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Bisphenol F is a substitute material for bisphenol A and is widely used in household products as a raw material for polycarbonate resin, epoxy resin, and plastic reinforcement. It is known to be mainly used in food containers, thermal paper for receipts, and coatings for water pipes. In some countries, bisphenol F has been detected in drinking water and human urine samples. However, due to the lack of safety evaluation data on bisphenol F, it is difficult to establish appropriate guidelines for the proper use of the substance, and social anxiety is increasing accordingly. This study investigated the use, exposure route, and distribution flow of bisphenol F, a household chemical. To determine the no-observed-adverse-effect level (NOAEL) and target organ of bisphenol F after exposure, a single-dose oral toxicity, dose-range finding (28 day oral), repeated dose toxicity (90 day oral), and genotoxicity (reverse mutation, chromosomal abnormality, in vivo micronucleus test) tests were performed. The pharmacokinetic profile was also obtained. The test results are as follows: in the pharmacokinetic study, it was confirmed that single oral exposure to BPF resulted in systemic exposure; in single oral dose toxicity test, the approximate lethal dose was found to be 4000 mg/kg and confusion and convulsion was shown in the test animals; NOAEL was determined to be 2 mg/kg/day for male and 5 mg/kg/day for female, and the no-observed-effect level (NOEL) was determined to be 2 mg/kg/day for males and 1 mg/kg/day for females, and the target organ was the small intestine; genotoxicity tests confirmed that BPF does not induce genotoxicity. [ABSTRACT FROM AUTHOR]

Nephrotoxicity is the most common side effect that severely limits the clinical application of tacrolimus (TAC), an immunosuppressive agent used in kidney transplant patients. This study aimed to explore the tolerated dose of nephrotoxicity of TAC in individuals with different CYP3A5 genotypes and liver conditions. We established a human whole-body physiological pharmacokinetic (WB-PBPK) model and validated it using data from previous clinical studies. Following the injection of 1 mg/kg TAC into the tail veins of male rats, we developed a rat PBPK model utilizing the drug concentration–time curve obtained by LC–MS/MS. Next, we converted the established rat PBPK model into the human kidney PBPK model. To establish renal concentrations, the BMCL5 of the in vitro CCK-8 toxicity response curve (drug concentration range: 2–80 mol/L) was extrapolated. To further investigate the acceptable levels of nephrotoxicity for several distinct CYP3A5 genotypes and varied hepatic function populations, oral dosing regimens were extrapolated utilizing in vitro-in vivo extrapolation (IVIVE). The PBPK model indicated the tolerated doses of nephrotoxicity were 0.14–0.185 mg/kg (CYP3A5 expressors) and 0.13–0.155 mg/kg (CYP3A5 non-expressors) in normal healthy subjects and 0.07–0.09 mg/kg (CYP3A5 expressors) and 0.06–0.08 mg/kg (CYP3A5 non-expressors) in patients with mild hepatic insufficiency. Further, patients with moderate hepatic insufficiency tolerated doses of 0.045–0.06 mg/kg (CYP3A5 expressors) and 0.04–0.05 mg/kg (CYP3A5 non-expressors), while in patients with moderate hepatic insufficiency, doses of 0.028–0.04 mg/kg (CYP3A5 expressors) and 0.022–0.03 mg/kg (CYP3A5 non-expressors) were tolerated. Overall, our study highlights the combined usage of the PBPK model and the IVIVE approach as a valuable tool for predicting toxicity tolerated doses of a drug in a specific group. [ABSTRACT FROM AUTHOR]

"Novichok" refers to a new group of nerve agents called the A-series agents. Their existence came to light in 2018 after incidents in the UK and again in 2020 in Russia. They are unique organophosphorus-based compounds developed during the Cold War in a program called Foliant in the USSR. This review is based on original chemical entities from Mirzayanov's memoirs published in 2008. Due to classified research, a considerable debate arose about their structures, and hence, various structural moieties were speculated. For this reason, the scientific literature is highly incomplete and, in some cases, contradictory. This review critically assesses the information published to date on this class of compounds. The scope of this work is to summarize all the available and relevant information, including the physicochemical properties, chemical synthesis, mechanism of action, toxicity, pharmacokinetics, and medical countermeasures used to date. The environmental stability of A-series agents, the lack of environmentally safe decontamination, their high toxicity, and the scarcity of information on post-contamination treatment pose a challenge for managing possible incidents. [ABSTRACT FROM AUTHOR]

Sinomenine is a bioactive alkaloid isolated from the Chinese medicinal plant Sinomenium acutum (Thunb.) Rehd. et Wils which exhibits significant analgesic, anti-inflammatory, and immunosuppressive effects. Sinomenine hydrochloride (SH) preparations, classified as natural disease-modifying antirheumatic drugs, are currently available for the treatment of rheumatoid arthritis and other rheumatic diseases. Our toxicity evaluation demonstrated that the median lethal dose of SH in female Sprague-Dawley (SD) rats was over 11 times greater than that in male SD rats, revealing striking sex-linked differences in the safety profile of SH. The present study was designed to investigate differences in the pharmacokinetics (PKs) and tissue distribution of SH between male and female SD rats after a single oral dose of 25 mg/kg. PK and tissue distribution studies were performed using a validated UPLC-MS/MS method. The results showed that SH-treated SD female rats displayed markedly greater drug exposure, and SH exhibited a longer half-life and slower clearance rate than comparable studies in male rats. Moreover, the tissue distribution study confirmed that the sinomenine concentration in female rats was considerably greater in the internal organs than in male rats. Our study demonstrates, for the first time, significant sex-related differences in the safety profile and PKs of SH, which may be associated with a distinct sex-dependent metabolic mechanism of sinomenine. [ABSTRACT FROM AUTHOR]

As a toxic substance, 4-n-nonylphenol (4-n-NP) or 4-nonylphenol (4-NP) is widely present in the environment. 4-n-NP is a single substance with a linear-alkyl side chain, but 4-NP usually refers to a random mixture containing various branched types. Unfortunately, human risk assessment and/or exposure level analysis for 4-n-NP (or 4-NP) were almost nonexistent, and related research was urgently needed. This study aimed to analyze the various exposures of 4-n-NP (or 4-NP) through development of a physiologically based-pharmacokinetic (PBPK) model considering gender difference in pharmacokinetics of 4-n-NP and its application to human risk assessment studies. A PBPK model was newly developed considering gender differences in 4-n-NP pharmacokinetics and applied to a human risk assessment for each gender. Exposure analysis was performed using a PBPK model that considered gender differences in 4-n-NP (or 4-NP) exposure and high variabilities in several countries. Furthermore, an extended application was attempted as a human risk assessment for random mixture 4-NP, which is difficult to accurately evaluate in reality. External-exposure and margin-of-safety estimated with the same internal exposure amount differed between genders, meaning the need for a differentiated risk assessment considering gender. Exposure analysis based on biomonitoring data confirmed large variability in exposure to 4-n-NP (or 4-NP) by country, group, and period. External-exposures estimated using PBPK model varied widely, ranging from 0.039 to 63.875 mg/kg/day (for 4-n-NP or 4-NP). By country, 4-n-NP (or 4-NP) exposure was higher in females than in males and the margin-of-safety tended to be low. Overall, exposure to 4-n-NP (or 4-NP) in populations was largely not safe, suggesting need for ongoing management and monitoring. Considering low in vivo accumulation confirmed by PBPK model, risk reduction of 4-n-NP is possible by reducing its use. [ABSTRACT FROM AUTHOR]

Bile acids (BA) fulfill a wide range of physiological functions, but are also involved in pathologies, such as cholestasis. Cholestasis is characterized by an intrahepatic accumulation of BAs and subsequent spillage to the systemic circulation. The aim of the present study was to develop physiologically based kinetic (PBK) models that would provide a tool to predict dose-dependent BA accumulation in humans upon treatment with a Bile Salt Export Pump (BSEP) inhibitor. We developed a PBK model describing the BA homeostasis using glycochenodeoxycholic acid as an exemplary BA. Population wide distributions of BSEP abundances were incorporated in the PBK model using Markov Chain Monte Carlo simulations, and alternatively the total amount of BAs was scaled empirically to describe interindividual differences in plasma BA levels. Next, the effects of the BSEP inhibitor bosentan on the BA levels were simulated. The PBK model developed adequately predicted the in vivo BA dynamics. Both the Markov Chain Monte Carlo simulations based on a distribution of BSEP abundances and empirical scaling of the total BA pool readily described the variations within and between data in human volunteers. Bosentan treatment disproportionally increased the maximum BA concentration in individuals with a large total BA pool or low BSEP abundance. Especially individuals having a large total BA pool size and a low BSEP abundance were predicted to be at risk for rapid saturation of BSEP and subsequent intrahepatic BA accumulation. This model provides a first estimate of personalized safe therapeutic external dose levels of compounds with BSEP-inhibitory properties. [ABSTRACT FROM AUTHOR]

Chlordecone (CD; Kepone™) is a carcinogenic organochlorine insecticide with neurological, reproductive, and developmental toxicity that was widely used in the French West Indies (FWI) from 1973 to 1993 to fight banana weevils. Although CD has not been used there for more than 25 years, it still persists in the environment and has polluted the waterways and soil of current and older banana fields. Today, human exposure to CD in the FWI mainly arises from consuming contaminated foodstuffs. The aims of this study were to develop a physiologically based pharmacokinetic (PBPK) model in the rat and extrapolate it to humans based on available pharmacokinetic data in the literature. A comparison of simulations using the rat model with published experimental datasets showed reasonable predictability for single and repetitive doses, and, thus, it was extrapolated to humans. The human PBPK model, which has seven compartments, is able to simulate the blood concentrations of CD in human populations and estimate the corresponding external dose using the reverse dosimetry approach. The human PBPK model will make it possible to improve quantitative health risk assessments for CD contamination and reassess the current chronic toxicological reference values to protect the FWI population. [ABSTRACT FROM AUTHOR]

N-benzylpiperazine (BZP) has become popular among recreational drug users as the major active ingredient of 'party pills' due to its stimulant and euphoric properties. Before BZP legal restrictions, these pills were sold as a safe and legal alternative to classical amphetamines like ecstasy. New Zealand, given the size of its legal market prior to BZP control, is the country that most contributed to the knowledge about the patterns of use, motivations and positive and adverse effects resulting from its consumption, though the interest in BZP-party pills was observed all over the world. The use of these pills has been associated with hospitalizations for adverse events and continued availability over the Internet makes this intoxication a continued concern. This paper provides a review on the characteristics of BZP recreational use, specifically the target population, patterns and motivations of use, and evolution of legal status. Moreover, the in vivo and in vitro studies performed in order to understand its pharmacology, toxicology and kinetics are also discussed. Lastly, analytical methodologies for the identification of BZP in clinical and forensic settings are addressed. [ABSTRACT FROM AUTHOR]

Regulatory toxicology seeks to ensure that exposures to chemicals encountered in the environment, in the workplace, or in products pose no significant hazards and produce no harm to humans or other organisms, i.e., that chemicals are used safely. The most practical and direct means of ensuring that hazards and harms are avoided is to identify the doses and conditions under which chemical toxicity does not occur so that chemical concentrations and exposures can be appropriately limited. Modern advancements in pharmacology and toxicology have revealed that the rates and mechanisms by which organisms absorb, distribute, metabolize and eliminate chemicals—i.e., the field of kinetics—often determine the doses and conditions under which hazard, and harm, are absent, i.e., the safe dose range. Since kinetics, like chemical hazard and toxicity, are extensive properties that depend on the amount of the chemical encountered, it is possible to identify the maximum dose under which organisms can efficiently metabolize and eliminate the chemicals to which they are exposed, a dose that has been referred to as the kinetic maximum dose, or KMD. This review explains the rationale that compels regulatory toxicology to embrace the advancements made possible by kinetics, why understanding the kinetic relationship between the blood level produced and the administered dose of a chemical is essential for identifying the safe dose range, and why dose-setting in regulatory toxicology studies should be informed by estimates of the KMD rather than rely on the flawed concept of maximum-tolerated toxic dose, or MTD. [ABSTRACT FROM AUTHOR]

Cathinone, the main psychoactive compound found in the plant Catha edulis Forsk. (khat), is a β-keto analogue of amphetamine, sharing not only the phenethylamine structure, but also the amphetamine-like stimulant effects. Synthetic cathinones are derivatives of the naturally occurring cathinone that largely entered the recreational drug market at the end of 2000s. The former "legal status", impressive marketing strategies and their commercial availability, either in the so-called "smartshops" or via the Internet, prompted their large spread, contributing to their increasing popularity in the following years. As their popularity increased, the risks posed for public health became clear, with several reports of intoxications and deaths involving these substances appearing both in the social media and scientific literature. The regulatory measures introduced thereafter to halt these trending drugs of abuse have proved to be of low impact, as a continuous emergence of new non-controlled derivatives keep appearing to replace those prohibited. Users resort to synthetic cathinones due to their psychostimulant properties but are often unaware of the dangers they may incur when using these substances. Therefore, studies aimed at unveiling the pharmacological and toxicological properties of these substances are imperative, as they will provide increased expertise to the clinicians that face this problem on a daily basis. The present work provides a comprehensive review on history and legal status, chemistry, pharmacokinetics, pharmacodynamics, adverse effects and lethality in humans, as well as on the current knowledge of the neurotoxic mechanisms of synthetic cathinones. [ABSTRACT FROM AUTHOR]

Long-term retrospective monitoring of exposure to organophosphorus nerve agents is challenging. We recently developed two highly sensitive analytical methods for regenerated sarin (GB) nerve agent in blood and its primary metabolite, isopropyl-methylphosphonic acid (IMPA), in urine. These methods were implemented in a toxicokinetics study carried out with sarin injected (i.v.) to rabbits at doses corresponding to 0.1, 0.5 or 0.9 LD50. The time frame for monitoring regenerated sarin from blood was 70 days for 0.1 LD50 and 0.5 LD50 and 77 days for 0.9 LD50, where rapid elimination occurred in the first 8 days with an initial average half-life of 1.2 days, followed by a second, slower elimination, with a terminal average half-life of 8.4 days. The time frame for monitoring IMPA in urine was 7, 15 and 16 days for 0.1 LD50, 0.5 LD50 and 0.9 LD50 intoxications, respectively. Rapid elimination of IMPA in urine occurred after exposure, with an average half-life of ~ 0.8 days on days 2–6. For the first time, a slower elimination route for IMPA, with an average half-life of ~ 4 days from day 6 onwards, was revealed. Both IMPA and regenerated sarin pharmacokinetics exhibit linearity with dose. The overlaid pharmacokinetic profiles of regenerated sarin in blood along with IMPA in urine emphasize the dominance of IMPA with a rapid decay in urine in the first week and the slower long-term decay of protein-bound sarin later in blood. To our knowledge, the two new sensitive methods exhibit the longest monitoring time frame reported in biological samples. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

2-Phenoxyethanol (PE), ethylene glycol monophenyl ether, is widely used as a preservative in cosmetic products as well as in non-cosmetics. Since PE has been used in many types of products, it can be absorbed via dermal or inhaled route for systemic exposures. In this study, the pharmacokinetic (PK) studies of PE and its major metabolite, phenoxyacetic acid (PAA), after dermal (30 mg and 100 mg) and inhaled administration (77 mg) of PE in rats were performed. PE was administered daily for 4 days and blood samples were collected at day 1 and day 4 for PK analysis. PE was rapidly absorbed and extensively metabolized to form PAA. After multiple dosing, the exposures of PE and PAA were decreased presumably due to the induction of metabolizing enzymes of PE and PAA. In dermal mass balance study using [14C]-phenoxyethanol ([14C]PE) as a microtracer, most of the PE and its derivatives were excreted in urine (73.03%) and rarely found in feces (0.66%). Based on these PK results, a whole-body physiologically-based pharmacokinetic (PBPK) model of PE and PAA after dermal application and inhalation in rats was successfully developed. Most of parameters were obtained from the literatures and experiments, and intrinsic clearance at steady-state (CLint,ss) were optimized based on the observed multiple PK data. With the developed model, systemic exposures of PE and PAA after dermal application and inhalation were simulated following no-observed-adverse-effect level (NOAEL) of 500 mg/kg/day for dermal application and that of 12.7 mg/kg/day for inhalation provided by the Environmental Protection Agency. The area under the concentration–time curve at steady state (AUCss) in kidney and liver (and lung for inhalations), which are known target organs of exhibiting toxicity of PE, as well as AUCss in plasma of PE and PAA were obtained from the model. [ABSTRACT FROM AUTHOR]

The dose-dependency of Tl kinetics was studied in rabbits by intravenous injection first of aTl tracer dose and 2 weeks later of a 5.5 μmol/kg dose. For either dose level, an open three compartment model was appropriate to describe the course of the plasma concentration curve. With the dosage increase a slight to moderate decrease in the distribution volumes (11.2 l/kg versus 9.7 l/kg) and in the plasma clearance (13 ml/min versus 9 ml/min) was found. Two days after injection of both the high and the low dose considerable amounts of Tl were found in the intestinal contents and only small amounts were found in the bile. [ABSTRACT FROM AUTHOR]

Physiology-based pharmacokinetic and toxicokinetic (PBPK/TK) models allow us to simulate the concentration of xenobiotica in the plasma and different tissues of an organism. PBPK/TK models are therefore routinely used in many fields of life sciences to simulate the physiological concentration of exogenous compounds in plasma and tissues. The application of PBTK models in ecotoxicology, however, is currently hampered by the limited availability of models for focal species. Here, we present a best practice workflow that describes how to build PBTK models for novel species. To this end, we extrapolated eight previously established rabbit models for several drugs to six additional mammalian species (human, beagle, rat, monkey, mouse, and minipig). We used established PBTK models for these species to account for the species-specific physiology. The parameter sensitivity in the resulting 56 PBTK models was systematically assessed to rank the relevance of the parameters on overall model performance. Interestingly, more than 80% of the 609 considered model parameters showed a negligible sensitivity throughout all models. Only approximately 5% of all parameters had a high sensitivity in at least one of the PBTK models. This approach allowed us to rank the relevance of the various parameters on overall model performance. We used this information to formulate a best practice guideline for the efficient development of PBTK models for novel animal species. We believe that the workflow proposed in this study will significantly support the development of PBTK models for new animal species in the future. [ABSTRACT FROM AUTHOR]

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 Highlights: Extensive 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. [ABSTRACT FROM AUTHOR]

Perfluoroalkyl and polyfluoroalkyl substances (PFASs) have been used in various industrial applications for many years. Long-chain PFASs are ubiquitous in wildlife and are reported to have a long elimination half-life in biological systems. Moreover, significant gender difference exists in the elimination of PFASs, where less is eliminated in male than in female. Recently, PFASs manufacturers and agencies have tried to replace the use of long-chain PFASs with short-chain PFASs, since they are expected to exhibit less bioaccumulation potential. Nevertheless, the potential risk and the pharmacokinetic (PK) characteristics of the short-chain PFASs still remain unknown. This study aims to fill the knowledge gap on short-chain PFASs, perfluoropentanoic acid (PFPeA), in terms of its PK properties using non-linear mixed-effect modeling and to explore gender differences in rats. Animal studies were carried out following oral or intravenous administration of PFPeA in male and female rats at a dose of 0.5–10 mg/kg. Plasma, urine, feces and nine tissues were collected and analyzed using ultra-performance liquid chromatography–tandem mass spectrometry. PK findings revealed that the clearance and the inter-compartmental clearance were 1.75 and 3.12 times higher in female rats than in male rats, respectively. According to the result, PFPeA is eliminated more rapidly in female rats than in male rats. Also, the tissue distribution study confirmed that distribution characteristics exhibited gender difference. This study provides scientific evidence for conducting further investigation into short-chain PFASs, biomonitoring plans and decision making regarding human health risk assessment. [ABSTRACT FROM AUTHOR]

The aim of this study was to newly identify and investigate the gender differences in pharmacokinetics (PKs) and tissue distribution of 4-n-nonylphenol (4-n-NP) in both male and female Sprague–Dawley rats. For this study, a UPLC–ESI–MS/MS system for 4-n-NP was developed as a sensitive and rapid analysis method and validated according to the accepted criteria of the international guidelines. The method was finally applied to the analysis of plasma, urine, feces, and nine different tissue samples of rats. PK parameters were calculated after single oral or intravenous administration of 4-n-NP at a dose of 10 or 50 mg/kg. Mean half-life of 4-n-NP in female rats was shorter and its clearance was larger for all doses than those in male rats. There were statistically significant differences in excretion patterns of urine and feces between male and female rats. Distribution of nine different tissues for 4-n-NP was greater in male than in female, and 4-n-NP was highly distributed in the liver or kidney. It was also specific that the distribution of 4-n-NP into brain was considerable. These results suggest that there are gender differences in the PKs of 4-n-NP in rats. Although, 4-n-NP is known to be a reproductive toxicant, reports on its PKs, excretion pattern, tissue distribution, and gender difference are limited. Therefore, our results will be useful data for gender differences as well as toxicokinetic information for 4-n-NP. In addition, it is expected to be very important for future risk assessment and PBPK model establishment of 4-n-NP. [ABSTRACT FROM AUTHOR]

In vitro studies are increasingly proposed to replace in vivo toxicity testing of substances. We set out to apply physiologically based pharmacokinetic (PBPK) modeling to predict the in vivo dose of amiodarone that leads to the same concentration–time profile in the supernatant and the cell lysate of cultured primary human hepatic cells (PHH). A PBPK human model was constructed based on the structure and tissue distribution of amiodarone in a rat model and using physiological human parameters. The predicted concentration–time profile in plasma was in agreement with human experimental data with the unbound fraction of amiodarone in plasma crucially affecting the goodness-of-fit. Using the validated kinetic model, we subsequently described the in vitro concentration–time data of amiodarone in PHH culture. However, this could be only appropriately modeled under conditions of zero protein binding and the very low clearance of the in vitro system in PHH culture. However, these represent unphysiological conditions and, thus, the main difference between the in vivo and the in vitro systems. Our results reveal that, for meaningful quantitative extrapolation from in vitro to in vivo conditions in PBPK studies, it is essential to avoid non-intended differences between these conditions. Specifically, clearance and protein binding, as demonstrated in our analysis of amiodarone modeling, are important parameters to consider. [ABSTRACT FROM AUTHOR]

Perfluorononanoic acid (PFNA) and perfluorodecanoic acid (PFDA), which are classified as perfluoroalkyl and polyfluoroalkyl substances (PFASs), have been widely used in industrial applications as a surface protectant. PFASs have been detected in wildlife and in humans around the globe. The purposes of this study are to develop and validate a physiologically based pharmacokinetic (PBPK) model for detecting PFNA and PFDA in male and female rats, and to apply the model to a human health risk assessment regarding the sex difference. A PBPK model of PFNA and PFDA was established based on an in vivo study in male and female rats. Analytes in biological samples (plasma, nine tissues, urine, and feces) were determined by ultra-liquid chromatography coupled tandem mass spectrometry (UPLC-MS/MS) method. PFNA and PFDA showed a gender differences in the elimination half-life and volume of distribution. The tissue-plasma partition coefficients were the highest in the liver in both male and female rats. The predicted rat plasma and urine concentrations simulated and fitted were in good agreement with the observed values. The PBPK models of PFNA and PFDA in male and female rats were then extrapolated to a human PBPK model based on human physiological parameters. The external doses were calculated at 3.35 ng/kg/day (male) and 17.0 ng/kg/day (female) for PFNA and 0.530 ng/kg/day (male) and 0.661 ng/kg/day (female) for PFDA. Human risk assessment was estimated using Korean biomonitoring values considering the gender differences. This study provides valuable insight into human health risk assessment regarding PFNA and PFDA exposure. [ABSTRACT FROM AUTHOR]

The antihistaminic drug methapyrilene was withdrawn from the market in 1979 because of hepatocarcinogenicity in rats. Since then, the drug has been used as a model hepatotoxin especially for transcriptomic analyses using material from in vivo studies. Much less transcriptomics data are available from in vitro studies, and no studies have investigated proteomic effects of methapyrilene in vitro. Thus, the present study was aimed to characterize the proteomic response of primary rat hepatocytes to methapyrilene, to broaden our knowledge on the molecular mechanisms of methapyrilene toxicity, and to compare the results of collagen sandwich-cultured hepatocytes to in vivo data. In vitro methapyrilene concentrations (0.39 µM, 6.25 µM, and 100 µM) were chosen to cover an in vivo-relevant range. Based on published pharmacokinetic data they correspond to concentrations in portal vein blood for previously in vivo-tested doses of methapyrilene, up to a concentration showing slight cytotoxicity. Analysis of proteomic alterations by two-dimensional gel electrophoresis and mass-spectrometric protein identification demonstrated consistent and concentration-dependent effects of methapyrilene, in particular on mitochondrial proteins. Data suggest substantial deregulation of amino acid and ammonia metabolism and effects on mitochondrial energy supply pathways. The effects identified in vitro concur well with into previous in vivo observations. Several effects, for example, the influence of methapyrilene on S-adenosylmethionine metabolism, have not been described previously. The data suggest that already non-toxic concentrations of methapyrilene alter components of the intermediary metabolism, such as branched-chain amino acid metabolism, as well as urea and tricarboxylic cycle enzymes. In summary, data substantially add to our knowledge on molecular mechanisms of methapyrilene hepatotoxicity at the protein level. [ABSTRACT FROM AUTHOR]

Perfluorohexanesulfonate (PFHxS), which belongs to the group of perfluoroalkyl and polyfluoroalkyl substances (PFASs), has been extensively used in industry and subsequently detected in the environment. Its use may be problematic, as PFHxS is known to induce neuronal cell death, and has been associated with early onset menopause in women and with attention deficit/hyperactivity disorder. Due to these impending issues, the aim of this study is to develop and evaluate a physiologically based pharmacokinetic (PBPK) model for PFHxS in male and female rats, and apply this to a human health risk assessment. We conducted this study in vivo after the oral or intravenous administration of PFHxS in male (dose of 10 mg/kg) and female rats (dose of 0.5-10 mg/kg). The biological samples consisted of plasma, nine tissues, urine, and feces. We analyzed the sample using ultra-liquid chromatography coupled tandem mass spectrometry (UPLC-MS/MS). Our findings showed the tissue-plasma partition coefficients for PFHxS were highest in the liver. The predicted rat plasma and tissue concentrations using a simulation fitted well with the observed values. We extrapolated the PBPK model in male and female rats to a human PBPK model of PFHxS based on human physiological parameters. The reference doses of 0.711 µg/kg/day (male) and 0.159 µg/kg/day (female) and external doses of 0.007 µg/kg/day (male) and 0.006 µg/kg/day (female) for human risk assessment were estimated using Korean biomonitoring values. This study provides valuable insight into human health risk assessment regarding PFHxS exposure. [ABSTRACT FROM AUTHOR]

Assessing the potential of a new drug to cause drug-induced liver injury (DILI) is a challenge for the pharmaceutical industry. We therefore determined whether cell models currently used in safety assessment (HepG2, HepaRG, Upcyte and primary human hepatocytes in conjunction with basic but commonly used endpoints) are actually able to distinguish between novel chemical entities (NCEs) with respect to their potential to cause DILI. A panel of thirteen compounds (nine DILI implicated and four non-DILI implicated in man) were selected for our study, which was conducted, for the first time, across multiple laboratories. None of the cell models could distinguish faithfully between DILI and non-DILI compounds. Only when nominal in vitro concentrations were adjusted for in vivo exposure levels were primary human hepatocytes (PHH) found to be the most accurate cell model, closely followed by HepG2. From a practical perspective, this study revealed significant inter-laboratory variation in the response of PHH, HepG2 and Upcyte cells, but not HepaRG cells. This variation was also observed to be compound dependent. Interestingly, differences between donors (hepatocytes), clones (HepG2) and the effect of cryopreservation (HepaRG and hepatocytes) were less important than differences between the cell models per se. In summary, these results demonstrate that basic cell health endpoints will not predict hepatotoxic risk in simple hepatic cells in the absence of pharmacokinetic data and that a multicenter assessment of more sophisticated signals of molecular initiating events is required to determine whether these cells can be incorporated in early safety assessment. [ABSTRACT FROM AUTHOR]

Understanding central mechanisms underlying drug-induced toxicity plays a crucial role in drug development and drug safety. However, a translation of cellular in vitro findings to an actual in vivo context remains challenging. Here, physiologically based pharmacokinetic (PBPK) modeling was used for in vivo contextualization of in vitro toxicity data (PICD) to quantitatively predict in vivo drug response over time by integrating multiple levels of biological organization. Explicitly, in vitro toxicity data at the cellular level were integrated into whole-body PBPK models at the organism level by coupling in vitro drug exposure with in vivo drug concentration-time profiles simulated in the extracellular environment within the organ. PICD was exemplarily applied on the hepatotoxicant azathioprine to quantitatively predict in vivo drug response of perturbed biological pathways and cellular processes in rats and humans. The predictive accuracy of PICD was assessed by comparing in vivo drug response predicted for rats with observed in vivo measurements. To demonstrate clinical applicability of PICD, in vivo drug responses of a critical toxicity-related pathway were predicted for eight patients following acute azathioprine overdoses. Moreover, acute liver failure after multiple dosing of azathioprine was investigated in a patient case study by use of own clinical data. Simulated pharmacokinetic profiles were therefore related to in vivo drug response predicted for genes associated with observed clinical symptoms and to clinical biomarkers measured in vivo. PICD provides a generic platform to investigate drug-induced toxicity at a patient level and thus may facilitate individualized risk assessment during drug development. [ABSTRACT FROM AUTHOR]

The article presents the author's thoughts on the issue of inhibition and induction of cytochrome P450 enzymes. This paper focuses on the failure in the development of pharmaceuticals which could result in various clinical response. It also explains the mechanisms in compromised pharmacokinetics inhibited and downregulated.

For centuries, 'khat sessions' have played a key role in the social and cultural traditions among several communities around Saudi Arabia and most East African countries. The identification of cathinone as the main psychoactive compound of khat leaves, exhibiting amphetamine-like pharmacological properties, resulted in the synthesis of several derivatives structurally similar to this so-called natural amphetamine. Synthetic cathinones were primarily developed for therapeutic purposes, but promptly started being misused and extensively abused for their euphoric effects. In the mid-2000's, synthetic cathinones emerged in the recreational drug markets as legal alternatives ('legal highs') to amphetamine, 'ecstasyʼ, or cocaine. Currently, they are sold as 'bath salts' or 'plant foodʼ, under ambiguous labels lacking information about their true contents. Cathinone derivatives are conveniently available online or at 'smartshops' and are much more affordable than the traditional illicit drugs. Despite the scarcity of scientific data on these 'legal highs', synthetic cathinones use became an increasingly popular practice worldwide. Additionally, criminalization of these derivatives is often useless since for each specific substance that gets legally controlled, one or more structurally modified analogs are introduced into the legal market. Chemically, these substances are structurally related to amphetamine. For this reason, cathinone derivatives share with this drug both central nervous system stimulating and sympathomimetic features. Reports of intoxication and deaths related to the use of 'bath salts' have been frequently described over the last years, and several attempts to apply a legislative control on synthetic cathinones have been made. However, further research on their pharmacological and toxicological properties is fully required in order to access the actual potential harm of synthetic cathinones to general public health. The present work provides a review on khat and synthetic cathinones, concerning their historical background, prevalence, patterns of use, legal status, chemistry, pharmacokinetics, pharmacodynamics, and their physiological and toxicological effects on animals and humans. [ABSTRACT FROM AUTHOR]

Amphetamines represent a class of psychotropic compounds, widely abused for their stimulant, euphoric, anorectic, and, in some cases, emphathogenic, entactogenic, and hallucinogenic properties. These compounds derive from the β-phenylethylamine core structure and are kinetically and dynamically characterized by easily crossing the blood-brain barrier, to resist brain biotransformation and to release monoamine neurotransmitters from nerve endings. Although amphetamines are widely acknowledged as synthetic drugs, of which amphetamine, methamphetamine, and 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) are well-known examples, humans have used natural amphetamines for several millenniums, through the consumption of amphetamines produced in plants, namely cathinone (khat), obtained from the plant Catha edulis and ephedrine, obtained from various plants in the genus Ephedra. More recently, a wave of new amphetamines has emerged in the market, mainly constituted of cathinone derivatives, including mephedrone, methylone, methedrone, and buthylone, among others. Although intoxications by amphetamines continue to be common causes of emergency department and hospital admissions, it is frequent to find the sophism that amphetamine derivatives, namely those appearing more recently, are relatively safe. However, human intoxications by these drugs are increasingly being reported, with similar patterns compared to those previously seen with classical amphetamines. That is not surprising, considering the similar structures and mechanisms of action among the different amphetamines, conferring similar toxicokinetic and toxicological profiles to these compounds. The aim of the present review is to give an insight into the pharmacokinetics, general mechanisms of biological and toxicological actions, and the main target organs for the toxicity of amphetamines. Although there is still scarce knowledge from novel amphetamines to draw mechanistic insights, the long-studied classical amphetamines-amphetamine itself, as well as methamphetamine and MDMA, provide plenty of data that may be useful to predict toxicological outcome to improvident abusers and are for that reason the main focus of this review. [ABSTRACT FROM AUTHOR]

To clarify the toxicological aspects of FYX-051, a xanthine oxidoreductase inhibitor, which is currently being developed as a therapeutic agent against gout and hyperuricemia, we performed the study focused on species differences in FYX-051-induced nephropathy. In the repeated toxicology testing by oral administration, nephropathy was seen at 1 mg/kg and more in rats and at 100 mg/kg in dogs, in contrast to no toxicity even at the practical maximum dose (300 mg/kg) in monkeys. The HPLC and LC-MS/MS analyses of intrarenal deposits in dogs have proven that the entity was xanthine. The study on dose dependency of pharmacokinetics, pharmacodynamics, urinary xanthine excretion, and kidney xanthine content by oral administration at 0.3, 1, and 3 mg/kg to rats revealed the involvement of xanthine in the occurrence of nephropathy, thus suggesting that plasma concentrations of FYX-051 can contribute to species differences. Regarding the possible factors of species differences, the daily urinary excretion of total purine metabolites was 30.5- and 6.3-fold greater in rats and dogs, respectively, than in monkeys. Urinary xanthine solubility was 2.3- and 6.3-fold higher in dogs and monkeys, respectively, than in rats. Plasma concentrations of FYX-051 were fivefold higher in rats than in dogs and monkeys, without differences between the latter two species. Therefore, the present study indicated that species differences in nephropathy were produced by the combined effects of purine metabolism, urinary xanthine solubility, and plasma concentrations of FYX-051. [ABSTRACT FROM AUTHOR]

Chemical exposure via breast milk is one of the great concerns in public health. Previously, we demonstrated that most body burden of PCB 153 can be transferred from the mother to the pups in mice during lactational period. Here we present a physiologically based pharmacokinetic (PBPK) model to describe the lactational transfer of PCB 153 with or without PCB 126 in mice. The model incorporated physiological changes on the volume and the blood flow into mammary tissues, and considered mechanistic information on the movement of PCB 153 from adipose tissue to the mammary gland during lactational period. The mechanistic consideration includes fat volume changes, binding of PCB 153 to very low density lipoprotein (VLDL) and increased uptake of VLDL in mammary tissues. Model parameters depicting physiological changes were obtained from research articles dealing with chemical transfer during lactational period in rodents. Chemical-specific parameters were derived from previous PBPK models focusing on the PCB disposition in rodents. The developed model adequately described the lactational transfer of PCB 153 with or without PCB 126 in mice. Our model will provide a useful mechanistic tool to estimate the disposition of PCBs in diverse experimental designs regarding PCB effects during developmental period and to improve quantitative risk assessment of PCBs in the developing organisms. [ABSTRACT FROM AUTHOR]

Garenoxacin is a des-F(6)-quinolone with a broad antibacterial spectrum, which has previously been shown to exhibit low chondrotoxicity in juvenile dogs compared with several other quinolones. A study was performed to determine whether the low chondrotoxicity observed in immature rats following garenoxacin treatment could be explained by poor penetration into cartilage tissue. Garenoxacin was orally administered to immature (4- to 5-week-old) Wistar rats as a single dose—or as doses given on 5 consecutive days—of 0 (vehicle), 200, 400, and 600 mg/kg (n=5 per dose level). Additional groups of rats were orally dosed with 600 mg/kg ofloxacin and ciprofloxacin. One knee joint of each animal (24 h after the last dose) was studied histologically after staining with Toluidine blue. The pharmacokinetics of garenoxacin in plasma (200, 400, and 600 mg/kg) and in knee joint cartilage (200 and 600 mg/kg) was assessed in separate groups of rats (n=55 per dose level). Concentrations of garenoxacin in plasma and cartilage were measured using an HPLC method. No signs of chondrotoxicity were observed in the immature rats treated with garenoxacin or ciprofloxacin for 5 days at the doses investigated in this study. However, ofloxacin was found to induce cartilage lesions that were typical of those seen for this quinolone. Systemic exposure to garenoxacin increased as a function of dose. Across dose and study day, mean garenoxacin plasma maximum concentration (Cmax) and area under the concentration–time curve (AUCtau) values were in the range 12–26 mg/l and 33–133 mg×h/l, respectively. Garenoxacin Cmax and AUC were similar on days 1 and 5, within each dose, indicating the absence of accumulation or reduction in the systemic exposure. Values determined for Tmax (0.25–1.0 h) and T1/2 (3.8–6.4 h) of garenoxacin in plasma did not vary with dose or study day. Although peak garenoxacin concentrations in cartilage were between equal levels to and 2.5-fold of those found in plasma, the observed ratios were somewhat lower than those reported for other quinolones, e.g. ofloxacin or sparfloxacin. Since garenoxacin appeared to be well absorbed following oral administration and concentrations in cartilage tended to be higher than those in plasma, it is unlikely that the low chondrotoxicity in comparison with other quinolones is explained by differences in the pharmacokinetics of these compounds. [ABSTRACT FROM AUTHOR]

The involvement of cytochrome P450 2E1 (CYP2E1) in the metabolism of N-methyl-2-pyrrolidone (NMP) was studied with three experimental approaches: in the rat, in vitro in human microsomes, and in human volunteers. NMP was administered dermally (40 mg/kg) to OFA rats to examine the influence of CYP2E1 inhibition (5 mg/kg diethyldithiocarbamate, DETC, 30 min before) and CYP2E1 induction (after 4 days of fasting). The main NMP metabolite 5-hydroxy-N-methylpyrrolidone (5HNMP) in the urine fractions collected during the following 48 h was analysed by gas chromatography-mass spectrometry. CYP2E1 inhibition led to a statistically significant retardation of 5HNMP excretion in urinary fractions collected during the first 12 h. In the group of fasted rats, a two-fold increase of CYP2E1 activity was observed in comparison with the control group. During the first 6 h after dermal administration of NMP to fasted rats, about 33% of the dose was excreted in urine versus 22% in controls. In vitro, NMP (15 mM) was incubated (up to120 min) with human liver microsomes and the formation of 5HNMP followed Michaelis-Menten kinetics with Vmax of 1.1 nmol/min per mg protein and Km of 2.4 mM. The formation of 5HNMP was inhibited by 35% in the presence of a monoclonal antibody against CYP2E1, but not by CYP1A2 antibody. In a dermal application experiment, 12 humans volunteers were exposed by means of a dermal patch to 300 mg NMP; five urine fractions were collected during the 48 h following the onset of application in order to measure the major metabolites 5HNMP and 2-hydroxymethylsuccinimide (2HMSI). Before NMP application, a blood sample was collected for the quantification of CYP2E1 mRNA in peripheral blood lymphocytes (PBLs). The mean dermal absorption of NMP was 67.9%. The highest amount of 5HNMP was excreted in urine in the fraction collected between 6–12 h (12.6% of dose), while 2HMSI peaked in fractions 12–24 h and 36–48 h (3.3 and 3.2% of dose, respectively). A significant relationship was found between CYP2E1 mRNA content in PBLs and the amount of both the metabolites excreted in urine within 24 h (r2=0.54, P<0.01). It is concluded that CYP2E1 is involved in the first steps of NMP metabolism in the rat and, to a lesser extent, in humans. Since large variations in CYP2E1 activity exist in the human population (at least 5-fold range), it seems justified to take into account the activity of this enzyme in an individual for an accurate interpretation of biological monitoring of exposure to NMP when relying on 5HNMP and/or 2HMSI determination in urine. [ABSTRACT FROM AUTHOR]

The pharmacokinetics and placental transfer of a single intravenous dose of 5.0 mg/kg (10 µCi/kg) ring-labeled [14C]chlorpyrifos were investigated in pregnant Sprague-Dawley rats at 11–13 days of gestation. Three rats were killed at 5, 15 or 30 min, or 1, 2, 4, 8, 12, 18, 24, 36, 48, 72 or 96 h after dosing. Radioactivity and 3,5,6-trichloropyridinol (TCP) were detected in all tissues 5 min after dosing. Chlorpyrifos was only found in maternal plasma and liver. Peak maternal plasma concentration of radioactivity (µg chlorpyrifos equivalents/ml) was 157 at 5 min, compared with 1.9 for fetal plasma at 15 min. The maximum concentrations of radioactivity (µg chlorpyrifos equivalents/g), detected in most tissues within 12 h of dosing, were, in descending order: liver (30), brain (29), placenta (21), and fetus (2). All peaks occurred at 5 min except for fetus and fetal plasma, which were at 15 min. TCP was detected by HPLC as the major compound identified in plasma and tissues. The maximum concentration detected was in plasma, at 12.4 µg/ml, and for the following tissues was: liver 4.3 ng/g fresh tissue, fetus 4 ng/g, placenta 2.97 ng/g, brain 1.68 ng/g, and fetal plasma 0.52 ng/g. All TCP peaks occurred at 5 min except for fetus at 30 min and fetal plasma at 15 min. Parent chlorpyrifos was detected in maternal plasma and liver at maximum concentrations of 5.1 µg/ml and 0.40 µg/g, respectively, at 5 min. Chlorpyrifos was detectable in maternal plasma up to 36 h after dosing, and in liver up to 24 h after dosing. Pharmacokinetic analysis best described radioactivity, chlorpyrifos, and TCP as disappearing biexponentially from plasma and tissues. The terminal elimination half-lives of radioactivity, chlorpyrifos and TCP from maternal plasma were 16, 18, and 16 h, respectively. The results indicate that (1) chlorpyrifos undergoes a rapid metabolism to its major metabolites (TCP); (2) chlorpyrifos and its metabolites are distributed to all maternal and fetal tissues and plasma; and (3) the elimination of chlorpyrifos and TCP is slow, with redistribution from lipid stores a likely determinant of elimination rates. [ABSTRACT FROM AUTHOR]

The volatile organic solvents trichloroethylene (TCE), tetrachloroethylene (perchloroethylene, PERC), and 1,1,1-trichloroethane (methylchloroform, MC) are widely distributed environmental pollutants and common contaminants of many chemical waste sites. To investigate the mode of pharmacokinetic interactions among TCE, PERC, and MC and to calculate defined "interaction thresholds", gas-uptake experiments were performed using a closed-chamber exposure system. In each experiment, two rats (Fischer 344, male, 8–9 weeks old) were exposed to different initial concentrations of TCE, PERC, and MC, applied singly or as a mixture, and their concentration in the gas phase of the chamber was monitored over a period of 6 h. A physiologically based pharmacokinetic (PBPK) model was developed to test multiple mechanisms of inhibitory interactions, i.e., competitive, non-competitive, or uncompetitive. All mixture exposure data were accurately described by a system of equations in which a PBPK model was provided for each chemical and each was regarded as an inhibitor of the others' metabolism. Sensitivity-analysis techniques were used to investigate the impact of key parameters on model output and optimize experimental design. Model simulations indicated that, among these three chemicals, the inhibition was competitive. The PBPK model was extended to assess occupationally relevant exposures at or below the current threshold-limit values (TLVs). Based on 10% elevation in TCE blood levels as a criterion for significant interaction and assuming TCE exposure is set at TLV of 50 ppm, the calculated interaction thresholds for PERC and MC were 25 and 135 ppm, respectively. TLV exposures to binary TCE/PERC mixture were below the 10% significance level. The interaction threshold for TCE and MC co-exposure would be reached at 50 and 175 ppm, respectively. Such interactive PBPK models should be of value in risk assessment of occupational and environmental exposure to solvent mixtures. [ABSTRACT FROM AUTHOR]

The gas 1,3-butadiene (BU) is an important industrial chemical and an environmental air pollutant. BU has been shown to be a weak carcinogen in the rat but a potent carcinogen in the B6C3F mouse. This species difference makes risk extrapolation to humans difficult and the underlying mechanism should be clarified before meaningful risk extrapolation to humans can be made. One possible explanation for the species differences in cancer response is that there are quantitative species differences in the formation of genotoxic epoxides. To investigate this possibility a physiologically based pharmacokinetic (pbpk) model for BU together with its first reactive metabolite l,2-epoxybutene-3 (butadiene monoxide, BMO) was developed. Previously reported values on hepatic glutathione (GSH) turnover, depletion of hepatic GSH in rodents exposed to BU, and in vitro metabolic data of BU and BMO were included in the model, which incorporates intrahepatic first-pass hydrolysis of BMO and the ordered sequential, ping-pong mechanism to describe the enzyme kinetics of BMO-GSH conjugation. In vitro studies were carried out to obtain tissue: air partition coefficients of BU and BMO in rat tissue homogenates. The simulated pharmacokinetics of BU, BMO, and GSH agreed with previously published experimental observations in rat and mouse obtained in closed and open chamber experiments. According to the model, the internal dose of BMO (expressed either as the concentration in mixed venous blood or as the area under the concentration-time curve) is approximately 1.6 times higher in the mouse than in the rat for exposure to BU below 1000 ppm. At higher exposure levels, GSH depletion occurs in the mouse, but not in the rat, after about 6-9 h. This GSH depletion results in up to 2-3 times higher internal doses in the mouse than in the rat. The clear but relatively small species difference in body burdens of BMO indicated from our model can only partly explain the marked species difference in cancer response between mice and rats exposed to BU. [ABSTRACT FROM AUTHOR]

Oral administration of retinol (50 mg/kg) to NMRI mice on day 11 of gestation (vaginal plug = day 0) led to the metabolic formation of high quantities of all- trans retinoic acid and all- trans-4-oxoretinoic acid, both known as potent teratogenic agents in the mouse. A 96% reduction of the area under the concentration-versus-timecurve (AUC) of metabolically generated all trans retinoic acid in maternal plasma, and an 84% decrease in the embryonic AUC were observed when mice had been pretreated with the alcohol dehydrogenase inhibitor 4-methylpyrazole. A similar reduction was observed for the major metabolite of all -trans retinoic acid in the mouse, all- trans-4-oxoretinoic acid. However, 4-methylpyrazole pretreatment decreased the AUC of retinol by 10% in maternal plasma and 15% in embryo. Treatment with retinol alone resulted in 55.6%, 43.9% and 56.0% skeletal anomalies of the forelimbs, hindlimbs and craniofacial structures, respectively. Pretreatment with 4-methylpyrazole lowered the retinol induced skeletal defects to 31.3%, 24.0% and 31.3%, respectively, in the forelimb, hindlimb and craniofacial region. Typical retinoid-induced malformations for gestational day 11, e.g. bent or reduced zeugopod or stylopod elements, or cleft palate, were significantly reduced by 4-methylpyrazole pretreatment but were still detected in significantly higher prevalence than in control mice. These data suggest that the teratogenic activity of a single high dose of vitamin A in mouse is partially but not exclusively dependent on the metabolic activation of retinol to all - trans retinoic acid. Thus it could be hypothesized that retinol is either a proximate teratogen or a coteratogen with all - trans retinoic acid. [ABSTRACT FROM AUTHOR]