Date Published: February 2, 2018
Publisher: Public Library of Science
Author(s): Ling Li, ZeBin Liao, Yu Yang, Lei Lv, YingYing Cao, ZhenYu Zhu, Chaminda Jayampath Seneviratne.
Candida albicans, one of the most common fungal pathogens, is responsible for several yeast infections in human hosts, being resistant to classically used antifungal drugs, such as azole drugs. Multifactorial and multistep alterations are involved in the azole resistance in Candida albicans. In this study, a FCZ-resistant C. albicans strain was obtained by serial cultures of a FCZ-susceptible C. albicans strain in incrementally increasing concentrations of FCZ. We performed an integrated profile of different classes of molecules related to azole resistance in C. albicans by combining several mass-spectrometry based methodologies. The comparative metabolomic study was performed with the sensitive and resistant strains of C.albicans to identify metabolites altered during the development of resistance to fluconazole, while the intervention strains and non-intervention strains of C.albicans to identify metabolites altered involved in cross-resistant to azole drugs. Our analysis of the different metabolites identified molecules mainly involved in metabolic processes such as amino acid metabolism, tricarboxylic acid cycle and phospholipid metabolism. We also compared the phospholipid composition of each group, revealing that the relative content of phospholipids significantly changed during the development of resistance to azole drugs. According with these results, we hypothesized that the metabolism shift might contribute to azole drugs resistance in C.albicans from multifactorial alterations. Our result paves the way to understand processes underlying the resistance to azole drugs in C. albicans, providing the basis for developing new antifungal drugs.
Candida albicans is an asexual opportunistic fungus that causes infections in immunocompromised and debilitated individuals. Azole drugs are widely used in clinical practice having a good antibacterial power and low side effects. Unfortunately, widespread uses of azole drugs have led to the rapid development of drug resistance which hampers the efficacy of current treatments for invasive mycoses. The considerable number of side effects mainly related to high-concentration use of drugs and prolonged therapies. The increase of drug resistance still make a serious clinical problem for fungal infections. A strong mobilization of the scientific community allowed elucidation of the molecular mechanisms underlying fluconazole resistance in the yeasts Candida, of which a number of them could be extrapolated to other azole drugs, such as mutations in the ERG11 gene, overexpression of efflux membrane transporters and overexpression of ERG11. Metabolomics is a systems biology approach to study small molecules. It is a rapidly growing field that aims to profile as many low molecular weight metabolites as possible, rather than focus on single metabolites in cells, biofluids and tissue extracts[5, 6]. Almost all metabolomics approaches can be classified as targeted or untargeted. Targeted analyses always focus on a subset of known metabolites, while untargeted are global screening approaches. Using bioinformatic and statistical tools, metabolomic profiles from different samples can be compared, identifying potential metabolite markers or patterns typical for a specific sample or condition. However, due to the wide range of metabolite concentrations and the diversity of their biochemical properties, no single analytical technique can provide a fully characterization of the metabolic profile of an organism. The best option is to use a combination of several analytical approaches. High-performance liquid chromatography mass spectrometry (HPLC-MS) and gas chromatography MS (GC-MS) are two widely used techniques for metabolomics analysis.
To investigate biological mechanisms of azole resistance in C. albicans, a laboratory azole resistant C. albicans strain was obtained by serial cultures of a FCZ susceptible C. albicans strain in inhibitory concentrations of FCZ. This resistant strain possessed high-level and stable resistant characteristic, as well as cross-resistance to two other azole antifungal agents. Comparative analysis of metabolomics in groups showed that the differentially expressed metabolites were found to be involved in multiple biochemical functions. It is reasonable to assume that many of the observed alternations are somewhat related to azole resistance in C. albicans.
In this study, different MS-based approaches were used to investigate the metabolic profile associated with azole resistance in C. albicans. Our results allowed, as a model containing potential biomarkers changing in azole resistance in C. albicans. that the majority of these potential biomarkers were involved in metabolic processes related to amino acid metabolism, sphingolipid metabolism and phospholipid metabolism. It is a complex process probably involving, reducing the endogenous ROS production, strengthening the expression of drug transporters, changing the function of cell membranes and mitochondria. Overall, our study explores global changes in metabolites involved in resistance to azole drugs, providing a more detailed understanding of the evolution of drug resistance in C. albicans.