The Effect of a Ceramide-Containing Product on Stratum Corneum Lipid Levels in Dry Legs.

Roughly equimolar concentrations of ceramides, cholesterol, and free fatty acids arranged in lamellar sheets form the intercellular lipid barrier in the stratum corneum (SC). Intercellular lipid deficiencies, specifically ceramides, and barrier disruption are associated with many dermatologic conditions, including dry skin. This study explored the relationship between the improvement in the signs of dry skin and the amounts of ceramides in the SC by combining clinical observations with a biochemical analysis to quantify the level of SC intercellular lipids. The efficacy of a multilamellar vesicular emulsion (MVE), ceramide-containing moisturizing cream was evaluated in a randomized, investigator-blinded, split-leg study on female subjects with dry, itchy skin. The cream increased skin hydration and demonstrated an immediate and sustained reduction in the visible signs of dry skin and subject perceived sensory discomfort. Additionally, ceramide, cholesterol and free fatty acid levels in the SC significantly increased after 4 weeks of moisturizer application. Thus, the clinical effect of the ceramide-containing moisturizing cream on dry, itchy skin was accompanied by an increase in SC intercellular lipid levels. J Drugs Dermatol. 2020;19(4):372-376. doi:10.36849/JDD.2020.4796.

Evaluating the Transport Kinetics of a Model Compound Released From Cellulosic Coacervate Compositions Into Artificial Sebum.

Complex coacervates of cationic polymers and anionic surfactants, which are produced spontaneously during the use of rinse-off formulations, represent an important delivery vehicle for topical agents to the skin surface and appendages. In this study, an artificial sebum-loaded cell culture insert method for determining the sebum diffusion properties of topical agents was optimized for in vitro release testing. This method was subsequently used to evaluate the transport kinetics of a model compound, kinetin, released from semi-solid coacervate formulations into sebum. Coacervate compositions were prepared with cationic-hydroxyethyl cellulose dodecyl sulfate (cat-HECDS), sodium dodecyl sulfate (NaDS), and water. Tested compositions ranged from 90 to 50 wt% water and had a cat-HECDS to NaDS wt% ratio of 2:1, 1:1, or 1:2, mimicking the in vivo hydration range and relative excess surfactant content expected from commercial rinse-off formulations. Steady-state flux of the model compound from each coacervate composition was found to vary with water content of the composition. When flux was plotted versus [(cat-HECDS:NaDS) × (1 - weight fraction water)]-1, a strong linear correlation (R2 = 0.89) emerged. The in vitro release testing method proved capable of discriminating between clinically relevant differences in transport kinetics from different coacervate formulations using a practical sample size.

The influence of cellulosic coacervate composition on the flux of an entrained agent through a coacervate/sebum barrier.

Complex coacervation is the primary mechanism used in rinse-off formulations to deliver topical agents to the skin and hair; this process produces polycation-surfactant anion coacervates that entrain the agent and enhance its substantivity at these sites. This study investigates the relationship between the transport of agents released from a coacervate vehicle into artificial sebum and the coacervate's composition and properties. The flux of a model compound, kinetin, through a variety of cellulosic coacervate/sebum composite barriers prepared on cell culture inserts was determined. These values were interpreted according to a semi-empirical model based on the composition of the coacervate, polymer properties, and the material stiffness. A multivariate analysis using composition and polymer descriptors yielded a strong correlation (r2=0.72) to the experimental kinetin transport data. Variables that describe the degree of entanglement of the surfactant-linked polymer chain web (specifically, the molar ratio of anions to cations and wt% water) emerged as important predictive variables for kinetin transport. According to the developed model, compositional or ingredient manipulations that expand and untangle the web favor a more rapid release of entrained agents from the coacervate into sebum and, consequently, higher bioavailability on the skin surface.