Quercetin, the active phenolic component in kiwifruit, prevents hydrogen peroxide-induced inhibition of gap-junction intercellular communication

Applicability of Scrape Loading-Dye Transfer Assay for Non-Genotoxic Carcinogen Testing

Dysregulation of gap junction intercellular communication (GJIC) is recognized as one of the key hallmarks for identifying non-genotoxic carcinogens (NGTxC). Currently, there is a demand for in vitro assays addressing the gap junction hallmark, which would have the potential to eventually become an integral part of an integrated approach to the testing and assessment (IATA) of NGTxC. The scrape loading-dye transfer (SL-DT) technique is a simple assay for the functional evaluation of GJIC in various in vitro cultured mammalian cells and represents an interesting candidate assay. Out of the various techniques for evaluating GJIC, the SL-DT assay has been used frequently to assess the effects of various chemicals on GJIC in toxicological and tumor promotion research. In this review, we systematically searched the existing literature to gather papers assessing GJIC using the SL-DT assay in a rat liver epithelial cell line, WB-F344, after treating with chemicals, especially environmental and food toxicants, drugs, reproductive-, cardio- and neuro-toxicants and chemical tumor promoters. We discuss findings derived from the SL-DT assay with the known knowledge about the tumor-promoting activity and carcinogenicity of the assessed chemicals to evaluate the predictive capacity of the SL-DT assay in terms of its sensitivity, specificity and accuracy for identifying carcinogens. These data represent important information with respect to the applicability of the SL-DT assay for the testing of NGTxC within the IATA framework.

Deciphering the in vivo redox behavior of human peroxiredoxins I and II by expressing in budding yeast

Peroxiredoxins (Prxs), scavenge cellular peroxides by forming recyclable disulfides but under high oxidative stress, hyperoxidation of their active-site Cys residue results in loss of their peroxidase activity. Saccharomyces cerevisiae deficient in human Prx (hPrx) orthologue TSA1 show growth defects under oxidative stress. They can be complemented with hPRXI but not by hPRXII, but it is not clear how the disulfide and hyperoxidation states of the hPrx vary in yeast under oxidative stress. To understand this, we used oxidative-stress sensitive tsa1tsa2Δ yeast strain to express hPRXI or hPRXII. We found that hPrxI in yeast exists as a mixture of disulfide-linked dimer and reduced monomer but becomes hyperoxidized upon elevated oxidative stress as analyzed under denaturing conditions (SDS-PAGE). In contrast, hPrxII was present predominantly as the disulfide in unstressed cells and readily converted to its hyperoxidized, peroxidase-inactive form even with mild oxidative stress. Interestingly, we found that plant extracts containing polyphenol antioxidants provided further protection against the growth defects of the tsa1tsa2Δ strain expressing hPrx and preserved the peroxidase-active forms of the Prxs. The extracts also helped to protect against hyperoxidation of hPrxs in HeLa cells. Based on these findings we can conclude that resistance to oxidative stress of yeast cells expressing individual hPrxs requires the hPrx to be maintained in a redox state that permits redox cycling and peroxidase activity. Peroxidase activity decreases as the hPrx becomes hyperoxidized and the limited protection by hPrxII compared with hPrxI can be explained by its greater sensitivity to hyperoxidation.

Actinidia chinensis Planch.: A Review of Chemistry and Pharmacology

Actinidia chinensis Planch. (A. chinensis), commonly known as Chinese kiwifruit, is a China native fruit, which becomes increasingly popular due to attractive economic, nutritional, and health benefits properties. The whole plant including fruits, leaves, vines, and roots of A. chinensis are used mainly as food or additive in food products and as folk medicine in China. It is a good source of triterpenoids, polyphenols, vitamin C, carbohydrate, amino acid, and minerals. These constituents render the A. chinensis with a wide range of pharmacological properties including antitumor, antioxidant, anti-inflammatory, immunoregulatory, hypolipemic, antidiabetic, and cardiovascular protective activities, suggesting that it may possibly be value in the prevention and treatment of pathologies associated to cancer, oxidative stress, and aging. This minireview provides a brief knowledge about the recent advances in chemistry, biological activities, utilization, and storage of Chinese kiwifruit. Future research directions on how to better use of this crop are suggested.

Vitamin E and caloric restriction promote hepatic homeostasis through expression of connexin 26, N-cad, E-cad and cholesterol metabolism genes

Connexins (Cx) and cadherins are responsible for cell homeostasis. The Cx activity is directly related to cholesterol. The present work investigates whether vitamin E, with or without caloric restriction (CR), alters the mRNA expression of Cx26, Cx32, Cx43, N-cadherins (N-cads), E-cadherins (E-cads) and alpha-smooth muscle actin (α-SMA), and evaluates their relation to cholesterol metabolism in rat liver. Animals were divided into different groups: control with ad libitum diet (C), control+vitamin E (CV), aloric restriction with intake to 60% of group C (CR), and the intake of group CR+vitamin E (RV). There were increases of manganese superoxide dismutase (Mn-SOD) and glutathione S-transferase mu 1, indicating antioxidant effects of CR and vitamin E. An increase of nitric oxide in the CR group was in agreement with the Mn-SOD data. Supplementation with vitamin E, with or without CR, upregulated the expression of Cx26 mRNA and increased low-density lipoprotein cholesterol (LDL-c) in the CV group. Reductions of Cx32 and Cx43 were associated with lower LDL-c. Increases in Hmgcr and low-density lipoprotein receptor (LDLr) in the CV and RV groups could be explained by the effect of vitamin E. A reduction of LDLr in the CR group was due to the reduced dietary intake. Increases in cadherins in the CV, CR and RV groups were indicative of tissue maintenance, which was also supported by increases of α-SMA in groups CV and RV. Finally, vitamin E, with or without CR, increased Cx26, probably modulated by expression of the Hmgcr and LDLr genes. This suggests important relationship of Cxs and cholesterol metabolism genes.

Influence of Geographical Location of Orchards on Green Kiwifruit Bioactive Components

Italy is one of the world's major kiwifruit producers and exporters with orchards located in different areas from the north to the south of the peninsula. This study sought to investigate for the first time the possible influence of the geographical location of kiwifruit orchards on some fruit components, selected because of their involvement in beneficial or negative effects on human health. The fruits harvested in 16 Italian areas were analyzed, and the results obtained show that the observed variations of the relative amounts of total proteins, kiwellin, the major allergen actinidin, ascorbate, polyphenols, and superoxide dismutase (SOD)-like activity seem not to be related to the geographical location of the orchards. In contrast, the high concentration of the nutraceutical peptide kissper seems to have some relationship with the cultivation area. In fact, its amount is much higher in the fruits from the Lazio region, thus providing added value to these kiwifruits.

Chemopreventive Agents Attenuate Rapid Inhibition of Gap Junctional Intercellular Communication Induced by Environmental Toxicants

Altered gap junctional intercellular communication (GJIC) has been associated with chemical carcinogenesis, where both chemical tumor promoters and chemopreventive agents (CPAs) are known to conversely modulate GJIC. The aim of this study was to investigate whether attenuation of chemically inhibited GJIC represents a common outcome induced by different CPAs, which could be effectively evaluated using in vitro methods. Rat liver epithelial cells WB-F344 were pretreated with a CPA for either 30 min or 24 h, and then exposed to GJIC-inhibiting concentration of a selected tumor promoter or environmental toxicant [12-O-tetradecanoylphorbol-13-acetate (TPA), lindane, fluoranthene, 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane (DDT), perfluorooctanoic acid (PFOA), or pentachlorophenol]. Out of nine CPAs tested, quercetin and silibinin elicited the most pronounced effects, preventing the dysregulation of GJIC by all the GJIC inhibitors, but DDT. Metformin and curcumin attenuated the effects of three GJIC inhibitors, whereas the other CPAs prevented the effects of two (diallyl sulfide, emodin) or one (indole-3-carbinol, thymoquinone) GJIC inhibitor. Significant attenuation of chemically induced inhibition of GJIC was observed in 27 (50%) out of 54 possible combinations of nine CPAs and six GJIC inhibitors. Our data demonstrate that in vitro evaluation of GJIC can be used as an effective screening tool for identification of chemicals with potential chemopreventive activity.

Effects of kiwi consumption on plasma lipids, fibrinogen and insulin resistance in the context of a normal diet

Background and aims

Among fruits, kiwi is one of the richest in vitamins and polyphenols and has strong anti-oxidant effects. We aimed to analyze the relationship between the consumption of kiwi and plasma lipid values, fibrinogen, and insulin resistance in adults within the context of a normal diet and physical-activity.

Methods

Cross-sectional study. Participants (N = 1469), who were free of cardiovascular diseases, completed a visit, which included the collection of information concerning the participant’s usual diet and kiwi consumption using a previously validated, semi-quantitative, 137-item food-frequency-questionnaire. Fasting laboratory determinations included plasma lipids, fibrinogen and insulin resistance. Regular physical-activity was determined using accelerometry.

Results

Consumers of at least 1 kiwi/week presented higher plasma values of HDL-cholesterol (mean difference 4.50 [95 % CI: 2.63 to 6.36]) and lower triglyceride values (mean difference −20.03 [95 % CI: −6.77 to −33.29]), fibrinogen values (mean difference −13.22 [95 % CI: −2.18 to −24.26]) and HOMAir values (mean difference −0.30 [95 % CI: −0.09 to −0.50]) (p < 0.05, for all comparisons) than those who consumed less than 1 kiwi per week. In an adjusted logistic regression analysis, this group had a lower odds-ratio for presenting plasmatic fibrinogen concentrations above 400 mg/dL (OR = 0.68, 95 % CI 0.49 to 0.95), HDL-Cholesterol plasma values below 45 mg/dL (OR = 0.57, 95 % CI 0.36 to 0.91) and a HOMAir above 3 (OR = 0.61, 95 % CI 0.37 to 1.00).

Conclusions

Consumption of at least one kiwi/week is associated with lower plasma concentrations of fibrinogen and improved plasma lipid profile in the context of a normal diet and regular exercise.

Intracellular Cleavage of the Cx43 C-Terminal Domain by Matrix-Metalloproteases: A Novel Contributor to Inflammation?

The coordination of tissue function is mediated by gap junctions (GJs) that enable direct cell-cell transfer of metabolic and electric signals. GJs are formed by connexin (Cx) proteins of which Cx43 is most widespread in the human body. Beyond its role in direct intercellular communication, Cx43 also forms nonjunctional hemichannels (HCs) in the plasma membrane that mediate the release of paracrine signaling molecules in the extracellular environment. Both HC and GJ channel function are regulated by protein-protein interactions and posttranslational modifications that predominantly take place in the C-terminal domain of Cx43. Matrix metalloproteases (MMPs) are a major group of zinc-dependent proteases, known to regulate not only extracellular matrix remodeling, but also processing of intracellular proteins. Together with Cx43 channels, both GJs and HCs, MMPs contribute to acute inflammation and a small number of studies reports on an MMP-Cx43 link. Here, we build further on these reports and present a novel hypothesis that describes proteolytic cleavage of the Cx43 C-terminal domain by MMPs and explores possibilities of how such cleavage events may affect Cx43 channel function. Finally, we set out how aberrant channel function resulting from cleavage can contribute to the acute inflammatory response during tissue injury.

Recovery effect of onion peel extract against H2 O2 -induced inhibition of gap-junctional intercellular communication is mediated through quercetin

Cellular oxidative damage mediated by reactive oxygen species has been reported to inhibit gap-junctional intercellular communication (GJIC). In turn, the inhibition of GJIC can be attenuated by functional food compounds with antioxidant properties. In this study, we compared the protective effects of onion peel extract (OPE) and onion flesh extract (OFE) on oxidative stress-mediated GJIC inhibition, and investigated the mechanisms of action responsible. OPE restored H2 O2 -induced GJIC inhibition to a higher degree than OFE in WB-F344 rat liver epithelial cells. OPE was found to inhibit H2 O2 -induced phosphorylation of ERK1/2 and Cx43. A radical scavenging assay demonstrated superiority of OPE over OFE, suggesting that the observed effects might be mediated via an antioxidant mechanism. Quercetin is the major compound that is likely to be responsible for the protective effect against H2 O2 -mediated GJIC inhibition. This study suggests that OPE, a material often discarded, may be of value for the future development of functional food products.

PRACTICAL APPLICATION

This study demonstrates that onion peel extract (OPE) exhibits a protective effect against the inhibition of gap-junctional intercellular communication (GJIC) mediated by H2 O2 , which is likely to occur via its antioxidant activity. OPE contains significant concentrations of bioactive phenolic compounds. Reductions in oxidative stress can lead to recovery of GJIC, which has been reported to be implicated in the prevention and treatment of cancers. These findings suggest that onion peel, a common waste product, could be used as potential resources for functional food development. Onion peel could be processed into a quercetin-rich powder or a pill for the prevention of cancer and other oxidative stress-related diseases.

The kiwi fruit peptide kissper displays anti-inflammatory and anti-oxidant effects in in-vitro and ex-vivo human intestinal models

Literature reports describe kiwi fruit as a food with significant effects on human health, including anti-oxidant and anti-inflammatory activity. Fresh fruit or raw kiwi fruit extracts have been used so far to investigate these effects, but the molecule(s) responsible for these health-promoting activities have not yet been identified. Kissper is a kiwi fruit peptide displaying pore-forming activity in synthetic lipid bilayers, the composition of which is similar to that found in intestinal cells. The objective of this study was to investigate the kissper influence on intestinal inflammation using cultured cells and ex-vivo tissues from healthy subjects and Crohn's disease (CD) patients. The anti-oxidant and anti-inflammatory properties of kissper were tested on Caco-2 cells and on the colonic mucosa from 23 patients with CD, by challenging with the lipopolysaccharide from Escherichia coli (EC-LPS) and monitoring the appropriate markers by Western blot and immunofluorescence. EC-LPS challenge determined an increase in the intracellular concentration of calcium and reactive oxygen species (ROS). The peptide kissper was highly effective in preventing the increase of LPS-induced ROS levels in both the Caco-2 cells and CD colonic mucosa. Moreover, it controls the calcium increase, p65-nuclear factor (NF)-kB induction and transglutaminase 2 (TG2) activation inflammatory response in Caco-2 cells and CD colonic mucosa. Kissper efficiently counteracts the oxidative stress and inflammatory response in valuable model systems consisting of intestinal cells and CD colonic mucosa. This study reports the first evidence supporting a possible correlation between some beneficial effects of kiwi fruit and a specific protein molecule rather than generic nutrients.

Comparison between the effects of quercetin on seizure threshold in acute and chronic seizure models

Flavonoids are important constituents of food and beverages, and several studies have shown that they have neuroactive properties. Many of these compounds are ligands for γ-aminobutyric acid type A receptors in the central nervous system. This study aimed to investigate the anticonvulsant effects of quercetin (3,3',4',5,7-pentahydroxyflavone), which is a flavonoid found in plants, in rats treated with pentylenetetrazole in acute and chronic seizure models. Single intraperitoneal administration of quercetin did not show anticonvulsive effects against acute seizure. Similarly, multiple oral pretreatment with quercetin did not have protective effects against acute seizure. However, multiple intraperitoneal administration of quercetin (25 and 50 mg/kg) significantly increased time to death compared with the control (p < 0.001). However, quercetin pretreatment had no significant effects on the pattern of convulsion development during all periods of kindling. But on the test day, quercetin (100 mg/kg) could significantly increase generalized tonic-clonic seizure onset (GTCS) and decrease GTCS duration compared with the control (p < 0.01, p < 0.05). We conclude that quercetin has a narrow therapeutic dose range for anticonvulsant activities in vivo, and it has different effects on the seizure threshold. The different effects of quercetin on seizure threshold may occur through several mechanisms.

A randomised cross-over pharmacokinetic bioavailability study of synthetic versus kiwifruit-derived vitamin C

Kiwifruit are a rich source of vitamin C and also contain numerous phytochemicals, such as flavonoids, which may influence the bioavailability of kiwifruit-derived vitamin C. The aim of this study was to compare the relative bioavailability of synthetic versus kiwifruit-derived vitamin C using a randomised cross-over pharmacokinetic study design. Nine non-smoking males (aged 18–35 years) received either a chewable tablet (200 mg vitamin C) or the equivalent dose from gold kiwifruit (Actinidia chinensis var. Sungold). Fasting blood and urine were collected half hourly to hourly over the eight hours following intervention. The ascorbate content of the plasma and urine was determined using HPLC with electrochemical detection. Plasma ascorbate levels increased from 0.5 h after the intervention (P = 0.008). No significant differences in the plasma time-concentration curves were observed between the two interventions (P = 0.645). An estimate of the total increase in plasma ascorbate indicated complete uptake of the ingested vitamin C tablet and kiwifruit-derived vitamin C. There was an increase in urinary ascorbate excretion, relative to urinary creatinine, from two hours post intervention (P < 0.001). There was also a significant difference between the two interventions, with enhanced ascorbate excretion observed in the kiwifruit group (P = 0.016). Urinary excretion was calculated as ~40% and ~50% of the ingested dose from the vitamin C tablet and kiwifruit arms, respectively. Overall, our pharmacokinetic study has shown comparable relative bioavailability of kiwifruit-derived vitamin C and synthetic vitamin C.

The kiwi fruit peptide kissper displays anti-inflammatory and anti-oxidant effects in in-vitro and ex-vivo human intestinal models

Literature reports describe kiwi fruit as a food with significant effects on human health, including anti-oxidant and anti-inflammatory activity. Fresh fruit or raw kiwi fruit extracts have been used so far to investigate these effects, but the molecule(s) responsible for these health-promoting activities have not yet been identified. Kissper is a kiwi fruit peptide displaying pore-forming activity in synthetic lipid bilayers, the composition of which is similar to that found in intestinal cells. The objective of this study was to investigate the kissper influence on intestinal inflammation using cultured cells and ex-vivo tissues from healthy subjects and Crohn's disease (CD) patients. The anti-oxidant and anti-inflammatory properties of kissper were tested on Caco-2 cells and on the colonic mucosa from 23 patients with CD, by challenging with the lipopolysaccharide from Escherichia coli (EC-LPS) and monitoring the appropriate markers by Western blot and immunofluorescence. EC-LPS challenge determined an increase in the intracellular concentration of calcium and reactive oxygen species (ROS). The peptide kissper was highly effective in preventing the increase of LPS-induced ROS levels in both the Caco-2 cells and CD colonic mucosa. Moreover, it controls the calcium increase, p65-nuclear factor (NF)-kB induction and transglutaminase 2 (TG2) activation inflammatory response in Caco-2 cells and CD colonic mucosa. Kissper efficiently counteracts the oxidative stress and inflammatory response in valuable model systems consisting of intestinal cells and CD colonic mucosa. This study reports the first evidence supporting a possible correlation between some beneficial effects of kiwi fruit and a specific protein molecule rather than generic nutrients.

Extract from the zooxanthellate jellyfish Cotylorhiza tuberculata modulates gap junction intercellular communication in human cell cultures

On a global scale, jellyfish populations in coastal marine ecosystems exhibit increasing trends of abundance. High-density outbreaks may directly or indirectly affect human economical and recreational activities, as well as public health. As the interest in biology of marine jellyfish grows, a number of jellyfish metabolites with healthy potential, such as anticancer or antioxidant activities, is increasingly reported. In this study, the Mediterranean “fried egg jellyfish” Cotylorhiza tuberculata (Macri, 1778) has been targeted in the search forputative valuable bioactive compounds. A medusa extract was obtained, fractionated, characterized by HPLC, GC-MS and SDS-PAGE and assayed for its biological activity on breast cancer cells (MCF-7) and human epidermal keratinocytes (HEKa). The composition of the jellyfish extract included photosynthetic pigments, valuable ω-3 and ω-6 fatty acids, and polypeptides derived either from jellyfish tissues and their algal symbionts. Extract fractions showed antioxidant activity and the ability to affect cell viability and intercellular communication mediated by gap junctions (GJIC) differentially in MCF-7and HEKa cells. A significantly higher cytotoxicity and GJIC enhancement in MCF-7 compared to HEKa cells was recorded. A putative action mechanism for the anticancer bioactivity through the modulation of GJIC has been hypothesized and its nutraceutical and pharmaceutical potential was discussed.

Cancer chemoprevention by polyphenols and their potential application as nanomedicine

Today cancer is a leading cause of death among the developed countries. Its highly complex nature makes it difficult to understand as it entails multiple cellular physiological systems such as cell signaling and apoptosis. The biggest challenges faced by cancer chemoprevention/chemotherapy is maintaining drug circulation and avoiding multidrug resistance. Overall there is modest evidence regarding the protective effects of nutrients from supplements against a number of cancers. Numerous scientific literatures available advocate the use of polyphenols for chemoprevention. Some groups have also suggested use of combination of nutrients in cancer prevention. However, we have yet to obtain the desired results in the line of cancer chemotherapy research. Nanotechnology can play a pivotal role in cancer treatment and prevention. Moreover, nanoparticles can be modified in various ways to prolong circulation, enhance drug localization, increase drug efficacy, and potentially decrease the chances of multidrug resistance. In this communication, we will cover the use of various polyphenols and nutrients in cancer chemoprevention. The application of nanotechnology in this regard will also be included. In view of available reports on the potential of nanoparticles, we suggest their usage along with different combination of nutrients as cancer chemotherapeutic agents.

In vitro antioxidant synergism and antagonism between food extracts can lead to similar activities in H2O2-induced cell death, caspase-3 and MMP-2 activities in H9c2 cells

BACKGROUND

The cardio-health-promoting activity of some foods may be due to their specific antioxidant content. The antioxidant activity of a mixture of plant extracts has been shown to differ from the activity of the individual extracts. As a result, the activity of the mixture can be described as synergistic, antagonistic or additive. This in vitro study evaluated the relationship between the in vitro antioxidant capacity of mixtures and their bioactivity when cardiomyocytes (H9c2) were challenged with H(2)O(2).

RESULTS

A mixture of raspberry and adzuki bean extracts produced a synergistic response and a mixture of broccoli and soybean extracts produced an antagonistic response in chemical-based antioxidant assays. When these extracts were tested in cell cultures, individually and in mixtures, the mixture of raspberry and adzuki bean protected the cardiomyocytes from H(2)O(2)-induced cell damage significantly better than the individual extracts. Conversely, the mixture of broccoli and soybean extracts was less effective in protecting H9c2 cells. The synergistic and antagonistic effects of the mixtures in protecting cell damage were brought about by enhanced or reduced ability in attenuating caspase-3 and matrix metalloproteinase-2 activities elevated by H(2)O(2).

CONCLUSION

Food mixtures with synergistic antioxidant activity and protective property against reactive oxygen species-induced cell death can potentially be incorporated into novel functional foods or beverages with optimum health benefit. The antagonistic effect of food mixtures can be a health concern and thus should be avoided.

Combination of quercetin with radiotherapy enhances tumor radiosensitivity in vitro and in vivo

PURPOSE

Quercetin (3, 3,' 4', 5, 7 - five-flavonoids) is one of the main components of flavonoids, with multifunctions on immune function, anti-oxidation, anti-viral, anti-inflammatory, and cardiovascular protection. We hypothesize that a combination of quercetin with radiation would increase tumor radiosensitivity. To test this hypothesis, we conducted in vitro and in vivo studies.

METHODS AND MATERIALS

The in vitro radio-sensitization activity of quercetin was tested in DLD1, HeLa and MCF-7 tumor cell lines by colony formation assays. The in vivo activity was assessed in the DLD-1 human colorectal cancer xenograft model in nude mice. Mechanistic studies were conducted in several cell lines using Western blot analysis and immunofluorescence microscopy.

RESULTS

We found that quercetin can significantly increase tumor radiosensitivity both in vitro and in vivo. The in vitro Sensitizing Enhancement Ratios in DLD1, HeLa and MCF-7 cells were 1.87, 1.65, and 1.74, respectively. The mean doubling time of tumor xenografts was significantly increased in irradiated mice treated with quercetin. At the cellular level, exposure to quercetin resulted in prolonged DNA repair. The mechanistic studies demonstrated that quercetin induced radio-sensitization is through inhibiting the ATM kinase, one of the critical DNA damage response proteins.

CONCLUSION

We demonstrate both in vitro and in vivo evidence that combination of quercetin with radiotherapy can enhance tumor radiosensitivity by targeting the ATM-mediated pathway in response to radiation.

Preventive effect of t,t-conjugated linoleic acid on 12-O-tetradecanoylphorbol-13-acetate-induced inhibition of gap junctional intercellular communication in human mammary epithelial MCF-10A cells

The anti-tumor promotional effects of t9,t11-conjugated linoleic acid (t9,t11-CLA) and t10,t12-CLA were evaluated on the 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced inhibition of gap junctional intercellular communication (GJIC) in the human mammary epithelial cell line MCF-10A. The results were compared to those obtained from c9,t11-CLA, which is a more effective anti-tumor promoter on TPA-induced GJIC inhibition in MCF-10A cells than t10,c12-CLA. Cells were treated with 20 μM t9,t11-CLA, t10,t12-CLA, or c9,t11-CLA for 24 h followed by 60 nM TPA for 1 h. Both t9,t11-CLA and t10,t12-CLA equally protected MCF-10A cells from TPA-induced inhibition of GJIC with inferior efficacy to c9,t11-CLA.The protection was due to the ameliorated phosphorylation of connexin43 via suppression of extracellular signal-regulated kinases (ERK1/2) activation. Suppression of TPA-induced reactive oxygen species (ROS) generation by t9,t11-CLA and t10,t12-CLA was less effective, relative to c9,t11-CLA. The results suggest that the anti-promotional activities of t9,t11-CLA and t10,t12-CLA are equal but less potent than c9,t11-CLA in TPA-treated MCF-10A cells. The activity might be mediated by the attenuation of ROS production in MCF-10A cells by preventing the downregulation of GJIC during the cancer promotion stage.

Polyphenols as small molecular inhibitors of signaling cascades in carcinogenesis

Multiple lines of evidences suggest that oxidative stress induced by reactive oxygen species are closely related to multi-stage carcinogenesis. Polyphenols, a group of chemicals with more than one phenol unit or building block per molecule, have been recognized for possessing many health benefits including cancer-preventive effects mainly due to their antioxidant activity. However, polyphenols can directly bind with signaling molecules involved in carcinogenesis and regulate its activity. Moreover, it is noteworthy that the binding between the polyphenol and the target protein is determined by their structural relationship, which implies that different polyphenols have different target proteins, leading to divergent chemopreventive effects. Extracellular stimuli transmit signals into a cell by activating their target signaling cascades involved in carcinogenesis. As an example, Src family kinase, a family of proto-oncogenic tyrosine kinases activated by a variety of oxidative stress and proinflammatory agents, is known to regulate cell proliferation, differentiation, survival and angiogenesis. Src family kinase subsequently activates downstream signal cascades including mitogen-activated protein kinase, phosphoinositol-3-kinase, and nuclear factor-kappaB, thereby inducing cell proliferation and causing cancer. Recent studies demonstrate that polyphenols can directly target signaling cascades involved in inflammation and the development of cancer. Inhibition of the kinases by polyphenols contributes to the attenuation of carcinogenesis. Therefore, the development of polyphenols as direct inhibitors against target proteins is regarded as a rational approach for chemoprevention. This review describes and discusses recent results about the direct interactions of polyphenols and protein kinases in cancer chemoprevention.