92 INSULIN-LIKE GROWTH FACTOR-1 PROTECTS BOVINE PRE-IMPLANTATION EMBRYOS PRODUCED IN VITRO FROM ANTI-DEVELOPMENTAL ACTIONS OF MENADIONE

Abstract

The objective of this study was to evaluate the protective effect of insulin-like growth factor (IGF-1) on blastocyst development and cryotolerance of bovine embryos in in vitro culture (IVC) under oxidative stress induced by menadione (MD). Cumulus-oocyte complexes (n = 1421) were matured in TCM-199 with bicarbonate, hormones, and 10% FCS for 22 h. After fertilization, the presumptive zygotes were cultured up to 7 days in SOF medium with 2.5% FCS and 0.5% BSA (control), and also supplemented with 100 μM IGF-1 (IGF). At Day 6, MD was included in the culture medium (0 μM, control; or 5.0 μM, MD) during 24 h. Cultures were conducted at 38.5°C in 5% CO₂ in air. The cleavage and blastocysts rates were evaluated, respectively, at Days 3 and 7 (IVF = Day 0). At Day 7, a sample of the blastocysts was stained with 5 μM H₂DCFDA (Molecular Probes, Canada) to evaluate the intracellular ROS levels or was stained for TUNEL (In Situ Cell Death Detection Kit, Roche, Indianapolis, IN, USA). Stained embryos were immediately evaluated under an epifluorescence microscope (excitation 495/550 nm and emission 404/590 nm, respectively, for ROS and TUNEL), and the images of embryos stained with H₂DCFDA were analysed by Q-Capture Pro image software for determining the fluorescent intensity. Other blastocysts were vitrified (Ingámed®, Maringá-PR, Brazil), and after warming, they were cultured for 24 h to evaluate the re-expansion rates. The results were compared by ANOVA followed by Student’s t-test (mean ± s.e.M) and re-expansion rates by chi-square test (P < 0.05). The cleavage rates did not differ (P > 0.05) among groups (77.1 ± 1.9% to 82.75 ± 2.2%). The blastocyst rates were similar between control (35.4 ± 2.0%) and IGF (34.5 ± 3.7%), and both were higher (P < 0.05) than MD (21.3 ± 2.7%); the IGF+MD group (28.3 ± 1.6%) was similar (P > 0.05) to all groups. The intracellular levels of ROS were higher (P < 0.05) for the MD group (21.7 ± 0.7) than for control (17.0 ± 1.6), and both were similar (P > 0.05) to the IGF (19.2 ± 0.6) and IGF+MD (18.0 ± 1.0) groups. The highest rates of apoptosis were found in the MD group (22.3% ± 2.3) and the smallest in IGF (9.1% ± 0.7), and both differed (P < 0.05) from control (12.8% ± 1.0), and IGF+MD (15.6% ± 1.6). The re-expansion rates were similar between control (77.4%) and IGF (69.2%), and both were higher (P < 0.05) than MD (49.1%); however, the IGF+MD group (57.6%) was similar (P > 0.05) to IGF and MD groups. In conclusion, the supplementation with IGF-1 during IVC reversed the detrimental effects of MD on embryonic levels of ROS and apoptosis, as well as improved the embryo development and cryotolerance of blastocysts under oxidative stress.

Financial support was provided by FAPESP (#2012/10083–8 and #2013/07382–6).