Oocyte cryopreservation and in vitro culture affect calcium signalling during human fertilization.

STUDY QUESTION: What are the precise patterns of calcium oscillations during the fertilization of human oocytes matured either in vivo or in vitro or aged in vitro and what is the effect of cryopreservation? SUMMARY ANSWER: Human oocytes matured in vivo exhibit a specific pattern of calcium oscillations, which is affected by in vitro maturation, in vitro ageing and cryopreservation. WHAT IS KNOWN ALREADY: Oscillations in cytoplasmic calcium concentration are crucial for oocyte activation and further embryonic development. While several studies have described in detail the calcium oscillation pattern during fertilization in animal models, studies with human oocytes are scarce. STUDY DESIGN, SIZE, DURATION: This was a laboratory-based study using human MII oocytes matured in vivo or in vitro either fresh or after cryopreservation with slow freezing or vitrification. Altogether, 205 human oocytes were included in the analysis. PARTICIPANTS/MATERIALS, SETTING, METHODS: In vivo and in vitro matured human oocytes were used for this research either fresh or following vitrification/warming (V/W) and slow freezing/thawing (F/T). Human oocytes were obtained following written informed consent from patients undergoing ovarian hyperstimulation. For the calcium pattern analysis, oocytes were loaded with the ratiometric calcium indicator fluorescent dye Fura-2. Following ICSI using sperm from a single donor, intracellular calcium was measured for 16 h at 37°C under 6% CO(2). The calcium oscillation parameters were calculated for all intact oocytes that showed calcium oscillations and were analyzed using the Mann-Whitney U-test. MAIN RESULTS AND THE ROLE OF CHANCE: Human in vivo MII oocytes display a specific pattern of calcium oscillations following ICSI. This pattern is significantly affected by in vitro ageing, with the calcium oscillations occurring over a longer period of time and with a lower frequency, shorter duration and higher amplitude (P < 0.05). In vitro matured oocytes from the GV and MI stage exhibit a different pattern of calcium oscillations with calcium transients being of lower frequency and shorter duration compared with in vivo matured MII. In MI oocytes that reached the MII stage within 3 h the calcium oscillations additionally appear over a longer period of time (P < 0.05). In vivo MII oocytes show a different calcium oscillation pattern following V/W with calcium oscillations occurring over a longer period of time, with a higher amplitude and a lower frequency (P < 0.05). In vitro matured oocytes, either from the GV or the MI stage, also display an altered pattern of calcium oscillations after V/W and the parameters that were similarly affected in all these oocyte groups are the frequency and the amplitude of the calcium transients. Slow freezing/thawing differentially affects the calcium oscillation pattern of in vitro matured and in vitro aged oocytes. LIMITATIONS, REASONS FOR CAUTION: The relationship between a specific pattern of calcium oscillations and subsequent human embryonic development could not be evaluated since the calcium indicator used and the high-intensity excitation light impair development. Furthermore, all oocytes were derived from stimulated cycles and immature oocytes were denuded prior to in vitro maturation. WIDER IMPLICATIONS OF THE FINDINGS: Our data show for the first time how calcium signalling during human fertilization is affected by oocyte in vitro maturation, in vitro ageing as well as V/W and slow freezing/thawing. The analysis of calcium oscillations could be used as an oocyte quality indicator to evaluate in vitro culture and cryopreservation techniques of human oocytes. STUDY FUNDING/COMPETING INTEREST(S): This work was supported by a clinical research mandate from the Flemish Foundation of Scientific Research (FWO-Vlaanderen, FWO09/ASP/063) to F.V.M, a fundamental clinical research mandate from the FWO-Vlaanderen (FWO05/FKM/001) to P.D.S and a Ghent University grant (KAN-BOF E/01321/01) to B.H. The authors have no conflict of interest to declare.

Comparison of pre- and post-implantation development following the application of three artificial activating stimuli in a mouse model with round-headed sperm cells deficient for oocyte activation.

STUDY QUESTION: Does the application of three different artificial activating stimuli lead to a difference in pre- and post-implantation embryo development in the wobbler mouse, a mouse model with oocyte activation deficient round-headed sperm cells similar to human globozoospermia? SUMMARY ANSWER: No gross differences were found between strontium chloride, electrical pulses or ionomycin with respect to the pre- and post-implantation development in the wobbler mouse. WHAT IS KNOWN ALREADY: Fertilization failure following intra-cytoplasmic sperm injection (ICSI) occurs in 1-3% of the ICSI cycles in human assisted reproduction technology (ART) and has been successfully overcome by different artificial activating stimuli. No comparison has been made yet in terms of their efficiency and safety. STUDY DESIGN, SIZE, DURATION: Calcium release and embryo development were compared between oocytes fertilized by wobbler and wild-type (WT) sperm following ICSI with or without three different artificial activating agents. Preimplantation development was assessed on 70 injected oocytes on average per group. On average, 10 foster mothers were used per activating group to compare post-implantation development. PARTICIPANTS/MATERIALS, SETTING, METHODS: We used the wobbler mouse model that possesses oocyte activation deficient round-headed sperm cells. First, the calcium release following ICSI using wobbler sperm was compared with that of WT sperm. Outcome measures were the percentage of oocytes that showed calcium release and their mean amount of calcium rises. Secondly, the pre- and post-implantation development was assessed following ICSI with wobbler sperm plus artificial oocyte activation using either: (i) strontium chloride (Wob-Sr), (ii) electrical pulses (Wob-E) or (iii) ionomycin (Wob-I). Outcome measures were the activation, cleavage and blastocyst rates and the assessment of blastocyst quality by differential staining. Following mouse embryo transfer, pregnancy and birth rates as well as mean litter sizes were examined. Finally, pups were followed up until 8 weeks of age and then mated with fertile controls to assess their fertility. MAIN RESULTS AND THE ROLE OF CHANCE: The percentage of oocytes showing calcium rises as well as the number of calcium rises per oscillating oocyte were significantly lower in the wobbler group when compared with the WT group (9.3 versus 96% and 2.1 calcium rises versus 31 calcium rises) (P < 0.001). The fertilization rate was significantly lower in the wobbler group (11.4%) when compared with the WT group (92.1%) and the artificial activation groups (strontium chloride: 99%, electrical pulses: 99% and ionomycin: 81%, respectively) (P < 0.001). Post-implantation development did not differ significantly between the WT and artificial activation groups, with pregnancy rates in favor of strontium chloride and electrical pulses. The weight of the male pups did not differ between the study groups, whereas the weight of the female pups originating from Wob-Sr embryos was significantly lower at weeks 2, 3 and 4 when compared with female pups originating from WT embryos. However, the latter difference was not observed at later time points, nor in the other artificial activating groups. All offspring mated successfully with fertile controls. LIMITATIONS, REASONS FOR CAUTION: Results in animal models should be extrapolated with caution to a subfertile human population. Also, ionomycin is currently the most widely used artificial oocyte activating agent in human ART. WIDER IMPLICATIONS OF THE FINDINGS: The low frequency of observed calcium rises and the low activation rate make the wobbler mouse a highly suitable model to study oocyte activation deficiency. Strontium chloride and electrical pulses were more efficient means to restore fertilization rates and to support pre- and post-implantation embryonic development than ionomycin. STUDY FUNDING/COMPETING INTEREST(S): This work was supported by the Flemish foundation of Scientific Research (FWO-Vlaanderen) (aspirant clinical research mandate to F.V.M., fundamental clinical research mandate to P.D.S.); and Ghent University grant (KAN-BOF E/01321/01 to B.H.). The authors have no competing interests to declare.

Diagnostic and prognostic value of calcium oscillatory pattern analysis for patients with ICSI fertilization failure.

STUDY QUESTION: Does calcium oscillatory pattern analysis following heterologous intra-cytoplasmic sperm injection (ICSI) of human sperm into mouse oocytes lead to diagnostic and prognostic information for patients suffering from ICSI fertilization failure? SUMMARY ANSWER: We found that calcium oscillatory pattern analysis following heterologous ICSI has the strength to reveal, for the individual patient, the most probable underlying reason for low or failed fertilization after conventional ICSI. WHAT IS KNOWN ALREADY: Fertilization failure occurs in 1-3% of the couples undergoing conventional ICSI, for whom the mouse oocyte activation test (MOAT) or a similar heterologous ICSI model is the only diagnostic test available to evaluate the oocyte-activating capacity of human sperm cells. The MOAT classifies the patients into three groups: a low (group 1), an intermediate (group 2) and a high (group 3) activating group. In MOAT group 1 patients, a sperm-related deficiency is likely to be the cause of previous fertilization failures, while in MOAT group 3 patients a sperm-related deficiency can most probably be refuted. For MOAT group 2 patients, the result is called inconclusive; hence, both sperm and oocyte deficiencies may still contribute to the previous ICSI fertilization failure. STUDY DESIGN, SIZE, DURATION: The calcium-releasing ability of sperm from 26 MOAT patients with a history of zero or low fertilization following conventional ICSI was compared with the calcium-releasing ability of sperm from 4 control patients, with proven oocyte activation potential. Per case an average of 19 mouse oocytes were injected. Calcium imaging started within 5-10 min after ICSI and continued for 2 h. PARTICIPANTS/MATERIALS, SETTING, METHODS: Human sperm were demembranated with 0.02% lysolecithin for 1 min immediately before heterologous piezo-driven ICSI. For calcium imaging, metaphase II oocytes from B6D2/F1 mice were loaded with fura-2 acetoxymethyl ester. The calcium oscillatory patterns following heterologous ICSI were scored per oocyte and per patient individually based on the presence of calcium spikes and their frequency and amplitude. MAIN RESULTS AND THE ROLE OF CHANCE: For patients with low or high MOAT activating capacity (MOAT group 1 or 3, respectively), calcium analysis confirmed the MOAT result. For patients with a former inconclusive intermediate MOAT activating capacity result (MOAT group 2), no or strongly dissimilar calcium oscillatory patterns were seen, with significantly lower amplitude and frequency compared with control sperm. When the product of the amplitude and the frequency of the calcium traces was compared between the groups, MOAT group 1 and 2 cases differed significantly from MOAT group 3 cases and the control sperm (P < 0.01). LIMITATIONS, REASONS FOR CAUTION: The results of the calcium analysis in mouse oocytes should not be directly extrapolated to human oocytes, since it is well known that human spermatozoa exhibit a greater activating potency in mouse oocytes compared with mouse spermatozoa. Furthermore, not much is known yet about the influence of aberrant calcium oscillatory patterns, such as found in MOAT group 2 patients, on pre- and post-implantation embryo development in the human. WIDER IMPLICATIONS OF THE FINDINGS: Based on the current calcium oscillatory pattern analysis, we found that the product of calcium spike amplitude with its frequency allowed us to create a new threshold value, which can assist in confirming or refuting, on a single patient base, a sperm-borne activation deficiency. The latter is especially interesting for patients with a former intermediate inconclusive MOAT result (MOAT group 2 patients), for whom calcium oscillatory pattern analysis should be considered. STUDY FUNDING/COMPETING INTEREST(S): F.V.M. is holder of an aspirant clinical research mandate by the Flemish foundation of Scientific Research (FWO-Vlaanderen). B.H. is supported by a Ghent University grant (KAN-BOF E/01321/01). P.D.S. is holder of a fundamental clinical research mandate by the same Flemish foundation of Scientific Research (FWO-Vlaanderen).

Assisted oocyte activation is not beneficial for all patients with a suspected oocyte-related activation deficiency.

BACKGROUND: Despite the success of ICSI, total fertilization failure (TFF) still occurs in 1-3% of all ICSI cycles. ICSI followed by assisted oocyte activation (ICSI-AOA) can restore fertilization, most efficiently in cases of sperm-related fertilization deficiency. The indication for ICSI-AOA is less obvious when the capacity of the sperm to activate oocytes is considered normal, as proved by a heterologous ICSI model, such as the mouse oocyte activation test (MOAT). In this study, we verified whether ICSI-AOA is beneficial for patients in whom an oocyte-related activation deficiency is suspected. METHODS: A prospective study was conducted including patients presenting with a history of TFF or low fertilization (LF) following conventional ICSI in our centre (in-house cases, n= 2) or elsewhere (out-house cases, n= 12). In all cases a sperm deficiency was refuted by the MOAT. In a next treatment cycle, ICSI-AOA was performed on half of the sibling metaphase II oocytes and conventional ICSI on the rest ('split ICSI-AOA cycle'). The main outcome parameters were fertilization, pregnancy and live birth rates. RESULTS: Overall, ICSI-AOA was able to improve fertilization rates in couples with a suspected oocyte-related fertilization problem, with a mean fertilization rate of 74.2% following ICSI-AOA compared with 43.5% following conventional ICSI (P< 0.001). Cumulative pregnancy rate and live birth rate per cycle were 35.7 and 14.3%, respectively. Considering the out-house patients only, fertilization rates with ICSI-AOA were higher in couples with previous TFF than with conventional ICSI (P< 0.001). Interestingly, for out-house patients who had experienced low, but not zero, fertilization elsewhere, ICSI-AOA could not enhance the fertilization rate. For the two in-house patients, both suffering from previous LF following conventional ICSI, the ICSI-AOA procedure enhanced the mean fertilization rate (25 versus 75%, respectively). CONCLUSIONS: For patients with a suspected oocyte-related activation deficiency, as diagnosed by a heterologuous ICSI model, the indication for ICSI-AOA still remains debatable. Our data show that ICSI-AOA is very efficient in patients with a suspected oocyte-related activation deficiency and previous TFF after conventional ICSI. In contrast, when there was a history of LF in another centre, one should be careful and test the efficiency of ICSI-AOA on half of the sibling oocytes, because ICSI-AOA is not always beneficial for patients with previous LF and a suspected oocyte-related activation deficiency. For these patients, a split ICSI-AOA cycle using sibling oocytes can help to distinguish between a molecular oocyte-related activation deficiency and a previous technical or other biological failure. Moreover, this split ICSI-AOA strategy enables us to set the appropriate strategy for future treatment cycles. Further research with larger groups of patients is now required.