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Parabens are used as preservatives in personal care and consumer products, food and pharmaceuticals. Their use is controversial because of possible endocrine disrupting properties. In this study, we investigated metabolism and urinary excretion of methyl paraben (MeP), iso -butyl paraben ( iso -BuP) and n -butyl paraben ( n -BuP) after oral dosage of deuterium-labeled analogs (10 mg). Each volunteer received one dosage per investigated paraben separately and at least 2 weeks apart. Consecutive urine samples were collected over 48 h. In addition to the parent parabens (free and conjugated) which are already used as biomarkers of internal exposure and the known but non-specific metabolites, p -hydroxybenzoic acid (PHBA) and p -hydroxyhippuric acid (PHHA), we identified new, oxidized metabolites with hydroxy groups on the alkyl side chain (3OH- n -BuP and 2OH- iso -BuP) and species with oxidative modifications on the aromatic ring. MeP represented 17.4 % of the dose excreted in urine, while iso -BuP represented only 6.8 % and n -BuP 5.6 %. Additionally, for iso -BuP, about 16 % was excreted as 2OH- iso -BuP and for n -BuP about 6 % as 3OH- n -BuP. Less than 1 % was excreted as ring-hydroxylated metabolites. In all cases, PHHA was identified as the major but non-specific metabolite (57.2–63.8 %). PHBA represented 3.0–7.2 %. For all parabens, the majority of the oral dose captured by the above metabolites was excreted in the first 24 h (80.5–85.3 %). Complementary to the parent parabens excreted in urine, alkyl-chain-oxidized metabolites of the butyl parabens are introduced as valuable and contamination-free biomarkers of exposure.

Crossover animal trials were performed with intravenous and oral administration of deoxynivalenol-3-β- d -glucoside (DON3G) and deoxynivalenol (DON) to broiler chickens and pigs. Systemic plasma concentrations of DON, DON3G and de-epoxy-DON were quantified using liquid chromatography–tandem mass spectrometry. Liquid chromatography coupled to high-resolution mass spectrometry was used to unravel phase II metabolism of DON. Additionally for pigs, portal plasma was analysed to study presystemic hydrolysis and metabolism. Data were processed via tailor-made compartmental toxicokinetic models. The results in broiler chickens indicate that DON3G is not hydrolysed to DON in vivo. Furthermore, the absolute oral bioavailability of DON3G in broiler chickens was low (3.79 ± 2.68 %) and comparable to that of DON (5.56 ± 2.05 %). After PO DON3G administration to pigs, only DON was detected in plasma, indicating a complete presystemic hydrolysis of the absorbed fraction of DON3G. However, the absorbed fraction of DON3G, recovered as DON, was approximately 5 times lower than after PO DON administration, 16.1 ± 5.4 compared with 81.3 ± 17.4 %. Analysis of phase II metabolites revealed that biotransformation of DON and DON3G in pigs mainly consists of glucuronidation, whereas in chickens predominantly conjugation with sulphate occurred. The extent of phase II metabolism is notably higher for chickens than for pigs, which might explain the differences in sensitivity of these species to DON. Although in vitro studies demonstrate a decreased toxicity of DON3G compared with DON, the species-dependent toxicokinetic data and in vivo hydrolysis to DON illustrate the toxicological relevance and consequently the need for further research to establish a tolerable daily intake.

Homosalate (HMS) is a UV filter used in sunscreens and personal care products as a mixture of cis- and trans-isomers. Systemic absorption after sunscreen use has been demonstrated in humans, and concerns have been raised about possible endocrine activity of HMS, making a general population exposure assessment desirable. In a previous study, it was shown that the oral bioavailability of cis-HMS (cHMS) is lower than that of trans-HMS (tHMS) by a factor of 10, calling for a separate evaluation of both isomers in exposure and risk assessment. The aim of the current study is the investigation of HMS toxicokinetics after dermal exposure. Four volunteers applied a commercial sunscreen containing 10% HMS to their whole body under regular-use conditions (18–40 mg HMS (kg bw)−1). Parent HMS isomers and hydroxylated and carboxylic acid metabolites were quantified using authentic standards and isotope dilution analysis. Further metabolites were investigated semi-quantitatively. Elimination was delayed and slower compared to the oral route, and terminal elimination half-times were around 24 h. After dermal exposure, the bioavailability of cHMS was a factor of 2 lower than that of tHMS. However, metabolite ratios in relation to the respective parent isomer were very similar to the oral route, supporting the applicability of the oral-route urinary excretion fractions for dermal-route exposure assessments. Exemplary calculations of intake doses showed margins of safety between 11 and 92 (depending on the approach) after single whole-body sunscreen application. Human biomonitoring can reliably quantify oral and dermal HMS exposures and support the monitoring of exposure reduction measures.

New synthetic opioids (NSOs) pose a public health concern since their emergence on the illicit drug market and are gaining increasing importance in forensic toxicology. Like many other new psychoactive substances, NSOs are consumed without any preclinical safety data or any knowledge on toxicokinetic (TK) data. Due to ethical reasons, controlled human TK studies cannot be performed for the assessment of these relevant data. As an alternative animal experimental approach, six pigs per drug received a single intravenous dose of 100 µg/kg body weight (BW) of U-47700 or 1000 µg/kg BW of tramadol to evaluate whether this species is suitable to assess the TK of NSOs. The drugs were determined in serum and whole blood using a fully validated method based on solid-phase extraction and LC–MS/MS. The concentration–time profiles and a population (pop) TK analysis revealed that a three-compartment model best described the TK data of both opioids. Central volumes of distribution were 0.94 L/kg for U-47700 and 1.25 L/kg for tramadol and central (metabolic) clearances were estimated at 1.57 L/h/kg and 1.85 L/h/kg for U-47700 and tramadol, respectively. The final popTK model parameters for pigs were upscaled via allometric scaling techniques. In comparison to published human data, concentration–time profiles for tramadol could successfully be predicted with single species allometric scaling. Furthermore, possible profiles for U-47700 in humans were simulated. The findings of this study indicate that unlike a multiple species scaling approach, pigs in conjunction with TK modeling are a suitable tool for the assessment of TK data of NSOs and the prediction of human TK data.

The merging of physiology and toxicokinetics, or pharmacokinetics, with computational modeling to characterize dosimetry has led to major advances for both the chemical and pharmaceutical research arenas. Driven by the mutual need to estimate internal exposures where in vivo data generation was simply not possible, the application of toxicokinetic modeling has grown exponentially in the past 30 years. In toxicology the need has been the derivation of quantitative estimates of toxicokinetic and toxicodynamic variability to evaluate the suitability of the tenfold uncertainty factor employed in risk assessment decision-making. Consideration of a host of physiologic, ontogenetic, genetic, and exposure factors are all required for comprehensive characterization. Fortunately, the underlying framework of physiologically based toxicokinetic models can accommodate these inputs, in addition to being amenable to capturing time-varying dynamics. Meanwhile, international interest in advancing new approach methodologies has fueled the generation of in vitro toxicity and toxicokinetic data that can be applied in in vitro-in vivo extrapolation approaches to provide human-specific risk-based information for historically data-poor chemicals. This review will provide a brief introduction to the structure and evolution of toxicokinetic and physiologically based toxicokinetic models as they advanced to incorporate variability and a wide range of complex exposure scenarios. This will be followed by a state of the science update describing current and emerging experimental and modeling strategies for population and life-stage variability, including the increasing application of in vitro-in vivo extrapolation with physiologically based toxicokinetic models in pharmaceutical and chemical safety research. The review will conclude with case study examples demonstrating novel applications of physiologically based toxicokinetic modeling and an update on its applications for regulatory decision-making. Physiologically based toxicokinetic modeling provides a sound framework for variability evaluation in chemical risk assessment.

Chlorfenapyr is a novel broad-spectrum insecticide derived from natural pyrrole derivatives produced by Streptomyces spp. It acts as a pro-insecticide and is metabolically converted to the active metabolite, tralopyril. Chlorfenapyr poisoning is known for its delayed neurological symptoms and high mortality. Unfortunately, information on the toxicokinetics, metabolism and tissue distribution of chlorfenapyr and tralopyril is still lacking. In this study, the metabolic profile, toxicokinetics and tissue distribution of chlorfenapyr and tralopyril after oral administration at a toxic dose in mice were investigated. Twenty metabolites were identified in plasma, urine and feces, which were mainly formed by dealkylation, oxidative dechlorination and reductive dechlorination. Toxicokinetic results showed that chlorfenapyr was rapidly converted to tralopyril after administration, and the in vivo half-life (t1/2), area under the curve (AUC) and peak concentration (Cmax) values of tralopyril were significantly higher than those of chlorfenapyr (P < 0.05). Tissue distribution experiments confirmed that the metabolite tralopyril had a longer half-life, a lower clearance and a wide distribution in different organs and tissues compared to chlorfenapyr. It was also able to cross the blood–brain barrier, suggesting a potential association with brain lesions. In addition, a sensitive and rapid LC–MS/MS analytical method was established for the detection of chlorfenapyr and tralopyril. In conclusion, this study provided valuable metabolic, toxicokinetic and tissue distribution information, contributing to future risk assessment and forensic identification in cases of chlorfenapyr poisoning. We recommend considering the assessment of tralopyril levels, which may be of greater therapeutic importance in the management of chlorfenapyr poisoning.

Hypoalbuminemia (HA) is frequently observed in systemic inflammatory diseases and in liver disease. However, the influence of HA on the pharmacokinetics and toxicity of compounds with high plasma albumin binding remained insufficiently studied. The ‘ lack-of-delivery-concept ’ postulates that HA leads to less carrier mediated uptake of albumin bound substances into hepatocytes and to less glomerular filtration; in contrast, the ‘ concept-of-higher-free-fraction ’ argues that increased concentrations of non-albumin bound compounds facilitate hepatocellular uptake and enhance glomerular filtration. To address this question, we performed intravital imaging on livers and kidneys of anesthetized mice to quantify the spatio-temporal tissue distribution of the mycotoxin ochratoxin A (OTA) based on its auto-fluorescence in albumin knockout and wild-type mice. HA strongly enhanced the uptake of OTA from the sinusoidal blood into hepatocytes, followed by faster secretion into bile canaliculi. These toxicokinetic changes were associated with increased hepatotoxicity in heterozygous albumin knockout mice for which serum albumin was reduced to a similar extent as in patients with severe hypoalbuminemia. HA also led to a shorter half-life of OTA in renal capillaries, increased glomerular filtration, and to enhanced uptake of OTA into tubular epithelial cells. In conclusion, the results favor the ‘ concept-of-higher-free-fraction ’ in HA; accordingly, HA causes an increased tissue uptake of compounds with high albumin binding and increased organ toxicity. It should be studied if this concept can be generalized to all compounds with high plasma albumin binding that are substrates of hepatocyte and renal tubular epithelial cell carriers.

In order to quantify the relative oral bioavailability of 3-chloropropane-1,2-diol (3-MCPD) from 3-MCPD fatty acid diesters in vivo, 1,2-dipalmitoyl-3-chloropropane-1,2-diol (3-MCPD diester) and 3-MCPD were orally applied to rats in equimolar doses. In both cases, the time courses of 3-MCPD concentrations were measured in blood, various organs, tissues and intestinal luminal contents. The results show that 3-MCPD is released by enzymatic hydrolysis from the 3-MCPD diester in the gastrointestinal tract and distributed to blood, organs and tissues. Based on the measurements in blood, the areas under the curve (AUC) for 3-MCPD were calculated. By comparing both AUC, the relative amount of 3-MCPD bioavailable from the 3-MCPD diester was calculated to be 86 % on average of the amount bioavailable following administration of 3-MCPD. In view of limited experimental data, it is justified for the purpose of risk assessment to assume complete hydrolysis of the diesters in the gastro-intestinal tract. Therefore, assessment of the extent of exposure to 3-MCPD released from its fatty acid esters should be performed in the same way as exposure to the same molar quantity of 3-MCPD.

Due to their unique physicochemical properties, graphene-family nanomaterials (GFNs) are widely used in many fields, especially in biomedical applications. Currently, many studies have investigated the biocompatibility and toxicity of GFNs in vivo and in intro. Generally, GFNs may exert different degrees of toxicity in animals or cell models by following with different administration routes and penetrating through physiological barriers, subsequently being distributed in tissues or located in cells, eventually being excreted out of the bodies. This review collects studies on the toxic effects of GFNs in several organs and cell models. We also point out that various factors determine the toxicity of GFNs including the lateral size, surface structure, functionalization, charge, impurities, aggregations, and corona effect ect. In addition, several typical mechanisms underlying GFN toxicity have been revealed, for instance, physical destruction, oxidative stress, DNA damage, inflammatory response, apoptosis, autophagy, and necrosis. In these mechanisms, (toll-like receptors-) TLR-, transforming growth factor β- (TGF-β-) and tumor necrosis factor-alpha (TNF-α) dependent-pathways are involved in the signalling pathway network, and oxidative stress plays a crucial role in these pathways. In this review, we summarize the available information on regulating factors and the mechanisms of GFNs toxicity, and propose some challenges and suggestions for further investigations of GFNs, with the aim of completing the toxicology mechanisms, and providing suggestions to improve the biological safety of GFNs and facilitate their wide application.

UDP-glucuronosyltransferases (UGTs) are involved in phase II conjugation reactions of xenobiotics and differences in their isoform activities result in interindividual kinetic differences of UGT probe substrates. Here, extensive literature searches were performed to identify probe substrates (14) for various UGT isoforms (UGT1A1, UGT1A3, UGT1A4, UGT1A6, UGT1A9, UGT2B7 and UGT2B15) and frequencies of human polymorphisms. Chemical-specific pharmacokinetic data were collected in a database to quantify interindividual differences in markers of acute (Cmax) and chronic (area under the curve, clearance) exposure. Using this database, UGT-related uncertainty factors were derived and compared to the default factor (i.e. 3.16) allowing for interindividual differences in kinetics. Overall, results show that pharmacokinetic data are predominantly available for Caucasian populations and scarce for other populations of different geographical ancestry. Furthermore, the relationships between UGT polymorphisms and pharmacokinetic parameters are rarely addressed in the included studies. The data show that UGT-related uncertainty factors were mostly below the default toxicokinetic uncertainty factor of 3.16, with the exception of five probe substrates (1-OH-midazolam, ezetimibe, raltegravir, SN38 and trifluoperazine), with three of these substrates being metabolised by the polymorphic isoform 1A1. Data gaps and future work to integrate UGT-related variability distributions with in vitro data to develop quantitative in vitro–in vivo extrapolations in chemical risk assessment are discussed.Article HighlightsExtensive literature search of human kinetic parameters for UGT probe substrates.Bayesian meta-analysis quantifying human variability in acute and chronic kinetic parameters.UGT isoform-related uncertainty factors were below the 3.16 kinetic default uncertainty factor for most probe substrates.Quantifying human variability in UGT polymorphisms.