Photodynamic Inactivation from ALA, on bacterial infections and skin wounds in an in vivo mouse model

ROBERTO TOMÁS, GABRIELA DI VENOSA, FERNANDA BUZZOLA, ADRIANA CASAS, LEANDRO MAMONE.

Congreso; LXVII REUNIÓN ANUAL DE LA SOCIEDAD ARGENTINA DE INVESTIGACIÓN CLÍNICA (SAIC); 2022

Photodynamic Inactivation (PDI)is a treatment that uses a photosensitizing compound (PS) that after absorbingvisible light in the presence of molecular oxygen generates reactive oxygenspecies, which cause damage and inactivation of microorganisms.5-aminolevulinic acid (ALA) is a precursor for the endogenous synthesis ofporphyrins, some of which can act as PSs in both eukaryotic cells and bacteria.The objective of this work was toevaluate the effect of ALA-PDI (visible light irradiation after topical ALAtreatment) on the progression of wounds caused by subcutaneous Staphylococcus aureus infection, in an in vivo model in mice.BALB/c mice were infected byintradermal inoculation of a suspension of S.aureus RN6390. After 48 h, 20 mg/ml ALA solution was applied to the skin,in the area of ​​infection, 4 h later, fluorescence emitted by the synthesizedporphyrins was detected. The PDI was performed employing a laser device (635 nm)at 300, 450 and 600 mW. The effect of ALA-PDI was determined by measuring thearea of wound (caused by infection) during four weeks after treatments. Porphyrinsproduced, were identified by fluorescence spectroscopy of skin homogenates. Theeffects of ALA-PDI on the bacteria present in the infection were determined bymeasuring the CFUs from skin homogenates.A higher amount of porphyrins wasobserved in the infected skins than in the non-infected ones. The mainporphyrin synthesized was protoporphyrin IX.It was observed that woundstreated with ALA-PDI begin to reduce the area immediately after being treated (in contrast tountreated or only irradiated controls). Time required to completely resolve theinfection in the ALA-PDI treated group was significantly less (p˂0.01) than inthe untreated control (14 vs 27 days). In addition, it was observed thatirradiated controls without ALA, also reduced the area of ​​the wounds earlierthan untreated controls. By employing an alternative model of uninfected skinwound, this enhancing effect of laser irradiation over wound healing wascorroborated.These results suggest that PDIusing ALA as a precursor of PSs porphyrins is a promising option to treatsuperficial infections.