Fruit active affects pigment pathways for lighter skin

 In recent years, we have learnt a lot about melanocytes, enzymes and others factors impacting melanogenesis. Besides, we know that pigmentation variations depend on melanin type, melanosomes size (Table 1) and their damage stage. Melanocytes located in the epidermal basal layer are contained within melanosomes and produce melanin, a pigment that protects the epidermis against external damages such as UV rays. They possess dendritic extensions that enable contact with other cells: the keratinocytes. There are various ways melanosomes are diffused, carried out by keratinocyte phagocytosis. For light skins, they are destroyed in the malpighi layer whereas for darker skins, they are moved one by one into the corneous layer, the upper level of the epidermis. When exposed, UV rays reinforce melanogenesis by activating tyrosinase, the key enzyme of the process. This glycoprotein located in the melanosome membrane has histidin residues and is linked to copper ions necessary for its activity. Tyrosinase catalyses the first two steps of melanin production: the hydroxylation of L-tyrosine, amino-acid, to L-DOPA followed by the oxidation of o-diphenol to the dopaquinone. After this formation, the pathway is divided into eumelanin synthesis, a black-brownish insoluble polymer, and pheomelanin synthesis, a red-yellow soluble polymer. Dopaquinone, spontaneously converted into dopachrome, favours the eumelanin formation via TRP1 and TRP2, which are tyrosinase related proteins. Pheomelanin formation branches from the L-dopaquinone which reacts with high sulphur level components, cystein or glutathione, to create cysteinyl-dopa1 (Fig. 1). Known as the reference chemical agent for depigmentation, kojic acid is mainly used for in vitro studies and can be incorporated in some cosmetic formulas. It is of interest to compare with natural substances, more particularly extracted from fruits, for instance AHAs (alpha hydroxy acids). These substances have been used for years as moisturising, emollient and exfoliating agents (stimulation of cellular renewal). Thus, it is plausible that a lightening effect is accentuated by the exfoliation increase2 which is favoured by dendritic relocation of the melanin located in the epithelial cells. Indeed, some recent studies3 proved the interaction of some AHAs, in particular lactic and ascorbic acids, with cutaneous pigmentation. The aim of this article is to highlight the influence of a fruit active rich in vitamin C and lactic acid (Melan’oWhite) on the pigmentation pathway. Studies will show the significant lightening action on the skin for a bright, luminous and uniform complexion.

Melano-modulatory effect

In the first study, in vitro evaluation, we measured the melanin synthesis on confluent monolayers of normal human melanocytes. This one is quantified with a spectrophotometric method at 405 nm and is expressed in percentage of inhibition. To that end, melanocytes are incubated for a 72-hour period at 37°C with and without the fruit active directly solubilised in the culture medium and then lysed with NaOH 1N. Model is evaluated with a reference product, kojic acid, tested at 250 M and validated by the calculation of normal synthesis which corresponds to the difference before incubation (D0) and the result after 72 hours (control) without any product. Melanin obtained from the various fruit active concentrations is measured in the cellular lysates after 72 hours of incubation and is compared to the control (incubation without any product) and the reference product, kojic acid. A standard curve of melanin is realised and helps to evaluate the melanin content (expressed in micrograms per milligram of proteins). The results obtained are then written down in Table 2. Protein content, present in the same previous lysates, is determined by a spectrocolorimetric method using Coomassie Brillant Blue (Bradford assay). The percentage of melanin synthesis inhibition in the sample is then calculated according to the % control of treated cells at T+72h on the % control of non-treated cells (Fig. 2). Inhibition % = (control – Melan’oWhite at 0.025%)/(control – D0) Also, a study of the non-specific adsorption of the fruit active has been made with a different protocol. Melanocytes from a pellet are lysed with ultrasound before being incubated with and without the active ingredient. Then, the pellet is rinsed off with PBS and then lysed again with NaOH 1N soda. As was done previously, quantities are determined by a spectrophotometric method at 405 nm. The following results (Fig. 3) show that the lightening effect of mango is not impacted by an adsorption specific to the melanocytes.