Photodynamic therapy can kill Cryptococcus neoformans in in vitro and in vivo models

Abstract

Cryptococcosis is an infection caused by the encapsulated yeast Cryptococcus neoformans and the most afflicted sites are lung, skin and central nervous system. A range of studies had reported that photodynamic therapy (PDT) can inactivate yeast cells; however, the in vivo experimental models of cryptococcosis photoinactivation are not commonly reported. The aim of this study was to investigate the ability of methylene blue (MB) combined with a low-power red laser to inactivate Cryptococcus neoformans in in vitro and in vivo experimental models. To perform the in vitro study, suspension of Cryptococcus neoformans ATCC-90112 (106cfu/mL) was used. The light source was a laser (Photon Lase III, DMC, São Carlos, Brazil) emitting at λ660nm with output power of 90mW for 6 and 9min of irradiation, resulting fluences at 108 and 162J/cm². As photosensitizer, 100μM MB was used. For the in vivo study, 10 BALB/c mice had the left paw inoculated with C. neoformans ATCC-90112 (107cfu). Twenty-four hours after inoculation, PDT was performed using 150μM MB and 100mW red laser with fluence at 180J/cm2. PDT was efficient in vitro against C. neoformans in both parameters used: 3 log reduction with 108J/cm² and 6 log reduction with 162J/cm². In the in vivo experiment, PDT was also effective; however, its effect was less expressive than in the in vitro study (about 1 log reduction). In conclusion, PDT seems to be a helpful alternative to treat dermal cryptococcosis; however, more effective parameters must be found in in vivo studies.