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STRATEGIES TO REDUCE OR REPLACE THE USE OF ANIMALS IN THE ENDOCRINE SCREENING AND TESTING PROGRAM.
GRAY, L. E. STRATEGIES TO REDUCE OR REPLACE THE USE OF ANIMALS IN THE ENDOCRINE SCREENING AND TESTING PROGRAM. Presented at TestSmart--Endocrine Disruptors, Reston, VA, March 13 - 15, 2006.
Abstract: The US Environmental Protection Agency (EPA) is developing a screening and testing program for endocrine disrupting chemicals (EDCs) to detect alterations of hypothalamic-pituitary-gonadal (HPG) function, estrogen, androgen and thyroid hormone synthesis and androgen (AR) and estrogen (ER) receptor-mediated effects in mammals and other animals. High priority chemicals would be evaluated in the Tier 1 Screening (T1S) battery and chemicals positive in T1S would then be tested in Tier 2 (T2). As equivocal screening results may require further evaluation, we have proposed that additional short-term screening assays be employed in T1.5 to eliminate any uncertainty about T1S results. This would reduce testing with animals of false positives in T2. T1 and T1.5 include both in vitro and in vivo assays. The proposed screening and testing batteries include short-term and multigenerational assays using the laboratory rat. Fish and amphibian assays also are being developed. This presentation will discuss strategies to reduce or replace the use of animals in endocrine screening and testing studies. In vitro assays in the EDSTAC T1 battery included ER and AR competitive binding and transcriptional activation assays to distinguish agonists from antagonists. It also included assays for assessment of steroidogenesis and aromatase. The in vitro assays in the EDSTAC battery propose using animal tissues as a source of ER and AR receptors and testis tissue to assess steroidogenesis. Since those protocols were drafted in 1998, in vitro assays have been developed that can assess AR and ER binding using recombinant receptors and cell lines can be used in place of animal derived testis tissue to evaluate steroidogenesis. In the proposed in vivo EDSTAC screening battery, the uterotropic assay detects estrogens and antiestrogens, while steroidogenesis, antithyroid activity, (anti) estrogenicity and hypothalamic-pituitary-gonadal (HPG) function are assessed in a Pubertal Female assay. (Anti) androgens are detected in the Hershberger Assay (weight of androgen-dependent tissues in castrate-immature-male rats). Several alternative mammalian in vivo assays were proposed in the EDSTAC Final Report. Of these, a short-term pubertal male rat assay appears most promising for inclusion in T1 or T1.5 to confirm T1 effects. An in utero-lactational screening protocol also is being evaluated but this assay is better suited for T1.5 or T2 due to the size, complexity and duration of the assay. The AAdult Intact Male@ assay, also was proposed as an alternative for T1, attempts to identify EDCs in a hormonal battery, however, this assay appears to be of limited value as a screen due to a lack of sensitivity and specificity. For Tier 2 testing, the number of endocrine sensitive endpoints and offspring (F1) examined in multigenerational tests needs to be thoughtfully modified for EDCs on a mode-of-action specific basis. Consideration should be given to tailoring T2, based on the results of T1S. One should be aware that this phase of the battery uses many more animals than does the screening phase and the numbers of animals used in different multigenerational/in utero/transgenerational protocols ranges from a few hundred to several thousands. For chemicals with a mode of action that is more likely to affect the offspring than the parent generation, 'enhanced' developmental protocols can provide the data critical for chemical risk assessments on EDCs with a minimum of animals by including a comprehensive assessment of all of the sensitive endpoints in all of the offspring. Consideration of approaches to reducing animal use in Tier I Screening and Tier 2 Testing Batteries. 1. Develop a comprehensive, robust in vitro battery of screening assays to prioritize chemicals for in vivo screening. 2. Limit the numbers of chemicals entering Tier 1 Screening to those with a real possibility of human or wildlife exposures 3. Minimize the numbers of animals used in each in vitro and vivo Tier 1 Screening Assay based upon data from research on these protocols. 4. Minimize the numbers of animals used in dose-range finding studies to a minimum. 5. Minimize the numbers of dose groups used in Tier 1 Screening. 6. Employ a strategy to eliminate the testing on Tier 2 of chemicals that were false positives in Tier 1. 7. Reduce animal use in Tier 2 Testing. a. Enhance the testing protocols such that they include all the endpoints that are sensitive to the endocrine activity seen in Tier 1 Screening. b. For modes of action that are expected to affect the F1 more the parent generation, reduce the numbers of litters used by half, but carefully examine all the animals after puberty, as warranted by the results of Tier 1 Screening. This is an abstract of a proposed presentation and does not necessarily reflect USEPA policy. Impact. The proceedings of the CAAT DNT meeting, including this slide presentation, will impact on the numbers of animals used in the EDSP program. If followed, the recommendations would allow the USEPA and other regulatory agencies to reduce animal use in the EDSP endocrine screening program to the minimum number required for screening and testing, hence, preventing unnecessary animal use but provide better data for risk assessments than do the current assays Impact. The proceedings of the CAAT DNT meeting, including this slide presentation, will impact on the numbers of animals used in the EDSP program. If followed, the recommendations would allow the USEPA and other regulatory agencies to reduce animal use in the EDSP endocrine screening program to the minimum number required for screening and testing, hence, preventing unnecessary animal use but provide better data for risk assessments than do the current assays.