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.

The physical and chemical properties of eumelanin

“…In addition, skin susceptibility to so-called photoaging may inversely correlate with pigmentation of the skin (Wlaschek et al, 2001). In cultured melanocytes, melanin was shown to offer protection against induction of major DNA lesions by UVB (Barker et al, 1995;Smit et al, 2001) and UVAinduced membrane damage (Kwam and Dahle, 2003). A significant inverse correlation between baseline skin pigmentation and the extent of UV-induced DNA damage was also reported by an independent study (Tadokoro et al, 2003).…”

Domain swapping between FEN-1 and XPG defines regions in XPG that mediate nucleotide excision repair activity and substrate specificity

“…XPG, FEN-1-XPG or FEN-1 transductants were exposed to a UV dose of 20 J/m 2 , and genomic DNA was isolated at various times thereafter. The DNA samples were then probed with monoclonal antibodies against the 6-4PPs (43,44). The disappearance of the signals for 6-4PPs over time indicates proper removal of these lesions by NER.…”

Photoprotection versus photodamage: updating an old but still unsolved controversy about melanin

“…Melanocytes from light‐skinned individuals containing mostly pheomelanin produced around twice as many CPDs upon UV exposure than did melanocytes from black skin. Moreover, the quantity and quality of melanin revealed that eumelanin concentration correlated better with DNA protection than pheomelanin . Skin type I to type VI melanocyte cells were irradiated with UVB, and the levels of the photoproducts were determined immediately and after 6 and 24 h. The induction of the photoproducts was inversely correlated with the skin type as it was mitigated by increased eumelanogenesis.…”