Quercetin inhibits human sperm functions by reducing sperm [Ca2+]i and tyrosine phosphorylation

Quercetin is widely known as potent natural antioxidant and scavenger of reactive oxygen species (ROS) and nitric oxide both in vitro and in vivo. Quercetin has a wide range of biological functions and health-promoting effects. There are more and more interests in the addition of this flavonol to various traditional food products. However, the in vitro toxicity of quercetin to mature human sperm remains unknown. In this study, we investigated the in vitro effects of quercetin on human sperm functions. The results showed that the total sperm motility were significantly inhibited compared to the controls following exposure to 100, 200 and 400µM quercetin for 6 and 12h; quercetin did not affect human sperm viability. The acrosome reaction and capacitation induced by progesterone were dose-dependently inhibited by quercetin. Furthermore, quercetin induced a significantly decrease of human sperm [Ca²⁺]_i after 2 min above 50 μM, and dose-dependently decreased the protein-tyrosine phosphorylation of human sperm. Our results indicated that quercetin may decrease sperm [Ca²⁺]_i, suppresse tyrosine phosphorylation, and subsequently inhibit sperm functions.