EPR (Electron Paramagnetic Resonance) as Method of Non-invasive Characterization of Melanin Content in Skins With Different Phototypes

Electron paramagnetic resonance (EPR), also known as electron spin resonance (ESR), is a spectrometric method enabling the observation of the absorption of energy by the free radicals contained by a sample immerged in a strong homogenous magnetic field. An EPR spectrum reveals only the presence of paramagnetic centers and can thus only be observed with samples containing lone unpaired electrons. In water-containing biological environments, most of free radicals are very reactive and have a very short life. To detect such species, a strategy is to use extrinsic molecules that will react with these species to form EPR measurable adducts. This technique is called "spin trapping". In contrast, the study of stable free radicals does not require the use of spin-trap agents. Melanins are part of the rare stable biological radicals directly observable with EPR. In practice, melanin is the only endogenous stable radical that can be detected using 1 GHz EPR.

The aim of the present study is to measure the EPR signal recorded from skin with different pigmentations. 45 healthy volunteers will be enrolled:

15 subjects with phototype 1-2, 15 subjects with phototypes 3-4, 15 subjects with phototypes 5-6. The parameters described hereafter will be investigated:

• g factor (resonance condition); expected g=2.005;
• shape of the signal, presence of a shoulder at g=2.01 due to pheomelanin;
• intensity of the signal (signal height, double integration, double integration relative to reference).

This will provide a database for other ongoing studies carried out in patients with suspicious lesion (nevi vs melanoma)