The haploinsufficiency profile of α-hederin suggests a caspofungin-like antifungal mode of action

α-Hederin regulates macrophage polarization to relieve sepsis-induced lung and liver injuries in mice

Sepsis is one of the most fatal inflammatory diseases with multiple organ failure caused by pathological infection. α-Hederin, a monodesmosidic triterpenoid saponin, has many biological activities including anti-inflammation. This study aimed to investigate the effect of α-Hederin on lung and liver injuries in septic mice. Mice underwent cecal ligation and puncture-induced sepsis were intraperitoneally injected with 0.3 or 3 mg/kg α-Hederin. α-Hederin treatment dose-dependently attenuated the lung and liver injuries in septic mice. Correspondingly, α-Hederin significantly decreased malondialdehyde production, increased the levels of superoxide dismutase and glutathione in lung tissues, reduced serum alanine aminotransferase and aspartate aminotransferase activities, and suppressed the levels of TNF-α and IL-6 in both tissues and in the serum. Moreover, α-Hederin augmented CD206 level and inhibited the productions of CD86 and iNOS in lung and liver tissues of septic mice. Importantly, p-p65/p65 was suppressed, whereas IκB was elevated by α-Hederin. In conclusion, α-Hederin could improve the lung and liver injuries in mice with sepsis by regulating macrophage M1/M2 polarization and inhibiting the activation of NF-κB signaling pathway.

Modes-of-action of antifungal compounds: Stressors and (target-site-specific) toxins, toxicants, or Toxin-stressors

Fungi and antifungal compounds are relevant to the United Nation's Sustainable Development Goals. However, the modes-of-action of antifungals-whether they are naturally occurring substances or anthropogenic fungicides-are often unknown or are misallocated in terms of their mechanistic category. Here, we consider the most effective approaches to identifying whether antifungal substances are cellular stressors, toxins/toxicants (that are target-site-specific), or have a hybrid mode-of-action as Toxin-stressors (that induce cellular stress yet are target-site-specific). This newly described 'toxin-stressor' category includes some photosensitisers that target the cell membrane and, once activated by light or ultraviolet radiation, cause oxidative damage. We provide a glossary of terms and a diagrammatic representation of diverse types of stressors, toxic substances, and Toxin-stressors, a classification that is pertinent to inhibitory substances not only for fungi but for all types of cellular life. A decision-tree approach can also be used to help differentiate toxic substances from cellular stressors (Curr Opin Biotechnol 2015 33: 228-259). For compounds that target specific sites in the cell, we evaluate the relative merits of using metabolite analyses, chemical genetics, chemoproteomics, transcriptomics, and the target-based drug-discovery approach (based on that used in pharmaceutical research), focusing on both ascomycete models and the less-studied basidiomycete fungi. Chemical genetic methods to elucidate modes-of-action currently have limited application for fungi where molecular tools are not yet available; we discuss ways to circumvent this bottleneck. We also discuss ecologically commonplace scenarios in which multiple substances act to limit the functionality of the fungal cell and a number of as-yet-unresolved questions about the modes-of-action of antifungal compounds pertaining to the Sustainable Development Goals.

A simplified and easy-to-use HIP HOP assay provides insights into chalcone antifungal mechanisms of action

Elucidating the mechanism of action of an antifungal or cytotoxic compound is a time-consuming process. Yeast chemogenomic profiling provides a compelling solution to the problem but is experimentally complex. Here, we demonstrate the use of a highly simplified yeast chemical genetic assay comprising just 89 yeast deletion strains, each diagnostic for a specific mechanism of action. We use the assay to investigate the mechanism of action of two antifungal chalcone compounds, trans-chalcone and 4'-hydroxychalcone, and narrow down the mechanism to transcriptional stress. Crucially, the assay eliminates mechanisms of action such as topoisomerase I inhibition and membrane disruption that have been suggested for related chalcone compounds. We propose this simplified assay as a useful tool to rapidly identify common off-target mechanisms.

An investigation of the antileishmanial properties of semi-synthetic saponins

Leishmaniasis is a neglected tropical disease caused by insect-vector borne protozoan parasites of the, Leishmania species. Whilst infection threatens and affects millions of the global poor, vaccines are absent and drug therapy limited. Extensive efforts have recently been made to discover new leads from small molecule synthetic compound libraries held by industry; however, the number of new chemical entities identified and entering development as anti-leishmanials has been very low. This has led to increased interest in the possibility of discovering naturally derived compounds with potent antileishmanial activity which may be developed towards clinical applications. Plant-derived triterpenoid and steroidal saponins have long been considered as anti-microbials and here we describe an investigation of a library of 137 natural (9) and semi-synthetic saponins (128) for activity against Leishmania mexicana, a causative agent of cutaneous leishmaniasis. The triterpenoid sapogenin, hederagenin, readily obtained in large quantities from Hedera helix (common ivy), was converted into a range of 128 derivatives. These semi-synthetic compounds, as well as saponins isolated from ivy, were examined with a phenotypic screening approach to identify potent and selective anti-leishmanial hits. This led to the identification of 12 compounds, including the natural saponin gypsogenin, demonstrating high potency (ED50 < 10.5 μM) against axenic L. mexicana amastigotes, the mammalian pathogenic form. One of these, hederagenin disuccinate, was sufficiently non-toxic to the macrophage host cell to facilitate further analyses, selectivity index (SI) > 10. Whilst this was not active in an infected cell model, the anti-leishmanial properties of hederagenin-derivatives have been demonstrated, and the possibility of improving the selectivity of natural hederagenin through chemical modification has been established.

De novo leaf and root transcriptome analysis to identify putative genes involved in triterpenoid saponins biosynthesis in Hedera helix L

Hedera helix L. is an important traditional medicinal plant in Europe. The main active components are triterpenoid saponins, but none of the potential enzymes involved in triterpenoid saponins biosynthesis have been discovered and annotated. Here is reported the first study of global transcriptome analyses using the Illumina HiSeq™ 2500 platform for H. helix. In total, over 24 million clean reads were produced and 96,333 unigenes were assembled, with an average length of 1385 nt; more than 79,085 unigenes had at least one significant match to an existing gene model. Differentially Expressed Gene analysis identified 6,222 and 7,012 unigenes which were expressed either higher or lower in leaf samples when compared with roots. After functional annotation and classification, two pathways and 410 unigenes related to triterpenoid saponins biosynthesis were discovered. The accuracy of these de novo sequences was validated by RT-qPCR analysis and a RACE clone. These data will enrich our knowledge of triterpenoid saponin biosynthesis and provide a theoretical foundation for molecular research on H. helix.

A rapid and sensitive liquid chromatography-tandem mass spectrometric method for the determination of hederasaponin B in rat plasma: Application to a pharmacokinetic study

A rapid, simple and sensitive ultra-high performance liquid chromatography-tandem mass spectrometric (UPLC-MS/MS) method was developed and validated for the determination of hederasaponin B, an active triterpenoid saponin widely existed in Hedera helix L. Plasma samples were processed by protein precipitation with acetonitrile and separated on a Thermo Hypersil GOLD C₁₈ (2.1 mm × 50 mm,1.9 µm) at flow rate of 0.3 ml/min, with a gradient elution consisting of acetonitrile and water containing 0.1% (v/v) formic acid at 30 °C and detected by electrospray ionization mass spectrometry in the positive multiple reaction monitoring (MRM) mode. The linearity was found to be within the concentration range of 0.5-5000 ng/ml with a lower limit of quantification of 0.5 ng/ml. The absolute oral bioavailability of hederasaponin B was 0.24 ± 0.49%. This indicated that the concentration-time course of the hederasaponin B existed a double-peak phenomenon. This method was further applied to the determination of hederasaponin B in rat plasma and showed good practicability, for the first time, after intragastric (25 mg/kg) and intravenous (2 mg/kg) administration in rats.

A Mini HIP HOP Assay Uncovers a Central Role for Copper and Zinc in the Antifungal Mode of Action of Allicin

Garlic contains the organosulfur compound allicin which exhibits potent antifungal activity. Here we demonstrate the use of a highly simplified yeast chemical genetic screen to characterize its mode of action. By screening 24 validated yeast gene deletion "signature" strains for which hypersensitivity is characteristic for common antifungal modes of action, yeast lacking the high affinity Cu²⁺ transporter Ctr1 was found to be hypersensitive to allicin. Focusing on transition metal related genes identified two more hypersensitive strains lacking the Cu²⁺ and Zn²⁺ transcription factors Mac1 and Zap1. Hypersensitivity in these strains was reversed by the addition of Cu²⁺ and Zn²⁺ ions, respectively. The results suggest the antifungal activity of allicin is mediated through restricted Cu²⁺ and Zn²⁺ uptake or inhibition of Cu²⁺ and Zn²⁺ metalloproteins. As certain antimicrobial modes of action are much more common than others, the approach taken here provides a useful way to identify them early on.