STRONTIUM-INDUCED OOCYTE ACTIVATION IN NON-MALE FACTOR ICSI CYCLES AND ADVANCED MATERNAL AGE

Abstract

Abnormal calcium (Ca2+) oscillations in aged oocytes may adversely affect fertilization and subsequent embryonic development. Strontium (Sr2+) induces Ca2+ oscillations via the InsP3 receptor and PLCζ activation. However, unlike the sperm factor and calcium ionophore induced Ca2+ oscillations, Sr2+ does not require putative maternal machinery. We investigated the role of Sr2+ for artificial oocyte activation (AOA) in aged oocytes among non-male factor infertility couples undergoing assisted reproduction technology (ART). Retrospective cohort study This study included infertility couples with non-male factor infertility and advanced maternal age (40 years and over) with at least one previous non-AOA failed ICSI cycle. Ovarian stimulation and laboratory protocols were similar between non-AOA and the Sr2+-AOA, except for the use of AOA. In the study group (Sr2+-AOA cycles) all injected oocytes were stimulated using 10 mM SrCl (Sigma-Aldrich, St Louis, MO, USA) for 60 min, immediately after ICSI. The zygotes were cultured up to the blastocyst stage, and the resulting embryos were subjected to trophectoderm biopsy for preimplantation genetic testing for aneuploidies using next-generation sequencing. Comparisons between Sr2+-AOA and previous non-AOA cycles were performed using the paired Student’s t-test. The primary endpoint was 2PN fertilization rates and the secondary endpoints were embryonic outcomes. Statistical analyses also included generalized linear and binary logistic regression models. Between September 2019 and March 2020, we performed 18 Sr2+-AOA cycles in 13 couples who have undergone an average of 1.9 previous failed ICSI without AOA (range 1–6 cycles). The 2PN fertilization rate after Sr2+-mediated AOA was significantly higher than that of the routine non-AOA ICSI procedure (81.0% vs. 67.1%, p=0.04). Adjusted linear regression models showed that fertilization rates were significantly and independently associated with Sr2+-AOA (β=19.85, p=0.007). Sr2+-mediated AOA had no negative impact on blastocyst formation rate (30.9% vs. 34.5%, p=0.67) and on the likelihood of having at least one euploid blastocyst for transfer (OR=1.46, 95% IC: 0.26-8.27). Age-related oocyte activation defects might adversely impact fertilization rates by ICSI, thus affecting the number of resulting embryos. Our results suggest that Sr2+-mediated AOA improves fertilization rates in aged oocytes, probably related to a sperm-independent activation. Our data corroborate previous studies on the safe utilization of Sr2+ on gametes and embryos cultured to the blastocyst stage. However, large-scale studies are warranted to evaluate the effectiveness of Sr2+-mediated AOA on pregnancy outcomes.