A specific and sensitive GC-MS/MS method for the quantitative determination of 2-phenoxyethanol and selected metabolites in human blood and urine

2-Phenoxyethanol (PhE) is widely used as a preservative in consumer products such as cosmetics as well as at the workplace as a component of metal-working fluids and hydraulic fluids. Therefore, both industry workers and consumers may potentially be exposed to PhE. An analytical method for the quantification of PhE and three selected metabolites, namely phenoxyacetic acid (PhAA), 4-hydroxyphenoxyacetic acid (4-OH-PhAA), and 4-hydroxyphenoxyethanol (4-OH-PhE) in human urine and blood was developed and validated. The sample preparation includes enzymatic hydrolysis of urine samples or protein precipitation of blood samples, followed by liquid-liquid extraction and silylation of the target analytes. Analyses of the extracts were carried out by gas chromatography with tandem mass spectrometry (GC-MS/MS). 3,4-Hydroxyphenoxyethanol, a probably minor PhE metabolite could not reliable be analyzed due to its instability. The limits of quantification (LOQ) of the analytes ranged between 0.5 and 6.1 μg/L and 2.0 and 3.9 μg/L in urine and blood, respectively. The method was successfully applied to spot urine samples of 50 individuals without occupational exposure to PhE and additionally to blood samples from seven volunteers. In urine, PhAA and 4-OH-PhAA could be quantified in all analyzed samples, whereas 4-OH-PhE and unchanged PhE were found in 36 % and 32 % of the samples, respectively. In blood, PhAA was also found in every sample in levels above the LOQ, whereas PhE itself was detected in three of seven samples only. Neither 4-OH-PhAA nor 4-OH-PhE were found in any of the analyzed blood samples. The developed method promises to be a valuable tool for PhE monitoring of urine and blood samples and may also enable an advanced investigation of PhE biotransformation pathways in humans.

Human Metabolism and Urinary Elimination Kinetics of the Fragrance Geraniol after Oral Dosage

Geraniol is a fragrance with a characteristic rose-like smell, naturally occurring in terpene oil and also chemically synthesized on a large scale. Geraniol is widely used in consumer products such as cosmetics, personal care products, and household cleaners and as an additive in foods. An experimental study in human volunteers was carried out to investigate the metabolism and elimination kinetics of geraniol. Three subjects were orally exposed to geraniol in two different dosages (25 or 250 mg). In each case, one pre-exposure urine sample and all urine voids for 72 h after exposure were collected separately. The geraniol metabolites Hildebrandt acid, geranic acid, 3-hydroxycitronellic acid, and 8-carboxygeraniol were analyzed in every sample after enzymatic hydrolysis and liquid-liquid extraction using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Maximum urinary concentrations of the metabolites were measured between 1 and 5 h after oral dosing, and elimination half-lives were determined to be about 2-4 h. The predominant metabolite found in urine was Hildebrandt acid with 34.4 ± 5.6% of the ingested dose, followed by geranic acid (12.7 ± 5.6%), 3-hydroxycitronellic acid (2.2 ± 0.4%), and 8-carboxygeraniol (0.19 ± 0.09%). In total, the four metabolites determined represent 41.7-55.5% of the ingested dose. Only 8-carboxygeraniol is, however, a specific metabolite, while the other three target analytes are also formed from other terpenes like citral. Within this study, conversion factors were calculated, which allow for a rough estimate of the total geraniol uptake by back-calculation from metabolite concentrations of spot urine samples. Taking the conversion factor for all four metabolites into account, a mean daily uptake of geraniol of 1.43 mg was estimated from 41 urine samples of occupationally nonexposed adults. The metabolites Hildebrandt acid, geranic acid, 3-hydroxycitronellic acid, and 8-carboxygeraniol in urine are suitable biomarkers of exposure for geraniol and can be used for human biomonitoring studies.

Human metabolism and excretion kinetics of the surfactant 2,4,7,9-tetramethyl-5-decyne-4,7-diol (TMDD) after oral and dermal administration

2,4,7,9-Tetramethyl-5-decyne-4,7-diol (TMDD) is a non-ionic surfactant with a wide range of applications. TMDD is considered a high-production chemical and, due to its low biodegradation rate, possesses a potentially high prevalence in the environment. However, despite its widespread use, toxicokinetic data and data on internal exposure to TMDD in the general population are completely lacking. Hence, we developed a human biomonitoring (HBM) method for TMDD. Our approach included a metabolism study with four subjects, who were administered an oral dose of 75 µg TMDD/kg body weight and a dermal dose of 750 µg/kg body weight. Terminal methyl-hydroxylated TMDD (1-OH-TMDD) was previously identified as the main urinary metabolite in our lab. The results of the oral and dermal applications were used to determine the toxicokinetic parameters of 1-OH-TMDD as a biomarker of exposure. Finally, the method was applied to 50 urine samples from non-occupationally exposed volunteers. Results show that TMDD was rapidly metabolized, with an average tmax of 1.7 h and a rapid and almost complete (96%) excretion of 1-OH-TMDD until 12 h after oral dosage. Elimination was bi-phasic, with half-lives of 0.75-1.6 h and 3.4-3.6 h for phases 1 and 2, respectively. The dermal application resulted in a delayed urinary excretion of this metabolite with a tmax of 12 h and complete excretion after about 48 h. The excreted amounts of 1-OH-TMDD represented 18% of the orally administered TMDD dose. The data of the metabolism study demonstrated a fast oral as well as substantial dermal resorption of TMDD. Moreover, the results indicated an effective metabolism of 1-OH-TMDD, which is excreted rapidly and completely via urine. Application of the method to 50 urine samples revealed a quantification rate of 90%, with an average concentration of 0.19 ng/mL (0.97 nmol/g creatinine). With the urinary excretion factor (Fue) derived from the metabolism study, we estimated an average daily intake of 1.65 µg TMDD from environmental and dietary sources. In conclusion, 1-OH-TMDD in urine is a suitable biomarker of exposure to TMDD and can be applied for biomonitoring of the general population.

Determination of a specific metabolite for the non-ionic surfactant 2,4,7,9-Tetramethyl-5-decyne-4,7-diol (TMDD) by UPLC-MS/MS

2,4,7,9-Tetramethyldec-5-yne-4,7-diol (TMDD) is a non-ionic surfactant commonly used as defoaming agent and numerous other applications. Effluents of wastewater treatment plants have been identified as one of the main sources of TMDD emissions into the environment. Due to its broad application in various fields, TMDD was selected for the development of a biomonitoring method for assessing human exposure within the frame of the cooperation project of the German Federal Ministry for the Environment, Nature Conservation, Building and Nuclear Safety (BMUB) and the German Chemical Industry Association (VCI) in 2020. This study aimed to identify a urinary metabolite for TMDD by UPLC-Q-Orbitrap-MS which can be used as a biomarker of TMDD exposure. Monohydroxylated TMDD (1-OH-TMDD) was deciphered as the most prominent metabolite of TMDD in humans in a series of in vitro and in vivo experiments. In a next step, a quantitative method for the determination of 1-OH-TMDD was developed and validated. Quantification was achieved by isotope dilution using D₃-1-OH-TMDD as internal standard. The method is characterized by a simple sample clean-up procedure and an enzymatic hydrolysis of possible metabolite conjugates with ß-glucuronidase. Method validation was performed according to international guidelines for bioanalytical method validation. The method proved its robustness, precision, accuracy and sensitivity for the intended purpose, i.e. the assessment of TMDD exposure in the general population by means of human biomonitoring.

Human metabolism and excretion kinetics of benzotriazole UV stabilizer UV-327 after single oral administration

UV-327 (2-(5-chloro-benzotriazol-2-yl)-4,6-di-(tert-butyl)phenol) is used as an ultraviolet (UV) absorber in plastic products and coatings. Due to its ubiquitous distribution in the environment, human exposure is conceivable. In the study presented herein, initial information on the human in vivo metabolism of UV-327 was obtained by single oral administration to three volunteers. Urine and blood samples were collected up to 72 h after exposure. One study participant additionally donated plasma samples. Maximum blood and plasma levels of UV-327 and its two monohydroxylated metabolites UV-327-6-mOH and UV-327-4-mOH were reached 6 h post-exposure. Almost the entire amount found in blood and plasma samples was identified as UV-327, whereas the two metabolites each accounted for only 0.04% of the total amount, indicating that UV-327 is well-absorbed from the intestine, but only partially metabolized. Plasma to blood ratios of UV-327, UV-327-6-mOH, and UV-327-4-mOH ranged from 1.5 to 1.6. Maximum urinary excretion rates of UV-327, UV-327-6-mOH, UV-327-4-mOH, and UV-327-4 + 6-diOH were reached 9-14 h post-exposure. However, only about 0.03% of the orally administered dose of UV-327 was recovered as UV-327 and its metabolites in urine, indicating that biliary excretion may be the major route of elimination of UV-327 and its hydroxylated metabolites. The present study complements the insight in the complex absorption, distribution, metabolism, and elimination (ADME) processes of benzotriazole UV stabilizers (BUVSs).

Reliable determination of the main metabolites of 2-phenoxyethanol in human blood and urine using LC-MS/MS analysis

2-Phenoxyethanol (PhE) is used as a broad-spectrum preservative in several consumer products like cosmetics and cleaning agents. To enable the analysis and assessment of human exposure to PhE, a fast and sensitive LC-MS/MS method for the quantification of two PhE metabolites, namely phenoxyacetic acid (PhAA) and 4-hydroxyphenoxyacetic acid (4-OH-PhAA) in human urine and blood was developed and validated. The method is based on liquid chromatography combined with tandem mass spectrometry (LC-MS/MS). Sample preparation was different for both matrices: either a simple "dilute&shoot"-approach for urine samples or a liquid-liquid-extraction (LLE) for blood samples was used. The limit of quantification (LOQ) is 10 μg L^-1 and 6 μg L^-1 for PhAA and 20 μg L^-1 and 10 μg L^-1 for 4-OH-PhAA in urine and blood, respectively. The method was applied to urine samples of 153 persons without occupational exposure to PhE and to blood samples of 7 additional volunteers. In blood, PhAA was detected in 57% of all samples (range: <LOQ - 0.017 mg L^-1), while 4-OH-PhAA was not detectable. In contrast to that, PhAA was found in 99% and 4-OH-PhAA in 95% of all urine samples. The median concentrations in urine were 0.99 mg L^-1 (range: <LOQ - 53.83 mg L^-1) for PhAA and 0.11 mg L^-1 (<LOQ - 4.98 mg L^-1) for 4-OH-PhAA, respectively. Analyses after acid hydrolysis showed that both urinary metabolites are excreted unconjugated.

Quantitative determination of urinary metabolites of geraniol by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS)

Geraniol is a fragrance which occurs in natural terpene oil or is chemically synthesized on a large scale. It is used in a wide variety of consumer products such as perfumes, deodorants, household products and cosmetics. Hence, not only industry workers in the production of geraniol, but also consumers can come into contact with the substance. Human biomonitoring (HBM), i.e. the analytical determination of substances and their metabolites in human biological material, is a key element in the analysis and assessment of the distribution and intensity of occupational and environmental exposure of humans. Therefore, a procedure for the quantitative determination of the urinary metabolites Hildebrandt acid, geranic acid, 3-hydroxycitronellic acid and 8-carboxygeraniol as potential biomarkers of geraniol exposure was developed and validated. The method is based on ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) after enzymatic hydrolysis and liquid-liquid extraction (LLE) of the target analytes. The limit of quantification (LOQ) is 1.5 μg L^-1 for 8-carboxygeraniol, 2.7 μg L^-1 each for Hildebrandt acid and geranic acid, and 1.8 μg L^-1 for 3-hydroxycitronellic acid. The method was applied to urine samples of 41 persons without occupational exposure to geraniol. Hildebrandt acid and geranic acid were detected in all samples, 8-carboxygeraniol in 83% and 3-hydroxycitronellic acid in 81% of the samples. Hildebrandt acid (median: 313 μg L^-1, range: 37-1966 μg L^-1) was the most abundant metabolite, followed by geranic acid (93 μg L^-1; 9-477 μg L^-1), 3-hydroxycitronellic acid (18 μg L^-1; <LOQ to 70 μg L^-1) and 8-carboxygeraniol (9 μg L^-1; <LOQ to 46 μg L^-1). Hildebrandt acid, geranic acid and 3-hydroxycitronellic acid apparently represent larger relative fractions of the eliminated metabolites, but they are not strictly specific for geraniol since they are metabolites of other terpenes as well, such as citral. In contrast, geraniol seems to be the only parent compound for 8-carboxygeraniol, which makes this metabolite a promising candidate for specific human biomonitoring and risk assessment.

Development of a human biomonitoring method for assessing the exposure to ethoxyquin in the general population

Ethoxyquin (EQ) is commonly used as an antioxidant in animal feeds. Although EQ is not permitted for usage in food products for humans within the EU, residues of EQ and its transformation products could be determined in food of animal origin. Despite its widespread use and concerns on its toxicological profile, no information about the systemic exposure to EQ in the general population is available. Hence, we developed a human biomonitoring (HBM) method for EQ. Our approach included a metabolism study with five subjects, who were administered an oral dose of 0.005 mg EQ/kg body weight. Unchanged EQ and the major metabolite 2,2,4-trimethyl-6(2H)-quinolinone (EQI) were identified as urinary excretion products of EQ. While small amounts of EQ could be determined in high concentrated samples from the metabolism study only, 28.5% of the orally applied EQ dose could be recovered as EQI. Toxicokinetic parameters were determined for EQI, the potential biomarker of exposure. In addition, an analytical method for EQI (LOQ = 0.03 µg/L) in urine based on UHPLC-MS/MS comprising enzymatic glucuronide hydrolysis and salt-assisted liquid-liquid extraction was developed, validated and applied to 53 urine samples from the general population. EQI could be quantified in 11 (21%) of the samples in levels up to 1.7 µg/L urine, proving the suitability of the developed method for the intended purpose.

Identification of in vitro phase I metabolites of benzotriazole UV stabilizer UV-327 using HPLC coupled with mass spectrometry

The benzotriazole UV stabilizer (BUVS) 2-(5-chloro-benzotriazol-2-yl)-4,6-di-(tert-butyl)phenol (UV-327) is used in various plastic products to protect them against harmful UV radiation. Meanwhile, there are concerns about potential adverse health effects on humans, as residues of UV-327 and other BUVSs have already been detected in various environmental matrices. However, information on the metabolism of UV-327 is not yet available. Therefore, in vitro experiments with human liver microsomes (HLMs) were performed in order to identify phase I metabolites to be used as specific biomarkers of exposure in biomonitoring studies. The samples were analyzed by HPLC coupled with mass spectrometry (HPLC/MS). Potential metabolites, which were formed by hydroxylation and further oxidation to carboxylic acid, were tentatively identified. Special metabolite structures were suspected and custom-synthesized as reference substances for verification. In total, seven phase I metabolites, which may be suitable biomarkers for the assessment of exposure to UV-327, have been identified and quantified. The results of the present study provide initial insights into the metabolic pathway of UV-327, which is essential for further research on its human metabolism.

Human metabolism and urinary excretion kinetics of the UV filter Uvinul A plus® after a single oral or dermal dosage

Hexyl 2-[4-(diethylamino)-2-hydroxybenzoyl]benzoate, better known under its trading name Uvinul A plus® is a UV filter mainly used in sunscreens, but also present in other cosmetic products with a maximum concentration of 10% (w/w) according to the EU directive. In this study we investigated the human metabolism after a single oral and a single dermal dose of Uvinul A plus®, respectively. Samples collected within 72 h of administration were analyzed with a newly developed UHPLC-MS/MS method. Results of the study revealed three major urinary metabolites, namely 2-(4-amino-2-hydroxybenzoyl)benzoic acid (AHB), 2-(4-(ethylamino)-2-hydroxybenzoyl)benzoic acid (EHB) and 2-(4-(diethylamino)-2-hydroxybenzoyl)benzoic acid (DHB), representing 52% of the administered oral dose. The three major metabolites are further converted into four minor metabolites with an additional hydroxyl group in the aniline moiety. Toxicokinetic parameters (amount excreted, t_max, elimination constant and half-life t_1/2) and conversion factors were determined for the three major metabolites. The conversion factors were used to estimate the mean daily exposure to Uvinul A plus® in spot urine samples from 58 volunteers not intentionally exposed to Uvinul A plus® derived from a pilot study. The three major metabolites were quantifiable in 26% of the samples. In 35% of the samples, at least one major metabolite could be quantified. The daily systemic exposure to Uvinul A plus® was estimated to approximately 8.1-9.3 μg/d by applying the combined conversion factor for all three major metabolites. In conclusion, a very low systemic exposure to DHHB was observed with regard to the no observed adverse effect level (NOAEL) as an established threshold for chronic uptake.

Derivation of safe exposure levels for potential migration of formaldehyde into food

Polyoxymethylene (POM) is a polymer of formaldehyde used inter alia for kitchenware and food processing machines. By migration into food, consumers may be exposed to small additional amounts of formaldehyde in food. In order to address such potential exposures, Specific Migration Limits are derived using all studies with oral exposure in mammals and birds. The assessment is not only based on local irritation observed in a 2-year rat study that has previously served to calculate acceptable exposure levels, but also on systemic effects, namely on effects on the kidney in adult rats and testes in birds before sexual maturity. At the relatively high oral exposure levels (up to 2000 ppm in drinking water) long-term effects caused by formic acid, the first step metabolite of formaldehyde, such as acidosis, cannot be excluded. The lowest Specific Migration Limit of 2.74 mg/dm², corresponding to 16.5 mg formaldehyde/kg food, is based upon kidney effects in rats, leading to potential exposures that range between 2900 and 4400 times below the endogenous turnover of formaldehyde. Lastly, a recent migration study with POM showed that migration of formaldehyde into food simulants is over an order of magnitude below the lowest Specific Migration Limit derived herein.

Oxidative phase I metabolism of the UV absorber 2-(2H-benzotriazol-2-yl)-4,6-di-tert-pentylphenol (UV 328) in an in vitro model with human liver microsomes

2-(2H-Benzotriazol-2-yl)-4,6-di-tert-pentylphenol (UV 328, CAS: 25973-55-1) is an ultraviolet light (UV) absorber which is used as an additive for plastics and other polymeric substances to prevent the host material from light induced degradation reactions. However, no information about human exposure, metabolism and kinetics is available for this substance so far. Therefore, in vitro experiments with human liver microsomes were performed to derive oxidative phase I metabolites of UV 328 in an explorative approach using liquid-chromatography coupled with tandem mass spectrometry. Initially, a suspect screening mode was applied to the incubated samples. Six metabolites with hydroxy or oxo groups as well as a metabolite carrying both hydroxy and carbonyl moieties at the alkyl side chains were postulated and custom synthesized as reference standards. Afterwards, the results were verified in a target screening approach. Thereby, five of the six investigated analyte structures were confirmed. Quantitative estimations of the generated transformation products revealed 2-(2H-benzotriazol-2-yl)-6-(3-hydroxy-2-methylbutan-2-yl)-4-(tert-pentyl)phenol (UV 328-6/3-OH), 2-(2H-benzotriazol-2-yl)-4-(3-hydroxy-2-methylbutan-2-yl)-6-(tert-pentyl)phenol (UV 328-4/3-OH) and 2-(2H-benzotriazol-2-yl)-4-(2-methylbutan-3-on-2-yl)-6-(3-hydroxy-2-methylbutan-2-yl)phenol (UV 328-4/3-CO-6/3-OH) as most promising parameters. In summary, oxidation of both alkyl side chains at the phenol moiety was proven, but no metabolic transformations at the benzotriazole moiety were observed.

Hexamoll® DINCH: Lack of in vivo evidence for obesogenic properties

Hexamoll^® DINCH is an important alternative to phthalate plasticizers. Although regulatory reviews have not identified any potential hazards even in sensitive populations, an in vitro study by Campioli et al. (2015) suggested Hexamoll^® DINCH might alter fat storage in adipocytes resulting in obesity. To evaluate this hypothesis, data from studies with Hexamoll^® DINCH were reviewed for evidence of deposition in fat, changes in body weight, or changes in serum chemistry reflecting altered metabolic status. Body weights of F1 and F2 pups in a two-generation study did not differ from controls even at 1000 mg Hexamoll^® DINCH/kg body weight. Mean relative liver weights from the 1000 and 300 mg/kg bw groups were increased, but without histopathologic changes. Triglyceride and cholesterol levels in serum were not affected. In addition, subchronic and chronic studies in rats did not give evidence of an obesogenic effect. Radioactivity from 20 or 1000 mg/kg bw ¹⁴C-labelled Hexamoll^® DINCH dosed orally remained 2-3 times longer in adipose tissue than in well-perfused tissues; however, levels were 20-500% below other tissues at 1 and 8 h post dosing. Radioactivity concentrations in organs and tissues excluding the GI tract declined rapidly and continuously, and decreased in parallel to the concentration in plasma during the following 20 h. Both, initial and terminal half-lives of radioactivity concentration do not indicate a potential for accumulation. Furthermore, a metabolomic comparison of Hexamoll^® DINCH with DEHP and other phthalates shows complete separation of the metabolomic profile of these two chemical classes, meaning that their effects on the body and the body's reaction to the substance are different. Hence, comprehensive in vivo data do not show any evidence of Hexamoll^® DINCH altering fat metabolism or having obesogenic properties.

A validated UPLC-MS/MS method for biomonitoring the exposure to the fragrance 7-hydroxycitronellal

7-Hydroxycitronellal is a synthetic fragrance (CAS No. 107-75-5) which is used commonly in cosmetics, washing- and cleaning agents and as flavoring in foods. Due to its broad application in various fields, 7-hydroxycitronellal was selected for the development of a biomonitoring method for the quantitative exposure assessment within the frame of the cooperation project of the German Federal Ministry for the Environment, Nature Conservation, Building and Nuclear Safety (BMUB) and the German Chemical Industry Association (VCI). For this purpose, an ultra performance liquid chromatography combined with tandem mass spectrometry (UPLC-MS/MS) based method was developed for the determination of potential biomarkers of 7-hydroxycitronellal (7-HC) in human urine samples. 7-Hydroxycitronellylic acid (7-HCA) turned out to be the quantitatively most important metabolite of 7-HC in human urine, occurring in 1000 times higher amounts than 7-hydroxycitronellol (7-HCO) or other potential metabolites. Therefore, an analytical method for 7-HCA was developed using stable isotope-labeled 7-HCA as internal standard (IS). The method includes a cleavage step of possible metabolite conjugates with an enzyme mix of ß-glucuronidase and arylsulfatase. Subsequent sample cleanup was performed by liquid-liquid extraction (LLE) with dichloromethane. The method was calibrated by calculating the linear regression between the analyte/IS ratio and the nominal 7-HCA concentrations in water. The method was validated according to approved standard guidelines and proved to be robust, reliable and sensitive for the human biomonitoring of 7-HC. The method was applied to urine samples of 40 adult volunteers from the general population. 7-HCA was quantifiable in urine of all subjects. Thus the developed method proved to be suitable for assessing the background exposure to 7-HC in the general population.

A comparison between in vitro rat and human and in vivo rat skin absorption studies

In vitro skin penetration rates in rat and man were compared to those obtained in vivo in rats. Saturation of absorption was frequently observed at higher exposure levels in in vitro and in vivo. Lipophilic compounds showed the highest penetration rates through rat skin in vitro. In all cases in vitro dermal penetration through rat skin was higher than in vivo. Thus, the in vitro study may serve as a first tier test. The in vivo data suggest an inverse relationship between molecular weight and the rate of dermal absorption for lipophilic as well as hydrophilic compounds. Rat skin was more permeable to all tested substances than human skin (mean difference 10.9-fold). Thus, the systemic exposure of humans may be significantly overestimated if risk assessment is based only on the results of an in vivo rat study, because human skin is less permeable than rat skin. It would appear, therefore, that an estimate of actual dermal penetration through human skin should be based on the combined use of in vivo and in vitro data, using the following equation:

%Human dermal penetration

=(%rat in vivo dermal penetration)

(See PDF for Formula)

A critical review finds styrene lacks direct endocrine disruptor activity

The European Commission lists styrene (S) as an endocrine disruptor based primarily on reports of increased prolactin (PRL) levels in S-exposed workers. The US Environmental Protection Agency included S in its list of chemicals to be tested for endocrine activity. Therefore, the database of S for potential endocrine activity is assessed. In vitro and in vivo screening studies, as well as non-guideline and guideline investigations in experimental animals indicate that S is not associated with (anti)estrogenic, (anti)androgenic, or thyroid-modulating activity or with an endocrine activity that may be relevant for the environment. Studies in exposed workers have suggested elevated PRL levels that have been further examined in a series of human and animal investigations. While there is only one definitively known physiological function of PRL, namely stimulation of milk production, many normal stress situations may lead to elevations without any chemical exposure. Animal studies on various aspects of dopamine (DA), the PRL-regulating neurotransmitter, in the central nervous system did not give mechanistic explanations on how S may affect PRL levels. Overall, a neuroendocrine disruption of PRL regulation cannot be deduced from a large experimental database. The effects in workers could not consistently be reproduced in experimental animals and the findings in humans represented acute reversible effects clearly below clinical and pathological levels. Therefore, unspecific acute workplace-related stress is proposed as an alternative mode of action for elevated PRL levels in workers.

Sensory irritation as a basis for setting occupational exposure limits

There is a need of guidance on how local irritancy data should be incorporated into risk assessment procedures, particularly with respect to the derivation of occupational exposure limits (OELs). Therefore, a board of experts from German committees in charge of the derivation of OELs discussed the major challenges of this particular end point for regulatory toxicology. As a result, this overview deals with the question of integrating results of local toxicity at the eyes and the upper respiratory tract (URT). Part 1 describes the morphology and physiology of the relevant target sites, i.e., the outer eye, nasal cavity, and larynx/pharynx in humans. Special emphasis is placed on sensory innervation, species differences between humans and rodents, and possible effects of obnoxious odor in humans. Based on this physiological basis, Part 2 describes a conceptual model for the causation of adverse health effects at these targets that is composed of two pathways. The first, “sensory irritation” pathway is initiated by the interaction of local irritants with receptors of the nervous system (e.g., trigeminal nerve endings) and a downstream cascade of reflexes and defense mechanisms (e.g., eyeblinks, coughing). While the first stages of this pathway are thought to be completely reversible, high or prolonged exposure can lead to neurogenic inflammation and subsequently tissue damage. The second, “tissue irritation” pathway starts with the interaction of the local irritant with the epithelial cell layers of the eyes and the URT. Adaptive changes are the first response on that pathway followed by inflammation and irreversible damages. Regardless of these initial steps, at high concentrations and prolonged exposures, the two pathways converge to the adverse effect of morphologically and biochemically ascertainable changes. Experimental exposure studies with human volunteers provide the empirical basis for effects along the sensory irritation pathway and thus, “sensory NOAEC_human” can be derived. In contrast, inhalation studies with rodents investigate the second pathway that yields an “irritative NOAEC_animal.” Usually the data for both pathways is not available and extrapolation across species is necessary. Part 3 comprises an empirical approach for the derivation of a default factor for interspecies differences. Therefore, from those substances under discussion in German scientific and regulatory bodies, 19 substances were identified known to be human irritants with available human and animal data. The evaluation started with three substances: ethyl acrylate, formaldehyde, and methyl methacrylate. For these substances, appropriate chronic animal and a controlled human exposure studies were available. The comparison of the sensory NOAEC_human with the irritative NOAEC_animal (chronic) resulted in an interspecies extrapolation factor (iEF) of 3 for extrapolating animal data concerning local sensory irritating effects. The adequacy of this iEF was confirmed by its application to additional substances with lower data density (acetaldehyde, ammonia, n-butyl acetate, hydrogen sulfide, and 2-ethylhexanol). Thus, extrapolating from animal studies, an iEF of 3 should be applied for local sensory irritants without reliable human data, unless individual data argue for a substance-specific approach.

Polyethylene glycol-polyvinyl alcohol grafted copolymer: study of the bioavailability after oral administration to rats

The absorption, urinary excretion, and the biliary excretion of a single oral dose of 10 or 1000 mg/kg bw of (14)C-polyethylene glycol-polyvinyl alcohol (PEG-PVA) grafted copolymer were studied in adult male and female rats. In a balance/excretion experiment, the total excretion of ingested radioactivity was determined over a period of 168 h and residual radioactivity was detected in selected tissues and the carcass. In a biliary excretion experiment, excretion of radioactivity via the bile duct was determined over a period of 48 h after administration of the substance to cannulated rats. Most, if not all, of the radioactivity (>100%) was excreted within 48 h via the feces regardless of sex or dose. Urinary excretion was very limited: 0.45-0.50% of dose at the low dose and 0.22-0.27% of dose at the high dose. At both dose levels, residual radioactivity in the carcass and all organs and tissues after 168 h was ≤ 0.02% of dose. Biliary excretion was 0.01-0.02% of dose. Based on these findings, the bioavailability of PEG-PVA grafted copolymer was determined to be <1% demonstrating that absorption was virtually negligible following a single oral administration to male and female rats.

In vitro metabolism, glutathione conjugation, and CYP isoform specificity of epoxidation of 4-vinylphenol

4-Vinylphenol (4VP) has been identified as a minor urinary metabolite of styrene in rat and human volunteers. This compound has been shown to be more hepatotoxic and pneumotoxic than both styrene and styrene oxide at lower doses in rats and mice. To explore the possible toxicity mechanism of 4VP, the current study was conducted to investigate the metabolism of 4VP, the glutathione (GSH) conjugation of the metabolites of 4VP and its cytochrome P(450) (CYP) specificity in epoxidation in different microsomes in vitro. Incubations of 4VP with mouse lung microsomes afforded two major metabolites which were identified as 4-(2-oxiranyl)-phenol of 4VP (4VPO) and 4VP catechol. 4VPO was found to react with GSH to form GSH conjugate and 4VP catechol was found to further be metabolized to electrophilic species which react with GSH to form the corresponding 4VP catechol GSH conjugates. Relative formation rates for those GSH conjugates and the regioisomer formation of 4VPO-GSH conjugates with both inhibitors of CYP 2F2 and CYP 2E1 in microsomal incubation condition were also investigated. This present study provides better insight on the lung toxicity seen with 4VP, the toxic metabolite of commercial styrene.

Generation and characterization of test atmospheres with nanomaterials

To ensure the product safety of nanomaterials, BASF has initiated an extensive program to study the potential inhalation toxicity of nanosize particles. As preparation work for upcoming inhalation studies, the following manufactured nanomaterials have been evaluated for their behavior in an exposure system designed for inhalation toxicity studies: titanium dioxide, carbon black, Aerosil R104, Aerosil R106, aluminum oxide, copper(II) oxide, amorphous silicon dioxide, zinc oxide, and zirconium(IV) oxide. As the physicochemical properties and the complex nature of ultrafine aerosols may substantially influence the toxic potential, the particle size, specific surface area, zeta potential, and morphology of each of the materials were determined. Aerosols of each material were generated using a dry powder aerosol generator and by nebulization of particle suspensions. The mass concentration of the particles in the inhalation atmosphere was determined gravimetrically and the particle size was determined using a cascade impactor, an optical particle counter, and a scanning mobility particle sizer. The dispersion techniques used generated fine aerosols with particle size distributions in the respiratory range. However, as a result of the significant agglomeration of nanoparticles in the test materials evaluated, no more than a few mass percent of the materials were present as single nanoparticles (i.e., < 100 nm). Considering the number, a greater percentage of nanoparticles was present. Based on the obtained results and experience with the equipment, a technical setup for inhalation studies with nanomaterials is proposed. Furthermore, a stepwise testing approach is recommended that also could reduce the number of animals used in testing.

The use of metabolomics for the discovery of new biomarkers of effect

Will metabolomics have a greater chance of success in toxicology and biomarker assessment than genomics and proteomics? Metabolomics has the advantage that (1) it analyses the last step in a series of changes following a toxic insult, (2) many of the metabolites have a known function and (3) changes are detectable in blood. If the analysis of a great number of individual organs can be replaced by one matrix then this will provide significant advantages (less invasive method, no need to kill animals, time course analysis possible). We have chosen to perform the analysis of blood metabolites in such a way as to minimize the risk of artifacts and to have a high number of known metabolites. We have also reduced the amount of variation in the biological system as well as during analysis. In a series of proof of concept studies it could be demonstrated that (1) the metabolome of control animals was stable of a period of nearly 1 year, with a remarkable differentiation between males and females, (2) a dose response relationship in metabolome changes was induced by phenobarbital and that (3) different modes of action could be distinguished by blood metabolome analysis. To investigate the potential of metabolomics to find biomarkers or specific patterns of change we have analyzed the blood metabolome of rats treated with HPPD inhibitors, a novel class of herbicides. The results demonstrated that a single metabolite, tyrosine, can be used as a biomarker. In addition to tyrosine we also found a specific pattern of change that involved nine metabolites. Though the extent of change was less than for tyrosine the consistent change of these metabolites is diagnostic for this (toxicological) mode of action.

Determination of pulmonary irritant threshold concentrations of hexamethylene-1,6-diisocyanate (HDI) prepolymers by bronchoalveolar lavage in acute rat inhalation studies according to TRGS 430

Pulmonary irritant threshold concentrations of two hexamethylene-1,6-diisocyanate (HDI)-based prepolymers (I: polymeric emulsfier modified and II: oligomeric allophanate modified) were determined in acute inhalation studies according to TRGS 430 (Dangerous Substances Technical Rule, isocyanates, Germany), based on benchmark extrapolation of bronchoalveolar lavage fluid (BALF) total protein. It was also investigated if the method is robust enough to be transferred to an independent laboratory. Five male Wistar rats per group were exposed nose-only to the test substances as liquid aerosols to concentrations of 0, 0.5, 3, 15 mg/m(3) for both test substances with an additional test group at 50 mg/m(3) for test substance I. The duration of the exposure was 6h, followed by serial sacrifices 1 day, 3 days and 7 days post exposure. BALF was analyzed for biochemical and cytological markers indicative for injury of the bronchoalveolar region. The exposure of rats to test substance I and II caused dose depended lung irritation with BALF total protein concentration being the most sensitive indicator of pulmonary effects. The extrapolated no observed adverse effect level of test substance I was 1.1 mg/m(3) and that of test substance II 2.3 mg/m(3). The acute pulmonary irritant threshold concentrations were found to be similar to those reported by [Pauluhn, J., 2004. Pulmonary irritant potency of polyisocyanate aerosols in rats: comparative assessment of irritant threshold concentrations by bronchoalveolar lavage. J. Appl. Toxicol. 24, 231-247] for HDI-homopolymers and other HDI-based polyisocyanates, and were at least 30 times higher than the MAK (occupational exposure limit) value for the HDI monomer (0.035 mg/m(3)). Thus the EBW (exposure assessment value) for these two HDI-based prepolymers can be established at 10x MAK, i.e. at 0.35 mg/m(3).

Analysis of biomarkers in rats and dogs exposed to polymeric methylenediphenyl diisocyanate (pMDI) and its glutathione adduct

Hemoglobin adducts (Hb-MDX) of monomeric methylenediphenyl diisocyanate (MDI) are often interpreted as indirect evidence of hydrolysis of the diisocyanate moiety to the respective amine (diphenylmethane-4,4'-diamine, 4,4'-MDA) which constitutes the rationale of using this biomarker as an internal dosimeter of exposure to putatively formed MDA. In contrast, more recently published data suggest that following inhalation the high concentration of glutathione (GSH) present in lungs favor an adduct formation with GSH and/or peptides/proteins rather than hydrolysis. The focus of this study was to test this alternate hypothesis, viz. whether Hb-MDX can also be formed by the GSH bis-adduct of monomeric MDI. The synthesized mMDI-GSH bis-adduct was administered to rats by single intratracheal instillation. Additional groups were dosed by gavage and intraperitoneal injection. Biomarkers of exposure were determined in blood (plasma protein and hemoglobin adducts) and urine after harsh alkaline and acid hydrolysis, respectively. Data from previous single inhalation exposure studies with aerosols of MDI and 4,4'-MDA in rats served as reference. As to whether N-acetylation plays any modifying role to yield these mMDI-specific biomarkers was addressed in similarly head-only exposed dogs, a species with no appreciable N-acetylation capacity whereas rats are strong N-acetylators. The results obtained suggest that biomarkers in blood from controlled exposures above current workplace standards of mMDI appear not to be suitable for reliable assessments of past exposures. The biomarkers typically used to assess past exposures to MDI were also identified following exposure to the MDI-GSH bis-adduct. Their yield was low but quite similar for MDI aerosol and the MDI-GSH bis-adduct, whilst that of MDA was distinctively higher. The findings of this study are supportive of a conceptual pathway that the MDI-derived biomarkers of exposure are formed through MDI-GSH adducts rather than MDA. Data from dogs support the findings from rats and show that N-acetylation does not appear to be an essential modifying factor. It is concluded that the yield of MDI-related markers of exposure is relatively low and dependent on the exposure dose (and route). MDA originating from hydrolyzed serum protein or hemoglobin appear to be confounded by false-positive background levels which are surmised to be associated with the method of hydrolysis. The determination of urinary biomarkers might be a useful tool to identify recent exposures (by any route). Due methodological uncertainties associated with the harsh hydrolysis of biological specimens may be reduced substantially when using incremental pre- to post-shift changes rather than relying solely on absolute data.

Absorption, distribution, metabolism and excretion of an inhalation dose of [14C] 4,4'-methylenediphenyl diisocyanate in the male rat

The received dose, tissue distribution, metabolism, routes and rates of excretion of [(14)C]-4, 4(')-methylenediphenyl diisocyanate (MDI) were investigated in the male rat following a 6-h inhalation exposure to [(14)C]-MDI at a target concentration of 2 mg m(-3). The mean dose received was equivalent to 0.078 mg MDI per animal, of this between 25 and 32% of radiolabelled material was available systemically. Radioactivity was distributed to all tissues examined with the highest proportions present in the respiratory and gastrointestinal tracts, suggesting that both oral ingestion and pulmonary absorption contributed to the systemic dose of [(14)C]-MDI derived material, with the oral ingestion and the majority of the internal dose resulting from ingestion of radiolabelled material by grooming the pelt after exposure. Radioactivity was excreted mainly via faeces (about 80% of the received dose). Excretion in bile and urine each accounted for less than 15% of the dose. MDI was extensively metabolized after uptake, with two routes of transformation evident; the proposed spontaneous formation of mixed molecular weight polyureas and the enzyme catalysed metabolism of systemically available MDI or MDI derivatives to give N-acetylated and N-acetylated hydroxylated products. No free MDA was detected in any of the biomatrices (urine, faeces, bile) investigated.

The in vitro absorption of microfine zinc oxide and titanium dioxide through porcine skin

Microfine metallic oxides such as titanium dioxide or zinc oxide have been found to be highly protective against harmful UV rays. Because their long-term use could potentially lead to health effects if significant amounts of these microfine metallic oxides would be absorbed through the skin, the in vitro absorption of microfine zinc oxide and titanium oxide in cosmetic formulations through porcine skin was investigated. In the experiments with a microfine zinc oxide formulation, the mean total recoveries of Zn were in the range from 102% to 107% of the total Zn applied. Virtually the total amount of applied Zn was recovered in the first five tape strips. The amounts of Zn found in the skin membrane and the receptor fluid were comparable in untreated, vehicle treated or test substance treated skin preparations. The absorption-time plots from diffusion cells treated with the vehicle did not differ from those treated with the ZnO containing formulation. In the experiments with microfine titanium dioxide formulations T-Lite SF-S and T-Lite SF, mean total recoveries of Ti ranged from 98% to 100% and 86% to 93% of the total Ti applied, respectively. Virtually the total amount of applied Ti could be removed from the skin surface by washing. The amounts of titanium found in the tape strips and skin preparations were in the order of the analytical determination limit. No Ti was found in the receptor fluid at any sampling time. The results show that neither zinc or titanium ions nor microfine zinc oxide or titanium dioxide particles were able to penetrate porcine stratum corneum. Therefore, from the absence of internal exposure we conclude that their use in sunscreens does not pose a health risk.

The effects of styrene on lung cells in female mice and rats

Styrene has been shown to cause an increase in the incidence of lung tumors in CD-1 mice following chronic exposure at 40 and 160 ppm, whereas no treatment-related increase in tumors in any organ was seen in rats chronically exposed to up to 1000 ppm styrene. So far most of the mechanistic studies have been performed with male animals. The aim of the present study was to further elucidate the target cell population in mouse lungs exposed to styrene, and to investigate possible differential in vivo effects (e.g., glutathione depletion, increased lipid peroxidation, and oxidative DNA damage). Groups of female CD-1 mice were exposed to styrene at concentrations of 0, 172 or 688 mg/m3 (0, 40 or 160 ppm) for 6 h per day on 1 day, 5 consecutive days or for 20 days during a 4 week period. Groups of female Crl:CD rats were exposed to styrene at concentrations of 0, 688 or 2150 mg/m3 (0, 160 or 500 ppm) for a single 6 h period or for 6 h per day on 5 consecutive days. No signs of lung toxicity were observed in rats. The cytology of cells in lung lavage fluid provided no signs of an inflammatory response in either rats or mice. In mice, both exposure levels caused decreased CC16 protein concentrations in lung lavage fluid after 1 and 5 exposures and in mouse blood serum throughout the study, suggesting that styrene may cause destruction of Clara cells in mice. Degenerative lesions in mouse Clara cells (vacuolar cell degeneration, cell necrosis) were revealed by electronmicroscopy. After 5 and 20 exposures of mice at 160 ppm, cellular crowding, expressed as an irregular epithelial lining and indicative of a very early hyperplasia was noted. Although a depletion of glutathione was noted in mouse lung homogenates after 20 exposures, there was no evidence of oxidative stress as indicated by unchanged concentrations of 8-OH-deoxyguanosine. Malondialdehyde, an indicator of lipid peroxidation, was slightly increased in mice after 1 exposure at 160 ppm only.

The significance of in vitro rat skin absorption studies to human risk assessment

The present paper reviews the comparative rates of skin penetration between rat and man for a total of 14 chemicals in in vitro absorption studies. The results showed that in vitro absorption assays are capable of demonstrating large differences in the rate of skin penetration. Saturation of absorption was also frequently observed at higher exposure levels. The highest absorption rates through rat and human epidermis were observed with compounds with a molecular weight of approximately 300, an aqueous solubility of approximately 1-6 mg/l, and a log10 (P(OCTANOL/WATER)) of approximately 3-4. When the absorption data for 3 compounds with a log10 (P(OCTANOL/WATER)) of 2.9-3.0 were compared, there appeared to be an inverse relationship between molecular weight/aqueous solubility and the rate of dermal absorption. Lipophilic compounds with low aqueous solubility (<4 mg/l) showed the highest penetration rates through rat skin, but this was not always the case for human skin. The human skin was invariably less permeable to all tested substances than rat skin, though no constant factor of difference could be identified. The factor of difference would not appear to be determined by molecular weight, lipophilicity, or aqueous solubility. The actual systemic exposure of humans may be significantly overestimated if risk assessment is based only on the results of an in vivo rat study. It would appear that dermal penetration through human skin should be based on the combined use of in vivo and in vitro data, using the following equation: %Human dermal penetration= [[% dermal penetration rat (in vivo)] x [rate dermal penetration human (in vitro)]] / [rate dermal penetration rat (in vitro)]

Absorption, distribution, metabolism and excretion of 4-chloro-2-methylphenoxyacetic acid (MCPA) in rats

The metabolism of 14C-MCPA (4-chloro-2-methylphenoxyacetic acid) in male and female rats was compared to that of 14C- MCPA dimethylamine salt (MCPA.DMA) or 14C-MCPA ethylhexyl ester (MCPA-EHE) in adsorption, distribution, metabolism and excretion studies. Compounds were administered by the oral route. The studies demonstrated the bioequivalence of the various forms of MCPA, established the extent of metabolism and metabolite identity. Following single or multiple oral administration of 5 mg/kg 14C-MCPA quantitative recovery of radioactivity, predominantly in urine, was obtained within 168 h. Rats dosed at 100 mg/kg showed similar absorption kinetics but apparent saturation of urinary excretion led to a prolonged elimination phase. MCPA was not extensively metabolised but the oxidation product HMCPA (4-chloro-2-hydroxymethylphenoxyacetic acid) was found at low levels, together with the glycine conjugate. These metabolites were more prominent shortly after dosing, suggesting that MCPA is not retained in the liver and that these metabolites may be excreted faster than MCPA itself. MCPA.DMA and MCPA-EHE were very rapidly converted into MCPA and toxicokinetics and metabolism were indistinguishable from parent compound.

Effect of cytochrome P-450 inhibition on tetrahydrofuran-induced hepatocellular proliferation in female mice

The studies presented were designed to investigate the effects of cytochrome P450 inhibition on tetrahydrofuran-induced hepatocellular proliferation in female B6C3F(1) mice. Groups of female B6C3F(1) mice were exposed to dynamic atmospheres containing tetrahydrofuran (THF) concentrations of 0, 5,400 or 15,000 mg/m(3) for 6 h per day, for 5 consecutive days. One-half of the animals in each THF exposure group were pretreated with the cytochrome P450 inhibitor 1-aminobenzotriazole (ABT) at 100 mg/kg (i.p.) 1 h before the start of each THF exposure period. Treatment with THF at 15,000 mg/m(3) caused marked microsomal enzyme induction in the liver. The cytochrome P450 content was nearly doubled (+98%), pentoxyresorufin-O-depentylase (PROD) and ethoxyresorufin-O-deethylase (EROD) activities were increased by 600% and 160%, respectively. ABT pretreatment effectively blocked microsomal enzyme induction at 15,000 mg/m(3). THF exposure had no effect on the subcellular morphology of hepatocytes, whereas ABT-pretreatment caused centrilobular fatty change. THF at 15,000 mg/m(3) caused increased cell proliferation in zone 3 (central vein region) of the liver (according to Rappaport), as indicated by a significantly higher PCNA (Proliferating Cell Nuclear Antigen) labelling index, but there were no effects at 5,400 ppm. ABT pretreatment prior to THF exposure at 15,000 mg/m(3) caused an exacerbated proliferative response of mouse liver, significantly higher PCNA labelling indices being observed in zones 2 (midzonal region) and 3. The exacerbated proliferative response of mouse liver under conditions of inhibited THF metabolism suggests that the mitogenic effects are related to prevailing THF tissue concentrations and not to the generation of THF oxidative metabolite(s).

Investigations on cell proliferation and enzyme induction in male rat kidney and female mouse liver caused by tetrahydrofuran

To elucidate possible mechanism(s) of carcinogenic action of tetrahydrofuran (THF) that had been demonstrated in previous inhalation studies, groups of male F344 rats and female B6C3F(1) mice were exposed to dynamic atmospheric concentrations of 0, 600, 1800, or 5400 mg/m(3) for 6 h per day, either for 5 consecutive days or for a period of 4 weeks (5 days per week). The reversibility of treatment-related changes was investigated in rats and mice exposed for 5 days and sacrificed 21 days after the last exposure. Female B6C3F(1) mice exposed to 5400 mg/m(3) showed significantly increased cytochrome P450 content, increased ethoxyresorufin-O-deethylase and pentoxyresorufin-O-depentylase activities, increased cell proliferation (5-bromo-2'-deoxyuridine-method) and an increased mitotic index in liver zones 2 (midzonal region) and 3 (central vein region). The changes were found to be reversible after a 3-week treatment-free period (cell proliferation examined, only). Male F344 rats showed dose-related alpha2u-globulin (alpha2u) accumulation in the renal cortex after 5 or 20 exposures, and there were no signs of reversal after a 3-week treatment-free period. After 20 exposures at 5400 mg/m(3), the alpha2u accumulation was found to be associated with increased cell proliferation in "hot spots" of the renal cortex and increased apoptosis. Increased cell proliferation was also detected after 20 exposures at 1800 mg/m(3). There were no effects at 600 mg/m(3). It is concluded that THF enhances tumor formation in male rat kidney and female mouse liver via induction of cell proliferation. These features present essential elements that should be taken into account for the carcinogenic risk assessment of THF.

NTA and Fe(III)NTA: differential patterns of renal toxicity in subchronic studies

Differential patterns in terms of nephropathology and 8-hydroxyguanine formation in the course of oral 28-day studies were observed with nitrilotriacetic acid (NTA) and FeNTA. FeNTA, but not NTA, caused enhanced 8-hydroxyguanine formation in kidney DNA after oral and intraperitoneal administration. Enhanced lipid peroxidation in the kidney homogenate was observed with FeNTA as well as with NTA. For NTA, the low dose (9 mg/kg per day) was without adverse effect. The kidney toxicity of oral FeNTA (50, 200, and 1000 mg/kg per day) was only mild, 50 mg/kg per day; however, it still led to an increased 8-hydroxyguanine content. The relevance of Iron(III) (Fe(III)) or Fe(III)NTA formation as a relevant mediator of NTA-related toxicity was excluded on the basis of these data. Also, a thermodynamic consideration presented here, supports the view that zinc (Zn), and not Fe, is likely to mediate the tubular cell cytotoxicity of NTA.

Different patterns of kidney toxicity after subacute administration of Na-nitrilotriacetic acid and Fe-nitrilotriacetic acid to Wistar rats

Na-nitrilotriacetic acid (Na3NTA) and Fe-nitrilotriacetic acid (FeNTA) have both been described to cause tumors in the urinary tract of rodents. However, these effects were observed using different modes of administration at extremely different dose levels and explained by different mechanisms. Whereas FeNTA causes an iron overload of cells and is genotoxic in various assays, Na3NTA is predominantly bound to zinc in vivo and thereby causes cytotoxic effects in the urinary tract. In contrast to FeNTA, Na3NTA requires high dose levels to produce tumors. The aim of this study was to compare the effects of Na3NTA and FeNTA on cellular proliferation, histopathology, lipid peroxidation, and 8-OH-2'-deoxyguanosine levels in the kidneys as well as on the urinary excretion of Ca, Fe, and Zn. For evaluation of DNA synthesis both compounds were administered for 1 or 4 weeks to 14-week-old male Wistar rats at a tumor causing dose, Na3NTA via the diet at 150 ppm and 20,000 ppm (approximately 9 and approximately 1000 mg/kg/day) and FeNTA i.p. at 25 mg/kg/day. An osmotic minipump, containing 20 mg/ml BrdU, was implanted subcutaneously 7 days before necropsy. Na3NTA showed nearly no effect on DNA replication after 1 week but a strong reaction after 4 weeks. The increase was 10- to 18-fold in different renal compartments. The enhancement of proliferation in the proximal tubules was nearly twice that in the distal tubules. In contrast, FeNTA caused DNA replication during the first week, and this was restricted to the proximal tubules. After 4 weeks there was an 18-fold increase in the outer stripe and no effect in the inner stripe of the outer medulla. The data presented give evidence to the assumption that both substances increase cell proliferation as a compensatory mechanism, causing different pattern of tubular proliferation in terms of time course and affected cell types. Both Na3NTA at 20,000 ppm and FeNTA led to increased lipid peroxidation, whereas increased levels of 8-OH-2'-deoxyguanosine were observed only after treatment with FeNTA. Urinary excretion of Zn was increased 30-fold after administration of 20,000 ppm Na3NTA but only 2-fold after administration of FeNTA. Urinary excretion of Ca and Fe remained unchanged after treatment with either Na3NTA and FeNTA. These results show that the Na3NTA-related proliferative effects are not mediated by an internal formation of FeNTA.

Phenobarbital transiently stimulates uptake of 2-aminoisobutyric acid in hepatocytes

Phenobarbital (PB) is a classical inducer of drug metabolizing enzymes and known to stimulate liver growth transiently in rodents. Previous studies have shown that regenerative liver growth after a partial hepatectomy is accompanied by the induction of the amino acid transport system A. In the present study we investigated whether amino acid transport is also increased by treatment of rats with PB. Na(+) -dependent hepatic uptake of the non-metabolizable amino acid 2-aminoisobutyric acid (AIB), which proceeds largely via transport system A, was studied in isolated hepatocytes from PB treated and untreated rats. Uptake of AIB (100 microM) was maximally induced (2.5-fold) 8 h after the beginning of PB treatment. Within 4 days, transport rates decreased to values similar to those determined in hepatocytes from untreated animals, despite the continuation of PB treatment. In contrast, induction of the PB-inducible cytochromes P450 2B1/2 was markedly increased during the entire experiment, as determined with the isoenzyme-selective substrate pentoxyresorufin. Kinetic analysis of AIB uptake revealed a "high" and a "low" affinity transport system. It is most likely that the high affinity system represents amino acid transport system A. Treatment with PB increased the V(max) value but did not affect the apparent Km value of the high affinity system. The present data suggest that the hepatic mitogen PB transiently induces amino acid transport system A.

Suppression of agonist induced Ca2+ oscillations in cultured hepatocytes by nafenopin: possible involvement of protein kinase C

The alpha 1-agonist phenylephrine (5 microM) induces an increase in the free cytosolic Ca2+ concentration, followed by repetitive transients of the cytoplasmic Ca2+ concentration, in single Fura-2 loaded hepatocytes. The tumor promoting, hypolipidemic drug nafenopin suppressed the cellular Ca2+ response to phenylephrine. The effect of nafenopin on the Ca2+ increase and Ca2+ oscillations was largely prevented by the specific protein kinase C inhibitor Gö 6976. This finding suggests involvement of protein kinase C in the action of nafenopin on phenylephrine induced Ca2+ mobilization.

Inhibition of intercellular communication of rat hepatocytes by nafenopin: involvement of protein kinase C

Peroxisome proliferators (PPs) have been shown to cause tumours in rodent liver. The mechanism of action of these chemicals is only poorly understood. Current evidence, however, suggests that they may cause tumours through a tumour promoting activity. In the present study we therefore evaluated the effect of three peroxisome proliferators on gap junctional intercellular communication (IC) of cultured hepatocytes. Interference with IC is thought to be one of the mechanisms involved in tumour promotion. IC was detected by dye coupling of hepatocytes using microinjection of Lucifer Yellow CH. Five hours after plating, coupling of the cells amounted to approximately 90%. Incubation of hepatocytes with the PPs mono(2-ethylhexyl)phthalate (MEHP), nafenopin and [4-chloro-6-(2,3- xylidino)-2-pyrimidylthio]acetic acid (Wy-14,643) decreased dye coupling of the hepatocytes. Half maximal effects were obtained at approximately 50 microM nafenopin, 150 microM Wy-14,643 and 200 microM MEHP. Addition of the specific inhibitor of Ca(2+)-dependent protein kinase C isoenzymes, Gö 6976 (2 microM), prevented inhibition of IC by nafenopin, but not by the two other peroxisome proliferators. Further studies suggest significant differences in the mechanisms underlying inhibition of dye coupling between hepatocytes by nafenopin and by phenobarbital, a known tumour promoter in the liver. The results show that the PPs nafenopin, MEHP and Wy-14,643 decrease IC between cultured hepatocytes. Inhibition of IC by nafenopin, but not by MEHP and Wy-14,643, is most likely mediated by Ca(2+)-dependent protein kinase C isoenzymes.

Inhibition of intercellular communication in rat hepatocytes by phenobarbital, 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) and gamma-hexachlorocyclohexane (lindane): modification by antioxidants and inhibitors of cyclo-oxygenase

Several tumour promoting chemicals have been shown to inhibit intercellular communication (IC) through gap junctions in cell cultures. In the present investigation we studied the effect of the hepatic tumour promoters phenobarbital (PB), 1,1,1-trichloro-2,2-(p-chlorophenyl)ethane (DDT) and gamma-hexachlorocyclohexane (lindane) on IC in rat hepatocyte cultures. IC was evaluated by microinjection of fluorescent Lucifer Yellow CH dye and visualization of dye spread to adjacent hepatocytes. Incubation of hepatocytes with PB (2 mM), DDT (30 microM) and lindane (25 microM) decreased dye-coupling of the cells by about 30%, 42% and 35%, respectively; dye-coupling in untreated cultures was 88.1 +/- 0.7%. Inhibition of IC was reversible when the xenobiotics were removed from the medium. The antioxidant vitamin E (100 microM) prevented inhibition of dye-coupling by PB and lindane and partially that by DDT. Superoxide dismutase (100 units/microliters) counteracted the effect on dye-coupling by PB, but not that by the insecticides. Similarly, the cyclo-oxygenase inhibitors indomethacin and aspirin only reversed the effect of PB on IC, but not that of DDT or lindane. As indicated by further experiments, prevention by non-steroidal anti-inflammatory agents of PB-induced inhibition of IC is most likely not mediated by inhibition of cyclo-oxygenase. The results indicate significant differences in the action of PB, DDT and lindane on IC in hepatocyte cultures. This is suggested by the differential effects of superoxide dismutase and non-steroidal anti-inflammatory agents on the action of the three tumour promoting chemicals. Whereas superoxide radicals may be involved in the inhibition of dye-coupling by PB, radical intermediates of the insecticides may be responsible for the decrease in dye-coupling by DDT and lindane.

Intercellular communication in primary cultures of putative preneoplastic and 'normal' hepatocytes

Gap junctional intercellular communication (IC) was studied in gamma-glutamyltranspeptidase (gamma-GT)-positive and -negative hepatocytes isolated from carcinogen-treated rats. Putative preneoplastic gamma-GT-positive hepatocytes were visualized in monolayer cultures by indirect immunofluorescence using anti-gamma-GT-antibodies. IC was evaluated by studying dye coupling of the cells. gamma-GT-positive hepatocytes showed a significantly lower dye coupling than did gamma-GT-negative liver cells. Spread of the dye Lucifer Yellow CH to neighboring cells was decreased further by the tumor-promoting chemical phenobarbital in both cell types in vitro. Also treatment in vivo with the barbiturate significantly reduced dye coupling of hepatocytes. The findings suggest that as a result of their decreased ability to communicate, preneoplastic hepatocytes may escape from growth control and differentiation signals given out by surrounding 'normal' cells.