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In Reply: Drs Tsikas and Rossi question the validity of the S-nitrosoglutathione assay and the clinical relevance of S-nitrosoglutathione for the blood pressure reduction described in our article. Our study reported only data from methods that have been validated according to established medical, analytical, or regulatory guidelines. To facilitate assessment of data quality for the methods used to measure main outcomes—including the S-nitrosoglutathione concentrations—essential validation parameters were presented. Requiring preceding publication of the complete validation process before allowing publication of clinical data would hamper clinically relevant "real-world" research without improving quality and clarity of the studies.

Regarding use of an internal standard, isotope-labeled standards are preferred for the liquid chromatography tandem mass spectrometry quantification of stable analytes. However, S-nitrosoglutathione undergoes transnitrosylation reactions. Thus, the addition of labeled S-nitrosoglutathione (such as S-[¹⁵N]nitrosoglutathione)¹ to the plasma samples leads to a reequilibration of nitric oxide (NO) . . . [Full Text of this Article]

Dirk Taubert, MD, PhD
dirk.taubert@medizin.uni-koeln.de
Department of Pharmacology

Norma Jung, MD
Department of Internal Medicine

Renate Roesen, PhD
Department of Pharmacology
University Hospital of Cologne
Cologne, Germany

RELATED LETTER

Cocoa Intake and Blood Pressure
Dimitrios Tsikas and Ranieri Rossi
JAMA. 2007;298(16):1862-1863.
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