Ultrastructural and molecular changes after oocyte vitrification protocol

Abstract

Kuwayama (2007) describe the vitrification method for oocytes and embryo cryopreservation. The aim of the present study was to compare ultrastructural and molecular changes that are present in oocytes from egg donors after vitrification in compare with fresh oocytes. Prospective and comparative cohort study. One hundred remanent oocytes from egg donation cycles were included in this study (2012-2013). Oocytes were selected from donors that had at least one previous donation cycle. Half of the oocytes were vitrified (V) by Cryotop method and the other half was evaluated in fresh (F). All oocytes were vitrified/thawed by the same operator. Ten oocytes of each group (V and F) were randomly selected for transmission electron microscopy in order to assess mitochondrial ultrastructural analysis. The rest of the oocytes were evaluated by immunocytochemistry for: DNA fragmentation (TUNEL), microtubules and metaphase plate organization (Tubulin antibodies and Hoechst). The survival rate after vitrification was 96% (CI95% 86.3-99.5). The comparison of the assessed variables are shown in table 1. The percentage of the quantified variables seems to be higher in the vitrified oocytes group, however, the differences were not statistically significant. Mitochondrial alterations, evidenced by the inner plasma membrane dilation and electron-dense appearance, are associated with the activation of apoptotic mechanisms. In both groups, most of the oocytes that showed chromosomal alignment anomalies had DNA damage at the same time.Tabled 1Fresh vs. Vitrified/Thawed oocytesFresh oocytesVit/Thawed oocytesp valueDNA fragmentation8.6%15.2%0.64Mitochondrial alterations13.3%20%0.62Metaphase plate disarrangements5.7%12.1%0.61Parthenogenetic activation0%3%0.31 Open table in a new tab Regarding the ultrastructural and molecular changes assessed in this study, no significant differences were detected between fresh or vitrified/thawed oocytes. Thus, in our experience, the vitrification technique appears to be safe, confirming the previous reports by other authors.