Nanoscale investigation of human skin and study of skin penetration of Janus nanoparticles.

Janus nanoparticles (JNP) are innovative nanocarriers with an interesting pharmaceutical and cosmetic potential. They are characterized by the presence of a lipid compartment associated with an aqueous compartment delimited by a phospholipid bilayer containing phospholipids and non-ionic surfactants. The hydrodynamic diameter of JNP varies between 150 and 300 nm. The purpose of this study was to answer the following questions: after cutaneous application, are JNP penetrating? If so, how deep? And in which state, intact or degraded? It was essential to understand these phenomena in order to control the rate and kinetics of diffusion of active ingredients, which can be encapsulated in this vehicle for pharmaceutical or cosmetic purposes. An innovative technique called AFM-IR, was used to elucidate the behavior of JNP after cutaneous application. This instrument, coupling atomic force microscopy and IR spectroscopy, allowing to perform chemical analysis at the nanometer scale thanks to local absorption measurements. The identification of organic molecules at the nanoscale is possible without any labelling. Before cutaneous application of JNP, the nano-structure of untreated human skin was investigated with AFM-IR. Then, in vitro human skin penetration of JNP was studied using Franz cells, and AFM-IR allowed us to perform ultra-local information investigations.

ATR-FTIR Characterization of Janus Nanoparticles-Part II: Follow-Up Skin Application.

Attenuated total reflection by Fourier transform infrared (ATR-FTIR) was used to implement reliable infrared descriptors over time of Janus nanoparticles (JNP), to follow their behavior before and after cutaneous application. In the last study, ATR-FTIR spectroscopic analysis allowed us to identify the evolution of intensity ratio of ν(C=O) at 1739 cm-1 and δ(H-O-H) at 1639 cm-1 as a spectroscopic descriptor, for JNP before cutaneous application (on the CaF2 window). This descriptor can be used to follow the physical stability (presence) of nanoparticles over time. The purpose of this study was to understand the behavior of JNP on the surface of the human skin. Therefore, a comparative study with the untreated skin and the skin after cutaneous application of lipophilic phase (Labrafil) of JNP was conducted using Franz cells. The suitability of the ATR-FTIR descriptor of JNP was evaluated, and a research of other descriptors was performed to understand the interaction that may exist between nanoparticles and the skin.

ATR-FTIR Characterization of Janus Nanoparticles. Part I: Implementation of Spectroscopic Descriptors.

The present work deals with original bicompartmental lipid Janus nanoparticles (JNPs), which are characterized by the presence of an oily compartment associated with an aqueous compartment delimited by a phospholipid-based bilayer. The size of JNP varies between 150 and 300 nm. As JNP are promising candidates for cutaneous application, the purpose of this study was to implement reliable infrared descriptors over time of JNP, to follow the physical stability of JNP in open air and over time. Therefore, a comparative study with the nanoemulsion and the physical mixture formulations was conducted by attenuated total reflection by FTIR spectroscopy. We defined herein spectroscopic descriptor reflecting the integrity of the JNP. Principal component analysis and orthogonal partial least square-discriminant analysis were used to validate the relevant descriptor and permitted to extract relevant and useful information from the spectral data. Dynamic light scattering measurements were also carried and gave supporting data for our conclusion on the fate of JNP over time.

Labeling of Hyaluronic Acids with a Rhenium-tricarbonyl Tag and Percutaneous Penetration Studied by Multimodal Imaging.

Hyaluronic acids were labeled with a rhenium-tricarbonyl used as single core multimodal probe for imaging and their penetration into human skin biopsies was studied using IR microscopy and fluorescence imaging (labeled SCoMPI). The penetration was shown to be dependent on the molecular weight of the molecule and limited to the upper layer of the skin.

An easy-to-detect nona-arginine peptide for epidermal targeting.

A correlative approach combining synchrotron radiation based IR microscopy and fluorescence microscopy enabled the successful detection and quantification of a nona-arginine peptide labelled with a Single Core Multimodal Probe for Imaging (SCoMPI) in skin biopsies. The topical penetration of the conjugate appeared to be time dependent and occurred most probably via the extracellular matrix.

Study of the potential of stratum corneum lipids and exogenous molecules interaction by fluorescence spectroscopy for the estimation of percutaneous penetration.

Considering that the skin barrier properties are closely linked to the ceramides composition and conformation within the SC, our work focused on developing a new evaluation criterion in complement of the Log Pow and MW: lipids retentive role within the SC. We developed an in vitro model to study exogenous molecules (Mol) and SC lipids interaction by fluorescence spectroscopy. As ceramides do not fluoresce, fluorescence probes that emit a fluorescence signal in contact with lipidic chains were selected for the study. A protocol was developed based on the exogenous molecule (cosmetic actives) affinity for the SC lipids. A fluorescence criterion (ΔI) was calculated from our results and compared to ex vivo skin penetration measurements realized with a Franz cell device. Our results indicated that polarity seems to be very representative of the ceramide and exogenous molecule interaction for most of the molecules tested. However, the ΔI calculated highlighted the particular interaction of some exogenous molecules with ceramides and their skin distribution. This particular behavior was not initially possible to estimate with the Log Pow and MW. This work aimed to develop a new alternative method to enhance the percutaneous penetration estimation of exogenous molecules for the risk analysis.

Effect of UVA or UVB irradiation on cutaneous lipids in films or in solution.

The barrier function of the skin is largely due to the stratum corneum which is essentially composed of lipids. Different external factors, such as UV irradiation, affect this skin layer and are responsible for a destabilization of the supramolecular organization of its constituted lipids. In this work, mass spectrometry and infrared spectroscopy are combined to study the correlation between the formation of oxidative compounds by UV irradiation and the lipid organization. Experiments were carried out on unsaturated lipids in film or solution form, exposed to UVA or UVB irradiation. UV exposure leads to the formation of oxygenated entities in the case of lipids with an unsaturated fatty acid moiety, resulting in a decrease in their packing which is greater when the lipids are in solution. The packing decrease is even greater following UVB irradiation.

Molecular interactions of penetration enhancers within ceramides organization: a FTIR approach.

The barrier function of the skin is related to the unique composition of the stratum corneum (SC) lipids and their complex structural arrangement. The high content of ceramides would seem to be ideally suited for the formation of ordered impermeable membrane. Skin penetration enhancers (PE) are molecules which reversibly remove the barrier resistance of the SC. Interactions with SC intercellular lipids are of crucial importance for the effectiveness of PE action. Their mode of action on the lipid bilayer may involve interactions at two sites, i.e., at or near the polar head groups of the lipid bilayer and/or between the hydrophobic tails of the bilayer. This paper discusses the local effect of four PE, among the most investigated, limonene, ethanol, oleic acid and DMSO. FTIR is used in this study to highlight the local effect of the PE on ceramides films. Lipophilic PE, i.e., oleic acid and limonene, both present a direct fluidizing action on the alkyl chains and an indirect action on the polar head groups resulting in a more spacing lipid packing. Hydrophilic PE, i.e., ethanol and DMSO, have no interaction on the lipid bilayer but show a complex action on the polar headgroup, weakening the H-bonds. Our most significant finding is that each PE we investigated interacted with the ceramide packing, depending of these structures. Such modifications contribute a share to interpretation, at the molecular level, of the decrease of skin barrier properties with PE described in published data.