Photobleaching during and re-appearance after photodynamic therapy of topical ALA-induced fluorescence in UVB-treated mouse skin.

Type:Uv phototherapy Time:2017-11-01 11:17:59

Photobleaching during and re-appearance after photodynamic therapy of topical ALA-induced fluorescence in UVB-treated

mouse skin.

Photodynamic therapy (PDT) using protoporphyrin IX (PpIX) induced by topically applied 5-aminolevulinic acid (ALA)

seems a promising alternative for the treatment of superficial non-melanoma skin cancer and actinic keratosis. In this

study, the kinetics of new PpIX fluorescence arising after a PDT treatment that had photobleached the original

fluorescence were determined. Our purpose was to examine the feasibility of multiple irradiations, following a single

topical ALA application, to increase PDT efficacy. In addition, photobleaching during PDT and the fluorescence spectra

during and after PDT were studied. As a model we used hairless mice with and without UVB-induced skin lesions. ALA was

applied to the skin for 4 hr. An illumination was delivered either immediately after application or 6 hr after the end

of the application (at interval of maximum fluorescence). During PDT, the fluorescence of normal skin decreased at a

faster rate than the fluorescence of the skin lesions. In the fluorescence study after PDT, the areas treated

immediately post-application showed a fluorescence increase over time similar to that in non-treated areas on the same

mice. A remarkable result was that the fluorescence of areas treated at maximum fluorescence increased, whereas the

fluorescence of non-treated areas did not increase over time. With both treatment intervals the new fluorescence

showed a characteristic PpIX spectrum. Our results demonstrate that a second illumination, when new PpIX fluorescence

has been formed, may increase PDT efficacy after topical ALA application. This finding has been demonstrated

previously for systemic ALA administration.

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