O papel do estresse oxidativo e nitrosativo gerado pelos antifúngicos em Cryptococcus gattii e sua influência na heterorresistência ao itraconazol

Abstract

Although the most accepted mechanisms of action of amphotericin B and azoles are related to ergosterol, it is possible that these drugs have other effects on the fungal cell. Moreover, heteroresistance is an adaptive mechanism developed by the microorganism to counteract the stress of increasing drug concentration in the environment. Since itraconazole is used in the therapy of cryptococcosis, the aim of this study was to evaluate the role of endogenous reactive oxygen species (ROS) and peroxynitrite produced by azoles and amphotericin B in the fungus C. gattii and its influence on emergence of heteroresistante clones to itraconazole. We studied distinct parameters to evaluate the effect of oxidative and nitrosative stresses induced by fluconazole, itraconazole and amphotericin B in C. gattii cells. The effects of the heteroresistance to itraconazole were studied by performing tests in vitro and in a murine model. Itraconazole reduces the level of ergosterol and led to ROS production in C. gattii cells in the early stages of the treatment, enhancing the antioxidant activity. The same did not happen with fluconazole. Amphotericin B caused lipid peroxidation in C. gattii cells through a greatly enhanced production of oxidative and nitrosative radicals with increased lipid peroxidation. Heteroresistance to itraconazole was intrinsic in all strains tested and changed pharmacodynamics parameters, diminished cell and capsule sizes, reduced ergosterol content and enhanced the antioxidant system of heteroresistant clones. Indeed, heteroresistance to itraconazole led to the increased internalization of cryptococcal cells by macrophages, but also to a prominent proliferation inside these phagocytic cells, culminating in the higher virulence of heteroresistant clones. Based on these results, we conclude that oxidative bursts play an important role in the antifungal activity of itraconazole and may be one of the mechanisms that lead to heteroresistance and the increased virulence of C. gattii.