Determination of S-nitrosothiols in biological and clinical samples using electron paramagnetic resonance spectrometry with spin trapping.

S-Nitroso moieties, such as the S-nitroso group within S-nitrosated albumin, constitute a potential endogenous reservoir of nitric oxide (NO.) in human tissues and other biological systems. Moreover, S-nitroso compounds are under investigation as therapeutic agents in humans. Therefore, it is important to be able to detect S-nitrosothiols (RSNOs) in human extracellular fluids, such as plasma and synovial fluid, as well as other biological samples. This chapter describes a method for the determination of S-nitrosothiols in biofluids. The method is based on electron paramagnetic resonance (EPR) spectrometry, in combination with spin trapping using a ferrous ion complex of the iron chelator N-methyl-d-glucamine dithiocarbamate under alkaline conditions. This iron complex mediates the decomposition of RSNO to NO., as well as spin trapping the generated NO.. The resulting spin adduct has a unique EPR signal that can be quantified.