Toxic effects of mycotoxin zearalenone and its derivatives on in vitro maturation of bovine oocytes and 17 beta- estradiol level in mural granulosa cell cultures.

Moulds parasites of livestock foodstuffs alter the quality of grains by synthetising mycotoxins. Zearalenone (ZEA) and its derivatives (a- and b-zearalenol, zeranol, taleranol and zearalanone) are produced by fungi of the genus Fusarium and, after ingestion via contaminated cereals, may lead to fertility disturbances and other reproductive pathologies. Zearalenone, a-zearalenol and zearalanone were tested, at levels ranging from 0.3 to 30 mg/ml, in order to evaluate the effect on the in vitro maturation (IVM) rate of bovine oocytes and on the formation of 17 b-estradiol in supernatants of mural granulosa cells (GC) cultures. These compounds induced dose-dependent oocyte maturation delay and chromatin abnormalities. Maturation of oocytes to metaphase II (M II) was inhibited in oocytes cultured in the presence of 30 mg/ml ZEA, a-zearalenol or zearalanone, with a significant increase in chromatin abnormalities occurring in the presence of ZEA (P<0.05) and a-zearalenol (P< 0.001). In preliminary trials on 17b-estradiol formation, at the same testing concentration, higher levels of 17 b-estradiol were found in the presence of a-zearalenol (mean value 1.6 ng/ml) with respect to ZEA and zearalanone (mean estradiol concentrations of 0.06 and 0.5 ng/ml, respectively). These data demonstrate a negative effect of ZEA and its derivatives on meiotic progression of bovine oocytes, possibly attributable to a toxic mechanism not related to the binding affinity of these compounds to estrogen receptor sites, and support previous observations thata-zearalenol acts as a stronger estrogenic inducer than the original molecule (ZEA).