title: In adenosine A2B knockouts acute treatment with inorganic nitrate improves glucose disposal, oxidative stress, and AMPK signaling in the liver.
abstract: BACKGROUND
  Accumulating studies suggest that nitric oxide (NO) deficiency and oxidative stress are central pathological mechanisms in type 2 diabetes (T2D). Recent findings demonstrate therapeutic effects by boosting the nitrate-nitrite-NO pathway, which is an alternative pathway for NO formation. This study aimed at investigating the acute effects of inorganic nitrate on glucose and insulin signaling in adenosine A2B receptor knockout mice (A(-/-) 2B), a genetic mouse model of impaired metabolic regulation.
  
  
  METHODS
  Acute effects of nitrate treatment were investigated in aged wild-type (WT) and A(-/-) 2B mice. One hour after injection with nitrate (0.1 mmol/kg, i.p.) or placebo, metabolic regulation was evaluated by intraperitoneal glucose and insulin tolerance tests. NADPH oxidase-mediated superoxide production and AMPK phosphorylation were measured in livers obtained from non-treated or glucose-treated mice, with or without prior nitrate injection. Plasma was used to determine insulin resistance (HOMA-IR) and NO signaling.
  
  
  RESULTS
  A(-/-) 2B displayed increased body weight, reduced glucose clearance, and attenuated overall insulin responses compared with age-matched WT mice. Nitrate treatment increased circulating levels of nitrate, nitrite and cGMP in the A(-/-) 2B, and improved glucose clearance. In WT mice, however, nitrate treatment did not influence glucose clearance. HOMA-IR increased following glucose injection in the A(-/-) 2B, but remained at basal levels in mice pretreated with nitrate. NADPH oxidase activity in livers from A(-/-) 2B, but not WT mice, was reduced by nitrate treatment. Livers from A(-/-) 2B displayed reduced AMPK phosphorylation compared with WT mice, and this was increased by nitrate treatment. Finally, injection with the anti-diabetic agent metformin induced similar therapeutic effects in the A(-/-) 2B as observed with nitrate.
  
  
  CONCLUSIONS
  The A(-/-) 2B mouse is a genetic mouse model of metabolic syndrome. Acute treatment with nitrate improved the metabolic profile in it, at least partly via reduction in oxidative stress and improved AMPK signaling in the liver.
authors: Department of Physiology and Pharmacology, Karolinska Institutet Stockholm, Sweden.
authors: Maria
authors: M
authors: Peleli
authors: Department of Physiology and Pharmacology, Karolinska Institutet Stockholm, Sweden.
authors: Michael
authors: M
authors: Hezel
authors: Department of Physiology and Pharmacology, Karolinska Institutet Stockholm, Sweden.
authors: Christa
authors: C
authors: Zollbrecht
authors: Department of Medical Cell Biology, Uppsala University Stockholm, Sweden.
authors: A Erik G
authors: AE
authors: Persson
authors: Department of Physiology and Pharmacology, Karolinska Institutet Stockholm, Sweden.
authors: Jon O
authors: JO
authors: Lundberg
authors: Department of Physiology and Pharmacology, Karolinska Institutet Stockholm, Sweden.
authors: Eddie
authors: E
authors: Weitzberg
authors: Department of Physiology and Pharmacology, Karolinska Institutet Stockholm, Sweden.
authors: Bertil B
authors: BB
authors: Fredholm
authors: Department of Physiology and Pharmacology, Karolinska Institutet Stockholm, Sweden.
authors: Mattias
authors: M
authors: Carlström
keywords: NADPH oxidase; insulin resistance; metabolic syndrome; nitric oxide; nitrite; obesity; superoxide; type 2 diabetes