Naringin is a natural polyphenol found in citrus fruits with a strong antioxidant activity and valuable biological actions making it a perfect candidate for a well aging strategy. However, due to its low water solubility, this molecule has been set aside from the cosmetic field.
To be able to take advantage of its beneficial activities, the Nagase group company Hayashibara glycosylated the naringin molecule to offer glucosyl naringin (GN), a natural and water soluble active.
GN has been shown to be effective in increasing elastin fiber compounds production as well as elastin fibers formation in monolayered fibroblasts.
Interestingly, this effect was then confirmed on a full thickness 3D skin equivalent. Indeed, using a unique model composed of an epidermis recovering a dermis obtained with fibroblasts seeded into a sponge made of collagen-glycosaminoglycans crosslinked with chitosan, GN enriched the dermal compartment. Thanks to this dynamic model allowing relevant investigations of dermal structure and composition, an increase in elastin and fibrillin-1 expression was observed. Thus, elastin expression appeared 42% higher when the samples were treated with GN (Figure 1). As well, fibrillin-1 expression increased by 44% compared to the untreated sample (Figure 2).
Figure 1: Elastin expression in skin equivalent samples treated or not with GN. Elastin appears in red and cell nucleus in blue.
Figure 2: Fibrillin-1 expression in skin equivalent treated or not with GN. Fibrillin-1 appears in green and cell nucleus in blue.
Biomechanical analysis using Atomic Force Microscopy showed that, as a result of dermal structure changes and elastin network improvement, the elastic modulus of the dermal compartment significantly increased (data not shown), supporting the firming effect of GN.
Consistent with these in vitro results, the topical application of a toner including GN on human volunteers of approximatively 49 y.o significantly enhanced skin firmness and elasticity after 8 weeks of treatment. Indeed, skin analysis using a cutometer revealed that (i) gross elasticity (parameter R2) significantly increased with GN application compared to day 0 and compared to placebo, while (ii) the portion of visco-elasticity on the elastic part of the curve (R6) significantly decreased compared to day 0 (Figure 3).
Figure 3: R2 and R6 parameters evolution after 8 weeks of topical application of a toner including GN or not, on human volunteers (age 49,2 ± 2,9 y.o) obtained with a cutometer MPA-580.
R2 is the recovery ratio of the skin length (or gross elasticity). The closer to 1 (100%) the more elastic is the skin. R6 is ratio of viscosity and elasticity part when elongated (or portion of visco-elasticity on the elastic part of the curve). The smaller the value the higher the elasticity. Source : Manual of Cutometer MPA-580.
To conclude, a combination of biomechanical analysis utilized on monolayered and 3D in vitro as well as on in vivo studies efficiently showed that GN helps developing the cutaneous elastin network leading to an enhancement of skin firmness and elasticity.
In this world where we want to feel good whatever our age and where social interactions are more important than ever, GN appears as a new solution to attenuate visible signs of aging and so, counteract their negative impact on self-esteem and social attractiveness.