Resveratrol inhibits drug-induced apoptosis in human leukemia cells by creating an intracellular milieu nonpermissive for death execution

Evaluation of oxidative stress-mediated cytotoxicity and genotoxicity of copper and flubendiamide: amelioration by antioxidants in vivo and in vitro

Present study was designed to evaluate toxic effects of copper (Cu) (@ 33 mg/kg b.wt.) and flubendimide (Flb) (@ 200 mg/kg b.wt.) alone and/or in combination on blood-biochemical indices, oxidative stress, and drug metabolizing enzymes (DMEs) in vivo in male Wistar rats following oral exposure continuously for 90 days and their immunotoxic (cyto-genotoxic and apoptotic) potential in vitro on thymocytes. In in vivo study, ameliorative potential of α-tocopherol was assessed, whereas α-tocopherol, curcumin, resveratrol, and catechin were evaluated for protective effect in vitro. Significantly (P < 0.05) increased AST activity and increment in total bilirubin, uric acid, creatinine, and BUN levels; however, reduction in total protein, GSH content, reduced activities of SOD and GST, and increased lipid peroxidation and GPx activity with severe degenerative changes in histopathological examination of liver and kidney in group of Cu and Flb were observed. Treatment with α-tocopherol improved biochemical variables, redox status, and histoarchitecture of liver and kidney tissues. Reduced hepatic CYP450, CYPb5, APH, UGT, and GST activities observed in both Cu and α-tocopherol alone and their combination groups, whereas significant increment in Flb alone, while α-tocopherol in combination with xenobiotics improved the activities of hepatic DMEs. Primary cell culture of thymocytes (106 cells/ml) exposed to Cu and Flb each @ 40 μM increased TUNEL+ve cells, micronuclei induction, DNA shearing, and comet formation establishes their apoptotic and genotoxic potential, whereas treatment with antioxidants showed concentration-dependent significant reduction and their order of potency on equimolar concentration (10 μM) basis is: curcumin > resveratrol > catechin = α-tocopherol.

A novel combined resveratrol/berberine phytochemotheraputic using the HePG2 cell line as a model for the treatment of hepatocarcinoma

The results presented herein show that at clinically relevant concentrations (0-30 µM), the well-tolerated phytochemical berberine (BER) induces cell death in cultured human hepatocarcinoma (HepG2) cells as a model for liver cancer, primarily via apoptosis. Similar, relatively low-concentration single treatments using the structurally related phytochemical resveratrol (RSV), had little or no effect on cell viability but inhibited the cell cycle, while simultaneously increasing the strength of cellular adhesion. When used in combination, an RSV/BER cotreatment appeared to retain the ability of a single RSV treatment to increase cellular adhesion, but also induced a massive loss in hepatocarcinoma cellular viability, inducing cell death in more than 90% of cells. This model, therefore, suggests that it may be possible to use RSV to stabilise hepatocarcinomas against metastasis while using cotreatment with BER to simultaneously induce cell death. By measuring the changes in the activity of the pleiotropic enzyme transglutaminase 2 (TGM2), which is known to be overexpressed in hepatocarcinoma and many other tumours, we hypothesise a role for this enzyme in the activities of these two phytochemicals, and propose the potential use of this RSV/BER cotreatment as a chemotherapeutic in TGM2+ hepatocarcinomas.

Towards resolving the enigma of the dichotomy of resveratrol: cis- and trans-resveratrol have opposite effects on TyrRS-regulated PARP1 activation

Unlike widely perceived, resveratrol (RSV) decreased the average lifespan and extended only the replicative lifespan in yeast. Similarly, although not widely discussed, RSV is also known to evoke neurite degeneration, kidney toxicity, atherosclerosis, premature senescence, and genotoxicity through yet unknown mechanisms. Nevertheless, in vivo animal models of diseases and human clinical trials demonstrate inconsistent protective and beneficial effects. Therefore, the mechanism of action of RSV that elicits beneficial effects remains an enigma. In a previously published work, we demonstrated structural similarities between RSV and tyrosine amino acid. RSV acts as a tyrosine antagonist and competes with it to bind to human tyrosyl-tRNA synthetase (TyrRS). Interestingly, although both isomers of RSV bind to TyrRS, only the cis-isomer evokes a unique structural change at the active site to promote its interaction with poly-ADP-ribose polymerase 1 (PARP1), a major determinant of cellular NAD+-dependent stress response. However, retention of trans-RSV in the active site of TyrRS mimics its tyrosine-bound conformation that inhibits the auto-poly-ADP-ribos(PAR)ylation of PARP1. Therefore, we proposed that cis-RSV-induced TyrRS-regulated auto-PARylation of PARP1 would contribute, at least in part, to the reported health benefits of RSV through the induction of protective stress response. This observation suggested that trans-RSV would inhibit TyrRS/PARP1-mediated protective stress response and would instead elicit an opposite effect compared to cis-RSV. Interestingly, most recent studies also confirmed the conversion of trans-RSV and its metabolites to cis-RSV in the physiological context. Therefore, the finding that cis-RSV and trans-RSV induce two distinct conformations of TyrRS with opposite effects on the auto-PARylation of PARP1 provides a potential molecular basis for the observed dichotomic effects of RSV under different experimental paradigms. However, the fact that natural RSV exists as a diastereomeric mixture of its cis and trans isomers and cis-RSV is also a physiologically relevant isoform has not yet gained much scientific attention.

Understanding the complicated relationship between antioxidants and carcinogenesis

Reactive oxygen species (ROS) are generated as by-product of cellular respiration and also due to the exposure of various xenobiotics, whereas mitochondrial electron transport chain is considered as the main source of ROS generation. The sequential addition to molecular oxygen gives rise to various forms of ROS like superoxide anion, peroxide, hydroxyl radical, hydroxyl ion, and so forth. However, the uncontrolled level of ROS generation and accumulation alters the body homeostasis. Excessive generation of ROS leads to oxidative stress and various kinds of diseases including cancer. To counteract ROS, enzymatic and nonenzymatic antioxidants' armory is available in our body. Apart from endogenous antioxidants, we are also consuming various exogenous antioxidants. Antioxidants protect us from ROS-mediated damages and inhibit ROS-induced carcinogenesis. Recent studies have revealed that antioxidants could also act as tumor-promoting agents. Various anticancer drugs are used to kill the cancer cells through the generation of oxidative stress in them, but the cancer cells can counteract the effect with the help of various endogenous as well as exogenous antioxidants. Our review will summarize the multifaceted relationship between antioxidants and carcinogenesis, and it will help to create new directions in antioxidant-based chemotherapy.

Resveratrol attenuates hydrogen peroxide-induced oxidative stress in TM3 Leydig cells in vitro

The objective of present study was to investigate in vitro protective potential of resveratrol in TM3 Leydig cells with induced oxidative stress using hydrogen peroxide (H₂O₂). Leydig cells experiencing oxidative stress exhibit reduced activities in androgens production, and become hypofunctional with age, which is also related to growing oxidative stress, while resveratrol has received growing attention as a cytoprotective agent. TM3 mouse Leydig cells were cultivated during 24 h in the presence of resveratrol (5, 10, 25, 50 and 100 μM) alone, or in combination with H₂O₂ (300/600 μM) to induce oxidative stress. Mitochondrial activity was evaluated using MTT test, triple assay was used in order to assess cell viability parameters, intracellular generation of superoxide was determined by the nitroblue-tetrazolium assay, and quantification of steroid hormones was performed by the enzyme- linked immunosorbent assay. Resveratrol alone treatment led to the most significantly improved values of all tested parameters in the cells of experimental group with addition of 10 μM of resveratrol in comparison to the control group. In the case of cells with induced oxidative stress (300 μM H₂O₂) resveratrol administration resulted in significantly increased (P < 0.05) metabolic activity, as well as cell membrane integrity at concentration 10 μM. Significantly improved (P < 0.001) lysosomal activity showed cells treated with 5 and 10 μM of resveratrol, and the level of both measured hormones was significantly higher (P < 0.05) in cells supplemented with 10 μM of resveratrol. Significant decline of superoxide radical production was observed in all experimental groups in comparison to the control exposed to H₂O₂ alone. With respect to cells exposed to higher concentration of H₂O₂ (600 μM)_, results showed positive effect of resveratrol only in biosynthesis of both androgens with significant increased values in experimental group treated with 5 μM (P < 0.05) and 10 μM (P < 0.01) of resveratrol, in addition, in the case of testosterone we recorded significant higher (P < 0.05) values in cells with addition of 25 and 50 μM resveratrol when compared to H₂O₂ control. More specific and systematic research focused especially on androgen biosynthesis is necessary related to the biological activity of resveratrol in male reproductive system due to inconsistent results of studies.

Superoxide induced inhibition of death receptor signaling is mediated via induced expression of apoptosis inhibitory protein cFLIP

The death inhibitory proteins, cFLIP and Bcl-2, canonically act at different steps to regulate receptor-mediated apoptosis in cancer cells. Here we report that pharmacological or genetic means to effect an increase in intracellular superoxide result in cFLIP upregulation. Interestingly, Bcl-2 overexpression is associated with a concomitant increase in cFLIP, and reducing superoxide sensitizes Bcl-2 overexpressing cancer cells to receptor-mediated apoptosis via downregulation of cFLIP. Moreover, inhibiting glycolytic flux overcomes apoptosis resistance by superoxide-dependent downregulation of cFLIP. Superoxide-induced upregulation of cFLIP is a function of enhanced transcription, as evidenced by increases in cFLIP promoter activity and mRNA abundance. The positive effect of superoxide on cFLIP is mediated through its reaction with nitric oxide to generate peroxynitrite. Corroborating these findings in cell lines, subjecting primary cells derived from lymphoma patients to glucose deprivation ex vivo, as a means to decrease superoxide, not only reduced cFLIP expression but also significantly enhanced death receptor sensitivity. Based on this novel mechanistic insight into the redox regulation of cancer cell fate, modulation of intracellular superoxide could have potential therapeutic implications in cancers in which these two death inhibitory proteins present a therapeutic challenge.

Gene expression analysis of heat-shock proteins and redox regulators reveals combinatorial prognostic markers in carcinomas of the gastrointestinal tract

Heat shock proteins (HSPs) are a large family of ubiquitously expressed proteins with diverse functions, including protein assembly and folding/unfolding. These proteins have been associated with the progression of various gastrointestinal tumours. Dysregulation of cellular redox has also been associated with gastrointestinal carcinogenesis, however, a link between HSPs and dysregulation of cellular redox in carcinogenesis remains unclear. In this study, we analysed mRNA co-expression and methylation patterns, as well as performed survival analysis and gene set enrichment analysis, on gastrointestinal cancer data sets (oesophageal, stomach and colorectal carcinomas) to determine whether HSP activity and cellular redox dysregulation are linked. A widespread relationship between HSPs and cellular redox was identified, with specific combinatorial co-expression patterns demonstrated to significantly alter patient survival outcomes. This comprehensive analysis provides the foundation for future studies aimed at deciphering the mechanisms of cooperativity between HSPs and redox regulatory enzymes, which may be a target for future therapeutic intervention for gastrointestinal tumours.

Clair WH, St. Clair DK. Redox Paradox: A Novel Approach to Therapeutics-Resistant Cancer

SIGNIFICANCE

Cancer cells that are resistant to radiation and chemotherapy are a major problem limiting the success of cancer therapy. Aggressive cancer cells depend on elevated intracellular levels of reactive oxygen species (ROS) to proliferate, self-renew, and metastasize. As a result, these aggressive cancers maintain high basal levels of ROS compared with normal cells. The prominence of the redox state in cancer cells led us to consider whether increasing the redox state to the condition of oxidative stress could be used as a successful adjuvant therapy for aggressive cancers. Recent Advances: Past attempts using antioxidant compounds to inhibit ROS levels in cancers as redox-based therapy have met with very limited success. However, recent clinical trials using pro-oxidant compounds reveal noteworthy results, which could have a significant impact on the development of strategies for redox-based therapies.

CRITICAL ISSUES

The major objective of this review is to discuss the role of the redox state in aggressive cancers and how to utilize the shift in redox state to improve cancer therapy. We also discuss the paradox of redox state parameters; that is, hydrogen peroxide (H2O2) as the driver molecule for cancer progression as well as a target for cancer treatment.

FUTURE DIRECTIONS

Based on the biological significance of the redox state, we postulate that this system could potentially be used to create a new avenue for targeted therapy, including the potential to incorporate personalized redox therapy for cancer treatment.

A Therapeutic Connection between Dietary Phytochemicals and ATP Synthase

For centuries, phytochemicals have been used to prevent and cure multiple health ailments. Phytochemicals have been reported to have antioxidant, antidiabetic, antitussive, antiparasitic, anticancer, and antimicrobial properties. Generally, the therapeutic use of phy-tochemicals is based on tradition or word of mouth with few evidence-based studies. Moreo-ver, molecular level interactions or molecular targets for the majority of phytochemicals are unknown. In recent years, antibiotic resistance by microbes has become a major healthcare concern. As such, the use of phytochemicals with antimicrobial properties has become perti-nent. Natural compounds from plants, vegetables, herbs, and spices with strong antimicrobial properties present an excellent opportunity for preventing and combating antibiotic resistant microbial infections. ATP synthase is the fundamental means of cellular energy. Inhibition of ATP synthase may deprive cells of required energy leading to cell death, and a variety of die-tary phytochemicals are known to inhibit ATP synthase. Structural modifications of phyto-chemicals have been shown to increase the inhibitory potency and extent of inhibition. Site-directed mutagenic analysis has elucidated the binding site(s) for some phytochemicals on ATP synthase. Amino acid variations in and around the phytochemical binding sites can re-sult in selective binding and inhibition of microbial ATP synthase. In this review, the therapeu-tic connection between dietary phytochemicals and ATP synthase is summarized based on the inhibition of ATP synthase by dietary phytochemicals. Research suggests selective target-ing of ATP synthase is a valuable alternative molecular level approach to combat antibiotic resistant microbial infections.

Reverse chemomodulatory effects of the SIRT1 activators resveratrol and SRT1720 in Ewing's sarcoma cells: resveratrol suppresses and SRT1720 enhances etoposide- and vincristine-induced anticancer activity

PURPOSE

SIRT1-activating compounds (STACs) may have potential in the management of cancer. However, the best-studied STAC, the naturally occurring compound resveratrol, is reported to have contradictory effects in combination chemotherapy regimens: It has been shown both to increase and to decrease the action of anticancer agents. To shed more light on this issue, we comparatively investigated the impact of resveratrol and the synthetic STAC SRT1720 on the responsiveness of Ewing's sarcoma (ES) cells to the chemotherapeutic drugs etoposide and vincristine.

METHODS

Because the effects of STACs can depend on the functionality of the tumor suppressor protein p53, we used three ES cell lines differing in their p53 status, i.e., wild-type p53 WE-68 cells, mutant p53 SK-ES-1 cells and p53 null SK-N-MC cells. Single agent and combination therapy effects were assessed by flow cytometric analyses of propidium iodide uptake and mitochondrial depolarization, by measuring caspase 3/7 activity and by gene expression profiling.

RESULTS

When applied as single agents, both STACs were effective in ES cells irrespective of their p53 status. Strikingly, however, when applied in conjunction with cytostatic agents, the STACs displayed reverse effects: SRT1720 largely enhanced etoposide- and vincristine-induced cell death, while resveratrol inhibited it. Combination index analyses validated the antipodal impact of the STACs on the effectiveness of the chemotherapeutics.

CONCLUSION

These findings suggest that the synthetic STAC SRT1720 may be useful to enhance the efficacy of anticancer therapy in ES. But they also suggest that the dietary intake of the natural STAC resveratrol may be detrimental during chemotherapy of ES.

Mechanisms of superoxide signaling in epigenetic processes: relation to aging and cancer

Superoxide is a precursor of many free radicals and reactive oxygen species (ROS) in biological systems. It has been shown that superoxide regulates major epigenetic processes of DNA methylation, histone methylation, and histone acetylation. We suggested that superoxide, being a radical anion and a strong nucleophile, could participate in DNA methylation and histone methylation and acetylation through mechanism of nucleophilic substitution and free radical abstraction. In nucleophilic reactions superoxide is able to neutralize positive charges of methyl donors S-adenosyl-L-methionine (SAM) and acetyl-coenzyme A (AcCoA) enhancing their nucleophilic capacity or to deprotonate cytosine. In the reversed free radical reactions of demethylation and deacetylation superoxide is formed catalytically by the (Tet) family of dioxygenates and converted into the iron form of hydroxyl radical with subsequent oxidation and final eradication of methyl substituents. Double role of superoxide in these epigenetic processes might be of importance for understanding of ROS effects under physiological and pathological conditions including cancer and aging.

Concentration-dependent biphasic effects of resveratrol on human natural killer cells in vitro

Resveratrol (RES) is a polyphenol phytoalexin from plants, which has been reported to possess a variety of biological effects. The properties of RES on human natural killer (NK) cells were assessed in this study. Results showed that RES has concentration-dependent biphasic effects on NK cells. In high concentration (50 μM), RES can inhibit viability and promoted apoptosis of NK cells and human lymphoblastoid T (Jurkat) cells, which may affect the caspase signaling pathway. The Jurkat cells were more sensitive than NK cells on the RES caused cell death. However, when the concentration range reduced from 3.13 to 1.56 μM, RES showed the positive effects on NK cells by increasing the NK cells cytotoxicity via up-regulating the expression of NKG2D and IFN-γ (in mRNA and protein levels). These results indicated that one needs to pay more attention to the dosage and biphasic effects when RES was applied as antitumor drugs or health products.

The multiple mechanisms of cell death triggered by resveratrol in lymphoma and leukemia

Lymphoma and leukemia represent a serious threat to human health and life expectancy. Resveratrol is, among the natural-derived chemopreventive molecules, one of the most effective and better studied. In this paper the main mechanisms of cell death triggered by- or linked to- resveratrol are reviewed and discussed. The main focus is on lymphoma and leukemia experimental models where resveratrol has been tested and investigated at the cellular, molecular or physiological levels. The most relevant in vivo challenges involving resveratrol are also reported and analyzed in order to define the key features of this polyphenol and the potential for the treatment of hematologic tumors.

Resveratrol: from basic studies to bedside

Plants produce a remarkable amount of low molecular mass natural products endowed with a large array of pivotal biological activities. Among these molecules, resveratrol (3,5,4'-trihydroxystilbene) has been identified as an important modulator of cell phenotype with a complex and pleiotropic mode of action. Extensive literature regarding its activity, mainly employing cellular models, suggests that this polyphenol controls cell proliferation, induces differentiation, and activates apoptosis and autophagy. The compound also modulates angiogenesis and inflammation. Similarly, studies on implanted cancers and chemical-induced tumors confirm the potential chemotherapeutical interest of the compound. Likewise, several reports clearly demonstrated, in animal models, that the compound might positively affect the development and evolution of chronic diseases including type 2 diabetes, obesity, coronary heart disease, metabolic syndrome, and neurogenerative pathologies. Finally, a number of investigations stated that the toxicity of the molecule is scarce. Despite these promising observations, few clinical trials have yet been performed to evaluate the effectiveness of the molecule both in prevention and treatment of human chronic disease. Preliminary findings therefore suggest the need for more extensive clinical investigations.

Hydroxytyrosol induces apoptosis in human colon cancer cells through ROS generation

Cancer cells are usually under higher levels of oxidative stress compared to normal cells.

Nutritional countermeasures targeting reactive oxygen species in cancer: from mechanisms to biomarkers and clinical evidence

Reactive oxygen species (ROS) exert various biological effects and contribute to signaling events during physiological and pathological processes. Enhanced levels of ROS are highly associated with different tumors, a Western lifestyle, and a nutritional regime. The supplementation of food with traditional antioxidants was shown to be protective against cancer in a number of studies both in vitro and in vivo. However, recent large-scale human trials in well-nourished populations did not confirm the beneficial role of antioxidants in cancer, whereas there is a well-established connection between longevity of several human populations and increased amount of antioxidants in their diets. Although our knowledge about ROS generators, ROS scavengers, and ROS signaling has improved, the knowledge about the direct link between nutrition, ROS levels, and cancer is limited. These limitations are partly due to lack of standardized reliable ROS measurement methods, easily usable biomarkers, knowledge of ROS action in cellular compartments, and individual genetic predispositions. The current review summarizes ROS formation due to nutrition with respect to macronutrients and antioxidant micronutrients in the context of cancer and discusses signaling mechanisms, used biomarkers, and its limitations along with large-scale human trials.

Phytochemicals as chemosensitizers: from molecular mechanism to clinical significance

This review provides an overview of the clinical relevance of chemosensitization, giving special reference to the phenolic phytochemicals, curcumin, genistein, epigallocatechin gallate, quercetin, emodin, and resveratrol, which are potential candidates due to their ability to regulate multiple survival pathways without inducing toxicity. We also give a brief summary of all the clinical trials related to the important phytochemicals that emerge as chemosensitizers. The mode of action of these phytochemicals in regulating the key players of the death receptor pathway and multidrug resistance proteins is also abridged. Rigorous efforts in identifying novel chemosensitizers and unraveling their molecular mechanism have resulted in some of the promising candidates such as curcumin, genistein, and polyphenon E, which have gone into clinical trials. Even though considerable research has been conducted in identifying the salient molecular players either contributing to drug efflux or inhibiting DNA repair and apoptosis, both of which ultimately lead to the development of chemoresistance, the interdependence of the molecular pathways leading to chemoresistance is still the impeding factor in the success of chemotherapy. Even though clinical trials are going on to evaluate the chemosensitizing efficacy of phytochemicals such as curcumin, genistein, and polyphenon E, recent results indicate that more intense study is required to confirm their clinical efficacy. Current reports also warrant intense investigation about the use of more phytochemicals such as quercetin, emodin, and resveratrol as chemosensitizers, as all of them have been shown to modulate one or more of the key regulators of chemoresistance.

A synergetic screening approach with companion effector for combination therapy: application to retinoblastoma

For many cancers, the lack of potency and the toxicity of current drugs limits the dose achievable in patients and the efficacy of treatment. Among them, retinoblastoma is a rare cancer of the eye for which better chemotherapeutic options are needed. Combination therapy is a compelling approach to enhance the efficacy of current treatment, however clinical trials to test rationally designed combinations of approved drugs are slow and expensive, and limited by our lack of in-depth knowledge of drug specificity. Since many patients already turn to nutraceuticals in hopes of improving their condition, we hypothesized that certain approved drugs could potentially synergize with widely consumed supplements. Following this hypothesis, we devised an alternative screening strategy aimed at taking advantage of a bait compound such as a nutraceutical with potential therapeutic benefits but low potency, by screening chemical libraries for approved drugs that synergize with this companion effector. As a proof of concept, we sought to identify approved drugs with synergetic therapeutic effects toward retinoblastoma cells in combination with the antioxidant resveratrol, popular as a supplement. We systematically tested FDA-approved drugs and known bioactives seeking to identify such pairs, which led to uncovering only a few additive combinations; but to our surprise, we identified a class of anticancer drugs widely used in the clinic whose therapeutic effect is antagonized with resveratrol. Our observations could explain in part why some patients do not respond well to treatment. Our results validate this alternative approach, and we expect that our companion effector strategy could significantly impact both drug discovery and the nutraceutical industry.

Redox regulation of p53, redox effectors regulated by p53: a subtle balance

SIGNIFICANCE

Reactive oxygen species (ROS), generated by cells as side products of biological reactions, function as secondary messengers by impacting a host of cellular networks involved in maintaining normal homeostatic growth as well as pathological disease states. Redox-sensitive proteins, such as the tumor suppressor protein p53, are susceptible to ROS-dependent modifications, which could impact their activities and/or biological functions.

RECENT ADVANCES

p53 is a transcription factor that controls a wide variety of target genes and regulates numerous cellular functions in response to stresses that lead to genomic instability. Thus, redox modifications of p53 could impact cell fate signaling and could have profound effects on pathways fundamental to maintaining cell and tissue integrity.

CRITICAL ISSUES

Recent studies present evidence that ROS function upstream of p53 in some model systems, while in others ROS production could be a downstream effect of p53 activation.

FUTURE DIRECTIONS

In this review, we describe how ROS production regulates p53 activity and how p53 can, in turn, influence cellular ROS production.

Mitochondria: redox metabolism and dysfunction

Mitochondria are the main intracellular location for fuel generation; however, they are not just power plants but involved in a range of other intracellular functions including regulation of redox homeostasis and cell fate. Dysfunction of mitochondria will result in oxidative stress which is one of the underlying causal factors for a variety of diseases including neurodegenerative diseases, diabetes, cardiovascular diseases, and cancer. In this paper, generation of reactive oxygen/nitrogen species (ROS/RNS) in the mitochondria, redox regulatory roles of certain mitochondrial proteins, and the impact on cell fate will be discussed. The current state of our understanding in mitochondrial dysfunction in pathological states and how we could target them for therapeutic purpose will also be briefly reviewed.

Resveratrol enhances the therapeutic effect of temozolomide against malignant glioma in vitro and in vivo by inhibiting autophagy

The alkylating agent temozolomide (TMZ) is the major chemotherapeutic drug used clinically in the treatment of malignant gliomas. This study investigated the mechanism behind TMZ-induced cell death and the possibility that resveratrol might increase TMZ efficacy. TMZ induced both apoptotic cell death and cytoprotective autophagy through a reactive oxygen species (ROS) burst and extracellular signal-regulated kinase (ERK) activation, which was suppressed by resveratrol, resulting in a decrease in autophagy and an increase in apoptosis, suggesting that the ROS/ERK pathway plays a crucial role in the fate of cells after TMZ treatment. Isobolographic analysis indicated that the combination of TMZ and resveratrol has a synergistic effect. Moreover, an in vivo mouse xenograft study also showed that coadministration of resveratrol and TMZ reduced tumor volumes by suppressing ROS/ERK-mediated autophagy and subsequently inducing apoptosis. Taken together, our data indicate that TMZ-induced ROS/ERK-mediated autophagy protected glioma cells from apoptosis, and the combination of resveratrol with TMZ could improve the efficacy of chemotherapy for brain tumors.

Bcl-2: a prime regulator of mitochondrial redox metabolism in cancer cells

SIGNIFICANCE

Mitochondria play a critical role as death amplifiers during drug-induced apoptosis in cancer cells by providing pro-apoptotic factors that are released from the mitochondrial inter-membranous space upon the induction of mitochondrial outer membrane permeabilization. This intrinsic death signaling pathway is the preferred mechanism employed by most anticancer compounds, and as such, resistance to drug-induced apoptosis is invariably associated with inhibition of mitochondrial death signaling network. The latter is a function of a balance between the pro- and the anti-apoptotic members of the Bcl-2 family. Bcl-2 is the prototype anti-apoptotic protein that localizes to the mitochondria and blocks the recruitment and activation of pro-apoptotic proteins, such as Bax, to the mitochondria.

RECENT ADVANCES AND CRITICAL ISSUES

Recent evidence has highlighted a novel mechanism of anti-apoptotic activity of Bcl-2 in addition to its canonical activity in regulating mitochondrial outer membrane permeabilization. This novel activity is a function of cellular redox regulation, in particular, mitochondrial metabolism in cancer cells.

FUTURE DIRECTIONS

Here we review the current state of our understanding of the death inhibitory activity of Bcl-2 and provide insight into the novel functional biology of this remarkable protein, which could have implications for designing innovative strategies to overcome the problem of drug resistance in the clinical settings.

Regulation of mitochondrial metabolism: yet another facet in the biology of the oncoprotein Bcl-2

The Bcl-2 (Bcl is B-cell lymphocytic-leukaemia proto-oncogene) family comprises two groups of proteins with distinct functional biology in cell-fate signalling. Bcl-2 protein was the first member to be discovered and associated with drug resistance in human lymphomas. Since then a host of other proteins such as Bcl-xL, Bcl-2A1 and Mcl-1 with similar anti-apoptotic functions have been identified. In contrast, the pro-apoptotic Bcl-2 proteins contain prototypic effector proteins such as Bax and Bak, and the BH3 (Bcl-2 homology)-only proteins comprising Bak, Bid, Bim, Puma and Noxa. A complex interplay between the association of pro-apoptotic and anti-apoptotic proteins with each other determines the sensitivity of cancer cells to drug-induced apoptosis. The canonical functional of Bcl-2 in terms of apoptosis inhibition is its ability to prevent mitochondrial permeabilization via inhibiting the translocation and oligomerization of pro-apoptotic proteins such as Bax; however, more recent evidence points to a novel mechanism of the anti-apoptotic activity of Bcl-2. Overexpression of Bcl-2 increases mitochondrial oxygen consumption and in doing so generates a slight pro-oxidant intracellular milieu, which promotes genomic instability and blocks death signalling. However, in the wake of overt oxidative stress, Bcl-2 regulates cellular redox status thereby preventing excessive build-up of ROS (reactive oxygen species), which is detrimental to cells and tissues. Taken together, the canonical and non-canonical activities of Bcl-2 imply a critical involvement of this protein in the processes of tumour initiation and progression. In the present paper we review these functionally distinct outcomes of Bcl-2 expression with implications for the chemotherapeutic management of cancers.

Chemosensitization of tumors by resveratrol

Because tumors develop resistance to chemotherapeutic agents, the cancer research community continues to search for effective chemosensitizers. One promising possibility is to use dietary agents that sensitize tumors to the chemotherapeutics. In this review, we discuss that the use of resveratrol can sensitize tumor cells to chemotherapeutic agents. The tumors shown to be sensitized by resveratrol include lung carcinoma, acute myeloid leukemia, promyelocytic leukemia, multiple myeloma, prostate cancer, oral epidermoid carcinoma, and pancreatic cancer. The chemotherapeutic agents include vincristine, adriamycin, paclitaxel, doxorubicin, cisplatin, gefitinib, 5-fluorouracil, velcade, and gemcitabine. The chemosensitization of tumor cells by resveratrol appears to be mediated through its ability to modulate multiple cell-signaling molecules, including drug transporters, cell survival proteins, cell proliferative proteins, and members of the NF-κB and STAT3 signaling pathways. Interestingly, this nutraceutical has also been reported to suppress apoptosis induced by paclitaxel, vincristine, and daunorubicin in some tumor cells. The potential mechanisms underlying this dual effect are discussed. Overall, studies suggest that resveratrol can be used to sensitize tumors to standard cancer chemotherapeutics.

Resveratrol in cancer management: where are we and where we go from here?

Resveratrol has been shown to afford protection against several diseases. A plethora of studies have suggested that resveratrol imparts cancer chemopreventive and therapeutic responses. However, an important issue with the future development of resveratrol for disease management is its low bioavailability due to its rapid metabolism in mammals. Therefore, efforts are needed to enhance its bioavailability in humans. In this direction, some possible scenarios include enhancing the bioavailability of resveratrol by novel mechanism-based combinations with agents that can inhibit the in vivo metabolism of resveratrol, nanoparticle-mediated delivery, use of naturally occurring or synthetic analogues of resveratrol, and use of conjugated metabolites of resveratrol, though these need to be carefully evaluated as they may need to be deconjugated from resveratrol at the target organ to elicit a biological response. Thus, concerted and multidisciplinary efforts are needed to take resveratrol to the next level, that is, from the "bench-to-bedside."

Resveratrol confers resistance against taxol via induction of cell cycle arrest in human cancer cell lines

Resveratrol, which is highly concentrated in the skin of grapes and is abundant in red wine, has been demonstrated to account for several beneficial properties, including antioxidant, anticoagulant, anti-inflammatory and anticancer effects. Taxol is a microtubule-stabilizing drug that has been extensively used as effective chemotherapeutic agents in the treatment of solid tumors. Here, we investigated whether the combination of the two compounds would yield increased antitumor efficacy in human cancer cells. Unexpectedly, resveratrol effectively prevented tumor cell death induced by taxol in 5637 bladder cancer cells. This pronounced antagonistic function of resveratrol against taxol was associated with changes in multiple signal transduction pathways, but not with tubulin polymerization. Importantly, cell cycle analysis showed that resveratrol prevented the cells from entering into mitosis, the phase in which taxol exerts its action. Furthermore, resveratrol blocked the cytotoxic effects of vinblastine but not cisplatin in 5637 cells. Interestingly, resveratrol pre-treatment followed by taxol resulted in synergistic cytotoxicity. Finally, we extended our studies to various human cancer cell lines. Taken together, our results indicate that resveratrol may have the potential to negate the therapeutic efficacy of taxol and suggest that consumption of resveratrol-related products may be contraindicated during cancer therapy with taxol.

Multifaceted approach to resveratrol bioactivity: Focus on antioxidant action, cell signaling and safety

Resveratrol (RVT) is a naturally occurring trihydroxy stilbene that displays a wide spectrum of physiological activity. Its ability to behave therapeutically as a component of red wine has attracted wide attention. The phenol acts as a protective agent involving various body constituents. Most attention has been given to beneficial effects in insults involving cancer, aging, cardiovascular system, inflammation and the central nervous system. One of the principal modes of action appears to be as antioxidant. Other mechanistic pathways entail cell signaling, apoptosis and gene expression. There is an intriguing dichotomy in relation to pro-oxidant property. Also discussed are metabolism, receptor binding, rationale for safety and suggestions for future work. This is the first comprehensive review of RVT based on a broad, unifying mechanism.

Bcl-2 modulates resveratrol-induced ROS production by regulating mitochondrial respiration in tumor cells

Resveratrol is a naturally occurring flavanoid with potent apoptosis-inducing activity against human tumor cells. We investigated the effect of resveratrol on human leukemia cell lines, in particular its ability to induce intracellular reactive oxygen species production and the effect of Bcl-2 overexpression on this model. Exposure of CEM cells to increasing concentrations of resveratrol (0-50 microM) resulted in an increase in mitochondrial superoxide production, decrease in transmembrane potential, and a concomitant decrease in cell viability. Whereas overexpression of Bcl-2 increased mitochondrial oxygen consumption and complex IV activity, CEM/Bcl-2 cells responded to the increased mitochondrial oxidative stress induced by resveratrol by significantly reducing mitochondrial respiration, complex IV activity, and O(2)(-) production, and promoted cell survival. The inhibitory effect of Bcl-2 on resveratrol-induced mitochondrial O(2)(-) production is further corroborated by the neutralization of this regulatory effect upon siRNA-mediated gene silencing of Bcl-2. These data provide evidence implicating mitochondrial metabolism in the anticancer activity of resveratrol, and underscore a novel regulatory role of Bcl-2 against exogenous oxidative stress through its ability to fine tune mitochondrial respiration, and by doing so maintaining mitochondrial O(2)(-) at a level optimal for survival.

Resveratrol: its biologic targets and functional activity

The polyphenolic phytoalexin resveratrol (RSV) and its analogues have received tremendous attention over the past couple of decades because of a number of reports highlighting their benefits in vitro and in vivo in a variety of human disease models, including cardio- and neuroprotection, immune regulation, and cancer chemoprevention. These studies have underscored the high degree of diversity in terms of the signaling networks and cellular effector mechanisms that are affected by RSV. The activity of RSV has been linked to cell-surface receptors, membrane signaling pathways, intracellular signal-transduction machinery, nuclear receptors, gene transcription, and metabolic pathways. The promise shown by RSV has prompted heightened interest in studies aimed at translating these observations to clinical settings. In this review, we present a comprehensive account of the basic chemistry of RSV, its bioavailability, and its multiple intracellular target proteins and signaling pathways.

Involvement of reactive oxygen species in apoptosis induced by pharmacological inhibition of protein kinase CK2

It has been reported that inhibition of protein kinase CK2 (CK2) with antisense oligodeoxynucleotides (ODN) is a potent inducer of apoptosis in cancer cells but not in normal cells. In this regard, the apoptotic-inducing effect is attributed to the catalytic activity of the enzyme, which phosphorylates proapoptotic proteins to inhibit their functions. In this study we investigate the role of intracellular redox status in the proapoptotic activity of CK2 inhibition in human leukemia Cem cells. We provide evidence that inhibition of CK2 activity induces apoptotic cell death as evident by activation of caspase 3, DNA fragmentation, and phosphatidylserine externalization. Inhibition of CK2 resulted in a significant increase in intracellular hydrogen peroxide production, which we show as a critical mediator of apoptosis. To that end, apoptotic hallmarks, like DNA fragmentation and phosphatidylserine externalization, were blocked with the specific hydrogen peroxide scavenger catalase. We also show that inhibition of CK2 reduces cytosolic intracellular superoxide, a precursor of hydrogen peroxide. In summary, decreasing CK2 activity increases intracellular hydrogen peroxide, creating an intracellular environment conducive for death execution. Taken together, these data provide information on novel pathways involved in CK2 biology with implications for effective tools against drug-resistant tumors.

Resveratrol regulates the expression of NHE-1 by repressing its promoter activity: critical involvement of intracellular H2O2 and caspases 3 and 6 in the absence of cell death

Na(+)/H(+) exchanger-1 (NHE-1) overexpression is associated with carcinogenesis and is an attractive target for intervention. We report that the chemopreventive agent resveratrol (RSV) downregulates NHE-1 in a caspase-dependent manner without inducing cell death. Resveratrol triggered early activation of caspase 3 and late activation of caspase 6, which were not inter-dependent. Whereas, caspase 3 activation appeared to be a direct effect of resveratrol, caspase 6 activation was mediated via intracellular hydrogen peroxide production and iron. Moreover, downregulation of NHE-1 expression was a function of resveratrol-induced repression of NHE-1 gene promoter activity. RNAi-mediated silencing of caspase 3 or 6 blocked the effect of resveratrol on NHE-1 expression, however the effect on NHE-1 promoter was observed at different phases of promoter repression with caspase 3 controlling the early phase (4-12 h) and caspase 6 regulating the late phase (12-24 h). Scavenging hydrogen peroxide or iron only reversed the late phase of resveratrol-induced NHE-1 promoter repression. Finally, an AP2 binding region within NHE-1 gene promoter was identified as the target of resveratrol. Collectively, these data could explain the anti-cancer activity of resveratrol in the light of the association of increased NHE-1 expression with carcinogenesis.

Resveratrol disrupts peroxynitrite-triggered mitochondrial apoptotic pathway: a role for Bcl-2

Resveratrol (3,4',5-trihydroxystilbene) is a phytochemical believed to be partly responsible for the cardioprotective effects of red wine due to its numerous biological activities. Here, we studied biochemical pathways underlying peroxynitrite-mediated apoptosis in endothelial cells and potential mechanisms responsible for resveratrol cytoprotective action. Peroxynitrite triggered endothelial cell apoptosis through caspases-8, -9 and -3 activation implying both mitochondrial and death receptor apoptotic pathways. Resveratrol was able to prevent peroxynitrite-induced caspases-3 and -9 activation, but not caspase-8 activation. Additionally, peroxynitrite increased intracellular levels of Bax without affecting those of Bcl-2, increasing consequently the Bax/Bcl-2 ratio. This ratio decreased when cells where pre-incubated with 10 and 50 muM resveratrol, mainly due to resveratrol ability per se to increase Bcl-2 intracellular levels without affecting Bax intracellular levels. These results propose an additional mechanism whereby resveratrol may exert its cardioprotective effects and suggest a key role for Bcl-2 in the resveratrol anti-apoptotic action, especially in disrupting peroxynitrite-triggered mitochondrial pathway.

Hypomethylation and apoptosis in 5-azacytidine-treated myeloid cells

OBJECTIVE

Although clinically approved for myelodysplastic syndromes (MDS), the mode of action of 5-azacytidine has not been well understood at the cellular level. The present study aimed at characterizing the mechanisms for 5-azacytidine-induced apoptosis, as well as the presence of a possible link between apoptosis and DNA hypomethylation.

MATERIALS AND METHODS

We investigated the effects of 5-azacytidine on a spectrum of specific apoptotic pathways, as well as on global DNA methylation, assessed by luminometric methylation assay, in myeloid (P39, HL60) and T cells (Jurkat).

RESULTS

5-Azacytidine induced dose-dependent apoptosis as well as non-dose-dependent global DNA hypomethylation at concentrations >or=0.5 microM. Hypomethylation was observed in the sorted apoptotic fraction (41% decrease with 1 microM after 24 hours), while nonapoptotic cells retained a methylation pattern similar to untreated cells (+/-6%). The induced apoptotic pattern involved several pathways: cleavage of Bcl-2 family proteins, activation of caspase-2 and -3-like, mitochondrial involvement characterized by loss of transmembrane potential (tetramethylrhodamine ethyl ester [TMRE]) and cytochrome release, and acidification of cytosol. Selective inhibition of caspase-3-like, -2, -8, -9, and pan-caspase activity, as well as stabilization of cytosolic pH by monensin completely failed to block apoptosis. Poly(ADP-ribose) polymerase (PARP) inhibitors only partially inhibited loss of TMRE (32% reduction) and caspase-2 activity (38% reduction); indicative of PARP operation (or action) upstream of caspase-2. Moreover, cytosine arabinoside induced a similar degree of apoptosis, while leaving methylation status mainly unaffected.

CONCLUSIONS

5-Azacytidine acts via multiple and separately regulated pathways, including parallel induction of hypomethylation. The broad action of 5-azacytidine may explain its therapeutic effects in poor-prognostic MDS.

Resveratrol protects against arsenic trioxide-induced cardiotoxicity in vitro and in vivo

BACKGROUND AND PURPOSE

The clinical use of arsenic trioxide (As(2)O(3)), a potent antineoplastic agent, is limited by its severe cardiotoxic effects. QT interval prolongation and apoptosis have been implicated in the cardiotoxicity of As(2)O(3). The present study was designed to evaluate the effects of resveratrol on As(2)O(3)-induced apoptosis and cardiac injury.

EXPERIMENTAL APPROACH

In a mouse model of As(2)O(3)-induced cardiomyopathy in vivo, QT intervals and plasma enzyme activities were measured; cardiac tissues were examined histologically and apoptosis assessed. In H9c2 cardiomyocyte cells, viability, apoptosis, generation of reactive oxygen species (ROS) and cellular calcium levels were measured.

KEY RESULTS

In the mouse model, resveratrol reduced As(2)O(3)-induced QT interval prolongation and cardiomyocyte injury (apoptosis, myofibrillar loss and vacuolization). In addition, increased lactate dehydrogenase activity and decreased activities of glutathione peroxidase, catalase and superoxide dismutase were observed in the plasma of As(2)O(3)-treated mice; these changes were prevented by pretreatment with resveratrol. In As(2)O(3)-treated H9c2 cardiomyocytes, resveratrol significantly increased cardiomyocyte viability and attenuated cell apoptosis as measured by acridine orange/ethidium bromide staining, TdT-mediated dUTP nick end labelling assay and caspase-3 activity. As(2)O(3)-induced generation of ROS and intracellular calcium mobilization in H9c2 cells was also suppressed by pretreatment with resveratrol.

CONCLUSIONS AND IMPLICATIONS

Our results showed that resveratrol significantly attenuated As(2)O(3)-induced QT prolongation, structural abnormalities and oxidative damage in the heart. In H9c2 cardiomyocytes, resveratrol also decreased apoptosis, production of ROS and intracellular calcium mobilization induced by treatment with As(2)O(3). These observations suggested that resveratrol has the potential to protect against cardiotoxicity in As(2)O(3)-exposed patients.

Predicting the physiological relevance of in vitro cancer preventive activities of phytochemicals

There is growing interest in the ability of phytochemicals to prevent chronic diseases, such as cancer and heart disease. However, some of these agents have poor bioavailability and many of the in-depth studies into their mechanisms of action have been carried out in vitro using doses which are unachievable in humans. In order to optimize the design of chemopreventive treatment, it is important to determine which of the many reported mechanisms of action are clinically relevant. In this review we consider the physiologically achievable doses for a few of the best studied agents (indole-3-carbinol, diindolylmethane, curcumin, epigallocatechin-3-gallate and resveratrol) and summarize the data derived from studies using these low concentrations in cell culture. We then cite examples of in vitro effects which have been observed in vivo. Finally, the ability of agent combinations to act synergistically or antagonistically is considered. We conclude that each of the compounds shows an encouraging range of activities in vitro at concentrations which are likely to be physiologically relevant. There are also many examples of in vivo studies which validate in vitro observations. An important consideration is that combinations of agents can result in significant activity at concentrations where any single agent is inactive. Thus, for each of the compounds reviewed here, in vitro studies have provided useful insights into their mechanisms of action in humans. However, data are lacking on the full range of activities at low doses in vitro and the benefits or otherwise of combinations in vivo.

Protein kinase CK2 modulates apoptosis induced by resveratrol and epigallocatechin-3-gallate in prostate cancer cells

Resveratrol and epigallocatechin-3-gallate (EGCG) are important candidates as chemopreventive agents by virtue of their ability to induce apoptosis in cancer cells. Casein kinase 2 (CK2) is a ubiquitous protein ser/thr kinase that plays diverse roles in cell proliferation and apoptosis. We have previously shown that overexpression of CK2 suppresses apoptosis induced by a variety of agents, whereas down-regulation of CK2 sensitizes cells to induction of apoptosis. We therefore investigated whether or not CK2 played a role in resveratrol and EGCG signaling in androgen-sensitive (ALVA-41) and androgen-insensitive (PC-3) prostate cancer cells. Resveratrol- and EGCG-induced apoptosis is associated with a significant down-regulation of CK2 activity and protein expression in both the ALVA-41 and PC-3 cells. Overexpression of CK2alpha protected prostatic cancer cells against resveratrol- and EGCG-induced apoptosis. Relatively low doses (10 mumol/L) of resveratrol and EGCG induced a modest proliferative response in cancer cells that could be switched to cell death by moderate inhibition of CK2. These findings characterize, for the first time, the effects of polyphenolic compounds on CK2 signaling in androgen-sensitive and androgen-insensitive prostatic carcinoma cells and suggest that resveratrol and EGCG may mediate their cellular activity, at least in part, via their targeting of CK2. Further, the data hint at the potential of using these polyphenols alongside CK2 inhibitors in combination chemotherapy.

Resveratrol increases vascular oxidative stress resistance

Epidemiological studies suggest that Mediterranean diets rich in resveratrol are associated with reduced risk of coronary artery disease. However, the mechanisms by which resveratrol exerts its vasculoprotective effects are not completely understood. Because oxidative stress and endothelial cell injury play a critical role in vascular aging and atherogenesis, we evaluated whether resveratrol inhibits oxidative stress-induced endothelial apoptosis. We found that oxidized LDL and TNF-α elicited significant increases in caspase-3/7 activity in endothelial cells and cultured rat aortas, which were prevented by resveratrol pretreatment (10−6–10−4 mol/l). The protective effect of resveratrol was attenuated by inhibition of glutathione peroxidase and heme oxygenase-1, suggesting a role for antioxidant systems in the antiapoptotic action of resveratrol. Indeed, resveratrol treatment protected cultured aortic segments and/or endothelial cells against increases in intracellular H2O2 levels and H2O2-mediated apoptotic cell death induced by oxidative stressors (exogenous H2O2, paraquat, and UV light). Resveratrol treatment also attenuated UV-induced DNA damage (comet assay). Resveratrol treatment upregulated the expression of glutathione peroxidase, catalase, and heme oxygenase-1 in cultured arteries, whereas it had no significant effect on the expression of SOD isoforms. Resveratrol also effectively scavenged H2O2 in vitro. Thus resveratrol seems to increase vascular oxidative stress resistance by scavenging H2O2 and preventing oxidative stress-induced endothelial cell death. We propose that the antioxidant and antiapoptotic effects of resveratrol, together with its previously described anti-inflammatory actions, are responsible, at least in part, for its cardioprotective effects.

Automated laser scanning cytometry: a powerful tool for multi-parameter analysis of drug-induced apoptosis

BACKGROUND

Simultaneous analysis of multiple intracellular events is critical for assessing the effect of biological response modifiers, including the efficacy of chemotherapy. Here we used the automated laser scanning cytometry (LSC) for multi-parameter analysis of drug-induced tumor cell apoptosis.

MATERIALS

Using 2-mercaptopyridine-N-oxide-hydrate sodium salt, or the commonly used chemotherapeutic agents etoposide and camptothecin, we performed simultaneous analyses of apoptosis-related morphological features as well as fluorescence-based biochemical changes in a 96-well format.

RESULTS

We demonstrate the scope of LSC as a platform for comparing multiple variables between different cell populations, distinguishing unique events at a single cell level within a sample population, and enabling simultaneous screenings in a single assay at multiple dosages and time-points.

CONCLUSION

These data underscore the power of LSC for simultaneous multi-parameter analysis, which could have implications for screening or assessing the efficacy of drug responses in heterogeneous cell populations and at the single cell level.

Phosphorylation of the survival kinase Akt by superoxide is dependent on an ascorbate-reversible oxidation of PTEN

In this report, we demonstrate that in serum-deprived mouse embryonic fibroblasts an increase in intracellular level of superoxide through pharmacological inhibition of the Cu/ZnSOD protein or the down-regulation of its expression using specific siRNA mimics growth factor-induced phosphorylation of Akt. Using the PI3K inhibitor LY294002 and PTEN knockout mouse embryonic fibroblasts, we show that phosphorylation of Akt by superoxide requires the production of PIP3 and that the target for the induction of Akt phosphorylation by O2.- is the phosphatase PTEN. Interestingly, the inhibition of PTEN involves an O2.--mediated oxidation of the phosphatase rather than regulation of its phosphorylation or decreased protein expression. Moreover, using differential reduction of oxidized protein by DTT and ascorbate, O2.--dependent oxidation of PTEN is shown to be due to S-nitrosylation of the protein. Finally, exposure of serum-deprived mouse embryonic fibroblasts to fetal bovine serum leads to a rapid and strong phosphorylation of Akt that is dependent on an ascorbate-reversible O2.--mediated oxidation of PTEN. These results support O2.- as a physiologically relevant second messenger for Akt activation through S-nitrosylation of PTEN and offer a mechanistic explanation for the mitogenic and prosurvival activities of O2.-.

Resveratrol in cell fate decisions

Resveratrol, a polyphenolic phytoalexin, is one of the most extensively studied natural products, with wide ranging biological activity and tremendous clinical potential. First identified from fruits and plants, in particular grapes and wines, its positive effects on a variety of disease states have been unraveled over the past decade or so. Most noticeable are its anti-thrombogenic, anti-inflammatory, cardio-protective, neuro-protective, anti-aging, and cancer preventive and therapeutic activities. Recent data also indicate that depending upon the concentration/dose, resveratrol can trigger or block cell death signaling in tumor cells. Considering the heightened interest in this compound, here we present a short review on the biological activity of this remarkable compound, with a specific focus on its effects on cell survival and death signals.

Time- and concentration-dependent effects of resveratrol in HL-60 and HepG2 cells

Resveratrol, a phytochemical present in grapes, has been demonstrated to inhibit tumourigenesis in animal models. However, the specific mechanism by which resveratrol exerts its anticarcinogenic effect has yet to be elucidated. In the present study, the inhibitory effects of resveratrol on cell proliferation and apoptosis were evaluated in the human leukaemia cell line HL-60 and the human hepatoma derived cell line HepG2. We found that after a 2 h incubation period, resveratrol inhibited DNA synthesis in a concentration-dependent manner. The IC50 value was 15 microm in both HL-60 and HepG2 cells. When the time of treatment was extended, an increase in IC50 value was observed; for example, at 24 h the IC50 value was 30 microm for HL-60 cells and 60 microm for HepG2 cells. Flow cytometry revealed that cells accumulated in different phases of the cell cycle depending on the resveratrol concentration. Furthermore, an increase in nuclear size and granularity was observed in the G1 and S phases of HL-60 treated and HepG2-treated cells. Apoptosis was also stimulated by resveratrol in a concentration-dependent manner in HL-60 and HepG2 cells. In conclusion, resveratrol inhibits cell proliferation in a concentration- and time-dependent manner by interfering with different stages of the cell cycle. Furthermore, resveratrol treatment causes stimulation of apoptosis as well as an increase in nuclear size and granularity.

Resveratrol: a review of preclinical studies for human cancer prevention

The search for novel and effective cancer chemopreventive agents has led to the identification of various naturally occurring compounds one of which is resveratrol (trans-3,4',5-trihydroxystilbene), a phytoalexin derived from the skin of grapes and other fruits. Resveratrol is known to have potent anti-inflammatory and antioxidant effects and to inhibit platelet aggregation and the growth of a variety of cancer cells. Its potential chemopreventive and chemotherapeutic activities have been demonstrated in all three stages of carcinogenesis (initiation, promotion, and progression), in both chemically and UVB-induced skin carcinogenesis in mice, as well as in various murine models of human cancers. Evidence from numerous in vitro and in vivo studies has confirmed its ability to modulate various targets and signaling pathways. This review discusses the current preclinical and mechanistic data available and assesses resveratrol's anticancer effects to support its potential as an anticancer agent in human populations.