Mechanistic studies of Candida albicans photodynamic inactivation with Porophyllum obscurum hexanic extract and its isolated thiophenic compounds

Abstract

Porophyllum obscurum (Spreng) DC (Asteraceae) hexanic extract (PoHex) from aerial parts has demonstrated antifungal activity under UVA irradiation against Candida spp. isolates from patients with oropharyngeal candidiasis and four thiophenes were isolated as responsible of the activity. In the present work, we studied the photomechanisms whereby PoHex and their thiophenes produce photoinactivation of C. albicans. Reactive Oxygen Species generation by PoHex and thiophenes was evaluated: the production of superoxide anion, employing the NBT reduction assay; hydrogen peroxide, through the formation of a red quinoneimine; and singlet oxygen by using the 1,3-DPBF bleaching method. The action of ROS in fungal cells was investigated by evaluating binding of photosensitizer, leakage, apoptosis and stress sensibility that were performed by following M27-A3 guidelines, in parallel under “light” and “darkness” conditions. Results showed that the photosensitive antifungal activity of PoHex required oxygen and both type I (production of superoxide anion and hydrogen peroxide) and type II (production of singlet oxygen) reactions were involved. In addition, we found that ROS generated by PoHex did not cause release of cytoplasmic components due to membrane damage nor apoptosis of C. albicans. Treatment with PoHex and UVA increased cells sensitivities to osmotic stressors; did not reduce resistance to additional oxidative stress and possibly affected the structure of the cell wall. In addition, 2,2′:5′2″terthiophene, the most active PS present in PoHex and the only one that generate single oxygen, at Minimal Fungicide Concentration, did not cause leakage nor apoptosis and did not increase sensitivities to osmotic and oxidative stressors. Results demonstrated that Photodynamic Inactivation employing PoHex under UVA does represent an alternative for topical antifungal therapy for oropharyngeal candidiasis.