Riparina 3 como um novo agente antifúngico e antibiofilme para controle de dermatófitos.

Abstract

Dermatophytoses are fungal infections involving the invasion and propagation of dermatophytes in keratinized structures. Despite the numerous medications available in the market for treating these conditions, resistance to conventional antifungals has been on the rise, leading to therapeutic failures. Currently, the ability of dermatophytes to produce biofilms is considered one of the most important factors involved in treatment failures, as these biofilms hinder the penetration of drugs into infected

tissues. Therefore, research aimed at finding new antifungal agents with potential anti- biofilm properties is crucial. In this regard, riparins, a class of alkaloids containing an

amide group, isolated from the green fruits of Aniba riparia, are promising phytochemicals. In this study, we assessed the antifungal and anti-biofilm activity of riparin 3 (RIP3) and its synthetic counterpart Nor-(NOR3) against clinically relevant dermatophytes Trichophyton rubrum, Microsporum canis, and Nannizzia gypsea. Cyclopirox (CPX) was used as the positive control. The effects of RIP3 and NOR3 on fungal growth were evaluated using the microdilution technique. The quantification of in vitro biofilm biomass was carried out using 0.5% crystal violet, and biofilm viability was assessed by quantifying the number of colony-forming units (CFUs). The ex vivo model was performed on human nail fragments, which were evaluated through light microscopy and quantification of CFUs (viability). Finally, it was determined whether

the test drugs inhibited the sulfite secretion by strains grown in M9 medium with L- cysteine, based on sulfite oxidation to sulfate and measurement of stable signal at 570

nm. The results showed that RIP3 is a fungicide, inhibiting the growth of T. rubrum and M. canis from 128 mg/L and N. gypsea from 256 mg/L onwards. Conversely, NOR3 showed no antifungal activity against the tested dermatophytes (MIC > 1024 mg/L). Regarding anti-biofilm activity, RIP3 inhibited the in vitro and ex vivo biofilm formation and viability compared to the control (p <0.05). Furthermore, RIP3 significantly inhibited sulfite secretion and was more potent than CPX. In conclusion, the results indicate that RIP3 is a promising antifungal agent against dermatophyte biofilms, and this action appears to involve the inhibition of sulfite secretion.