A Practical Approach, Second Edition=Ronald D. Ho.pdf

THE U.S. EPA ENDOCRINE DISRUPTOR SCREENING PROGRAM 515tested include whether some effects might be detected more easily in the adult as compared withthe weanling, and if increasing the number of males observed at either age would be beneficial.Data from these studies may ultimately increase the sensitivity of the mammalian multigenerationtest for the detection of endocrine disrupting chemicals.Potential alternatives to the standard mammalian two-generation test include several transgenerationalprotocols that have been developed recently. Many of these protocols typically use fewerlitters (7 to 10 per dosage group) but examine all animals in the litter. 147–150 Even though theprotocols employ fewer animals, they provide more statistical power to detect reproductive effectsin the F 1 generation. In addition, the measurement of anogenital distance (AGD) at 1 to 2 days ofage and areolae and nipples at 12 to 13 days of age in the F 1 generation are included. Theseendpoints are not only extremely useful “biomarkers” of an effect on androgen function, but alsothe changes in AGD and nipples can be permanent. Moreover, these endpoints are highly correlatedwith malformations and other alterations in androgen-dependent tissues. 148 Unfortunately neitherof these markers is measured in the F 1 generation under the EPA standard two-generation testguidelines. In this regard, the proposal that the Tier II testing assays should be based upon theresults of TIS remains an important consideration for obtaining the most relative data on thesuspected mode of action. Another transgenerational protocol, described as alternative reproductiontest (ART) 140,151 or alternative mammalian reproductive test (ARMT), 3 has been used to studyxenoestrogens, such as the phthalates, the herbicide, linuron, and the fungicide, fenarimol. Thisprotocol initiates oral exposure by daily gavage of P 0 male and female rats at weaning and continuesthrough puberty, mating, gestation, and lactation. The F 1 are monitored throughout life but notdosed. While this protocol is longer than the in utero/lactational protocol, it may be appropriatefor xenoestrogens and inhibitors of steroidogenesis that affect the P 0 as well as the F 1 generationin the lower dosage groups.V. SUMMARYIn this chapter we have briefly discussed the in vitro and in vivo assays that are currently underconsideration for use in the TIS battery of the EPA’s EDSP. The current TIS battery represents theproduct of considerable scientific evaluation and deliberations by the EDSTAC, EDMVS, OECD,ICCVAM, and the EPA’s EDSP. The strengths and limitations of these assays, as well as their usefulnessfor detecting known modes of action for the disruption of the mammalian endocrine system, have beendescribed. The assays are currently in various stages of the validation process that will document thebiological relevance and quantify intra- and interlaboratory variance as measures of assay reliability.The ultimate goal of the EPA is to provide a set of assays that will be capable of detecting chemicalswith endocrine disrupting activity, while minimizing the occurrence of false negatives.The EPA issued a notice of its approach for selecting the chemicals for the initial round ofscreening. 152 Of the approximately 87,000 chemicals under its regulatory purview, the agency isproposing to select and screen 50 to 100 chemicals drawn from pesticide active ingredients andhigh production volume chemicals, with some having pesticide inert uses. As previously recommendedby the SAP subcommittee, data resulting from the screening process will be evaluated byan independent external panel of experts to determine whether the program needs to be improvedor further optimized. In addition, as the agency moves forward with its EDSP, new methods andstate-of-the-art approaches will continue to be evaluated for possible substitution in the TIS andTier II testing batteries. New approaches that will reduce animal use, such as using QSAR modelsor HTS technology, will continued to be developed and evaluated to identify chemicals likely todisrupt the endocrine system. Thus, the assays used in the EDSP will continue to be refined andupdated as the program evolves toward full implementation.© 2006 by Taylor & Francis Group, LLC