Cholesterol Import by Aspergillus fumigatus and Its Influence on Antifungal Potency of Sterol Biosynthesis Inhibitors

Abstract

High mortality rates from invasive aspergillosis in immunocompromised patients are prompting research toward improved antifungal therapy and better understanding of fungal physiology. Herein we show that Aspergillus fumigatus, the major pathogen in aspergillosis, imports exogenous cholesterol under aerobic conditions and thus compromises the antifungal potency of sterol biosynthesis inhibitors. Adding serum to RPMI medium led to enhanced growth of A. fumigatus and extensive import of cholesterol, most of which was stored as ester. Growth enhancement and sterol import also occurred when the medium was supplemented with purified cholesterol instead of serum. Cells cultured in RPMI medium with the sterol biosynthesis inhibitors itraconazole or voriconazole showed retarded growth, a dose-dependent decrease in ergosterol levels, and accumulation of aberrant sterol intermediates. Adding serum or cholesterol to the medium partially rescued the cells from the drug-induced growth inhibition. We conclude that cholesterol import attenuates the potency of sterol biosynthesis inhibitors, perhaps in part by providing a substitute for membrane ergosterol. Our findings establish significant differences in sterol homeostasis between filamentous fungi and yeast. These differences indicate the potential value of screening aspergillosis antifungal agents in serum or other cholesterol-containing medium. Our results also suggest an explanation for the antagonism between itraconazole and amphotericin B, the potential use of Aspergillus as a model for sterol trafficking, and new insights for antifungal drug development.

Cholesterol import fails to prevent catalyst-based inhibition of ergosterol synthesis and cell proliferation of Trypanosoma brucei

“…In a related study on cholesterol import by Aspergillus fumigatus and its influence on the antifungal potency of ergosterol biosynthesis inhibitors, specifically 14a-demethylase inhibitors, it was concluded that adding serum or cholesterol to the medium partially rescues fungal cells from the drug-induced growth inhibition (33), a finding that is contrary to the observations described here with TB. However, the possibility that cholesterol can serve as an ergosterol surrogate for the cell membrane is entirely consistent with our view (29) and that of others (30)(31)(32) that distinct sterol structures are involved with multiple functions.…”

Inhibitory and Fungicidal Effects of Antifungal Drugs against Aspergillus Species in the Presence of Serum

“…However, be- (19,20). Another effect of serum on Aspergillus growth is the exogenous import of human cholesterol by A. fumigatus, providing a substitute for fungal membrane ergosterol (27). This effect may contribute to the decreased antifungal activity of amphotericin B in the presence of serum found in the present study, since cholesterol has a lower affinity for amphotericin B (28).…”

Facultative Sterol Uptake in an Ergosterol-Deficient Clinical Isolate of Candida glabrata Harboring a Missense Mutation in ERG11 and Exhibiting Cross-Resistance to Azoles and Amphotericin B

“…It has been proposed that aerobic uptake of exogenous sterol (e.g., host cholesterol) contributes to azole (1,26) and polyene (12) resistance in vivo, and a putative sterol transporter gene for C. glabrata (AUS1) has been identified (26). The genetic controls and biological consequences of obligate and facultative sterol uptake in C. glabrata require further investigation, not least because the potential exists for similarities with other opportunistic pathogens, such as Aspergillus fumigatus (41) and Pneumocystis jirovecii (14).…”