Prediction of carcinogenic potential of chemicals using repeated-dose (13-week) toxicity data

AbstractSub-chronic toxicity studies of 163 non-genotoxic chemicals were evaluated in order to predict the tumour outcome of 24-month rat carcinogenicity studies obtained from the EFSA and ToxRef databases. Hundred eleven of the 148 chemicals that did not induce putative preneoplastic lesions in the sub-chronic study also did not induce tumours in the carcinogenicity study (True Negatives). Cellular hypertrophy appeared to be an unreliable predictor of carcinogenicity. The negative predictivity, the measure of the compounds evaluated that did not show any putative preneoplastic lesion in de sub-chronic studies and were negative in the carcinogenicity studies, was 75%, whereas the sensitivity, a measure of the sub-chronic study to predict a positive carcinogenicity outcome was only 5%. The specificity, the accuracy of the sub-chronic study to correctly identify non-carcinogens was 90%. When the chemicals which induced tumours generally considered not relevant for humans (33 out of 37 False Negatives) are classified as True Negatives, the negative predictivity amounts to 97%. Overall, the results of this retrospective study support the concept that chemicals showing no histopathological risk factors for neoplasia in a sub-chronic study in rats may be considered non-carcinogenic and do not require further testing in a carcinogenicity study

Effects of orchiectomy, alone or in combination with testosterone, and cyproterone acetate on exocrine pancreatic carcinogenesis in rats and hamsters

The results of a previous 4-mo study in azaserine-treated rats and BOP-treated hamsters indicated that orchiectomy inhibited pancreatic growth and development of putative preneoplastic lesions in the exocrine pancreas of rats but not hamsters. This 12-mo study was carried out to investigate the effects of orchiectomy, alone and in combination with testosterone, and of treatment with cyproterone acetate on pancreatic carcinogenesis in azaserine-treated rats and BOP-treated hamsters. Treatment started 4 mo after injection of the carcinogen. In orchiectomized rats, pancreatic wt was lower than in controls, whereas pancreatic wt of orchiectomized rats treated with testosterone was similar to that of controls. Both orchiectomy and cyproterone acetate caused a decrease in body wt gain and had an inhibitory effect on pancreatic carcinogenesis. Testosterone treatment did not influence the inhibitory effects of orchiectomy on body wt gain and on pancreatic carcinogenesis. In hamsters, neither orchiectomy, alone or in combination with testosterone, nor cyproterone acetate (CA) affected pancreatic growth or pancreatic carcinogenesis. This study indicates that testosterone plays a minor role in the development of pancreatic tumors induced in rats by azaserine but not in that of pancreatic tumors induced in hamsters by BOP

Bioavailability and biodistribution of differently charged polystyrene nanoparticles upon oral exposure in rats

The likelihood of oral exposure to nanoparticles (NPs) is increasing, and it is necessary to evaluate the oral bioavailability of NPs. In vitro approaches could help reducing animal studies, but validation against in vivo studies is essential. Previously, we assessed the translocation of 50 nm polystyrene NPs of different charges (neutral, positive and negative) using a Caco-2/HT29-MTX in vitro intestinal translocation model. The NPs translocated in a surface charge-dependent manner. The present study aimed to validate this in vitro intestinal model by an in vivo study. For this, rats were orally exposed to a single dose of these polystyrene NPs and the uptake in organs was determined. A negatively charged NP was taken up more than other NPs, with the highest amounts in kidney (37.4 µg/g tissue), heart (52.8 µg/g tissue), stomach wall (98.3 µg/g tissue) and small intestinal wall (94.4 µg/g tissue). This partly confirms our in vitro findings, where the same NPs translocated to the highest extent. The estimated bioavailability of different types of NPs ranged from 0.2 to 1.7 % in vivo, which was much lower than in vitro (1.6–12.3 %). Therefore, the integrated in vitro model cannot be used for a direct prediction of the bioavailability of orally administered NPs. However, the model can be used for prioritizing NPs before further in vivo testing for risk assessment. © 2015, The Author(s)

The assessment of the safety for the consumer of feed additives and additives added to foods of animal origin

Safe animal feed is important for the health of animals, the safety of the consumer of food of animal origin and for the environment. There is a close link between the safety of animal feed and the foods derived from the animals given this fodder. Additives are purposely added to animal feed or to food of animal origin with the aim to improve the quality of the feed and the quality of the food of animal origin. Assessing the safety of feed additives or additives added to food of animal origin requires a multidisciplinary approach to asses all aspects relevant to the intended use of that compound. The principles of the assessment of the safety of the consumer exposed to compounds via food from animal origin are described. An overview is given of the toxicity studies that are used to assess the safety, including the method to derive the safe intake for the consumer based on the outcome of the toxicity studies. The approach is illustrated by four examples of commercially available additives in order to illustrate how regulatory authorities, i.e. the European Food Safety Authority, evaluate the (absence of) potential health effects for consumers

Development of a combined in Vitro Physiologically Based Kinetic (PBK) and Monte Carlo modelling approach to predict interindividual human variation in phenol-induced developmental toxicity

With our recently developed in vitro physiologically based kinetic (PBK) modelling approach, we could extrapolate in vitro toxicity data to human toxicity values applying PBK-based reverse dosimetry. Ideally information on kinetic differences among human individuals within a population should be considered. In the present study, we demonstrated a modelling approach that integrated in vitro toxicity data, PBK modelling and Monte Carlo simulations to obtain insight in interindividual human kinetic variation and derive chemical specific adjustment factors (CSAFs) for phenol-induced developmental toxicity. The present study revealed that UGT1A6 is the primary enzyme responsible for the glucuronidation of phenol in humans followed by UGT1A9. Monte Carlo simulations were performed taking into account interindividual variation in glucuronidation by these specific UGTs and in the oral absorption coefficient. Linking Monte Carlo simulations with PBK modelling, population variability in the maximum plasma concentration of phenol for the human population could be predicted. This approach provided a CSAF for interindividual variation of 2.0 which covers the 99th percentile of the population, which is lower than the default safety factor of 3.16 for interindividual human kinetic differences. Dividing the dose-response curve data obtained with in vitro PBK-based reverse dosimetry, with the CSAF provided a dose-response curve that reflects the consequences of the interindividual variability in phenol kinetics for the developmental toxicity of phenol. The strength of the presented approach is that it provides insight in the effect of interindividual variation in kinetics for phenol-induced developmental toxicity, based on only in vitro and in silico testing.</p

The Isolated Chicken Eye test to replace the Draize test in rabbits

In 1944, Draize et al., published a paper entitled “Methods for the study of irritation and toxicity of substances applied topically to the skin and mucous membranes”. The Organization for Economic Co-operation and Development published their first guideline on eye irritation in 1981, using rabbits. In the early eighties the development of alternative non-animal tests to replace the Draize eye test started. The first attempts to validate alternative tests for eye irritation were considered to be relatively simple by comparing in vitro and in vivo irritation index scores. In the early nineteen-eighties, we introduced the use of isolated eyes as an alternative test for the Draize eye irritation test. What was expected to be a process of several years, however, turned out to be a decades spanning process still not fully completed. For a large part, this can be attributed to the nature of the in vivo test in rabbits, which is more complicated and compromised than originally believed. This paper describes, most chronologically, the development, performance, validation and application of the Isolated Eye Test and, in broader perspective, the international validation and acceptance of this alternative test by regulatory authorities and agencies.</p

Integrating in vitro data and physiologically based kinetic (PBK) modelling to assess the in vivo potential developmental toxicity of a series of phenols

Toxicity outcomes derived in vitro do not always reflect in vivo toxicity values, which was previously observed for a series of phenols tested in the embryonic stem cell test (EST). Translation of in vitro data to the in vivo situation is therefore an important, but still limiting step for the use of in vitro toxicity outcomes in the safety assessment of chemicals. The aim of the present study was to translate in vitro embryotoxicity data for a series of phenols to in vivo developmental toxic potency values for the rat by physiologically based kinetic (PBK) modelling-based reverse dosimetry. To this purpose, PBK models were developed for each of the phenols. The models were parameterised with in vitro-derived values defining metabolism and transport of the compounds across the intestinal and placental barrier and with in silico predictions and data from the literature. Using PBK-based reverse dosimetry, in vitro concentration–response curves from the EST were translated into in vivo dose–response curves from which points of departure (PoDs) were derived. The predicted PoDs differed less than 3.6-fold from PoDs derived from in vivo toxicity data for the phenols available in the literature. Moreover, the in vitro PBK-based reverse dosimetry approach could overcome the large disparity that was observed previously between the in vitro and the in vivo relative potency of the series of phenols. In conclusion, this study shows another proof-of-principle that the in vitro PBK approach is a promising strategy for non-animal-based safety assessment of chemicals