OBJECTIVETo investigate the potential protective effect of water-soluble vitamin E (Trolox) against oxidative stress injury in post-thawing human sperm and its mechanism.

METHODSSemen samples from 16 fertile men were mixed with modified cryoprotectant and each sample was equally divided into groups 0 (G0), 1 (G1), 2 (G2) and 3 (G3) according to the concentration of Trolox measured by computer-assisted semen analysis (CASA). G0, with no Trolox in the mixed cryoprotectant, served as the control, while G1, G2 and G3 contained 50, 100 and 200 micromol/L of Trolox, respectively. Before and after thawing, the semen samples were subjected to CASA for sperm kinematics, flow cytometry for reactive oxygen species (ROS), and thiobarbituric acid assay for the concentration of malondialdehyde (MDA).

RESULTSAfter cryopreservation, sperm motility was markedly decreased in all the groups (P < (0.01), but less in G2 than in the control ([53.33 +/- 5.63]% vs [47.85 +/- 5.09]%, P < 0.05). Curvilinear velocity and average path velocity were remarkably higher in G2 (P < 0.05), and ROS and MDA significantly lower in G2 and G3 than in the control (P < 0.05).

CONCLUSIONAddition of vitamin E (Trolox) to freezing extender at a moderate concentration may decrease surplus ROS in the freezing-thawing process, ease ROS-induced oxidative stress injury to the plasma membrane, and improve sperm motility and kinematic parameters after cryopreservation.