Terapia fotodinâmica mediada por azul de ortotoluidina: influência do regime de tratamento, superfície e matriz extracelular em biofilme de cândida albicans in vitro e toxicidade em modelo animal

Abstract

Candida albicans infections treatments is challenging due to the high recurrence rates. The antimicrobial photodynamic therapy (aPDT) has been suggested as an alternative approach for these infections. Thus, this thesis, comprised by 4 chapters, aimed: (1) Comparing aPDT results against C. albicans biofilms formed on two different substrates – acrylic resin or polystyrene plate; and two aPDT application regimens – twice-daily over the course of 48 hours or one time after 48 hours biofilm formation (2) Comparing the outcomes of aPDT on biofilms of C. albicans wild-type strain and two mutant strains with reduced extracellular matrix components. (3) Assessing the local and/or systemic toxicity of aPDT in vivo. (4) Developing a device patent design adapted to oral cavity to applied aPDT. In study 1, C. albicans biofilms were incubated with the photosensitizer toluidine blue O (TBO; 44 μM) before having light (635 nm; 175.2 J/cm2). As a negative control, ultrapure water, and as a positive control 0.12% chlorhexidine were used. Biofilms were evaluated for colony forming units (CFU), dry weight (DW). Confocal scanning laser microscopy (CLSM) was performed. In study 2, biofilms treated with aPDT were incubated with TBO (44 μM) before light (635 nm; 87.6 J/cm² and 175.2 J/cm2). As a negative control, ultrapure water, and as a positive control 0.12% chlorhexidine were used. The effect of TBO and light alone were also assessed. Biofilms were evaluated for CFU, DW, extracellular DNA, soluble and insoluble protein, water-soluble polysaccharides, alkali-soluble polysaccharide and CSLM. In study 3, oral and topical administration of TBO (22 μM) were performed in mice during seven consecutive days. In the animals treated with aPDT, first the TBO was applied and then the light (635 nm; 152 J/cm2). As negative control, the animals were treated with sterile saline solution and as a positive control with oral nystatin. The effects of TBO alone and of light alone were also assessed. After the topical applications, 0.3 ml of each solution was administrated by gavage for all groups. Local and systemic toxicity were evaluated for histological analysis and body/organs mass variation. The study 1 demonstrated that the biofilms formed on polystyrene plate are more resistant to aPDT than biofilms formed on acrylic resin. The result of the study 2 showed that the mutant strain was more susceptible to aPDT than the wide type strain. The third manuscript showed that aPDT did not affect the development body weight and the weight of organs; however, the direct application of light in contact with the palate caused a decrease of epithelium thickness. In conclusion, the results of these studies suggest that aPDT is a safe and promising therapeutic approach against C. albicans.