Surfactin-methylene blue complex under LED illumination for antibacterial photodynamic therapy: Enhanced methylene blue transcellular accumulation assisted by surfactin

Sodium Cholate-Mediated Ion-Pairing for Skin Delivery of Methylene Blue: Physicochemical Characterization and Influence on Skin Barrier and Skin Penetration

Methylene blue (MB)-based photodynamic therapy has proven to be effective and promising for the treatment of non-melanoma skin neoplasms. However, the topical application of MB has certain challenges. MB is a cationic and water-soluble molecule. These properties limit its partition and diffusion through the layers of the skin, limiting it from reaching the neoplastic cells at therapeutic concentration. Sodium cholate (CNa), a bile salt, enables ion-pairing with cationic drugs, such as MB, through electrostatic interactions. The complex formed modifies the physicochemical properties of MB, which may enable its partition and diffusion through the layers of the skin. Thus, we proposed to investigate the interaction between CNa and MB as a function of CNa concentration and its effect on the partition coefficient, solubility, skin barrier and skin delivery of MB. Spectroscopic and thermal studies of MB/CNa dispersions suggest intermolecular interactions between MB and CNa. CNa causes an increase in the partition coefficient of MB and reduces its solubility in water. CNa at the concentrations used does not cause significant changes in electrical resistance or the profile of FTIR spectra related to the lipids and the proteins of the stratum corneum. The use of CNa at the critical micelle concentration causes a reduction in the release and cutaneous delivery of MB; and, at a concentration below the critical micelle concentration, it does not significantly influence the release, but promotes the cutaneous delivery of MB.

Photosensitizer associated with efflux pump inhibitors as a strategy for photodynamic therapy against bacterial resistance

Antimicrobial resistance is currently one of the biggest challenges in controlling infectious diseases and was listed among the top 10 threats to global health by the World Health Organization (WHO) in 2023. The antibiotics misuse has led to the widespread emergence of antimicrobial resistance, marking the beginning of the alarming increase in antibiotic resistance. In this context, Antimicrobial Photodynamic Therapy (aPDT) has garnered significant attention from the scientific community due to its potential to effectively eliminate multidrug-resistant pathogenic bacteria and its low propensity to induce drug resistance, which bacteria can quickly develop against traditional antibiotic treatments. However, some efflux pumps can expel diverse substrates from inside the cell, including photosensitizers used in aPDT, contributing to multidrug-resistance mechanisms. Efflux Pump Inhibitors are potential solutions to combat resistance mediated by these pumps and can play a crucial role in enhancing aPDT's effectiveness against multidrug-resistant bacteria. Therefore, combining efflux pumps inhibitors with photosensitizers can possible to eliminate the pathogen more efficiently. This review summarizes the mechanisms in which bacteria resist conventional antibiotic treatment, with a particular emphasis on efflux pump-mediated resistance, and present aPDT as a promising strategy to combat antibiotic resistance. Additionally, we highlighted several molecules of photosensitizer associated with efflux pump inhibitors as potential strategies to optimize aPDT, aiming to offer a perspective on future research directions on aPDT for overcoming the limitations of antibiotic resistance.

Highly Efficient AIE-Active palmatine photosensitizer for photodynamic inactivation of Listeria monocytogenes in apple juice preservation

Photodynamic sterilization is a promising alternative to conventional antibacterial approaches with merits of high efficiency and safety. The exploration of aggregation-induced emission (AIE)-type photosensitizers from natural sources is highly valued by researchers and food industry. Herein, the use of palmatine (PA), an aggregation-induced emission-active natural product from traditional Chinese medicine, as photosensitizers for photodynamic inactivation of a tenacious foodborne pathogen of Listeria monocytogenes is investigated. Antibacterial and antibiofilm activity against L. monocytogenes of PA-mediated photodynamic process were first assessed. The results showed that PA-mediated photodynamic process could inhibit the growth of L. monocytogenes, and the minimum bactericidal concentration was determined as 80 μM. At this PA dosing level, well-established biofilms of L. monocytogenes can be effectively destroyed under light irritation. Afterward, cell- and gene-level investigations were conducted to explore the antibacterial mechanism. It is concluded that the exceptional photodynamic antibacterial activity of PA against L. monocytogenes is attributed to the disruption of the cell wall and membrane, increased cell permeability, leakage of functional proteins, and damage to DNA structure. Subsequently, PA-mediated photodynamic process was applied to reduce bacterial activity in apple juice while preserving its quality. Overall, this work highlights the significant potential of PA-mediated photodynamic strategy for controlling foodborne pathogens in food systems.

Sophorolipid-toluidine blue conjugates for improved antibacterial photodynamic therapy through high accumulation

Anti-bacterial photodynamic therapy is the most promising treatment protocol for bacterial infection, but low accumulation of photosensitizers has seriously hindered their development in clinical application. Here, with inherent outstanding affinity to bacterial cell envelope, sophorolipid produced from Candida bombicola has been conjugated to toluidine blue (SL-TB) through amidation reaction. The structure of SL-TB conjugates was identified by ¹H-NMR, FT-IR and ESI-HRMS. The interfacial assembly and photophysical properties of SL-TB conjugates have been disclosed through surface tension, micro-polarity, electronic and fluorescence spectra. After light irradiation, the log₁₀ (reduced CFU) of free toluidine blue to P. aeruginosa and S. aureus were 4.5 and 7.9, respectively. In contrast, SL-TB conjugates showed a higher bactericidal activity, with a reduction of 6.3 and 9.7 log₁₀ units of CFU against P. aeruginosa and S. aureus, respectively. The fluorescence quantitative results showed that SL-TB could accumulate 2850 nmol/10¹¹ cells and 4360 nmol/10¹¹ cells by P. aeruginosa and S. aureus, which was much higher than the accumulation of 462 nmol/10¹¹ cells and 827 nmol/10¹¹ cells of free toluidine blue. Through the cooperation of triple factors, including sophorose affinity to bacterial cells, hydrophobic association with plasma membrane, and electrostatic attraction, higher SL-TB accumulation was acquired, which has enhanced antibacterial photodynamic efficiencies.

Amphiphilic di-cationic methylene blue for improving antibacterial photodynamic efficiency through high accumulation and low aggregation on bacterial cell surfaces

The aggregation state of photosensitizers on the surface of bacterial cells is an important scientific problem for antibacterial photodynamic therapy (APDT). High accumulation and high photoactive state maintenance of photosensitizers are the prerequisite of high APDT efficiency. In this study, an amphiphilic di-cationic methylene blue photosensitizer (C12-MB) was synthesized through quaternization, and its structure, interface properties, photophysical properties and antibacterial photodynamic properties were studied. The results showed that C12-MB could reduce 4.27 log10 CFU and 4.8 log10 CFU for P. aeruginosa and S. aureus under irradiation of light at 660 nm, higher than the parent methylene blue. Through a spectroscopic study on photosensitizer adsorption over the bacterial surface, C12-MB can be accumulated with higher concentration, and the photo-active monomer content is 73% and 70% over P. aeruginosa and S. aureus, higher than those of methylene blue: 25% and 49%, respectively. The higher content of non-aggregated photo-active monomer could contribute to higher antibacterial photodynamic efficiency. For C12-MB adsorbed over bacterial surfaces, planar packing inhibition and electrostatic repulsion could contribute to lower C12-MB aggregation, which provides an useful reference for the structural design of high-efficiency photosensitizers.

Cationic porphyrin-based nanoparticles for photodynamic inactivation and identification of bacteria strains

The emergence of antibiotic drug resistance has undermined the efficacy of antibiotics, and is becoming a severe threat to public health. To combat antibiotic drug resistance and to replace traditional antibiotic treatment, an alternative strategy based on antibacterial photodynamic therapy (APDT), which has broad applicability, high efficiency and less potential of developing antibiotic drug resistance, has been developed. In this work, the cationic porphyrin-based nanoparticles (NPs) were prepared by epoxy-amine chain extension polymerization of diepoxy-terminated poly(ethylene glycol) (PEG) and tetraamino-containing porphyrin, followed by quaternization with methyl iodine and butyl bromide. The as-obtained cationic porphyrin NPs preserved the photophysical properties of porphyrin derivatives, and can efficiently generate singlet oxygen (¹O₂) under 635 nm laser irradiation. The cationic porphyrin-based NPs displayed intrinsic antibacterial properties, and exhibited strong APDT effect on Gram-positive bacteria by destroying the bacterial cell membranes. Upon incubation with different bacterial strains, it was found that they could be utilized to identify Gram-positive bacteria by observing the sedimentation behavior of their mixtures, and visualizing their co-cultured and centrifugal bacteria cakes. In addition, the cationic porphyrin-based NPs had good hemocompatibility and low dark cytotoxicity.

Sensitization of Antibiotic-Resistant Gram-Negative Bacteria to Photodynamic Therapy via Perfluorocarbon Nanoemulsion

With the merits of excellent efficacy, safety, and facile implementation, antibacterial photodynamic therapy (APDT) represents a promising means for treating bacterial infections. However, APDT shows an unsatisfactory efficacy in combating antibiotic-resistant Gram-negative bacteria due to their specific cell wall structure. In this work, we report a perfluorocarbon nanoemulsion (Ce6@FDC) used as a multifunctional nanocargo of photosensitizer and oxygen for sensitizing antibiotic-resistant Gram-negative bacteria to APDT. Ce6@FDC was fabricated via ultrasonic emulsification with good colloidal stability, efficient Ce6 and oxygen delivery, and excellent photodynamic activity. Meanwhile, Ce6@FDC could strongly bind with Gram-negative Acinetobacter baumannii (A. baumannii) and Escherichia coli (E. coli) via electrostatic interaction, thus leading to notable photodynamic bactericidal potency upon irradiation. In addition, oxygenated Ce6@FDC also exhibited a remarkable efficacy in eradicating Gram-negative bacteria biofilm, averaging five log units lower than the Ce6 group under identical conditions. Taken together, we demonstrate that photodynamic perfluorocarbon nanoemulsion with oxygen-delivery ability could effectively kill planktonic bacteria and remove biofilm, representing a novel strategy in fighting against antibiotic-resistant Gram-negative bacteria.