Design, synthesis and biological evaluation of reactive selenium species (RSeS)

Naturally occurring RSeS form an interesting alcove of redox biology in living cells. These species provide interesting information for the design and synthesis of RSeS which modulate the redox state of cells and further grant important insights on lead structures in the hunt for active agents against infectious diseases associated with Oxidative Stress (OS). In the present study, several synthetic RSeS were prepared and, thereafter, evaluated biologically against a plethora of targets. The synthetic compounds belong to different classes of organo-selenium compounds ranging from simple aromatic selenocyanates to ebselen-like selenazolinium salts and even rather complicated multi-component hybrid redox catalysts. These organic RSeS and some inorganic salts of selenium and tellurium were evaluated against a broad spectrum of microorganisms, including Gram-positive and Gram-negative bacteria of the notorious ESKAPE family, yeasts and multicellular nematodes. Some of the compounds, such as aryl methyl selenocyanates, were also investigated for cytotoxic activity against normal and cancer cell lines. Generally, all the synthetic RSeS exhibited excellent activity against the selected targets. The preliminary mechanistic studies revealed that such compounds interact with the cellular thiolstat of the target organism. The interaction of selenium-based agents with intracellular thiolstat sets forth novel possibilities to tailor potent, efficient and target-oriented multifunctional RSeS.Natürlich vorkommende RSeS bilden eine interessante Nische der Redox-Biologie in lebenden Zellen. Diese Spezies liefern interessante Informationen für das Design und die Synthese von RSeS, die den Redox-Zustand der Zellen modulieren und wichtige Erkenntnisse über Leitstrukturen bei der Suche nach Wirkstoffen gegen Infektionskrankheiten im Zusammenhang mit Oxidativem Stress liefern. In der vorliegenden Arbeit wurden mehrere synthetische RSeS vorbereitet und anschließend gegen eine Vielzahl von biologischen Targets bewertet. Die synthetischen Verbindungen gehören zu verschiedenen Klassen von Organoselenverbindungen, die von einfachen aromatischen Selenocyanaten über ebselenartige Selenazolinium Salze bis hin zu komplexeren mehrkomponentige Hybrid-Redoxkatalysatoren reichen. Diese Verbindungen wurden anhand eines breiten Spektrums an Mikroorganismen bewertet, darunter Gram-positiv und Gram-negativ Bakterien der berüchtigten ESKAPE-Familie, Hefen und Nematoden. Einige der Verbindungen, wie beispielsweise Arylmethylselenocyanate, wurden auch auf zytotoxische Aktivität gegen normale und Krebs-Zelllinien untersucht. Im Allgemeinen zeigten alle synthetischen RSeS eine ausgezeichnete Aktivität gegenüber den ausgewählten Zielen. Die mechanistischen Vorstudien zeigten, dass solche Verbindungen mit dem zellulären Thiolstat des Zielorganismus interagieren. Diese Interaktionen eröffnen neue Möglichkeiten, potente, effiziente und zielgerichtete multifunktionale RSeS zu gestalten

Yeast Chemogenetic Screening as a Tool to Unravel the Antifungal Mode of Action of Two Selected Selenocyanates

During recent decades, selenium-containing compounds, as with the chemically similar sulfur-containing compounds, have gained considerable interest as cytotoxic and anticancer agents. Selenocyanates represent a well-established class of organic selenium compounds. These agents exhibit a wide range of biological activities. Classically, selenocyanates may cause an increase in the intracellular levels of reactive oxygen species (ROS) and exert cytotoxic activities, thus, acting as pro-oxidants. In this study, chemogenetic profiling was carried out to decipher the resistance mechanisms as central part of the antifungal mode of action against two selected selenocyanates. If a mutant line is less resistant against a compound compared to the wildtype, the gene deleted in that strain seems to be correlated with the resistance. Yeast mutants carrying gene deletions for specific redox-related protein function were employed in the chemogenetic screening. The results of screening reveal the hypersensitivity of mutants carrying deletions for glutathione pool and metabolism. To confirm the results, Arabidopsis mutants deficient in glutathione were subjected to various concentrations of selenocyanates to observe their effects on mutants and the wildtype. A significant dose dependent inhibition in Arabidopsis mutants compared to the wildtype confirmed the findings of the chemogenetic screening. The data suggest that the two representatives of organoselenium compounds cause oxidative stress in yeast cells and glutathione participates towards the development of resistance against the chemicals

Efficacy of Allicin against Plant Pathogenic Fungi and Unveiling the Underlying Mode of Action Employing Yeast Based Chemogenetic Profiling Approach

Allicin (diallylthiosulfinate) is the principal organosulfur compound present in freshly damaged garlic tissue which exhibits a wide range of biological actions including antibacterial, antifungal, antiviral and anticancer properties. The antifungal activities of allicin were investigated against plant pathogenic fungi of agriculture importance. Furthermore, a yeast genome haploinsufficiency screening was also employed to decipher the antifungal mode of action of allicin. Wildtype and 1152 yeast mutant strains (each deprived of one specific allele of an essential gene in a diploid strain) were screened against allicin. Allicin exhibited promising antifungal properties against all the tested plant pathogens. Haploinsufficiency screening revealed three hypersensitive yeast mutants with gene deletions coding for proteins involved in DNA replication, mitochondrial translation and chromatids cohesion. These processes play a vital role in the cell cycle, growth and viability of yeast cells. Taken together, the results of the present study unravel the excellent antifungal activities and mechanisms and modes of action of allicin. These findings also indicate the potential use of allicin as an alternative “green” fungicide (fumigant) in agriculture

The Reactive Sulfur Species Concept: 15 Years On

Fifteen years ago, in 2001, the concept of “Reactive Sulfur Species” or RSS was advocated as a working hypothesis. Since then various organic as well as inorganic RSS have attracted considerable interest and stimulated many new and often unexpected avenues in research and product development. During this time, it has become apparent that molecules with sulfur-containing functional groups are not just the passive “victims” of oxidative stress or simple conveyors of signals in cells, but can also be stressors in their own right, with pivotal roles in cellular function and homeostasis. Many “exotic” sulfur-based compounds, often of natural origin, have entered the fray in the context of nutrition, ageing, chemoprevention and therapy. In parallel, the field of inorganic RSS has come to the forefront of research, with short-lived yet metabolically important intermediates, such as various sulfur-nitrogen species and polysulfides (Sx2−), playing important roles. Between 2003 and 2005 several breath-taking discoveries emerged characterising unusual sulfur redox states in biology, and since then the truly unique role of sulfur-dependent redox systems has become apparent. Following these discoveries, over the last decade a “hunt” and, more recently, mining for such modifications has begun—and still continues—often in conjunction with new, innovative and complex labelling and analytical methods to capture the (entire) sulfur “redoxome”. A key distinction for RSS is that, unlike oxygen or nitrogen, sulfur not only forms a plethora of specific reactive species, but sulfur also targets itself, as sulfur containing molecules, i.e., peptides, proteins and enzymes, preferentially react with RSS. Not surprisingly, today this sulfur-centred redox signalling and control inside the living cell is a burning issue, which has moved on from the predominantly thiol/disulfide biochemistry of the past to a complex labyrinth of interacting signalling and control pathways which involve various sulfur oxidation states, sulfur species and reactions. RSS are omnipresent and, in some instances, are even considered as the true bearers of redox control, perhaps being more important than the Reactive Oxygen Species (ROS) or Reactive Nitrogen Species (RNS) which for decades have dominated the redox field. In other(s) words, in 2017, sulfur redox is “on the rise”, and the idea of RSS resonates throughout the Life Sciences. Still, the RSS story isn’t over yet. Many RSS are at the heart of “mistaken identities” which urgently require clarification and may even provide the foundations for further scientific revolutions in the years to come. In light of these developments, it is therefore the perfect time to revisit the original hypotheses, to select highlights in the field and to question and eventually update our concept of “Reactive Sulfur Species”

The Pioneering Role of Sci in Post Publication Public Peer Review (P4R)

Scientists observe, discover, justify and eventually share their findings with the scientific community. Dissemination is an integral aspect of scientific discovery, since discoveries which go unnoticed have no or little impact on science. Today, peer review is part of this process of scientific dissemination as it contributes proactively to the quality of a scientific article. As the numbers of scientific journals and scientific articles published therein are increasing steadily, processes such as the single-blind or double-blind peer review are facing a near collapse situation. In fact, these traditional forms of reviewing have reached their limits and, because of this, are also increasingly considered as unfair, sloppy, superficial and even biased. In this manuscript, we propose forms of post-publication public peer review (P4R) as valuable alternatives to the traditional blind peer review system. We describe how the journal Sci has explored such an approach and provide first empirical evidence of the benefits and also challenges, such a P4R approach faces

To Cut the Mustard : Antimicrobial Activity of Selenocyanates on the Plate and in the Gas Phase

Organic selenocyanates (RSeCN) are among the most reactive and biologically active Se species, often exhibiting a pronounced cytotoxic activity against mammalian cells and microorganisms. Various aromatic selenocyanates have been synthesized and, similar to some of the most Reactive Sulfur Species (RSS), such as allicin, found to be active against a range of bacteria, including Escherichia coli, Pseudomonas syringae and Micrococcus luteus, and fungi, including Verticillium dahlia, Verticillium longisporum, Alternaria brassicicola, and Botrytis cinerea, even via the gas phase. The highest antimicrobial activity has been observed for benzyl selenocyanate, which inhibited the growth of all bacteria considerably, even at the lowest tested concentration of 50 µM. Notably, neither the analogues thiocyanate (BTC) nor isothiocyanate (BITC) show any of these activities, rendering this selenium motif rather special in activity and mode of action. Eventually, these findings advocate a range of potential applications of organic selenocyanates in medicine and agriculture

Inspired by Nature: Redox Modulators and Natural Nanoparticles

Numerous secondary metabolites found in edible plants modulate intracellular redox processes and are suggested to prevent certain diseases, especially in ageing organisms. Since such nutraceuticals provide the basis for new and innovative designer diets and therapies, extracting these substances and their potential from plants has become a focus of research, with nanotechnology and natural nanoparticles at the centre of some of these developments

Small Molecule Catalysts with Therapeutic Potential

Catalysts are employed in many areas of research and development where they combine high efficiency with often astonishing selectivity for their respective substrates. In biology, biocatalysts are omnipresent. Enzymes facilitate highly controlled, sophisticated cellular processes, such as metabolic conversions, sensing and signalling, and are prominent targets in drug development. In contrast, the therapeutic use of catalysts per se is still rather limited. Recent research has shown that small molecule catalytic agents able to modulate the redox state of the target cell bear considerable promise, particularly in the context of inflammatory and infectious diseases, stroke, ageing and even cancer. Rather than being “active” on their own in a more traditional sense, such agents develop their activity by initiating, promoting, enhancing or redirecting reactions between biomolecules already present in the cell, and their activity therefore depends critically on the predisposition of the target cell itself. Redox catalysts, for instance, preferably target cells with a distinct sensitivity towards changes in an already disturbed redox balance and/or increased levels of reactive oxygen species. Indeed, certain transition metal, chalcogen and quinone agents may activate an antioxidant response in normal cells whilst at the same time triggering apoptosis in cancer cells with a different pre-existing “biochemical redox signature” and closer to the internal redox threshold. In pharmacy, catalysts therefore stand out as promising lead structures, as sensor/effector agents which are highly effective, fairly selective, active in catalytic, i.e., often nanomolar concentrations and also very flexible in their structural design

Selenomethionine: A Pink Trojan Redox Horse with Implications in Aging and Various Age-Related Diseases

Selenium is an essential trace element. Although this chalcogen forms a wide variety of compounds, there are surprisingly few small-molecule organic selenium compounds (OSeCs) in biology. Besides its more prominent relative selenocysteine (SeCys), the amino acid selenomethionine (SeMet) is one example. SeMet is synthesized in plants and some fungi and, via nutrition, finds its way into mammalian cells. In contrast to its sulfur analog methionine (Met), SeMet is extraordinarily redox active under physiological conditions and via its catalytic selenide (RSeR’)/selenoxide (RSe(O)R’) couple provides protection against reactive oxygen species (ROS) and other possibly harmful oxidants. In contrast to SeCys, which is incorporated via an eloquent ribosomal mechanism, SeMet can enter such biomolecules by simply replacing proteinogenic Met. Interestingly, eukaryotes, such as yeast and mammals, also metabolize SeMet to a small family of reactive selenium species (RSeS). Together, SeMet, proteins containing SeMet and metabolites of SeMet form a powerful triad of redox-active metabolites with a plethora of biological implications. In any case, SeMet and its family of natural RSeS provide plenty of opportunities for studies in the fields of nutrition, aging, health and redox biology

Unleashing the Biological Potential of Fomes fomentarius via Dry and Wet Milling

Fomes fomentarius, usually referred to as tinder conk, is a common wood-based fungus rich in many interesting phytochemicals and with an unique porous structure. Dry or wet ball milling of this sponge on a planetary mill results in small particles with sizes in the range of 10 µm or below. Suspended in water and without preservatives or other stabilizers, the resulting micro-suspensions are sterile for around six days, probably due to the increased temperatures of around 80 ◦C especially during the wet milling process. The suspensions also exhibit excellent antioxidant activities as determined in the DPPH, ferric reducing antioxidant potential (FRAP) and 2,20 -azino-bis(3-ethylbenzothiazoline-6-sulfonic acid (ABTS) assays. In the DPPH assay, IC50 values of 0.02–0.04% w/v and 0.04% w/v were observed for dry and wet milled samples, respectively. In the FRAP assay, IC50 values of <0.02% w/v and 0.04% w/v were observed for dry and wet milled samples, respectively. In contrast, the ABTS assay provided IC50 values of 0.04% w/v and 0.005% w/v, respectively. Notably, this activity is mostly—albeit not exclusively—associated with the highly porous particles and their large surfaces, although some active ingredients also diffuse into the surrounding aqueous medium. Such suspensions of natural particles carrying otherwise insoluble antioxidants on their surfaces provide an interesting avenue to unleash the antioxidant potential of materials such as sponges and barks. As dry milling also enables longer storage and transport, applications in the fields of medicine, nutrition, agriculture, materials and cosmetics are feasible