Alternative sources of NO in the lung

Transcription

1 Vasoactivity Reduce, of Reuse, circulating and Recycle: species. Alternative sources of in the lung Smooth Muscle Vasodilation i Endothelium Plasma L-Arginine Arlin B. Blood, PhD Associate Professor Department of Pediatrics Division of Neonatology Loma Linda University School of Medicine half-life in blood = <10 milliseconds Blood transit time from lung to periphery ~ 5-15 seconds Evidence for peripheral effects of i i Smooth Muscle Endothelium Plasma L-Arginine R-SH 2 - (Nitrite) H + R-S (S-nitrosothiols) McMahon and Doctor, PNAS, 2006;3:

2 S-Nitrosothiol production Nitrosated albumin carries in plasma Inhaled GS Cys R-S (Transnitrosation) S-Hemoglobin; a circulating carrier Artery-vein gradient for S-Hb in rats Hb S-Hb β β α Stamler et al, 1997, Science, 276:2034 2

3 S-Hb exports via anion exchanger Transport of i into lungs as Cys Cys i + Cys Venous blood (T-state, Hb) Arterial blood (R-state, S-Hb) Tissues (T-state, export) amino acid transporter Modified from review by Doctor & Stamler, Compr Physiol, : Alveolar Epithelium S-Hb concentrations are increased in infants during i therapy Controversy surrounding S-Hb concentrations Triiodide methods Photolysis methods... but adult reports are conflicting Ibrahim, et al, J Pediatr 2012 Feb;160(2): Cannon, et al, J Clin Invest : picomolar to low nanomolar levels midnanomolar to low micromolar levels 3

4 S-Hb knockout mouse S-Hb knockout mouse Knockouts had no difference in excercise stress tests, systemic blood pressure, and no evidence of pulmonary hypertension......but knockouts also had evidence of compensations in the RBC S pool. Isbell et al, 2008, Nat Med, 14(7): Isbell et al, 2008, Nat Med, 14(7): Nitrite as a circulating source of i Mammalian Blood Nitrite Concentrations Smooth Muscle Vasodilation Endothelium Plasma L-Arginine 2 - (Nitrite) Hb MetHb + Kleinbongard et al Free Rad Biol & Med 35:7,

5 Effect of i therapy on plasma and CSF nitrite Nitrite is a vasodilator in the human forearm Newborn lambs Infants with PPHN Nitrite + DeoxyHb + H + + MetHb + OH - Exercising forearm blood flow Cosby, et al, Nature Med Dec 9 (12): Dejam et al, Circulation 2007;116: Conahey, et al, Ped Res : Ibrahim, et al, J Pediatr 2012 Feb;160(2): Hypothesis Pulmonary hypertension will be alleviated by inhaled sodium nitrite. Inhaled nitrite is a pulmonary vasodilator in newborn lambs Hunter et al, 2004 Nature Med, 10:10,

6 Hypothesis Pulmonary hypertension will be alleviated by intravenous nitrite. Intravenous nitrite is T a pulmonary vasodilator in newborn lambs Blood et al, 2011 Circulation, 123: Current Working Model Inhaled nitrite is reduced to in the airway Nitrite as a circulating source of i Smooth Muscle Vasodilation Endothelium L-Arginine Plasma 2 - (Nitrite)? Hb MetHb + K ~ 0.1 M -1 s -1 Hb + Hb K ~ 10 HbO2 + MetHb M -1 s -1 6

7 Hypothesis Nitrite is a vasodilator in the femoral vasculature of the adult sheep Exogenous nitrite is T a vasodilator in adult sheep femoral vasculature Blood Pressure Ipsilateral / Contralateral Blood Flow Sheep vs Human RBCs: current working model Nitrite is protective during ischemic stress AE-1 binds to hemoglobin at the same binding site used by 2,3-DPG Sheep hemoglobin does not bind to 2,3-DPG...?? Hb Modified from review by Doctor & Stamler, Compr Physiol, : Lundberg and Weitzberg, Biochem Biophys Res Comm, 2010;396:

8 Extravascular pathways of nitrite reduction to Putative protective pathways of nitrite Deoxymyoglobin Xanthine Oxidase Neuroglobin Cytoglobin Cytochrome c Oxidase Aldehyde Dehydrogenase Carbonic Anhydrase 2 - Hypoxia H + pka = 3.3 H2 OH - + Lundberg et al, 2008 Nat Rev Drug Discov, Feb;7(2): Conclusions Acknowledgements S-Hb is a potential carrier of bioactive in the blood Lack of consensus lingers due to assay methodological issues Nitrite is a potential carrier of bioactive Its vasoactive properties are questionable There is growing consensus on its protection against ischemia/reperfusion injury Gordon Power Hobe Schroeder Andrew Hopper Janet Ninnis T. Allen Merritt Doug Deming Shannon Bragg Kurt Vrancken Jesica Kanady Laura Kirby Giang Truong Jonathon Ross Taiming Liu Yomna Ibrahim Daniel Hunt Michael Terry Jeanette Merrill-Henry Lawrence Longo Sean Wilson Department of Pediatrics Division of Neonatology NIH R01 HL (ABB) Mark Gladwin Mauro Tiso Andre Dejam Christian Hunter Wake Forest University Daniel Kim-Shapiro Landon Bellavia Ivan Azarov Mahesh Joshi Tim McMahon Amy Zhang 8