Human Reproduction, Vol. 16, No. 8, 1778-1779,
August 2001
© 2001 European Society of Human Reproduction and Embryology
Letters to the editor |
Vitrification of embryos and oocytes with 5.5 mol/l ethylene glycol and 1.0 mol/l sucrose
Department of Obstetrics and Gynecology, National Taiwan University Hospital, No. 7, Chung-Shan South Road, Taipei, Taiwan
Dear Sir,
In the article of `Open pulled straws (OPS) for vitrification of mature mouse oocytes preserve patterns of meiotic spindles and chromosomes better than conventional straws' (Chen et al., 2000b
), we used the vitrification solution of 5.5 mol/l ethylene glycol and 1.0 mol/l sucrose (EG5.5) and cited the appropriate reference (Martino et al.1996). The recently developed OPS (Vajta et al.1998) achieving more rapid cooling and warming rates may alleviate the chilling injury of meiotic spindles of oocytes. In addition, OPS expedite the procedures for loading and releasing oocytes that can reduce the exposure of a highly concentrated solution. In our previous study, we employed EG5.5 for vitrification of mature human oocytes using conventional straws, and achieved a high morphological survival rate, fertilization, and early cleavage of vitrified oocytes (Chen et al.2000a).
Martino et al. (1996) vitrified bovine oocytes using EG5.5 with a support of the microscope copper grid (Martino et al.1996). With rapid passage of the dangerous temperature zone, the chill-sensitive bovine oocytes reached better growth potential to blastocysts, compared with those using a conventional straw. However, they did not point out the originality of EG5.5. Hong et al. (1999) attained live births from vitrified human oocytes with reference to the above method (Martino et al.1996; Hong et al.1999).
Recently, we received the information that the original formulation of EG5.5—called VS14—was devised by Ali and Shelton (1993). Rall and Fahy (1985) first successfully vitrified mouse embryos with the medium consisting of dimethylsulphoxide (DMSO), acetamide and propylene glycol and polyethylene glycol, which required a low temperature of 4°C during the equilibration (Rall and Fahy, 1985). Subsequent investigators made a significant improvement in adjustment of cryoprotectants for reducing toxicity that permitted the equilibration steps performed at the room temperature or 35°C (Kasai et al.1990; Ali and Shelton, 1993; Ishimori et al.1993; Vajta et al.1998; Park et al.2000; Yokota et al.2000).
Ethylene glycol, with the characteristics of low toxicity and rapid permeation of the cell, became an important component of vitrification solutions. Some authors used sucrose as a non-permeating agent to facilitate dehydration and vitrification that further reduced the toxicity of ethylene glycol by decreasing its concentration (Ali and Shelton et al.1993). Some authors mixed other permeating agents, such as DMSO, to reduce the concentration of single cryoprotectant (Ishimori et al.1993; Vajta et al.1998; Yokota et al.2000). The other investigators added a macromolecule, such as Ficoll, in a vitrification solution that was thought to stabilize the glass formation and form a protective coating around embryos (Kasai et al.1990; Park et al.2000). The superiority among these vitrification solutions is not clear and may merit further studies.
Ali and Shelton developed VS14 (EG5.5) after systematic examinations of various cryoprotectants and combinations, and demonstrated it to be excellent for the vitrification of mouse and sheep embryos (Ali and Shelton, 1993). Because of its low toxicity and high efficiency, many researchers have applied VS14 (EG5.5) for vitrification of oocytes and embryos. We agree that Ali and Shelton have made a great contribution to the original development of VS14 (EG5.5). We have changed the quotation to Ali and Shelton (1993) in our next manuscripts.
Notes
1 To whom correspondence should be addressed. E-mail: ysyang{at}ha.mc.ntu.edu.tw 
References
Ali, J. and Shelton, J.N. (1993) Design of vitrification solutions for the cryopreservation of embryos. J. Reprod. Fertil., 99, 471–477.
Chen, S.U., Lien, Y.L., Chao, K.H. et al. (2000a) Cryopreservation of mature human oocytes by vitrification with ethylene glycol in straws. Fertil. Steril., 74, 804–808.[Web of Science][Medline]
Chen, S.U., Lien, Y.L., Chen, H.F. et al. (2000b) Open pulled straws for vitrification of mature mouse oocytes preserve patterns of meiotic spindles and chromosomes better than conventional straws. Hum. Reprod., 12, 2598–2603.
Hong, S.W., Chung, H.M., Lim, J.M. et al. (1999) Improved human oocyte development after vitrification: a comparison of thawing methods. Fertil. Steril., 72, 142–146.[Web of Science][Medline]
Ishimori, H., Saeki, K., Inai, M. et al. (1993) Vitrification of bovine embryos in a mixture of ethylene glycol and dimethyl sulfoxide. Theriogenolgy, 40, 427–433.
Kasai, M., Komi, J.H., Takakamo, A. et al. (1990) A simple method for mouse embryo cryopreservation in a low toxicity vitrification solution, without appreciable loss of viability. J. Reprod. Fertil., 89, 91–97.
Martino, A., Songsasen, N. and Leibo, S.P. (1996) Development into blastocysts of bovine oocytes cryopreserved by ultra-rapid cooling. Biol. Reprod., 54, 1059–1069.[Abstract]
Park, S.P., Kim, E.Y., Oh, J.H. et al. (2000) Ultra-rapid freezing of human multipronuclear zygotes using electron microscope grids. Hum. Reprod., 15, 1787–1790.
Rall, W.F. and Fahy, G.M. (1985) Ice-free cryopreservation of mouse embryos at –196 °C by vitrification. Nature, 313, 573–575.[Medline]
Vajta, G., Holm, P., Kuwayama, M. et al. (1998) Open pulled straw (OPS) vitrification: a new way to reduce cryoinjuries of bovine ova and embryos. Mol. Reprod. Dev., 51, 53–58.[Web of Science][Medline]
Yokota, Y., Sato, S., Yokota, M. et al. (2000) Successful pregnancy following blastocyst vitrification: case report. Hum. Reprod., 15, 1802–1803.
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