Evaluation of the developmental toxicity of five compounds with the frog embryo teratogenesis assay: Xenopus (FETAX) and a metabolic activation system

Abstract

The potential teratogenic hazard of five compounds was evaluated using the Frog Embryo Teratogenesis Assay--Xenopus (FETAX) and a metabolic activation system. Embryos of the South African clawed frog, Xenopus laevis, were exposed to (i) three compounds suspected to be proteratogenic in mammalian test systems--[2-acetylaminofluorene (2-AAF), rifampicin (RA) and benzo[a]pyrene (BP)] for 96 h; (ii) one compound unaffected by mixed-functional oxidase (MFO) metabolism--ZnSO4; (iii) one compound thought to be inactivated by cytochrome P-450--cytochalasin D (CD). Two separate static renewal tests were conducted with and without the presence of an exogenous metabolic activation system (MAS). The metabolic activation system consisted of Aroclor 1254-induced rat liver microsomes. The teratogenic potential of each compound and the effects of metabolic activation were based on teratogenic indices [TI = 96 h LC50/96 h EC50 (malformation)], types and severity of malformation, and effects on embryo growth. Metabolic activation increased the potential teratogenic hazard of 2-AAF, RA and BP by TI factors of 1.3, 2.8 and 6.8, respectively. The teratogenic potential of ZnSO4 was virtually unaffected by the MAS. The MAS significantly reduced the teratogenic potential of CD by a TI factor of 2.7. These results demonstrate the utility and importance of a MAS for in vitro developmental toxicity screens such as FETAX. Consistent use of a MAS with FETAX should reduce the number of potential false-positive and false-negative test results.

Comparative sensitivity of Xenopus tropicalis and Xenopus laevis as test species for the FETAX model

“…It is interesting to note that growth-inhibiting potential in the present study directly follows the trend in teratogenic potential. The same similarity in trends was identified during validation of FETAX with X. laevis (Dawson and Bantle, 1987;Dawson et al, 1989;Fort et al, 1989Fort et al, , 1990Fort et al, , 1992Bantle et al, 1990;Sunderman et al, 1991;Dresser et al, 1992).…”

“…The Frog Embryo Teratogenesis Assay -Xenopus (FETAX) model was originally developed by Dumont et al (1983), standardized via the American Society of Testing and Materials (ASTM, 1998) and validated as an alternative developmental toxicity screening test to determine the relative developmental toxicity hazard of chemical agents and complex mixtures (Dawson et al, 1989;Fort et al, 1989;Bantle et al, 1990Sunderman et al, 1991;Dresser et al, 1992;Fort et al, 1992Morgan et al, 1996). Interlaboratory validation studies have strongly supported the FETAX as a promising alternative prescreening test system capable of minimizing the cost and time restraints associated with the use of conventional mammalian test organisms, as well as the number of mammalian specimens used in developmental toxicity testing (Bantle et al, 1994a(Bantle et al, ,b, 1996(Bantle et al, , 1999Fort et al, 1998).…”

A toxicity and hazard assessment of fourteen pharmaceuticals to Xenopus laevis larvae

“…In all experiments, the concentration of the solvent did not exceed 1% (v/v), per ASTM (2002) guidelines. These concentrations have been found not to cause any adverse effects in FETAX (Fort et al 1989). Solvent controls did not have significant effects on normal Xenopus development (i.e., at least 90% of controls survived without deformities throughout the duration of the test).…”

Assessing the predictive validity of frog embryo teratogenesis assay?Xenopus (FETAX)

“…Specific aliquots of the Aroclor 1254-induced microsomes were pretreated with carbon monoxide (CO) to selectively modulate mixed function oxidase (MFO) activity. Inhibition with CO was achieved by chemically reducing 3 Teratogenic Index = LC50/EC50 (malformation). 4 Minimum concentration to inhibit growth determined using ANOVA -Dunnett's Test, P < 0.05.…”

“…Endpoints measured include mortality, malformation, and growth. Validation studies have shown FETAX to have value in screening for chemical teratogens, determining teratogenic interactions, evaluating the developmental toxicity of complex environmental mixtures, and developing structure-activity relationships [2][3][4][5][6][7][8][9][10][11].…”