Allicin and derivates are cysteine protease inhibitors with antiparasitic activity

Allicin: a promising modulator of apoptosis and survival signaling in cancer

According to the World Health Organization, cancer is the foremost cause of mortality globally. Various phytochemicals from natural sources have been extensively studied for their anticancer properties. Allicin, a powerful organosulfur compound derived from garlic, exhibits anticancer, antioxidant, anti-inflammatory, antifungal, and antibacterial properties. This review aims to update and evaluate the chemistry, composition, mechanisms of action, and pharmacokinetics Allicin. Allicin has garnered significant attention for its potential role in modulating Fas-FasL, Bcl2-Bax, PI3K-Akt-mTOR, autophagy, and miRNA pathways. At the molecular level, allicin induces the release of cytochrome c from the mitochondria and enhances the activation of caspases-3, -8, and -9. This is accompanied by the simultaneous upregulation of Bax and Fas expression in tumor cells. Allicin can inhibit excessive autophagy by activating the PI3K/Akt/mTOR and MAPK/ERK/mTOR signaling pathways. Allicin-loaded nano-formulations efficiently induce apoptosis in cancer cells while minimizing toxicity to normal cells. Safety and clinical aspects are meticulously scrutinized, providing insights into the tolerability and adverse effects associated with allicin administration, along with an overview of current clinical trials evaluating its therapeutic potential. In conclusion, this review underscores the promising prospects of allicin as a dietary-derived medicinal compound for cancer therapy. It emphasizes the need for further research to elucidate its precise mechanisms of action, optimize delivery strategies, and validate its efficacy in clinical settings.

Anti-Malarial Activity of Allyl Isothiocyanate and N-acetyl-S-(N-allylthiocarbamoyl)-l-Cysteine

SCOPE

Malaria remains one of the most important infectious diseases in the world. Allyl isothiocyanate (AITC) is a main ingredient of traditional spice Wasabia japonica, which is reported to have anti-bacterial and antiparasitic activities. However, there is no information on effects of AITC against malaria. The present study investigates the anti-malarial activity of dietary AITC in vivo and that of AITC metabolites in vitro.

METHODS AND RESULTS

The ad libitum administration of 35, 175, or 350 µM AITC-containing drinking water to ICR mice significantly inhibit the parasitemia induced after infection with Plasmodium berghei. On the other hand, after single oral administration of AITC (20 mg kg-1 body weight), N-acetyl-S-(N-allylthiocarbamoyl)-l-cysteine (NAC-AITC) as one of the AITC metabolites displays a serum Cmax of 11.4 µM at a Tmax of 0.5 h, but AITC is not detected at any time point. Moreover, NAC-AITC shows anti-malarial activity against Plasmodium falciparum in vitro, and its 50% inhibitory concentration (IC50 ) against parasitemia is 12.6 µM.

CONCLUSIONS

These results indicate that orally administered AITC is metabolized to NAC-AITC and exerts anti-malarial activity against malaria parasites in blood, suggesting that the consumption of AITC-containing food stuffs such as cruciferous plants may prevent malaria.

Regional variation in the antibacterial activity of a wild plant, wild garlic (Allium ursinum L.)

Antibacterial activity is a common and highly studied property of plant secondary metabolites. Despite the extensive literature focusing on identifying novel antibacterial metabolites, little work has been undertaken to examine variation in levels of antibacterial activity in any plant species. Here, we used large-scale sampling of leaves of the antibacterial plant, wild garlic (Allium ursinum L.), assembling a set of tissue extracts from 168 plants, with 504 leaves collected and analysed. We assayed extracts for antibacterial activity against Bacillus subtilis and used LC-MS to carry out a chemometric analysis examining variation in individual metabolites, comparing them with several ecological parameters. We found that allicin was the only metabolite which was positively related to antibacterial activity. Soil temperature was a key determinant of variability in the concentrations of many foliar metabolites, however, neither allicin concentrations nor antibacterial activity was related to any of our measured ecological parameters, other than roadside proximity. We suggest that the synthesis of allicin precursors may be largely independent of growing conditions. This may be to ensure that allicin is synthesised rapidly and in sufficiently high concentrations to effectively prevent herbivory and pest damage. This finding contrasts with flavonoids which were found to vary greatly between plants and across sites. Our findings suggest that key biologically active metabolites are constrained in their concentration range compared to other compounds in the metabolome. This has important implications for the development of wild garlic as a health supplement or animal feed additive.

Allicin-inspired disulfide derivatives containing quinazolin-4(3H)-one as a bacteriostat against Xanthomonas oryzae pv. oryzae

BACKGROUND

Plant bacterial diseases have seriously affected the yield and quality of crops, among which rice bacterial leaf blight (BLB), caused by Xanthomonas oryzae pv. oryzae has seriously affected the yield of rice. As plant-pathogenic bacteria gradually become resistant to existing bactericides, it is necessary to find effective bactericides with novel structures.

RESULTS

Herein, a series of compounds containing quinazolin-4(3H)-one and disulfide moieties were designed and synthesized using a facile synthetic method. The bioassay results revealed that most target compounds possessed noticeable antibacterial activity against Xanthomonas oryzae pv. oryzae. Particularly, compound 2-(butyldisulfanyl) quinazolin-4(3H)-one (1) exhibited remarkable antibacterial activity with the half effective concentration (EC₅₀ ) of 0.52 μg mL^-1 . Additionally, compound 1 was confirmed to inhibit the growth of the bacteria, change the bacterial morphology, and increase the level of reactive oxygen species. Proteomics, and RT-qPCR analysis results indicated that compound 1 could downregulate the expression of Pil-Chp histidine kinase chpA encoded by the pilL gene, and the potting experiments proved that compound 1 exhibits significant protective activity against BLB.

CONCLUSIONS

Compound 1 may weaken the pathogenicity of Xanthomonas oryzae pv. oryzae by inhibiting the bacterial growth and blocking the pili-mediated twitching motility without inducing the bacterial apoptosis. This study indicates that such derivatives could be a promising scaffold to develop a bacteriostat to control BLB. © 2022 Society of Chemical Industry.

In Vitro Antiparasitic Activity of Propyl-Propane-Thiosulfinate (PTS) and Propyl-Propane-Thiosulfonate (PTSO) from Allium cepa against Eimeria acervulina Sporozoites

Among the alternatives to control avian coccidiosis, alliaceous extracts stand out due to their functional properties. Despite this, most of the references are focused just on garlic. In this study, we analyze the in vitro effects of propyl-propane thiosulfinate (PTS) and propyl-propane thiosulfonate (PTSO), two organosulfur compounds from onion, on MDBK cells infected with sporozoites of Eimeria acervulina. To this aim, two different experiments were performed. In the first experiment, sporozoites were previously incubated for 1 h at 1, 5 and 10 µg/mL of PTS or PTSO and added to MDBK cells. In the second experiment, MDBK cells were first incubated for 24 h at different concentrations of PTS or PTSO and then infected with E. acervulina sporozoites. Then, 24 h after inoculation, the presence of E. acervulina was quantified by qPCR. MDBK viability was measured at 72 h post-infection. Sporozoites incubated at 10 µg/mL of PTS and PTSO inhibited the capability to penetrate the cells up to 75.2% ± 6.44 and 71.7% ± 6.03, respectively. The incubation of MDBK with each compound resulted in a preventive effect against sporozoite invasion at 1 µg/mL of PTS and 1 and 10 µg/mL of PTSO. Cells incubated with PTSO obtained similar viability percentages to uninfected cells. These results suggest that the use of PTS and PTSO is a promising alternative to coccidiosis treatment, although further in vivo studies need to be performed.

Allicin-Inspired Heterocyclic Disulfides as Novel Antimicrobial Agents

In this work, a series of derivatives with disulfide bonds containing pyridine, pyrimidine, thiophene, thiazole, benzothiazole, and quinoline were designed and synthesized based on the various biological activities of allicin disulfide bond functional groups. The antimicrobial activities of the target compounds were determined, and the structure-activity relationships were discussed. Among them, compound S8 demonstrated the most potent antifungal activity in vitro against Monilinia fructicola (M. fructicola), with an EC₅₀ value of 5.92 μg/mL. Furthermore, an in vivo bioassay revealed that compound S8 exhibited equivalent curative and higher protective effects as the positive drug thiophanate methyl at a concentration of 200 μg/mL. The preliminary mechanism experiments showed that compound S8 could inhibit the growth of M. fructicola' s hyphae in a time- and concentration-dependent manner, and compound S8 could induce the shrinkage of hyphae, disrupt the integrity of the plasma membrane, and cause the damage and leakage of cell contents. More than that, compound S5 also demonstrated an excellent antibacterial effect on Xanthomonas oryzae (X. oryzae), with a MIC₉₀ value of 1.56 μg/mL, which was superior to the positive control, thiodiazole copper.

Two-component carnitine monooxygenase from Escherichia coli: Functional characterization, Inhibition and mutagenesis of the molecular interface

Gut microbial production of trimethylamine (TMA) from l-carnitine is directly linked to cardiovascular disease. TMA formation is facilitated by carnitine monooxygenase, which was proposed as a target for the development of new cardioprotective compounds. Therefore, the molecular understanding of the two-component Rieske-type enzyme from Escherichia coli was intended. The redox cofactors of the reductase YeaX (FMN, plant-type [2Fe-2S] cluster) and of the oxygenase YeaW (Rieske-type [2Fe-2S] and mononuclear [Fe] center) were identified. Compounds meldonium and the garlic-derived molecule allicin were recently shown to suppress microbiota-dependent TMA formation. Based on two independent carnitine monooxygenase activity assays, enzyme inhibition by meldonium or allicin was demonstrated. Subsequently, the molecular interplay of the reductase YeaX and the oxygenase YeaW was addressed. Chimeric carnitine monooxygenase activity was efficiently reconstituted by combining YeaX (or YeaW) with the orthologous oxygenase CntA (or reductase CntB) from Acinetobacter baumannii. Partial conservation of the reductase/oxygenase docking interface was concluded. A structure guided mutagenesis approach was used to further investigate the interaction and electron transfer between YeaX and YeaW. Based on AlphaFold structure predictions, a total of 28 site-directed variants of YeaX and YeaW were kinetically analyzed. Functional relevance of YeaX residues Arg²⁷¹, Lys³¹³ and Asp³²⁰ was concluded. Concerning YeaW, a docking surface centered around residues Arg⁸³, Lys¹⁰⁴ and Lys¹¹⁷ was hypothesized. The presented results might contribute to the development of TMA-lowering strategies that could reduce the risk for cardiovascular disease.

Allicin in Digestive System Cancer: From Biological Effects to Clinical Treatment

Allicin is the main active ingredient in freshly-crushed garlic and some other allium plants, and its anticancer effect on cancers of digestive system has been confirmed in many studies. The aim of this review is to summarize epidemiological studies and in vitro and in vivo investigations on the anticancer effects of allicin and its secondary metabolites, as well as their biological functions. In epidemiological studies of esophageal cancer, liver cancer, pancreatic cancer, and biliary tract cancer, the anticancer effect of garlic has been confirmed consistently. However, the results obtained from epidemiological studies in gastric cancer and colon cancer are inconsistent. In vitro studies demonstrated that allicin and its secondary metabolites play an antitumor role by inhibiting tumor cell proliferation, inducing apoptosis, controlling tumor invasion and metastasis, decreasing angiogenesis, suppressing Helicobacter pylori, enhancing the efficacy of chemotherapeutic drugs, and reducing the damage caused by chemotherapeutic drugs. In vivo studies further demonstrate that allicin and its secondary metabolites inhibit cancers of the digestive system. This review describes the mechanisms against cancers of digestive system and therapeutic potential of allicin and its secondary metabolites.

Effect of Allicin and Artesunate Combination Treatment on Experimental Mice Infected with Plasmodium berghei

Malaria is still a significant health problem in endemic countries and increases Plasmodium resistance to the available antimalarial drugs. Hence, this study aimed to investigate the antimalarial activity of allicin and its combination with artesunate (ART) against rodent malaria Plasmodium berghei ANKA (PbANKA) infected mice. Allicin was prepared in 20% Tween-80. Balb/c mice were inoculated intraperitoneally with 1×10⁷ PbANKA-infected erythrocytes and orally given by gavage with the chosen doses of 1, 10, 50, and 100 mg/kg of allicin and 1, 5, 10, and 20 mg/kg of ART once a day for 4 consecutive days. Effective dose 50 (ED₅₀) of allicin and ART was subsequently investigated. Moreover, the combination (1 : 1) of allicin and ART at the doses of their respective ED₅₀, ED₅₀ 1/2, ED₅₀ 1/4, and ED₅₀ 1/8 was also carried out. The untreated control was given 20% Tween-80. The results showed that allicin presented a dose-dependent antimalarial activity with significance (p < 0.05). The ED₅₀ values of allicin and ART were about 14 and 5 mg/kg, respectively. For combination, allicin and ART showed a synergistic effect at the combination doses of ED₅₀, ED₅₀ 1/2, and ED₅₀ 1/4 with significantly (p < 0.01) prevented reduction of packed cell volume, bodyweight loss, rapid dropping of rectal temperature, and markedly prolonged mean survival time, compared with the untreated control and single treatment. It can be concluded that allicin exerted potential antimalarial activity in single and its combination with ART.

Evaluation of Allicin Against Alveolar Echinococcosis In Vitro and in a Mouse Model

Purpose

At present, the chemotherapy for alveolar echinococcosis (AE) is mainly based on albendazole (ABZ). However, more than 20% of patients fail chemotherapy. Therefore, new and more effective treatments are urgently needed. Allicin has been reported to have antibacterial and antiparasitic effects. The objectives of the present study were to investigate the in vivo and in vitro efficacy of allicin against Echinococcus multilocularis (E. multilocularis).

Methods

The effects of allicin on protoscolex survival and structural changes were evaluated in vitro. The 4-week-old BALB/c male mice used for in vivo modelling underwent inoculation of E. multilocularis protoscoleces by intraperitoneal injection, followed by intragastric administration of allicin for 6 weeks. Then, the effects of allicin on lymphocyte subsets, metacestode growth and host tissue matrix metalloproteinase 2 (MMP2)/MMP9 expression around metacestodes in mice were evaluated. The toxicity of allicin was further evaluated in vivo and in vitro.

Results

Att 40 μg/mL, allicin showed a killing effect on protoscoleces in vitro and treatment resulted in the destruction of protoscolex structure. Molecular docking showed that allicin could form hydrogen bonds with E. multilocularis cysteine enzymes. After 6 weeks of in vivo allicin treatment, the spleen index of mice was increased and the weight of metacestodes was reduced. Allicin increased the proportion of CD4⁺ T cells and decreased the proportion of CD8⁺ T cells in the peripheral blood and spleen. Pathological analysis of the metacestodes showed structural disruption of the germinal and laminated layers after allicin treatment. In addition, allicin inhibited the expression of MMP2 and MMP9 in metacestode-surrounding host tissues. At 160 μg/mL, allicin had no significant toxicity to normal hepatocytes but could inhibit hepatoma cell proliferation. At 30 mg/kg, allicin had no significant hepatorenal toxicity in vivo.

Conclusion

These results suggest that allicin exerts anti-E. multilocularis effects in vitro and in vivo and can enhance immune function in mice, with the potential to be developed as a lead compound against echinococcosis.

Direct Bis-Alkyl Thiolation for Indoles with Sulfinothioates under Pummerer-Type Conditions

A base-free bis-alkyl thiolation reaction of indoles with sulfinothioates under Pummerer-type conditions is described. Sulfinothioates, activated with 2,2,2-trifluoroacetic anhydride, are demonstrated to be an efficient thiolation reagent for wide applications. This approach enabled double C-H thiolation at the C2 and C3 of the indole in one pot. The mechanism studies suggested the thiolation was realized through the sulfoxonium salt rather than sulfenyl carboxylate.

A Comparative Review on Current and Future Drug Targets Against Bacteria & Malaria

Long before the discovery of drugs like 'antibiotic and anti-parasitic drugs', the infectious diseases caused by pathogenic bacteria and parasites remain as one of the major causes of morbidity and mortality in developing and underdeveloped countries. The phenomenon by which the organism exerts resistance against two or more structurally unrelated drugs is called multidrug resistance (MDR) and its emergence has further complicated the treatment scenario of infectious diseases. Resistance towards the available set of treatment options and poor pipeline of novel drug development puts an alarming situation. A universal goal in the post-genomic era is to identify novel targets/drugs for various life-threatening diseases caused by such pathogens. This review is conceptualized in the backdrop of drug resistance in two major pathogens i.e. "Pseudomonas aeruginosa" and "Plasmodium falciparum". In this review, the available targets and key mechanisms of resistance of these pathogens have been discussed in detail. An attempt has also been made to analyze the common drug targets of bacteria and malaria parasite to overcome the current drug resistance scenario. The solution is also hypothesized in terms of a present pipeline of drugs and efforts made by scientific community.

Antifungal activity of an allicin derivative against Penicillium expansum via induction of oxidative stress

The application of natural preservatives has become an attractive method for controlling postharvest decay of fruits and vegetables. Allicin, the main active ingredient of allium plants, has broad-spectrum antifungal activity. However, the unstable properties of allicin limit its wide application. In this study, 1-[(R)-ethylsulfinyl]sulfanylethane, a structurally stable derivative of allicin, was used to explore its antifungal activity and potential mechanism on the expansion of Penicillium expansum. We demonstrated the antifungal activity of 1-[(R)-ethylsulfinyl]sulfanylethane through in vitro antifungal experiments. At the concentration is 2 mg/L, 1-[((R)-ethylsulfinyl]sulfanyl]ethane can completely inhibit spore germination and mycelial growth, whereas the concentration of allicin needs to reach 16 mg/L. Fungal Biochemical assay indicated that decrease of mitochondrial membrane potential, overgeneration of reactive oxygen species, decrease of adenosine triphosphate and glutathione content, increase of superoxide dismutase, catalase, and malondialdehyde content. The results revealed that 1-[(R)-ethylsulfinyl]sulfanylethane induced mitochondrial dysfunction and oxidative stress in P. expansum. Due to its excellent antifungal activity, 1-[((R)-ethylsulfinyl]sulfanyl]ethane might be developed as a substitute for fungicides against P. expansum in postharvest fruit storage.

Potential effect of Allium sativum bulb for the treatment of biofilm forming clinical pathogens recovered from periodontal and dental caries

Biofilm producing clinical bacterial isolates were isolated from periodontal and dental caries samples and identified as, Lactobacillus acidophilus, Streptococcus sanguis, S. salivarius, S. mutansand Staphylococcus aureus. Among the identified bacterial species, S. aureus and S. mutansshowed strong biofilm producing capacity. The other isolated bacteria, Streptococcus sanguis, S. salivarius showed moderate biofilm formation. These pathogens were subjected for the production of extracellular polysaccharides (EPS) in nutrient broth medium and the strain S. aureus synthesized more amounts of EPS (610 ± 11.2 µg/ml) than S. sanguis (480 ± 5.8 µg/ml).EPS production was found to be less in S. salivarius (52 ± 3.8 µg/ml).The solvent extract of A. sativum bulb showed the phytochemicals such as, carbohydrate, total protein, alkaloids, saponins, flavonoids, tannins and sterioids. The solvent extract of A. sativum bulb showed wide ranges of activity against the selected dental pathogens. The difference in antibacterial activity of the solvent extract revealed differences in solubility of phytochemicals in organic solvents. Ethanol extract was highly active againstS. aureus (25 ± 2 mm). The Minimum Inhibitory Concentration (MIC) of crude garlic bulb varied widely and this clearly showed that bacteria exhibits different level of susceptibility to secondary metabolites. MIC value ranged between 20 ± 2 mg/ml and 120 ± 6 mg/ml and Minimum Bactericidal Concentration (MBC) value ranged from 60 ± 5 mg/l to 215 ± 7 mg/ml. To conclude, A. sativum bulb can be effectively used to treat periodontal and dental caries infections.

Asymmetric Disulfanylbenzamides as Irreversible and Selective Inhibitors of Staphylococcus aureus Sortase A

Staphylococcus aureus is one of the most frequent causes of nosocomial and community-acquired infections, with drug-resistant strains being responsible for tens of thousands of deaths per year. S. aureus sortase A inhibitors are designed to interfere with virulence determinants. We have identified disulfanylbenzamides as a new class of potent inhibitors against sortase A that act by covalent modification of the active-site cysteine. A broad series of derivatives were synthesized to derive structure-activity relationships (SAR). In vitro and in silico methods allowed the experimentally observed binding affinities and selectivities to be rationalized. The most active compounds were found to have single-digit micromolar Ki values and caused up to a 66 % reduction of S. aureus fibrinogen attachment at an effective inhibitor concentration of 10 μM. This new molecule class exhibited minimal cytotoxicity, low bacterial growth inhibition and impaired sortase-mediated adherence of S. aureus cells.

Effects of Feeding Garlic Powder on Growth Performance, Rumen Fermentation, and the Health Status of Lambs Infected by Gastrointestinal Nematodes

Simple Summary

Non-chemical strategies to control gastrointestinal nematodes (GINs) infection are urgently needed to support the sustainable development of the livestock industry. The potential anti-parasitic properties in garlic powder to control sheep GINs was investigated in this study. The key finding of this study was that feeding garlic powder increased growth performance of lambs infected with GINs by decreasing fecal egg counts and improving feed digestion, rumen fermentation, and the health status of lambs.

Abstract

For the study, forty lambs were weighed and assigned into two treatments to determine the effects of feeding garlic powder on growth performance, rumen fermentation, and the health status of lambs infected with gastrointestinal nematodes (GINs). The lambs were fed with a basal diet without or with 50 g/kg garlic powder for 84 d. Data were analyzed by a general linear or mixed model of SAS software and differences were considered statistically significant if p ≤ 0.05. Results showed that garlic powder supplementation increased the lambs’ average daily gain (p = 0.025), digestibility of dry matter (p = 0.019), and crude protein (p = 0.007). No significant changes were observed on the dry matter intake, feed conversion ratio, as well as the apparent digestibility of lipid and fiber. An interactive effect between treatment and feeding day was observed on ruminal pH (p < 0.001) and ammonia nitrogen concentration (p < 0.001). Ruminal pH (p < 0.001) and ammonia nitrogen concentration (p < 0.001) decreased with garlic powder supplementation, while ammonia nitrogen concentration increased (p = 0.001) with the extension of the feeding period. Garlic powder supplementation increased the total volatile fatty acid concentration (p < 0.001) in the rumen fluid, the molar proportion of acetic acid (p = 0.002), propionic acid (p < 0.001), and isovaleric acid (p = 0.049), but it decreased the ratio of acetic acid to propionic acid (p = 0.015). The lambs’ fecal egg count decreased (p < 0.001), but the packed cell volume and body condition scores of lambs increased (p < 0.001) with garlic powder supplementation. In conclusion, feeding garlic powder increased growth performance, feed digestion, rumen fermentation, and the health status of lambs infected with GINs.

Activity of Thioallyl Compounds From Garlic Against Giardia duodenalis Trophozoites and in Experimental Giardiasis

Fresh aqueous extracts (AGEs) and several thioallyl compounds (TACs) from garlic have an important antimicrobial activity that likely involves their interaction with exposed thiol groups at single aminoacids or target proteins. Since these groups are present in Giardia duodenalis trophozoites, in this work we evaluated the anti-giardial activity of AGE and several garlic's TACs. In vitro susceptibility assays showed that AGE affected trophozoite viability initially by a mechanism impairing cell integrity and oxidoreductase activities while diesterase activities were abrogated at higher AGE concentrations. The giardicidal activities of seven TACs were related to the molecular descriptor HOMO (Highest Occupied Molecular Orbital) energy and with their capacity to modify the -SH groups exposed in giardial proteins. Interestingly, the activity of several cysteine proteases in trophozoite lysates was inhibited by representative TACs as well as the cytopathic effect of the virulence factor giardipain-1. Of these, allicin showed the highest anti-giardial activity, the lower HOMO value, the highest thiol-modifying activity and the greatest inhibition of cysteine proteases. Allicin had a cytolytic mechanism in trophozoites with subsequent impairment of diesterase and oxidoreductase activities in a similar way to AGE. In addition, by electron microscopy a marked destruction of plasma membrane and endomembranes was observed in allicin-treated trophozoites while cytoskeletal elements were not affected. In further flow cytometry analyses pro-apoptotic effects of allicin concomitant to partial cell cycle arrest at G2 phase with the absence of oxidative stress were observed. In experimental infections of gerbils, the intragastric administration of AGE or allicin decreased parasite numbers and eliminated trophozoites in experimentally infected animals, respectively. These data suggest a potential use of TACs from garlic against G. duodenalis and in the treatment of giardiasis along with their additional benefits in the host's health.

Medicinal plants used by the people of Nsukka Local Government Area, south-eastern Nigeria for the treatment of malaria: An ethnobotanical survey

ETHNOBOTANICAL RELEVANCE

Malaria is a serious public health problem especially in sub-Saharan African countries such as Nigeria. The causative parasite is increasingly developing resistance to the existing drugs. There is urgent need for alternative and affordable therapy from medicinal plants which have been used by the indigenous people for many years.

AIM OF STUDY

This study was conducted to document the medicinal plant species traditionally used by the people of Nsukka Local Government Area in south-eastern Nigeria for the treatment of malaria.

METHODS

A total of 213 respondents, represented by women (59.2%) and men (40.8%), were interviewed using a semi-structured questionnaire. The results were analysed and discussed in the context of previously published information on anti-malarial and phytochemical studies of the identified plants.

RESULTS

The survey revealed that 50 plant species belonging to 30 botanical families were used in this region for the treatment of malaria. The most cited families were Apocynaceae (13.3%), Annonaceae (10.0%), Asteraceae (10.0%), Lamiaceae (10.0%), Poaceae (10.0%), Rubiaceae (10.0%) and Rutaceae (10.0%). The most cited plant species were Azadirachta indica (11.3%), Mangifera indica (9.1%), Carica papaya (8.5%), Cymbopogon citratus (8.5%) and Psidium guajava (8.5%).

CONCLUSION

The present findings showed that the people of Nsukka use a large variety of plants for the treatment of malaria. The identified plants are currently undergoing screening for anti-malarial, toxicity and chemical studies in our laboratory.

A Comparison of the Antibacterial and Antifungal Activities of Thiosulfinate Analogues of Allicin

Allicin (diallylthiosulfinate) is a defence molecule from garlic (Allium sativum L.) with broad antimicrobial activities in the low µM range against Gram-positive and -negative bacteria, including antibiotic resistant strains, and fungi. Allicin reacts with thiol groups and can inactivate essential enzymes. However, allicin is unstable at room temperature and antimicrobial activity is lost within minutes upon heating to >80 °C. Allicin's antimicrobial activity is due to the thiosulfinate group, so we synthesized a series of allicin analogues and tested their antimicrobial properties and thermal stability. Dimethyl-, diethyl-, diallyl-, dipropyl- and dibenzyl-thiosulfinates were synthesized and tested in vitro against bacteria and the model fungus Saccharomyces cerevisiae, human and plant cells in culture and Arabidopsis root growth. The more volatile compounds showed significant antimicrobial properties via the gas phase. A chemogenetic screen with selected yeast mutants showed that the mode of action of the analogues was similar to that of allicin and that the glutathione pool and glutathione metabolism were of central importance for resistance against them. Thiosulfinates differed in their effectivity against specific organisms and some were thermally more stable than allicin. These analogues could be suitable for applications in medicine and agriculture either singly or in combination with other antimicrobials.

Synthesis and in vitro biological evaluation of thiosulfinate derivatives for the treatment of human multidrug-resistant breast cancer

Organosulfur compounds derived from Allium vegetables have long been recognized for various therapeutic effects, including anticancer activity. Allicin, one of the main biologically active components of garlic, shows promise as an anticancer agent; however, instability makes it unsuitable for clinical application. The aim of this study was to investigate the effect of stabilized allicin derivatives on human breast cancer cells in vitro. In this study, a total of 22 stabilized thiosulfinate derivatives were synthesized and screened for their in vitro antiproliferative activities against drug-sensitive (MCF-7) and multidrug-resistant (MCF-7/Dx) human adenocarcinoma breast cancer cells. Assays for cell death, apoptosis, cell cycle progression and mitochondrial bioenergetic function were performed. Seven compounds (4b, 7b, 8b, 13b, 14b, 15b and 18b) showed greater antiproliferative activity against MCF-7/Dx cells than allicin. These compounds were also selective towards multidrug-resistant (MDR) cells, a consequence attributed to collateral sensitivity. Among them, 13b exhibited the greatest anticancer activity in both MCF-7/Dx and MCF-7 cells, with IC₅₀ values of 18.54±0.24 and 46.50±1.98 μmol/L, respectively. 13b altered cellular morphology and arrested the cell cycle at the G₂/M phase. Additionally, 13b dose-dependently induced apoptosis, and inhibited cellular mitochondrial respiration in cells at rest and under stress. MDR presents a significant obstacle to the successful treatment of cancer clinically. These results demonstrate that thiosulfinate derivatives have potential as novel anticancer agents and may offer new therapeutic strategies for the treatment of chemoresistant cancers.

Disulfide Bond-Containing Ajoene Analogues As Novel Quorum Sensing Inhibitors of Pseudomonas aeruginosa

Since its discovery 22 years ago, the bacterial cell-to-cell communication system, termed quorum sensing (QS), has shown potential as antipathogenic target. Previous studies reported that ajoene from garlic inhibits QS in opportunistic human pathogen Pseudomonas aeruginosa. In this study, screening of an in-house compound library revealed two sulfur-containing compounds which possess structural resemblance with ajoene and inhibit QS in bioreporter assay. Following a quantitative structure-activity relationship (SAR) study, 25 disulfide bond-containing analogues were synthesized and tested for QS inhibition activities. SAR study indicated that the allyl group could be replaced with other substituents, with the most active being benzothiazole derivative (IC₅₀ = 0.56 μM). The compounds were able to reduce QS-regulated virulence factors (elastase, rhamnolipid, and pyocyanin) and successfully inhibit P. aeruginosa infection in murine model of implant-associated infection. Altogether, the QS inhibition activity of the synthesized compounds is encouraging for further exploration of novel analogues in antimicrobial drug development.

Allicin Induces Calcium and Mitochondrial Dysregulation Causing Necrotic Death in Leishmania

Background

Allicin has shown antileishmanial activity in vitro and in vivo. However the mechanism of action underlying its antiproliferative effect against Leishmania has been virtually unexplored. In this paper, we present the results obtained in L.infantum and a mechanistic basis is proposed.

Methodology/Principal Finding

Exposure of the parasites to allicin led to high Ca²⁺ levels and mitochondrial reactive oxygen species (ROS), collapse of the mitochondrial membrane potential, reduced production of ATP and elevation of cytosolic ROS. The incubation of the promastigotes with SYTOX Green revealed that decrease of ATP was not associated with plasma membrane permeabilization. Annexin V and propidium iodide (PI) staining indicated that allicin did not induce phospholipids exposure on the plasma membrane. Moreover, DNA agarose gel electrophoresis and TUNEL analysis demonstrated that allicin did not provoke DNA fragmentation. Analysis of the cell cycle with PI staining showed that allicin induced cell cycle arrest in the G₂/M phase.

Conclusions/Significance

We conclude that allicin induces dysregulation of calcium homeostasis and oxidative stress, uncontrolled by the antioxidant defense of the cell, which leads to mitochondrial dysfunction and a bioenergetic catastrophe leading to cell necrosis and cell cycle arrest in the premitotic phase.

Leishmaniasis is a vectorial parasitic disease caused by flagellate organisms from the genus Leishmania. Infection is present in over 80 countries and visceral forms are the second most fatal human parasitic disease. Control relies on chemotherapy but available drugs have important shortcomings such as toxicity, side effects, unaffordable price of the safest presentations and increasing reports of parasite resistance and clinical failures. Thus, new drugs are needed. Allicin, a molecule obtained from garlic, has shown antiproliferative effect against different cancer cells, bacteria, fungi and Protista including Leishmania. Insofar its mechanism of action is poorly known. Our results with L.infantum point towards allicin inducing high levels of intracellular calcium, redox inbalance, and mitochondrial dysfunction with reduction of ATP. These events lead to cell necrosis without evidence of apoptotic-like markers. The proposed model suggests the potential use of allicin against leishmaniasis, alone or in combination with other drugs with different mechanisms of action.

A structure guided drug-discovery approach towards identification of Plasmodium inhibitors

This article provides a comprehensive review of inhibitors from natural, semisynthetic or synthetic sources against key targets ofPlasmodium falciparum.

Antileishmanial and Immunomodulatory Activity of Allium sativum (Garlic): A Review

Leishmaniasis is caused by an obligate intracellular protozoa belonging to Leishmania genus. The current drugs for treatment of leishmaniasis possess many disadvantages; therefore, researchers are continuously looking for the more effective and safer drugs. The aim of this study is to review the effectiveness, toxicities, and possible mechanisms of pharmaceutical actions of different garlic extracts and organosulfur compounds isolated from garlic against Leishmania spp. in a variety of in vitro, in vivo and clinical trials reports. All relevant databases were searched using the terms "Allium sativum," "Garlic," "Allicin," "Ajoene," "Leishmania," "in vitro," "in vivo," and "clinical trial," alone or in combination from 5 English databases (Web of Science, PubMed, Science Direct, Scopus, Google Scholar) and 3 Persian databases (Scientific Information Database, Iran Medex, and Magiran) from 1990 to 2014. In summary, garlic with immunomodulatory effects and apoptosis induction contributes to the treatment of leishmaniasis.

Development of a New Antileishmanial Aziridine-2,3-Dicarboxylate-Based Inhibitor with High Selectivity for Parasite Cysteine Proteases

Leishmaniasis is one of the major neglected tropical diseases of the world. Druggable targets are the parasite cysteine proteases (CPs) of clan CA, family C1 (CAC1). In previous studies, we identified two peptidomimetic compounds, the aziridine-2,3-dicarboxylate compounds 13b and 13e, in a series of inhibitors of the cathepsin L (CL) subfamily of the papain clan CAC1. Both displayed antileishmanial activity in vitro while not showing cytotoxicity against host cells. In further investigations, the mode of action was characterized in Leishmania major. It was demonstrated that aziridines 13b and 13e mainly inhibited the parasitic cathepsin B (CB)-like CPC enzyme and, additionally, mammalian CL. Although these compounds induced cell death of Leishmania promastigotes and amastigotes in vitro, the induction of a proleishmanial T helper type 2 (Th2) response caused by host CL inhibition was observed in vivo. Therefore, we describe here the synthesis of a new library of more selective peptidomimetic aziridine-2,3-dicarboxylates discriminating between host and parasite CPs. The new compounds are based on 13b and 13e as lead structures. One of the most promising compounds of this series is compound s9, showing selective inhibition of the parasite CPs LmaCatB (a CB-like enzyme of L. major; also named L. major CPC) and LmCPB2.8 (a CL-like enzyme of Leishmania mexicana) while not affecting mammalian CL and CB. It displayed excellent leishmanicidal activities against L. major promastigotes (50% inhibitory concentration [IC50] = 37.4 μM) and amastigotes (IC50 = 2.3 μM). In summary, we demonstrate a new selective aziridine-2,3-dicarboxylate, compound s9, which might be a good candidate for future in vivo studies.

Oxidation of Disulfides to Thiolsulfinates with Hydrogen Peroxide and a Cyclic Seleninate Ester Catalyst

Cyclic seleninate esters function as mimetics of the antioxidant selenoenzyme glutathione peroxidase. They catalyze the reduction of harmful peroxides with thiols, which are converted to disulfides in the process. The possibility that the seleninate esters could also catalyze the further oxidation of disulfides to thiolsulfinates and other overoxidation products under these conditions was investigated. This has ramifications in potential medicinal applications of seleninate esters because of the possibility of catalyzing the unwanted oxidation of disulfide-containing spectator peptides and proteins. A variety of aryl and alkyl disulfides underwent facile oxidation with hydrogen peroxide in the presence of catalytic benzo-1,2-oxaselenolane Se-oxide affording the corresponding thiolsulfinates as the principal products. Unsymmetrical disulfides typically afforded mixtures of regioisomers. Lipoic acid and N,N′-dibenzoylcystine dimethyl ester were oxidized readily under similar conditions. Although isolated yields of the product thiolsulfinates were generally modest, these experiments demonstrate that the method nevertheless has preparative value because of its mild conditions. The results also confirm the possibility that cyclic seleninate esters could catalyze the further undesired oxidation of disulfides in vivo.

Immunomodulatory and antiparasitic effects of garlic extract on Eimeria vermiformis-infected mice

We investigated the immunomodulatory and parasiticidal effects of garlic extract on coccidiosis caused by Eimeria vermiformis infection in male ICR mice. One group received garlic extract daily until the end of the experiment by the oral route from 10 days prior to oral infection with 300 sporulated E. vermiformis oocysts (infected-garlic(+)). The other group served as a control positive with E. vermiformis infection alone (infected-garlic(-)). In the infected-garlic(+) group, garlic extract treatment induced a significant reduction in fecal oocyst output when compared with the infected-garlic(-) group. Histopathological, immunohistochemical, and gene expression analysis for inflammatory cytokines in ileal tissues showed that the garlic extract treatment impaired intracellular development of E. vermiformis during the early stages by increasing the number of intraepithelial CD8(+) T cells and decreasing IL-10 expression. This induced cell cytotoxicity which was reflected by a decrease in oocyst numbers in the intestinal villi and the feces, indicating anticoccidial effects of the garlic extract. However, further studies to explore the precise mechanism of the observed effects of garlic treatment during Eimeria infection are needed to verify our results.

Garlic revisited: antimicrobial activity of allicin-containing garlic extracts against Burkholderia cepacia complex

The antimicrobial activities of garlic and other plant alliums are primarily based on allicin, a thiosulphinate present in crushed garlic bulbs. We set out to determine if pure allicin and aqueous garlic extracts (AGE) exhibit antimicrobial properties against the Burkholderia cepacia complex (Bcc), the major bacterial phytopathogen for alliums and an intrinsically multiresistant and life-threatening human pathogen. We prepared an AGE from commercial garlic bulbs and used HPLC to quantify the amount of allicin therein using an aqueous allicin standard (AAS). Initially we determined the minimum inhibitory concentrations (MICs) of the AGE against 38 Bcc isolates; these MICs ranged from 0.5 to 3% (v/v). The antimicrobial activity of pure allicin (AAS) was confirmed by MIC and minimum bactericidal concentration (MBC) assays against a smaller panel of five Bcc isolates; these included three representative strains of the most clinically important species, B. cenocepacia. Time kill assays, in the presence of ten times MIC, showed that the bactericidal activity of AGE and AAS against B. cenocepacia C6433 correlated with the concentration of allicin. We also used protein mass spectrometry analysis to begin to investigate the possible molecular mechanisms of allicin with a recombinant form of a thiol-dependent peroxiredoxin (BCP, Prx) from B. cenocepacia. This revealed that AAS and AGE modifies an essential BCP catalytic cysteine residue and suggests a role for allicin as a general electrophilic reagent that targets protein thiols. To our knowledge, we report the first evidence that allicin and allicin-containing garlic extracts possess inhibitory and bactericidal activities against the Bcc. Present therapeutic options against these life-threatening pathogens are limited; thus, allicin-containing compounds merit investigation as adjuncts to existing antibiotics.

Efficacy of low doses of amphotericin B plus allicin against experimental visceral leishmaniasis

OBJECTIVES

To evaluate the efficacy of the combination of allicin and amphotericin deoxycholate (AmB) in the chemotherapy of Leishmania infantum infection with the final aim of reducing the dose of AmB in the chemotherapy of visceral leishmaniasis.

METHODS

Hamsters were intraperitoneally (ip) infected with L. infantum (10(7) stationary phase promastigotes). On day 45 post-infection animals were treated ip with AmB (1 or 5 mg/kg/day), allicin (5 mg/kg/day) or a combination of AmB (1 mg/kg/day) + allicin (5 mg/kg/day) for 5 days. Animals were clinically and biopathologically monitored and the antibody response (IgG, IgG1, IgG2) was determined. Parasite burdens were estimated by limiting dilution and AmB biodistribution was determined by HPLC in plasma, kidney, spleen and liver.

RESULTS

No clinical signs or liver and kidney alterations were observed. AmB (1 mg/kg/day) did not clear the Leishmania infection and no parasites were detected in two animals treated with 5 mg/kg/day allicin. Combination therapy (5 mg/kg allicin + 1 mg/kg AmB) reduced the L. infantum burden by >95%. Antileishmanial activity of the combination was comparable (P < 0.05) to the standard AmB treatment (5 mg/kg).

CONCLUSIONS

Allicin alone (5 mg/kg/day for 5 days) significantly reduced the Leishmania burden in spleen and liver of infected hamsters. Co-administration of allicin (5 mg/kg/day for 5 days) and AmB (1 mg/kg/day for 5 days) showed a partial additive effect on the reduction of leishmanial burden in both target organs.

Drug discovery and human African trypanosomiasis: a disease less neglected?

Human African trypanosomiasis (HAT) has been neglected for a long time. The most recent drug to treat this disease, eflornithine, was approved by the US FDA in 2000. Current treatments exhibit numerous problematic side effects and are often ineffective against the debilitating CNS resident stage of the disease. Fortunately, several partnerships and initiatives have been formed over the last 20 years in an effort to eradicate HAT, along with a number of other neglected diseases. This has led to an increasing number of foundations and research institutions that are currently working on the development of new drugs for HAT and tools with which to diagnose and treat patients. New biochemical pathways as therapeutic targets are emerging, accompanied by increasing numbers of new antitrypanosomal compound classes. The future looks promising that this collaborative approach will facilitate eagerly awaited breakthroughs in the treatment of HAT.

In vitro synergistic effect of amphotericin B and allicin on Leishmania donovani and L. infantum

Current monotherapy against visceral leishmaniasis has serious side effects, and resistant Leishmania strains have been identified. Amphotericin B (AmB) has shown an extraordinary antileishmanial efficacy without emergence of resistance; however, toxicity has limited its general use. Results obtained showed, using a fixed-ratio analysis, that the combination of diallyl thiosulfinate (allicin) and AmB ranged from moderately synergic to synergic at low concentrations (0.07 μM AmB plus 35.45 μM allicin induced 95% growth inhibition). None of the treatments, alone or in combination, had noticeable adverse effects on macrophages (M) in the concentration range examined (allicin, 0.5, 1, 5 and 10 μM; AmB, 0.05, 0.075, and 0.1 μM). Allicin, AmB, or the combination did not affect the infection rate (percentage of infected M) of Leishmania. Allicin enhanced the activity of AmB on intracellular amastigotes of Leishmania donovani and L. infantum (ca. 45% reduction of amastigote burden with 0.05 μM AmB plus 10 μM allicin); this represented nearly a 2-fold reduction in the 50% inhibitory concentration (IC50) of the antibiotic added alone. Results point toward the possible utility of testing this combination in vivo to reduce the toxicity associated with monotherapy with AmB.

Effect of allicin on promastigotes and intracellular amastigotes of Leishmania donovani and L. infantum

Anti-leishmanial activity of allicin (=diallyl thiosulphinate) has been tested in vitro against promastigotes and intracellular amastigotes of Leishmania donovani and Leishmania infantum. Macrophage infections have been carried out in vitro in the murine cell line J774 and ex vivo with peritoneal macrophages from BALB/c mice with a modified method to isolate metacyclic promastigotes. The compound has shown a significant in vitro effect on the multiplication of promastigotes of L. donovani and L. infantum in a time- and dose-dependent manner. It has been shown for the first time the inhibition of multiplication of intracellular amastigotes of Leishmania by allicin. Inhibitory concentrations of the compound were in the micromolar range (10-30 μM) for both Leishmania species. Antileishmanial effect of allicin apparently was not related to products of degradation of the molecule as assessed by mass spectrometry analysis. Inhibitory activity of allicin against promastigotes and intracellular amastigotes increased when the compound was added to the cultures every 24 h. Two administrations of 5 μM allicin inhibited by ca. 50% the proliferation of Leishmania amastigotes. Low toxicity for mammalian cells of this compound suggests the interest of exploring the value of allicin in combined therapy against leishmanial infections.

Allicin enhances host pro-inflammatory immune responses and protects against acute murine malaria infection

Background

During malaria infection, multiple pro-inflammatory mediators including IFN-γ, TNF and nitric oxide (NO) play a crucial role in the protection against the parasites. Modulation of host immunity is an important strategy to improve the outcome of malaria infection. Allicin is the major biologically active component of garlic and shows anti-microbial activity. Allicin is also active against protozoan parasites including Plasmodium, which is thought to be mediated by inhibiting cysteine proteases. In this study, the immunomodulatory activities of allicin were assessed during acute malaria infection using a rodent malaria model Plasmodium yoelii 17XL.

Methods

To determine whether allicin modulates host immune responses against malaria infection, mice were treated with allicin after infection with P. yoelii 17XL. Mortality was checked daily and parasitaemia was determined every other day. Pro-inflammatory mediators and IL-4 were quantified by ELISA, while NO level was determined by the Griess method. The populations of dendritic cells (DCs), macrophages, CD4⁺ T and regulatory T cells (Treg) were assessed by FACS.

Results

Allicin reduced parasitaemia and prolonged survival of the host in a dose-dependent manner. This effect is at least partially due to improved host immune responses. Results showed that allicin treatment enhanced the production of pro-inflammatory mediators such as IFN-γ, TNF, IL-12p70 and NO. The absolute numbers of CD4⁺ T cells, DCs and macrophages were significantly higher in allicin-treated mice. In addition, allicin promoted the maturation of CD11c⁺ DCs, whereas it did not cause major changes in IL-4 and the level of anti-inflammatory cytokine IL-10.

Conclusions

Allicin could partially protect host against P. yoelii 17XL through enhancement of the host innate and adaptive immune responses.

Thiol-reactive compounds from garlic inhibit the epithelial sodium channel (ENaC)

The epithelial sodium channel (ENaC) is a key factor in the transepithelial movement of sodium, and consequently salt and water homeostasis in various organs. Dysregulated activity of ENaC is associated with human diseases such as hypertension, the salt-wasting syndrome pseudohypoaldosteronism type 1, cystic fibrosis, pulmonary oedema or intestinal disorders. Therefore it is important to identify novel compounds that affect ENaC activity. This study investigated if garlic (Allium sativum) and its characteristic organosulfur compounds have impact on ENaCs. Human ENaCs were heterologously expressed in Xenopus oocytes and their activity was measured as transmembrane currents by the two-electrode voltage-clamp technique. The application of freshly prepared extract from 5g of fresh garlic (1% final concentration) decreased transmembrane currents of ENaC-expressing oocytes within 10 min. This effect was dose-dependent and irreversible. It was fully sensitive to the ENaC-inhibitor amiloride and was not apparent on native control oocytes. The effect of garlic was blocked by dithiothreitol and l-cysteine indicating involvement of thiol-reactive compounds. The garlic organosulsur compounds S-allylcysteine, alliin and diallyl sulfides had no effect on ENaC. By contrast, the thiol-reactive garlic compound allicin significantly inhibited ENaC to a similar extent as garlic extract. These data indicate that thiol-reactive compounds which are present in garlic inhibit ENaC.

Antimicrobial properties of allium species

The antimicrobial activity of Allium species has long been recognized, with allicin, other thiosulfinates, and their transformation products having antimicrobial activity. Alliums are inhibitory against all tested microorganisms such as bacteria, fungi, viruses, and parasites. Alliums inhibit multi-drug-resistant microorganisms and often work synergistically with common antimicrobials. Allium-derived antimicrobial compounds inhibit microorganisms by reacting with the sulfhydryl (SH) groups of cellular proteins. It used to be thought that allicin reacts only with cysteine and not with non-SH amino acids, but evidence has accumulated that allicin and other thiosulfinates also react with non-SH amino acids.

Low-frequency and low-intensity ultrasound accelerates alliinase-catalysed synthesis of allicin in freshly crushed garlic

BACKGROUND

The well-known chemically and therapeutically active compound allicin is formed in crushed garlic by the interaction of alliin with alliinase. In this study, low-frequency and low-intensity ultrasound was employed to accelerate the alliinase-catalysed synthesis of allicin in freshly crushed garlic.

RESULTS

The optimal conditions for improvement of the alliinase-catalysed synthesis of allicin in freshly crushed garlic were found to be as follows: ultrasound intensity 0.4 W cm⁻², ultrasound frequency 50 kHz, enzymatic reaction temperature 35 °C and reaction time 30 min. Under these conditions the yield of allicin was increased by about 25.2% compared with the control without ultrasound. Alliinase in the freshly crushed garlic was purified by ammonium sulfate precipitation and gel filtration on a Sephacryl S-200 column. The employed ultrasound increased the activity of the purified alliinase by about 42.8%, did not affect the enzyme's temperature optimum and improved its thermal stability.

CONCLUSION

The results of this study indicated that the activity of alliinase in freshly crushed garlic might be enhanced by low-frequency and low-intensity ultrasound, thereby accelerating the alliinase-catalysed conversion of alliin in garlic to allicin.