Apoptosis of human dermal endothelial cells as a potential side effect following therapeutic administration of UVA1 irradiation: preliminary results

Apoptosis is a highly selective form of cell suicide with characteristic morphological and biochemical features. UVA1 phototherapy has been introduced into the treatment of many T cell-derived skin diseases. The aim of our pilot study was to assess apoptosis of endothelial cells in relation to time after irradiation with medium-dose UVA1 using four different staining techniques. With in situ nick end labelling (ISEL) and Hoechst 33342 staining we investigated DNA degradation during apoptosis and used M30 CytoDEATH to selectively stain the cytoplasm of apoptotic cells. Additionally, the expression of the tumour suppressor gene p53 was determined. ISEL and Hoechst 33342 revealed only a few positive endothelial cells 3 h after UVA1 irradiation. After 6 h almost all vessels were positively stained. By 12 h after irradiation this peak concentration had lowered again. The first p53-positive endothelial cells were seen 6 h after UVA1 irradiation and reached a maximum at 12 h after irradiation. Fibroblasts of the lower dermis were positively stained after 6 and 12 h. M30-positive endothelial cells were found from 3 to 12 hours after irradiation. ISEL and Hoechst 33342 staining clearly revealed UVA1-induced apoptotic cell elimination predominantly restricted to endothelial cells as a possible side effect of UVA1 irradiation. The induction of apoptosis was specifically verified by M30 immunostaining of early caspase cleavage. Whereas the p53-positive endothelial cells underwent programmed cell death as demonstrated by M30, ISEL and Hoechst 33342, some fibroblasts seemed to accumulate the p53 antibody, but this did not induce apoptotic cascades.