Melanin Offers Protection Against Induction of Cyclobutane Pyrimidine Dimers and 6-4 Photoproducts by UVB in Cultured Human Melanocytes¶

Abstract

The goal of this investigation was to correlate the melanin content in human pigmentary cells with the generation of UVB‐induced photoproducts and to examine the relationship between the melanin content and the removal of the photoproducts. Cultured melanocytes from light‐skinned individuals synthesized less melanin and produced more cyclobutane pyrimidine dimers and 6–4 photoproducts upon UVB exposure than did melanocytes from black skin. Tyrosine‐stimulated melanogenesis provided protection against DNA damage in both cell types. In another set of pigmented cell lines a ratio between eumelanin and pheomelanin was determined. The assessment of association between DNA damage induction and the quantity and quality of melanin revealed that eumelanin concentration correlated better with DNA protection than pheomelanin. Skin type–I and skin type–VI melanocytes, congenital nevus (CN)‐derived cells and skin type–II melanocytes from a multiple‐melanoma patient were grown in media with low or high l‐tyrosine concentration. The cells were irradiated with 200 J/m2 UVB, and the levels of the photoproducts were determined immediately and after 6 and 24 h. Once again the induction of the photoproducts was mitigated by increased melanogenesis, and it was inversely correlated with the skin type. No significant differences were found for the removal of photoproducts in the cultures of skin types I and VI and CN cells. No indications of a delay in the removal of photoproducts in the melanocytes from the multiple‐melanoma patient were found either.

Effect of Intense Pulsed-Light Exposure on Lipid Peroxides and Thymine Dimers in Human Skin In Vivo

“…then thymine dimers were detected in 100 ng of DNA by immunoslot blots using the aforementioned antibody, as described by Smit et al 6 The quantitation of immunoslot blots was performed with a densitometer and the software ImageQuant from Molecular Dynamics (Redwood City, Calif).…”

Photoprotection of bacterial‐derived melanin against ultraviolet A–induced cell death and its potential application as an active sunscreen

“…Most melanins appear to be mixed polymers based on indoles but contain variable amounts of other preindole products of the synthetic pathway 14 . Many studies have demonstrated that melanin plays a role as a photoprotector against radiation in organisms and cells, especially in the UV region of the spectrum 15,16 . Melanin is thought to filter out UV radiation and scavenge reactive oxygen species (ROS), thereby reducing UV damage in vivo 17 .…”

Inhibition of melanogenesis as a radiation sensitizer for melanoma therapy

“…10,11 The major role of cutaneous melanin is protection against the harmful actions of solar radiation, by acting as a filter against ultraviolet radiation (UVR), preventing its penetration and genotoxicity (formation of UV-induced DNA dimmers). [11][12][13][14][15][16] Melanin also neutralizes reactive oxygen species (ROS) generated mostly by UVA, through its antioxidative and free-radical scavenging actions. 13,16,17 Overall, melanin protects against epidermal carcinogenesis or melanomagenesis.…”