Georgios N. Stamatas

Barrier Function and Water-Holding and Transport Properties of Infant Stratum Corneum Are Different from Adult and Continue to Develop through the First Year of Life

Skin water barrier development begins in utero and is believed to be complete by week 34 of gestational age. The goal of this investigation was to assess the dynamic transport and distribution of water of the stratum corneum of infants and compare it to those of adults. The interaction of water with the stratum corneum was assessed by measuring capacitance, transepidermal water loss (TEWL), rates of absorption-desorption as well as Raman spectra as a function of depth (a total of 124 infants (3-12 months) and 104 adults (14-73 years)). The results show that capacitance, TEWL, and absorption-desorption rates had larger values consistently for infant stratum corneum throughout the first year of life and showed greater variation than those of adults. The Raman spectra analyzed for water and for the components of natural moisturizing factor (NMF) showed the distribution of water to be higher and have a steeper gradient in infants than in adults; the concentration of NMF was significantly lower in infants. The results suggest that although the stratum corneum of infants may appear intact shortly after birth (<1 month), the way it stores and transports water becomes adult-like only after the first year of life.

In vivo spectrofluorimetry reveals endogenous biomarkers that report healthspan and dietary restriction in Caenorhabditis elegans.

Autofluorescent lipofuscin and advanced glycation end‐products (age pigments) accumulate with age across phyla, yet little is understood about their formation under physiological conditions and their specific contributions to the aging process. We used in vivo spectrofluorimetry to quantitate autofluorescence in wild‐type Caenorhabditis elegans and longevity mutants disrupted for distinct aspects of the aging process. In wild‐type animals, age pigments increase into adulthood, accumulating slowly during the reproductive phase and more rapidly during the post‐reproductive period. As in humans, insulin signaling influences age pigment accumulation – mutations that lower efficacy of insulin signaling and extend lifespan [daf‐2(e1370) insulin receptor and age‐1(hx546) PI3‐kinase] dramatically lower age pigment accumulation; conversely, elimination of the insulin‐inhibited DAF‐16/FOXO transcription factor causes a huge increase in age pigment accumulation, supporting that the short‐lived daf‐16 null mutant is truly progeric. By contrast, mutations that increase mitochondrial reactive oxygen species production do not affect age pigment accumulation, challenging assumptions about the role of oxidative stress in generating these species in vivo. Dietary restriction reduces age pigment levels significantly and is associated with a unique spectral shift that might serve as a rapidly scored reporter of the dietary restricted state. Unexpectedly, genetically identical siblings that age poorly (as judged by decrepit locomotory capacity) have dramatically higher levels of age pigments than their same‐aged siblings that appear to have aged more gracefully and move youthfully. Thus, high age pigment levels indicate a physiologically aged state rather than simply marking chronological time, and age pigments are valid reporters of nematode healthspan.

Diversity of the Human Skin Microbiome Early in Life

Within days after birth, rapid surface colonization of infant skin coincides with significant functional changes. Gradual maturation of skin function, structure, and composition continues throughout the first years of life. Recent reports have revealed topographical and temporal variations in the adult skin microbiome. Here we address the question of how the human skin microbiome develops early in life. We show that the composition of cutaneous microbial communities evolves over the first year of life, showing increasing diversity with age. Although early colonization is dominated by Staphylococci, their significant decline contributes to increased population evenness by the end of the first year. Similar to what has been shown in adults, the composition of infant skin microflora appears to be site specific. In contrast to adults, we find that Firmicutes predominate on infant skin. Timely and proper establishment of healthy skin microbiome during this early period might have a pivotal role in denying access to potentially infectious microbes and could affect microbiome composition and stability extending into adulthood. Bacterial communities contribute to the establishment of cutaneous homeostasis and modulate inflammatory responses. Early microbial colonization is therefore expected to critically affect the development of the skin immune function.

Fluorescence spectroscopy of skin

The fluorescence properties of skin both human and of an animal model are reviewed in this article. Fluorescence spectroscopy is a valuable tool for the investigation of the optical properties of the skin in the ultraviolet range of the spectrum because the absorption bands are confluent. Epidermal and dermal fluorescence signals are each produced in distinct spectral regions. Biological processes modulate the fluorescence signals in predictable ways. Such cases include aging, epidermal proliferation, and photoaging as well as diseases such as psoriasis, acne and non-melanoma skin cancer. Fluorescence excitation spectroscopy has proved a valuable approach in the study of the structure and function of human skin.

Infant skin physiology and development during the first years of life: a review of recent findings based on in vivo studies

Infant skin is often presented as the cosmetic ideal for adults. However, compared to adult skin it seems to be more prone to develop certain pathological conditions, such as atopic dermatitis and irritant contact dermatitis. Therefore, understanding the physiology of healthy infant skin as a point of reference is of interest both from the cosmetic as well as from the clinical point of view. Clinical research on healthy infants is, however, limited because of ethical considerations of using invasive methods and therefore until recently data has been scarce. Technical innovations and the availability of non‐invasive in vivo techniques, such as evaporimetry, electrical impedance measurement, in vivo video and confocal microscopy, and in vivo fibre‐optic based spectroscopy, opened up the field of in vivo infant skin physiology research. Studies incorporating such methods have demonstrated that compared to adult, infant skin continues to develop during the first years of life. Specifically, infant skin appears to have thinner epidermis and stratum corneum (SC) as well as smaller corneocytes at least until the second year of life. The water‐handling properties are not fully developed before the end of the first year and infant SC contains more water and less amounts of natural moisturizing factors. Such findings re‐evaluate the old notions that skin is fully matured at birth. Armed with this knowledge, we are in a position not only to better understand infant dermatological conditions but also to design better skin care products respecting the distinct qualities of infant skin.

In vivo measurement of skin erythema and pigmentation: new means of implementation of diffuse reflectance spectroscopy with a commercial instrument

Background  Various physical, chemical and biological insults, including exposure to ultraviolet (UV) radiation, cause erythema and change in pigmentation in human skin. These reactions provide an important measure of the cutaneous response to the insult.

Lipid uptake and skin occlusion following topical application of oils on adult and infant skin

BACKGROUND Topical application of oils and oil-based formulations is common practice in skin care for both adults and infants. Only limited knowledge however is available regarding skin penetration and occlusive potential of oils and common methods for measuring skin moisturization fall short when it comes to the moisturizing effect of oils. OBJECTIVE In this study we used in vivo confocal Raman microspectroscopy to test the efficacy of paraffin oil (mineral oil) and two vegetable oils in terms of skin penetration and occlusion. Petrolatum was used as a positive control. METHODS The products were applied topically on the forearms of nine volunteers and seven infants and Raman spectra were acquired before and at 30 and 90 min following application. Depth concentration profiles for lipid and water were calculated from the Raman spectra. Skin occlusion was assessed from the amount of stratum corneum (SC) swelling measured from the water concentration profiles. RESULTS The paraffin oil and the vegetable oils penetrate the top layers of the SC with similar concentration profiles, a result that was confirmed both for adult and infant skin. The three oils tested demonstrated modest SC swelling (10-20%) compared to moderate swelling (40-60%) for petrolatum. CONCLUSION These data indicate that there is no statistical difference between the paraffin oil and vegetable oils in terms of skin penetration and skin occlusion. The results for petrolatum show that in vivo confocal Raman microspectroscopy is sensitive and specific enough to measure both lipid uptake and skin occlusion events following topical application.

Skin Viscoelasticity Displays Site- and Age-Dependent Angular Anisotropy

One of the dominant characteristics of skin aging is loss of elasticity. Although the changes in the mechanical properties of the skin over several decades of life are substantial, objective measurements have failed to capture their magnitude thus far. Moreover, the mechanical properties of the skin are not uniform in all directions, and there is a need to understand this angular anisotropy. In this work we present a methodology of documenting the angular anisotropy of skin elasticity with high sensitivity and dynamic range using the Reviscometer® RVM 600 (Courage & Khazaka Electronic GmbH, Cologne, Germany). The method is based on determining the directional dependence of the speed of an acoustic shear wave on the skin surface at intervals of 3°. Based on the angular distribution of the resonance running time, we define two parameters: the anisotropy and the angular dispersion width. We find that with increasing age the anisotropy increases, while the angular dispersion width decreases. The ratio of these values provides a sensitive parameter for the assessment of the directional behavior of the skin mechanical properties. This parameter provides a large effective dynamic range capable of demonstrating close to an order of magnitude differences in skin viscoelasticity from infants up to adults 75 years of age. Furthermore, we show that the direction of the angular anisotropy relates to the direction of the dermal cleavage lines as defined by Langer, indicating that the anisotropy of the mechanical properties of skin stems from structural parameters. Based on these results, we conclude that the proposed methodology is able to capture accurately the age-dependent changes of the mechanical properties of the skin and to demonstrate a structure-function relationship.

Age-dependent changes in stratum corneum barrier function

The Stratum Corneum (SC) barrier function mainly depends on the SC structure at the tissue level, its composition, and the organization of intercellular lipidic cement at the molecular level. The goal of this study was to assess the age‐dependent changes of the SC barrier function and the associated physiological parameters.

In vivo documentation of cutaneous inflammation using spectral imaging

Typical manifestations of cutaneous inflammation include erythema and edema. While erythema is the result of capillary dilation and local increase of oxygenated hemoglobin concentration, edema is characterized by an increase in extracellular fluid in the dermis, leading to local tissue swelling. Both of these inflammatory reactions are typically graded visually. We demonstrate the potential of spectral imaging as an objective noninvasive method for quantitative documentation of both erythema and edema. As examples of dermatological conditions that exhibit skin inflammation we applied this method on patients suffering from (1) allergic dermatitis (poison ivy rashes), (2) inflammatory acne, and (3) viral infection (herpes zoster). Spectral images are acquired in the visible and near-IR part of the spectrum. Based on a spectral decomposition algorithm, apparent concentrations maps are constructed for oxyhemoglobin, deoxyhemoglobin, melanin, optical scattering, and water. In each dermatological condition examined, the concentration maps of oxyhemoglobin and water represent quantitative visualizations of the intensity and extent of erythema and cutaneous edema, correspondingly. We demonstrate that spectral imaging can be used to quantitatively document parameters relevant to skin inflammation. Applications may include monitoring of disease progression as well as screening for efficacy of treatments.