Lucyanna Barbosa-Barros

Conformational Changes in Stratum Corneum Lipids by Effect of Bicellar Systems

Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy was applied to study the effects of the bicelles formed by dimyristoyl-glycero-phosphocholine (DMPC) and dihexanoyl-glycero-phosphocholine (DHPC) in porcine stratum corneum (SC) in vitro. A comparison of skin samples treated and untreated with bicelles at different temperatures was carried out. The analysis of variations after treatment in the position of the symmetric CH2 stretching, CH2 scissoring, and CH2 rocking vibrations reported important information about the effect of bicelles on the skin. Bicellar systems caused a phase transition from the gel or solid state to the liquid crystalline state in the lipid conformation of SC, reflecting the major order-disorder transition from hexagonally packed to disordered chains. Grazing incidence small and wide X-ray scattering (GISAXS and GIWAXS) techniques confirmed this effect of bicelles on the SC. These results are probably related to with the permeabilizing effect previously described for the DMPC/DHPC bicelles.

Bicelles: Lipid Nanostructured Platforms with Potential Dermal Applications

Bicelles emerge as promising membrane models, and because of their attractive combination of lipid composition, small size and morphological versatility, they become new targets in skin research. Bicelles are able to modify skin biophysical parameters and modulate the skins barrier function, acting to enhance drug penetration. Because of their nanostructured assemblies, bicelles have the ability to penetrate through the narrow intercellular spaces of the stratum corneum of the skin to reinforce its lipid lamellae. The bicelle structure also allows for the incorporation of different molecules that can be carried through the skin layers. All of these characteristics can be modulated by varying the lipid composition and experimental conditions. The remarkable versatility of bicelles is their most important characteristic, which makes their use possible in various fields. This system represents a platform for dermal applications. In this review, an overview of the main properties of bicelles and their effects on the skin are presented.

Lipid Nanostructures: Self-Assembly and Effect on Skin Properties

This work evaluates the relation between the composition and the self-assembly of some lipid aggregates with their effects on the skin. To this end, liposomes, bicelles and micelles formed by dipalmitoylphosphatidylcholine (DPPC), dimyristoylphosphatidylcholine (DMPC) and dihexanoylphosphatidylcholine (DHPC) were characterized by electron microscopy and dynamic light scattering techniques, and applied on the skin. The results revealed that nanostructures with similar assembly but different composition caused different effects on the skin parameters. In general, samples containing DMPC affected the barrier function to a greater extent than systems containing DPPC. Additionally, our results showed that samples with the same lipid composition but different assembly exerted different effects on the skin. Liposomes decreased or did not modify the transepidermal water loss (TEWL), while bicelles and micelles increased this parameter. Hydration of the skin diminished especially after the application of micellar and bicellar samples. In vitro experiments showed structures like vesicles inside cutaneous SC (stratum corneum) incubated with DPPC/DHPC bicelles. These structures were not detected in SC samples incubated with DMPC/DHPC bicelles probably due to the different thermotropic behavior of DMPC and DPPC at physiological temperatures. Results reported in this work should be considered in terms of design of more efficient and specific skin delivery systems.

Bicosomes: Bicelles in dilute systems

Bicelles are discoidal phospholipid nanostructures at high lipid concentrations. Under dilute conditions, bicelles become larger and adopt a variety of morphologies. This work proposes a strategy to preserve the discoidal morphology of bicelles in environments with high water content. Bicelles were formed in concentrated conditions and subsequently encapsulated in liposomes. Later dilution of these new structures, called bicosomes, demonstrated that lipid vesicles were able to isolate and protect bicelles entrapped inside them from the medium. Characterization of systems before and after dilution by dynamic light-scattering spectroscopy and cryo-transmission electron microscopy showed that free bicelles changed in size and morphology, whereas encapsulated bicelles remained unaltered by the effect of dilution. Free and entrapped bicelles (containing the paramagnetic contrast agent gadodiamide) were injected into rat brain lateral ventricles. Coronal and sagittal visualization was performed by magnetic resonance imaging. Whereas rats injected with free bicelles did not survive the surgery, those injected with bicosomes did, and a hyperintensity effect due to gadodiamide was observed in the cerebrospinal fluid. These results indicate that bicosomes are a good means of preserving the morphology of bicelles under dilution conditions.

Bicellar systems as modifiers of skin lipid structure.

The characterization of different bicellar aggregates and the effects of these systems on the stratum corneum (SC) microstructure have been studied. Dynamic light scattering (DLS) and freeze fracture electron microscopy (FFEM) techniques showed that both of the systems studied, dimyristoyl-phosphatidylcholine/dihexanoyl-phosphocholine (DMPC/DHPC) and dipalmitoyl-phosphocholine (DPPC)/DHPC, were formed by small discoidal aggregates at room temperature (20°C). Treating skin with DMPC/DHPC bicelles does not affect the SC lipid microstructure, whereas bicellar systems formed by DPPC and DHPC can promote the formation of new structures in the SC lipid domains. This indicates the passage of lipids from bicelles through the SC layers and also a possible interaction of these lipids with the SC lipids. Given the absence of surfactant in the bicellar composition and the small size of these structures, the use of these smart nano-systems offers great advantages over other lipid systems for dermatological purposes. Bicelles could be promising applications as drug carriers through the skin. This contribution, based on the new biological use of bicelles, may be useful to scientists engaged in colloid science and offers a new tool for different applications in skin and cosmetic research.

Bicellar systems as a new colloidal delivery strategy for skin

The presented work evaluates the use of bicellar systems as new delivery vectors for controlled release of compounds through the skin. Two different active principles were introduced into the bicellar systems: diclofenac diethylamine (DDEA) and flufenamic acid (Ffa). Bicellar systems are discoidal aggregates formed by long and short alkyl chain phospholipids. Characterization of the bicellar systems by dynamic light scattering (DLS) and cryogenic transmission electron microscopy (Cryo-TEM) showed that particle size decreased when DDEA was encapsulated and increased when Ffa was included in the bicellar systems. Percutaneous absorption studies demonstrated a lower penetration of DDEA and Ffa through the skin when the drugs were included in the bicellar systems than when the drugs were applied in an aqueous solution (DDEA) and in an ethanolic solution (Ffa); the reduction in penetration was more pronounced with Ffa. These bicellar systems may have retardant effects on percutaneous absorption, which result in a promising strategy for future drug or cosmetic delivery applications.

Lamellar body mimetic system: An up-to-down repairing strategy of the stratum corneum lipid structure

Epidermal lamellar bodies (LBs) are organelles that secrete their content, mainly lipids and enzymes, into the intercorneocyte space of the stratum corneum (SC) to form the lamellar structure of this tissue. Thus, LBs have a key role in permeability and the microbial cutaneous barrier. In this work, a complex lipid system that mimics the morphology, structure and composition of LBs has been designed. To evaluate the effect of this system on delipidized SC, in vitro experiments using porcine skin were performed. The microstructure of SC samples (native, delipidized and, delipidized after treatment) was evaluated by freeze substitution transmission electron microscopy (FSTEM) and grazing-incidence small-angle X-ray scattering (GISAXS). Delipidized SC samples showed no evidence of lipid lamellae after extraction with organic solvents. However, after treatment with the LB mimetic system, new lamellar structures between corneocytes were detected by FSTEM, and high intensity peaks and reflections were found in the GISAXS pattern. These results demonstrate a strong effect of the treatment in repairing part of the lipid lamellar structure of the SC. Accordingly, future research could extend the use of this system to repair skin barrier dysfunction.

Bicellar systems as vehicle for the treatment of impaired skin.

This study assesses the potential usefulness of bicellar systems to retard the penetration of drugs into damaged skin. The active compound used in this study was diclofenac diethylamine (DDEA). Initially, physicochemical characterisation of the DDEA bicellar systems was performed at different temperatures by small-angle X-ray scattering (SAXS), wide-angle X-ray scattering (WAXS) and differential scanning calorimetry (DSC) techniques. Subsequently, in vitro percutaneous absorption of bicellar systems into in vitro damaged skin was studied. SAXS results indicated a slight decrease in the width of their bilayers with increasing temperature, with no apparent stacking in those systems. WAXS patterns were compatible with an orthorhombic lateral packing of the nanoaggregates. The thermogram obtained by DSC indicated a decrease in gel-to-liquid crystalline transition temperature (Tm) when the drug was included into bicellar systems. A retardation effect for DDEA was detected by in vitro percutaneous absorption studies when DDEA was vehiculised in the bicellar systems with respect to an aqueous solution of the drug. It seems that the use of bicellar systems as a vehicle for topical application of DDEA on skin with an impaired barrier function may inhibit the penetration of DDEA to the systemic level. Such systems may consequently repair stratum corneum barrier function to some extent. The use of these systems could be considered a new alternative strategy to treat topically pathological skin with different drugs.

Bicelles and bicosomes as free radical scavengers in the skin

In the present work, β-carotene antioxidant was incorporated in two different lipid nanoaggregates, bicelles and bicosomes, and its effectiveness against free radical formation in porcine skin in vitro was determined using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) spin trap and Electron Paramagnetic Resonance spectroscopy (EPR). Bicelles are discoidal nanostructures formed by self-assembly of phospholipids dispersed in aqueous solution. Bicosomes emerge as a strategy to stabilize and protect bicelles encapsulating these nanostructures in liposomes. Results from Dynamic Light Scattering (DLS) and cryo Transmission Electron Microscopy (cryo-TEM) demonstrated a slight modification in the size of both systems when β-carotene was incorporated. EPR revealed that after skin irradiation both systems presented free radical scavenging activity. This activity was statistically significant for bicosomes containing β-carotene. Differences regarding this scavenging activity between bicelles and bicosomes would probably be due to the different interaction of both systems with the skin. In this study, six different radicals were identified in skin spectra: two originated from oxygen centred radicals (primary/secondary and tertiary alkoxyl radicals) and another from carbon-centred radicals. Additionally, the presence of 5,5-dimethyl-2-oxo-pyrroline-1-hydroxyl (DMPO-OH), 5,5-dimethyl-2-oxo-pyrroline-1-hydrogen (DMPO-H) adducts and aminoxyl radicals (RR′NO˙) were detected. Considering these results, bicelles and bicosomes could be useful lipid systems for future dermopharmaceutical applications.

Reducing the Harmful Effects of Infrared Radiation on the Skin Using Bicosomes Incorporating β-Carotene.

Aim: In this work the effect of infrared (IR) radiation, at temperatures between 25 and 30°C, on the formation of free radicals (FRs) in the skin is studied. Additionally, the influence of IR radiation at high temperatures in the degradation of skin collagen is evaluated. In both experiments the protective effect against IR radiation of phospholipid nanostructures (bicosomes) incorporating β-carotene (Bcb) is also evaluated. Methods: The formation of FRs in skin under IR exposure was measured near physiological temperatures (25-30°C) using 5,5-dimethyl-1-pyrroline-N-oxide spin trap and electron paramagnetic resonance (EPR) spectroscopy. The study of the collagen structure was performed by small-angle X-ray scattering using synchrotron radiation. Results: EPR results showed an increase in the hydroxyl radical in the irradiated skin compared to the native skin. The skin collagen was degraded by IR exposure at high temperatures of approximately 65°C. The treatment with Bcb reduced the formation of FRs and kept the structure of collagen. Conclusions: The formation of FRs by IR radiation does not depend on the increase of skin temperature. The decrease of FRs and the preservation of collagen fibers in the skin treated with Bcb indicate the potential of this lipid system to protect skin under IR exposure.