Ovarian function and response to gonadotropins after prolonged perfusion of whole ewe ovaries in a bioreactor

Fertility preservation for pre-pubertal girls undergoing gonadotoxic cancer treatments and women with systemic cancers at high risk for ovarian metastasis remains limited. Current options, such as ovarian cortex transplantation, risk reintroducing malignant cells. This study presents a novel approach focusing on ex vivo folliculogenesis and mature oocyte retrieval for cryopreservation, mitigating this risk.

This experimental study optimized an ex vivo ovarian perfusion system in sheep, refining gonadotropin stimulation to yield mature oocytes. Eleven ovaries were divided into two experimental subgroups: Group 1 (n = 5) and Group 2 (n = 6). Both groups were perfused in a bioreactor for 4 to 8 days under distinct perfusion protocols, differing in gonadotropin administration overnight-Group 1 did not receive overnight gonadotropin stimulation, whereas Group 2 received basal gonadotropin stimulation overnight. Assessments included follicular proliferation, oocyte maturity, apoptosis, ovarian function-related gene expression, and the levels of hormones, metabolites, and electrolytes in the culture medium, compared across subgroups.

The protocol without overnight ovarian stimulation yielded mature MII oocytes, despite fewer secondary follicles and overexpression of the pro-apoptotic BAX gene. Conversely, ovaries with overnight stimulation yielded mostly GV-MI oocytes and exhibited reduced secondary follicle proliferation and higher HIF1A expression. Hormone levels, metabolites, and electrolytes remained stable across groups and time.

This study is the first to report the successful harvesting of MII oocytes following extended ex vivo perfusion of intact ewe ovaries, highlighting the potential of the perfusion model to support advanced follicular development. Further investigations are warranted to elucidate underlying mechanisms and refine protocol efficiency.