| ObjectivesEpidemiological evidence has implicated ultraviolet light ( UV) irradiation as one of the environmental factors in human cataractogenesis. Long - term chronic ultraviolet exposure is believed to be the major cause of senile cataract. But till today, the mechanism by which ultraviolet induces cataract remains unknown. UV is one kind of electromagnetic wave. UV mainly come from nature light of solar radiation. The effect of UV - irradiation on crystalline lens is long - term chronic cumulative process of oxidative stress, it is reasonable to assume that the defense system in the crystalline lens remains sufficiently protective until the cumulative effects exceed a critical level. Then irreversible damage occurs. The mechanisms of UV - irradiation on crystalline lens are direct photochemistry damage and light oxidative stress. Exposure to light in mammalian cells can lead to DNA damage, the severity of which is dependent on the wavelength and the internal or external cellular environment. UV - C ( 100 ~ 290nm) radiation is ecologically not relevant since it is quantitatively absorbed by oxygen and ozone in the Earth's atmosphere, the longer wavelength UV - B (290 ~320nm) and UV - A (320 ~400nm) radiation can have significant effects on the biota. Lens epithelial cells provide a good model for relatively early age - related increase in oxidative stress. Stress has been shown to be associated with DNA damage. Compensatory antioxidant defenses, such as glutathione, catalase and superox-ide dismutase are released in response to light - induced oxidative stress that would result in macromolecular damage ( DNA, crystalline). Also, it is likely that several DNA repair enzymes are induced by exposure to light, in order to maintain the long - term functionality of the lens epithelial cells. Compromisedanti oxidant defenses can lead to excessive DNA damage in lens epithelial cells. The most abundant lesion produced is DNA single strand breakage, which can be sensitively detected by the alkaline microgel electrophoresis (COMET) assay. It is generally accepted that UV irradiation generates active oxygen species including hydrogen peroxide and superoxide ion. These reactive oxygen species induces various cellular responses in eukaryotes, which includes damage of DNA and proteins, triggering of signal transduction pathways, and activation of gene expression. Recent studies have suggested that the lens epithelium may be the site of initiation for cataract development. DNA is obviously one of the most sensitive target for UV - induced damage in lens epithelial cells. It is therefore important to study the mechanism of UV - induced DNA damage and repair in human lens epithelial cell and to investigate the change and role of telomerase and other stress - related proteins. Powerful antioxidants are searched to defense DNA damage UV - induced. To delay the onset and retard the progression of cataract is valuable.Methods1. Human lens epithelial cells were irradiated at UV - doses 0. 0( control group) and 2.5 >5.0 ^7. 5 N10.0 mj/cm2(treated 1 ~4group). With the alkaline comet assay, the amounts of DNA single strand breaks ( SSB) were quantified, the spontaneous repair of DNA SSB after exposure to 10. OmJ/cm2 was also determined in human lens epithelial cells. Human lens epithelial cells were irradiated at UV - doses 0.0( control group) and 2.5,5.0,10.0 mj/cm (treated 1 ~ 3group) ,the distribution of cell cycles UV - induced DNA damage and repair in lens epithelial cells was assayed by flow cytometry(FCM).2. The degree of DNA damage was examined with the alkaline comet assay. Human lens epithelial cells were treated with different concentration of Vi-taminC, taurineN Superoxide dismutase ( SOD) and epigallocatechin gallate ( EGCG) before and after ultraviolet radiation ,the effect of antioxidants on DNA damage degree was examined with alkaline comet assay.3. Human lens epithelial cells were irradiated at UV - doses 0. 0( controlgroup) and 0.5,1. 5,2. 5,3. 5,5. 0,7. 5,10.0 mj/cm2(treated 1 ~7group). telomerase activity was determined by Telomeric Repeat Amplification Protocol -Enzyme Linked Immunosorbent Assay (TRAP -ELJSA) ,P53,P21, growth arrest and DNA damage inducible ( GADD45), proliferating cell nuclear antigen (PCNA) and PI 6 protein levels were analyzed by Western blotting.Results1. The amount of DNA SSB in control group and treated 1 ~ 4group showed increased tendency. The differences of DNA SSB were significantly ( P < 0. 01). UV - induced DNA SSB at UV - doses 10. 0 mj/cm2 in human lens epithelial cells, the half repair time was 60 minute. Human lens epithelial cells UV- induced were arrested at Gj phases of the cell cycle, the percentage in control and experimental guoup of G, phases cell were 51. 5% ,52. 9% ,52. 5% and 50. 0% immediately after UV irradiation; were 43. 7% ,45. 8% ,50. 0% and 51. 1% 2h after UV irradiation; were 38. 7,43. 1% ,47. 1% and 50. 8% 4h after UV irradiation; were 29.80% ,39. 8% ,48.5% and 50.4% 8h after UV irradiation ; were 56.6% ,48.0% ,30.0% and 26.3% 24h after UV irradiation;2. Human lens epithelial cells were treated with different concentration of taurine, SOD and EGCG before ultraviolet radiation, the differences of antioxida-nts effect on DNA in control and treated group were significantly (P <0. 01). Human lens epithelial cells were treated with different concentration of VitC, taurine>,SOD and EGCG after ultraviolet radiation, the differences of antioxida-nts effects on DNA between the control and treated group were significantly (P<0.01). The differences of effect on DNA in four kinds of antioxidants before UV irradiation were significantly (P <0.01); The differences of effect on DNA in four kinds of antioxidants after UV irradiation were not significantly (P >0. 05).3. Telomerase activity in control group and treated 1 ~ 7 group showed increased tendency, the differences of telomerase activity in 8 groups were significantly (P < 0.01). The expression of P53, P21, GADD45, PCNA, P16 proteins showed increased tendency in experimental group, compairing with the control...
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