Pro-oxidant effects of Verbascoside, a bioactive compound from olive oil mill wastewater, on in vitro developmental potential of ovine prepubertal oocytes and bioenergetic/oxidative stress parameters of fresh and vitrified oocytes

Verbascoside (VB) is a bioactive compound from olive oil mill wastewater with known antioxidant activity. Oxidative stress in germ cell in vitro culture and cryopreservation procedures is an emerging problem in assisted reproductive technology (ART). Juvenile in vitro embryo production from oocytes of prepubertal subjects is a promising ART because, in farm animals, it reduces the generation gap and in human reproductive medicine, it helps to overcome premature ovarian failure. The aim of this study was to test the effects of VB on the developmental competence of ovine prepubertal oocytes and the bioenergetic/oxidative stress status of fresh and vitrified oocytes. In fresh oocytes, when used at high concentration, VB exerted pro-oxidant short-term effects, i.e. catalase activity increase and uncoupled increases of ooplasmic mitochondria and reactive oxygen species (ROS) specific fluorescence signals and long-term effects, i.e reduced blastocyst formation rate. In vitrified oocytes, it increased ROS levels. Pro-oxidant VB effects in ovine prpubertal oocytes could be related to higher VB accumulation, which was found as being almost one thousand times higher than that reported in other cell systems in previous studies. Also, long exposure times of oocytes to VB, throughout the duration of in vitro maturation (IVM) culture, may have contributed to significantly increase oocyte oxidation. Further studies are needed to identify suitable conditions, lower concentrations and/or shorter exposure times, to figure out VB antioxidant effects in juvenile ARTs.