156 PRETREATMENT WITH THE ANTIOXIDANT EPIGALLOCATECHIN GALLATE (EGCG) COUNTERACTS THE NEGATIVE EFFECTS OF MATERNAL HYPERTHERMIA ON EMBRYONIC DEVELOPMENT IN MICE

Abstract

Hyperthermia-induced oxidative stress is one of the suggested mechanisms underlying the loss of developmental competence in heat-stressed embryos. The objective of the present study was to determine whether pretreatment with the antioxidant epigallocatechin gallate (EGCG) would counteract the negative effects of maternal hyperthermia on oocyte competence and improve subsequent embryonic development. Exp. 1 examined the effect of pretreatment with EGCG on ex vivo embryonic development under normal culture conditions (KSOM, 37°C, 5% CO2, 95% RH in air). Female mice (CB6F1) were synchronized (PMSG + hCG) and injected with 0.4 mL EGCG (100 mg/kg body weight) or with saline. Both EGCG- and saline-treated females were paired with stud males overnight. Mated mice were sacrificed and putative zygotes recovered and cultured in vitro. Cleavage and blastocyst formation rates were recorded on Days 1 and 5 post-fertilization, respectively. The percentage of putative zygotes that cleaved into the two-cell stage did not differ between the groups; however, blastocyst formation rate was higher (P < 0.05) in the EGCG group (85 ± 2%) than in the saline group (75 ± 2%). In Exp. 2 (a 2 × 2 factorial study), both EGCG- and saline-treated mice were exposed to normo-thermal conditions (NT; 22°C, 45% RH) or heat stress (HS; 40°C, 70% RH) for 1.5 to 2 h, the latter to induce a rise of 2°C in body temperature. Synchronized mice were paired with stud males overnight and mated mice were then sacrificed. Putative zygotes were recovered and cultured in vitro as described above. The number of putative zygotes recovered, cleavage and blastocyst formation rates and percentage of hatched blastocysts are presented in Table 1. Blastocyst formation rate was higher (P < 0.05) in the HS-EGCG group than in the HS-saline group. In addition, HS-EGCG embryos exhibited developmental competence similar to that of embryos from both NT groups. In summary, pretreatment with EGCG improved developmental competence under the described culture conditions. Furthermore, pretreatment with the antioxidant EGCG counteracted the negative effects of maternal hyperthermia. Further studies are warranted to evaluate the effect of pretreatment with EGCG on embryo quality. Table 1. Effect of pretreatment with EGCG on developmental competence of heat stressed oocytes