327 UNSATURATED AND SATURATED NON-ESTERIFIED FATTY ACIDS DIFFERENTLY AFFECT LIPID STORAGE AND DEVELOPMENTAL COMPETENCE OF BOVINE OOCYTES

Abstract

Fertility in high-producing dairy cows has declined over the last decades. An increased serum and follicular fluid concentration of non-esterified fatty acids (NEFAs), due to body fat mobilization in the early post partum period, has been postulated as a cause for this fertility decline. NEFA concentrations and composition may change in the environment of the oocyte and thus might affect the storage depots of esterified NEFAs in the oocyte. We exposed COCs to unsaturated (oleic acid) or saturated (palmitic acid) NEFAs during maturation and subsequently examined lipid droplets and developmental competence of the oocytes. COCs from 3-8 mm follicles of slaughterhouse ovaries were cultured in control maturation medium (TCM-199) and medium containing 100, 250, or 500 μM oleic and/or palmitic acid (10 mM fatty acid was bound to 10% BSA fatty acid free). These concentrations were based on in vivo measured NEFA concentrations in follicular fluid in the early post partum period (Leroy et al. 2005 Reproduction 130, 485-495). After 23 h of maturation, COCs were fertilized (450 per group) and cultured till the blastocyst stage, or fixed (80 per group) for lipid droplet staining with C1-BODIPY^® 500/510 C12. Confocal microscopy was performed to determine lipid droplet size in (im(mean) and the number of lipid droplets per oocyte. Lipid droplet number and the log of size were analyzed using analysis of variances with condition as fixed factor. Variation was described as the standard error of the mean. Similar concentrations of palmitic or oleic acid had an opposite effect on the size of lipid droplets in oocytes. The number of lipid droplets dramatically decreased in oocytes exposed to 500 μM palmitic acid (178 ± 20), whereas the number increased after exposure to 500 μM oleic acid (554 ± 15). The number of lipid droplets of oocytes exposed to a combination of 250 μM palmitic acid and 250 μM oleic acid (421 ± 23) was comparable with the control and lower oleic and palmitic acid concentrations. Exposure of COCs to palmitic acid during maturation resulted in reduced blastocyst development in a dose-dependent manner (from 18 ± 1.4%, 13 ± 2.4% to 2.8 ± 1.3% after exposure to 500 μM) when compared to control (20 ± 2.2%) or oocytes exposed to oleic acid (from 23 ± 1.6%, 23 ± 3.3% till 28 ± 3.3%). Negative effects of palmitic acid were counteracted by simultaneous exposure to oleic acid during in vitro oocyte maturation (26 ± 5.5%). We conclude that palmitic acid elicited negative effects on early embryonic development, possibly because it induces a reduction in the number of lipid droplets. These adverse effects can be offset by oleic acid during maturation. Moreover a high oleic acid concentration increased the number and size of lipid droplets of oocytes. The regulatory pathways involved in the noted differences in lipid storage features of in vitro-matured oocytes as well as the adverse effects of palmitic acid on early embryonic development are currently under research.