Tricyclic antidepressants inhibit Candida albicans growth and biofilm formation

Candida albicans is a commensal yeast of the human body, able to form biofilms on solid surfaces such as implanted medical devices, and contributes to nosocomial infections. Biofilms have the capacity to resist higher levels of antifungals compared with planktonic cells, and can develop tolerance to commonly used treatments. The necessity to overcome acquired drug resistance and identify new active molecules with low toxicity is a significant problem. It has been reported that some antidepressants have antibacterial properties, but little is known regarding the effect of these drugs on fungi. This study demonstrated the capacity of three tricyclic antidepressants (doxepin, imipramine and nortriptyline) to inhibit the growth and biofilm formation of Candida spp. The antimicrobial potential of the drugs was assessed by studying gene expression, hyphae formation, biofilm growth and maturation. Their negative impact on the growth of C. albicans and other Candida spp. is shown in vitro and with the hepatic S9 system, which is preliminary to any in-vivo test. This study found that the antidepressants considered can inhibit not only hyphae and biofilm formation, but also kill cells in a mature biofilm. Moreover, cell lysis by nortriptyline was observed, along with its synergistic activity with amphotericin B. These findings suggest that tricyclic antidepressants, particularly nortriptyline, should be studied further in drug repositioning programmes to assess their antimycotic capacity in full.