It is the purpose of this presentation to: (1) describe the nature and conduct of the Hydra Assay, and (2) offer a procedure for assuring and documenting its quality.
The Hydra Developmental Toxicity Assay provides a rapid and reliable prescreening system for teratogenic hazard. Fresh water Hydra attenuata polyps are dissociated into component cells that can be randomly reaggregated into an “artificial embryo” that will produce new adult polyps in approximately one week. During this whole-body regeneration, the artificial embryo achieves most of the developmental phenomena required during mammalian organogenesis.
By determining the minimal affective concentration (MAC) of the substance, both for adult Hydra and embryos, it is possible to determine the substance's ability to disrupt developmental phenomena (developmental toxicity) and determine an A/D ratio, the same ratio as that obtained through the use of mammalian test systems. The A/D ratio is calculated on the basis of the adult (A) and the developmental (D) minimal affective concentrations. An A/D ratio near unity indicates that the substance tested can disrupt development only at doses that also produce overt adult toxicity, and that it constitutes no unique hazard to the conceptus. An A/D ratio of 10.0 or more generally indicates that the substance tested represents a unique hazard to the conceptus, although the concentrations of the test substance required to produce this ratio may bear no direct relationship to the concentrations needed to achieve the same results in mammals.
The phases of the Hydra Assay that are deemed “critical,” and that therefore require audit or inspection, or both, include: (1) protocol review, (2) preparation of media, (3) preparation of the test substance concentrations, (4) preparation of adult and embryo Hydra for use, (5) examination and evaluation of Hydra specimens at periodic intervals, (6) test substance administration, (7) documentation of the environmental conditions and maintenance of the Hydra farm, and (8) report and raw data audit.
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