Original Contribution Serial measurements of whole blood nitrite in an intensive care setting Eva S. Kehmeier a , Martina Kropp a , Petra Kleinbongard a , Thomas Lauer a , Jan Balzer a , Marc W. Merx a , Gerd Heusch b , Malte Kelm a , Wolfgang Lepper a , Tienush Rassaf a, ⁎ a University Hospital Aachen, Department of Medicine, Division of Cardiology, Pulmonary Diseases, and Vascular Medicine, D-52074 Aachen, Germany b Institute of Pathophysiology, Center of Internal Medicine, University of Essen Medical School, 45122 Essen, Germany article info abstract Article history: Received 13 January 2008 Revised 22 February 2008 Accepted 23 February 2008 Available online 18 March 2008 Nitrite plays an eminent role in cardiovascular physiology and pathology, mediating hypoxic vasodilation, reducing ischemia–reperfusion injury, and regulating cardiac energetics and function. The role of circulating nitrite in critically ill patients has not been examined so far. To investigate whether whole blood nitrite can be determined reproducibly in an intensive care setting, 30 patients from a cardiology intensive care unit were enrolled in this study, no matter what the underlying disease. Blood was drawn from an arterial catheter and whole blood nitrite was determined, using a tri-iodide/ozone-based chemiluminescence assay after incubation with a ferricyanide-containing stabilization solution. Whole blood nitrite levels ranged from 35 to 1193 nmol/L (mean ± SEM: 220 ± 20 nmol/L). Myocardial infarction was associated with lower whole blood nitrite levels (200 ± 53 nmol/L for elevated serum CK MB levels vs 432 ± 95 nmol/L in the normal CK MB range, p = 0.039). Neither impaired kidney function nor an inflammatory state was associated with higher or lower whole blood nitrite levels. In conclusion, whole blood nitrite can be measured easily and reproducibly in critically ill patients, regardless of renal function and inflammation. The origin of decreased nitrite levels in myocardial infarction is currently unclear and needs to be further elucidated. © 2008 Elsevier Inc. All rights reserved. Keywords: Nitrite Nitric oxide Ischemia–reperfusion Free radicals Introduction The generation of nitric oxide (NO) by both endothelial and in- ducible NO synthase in the cardiovascular system is well appreciated [1]. Over the past years, accumulating data have suggested that nitrite represents a large bioactive storage reservoir of NO in blood and tissue [2,3]. Under hypoxic conditions, nitrite may be reduced to NO via reactions with hemoglobin [2], myoglobin [4], and xanthine oxidoreductase [5] and by acidic reduction [6]. Beyond its function in storage and intravascular NO transport, nitrite has also been shown to regulate cardiac energetics and function [4] and to exert cytopro- tective effects in experimental ischemia–reperfusion (I/R) models [5,7–12]. In an intensive care setting, in which diseases with critical de- creases in blood flow with regional or general hypoxia and acidosis are commonly found (e.g., myocardial infarction, shock syndromes with multiorgan dysfunction), the role of circulating nitrite has not been studied so far. One reason for this is the lack of a reliable and simple method combined with simple sample preparation proce- dures that can be utilized in the clinical setting to examine nitrite homeostasis. Measuring whole blood nitrite has been shown to be reliable in assessing nitrite homeostasis in healthy subjects [13]. Patients with lower nitrite levels may be more prone to myocardial infarction. Vice versa, myocardial infarction may result in endothelial dysfunction, which may lead to disturbances in endothelium-derived nitric oxide and thus nitrite levels. In the present study we therefore investigated the impact of myo- cardial infarction on whole blood nitrite and examined whether whole blood nitrite can be determined reproducibly in critical ill patients, in particular without interference from factors such as renal function or inflammation, which are known to affect plasma NOx (the sum of plasma nitrite and nitrate) levels [14–17]. Materials and methods Study population The study population was recruited in two sets. An initial study population consisted of five young healthy vo- lunteers recruited from hospital staff and medical students of the University Hospital Aachen. Results from these initial experiments were used to validate the ferricyanide-based hemoglobin oxidation assay. None of the volunteers was on a regular medication nor revealed present or past evidence of cardiovascular disease. No organ Free Radical Biology & Medicine 44 (2008) 1945–1950 ⁎ Corresponding author. Fax: +49 241 80 82303. E-mail address: trassaf@ukaachen.de (T. Rassaf). Abbreviations: CK, creatine kinase; CRP, C-reactive protein; GFR, glomerular filtration rate; I/R, ischemia–reperfusion; ICU, intensive care unit; NEM, N-ethylmalei- mide; NOx, sum of plasma nitrite and nitrate; PCT, procalcitonin; RRT, renal replacement therapy; SIRS, systemic inflammatory response syndrome. 0891-5849/$ – see front matter © 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.freeradbiomed.2008.02.014 Contents lists available at ScienceDirect Free Radical Biology & Medicine journal homepage: www.elsevier.com/locate/freeradbiomed