Inhibition of Rho-associated protein kinase increases the ratio of formation of blastocysts from single human blastomeres

Y-27632 is a specific inhibitor of Rho-associated protein kinases (ROCKs), which are downstream effectors of Rho GTPase. The present study aimed to determine the effect of the specific ROCK inhibitor, Y-27632, on fresh human embryos and on single blastomeres obtained from discarded human embryos. A total of 784 poor-quality embryos were included, of which 526 were allocated to blastocyst culture directly and the remaining 258 were allocated to blastomere isolation. Embryos and single blastomeres were cultured either with, or without, Y-27632. Embryonic development was observed and recorded daily from day 5 onwards. Y-27632 did not affect the ratio of blastocyst formation or the quality of the human embryos. The duration of blastocyst formation was compared between the two groups in the embryo culture. On day 5, the blastocyst formation ratio in the experimental group was 11.4% (26/228), which was significantly (P=0.015) lower than the corresponding rate (19.7%; 44/223) in the control group. Survival analysis of the blastocyst formation duration showed that the median formation duration in the experimental group was significantly higher than that of the control group. The present study also obtained 1,192 blastomeres from 258 discarded day 3 embryos, and sibling blastomeres of similar sizes were equally allocated to experimental and control groups (n=596 in each). Treatment with Y-27632 increased the blastocyst formation ratio of human individual blastomeres, with 82 blastocysts of 596 blastomeres (13.8%), and 51 blastocysts of 596 blastomeres (8.6%) formed in the presence and absence of Y-27632, respectively (P=0.004). Compared with the control group, the mRNA and protein expression levels of E-cadherin in the blastocysts from blastomeres were enhanced by Y-27632 (P=0.022). In conclusion, the present study demonstrated that Y-27632 has different effects on the cleavage-stage of embryos and single blastomeres. Y-27632 increases the ratio of formation of blastocysts from single human blastomeres, but inhibits the direct formation of blastocysts from discarded human embryos.