Toxic effects of the mycotoxin zearalenone and its derivatives on in vitro maturation of bovine oocytes and 17β-estradiol levels in mural granulosa cell cultures

Moulds parasites of livestock foodstuffs alter the quality of grains by synthetising mycotoxins. Zearalenone (ZEA) and its derivatives (alpha- and beta -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, alpha -zearalenol and zearalanone were tested, at levels ranging from 0.3 to 30 mug/ml, in order to evaluate the effect on the in vitro maturation (IVM) rate of bovine oocytes and on the formation of 17 beta -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 mug/ml ZEA, alpha -zearalenol or zearalanone, with a significant increase in chromatin abnormalities occurring in the presence of ZEA (P<0.05) and <alpha>-zearalenol (P<0.001). In preliminary trials on 17<beta>-estradiol formation, at the same testing concentration, higher levels of 17 beta -estradiol were found in the presence of alpha -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 that alpha -zearalenol acts as a stronger estrogenic inducer than the original molecule (ZEA). (C) 2001 Elsevier Science Ltd. All rights reserved.