Characterization of in-vitro spermicidal activity of chelating agent against human sperm.

The effect of ethylenediaminetetraacetic acid (EDTA), a cationic chelating agent, on sperm motility and sperm penetration through cervical mucus was evaluated. EDTA exerted a relatively mild dose-dependent effect on sperm motility. Total loss of sperm motility (EC100) was achieved at a concentration of about 5.0 mg/mL of EDTA, which is much greater than the 200 micrograms/mL concentration of Nonoxynol-9 (N-9). EDTA salts, such as EDTA-Na2 and EDTA-Na4, showed weak spermicidal activity, while EDTA-K2 and EDTA-Ca had no spermicidal activity at concentrations up to 5.0 mg/mL. EDTA appeared to decrease the in vitro percentage of motile sperm as a function of exposure time. EDTA completely impeded the penetration of sperm into cervical mucus at a concentration much lower than that for 100% inhibition of sperm motility in semen. In the presence of 500-3200 micrograms/mL extra calcium, the first-order rate constant for sperm immobilization, which was derived from the slopes of a relative sperm motility curve, was reduced by 38.9--55.6% of the control and was inversely proportional to calcium concentration. After exposure to EDTA, the calcium ion concentration in semen was reduced as a function of EDTA concentration, which yielded a linear reduction of sperm motility. A decrease of approximately 65% in calcium ion concentration in semen seemed to be the threshold at which total loss of sperm motility occurred. Calcium ion was shown to play an essential role in regulating sperm molitility in semen, and EDTA was demonstrated to exert spermicidal activity by modulating calcium ion concentration in semen.