[28] In vivo measurement of oxidative stress status in human skin

The chapter describes an electron paramagnetic resonance- (EPR) based assay to evaluate the oxidative stress status in human skin before and after exposure to solar-simulated light. For EPR in vivo measurements in human skin, two different experimental approaches have been used. The microwave penetration depth in the X-band region is about 0.5–1.0 mm in human skin and about 5 mm for S-band frequency. Thus, the X band is restricted to the upper layer of the skin (the human epidermis), whereas the S band is suited for deeper layers (the human dermis and subcutis). At the S band, the probe head is a 90° bent surface coil with an electronically matched system. Ultraviolet radiation is well known to cause oxidative stress that decreases the antioxidant capacity and the radical-scavenging activity of skin. Uncharged piperidine-type nitroxides are used preferentially, because of their redox properties, to measure tissue antioxidant activity. They possess the right reduction potential, polarity, and permeability through the wall of membranes and the horny layer of the skin. The chapter mentions the successful imaging of the distribution and metabolism of nitroxides in human skin in vivo. The chapter concludes by stating that this technique and application hold great promise in the study of cutaneous redox state, skin diseases, and development of topical pharmaceutical and cosmetic products.