Phase III interlaboratory study of FETAX part 3. FETAX validation using 12 compounds with and without an exogenous metabolic activation system

Abstract

FETAX (Frog Embryo Teratogenesis Assay—Xenopus) is a 96‐h whole‐embryo developmental toxicity screening assay that can be used in ecotoxicology and in detecting mammalian developmental toxicants when an in vitro metabolic activation system is employed. A standardized American Society for Testing and Materials (ASTM) guide for the conduct of FETAX has been published, along with a companion atlas that helps in embryo staging and in identifying malformations. As part of the ASTM process, an interlaboratory validation study was undertaken to evaluate the repeatability and reliability of FETAX and to evaluate the potential teratogenic hazard of 12 compounds. Three different laboratories participated in the study. All three participating laboratories had extensive experience with the assay. FETAX intralaboratory and interlaboratory variability, as judged by coefficients of variation, were very low. Potential teratogenic hazard was evaluated using two major criteria from FETAX experiments employing metabolic activation systems (MAS). These were the teratogenic index TI (TI = 96‐h lc50/96‐h ec50 (malformation)) and the minimum concentration that inhibits growth (MCIG). A compound was considered teratogenic by this criterion when the MCIG was significantly different from controls at concentrations below the 30% level of the MAS 96‐h lc50. Based on the results of this and other studies, a decision table was constructed in order to evaluate additional studies. Severity of malformations caused, especially near the MAS 96‐h ec50 (malformation), were also evaluated. Four compounds were non‐teratogenic but two compounds were clearly teratogenic. The remaining six compounds were ranked as equivocal teratogens. The results were discussed in light of the difficulty of producing an adequate decision table. FETAX proved to yield repeatable and reliable data as long as care was taken during range‐finding and technicians were adequately trained. The MAS was essential in using FETAX to predict developmental hazard in mammals, and still requires further development. Copyright © 1999 John Wiley & Sons, Ltd.

Development of a Reproductive Toxicity Test Using Xenopus

“…The teratogenic effects noted in studies applying post-fertilization exposure are significantly more dramatic in terms of the incidence of malformation and the severity of effects. 31 Effects on the testis have been observed in both subchronic and chronic studies in rats and mice exposed to B. 32 After 14 d of treatment, doses of 93 mg B/Kg/d caused a reduction in spermiation.…”

“…Based on these studies, it appears that both male and female gonads Interestingly, similar effects have been induced in normal-appearing X. laevis embryos from unexposed mothers exposed to 500.0 mg B/L in the FETAX model. 31 These results suggest that similar modes of action on the developing embryo are occurring, regardless of whether exposure is provided through the mother to the oocyte or directly to the developing embryo following fertilization. The teratogenic effects noted in studies applying post-fertilization exposure are significantly more dramatic in terms of the incidence of malformation and the severity of effects.…”

Acute Toxic Effects of the Herbicide Formulation and the Active Ingredient Used in Cycloxydim-Tolerant Maize Cultivation on Embryos and Larvae of the African Clawed Frog, Xenopus laevis

“…Therefore, the calculated Teratogenic Index (TI = 96-h LC50/96-h TC50) was 0.94. According to Bantle et al (1999) the compound can be considered as non-teratogenic. However, it has to be taken into account that mortality may camouflage teratogenic effects at an early stage before they are visible as diagnosable morphological changes.…”

“…We conducted the first experimental trials to investigate the toxicity of Focus Ò Ultra on embryos and early larvae of the African clawed frog (Xenopus laevis). The developmental stages of X. laevis can be used as surrogates for other aquatic organisms because of their high sensitivity to pesticides and their availability as a laboratory species (ASTM 1998;Bantle et al 1998Bantle et al , 1999Wagner et al 2013).…”

Acute Toxic Effects of the Herbicide Formulation Focus® Ultra on Embryos and Larvae of the Moroccan Painted Frog, Discoglossus scovazzi

“…Early developmental stages of the African clawed frog [X. laevis (Daudin 1802) Pipidae] are commonly used in toxicological studies as surrogates for other aquatic organisms, including amphibians, because of their high sensitivity to pesticides and their availability for use in the laboratory (ASTM 1998;Bantle et al 1998Bantle et al , 1999OECD 2009;Wagner et al 2015). Xenopus larvae [larval type I (pipid type)] are understood as derived within anurans and the larval types IV and III as the phylogenetically basic morphotypes (Roelants et al 2011).…”