17BIPHE2, an engineered cathelicidin antimicrobial peptide with low susceptibility to proteases, is an effective spermicide and microbicide against Neisseria gonorrhoeae

STUDY QUESTION

Is 17BIPHE2, an engineered cathelicidin antimicrobial peptide with low susceptibility to proteases, a better spermicide in cervicovaginal fluid (CVF) than its parental peptides, LL-37 and GF-17?

SUMMARY ANSWER

At the same mass concentration, 17BIPHE2 exhibited the highest spermicidal activity on human sperm resuspended in CVF-containing medium.

WHAT IS KNOWN ALREADY

LL-37 and its truncated peptide GF-17 exert both spermicidal and microbicidal activities, although they are prone to proteolytic degradation in body fluids.

STUDY DESIGN, SIZE, DURATION

Spermicidal activities of 17BIPHE2 were evaluated in vitro in mouse and human sperm, both resuspended in medium, and then on human sperm incubated in CVF-containing medium; in the latter condition, the spermicidal activity and peptide stability in CVF of 17BIPHE2 were compared with that of LL-37 and GF-17. The in vivo contraceptive effects of 17BIPHE2 and the reversibility thereof were then assessed in mice. Finally, in vitro microbicidal effects of 17BIPHE2 on Neisseria gonorrhoeae were determined.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Sperm motility and plasma membrane integrity were assessed by videomicroscopy and exclusion of Sytox Green, a membrane-impermeable fluorescent dye, respectively. Successful in vitro fertilization (IVF) was determined by the presence of two pronuclei in oocytes following their coincubation with capacitated untreated or 17BIPHE2-treated sperm. Sperm alone or with 17BIPHE2 were transcervically injected into female mice and successful in vivo fertilization was indicated by the formation of two-cell embryos 42-h postinjection, and by pregnancy through pup delivery 21-25 days afterwards. Peptide intactness was assessed by immunoblotting and HPLC. Reversibility of the contraceptive effects of 17BIPHE2 was evaluated by resumption of pregnancy of the female mice, pretranscervically injected with 17BIPHE2, following natural mating with fertile males. Minimum inhibitory/bactericidal concentrations of 17BIPHE2 on N. gonorrhoeae were obtained through microdilution broth assay.

MAIN RESULTS AND THE ROLE OF CHANCE

At the same mass concentration, 17BIPHE2 was a more effective spermicide than LL-37 or GF-17 on human sperm resuspended in CVF-containing medium, with the spermicidal concentration of 32.4 µM. This was mainly due to lower susceptibility of 17BIPHE2 to CVF proteases. Importantly, the reproductive tract of mouse females treated three times with 32.4 µM 17BIPHE2 remained normal and their fecundity resumed after stopping 17BIPHE2 treatment.

LIMITATIONS, REASONS FOR CAUTION

For ethical reasons, the inhibitory effects of 17BIPHE2 on fertilization and pregnancy cannot presently be performed in women. Also, while our study has proven the effectiveness of 17BIPHE2 as a spermicide for mouse and human sperm in vitro, dosage formulation (e.g. in hydrogel) of 17BIPHE2 still needs to be developed to allow 17BIPHE2 to remain in the vagina/uterine cavity with controlled release for its spermicidal action.

WIDER IMPLICATIONS OF THE FINDINGS

Since 17BIPHE2 also exerted bactericidal activity against N. gonorrhoeae at its spermicidal concentration, it is a promising candidate to be developed into a vaginal multipurpose prevention technology agent, thus empowering women against unplanned pregnancies and sexually transmitted infections.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the Canadian Institutes of Health Research (PJT 173268 to N.T.). There are no competing interests to declare.

TRIAL REGISTRATION NUMBER

N/A.

Evaluation of the novel vaginal contraceptive agent PPCM in preclinical studies using sperm hyaluronan binding and acrosome status assays

Background

Polyphenylene carboxymethylene (PPCM) sodium salt is a promising multipurpose technology for prevention of both sexually transmitted infections (STIs) and pregnancy. In preclinical studies, PPCM has demonstrated significant (1) antimicrobial activity against several important viral and bacterial pathogens and (2) contraceptive activity associated with premature acrosome loss.

Objective

To further evaluate a vaginal antimicrobial compound as a contraceptive agent in preclinical studies utilizing a repurposed hyaluronan binding assay (HBA).

Materials and methods

Semen samples containing either neat semen or washed spermatozoa were treated with increasing concentrations of PPCM or calcium ionophore A23187 (positive control). Sperm inactivation was measured by two methods: (1) double acrosome staining (AS), and (2) a hyaluronan binding assay (HBA^®). Percentage of inactivated sperm was compared between untreated control sperm and those treated with PPCM or A23187.

Results

PPCM had a significant (p < 0.05) and dose‐dependent effect on sperm inactivation in both assays, with HBA detecting a higher proportion of inactivated sperm than AS. PPCM did not affect sperm motility and exhibited equivalent responses in the neat and washed samples.

Discussion

Both HBA and AS confirmed that spermatozoa were rapidly inactivated at PPCM concentrations likely present in the vagina under actual use conditions and in a time‐frame comparable to in vivo migration of spermatozoa out of seminal plasma into cervical mucus.

Conclusion

PPCM vaginal gel may provide contraceptive protection as well as help with STI prevention. HBA may be a sensitive and much needed biomarker for sperm activity in future contraceptive development.

Antimicrobial peptide LL-37 and its truncated forms, GI-20 and GF-17, exert spermicidal effects and microbicidal activity against Neisseria gonorrhoeae

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.

Potential Use of Antimicrobial Peptides as Vaginal Spermicides/Microbicides

The concurrent increases in global population and sexually transmitted infection (STI) demand a search for agents with dual spermicidal and microbicidal properties for topical vaginal application. Previous attempts to develop the surfactant spermicide, nonoxynol-9 (N-9), into a vaginal microbicide were unsuccessful largely due to its inefficiency to kill microbes. Furthermore, N-9 causes damage to the vaginal epithelium, thus accelerating microbes to enter the women's body. For this reason, antimicrobial peptides (AMPs), naturally secreted by all forms of life as part of innate immunity, deserve evaluation for their potential spermicidal effects. To date, twelve spermicidal AMPs have been described including LL-37, magainin 2 and nisin A. Human cathelicidin LL-37 is the most promising spermicidal AMP to be further developed for vaginal use for the following reasons. First, it is a human AMP naturally produced in the vagina after intercourse. Second, LL-37 exerts microbicidal effects to numerous microbes including those that cause STI. Third, its cytotoxicity is selective to sperm and not to the female reproductive tract. Furthermore, the spermicidal effects of LL-37 have been demonstrated in vivo in mice. Therefore, the availability of LL-37 as a vaginal spermicide/microbicide will empower women for self-protection against unwanted pregnancies and STI.

Antimicrobial host defence peptide, LL-37, as a potential vaginal contraceptive

STUDY QUESTION

Does antimicrobial peptide, LL-37, inhibit sperm fertilizing ability?

SUMMARY ANSWER

Our results indicate that LL-37 inhibits mouse and human sperm fertilizing ability.

WHAT IS KNOWN ALREADY

LL-37, a cationic antimicrobial peptide, exerts its microbicidal effects through the disruption of microbial cytoplasmic membranes following its interaction with microbial surface anionic phospholipids. ALL-38 (an LL-37 close analogue: LL-37 + Ala at the N-terminus) is produced in the vagina 2-6 h post-intercourse from its precursor hCAP-18, a seminal plasma component. At this time, motile sperm have already swum into the uterine cavity, thus unexposed to ALL-38. Since sperm contain a substantial amount of acidic sulfogalactosylglycerolipid (SGG) on their surface, treatment of sperm with LL-37 may cause their membrane disruption in an analogous manner to that occurring on microbial membranes.

STUDY DESIGN, SIZE AND DURATION

Mouse/human sperm treated (2-30 min) with LL-37 in a physiological concentration range (up to 10.8 µM) were assessed for SGG-dependent LL-37 binding, and parameters relevant to fertilizing ability, namely motility and intactness of the sperm acrosome and plasma membrane. Ability of mouse sperm to fertilize eggs in vitro was also evaluated. Each study was performed with greater than or equal to three different sperm samples. The efficacy of LL-37 to inhibit sperm fertilizing ability in vivo was determined in female mice (n = 26 each for LL-37 treatment and no treatment), using sperm retrieved from 26 males.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Human sperm samples were donated by fertile men. LL-37 was chemically synthesized and was biotinylated for sperm binding studies. Sperm motility was assessed by videomicroscopy and the acrosomal status by Coomassie blue staining of acrosome-intact mouse sperm or the exposure of CD46, an inner acrosomal membrane protein, of acrosome reacted human sperm. Sperm membrane permeabilization/disruption was assessed by the loss of hypo-osmotic swelling response, an incorporation of Sytox Green (a membrane impermeable fluorescent DNA dye), and electron microscopy. Mouse IVF was scored by the presence of two pronuclei in eggs 6 h post-insemination. Ability of mouse sperm to fertilize eggs in vivo was determined by the pregnancy outcome of female mice injected transcervically with sperm with or without LL-37.

MAIN RESULTS AND THE ROLE OF CHANCE

Biotinylated LL-37 bound to both mouse and human sperm and the binding was partially dependent on sperm surface SGG. Mouse and human sperm became immotile and underwent a premature acrosome reaction upon treatment with LL-37 at 3.6 and 10.8 µM, respectively. The initial action of LL-37 on both mouse and human sperm appeared to be through permeabilization/disruption of sperm surface membranes evidenced by the loss of hypo-osmotic swelling response, Sytox Green staining and electron microscopy revealing ultrastructural damage. Mouse sperm treated with 3.6 µM LL-37 lost the ability to fertilize eggs both in vitro and in vivo. All 26 female mice inseminated with sperm and LL-37 did not become pregnant. No apparent damage to the reproductive tract was observed as revealed by histological characterization in LL-37-inseminated mice and these females resumed fecundity following mating with fertile males.

LIMITATIONS, REASONS FOR CAUTION

Direct demonstration that LL-37 treated human sperm fail to fertilize eggs was limited by legal restrictions on obtaining human eggs for such use.

WIDER IMPLICATIONS OF THE FINDINGS

Our results reveal selective inhibitory effects of LL-37 on sperm fertilizing ability in mice without apparent impairment to the female reproductive tract. LL-37 is therefore a promising candidate to be developed into a vaginal contraceptive with microbicidal activity.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by Grand Challenges Explorations grant from the Bill & Melinda Gates Foundation (OPP1024509), Canadian Institutes of Health Research (MOP119438 & CCI82413) and International Collaboration and Exchanges NSFC of China (No.30611120525). There are no competing interests to declare.