Effect of zinc on sperm recovered by swim-up

Zinc is known to influence chromatin stability, motility and protection against oxidative stress. While swim-up remains the preferred method for selecting sperm in Assisted Reproductive Technologies (ART), concerns arise regarding sperm DNA fragmentation associated with this procedure. Given zinc's significant role in protecting sperm DNA integrity and motility, we aimed to investigate the impact of zinc supplementation during the swim-up process on sperm quality.

Semen samples from 203 normozoospermic men were used. Samples were divided into fractions and swim-up procedure was applied using human tubal fluid (mHTF) supplemented with three different concentrations of zinc or medium without supplementation as control. DNA fragmentation, chromatin maturity, reactive oxygen species (ROS) levels, motility and protein phosphorylation levels analyses were addressed to each fraction.

The sperm DNA fragmentation was reduced in sperm recovered by swim-up in media with all concentrations of zinc assayed with respect to the control (p < 0.0001). Aniline blue staining showed better chromatin maturity in sperm recovered with 2.5- and 3.5-mM zinc (p = 0.045; p = 0.021). Kinematic parameters such as curvilinear velocity and beat-cross frequency showed improvement with 2.5 mM zinc (p = 0.0080 and p = 0.0400), whereas straightness, linearity, and hypermotility showed improvement with 5 mM zinc (p = 0.0075, p = 0.0069, and p = 0.0244). Protein phosphorylation patterns showed changes associated with treatment with zinc, and only 5 mM zinc treatment showed a decrease in ROS levels.

The addition of zinc to mHTF provided optimal physiological conditions for sperm recovered through swim-up. This supplementation should be considered for selecting sperm for use in ART.