Bypass of Dfi1 Regulation of Candida albicans Invasive Filamentation by Iron Limitation.

Candida albicans filamentation, the ability to convert from oval yeast cells to elongated hyphal cells, is a key factor in its pathogenesis. Previous work has shown that the integral membrane protein Dfi1 is required for filamentation in cells grown in contact with a semisolid surface. Investigations into the downstream targets of the Dfi1 pathway revealed potential links to two transcription factors, Sef1 and Czf1. Sef1 regulates iron uptake and iron utilization genes under low-iron conditions, leading us to hypothesize that there exists a link between iron availability and contact-dependent invasive filamentation. In this study, we showed that Sef1 was not required for contact-dependent filamentation, but it was required for wild-type (WT) expression levels of a number of genes during growth under contact conditions. Czf1 is required for contact-dependent filamentation and for WT levels of expression of several genes. Constitutive expression and activation of either Sef1 or Czf1 individually in a dfi1 null strain resulted in a complete rescue of the dfi1 null filamentation defect. Because Sef1 is normally activated in low-iron environments, we embedded WT and dfi1 null cells in iron-free agar medium supplemented with various concentrations of ferrous ammonium sulfate (FAS). dfi1 null cells embedded in media with a low concentration of iron (20 µM FAS) showed increased filamentation in comparison to mutant cells embedded in higher concentrations of iron (50 to 500 µM). WT cells produced filamentous colonies in all concentrations. Together, the data indicate that Dfi1, Czf1, Sef1, and environmental iron regulate C. albicans contact-dependent filamentation. IMPORTANCE Candida albicans is an opportunistic pathogen responsible for a larger proportion of candidiasis and candidemia cases than any other Candida species. The ability of C. albicans cells to invade and cause disease is linked to their ability to filament. Despite this, there are gaps in our knowledge of the environmental cues and intracellular signaling that triggers the switch from commensal organism to filamentous pathogen. In this study, we identified a link between contact-dependent filamentation and iron availability. Over the course of tissue invasion, C. albicans cells encounter a number of different iron microenvironments, from the iron-rich gut to iron-poor tissues. Increased expression of Sef1-dependent iron uptake genes as a result of contact-dependent signaling will promote the adaptation of C. albicans cells to a low-iron-availability environment.

In Vitro and In Vivo Study of Amphotericin B Formulation with Quaternized Bioreducible Lipidoids.

Invasive fungal infections are well-known causes of morbidity and mortality in immunocompromised patients. Amphotericin B (AmB) is a polyene fungicidal agent with excellent properties of the broad antifungal spectrum, high activity, and relatively rare drug resistance. However, significant toxicities limit the clinical application of AmB and its conventional formulation AmB deoxycholate (Fungizone). Here we investigated nanoparticle formulations of AmB using synthetic biodegradable lipidoids and evaluated their stability, in vitro antifungal efficacy, and in vivo toxicity and pharmacokinetics. We found that the AmB formulated using a mixture of quaternized lipidoid (Q78-O14B) and DSPE-PEG2000 has the size around 70-100 nm and is stable during storage. The formulation showed no hemotoxicity to red blood cells (RBCs) in vitro. It also possesses the highest antifungal activity (in vitro) and lowest toxicity (both in vitro and in vivo). These metrics are significantly superior to the commercial antifungal product Fungizone. Meanwhile, AmB/Q78-O14B-P exhibited prolonged blood circulation in comparison to Fungizone in vivo. In AmB/Q78-O14B-P formulation, AmB was still detectable in the liver, spleen, and lung tissues with a concentration above the minimum inhibitory concentrations 72 h after low-dose intravenous injection. Based on these results, AmB in lipidoid nanoparticle formulation may produce sustained antifungal activity against blood-borne and systemic organ infections. Moreover, the new AmB formulation showed low nephrotoxicity and hepatotoxicity in rats even at high doses, allowing a dramatically wider and safer therapeutic window than Fungizone. This method provides a means to develop much needed antifungal agents that will be more therapeutically efficacious, more affordable (than AmBisome), and less toxic (than Fungizone) for the treatment of systemic fungal infections.