Blastocyst production by in vitro maturation and development of porcine oocytes in defined media following intracytoplasmic sperm injection

Impact of oxidative stress on oocyte competence for in vitro embryo production programs

Producing high-competent oocytes during the in vitro maturation (IVM) is considered a key step for the success of the in vitro production (IVP) of embryos. One of the known disruptors of oocyte developmental competence on IVP is oxidative stress (OS), which appears due to the imbalance between the production and neutralization of reactive oxygen species (ROS). The in vitro conditions induce supraphysiological ROS levels due to the exposure to an oxidative environment and the isolation of the oocyte from the follicle protective antioxidant milieu. In juvenile in vitro embryo transfer (JIVET), which aims to produce embryos from prepubertal females, the oocytes are more sensitive to OS as they have inherent lower quality. Therefore, the IVM strategies that aim to prevent OS have great interest for both IVP and JIVET programs. The focus of this review is on the effects of ROS on oocyte IVM and the main antioxidants that have been tested for protecting the oocyte from OS. Considering the importance that OS has on oocyte competence, it is crucial to create standardized antioxidant IVM systems for improving the overall IVP success.

Using cysteine/cystine to overcome oxidative stress in goat oocytes and embryos cultured in vitro

Assisted reproductive techniques expose gametes to excessive concentrations of reactive oxygen species. The present study aimed to evaluate the effects of oxidative stress on apoptosis in goat oocytes and embryonic development. The results demonstrated that the addition of 100 µM hydrogen peroxide (H2O2) into media produces an oxidative environment during oocyte maturation. The number of cumulus cells positive for terminal deoxynucleotidyl transferase UTP nick end labeling, and the activity of caspase 3 in mature oocytes were increased, compared with the control group (P<0.05). In addition, the expression levels of mitochondrial regulators, including peroxisome proliferator‑activated receptor γ coactivator-1 α (PGC-1α) and nuclear respiratory factor‑1 (NRF‑1) were increased in the oxidative oocytes, compared with those in the control group (P<0.05). The ratio of the proapoptotic gene, B cell lymphoma (Bcl-2)-associated X protein (BAX), to the anti‑apoptotic gene, BCL‑2, was higher in the H2O2 group, compared with the control group (P<0.05). To overcome oxidative stress in oocytes and embryos cultured in vitro, 200 µM cysteine and 200 µM cystine were added to the media, thereby increasing the concentration of intracellular glutathione (GSH) and assisting in maintaining the redox state of the cells. In conclusion, cysteine and cystine reduced the oxygen tension caused by H2O2, thereby providing a novel strategy for optimizing in vitro embryonic development systems.

Cysteamine supplementation during in vitro maturation (IVM) of rabbit oocyte improves the developmental capacity after intracytoplasmic sperm injection

Purpose

Current approaches to in vitro maturation (IVM) may result in low efficiency and inadequate quality of the oocytes due to insufficient cytoplasmic maturation. Although positive effects of the cysteamine supplementation in IVM medium for oocyte nuclear maturation or male pronuclear formation have been confirmed, it is still controversial whether the cysteamine addition affects embryo development after IVM. We aimed here to confirm the effect of cysteamine addition into IVM medium for subsequent embryo development in vitro.

Methods

We administered the cysteamine to the IVM culture of rabbit immature oocytes at various concentrations and observed the developmental rate, speed to reach blastocyst stage and cell numbers at the blastocyst stage.

Results

Cysteamine supplementation improved developmental rate to blastocyst stage of the IVM oocytes. On the other hand, addition of glutathione (GSH) inhibitor buthionine sulfoximine inhibited GSH accumulation in the oocytes and subsequent embryo development to the blastocyst stage.

Conclusions

Controlling the GSH quantity of IVM oocytes may be an important factor for success of embryo development, and it is quite probable that a cysteamine supplementation can contribute to an increase of GSH content in oocyte.

Effect of lycopene on cytoplasmic maturation of porcine oocytes in vitro

The aim of the present study was to improve cytoplasmic maturation of porcine oocytes by the addition of lycopene into in vitro maturation (IVM) media. We designed six experimental groups; IVM medium was supplemented with 10 IU/ml FSH, FSH and 10 IU/ml human chorionic gonadotrophin (hCG), or FSH and 7 μm lycopene in the first half of the IVM culture (0-22 h) followed by further culture (22-44 h) with or without hCG. The addition of lycopene into IVM media delayed the interruption of communication between an oocyte and the cumulus cells. Although meiotic competence was similar among the six groups, the glutathione level of matured oocytes was significantly higher in the lycopene-supplemented group (9.89 pmol per oocyte) than that in other groups (7.25 and 7.81 pmol per oocyte). Fertilization rate was significantly improved in lycopene-supplemented groups (58.3%) more than that in the group supplemented with FSH only (43.1%), whereas there were no differences in developmental competence among the groups (blastocyst rate: 20.1-29.5%). These results indicate that insufficient cytoplasmic maturation during conventional IVM resulted by disconnection of the gap junction between an oocyte and the cumulus cells in the early phase during IVM culture. We concluded that lycopene induced a prolonged sustainment of gap junctional communication between an oocyte and the cumulus cells during porcine IVM culture, which was an effective cytoplasmic maturation of porcine IVM oocytes.

Acetylation of H4K12 in porcine oocytes during in vitro aging: potential role of ooplasmic reactive oxygen species

Deterioration in the quality of mammalian mature oocytes during metaphase-II (M-II) arrest is called "oocyte aging". Although histone acetylation may affect the progression of aging in murine oocytes, the mechanism is unknown. The objective was to determine the role of ooplasmic reactive oxygen species (ROS) in acetylation of histone H4 at lysine 12 (acH4K12) in porcine aged oocytes in vitro. Based on immunostaining with a specific antibody, acetylation of H4K12 in porcine oocytes increased during in vitro aging, which coincided with changing patterns of ooplasmic ROS content. Furthermore, both hydrogen peroxide (H(2)O(2)), and the mitochondrial membrane potential disrupter, carbonyl cyanide 3-chlorophenylhydrazone (CCCP), which can moderately elevate oocyte ROS content, significantly increased acetylation levels of H4K12 in porcine oocytes. It was noteworthy that acetylation in the CCCP group was decreased when ROS was counteracted by cysteine, a common antioxidant. In addition, the intracellular mRNA abundance of acetyltransferase gene HAT1 in aged and H(2)O(2) treated oocytes was higher than in M-II phase oocytes, suggesting that HAT1 was involved in this reaction. After parthenogenetic activation, a lower proportion of oocytes developed to the blastocyst stage after CCCP or H(2)O(2) treatment when compared with M-II phase oocytes (20 and 0% for CCCP and H(2)O(2) groups, respectively, versus 42% for the M-II group, P < 0.05). In conclusion, elevated levels of H4K12 acetylation were attributed to increased ooplasmic ROS content during porcine oocyte aging in vitro.

Developmental competence of porcine oocytes selected by brilliant cresyl blue and matured individually in a chemically defined culture medium

The objective of this study was to investigate the effects of oocyte selection using brilliant cresyl blue (BCB) and culture density during individual in vitro maturation (IVM) on porcine oocyte maturity and subsequent embryo development using a chemically defined medium. Cumulus-oocyte complexes (COCs) were classified as BCB-positive or BCB-negative after exposure to a BCB solution for 90 min. The classified COCs were matured in a group (15 COCs per 100-microL droplet) or individually (1 COC per 1-, 2.5-, 5-, or 10-microL droplet). Meiotic competence, intraoocyte glutathione concentration, and developmental competence after intracytoplasmic sperm injection were monitored. The BCB selected oocytes competent for nuclear and cytoplasmic maturation. Furthermore, meiotic competence for oocytes matured individually in a 5-microL droplet was superior (P<0.05) to that of oocytes matured in a 1-microL droplet. Also, the culture density in a 5-microL droplet during IVM resulted in a higher (P<0.05) rate of cleaved embryos than that in a 1-microL droplet and produced a similar rate of blastocysts compared with that of a group culture system. Conversely, BCB selection did not improve cleavage and blastocyst formation. In conclusion, it was possible to predict porcine oocytes competent for maturation using oocyte selection with BCB. Moreover, a 5-microL droplet during the individual IVM culture was most suitable for oocyte maturation and subsequent embryo development, although every culture density used in this study supported development up to the blastocyst stage.