Study question: Do the truncated LL-37 peptides, GI-20 and GF-17, have spermicidal activity and microbicidal effects on the sexually transmitted infection (STI) pathogen Neisseria gonorrhoeae with equivalent potency to LL-37?
Summary answer: GI-20 and GF-17 exhibited spermicidal effects on both mouse and human sperm as well as microbicidal action on N. gonorrhoeae with the same efficacy as LL-37.
What is known already: The antimicrobial peptide LL-37 exerts microbicidal activity against various STI pathogens as well as spermicidal effects on both mouse and human sperm.
Study design, size, duration: Spermicidal activities of GI-20 and GF-17 were evaluated in vitro in mouse and human sperm and in vivo in mice. Finally, in vitro antimicrobial effects of LL-37, GI-20 and GF-17 on an STI pathogen, N. gonorrhoeae were determined. All experiments were repeated three times or more. In particular, sperm samples from different males were used on each experimental day.
Participants/materials, setting, methods: The plasma membrane integrity of peptide-treated sperm was assessed by cellular exclusion of Sytox Green, a membrane impermeable fluorescent DNA dye. Successful mouse in vitro fertilization was revealed by the presence of two pronuclei in oocytes following co-incubation with capacitated untreated/peptide-pretreated sperm. Sperm plus each peptide were transcervically injected into female mice and the success of in vivo fertilization was scored by the formation of 2-4 cell embryos 42 h afterward. Reproductive tract tissues of peptide pre-exposed females were then assessed histologically for any damage. Minimal inhibitory/bactericidal concentrations of LL-37, GI-20 and GF-17 on N. gonorrhoeae were determined by a standard method.
Main results and the role of chance: Like LL-37, treatment of sperm with GI-20 and GF-17 resulted in dose-dependent increases in sperm plasma membrane permeabilization, reaching the maximum at 18 and 3.6 μM for human and mouse sperm, respectively (P < 0.0001, as compared with untreated sperm). Mouse sperm treated with 3.6 μM GI-20 or GF-17 did not fertilize oocytes either in vitro or in vivo. Moreover, reproductive tract tissues of female mice pre-exposed to 3.6 μM GI-20 or GF-17 remained intact with no lesions, erosions or ulcerations. At 1.8-7.2 μM, LL-37, GI-20 and GF-17 exerted bactericidal effects on N. gonorrhoeae.
Large scale data: N/A.
Limitations, reasons for caution: Direct demonstration of the inhibitory effects of GI-20 and GF-17 on human in vitro and in vivo fertilization cannot be performed due to ethical issues.
Wider implications of the findings: Like LL-37, GI-20 and GF-17 acted as spermicides and microbicides against N. gonorrhoeae, without adverse effects on female reproductive tissues. With lower synthesis costs, GI-20 and GF-17 are attractive peptides for further development into vaginal spermicides/microbicides.
Study funding/competing interest(s): This work was supported by Canadian Institutes of Health Research (MOP119438 and CCI82413 to N.T.) and NIH (R01 AI105147 to G.W.). There are no competing interests to declare.