Measurement of S-nitrosothiols in extracellular fluids from healthy human volunteers and rheumatoid arthritis patients, using electron paramagnetic resonance spectrometry

In human tissues, S-nitrosothiols (RSNOs) are generated by the nitric oxide (NOcenter dot)-dependent S-nitrosation of thiol-containing species. Here, a novel electron paramagnetic resonance spectrometry assay for RSNOs is described, together with its application to studies of human health and disease. The assay involves degrading RSNOs using N-methyl-D-glucamine dithiocarbamate (MGD) at high pH and spin trapping the NOcenter dot released using (MGD)(2)-Fe2+. Because dietary nitrate might contribute to tissue RSNOs, the assay was used to monitor the effect of (NaNO3)-N-15 ingestion on plasma and gastric juice RSNOs in healthy human volunteers. (NaNO3)-N-15 ingestion (2 mmol) increased gastric (RSNO)-N-15 concentrations (p < 0.01), but there was no significant effect on plasma (RSNO)-N-15 concentrations. Having established that dietary nitrate was not a confounding factor, we applied the RSNO assay to matched plasma and knee-joint synovial fluid (SF) from rheumatoid arthritis (RA) patients, with healthy subjects as controls. Clinical markers of RA inflammatory disease activity were quantified, as were plasma and SF NO2- and NO3-. Median RSNO concentrations were 0 (interquartile range 68) nM, 109 (282) nM, and 309 (470) nM in normal plasma, RA plasma, and SF, respectively. The median RSNO concentration was significantly elevated in RA SF compared with RA plasma (p < 0.05) and in RA plasma compared with normal plasma (p < 0.05). SF RSNO concentrations correlated positively with SF neutrophil counts (r(s) = 0.55,p < 0.05) and inversely with blood hemoglobin concentrations (r(s) = -0.52, p < 0.05), but not with NO2- orNO(3)(-). Thus the raised levels of RSNOs in RA SF correlate with some established markers of inflammation, suggesting the described RSNO assay may have applications in rapid clinical monitoring of NO metabolism in human inflammatory conditions. (c) 2005 Elsevier Inc. All rights reserved.