Human oocyte-derived sperm chemoattractant is a hydrophobic molecule associated with a carrier protein

Objective To characterize the nature of the human oocyte-derived chemoattractant. Design Laboratory in vitro study. Setting Academic research institute. Patient(s) Ten healthy sperm donors. Oocyte-conditioned media from women undergoing IVF treatment because of male factor infertility. Intervention(s) Sperm samples were processed by the migration-sedimentation technique. Oocyte-conditioned media were collected 2-3 hours after oocyte stripping. Main Outcome Measure(s) Sperm chemotaxis was assayed in a μ-slide chamber according to the direction of swimming relative to that of the chemical gradient. Result(s) Oocyte-conditioned media treated with proteases did not lose their chemotactic activity; on the contrary, they became more active, with the activity shifted to lower concentrations. When oocyte-conditioned media were subjected to hexane extraction, chemotactic activity was found in both the hydrophobic and aqueous phases. Known mammalian sperm chemoattractants were ruled out as oocyte-derived chemoattractants. Conclusion(s) Our results suggest that the oocyte-derived chemoattractant is a hydrophobic nonpeptide molecule that, in an oocyte-conditioned medium, is associated with a carrier protein that enables its presence in a hydrophilic environment.