Antimicrobial properties of membrane-active dodecapeptides derived from MSI-78

Peptide-based self-assembled monolayers (SAMs): what peptides can do for SAMs and vice versa

Self-assembled monolayers (SAMs) represent highly ordered molecular materials with versatile biochemical features and multidisciplinary applications. Research on SAMs has made much progress since the early begginings of Au substrates and alkanethiols, and numerous examples of peptide-displaying SAMs can be found in the literature. Peptides, presenting increasing structural complexity, stimuli-responsiveness, and biological relevance, represent versatile functional components in SAMs-based platforms. This review examines the major findings and progress made on the use of peptide building blocks displayed as part of SAMs with specific functions, such as selective cell adhesion, migration and differentiation, biomolecular binding, advanced biosensing, molecular electronics, antimicrobial, osteointegrative and antifouling surfaces, among others. Peptide selection and design, functionalisation strategies, as well as structural and functional characteristics from selected examples are discussed. Additionally, advanced fabrication methods for dynamic peptide spatiotemporal presentation are presented, as well as a number of characterisation techniques. All together, these features and approaches enable the preparation and use of increasingly complex peptide-based SAMs to mimic and study biological processes, and provide convergent platforms for high throughput screening discovery and validation of promising therapeutics and technologies.

GATR-3, a Peptide That Eradicates Preformed Biofilms of Multidrug-Resistant Acinetobacter baumannii

Acinetobacter baumannii is a gram-negative bacterium that causes hospital-acquired and opportunistic infections, resulting in pneumonia, sepsis, and severe wound infections that can be difficult to treat due to antimicrobial resistance and the formation of biofilms. There is an urgent need to develop novel antimicrobials to tackle the rapid increase in antimicrobial resistance, and antimicrobial peptides (AMPs) represent an additional class of potential agents with direct antimicrobial and/or host-defense activating activities. In this study, we present GATR-3, a synthetic, designed AMP that was modified from a cryptic peptide discovered in American alligator, as our lead peptide to target multidrug-resistant (MDR) A. baumannii. Antimicrobial susceptibility testing and antibiofilm assays were performed to assess GATR-3 against a panel of 8 MDR A. baumannii strains, including AB5075 and some clinical strains. The GATR-3 mechanism of action was determined to be via loss of membrane integrity as measured by DiSC3(5) and ethidium bromide assays. GATR-3 exhibited potent antimicrobial activity against all tested multidrug-resistant A. baumannii strains with rapid killing. Biofilms are difficult to treat and eradicate. Excitingly, GATR-3 inhibited biofilm formation and, more importantly, eradicated preformed biofilms of MDR A. baumannii AB5075, as evidenced by MBEC assays and scanning electron micrographs. GATR3 did not induce resistance in MDR A. baumannii, unlike colistin. Additionally, the toxicity of GATR-3 was evaluated using human red blood cells, HepG2 cells, and waxworms using hemolysis and MTT assays. GATR-3 demonstrated little to no cytotoxicity against HepG2 and red blood cells, even at 100 μg/mL. GATR-3 injection showed little toxicity in the waxworm model, resulting in a 90% survival rate. The therapeutic index of GATR-3 was estimated (based on the HC50/MIC against human RBCs) to be 1250. Overall, GATR-3 is a promising candidate to advance to preclinical testing to potentially treat MDR A. baumannii infections.

The role of hydrophobic patches of de novo designed MSI-78 and VG16KRKP antimicrobial peptides on fragmenting model bilayer membranes

Antimicrobial peptides (AMPs) with cell membrane lysing capability are considered potential candidates for the development of the next generation of antibiotics. Designing novel AMPs requires an in-depth understanding of the mechanism of action of the peptides. In this work, we used various biophysical techniques including ³¹P solid-state NMR to examine the interaction of model membranes with amphipathic de novo-designed peptides. Two such peptides, MSI-78 and VG16KRKP, were designed with different hydrophobicity and positive charges. The model lipid membranes were constituted by mixing lipids of varying degrees of 'area per lipid' (APL), which directly affected the packing properties of the membrane. The observed emergence of the isotropic peak in ³¹P NMR spectra as a function of time is a consequence of the fragmentation of the membrane mediated by the peptide interaction. The factors such as the charges, overall hydrophilicity of the AMPs, as well as lipid membrane packing, contributed to the kinetics of membrane fragmentation. Furthermore, we anticipate the designed AMPs follow the carpet and toroidal pore mechanisms when lysing the cell membrane. This study highlights the significance of the effect of the overall charges and the hydrophobicity of the novel AMPs designed for antimicrobial activity.

The Unusual Aggregation and Fusion Activity of the Antimicrobial Peptide W-BP100 in Anionic Vesicles

Cationic antimicrobial peptides (CAMPs) offer a promising strategy to counteract bacterial resistance, mostly due to their membrane-targeting activity. W-BP100 is a potent broad-spectrum cecropin-melittin CAMP bearing a single N-terminal Trp, which was previously found to improve its antibacterial activity. W-BP100 has high affinity toward anionic membranes, inducing membrane saturation at low peptide-to-lipid (P/L) ratios and membrane permeabilization, with the unique property of promoting the aggregation of anionic vesicles only at specific P/L ratios. Herein, we aimed to investigate this unusual behavior of W-BP100 by studying its aggregation and fusion properties with negatively-charged large (LUVs) or giant (GUVs) unilamellar vesicles using biophysical tools. Circular dichroism (CD) showed that W-BP100 adopted an α-helical conformation in anionic LUVs, neutralizing its surface charge at the aggregation P/L ratio. Its fusion activity, assessed by Förster resonance energy transfer (FRET) using steady-state fluorescence spectroscopy, occurred mainly at the membrane saturation/aggregation P/L ratio. Confocal microscopy studies confirmed that W-BP100 displays aggregation and detergent-like effects at a critical P/L ratio, above which it induces the formation of new lipid aggregates. Our data suggest that W-BP100 promotes the aggregation and fusion of anionic vesicles at specific P/L ratios, being able to reshape the morphology of GUVs into new lipid structures.

Antimicrobial-wound healing peptides: Dual-function molecules for the treatment of skin injuries

Chronic non-healing wounds caused by microbial infections extend the necessity for hospital care and constitute a public health problem and a great financial burden. Classic therapies include a wide range of approaches, from wound debridement to vascular surgery. Antimicrobial peptides (AMPs) are a preserved trait of the innate immune response among different animal species, with known effects on the immune system and microorganisms. Thus, AMPs may represent promising candidates for the treatment of chronic wounds with dual functionality in two of the main agents that lead to this condition, proliferation of microorganisms and uncontrolled inflammation. Here, our goal is to critically review AMPs with wound healing properties. We strongly believe that these dual-function peptides alone, or in combination with other wound healing strategies, constitute an underexplored field that researchers can take advantage of.

Grafting MSI-78A onto chitosan microspheres enhances its antimicrobial activity

MSI-78A (Pexiganan A) is one of the few antimicrobial peptides (AMPs) able to kill Helicobacter pylori, a pathogenic bacterium that colonizes the gastric mucosa of half of the world's population. Antibiotics fail in 20-40% of H. pylori-infected patients, reinforcing the need for alternative treatments. Herein, a bioengineered approach was developed. MSI-78A with a C-terminal cysteine was grafted onto chitosan microspheres (AMP-ChMic) by thiol-maleimide (Michael-addition) chemistry using a long heterobifunctional spacer (NHS-PEG₁₁₃-MAL). Microspheres with ∼4 µm diameter (near H. pylori length) and stable at low pH were produced by spray drying using a chitosan solution with an incomplete genipin crosslinking. A 3 × 10^-5 µg AMP/microsphere grafting was estimated/confirmed by UV/Vis and FTIR spectroscopies. AMP-ChMic were bactericidal against H. pylori J99 (highly pathogenic human strain) at lower concentrations than the free peptide (∼277 µg grafted MSI-78A-SH/mL vs 512 µg free MSI-78A-SH/mL), even after pre-incubation in simulated gastric conditions with pepsin. AMP-ChMic killed H. pylori by membrane destabilization and cytoplasm release in a ratio of ∼10 bacteria/microsphere. This can be attributed to H. pylori attraction to chitosan, facilitating the interaction of grafted AMP with bacterium membrane. Overall, it was demonstrated that the peptide-microsphere conjugation chemistry did not compromise the MSI-78A antimicrobial activity, instead it boosted its bactericidal performance against H. pylori. STATEMENT OF SIGNIFICANCE: Half of the world's population is infected with Helicobacter pylori, a gastric bacterium that is responsible for 90% of non-cardia gastric cancers. Therefore, H. pylori eradication is now advocated in all infected individuals. However, available antibiotic therapies fail in up to 40% patients. Antimicrobial peptides (AMPs) are appealing alternatives to antibiotics, but their high susceptibility in vivo limits their clinical translation. AMP immobilization onto biomaterials surface will overcome this problem. Herein, we demonstrate that immobilization of MSI-78A (one of the few AMPs with activity against H. pylori) onto chitosan microspheres (AMP-ChMic) enhances its anti-H. pylori activity even at acidic pH (gastric settings). These results highlight the strong potential of AMP-ChMic as an antibiotic alternative for H. pylori eradication.

Activity of MSI-78, h-Lf1-11 and cecropin B antimicrobial peptides alone and in combination with voriconazole and amphotericin B against clinical isolates of Fusarium solani

Fusarium infections have been associated with high mortality rates due to the lack of definition of an ideal treatment strategy. Antimicrobial peptides (AMPs) have potential antifungal activity. Therefore, investigating the in vitro activity of these molecules alone and in association with conventional antifungals against clinical isolates of Fusarium was the aim of this study. Fusarium solani (n=10) strains were tested against the AMPs, MSI-78, h-Lf1-11 and cecropin B in accordance with CLSI protocol. Further, a checkerboard assay for its combination with amphotericin B or voriconazole, was carried out. MSI-78, h-Lf1-11 and cecropin B exhibited antifungal activity against F. solani strains tested with MICs ranging from 20 to 320mg/L. Satisfactory percentage of synergism was demonstrated for all evaluated combinations, ranging from 70 to 100%. The use of AMPs combined with amphotericin B and voriconazole antifungals has great synergistic potential and deserve to be evaluated in murine models of fusariosis.

Short communication: Algicide activity of antimicrobial peptides compounds against Prototheca bovis

This study evaluated the in vitro activity of antimicrobial peptides pexiganan (MSI-78), h-Lf1-11, LL-37, cecropin B, magainin-2, and fengycin B against the veterinary mastitis agent Prototheca bovis. The results showed that pexiganan, h-Lf1-11, LL-37, and cecropin B were able to inhibit the growth and had effect on algicide P. bovis isolates (n = 32). The minimum inhibitory concentration ranged from 5 to 10 µg/mL for pexiganan, and algicide effect was detected from 5 to 20 µg/mL. The minimum inhibitory concentration ranged from 10 to 80 µg/mL for h-Lf1-11, 20 to 80 µg/mL for LL-37, and 40 to 160 µg/mL for cecropin B. These findings present a promising and novel alternative for P. bovis treatment and growth control.

Antibacterial nanotruffles for treatment of intracellular bacterial infection

Bacterial pathogens residing in host macrophages in intracellular infections are hard to eradicate because traditional antibiotics do not readily enter the cells or get eliminated via efflux pumps. To overcome this challenge, we developed a new particle formulation with a size amenable to selective macrophage uptake, loaded with two antibacterial agents - pexiganan and silver (Ag) nanoparticles. Here, pexiganan was loaded in 600 nm poly(lactic-co-glycolic acid) (PLGA) particles (NP), and the particle surface was modified with an iron-tannic acid supramolecular complex (pTA) that help attach Ag nanoparticles. PLGA particles coated with Ag (NP-pTA-Ag) were taken up by macrophages, but not by non-phagocytic cells, such as fibroblasts, reducing non-specific toxicity associated with Ag nanoparticles. NP-pTA-Ag loaded with pexiganan (Pex@NP-pTA-Ag) showed more potent antibacterial activity against various intracellular pathogens than NP-pTA-Ag or Pex@NP (pexiganan-loaded NP with no Ag), suggesting a collaborative function between pexiganan and Ag nanoparticles. Mouse whole-body imaging demonstrated that, upon intravenous injection, NP-pTA-Ag quickly accumulated in the liver and spleen, where intracellular bacteria tend to reside. These results support that Pex@NP-pTA-Ag is a promising strategy for the treatment of intracellular bacterial infection.

Activity of Specialized Biomolecules against Gram-Positive and Gram-Negative Bacteria

The increased resistance of bacteria against conventional pharmaceutical solutions, the antibiotics, has raised serious health concerns. This has stimulated interest in the development of bio-based therapeutics with limited resistance, namely, essential oils (EOs) or antimicrobial peptides (AMPs). This study envisaged the evaluation of the antimicrobial efficacy of selected biomolecules, namely LL37, pexiganan, tea tree oil (TTO), cinnamon leaf oil (CLO) and niaouli oil (NO), against four bacteria commonly associated to nosocomial infections: Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli and Pseudomonas aeruginosa. The antibiotic vancomycin and silver nanoparticles (AgNPs) were used as control compounds for comparison purposes. The biomolecules were initially screened for their antibacterial efficacy using the agar-diffusion test, followed by the determination of minimal inhibitory concentrations (MICs), kill-time kinetics and the evaluation of the cell morphology upon 24 h exposure. All agents were effective against the selected bacteria. Interestingly, the AgNPs required a higher concentration (4000-1250 µg/mL) to induce the same effects as the AMPs (500-7.8 µg/mL) or EOs (365.2-19.7 µg/mL). Pexiganan and CLO were the most effective biomolecules, requiring lower concentrations to kill both Gram-positive and Gram-negative bacteria (62.5-7.8 µg/mL and 39.3-19.7 µg/mL, respectively), within a short period of time (averaging 2 h 15 min for all bacteria). Most biomolecules apparently disrupted the bacteria membrane stability due to the observed cell morphology deformation and by effecting on the intracellular space. AMPs were observed to induce morphological deformations and cellular content release, while EOs were seen to split and completely envelope bacteria. Data unraveled more of the potential of these new biomolecules as replacements for the conventional antibiotics and allowed us to take a step forward in the understanding of their mechanisms of action against infection-related bacteria.

Surface Grafted MSI-78A Antimicrobial Peptide has High Potential for Gastric Infection Management

As we approach the end of the antibiotic era, newer therapeutic options, such as antimicrobial peptides (AMPs), are in urgent demand. AMP surface grafting onto biomaterials has been described as a good strategy to overcome problems associated with their in vivo stability. Helicobacter pylori is among the bacteria that pose greatest threat to human health, being MSI-78A one of the few bactericidal AMPs against this bacterium. Here, we report that MSI-78A grafted onto model surfaces (Self-Assembled Monolayers –SAMs), in a concentration of 30.3 ± 1.2 ng/cm² determined by quartz crystal microbalance with dissipation (QCM-D), was able to kill, by contact, 98% of planktonic H. pylori in only 2 h. This fact was not verified against the control bacteria (Staphylococcus epidermidis), although the minimal inhibitory concentration (MIC) of MSI-78A in solution is much lower for S. epidermidis (2 μg/mL) than for H. pylori (64 μg/mL). Our results also demonstrated that, in opposite to other bacteria, H. pylori cells were attracted to ethylene glycol terminated (antiadhesive) surfaces, which can explain the high bactericidal potential of grafted MSI-78A. This proof of concept study establishes the foundations for development of MSI-78A grafted nanoparticles for gastric infection management within a targeted nanomedicine concept.

Prevention of urinary catheter-associated infections by coating antimicrobial peptides from crowberry endophytes

Urinary catheters are extensively used in hospitals, being responsible for about 75% of hospital-acquired infections. In this work, a de novo designed antimicrobial peptide (AMP) Chain201D was studied in the context of urinary catheter-associated infections. Chain201D showed excellent antimicrobial activity against relevant ATCC strains and clinical isolates of bacteria and yeast and demonstrated high stability in a wide range of temperatures, pH and salt concentrations. Moreover, the bactericidal activity of Chain201D immobilized on a model surface was studied against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), some of the most prevalent strains found in urinary catheter-associated infections. Chain201D was successfully tethered to ((1-mercapto-11-undecyl)-(tetra(ethylene glycol) (EG4)) terminated self-assembled monolayers (SAMs), (EG4-SAMs), activated by 1,1'-Carbonyldiimidazole (CDI) at different concentrations. Chain201D surfaces can bind and kill by contact a high percentage of adherent bacteria. These achievements are obtained without any peptide modification (for chemoselective conjugation) and without the use of a spacer. Moreover, increased amounts of immobilized AMP lead to higher numbers of adhered/dead bacteria, revealing a concentration-dependent behaviour and demonstrating that Chain201D has excellent potential for developing antimicrobial urinary catheters.

Self-disinfecting surfaces and infection control

According to World Health Organization, every year in the European Union, 4 million patients acquire a healthcare associated infection. Even though some microorganisms represent no threat to healthy people, hospitals harbor different levels of immunocompetent individuals, namely patients receiving immunosuppressors, with previous infections, or those with extremes of age (young children and elderly), requiring the implementation of effective control measures. Public spaces have also been found an important source of infectious disease outbreaks due to poor or none infection control measures applied. In both places, surfaces play a major role on microorganisms' propagation, yet they are very often neglected, with very few guidelines about efficient cleaning measures and microbiological assessment available. To overcome surface contamination problems, new strategies are being designed to limit the microorganisms' ability to survive over surfaces and materials. Surface modification and/or functionalization to prevent contamination is a hot-topic of research and several different approaches have been developed lately. Surfaces with anti-adhesive properties, with incorporated antimicrobial substances or modified with biological active metals are some of the strategies recently proposed. This review intends to summarize the problems associated with contaminated surfaces and their importance on infection spreading, and to present some of the strategies developed to prevent this public health problem, namely some already being commercialized.

Development of a novel short 12-meric papiliocin-derived peptide that is effective against Gram-negative sepsis

The development of novel peptide antibiotics with potent activity against multidrug-resistant Gram-negative bacteria and anti-septic activity is urgently needed. In this study, we designed short, 12-meric antimicrobial peptides by substituting amino acids from the N-terminal 12 residues of the papiliocin (Pap12-1) peptide to alter cationicity and amphipathicity and improve antibacterial activity and bacterial membrane interactions. Pap12-6, with an amphipathic α-helical structure and Trp¹² at the C-terminus, showed broad-spectrum antibacterial activity, especially against multidrug-resistant Gram-negative bacteria. Dye leakage, membrane depolarization, and electron microscopy data proved that Pap12-6 kills bacteria by permeabilizing the bacterial membrane. Additionally, Pap12-6 significantly reduced the secretion of NO, TNF-α, and IL-6 and secreted alkaline phosphatase reporter gene activity confirmed that Pap12-6 shows anti-inflammatory activity via a TLR4-mediated NF-κB signaling pathway. In a mouse sepsis model, Pap12-6 significantly improved survival, reduced bacterial growth in organs, and reduced LPS and inflammatory cytokine levels in the serum and organs. Pap12-6 showed minimal cytotoxicity towards mammalian cells and controlled liver and kidney damage, proving its high bacterial selectivity. Our results suggest that Pap12-6 is a promising peptide antibiotic for the therapeutic treatment of Gram-negative sepsis via dual bactericidal and immunomodulatory effects on the host.

Review of antimicrobial peptides with anti-Helicobacter pylori activity

BACKGROUND

The emergence of antibiotic-resistant Helicobacter pylori strains in recent years has increased the need for finding an alternative in the post-antibiotic era. One of the fields being considered for this purpose is antimicrobial peptides. The aim of this review was to provide an obvious scheme from the studied anti-H. pylori peptides and to investigate their common features.

METHOD

First, all of the antimicrobial peptides with their anti-H. pylori effects have been proved up to September 2018 were selected and their information including structure, mechanism of action, and function was reviewed. To achieve this, three databases of PubMed, Scopus, and Web of science were used.

RESULTS

A total of 9 groups containing 22 antimicrobial peptides were found with demonstrated anti-H. pylori effects. The nine groups included pexiganan, tilapia piscidins, epinecidin-1, cathelicidins, defensins, bicarinalin, odorranain-HP, PGLa-AM1, and bacteriocins. Most of the antimicrobial peptides, not all, had common features such as the ability to kill antibiotic-resistant strains, having α-helical structure, being cationic, with high positive charge and isoelectric point.

CONCLUSION

Antimicrobial peptides with anti-H. pylori effects have the potential to replace the antibiotics, especially in the post-antibiotic era, if a rapid and low-cost production method would be found.

Antimicrobial coatings prepared from Dhvar-5-click-grafted chitosan powders

Antimicrobial peptides (AMP) are powerful components of the innate immune system, as they display wide activity spectrum and low tendency to induce pathogen resistance. Hence, the development of AMP-based coatings is a very promising strategy to prevent biomaterials-associated infections. This work aims to investigate if Dhvar-5-chitosan conjugates, previously synthesized by us via azide-alkyne "click" reaction, can be applied as antimicrobial coatings. Ultrathin coatings were prepared by spin coater after dissolving Dhvar-5-chitosan conjugate powder in aqueous acetic acid. Peptide orientation and exposure from the surface was confirmed by ellipsometry and contact angle measurements. Bactericidal activity was evaluated against Staphylococcus epidermidis, Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa, the most prevalent pathogens in implant-associated infections. Results showed that Dhvar-5-chitosan coatings displayed bactericidal effect. Moreover, since Dhvar-5 has head-to-tail amphipathicity, it was clear that the bactericidal potency was dependent on which domain of the peptide (cationic or hydrophobic) was exposed. In this context, Dhvar-5 immobilized through its C-terminus (exposing its hydrophobic end) presented higher antimicrobial activity against Gram-positive bacteria and reduced adhesion of Gram-negative bacteria. This orientation-dependent antimicrobial activity was further corroborated by the anti-biofilm assay, as covalent immobilization of Dhvar-5 through its C-terminus provided anti-biofilm properties to the chitosan thin film. Immobilization of Dhvar-5 showed no cytotoxic effect against HFF-1 cells, as both metabolic activity and cell morphology were similar to control. In conclusion, Dhvar-5-chitosan coatings are promising antimicrobial surfaces without cytotoxic effects against human cells. STATEMENT OF SIGNIFICANCE: AMP-tethering onto ground biomaterial is still a poorly explored strategy in research. In this work, AMP-tethered ground chitosan is used to produce highly antibacterial ultrathin films. Powdered AMP-tethered chitosan appears as an alternative solution for antimicrobial devices production, as it is suitable for large scale production, being easier to handle for fabrication of different coatings and materials with antimicrobial properties and without inducing toxicity.

Wound-Healing Peptides for Treatment of Chronic Diabetic Foot Ulcers and Other Infected Skin Injuries

As the incidence of diabetes continues to increase in the western world, the prevalence of chronic wounds related to this condition continues to be a major focus of wound care research. Additionally, over 50% of chronic wounds exhibit signs and symptoms that are consistent with localized bacterial biofilms underlying severe infections that contribute to tissue destruction, delayed wound-healing and other serious complications. Most current biomedical approaches for advanced wound care aim at providing antimicrobial protection to the open wound together with a matrix scaffold (often collagen-based) to boost reestablishment of the skin tissue. Therefore, the present review is focused on the efforts that have been made over the past years to find peptides possessing wound-healing properties, towards the development of new and effective wound care treatments for diabetic foot ulcers and other skin and soft tissue infections.

New Potent Membrane-Targeting Antibacterial Peptides from Viral Capsid Proteins

The increasing prevalence of multidrug-resistant bacteria urges the development of new antibacterial agents. With a broad spectrum activity, antimicrobial peptides have been considered potential antibacterial drug leads. Using bioinformatic tools we have previously shown that viral structural proteins are a rich source for new bioactive peptide sequences, namely antimicrobial and cell-penetrating peptides. Here, we test the efficacy and mechanism of action of the most promising peptides among those previously identified against both Gram-positive and Gram-negative bacteria. Two cell-penetrating peptides, vCPP 0769 and vCPP 2319, have high antibacterial activity against Staphylococcus aureus, MRSA, Escherichia coli, and Pseudomonas aeruginosa, being thus multifunctional. The antibacterial mechanism of action of the two most active viral protein-derived peptides, vAMP 059 and vCPP 2319, was studied in detail. Both peptides act on both Gram-positive S. aureus and Gram-negative P. aeruginosa, with bacterial cell death occurring within minutes. Also, these peptides cause bacterial membrane permeabilization and damage of the bacterial envelope of P. aeruginosa cells. Overall, the results show that structural viral proteins are an abundant source for membrane-active peptides sequences with strong antibacterial properties.

Polymer surface adsorption as a strategy to improve the biocompatibility of graphene nanoplatelets

The biointeractions of graphene-based materials depend on their physico-chemical properties. These properties can be manipulated by polymer adsorption. Graphene nanoplatelets (GNP-C) were modified with PVA, HEC, PEG, PVP, chondroitin, glucosamine, and hyaluronic acid. These materials were characterized by SEM, DLS, XPS, Raman spectroscopy, and TGA. Surface adsorption was confirmed for all polymers. Biocompatibility evaluation showed that all of these materials induced low haemolysis (<1.7%) at concentrations up to 500μgmL(-1). GNP-C-PVA and GNP-C-HEC presented the lowest haemolysis percentages and were therefore more thoroughly studied. The morphology of HFF-1 cells was investigated by microscopy (optical, fluorescence, TEM) in order to evaluate interactions with GNP materials. Small GNP-C nanoplatelets were observed to enter cells independently of the surface treatment. For pristine GNP-C at a concentration of 50μgmL(-1), ROS production increased 4.4-fold. This effect is lower for GNP-C-PVA (3.3-fold) and higher for GNP-C-HEC (5.1-fold). Resazurin assays showed that GNP-C caused toxicity in HFF-1 cells at concentrations above 20μgmL(-1) at 24h, which decreased at 48 and 72h. PVA surface adsorption rendered GNP-C non-toxic at concentrations up to 50μgmL(-1). LIVE/DEAD assays showed that at 20 and 50μgmL(-1) cell death is significantly lower for GNP-C-PVA compared to pristine GNP-C. Modification of nanoplatelets with HEC resulted in no benefit in terms of biocompatibility, whereas PVA considerably improved the biocompatibility.

Lysine-Based Small Molecules That Disrupt Biofilms and Kill both Actively Growing Planktonic and Nondividing Stationary Phase Bacteria

The emergence of bacterial resistance is a major threat to global health. Alongside this issue, formation of bacterial biofilms is another cause of concern because most antibiotics are ineffective against these recalcitrant microbial communities. Ideal future antibacterial therapeutics should possess both antibacterial and anti-biofilm activities. In this study we engineered lysine-based small molecules, which showed not only commendable broad-spectrum antibacterial activity but also potent biofilm-disrupting properties. Synthesis of these lipophilic lysine-norspermidine conjugates was achieved in three simple reaction steps, and the resultant molecules displayed potent antibacterial activity against various Gram-positive (Staphylococcus aureus, Enterococcus faecium) and Gram-negative bacteria (Escherichia coli) including drug-resistant superbugs MRSA (methicillin-resistant S. aureus), VRE (vancomycin-resistant E. faecium), and β-lactam-resistant Klebsiella pneumoniae. An optimized compound in the series showed activity against planktonic bacteria in the concentration range of 3-10 μg/mL, and bactericidal activity against stationary phase S. aureus was observed within an hour. The compound also displayed about 120-fold selectivity toward both classes of bacteria (S. aureus and E. coli) over human erythrocytes. This rapidly bactericidal compound primarily acts on bacteria by causing significant membrane depolarization and K(+) leakage. Most importantly, the compound disrupted preformed biofilms of S. aureus and did not trigger bacterial resistance. Therefore, this class of compounds has high potential to be developed as future antibacterial drugs for treating infections caused by planktonic bacteria as well as bacterial biofilms.