Flow cytometric analysis of pig epidermal keratinocytes: effects of ultraviolet B irradiation (UVB) and topical PUVA treatment.

The effects of a single application of ultraviolet B irradiation (UVB) and topical PUVA treatment on pig epidermal cell kinetics were studied by DNA-flow cytometry (FCM), 3H-thymidine uptake, mitotic counts and 2-3H-deoxy-D-glucose uptake. Following UVB irradiation (2MED: 250 mJ/cm2) and PUVA (0.9, 1.4 J/cm2) treatment, thymidine uptake and mitosis were markedly decreased. This was followed by a transient increase in all of these parameters. The maximal increase was observed at 96 h following the UVB irradiation and at 168 h following the PUVA treatment (0.9 J/cm2), respectively. The suppression of DNA synthesis and mitosis persisted for a longer period in PUVA-treated than in UVB-treated epidermis. At 48-72 h after the UVB irradiation and 72-144 h after the PUVA treatment, an increase in the cells of the G2/M fraction was observed. This was associated with the decreased mitotic counts, suggesting accumulation of G2-blocked cells. Histologically, PUVA-treated epidermis showed a considerable degenerative change. Mild acanthosis was noted at 72-96 h in UVB-treated epidermis and at 168 h in PUVA-treated epidermis. These results indicate that the inhibition of DNA synthesis and increase in G2-phase cells are associated with the UVB and PUVA induced suppression of epidermal cell proliferation. These suppressive effects that persisted longer in PUVA-treated, than in UVB-treated epidermis, were followed by an increased epidermal keratinocyte proliferation of pig skin in vivo.