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Photoinstability of S-Nitrosothiols during Sampling of Whole Blood: A Likely Source of Error and Variability in S-Nitrosothiol Measurements

¹ Department of Chemistry, the University of Michigan, Ann Arbor, MI; ² Department of Internal Medicine, University of Cincinnati, Cincinnati, OH; ³ College of Pharmacy, University of Michigan, Ann Arbor, MI;

^aaddress correspondence to this author at: Department of Chemistry, the University of Michigan, Ann Arbor, MI 48109-1055. Fax 734-647-4865; e-mail: mmeyerho{at}umich.edu

Abstract

Background: The determination of reference intervals for the concentration of total S-nitrosothiols (RSNOs) in blood is a highly controversial topic, likely because of the inherent instability of these species. Most currently available techniques to quantify RSNOs in blood require considerable sample handling and multiple pretreatment steps during which light exposure is difficult to completely eliminate. We investigated the effect of brief light exposure on the stability of RSNO species in blood during the initial sampling process.

Methods: A novel amperometric RSNO sensor, based on an immobilized organoselenium catalyst at the distal tip of an electrochemical nitric oxide detector, was used to determine RSNO species in diluted whole blood without centrifugation or pretreatment. Porcine blood was collected into aluminum foil–wrapped syringes via a 12-inch butterfly needle tube assembly. Two blood samples were collected from the same animal—one with the butterfly needle tubing wrapped in aluminum foil and one with the tubing exposed to ambient room light. The RSNO concentrations in these sequential blood samples were determined by a standard addition procedure.

Results: Eight sets of measurements were made in 6 animals. Samples exposed to light yielded RSNO concentrations only 23.6% (7.2%) [mean (SD)] of the RSNO concentrations determined in samples that were shielded from light and obtained from the same animals.

Conclusions: These results suggest significant photoinstablity of RSNOs in whole blood and indicate the critical importance of proper light protection during sampling and processing of blood samples for the accurate determinations of endogenous RSNO concentrations.

The following articles in journals at HighWire Press have cited this article:

				D. T. Hess, M. W. Foster, and J. S. Stamler Assays for S-Nitrosothiols and S-Nitrosylated Proteins and Mechanistic Insights Into Cardioprotection Circulation, July 21, 2009; 120(3): 190 - 193. [Full Text] [PDF]

				R. Rossi and D. Tsikas S-Nitrosothiols in Blood: Does Photosensitivity Explain a 4-Order-of-Magnitude Concentration Range? Clin. Chem., May 1, 2009; 55(5): 1036 - 1038. [Full Text] [PDF]

				Y. Wu, W. Cha, F. Zhang, and M. E. Meyerhoff In Reply Clin. Chem., May 1, 2009; 55(5): 1038 - 1040. [Full Text] [PDF]