2.9. Analysis of DNA damage
Analysis of DNA damage was carried out by using the comet assay in the murine embryonic fibroblast line, 3T3-L1 (ATCC). The 3T3-L1 cells were cultured in 12-well tissue culture plates (1 _ 105 cells/well) for 24 h at 37 _C, in a humidified atmosphere containing 5% CO2. Then the cells were pre-treated for 24 h with WTE at concentrations of 5–25 lg/ml. After 24 h of incubation, the cells were treated with 100 lM of H2O2 for 60 min in an ice bath to prevent the action of DNA repair mechanisms and then harvested using trypsin– EDTA, centrifuged for 5 min at 1500 rpm and resuspended in 1 ml of PBS. A volume of 25 ll of cell suspension was mixed with 75 ll of 0.6% low melting agarose. The suspension was spread on a frosted microscopic slide pre-coated with 250 ll of 0.8% normal melting agarose, covered with a cover slip, and then allowed to solidify on ice for 10 min. The cover slips were then removed and the slides were immersed in cold lysis solution containing 1% sodium dodecyl sulphate, 2.5 M NaCl, 100 mM Na2EDTA, 1% Triton X-100, and 10% DMSO, with the DMSO for 1 h at 4 _C in the dark. The slides were arranged in an electrophoresis tank filled with pre-chilled electrophoretic buffer (1 mM Na2EDTA and 300 mM NaOH) and incubated for 20 min. Electrophoresis was conducted at 25 V (300 mA) for 20 min using a power supply. The slides were washed with 0.4 M Tris–HCl (pH 7.5) and stained with 20 lg/ml ethidium bromide. An Olympus BX50 fluorescence microscope was used for viewing the slides. A total of 50 cells in triplicate per group were used to calculate the DNA damage induced by hydrogen peroxide. The comet tail length was measured using an ocular micrometer and the DNA damage was calculated by the following formula: Comet tail length ผ maximum total length _ head diameter
2.9. Analysis of DNA damage
Analysis of DNA damage was carried out by using the comet assay in the murine embryonic fibroblast line, 3T3-L1 (ATCC). The 3T3-L1 cells were cultured in 12-well tissue culture plates (1 _ 105 cells/well) for 24 h at 37 _C, in a humidified atmosphere containing 5% CO2. Then the cells were pre-treated for 24 h with WTE at concentrations of 5–25 lg/ml. After 24 h of incubation, the cells were treated with 100 lM of H2O2 for 60 min in an ice bath to prevent the action of DNA repair mechanisms and then harvested using trypsin– EDTA, centrifuged for 5 min at 1500 rpm and resuspended in 1 ml of PBS. A volume of 25 ll of cell suspension was mixed with 75 ll of 0.6% low melting agarose. The suspension was spread on a frosted microscopic slide pre-coated with 250 ll of 0.8% normal melting agarose, covered with a cover slip, and then allowed to solidify on ice for 10 min. The cover slips were then removed and the slides were immersed in cold lysis solution containing 1% sodium dodecyl sulphate, 2.5 M NaCl, 100 mM Na2EDTA, 1% Triton X-100, and 10% DMSO, with the DMSO for 1 h at 4 _C in the dark. The slides were arranged in an electrophoresis tank filled with pre-chilled electrophoretic buffer (1 mM Na2EDTA and 300 mM NaOH) and incubated for 20 min. Electrophoresis was conducted at 25 V (300 mA) for 20 min using a power supply. The slides were washed with 0.4 M Tris–HCl (pH 7.5) and stained with 20 lg/ml ethidium bromide. An Olympus BX50 fluorescence microscope was used for viewing the slides. A total of 50 cells in triplicate per group were used to calculate the DNA damage induced by hydrogen peroxide. The comet tail length was measured using an ocular micrometer and the DNA damage was calculated by the following formula: Comet tail length ผ maximum total length _ head diameter
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