title: Dietary nitrate increases arginine availability and protects mitochondrial complex I and energetics in the hypoxic rat heart.
abstract: Hypoxic exposure is associated with impaired cardiac energetics in humans and altered mitochondrial function, with suppressed complex I-supported respiration, in rat heart. This response might limit reactive oxygen species generation, but at the cost of impaired electron transport chain (ETC) activity. Dietary nitrate supplementation improves mitochondrial efficiency and can promote tissue oxygenation by enhancing blood flow. We therefore hypothesised that ETC dysfunction, impaired energetics and oxidative damage in the hearts of rats exposed to chronic hypoxia could be alleviated by sustained administration of a moderate dose of dietary nitrate. Male Wistar rats (n = 40) were given water supplemented with 0.7 mmol l(-1) NaCl (as control) or 0.7 mmol l(-1) NaNO3, elevating plasma nitrate levels by 80%, and were exposed to 13% O2 (hypoxia) or normoxia (n = 10 per group) for 14 days. Respiration rates, ETC protein levels, mitochondrial density, ATP content and protein carbonylation were measured in cardiac muscle. Complex I respiration rates and protein levels were 33% lower in hypoxic/NaCl rats compared with normoxic/NaCl controls. Protein carbonylation was 65% higher in hearts of hypoxic rats compared with controls, indicating increased oxidative stress, whilst ATP levels were 62% lower. Respiration rates, complex I protein and activity, protein carbonylation and ATP levels were all fully protected in the hearts of nitrate-supplemented hypoxic rats. Both in normoxia and hypoxia, dietary nitrate suppressed cardiac arginase expression and activity and markedly elevated cardiac l-arginine concentrations, unmasking a novel mechanism of action by which nitrate enhances tissue NO bioavailability. Dietary nitrate therefore alleviates metabolic abnormalities in the hypoxic heart, improving myocardial energetics.
authors.affiliation: Department of Physiology, Development & Neuroscience, University of Cambridge, UK Department of Biochemistry, University of Cambridge, UK.
authors.forename: Tom
authors.initials: T
authors.lastname: Ashmore
authors.affiliation: Faculty of Medicine, Clinical & Experimental Sciences, University of Southampton, UK.
authors.forename: Bernadette O
authors.initials: BO
authors.lastname: Fernandez
authors.affiliation: Department of Physiology, Development & Neuroscience, University of Cambridge, UK.
authors.forename: Cristina
authors.initials: C
authors.lastname: Branco-Price
authors.affiliation: Department of Biochemistry, University of Cambridge, UK MRC-Human Nutrition Research, Elsie Widdowson Laboratory, Cambridge, UK.
authors.forename: James A
authors.initials: JA
authors.lastname: West
authors.affiliation: Department of Physiology, Development & Neuroscience, University of Cambridge, UK.
authors.forename: Andrew S
authors.initials: AS
authors.lastname: Cowburn
authors.affiliation: Department of Physiology, Anatomy & Genetics, University of Oxford, UK.
authors.forename: Lisa C
authors.initials: LC
authors.lastname: Heather
authors.affiliation: Department of Biochemistry, University of Cambridge, UK MRC-Human Nutrition Research, Elsie Widdowson Laboratory, Cambridge, UK.
authors.forename: Julian L
authors.initials: JL
authors.lastname: Griffin
authors.affiliation: Department of Physiology, Development & Neuroscience, University of Cambridge, UK.
authors.forename: Randall S
authors.initials: RS
authors.lastname: Johnson
authors.affiliation: Faculty of Medicine, Clinical & Experimental Sciences, University of Southampton, UK.
authors.forename: Martin
authors.initials: M
authors.lastname: Feelisch
authors.affiliation: Department of Physiology, Development & Neuroscience, University of Cambridge, UK ajm267@cam.ac.uk.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Murray
mesh_terms: D000818:Animals; D001119:Arginase / Q000235:genetics / Q000378:metabolism; D001120:Arginine / Q000378:metabolism*; D004032:Diet; D042967:Electron Transport Complex I / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects; D006321:Heart / Q000187:drug effects* / Q000502:physiology; D051793:Hypoxia-Inducible Factor 1 / Q000235:genetics / Q000378:metabolism; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D009566:Nitrates / Q000008:administration & dosage / Q000494:pharmacology*; D009573:Nitrites / Q000737:chemistry / Q000378:metabolism; D018384:Oxidative Stress; D010100:Oxygen; D051381:Rats; D017208:Rats, Wistar
chemical_list: D051793:Hypoxia-Inducible Factor 1; D009566:Nitrates; D009573:Nitrites; D001120:Arginine; D001119:Arginase; D042967:Electron Transport Complex I; D010100:Oxygen