Allicin purified from fresh garlic cloves induces apoptosis in colon cancer cells via Nrf2

Allicin (diallyl thiosulfinate) is the best-known biologically active component in freshly crushed garlic extract. We developed a novel, simple method to isolate active allicin, which yielded a stable compound in aqueous solution amenable for use in in vitro and in vivo studies. We focused on the in vitro effects of allicin on cell proliferation of colon cancer cell lines HCT-116, LS174T, HT-29, and Caco-2 and assessed the underlying mechanisms. This allicin preparation exerted a time- and dose-dependent cytostatic effect on these cells at concentrations ranging from 6.2 to 310 μM. Treatment with allicin resulted in HCT-116 apoptotic cell death as demonstrated by enhanced hypodiploid DNA content, decreased levels of B-cell non-Hodgkin lymphoma-2 (Bcl-2), increased levels of bax and increased capability of releasing cytochrome c from mitochondria to the cytosol. Allicin also induced translocation of NF-E2-related factor-2 (Nrf2) to the nuclei of HCT-116 cells. Luciferase reporter gene assay showed that allicin induces Nrf2-mediated luciferase transactivation activity. SiRNA knock down of Nrf2 significantly affected the capacity of allicin to inhibit HCT-116 proliferation. These results suggest that Nrf2 mediates the allicin-induced apoptotic death of colon cancer cells.     

Effect of purified allicin, the major ingredient of freshly crushed garlic, on cancer cell proliferation

The diverse health benefit effects of garlic include its anticancer activity. However, very little is known about such activity of isolated garlic compounds, among which allicin (the major ingredient of crushed garlic) has been the least studied. The aim of this work was to determine whether pure allicin exhibits the antiproliferative effect reported for garlic in in vitro models. Allicin, but not its precursor alliin, inhibited proliferation of human mammary (MCF-7), endometrial (Ishikawa), and colon (HT-29) cancer cells (50% inhibitory concentration = 10-25 microM). Two of three tested primary lines of human fibroblasts displayed a similar response to allicin (50% inhibitory concentration = 16-40 microM), whereas the third line was almost unaffected by this compound. The pure allicin and water extract of garlic powder with equivalent allicin concentrations displayed a similar potency, suggesting that allicin is responsible for the antiproliferative effect of the extract. The growth inhibition was accompanied by accumulation of cells in the G0/G1 and G2/M phases of the cell cycle (MCF-7 cells) and not by a significant increase in cell death. Allicin caused a transient drop in the intracellular glutathione (GSH) level, the magnitude and kinetics of which significantly varied depending on cell type. The extent of the decrease in GSH levels correlated well (r = 0.75) with the growth inhibitory activity of allicin. On the basis of these findings, we suggest that allicin plays a major role in the antiproliferative effect of water-soluble garlic preparations and that this effect may be attributed to the ability of allicin to transiently deplete the intracellular GSH level.     

Anticolon Cancer Effect of Korean Red Ginseng via Autophagy- and Apoptosis-Mediated Cell Death

Ginseng (Panax ginseng Meyer) has been used in East Asian traditional medicine for a long time. Korean red ginseng (KRG) is effective against several disorders, including cancer. The cytotoxic effects of KRG extract in terms of autophagy- and apoptosis-mediated cell death and its mechanisms were investigated using human colorectal cancer lines. KRG induced autophagy-mediated cell death with enhanced expression of Atg5, Beclin-1, and LC3, and formed characteristic vacuoles in HCT-116 and SNU-1033 cells. An autophagy inhibitor prevented cell death induced by KRG. KRG generated mitochondrial reactive oxygen species (ROS); antioxidant countered this effect and decreased autophagy. KRG caused apoptotic cell death by increasing apoptotic cells and sub-G₁ cells, and by activating caspases. A caspase inhibitor suppressed cell death induced by KRG. KRG increased phospho-Bcl-2 expression, but decreased Bcl-2 expression. Moreover, interaction of Bcl-2 with Beclin-1 was attenuated by KRG. Ginsenoside Rg2 was the most effective ginsenoside responsible for KRG-induced autophagy- and apoptosis-mediated cell death. KRG induced autophagy- and apoptosis-mediated cell death via mitochondrial ROS generation, and thus its administration may inhibit colon carcinogenesis.     

Colon cancer proliferating desulfosinigrin in wasabi (Wasabia japonica)

A reduced incidence of different types of cancer has been linked to consumption of Brassica vegetables, and there is evidence that glucosinolates (GSLs) and their hydrolysis products play a role in reducing cancer risk. Wasabi (Wasabia japonica) and horseradish (Armoracia rusticana), both Brassica vegetables, are widely used condiments both in Japanese cuisine and in the United States. Desulfosinigrin (DSS) (1) was isolated from a commercially available wasabi powder and from fresh wasabi roots. Sinigrin (2) was isolated from horseradish roots. DSS and sinigrin were evaluated for their inhibitory effects on cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2) enzymes, on lipid peroxidation, and on the proliferation of human colon (HCT-116), breast (MCF-7), lung (NCIH460), and central nervous system (CNS, SF-268) cancer cell lines. DSS did not inhibit COX enzymes or lipid peroxidation at 250 microg/ml. Sinigrin inhibited lipid peroxidation by 71% at 250 microg/ml. However, DSS promoted the growth of HCT-116 (colon) and NCI H460 (lung) human cancer cells as determined by the MTT assay in a concentration-dependent manner. At 3.72 microg/ml, a 27% increase in the number of viable human HCT-116 colon cancer cells was observed; the corresponding increases at 7.50 and 15 microg/ml were 42 and 69%, respectively. At 60 microg/ml, DSS doubled the number of HCT-16 colon cancer cells. For NCI H460 human lung cancer cells, DSS at 60 microg/ml increased the cell number by 20%. Sinigrin showed no proliferating effect on the tumor cells tested. This is the first report of the tumor cell-proliferating activity by a desulfoglucosinolate, the biosynthetic precursor of GSLs found in Brassica spp.     

Allicin up-regulates cellular glutathione level in vascular endothelial cells

Background  Allicin in garlic is the primary active compound known to rapidly interact with free thiols. Aims of the study  To examine the effect of allicin on gene expression and glutathione cellular level in vascular endothelial cells. Methods  Cultured endothelial cells were exposed to allicin; mRNA was prepared and subjected to Micro-array and Real-Time PCR. Glutathione cellular level was determined on cell lysates. Results  Micro-array analysis demonstrated allicin-induced up- and down-regulation of 116 and 100 genes, respectively. Up-regulated genes included the phase II detoxifying enzymes thioredoxin reductase 1 and 2, heme oxygenase-1 and glutamate cysteine lygaze modifier subunit, the rate limiting enzyme in glutathione biosynthesis. Endothelial cells exposed to allicin and its derivatives containing glutathione or cysteine residues increased cellular glutathione. Allicin increased the glutathione level in a concentration and time-dependent manner up to 8-fold at a concentration of 10–20 μM after 28 h exposure. Furthermore, allicin derivative-treated cultures demonstrated a 50% decrease in tBuOOH cytotoxicity. Conclusions  These results may suggest a putative role for allicin and its derivatives in preventing reactive oxygen species damage by up-regulating the phase II detoxifying enzymes and increasing the cellular glutathione level.     

大蒜素对子宫颈癌Hela细胞增殖的影响

目的:探讨大蒜素对宫颈癌Hela细胞增殖的影响。方法:不同浓度的大蒜素作用于体外培养的Hela细胞,倒置显微镜下观察Hela细胞的形态学变化;采用MTT法检测大蒜素对Hela细胞增殖抑制能力,采用流式细胞术分析大蒜素对Hela细胞凋亡的影响。结果:MTT显示大蒜素能抑制人宫颈癌Hela细胞的增殖,并具有时间-剂量依赖性;流式细胞术测定结果显示50μg/ml浓度的大蒜素可明显诱导Hela细胞凋亡,并将细胞周期阻滞在G2/M期。结论:大蒜素对人宫颈癌Hela细胞的生长有抑制作用,其抑制作用与诱导Hela细胞凋亡和阻抑细胞周期有关。     

Piceatannol, a natural analog of resveratrol, inhibits progression through the S phase of the cell cycle in colorectal cancer cell lines

Piceatannol, a naturally occurring analog of resveratrol, was previously identified as the active ingredient in herbal preparations in folk medicine and as an inhibitor of p72(Syk). We studied the effects of piceatannol on growth, proliferation, differentiation and cell cycle distribution profile of the human colon carcinoma cell line Caco-2. Growth of Caco-2 and HCT-116 cells was analyzed by crystal violet assay, which demonstrated dose- and time-dependent decreases in cell numbers. Treatment of Caco-2 cells with piceatannol reduced proliferation rate. No effect on differentiation was observed. Determination of cell cycle distribution by flow cytometry revealed an accumulation of cells in the S phase. Immunoblotting demonstrated that cyclin-dependent kinases (cdk) 2 and 6, as well as cdc2 were expressed at steady-state levels, whereas cyclin D1, cyclin B1 and cdk 4 were downregulated. The abundance of p27(Kip1) was also reduced, whereas the protein level of cyclin E was enhanced. Cyclin A levels were enhanced only at concentrations up to 100 micromol/L. These changes also were observed in studies with HCT-116 cells. On the basis of our findings, piceatannol can be considered to be a promising chemopreventive or anticancer agent.     

Phosphatidylinositol 3-Kinase Mediates the Ability of Retinol to Decrease Colorectal Cancer Cell Invasion

Previously, we showed that retinol (vitamin A) decreased both colorectal cancer cell invasion and phosphatidylinositol 3-kinase (PI3K) activity through a retinoic acid receptor–independent mechanism. Here, we determined if these phenomena were related by using parental HCT-116 cells that harbor 1 allele of wild-type PI3K and 1 allele of constitutively active (ca) PI3K and 2 mutant HCT-116 cell lines homozygous for caPI3K. In vitro, treatment of parental HCT-116 cells with 10 μM retinol reduced cell invasion whereas treatment of mutant HCT-116 cell lines with retinol did not. Treatment with 10 μM retinol also decreased the activity of matrixmetalloproteinase-9 and increased tissue inhibitor of matrixmetalloproteinase-I levels in parental, but not mutant, HCT-116 cells. Finally, parental or mutant cells were intrasplenically injected into athymic mice consuming diets with or without supplemental vitamin A. As expected, vitamin A supplementation tended (P = 0.18) to reduce the incidence of metastases in mice injected with the parental cell line and consuming the supplemented diet. In contrast, metastatic incidence was not affected (P = 1.00) by vitamin A supplementation in mice injected with mutant cells. These data indicate that the capacity of retinol to inhibit PI3K activity confers its ability to decrease colorectal cancer metastasis.     

Allicin inhibits spontaneous and TNF-alpha induced secretion of proinflammatory cytokines and chemokines from intestinal epithelial cells

BACKGROUND & AIMS: Allicin, the active substance of fresh crushed garlic has different biological activities and was implicated as an anti-inflammatory agent. Epithelial cells have an important role in intestinal inflammation. The aim of this study was to assess the immunomodulatory effect of allicin on intestinal epithelial cells. METHODS: The spontaneous and TNF-alpha-stimulated secretion of IL-1beta, IL-8, IP-10 and MIG from HT-29 and Caco-2 cells was tested with, or without pretreatment with allicin. Cytokine secretion was assessed using ELISA and expression of mRNA was determined by an RNA protection assay. RESULTS: Allicin markedly inhibited the spontaneous and TNF-alpha -induced secretion of IL-1beta, IL-8, IP-10 and MIG from the two different cell lines in a dose-dependent manner and suppressed the expression of IL-8 and IL-1beta mRNA levels. In addition, allicin suppressed the degradation of IkappaB. No effect on cell viability was noted. CONCLUSIONS: These observations indicate that allicin exerts an inhibitory immunomodulatory effect on intestinal epithelial cells and suggest that allicin may have the potential to attenuate intestinal inflammation.     

Dual Effects of Resveratrol on Cell Death and Proliferation of Colon Cancer Cells

Colorectal cancer remains a main cause of deaths worldwide, and novel agents are being searched to treat this disease. Polyphenols have emerged as promising therapeutic tools in cancer. Resveratrol (3,5,4′-trihydoxy-trans-stilbene) induces cell death in different tumor cell lines, and it also stimulates the proliferation of specific breast and prostate cancer cell lines. Here, we studied the impact of resveratrol over a 100-fold concentration range on cell death and proliferation of HT-29 colorectal adenocarcinoma cells. After 96 h of treatment, a biphasic pattern was observed. At lower concentrations (1 and 10 μmol/l), resveratrol increased the cell number, as did the polyphenol quercetin. At 50 or 100 μmol/l, resveratrol reduced the cell number and increased the percentage of apoptotic or necrotic cells, thus indicating cytotoxicity. On HCT116 colon cancer cells, however, no proliferative properties of resveratrol were observed. Resveratrol-induced cytotoxicity on HT-29 cells was associated with NADPH oxidase activation and increased levels of histone γH2AX, a marker of DNA damage, paralleled by enhanced sirtuin 6 levels, likely as a repair mechanism. Overall, resveratrol may be an effective tool in anti-tumor chemotherapy. However, since under some conditions it may favor tumor cell growth, appropriate local concentrations must be achieved to minimize unwanted effects of resveratrol.     

Curcumin Synergizes With Resveratrol to Inhibit Colon Cancer

Development and progression of many malignancies, including colorectal cancer, are associated with activation of multiple signaling pathways. Therefore, inhibition of these signaling pathways with noncytotoxic natural products represents a logical preventive and/or therapeutic approach for colon cancer. Curcumin and resveratrol, both of which inhibit the growth of transformed cells and colon carcinogenesis, were selected to examine whether combining them would be an effective preventive and/or therapeutic strategy for colon cancer. Indeed, the combination of curcumin and resveratrol was found to be more effective in inhibiting growth of p53-positive (wt) and p53-negative colon cancer HCT-116 cells in vitro and in vivo in SCID xenografts of colon cancer HCT-116 (wt) cells than either agent alone. Analysis by Calcusyn software showed synergism between curcumin and resveratrol. The inhibition of tumors in response to curcumin and/or resveratrol was associated with the reduction in proliferation and stimulation of apoptosis accompanied by attenuation of NF-κB activity. In vitro studies have further demonstrated that the combinatorial treatment caused a greater inhibition of constitutive activation of EGFR and its family members as well as IGF-1R. Our current data suggest that the combination of curcumin and resveratrol could be an effective preventive/therapeutic strategy for colon cancer.     

c-Fos对结直肠癌细胞HCT-116影响

目的 探讨AP-1转录因子组成成分之一c-Fos对结直肠癌细胞增殖和凋亡的影响。方法 将合成的siRNA转染入HCT-116细胞中,实时定量PCR法检测其中c-Fos的含量;利用四甲基偶氮唑盐（MTT）显色法检测c-Fos被敲低后对细胞生长增殖的影响;Etoposide诱导细胞凋亡,溴化丙啶（PI）染色、流式细胞仪检测细胞凋亡的改变。结果 siRNA转染结直肠癌细胞HCT-116 48 h后,与对照组相比,c-Fos的含量降低约50%;MTT实验中RNAi组细胞增殖速度时间增加,加入etoposide（100 μmol/L）12 h后,对照组细胞凋亡率为（27.6±2.07）%,RNAi组细胞的凋亡率为（39.1±4.84）%,凋亡率降低。结论 c-Fos在HCT-116细胞中发挥着促进细胞生长和抑制凋亡的作用。     

The effects of short-chain fatty acids on human colon cancer cell phenotype are associated with histone hyperacetylation

The short-chain fatty acid (SCFA) butyrate is produced via anaerobic bacterial fermentation within the colon and is thought to be protective in regard to colon carcinogenesis. Although butyrate (C4) is considered the most potent of the SCFA, a variety of other SCFA also exist in the colonic lumen. Butyrate is thought to exert its cellular effects through the induction of histone hyperacetylation. We sought to determine the effects of a variety of the SCFA on colon carcinoma cell growth, differentiation and apoptosis. HT-29 or HCT-116 (wild-type and p21-deleted) cells were treated with physiologically relevant concentrations of various SCFA, and histone acetylation state was assayed by acid-urea-triton-X gel electrophoresis and immunoblotting. Growth and apoptotic effects were studied by flow cytometry, and differentiation effects were assessed using transient transfections and Northern blotting. Propionate (C3) and valerate (C5) caused growth arrest and differentiation in human colon carcinoma cells. The magnitude of their effects was associated with a lesser degree of histone hyperacetylation compared with butyrate. Acetate (C2) and caproate (C6), in contrast, did not cause histone hyperacetylation and also had no appreciable effects on cell growth or differentiation. SCFA-induced transactivation of the differentiation marker gene, intestinal alkaline phosphatase (IAP), was blocked by histone deacetylase (HDAC), further supporting the critical link between SCFA and histones. Butyrate also significantly increased apoptosis, whereas the other SCFA studied did not. The growth arrest induced by the SCFA was characterized by an increase in the expression of the p21 cell-cycle inhibitor and down-regulation of cyclin B1 (CB1). In p21-deleted HCT-116 colon cancer cells, the SCFA did not alter the rate of proliferation. These data suggest that the antiproliferative, apoptotic and differentiating properties of the various SCFA are linked to the degree of induced histone hyperacetylation. Furthermore, SCFA-mediated growth arrest in colon carcinoma cells requires the p21 gene.     

重组人生长激素体外激活人结肠癌细胞JAK2-STAT3通路

目的探讨重组人生长激素（rhGH）对不同生长激素受体（GHR）表达状态的人结肠癌细胞生长及JAK2-STAT3通路的影响。方法采用流式细胞术根据GHR表达状态不同筛选结肠癌细胞株,选择LOVO细胞株和HCT-8细胞株进入实验,采用MTT法分析rhGH对人结肠癌细胞生长的作用,采用流式细胞术进行细胞增殖指数（PI）、细胞周期分析及凋亡检测,采用蛋白质印迹法分析JAK2-STAT3通路相关分子的蛋白水平变化。结果HCT-8细胞株GHR呈阳性表达（59．6％）,LOVO细胞株GHR呈阴性表达（3．5％）。rhGH显著促进HCT-8细胞生长,G2／M期比例明显高于未处理组（P=0．0073）,PI升高,凋亡率降低,且pJAK2、pSTAT3、VEGF、CyelinD1、Bcl-xL蛋白表达增加。经rhGH处理后,LOVO细胞的上述各项检测指标未出现明显变化。结论rhGH促进GHR表达较高的HCT-8细胞生长,上调JAK2-STAT3信号转导通路多个关键节点的基因表达;不促进GHR低表达的LOVO细胞生长及JAK2-STAT3通路因子表达变化。     

Prolonged sulforaphane treatment activates survival signaling in nontumorigenic NCM460 colon cells but apoptotic signaling in tumorigenic HCT116 colon cells

Sulforaphane (SFN) is a naturally occurring chemopreventive agent; the induction of cell cycle arrest and apoptosis is a key mechanism by which SFN exerts its colon cancer prevention. However, little is known about the differential effects of SFN on colon cancer and normal cells. In this study, we demonstrated that SFN (15 μmol/L) exposure (72 h) inhibited cell proliferation by up to 95% in colon cancer cells (HCT116) and by 52% in normal colon mucosa-derived (NCM460) cells. Our data also showed that SFN exposure (5 and 10 μmol/L) led to the reduction of G1 phase cell distribution and an induction of apoptosis in HCT116 cells, but to a much lesser extent in NCM460 cells. Furthermore, the examination of mitogen-activated protein kinase (MAPK) signaling status revealed that SFN upregulated the phosphorylation of extracellular-regulated kinase 1/2 (ERK1/2) in NCM460 cells but not in HCT116 cells. In contrast, SFN enhanced the phosphorylation of stress-activated protein kinase (SAPK) and decreased cellular myelocytomatosis oncogene (c-Myc) expression in HCT116 cells but not NCM460 cells. Taken together, the activation of survival signaling in NCM460 cells and apoptotic signaling in HCT116 cells may play a critical role in SFN's stronger potential of inhibiting cell proliferation in colon cancer cells than in normal colon cells.     

Superior inhibitory efficacy of butyrate over propionate and acetate against human colon cancer cell proliferation via cell cycle arrest and apoptosis: linking dietary fiber to cancer prevention

Intake of dietary fiber may protect against colon cancer. The anticancer property is associated with an increased production of short chain fatty acids (SCFAs), including acetate, propionate and butyrate, during dietary fiber fermentation in the colon. However, the mechanisms remain to be determined. We hypothesized that butyrate exhibits a stronger inhibitory potential against colon cancer cell proliferation compared with acetate and propionate. We determined the half maximal inhibitory concentrations (IC₅₀) of SCFAs in HCT116 human colon cancer cell proliferation by examining cell growth curves. At 24- and 48-hour time points, IC₅₀ (mmol/L) concentrations of acetate, propionate, and butyrate were [66.0 and 29.0], [9.2 and 3.6], and [2.5 and 1.3], respectively. Consistent with the greater anti-proliferative effect, butyrate exhibits >3-fold stronger potential for inducing cell cycle arrest at the G2 phase with a drop in S-phase fraction (including c-Myc/p21 signaling) and apoptosis when compared with acetate and propionate. Subsequently, we focused on the effect of butyrate on apoptotic gene expression. Using a PCR array analysis, we identified 17 pro-apoptotic genes, 6 anti-apoptotic genes, and 4 cellular mediator genes with >1-fold increase or decrease in mRNA levels out of 93 apoptosis related genes in butyrate-treated HCT116 cells when compared with untreated HCT116 cells. These genes were mainly involved in the TNF, NFκB, CARD, and BCL-2 regulated pathways. Taken together, our data indicate a greater inhibitory efficacy of butyrate over propionate and acetate against human colon cancer cell proliferation via cell cycle arrest and apoptosis.     

The growth-inhibitory effects of tomatoes digested in vitro in colon adenocarcinoma cells occur through down regulation of cyclin D1, Bcl-2 and Bcl-xL

In the present study, we utilised an in vitro digestion procedure to deliver molecules contained in tomatoes to cultured cells and to analyse potential mechanisms underlying the antitumoural effects of tomatoes reported in the literature. Ripe tomatoes underwent in vitro simulated digestion and the aqueous fraction obtained was delivered to HT-29 and HCT-116 colon adenocarcinoma cells. The amount of lycopene released during digestion and transferred to the aqueous fraction during digestion was 10-fold lower than that present in tomato homogenate before digestion. The carotenoid was accumulated by colon adenocarcinoma cells in a dose-dependent manner after the addition of tomato digestate (20-100 ml/l) for 24 h. Tomato digestate inhibited the growth of HT-29 and HCT-116 cells in a dose-dependent manner. Growth inhibition resulted from an arrest of cell cycle progression at the G0/G1 phase and by apoptosis induction. A down regulation of cyclin D1, Bcl-2 and Bcl-xL expression was also observed, without apparent changes in p53, p21, p27 and Bax. In conclusion, the present data demonstrate that the in vitro digestion procedure represents a useful approach to supply tomato to colon cultured cells. Moreover, we have shown that tomato digestate is able to inhibit the growth of colon cancer cells by modulating the expression of regulators of the cell cycle and apoptosis.     

金雀异黄酮对结肠癌细胞HT-29增殖及凋亡的影响

目的观察植物雌激素金雀异黄酮(GS)对人结肠癌细胞HT-29增殖及凋亡的影响,并初步探讨其分子生物学作用机制。方法采用MTT比色法和流式细胞术检测GS对HT-29细胞增殖活力和细胞周期分布的影响;CellDeathELISA和流式细胞术从不同方面检测GS对HT-29细胞凋亡的影响;RT-PCR和Western-blot技术检测GS对核增殖抗原PCNA、bcl-2和baxmRNA和蛋白质表达的影响。结果与对照组相比,在15~120μmol/L浓度范围内,GS能够抑制HT-29细胞增殖活力;降低S细胞分布比例,将细胞周期滞留在G2/M期;显著性诱导HT-29细胞凋亡(>30μmol/L,P<0.05),并呈现出良好的剂量-效应关系。检测GS对PCNA、bcl-2和bax表达的影响显示,GS能够抑制PCNA和bcl-2mRNA和蛋白质表达,对bax的表达则表现出促进作用。结论GS通过诱导HT-29细胞凋亡而抑制其增殖活力,这些效应与PCNA、bcl-2和bax的表达变化有关。这些资料可为结肠癌的早期预防提供膳食干预新途径,并为临床新药的开发提供新方案。