Supplementation of in vitro maturation (IVM) medium with linolenic acid (ALA) has been used in order to reduce oocyte lipid content and have beneficial effects on maturation and acquisition of competence for embryonic development. Besides the effect of reducing cellular lipid content, l-carnitine (l-car) has an antioxidant effect by reducing the levels of reactive oxygen species (ROS) and protecting cells from apoptosis. However, the association of ALA and l-car has never been tested. This study was conducted to evaluate the effects of supplementation of IVM medium of bovine oocytes with ALA, l-car or the association of both (ALA+l-car) on embryonic development and blastocysts reactive oxygen species (ROS) levels and occurrence of apoptosis. Cumulus-oocyte complexes (n = 2241, in 11 replicates) were matured during 22 h at 38.5°C and 5% CO2 in air, in TCM-199 medium with bicarbonate, hormones and 10% FCS (control group), also supplemented with 100 μM ALA group; or 5 mM l-car (l-car group); or 100 μM ALA associated with 5 mM l-car (ALA+l-car group). After fertilisation (Day 0), zygotes were cultured 7 days in SOF that was supplemented with 0.5% BSA and 2.5% FCS, in 5% CO2 in air at 38.5°C. The cleavage and blastocysts rates were evaluated, respectively, at Days 3 and 7. Blastocysts were stained with 5 mM of H2DCFDA (Molecular Probes, Invitrogen, Carlsbad, CA, USA) and TUNEL (In Situ Cell Death Detection Kit, Roche Applied Science, Boston, MA, USA), to evaluate the ROS levels and the blastomers apoptotic index, respectively. The ROS (n = 115) and TUNEL (n = 102) stained blastocysts were evaluated under an epifluorescence microscope (excitation 495 nm/510–550 nm and emission 404 nm/590 nm), and the ROS levels (expressed as arbitrary fluorescence units) were measured by Q-Capture Pro image software (Q Imaging, Surrey, BC, Canada). The fluorescence intensity values were subtracted from mean values of background in the images. The variables were analysed by ANOVA followed by Tukey’s test (P < 0.05) and data are presented as mean ± s.e.m. There was no effect (P > 0.05) of the supplements during IVM on cleavage and blastocysts rates (%), respectively, for control (81.1 ± 1.8 and 29.0 ± 3.1), ALA (80.5 ± 2.1 and 29.7 ± 2.3), l-car (79.5 ± 2.8 and 29.2 ± 2.3), and ALA+l-car (82.2 ± 1.1 and 30.5 ± 2.0) groups. The oocytes supplementation resulted in a decrease (P < 0.05) in ROS levels for ALA (0.84 ± 0.04), l-car (0.85 ± 0.03) and ALA+l-car (0.82 ± 0.02) groups, compared to the Control (1.00 ± 0.05). Consequently, the percentage of apoptotic blastomeres decreased (P < 0.05) after ALA (6.9 ± 1.0%), l-car (7.5 ± 1.2%) and ALA+l-car (4.6 ± 0.7%) supplementations, unlike to the Control group (12.0 ± 1.2%). In conclusion, the supplementation with ALA, l-car or ALA+l-car during IVM did not affect the blastocyst development, but led to a reduction in ROS levels and in the apoptotic index of such blastocysts. These findings may be due to some antioxidant effect of these supplements in the oocytes and/or the produced embryos.
Financial support was through FAPESP (#2012/10084–4 and #2013/07382–6).
Alpha-linolenic acid enhances maturation and developmental competence via regulation of glutathione, cAMP and fatty acid accumulation during in vitro maturation of porcine oocytes