What is tanning?

Tanning can be observed after stimulation of melanin production in the skin. It can also be stimulated in vitro. Epidermal skin equivalents including melanocytes can be cultured for a few weeks at airlift culture and provide sufficient time to study skin differentiation, pigmentation or de-pigmentation.

How is tanning induced in skin models?

Spontaneous pigmentation of in vitro skin models is visible during tissue culture (see epiCS-M characterisation section). Pigmentation can be induced by different means.

In most cases stimulation of melanin production (i.e., tanning) is done using α-MSH (Melanin Stimulating Hormone) to study the tanning potential of the model. Generally 7 to 14 days of α-MSH exposure is sufficient to obtain these effects (Fig. 1). Alternatively, incubation with IBMX (3-Isobutyl-1-Methyl-Xanthine) or UV light (30 to 45 mJ/cm 2) stimulates melanin production (Fig. 2, Fig. 3).

How can melanin production be quantified?

The most common method to quantify the melanin content of the models is solvent extraction (e.g., 60 min, 100°C). Commercially available melanin can be used to generate a standard curve. The optical density can be determined at 492 nm wavelength to calculate the melanin content of single epiCS-M tissues (bar graphs of melanin measurements using this method are shown below). Alternatively, the melanin content can be quantified by digital image analysis of tissue slices stained with Fontana-Masson (an example is shown in the lightening section).

Examples of tanning experiments using chemicals or UV light:

Fig. 1 α-MSH: 10 nM systemically applied

Fig. 2 IBMX: 50 µM systemically applied for 14 days

Fig. 3 UV light: Repeated exposure for 12 days