The Capacity of Red Blood Cells to Reduce Nitrite Determines Nitric Oxide Generation under Hypoxic Conditions

• Type of Material: Article
• Authors: Marcel H. Fens, Children's Hospital Oakland Research Institute; Sandra K. Larkin, Children's Hospital Oakland Research Institute; Bryan Oronsky, RadioRx Inc; Jan Scicinski, RadioRx Inc; Claudia Morris, Emory University; Frans A. Kuypers, Children's Hospital Oakland Research Institute
• Language: English
• Date: 2014-07-09
• Publisher: Public Library of Science
• Publication Version: Final Published Version
• Copyright Statement: © 2014 Fens et al.
• License: Creative Commons Attribution 4.0 International
• Final Published Version (URL): http://dx.doi.org/10.1371/journal.pone.0101626
• Title of Journal or Parent Work: PLoS ONE
• ISSN: 1932-6203
• Volume: 9
• Issue: 7
• Start Page: e101626
• End Page: e101626
• Grant/Funding Information: MHF is supported by the Netherlands Organisation for Scientific Research, The Hague, The Netherlands.
• Keywords: MULTIDISCIPLINARY SCIENCES; Multidisciplinary Sciences; Science & Technology - Other Topics; HEMOGLOBIN; RELAXING FACTOR; SYNTHASE; PULMONARY-HYPERTENSION; FLOW REGULATION; DISEASE; MECHANISMS; RELEASE; Science & Technology; NO; S-NITROSOHEMOGLOBIN
• Research Categories: Health Sciences, General; Health Sciences, Human Development

Abstract

Nitric oxide (NO) is a key regulator of vascular tone. Endothelial nitric oxide synthase (eNOS) is responsible for NO generation under normoxic conditions. Under hypoxia however, eNOS is inactive and red blood cells (RBC) provide an alternative NO generation pathway from nitrite to regulate hypoxic vasodilation. While nitrite reductase activity of hemoglobin is well acknowledged, little is known about generation of NO by intact RBC with physiological hemoglobin concentrations. We aimed to develop and apply a new approach to provide insights in the ability of RBC to convert nitrite into NO under hypoxic conditions. We established a novel experimental setup to evaluate nitrite uptake and the release of NO from RBC into the gas-phase under different conditions. NO measurements were similar to well-established clinical measurements of exhaled NO. Nitrite uptake was rapid, and after an initial lag phase NO release from RBC was constant in time under hypoxic conditions. The presence of oxygen greatly reduced NO release, whereas inhibition of eNOS and xanthine oxidoreductase (XOR) did not affect NO release. A decreased pH increased NO release under hypoxic conditions. Hypothermia lowered NO release, while hyperthermia increased NO release. Whereas fetal hemoglobin did not alter NO release compared to adult hemoglobin, sickle RBC showed an increased ability to release NO. Under all conditions nitrite uptake by RBC was similar. This study shows that nitrite uptake into RBC is rapid and release of NO into the gas-phase continues for prolonged periods of time under hypoxic conditions. Changes in the RBC environment such as pH, temperature or hemoglobin type, affect NO release.