34 Effects of sericin supplementation on in vitro maturation of feline oocytes

The development of assisted reproductive technologies (ARTs) in felidae species has been proposed to guarantee the genetic viability of species that are on the verge of extinction. However, during the in vitro maturation (IVM) process, elevated levels of reactive oxygen species (ROS) are generated, which can negatively affect the viability and quality of the oocytes. Previous study in our laboratory demonstrated the efficiency of sericin (silk protein derived from silkworms) supplementation in the IVM medium and embryo culture in bovine (Velasquez Vasquez et al. 2023 Reprod. Fert. Dev. 35, 181–181, https://doi.org/10.1071/RDv35n2Ab108). The objective of this study was to evaluate the effects of sericin supplementation in the IVM medium. Bovine serum albumin (BSA), sericin + BSA (SER + BSA), and the absence of a protein source (WPS) were also evaluated. Ovaries were obtained from ovariohysterectomy at veterinary clinics and transport to the laboratory within 2 h. Cumulus–oocyte complex (COCs) were matured in vitro for 22 h in tissue culture medium 199 (TCM 199) supplemented with 1 IU/mL human chorionic gonadotrophin, 10 ng/mL equine chorionic gonadotrophin, 1 µL/mL insulin-transferrin-selenium (ITS), 1% vol/vol ATB and divided into four groups: (1) 1% sericin, (2) 0.3% BSA, (3) 0.3% BSA+1% sericin, and (4) WPS. The maturation process was conducted at 38.5°C in humidified air with 6.5% CO₂. Oocyte maturation was assessed by the first polar body extrusion, and degenerated and parthenogenetically activated oocytes were also evaluated. Mature and immature oocytes were separated and treated with CellTracker^TM Blue and fluorescein diacetate to measure glutathione (GSH) and ROS levels. Infinity Analyzer software was used to measure GSH and ROS levels. Data were analysed by Fisher’s exact test using GraphPad Prism 6.0 (GraphPad Inc.) and differences were considered significant at P < 0.05. The experiment was replicated five times. Significant differences were observed in the maturation rate between sericin (150/255, 59%) and WPS group (118/237, 49.8%). No significant differences were found in parthenogenetic and degenerated oocytes between all groups. Sericin and SER+BSA groups, regardless of maturation status, showed higher levels of GSH compared with BSA. In mature oocytes, sericin, and WPS showed higher levels of ROS than in BSA group. Additionally, ROS levels of immature oocyte were lower in the BSA compared with WPS and SER + BSA groups. To our knowledge this is the first time sericin was used in IVM of cat oocytes. Our results suggest that the use of sericin in the IVM medium increase maturation rates and GSH levels. Further studies are required to evaluate sericin effect in felidae in vitro embryo development.