TOPICAL DELIVERY OF ANTI-INFLAMMATORY COMPOUNDS 347 To better outline the results obtained, the PIE was calculated from the AUC values using equation (3): (C) (T) (C) AUC - AUC Inhibition (%) 100 AUC = × (3) where AUC(C) is the area under the response/time curve of the vehicle-treated site (con- trol) and AUC(T) is the area under the response/time curve of the drug-treated site. Statis- tical differences of in vivo data were determined using repeated measure analysis of variance (ANOVA) followed by the Bonferroni–Dunn post hoc pairwise comparison pro- cedure. A probability, p, of less than 0.05 was considered signifi cant in this study. HPLC ANALYSES DG quantifi cation was effected by HPLC. The HPLC apparatus consisted of a Shimadzu LC-10 AT VP (equipped with a 20-μl loop injector and a SPD-M10A VP Shimadzu pho- todiode array UV detector. Chromatography was performed using a Symmetry Shield C18 RP column (particle size, 5 μm, 250 × 4.6 mm i.d.. Phenomenex, Torrance, CA). The mobile phase was composed of 30% water (pH 3 adjusted with phosphoric acid) and 70% acetonitrile and the detection was effected at 250 nm. The fl ow rate was set at 1 ml/ min. The retention time was 7.5 min. UV ANALYSES SG quantifi cation was effected by UV analyses. The UV apparatus consisted of a spectro- photometer UV-1700 PharmaSpec, Shimadzu. Calibration curves for validated UV assays of SG were performed on fi ve solutions in the concentration range 8—80 mg/ml using a wavelength of 240 nm. The correlation coeffi cient was greater than 0.990. Each point represented the average of three measurements, and the error was calculated as standard deviation (±SD). RESULTS AND DISCUSSION PREPARATION AND CHARACTERIZATION OF SG-LOADED SLN SG-loaded SLN were prepared with Compritol® 888 ATO (glyceryl behenate, tribe- henin), a mixture of mono-, di-, and triglycerides of behenic acid (C22) as the solid lipid and Pluronic® F68 (poloxamer 188) as the surfactant. We decided to use these ingredients after a lipid screening for the identifi cation of matrices for SG incorpora- tion, which pointed out a high affi nity of the active compounds toward Compritol® 888 ATO (data not shown). The use of SLN strategy to optimize DG permeation profi le resulted to be diffi cult, because the active ingredient, even if showed a chem- ical structure similar to SG, was very hydrophilic and consequently unsuitable to be formulated in a SLN system.
JOURNAL OF COSMETIC SCIENCE 348 Notwithstanding that the hot high pressure homogenization method is recognized as the most suitable procedure to produce lipid nanoparticles because of its easy scalability, the US method, in our experience, is a “cheap and fast” method suitable for the production of lipid nanoparticles. Mean particle size data of SG-loaded SLN were obtained by PCS analyses. The results confi rmed the effi ciency of the US method: not loaded SLN showed a mean diameter of 280.9 ± 25.4 nm (polydispersity index: 0.237 ± 0.03) while for SG-loaded SLN a popula- tion with a mean diameter of 185.4 ± 12.8 nm was obtained (polydispersity index: 0.395 ± 0.01). As regards the drug loading, the SLN produced by the US method had a high incorporation effi ciency showing drug recovery of 88%. IN VITRO PERCUTANEOUS ABSORPTION STUDY In vitro skin permeation experiments were performed using human SCE membranes in- stead of full-thickness skin because, as reported by others, the dermis in vitro can act as a signifi cant artifi cial barrier to the absorption of lipophilic compounds (23). In Figs 1 and 2, the cumulative amounts (Q24) of SG and DG permeated through human SCE membrane are shown, respectively. From the results obtained, all the formulation containing Lecinol® S-10 (H, D, G, and C) produced an increase of per- cutaneous absorption of SG and DG compared to control formulations (F, B, E, and A), respectively. Figure 1. Cumulative amount (Q24) of SG 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).
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