Topical Application of 5-Aminolevulinic Acid Hexyl Ester and 5-Aminolevulinic Acid to Normal Nude Mouse Skin: Differences in Protoporphyrin IX Fluorescence Kinetics and the Role of the Stratum Corneum¶

Abstract

An important limitation of topical 5‐aminolevulinic acid (ALA)‐based photodetection and photodynamic therapy is that the amount of the fluorescing and photosensitizing product protoporphyrin IX (PpIX) formed is limited. The reason for this is probably the limited diffusion of ALA through the stratum corneum. A solution to this problem might be found in the use of ALA derivatives, as these compounds are more lipophilic and therefore might have better penetration properties than ALA itself. Previous studies have shown that ALA hexyl ester (ALAHE) is more successful than ALA for photodetection of early (pre)malignant lesions in the bladder. However, ALA pentyl ester slightly increased the in vivo PpIX fluorescence in early (pre)malignant lesions in hairless mouse skin compared to ALA. The increased PpIX fluorescence is located in the stratum corneum and not in the dysplastic epidermal layer. In the present study, ALA‐ and ALAHE‐induced PpIX fluorescence kinetics are compared in the normal nude mouse skin, of which the permeability properties differ from the bladder. Application times and ALA(HE) concentrations were varied, the effect of a penetration enhancer and the effect of tape stripping the skin before or after application were investigated. Only during application for 24 h, did ALAHE induce slightly more PpIX fluorescence than ALA. After application times ranging from 1 to 60 min, ALA‐induced PpIX fluorescence was higher than ALAHE‐induced PpIX fluorescence. ALA also induced higher PpIX production than ALAHE after 10 min of application with concentrations ranging from 0.5 to 40%. The results of experiments with the penetration enhancer and tape stripping indicated that the stratum corneum acts a barrier against ALA and ALAHE. Use of penetration enhancer or tape stripping enhanced the PpIX production more in the case of ALAHE application than in the case of ALA application. This, together with the results from the different application times and concentrations indicates that ALAHE diffuses more slowly across the stratum corneum than ALA.

ALA and ALA hexyl ester induction of porphyrins after their systemic administration to tumour bearing mice

“…It has already been demonstrated (van den Akker et al, 2000) that after topical application of He-ALA, the stratum corneum of the skin acts as a barrier impairing its penetration through the skin. It has also been observed that topical use of He-ALA restricts porphyrin accumulation to the site of application (Casas et al, 2001b;Moan et al, 2001), but the same intensity of PpIX fluorescence using lower concentrations of ALA esters compared to ALA was obtained in the tissue layers of normal rat colon (Endlicher et al, 2001).…”

An Evaluation of Exogenous Application of Protoporphyrin IX and its Dimethyl Ester as a Photodynamic Diagnostic Agent in Poorly Differentiated Human Nasopharyngeal Carcinoma¶

“…i.v. or topical formulations, could be further developed to allow rapid and even distribution of photosensitizer across the tumor by using specific penetrant enhancers ( 25 ). In addition, modification of the delivery vehicle gel‐1 to enhance normal tissue clearance of PME could be further investigated for application in PDD.…”

Drug Delivery of Aminolevulinic Acid from Topical Formulations Intended for Photodynamic Therapy¶

“…The formulation is generally left in place for 4–6 h before a biopsy is taken from the application site. Sectioning of the biopsy allows the fluorescence intensity of PpIX to be evaluated using suitable microscopy with excitation wavelengths around 400 nm and emission wavelengths from 600 to 700 nm (3,65). Alternatively, PpIX is extracted from dissolved tissue samples and determined using fluorescence spectrophotometry with similar excitation and emission wavelengths as above (33,66,67).…”

“…Their purpose is to remove the stratum corneum and keratinized debris overlying lesions and, thereby, enhance drug penetration (43,60,62,136,137). In a semiquantitative study, Van den Akker et al (65) demonstrated reduced PpIX production due to the reservoir capacity of the stratum comeum after topical application of hexyl ALA. When the stratum comeum was removed by tape stripping, PpIX production equalized between topically applied hexyl ALA and ALA. De Rosa et al (91) quantified the amounts of topically applied ALA or ALA esters retained in the stratum comeum in vitro .…”