Evaluation of the effect of lecithin and nanolecithin in repairing membrane damage, maintaining membrane integrity, and improving human sperm function in the freezing-thawing process.

Purpose: Our study aimed to evaluate the effects of lecithin nanoparticles on sperm quality during cryopreservation.

Methods: In phase one, sperm-freezing media were prepared with lecithin concentrations (0.5%, 1%, and 2%) and lecithin nanoparticles of various sizes (50-100, 100-200, and ≥ 200 nm). Post-thaw, sperm motility, viability, mitochondrial membrane potential (MMP), lipid peroxidation (measured by malondialdehyde, MDA), and DNA fragmentation were evaluated. In phase two, the acrosomal reaction was assessed in the best and worst-performing groups from phase one. DiI labeling detected interactions between lecithin nanoparticles and the sperm membrane. Field emission scanning electron microscopy (FESEM) examined the sperm membrane's surface structure and lecithin binding sites. Atomic force microscopy (AFM) assessed height differences in the sperm surface layer in the best-performing group from phase one.

Results: The group treated with 1% lecithin nanoparticles (50-100 nm) showed significantly increased viability post-thaw compared to other groups, with reduced DNA fragmentation and MDA levels. While motility significantly decreased in all groups compared to before freezing levels, lower concentrations, and smaller particle sizes yielded better results. MMP also significantly decreased across all groups with no significant differences. The acrosomal reaction significantly decreased with 1% lecithin nanoparticles (50-100 nm) compared to the 2% (≥ 200 nm) group. DiI-labeled nanoparticles and FESEM revealed that lecithin nanoparticles primarily bound to and infiltrated the sperm membrane, particularly in the head and postacrosomal regions.

Conclusions: Lecithin nanoparticles effectively bind to the sperm membrane, protecting it during the freeze-thaw process and improving sperm viability.