Lipid-based Janus nanoparticles for pharmaceutical and cosmetic applications: Kinetics and mechanisms of destabilization with time and temperature.

The aim of this paper is to investigate the time and thermal stability of innovative multicompartmental nanoparticles. These particles, having a hydrophilic side and a hydrophobic side, belong to the family of Janus particles and are promising tools to carry active ingredients with opposite solubilities in a unique nanocarrier. The stability of nanoparticles obtained with mainly two types of polyoxylglycerides (Labrafil® M2125 CS and Labrafil® M1944 CS) has been investigated. The suspensions describe a two-step maturation/destabilization process with an Ostwald ripening phase followed by the coalescence of the particles. The effect of lipid composition and temperature on these steps has been investigated in deep as stability with temperature is a critical parameter to consider in order to envisage the development of any formulation for pharmaceutical or cosmetic uses. These nanoparticles were particularly stable at room temperature as their hydrodynamic diameter did not change significantly for 20 months. Contrarily, a strong dependency to temperature appears when storage temperature increases from 25 °C to 43 °C. Indeed, Labrafil® M1944 CS seemed to undergo a progressive destabilization where a significant increase of particles size is visible from 25 °C and phase separation occurred after 4 months at 32 °C. At the opposite, Labrafil® M2125 CS remained stable until 36 °C and reached a threshold temperature between 32 °C and 36 °C after which Labrafil® M2125 CS underwent a consequent increase of particles size at the longer time, i.e. after 6 months. Moreover, Labrafil® M2125 CS formulation was stable at least 3 months at 43 °C.

Development of a percutaneous penetration predictive model by SR-FTIR.

This work focused on developing a new evaluation criterion of percutaneous penetration, in complement to Log Pow and MW and based on high spatial resolution Fourier transformed infrared (FTIR) microspectroscopy with a synchrotron source (SR-FTIR). Classic Franz cell experiments were run and after 22 h molecule distribution in skin was determined either by HPLC or by SR-FTIR. HPLC data served as reference. HPLC and SR-FTIR results were compared and a new predictive criterion based from SR-FTIR results, named S(index), was determined using a multi-block data analysis technique (ComDim). A predictive cartography of the distribution of molecules in the skin was built and compared to OECD predictive cartography. This new criterion S(index) and the cartography using SR-FTIR/HPLC results provides relevant information for risk analysis regarding prediction of percutaneous penetration and could be used to build a new mathematical model.

Spectral monitoring of photoirradiated skin lipids: MS and IR approaches.

An investigation of the effects of UV(A) irradiation on the stratum corneum lipids was carried out in vitro on films. The modifications of their conformational order were studied by FTIR and the formation of new entities was detected by mass spectroscopy. The results show not only differences in behaviour of the three lipid classes (fatty acids (FA), ceramides (CER), and cholesterol), but also variation within a class, depending on the molecules structure. Upon UV(A) irradiation, beta scission occurs on all the components, saturated and unsaturated. Moreover, unsaturated FA or CER having a double bond on their FA moiety may become saturated or may be transformed into their free radical form. Unsaturated FA are more sensitive to UV(A) and lead more easily to oxygenated components than unsaturated CER. The chemical effects are irradiation dose dependent but do not deeply influence the supramolecular organisation of these lipids. The global conformation of the lipids stays in an orthorhombic state, a decrease of the packing density however is observed.

Role of ceramide structure and its microenvironment on the conformational order of model stratum corneum lipids mixtures: an approach by FTIR spectroscopy.

The aim of this study is to investigate the influence of ceramide head group architecture and free fatty acid (another main class of stratum corneum lipids) or protein (keratin), on the lamellar organization of the ceramide auto-associated in model films mimicking lipid organization within the stratum corneum. FTIR spectroscopy is a powerful technique for investigating the structure of such systems. This technique has already been used to characterize phase transitions of the SC and of related model systems. As temperature is known to modify the conformational order of lipids, we used it as a variable parameter to monitor the differences in the conformational stability of ceramides. Our study included four ceramides: ceramide 2, 3, 5 and 6 which differ by their head group architecture. Two kinds of lipid-lipid interactions were studied: non-polar and polar. We noted some structural factors which participated to the organizational behavior: insaturation of alkyl chain, alpha-hydroxyl on fatty acid moiety and sphingosine or phytosphingosine head group. There is a direct interaction of palmitic acid on alkyl chains organization and a weak interaction with polar head group in presence of keratin, both provoking a destabilization of the ceramidic orthorhombic organization.

ATR-FTIR spectroscopy: a chemometric approach for studying the lipid organisation of the stratum corneum.

The barrier function of skin resides in the lipid components of the stratum corneum, particularly their spatial organisation. FTIR spectroscopy has already been used as a relevant tool to study this lipid organisation: IR vibration band shifts have been attributed to the variations in lipid organisation induced by temperature. Our study included a stratum corneum model, composed of the three main lipids: palmitic acid as an example of fatty acids, cholesterol and ceramide III as an example of ceramide. Different films with various ratios of these lipids were studied. In our analytical strategy, the interest of using a chemometric analysis of global data obtained from ATR-FTIR spectra to highlight the main interactions involved in the molecular organisation of lipids has been demonstrated. Two kinds of interaction between the three main lipids have been shown: a non polar interaction between the long hydrocarbon chains and a polar interaction as the hydrogen bonding between polar functional groups. By varying the lipid ratio, we have shown first that the relative importance of each interaction was modified, second, that the induced modification of organisation can be detected by chemometric analysis of the ATR-FTIR spectra. The role of each kind of lipid in the organisation has been discussed. In conclusion, associating the ATR-FTIR with chemometric treatment is a promising tool: firstly, to understand the consequence of lipid relative compositions on the structural organisation of the stratum corneum, secondly, to show the relationship between lipid organisation and percutaneous penetration data. Indeed, this methodology will be transposed to in vivo studies with IR measurements through a probe.

The stripping technique: in vitro absorption and penetration of five UV filters on excised fresh human skin.

This article gives the results of a study whose aim was to compare the compartmental distribution and absorption of 5 UV filters, in vitro, by fresh human skin, after exposure times of 30 min and 16 h. These UV filters from BASF (octyl methoxycinnamate, benzophenone 4, benzophenone 3, octyl triazone and octocrylene) were incorporated separately in a simple oil-in-water emulsion. The composition of the emulsions was designed in order to obtain a sun protection factor of 5. Therefore the UV filters were introduced into the emulsions at different concentrations. We show that the affinity for each skin level [stratum corneum (SC), viable epidermis, dermis and receptor fluid] is different according to the test substance used. Some substances accumulated in the SC, whereas others passed through the skin very quickly and were quantified in the receptor fluid. The stripping technique allowed us to see that more than 94% of the chemical compound in the SC was in the first eight tapes. The problem of individual values below the limit of detection was raised, a correlation between the two exposure times was found (y = 1.702x - 0.105; R = 0.94) and a classification of products according to their affinity for the SC was determined.

In vitro release of caffeine from concentrated W/O emulsions: effect of formulation parameters.

Concentrated water in oil emulsions have been obtained with four different emulsifiers to study the effect of formulation parameters on the in vitro release of caffeine. The in vitro release was studied on polysulfone membranes. Among the four emulsifiers, only one gave a statistically higher release of caffeine after 15 h (at a fixed percentage of dispersed phase). The concentration of the emulsifier does not have a significant effect on the release of caffeine. In contrast, diffusion of caffeine from concentrated W/O emulsions has been found to be highly dependent on the internal phase volume. The flux of caffeine increases with the percentage internal water phase. The droplet diameter decreases and the apparent viscosity increases with the percentage of the dispersed phase. And, the shape of the droplets goes from spherical to polyhedral as the percentage dispersed phase is increased. However, the flux could be correlated neither with the apparent viscosity nor with the droplet diameter at a fixed percentage of the dispersed phase. Results suggest that the shape factor may have an influence on the release of caffeine from concentrated emulsions. All the release profiles followed a zero-order kinetic.

Influence of three synthetic membranes on the release of caffeine from concentrated W/O emulsions.

We measured the release rate characteristics of caffeine from concentrated emulsions using three different sources of synthetic membranes. The formulations tested included, on the one hand, two stable cosmetic concentrated W/O emulsions (90% w/w) - one with a non ionic surfactant and one with a silicone surfactant - and on the other hand, a commercially available hydroalcoholic gel. All formulations contained 5% caffeine. In vitro diffusion measurements (24 h) were performed with static diffusion Franz cells. A silicone membrane could not allow us to differentiate the two concentrated emulsions (CE), but the two other membranes, not rate limiting, showed difference in the release profile of caffeine from the two CE. Results with the cellulose and polysulfone membrane showed that in vitro release of caffeine is influenced by the nature of the emulsifier in the concentrated emulsion, the non ionic surfactant being more efficient than the silicone surfactant. The polysulfone membrane was the only one that allows statistical differentiation of the three products. For further studies the polysulfone membrane will be use to make screening on concentrated emulsions.

Modulated release of triterpenic compounds from a O/W/O multiple emulsion formulated with dimethicones: infrared spectrophotometric and differential calorimetric approaches.

From the use of silicones within O/W/O multiple emulsions, we can expect, two principal advantages: (1) the silicones with the lowest molecular weight decrease the oily touch; (2) due to the large range of viscosity, this excipient should influence the skin distribution of actives after topical application. The purpose of our work is to highlight these advantages. Multiple emulsions were formulated with several dimethicones and with drug model. Firstly, the effects of different dimethicones incorporated within multiple emulsions were studied, through in vitro penetration results. Secondly, we investigated the residual film on the skin by Differential Scanning Calorimetry (DSC) and by Fourier Transform Infrared (FTIR) to determine its structure. Correlations were established between the silicone structure and the distribution of drugs in different skin levels or between the silicone structure and the percutaneous penetration. The incorporation of silicones within O/W/O multiple emulsions seems to be an efficient means of modulating the penetration and the distribution of drugs in the skin.

Quantitative HPLC analysis of sunscreens and caffeine during in vitro percutaneous penetration studies.

This report describes rapid analytical HPLC for the quantification of five UV filters (octyl methoxycinnamate, benzophenone-3, benzophenone-4, octyl triazone and octocrylene) and of caffeine in various skin layers (stratum corneum, dermis, epidermis and receptor fluid) and in cosmetic preparations. The predominant purpose of the study was to establish standard operating procedures for rapid analysis of the compounds in various skin samples. Particular attention was paid to the preparation of biological samples whose natural constitution could interfere with the quantitative analysis. Our methods used the isocratic chromatographic mode in an RP-HPLC with UV detection and did not involve centrifugation or evaporation. Our results were validated in terms of specificity, linearity, precision, accuracy and limits of detection and quantification. The first results, obtained after in vitro experiments, are presented in this report.

In vitro topical delivery of non-steroidal anti-inflammatory drugs through human skin.

The objective of the present study was to evaluate in vitro the percutaneous absorption, across human skin, of 5 non-steroidal anti-inflammatory drugs (NSAIDs) formulated as gels: ketoprofen (CAS 22071-15-4), epolamine diclofenac (CAS 15307-86-5), piroxicam (CAS 36322-90-4) and niflumic acid (CAS 4394-00-7) or as emulgel: diclofenac sodium (CAS 15307-79-6) and to compare the different formulations as drug delivery systems. Because the concentrations of the NSAIDs in the different excipients were not identical, the comparison of their diffusional properties was expressed in term of release efficiency (or diffusion efficacy). The results obtained show that, across human skin under standardized experimental conditions, ketoprofen and piroxicam have the best rank order followed by niflumic acid, diclofenac sodium and epolamine diclofenac.

Incorporation of triterpenic derivatives within an o/w/o multiple emulsion: structure and release studies.

Triterpenic derivatives stimulate the total collagen synthesis of skin fibroblasts. Their incorporation within an o/ w/o multiple emulsion should protect them against oxidation, particularly for unsaturated derivatives and should lead to a modulated release after topical application. The influence of the incorporation of madecassic acid, asiaticoside and asiatic acid on the viscosity and the stability of a multiple o/w/o emulsion was studied. Rheological analyses were carried out by flow experiments in order to obtain the apparent viscosity and by the oscillatory technique to calculate the basic visceolastic parameters. The comparative stability study was assessed by the tracer release method with phthalic acid diethyl ester previously incorporated in the internal phase of the emulsions. Six months storage at room temperature and at 40 degrees C did not affect the stability of emulsions with triterpenic substances. The in vitro percutaneous absorption of triterpenic derivatives was investigated by Franz diffusion cells in hairless rats. Triterpenic derivatives were analysed in stratum corneum, epidermis and dermis, by liquid chromatography. Correlations were established between the triterpenic derivatives structure (glycosylated or not) and their percutaneous absorption. O/w/o multiple emulsion seems to be an efficient vehicle to preserve these active substances and to control their distribution in the skin.