Toxicity and sister-chromatid exchange in cultured preimplantation mouse embryos exposed to serum from cyclophosphamide-treated rats: possible implications for testing maternal serum genotoxicity

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Abstract
We have worked out a simplified method to detect embryotoxicity associated with blood serum. Here we report results for serum from female rats treated with 0, 25, 250 and 500 mg/kg cyclophosphamide (CP) as a control experiment in order to evaluate the feasibility of this protocol. Eight-cell mouse embryos were cultured for 48 h in medium supplemented with 10% rat serum and 10−6 M 5-bromodeoxyuridine (BrdU). Colchicine (0.2 μM) was added 3 h prior to harvesting the cells for chromosome preparation, and differentially stained sister chromatids were visualized after fluorescence-plus-Giemsa staining. Rats treated with increasing doses of CP yielded serum which had increasing mutagenic [as evaluated by sister-chromatid exchange (SCE)] and toxic effects on mouse embryos during 48-h in vitro cultures. The SCEs/cell (based on 40 chromosomes) ranged from 17.6 ± 0.31 (mean ± SE) for serum from control (0 mg/kg CP) rats to 40.4 ± 0.22 for serum from rats given 250 mg/kg CP. Serum from rats treated with 500 mg/kg CP was essentially lethal on mouse embryos. The percentage embryo survival decreased from 79.8 ±0.31%(mean ± SE) for serum from control rats to 8.4 ± 0.42% for serum from rats given 500 mg/kg CP. These results indicate that after appropriate testing, this protocol could be used for the possible detection of embryo genotoxicity associated with any human serum. If successful, the evaluation of mouse embryo survival and SCE in the presence of human female sera could become an ’early warning' system for possible reproductive problems (e.g. recurrent abortions, low birth weight and malformations) of unknown aetiologies. Such information could be the basis for corrective measures and selection of sera for in vitro fertilization programmes.