EPR Spectroscopy as a Method for ROS Quantification in the Skin

Wavelength, dose, skin type and skin model related radical formation in skin

“…The use of, e.g., nitroxide spin probes allows statements about the formation of radicals (Haag et al 2010 ; Lohan et al 2016 ; Lohan et al 2021a, b , c ) or the endogenous redox state (Lauer et al 2013 ; Lohan et al 2020 ). In general, nitroxides are paramagnetic species with a free, unpaired electron in the outer shell of the oxygen atom.…”

“…With the EPR technology, semi-quantitative (Lohan et al 2021a, b , c ) but also quantitative measurements of free radicals in the skin (Albrecht et al 2019a , b ) can be made. Therefore, the quantitative EPR measurements have to be calibrated with an alanine standard with a defined spin number (2.01 × 10 17 spins) (Albrecht et al 2019a , b ; Lohan et al 2021a, b , c ). The accuracy of this quantification method is guaranteed by using a PCA solution with known concentration.…”

“…Spin traps can be used to determine the types of radicals. For example, the spin trap DMPO (5,5-dimethyl-1-pyrroline-N-oxide) can be used to differentiate between reactive oxygen species (ROS) and lipid oxygen species (LOS) in the skin (Albrecht et al 2019a , b ; Lohan et al 2021a, b , c ; Lohan et al 2021a, b , c ) (Fig. 1 ).…”

“…The adducts formed, however, often only have a short half-life of seconds to a few minutes, depending on the spin trap, and are unstable and break down into further adducts (Bacic et al 2008 ). In order to be able to detect the adducts of interest, optimized EPR settings with high sensitivity and an in situ stress application are required (Lohan et al 2021a, b , c ). Spin traps are currently only very rarely used in vivo, due to their instability in living tissue and their toxicity potential (Berliner et al 2001 ; Khan et al 2003 ).…”

“…3 Characterization of radicals. A Relative radical concentration *OH/*CCR in % for RHS, human and porcine ( n = 3 each), measured with DMPO (dose 0.53–1.0 MED (right) using an irradiance of 49 mW/cm 2 (UVB-NIR), 0.24 mW/cm 2 (UVB), 2.4 mW/cm 2 (UVA)(Albrecht et al 2019a , b ); B percentage of radical species and progression of reactive oxygen (ROS) and lipid oxygen species (LOS) after irradiation of unstressed and stressed porcine skin ( n = 10) with UVA (365 nm, 244 mW/cm 2 ) (Lohan et al 2021a, b , c ). Mean value ± s tandard error of mean, *** p ≤ 0.001 …”