Nitric oxide suppresses apoptosis in human colon cancer cells by scavenging mitochondrial superoxide anions

Inflammation-Associated Cytotoxic Agents in Tumorigenesis

Chronic inflammatory processes are related to all stages of tumorigenesis. As inflammation is closely associated with the activation and release of different cytotoxic agents, the interplay between cytotoxic agents and antagonizing principles is highlighted in this review to address the question of how tumor cells overcome the enhanced values of cytotoxic agents in tumors. In tumor cells, the enhanced formation of mitochondrial-derived reactive species and elevated values of iron ions and free heme are antagonized by an overexpression of enzymes and proteins, contributing to the antioxidative defense and maintenance of redox homeostasis. Through these mechanisms, tumor cells can even survive additional stress caused by radio- and chemotherapy. Through the secretion of active agents from tumor cells, immune cells are suppressed in the tumor microenvironment and an enhanced formation of extracellular matrix components is induced. Different oxidant- and protease-based cytotoxic agents are involved in tumor-mediated immunosuppression, tumor growth, tumor cell invasion, and metastasis. Considering the special metabolic conditions in tumors, the main focus here was directed on the disturbed balance between the cytotoxic agents and protective mechanisms in late-stage tumors. This knowledge is mandatory for the implementation of novel anti-cancerous therapeutic approaches.

Gasotransmitters in the tumor microenvironment: Impacts on cancer chemotherapy (Review)

Nitric oxide, carbon monoxide and hydrogen sulfide are three endogenous gasotransmitters that serve a role in regulating normal and pathological cellular activities. They can stimulate or inhibit cancer cell proliferation and invasion, as well as interfere with cancer cell responses to drug treatments. Understanding the molecular pathways governing the interactions between these gases and the tumor microenvironment can be utilized for the identification of a novel technique to disrupt cancer cell interactions and may contribute to the conception of effective and safe cancer therapy strategies. The present review discusses the effects of these gases in modulating the action of chemotherapies, as well as prospective pharmacological and therapeutic interfering approaches. A deeper knowledge of the mechanisms that underpin the cellular and pharmacological effects, as well as interactions, of each of the three gases could pave the way for therapeutic treatments and translational research.

Treatment with ascorbic acid normalizes the aerobic capacity, antioxidant defence, and cell death pathways in thermally stressed Mytilus galloprovincialis

Considering temperature's upcoming increase due to climate change, combined with the fact that Mediterranean mussels Mytilus galloprovincialis (Lamarck, 1819) live at their upper limits [critical temperatures (Tc) beyond 25 °C], we cannot be sure of this species' sustainable future in the Mediterranean Sea. Deviation from optimum temperatures leads to cellular damage due to oxidative stress. Although ascorbic acid (AA) is a major scavenger of reactive oxygen species (ROS), its capacity to minimize oxidative stress effects is scarcely studied in aquatic organisms. Thus, treatment with 5 mM and 10 mM AA of thermally stressed molluscs had been employed in order to examine its antioxidant capacity. While 5 mM had no effect, 10 mM normalized COX1 and ND2 relative mRNA levels, and superoxide dismutase (SOD), catalase, and glutathione reductase (GR) enzymatic activity levels in both examined tissues: posterior adductor muscle (PAM) and mantle. ATP levels, probably providing the adequate energy for antioxidant defence in thermally stressed mussels, is also normalized under 10 mM AA treatment. Moreover, autophagic indicators such as LC3 II/I and SQSTM1/p62 levels are normalized, indicating autophagy amelioration. Apoptosis also seems to be inhibited since both Bax/Bcl-2 and cleaved caspase substrate levels decrease with 10 mM AA treatment. Therefore, treatment of mussels with AA seems to produce threshold effects, although the precise underlying mechanisms must be elucidated in future studies. These findings show that treatment of mussels with effective antioxidants can be useful as a strategic approach for the reduction of the deleterious effects on mussels' summer mortality in aquaculture zones.

Mitochondrial NOS1 suppresses apoptosis in colon cancer cells through increasing SIRT3 activity

Previous studies have suggested that nitric oxide (NO) which is synthetized by nitric oxide synthase (NOS) is closely related to the carcinogenesis and progression of colon cancer. However, the precise physiopathological role of NO on colon cancer remains unclear, and a lot of related studies focused on NOS2 and NOS3, but little on NOS1. Here, stable overexpression NOS1 of colon cancer cells were constructed to investigate whether NOS1 plays a special role in colon cancer. We observed that NOS1 protein was presented in mitochondria. Both the basal and cisplatin-induced mitochondrial superoxide were inhibited by NOS1, and the cisplatin-induced apoptosis was also inhibited by NOS1. Geldanamycin, a Hsp90 N-terminal inhibitor, was able to impede NOS1 translocation into mitochondria and reverse NOS1-induced apoptosis resistance. Importantly, SIRT3 activity was enhanced by NOS1, which contributes to the low level of mitochondrial superoxide and apoptosis resistance. Our data suggest a link between NOS1 and apoptosis resistance in colon cancer cells through mtNOS1-SIRT3-SOD2 axis. Furthermore, NOS1-induced apoptosis resistance could be reversed by inhibiting mitochondrial translocation of NOS1.

Flavone inhibits nitric oxide synthase (NOS) activity, nitric oxide production and protein S-nitrosylation in breast cancer cells

As the core structure of flavonoids, flavone has been proved to possess anticancer effects. Flavone's growth inhibitory functions are related to NO. NO is synthesized by nitric oxide synthase (NOS), and generally increased in a variety of cancer cells. NO regulates multiple cellular responses by S-nitrosylation. In this study, we explored flavone-induced regulations on nitric oxide (NO)-related cellular processes in breast cancer cells. Our results showed that, flavone suppresses breast cancer cell proliferation and induces apoptosis. Flavone restrains NO synthesis by does-dependent inhibiting NOS enzymatic activity. The decrease of NO generation was detected by fluorescence microscopy and flow cytometry. Flavone-induced inhibitory effect on NOS activity is dependent on intact cell structure. For the NO-induced protein modification, flavone treatment significantly down-regulated protein S-nitrosylation, which was detected by "Biotin-switch" method. The present study provides a novel, NO-related mechanism for the anticancer function of flavone.

Arctigenin promotes apoptosis in ovarian cancer cells via the iNOS/NO/STAT3/survivin signalling

Arctigenin is a biologically active lignan extracted from the seeds of Arctium lappa and shows anticancer activity against a variety of human cancers. The aim of this study was to determine the effects of arctigenin on ovarian cancer cell proliferation and survival and associated molecular mechanisms. Human ovarian cancer OVCAR3 and SKOV3 cells were treated with arctigenin, and cell proliferation and apoptosis were assessed. Western blot analysis was used to examine signal transducer and activator of transcription-3 (STAT3) phosphorylation and survivin and inducible nitric oxide synthase (iNOS) expression. The involvement of STAT3/survivin/iNOS/NO signalling in arctigenin action was checked. Arctigenin treatment resulted in a significant and dose-dependent inhibition of cell proliferation. Arctigenin-treated cells showed a 4-6 times increase in the percentage of apoptosis, compared with control cells. Pre-treatment with Ac-DEVD-CHO, a specific inhibitor of caspase-3, counteracted the induction of apoptosis by arctigenin. Arctigenin treatment significantly inhibited STAT3 phosphorylation and survivin and iNOS expression. Arctigenin-induced apoptosis was impaired by pre-transfection with survivin-expressing plasmid or addition of chemical nitric oxide (NO) donors. Additionally, exogenous NO prevented the suppression of STAT3 phosphorylation and survivin expression by arctigenin. Arctigenin treatment inhibits the proliferation and induces caspase-3-dependent apoptosis of ovarian cancer cells. Suppression of iNOS/NO/STAT3/survivin signalling is causally linked to the anticancer activity of arctigenin. Therefore, arctigenin may be applicable to anticancer therapy for ovarian cancer.

Pro-oxidative synergic bactericidal effect of NO: kinetics and inhibition by nitroxides

NO plays diverse roles in physiological and pathological processes, occasionally resulting in opposing effects, particularly in cells subjected to oxidative stress. NO mostly protects eukaryotes against oxidative injury, but was demonstrated to kill prokaryotes synergistically with H2O2. This could be a promising therapeutic avenue. However, recent conflicting findings were reported describing dramatic protective activity of NO. The previous studies of NO effects on prokaryotes applied a transient oxidative stress while arbitrarily checking the residual bacterial viability after 30 or 60min and ignoring the process kinetics. If NO-induced synergy and the oxidative stress are time-dependent, the elucidation of the cell killing kinetics is essential, particularly for survival curves exhibiting a "shoulder" sometimes reflecting sublethal damage as in the linear-quadratic survival models. We studied the kinetics of NO synergic effects on H2O2-induced killing of microbial pathogens. A synergic pro-oxidative activity toward gram-negative and gram-positive cells is demonstrated even at sub-μM/min flux of NO. For certain strains, the synergic effect progressively increased with the duration of cell exposure, and the linear-quadratic survival model best fit the observed survival data. In contrast to the failure of SOD to affect the bactericidal process, nitroxide SOD mimics abrogated the pro-oxidative synergy of NO/H2O2. These cell-permeative antioxidants, which hardly react with diamagnetic species and react neither with NO nor with H2O2, can detoxify redox-active transition metals and catalytically remove intracellular superoxide and nitrogen-derived reactive species such as (•)NO2 or peroxynitrite. The possible mechanism underlying the bactericidal NO synergy under oxidative stress and the potential therapeutic gain are discussed.

iNOS-selective inhibitors for cancer prevention: promise and progress

Nitric oxide (NO) is involved in various physiological functions and its role in tumorigenesis has been well studied. A large majority of human and experimental tumors appear to progress owing to NO resulting from iNOS, further stimulated by proinflammatory cytokines. Conversely, in some cases, NO is associated with induction of apoptosis and tumor regression. This dichotomy of NO is largely explained by the complexity of signaling pathways in tumor cells, which respond to NO very differently depending on its concentration. In addition, NO alters many signaling pathways through chemical modifications, such as the addition of S-nitrosothiols and nitrosotyrosine to target proteins altering various biological pathways. Hence, iNOS inhibitors are designed and developed to inhibit various organ site cancers including the colon. Here, we review iNOS expression, generation of NO, involvement of NO in altering signaling pathways, and iNOS select inhibitors and their possible use for the prevention and treatment of various cancers.

Effect of early acute high concentrations of iodide exposure on mitochondrial superoxide production in FRTL cells

Excessive oxidative stress has been suggested as one of the underlying mechanisms in the development of thyroid cytotoxicity. Although the involvement of mitochondria has been hypothesized, the effect of early acute high concentrations of iodide on mitochondrial superoxide production remains largely unknown, especially within a 24 h time frame. By using a novel fluorescent probe, MitoSOX Red, we demonstrated the concentration response and time-course response of KI-induced mitochondrial superoxide production in the Fischer rat thyroid cell line (FRTL). A strong increase of MitoSOX Red fluorescence intensity in FRTL cells can be seen at 2 h following high concentrations of iodide exposure. Besides, we indicated that 6-propyl-2-thiouracil (PTU, 300 μM), thyroid-stimulating hormone (TSH, 10 mU/ml), and perchlorate (KClO(4), 30 μM) can inhibit excessive iodide-induced strong mitochondrial superoxide production; however, diethyldithiocarbamic acid (DETC, 2 mM) can further increase excessive iodide-induced mitochondrial superoxide production. By using transmission electron microscopy (TEM), we noted accumulated myelinoid bodies with lipid droplets and numerous apoptotic nuclear bodies at 24 h in FRTL cells. In addition, we demonstrated a significant decrease in cytochrome c (cyt c) content in the mitochondria by enzyme linked immunosorbent assay (ELISA), and DNA fragments and significant increases in lactate dehydrogenase (LDH) activity were detected. We propose a sequence of events mediated by a strong mitochondrial superoxide production at 2 h, followed by lipid peroxidation, cell membrane damage with significant cyt c release, culminating in DNA fragmentation and apoptotic nuclear formation at 24 h, which may partly contribute to the underlying mechanisms of early acute iodide excess.

Colorectal cancer chemoprevention by trans-resveratrol

trans-Resveratrol (trans-3,4',5-trihydroxystilbene) is a natural phytoalexin present in grapes, red wine, berries and peanuts with health protecting properties. The low oral bioavailability indicated for this polyphenol, with the intestine as a bottleneck to its absorption, has promoted the large intestine as a potential target site for its chemopreventive activity. This review recapitulates the current evidence of the effects of trans-resveratrol on colon cancer. First, we describe the studies conducted in vitro which show that the protective activity takes place by inhibition of proliferation and induction of apoptosis. Secondly, the chemopreventive activity in animal models of colon carcinogenesis is revised. trans-Resveratrol not only reduces the number of preneoplastic lesions but also the incidence and multiplicity of tumors. Lastly, the article also reviews the available data on clinical trials. Altogether, the present findings support the hypothesis that the oral administration of trans-resveratrol might contribute to the prevention of colon carcinogenesis.

Release of NO from a nitrosyl ruthenium complex through oxidation of mitochondrial NADH and effects on mitochondria

Nitrosyl ruthenium complexes are promising NO donor agents with numerous advantages for the biologic applications of NO. We have characterized the NO release from the nitrosyl ruthenium complex [Ru(NO(2))(bpy)(2)(4-pic)](+) (I) and the reactive oxygen/nitrogen species (ROS/RNS)-mediated NO actions on isolated rat liver mitochondria. The results indicated that oxidation of mitochondrial NADH promotes NO release from (I) in a manner mediated by NO(2) formation (at neutral pH) as in mammalian cells, followed by an oxygen atom transfer mechanism (OAT). The NO released from (I) uncoupled mitochondria at low concentrations/incubation times and inhibited the respiratory chain at high concentrations/incubation times. In the presence of ROS generated by mitochondria NO gave rise to peroxynitrite, which, in turn, inhibited the respiratory chain and oxidized membrane protein-thiols to elicit a Ca(2+)-independent mitochondrial permeability transition; this process was only partially inhibited by cyclosporine-A, almost fully inhibited by the thiol reagent N-ethylmaleimide (NEM) and fully inhibited by the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO). These actions correlated with the release of cytochrome c from isolated mitochondria as detected by Western blotting analysis. These events, typically involved in cell necrosis and/or apoptosis denote a potential specific action of (I) and analogs against tumor cells via mitochondria-mediated processes.

A novel quinone-based derivative (DTNQ-Pro) induces apoptotic death via modulation of heat shock protein expression in Caco-2 cells

BACKGROUND AND PURPOSE

The resistance of human colon adenocarcinoma cells to antineoplastic agents may be related to the high endogenous expression of stress proteins, including the family of heat shock proteins (HSPs). Recently, a quinone-based pentacyclic derivative, DTNQ-Pro, showed high cytotoxic activity in human colon carcinoma cell lines. The aim of the present study was to determine the precise cellular mechanisms of this cytotoxic action of DTNQ-Pro.

EXPERIMENTAL APPROACH

Using human colorectal carcinoma-derived Caco-2 cells as a model, we studied the effects of DTNQ-Pro on cellular viability and oxidative stress; HSP70 and HSP27 accumulation; and cell cycle, differentiation and apoptosis.

KEY RESULTS

Incubation of Caco-2 cells with DTNQ-Pro reduced cell growth and increased the levels of reactive oxygen species in mitochondria. After 48 h of treatment, cells surviving showed an increased expression of Mn-superoxide dismutase (SOD), nitric oxide production and membrane lipid peroxidation. Treatment with DTNQ-Pro decreased HSP70 expression, and redistributed HSP27 and vimentin within the cell. DTNQ-Pro down-regulated the expression of A and B cyclins with arrest of the cell cycle in S phase and increased cellular differentiation. A second treatment of Caco-2 cells with DTNQ-Pro induced cellular death by activation of the apoptotic pathway.

CONCLUSIONS AND IMPLICATIONS

DTNQ-Pro causes Caco-2 cell death by induction of apoptosis via inhibition of HSP70 accumulation and the intracellular redistribution of HSP27. These findings suggest the potential use of DTNQ-Pro in combination chemotherapy for colon cancer.

Flavone induces changes in intermediary metabolism that prevent microadenoma formation in colonic tissue of carcinogen-treated mice

SCOPE

Colorectal cancer is a major cause of cancer deaths worldwide with the need for improved therapeutics and adjuvants.

METHODS AND RESULTS

We here tested whether the secondary plant compound flavone affects the development of aberrant crypt foci and microadenomas triggered in C57BL/6J mice by 1,2-dimethylhydrazine. Ten weeks after the last 1,2-dimethylhydrazine injection, flavone was applied at 400 mg/kg body weight over 4 wk by gavage. Flavone was found to increase apoptosis and to reduce the rate of proliferation and aberrant crypt formation. More importantly, development of microadenomas was completely suppressed by flavone. Proteome analysis by 2-DE with mass spectrometric identification of regulated proteins suggests a downregulation of tricarboxylic acid cycle activity in colonocytes with compensation by increased FADH(2) production via a partial beta-oxidation of long-chain fatty acids to meet energy demands. Transcriptome analysis, using a Gene Chip expression array with 24,000 gene probes confirmed the proteome data and moreover revealed the increased expression of various solute transporters, suggesting increased substrate supply to be used for tricarboxylic acid cycle-independent energy production.

CONCLUSION

In conclusion, changes in the levels of proteins from intermediary metabolism or their encoding mRNAs are linked to flavone-induced apoptosis and the prevention of microadenoma formation in transformed colonocytes of mice.

Protection by pentoxifylline of malathion-induced toxic stress and mitochondrial damage in rat brain

OBJECTIVE

The objective of this study was to investigate the possible protective effects of pentoxifylline as a phosphodiesterase-5 inhibitor on malathion-induced oxidative damage to rat brain mitochondria.

METHODS

Rats received malathion (200 mg/kg/day) and pentoxifylline (PTX, 50 mg/kg/day) in combination or alone. Alpha-tocopherol (AT, 15 mg/kg/day) was used as a positive standard. After 1 week of treatment, blood, whole brain tissue, and brain mitochondria were isolated. The activity of enzymatic scavengers such as glutathione peroxidase (GPx), catalase (CAT), copper-zinc superoxide dismutase (Cu/ZnSOD), and manganese superoxide dismutase (MnSOD) were measured. The extents of cellular lipid peroxidation (LPO), nitrotyrosine (NOx), and the ratio of reduced versus oxidized glutathione (GSH/GSSG) were determined. The protein expression of MnSOD was determined in brain mitochondria.

RESULTS

Malathion stimulated activities of CAT, Cu/ZnSOD, GPx, and increased LPO and NOx, and decreased GSH/GSSG in whole brain homogenate. The changes in CAT, LPO, GPx, and GSH/GSSG were restored by PTX and AT. In plasma samples, malathion increased CAT, Cu/ZnSOD, and GPx activities, increased LPO, and decreased GSH/GSSG, while PTX and AT attenuated malathion-induced changes in GPx, Cu/ZnSOD, LPO, and GSH/GSSG. In brain mitochondria, malathion enhanced LPO, NOx, CAT, GPx, and MnSOD and decreased GSH/GSSG as compared to controls, whereas PTX and AT restored malathion-induced changes in GSH/GSSG, NOx, GPx, and CAT. Malathion noticeably enhanced expression of MnSOD protein as compared to controls. Malathion decreased viability of mitochondria that was recovered by AT. It is concluded that oxidative damage is at least in part the mechanism of toxicity of malathion in the mitochondria that can be recovered by PTX comparable to AT.

Effects on mitochondria of mitochondria-induced nitric oxide release from a ruthenium nitrosyl complex

The ruthenium nitrosyl complex trans-[Ru(NO)(NH(3))(4)(py)](PF(6))(3) (pyNO), a nitric oxide (NO) donor, was studied in regard to the release of NO and its impact both on isolated mitochondria and HepG2 cells. In isolated mitochondria, NO release from pyNO was concomitant with NAD(P)H oxidation and, in the 25-100 microM range, it resulted in dissipation of mitochondrial membrane potential, inhibition of state 3 respiration, ATP depletion and reactive oxygen species (ROS) generation. In the presence of Ca(2+), mitochondrial permeability transition (MPT), an unspecific membrane permeabilization involved in cell necrosis and some types of apoptosis, was elicited. As demonstrated by externalization of phosphatidylserine and activation of caspase-9 and caspase-3, pyNO (50-100 microM) induced HepG2 cell death, mainly by apoptosis. The combined action of the NO itself, the peroxynitrite yielded by NO in the presence of reactive oxygen species (ROS) and the oxidative stress generated by the NAD(P)H oxidation is proposed to be involved in cell death by pyNO, both via respiratory chain inhibition and ROS levels increase, or even via MPT, if Ca(2+) is present.

The Fas death signaling pathway connecting reactive oxygen species generation and FLICE inhibitory protein down-regulation

Fas-mediated apoptosis plays an important role in normal tissue homeostasis, and disruption of this death pathway contributes to many human diseases. Induction of apoptosis via Fas activation has been associated with reactive oxygen species (ROS) generation and down-regulation of FLICE inhibitory protein (FLIP); however, the relationship between these two events and their role in Fas-mediated apoptosis are unclear. We show herein that ROS are required for FLIP down-regulation and apoptosis induction by Fas ligand (FasL) in primary lung epithelial cells. ROS mediate the down-regulation of FLIP by ubiquitination and subsequent degradation by proteasome. Inhibition of ROS by antioxidants or by ectopic expression of ROS-scavenging enzymes glutathione peroxidase and superoxide dismutase effectively inhibited FLIP down-regulation and apoptosis induction by FasL. Hydrogen peroxide is a primary oxidative species responsible for FLIP down-regulation, whereas superoxide serves as a source of peroxide and a scavenger of NO, which positively regulates FLIP via S-nitrosylation. NADPH oxidase is a key source of ROS generation induced by FasL, and its inhibition by dominant-negative Rac1 expression or by chemical inhibitor decreased the cell death response to FasL. Taken together, our results indicate a novel pathway of FLIP regulation by an interactive network of reactive oxygen and nitrogen species that provides a key mechanism of apoptosis regulation in Fas-induced cell death and related apoptosis disorders.

Hesperetin exerts dose dependent chemopreventive effect against 1,2-dimethyl hydrazine induced rat colon carcinogenesis

Colon cancer is still one of the leading causes of death in USA and is increasing at an alarming rate in Asia. It is one of the major causes of death in industrialized countries, and its etiology is known to be a combination of hereditary, environmental, dietary factors and lack of physical activity. Chemoprevention plays a potential role in colorectal cancer. The present study was performed to evaluate the efficacy of hesperetin supplementation on colonic aberrant crypt foci, lipid peroxidation and antioxidant defense system in 1,2-dimethylhydrazine (DMH) induced colon carcinogenesis in male Wistar rats. The rats were segregated into six groups viz., group 1, control rats received modified pellet diet; group 2 rats received modified pellet diet along with hesperetin (30 mg/kg body weight/day); groups 3-6 administrated DMH (20 mg/kg body weight) subcutaneous injection once a week for the first 4 weeks; in addition groups 4-6 received hesperetin at three different doses of 10, 20 and 30 mg/kg body weight/day for 16 weeks. All the rats were sacrificed at the end of the experimental period of 16 weeks. Increased tumor incidence and increased number aberrant crypt foci (ACF) accompanied by a decrease in the tissue lipid peroxidation, glutathione S-transferase (GST), glutathione peroxidase (GPx), superoxide dismutase (SOD), and catalase (CAT) activities were observed in DMH-treated rats. Administration of hesperetin to DMH treated rats significantly decreased the tumor incidence, the number of aberrant crypt foci with simultaneous enhancement of tissue lipid peroxidation, GST, GPx, SOD, and CAT activities. The results of this study suggest that hesperetin at a dose of 20 mg/kg body weight showed a significant beneficial effect against chemically induced colonic carcinogenesis in rats as compared to the other two doses.

Resveratrol induces apoptosis through ROS-dependent mitochondria pathway in HT-29 human colorectal carcinoma cells

trans-Resveratrol is a polyphenol found in blueberries, grapes, and wine with cancer chemopreventive properties. The low bioavailability of this compound enhances its concentration in the luminal content and becomes a potential chemopreventive agent against colon cancer. In the present study, the antiproliferative and pro-apoptotic effects on the human colorectal carcinoma HT-29 cells as well as the mechanisms underlying these effects were examined. Proliferation, cytotoxicity, and apoptosis were measured by fluorescence-based techniques. Studies of dose-dependent effects of trans-resveratrol showed antiproliferative activity with an EC 50 value of 78.9 +/- 5.4 microM. Caspase-3 was activated in a dose-dependent manner after incubation for 24 h giving an EC 50 value of 276.1 +/- 1.7 microM. Apoptosis was also confirmed with microscopic observation of changes in membrane permeability and detection of DNA fragmentation. The activity of trans-resveratrol on the mitochondria apoptosis pathway was evidenced by the production of superoxide anions in the mitochondria of cells undergoing apoptosis. In conclusion, trans-resveratrol inhibits cell proliferation without cytotoxicity and induces apoptosis in HT-29. Results of the present study provide evidence demonstrating the antitumor effect of trans-resveratrol via a ROS-dependent apoptosis pathway in colorectal carcinoma.

Increased inducible nitric oxide synthase in lung carcinoma of smokers

BACKGROUND

Cigarette smoking is well known to play an important role in the development of lung cancer. Inducible nitric oxide synthase (iNOS) can either promote or inhibit cell proliferation and growth, which makes its role in the development of malignant tumors controversial. The relation between cigarette smoking and iNOS in human lung cancer is unknown.

METHODS

The study examined the levels of iNOS/NO in nonsmall-cell lung cancer (NSCLC) tissues of smokers and nonsmokers and in NSCLC cells (NCI-H23) treated by 4-(N-Methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK), a potent tobacco-specific carcinogen.

RESULTS

The level of iNOS/NO was significantly higher in lung cancer tissues of smokers than that of nonsmokers. Unlike iNOS/NO, the activity of caspase-3 was reduced in the former compared with the latter. The expression of the cleaved caspase-3 was deceased in NCI-H23 cells treated with S-Nitroso-N-acetylpenicillamine (SNAP), an NO donor, whereas treatment with NG-methyl-L-arginine (NMA), an NO inhibitor, caused an increase in cleaved caspase-3. Consistent with the change in caspase-3, SNAP treatment inhibited cell death induced by UCN01, a potent cell death-inducer. NMA treatment greatly enhanced the sensitivity of the cells to UCN01. Further, the cells treated by NNK showed an increase in iNOS protein, accompanied by an elevation of cell proliferation.

CONCLUSIONS

The study demonstrates that cigarette smoking promotes the level of iNOS/NO but suppresses the activity of caspase-3, which may lead to the proliferation and growth of lung cancer cells.

Pros and cons of L-arginine supplementation in disease

The amino acid arginine and one of its metabolites NO have gathered broad attention in the last decade. Although arginine is regarded as a conditionally essential amino acid in disease, L-arginine supplementation in severe illness has not found its way into clinical practice. This might be due to the invalid interpretation of results from studies with immune-enhancing diets containing L-arginine amongst other pharmaconutrients. However, not much attention is given to research using L-arginine as a monotherapy and the possibility of the alternative hypothesis: that L-arginine supplementation is beneficial in disease. The present review will discuss data from studies in healthy and diseased animals and patients with monotherapy of L-arginine to come to an objective overview of positive and negative aspects of L-arginine supplementation in disease with special emphasis on sepsis, cancer, liver failure and wound healing.

Proteomic characterization of Sophoraflavone J-induced apoptosis in HepG2 cells

Chinese herb Radix sophorae is widely applied as an anticarcinogenic/antimetastatic agent against liver cancers. In the current study, Sophoraflavone J, a flavonoid constituent enriched in the root of Radix sophorae, induced apoptosis in human hepatoma HepG2 cells via the intrinsic mitochondrial death pathway. The molecular mechanism of the cytotoxic effect was further investigated by a comparative proteomic approach. Differentially expressed proteins identified included membrane proteins/antigens, structural proteins, transcriptional factors, glycolytic enzymes, heat-shock chaperon proteins, ROS-related proteins and proteosomes, etc. These findings were further validated by Western blot analysis and real-time PCR. Preliminary experiments to characterize the roles of these proteins were conducted. Our data suggested that Sophoraflavone J treatment triggered nutrient depletion and generation of ROS in cells, which subsequently led to mitochondrial dysfunction and apoptosis.

The suppression of aberrant crypt multiplicity in colonic tissue of 1,2-dimethylhydrazine-treated C57BL/6J mice by dietary flavone is associated with an increased expression of Krebs cycle enzymes

Colorectal cancer is the second leading cause of cancer deaths worldwide with diet playing a prominent role in disease initiation and progression. Flavonoids are secondary plant compounds that are suggested as protective ingredients of a diet rich in fruits and vegetables. We here tested whether flavone, a flavonoid that proved to be an effective apoptosis inducer in colon cancer cells in culture, can affect the development of aberrant crypt foci (ACFs) in C57BL/6J mice in vivo when preneoplastic lesions were induced by the carcinogen 1,2-dimethylhydrazine (DMH). Flavone applied at either a low dose (15 mg/kg body wt per day) or a high dose (400 mg/kg body wt per day) reduced the numbers of ACFs significantly, independent of whether it was supplied simultaneously with the carcinogen (blocking group) or subsequent to the tumor induction phase (suppressing group). Proteome analysis performed in colonic tissue samples revealed that flavone treatment increased the expression of a number of Krebs cycle enzymes in the suppressing group and this was associated with reduced crypt multiplicity. It suggests that mitochondrial substrate oxidation is increased by flavone in colonic cells in vivo as already observed in HT-29 cells in vitro as the prime mechanism underlying tumor cell apoptosis induction by flavone. In conclusion, flavone reduces the number of ACFs in DMH-treated mice at doses that can be achieved for flavonoids by a diet rich in fruits and vegetables. Moreover, reduction in crypt multiplicity by flavone is most probably due to the preservation of a normal oxidative metabolism.

Nitric oxide, a double edged sword in cancer biology: Searching for therapeutic opportunities

Nitric oxide (NO) is a pleiotropic molecule critical to a number of physiological and pathological processes. The last decade has witnessed major advances in dissecting NO biology and its role in cancer pathogenesis. However, the complexity of the interactions between different levels of NO and several aspects of tumor development/progression has led to apparently conflicting findings. Furthermore, both anti-NO and NO-based anticancer strategies appear effective in several preclinical models. This paradoxical dichotomy is leaving investigators with a double challenge: to determine the net impact of NO on cancer behavior and to define the therapeutic role of NO-centered anticancer strategies. Only a comprehensive and dynamic view of the cascade of molecular and cellular events underlying tumor biology and affected by NO will allow investigators to exploit the potential antitumor properties of drugs interfering with NO metabolism. Available data suggest that NO should be considered neither a universal target nor a magic bullet, but rather a signal transducer to be modulated according to the molecular makeup of each individual cancer and the interplay with conventional antineoplastic agents.

WP760, a melanoma selective drug

PURPOSE

Our goal was to perform studies on the specificity and antimelanoma mechanism of a novel bis-anthracycline, WP760. WP760 initially identified in the NCI 160 screen as anti-melanoma.

METHODS

The methyl thiazolyl tetrazolium reduction (MTT) assay was used to test tumor cell growth inhibition; confocal microscopy to view WP760 intracellular distribution; flow cytometry for cell-cycle arrest and apoptosis; and Western blotting was employed to identify and compare quantities and kinetics of cell growth related molecule levels.

RESULTS

WP760 induced G(2)/M-phase cell-cycle arrest and apoptosis in melanoma cell lines and short-term melanoma explants established from clinical specimens in a time and concentration dependent manner at nM concentrations. In contrast, effects on fibroblasts and A549 lung cancer cells required higher concentrations, suggesting that WP760 possesses selectivity for melanoma. Molecular studies indicated that WP760 induced p53 stabilization, checkpoint kinase 2 and p27(Kip1) protein upregulation, and activation of caspase-3. Endogenous nitric oxide (NO) production has been implicated in the chemoresistance of melanoma; WP760 caused inhibition of the inducible nitric oxide synthase (iNOS) protein as well as inhibition of phosphorylation of ERK, known to drive the iNOS pathway. Based on WP760 localization into mitochondria, and caspase-3 inhibitor block the killing of WP760, the intrinsic pathway of apoptosis appears to have been activated.

CONCLUSIONS

Our results indicate that WP760 affects a critical and unique set of growth regulatory effects in melanoma, and is a promising candidate for further preclinical studies.

Functional interaction between nitric oxide-induced iron homeostasis and heme oxygenase-1 in immortalized and malignant oral keratinocytes

Heme oxygenase-1 (HO-1) is involved in a variety of regulatory and protective cellular mechanisms as a stress-responsive protein. Whether HO-1 plays a protective role against NO-induced cytotoxicity in oral cancer cells has not yet been established. We used sodium nitroprusside (SNP) as a source of exogenous NO in studies of NO-induced cytotoxicity in immortalized (IHOK) and malignant oral keratinocytes (HN12). The roles of the caspase pathway, of regulatory proteins of iron metabolism (iron regulatory protein (IRP)1, IRP2, transferrin receptor (TfR), and ferritin), and of HO-1 in protection against NO-induced cytotoxicity were assessed. The SNP-induced growth inhibition and apoptosis of IHOK and HN12 cells was reduced by addition of ferric citrate (FC). At low concentrations (< 1 mM), SNP up-regulated cellular iron metabolism by increasing expression of IRP1, IRP2, and TfR, whereas at high concentrations (> 2 mM), SNP down-regulated expression of these proteins. A consistent correlation between decreased levels of IRP1, IRP2, and TfR and increased NO-induced cytotoxicity and apoptosis was observed. Addition of FC inhibited the NO-induced decrease in IRP1, IRP2, and TfR levels. Moreover, SNP increased the expression of HO-1 and ferritin in IHOK and HN12 cells in a concentration-dependent manner. NO-induced cytotoxicity was also inhibited by hemin (an HO-1 agonist) and was enhanced by zinc protoporphyrin IX (an HO-1 inhibitor). Based on these results, we conclude that HO-1 plays a major role in mediating cytoprotection and iron homeostasis against NO toxicity in immortalized and malignant oral keratinocytes.

Olive fruit extracts inhibit proliferation and induce apoptosis in HT-29 human colon cancer cells

Olives and their derivatives represent an important component of the Mediterranean diet that has been considered to be protective against cancer. We investigated the effect on cell proliferation and apoptosis in HT-29 cells of an extract from the skin of olives composed of pentacyclic triterpenes with the main components maslinic acid (73.25%) and oleanolic acid (25.75%). Studies of the dose-dependent effects showed antiproliferative activity at an EC50 value of 73.96 +/- 3.19 micromol/L of maslinic acid and 26.56 +/- 2.55 micromol/L of oleanolic acid without displaying necrosis. Apoptosis was confirmed by the microscopic observation of changes in membrane permeability in 40.9 +/- 3.9% and detection of DNA fragmentation in 24.5 +/- 1.5% of HT-29 cells incubated for 24 h with olive fruit extract containing 150 and 55.5 micromol/L of maslinic and oleanolic acids, respectively. Caspase-3 was activated in a dose-dependent manner after incubation for 24 h. The extract containing 200 micromol/L maslinic acid and 74 micromol/L oleanolic acid increased caspase-3-like activity to 6-fold that of control cells. Programmed cell death was induced by the intrinsic pathway, as evidenced by the production of superoxide anions in the mitochondria of cells treated with olive fruit extracts containing 150 and 55.5 micromol/L of maslinic and oleanolic acids, respectively. Our results report for the first time, to our knowledge, the inhibition of cell proliferation without cytotoxicity and the restoration of apoptosis in colon cancer cells by maslinic and oleanolic acids present in olive fruit extracts.

Dual effect of nitric oxide in immortalized and malignant human oral keratinocytes: induction of apoptosis and differentiation

BACKGROUND

Nitric oxide (NO) is known to act cytostatically on several tumor cell when functioning as an effector molecule of activated macrophages, but the differential effects of NO on immortalized and malignant oral keratinocytes have not been examined.

METHODS

We investigated the influence of NO on the proliferation, cell cycle, apoptosis, and differentiation of immortalized human oral keratinocytes (IHOK) and primary oral cancer cells (HN4) using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, sulforhodamine B (SRB) assay, flow cytometry, nuclear DNA staining, and Western blotting.

RESULTS

The MTT and SRB assays indicated inhibited growth of IHOK and HN4 cells that were treated with sodium nitroprusside (SNP) at concentrations higher than 1 mM but not at lower SNP concentrations. The higher concentrations of SNP up-regulated the apoptosis-related protein expression, which is consistent with the analyses of sub-G(1) phase arrest, annexin V-FITC (fluorescein isothiocynate) staining, nuclear staining, and DNA fragmentation. On the other hand, the lower concentrations of SNP enhanced the expression of keratinocyte differentiation markers in IHOK and HN4 cells.

CONCLUSIONS

These data suggest that high concentrations of NO can inhibit the growth of IHOK and HN4 cells through the induction of apoptosis, while low concentrations of NO can induce cytodifferentiation. The dual effects of NO, namely, the induction of apoptosis or cytodifferentiation, have important implications for the possible anti-oral cancer treatment.

Nitric oxide promotes resistance to tumor suppression by CTLs

Many human tumors express inducible NO synthetase (NOS2), but the roles of NO in tumor development are not fully elucidated. An important step during tumor development is the acquisition of apoptosis resistance. We investigated the dose-dependent effects of endogenously produced NO on apoptosis using ecdysone-inducible NOS2 cell lines. Our results show that short-term NOS2 expression enhances CD95-mediated apoptosis and T cell cytotoxicity dose dependently. Furthermore, we could show that during chronic exposure to NO, besides the primary cytotoxic NO effect, there is selection of cell clones resistant to NO that show cross-resistance to CD95-induced apoptosis and the killing by CTLs. We propose that NO production could initially act as an autocrine suicide or paracrine killing mechanism in cells undergoing malignant transformation. However, once failed, the outcome is fatal. NO promotes tumor formation by enhancing the selection of cells that can evade immune attack by acquiring apoptosis resistance.

Proline oxidase activates both intrinsic and extrinsic pathways for apoptosis: the role of ROS/superoxides, NFAT and MEK/ERK signaling

Proline oxidase (POX), often considered a 'housekeeping enzyme' might play an important role in apoptosis. We have shown that POX generated proline-dependent reactive oxygen species (ROS), specifically superoxide radicals, and induced apoptosis through the mitochondrial (intrinsic) pathway. In our current report, we used DLD-1 colorectal cancer cells stably transfected with the POX gene under the control of a tetracycline-inducible promoter and found POX-stimulated expression of tumor necrosis factor-related apoptosis inducing ligand (TRAIL), DR5 and cleavage of caspase-8. Importantly, apoptosis measured by flow cytometry was partially inhibited by Z-IETD-FMK, a specific inhibitor of caspase-8. These findings suggest that the extrinsic (death receptor) pathway also is activated by POX. Furthermore, the mechanism of this effect on the extrinsic pathway, specifically, the induction of TRAIL by POX, may be mediated by NFAT transcription factors. Additionally, POX expression also dramatically decreased phosphorylation of MEK and ERK, and the decrease was partially reversed by expression of manganese superoxide dismutase (MnSOD). Overexpression of constitutively active form of MEK, acMEK, partially blocked POX-induced apoptosis. These findings suggest the involvement of MEK/ERK signaling and further confirm the role of ROS/superoxides in POX-induced apoptosis. Combined with previously published data, we conclude that POX may induce apoptosis through both intrinsic and extrinsic pathways and is involved in nuclear factor of activated T cells (NFAT) signaling and regulation of the MEK/ERK pathway. It is suggested that, as a nutrition factor, POX may modulate apoptosis signals induced by p53 or other anti-cancer agents and enhance apoptosis in stress situations.

The role of NO synthases in arginine-dependent small intestinal and colonic carcinogenesis

Arginine is catabolized by NOS2 and other nitric oxide synthases to form nitric oxide. We evaluated the roles of dietary arginine and Nos2 in Apc-dependent intestinal tumorigenesis in Min mice with and without a functional Nos2 gene. NOS2 protein was expressed only in intestinal tissues of Apc(Min/+) Nos2+/+ mice. NOS3 expression was higher in intestinal tissues of mice lacking Nos2, mainly in the small intestine. When diet was supplemented with arginine (0.2% and 2% in drinking water), lack of Nos2 results in decreased tumorigenesis in both small intestine and colon. In Nos2 knockout mice, supplemental arginine (up to 2%) caused a decrease in small intestinal tumor number and size. The arginine-dependent decrease was associated with an increase in nitrotyrosine formation and apoptosis in the region of intestinal stem cells. Mice expressing Nos2 did not show these changes. These mice did, however, show an arginine-dependent increase in colon tumor number and incidence, while no effect on apoptosis was seen. These changes were associated with increased nitrotyrosine formation in epithelial cells. Mice lacking Nos2 did not show changes in tumorigenesis or nitrotyrosine formation, while demonstrating an arginine-dependent increase in apoptosis. These data suggest that Nos2 and dietary arginine have significant effects on intestinal and colonic tumorigenesis in Min mice. In both tissues, loss of Nos2 is associated with decreased tumorigenesis when mice are supplemented with dietary arginine. In the small intestine, Nos2 prevents the arginine-induced decrease in tumor number and size, which is associated with NOS3 expression and increased apoptosis. In the colon, Nos2 is required for the arginine-induced increase in tumor number and incidence.

alpha-Lipoic acid induces apoptosis in human colon cancer cells by increasing mitochondrial respiration with a concomitant O2-*-generation

The antioxidant alpha-lipoic acid (ALA) has been shown to affect a variety of biological processes associated with oxidative stress including cancer. We determined in HT-29 human colon cancer cells whether ALA is able to affect apoptosis, as an important parameter disregulated in tumour development. Exposure of cells to ALA or its reduced form dihydrolipoic acid (DHLA) for 24 h dose dependently increased caspase-3-like activity and was associated with DNA-fragmentation. DHLA but not ALA was able to scavenge cytosolic O2-* in HT-29 cells whereas both compounds increased O2-*-generation inside mitochondria. Increased mitochondrial O2-*-production was preceded by an increased influx of lactate or pyruvate into mitochondria and resulted in the down-regulation of the anti-apoptotic protein bcl-X(L). Mitochondrial O2-*-generation and apoptosis induced by ALA and DHLA could be prevented by the O2-*-scavenger benzoquinone. Moreover, when the lactate/pyruvate transporter was inhibited by 5-nitro-2-(3-phenylpropylamino) benzoate, ALA- and DHLA-induced mitochondrial ROS-production and apoptosis were blocked. In contrast to HT-29 cells, no apoptosis was observed in non-transformed human colonocytes in response to ALA or DHLA addition. In conclusion, our study provides evidence that ALA and DHLA can effectively induce apoptosis in human colon cancer cells by a prooxidant mechanism that is initiated by an increased uptake of oxidizable substrates into mitochondria.

NO-donating aspirin inhibits both the expression and catalytic activity of inducible nitric oxide synthase in HT-29 human colon cancer cells

Nitric oxide-releasing aspirin (NO-ASA) is emerging as a potentially important chemopreventive agent against colon cancer. We examined in HT-29 human colon adenocarcinoma cells the effect of NO-ASA on the inducible form of nitric oxide synthase (NOS2), an enzyme implicated in colon carcinogenesis. NO-ASA inhibited in a time- and concentration-dependent manner the expression of NOS2 up to 70% compared to control (IC50 for this effect = 46 microM). NO-ASA also decreased the corresponding steady-state mRNA levels and this reduction preceded the reduction of protein levels by at least 6 h. NO-ASA also reduced the enzymatic activity of NOS2, as determined by a direct enzyme assay (maximal reduction = 80%) and by determining the accumulation of NO in the culture medium (IC50 for this effect = 36 microM). These effects of NO-ASA on NOS2 were paralleled by inhibition in cell growth (IC50 = 8.5 microM). These findings indicate that NO-ASA profoundly inhibits both the expression and enzymatic activity of NOS2 and suggest that these effects may represent an important mechanism for the colon cancer chemopreventive effect of NO-ASA.

Melatonin potentiates flavone-induced apoptosis in human colon cancer cells by increasing the level of glycolytic end products

Melatonin is a natural compound synthesized by a variety of organs. It has been described to possess cell protecting activity in normal cells but was shown to induce apoptotic cell death in cancer cells. We determined to which extent and based on which molecular mechanisms melatonin is able to cause apoptosis in HT-29 human colon cancer cells. Induction of apoptosis was assessed by caspase-3-like activity, nuclear fragmentation and chromatin condensation. Melatonin, when given alone at a concentration of 1 mM, did not affect any of the apoptosis markers. It potentiated apoptosis induced by the flavonoid flavone significantly. Whereas flavone alone at a concentration of 150 microM led to a 8-fold increase in caspase-3-like activity associated with around 40% of cells displaying DNA-fragmentation, a combination of flavone and melatonin increased caspase-3-like activity 30-fold and 80% of cells exhibited fragmentation of DNA when compared to untreated controls. Melatonin caused an increase in cytosolic lactate levels that most likely allows the flavone-induced activation of the mitochondrial pyruvate/lactate importer to deliver more substrates to mitochondrial respiration. The subsequent increased production of mitochondrial O2-* in the presence of flavone was further increased by melatonin. Scavenging mitochondrial O2-* by benzoquinone or blocking the lactate/pyruvate transporter by 5-nitro-2-(3-phenylpropylamino) benzoate inhibited mitochondrial O2-* -generation and apoptosis execution mediated by flavone and melatonin. Our study provides evidence that melatonin potentiates flavone-induced apoptosis in HT-29 human colon cancer cells by enhancing the level of oxidizable substrates that can be transported into mitochondria in the presence of flavone.

Effects of increased cellular zinc levels on gene and protein expression in HT-29 cells

High cellular zinc concentrations lead to impairments in ATP synthesis and cell cycle control particularly in neurons and epithelial cells. The molecular basis for these dysfunctions is still not fully elucidated. Here we analyzed the effects of a high zinc exposure (10 ppm) on gene and protein expression in the human epithelial cell line HT-29. Of the 1176 genes analyzed with cDNA arrays, nine differentially expressed genes were identified. Proteome analysis based on 1310 detected proteins identified 11 molecular targets. Most of the identified genes/proteins have not been linked to cellular zinc status before (e.g. PEC-60, R-ras3). More than half of the targets participate in ATP production or stress response. Therefore, it appears that higher zinc concentrations mediate their effects mainly via impairments in cellular energy metabolism and stress response.

MnSOD inhibits proline oxidase-induced apoptosis in colorectal cancer cells

Proline oxidase (POX), localized on inner mitochondrial membranes, is encoded by a p53-induced gene and metabolically participates in p53-induced apoptosis. Previously, we showed that POX catalyzed the generation of reactive oxygen species (ROS). We and others have demonstrated that overexpression of POX, independent of p53, causes apoptotic cell death in a variety of cancer cells. But a necessary role for ROS remains uncertain. Therefore, we asked whether superoxide dismutases (SOD) and catalase (CAT), important antioxidant enzymes, might interfere with the POX-dependent induction of apoptosis. In this study, we used DLD-1 colorectal cancer cells stably transfected with the POX gene under the control of a tetracycline-inducible promoter. When doxycycline was removed from the culture medium and the expression of POX was induced, apoptotic cell death was initiated. To examine the importance of the ROS-dependent component of the pathway, we infected DLD-1 POX cells with recombinant adenoviruses containing MnSOD, CuZnSOD, CAT or varying combinations of these adenoviruses followed by induced expression of POX. The expression of MnSOD inhibited POX-induced apoptosis, but others did not. Mechanistically, mitochondria-localized MnSOD dramatically reduced the release of cytochrome c to cytosol by POX. Compared with control cells, MnSOD-expressing DLD-1 POX cells generated a higher concentration of H2O2 owing to dismutation of superoxide radicals, which was elevated by POX. Thus, these data further suggest that the generation of superoxide radicals plays a crucial role in POX-induced apoptosis and the process is partially blocked by MnSOD.

Palmitate increases nitric oxide synthase activity that is involved in palmitate-induced cell death in cardiomyocytes

The objective of this study was to test the hypothesis that nitric oxide synthase (NOS) is subjected to regulatory control by palmitate, and that nitric oxide (NO) is operative in palmitate-induced cell death. Palmitate induced a significant ( p<0.05 ) concentration-dependent increase in NOS activity measured by the conversion of [(3)H]arginine to [3H]citrulline in embryonic chick cardiomyocytes. Cellular eNOS and iNOS, determined by immunocytochemistry, were increased by palmitate. Western blotting also showed that palmitate, 500 microM for 4h, significantly increased the amount of cellular of eNOS and iNOS by 36.2+/-6.5% ( p<0.001 ) and 38.4+/-14.4% ( p<0.05 ), respectively. The NOS inhibitor L-NAME significantly ( p<0.05 ) accentuated palmitate-induced cell death These data suggest that palmitate has a bifunctional effect on cell viability--in addition to loss of cell viability, palmitate stimulates NOS activity by inducing an increase in cellular eNOS and iNOS with the resultant NO production serving to protect cardiomyocytes from palmitate-induced cell death.

Identification of biomarkers for the initiation of apoptosis in human preneoplastic colonocytes by proteome analysis

Development of resistance of cells toward proapoptotic signals is regarded as one of the key processes that allow tumor development. To identify proteins that are crucial for the initiation of apoptosis in NCOL-1 human preneoplastic colonocytes, we analyzed the proteome of cells exposed to the flavonoids flavone and quercetin that differ in their ability to induce apoptosis although they possess similar structures. Both flavonoids inhibited proliferation and induced differentiation of NCOL-1 cells but only quercetin committed the cells to apoptosis. The accessible proteome of NCOL-1 cells was separated by 2D-polyacrylamide-gelelectrophoresis and proteins with changed expression level were identified by peptide mass fingerprints of tryptic digests of the protein spots. A pre-fractionation of soluble and lipophilic proteins was used to enhance the resolution of analysis. After exposure to the test compounds for 24 hr, 73 proteins displayed changed steady state levels in case of quercetin and 32 in case of flavone. Several heat-shock proteins, annexins and cytoskeletal caspase substrates were regulated by quercetin but not by flavone and these protein classes are known to play a role in apoptosis induction and execution. Whereas proteins like lamin A, C and desmoplakin, are indicators that apoptosis has already proceeded, others, such as annexin IV or protein kinase C-beta play a pivotal role in the early phases of apoptosis. In conclusion, proteome analysis allowed the identification of marker proteins that are involved in the initiation of apoptotic cell death in preneoplastic colonocytes and those may help to develop new strategies for cancer prevention.

Nitric oxide levels in human preneoplastic colonocytes determine their susceptibility toward antineoplastic agents

The efficacy of antineoplastic compounds can depend heavily on the genetic background of the cells exposed to the drugs. This becomes evident by the fact that HT-29 human colon cancer cells but not primary murine nontransformed colonocytes are efficiently submitted to apoptosis by the flavonoid flavone. By determining caspase-3 activation, plasma membrane disintegration, and nuclear fragmentation, we show here that flavone also does not promote apoptosis in preneoplastic NCOL-1 colonocytes derived from a nontransformed human biopsy specimen. In clear contrast, the antitumor drug camptothecin potently induces apoptosis in NCOL-1 cells associated with a specific down-regulation of the antiapoptotic factor bcl-XL at the mRNA and protein levels and with the activation of the mitochondrial apoptosis pathway. Confocal microscopy revealed an increased production of superoxide anion radicals in the mitochondria of NCOL-1 cells that preceded the apoptotic events. However, in the case of flavone, the mitochondrial oxygen radicals were effectively scavenged by physiological concentrations of nitric oxide (NO), whereas in the case of camptothecin, the available nitric oxide was rapidly scavenged by the production of large quantities of cytosolic superoxide anions. Increasing the levels of nitric oxide inside NCOL-1 cells by sodium nitroprusside prevented the apoptosis induction by camptothecin. Reducing the levels of nitric oxide by using the NO synthase inhibitor, Nomega-nitro-l-arginine methyl ester in NCOL-1 cells or using HT-29 cells that intrinsically have low NO levels enabled flavone to trigger the apoptosis pathway. In conclusion, our studies demonstrate that the intracellular levels of nitric oxide significantly change the apoptotic response to antineoplastic agents in colonic cells.

Identification of genes responsive to intracellular zinc depletion in the human colon adenocarcinoma cell line HT-29

Zinc is essential for the structural and functional integrity of cells and plays a pivotal role in the control of gene expression. To identify genes with altered mRNA expression level after zinc depletion, we employed oligonucleotide arrays with approximately 10,000 targets and used the human colon adenocarcinoma epithelial cell line HT-29 as a model. A low intracellular zinc concentration caused alterations in the steady-state mRNA levels of 309 genes at a threshold factor of 2.0. Northern blot analysis and/or real-time RT-PCR confirmed the array results for 12 of 14 selected targets. Genes identified as regulated based on microarray data encode mainly proteins involved in central pathways of intermediary metabolism (79 genes) including protein metabolism (21). We also identified five groups of genes important for basic cellular functions such as signaling (30), cell cycle control and growth (15), vesicular trafficking (15), cell-cell interaction (13), cytoskeleton (10) and transcription control (19). The latter group comprises several zinc finger-containing transcription factors of which the Kruppel-like factor 4 showed the most pronounced changes. Western blot analysis confirmed the increased expression level of this protein in cells grown under low zinc conditions. Our findings in a homogeneous cell population demonstrate that the molecular mechanisms by which cellular functions are altered at a low zinc status, occur via pleiotropic effects on gene expression. In conclusion, the pattern of zinc-affected genes may represent a reference for further studies to define the zinc regulon in mammalian cells.

Activation of mitochondrial lactate uptake by flavone induces apoptosis in human colon cancer cells

Lactate production from glucose even in the presence of oxygen is a characteristic of cancer cell metabolism and an important feature for tumor progression. Here, we describe that an increased uptake of lactate into mitochondria of HT-29 human colon cancer cells by treatment of cells with the flavonoid flavone is associated with an increased production of mitochondrial superoxide anions and apoptotic cell death. In search of the mitochondrial transporter that could promote enhanced lactate uptake and energetic flow through the electron transport chain, we used fluorescein as a model substrate. Flavone increased fluorescein uptake at pH 7.4 into mitochondria of HT-29 cells almost tenfold while lactate inhibited uptake significantly. Uptake of fluorescein in the absence or presence of flavone was strongly increased by lowering pH from 7.4 to 6.0 and almost abolished by the protonophore carbonyl cyanide m-chlorophenylhydrazone (CCCP). The lactate-sensitive part of fluorescein transport was completely blocked by p-chloromercuribenzenesulfonic acid (pCMBS), a specific inhibitor of the monocarboxylate transporter-1 (MCT-1) that by Western blotting and immunofluorescence was identified in mitochondria of HT-29 cells. Finally, lactate increased and pCMBS inhibited the flavone-induced generation of mitochondrial O2-* radicals and in turn blunted the apoptotic response. In conclusion, our studies provide evidence that flavone reverts the metabolic phenotype of transformed colonocytes towards a phenotype characteristic for normal cells. Transformed colonocytes, however, seem especially vulnerable to O2-*, produced in mitochondria as a consequence of these metabolic alterations, and respond with the induction of apoptosis.