J. Cosmet. Sci., 59, 217-224 (May/June 2008) In vivo spectrophotometric evaluation of skin barrier recovery after topical application of soybean phytosterols CARMELO PUGLIA and FRANCESCO BONINA, Department of Pharmaceutical Sciences, School of Pharmacy, University of Catania, Viale A. Doria No. 6, 95125, Catania, Italy. Accepted for publication January 28, 2008. Synopsis The skin's uppermost thin layer, stratum corneum, plays a crucial role in protecting the body against unwanted influences from the environment. Disruption of the stratum corneum, by tape stripping or chemical injury, results in epidermal recovery of the skin barrier. Soy phytosterols are widely used in the cosmetic field as active ingredients in creams and lipsticks. Furthermore, they deserve an important place among nutracosmeceuticals in fact, after their absorption from the diet they are transferred from the plasma to the skin, playing an important role in the constitution of skin surface lipids. The aim of the present work was to study the effect of the topical application of soybean phytosterols on skin barrier recovery in human volunteers using the extent of methyl nicotinate (MN)-induced erythema in damaged skin as a parameter to evaluate the rate of stratum corneum recovery. MN was chosen as an erythematogenous substance for its capability to cause an erythema whose intensity and duration are proportional to the quantity of the substance that has entered the living epidermis over time. MN-induced erythema was monitored using reflectance spectrophotometry as a noninvasive instrumental technique. The results show clearly that soy phytosterols exert positive results on skin repair in fact, three days after tape stripping, the sites treated with a formulation containing phytosterols showed an appreciable recovery of barrier function compared to those treated with a vehicle control without soy phytosterols. INTRODUCTION The permeability barrier of the skin is localized in the stratum corneum (SC), a compact mass of metabolically inactive cells embedded in an extracellular matrix of non-polar continuous lamellar lipid layers (1). These structures are viewed as the major obstacle against the penetration of exogenous substances through the skin (2,3). This feature of the stratum corneum is dependent on its elasticity, determined by the content of fats and inorganic salts, as well as by the hydratation state (3 ). Besides, skin Address all correspondence to Carmelo Puglia. 217

218 JOURNAL OF COSMETIC SCIENCE moisturization depends on lipid presence in the stratum corneum, and it guarantees a softer and healthy skin with a more pleasing appearance (4). When the barrier function is damaged by a surfactant, organic solvent, or tape stripping, a series of homeostatic systems is accelerated and the barrier function recovers its original level (5). First, exocytosis of lipid-containing granules, lamellar bodies, is accelerated and the inside lipids are secreted into the intercellular domain between the stratum granu­ losum and the stratum corneum and form a water-impermeable membrane (5). Then, lipid synthesis and processing are speeded up. Finally, the barrier function recovers to its original level. In order to increase the rate of the homeostatic response in the epidermis and the return of the barrier function to normal, different strategies have been studied. Many research­ ers (6-8) demonstrated that a topically applied mixture of stratum corneum lipids, i.e, ceramide, cholesterol, and free fatty acids, accelerated repair of the barrier function after its damage. Furthermore, Yang et al. demonstrated the efficacy of an optimal non­ physiological lipid mixture in increasing the recovery rate of the disrupted skin barrier (9). Soybean-germ oil deserves an important place among nutraceuticals because of its very high content of tocopherols, phytosterols, polyunsaturated fatty acids, carotenoids, and other vitamins (10). This pool of substances represents a natural defense against oxidative damage caused by free radicals derived from cellular aging (10). Particularly, various scientific works have demonstrated the efficacy of soy phytosterols, such as �-sitosterol, in the treatment of erythema, chilblains, and chapping, and as ingredients in topic formulations in the treatment of burns (11-13). As previously observed, the stratum corneum represents a valid shield against the penetration of exogenous and toxic substances and its removal is often followed by an amplification of skin irritant phenomena compared to normal conditions. Therefore, the aim of the present work was to study the effect of the topical application of soybean phytosterols on skin barrier recovery in human volunteers using the extent of methyl nicotinate (MN)-induced erythema in damaged skin as a parameter to evaluate the rate of stratum corneum recovery. MN was chosen as an erythematogenous substance for its capability to cause an erythema whose intensity and duration are proportional to the quantity of the substance that has entered the living epidermis over time (14). MN­ induced erythema was monitored using reflectance spectrophotometry as a noninvasive instrumental technique. MATERIALS AND METHODS MATERIALS Soy phytosterol mixture was obtained from Sochim International (Milan, Italy) and its composition is reported in Table I methyl nicotinate (MN) was obtained from Fluka (Switzerland) Cetiol B (d-n-butyl adipate) was obtained from Henkel (Dusseldorf, Ger­ many). All other chemicals were of reagent grade. INSTRUMENTATION MN-induced skin erythema was monitored by using a reflectance visible spectropho-