported previously, were identified through this study. This report will serve as a useful reference for future DiDP environmental regulation and scientific human risk assessment studies.

Human risk assessment of di-isobutyl phthalate through the application of a developed physiologically based pharmacokinetic model of di-isobutyl phthalate and its major metabolite mono-isobutyl phthalate

Di-isobutyl phthalate (DiBP) is a substance used in the production of objects frequently used in human life. Mono-isobutyl phthalate (MiBP), a major in vivo metabolite of DiBP, is a biomarker for DiBP exposure assessment. Therefore, risk assessment studies on DiBP and MiBP, which have not yet been reported in detail, are needed. The aim of this study was to develop and evaluate a physiologically based pharmacokinetic (PBPK) model for DiBP and MiBP in rats and extend this to human risk assessment based on human exposure. Pharmacokinetic studies were performed in male rats following the administration of 5-100 mg/kg DiBP, and these results were used for the development and validation of the PBPK model. In addition, the previous pharmacokinetic results in female rats following DiBP administration and the pharmacokinetic results in both males and females according to multiple exposures to DiBP were used to develop and validate the PBPK model. The metabolism of DiBP to MiBP in the body was very significant and rapid, and the biodistribution of MiBP was broad and major. Furthermore, the amount of MiBP in the body showed a correlation with DiBP exposure, and from this, a PBPK model was developed to evaluate the external exposure of DiBP from the internal exposure of MiBP. The predicted rat plasma, urine, fecal, and tissue concentrations using the developed PBPK model fitted well with the observed values. The established PBPK model for rats was extrapolated to a human PBPK model of DiBP and MiBP based on human physiological parameters and allometric scaling. The reference dose of 0.512 mg/kg/day of DiBP and external doses of 6.14-280.90 μg/kg/day DiBP for human risk assessment were estimated using Korean biomonitoring values. Valuable insight and approaches to assessing human health risks associated with DiBP exposure were provided by this study.

In vivo and in vitro studies of Banhahoobak-tang tablets using UPLC-ESI-MS/MS with polarity switching

Banhahoobak-tang is the most prescribed herbal drug in East Asia when individuals experience sudden symptoms such as sore throat or neurological symptoms. The low toxicity and high in-vivo safety of this herbal medicine has made it more attractive to patients, and it has recently been formulated as tablets. In addition, Banhahoobak-tang tablets are registered as health insurance drugs in South Korea, and clinical prescriptions and demand are increasing. However, there are very few clinical trial data as well as very little accurate content analysis and results for Banhahoobak-tang tablets. The purpose of this study was to perform in-vitro and in-vivo studies on Banhahoobak-tang tablets, including content analysis, pharmacokinetics in humans, and plasma protein binding. For this study, a UPLC-ESI-MS/MS method with polarity switching was developed for simultaneous analysis of 18 components of Banhahoobak-tang. To separate the analytes, a C₈ reverse-phase column was used as the stationary phase, 0.1 % aqueous formic acid and acetonitrile as the mobile phase, and ionization and multiple reaction monitoring for quantification. The developed method was able to isolate and quantify the 18 components with good sensitivity and selectivity and was fully validated according to international analytical standards. Stability tests were also conducted on the analytes. Finally, the method was applied to in-vitro and in-vivo studies of Banhahoobak-tang tablets, and the tablet components were 52.49 ng/g to 91.00 μg/g on average. The detected components showed rapid oral absorption in humans as well as high plasma protein binding ratio overall. These results and methods can be useful not only for effectiveness and safety evaluation but also for quality control of Banhahoobak-tang tablets.

Risk assessment for humans using physiologically based pharmacokinetic model of diethyl phthalate and its major metabolite, monoethyl phthalate

Diethyl phthalate (DEP) belongs to phthalates with short alkyl chains. It is a substance frequently used to make various products. Thus, humans are widely exposed to DEP from the surrounding environment such as food, soil, air, and water. As previously reported in many studies, DEP is an endocrine disruptor with reproductive toxicity. Monoethyl phthalate (MEP), a major metabolite of DEP in vivo, is a biomarker for DEP exposure assessment. It is also an endocrine disruptor with reproductive toxicity, similar to DEP. However, toxicokinetic studies on both MEP and DEP have not been reported in detail yet. Therefore, the objective of this study was to evaluate and develop physiologically based pharmacokinetic (PBPK) model for both DEP and MEP in rats and extend this to human risk assessment based on human exposure. This study was conducted in vivo after intravenous or oral administration of DEP into female (2 mg/kg dose) and male (0.1-10 mg/kg dose) rats. Biological samples consisted of urine, plasma, and 11 different tissues. These samples were analyzed using UPLC-ESI-MS/MS method. For DEP, the tissue to plasma partition coefficient was the highest in the kidney, followed by that in the liver. For MEP, the tissue to plasma partition coefficient was the highest in the liver. It was less than unity in all other tissues. Plasma, urine, and fecal samples were also obtained after IV administration of MEP (10 mg/kg dose) to male rats. All results were reflected in a model developed in this study, including in vivo conversion from DEP to MEP. Predicted concentrations of DEP and MEP in rat urine, plasma, and tissue samples using the developed PBPK model fitted well with observed values. We then extrapolated the PBPK model in rats to a human PBPK model of DEP and MEP based on human physiological parameters. Reference dose of 0.63 mg/kg/day (or 0.18 mg/kg/day) for DEP and external doses of 0.246 μg/kg/day (pregnant), 0.193 μg/kg/day (fetus), 1.005-1.253 μg/kg/day (adults), 0.356-0.376 μg/kg/day (adolescents), and 0.595-0.603 μg/kg/day (children) for DEP for human risk assessment were estimated using Korean biomonitoring values. Our study provides valuable insight into human health risk assessment regarding DEP exposure.