[Show abstract][Hide abstract] ABSTRACT: RIVM's investigation of integrated testing strategies (ITS) to reduce the use of experimental animals in the risk assessment of chemical substance focuses on the application of alternative and improved test methods. This research is highly desirable for the contribution it can make to the successful implementation of the new EU legislation for industrial chemicals, REACH, as of June 1, 2007. In this way RIVM will contribute to EU and OECD research into testing strategies. Integrated, or Intelligent, Testing Strategies (ITS) are strategies for the effective testing of the hazards of chemical substances. Such strategies show what tests or mathematical methods should be used for a particular substance, and in what order. ITS are intended as an answer to the ever-increasing demand for testing in regulations for a great number of substances with limited databases. The focus of ITS is especially on the development of strategies on the basis of test methods at cellular level (in vitro) and mathematical methods (in silico). The mathematical methods are needed for the assessment of exposure and of the relation between effects and chemical structure. Some tests with experimental animals (in vivo) will also remain necessary. Knowledge on the effects of chemical substances can be derived with sufficient certainty by smartly coupling these methods with each other. In this way, the expectation is that chemical substances will be assessed cheaper and faster, with less use of experimental animals. The report first describes how to deal with uncertainties in the results of tests and methods used in each step of a particular ITS. Next it focuses on testing strategies for the assessment of: 1) environmental degradation 2) sensitization and 3) adverse effects on fertility and progeny. Het RIVM heeft teststrategieen onderzocht (ITS) om de risicobeoordeling van chemicalien proefdiervriendelijker te maken. Het wil hiermee bijdragen aan onderzoeksprogramma's hiernaar van de EU en de OESO. Het accent ligt daarbij op de toepassing van alternatieve methoden en de verbetering van bestaande testmethoden. Dit onderzoek is hard nodig om de nieuwe Europese wetgeving voor industriele stoffen, REACH, te laten slagen, welke op 1 juni 2007 in werking treedt. ITS staat voor geintegreerde of intelligente Teststrategieen. Het zijn strategieen op papier waarmee chemische stoffen zo effectief mogelijk kunnen worden getest op mogelijke gevaren. Die strategieen maken inzichtelijk welke testen of wiskundige methoden voor een bepaalde stof moeten worden gebruikt, en in welke volgorde. ITS wil een antwoord zijn op de toenemende testvereisten in de regelgeving voor grote aantallen stoffen waarover weinig fysisch-chemische en (eco)toxicologische gegevens bekend zijn. Het gaat dan vooral om de ontwikkeling van strategieen waarvoor testmethoden op celniveau (in vitro) en wiskundige testmethoden (in silico) gebruikt worden. De wiskundige methoden zijn nodig om de blootstelling aan stoffen en de relatie tussen effecten hiervan en chemische structuur in te kunnen schatten. Daarnaast blijft proefdiergebruik (in vivo) in sommige gevallen nodig. Door de resultaten van al deze methoden op slimme wijze aan elkaar te koppelen kan met voldoende zekerheid inzicht worden verkregen in de effecten van chemische stoffen. En daarmee kunnen, naar verwacht, stoffen met minder proefdieren, goedkoper en sneller op hun veiligheid worden beoordeeld. Het rapport beschrijft hoe in elke stap van de teststrategie zo verantwoord mogelijk kan worden omgegaan met de onzekerheden in de gebruikte resultaten van testen en methoden. Vervolgens worden teststrategieen besproken voor de beoordeling van 1) de afbraak van chemicalien in het milieu, 2) overgevoeligheid van huid en ademhalingswegen en 3) nadelige effecten op de vruchtbaarheid en op het nageslacht.
[Show abstract][Hide abstract] ABSTRACT: Workshops on maternal toxicity were held at the annual Society of Toxicology, Teratology Society, and European Teratology Society meetings in 2009. Speakers presented background information prior to a general discussion on this topic.
The following recommendations/options are based on the outcome of the discussions at the workshops:
Birth Defects Research Part B Developmental and Reproductive Toxicology 02/2011; 92(1):36-51. DOI:10.1002/bdrb.20281 · 1.17 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Risk managers need detailed information on (1) the type of effect, (2) the size (severity) of the expected effect(s) and (3) the fraction of the population at risk to decide on well-balanced risk reduction measures. A previously developed integrated probabilistic risk assessment (IPRA) model provides quantitative information on these three parameters. A semi-quantitative tool is presented that combines information on these parameters into easy-readable charts that will facilitate risk evaluations of exposure situations and decisions on risk reduction measures. This tool is based on a concept of health impact categorization that has been successfully in force for several years within several emergency planning programs. Four health impact categories are distinguished: No-Health Impact, Low-Health Impact, Moderate-Health Impact and Severe-Health Impact. Two different charts are presented to graphically present the information on the three parameters of interest. A bar plot provides an overview of all health effects involved, including information on the fraction of the exposed population in each of the four health impact categories. Secondly, a Health Impact Chart is presented to provide more detailed information on the estimated health impact in a given exposure situation. These graphs will facilitate the discussions on appropriate risk reduction measures to be taken.
Food and chemical toxicology: an international journal published for the British Industrial Biological Research Association 04/2009; 47(12):2941-50. DOI:10.1016/j.fct.2009.03.009 · 2.61 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The implementation of in vitro alternatives in the safety evaluation of chemicals in the animal intensive area of reproductive toxicity testing is highly desirable, but has been limited by issues around predictivity and applicability domains. The validation of alternatives may gain from a category approach, in which, rather than validating a test for the universe of chemicals, its predictive value is assessed for each class of chemicals for which the test represents relevant end point(s). We studied the embryotoxicity in rodent postimplantation whole embryo culture (WEC) of a series of phthalates and their metabolites. Phthalate diesters are widely applied industrial chemicals, their monoester derivatives being considered as their embryotoxic metabolites. The relative in vitro potency of three out of four monophthalates was found to mimick that of corresponding diphthalates tested in vivo. The phthalate that deviated from this ranking, monoethylhexylphthalate (MEHP), showed a relatively high in vitro toxicity as compared to in vivo data. This deviation could be explained through kinetic differences among phthalates, as shown between MEHP and monobutylphthalate. In addition, in vitro testing of specific secondary MEHP metabolites showed that they were all less potent than MEHP. This finding confirmed that MEHP in vitro embryotoxicity is most likely the best correlate to DEHP in vivo embryotoxicity. This study shows that a category approach in the assessment of the validation of in vitro alternatives is feasible, and can be improved when kinetic considerations are taken into account.
Toxicology in Vitro 08/2008; 22(7):1797-805. DOI:10.1016/j.tiv.2008.07.007 · 3.21 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In contrast to most toxicological tests, developmental studies are usually required in both a rodent and a non-rodent species. This study retrospectively assessed the added value of the rabbit developmental test when a rat developmental test is available. In contrast with previous reviews, we looked at developmental toxicity instead of teratogenicity, and took into account maternal toxicity in the evaluation of developmental toxicity. We analyzed data for 54 substances classified for developmental toxicity and 73 substances considered to be teratogenic in the rabbit and not in the rat in two previous reviews. On average, the rat and the rabbit developmental toxicity studies were similarly sensitive: the average ratio of the NOAELs between the two species was about one, and for most compounds there were no differences between rat and rabbit studies in terms of classification for developmental toxicity. For certain substances the developmental study in either one of the two species appeared to be more sensitive than in the other species. However, these differences are partly due to differences between studies other than the test species used. Overall, our analysis does not clearly indicate that the evaluation of developmental toxicity, as opposed to other types of toxicity, would specifically require the rabbit as an additional test species. The discrimination between direct and indirect (i.e., as a consequence of maternal toxicity) developmental effects was often doubtful, and is one of the factors that could explain the apparent differences between the two species. A more accurate assessment of maternal toxicity might improve the reliability of the results from a single developmental toxicity study. More knowledge about the interaction between maternal and developmental effects is required before decisions on omitting the requirement for the developmental toxicity testing in a second species can be considered.
[Show abstract][Hide abstract] ABSTRACT: If in vitro data are to be used as a basis for hazard characterization, a translation of an in vitro concentration toward an in vivo dose must be made. In this study we examined the correlation between dose descriptors from the in vitro Whole Embryo Culture (WEC) test and in vivo developmental toxicity tests. We applied the Benchmark Dose (BMD) approach to estimate equipotent in vitro concentrations (Benchmark Concentrations [BMCs]) and equipotent in vivo doses (BMDs). Using the data generated in an European Center for the Validation of Alternative Methods validation study we found that the BMCs were highly reproducible among laboratories. The three endpoints analyzed (head length, crown-rump length, and total morphological score) were strongly correlated. A clear in vitro-in vivo correlation was found between BMCs and BMDs. However, a considerable uncertainty would remain if the BMDs were estimated from the BMC using this correlation: the confidence interval of such an in vivo dose estimate would span various orders of magnitude. Differences in toxicokinetic properties among the compounds explained at least part of the scatter of the in vitro-in vivo correlation. But also heterogeneity in the design of the available in vivo studies underlies much of the scatter, and this puts a limit on validating in vitro data as predictors of in vivo data. Further analysis of the in vitro-in vivo correlation would therefore require high-quality in vivo data, generated by appropriate (and similar) study designs.
[Show abstract][Hide abstract] ABSTRACT: Increasing pressure is exerted by some stakeholders to reduce the two-generation study to a one-generation study, a measure that would considerably reduce the number of animals and other costs involved in these lengthy studies. The present study retrospectively evaluates 176 multi-generation studies to assess potential differences between the first and the second generation, both in terms of the types of effects observed and in terms of the effective doses. All substances classified as reproductive toxicants by the Directive 92/32/EEC or considered as toxic to fertility by the California EPA for which we found a multi-generation study were included (n=58 studies). The second generation in the two-generation studies considered affected neither the overall NOAEL nor the critical effect. Therefore, it had no impact on the ensuing risk assessment, nor on classification and labeling. However, several substances did show an increased sensitivity of the F(1) adults in comparison to the P(0). These results support the proposal of replacing the current two-generation study by a one-generation study with a more extensive assessment of parameters at F(1) adulthood.
[Show abstract][Hide abstract] ABSTRACT: This study aims to evaluate the added value of the two-generation reproductive toxicity study when a subchronic study (90-day repeated dose toxicity study) is available. The analysis includes a total of 47 reproductive toxic and 75 non-reproductive toxic substances, for which a two-generation study was available. For each of these compounds the outcomes of both study types were compared, in view of the question what the impact would have been both for the derived NOAEL and for classification regarding toxicity to fertility. On average, only a small difference (less than twofold) in overall NOAELs was found between the rat two-generation study and the rat subchronic study. For individual compounds the differences could be larger (up to around a factor of 10), but differences of this magnitude equally occur between NOAELs of subchronic studies (testing the same substance). The two generation study did have an impact on classification for toxicity to fertility: about one-third of the substances shown to be toxic to fertility in the two-generation study did not show any sign of that in the 90-day study. If the subchronic study did show toxicity to reproductive organs this often occurred at (much) higher doses than other toxic effects in the same study. Therefore, apart from including more fertility endpoints, a larger dose spacing (or more dose groups) in the subchronic study might increase its detection rate of fertility toxic substances. The consequences that these findings may have for risk assessment and risk management are discussed, especially in the context of REACH.