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Keywords:

  • resveratrol;
  • chemoprevention;
  • experimental animals

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Colon cancer chemopreventive effects
  5. Conclusion
  6. Conflicts of interest
  7. References

The potential cancer-preventive effects of resveratrol, evident from the data obtained by various studies, are summarized in this review. Resveratrol (trans-3,5,4′-trihydroxystilbene), a naturally occurring polyphenolic compound, was first isolated in 1940 as a constituent of the roots of white Hellebore (Veratrum grandiflorum O. Loes), and is now found to be present in various plants including grapes, berries, peanuts, and red wine. This review first briefly describes the current evidence on the link between resveratrol and cancer occurrence, based on epidemiological studies. Subsequently, investigations with resveratrol in animal models of colon carcinogenesis are presented, followed by a comprehensive compilation of resveratrol on cancer. In the second part, the article focuses on results from investigations on cancer-preventive mechanisms of resveratrol. Biological activities including antioxidant effects, modulation of carcinogen metabolism, anti-inflammatory potential, antioxidant properties, antiproliferative mechanisms by induction of apoptosis, and cell differentiation are discussed. Some novel information on its modulating effects on cell signaling pathway, metabolism studies, bioavailability, and cancer-preventive efficacy is also provided. Based on these findings, resveratrol may be used as a promising candidate for cancer chemoprevention.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Colon cancer chemopreventive effects
  5. Conclusion
  6. Conflicts of interest
  7. References

Cancer chemoprevention

Cancer chemoprevention can be defined as the prevention, inhibition, or reversal of carcinogenesis by administration of one or more chemical entities, either as individual drugs or as naturally occurring constituents of the diet.1 The concept of chemoprevention, which is the use of natural or synthetic compounds to block, reverse, or prevent the development of cancers, has great appeal. There are at least two major mechanisms for cancer chemoprevention.2,3 One is antimutagenesis. It includes the inhibition of the uptake of carcinogens, the formation/activation of carcinogens, the deactivation/detoxification of carcinogens, the blocking of carcinogen-DNA bindings, and the enhancement of fidelity of DNA repair. Another mechanism is antiproliferation/antiprogression. Examples are the modulation of hormone/growth factor activity, the modification of signal transduction, the inhibition of oncogene activity, the promotion of the cellular differentiation, the modulation of arachidonic acid metabolism, and the enhancement of apoptosis.4

Classes of chemopreventive agents

Absolute classification of chemopreventive agents is difficult because the precise mechanisms of action are not known for many compounds. In addition, many chemopreventive agents act through more than one mechanism, making it difficult to establish the most effective mode of action. On this basis, the chemopreventive agents are classified as (1) inhibitors of carcinogen formation; (2) blocking agent-inhibitors of tumor initiation; and (3) suppressing agent-inhibitors of tumor promotion/progression.5

Phytochemicals Several studies have demonstrated that generous consumption of vegetables and fruits reduces the risk of colon cancer.6 Although the nature of the constituents that are responsible for reduced risk has not been fully elucidated, it is clear that plant foods contain chemopreventive agents, including several micronutrients, such as vitamins and minerals, and also nonnutrients, such as organosulfur compounds, polyphenols, and isoflavones, to cite a few. The diversity of these compounds is a positive feature, indicating that a variety of approaches to cancer prevention by these agents may be made so that the optimal selection will emerge.

History of resveratrol

Resveratrol (3,5,4′-trihydroxystilbene) is a naturally occurring phytoalexin produced by a variety of plants such as grapes (Vitis vinifera), peanuts (Arachis hypogaea), and mulberries in response to stress, injury, ultraviolet (UV) irradiation, and fungal (e.g., Botrytis cinerea) infection. Although phytoalexins have long been inferred to be important in the defense of plants against fungal infection, few reports show that they provide resistance to infection. Several plants, including grapevine, synthesize the stilbene-type phytoalexin, resveratrol, when attacked by pathogens.7

Chemistry Resveratrol is found widely in nature, and a number of its natural and synthetic analogues, isomers, adducts, derivatives, and conjugates are known. It is an off-white powder with a melting point of 253–255° C and molecular weight of 228 kDa. Resveratrol is insoluble in water but dissolves in ethanol, carboxymethylcellulose, and dimethylsulphoxide. The stilbene-based structure of resveratrol consists of two phenolic rings linked by a styrene double bond to generate 3,5,4′-trihydroxy-trans-stilbene (Fig. 1). Although the presence of the double bond facilitates trans- and cis-isomeric forms of resveratrol [(E)- and (Z)-diastereoisomers, respectively], the trans-isomer is sterically the most stable form.8

image

Figure 1. Structure of resveratrol.

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Metabolism, pharmacokinetics, tissue distribution, and clearance Numerous studies have examined the metabolism, pharmacokinetics, tissue distribution, and clearance of resveratrol.9,10 Bertelli et al. studied the plasma kinetics and tissue bioavailability of this compound after oral administration in rats.9 Resveratrol concentrations were measured in the plasma, heart, liver, intestine, and kidneys. Tissue concentrations of resveratrol showed a significant bioavailability and strong affinity for the liver and kidneys. The majority of the absorbed resveratrol was conjugated to yield resveratrol glucuronide (16.8%) and lesser amounts of resveratrol sulfate (3%). Only a small amount of resveratrol was absorbed and metabolized across the enterocyte of the jejunum and ileum. These findings suggest that resveratrol is most likely to be in the form of glucuronide conjugate after crossing the small intestine and entering the blood circulation. This may account for its significantly higher levels in the plasma, liver, intestine, and colon. Moreover, abundant trans-resveratrol-3-O-glucuronide and trans-resveratrol-3-O-sulfate were identified in rat urine. Virtually no unconjugated resveratrol was detected in the urine or serum samples.10

Biological and pharmacological effects Several in vivo and in vitro studies describe various biological functions of resveratrol. Resveratrol is notable for its diverse biological actions in preclinical models at a very wide range of physiologically attainable and supraphysiological doses (Table 1).

Table 1.  Biological effects of resveratrol
Therapeutic activities of resveratrolReferences
Antibacterial and antifungicidal activitiesCreasy and Coffee181
Antioxidant activityChanvitayapongs et al.82
Free radical scavenging activityBelguendouz et al.83
Inhibition of lipid peroxidationFrankel et al.84
Inhibition of eicosanoid synthesisKimura et al.85
Inhibition of platelet aggregationChung et al.86
Chelation of copperBelguendouz et al.83
Anti-inflammatory propertyJang et al.14
Vasorelaxing activityChen and Pace-Asciak87
Modulation of lipids and lipoprotein metabolismFrankel et al.84
Inhibition of rat gastric H+, K+-ATPaseMurakami et al.88
Inhibition of protein-tyrosine kinase and protein kinase CJayatilake et al.89

Toxicity To date, few studies have evaluated the toxicity of resveratrol in animals. A single dose of 2,000 mg resveratrol/kg body weight (bw) did not cause any detectable, toxicologically significant changes in rats.11 Moreover, Crowell et al. have reported that oral administration of 300 mg resveratrol/kg bw for 28 days was nontoxic.12

Anticancer activity Besides many other biological properties, resveratrol exhibits anticancer properties, as suggested by its ability to suppress cell proliferation in a wide variety of tumor cells, including lymphoid and myeloid cancers, multiple myeloma, cancers of the breast, prostate, stomach, colon, pancreas, and thyroid, melanoma, head and neck squamous cell carcinoma, ovarian carcinoma, and cervical carcinoma. In general, the anticancer activity of resveratrol has been attributed to the suppression of cell proliferation and induction of apoptosis.13 Moreover, Jang et al. proved that resveratrol acts as an effective chemopreventive agent against mouse skin cancer model by blocking cancer development and formation at various stages, including initiation, promotion, and progression.14 Recently, resveratrol was found to block the development of pre-neoplastic lesions in carcinogen-treated mouse mammary glands.15 Although the anticarcinogenic function of resveratrol has been well-established to some degree, the mechanism by which resveratrol exerts its chemopreventive effects remain largely unknown. At present, many key molecular targets associated with anticancer activity has been revealed (Fig. 2).

image

Figure 2. Molecular targets of resveratrol (Aggarwal et al.90).

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Clinical trials Many data are available from in vitro studies, experimental animal model studies, and few clinical trials in humans on the anticancer effects of resveratrol. Gautam et al. found that the ex vivo origin of contaminating tumor cells may reduce the incidence of relapse in patients undergoing bone marrow transplantation and demonstrated that resveratrol exhibits antileukemic activity.16 A study by Wang et al. suggested that resveratrol significantly inhibits in vivo platelet aggregation induced by collagen.17 Resveratrol also causes an increase in plasma adenosine levels and blood nucleosides in human subjects.18

Several reports show that the cancer preventive activities of resveratrol could be attributed to its ability to trigger apoptosis in carcinoma cells.19,20 Resveratrol is metabolized by the enzyme cytochrome P450 1B1 (CYP1B1), found in a variety of different tumors, to form an antileukemic agent, piceatannol.21,22 This observation provides a novel explanation for the cancer preventive property of resveratrol.

Cancer chemopreventive effect

Many studies have revealed the cancer chemopreventive and/or therapeutic potential of resveratrol. Jang et al. showed that resveratrol influences antiproliferative effects on human breast epithelial cells.14 Carbo et al. have demonstrated that resveratrol administration to male Wistar rats inoculated with Yoshida AH-130 ascites hepatoma tumors resulted in a significant decrease in tumor cell content, and this response was found to be associated with a G2/M phase arrest and apoptosis.23 Elattar and Virji20,21 have shown that resveratrol induces significant dose-dependent inhibition in human oral squamous carcinoma cell (SCC-25) growth and DNA synthesis.24,25 Resveratrol is also known to reduce the viability and DNA synthesizing capability of human promyelocytic leukemia (HL-60) cells via induction of apoptosis through the BCl-2 pathway.26 Hsieh and Wu9 investigated the effects of resveratrol on growth, induction of apoptosis, and modulation of prostate-specific gene expression using DU-145, PC-3, and JCA-1 human CaP cells.27 This study suggests that resveratrol negatively modulates CaP cell growth by affecting mitogenesis as well as inducing apoptosis in a prostate cell type-specific manner. Resveratrol has also been shown to regulate PSA gene expression by an AR-independent mechanism.27 In another study, Mitchell et al. demonstrated the inhibitory effects of resveratrol on androgen action in LNCaP cells.28 This study observed that resveratrol represses different classes of androgen-regulated genes at the protein or mRNA level, including PSA, human glandular kallikrein-2, AR-specific coactivator ARA70, and the WAF1/p21.28 In another study, Kampa et al. have shown that many antioxidant polyphenols present in wine, including resveratrol, inhibits the proliferation of human prostate cancer cell lines.29

Colon cancer chemopreventive effects

  1. Top of page
  2. Abstract
  3. Introduction
  4. Colon cancer chemopreventive effects
  5. Conclusion
  6. Conflicts of interest
  7. References

Resveratrol on pre-neoplastic changes

Reliable intermediate biomarkers for colon carcinogenesis need to be identified in order to use them to evaluate several agents for their carcinogenic or potential chemopreventive efficacy against colon tumors.30 Aberrant crypt foci (ACF) are microscopic lesions that have been postulated to precede the development of adenomas and are considered as earliest premalignant lesions in colon carcinogenesis.31 Furthermore, specificity studies showed that several other colon-specific carcinogens such as 1,2-dimethylhydrazine, 4-aminobiphenyl, N-nitroso-N-methylurea and 3-methylcholanthrene also induce ACF, indicating that development of these lesions in the colon is clearly related to the genotoxic events.32 Multiplicity of ACF increases with time and appears to be a predictor of tumor outcome.33 These observations justify the use of the colonic ACF assay as a useful tool for the evaluation of agents with potential chemopreventive properties in colon cancer prior to clinical studies.

Resveratrol was supplemented to 1,2-dimethylhydrazine-induced colon cancer rats to evaluate its effect on the preneoplastistic changes. The number of aberrant crypts (AC), AC/ACF (crypt multiplicity) and percentage of ACF inhibition in experimental groups were determined. Rats treated with the carcinogen showed 100% ACF incidence, in contrast to the complete lack of such lesions in control groups (Table 2). The number of ACF consisting of six or more aberrant crypts per rat in resveratrol-supplemented groups [group 6 (6.2 ± 1.4), group 5 (7.7 ± 1.0), and group 4 (8.2 ± 1.4)] were significantly (P < 0.05) lower than that of carcinogen-alone–treated rats (22.3 ± 2.4) (Table 3). The statistically significant (P < 0.01) reduction in the total number of ACF was higher in rats supplemented with resveratrol for the entire period (group 6).34 Resveratrol supplementation for the entire period of the study caused a significant decrease in the total number of ACF, AC, and AC/ACF with increased percentage of inhibition.34

Table 2.  Resveratrol on aberrant crypt foci formation in rat colon
GroupsACF incidence (%)Total no. of ACFNo. of ACCrypt multiplicity (AC/ACF)Percent of ACF inhibition
  1. Data are presented as means ± SD of 10 rats in each group.

  2. a–dP < 0.05; values not sharing a common superscript letter are significantly different.

  3. *P < 0.01; values are significantly different as compared to DMH-alone–treated group.

DMH10/10 (100)100.3 ± 10.2a180.5 ± 14.5a1.8 ± 0.08a
DMH + RES (I)10/10 (100)50.4 ± 5.3b85.6 ± 7.6b1.7 ± 0.08ab49.75
DMH + RES (PI)10/10 (100)39.4 ± 5.4c63.0 ± 20.9c1.6 ± 0.08b60.71
DMH + RES (EP)10/10 (100)28.5 ± 5.1d*37.0 ± 14.3d*1.3 ± 0.07c*71.58
Table 3.  Resveratrol on ACF distribution in proximal, middle, and distal rat colon
ACF DistributionDMHDMH+RES (I)DMH+RES (PI)DMH+RES (EP)
  1. Data are presented as means ± SD of 10 rats in each group.

  2. a–dP < 0.01; values not sharing a common superscript letter are significantly different.

Proximal colon11.7 ± 0.9a6.7 ± 0.6b4.2 ± 1.3c1.7 ± 0.6d
 Small9.2 ± 0.64.1 ± 0.33.2 ± 1.01.0 ± 0.4
 Medium1.5 ± 0.21.4 ± 0.20.7 ± 0.20.7 ± 0.2
 Large1.0 ± 0.11.2 ± 0.10.3 ± 0.1
Middle colon30.1 ± 3.2a14.3 ± 1.6b12.3 ± 1.5c10.2 ± 1.6d
 Small11.1 ± 1.28.3 ± 1.08.2 ± 1.02.8 ± 0.4
 Medium15.3 ± 1.95.0 ± 0.42.6 ± 0.35.3 ± 0.9
 Large3.7 ± 0.11.0 ± 0.21.5 ± 0.22.1 ± 0.3
Distal colon58.5 ± 6.1a29.4 ± 3.1b22.9 ± 2.6c16.6 ± 2.9d
 Small15.3 ± 1.613.3 ± 1.96.2 ± 0.38.3 ± 1.5
 Medium25.6 ± 3.510.1 ± 0.510.8 ± 1.64.2 ± 0.5
 Large17.6 ± 1.06.0 ± 0.75.9 ± 0.74.1 ± 0.9

Total number of ACF, number of larger ACF and number of AC/ACF (crypt multiplicity) were used to evaluate the potency of colon cancer preventive agents. Accordingly, Sengottuvelan et al. also showed that resveratrol not only inhibited the growth of ACF by decreasing the total number of ACF consisting of various number of crypts (small, medium and large), but also inhibited its distribution in proximal, middle and distal regions of colon.34 ACF develops as early as 2–4 weeks after carcinogen administration and appears predominantly in the medial colon during early time points. But as time progresses, ACF appears in the distal and proximal colon, and a proportion of ACF starts to exhibit focal expansion and may contain one to several crypts.35 Resveratrol supplementation throughout the study period to colon cancer rats suppressed the formation of ACF in the distal colon, suggesting that resveratrol may intervene in the development of ACF at a later time point. These findings suggest that resveratrol suppresses early events (development of smaller ACFs) in colon carcinogenesis and also the formation of tumors.

In several studies, reduction in the number of multiple crypts (four or more), total, and regional distribution of ACF were used to define efficacy end points to predict the sensitivity and specificity of potential chemopreventive agents.36 The expression of larger ACF (six or more aberrant crypts per focus) is considered more likely to progress to tumors.37,38 In this study, resveratrol feeding showed a significant inhibition on the formation of larger ACF in the distal colon.

Hyperplasia was assessed by counting the number of cells per crypt column (crypt height). The number of cells in the crypt column was decreased on resveratrol supplementation. In this context, the decrease in crypt height might be correlated with a significant decrease in hyperplastic lesions.39

Although the mechanisms involved in the protective effects of resveratrol against ACF and tumor formation are not clearly understood, the inhibitory actions of resveratrol could be explained as follows: resveratrol is known to (i) affect bax and p21CIP expression in both ACF and surrounding mucosa; (ii) inhibit enzymes such as ribonucleotide reductase and DNA polymerases; (iii) modulate protein kinase C and cyclooxygenase-2 (COX-2) expression; (iv) inhibit ROS-mediated carcinogenesis; (v) inhibit tumor cell division; (vi) activate apoptotic cell death; and (vii) reduce carcinogen-induced luminal mutations.

Antioxidant activity of resveratrol

Cancer can be inhibited at different stages of its development. Induction of antioxidants and detoxifying enzymes by anticarcinogens appear to be a form of adaptation to metabolic stress.40 An inverse relationship between the concentration of lipid peroxides and the rate of cell proliferation41 and differentiation42 is well documented. Moreover, a number of studies have demonstrated that tumor cells have reduced levels of phospholipids and polyunsaturated fatty acids (PUFA). The low content of PUFA in tumor cells can be attributed to the loss or decreased activity of δ-6- and δ-6–5- desaturases,43 lending support to the concept that the rate of lipid peroxidation is generally low in tumor cells.

The enzymes SOD and CAT and the glutathione system play key roles in the cellular defense against free radical damage.44 Many data indicate that animal tumor cells lack complex enzyme systems, which normally exert protection by scavenging toxic oxygen species such as superoxide radicals, hydrogen peroxide, and lipid hydroperoxides.45 The antioxidant activity against DMH-induced colon cancer showed a significant decrease in the activities of SOD, CAT, and GR, while the activities of glutathione dependent enzymes such as GPx and GST were significantly increased (almost doubled) in carcinogen-treated rats and served as markers of neoplastic tissues.44 Colonic mucosal GSH (ubiquitous cellular reductant) levels were lowered in carcinogen-treated rats, which suggests that this tripeptide may be involved in the detoxification and possible repair mechanisms in the colonic mucosa.45

SOD, CAT, GSH, and GR replenishment (increase) upon resveratrol supplementation throughout the experimental period reflects a favorable balance between potentially harmful oxidants and protective antioxidants. Furthermore, elevated SOD and CAT activities can play an inhibitory role on cell transformation. CAT has been found to significantly decrease chromosomal aberrations and also delay or prevent the onset of spontaneous neoplastic transformation in mouse fibroblasts and epidermal keratinocytes.46 The available reports suggest that the anticarcinogenic effect of resveratrol may be mediated by the induction of GSH because this endogenous tripeptide molecule can detoxify various carcinogens, serve as an intracellular antioxidant, and also regulate DNA and protein synthesis.47

Many findings report that decreased CAT activity in tumor cells is somehow compensated by an increase in GPx activity, which in turn prevents tumor cells from peroxidative attack. The overexpression of GST enhances the production of eicosanoids, another common attribute observed in many tumors.47 Furthermore, the ratio among these antioxidant enzymes is important, as any imbalance will result in the accumulation of toxic free radicals that cause cell damage.44 Previous findings firmly established GST inhibition as one of the major mechanisms to explain the chemopreventive efficacy of phytochemicals.48 Reduction in GPx and GST activities on resveratrol supplementation shows that resveratrol may play a role in maintaining the balance between these antioxidant enzymes, which is in harmony with the previous reports.48 However, the changes in GPx and GST enzyme activities might be due to the malignant state, and recovery of the enzyme activities could help to reverse malignancy.

Several studies have demonstrated that resveratrol exhibits a wide range of biological activities including anti-inflammatory and antitumor effects.14 Polyphenols and flavonoids can prevent oxidative damage by their ability to scavenge reactive oxygen species such as hydroxyl radical and superoxide anion. The cytotoxic action of resveratrol against cancer cells may be through mobilization of endogenous copper and the consequent prooxidant action, which might be one of the mechanisms involved in ROS mediated tumor cell apoptosis and cancer chemoprevention.49 Thus the significant increase in tissue (intestine and colon) lipid peroxidation products observed on chronic resveratrol supplementation may be correlated with its pro-oxidant property.47

Resveratrol on bacterial enzymes

Epidemiological studies and laboratory research have indicated a strong association between the metabolic activity of the intestinal microflora and cancer of the large bowel.50 The activation of procarcinogens could be mediated enzymatically by intestinal bacteria and the activities of colonic bacterial enzymes are increased by dietary fat.50 Increased expression of intestinal mucosal β-glucuronidase, β-glucosidase, and β-galactosidase in a population with a high risk of colon cancer is well documented. In addition, it has been reported that E. coli, a β-glucuronidase positive bacterium, increases the production of active carcinogenic metabolites in the colon and is thus responsible for colon carcinogenesis.51

Several other enzymes such as nitroreductase and sulphatases have also been implicated in the carcinogenic process, which are known to retoxify and release carcinogens in the gastrointestinal tract.52 The carcinogens, on being reduced, may be converted into highly reactive intermediates, which inturn can react with proteins and nucleic acids.53 Fecal sulfatase activity should also be considered in the desulfation of conjugated toxins and in the degradation of sulfated mucins. Changes in the expression of sulfated molecules such as mucins and other glycoconjugates have been demonstrated in transformed colonic epithelial cells.54 A change in mucinase activity is accompanied by a change in the rate of mucin degradation, leading to a shift in the balance between mucin secretion and degradation.53,67 Enhanced degradation of the mucosal lining of colonic epithelial cells (mucin) ensures greater contact of the toxic carcinogen with the colonocytes. This may be accompanied by increased susceptibility of the colonic cells to being transformed.53

Measurement of colonic and fecal biotransforming enzyme activities in carcinogen exposed rats was found to be higher by several-fold compared to the control rats. The influence of diet on tumor development and carcinogen retoxifying enzymes have been evaluated for their influence on colon carcinogenesis.55 The activities of these bacterial enzymes were significantly decreased following resveratrol supplementation, especially when 8 mg/kg body weight was supplemented throughout the study period.56 Apart from antioxidant and antiproliferative properties, resveratrol is also known to modulate cytochrome P450 metabolic activity, thus preventing the activation of procarcinogenic substrates to carcinogens. This may just as well explain the protective action of resveratrol on carcinogen-induced colon carcinogenesis.

Resveratrol is also known to have strong antimicrobial activity.11 Thus, the success of resveratrol supplementation is credited in part to its antibacterial effects. Furthermore, Onoue et al. suggested that reduction of bacterial enzyme activity is paralleled by a decrease in the frequency of colonic ACF.49 Thus, one of the plausible explanations for the reduction in tumor incidence and ACF development may be associated with the reduced activities of fecal and colonic mucosal enzymes on resveratrol supplementation to carcinogen-treated rats. A strategy for colon-specific drug delivery is another way of releasing bioactive compounds/molecules into the colon. Resveratrol is readily absorbed and immediately glucuronidated and sulfated by intestinal cells and/or by the liver.9 This conjugation makes resveratrol more hydrophilic and easily accessible to the intracellular targets. Nevertheless, hydrolytic enzymes such as β-glucuronidase and sulfatases are expressed at high levels in the extracellular space of certain bulky tumors, including ovarian cancers.57,58 These enzymes may be capable of converting the resveratrol metabolites back to trans-resveratrol, providing tumor-selective bioactivation and a sufficient concentration of active drug to induce autophagy.

Antiproliferative activities of resveratrol

Ornithine decarboxylase (ODC) is found to be increasingly expressed in a variety of cancers and is considered to be important for carcinogenesis. ODC has been evaluated as an intermediate biomarker of cell proliferation in cancer chemopreventive studies.59 Carcinogen exposure to rats resulted in increased expression of colonic ODC compared to the control group.60 A significant decrease of ODC activity observed on resveratrol supplementation61,74 could be, at least in part, related to the accumulation of cells at the S/G2 phase transition and suppression of the activity of nuclear transition factors, which are involved in a number of different signaling pathways associated with proliferation, differentiation, neuronal excitation, and cell death.

Colonic epithelial cell proliferation changes are considered to be indicators of increased risk of colon cancer.62 Many studies showed that morphometric analysis of argyrophilic nucleolar organizing region-associated protein (AgNOR) was used as a marker for cell proliferation, which aids in the identification of cells with neoplastic potential. At 30 weeks, AgNOR expression was visualized as black dots in silver-stained histological sections. The number of AgNOR dots was consistently enhanced in nonlesional colonic crypts of carcinogen-treated rats, which reflects increased cell proliferation.60

Our data indicating a reduced number of AgNORs/nucleus during the entire period of resveratrol supplementation suggest that the mechanism of reduction of ACF number by resveratrol may be by reducing increased cell proliferation of the colonic epithelium.60 Resveratrol downregulates the expression of cyclins D1 and D2, which are directly involved in cell cycle progression,63 generally stimulated during malignancy,64 and repressed by anticancer phytochemicals.65 Resveratrol is also known to significantly reduce expression of transcription factors, including DP-1, involved in the control of cell proliferation.66 In addition, resveratrol is known to possess antiproliferative and cell cycle-arresting properties in vitro, in several cancer cell lines.13 Furthermore, resveratrol can inhibit several enzyme activities associated with cell proliferation and DNA replication.

Proapoptotic effects of resveratrol

Colon cancer reflects one or more disturbances in colonic tissue homeostasis. Changes in the rates of colonocyte proliferation, apoptosis, or both are involved in colon tumorigenesis. Indeed, a defect in an apoptosis mechanism is recognized as an important cause of carcinogenesis.68 Dysregulation of proliferation alone is not sufficient for cancer formation; suppression of apoptotic signaling is also needed.67 The proapototic effector molecule caspase 3 plays an important role in downstream apoptotic signaling by cleaving proteins vital for cell survival, by activating poly (ADP-ribose) polymerase (PARP), and by activating DNA fragmentation factors.68 Following carcinogen administration, colonic expression of caspase 3 was downregulated. Several studies show that induction of apoptotic processes by activation of apoptosis-regulating molecules such as caspases can induce cancer cell death.69 The mechanism responsible for the induction of caspase 3 by resveratrol is not known; however, it is possible that inhibition of cholesterol formation by resveratrol may alter the integrity of cell membranes (cell/mitochondrial) of tumor cells, thereby leading to activation of the proapoptotic effector molecules, including caspase 3. Dorrie et al. showed that resveratrol induced extensive apoptosis by depolarizing mitochondrial membranes and activating caspase cascade in several cancer cell lines.70 Induction of p53 at the mRNA and protein levels is a commonly observed effect of resveratrol and may be considered a major cause of apoptosis.

Heat shock proteins (HSPs) are a family of chaperones induced by heat and other stresses; these proteins thus serve essential functions under stress (and nonstress) conditions. Several HSPs are differentially expressed and/or regulated during cell cycle and at various stages of development and differentiation.71 The normal cellular functions of HSP70 and HSP27 are not completely understood. Over-expression of HSP70, an anti-apoptotic heat shock protein, may lead to accumulation of damaged cells and, therefore, enhanced cancer risk. Over-expression of HSP27 may increase cell tumorigenicity, possibly as a result of a drastic decrease in tumor cell apoptosis.71 Furthermore, Lee et al. have shown that over-expression of HSP70 may be associated with abnormal p53 expression by tumor cells.72 Accumulation of HSP27 in colon cancer cells reaching confluence is involved in their resistance to cytotoxic drugs. Moreover, over-expression of HSP70, with low levels of caspase 3 activity, is known to play an antiapoptotic role in malignant human tumors of various origins. It has been shown that HSP70 over-production can ameliorate apoptotic cell death and inhibit caspase 3 activation, leading to reduced apoptosis.73

Induction and activation of some HSPs in tumor cells may be controlled by several regulatory factors, including oncogenes such as c-myc, ras, and tumor suppressor genes (e.g., p53). In this regard, Sengottuvelan et al.61 investigated the effect of resveratrol on HSP70 and HSP27 expression in carcinogen-induced rat colon carcinogenesis. An elevated expression of HSP70 and HSP27 in the colonic mucosa of carcinogen-exposed rats was observed at the end of 30 weeks.61 Resveratrol supplementation suppressed the accumulation of HSP70 and HSP27 in carcinogen-treated rats. The inhibitory effect was most prominent when resveratrol was supplemented throughout the experimental period. This could be attributed to its antitumor activity, thus highlighting the chemotherapeutic potential of resveratrol, in addition to its chemopreventive activity.

Resveratrol on cell signaling and inflammatory markers

Protein kinase C (PKC), a serine/threonine-specific kinase known to exist as at least nine isoenzymes with different properties and subcellular localizations, appears to participate in signaling pathways involved in cell proliferation, differentiation, apoptosis, and malignant transformation.74 The changes in PKC distribution, followed by a decrease in cytosolic kinase expression in carcinogen-exposed rats, is consistent with an apparent down-regulation of PKC, which has been noted in several cultured cells treated with tumor promoters. Kahl-Rainer et al. have suggested that PKC may diffuse from the cytoplasm to the nucleus of the cell and thereby transmit signals from the cytosolic side of the plasma membrane to the nucleus and induce malignant transformation.75 Doi et al. have also recently speculated that altered regulation of PKC, or a process closely linked to this phenomenon, may be important in the process of multi-stage carcinogenesis.76

1,2-Dimethylhydrazine (DMH) is known to stimulate colonic epithelial cell proliferation, and it is possible that the PKC alterations noted in the previous experiments are secondary to proliferative changes induced by DMH. The signaling events leading to apoptotic cell death upon exposure to antiproliferative agents has emerged as a target candidate for chemopreventive agents. Sengottuvelan et al.77,78 have shown that resveratrol suppresses the translocation and overexpression of membrane PKC in carcinogen-exposed rats. This action of resveratrol may be due to the suppression of colonic mucosal turnover of phosphoinositides and diacylglycerol mass or to its modulatory action on PKC enzyme expression.77,78 This inhibitory effect could also be explained, in part, by the antiproliferative and antioxidant property of resveratrol as other phenolic antioxidants inhibit phorbol ester-mediated activation of PKC.

The enzyme cyclooxygenase-2 (COX-2), an inducible early-response protein, plays an important role in inflammation and in carcinogenesis.79 Assay of COX-2 expression can be used to monitor the process of carcinogenesis, and suppression of COX-2 expression has become a target for cancer chemoprevention. It is known that COX-2 activity is elevated in carcinogen-induced rodents and in human colorectal tumors. Sengottuvelan et al. showed that the expression pattern of COX-2 was elevated in DMH-treated rats.78 Over-expression of COX-2 can result in the inhibition of programmed cell death in prostate cancer cells. Evidence from in vitro and animal model studies suggests that the COX-2 inhibition may suppress carcinogenesis by affecting/promoting a number of pathways such as angiogenesis, tumor invasion, and apoptosis. Resveratrol supplementation inhibited the over-expression of COX-2 in carcinogen-treated rats. Several studies have shown that inhibition of COX-2 activity in different cancer models is effective in the treatment of cancer initiation, promotion, and progression.80 Reduced expression of COX-2 by the colonic cells may be due to the anti-oxidant, anti-inflammatory, or immunomodulatory effects of resveratrol. In addition, decreased COX-2 expression on resveratrol supplementation may also be attributed to the ability of resveratrol to inhibit cell proliferation.

Conclusion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Colon cancer chemopreventive effects
  5. Conclusion
  6. Conflicts of interest
  7. References

Many phenolic compounds present in food and vegetables are known to possess potent and desirable biological activities against cancer and cardiovascular disease. The most universal property is related to their functions as antioxidants, manifested by their ability to trap free radicals. There are several mechanisms that may account for the biological properties of resveratrol, such as anticancer, antihyperlipidemic, and anti-inflammatory effects. The possible signal transduction pathways inhibited by resveratrol may include (1) scavenging ROS; (2) inhibition of cell proliferation; (3) induction of apoptosis; or (4) inhibition of protein kinases. Based on the findings that signal transduction may be affected by resveratrol, further studies are needed to determine how effective resveratrol or its analogues are in preventing or treating inflammation, cardiovascular disease, and cancer.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Colon cancer chemopreventive effects
  5. Conclusion
  6. Conflicts of interest
  7. References