Effects of hydroxyapatite nanoparticles on the vitrification of bovine metaphase II oocytes

Abstract

Context Although vitrification is commonly used for oocyte cryopreservation, the cryogenic damage results in poor developmental capacity of oocytes after freezing. Nano-cryopreservation is one of the new methods of vitrification developed in recent years. However, the effect of nano-cryopreservation on mature bovine oocytes remains to be elucidated. Aims This study aimed to verify the effect of using hydroxyapatite (HA) nanoparticles (NPs) on the vitrification of bovine metaphase II (MII)-stage oocytes. Methods Bovine MII-stage oocytes were exposed to different HA concentrations (0.01%, 0.05%, and 0.10%) in vitrification solution (VS). After IVF (in vitro fertilisation) and IVC (in vitro culture), the toxicity of HA was assessed by cleavage and blastocyst rates. A suitable concentration of HA nanoparticles was selected according to the results of the first experiment. and then vitrification-thawing was measured. The effect of HA on the developmental capacity of oocytes was assessed by oocyte cleavage rate and blastocyst rate. The mitochondrial membrane potential (MMP) and the intracellular reactive oxygen levels (ROS) of oocytes were measured by staining with a fluorescence probe (JC-1) and an ROS kit after nano-cryopreservation. Key results The addition of 0.05% HA to the VS did not affect the oocyte morphology; the proportion of oocytes developing with normal morphology was 96.72%. In contrast, this proportion it significantly decreased at a concentration of 0.1% HA in VS (91.69%; P < 0.05). The cleavage rates (56.95% vs 51.20%, 50.67%; P < 0.05) of bovine oocytes exposed to 0.05% HA were significantly higher than in the VS group and VS + 0.1% HA group. After the vitrification-thawing, the oocyte cleavage rates (41.07% vs 33.97%; P < 0.05) and blastocyst rates (12.35% vs 7.38%; P < 0.05) were significantly higher in the VS + 0.05% HA group compared to the VS group. At the 0.05% HA concentration, nano-cryopreserved oocytes had significantly higher MMP (1.35 ± 0.24) and significantly lower ROS (1.43 ± 0.05) than the VS group (P < 0.05, mean ± s.e.m.). Conclusions The addition of 0.05% HA-NPs in VS could promote bovine MII-stage oocytes’ developmental ability after vitrification. This effect may be caused partly by increased mitochondrial membrane activity and decreased ROS. Implications HA-NPs may be a new class of cryoprotective agent suitable as components for oocyte vitrification.