The relationship between UVB screening and cytoprotection by microcorpuscular ZnO or ascorbate against DNA photodamage and membrane injuries in keratinocytes by oxidative stress.
Decreased cell viability and increased formation of cyclobutane-type pyrimidine dimers (CPDs) in DNA of UVB-irradiated keratinocytes were shown to be appreciably restored by the addition of w/o emulsion of microcorpuscular zinc oxide (mcZnO) with a corpuscle diameter of 0.15 microm. The cytoprotection was exerted only by 20 wt/wt% mcZnO at levels equivalent to 40- to 100-microm-thick emulsion layers, which screened 90-92% of the incident UVB. However, protection was not seen by mcZnO below 20-microm thickness, which, unexpectedly, screened 79% of the incident radiation. This suggests that thorough UVB screening is necessary for cytoprotection. This may be attributable to involvement of intracellular reactive oxygen species (ROS) secondarily generated from UVB-irradiated mcZnO. Intracellular ROS was increased in mcZnO-added cells in a time-dependent manner even after UVB irradiation, contrasting with reduction of intracellular ROS in ascorbic acid-added cells. UVB-induced disruption of cell membrane integrity was reduced by mcZnO at 100-microm thickness, equivalent to the addition of ascorbic acid of 50 microM. Thus, mcZnO was thought to be cytoprotective through reductions of intracellular ROS generation, CPD formation and cell membrane disintegration when added so abundantly so as to achieve UVB-screening more than 90%.
Hayashi
S
S
Division of Cell Biochemistry, Hiroshima Prefectural University School of BioSciences, Shobara, 727-0023, Hiroshima, Japan.
Takeshita
H
H
Nagao
N
N
Nikaido
O
O
Miwa
N
N
D000818:Animals; D001205:Ascorbic Acid / Q000494:pharmacology*; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D002478:Cells, Cultured; D004249:DNA Damage / Q000187:drug effects / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D015603:Keratinocytes / Q000166:cytology / Q000187:drug effects* / Q000528:radiation effects; D051379:Mice; D018384:Oxidative Stress / Q000187:drug effects* / Q000528:radiation effects; D011740:Pyrimidine Dimers / Q000528:radiation effects; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D012867:Skin / Q000166:cytology / Q000187:drug effects / Q000528:radiation effects; D013473:Sunscreening Agents / Q000494:pharmacology*; D014466:Ultraviolet Rays; D015034:Zinc Oxide / Q000494:pharmacology*
D011740:Pyrimidine Dimers; D011838:Radiation-Sensitizing Agents; D013473:Sunscreening Agents; D001205:Ascorbic Acid; D015034:Zinc Oxide