Endogenous skin flourescence includes bansds that may serve as quantitative markers of aging and photoaging

Abstract

Aging and photoaging cause distinct changes in skin cells and extracellular matrix. Changes in hairless mouse skin as a function of age and chronic UVB exposure were investigated by flourescence excitation spectroscopy. Fluorescence excitation spectra were measured in vivo, on heat- separated epidermis and dermis, and on extracts of mouse skin to characterize the absorption spectra obtained in vivo on 6 wk old mouse skin had maxima at 295, 340, and 360 nm; the 295 nm band was the dominant band. Using heat separated tissue, the 295 nm band predominantly originated in the epidermis and the bands at 340 nm band to pepsin digestable collagen cross-links flourescence and the 360 nm band to collagenase digestable collagen cross- links flourescence. Fluorescence excitation maxima remained unchanged in chronologically aged mice (34-38 wk old), whereas the 295 nm band decreased in intensity with age. In contrast, fluorescence excitation spectra of chronically UVB exposed mices showed a large increase in the 295 nm band compared with age-matched controls and the bands at 340 and 350 nm were no longer distinct. Two new bands appeared in the chronically exposed mice at 270 nm and at 305 nm. These reproducible changes in skin autofluorescence suggest that aging causes predictable alterations in both epidermal and dermal fluorescence, whereas chronic UV exposure induces the appearance of new fluorphores.