Potato aspartic proteases (StAPs) exert cytotoxic activity on bovine and human spermatozoa

Objective To evaluate the in vitro spermicidal activity of Solanum tuberosum aspartic proteinases ( St APs) on bovine and human sperm. Design Controlled laboratory study. Setting Three research laboratories at a university of biologic science. Animal(s) and Donor(s) Frozen semen from five Aberdeen Angus bulls and six proven fertile men volunteers. Intervention(s) The effect of St APs on sperm motility was studied in vitro by incubation of different concentrations of St APs with sperm suspensions, and motility was assessed by direct microscopic observation. Membrane integrity was analyzed by SYTOX Green uptake after incubation with different St AP concentrations. The effect of St APs was evaluated by human erythrocyte lysis, as a control in somatic cells. The St APs binding was monitored by fluorescence. Main Outcome Measure(s) Total and progressive sperm motility; hypoosmotic swelling test and SYTOX Green uptake as a measure of membrane damage; fluorescein isothiocyanate-labeled St AP binding by an optical microscopy. Result(s) The St APs reduced sperm motility in a dose-dependent manner, and 25 μM of St AP1 and 35 μM of St AP3 completely abolished the progressive motility. The St APs were able to bind in the postacrosomal and midpiece region only in bovine sperm. Also, St APs caused spermatozoa agglutination. In vitro cell toxicity was observed by a dose-dependent increase in hypoosmotic swelling negative sperm and SYTOX Green uptake in both human and bovine spermatozoa; however, no toxic effect was observed on erythrocytes. Conclusion(s) The spermicidal effect of St APs involves plasma membrane permeabilization.