Evaluation of skin damage caused by percutaneous absorption enhancers using fractal analysis

Fractal analysis of the cross-sectional morphology of rat skin was conducte d to evaluate pathologic changes evoked by percutaneous absorption enhancer s. Male hairless rats (WBN/Ht-ILA), 8 weeks old, weighing 160 to 180 g were used. Under anesthetization, glass cells (10-mm inner diameter) were attac hed to the rats' abdomens, and test solutions containing various mixtures o f the percutaneous absorption enhancers, sodium lauryl sulfate, isopropanol , 2-methyl-1-butanol, and sodium myristate were applied. Six hours after ap plication, the solutions were removed and the abdominal skin was excised. S kin cross sections were analyzed with a charge-coupled device (CCD) camera. Image data taken by the CCD camera were fed into a desktop digital compute r; then the fractal dimension of each skin cross section was determined on the basis of the box-counting algorithm. A pathologic study was also perfor med on the skin treated with the test solution. All sections of skin were e xamined with an optical photo microscope. Pathologic findings were classifi ed into five levels. The total irritation score (TIS) was defined as the su mmation of damage levels in all regions. Only with the administration of hy drogel containing 2-methyl-1-butanol or sodium lauryl sulfate were positive values of TIS observed. However, the TIS values were independent of the co ncentration of these components. The most severe skin damage was evoked by application of sodium lauryl sulfate. Noticeable skin damage was also seen with 2-methyl-1-butanol. No irritation to the skin resulted from treatment with isopropanol or sodium myristate. When test solution containing sodium lauryl sulfate was applied to the skin, a remarkable increment in fractal d imensions was noted. This may suggest that the structure of the skin was gr eatly compromised as a result of sodium lauryl sulfate application. Althoug h no change in fractal dimension was observed as a result of application of the test solution containing only 25% isopropanol, the fractal dimension o f skin cross section gradually increased with increasing concentrations of isopropanol, 2-methyl-1-butanol or sodium myristate in the test solutions. The increment of fractal dimension was around 0.4. Thus, the skin structure was also altered by the application of high concentrations of these compou nds. Although the relevance to humans is not known, fractal analysis of ski n structure is thought to be useful as a novel method for detecting skin da mage that is brought about by the application of percutaneous absorption en hancers. Copyright (C) 2000 Wiley-Liss, Inc. and the American Pharmaceutica l Association J Pharm Sci 89: 556-561, 2000.