title: Circulating adenosine increases during human experimental endotoxemia but blockade of its receptor does not influence the immune response and subsequent organ injury.
abstract: BACKGROUND
  Preclinical studies have shown that the endogenous nucleoside adenosine prevents excessive tissue injury during systemic inflammation. We aimed to study whether endogenous adenosine also limits tissue injury in a human in vivo model of systemic inflammation. In addition, we studied whether subjects with the common 34C > T nonsense variant (rs17602729) of adenosine monophosphate deaminase (AMPD1), which predicts increased adenosine formation, have less inflammation-induced injury.
  
  
  METHODS
  In a randomized double-blinded design, healthy male volunteers received 2 ng/kg E. Coli LPS intravenously with (n = 10) or without (n = 10) pretreatment with the adenosine receptor antagonist caffeine (4 mg/kg body weight). In addition, lipopolysaccharide (LPS) was administered to 10 subjects heterozygous for the AMPD1 34C > T variant.
  
  
  RESULTS
  The increase in adenosine levels tended to be more pronounced in the subjects heterozygous for the AMPD1 34C > T variant (71 ± 22%, P=0.04), compared to placebo- (59 ± 29%, P=0.012) and caffeine-treated (53 ± 47%, P=0.29) subjects, but this difference between groups did not reach statistical significance. Also the LPS-induced increase in circulating cytokines was similar in the LPS-placebo, LPS-caffeine and LPS-AMPD1-groups. Endotoxemia resulted in an increase in circulating plasma markers of endothelial activation [intercellular adhesion molecule (ICAM) and vascular cell adhesion molecule (VCAM)], and in subclinical renal injury, measured by increased urinary excretion of tubular injury markers. The LPS-induced increase of these markers did not differ between the three groups.
  
  
  CONCLUSIONS
  Human experimental endotoxemia induces an increase in circulating cytokine levels and subclinical endothelial and renal injury. Although the plasma adenosine concentration is elevated during systemic inflammation, co-administration of caffeine or the presence of the 34C > T variant of AMPD1 does not affect the observed subclinical organ damage, suggesting that adenosine does not affect the inflammatory response and subclinical endothelial and renal injury during human experimental endotoxemia.
  
  
  BACKGROUND
  ClinicalTrials (NCT): NCT00513110.
authors.affiliation: Department of Intensive Care Medicine, Radboud University Nijmegen Medical Center, Geert Grooteplein 10, 6500 HB Nijmegen, The Netherlands. p.pickkers@ic.umcn.nl
authors.forename: Bart P
authors.initials: BP
authors.lastname: Ramakers
authors.forename: Niels P
authors.initials: NP
authors.lastname: Riksen
authors.forename: Petra
authors.initials: P
authors.lastname: van den Broek
authors.forename: Barbara
authors.initials: B
authors.lastname: Franke
authors.forename: Wilbert H M
authors.initials: WH
authors.lastname: Peters
authors.forename: Johannes G
authors.initials: JG
authors.lastname: van der Hoeven
authors.forename: Paul
authors.initials: P
authors.lastname: Smits
authors.forename: Peter
authors.initials: P
authors.lastname: Pickkers
mesh_terms: D000659:AMP Deaminase / Q000235:genetics; D000241:Adenosine / Q000097:blood*; D002110:Caffeine / Q000494:pharmacology*; D004311:Double-Blind Method; D019446:Endotoxemia / Q000097:blood*; D004926:Escherichia coli; D006801:Humans; D007113:Immunity, Innate; D007249:Inflammation / Q000150:complications; D007668:Kidney / Q000293:injuries; D008070:Lipopolysaccharides; D008297:Male; D058915:Purinergic P1 Receptor Antagonists / Q000494:pharmacology*; D018047:Receptors, Purinergic P1 / Q000187:drug effects*
chemical_list: D008070:Lipopolysaccharides; D058915:Purinergic P1 Receptor Antagonists; D018047:Receptors, Purinergic P1; D002110:Caffeine; D000659:AMP Deaminase; C514117:AMPD1 protein, human; D000241:Adenosine