Brilliant Cresyl Blue Negative Oocytes Show a Reduced Competence for Embryo Development after In Vitro Fertilisation with Sperm Exposed to Oxidative Stress

Simple Summary: Oxidatively stressed sperm can fertilise oocytes and, hence, transfer its damaged genome to a progeny. Sperm cannot repair its own genome, therefore the oocyte's capacity to deal with damaged sperm influences the outcome of a fertilisation. We distinguished bovine oocytes of different qualities in vitro using Brilliant Cresyl Blue (BCB) staining and in vitro fertilised them with non-oxidised and oxidised bovine semen. BCB-negative oocytes were less able to support embryo development after fertilisation with oxidatively stressed bovine semen, demonstrated by lower cleavage and blastocyst rates, a delay in development and lower blastocyst quality. These results support a further description of the oocytes' quality in regard of their capacity to deal with damaged sperm, which will help in selecting the best oocytes when damaged sperm have to be used in assisted reproduction. The extent of oxidative damage transferred by the damaged sperm to the progeny is likely to be limited by the oocyte's repair and antioxidative capacity. We aimed to assess the association between Brilliant Cresyl Blue (BCB) staining in oocytes and their competence for embryo development after in vitro fertilisation (IVF) with damaged sperm. For this purpose, bovine sperm were incubated without (non-oxidised sperm, NOX S) or with 100 mu M H2O2 (oxidised sperm, OX S) and were used to fertilise in-vitro-matured bovine oocytes (BCB-pos./BCB-neg.). Unstained oocytes served as controls (US). Development was assessed at 30, 46, 60 h and on Days (D) 7 and 8 after IVF. Total cell number and apoptotic index were analysed in D7 blastocysts. BCB-neg. oocytes showed lower cleavage rates and blastocyst rates than unstained oocytes after IVF with NOX S (p < 0.05). They showed the highest reduction in D7 blastocyst rate upon fertilisation with OX S and showed a delayed embryo development at 46 and 60 h after IVF compared to embryos produced with NOX S (p < 0.05). Total cell number in blastocysts produced with BCB-neg. oocytes was lower (p < 0.05) in the embryos produced with OX S than in embryos after IVF with NOX S. In conclusion, BCB-neg. oocytes have a lower competence to support embryo development after in vitro fertilisation with oxidised sperm.

Automated summary

Oxidatively stressed sperm can negatively impact embryo development when fertilizing oocytes, and the oocyte's ability to handle this damage plays a significant role in the outcome. By using Brilliant Cresyl Blue (BCB) staining to differentiate oocytes of different qualities, this study found that BCB-negative oocytes had lower embryo development rates and lower blastocyst quality when fertilized with oxidatively stressed sperm. These findings can help in selecting high-quality oocytes for assisted reproduction involving damaged sperm, while also highlighting the importance of oocyte repair and antioxidative capacity in limiting oxidative damage to the progeny.