The measurement of oxygen-derived free radicals and related substances in medicine

Due to the high reactivity of the chemical species and the presence of multiple potentially interfering substances, the measurement of oxygen-derived free radicals in biological material requires highly developed techniques. The currently employed methods are reviewed according to the reactions upon which they are based, the assays, possible interferences and their use in medical research. Detection of the emission of light is a very popular method. Although it is in principle unspecific, there are modifications to measure individual radical species. The only direct way to detect radicals is electron spin resonance spectroscopy. Among the specific assays for O2- the reductions of nitroblue tetrazolium or cytochrome c are predominant. For the detection of H2O2 different techniques are employed for either intracellular or extracellular determination. An array of substances has been used for the measurement of OH. Which of them is the most useful depends on the question to be answered. There are also indirect methods that determine free radicals based on chemical modifications caused by them; the most important assays of this kind quantify lipid peroxides. In addition, assays for thiobarbituric acid-reactive substances and DNA strand breaks and interstrand crosslinks are used.