Consequences of copper and zinc co-supplementation on DNA integrity and apoptosis of bovine cumulus cells during oocyte in vitro maturation

Abstract

Minerals such as copper (Cu) and zinc (Zn) are essential trace elements with specific roles in the antioxidant defense system. They are also vital for the health and growth of dairy cattle. We hypothesised that simultaneously increased Cu and Zn concentrations would reduce DNA damage and apoptosis in cumulus cells (CC) during oocyte in vitro maturation (IVM). Cumulus oocyte complexes (COC) were aspirated from follicles and only intact ones were selected for IVM. Groups of 10 COC were transferred into 50 μL of IVM medium and cultured in 5% CO 2 at 39°C for 24 h. The final concentrations of Cu and Zn were 0.2 and 0.7 μg/mL, 0.5 and 1.0 μg/mL, and 0.8 and 1.5 μg/mL, respectively. DNA integrity was analysed with the alkaline comet assay. Early apoptosis induction was studied by annexin-V binding. The results obtained showed that whereas joint Cu/Zn supplementation at a ratio not greater than 0.3 could be beneficial for DNA integrity and prevent the onset of apoptosis in CC during IVM, a Cu/Zn ratio greater than 0.5 induced DNA damage and cell death.