38. Arch Biochem Biophys. 2011 Apr 15;508(2):152-8. Epub 2010 Nov 19.  Green tea prevents non-melanoma skin cancer by enhancing DNA repair.  Katiyar SK.  Birmingham Veterans Affairs Medical Center, Birmingham, AL 35294, USA. skatiyar@uab.edu 

Excessive exposure of the skin to solar ultraviolet (UV) radiation is one of the major factors for the development of skin cancers, including non-melanoma. For the last several centuries the consumption of dietary phytochemicals has been linked to numerous health benefits including the photoprotection of the skin. Green tea has been consumed as a popular beverage world-wide and skin photoprotection by green tea polyphenols (GTPs) has been widely investigated. In this article, we have discussed the recent investigations and mechanistic studies which define the potential efficacy of GTPs on the prevention of non-melanoma skin cancer. UV-induced DNA damage, particularly the formation of cyclobutane pyrimidine dimers, has been implicated in immunosuppression and initiation of skin cancer. Topical application or oral administration of green tea through drinking water of mice prevents UVB-induced skin tumor development, and this prevention is mediated, at least in part, through rapid repair of DNA. The DNA repair by GTPs is mediated through the induction of interleukin (IL)-12 which has been shown to have DNA repair ability. The new mechanistic investigations support and explain the anti-photocarcinogenic activity, in particular anti-non-melanoma skin cancer, of green tea and explain the benefits of green tea for human health.  Copyright © 2010 Elsevier Inc. All rights reserved.  PMCID: PMC3077767 PMID: 21094124  [PubMed - indexed for MEDLINE]

37. Int J Clin Exp Pathol. 2010 Aug 5;3(7):705-9.  Anti-angiogenic effects of epigallocatechin-3-gallate in human skin.  Domingo DS, Camouse MM, Hsia AH, Matsui M, Maes D, Ward NL, Cooper KD, Baron ED.  University Hospitals Case Medical Center, Department of Dermatology, Cleveland, OH 44106, USA.

 Epigallocatechin-3-gallate (EGCG) is the main polyphenol component of green tea.  This compound exhibits antioxidant, immunomodulatory, photoprotective, anti-angiogenic, and anti-inflammatory properties. We conducted a small randomized, double blind, split face trial using a cream containing 2.5% w/w of EGCG. Four healthy volunteers with significant erythema and telangiectasia on the face applied EGCG cream to one side of the face, and vehicle control cream to the other, twice daily for six weeks. After six weeks, biopsies were taken from EGCG and vehicle treated sites. Immunohistochemistry was used to measure VEGF and HIF-1 α. HIF-1 α expression was decreased in EGCG treated sites, such that 28.4% of the epidermis showed positive staining in vehicle treated vs. 13.8% in EGCG treated sites (p<0.001). A similar decrease in VEGF expression was found (6.7% in EGCG vs. 11.0%in in vehicle-treated skin (p<0.005). EGCG topical treatments influence HIF-1 α induction and VEGF expression and may serve as a potential agent in the prevention of telangiectasias.  PMCID: PMC2933390 PMID: 20830241  [PubMed - indexed for MEDLINE]

36. Arch Dermatol Res. 2010 Mar;302(2):71-83. Epub 2009 Nov 7.  Skin photoprotection by natural polyphenols: anti-inflammatory, antioxidant and DNA repair mechanisms.  Nichols JA, Katiyar SK.  Department of Dermatology, University of Alabama at Birmingham, 1670 University Boulevard, Volker Hall 557, PO Box 202, Birmingham, AL 35294, USA. 

Epidemiological, clinical and laboratory studies have implicated solar ultraviolet (UV) radiation in various skin diseases including, premature aging of the skin and melanoma and non-melanoma skin cancers. Chronic UV radiation exposure-induced skin diseases or skin disorders are caused by the excessive induction of inflammation, oxidative stress and DNA damage, etc. The use of chemopreventive agents, such as plant polyphenols, to inhibit these events in UV-exposed skin is gaining attention. Chemoprevention refers to the use of agents that can inhibit, reverse or retard the process of these harmful events in the UV-exposed skin. A wide variety of polyphenols or phytochemicals, most of which are dietary supplements, have been reported to possess substantial skin photoprotective effects. This review article summarizes the photoprotective effects of some selected polyphenols, such as green tea polyphenols, grape seed proanthocyanidins, resveratrol, silymarin and genistein, on UV-induced skin inflammation, oxidative stress and DNA damage, etc., with a focus on mechanisms underlying the photoprotective effects of these polyphenols. The laboratory studies conducted in animal models suggest that these polyphenols have the ability to protect the skin from the adverse effects of UV radiation, including the risk of skin cancers. It is suggested that polyphenols may favorably supplement sunscreens protection, and may be useful for skin diseases associated with solar UV radiation-induced inflammation, oxidative stress and DNA damage.  PMCID: PMC2813915 PMID: 19898857  [PubMed - indexed for MEDLINE]

35. Exp Dermatol. 2009 Jun;18(6):522-6.  Topical application of green and white tea extracts provides protection from solar-simulated ultraviolet light in human skin.  Camouse MM, Domingo DS, Swain FR, Conrad EP, Matsui MS, Maes D, Declercq L, Cooper KD, Stevens SR, Baron ED.  Department of Dermatology, University Hospitals Case Medical Center Cleveland, OH 44106, USA. 

BACKGROUND: Tea polyphenols have been found to exert beneficial effects on the skin via their antioxidant properties. AIMS: We sought to determine whether topical application of green tea or white tea extracts would prevent simulated solar radiation-induced oxidative damages to DNA and Langerhans cells that may lead to immune suppression and carcinogenesis.

METHODS: Skin samples were analysed from volunteers or skin explants treated with white tea or green tea after UV irradiation. In another group of patients, the in vivo immune protective effects of green and white tea were evaluated using contact hypersensitivity to dinitrochlorobenzene.

 RESULTS: Topical application of green and white tea offered protection against detrimental effects of UV on cutaneous immunity. Such protection is not because of direct UV absorption or sunscreen effects as both products showed a sun protection factor of 1. There was no significant difference in the levels of protection afforded by the two agents. Hence, both green tea and white tea are potential photoprotective agents that may be used in conjunction with established methods of sun protection.  PMID: 19492999  [PubMed - indexed for MEDLINE]

34. J Invest Dermatol. 2008 Oct;128(10):2429-41. Epub 2008 May 8.  Green tea polyphenol epigallocatechin-3-gallate suppresses collagen production and proliferation in keloid fibroblasts via inhibition of the STAT3-signaling pathway.  Park G, Yoon BS, Moon JH, Kim B, Jun EK, Oh S, Kim H, Song HJ, Noh JY, Oh C, You  S.  Department of Dermatology, School of Medicine, Korea University, Seoul, Korea. 

Keloids are benign skin tumors characterized by collagen accumulation and hyperproliferation of fibroblasts. To find an effective therapy for keloids, we explored the pharmacological potential of (-)-epigallocatechin-3-gallate (EGCG),  a widely investigated tumor-preventive agent. When applied to normal and keloid fibroblasts (KFs) in vitro, proliferation and migration of KFs were more strongly suppressed by EGCG than normal fibroblast proliferation and migration (IC(50): 54.4 microM (keloid fibroblast (KF)) versus 63.0 microM (NF)). The level of Smad2/3, signal transducer and activator of transcription-3 (STAT3), and p38 phosphorylation is more enhanced in KFs, and EGCG inhibited phosphorylation of phosphatidylinositol-3-kinase (PI3K), extracellular signal-regulated protein kinase 1/2 (ERK1/2), and STAT3 (Tyr705 and Ser727). To evaluate the contribution  of these pathways to keloid pathology, we treated KFs with specific inhibitors for PI3K, ERK1/2, or STAT3. Although a PI3K inhibitor significantly suppressed proliferation, PI3K and MEK/ERK inhibitors had a minor effect on migration and collagen production. However, a JAK2/STAT3 inhibitor and a STAT3 siRNA strongly suppressed proliferation, migration, and collagen production by KFs. We also found that treatment with EGCG suppressed growth and collagen production in the in vivo keloid model. This study demonstrates that EGCG suppresses the pathological characteristics of keloids through inhibition of the STAT3-signaling pathway. We propose that EGCG has potential in the treatment and prevention of keloids.  PMID: 18463684  [PubMed - indexed for MEDLINE]

33. Exp Dermatol. 2007 Aug;16(8):678-84.  Green tea polyphenol induces caspase 14 in epidermal keratinocytes via MAPK pathways and reduces psoriasiform lesions in the flaky skin mouse model.  Hsu S, Dickinson D, Borke J, Walsh DS, Wood J, Qin H, Winger J, Pearl H, Schuster G, Bollag WB.  Department of Oral Biology and Maxillofacial Pathology, School of Dentistry, Medical College of Georgia, Augusta, GA 30912, USA. shsu@mail.mcg.edu 

Psoriasiform lesions are characterized by hyperproliferation and aberrant differentiation of epidermal keratinocytes, accompanied by inflammation, leading  to a disrupted skin barrier with an abnormal stratum corneum. The expression and  proteolytic processing of caspase 14, a member of the caspase family which is associated with epithelial cell differentiation, planned cell death, and barrier  formation, is altered in psoriatic epidermis. We recently reported that human psoriatic tissues lack normal expression of caspase 14 [J Dermatol Sci37 (2005) 61], and caspase 14 is induced by EGCG, a green tea polyphenol (GTP), in exponentially growing normal human epidermal keratinocytes (NHEK) [J Pharmacol Exp Ther315 (2005) 805]. This suggests that GTPs may have beneficial effects on psoriasiform lesions. The current study aimed to determine whether MAPK pathways  are required for GTP-induced caspase 14 expression in NHEK and if GTPs can modulate the expression of pathological markers in the psoriasiform lesions that  develop in the flaky skin mouse. The results indicate that the p38 and JNK MAPK pathways are required for EGCG-induced expression of caspase 14 in NHEK. Importantly, topical application of 0.5% GTPs significantly reduced the symptoms  of epidermal pathology in the flaky skin mice, associated with efficient caspase  14 processing and reduction in proliferating cell nuclear antigen levels. This suggests that GTP-activated pathways may be potential targets for novel therapeutic approaches to the treatment of some psoriasiform skin disorders.  PMID: 17620095  [PubMed - indexed for MEDLINE]

32. Phytomedicine. 2007 Aug;14(7-8):551-5. Epub 2006 Nov 7.  Human hair growth enhancement in vitro by green tea epigallocatechin-3-gallate (EGCG).  Kwon OS, Han JH, Yoo HG, Chung JH, Cho KH, Eun HC, Kim KH.  Department of Dermatology, Seoul National University College of Medicine, Laboratory of Cutaneous Aging and Hair Research, Seoul National University Hospital, Institute of Dermatological Science, Seoul National University, 110-744 Seoul, Republic of Korea. 

Green tea is a popular worldwide beverage, and its potential beneficial effects such as anti-cancer and anti-oxidant properties are believed to be mediated by epigallocatechin-3-gallate (EGCG), a major constituent of polyphenols. Recently,  it was reported that EGCG might be useful in the prevention or treatment of androgenetic alopecia by selectively inhibiting 5alpha-reductase activity. However, no report has been issued to date on the effect of EGCG on human hair growth. This study was undertaken to measure the effect of EGCG on hair growth in vitro and to investigate its effect on human dermal papilla cells (DPCs) in vivo  and in vitro. EGCG promoted hair growth in hair follicles ex vivo culture and the proliferation of cultured DPCs. The growth stimulation of DPCs by EGCG in vitro may be mediated through the upregulations of phosphorylated Erk and Akt and by an increase in the ratio of Bcl-2/Bax ratio. Similar results were also obtained in in vivo dermal papillae of human scalps. Thus, we suggest that EGCG stimulates human hair growth through these dual proliferative and anti-apoptotic effects on  DPCs.  PMID: 17092697  [PubMed - indexed for MEDLINE]

  31. J Eur Acad Dermatol Venereol. 2007 May;21(5):650-6.  Effects of polyphenols on skin damage due to ultraviolet A rays: an experimental  study on rats.  Sevin A, Oztaş P, Senen D, Han U, Karaman C, Tarimci N, Kartal M, Erdoğan B.  1st Plastic and Reconstructive Surgery Department, Ankara Numune Education and Research Hospital, Ankara, Turkey.

BACKGROUND: Ultraviolet (UV) radiation causes many acute and chronic conditions such as oedema of the skin, sunburn, immunosuppression, photo-ageing and skin cancer. The use of antioxidants has become of paramount importance in prevention  of the damage caused by ultraviolet radiation. Epigallocatechin-3-gallate (EGCG one of the main components of green tea, has been reported to have anti-inflammatory, antioxidant and anticarcinogenic properties.

AIM: The aim of this experimental study was to investigate to what extent EGCG prevented acute skin damage caused by UVA.

MATERIAL AND METHOD: The sample contained 2% EGCG, which was prepared in hydrophilic ointment (USP XXIV) as the vehicle. Twenty-four 12-week-old Wistar albino rats are included in the study and divided into four groups, each containing six rats. Group I was formed to be the control group, which was not applied any topical medication or exposed to UV radiation. Group II was formed to observe acute effects of UVA on the skin, Group III was formed to observe effectiveness of topical EGCG on the skin applied 30 min after exposure to UVA, and Group IV was formed to observe topical EGCG applied 30 min before exposure to UVA. All groups were examined for sunburn cells, leucocyte infiltration, dermo-epidermal activity, collagen changes and elastic fibre pathologies on 24 and 72 h. Statistical analysis was performed using spss 11.5, and chi-squared test was used for the evaluation of parameters. RESULTS: Group IV showed a statistically significant decrease in sunburn cells and dermo-epidermal activation compared with Group II. Group II showed significant increase in all parameters compared with Group I, showing the effects of UV exposure alone, and no difference was detected in Group II and III.

CONCLUSION: These results show a protective effect of EGCG when applied topically before UVA exposure. No benefit was detected when EGCG was applied after UV exposure.  PMID: 17447979  [PubMed - indexed for MEDLINE]

30. J Nutr Biochem. 2007 May;18(5):287-96. Epub 2006 Oct 17.  Green tea and skin cancer: photoimmunology, angiogenesis and DNA repair.  Katiyar S, Elmets CA, Katiyar SK.  Department of Dermatology, University of Alabama at Birmingham, Birmingham, AL 35294, USA. skatiyar@uab.edu  

Human skin is constantly exposed to numerous noxious physical, chemical and environmental agents. Some of these agents directly or indirectly adversely affect the skin. Cutaneous overexposure to environmental solar ultraviolet (UV) radiation (290-400 nm) has a variety of adverse effects on human health, including the development of melanoma and nonmelanoma skin cancers. Therefore, there is a need to develop measures or strategies, and nutritional components are increasingly being explored for this purpose. The polyphenols present in green tea (Camellia sinensis) have been shown to have numerous health benefits, including protection from UV carcinogenesis. (-)-Epigallocatechin-3-gallate (EGCG) is the major and most photoprotective polyphenolic component of green tea. In this review article, we have discussed the most recent investigations and mechanistic studies that define and support the photoprotective efficacy of green tea polyphenols (GTPs) against UV carcinogenesis. The oral administration of GTPs in drinking water or the topical application of EGCG prevents UVB-induced skin tumor development in mice, and this prevention is mediated through: (a) the induction of immunoregulatory cytokine interleukin (IL) 12; (b) IL-12-dependent DNA repair following nucleotide excision repair mechanism; (c) the inhibition of  UV-induced immunosuppression through IL-12-dependent DNA repair; (d) the inhibition of angiogenic factors; and (e) the stimulation of cytotoxic T cells in a tumor microenvironment. New mechanistic information strongly supports and explains the chemopreventive activity of GTPs against photocarcinogenesis.  PMID: 17049833  [PubMed - indexed for MEDLINE]

29. Photodermatol Photoimmunol Photomed. 2007 Feb;23(1):48-56.  Photoprotective effects of green tea polyphenols.  Yusuf N, Irby C, Katiyar SK, Elmets CA.  Department of Dermatology, University of Alabama at Birmingham, Birmingham, AL 35294, USA. nabiha@uab.edu 

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.  PMID: 17254040  [PubMed - indexed for MEDLINE]

28. J Invest Dermatol. 2006 Dec;126(12):2607-13. Epub 2006 Jul 13.  Green tea extract and (-)-epigallocatechin-3-gallate inhibit mast cell-stimulated type I collagen expression in keloid fibroblasts via blocking PI-3K/AkT signaling pathways.  Zhang Q, Kelly AP, Wang L, French SW, Tang X, Duong HS, Messadi DV, Le AD.  Center for Craniofacial Molecular Biology, University of Southern California, School of Dentistry, Los Angeles, California 90033, USA. 

Keloid, a chronic fibro-proliferative disease, exhibits distinctive histological  features characterized by an abundant extracellular matrix stroma, a local infiltration of inflammatory cells including mast cells (MCs), and a milieu of enriched cytokines. Previous studies have demonstrated that co-culture with MCs stimulate type I collagen synthesis in fibroblasts, but the signaling mechanisms  remain largely unknown. In this study, we investigated the signaling pathways involved in MC-stimulated type I collagen synthesis and the effects of green tea  extract (GTE) and its major catechin, (-)-epigallocatechin-3-gallate (EGCG), on collagen homeostasis in keloid fibroblasts. Our results showed that MCs significantly stimulated type I collagen expression in keloid fibroblasts, and the upregulation of type I collagen was significantly attenuated by blockade of phosphatidylinositol-3-kinase (PI-3K), mammalian target of rapamycin (mTOR), and  p38 MAPK signaling pathways, but not by blockade of ERK1/2 pathway. Furthermore,  GTE and EGCG dramatically inhibited type I collagen production possibly by interfering with the PI-3K/Akt/mTOR signaling pathway. Our findings suggest that  interaction between MCs and keloid fibroblasts may contribute to excessive collagen accumulation in keloids and imply a therapeutic potential of green tea for the intervention and prevention of keloids and other fibrotic diseases.  PMID: 16841034  [PubMed - indexed for MEDLINE]

27. Cancer Res. 2006 May 15;66(10):5512-20.  (-)-Epigallocatechin-3-gallate prevents photocarcinogenesis in mice through interleukin-12-dependent DNA repair.  Meeran SM, Mantena SK, Elmets CA, Katiyar SK.  Department of Dermatology, University of Alabama at Birmingham and Birmingham VA  Medical Center, Birmingham, Alabama 35294, USA. 

We have shown previously that topical application of (-)-epigallocatechin-3-gallate (EGCG), the major polyphenol of green tea, prevents photocarcinogenesis in mice. EGCG prevents UVB-induced immunosuppression by inducing interleukin-12 (IL-12). As immunosuppression is a risk factor for photocarcinogenesis, we investigated the possibility that EGCG also prevents UVB-induced photocarcinogenesis through an IL-12-dependent DNA repair mechanism.  To investigate this possibility, we determined the effects of EGCG on photocarcinogenesis in IL-12 knockout (KO) mice using the formation of cyclobutane pyrimidine dimers (CPD) as an indicator of the extent of UVB-induced  DNA damage. Topical application of EGCG (1 mg/cm(2) skin) prevented photocarcinogenesis in wild-type (C3H/HeN) mice in terms of tumor incidence and tumor multiplicity but did not prevent photocarcinogenesis in IL-12 KO mice. UVB-induced DNA damage, as determined by the formation of CPDs and the number of  sunburn cells, was resolved more rapidly in the skin of wild-type mice treated with EGCG than untreated control mice. In contrast, the extent of UVB-induced DNA damage and the numbers of sunburn cells were not significantly different in the EGCG-treated IL-12 KO mice and untreated control mice. In addition, treatment of  XPA-proficient human fibroblast cells with EGCG promoted repair of UVB-induced CPDs in a dose-dependent manner but not in an XPA-deficient cells, indicating that the nucleotide excision repair mechanism is involved in EGCG-mediated DNA repair. Taken together, these results indicate for the first time that EGCG can prevent photocarcinogenesis through an EGCG-induced IL-12-dependent DNA repair mechanism.  PMID: 16707481  [PubMed - indexed for MEDLINE]

26. Clin Cancer Res. 2006 Apr 1;12(7 Pt 1):2272-80.  Prevention of ultraviolet radiation-induced immunosuppression by (-)-epigallocatechin-3-gallate in mice is mediated through interleukin 12-dependent DNA repair.  Meeran SM, Mantena SK, Katiyar SK.  Department of Dermatology, University of Alabama at Birmingham and Birmingham Veterans Affairs Medical Center, Birmingham, Alabama, USA. 

PURPOSE: Solar UV radiation-induced immunosuppression is considered to be a risk  factor for melanoma and nonmelanoma skin cancers. We previously have shown that topical application of (-)-epigallocatechin-3-gallate (EGCG) prevents UV-induced  immunosuppression in mice. We studied whether prevention of UV-induced immunosuppression by EGCG is mediated through interleukin 12 (IL-12)-dependent DNA repair.

EXPERIMENTAL DESIGN: IL-12 knockout (KO) mice on C3H/HeN background and DNA repair-deficient cells from xeroderma pigmentosum complementation group A (XPA) patients were used in this study. The effect of EGCG was determined on UV-induced suppression of contact hypersensitivity and UV-induced DNA damage in the form of  cyclobutane pyrimidine dimers (CPD) in mice and XPA-deficient cells using immunohistochemistry and dot-blot analysis.

RESULTS: Topical treatment with EGCG prevented UV-induced suppression of the contact hypersensitivity in wild-type (WT) mice but did not prevent it in IL-12 KO mice. Injection of anti-IL-12 monoclonal antibody to WT mice blocked the preventive effect of EGCG on UV-induced immunosuppression. EGCG reduced or repaired UV-induced DNA damage in skin faster in WT mice as shown by reduced number of CPDs(+) cells and reduced the migration of CPD(+) antigen-presenting cells from the skin to draining lymph nodes. In contrast, this effect of EGCG was not seen in IL-12 KO mice. Further, EGCG was able to repair UV-induced CPDs in XPA-proficient cells obtained from healthy person but did not repair in XPA-deficient cells, indicating that nucleotide excision repair mechanism is involved in DNA repair. CONCLUSIONS: These data identify a new mechanism by which EGCG prevents UV-induced immunosuppression, and this may contribute to the chemopreventive activity of EGCG in prevention of photocarcinogenesis.  PMID: 16609044  [PubMed - indexed for MEDLINE]

25. Chin Med J (Engl). 2006 Feb 20;119(4):282-7.  Green tea polyphenol epigallocatechin-3-gallate inhibits the expression of nitric oxide synthase and generation of nitric oxide induced by ultraviolet B in HaCaT cells.  Song XZ, Bi ZG, Xu AE.  Department of Dermatology, Third Hospital of Hangzhou, Hangzhou 310009, China. songxiuzu@sina.com  Comment in     Chin Med J (Engl). 2006 Jun 20;119(12):1056.

 BACKGROUND: Nitic oxide (NO) has been implicated in the pathogenesis of various inflammatory diseases, including sunburn and pigmentation induced by ultraviolet  irradiation. Epigallocatechin-3-gallate (EGCG) is the major effective component in green tea and can protect skin from ultraviolet-induced damage. The purpose of this study was to investigate the protective mechanisms of EGCG on inducible nitric oxide synthase (iNOS) expression and NO generation by ultraviolet B (UVB)  irradiation in HaCaT cells.

METHODS: HaCaT cells were irradiated with UVB 30 mJ/cm 2 and pretreated with EGCG at varying concentrations. The iNOS mRNA was detected by reverse transcriptase polymerase chain reaction (RT-PCR) and NO production was quantified by spectrophotometric method. The expression of NF-kappaB P65 was measured by immunofluorescence cytochemistry staining. RESULTS: The expression of iNOS mRNA and generation of NO in HaCaT cells were increased by UVB irradiation. EGCG down regulated the UVB-induced iNOS mRNA synthesis and NO generation in a dose dependent manner. The UVB-induced ctivation and translocation of NF-kappaB were also down regulated by EGCG treatment in HaCaT cells (P < 0.01).

CONCLUSIONS: Green tea derived-EGCG can inhibit and down regulate the UVB-induced activation and translocation of NF-kappaB, expression of iNOS mRNA and generation of NO respectively, indicating EGCG may play a protective role from UVB-induced skin damage.  PMID: 16537022  [PubMed - indexed for MEDLINE]

24. Int J Mol Med. 2005 Nov;16(5):943-50.  UV-induced NF-kappaB activation and expression of IL-6 is attenuated by (-)-epigallocatechin-3-gallate in cultured human keratinocytes in vitro.  Xia J, Song X, Bi Z, Chu W, Wan Y.  Department of Dermatology, The First Affiliated Hospital of Nanjing Medical University, Nanjing 210029, Jiangsu Province, PR China. 

Ultraviolet (UV) radiation from the sun is widely considered as a major cause of  human skin photoaging and skin cancer. UV radiation-induced proinflammatory cytokines mediated by NF-kappaB reportedly play important roles in photoaging and cancer. NF-kappaB and cytokines have been thus perceived as molecular targets for pharmacological intervention. With an increasing amount of knowledge of the actions of green tea extracts at cellular and molecular levels, the beneficial effect of drinking green tea has become well recognized if not completely accepted. The components in green tea have even been added to skin-care products unregulated, while the molecular mechanisms of the actions of those components on human skin are being unraveled. Using cultured human keratinocytes, we investigated the effects of (-)-epigallocatechin-3-gallate (EGCG), a major polyphenolic constituent in green tea, on UV-induced activation of transcription  factor NF-kappaB and proinflammatory pathway by measuring nuclear translocation of NF-kappaB and IL-6 secretion in vitro. Immunohistochemical and Western blot analysis and ELISA indicated that both nuclear p65 and secreted IL-6 were significantly (p<0.05) induced by UVB (20, 30 mJ/cm2) and UVA irradiation (10, 20 J/cm2). NF-kappaB nuclear translocation and IL-6 secretion induced by UVB and UVA were dramatically inhibited by treatment of EGCG. FACS analysis showed that EGCG also inhibited UVB-induced apoptosis. EGCG recovered UV-induced loss of anti-apoptotic component, bcl-2, and inhibited UV-induced apoptotic component, Fas ligand, expression. Collectively, we conclude that EGCG inhibits UVB- and UVA-induced proinflammatory pathway and inhibits apoptosis in cultured human keratinocytes in vitro. Our data suggest that EGCG be added to cosmetic or skin-care products for prevention from UV-induced skin photoaging if this activity can be further confirmed and no cytotoxicity is reported in human skin in vivo.  PMID: 16211268  [PubMed - indexed for MEDLINE]

23. Photochem Photobiol. 2005 Sep-Oct;81(5):1174-9.  Epigallocatechin-3-gallate inhibits photocarcinogenesis through inhibition of angiogenic factors and activation of CD8+ T cells in tumors.  Mantena SK, Roy AM, Katiyar SK.  Department of Dermatology, University of Alabama at Birmingham, Birmingham, AL, USA. 

There has been considerable interest in the use of botanical supplements to protect skin from the adverse effects of solar UV radiation, including photocarcinogenesis. We and others have shown that topical application of (-)-epigallocatechin-3-gallate (EGCG) from green tea prevents photocarcinogenesis in mice; however, the chemopreventive mechanism of EGCG in an in vivo tumor model is not clearly understood. In this study, UV-B-induced skin tumors with and without treatment of EGCG ( approximately 1 mg/cm(2)) and age-matched skin biopsies from SKH-1 hairless mice were used to identify potential molecular targets of skin cancer prevention by EGCG. These biopsies were analyzed for various biomarkers of angiogenesis and antitumor immune response using immunostaining, Western blotting and gelatinolytic zymography. We report that compared to non-EGCG-treated tumors, topical application of EGCG in UV-induced tumors resulted in inhibition of protein expression and activity of matrix metalloproteinase (MMP)-2 and MMP-9, which play crucial roles in tumor growth and metastasis. In contrast, tissue inhibitor of MMP-1 (TIMP-1), which inhibits MMP activity, was increased in tumors. With respect to the tumor vasculature, EGCG decreased the expression of CD31, a cell surface marker of vascular endothelial cells, and inhibited the expression of vascular endothelial growth factor in tumors, which are essential for angiogenesis. EGCG inhibited proliferating cell nuclear antigen in UV-B-induced tumors as well. Additionally, higher numbers of cytotoxic T lymphocytes (CD8(+) T cells) were detected in EGCG-treated tumors compared with non-EGCG-treated tumors. Together, these in vivo tumor data suggested that inhibition of photocarcinogenesis in mice by EGCG is associated with inhibition of angiogenic factors and induction of antitumor immune reactivity.  PMID: 15938647  [PubMed - indexed for MEDLINE]

22. Dermatol Surg. 2005 Jul;31(7 Pt 2):855-60; discussion 860.  Double-blinded, placebo-controlled trial of green tea extracts in the clinical and histologic appearance of photoaging skin.  Chiu AE, Chan JL, Kern DG, Kohler S, Rehmus WE, Kimball AB.  Department of Dermatology, Emory University, USA. 

BACKGROUND: Green tea extracts have gained popularity as ingredients in topical skin care preparations to treat aging skin. Green tea polyphenolic compounds have significant antioxidant and anti-inflammatory activities, and studies suggest that these extracts help mediate ultraviolet radiation damage.

OBJECTIVE: To evaluate the effects of a combination regimen of topical and oral green tea supplementation on the clinical and histologic characteristics of photoaging.

METHODS: Forty women with moderate photoaging were randomized to either a combination regimen of 10% green tea cream and 300 mg twice-daily green tea oral  supplementation or a placebo regimen for 8 weeks.

RESULTS: No significant differences in clinical grading were found between the green tea-treated and placebo groups, other than higher subjective scores of irritation in the green tea-treated group. Histologic grading of skin biopsies did show significant improvement in the elastic tissue content of treated specimens (p<.05).

CONCLUSION: Participants treated with a combination regimen of topical and oral green tea showed histologic improvement in elastic tissue content. Green tea polyphenols have been postulated to protect human skin from the cutaneous signs of photoaging, but clinically significant changes could not be detected. Longer supplementation may be required for clinically observable improvements.  PMID: 16029678  [PubMed - indexed for MEDLINE]

21. Int J Cancer. 2005 Apr 20;114(4):513-21.  Anti-proliferative and proapoptotic effects of (-)-epigallocatechin-3-gallate on  human melanoma: possible implications for the chemoprevention of melanoma.  Nihal M, Ahmad N, Mukhtar H, Wood GS.  Department of Dermatology, University of Wisconsin and William S. Middleton Veterans Memorial Hospital, Madison, WI 53706, USA. 

Melanoma accounts for only about 4% of all skin cancer cases but most of skin cancer-related deaths. Standard systemic therapies such as interferon (IFN) have  not been adequately effective in the management of melanoma. Therefore, novel approaches are needed for prevention and treatment of this disease. Chemoprevention by naturally occurring agents present in food and beverages has shown benefits in certain cancers including nonmelanoma skin cancers. Here, employing 2 human melanoma cell lines (A-375 amelanotic malignant melanoma and Hs-294T metastatic melanoma) and normal human epidermal melanocytes (NHEM), we studied the antiproliferative effects of epigallocatechin-3-gallate (EGCG), the major polyphenolic antioxidant present in green tea. EGCG treatment was found to  result in a dose-dependent decrease in the viability and growth of both melanoma  cell lines. Interestingly, at similar EGCG concentrations, the normal melanocytes were not affected. EGCG treatment of the melanoma cell lines resulted in decreased cell proliferation (as assessed by Ki-67 and PCNA protein levels) and induction of apoptosis (as assessed cleavage of PARP, TUNEL assay and JC-1 assay). EGCG also significantly inhibited the colony formation ability of the melanoma cells studied. EGCG treatment of melanoma cells resulted in a downmodulation of anti-apoptotic protein Bcl2, upregulation of proapoptotic Bax and activation of caspases -3, -7 and -9. Furthermore, our data demonstrated that EGCG treatment resulted in a significant, dose-dependent decrease in cyclin D1 and cdk2 protein levels and induction of cyclin kinase inhibitors (ckis) p16INK4a, p21WAF1/CIP1 and p27KIP1. Our data suggest that EGCG causes significant induction of cell cycle arrest and apoptosis of melanoma cells that is mediated via modulations in the cki-cyclin-cdk network and Bcl2 family proteins. Thus, EGCG, alone or in conjunction with current therapies, could be useful for the management of melanoma.  PMID: 15609335  [PubMed - indexed for MEDLINE]

20. Arch Dermatol Res. 2005 Apr;296(10):473-81. Epub 2005 Feb 22.  Protective effects of (-)-epicatechin-3-gallate on UVA-induced damage in HaCaT keratinocytes.  Huang CC, Fang JY, Wu WB, Chiang HS, Wei YJ, Hung CF.  Department of Dermatology, Shin Kong Wu Ho-Su Memorial Hospital, Taipei County, Taiwan. 

(-)-Epigallocatechin-3-gallate (EGCG), a constituent of green tea, has been extensively studied and shown to be a powerful antioxidant protecting skin cells  against photodamage. In this study, however, we demonstrated that another gallated catechin, (-)-epicatechin-3-gallate (ECG), was also able to protect human keratinocytes against damage induced by ultraviolet A (UVA) light. We found that ECG dose-dependently inhibited UVA-induced keratinocyte death as determined  by cell viability assay. Moreover, ECG had similar potency to EGCG in inhibiting  UVA-induced cell death. Therefore, the mechanism of action of ECG was further investigated. As assayed by flow cytometry, UVA-induced hydrogen peroxide (H2O2)  production in keratinocytes was inhibited by ECG in a concentration-dependent manner, suggesting that ECG can act as a free radical scavenger while keratinocytes were photodamaged. The scavenging effect of ECG was confirmed by  the fact that ECG treatment attenuated cell damage induced by H2O2 and hypoxanthine-xanthine oxidase. In a parallel experiment, UVA-induced activation of extracellular signal-regulated kinase in keratinocytes was blocked by ECG. We provided here the first evidence that ECG is a potent protectant that protects keratinocytes from photodamage. Because ECG is abundant in green tea, we believe  that this compound is beneficial for skin care.   PMID: 15726391  [PubMed - indexed for MEDLINE]

19. Photodermatol Photoimmunol Photomed. 2005 Feb;21(1):15-22.  The green tea polyphenol (-)-epigallocatechin gallate and green tea can protect human cellular DNA from ultraviolet and visible radiation-induced damage.  Morley N, Clifford T, Salter L, Campbell S, Gould D, Curnow A.  Cornwall Dermatology Research Project, Polgooth Ward, Royal Cornwall Hospital, Treliske, Truro, Cornwall TR1 3LJ, UK. 

BACKGROUND: Antioxidant compounds in green tea may be able to protect against skin carcinogenesis and it is of interest to investigate the mechanisms involved. A study was therefore conducted to determine whether the isolated green tea polyphenol (-)-epigallocatechin gallate (EGCG) could prevent ultraviolet radiation (UVR)-induced DNA damage in cultured human cells. This work was then extended to investigate whether drinking green tea could afford any UVR protection to human peripheral blood cells collected after tea ingestion.

METHODS: The alkaline comet assay was used to compare the DNA damage induced by UVR in cultured human cells with and without the presence of EGCG. The same assay technique was then employed to assess UVR-induced DNA damage in peripheral leucocytes isolated from 10 adult human volunteers before and after drinking 540  ml of green tea.

RESULTS: Initial trials found that EGCG afforded concentration-dependent photoprotection to cultured human cells with a maximal activity at a culture concentration of 250 microM. The cells types tested (lung fibroblasts, skin fibroblasts and epidermal keratinocytes) demonstrated varying susceptibility to the UVR insult provided. The in vivo trials of green tea also demonstrated a photoprotective effect, with samples of peripheral blood cells taken after green  tea consumption showing lower levels of DNA damage than those taken prior to ingestion when exposed to 12 min ultraviolet A (UVA) radiation.

CONCLUSION: The studies showed that green tea and/or some constituents can offer  some protection against UV-induced DNA damage in human cell cultures and also in  human peripheral blood samples taken post-tea ingestion.  PMID: 15634219  [PubMed - indexed for MEDLINE]

18. FASEB J. 2003 Oct;17(13):1913-5. Epub 2003 Aug 1.  Dual mechanisms of green tea extract (EGCG)-induced cell survival in human epidermal keratinocytes.  Chung JH, Han JH, Hwang EJ, Seo JY, Cho KH, Kim KH, Youn JI, Eun HC.  Department of Dermatology, Seoul National University College of Medicine, and Laboratory of Cutaneous Aging Research, Clinical Research Institute, Seoul National University Hospital, Seoul, Korea. 

Beneficial effects attributed to green tea, such as its anticancer and antioxidant properties, may be mediated by (-)-epigallocatechin-3-gallate (EGCG). In this study, the effects of EGCG on cell proliferation and UV-induced apoptosis were investigated in normal epidermal keratinocytes. When topically applied to aged human skin, EGCG stimulated the proliferation of epidermal keratinocytes, which increased the epidermal thickness. In addition, this topical application also inhibited the UV-induced apoptosis of epidermal keratinocytes. EGCG was found to increase the phosphorylation of Bad protein at the Ser112 and Ser136. Moreover, EGCG-induced Erk phosphorylation was found to be critical for the phosphorylation of Ser112 in Bad protein, and the EGCG-induced activation of the  Akt pathway was found to be involved in the phosphorylation of Ser136. Furthermore, EGCG increased Bcl-2 expression but decreased Bax expression, causing an increase in the Bcl-2-to-Bax ratio. In addition, we demonstrate the differential growth inhibitory effects of EGCG on cancer cells. In conclusion, this study demonstrates that EGCG promotes keratinocyte survival and inhibits the UV-induced apoptosis via two mechanisms: by phosphorylating Ser112 and Ser136 of  Bad protein through Erk and Akt pathways, respectively, and by increasing the Bcl-2-to-Bax ratio. Moreover, these two proposed mechanisms of EGCG-induced cell  proliferation may differ kinetically to promote keratinocyte survival.  PMID: 12897059  [PubMed - indexed for MEDLINE]

17. Curr Drug Targets Immune Endocr Metabol Disord. 2003 Sep;3(3):234-42.  Skin photoprotection by green tea: antioxidant and immunomodulatory effects.  Katiyar SK.  Department of Dermatology, University of Alabama at Birmingham, Birmingham, AL 35294, USA. skatiyar@uab.edu  

Because of a characteristic aroma and health benefits, green tea is consumed worldwide as a popular beverage. The epicatechin derivatives, commonly called polyphenols, present in green tea possess antioxidant, anti-inflammatory and anti-carcinogenic properties. The major and most highly chemopreventive constituent in green tea responsible for the biochemical or pharmacological effects is (-)-epigallocatechin-3-gallate (EGCG). Epidemiological, clinical and biological studies have implicated that solar ultraviolet (UV) light is a complete carcinogen and repeated exposure can lead to the development of various  skin disorders including melanoma and nonmelanoma skin cancers. We and others have shown that topical treatment or oral consumption of green tea polyphenols (GTP) inhibit chemical carcinogen- or UV radiation-induced skin carcinogenesis in different laboratory animal models. Topical treatment of GTP and EGCG or oral consumption of GTP resulted in prevention of UVB-induced inflammatory responses,  immunosuppression and oxidative stress, which are the biomarkers of several skin  disease states. Topical application of GTP and EGCG prior to exposure of UVB protects against UVB-induced local as well as systemic immune suppression in laboratory animals, which was associated with the inhibition of UVB-induced infiltration of inflammatory leukocytes. Prevention of UVB-induced suppression of immune responses by EGCG was also associated with the reduction in immunosuppressive cytokine interleukin (IL)-10 production at UV irradiated skin and draining lymph nodes, whereas IL-12 production was significantly enhanced in  draining lymph nodes. Antioxidant and anti-inflammatory effects of green tea were also observed in human skin. Treatment of EGCG to human skin resulted in the inhibition of UVB-induced erythema, oxidative stress and infiltration of inflammatory leukocytes. We also showed that treatment of GTP to human skin prevents UVB-induced cyclobutane pyrimidine dimers formation, which are considered to be mediators of UVB-induced immune suppression and skin cancer induction. The in vitro and in vivo animal and human studies suggest that green tea polyphenols are photoprotective in nature, and can be used as pharmacological agents for the prevention of solar UVB light-induced skin disorders including photoaging, melanoma and nonmelanoma skin cancers after more clinical trials in humans.  PMID: 12871030  [PubMed - indexed for MEDLINE]

16. J Pharmacol Exp Ther. 2003 Jul;306(1):29-34. Epub 2003 Mar 27.  Green tea polyphenols induce differentiation and proliferation in epidermal keratinocytes.  Hsu S, Bollag WB, Lewis J, Huang Q, Singh B, Sharawy M, Yamamoto T, Schuster G.  Department of Oral Biology and Maxillofacial Pathology, School of Dentistry, AD1443. Medical College of Georgia, Augusta, GA 30912-1126, USA. shsu@mail.mcg.edu  

The most abundant green tea polyphenol, epigallocatechin-3-gallate (EGCG), was found to induce differential effects between tumor cells and normal cells. Nevertheless, how normal epithelial cells respond to the polyphenol at concentrations for which tumor cells undergo apoptosis is undefined. The current  study tested exponentially growing and aged primary human epidermal keratinocytes in response to EGCG or a mixture of the four major green tea polyphenols. EGCG elicited cell differentiation with associated induction of p57/KIP2 within 24 h in growing keratinocytes, measured by the expression of keratin 1, filaggrin, and transglutaminase activity. Aged keratinocytes, which exhibited low basal cellular activities after culturing in growth medium for up to 25 days, renewed DNA synthesis and activated succinate dehydrogenase up to 37-fold upon exposure to either EGCG or the polyphenols. These results suggest that tea polyphenols may be used for treatment of wounds or certain skin conditions characterized by altered  cellular activities or metabolism.  PMID: 12663686  [PubMed - indexed for MEDLINE]

15. Carcinogenesis. 2003 May;24(5):927-36.  Treatment of green tea polyphenols in hydrophilic cream prevents UVB-induced oxidation of lipids and proteins, depletion of antioxidant enzymes and phosphorylation of MAPK proteins in SKH-1 hairless mouse skin.  Vayalil PK, Elmets CA, Katiyar SK.  Department of Dermatology, University of Alabama at Birmingham, 1670 University Blvd, Volker Hall 557, 35294, USA. 

The use of botanical supplements has received immense interest in recent years to protect human skin from adverse biological effects of solar ultraviolet (UV) radiation. The polyphenols from green tea are one of them and have been shown to  prevent photocarcinogenesis in animal models but their mechanism of photoprotection is not well understood. To determine the mechanism of photoprotection in in vivo mouse model, topical treatment of polyphenols from green tea (GTP) or its most chemopreventive constituent (-)-epigallocatechin-3-gallate (EGCG) (1 mg/cm(2) skin area) in hydrophilic ointment USP before single (180 mJ/cm(2)) or multiple UVB exposures (180 mJ/cm(2), daily for 10 days) resulted in significant prevention of UVB-induced depletion of antioxidant enzymes such as glutathione peroxidase (78-100%, P < 0.005-0.001), catalase (51-92%, P < 0.001) and glutathione level (87-100%, P < 0.005). Treatment of EGCG or GTP also inhibited UVB-induced oxidative stress when measured in terms of lipid peroxidation (76-95%, P < 0.001), and protein oxidation (67-75%, P > 0.001). Further, to delineate the inhibition of UVB-induced oxidative stress with cell signaling pathways, treatment of EGCG to mouse skin resulted in marked inhibition of a single UVB irradiation-induced phosphorylation of ERK1/2 (16-95%), JNK (46-100%) and p38 (100%) proteins of MAPK family in a time-dependent manner. Identical photoprotective effects of EGCG or GTP were also observed against multiple UVB irradiation-induced phosphorylation of the proteins of MAPK family in vivo mouse skin. Photoprotective efficacy of GTP given in drinking water (d.w.) (0.2%, w/v) was also determined and compared with that of topical treatment of EGCG and GTP. Treatment of GTP in d.w. also significantly prevented single or multiple UVB irradiation-induced depletion of antioxidant enzymes (44-61%, P < 0.01-0.001), oxidative stress (33-71%, P < 0.01) and phosphorylation of ERK1/2, JNK and p38 proteins of MAPK family but the photoprotective efficacy was comparatively less than that of topical treatments of EGCG and GTP. Lesser photoprotective efficacy of GTP in d.w. in comparison with topical application may be due to its less bioavailability in skin target cells. Together, for the first time a cream based formulation of green tea polyphenols was tested in this study to explore the possibility of its use for the humans, and the data obtained from this in vivo study further suggest that GTP could be useful in attenuation of solar UVB light-induced oxidative stress-mediated and MAPK-caused skin disorders in humans.  PMID: 12771038  [PubMed - indexed for MEDLINE]

14. Oncogene. 2003 Feb 20;22(7):1035-44.  Inhibition of ultraviolet B-mediated activation of nuclear factor kappaB in normal human epidermal keratinocytes by green tea Constituent (-)-epigallocatechin-3-gallate.  Afaq F, Adhami VM, Ahmad N, Mukhtar H.  Department of Dermatology, University of Wisconsin, Madison, WI 53706, USA. 

Epigallocatechin-3-gallate (EGCG), the major constituent of green tea, possesses  significant anti-inflammatory and cancer chemopreventive properties. Studies have shown the photochemopreventive effects of green tea and EGCG in cell culture, animal models, and human skin. The molecular mechanism(s) of photochemopreventive effects of EGCG are incompletely understood. We recently showed that EGCG treatment of the normal human epidermal keratinocytes (NHEK) inhibits ultraviolet (UV)B-mediated activation of the mitogen-activated protein kinase (MAPK) pathway. In this study, we evaluated the effect of EGCG on UVB-mediated modulation of the  nuclear factor kappa B (NF-kappaB) pathway, which is known to play a critical role in a variety of physiological functions and is involved in inflammation and  development of cancer. Immunoblot analysis demonstrated that the treatment of NHEK with EGCG (10-40 microM) for 24 h resulted in a significant inhibition of UVB (40 mJ/cm(2))-mediated degradation and phosphorylation of IkappaBalpha and activation of IKKalpha, in a dose-dependent manner. UVB-mediated degradation and  phosphorylation of IkappaBalpha and activation of IKKalpha was also observed in a time-dependent protocol (15 and 30 min, 1, 2, 3, 6, 12 h post-UVB exposure). Employing immunoblot analysis, enzyme-linked immunosorbent assay, and gel shift assay, we demonstrate that EGCG treatment of the cells resulted in a significant  dose- and time-dependent inhibition of UVB-mediated activation and nuclear translocation of a NF-kappaB/p65. Our data suggest that EGCG protects against the adverse effects of UV radiation via modulations in NF-kappaB pathway, and provide a molecular basis for the photochemopreventive effect of EGCG.  PMID: 12592390  [PubMed - indexed for MEDLINE]

13. Int J Cancer. 2002 Dec 10;102(5):439-44.  The green tea polyphenol, epigallocatechin-3-gallate, protects against the oxidative cellular and genotoxic damage of UVA radiation.  Tobi SE, Gilbert M, Paul N, McMillan TJ.  Department of Biological Sciences, Institute of Environmental and Natural Sciences, Lancaster University, Lancaster, United Kingdom. 

A number of biological activities have been ascribed to the major green tea polyphenol epigallocatechin-3-gallate (EGCG) to explain its chemopreventive properties. Its antioxidant properties emerge as a potentially important mode of  action. We have examined the effect of EGCG treatment on the damaging oxidative effects of UVA radiation in a human keratinocyte line (HaCaT). Using the ROS-sensitive probes dihydrorhodamine 123 (DHR) and 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA), we detected a reduction in  fluorescence in UVA-irradiated (100 kJ/m(2)) cells in the case of the former but  not the latter probe after a 24-hr treatment with EGCG (e.g., 14%, [p < 0.05] after 10 microM EGCG). In the absence of UVA, however, both DHR and DCFH detected a pro-oxidant effect of EGCG at the highest concentration used of 50 microM. Measurements of DNA damage in UVA-exposed cells using the single cell gel electrophoresis assay (comet assay) also showed the protective effects of EGCG. A concentration of 10 microM EGCG decreased the level of DNA single strand breaks and alkali-labile sites to 62% of the level observed in non-EGCG, irradiated cells (p < 0.001) with a 5-fold higher concentration producing little further effect. Correspondingly, EGCG ablated the mutagenic effects of UVA (500 kJ/m(2))  reducing an induced hypoxanthine-guanine phosphoribosyl transferase (HPRT) mutant frequency of (3.39 +/- 0.73) x 10(-6) to spontaneous levels (1.09 +/- 0.19) x 10(-6). Despite having an antiproliferative effect in the absence of UVA, EGCG also served to protect against the cytotoxic effects of UVA radiation. Our data demonstrate the ability of EGCG to modify endpoints directly relevant to the carcinogenic process in skin.  Copyright 2002 Wiley-Liss, Inc.  PMID: 12432544  [PubMed - indexed for MEDLINE]

12. J Photochem Photobiol B. 2001 Dec 31;65(2-3):109-14.  Green tea polyphenols: DNA photodamage and photoimmunology.  Katiyar SK, Bergamo BM, Vyalil PK, Elmets CA.  Department of Dermatology, School of Medicine, University of Alabama at Birmingham, 1670 University Blvd., VH501, Box 202, Birmingham, AL 35294, USA. skatiyar@uab.edu  

Green tea is a popular beverage consumed worldwide. The epicatechin derivatives,  which are commonly called 'polyphenols', are the active ingredients in green tea  and possess antioxidant, anti-inflammatory and anti-carcinogenic properties. Studies conducted by our group on human skin have demonstrated that green tea polyphenols (GTP) prevent ultraviolet (UV)-B-induced cyclobutane pyrimidine dimers (CPD), which are considered to be mediators of UVB-induced immune suppression and skin cancer induction. GTP treated human skin prevented penetration of UV radiation, which was demonstrated by the absence of immunostaining for CPD in the reticular dermis. The topical application of GTP or its most potent chemopreventive constituent (-)-epigallocatechin-3-gallate (EGCG) prior to exposure to UVB protects against UVB-induced local as well as systemic immune suppression in laboratory animals. Additionally, studies have shown that EGCG treatment of mouse skin inhibits UVB-induced infiltration of CD11b+ cells. CD11b is a cell surface marker for activated macrophages and neutrophils, which are associated with induction of UVB-induced suppression of contact hypersensitivity responses. EGCG treatment also results in reduction of the UVB-induced immunoregulatory cytokine interleukin (IL)-10 in skin as well as in draining lymph nodes, and an elevated amount of IL-12 in draining lymph nodes. These in vivo observations suggest that GTPs are photoprotective, and can be used as pharmacological agents for the prevention of solar UVB light-induced skin disorders associated with immune suppression and DNA damage.  PMID: 11809367  [PubMed - indexed for MEDLINE]

11. Toxicol Appl Pharmacol. 2001 Oct 15;176(2):110-7.  Inhibition of UVB-induced oxidative stress-mediated phosphorylation of mitogen-activated protein kinase signaling pathways in cultured human epidermal keratinocytes by green tea polyphenol (-)-epigallocatechin-3-gallate.  Katiyar SK, Afaq F, Azizuddin K, Mukhtar H.  Department of Dermatology, Case Western Reserve University, Cleveland, Ohio 44106, USA. shatiyar@uab.edu  

Exposure of normal human epidermal keratinocytes (NHEK) to UVB radiation induces  intracellular release of hydrogen peroxide (oxidative stress) and phosphorylation of mitogen-activated protein kinase cell signaling pathways. Here, we demonstrate that pretreatment of NHEK with (-)-epigallocatechin-3-gallate (EGCG), an antioxidant from green tea, inhibits UVB-induced hydrogen peroxide (H(2)O(2)) production and H(2)O(2)-mediated phosphorylation of MAPK signaling pathways. We found that treatment of EGCG (20 microg/ml of media) to NHEK before UVB (30 mJ/cm(2)) exposure inhibited UVB-induced H(2)O(2) production (66-80%) concomitant with the inhibition of UVB-induced phosphorylation of ERK1/2 (57-80%), JNK (53-83%), and p38 (50-77%) proteins. To demonstrate whether UVB-induced phosphorylation of MAPK occurs via UVB-induced H(2)O(2) (oxidative stress) production, NHEK were treated with the oxidant H(2)O(2). Treatment of H(2)O(2) to NHEK resulted in phosphorylation of ERK1/2, JNK, and p38. Using the same in vitro system, when these cells were pretreated with EGCG or with the known antioxidant  ascorbic acid (as positive control), H(2)O(2)-induced phosphorylation of ERK1/2,  JNK, and p38 was found to be significantly inhibited. These findings demonstrate  that EGCG has the potential to inhibit UVB-induced oxidative stress-mediated phosphorylation of MAPK signaling pathways, suggesting that EGCG could be useful  in attenuation of oxidative stress-mediated and MAPK-caused skin disorders in humans.  Copyright 2001 Academic Press.  PMID: 11601887  [PubMed - indexed for MEDLINE]

10. J Leukoc Biol. 2001 May;69(5):719-26.  Green tea polyphenol (-)-epigallocatechin-3-gallate treatment to mouse skin prevents UVB-induced infiltration of leukocytes, depletion of antigen-presenting  cells, and oxidative stress.  Katiyar SK, Mukhtar H.  Department of Dermatology, School of Medicine, Case Western Reserve University, Cleveland, OH 44106, USA. skatiyar@uab.edu  

Ultraviolet (UV) radiation-induced infiltrating leukocytes, depletion of antigen-presenting cells, and oxidative stress in the skin play an important role in the induction of immune suppression and photocarcinogenesis. Earlier we have shown that topical application of polyphenols from green tea or its major chemopreventive constituent (-)-epigallocatechin-3-gallate (EGCG) prevents UV-B-induced immunosuppression in mice. To define the mechanism of prevention, we found that topical application of EGCG (3 mg/mouse/3 cm(2) of skin area) to C3H/HeN mice before a single dose of UV-B (90 mJ/cm(2)) exposure inhibited UV-B-induced infiltration of leukocytes, specifically the CD11b+ cell type, and myeloperoxidase activity, a marker of tissue infiltration of leukocytes. EGCG treatment was also found to prevent UV-B-induced depletion in the number of antigen-presenting cells when immunohistochemically detected as class II MHC+ Ia+ cells. UV-B-induced infiltrating cell production of H2O2 and nitric oxide (NO) was determined as a marker of oxidative stress. We found that pretreatment of EGCG decreased the number of UV-B-induced increases in H2O2-producing cells and inducible nitric oxide synthase-expressing cells and the production of H2O2 and NO in both epidermis and dermis at a UV-B-irradiated site. Together, these data suggest that prevention of UV-B-induced infiltrating leukocytes, antigen-presenting cells, and oxidative stress by EGCG treatment of mouse skin may be associated with the prevention of UV-B-induced immunosuppression and photocarcinogenesis.  PMID: 11358979  [PubMed - indexed for MEDLINE]

9. J Am Acad Dermatol. 2001 Mar;44(3):425-32.  Cutaneous photoprotection from ultraviolet injury by green tea polyphenols.  Elmets CA, Singh D, Tubesing K, Matsui M, Katiyar S, Mukhtar H.  Department of Dermatology, Case Western Reserve, Cleveland, Ohio, USA.  

BACKGROUND: In animal models, extracts from green tea have been shown to be remarkably effective at reducing the severity of adverse human health effects of overexposure to ultraviolet (UV) radiation. Although sunscreens and other photoprotective measures have traditionally been used for this purpose, there is  a need for additional measures and natural products are increasingly being explored for that purpose.

OBJECTIVE: Our purpose was to evaluate the effect of polyphenols from green tea on parameters associated with acute UV injury.

METHODS: Areas of skin of normal volunteers were treated with an extract of green tea or one of its constituents. Thirty minutes later, the treated sites were exposed to a 2 minimal erythema dose solar simulated radiation. UV-treated skin was examined clinically for UV-induced erythema, histologically for the presence  of sunburn cells or Langerhans cell distributions, or biochemically for UV-induced DNA damage. RESULTS: Application of green tea extracts resulted in a dose-dependent inhibition of the erythema response evoked by UV radiation. The (-)-epigallocatechin-3-gallate (EGCG) and (-)-epicatechin-3-gallate (ECG) polyphenolic fractions were most efficient at inhibiting erythema, whereas (-)-epigallocatechin (EGC) and (-)-epicatechin (EC) had little effect. On histologic examination, skin treated with green tea extracts reduced the number of sunburn cells and protected epidermal Langerhans cells from UV damage. Green tea extracts also reduced the DNA damage that formed after UV radiation.

CONCLUSION: Polyphenolic extracts of green tea are effective chemopreventive agents for many of the adverse effects of sunlight on human health and may thus serve as natural alternatives for photoprotection.  PMID: 11209110  [PubMed - indexed for MEDLINE]

8. Carcinogenesis. 2001 Feb;22(2):287-94.  Green tea polyphenol (-)-epigallocatechin-3-gallate treatment of human skin inhibits ultraviolet radiation-induced oxidative stress.  Katiyar SK, Afaq F, Perez A, Mukhtar H.  Department of Dermatology, Volker Hall 501, 1530 3rd Ave S, The University of Alabama at Birmingham, Birmingham, AL 35294-0019, USA. sxk32@po.cwru.edu  

The use of naturally occurring botanicals with substantial antioxidant activity to afford protection to human skin against UV damage is receiving increasing attention. The green tea constituent (-)-epigallocatechin-3-gallate (EGCG) is a potent antioxidant and has shown remarkable preventive effects against photocarcinogenesis and phototoxicity in mouse models. In this study we have investigated the effects of topical application of EGCG, the major polyphenol present in green tea, to human skin before UV irradiation on UV-induced markers of oxidative stress and antioxidant enzymes. Using immunohistochemistry and analytical enzyme assays, we found that application of EGCG (mg/cm(2) skin) before a single UV exposure of 4x minimal erythema dose (MED) markedly decreases  UV-induced production of hydrogen peroxide (68-90%, P < 0.025-0.005) and nitric oxide (30-100%, P < 0.025-0.005) in both epidermis and dermis in a time-dependent manner. EGCG pretreatment also inhibits UV-induced infiltration of inflammatory leukocytes, particularly CD11b(+) cells (a surface marker of monocytes/macrophages and neutrophils), into the skin, which are considered to be the major producers of reactive oxygen species. EGCG treatment was also found to  inhibit UV-induced epidermal lipid peroxidation at each time point studied (41-84%, P < 0.05). A single UV exposure of 4x MED to human skin was found to increase catalase activity (109-145%) and decrease glutathione peroxidase (GPx) activity (36-54%) and total glutathione (GSH) level (13-36%) at different time points studied. Pretreatment with EGCG was found to restore the UV-induced decrease in GSH level and afforded protection to the antioxidant enzyme GPx. Further studies are warranted to study the preventive effects of EGCG against multiple exposures to UV light of human skin.  PMID: 11181450  [PubMed - indexed for MEDLINE]

7. Skin Pharmacol Appl Skin Physiol. 2001 Jan-Feb;14(1):11-9.  Protective effects of (-)-epigallocatechin-3-gallate on UVA- and UVB-induced skin damage.  Kim J, Hwang JS, Cho YK, Han Y, Jeon YJ, Yang KH.  Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Taejon, Korea.

It has been known that green tea and its components possess significant chemopreventive effects against chemical carcinogens and photo-caused skin tumor  formation. In this study, the protective effects of (-)-epigallocatechin-3-gallate (EGCG), a major green tea catechin, on the ultraviolet (UV)-induced skin damage (photoaging) were studied in guinea pigs, hairless mice and human dermal fibroblast cultures. The lipid peroxidation was significantly reduced in the EGCG-treated group. The amount of lipid peroxides produced in the control and EGCG treated group were 838 +/- 144 and 286 +/- 57 nmol/mg at 18 h after UV irradiation, respectively. UVB-induced erythema was also significantly reduced in the EGCG treated group. The erythema relative index of the control and the EGCG treated group were 311 +/- 45 and 191 +/- 49 at 16 h after UV irradiation, respectively. EGCG treatment reduced UVA-induced skin damage (roughness and sagginess) and protected from the decrease of dermal collagen in hairless mouse skin. EGCG treatment blocked the UV-induced increase of collagen secretion and collagenase mRNA level in fibroblast culture. The nuclear transcription factors NF-kappaB and AP-1 binding activities were also inhibited by EGCG treatment.  Copyright 2001 S. Karger AG, Basel  PMID: 11174086  [PubMed - indexed for MEDLINE]

6. Arch Dermatol. 2000 Aug;136(8):989-94.  Green tea and skin.  Katiyar SK, Ahmad N, Mukhtar H.  Department of Dermatology, Case Western Reserve University, Cleveland, OH 44106,  USA.  Comment in     Arch Dermatol. 2001 May;137(5):664.     Arch Dermatol. 2000 Aug;136(8):1051. 

OBJECTIVE: To discuss the current knowledge of polyphenolic compounds present in  green tea as anti-inflammatory, antioxidant, and anticarcinogenic in skin.

DATA SOURCES: References identified from bibliographies of pertinent articles, including our work in related fields.

STUDY SELECTION AND DATA EXTRACTION: Articles were selected based on the use of green tea or its polyphenolic constituents for prevention against inflammation and cancer in the skin. Also discussed is the possible use of green tea to treat  various inflammatory dermatoses.

DATA SYNTHESIS: The polyphenolic compounds from green tea were tested against chemical carcinogenesis and photocarcinogenesis in murine skin. These green tea polyphenols were found to afford protection against chemical carcinogenesis as well as photocarcinogenesis in mouse skin. A few experimental studies were conducted in human skin in our laboratory. Analysis of published studies demonstrates that green tea polyphenols have anti-inflammatory and anticarcinogenic properties. These effects appear to correlate with antioxidant properties of green tea polyphenols.

CONCLUSIONS: The outcome of the several experimental studies suggests that green  tea possess anti-inflammatory and anticarcinogenic potential, which can be exploited against a variety of skin disorders. Although more clinical studies are needed, supplementation of skin care products with green tea may have a profound  impact on various skin disorders in the years to come. Arch Dermatol. 2000;136:989-994  PMID: 10926734  [PubMed - indexed for MEDLINE]

5. J Invest Dermatol. 1999 Dec;113(6):1070-5.  Green tea protects against psoralen plus ultraviolet A-induced photochemical damage to skin.  Zhao JF, Zhang YJ, Jin XH, Athar M, Santella RM, Bickers DR, Wang ZY.  Department of Dermatology, Columbia University, New York, NY, USA. 

The use of psoralens combined with exposure to ultraviolet A radiation is a major form of treatment for psoriasis and a number of other common skin diseases. Although psoralen plus ultraviolet A treatment is highly effective, careful follow-up cohort studies have shown that it greatly increases risk for the development of cutaneous squamous cell carcinoma and melanoma. Strategies to reduce the risk of cancer development in psoralen plus ultraviolet A-treated populations are highly desirable. In prior studies, we demonstrated that green tea and constituent polyphenols protect against ultraviolet B-induced carcinogenesis and reduce the growth rate of established tumors in skin. In this  study, we show that pre- and post-treatment with standardized green tea extract in psoralen plus ultraviolet A treatment populations abrogates the psoralen plus  ultraviolet A-induced photochemical damage to skin. Intact mouse and human skin and reconstituted human skin were employed to assess the effect of both topical and oral administration of standardized green tea extract against psoralen plus ultraviolet A-induced photodamage. Oral administration of standardized green tea  extract prior to and during multiple psoralen plus ultraviolet A treatments reduced hyperplasia and hyperkeratosis in murine skin. Standardized green tea extract treatment also inhibited accumulation of c-fos and p53 protein induction  following a single exposure to psoralen plus ultraviolet A. c-fos and p53 positive cells in psoralen plus ultraviolet A-treated skin were found to be increased by 55.4 +/- 13. 6% and 62.3 +/- 10.5%, respectively, compared with saline-treated unexposed control skin. Oral administration of 0.4 or 0.8% standardized green tea extract inhibited c-fos protein accumulation by 18.5% and  46.2% (p < 0.05), respectively, and p53 protein accumulation by 26.1% and 54.3% (p < 0.05), respectively. Similarly proliferating cell nuclear antigen staining,  a marker of cell proliferation was induced (73.7%) in psoralen plus ultraviolet A-treated skin. Oral administration of 0.4% or 0.8% standardized green tea extract 1 d after psoralen plus ultraviolet A treatment was effective in reducing psoralen plus ultraviolet A-induced inflammatory responses including erythema and edema formation. When standardized green tea extract was applied to EpiDerm, a reconstituted human skin equivalent, psoralen plus ultraviolet A-induced 8-methoxypsoralen-DNA adduct formation and p53 protein accumulation were inhibited. Topical application of 0.2 mg 8-methoxypsoralen per cm2 followed by exposure to ultraviolet A (2.5 J per cm2) resulted in delayed erythema formation  in human subjects. Pretreatment of human skin with topical application of 0.2 mg  standardized green tea extract per cm2 30 min prior to psoralen plus ultraviolet  A treatment resulted in an almost complete abrogation of psoralen plus ultraviolet A-induced erythema. In summary, these data demonstrate that standardized green tea extract protects against psoralen plus ultraviolet A-induced phototoxicity by inhibiting DNA damage and diminishing the inflammatory effects of this modality.  PMID: 10594754  [PubMed - indexed for MEDLINE]

4. Carcinogenesis. 1999 Nov;20(11):2117-24.  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.  Katiyar SK, Challa A, McCormick TS, Cooper KD, Mukhtar H.  Department of Dermatology, Case Western Reserve University, 11100 Euclid Avenue,  Cleveland and University Hospitals of Cleveland and VA Hospital, Cleveland, OH 44106, USA. sxk32@po.cwru.edu  

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.  PMID: 10545414  [PubMed - indexed for MEDLINE]

3. Photochem Photobiol. 1999 Feb;69(2):148-53.  Polyphenolic antioxidant (-)-epigallocatechin-3-gallate from green tea reduces UVB-induced inflammatory responses and infiltration of leukocytes in human skin.  Katiyar SK, Matsui MS, Elmets CA, Mukhtar H.  Department of Dermatology, Case Western Reserve University, Cleveland, OH 44106,  USA. 

Identification of natural products capable of affording protection against UVB radiation-induced inflammatory responses and generation of oxidative stress may have important human health implications. The UVB exposure-induced skin injury and oxidative stress has been associated with a variety of skin disease conditions including photoaging, inflammation and cancer. Tea is a popular beverage consumed worldwide. In several mouse skin models, topical application as well as oral consumption of green tea has been shown to afford protection against chemical and UVB-induced carcinogenesis and inflammatory responses. In the present study, we investigated in human skin, whether topical application of (-)-epigallocatechin-3-gallate (EGCG), the major polyphenolic constituent in green tea, inhibits UVB-induced infiltration of leukocytes (macrophage/neutrophils), a potential source of generation of reactive oxygen species (ROS), and generation of prostaglandin (PG) metabolites. Human subjects were UVB irradiated on sun-protected skin to four times their minimal erythema dosage (MED) and skin biopsies or keratomes were obtained either 24 h or 48 h later. We found that topical application of EGCG (3 mg/2.5 cm2) before UVB (4 MED) exposure to human skin significantly blocked UVB-induced infiltration of leukocytes and reduced myeloperoxidase activity. These infiltrating leukocytes are considered to be the major source of generation of ROS. In the same set of experiments we found that topical application of EGCG before UVB exposure decreased UVB-induced erythema. In additional experiments, we found that microsomes from EGCG pretreated human skin and exposed to UVB, compared to UVB exposure alone, produced significantly reduced PG metabolites, particularly PGE2. The PG metabolites play a critical role in free radical generation and skin tumor promotion in multistage skin carcinogenesis. Careful microscopic examination of skin sections, stained with hematoxylin and eosin, under higher magnification (x400) also revealed that EGCG pretreated and UVB-exposed human skin contained fewer dead cells in the epidermis with comparison to nonpretreated UVB-exposed skin. Taken together, our data demonstrate that EGCG has the potential to block the UVB-induced infiltration of leukocytes and the subsequent generation of ROS in human skin. This may explain the possible mechanism involved in anti-inflammatory effects of green tea. We suggest that EGCG may be useful as a topical agent for protection against UVB-induced ROS-associated inflammatory dermatoses, photoaging and photocarcinogenesis. Further studies are warranted in  this direction.  PMID: 10048310  [PubMed - indexed for MEDLINE]

2. Carcinogenesis. 1998 Dec;19(12):2201-4.  (-)-Epigallocatechin-3-gallate inhibition of ultraviolet B-induced AP-1 activity.  Barthelman M, Bair WB 3rd, Stickland KK, Chen W, Timmermann BN, Valcic S, Dong Z, Bowden GT.  Department of Radiation Oncology, University of Arizona Health Sciences Center, Tucson 85724, USA. 

Green tea polyphenols have been shown to inhibit cancer in a variety of tumor models, including ultraviolet B (UVB)-induced non-melanoma skin cancer. In green  tea extracts, the major dry mass constituent is the family of catechins, of which (-)-epigallocatechin-(3)-gallate (EGCG) is considered to be important for the chemopreventive activity. EGCG has been shown to have antioxidant properties, but there has been little progress toward identifying the specific targets and mechanisms of its action. Using cultured human keratinocytes, we show that UVB-induced AP-1 activity is inhibited by EGCG in a dose range of 5.45 nM to 54.5 microM. EGCG is effective at inhibiting AP-1 activity when applied before, after  or both before and after UVB irradiation. EGCG also inhibits AP-1 activity in the epidermis of a transgenic mouse model. This work begins to define a mechanism by  which EGCG could be acting to inhibit UVB-induced tumor formation.  PMID: 9886579  [PubMed - indexed for MEDLINE]

1. Photochem Photobiol. 1995 Nov;62(5):855-61.  Protection against ultraviolet-B radiation-induced local and systemic suppression of contact hypersensitivity and edema responses in C3H/HeN mice by green tea polyphenols.  Katiyar SK, Elmets CA, Agarwal R, Mukhtar H.  Department of Dermatology, University Hospitals of Cleveland, Case Western Reserve University, OH 44106, USA. 

Exposure of skin to UV radiation can cause diverse biological effects, including  induction of inflammation, alteration in cutaneous immune cells and impairment of contact hypersensitivity (CHS) responses. Our laboratory has demonstrated that oral feeding as well as topical application of a polyphenolic fraction isolated from green tea (GTP) affords protection against the carcinogenic effects of UVB (280-320 nm) radiation. In this study, we investigated whether GTP could protect  against UVB-induced immunosuppression and cutaneous inflammatory responses in C3H mice. Immunosuppression was assessed by contact sensitization with 2,4-dinitrofluorobenzene applied to UVB-irradiated skin (local suppression) or to a distant site (systemic suppression), while double skin-fold swelling was used as the measure of UVB-induced inflammation. Topical application of GTP (1-6 mg/animal), 30 min prior to or 30 min after exposure to a single dose of UVB (2 kJ/m2) resulted in significant protection against local (25-90%) and systemic suppression (23-95%) of CHS and inflammation in mouse dorsal skin (70-80%). These protective effects were dependent on the dose of GTP employed; increasing the dose (1-6 mg/animal) resulted in an increased protective effect (25-93%). The protective effects were also dependent on the dose of UVB (2-32 kJ/m2). Among the four major epicatechin derivatives present in GTP, (-)-epigallocatechin-3-gallate, the major constituent in GTP, was found to be the most effective in affording protection against UVB-caused CHS and inflammatory responses. Our study suggests that green tea, specifically polyphenols present therein, may be useful against inflammatory dermatoses and immunosuppression caused by solar radiation.  PMID: 8570723  [PubMed - indexed for MEDLINE]