|
G Coticchio, MA Bonu, E Sereni, R Sciajno, A Borini
Tecnobios Procreazione, Via Dante 15, 40125 Bologna, Italy
The mammalian oocyte is especially sensitive to cryopreservation. Because of its size and physiology, it can easily undergo cell death or sub-lethal damage as a consequence of intracellular ice formation, increase in the concentration of solutes, a phenomenon referred to as solution effect, and other undesired effects occurring during the conversion of extracellular water into ice. This has generated the belief that oocyte storage cannot be achieved with the necessary efficiency and safety. However, many of the concerns raised by oocyte freezing are in fact the result of unproven hypotheses or observations conducted under conditions not always appropriate. For instance, to some extent spindle organization can in effect undergo damage under certain freezing conditions, but in fact with some protocols such a problem appears to be circumvented. The suggestion that cryopreservation induces cortical granules discharge and zona pellucida hardening remains controversial, somehow questioning the routine use of sperm microinjection to achieve fertilization. Damage of mouse oocytes caused by the solution effect is well documented, but in the human there is no solid evidence that modifications of freezing mixtures aiming at preventing this problem provide an actual advantage. The hope of developing oocyte cryopreservation as a major IVF treatment option is becoming increasingly realistic, but major efforts are still required to clarify the authentic implications of oocyte cryopreservation at the cellular level and identify freezing conditions compatible with the preservation of viability and developmental ability.
Keywords: calcium, cryopreservation, cryoprotectant, intracellular ice formation, oocyte, solute concentration
Source: Reproductive Biomedicine Online
|
