FORMULATING FOR MILDNESS
Mild retinol alternative for global compliance
Marcie Natale, Stephanie Clendennen - Eastman
Retinoids are the gold standard for reducing signs of aging when applied topically to the skin. Familiar examples of retinoids are retinoic acid, retinol, and retinol esters like retinyl palmitate. Retinol is highly effective, but it can be unstable in formulation and irritating to skin at cosmetically useful levels. In one review of published studies, retinol
was associated with skin redness, dryness and flaking.1
Derivatizing retinol can reduce its
potential for irritation and improve its stability. In particular, fatty acid derivatives of retinol can deliver high efficacy without the irritation.2 Retinyl linoleate is a compound composed
of retinol and high-purity linoleic acid from safflower oil joined by an ester bond. Retinyl linoleate is a biobased, formulation-stable, easy-to-handle, nonirritating antiaging ingredient. Retinyl linoleate is historically known to be non-irritating and stable in formulation.3 Eastman GEM™ retinyl linoleate is
manufactured under exceptionally mild conditions, preserving the product purity and not introducing any unwanted by-products. At room temperature, it is a pourable liquid and is supplied as a high-purity (>95%) assay; therefore, it is free of solvent, diluents, and carriers. The fatty acid component of retinyl linoleate
is a polyunsaturated fatty acid, proposed to offer better solubility in skin lipids for good skin delivery. Better bioavailability will lead to enhanced biological action in skin cells. To confirm the bio-activity of retinyl linoleate, we first used in vitro methods to predict the cosmetic effect of retinyl ester treatments at the molecular level. A global gene expression profiling study
was performed in a cultured skin model treated topically with retinyl linoleate. The induction of genes associated with cell proliferation and known retinol marker genes, points to very specific physiological changes after the retinyl ester treatment. From the in vitro data, we predicted that the
observed changes may translate into desired cosmetic benefits. To confirm those benefits, the in vitro tests were followed by a clinical study that confirmed improvement in multiple signs of aging over the course of 12 weeks.
Experimental methods Materials Cultured skin models were purchased from MatTek. Retinyl linoleate was from Eastman
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the tissue and shaken at 35°C in a humidified incubator. After 24 hours, the cultured skin disc was rinsed and subjected to RNA isolation and cDNA synthesis. The cDNA was labeled and hybridized with a human whole gene array analysis (Roche/NimbleGen Systems). Over 47,000 features per chip were represented in each data set, theoretically representing each known human gene (37,000) at least once.
In vitro permeation and hydrolysis in a skin model
The permeation and hydrolysis of experimental retinyl esters was evaluated in an in vitro human skin model by monitoring esters and hydrolysis products in the tissue. EpiDerm differentiated cultured human skin tissue was purchased from MatTek Corporation and used according to the supplier’s protocols. The percutaneous absorption protocol
Chemical Company. Retinyl palmitate was purchased from Sigma-Aldrich. Other reagents were ACS grade or higher purity.
Formulations for in vitro studies Retinyl esters were first dissolved in isopropanol (IPA) at a final concentration of 10% or 20% (w/v). An emulsion in water was made right before application. The vehicle contained 90% deionized water, 8% Triacetin, 1% IPA, and 1% lecithin. In the test samples, the final concentration
of retinyl ester in the vehicle was either 0.2% (2mg/ml) for gene expression or 0.1% (1
mg.ml) for permeation studies.
In vitro gene expression A cultured human skin model containing both fibroblasts and differentiated keratinocytes was subjected to retinyl ester treatments and subsequent gene expression profiling. MatTek EpiDerm300FT full thickness cultured skin was treated according to supplier’s protocols. Topical treatments for global gene
expression profiling included vehicle only, 0.2% retinyl linoleate, and 0.2% retinyl palmitate. A retinyl ester or vehicle only emulsion was added to the upper surface of
supplied with the EpiDerm tissue was followed using MatTek permeation devices. A 0.4 ml sample of the test formulation containing 0.1% of the test retinyl ester was applied to the upper surface of the tissue. Plates were incubated at 37°C, loosely covered, and rotated at 60rpm. After a 24-hour sample, each permeation
device was disassembled, the skin disc was removed from the insert membrane with fine forceps and rinsed in 1ml fresh PBS. Then, the tissue discs were extracted in 1ml ethyl acetate by sonication and stored at -20°C prior to LC/MS/MS analysis. Treatments were performed in triplicate. The relative levels of retinol/retinaldehyde and retinyl esters were determined by LC/MS/MS and identified using authentic standards.
Clinical study A clinical study was conducted to assess the efficacy of a formulated skin cream containing 0.1% retinyl linoleate (Figure 1). Panelists applied the cream twice daily over a 12-week period. A daily sunscreen was part of the regimen. Experts graded the panelists at baseline and
after 12 weeks of home use on a scale from 0 (very clear, no wrinkles or spots) to 9 (Extremely visible dark spots, severe wrinkles). Twenty- one subjects of diverse age and skin types completed the study.
Results and discussion Global gene expression analysis Retinoids can reduce the appearance of fine
April 2023 PERSONAL CARE
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