Kaempferol Enhances Sperm Post-Thaw Survival by Its Cryoprotective and Antioxidant Behavior

This study examined the effects of three selected doses of kaempferol (KAE; 12.5, 25 or 50 μM) on bovine sperm motility and oxidative profile directly related to cold storage. We also elucidated the effect of KAE on the expression profiles of heat shock proteins (HSPs) 70 and 90 as well as the pro-apoptotic BCL2-associated X (BAX) protein and the anti-apoptotic B-cell lymphoma 2 (Bcl-2) protein. Frozen samples supplemented with KAE were compared with a native control (fresh spermatozoa) and a cryopreserved control, frozen in the absence of KAE. Our results demonstrate that the administration of all KAE doses led to a higher degree of sperm motility (p < 0.05) when compared with the cryopreserved control. The highest levels of protection of sperm DNA (p < 0.05), lipids (p < 0.05) and proteins (p < 0.05) were detected in samples exposed to 25 μM KAE when compared with samples frozen without KAE. Administration of 25 μM KAE led to a significant increase in HSP70 and HSP90 (p < 0.05) when compared with the unsupplemented frozen control. No significant differences were observed in the expression patterns of BAX; however, a significant up-regulation of Bcl-2 protein was observed in the frozen samples enriched with 25 μM KAE when compared with the cryopreserved control (p < 0.05). In summary, we may consider KAE as an effective agent in stabilizing the sperm membranes by preventing reactive oxygen species (ROS) overproduction in the mitochondria and subsequent oxidative damage to molecules critical for a proper sperm architecture and function. These protective properties of KAE may lead to higher post-thaw sperm activity and viability.