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

The present study aimed to evaluate the effect of methyl-beta-cyclodextrin (M beta CD) 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 M beta CD 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 M beta CD 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 2 mg/mL of M beta CD compared to the group exposed to 0 mg/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 M beta CD and then, vitrified (cryotop). After warming, we observed that the ability to reach MII and chromatin degeneration were altered (P < 0.05) by M beta CD. The blastocysts rate (P < 0.05) on D7 was higher in the 2 mg/mL M beta CD group, but an identical finding was not observed on D8 (P > 0.05). Chromatin degeneration was higher in the vitrification groups. We conclude that M beta CD improved nuclear maturation by reducing oocyte degeneration after cold stress or vitrification; however, more studies are required to clarify the usefulness of M beta CD use in oocyte cryopreservation. (C) 2012 Elsevier Inc. All rights reserved.