Date Published: October 17, 2012
Publisher: Public Library of Science
Author(s): Rok Devjak, Klementina Fon Tacer, Peter Juvan, Irma Virant Klun, Damjana Rozman, Eda Vrtačnik Bokal, Jason Glenn Knott. http://doi.org/10.1371/journal.pone.0047106
In in vitro fertilization (IVF) cycles controlled ovarian hyperstimulation (COH) is established by gonadotropins in combination with gonadotropin-releasing hormone (GnRH) agonists or antagonists, to prevent premature luteinizing hormone (LH) surge. The aim of our study was to improve the understanding of gene expression profile of cumulus cells (CC) in terms of ovarian stimulation protocol and oocyte maturity. We applied Affymetrix gene expression profiling in CC of oocytes at different maturation stages using either GnRH agonists or GnRH antagonists. Two analyses were performed: the first involved CC of immature metaphase I (MI) and mature metaphase II (MII) oocytes where 359 genes were differentially expressed, and the second involved the two GnRH analogues where no differentially expressed genes were observed at the entire transcriptome level. A further analysis of 359 differentially genes was performed, focusing on anti-Müllerian hormone receptor 2 (AMHR2), follicle stimulating hormone receptor (FSHR), vascular endothelial growth factor C (VEGFC) and serine protease inhibitor E2 (SERPINE2). Among other differentially expressed genes we observed a marked number of new genes connected to cell adhesion and neurotransmitters such as dopamine, glycine and γ-Aminobutyric acid (GABA). No differential expression in CC between the two GnRH analogues supports the findings of clinical studies where no significant difference in live birth rates between both GnRH analogues has been proven.
In vitro fertilization (IVF) has become one of the most common treatments of infertility. In an IVF cycle, ovarian stimulation is established by gonadotropins in combination with gonadotropin-releasing hormone (GnRH) analogues, i.e. GnRH agonists or GnRH antagonists. GnRH analogues are used to prevent premature luteinizing hormone (LH) surge during ovarian stimulation, which improves oocyte yield and increases pregnancy rate . In the 1980s a long protocol of GnRH agonists was used starting in the midluteal phase of the preceding cycle . In the 1990s, GnRH antagonists were introduced into clinical practice and proved to be safe and effective , , . In contrast to GnRH agonists, GnRH antagonists cause immediate and rapid gonadotropin suppression without an initial period of gonadotropin hypersecretion. GnRH antagonists have several advantageous effects over GnRH agonists , , of which the most important is having fewer follicles and lower oestradiol level on the day of human chorionic gonadotropin (hCG) application  leading to a lower incidence of ovarian hyperstimulation syndrome (OHSS) , a serious complication of assisted reproductive therapy. Further, with a shorter period of application GnRH antagonists are friendlier to patients. Earlier studies have shown that GnRH antagonists result in lower pregnancy and delivery rates compared to GnRH agonists , whereas recent meta analyses show that the difference between them is not significant , .
As patients were randomly assigned to either the GnRH agonist or GnRH antagonist group, we first assessed the baseline characteristics of the two treatment groups. The groups did not differ in age, BMI, pregnancy rate and delivery rate (Table 2). The number of retrieved oocytes was higher in the GnRH agonist group at a borderline significance level (p = 0.08). The proportions of degenerated, MI, MII, MII-NF and MII-BL oocytes were similar in both groups. The fertilization rate was by 30% higher in the GnRH agonist group (0.65 vs. 0.5; p = 0.06), which almost reached statistical significance.
To our knowledge, this is the first prospective study comparing the effects of two different GnRH analogues and maturity stage of the oocyte at the level of gene expression in CC. Considering oocyte maturity we observed 359 differentially expressed genes between CC MI and CC MII. Using either GnRH agonists or GnRH antagonists, we have not observed differentially expressed genes. Moreover, we have not observed differentially expressed genes at any level of maturity stage of the oocyte (MI, MII-NF and MII-BL) between the two GnRH analogues used. Since only MII oocytes are capable of fertilization, our results support and supplement the clinical studies on GnRH analogues ,  by showing that no significant differences between CC of MII oocytes exist at the transcriptome level. However, the GnRH antagonist protocol is more patient friendly because of shorter stimulation time, and is also considered safer because of a lower incidence of OHSS.