The International Society for Stratum Corneum Research held its seventh biannual Stratum Corneum (SC) conference on Sept. 10–12 as a joint meeting with the Skin Forum. The event’s namesake is the top layer of the skin that functions primarily as the skin barrier, and it plays a vital role in many aspects of personal care.
The three-day conference was attended by researchers working in basic and applied research of SC biology, organization and function, transdermal absorption and their applications in personal care, pharmaceutical technology and dermatology. Ronald Marks, PhD, of Cutest Systems Ltd., opened the event and set the scene in defining the SC as an important barrier membrane, acting also as “a canvas on which we paint a pleasing supplement to our aesthetic selves.” The SC has impressive protective functions, including: mechanical (preventing incisional, torsional and scratch injury), antimicrobial and ultraviolet. In addition, it also has an impressive viscoelastic nature and pliability, allowing digits to move without cracking.
The SC also has an ability to differentiate at specific anatomical sites. Jean-Luc Lévêque, PhD, of Skindata elaborated on the SC mechanical function. It is a bio-composite membrane made of reinforced corneocytes bound together by proteic plugs and lipids of a complex, ordered structure. Synergy of these building blocks allows SC to remain cohesive while ensuring its barrier properties when strained by external mechanical stimuli. SC transmits weak tactile stimuli from its surface and has frictional properties to allow an efficient grasp and sensing of objects.
Organization and Function of SC
Marek Haftek, PhD, MD, of CNRS and his group presented their research of electron microscopy of the barrier and detection and functionality of epidermal tight junctions. The barrier is located in stratum compactum with lipid molecules arranged in quasi-continuous multilayered sheets and hydrophilic lacunae. Tight junctions in the stratum granulosum are involved in the process of SC formation and may constitute a secondary barrier beneath SC. Mila Boncheva, PhD, of Firmenich elaborated on the physical chemistry of barrier lipids, reviewing current understanding of their composition, self-assembly and molecular organization related to skin barrier integrity.
The processes of epidermal differentiation and apoptosis were explored by Professor Wim Declercq, PhD, of Ghent University. Caspases, proteinases with a role in inflammation and apoptosis are also implicated in keratinocyte differentiation. It is a pathway that differs from the classical cell death.
In the Desquamation session, which was supported by DSM, Michel Simon, PhD, of University of Toulouse reported on properties and functions of filaggrin-related proteins (filaggrin-2 and hornerin) that are important for keratinocyte differentiation. Their decreased expression may contribute to barrier defects in atopic dermatitis (AD). Ulf Meyer-Hoffert, PhD, from the University of Kiel looked at inhibition of kallikrein-related peptidases, involved in inflammation and desquamation, to maintain the epidermal homeostasis. Mark Donovan, PhD, of L’Oréal Recherche outlined new perspectives on desquamation, studying the degradation of the corneo-desmosomal proteins through a combination of proteomics and atomic force microscopy in normal and aged skin.
A comprehensive review of SC antimicrobial peptides by Jens Schroder, PhD, of the University of Kiel, discussed the SC being covered with microorganisms that do not infect the skin. The antimicrobial barrier preferentially kills or inhibits potentially pathogenic bacteria from the gastrointestinal system. Three distinct peptide barrier systems, at specific locations within the SC, constitute the innate defense system of healthy skin.
Transdermal Absorption Through SC
The Skin Forum session was introduced by Professor Jonathan Hadgraft, PhD, of the University of London, sharing the work of the late Professor Johann Wiechers, PhD. The skin, as an effective barrier, presents a challenge for the formulator of topical and transdermal products. The solubility of the active compound is important. It has to pass sequentially through hydrophilic and lipophilic domains of structured lipid bilayers that can be modified by excipients when “formulating for efficacy.” The session further explored issues of transdermal absorption in vitro and micro-needle delivery.
Penetration of lipophilic and hydrophilic actives into skin was also discussed by Franziska Fleischli, PhD, of the Zurich University of Applied Sciences. Cosmetic and pharmaceutical products are applied for different purposes, and the depth of the penetration depends on the active compound as well as the formulation. She compared the penetration into skin models in vitro and human skin in vivo, confirming different penetration profiles.
Barrier Function in Adult and Baby SC
Neelam Muizziddin, PhD, of Esteé Lauder Companies looked at the adaptation of skin to climates and seasons. Basal transepidermal water loss (TEWL) is reduced in a dry versus humid environment; skin chronically exposed to hot, dry climate exhibits a stronger barrier. Skin barrier is weaker in winter than in summer.
Biophysical and biochemical properties of female intimate skin were explored by Ray Warren of P&G, and research into variations in residual skin surface components (the mixture of sebum and sweat residue) based on age, gender and ethnicity was presented by Matt Traynor, PhD, of University of Hertfordshire.
Martin Albrecht of GSK discussed enhanced recovery of intercellular lipid damage of the SC by topical application of phospholipids showing advantages compared to classical emulsifier/surfactant based systems. Russell Elliott, PhD, of Johnson & Johnson studied benefits of glycerin in xerotic skin, improving barrier function and hydration and inhibiting the transition of SC lipids from liquid to solid phase.
Georgios Stamatas, PhD, of Johnson & Johnson explored the intricacies of infant skin physiology and structure. Compared to adult skin, the higher epidermal cell turnover gives rise to smaller, less mature corneocytes and thinner SC layers. This translates to weaker barrier and increased skin hydration, softer SC and a difference in microbial colonization. Factors influencing SC integrity and maturation in neonates were discussed by Marty Visscher, MD, of the Cincinnati Children Hospital. Neonatal SC provides innate immunity and protection, and it enables life-supporting tactile discrimination, critically important for premature infant survival. An understanding of the SC adaptive changes is essential for the development of evidence-based practices on the neonatal units.
Dematological and Cosmetic Aspects of SC
Professor Mike Cork, PhD, from the University of Sheffield, gave a talk about skin barrier breakdown in AD and the effect of topical products. AD develops as a result of gene-environment interactions, which leads to a breakdown of the barrier. The first line treatment is to repair the defective skin barrier. There is a lack of evidence for the effect topical products have on the skin barrier, and some formulations have a detrimental effect. The challenge is to educate clinicians, patients and consumers. A comprehensive review of skin lipid barrier was presented by Professor Joke Bouwstra, PhD, from Leiden University, demonstrating that changes in ceramide composition and lipid organization play a role in the barrier impairment in AD. Carmen Martinezlerga of Croda Europe Ltd. studied the impact of emulsifiers, generating “a spectrum of skin mildness” for different end formulations (e.g., leave- on or wash-off product). Her goal is to change the formulator’s priorities; to be influenced not only by the formulation stability and aesthetic but also its interaction with the skin.
Lisa Kroll of Kimberly-Clark Corp. talked about SC changes after mechanical damage with emery paper. She described significant biophysical but no biochemical changes immediately after the abrasion. In the days after, there was a decrease of natural moisturizing factor (NMF) components. Barrier function recovered within a week, but NMF has not been restored, even after 11 days. Izabela Buraczewska-Norin of ACO Hud Nordic AB reiterated that sensory properties of moisturizers influence compliance and treatment effectiveness; these should meet consumers’ preferences. The lack of correlation between instrumental and sensory analysis suggests that “skin feel” is hard to measure by objective methods.
Kristien De Paepe, PhD, of Vrije Universiteit reviewed silicone preparations used in personal care for their emollient and skin conditioning properties. Persistent misconception exists that silicones are occlusive, and the industry has to differentiate between occlusive and water-resistant (skin protecting) properties when communicating to consumers.
All presentation abstracts are available in the International Journal of Cosmetic Science’s August 2012 issue. For more information about the International Society for Stratum Corneum Research, visit www.stratumcorneumsociety.com.