Auemduan Prawan

Increased Susceptibility of Nrf2 Knockout Mice to Colitis-Associated Colorectal Cancer

The nuclear factor-erythroid 2-related factor 2 (Nrf2) plays a critical role in protecting various tissues against inflammation, which is a potential risk factor for colorectal and other cancers. Our previously published mouse model work showed that Nrf2 helps protect against dextran sulfate sodium (DSS)–induced colitis/inflammation, and others have shown that Nrf2 helps protect against inflammation-associated colorectal carcinogenesis (aberrant crypt foci). The present study extended these important earlier findings by exploring the role of Nrf2 in colitis-associated colorectal cancer in a mouse model involving azoxymethane/DSS–induced colorectal carcinogenesis in Nrf2 knockout mice. Azoxymethane/DSS–treated Nrf2 knockout mice had increased incidence, multiplicity, and size of all colorectal tumors, including adenomas, versus treated wild-type (WT) mice, and the proportion of tumors that were adenocarcinoma was much higher in knockout (80%) versus WT (29%) mice. Compared with WT mice, knockout mice also had increased markers of inflammation in tumor tissue (cyclooxygenase-2 and 5-lipoxygenase expressions and prostaglandin E2 and leukotriene B4 levels) and in inflamed colonic mucosa (nitrotyrosine expression), supporting the association of knockout mouse tumor formation with inflammation. The phase II detoxifying/antioxidant enzymes NAD(P)H-quinone reductase 1 and UDP-glucurosyltransferase 1A1 were elevated in the normal mucosa of WT, but not Nrf 2 knockout, mice treated with azoxymethane/DSS. Our findings show that Nrf2 plays a critical role in protecting against inflammation-associated colorectal cancer.

Structural Influence of Isothiocyanates on the Antioxidant Response Element (ARE)-Mediated Heme Oxygenase-1 (HO-1) Expression

PurposeIsothiocyanates (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.Materials and MethodsAfter exposure of HepG2-C8 cells to ITCs, cell viability, luciferase reporter assay, Western blot analysis and quantitative real-time PCR were conducted.ResultsTreatments 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.ConclusionCollectively, 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.

Quercetin and EGCG exhibit chemopreventive effects in cholangiocarcinoma cells via suppression of JAK/STAT signaling pathway.

Quercetin and epigallocatechin‐3‐gallate (EGCG) are dietary phytochemicals with antiinflammatory and antitumor effects. In the present study, we examined the effects of these two compounds on Janus‐like kinase (JAK)/signal transduction and transcription (STAT) pathway of cholangiocarcinoma (CCA) cells, because CCA is one of the aggressive cancers with very poor prognosis and JAK/STAT pathway is critically important in inflammation and carcinogenesis. The results showed that the JAK/STAT pathway activation by proinflammatory cytokine interleukin‐6 and interferon‐γ in CCA cells was suppressed by pretreatment with quercetin and EGCG, evidently by a decrease of the elevated phosphorylated‐STAT1 and STAT3 proteins in a dose‐dependent manner. The cytokine‐mediated up‐regulation of inducible nitric oxide synthase (iNOS) and intercellular adhesion molecule‐1 (ICAM‐1) via JAK/STAT cascade was abolished by both quercetin and EGCG pretreatment. Moreover, these flavonoids also could inhibit growth and cytokine‐induced migration of CCA cells. Pretreatment with specific JAK inhibitors, AG490 and piceatannol, abolished cytokine‐induced iNOS and ICAM‐1 expression. These results demonstrate beneficial effects of quercetin and EGCG in the suppression of JAK/STAT cascade of CCA cells. Quercetin and EGCG would be potentially useful as cancer chemopreventive agents against CCA. Copyright

Crucial role of heme oxygenase-1 on the sensitivity of cholangiocarcinoma cells to chemotherapeutic agents.

Cancer cells acquire drug resistance via various mechanisms including enhanced cellular cytoprotective and antioxidant activities. Heme oxygenase-1 (HO-1) is a key enzyme exerting potent cytoprotection, cell proliferation and drug resistance. We aimed to investigate roles of HO-1 in human cholangiocarcinoma (CCA) cells for cytoprotection against chemotherapeutic agents. KKU-100 and KKU-M214 CCA cell lines with high and low HO-1 expression levels, respectively, were used to evaluate the sensitivity to chemotherapeutic agents, gemcitabine (Gem) and doxorubicin. Inhibition of HO-1 by zinc protoporphyrin IX (ZnPP) sensitized both cell types to the cytotoxicity of chemotherapeutic agents. HO-1 gene silencing by siRNA validated the cytoprotective effect of HO-1 on CCA cells against Gem. Induction of HO-1 protein expression by stannous chloride enhanced the cytoprotection and suppression of apoptosis caused by anticancer agents. The sensitizing effect of ZnPP was associated with increased ROS formation and loss of mitochondrial transmembrane potential, while Gem alone did not show any effects. A ROS scavenger, Tempol, abolished the sensitizing effect of ZnPP on Gem. Combination of ZnPP and Gem enhanced the release of cytochrome c and increased p21 levels. The results show that HO-1 played a critical role in cytoprotection in CCA cells against chemotherapeutic agents. Targeted inhibition of HO-1 may be a strategy to overcome drug resistance in chemotherapy of bile duct cancer.

Mulberry leaf extract stimulates glucose uptake and GLUT4 translocation in rat adipocytes.

Mulberry (Morus alba L.) leaf tea is promoted for its health benefits and the control of diabetes in Asian nations. The blood glucose lowering activity of mulberry leaf extract (MA) has been proven; however, the molecular basis underlying this effect remains unclear. The aim of the present work is to elucidate its mechanism of the antihyperglycemic action, by examining the effect of MA on glucose uptake and the translocation of glucose transporter 4 protein (GLUT4) to the plasma membrane of adipocytes isolated from diabetic rats. The incubation of adipocytes with 5-45 μg/ml MA resulted in 31-54% increase of glucose uptake in a dose-dependent manner. This glucose uptake enhancing effect was inhibited by the phosphoinositol 3-kinase (PI3-K) inhibitor, wortmannin (100 nM). The GLUT4 protein on the plasma membrane fraction of adipocytes was markedly increased after treatment with 15 μg/ml MA extract. Interestingly, gallic acid, one of the phenolic compounds found in MA extract, increased glucose uptake and enhanced the translocation of GLUT4 at concentrations comparable to the amount of gallic acid in the effective concentration ranges of MA. Thus, it is likely that gallic acid contributes, at least in part, to its antihyperglycemic activity. The present results suggest that the antihyperglycemic action of MA is mediated by increasing glucose uptake via the activation of PI3-K signaling pathway and translocation of GLUT4 to the plasma membrane. These findings are the first molecular evidence supporting the mulberry tea as herbal medicine for diabetic patients.

Redox modulation and human bile duct cancer inhibition by curcumin

Curcumin, a major component from tumeric and well-known dietary spice, possesses various pharmacological effects. The cancer chemoprevention effect is suggested to act through its pro-oxidant property. The study was to clarify effects of curcumin on cholangiocarcinoma cells, a cancer of the bile duct that refractory to chemotherapeutic drugs. We examined time-course of oxidant formation in relation to antitumor and the adaptive antioxidant response of the cells. Curcumin induced antiproliferation and apoptosis in KKU-M214 CCA cells with concentration- and time- dependent manners. The antiproliferative effect of curcumin was observed at concentrations as low as 3 microM and was not necessarily associated with oxidative stress, while induction of apoptosis required significant production of superoxide anion, suppression of cellular redox and collapse of mitochondrial transmembrane potential. Western blot analysis showed a temporal relationship between the suppression of nuclear NF-kappaB with Bcl-XL protein levels. Up-regulation of p53 and Bax was associated with marked oxidative stress and apoptosis. Curcumin also induced Nrf2 protein expression with up-regulation of gamma-glutamylcysteine ligase mRNA and increased cellular antioxidant, glutathione. The study suggests that curcumin could be developed into an effective chemoprevention against CCA.

Luteolin Arrests Cell Cycling, Induces Apoptosis and Inhibits the JAK/STAT3 Pathway in Human Cholangiocarcinoma Cells

Cholangiocarcinoma (CCA) is one of the aggressive cancers with a very poor prognosis. Several efforts have been made to identify and develop new agents for prevention and treatment of this deadly disease. In the present study, we examined the anticancer effect of luteolin on human CCA, KKU-M156 cells. Sulforhodamine B assays showed that luteolin had potent cytotoxicity on CCA cells with IC50 values of 10.5±5.0 and 8.7±3.5 μM at 24 and 48 h, respectively. Treatment with luteolin also caused a concentration-dependent decline in colony forming ability. Consistent with growth inhibitory effects, luteolin arrested cell cycle progression at the G2/M phase in a dose-dependent manner as assessed by flow cytometry analysis. Protein expression of cyclin A and Cdc25A was down-regulated after luteolin treatment, supporting the arrest of cells at the G2/M boundary. Besides evident G2/M arrest, luteolin induced apoptosis of KKU-M156 cells, demonstrated by a distinct sub-G1 apoptotic peak and fluorescent dye staining. A decrease in the level of anti-apoptotic Bcl-2 protein was implicated in luteolin- induced apoptosis. We further investigated the effect of luteolin on JAK/STAT3, which is an important pathway involved in the development of CCA. The results showed that interleukin-6 (IL-6)-induced JAK/STAT3 activation in KKU-M156 cells was suppressed by treatment with luteolin. Treatment with a specific JAK inhibitor, AG490, and luteolin diminished IL-6-stimulated CCA cell migration as assessed by wound healing assay. These data revealed anticancer activity of luteolin against CCA so the agent might have potential for CCA prevention and therapy.

Suppression of NAD(P)H-quinone oxidoreductase 1 enhanced the susceptibility of cholangiocarcinoma cells to chemotherapeutic agents

BackgroundCholangiocarcinoma (CCA) is highly resistant to most of the known chemotherapeutic treatments. NAD(P)H-quinone oxidoreductase 1 (NQO1) is an antioxidant/detoxifying enzyme recently recognized as an important contributor to chemoresistance in some human cancers. However, the contribution of NQO1 to chemotherapy resistance in CCA is unknown.MethodsTwo CCA cell lines, KKU-100 and KKU-M214, with high and low NQO1 expression levels, respectively, were used to evaluate the sensitivity to chemotherapeutic agents; 5-fluorouracil (5-FU), doxorubicin (Doxo), and gemcitabine (Gem). NQO1 and/or p53 expression in KKU-100 cells were knocked down by siRNA. NQO1 was over-expressed in KKU-M214 cells by transfection with pCMV6-XL5-NQO1 expression vector. CCA cells with modulated NQO1 and/or p53 expression were treated with chemotherapeutic agents, and the cytotoxicity was assessed by SRB assay. The mechanism of enhanced chemosensitivity was evaluated by Western blot analysis.ResultsWhen NQO1 was knocked down, KKU-100 cells became more susceptible to all chemotherapeutic agents. Conversely, with over-expression of NQO1 made KKU-M214 cells more resistant to chemotherapeutic agents. Western blot analysis suggested that enhanced chemosensitivity was probably due to the activation of p53-mediated cell death. Enhanced susceptibility to chemotherapeutic agents by NQO1 silencing was abolished by knockdown of p53.ConclusionsThese results suggest that inhibition of NQO1 could enhance the susceptibility of CCA to an array of chemotherapeutic agents.

Phenethyl isothiocyanate induces apoptosis of cholangiocarcinoma cells through interruption of glutathione and mitochondrial pathway

Phenethyl isothiocyanate (PEITC) is a natural isothiocyanate with anticancer activity against many drug-resistant cancer cells. A body of evidence suggests that PEITC enhances oxidative stress leading to cancer cell death. Cholangiocarcinoma (CCA) is an aggressive bile duct cancer with resistance to chemotherapeutic drugs. PEITC rapidly kills KKU-100 CCA cells with concurrent induction of cellular glutathione depletion, superoxide formation, and loss of mitochondrial transmembrane potential. The loss was associated with increased Bax and decreased Bcl-xl proteins followed by the release of cytochrome c and the activation of caspase-9 and -3. Although TEMPOL could prevent superoxide formation, it did not prevent the disruption of glutathione (GSH) redox, mitochondrial dysfunction, and cell death. On the other hand, N-acetylcysteine could prevent the events and cell death. It was concluded that disruption of GSH redox but not superoxide formation may be an initial step leading to mitochondrial injury. PEITC could be a promising chemopreventive agent for CCA.

Phenethyl isothiocyanate induces calcium mobilization and mitochondrial cell death pathway in cholangiocarcinoma KKU-M214 cells

BackgroundPhenethyl isothiocyanate (PEITC) is a cancer chemopreventive agent from cruciferous vegetables. Cholangiocarcinoma (CCA) is a chemo-resistant cancer with very poor prognosis. We evaluated the effects of PEITC on induction of apoptotic cell death in relation to cellular glutathione (GSH) and mitochondrial function of a CCA cell line, KKU-M214.MethodsCytotoxic effects of PEITC on a CCA cell line, KKU-M214, and a reference cell line, Chang cells were evaluated. To delineate mechanisms of cell death, the following parameters were measured; GSH and superoxide levels as the oxidative status parameters, apoptosis related proteins levels using Western blotting. Cellular free calcium level and mitochondrial transmembrane potential were also measured.ResultsPEITC induced apoptotic cell death of both KKU-M214 and Chang cells. After PEITC treatment, both cells showed decrease of Bcl-xl and increase of Bax levels. While KKU-M214 cells released AIF, Chang cells released cytochrome c, with subsequent activation of caspase 3 and 9, upon PEITC treatment. PEITC induced superoxide formation in both cells, although it seemed not play a role in cell death. PEITC caused GSH redox stress in different ways in two cell types, because N-acetylcysteine (NAC) prevented redox stress in Chang but not in KKU-M214 cells. The loss of mitochondrial transmembrane potential was induced by PEITC concurrent with GSH stress, but was not a primary cause of cell death. The rapid increase of free calcium level in cytosol was associated with cell death in both cell lines. These events were prevented by NAC in Chang cells, but not in KKU-M214 cells.ConclusionPEITC induced cell death KKU-M214 cells and Chang cells via increase of cellular calcium mobilization and activation of mitochondrial cell death pathway. The effects of PEITC on the redox stress was mediated via different ways in CCA and Chang cells because NAC could prevent redox stress in Chang cells, but not in KKU-M214 cells. The multiple effects of PEITC may be useful for the development of novel chemotherapy for CCA.