Easy and versatile cellulosic support inhibiting broad spectrum strains: synergy between photodynamic antimicrobial therapy and polymyxin B

Despite advances achieved in the health field over the last decade, infections caused by resistant bacterial strains are an increasingly important societal issue that needs to be addressed. New approaches have already been developed to overcome this problem. Photodynamic antimicrobial chemotherapy (PACT) could provide a promising alternative method to eradicate microbes. This approach has already inspired the development of innovative surfaces. Interesting results were achieved against Gram-positive bacteria, but it also appeared that Gram-negative strains, especially Pseudomonas aeruginosa, were less sensitive to PACT. However, materials coated with cationic porphyrins have already proven their wide-spectrum activity, but these materials were not suitable for industrial-scale production. The main aim of this work was the design of a large-scale evolutionary material based on PACT and antibiotic prophylaxis. Transparent regenerated cellulose has been simply impregnated with a usual cationic porphyrin (N-methylpyridyl) and an antimicrobial peptide (polymyxin B). In addition to its photophysical properties, this film exhibited a wide-spectrum bactericidal activity over 4 days despite daily application of fresh bacterial inoculums. The efficiency of PACT and polymyxin B combination could help to reduce the emergence of bacterial multi-resistant strains and we believe that this kind of material would provide an excellent opportunity to prevent bacterial contamination of bandages or packaging.

A Review of Phototoxic Plants, Their Phototoxic Metabolites, and Possible Developments as Photosensitizers

This study provides a comprehensive overview of the current knowledge regarding phototoxic terrestrial plants and their phototoxic and photosensitizing metabolites. Within the 435,000 land plant species, only around 250 vascular plants have been documented as phototoxic or implicated in phototoxic occurrences in humans and animals. This work compiles a comprehensive catalog of these phototoxic plant species, organized alphabetically based on their taxonomic family. The dataset encompasses meticulous details including taxonomy, geographical distribution, vernacular names, and information on the nature and structure of their phototoxic and photosensitizing molecule(s). Subsequently, this study undertook an in-depth investigation into phototoxic molecules, resulting in the compilation of a comprehensive and up-to-date list of phytochemicals exhibiting phototoxic or photosensitizing activity synthesized by terrestrial plants. For each identified molecule, an extensive review was conducted, encompassing discussions on its phototoxic activity, chemical family, occurrence in plant families or species, distribution within different plant tissues and organs, as well as the biogeographical locations of the producer species worldwide. The analysis also includes a thorough discussion on the potential use of these molecules for the development of new photosensitizers that could be used in topical or injectable formulations for antimicrobial and anticancer phototherapy as well as manufacturing of photoactive devices.

Porphyrin Photosensitizers Grafted in Cellulose Supports: A Review

Cellulose is the most abundant natural biopolymer and owing to its compatibility with biological tissues, it is considered a versatile starting material for developing new and sustainable materials from renewable resources. With the advent of drug-resistance among pathogenic microorganisms, recent strategies have focused on the development of novel treatment options and alternative antimicrobial therapies, such as antimicrobial photodynamic therapy (aPDT). This approach encompasses the combination of photoactive dyes and harmless visible light, in the presence of dioxygen, to produce reactive oxygen species that can selectively kill microorganisms. Photosensitizers for aPDT can be adsorbed, entrapped, or linked to cellulose-like supports, providing an increase in the surface area, with improved mechanical strength, barrier, and antimicrobial properties, paving the way to new applications, such as wound disinfection, sterilization of medical materials and surfaces in different contexts (industrial, household and hospital), or prevention of microbial contamination in packaged food. This review will report the development of porphyrinic photosensitizers supported on cellulose/cellulose derivative materials to achieve effective photoinactivation. A brief overview of the efficiency of cellulose based photoactive dyes for cancer, using photodynamic therapy (PDT), will be also discussed. Particular attention will be devoted to the synthetic routes behind the preparation of the photosensitizer-cellulose functional materials.

Xylan-Based Cross-Linked Hydrogel for Photodynamic Antimicrobial Chemotherapy

Photodynamic antimicrobial chemotherapy or PACT has been shown to be a promising antibacterial treatment that could overcome the challenge of multidrug-resistant bacteria. However, the use of most existing photosensitizers has been severely hampered by their significant self-quenching effect, poor water solubility, lack of selectivity against bacterial cells, and possible damage to the surrounding tissues. The use of hydrogels may overcome some of these limitations. We herein report a simple strategy to synthesize a cross-linked hydrogel from beech xylan. The hydrogel showed a high swelling ratio, up to 62, an interconnected porous structure, and good mechanical integrity, and 5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin tetraiodide (TMPyP) was chosen as a model of hydrophilic photosensitizer (PS) and was encapsulated inside the xylan-based hydrogel. TMPyP-loaded hydrogel prolonged release of PS up to 24 h with a cumulative amount that could reach 100%. TMPyP-loaded hydrogel showed a photocytotoxic effect against Pseudomonas aeruginosa, Escherichia coli, Staphylococcus aureus strains, and Bacillus cereus, while no cytotoxicity was observed in the dark.

A new antibacterial nano-system based on hematoporphyrin-carboxymethyl chitosan conjugate for enhanced photostability and photodynamic activity

To promote bactericidal activity, improve photostability and safety, novel antibacterial nanoparticle system based on photodynamic action (PDA) was prepared here through conjugation of photosensitizer hematoporphyrin (HP) onto carboxymethyl chitosan (CMCS) via amide linkage and followed by ultrasonic treatment. The system was stable in PBS (pH 7.4) and could effectively inhibit the photodegradation of conjugated HP because of aggregation-caused quenching effect. ROS produced by the conjugated HP under light exposure could change the structure of nanoparticles by oxidizing the CMCS skeleton and thereby significantly promote the photodynamic activity of HP and its photodynamic activity after 6 h was higher than that of HP·2HCl under the same conditions. Antibacterial experiments showed that CMCS-HP nanoparticles had excellent photodynamic antibacterial activity, and the bacterial inhibition rates after 60 min of light exposure were greater than 97%. Safety evaluation exhibited that the nanoparticles were safe to mammalian cells, showing great potential for antibacterial therapy.

Chemical synthesis of NiFe2 O4 /NG/cellulose nanocomposite and its antibacterial potential against bacterial pathogens

In this work, a nickel ferrite (NiFe₂ O₄ )/nitrogen-doped-graphene (NG)/cellulose composite (NiFe₂ O₄ /NG/cellulose) was successfully synthesized through a facile chemical route, and its antibacterial potential was evaluated. The synthesized NiFe₂ O₄ /NG/cellulose composite was characterized by performing morphological and structural analyses. The results showed the successful formation of NiFe₂ O₄ -nanoparticles with a spherical shape and a size ranging from 15 to 200 nm. Energy-dispersive X-ray results confirmed the presence of various elements (carbon, nitrogen, oxygen, iron, and nickel) in the reaction mixture. The X-ray diffraction pattern showed the face-centered-cubic nature of the particles. In addition, antibacterial activity against Escherichia coli (Gram-negative bacteria) and Bacillus subtilis (Gram-positive bacteria) was evaluated with different concentrations of NiFe₂ O₄ /NG/cellulose composite (0-50 μg/mL). Inhibitory activity increased with increasing concentrations of NiFe₂ O₄ /NG/cellulose. The composite's inhibitory activity was slightly higher in E. coli than in B. subtilis due to the differing nature of their cell wall structures. Overall, the chemically synthesized NiFe₂ O₄ /NG/cellulose composite has the potential as an efficient antibacterial agent for controlling the growth of pathogenic bacteria.

Acetylated lignin nanoparticles as a possible vehicle for photosensitizing molecules

Lignins are underused and abundant bio-sourced polymers with various potential applications. An attractive one is the development of nanoparticles for bioactive compound delivery. Here, we optimized the synthesis of hydrodispersible nanoparticles of acetylated lignin by comparing different lignin sources, degrees of acetylation and preparation methods. The formation of acetylated lignin nanoparticles in various solvents was probed by both experiments and, for the first time, a molecular dynamics simulation. We showed that dialysis is more suitable to obtain these nanoparticles than anti-solvent addition. The encapsulation of hydrophobic photosensitizing porphyrin in these nanoparticles was also demonstrated and rationalized at the molecular level, together with experiments, docking and molecular dynamics simulations. As acetylated lignin has been demonstrated to exhibit photosensitizing activity, the encapsulation of bioactive compounds in lignin nanoparticles opens the doors to a broad range of potential applications.

Porphyrin-Loaded Lignin Nanoparticles Against Bacteria: A Photodynamic Antimicrobial Chemotherapy Application

The need for alternative strategies to fight bacteria is evident from the emergence of antimicrobial resistance. To that respect, photodynamic antimicrobial chemotherapy steadily rises in bacterial eradication by using light, a photosensitizer and oxygen, which generates reactive oxygen species that may kill bacteria. Herein, we report the encapsulation of 5,10,15,20-tetrakis(4-hydroxyphenyl)-21H,23H-porphyrin into acetylated lignin water-dispersible nanoparticles (THPP@AcLi), with characterization of those systems by standard spectroscopic and microscopic techniques. We observed that THPP@AcLi retained porphyrin's photophysical/photochemical properties, including singlet oxygen generation and fluorescence. Besides, the nanoparticles demonstrated enhanced stability on storage and light bleaching. THPP@AcLi were evaluated as photosensitizers against two Gram-negative bacteria, Escherichia coli and Pseudomonas aeruginosa, and against three Gram-positive bacteria, Staphylococcus aureus, Staphylococcus epidermidis, and Enterococcus faecalis. THPP@AcLi were able to diminish Gram-positive bacterial survival to 0.1% when exposed to low white LED light doses (4.16 J/cm2), requiring concentrations below 5 μM. Nevertheless, the obtained nanoparticles were unable to diminish the survival of Gram-negative bacteria. Through transmission electron microscopy observations, we could demonstrate that nanoparticles did not penetrate inside the bacterial cell, exerting their destructive effect on the bacterial wall; also, a high affinity between acetylated lignin nanoparticles and bacteria was observed, leading to bacterial flocculation. Altogether, these findings allow to establish a photodynamic antimicrobial chemotherapy alternative that can be used effectively against Gram-positive topic infections using the widely available natural polymeric lignin as a drug carrier. Further research, aimed to inhibit the growth and survival of Gram-negative bacteria, is likely to enhance the wideness of acetylated lignin nanoparticle applications.

The Red Color of Life Transformed - Synthetic Advances and Emerging Applications of Protoporphyrin IX in Chemical Biology

Protoporphyrin IX (PPIX) is the porphyrin scaffold of heme b, a ubiquitous prosthetic group of proteins responsible for oxygen binding (hemoglobin, myoglobin), electron transfer (cytochrome c) and catalysis (cytochrome P450, catalases, peroxidases). PPIX and its metallated derivatives frequently find application as therapeutic agents, imaging tools, catalysts, sensors and in light harvesting. The vast toolkit of accessible porphyrin functionalization reactions enables easy synthetic modification of PPIX to meet the requirements for its multiple uses. In the past few years, particular interest has arisen in exploiting the interaction of PPIX and its synthetic derivatives with biomolecules such as DNA and heme-binding proteins to evolve molecular devices with new functions as well as to uncover potential therapeutic toeholds. This review strives to shine a light on the most recent developments in the synthetic chemistry of PPIX and its uses in selected fields of chemical biology.

Conjugating biomaterials with photosensitizers: advances and perspectives for photodynamic antimicrobial chemotherapy

Antimicrobial resistance is threatening to overshadow last century's medical advances. Previously eradicated infectious diseases are now resurgent as multi-drug resistant strains, leading to expensive, toxic and, in some cases, ineffective antimicrobial treatments. Given this outlook, researchers are willing to investigate novel antimicrobial treatments that may be able to deal with antimicrobial resistance, namely photodynamic therapy (PDT). PDT relies on the generation of toxic reactive oxygen species (ROS) in the presence of light and a photosensitizer (PS) molecule. PDT has been known for almost a century, but most of its applications have been directed towards the treatment of cancer and topical diseases. Unlike classical antimicrobial chemotherapy treatments, photodynamic antimicrobial chemotherapy (PACT) has a non-target specific mechanism of action, based on the generation of ROS, working against cellular membranes, walls, proteins, lipids and nucleic acids. This non-specific mechanism diminishes the chances of bacteria developing resistance. However, PSs usually are large molecules, prone to aggregation, diminishing their efficiency. This review will report the development of materials obtained from natural sources, as delivery systems for photosensitizing molecules against microorganisms. The present work emphasizes on the biological results rather than on the synthesis routes to prepare the conjugates. Also, it discusses the current state of the art, providing our perspective on the field.