Lightening and Illuminating Skin With Acetylated Hydroxystilbenes From Rheum rhaponticum

Sep 1, 2011 | Contact Author | By: Giorgio Dell’Acqua, PhD, and Christian Wagner, Induchem AG
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Title: Lightening and Illuminating Skin With Acetylated Hydroxystilbenes From Rheum rhaponticum
melanogenesisx pigmentationx melaninx stilbenesx brighteningx
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Keywords: melanogenesis | pigmentation | melanin | stilbenes | brightening

Abstract: Skin discoloration and excessive pigmentation due to increased melanin production is associated with skin inflammation and aging. Therefore, an extract rich in acetylated hydroxystilbenes from Rheum rhaponticum was combined with panthenyl triacetate to test in the melanogenesis pathway. The complex strongly reduced melanogenesis and melanin accumulation in human skin explants, decreased melanin content in pigmented spots, increased skin brightness and enhanced skin radiance on the face of human volunteers in a double-blind clinical study.

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G Dell'Acqua and C Wagner, Lightening and Illuminating Skin With Acetylated Hydroxystilbenes From Rheum rhaponticum, Cosm & Toil 126(9) 634 (2011)

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Increased melanin pigmentation is a physiological mechanism that the skin adopts to protect itself from the damaging effect of sustained and prolonged UV light exposure. Melanin pigment, produced by melanocyte cells in the basal layers of the epidermis, is transferred to the keratinocytes in the epidermis and sits on the top of the keratinocyte’s nucleus to protect the cell’s DNA. However, in some conditions (i.e., inflammation or a hormonal imbalance) and with increasing age, the deposition of melanin in the epidermis increases. This is particularly evident in extreme cases such as melasma, where patchy melanin formation on skin is observed.1 Skin inflammation and sustained damage can also be a fundamental trigger for excessive pigmentation,2, 3 with clinical relevance in the case of post inflammatory pigmentation.4 Other examples of increased pigmentation due to skin irritation and/or inflammation are documented in women developing axillary melanin spots due to hair removal irritation5 or in individuals suffering from acne.6

Those experiencing skin pigmentation as a result of inflammation or irritation are often associated with phototypes III–IV on the Fitzpatrick Scale. In order to even skin tone, decrease skin pigmentation and reduce the formation of dark spots, a series of lightening and depigmenting agents have been developed over the years targeting different steps of the melanogenesis process.7, 8 Among the agents most utilized for this purpose are: hydroquinone, kojic acid, arbutin, vitamin C, etc. However, many of these agents have been questioned for their safety7, 9 and have been restricted for their use in many countries. Therefore novel skin lighteners and depigmenting agents with a proven efficacy and safety profile remain a prominent need in personal care.

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Table 1. Semiquantitative analysis by score for pigmentation steps in irradiated human skin explants after six days (+++) highest (-) lowest

Table 1. Semiquantitative analysis by score for pigmentation steps in irradiated human skin explants after six days (+++) highest (-) lowest

Treatments were every other day for six days with a 2 mg/cm2 cream formulated with or without 1% R. rhaponticum complex, as shown in Table 1.

Table 2. R. rhaponticum complex and placebo cream formulations

Table 2. <em>R. rhaponticum</em> complex and placebo cream formulations

Based on these images, treatment differences were evaluated with microscopic observations followed by a score (see experimental methods). Results are summarized in Table 2.

Figure 1. The effect of acetylation of R. rhaponticum on melanogenisis

Figure 1. The effect of acetylation of <em>R. rhaponticum</em> on melanogenisis

Incubation of 50 μg/ml R. rhaponticum hydroxystilbenes extract with NDP-MSHinduced B16 melanocytes produced a clear inhibition of melanin synthesis (both intracellular and secreted) as shown in Figure 1.

Figure 2. Effect of R. rhaponticum complex., kojic acid or placebo on melanin content in basal layer keratinoctyes

Figure 2. Effect of <em>R. rhaponticum</em> complex., kojic acid or placebo on melanin content in basal layer keratinoctyes

In Figure 2, histology cuts with the different treatments are shown.

Figure 3. Effect of R. rhaponticum complex., kojic acid or placebo on melanin content in basal layer keratinoctyes

Figure 3. Effect of <em>R. rhaponticum</em> complex., kojic acid or placebo on melanin content in basal layer keratinoctyes

When image analysis for % melanin in keratinocytes’ basal layer was concluded, the different treatments were proven to inhibit melanin accumulation, as shown in Figure 3.

Figure 4. Melanin content in skin pigmented spots after treatment with R. rhaponticum complex

Figure 4. Melanin content in skin pigmented spots after treatment with <em>R. rhaponticum</em> complex

A panel was run to test the activity of a cream with or without the R. rhaponticum complex by daily measuring melanin index in pigmented spots (Figure 4), skin brightness (Figure 5) and skin radiance (Figure 6) daily.

Figure 5. Skin brightness (L*) with R. rhaponticum complex treatment

Figure 5. Skin brightness (L*) with <em>R. rhaponticum</em> complex treatment

A panel was run to test the activity of a cream with or without the R. rhaponticum complex by daily measuring melanin index in pigmented spots (Figure 4), skin brightness (Figure 5) and skin radiance (Figure 6) daily.

Figure 6. Skin radiance after treatment with R. rhaponticum

Figure 6. Skin radiance after treatment with <em>R. rhaponticum</em>

A panel was run to test the activity of a cream with or without the R. rhaponticum complex by daily measuring melanin index in pigmented spots (Figure 4), skin brightness (Figure 5) and skin radiance (Figure 6) daily.

Melanin Index

The measurement of the melanin index is based on the absorption principle. A special probe emits light of three defined wavelengths, and a receiver measures the light reflected by the skin. For the melanin index measurement, two different wavelengths are used, corresponding to the melanin absorption peaks. The instrument then calculates the melanin index on the basis of the absorption data.

Footnotes (CT1109 Dell'Acqua)

a Unilucent PA-13 (INCI: Panthenyl Triacetate (and) Acetyl Rheum Rhaponticum Root Extract) is a product of Induchem, Zürich, Switzerland.
b RMX-3W is a radiometer manufactured by Vilbert Lourmat, Marne-la-Vallée Cedex, France.
c The Orthoplan 25x is a microscope that was once manufactured by Ernst Leitz GmbH, now Leica Microsystems AG, Wetzlar, Germany.
d DXC-390P is a camera manufactured by Sony, Tokyo.
e QWin-Pro V2.4 Imagin Solution is a software manufactured by Leica Microsystems AG, Wetzlar, Germany.
f Mexameter MX 18 is a probe manufactured by Courage + Khazaka electronic GmbH, Köln, Germany.
g CM-700d is a spectrophotometer manufactured by Konica Minolta, Tokyo.

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