Kinetics and localisation of PpIX fluorescence after topical and systemic ALA application, observed in skin and skin tumours of UVB-treated mice

Abstract

SummaryIn this study the kinetics and localisation of protoporphyrin IX (PpIX) fluorescence in skin and skin tumours were examined after topically (20% for 4 h) or systemically (200 mg kg-', i.p.) administered 5-aminolaevulinic acid (ALA). As a model we used hairless mice with skin lesions (actinic keratoses and squamous cell carcinoma), which were induced by daily UVB irradiation. The epidermis of the skin surrounding the tumours (T) was altered (AS); owing to the UVB irradiation, the epidermis was thicker and less elastic. Therefore, non-UVBirradiated mice were used to assess fluorescence of normal skin (NS). Light from a halogen lamp was used to excite at 500 + 20 nm and fluorescence was detected through a filter that passes light of 670 + 50 nm. Maximal fluorescence following i.p. ALA was observed 2 h post injection (p.i.) and was three times less than after topically applied ALA. Furthermore, after i.p. ALA a lower T selectively (T/NS) could be obtained than after topically applied ALA. Maximal fluorescence following topically applied ALA was achieved 6 h after the end of the 4 h application time. At that interval fluorescence of T was twice as high as directly after the application period. Furthermore, T selectivity (T/NS) after topical ALA at the interval of maximal fluorescence was higher than at the interval directly after application. With fluorescence cryomicroscopy localisation of fluorescence in the skin at the interval of maximal fluorescence was determined after both administration routes. For both cases fluorescence was mainly located in T, epidermis and hair follicles. Fluorescence in subcutis could only be observed at 2 h post i.p. ALA and at 6 h post topical ALA. No fluorescence could be observed in muscle. We conclude that, in this model and with these ALA doses, a higher fluorescence intensity and selectivity (T/NS) was achieved after topically applied ALA than after systemically administered ALA. These results make topically applied ALA more favourable for ALA-PDT of superficial skin tumours in this model. In general these results imply that by optimising the time after ALA application the efficacy and selectivity of topical ALA-PDT for skin tumours may be improved.

Kinetics of 5-Aminolevulinic Acid-Induced Fluorescence in Organ Cultures of Bronchial Epithelium and Tumor

“…We also showed that PPIX fluorescence kinetics depend on the time of exposure to 5-ALA in cultures of normal bronchial epithelium. PPIX fluorescence kinetics might also depend on the application modalities of 5-ALA [18]. The results of our experiments may better apply to topical application of 5-ALA (for example inhalation of 5-ALA), since the patterns of 5-ALA transport by blood are not taken into consideration in our system.…”

Therapeutic and immune effects of 5‐aminolevulinic acid photodynamic therapy on UVB‐induced squamous cell carcinomas in hairless mice

“…Six mice were used for identifying visual features of SCCs and nine for in situ PpIX fluorescence examination (17,18). To study the therapeutic efficacy, 24 mice were divided into four groups: untreated, ALA only, light only and PDT.…”

Acceleration of ALA‐induced PpIX fluorescence development in the oral mucosa

“…The resulting tissue-specific photosensitization permits photodynamic diagnosis and therapy, whereby far lower light doses are used for diagnosis. Animal studies have demonstrated stronger PpIX fluorescence after application of ALA in colon [8], bladder [9], and skin tumors [10]. ALA can induce strong PpIX fluorescence in tumors of the bronchi, skin, and mammary tissue [7,[11][12][13][14].…”

“…The safety of ALA as a topical or systemic photosensitizer has been established in multiple clinical trials [7][8][9][10][11][12][13][14]. PpIX is normally present in tissues of the body.…”