Non-animal test methods for predicting skin sensitization potentials

Contact allergies are complex diseases, and it is estimated that 15-20 % of the general population suffers from contact allergy, with increasing prevalence. Evaluation of the sensitization potential of a substance is usually carried out in animal models. Nowadays, there is much interest in reducing and ultimately replacing current animal tests. Furthermore, as of 2013, the EU has posed a ban on animal testing of cosmetic ingredients that includes skin sensitization. Therefore, predictive and robust in vitro tests are urgently needed. In order to establish alternatives to animal testing, the in vitro tests must mimic the very complex interactions between the sensitizing chemical and the different parts of the immune system. This review article summarizes recent efforts to develop in vitro tests for predicting skin sensitizers. Cell-based assays, in chemico methods and, to a lesser extent, in silico methods are presented together with a discussion of their current status. With considerable progress having been achieved during the last years, the rationale today is that data from different non-animal test methods will have to be combined in order to obtain reliable hazard and potency information on potential skin sensitizers.

Relevance of xenobiotic enzymes in human skin in vitro models to activate pro-sensitizers

Skin exposure to sensitizing chemicals can induce allergic reactions. Certain chemicals, so called pro-sensitizers, need metabolic activation to become allergenic. Their metabolic activation occurs in skin cells such as keratinocytes or dendritic cells. These cell types are also incorporated into dermal in vitro test systems used to assess the sensitizing potential of chemicals for humans. In vitrosystems range from single cell cultures to organotypic multi-cellular reconstructed skin models. Until now, their metabolic competence to unmask sensitizing potential of pro-sensitizers was rarely investigated. This review aims to summarize current information on available skin in vitro models and the relevance of xenobiotic metabolizing enzymes for the activation of pro-sensitizers such as eugenol, 4-allylanisole, and ethylendiamine. Among others, these chemicals are discussed as performance standards to validate new coming in vitro systems for their potential to identify pro-sensitizers.

Health and nutritional status of Wistar rats following subchronic exposure to CV127 soybeans

This subchronic duration feeding study evaluated the nutritional and health status of rats fed diets containing CV127 at incorporation levels of 11% and 33%. For control comparisons, rats were also exposed to similar incorporation levels of the near isogenic conventional soybean variety (Conquista) and two other conventional soybean varieties (Monsoy, Coodetec). In spite of phenotypic differences among these four soybean varieties, there were no quantitative differences in their respective proximate and other compositional properties, including proteins, amino acids, antinutrients and nutritional cofactors. All diets were prepared by blending the respective processed soybean meal with ground Kliba maintenance meal at high (33%) and low (11%) incorporation levels, and the blended diets were fed to Wistar rats for about 91 days. Although there were some isolated parameters indicating statistically significant changes, these lacked consistency and a plausible mechanism and were thus assessed to be incidental. The totality of results demonstrate that CV127 soybeans are similar with respect to their nutritional value and systemic effects as its near isogenic conventional counterpart, as well as other conventional soybean varieties. Hence, introduction of AHAS gene into soybeans does not substantially alter its compositional properties, nor adversely affect its nutritional or safety status to mammals.

Short-term rat inhalation study with aerosols of acrylic ester-based polymer dispersions containing a fraction of nanoparticles

Aqueous polymer dispersions are important raw materials used in a variety of industrial processes. They may contain particles with diameters ranging from 10 to 1500 nm. Polymer exposure alone may cause pulmonary lesions after inhalation exposure. Polymer dispersions with increased proportions of nano-sized particles are being developed for improved material characteristics, and this may pose even increased pulmonary hazards upon potential inhalation exposure. In a 5-day screening study, male rats were nose-only exposed to aerosols generated from 2 dispersions of acrylic ester polymers with identical chemical composition but different nano-sized particle proportions at particle concentrations of 3 and 10 mg/m³. Immediately and 19 days after the end of inhalation, necropsies were conducted with major emphasis on respiratory tract histopathology. Three and 23 days after the end of inhalation, bronchoalveolar lavage was performed to screen for early pulmonary injury and inflammation. In contrast to the adverse effects known for other materials in short-term inhalation studies, none of the tested preparations of acrylic ester polymers elicited any adverse effect at the end of the inhalation or postinhalation periods. No shift in toxicity could be observed by the increased proportion of nano-sized polymer particles. Under the conditions of this study, the no observable adverse effect levels for both preparations were >10 mg/m³, that is 2- to 3-fold beyond current nuisance dust threshold limit values.

In-house validation of the EpiOcular(TM) eye irritation test and its combination with the bovine corneal opacity and permeability test for the assessment of ocular irritation

In 2009, the Bovine Corneal Opacity and Permeability (BCOP) test was accepted by the regulatory bodies for the identification of corrosive and severe ocular irritants (Global Harmonised System [GHS] Category 1). However, no in vitro test is currently accepted for the differentiation of ocular irritants (GHS Category 2) and non-irritants (GHS No Category). Human reconstructed tissue models have been suggested for incorporation into a tiered testing strategy to ultimately replace the Draize rabbit eye irritation test (OECD TG 405). The purpose of this study was to evaluate whether the EpiOcular(TM) reconstructed cornea-like tissue model and the COLIPA pre-validated EpiOcular Eye Irritation Test (EpiOcular-EIT) could be used as suitable components of this testing strategy. The in-house validation of the EpiOcular-EIT was performed by using 60 test substances, including a broad variety of chemicals and formulations for which in vivo data (from the Draize rabbit eye irritation test) were available. The test substances fell into the following categories: 18 severe irritants/corrosives (Category 1), 21 irritants (Category 2), and 21 non-irritants (No Category). Test substances that decreased tissue viability to ≤ 60% (compared to the negative control tissue) were considered to be eye irritants (Category 1/2). Test substances resulting in tissue viability of > 60% were considered to be non-irritants (No Category). For the assessed dataset and the classification cut-off of 60% viability, the EpiOcular-EIT provided 98% and 84% sensitivity, 64% and 90% specificity, and 85% and 86% overall accuracy for the literature reference and BASF proprietary substances, respectively. Applying a 50% tissue viability cut-off to distinguish between irritants and non-irritants resulted in 93% and 82% sensitivity, 68% and 100% specificity, and 84% and 88% accuracy for the literature reference and BASF proprietary substances, respectively. Further, in the EpiOcular-EIT (60% cut-off), 100% of severely irritating substances under-predicted by the BCOP assay were classified as Category 1/2. The results obtained in this study, based on 60 test substances, indicate that the EpiOcular-EIT and the BCOP assay can be combined in a testing strategy to identify strong/severe eye irritants (Category 1), moderate and mild eye irritants (Category 2), and non-irritants (No Category) in routine testing. In particular, when the bottom-up strategy with the 60% viability cut-off was employed, none of the severely irritating substances (Category 1) were under-predicted to be non-irritant. Sensitivity for Category 1/2 substances was 100% for literature reference substances and 89% for BASF SE proprietary substances.

Refinement and Reduction of Acute Oral Toxicity Testing: A Critical Review of the Use of Cytotoxicity Data

Acute oral toxicity testing is still required for the classification and labelling of chemicals, agrochemicals and related formulations. There have been increasing efforts over the last two decades to reduce the number of animals needed for this testing, according to the Three Rs concept. To evaluate the utility of an in vitro cytotoxicity test in our routine testing for acute oral toxicity, we have implemented in our laboratory the neutral red uptake (NRU) method, with Balb/c 3T3 fibroblasts after a 48-hour exposure, which was recommended in ICCVAM Report 07-4519, 2006. Initially, we tested 16 substances that had existing in vivo and in vitro data available, to prove our technical proficiency with the in vitro test. Then, testing was performed with 187 test substances, including a broad variety of chemicals, agrochemicals and formulations. The starting dose for acute oral systemic toxicity assays in rats (LD50) was estimated by using the prediction model presented in the ICCVAM validation study, and subsequently compared to the results obtained by in vivo testing performed according to, or similar to, OECD Test Guideline 423. Comparison of all of the 203 predicted LD50 values that were deduced from the in vitro IC50 values, with the in vivo results from oral toxicity studies in rats, resulted in a low overall concordance of 35%. The in vitro cytotoxicity assay achieved a good concordance of 74%, only for the weakly toxic substances (EU-GHS Cat. 4). However, it must be noted that 71% of the substances tested (i.e. 145/203) were classified as being weakly toxic in vitro. We further analysed the utility of the in vitro test for predicting the starting dose for an in vivo study, and the potential reduction in animal usage that this would engender. In this regard, the prediction by the cytotoxicity test was useful for 59% of the substances. However, the use of a standard starting dose of 300mg/kg bw by default (without previous cytotoxicity testing) would have been almost as useful (50%). In contrast, the prediction by an experienced toxicologist was correct for 95% of the substances. However, this was only performed for 40% of the substances, mainly those of no to low toxicity. Calculating the theoretical animal numbers needed in several scenarios supported these results. The additional analysis, considering some physicochemical data (solubility, molecular weight, log POW), substance class and mode of action, revealed no specific applicability domains. In summary, the use of the 3T3 NRU cytotoxicity data alone did not sufficiently contribute to refinement and reduction in the acute oral toxicity testing of the substance portfolio tested routinely in our laboratory.

The bovine corneal opacity and permeability test in routine ocular irritation testing and its improvement within the limits of OECD test guideline 437

Data on eye irritation are generally needed for the hazard identification of chemicals. As the Bovine Corneal Opacity and Permeability (BCOP) test has been accepted by many regulatory agencies for the identification of corrosive and severe ocular irritants since September 2009 (OECD Test Guideline 437, TG 437), we evaluated this alternative method for routine testing at BASF. We demonstrated our technical proficiency by testing the reference standards recommended in TG 437, and 21 additional materials with published BCOP and in vivo data. Our results matched the published in vitro data very well, but with some intentionally selected false negatives (FNs) and false positives (FPs), the concordance was 77% (24/31), with FN and FP rates of 20% (2/10) and 24% (5/21), respectively. In addition, we tested 21 in-house materials, demonstrating the utility of the BCOP assay for our own test material panel. Histopathological assessment of the corneas by light microscopy was also conducted, as this was suggested as a means of improving the identification of FNs. The histopathology corrected the classification of some FNs, but also increased the number of FPs. Parallel to the test method evaluation, we compared three new opacitometer models with the current standard device. We recommend the use of an opacitometer developed in our BASF laboratory, which has certified components and electronic data storage, resulting in what we consider to be excellent sensitivity, stability and reproducibility.

Initiatives to decrease redundancy in animal testing of pesticides

Two well-documented examples of studies that can be eliminated from the data requirement list without apparent impact on the quality of risk assessment are presented. Database evaluations demonstrated no clear difference in sensitivity between 3-month and 12-month dog studies. From a regulatory perspective, only two compounds were identified in which the NOAEL for the 12-month dog study was more than 2-fold lower than in any other study. Evaluation of the contribution of the mouse cancer study demonstrated that in 5% of all cases the mouse cancer study was used for reference dose setting and in 1.5% it was used for selective cancer classification. It is suggested that regulatory agencies periodically review their study requirements for redundant studies.

Inhalation toxicity of multiwall carbon nanotubes in rats exposed for 3 months

Carbon nanotubes (CNT) are of great commercial interest. Theoretically, during processing and handling of CNT and in abrasion processes on composites containing CNT, inhalable CNT particles might be set free. For hazard assessment, we performed a 90-day inhalation toxicity study with a multiwall CNT (MWCNT) material (Nanocyl NC 7000) according to Organisation for Economic Co-operation and Development test guideline 413. Wistar rats were head-nose exposed for 6 h/day, 5 days/week, 13 weeks, total 65 exposures, to MWCNT concentrations of 0 (control), 0.1, 0.5, or 2.5 mg/m(3). Highly respirable dust aerosols were produced with a proprietary brush generator which neither damaged the tube structure nor increased reactive oxygen species on the surface. Inhalation exposure to MWCNT produced no systemic toxicity. However, increased lung weights, pronounced multifocal granulomatous inflammation, diffuse histiocytic and neutrophilic inflammation, and intra-alveolar lipoproteinosis were observed in lung and lung-associated lymph nodes at 0.5 and 2.5 mg/m(3). These effects were accompanied by slight blood neutrophilia at 2.5 mg/m(3). Incidence and severity of the effects were concentration related. At 0.1 mg/m(3), there was still minimal granulomatous inflammation in the lung and in lung-associated lymph nodes; a no observed effect concentration was therefore not established in this study. The test substance has low dust-forming potential, as demonstrated by dustiness measurements, but nonetheless strict industrial hygiene measures must be taken during handling and processing. Toxicity and dustiness data such as these can be used to compare different MWCNT materials and to select the material with the lowest risk potential for a given application.

Development of a short-term inhalation test in the rat using nano-titanium dioxide as a model substance

Evidence suggests that short-term inhalation studies may provide comparable prediction of respiratory tract toxicity to 90-day studies, presenting the opportunity to save time and resources in screening inhalation toxicity of test substances. The aim of this study was to develop a short-term inhalation test that could be employed to provide early evidence on respiratory tract effects which might occur from long-term exposure to aerosols of nano-materials. Male Wistar rats were exposed to aerosols of 0 (control), 2, 10 and 50 mg/m(3) nano-titanium dioxide (TiO2) by inhalation for 6 h/day for 5 days. Necropsies were performed either immediately after the last exposure or after 3 and 16 days post exposure (study days 5, 8 and 21, respectively). Treatment with nano-TiO2 resulted in morphological changes in the lung, with 50 mg/m(3) nano-TiO2 producing an increase in lung weight. Lung inflammation was associated with dose-dependent increases in bronchoalveolar lavage fluid (BALF) total cell and neutrophil counts, total protein content, enzyme activities and levels of a number of cell mediators. No indications of systemic effects could be found by measurement of appropriate clinical pathology parameters. Cell replication (determined by incorporation of 5-bromo-2'-deoxyuridine) was increased at all nano-TiO2 dose levels in large/medium bronchi and terminal bronchioles. The effects on the parameters measured were most prominent either on study day 5 or 8, with some endpoints returning to control levels by day 21. Overall, the pulmonary effects of nano-TiO2 observed in this short-term study were comparable to those previously reported in subchronic inhalation studies.

Vinclozolin--the lack of a transgenerational effect after oral maternal exposure during organogenesis

The purpose of the study was to investigate a possible transgenerational effect of the fungicide vinclozolin on the male reproductive system following oral exposure since this effect was reported by Anway et al. [Anway MD, Cupp AS, Uzumcu M, Skinner MK. Epigenetic transgenerational actions of endocrine disruptors and male fertility. Science 2005;308(5727 (June 3)):1466-9] after intraperitoneal administration. Pregnant Wistar rats were dosed by oral gavage with vinclozolin 0, 4 or 100mg/(kg bw day) on days 6-15 post coitum (p.c.). F1 male offspring was mated with untreated females to produce F2, which were then similarly mated to produce F3 offspring. F0 maternal treatment had no effect on mating and fertility indices or male offspring sexual development, mean sperm parameters, or histopathology of the sexual organs in F1, F2 or F3 males (at age 127-134 days). Apoptotic germ cell counts were statistically significantly lower in F1, F2 and F3 generations, however, control values showed a pronounced variance over time. Also, as anti-androgenic compounds are more likely to induce the opposite effect (increased apoptosis), this observation is not considered to be treatment related. Consequently, spermatogenesis was not affected by vinclozolin exposure in utero. As vinclozolin has been shown to induce clear anti-androgenic effects in offspring following treatment with 100mg/(kg bw day) during entire gestation, the lack of effects in this study indicates that the window of sensitivity for anti-androgenic effects is from days 16-20 p.c. No transgenerational effect on the male reproductive system was found. The NOAEL was >100mg/(kg bw day) for fertility and reproductive performance, for systemic parental and developmental toxicity in F1, F2 and F3 males.

Ethylbenzene: 4- and 13-week rat oral toxicity

Ethylbenzene was administered to groups of male and female Wistar rats by gavage for 4 (n = 5/dose/sex) and 13 weeks (n = 10/dose/sex) (OECD 408) at doses of 0 (vehicle control), 75, 250, and 750 mg/kg bodyweight/day (mg/kg bw/day), administered am/pm as half doses. In the 4-week study, > or =250 mg/kg increased serum alanine aminotransferase, total bilirubin and cholesterol, liver weights and centrilobular hepatocyte hypertrophy, and kidney weights; males also had post-dose salivation, increased urinary epithelial cell casts and cells, and hyaline droplet nephropathy. In the 13-week study, > or =250 mg/kg increased water consumption and produced post-dose salivation. Liver-related effects: increased serum alanine aminotransferase, gamma-glutamyltransferase, bilirubin, total protein, albumin and globulins, cholesterol, liver weights and centrilobular hepatocyte hypertrophy, and reduced prothrombin times. Kidney-related effects: increased serum potassium, calcium, magnesium, kidney weights, and (males only) urea and hyaline droplets in renal tubular epithelium, and reduced sodium (females only); creatinine was reduced in 750 mg/kg males. The NOAEL of ethylbenzene in these studies, based on hepatocyte hypertrophy and liver- and kidney-related clinical chemistry changes, was 75 mg/kg bw/day.

A tiered approach to systemic toxicity testing for agricultural chemical safety assessment

A proposal has been developed by the Agricultural Chemical Safety Assessment (ACSA) Technical Committee of the ILSI Health and Environmental Sciences Institute (HESI) for an improved approach to assessing the safety of crop protection chemicals. The goal is to ensure that studies are scientifically appropriate and necessary without being redundant, and that tests emphasize toxicological endpoints and exposure durations that are relevant for risk assessment. The ACSA Systemic Toxicity Task Force proposes an approach to systemic toxicity testing as one part of the overall assessment of a compound's potential to cause adverse effects on health. The approach is designed to provide more relevant data for deriving reference doses for shorter time periods of human exposure, and includes fewer studies for deriving longer term reference doses-that is, neither a 12-month dog study nor a mouse carcinogenicity study is recommended. All available data, including toxicokinetics and metabolism data and life stages information, are taken into account. The proposed tiered testing approach has the potential to provide new risk assessment information for shorter human exposure durations while reducing the number of animals used and without compromising the sensitivity of the determination of longer term reference doses.

Octyl methoxycinnamate: Two generation reproduction toxicity in Wistar rats by dietary administration

Wistar rats continuously received octyl methoxycinnamate (OMC) in the diet through two successive generations at nominal doses of 0, 150, 450 or 1000 mg/kg bw/day. OMC had no adverse effects on estrous cycles, mating behavior, conception, parturition, lactation and weaning, sperm and follicle parameters, macropathology and histopathology of the sexual organs. 1000 mg/kg bw/day reduced parental food consumption and body weight (-14% to -16% in males, -4% to -5% females), increased liver weight, produced hepatic cytoplasmic eosinophilia and erosion/ulceration of glandular stomach mucosa. and led to a slightly decreased implantation rate in the top dose F0 and F1 dams. The high dose F1 and F2 pups had reduced lactation weight gain and organ weights and delayed sexual maturation landmarks. There was no evidence of a selective influence of the test compound on pups' sexual landmarks. The NOAEL (no observed adverse effect level) is 450 mg/kg bw/day for fertility and reproductive performance, for systemic parental and developmental toxicity.

The stability of historical control data for common neoplasms in laboratory rats and the implications for carcinogenic risk assessment

Time-related changes in the incidences of spontaneous neoplasms in skin (fibroma and keratoacanthoma), thyroid (C-cell and follicular cell adenomas/carcinomas), uterus (stromal polyp), testes (Leydig cell tumor) and hemolymphoreticular system (mesenteric lymph node hemangioma and malignant granular lymphocytic leukemia) were assessed statistically in Wistar, Sprague-Dawley and F344 rats employed by the BASF, Germany and major European contract research organizations over the last 20 years. Negative trends (5 out of 80 cases) were observed for skin fibromas in F344 males, for follicular cell adenomas in Han Wistar females and in Sprague-Dawley males and females, and for follicular cell carcinomas in Sprague-Dawley males. Positive trends (8 out of 80 cases) were observed for skin keratoacanthomas in Han Wistar males, for C-cell adenomas in BASF Wistar males and females, for stromal polyps in Han Wistar and Sprague-Dawley females, and for mesenteric lymph node hemangiomas in Han Wistar and Sprague-Dawley males and in BASF Wistar females. In 67 out of 80 cases there were no statistically significant trends. Tumor drift was not common but occurred far more often in outbred rat strains (Wistar and Sprague-Dawley) than in the inbred rat strain (F344). This observation suggests that tumor predisposition is genetically determined, that tumor drift is primarily caused by genetic drift and that non-genotoxic carcinogens operate by facilitating the expression of tumor predisposition in target cells.

The stability of historical control data for common neoplasms in laboratory rats: adrenal gland (medulla), mammary gland, liver, endocrine pancreas, and pituitary gland

Time-related changes in the incidences of spontaneous neoplasms in adrenals (medulla), mamma, liver, pituitary, and (endocrine) pancreas were assessed statistically in Wistar, Sprague-Dawley, and F344 rats employed by BASF, Germany and major European contract research organizations over the last 20 years. Negative trends (7 of 80 cases) were observed for pituitary pars distalis adenomas in Sprague-Dawley males and females, for pancreas islet cell adenomas in BASF Wistar males and females, for benign adrenal pheochromocytomas in Sprague-Dawley males, for malignant pheochromocytomas in F344 males, and for mammary gland fibroadenomas in BASF Wistar females. Positive trends (13 of 80 cases) were observed for benign pheochromocytomas, mammary gland adenocarcinomas, and pancreas islet cell carcinomas in HanWistar females, for malignant pheochromocytomas and islet cell carcinomas in BASF Wistar males, for benign pheochromocytomas and islet cell adenomas in F344 males, for mammary gland fibroadenomas in Sprague-Dawley females, and for benign hepatocellular tumors in HanWistar males and females, and in BASF Wistar and Sprague-Dawley females. In 60 of 80 cases there were no statistically significant trends. These results indicate that the majority of tumor types showed no time trends and that, in each rat strain, certain tumor types are susceptible to slight positive or negative time trends. Accordingly, the validity and use of historical control data should be based on an organ- and strain-specific statistical analysis of tumor incidence over time.

A Wistar rat strain prone to spontaneous liver tumor development: implications for carcinogenic risk assessment

The European Union legislation considers nongenotoxic substances that only cause liver tumors in certain sensitive strains of mice as raising no concern for man. The EU legislation, however, also clearly stipulates that cases where the only available tumor data are the occurrence of neoplasms at sites and in strains where they are well known to occur spontaneously with a high incidence are relevant arguments which exclude a concern for man. We have analyzed the spontaneous liver tumor incidence in Wistar rats and in B6C3F(1) and C57Bl mice used in carcinogenicity trials at the BASF facility in Ludwigshafen, Germany, over the past 15 years and compared the spontaneous liver tumor incidence in BASF Wistar rats with those observed in rat strains employed in major European contract research organizations (CROs). The results of these analyses indicate that the incidence of spontaneous liver tumors in the BASF Wistar rat strain is very high, similar to that seen in the B6C3F(1) mouse and much higher than that seen in the C57Bl mouse and other commonly used strains of rat. The analyses also revealed signs of increasing variability and liver tumor drift in several rat strains. Moreover, the incidence of spontaneous preneoplastic liver cell foci was far higher in the BASF Wistar rat strain than reported for other rat strains in the literature. The analyses provide relevant arguments which exclude a concern for man for nongenotoxic chemicals that only tested positive for liver tumors in this sensitive rat strain.