| Chapter OneBackgroundUV radiation is an important environmental factor with inducible health hazards for mankind, particularly UVB has been demonstrated to be the pivotal casual factor in human. UVB exposure has been established to induce adverse effects, such as erythema, edema, blistering, skin pigmentation, sunburn cell formation, hyperplasia, photoaging and nonmelanoma skin cancer. Substantial UVB exposure may lead to detrimental acute effects such as tissue damage owing in part to the organism's surveillance mechanism(s) attempting to eliminate damaged cells through apoptosis and inflammation. Scientific interest in UV-induced information highways from the cell surface to the nucleus has explored over the past years, one of the best-studied signaling routes is the mitogen activated protein kinase (MAPK) signal transduction pathway, which plays a crucial role in the regulation of the multitude of UV-induced cellular responses. MAPK is composed of at least four families that include extracellular signal-regulated kinase (ERK), c-Jun NH2-terminal kinase (JNK), p38, and ERK5/BMK1. P38 mediated apoptosis and inflammation are critical in protecting the integrity of the epidermis against the tumorigenic effects of UV-induced damage. Green tea is one of the most widely consumed beverages worldwide. The polyphenols in green tea are catechins, a family of compounds which includes (-)-epigallocatechin-3-gallate (EGCG), (-)-epigallocatechin, (-)-epicatechin-3-gallate, (-)-epicatechin . EGCG , which are known to be effective free radical scavengers and potent antioxidants, protect against chemical carcinogenesis and UV-induced oxidative stress. Here We used HaCaT cells to assess the effects of EGCG on UVB-induced damage, such as apoptosis and cytokine secretion. We also attempted to ascertain the regulation mechanism of p38MAPK pathways, by which UVB irradiation and EGCG treatment could function in HaCaT cell culture system.Objectives: Part I to investigate the incidence of apoptosis, secretion of cytokine, expression of p38MAPK and pp38MAPK induced by UVB irradiation in HaCaT cells; Part IIto investigate the EGCG effects on the apoptosis, secretion of cytokine and expression of p38MAPK.Methods: Flow cytometry was used to detect the apoptosis of the cells. ELISA was used to detect the TNF-αconcentration. Western blot analysis was performed to determine the expression of p38 mitogen-activated protein kinase (MAPK).Results: PartⅠ: After UVB irradiation P38MAPK phosphorylation was detectable immediately and peaked at one hour. Again TNF-α, IL-1β, IL-6 secretion and cell apoptosis were significantly increased. P38 inhibitor, SB203580 inhibited the activity of p38MAPK, reduced cytokine secretion of TNF-α, IL-1β, IL-6 and decreased cell apoptosis. These data suggest that p38 MAPK activation is one aspect of the signaling cascade which culminates in the secretion of TNF-α, IL-1β, IL-6 and contributes to cell apoptosis after UVB irradiation. PartⅡ:We found that EGCG reduced levels of the phosphorylation of UVB-induced p38 MAPK. coupled with a marked down-regulation of UVB-induced cytokine secretion and apoptosis.Conclusions: These data suggest p38 MAPK activation is one aspect of the signaling cascade that culminates in the secretion of cytokine and contributes to cell apoptosis after UVB irradiation and demonstrate that EGCG exerts photoprotective effects against UVB irradiation. Pretreatment with EGCG protects against UVB irradiation via the suppression p38 MAPK activation. Our results suggest that EGCG may be useful in the prevention of UVB-induced human skin damage.Chapter TwoBackgroundProtection against UVA exposure is also important since UVA radiation (320-400 nm), which makes up 95% of natural sunlight, is not filtered by standard glass. UVA is a potent inducer of reactive oxygen species (ROS), which can induce various biological processes. Chronic UVA irradiation has been reported to induce photoaging and photocarcinogenesis, because of its capacity to reach dermal layers, unlike UVB (290-320 run) which is absorbed in the epidermis. Clinically and histopathologically, photoaging and photocarcinogenesis behaved themselves many characteristics. Our researches have proved that EGCG cream showed photoprotections in BALB/c mice skin induced by acute and chronic UVB irradiation, such as reduced apoptosis,etc.Here we evaluated the photoprotective effects of EGCG cream against chronic UVA-induced damages in BALB/c mice.Objective: To investigate the potency of EGCG cream in reducing the degradative changes photoaging induced in BALB/c mouse skin upon exposure to chronic UVA radiation for 12 weeks.Methods: EGCG was prepared in hydrophilic ointment as the vehicle. Mice were divided into 6 groups and each group has 5 mice. The first received no treatment and was the control group. The second and third groups received EGCG and vehicle treatment ,respectively. The fourth , fifth and sixth group received UVA treatment only, UVA+EGCG treatment and UVA+vehicle, respectively. After 12 weeks' treatment as above, all mice were sacrificed and the skin specimens were examined by scanning electron microscope and common light microscope.Results: Upon exposure of mice to UVA radiation, the results of common light microscope and scanning electron microscope indicated that among groups one ,four, and five, the thickness of dermal layers have significant difference. There are elastosis with accumulation of elastotic fibers. Comparison of Groups one, two and three shows similar results.Conclusions: It can be concluded that topical EGCG cream is capable of preventing the structural damage caused by chronic UVA irradiation and EGCG is also found very useful in decelerating the photoaging process. |
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