Establishment of Photoaging In Vitro by Repetitive UVA Irradiation: Induction of Characteristic Markers of Senescence and its Prevention by PAPLAL with Potent Catalase Activity

Abstract To understand a role of UVA radiation in photoaging of the skin, we established a model of photoaging cells using cultured human dermal fibroblasts. Repeated low‐dose UVA radiation for 10 consecutive days induced senescence in fibroblasts, characterized with (1) increased level of senescence‐associated β ‐galactosidase, (2) flattened large cell shape, (3) accumulation of reactive oxygen species, (4) yellowish coloration and (5) expression of p16. These were also observed in chronologically aged fibroblasts (doubling times >20), whereas none of these were detected in young cells (doubling times <10). Collectively, we propose that fibroblasts exposed to repetitive UVA radiation may be a good model of aged cells to study the mechanism of aging and photoaging and further to search for novel agents preventing cellular senescence. In addition, H 2 O 2 was produced in the culture medium by a single low dose of UVA irradiation. Further, PAPLAL , a nanoparticle of platinum and palladium having potent catalase‐like activity, significantly delayed the onset of H 2 O 2 ‐induced cell senescence. The present study strongly indicates that repetitive short‐term UVA irradiation induces aging of cells possibly via H 2 O 2 and may be suppressed by potent anti‐H 2 O 2 agents.