Effect of Organic Solvents on Normal Human Stratum Corneum: Evaluation by the Corneoxenometry Bioassay

Abstract

Background: Organic solvents alter the stratum corneum structure and barrier function. Objective: To measure the effect of various solvents upon human stratum corneum using the ex vivo corneoxenometry bioassay which is a variant of corneosurfametry. Methods: Corneoxenometry entails collection of human stratum corneum by cyanoacrylate. The material is immersed in organic solvents for periods ranging from 1 to 120 min. After staining the samples with a toluidine blue-basic fuchsin solution, the color is measured using reflectance colorimetry. Solvent aggressivity to the stratum corneum correlates with the color darkening of the samples. Results: The least aggressive solvent was hexane, followed by ethanol, methanol, hexane-ethanol, chloroform, chloroform-methanol and hexane-methanol. The influence of contact time between solvents and the stratum corneum showed a logarithmic pattern which varied according to the solvent. Conclusion: Data are in line with previous experiments conducted in vivo and in vitro, thus indicating the predictive value of corneoxenometry. Such a bioassay may avoid hazards of some in vivo human testings.

Corneosurfametry and Corneoxenometry

“…Chloroform-methanol is well known as the most potent extraction mixture for lipids in biological samples. However, it did not reach the top rank using the CXM bioassay [ 16 ]. Such a fi nding further illustrated the fact that organic solvents may alter other biological components which in turn affect the CXM data.…”

“…In particular, they were compared using CXM [ 16 ]. Series of CSSS were immersed for 1, 5, 10, 30, 60, or 120 min in vials containing deionized water or an organic solvent including chloroform, ethanol, hexane, methanol, chloroform-methanol (2:1, v/v), hexaneethanol (2:3, v/v), and hexane-methanol (2:3, v/v).…”

“…After contact with the selected solvent for one of the predetermined duration, CSSS were thoroughly rinsed under running tap water for 20 s, air-dried, and stained for 3 min with toluidine blue-basic fuchsin dyes. The ranking from the least to the most aggressive solvent according to the mean CIM was as follows: hexane (40.7), ethanol (26.5), methanol (23.5), hexane-ethanol (23.3), chloroform (20.8), chloroform-methanol (15.5), and hexanemethanol (7.8) [ 16 ]. CIM values showed that the effect of hexane-methanol on SC was signifi cantly higher ( p < 0.01) than those of any other solvent with the exception of chloroformmethanol.…”

“…Despite interindividual inconsistencies in corneocyte alterations, signifi cant differences were reported among solvents using the CXM bioassay [ 16 ]. The test organic solvents are recognized to extract lipids [ 26 , 27 , 34 -37 ].…”

“…In addition, alterations in the SC other than pure lipid extraction are likely [ 27 ]. Large interindividual differences in CIM were found for any of the solvents or mixtures [ 16 ] suggesting the variability in the overall lipid extraction by these compounds [ 26 ]. The alterations induced in the human SC by solvents at the CXM bioassay were indeed reported to be more variable in extent that those induced by diluted surfactants as shown at the CSM bioassay on normal subjects [ 13 , 16 ].…”