DL-alpha-tocopherol acetate mitigates maternal hyperthermia-induced pre-implantation embryonic death accompanied by a reduction of physiological oxidative stress in mice

Maternal hyperthermia induces pre-implantation embryo death, which is accompanied by enhanced physiological oxidative stress. We evaluated whether the administration of DL-alpha-tocopherol acetate (TA) to hyperthermic mothers mitigated pre-implantation embryo death. Mice were exposed to heat stress (35 degrees C, 60% relative humidity) for 12 h or not heated (25 degrees C) on the day of mating. Twelve hours before the beginning of temperature treatment, TA was injected intraperitoneally at a dose of 1 g/kg body weight. After the treatment, zygotes were recovered and the developmental abilities and intracellular glutathione (GSH) levels were evaluated. Another set of mice, with or without TA treatment, was exposed to heat stress for 12, 24 and 36 h, and the urinary levels of the oxidative stress marker 8-hydroxy-2'-deoxyguanosine (8-OHdG) were measured. Heat stress significantly decreased the blastocyst development rate and the GSH content in zygotes, as compared with the non-heat-stressed embryos, while TA administration significantly mitigated the deleterious effects of heat stress with regard to both parameters. Moreover, although the urinary levels of 8-OHdG gradually increased according to the duration of heat exposure, with or without TA administration, the levels were lower in the TA-administered group than in the placebo-injected mice. These results suggest that heat stress enhances physiological oxidative stress, and that TA administration alleviates the hyperthermia-induced death of pre-implantation embryos by reducing physiological oxidative stress.

153 ALLEVIATIVE EFFECTS OF ANTIOXIDANT ADMINISTRATION ON MATERNAL HYPERTHERMIA-INDUCED EARLY EMBRYONIC DEATH IN MICE

Hyperthermia-induced early embryonic death is generally ascribed to the high susceptibility of early embryos to elevated maternal body temperature. However, recent studies have indicated that the disruption of embryonic development by maternal hyperthermia has relevance to not only high temperature exposure to the embryo, but also hyperthermia-associated changes in the maternal body. Hyperthermia enhances physiological production of reactive oxygen species (ROS) systemically. Early embryos are susceptible to oxidative stress and it becomes easy to arrest their development when the oxidative stress is exposed. These findings led us to speculate that maternal hyperthermia-induced early embryonic death is caused by an increase in oxidative stress to the embryo. Vitamin E and melatonin are both well known to function as antioxidants in vivo when they are administered exogenously. In this study, we administered vitamin E or melatonin to heat-stressed pregnant mice, aiming to alleviate the hyperthermia-induced embryonic death. Female mice were heat-stressed (35�C with 60% relative humidity) for 12 h on the day of mating. In Experiment 1, vitamin E (1000 mg/kg body weight) was injected intraperitoneally just before stress treatment, or melatonin (3 mg/kg body weight) was injected subcutaneously for every 2 h during heat exposure. Then, zygotes were collected and in vitro developmental ability was assessed. In Experiment 2, intracellular glutathione (GSH) content in the zygote, ROS level and free radical scavenging activity (FRSA) in the oviduct, and lipid peroxidation level in the liver were measured to evaluate the effects of melatonin administration on physiological redox status. All data were analyzed using one-way ANOVA followed by Fisher's protected least-significant test. The percentage of embryos that developed to the morula or blastocyst stage was significantly (P < 0.01) increased by administration of either vitamin E (58.6%) or melatonin (47.9%) compared with that in heat-stressed mice that were administered placebos (14.8%). Intracellular GSH content in zygotes derived from melatonin-administered mice was not significantly different from that in unstressed mice (1.67 and 1.82 pmol/zygote, respectively), whereas in heat-stressed mice that were administered placebo, intracellular GSH content was significantly decreased (1.48 pmol/zygote, P < 0.05) compared to that in unstressed mice. There were no significant differences in lipid peroxidation levels in the liver and in ROS levels in the oviduct between melatonin-administered stressed mice and unstressed mice, although these parameters in heat-stressed mice with placebo were significantly higher than in unstressed mice (P < 0.05). Furthermore, FRSA in the oviduct was significantly (P < 0.05) higher in the melatonin-administered mice than in the heat-stressed mice. These findings suggest that antioxidant administration to heat-stressed mice alleviates the hyperthermia-induced early embryonic death, and this may be accomplished in part by maintaining a neutral redox status within the mother.

Alleviation of maternal hyperthermia-induced early embryonic death by administration of melatonin to mice

Maternal hyperthermia induces early embryonic death via increased oxidative stress to the embryo. In this study, we examined whether melatonin administered to heat-stressed pregnant mice would reduce hyperthermia-induced embryonic death. Mice were heat stressed (12 hr at 35 degrees C, 60% relative humidity) on the day of mating and melatonin (3 mg/kg body weight) was injected subcutaneously every 2 hr during heat exposure. Thereafter, zygotes were collected, and in vitro developmental ability and intracellular glutathione (GSH) content were assessed. In addition, reactive oxygen species (ROS) levels and free radical scavenging activity (FRSA) in the oviduct as well as lipid peroxidation in the liver were measured. Melatonin administration was associated with a tendency for higher intracellular GSH content in zygotes (1.67 pmol/zygote) and a significantly higher percentage of embryos that developed to the morula or blastocyst stage (47.91%; P < 0.01) compared with the parameters in heat-stressed mice that were administered a placebo (1.48 pmol GSH/zygote and 14.78% development). Lipid peroxidation levels in the liver and ROS levels in the oviduct were the same in melatonin-treated stressed mice and the controls, while these parameters were significantly higher in heat-stressed mice that were not treated with melatonin. Furthermore, FRSA in the oviduct was significantly (P < 0.05) higher in the melatonin-treated mice than in the controls. These results suggest that administration of melatonin to heat-stressed mice alleviates hyperthermia-induced early embryonic death and that this is accomplished in part by maintaining a neutral redox status within the mother.

Effects of heat stress on the redox status in the oviduct and early embryonic development in mice

This study examined the association between redox status in the oviduct and early embryonic death in heat-stressed mice. In Experiment 1, non-pregnant mice were heat-stressed at 35 C with 60% relative humidity for 12, 24, or 36 h, and the maternal redox status was verified by measuring the levels of reactive oxygen species (ROS) and free radical scavenging activity (FRSA) in the oviduct, and thiobarbituric acid reactive substances (TBARS) and glutathione peroxidase (GSH-Px) activity in the liver. In Experiment 2, zygotes were collected from mice heat-stressed for 12 h on the day of pregnancy, and their developmental abilities were assessed in vitro, along with the intensity of DNA damage at the 2-cell stage. The TBARS value and GSH-Px activity in the liver, and ROS level in the oviduct were significantly higher in heat-stressed mice, and this increase appeared to depend on the duration of the heat stress. Maternal heat stress significantly reduced the percentage of zygotes that developed to the morula and blastocyst and the total cell number in the blastocyst. In addition, DNA damage at the 2-cell stage was significantly higher in maternally heat-stressed embryos. These results suggest that heat stress induces systemic changes in redox status in the maternal body, and the resultant increase in oxidative stress in the oviduct is possibly involved in heat stress-induced early embryonic death .