B159
Direct mechanisms of UVA- and solar radiation-induced protein, lipid and DNA oxidation relevant to human skin photodamage
Rachel Haywood, Carima Andrady
RAFT Institute, Middlesex, UK
Ultraviolet-A (UVA) exposure is a public health issue, with the continued popularity of sunscreens, which protect against UVB-induced erythema but provide inadequate UVA and visible light protection. We have shown that ESR/spin trapping can be used to detect lipid and protein radicals in UVA-irradiated human Caucasian skin (which were lower in Afro-Caribbean skin). In highly pigmented skin, however, radicals with characteristics of stable DNA radicals could be present (also detected in DNA-melanin systems) [1]. Here we investigated the UVA/visible- and broad spectral irradiation of human skin, skin substitutes, proteins (and component amino-acids), fats, oils and DNA-melanin systems in the presence of the spin trap DMPO. Radical-damage to Caucasian skin was identified as previously, and to a higher intensity (6 mW/cm2) where damage was observed almost immediately in non-pigmented skin, whilst pigmented skin remained mostly protected. Protein radicals, comparable to radicals detected in skin and skin substitutes, were detected in bovine serum albumin (664 mg/ml) exposed to UVA/visible light; and in gelatine and elastin exposed to solar-irradiation. Sunflower oil and lard absorbed UVA radiation (≈320 – 380 nm) and were photoreactive. UVA/visible irradiation of human DNA +/- melanin demonstrated melanin photocatalysis of DNA oxidation, with oxygen acting as an electron acceptor (confirmed by the detection of superoxide radical-adducts in the presence of melanin which were abolished by superoxide-dismutase). These preliminary findings support direct mechanisms of lipid, protein and DNA (in the presence of melanin) oxidation by UVA irradiation. This is new evidence to support the need for effective UVA protection by sunscreens.
References
[1] Haywood R., F. Rogge and M. Lee (2008). Protein, lipid and DNA radicals to measure skin UVA damage and modulation by melanin. Free Radical Biology and Medicine 44, 990-1000.
