Anti-HIV effect of gramicidin in vitro: potential for spermicide use

In Silico and In Vitro Inhibition of SARS-CoV-2 PLpro with Gramicidin D

Finding an effective drug to prevent or treat COVID-19 is of utmost importance in tcurrent pandemic. Since developing a new treatment takes a significant amount of time, drug repurposing can be an effective option for achieving a rapid response. This study used a combined in silico virtual screening protocol for candidate SARS-CoV-2 PL^pro inhibitors. The Drugbank database was searched first, using the Informational Spectrum Method for Small Molecules, followed by molecular docking. Gramicidin D was selected as a peptide drug, showing the best in silico interaction profile with PL^pro. After the expression and purification of PL^pro, gramicidin D was screened for protease inhibition in vitro and was found to be active against PL^pro. The current study's findings are significant because it is critical to identify COVID-19 therapies that are efficient, affordable, and have a favorable safety profile.

Antiviral Activity of Approved Antibacterial, Antifungal, Antiprotozoal and Anthelmintic Drugs: Chances for Drug Repurposing for Antiviral Drug Discovery

Drug repurposing process aims to identify new uses for the existing drugs to overcome traditional de novo drug discovery and development challenges. At the same time, as viral infections became a serious threat to humans and the viral organism itself has a high ability to mutate genetically, and due to serious adverse effects that result from antiviral drugs, there are crucial needs for the discovery of new antiviral drugs, and to identify new antiviral effects for the exciting approved drugs towards different types of viral infections depending on the observed antiviral activity in preclinical studies or clinical findings is one of the approaches to counter the viral infections problems. This narrative review article summarized mainly the published preclinical studies that evaluated the antiviral activity of drugs that are approved and used mainly as antibacterial, antifungal, antiprotozoal, and anthelmintic drugs, and the preclinical studies included the in silico, in vitro, and in vivo findings, additionally some clinical observations were also included while trying to relate them to the preclinical findings. Finally, the structure used for writing about the antiviral activity of the drugs was according to the families of the viruses used in the studies to form a better image for the target of antiviral activity of different drugs in the different kinds of viruses and to relate between the antiviral activity of the drugs against different strains of viruses within the same viral family.

The antimicrobial and immunomodulatory effects of Ionophores for the treatment of human infection

Ionophores are a diverse class of synthetic and naturally occurring ion transporter compounds which demonstrate both direct and in-direct antimicrobial properties against a broad panel of bacterial, fungal, viral and parasitic pathogens. In addition, ionophores can regulate the host-immune response during communicable and non-communicable disease states. Although the clinical use of ionophores such as Amphotericin B, Bedaquiline and Ivermectin highlight the utility of ionophores in modern medicine, for many other ionophore compounds issues surrounding toxicity, bioavailability or lack of in vivo efficacy studies have hindered clinical development. The antimicrobial and immunomodulating properties of a range of compounds with characteristics of ionophores remain largely unexplored. As such, ionophores remain a latent therapeutic avenue to address both the global burden of antimicrobial resistance, and the unmet clinical need for new antimicrobial therapies. This review will provide an overview of the broad-spectrum antimicrobial and immunomodulatory properties of ionophores, and their potential uses in clinical medicine for combatting infection.

The Effect of Cellular Stress on T and B Cell Memory Pathways in Immunized and Unimmunized BALB/c Mice

Immunological memory is a fundamental function of vaccination. The antigenic breakdown products of the vaccine may not persist, and undefined tonic stimulation has been proposed to maintain the specific memory. We have suggested that cellular stress agents to which the immune cells are constantly exposed may be responsible for tonic stimulation. Here we have studied four stress agents: sodium arsenite, an oxidative agent; Gramicidin, eliciting K⁺ efflux and calcium influx; dithiocarbamate, a metal ionophore; and aluminum hydroxide (alum), an immunological adjuvant. The aims of this study are to extend these investigations to T and B cell responses of unimmunized and ovalbumin (OVA)-immunized BALB/c mice, and furthermore, to ascertain whether stress is involved in optimal expression of memory B cells, as demonstrated in CD4⁺ T cells. Examination of the homeostatic pathway defined by IL-15/IL-15R (IL-15 receptor) interaction and the inflammasome pathway defined by the IL-1-IL-1R interaction between dendritic cells (DC) and CD4⁺ T cells suggests that both pathways are involved in the development of optimal expression of CD4⁺CD45RO⁺ memory T cells in unimmunized and OVA-immunized BALB/c mice. Furthermore, significant direct correlation was found between CD4⁺CD44⁺ memory T cells and both IL-15 of the homeostatic and IL-1β of the inflammasome pathways. However, CD19⁺CD27⁺ memory B cells in vivo seem to utilize only the IL-15/IL-15R homeostatic pathway, although the proliferative responses are enhanced by the stress agents. Altogether, stress agents may up-regulate unimmunized and OVA-immunized CD4⁺CD44⁺ memory T cells by the homeostatic and inflammasome pathways. However, the CD19⁺CD27⁺ memory B cells utilize only the homeostatic pathway.

Roles of d-Amino Acids on the Bioactivity of Host Defense Peptides

Host defense peptides (HDPs) are positively-charged and amphipathic components of the innate immune system that have demonstrated great potential to become the next generation of broad spectrum therapeutic agents effective against a vast array of pathogens and tumor. As such, many approaches have been taken to improve the therapeutic efficacy of HDPs. Amongst these methods, the incorporation of d-amino acids (d-AA) is an approach that has demonstrated consistent success in improving HDPs. Although, virtually all HDP review articles briefly mentioned about the role of d-AA, however it is rather surprising that no systematic review specifically dedicated to this topic exists. Given the impact that d-AA incorporation has on HDPs, this review aims to fill that void with a systematic discussion of the impact of d-AA on HDPs.

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.

Enhanced eryptosis following gramicidin exposure

The peptide antibiotic and ionophore gramicidin has previously been shown to trigger apoptosis of nucleated cells. In analogy to apoptosis, the suicidal death of erythrocytes or eryptosis involves cell shrinkage and cell membrane scrambling with phosphatidylserine translocation to the erythrocyte surface. Triggers of eryptosis include oxidative stress, increase of cytosolic Ca²⁺ activity ([Ca²⁺]_i), and ceramide. The present study explored, whether gramicidin triggers eryptosis. To this end phosphatidylserine exposure at the cell surface was estimated from annexin V binding, cell volume from forward scatter, red blood cell distribution width (RDW) from electronic particle counting, reactive oxidant species (ROS) from 2',7'-dichlorodihydrofluorescein diacetate (DCFDA) fluorescence, [Ca²⁺]_i from Fluo3- and Fluo4 fluorescence, and ceramide abundance from binding of specific antibodies. As a result, a 24 h exposure of human erythrocytes to gramicidin significantly increased the percentage of annexin-V-binding cells (≥1 µg/mL), forward scatter (≥0.5 µg/mL) and hemolysis. Gramicidin enhanced ROS activity, [Ca²⁺]_i and ceramide abundance at the erythrocyte surface. The stimulation of annexin-V-binding by gramicidin was significantly blunted but not abolished by removal of extracellular Ca²⁺. In conclusion, gramicidin stimulates phospholipid scrambling of the erythrocyte cell membrane, an effect at least partially due to induction of oxidative stress, increase of [Ca²⁺]_i and up-regulation of ceramide abundance. Despite increase of [Ca²⁺]_i, gramicidin increases cell volume and slightly reduces RWD.

Channel-forming bacterial toxins in biosensing and macromolecule delivery

To intoxicate cells, pore-forming bacterial toxins are evolved to allow for the transmembrane traffic of different substrates, ranging from small inorganic ions to cell-specific polypeptides. Recent developments in single-channel electrical recordings, X-ray crystallography, protein engineering, and computational methods have generated a large body of knowledge about the basic principles of channel-mediated molecular transport. These discoveries provide a robust framework for expansion of the described principles and methods toward use of biological nanopores in the growing field of nanobiotechnology. This article, written for a special volume on "Intracellular Traffic and Transport of Bacterial Protein Toxins", reviews the current state of applications of pore-forming bacterial toxins in small- and macromolecule-sensing, targeted cancer therapy, and drug delivery. We discuss the electrophysiological studies that explore molecular details of channel-facilitated protein and polymer transport across cellular membranes using both natural and foreign substrates. The review focuses on the structurally and functionally different bacterial toxins: gramicidin A of Bacillus brevis, α-hemolysin of Staphylococcus aureus, and binary toxin of Bacillus anthracis, which have found their "second life" in a variety of developing medical and technological applications.

Mechanisms and modifications of naturally occurring host defense peptides for anti-HIV microbicide development

Despite advances in the treatment of HIV infection, heterosexual transmission of HIV remains high, and vaccines to prevent HIV acquisition have been unfruitful. Vaginal microbicides, on the other hand, have demonstrated considerable potential for HIV prevention, and a variety of compounds have been screened for their activity and safety as anti-HIV microbicides. Among these are the naturally occurring host defense peptides, small peptides from diverse lineages with intrinsic antiviral activity. Naturally occurring host defense peptides with anti-HIV activity are promising candidates for vaginal microbicide development. Their structural variance and accompanying mechanistic diversity provide a wide range of inhibitors whose antiviral activity can be exerted at nearly every stage of the HIV lifecycle. Additionally, peptide modification has been explored as a method for improving the anti-HIV activity of host defense peptides. Structure- and sequence-based alterations have achieved varying success in improving the potency and specificity of anti-HIV peptides. Overall, peptides have been discovered or engineered to inhibit HIV with therapeutic indices of > 1000, encouraging their advancement toward clinical trials. Here we review the naturally occurring anti-HIV host defense peptides, demonstrating their breadth of mechanistic diversity, and exploring approaches to enhance and optimize their activity in order to expedite their development as safe and effective anti-HIV vaginal microbicides.

Role of ions on structure and stability of a synthetic gramicidin ion channel in solution. A molecular dynamics study

We performed a molecular dynamics (MD) simulation to the investigate structure and stability of a synthetic gramicidin-like peptide in solution with and without ions. The starting structures of the MD simulations were taken from two recently solved NMR structures of this peptide in isotropic solution, which forms stable monomers or dimers in the presence or absence of ions, respectively. The monomeric structure is channel-like and is assumed to be stabilized by the presence of two Cs(+) ions bound in the channel, each one close to one channel entrance. In our MD simulations, we observed how the Cs(+) ions bind in the channel formed by the monomeric gramicidin-like peptide using implicit solvent and explicit ions with a concentration of 2 M. MD simulations were performed with and without explicit ions but with an implicit solvent model defined by the generalized Born approximation, which was used to mimic the dielectric properties of the solvent and to speed up the computations.

Minidefensins and other antimicrobial peptides: candidate anti-HIV microbicides

Antimicrobial peptides have long been presumed to act as effector molecules of innate immunity. However, direct evidence that antimicrobial peptides have central roles in host defence has only recently become available. An overview of the types and characteristics of endogenous human antimicrobial peptides and proteins is presented, with particular emphasis on peptides that are active against HIV. These antiviral peptides are discussed in the context of utilising natural peptides for the design of effective topical microbicides for the treatment of sexually transmitted infections (STIs). Several antimicrobial peptides, termed minidefensins, are potently active against HIV, and bear structural similarity to their larger defensin cousins. Strategies to develop potent peptide antibiotics based on defensin and minidefensin templates are promising in the development of antiviral therapeutics and preventatives.

Considerations and development of topical microbicides to inhibit the sexual transmission of HIV

The increased incidence of HIV/AIDS disease in women aged 15 - 49 years has identified the urgent need for a female-controlled, efficacious and safe vaginal topical microbicide. To meet this challenge, new topical microbicide candidates consisting of molecules or formulations that modify the genital environment (BufferGel, engineered Lactobacillus, over-the-counter lubricants), surfactants (C31D/Savvy, sodium dodecyl sulfate, sodium lauryl sulfate), polyanionic polymers (PRO 2000, beta-cyclodextrin, Carraguard, CAP, D2S, SPL-7013), proteins (cyanovirin-N, monoclonal antibodies, thromspondin-1 peptides, Pokeweed antiviral protein and others), reverse transcription inhibitors (PMPA [Tenofovir ]), UC-781, SJ-3366, DABO and thiourea) and other molecules (NCp7-specific virucides, chemokine receptor agonists/antagonists, WHI-05 and WHI-07) are currently being investigated for activity, safety and efficacy. This review will assess the development of these molecules in the context of cervicovaginal defences and the clinical failure of nonoxynol-9.

Women, contraception and STDs including HIV

It is estimated that eight million women are infected with the human immunodeficiency virus (HIV) worldwide. Heterosexual transmission is the predominant mode of HIV transmission on a global basis and is becoming increasingly important in the Western world. Women have long used contraceptives as a means of protection against an unwanted pregnancy, some of which may also protect against sexually transmitted disease (STD) including HIV. We review the relationship between contraceptive methods and STD acquisition and transmission; HIV acquisition and transmission; and the implications of contraceptive use, particularly regarding disease progression, in those women who are already infected with the virus. It is important for all women that protection against both unwanted pregnancy and HIV acquisition and transmission are considered together and not in isolation as nowhere is the argument for a broad based multi-disciplinary approach more cogent.

Acrosin inhibitor, 4'-acetamidophenyl 4-guanidinobenzoate, an experimental vaginal contraceptive with anti-HIV activity

Serine proteases are involved in a wide variety of seemingly unrelated physiological functions including capacitation of the spermatozoa and potentiation of human immunodeficiency virus (HIV) infection. The experimental vaginal contraceptives derived from 4-guanidinobenzoic acid act through inhibition of acrosin--a serine protease from the sperm. The serial ten-fold dilutions of 4'-acetamidophenyl 4-guanidinobenzoate (AGB) were tested in vitro for the effect against HIV infection by assaying the suppression of de novo p24 synthesis in virus-inoculated MT-4 T lymphocytes. The results reveal that complete inhibition of HIV occurred at 100 micrograms/ml--a dose corresponding to previously reported concentrations responsible for preventing fertilization in rabbits. These findings suggest that serine protease inhibitors and in particular the guanidinobenzoates, reported to be up to 100-fold more potent and less irritating than nonoxynol-9, can be potentially operative against sexual transmission of HIV.