Synergistic fungicidal activity of Cu(2+) and allicin, an allyl sulfur compound from garlic, and its relation to the role of alkyl hydroperoxide reductase 1 as a cell surface defense in Saccharomyces cerevisiae

Anticandidal Activity of In Situ Methionine γ-Lyase-Based Thiosulfinate Generation System vs. Synthetic Thiosulfinates

Candida albicans and non-albicans Candida species are a common cause of human mucosal infections, as well as bloodstream infections and deep mycoses. The emergence of resistance of Candida spp. to antifungal drugs used in practice requires the search for new antimycotics. The present study unravels the antifungal potential of the synthetic dialk(en)ylthiosulfinates in comparison with an enzymatic in situ methionine γ-lyase-based thiosulfinate generation system (TGS). The kinetics of the TGS reaction, namely, the methionine γ-lyase-catalyzed β-elimination of S-alk(en)yl-L-cysteine sulfoxides, was investigated via 1H NMR spectroscopy for the first time, revealing fast conversion rates and the efficient production of anticandidal dialk(en)ylthiosulfinates. The anticandidal potential of this system vs. synthetic thiosulfinates was investigated through an in vitro assay. TGS proved to be more effective (MIC range 0.36-1.1 μg/mL) than individual substances (MIC range 0.69-3.31 μg/mL). The tested preparations had an additive effect with the commercial antimycotics fluconazole, amphotericin B and 5-flucytosine demonstrating a fractional inhibitory coefficient index in the range of 0.5-2 μg/mL. TGS can be regarded as an attractive candidate for the targeted delivery of antimycotic thiosulfinates and for further implementation onto medically implanted devices.

Dithiosulfinates and Sulfoxides with Antifungal Activity from Bulbs of Allium sativum L. var. Voghiera

A bioassay guided phytochemical analysis of the bulbs of Allium sativum L. var. Voghiera, typical of Voghiera, Ferrara (Italy), allowed the isolation of six new sulfur compounds with dithiosulfinates and sulfoxides functionalities. Structure elucidation of the isolated compounds was carried out by spectroscopic analyses, including NMR spectroscopy and MS spectrometry. Compounds showed significant antimicrobial activity towards two fungal species, the air-borne pathogen Botrytis cinerea and the beneficial fungus Trichoderma harzianum.

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.

Allicin: chemistry and biological properties

Allicin (diallylthiosulfinate) is a defence molecule from garlic (Allium sativum L.) with a broad range of biological activities. Allicin is produced upon tissue damage from the non-proteinogenic amino acid alliin (S-allylcysteine sulfoxide) in a reaction that is catalyzed by the enzyme alliinase. Current understanding of the allicin biosynthetic pathway will be presented in this review. Being a thiosulfinate, allicin is a reactive sulfur species (RSS) and undergoes a redox-reaction with thiol groups in glutathione and proteins that is thought to be essential for its biological activity. Allicin is physiologically active in microbial, plant and mammalian cells. In a dose-dependent manner allicin can inhibit the proliferation of both bacteria and fungi or kill cells outright, including antibiotic-resistant strains like methicillin-resistant Staphylococcus aureus (MRSA). Furthermore, in mammalian cell lines, including cancer cells, allicin induces cell-death and inhibits cell proliferation. In plants allicin inhibits seed germination and attenuates root-development. The majority of allicin's effects are believed to be mediated via redox-dependent mechanisms. In sub-lethal concentrations, allicin has a variety of health-promoting properties, for example cholesterol- and blood pressure-lowering effects that are advantageous for the cardio-vascular system. Clearly, allicin has wide-ranging and interesting applications in medicine and (green) agriculture, hence the detailed discussion of its enormous potential in this review. Taken together, allicin is a fascinating biologically active compound whose properties are a direct consequence of the molecule's chemistry.

Visualization analysis of the vacuole-targeting fungicidal activity of amphotericin B against the parent strain and an ergosterol-less mutant of Saccharomyces cerevisiae

Here, we sought to investigate the vacuole-targeting fungicidal activity of amphotericin B (AmB) in the parent strain and AmB-resistant mutant of Saccharomyces cerevisiae and elucidate the mechanisms involved in this process. Our data demonstrated that the vacuole-targeting fungicidal activity of AmB was markedly enhanced by N-methyl-N″-dodecylguanidine (MC12), a synthetic analogue of the alkyl side chain in niphimycin, as represented by the synergy in their antifungal activities against parent cells of S. cerevisiae. Indifference was observed only with Δerg3 cells, indicating that the replacement of ergosterol with episterol facilitated their resistance to the combined lethal actions of AmB and MC12. Dansyl-labelled amphotericin B (AmB-Ds) was concentrated into normal rounded vacuoles when parent cells were treated with AmB-Ds alone, even at a non-lethal concentration. The additional supplementation of MC12 resulted in a marked loss of cell viability and vacuole disruption, as judged by the fluorescence from AmB-Ds scattered throughout the cytoplasm. In Δerg3 cells, AmB-Ds was scarcely detected in the cytoplasm, even with the addition of MC12, reflecting its failure to normally incorporate across the plasma membrane into the vacuole. Thus, this study supported the hypothesis that ergosterol is involved in the mobilization of AmB into the vacuolar membrane so that AmB-dependent vacuole disruption can be fully enhanced by cotreatment with MC12.

A comprehensive review on pharmacotherapeutics of herbal bioenhancers

In India, Ayurveda has made a major contribution to the drug discovery process with new means of identifying active compounds. Recent advancement in bioavailability enhancement of drugs by compounds of herbal origin has produced a revolutionary shift in the way of therapeutics. Thus, bibliographic investigation was carried out by analyzing classical text books and peer-reviewed papers, consulting worldwide-accepted scientific databases from last 30 years. Herbal bioenhancers have been shown to enhance bioavailability and bioefficacy of different classes of drugs, such as antibiotics, antituberculosis, antiviral, antifungal, and anticancerous drugs at low doses. They have also improved oral absorption of nutraceuticals like vitamins, minerals, amino acids, and certain herbal compounds. Their mechanism of action is mainly through absorption process, drug metabolism, and action on drug target. This paper clearly indicates that scientific researchers and pharmaceutical industries have to give emphasis on experimental studies to find out novel active principles from such a vast array of unexploited plants having a role as a bioavailability and bioefficacy enhancer. Also, the mechanisms of action by which bioenhancer compounds exert bioenhancing effects remain to be explored.

Quantitative and qualitative analysis of the antifungal activity of allicin alone and in combination with antifungal drugs

The antifungal activity of allicin and its synergistic effects with the antifungal agents flucytosine and amphotericin B (AmB) were investigated in Candida albicans (C. albicans). C. albicans was treated with different conditions of compounds alone and in combination (allicin, AmB, flucytosine, allicin + AmB, allicin + flucytosine, allicin + AmB + flucytosine). After a 24-hour treatment, cells were examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM) to measure morphological and biophysical properties associated with cell death. The clearing assay was conducted to confirm the effects of allicin. The viability of C. albicans treated by allicin alone or with one antifungal drug (AmB, flucytosine) in addition was more than 40% after a 24-hr treatment, but the viability of groups treated with combinations of more than two drugs was less than 32%. When the cells were treated with allicin alone or one type of drug, the morphology of the cells did not change noticeably, but when cells were treated with combinations of drugs, there were noticeable morphological changes. In particular, cells treated with allicin + AmB had significant membrane damage (burst or collapsed membranes). Classification of cells according to their cell death phase (CDP) allowed us to determine the relationship between cell viability and treatment conditions in detail. The adhesive force was decreased by the treatment in all groups compare to the control. Cells treated with AmB + allicin had a greater adhesive force than cells treated with AmB alone because of the secretion of molecules due to collapsed membranes. All cells treated with allicin or drugs were softer than the control cells. These results suggest that allicin can reduce MIC of AmB while keeping the same efficacy.

Enhancing effects on vacuole-targeting fungicidal activity of amphotericin B

Invasive fungal infections are major threats for immunocompromised patients as well as for those undergoing cancer chemotherapy. Amphotericin B (AmB), a classical antifungal drug with a polyene macrolide structure, is widely used for the control of serious fungal infections. However, the clinical use of this antifungal drug is limited by its side effects and the emergence of drug-resistant strains. AmB lethality has been generally attributed to alterations in plasma membrane ion permeability due to its specific binding to plasma membrane ergosterol. Recent studies with Saccharomyces cerevisiae and Candida albicans reveal the vacuole disruptive action as another cause of AmB lethality on the basis of marked amplification of its activity in combination with allicin, an allyl-sulfur compound from garlic. The enhancing effect of allicin is dependent on the inhibition of ergosterol-trafficking from the plasma membrane to the vacuole membrane, which is considered to be a cellular response to protect against disintegration of the vacuole membrane. The polyol macrolide niphimycin (NM) also possesses vacuole-targeting fungicidal activity, which is greater than that of AmB and nystatin. The alkyl side chain attached to the macrolide ring of NM is considered to possess an allicin-like inhibitory effect on the intracellular trafficking of ergosterol. The vacuole-targeting fungicidal activity was additionally detected with a bactericidal cyclic peptide polymyxin B (PMB), and was markedly enhanced when administered together with allicin, monensin, or salinomycin. The synergistic fungicidal activities of AmB and allicin may have significant implications for the development of vacuole-targeting chemotherapy against fungal infections.

Efficacy of allicin from garlic against Ascaridia galli infection in chickens

The use of garlic as a treatment against helminth infections is increasing in organic layer farms in several European countries. Its efficacy against these parasites, however, has not been demonstrated thus far. Therefore, a study was conducted to determine the efficacy of a commercially available garlic product consisting of a high concentration of allicin (i.e., the main active component of garlic) against experimentally induced Ascaridia galli infection in chickens. In total, 450 Lohmann LSL-Classic cockerels were used. Group 1, the uninfected, untreated group, consisted of 50 chickens. Groups 2 to 5, each consisting of approximately 100 chickens, were inoculated with 300 embryonated A. galli eggs/chicken at 6 wk of age. Group 2 was not treated, whereas groups 3 through 5 were given daily individual oral treatments from 13 wk of age onward. Group 3 received the recommended dose of allicin for 2 wk, whereas group 4 received a 10-fold dose of allicin. Group 5 was given 10 mg of flubendazole/kg of BW for 1 wk. Necropsy of 20 birds of all groups was performed weekly between 13 and 16 wk of age to determine adult worm loads. Group 1 remained free of A. galli. The experimental infection in the other groups resulted in a mean adult worm load of approximately 16 worms/bird. No significant differences were observed in worm counts of the allicin-treated groups (groups 3 and 4) compared with the infected, untreated group (group 2) at any week (P > 0.05). In contrast, no worms were found in chickens after flubendazole treatment (group 5). It was concluded that allicin does not represent an alternative to flubendazole for the treatment of A. galli infections in chickens.

Amplification of vacuole-targeting fungicidal activity of antibacterial antibiotic polymyxin B by allicin, an allyl sulfur compound from garlic

A cationic antibacterial peptide, polymyxin B (PMB), was evaluated as an antifungal antibiotic against various yeasts and filamentous fungi when used in combination with allicin, an allyl sulfur compound from garlic. Allicin was not lethal but could markedly amplify the fungicidal activity of PMB, which was weakly detected with the increase in the plasma membrane permeability in Saccharomyces cerevisiae. Their combined actions caused a dynamic structural damage to the yeast vacuole as judged by the disappearance of its swollen spherical architecture. The vacuole-targeting activity of PMB was similarly amplified in medium with t-butyl hydroperoxide as a substitute for the action of allicin. These findings suggest that the allicin-mediated lipoperoxide production in fungal plasma membrane is the cause of the enhancement in the cellular uptake of PMB as well as its action against the vacuole.

Synergistic Fungicidal Activities of Amphotericin B and N-Methyl-N″-dodecylguanidine: A Constituent of Polyol Macrolide Antibiotic Niphimycin

The synergy between the alkylguanidinium chain of niphimycin (NM), a polyol macrolide antibiotic, and polyene macrolide amphotericin B (AmB) without such an alkyl side chain was examined using N-methyl-N"-alkylguanidines as its synthetic analogs. Among the analogs, N-methyl-N"-dodecylguanidine (MC12) most strongly inhibited the growth of Saccharomyces cerevisiae cells and those of other fungal strains in synergy with AmB. MC12 itself was not lethal but the analog could be a cause of a rapid cell death progression of yeast cells in the presence of AmB at a nonlethal concentration. Their combined actions resulted in the generation of NM-like fungicidal activity that depended on plasma membrane disability and cellular reactive oxygen species production. We also found an aberrant vacuolar morphogenesis and an associated vacuolar membrane disability in cells treated simultaneously with MC12 and AmB, as in the case of NM-treated cells. These findings support the idea that the alkylguanidinium chain plays a major role in the fungicidal activity of NM in cooperation with the polyol lactone ring as its enhancer.

Characterization of cell wall associated proteins of a Staphylococcus aureus isolated from bovine mastitis case by a proteomic approach

Staphylococcus aureus causes different pathologies in humans and animals. In particular, it is involved in intramammary infections in cows, causing economic losses and milk-safety problems. Although it is well-known that surface components (proteins and capsular polysaccharides) and exotoxins are virulence factors involved in the pathogenesis of bovine mastitis, less is known about the precise biochemical identity of such molecules. Therefore, mapping of surface proteins using specific disease- and environment-isolates provides a benchmark for strain comparison of pathogens with different pathogenic characteristics and antibiotic resistance mechanism and can aid in defining specific vaccine and therapeutic targets. In this study, we used a proteomic approach on protein extracts of lysostaphin-treated S. aureus in isotonic conditions, to produce a reproducible and well resolved 2-D electrophoresis (2-DE) reference map of surface associated proteins of isolated S. aureus from a case of bovine mastitis. The most abundant protein components were identified by Matrix assisted laser desorption ionisation-time of flight (MALDI-TOF) mass spectrometry.