Hydroxypropyl cellulose as a macromolecular supplement for cryopreservation by vitrification of bovine ooytes and blastocysts and human oocytes

Abstract

Vitrification is an alternative cryopreservation in human ART resulting in significantly improved survival of oocytes and embryos, and excellent clinical outcomes. To reduce possible risk of viral contamination resulting from media containing biological macromolecules, government regulators in some countries have stipulated that non-serum substitutes must be used. The purpose of this study was to test the efficacy of hydroxypropyl cellulose (HPC), for vitrification of oocytes and embryos. Bovine oocytes, blastocysts and human oocytes were vitrified with HPC, Synthetic Serum Substitute (SSS) or no added macromolecule, and post-thaw survival and in vitro development were tabulated. Three experiments were conducted using bovine IVM oocytes, blastocysts, and human oocytes with informed consent. In each of two experiments, three groups of 90 bovine oocytes (Exp. 1) and 90 blastocysts (Exp. 2) were vitrified with the Cryotop method. In Group 1, the vitrification medium was supplemented with 0.6 mg/ml HPC, and in Group 2, with 1% SSS; Group 3 contained no added macromolecule. In Exp. 3, 60 human oocytes were vitrified with or without HPC. After vitrification, survival was based on development into blastocysts of oocytes subjected to IVF and IVC. Blastocysts were classified as survivors if they reformed a blastocoelic cavity after culture. In Exp. 1, the survival rates of oocytes in Groups 1, 2 and 3 were 100, 100 and 87%. The two-cell and blastocyst rates in the three groups were 63, 67 and 37%, and 20, 17 and 7%. In Exp. 2, the survival rates of bovine blastocysts of the groups were 100, 100 and 93%. In Exp. 3, all 30 human oocytes vitrified in HPC exhibited survived vitrification (100%) but not in non-added group (27/30, 90%). High morphological and functional survival of bovine oocytes vitrified with HPC, as well as morphological survival of bovine blastocysts and human oocytes suggest that HPC may be a safe and effective supplement for vitrification in human ART.