Usnic acid activity on oxidative and nitrosative stress of azole-resistant Candida albicans biofilm

MARIANA ANDREA PERALTA, MARÍA ANGEL DA SILVA, MARÍA GABRIELA ORTEGA, JOSÉ LUIS CABRERA, MARÍA GABRIELA PARAJE.

PLANTA MEDICA

GEORG THIEME VERLAG KG

Año: 2017 vol. 20

0032-0943

Severalstudies report about that (+)-usnic acid (UA), asecondary metabolite produced by lichens, inhibits growth of differentbacteria and fungi; however, mechanism of its antimicrobial activity remainsunknown. In the present study,we have explored the ability of UA, obtained from Usnea amblyoclada, as an antibiofilm agent against azole-resistant(RCa) and azole-sensitive (SCa) Candida albicans strainsby studying the cellular stress and antioxidant response in biofilms. Thebiofilm inhibitory concentration (BIC) of UA (4 µg/mL) exhibited a significant biofilm inhibition, 71.08% for RCa and 87.84% for SCa. Confocalscanning laser microscopy (CSLM) showed that the morphology of mature biofilmwas altered (reduced the biomass and thickness) in the presence of UA. The antifungal effectwas mediated by an oxidativeand nitrosative stress, with a significant accumulation of intracellular andextracellular ROS detected by CSLM and by nitroblue tetrazolium, respectively. In fact, RCa and SCa biofilms treated atBIC of UA (4 µg/mL) presented ROS measurements with an increase of 30-fold and10-fold compared to basal levels, respectively. Also SCa and RCa biofilms treated with UA at 4 µg/mL exhibitedan important NO generation with 60-fold and 25-fold increase with respect tothe controls, respectively.  Non-enzymatic and enzymatic antioxidant defenses were increased inboth strains compared to biofilm basal levels as response to the increase ofoxidant metabolites. Thepresent study shows, for the first time, that UA can alter the prooxidant-antioxidant balance, which may be the cause of theirreversible cell damage and lead to cell death. Our results suggest that UA could be an alternative for theCandida infections treatment, whichdeserves further investigation.