BEAUVERICIN DISTURBS NUCLEAR AND CYTOPLASMIC MATURATION OF PREBUPERTAL SHEEP OOCYTES

Beauvericin (BEA) is a mycotoxin produced by several Fusarium species and a common contaminant of food and feed. Due to its ionophoric properties it can disturb mitochondrial function, and enhance reactive oxygen species (ROS) production and membrane lipid peroxidation [1]. It has been reported that BEA may affect the quality of oocytes by reducing granulosa cell function in pigs [1]. Here we determined the effect of BEA on meiotic competence and cytoplasmic maturation of oocytes from pre-pubertal sheep. Cumulusoocyte complexes (COCs) recovered at local slaughterhouses from the ovaries of sheep younger than 6 months were underwent in vitro maturation (IVM) [2]. COCs were exposed to BEA concentrations selected on the basis of previous studies (0.5, 1, 3, 5 μM) [3]. COCs cultured in IVM medium with 0.02% DMSO (vehicle) were used as controls. After IVM, cumulus cells were removed and oocytes stained with MitoTracker Orange CMTM Ros, 2′,7′- dichlorodihydrofluorescein diacetate and Hoechst 33258 and fixed in 2% paraformaldehyde in PBS. Oocytes at the metaphase II stage were analyzed by confocal laser scanning microscopy for their cytoplasmic maturation expressed as mitochondria (mt) distribution pattern [2]. Data were analysed by Chi-square test and differences were considered to be significant when P<0.05. A total of 464 oocytes were analyzed in four replicates. BEA, at 5 μM, was found to reduce the maturation rate (45/94, 47.9% vs 59/93, 63.4%, for exposed and controls, respectively; P<0.05) whereas it was not effective at the lower tested concentrations (58/94, 61.7%; 45/93, 48.4%; 47/90, 52.2% for 0.5, 1 and 3 μM, respectively; P>0.05). In addition, BEA at 5 μM affected the bioenergetic status of oocytes, as it increased the rate of oocytes showing abnormal mt pattern (5/45, 11% vs 0/59, 0%, for exposed and controls, respectively; P<0.05) and reduced the rate of oocytes with healthy perinuclear/pericortical mt pattern (20/45, 44% vs 39/59, 66%, for exposed and controls, respectively; P<0.05). No effects were noticed on mt pattern at lower tested concentrations (37/58, 64%; 25/45, 56%; 29/47, 62%, for 0.5, 1 and 3 μM respectively; P>0.05). These data indicate that BEA, in the exposure conditions used in the present study, hinder nuclear and cytoplasmic maturation in prepubertal sheep oocytes