CHAPTER 2: Quantifying Peroxynitrite: Bridging the Gap Between Chemistry, Biology and Immunology

Quantifying reactive nitrogen species (RNS) and reactive oxygen species (ROS) still remains a challenge even though there are a variety of detection principles available today. The quest for substantial cause–effect relationships is not trivial, especially in the context of biologically relevant samples: monitoring the complex reactions of RNS and ROS in biological matrices such as cell culture, body fluids, or tissue. Peroxynitrite (ONOO⁻), which is not a radical species, is a very interesting candidate as a signaling or immunological molecule because it acts in an oxidizing as well as nitrating manner. Furthermore, it can selectively react with other biological target molecules. The impact of peroxynitrite on biological systems strongly depends on the local microenvironment, the nature and status of the target as well as the local concentration, spatial and temporal distribution of ONOO⁻. To unambiguously differentiate between the influences of ONOO⁻, its precursors nitric oxide and superoxide, or the decomposition products of ONOO⁻ is very demanding. The lifetime of the molecule is of further importance and is not negligible with respect to sample preparation and storage procedures. The focus of this book chapter is: (a) to highlight the complex chemical nature of peroxynitrite for biologists and immunologists; (b) to explain the biological impact and complexity of peroxynitrite in biological matrices for chemists; and (c) to derive guiding principles for optimizing quantitative assays in a reasonable fashion.