Perceived age and perceived health among a Chinese cohort: Does it mean the same thing?

BACKGROUND & AIMS: Previous investigations have aimed at investigating parameters affecting age perception on several ethnicities. Perceived health has been a newer focus on Caucasian skin, yet little is known on the skin features used to estimate the health status of Chinese women and we aimed to investigate whether these cues are the same as those used for age perception. METHODS: Age and health appearance of 276 Chinese female volunteers were estimated from their photographs by 1025 female naïve Chinese graders 20-69 years old. Models were built to predict perceived age and health from topographic, colour and biophysical measured variables, in two subsets of the studied volunteers: below and above 50 years. Machine learning-based predictive models for age and health perception were built on the collected data, and the interpretability of the models was established by measuring feature importance. RESULTS: Age perception was mostly driven by topographic features, particularly eye bags and eyelid sagging in the group below 50 years old. Wrinkles, notably from the lower part of the face and oval of the lower face, were found to be more relevant in the group above 50 years. Health appearance was primarily signalled by skin imperfections and global pigmentation in the subset below 50 years, whereas colour-related parameters and skin hydration acted as health cues for the subset above 50 years. CONCLUSION: Distinct skin features were acting as cues for age perception and/or health perception and varied per age subset. Their contribution should be borne in mind when designing products for 'younger looking skin' and 'healthier looking skin'.

OBJECTIF: Des études se sont penchées sur les paramètres cutanés influant sur la perception de l'âge, et ce sur plusieurs groups ethniques. La santé perçue quant à elle est un focus plus récent, avec des données publiées sur les peaux caucasiennes, au contraire des peaux chinoises. Nous avons donc décidé d'étudier quels sont ces paramètres cutanés influant sur la santé perçue et s'ils diffèrent de ceux utilisés dans la perception de l'âge, au sein d'un panel de femmes chinoises. MÉTHODES: L'âge et la santé cutanée de 276 femmes chinoises ont été estimés à partir de leurs photographies par un panel de 1025 évaluatrices naïves âgées de 20 à 69 ans. Des modèles ont été construits pour prédire l'âge et la santé perçus à partir de paramètres cutanés topographiques, de couleur et biophysiques, dans deux groupes d'âges différents : en dessous et au-dessus de 50 ans. Des modèles prédictifs basés sur l'apprentissage automatique (Machine learning) pour la perception de l'âge et de la santé ont été construits à partir des données collectées et l'interprétabilité des modèles a été établie en mesurant l'importance des paramètres cutanés. RÉSULTATS: Nos résultats montrent que la perception de l'âge repose principalement sur des paramètres topographiques, en particulier les poches sous les yeux et l'affaissement de la paupière, pour le groupe âgé de moins de 50 ans. Les rides, notamment celles de la partie basse du visage et le contour de la partie basse du visage se sont montrés pertinents pour estimer l'âge dans le groupe âgé de plus de 50 ans. La perception de la santé est principalement affectée par les imperfections cutanées et la pigmentation dans le groupe âgé de moins de 50 ans, tandis que des paramètres liés à la couleur et l'hydratation prennent le relais pour le groupe âgé de plus de 50 ans. CONCLUSION: Des paramètres cutanés de nature diverse sont pris en compte selon que l'on essaye d'estimer l'âge ou la santé, et ce en fonction du groupe d'âge étudié. Leur contribution doit être prise en compte lors de la conception de produits pour une «peau d'apparence plus jeune¼ et une «peau d'apparence plus saine¼.

Ageing profiles of Caucasian and Chinese cohorts - focus on hands skin.

OBJECTIVE: In spite of hand care being a dynamic segment of skin care, hands skin physiology has been receiving little attention in comparison to facial skin. In the present study, we aimed at gathering a comprehensive set of skin data from the dorsal part of the hand to study age related-changes in two ethnic groups (Caucasian and Chinese). METHODS: Skin topographic, skin colour/colour heterogeneities, skin chromophores and skin biophysical measurements of 116 Caucasian and Chinese female volunteers aged 30-65 years old were collected in Ireland and in China as part of a cross-sectional study. RESULTS: Topographic alterations happened at both micro and macro scales with a noticeable delay in the onset of 10 years for the Chinese cohort. Similar evolution of skin colour with ageing was observed between the two cohorts and strong dissimilarities were seen when it came to colour heterogeneities and melanin hyper concentration, with a 20-year delay in severity for the Chinese cohort. A similar sharp drop of skin hydration occurred when reaching the 60's regardless of the group and substantial differences were recorded for skin biomechanical properties of the skin. CONCLUSION: These results provide additional insights about hand skin physiology in relation to ageing and ethnic differences, especially when put into perspective with what is currently known about facial ageing. This research yield additional material for hand cream product rationale and strategies for mitigating the appearance of ageing hands.

OBJECTIF: Même si le soin pour les mains demeure un segment dynamique en termes de ventes de produits cosmétiques, peu d'études se sont penchées sur la physiologie de la peau des mains en comparaison du visage. Le but de cette étude est d'élucider les changements de la partie dorsale de la main induits par le vieillissement, au sein de deux groupes ethniques (Caucasienne et Chinoise). METHODES: Des mesures de la topographie, de couleur et de distribution de la couleur, de chromophores et des propriétés biophysiques de la peau de la main ont été collectées sur 116 sujets féminins d'origine caucasienne ou chinoise, âgées entre 30 et 65 ans, en Irlande et en Chine dans le cadre d'une étude cross-sectionnelle. RESULTATS: Des altérations de la topographie de la peau ont été observés à plusieurs échelles, micro et macroscopique, avec néanmoins un délai de 10 ans dans la détérioration de la peau en faveur du panel Chinois. Au niveau de la couleur, des évolutions similaires ont été mesurées dans les deux panels, avec cependant de fortes dissimilarités pour ce qui est de la distribution de la couleur de la peau et de l'hyperconcentration de mélanine, avec des changements retardés de 20 ans en faveur du panel d'origine chinoise. Un déclin d'hydratation significatif s'est produit à partir de la soixantaine dans les deux panels étudiés tandis que des différences flagrantes ont été relevées en ce qui concerne les propriétés biomécaniques de la peau. CONCLUSION: Ces résultats offre des données supplémentaires sur la physiologie de la peau des mains lors du vieillissement cutané et sur les différences à prendre en compte entre deux groupes ethniques très distincts, surtout si l'on considère les différences avec le vieillissement du visage. Cette étude fournit un support additionnel pour la conception de crèmes pour les mains et les stratégies à mettre en place pour atténuer l'apparence de mains âgées.

Antera 3D capabilities for pore measurements.

BACKGROUND: The cause of enlarged pores remains obscure but still remains of concern for women. To complement subjective methods, bioengineered methods are needed for quantification of pores visibility following treatments. The study objective was to demonstrate the suitability of pore measurements from the Antera 3D. MATERIAL AND METHODS: Pore measurements were collected on 22 female volunteers aged 18-65 years with the Antera 3D, the DermaTOP and image analysis on photographs. Additionally, 4 raters graded pore size on photographs on a scale 0-5. Repeatability of Antera 3D parameters was ascertained and the benefit of a pore minimizer product on the cheek was assessed on a sub panel of seven female volunteers. RESULTS: Pore parameters using the Antera were shown to depict pore severity similar to raters on photographs, except for Max Depth. Mean pore volume, mean pore area and count were moderately correlated with DermaTOP parameters (up to r = .50). No relationship was seen between the Antera 3D and pore visibility analysis on photographs. The most repeatable parameters were found to be mean pore volume, mean pore area and max depth, especially for the small and medium filters. The benefits of a pore minimizer product were the most striking for mean pore volume and mean pore area when using the small filter for analysis, rather than the medium/large ones. CONCLUSION: Pore measurements with the Antera 3D represent a reliable tool for efficacy and field studies, with an emphasis of the small filter for analysis for the mean pore volume/mean pore area parameters.

Wrinkle and roughness measurement by the Antera 3D and its application for evaluation of cosmetic products.

BACKGROUND: Skin topographic measurements are of paramount importance in the field of dermo-cosmetic evaluation. The aim of this study was to investigate how the Antera 3D, a multi-purpose handheld camera, correlates with other topographic techniques and changes in skin topography following the use of a cosmetic product. METHODS: Skin topographic measurements were collected on 26 female volunteers aged 45-70 years with the Antera 3D, the DermaTOP and image analysis on parallel-polarized pictures. Different filters for analysis from the Antera 3D were investigated for repeatability, correlations with other imaging techniques and ability to detect improvements of skin topography following application of a serum. RESULTS: Most of Antera 3D parameters were found to be strongly correlated with the DermaTOP parameters. No association was found between the Antera 3D parameters and measurements on parallel-polarized photographs. The measurements repeatability was comparable among the different filters for analysis, with the exception of wrinkle max depth and roughness Rt. Following a single application of a tightening serum, both Antera 3D wrinkles and texture parameters were able to record significant improvements, with the best improvements observed with the large filter. CONCLUSION: The Antera 3D demonstrated its relevance for cosmetic product evaluation. We also provide recommendations for the analysis based on our findings.

Evaluation of skin firmness by the DynaSKIN, a novel non-contact compression device, and its use in revealing the efficacy of a skincare regimen featuring a novel anti-ageing ingredient, acetyl aspartic acid.

BACKGROUND: One of the key strategies for anti-ageing in the cosmetics industry today is to target the structural changes responsible for ptosis of the skin, given its impact on age perception. Several objective and non-invasive methods are available to characterise the biomechanical properties of the skin, which are operator-dependent, involving skin contact and providing single-dimensional numerical descriptions of skin behaviour. The research introduces the DynaSKIN, a device using non-contact mechanical pressure in combination with fringe projection to quantify and visualise the skin response in 3-dimensions. We examine the age correlation of the measurements, how they compare with the Cutometer® , and measure skin dynamics following application of a skincare regimen containing established anti-ageing ingredients. METHODS: DynaSKIN and Cutometer® measurements were made on the cheek of 80 Caucasian women (18-64 years). DynaSKIN volume, mean depth and maximum depth parameters were correlated with age and 15 Cutometer® parameters. Subsequently, the firming efficacy of a skincare regimen featuring acetyl aspartic acid (AAA) and a peptide complex was examined in a cohort of 41 volunteers. RESULTS: DynaSKIN volume, mean depth and maximum depth parameters correlate with age and the Cutometer® parameters that are associated with the skin relaxation phase (R1, R2, R4, R5, R7 and F3). Furthermore, the DynaSKIN captured significant improvements in skin firmness delivered by the skincare regimen. CONCLUSION: The DynaSKIN is a novel device capable of capturing skin biomechanics at a high level of specificity and successfully detected the firming properties of a skincare regimen. Its independent measuring principle, consumer relevance and skin firmness 3D visualisation capabilities bring objectivity and novelty to product efficacy substantiation evaluation.

Structural activity relationship analysis (SAR) and in vitro testing reveal the anti-ageing potential activity of acetyl aspartic acid.

BACKGROUND: Acetyl aspartic acid (A-A-A) was discovered through gene array analysis with corresponding connectivity mapping (Cmap), aiming for identification of new compounds with anti-ageing properties. OBJECTIVE: The aim of this study was to use structural activity relationship (SAR) analysis to identify a predictive mechanism of action of A-A-A. The findings from SAR will be further characterized by in vitro activity testing. Furthermore, we aimed to investigate the role of polymerized filamentous F-actin in ageing fibroblasts and to evaluate the effect of A-A-A on this model. METHODS: To predict the mode of action of A-A-A, we used the PASS computer program as a SAR model. In vitro, scratch motility tests with immortalized keratinocytes were used as a model for wound healing potential. Matrix metalloproteinase 1-3 (MMP 1-3) was analysed using multiplex protein assays (Luminex), and polymerized actin was detected by phalloidin staining in dermal fibroblasts (HDF). RESULTS: SAR analysis predicted that A-A-A would possess both epidermal and dermal activities with identification of wound healing and MMP inhibition potential. Further in vitro studies confirmed the wound healing potential using keratinocyte scratch motility assays. We were also able to confirm the dermal activities predicted by inhibition of MMP (MMP 1-3) in HDF by A-A-A. In addition, we found a positive relationship between age and F-actin expression. We also discovered that stimulation of HDF with A-A-A for 72 h significantly reduced the polymerized cytoskeletal network as visualized by inhibition of F-actin expression. In fact, A-A-A leveraged the expression of F-actin in middle-aged female fibroblasts (50 years of age) to the level of young female fibroblasts (30 years of age), corresponding to a 40% reduction in F-actin expression. CONCLUSION: Using an in silico and in vitro approach, we were able to demonstrate that A-A-A has the capacity to target different compartments of the skin through keratinocyte regeneration, MMP inhibition and relief in fibroblasts stiffness by reduction of F-actin cytoskeletal network in HDF.

In vivo topical application of acetyl aspartic acid increases fibrillin-1 and collagen IV deposition leading to a significant improvement of skin firmness.

OBJECTIVE: Acetyl aspartic acid (A-A-A) was discovered through gene array analysis with corresponding Cmap analysis. We found that A-A-A increased keratinocyte regeneration, inhibited dermal matrix metalloprotease (MMP) expression and relieved fibroblast stiffness through reduction of the fibroblast stiffness marker F-actin. Dermal absorption studies showed successful delivery to both the epidermal and dermal regions, and in-use trial demonstrated that 1% A-A-A was well tolerated. In this study, the aim was to investigate whether A-A-A could stimulate the synthesis of extracellular matrix supporting proteins in vivo and thereby improving the viscoelastic properties of human skin by conducting a dual histological and biophysical clinical study. METHOD: Two separate double-blind vehicle-controlled in vivo studies were conducted using a 1% A-A-A containing oil-in-water (o/w) emulsion. In the histological study, 16 female volunteers (>55 years of age) exhibiting photodamaged skin on their forearm were included, investigating the effect of a 12-day treatment of A-A-A on collagen IV (COLIV) and fibrillin-1. In a subsequent pilot study, 0.1% retinol was used for comparison to A-A-A (1%). The biomechanical properties of the skin were assessed in a panel of 16 women (>45 years of age) using the standard Cutometer MPA580 after topical application of the test products for 28 days. The use of multiple suction enabled the assessment of F4, an area parameter specifically representing skin firmness. RESULTS: Twelve-day topical application of 1% A-A-A significantly increased COLIV and fibrillin with 13% and 6%, respectively, compared to vehicle. 1% A-A-A and 0.1% retinol were found to significantly reduce F4 after 28 days of treatment by 15.8% and 14.7%, respectively, in the pilot Cutometer study. No significant difference was found between retinol and A-A-A. However, only A-A-A exhibited a significant effect vs. vehicle on skin firmness which indicated the incremental benefit of A-A-A as a skin-firming active ingredient. CONCLUSION: In this study, we showed the in vivo efficacy of 1% A-A-A both on a protein level (fibrillin and collagen IV) and on a clinical end point, specifically skin firmness, providing proof that, acetyl aspartic acid has a strong potential as an anti-ageing 'cosmeceutical' ingredient answering the needs of our key consumer base.

Acetyl aspartic acid, a novel active ingredient, demonstrates potential to improve signs of skin ageing: from consumer need to clinical proof.

BACKGROUND: The megatrend of population ageing is leading to a growing demand for "anti-ageing" treatments, especially to prevent or treat skin ageing. Facing an increasing offer, consumers are choosing more and more skin care products supported by a scientific rationale, active ingredients and clinical proof of efficacy. OBJECTIVE: Considering consumer expectations, this research led to the discovery of acetyl aspartic acid (A-A-A), a novel active ingredient to improve sagging skin and loss of skin firmness. RESULTS: This supplement is featuring seven manuscripts aiming at presenting the research and investigations from consumer insights, discovery of A-A-A, its in vitro activity confirmation, safety assessment, formulation and its dermal absorption to the clinical proof of efficacy, investigated through two pilots' double bind randomized and placebo controlled studies on photo-aged skin. CONCLUSION: This extensive research enabled us to discover A-A-A, as an active ingredient with potential to repair sign of skin ageing and supported by clinical proof of efficacy. This active ingredient will be soon launched in a commercial innovative skin care range, delivering desirable anti-wrinkle and skin lifting benefits.

In vitro and in vivo dermal absorption assessment of acetyl aspartic acid: a compartmental study.

OBJECTIVE: The purpose of this study was to evaluate the dermal absorption of acetyl aspartic acid (A-A-A) through an in vitro and in vivo evaluation with human skin after 6 and 24 h of topical application of a cosmetic formulation containing A-A-A at 1%. METHODS: The in vitro experiment was carried out using the Franz diffusion cells system with ex vivo human skin samples. The profile of diffusion of A-A-A was evaluated after 6 and 24 h. The in vivo experiment was performed on human volunteers following a tape-stripping protocol after 6 h of topical application. A-A-A was quantified in the main skin compartments, that is the skin surface, the stratum corneum, the skin and the receptor fluid using LC-MS analysis. RESULTS: The 24-h in vitro experiment confirmed the great penetration potential of A-A-A in all skin compartments. After 6 h of topical application, the removed tape strips from both in vitro and in vivo experiments were analysed and the profile of diffusion of A-A-A was determined, allowing also an in vitro/in vivo comparison. The diffusion profile observed on the in vitro skin penetration test is highly representative of the in vivo situation evaluated on volunteers. CONCLUSION: The combination of in vitro with in vivo data confirmed that A-A-A has the capacity to diffuse through the skin after topical application and reach the dermis as the targeted skin layer for potential anti-ageing benefits.

Pre-clinical formulation screening, development and stability of acetyl aspartic acid for cosmetic application.

BACKGROUND: Acetyl aspartic acid (A-A-A) was discovered through gene array analysis with corresponding connectivity mapping (Cmap). Using an in silico and in vitro approach, A-A-A was found increased keratinocyte regeneration, inhibited dermal expression of MMP making this compound a potential active ingredient for cosmetic application. OBJECTIVES: To determine the conditions to successfully formulate A-A-A for skin delivery investigation and in vivo clinical assessment by the systematic approach of pre-formulation testing of the active, screening of formulation type on active delivery and stability evaluations. METHODS: Analytical evaluation of A-A-A was undertaken using LC-MS ESI method. Formulation stability was evaluated using Brookfield viscometer, pH analysis, optical microscopy and organoleptic evaluations. RESULTS: Analytical evaluation of A-A-A shows that pH significantly impacts chemical stability of the molecule. A-A-A containing formulae show minimal differences to vehicle product throughout the testing. CONCLUSION: A-A-A is an active that can be successfully formulated in a cosmetic o/w emulsion within defined pH considerations.

The use of gene arrays and corresponding connectivity mapping (Cmap) to identify novel anti-ageing ingredients.

OBJECTIVE: The need for effective 'anti-ageing' treatments, in particular for the management of photodamaged skin, prompted us to develop a novel method to identify new active ingredients. The model utilized a gene profiling study with corresponding connectivity mapping (Cmap) to identify novel anti-ageing compounds using all-trans retinoic acid (RA) as the lead compound due to its beneficial effect on photodamaged skin and skin firmness. METHOD: A vehicle-controlled clinical study including nine healthy Caucasian female volunteers aged 57 ± 7 (mean ± SEM) exhibiting photodamage on their lower outer forearms was conducted. The volunteers applied RA once daily on photodamaged skin for 7 days, and biopsies were subjected to Affymetrix gene arrays. Connectivity mapping (Cmap), examining hundreds of gene expression profiles, was run on the gene signature of RA-treated photodamaged skin to identify small bioactive compounds. RESULTS: Affymetrix gene array identified 19 genes significantly differentially expressed after application of RA. Corresponding Cmap analysis revealed six natural bioactive compounds including N-acetyl aspartic acid (A-A-A) showing similar activity to RA on the differentially expressed genes identified. CONCLUSION: Based on RA mimicking gene array activity, potential use within skincare on molecular size, safety assessment and sourcing, we identified the natural amino acid, A-A-A as a potential candidate to treat ageing skin.

Influence of facial skin ageing characteristics on the perceived age in a Russian female population.

OBJECTIVE: The desire for a youthful look remains a powerful motivator in the purchase of cosmetics by women globally. To develop an anti-ageing solution that targets the need of end consumers, it is critical to understand which signs of ageing really matter to them and which influence their age perception. To date, such research has not been performed in a Russian population. The aim of this work was to identify the signs of ageing that contribute the most to an 'older' or 'younger' look for Russian women aged 40 years old and above. METHODS: The age of 203 Russian female volunteers was estimated from their standard photographs by a total of 629 female naïve assessors aged 20-65 years old. Perceived age data were related to 23 facial skin features previously measured using linear correlation coefficients. Differences in average severity of the correlating skin ageing features were evaluated between women perceived older and women perceived younger than their chronological age. Volunteers' responses to a ranking question on their key ageing skin concerns previously collected were analysed to provide an additional view on facial ageing from the consumer perspective. RESULTS: Nine facial skin ageing features were found to correlate the most with perceived age out of the 23 measured. Such results showed the importance of wrinkles in the upper part of the face (crow's feet, glabellar, under eye and forehead wrinkles), but also wrinkles in the lower half of the face associated with facial sagging (upper lip, nasolabial fold). Sagging was confirmed of key importance to female volunteers aged 41-65 years old who were mostly concerned by the sagging of their jawline, ahead of under eye and crow's feet wrinkle. The severity of hyperpigmented spots, red and brown, was also found to contribute to perceived age although to a weaker extent. CONCLUSION: By providing a clear view on the signs of ageing really matter to Russian women who are aged 40 years old and above, this research offers key information for the development of relevant anti-ageing solutions specifically targeting their needs and their desire to achieve younger-looking skin.

Transcriptional changes in organoculture of full-thickness human skin following topical application of all-trans retinoic acid.

In this study, we developed an organoculture of human skin to investigate the effect of topical applied all-trans retinoic acid using a gene array approach. We could by using this approach confirm previous studies on genes activated by RA in keratinocyte monocultures and also provide new insights on genes that are relevant to RA-activation in human skin. The results in the present study show this model represent a valuable pre-clinical model for studying the effects of retinoids in skin.

Effect of skin metabolism on dermal delivery of testosterone: qualitative assessment using a new short-term skin model.

The skin is a metabolically active organ expressing biotransformation enzymes able to metabolize both endogenous molecules and xenobiotics. We investigated the impact of metabolism on the delivery of testosterone through the skin with an ex vivo pig ear skin system as an alternative model for human skin. Penetration, absorption and metabolic capabilities were investigated up to 72 h after application of [(14)C]-testosterone doses of 50-800 nmol on either fresh or frozen skin, with the latter model being metabolically inactive. Testosterone absorption and metabolite production were monitored by radio-HPLC and gas chromatography-mass spectrometry. Testosterone absorption through frozen skin was much lower, irrespective of the dose of testosterone applied, compared to fresh skin. Using fresh skin samples, >95% of the radioactivity recovered in culture media, as well as the skin itself, corresponded to metabolites. These results were compared with the metabolic data obtained from other in vitro systems (liver and skin microsomes). The present work leads to the conclusion that most of the enzymatic activities expressed in liver fractions are also expressed in pig and human skin. The metabolic activity of the skin can modulate the biological activity of pharmaceuticals (and xenobiotics). Consequently, it can also greatly affect transdermal drug delivery.

Comparative analysis of solar radiation-induced cellular damage between ex vivo porcine skin organ culture and in vitro reconstructed human epidermis.

Reconstructed human epidermis models (RHE) constitute an innovative alternative to study phototoxicity and photoprotection in the cosmetic industry. However, little information is currently available concerning the harmful effects of solar-simulated radiation (SSR) in these in vitro skin models. In this study, the phototoxic effects of a single acute SSR dose of 275 kJ m(-2) were evaluated in a validated RHE model (from SkinEthic), and were compared with those obtained from an ex vivo skin organ culture recently developed from domestic pig ears. The RHE model was well differentiated in vitro and released a significant level of the cytosolic enzymes lactate dehydrogenase (LDH) and extracellular signal-related kinase 2 (ERK2) protein in the culture medium 24 h after SSR exposure. The SSR-induced cytotoxicity was related to the formation of sunburn cells and the appearance of DNA damage (thymine dimer and DNA fragmentation) in keratinocytes. Interestingly, these DNA alterations were associated with the activation of the caspase-3 protease, mainly in the basal layers of the epidermis. In addition, the RHE model responses were comparable with porcine skin following solar irradiation, and none of the above cellular responses was observed in non-irradiated skin models. Finally, topical application of a broad-spectrum UVB + A sunscreen formulation efficiently protected both the RHE and pig skin against the deleterious effects of SSR. Thus, both RHE and ex vivo pig skin organ culture models are complementary tools in the assessment of SSR-induced DNA damage and apoptosis, and they may be used to evaluate the photoprotective capacity of cosmetic formulations.

In vitro percutaneous absorption and in vivo stratum corneum distribution of an organic and a mineral sunscreen.

Sunscreens, whose main function is to protect the skin against the harmful effects of solar irradiation, should remain at the skin surface or impregnate the first layers of the stratum corneum only and not penetrate into the underlying living tissue. The goal of this work was to assess the penetration of titanium dioxide (TiO(2)) and methylene bis-benzotriazoyl tetramethylbutylphenol (MBBT), included in a broad-spectrum sunscreen formulation, into human skin in vivo, using the tape stripping method, and in vitro, using a compartmental approach. An additional objective was to propose an easy and minimally invasive approach to determining the percutaneous uptake of sunscreens following topical application. TiO(2) and MBBT were quantified using colorimetric assay and HPLC analysis, respectively. The transmission electron microscopy and particle-induced X-ray emission techniques were used to localize the TiO(2) in skin sections. More than 90% of both sunscreens was recovered in the first 15 tape strippings. In addition we have shown that the remaining 10% did not penetrate the viable tissue, but was localized in the furrows and in the opened infundibulum. Less than 0.1% of MBBT was detected in the receptor medium, and no TiO(2) was detected in the follicle, viable epidermis or dermis. Thus, this in vivo and in vitro penetration study showed an absence of TiO(2) penetration into the viable skin layers through either transcorneal or transfollicular pathways and negligible transcutaneous absorption of MBBT. However, differences in distribution within the stratum corneum reinforced the need for a complementary approach, using minimally invasive in vivo methodology and in vitro compartmental analysis. This combination represents a well-adapted method for testing the safety of topically applied sunscreen formulations in real-life conditions.

Transfollicular delivery of linoleic acid in human scalp skin: permeation study and microautoradiographic analysis.

There are a large number of studies on the pharmacological activity of lineolic acid (LA) on the skin; however, very little work has been carried out to determine how LA targets the follicular structure. The aim of this study was to identify the preferred route of penetration of LA and to localize the molecule, using a microautoradiographic technique associated with a compartmental approach. In an in vitro test using topical application of 0.05 g of a formulation containing 1% of LA, 10% of the total recovery was found in the stratum corneum and dermis after 6 h. Microautoradiographic analysis of a 'virtual' slide showed most of the silver grains, i.e. LA, at the hair sheath, and none in the dermal compartment, confirming the diffusion of LA through a preferred transfollicular route. These results show, for the first time on human scalp skin, that the combination of compartmental analysis and microautoradiography points to a preferred transfollicular route of diffusion of topically applied LA. Thanks to its high-resolution, microautoradiography offers the advantage of providing detailed in situ information on the delivery of LA in the skin, including the cellular location of the molecule.

Diffusion of E and Z urocanic amphiphiles through skin and their insertion in a membrane model.

The incorporation of synthetic urocanic amphiphiles into a membrane model is described. A monomolecular film of dipalmitoyl phosphatidylcholine (DPPC) and cholesterol was formed at the air-water interface and used as a model. In parallel, diffusion of these derivatives through the skin was studied using rat skin on flow-through diffusion cells. The flux and the cumulative amount were determined. Although the structure and the composition of the DPPC/cholesterol monolayer differed greatly from multilayers of epidermal lipids, the results obtained in the incorporation and diffusion studies were similar. The structure of the urocanic amphiphiles was very close, but the membranes led to the following flux or insertion classification: Ester E > Ester Z >> Amide E. From the results obtained and for simplicity, the technique of Langmuir monolayers seems to be highly suited to the primary screening of amphiphilic compounds.

In vitro study of low-frequency ultrasound-enhanced transdermal transport of fentanyl and caffeine across human and hairless rat skin.

The effect of low-frequency sonophoresis on fentanyl and caffeine permeation through human and hairless rat skin was studied in vitro. Experiments were performed using 20 kHz ultrasound applied at either continuous or discontinuous mode and with an average intensity of 2.5 W/cm(2). The results showed that low-frequency ultrasound enhanced the transdermal transport of both fentanyl and caffeine across human and hairless rat skin. This was explained by both increasing flux during sonication and shortening the lag time. Discontinuous mode was found to be more effective in increasing transdermal penetration of fentanyl while transdermal transport of caffeine was enhanced by both continuous and pulsed mode. Histological and electron microscopy studies showed that human and hairless rat skin was unaffected by ultrasound exposure. Further studies will be necessary to determine the relative contribution of ultrasound parameters in low-frequency ultrasound-induced percutaneous enhancement of drug transport.

Wetting of biological lipids on aqueous substrates.

We study the dynamics and final wetting state of skin lipids on water and brine by fluorescence microscopy and ellipsometry. When a lipid droplet is brought into contact with the water surface, a lipid wetting film spreads out rapidly by a Marangoni effect. Subsequently, this film undergoes a dewetting instability. However, the final equilibrium is not partial wetting. The film breaks up into droplets with a mesoscopic (approximately 50 A) film in between. These observations result from a subtle interplay between short- and long-range forces: surfactants naturally present in the lipids favor wetting, while the van der Waals forces oppose it. In addition, this reveals the likely organization of the hydrolipid film that covers and protects the skin.