The effect of platelet releasate on oocytes has a detrimental impact on early mammalian embryos

Background: Blood-derived products are a growing area of therapeutic treatments for a diverse range of conditions, including hair loss, scarring, muscle injury, wounds, arthritis, and symptoms related to the menopause. Platelet-rich plasma (PRP) is one blood product being trialled on the menopausal ovary. Emerging data from ongoing trials suggest that PRP injection might promote resumption in ovarian function, and an increase in both spontaneous and assisted conception. However, knowledge of the direct cellular effects of PRP on oocytes and early embryos is limited. Hypothesis & Aim: We hypothesised that platelet releasate would influence embryo development. This study aimed to determine the extent to which the embryo is affected by releasate. We further hypothesised that oocytes (mature and dead) and cumulus cells would activate platelets. This study aimed to determine the extent to which oocytes and cumulus cells were able to induce platelet activation. Method: Oocytes were collected from abattoir-derived bovine ovarian tissue and incubated for 22 hours in in the presence of either 10% platelet releasate (derived from whole human blood) or 10% foetal calf serum (FCS) (control). A proportion of oocytes were selected for nuclear staining to establish maturation status. The majority of the oocytes were fertilised with bull sperm and allowed to develop into embryos. The number of embryos that reached the 2-cell stage by day 2 (cleavage rate) and blastocyst stage by day 9 (blastocyst rate) were recorded, as were a variety of blastocyst endpoints: blastocyst metabolism, mitochondrial function, and expression of the epigenetic marker, H3K27me3. Separately, the effect of oocytes on platelets was investigated. Mature oocytes, dead (unexpanded) oocytes, culture media, and cumulus cells were added to PRP to determine their capability to activate platelets via a series of aggregations. Results: Platelet releasate had no discernable effect on metaphase II rate in oocytes matured in vitro. There was no significant difference between the cleavage rate of platelet releasate and FCS derived oocytes, however the blastocyst rate of platelet releasate derived embryos was significantly lower than that of the FCS group. No significant difference was found in lactate release and pyruvate depletion of platelet ii releasate and FCS derived embryos. However, glucose depletion was significantly reduced in platelet releasate derived embryos in comparison to the FCS control. Oxygen consumption rate, used as a measure of mitochondrial function, did not differ significantly between the groups, and neither did H3K27me3 expression – both platelet releasate derived embryos and FCS derived embryos expressed the modification. No significant difference in platelet activation of PRP was observed between mature oocytes, dead oocytes, culture media, and cumulus cells exposure, although repeats were inconsistent. Conclusion: Oocyte exposure to platelet releasate did not lead to differences in nuclear maturation, the oocytes’ capability to be fertilised was similar between the releasate group and FCS control. The number of oocytes that were able to cleave after fertilisation was unaffected by prior supplementation with platelet releasate. However, platelet releasate derived embryos were significantly less likely to develop into blastocysts. In comparison with the FCS control, platelet releasate derived embryos that did develop into blastocysts, had a reduced consumption of glucose but a normal pyruvate consumption and lactate production, they also had a normal oxygen consumption rate and normal H3K27me3 expression. Neither mature oocytes, nor dead oocytes, nor cumulus cells, showed ability to activate platelets to a further extent than culture media. While platelet-derived factors injected into the ovary might stimulate resumption of ovarian activity, the oocytes exposed to such factors may have diminished developmental competence once they form embryos.