Lichen-derived compounds, lichesterinic and protolichesterinic, mediate pigmentation in B16 melanoma cells

Protection against melanoma, one of the most aggressive skin cancers is afforded in part by the tanning response in which UV irradiation triggers melanocytes to increase production of melanin [1,2]. The identification of new natural compounds that positively regulate the tanning response is important in overcoming the deleterious effect of solar exposure. Lichens provide a particularly attractive source for novel photo-protective compounds because they have developed protective tools to enable their survival in high UV-index regions [3,4]. In this study, using B16 melanoma cells we have identified two aliphatic lactones, lichesterinic and protolichesterinic acids, isolated from the lichen Cetraria islandica, as positive mediators of pigmentation. The cytotoxicity of both lichesterinic and protolichesterinic acids was determined using the MTT assay and a non-toxic dose of 5µM was utilized in all assays tested. A significant increase (p<0.05) in melanin content was observed for both compounds in the presence and absence of UVB irradiation compared to the control cells. Interestingly, the observed increased in melanin content in these cells did not correlate with an increase in tyrosinase activity. Taken together, these results implicate the lichen compounds, lichesterinic and protolichesterinic acids, as novel mediators of pigmentation and may also indicate a photo-protective role of these compounds in response to UV irradiation.

Acknowledgements: This work was supported by a postdoctoral grant (to Amaal Abrahams) from the University of Rennes 1.

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4. Boustie, J. and Grube, M. (2005) Plant Genetic Resources 3: 273–287.