358 THE CONSEQUENCE OF HIGH NON-ESTERIFIED FATTY ACID CONCENTRATIONS DURING OOCYTE IN VITRO MATURATION ON BOVINE EMBRYO QUALITY

Abstract

High non-esterified fatty acid (NEFA) concentrations in the blood, associated with negative energy balance (NEB), obesity or diabetes Type II are known to alter the follicular micro-environment. These environmental changes have been associated with disappointing fertility outcome through disabled ovarian cell function and oocyte’s developmental competence. Our hypothesis was that elevated NEFA concentrations during final oocyte maturation might hamper the quality of the pre-implantation embryo as well. To assess embryo quality, the present study focused on total cell number and apoptotic index in 7-day-old embryos. Applied NEFA concentrations in the maturation medium were based on analyses in the follicular fluid of high yielding dairy cows early post partum during NEB. Bovine cumulus-oocyte complexes were exposed to 1) physiological NEFA concentrations, i.e. a combination of basal palmitic (25 μM), stearic (50 μM) and oleic acid (75 μM) concentrations (CONTROL), 2) elevated NEFA concentrations, i.e. a combination of high palmitic (75 μM), stearic (150 μM) and oleic acid (200 μM) concentrations (HIGH COMBI) and 3) elevated palmitic acid (75 μM) concentrations (HIGH PA). Palmitic acid has been recognized as a major saturated fatty acid in terms of cellular toxicity. After serum-free in vitro maturation (24 h) and fertilization (22 h), zygotes were cultured in SOF medium with 5% serum for 7 days. Blastocysts were evaluated for developmental competence, total cell number (by Propidium Iodide staining) and apoptotic index (by TUNEL detection kit). In total, 684 oocytes were cultured in 3 replicates. Data were analyzed with binary logistic regression and a mixed model ANOVA. Preliminary research showed that maturation in a combination of basal NEFA concentrations has no effect on oocyte’s developmental competence compared to the standard serum free maturation system. In the present study, maturation in HIGH COMBI resulted in significantly lower blastocyst rates (21.4%) compared to CONTROL (30.1%) (P = 0.03). No significant effect of HIGH PA maturation on blastocyst rate (24.1%) could be found. Also total cell number tended to be lower in the HIGH COMBI (104.7 ± 26.1) compared to CONTROL (125.8 ± 29.4) (P = 0.08). The apoptotic index was significantly increased in the HIGH PA group (0.22 ± 0.12) compared to the CONTROL group (0.11 ± 0.07) (P = 0.02) and tended to be higher than the HIGH COMBI group (0.14 ± 0.12) (P = 0.06). Maternal metabolic conditions, leading to increased lipolysis and high NEFA concentrations, can hamper fertility through a reduction of the oocyte’s developmental competence. The data of the present study furthermore suggest that elevated NEFAs might induce a negative carry over effect from the oocyte during its maturation to the embryo quality. This may ultimately lead to embryonic mortality and thus to a disappointing fertility outcome.

Veerle Van Hoeck is supported by the Special Research Fund, University of Antwerp (Grant 22590).