In vivo EPR imaging of the distribution and metabolism of nitroxide radicals in human skin

While altered cellular free radical and redox metabolism are critical facto rs in many human diseases, it has not been previously possible to both meas ure and image these processes in humans. The development and application of electron paramagnetic resonance instrumentation capable of in vivo spectro scopy and imaging of free radicals in human skin are reported. The instrume ntation uses a specially designed topical resonator and a 2.2-GHz microwave bridge. Noninvasive measurements of the distribution and metabolism of the topically applied nitroxide, N-15-perdeuterated tempone (100 mM), in forea rm skin were performed. A single broad peak due to the concentrated label a t the skin surface was initially observed, followed by a sharp doublet from the diluted label that permeated the skin. The penetration of the label in to the skin and its metabolic clearance were modeled using kinetic equation s. It was observed that the penetration process from the skin surface into the dermis and subcutaneous regions, as well as its clearance from these re gions, could be described by single exponential functions, Phantom imaging experiments using the nitroxide showed that a spatial resolution of up to 5 0 mum could be achieved. The skin imaging measurements showed two bands in the distribution of the label along the skin depth. The first band appeared in the outer 400 mum of the skin, the epidermis region, whereas the second band was centered at a depth of 1000 mum in the subcutaneous region with a thickness about 400 mum. These two bands decayed and merged into a single band with time. The results are important in the understanding of the perme ability and metabolism of free radicals in human skin. (C) 2001 Academic Pr ess.