LIPO-AMINO ACID CIIOLESTERYL DERIVATIVES 359 Petrolatum Control Model A Model B Figure 7. Visual appearance of damaged skin treated with Models A and B (day 7). A and B recovered from "well-defined erythema" to "barely perceptible erythema" within three days. Models A and B induced a significant increase in water-holding capacity in damaged skin compared with petrolatum (day 3 p 0.05). No significant differences were observed between models A and B with respect to recovery of water- holding capacity or TEWL (Figures 8, 9). A significant decrease in TEWL was observed for models A and B when compared with the no-treatment condition. DISCUSSION EFFECT OF CHOLESTERYL DERIVATIVES ON DAMAGED SKIN Damaged skin shows a marked decrease in water-holding capacity in the stratum cor- neum accompanied by considerable and selective loss of intercellular lipids such as ceramide, cholesterol, cholesterol esters, and polar lipids. In contrast, a similar signifi- cant decrease in water-holding capacity could not be induced by a loss of lipids such as wax esters, squalene, or triglycerides (8). The present study evaluated the possibility of using cholesteryl derivatives to promote the recovery effect in damaged skin, and whether lipo-amino acid cholesteryl derivatives (AGCEs) could be used as a substitute for ceramide. The results showed that AGCEs are more effective than cholesteryl hydroxy stearate or petrolatum in promoting the recovery of water-holding capacity, as shown in Figures 2, 3, and 4. Occlusive agents such as petrolatum increase the water content in the stratum corneum simply by forming an occlusive film that traps beneath it the water already present in the skin (2). The ability

360 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS O 40 30 20' 10' mean+S.E. ! ! ! ! ß i -1 0 1 2 3 days after application = blank • Model A o Model B [] Petrolatum Figure 8. Water-holding capacity following application of stratum comeurn lipid models. of petrolatum to promote recovery in damaged skin is thought to be due to this occlusiveness. Cholesteryl esters showed better recovery effect upon visual and instrumental assessment than petrolatum. As reported before, cholesteryl esters spread on a cellophane film showed water permeability, and the recovery effect for this class of molecule can be attributed to the emollient effect combined with water in the stratum corneum rather than simple occlusion. AGCE, which has a higher water-holding capacity and water permeability, showed better recovery effect than cholesteryl hydroxy stearate. These results indicate that cholesterol esters applied on damaged skin may be incorporated into the lipid component in the stratum corneum to reconstruct damaged lipid layers. CHARACTERIZATION AND EFFECT OF STRATUM CORNEUM LIPID MODEL AGCEs are derivatives of an amino acid (glutamic acid) bearing an amide group and having structural resemblance to ceramide. Ceramides have been reported to be the main component in stratum corneum lipids that form the lameliar structure. The results in Figure 5 suggest that stratum corneum lipid models A (ceramide) and B (AGCE sub-