Ascorbic acid (AA) is widely used in cosmetic formulations due to its antioxidant property and ability to increase collagen synthesis. Here, we encapsulated AA in vesicles with different lipid compositions. Negative liposome charge favored AA skin retention, with accumulation of 37 ± 12 and 74 ± 23 μg/cm2 in the epidermis and dermis, respectively, after 6 hours. Drug flux was influenced by the formulation composition, and both the presence of cholesterol and the liposomes surface charge were able to increase the amount of AA crossing the skin. The formulation was stable for at least 30 days and promoted a 7-fold increase in flux compared to free AA. Additionally, liposomes were able to interact better with keratinocytes and fibroblasts membranes. In vitro efficacy studies demonstrated that associating AA to these liposomes resulted in increased effectiveness of type I collagen synthesis by fibroblasts and regeneration of UVA-induced damage in keratinocytes. Our results demonstrate the applicability of AA-negatively charged liposomes in promoting AA cutaneous permeation and increasing the retention and flux of this molecule in the skin. This formulation also increased AA stability and effectiveness, opening new perspectives for its application in view of reducing certain skin ageing outcomes.

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Genistein (GEN) has potential advantages for topical skin delivery, but no literature data are available for its quantitation in different skin layers, such as the stratum corneum (SC). Therefore, a simple, rapid, selective and sensitive bioanalytical method was developed and validated for GEN quantitation in porcine skin samples following in vitro permeation studies. GEN was assayed by HPLC with UV-Vis detection (270 nm) using 0.5% acetic acid in water-n-propanol-acetonitrile (50 : 2 : 48, v/v/v) as mobile phase (flowrate of 1.0 mL/min). Specificity was demonstrated since endogenous skin components did not interfere with GEN peak. Standard analytical curve was linear over the concentration range (0.1-60 µg/mL) and the lower limit of quantitation was determined for different skin layers (100 ng/mL). GEN recovery from skin layers ranged from 95.57 to 97.57%. Permeation studies were carried out using an automated vertical diffusion cell apparatus. No fluctuation on the amount of GEN retained in the SC was observed over time, but increasing amounts of the drug were found in deeper layers of the skin. The method was reliable and reproducible for the quantitation GEN in skin samples enabling the determination of the cutaneous penetration profile of this drug in permeation experiments.Key words genistein; HPLC quantitation; bioanalytical validation; skin layer Genistein (GEN) (Fig. 1) is the main isoflavone found in soybeans with several beneficial effects in cardiovascular diseases, osteoporosis and postmenopausal syndrome. Potential advantages of GEN have been reported in different types of cancer, such as breast and prostate, as well as skin cancer. 1) GEN acts in carcinogenesis through different mechanisms such as induction of differentiation, inhibition of topoisomerase II, protein tyrosine kinase activity and angiogenesis. 1,2)Skin cancer arises predominantly from cells located within the epidermis.3) Thus, to reach skin malignancies and achieve therapeutic benefits, antitumoral drugs, such as GEN, have to penetrate the stratum corneum and reach deeper layers of the epidermis. 4) In general, topical administration is a challenge in pharmaceutics. 5) Regardless, previous studies have demonstrated GEN's viability for topical 6) and transdermal permeation from different kinds of vehicles.7) Thus, with the purpose of conducting percutaneous permeation studies, the quantitative determination of the drug in the skin is necessary in order to evaluate the efficiency of the proposed formulations. 8)Due to the complexity of the skin matrices and the need to quantify low levels of the drug in the epidermis, 9) a highly selective analytical tool is required, since most samples usually contain several endogenous components of the skin. In addition, the analytical method must present enough sensitivity, due to possible very low concentrations of the drug present in each skin layer. 10) Considering the complexity and heterogeneity of the skin tissue, an effective extraction procedure to completely recover the analyte from the ...

The electron paramagnetic resonance (EPR) spin labeling methodology was used to analyze the interactions of phosphatidylcholine (PC) liposomal formulations that are commonly used as transepidermal drug delivery systems with stratum corneum (SC) membranes. The lipid dynamics of five liposome formulations were evaluated to study the influences of sorbitan monooleate (Span80), cholesterol, and cholesterol with the charged lipids 2-dioleoyl-3-trimethylammonium-propane (DOTAP) and 1,2-distearoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (DSPG) on the molecular dynamics of PC vesicles. The EPR spectra of 5-doxyl-stearic acid (5-DSA) showed that the addition of Span80 to the liposomes increased the lipid fluidity, whereas cholesterol had the opposite effect, and the combination of charged lipids and cholesterol did not additionally influence the lipid bilayer dynamics. Fatty acid spin-labeled SC membranes were treated with the liposome formulations, leading to migration of the spin label to the molecular environment of the formulation and the presence of two spectral components representing distinct mobility states. In terms of molecular dynamics, these environments correspond to the lipid domains of the untreated SC and the liposome, indicating a poor interaction between the liposome and SC membranes. However, the contact was sufficient to allow a pronounced exchange of the spin-labeled fatty acid. Our data suggest that flexible liposomes may access the inner intercellular membranes of the SC and facilitate mutual lipid exchange without losing their relative liposomal integrity.