Biological effects of polyphenol-rich extract and fractions from an oenological oak-derived tannin on in vitro swine sperm capacitation and fertilizing ability

Although excessive ROS levels induce sperm damage, sperm capacitation is an oxidative event that requires low amounts of ROS. As the antioxidant activity of the ethanol extract (TRE) of a commercial oenological tannin (Quercus robur toasted oak wood, Tan'Activ R^®) and its four fractions (FA, FB, FC, FD) has been recently reported, the present study was set up to investigate the biological effects of TRE and its fractions in an in vitro model of sperm capacitation and fertilization. Boar sperm capacitation or gamete coincubation were performed in presence of TRE or its fractions (0, 1, 10, 100 μg/ml). TRE at the concentration of 10 μg/ml (TRE10) stimulated sperm capacitation, as it increased (p < .001) the percentage of spermatozoa with tyrosine-phosphorylated protein positivity in the tail principal piece (B pattern) (67.0 ± 10.6 vs. 48.6 ± 9.0, mean ± SD for TRE10 vs. Ctr respectively). Moreover T10 significantly (p < .001) increased oocyte fertilization rate (91.9 ± 4.0 vs. 69.0 ± 14.8, TRE10 vs. Ctr respectively). An opposite effect of TRE at the concentration of 100 μg/ml (TRE100) on both sperm capacitation (B pattern cell percentage 33.3 ± 29.2) and fertilizing ability (fertilization rate 4.9 ± 8.3), associated with a higher sperm viability (66.9 ± 9.3 vs. 35.4 ± 10.8, TRE100 vs. Ctr respectively) (p < .001), was recorded. The potency of the TRE fractions seems to be highest in FB followed by FC, faint in FD and nearly absent in FA. Our results show that TRE and its fractions, in a different extent, exert a powerful biological effect in finely modulating capacitation and sperm fertilizing ability.