Spermicidal Activity of nonoxynol-9 and Analogs: Quantitative Assessments by Flow Cytometry

Abstract A flow cytometer-based method was developed for the quantitative assessment of spermicidal action of nonoxynol-9 (N-9) against human sperm. Two fluorescent dyes were chosen: carboxyfluorescein diacetate (CFDA) was employed as an indicator for viable sperm, while propidium iodide (PI) identified the sperm membrane integrity disrupted by spermicidal agents. Living, motile sperm were identified by the green fluorescence of CFDA, while the red fluorescence of PI reflected the ability of the spermicide to kill sperm. Both living and dead sperm were effectively resolved from the acellular components of seminal fluid. N-9 was used as a model spermicidal agent to study the feasibility as well as establish the various technical aspects of this method. Further studies with a series of structurally-related nonoxynol analogs, using the method established, demonstrated that N-9 is the most effective spermicidal agent. The spermicidal activity of N-9 and analogs was also determined by a a computer-assisted semen analysis (CASA) method for comparison. This conventional CASA method is designed to detect sperm motility, in contrast to the flow cytometry method which is capable of identifying the loss of membrane integrity. A discrepancy in the concentration needed for comparable spermicidal action between these assay methods was observed, which could imply that there is a concentration dependency on the disruption of membrane integrity and the complete loss of motility.