Effects of antifungal agents on the fungal proteome: informing on mechanisms of sensitivity and resistance

INTRODUCTION

Antifungal agents are essential in the fight against serious fungal disease, however emerging resistance is threatening an already limited collection of therapeutics. Proteomic analyses of effects of antifungal agents can expand our understanding of multifactorial mechanisms of action and have also proven valuable to elucidate proteomic changes associated with antifungal resistance.

AREAS COVERED

This review covers the application of proteomic techniques to examine sensitivity and resistance to antifungals including commonly used therapeutics, amphotericin B, echinocandins and the azoles, based predominantly on studies involving Aspergillus fumigatus, Candida albicans and Candida glabrata from the last 10 years. In addition, non-clinical antimicrobial agents are also discussed, which highlight the potential of proteomics to identify new antifungal targets.

EXPERT COMMENTARY

Fungal proteomics has evolved in the last decade with increased genome availability and developments in mass spectrometry. Collectively, these have led to the advancement of proteomic techniques, allowing increased coverage of the proteome. Gel-based proteomics laid the foundation for these types of studies, which has now shifted to the more powerful gel-free proteomics. This has resulted in the identification of key mediators and potential biomarkers of antifungal resistance, as well as elucidating the mechanisms of action of novel and established antifungal agents.

Update on Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry Identification of Filamentous Fungi

Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS)-based species identification has found its place in many clinical routine diagnostic laboratories over the past years, allowing significantly reduced turnaround times and high-precision results. With regard to MALDI-TOF MS for filamentous fungi, here, we discuss different approaches for sample processing and growth conditions before analysis. In particular, we review the performances of different commercially available databases as well as the potential of complementary (self-constructed) in-house databases.

Resistance mechanism and proteins in Aspergillus species against antifungal agents

Aspergillus

species contain pathogenic and opportunistic fungal pathogens which have the potential to cause mycosis (invasive aspergillosis) in humans. The existing antifungal drugs have limitation largely due to the development of drug-resistant isolates. To gain insight into the mechanism of action and antifungal drug resistance in Aspergillus species including biofilm formation, we have reviewed protein data of Aspergillus species during interaction with antifungals drugs (polynes, azoles and echinocandin) and phytochemicals (artemisinin, coumarin and quercetin). Our analyses provided a list of Aspergillus proteins (72 proteins) that were abundant during interaction with different antifungal agents. On the other hand, there are 26 proteins, expression level of which is affected by more than two antifungal agents, suggesting the more general response to the stress induced by the antifungal agents. Our analysis showed enzymes from cell wall remodelling, oxidative stress response and energy metabolism are the responsible factors for providing resistance against antifungal drugs in Aspergillus species and could be explored further in clinical isolates. Also, these findings have clinical importance since the effect of drug targeting different proteins can be potentiated by combination therapy. We have also discussed the opportunities ahead to study the functional role of proteins from environmental and clinical isolates of Aspergillus during its interaction with the antifungal drugs.

Abbreviations

IPA: invasive pulmonary aspergillosis; IA: invasive aspergillosis; AmB: Amphotericin B; CAS: Caspofungin; VRC: Voriconazole; ITC: Itraconazole; POS: Posaconazole; ART: Artemisinin; QRT: Quercetin; CMR: Coumarin; MIC: minimal inhibitory concentration