Mechanism of differential efficacy of garlic organosulfides in preventing benzo(a)pyrene-induced cancer in mice

Diallyl Trisulfide Induces ROS-Mediated Mitotic Arrest and Apoptosis and Inhibits HNSCC Tumor Growth and Cancer Stemness

Despite advances in therapeutic approaches, the five-year survival rate for head and neck squamous cell carcinoma (HNSCC) patients is still less than fifty percent. Research has indicated that the consumption of Allium vegetables or processed garlic containing diallyl trisulfide (DATS) can lower the risk of multiple types of cancer. Nevertheless, the effectiveness and underlying mechanisms of DATS against HNSCC have not been thoroughly explored until the current study. In this research, it was found that DATS notably curtailed the growth and viability of HNSCC cells. Additionally, DATS triggered a significant G2/M cell cycle arrest in these cells, accumulating cyclin B1, Cip1/p21, and Ser-10 phospho-histone H3-this was indicative of mitotic arrest attenuated by NAC pretreatment, suggesting the role of reactive oxygen species (ROS) induction. The production of ROS induced by DATS led to DNA damage and apoptosis, a process associated with elevated levels of cleaved caspase-3 and cleaved PARP, along with reduced XIAP. When HNSCC cells were exposed to pharmacological concentrations of DATS, it resulted in the suppression of cancer stem cell (CSC) populations, as indicated by a decrease in the CD133high/CD44high cell fraction, reduced aldehyde dehydrogenase 1 (ALDH1) activity, inhibited spheroid formation and downregulated SOX2 and Oct4 expression. Furthermore, the administration of DATS to tumor xenografts demonstrated its in vivo capacity to hinder CSCs. Further, DATS treatment inhibited the growth of UMSCC-22B head and neck cancer tumor xenograft in immunocompromised mice. Overall, DATS inhibited cell proliferation; induced cell cycle mitotic arrest and apoptosis involving DNA damage through ROS generation; reduced the CSC fraction and spheroid formation; and downregulated SOX2 and Oct4 expression. More importantly, DATS inhibited HNSCC tumor growth and CSC fraction in vivo. Thus, DATS could be a potential anticancer agent that can be used against head and neck cancer.

Chemical constituents and medicinal properties of Allium species

Allium species, belonging to Alliaceae family, are among the oldest cultivated vegetables used as food. Garlic, onions, leeks and chives, which belong to this family, have been reported to have medicinal properties. The Allium species constituents have been shown to have antibacterial and antioxidant activities, and, in addition, other biological properties. These activities are related to their rich organosulfur compounds. These organosulfur compounds are believed to prevent the development of cancer, cardiovascular, neurological, diabetes, liver diseases as well as allergy and arthritis. There have also been reports on toxicities of these compounds. The major active compounds of Allium species includes, diallyl disulfide, diallyl trisulfide, diallyl sulfide, dipropyl disulfide, dipropyl trisulfide, 1-propenylpropyl disulfide, allyl methyl disulfide and dimethyl disulfide. The aim of this review is to focus on a variety of experimental and clinical reports on the effectiveness, toxicities and possible mechanisms of actions of the active compounds of garlic, onions, leek and chives.

Protective and Restorative Effects of Nutrients and Phytochemicals

Intoroduction:

Dietary intake fundamentally provides reintegration of energy and essential nutrients to human organisms. However, its qualitative and quantitative composition strongly affects individual’s health, possibly being either a preventive or a risk factor. It was shown that nutritional status resulting from long-term exposition to specific diet formulations can outstandingly reduce incidences of most common and most important diseases of the developed world, such as cardiovascular and neoplastic diseases. Diet formulations result from different food combinations which bring specific nutrient molecules. Numerous molecules, mostly but not exclusively from vegetal foods, have been characterized among nutritional components as being particularly responsible for diet capabilities to exert risk reduction. These “bioactive nutrients” are able to produce effects which go beyond basic reintegration tasks, i.e. energetic and/or structural, but are specifically pharmacologically active within pathophysiological pathways related to many diseases, being able to selectively affect processes such as cell proliferation, apoptosis, inflammation, differentiation, angiogenesis, DNA repair and carcinogens activation.

Conclusion:

The present review was aimed to know the molecular mechanisms and pathways of activity of bioactive molecules; which will firstly allow search for optimal food composition and intake, and then use them as possible therapeutical targets and/or diagnostics. Also, the present review discussed the therapeutic effect of both nutrients and phytochemicals.

Dietary Bioactive Diallyl Trisulfide in Cancer Prevention and Treatment

Bioactive dietary agents have been shown to regulate multiple cancer hallmark pathways. Epidemiologic studies have linked consumption of Allium vegetables, such as garlic and onions, to decreased incidence of cancer. Diallyl trisulfide (DATS), a bioactive compound derived from Allium vegetables, has been investigated as an anti-cancer and chemopreventive agent. Preclinical studies provide ample evidence that DATS regulates multiple cancer hallmark pathways including cell cycle, apoptosis, angiogenesis, invasion, and metastasis. DATS has been shown to arrest cancer cells at multiple stages of the cell cycle with the G2/M arrest being the most widely reported. Additionally, increased pro-apoptotic capacity as a result of regulating intrinsic and extrinsic apoptotic pathway components has been widely reported following DATS treatment. Invasion, migration, and angiogenesis represent emerging targets of DATS and support its anti-cancer properties. This review summarizes DATS mechanisms of action as an anti-cancer and chemopreventive agent. These studies provide rationale for future investigation into its use as a cancer chemopreventive agent.

Diallyl trisulfide protects the liver against hepatotoxicity induced by isoniazid and rifampin in mice by reducing oxidative stress and activating Kupffer cells

Background & Aim: Diallyl trisulfide (DATS) has been verified to ameliorate hepatotoxicity induced by many drugs, but the protective actions of isoniazid (INH) and rifampicin (RFP) have not been reported. We attempted to elucidate the potential effects and mechanisms of DATS against INH&RFP-caused hepatotoxicity. Methods: Male Kunming mice weighing 18-22 g were divided into 6 groups. For the hepatic-protective study, DATS (10 mg per kg, 20 mg per kg, and 40 mg per kg bw, respectively) was orally administered two hours before the INH&RFP (100 mg per kg, 100 mg per kg bw, respectively) treatments. After 11 days of treatment, 10 mice in each group were taken for the carbon clearance test, while the other 10 mice were sacrificed for the collection of serum and livers for further measurements, including the levels of serum alanine aminotransferase (ALT), aspartate transaminase (AST) and total bilirubin (T.Bili), the liver index, and liver histopathological examination. Malondialdehyde (MDA), glutathione (GSH), and the level of interleukin 1-β (IL-1-β) were measured, the carbon clearance test was performed and the immunohistochemistry of F4/80 marker for activated Kupffer cells (KCs) was analyzed to investigate potential mechanisms. Results: DATS co-administration significantly inhibited the increase of liver index and elevation of serum ALT, AST and T.Bili levels induced by INH&RFP, as well as improved the hepatocellular structure. The further mechanistic studies demonstrated that DATS co-administration counteracted INH&RFP-induced oxidative stress in mice, which was illustrated by the restoration of GSH levels, and the reduction of MDA levels in the liver. Furthermore, DATS co-administration reactivated the KCs inhibited by INH&RFP, which was illustrated by the increase of carbon phagocytosis, and the restoration of the number of activated KCs and IL-1-β levels in the liver. Conclusion: DATS effectively protected the liver against INH&RFP-induced hepatotoxicity, which might be due to its antioxidant effect and enhancement of KCs' activities.

Garlic oil suppressed the hematological disorders induced by chemotherapy and radiotherapy in tumor-bearing mice

Although the anticancer effects of garlic and its products have been demonstrated by a variety of studies; however, few studies were conducted to investigate the effects of garlic on the adverse effects of chemo/radiotherapy. In order to clarify the above question and make a more comprehensive understanding of the anticancer effects of garlic, tumor xenograft mice model was established by subcutaneous injection of H22 tumor cells, and was used for the investigation of effects of garlic oil (GO) on the chemo/radiotherapy. In the chemotherapy test, tumor-bearing mice were treated with cyclophosphamide (CTX) or CTX plus GO (25 or 50 mg/kg bw) for 14 d, while the mice received a single 5 Gy total body radiation or radiation plus GO (25 or 50 mg/kg bw) in radiotherapy test. The results showed that GO did not increase the tumor inhibitory rate of CTX/radiation, which indicated that GO could not enhance the chemo/radiosensitivity of cancer cells. However, the decrease of the peripheral total white blood cells (WBCs) count induced by CTX/radiation was significantly suppressed by GO cotreatment. Furthermore, GO cotreatment significantly inhibited the decrease of the DNA contents and the micronuclei ratio of the bone marrow. Lastly, the reduction of the endogenous spleen colonies induced by CTX/radiation was significantly suppressed by GO cotreatment. These findings support the idea that GO consumption may benefit for the cancer patients receiving chemotherapy or radiotherapy.

Role of di-allyl disulfide, a garlic component in NF-κB mediated transient G2-M phase arrest and apoptosis in human leukemic cell-lines

Diallyl disulfide (DADS), the major organosulfur component of processed garlic is very effective in chemoprevention of several types of cancers; however, its detailed mechanism is yet to be divulged. Present study shows antiproliferative activity of DADS against human leukemic cell-lines, mainly U937. DADS induced transient G2/M phase arrest, which is evident from FACS analysis. The results revealed that a significant transcriptional induction of p21 happened in early hours of treatment, which is due to increased nuclear translocation of NF-κB and its specific binding to p21 promoter. However, in the later hours, G2/M arrest is lost leading to apoptosis via intrinsic mitochondria-mediated pathway through generation of reactive oxygen species followed by changes in mitochondrial membrane potential. Western blots indicate release of cytochrome-c, activation of caspase-3, cleavage of PARP1, and finally decrease in bcl-2 levels. In addition, inactivation of NF-κB by its inhibitor BAY 11-7085 causes early onset of apoptosis without any transient G2/M arrest. Thus, in conclusion, DADS induces reversible G2/M arrest through NF-κB mediated pathway in human leukemic cell lines, like U937, K562, and Jurkat, lacking wild type p53. However, G2/M arrest is lost owing to the incapability of the damage repair system that leads to apoptosis.

Diallylsulfide attenuates excessive collagen production and apoptosis in a rat model of bleomycin induced pulmonary fibrosis through the involvement of protease activated receptor-2

Pulmonary fibrosis (PF) can be a devastating lung disease. It is primarily caused by inflammation leading to severe damage of the alveolar epithelial cells. The pathophysiology of PF is not yet been clearly defined, but studying lung parenchymal injury by involving reactive oxygen species (ROS) through the activation of protease activated receptor-2 (PAR-2) may provide promising results. PAR-2 is a G-protein coupled receptor is known to play an important role in the development of PF. In this study, we investigated the inhibitory role of diallylsulfide (DAS) against ROS mediated activation of PAR-2 and collagen production accompanied by epithelial cell apoptosis. Bleomycin induced ROS levels may prompt to induce the expression of PAR-2 as well as extracellular matrix proteins (ECM), such as MMP 2 and 9, collagen specific proteins HSP-47, α-SMA, and cytokines IL-6, and IL-8RA. Importantly DAS treatment effectively decreased the expression of all these proteins. The inhibitory effect of DAS on profibrotic molecules is mediated by blocking the ROS level. To identify apoptotic signaling as a mediator of PF induction, we performed apoptotic protein expression, DNA fragmentation analysis and ultrastructural details of the lung tissue were performed. DAS treatment restored all these changes to near normalcy. In conclusion, treatment of PF bearing rats with DAS results in amelioration of the ROS production, PAR-2 activation, ECM production, collagen synthesis and alveolar epithelial cell apoptosis during bleomycin induction. We attained the first evidence that treatment of DAS decreases the ROS levels and may provide a potential therapeutic effect attenuating bleomycin induced PF.

Effect of allyl sulfides from garlic essential oil on intracellular ca2+ levels in renal tubular cells

Diallyl sulfide (1), diallyl disulfide (2), and diallyl trisulfide (3), which are major organosulfur compounds of garlic (Allium sativum), are recognized as a group of potential chemopreventive compounds. In this study, the early signaling effects of 3 were examined on Madin-Darby canine kidney (MDCK) cells loaded with the Ca(2+)-sensitive dye fura-2. It was found that 3 caused an immediate and sustained increase of [Ca(2+)](i) in a concentration-dependent manner (EC(50) = 40 μM). Compound 3 also induced a [Ca(2+)](i) elevation when extracellular Ca(2+) was removed, but the magnitude was reduced by 45%. In Ca(2+)-free medium, the 3-induced [Ca(2+)](i) level was abolished by depleting stored Ca(2+) with 1 μM thapsigargin (an endoplasmic reticulum Ca(2+) pump inhibitor). Elevation of [Ca(2+)](i) caused by 3 in the Ca(2+)-containing medium was not affected by modulation of protein kinase C activity. The 3-induced Ca(2+) influx was inhibited by nifedipine and nicardipine (1 μM). U73122, an inhibitor of phospholipase C, abolished ATP (but not the 3-induced [Ca(2+)](i) level). These findings suggest that 3 induced a significant [Ca(2+)](i) elevation in MDCK renal tubular cells by stimulating both extracellular Ca(2+) influx and thapsigargin-sensitive intracellular Ca(2+) release via as yet unidentified mechanisms. Furthermore, the order of the allyl sulfide-induced [Ca(2+)](i) elevation and cell viability was 1 < 2 < 3. The differential effect of allyl sulfides on Ca(2+) signaling and cell death appears to correlate with the number of sulfur atoms in the structure of these allyl sulfides.

The attenuation of early benzo(a)pyrene-induced carcinogenic insults by diallyl disulfide (DADS) in MCF-10A cells

Diallyl disulfide (DADS), a garlic organosulfur compound, has been researched as a cancer prevention agent; however, the role of DADS in the suppression of cancer initiation in nonneoplastic cells has not been elucidated. To evaluate DADS inhibition of early carcinogenic events, MCF-10A cells were pretreated (PreTx) with DADS followed by the ubiquitous carcinogen benzo(a)pyrene (BaP), or cotreated (CoTx) with DADS and BaP for up to 24 h. The cells were evaluated for changes in cell viability/proliferation, cell cycle, induction of peroxide formation, and DNA damage. BaP induced a statistically significant increase in cell proliferation at 6 h, which was attenuated with DADS CoTx. PreTx with 6 and 60 μM of DADS inhibited BaP-induced G2/M arrest by 68% and 78%, respectively. DADS, regardless of concentration or method, inhibited BaP-induced extracellular aqueous peroxide formation within 24 h. DADS attenuated BaP-induced DNA single-strand breaks at all time points through both DADS Pre- and CoTx, with significant inhibition for all treatments sustained after 6 h. DADS was effective in inhibiting BaP-induced cell proliferation, cell cycle transitions, reactive oxygen species, and DNA damage in a normal cell line, and thus may inhibit environmentally induced breast cancer initiation.

Hydrogen sulfide-releasing aspirin modulates xenobiotic metabolizing enzymes in vitro and in vivo

The balance between phase-I carcinogen-activating and phase-II detoxifying xenobiotic metabolizing enzymes is critical to determining an individual's risk for cancer. We evaluated the effect of Hydrogen sulfide-releasing aspirin (HS-ASA) on xenobiotic metabolizing enzymes in HT-29 human colon and Hepa 1c1c7 mouse liver adenocarcinoma cells and in Wistar rats. HS-ASA inhibited the growth of HT-29 and Hepa 1c1c7 cells, with an IC(50) of 3.2 ± 0.3 μM and 4.2 ± 0.4 μM, respectively. The IC(50) for ASA in both cell lines was greater than 5000 μM at 24h. In these cell lines, HS-ASA caused a dose-dependent increase in activity and expression of the phase-II enzymes glutathione S-transferase (GST) and NAD(P)H:quinoneoxireductase (NQO1). It also caused an increase in UDP-glucuronosyltransferase (UGT) expression. The levels of CYP 1A1 a phase-I enzyme was increased by HS-ASA in both cell lines. Pretreatment of cells with NaF, an esterase inhibitor, abrogated the HS-ASA-mediated increases in NQO1 enzyme activity. HS-ASA increased the protein levels of the transcription factor Nrf2, which is a regulator of the phase-II enzymes. In vivo, HS-ASA at 100mg/kg/day had no effect on rat's weights; it induced a 3.4-fold and 1.4-fold increase in hepatic GST and NQO1 enzyme activities, respectively. GST and NQO1 protein levels were also increased. In contrast to that in cultured cells, CYP 1A1 protein levels were not altered in vivo. Therefore, HS-ASA induces phase-II enzymes, at least in part, through the action of H(2)S and by modulating Nrf2; these effects may be part of its mechanism of action against carcinogenesis.

Harmful and beneficial effects of organic monosulfides, disulfides, and polysulfides in animals and humans

Many organic sulfides (mono-, di-, and polysulfides) are present in our environment. Simple derivatives are produced by some plants and animals, while complex sulfides are secondary metabolites of several genera of bacteria and fungi. Sulfides play an important role in the smell and taste of food, and many such compounds are used as food flavorings. Some sulfides are toxic, and there is evidence that such toxicity is caused by the ability of these substances to generate reactive oxygen species. Some sulfides, however, have been shown to protect against toxicants and carcinogens. These beneficial effects are believed to involve, at least in part, the ability of sulfides to inhibit the enzymatic activation of pro-toxicants and to increase tissue activities of enzymes that protect against electrophiles. Some sulfides also have potential as cancer chemotherapeutics. In this review, the toxic and beneficial effects of sulfides in animals are described, and the possible value of sulfides in cancer chemoprotection and cancer chemotherapy is discussed.

Garlic in health and disease

The present article reviews the historical and popular uses of garlic, its antioxidant, haematological, antimicrobial, hepatoprotective and antineoplastic properties and its potential toxicity (from sulfoxide). Garlic has been suggested to affect several cardiovascular risk factors. It has also been shown that garlic and its organic allyl sulfur components are effective inhibitors of the cancer process. Since garlic and its constituents can suppress carcinogen formation, bioactivation and tumour proliferation, it is imperative that biomarkers be established to identify which individuals might benefit most. Garlic powder, aged garlic and garlic oil have demonstrated antiplatelet and anticoagulant effects by interfering with cyclo-oxygenase-mediated thromboxane synthesis. Garlic has also been found to have synergistic effects against Helicobacter pylori with a proton pump inhibitor. The active compound allicin may affect atherosclerosis not only by acting as an antioxidant, but also by other mechanisms, such as lipoprotein modification and inhibition of LDL uptake and degradation by macrophages. Freshly prepared garlic homogenate protects against isoniazid+rifampicin-induced liver injury in experimental animal models. Several mechanisms are likely to account for this protection.

Structure and function relationship study of allium organosulfur compounds on upregulating the pi class of glutathione S-transferase expression

Allium organosulfides are potential chemopreventive compounds due to their effectiveness on the induction of phase II detoxification enzyme expression. In this study, we examined the structure and function relationship among various alk(en)yl sulfides on the expression of the pi class of glutathione S-transferase (GSTP) in rat Clone 9 cells, and what mechanism is involved. Cells were treated with 300 μM dipropyl sulfide (DPS), dipropyl disulfide (DPDS), propyl methyl sulfide (PMS), and propyl methyl disulfide (PMDS) for 48 h. DPDS and PMDS displayed more potency on GSTP protein and mRNA induction than that of DPS and PMS. Next, we compared the effectiveness of DPDS, PMDS, and diallyl disulfide (DADS), which have the same number of sulfur atoms but differ in the side alk(en)yl groups. The maximum increases on protein expression, mRNA level, and enzyme activity were noted in cells treated with DADS, followed by DPDS and PMDS. A reporter assay showed that three disulfides increased GSTP enhancer I (GPE I) activity (P < 0.05) in the order DADS > DPDS ≥ PMDS. Electromobility gel shift assays showed that the DNA binding of GPE I to nuclear proteins reached a maximum at 1 to 3 h after alk(en)yl disulfide treatment. Supershift assay revealed that c-jun bound to GPE I. Silencing of extracellular signal-regulated kinase (ERK) 2 expression inhibited c-jun activation and GSTP induction. Results suggest that both the type of alk(en)yl groups and number of sulfur atoms are determining factors of allium organosulfides on inducing GSTP expression, and it is likely related to the ERK-c-Jun-GPE I pathway.

Consumption of S-allylcysteine inhibits the growth of human non-small-cell lung carcinoma in a mouse xenograft model

Lung cancer is one of the leading causes of cancer death in the world. Human non-small-cell lung carcinoma (NSCLC) accounts for almost 80% of lung cancer cases. Aberrant phosphoinositide 3-kinase (PI3K)/Akt/mTOR signaling pathways play important roles and have been widely observed in the development of NSCLC. Previous studies indicated that garlic extracts such as diallyl disulfide (DADS) and diallyl trisulfide (DATS) could inhibit the proliferation of several types of cancer in vitro. However, the inhibitory effects of S-allylcysteine (SAC) on the growth of NSCLC have not been demonstrated yet. Therefore, this study investigated whether consumption of SAC could prevent the growth of NSCLC in both in vitro and in vivo models. It was found that SAC significantly inhibited the proliferation of human NSCLC A-549 cells in vitro. Treatment of the NF-κB inhibitor, Bay-11-7082, could significantly inhibit the proliferation of NSCLC A-549 cells. The results demonstrated that SAC significantly suppressed the activation of mTOR, NF-κB, and cyclin D1 molecules in vitro. Furthermore, the results demonstrated that consumption of SAC significantly inhibited the growth of highly metastatic human NSCLC cells in tumor-bearing mice. Bioluminescence imaging and pathological and immunohistochemical (IHC) staining results also indicated that SAC could effectively suppress the growth and malignant progression of human NSCLC in vivo. The chemopreventive effects of SAC were associated with suppression of mTOR and NF-κB molecules in vivo. These results suggested that SAC could act as an effective agent against the malignant progression of human NSCLC in both in vitro and in vivo models.

Organosulfur compounds and possible mechanism of garlic in cancer

Garlic (Allium sativum), a member of the family Liliaceae, contains an abundance of chemical compounds that have been shown to possess beneficial effects to protect against several diseases, including cancer. Evidence supports the protective effects of garlic in stomach, colorectal, breast cancer in humans. The protective effects appear to be related to the presence of organosulfur compounds, predominantly allyl derivatives, which also have been shown to inhibit carcinogenesis in forestomach, esophagus, colon, mammary gland and lung of experimental animals. The exact mechanisms of the cancer-preventive effects are not clear, although several hypotheses have been proposed. Organosulfur compounds modulate the activity of several metabolizing enzymes that activate (cytochrome P450s) or detoxify (glutathione S-transferases) carcinogens and inhibit the formation of DNA adducts in several target tissues. Antiproliferative activity has been described in several tumor cell lines, which is possibly mediated by induction of apoptosis and alterations of the cell cycle. Organosulfur compounds in garlic are thus possible cancer-preventive agents. Clinical trials will be required to define the effective dose that has no toxicity in humans.

Induction of drug-metabolizing enzymes by garlic and allyl sulfide compounds via activation of constitutive androstane receptor and nuclear factor E2-related factor 2

Garlic oil (GO) contains several linear sulfur compounds, including diallyl sulfide (DAS), diallyl disulfide (DADS), and diallyl trisulfide (DATS), that induce drug-metabolizing enzymes such as CYP2B and NAD(P)H quinone oxidoreductase 1 (NQO1). CYP2B and NQO1 are primarily regulated by constitutive androstane receptor (CAR) and nuclear factor E2-related factor 2 (Nrf2) transcription factors, respectively. The purpose of this study was to determine whether GO and its specific constituents induce these two enzymes via CAR and Nrf2 activation. Female Wistar-Kyoto (WKY) rats express little CAR protein and exhibit less induction of CYP2B1/2 than males. GO, DAS, and DADS, but not DATS, induced CYP2B1/2 mRNA levels to a greater extent in WKY males than in females, suggesting CAR activation. Conversely, DAS induced NQO1 levels equally in WKY males and females, indicating CAR-independent induction in rats. DAS, but not GO, DADS, or DATS, induced CYP2B10 mRNA levels 530-fold in wild-type (WT) mice, whereas this induction was attenuated in CAR(-/-) mice. DAS induced NQO1 in WT and CAR(-/-) mice equally, suggesting CAR-independent induction in mice. DAS induced NQO1 5-fold in WT mice, whereas induction was completely absent in Nrf2(-/-) mice, indicating DAS also activates Nrf2. DAS induction of CYP2B10 mRNA was independent of Nrf2 presence or absence. In in vivo transcription assays, DAS activated the human CYP2B6 promoter, and the antioxidant response element of the human NQO1 promoter, respectively. These studies indicate that GO constituents, particularly DAS, activate CAR and Nrf2 to induce drug-metabolizing enzymes.

A proteomic investigation into a human gastric cancer cell line BGC823 treated with diallyl trisulfide

Garlic is generally used as a therapeutic reagent against various diseases worldwide. Although a great effort is made to understand the pharmaceutical mechanisms of garlic and its derivatives, there are many mysteries to be uncovered. Using proteomic means, herein we have systematically studied the responses of protein expression in BGC823 cells, a gastric cancer cell line, induced by diallyl trisulfide (DATS), a major component of garlic derivatives. A total of 41 unique proteins in BGC823 were detected with significant changes in their expression levels corresponding with DATS administration. Of these proteins, five typical ones, glutathione S-transferase-pi (GST-pi), voltage-dependent anion channel-1 (VDAC-1), Annexin I, Galectin and S100A11, were further examined by Western blotting, resulting in coincident data with the proteomic evidence. Moreover quantitative real-time RT-PCR experiments offered dynamic data of mRNA expression, indicating the responses of Annexin I and GST-pi expression within a short period after DATS treatment. Interestingly, approximately 50% of DATS-sensitive proteins (19/41) in BGC823 are tightly associated with apoptotic pathways. These proteomic results presented, therefore, provide additional support to the hypothesis that garlic is a strong inducer of apoptosis in tumor cells.

Diallyl trisulfide suppresses the proliferation and induces apoptosis of human colon cancer cells through oxidative modification of beta-tubulin

Allyl sulfides are characteristic flavor components obtained from garlic. These sulfides are thought to be responsible for their epidemiologically proven anticancer effect on garlic eaters. This study was aimed at clarifying the molecular basis of this anticancer effect of garlic by using human colon cancer cell lines HCT-15 and DLD-1. The growth of the cells was significantly suppressed by diallyl trisulfide (DATS, HCT-15 IC50 = 11.5 microM, DLD-1 IC50 = 13.3 microM); however, neither diallyl monosulfide nor diallyl disulfide showed such an effect. The proportion of HCT-15 and that of DLD-1 cells residing at the G1 and S phases were decreased by DATS, and their populations at the G2/M phase were markedly increased for up to 12 h. The cells with a sub-G1 DNA content were increased thereafter. Caspase-3 activity was also dramatically increased by DATS. Fluorescence-activated cell sorter analysis performed on the cells arrested at the G1/S boundary revealed cell cycle-dependent induction of apoptosis through the transition of the G2/M phase to the G1 phase by DATS. DATS inhibited tubulin polymerization in an in vitro cell-free system. DATS disrupted microtubule network formation of the cells, and microtubule fragments could be seen at the interphase. Peptide mass mapping by liquid chromatography-tandem mass spectrometry analysis for DATS-treated tubulin demonstrated that there was a specific oxidative modification of cysteine residues Cys-12beta and Cys-354beta to form S-allylmercaptocysteine with a peptide mass increase of 72.1 Da. The potent antitumor activity of DATS was also demonstrated in nude mice bearing HCT-15 xenografts. This is the first paper describing intracellular target molecules directly modified by garlic components.

Effects of a series of organosulfur compounds on mitotic arrest and induction of apoptosis in colon cancer cells

We previously reported that the garlic-derived compound S-allylmercaptocysteine (SAMC) causes growth inhibition, mitotic arrest, and induction of apoptosis in SW480 human colon cancer cells by inducing microtubule depolymerization and c-Jun NH(2) terminus kinase-1 activation. In the present study, we compared the aforementioned effects of SAMC to those of a series of garlic-derived and other organosulfur compounds. Among the 10 compounds tested, only SAMC, diallyl disulfide (DADS), and S-trityl-L-cysteine (trityl-cys) cause significant inhibition of cell growth with IC(50) values of 150, 56, and 0.9 micromol/L, respectively. These three compounds also induce G(2)-M cell cycle arrest and apoptosis. Further studies reveal that, like SAMC, the garlic-derived compound DADS exerts antiproliferative effects by binding directly to tubulin and disrupting the microtubule assembly, thus arresting cells in mitosis and triggering mitochondria-mediated signaling pathways that lead to apoptosis. However, the synthetic compound trityl-cys exerts its effect on M-phase arrest and growth inhibition by mechanisms that involve spindle impairment but do not involve disruption of microtubule structure or dynamics. Furthermore, trityl-cys does not induce marked loss of mitochondrial membrane potential or release of cytochrome c, but it does induce caspase-3 activation and poly(ADP-ribose) polymerase cleavage. Structure-function analysis suggests that both the allyl and the disulfide moieties are important features for the antiproliferative effects of SAMC and DADS. These findings may be useful in the identification, synthesis, and development of organosulfur compounds that have anticancer activity.

Bioactive S-alk(en)yl cysteine sulfoxide metabolites in the genus Allium: the chemistry of potential therapeutic agents

S-Alk(en)yl cysteine sulfoxides are odourless, non-protein sulfur amino acids typically found in members of the family Alliaceae and are the precursors to the lachrymatory and flavour compounds found in the agronomically important genus Allium. Traditionally, Allium species, particularly the onion (Allium cepa) and garlic (A. sativum), have been used for centuries in European, Asian and American folk medicines for the treatment of numerous human pathologies, however it is only recently that any significant progress has been made in determining their mechanisms of action. Indeed, our understanding of the role of Allium species in human health undoubtedly comes from the combination of several academic disciplines including botany, biochemistry and nutrition. During tissue damage, S-alk(en)yl cysteine sulfoxides are converted to their respective thiosulfinates or propanethial-S-oxide by the action of the enzyme alliinase (EC 4.4.1.4). Depending on the Allium species, and under differing conditions, thiosulfinates can decompose to form additional sulfur constituents including diallyl, methyl allyl, and diethyl mono-, di-, tri-, tetra-, penta-, and hexasulfides, the vinyldithiins and (E)- and (Z)-ajoene. Recent reports have shown onion and garlic extracts, along with several principal sulfur constituents, can induce phase II detoxification enzymes like glutathione-S-transferases (EC 2.5.1.18) and quinone reductase (QR) NAD(P)H: (quinine acceptor) oxidoreductase (EC 1.6.99.2) in mammalian tissues, as well as also influencing cell cycle arrest and apoptosis in numerous in vitro cancer cell models. Moreover, studies are also beginning to highlight a role of Allium-derived sulfur compounds in cardiovascular protection. In this review, we discuss the chemical diversity of S-alk(en)yl cysteine sulfoxide metabolites in the context of their biochemical and pharmacological mechanisms.

Anticarcinogenic properties of garlic: a review

Garlic is a popular spice added to several edible preparations and is a remedy for a variety of ailments. Epidemeological as well as laboratory studies have shown that garlic consumption reduces certain cancer incidences in the stomach, colon, mammary, cervical, etc. This article focuses on the general chemistry, metabolism, anticarcinogenic properties, mechanism of action behind the anticarcinogenic effects, functional foods based on garlic; and future areas of research. Garlic has been shown to metabolized into N-aceryl-S-allyl cysteine, allyl mercaptan, diallyl disulfide, diallyl sulfide, diallyl sulfoxide, diallyl sulfone, and allyl methyl sulfide. Garlic has been thought to bring about its anticarcinogenic effect through a number of mechanisms, such as the scavenging of radicals, increasing gluathione levels, increasing the activities of enzymes such as glutathione S-transferase, catalase, inhibition of cytochrome p4502E1, DNA repair mechanisms, prevention of chromosomal damage etc. Future research should standardize the dosage of garlic and type, ie., whether it should be taken fresh, cooked, or aged. The formulation of odorless functional foods with the retention of anticarcinogenic activity should be further studied.

Differential effects of allyl sulfides from garlic essential oil on cell cycle regulation in human liver tumor cells

In this study, diallyl sulfide (DAS), diallyl disulfide (DADS) and diallyl trisulfide (DATS), which are major organosulfur compounds (OSCs) of garlic, were used as experimental materials to investigate their modulation effects on cell viability and cell cycle in human liver tumor cells (J5). According to the results of cell viability assay, 50 or 100 microM DATS significantly decreased the cell viability as compared with the control (P < 0.05) in dose and time dependent relations. Phenomena of cell number loss, shape deformation and lysis were observed after treatment with 100 microM DATS for 24 h. Cell cycle studies showed that J5 cells were significantly arrested in G2/M phase as the cells were treated with 100 microM DADS, 10, 50 or 100 microM DATS for 24 h (P < 0.05). DATS was more effective in arresting cells in G2/M phase than DADS, and the phenomena of arresting J5 cells in G2/M phase increased obviously in dose and time dependent relations. According to the Western blot analysis, DATS decreased cyclin-dependent kinase (Cdks)-Cdk7 (i.e. Cdc2 activate kinase) protein levels in J5 cells but increased cyclin B1 protein level. The modulation potency to cyclin B1 and Cdk7 expressions was in the order of DATS > DADS > DAS. The modulation potency to cyclin B1 and Cdk7 protein levels increased with increasing in DATS concentration and culture time. In conclusion, DATS might affect cell viability and cell morphological changes in J5 cells and lead cells to be arrested in G2/M phase via controlling the expression of cyclin B1 and Cdk7 in J5 cells, and the controlling action might relate to the sulfuric atom numbers in the structures of all these allyl sulfides.

Garlic attenuates chrysotile-mediated pulmonary toxicity in rats by altering the phase I and phase II drug metabolizing enzyme system

Asbestos and its carcinogenic properties have been extensively documented. Asbestos exposure induces diverse cellular events associated with lung injury. Previously, we have shown that treatment with chrysotile shows significant alteration in phase I and phase II drug metabolizing enzyme system. In this study we have examined some potential mechanisms by which garlic treatment attenuates chrysotile-mediated pulmonary toxicity in rat. Female Wistar rats received an intratracheal instillation of 5 mg chrysotile (0.5 mL saline) as well as intragastric garlic treatment (1% body weight (v/w); 6 days per week). Effect of garlic treatment was evaluated after 1, 15, 30, 90, and 180 days by assaying aryl hydrocarbon hydroxylase (AHH), glutathione (GSH), glutathione S-transferase (GST), and production of thiobarbituric acid reactive substances (TBARS) in rat lung microsome. The results showed that AHH and TBARS formation were significantly reduced at day 90 and day 180 in chrysotile treated garlic cofed rats; GSH recovered 15 days later to the near normal level and GST elevated significantly after treatment of garlic as compared to chrysotile alone treated rat lung microsome. The data obtained shows that inhibition of AHH activity and induction of GST activity could be contributing factor in chrysotile-mediated pulmonary toxicity in garlic cofed rats. However, recovery of GSH and inhibition of TBARS formation by garlic and its constituent(s) showed that garlic may give protection by altering the drug metabolizing enzyme system.

Diallyl trisulfide modulates cell viability and the antioxidation and detoxification systems of rat primary hepatocytes

This study investigated the effects of various concentrations of diallyl trisulfide (DATS) and incubation times on cell viability, glutathione (GSH) content, and GSH-related enzyme activity in rat primary hepatocytes. Isolated and cultured primary rat hepatocytes were used as an experimental model. Cells were treated with 0 (control), 0.025, 0.05, or 0.25 mmol/L DATS for 0, 4, 8, or 24 h. After 24 h of treatment, some cells were incubated in fresh medium without DATS for an additional 24 h (48-h incubations). Based on lactate dehydrogenase (LDH) leakage and morphological examination, hepatocytes treated with 0.025 mmol/L DATS did not differ from the control cells at 4, 8, 24, and 48 h of incubation. However, LDH leakage was higher than in the control cells (P < 0.05) when the hepatocytes were treated with 0.05 or 0.25 mmol/L DATS for 4 h or more. The intracellular GSH levels of hepatocytes treated with 0.025 or 0.05 mmol/L DATS were higher than those of the control cells (P < 0.05), whereas those treated with 0.25 mmol/L DATS did not differ. The activity of glutathione reductase (GRd) was higher than in the control cells at 24 h (P < 0.05) when the hepatocytes were treated with 0.025 mmol/L DATS. When the hepatocytes were treated with 0.025 mmol/L DATS, the activity of glutathione S-transferase (GST) was higher than in the control cells at 48 h (P < 0.05). In hepatocytes treated with 0.05 mmol/L DATS, the activity of GST and glutathione peroxidase (GPx) was higher than in the control cells (P < 0.05) at 24 and 48 h of incubation. The results indicate that 0.025 or 0.05 mmol/L DATS could enhance antioxidation and detoxification capabilities by increasing the intracellular GSH level and the activity of GPx, GRd, or GST in rat primary hepatocytes. However, 0.05 or 0.25 mmol/L DATS might adversely affect the viability of hepatocytes.

Oxathiolene oxides: a novel family of compounds that induce ferritin, glutathione S-transferase, and other proteins of the phase II response

Compounds that induce the synthesis of cytoprotective phase II enzymes have shown promise as cancer chemopreventive agents. Although chemically diverse, phase II enzyme inducers are capable of participating in Michael reaction chemistry. We have synthesized a novel class of organosulfur compounds, termed oxathiolene oxides (OTEOs). Based on their chemical properties, we hypothesized that these compounds could function as phase II enzyme inducers. Northern blot analysis showed that oxathiolene oxides induce the phase II enzymes glutathione S-transferase (GST), NAD(P)H:quinone oxidoreductase 1 (NQO1), and ferritin H and L mRNA in a concentration-dependent fashion in a normal embryonic mouse liver cell line, BNLCL.2. OTEO-562 (3-cyclohexenyl-4-methyl-1,2-oxathiol-3-ene-2-oxide) was the strongest inducer. Western blot analysis demonstrated that GST-alpha and ferritin H protein levels were also induced in cells treated with OTEO-562, as was total GST and NQO1 enzyme activity. Further, induction of NQO1 activity by OTEO-562 was equivalent in aromatic hydrocarbon (Ah) receptor wild-type and Ah receptor mutant cell lines, suggesting that oxathiolene oxides activate phase II enzymes by an Ah receptor-independent mechanism. Consistent with this observation, OTEO-562 failed to induce cytochrome P450 1A1 mRNA. These results suggest that oxathiolene oxides may merit further investigation as candidate chemopreventive agents.

Prevention of chemical carcinogen DNA binding and inhibition of nuclear RNA polymerase activity by organosulfur compounds as the possible mechanisms for their anticancer initiation and proliferation effects

This report examines the transcriptional roles and DNA binding properties of the three major organosulfur compounds (OSCs) from garlic, diallyl sulfide (DAS), diallyl disulfide (DADS) and diallyl trisulfide (DATS). We found DADS and DATS, but not DAS, could be activated by the versatile epoxide-forming oxidant dimethyldioxirane (DMDO) and could strongly inhibit nuclear RNA synthesis in vitro. We also found that when incubated together with [3H]-labeled 17beta-estradiol (E(2)) for activation by DMDO, DADS and DATS, but not DAS, were able to prevent the binding of [3H]E(2) to DNA. This preventive effect of DADS and DATS was confirmed when liver microsomes were used, and further verified by 32P post-labeling analysis. Additionally, we discovered that the DMDO treated DADS and DATS, but not DAS, were able to directly inhibit the enzyme RNA polymerase per se. These novel findings provide new insights into the potential mechanisms of the preventive effects of OSCs on tumor initiation and promotion.

Relative activities of organosulfur compounds derived from onions and garlic in increasing tissue activities of quinone reductase and glutathione transferase in rat tissues

There is evidence that onions and garlic protect against cancer in humans. It has been suggested that this effect is due to the organosulfur compounds in these vegetables and that these substances act through induction of phase II detoxification enzymes. In the present studies, we have compared the ability of diallyl sulfide, dially disulfide, and diallyl trisulfide, compounds that are derived from garlic, to increase the activity of the phase II enzymes quinone reductase and glutathione transferase in a variety of rat tissues. We have also examined the onion-derived substances, dipropyl sulfide, dipropyl disulfide, dipropenyl sulfide, and dipropenyl disulfide, under identical conditions. Diallyl trisulfide and diallyl disulfide were potent inducers of the phase II enzymes. Dipropenyl disulfide was much less active, while little effect on enzyme activity was seen in animals dosed with dipropyl disulfide. Diallyl sulfide and dipropyl sulfide were weak inducers of quinone reductase and glutathione transferase, but dipropenyl sulfide was very active, with an effect similar to that of diallyl disulfide. It is possible that diallyl disulfide and diallyl trisulfide are important in the anticancer action of garlic, while dipropenyl sulfide could be involved in the beneficial action of onions.

Diallyl disulfide (DADS) induces the antitumorigenic NSAID-activated gene (NAG-1) by a p53-dependent mechanism in human colorectal HCT 116 cells

Garlic is appealing as an anti-carcinogenic agent due to its ability to induce apoptosis in vitro and inhibit the formation and growth of tumors in animals in vivo. Diallyl disulfide (DADS) is a constituent of garlic that suppresses neoplastic cell growth and induces apoptosis. We examined the effects of DADS on various cancer cell lines to better understand its effect on apoptosis and apoptosis-related genes. The nonsteroidal anti-inflammatory drug (NSAID)-activated gene (NAG-1) has proapoptotic and antitumorigenic activities and is upregulated by anticancer agents such as NSAIDs. In this study, human colorectal HCT-116 (wild-type p53), HCT-15 (p53 mutant) and human prostate PC-3 (p53 mutant) cells were exposed to DADS. DADS inhibited cell proliferation in all cell lines albeit to a lesser extent in HCT-15 and PC-3 cells at 11.5 and 23 micromol/L. In HCT-116 cells, DADS induced p53 and NAG-1 in a dose-dependent manner and the induction of p53 preceded that of NAG-1. In HCT-116 cells, NAG-1 protein expression was increased 2.4-fold +/- 0.6 at 4.6 micromol/L and 6.1-fold +/- 1.7 at 23 micromol/L DADS, whereas p53 was induced 1.5-fold +/- 0.1 and 2.3-fold +/- 0.4. DADS did not induce NAG-1 or p53 in p53 mutant cell lines; however, NAG-1 expression was induced by sulindac sulfide. HCT-116 cells treated with 4.6 and 23 micromol/L DADS resulted in a 1.9- and 2.9-fold increase in apoptosis, respectively. In contrast, 23 micromol/L DADS induced apoptosis only 1.8-fold in HCT-15 cells and not at all in PC-3 cells. Thus, DADS-induced apoptosis and NAG-1 protein expression appear to occur via p53.

Differential effects of garlic oil and its three major organosulfur components on the hepatic detoxification system in rats

The objective of this study was to compare the modulatory effect of garlic oil and its three organosulfur compounds, diallyl sulfide (DAS), diallyl disulfide (DADS), and diallyl trisulfide (DATS), on rat hepatic detoxification enzyme activity, and protein and mRNA expression. Rats were orally administered garlic oil (80 or 200 mg/kg bw), DAS (20 or 80 mg/kg bw), DADS (80 mg/kg bw), or DATS (70 mg/kg bw) three times a week for 6 weeks. Control rats received corn oil. According to the results, garlic oil and DAS in dosages of 200 and 80 mg/kg bw, respectively, significantly increased pentoxyresorufin O-dealkylase (PROD) activity as compared with the that of the control rats (P < 0.05). In contrast, N-nitrosodimethylamine demethylase activity in rats that received DADS and DATS was significantly lower than that in the control rats (P < 0.05). Ethoxyresorufin O-deethylase and erythromycin demethylase activities were not influenced by garlic oil, DAS, DADS, or DATS. To the phase II enzyme, garlic oil, DADS, and DATS significantly increased the glutathione S-transferase (GST) activity toward ethacrynic aicd (P < 0.05). Immunoblot assay showed that the protein contents of cytochrome P450 1A1, 2B1, and 3A1 were increased by garlic oil and each of three allyl sulfides, and the change among the allyl sulfides was in the order of DAS > DADS > DATS. The placental form of GST (PGST) level was also increased by garlic oil and the three allyl sulfides, but the increase among the allyl sulfides was DATS congruent with DADS > DAS. P450 2E1, however, was suppressed by each garlic component. Northern blot results indicated that the changes in P450 1A1, 2B1, 3A1, and PGST mRNA levels by garlic components were similar to those noted in the protein levels. These results indicate that the modulatory effect of garlic oil on hepatic drug-metabolizing enzymes can be attributed to its three major allyl sulfide components DAS, DADS, and DATS. These three allyl sulfides vary in modulatory activity, and this variation is related to the number of sulfur atoms in the molecule.

Modulation of cytochrome P4501-mediated bioactivation of benzo[a]pyrene by volatile allyl sulfides in human hepatoma cells

Allyl sulfides such as diallyl sulfide (DAS), diallyl disulfide (DADS), and diallyl trisulfide (DATS), typical flavor components of Allium vegetables, have been shown to inhibit benzo[a]pyrene (B[a]P)-induced carcinogenesis in animal models. As a possible mechanism of this inhibition, the effect of these volatile substances on cytochrome P450 (CYP)1 (CYP1A1, 1A2 and 1B1)-mediated bioactivation of B[a]P was investigated using a human hepatoma cell model (HepG2). DADS and DATS inhibited the B[a]P-induced ethoxyresorufin O-deethylase (EROD) activity, a marker enzyme for CYP1, by 30-90% and 70-95% at 100-1,000 microM concentration, respectively. The cell viability, an indicator of the capacity to inhibit B[a]P bioactivation, was increased by treatments of 100-1,000 microM DADS and 10-100 microM DATS. Immunoblot results indicated that the B[a]P inducible CYP1A2 protein was suppressed by 100-1,000 microM of DADS and 10-100 microM of DATS, but CYP1A1 and 1B1 were not detectable in any microsomes. Analysis of B[a]P metabolites revealed that the level of 7,8-diol formed was significantly reduced in the DADS and DATS treated microsomes as compared to the control. The level of 9,10-diol and 4,5-diol formed was also lowered by the allyl sulfide treatments. These results suggest that the protective mechanism of allyl sulfides on B[a]P-induced carcinogenesis is possibly related with the modulation of CYP1-mediated bioactivation of B[a]P.

Effects of organosulfur compounds from garlic oil on the antioxidation system in rat liver and red blood cells

The modulation of garlic oil (GO) and three allyl compounds, diallyl sulfide (DAS), diallyl disulfide (DADS) and diallyl trisulfide (DATS), on the antioxidation system in rat livers and red blood cells was examined. Rats were orally administered GO (200 mg/kg body weight), DAS (20, 80 mg/kg body weight), DADS (80 mg/kg body weight) or DATS (70 mg/kg body weight) three times a week for 6 weeks. Control rats received corn oil (2 ml/kg body weight) alone. GO, DADS and DATS treatment significantly increased the glutathione (GSH) content (48-84%) in red blood cells (P < 0.05). DATS displayed a greater enhancement than GO and DADS (P < 0.05). Hemolysis induced by tert-butyl hydroperoxide was not suppressed by GO or allyl compound treatment although higher GSH content was evident. Hepatic GSH was not influenced by garlic components. In rat livers, DADS and DATS significantly increased the activity of GSH reductase (46 and 54%, respectively) and of GSH S-transferase (GST) (63 and 103%, respectively), but decreased the GSH peroxidase activity (27 and 28%, respectively). In contrast, GSH reductase and GST activities in the DAS group, either 20 or 80 mg/kg body weight, were similar to the control group. A decrease of GSH peroxidase activity was observed in rats dosed with 80 mg/kg body weight (P < 0.05). An increase in GST activity and a decrease in GSH peroxidase activities were also noted in GO-treated rats (P < 0.05). In red blood cells, three GSH-related antioxidant enzyme activities were not affected by garlic oil and its organosulfur components. Immunoblot assay showed that, accompanying the increase in hepatic GST activity, GO, DADS, DAS (80 mg/kg body weight) and DATS increased the expression of GST Ya, Yb1 and Yc proteins. Results indicate that GO and three allyl compounds play a differential role in modulation of the GSH-related antioxidant system in rat livers and red blood cells.

Organosulfur compounds from Allium and the chemoprevention of cancer

Allium vegetables and their associated organosulfur constituents are extensively studied for their chemopreventive potential against cancer. This article overviews their anticarcinogenic and antigenotoxic properties. Epidemiological studies (mostly case-control studies) provide strong evidence that Allium vegetable consumption reduces the incidence of gastric and colon cancer while the association between Allium vegetable consumption and other cancers is less convincing. Furthermore, many experimental studies have demonstrated that organosulfur compounds and Allium extracts have inhibitory effects on carcinogenesis in animals. These inhibitory effects are supported by many diverse mechanisms, including inhibition of carcinogen formation, modulation of carcinogen metabolism, inhibition of mutagenesis and genotoxicity, inhibition of cell proliferation and increase of apoptosis, inhibition of angiogenesis, and immune system enhancement. Before such constituents or extracts can be used in chemopreventive trials, it is important to verify their lack of toxicity and to investigate further their precise mechanisms of action throughout the whole process of carcinogenesis.

Effect of organosulfur compounds from garlic and cruciferous vegetables on drug metabolism enzymes

The frequent consumption of cruciferous vegetables and garlic is associated with several health benefits. These foods contain organosulfur compounds that are known to affect the biotransformation of xenobiotics, and therefore can influence the toxicity and carcinogenicity of environmental chemicals. In this article, we review the effects of isothiocyanates and diallyl sulfide on xenobiotic metabolism and the enzymes involved in the process. Isothiocyanates and diallyl sulfide can modulate the levels of phase I and phase II drug-metabolizing enzymes by affecting the transcriptional rates of their genes, the turnover rates of specific mRNAs or enzymes, or the enzyme activity. These compounds are not general enzyme inhibitors or inducers. They elicit selectivity in their mode of action. Elucidating the mechanisms involved in the alteration of drug-metabolizing enzymes by isothiocyanates and diallyl sulfide will increase our understanding of their possible effects on the biotransformation of drugs as well as the potential beneficial or detrimental effects of these organosulfur compounds.

Mechanisms of inhibition of chemical toxicity and carcinogenesis by diallyl sulfide (DAS) and related compounds from garlic

Diallyl sulfide (DAS) is a flavor compound derived from garlic and is sequentially converted to diallyl sulfoxide (DASO) and diallyl sulfone (DASO(2)) by cytochrome P(450) 2E1 (CYP2E1). These compounds have been shown to reduce the incidence of a multitude of chemically induced tumors in animal models. The impediment of phase I activation of these carcinogens is hypothesized to be accountable for the reduction in tumor incidence. Indeed, DAS, DASO and DASO(2) are competitive inhibitors of CYP2E1. DASO(2), in addition, is a suicide inhibitor of CYP2E1. These compounds have been shown to reduce carbon tetrachloride-, N-nitrosodimethylamine- and acetaminophen-induced toxicity in rodents. All three chemicals are substrates for CYP2E1. The protective effect was observed when the organosulfur compounds were given before, during or soon after chemical treatment. DAS and DASO(2) inhibited the bioactivation of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and related lung tumorigenesis in A/J mice. Because CYP2E1 does not play a key role in NNK activation, the inhibition of other CYP enzymes active in NNK metabolism is likely. DAS also has been shown to induce other CYP and phase II enzymes as well as decrease hepatic catalase activity. All of these effects are observed at concentrations much higher than what is normally ingested by humans. The biological activities of garlic and its related compounds at lower concentrations that mimic human consumption remain to be studied further.

Diet and apoptosis

A range of compounds in or derived from the diet modulates apoptosis in cell cultures in vitro. These observations have important implications concerning the mechanisms whereby dietary components affect health. Proapoptotic compounds could protect against cancer by enhancing elimination of initiated, precancerous cells, and antiapoptotic compounds could promote tumor formation by inhibiting apoptosis in genetically damaged cells. Proapoptotic compounds could also contribute to age-related degenerative diseases by activating cell death in postmitotic cells or shifting the normal balance of mitosis and apoptosis in tissues with regenerative capacity. Many age-related diseases, for example macular degeneration and Parkinson's disease, appear to have oxidative stress as an underlying component that interacts with genetic, dietary, and environmental factors to determine relative risk in an individual. Oxidative stress activates apoptosis, and antioxidants protect against apoptosis in vitro; thus, a central role of dietary antioxidants may be to protect against apoptosis. However, little in vivo data are available to directly link diet with altered apoptosis as an underlying determinant of disease. Moreover, the possible antagonistic effects of different dietary components and the uncertainty about whether proapoptotic compounds that may protect against cancer could contribute to degenerative diseases and vice versa indicate that there is a great need for better in vivo assessment of apoptosis and that caution should be exercised when extrapolating in vitro data on apoptosis to in vivo dietary recommendations.

Purification and bioassays of a diuretic and natriuretic fraction from garlic (Allium sativum)

The intravenous administration of a purified fraction (6 microg/kg) to anaesthesized dogs was followed by a significant biphasic diuretic and natriuretic response which reached a maximum at 180 min after injection. Chloride, but not potassium ions, followed the natriuretic profile. No changes were observed in arterial blood pressure or in the electrocardiogram. The purified garlic fraction also induced an inhibitory dose-dependent effect on kidney Na, K-ATPase.

Inhibition of cholesterol biosynthesis by organosulfur compounds derived from garlic

The study was undertaken to test the inhibitory potential on cholesterogenesis of organosulfur compounds derived from garlic. The primary rat hepatocytes maintained in Dulbecco's modified Eagle's medium were treated with [2-14C]acetate as substrate for cholesterol synthesis in the presence or absence of test compounds at 0.05 to 4.0 mmol/L. Eleven water-soluble and six lipid-soluble compounds of garlic were tested. Among water-soluble compounds, S-allyl cysteine (SAC), S-ethyl cysteine (SEC), and S-propyl cysteine (SPC) inhibited [2-14C]acetate incorporation into cholesterol in a concentration-dependent manner, achieving 42 to 55% maximal inhibition. Gamma-glutamyl-S-allyl cysteine, gamma-glutamyl-S-methyl cysteine, and gamma-glutamyl-S-propyl cysteine were less potent, exerting only 16 to 29% maximal inhibitions. Alliin, S-allyl-N-acetyl cysteine, S-allylsulfonyl alanine, and S-methyl cysteine had no effect on cholesterol synthesis. Of the lipid-soluble compounds, diallyl disulfide (DADS), diallyl trisulfide (DATS), and dipropyl disulfide (DPDS) depressed cholesterol synthesis by 10 to 25% at low concentrations (< or =0.5 mmol/L), and abolished the synthesis at high concentrations (> or =1.0 mmol/L). Diallyl sulfide, dipropyl sulfide, and methyl allyl sulfide slightly inhibited [2-14C]acetate incorporation into cholesterol only at high concentrations. The complete depression of cholesterol synthesis by DADS, DATS, and DPDS was associated with cytotoxicity as indicated by marked increase in cellular LDH release. There was no apparent increase in LDH secretion by water-soluble compounds except S-allyl mercaptocysteine, which also abolished cholesterol synthesis. Judging from maximal inhibition and IC50 (concentration required for 50% of maximal inhibition), SAC, SEC, and SPC are equally potent in inhibiting cholesterol synthesis.

Tissue distribution of silibinin, the major active constituent of silymarin, in mice and its association with enhancement of phase II enzymes: implications in cancer chemoprevention

Polyphenolic antioxidants are being identified as cancer preventive agents. Recent studies in our laboratory have identified and defined the cancer preventive and anticarcinogenic potential of a polyphenolic flavonoid antioxidant, silymarin (isolated from milk thistle). More recent studies by us found that these effects of silymarin are due to the major active constituent, silibinin, present therein. Here, studies are done in mice to determine the distribution and conjugate formation of systemically administered silibinin in liver, lung, stomach, skin, prostate and pancreas. Additional studies were then performed to assess the effect of orally administered silibinin on phase II enzyme activity in liver, lung, stomach, skin and small bowel. For tissue distribution studies, SENCAR mice were starved for 24 h, orally fed with silibinin (50 mg/kg dose) and killed after 0.5, 1, 2, 3, 4 and 8 h. The desired tissues were collected, homogenized and parts of the homogenates were extracted with butanol:methanol followed by HPLC analysis. The column eluates were detected by UV followed by electrochemical detection. The remaining homogenates were digested with sulfatase and beta-glucuronidase followed by analysis and quantification. Peak levels of free silibinin were observed at 0.5 h after administration in liver, lung, stomach and pancreas, accounting for 8.8 +/- 1.6, 4. 3 +/- 0.8, 123 +/- 21 and 5.8 +/- 1.1 (mean +/- SD) microg silibinin/g tissue, respectively. In the case of skin and prostate, the peak levels of silibinin were 1.4 +/- 0.5 and 2.5 +/- 0.4, respectively, and were achieved 1 h after administration. With regard to sulfate and beta-glucuronidate conjugates of silibinin, other than lung and stomach showing peak levels at 0.5 h, all other tissues showed peak levels at 1 h after silibinin administration. The levels of both free and conjugated silibinin declined after 0.5 or 1 h in an exponential fashion with an elimination half-life (t((1/2))) of 57-127 min for free and 45-94 min for conjugated silibinin in different tissues. In the studies examining the effect of silibinin on phase II enzymes, oral feeding of silibinin at doses of 100 and 200 mg/kg/day showed a moderate to highly significant (P < 0.1-0.001, Student's t-test) increase in both glutathione S-transferase and quinone reductase activities in liver, lung, stomach, skin and small bowel in a dose- and time-dependent manner. Taken together, the results of the present study clearly demonstrate the bioavailability of and phase II enzyme induction by systemically administered silibinin in different tissues, including skin, where silymarin has been shown to be a strong cancer chemopreventive agent, and suggest further studies to assess the cancer preventive and anticarcinogenic effects of silibinin in different cancer models.

Low doses of diallyl disulfide, a compound derived from garlic, increase tissue activities of quinone reductase and glutathione transferase in the gastrointestinal tract of the rat

Diallyl disulfide (DADS), a substance that is formed from the organosulfur compounds present in garlic, is known to increase tissue activities of the phase II detoxification enzymes quinone reductase (QR) and glutathione transferase (GT) in animals. In previous experiments, however, high doses of DADS were employed and only a limited range of tissues were examined. In the present studies, increased activities of QR and GT were recorded in the forestomach, glandular stomach, duodenum, jejunum, ileum, cecum, colon, liver, kidneys, spleen, heart, lungs, and urinary bladder of rats given DADS over a wide range of dose levels. Large variations in response were recorded among the different organs, with forestomach, duodenum, and jejunum being the most sensitive to enzyme induction by DADS. In these organs, significant increases in QR activity were observed at a dose of only 0.3 mg/kg/day. Such a dose level is close to that which may be achieved through human consumption of garlic, suggesting that induction of phase II enzymes may contribute to the protection that is afforded by this vegetable against cancer of the gastrointestinal tract in humans.

Modulation of phase II enzymes by organosulfur compounds from allium vegetables in rat tissues

The naturally occurring organosulfur compounds (OSCs) diallyl sulfide (DAS), diallyl disulfide (DADS), dipropyl sulfide (DPS), and dipropyl disulfide (DPDS) were studied with respect to their effects on hepatic, intestinal, renal, and pulmonary phase II drug metabolizing enzymes, i.e., glutathione S-transferase (GST), microsomal epoxide hydrolase (mEH), quinone reductase (QR), and UDP-glucuronosyltransferase (UGT). OSCs were administered po to male SPF Wistar rats. In addition to assays of total enzyme activity, the ability of OSCs to modify the levels of mEH and rGSTA1/A2, A3/A5, M1, M2, and P1 was assessed by Western blotting. Remarkably, DADS significantly increased all Phase II enzyme activities, except the pulmonary mEH. It was noteworthy that only DADS induced QR activity. DAS, DPS, and DPDS induced mEH, GST, and UGT activities in the liver. Interestingly, DAS, DPS, and DPDS significantly decreased renal GST activity. In the same manner, DAS, DPS, and DPDS decreased rGSTA1/A2 and A3/A5 levels in the kidney. Conversely, all OSCs were able to induce GST of alpha and mu classes in the liver. In the intestine, DADS and DAS increased rGSTA1/A2, M2, and P1, while rGSTA3/A5 and M2 were only increased by DADS. In addition, DADS induced rGSTP1 dramatically in the four tissues analyzed. DADS also increased the mEH levels in the liver, intestine, and kidney, while DAS and DPS moderately induced mEH level in the liver. This study brings additional insights into the effects of OSCs on Phase II enzymes and suggests that DADS could be a promising chemopreventive agent considering its pleiotropic capacity of induction.

Protective effects of diallyl sulfide on N-nitrosodimethylamine-induced immunosuppression in mice

Diallyl sulfide (DAS), a flavor component of garlic that has been used as a food additive, exerts chemopreventive effects at several organ sites in rodents after administration of chemical carcinogens possibly by inhibiting carcinogen activation via cytochrome P450-mediated oxidative metabolism. In this study, we investigated the protective effect of DAS on the N-nitrosodimethylamine (NDMA)-induced immunosuppression of humoral and cellular responses in BALB/c mice and the possible mechanisms involved in this protection. We observed that oral administration of DAS prior to NDMA treatment for 14 consecutive days blocked the NDMA-induced suppression of the antibody response to a T-cell-dependent antigen, sheep erythrocytes, and the lymphoproliferative response to the T-cell and the B-cell mitogens in dose-dependent manners. Treatment of mice with DAS resulted in a significant decrease of cytochrome P450 2E1-dependent p-nitrophenol hydroxylase and NDMA demethylase activities. The results show that the protective effects of DAS against the NDMA-induced immunotoxicity may, at least in part, be due to its ability to block bioactivation of NDMA mainly by the inhibition of cytochrome P450 2E1.

Antitumour activity of diallyl sulfide on polycyclic aromatic hydrocarbon-induced mouse skin carcinogenesis

Diallyl sulfide (DAS), a major flavour component of garlic, is known to modulate xenobiotic metabolism and possess antitoxic, bactericidal, antineoplastic, hypolipidemic and hypocholesteromic effects. In the present study, the anticarcinogenic activity of DAS on a 7,12-dimethylbenzanthracene (DMBA)- or benzo[a]pyrene (B(a)P)-induced mouse skin model of carcinogenesis was evaluated. DAS was applied topically either 1 h prior to or 1 h after the administration of DMBA or B(a)P. A significant protection from neoplasia was observed in DAS- and DMBA/B(a)P-exposed animals when DAS was applied topically compared to the animals exposed only to DMBA/B(a)P. In the animals where DAS was applied 1 h prior to the application of DMBA, a lower magnitude of neoplasia was recorded in terms of the cumulative number of tumours and average number of tumours per mouse during the entire period of study (28 weeks) compared to the animals exposed to DAS 1 h later, while in B(a)P-exposed animals, the antitumorigenic potential of DAS was more evident in the mice treated with DAS 1 h after the B(a)P exposure compared to the animals treated with DAS 1 h prior to B(a)P. The antitumour activity of DAS was of a much higher magnitude in B(a)P-induced carcinogenesis in comparison to animals exposed to DMBA in terms of tumour incidence, cumulative number of tumours and average number of tumours per mouse. The results suggest that DAS has a protective effect in PAH-induced mouse skin carcinogenesis.

Differential induction of NAD(P)H:quinone oxidoreductase by anti-carcinogenic organosulfides from garlic

This study was undertaken to elucidate the mechanism of organ specificity and differential efficacy of garlic organosulfides (OSCs) [diallyl sulfide (DAS), diallyl disulfide (DADS), diallyl trisulfide (DATS), dipropyl sulfide (DPS) and dipropyl disulfide (DPDS)] in preventing benzo(a)pyrene (BP)-induced tumorigenesis in mice. The results of the present study reveal a good correlation between chemopreventive efficacies of garlic OSCs and their inductive effects on the expression of NAD(P)H:quinone oxidoreductase (NQO), an enzyme implicated in the detoxification of activated quinone metabolites of BP. Treatment of mice with DADS and DATS, which are potent inhibitors of BP-induced forestomach tumorigenesis, resulted in a statistically significant increase (2.4- and 1.5-fold, respectively) in forestomach NQO activity. In addition, DADS and DATS were much more potent inducers of forestomach NQO activity than DAS, which is a weak inhibitor of BP-induced forestomach tumorigenesis than the former compounds. Propyl-group containing OSCs (DPS and DPDS), which do not inhibit BP-induced tumorigenesis, did not affect forestomach NQO activity. Similar to forestomach, a good correlation was also observed between effects of these OSCs against BP-induced pulmonary tumorigenesis and their effects on NQO expression in the lung. For example, treatment of mice with DAS, which is a potent inhibitor of BP-induced pulmonary tumorigenesis, resulted in about 3.2-fold increase in pulmonary NQO activity. On the other hand, this activity was increased by about 1.5-fold upon DATS administration, which does not inhibit BP-induced cancer of the lung. In conclusion, our results suggest that induction of NQO may be important in anti-cancer effects of garlic OSCs.