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Garlic (Allium sativum L.) has been used as a spice and medicinal plant since ancient times. Garlic produces the thiol-reactive defence substance, allicin, upon wounding. The effects of allicin on human lung epithelium carcinoma (A549), mouse fibroblast (3T3), human umbilical vein endothelial cell (HUVEC), human colon carcinoma (HT29) and human breast cancer (MCF7) cell lines were tested. To estimate toxic effects of allicin, we used a standard MTT-test (methylthiazoltetrazolium) for cell viability and 3H-thymidine incorporation for cell proliferation. The glutathione pool was measured using monobromobimane and the formation of reactive species was identified using 2',7'-dichlorofluoresceine-diacetate. The YO-PRO-1 iodide staining procedure was used to estimate apoptosis. Allicin reduced cell viability and cell proliferation in a concentration dependent manner. In the bimane test, it was observed that cells treated with allicin showed reduced fluorescence, suggesting glutathione oxidation. The cell lines tested differed in sensitivity to allicin in regard to viability, cell proliferation and glutathione oxidation. The 3T3 and MCF-7 cells showed a higher proportion of apoptosis compared to the other cell types. These data show that mammalian cell lines differ in their sensitivity and responses to allicin. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The volatile organic sulfur compound allicin (diallyl thiosulfinate) is produced as a defense substance when garlic (Allium sativum) tissues are damaged, for example by the activities of pathogens or pests. Allicin gives crushed garlic its characteristic odor, is membrane permeable and readily taken up by exposed cells. It is a reactive thiol-trapping sulfur compound that S-thioallylates accessible cysteine residues in proteins and low molecular weight thiols including the cellular redox buffer glutathione (GSH) in eukaryotes and Gram-negative bacteria, as well as bacillithiol (BSH) in Gram-positive firmicutes. Allicin shows dose-dependent antimicrobial activity. At higher doses in eukaryotes allicin can induce apoptosis or necrosis, whereas lower, biocompatible amounts can modulate the activity of redox-sensitive proteins and affect cellular signaling. This review summarizes our current knowledge of how bacterial and eukaryotic cells are specifically affected by, and respond to, allicin. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editor discusses various topics in the issue including physiological activity of fluorinated analogues of garlic organosulfur compounds; activation of the unfolded protein response associated with cytotoxicity; and constituents of aged black garlic.

Allicin (diallylthiosulfinate) is a potent thiol reagent and natural defense substance produced by garlic (Allium sativum) tissues when damaged. Allicin acts as a redox toxin and oxidizes the cellular glutathione (GSH) pool producing S-allylmercaptoglutathione (GSSA). The cellular enzyme glutathione reductase (GR) uses NADPH to reduce glutathione disulfide (GSSG) back to GSH and replenishes the GSH pool. It was not known whether GR could accept GSSA as a substrate. Here, we report that GR from yeast (Saccharomyces cerevisiae) shows Michaelis–Menten kinetics with GSSA as substrate in vitro (Km = 0.50 mM), but that GSSA is not as good a substrate as GSSG (Km = 0.07 mM). Furthermore, cells unable to synthesize GSH because the γ-glutamylcysteine synthetase (GSH1) gene is deleted, cannot grow without GSH supplementation and we show that the auxotrophic requirement for GSH in Δgsh1 mutants can be met by GSSA in the growth medium, suggesting that GSSA can be reduced to GSH in vivo. [ABSTRACT FROM AUTHOR]

Allicin is a natural antibiotic produced by garlic as a defence against pathogens and pests. Due to the worldwide increase in antibiotic resistance, new antibiotics are desperately required. Allicin is such a candidate and is active against several multidrug-resistant (MDR) strains of human pathogens, including methicillin-resistant Staphylococcus aureus (MRSA). When administered orally, allicin is titrated out by glutathione in the cells and blood, and effective therapeutic concentrations are difficult to achieve at the site of an infection. However, in the case of lung infections, allicin can be delivered directly to pathogens via the pulmonary route. In this study, we designed and constructed an in vitro lung test rig, which allowed us to model accurately the exposure of lung air-passage surfaces to allicin and gentamicin, in order to examine the feasibility of combating lung infections by direct inhalation. A prototype test rig of lung bronchi with three bifurcations was constructed, which could be coated internally with a thin layer of bacteria-seeded agar medium. The deposition of antimicrobial aerosols on the modelled bronchial surfaces was followed in preliminary tests without the need for animal experiments. The differential sensitivity of the test bacteria to different antibiotics and the dose-dependency of inhibition was shown using the model. Furthermore, a synergistic effect of allicin vapour and ethanol in inhibiting bacterial growth was demonstrated. The modelling of the axial velocity air-flow distribution correlated with the regions indicating the inhibition of bacterial growth, demonstrating that the model has predictive value and can reduce the requirement for animal sacrifice in pre-clinical trials of novel antibiotics., (Copyright: © Reiter et al.)

A single clove of edible garlic (Allium sativum L.) of about 10 g produces up to 5 mg of allicin (diallylthiosulfinate), a thiol-reactive sulfur-containing defence substance that gives injured garlic tissue its characteristic smell. Allicin induces apoptosis or necrosis in a dose-dependent manner but biocompatible doses influence cellular metabolism and signalling cascades. Oxidation of protein thiols and depletion of the glutathione pool are thought to be responsible for allicin's physiological effects. Here, we studied the effect of allicin on post-translational thiol-modification in human Jurkat T-cells using shotgun LC-MS/MS analyses. We identified 332 proteins that were modified by S-thioallylation in the Jurkat cell proteome which causes a mass shift of 72 Da on cysteines. Many S-thioallylated proteins are highly abundant proteins, including cytoskeletal proteins tubulin, actin, cofilin, filamin and plastin-2, the heat shock chaperones HSP90 and HSPA4, the glycolytic enzymes GAPDH, ALDOA, PKM as well the protein translation factor EEF2. Allicin disrupted the actin cytoskeleton in murine L929 fibroblasts. Allicin stimulated the immune response by causing Zn 2+ release from proteins and increasing the Zn 2+ -dependent IL-1-triggered production of IL-2 in murine EL-4 T-cells. Furthermore, allicin caused inhibition of enolase activity, an enzyme considered a cancer therapy target. In conclusion, our study revealed the widespread extent of S-thioallylation in the human Jurkat cell proteome and showed effects of allicin exposure on essential cellular functions of selected targets, many of which are targets for cancer therapy., (Copyright © 2018 The Authors. Published by Elsevier Inc. All rights reserved.)

Allicin is a thiol-reactive sulfur-containing natural product from garlic with a broad range of antimicrobial effects against prokaryotes and eukaryotes. Previous work showed that the S. cerevisiae OSI1 gene is highly induced by allicin and other thiol-reactive compounds, and in silico analysis revealed multiple Yap1p binding motifs in the OSI1 promoter sequence. An OSI1-promoter::luciferase reporter construct expressed in Wt and Δyap1 cells showed absolute Yap1p-dependence for allicin-induced OSI1-expression., A Gfp: Yap1p fusion protein accumulated in the nucleus within 10min of allicin treatment and a Δyap1 mutant was highly sensitive to allicin. Yap1p regulates glutathione (GSH) metabolism genes, and Δgsh1, Δgsh2 and Δglr1 mutants showed increased sensitivity to allicin. Allicin activated the OSI1-promoter::luciferase reporter construct in Δgpx3 and Δybp1 cells, indicating that allicin activates Yap1p directly rather than via H 2 O 2 production. A systematic series of C-to-A Yap1p exchange mutants showed that the C-term C598 and C620 residues were necessary for allicin activation. These data suggest that Yap1p is an important transcriptional regulator for the resistance of yeast cells to allicin, and that activation occurs by direct modification of C-term cysteines as shown for other electrophiles., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Garlic ( Allium sativum L.) has been used as a spice and medicinal plant since ancient times. Garlic produces the thiol-reactive defence substance, allicin, upon wounding. The effects of allicin on human lung epithelium carcinoma (A549), mouse fibroblast (3T3), human umbilical vein endothelial cell (HUVEC), human colon carcinoma (HT29) and human breast cancer (MCF7) cell lines were tested. To estimate toxic effects of allicin, we used a standard MTT-test (methylthiazoltetrazolium) for cell viability and ³H-thymidine incorporation for cell proliferation. The glutathione pool was measured using monobromobimane and the formation of reactive species was identified using 2',7'-dichlorofluoresceine-diacetate. The YO-PRO-1 iodide staining procedure was used to estimate apoptosis. Allicin reduced cell viability and cell proliferation in a concentration dependent manner. In the bimane test, it was observed that cells treated with allicin showed reduced fluorescence, suggesting glutathione oxidation. The cell lines tested differed in sensitivity to allicin in regard to viability, cell proliferation and glutathione oxidation. The 3T3 and MCF-7 cells showed a higher proportion of apoptosis compared to the other cell types. These data show that mammalian cell lines differ in their sensitivity and responses to allicin.

Background: Allicin (diallylthiosulfinate) is the major volatile- and antimicrobial substance produced by garlic cells upon wounding. We tested the hypothesis that allicin affects membrane function and investigated 1) betanine pigment leakage from beetroot (Beta vulgaris) tissue, 2) the semipermeability of the vacuolar membrane of Rhoeo discolor cells, 3) the electrophysiology of plasmalemma and tonoplast of Chara corallina and 4) electrical conductivity of artificial lipid bilayers., Methods: Garlic juice and chemically synthesized allicin were used and betanine loss into the medium was monitored spectrophotometrically. Rhoeo cells were studied microscopically and Chara- and artificial membranes were patch clamped., Results: Beet cell membranes were approximately 200-fold more sensitive to allicin on a mol-for-mol basis than to dimethyl sulfoxide (DMSO) and approximately 400-fold more sensitive to allicin than to ethanol. Allicin-treated Rhoeo discolor cells lost the ability to plasmolyse in an osmoticum, confirming that their membranes had lost semipermeability after allicin treatment. Furthermore, allicin and garlic juice diluted in artificial pond water caused an immediate strong depolarization, and a decrease in membrane resistance at the plasmalemma of Chara, and caused pore formation in the tonoplast and artificial lipid bilayers., Conclusions: Allicin increases the permeability of membranes., General Significance: Since garlic is a common foodstuff the physiological effects of its constituents are important. Allicin's ability to permeabilize cell membranes may contribute to its antimicrobial activity independently of its activity as a thiol reagent., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Sulfur is an essential and quantitatively important element for living organisms. Plants contain on average approximately 1 g S kg⁻¹ dry weight (for comparison plants contain approximately 15 g N kg⁻¹ dry weight). Sulfur is a constituent of many organic molecules, for example amino acids such as cysteine and methionine and the small tripeptide glutathione, but sulfur is also essential in the form of Fe-S clusters for the activity of many enzymes, particularly those involved in redox reactions. Sulfur chemistry is therefore important. In particular, sulfur in the form of thiol groups is central to manifold aspects of metabolism. Because thiol groups are oxidized and reduced easily and reversibly, the redox control of cellular metabolism has become an increasing focus of research. In the same way that oxygen and nitrogen have reactive species (ROS and RNS), sulfur too can form reactive molecular species (RSS), for example when a -SH group is oxidized. Indeed, several redox reactions occur via RSS intermediates. Several naturally occurring S-containing molecules are themselves RSS and because they are physiologically active they make up part of the intrinsic plant defence repertoire against herbivore and pathogen attack. Furthermore, RSS can also be used as redox-active pharmacological tools to study cell metabolism. The aim of this review is to familiarize the general reader with some of the chemical concepts, terminology and biology of selected RSS., (Copyright © 2012 Elsevier Masson SAS. All rights reserved.)

The volatile substance allicin gives crushed garlic (Allium sativum) its characteristic odor and is a pro-oxidant that undergoes thiol-disulfide exchange reactions with -SH groups in proteins and glutathione. The antimicrobial activity of allicin is suspected to be due to the oxidative inactivation of essential thiol-containing enzymes. We investigated the hypothesis that at threshold inhibitory levels allicin can shunt yeast cells into apoptosis by altering their overall redox status. Yeast cells were treated either with chemically synthesized, pure allicin or with allicin in garlic juice. Allicin-dependent cell oxidation was demonstrated with a redox-sensitive GFP construct and the shift in cellular electrochemical potential (E(hc)) from less than -215 to -181mV was calculated using the Nernst equation after the glutathione/glutathione disulfide couple (2GSH/GSSG) in the cell was quantified. Caspase activation occurred after allicin treatment, and yeast expressing a human antiapoptotic Bcl-XL construct was rendered more resistant to allicin. Also, a yeast apoptosis-inducing factor deletion mutant was more resistant to allicin than wild-type cells. We conclude that allicin in garlic juice can activate apoptosis in yeast cells through its oxidizing properties and that this presents an alternative cell-killing mechanism to the previously proposed specific oxidative inactivation of essential enzymes., (Copyright © 2010 Elsevier Inc. All rights reserved.)