Treatment of infected and non-infected wounds using light-mediated therapies.

TOMÁS RS; MAMONE L; DI VENOSA G; BUZZOLA F; AGUAYO FRÍAS T; GONZÁLEZ MAGLIO D; CASAS A

Encuentro; XV Encuentro Latinoamericano de Fotoquímica y Fotobiología (ELAFOT); 2023

Photodynamic Inactivation (PDI) combines the action of a photosensitizer with visible light, generating radical species that cause the inactivation of microorganisms. Near Infrared Therapy (NIRT) employs infrared light that delivers thermal energy to the organisms, exciting water molecules and bacterial chromophores.The 5-aminolevulinic acid (ALA) is a precursor in the endogenous biosynthesis of porphyrins. After its incorporation into bacterial cells, an increase in porphyrin levels is produced. In Staphylococci, the main porphyrin accumulated is Coproporphyrin. The aim of this work was to employ a combination of NIRT and PDI as an alternative approach to increase PDI efficiency to eradicate Staphylococcus aureus, a relevant human opportunistic pathogen. Response to PDI of S. aureus RN6390 biofilms grown on polystyrene surface was determined after incubation with ALA (2 mM) and irradiation with non-coherent visible light (58 J/cm2; quartz halogen lamps). This treatment did not induce any significant effects on biofilm viability. However, employing a 630 nm laser (19.3 J/cm2), a 1-log decrease in biofilm viability was observed. Biofilms sequentially treated with NIRT and ALA-PDI suffered a 2-log reduction of biofilm viability. Furthermore, NIRT + ALA- PDI reduced 3-logs the viability of S. aureus biofilms growing on titanium surfaces. The synergistic action of NIRT on ALA-PDI is presumably ascribed to the increase of bacterial porphyrins due to the higher permeation of ALA induced by the photothermic effect. An inoculum of 108 CFUs of S. aureus RN6390 was subcutaneously injected into CF1 mice to induce a skin and soft tissue infection model. After 48 h, the lesions were superficially treated with 1.5 mg ALA followed by NIRT (980 nm laser, 91 J/cm2), to induce ALA penetration through the abscess, and after 1 h, the lesion was treated with 630 nm laser. The progression of the infected area was monitored in control and treated mice. At 2, 7 and 14 days after treatment, representative mice were killed to assess the CFU counts in the abscess. A significant decrease in the time of infection resolution was found employing ALA-PDI (19.3 J/cm2) and red light alone (14.1 J/cm2). However, NIRT after ALA application did not improve the outcome of PDI. Since the CFU number did not increase after ALA-PDI, we are currently evaluating the immune system role in the resolution of infected wounds. We also found that red light alone (44.8 J/cm2) but not ALA-PDI have a significant impact on the healing of non-infected wounds (scalpel incision).We propose the use of ALA-PDI for the treatment of infected wounds and 630 nm light for wound healing.