Using EPR to measure a critical but often unmeasured component of oxidative damage: oxygen.

Oxygen is a critical variable in oxidative damage. It can be a direct reactant in one or more of the pertinent reactions that result in oxidative damage. It also is an essential substrate for mitochondrial respiration and many other essential synthetic and degradative reactions. The level of oxygen can have a regulatory role, affecting the rate and direction of metabolic processes and physiological functions that are germane to the pathophysiological processes that are being studied. Its supply to tissue and to cells is therefore a critical parameter governing normal homeostasis. The level of oxygen at specific sites may affect cell signaling. It therefore seems clear that it can be very useful to measure oxygen when studying oxidative damage. In order for the measurements of oxygen to be most useful, it often is essential to measure the amount of oxygen at particular sites and under appropriate conditions. These needs require methodology that can make sensitive and localized measurements of oxygen. Electron paramagnetic resonance (EPR) oximetry is such a technique, plus it has the capability of making repeated measurements from the same site non-invasively. The principles and applications of EPR oximetry to viable systems, including cell suspensions and intact animals, are described in this paper.