Lipid composition and cell surface hydrophobicity of Candida albicans influence the efficacy of fluconazole–gentamicin treatment

Abstract

Adherence of the fungus, Candida albicans, to biotic (e.g. human tissues) and abiotic (e.g. catheters) surfaces can lead to emergence of opportunistic infections in humans.The process of adhesion and further biofilm development depends, in part, on cell surface hydrophobicity (CSH). In this study, we compared the resistance of C. albicans strains with different CSH to the most commonly prescribed antifungal drug, fluconazole, and the newly described synergistic combination, fluconazole and gentamicin. The hydrophobic strain was more resistant to fluconazole due to, among others, overexpression of the ERG11 gene encoding the fluconazole target protein (CYP51A1, Erg11p), which leads to overproduction of ergosterol in this strain.Additionally, the hydrophobic strain displayed high efflux activity of the multidrug resistance Cdr1 pump due to high expression of the CDR1 gene. On the other hand, the hydrophobic C. albicans strain was more susceptible to fluconazole-gentamicin combination because of its different effect on lipid content in the two strains. The combination resulted in ergosterol depletion with subsequent Cdr1p mislocalization and loss of activity in the hydrophobic strain. We propose that C. albicans strains with different CSH may possess altered lipid metabolism and consequently may differ in their response to treatment. K E Y W O R D SCandida albicans, Cdr1, cell surface hydrophobicity, ergosterol, fluconazole synergism, gentamicin

Mitochondria-Mediated Azole Drug Resistance and Fungal Pathogenicity: Opportunities for Therapeutic Development

“…On the other hand, activation of the Pdr pathway regulates the expression of genes required for the homeostasis of two key lipid components of plasma membranes, phospholipids, and sphingolipids ( Figure 3 ) [ 15 , 50 ]. Because plasma membrane lipid components are crucial for surface localization of drug efflux pumps [ 50 , 51 ], the Pdr pathway may provide coordinate control of plasma membrane lipid composition through modulation of sphingolipid and phospholipid homeostasis and of drug efflux pump proteins that function in the resulting membrane lipid environment, which may contribute to Pdr-mediated azole resistance upon mitochondrial dysfunction. Taken together, mitochondrial function plays an important role in membrane lipid composition, and activation of lipid homeostasis by the Pdr pathway may serve to compensate for the changes to membrane lipid structure and composition upon mitochondrial dysfunction, which may be the reason why fungi activate the Pdr pathway upon mitochondrial dysfunction.…”

Sphingolipids: Regulators of azole drug resistance and fungal pathogenicity

“…Membrane sphingolipid–ergosterol interactions are required for azole resistance . Various studies have confirmed that the action of azole drugs can be modulated by subtle modification of the plasma membrane lipid composition (Khandelwal et al ., 2018; Kundu et al ., 2020; Suchodolski et al ., 2020). Some clinical azole‐resistant isolates of pathogenic fungi exhibit altered plasma membrane lipid composition (Mishra et al ., 2008; Eddouzi et al ., 2013; Hull et al ., 2012).…”

“…Depletion of either of these plasma membrane lipid components results in disruption of this interaction, which in turn increases the susceptibility to azole drugs (Mukhopadhyay et al ., 2004). Therefore, changes in plasma membrane sphingolipid and ergosterol composition may be responsible for azole resistance (Mukhopadhyay et al ., 2004; Suchodolski et al ., 2020). Since lipid raft domains enriched in sphingolipids and ergosterol are crucial for the localization of drug efflux pump proteins (Panwar et al ., 2008; Singh et al ., 2017; Suchodolski et al ., 2020), the increased azole susceptibility caused by the disruption of this interaction might be due to interference with proper surface localization of drug efflux pumps.…”

“…Therefore, changes in plasma membrane sphingolipid and ergosterol composition may be responsible for azole resistance (Mukhopadhyay et al ., 2004; Suchodolski et al ., 2020). Since lipid raft domains enriched in sphingolipids and ergosterol are crucial for the localization of drug efflux pump proteins (Panwar et al ., 2008; Singh et al ., 2017; Suchodolski et al ., 2020), the increased azole susceptibility caused by the disruption of this interaction might be due to interference with proper surface localization of drug efflux pumps. For example, when ergosterol and sphingolipid biosynthesis genes were disrupted, the multidrug ABC transporter Cdr1 was poorly localized and the efflux of azole drugs was severely hampered in Candida cells (Mukhopadhyay et al ., 2004; Prasad et al ., 2005; Pasrija et al ., 2008; Suchodolski et al ., 2020), indicating that membrane sphingolipid–ergosterol interactions are required for surface localization of Cdr1.…”

“…Since lipid raft domains enriched in sphingolipids and ergosterol are crucial for the localization of drug efflux pump proteins (Panwar et al ., 2008; Singh et al ., 2017; Suchodolski et al ., 2020), the increased azole susceptibility caused by the disruption of this interaction might be due to interference with proper surface localization of drug efflux pumps. For example, when ergosterol and sphingolipid biosynthesis genes were disrupted, the multidrug ABC transporter Cdr1 was poorly localized and the efflux of azole drugs was severely hampered in Candida cells (Mukhopadhyay et al ., 2004; Prasad et al ., 2005; Pasrija et al ., 2008; Suchodolski et al ., 2020), indicating that membrane sphingolipid–ergosterol interactions are required for surface localization of Cdr1. Taken together, there is a strong correlation between plasma membrane lipid components and proper surface localization of drug efflux pump proteins (Figure 2a), and sphingolipid and ergosterol as individual components—as well as their mutual interactions—are critical in the sorting and functioning of drug efflux pump proteins.…”