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Ranieri Rossi, Dimitrios Tsikas, S-Nitrosothiols in Blood: Does Photosensitivity Explain a 4-Order-of-Magnitude Concentration Range?, Clinical Chemistry, Volume 55, Issue 5, 1 May 2009, Pages 1036–1038, https://doi.org/10.1373/clinchem.2008.114462
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To the Editor:
S-nitrosothiols such as S-nitrosoglutathione (GSNO) are nitric oxide derivates with potent biological actions. There is disagreement regarding the blood concentrations of nitrosothiols, which are reported to range between nondetectable and approximately 10 000 nmol/L (1). Problems and pitfalls in the analysis of nitrosothiols have been attributed to their wide concentration range in biological samples (1). Many of these analytical problems arise from the chemical nature of S-nitrosothiols and are difficult to control, but other problems may be avoidable (1).
Wu and coworkers recently reported that the photoinstability of S-nitrosothiols during sampling of whole blood may be a likely source of error and variation in S-nitrosothiol measurement (2). In general, we think that the findings of this study (2) are incorrect and suffer from analytical and methodologic shortcomings, as are discussed below.
1. selectivity
Wu and coworkers assumed that their electrochemical method was selective for S-nitrosothiols and that any signal obtained was attributable to S-nitrosothiols (2). They reported that the ammonium/ammonia system may interfere with S-nitrosothiol analysis by this method (3) but did not report on a quantitative basis the potential contributions by NH3, NH2CH3, NH(CH3)2, and other volatile, labile, and readily oxidizable substances present in porcine blood. For instance, carbamino compounds are abundant in blood and spontaneously decompose to NH3 and CO2. Additionally, the authors did not report experiments that demonstrated the selectivity of this method for S-nitrosothiols [e.g., the use of HgCl2 (1)]. Given the potential nonselectivity of the method and the lack of additional experiments, we do not agree with the authors’ conclusion that “… the only plausible explanation … is the photodecomposition …” (2).
