TOPICAL DELIVERY OF ANTI-INFLAMMATORY COMPOUNDS 349 This result is in line with the evidences reported in literature that point out a penetration enhancer effect of soy lecithin toward topically applied active substances (6). Lecithin interacts directly with stratum corneum packing and occludes the skin surface thus in- creasing tissue hydration, and consequently, the permeation of actives. As regards SLN based formulations (Fig. 3), SG inclusion in lipid matrix of solid lipid nanoparticles (SLN-IN) produced an enhancement of active percutaneous absorption Figure 2. Cumulative amount (Q24) of DG permeated during 24 h from F (gel containing 0.5% of SG), H (gel containing 0.5% of SG and 1% of soy lecithins), B (O/W emulsion containing 0.5% of SG), and D (O/W emulsion containing 0.5% of SG and 1% of soy lecithins). Figure 3. Cumulative amount (Q24) of SG permeated during 24 h from SLN-IN (viscosized suspension of SG-loaded SLN) and SLN-OUT (viscosized suspension of not loaded SLN and “free” SG).

JOURNAL OF COSMETIC SCIENCE 350 through the skin with respect to the formulation characterized by not loaded SLN and free SG suspension (SLN-OUT). A different mechanism could explain the permeation enhancer effect of SLN observed in this study. Once applied to the stratum corneum the SLN, made of high biocompatible lipids, can fuse with stratum corneum lipids. This collapse of structure liberates permeant into a medium in which the active is poorly soluble. In these conditions an increase of SG thermodynamic activity is observed so facilitating the delivery. IN VIVO ANTI-INFLAMMATORY ACTIVITY Formulation D, G, SLN-IN, and SLN-OUT, showing the best in vitro profi le, were fur- ther studied in vivo to determine their ability to inhibit the UVB-induced skin erythema on healthy human volunteers. Skin refl ectance spectrophotometry was used to determine the extent of the erythema and to assess the inhibition capacity of the formulations after their preventive application onto the skin. The AUC was determined for each subject plotting ΔEI values versus time. An inverse relationship was found between the AUC and the inhibition of UVB-induced erythema (Table III). Fig. 4 reports the PIE values. Formulations D and G, containing SG and DG respectively, showed to be more effective than SLN-IN and SLN-OUT formulations, containing SG, in inhibiting the induced erythema 1 h after gel removal (p 0.05), while at 3 and 6 h, the formulation SLN-IN showed the best inhibitory ability (p 0.05 Fig. 4, Table III). The mechanism described to justify the in vitro evidences appears to be useful also to fi nd an explanation of in vivo results. In fact, soy lecithin, increasing skin hydration, produced Figure 4. Percentage of inhibition of the UVB-induced erythema (PIE) by formulation D, SLN-IN, and SLN-OUT containing SG (0.5% w/w) or with formulation G containing DG (0.5% w/w). Data represent the mean for 10 subjects.