Envolvimento da defesa antioxidante de fungos na formação de biofilme

Abstract

The early reactive oxygen/nitrogen species (ROS/RNS) produced by phagocytes are superoxide anions, from which are derived other oxidant compounds that are potent microbicides. In response to oxidative/nitrosative stress, all cells present endogenous antioxidant defense capacity. Some fungi are able to modulate their antioxidant defense, increasing their pathogenicity forward to the oxidant host organism attack. Attention has been given to the ability of Candida albicans biofilms modulate their antioxidant defense, associated to the increase of morbidity and mortality of infected patients. Nitroxides are synthetic antioxidants that modulate the activity of Nox2 in phagocytes, reducing the production of superoxide anions. This effect of nitroxides decreases the harmful effects of ROS/RNS during an inflammatory process, but could compromise the microbicidal capacity of phagocytes. The aim of this work was to study the interaction between human phagocytes and C. albicans in both, planktonic and biofilm, forms. Also, the effect of nitroxide 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl (Tempol) was tested in order to verify the hypothesis of interference of this antioxidant in the host immune defense. The antioxidant enzymes catalase (CAT) and superoxide dismutases (SOD) were evaluated in yeasts and neutrophils, either in presence or absence of Tempol. Neutrophil respiratory burst was monitored to determine the effects of the nitroxide on superoxide anion production. Killing assay of C. albicans was performed by cultivating yeast in the presence of human neutrophils with or without Tempol addition, followed by colony forming units counting. The results showed a high activity of SOD and CAT in the fungus, which was stronger when biofilm form was established than that planktonic one. In addition, the exposure to yeast caused a decrease on antioxidant enzymes activities of human neutrophils. Tempol addition caused a significant impairment on both antioxidant enzymatic activities, as in neutrophil suspensions as in cultured fungi. Exposure to C. albicans biofilms stimulated a larger neutrophil superoxide anion formation than correspondent planktonic form, an event that was inhibited by Tempol. Nitroxide addition partially deleted neutrophil fungicide capability, suggesting a deleterious action on phagocytic fulfillment on host defence.