Chemopreventive activity of very low dose dietary tannic acid administration in hepatoma bearing C3H male mice

Tannic acid-fortified zein-pectin nanoparticles: Stability, properties, antioxidant activity, and in vitro digestion

Tannic acid was loaded into zein nanoparticles using antisolvent precipitation and then these particles were coated by anionic pectin using electrostatic deposition. The resulting core-shell nanoparticles were near spherical and had an average diameter of 166 nm, a particle yield of 95%, a tannic acid content of 5.4%, and a tannic acid loading efficiency of 89%. Circular dichroism revealed that the presence of tannic acid caused little change in the secondary structure of the zein within the nanoparticles. Fluorescence spectroscopy suggested the formation of a molecular complex between the zein and tannic acid molecules. Fourier transform infrared spectroscopy indicated that hydrogen bonding was the main force holding these complexes together. The core-shell nanoparticles remained resistant to flocculation from pH 2 to 8, when heated at 80 °C for 2 h, and when the NaCl concentration was below 30 mM. The encapsulated tannic acid preserved its high antioxidant capacity. The tannic acid was progressively released from the core-shell nanoparticles under simulated gastrointestinal conditions, with the majority of release occurring within the small intestine. Overall, this research suggests that pectin-coated zein nanoparticles may be effective encapsulation and delivery systems for hydrophilic polyphenols in nutraceutical, supplements, or pharmaceutical formulations.

Tannic Acid: Specific Form of Tannins in Cancer Chemoprevention and Therapy-Old and New Applications

Purpose of Review

This short review is aimed at providing an updated and comprehensive report on tannic acid biological activities and molecular mechanisms of action most important for cancer prevention and adjuvant therapy.

Recent Findings

Tannic acid (TA), a mixture of digallic acid esters of glucose, is a common ingredient of many foods. The early studies of its anti-mutagenic and anti-tumorigenic activity were mostly demonstrated in the mouse skin model. This activity has been explained by its ability to inhibit carcinogens activation, as well as antioxidant and anti-inflammatory properties. Recently, the cell cycle arrest, apoptosis induction, reduced rate of proliferation, and cell migration and adhesion of several cancer cell lines as a result of TA treatment were described. The underlining mechanisms include modulation of signaling pathways such as EGFR/Jak2/STATs, or inhibition of PKM2 glycolytic enzyme. Moreover, epithelial-to-mesenchymal transition prevention and decrease of cancer stem cells formation by TA were also reported. Besides, TA was found to be potent chemosensitizer overcoming multidrug resistance. Eventually, its specific physicochemical features were found useful for generation of drug-loaded nanoparticles.

Summary

TA was shown to be a very versatile molecule with possible application not only in cancer prophylaxis, as was initially thought, but also in adjuvant cancer therapy. The latter may refer to chemosensitization and its application as a part of drug delivery systems. More studies are required to better explore this subject. In addition, the effect of TA on normal cells and its bioavailability have to better characterized.

Streptococcus gallolyticus abrogates anti-carcinogenic properties of tannic acid on low-passage colorectal carcinomas

The tannase-producing Gram-positive bacterial species Streptococcus gallolyticus subsp. gallolyticus (Sgg) is an opportunistic pathogen of the human gut and strongly associated with colorectal cancer (CRC). A unique feature of Sgg is its ability to degrade tannic acids (TA). TA constitute an important part of the human diet with known anti-tumorigenic properties. Here, we examined whether Sgg is able to protect tumor cells from the toxic effect of TA and thus drive tumorigenesis indirectly. Human CRC cell lines (n = 8) were treated with increasing concentrations of TA. We confirmed the cytotoxic activity of TA in a dose-dependent manner. In virtually all cell lines, viability decreased significantly (>60% inhibition). Moreover, pyrogallol, the degradation product of TA, had no effect on the tested cell lines. This suggests a specific effect of TA. Cytotoxicity was due to necrosis and induction of senescence in residual cells. Finally, when TA was degraded by Sgg, the cytotoxic effect could be abolished. Tumor cells even responded with boosted cell proliferation, highlighting the impact of Sgg on CRC progression. We here provide another piece of evidence for the active interplay between Sgg and cancer preventive components. These data will help to move forward in designing concepts for therapeutic and eventually also prophylactic approaches to combat gastrointestinal malignancies.

Tannic Acid Promotes TRAIL-Induced Extrinsic Apoptosis by Regulating Mitochondrial ROS in Human Embryonic Carcinoma Cells

: Human embryonic carcinoma (EC; NCCIT) cells have self-renewal ability and pluripotency. Cancer stem cell markers are highly expressed in NCCIT cells, imparting them with the pluripotent nature to differentiate into other cancer types, including breast cancer. As one of the main cancer stem cell pathways, Wnt/β-catenin is also overexpressed in NCCIT cells. Thus, inhibition of these pathways defines the ability of a drug to target cancer stem cells. Tannic acid (TA) is a natural polyphenol present in foods, fruits, and vegetables that has anti-cancer activity. Through Western blotting and PCR, we demonstrate that TA inhibits cancer stem cell markers and the Wnt/β-catenin signaling pathway in NCCIT cells and through a fluorescence-activated cell sorting analysis we demonstrated that TA induces sub-G1 cell cycle arrest and apoptosis. The mechanism underlying this is the induction of mitochondrial reactive oxygen species (ROS) (mROS), which then induce the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-mediated extrinsic apoptosis pathway instead of intrinsic mitochondrial apoptosis pathway. Moreover, ribonucleic acid sequencing data with TA in NCCIT cells show an elevation in TRAIL-induced extrinsic apoptosis, which we confirm by Western blotting and real-time PCR. The induction of human TRAIL also proves that TA can induce extrinsic apoptosis in NCCIT cells by regulating mROS.

Mechanistic Insights into Oxidative Stress and Apoptosis Mediated by Tannic Acid in Human Liver Hepatocellular Carcinoma Cells

The study investigated the cytotoxic effect of a natural polyphenolic compound Tannic acid (TA) on human liver hepatocellular carcinoma (HepG2) cells and elucidated the possible mechanisms that lead to apoptosis and oxidative stress HepG2 cell. The HepG2 cells were treated with TA for 24 h and various assays were conducted to determine whether TA could induce cell death and oxidative stress. The cell viability assay was used to determine the half maximal inhibitory concentration (IC₅₀), caspase activity and cellular ATP were determined by luminometry. Microscopy was employed to determine deoxyribonucleic acid (DNA) integrity, while thiobarbituric acid (TBARS) and nitric oxide synthase (NOS) assays were used to elucidate cellular reactive oxygen species (ROS) and reactive nitrogen species (RNS), respectively. Western blotting was used to confirm protein expression. The results revealed that tannic acid induced caspase activation and increased the presence of cellular ROS and RNS, while downregulating antioxidant expression. Tannic acid also showed increased cell death and increased DNA fragmentation. In conclusion, TA was able to induce apoptosis by DNA fragmentation via caspase-dependent and caspase-independent mechanism. It was also able to induce oxidative stress, consequently contributing to cell death.

Aqueous extract from pecan nut [Carya illinoinensis (Wangenh) C. Koch] shell show activity against breast cancer cell line MCF-7 and Ehrlich ascites tumor in Balb-C mice

ETHNOPHARMACOLOGICAL RELEVANCE

In Brazil many health disorders are treated with the consumption of different varieties of tea. Shell extracts of pecan nut (Carya illinoinensis), which have significant amounts of phenolic compounds in their composition, are popularly taken as tea to prevent diverse pathologies.

AIM OF THE STUDY

Phenolic compounds from pecan nut shell extract have been associated with diverse biological effects but the effect on tumor cells has not been reported yet. The aim of the current work was to evaluate the relationship between DNA fragmentation, cell cycle arrest and apoptosis induced by pecan nut shell extract and its antitumor activity.

MATERIALS AND METHODS

Cytotoxicity, proliferation, cell death and cell cycle were evaluated in MCF-7 cells by MTT, colony assay, differential coloring and flow cytometry assays, respectively. DNA damage effects were evaluated through intercalation into CT-DNA and plasmid DNA cleavage. Tumor growth inhibition, survival time increase, apoptosis and cell cycle arrest were assessed in Ehrlich ascites tumor in Balb/C mice.

RESULTS

The cytotoxic effect of pecan nut shell extracts, the induction of cell death by apoptosis and also the cell cycle arrest in MCF-7 cells have been demonstrated. The survival time in mice with Ehrlich ascites tumor increased by 67%. DNA damage was observed in the CT-DNA, plasmid DNA and comet assays. The mechanism involved in the antitumor effect of pecan nut shell extracts may be related to the activation of key proteins involved in apoptosis cell death (Bcl-XL, Bax and p53) and on the cell cycle regulation (cyclin A, cyclin B and CDK2).

CONCLUSIONS

These results were attributed to the phenolic profile of the extract, which presented compounds such as gallic, 4-hydroxybenzoic, chlorogenic, vanillic, caffeic and ellagic acid, and catechin, epicatechin, epigallocatechin and epicatechin gallate. The results indicated that pecan nut shell extracts are effective against tumor cells growth and may be considered as an alternative to the treatment of cancer.

Cistus incanus from Strandja Mountain as a Source of Bioactive Antioxidants

The purpose of the present study is to survey the extraction conditions and explore the antioxidant potential of the wild herb Cistus incanus, which is non-traditional in Bulgarian ethnomedicine and widespread in the Strandja Mountain. The influence of the extraction time (0–500 min) and solvent composition (0–50% ethanol in water) on the polyphenols, flavonoid yields and on the antioxidant capacity of the extracts of leaves, stalks (wood parts) and bud mixture were studied. The antioxidant capacity (AOC) was evaluated by use of scavenging assays of 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals. Total polyphenol and flavonoid contents were quantified using UV–vis (ultraviolet-visible) spectrophotometry. The optimal yield of the desired components was obtained with 30% ethanol in water solvent at the 390th min of extraction time. In addition, the influence of seasonality (winter and summer Cistus incanus), and of the different aerial parts—hard-coated seeds, buds, and a mixture of leaves and stalks of the wild plant—on the presence of polyphenols, flavonoids, and AOC were investigated. The present work revealed that the high values of polyphenols, flavonoids and the high AOC occurred not only in the summer leaves, but were also found in the winter leaves, hard-coated seeds, buds, and stalks. Based on the obtained results, the Cistus incanus from Strandja Mountain could be an excellent new source of natural antioxidants in food and for the pharmaceutical industries.

Identity-based High-performance thin Layer Chromatography Fingerprinting Profile and Tumor Inhibitory Potential of Anisochilus carnosus (L.f.) wall Against Ehrlich Ascites Carcinoma

CONTEXT

Anisochilus carnosus (L.f.) wall belonging to the family Lamiaceae is a plant that is widely used in folk medicine for treating eczema, cold, cough, and fever.

OBJECTIVE

In the present study, we explored the anticancer potential of A. carnosus leaves against Ehrlich ascites carcinoma (EAC) and estimated the quantity of luteolin present in various extracts and fractions of A. carnosus by high-performance thin layer chromatography (HPTLC) fingerprinting.

MATERIALS AND METHODS

Various factors such as tumor volume, tumor cell viability, tumor weight, prolongation of lifespan, and hematological parameters were assessed.

RESULT

We observed a significant lowering in tumor volume, tumor weight, and cell viability in EAC-induced mice following intervention with A. carnosus extracts. Also, there was a considerable prolongation of host lifespan and restoration of hematological parameters to almost normal levels with A. carnosus treatment. HPTLC fingerprinting of various extracts and fractions of A. carnosus along with luteolin as the reference standard revealed the occurrence of luteolin in all tested extracts and fractions of A. carnosus with the highest concentration being reported in the ethanol fraction.

CONCLUSION

A. carnosus exhibits potent anti-tumor potential which can most likely be attributed to the occurrence of different phytochemicals such as phytosterols, terpenoids, and flavonoids in the plant. Further studies to isolate compounds from A. carnosus and understand the mechanism of anti-tumor activity would be worthwhile.

SUMMARY

EAC induced mice that received A. carnosus treatment exhibited significant reduction in tumor volume, tumor weight and tumor cell viability. Their life span was considerably prolonged. We detected luteolin in A. carnosus aqueous and ethanol extract using HPTLC. Hence, anticancer activity of A. carnosus can be partly attributed to the presence of luteolin.

Enhanced drug encapsulation and extended release profiles of calcium-alginate nanoparticles by using tannic acid as a bridging cross-linking agent

Calcium alginate nanoparticles (NPs) suffer from sub-optimal stability in bio-relevant media leading to low drug encapsulation efficiency and uncontrolled release profiles. To sort out these drawbacks, a novel approach is proposed herein based on introducing tannic acid into these NPs to act as a bridging cross-linking aid agent. Calcium-alginate NPs were prepared by the ionotropic gelation method and loaded with diltiazem hydrochloride as a model drug. These NPs were characterized in terms of particle size, zeta potential, and morphology, and results were explained in accordance with Fourier-transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). The incorporation of tannic acid led to more than four folds increase in drug encapsulation efficiency (i.e. from 15.3% to 69.5%) and reduced burst drug release from 44% to around 10% within the first 30 min. These findings suggest the possibility of improving the properties of Ca-alginate NPs by incorporating cross-linking aid agents under mild conditions.

Preventive effect of tannic acid on 2-acetylaminofluorene induced antioxidant level, tumor promotion and hepatotoxicity: a chemopreventive study

Tannic acid, present in almost every food derived from plants, has been widely investigated as a chemopreventive agent because, apart from its use as a food additive, pharmacological studies have demonstrated its many health-promoting properties. In this study, we show the modulatory effect of tannic acid on 2-acetylaminofluorene (2-AAF)-mediated hepatic oxidative stress and cell proliferation in rats. 2-AAF (50 mg/kg body weight) caused reduction in hepatic glutathione content and the activities of hepatic anti-oxidant enzymes and phase-II metabolizing enzymes with an enhancement of xanthine oxidase activity, lipid peroxidation and hydrogen peroxide content. 2-AAF treatment also induced serum oxaloacetate and pyruvate transaminase, lactate dehydrogenase and gamma-glutamyl transpeptidase. Treatment of rats orally with tannic acid (125 and 250 mg/kg body weight) resulted in significant recovery of hepatic glutathione content, antioxidant and phase-II metabolizing enzymes. Also, significant decreases in lipid peroxidation, xanthine oxidase, hydrogen peroxide generation and liver damage marker enzymes were observed. The antiproliferative efficacy of the tannic acid was also evaluated. The promotion parameters induced (ornithine decarboxylase activity and DNA synthesis) by 2-AAF administration in the diet with partial hepatectomy (PH) were also significantly suppressed, dose dependently, by tannic acid. Hence, we propose that tannic acid might suppress the promotion stage via inhibition of oxidative stress and polyamine biosynthetic pathway.

Tannic acid is a natural β-secretase inhibitor that prevents cognitive impairment and mitigates Alzheimer-like pathology in transgenic mice

Amyloid precursor protein (APP) proteolysis is essential for production of amyloid-β (Aβ) peptides that form β-amyloid plaques in brains of Alzheimer disease (AD) patients. Recent focus has been directed toward a group of naturally occurring anti-amyloidogenic polyphenols known as flavonoids. We orally administered the flavonoid tannic acid (TA) to the transgenic PSAPP mouse model of cerebral amyloidosis (bearing mutant human APP and presenilin-1 transgenes) and evaluated cognitive function and AD-like pathology. Consumption of TA for 6 months prevented transgene-associated behavioral impairment including hyperactivity, decreased object recognition, and defective spatial reference memory, but did not alter nontransgenic mouse behavior. Accordingly, brain parenchymal and cerebral vascular β-amyloid deposits and abundance of various Aβ species including oligomers were mitigated in TA-treated PSAPP mice. These effects occurred with decreased cleavage of the β-carboxyl-terminal APP fragment, lowered soluble APP-β production, reduced β-site APP cleaving enzyme 1 protein stability and activity, and attenuated neuroinflammation. As in vitro validation, we treated well characterized mutant human APP-overexpressing murine neuron-like cells with TA and found significantly reduced Aβ production associated with less amyloidogenic APP proteolysis. Taken together, these results raise the possibility that dietary supplementation with TA may be prophylactic for AD by inhibiting β-secretase activity and neuroinflammation and thereby mitigating AD pathology.

Inhibition of ozone-induced SP-A oxidation by plant polyphenols

Surfactant protein-A (SP-A) is the best studied and most abundant of the protein components of lung surfactant and plays an important role in host defense of the lung. It has been shown that ozone-induced oxidation of SP-A protein changes its functional and biochemical properties. In the present study, eight plant polyphenols (three flavonoids, three hydroxycinnamic acids, and two hydroxybenzoic acids) known as strong antioxidants, were tested for their ability to inhibit ozone-induced SP-A oxidation as a mechanism for chemoprevention against lung damage. SP-A isolated from alveolar proteinosis patients was exposed to ozone (1 ppm) for 4 h. The flavonoids protected SP-A from oxidation in a dose dependent manner. ( - )-Epicatechin was the most potent flavonoid and exhibited inhibition of ozone-induced formation of carbonyls by 35% at a concentration as low as 5 microM. Hydroxybenzoic acids inhibited SP-A oxidation in a dose-dependent manner although they were less potent than flavonoids. On the other hand, hydroxycinnamic acids exhibited a different inhibitory pattern. Inhibition was observed only at medium concentrations. The results indicate that inhibition of SP-A oxidation by plant polyphenols may be a mechanism accounting for the protective activity of natural antioxidants against the effects of ozone exposure on lungs.

Tannic acid incorporation in chitosan-based microparticles and in vitro controlled release

Chitosan, a natural polycationic polysaccharide, was coupled with two polyanionic polymers: Na-alginate and carboxymethylcellulose (CMC) and with tannic acid (TA) obtaining three species of self-assembled complexes: chitosan/alginate/TA (sample 1), chitosan/TA (sample 2) and chitosan/CMC/TA (sample 3). The microparticle formation was achieved by dropwise addition of one solution into other by using a coaxial airflow sprayer. These systems were characterized with regard to particle size distribution, thermal stability, tannic acid entrapment efficiency. Sample 2 showed quite a different behavior compared to the other two samples; the particle diameter is located in the nanometric region, the quantity of incorporated tannic acid is higher than in the other two samples and the material shows better thermal stability. The release of tannic acid from these complexes was studied in water (pH = 5.89), phosphates buffer (pH = 7.04) and acetate buffer (pH = 4.11). These studies revealed two distinct periods in tannic acid delivery process: an initial period, varying between 4 and 10 h, characterized by a high release rate with a delivered tannic acid amount of approximately 80% of the incorporated polyphenol and a second period, which starts after 20 to 30 h of delivery and it ends after approximately 120 h, when the release process takes place with low and constant rate and the kinetic curve is linear--characteristic for a zero order kinetic.

Tannic acid facilitates expression of the polypyrimidine tract binding protein and alleviates deleterious inclusion of CHRNA1 exon P3A due to an hnRNP H-disrupting mutation in congenital myasthenic syndrome

We recently reported that the intronic splice-site mutation IVS3-8G>A of CHRNA1 that encodes the muscle nicotinic acetylcholine receptor alpha subunit disrupts binding of a splicing repressor, hnRNP H. This, in turn, results in exclusive inclusion of the downstream exon P3A. The P3A(+) transcript encodes a non-functional alpha subunit that comprises 50% of the transcripts in normal human skeletal muscle, but its functional significance remains undetermined. In an effort to search for a potential therapy, we screened off-label effects of 960 bioactive chemical compounds and found that tannic acid ameliorates the aberrant splicing due to IVS3-8G>A but without altering the expression of hnRNP H. Therefore, we searched for another splicing trans-factor. We found that the polypyrimidine tract binding protein (PTB) binds close to the 3' end of CHRNA1 intron 3, that PTB induces skipping of exon P3A and that tannic acid increases the expression of PTB in a dose-dependent manner. Deletion assays of the PTB promoter region revealed that the tannic acid-responsive element is between positions -232 and -74 from the translation initiation site. These observations open the door to the discovery of novel therapies based on PTB overexpression and to detecting possible untoward effects of the overexpression.

Tannic acid-induced apoptosis and -enhanced sensitivity to arsenic trioxide in human leukemia HL-60 cells

Tannic acid (TA), a glucoside of gallic acid polymer, has been shown to possess anti-bacterial, anti-enzymatic, anti-tumor and astringent properties. However, the anti-cancer activity of TA in leukemia is still obscure. In this study, we showed TA-induced apoptotic death in acute myeloid leukemia (AML) HL-60 cells via dose- and time-dependent manner as well as increase of sub-G1 fraction, chromosome condensation, and DNA fragmentation. Further analysis demonstrated the involvement of activation of caspase cascade, cleavage of poly (ADP-ribose) polymerase (PARP), disruption of mitochondrial membrane potential, and release of Cytochrome C, in TA-induced apoptosis. These effects were probably associated with the increase of intracellular superoxide in mitochondrial signaling pathway which attributed to the down-regulation of superoxide dismutase (SOD). Notably, a low dose of TA is sufficient to aggravate arsenic trioxide (As(2)O(3))-induced cytotoxicity in HL-60 cells. Altogether, this study suggested the effects of TA to induce apoptosis in HL-60 and therapeutic potential in AML by being an adjunct to As(2)O(3).

Cytogenetic effects of grape extracts (Vitis vinifera) and polyphenols on mitomycin C-induced sister chromatid exchanges (SCEs) in human blood lymphocytes

In the present study, the effects of extracts and polyphenol-rich fractions as well as monomer polyphenols identified in them, from both red and white grapes, on mitomycin C (MMC) induced sister chromatid exchanges (SCEs) in human peripheral blood lymphocytes were investigated. The grape extracts and two of the three polyphenol-rich fractions promoted MMC-induced SCEs at concentrations from 75 to 300 microg/mL. However, none of the extracts or fractions alone induced SCEs. Thus, these results suggest caution especially with regard to the use of grape extracts as dietary supplements. On the other hand, the fact that these extracts were not genotoxic alone may indicate a selective activity against genetically damaged cells. This is the first study regarding the clastogenic effects of grape extracts in human cells. Moreover, from the tested polyphenols, caffeic acid, gallic acid, and rutin hydrate enhanced MMC-induced clastogenicity, whereas ferulic acid, protocatechuic acid, (+)-catechin, (-)-epicatechin, and trans-resveratrol had no effect at concentrations between 5 and 100 microM. The differences in the chemical structures of the tested polyphenols may account for their differential effects on MMC clastogenicity.

Molecular mechanisms of the chemopreventive effect on hepatocellular carcinoma development in Mdr2 knockout mice

Dietary antioxidants and selenium compounds were shown to have a therapeutic effect against hepatocellular carcinoma in several mouse models. We tested the effects of tannic acid and selenomethionine on hepatocellular carcinoma development in Mdr2 knockout (Mdr2-KO) mice. Mdr2-KO and age-matched Mdr2 heterozygous control mice were fed with tannic acid or selenomethionine during the first 3 months of life. Then, several mice from each group were sacrificed, and liver tissue samples were removed for analysis. The remaining mice were fed a regular diet until the age of 16 months, at which time the number and size of liver tumors were determined. Liver tissue samples of 3-month-old mice were subjected to gene expression profiling analysis using cDNA macroarrays containing probes for 240 genes that regulate responses to oxidative stress and inflammation or lipid metabolism. Both tannic acid and selenomethionine had partial chemopreventive effect on development of hepatocellular carcinoma in Mdr2-KO mice: they reduced the incidence of large tumor nodules (diameter >1 cm) at age 16 months. Both agents inhibited gene expression and reversed up-regulation of many genes that control inflammation or response to oxidative stress in Mdr2-KO livers at age 3 months. This inhibitory effect on gene expression correlated with the ability of agents to reduce incidence of large tumors: selenomethionine was more active than tannic acid in both aspects. Understanding the molecular mechanism of chemoprevention effect could improve our therapeutic modalities while using these agents.

Tannic acid inhibits in vitro iron-dependent free radical formation

The antioxidant activity of tannic acid (TA), a plant polyphenol claimed to possess antimutagenic and anticarcinogenic activities, was studied by monitoring (i) 2-deoxyribose degradation (a technique for OH detection), (ii) ascorbate oxidation, (iii) ascorbate radical formation (determined by EPR analysis) and (iv) oxygen uptake induced by the system, which comprised Fe(III) complexes (EDTA, nitrilotriacetic acid (NTA) or citrate as co-chelators), ascorbate and oxygen. TA removes Fe(III) from the co-chelators (in the case of EDTA, this removal is slower than with NTA or citrate), forming an iron-TA complex less capable of oxidizing ascorbate into ascorbate radical or mediating 2-deoxyribose degradation. The effectiveness of TA against 2-deoxyribose degradation, ascorbate oxidation and ascorbate radical formation was substantially higher in the presence of iron-NTA (or iron-citrate) than with iron-EDTA, which is consistent with the known formation constants of the iron complexes with the co-chelators. Oxygen uptake and 2-deoxyribose degradation induced by Fe(II) autoxidation were also inhibited by TA. These results indicate that TA inhibits OH formation induced by Fe(III)/ascorbate/O(2) mainly by arresting Fe(III)-induced ascorbate oxidation and Fe(II) autoxidation (which generates Fe(II) and H(2)O(2), respectively), thus limiting the production of Fenton reagents and OH formation. We also hypothesize that the Fe(II) complex with TA exhibits an OH trapping activity, which explains the effect of TA on the Fenton reaction.

Tannic acid inhibits cholangiocyte proliferation after bile duct ligation via a cyclic adenosine 5',3'-monophosphate-dependent pathway

Chronic cholestatic diseases are characterized by morphological changes involving cholangiocyte proliferation and functional alterations of secretory capacity. The plant polyphenol tannic acid inhibits the growth of malignant human cholangiocytes. However, the mechanisms by which tannic acid limits excessive cholangiocyte proliferation are unknown. In this study we assessed the effect of tannic acid on cholangiocyte proliferation after bile duct ligation in rats. Tannic acid feeding decreased cholangiocyte proliferation and ductal mass in vivo after bile duct ligation. These changes were associated with functional changes in bile secretion and with decreases of intracellular cyclic adenosine 5',3'-monophosphate. The anti-proliferative effect of tannic acid was associated with a reduction of ERK1,2 phosphorylation. Additionally, tannic acid feeding decreased protein kinase A phosphorylation and activity. Similar changes were observed in isolated cholangiocytes during in vitro incubation with tannic acid. Furthermore, forskolin abolished the anti-proliferative effect of tannic acid on cholangiocyte proliferation after bile duct ligation. In conclusion, the anti-proliferative effects of tannic acid in cholangiocytes involve modulation of ERK1,2 by a cyclic adenosine 5',3'-monophosphate-protein kinase A-dependent pathway. These data suggest that tannic acid may be useful in limiting excessive cholangiocyte proliferation and modulating secretion during cholestasis.

Inhibition of cholangiocarcinoma growth by tannic acid

Cholangiocarcinoma is an aggressive malignancy of the biliary tract for which effective treatment is lacking. Tannic acid (TA) is a naturally occurring polyphenolic compound with antioxidant and radical scavenging properties as well as anticarcinogenic effects. TA inhibited proliferation of malignant human cholangiocytes in vitro. Furthermore, the growth rate of Mz-ChA-1 cholangiocarcinoma xenografts in balb/c athymic mice was reduced from 10.9 +/- 1.8 mm(3)/d in mice fed with normal water to 5.5 +/- 1.2 mm(3)/d in mice fed with water containing 0.05% TA. Pretreatment with 50 microg/mL TA for 24 hours before xenograft implantation increased tumor latency by 2.5-fold compared with untreated controls, and decreased subsequent growth rates compared with controls in the absence of TA feeding. TA was not cytotoxic to Mz-ChA-1 cells in vitro, but enhanced sensitivity to camptothecin cytotoxicity. TA potently inhibited cell cycle progression, and increased expression of the cyclin-dependent kinase inhibitor p27(KIP1). In addition, TA (0-50 microg/mL) inhibited proteasomal activity in cholangiocyte cell extracts in a concentration-dependent manner. In conclusion, the growth inhibitory effects of TA may result from dysregulation of cell cycle progression due to altered proteasomal degradation of these cell cycle regulatory proteins. TA warrants evaluation as a candidate for the treatment of human cholangiocarcinoma either by itself or in combination with other chemotherapeutic agents.

Inhibition of cancer cell growth by crude extract and the phenolics of Terminalia chebula retz. fruit

A 70% methanol extract of Terminalia chebula fruit, was studied for its effects on growth in several malignant cell lines including a human (MCF-7) and mouse (S115) breast cancer cell line, a human osteosarcoma cell line (HOS-1), a human prostate cancer cell line (PC-3) and a non-tumorigenic, immortalized human prostate cell line (PNT1A) using assays for proliferation ([(3)H]-thymidine incorporation and coulter counting), cell viability (ATP determination) and cell death (flow cytometry and Hoechst DNA staining). In all cell lines studied, the extract decreased cell viability, inhibited cell proliferation, and induced cell death in a dose dependent manner. Flow cytometry and other analyses showed that some apoptosis was induced by the extract at lower concentrations, but at higher concentrations, necrosis was the major mechanism of cell death. ATP assay guided chromatographic fractionation of the extract yielded ellagic acid, 2,4-chebulyl-beta-D-glucopyranose (a new natural product), and chebulinic acid which were tested by ATP assay on HOS-1 cell line in comparison to three known antigrowth phenolics of Terminalia, gallic acid, ethyl gallate, luteolin, and tannic acid. Chebulinic acid (IC(50) = 53.2 microM +/- 0.16) > tannic acid (IC(50) = 59.0 microg/ml +/- 0.19) > and ellagic acid (IC(50) = 78.5 microM +/- 0.24), were the most growth inhibitory phenolics of T. chebula fruit in our study.

Tannins, xenobiotic metabolism and cancer chemoprevention in experimental animals

Tannins are plant polyphenolic compounds that are contained in large quantities in food and beverages (tea, red wine, nuts, etc.) consumed by humans daily. It has been shown that various tannins exert broad cancer chemoprotective activity in a number of animal models. This review summarizes the recent literature regarding both the mechanisms involved, and the specific organ cancer models used in laboratory animals. An increasing body of evidence demonstrates that tannins act as both anti-initiating and antipromoting agents. In view of the fact that tannins may be of valid medicinal efficacy in human clinical trials, the present review attempts to integrate results from animal studies, and considers their possible application in humans.