Melittin: a membrane-active peptide with diverse functions

Light-Controlled Release of Therapeutic Proteins from Red Blood Cells

Protein therapeutics are a powerful class of drugs known for their selectivity and potency. However, the potential efficacy of these therapeutics is commonly offset by short circulatory half-lives and undesired action at otherwise healthy tissue. We describe herein a targeted protein delivery system that employs engineered red blood cells (RBCs) as carriers and light as the external trigger that promotes hemolysis and drug release. RBCs internally loaded with therapeutic proteins are readily surface modified with a dormant hemolytic peptide. The latter is activated via easily assigned wavelengths that extend into the optical window of tissue. We have demonstrated that photorelease transpires with spatiotemporal control and that the liberated proteins display the anticipated biological effects in vitro. Furthermore, we have confirmed targeted delivery of a clot-inducing enzyme in a mouse model. Finally, we anticipate that this strategy is not limited to RBC carriers but also should be applicable to nano- and microtransporters comprised of bilayer lipid membranes.

Novel insights in linking solvent relaxation dynamics and protein conformations utilizing red edge excitation shift approach

Protein hydration dynamics plays an important role in many physiological processes since protein fluctuations, slow solvation, and the dynamics of hydrating water are all intrinsically related. Red edge excitation shift (REES) is a unique and powerful wavelength-selective (i.e. excitation-energy dependent) fluorescence approach that can be used to directly monitor the environment-induced restriction and dynamics around a polar fluorophore in a complex biological system. This review is mainly focused on recent applications of REES and a novel analysis of REES data to monitor the structural dynamics, functionally relevant conformational transitions and to unmask the structural ensembles in proteins. In addition, the novel utility of REES in imaging protein aggregates in a cellular context is discussed. We believe that the enormous potential of REES approach showcased in this review will engage more researchers, particularly from life sciences.

Mobitz Type-2 Heart Block After a Bee-Sting

We report the case of a patient who developed symptomatic bradycardia and Mobitz type 2 heart block one week after a single bee sting. This required implantation of a permanent pacemaker. The patient had no significant past medical history, and previous electrocardiogram (ECGs) did not show heart block or bradycardia. He has been physically active in the past and denied any such symptoms. We presume bee sting to be the cause of his symptomatic bradycardia and heart block. We also think that his heart block was reversible and has since resolved, as his most recent device check showed minimal V-pacing. The cause of his heart block can be either Kounis syndrome or Apamin-mediated calcium channel block. A detailed discussion is done separately.

Venom peptides in cancer therapy: An updated review on cellular and molecular aspects

Based on the high incidence and mortality rates of cancer, its therapy remains one of the most vital challenges in the field of medicine. Consequently, enhancing the efficacy of currently applied treatments and finding novel strategies are of great importance for cancer treatment. Venoms are important sources of a variety of bioactive compounds including salts, small molecules, macromolecules, proteins, and peptides that are defined as toxins. They can exhibit different pharmacological effects, and in recent years, their anti-tumor activities have gained significant attention. Several different compounds are responsible for the anti-tumor activity of venoms, and peptides are one of them. In the present review, we discuss the possible anti-tumor activities of venom peptides by highlighting molecular pathways and mechanisms through which these molecules can act effectively. Venom peptides can induce cell death in cancer cells and can substantially enhance the efficacy of chemotherapy and radiotherapy. Also, the venom peptides can mitigate the migration of cancer cells via suppression of angiogenesis and epithelial-to-mesenchymal transition. Notably, nanoparticles have been applied in enhancing the bioavailability of venom peptides and providing targeted delivery, thereby leading to their elevated anti-tumor activity and potential application for cancer therapy.

Bee Venom: An Updating Review of Its Bioactive Molecules and Its Health Applications

Bee venom (BV) is usually associated with pain since, when humans are stung by bees, local inflammation and even an allergic reaction can be produced. BV has been traditionally used in ancient medicine and in acupuncture. It consists of a mixture of substances, principally of proteins and peptides, including enzymes as well as other types of molecules in a very low concentration. Melittin and phospholipase A2 (PLA2) are the most abundant and studied compounds of BV. Literature of the main biological activities exerted by BV shows that most studies focuses on the comprehension and test of anti-inflammatory effects and its mechanisms of action. Other properties such as antioxidant, antimicrobial, neuroprotective or antitumor effects have also been assessed, both in vitro and in vivo. Moreover, human trials are necessary to confirm those clinical applications. However, notwithstanding the therapeutic potential of BV, there are certain problems regarding its safety and the possible appearance of adverse effects. On this perspective, new approaches have been developed to avoid these complications. This manuscript is aimed at reviewing the actual knowledge on BV components and its associated biological activities as well as the latest advances on this subject.

Targeted and Intracellular Antibacterial Activity against S. agalactiae of the Chimeric Peptides Based on Pheromone and Cell-Penetrating Peptides

The significance of the complex bacterial ecosystem in the human body and the impediment of the mammalian membrane against many antibiotics together emphasize the necessity to develop antimicrobial agents with precise antimicrobial and cell-penetrating activities. A simple and feasible method for generating dual-function antimicrobial peptides inspired by highly hydrophobic peptide pheromone and cationic cell-penetrating peptides is presented. Furthermore, the extension of the peptide candidate library is achieved by modifying the charged domain. The bacteria-selective peptides L1, L2, L10, and L11 kill Streptococcus agalactiae by disrupting the membrane structure, and the targeted mechanism is suggested where the peptides offset the entrapment of S. agalactiae rather than of other bacteria. Moreover, L2 and L10 possess intracellular antibacterial activity and carrier property, which is mainly dependent on endocytosis. Given their suitable biocompatibility, high tolerance, no drug resistance, and effective antimicrobial capacity in a mouse mastitis model, L2 and L10 can be powerful weapons against S. agalactiae pathogen infection.

Activity of five antimicrobial peptides against periodontal as well as non-periodontal pathogenic strains

Background: Due to the increasing emergence of multi-resistant bacteria the search for alternative antimicrobial substances is of high interest. Promising agents are antimicrobial peptides which are host defense molecules of the innate immune system in a wide range of different species. Objectives: The aim of this study was to assess the activity of nisin, melittin, lactoferrin, parasin-1 and LL-37 against 35 oral bacteria and Candida albicans employing the gold standard method for anaerobic susceptibility testing. Methods: The activity of the peptides was determined by an agar dilution method under anaerobic and aerobic conditions. The test media contained final peptide concentrations between 0.125 µg/ml and 8 µg/ml (melittin, lactoferrin, parasin-1, LL-37) and between 0.125 µg/ml and 128 µg/ml (nisin). Results: Nisin completely inhibited the growth of Megasphaera sp., Bifidobacterium longum, Parvimonas micra, Actinomyces israelii, Actinomyces naeslundii, Actinomyces odontolyticus, Prevotella intermedia, Streptococcus anginosus, Streptococcus constellatus and Staphylococcus aureus. Melittin and lactoferrin reduced the growth of Megasphaera sp., P. micra, B. longum (melittin) and Selenomonas flueggei (lactoferrin). Parasin-1 and LL-37 showed no activity. Conclusion: AMPs, especially nisin and to a smaller degree lactoferrin, might be promising alternatives to antibiotics because of their antimicrobial activity, high resistance to environmental conditions and partially low costs.

Antiulcerogenic effect of melittin via mitigating TLR4/TRAF6 mediated NF-κB and p38MAPK pathways in acetic acid-induced ulcerative colitis in mice

Ulcerative colitis (UC) is a chronic disease driven primarily by uncontrolled pervasive inflammatory responses affecting the colon and rectum. Currently available medications carry multiple detrimental adverse effects, which have emphasized the mandatory need for safer and more efficient novel therapeutic alternatives. Melittin is the main constituent of bee venom and exhibits potent anti-inflammatory properties. The antiulcerogenic effect of oral melittin (40 μg/kg) was explored in the current study using the acetic acid-induced colitis model. Increase in body weight and decrease in colon mass index were observed in the melittin group. Microscopically, melittin ameliorated acetic acid-induced histological damage. Melittin administration has efficiently amended the elevated levels of the cytokines, tumor necrosis factor (TNF-α) and interleukin 6 (IL-6) seen in the colitis group. This was accompanied by inhibition of the upstream signaling molecules, Toll-like receptor 4 (TLR4), tumor necrosis factor receptor (TNF-R)-associated factor (TRAF6), mitogen-activated protein kinase 38 (p38 MAPK), and nuclear factor kappaB (NF-κB) in the melittin group. Moreover, treatment with melittin resulted in marked decrease in colonic level of prostaglandin E2 (PGE2) together with the enzymes involved in its synthesis, secretory phospholipase A2 (sPLA2) and cyclooxygenase 2 (COX-2). Additionally, melittin has attenuated acetic acid-induced oxidative stress as manifested by the significant diminishment in malondialdehyde (MDA) as well as the increase in superoxide dismutase (SOD) and reduced glutathione (GSH) levels. Therefore, melittin mitigated UC pathogenesis and could be considered as a potent and promising therapeutic alternative for UC treatment.

Melittin from Apis florea Venom as a Promising Therapeutic Agent for Skin Cancer Treatment

Melittin, a major component found in bee venom, is produced by the Apis species of the honey bee. In this study, the effect of melittin derived from Apis florea (Mel-AF), which is a wild honey bee species that is indigenous to Thailand, was investigated against human malignant melanoma (A375) cells. In this study, Mel-AF exhibited considerable potential in the anti-proliferative action of A375 cells. Subsequently, the cellular mechanism of Mel-AF that induced cell death was investigated in terms of apoptosis. As a result, gene and protein expression levels, which indicated the activation of cytochrome-c release and caspase-9 expression, eventually triggered the release of the caspase-3 executioner upon Mel-AF. We then determined that apoptosis-mediated cell death was carried out through the intrinsic mitochondrial pathway. Moreover, advanced abilities, including cell motility and invasion, were significantly suppressed. Mel-AF manipulated the actin arrangement via the trapping of stress fibers that were found underneath the membrane, which resulted in the defective actin cytoskeleton organization. Consequently, the expression of EGFR, a binding protein to F-actin, was also found to be suppressed. This outcome strongly supports the effects of Mel-AF in the inhibition of progressive malignant activity through the disruption of actin cytoskeleton-EGFR interaction and the EGFR signaling system. Thus, the findings of our current study indicate the potential usefulness of Mel-AF in cancer treatments as an apoptosis inducer and a potential actin-targeting agent.

Antibacterial and Anti-Inflammatory Effects of Novel Peptide Toxin from the Spider Pardosa astrigera

The prevalence of antibiotic-resistant bacteria has become an immediate threat to public health. Antimicrobial peptides are attracting attention as a new source of antibiotics due to their ability to prevent drug-resistances with fewer side effects. Spider venom is composed of various bioactive substances with multiple functionalities such as antimicrobial and anti-inflammatory effects. Here, RNA sequencing was conducted on the venom gland of the spider Pardosa astrigera, and a potential toxin peptide with antibacterial properties was selected via homology and in silico analysis. A novel toxin, Lycotoxin-Pa4a, inhibited both gram-negative and gram-positive bacteria by disrupting the outer and bacterial cytoplasmic membrane. Moreover, the peptide downregulated the expression of pro-inflammatory mediators while upregulating the level of anti-inflammatory cytokine by inactivating mitogen-activated protein kinase signaling in a lipopolysaccharide-stimulated murine macrophage cell line. In this research, we identified a novel peptide toxin, Lycotoxin-pa4a, with antibacterial and anti-inflammatory properties, suggesting its potential for the development of a new antibiotics, as well as offering insights into the utilization of biological resources.

In vitro exposure to Hymenoptera venom and constituents activates discrete ionotropic pathways in mast cells

Calcium entry is central to the functional processes in mast cells and basophils that contribute to the induction and maintenance of inflammatory responses. Mast cells and basophils express an array of calcium channels, which mediate responses to diverse stimuli triggered by small bioactive molecules, physicochemical stimuli and immunological inputs including antigens and direct immune cell interactions. These cells are also highly responsive to certain venoms (such as Hymenoptera envenomations), which cause histamine secretion, cytokine release and an array of pro-inflammatory functional responses. There are gaps in our understanding of the coupling of venom exposure to specific signaling pathways such as activation of calcium channels. In the present study, we performed a current survey of a model mast cell line selected for its pleiotropic responsiveness to multiple pro-inflammatory inputs. As a heterogenous stimulus, Hymenoptera venom activates multiple classes of conductance at the population level but tend to lead to the measurement of only one type of conductance per cell, despite the cell co-expressing multiple channel types. The data show that I_CRAC, I_ARC, and TRPV-like currents are present in the model mast cell populations and respond to venom exposure. We further assessed individual venom components, specifically secretagogues and arachidonic acid, and identified the conductances associated with these stimuli in mast cells. Single-cell calcium assays and immunofluorescence analysis show that there is heterogeneity of channel expression across the cell population, but this heterogeneity does not explain the apparent selectivity for specific channels in response to exposure to venom as a composite stimulus.

Bee venom-derived antimicrobial peptide melectin has broad-spectrum potency, cell selectivity, and salt-resistant properties

Antimicrobial peptides have attracted attention as alternatives to conventional antibiotics. Previously, a novel antimicrobial peptide, melectin, consisting of 18 amino acids was isolated from the venom of a bee, Melecta albifrons. Here, we investigated the antibacterial activity of melectin against drug-resistant bacteria. Melectin showed broad-spectrum antimicrobial activity but low cytotoxicity and no hemolytic activity. Melectin maintained its antimicrobial activity at physiological salt concentrations. Melectin is an α-helical structure that binds to the bacterial membrane via electrostatic interactions and kills bacteria in a short time by bacterial membrane targeting. Collectively, our results suggest that melectin has antibacterial activity and anti-inflammatory activity.

Anti-fungal properties and mechanisms of melittin

Many fungal diseases remain poorly addressed by public health authorities, despite posing a substantial threat to humans, animals, and plants. More worryingly, few classes of anti-fungals have been developed to combat fungal infections thus far. These medications also have certain drawbacks in terms of toxicity, spectrum of activity, and pharmacokinetic properties. Hence, there is a dire need for discovery of novel anti-fungal agents. Melittin, the main constituent in the venom of European honeybee Apis mellifera, has attracted considerable attention among researchers owing to its potential therapeutic applications. To our knowledge, there has been no review pertinent to anti-fungal properties of melittin, prompting us to synopsize the results of experimental investigations with a special emphasis upon underlying mechanisms. In this respect, melittin inhibits a broad spectrum of fungal genera including Aspergillus, Botrytis, Candida, Colletotrichum, Fusarium, Malassezia, Neurospora, Penicillium, Saccharomyces, Trichoderma, Trichophyton, and Trichosporon. Melittin hinders fungal growth by several mechanisms such as membrane permeabilization, apoptosis induction by reactive oxygen species-mediated mitochondria/caspase-dependent pathway, inhibition of (1,3)-β-D-glucan synthase, and alterations in fungal gene expression. Overall, melittin will definitely open up new avenues for various biomedical applications, from medicine to agriculture. KEYPOINTS: • Venom-derived peptides have potential for development of anti-microbial agents. • Many fungal pathogens are susceptible to melittin at micromolar concentrations. • Melittin possesses multi-target mechanism of action against fungal cells.

Effectual Anticancer Potentiality of Loaded Bee Venom onto Fungal Chitosan Nanoparticles

Chitosan and its nanoparticles (NPs) could be extracted from numerous fungal species and used as effectual carriers for bioactive compounds. The fungal chitosan (FC) was innovatively acquired from Fusarium oxysporum grown mycelia, characterized and used for NP synthesis and loading with bee venom (BV). The nano-FC (NFC) had 192.4 nm mean NP diameter, 38.22% loading capacity, and 92.42% entrapment efficiency. BV release from NFC was pH and time dependent; burst BV release was detected at the first 6 h, followed by gradual releases up to 30 h. The in vitro anticancer potentiality valuation, of NFC, BV, and NFC/BV nanoconjugates against HeLa cervix carcinoma, revealed that they all had potent dose-dependent anticancer activity; BV/NFC nanoconjugates were the most effective with IC50=200 μg/mL. The fluorescent staining of treated HeLa cells with BV/NFC nanoconjugates, with DAPI and acridine orange/propidium iodide combination, indicated the appearance of early apoptosis, secondary apoptosis, and secondary necrosis markers and their increment with exposure prolongation. The production of NFC from F. oxysporum and their loading with BV are strongly counseled for production of potent natural antitumor agent with augmented activity against cervix carcinoma.

The Effect of Bee Venom Peptides Melittin, Tertiapin, and Apamin on the Human Erythrocytes Ghosts: A Preliminary Study

Red blood cells (RBCs) are the most abundant cells in the human blood that have been extensively studied under morphology, ultrastructure, biochemical and molecular functions. Therefore, RBCs are excellent cell models in the study of biologically active compounds like drugs and toxins on the structure and function of the cell membrane. The aim of the present study was to explore erythrocyte ghost’s proteome to identify changes occurring under the influence of three bee venom peptides-melittin, tertiapin, and apamin. We conducted preliminary experiments on the erythrocyte ghosts incubated with these peptides at their non-hemolytic concentrations. Such preparations were analyzed using liquid chromatography coupled with tandem mass spectrometry. It was found that when higher concentrations of melittin and apamin were used, fewer proteins were identified. Moreover, the results clearly indicated that apamin demonstrates the greatest influence on the RBCs ghosts proteome. Interestingly, the data also suggest that tertiapin exerted a stabilizing effect on the erythrocyte membrane. The experiments carried out show the great potential of proteomic research in the projects focused on the toxin’s properties as membrane active agents. However, to determine the specificity of the effect of selected bee venom peptides on the erythrocyte ghosts, further proteomic research should be focused on the quantitative analysis.

Antibacterial activity and mechanism of the cell-penetrating peptide CF-14 on the gram-negative bacteria, Escherichia coli

In the present study, we characterized CF-14, a novel antimicrobial peptide derived from the catfish skin mucus. The objective of this study was to explore the antimicrobial mechanism of CF-14 against Escherichia coli. The agar-diffusion assay and the microdilution method were used to evaluate the antimicrobial activity and the minimum inhibitory concentration (MIC) of CF-14 against E. coli, respectively. In addition, the absorbance of the bacterial suspension filtrate at 260 nm was measured to quantify the leakage of bacterial cytoplasmic components. The bacterial morphological changes were observed by scanning electron microscopy, while confocal microscopy was used to investigate the localization site of CF-14 in E.coli. The DNA binding ability of CF-14 was evaluated using gel retardation assay and the binding of CF-14 to DnaK was evaluated using Discovery Studio. The results demonstrated that CF-14 exhibited strong antimicrobial activity against E.coli with an MIC of 31.3 μg/mL. Unlike common cationic anti-microbial peptides (AMPs) that target the cellmembrane, CF-14 penetrated the E.coli cell membrane and induced only minormembrane perturbations. Furthermore, the antimicrobial mechanism of CF-14 against E.coli involved DNA binding and competitive inhibition of bacterial DnaK. Finally, by deleting or replacing the amino acid sequence, the antibacterial activity of CF-14 was affected, which helped the optimization of amino acid sequence. Therefore, CF-14 can be a potential antimicrobial peptide.

Membrane morphology effects in quartz crystal microbalance characterization of antimicrobial peptide activity

The mechanism of action of membrane disrupting antimicrobial peptides (AMPs) and the basis of their specificity and selectivity to pathogens are often studied by using biomimetic model membranes. It is often assumed that all model membrane morphologies, e.g. liposomes, supported bilayers, tethered bilayers etc. are equivalent. In this work the validity of this assumption was assessed. Melittin was used as the reference AMP as it can disrupt both bacterial and mammalian-mimetic membranes. Quartz crystal microbalance (QCM) viscoelastic fingerprints show characteristic differences between the three model morphologies: single bilayer membranes, multilamellar membrane stacks and unilamellar liposomes. In the second and third case, initial trends show material removal instead of material addition as in the single bilayer case, consistent with dissolution of some bilayers, and bursting liposomes, respectively. The latter is accompanied by a characteristic drop in the dissipation signal as the liposomes collapse. The results also highlight an important limitation of the QCM method, the need for a well established reference system for qualitative analysis of the viscoelastic fingerprints, and thus the importance of using the right model system, i.e. single bilayer membrane, for studies of the mechanism of action of AMPs.

Rational Substitution of ε-Lysine for α-Lysine Enhances the Cell and Membrane Selectivity of Pore-Forming Melittin

Here, we present a rational approach that enhances the membrane selectivity of a prolific pore-forming peptide, melittin, based on experimental observations that the cationic polymer, ε-polylysine, disrupts bacterial membranes with greater affinity over mammalian cells when compared to poly-l-lysine and poly-d-lysine. We systematically replaced three α-lysine residues in melittin with ε-lysine residues and identified key residues that are important for cytotoxicity. We then assessed the antimicrobial properties of the modified peptides which carry two or three ε-lysyl residues. Two modified melittin peptides displayed rapid bactericidal properties against antibiotic-resistant strains, low innate resistance development by pathogenic bacteria, remained nonimmunogenic for T lymphocytes, and increased bioavailability in tear fluids. In proof-of-concept in vivo experiments, one of the peptides was noncytotoxic for ocular surfaces and had comparable antimicrobial efficacy to that of fluoroquinolone antibiotics. The results uncover a simple and potential strategy that can enhance the membrane selectivity of cytolytic peptides by ε-lysylation.

Neuroinflammation: An overview of neurodegenerative and metabolic diseases and of biotechnological studies

Neuroinflammation is an important factor contributing to cognitive impairment and neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), Amyotrophic lateral sclerosis (ALS), ischemic injury, and multiple sclerosis (MS). These diseases are characterized by inexorable progressive injury of neuron cells, and loss of motor or cognitive functions. Microglia, which are the resident macrophages in the brain, play an important role in both physiological and pathological conditions. In this review, we provide an updated discussion on the role of ROS and metabolic disease in the pathological mechanisms of activation of the microglial cells and release of cytotoxins, leading to the neurodegenerative process. In addition, we also discuss in vivo models, such as zebrafish and Caenorhabditis elegans, and provide new insights into therapeutics bioinspired by neuropeptides from venomous animals, supporting high throughput drug screening in the near future, searching for a complementary approach to elucidating crucial mechanisms associated with neurodegenerative disorders.

What Makes a Good Pore Former: A Study of Synthetic Melittin Derivatives

Pore formation by membrane-active peptides, naturally encountered in innate immunity and infection, could have important medical and technological applications. Recently, the well-studied lytic peptide melittin has formed the basis for the development of combinatorial libraries from which potent pore-forming peptides have been derived, optimized to work under different conditions. We investigate three such peptides, macrolittin70, which is most active at neutral pH; pHD15, which is active only at low pH; and MelP5_Δ6, which was rationally designed to be active at low pH but formed only small pores. There are three, six, and six acidic residues in macrolittin70, pHD15, and MelP5_Δ6, respectively. We perform multi-microsecond simulations in 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) of hexamers of these peptides starting from transmembrane orientations at neutral pH (all residues at standard protonation), low pH (acidic residues and His protonated), and highly acidic environments in which C-termini are also protonated. Previous simulations of the parent peptides melittin and MelP5 in 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) are repeated in POPC. We find that the most potent pore-forming peptides exhibit strong interpeptide interactions, including salt bridges, H-bonds, and polar interactions. Protonation of the C-terminus promotes helicity and pore size. The proximity of the peptides allows fewer lipid headgroups to line the pores than in previous simulations, making the pores intermediate between barrel stave and toroidal. Based on these structures and geometrical arguments, we attempt to rationalize the factors that under different conditions can increase or decrease pore stability and propose mutations that could be tested experimentally.

Design and use of model membranes to study biomolecular interactions using complementary surface-sensitive techniques

Cellular membranes are complex structures and simplified analogues in the form of model membranes or biomembranes are used as platforms to understand fundamental properties of the membrane itself as well as interactions with various biomolecules such as drugs, peptides and proteins. Model membranes at the air-liquid and solid-liquid interfaces can be studied using a range of complementary surface-sensitive techniques to give a detailed picture of both the structure and physicochemical properties of the membrane and its resulting interactions. In this review, we will present the main planar model membranes used in the field to date with a focus on monolayers at the air-liquid interface, supported lipid bilayers at the solid-liquid interface and advanced membrane models such as tethered and floating membranes. We will then briefly present the principles as well as the main type of information on molecular interactions at model membranes accessible using a Langmuir trough, quartz crystal microbalance with dissipation monitoring, ellipsometry, atomic force microscopy, Brewster angle microscopy, Infrared spectroscopy, and neutron and X-ray reflectometry. A consistent example for following biomolecular interactions at model membranes is used across many of the techniques in terms of the well-studied antimicrobial peptide Melittin. The overall objective is to establish an understanding of the information accessible from each technique, their respective advantages and limitations, and their complementarity.

Selective anticancer activity of synthetic peptides derived from the host defence peptide tritrpticin

Antimicrobial peptides (AMPs) constitute a diverse family of peptides with the ability to protect their host against microbial infections. In addition to their ability to kill microorganisms, several AMPs also exhibit selective cytotoxicity towards cancer cells and are collectively referred to as anticancer peptides (ACPs). Here a large library of AMPs, mainly derived from the porcine cathelicidin peptide, tritrpticin (VRRFPWWWPFLRR), were assessed for their anticancer activity against the Jurkat T cell leukemia line. These anticancer potencies were compared to the cytotoxicity of the peptides towards normal cells isolated from healthy donors, namely peripheral blood mononuclear cells (PBMCs) and red blood cells (RBCs; where hemolytic activity was assessed). Among the active tritrpticin derivatives, substitution of Arg by Lys enhanced the selectivity of the peptides towards Jurkat cells when compared to PBMCs. Additionally, the side chain length of the Lys residues was also optimized to further enhance the tritrpticin ACP selectivity at low concentrations. The mechanism of action of the peptides with high selectivity involved the permeabilization of the cytoplasmic membrane of Jurkat cells, without formation of apoptotic bodies. The incorporation of non-natural Lys-based cationic amino acids could provide a new strategy to improve the selectivity of other synthetic ACPs to enhance their potential for therapeutic use against leukemia cells.

A Rapid Fluorescence-Based Microplate Assay to Investigate the Interaction of Membrane Active Antimicrobial Peptides with Whole Gram-Positive Bacteria

Background: Membrane-active antimicrobial peptides (AMPs) are interesting candidates for the development of novel antimicrobials. Although their effects were extensively investigated in model membrane systems, interactions of AMPs with living microbial membranes are less known due to their complexity. The aim of the present study was to develop a rapid fluorescence-based microplate assay to analyze the membrane effects of AMPs in whole Staphylococcus aureus and Staphylococcus epidermidis. Methods: Bacteria were exposed to bactericidal and sub-inhibitory concentrations of two membrane-active AMPs in the presence of the potential-sensitive dye 3,3′-dipropylthiadicarbocyanine iodide (diSC₃(5)) and the DNA staining dye propidium iodide (PI), to simultaneously monitor and possibly distinguish membrane depolarization and membrane permeabilization. Results: The ion channel-forming gramicidin D induced a rapid increase of diSC₃(5), but not PI fluorescence, with slower kinetics at descending peptide concentrations, confirming killing due to membrane depolarization. The pore-forming melittin, at sub-MIC and bactericidal concentrations, caused, respectively, an increase of PI fluorescence in one or both dyes simultaneously, suggesting membrane permeabilization as a key event. Conclusions: This assay allowed the distinction between specific membrane effects, and it could be applied in the mode of action studies as well as in the screening of novel membrane-active AMPs.

Melittin-A Natural Peptide from Bee Venom Which Induces Apoptosis in Human Leukaemia Cells

Bee venom is a very complex mixture produced and secreted by the honeybee (Apis mellifera). Melittin is a major component of bee venom that accounts for about 52% of its dry mass. A vast number of studies have been dedicated to the effects of melittin’s regulation of apoptosis and to the factors that induce apoptosis in various types of cancer such as breast, ovarian, prostate, lung. The latest evidence indicates its potential as a therapeutic agent in the treatment of leukaemia. The aim of our present study is to evaluate melittin’s ability to induce apoptosis in leukaemia cell lines of different origin acute lymphoblastic leukaemia (CCRF-CEM) and chronic myelogenous leukaemia (K-562). We demonstrated that melittin strongly reduced cell viability in both leukaemia cell lines but not in physiological peripheral blood mononuclear cells (PMBCs). Subsequent estimated parameters (mitochondrial membrane potential, Annexin V binding and Caspases 3/7 activity) clearly demonstrated that melittin induced apoptosis in leukaemia cells. This is a very important step for research into the development of new potential anti-leukaemia as well as anticancer therapies. Further analyses on the molecular level have been also planned (analysis of proapoptotic genes expression and DNA damages) for our next research project, which will also focus on melittin.

Revisiting the Interaction of Melittin with Phospholipid Bilayers: The Effects of Concentration and Ionic Strength

Melittin is an anti-microbial peptide (AMP) and one of the most studied membrane-disrupting peptides. There is, however, a lack of accurate measurements of the concentration-dependent kinetics and affinity of binding of melittin to phospholipid membranes. In this study, we used surface plasmon resonance spectroscopy to determine the concentration-dependent effect on the binding of melittin to 1-palmitoyl-2-oleoyl-glycero-3-phosphocholine (POPC) bilayers in vesicles. Three concentration ranges were considered, and when combined, covered two orders of magnitudes (0.04 µM to 8 µM), corresponding to concentrations relevant to the membrane-disrupting and anti-microbial activities of melittin. Binding kinetics data were analysed using a 1:1 Langmuir-binding model and a two-state reaction model. Using in-depth quantitative analysis, we characterised the effect of peptide concentration, the addition of NaCl at physiological ionic strength and the choice of kinetic binding model on the reliability of the calculated kinetics and affinity of binding parameters. The apparent binding affinity of melittin for POPC bilayers was observed to decrease with increasing peptide/lipid (P/L) ratio, primarily due to the marked decrease in the association rate. At all concentration ranges, the two-state reaction model provided a better fit to the data and, thus, a more reliable estimate of binding affinity. Addition of NaCl significantly reduced the signal response during the association phase; however, no substantial effect on the binding affinity of melittin to the POPC bilayers was observed. These findings based on POPC bilayers could have important implications for our understanding of the mechanism of action of melittin on more complex model cell membranes of higher physiological relevance.

18F-Trifluoromethanesulfinate Enables Direct C-H 18F-Trifluoromethylation of Native Aromatic Residues in Peptides

18F labeling strategies for unmodified peptides with [18F]fluoride require 18F-labeled prosthetics for bioconjugation more often with cysteine thiols or lysine amines. Here we explore selective radical chemistry to target aromatic residues applying C-H 18F-trifluoromethylation. We report a one-step route to [18F]CF3SO2NH4 from [18F]fluoride and its application to direct [18F]CF3 incorporation at tryptophan or tyrosine residues using unmodified peptides as complex as recombinant human insulin. The fully automated radiosynthesis of octreotide[Trp(2-CF218F)] enables in vivo positron emission tomography imaging.

Development and Challenges of Antimicrobial Peptides for Therapeutic Applications

More than 3000 antimicrobial peptides (AMPs) have been discovered, seven of which have been approved by the U.S. Food and Drug Administration (FDA). Now commercialized, these seven peptides have mostly been utilized for topical medications, though some have been injected into the body to treat severe bacterial infections. To understand the translational potential for AMPs, we analyzed FDA-approved drugs in the FDA drug database. We examined their physicochemical properties, secondary structures, and mechanisms of action, and compared them with the peptides in the AMP database. All FDA-approved AMPs were discovered in Gram-positive soil bacteria, and 98% of known AMPs also come from natural sources (skin secretions of frogs and toxins from different species). However, AMPs can have undesirable properties as drugs, including instability and toxicity. Thus, the design and construction of effective AMPs require an understanding of the mechanisms of known peptides and their effects on the human body. This review provides an overview to guide the development of AMPs that can potentially be used as antimicrobial drugs.

Melittin: a venom-derived peptide with promising anti-viral properties

Despite tremendous advances in the development of anti-viral therapeutics, viral infections remain a chief culprit accounting for ongoing morbidity and mortality worldwide. Natural products, in particular animal venoms, embody a veritable cornucopia of exotic constituents, suggesting an immensurable source of anti-infective drugs. In this context, melittin, the principal constituent in the venom of the European honeybee Apis mellifera, has been demonstrated to exert anti-cancer, anti-inflammatory, anti-diabetic, anti-infective, and adjuvant properties. To our knowledge, there is no review appertaining to effects of melittin against viruses, prompting us to synopsize experimental investigations on its anti-viral activity throughout the past decades. Accumulating evidence indicates that melittin curbs infectivity of a diverse array of viruses including coxsackievirus, enterovirus, influenza A viruses, human immunodeficiency virus (HIV), herpes simplex virus (HSV), Junín virus (JV), respiratory syncytial virus (RSV), vesicular stomatitis virus (VSV), and tobacco mosaic virus (TMV). However, medication safety, different routes of administrations, and molecular mechanisms behind the anti-viral activity of melittin should be scrutinized in future studies.

The Effect of Charge on Melittin-Induced Changes in Membrane Structure and Morphology

The binding of melittin to a range of phospholipid bilayers was studied using dual polarisation interferometry and atomic force microscopy. The phospholipid model membranes included zwitterionic dimyristylphosphatidylcholine (DMPC), together with mixtures of DMPC/dimyristylphosphatidylglycerol (DMPG) and DMPC/DMPG/cholesterol. Melittin caused significant disruption on all bilayers, but differences in morphological changes during binding were different on each membrane. Overall, the results demonstrate that the process of membrane disruption follows distinct structural changes for different lipid mixtures irrespective of the strength of binding to the membrane surface.

Use of Selected Carbon Nanoparticles as Melittin Carriers for MCF-7 and MDA-MB-231 Human Breast Cancer Cells

Despite advanced techniques in medicine, breast cancer caused the deaths of 627,000 women in 2018. Melittin, the main component of bee venom, has lytic properties for many types of cells, including cancer cells. To increase its toxic effect, carbon nanoparticles, graphene oxide, pristine graphene, and diamond were used as carriers of melittin to breast cancer cells. To date, the effects of carbon nanoparticles as carriers of melittin on cancer cells have not been studied. The present study was carried out on MCF-7 and MDA-MB-231 cell lines. The investigation consisted of structural analysis of complexes using transmission electron microscopy, zeta potential measurements, evaluation of cell morphology, assessment of cell viability and membrane integrity, investigation of reactive oxygen species production, and investigation of mitochondrial membrane potential. Cell death was examined by flow cytometry and a membrane test for 43 apoptotic proteins. The results indicate that melittin complex with nanographene oxide has a stronger toxic effect on breast cancer cells than melittin alone. Moreover, nanodiamonds can protect cells against the lytic effects of melittin. All complexes reduced, but not completely eliminated the level of necrosis, compared to melittin. Thus, results suggest that the use of carbon nanoparticles as carriers for melittin may find use in medicine in the future.

Differential sensitivity of pHLIP to ester and ether lipids

pH (low) insertion peptide (pHLIP) is a polypeptide from the third transmembrane helix of bacteriorhodopsin. The pH-dependent membrane insertion of pHLIP has been conveniently exploited for translocation of cargo molecules and as a novel imaging agent in cancer biology due to low extracellular pH in cancer tissues. Although the application of pHLIP for imaging tumor and targeted drug delivery is well studied, literature on pHLIP-membrane interaction is relatively less studied. Keeping this in mind, we explored the differential interaction of pHLIP with ester and ether lipid membranes utilizing fluorescence and CD spectroscopy. We report, for the first time, higher binding affinity of pHLIP toward ether lipid relative to ester lipid membranes. There results gain relevance since Halobacterium halobium (source of bacteriorhodopsin) is enriched with ether lipids. In addition, we monitored the difference in microenvironment around pHLIP tryptophans utilizing red edge excitation shift and observed increased motional restriction of water molecules in the interfacial region in ether lipid membranes. These changes were accompanied with increase in helicity of pHLIP in ether lipid relative to ester lipid membranes. Our results assume further relevance since ether lipids are upregulated in cancer cells and have emerged as potential biomarkers of various diseases including cancer.

Applications of RNA interference in the treatment of arthritis

RNA interference (RNAi) is a cellular mechanism for post-transcriptional gene regulation mediated by small interfering RNA (siRNA) and microRNA. siRNA-based therapy holds significant promise for the treatment of a wide-range of arthritic diseases. siRNA selectively suppresses the expression of a gene product and can thus achieve the specificity that is lacking in small molecule inhibitors. The potential use of siRNA-based therapy in arthritis, however, has not progressed to clinical trials despite ample evidence for efficacy in preclinical studies. One of the main challenges to clinical translation is the lack of a suitable delivery vehicle to efficiently and safely access diverse pathologies. Moreover, the ideal targets in treatment of arthritides remain elusive given the complexity and heterogeneity of these disease pathogeneses. Herein, we review recent preclinical studies that use RNAi-based drug delivery systems to mitigate inflammation in models of rheumatoid arthritis and osteoarthritis. We discuss a self-assembling peptide-based nanostructure that demonstrates the potential of overcoming many of the critical barriers preventing the translation of this technology to the clinic.

Co-delivery of Bee Venom Melittin and a Photosensitizer with an Organic-Inorganic Hybrid Nanocarrier for Photodynamic Therapy and Immunotherapy

Photodynamic therapy (PDT) is a clinical cancer treatment modality based on the induction of therapeutic reactive oxygen species (ROS), which can trigger immunogenic cell death (ICD). With the aim of simultaneously improving both PDT-mediated intracellular ROS production and ICD levels, we designed a serum albumin (SA)-coated boehmite ("B"; aluminum hydroxide oxide) organic-inorganic scaffold that could be loaded with chlorin e6 (Ce6), a photosensitizer, and a honey bee venom melittin (MLT) peptide, denoted Ce6/MLT@SAB. Ce6/MLT@SAB was anchored by a boehmite nanorod structure and exhibited particle size of approximately 180 nm. Ce6/MLT@SAB could significantly reduce hemolysis relative to that of free MLT, while providing MLT-enhanced PDT antitumor effects in vitro. Compared with Ce6@SAB, Ce6/MLT@SAB improved Ce6 penetration of cancer cells both in vitro and in vivo, thereby providing enhanced intracellular ROS generation with 660 nm light treatment. Following phototreatment, Ce6/MLT@SAB-treated cells displayed significantly improved levels of ICD and abilities to activate dendritic cells. In the absence of laser irradiation, multidose injection of Ce6/MLT@SAB could delay the growth of subcutaneous murine tumors by more than 60%, compared to controls. When combined with laser irradiation, a single injection and phototreatment with Ce6/MLT@SAB eradicated one-third of subcutaneous tumors in treated mice. The addition of an immune checkpoint blockade to Ce6/MLT@SAB phototreatment further augmented antitumor effects, generating increased numbers of CD4⁺ and CD8⁺ T cells in tumors with concomitant reduction of myeloid-derived suppressor cells.

Melittin inhibits proliferation, migration and invasion of bladder cancer cells by regulating key genes based on bioinformatics and experimental assays

The antitumour effect of melittin (MEL) has recently attracted considerable attention. Nonetheless, information regarding the functional role of MEL in bladder cancer (BC) is currently limited. Herein, we investigated the effect of MEL on critical module genes identified in BC. In total, 2015 and 4679 differentially expressed genes (DEGs) associated with BC were identified from the GSE31189 set and The Cancer Genome Atlas database, respectively. GSE‐identified DEGs were mapped and analysed using Gene Ontology and Kyoto Encyclopaedia of Genes and Genomes analyses to determine BC‐involved crucial genes and signal pathways. Coupled with protein–protein interaction network and Molecular Complex Detection analyses, Modules 2 and 4 were highlighted in the progression of BC. In in‐vitro experiments, MEL inhibited the proliferation, migration, and invasion of UM‐UC‐3 and 5637 cells. The expression of NRAS, PAK2, EGFR and PAK1 in Module 4—enriched in the MAPK signalling pathway—was significantly reduced after treatment with MEL at concentrations of 4 or 6 μg/mL. Finally, quantitative reverse transcription‐polymerase chain reaction and Western blotting analyses revealed MEL inhibited the expression of genes at the mRNA (ERK1/2, ERK5, JNK and MEK5), protein (ERK5, MEK5, JNK and ERK1/2) and phosphorylation (p‐ERK1/2, p‐JNK, and p‐38) levels. This novel evidence indicates MEL exerts effects on the ERK5‐MAK pathway—a branch of MAPK signalling pathway. Collectively, these findings provide a theoretical basis for MEL application in BC treatment.

Site-Directed Fluorescence Approaches for Dynamic Structural Biology of Membrane Peptides and Proteins

Membrane proteins mediate a number of cellular functions and are associated with several diseases and also play a crucial role in pathogenicity. Due to their importance in cellular structure and function, they are important drug targets for ~60% of drugs available in the market. Despite the technological advancement and recent successful outcomes in determining the high-resolution structural snapshot of membrane proteins, the mechanistic details underlining the complex functionalities of membrane proteins is least understood. This is largely due to lack of structural dynamics information pertaining to different functional states of membrane proteins in a membrane environment. Fluorescence spectroscopy is a widely used technique in the analysis of functionally-relevant structure and dynamics of membrane protein. This review is focused on various site-directed fluorescence (SDFL) approaches and their applications to explore structural information, conformational changes, hydration dynamics, and lipid-protein interactions of important classes of membrane proteins that include the pore-forming peptides/proteins, ion channels/transporters and G-protein coupled receptors.

Bee Updated: Current Knowledge on Bee Venom and Bee Envenoming Therapy

Honey bees can be found all around the world and fulfill key pollination roles within their natural ecosystems, as well as in agriculture. Most species are typically docile, and most interactions between humans and bees are unproblematic, despite their ability to inject a complex venom into their victims as a defensive mechanism. Nevertheless, incidences of bee stings have been on the rise since the accidental release of Africanized bees to Brazil in 1956 and their subsequent spread across the Americas. These bee hybrids are more aggressive and are prone to attack, presenting a significant healthcare burden to the countries they have colonized. To date, treatment of such stings typically focuses on controlling potential allergic reactions, as no specific antivenoms against bee venom currently exist. Researchers have investigated the possibility of developing bee antivenoms, but this has been complicated by the very low immunogenicity of the key bee toxins, which fail to induce a strong antibody response in the immunized animals. However, with current cutting-edge technologies, such as phage display, alongside the rise of monoclonal antibody therapeutics, the development of a recombinant bee antivenom is achievable, and promising results towards this goal have been reported in recent years. Here, current knowledge on the venom biology of Africanized bees and current treatment options against bee envenoming are reviewed. Additionally, recent developments within next-generation bee antivenoms are presented and discussed.

Effects of Peptide Charge, Orientation, and Concentration on Melittin Transmembrane Pores

Melittin is a short cationic peptide that exerts cytolytic effects on bacterial and eukaryotic cells. Experiments suggest that in zwitterionic membranes, melittin forms transmembrane toroidal pores supported by four to eight peptides. A recently constructed melittin variant with a reduced cationic charge, MelP5, is active at 10-fold lower concentrations. In previous work, we performed molecular dynamics simulations on the microsecond timescale to examine the supramolecular pore structure of a melittin tetramer in zwitterionic and partially anionic membranes. We now extend that study to include the effects of peptide charge, initial orientation, and number of monomers on the pore formation and stabilization processes. Our results show that parallel transmembrane orientations of melittin and MelP5 are more consistent with experimental data. Whereas a MelP5 parallel hexamer forms a large stable pore during the 5-μs simulation time, a melittin hexamer and an octamer are not fully stable, with several monomers dissociating during the simulation time. Interaction-energy analysis shows that this difference in behavior between melittin and MelP5 is not due to stronger electrostatic repulsion between neighboring melittin peptides but to peptide-lipid interactions that disfavor the isolated MelP5 transmembrane monomer. The ability of melittin monomers to diffuse freely in the 1,2-dimyristoyl-SN-glycero-3-phosphocholine membrane leads to dynamic pores with varying molecularity.

Bee Venom: Overview of Main Compounds and Bioactivities for Therapeutic Interests

Apitherapy is an alternate therapy that relies on the usage of honeybee products, most importantly bee venom for the treatment of many human diseases. The venom can be introduced into the human body by manual injection or by direct bee stings. Bee venom contains several active molecules such as peptides and enzymes that have advantageous potential in treating inflammation and central nervous system diseases, such as Parkinson's disease, Alzheimer's disease, and amyotrophic lateral sclerosis. Moreover, bee venom has shown promising benefits against different types of cancer as well as anti-viral activity, even against the challenging human immunodeficiency virus (HIV). Many studies described biological activities of bee venom components and launched preclinical trials to improve the potential use of apitoxin and its constituents as the next generation of drugs. The aim of this review is to summarize the main compounds of bee venom, their primary biological properties, mechanisms of action, and their therapeutic values in alternative therapy strategies.

Anti-Tumor Effects of Melittin and Its Potential Applications in Clinic

Melittin, a major component of bee venom, is a water-soluble toxic peptide of which a various biological effects have been identified to be useful in anti-tumor therapy. In addition, Melittin also has anti-parasitic, anti-bacterial, anti-viral, and anti-inflammatory activities. Therefore, it is a very attractive therapeutic candidate for human diseases. However, melittin induces extensive hemolysis, a severe side effect that dampens its future development and clinical application. Thus, studies of melittin derivatives and new drug delivery systems have been conducted to explore approaches for optimizing the efficacy of this compound, while reducing its toxicity. A number of reviews have focused on each side, respectively. In this review, we summarize the research progress on the anti-tumor effects of melittin and its derivatives, and discuss its future potential clinical applications.

α1-Acid Glycoprotein Has the Potential to Serve as a Biomimetic Drug Delivery Carrier for Anticancer Agents

Nanosize plasma proteins could be used as a biomimetic drug delivery system (DDS) for cancer treatment when loaded with anticancer drugs based on the fact that plasma proteins can serve as a source of nutrients for cancer cells. This prompted us to investigate the potential of α₁-acid glycoprotein (AGP) for this role because it is a nanosize plasma protein and binds a variety of anticancer agents. Pharmacokinetic analyses indicated that AGP is distributed more extensively in tumor tissue than human serum albumin, which was already established as a cancer DDS carrier. AGP is possibly being incorporated into tumor cells via endocytosis pathways. Moreover, a synthetic AGP-derived peptide which possesses a high ability to form an α-helix, as deduced from the primary structure of AGP, was also taken up by the tumor cells. AGP loaded with anticancer agents, such as paclitaxel or nitric oxide, efficiently induced tumor cell death. These results suggest that AGP has the potential to be a novel DDS carrier for anticancer agents.

Coming in and Finding Out: Blending Receptor-Targeted Delivery and Efficient Endosomal Escape in a Novel Bio-Responsive siRNA Delivery System for Gene Knockdown in Pulmonary T Cells

RNA interference (RNAi) offers the potential to selectively silence disease-related genes in defined cell subsets. Translation into the clinical routine is, however, still hampered by the lack of efficient carrier systems for therapeutic siRNA, endosomal entrapment presenting a major hurdle. A promising siRNA delivery system has previously been developed on the base of polyethylenimine (PEI) and the targeting ligand transferrin (Tf) to specifically reach activated T cells in the lung. In the present work, the focus is on optimizing Tf-PEI polyplexes for gene knockdown in primary activated T cells by improving their endosomal escape properties. Blending of the conjugate with membrane lytic melittin significantly enhanced endosomal release and thereby cytoplasmic delivery, while maintaining selective T cell targeting abilities and overall cell tolerability. The gathered data furthermore demonstrate that melittin addition also distinctly improves several other essential particle characteristics, such as siRNA encapsulation efficiency and stability in lung lining fluids. In conclusion, this results in a novel upgraded siRNA delivery system that is not only able to specifically deliver its payload to the desired target cells via receptor-mediated endocytosis, but also shows enhanced release from endosomal vesicles in order to initiate RNAi in the cytoplasm.

Potential Therapeutic Applications of Bee Venom on Skin Disease and Its Mechanisms: A Literature Review

Skin is larger than any other organ in humans. Like other organs, various bacterial, viral, and inflammatory diseases, as well as cancer, affect the skin. Skin diseases like acne, atopic dermatitis, and psoriasis often reduce the quality of life seriously. Therefore, effective treatment of skin disorders is important despite them not being life-threatening. Conventional medicines for skin diseases include corticosteroids and antimicrobial drugs, which are effective in treating many inflammatory and infectious skin diseases; however, there are growing concerns about the side effects of these therapies, especially during long-term use in relapsing or intractable diseases. Hence, many researchers are trying to develop alternative treatments, especially from natural sources, to resolve these limitations. Bee venom (BV) is an attractive candidate because many experimental and clinical reports show that BV exhibits anti-inflammatory, anti-apoptotic, anti-fibrotic, antibacterial, antiviral, antifungal, and anticancer effects. Here, we review the therapeutic applications of BV in skin diseases, including acne, alopecia, atopic dermatitis, melanoma, morphea, photoaging, psoriasis, wounds, wrinkles, and vitiligo. Moreover, we explore the therapeutic mechanisms of BV in the treatment of skin diseases and killing effects of BV on skin disease-causing pathogens, including bacteria, fungi and viruses.

Hydrogels Embedded With Melittin and Tobramycin Are Effective Against Pseudomonas aeruginosa Biofilms in an Animal Wound Model

We demonstrate that the antimicrobial peptide, melittin, is effective alone and in combination with the aminoglycosides tobramycin to kill Pseudomonas aeruginosa growing as biofilms both in vitro and in vivo. Melittin and tobramycin show enhanced in vitro activity in combination at micromolar concentrations, resulting in a 2-log10 reduction in the number of cells within mature PAO1 P. aeruginosa biofilms after 6-h of treatment. Alternatively, either agent alone resulted in half-a-log10 reduction. Time-killing assays demonstrated that the combination of melittin and tobramycin was effective at 2-h whereas tobramycin was not effective until after 6-h of treatment. We also found the combination was more effective than tobramycin alone against biofilms of 7 P. aeruginosa cystic fibrosis clinical isolates, resulting in a maximum 1.5-log10 cellular reduction. Additionally, melittin alone was effective at killing biofilms of 4 Staphylococcus aureus isolates, resulting in a maximum 2-log10 cellular reduction. Finally, melittin in combination with tobramycin embedded in an agarose-based hydrogel resulted in a 4-fold reduction in bioluminescent P. aeruginosa colonizing mouse wounds by 4-h. In contrast, tobramycin or melittin treatment alone did not cause a statistically significant reduction in bioluminescence. These data demonstrate that melittin in combination with tobramycin embedded in a hydrogel is a potential treatment for biofilm-associated wound infections.

Comparison of the Protective Effects of Bee Venom Extracts with Varying PLA2 Compositions in a Mouse Model of Parkinson's Disease

Bee venom contains a number of pharmacologically active components, including enzymes and polypeptides such as phospholipase A₂ (PLA₂) and melittin, which have been shown to exhibit therapeutic benefits, mainly via attenuation of inflammation, neurotoxicity, and nociception. The individual components of bee venom may manifest distinct biological actions and therapeutic potential. In this study, the potential mechanisms of action of PLA₂ and melittin, among different compounds purified from honey bee venom, were evaluated against Parkinson’s disease (PD). Notably, bee venom PLA₂ (bvPLA₂), but not melittin, exhibited neuroprotective activity against PD in a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD. MPTP-induced behavioral deficits were also abolished after bvPLA₂ treatment, depending on the PLA₂ content. Further, bvPLA₂ administration activated regulatory T cells (Tregs) while inhibiting inflammatory T helper (Th) 1 and Th17 cells in the MPTP mouse model of PD. These results indicate that bvPLA₂, but not melittin, protected against MPTP and alleviated inflammation in PD. Thus, bvPLA₂ is a promising and effective therapeutic agent in Parkinson’s disease.

Designing Melittin-Graphene Hybrid Complexes for Enhanced Antibacterial Activity

Antimicrobial peptides (AMPs) promise a fundamental solution to the devastating threat of drug-resistant bacteria. However, drawbacks of AMPs (e.g., poor cell membrane penetration efficiency) seriously block their clinical use. In this work, rational design of a hybrid complex of melittin (as a representative AMP) and graphene or graphene oxide (Gra or GO) nanosheets for enhanced antibacterial ability is achieved, via combining in-silico prediction and in-tube test. In comparison to pristine melittin, the specifically designed AMP-Gra (/GO) complex exhibits remarkable efficiency in transmembrane perforation with an over tenfold decrease in the threshold working concentration of peptide; moreover, it has an up to 20-fold enhancement in antibacterial activity against both Gram-negative and Gram-positive bacteria. Such improvement is ascribed to the synergetic insertion of nanosheets and melittin due to similarity in antibacterial mechanism between them and is further regulated by the structural factors of the complex, including the intersheet spacing and surface functionalization of the Gra/GO sheets, etc. These results provide practical guidelines to engineer AMPs with nanotechnology for improved antimicrobial performances, especially based on targeted functionalization of the Gra/GO nanosheets.