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ABSTRACT: In the present study, we have evaluated the pharmacokinetics and the in vivo prostate chemopreventive activity of broccoli sprouts.
The in vivo pharmacokinetic profiles of sulforaphane (SFN) and SFN- glutathione (GSH) conjugate in rats after oral administration of 200 mg and 500 mg broccoli sprouts were analyzed. Next, 8-week old TRAMP mice were fed with dietary broccoli sprouts at two dosages (60 and 240 mg/mouse/day) for 16 weeks, and the mice were sacrificed to examine the pharmacodynamic response on prostate tumor and some biomarkers.
SFN was readily released and conjugated with GSH in the rats after oral administration of broccoli sprouts. TRAMP mice fed with 240 mg broccoli sprouts/mouse/day exhibited a significant retardation of prostate tumor growth. Western blot analysis revealed that the expression levels of Nrf2, HO-1, cleaved-Caspase-3, cleaved-PARP and Bax proteins were increased, but that of Keap1 and Bcl-XL proteins were decreased. In addition, the phosphorylation and/or the expression level of Akt and its downstream kinase and target proteins, e.g. mTOR, 4E-BP1 and cyclin D1, were reduced.
Our findings indicate that broccoli sprouts can serve as a good dietary source of SFN in vivo and that they have significant inhibitory effects on prostate tumorigenesis.
Pharmaceutical Research 09/2009; 26(10):2324-31. · 4.09 Impact Factor
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ABSTRACT: Many cancer chemopreventive agents have been associated with lower cancer risk by suppressing nuclear factor-kappaB (NF-kappaB) signaling pathways, which subsequently leads to attenuated pro-inflammatory mediators and activities. Of the natural compounds, the isothiocyanates (ITCs) found in cruciferous vegetables have received particular attention because of their potential anti-cancer effects. However, limited studies regarding the influence of ITCs structure on NF-kappaB transactivation and anti-inflammatory action are reported. In the present study, the anti-inflammatory potential of ten structurally divergent synthetic ITCs were evaluated in HT-29-N9 human colon cancer cells and RAW 264.7 murine macrophages. The effect of ITCs on the basal transcriptional activation of NF-kappaB and the inflammatory response to bacterial lipopolysaccharide (LPS) were assessed. The synthetic ITC analogs suppressed NF-kappaB-mediated pro-inflammatory gene transcription. Among the ITC analogs, tetrahydrofurfuryl isothiocyanate, methyl-3-isothiocyanatopropionate, 3-morpholinopropyl isothiocyanate and 3,4-methyelendioxybenzyl isothiocyanate showed stronger NF-kappaB inhibition as compared to the parent compound, phenylethyl isothiocyanate (PEITC). Molecular analysis revealed that several of the pro-inflammatory mediators and cytokines (iNOS, COX-2, IL-1beta, IL-6 and TNF-alpha) were reduced by ITCs, and correlated with the downregulation of NF-kappaB signaling pathways. Immunoblotting showed that ITCs suppressed LPS-induced phosphorylation and degradation of IkappaB alpha and decreased nuclear translocation of p65. In parallel, ITCs suppressed the phosphorylation of IkappaB kinase alpha/beta (IKKalpha/beta). Taken together, our findings provide the possibility that synthetic ITC analogs might have promising cancer chemopreventive potential, based on their stronger anti-NF-kappaB and anti-inflammatory activities, than the natural ITCs.
Chemico-biological interactions 01/2009; 179(2-3):202-11. · 2.46 Impact Factor
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ABSTRACT: Recently, considerable attention has been focused on identifying dietary and medicinal phytochemicals that can inhibit, retard or reverse the multi-stage carcinogenesis. Spices and herbs contain phenolic substances with potent antioxidative and chemopreventive properties. Curcumin, a yellow colouring agent from turmeric and capsaicin, a pungent principle of red pepper exhibit profound anticarcinogenic and antimutagenic activities. Two well-defined eukaryotic transcription factors, nuclear factor-kappa B (NF-κB) and activator protein 1 (AP-1) have been implicated in pathogenesis of many human diseases including cancer. These transcription factors are known to be activated by a wide array of external stimuli, such as tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA), tumor necrosis factor, reactive oxygen species, bacterial lipopolysaccharide, and ultraviolet. In the present study, we found that topical application of TPA onto dorsal skin of female ICR mice resulted in marked activation of epidermal NF-κB and AP-1. Curcumin and capsaicin, when topically applied prior to TPA, significantly attenuated TPA-induced activation of each transcription factor in mouse skin. Likewise, both compounds inhibited NF-κB and AP-1 activation in cultured human promyelocytic leukemia (HL-60) cells stimulated with TPA. Based on these findings, it is likely that curcumin and capsaicin exert anti-tumor promotional effects through suppression of the tumor promoter-induced activation of transcription factors, NF-κB and AP-1.
BioFactors 12/2008; 12(1‐4):107 - 112. · 4.93 Impact Factor
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ABSTRACT: PurposePrior studies from our laboratory have demonstrated the efficacy of a combined treatment of low doses of dietary agents curcumin
and phenylethylisothiocyanate in effectively suppressing prostate cancer in vitro in human prostate cancer PC3 cells as well as in vivo in immunodeficient mice implanted with PC3 cells. Hence, this study was undertaken to examine the potential chemopreventive
properties of the two agents against transgenic adenocarcinoma of the mouse prostate.
Materials and MethodsThe efficacy of AIN-76A diet supplemented with 2% curcumin or 0.05% PEITC or a combination of 1% curcumin and 0.025% PEITC
for periods of 10 and 16weeks was tested against adenocarcinoma of the mouse prostate. Immunohistochemistry and Western blot
analysis were used to examine the expression of proliferation and apoptotic biomarkers. All statistical tests were two-sided.
ResultsSupplementing AIN-76A diet with dietary phytochemicals curcumin or PEITC either alone or in combination, significantly decreased
incidence of prostate tumor formation (P = 0.0064). Immunohistochemistry revealed a significant inhibition of high-grade PIN (P = 0.0006, 0.000069, 0.00029 for a treatment period of 10weeks and P = 0.02582, 0.022179, 0.0317 for a treatment period of 16weeks) along with decreased proliferation and increased apoptotic
index in the curcumin, PEITC or curcumin and PEITC treated animals, respectively. Furthermore, Western blot analysis revealed
that downregulation of the Akt signaling pathway may in part play a role in decreasing cell proliferation ultimately retarding
prostate tumor formation.
ConclusionOur data lucidly evidence the chemopreventive merits of dietary phytochemicals curcumin and PEITC in suppressing prostate
adenocarcinoma.
Pharmaceutical Research 08/2008; 25(9):2181-2189. · 4.09 Impact Factor
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ABSTRACT: Isothiocyanates (ITCs), existing abundantly in cruciferous vegetables, is one class of promising dietary cancer chemopreventive agents that possess strong cancer protective effects by modulation of phase II detoxifying/antioxidant enzyme activities. However, limited studies regarding to the structure-activity relationship (SAR) of ITCs on the induction of phase II detoxifying/antioxidant enzymes are reported. In this study, the effects of ten structurally related isothiocyanates on the antioxidant response element (ARE)-mediated antioxidant enzyme heme oxygenase-1 (HO-1) induction in human hepatoma HepG2-C8 cells were evaluated.
After exposure of HepG2-C8 cells to ITCs, cell viability, luciferase reporter assay, Western blot analysis and quantitative real-time PCR were conducted.
Treatments with most ITCs significantly activated ARE-mediated luciferase activity with different maximal degree of ARE induction. In addition, ITCs caused a substantial induction of HO-1 protein, which was closely correlated with inductive level of Nrf2 protein. Real-time PCR revealed that the expression of HO-1 mRNA and protein was significantly increased after treatments with ITCs, although not directly correlated. HO-1 induction by ITCs was attenuated in HepG2-C8 cells transiently transfected with a dominant negative mutant of Nrf2 (Nrf2-M4), whereas it was totally absent in Nrf2 -/- mouse embryonic fibroblasts. In addition, ARE activation by ITCs was associated with the depletion of intracellular glutathione.
Collectively, our results demonstrate that the ITC class of compounds activates ARE-mediated HO-1 gene transcription through Nrf2/ARE signaling pathway, however, their inductive effects are quite specific, depending on the chemical structure. These results suggest the possibility that some synthetic ITCs might have superior chemopreventive activity than natural ITCs.
Pharmaceutical Research 05/2008; 25(4):836-44. · 4.09 Impact Factor
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ABSTRACT: The induction of NF-E2-related factor-2 (Nrf2)-mediated detoxifying/antioxidant enzymes is recognized as an effective strategy for cancer chemoprevention. Here, we report that 3-morpholinopropyl isothiocyanate (3MP-ITC) is an exceptionally strong chemical inducer of these enzymes. Exposure of 3MP-ITC in HepG2C8 cells not only induced endogenous Nrf2 protein but also suppressed endogenous Kelch-like ECH-associated protein 1, resulting in an increased nuclear accumulation of Nrf2. Using chemical inhibitors of protein synthesis (cycloheximide) and 26S proteosomal degradation (MG-132), we observed that the induction of Nrf2 protein by 3MP-ITC appeared to be post-translationally regulated. 3MP-ITC activated ERK1/2 and JNK1/2 and the activation of antioxidant response element (ARE) by 3MP-ITC was significantly attenuated by chemical inhibition of PKC and PI3K signaling pathways in HepG2C8 cells. Treatment with 3MP-ITC significantly depleted the intracellular level of glutathione (GSH) in HepG2C8 cells and oral administration of 3MP-ITC increased the protein expression of hepatic NAD[P]H:quinone oxidoreductase-1 and Nrf2 in Nrf2 (+/+) but not in Nrf2 (-/-) mice, whereas UDP-glucuronosyl transferase 1A1 was induced in both genotypes. Our results indicate that 3MP-ITC is a novel ITC that strongly induces Nrf2-dependent ARE-mediated detoxifying/antioxidant enzymes in vitro and in vivo via the Nrf2 signaling pathway coupled with GSH depletion and activation of multiple signaling kinase pathways, which could be potentially useful agent for cancer chemoprevention.
Carcinogenesis 04/2008; 29(3):594-9. · 5.70 Impact Factor
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ABSTRACT: This study was aimed to investigate the effects of a phenolic antioxidant, butylated hydroxyanisole (BHA) and its metabolite, tert-butylhydroquinone (tBHQ) on the induction of HO-1, NQO1 and Nrf2 proteins and their regulatory mechanisms in primary-cultured hepatocytes.
After exposure of BHA and tBHQ to primary-cultured rat and human hepatocytes and mouse neonatal fibroblasts (MFs), Western blot, semi-quantitative RT-PCR and microarray analysis were conducted.
Induction of HO-1, NQO1 and Nrf2 proteins and activation of ERK1/2 and JNK1/2 were observed after BHA and tBHQ treatments in primary-cultured rat and human hepatocytes. Semi-quantitative RT-PCR study and microarray analysis revealed that HO-1 and NQO1 were transcriptionally activated in primary-cultured rat hepatocytes and a substantial transcriptional activation, including HO-1 occurred in primary-cultured human hepatocytes after BHA treatment. Whereas BHA failed to induce HO-1 in wild-type and Nrf2 knock-out MFs, tBHQ strongly induced HO-1 in wild-type, but not in Nrf2 knock-out MFs.
Our data demonstrate that both BHA and tBHQ are strong chemical inducers of HO-1, NQO1 and Nrf2 proteins in primary-cultured human and rat hepatocytes with the activation of MAPK ERK1/2 and JNK1/2. However, in MFs, BHA failed to induce HO-1, whereas tBHQ strongly induced HO-1 in Nrf2 wild-type but not in Nrf2 knock-out, suggesting that Nrf2 is indispensable for tBHQ-induced HO-1 in MF.
Pharmaceutical Research 12/2006; 23(11):2586-94. · 4.09 Impact Factor
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Sujit Nair,
Changjiang Xu,
Guoxiang Shen,
Vidya Hebbar,
Avantika Gopalakrishnan,
Rong Hu,
Mohit Raja Jain,
Wen Lin, Young-Sam Keum,
Celine Liew,
Jefferson Y Chan,
Ah-Ng Tony Kong
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ABSTRACT: The objective of this study was to investigate the pharmacogenomics and the spatial regulation of global gene expression profiles elicited by cancer chemopreventive agent butylated hydroxyanisole (BHA) in mouse small intestine and liver as well as to identify BHA-modulated nuclear factor-E2-related factor 2 (Nrf2)-dependent genes.
C57BL/6J (+/+; wildtype) and C57BL/6J/Nrf2(-/-; knockout) mice were administered a single 200 mg/kg oral dose of BHA or only vehicle. Both small intestine and liver were collected at 3 h after treatment and total RNA was extracted. Gene expression profiles were analyzed using 45,000 Affymetrix mouse genome 430 2.0 array and GeneSpring 7.2 software. Microarray results were validated by quantitative real-time reverse transcription-PCR analyses.
Clusters of genes that were either induced or suppressed more than two fold by BHA treatment compared with vehicle in C57BL/6J/Nrf2(-/-; knockout) and C57BL/6J Nrf2 (+/+; wildtype) mice genotypes were identified. Amongst these, in small intestine and liver, 1,490 and 493 genes respectively were identified as Nrf2-dependent and upregulated, and 1,090 and 824 genes respectively as Nrf2-dependent and downregulated. Based on their biological functions, these genes can be categorized into ubiquitination/proteolysis, apoptosis/cell cycle, electron transport, detoxification, cell growth/differentiation, transcription factors/interacting partners, kinases and phosphatases, transport, biosynthesis/metabolism, RNA/protein processing and nuclear assembly, and DNA replication genes. Phase II detoxification/antioxidant genes as well as novel molecular target genes, including putative interacting partners of Nrf2 such as nuclear corepressors and coactivators, were also identified as Nrf2-dependent genes.
The identification of BHA-regulated and Nrf2-dependent genes not only provides potential novel insights into the gestalt biological effects of BHA on the pharmacogenomics and spatial regulation of global gene expression profiles in cancer chemoprevention, but also points to the pivotal role of Nrf2 in these biological processes.
Pharmaceutical Research 12/2006; 23(11):2621-37. · 4.09 Impact Factor
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ABSTRACT: Many natural and synthetic cancer chemopreventive compounds are potent inducers of phase II detoxifying and antioxidant stress responsive genes. The phase II/antioxidant gene expression plays critical role in chemoprevention of carcinogenesis. The antioxidant responsive element (ARE), located on many phase II/antioxidant genes, binds with the transcription factor Nrf2, and is required for the activation of these phase II/antioxidant gene expression induced by many natural and synthetic cancer chemopreventive compounds. In this study, we investigated the potential roles of extracellular signal-regulated kinase (ERK) and c-jun N-terminal kinase (JNK) in the regulation of butylated hydroxyanisole (BHA)-induced and Nrf2-dependent ARE transcriptional activity and ARE-mediated endogenous heme oxygenase-1 (HO-1) protein expression in HepG2 cells. ARE transcriptional activity and HO-1 protein expression were increased dose dependently after treatment with BHA in HepG2 cells. Dose-response and time-course experiments showed that BHA increased the accumulation of Nrf2, and concomitantly decreased the protein level of Keap1. We next examined the phosphorylation of the MAPKs, and found that BHA significantly increased the phosphorylation levels of ERK1/2 and JNK1/2. Importantly BHA-induced ARE transcriptional activity was attenuated by the inhibition of ERK and JNK signaling using biochemical inhibitors and their dominant-negative mutants. Using confocal microscopy technique, treatment with BHA showed the release of Nrf2 sequestered by Keap1 in the cytosol, and that Nrf2 translocated into the nucleus. Importantly, cDNA transfections of ERK and JNK signaling pathways similarly released Nrf2 from Keap1 cytosolic sequestration and translocating Nrf2 into the nucleus. Taken together, these results strongly suggested that ERK and JNK signaling pathways played important and positive roles in BHA-induced and Nrf2-dependent regulation of ARE-mediated gene expression, as well as the nuclear translocation of Nrf2 in HepG2 cells.
Molecular Carcinogenesis 12/2006; 45(11):841-50. · 3.16 Impact Factor
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ABSTRACT: Exposure of sulforaphane to HepG2 cells increased heme oxygenase-1 (HO-1) expression by activating antioxidant response element (ARE) through induction of Nrf2 and suppression of Kelch-like ECH-associated protein 1 (Keap1). Using human HO-1 promoter reporter plasmids and ChIP assay, we have identified that sulforaphane transcriptionally activated the upstream ARE-rich enhancer region, located at -9.0 kb upstream human HO-1 promoter. Induction of HO-1 by sulforaphane was attenuated by overexpression of mutant Nrf2 plasmid in HepG2 cells and totally abolished in Nrf2 knockout mouse embryonic keratinocytes and fibroblasts. Overexpression of individual p38 mitogen-activated protein (MAP) kinase (MAPK) isoforms also suppressed constitutive as well as sulforaphane- or Nrf2-induced ARE-dependent gene expression. Among the upstream kinases, although MKK3 was not involved in suppression of ARE by any of p38 MAPK isoforms, MKK6 selectively suppressed ARE by p38 gamma or p38 delta, but not by p38 alpha or p38 beta. Importantly, sulforaphane not only activated MAP/extracellular signal-regulated kinase (ERK) kinases 1/2 and ERK1/2, but also strongly suppressed anisomycin-induced activation of p38 MAPK isoforms by blocking phosphorylation of upstream kinases, MKK3/6. Finally, we found that stimulation of p38 MAPK isoforms phosphorylated purified Nrf2 protein and caused an increase in the interaction between Nrf2 and Keap1 in vitro and the suppression of Nrf2 translocation into the nucleus. Collectively, our results indicate that transcriptional activation of Nrf2/ARE is critical in sulforaphane-mediated induction of HO-1, which can be modulated in part by the blockade of p38 MAPK signaling pathway. In addition, our study shows that p38 MAPK can phosphorylate Nrf2 and promotes the association between Nrf2 and Keap1 proteins, thereby potentially inhibiting nuclear translocation of Nrf2.
Cancer Research 10/2006; 66(17):8804-13. · 7.86 Impact Factor
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ABSTRACT: Many naturally occurring compounds, including beta-phenylethyl isothiocyanate (PEITC) and curcumin, exhibit significant anti-cancer chemopreventive effects. In this study, we investigated the combined effects of PEITC and curcumin in PC-3 human prostate cancer cells and in PC-3 cells that were stably transfected with an NF-kappaB luciferase plasmid (PC-3 C4). We found an additive effect of PEITC and curcumin for the induction of apoptosis. To elucidate the potential mechanisms of this effect, we studied several critical cellular signaling pathways, including the critical NF-kappaB cell survival signal that is hyper-activated in PC-3 cells and many other cancers. PEITC and curcumin additively inhibited NF-kappaB luciferase activity. Furthermore, the combined treatment significantly increased the activity of poly(ADP-Ribose) polymerase and cleavage of caspase-3 in correlation with apoptotic cell death. Studying upstream signaling events, we found that the phosphorylations of IkappaBalpha and Akt (Ser473, Thr308) were significantly attenuated by the combination of PEITC and curcumin. As these events can be downstream of the activation of epidermal growth factor receptor (EGFR), we pretreated PC-3 cells with PEITC and curcumin and then stimulated them with EGF. EGFR phosphorylations (Y845 and Y1068) were dramatically suppressed by PEITC or curcumin, and more so by the combination. Importantly, the degree of Akt and PI3K phosphorylations induced by EGF were also significantly suppressed. We conclude that the simultaneous targeting of EGFR, Akt and NF-kappaB signaling pathways by PEITC and curcumin could be the molecular targets by which PEITC and curcumin exert their additive inhibitory effects on cell proliferation and ultimately lead to programmed cell death of tumor cells.
Carcinogenesis 04/2006; 27(3):475-82. · 5.70 Impact Factor
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ABSTRACT: Many isothiocyanates (ITCs) such as sulforaphane (SFN), phenethyl isothiocyanate (PEITC) and allyl isothiocyanate (AITC) are highly effectively in chemoprevention or reduction of the risk of cancer and possess antitumor activities in vitro and in vivo. The activator protein 1 (AP-1) and MAPK signaling pathways are believed to play an important role in cancer chemoprevention and chemotherapy due to their involvement in tumor cell growth, proliferation, apoptosis and survival. In the present study, we determined the effects of SFN, PEITC and AITC on AP-1 activation, and investigated the roles of extracellular signal-regulated protein kinase (ERK) and c-Jun N-terminal kinase (JNK) signaling pathways in the regulation of AP-1 activation and cell death elicited by these ITCs in human prostate cancer PC-3 cells. SFN, PEITC and AITC each induced AP-1 activity potently and caused a significant elevation in the phosphorylation of ERK1/2, JNK1/2, Elk-1 and c-Jun. Transfection with ERK2 and upstream kinase DNEE-MEK1 activated AP-1 activity, and transfection with dominant-negative mutant ERK2 (dnERK2) potently decreased AP-1 activation induced by SFN, PEITC and AITC. Transfection with JNK1 and upstream kinase MKK7 activated AP-1 activity, and transfection with dominant-negative mutant JNK1-APF significantly attenuated AP-1 activation induced by SFN, PEITC and AITC. Pretreatment with MEK1-ERK inhibitor U0126 and JNK inhibitor SP600125 substantially attenuated the decrease in cell viability induced by SFN, PEITC and AITC. Transfection with dnERK2 and JNK1-APF significantly reversed the decrease of Bcl-2 expression elicited by these ITCs. Furthermore, transfection with dnERK2 and JNK1-APF blocked the apoptosis induced by these ITCs in PC-3 cells. Taken together, our results indicate that the activation of the ERK and JNK signaling pathways is important for transcriptional activity of AP-1 and is involved in the regulation of cell death elicited by ITCs in PC-3 cells.
Carcinogenesis 04/2006; 27(3):437-45. · 5.70 Impact Factor
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Tin Oo Khor, Young-Sam Keum,
Wen Lin,
Jung-Hwan Kim,
Rong Hu,
Guoxiang Shen,
Changjiang Xu,
Avanthika Gopalakrishnan,
Bandaru Reddy,
Xi Zheng,
Allan H Conney,
Ah-Ng Tony Kong
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ABSTRACT: Earlier studies using prostate cancer cells in culture showed that phenethyl isothiocyanate (PEITC) and curcumin have significant chemopreventive and possibly chemotherapeutic effects. However, their in vivo effects are still lacking. Hence, this study was undertaken to determine the possible in vivo efficacy of prostate cancer-prevention as well as cancer-therapeutic treatment by PEITC and curcumin alone or in combination. We evaluated the effects on tumor growth in vivo, using NCr immunodeficient (nu/nu) mice bearing s.c. xenografts of PC-3 human prostate cancer cells. Molecular biomarkers representing proliferation and apoptosis were determined. Continued i.p. injection of curcumin or PEITC (6 and 5 mumol; thrice a week for 28 days), beginning a day before tumor implantation significantly retarded the growth of PC-3 xenografts. Combination of i.p. administration of PEITC (2.5 mumol) and curcumin (3 mumol) showed stronger growth-inhibitory effects. Next, we evaluated the cancer-therapeutic potential of curcumin and PEITC in mice with well-established tumors, and the results showed that PEITC or curcumin alone had little effect, whereas combination of curcumin and PEITC significantly reduced the growth of PC-3 xenografts. Immunohistochemistry staining and Western blot analysis revealed that the inhibition of Akt and nuclear factor-kappaB signaling pathways could contribute to the inhibition of cell proliferation and induction of apoptosis. Taken together, our results show that PEITC and curcumin alone or in combination possess significant cancer-preventive activities in the PC-3 prostate tumor xenografts. Furthermore, we found that combination of PEITC and curcumin could be effective in the cancer-therapeutic treatment of prostate cancers.
Cancer Research 02/2006; 66(2):613-21. · 7.86 Impact Factor
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ABSTRACT: Numerous animal and epidemiological studies have demonstrated that consumption of cruciferous vegetables is inversely correlated with the cancer incidence. Strong anticarcinogenic activities of cruciferous vegetables are attributed to the high abundance of glucosinolates. Upon consumption, glucosinolates are hydrolyzed into iso-thiocyanates (ITCs), which in turn are conjugated with intracellular glutathione and excreted via mercapturic acid pathway. On the basis of the principle that ITCs can interact with 1,2-benzenedithiole to produce 1,3-benzodithiole-2-thione, a simple high-pressure liquid chromatography-based assay (namely cyclocondensation assay) has been devised to carry out the accurate measurement of the intracellular ITC accumulation. This assay has been adopted to assess the pharmacokinetic profiles of ITCs in humans, to evaluate the enzymatic efficiency of glucosinolate breakdown by myrosinase and to investigate the intracellular absorption and elimination mechanisms of ITCs. In addition, LC-MS-MS has recently been introduced as an alternative quantitative method for ITCs and proved to be superior to cyclocondensation assay, in terms of sensitivity as well as selectivity. Among several possible cellular mechanisms, both the modulation of nuclear factor kappaB (NF-kappaB) and activator protein-1 (AP-1) and the induction of phase II cellular detoxification and antioxidant enzymes (in brief phase II enzymes) have been proposed as potential molecular mechanisms of chemoprevention by ITCs. In the present review, we describe how ITCs modulate the activity of NF-kappaB and AP-1 and discuss how Nrf2/ARE module was discovered as the central core in the transcriptional regulation of phase II cellular detoxification and antioxidant enzymes.
Drug News & Perspectives 10/2005; 18(7):445-51. · 2.21 Impact Factor
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ABSTRACT: Nuclear factor-E2-related factor 2 (Nrf2) is known as a key regulator of ARE-mediated gene expression and the induction of Phase II detoxifying enzymes and antioxidant enzymes, which is also a common property of many chemopreventive agents. In the present study, we investigated the regulatory role of different chemopreventive agents including sulforaphane (SUL), allyl isothiocyanate (AITC), indole-3-carbinol (I3C), and parthenolide (PTL), in the expression and degradation of Nrf2 and the induction of the antioxidant enzyme HO-1. SUL strongly induced Nrf2 protein expression and ARE-mediated transcription activation, retarded degradation of Nrf2 through inhibiting Keap1, and thereby activating the transcriptional expression of HO-1. AITC was also a potent inducer of Nrf2 protein expression, ARE-reporter gene and HO-1 but had little effect on delaying the degradation of Nrf2 protein. Although PTL and I3C could induce AREreporter gene expression and Nrf2 to some extent, they were not as potent as SUL and AITC. However, PTL dramatically induced the HO-1 expression, which was comparable to SUL, while I3C had no effect. In addition, when treated with SUL and PTL, inhibition of proteasome by MG132 did not cause additional accumulation of Nrf2, suggesting the involvement of other degradation mechanism(s) in the presence of these compounds such as SUL and PTL. In summary, the results of our current study indicated that different chemopreventive compounds have different regulatory properties on the accumulation and degradation of Nrf2 as well as the induction of cellular antioxidant enzyme HO-1.
Journal of biochemistry and molecular biology 04/2005; 38(2):167-76. · 2.02 Impact Factor
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ABSTRACT: Chemoprevention is a cancer preventive strategy to inhibit, delay or reverse carcinogenesis using naturally occurring or synthetic chemical agents. Numerous epidemiological studies as well as experimental animal studies clearly demonstrate that high intake of cruciferous vegetables protects against tumorigenesis. Thus, cruciferous vegetables have been of great interest for potential use in the chemoprevention of cancer. Cruciferous vegetables are rich source of glucosinolates, which are degraded into isothiocyanates by enzymatic action of plant-specific myrosinase or intestinal flora in the body. It appears that significant portion of the chemopreventive effects of isothiocyanates may be associated with the inhibition of the metabolic activation of carcinogens by cytochrome P450s (Phase I), coupled with strong induction of Phase II detoxifying and cellular defensive enzymes. Inductions of Phase II cellular enzymes are largely mediated by the antioxidant responsive element (ARE), which is regulated by the transcriptional factor, Nrf2. Additional potent regulatory mechanisms of Nrf2 include the different signaling kinase pathways (MAPK, PI3K, PKC and PERK) as well as other non-kinase dependent mechanisms. Moreover, apoptosis and cell cycle perturbations appear to be yet another potential chemopreventive mechanisms elicited by isothiocyanates, especially with respect to the effects on pre-initiated or initiated tumor cells. Finally, modulation of other critical signaling mediators, including the NF-kappaB and AP-1 by a wide array of chemopreventive agents including isothiocyanates may also contribute to the overall chemopreventive mechanisms.
Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis 12/2004; 555(1-2):191-202. · 2.85 Impact Factor
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ABSTRACT: Transcription factor NF-E2-related factor 2 (Nrf2) regulates the induction of Phase II detoxifying enzymes as well as anti-oxidative enzymes. In this study, we investigated the transactivation potential of different Nrf2 transactivation domain regions by using the Gal4-Nrf2 chimeras and Gal4-Luc reporter co-transfection assay system in HepG2 cells. The results indicated that chimera Gal4-Nrf2-(1-370), which contains the full transactivation domain showed very potent transactivation activity. The high transactivation activity of Gal4-Nrf2-(113-251) and the diminished transactivation activities of chimera Gal4-Nrf2-(1-126) and Gal4-Nrf2-(230-370) suggested that the Nrf2 N-terminal 113-251 amino acids region is critical in maintaining its transactivation activity. Overexpression of upstream MAPKs such as Raf, MEKK1, TAK1-DeltaN, and ASK1 up-regulated the transactivation activities of Gal4-Nrf2-(1-370) and Gal4-Nrf2-(113-251) in a dose-dependent manner. Further investigation on the effects of the three MAPK pathways on Nrf2 transactivation domain activity demonstrated that both ERK and JNK signaling pathways stimulated the Gal4-Nrf2-(1-370) transactivation activity while the p38 pathway played a negative role. Site-directed mutagenesis studies on potential MAPK phosphorylation sites of Gal4-Nrf2-(113-251) showed no significant effect on its basal transactivation activity or the fold of induction by Raf. Interestingly, the nuclear transcription coactivator CREB-binding protein (CBP), which can bind to Nrf2 transactivation domain and can be activated by ERK cascade, showed synergistic stimulation with Raf on the transactivation activities of both the chimera Gal4-Nrf2-(1-370) and the full-length Nrf2. Taken together, this study clearly demonstrated that different segments of Nrf2 transactivation domain have different transactivation potential and different MAPKs have differential effects on Nrf2 transcriptional activity. It also suggested that the up-regulation of Nrf2 transactivation domain activity by upstream MAPKs such as Raf may not be mediated by direct phosphorylation of the Nrf2 transactivation domain, but rather by regulation of the transcriptional activity of coactivator CBP.
Journal of Biological Chemistry 06/2004; 279(22):23052-60. · 4.77 Impact Factor
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ABSTRACT: Transcription factor NF-E2-related factor 2 (Nrf2) regulates the induction of Phase II detoxifying enzymes as well as anti-oxidative
enzymes. In this study, we investigated the transactivation potential of different Nrf2 transactivation domain regions by
using the Gal4-Nrf2 chimeras and Gal4-Luc reporter co-transfection assay system in HepG2 cells. The results indicated that
chimera Gal4-Nrf2-(1–370), which contains the full transactivation domain showed very potent transactivation activity. The
high transactivation activity of Gal4-Nrf2-(113–251) and the diminished transactivation activities of chimera Gal4-Nrf2-(1–126)
and Gal4-Nrf2-(230–370) suggested that the Nrf2 N-terminal 113–251 amino acids region is critical in maintaining its transactivation
activity. Overexpression of upstream MAPKs such as Raf, MEKK1, TAK1-ΔN, and ASK1 up-regulated the transactivation activities
of Gal4-Nrf2-(1–370) and Gal4-Nrf2-(113–251) in a dose-dependent manner. Further investigation on the effects of the three
MAPK pathways on Nrf2 transactivation domain activity demonstrated that both ERK and JNK signaling pathways stimulated the
Gal4-Nrf2-(1–370) transactivation activity while the p38 pathway played a negative role. Site-directed mutagenesis studies
on potential MAPK phosphorylation sites of Gal4-Nrf2-(113–251) showed no significant effect on its basal transactivation activity
or the fold of induction by Raf. Interestingly, the nuclear transcription coactivator CREB-binding protein (CBP), which can
bind to Nrf2 transactivation domain and can be activated by ERK cascade, showed synergistic stimulation with Raf on the transactivation
activities of both the chimera Gal4-Nrf2-(1–370) and the full-length Nrf2. Taken together, this study clearly demonstrated
that different segments of Nrf2 transactivation domain have different transactivation potential and different MAPKs have differential
effects on Nrf2 transcriptional activity. It also suggested that the up-regulation of Nrf2 transactivation domain activity
by upstream MAPKs such as Raf may not be mediated by direct phosphorylation of the Nrf2 transactivation domain, but rather
by regulation of the transcriptional activity of coactivator CBP.
Journal of Biological Chemistry 05/2004; 279(22):23052-23060. · 4.77 Impact Factor
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ABSTRACT: Sulforaphane (SFN) and its N-acetyl-L-cysteine (NAC) conjugate are effective inhibitors of tumorigenesis in animal models. These compounds induce the expression of the antioxidant response element (ARE)-related genes and cause apoptosis. We studied the role of reduced glutathione (GSH) in the activations of ARE-mediated gene expression, apoptosis, and the activation of c-Jun NH(2)-terminal kinase (JNK) in HepG2-C8 cells. The cellular level of GSH decreased transiently when cells were exposed to SFN and then increased from 4 h, reaching 2.2-fold over control at 24 h. In contrast, SFN-NAC did not change the GSH level substantially during the time of incubation. ARE expression was increased in a dose-dependent manner up to 35 micro M SFN and 75 micro M SFN-NAC, respectively. The induction of ARE by SFN was 8.6-fold higher than that by SFN-NAC. Pretreatment with L-buthionine sulfoximine increased SFN-induced ARE expression significantly. The decrease in ARE expression at higher concentrations of SFN and SFN-NAC was correlated with accelerated apoptotic cell death, with a dose-dependent activation of caspase 3 activity by SFN. On addition of extracellular GSH within 6 h of treatment with SFN, the effect on ARE expression was blocked almost completely. SFN was able to activate JNK1/2, and that activation was blocked by treatment with exogenous GSH. Taken together, these results suggest that the biological effects of SFN and SFN-NAC on the induction of ARE-related gene expression and apoptosis could be different from each other; however, the different effects on ARE-related gene expression and apoptosis elicited by SFN can be blocked by the addition of GSH.
Cancer Research 12/2003; 63(21):7520-5. · 7.86 Impact Factor
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ABSTRACT: Recently, there have been considerable efforts to search for naturally occurring substances for the intervention of carcinogenesis. Many components derived from dietary or medicinal plants have been found to possess substantial chemopreventive properties. Curcumin, a yellow coloring ingredient of turmeric (Curcuma longa L., Zingiberaceae), has been shown to inhibit experimental carcinogenesis and mutagenesis, but molecular mechanisms underlying its chemopreventive activities remain unclear. In the present work, we assessed the effects of curcumin on 12-O- tetradecanoylphorbol-13-acetate (TPA)-induced expression of cyclooxygenase-2 (COX-2) in female ICR mouse skin. Topical application of the dorsal skin of female ICR mice with 10 nmol TPA led to maximal induction of cox-2 mRNA and protein expression at approximately 1 and 4 h, respectively. When applied topically onto shaven backs of mice 30 min prior to TPA, curcumin inhibited the expression of COX-2 protein in a dose-related manner. Immunohistochemical analysis of TPA-treated mouse skin revealed enhanced expression of COX-2 localized primarily in epidermal layer, which was markedly suppressed by curcumin pre-treatment. Curcumin treatment attenuated TPA- stimulated NF-kappaB activation in mouse skin, which was associated with its blockade of degradation of the inhibitory protein IkappaBalpha and also of subsequent translocation of the p65 subunit to nucleus. TPA treatment resulted in rapid activation via phosphorylation of extracellular signal-regulated kinase (ERK)1/2 and p38 mitogen-activated protein (MAP) kinases, which are upstream of NF-kappaB. The MEK1/2 inhibitor U0126 strongly inhibited NF-kappaB activation, while p38 inhibitor SB203580 failed to block TPA-induced NF-kappaB activation in mouse skin. Furthermore, U0126 blocked the IkappaBalpha phosphorylation by TPA, thereby blocking the nuclear translocation of NF-kappaB. Curcumin inhibited the catalytic activity of ERK1/2 in mouse skin. Taken together, suppression of COX-2 expression by inhibiting ERK activity and NF-kappaB activation may represent molecular mechanisms underlying previously reported antitumor promoting effects of this phytochemical in mouse skin tumorigenesis.
Carcinogenesis 10/2003; 24(9):1515-24. · 5.70 Impact Factor
