title: Nitrate enhances skeletal muscle fatty acid oxidation via a nitric oxide-cGMP-PPAR-mediated mechanism.
abstract: BACKGROUND
  Insulin sensitivity in skeletal muscle is associated with metabolic flexibility, including a high capacity to increase fatty acid (FA) oxidation in response to increased lipid supply. Lipid overload, however, can result in incomplete FA oxidation and accumulation of potentially harmful intermediates where mitochondrial tricarboxylic acid cycle capacity cannot keep pace with rates of β-oxidation. Enhancement of muscle FA oxidation in combination with mitochondrial biogenesis is therefore emerging as a strategy to treat metabolic disease. Dietary inorganic nitrate was recently shown to reverse aspects of the metabolic syndrome in rodents by as yet incompletely defined mechanisms.
  
  
  RESULTS
  Herein, we report that nitrate enhances skeletal muscle FA oxidation in rodents in a dose-dependent manner. We show that nitrate induces FA oxidation through a soluble guanylate cyclase (sGC)/cGMP-mediated PPARβ/δ- and PPARα-dependent mechanism. Enhanced PPARβ/δ and PPARα expression and DNA binding induces expression of FA oxidation enzymes, increasing muscle carnitine and lowering tissue malonyl-CoA concentrations, thereby supporting intra-mitochondrial pathways of FA oxidation and enhancing mitochondrial respiration. At higher doses, nitrate induces mitochondrial biogenesis, further increasing FA oxidation and lowering long-chain FA concentrations. Meanwhile, nitrate did not affect mitochondrial FA oxidation in PPARα(-/-) mice. In C2C12 myotubes, nitrate increased expression of the PPARα targets Cpt1b, Acadl, Hadh and Ucp3, and enhanced oxidative phosphorylation rates with palmitoyl-carnitine; however, these changes in gene expression and respiration were prevented by inhibition of either sGC or protein kinase G. Elevation of cGMP, via the inhibition of phosphodiesterase 5 by sildenafil, also increased expression of Cpt1b, Acadl and Ucp3, as well as CPT1B protein levels, and further enhanced the effect of nitrate supplementation.
  
  
  CONCLUSIONS
  Nitrate may therefore be effective in the treatment of metabolic disease by inducing FA oxidation in muscle.
authors.affiliation: Department of Physiology, Development & Neuroscience, University of Cambridge, Downing Street, Cambridge, CB2 3EG, UK.|Department of Biochemistry, University of Cambridge, Cambridge, UK.
authors.forename: Tom
authors.initials: T
authors.lastname: Ashmore
authors.affiliation: Department of Biochemistry, University of Cambridge, Cambridge, UK.|MRC-Human Nutrition Research, University of Cambridge, Cambridge, UK.
authors.forename: Lee D
authors.initials: LD
authors.lastname: Roberts
authors.affiliation: Department of Physiology, Development & Neuroscience, University of Cambridge, Downing Street, Cambridge, CB2 3EG, UK.
authors.forename: Andrea J
authors.initials: AJ
authors.lastname: Morash
authors.affiliation: Department of Physiology, Development & Neuroscience, University of Cambridge, Downing Street, Cambridge, CB2 3EG, UK.
authors.forename: Aleksandra O
authors.initials: AO
authors.lastname: Kotwica
authors.affiliation: Department of Physiology, Development & Neuroscience, University of Cambridge, Downing Street, Cambridge, CB2 3EG, UK.
authors.forename: John
authors.initials: J
authors.lastname: Finnerty
authors.affiliation: Department of Biochemistry, University of Cambridge, Cambridge, UK.
authors.forename: James A
authors.initials: JA
authors.lastname: West
authors.affiliation: Department of Biochemistry, University of Cambridge, Cambridge, UK.
authors.forename: Steven A
authors.initials: SA
authors.lastname: Murfitt
authors.affiliation: Faculty of Medicine, Clinical & Experimental Sciences, University of Southampton, Southampton, UK.
authors.forename: Bernadette O
authors.initials: BO
authors.lastname: Fernandez
authors.affiliation: Department of Physiology, Development & Neuroscience, University of Cambridge, Downing Street, Cambridge, CB2 3EG, UK.
authors.forename: Cristina
authors.initials: C
authors.lastname: Branco
authors.affiliation: Department of Physiology, Development & Neuroscience, University of Cambridge, Downing Street, Cambridge, CB2 3EG, UK.
authors.forename: Andrew S
authors.initials: AS
authors.lastname: Cowburn
authors.affiliation: Department of Physiology, Anatomy & Genetics, University of Oxford, Oxford, UK.
authors.forename: Kieran
authors.initials: K
authors.lastname: Clarke
authors.affiliation: Department of Physiology, Development & Neuroscience, University of Cambridge, Downing Street, Cambridge, CB2 3EG, UK.
authors.forename: Randall S
authors.initials: RS
authors.lastname: Johnson
authors.affiliation: Faculty of Medicine, Clinical & Experimental Sciences, University of Southampton, Southampton, UK.
authors.forename: Martin
authors.initials: M
authors.lastname: Feelisch
authors.affiliation: Department of Biochemistry, University of Cambridge, Cambridge, UK.|MRC-Human Nutrition Research, University of Cambridge, Cambridge, UK.
authors.forename: Julian L
authors.initials: JL
authors.lastname: Griffin
authors.affiliation: Department of Physiology, Development & Neuroscience, University of Cambridge, Downing Street, Cambridge, CB2 3EG, UK. ajm267@cam.ac.uk.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Murray
mesh_terms: D000821:Animal Feed / Q000032:analysis; D000818:Animals; D006152:Cyclic GMP / Q000378:metabolism*; D004032:Diet; D004305:Dose-Response Relationship, Drug; D005227:Fatty Acids / Q000378:metabolism*; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism*; D009566:Nitrates / Q000378:metabolism*; D009569:Nitric Oxide / Q000378:metabolism*; D001678:Organelle Biogenesis; D010084:Oxidation-Reduction; D047492:Peroxisome Proliferator-Activated Receptors / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
chemical_list: D005227:Fatty Acids; D009566:Nitrates; D047492:Peroxisome Proliferator-Activated Receptors; D009569:Nitric Oxide; D006152:Cyclic GMP