Shin-ya Kawakami*, Chihiro Nansai and Sueo Niimura
Inhibitors of the enzyme 20α-HSD (AKR1C18) are required to investigate AKR1C18 activity that occurs with meiotic resumption and progression in mouse oocytes. However, currently, no effective inhibitors of AKR1C18 are available. Therefore, we treated mouse oocytes with 3-bromo-5-phenylsalicylic acid (5-PBSA), an inhibitor of human 20α-HSD (AKR1C1), to ascertain whether it suppressed AKR1C18 activity. We also examined the effect of this inhibitor on oocyte maturation and viability.
In the germinal vesicle stage of mouse oocytes treated with 300 and 400 μM 5-PBSA, the number of oocytes showing AKR1C18 activity in the cytoplasm was 0 (0/34 and 0/35); the activity was significantly suppressed as compared with AKR1C18 activity in the control (25/29, 86.2%). In oocytes treated with >200 μM 5-PBSA, the number of degenerated oocytes was significantly increased compared with that in the control, and 17/37 (45.9%) of the oocytes treated with 300 μM were degenerated. In addition, in oocytes treated with 300 and 400 μM 5-PBSA, the number of oocytes that resumed meiosis was 2/20 (10%) and 0/16 (0%), respectively, and the resumption of meiosis was significantly suppressed compared with that in the controls (29/32, 90.6%).
These results revealed that 5-PBSA inhibits not only human AKR1C1 but also mouse AKR1C18 activity. In addition, suppression of meiotic resumption by treatment with 300 μM 5-PBSA suggests that AKR1C18 activity was involved in meiotic resumption. However, because 5-PBSA concentrations as high as 300 μM may also inhibit the activity of the AKR1C subfamily other than AKR1C18, the effects of 5-PBSA on these phylogenetically similar subfamilies must be investigated in the future.
