Requirement for Ergosterol in Berberine Tolerance Underlies Synergism of Fluconazole and Berberine against Fluconazole-Resistant Candida albicans Isolates.

Yi Xu,Jianjiang Xu,Hua Quan,Yan Wang,Hua Zhong,Yuanying Jiang,Nuan Jia,Jun Sun

doi:10.3389/fcimb.2017.00491

Abstract

Candida albicans is one of the most common fungal pathogens. Our previous study demonstrated that concomitant use of berberine (BBR) and fluconazole (FLC) showed a synergistic action against FLC-resistant C. albicans in vitro and BBR had a major antifungal effect in the synergism, while FLC played a role of increasing the intracellular BBR concentration. Since the antifungal activity of BBR alone is very weak (MIC > 128 μg/mL), it was assumed that FLC-resistant C. albicans was naturally tolerant to BBR, and this tolerance could be reversed by FLC. The present study aimed to elucidate the mechanism underlying BBR tolerance in FLC-resistant C. albicans and its disruption by FLC. The ergosterol quantitative analysis showed that the BBR monotreatment could increase the content of cellular ergosterol. Real-time RT-PCR revealed a global upregulation of ergosterol synthesis genes in response to BBR exposure. In addition, exogenous ergosterol could decrease intracellular BBR concentration and increase the expression of drug efflux pump genes, further reducing the susceptibility of C. albicans to BBR. Similar to FLC, other antifungal agents acting on ergosterol were able to synergize with BBR against FLC-resistant C. albicans. However, the antifungal agents not acting on ergosterol were not synergistic with BBR. These results suggested that ergosterol was required for BBR tolerance, and FLC could enhance the susceptibility of FLC-resistant C. albicans to BBR by inhibiting ergosterol synthesis.

Highlights

Candida albicans is one of the most common clinical fungal pathogens and causes superficial mycoses, invasive mucosal infections, and disseminated systemic disease (Wilson et al, 2002; Gudlaugsson et al, 2003; Wisplinghoff et al, 2004; Pfaller and Diekema, 2007)
The findings suggested that BBR monotreatment resulted in marked augmentation of cellular ergosterol content in FLCresistant C. albicans
The results showed that BBR monotreatment induced increased expression of ergosterol synthesis genes and higher cellular ergosterol level, and promoted fusion of intracellular vacuoles in clinical FLC-resistant isolates

Summary

Introduction

Candida albicans is one of the most common clinical fungal pathogens and causes superficial mycoses, invasive mucosal infections, and disseminated systemic disease (Wilson et al, 2002; Gudlaugsson et al, 2003; Wisplinghoff et al, 2004; Pfaller and Diekema, 2007). Fluconazole (FLC), a classic antifungal agent, has been widely used in the clinic due to its Tolerance to Berberine Requires Ergosterol high bioavailability and low toxicity (Avmeet et al, 2002; White et al, 2002). Drug-resistant isolates are emerging rapidly with the increasing clinical use of FLC (Horn et al, 2009). With the deepening of the research, we further found that BBR played a major role in the synergism by causing cell cycle arrest and DNA damage, while FLC played a role of increasing the intracellular BBR concentration by damaging the cell membrane of drug-resistant C. albicans isolates (Li et al, 2013). Considering the weak antifungal effect of BBR monotherapy, we hypothesized that a natural BBR-tolerant mechanism might exist in FLC-resistant C. albicans, which could be disrupted by FLC

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