Abstract
Deleterious effects of UV radiation in tissue are usually attributed to different mechanisms. Absorption of UVB radiation in cell constituents like DNA causes photochemical reactions. Absorption of UVA radiation in endogenous photosensitizers like vitamins generates singlet oxygen via photosensitized reactions. We investigated two further mechanisms that might be involved in UV mediated cell tissue damage. Firstly, UVB radiation and vitamins also generate singlet oxygen. Secondly, UVB radiation may change the chemical structure of vitamins that may change the role of such endogenous photosensitizers in UVA mediated mechanisms. Vitamins were irradiated in solution using monochromatic UVB (308 nm) or UVA (330, 355, or 370 nm) radiation. Singlet oxygen was directly detected and quantified by its luminescence at 1270 nm. All investigated molecules generated singlet oxygen with a quantum yield ranging from 0.007 (vitamin D3) to 0.64 (nicotinamide) independent of the excitation wavelength. Moreover, pre-irradiation of vitamins with UVB changed their absorption in the UVB and UVA spectral range. Subsequently, molecules such as vitamin E and vitamin K1, which normally exhibit no singlet oxygen generation in the UVA, now produce singlet oxygen when exposed to UVA at 355 nm. This interplay of different UV sources is inevitable when applying serial or parallel irradiation with UVA and UVB in experiments in vitro. These results should be of particular importance for parallel irradiation with UVA and UVB in vivo, e.g. when exposing the skin to solar radiation.
Highlights
Radiation of the ultraviolet spectral range is known to be hazardous to human health by inducing inflammation, cataract formation in the eye, premature skin aging and skin cancer.[1,2] In the US, skin cancer is the most frequent cancer showing an incidence of about 40 percent of all diagnosed human cancers.[3]
It is commonly accepted that UVB radiation is directly absorbed in cellular DNA, which typically leads to the formation of cyclobutane pyrimidine dimers (CPD) and pyrimidine(6-4)pyrimidone photoproducts (6-4PP).[7]
In case such a molecule can act as an endogenous photosensitizer, energy or charge transfer may occur from its triplet T1 state to other adjacent molecules yielding reactive oxygen species (ROS), in particular singlet oxygen (1O2).[8,9,10]
Summary
Radiation of the ultraviolet spectral range is known to be hazardous to human health by inducing inflammation, cataract formation in the eye, premature skin aging and skin cancer.[1,2] In the US, skin cancer is the most frequent cancer showing an incidence of about 40 percent of all diagnosed human cancers.[3]. It is commonly accepted that UVB radiation is directly absorbed in cellular DNA, which typically leads to the formation of cyclobutane pyrimidine dimers (CPD) and pyrimidine(6-4)pyrimidone photoproducts (6-4PP).[7] Since UVA is only poorly absorbed by DNA or proteins, other molecules in tissue may absorb that radiation In case such a molecule can act as an endogenous photosensitizer, energy or charge transfer may occur from its triplet T1 state to other adjacent molecules yielding reactive oxygen species (ROS), in particular singlet oxygen (1O2).[8,9,10] The deleterious biological effects of UVA radiation are mediated by these ROS; among them, 1O2 plays a major role.[11,12,13,14]. This in turn may lead to a change of the absorption coefficient of such molecules in the entire range of ultraviolet radiation and change the ability to generate 1O2.23 we pre-irradiated the vitamins with UVB and determined subsequently the quantum yield of 1O2 generation for UVA radiation
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