183 ADDITION OF DIPHENYLENEIODONIUM OR DEHYDROEPIANDROSTERONE TO CULTURE MEDIA INHIBITS REACTIVE OXYGEN SPECIES PRODUCTION DURING THE EARLY CLEAVAGE STAGES OF IN VITRO-PRODUCED PORCINE EMBRYOS

Abstract

Nicotinamide adenine dinucleotide phosphate-oxidase (NADPH oxidase), an enzyme required to catalyze the oxidation of NADPH to NADP during the metabolism of glucose via the pentose phosphate pathway (PPP), was considered as contributing to intracellular reactive oxygen species (ROS) production. Production of superoxide anion and H₂O₂ via NADPH oxidase has been reported on a rabbit blastocyst surface (Manes and Lai 1995 J. Reprod. Fertil. 104, 69–75). The objective of this study was to examine the effects on in vitro development and intracellular ROS content after the addition of diphenyleneiodonium (DPI), an inhibitor of NADPH oxidase, or dehydroepiandrosterone (DHEA), an inhibitor of glucose-6-phosphate dehydrogenase (G6PDH), to culture medium during the early embryonic development of in vitro-produced (IVP) porcine embryos. To confirm that these inhibitors lead to reduction in NADPH concentration in the embryo and hence likely to be inhibiting the PPP, a brilliant cresyl blue (BCB) test was performed on Day 2 (the day of insemination = Day 0) of culture. Porcine cumulus–oocyte complexes were matured and fertilized in vitro as described previously (Kikuchi et al. 2002 Biol. Reprod. 66, 1033–1041). Prezumptive zygotes were then cultured in NCSU-37 supplemented with 5.5 mM glucose and DPI at concentrations of 0.5 or 1 nM or DHEA at concentrations of 10 or 100 µM (DPI-0.5, DPI-1, DHEA-10 and DHEA-100 groups, respectively) from Day 0 to Day 2 of culture. All of the embryos were cultured subsequently until Day 6 in NCSU-37 supplemented with only 5.5 mM glucose. Data were analyzed by ANOVA. On Day 6, the development to the blastocyst stage of embryos in DPI-0.5, DPI-1, DHEA-10, and DHEA-100 groups were 16.1, 17.6, 16.1, and 19.5%, respectively, which were not significantly different from that of the control group (17.5%) (n d 165 per group, 5 replicates). However, the mean cell number in blastocysts derived from DPI-1, DHEA-10, and DHEA-100 groups (40.8 ± 2.3, 39.3 ± 1.7, and 42.5 ± 2.7, respectively) was significantly higher (P < 0.01) than those in the control (33.4 ± 1.6) and DPI-0.5 (32.7 ± 1.6) groups. At 20 min after an exposure to BCB, the percentage of BCB+ embryos in DPI-1, DHEA-10, and DHEA-100 groups (73.8, 79.9, and 77.8%, respectively) were significantly higher (P < 0.01) than those in the control and DPI-0.5 groups (42% and 53.9%, respectively) (n = 81-92 per group, 6 replicates), indicating that these two inhibitors effectively induce the reduction of NADPH concentration in the embryos. Moreover, the addition of DPI at 1 nM or DHEA at 10 or 100 µM significantly decreased the H₂O₂ content of Day 2 embryos as compared with control embryos (n = 48-53 per group, 7 replicates). These results suggest that the addition of either DPI or DHEA to the medium during the first 2 days of culture did not impair the development of the embryos to the blastocyst stage. Decrease of cellular ROS production in Day 2 embryos in this study is interpreted as a result of inhibition of the NADPH oxidase by DPI or of the G6PDH by DHEA.