Preventive effect of epicatechin and ginsenoside Rb(2) on the inhibition of gap junctional intercellular communication by TPA and H(2)O(2)

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.

Role of ROS/RNS in Preeclampsia: Are Connexins the Missing Piece?

Preeclampsia is a pregnancy complication that appears after 20 weeks of gestation and is characterized by hypertension and proteinuria, affecting both mother and offspring. The cellular and molecular mechanisms that cause the development of preeclampsia are poorly understood. An important feature of preeclampsia is an increase in oxygen and nitrogen derived free radicals (reactive oxygen species/reactive nitrogen species (ROS/RNS), which seem to be central players setting the development and progression of preeclampsia. Cell-to-cell communication may be disrupted as well. Connexins (Cxs), a family of transmembrane proteins that form hemichannels and gap junction channels (GJCs), are essential in paracrine and autocrine cell communication, allowing the movement of signaling molecules between cells as well as between the cytoplasm and the extracellular media. GJCs and hemichannels are fundamental for communication between endothelial and smooth muscle cells and, therefore, in the control of vascular contraction and relaxation. In systemic vasculature, the activity of GJCs and hemichannels is modulated by ROS and RNS. Cxs participate in the development of the placenta and are expressed in placental vasculature. However, it is unknown whether Cxs are modulated by ROS/RNS in the placenta, or whether this potential modulation contributes to the pathogenesis of preeclampsia. Our review addresses the possible role of Cxs in preeclampsia, and the plausible modulation of Cxs-formed channels by ROS and RNS. We suggest these factors may contribute to the development of preeclampsia.

Gadolinium Chloride Restores the Function of the Gap Junctional Intercellular Communication between Hepatocytes in a Liver Injury

BACKGROUND

Gadolinium chloride (GdCl3) has been reported to attenuate liver injury caused by a variety of toxicants. Gap junctional intercellular communication (GJIC) is thought to be essential in controlling liver homeostasis and pathology. Here we evaluate the effects of GdCl3 on functional GJIC and connexin expression in mouse models and primary hepatocytes.

METHODS

Mice were administered GdCl3 intraperitoneally the day before a carbon tetrachloride (CCl4) injection or bile duct ligation (BDL) operation. Primary hepatocytes were treated with CCl4 or lipopolysaccharides (LPS), with or without GdCl3. A scrape loading/dye transfer assay was performed to assess the GJIC function. The expression of connexins was examined by real-time reverse transcription polymerase chain reaction (RT-PCR), western blot and immunofluorescent staining.

RESULTS

CCl4 treatment or the BDL operation led to the dysfunction of GJIC and a down-regulation of Cx32 and Cx26 in injured liver. GdCl3 administration restored GJIC function between hepatocytes by facilitating the transfer of fluorescent dye from one cell into adjacent cells via GJIC, and markedly prevented the decrease of Cx32 and Cx26 in injured liver. In primary hepatocytes, CCl4 or LPS treatment induced an obvious decline of Cx32 and Cx26, whereas GdCl3 pretreatment prevented the down-regulation of connexins. In vivo GdCl3 protected hepatocytes and attenuated the liver inflammation and fibrosis in liver injury mouse models.

CONCLUSION

GdCl3 administration protects functional GJIC between hepatocytes, and prevents the decrease of connexin proteins at mRNA and protein levels during liver injury, leading to the alleviation of chronic liver injury.

Simultaneous quantification of six nonpolar ginsenosides in white ginseng by reverse-phase high-performance liquid chromatography coupled with integrated pulsed amperometric detection

Background

White ginseng consists of the roots and rhizomes of the Panax species, and red ginseng is made by steaming and drying white ginseng. While red ginseng has both polar and nonpolar ginsenosides, previous studies showed white ginseng to have only polar ginsenosides. Because nonpolar ginsenosides are formed through the manufacture of red ginseng from white ginseng, researchers have generally thought that nonpolar ginsenosides do not exist in white ginseng.

Methods

We developed a simultaneous quantitative method for six nonpolar ginsenosides in white ginseng using reverse-phase high-performance liquid chromatography coupled with integrated pulsed amperometric detection. The nonpolar ginsenosides of white ginseng were extracted for 4 h under reflux with 50% methanol.

Results

Using the gradient elution system, all target components were completely separated within 50 min. Nonpolar ginsenosides were determined in the rhizome head (RH), main root (MR), lateral root, and hairy root (HR) of 6-year-old white ginseng samples obtained from several regions (Geumsan, Punggi, and Kanghwa). The total content in the HR of white ginseng was 37.8–56.8% of that in the HR of red ginseng. The total content in the MR of white ginseng was 5.9–24.3% of that in the MR of red ginseng. In addition, the total content in the RH of white ginseng was 28.5–35.8% of that in the HR of red ginseng

Conclusion

It was confirmed that nonpolar ginsenosides known to be specific components of red ginseng were present at substantial concentrations in the HR or RH of white ginseng.

Method development for the certification of a ginsenoside calibration solution via liquid chromatography with absorbance and mass spectrometric detection

The research presented here describes the development of two analytical methods for use in the certification of a ginsenoside calibration solution Standard Reference Material (SRM) 3389 consisting of seven ginsenosides: Rg1, Re, Rf, Rb1, Rc, Rb2, and Rd. The new methods utilized the liquid chromatographic (LC) separation of ginsenoside mixtures with absorbance detection (UV) and mass spectrometry (MS). Ginsenosides Rb3, Rg2, Rg3, Rh1, and Rh2 were evaluated for use as internal standards for LC/MS measurements. The 12 ginsenosides were baseline resolved by gradient elution LC/UV, with an initial mobile phase composition of 22% acetonitrile and 78% water, flow rate of 0.7 mL/min, and column temperature of 25 °C. The work presented here includes a detailed investigation into the optimization of the chromatographic conditions to minimize measurement biases that result from unresolved constituents. Temperature and mobile phase composition are known to play a significant role in column selectivity; however, flow rate is expected to influence primarily the separation efficiency and detection sensitivity. In the current study, column selectivity changed with changes in flow rate and the relative retention of ginsenoside Rg2 and Rh1 changed as the flow rate increased from 0.6 mL/min to 1.0 mL/min.

Catechins and Their Therapeutic Benefits to Inflammatory Bowel Disease

Catechins are natural polyphenolic phytochemicals that exist in food and medicinal plants, such as tea, legume and rubiaceae. An increasing number of studies have associated the intake of catechins-rich foods with the prevention and treatment of chronic diseases in humans, such as inflammatory bowel disease (IBD). Some studies have demonstrated that catechins could significantly inhibit the excessive oxidative stress through direct or indirect antioxidant effects and promote the activation of the antioxidative substances such as glutathione peroxidases (GPO) and glutathione (GSH), reducing the oxidative damages to the colon. In addition, catechins can also regulate the infiltration and proliferation of immune related-cells, such as neutrophils, colonic epithelial cells, macrophages, and T lymphocytes, helping reduce the inflammatory relations and provide benefits to IBD. Perhaps catechins can further inhibit the deterioration of intestinal lesions through regulating the cell gap junctions. Furthermore, catechins can exert their significant anti-inflammatory properties by regulating the activation or deactivation of inflammation-related oxidative stress-related cell signaling pathways, such as nuclear factor-kappa B (NF-κB), mitogen activated protein kinases (MAPKs), transcription factor nuclear factor (erythroid-derived 2)-like 2 (Nrf2), signal transducer and the activator of transcription 1/3 (STAT1/3) pathways. Finally, catechins can also stabilize the structure of the gastrointestinal micro-ecological environment via promoting the proliferation of beneficial intestinal bacteria and regulating the balance of intestinal flora, so as to relieve the IBD. Furthermore, catechins may regulate the tight junctions (TJ) in the epithelium. This paper elaborates the currently known possible molecular mechanisms of catechins in favor of IBD.

Ginseng for Liver Injury: Friend or Foe?

Panax sp., including Panax ginseng Meyer, Panax quiquifolius L., or Panax notoginseng (Burk.) FH Chen, have been used as functional foods or for traditional Chinese medicine for diabetes, inflammation, stress, aging, hepatic injury, and cancer. In recent decades, a number of both in vitro and in vivo experiments as well as human studies have been conducted to investigate the efficacy and safety of various types of ginseng samples and their components. Of these, the hepatoprotective and hepatotoxic effects of ginseng and their ginsenosides and polysaccharides are reviewed and summarized.

Anticancer Activities of Protopanaxadiol- and Protopanaxatriol-Type Ginsenosides and Their Metabolites

Recently, most anticancer drugs are derived from natural resources such as marine, microbial, and botanical sources, but the low success rates of chemotherapies and the development of multidrug resistance emphasize the importance of discovering new compounds that are both safe and effective against cancer. Ginseng types, including Asian ginseng, American ginseng, and notoginseng, have been used traditionally to treat various diseases, due to their immunomodulatory, neuroprotective, antioxidative, and antitumor activities. Accumulating reports have shown that ginsenosides, the major active component of ginseng, were helpful for tumor treatment. 20(S)-Protopanaxadiol (PDS) and 20(S)-protopanaxatriol saponins (PTS) are two characteristic types of triterpenoid saponins in ginsenosides. PTS holds capacity to interfere with crucial metabolism, while PDS could affect cell cycle distribution and prodeath signaling. This review aims at providing an overview of PTS and PDS, as well as their metabolites, regarding their different anticancer effects with the proposal that these compounds might be potent additions to the current chemotherapeutic strategy against cancer.

Soyasaponins prevent H₂O₂-induced inhibition of gap junctional intercellular communication by scavenging reactive oxygen species in rat liver cells

It appears to be more practical and effective to prevent carcinogenesis by targeting the tumor promotion stage. Gap junctional intercellular communication (GJIC) is strongly involved in carcinogenesis, especially the tumor promotion stage. Considerable interest has been focused on the chemoprevention activities of soyasaponin (SS), which are major phytochemicals found in soybeans and soy products. However, less is known about the preventive effects of SS (especially SS with different chemical structures) against tumor promoter-induced inhibition of GJIC. We investigated the protective effects of SS-A1, SS-A2, and SS-I against hydrogen peroxide (H2O2)-induced GJIC inhibition and reactive oxygen species (ROS) production in Buffalo rat liver (BRL) cells. The present results clearly show for the first time that SS-A1, SS-A2, and SS-I prevent the H2O2-induced GJIC inhibition by scavenging ROS in BRL cells in a dose-dependent manner at the concentration range of from 25 to 100 μg/mL. Soyasaponins attenuated the H2O2-induced ROS through potentiating the activities of superoxide dismutase and glutathione peroxidase. This may be an important mechanism by which SS protects against tumor promotion. In addition, various chemical structures of SS appear to exhibit different protective abilities against GJIC inhibition. This may partly attribute to their differences in ROS-scavenging activities.

Ginsenoside-Rb2 displays anti-osteoporosis effects through reducing oxidative damage and bone-resorbing cytokines during osteogenesis

Reactive oxygen species (ROS) are a significant pathogenic factor of osteoporosis. Ginsenoside-Rb2 (Rb2), a 20(S)-protopanaxadiol glycoside extracted from ginseng, is a potent antioxidant that generates interest regarding the bone metabolism area. We tested the potential anti-osteoporosis effects of Rb2 and its underlying mechanism in this study. We produced an oxidative damage model induced by hydrogen peroxide (H2O2) in osteoblastic MC3T3-E1 cells to test the essential anti-osteoporosis effects of Rb2in vitro. The results indicated that treatment of 0.1 to 10μM Rb2 promoted the proliferation of MC3T3-E1 cells, improved alkaline phosphatase (ALP) expression, elevated calcium mineralization and mRNA expressions of Alp, Col1a1, osteocalcin (Ocn) and osteopontin (Opn) against oxidative damage induced by H2O2. Importantly, Rb2 reduced the expression levels of receptor activator of nuclear factor kappa-B ligand (RANKL) and IL-6 and inhibited the H2O2-induced production of ROS. The in vivo study indicated that the Rb2 administered for 12weeks partially decreased blood malondialdehyde (MDA) activity and elevated the activity of reduced glutathione (GSH) in ovariectomized (OVX) mice. Moreover, Rb2 improved the micro-architecture of trabecular bones and increased bone mineral density (BMD) of the 4th lumbar vertebrae (L4) and the distal femur. Altogether, these results demonstrated that the potential anti-osteoporosis effects of Rb2 were linked to a reduction of oxidative damage and bone-resorbing cytokines, which suggests that Rb2 might be effective in preventing and alleviating osteoporosis.

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.

Evaluation of liquid chromatography-ion trap-time of flight hybrid mass spectrometry on the quantitative analysis for ginsenosides

It is ideal and desirable for a single instrument to meet the requirement of both qualitative and quantitative analysis of complicated components in pharmacokinetic research for herbal medicine. Liquid chromatography combined with hybrid ion trap and time-of-flight mass spectrometry (LCMS-IT-TOF) was recently confirmed as a very powerful tool for the qualitative analysis of both target and nontarget components in herbal medicines. The present study was designed to investigate the feasibility of LCMS-IT-TOF on quantitative analysis of ginsenosides in biological matrices. A simple liquid-liquid extraction procedure was followed by injection of the extracts onto a C₁₈ column with gradient elution and detection based on LCMS-IT-TOF system in negative scan mode. The developed method was validated with respect to the limit of quantification, linear dynamic range, precision, accuracy, matrix effects and stabilities. All the results suggested that the presently developed method was sufficiently sensitive and robust enough to simultaneously monitor 15 ginsenosides with diverse properties and a large range of concentration differences. Therefore, this method would be expected to be highly useful for comprehensive studies of ginsenosides in complicated matrix.

Gap junction intercellular communication mediated by connexin43 in astrocytes is essential for their resistance to oxidative stress

Oxidative stress induced by reactive oxygen species (ROS) is associated with various neurological disorders including aging, neurodegenerative diseases, as well as traumatic and ischemic insults. Astrocytes have an important role in the anti-oxidative defense in the brain. The gap junction protein connexin43 (Cx43) forms intercellular channels as well as hemichannels in astrocytes. In the present study, we investigated the contribution of Cx43 to astrocytic death induced by the ROS hydrogen peroxide (H2O2) and the mechanism by which Cx43 exerts its effects. Lack of Cx43 expression or blockage of Cx43 channels resulted in increased ROS-induced astrocytic death, supporting a cell protective effect of functional Cx43 channels. H2O2 transiently increased hemichannel activity, but reduced gap junction intercellular communication (GJIC). GJIC in wild-type astrocytes recovered after 7 h, but was absent in Cx43 knock-out astrocytes. Blockage of Cx43 hemichannels incompletely inhibited H2O2-induced hemichannel activity, indicating the presence of other hemichannel proteins. Panx1, which is predicted to be a major hemichannel contributor in astrocytes, did not appear to have any cell protective effect from H2O2 insults. Our data suggest that GJIC is important for Cx43-mediated ROS resistance. In contrast to hypoxia/reoxygenation, H2O2 treatment decreased the ratio of the hypophosphorylated isoform to total Cx43 level. Cx43 has been reported to promote astrocytic death induced by hypoxia/reoxygenation. We therefore speculate the increase in Cx43 dephosphorylation may account for the facilitation of astrocytic death. Our findings suggest that the role of Cx43 in response to cellular stress is dependent on the activation of signaling pathways leading to alteration of Cx43 phosphorylation states.

Fucoidan induces G1 phase arrest and apoptosis through caspases-dependent pathway and ROS induction in human breast cancer MCF-7 cells

Fucoidan is an active component of seaweed, which inhibits proliferation and induces apoptosis of several tumor cells while the detailed mechanisms underlying this process are still not clear. In this study, the effect of Fucoidan on the proliferation and apoptosis of human breast cancer MCF-7 cells and the molecular mechanism of Fucoidan action were investigated. Viable cell number of MCF-7 cells was decreased by Fucoidan treatment in a dose-dependent manner as measured by MTT assay. Fucoidan treatment resulted in G1 phase arrest of MCF-7 cells as revealed by flow cytometry, which was associated with the decrease in the gene expression of cyclin D1 and CDK-4. Annexin V/PI staining results showed that the number of apoptotic cells was associated with regulation of cytochrome C, caspase-8, Bax and Bcl-2 at transcriptional and translational levels. Both morphologic observation and Hoechst 33258 assay results confirmed the pro-apoptotic effect of Fucoidan. Meanwhile, the ROS production was also increased by Fucoidan treatment, which suggested that Fucoidan induced oxidative damage in MCF-7 cells. The results of present study demonstrated that Fucoidan could induce G1 phase arrest and apoptosis in MCF-7 cells through regulating the cell cycle and apoptosis-related genes or proteins expression, and ROS generation is also involved in these processes.

Bioactive carotenoids: potent antioxidants and regulators of gene expression

Carotenoids are plant pigments, some of which act as a vital source of vitamin A to all animals, that appear to have additional benefits to primates. They are potent antioxidants and photoprotectants and can additionally modulate gene activity resulting in protection from experimentally-induced inflammatory damage and neoplastic transformation. Anti-neoplastic properties appear tightly correlated to their ability to induce the gap junctional protein connexin 43 (Cx43). This when upregulated leads to decreased proliferation and decreased indices of neoplasia in animal and human cells. Delivery of natural carotenoids can be compromised by poor bioavailability. To overcome this, a synthetic water-dispersible derivative of astaxanthin has been synthesized and shown to be: highly bioavailable; a potent antioxidant; protective against experimental ischemia-reperfusion injury and capable of inducing Cx43, suggesting antineoplastic potential. The ability to deliver biologically active carotenoids at high concentration and with good reproducibility appears to have been achieved.

Epicatechin used in the treatment of intestinal inflammatory disease: an analysis by experimental models

Background. This study was pathway of (−)-epicatechin (EC) in the prevention and treatment of intestine inflammation in acute and chronic rat models. Methods. Intestine inflammation was induced in rats using TNBS. The morphological, inflammatory, immunohistochemical, and immunoblotting characteristics of colon samples were examined. The effects of EC were evaluated in an acute model at doses of 5, 10, 25, and 50 mg/kg by gavage for 5 days. The chronic colitis model was induced 1st day, and treated for 21 days. For the colitis relapse model, the induction was repeated on 14th. Results. EC10 and EC50 effectively reduced the lesion size, as assessed macroscopically; and confirmed by microscopy for EC10. The glutathione levels were higher in EC10 group but decreased COX-2 expression and increased cell proliferation (PC) were observed, indicating an anti-inflammatory activity and a proliferation-stimulating effect. In the chronic colitis model, EC10 showed lower macroscopic and microscopic lesion scores and increase in glutathione levels. As in the acute model, a decrease in COX-2 expression and an increase in PC in EC10, the chronic model this increase maybe by the pathway EGF expression. Conclusion. These results confirm the activity of EC as an antioxidant that reduces of the lesion and that has the potential to stimulate tissue healing, indicating useful for preventing and treating intestine inflammation.

Simultaneous analysis method for polar and non-polar ginsenosides in red ginseng by reversed-phase HPLC-PAD

The paper describes the development of a simultaneous determination method for polar and non-polar ginsenosides in red ginseng with a reversed-phase high-performance liquid chromatography-pulsed amperometric detection method. This method could be applied directly without any pretreatment steps and enabled the performance of highly sensitive analysis within 1h. The detection (S/N=3) and quantification (S/N=10) limits for the ginsenosides ranged 0.02-0.10 ng and 0.1-0.3 ng, respectively. The linear regression coefficients ranged 0.9975-0.9998. Intra- and inter-day precisions were <9.91%. The mean recoveries ranged 98.08-103.06%. The total amount of ginsenosides in the hairy root of red ginseng was higher than that in the main root.

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.

Stem cells in toxicology: fundamental biology and practical considerations

This "Commentary" has examined the use of human stem cells for detection of toxicities of physical, chemical, and biological toxins/toxicants in response to the challenge posed by the NRC Report, "Toxicity Testing in the 21st Century: A vision and Strategy." Before widespread application of the use of human embryonic, pluripotent, "iPS," or adult stem cells be considered, the basic characterization of stem cell biology should be undertaken. Because no in vitro system can mimic all factors that influence cells in vivo (individual genetic, gender, developmental, immunological and diurnal states; niche conditions; complex intercellular interactions between stem, progenitor, terminal differentiated cells, and the signaling from extracellular matrices, oxygen tensions, etc.), attempts should be made to use both embryonic and adult stem cells, grown in three dimension under "niche-like" conditions. Because many toxins and toxicants work by "epigenetic" mechanisms and that epigenetic mechanisms play important roles in regulating gene expression and in the pathogenesis of many human diseases, epigenetic toxicity must be incorporated in toxicity testing. Because modulation of gap junctional intercellular communication by epigenetic agents plays a major role in homeostatic regulation of both stem and progenitor cells in normal tissues, the modulation of this biological process by both endogenous and endogenous chemicals should be incorporated as an end point to monitor for potential toxicities or chemo-preventive attributes. In addition, modulation of quantity, as well as the quality, of stem cells should be considered as potential source of a chemical's toxic potential in affecting any stem cell-based pathology, such as cancer.

Attenuation of 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced gap junctional intercellular communication (GJIC) inhibition in MCF-10A cells by c9,t11-conjugated linoleic acid

The protective effect of c9,t11-conjugated linoleic acid (CLA) on the inhibition of gap junctional intercellular communication (GJIC) was examined in a human mammary epithelial cell line (MCF-10A) treated with 12-O-tetradecanoylphorbol-13-acetate (TPA), relative to t10,c12-CLA isomer. TPA inhibited GJIC in a dose-dependent and reversible manner and was associated with connexin 43 phosphorylation. Pretreatment of 20 μM c9,t11-CLA for 24 h prior to 60 nM TPA for 1 h prevented the inhibition of GJIC by reducing the phosphorylation of connexin 43 via suppressing extracellular signal-regulated kinases (ERK1/2) activation. Reactive oxygen species (ROS) accumulation by TPA was attenuated by c9,t11-CLA. The efficacy of c9,t11-CLA in protecting inhibition of GJIC, connexin 43 phosphorylation, and ROS production was superior to that of t10,c12-CLA. These results suggest that c9,t11-CLA, including t10,c12-CLA, prevents the carcinogenesis of MCF-10A cells by protecting down-regulation of GJIC during the cancer promotion stage, and lack of their toxicities could be an excellent indicator for the chemoprevention of breast cancer.

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

We evaluated the effects of the two main kiwifruit cultivars (gold kiwifruit (GOK) and green kiwifruit (GRK)) and their active phenolic compound, quercetin, on H2O2-induced inhibition of gap-junction intercellular communication (GJIC) in WB-F344 rat liver epithelial cells. We found that both GOK and GRK protect WB-F344 cells from H2O2-induced inhibition of GJIC. The extracellular signal-regulated protein kinase 1/2 (ERK1/2)-connexin 43 (Cx43) signalling pathway is crucial for the regulation of GJIC, and both GOK and GRK blocked the H2O2-induced phosphorylation of Cx43 and ERK1/2 in WB-F344 cells. Quercetin alone attenuated the H2O2-mediated ERK1/2-Cx43 signalling pathway and consequently reversed H2O2-mediated inhibition of GJIC in WB-F344 cells. A free radical-scavenging assay using 1,1-diphenyl-2-picrylhydrazyl showed that the scavenging activity of quercetin was higher than that of a synthetic antioxidant, butylated hydroxytoluene, per mol, suggesting that the chemopreventive effect of quercetin on H2O2-mediated inhibition of ERK1/2-Cx43 signalling and GJIC may be mediated through its free radical-scavenging activity. Since the carcinogenicity of reactive oxygen species such as H2O2 is attributable to the inhibition of GJIC, GOK, GRK and quercetin may have chemopreventive potential by preventing the inhibition of GJIC.

Differential regulation of the hydrogen-peroxide-induced inhibition of gap-junction intercellular communication by resveratrol and butylated hydroxyanisole

The present study was performed to evaluate the effects of two different phenolic antioxidants, resveratrol (3,5,4'-trihydroxystilbene) and butylated hydroxyanisole (BHA), on the hydrogen peroxide (H2O2)-induced inhibition of gap-junction intercellular communication (GJIC) in WB-F344 rat liver epithelial cells (WB-F344). Resveratrol is a naturally occurring polyphenolic antioxidant; on the other hand, BHA is a synthetic phenolic compound. We found that only resveratrol protects WB-F344 cells from H2O2-induced inhibition of GJIC, and BHA has no effect. The extracellular-signal-regulated protein kinase 1/2 (ERK1/2)-connexin 43 (Cx43) signaling pathway is crucial for the regulation of GJIC in rat liver epithelial cells, and resveratrol, but not BHA, blocked the H2O2-induced phosphorylation of Cx43, a critical regulator of GJIC, and ERK1/2 in WB-F344 cells. Resveratrol appears to attenuate the H2O2-mediated ERK1/2-Cx43 signaling pathway and consequently reverses H2O2-mediated inhibition of GJIC. DPPH and ABTS radical-scavenging assays revealed that the protective effect of resveratrol on the H2O2-mediated inhibition of GJIC was not mediated through its free radical-scavenging activity.

Targeting specific cell signaling transduction pathways by dietary and medicinal phytochemicals in cancer chemoprevention

Natural phytochemicals derived from dietary sources or medicinal plants have gained significant recognition in the potential management of several human clinical conditions. Much research has also been geared towards the evaluation of plant extracts as effective prophylactic agents since they can act on specific and/or multiple molecular and cellular targets. Plants have been an abundant source of highly effective phytochemicals which offer great potential in the fight against cancer by inhibiting the process of carcinogenesis through the upregulation of cytoprotective genes that encode for carcinogen detoxifying enzymes and antioxidant enzymes. The mechanistic insight into chemoprevention further includes induction of cell cycle arrest and apoptosis or inhibition of signal transduction pathways mainly the mitogen-activated protein kinases (MAPK), protein kinases C (PKC), phosphoinositide 3-kinase (PI3K), glycogen synthase kinase (GSK) which lead to abnormal cyclooxygenase-2 (COX-2), activator protein-1 (AP-1), nuclear factor-kappaB (NF-κB) and c-myc expression. Effectiveness of chemopreventive agents reflects their ability to counteract certain upstream signals that leads to genotoxic damage, redox imbalances and other forms of cellular stress. Targeting malfunctioning molecules along the disrupted signal transduction pathway in cancer represent a rational strategy in chemoprevention. NF-κB and AP-1 provide mechanistic links between inflammation and cancer, and moreover regulate tumor angiogenesis and invasiveness, indicating that signaling pathways that mediate their activation provide attractive targets for new chemotherapeutic approaches. Thus cell signaling cascades and their interacting factors have become important targets of chemoprevention and phenolic phytochemicals and plant extracts seem to be promising in this endeavor.

Gap junctional intercellular communication as a target for liver toxicity and carcinogenicity

Direct communication between hepatocytes, mediated by gap junctions, constitutes a major regulatory platform in the control of liver homeostasis, ranging from hepatocellular proliferation to hepatocyte cell death. Inherent to this pivotal task, gap junction functionality is frequently disrupted upon impairment of the homeostatic balance, as occurs during liver toxicity and carcinogenicity. In the present paper, the deleterious effects of a number of chemical and biological toxic compounds on hepatic gap junctions are discussed, including environmental pollutants, biological toxins, organic solvents, pesticides, pharmaceuticals, peroxides, metals and phthalates. Particular attention is paid to the molecular mechanisms that underlie the abrogation of gap junction functionality. Since hepatic gap junctions are specifically targeted by tumor promoters and epigenetic carcinogens, both in vivo and in vitro, inhibition of gap junction functionality is considered as a suitable indicator for the detection of nongenotoxic hepatocarcinogenicity.

Pfaffia paniculata (Brazilian ginseng) roots decrease proliferation and increase apoptosis but do not affect cell communication in murine hepatocarcinogenesis

Pfaffia paniculata (Brazilian ginseng) roots and/or its extracts have shown anti-neoplastic, chemopreventive, and anti-angiogenic properties. The aim of this work was to investigate the chemopreventive mechanisms of this root in mice submitted to the infant model of hepatocarcinogenesis, evaluating the effects on cellular proliferation, apoptosis, and intercellular communication. Fifteen-day-old BALB/c male mice were given, i.p., 10mug/g of the carcinogen N-nitrosodiethylamine (DEN). Animals were separated into three groups at weaning and were given different concentrations of powdered P. paniculata root (0%, 2%, or 10%) added to commercial food for 27 weeks. Control group (CT) was not exposed to the carcinogen and was given ration without the root. After euthanasia, the animals' liver and body weight were measured. Liver fragments were sampled to study intercellular communication, molecular biology, and histopathological analysis. Cellular proliferation was evaluated by immunohistochemistry for PCNA, apoptosis was evaluated by apoptotic bodies count and alkaline comet technique, and intercellular communication by diffusion of lucifer yellow dye, immunofluorescence, western blot and real-time PCR for connexins 26 and 32. Chronic treatment with powdered P. paniculata root reduced cellular proliferation and increased apoptosis in the 2% group. Animals in the 10% group had an increase in apoptosis with chronic inflammatory process. Intercellular communication showed no alterations in any of the groups analyzed. These results indicate that chemopreventive effects of P. paniculata are related to the control of cellular proliferation and apoptosis, but not to cell communication and/or connexin expression, and are directly influenced by the root concentration.

Drinking green tea modestly reduces breast cancer risk

Green tea is a commonly consumed beverage in China. Epidemiological and animal data suggest tea and tea polyphenols may be preventive against various cancers, including breast cancer. Catechol-O-methyltransferase (COMT) catalyzes catechol estrogens and tea polyphenols. The COMT rs4680 AA genotype leads to lower COMT activity, which may affect the relationship between green tea consumption and breast cancer risk. We evaluated whether regular green tea consumption was associated with breast cancer risk among 3454 incident cases and 3474 controls aged 20-74 y in a population-based case-control study conducted in Shanghai, China during 1996-2005. All participants were interviewed in person about green tea consumption habits, including age of initiation, duration of use, brew strength, and quantity of tea. Odds ratios (OR) and 95% CI were calculated for green tea consumption measures and adjusted for age and other confounding factors. Compared with nondrinkers, regular drinking of green tea was associated with a slightly decreased risk for breast cancer (OR, 0.88; 95% CI, 0.79-0.98). Among premenopausal women, reduced risk was observed for years of green tea drinking (P-trend = 0.02) and a dose-response relationship with the amount of tea consumed per month was also observed (P-trend = 0.046). COMT rs4680 genotypes did not have a modifying effect on the association of green tea intake with breast cancer risk. Drinking green tea may be weakly associated with a decreased risk of breast cancer.

Ascorbic acid 6-palmitate suppresses gap-junctional intercellular communication through phosphorylation of connexin 43 via activation of the MEK-ERK pathway

Although the health benefits of dietary antioxidants have been extensively studied, their potential negative effects remain unclear. L-Ascorbic acid 6-palmitate (AAP), a synthetic derivative of ascorbic acid (AA), is widely used as an antioxidant and preservative in foods, vitamins, drugs, and cosmetics. Previously, we found that AA exerted an antitumor effect by protecting inhibition of gap-junctional intercellular communication (GJIC), which is closely associated with tumor progression. In this study, we examined whether AAP, an amphipathic derivative of AA, has chemopreventive effects using a GJIC model. AAP and AA exhibited dose-dependent free radical-scavenging activities and inhibited hydrogen peroxide (H(2)O(2))-induced intracellular reactive oxygen species (ROS) production in normal rat liver epithelial cells. Unexpectedly, however, AAP did not protect against the inhibition of GJIC induced by H(2)O(2); instead, it inhibited GJIC synergistically with H(2)O(2). AAP inhibited GJIC in a dose-dependent and reversible manner. This inhibitory effect was not due to the conjugated lipid structure of AAP, as treatment with palmitic acid alone failed to inhibit GJIC under the same conditions. The inhibition of GJIC by AAP was restored in the presence of mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) kinase (MEK) inhibitor U0126, but not in the presence of other signal inhibitors and antioxidant (PKC inhibitors, EGFR inhibitor, NADPH oxidase inhibitor, catalase, vitamin E, or AA), indicating the critical involvement of MEK signaling in the GJIC inhibitory activity of AAP. Phosphorylation of ERK and connexin 43 (Cx43) was observed following AAP treatment, and this was reversed by U0126. These results suggest that the AAP-induced inhibition of GJIC is mediated by the phosphorylation of Cx43 via activation of the MEK-ERK pathway. Taken together, our results indicate that AAP has a potent carcinogenic effect, and that the influence of dietary antioxidants on carcinogenesis may be paradoxical.

Effect of ginsam, a vinegar extract from Panax ginseng, on body weight and glucose homeostasis in an obese insulin-resistant rat model

Extracts of ginseng species show antihyperglycemic activity. We evaluated the antihyperglycemic and antiobesity effects of ginsam, a component of Panax ginseng produced by vinegar extraction, which is enriched in the ginsenoside Rg3. Otsuka Long-Evans Tokushima Fatty rats, an obese insulin-resistant rat model, were assigned into 1 of 3 groups (n = 8 each): controls (isotonic sodium chloride solution, 5 mL/d), rats given 300 mg/(kg d) ginsam, and rats given 500 mg/(kg d) ginsam. An intraperitoneal 2-hour glucose tolerance test was performed at the end of the 6-week treatment. After 8 weeks, body and liver weights, visceral fat measured by computed tomography, and fasting glucose and insulin concentrations and lipid profiles were recorded. Insulin-resistant rats treated with ginsam had lower fasting and postprandial glucose concentrations compared with vehicle-treated rats. Importantly, overall glucose excursion during the intraperitoneal 2-hour glucose tolerance test decreased by 21.5% (P < .01) in the treated rats, indicating improved glucose tolerance. Plasma insulin concentration was significantly lower in ginsam-treated rats. These changes may be related to increased glucose transporter 4 expression in skeletal muscle. Interestingly, when the data from both ginsam-treated groups were combined, body weight was 60% lower in the ginsam-treated rats than in the controls (P < .01). Liver weight and serum alanine aminotransferase concentrations were also lower in the ginsam-treated rats. These effects were associated with increased peroxisome proliferator-activated receptor gamma expression and adenosine monophosphate-activated protein kinase phosphorylation in liver and muscle. Our data suggest that ginsam has distinct beneficial effects on glucose metabolism and body weight control in an obese animal model of insulin resistance by changing the expression of genes involved in glucose and fatty acid metabolism.

Inhibition of gap junctional intercellular communication by the green tea polyphenol (-)-epigallocatechin gallate in normal rat liver epithelial cells

(-)-Epigallocatechin gallate (EGCG), a polyphenolic compound found in green tea, is a promising chemopreventive agent against cancer due to its strong antiproliferative effects on cancer cells; however, its possible toxicity and carcinogenicity must be investigated before EGCG can be used as a dietary supplement for chemoprevention. The inhibition of gap junctional intercellular communication (GJIC) is strongly associated with carcinogenesis, particularly the tumor promotion process; thus, we investigated the effects of EGCG on GJIC in WB-F344 normal rat liver epithelial (RLE) cells. EGCG, but not (-)-epicatechin (EC), another polyphenol found in green tea, inhibited GJIC in a dose-dependent and reversible manner in RLE cells. EGCG also induced the phosphorylation of connexin 43 (Cx43), a major regulator of GJIC. The phosphorylation of extracellular signal-regulated protein kinase 1/2 (ERK1/2) was also observed in EGCG-treated RLE cells. The inhibition of GJIC and phosphorylation of Cx43 and ERK1/2 by EGCG were completely blocked by U0126, a pharmacological inhibitor of mitogen-activated protein kinase/ERK kinase. EGCG generated a larger amount of hydrogen peroxide than EC in a dose-dependent manner. Furthermore, catalase partially inhibited the EGCG-induced inhibition of GJIC and the phosphorylation of Cx43 and ERK1/2. These results indicated that EGCG inhibited GJIC mainly due to its prooxidant activity.

Complementary and alternative medicine in present day oncology care: promises and pitfalls

Cancer is already a well-recognized global phenomenon. The traditional approaches to cancer therapy have been surgery, radiotherapy and chemotherapy. These modalities have shown considerable promise and presently form cornerstones of management of most malignancies. However, these conventional approaches have associated toxicities and suffer from limitations in curing advanced lesions. Complementary and alternative medicine (CAM), for reasons varying from cost to accessibility, has assumed significant importance in cancer therapy. In this article, we review the prominent modalities in CAM in present day cancer management and critically analyze their emerging potential into an evidence-based oncology practice.

Gallic acid, a metabolite of the antioxidant propyl gallate, inhibits gap junctional intercellular communication via phosphorylation of connexin 43 and extracellular-signal-regulated kinase1/2 in rat liver epithelial cells

Propyl gallate and its metabolite, gallic acid, are widely used as antioxidants in the food industry, but they have been shown to exhibit liver toxicity and enhance carcinogenesis. In the present study, we investigated the possible undesirable effects of propyl gallate and gallic acid on gap junctional intercellular communication (GJIC), inhibition of which is closely linked to carcinogenesis. Gallic acid and propyl gallate exhibited dose-dependent free-radical-scavenging activities as determined by 1,1-diphenyl-2-picrylhydrazyl- or 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)-radical-scavenging assays, and the free-radical-scavenging activity of gallic acid was stronger than that of propyl gallate. However, using WB-F344 rat liver epithelial cells, gallic acid inhibited GJIC in a dose-dependent manner, while propyl gallate had no significant effect compared with untreated controls. The gallic-acid-induced inhibition of GJIC was reversible, with a recovery of nearly 65% after 120 min. Gallic acid induced the phosphorylation of connexin 43 (Cx43) and phosphorylation of extracellular-signal-regulated kinase1/2 (ERK1/2). The gallic-acid-induced inhibition of GJIC was attenuated by treatment with mitogen-activated protein kinase kinase inhibitors (U0126 and PD098059). U0126 blocked the gallic-acid-induced phosphorylation of Cx43 and ERK1/2, indicating that the gallic-acid-induced inhibition of GJIC is mediated by phosphorylation of Cx43 via activation of ERK1/2. In addition, gallic-acid-induced inhibition of GJIC was protected by ascorbic acid and quercetin, which might represent a simple example of the different effects of natural antioxidants in carcinogenesis.

Ginsenoside 20(S)-protopanaxadiol inhibits the proliferation and invasion of human fibrosarcoma HT1080 cells

Ginsenoside 20(S)-protopanaxadiol, one of metabolites of ginseng saponins, has been well characterized to possess the pleiotropic anticancer capabilities in several cancer cell lines. The object of this study was to investigate the effects of ginsenoside 20(S)-protopanaxadiol on the invasion in vitro and the expression of matrix metalloproteinase-2 in human fibrosarcoma HT1080 cells in absence of cytotoxicity. Our results showed that ginsenoside 20(S)-protopanaxadiol exerted a concentration-dependent inhibitory effect on the proliferation of HT1080 cells (IC50 was 76.78+/-2.24 microM, 48 hr). Treatment with 20(S)-protopanaxadiol significantly declined the invasive capacity of HT1080 cells compared to the control cells (P<0.01) in the in vitro invasion assay. Further analysis with gelatin zymography and western blotting revealed that both the activity and the expression of matrix metalloproteinase-2 decreased dramatically in a concentration-dependent manner (P<0.01). Taken together, these results indicated that ginsenoside 20(S)-protopanaxadiol is able to inhibit the invasiveness of HT1080 cells significantly in vitro and this action may be primarily due to down-regulating the expression of matrix metalloproteinase-2. Ginsenoside 20(S)-protopanaxadiol, a metabolite of ginseng, may be applied as a potential therapeutic agent in the prevention and treatment of cancer.

Chemopreventive effect of bicyclol on malignant transformation of WB-F344 rat liver epithelial cells and its effect on related signal transduction in vitro

The preventive effect of bicyclol, a novel anti-hepatitis drug, on hepatocarcinogenesis and its mechanism of action was studied in vitro. The results clearly indicated that bicyclol at non-toxic doses prevented the malignant transformation of WB-F344 cells (WB cells) induced by 3-methylcholanthrene (3MC) and 12-O-tetradecanoyl phorbol 13-acetate (TPA). Furthermore, bicyclol inhibited proliferation of quiescent WB cells stimulated by TPA and blocked TPA-induced down-regulation of the gap junctional intercellular communication (GJIC). Immunoblot analysis demonstrated that bicyclol exhibited a remarkable reversing effect on TPA-induced cPKC-alpha and phosphor-ERK1/2 expressions. In addition, bicyclol attenuated TPA-induced IkappaB-alpha degradation. In conclusion, our results support that bicyclol has chemopreventive action against hepatocarcinogenesis through inhibition of related signal transduction.

The roles of polyphenols in cancer chemoprevention

Oxidative stress imposed by reactive oxygen species (ROS) plays a crucial role in the pathophysiology associated with neoplasia, atherosclerosis, and neurodegenerative diseases. The ROS-induced development of cancer involves malignant transformation due to altered gene expression through epigenetic mechanisms as well as DNA mutations. Considerable attention has been focused on identifying naturally occurring antioxidative phenolic phytochemicals that are able to decrease ROS levels, but the efficacies of antioxidant therapies have been equivocal at best. Several studies have shown that some antioxidants exhibit prooxidant activity under certain conditions and potential carcinogenicity under others, and that dietary supplementation with large amounts of a single antioxidant may be deleterious to human health. This article reviews the intracellular signaling pathways that respond to oxidative stress and how they are modulated by naturally occurring polyphenols. The possible toxicity and carcinogenicity of polyphenols is also discussed.

Astaxanthin diminishes gap junctional intercellular communication in primary human fibroblasts

Astaxanthin is a carotenoid found in plants and algae; it provides the color of marine seafood such as salmon, lobster, or shrimp. Carotenoids are antioxidants and exhibit other biological functions, including effects on gap junctional communication important for homeostasis, growth control, and development of cells. Cancer cells have an impaired gap junctional intercellular communication. The objective of the present study was to determine the effects of astaxanthin and canthaxanthin on gap junctional intercellular communication in vitro. Primary human skin fibroblasts were exposed to carotenoids from 0.001 to 10 micromol/L, and gap junctional communication was measured with a dye transfer assay. After incubation with canthaxanthin for 24 and 72 h, intercellular communication increased, whereas it was strongly diminished by astaxanthin at levels > 0.1 micromol/L. Inhibition was reversed when astaxanthin was withdrawn. Western blot analysis showed that after exposure to canthaxanthin, the amount of the gap junction protein connexin43 was increased. Incubation with astaxanthin led to a change in the phosphorylation pattern of connexin43, shifting from higher to lower phosphorylation states. We suggest that astaxanthin affects channel function by changing the phosphorylation pattern of connexin43.

Chemopreventive effect of dimethyl dicarboxylate biphenyl on malignant transformation of WB-F344 rat liver epithelial cells

AIM

To study the potential chemopreventive effect of dimethyl dicarboxylate biphenyl (DDB), an anti-hepatitis drug, on hepatocarcinogenesis in vitro.

METHODS

The anti-carcinogenesis effect of DDB was assessed on a two-stage chemical oncogenesis model induced by 3-methylcholanthrene and 12-O-tetradecanoyl phorbol 13-acetate (TPA) with WB-F344 rat liver epithelial cells (WB-F344 cells) in vitro. A soft-agar colony formation assay was used to determine the tumorigenic potential of the transformed WB-F344 cells. The gap junctional intercellular communication (GJIC) was detected using the scrape loading/dye transfer technique.

RESULTS

DDB at 1 micromol/L, 2 micromol/L, and 4 micromol/L significantly prevented the malignant transformation of WB-F344 cells induced by 3-methylcholanthrene and TPA. The average number of transformed foci decreased dramatically by 10.0%, 37.2%, and 47.4%, respectively. In soft agar, a remarkable decrease in colony numbers was observed in transformed cells treated with 2 micromol/L and 4 micromol/L DDB. DDB at 1 micromol/L, 2 micromol/L, and 4 micromol/L inhibited the downregulation of GJIC induced by TPA in a dose-dependent manner. The GJIC recovered to 25.6%, 34.6%, and 44.9%, respectively, of the control WB-F344 cells by DDB.

CONCLUSION

DDB has a potential chemopreventive effect on hepato-carcinogenesis induced by carcinogens in vitro.

Role of gap junctional intercellular communication (GJIC) through p38 and ERK1/2 pathway in the differentiation of rat neuronal stem cells

Gap junctional intercellular communications (GJIC) contributes to neural function in development and differentiation of CNS. In this study, we have investigated the expression of GJIC during the differentiation of neuronal stem cells and 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced neuronal stem cell-derived cells from rat brain. During neuronal stem cell differentiation, expressions of Cx43 and 32 were increased for the duration of 72 hr, however the effect were decreased on the 7d. In the neuronal stem cell-derived cells, pretreatments with p38 MAP kinase inhibitor, SB203580, and MEK inhibitor, PD98059, could protect GJIC against TPA-induced inhibition of GJIC. Our data suggest that GJIC plays an important role during neuronal stem cell differentiation, and ERK1/2 and p38 MAP kinase signaling pathway may be closely related functionally to regulate gap junction in rat neuronal stem cell-derived cells.

Protective effects of green tea extracts (polyphenon E and EGCG) on human cervical lesions

We investigated clinical efficacy of green tea extracts (polyphenon E; poly E and (-)-epigallocatechin-3-gallate [EGCG]) delivered in a form of ointment or capsule in patients with human papilloma virus (HPV) infected cervical lesions. Fifty-one patients with cervical lesions (chronic cervicitis, mild dysplasia, moderate dysplasia and severe dysplasia) were divided into four groups, as compared with 39 untreated patients as a control. Poly E ointment was applied locally to 27 patients twice a week. For oral delivery, a 200 mg of poly E or EGCG capsule was taken orally every day for eight to 12 weeks. In the study, 20 out of 27 patients (74%) under poly E ointment therapy showed a response. Six out of eight patients under poly E ointment plus poly E capsule therapy (75%) showed a response, and three out of six patients (50%) under poly E capsule therapy showed a response. Six out of 10 patients (60%) under EGCG capsule therapy showed a response. Overall, a 69% response rate (35/51) was noted for treatment with green tea extracts, as compared with a 10% response rate (4/39) in untreated controls (P<0.05). Thus, the data collected here demonstrated that green tea extracts in a form of ointment and capsule are effective for treating cervical lesions, suggesting that green tea extracts can be a potential therapy regimen for patients with HPV infected cervical lesions.

Hydrogen peroxide increases gap junctional communication and induces astrocyte toxicity: regulation by brain macrophages

Cultured astrocytes are highly coupled by gap junction channels mainly constituted by connexin 43. We have previously shown that gap junctional communication (GJC) represents a functional property of astrocytes that is a target for their interaction with other brain cell types, including neurons and brain macrophages. In pathological situations, neurons as well as brain macrophages produce superoxide ions leading to the formation of hydrogen peroxide (H2O2) that can be cytotoxic. We report here that 10-min exposure to 100 microM H2O2 increases GJC in astrocytes. Moreover, 30-min exposure to 100 microM H2O2 induces, 24 h later, an astrocyte cell death by both apoptosis and necrosis. This H2O2-induced astrocyte cell death is not affected when gap junctions are inhibited by several uncoupling agents, including 18alpha-glycyrrhetinic acid, halothane, heptanol, and endothelin-1, indicating that the proportion of cell death is not related to the level of GJC. The effect of H2O2 on gap junction channels does not result from the production of free radicals but is rather linked to modification of the redox equilibrium in astrocytes. Indeed, an oxidative agent reproduces the H2O2-evoked response while reducing agents prevent the effect of H2O2. Finally, when astrocytes are cocultured with brain macrophages, the effects of H2O2 on both GJC and toxicity are not observed, revealing a new protective role of brain macrophages during oxidative stress.

Panax ginseng: a role in cancer therapy?

Panax ginseng is a plant that has been used in traditional medicine in China for thousands of years. It is used as a general tonic or adaptogen with chronically ill patients and is frequently featured in traditional medicine prescriptions from China, Japan, and Korea used by cancer patients. The putative active compounds are the ginsenosides, of which there are more than two dozen. These compounds are found in both Panax ginseng and in other Panax species that are used in herbal medicine. Analysis of ginsenosides is being used in developing quality control assessments for ginseng, which has frequently been adulterated due to its high cost; many currently available standardized extracts do appear to contain the amounts of ginsenosides listed on package labeling. The toxicity of ginseng appears to be low: some of the reports of toxic episodes of ginseng may actually pertain to other components of multicomponent preparations. Very low incidence of toxicity has been observed in ginseng clinical trials using well-characterized preparations. Numerous pharmacological activities of ginseng and the ginsenosides have been explored: the authors review here the activities relating to cancer. Immune system modulation, antistress activities, and antihyperglycemic activities are among the most notable features of ginseng noted in laboratory and clinical analyses. Much testing has been done in humans to explore ginseng's purported antifatigue properties, but this area remains controversial. A number of investigations point to antitumor properties and other pharmacological activities related to cancer, but no trials have yet confirmed a clinically significant anticancer activity. Cancer patients may empirically find ginseng to be useful when they are fatigued, although clinical trials should be conducted to confirm its benefits.

Ganoderma lucidum extract induces cell cycle arrest and apoptosis in MCF-7 human breast cancer cell

Although the pharmacology and clinical application of water extracts of Ganoderma lucidum have been extensively documented, little is known regarding its alcohol extract. In the present study, the anti-tumor effect of an alcohol extract of Ganoderma lucidum was investigated using MCF-7 cells. We found that the alcohol extract of Ganoderma lucidum inhibited cell proliferation in a dose- and time-dependent manner, which might be mediated through up-regulation of p21/Waf1 and down-regulation of cyclin D1. Furthermore, this compound can directly induce apoptosis in MCF-7 cells, which might be mediated through up-regulation of a pro-apoptotic Bax protein and not by the immune system. Our findings suggest that there are multiple mechanisms underlying the anti-tumor effects of Ganoderma lucidum.

Palgin sensitizes the adriamycin-induced apoptosis via the enhancement of Fas/Fas ligand expression

This study was designed to evaluate the synergistic cytotoxicity of herb prescription, Palgin, in adriamycin-treated cancer cells. The combination of Palgin and adriamycin synergistically augmented the cytotoxicity of Chang and HL-60 cells, but not in Hep3B and Alexander cells. The cytotoxicity of two drugs was revealed as apoptosis characterized by nuclear fragmentation. The apoptotic cell death was accompanied by the activation of caspase-3 as well as cleavage of poly(ADP) ribose polymerase (PARP) in Chang cells. Interestingly, a synergistic increase in apoptosis by the combination of two drugs was accompanied by the enhancement of Fas and Fas ligand (FasL) expression in Chang cells. Taken together, the combination of Palgin and adriamycin significantly augmented the apoptotic cytotoxicity of Fas-positive cells, such as Chang and HL-60 cells, via activation of caspase signaling pathway. This notion will provide a new trial to treat cancer patients in clinical fields as a complementary treatment of Western and Oriental medicine.

(-)-Epicatechin effects in rat liver epithelial cells: stimulation of gap junctional communication and counteraction of its loss due to the tumor promoter 12-O-tetradecanoylphorbol-13-acetate

Gap junctional intercellular communication (GJIC) is a direct signaling pathway for neighboring cells. Disturbances in GJIC are suggested to play a role in carcinogenesis and may be involved in cardiac arrhythmia. Tumor promoters like 12-O-tetradecanoylphorbol-13-acetate (TPA) are capable of inhibiting GJIC, whereas GJIC is stimulated by several micronutrients like genistein, retinoids or carotenoids. (-)-Epicatechin (4-40 microM), a major flavonoid in cocoa and green tea, exhibited stimulatory effects on GJIC in WB-F344 rat liver epithelial cells after 24-72hr of incubation; no change was observed after 90 min. However, treatment of cells for 90 min with TPA (5 or 10nM) led to complete loss of GJIC, whereas 40% loss was found with 1nM. These inhibitory effects of TPA were largely suppressed when (-)-epicatechin or genistein (40 microM) were present during the incubation. In communicating WB-F344 cells, most of the major gap junction protein connexin43 (Cx43) was located in the plasma membrane. When the cells were exposed to TPA, considerably less protein was found in the membrane. Such a delocalization of Cx43 proteins was not observed when TPA was coincubated with the flavonoids, (-)-epicatechin or genistein. It is concluded that TPA affects Cx43 trafficking between cellular compartments, and that this effect is counteracted by (-)-epicatechin or genistein.

DI-(2-ethylhexyl) phthalate-induced cell proliferation is involved in the inhibition of gap junctional intercellular communication and blockage of apoptosis in mouse Sertoli cells

Di-(2-ethylhexyl) phthalate (DEHP) has been studied on gap junctional intercellular communication (GJIC) and apoptosis in cultured normal mouse Sertoli cells. Since the inhibition of GJIC and programmed cell death or apoptosis play important roles in tumor promotion and developmental toxicity, it has been hypothesized that tumor promoters may inhibit apoptosis by blocking GJIC. The results showed that the most significant downregulation of GJIC was detected at 9 h after DEHP treatment. However, a significant concentration-dependent pattern was not observed at concentrations of 100 and 500 microM, but there was a time-dependent recovery of GJIC. DEHP inhibited the apoptotic changes in the cells such as chromatin condensation, nuclear fragmentation, and the cleavage of poly(ADP-ribose) polymerase. Morphological changes related to apoptosis appeared in the nontreated cells after 12 h of serum deprivation. These morphological changes were significantly reduced in the TM5 Sertoli cells treated with 500 microM DEHP for 24 h. These results suggest that DEHP inhibited apoptosis in this cell line, preceded by the downregulation of GJIC. It was also found that DEHP reduced the phosphorylation of Cx43, which might partly explain the mechanism of inhibition of GJIC.

Effects and neuro-toxic mechanisms of 2, 2', 4, 4', 5, 5'-hexachlorobiphenyl and endosulfan in neuronal stem cells

Endocrine disrupters are exogenous compounds thought to mimic the action of estrogen or other hormones and influence endocrine activity in the body (Juberg, 2000). These chemicals have adverse effects not only in the reproductive system but also in the central nervous system during development and throughout life. Polychlorinated biphenyls (PCBs) are a class of environmentally persistent and widespread halogenated hydrocarbons. It has been reported that PCBs are potential neurotoxicants. Endosulfan is an organochlorine insecticide that is extensively used to control pests in vegetables, cotton, and fruits. To determine the effect of 2, 2', 4, 4', 5, 5',-hexachlorobiphenyl(2, 4, 5-HCB) and endosulfan on embryo nervous system, we isolated neural stem cells from rat brain at embryonic day 17. Isolated neural stem cells showed pluripotenty. Stem cells could differentiate into neurons and glia. Neurite formation in endosulfan and 2, 4, 5-HCB treated cells. And it appeared to be decreased as compared with that in untreated cells. In order to know the neuro-toxic mechanisms of 2, 4, 5-HCB and endosulfan in neuronal stem cells, we investigated mitogen-activated protein kinase activity (MAPK) and gap junctional intercellular communication (GJIC). Endosulfan decreased the MAPK activity in dose dependent manner. Endosulfan and 2, 4, 5-HCB inhibited GJIC compared to the untreated cell by scrape loading dye transfer (SL/DT). 2, 4, 5-HCB and endosulfan decreased the expression of connexin 43 in dose dependent manner. These results indicated that 2, 4, 5-HCB and endosulfan may inhibit differentiation and proliferation of neural stem cells and gap junctional intercellular communication which play a crucial role in the maintenance of cellular homeostasis.