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UVA-induced Carbon-Centered Radicals in Lightly Pigmented Cells detected using ESR Spectroscopy

Lookup NU author(s): Professor Mark Birch-MachinORCiD



This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND).


Ultraviolet-A and melanin are implicated in melanoma, but whether melanin in vivo screens or acts as a UVA photosensitiser is debated. Here, we investigate the effect of UVA-irradiation on non-pigmented, lightly and darkly pigmented melanocytes and melanoma cells using electron spin resonance (ESR) spectroscopy. Using the spin trap 5,5 Dimethyl-1-pyrroline N-oxide (DMPO), carbon adducts were detected in all cells. However, higher levels of carbon adducts were detected in lightly pigmented cells than in non-pigmented or darkly pigmented cells. Nevertheless, when melanin levels were artificially increased in lightly pigmented cells by incubation with L-Tyrosine, the levels of carbon adducts decreased significantly. Carbon adducts were also detected in UVA-irradiated melanin-free cell nuclei, DNA-melanin systems, and the nucleoside 2’-deoxyguanosine combined with melanin, whereas they were only weakly detected in irradiated synthetic melanin and not at all in irradiated 2’-deoxyguanosine. The similarity of these carbon adducts suggests they may be derived from nucleic acid– guanine – radicals. These observations suggest that melanin is not consistently a UVA screen against free-radical formation in pigmented cells, but may also act as a photosensitizer for the formation of nucleic acid radicals in addition to superoxide. The findings are important for our understanding of the mechanism of damage caused by the UVA component of sunlight in non-melanoma and melanoma cells, and hence the causes of skin cancer.

Publication metadata

Author(s): Kassouf N, Kay CWM, Volkov A, Chiang S-C, birch-Machin MA, El-Khamisy SFE, Haywod RM

Publication type: Article

Publication status: Published

Journal: Free Radical Biology and Medicine

Year: 2018

Volume: 126

Pages: 153-165

Print publication date: 01/10/2018

Online publication date: 25/07/2018

Acceptance date: 24/07/2018

Date deposited: 02/08/2018

ISSN (print): 0891-5849

ISSN (electronic): 1873-4596

Publisher: Elsevier


DOI: 10.1016/j.freeradbiomed.2018.07.019

PubMed id: 30055236


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