Antimicrobial Organometallic Dendrimers with Tunable Activity against Multidrug-Resistant Bacteria

The antibacterial properties of branched peptides based on poly(l-arginine): In vitro antibacterial evaluation and molecular dynamic simulations

The emergence of bacterial strains resistant to antibiotics is a major issue in the medical field. Antimicrobial peptides are widely studied as they do not generate as much resistant bacterial strains as conventional antibiotics and present a broad range of activity. Among them, the homopolypeptide poly(l-arginine) presents promising antibacterial properties, especially in the perspective of its use in biomaterials. Linear poly(l-arginine) has been extensively studied but the impact of its 3D structure remains unknown. In this study, the antibacterial properties of newly synthesized branched poly(l-arginine) peptides, belonging to the family of multiple antigenic peptides, are evaluated. First, in vitro activities of the peptides shows that branched poly(l-arginine) is more efficient than linear poly(l-arginine) containing the same number of arginine residues. Surprisingly, peptides with more arms and more residues are not the most effective. To better understand these unexpected results, interactions between these peptides and the membranes of Gram positive and Gram negative bacteria are simulated thanks to molecular dynamic. It is observed that the bacterial membrane is more distorted by the branched structure than by the linear one and by peptides containing smaller arms. This mechanism of action is in full agreement with in vitro results and suggest that our simulations form a robust model to evaluate peptide efficiency towards pathogenic bacteria.

Advanced bioactive nanomaterials for diagnosis and treatment of major chronic diseases

With the rapid innovation of nanoscience and technology, nanomaterials have also been deeply applied in the medical and health industry and become one of the innovative methods to treat many diseases. In recent years, bioactive nanomaterials have attracted extensive attention and have made some progress in the treatment of some major chronic diseases, such as nervous system diseases and various malignant tumors. Bioactive nanomaterials depend on their physical and chemical properties (crystal structure, surface charge, surface functional groups, morphology, and size, etc.) and direct produce biological activity and play to the role of the treatment of diseases, compared with the traditional nanometer pharmaceutical preparations, biological active nano materials don't exert effects through drug release, way more directly, also is expected to be more effective for the treatment of diseases. However, further studies are needed in the evaluation of biological effects, fate in vivo, structure-activity relationship and clinical transformation of bionanomaterials. Based on the latest research reports, this paper reviews the application of bioactive nanomaterials in the diagnosis and treatment of major chronic diseases and analyzes the technical challenges and key scientific issues faced by bioactive nanomaterials in the diagnosis and treatment of diseases, to provide suggestions for the future development of this field.

Regulation of Staphylococcus aureus Virulence and Application of Nanotherapeutics to Eradicate S. aureus Infection

Staphylococcus aureus is a versatile pathogen known to cause hospital- and community-acquired, foodborne, and zoonotic infections. The clinical infections by S. aureus cause an increase in morbidity and mortality rates and treatment costs, aggravated by the emergence of drug-resistant strains. As a multi-faceted pathogen, it is imperative to consolidate the knowledge on its pathogenesis, including the mechanisms of virulence regulation, development of antimicrobial resistance, and biofilm formation, to make it amenable to different treatment strategies. Nanomaterials provide a suitable platform to address this challenge, with the potential to control intracellular parasitism and multidrug resistance where conventional therapies show limited efficacy. In a nutshell, the first part of this review focuses on the impact of S. aureus on human health and the role of virulence factors and biofilms during pathogenesis. The second part discusses the large diversity of nanoparticles and their applications in controlling S. aureus infections, including combination with antibiotics and phytochemicals and the incorporation of antimicrobial coatings for biomaterials. Finally, the limitations and prospects using nanomaterials are highlighted, aiming to foster the development of novel nanotechnology-driven therapies against multidrug-resistant S. aureus.

Membrane-Active Cyclic Amphiphilic Peptides: Broad-Spectrum Antibacterial Activity Alone and in Combination with Antibiotics

We designed a library of 24 cyclic peptides containing arginine (R) and tryptophan (W) residues in a sequential manner [R_nW_n] (n = 2-7) to study the impact of the hydrophilic/hydrophobic ratio, charge, and ring size on the antibacterial activity against Gram-positive and Gram-negative strains. Among peptides, 5a and 6a demonstrated the highest antimicrobial activity. In combination with 11 commercially available antibiotics, 5a and 6a showed remarkable synergism against a large panel of resistant pathogens. Hemolysis (HC₅₀ = 340 μg/mL) and cell viability against mammalian cells demonstrated the selective lethal action of 5a against bacteria over mammalian cells. Calcein dye leakage and scanning electron microscopy studies revealed the membranolytic effect of 5a. Moreover, the stability in human plasma (t_1/2 = 3 h) and the negligible ability of pathogens to develop resistance further reflect the potential of 5a for further development as a peptide-based antibiotic.

Antifungal Effect of Nanoparticles against COVID-19 Linked Black Fungus: A Perspective on Biomedical Applications

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a highly transmissible and pathogenic coronavirus that has caused a 'coronavirus disease 2019' (COVID-19) pandemic in multiple waves, which threatens human health and public safety. During this pandemic, some patients with COVID-19 acquired secondary infections, such as mucormycosis, also known as black fungus disease. Mucormycosis is a serious, acute, and deadly fungal infection caused by Mucorales-related fungal species, and it spreads rapidly. Hence, prompt diagnosis and treatment are necessary to avoid high mortality and morbidity rates. Major risk factors for this disease include uncontrolled diabetes mellitus and immunosuppression that can also facilitate increases in mucormycosis infections. The extensive use of steroids to prevent the worsening of COVID-19 can lead to black fungus infection. Generally, antifungal agents dedicated to medical applications must be biocompatible, non-toxic, easily soluble, efficient, and hypoallergenic. They should also provide long-term protection against fungal growth. COVID-19-related black fungus infection causes a severe increase in fatalities. Therefore, there is a strong need for the development of novel and efficient antimicrobial agents. Recently, nanoparticle-containing products available in the market have been used as antimicrobial agents to prevent bacterial growth, but little is known about their efficacy with respect to preventing fungal growth, especially black fungus. The present review focuses on the effect of various types of metal nanoparticles, specifically those containing silver, zinc oxide, gold, copper, titanium, magnetic, iron, and carbon, on the growth of various types of fungi. We particularly focused on how these nanoparticles can impact the growth of black fungus. We also discussed black fungus co-infection in the context of the global COVID-19 outbreak, and management and guidelines to help control COVID-19-associated black fungus infection. Finally, this review aimed to elucidate the relationship between COVID-19 and mucormycosis.

New Antimicrobial Peptide with Two CRAC Motifs: Activity against Escherichia coli and Bacillus subtilis

Due to the emergence of multiple antibiotic resistance in many pathogens, the studies on new antimicrobial peptides (AMPs) have become a priority scientific direction in fundamental and applied biology. Diverse mechanisms underlie the antibacterial action of AMPs. Among them are the effects that AMPs cause on bacterial cell membranes. In this work, we studied the antibacterial activity of a peptide named P4 with the following sequence RTKLWEMLVELGNMDKAVKLWRKLKR that was constructed from two alpha-helical fragments of the influenza virus protein M1 and containing two cholesterol-recognizing amino-acid consensus (CRAC) motifs. Previously we have shown that 50 μM of peptide P4 is toxic to cultured mouse macrophages. In the present work, we have found that peptide P4 inhibits the growth of E. coli and B. subtilis strains at concentrations that are significantly lower than the cytotoxic concentration that was found for macrophages. The half-maximal inhibitory concentration (IC50) for B. subtilis and E. coli cells were 0.07 ± 0.01 μM and 1.9 ± 0.4 μM, respectively. Scramble peptide without CRAC motifs did not inhibit the growth of E. coli cells and was not cytotoxic for macrophages but had an inhibitory effect on the growth of B. subtilis cells (IC50 0.4 ± 0.2 μM). A possible involvement of CRAC motifs and membrane sterols in the mechanism of the antimicrobial action of the P4 peptide is discussed. We assume that in the case of the Gram-negative bacterium E. coli, the mechanism of the toxic action of peptide P4 is related to the interaction of CRAC motifs with sterols that are present in the bacterial membrane, whereas in the case of the Gram-positive bacterium B. subtilis, which lacks sterols, the toxic action of peptide P4 is based on membrane permeabilization through the interaction of the peptide cationic domain and anionic lipids of the bacterial membrane. Whatever the mechanism can be, we report antimicrobial activity of the peptide P4 against the representatives of Gram-positive (B. subtilis) and Gram-negative (E. coli) bacteria.

Graphene oxide/gallium nanoderivative as a multifunctional modulator of osteoblastogenesis and osteoclastogenesis for the synergistic therapy of implant-related bone infection

Currently, implant-associated bacterial infections account for most hospital-acquired infections in patients suffering from bone fractures or defects. Poor osseointegration and aggravated osteolysis remain great challenges for the success of implants in infectious scenarios. Consequently, developing an effective surface modification strategy for implants is urgently needed. Here, a novel nanoplatform (GO/Ga) consisting of graphene oxide (GO) and gallium nanoparticles (GaNPs) was reported, followed by investigations of its in vitro antibacterial activity and potential bacterium inactivation mechanisms, cytocompatibility and regulatory actions on osteoblastogenesis and osteoclastogenesis. In addition, the possible molecular mechanisms underlying the regulatory effects of GO/Ga nanocomposites on osteoblast differentiation and osteoclast formation were clarified. Moreover, an in vivo infectious microenvironment was established in a rat model of implant-related femoral osteomyelitis to determine the therapeutic efficacy and biosafety of GO/Ga nanocomposites. Our results indicate that GO/Ga nanocomposites with excellent antibacterial potency have evident osteogenic potential and inhibitory effects on osteoclast differentiation by modulating the BMP/Smad, MAPK and NF-κB signaling pathways. The in vivo experiments revealed that the administration of GO/Ga nanocomposites significantly inhibited bone infections, reduced osteolysis, promoted osseointegration located in implant-bone interfaces, and resulted in satisfactory biocompatibility. In summary, this synergistic therapeutic system could accelerate the bone healing process in implant-associated infections and can significantly guide the future surface modification of implants used in bacteria-infected environments.

Surface-Decorated Graphene Oxide Sheets with Copper Nanoderivatives for Bone Regeneration: An In Vitro and In Vivo Study Regarding Molecular Mechanisms, Osteogenesis, and Anti-infection Potential

It has been previously reported that graphene oxide/copper nanoderivative (GO/Cu)-incorporated chitosan/hyaluronic acid scaffolds might be promising wound dressings for the management of infected wound healing. The aim of the present research is to deeply explore the potential antimicrobial mechanisms and synergistic osteogenic activity, as well as the in vivo anti-infective behavior of GO/Cu nanocomposites, making them possible candidates for establishing implantable biomaterials for the repair of infected bone defects. The antibacterial mechanisms of the nanocomposites were explored through the examination of membrane integrity, oxidative stress, and metabolic enzyme activities. Then, the cytocompatibility with bone mesenchymal stem cells (rBMSCs) and osteogenic potential were confirmed, and a subcutaneous bacterial infection model in rats was also established to verify the in vivo anti-infective property and biosafety of the nanocomposites. It was found that leakage of adenosine triphosphate, proteins, and reducing sugars from the bacterial cells, indicative of damaged permeability of bacterial membranes, and promoted production of reactive oxygen species and disordered metabolic enzyme activities in response to oxidative stress were possible molecular mechanisms responsible for the synergistic antibacterial effects of the GO/Cu nanocomposites. Additionally, good cytocompatibility with rBMSCs and promoted osteogenic differentiation were found in GO/Cu nanocomposites (mass ratio = 2:1), which also demonstrated satisfactory in vivo anti-infective performance, reduced inflammation, and acceptable biosafety. Based on our results, damaged bacterial membranes, increased ROS production, and disorders of crucial enzyme metabolism were the main antibacterial mechanisms involved in the bacterium-killing events caused by the GO/Cu nanocomposites, which also showed enhanced osteogenic activity, in vivo anti-infective capability, and acceptable cytocompatibility and biosafety. Therefore, GO/Cu (2:1) nanocomposites are a potential strategy for improving the biological performance of current bone substitutes used for combating bacterial-contaminated bone defects.

Conjugation of Gentamicin to Polyamidoamine Dendrimers Improved Anti-bacterial Properties against Pseudomonas aeruginosa

Purpose: This study aimed to design gentamicin-conjugated poly (amidoamine) (PAMAM) dendrimers to increase the therapeutic efficiency of gentamicin against Pseudomonas aeruginosa.

Methods: Gentamicin-presenting dendrimers were synthesized using MAL-PEG₃₄₀₀-NHS as a redox-sensitive linker to attach gentamicin to the surface of G4 PAMAM dendrimers. The gentamicin molecules were thiolated by using Traut reagent. Then, the functionalized gentamicin molecules were attached to PEGylated PAMAM dendrimers through simple and high selectively maleimide (MAL)-thiol reaction. The structure of gentamicin-conjugated PAMAM dendrimers was characterized and confirmed using nuclear magnetic resonance (NMR), dynamic light scattering (DLS), zeta potential analysis, and transmission electron microscopy (TEM) imaging. The antibacterial properties of the synthesized complex were examined on P. aeruginosa and compared to gentamycin alone.

Results: NMR, DLS, zeta potential analysis, and TEM imaging revealed the successful conjugation of gentamicin to PAMAM dendrimers. Data showed the appropriate physicochemical properties of the synthesized nanoparticles. We found a 3-fold increase in the antibacterial properties of gentamicin conjugated to the surface of PAMAM dendrimers compared to non-conjugated gentamicin. Based on data, the anti-biofilm effects of PAMAM-Gentamicin dendrimers increased at least 13 times more than the gentamicin in normal conditions.

Conclusion: Data confirmed that PAMAM dendrimer harboring gentamicin could be touted as a novel smart drug delivery system in infectious conditions.

Development of Ferromagnetic Materials Containing Co2P, Fe2P Phases from Organometallic Dendrimers Precursors

The development of synthesis methods to access advanced materials, such as magnetic materials that combine multimetallic phosphide phases, remains a worthy research challenge. The most widely used strategies for the synthesis of magnetic transition metal phosphides (TMPs) are organometallic approaches. In this study, Fe-containing homometallic dendrimers and Fe/Co-containing heterometallic dendrimers were used to synthesize magnetic materials containing multimetallic phosphide phases. The crystalline nature of the nearly aggregated particles was indicated for both designed magnetic samples. In contrast to heterometallic samples, homometallic samples showed dendritic effects on their magnetic properties. Specifically, saturation magnetization (M_s) and coercivity (H_c) decrease as dendritic generation increases. Incorporating cobalt into the homometallic dendrimers to prepare the heterometallic dendrimers markedly increases the magnetic properties of the magnetic materials from 60 to 75 emu/g. Ferromagnetism in homometallic and heterometallic particles shows different responses to temperature changes. For example, heterometallic samples were less sensitive to temperature changes due to the presence of Co₂P in contrast to the homometallic ones, which show an abrupt change in their slopes at a temperature close to 209 K, which appears to be related to the Fe₂P ratios. This study presents dendrimers as a new type of precursor for the assembly of magnetic materials containing a mixture of iron- and cobalt-phosphides phases with tunable magnetism, and provides an opportunity to understand magnetism in such materials.

Aspirin-Based Organoiron Dendrimers as Promising Anti-Inflammatory, Anticancer, and Antimicrobial Drugs

Designing nanocarriers with actions directed at a specific organ or tissue is a very promising strategy since it can significantly reduce the toxicity of a bioactive drug. In this study, an organometallic dendrimer was used to synthesize a biocompatible drug delivery system by attaching aspirin to the periphery of the dendrimer. Our goal is to enhance the bioavailability and anticancer activity of aspirin and reduce its toxicity through successive generations of organoiron dendrimers. The biological activity of aspirin-based dendrimer complexes was evaluated. The result of antimicrobial activity of the synthesized dendrimers also demonstrated an increase in their antimicrobial activity with increased generation of the dendrimers for most types of microorganisms. This study reveals for the first time that organoiron dendrimers linked with aspirin exhibit an excellent Gram-negative activity comparable to the reference drug Gentamicin. All synthesized dendrimers were tested for their anticancer activity against breast cancer cell lines (MCF-7), hepatocellular cell lines (Hep-G2), and a non-cancer cell line, Human Embryonic Kidney (HEK293), using the MTT cell viability assay and compared against a standard anticancer drug, Doxorubicin. Compounds G3-D9-Asp and G4-D12-Asp exhibited noticeable activity against both cell lines, both of which were more effective than aspirin itself. In addition, the in vivo anti-inflammatory activity and histopathology of swollen paws showed that the designed aspirin-based dendrimers displayed significant anti-inflammatory activity; however, G2-D6-Asp showed the best anti-inflammatory activity, which was more potent than the reference drug aspirin during the same period. Moreover, the coupling of aspirin to the periphery of organoiron dendrimers showed a significant reduction in the toxicity of aspirin on the stomach.

Antibacterial photodynamic activity of hydrophobic carbon quantum dots and polycaprolactone based nanocomposite processed via both electrospinning and solvent casting method

Inhabitation of various types of bacteria on different surfaces causes vital health problems worldwide. In this work, a wound dressing defeating bacterial infection had been fabricated. The antibacterial effect of polycaprolactone and hydrophobic carbon quantum dots (hCQDs) based nanocomposite has been presented. The nanocomposite was fabricated both via solvent casting and electrospinning method. Nanocomposites with and without hCQDs had been investigated. A detailed study on their morphology and surface properties were performed by scanning electron microscopy, atomic force microscopy and Raman spectroscopy. Prepared nanocomposites had been evaluated by the contact angle, UV-Vis spectroscopy, electron paramagnetic resonance spectroscopy, and antibacterial activity. It was found that nanocomposites were able to produce singlet oxygen upon blue light irradiation at 470 nm, and they were effective in the eradication of Gram positive (Staphylococcus aureus, Listeria monocytogenes) and Gram negative (Escherichia coli, Klebsiella pneumoniae) bacteria.

Trp-Containing Antibacterial Peptides Impair Quorum Sensing and Biofilm Development in Multidrug-Resistant Pseudomonas aeruginosa and Exhibit Synergistic Effects With Antibiotics

Pseudomonas aeruginosa uses quorum sensing (QS) to control virulence, biofilm formation and antibiotic efflux pump expression. The development of effective small molecules targeting the QS system and biofilm formation represents a novel attractive strategy. In this present study, the effects of a series of Trp-containing peptides on the QS-regulated virulence and biofilm development of multidrug-resistant P. aeruginosa, as well as their synergistic antibacterial activity with three classes of traditional chemical antibiotics were investigated. The results showed that Trp-containing peptides at low concentrations reduced the production of QS-regulated virulence factors by downregulating the gene expression of both the las and rhl systems in the strain MRPA0108. Biofilm formation was inhibited in a concentration-dependent manner, which was associated with extracellular polysaccharide production inhibition by downregulating pelA, algD, and pslA transcription. These changes correlated with alterations in the extracellular production of pseudomonal virulence factors and swarming motility. In addition, the combination of Trp-containing peptides at low concentration with the antibiotics ceftazidime and piperacillin provided synergistic effects. Notably, L11W and L12W showed the highest synergy with ceftazidime and piperacillin. A mechanistic study demonstrated that the Trp-containing peptides, especially L12W, significantly decreased β-lactamase activity and expression of efflux pump genes OprM, MexX, and MexA, resulting in a reduction in antibiotic efflux from MRPA0108 cells and thus increasing the antibacterial activity of these antibiotics against MRPA0108.

Dendrimers against fungi - A state of the art review

Fungal based diseases currently affect nearly a quarter of the population around the world, which diseases are usually limited to superficial infections. Perversely, along with the development of modern medicine, cases of life-threatening systemic fungi are more and more often encountered. Compared to antibacterial drugs, significantly fewer fungicides are tested and introduced to clinical practice. At the same time, the drug resistance of pathological fungi is constantly growing. In addition to obtaining new derivatives of already-established classes of drugs, such as azoles, there is a growing interest in new compounds with potentially new mechanisms and application possibilities. Polymers are included in the flow of these studies, and among them - dendrimers. Dendrimers are a special type of polymers with a strictly defined structure and a plethora of functionalization possibilities. This allows them to not only be used as effective antifungal drug carriers but also enables them to exhibit antifungal activity per se. In this review, we have introduced to the epidemiology of fungal infections and summarized the aspects related to their control and therapy. Various polymers and dendrimers with antifungal activity were presented. In the subsequent sections antifungal acting dendrimers were discussed within three subchapters, based on their chemical structure: (i) amino acid-based dendrimers, (ii) amino based dendrimers, and (iii) other, which do not share similarities in structure. We have gathered and summarized the reports regarding the direct action of dendrimers on infectious fungi, as well as their effect when used as solubilizers, carriers or adjuvants with currently used antifungals. Use of dendrimers for the sensing of fungi or their metabolites are also considered. Special attention was also paid to the applications of dendrimers together with photosensitizers in antimicrobial photodynamic therapy.

Pharmacological Evaluation of Novel Organoiron Dendrimers as Antimicrobial and Anti-Inflammatory Agents

The synthesis of a novel and attractive class of nonsteroidal anti-inflammatory and antimicrobial organoiron dendrimers attached to the well-known drug ibuprofen is achieved. The structures of these dendrimers are established by spectroscopic and analytical techniques. The antimicrobial activity of these dendrimers is investigated and tested against five human pathogenic Gram-positive and Gram-negative bacteria, and minimum inhibitory concentrations are reported. Some of these synthesized dendrimers exhibit higher inhibitory activity against methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus faecium, and Staphylococcus warneri compare to the reference drugs. As well, the in vitro and in vivo anti-inflammatory activities of these dendrimers are evaluated. The results of in vivo anti-inflammatory activity and histopathology of inflamed paws show that all dendrimers display considerable anti-inflammatory activity; however, second-generation dendrimer (G2-D6) shows the best anti-inflammatory activity, which is more potent than the commercial drug ibuprofen at the same tested dose. Results of the toxicity study reveal that G2-D6 is the safest drug on biological tissues.

From Nanobiotechnology, Positively Charged Biomimetic Dendrimers as Novel Antibacterial Agents: A Review

The alarming increase in antimicrobial resistance, based on the built-in abilities of bacteria to nullify the activity of current antibiotics, leaves a growing number of bacterial infections untreatable. An appealing approach, advanced in recent decades, concerns the development of novel agents able to interact with the external layers of bacteria, causing irreparable damage. Regarding this, some natural cationic antimicrobial peptides (CAMPs) have been reconsidered, and synthetic cationic polymers, mimicking CAMPs and able to kill bacteria by non-specific detrimental interaction with the negative bacterial membranes, have been proposed as promising solutions. Lately, also dendrimers were considered suitable macromolecules for the preparation of more advanced cationic biomimetic nanoparticles, able to harmonize the typical properties of dendrimers, including nanosize, mono-dispersion, long-term stability, high functionality, and the non-specific mechanism of action of CAMPs. Although cationic dendrimers are extensively applied in nanomedicine for drug or gene delivery, their application as antimicrobial agents is still in its infancy. The state of the art of their potential applications in this important field has therefore been reviewed here, with particular attention to the innovative case studies in the literature including also amino acid-modified polyester-based dendrimers, practically unexplored as membrane-active antimicrobials and able to kill bacteria on contact.

Design of Organoiron Dendrimers Containing Paracetamol for Enhanced Antibacterial Efficacy

Paracetamol (acetaminophen) is a common painkiller and antipyretic drug used globally. Attachment of paracetamol to a series of organoiron dendrimers was successfully synthesized. The aim of this study is to combine the benefits of the presence of these redox-active organoiron dendrimers, their antimicrobial activities against some human pathogenic Gram-positive, and the therapeutic characteristics of paracetamol. The antimicrobial activity of these dendrimers was investigated and tested with a minimum inhibitory concentration and this has been reported. Some of these newly synthesized dendrimers exhibited the highest inhibitory activity against methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus faecium (VRE), and Staphylococcus warneri compared to reference drugs. The results of this study indicate that the antimicrobial efficacy of the dendrimers is dependent on the size of the redox-active organoiron dendrimer and its terminal functionalities. The best result has been recorded for the fourth-generation dendrimer 11, which attached to 48 paracetamol end groups and has 90 units composed of the η⁶-aryl-η⁵-cyclopentadienyliron (II) complex. This dendrimer presented inhibition of 50% of the growth (IC₅₀) of 0.52 μM for MRSA, 1.02 μM for VRE, and 0.73 μM for Staphylococcus warneri. The structures of the dendrimers were characterized by elemental analysis, Fourier transform infrared (FT-IR), nuclear magnetic resonance (¹H-NMR), and ¹³C-NMR spectroscopic techniques. In addition, all synthesized dendrimers displayed good thermal stability in the range of 300–350 °C following the degradation of the cationic iron moieties which occurred around 200 °C.

S-benzyldithiocarbazate imine coordinated metal complexes kill Candida albicans by causing cellular apoptosis and necrosis

Development of new chemotherapeutic agents and strategies are urgently needed to curb and halt the growing menace caused by hard-to-treat microbes. Coordination of metals to bioactive organic ligands is now considered to be an efficient strategy for delivering bioactive compounds inside the microbial cell membranes. Metal complexes have been effectively used to treat many dreadful diseases were other treatment modalities had failed. Use of metal complexes to treat microbial infections is now conceived to be an alternative and efficient strategy. Towards this, some new homoleptic transition metal complexes, obtained by coordination of metal ions to bioactive S-benzyldithiocarbazate Schiff-base ligands were evaluated for their anti-Candida activity and their potential to disrupt the membrane architecture. The complexes displayed remarkable antifungal activity against a wide spectrum of fluconazole susceptible and resistant Candida albicans isolates, with Ni complex (dtc3) being highly active with minimum inhibitory concentration (MIC) values ranging from 1 to 32 µg/mL. Cell viability assay confirmed the fungicidal activity of these metal complexes, especially the complex dtc3. These metal complexes kill Candida albicans by inducing cellular apoptosis and necrosis thereby causing phosphatidylserine externalization as revealed by Annexin V-FITC and propidium iodide staining assays.

Coordinating Ability of Anions, Solvents, Amino Acids, and Gases towards Alkaline and Alkaline-Earth Elements, Transition Metals, and Lanthanides

After briefly reviewing the applications of the coordination ability indices proposed earlier for anions and solvents toward transition metals and lanthanides, a new analysis of crystal structures is applied now to a much larger number of coordinating species: anions (including those that are present in ionic solvents), solvents, amino acids, gases, and a sample of neutral ligands. The coordinating ability towards s-block elements is now also considered. The effect of several factors on the coordinating ability will be discussed: (a) the charge of an anion, (b) the chelating nature of anions and solvents, (c) the degree of protonation of oxo-anions, carboxylates and amino carboxylates, and (d) the substitution of hydrogen atoms by methyl groups in NH₃ , ethylenediamine, benzene, ethylene, pyridine and aldehydes. Hit parades of solvents and anions most commonly used in the areas of transition metal, s-block and lanthanide chemistry are deduced from the statistics of their presence in crystal structures.

Synergistic Antibacterial Activity of Designed Trp-Containing Antibacterial Peptides in Combination With Antibiotics Against Multidrug-Resistant Staphylococcus epidermidis

Multidrug resistance among various bacterial strains is leading to worldwide resistance to a wide range of antibiotics. Combination therapy involving current antibiotics and other biological or chemical molecules represents an attractive novel strategy. In this study, we investigated the synergistic antibacterial activity of a series of Trp-containing antimicrobial peptides (AMPs) with four classes of traditional chemical antibiotics that are inactive against multidrug-resistant Staphylococcus epidermidis (MRSE) in vitro and in vivo. Among the antibiotics that we studied, penicillin, ampicillin and erythromycin showed a distinct synergistic effect in combination with all of the Trp-containing AMPs, represented by a fractional inhibitory concentration index (FICI) of <0.5. The antibacterial activities were noticeably improved, with 32-to 64-fold reductions in the MIC values for ampicillin and 16- to 32-fold reductions in the MIC values for erythromycin and penicillin. Tetracycline showed synergistic activity with only I1WL5W but additive activity with L11W, L12W, and I4WL5W. Ceftazidime exhibited additive activity with the Trp-containing peptides. In addition, the antibiotics in combination with the peptide significantly inhibited biofilm formation by MRSE 1208. A mechanistic study demonstrated that the Trp-containing peptides, especially I1WL5W and I4WL5W, which contain two tryptophan residues, disrupted bacterial inner and outer membranes, which promoted antibiotic delivery into the cytoplasm and access to cytoplasmic targets; however, L11W and L12W may have increased intracellular antibiotic concentrations by decreasing blaZ, tet(m) and msrA expression. Importantly, strong synergistic activity against the MRSE 1208 strain was observed for the combination of I1WL5W and penicillin in a mouse infection model. Thus, the combination of AMPs and traditional antibiotics could be a promising option for the prevention of acute and chronic infections caused by MRSE.

Metallopolymers for advanced sustainable applications

Since the development of metallopolymers, there has been tremendous interest in the applications of this type of materials. The interest in these materials stems from their potential use in industry as catalysts, biomedical agents in healthcare, energy storage and production as well as climate change mitigation. The past two decades have clearly shown exponential growth in the development of many new classes of metallopolymers that address these issues. Today, metallopolymers are considered to be at the forefront for discovering new and sustainable heterogeneous catalysts, therapeutics for drug-resistant diseases, energy storage and photovoltaics, molecular barometers and thermometers, as well as carbon dioxide sequesters. The focus of this review is to highlight the advances in design of metallopolymers with specific sustainable applications.

Metallo-polyelectrolytes as a class of ionic macromolecules for functional materials

The fields of soft polymers and macromolecular sciences have enjoyed a unique combination of metals and organic frameworks in the name of metallopolymers or organometallic polymers. When metallopolymers carry charged groups, they form a class of metal-containing polyelectrolytes or metallo-polyelectrolytes. This review identifies the unique properties and functions of metallo-polyelectrolytes compared with conventional organo-polyelectrolytes, in the hope of shedding light on the formation of functional materials with intriguing applications and potential benefits. It concludes with a critical perspective on the challenges and hurdles for metallo-polyelectrolytes, especially experimental quantitative analysis and theoretical modeling of ionic binding.

Macromolecular agents with antimicrobial potentialities: A drive to combat antimicrobial resistance

In recent years, the antimicrobial resistance (AMR) or multidrug resistance (MDR) has become a serious health concern and major challenging issue, worldwide. After decades of negligence, the AMR has now captured global attention. The increasing number of antibiotic-resistant strains has threatened the achievements of science and medicine since it inactivates conventional antimicrobial therapeutics. Scientists are trying to respond to AMR/MDR threat by exploring innovative platforms and new therapeutic strategies to tackle infections from these resistant strains and bypass treatment limitations related to these pathologies. The present review focuses on the utilization of bio-inspired novel constructs and their potential applications as novel antimicrobial agents. The first part of the review describes plant-based biological macromolecules containing an immense variety of secondary metabolites, which could be potentially used as alternative strategies to combat antimicrobial resistance. The second part discusses the potential of metal-based macromolecules as effective antimicrobial platforms for preventing infections from resistant strains. The third part comprehensively elucidates how nanoparticles, in particular, metal-integrated nanoparticles can overcome this AMR or MDR issue. Towards the end, information is given with critical concluding remarks, gaps, and finally envisioned with future considerations.

A Cationic Polymer That Shows High Antifungal Activity against Diverse Human Pathogens

Invasive fungal diseases are generally difficult to treat and often fatal. The therapeutic agents available to treat fungi are limited, and there is a critical need for new agents to combat these deadly infections. Antifungal compound development has been hindered by the challenge of creating agents that are highly active against fungal pathogens but not toxic to the host. Host defense peptides (HDPs) are produced by eukaryotes as a component of the innate immune response to pathogens and have served as inspiration for the development of many new antibacterial compounds. HDP mimics, however, have largely failed to exhibit potent and selective antifungal activity. Here, we present an HDP-like nylon-3 copolymer that is effective against diverse fungi while displaying only mild to moderate toxicity toward mammalian cells. This polymer is active on its own and in synergy with existing antifungal drugs against multiple species of Candida and Cryptococcus, reaching levels of efficacy comparable to those of the clinical agents amphotericin B and fluconazole in some cases. In addition, the polymer acts synergistically with azoles against different species of Aspergillus, including some azole-resistant strains. These findings indicate that nylon-3 polymers are a promising lead for development of new antifungal therapeutic strategies.

Function Oriented Molecular Design: Dendrimers as Novel Antimicrobials

In recent years innovative nanostructures are attracting increasing interest and, among them, dendrimers have shown several fields of application. Dendrimers can be designed and modified in plentiful ways giving rise to hundreds of different molecules with specific characteristics and functionalities. Biomedicine is probably the field where these molecules find extraordinary applicability, and this is probably due to their multi-valency and to the fact that several other chemicals can be coupled to them to obtain desired compounds. In this review we will describe the different production strategies and the tools and technologies for the study of their characteristics. Finally, we provide a panoramic overview of their applications to meet biomedical needs, especially their use as novel antimicrobials.

Antibacterial activity of chensinin-1b, a peptide with a random coil conformation, against multiple-drug-resistant Pseudomonas aeruginosa

Nosocomial infections caused by Pseudomonas aeruginosa are difficult to treat due to the low permeability of its outer membrane as well as to its remarkable ability to acquire further resistance to antibiotics. Chensinin-1b exhibited antibacterial activity against the tested multiple-drug-resistant bacteria with a MIC ranging between 1.56 and 50μM, except E. cloacae strain 0320 (MREC0320), P. fluorescens strain 0322 (MRPF0322) and E. aerogenes strain 0320 (MREA0320). However, the MIC (25μM) of chensinin-1b to multiple-drug-resistant P. aeruginosa strain (MRPA 0108) was 16-fold higher than that observed to P. aeruginosa susceptible strain CGMCC 1.860 (PA1860). Chensinin-1b was able to disturb the integration of the cytoplasmic membrane of PA1860 and MRPA0108 cells similarly, but the outer membrane permeability of MRPA0108 cells was significantly lower. This low permeability was associated with increased expression of lipopolysaccharide (LPS) in the outer membrane and a decrease in negatively charged phospholipids in the outer membrane leaflet. In addition, the biofilm of MRPA0108 was responsible for the reduced susceptibility to chensinin-1b. A higher concentration of chensinin-1b (12.5µM) was required to maximally inhibit the formation of MRPA0108 biofilm. Notably, chensinin-1b inhibited the formation of MRPA0108 biofilm at concentrations below its MIC value by down-regulating the level of PelA, algD, and PslA gene transcription. Importantly, chensinin-1b had a significant antibacterial effect against MRPA0108 in vivo. Administration of chensinin-1b to mice infected with MRPA 0108 significantly increased survival by 50-70%. Moreover, chensinin-1b reduced the production of pro-inflammatory mediators and correspondingly reduced lung and liver tissue damage in the mouse model of septic shock induced by MRPA 0108. Collectively, these results suggest that chensinin-1b could be an effective antibiotic against multiple-drug-resistant bacterial strains.

Effect of tacticity-derived topological constraints in bactericidal peptides

Topology is a key element in structure-activity relationship estimation while designing physiologically-active molecular constructs. Peptides may be a preferred choice for therapeutics, principally due to their biocompatibility, low toxicity and predictable metabolism. Peptide design only guarantees functional group constitution by opting specific amino acid sequence, and not their spatial orientation to bind and incite physiological response on chosen targets. This is principally because peptide conformation is subject to external flux, due to the isotactic stereochemistry of the peptide chain. Stereochemical engineering of the peptide main chain offers the possibility of multiplying the structural space of a typical sequence to many orders of magnitude, and limiting the otherwise fluxional non-specific functional group dispensation in space by offering greater conformational rigidity. We put to test, this conceptual possibility already established in theoretical models, by designing amphipathic peptide systems and experimenting with them on Gram-positive, Gram-negative and antibiotic-resistant bacteria. The unusual conformational rigidity and stability of syndiotactic peptides enable them to retain the designed electrostatic environment, while they encounter the membrane surface. All the six designed systems exhibited bactericidal activity, pointing to the utility and specificity of stereo-engineered peptide systems for therapeutic applications. Overall, we hope that this work provides important insights and useful directives in designing novel peptide systems with antimicrobial activity, by expanding the design space, incorporating D-amino acid as an additional design variable.

Phosphonium-Functionalized Polymer Micelles with Intrinsic Antibacterial Activity

New approaches to treat bacterial infections are badly needed to address the increasing problem of antibiotic resistance. This study explores phosphonium-functionalized block copolymer micelles as intrinsically antibacterial polymer assemblies. Phosphonium cations with varying alkyl lengths were conjugated to the terminus of a poly(ethylene oxide)-polycaprolactone block copolymer, and the phosphonium-functionalized block copolymers were self-assembled to form micelles in aqueous solution. The size, morphology, and ζ-potential of the assemblies were studied, and their abilities to kill Escherichia coli and Staphylococcus aureus were evaluated. It was found that the minimum bactericidal concentration depended on the phosphonium alkyl chain length, and different trends were observed for Gram-negative and Gram-positive bacteria. The most active assemblies exhibited no hemolysis of red blood cells above the bactericidal concentrations, indicating that they can selectively disrupt the membranes of bacteria. Furthermore, it was possible to encapsulate and release the antibiotic tetracycline using the assemblies, providing a potential multimechanistic approach to bacterial killing.

Rapid bactericidal activity of an amphiphilic polyacrylate terpolymer system comprised of same-centered comonomers with 2-carbon and 6-carbon spacer arms and an uncharged repeat unit

Cationic amphiphilic polyacrylate terpolymers with rapid bactericidal activity against E. coli and S. aureus.

Tunable room-temperature soft ferromagnetism in magnetoceramics of organometallic dendrimers

This article represents an introduction of new dendrimeric precursors to magnetic ceramics, and homometallic and heterometallic dendrimers with tunable magnetic properties.

Metal-containing and related polymers for biomedical applications

A survey of the most recent progress in the biomedical applications of metal-containing polymers is given. Due to the unique optical, electrochemical, and magnetic properties, at least 30 different metal elements, most of them transition metals, are introduced into polymeric frameworks for interactions with biology-relevant substrates via various means. Inspired by the advance of metal-containing small molecular drugs and promoted by the great progress in polymer chemistry, metal-containing polymers have gained momentum during recent decades. According to their different applications, this review summarizes the following biomedical applications: (1) metal-containing polymers as drug delivery vehicles; (2) metal-containing polymeric drugs and biocides, including antimicrobial and antiviral agents, anticancer drugs, photodynamic therapy agents, radiotherapy agents and biocides; (3) metal-containing polymers as biosensors, and (4) metal-containing polymers in bioimaging.

Chitosan Derivatives Active against Multidrug-Resistant Bacteria and Pathogenic Fungi: In Vivo Evaluation as Topical Antimicrobials

The continuous rise of antimicrobial resistance and the dearth of new antibiotics in the clinical pipeline raise an urgent call for the development of potent antimicrobial agents. Cationic chitosan derivatives, N-(2-hydroxypropyl)-3-trimethylammonium chitosan chlorides (HTCC), have been widely studied as potent antibacterial agents. However, their systemic structure-activity relationship, activity toward drug-resistant bacteria and fungi, and mode of action are very rare. Moreover, toxicity and efficacy of these polymers under in vivo conditions are yet to be established. Herein, we investigated antibacterial and antifungal efficacies of the HTCC polymers against multidrug resistant bacteria including clinical isolates and pathogenic fungi, studied their mechanism of action, and evaluated cytotoxic and antimicrobial activities in vitro and in vivo. The polymers were found to be active against both bacteria and fungi (MIC = 125-250 μg/mL) and displayed rapid microbicidal kinetics, killing pathogens within 60-120 min. Moreover, the polymers were shown to target both bacterial and fungal cell membrane leading to membrane disruption and found to be effective in hindering bacterial resistance development. Importantly, very low toxicity toward human erythrocytes (HC₅₀ = >10000 μg/mL) and embryo kidney cells were observed for the cationic polymers in vitro. Further, no inflammation toward skin tissue was observed in vivo for the most active polymer even at 200 mg/kg when applied on the mice skin. In a murine model of superficial skin infection, the polymer showed significant reduction of methicillin-resistant Staphylococcus aureus (MRSA) burden (3.2 log MRSA reduction at 100 mg/kg) with no to minimal inflammation. Taken together, these selectively active polymers show promise to be used as potent antimicrobial agents in topical and other infections.

Recent advances in thromboresistant and antimicrobial polymers for biomedical applications: just say yes to nitric oxide (NO)

Biomedical devices are essential for patient diagnosis and treatment; however, when blood comes in contact with foreign surfaces or homeostasis is disrupted, complications including thrombus formation and bacterial infections can interrupt device functionality, causing false readings and/or shorten device lifetime. Here, we review some of the current approaches for developing antithrombotic and antibacterial materials for biomedical applications. Special emphasis is given to materials that release or generate low levels of nitric oxide (NO). Nitric oxide is an endogenous gas molecule that can inhibit platelet activation as well as bacterial proliferation and adhesion. Various NO delivery vehicles have been developed to improve NO's therapeutic potential. In this review, we provide a summary of the NO releasing and NO generating polymeric materials developed to date, with a focus on the chemistry of different NO donors, the polymer preparation processes, and in vitro and in vivo applications of the two most promising types of NO donors studied thus far, N-diazeniumdiolates (NONOates) and S-nitrosothiols (RSNOs).

Biological processing of dinuclear ruthenium complexes in eukaryotic cells

The biological processing - mechanism of cellular uptake, effects on the cytoplasmic and mitochondrial membranes, intracellular sites of localisation and induction of reactive oxygen species - of two dinuclear polypyridylruthenium(ii) complexes has been examined in three eukaryotic cells lines. Flow cytometry was used to determine the uptake of [{Ru(phen)2}2{μ-bb12}](4+) (Rubb12) and [Ru(phen)2(μ-bb7)Ru(tpy)Cl](3+) {Rubb7-Cl, where phen = 1,10-phenanthroline, tpy = 2,2':6',2''-terpyridine and bbn = bis[4(4'-methyl-2,2'-bipyridyl)]-1,n-alkane} in baby hamster kidney (BHK), human embryonic kidney (HEK-293) and liver carcinoma (HepG2) cell lines. The results demonstrated that the major uptake mechanism for Rubb12 and Rubb7-Cl was active transport, although with a significant contribution from carrier-assisted diffusion for Rubb12 and passive diffusion for Rubb7-Cl. Flow cytometry coupled with Annexin V/TO-PRO-3 double-staining was used to compare cell death by membrane damage or apoptosis. Rubb12 induced significant direct membrane damage, particularly with HepG2 cells, while Rubb7-Cl caused considerably less membrane damage but induced greater levels of apoptosis. Confocal microscopy, coupled with JC-1 assays, demonstrated that Rubb12 depolarises the mitochondrial membrane, whereas Rubb7-Cl had a much smaller affect. Cellular localisation experiments indicated that Rubb12 did not accumulate in the mitochondria, whereas significant mitochondrial accumulation was observed for Rubb7-Cl. The effect of Rubb12 and Rubb7-Cl on intracellular superoxide dismutase activity showed that the ruthenium complexes could induce cell death via a reactive oxygen species-mediated pathway. The results of this study demonstrate that Rubb12 predominantly kills eukaryotic cells by damaging the cytoplasmic membrane. As this dinuclear ruthenium complex has been previously shown to exhibit greater toxicity towards bacteria than eukaryotic cells, the results of the present study suggest that metal-based cationic oligomers can achieve selective toxicity against bacteria, despite exhibiting a non-specific membrane damage mechanism of action.

Diblock metallocopolymers containing various iron sandwich complexes: living ROMP synthesis and selective reversible oxidation

New diblock copolymers containing two iron-sandwich complexes in the side chain have been synthesized and oxidized to obtain mixed-valent Fe^II–Fe^III copolymers.