Resveratrol prevents capacitation-like changes and improves in vitro fertilizing capability of buffalo frozen-thawed sperm

The aim of this study was to evaluate the effect of resveratrol supplementation of semen extender on fertility parameters of frozen-thawed buffalo sperm. After the initial semen assessment, buffalo semen was cryopreserved in BioXcell containing 0 (control group), 0.5, 1, 10, and 50-μM resveratrol. After thawing, viability, motility, and capacitation status (assessed by localization of phosphotyrosine-containing proteins) were evaluated. Based on the results of the dose-response trial, the concentration of 50 μM was selected for further assessments, such as membrane integrity, total antioxidant capacity, reactive oxygen species, and lipid peroxidation (LPO) levels. Moreover, in vitro fertilizing ability by heterologous IVF and in vivo fertility were assessed. No differences among groups were recorded in sperm motility and viability (on average 52.3 ± 2.1% and 76.6 ± 1.3%, respectively). However, data showed a resveratrol dose-dependent effect on sperm capacitation status, with a significant reduction of the cryopreservation-induced capacitation with the higher concentrations tested. In particular, both 10- and 50-μM resveratrol increased (P < 0.01) the percentage of sperm displaying pattern A (low capacitation level), but treatment with 50-μM resveratrol also decreased (P < 0.01) the proportion of sperm exhibiting pattern EA (high-capacitation level) compared with the control. Interestingly, supplementation of semen extender with resveratrol increased membrane integrity, indicated by the higher percentage of hypo-osmotic swelling positive sperm (55.6 ± 0.6 vs. 48.4 ± 0.7; P < 0.01), and total antioxidant capacity (1.36 ± 0.01 vs. 1.32 ± 0.02 mM/L; P < 0.05) compared with the control. Intracellular reactive oxygen species decreased in resveratrol-treated sperm compared with the control, as indicated by dihydroethidium values (0.17 ± 0.01 and 0.22 ± 0.01 μM/μL dihydroethidium, respectively; P < 0.01). Moreover, when IVF was carried out by using semen treated with 50 μM resveratrol, the normal fertilization rate considerably improved (60.8%, P < 0.05) compared with the control (51.3%). However, no differences were recorded in pregnancy rates at 60 days post-AI with resveratrol-treated semen (50 μM) compared with the control (48.7 vs. 46.5%, respectively). In conclusion, the inclusion of 50-μM resveratrol in the extender decreases capacitation-like changes and oxidative stress, improving membrane stability and in vitro fertilizing ability of buffalo semen.