Photodynamic treatment of the fungal opportunistic pathogen Candida

Abstract

Thesis (Ph. D.)--University of Rochester. School of Medicine and Dentistry. Dept. of Microbiology and Immunology, 2008.Infection of the mucosal epithelium by the opportunistic fungus Candida results from fungal overgrowth and penetration of epithelium when the body's physical and immunological defenses become compromised. Treatment of Candida infections has become increasingly problematic given the inherent and acquired resistance to antifungals, especially to azoles, of the most commonly seen Candida species, C. albicans and C. glabrata. Meeting the challenge of increased resistance to currently used antifungal agents will require the development of novel strategies for control of the infection. Photodynamic treatment (PDT), the activation of a photosensitizing agent by a specific wavelength of light to kill a target cell via the production of reactive oxygen species, presents a new therapeutic approach for mucocutaneous and cutaneous candidiasis. The present work focused on investigating the efficacy of PDT against Candida employing structurally different photosensitizers, examining the effect of respiratory deficiency and azole resistance as contributing factors to enhanced sensitivity to PDT, and understanding the different pathways involved in respiratory deficiency that might induce hypersensitivity to PDT. We demonstrated the ability to effectively photosensitize Candida using two structurally different porphyrin based photosensitizers, Photofrin® and TMP-1363. We report a differential in PDT susceptibility between the different C. albicans morphologies and Candida species. Our studies revealed that the increased sensitivity to oxidative stress induced by PDT is independent of both inherent and acquired fluconazole resistance of Candida to azoles. In addition, we demonstrate that azole-resistant, respiratory deficient organisms are hypersensitive to photooxidative damage induced by PDT. Furthermore, we investigated specific pathways implicated in innate protection against oxidative stress that, if altered, cause respiratory deficiency and enhanced sensitivity to PDT. We focused on cytochrome c respiratory chain assembly and function, oxidative phosphorylation and mitochondrial redox balance pathways. We demonstrate that alterations in these pathways, in yeasts, induce respiratory deficiency as well as enhanced sensitivity to photooxidative damage induced by PDT. The data presented here reveals the success of effectively photosensitizing Candida independently of its resistance to antifungals, and the importance of intact mitochondrial function to provide a basal level of anti-oxidant defense against PDT-induced phototoxicity in Candida