Human skin pigmentation is caused by the synthesis of melanin (a natural pigment) and by its distribution in skin and in hair follicles. Melanin synthesis, also called melanogenesis, is an enzymatic process that is catalyzed mainly by tyrosinase, tyrosinase-related protein 1 (TYRP1) and dopachrome tautomerase (DCT). These enzymes allow the biotransformation of tyrosine into melanin within melanocytes, and more particularly in melanosomes, which are lysosomal vesicles.
Mature melanosomes containing melanin are transported via a microtubule network to the melanocyte dendritic extremities, in order to be transferred to keratinocytes and thereby provide skin pigmentation and photoprotection.
Melanin plays an essential role in skin tone evenness, in hair pigmentation and in photoprotection against UV-induced DNA damage. Melanin production can be altered by some internal factors (inflammatory or hormonal reactions) or by external factors (sun exposure). This altered melanin production can cause pigmentation damage (hair greying, vitiligo, etc.) or hyperpigmentation marks (age spots, melasma, acne lesions, etc.), which require skin care treatment.
A panel of complementary assays can evaluate the depigmenting effects (whitening/lightening/anti-spots) or pro-pigmenting effects of an active ingredient or cosmetic compound.
Skin pigmentation: in vitro models and assays
Bioalternatives has many in vitro or ex vivo models at your disposal:
- melanocyte cell lines (B16, etc.)
- normal human epidermal melanocytes (NHEM)
- co-culture of normal human epidermal keratinocytes and melanocytes (NHEK/NHEM)
- melanocyte-containing reconstructed epidermis (RHEm)
- skin explants (ex vivo)
- hair follicle (ex vivo)
on which we can evaluate the whitening or pro-pigmenting effect of active cosmetic compounds or formulations by measuring:
- the expression of specific markers of melanogenesis: TYR, TRP-1, Pmel17, MITF, etc.
- tyrosinase activity and expression
- melanin synthesis
- melanocyte dendricity
- melanosome transfer
Here are a few examples among all assays proposed by Bioalternatives in the field of skin pigmentation: