Combined nonoxynol-9 and antimicrobial peptide LL-37 for barrier contraception.

Abstract: Birth control and sexually transmitted infections are global concerns. Nonoxynol-9 (N-9) is the most commonly used component in spermicides, with controversial safety and efficacy. LL-37 has been considered the most promising antimicrobial peptide for developing spermicides. Thus, we aimed to refine the regime of N-9 through the adjunction of LL-37 with higher spermicidal efficacy, safety, and antimicrobial activity. Processed sperm from density gradient centrifugation were treated with nonoxynol-9, LL-37, or the combination for the spermicidal activity. Acrosome reaction, DNA fragmentation, and hemizona binding were evaluated. Minimal inhibitory concentrations were measured using E. coli. Mouse experiments were conducted to investigate skin and vagina irritations. The spermicidal activities of nonoxynol-9 and LL-37 were dose-dependent. Premature acrosome reactions were shown in both groups by increasing acrosome-reacted sperm at around 9 and 21% significantly, and interestingly, the combined group showed a synergistic effect by raising over 60%. In the DNA fragmentation, although there were no significant changes in the nonoxynol-9 or LL-37 groups, the combined group showed a 3% increase at a significant level. Both nonoxynol-9 and LL-37 showed reduced binding capacity with the hemizona-binding indexes at 43.2 and 8.0, and the combined group showed the lowest capacity at 5.6. In animal experiments, the addition of LL-37 to the nonoxynol-9 could alleviate the disruptions caused by nonoxynol-9 in reducing skin epidermal hyperplasia and vaginal irritation. However, the presence of nonoxynol-9 would reduce the antibacterial activity of LL-37. This refined regime showed enhanced spermicidal effects and reduced irritations, but only limited antimicrobial activity. Lay summary: Birth control and sexually transmitted infections are global concerns. One of the most common components used in spermicides to kill sperm is nonoxynol-9, but there have been questions about safety and efficacy. LL-37 has been considered a promising component, together with its function in killing microbes. We aimed to design a spermicide using N-9 and LL-37 together, with potentially higher efficacy and safety. This refined regime showed improvements in killing sperm and improved effects on sperm functions. It also reduced the irritation to the skin and vagina, but only showed limited activity in killing the microbes.