Dr Sergio Amari, Alain Thibodeau Ph.D. – B&T, Italy
The skin is externally located and thus serves as a sheath separating internal organs from direct contact with the environment.
Despite this perception as an inert envelop, the skin is a very complex and metabolically active tissue endowed with both intracrine and paracrine capabilities. The main roles of the skin are: protection from UV radiation (melanogenesis), immune defence and a barrier function preventing the penetration of foreign particles.
From this point, I will refer to those structures formed by cetearyl olivate, sorbitan olivate as bio-compatible liquid crystals.
The clinical efficacy of the biocompatible liquid crystals generated by cetearyl olivate, sorbitan olivate was clinically tested. First, its skin biocompatibility was verified in assessing its effect on the trans-epidermal water loss (TEWL) in comparison to other lipid compositions. TEWL is a validated method to assess the skin permeability barrier function (Fluhr, 2006). Ten volunteers topically applied identical concentrations (5%) of the following ingredients: cetearyl olivate, sorbitan olivate; cetearyl alcohol, cetearyl glucoside and polyglyceryl-3 methylglucose distearate. Results have shown that the application of cetearyl olivate, sorbitan olivate reduced the TEWL increase by 29% compared to the control formulae (Figure 2).
Those results support the need for a physiological compatibility between the topically applied lipid composition and the skin. Cetearyl alcohol, cetearyl glucoside and polyglyceryl-3 methylglucose distearate can be categorised as non-compatible lipid compositions as they trigger excessive water loss on application. This could be interpreted as a transient destabilisation of the barrier integrity leading to the formation of micropores through which water can escape. TEWL progressively recovers toward baseline values as the barrier integrity re-establishes. The importance of lipid composition made of the appropriate – skin-compatible – lipid composition and ratio has been demonstrated (Mao Qiang, 1995; De Paepe, 2002). The compatibility of cetearyl olivate, sorbitan olivate with the skin lipid composition is revealed by a relatively low level of induced TEWL. As the global skin hydration level relies on a tight barrier function and the waterholding capacity, compared was the skin hydration effect of cetearyl olivate, sorbitan olivate to that of glycerin using corneometry. Glycerin is processed and secereted by sebaceous glands and acts as a natural humectant for the skin (Fluhr, 2003). Ten volunteers applied a solution made of 2% glycerin and 0.4% xantham gum and an emulsion of 4% cetearyl olivate, sorbitan olivate on different sites of the volar aspect of the forearm. As expected, the glycerin solution produced a rapid increase in the skin surface hydration (Figure 3).
This peak in skin hydration progressively disappeared reaching values significantly lower than cetearyl olivate, sorbitan olivate from 45 minutes up to 7 hours post-application. The cetearyl olivate, sorbitan olivate emulsion did not yield a transient peak in hydration but resulted in a more sustained, long-term, effect. This effect can be interpreted by a physiological penetration and integration of the skin-compatible liquid crystals formed by cetearyl olivate, sorbitan olivate thus improving the SC barrier integrity. The “barrier” effect of cetearyl olivate, sorbitan olivate is clearly different from the “humecting” characteristic of glycerin. In a concerted action, glycerin as a natural skin humectant and cetearyl olivate, sorbitan olivate as a natural SC barrier constituent may thus complement each other in fulfilling two important skin hydration mechanisms.
The efficacy of cetearyl olivate, sorbitan olivate was further clinically investigated for its functional hydration effect. Ten volunteers applied an emulsion made of cetearyl olivate, sorbitan olivate on one half of the face and ceteareth-20, cetearyl alcohol on the other half, twice daily, for a period of up to 45 days.
Skin hydration was increased by 24.7% and 27.3% after 15 days and 45 days, respectively (p=<0.05), on application of cetearyl olivate, sorbitan olivate (Figure 4). Non-significant effects of 2.2% (Day 15) and 4.5% (Day 45) were observed with the control ceteareth- 20, cetearyl alcohol. Parallel to that, the formulation containing 2.5% cetearyl olivate, sorbitan olivate increased by 40% the sensorial appreciation level as judged by subjects themselves. The results obtained in this trial are consistent with an increased SC barrier function on application of skincompatible liquid crystals formed by cetearyl olivate, sorbitan olivate leading to an improved, long-term, hydration.
Conclusion
Skin homeostasis largely relies on the integrity of the SC barrier that consists of keratinocytes embedded within a lipidrich matrix. Its integrity insures protection from environmental insults and prevents from excessive trans-epidermal water loss. Barrier function can be disturbed by external factors such as pollutants, harsh cleansers and ageing thereby affecting water evaporation rate, skin sensitivity level and cell functions. Ultimately, this may translate into skin dryness, skin irritation and lower physiological responses.
Skin-compatible liquid crystals that mimic both the skin surface lipid composition and the molecular organisation of the SC intercellular lipid lamellae have been generated. The cetearyl olivate, sorbitan olivate liquid crystals have the property to physiologically integrate into the skin lipid barrier. They act as biomimetic restructuring agents and restore the optimal integrity of the skin barrier function. Furthermore, their similarity with the skin surface lipid composition allows those liquid crystals to improve the sensorial appreciation when part of the formulation.
The dermatological compatibility of cetearyl olivate, sorbitan olivate makes it a key ingredient in formulating products that respect the chemical and structural homeostasis of the skin lipid barrier and is thus highly physiologically adequate.
References
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ABSTRACT
Skin homeostasis largely relies on the integrity of the surface barrier found in the stratum corneum (SC). This barrier is composed of keratinocytes embedded in a lipid-rich extracellular matrix and its integrity insures protection from environmental insults and prevents excessive transepidermal water loss.
At the same time, this barrier may impede the penetration of biologically active substances and the binding with their targets in deeper epidermal layers. On the other hand, penetration enhancers may disrupt the barrier integrity thereby weakening skin homeostasis. Ideally, a topical formulation would maintain optimal skin barrier homeostasis while promoting optimal delivery.
Olive oil exhibits a fatty acid composition physiologically close to what is found at the surface the skin. A series of olive oil-derived functional ingredients, that have the ability to increase the skin lipid barrier integrity, has been developed. One of these ingredients (INCI: cetearyl olivate, sorbitan olivate) has the ability to generate liquid crystal structures that mimic the SC extracellular lipid matrix tridimensional organisation. Liquid crystals having a “skin-like” fatty acid composition represent a unique double-characteristic: improving skin barrier integrity and promoting delivery through SC layers. Topical application of an emulsion made of cetearyl olivate, sorbitan olivate achieved a significant increase in skin hydration (corneometry) (27.3%) and reduced TEWL (¯29%) vs placebo. Presented is a biomimetic model describing how skin-compatible liquid crystals generated by cetearyl olivate, sorbitan olivate physiologically integrate into the upper layers of the SC and merge with the lamellar extracellular lipid matrix.
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