Topical applications of caffeine or (-)-epigallocatechin gallate (EGCG) inhibit carcinogenesis and selectively increase apoptosis in UVB-induced skin tumors in mice

An updated systematic review of the pharmacology of silymarin

BACKGROUND

Recent years have seen an explosion of scientific papers that deal with drugs from the fruits of milk thistle and its active substances silymarin (standardized mixture of flavonolignanes), thus justifying an updated systematic review.

METHODS

Electronic databases identified silymarin, silibinin, silicristin or milk thistle as descriptors in >700 papers (34% published in last 5 years; 92% dealt with animal pharmacological). Only papers adequately reporting on experimental conditions, dosing, variables tested and statistics were analysed.

RESULTS

Silymarin was found to modify specifically the functions related to various transporters and receptors located in the cell membranes; that is, organic anion uptake transporter peptides (OATP), ABC transporters (P-gp), bile salt export pump, as well as TNF-alpha-dependent and possibly selectin-dependent phenomena. In the cytoplasm, some antioxidant properties and the inhibition of the lipoxygenase pathway seem quite selective and could concur to the antitoxic effects. Some effects like the inhibition of inducible nitric-oxide synthase, of nuclear factor kappa B, and reduction of collagen synthesis are indicative of DNA/RNA-mediated effects. Several studies using 'in vitro' and 'in vivo' cancer models suggest a potential of silymarin in such diseases. Topical and systemic silymarin has skin protective properties against UV-induced damage in epidermis and causes an up-regulation of tumour-suppressor genes p53- and p21CIP1. There were no data on hepatic viral replication, viremia or spontaneous tumours in the data examined.

CONCLUSIONS

Data presented here do not solve the question about the complex mechanism(s) of action of the medicinal herbal drug silymarin. Silymarin may be a natural multi-functional and multi-target drug.

Protection from photodamage by topical application of caffeine after ultraviolet irradiation

BACKGROUND

Characterization of mechanisms that can reverse residual damage from prior skin exposure to ultraviolet (UV) would be of considerable biological and therapeutic interest. Topical caffeine application to mouse skin that had previously been treated with UV has been shown to inhibit the subsequent development of squamous cell carcinomas.

OBJECTIVES

We used an established mouse photodamage model to investigate other possible effects of topical caffeine application after UV.

METHODS

SKH-1 hairless mice were treated with ultraviolet B (UVB) followed immediately by topical application of caffeine or vehicle three times weekly for 11 weeks.

RESULTS

Caffeine applied topically after UV treatment resulted in a significant decrease in UV-induced skin roughness/transverse rhytides as assessed by treatment-blinded examiners. Histologically, topical caffeine application after a single dose of UVB more than doubled the number of apoptotic keratinocytes as evaluated by sunburn cell formation, caspase 3 cleavage and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labelling (TUNEL) staining. A trend towards decreased solar elastosis was noted in the caffeine-treated group although this was not statistically significant. Other histological parameters including epidermal hyperplasia, solar elastosis and angiogenesis were increased in mice treated with UV but topical application of caffeine did not alter these particular UV effects.

CONCLUSIONS

These findings support the concept that topical application of caffeine to mouse skin after UV irradiation promotes the deletion of DNA-damaged keratinocytes and may partially diminish photodamage as well as photocarcinogenesis.

The enigmatic effects of caffeine in cell cycle and cancer

Caffeine may very well be the most frequently ingested neuroactive drug in the world. Mechanistically, caffeine has been reported to affect cell cycle function, induce programmed cell death or apoptosis and perturb key cell cycle regulatory proteins. Although the effects of caffeine have been heavily investigated, much of the research data regarding caffeine's effects on cell cycle and proliferation seem ambiguous. One important factor may be that caffeine has been used experimentally in numerous cell types under a variety of conditions at concentrations ranging from micromolar to high millimolar. Physiologically, achieving experimental blood levels of caffeine would be extremely difficult without adverse side effects. Therefore, the relevance of experimental data obtained by using high concentrations of caffeine is not clear and may account for some of the discrepancies in the literature. This review attempts to reconcile data regarding the cellular effects of caffeine by examining reported effects on cell cycle, proliferation and apoptosis with careful attention to differences in experimental conditions and caffeine concentration utilized.

Photoprotective effects of green tea polyphenols

Non-melanoma skin cancer is the most common malignancy in humans and is equivalent to the incidence of malignancies in all other organs combined in the United States. Current methods of prevention depend on sunscreens in humans, efficacy of which is largely undetermined for non-melanoma skin cancers. Green tea polyphenols have the greatest effect with respect to chemoprevention and have been found to be most potent at suppressing the carcinogenic activity of UV radiation. They protect against many of the other damaging effects of UV radiation such as UV-induced sunburn response, UV-induced immunosuppression and photoaging of the skin. They exert their photoprotective effects by various cellular, molecular and biochemical mechanisms in in vitro and in vivo systems. Green tea polyphenols thus have the potential, when used in conjunction with traditional sunscreens, to further protect the skin against the adverse effects of ultraviolet radiation.

Activation of PKCδ and p38δ MAPK during okadaic acid dependent keratinocyte apoptosis

There is substantial interest in identifying agents that differentially activate keratinocyte differentiation versus apoptosis. Okadaic acid (OA) is a tumor promoter in mouse skin that also stimulates apoptosis of murine keratinocytes. OA also enhances human keratinocyte differentiation; however, the impact of OA treatment on apoptosis in these cells has not been examined. We show that OA promotes normal human keratinocyte apoptosis as evidenced by increased accumulation of cells having sub-G1/S DNA content, decreased mitochondrial integrity, increased annexin V binding, increased cytoplasmic cytochrome c level, and increased procaspase 3 and PARP cleavage. Cyclin A, cyclin D1, cdk2, cdk4, p53 and p21 levels are reduced. These changes are associated with release of the PKCdelta catalytic domain and increased phosphorylation of PKCdelta-T(505)-responses consistent with PKCdelta activation. In contrast, phosphorylation of PKCdelta-Y(311) is not increased. The apoptotic response is enhanced in OA treated cells in the presence of p38delta, a PKCdelta target. OA treatment selectively activated p38delta, and OA-dependent apoptosis is not inhibited by treatment with the p38alpha/beta inhibitor, SB203580. These findings are consistent with the idea that the response is mediated by p38delta. Our data indicate that OA is an agent that regulates both keratinocyte differentiation and apoptosis, and that this regulation is mediated via activation of a PKCdelta/p38delta signaling cascade.

Inhibition of adenoma progression to adenocarcinoma in a 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone-induced lung tumorigenesis model in A/J mice by tea polyphenols and caffeine

The present study investigated the inhibitory effects of Polyphenon E [a standardized green tea polyphenol preparation containing 65% (-)-epigallocatechin-3-gallate] and caffeine on 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)-induced lung tumor progression from adenoma to adenocarcinoma. Female A/J mice were treated with a single dose of NNK (103 mg/kg body weight, i.p.) and kept for 20 weeks for the mice to develop lung adenomas. The mice were then given a solution of 0.5% Polyphenon E or 0.044% caffeine as the sole source of drinking fluid until week 52. Both treatments significantly decreased the number of visible lung tumors. Histopathologic analysis indicated that Polyphenon E administration significantly reduced the incidence (by 52%) and multiplicity (by 63%) of lung adenocarcinoma. Caffeine also showed marginal inhibitory effects in incidence and multiplicity of adenocarcinoma (by 48% and 49%, respectively). Markers of cell proliferation, apoptosis, and related cell signaling were studied by immunohistochemistry, and the labeling index and staining intensity were quantified by the Image-Pro system. Polyphenon E and caffeine treatment inhibited cell proliferation (by 57% and 50%, respectively) in adenocarcinomas, enhanced apoptosis in adenocarcinomas (by 2.6- and 4-fold, respectively) and adenomas (both by 2.5-fold), and lowered levels of c-Jun and extracellular signal-regulated kinase (Erk) 1/2 phosphorylation. In the normal lung tissues, neither agent had a significant effect on cell proliferation or apoptosis. The results show that tea polyphenols (and perhaps caffeine) inhibit the progression of NNK-induced lung adenoma to adenocarcinoma. This effect is closely associated with decreased cell proliferation, enhanced apoptosis, and lowered levels of c-Jun and Erk1/2 phosphorylation.

(-)-Epigallocatechin-3-gallate protects mice from concanavalin A-induced hepatitis through suppressing immune-mediated liver injury

(-)-Epigallocatechin-3-gallate (EGCG) is the major active component of green tea. Increasing evidence has suggested that EGCG exhibits anti-inflammatory, anti-oxidant and immunosuppressive effects. In this study, we investigated the effect of EGCG on concanavalin A (ConA)-induced hepatitis (CIH) in mice, a model of immune-mediated liver injury in humans. We pretreated mice with EGCG before ConA injection, and then measured alanine aminotransferase (ALT) levels in plasma, inflammatory infiltration and hepatocyte apoptosis in liver. Potential therapeutic mechanisms were elucidated further by measuring several inflammatory mediators. Mice pretreated with EGCG exhibited much less increased ALT levels in plasma, reduced inflammatory infiltration and hepatocyte apoptosis in liver compared with control mice pretreated with vehicle solutions. We further investigated the mechanisms of the protective effects of EGCG. In EGCG-pretreated mice, we found abrogated tumour necrosis factor (TNF)-alpha and interferon (IFN)-gamma at both protein levels in plasma and mRNA levels in liver. At the same time, the concentration of nitrite in plasma and inducible nitric oxide synthase production in liver were both down-regulated in these mice. Moreover, IFN-inducible protein-10 and macrophage inflammatory protein-1alpha expressions in liver were decreased significantly. Therefore, EGCG is capable of regulating immune-mediated liver injury in vivo. The protective effect depended on its suppressive effect on the production of important inflammatory mediators.

Neuro-bioenergetic concepts in cancer prevention and treatment

Cancer remains one of the most difficult and elusive disorders to prevent and treat, despite great efforts in research and treatment over the last 30 years. Researchers have tried to understand the pathogenesis of cancer by discovering the single cellular mechanism or pathway derived from a genetic mutation. There are limited efforts made toward discovering a unified concept of cancer. We propose a neuro-bioenergetic concept of cancer pathogenesis based on the central mechanism of cellular hyperexcitability via inducible overexpression of voltage-gated ion channels, ligand-gated channels and neurotransmitters. Exploration of this concept could lead to a better understanding of the cause of cancer as well as developing more effective and specific strategies toward cancer prevention and treatment.

Stimulatory effect of voluntary exercise or fat removal (partial lipectomy) on apoptosis in the skin of UVB light-irradiated mice

Earlier studies indicated that high dietary fat and obesity are associated with an increased risk of cancer at several organ sites in experimental animals and in humans. In a recent study we found that voluntary running wheel exercise decreased body fat and inhibited ultraviolet B light (UVB)-induced carcinogenesis in the epidermis of SKH-1 mice. In the present study we demonstrate that voluntary running wheel exercise stimulated UVB-induced apoptosis in the epidermis by a p53-independent mechanism, and voluntary exercise also stimulated apoptosis in UVB-induced tumors in tumor-bearing mice. Exercise had no effect in non-UVB-treated epidermis or in areas of the epidermis away from tumors in tumor-bearing mice. In addition, we found that removal of the parametrial fat pads (partial lipectomy) 2 weeks before UVB irradiation enhanced UVB-induced apoptosis. The results of our studies suggest that fat cells secrete substances that inhibit apoptosis in cells with DNA damage and possibly also in tumors. Our results help explain why exercise or various dietary regimens that decrease tissue fat inhibit carcinogenesis.

Protection against UV-light-induced skin carcinogenesis in SKH-1 high-risk mice by sulforaphane-containing broccoli sprout extracts

Aerobic life, UV solar radiation, genetic susceptibility, and immune status contribute collectively to the development of human skin cancers. In addition to direct DNA damage, UV radiation promotes the generation of reactive oxygen intermediates that can cause oxidative damage and inflammation, and ultimately lead to tumor formation. Treatment of murine and human keratinocytes with the isothiocyanate sulforaphane elevated phase 2 enzymes and glutathione and protected against oxidant toxicity. Topical application of sulforaphane-containing broccoli sprouts extracts induced the phase 2 response in mouse skin in vivo. Sulforaphane inhibited cytokine-dependent (gamma-interferon or lipopolysaccharide) induction of iNOS in RAW 264.7 macrophages. The UV-radiation-induced skin carcinogenesis in "initiated high-risk mice" was substantially inhibited by broccoli sprout extracts containing sulforaphane. After completion of the UV irradiation schedule (30 mJ/cm(2)/session twice a week for 20 weeks), groups of approximately 30 mice were treated topically on their backs (5 days a week for 11 weeks) with broccoli sprout extract containing either the equivalent to 0.3 micromol (low dose) or 1.0 micromol (high dose) sulforaphane, respectively. At this time point, the tumor incidence had reached 100% in the control mice. Tumor burden, incidence, and multiplicity were reduced by 50% in the animals that received the high dose of protector. Tumor incidence and multiplicity did not differ between the low dose-treated and the control groups, but the low dose treatment resulted in a substantial reduction of the overall tumor burden. Thus, topical application of sulforaphane-containing broccoli sprout extracts is a promising strategy for protecting against skin tumor formation after exposure to UV radiation.

Protective effects of EGCG on UVB-induced damage in living skin equivalents

In this study, we evaluate the effects of (-)-epigallocatechin-3-gallate (EGCG) on ultraviolet B (UVB)-irradiated living skin equivalents (LSEs). Histologically, UVB irradiation induced thinning of the LSE epidermis, whereas EGCG treatment led to thickening of the epidermis. Moreover, EGCG treatment protected LSEs against damage and breakdown caused by UVB exposure. Immunohistochemically, UVB-exposed LSEs expressed p53, Fas, and 8-hydroxy-deoxyguanosine (8-OHdG), all of which are associated with apoptosis. However, EGCG treatment reduced the levels of UVB-induced apoptotic markers in the LSEs. In order to determine the signaling pathways induced by UVB, Western blot analysis was performed for both c-Jun NH2-terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK), which are associated with UVB-induced oxidative stress. UVB activated JNK in the epidermis and dermis of the LSEs, and EGCG treatment reduced the UVB-induced phosphorylation of JNK. In addition, p38 MAPK was also found to have increased in the UVB-exposed LSEs. Also, EGCG reduced levels of the phosphorylation of UVB-induced p38 MAPK. In conclusion, pretreatment with EGCG protects against UVB irradiation via the suppression of JNK and p38 MAPK activation. Our results suggest that EGCG may be useful in the prevention of UVB-induced human skin damage, and LSEs may constitute a potential substitute for animal and human studies.

Chemoprevention of nonmelanoma skin cancer

Skin cancer is the most common cancer in human beings. The increased incidence of skin cancer has brought much attention to the process by which these tumors develop and how they can be prevented. Efforts have been made to educate the public about the importance of protecting skin from excessive ultraviolet light. Despite this work, the incidence of skin cancer continues to increase. Available compounds may be useful in the chemoprevention of skin cancer. Chemoprevention is defined as oral or topical use of dietary or pharmacologic agents to inhibit or reverse the development of cancer. Potential agents included are the retinoids; difluoromethylornithine; T4 endonuclease V; polyphenolic antioxidants, such as (-)-epigallocatechin gallate, found in green tea and grape seed extract; silymarin; isoflavone genestein; nonsteroidal anti-inflammatory drugs; curcumin; lycopene; vitamin E; beta-carotene; and selenium. Many of these agents are available over the counter as topical or oral preparations.

LEARNING OBJECTIVE

At the conclusion of this activity, participants should be familiar with the chemopreventive agents and their efficacy, as well as any significant side effects associated with them.

Cyanidin-3-glucoside, a natural product derived from blackberry, exhibits chemopreventive and chemotherapeutic activity

Epidemiological data suggest that consumption of fruits and vegetables has been associated with a lower incidence of cancer. Cyanidin-3-glucoside (C3G), a compound found in blackberry and other food products, was shown to possess chemopreventive and chemotherapeutic activity in the present study. In cultured JB6 cells, C3G was able to scavenge ultraviolet B-induced *OH and O2-* radicals. In vivo studies indicated that C3G treatment decreased the number of non-malignant and malignant skin tumors per mouse induced by 12-O-tetradecanolyphorbol-13-acetate (TPA) in 7,12-dimethylbenz[a]anthracene-initiated mouse skin. Pretreatment of JB6 cells with C3G inhibited UVB- and TPA-induced transactivation of NF-kappaB and AP-1 and expression of cyclooxygenase-2 and tumor necrosis factor-alpha. These inhibitory effects appear to be mediated through the inhibition of MAPK activity. C3G also blocked TPA-induced neoplastic transformation in JB6 cells. In addition, C3G inhibited proliferation of a human lung carcinoma cell line, A549. Animal studies showed that C3G reduced the size of A549 tumor xenograft growth and significantly inhibited metastasis in nude mice. Mechanistic studies indicated that C3G inhibited migration and invasion of A549 tumor cells. These finding demonstrate for the first time that a purified compound of anthocyanin inhibits tumor promoter-induced carcinogenesis and tumor metastasis in vivo.

Protective effects of tea polyphenols and caffeine

Compounds derived from botanical sources, such as polyphenols from tea, have been of interest as possible therapeutic agents. Their benefits in terms of cancer chemoprevention have also been investigated primarily through in vitro and animal in vivo studies. Ultraviolet light from solar radiation has been proven to initiate and promote skin cancer, which is the most common malignancy in light-skinned populations. This review discusses the effects of tea polyphenols in preventing cutaneous carcinogenesis. Although many of the mechanisms and pathways discussed may be applicable to other carcinogens, this review focuses mainly on those related to ultraviolet light-induced processes and potential action sites for tea polyphenols. Since caffeine is a component of tea, and has also been suggested as a possible chemoprotective agent, it is included in this review. Based on data from numerous studies published in the scientific literature, tea polyphenols are promising chemopreventive agents against ultraviolet-induced skin cancers. Their antioxidant properties, inhibitory effects on signal transduction pathways, cell proliferation, angiogenesis and capacity for apoptosis induction, as well as possible immune protective effects, are among the mechanisms that contribute to skin cancer prevention.

Possible mechanisms of the cancer-preventive activities of green tea

The cancer-preventive activities of tea and some tea constituents, such as caffeine and (-)-epigallocatechin-3-gallate (EGCG), have been demonstrated in animal models. The mechanisms of action of the tea constituents have been extensively investigated, but the mechanisms for the cancer-preventive activity of tea are not clearly understood. This chapter discusses some of the reported studies on the green tea polyphenol, EGCG, and the major issues in the interpretation of these data. Among the different activities of EGCG observed in cell culture systems, we need to select the physiologically relevant ones based on the biological importance of the target as well as the effective concentration and whether the reaction can take place in vivo because of the limited bioavailability of EGCG. We also need to distinguish between primary and subsequent events. Possible artifacts should be recognized. The cancer-preventive mechanisms need to be validated in animal models or human samples.

Intracellular signaling network as a prime chemopreventive target of (–)-epigallocatechin gallate

Chemoprevention is an attempt to use either naturally occurring or synthetic substances or their mixtures to intervene in the progress of carcinogenesis. Recently, it has been shown that some edible phytochemicals alter gene expression, directly or indirectly, thereby regulating the carcinogenic processes. (-)-Epigallocatechin gallate (EGCG), a principal antioxidant derived from green tea, is one of the most extensively investigated chemopreventive phytochemicals. EGCG has been known to block each stage of carcinogenesis by modulating signal transduction pathways involved in cell proliferation, transformation, inflammation, apoptosis, metastasis and invasion. This review addresses the molecular target-based chemoprevention with EGCG by focusing on the common events mediated by transcription factors, such as NF-kappa B, activator protein-1 and nuclear factor erythroid 2 p45-related factor, and upstream kinases involved in the cellular signaling network.

Safety studies on epigallocatechin gallate (EGCG) preparations. Part 2: dermal, acute and short-term toxicity studies

Green tea extract and its principal active ingredient, epigallocatechin gallate (EGCG), are gaining attention and increased usage due to their healthful properties. Despite the increasing demand for these products, few studies have examined their safety. The toxicity of purified green tea extracts containing high concentrations of EGCG have been evaluated in a series of studies in order to define the safety of Teavigo, a high-concentration EGCG extract produced by the same novel method. Topical EGCG preparations caused minor dermal irritation in rats and guinea pigs, but not rabbits, and was a moderate dermal sensitizing agent in the guinea pig maximization test. A rabbit eye irritation test produced a strong enough response to not warrant any further testing in this assay. An oral dose delivering 2000 mg EGCG preparation/kg was lethal to rats; whereas, a dose of 200 mg EGCG/kg induced no toxicity. The dietary administration of EGCG preparation to rats for 13 weeks was not toxic at doses up to 500 mg/kg/day. Similarly, no adverse effects were noted when 500 mg EGCG preparation/kg/day was administered to pre-fed dogs in divided doses. This dose caused morbidity when administered to fasted dogs as a single bolus dose, although this model was considered an unrealistic comparison to the human condition. From these studies a no-observed adverse effect level of 500 mg EGCG preparation/kg/day was established.

Chemoprevention of photocarcinogenesis by selected dietary botanicals

Epidemiological, clinical and laboratory studies have implicated solar ultraviolet (UV) radiation as a tumor initiator, tumor promoter and complete carcinogen, and their excessive exposure can lead to the development of various skin disorders including melanoma and nonmelanoma skin cancers. Sunscreens are useful, but their protection is not adequate to prevent the risk of UV-induced skin cancer. It may be because of inadequate use, incomplete spectral protection and toxicity. Therefore new chemopreventive methods are necessary to protect the skin from photodamaging effects of solar UV radiation. Chemoprevention refers to the use of agents that can inhibit, reverse or retard the process of skin carcinogenesis. In recent years, considerable interest has been focused on identifying naturally occurring botanicals, specifically dietary, for the prevention of photocarcinogenesis. A wide variety of botanicals, mostly dietary flavonoids or phenolic substances, have been reported to possess substantial anticarcinogenic and antimutagenic activities because of their antioxidant and antiinflammatory properties. This review summarizes chemopreventive effects of some selected botanicals, such as apigenin, curcumin, grape seed proanthocyanidins, resveratrol, silymarin, and green tea polyphenols, against photocarcinogenesis in in vitro and in vivo systems. Attention has also been focused on highlighting the mechanism of chemopreventive action of these dietary botanicals. We suggest that in addition to the use of these botanicals as dietary supplements for the protection of photocarcinogenesis, these botanicals may favorably supplement sunscreens protection and may provide additional antiphotocarcinogenic protection including the protection against other skin disorders caused by solar UV radiation.

Dietary polyphenolic phytochemicals—promising cancer chemopreventive agents in humans? A review of their clinical properties

Epidemiological and preclinical evidence suggests that polyphenolic phytochemicals exemplified by epigallocatechin gallate from tea, curcumin from curry and soya isoflavones possess cancer chemopreventive properties. Whilst such naturally occurring polyphenols have been the subject of numerous mechanistic studies in cells, information on their clinical properties, which might help assess their promise as human cancer chemopreventive agents, is scarce. Therefore, we present a review of pilot studies and trials with a cancer chemoprevention-related rationale, in which either healthy individuals or patients with premalignant conditions or cancer received polyphenolic phytochemicals. The review identifies trial design elements specifically applicable to polyphenolic phytochemicals. The available evidence for tea polyphenols tentatively supports their advancement into phase III clinical intervention trials aimed at the prevention of progression of prostate intraepithelial neoplasia, leukoplakia or premalignant cervical disease. In the case of curcumin and soya isoflavones more studies in premalignacies seem appropriate to optimise the nature and design of suitable phase III trials. The abundance of flavonoids and related polyphenols in the plant kingdom makes it possible that several hitherto uncharacterised agents with chemopreventive efficacy are still to be identified, which may constitute attractive alternatives to currently used chemopreventive drugs.

Modulation of apoptosis by cancer chemopreventive agents

A review of almost 2000 studies showed that the large majority of 39 putative cancer chemopreventive agents induced "spontaneous" apoptosis. Inhibition of the programmed cell death triggered by a variety of stimuli was consistently reported only with ascorbic acid, alpha-tocopherol, and N-acetylcysteine (NAC). We performed experimental studies in rodents exposed to cigarette smoke, either mainstream (MCS) or environmental (ECS), and UV-A/B-containing light. The nonsteroidal anti-inflammatory drug sulindac did not affect the apoptotic process in the skin of light-exposed mice and in the lungs of ECS-exposed mice. Likewise, 5,6-benzoflavone, indole-3-carbinol, 1,2-dithiole-3-thione and oltipraz failed to modulate apoptosis in the respiratory tract of ECS-exposed rats. Phenethyl isothiocyanate further enhanced the frequency of apoptosis in pulmonary alveolar macrophages and bronchial epithelial cells, and upregulated several genes in the lung of ECS-exposed rats. Both individually and in combination with oltipraz, NAC inhibited apoptosis in the respiratory tract of rats exposed either to MCS or ECS. Moreover, NAC attenuated the ECS-related overexpression of proapoptotic genes and normalized the levels of proapoptotic proteins in rat lung. The transplacental administration of NAC to mice considerably attenuated gene overexpression in the liver of fetuses exposed to ECS throughout pregnancy. Inhibition of apoptosis by chemopreventive agents reflects their ability to counteract certain upstream signals, such as genotoxic damage, redox imbalances, and other forms of cellular stress that trigger apoptosis. On the other hand, enhancement of apoptosis is a double-edged sword, since it represents a protective mechanism in carcinogenesis but may contribute to the pathogenesis of other degenerative diseases. We suggest that stimulation of apoptosis by so many chemopreventive agents, as reported in the literature, may often reflect the occurrence of toxic effects at high doses.

Mechanisms and preclinical efficacy of silibinin in preventing skin cancer

Eukaryotic cellular machineries including the genome face continuous challenge from environmental deleterious agents, as well as from the by products of their own metabolism. Our skin is the most important barrier. It protects us from xenobiotic and genotoxic agents including ultraviolet (UV) solar radiation and potential carcinogens, which are notorious for causing skin cancer. There is a rise in non-melanoma skin cancer (NMSC), which is diagnosed in more than a million people every year in the United States alone, and is also prevalent in the other Western countries. In addition to sunscreens, chemoprevention of skin cancer by natural non-toxic compounds is suggested as an effective strategy to prevent the incidence of skin cancer. Our extensive animal studies on silibinin, a non-toxic bioactive component in milk thistle, suggest that it has a strong potential to prevent skin cancer incidence, promotion and progression in response to chemical carcinogens and tumour promoters as well as UV radiation. Our data suggest that silibinin has multiple targets in the cell, and can be protective against the harmful effects of cytotoxic agents such as reactive oxygen species and inflammation. Further, silibinin modulates mitogenic and survival signalling, p53, Cip1/p21 and other cell cycle regulatory molecules to prevent UVB-induced skin carcinogenesis. Our ongoing studies also suggest the positive effect of silibinin on the repair of UVB-induced DNA damage in mouse skin. Overall, the protective efficacy of silibinin against skin cancer is supported by sound mechanistic rationale in animal and cell culture studies, and suggests its potential use for humans.

Redox properties of tea polyphenols and related biological activities

Plant polyphenolic compounds are known to be strong antioxidants. Because oxidative stress is believed to contribute to many acute and chronic diseases, these polyphenols have been postulated to have many beneficial health effects, such as the prevention of cancer and cardiovascular diseases. Indeed, some of these beneficial effects have been demonstrated in animal models and in some, but not all, epidemiological studies. Nevertheless, only some of these activities have been demonstrated to be associated with the antioxidative activities of polyphenols. In studies with cell lines in culture, some of the observed activities may be due to superoxide and hydrogen peroxide produced during the autooxidation of polyphenols. Such pro-oxidation-dependent reactions may not happen in tissues where the oxygen partial pressure is much lower than that in cell culture medium. This review will use the well-studied tea polyphenol, (-)-epigallocatechin-3-gallate, as an example to illustrate the redox properties of polyphenols and their influence on signaling pathways related to anti-cancer activities. Existing data suggest, however, that most of the relevant mechanisms of cancer prevention by tea polyphenols are not related to their redox properties, but are due to the direct binding of the polyphenol to target molecules, including the inhibition of selected protein kinases, matrix metalloproteinases, and DNA methyltransferases.

Comparison of (-)-epigallocatechin-3-gallate elicited liver and small intestine gene expression profiles between C57BL/6J mice and C57BL/6J/Nrf2 (-/-) mice

PURPOSE

This study was conducted to study global gene expression profiles elicited by (-)-epigallocatechin-3-gallate (EGCG) in mouse liver and small intestine, as well as to identify EGCG-regulated Nrf2-dependent genes.

METHODS

C57BL/6J and C57BL/6J/Nrf2(-/-) mice were given an oral dose of EGCG at 200 mg/kg or treated with vehicle. Both liver and small intestine were collected 3 h and 12 h after treatment. Total RNA was extracted from the tissues and gene expression profiles were analyzed using Affymetrix mouse genome 430 2.0 array and GeneSpring 6.1 software. Microarray data were validated using quantitative real-time reverse transcription-PCR chain reaction analysis.

RESULTS

Genes that were either induced or suppressed more than two fold by EGCG treatment compared with vehicle treatment in the same genotype group were filtered using the GeneSpring software. Among these well-defined genes, 671 EGCG-regulated Nrf2-dependent genes and 256 EGCG-regulated Nrf2-independent genes were identified in liver, whereas 228 EGCG-regulated Nrf2-dependent genes and 98 EGCG-regulated Nrf2-independent genes were identified in the small intestine. Based on their biological functions, these genes mainly fall into the category of ubiquitination and proteolysis, electron transport, detoxification, transport, cell growth and apoptosis, cell adhesion, kinase and phosphatases, and transcription factors.

CONCLUSIONS

Genes expressed in mouse liver are more responsive to oral treatment of EGCG than those expressed in small intestine. EGCG could regulate many genes in both organs in an Nrf2-dependent manner. The identification of genes related to detoxification, transport, cell growth and apoptosis, cell adhesion, kinase, and transcription regulated by EGCG not only provide potential novel insight into the effect of EGCG on global gene expression and chemopreventive effects, but also point to the potential role of Nrf2 in these processes.

Dietary cancer-chemopreventive compounds: from signaling and gene expression to pharmacological effects

The process of cancer development (carcinogenesis leading to advanced metastasized cancers) in humans generally takes many years through initiation, promotion and progression. Because advanced metastasized cancers are almost impossible to treat, cancer chemoprevention for the control and containment of early cancer development is highly desirable. Recent studies have provided strong evidence that many daily-consumed dietary compounds possess cancer-protective properties that might interrupt the carcinogenesis process. These properties include the induction of cellular defense detoxifying and antioxidant enzymes, which can protect against cellular damage caused by environmental carcinogens or endogenously generated reactive oxygen species. These compounds can also affect cell-death signaling pathways, which could prevent the proliferation of tumor cells. In this review, we will summarize current knowledge on dietary cancer-chemopreventive compounds and their induction of detoxifying enzymes and anti-proliferative effects, and discuss the challenges in translating these signaling and gene-expression events to pharmacological effects.

Effect of administration of caffeine or green tea on the mutation profile in the p53 gene in early mutant p53-positive patches of epidermal cells induced by chronic UVB-irradiation of hairless SKH-1 mice

Irradiation of SKH-1 mice with UVB light for 20 weeks resulted in a large number of patches of epidermal cells, which was visualized with an antibody that recognizes mutated p53 protein. Oral treatment of mice with caffeine (0.4 mg/ml) or green tea (6 mg tea solids/ml) as the drinking fluid during UVB irradiation decreased the number of patches by approximately 40%. Sequencing analysis of the p53 gene (exons 3 to 9) detected 88, 82 or 39 point mutations in 67, 70 or 29 patches from water, caffeine or tea treated mice, respectively. A major hotspot at codon 270 (Arg-->Cys) accounted for 47.7% (water), 70.7% (caffeine) or 46.2% (tea) of all mutations. Patches from caffeine treated mice had fewer types of mutations than patches from mice treated with water or tea. Administration of caffeine or tea during 20 weeks of UVB irradiation eliminated mutations at codons 149 (Pro-->Ser) and 210 (Arg-->Cys) but increased the frequency of mutations at codon 238 (Ser-->Phe). Topical applications of caffeine (1.2 mg in 100 microl acetone) once a day, five times a week for 6 weeks after stopping UVB decreased the number of patches by 63% when compared with mice treated with acetone. DNA sequencing analysis detected 63 and 68 mutations in 48 and 57 patches from acetone or caffeine treated mice, respectively. Although no differences in the frequency, position or types of mutations were observed, the caffeine group harbored less homozygous mutations (12.3% of the total) than the acetone group (31.3% of the total, P = 0.029). In summary, oral treatment of mice with caffeine or green tea during chronic UVB irradiation changed the mutation profile of the p53 gene in early mutant p53 positive epidermal patches, and topical applications of caffeine after discontinuation of chronic UVB irradiation specifically eliminated patches harboring homozygous p53 mutations.

Green tea and the skin

Plant extracts have been widely used as topical applications for wound-healing, anti-aging, and disease treatments. Examples of these include ginkgo biloba, echinacea, ginseng, grape seed, green tea, lemon, lavender, rosemary, thuja, sarsaparilla, soy, prickly pear, sagebrush, jojoba, aloe vera, allantoin, feverwort, bloodroot, apache plume, and papaya. These plants share a common character: they all produce flavonoid compounds with phenolic structures. These phytochemicals are highly reactive with other compounds, such as reactive oxygen species and biologic macromolecules, to neutralize free radicals or initiate biological effects. A short list of phenolic phytochemicals with promising properties to benefit human health includes a group of polyphenol compounds, called catechins, found in green tea. This article summarizes the findings of studies using green tea polyphenols as chemopreventive, natural healing, and anti-aging agents for human skin, and discusses possible mechanisms of action.

Photoprotection

Many agents affect the transmission of ultraviolet light to human skin. These include naturally occurring photoprotective agents (ozone, pollutants, clouds, and fog), naturally occurring biologic agents (epidermal chromophores), physical photoprotective agents (clothing, hats, make-ups, sunglasses, and window glass), and ultraviolet light filters (sunscreen ingredients and sunless tanning agents). In addition, there are agents that can modulate the effects of ultraviolet light on the skin (antioxidants and others). All of the above are reviewed in this article.

LEARNING OBJECTIVE

At the conclusion of this learning activity, participants should be able to provide an overview of all aspects of photoprotection.

Cytotoxicity of epigallocatechin-3-gallate to LNCaP cells in the presence of Cu2+

Epigallocatechin-3-gallate (EGCG) has shown remarkably anti-cancer activity, with its bioactivity being related to reactive conditions, such as pH and metal ions. The present study investigated the degradation of EGCG and its effect on prostate cancer cell in the presence of Cu2+. EGCG was incubated with prostate cancer cells, LNCaP, pretreated with or without Cu2+. EGCG in F-12 medium was quantified using HPLC and the viability of cells was assessed by gel electrophoresis, flow cytometry, and electron microscope. The results of HPLC showed that EGCG degraded completely within 12 h in F-12 medium with or without Cu2+. Gel electrophoresis and flow cytometry did not detect apoptosis of LNCaP cells when they were incubated with EGCG. Electron microscopy examination revealed that EGCG-Cu2+ complex led to damage of cytoplasm membrane in LNCaP cells. It was speculated that not EGCG, but its oxide and complex with Cu2+, are the bioactive components responsible for its cytotoxicity to LNCaP prostate cancer cells.

Inhibition of lung tumorigenesis by tea

Tea and tea constituents have been shown by different investigators to inhibit lung tumorigenesis in different animal model systems. This includes lung tumorigenesis in A/J mice induced by 4-(methylnitrosamino)-1-(3pyridyl)-1-butanone (NNK), N-nitrosodiethylamine, benzo[a]pyrene, N-nitrosomethylurea, or cisplatin. Inhibition of lung tumorigenesis has also been demonstrated in C3H mice treated with N-nitrosodiethylamine. In most of these experiments, reduction in tumor number and tumor size has been observed in the tea-treated group, and in some experiments, decreased tumor incidence has also been observed. The green tea constituent, epigallocatechin-3-gallate (EGCG), and the black tea constituent, theaflavins, have also been shown to be effective. Black tea preparations have been shown to reduce the incidence and number of spontaneously generated lung adenocarcinomas and rhabdomyosarcoma in A/J mice, as well as inhibit the progression of lung adenoma to adenocarcinoma. The mechanisms for the inhibitory action have not been well elucidated. It may be related to the antiproliferative, proapoptotic, and antiangiogenic activities of tea constituents that have been demonstrated in some experiments. These activities may be a result of the inhibition of key protein kinases involved in signal transduction and cell cycle regulation. Tea catechins, such as EGCG, have been suggested to be the effective components. However, a study suggests that caffeine is the key effective constituent for the inhibitory activity of lung tumorigenesis in Fisher 344 rats by black tea. In many of the experiments, tea consumption resulted in the reduction of body fat and body weight; these factors may also contribute to the inhibition of tumorigenesis.

Administration of green tea or caffeine enhances the disappearance of UVB-induced patches of mutant p53 positive epidermal cells in SKH-1 mice

Irradiation of female SKH-1 hairless mice with UVB (30 mJ/cm2) twice a week for 10-20 weeks resulted in the formation of a large number of cellular patches (>8 adjacent cells/patch) that are recognized with an antibody (Pab240) which recognizes mutated but not wild-type p53 protein. These patches are not recognized by an antibody (Pab1620) to wild-type p53 protein. The patches, which are considered putative early cellular markers of the beginning of tumor formation, started appearing after 4-6 weeks of UVB treatment, and multiple patches were observed after treatment for 10 weeks. The number and size of the patches increased progressively with continued UVB treatment. Discontinuation of UVB for 4 weeks resulted in an 80-90% decrease in the number of these patches. The number of the remaining patches did not decrease any further but remained relatively constant for at least 4-9 weeks. Oral administration of green tea (6 mg tea solids/ml) or caffeine (0.4 mg/ml) as the sole source of drinking fluid during irradiation with UVB, twice a week for 20 weeks, inhibited UVB-induced formation of mutant p53 positive patches by approximately 40%. Oral administration of green tea (6 mg tea solids/ml) as the sole source of drinking fluid or topical applications of caffeine (6.2 micromol) once a day 5 days a week starting immediately after discontinuation of UVB treatment enhanced the rate and extent of disappearance of the mutant p53-positive patches. Topical applications of caffeine to the dorsal skin of mice pretreated with UVB for 20 weeks resulted in enhanced apoptosis selectively in focal basal cell hyperplastic areas of the epidermis (putative precancerous lesions), but not in areas of the epidermis that only had diffuse hyperplasia. Our studies indicate that the chemopreventive effect of caffeine or green tea may occur by a proapoptotic effect preferentially in early precancerous lesions.

Contrasting action of flavonoids on phototoxic effects induced in human skin fibroblasts by UVA alone or UVA plus cyamemazine, a phototoxic neuroleptic

The potential protective effects of the flavanol catechin, the flavonol quercetin, the flavones, luteolin and rutin, and the isoflavones, genistein and daidzein, against the photo-oxidative stress induced by ultraviolet A radiation (UVA) and by phototoxic reactions resulting from the interaction of UVA with drugs and chemicals, has been assessed with cultured human skin fibroblasts. Lipid peroxidation and cell death have been chosen as model photobiological damage induced by UVA alone or photosensitized by cyamemazine (CMZ) and its photoproduct possessing phototoxic properties. Contrasting effects of flavonoids are observed. The flavanol, the flavonol and the flavones may protect against lipid peroxidation and cell death induced by 30 J cm(-2) of UVA alone or CMZ plus 10 J cm(-2) UVA. On the other hand, an amplification of the photodamage may be observed with isoflavones. A concentration-dependence study demonstrates that among the protective flavonoids, quercetin is the most efficient. The very effective protection brought by quercetin may result from its ability to scavenge reactive oxygen species produced by the photo-oxidative stress. However, the modification of membrane properties and the alteration of the lysosomal function by quercetin may not be neglected in these protective effects. The amplification of the photodamage by isoflavones is in sharp contrast with previous literature data demonstrating photoprotection by genistein. As a consequence, it may be concluded that an eventual antioxidant action of genistein may strongly depend on cells and photosensitizers. Furthermore such contrasting pro-versus anti-oxidant effects have to be taken into account when using flavonoid mixtures of plant extracts.

Ablation of either p21 or Bax prevents p53-dependent apoptosis induced by green tea polyphenol epigallocatechin-3-gallate

Treatment with epigallocatechin-3-gallate (EGCG), a polyphenolic compound of green tea, results in activation of p53 and induction of apoptosis in prostate cancer LnCaP cells. However, no direct evidence has delineated the role of p53 and p53-dependent pathways in EGCG-mediated apoptosis. To understand the mechanism of negative growth regulation of prostate cancer cells by EGCG we undertook a genetic approach and generated an isogenic pair of prostate carcinoma cells PC3 (p53-/-) by stably introducing a cDNA encoding wild-type p53. Treatment of the resultant cells, PC3-p53, with EGCG led to, as reported earlier in LnCaP cells, an increase in p53 protein, which exacerbated both G1 arrest and apoptosis. This response was accompanied by an increase in the levels of p21 and Bax. The cells lacking p53 continued to cycle and did not undergo apoptosis upon treatment with similar concentrations of EGCG, thus establishing the action of EGCG in a p53-dependent manner. This observation was revalidated in another prostate cancer LNCaP cells harboring wild-type p53. Inactivation of p53 using small interfering RNA (siRNA) rendered these cells resistant to EGCG-mediated apoptosis. Because p53 activation led to increase in p21 and Bax, we investigated whether these two proteins are important in this process. Ablation of p21 protein by siRNA prevented G1 arrest and apoptosis in PC3-p53 cells. The p53-dependent increase in Bax expression altered the Bax/Bcl-2 ratio and paralleled the activation of caspase 9 and 3 and cleavage of PARP. Transfection of cells with Bax siRNA abolished these effects and inhibited apoptosis but did not affect the accumulation of the cells in G1. In summary, using isogenic cell lines and siRNA, we have clearly demonstrated that EGCG activates growth arrest and apoptosis primarily via p53-dependent pathway that involves the function of both p21 and Bax such that down-regulation of either molecule confers a growth advantage to the cells.

Coffee, tea, and caffeine consumption and incidence of colon and rectal cancer

BACKGROUND

Frequent coffee consumption has been associated with a reduced risk of colorectal cancer in a number of case-control studies. Cohort studies have not revealed such an association but were limited in size. We explored the association between consumption of coffee and tea and the incidence of colorectal cancer in two large prospective cohorts of women and men.

METHODS

We used data from the Nurses' Health Study (women) and the Health Professionals' Follow-up Study (men). Consumption of coffee and tea and total caffeine intake were assessed and updated in 1980, 1984, 1986, 1990, and 1994 among women and in 1986, 1990, and 1994 among men. The incidence of cancer of the colon or rectum was ascertained through 1998. Hazard ratios were calculated using Cox proportional hazards models that adjusted for potential confounders. All tests of statistical significance were two-sided.

RESULTS

During almost 2 million person-years of follow-up, 1438 cases of colorectal cancer were observed. Consumption of caffeinated coffee or tea with caffeine or caffeine intake was not associated with the incidence of colon or rectal cancer in either cohort. For both cohorts combined, the covariate-adjusted hazard ratio for colorectal cancer associated with consumption of each additional cup of caffeinated coffee was 0.99 (95% confidence interval [CI] = 0.96 to 1.03). However, participants who regularly consumed two or more cups of decaffeinated coffee per day had a 52% (95% CI = 19% to 71%) lower incidence of rectal cancer than those who never consumed decaffeinated coffee.

CONCLUSIONS

Consumption of caffeinated coffee, tea with caffeine, or caffeine was not associated with incidence of colon of rectal cancer, whereas regular consumption of decaffeinated coffee was associated with a reduced incidence of rectal cancer.

Epigallocatechin gallate induces telomere fragmentation in HeLa and 293 but not in MRC-5 cells

Telomeres are the tandem repetitive sequence at the end of chromosomes and its integrity is crucial for cell vitality. We studied the effect of (-)-epigallocatechin-3-gallate (EGCG), one of the major tea polyphenols, on telomeres in HeLa, 293 cells and MRC-5 fibroblasts. At concentrations of above 50 microM, EGCG was found to causes telomere fragmentation in HeLa cells as a result of single-strand breaks in a dose-dependent manner. Treatment of EGCG also caused telomere fragmentation in 293 cells but had little or only marginal effect on MRC-5 fibroblasts. The telomere fragments detected by electrophoresis showed a unique size distribution that seems to suggest that the strand breaks were not produced randomly, but with preference at some specific sites. We speculate that the differential effect of EGCG in inducing telomere fragmentation in HeLa and 293 verse MRC-5 cells might be relevant to the apoptosis-inducing effect of EGCG on cancerous cells but not on normal cells.

Inhibition of carcinogenesis by polyphenols: evidence from laboratory investigations

Many plant polyphenolic compounds have been shown to have cancer-preventing activities in laboratory studies. For example, tea and tea preparations have been shown to inhibit tumorigenesis in a variety of animal models of carcinogenesis, involving organ sites such as the skin, lungs, oral cavity, esophagus, stomach, liver, pancreas, small intestine, colon, and prostate. In some of these models, inhibitory activity was demonstrated when tea was administered during the initiation, promotion, or progression stage of carcinogenesis. The cancer-preventing activities of these and other polyphenols, such as curcumin, genistein, and quercetin, are reviewed. In studies in vitro, many of these compounds have been shown to affect signal transduction pathways, leading to inhibition of cell growth and transformation, enhanced apoptosis, reduced invasive behavior, and slowed angiogenesis. However, the concentrations used in cell culture studies were much higher than those found in vivo. If we propose mechanisms for cancer prevention on the basis of cell line experiments, then these activities must be demonstrated in vivo. The bioavailability, ie, tissue and cellular concentrations, of dietary polyphenols is a determining factor in their cancer-preventing activity in vivo. For example, compounds such as curcumin are effective when applied topically to the skin or administered orally to affect the colon but are not effective in internal organs such as the lungs. More in-depth studies on bioavailability should facilitate correlation of mechanisms determined in vitro with in vivo situations, increase our understanding of dose-response relationships, and facilitate extrapolation of results from animal studies to human situations.

Molecular and cellular effects of green tea on oral cells of smokers: A pilot study

Studies in cell culture and laboratory animals have shown that green tea and its major component, epigallocatechin-3-gallate, inhibit cell growth and reduce tumor incidence. However, results of epidemiological studies have generated inconsistent, sometimes conflicting data regarding protection by green tea against human cancers. To clarify the findings of these laboratory studies in application to humans, we conducted a pilot intervention study with three heavy smokers (> 10 cigarettes/day) and three nonsmokers (never smokers) in order to evaluate the molecular and cellular effects of drinking green tea using human oral cells as an investigative tool. Green tea total extract (400-500 mg/cup, 5 cups/day) was administered in drinking water to the subjects for four weeks. Two oral cytology samples were taken weekly for measurements of tobacco carcinogen-induced DNA damage, including bulky adducts and oxidized bases, cell growth, DNA content, and apoptosis. The study showed that during the course of green tea administration smoking-induced DNA damage was decreased, cell growth was inhibited, and the percentage of cells in S phase was reduced, cells accumulated in G1 phase (cyclin D1 positive), DNA content became more diploid and less aneuploid, and p53, Caspase-3, and TUNEL, markers of apoptosis, were increased. The study, although preliminary, indicates that drinking green tea reduced the number of damaged cells in smokers by inducing cell growth arrest and apoptosis, a mechanism similar to that observed in cultured cells and animals. These results warrant a large-scale intervention trial to further verify the role of green tea in the prevention of oral cancer in smokers.

Effects of tea polyphenols on signal transduction pathways related to cancer chemoprevention

The inhibition of carcinogenesis by tea and tea polyphenols has been demonstrated in different animal models by many investigators. The mechanisms of this inhibitory activity have also been investigated extensively, mostly in cell culture systems, but no clear conclusion can be reached concerning the cancer preventive mechanisms in vivo. In this article, we reviewed the possible mechanisms, which include the inhibition of specific protein kinase activities, blocking receptor-mediated functions, and inhibition of proteases. These events may lead to cell cycle regulation, growth inhibition, enhanced apoptosis, inhibition of angiogenesis, and inhibition of invasion and metastases. The possible complications of translating results obtained in cell culture studies to animals and humans are discussed. It is likely that multiple signal transduction pathways are involved in the inhibition of carcinogenesis by tea constituents. The relative importance of these pathways needs to be determined in vivo.

Green Tea Epigallocatechin-3-Gallate Mediates T Cellular NF-κB Inhibition and Exerts Neuroprotection in Autoimmune Encephalomyelitis

Recent studies in multiple sclerosis and its animal model, experimental autoimmune encephalomyelitis (EAE), point to the fact that even in the early phase of inflammation, neuronal pathology plays a pivotal role in the sustained disability of affected individuals. We show that the major green tea constituent, (-)-epigallocatechin-3-gallate (EGCG), dramatically suppresses EAE induced by proteolipid protein 139-151. EGCG reduced clinical severity when given at initiation or after the onset of EAE by both limiting brain inflammation and reducing neuronal damage. In orally treated mice, we found abrogated proliferation and TNF-alpha production of encephalitogenic T cells. In human myelin-specific CD4+ T cells, cell cycle arrest was induced, down-regulating the cyclin-dependent kinase 4. Interference with both T cell growth and effector function was mediated by blockade of the catalytic activities of the 20S/26S proteasome complex, resulting in intracellular accumulation of IkappaB-alpha and subsequent inhibition of NF-kappaB activation. Because its structure implicates additional antioxidative properties, EGCG was capable of protecting against neuronal injury in living brain tissue induced by N-methyl-D-aspartate or TRAIL and of directly blocking the formation of neurotoxic reactive oxygen species in neurons. Thus, a natural green tea constituent may open up a new therapeutic avenue for young disabled adults with inflammatory brain disease by combining, on one hand, anti-inflammatory and, on the other hand, neuroprotective capacities.

Melanin acts as a potent UVB photosensitizer to cause an atypical mode of cell death in murine skin

Melanin protects the skin against DNA damage induced by direct absorption of sunlight's UV radiation. Yet, irradiating melanin in vitro or in cultured cells also generates active oxygen species such as superoxide, which can indirectly induce oxidative base lesions and DNA strand breaks. This photosensitization is greater for pheomelanin (yellow and red melanin) than for eumelanin (brown and black). The in vivo photosensitizing ability of melanin is unknown. We used congenic mice of black, yellow, and albino coat colors to investigate the induction of DNA lesions and apoptosis after exposure to predominantly UVB (280-320 nm) or UVA (320-400 nm) radiation. Cyclobutane pyrimidine dimers induced by direct UVB absorption were equal in all three strains, as was apoptosis measured as sunburn cells or as keratinocytes containing active caspase-3. However, terminal deoxynucleotidyltransferase-mediated dUTP nick end-labeling (TUNEL)-positive cells were approximately 3-fold more frequent in black and yellow mice after UVB or UVA irradiation than in albino. In epidermal sheets, TUNEL-positive cells lined the upper portion of the hair follicle, consistent with UV-induced photosensitization by melanin in the hair shaft. Because the concentration of eumelanin in black mice was three times that of pheomelanin in yellow mice, pheomelanin had 3-fold greater specific activity. We conclude that UV-irradiated melanin, particularly pheomelanin, photosensitizes adjacent cells to caspase-3 independent apoptosis, and this occurs at a frequency greater than the apoptosis induced by direct DNA absorption of UV. Melanin-induced apoptosis may contribute to the increased sensitivity of individuals with blonde and red hair to sunburn and skin cancer.

Silibinin protects against photocarcinogenesis via modulation of cell cycle regulators, mitogen-activated protein kinases, and Akt signaling

Here, we assessed the protective effect of silibinin on UVB-induced skin carcinogenesis in SKH-1 hairless mice. Topical application of silibinin before or immediately after UVB exposure or its dietary feeding resulted in a strong protection against photocarcinogenesis, in terms of tumor multiplicity (60-66%; P < 0.001), tumor volume per mouse (93-97%; P < 0.001) and tumor volume per tumor (80-91%; P < 0.001). Silibinin also moderately inhibited tumor incidence (5-15%; P < 0.01) and delayed tumor latency period (up to 4 weeks; P < 0.01-0.001). To investigate in vivo molecular mechanisms of silibinin efficacy, tumors and uninvolved skin from tumor-bearing mice were examined immunohistochemically for proliferation, p53, apoptosis, and activated caspase-3. Silibinin treatment showed a strong decrease (P < 0.001) in proliferating cell nuclear antigen-positive cells and an increase in p53-positive (P < 0.005-0.001), terminal deoxynucleotidyltransferase-mediated nick end labeling-positive (P < 0.005-0.001), and cleaved caspase-3-positive cells (P < 0.001). Western blot analysis of normal skin and tumor lysates showed that silibinin decreases the levels of cyclin-dependent kinase 2 and cyclin-dependent kinase 4 and associated cyclins A, E, and D1, together with an up-regulation of Cip1/p21, Kip1/p27, and p53. Silibinin also showed a strong phosphorylation of extracellular signal-regulated protein kinase 1/2, stress-activated protein kinase/c-JUN NH2-terminal kinase 1/2, and p38 mitogen-activated protein kinases but inhibited Akt phosphorylation and decreased survivin levels with an increase in cleaved caspase-3. Together, these results show a strong preventive efficacy of silibinin against photocarcinogenesis, which involves the inhibition of DNA synthesis, cell proliferation, and cell cycle progression and an induction of apoptosis. Furthermore, these results also identify in vivo molecular mechanisms of silibinin efficacy against photocarcinogenesis.

In vitro transdermal delivery of the major catechins and caffeine from extract of Camellia sinensis

The aim of this study was to investigate the feasibility of the transdermal delivery of catechins and caffeine from green tea extract. Drug-in-adhesive patches containing 1.35, 1.03, 0.68, and 0.32 mg cm(-2) green tea extract were formulated and the dissolution of (-)-epigallocatechin gallate (EGCg), (-)-epigallocatechin (EGC) and (-)-epicatechin (EC) from these was determined. Transdermal delivery was determined across full thickness pig ear skin from saturated solutions of green tea extract in pH 5.5 citrate-phosphate buffer, polyethylene glycol 400 and a 50:50 mixture of the citrate phosphate buffer and polyethylene glycol in addition to patches containing 1.35 mg cm(-2) green tea extract. Dissolution experiments indicated first order release which was dose dependent in respect of the loading level, although the amounts permeated were not always proportional to the amounts in the formulation. The highest percentage permeation of EGCg was found to be from the patch formulation. EGCg, EGC and EC were all successfully delivered transdermally from saturated solutions and adhesive patches containing green tea extract in this study. There was some evidence for the dermal metabolism of EGCg, but after 24 h 0.1% permeated from the patches containing 1.35 mg cm(-2) green tea extract. This was equivalent to the percentage absorbed after intragastric administration of green tea extract in rats. In addition, the concentration of EGCg in the Franz cell receptor chamber after 24 h permeation from the 0.9 cm diameter patch containing 1.35 mg cm(-2) was within the range of Cmax plasma levels achieved after oral dosing of 2.2-4.2 gm(-2) green tea extract. Caffeine was also delivered at concentrations above those previously reported.

Stimulatory Effect of Topical Application of Caffeine on UVB-Induced Apoptosis in the Epidermis of p53 and Bax Knockout Mice

Shaved male or female p53(-/-) C57BL/6J mice and their wild-type littermates were irradiated once with UVB (60 mJ/cm(2)). The UVB-induced increase in apoptotic sunburn cells in p53(-/-) mice at 6-10 h after exposure to UVB was only 10-30% of that observed after treatment of p53(+/+) mice with UVB. Topical applications of caffeine immediately after UVB irradiation in female p53(+/+) or p53(-/-) mice enhanced the UVB-induced increase in apoptotic sunburn cells 6 h later by 127% and 563%, respectively. In another study, shaved female Bax(-/-) C57BL/6J mice and their wild-type littermates were irradiated once with UVB (60 mJ/cm(2)). The UVB-induced increase in apoptotic sunburn cells in Bax(-/-) mice at 6 h after exposure to UVB was only 14% of that observed after treatment of Bax(+/+) mice with UVB. Topical application of caffeine immediately after irradiation of Bax(+/+) or Bax(-/-) mice with UVB enhanced the UVB-induced increases in apoptotic sunburn cells at 6 h by 214% and 467%, respectively, and topical application of caffeine immediately after irradiation of Bax(+/+) or Bax(-/-) mice with UVB enhanced the UVB-induced increase in caspase 3 (active form) positive cells at 6 h by 253% and 750%, respectively. The results indicate that UVB-induced increases in apoptosis in the epidermis of wild-type mice are predominantly (but not entirely) by p53- and Bax-dependent pathways and that topical application of caffeine can enhance UVB-induced increases in apoptosis by p53- and Bax-independent pathways.

Caffeine inhibits cell proliferation by G0/G1 phase arrest in JB6 cells

Caffeine is a major biologically active constituent in coffee and tea. Because caffeine has been reported to inhibit carcinogenesis in UVB-exposed mice, the cancer-preventing effect of caffeine has attracted considerable attention. In the present study, the effect of caffeine in quiescent (G0 phase) cells was investigated. Pretreatment with caffeine suppressed cell proliferation in a dose-dependent manner 36 h after addition of fetal bovine serum as a cell growth stimulator. Analysis by flow cytometry showed that caffeine suppressed cell cycle progression at the G0/G1 phase, i.e., 18 h after addition of fetal bovine serum, the percentages of cells in G0/G1 phase in 1 mM caffeine-treated cells and in caffeine-untreated cells were 61.7 and 29.0, respectively. The percentage of cells in G0/G1 phase at 0 h was 75.5. Caffeine inhibited phosphorylation of retinoblastoma protein at Ser780 and Ser807/Ser811, the sites where retinoblastoma protein has been reported to be phosphorylated by cyclin-dependent kinase 4 (cdk4). Furthermore, caffeine inhibited the activation of the cyclin D1-cdk4 complex in a dose-dependent manner. However this compound did not directly inhibit the activity of this complex. In addition, caffeine did not affect p16INK4 or p27Kip1 protein levels, but inhibited the phosphorylation of protein kinase B (Akt) and glycogen synthase kinase 3beta. Our results showed that caffeine suppressed the progression of quiescent cells into the cell cycle. The inhibitory mechanism may be due to the inhibition of cell growth signal-induced activation of cdk4, which may be involved in the inhibition of carcinogenesis in vivo.

Apoptosis as a novel target for cancer chemoprevention

Cancer chemopreventive agents are typically natural products or their synthetic analogs that inhibit the transformation of normal cells to premalignant cells or the progression of premalignant cells to malignant cells. These agents are believed to function by modulating processes associated with xenobiotic biotransformation, with the protection of cellular elements from oxidative damage, or with the promotion of a more differentiated phenotype in target cells. However, an increasing number of chemopreventive agents (e.g., certain retinoids, nonsteroidal anti-inflammatory drugs, polyphenols, and vanilloids) have been shown to stimulate apoptosis in premalignant and malignant cells in vitro or in vivo. Apoptosis is arguably the most potent defense against cancer because it is the mechanism used by metazoans to eliminate deleterious cells. Many chemopreventive agents appear to target signaling intermediates in apoptosis-inducing pathways. Inherently, the process of carcinogenesis selects against apoptosis to initiate, promote, and perpetuate the malignant phenotype. Thus, targeting apoptosis pathways in premalignant cells--in which these pathways are still relatively intact--may be an effective method of cancer prevention. In this review, we construct a paradigm supporting apoptosis as a novel target for cancer chemoprevention by highlighting recent studies of several chemopreventive agents that engage apoptosis pathways.

Strong inhibitory effects of common tea catechins and bioflavonoids on the O-methylation of catechol estrogens catalyzed by human liver cytosolic catechol-O-methyltransferase

In the present investigation, we studied the inhibitory effects of three tea catechins [catechin, epicatechin, and (-)-epigallocatechin-3-O-gallate] and two bioflavonoids (quercetin and fisetin) on the O-methylation of 2- and 4-hydroxyestradiol (2-OH-E(2) and 4-OH-E(2), respectively) by human liver cytosolic catechol-O-methyltransferase (COMT). We found that catechin and epicatechin each inhibited the O-methylation of 2-OH-E(2) and 4-OH-E(2) in a concentration-dependent manner. The IC(50) values for inhibition of 2-OH-E(2) methylation by catechin and epicatechin were 14 to 17 microM and 44 to 65 microM, respectively, and their IC(50) values for inhibition of 4-OH-E(2) methylation were 5 to 7 microM and 10 to 18 microM, respectively. Our data showed that these two catechins had 2- to 6-fold higher inhibition potency for the O-methylation of 4-OH-E(2) than for the O-methylation of 2-OH-E(2). (-)-Epigallocatechin-3-O-gallate was found to have a distinctly high inhibition potency for the O-methylation of 2- and 4-OH-E(2) (IC(50) values of 0.04-0.07 microM and 0.2-0.5 microM, respectively). The crude extracts from green tea and black tea also showed very strong activity in inhibiting human liver COMT-mediated O-methylation of catechol estrogens. We also determined, for comparison, two common bioflavonoids (quercetin and fisetin) for their inhibitory effects on human liver COMT-mediated O-methylation of catechol estrogens. The IC(50) values for quercetin and fisetin were 0.9 to 1.5 microM and 3.3 to 4.5 microM, respectively, for inhibiting the O-methylation of 2-OH-E(2), and 0.5 to 1.2 microM and 2.6 to 4.2 microM, respectively, for inhibiting the O-methylation of 4-OH-E(2). Enzyme kinetic analyses showed that both tea catechins and bioflavonoids inhibited human liver COMT-mediated O-methylation of 4-OH-E(2) (a representative substrate) with a mixed mechanism of inhibition (competitive plus noncompetitive). In summary, the catechol-containing tea catechins and bioflavonoids are strong inhibitors of human liver COMT-mediated O-methylation of catechol estrogens. More studies are warranted to determine the extent of such inhibition in human subjects and the potential biological consequences.

Bioadhesive Transdermal Film Containing Caffeine

The aim of this work was to investigate in vitro the transdermal permeation of caffeine from a new bioadhesive film, using rabbit ear skin as a barrier. The effects of film composition and of the presence of penetration enhancers in the formulation were studied. The obtained fluxes were compared with those shown by commercial formulations. The results obtained indicate that the bioadhesive film gave rise to a higher transdermal permeation compared to a commercial gel and to a saturated solution of caffeine in water. Additionally, the film did not present the typical time lag of solution and gel. Another peculiar feature of the film is that the percentage of permeated active substance is much higher than that obtained from commercial formulations. Finally, it was possible to modulate caffeine permeation from the film by adding different enhancers/solvents.

Exceptionally high protection of photocarcinogenesis by topical application of (--)-epigallocatechin-3-gallate in hydrophilic cream in SKH-1 hairless mouse model: relationship to inhibition of UVB-induced global DNA hypomethylation

(--)-Epigallocatechin-3-gallate (EGCG) has been shown to have potent antiphotocarcinogenic activity, but it was required to develop a cream-based formulation for topical application. For topical application, we tested hydrophilic cream as a vehicle for EGCG. Treatment with EGCG ( approximately 1 mg/cm(2) skin area) in hydrophilic cream resulted in exceptionally high protection against photocarcinogenesis when determined in terms of tumor incidence, tumor multiplicity, and tumor size in a SKH-1 hairless mouse model. EGCG also inhibited malignant transformation of ultraviolet B (UVB)-induced papillomas to carcinomas. In order to determine the mechanism of prevention of photocarcinogenesis, we determined the effect of EGCG on global DNA methylation pattern using monoclonal antibodies against 5-methyl cytosine and DNA methyltransferase in the long-term UV-irradiated skin because altered DNA methylation silencing is recognized as a molecular hallmark of human cancer. We found that treatment with EGCG resulted in significant inhibition of UVB-induced global DNA hypomethylation pattern. Long-term application of EGCG did not show any apparent sign of toxicity in mice when determined in terms of skin appearance, lean mass, total bone mineral content, and total bone mineral density but showed reduction in fat mass when analyzed using dual-energy X-ray absorptiometry. These data suggest that hydrophilic cream could be a suitable vehicle for topical application of EGCG, and that EGCG is a promising candidate for future cancer therapies based on its influence on the epigenetic pathway.

Peroxisome proliferator-activated receptor beta (delta)-dependent regulation of ubiquitin C expression contributes to attenuation of skin carcinogenesis

The role of peroxisome proliferator-activated receptor-beta (PPARbeta) in the molecular regulation of skin carcinogenesis was examined. Increased caspase-3 activity associated with apoptosis was found in the skin of wild-type mice after tumor promotion with 12-O-tetradecanoylphorbol-13-acetate, and this effect was diminished in PPARbeta-null mice. The onset of tumor formation, tumor size, and tumor multiplicity induced from a two-stage carcinogen bioassay (7,12-dimethylbenz[a]anthracene/12-O-tetradecanoylphorbol-13-acetate) were significantly enhanced in PPARbeta-null mice compared with wild-type mice. To begin to characterize the molecular changes underlying this PPARbeta-dependent phenotype, microarray analysis was performed and a number of differentially regulated gene products were identified including ubiquitin C. Subsequent promoter analysis, reporter gene assays, site-directed mutagenesis, and electrophoretic mobility shift assays provide evidence that PPARbeta regulates ubiquitin C expression, and that ubiquitination of proteins is influenced by PPARbeta. These results strongly suggest that activation of PPARbeta-dependent target genes provides a novel strategy to inhibit tumor promotion and carcinogenesis.

Inhibition of AP-1 and Neoplastic Transformation by Fresh Apple Peel Extract

Consumption of fruits and vegetables has been associated with a low incidence of cancers and other chronic diseases. Previous studies suggested that fresh apples inhibit tumor cell proliferation. Here we report that oral administration of apple peel extracts decreased the number of nonmalignant and malignant skin tumors per mouse induced by 12-O-tetradecanolyphorbol-13-acetate (TPA) in 7,12-dimethylbenz(a)anthracene-initiated mouse skin. ESR analysis indicated that apple extract strongly scavenged hydroxyl (OH) and superoxide (O(2)(-)) radicals. Mechanistic studies showed that pretreatment with apple peel extract inhibited AP-1 transactivation induced by ultraviolet B irradiation or TPA in JB6 cells and AP-1-luciferase reporter transgenic mice. This inhibitory effect appears to be mediated by the inhibition of ERKs and JNK activity. The results provide the first evidence that an extract from fresh apple peel extract may inhibit tumor promoter-induced carcinogenesis and associated cell signaling, and suggest that the chemopreventive effects of fresh apple may be through its antioxidant properties by blocking reactive oxygen species-mediated AP-1-MAPK activation.