Comparative permeation studies for delta-aminolevulinic acid and its n-butylester through stratum corneum and artificial skin constructs.

The improvement of the permeation properties through excised human stratum corneum and artificial skin constructs (ASC) of delta-aminolevulinic-n-butylester (ABE) compared with delta-aminolevulinic acid (ALA) was investigated. For this purpose the permeated amounts of each substance were determined depending on time in a Franz diffusion cell experiment with stratum corneum and ASC, respectively. Furthermore the barrier properties of ASC were compared with those of stratum corneum. Detection of both substances was performed by high-performance liquid chromatography (HPLC) analysis. For the determination of ABE a new HPLC method was developed. ABE could be determined with the new HPLC method with sufficient sensitivity (detection limit: 0.1 microg/ml) after derivatisation with o-phthalaldehyde (OPA). Stratum corneum and ASC were more permeable for ABE than for ALA. The permeation coefficient P of ABE through stratum corneum was nearly ten-fold higher than that of ALA. Using ASC as permeation barrier the permeation coefficient of ABE was about 22-fold higher than that of ALA. ABE and ALA permeated 142-fold and 64-fold, respectively, faster through ASC than through stratum corneum.