Effect of slow freeze versus vitrification on the oocyte: an animal model

Capsule:
This study adds to the increasing body of evidence that cryopreservation protocols vary in their impact upon the oocyte.

Authors:
Weihong Hu, M.D., Ph.D., Dennis Marchesi, Ph.D., Jie Qiao, M.D., Ph.D., Huai L. Feng, Ph.D., H.C.L.D., E.L.D.

Volume 98, Issue 3, Pages 752-760.e3, September 2012

Abstract:

Objective:
To determine whether there is a deleterious effect on dynamic events in the nucleus and cytoplasm of oocytes by using different cryopreservation protocols in an animal model.

Design:
Prospective study

Setting:
University hospitals

Intervention(s):
Immunostaining and confocal laser scanning microscope techniques were used.

Main outcome measure(s):
The spindle and chromosomal configurations, as well as dynamic changes of the cortical granules (CGs) and mitochondria in different cryo groups.

Result(s):
After thawing/warming of bovine oocytes, CGs became more dispersed in the cytoplasm, particularly in the DMSO group. A significant reduction in normal spindle and chromosomal configurations was observed in all three cryo-groups, particularly in the PROH group, when compared with the Fresh group. Global DNA methylation levels were significantly reduced in the Slow and DMSO groups, as compared to the Fresh grouphowever, methylation levels were significantly increased in the PROH group. The proportion of severely apoptotic oocytes was dramatically increased in all three cryo-groups, compared with Fresh group.

Conclusion(s):
Overall, results demonstrate that using DMSO as the cryoprotectant is better in preserving the cellular and nuclear integrity of the oocyte. The PROH method makes the oocyte more vulnerable to increased DNA methylation, which may be associated with imprinting gene alteration. This study adds to the increasing body of evidence that cryopreservation protocols vary in their impact upon the oocyte.

  • Ana Cobo

    I really enjoyed this work. Studies evaluating the effects of
    cryopreservation at the subcellular level are very welcome as
    they provide very strong evidence about the impact of different methods on cell physiology. The authors conclude that
    DMSO is better to preserve the nuclear and cell integrity. However, just as the cryoprotectant used is a key to success, the
    cryopreservation method is also a determining factor. In this sense, the vitrification method used by the authors has proved inefficient in survival and clinical outcome. The most efficient vitrification methods are those that use minimum volume.
    Both survival and clinical results are comparable to those obtained with fresh oocytes, so I would expect a correlation between the impact of vitrification at the subcellular level and the clinic. So probably the authors’ conclusions would be different using a different methodology to vitrify. Another interesting aspect is that authors vitrified the oocytes partially denuded. Could this affect the diffusion of permeable cryoprotectant and dehydration-rehydration processes?

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