Eicosatetraynoic and eicosatriynoic acids, lipoxygenase inhibitors, block meiosis via antioxidant action

We previously showed that nordihydroguaiaretic acid (NDGA) and other antiox idants inhibit the resumption of meiosis in oocyte-cumulus complexes (OCC) and denuded oocytes (DO). Because NDGA is well known to be an inhibitor of lipoxygenases (LOX), we assessed whether other LOX inhibitors influence spo ntaneous germinal vesicle breakdown (GVBD) in OCC and DO. Spontaneous GVBD in rat OCC obtained from preovulatory follicles was significantly and rever sibly inhibited by the minimum effective doses of 80 and 100 mu M 5,8,11,14 -eicosatetraynoic acid (ETYA) and 5,8,11-eicosatriynoic acid (ETI), respect ively. In DO, GVBD was significantly inhibited by 100 mu M ETYA or ETI. The minimum effective concentrations of ETYA and ETI for inhibition of GVBD in either OCC or DO are similar to 30- to 50-fold higher than the concentrati ons necessary to inhibit LOX activity by 50% in intact cells. Because re pr eviously showed that NDGA and other antioxidants inhibit the spontaneous re sumption of meiosis, we assessed whether ETYA and ETI may act similarly as scavengers of reactive oxygen species (ROS). Luminol-amplified chemilumines cence showed that 50 mu M of either ETYA or ETI markedly and significantly reduced ROS generated with 10 mM 2,2'-azobis(2-amidinopropane)dihydrochlori de (AAPH). Moreover, incubation of DO with 30 mm AAPH reversed the inhibiti on of GVBD produced by 100 mu M ETYA or ETI. These findings support the con clusion that ETYA and ETI inhibit oocyte maturation by acting as antioxidan ts rather than by inhibiting LOX.