Alternative pathways of sterol synthesis in yeast. Use of C(27) sterol tracers to study aberrant double-bond migrations and evaluate their relative importance

Benzylamines as highly potent inhibitors of the sterol biosynthesis pathway in Leishmania amazonensis leading to oxidative stress and ultrastructural alterations

Leishmaniasis is a neglected disease caused by protozoan parasites of the Leishmania genus. Benzylamines are a class of compounds selectively designed to inhibit the squalene synthase (SQS) that catalyzes the first committed reaction on the sterol biosynthesis pathway. Herein, we studied seven new benzylamines (SBC 37–43) against Leishmania amazonensis. After the first screening of cell viability, two inhibitors (SBC 39 and SBC 40) were selected. Against intracellular amastigotes, SBC 39 and SBC 40 presented selectivity indexes of 117.7 and 180, respectively, indicating high selectivity. Analysis of the sterol composition revealed a depletion of endogenous 24-alkylated sterols such as episterol and 5-dehydroepisterol, with a concomitant accumulation of fecosterol, implying a disturbance in cellular lipid content. This result suggests a blockade of de novo sterol synthesis at the level of SQS and C-5 desaturase. Furthermore, physiological analysis and electron microscopy revealed three main alterations: (1) in the mitochondrion; (2) the presence of lipid bodies and autophagosomes; and (3) the appearance of projections in the plasma membrane. In conclusion, our results support the notion that benzylamines have a potent effect against Leishmania amazonensis and should be an exciting novel pharmaceutical lead for developing new chemotherapeutic alternatives to treat leishmaniasis.

Antifungal drug testing by combining minimal inhibitory concentration testing with target identification by gas chromatography-mass spectrometry

Fungal infections and their increasing resistance to antibiotics are an emerging threat to public health. Novel antifungal drugs, as well technologies that can help us bolster the antimicrobial pipeline and understand resistance mechanisms, are needed. The ergosterol biosynthetic pathway is one potential target for antifungal drugs. Here we describe how antifungal susceptibility testing can be combined with target identification in distal ergosterol biosynthesis by means of gas chromatography-mass spectrometry. The fungi are treated with sublethal doses of active components that block ergosterol biosynthesis, and the ergosterol biosynthesis intermediates are analyzed in a targeted metabolomics manner after derivatization (trimethylsilylation). Drug treatment results in distinct sterol patterns that are characteristic of the affected enzyme. Sterol identification based on relative retention times and electron ionization (EI) mass spectra, as well as semiquantitative assessment of ergosterol intermediates, is described. The protocol is applicable to yeasts and molds. The overall analysis time from incubation to test result is not more than 3 d. The assay can be used to determine whether an antifungal compound of interest targets sterol biosynthesis, and, if so, to determine which enzyme in the pathway it targets.

Cell-type-specific transcriptional profiles of the dimorphic pathogen Penicillium marneffei reflect distinct reproductive, morphological, and environmental demands

Penicillium marneffei is an opportunistic human pathogen endemic to Southeast Asia. At 25° P. marneffei grows in a filamentous hyphal form and can undergo asexual development (conidiation) to produce spores (conidia), the infectious agent. At 37° P. marneffei grows in the pathogenic yeast cell form that replicates by fission. Switching between these growth forms, known as dimorphic switching, is dependent on temperature. To understand the process of dimorphic switching and the physiological capacity of the different cell types, two microarray-based profiling experiments covering approximately 42% of the genome were performed. The first experiment compared cells from the hyphal, yeast, and conidiation phases to identify "phase or cell-state-specific" gene expression. The second experiment examined gene expression during the dimorphic switch from one morphological state to another. The data identified a variety of differentially expressed genes that have been organized into metabolic clusters based on predicted function and expression patterns. In particular, C-14 sterol reductase-encoding gene ergM of the ergosterol biosynthesis pathway showed high-level expression throughout yeast morphogenesis compared to hyphal. Deletion of ergM resulted in severe growth defects with increased sensitivity to azole-type antifungal agents but not amphotericin B. The data defined gene classes based on spatio-temporal expression such as those expressed early in the dimorphic switch but not in the terminal cell types and those expressed late. Such classifications have been helpful in linking a given gene of interest to its expression pattern throughout the P. marneffei dimorphic life cycle and its likely role in pathogenicity.

Ergosterol biosynthesis pathway in Aspergillus fumigatus

The sterol composition of Aspergillus fumigatus for the biosynthesis of ergosterol is of interest since this pathway is the target for many antifungal drugs in clinical use. The sterol composition of this fungal species was analyzed by gas chromatography-mass spectrometry in different strains (susceptible and resistant to azole drugs). Also, sterols were analyzed in several A. fumigatus mutant strains deficient in enzymatic steps of the ergosterol biosynthesis pathway such as 14-alpha sterol demethylases (Cyp51A and Cyp51B) and C-5 sterol desaturases (Erg3A, Erg3B and Erg3C). All sterols identified from azole-resistant A. fumigatus strains were qualitatively and quantitatively similar to the susceptible strain (CM-237). However, sterol composition of mutants strains were different depending on the lacking enzyme. The analysis of the sterol composition in these mutant strains led to a better understanding of the ergosterol biosynthesis pathway in this important fungus.