The effectiveness of cosmetic products in alleviating a range of skin dryness conditions as determined by clinical and instrumental techniques.

Synopsis A vast array of cosmetic products are used routinely by consumers to alleviate a range of skin care problems. Consumer concern ranges from age-associated skin changes to complexion (e.g., spots and pimples) and dryness. However, a major cause for concern amongst European female consumers is skin dryness, which spans all age ranges and skin types. Utilizing instrumental procedures (Squametry and Image Analysis) the severity of skin dryness has been correlated with expert assessment and consumer perception of dryness. The sensitivity of these techniques enables one to follow the progression of dryness alleviation for a range of product forms (e.g., creams and lotions) as well as the purported mechanism of action of various ingredient systems (e.g., occlusivity, moisturization). While conventional cosmetic products are shown to be effective, these techniques can be used to aid in the assessment and formulation of more effective products. Efficacité des produit cosmétiques à l'allégement d'un spectre d'états de peau sèche selon des measures cliniques et au moyen d'instruments.

Location and nature of the epidermal permeability barrier.

Synopsis The lowest region of human and pig stratum corneum has been isolated as an integral layer, referred to as the stratum compactum. This preparation is resistant to disruption by enzymes, 6M urea, Triton X-100 and organic solvents. Our evidence suggests that penetration of materials to and through the corneum depend on the state of cohesion between cells, and of the organization of intercellular lipid species. As the cells move up towards the outside of the stratum corneum, the cohesive forces are reduced due to desmosome degradation and lipid modifications, with ultimate dyshesion and sloughing of individual cells. A number of linoleate-rich lipids have been identified within human and pig epidermis which could contribute to the formation or maintenance of an epidermal permeability barrier. Our current belief is that the molecule key to barrier function is a hydroxylated linoleate derivative which appears to be formed in the stratum compactum region.

Identification, isolation and characterization of epidermal lipids containing linoleic acid.

Three specific linoleate-rich lipids have been identified in pig epidermis and are referred to as O-acylglucosyl ceramide, O-acyl ceramide, and O-acyl acid. The acid moiety is up to 70% linoleic acid and linked via the hydroxyl group of a omega-OH long-chain fatty acid, which itself is linked to sphingosine or glucosyl sphingosine. The identification of O-acyl ceramide confirmed the findings of another group, whereas the structural configuration of the O-acylglucosyl ceramide is different to previous reports. The identification of an O-acyl acid in epidermis is novel. Our evidence allows us to speculate that a hydroxylated derivative of the O-acyl ceramide may be intimately involved in the permeability barrier of skin, perhaps providing sufficient polarity to maintain a lamellar phase in the intercellular space of the lower stratum corneum region, and that it is specifically in this form that linoleic acid is involved in skin barrier function. Alternatively, or concurrently, this species may act as a signal for late keratinisation events.

Isolation, barrier properties and lipid analysis of stratum compactum, a discrete region of the stratum corneum.

We have isolated the lowest region of human and pig stratum corneum as an integral layer which we have termed the stratum compactum. This preparation is resistant to disruption by enzymes, 6 M urea, Triton X-100 and solvents. Our evidence suggests that all cells of the stratum corneum may be equally permeable to aqueous soluble materials but that penetration of materials through the corneum depends on the state of cohesion between cells and of the organization of intercellular lipid species. As the cells move up towards the outside of the stratum corneum the cohesive forces are reduced due to desmosome degradation and lipid modifications with ultimate dyshesion and sloughing of individual cells.

Sphingomyelinase in pig and human epidermis.

The enzyme sphingomyelinase (sphingomyelin phosphorylcholine phosphohydrolase E.C.3.1.4.12) which hydrolyzes sphingomyelin to ceramide (N-acylsphingosine) and phosphorylcholine was identified in the subcellular fractions of pig and human epidermis. The enzyme has an optimum pH of 4.5 to 5 and is activated by Triton X-100 (0.1% w/v). Approximately two-thirds of the enzyme activity in both the pig and human epidermal homogenates was in the soluble subcellular fraction and more than half of the enzyme activity in the subcellular particulate fraction was solubilized by freeze-thawing. The pH optimum suggests that epidermal sphingomyelinase is probably a lysozomal enzyme. The enzymes in both pig and human epidermis exhibited Michaelis-Menten kinetics. The soluble sphingomyelinase in pig epidermis had an apparent Km, 4.5 X 10(-5) M and that in human epidermis an apparent Km 7.7 X 10(-5) M. The pig epidermal sphingomyelinase had no special requirement for either divalent or heavy metal ions and was not inhibited by sulfydryl group-blocking agents but it was moderately inhibited by dithiothreitol. No evidence was found in either pig or human epidermis for the presence of a phospholipase C (E.C.3.1.4.3) which hydrolyzes phosphatidylcholine to diglyceride and phosphorylcholine but there was suggestive evidence of another catabolic pathway for phosphatidylcholine.