Quantitative analysis of UVB-induced apoptosis in human epidermis

The quantitative measurement of the induction of apoptosis in cells grown i n vitro can be accomplished using a variety of proven methods. However, the quantitative assay of apoptosis within an intact tissue is very laborious and the results can be misleading. We have established a method to quantita tively analyze the induction of apoptosis in human epidermis following UVB irradiation. The assay is based on the activation of the apoptotically indu ced enzyme caspase 3, using a synthetic caspase 3 substrate. The activation of caspase 3 was shown to correlate with the induction of apoptosis in hum an keratinocytes cultures as a monolayer. We then demonstrated that the act ivation of caspase 3 could be measured from UVB-irradiated whole skin. The induction of apoptosis was confirmed by cellular morphology and terminal de oxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labe ling. Therefore, we concluded that the measurement of caspase 3 specific ac tivity in UVB-irradiated human epidermis was an efficient, inexpensive, and accurate method to quantitate UVB-induced apoptosis in vivo.