1521-0081/72/3/692–766$35.00 https://doi.org/10.1124/pr.120.019240 PHARMACOLOGICAL REVIEWS Pharmacol Rev 72:692–766, July 2020 Copyright © 2020 by The Author(s) This is an open access article distributed under the CC BY-NC Attribution 4.0 International license. ASSOCIATE EDITOR: CHRISTOPHER J. GARLAND The Noncanonical Pathway for In Vivo Nitric Oxide Generation: The Nitrate-Nitrite-Nitric Oxide Pathway V. Kapil, R. S. Khambata, D. A. Jones, K. Rathod, C. Primus, G. Massimo, J. M. Fukuto, and A. Ahluwalia William Harvey Research Institute, Barts and The London School of Medicine and Dentistry, Queen Mary University London, London, United Kingdom (V.K., R.S.K., D.A.J., K.R., C.P., G.M., A.A.) and Department of Chemistry, Sonoma State University, Rohnert Park, California (J.M.F.) Abstract ...................................................................................694 Significance Statement. ..................................................................694 I. Introduction . ..............................................................................694 A. Chemistry of ·NO and Its Metabolism to Nitrite and Nitrate . .........................695 II. Inorganic Nitrite and Nitrate . ............................................................697 A. Historical Uses of Inorganic Nitrite.....................................................697 B. Historical Uses of Inorganic Nitrate ....................................................698 III. Sources and Pharmacokinetics of Nitrate . ................................................698 Downloaded from A. Endogenously Derived Nitrate..........................................................698 B. Exogenous Sources of Nitrate ..........................................................699 1. Dietary Intake ......................................................................699 2. Water Supplies . ..................................................................699 C. Pharmacokinetics of Nitrate ............................................................699 D. Enterosalivary Circulation and Oral Reduction of Nitrate ...............................700 by guest on October 2, 2021 E. Nitrate Reductases. ..................................................................702 1. Prokaryotic Nitrate Reductases .....................................................702 2. Mammalian Nitrate Reductase Activity . ..........................................702 IV. Sources and Pharmacokinetics of Nitrite . ................................................703 A. Endogenously Derived Nitrite from the Enterosalivary Circuit . .........................703 B. Endogenously Derived Nitrite from NOS Activity . .....................................704 C. Exogenous Sources of Nitrite ...........................................................704 D. Systemic Nitrite Absorption ............................................................705 V. Mechanisms of Nitrite Bioactivation. ......................................................706 A. Nonenzymatic Nitrite Reduction. ......................................................706 B. Mammalian Nitrite Reductases. ......................................................706 1. Molybdenum-Containing Oxidase Enzymes ..........................................706 a. Xanthine oxidoreductase. ......................................................706 b. Aldehyde oxidase ................................................................708 c. Sulfite oxidase. ..................................................................709 d. Mitochondrial amidoxime reducing component ...................................709 2. Mitochondrial Respiratory Chain Enzymes ..........................................709 3. Globins .............................................................................709 a. Hemoglobin . ..................................................................709 b. Myoglobin .......................................................................710 c. Neuroglobin . ..................................................................710 d. Cytoglobin.......................................................................710 4. Indoleamine 2,3-Dioxygenase 1......................................................711 Address correspondence to: A. Ahluwalia, Centre for Cardiac Medicines and Device Innovation, William Harvey Research Institute, Charterhouse Square, London EC1M 6BQ, UK. E-mail: [email protected] V.K. and D.A.J. were supported by a Barts Charity Programme grant, C.P. by a Derek Willoughby clinical research training fellowship, and K.R. by a National Institute for Health Academic Clinical Lectureship award. https://doi.org/10.1124/pr.120.019240. 692 Nitrate-Nitrite-Nitric Oxide Pathway 693 5. Nitric Oxide Synthase . ............................................................711 6. Carbonic Anhydrase ................................................................711 VI. Functional Effects of the Noncanonical ·NO Pathway and Clinical Translation . .............712 A. Nitrite, Nitrate, and the CV System ....................................................712 1. Vasodilation ........................................................................712 2. Blood Pressure . ..................................................................714 3. Enterosalivary Generation of Nitrite Regulates Basal BP . .........................719 4. Endothelial Dysfunction ............................................................720 5. Arterial Stiffness . ..................................................................720 6. Cerebral Blood Flow ................................................................721 B. Nitrite and Nitrate in Exercise and Muscle Biology .....................................721 1. Nitrate and Exercise Performance on Moderately Trained Athletes ..................722 a. Mechanisms for enhanced exercise performance after nitrate supplementation . 723 2. Nitrate and Exercise Performance in Patient Populations. .........................724 3. Cardiac Muscle Function and Heart Failure .........................................725 a. ·NO as an inotrope . ............................................................725 b. Cardiac hypertrophy and ·NO....................................................727 c. Positive inotropic and antihypertrophic effects of nitrite and nitrate . .............727 d. Preclinical studies: cardiac dysfunction, nitrite, and nitrate.......................727 e. Clinical translation . ............................................................730 C. Nitrite and Nitrate in Inflammation ....................................................731 1. Thrombosis . ........................................................................735 2. Peripheral Arterial Disease . ......................................................737 3. Atherosclerosis . ..................................................................737 D. Nitrite and Nitrate in the Respiratory System ..........................................738 1. Pulmonary Hypertension............................................................739 2. Chronic Obstructive Pulmonary Disease . ..........................................740 3. Sleep-Disordered Breathing . ......................................................740 4. Toxic Lung Injury. ..................................................................741 E. Nitrite and Nitrate in the GI System . ................................................741 F. Nitrite and Nitrate in Metabolic Diseases...............................................742 G. Nitrite and Nitrate in I/R Injury. ......................................................743 1. Cytoprotection ......................................................................743 2. Potential Mechanisms for Nitrite-Induced Reduction in I/R Injury ...................743 3. Potential Mechanisms for Nitrite-Induced Cytoprotection in I/R Injury . .............744 a. Improved mitochondrial function. ................................................744 b. Antiplatelet effects . ............................................................745 ABBREVIATIONS: ABP, ambulatory blood pressure; ADI, acceptable daily intake; AMI, acute myocardial infarction; AMPK, AMP- activated protein kinase; AO, aldehyde oxidase; ApoE, apolipoprotein E; BNP, brain natriuretic peptide; BP, blood pressure; CABG, coronary artery bypass grafting; CCL2, chemokine (C-C motif) ligand 2; cGMP, cyclic GMP; COPD, chronic obstructive pulmonary disease; C-PTIO, 2- (4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide; CV, cardiovascular; CVD, cardiovascular disease; CXCL2, chemokine (C-X-C motif) ligand 2; DASH, Dietary Approaches to Stop Hypertension; DBP, diastolic blood pressure; deoxyHb, deoxyhemoglobin; deoxyMb, deoxymyoglobin; dP/dt, rate of change of pressure; DOCA, deoxycorticosterone acetate; EDRF, endothelium-derived relaxing factor; eNOS, endothelial nitric oxide synthase; Fe(II), ferrous; Fe(III), ferric; FMD, flow-mediated dilation; GAG, glycosaminoglycan; GC-1, soluble guanylyl cyclase; GI, gastrointestinal; GTN, glyceryl trinitrate; HF, heart failure; HFpEF, heart failure with preserved ejection fraction; HFrEF, heart failure with reduced ejection fraction; ICAM-1, intercellular adhesion molecule-1; IDO1, indoleamine 2,3-dioxygenase 1; IL, interleukin; iNO, 1 inhaled·NO; iNOS, inducible nitric oxide synthase; I/R, ischemia/reperfusion; KATP, ATP-sensitive K ; KO, knockout; L-NAME, N(g)--nitro-L- arginine methyl ester; LV, left ventricular; LVEF, left ventricular ejection fraction; MAP, mean arterial