The effect of dimethylsulfoxide, 1-[2-(decylthio)ethyl]azacyclopentan-2-one and Labrafac^®CC on porphyrin formation in normal mouse skin during topical application of methyl 5-aminolevulinate: A fluorescence and extraction study

Summary 

In this work, the effect of 10% of dimethylsulfoxide (DMSO), 1-[2-(decylthio)ethyl]azacyclopentan-2-one (HPE-101) and Labrafac^®CC (a mixture of caprylic and capric acid triglycerides) on porphyrin formation in mouse skin during topical application of methyl 5-aminolevulinate (MAL) was studied. The porphyrin level in mouse skin was determined by measuring directly fluorescence and by extraction method.

The porphyrin fluorescence kinetics during continuous application of MAL in creams in concentrations 2, 10 and 20% (wt./wt.) for up to 7h showed that in this concentration range the kinetics of porphyrin production in the site of application does not depend significantly on the MAL concentration. After 24h of application of all studied creams the porphyrin fluorescence in the area of treatment was dramatically reduced to be about two-fold higher than the skin autofluorescence, suggesting a significant decrease of the porphyrin concentration in these sites, although in all cases traces of porphyrins were found.

It was found by extraction method that a 10% MAL cream with 10% DMSO for 4h increased the concentration of porphyrin about four-fold compared with 10% MAL cream alone. The presence of 10% HPE-101 or 10% Labrafac^®CC in the 10% MAL cream increased the porphyrin concentration in the area of application about 2.5- and 2-fold, respectively, as compared with MAL cream without enhancers. No statistically significant difference was found between the effects of the creams containing 10% MAL with 10% HPE-101 or 10% Labrafac^®CC. The results obtained after 24h of mouse skin treatment with the same creams showed a large decrease of porphyrin formation in comparison with results found after 4h. All porphyrin concentrations measured after this time of MAL creams application were similar. Skin erythema was observed using MAL cream with DMSO and HPE-101, but not with Labrafac^®CC.

Our work suggests that the new penetration enhancer Labrafac^®CC in creams with MAL may be used to increase the penetration of MAL through the mouse skin and at the same time increase production of porphyrin in the skin. This may reduce skin erythema, which is induced by DMSO and HPE-101.

Abbreviations: ALA, 5-aminolevulinic acid, ALA-PDT, photodynamic therapy induced by 5-aminolevulinic acid, DMSO, dimethylsulfoxide, hexyl-ALA, hexyl 5-aminolevulinate, HPE-101, 1-[2-(decylthio)ethyl]azacyclopentan-2-one, MAL, methyl 5-aminolevulinate, PDT, photodynamic therapy, PpIX, protoporphyrin IX, v/v, volume/volume concentration, wt./wt., weight/weight concentration

Keywords: Porphyrin, Normal mouse skin extraction, Methyl 5-aminolevulinate, Topical application, Permeation enhancers