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Methylene blue-containing liposomes as new photodynamic anti-bacterial agents
Giulia Boccalini1, Luca Conti, Costanza Montis
1Department of Experimental & Clinical Medicine, Research Unit of Histology & Embryology, University of Florence, Italy.
Abstract:
Methylene blue (MB) can be employed as a photo-activatable antimicrobial drug in photodynamic therapy (PDT) due to its ability to release oxygen free radicals upon photo-activation. However, its poor ability to penetrate bacterial cell walls and bacterial biofilms limits its antimicrobial activity. To overcome these limitations, we propose some formulations of MB based on different cationic liposomes. The liposome-MB systems were characterized using dynamic light scattering (DLS), zeta potential analysis and UV-visible spectroscopy. Their ability to penetrate inside the cytoplasm of E. coli, taken as a bacterial model for Gram-negative strains, was investigated through laser scanning confocal microscopy (CLSM) and compared to the penetration of naked MB. Then, MB-loaded liposomes were photo-activated and their antimicrobial activity was tested against E. coli, showing a strong improvement with respect to MB solutions. The liposomal formulations dramatically enhance MB penetration in bacterial biofilms and reduce the inflammatory response due to lipopolysaccharide exposure in mammalian cells. The observed antimicrobial and anti-inflammatory efficacies show a clear correlation with some structural features of the carriers, namely the size and the surface charge density. Overall, these results provide fundamental knowledge that enables the design of novel efficient PDT treatments, which potentially overcome the rising incidence of antibiotic resistance of bacterial strains.
Insights
Cationic liposomes enhance methylene blue (MB) penetration into bacterial cells and biofilms, improving photodynamic therapy (PDT) efficacy against E. coli. This approach offers a promising strategy to combat antibiotic resistance.
Area of Science:
- Biomedical Engineering
- Photodynamic Therapy
- Drug Delivery Systems
Background:
- Methylene blue (MB) is a photosensitizer used in photodynamic therapy (PDT) for antimicrobial applications.
- Poor penetration of MB into bacterial cell walls and biofilms limits its effectiveness.
- Antibiotic resistance necessitates the development of novel therapeutic strategies.
Purpose of the Study:
- To develop and characterize cationic liposome formulations of MB to enhance antimicrobial activity.
- To investigate the penetration capabilities of liposome-MB systems into bacterial cells and biofilms.
- To evaluate the antimicrobial and anti-inflammatory effects of MB-loaded liposomes in a photodynamic therapy context.
Main Methods:
- Formulation of MB-loaded cationic liposomes.
- Characterization using dynamic light scattering (DLS), zeta potential analysis, and UV-visible spectroscopy.
- Investigation of bacterial penetration using laser scanning confocal microscopy (CLSM).
- Assessment of antimicrobial activity against E. coli post-photoactivation.
- Evaluation of anti-inflammatory response in mammalian cells.
Main Results:
- Liposomal formulations significantly improved MB penetration into E. coli cytoplasm and biofilms compared to naked MB.
- Photo-activated MB-loaded liposomes demonstrated enhanced antimicrobial activity against E. coli.
- Liposomal MB reduced inflammatory responses induced by lipopolysaccharide exposure.
- Antimicrobial and anti-inflammatory efficacies correlated with liposome size and surface charge density.
Conclusions:
- Cationic liposomes effectively enhance MB delivery for photodynamic therapy.
- Liposome-mediated MB delivery overcomes bacterial penetration barriers and improves antimicrobial outcomes.
- This strategy holds potential for developing new treatments against antibiotic-resistant bacteria and reducing inflammation.
