Tea polyphenols: prevention of cancer and optimizing health

The tea plant Camellia sinesis is cultivated in >30 countries. Epidemiologic observations and laboratory studies have indicated that polyphenolic compounds present in tea may reduce the risk of a variety of illnesses, including cancer and coronary heart disease. Most studies involved green tea, however; only a few evaluated black tea. Results from studies in rats, mice, and hamsters showed that tea consumption protects against lung, forestomach, esophagus, duodenum, pancreas, liver, breast, colon, and skin cancers induced by chemical carcinogens. Other studies showed the preventive effect of green tea consumption against atherosclerosis and coronary heart disease, high blood cholesterol concentrations, and high blood pressure. Because the epidemiologic studies and research findings in laboratory animals have shown the chemopreventive potential of tea polyphenols in cancer, the usefulness of tea polyphenols for humans should be evaluated in clinical trials. One such phase 1 clinical trial is currently under way at the MD Anderson Cancer Center in collaboration with Memorial Sloan-Kettering Cancer Center. This study will examine the safety and possible efficacy of consuming the equivalent of > or =10 cups (> or =2.4 L) of green tea per day. The usefulness of tea polyphenols may be extended by combining them with other consumer products such as food items and vitamin supplements. This "designer-item" approach may be useful for human populations, but it requires further study.

Photodynamic therapy with the phthalocyanine photosensitizer Pc 4 of SW480 human colon cancer xenografts in athymic mice

Photodynamic therapy (PDT) using the silicon phthalocyanine photosensitizer Pc 4 [HOSiPcOSi(CH3)2(CH2)3N-(CH3)2] is an oxidative stress associated with induction of apoptosis in various cell types. We assessed the effectiveness of Pc 4-PDT on SW480 colon cancer xenografts grown in athymic nude mice. Animals bearing xenografts were treated with 1 mg/kg body weight Pc 4 and 48 h later were irradiated with 150 J/cm2 672-nm light from a diode laser delivered at 150 mW/cm2. Biochemical studies were performed in xenografts resected at various time points up to 26 h after Pc 4-PDT treatment, whereas tumor size was evaluated over a 4-week period in parallel experiments. In the tumors resected for biochemical studies, apoptosis was visualized by activation of caspase-9 and caspase-3 and a gradual increase in the cleavage of the nuclear enzyme poly(ADP-ribose) polymerase (PARP) to a maximum of approximately 60% of the total PARP present at approximately 26 h. At that time all Pc 4-PDT-treated tumors had regressed significantly. Two signaling responses that have previously been shown to be associated with Pc 4-PDT-induced apoptosis in cultured cells, p38 mitogen-activated protein kinase and p21/WAF1/Cip1, were examined. A marked increase in phosphorylation of p38 was observed within 1 h after Pc 4-PDT without changes in levels of the p38 protein. Levels of p21 were not altered in the xenografts in correspondence with the presence of mutant p53 in SW480 cells. Evaluation of tumor size showed that tumor growth resumed after a delay of 9-15 days. Our results suggest that: (a) Pc 4-PDT is effective in the treatment of SW480 human colon cancer xenografts independent of p53 status; (b) PARP cleavage may be mediated by caspase-9 and caspase-3 activation in the Pc 4-PDT-treated tumors; and (c) p38 phosphorylation may be a trigger of apoptosis in response to PDT in vivo in this tumor model.

Biomelanin antioxidants in cosmetics: assessment based on inhibition of lipid peroxidation

Acute adverse effects of ultraviolet (UV) radiation in humans include sunburn, photosensitivity reactions and immunological suppression. Chronic exposure to UV light, particularly the UVB (290-320 nm) component of the UV radiation, and certain environmental chemicals increase the risk of nonmelanoma skin cancer and play a major role in cutaneous aging. The lipid peroxidation (LPO) of biomembranes, mediated by reactive oxygen species and free radicals, is one of the major causes of cellular damage induced by UV radiation and toxins. Antioxidants, such as vitamin E, vitamin C and melanins, are reactive oxygen and radical scavengers, thereby minimizing the light- and toxin-induced tissue destruction. We examined the influence of 8 biotechnically produced polyphenolic melanins on the LPO of microsomal membranes in comparison with alpha-tocopherol, ascorbate and synthetic melanin. All biomelanins showed better inhibition of peroxidative damage than synthetic melanin. Three of the 8 tested drugs inhibited the LPO at least as effectively as vitamin C and vitamin E. The combination of the most effective biomelanin with both vitamin C and vitamin E resulted in greater LPO inhibition than caused by each agent alone. Our data show that biomelanins are potent inhibitors of the peroxidative destruction of biomembranes, indicating that these compounds may be useful antioxidative agents in cosmetic preparations.

Involvement of caspase-3 in epigallocatechin-3-gallate-mediated apoptosis of human chondrosarcoma cells

Green tea polyphenol-(-)epigallocatechin-3-gallate (EGCG)-is a potent chemopreventive agent in many test systems and has been shown to inhibit tumor promotion and induce apoptosis. In this study we describe a novel observation that EGCG displayed strong inhibitory effects on the proliferation and viability of HTB-94 human chondrosarcoma cells in a dose-dependent manner and induced apoptosis. Investigation of the mechanism of EGCG-induced apoptosis revealed that treatment with EGCG resulted in DNA fragmentation, induction of caspase-3/CPP32 activity, and cleavage of the death substrate poly(ADP-ribose)polymerase (PARP). Pretreatment of cells with a synthetic pan-caspase inhibitor (Z-VAD-FMK) and a caspase-3-specific inhibitor (DEVD-CHO) prevented EGCG-induced PARP cleavage. The induction of apoptosis by EGCG via activation of caspase-3/CPP32-like proteases may provide a mechanistic explanation for its antitumor effects.

Green tea polyphenol epigallocatechin-3-gallate differentially modulates nuclear factor kappaB in cancer cells versus normal cells

Green tea has shown remarkable anti-inflammatory and cancer chemopreventive effects in many animal tumor bioassays, cell culture systems, and epidemiological studies. Many of these biological effects of green tea are mediated by epigallocatechin 3-gallate (EGCG), the major polyphenol present therein. We have earlier shown that EGCG treatment results in apoptosis of several cancer cells, but not of normal cells (J. Natl. Cancer Inst. 89, 1881-1886 (1997)). The mechanism of this differential response of EGCG is not known. In this study, we investigated the involvement of NF-kappaB during these differential responses of EGCG. EGCG treatment resulted in a dose-dependent (i) inhibition of cell growth, (ii) G0/G1-phase arrest of the cell cycle, and (iii) induction of apoptosis in human epidermoid carcinoma (A431) cells, but not in normal human epidermal keratinocytes (NHEK). Electromobility shift assay revealed that EGCG (10-80 microM) treatment results in lowering of NF-kappaB levels in both the cytoplasm and nucleus in a dose-dependent manner in both A431 cells and NHEK, albeit at different concentrations. EGCG treatment was found to result in a dose-based differential inhibition of TNF-alpha- and LPS-mediated activation of NF-kappaB in these cells. The inhibition of NF-kappaB constitutive expression and activation in NHEK was observed only at high concentrations. The immunoblot analysis also demonstrated a similar pattern of inhibition of the constitutive expression as well as activation of NF-kappaB/p65 nuclear protein. This inhibition of TNF-alpha-caused NF-kappaB activation was mediated via the phosphorylative degradation of its inhibitory protein IkappaBalpha. Taken together, EGCG was found to impart differential dose-based NF-kappaB inhibitory response in cancer cells vs normal cells; i.e., EGCG-mediated inhibition of NF-kappaB constitutive expression and activation was found to occur at much higher dose of EGCG in NHEK as compared to A431 cells. This study suggests that EGCG-caused cell cycle deregulation and apoptosis of cancer cells may be mediated through NF-kappaB inhibition.

Differential antiproliferative and apoptotic response of sanguinarine for cancer cells versus normal cells

Sanguinarine, derived from the root of Sanguinaria canadendid, has been shown to possess antimicrobial, anti-inflammatory, and antioxidant properties. Here we compared the antiproliferative and apoptotic potential of sanguinarine against human epidermoid carcinoma (A431) cells and normal human epidermal keratinocytes (NHEKs). Sanguinarine treatment was found to result in a dose-dependent decrease in the viability of A431 cells as well as NHEKs albeit at different levels because sanguinarine-mediated loss of viability occurred at lower doses and was much more pronounced in the A431 carcinoma cells than in the normal keratinocytes. DNA ladder assay demonstrated that compared to vehicle-treated control, sanguinarine treatment of A431 cells resulted in an induction of apoptosis at 1-, 2-, and 5-microM doses. Sanguinarine treatment did not result in the formation of a DNA ladder in NHEKs, even at the very high dose of 10 microM. The induction of apoptosis by sanguinarine was also evident by confocal microscopy after labeling the cells with annexin V. This method also identified necrotic cells, and sanguinarine treatment also resulted in the necrosis of A431 cells. The NHEKs showed exclusively necrotic staining at high doses (2 and 5 microM). We also explored the possibility of cell cycle perturbation by sanguinarine in A431 cells. The DNA cell cycle analysis revealed that sanguinarine treatment did not significantly affect the distribution of cells among the different phases of the cell cycle in A431 cells. We suggest that sanguinarine could be developed as an anticancer drug.

Growth inhibition, cell-cycle dysregulation, and induction of apoptosis by green tea constituent (-)-epigallocatechin-3-gallate in androgen-sensitive and androgen-insensitive human prostate carcinoma cells

Prostate cancer (PCA) is the most prevalent cancer diagnosed and the second leading cause of cancer-related deaths among men in the United States. Descriptive epidemiological data suggest that androgens and environmental exposures play a key role in prostatic carcinogenesis. Since androgen action is intimately associated with proliferation and differentiation, at the time of clinical diagnosis in humans most PCA represent themselves as a mixture of androgen-sensitive and androgen-insensitive cells. Androgen-sensitive cells undergo rapid apoptosis upon androgen withdrawal. On the other hand, the androgen-insensitive cells do not undergo apoptosis upon androgen blocking, but maintain the molecular machinery of apoptosis. Thus, agents capable of inhibiting growth and/or inducing apoptosis in both androgen-sensitive and androgen-insensitive cells will be useful for the management of PCA. In the present study, we show that (-)-epigallocatechin-3-gallate (EGCG), the major polyphenolic constituent present in green tea, imparts antiproliferative effects against both androgen-sensitive and androgen-insensitive human PCA cells, and this effect is mediated by deregulation in cell cycle and induction of apoptosis. EGCG treatment was found to result in a dose-dependent inhibition of cell growth in both androgen-insensitive DU145 and androgen-sensitive LNCaP cells. In both the cell types, EGCG treatment also resulted in a dose-dependent G(0)/G(1)-phase arrest of the cell cycle as observed by DNA cell-cycle analysis. As evident by DNA ladder assay, confocal microscopy, and flow cytometry, the treatment of both DU145 and LNCaP cells with EGCG resulted in a dose-dependent apoptosis. Western blot analysis revealed that EGCG treatment resulted in (i) a dose-dependent increase of p53 in LNCaP cells (carrying wild-type p53), but not in DU145 cells (carrying mutant p53), and (ii) induction of cyclin kinase inhibitor WAF1/p21 in both cell types. These results suggest that EGCG negatively modulates PCA cell growth, by affecting mitogenesis as well as inducing apoptosis, in cell-type-specific manner which may be mediated by WAF1/p21-caused G(0)/G(1)-phase cell-cycle arrest, irrespective of the androgen association or p53 status of the cells.

Photodynamic therapy in dermatology

The combination of light and chemicals to treat skin diseases is widely practiced in dermatology. Within this broad use of light and drugs, in recent years the concept of photodynamic therapy (PDT) has emerged. PDT is a promising modality for the management of various tumors and nonmalignant diseases, based on the combination of a photosensitizer that is selectively localized in the target tissue and illumination of the lesion with visible light, resulting in photodamage and subsequent cell death. Moreover, the fluorescence of photosensitizing compounds is also utilized as a helpful diagnostic tool for the detection of neoplastic tissue. Intensive basic and clinical research culminated in the worldwide approval of PDT for bladder, esophageal, and lung cancer. The expanding use of this relatively new therapeutic modality in dermatology at many centers around the world has revealed its efficacy for the treatment of cutaneous precancer and cancer, as well as selected benign skin disorders. The following article summarizes the main principles of PDT considering the most recent developments and provides a comprehensive synopsis of the present status of the use of PDT in dermatology. (J Am Acad Dermatol 2000;42:389-413.)

LEARNING OBJECTIVE

At the conclusion of this learning activity, participants should be able to describe the basic concepts of PDT, including fundamental knowledge of the most relevant photosensitizers, the light sources, the mechanisms involved in PDT-mediated cell destruction, as well as the indications and limitations of photodynamic treatment of skin diseases.

Ultraviolet-B exposure of human skin induces cytochromes P450 1A1 and 1B1

The cytochromes P450 belong to a multigene superfamily and are responsible for the metabolic activation of both xenobiotics and endobiotics. The expression of cytochrome P450 genes in target cells is an important determinant of human susceptibility to cancers and other chemically initiated diseases. In this study using immunohistochemistry, reverse transcription polymerase chain reaction, and western blot analysis, we investigated the cellular distribution and localization of cytochrome P450 1A1 and cytochrome P450 1B1 in human skin, and their induction by ultraviolet-B. Through the use of immunohistochemistry, cytochrome P450 1A1 was found to be primarily localized in the basal cell layer of the epidermis in non-ultraviolet-B exposed skin, whereas cytochrome P450 1B1 was localized in the epidermal cells other than the basal cell layer. Thus, localizations of cytochrome P450 1A1 and cytochrome P450 1B1 in human skin are different and may be related to keratinocyte differentiation. Ultraviolet-B exposure to solar-ultraviolet-protected skin (buttock site) resulted in an ultraviolet-B dose-dependent (0-4 minimal erythema doses) and time-dependent (0-48 h) induction of both cytochrome P450 1A1 and cytochrome P450 1B1 in the epidermis. Reverse transcription polymerase chain reaction and western blot analyses revealed that exposure of human skin to ultraviolet-B (4 minimal erythema doses) resulted in enhanced expression of mRNA and protein of both cytochrome P450 1A1 and cytochrome P450 1B1 in the epidermis. Ultraviolet-B induction of both cytochrome P450 1A1 and cytochrome P450 1B1 in human skin will probably result in enhanced bioactivation of polycyclic aromatic hydrocarbons and other environmental pollutants to which humans are exposed, which in turn could make the human skin more susceptible to ultraviolet-B-induced skin cancers or allergic and irritant contact dermatitis.

Phthalocyanine 4-photodynamic therapy induces ceramide generation and apoptosis in acid sphingomyelinase-deficient mouse embryonic fibroblasts

Photodynamic therapy (PDT), a novel cancer treatment using a photosensitizer and visible light, produces an oxidative stress in cells that can lead to apoptosis. PDT with the phthalocyanine photosensitizer Pc 4 (Pc 4-PDT), causes increased generation of ceramide, a lipid mediator, and subsequent induction of apoptosis in various cell types. Formation of ceramide by acid sphingomyelinase (ASMase) in response to stress has been implicated in apoptotic cell death. We assessed the role of ASMase in photocytotoxicity using mouse embryonic fibroblasts (MEFs) isolated from ASMase knockout (k/o) and wild-type (wt) mice. Exposure of wt or k/o MEFs to Pc 4-PDT led to increased caspase-3 activity and subsequent apoptosis. Similarly, ceramide levels were elevated in both cell types post-PDT. We suggest that in MEFs, ASMase is dispensable for ceramide accumulation and induction of apoptosis after Pc 4-PDT.

Over-expression of cyclooxygenase-2 in human prostate adenocarcinoma

Aberrant or increased expression of cyclooxygenase (COX)-2 has been implicated in the pathogenesis of many diseases including carcinogenesis. COX-2 has been shown to be over-expressed in some human cancers. Employing semi-quantitative reverse transcription-PCR, immunoblotting, and immunohistochemistry we assessed COX-2 expression in samples of pair-matched benign and cancer tissue obtained from the same prostate cancer patient. Mean levels of COX-2 mRNA were 3.4-fold higher in prostate cancer tissue (n = 12) compared with the paired benign tissue. The immunoblot analysis demonstrated that as compared to benign tissue COX-2 protein was over-expressed in 10 of 12 samples examined. Immunohistochemical analysis also verified COX-2 over-expression in cancer than in benign tissue. To our knowledge, this is the first in vivo study showing an over-expression of COX-2 in prostate cancer. These data suggest that COX-2 inhibitors may be useful for prevention or therapy of prostate cancer in humans.

Green tea in chemoprevention of cancer

The concept of prevention of cancer using naturally occurring substances that could be included in the diet consumed by the human population is gaining increasing attention. Tea, next to water, is the most popularly consumed beverage in the world and it is grown in about 30 countries. Abundant data, amassed from several laboratories around the world in the last ten years, provided convincing evidence that polyphenolic antioxidants present in tea afford protection against cancer risk in many animal-tumor bioassay systems. The epidemiological studies, though inconclusive, have also suggested that the consumption of tea is associated with a lowered risk of cancer. Much of this work has been done on green tea; less is known about black tea. Green tea contains many polyphenolic antioxidants, and (-)-epigallocatechin-3-gallate (EGCG) is the key polyphenolic antioxidant believed to be responsible for most of the cancer chemopreventive properties of green tea. This review will discuss these effects and the molecular mechanisms associated with the biological response to green-tea polyphenols.

Prevention of UVB-induced immunosuppression in mice by the green tea polyphenol (-)-epigallocatechin-3-gallate may be associated with alterations in IL-10 and IL-12 production

UV exposure of the skin, particularly UVB (290-320 nm), causes adverse biological effects, including alterations in cutaneous immune cells, photoaging and photocarcinogenesis. Several studies have shown that polyphenolic compounds isolated from green tea afford protection against UVB-induced inflammatory responses and photocarcinogenesis in murine models. In this study we show that topical application of (-)-epigallocatechin-3-gallate (EGCG) (3 mg/mouse), a major polyphenolic component of green tea, before a single low dose UVB exposure (72 mJ/cm(2)) to C3H/HeN mice prevented UVB-induced inhibition of the contact hypersensitivity response and tolerance induction to the contact sensitizer 2, 4-dinitrofluorobenzene. Topical application of EGCG before UVB exposure reduced the number of CD11b+ monocytes/macrophages and neutrophils infiltrating into skin inflammatory lesions, which are considered to be responsible for creating the UV-induced immunosuppressive state. In addition, application of EGCG before UVB exposure decreased UVB-induced production of the immunomodulatory cytokine interleukin (IL)-10 in skin as well as in draining lymph nodes (DLN), whereas production of IL-12, which is considered to be a mediator and adjuvant for induction of contact sensitivity, was found to be markedly increased in DLN when compared with UVB alone-exposed mice. Taken together, our data demonstrate that EGCG protects against UVB-induced immunosuppression and tolerance induction by: (i) blocking UVB-induced infiltration of CD11b+ cells into the skin; (ii) reducing IL-10 production in skin as well as in DLN; (iii) markedly increasing IL-12 production in DLN. Protection against UVB-induced immunosuppression by EGCG may be associated with protection against UVB-induced photocarcinogenesis.

Photoprotective effect of black tea extracts against UVB-induced phototoxicity in skin

In previous studies, we showed that green tea and black tea extracts and their major polyphenolic constituents protect against UVB light-induced carcinogenesis in murine skin. All of these studies required chronic administration of tea extracts or specific constituents either topically or orally. However, it is not known whether acute or subchronic administration of black tea extracts or constituents can ameliorate UVB-induced early effects in skin. In the present study, cultured keratinocytes and mouse and human skin were employed to assess the effect of both oral and topical administration of standardized black tea extract (SBTE) and its two major polyphenolic subfractions namely BTF1 and BTF2 against UVB-induced photodamage. In SKH-1 hairless mice, topical application of SBTE (0.2 mg/cm2) prior to UVB exposure (180 mJ/cm2) resulted in 40% reduced incidence and 64% reduced severity of erythema and 50% reduction in skinfold thickness by day 6 when compared to nontreated UVB-exposed animals. The SBTE was also effective in protecting against UVB-induced erythema in human volunteers. Administration of SBTE 5 min after UVB irradiation was similarly effective in reducing UVB-induced inflammation in both murine and human skin. The major polyphenolic subfractions, BTF1 and BTF2, were also effective in protecting in mouse skin. The SBTE subfractions inhibited UVB-induced tyrosine phosphorylation of epidermal growth factor receptor (EGFR). The UVB irradiation of human epidermoid carcinoma cells resulted in 3.3-fold induction of tyrosine phosphorylation of EGFR. Pretreatment with BTF1 and BTF2 reduced tyrosine phosphorylation of EGFR by 53% and 31%, respectively. The UVB-mediated enhanced expression of the early response genes, c-fos and c-jun in human epidermal keratinocytes was reduced in a dose-dependent manner by SBTE. Topical application of SBTE was also effective in reducing accumulation of c-fos and p53 proteins by 82% and 78%, respectively, in UVB-exposed mouse skin. These data provide evidence that constituents of black tea can abrogate UVB-induced erythema and associated early events in murine and human skin.

Upregulation of E2F transcription factors in chemically induced mouse skin tumors

E2F family of transcription factors plays an important role in cell cycle regulation, oncogenesis and differentiation. E2Fs are a family of heterodimeric transcription factors composed of E2F-like and DP-like subunits. They regulate expression of specific genes controlling cellular proliferation by binding to specific sequences within the promoter regions of these target genes and affecting their transcription in a cell cycle dependent manner. Recent studies have suggested an essential role of Rb/E2F pathway in the passage of cells through the G1 phase of the cell cycle. To better understand the role of these transcription factors in epithelial tumorigenesis, we compared the expression of various proteins involved in the Rb/E2F pathway in epidermis and 7,12-dimethylbenz(a)anthracene (DMBA)-initiated and 12-O-tetradecanoylphorbol-13-acetate (TPA) promoted papillomas on SENCAR mouse skin. Western blot analysis data showed 3.0- to 7.6-fold upregulation of E2F-1, E2F-2, E2F-3, E2F-4 and E2F-5 in tumors compared to normal epidermis. In tumors, the protein expression of DP-1 did not show significant change whereas that of DP-2 showed a 2.2-fold increase. Compared to normal epidermis, a significant upregulation of pRb (6.3-fold) and p107 (13-fold) was also observed in tumors. The protein expression of p130 was not detectable either in normal epidermis or in tumors. These data suggest that the overexpression of E2F proteins may be involved in the G1-S phase dysregulation that occurs during mouse skin tumorigenesis.

Prostate cancer chemoprevention by green tea: in vitro and in vivo inhibition of testosterone-mediated induction of ornithine decarboxylase

Recently, we have shown that ornithine decarboxylase (ODC), a rate-controlling enzyme in the polyamine biosynthetic pathway, is overexpressed in prostate cancer (PCA) and prostatic fluid in humans (R. R. Mohan et al., Clin. Cancer Res., 5: 143-147, 1999). ODC is also characterized as an androgen-responsive gene, and the androgenic stimulation regulates the development and growth of both normal and tumorigenic prostate cells. Thus, chemopreventive approaches aimed toward the modulation of ODC could be effective against PCA. Green tea polyphenols (GTPs) possess strong chemopreventive properties against a variety of animal tumor models and in some human epidemiological studies. At least two epidemiological studies have suggested that people who consume tea regularly may have a decreased risk of PCA. In this study, we investigated the effect of GTPs against testosterone-mediated induction of ODC in human prostate carcinoma cells, LNCaP as an in vitro model, and in Cpb:WU rats and C57BL/6 mice as in vivo models. Treatment of LNCaP cells with testosterone resulted in induction of ODC activity in a dose-dependent manner. Pretreatment of the cells with GTPs resulted in a significant inhibition of testosterone-caused induction of ODC activity in a dose-dependent manner. Similar effects of GTPs were observed in anchorage-independent growth assay of LNCaP cells where pretreatment of the cells with GTP was found to result in dose-dependent inhibition of colony formation. Testosterone treatment of the cells resulted in a significant increase in the level of ODC mRNA, and this increase was almost completely abolished by prior treatment of the cells with GTPs. The administration of testosterone (10 mg/kg body weight, i.p.) to sham-operated and castrated Cpb:WU rats resulted in 2- and 38-fold increases in ODC activity, respectively, in the ventral prostate. Oral feeding of 0.2% GTPs in drinking water for 7 days before testosterone administration resulted in 20 and 54% decreases in testosterone-caused induction of ODC activity in sham-operated and castrated rats, respectively. Similar results were obtained with C57BL/6 mice, where testosterone treatment at similar dosage resulted in a 2-fold increase in ODC activity in the ventral prostate and prior oral feeding with 0.2% GTPs resulted in 40% inhibition in this induction.

Prostate cancer chemoprevention by green tea

Prostate cancer (PCA) is one of the most invasive cancers and the second leading cause of cancer-related deaths among males in the United States. According to an estimate, 1 of every 11 American men will eventually develop PCA. One way to reduce the occurrence of cancer is through chemoprevention. PCA represents an excellent candidate disease for chemoprevention because it is typically diagnosed in men over 50 years of age, and therefore even a modest delay in neoplastic development achieved through pharmacological or nutritional intervention could result in a substantial reduction in the incidence of clinically detectable disease. The ideal agent(s) suitable for chemoprevention of PCA should be the one(s) that has proven efficacy in the laboratory experiments on one hand, and also possesses proven epidemiological basis on the other hand. This review attempts to address the issue of possible uses of tea, especially green tea, for the prevention of PCA. We are providing the experimental as well as the epidemiological basis for this possibility. Many laboratory experiments conducted in cell culture systems and in animal models have shown the usefulness of green tea, and the polyphenols present therein, against PCA. The epidemiological basis for this possibility is twofold. First, some epidemiological observations have suggested that people who consume tea regularly have a lower risk of PCA-related deaths. Second, the incidence of PCA in China, a population that consumes green tea on a regular basis, is lowest in the world.

Prevention of collagen-induced arthritis in mice by a polyphenolic fraction from green tea

Identification of common dietary substances capable of affording protection or modulating the onset and severity of arthritis may have important human health implications. An antioxidant-rich polyphenolic fraction isolated from green tea (green tea polyphenols, GTPs) has been shown to possess anti-inflammatory and anticarcinogenic properties in experimental animals. In this study we determined the effect of oral consumption of GTP on collagen-induced arthritis in mice. In three independent experiments mice given GTP in water exhibited significantly reduced incidence of arthritis (33% to 50%) as compared with mice not given GTP in water (84% to 100%). The arthritis index also was significantly lower in GTP-fed animals. Western blot analysis showed a marked reduction in the expression of inflammatory mediators such as cyclooxygenase 2, IFN-gamma, and tumor necrosis factor alpha in arthritic joints of GTP-fed mice. Histologic and immunohistochemical analysis of the arthritic joints in GTP-fed mice demonstrated only marginal joint infiltration by IFN-gamma and tumor necrosis factor alpha-producing cells as opposed to massive cellular infiltration and fully developed pannus in arthritic joints of non-GTP-fed mice. The neutral endopeptidase activity was approximately 7-fold higher in arthritic joints of non-GTP-fed mice in comparison to nonarthritic joints of unimmunized mice whereas it was only 2-fold higher in the arthritic joints of GTP-fed mice. Additionally, total IgG and type II collagen-specific IgG levels were lower in serum and arthritic joints of GTP-fed mice. Taken together our studies suggest that a polyphenolic fraction from green tea that is rich in antioxidants may be useful in the prevention of onset and severity of arthritis.

Involvement of retinoblastoma (Rb) and E2F transcription factors during photodynamic therapy of human epidermoid carcinoma cells A431

Photodynamic therapy (PDT), a promising new therapeutic modality for the management of a variety of solid malignancies and many non-malignant diseases, is a bimodal therapy using a porphyrin based photosensitizing chemical and visible light. The proper understanding of the mechanism of PDT-mediated cancer cell-kill may result in improving the efficacy of this treatment modality. Earlier we have shown (Proc. Natl. Acad. Sci. USA; 95: 6977-6982, 1998) that silicon phthalocyanine (Pc4)-PDT results in an induction of the cyclin kinase inhibitor WAF1/CIP1/p21 which, by inhibiting cyclins (E and D1) and cyclin dependent kinases (cdk2 and cdk6), results in a G0/G1-phase arrest followed by apoptosis in human epidermoid carcinoma cells A431. We have also demonstrated the generation of nitric oxide during PDT-mediated apoptosis (Cancer Res.; 58: 1785-1788, 1998). Retinoblastoma (pRb) and E2F family transcription factors are important proteins, which regulate the G1-->S transition in the cell cycle. Here, we provide evidence for the involvement of pRb-E2F/DP machinery as an important contributor of PDT-mediated cell cycle arrest and apoptosis. Western blot analysis demonstrated a decrease in the hyper-phosphorylated form of pRb at 3, 6 and 12 h post-PDT with a relative increase in hypo-phosphorylated pRb. Western blot analysis also revealed that PDT-caused decrease in phosphorylation of pRb occurs at serine-780. The ELISA data demonstrated a time dependent accumulation of hypo-phosphorylated pRb by PDT. This response was accompanied with down-regulation in the protein expression of all five E2F (1-5) family transcription factors, and their heterodimeric partners DP1 and DP2. These results suggest that Pc4-PDT of A431 cells results in a down regulation of hyper-phosphorylated pRb protein with a relative increase in hypo-phosphorylated pRb that, in turn, compromises with the availability of free E2F. We suggest that these events result in a stoppage of the cell cycle progression at G1-->S transition thereby leading to a G0/G1 phase arrest and a subsequent apoptotic cell death. These data provide an evidence for the involvement of pRb-E2F/DP machinery in PDT-mediated cell cycle arrest leading to apoptosis.

Green tea polyphenols and cancer: biologic mechanisms and practical implications

Polyphenolic compounds in fruits and vegetables have been associated with lower risk of some diseases, including cancer. Recent research has shown that the polyphenolic antioxidants in green tea possess cancer chemopreventive effects. This review discusses the cancer chemopreventive effects associated with green tea and the molecular mechanisms that underlie the broad anticarcinogenic effect of polyphenols in green tea.