Cilostamide, a phosphodiesterase 3A inhibitor, sustains meiotic arrest of rat oocytes by modulating cyclic adenosine monophosphate level and the key regulators of maturation promoting factor.

ABSTRACT

Cilostamide, a phosphodiesterase 3A (Pde3A) inhibitor, is known to increase intraoocyte cyclic adenosine monophosphate (cAMP) level which is involved in sustaining meiotic arrest of the oocytes. To explore the mechanisms involved in the cilostamide-mediated meiotic arrest of the oocytes, the present study describes the effects of cilostamide on cAMP level and related factors involved in maturation of the oocytes at its different meiotic stages; diplotene, metaphase I (MI) and metaphase II (MII). The oocytes from these three stages were collected from rat ovary and incubated with 10 µM cilostamide for 3 h in CO2 incubator. The levels of cAMP, cyclic guanosine monophosphate (cGMP) and the key players of maintaining meiotic arrest during oocyte maturation; Emi2, Apc, Cyclin B1, and Cdk1, were analyzed in diplotene, MI and MII stages. Pde3A was found to be expressed at all three stages but with the lowest level in MI oocyte. As compared to the control sets, the cAMP concentration was found to be highest in MII whereas cGMP was highest in the diplotene stage of cilostamide-treated group. The treated group showed declined reactive oxygen species level as compared with the control counterparts. Relatively increased levels of the Emi2, Cyclin B1, and phosphorylated thr161 of Cdk1 versus declined levels of phosphorylated thr14/tyr15 of Cdk1 in diplotene and MII stage oocytes are known to be involved in maintaining meiotic arrest and all these factors were found to undergo similar pattern of change due to the treatment with cilostamide. The findings thus suggest that cilostamide treatment promotes meiotic arrest by Pde3A inhibition led increase of both cAMP and cGMP level vis-a-vis modulation of the related regulatory factors such as Emi2, CyclinB1, and phosphorylated status of Cdk1 in diplotene and MII stage oocytes. Such a mechanism of meiotic arrest could allow the oocyte to prepare itself for meiotic maturation and thereby to improve oocyte quality.