In vitro testing of skin whitening agents
Biologically active substances with scientifically proven efficacy are already among the stars of the market for skin care ingredients. A particularity of the Asian skincare markets is the leading role of face-whitening products – up to 80% of Asian consumers consider skin whitening to be the most important property of skincare cosmetics. In recent decades whitening properties are becoming important also in Europe and North America. Skin whitening products are used not only to overall lighten skin tone, but also to reduce hyperpigmentation caused by skin ageing.
Traditional depigmenting agents, such as hydroquinone, corticosteroids, and kojic acid, although effective, raise several safety concerns. Adverse effects associated with the use of traditional skin whitening agents include skin irritation, contact dermatitis, leukoderma. As awareness of negative side effects of widely used skin whitening agents raise, more attention is being paid to safe and natural sources of active substances. Ban to use several active substances in cosmetics (e.g. hydroquinone, tretionin are considered illegal according to current European cosmetic legislation) further promotes studies of safety and efficacy of natural skin whitening agents.
Skin color is one of the most conspicuous ways in which humans vary and has been used to define human races. Pigment melanin accounts for most of the variation in the visual appearance of human skin. Pigmentation is related to the metabolic activity of a lineage of cells known as melanocytes. These cells are located in the basal layer of epidermis and epidermal appendages, i.e. sebaceous glands and hair follicles. Melanocytes extend dendrites from the cell body and create contact with the surrounding keratinocytes. This close anatomical relationship between these two cell types is called the “epidermal melanin unit”. Melanocytes produce the pigment melanin and transfer it via their dendritic processes to keratinocytes. Melanin synthesis takes place in the melanosome, a highly specialised organelle which is unique to pigment cells. Melanin production in is a process involving a series of enzymatic and biochemical events, with tyrosinase being the key enzyme responsible for melanogenesis (see ref. 1-2).
Evaluation of skin whitening properties of active substances
Their main mechanism of action of skin whitening active substances is inhibition of enzymes essential for melanin formation. Activity of tyrosinase is a target for the majority of ingredients developed for skin pigmentation altering cosmetic formulations. Other modes of action include inhibition of melanosome transfer form melanocytes to keratinocytes, inhibition of melanocyte proliferation.
To evaluate the skin whitening efficacy of active substances InCell offers the following tests:
- Tyrosinase inhibition assay
- Assessment of melanocyte proliferation and migration
- Evaluation of pigment granule trasfert from melanocytes to keratinocytes
- Expression analysis of genes related to melanogenesis (TYR, TRP-1, TR-2, PMEL, MART etc)
- Analysis of pigmentation modulation in 3D skin tissue models
1. Screening of plant extracts for human tyrosinase inhibiting effects Kim M et al. International Journal of Cosmetic Science, 2012
2. Melanocyte biology and skin pigmentation. Lin JY et al. Nature, 2007