Allicin as a Volatile or Nebulisable Antimycotic for the Treatment of Pulmonary Mycoses: In Vitro Studies Using a Lung Flow Test Rig.

Fungal infections of the lung are an increasing problem worldwide and the search for novel therapeutic agents is a current challenge due to emerging resistance to current antimycotics. The volatile defence substance allicin is formed naturally by freshly injured garlic plants and exhibits broad antimicrobial potency. Chemically synthesised allicin was active against selected fungi upon direct contact and via the gas phase at comparable concentrations to the pharmaceutically used antimycotic amphotericin B. We investigated the suppression of fungal growth by allicin vapour and aerosols in vitro in a test rig at air flow conditions mimicking the human lung. The effect of allicin via the gas phase was enhanced by ethanol. Our results suggest that allicin is a potential candidate for development for use in antifungal therapy for lung and upper respiratory tract infections.

Allicin, the Odor of Freshly Crushed Garlic: A Review of Recent Progress in Understanding Allicin's Effects on Cells.

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.

Feasibility study of a surface-coated lung model to quantify active agent deposition for preclinical studies.

BACKGROUND: Multiple drug resistance of a growing number of bacterial pathogens represents an increasing challenge in conventional curative treatments of infectious diseases. However, the development and testing of new antibiotics is associated with a high number of animal experiments. METHODS: A symmetrical parametrized lung test rig allowing the exposure of air-passage surfaces to antibiotics was designed and tested to demonstrate proof-of-principle with aerosols containing allicin, which is an antimicrobial natural product from garlic. An artificial lung surface is coated with bacteria embedded in a hydrogel and growth inhibition is visualized by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, that is reduced from colourless to the dark blue formazan in the presence of metabolically active, living cells. A nebulizer is used to generate the aerosols. FINDINGS: The results show that allicin has an antibiotic effect as an aerosol and that the deposition pattern of the active agent occurred mainly around the carinal regions. INTERPRETATION: The model represents an integral system for continuous, spatial detection of aerosol deposition and allows the analysis of bacterial behaviour and the toxicity of the active agent. Thus, the deposition of antimicrobial aerosols on the bronchial surfaces is characterized in preliminary tests without any animal experiments.

Investigation of the deposition behaviour and antibacterial effectivity of allicin aerosols and vapour using a lung model.

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.

Allicin, a natural antimicrobial defence substance from garlic, inhibits DNA gyrase activity in bacteria.

Allicin (diallylthiosulfinate) is a potent antimicrobial substance, produced by garlic tissues upon wounding as a defence against pathogens and pests. Allicin is a reactive sulfur species (RSS) that oxidizes accessible cysteines in glutathione and proteins. We used a differential isotopic labelling method (OxICAT) to identify allicin targets in the bacterial proteome. We compared the proteomes of allicin-susceptible Pseudomonas fluorescens Pf0-1 and allicin-tolerant PfAR-1 after a sublethal allicin exposure. Before exposure to allicin, proteins were in a predominantly reduced state, with approximately 77% of proteins showing less than 20% cysteine oxidation. Protein oxidation increased after exposure to allicin, and only 50% of proteins from allicin-susceptible Pf0-1, but 65% from allicin-tolerant PfAR-1, remained less than 20% oxidised. DNA gyrase was identified as an allicin target. Cys433 in DNA gyrase subunit A (GyrA) was approximately 6% oxidized in untreated bacteria. After allicin treatment the degree of Cys433 oxidation increased to 55% in susceptible Pf0-1 but only to 10% in tolerant PfAR-1. Allicin inhibited E. coli DNA gyrase activity in vitro in the same concentration range as nalidixic acid. Purified PfAR-1 DNA gyrase was inhibited to greater extent by allicin in vitro than the Pf0-1 enzyme. Substituting PfAR-1 GyrA into Pf0-1 rendered the exchange mutants more susceptible to allicin than the Pf0-1 wild type. Taken together, these results suggest that GyrA was protected from oxidation in vivo in the allicin-tolerant PfAR-1 background, rather than the PfAR-1 GyrA subunit being intrinsically less susceptible to oxidation by allicin than the Pf0-1 GyrA subunit. DNA gyrase is a target for medicinally important antibiotics; thus, allicin and its analogues may have potential to be developed as gyrase inhibitors, either alone or in conjunction with other therapeutics.

Diallylthiosulfinate (Allicin), a Volatile Antimicrobial from Garlic (Allium sativum), Kills Human Lung Pathogenic Bacteria, Including MDR Strains, as a Vapor.

Garlic (Allium sativum) has potent antimicrobial activity due to allicin (diallylthiosulfinate) synthesized by enzyme catalysis in damaged garlic tissues. Allicin gives crushed garlic its characteristic odor and its volatility makes it potentially useful for combating lung infections. Allicin was synthesized (>98% pure) by oxidation of diallyl disulfide by H2O2 using formic acid as a catalyst and the growth inhibitory effect of allicin vapor and allicin in solution to clinical isolates of lung pathogenic bacteria from the genera Pseudomonas, Streptococcus, and Staphylococcus, including multi-drug resistant (MDR) strains, was demonstrated. Minimal inhibitory (MIC) and minimal bactericidal concentrations (MBC) were determined and compared to clinical antibiotics using standard European Committee on Antimicrobial Susceptibility Testing (EUCAST) procedures. The cytotoxicity of allicin to human lung and colon epithelial and murine fibroblast cells was tested in vitro and shown to be ameliorated by glutathione (GSH). Similarly, the sensitivity of rat precision-cut lung slices (PCLS) to allicin was decreased by raising the [GSH] to the approximate blood plasma level of 1 mM. Because allicin inhibited bacterial growth as a vapor, it could be used to combat bacterial lung infections via direct inhalation. Since there are no volatile antibiotics available to treat pulmonary infections, allicin, particularly at sublethal doses in combination with oral antibiotics, could make a valuable addition to currently available treatments.