Effect of cysteamine during in vitro maturation of bovine oocytes on embryo development

In in vitro embryo production (IVP), oxidative modifications via increased reactive oxygen species (ROS) represent a major culture induced stress. Anti-oxidant systems such as glutathione (GSH) can attenuate deleterious effects of oxidative stress decreasing ROS thus protecting the zygote and early embryo. Previous studies suggest that addition of cysteamine to in vitro maturation (IVM) medium can increase intracellular GSH synthesis, improving pronucleus formation, cleavage rates and embryo development. The aim of the present work was to investigate the effects of cysteamine during IVM with conventional FSH stimulation or utilizing the IVM phase of the follicular system (FS), recently proposed by Ovarian Molecular Physiology Laboratory research group. The FS base medium consisted of TCM199 (with Earle's salts, bovine serum albumin, amikacin, pyruvate) supplemented with rhFSH, amphiregulin, insulin-like growth factor 1, estradiol and progesterone (Soares et al., Reproduction, Fertility and Development, 29:2217-2224, 2017). Five replicates were performed to compare four experimental groups: FSH (basic medium supplemented with rhFSH 10-1 UI/mL); FSH+C (FSH medium supplemented with cysteamine 1 mM/mL); FS and FS+C (FS medium supplemented with cysteamine 1 mM/mL). Ovaries were obtained from a slaughterhouse and COCs recovered by aspiration were submitted to IVM for 24h, followed by in vitro fertilization for 18h and in vitro culture (IVC) for seven days. Blastocyst rate was calculated in relation to total oocytes subjected to IVM and blastocyst cell numbers were assessed by Hoechst 33342 staining. Rates of expanded and hatched blastocysts were calculated in relation to total blastocysts. Data were arcsine transformed and compared with Tukey (parametric data) or Wilcoxon (non-parametric data) tests. Differences were considered significant when P≤0.05. Addition of cysteamine did not alter blastocyst rate (P>0.05; FSH 24.67±5.37; FSH+C 33.50±4.95; FS 25.96±4.92; FS+C 22.95±5.56), expanded and hatched blastocysts rates (P>0.05; FSH 94.44±3.51; FSH+C 83.57±5.61; FS 85.83±4.86; FS+C 83.36±7.65), nor the total number of embryonic cells (P>0.05; FSH 118.40±7.41; FSH+C 123.39±7.36; SF 124.97±9.75; SF+C 124.37±9.63). In conclusion, addition of cysteamine to the IVM medium did not improve embryo production. Supported by FAPESP 2017/07588-4.