Antifungal activity of Cardiospermum halicacabum L. (Sapindaceae) against Trichophyton rubrum occurs through molecular interaction with fungal Hsp90

Roberta Gaziano,1,* Elena Campione,2,* Federico Iacovelli,3 Daniele Marino,1 Francesca Pica,1 Paolo Di Francesco,1 Stefano Aquaro,4 Francesco Menichini,4 Mattia Falconi,3 Luca Bianchi2 1Microbiology Section, Department of Experimental Medicine and Surgery, University of Rome ‘Tor Vergata’, Rome, Italy; 2Department of Systems Medicine, University of Rome ‘Tor Vergata’, Rome, Italy; 3Department of Biology, University of Rome ‘Tor Vergata’, Rome, Italy; 4Department of Pharmacy, Health and Nutritional Sciences, University of Calabria, Rende, Italy *These authors contributed equally to this work Introduction: Dermatophytosis is a superficial fungal infection limited to the stratum corneum of the epidermis, or to the hair and nails, and constitutes an important public health problem because of its high prevalence and associated morbidity. Dermatophyte fungi, especially 2 species, Trichophyton rubrum and Trichophyton mentagrophytes, are the predominant pathogens. Topical antifungal drugs, mainly azoles or allyamines, are currently used for the treatment of dermatophytoses, although in some cases, such as in nail and hair involvement, systemic treatment is required. However, therapeutic efficacy of current antifungal agents can be limited by their side effects, costs, and the emergence of drug resistance among fungi. Plant extracts represent a potential source of active antimicrobial agents, due to the presence of a variety of chemical bioactive compounds. In the present work, we evaluated in silico and in vitro the antifungal activity of an extract of the medicinal plant Cardiospermum halicacabum against T. rubrum suggesting a potential interaction with Hsp90 as playing an important role in both pathogenicity and drug susceptibility of T. rubrum. Methods: We investigated in vitro the effect of different concentrations of C. halicacabum (from 500 to 31.25 µg) against a clinical isolate of T. rubrum. Furthermore, using a computational assessment, the interaction between different C. halicacabum active compounds and the fungal Hsp90 was also investigated. Results: Our results indicate a clear-cut antifungal activity of the total plant extract at the highest concentrations (500 and 250 µg). Among all tested C. halicacabum compounds, the luteolin and rutin molecules have been identified in silico as the most important potential inhibitors of Hsp90. Based on these data, luteolin and rutin were also individually assessed for their antifungal activity. Results demonstrate that both substances display an antifungal effect, even if lower than that of the total plant extract. Conclusion: Our data indicate a strong fungistatic effect of C. halicacabum against T. rubrum, suggesting its potential therapeutic efficacy in the treatment of dermatophytoses. Additionally, C. halicacabum compounds, and particularly luteolin and rutin, are all possible Hsp90 interactors, explaining their fungistatic activity. Keywords: Trichophyton rubrum, dermatophytoses, Cardiospermum halicacabum, antifungal activity, Hsp90, molecular modeling, molecular docking, rutin, luteolin