title: Intensity-dependent direct solar radiation- and UVA-induced radical damage to human skin and DNA, lipids and proteins.
abstract: Skin can be exposed to high-intensity UV-radiation in hot countries and during sunbed use; however, the free-radical damage at these intensities is unknown. We used electron spin resonance spectroscopy to measure free-radical generation in ex vivo human skin/substitutes +/- the spin-trap 5,5 dimethyl-1-pyrroline N-oxide (DMPO) exposed to solar-irradiation equivalent to Mediterranean sunlight. Skin-substitutes, model DNA-photosensitizer systems, lipids and proteins were also irradiated with low-intensity UVA/visible light. Without DMPO a broad singlet was detected (using both irradiations) in skin/substitutes, nail-keratin, tendon-collagen, phospholipid and DNA+melanin or riboflavin. In addition to lipid-derived (tentatively tert-alkoxyl/acyl-) and protein radicals detected with DMPO at lower intensities, isotropic carbon-, additional oxygen- and hydrogen-adducts were detected in solar-irradiated skin/substitutes at higher intensities. Carbon-adducts were detected in UVA-irradiated human skin cells, DNA+melanin or riboflavin and soybean-phospholipid. Anisotropic protein-adducts, comparable to adducts in solar-irradiated tendon-collagen, were absent in UVA-irradiated skin fibroblasts suggesting the trapping of extracellular collagen radicals. Absence of hydrogen-adducts in fibroblasts implies formation in the extracellular compartment. We conclude damage at high intensities is part cellular (carbon- and oxygen-radicals) and part extracellular (protein- and hydrogen/H(+)+e(-) ), and skin substitutes are suitable for sunscreen testing. While UVA absorption and lipid-oxidation is direct, DNA and protein-oxidation require photosensitisation.
authors.affiliation: RAFT Institute, Mount Vernon Hospital, Northwood, Middlesex, UK. haywoodr@raft.ac.uk
authors.forename: Rachel
authors.initials: R
authors.lastname: Haywood
authors.forename: Carima
authors.initials: C
authors.lastname: Andrady
authors.forename: Nick
authors.initials: N
authors.lastname: Kassouf
authors.forename: Nick
authors.initials: N
authors.lastname: Sheppard
mesh_terms: D006801:Humans; D050356:Lipid Metabolism / Q000528:radiation effects*; D011506:Proteins / Q000378:metabolism / Q000528:radiation effects*; D012867:Skin / Q000378:metabolism / Q000528:radiation effects*; D013472:Sunlight
chemical_list: D011506:Proteins