Interaction of contraceptive antimicrobial peptide nisin with target cell membranes: implications for use as vaginal microbicide

Nisin variants: What makes them different and unique?

Nisin A is a lantibiotic bacteriocin typically produced by strains of Lactococcus lactis. This bacteriocin has been approved as a natural food preservative since the late 1980 s and shows antimicrobial activity against a range of food-borne spoilage and pathogenic microorganisms. The therapeutic potential of nisin A has also been explored increasingly both in human and veterinary medicine. Nisin has been shown to be effective in treating bovine mastitis, dental caries, cancer, and skin infections. Recently, it was demonstrated that nisin has an affinity for the same receptor used by SARS-CoV-2 to enter human cells and was proposed as a blocker of the viral infection. Several nisin variants produced by distinct bacterial strains or modified by bioengineering have been described since the discovery of nisin A. These variants present modifications in the peptide structure, biosynthesis, mode of action, and spectrum of activity. Given the importance of nisin for industrial and therapeutic applications, the objective of this study was to describe the characteristics of the nisin variants, highlighting the main differences between these molecules and their potential applications. This review will be useful to researchers interested in studying the specifics of nisin A and its variants.

Antimicrobial peptide nisin induces spherical distribution of macropinocytosis-like cytokeratin 5 and cytokeratin 17 following immediate derangement of the cell membrane

The anti-aging effects of Lactococcus lactis are extensively investigated. Nisin is an antimicrobial peptide produced by L. lactis subsp. lactis. We previously reported that 24-hour nisin treatment disturbs the intermediate filament distribution in human keratinocytes. Additionally, we showed that the ring-like distribution of the intermediate filament proteins, cytokeratin (CK) 5 and CK17 is a marker of nisin action. However, two questions remained unanswered: 1) What do the CK5 and CK17 ring-like distributions indicate? 2) Is nisin ineffective under the experimental conditions wherein CK5 and CK17 do not exhibit a ring-like distribution? Super resolution microscopy revealed that nisin treatment altered CK5 and CK17 distribution, making them spherical rather than ring-like, along with actin incorporation. This spherical distribution was not induced by the suppression of endocytosis. The possibility of a macropinocytosis-like phenomenon was indicated, because the spherical distribution was >1 µm in diameter and the spherical distribution was suppressed by macropinocytosis inhibiting conditions, such as the inclusion of an actin polymerization inhibitor and cell migration. Even when the spherical distribution of CK5 and CK17 was not induced, nisin induced derangement of the cell membrane. Nisin treatment for 30 minutes deranged the regular arrangement of the lipid layer (flip-flop); the transmembrane structure of the CK5-desmosome or CK17-desmosome protein complex was disturbed. To the best of our knowledge, this is the first study to report that CK5 and CK17 in a spherical distribution could be involved in a macropinosome-like structure, under certain conditions of nisin action in keratinocytes.

Contraceptive efficacy of sperm agglutinating factor from Staphylococcus warneri, isolated from the cervix of a woman with inexplicable infertility

BACKGROUND

Voluntary control of fertility is of paramount importance to the modern society. But since the contraceptive methods available for women have their limitations such as urinary tract infections, allergies, cervical erosion and discomfort, a desperate need exists to develop safe methods. Vaginal contraceptives may be the answer to this problem, as these are the oldest ways of fertility regulation, practiced over the centuries. With minimal systemic involvement, these are also the safest. Natural substances blocking or impairing the sperm motility offer as valuable non-cytotoxic vaginal contraceptives. Antimicrobial peptides (AMPs) isolated from plants, animals and microorganisms are known to possess sperm immobilizing and spermicidal properties. Following this, in the quest for alternative means, we have cloned, over expressed and purified the recombinant sperm agglutinating factor (SAF) from Staphylococcus warneri, isolated from the cervix of a woman with unexplained infertility.

METHODS

Genomic library of Staphylococcus warneri was generated in Escherichia coli using pSMART vector and screened for sperm agglutinating factor (SAF). The insert in sperm agglutinating transformant was sequenced and was found to express ribonucleotide-diphosphate reductase-α sub unit. The ORF was sub-cloned in pET28a vector, expressed and purified. The effect of rSAF on motility, viability, morphology, Mg⁺⁺-dependent ATPase activity and acrosome status of human sperms was analyzed in vitro and contraceptive efficacy was evaluated in vivo in female BALB/c mice.

RESULTS

The 80 kDa rSAF showed complete sperm agglutination, inhibited its Mg²⁺-ATPase activity, caused premature sperm acrosomal loss in vitro and mimicked the pattern in vivo showing 100% contraception in BALB/c mice resulting in prevention of pregnancy. The FITC labeled SAF was found to bind the entire surface of spermatozoa. Vaginal application and oral administration of rSAF to mice for 14 successive days did not demonstrate any significant change in vaginal cell morphology, organ weight and tissue histology of reproductive and non-reproductive organs and had no negative impact in the dermal and penile irritation tests.

CONCLUSION

The Sperm Agglutinating Factor from Staphylococcus warneri, natural microflora of human cervix, showed extensive potential to be employed as a safe vaginal contraceptive.

Development and Characterization of Nisin Nanoparticles as Potential Alternative for the Recurrent Vaginal Candidiasis Treatment

The aim of this work was the development and characterization of nisin-loaded nanoparticles and the evaluation of its potential antifungal activity. Candidiasis is a fungal infection caused by Candida sp. considered as one of the major public health problem currently. The discovery of antifungal agents that present a reduced or null resistance of Candida sp. and the development of more efficient drug release mechanisms are necessary for the improvement of candidiasis treatment. Nisin, a bacteriocin commercially available for more than 50 years, exhibits antibacterial action in food products with potential antifungal activity. Among several alternatives used to modulate antifungal activity of bacteriocins, polymeric nanoparticles have received great attention due to an effective drug release control and reduction of therapeutic dose, besides the minimization of adverse effects by the preferential accumulation in specific tissues. The nisin nanoparticles were prepared by double emulsification and solvent evaporation methods. Nanoparticles were characterized by dynamic light scattering, zeta potential, Fourier transform infrared, X-ray diffraction, differential scanning calorimetry, and scanning electron microscopy. Antifungal activity was accessed by pour plate method and cell counting using Candida albicans strains. The in vitro release profile and in vitro permeation studies were performed using dialysis bag method and pig vaginal mucosa in Franz diffusion cell, respectively. The results revealed nisin nanoparticles (300 nm) with spherical shape and high loading efficiency (93.88 ± 3.26%). In vitro test results suggest a promising application of these nanosystems as a prophylactic agent in recurrent vulvovaginal candidiasis and other gynecological diseases.

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.

Converting a Staphylococcus aureus toxin into effective cyclic pseudopeptide antibiotics

Staphylococcus aureus produces peptide toxins that it uses to respond to environmental cues. We previously characterized PepA1, a peptide toxin from S. aureus, that induces lytic cell death of both bacterial and host cells. That led us to suggest that PepA1 has an antibacterial activity. Here, we demonstrate that exogenously provided PepA1 has activity against both Gram-positive and Gram-negative bacteria. We also see that PepA1 is significantly hemolytic, thus limiting its use as an antibacterial agent. To overcome these limitations, we converted PepA1 into nonhemolytic derivatives. Our most promising derivative is a cyclic heptapseudopeptide with inconsequential toxicity to human cells, enhanced stability in human sera, and sharp antibacterial activity. Mechanistically, linear and helical PepA1 derivatives form pores at the bacterial and erythrocyte surfaces, while the cyclic peptide induces bacterial envelope reorganization, with insignificant action on the erythrocytes. Our work demonstrates that bacterial toxins might be an attractive starting point for antibacterial drug development.

Antimicrobial peptides: versatile biological properties

Antimicrobial peptides are diverse group of biologically active molecules with multidimensional properties. In recent past, a wide variety of AMPs with diverse structures have been reported from different sources such as plants, animals, mammals, and microorganisms. The presence of unusual amino acids and structural motifs in AMPs confers unique structural properties to the peptide that attribute for their specific mode of action. The ability of these active AMPs to act as multifunctional effector molecules such as signalling molecule, immune modulators, mitogen, antitumor, and contraceptive agent makes it an interesting candidate to study every aspect of their structural and biological properties for prophylactic and therapeutic applications. In addition, easy cloning and recombinant expression of AMPs in heterologous plant host systems provided a pipeline for production of disease resistant transgenic plants. Besides these properties, AMPs were also used as drug delivery vectors to deliver cell impermeable drugs to cell interior. The present review focuses on the diversity and broad spectrum antimicrobial activity of AMPs along with its multidimensional properties that could be exploited for the application of these bioactive peptides as a potential and promising drug candidate in pharmaceutical industries.

Evaluating the feasibility of lantibiotics as an alternative therapy against bacterial infections in humans

Since the commercialization and ubiquitous use of antibiotics in the 20th century, there has been a steady increase in the number of reports on resistant bacteria. In recent years, this situation has become even more dramatic. The relatively slow development of new drugs, especially those with novel modes of action on target bacteria, is not paired with the rapid rate of resistance appearance. Lantibiotics form a group of antimicrobial peptides of bacterial origin with a dual mechanism of action not shared by other therapeutic compounds in use. They have a high potency to inhibit diverse (multidrug resistant) bacteria, combined with a low tendency to generate resistance. These properties make lantibiotics attractive candidates for clinical applications. This paper discusses some of the most recent results obtained in lantibiotic clinical application, paying special attention to the pharmacokinetic and pharmacodynamic properties they display. The objective of this paper is to give insight into the actual clinical applicability of lantibiotics and to point to the unexplored aspects that should be addressed in future research. The authors feel that lantibiotics could increase the number of second line antibiotics for systemic use in the future; however, further research is still needed before this is possible.

Effect of antimicrobial Peptide, nisin, on the reproductive functions of rats

Our previous studies have demonstrated that naturally occurring peptide, Nisin possess antibacterial activity and did not interfere with rabbit vaginal mucosa. In this study, the reproductive toxicity of the Nisin in male rats was evaluated. Rats were fed orally with Nisin (10, 25, and 50 mg/kg/day) for 13 weeks. No treatment related mortality was observed. The body weight gain, food consumption and serum biochemical parameters were at par with the control group. Histomorphology of the selected reproductive (testis, epididymis, ventral prostate, and seminal vesicle) and nonreproductive (liver and kidney) tissues was observed to be normal. There was no treatment-related increase or decrease in the expression of testis-specific genes (c-Kit, GATA-1, and HILS-1) and the activity levels of epididymal α-glucosidase, ventral prostate alkaline phosphatase (AlP), liver alanine aminotransferase (AlAT) and aspartate aminotransferase (AAT). Fructose and lactic acid levels in the seminal vesicles also remained unchanged. These studies suggest that Nisin did not affect the normal physiology of these organs. In addition, no adverse effects were observed on the reproductive performance of Nisin-treated male rats and their offspring. In conclusion, the current studies support our earlier studies, which demonstrated suitability of Nisin as a safe and effective microbicide.

The importance of bacterial membrane composition in the structure and function of aurein 2.2 and selected variants

For cationic antimicrobial peptides to become useful therapeutic agents, it is important to understand their mechanism of action. To obtain high resolution data, this involves studying the structure and membrane interaction of these peptides in tractable model bacterial membranes rather than directly utilizing more complex bacterial surfaces. A number of lipid mixtures have been used as bacterial mimetics, including a range of lipid headgroups, and different ratios of neutral to negatively charged headgroups. Here we examine how the structure and membrane interaction of aurein 2.2 and some of its variants depend on the choice of lipids, and how these models correlate with activity data in intact bacteria (MICs, membrane depolarization). Specifically, we investigated the structure and membrane interaction of aurein 2.2 and aurein 2.3 in 1:1 cardiolipin/1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (CL/POPG) (mol/mol), as an alternative to 1:1 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine(POPC)/POPG and a potential model for Gram positive bacteria such as S. aureus. The structure and membrane interaction of aurein 2.2, aurein 2.3, and five variants of aurein 2.2 were also investigated in 1:1 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE)/POPG (mol/mol) lipids as a possible model for other Gram positive bacteria, such as Bacillus cereus. Solution circular dichroism (CD) results demonstrated that the aurein peptides adopted α-helical structure in all lipid membranes examined, but demonstrated a greater helical content in the presence of POPE/POPG membranes. Oriented CD and ³¹P NMR results showed that the aurein peptides had similar membrane insertion profiles and headgroup disordering effects on POPC/POPG and CL/POPG bilayers, but demonstrated reduced membrane insertion and decreased headgroup disordering on mixing with POPE/POPG bilayers at low peptide concentrations. Since the aurein peptides behaved very differently in POPE/POPG membrane, minimal inhibitory concentrations (MICs) of the aurein peptides in B. cereus strain C737 were determined. The MIC results indicated that all aurein peptides are significantly less active against B. cereus than against S. aureus and S. epidermidis. Overall, the data suggest that it is important to use a relevant model for bacterial membranes to gain insight into the mode of action of a given antimicrobial peptide in specific bacteria.

Identification and characterization of anti-microbial peptides from rabbit vaginal fluid

Antimicrobial peptides (AMPs) serve as a first line of host defense and represent an important, though poorly understood components of the innate immune system. The present study was an attempt to identify and characterize the major molecules having anti-bacterial activities from the vaginal fluid of rabbit, Oryctologus cuniculus. AMPs from the rabbit vaginal fluid (RVF) were identified in the acid extracts of pooled RVF samples after RP-HPLC purification. The protein, RVFAMP was effective against gram negative (Escherichia coli and Pseudomonas aeruginosa) and gram positive (Staphylococcus aureus and Streptococcus pyogenes) bacteria. The results of acid urea-PAGE-gel overlay assay (AU-PAGE-GOA) demonstrated clear zone of growth inhibition of E. coli corresponding to 6 and 15 kDa protein bands. LC-MS data of these proteins indicated that 15 kDa protein consists of lysozyme, lipopolysaccharide binding protein (LBP), hemoglobin-α and β subunits (Hb-α/β), whereas 9 kDa protein band consists of transthyretin and calcyclin while uteroglobulin and neutrophil antibacterial peptide-5 (NAMP-5) are present in the 6 kDa protein band. Of the eight proteins, Hb-α derived protein was further characterized, as it showed the highest Probability Based Mowse Score (PBMS) of 288. A 25mer peptide, RVFHbαp was active against several clinical pathogens as demonstrated by minimum inhibitory concentration (MIC) and radial diffusion assays (RDA). The interaction of RVFHbαP with bacterial liposome membrane was assessed by calcein dye leakage assay. RVFHbαP did not show cytotoxicity against human endocervical cells (End1/E6E7) or erythrocytes. RT-PCR and immunofluorescence results revealed the expression of RVFHbαP mRNA and protein in rabbit vaginal tissue. To the best our knowledge, this is the first report describing the detection of AMPs in RVFs. In conclusion, these studies indicated that vaginal epithelial cells (VEC) derived RVFHbαP may have therapeutic potential in the management of reproductive well being of rabbits. The major reason for undertaking this study in rabbits is that, it forms an excellent in vivo model system for human's studies.

Studies with bioengineered Nisin peptides highlight the broad-spectrum potency of Nisin V

Nisin A is the most thoroughly investigated member of the lantibiotic family of antimicrobial peptides. In addition to a long history of safe use as a food antimicrobial, its activity against multi-drug resistant pathogens has resulted in a renewed interest in applying nisin as a chemotherapeutic to treat bacterial infections. The wealth of Nisin-related information that has been generated has also led to the development of the biotechnological capacity to engineer novel Nisin variants with a view to improving the function and physicochemical properties of this already potent peptide. However, the identification of bioengineered Nisin derivatives with enhanced antimicrobial activity against Gram-positive targets is a recent event. In this study, we created stable producers of the most promising derivatives of Nisin A generated to date [M21V (hereafter Nisin V) and K22T (hereafter Nisin T)] and assessed their potency against a range of drug-resistant clinical, veterinary and food pathogens. Nisin T exhibited increased activity against all veterinary isolates, including streptococci and staphylococci, and against a number of multi-drug resistant clinical isolates including MRSA, but not vancomycin-resistant enterococci. In contrast, Nisin V displayed increased potency against all targets tested including hVISA strains and the hyper-virulent Clostridium difficile ribotype 027 and against important food pathogens such as Listeria monocytogenes and Bacillus cereus. Significantly, this enhanced activity was validated in a model food system against L. monocytogenes. We conclude that Nisin V possesses significant potential as a novel preservative or chemotherapeutic compound.

Potent spermicidal effect of oleanolic acid 3-beta-D-glucuronide, an active principle isolated from the plant Sesbania sesban Merrill

BACKGROUND

The spermicidal activity of oleanolic acid 3-β-D-glucuronide (OAG), an active principle isolated from root extracts of Sesbania sesban, was evaluated.

STUDY DESIGN

Under the Sander-Cramer test criteria, the sperm-immobilizing activity of OAG was studied using highly motile rat sperm. Sperm mortality and membrane integrity were assessed by supravital staining, hypo-osmotic swelling (HOS), transmission electron microscopy (TEM) and sperm membrane lipid peroxidation (LPO). In vitro microbicidal potential and hemolytic index of OAG were examined in Lactobacillus culture and rat red blood corpuscles (RBCs), respectively. Post-intravaginal OAG application, the in vivo contraceptive efficacy was evaluated in rats. Ames test determined the carcinogenic potential of OAG.

RESULTS

The minimum effective concentration (MEC) of OAG was 50 mcg/mL. More than 97% of the OAG-treated sperm lost their HOS responsiveness in a dose-dependent manner. TEM and LPO revealed that OAG affected the sperm membrane integrity. OAG declined fertility to zero, was nonmutagenic and was not harmful to lactobacillus.

CONCLUSION

OAG has significant spermicidal activity that may be explored further.