Fluorescence excitation spectroscopy for the measurement of epidermal proliferation

Fluorescence excitation spectroscopy was used to assess cellular turnover i n human skin by monitoring changes of endogenous fluorescence. Epidermal pr oliferation was induced with alpha -hydroxy acids. Commercially available g lycolic acid creams (8 and 4% wt/wt concentration) and a vehicle cream (pla cebo) were applied in a randomized double blinded fashion on subjects' fore arms, twice daily for 21 days. Excitation spectra were recorded (excitation 250-360 nm, emission 380 nm) at days 0, 1, 3, 7, 10, 11, 14, 17 and 21, Th e 295 nm excitation band (assigned to tryptophan moieties) was used in this study as a marker for cellular proliferation, To further reduce the day-to day variability of the skin fluorescence the intensity of the 295 nm band w as normalized to the 334 nm band (assigned to collagen crosslinks), The flu orescence emission intensity from placebo-treated skin remained practically unchanged over the period of the measurements while the fluorescence inten sity measured from the glycolic acid-treated skin increased monotonically w ith treatment. The rate of increase of the excitation intensity with treatm ent was found to be dose dependent. The epidermal 295 nm band may be used a s a quantitative marker to monitor the rate of proliferation of epidermal k eratinocytes noninvasively.