Effect of the exposure to methyl-ß-cyclodextrin prior to chilling or vitrification on the viability of bovine immature oocytes.

ABSTRACT

The present study aimed to evaluate the effect of methyl-ß-cyclodextrin (MßCD) as a cholesterol loader to change oocyte plasma membrane and increase its tolerance toward cryopreservation. The first and second experiments were conducted to investigate if MßCD could improve nuclear and cytoplasmic maturation after oocyte exposure to cold stress for 10 or 30 min, respectively. No differences (P>0.05) in either experiment in the metaphase II (MII) rate of oocytes exposed to MßCD and cold stress; but these oocytes presented lower maturation rates than control groups. In the second experiment, a lower percentage of oocytes showed degenerated chromatin (P<0.05) after exposure to 2mg/mL of MßCD compared to the group exposed to 0mg/mL. However, no differences among treatments were observed in cytoplasmic maturation. Groups exposed to cold stress demonstrated a lower (P<0.05) capacity for embryonic development compared to the control groups. In the third experiment immature oocytes were exposed to MßCD and then, vitrified (cryotop). After warming, we observed that the ability to reach MII and chromatin degeneration were altered (P<0.05) by MßCD. The blastocysts rate (P<0.05) on D7 was higher in the 2 mg/mL MßCD group, but an identical finding was not observed on D8 (P>0.05). Chromatin degeneration was higher in the vitrification groups. We conclude that MßCD improved nuclear maturation by reducing oocyte degeneration after cold stress or vitrification; however, more studies are required to clarify the usefulness of MßCD use in oocyte cryopreservation.