cyclic-gmp and Bacteremia

Pattern recognition receptor nucleotide-binding oligomerization domain 2 (NOD2) is well investigated in immunity, but its expression and function in platelets has never been explored.. Using reverse transcription polymerase chain reaction and Western blot, we show that both human and mouse platelets express NOD2, and its agonist muramyl dipeptide induced NOD2 activation as evidenced by receptor dimerization. NOD2 activation potentiates platelet aggregation and secretion induced by low concentrations of thrombin or collagen, and clot retraction, as well. These potentiating effects of muramyl dipeptide were not seen in platelets from NOD2-deficient mice. Plasma from septic patients also potentiates platelet aggregation induced by thrombin or collagen NOD2 dependently. Using intravital microscopy, we found that muramyl dipeptide administration accelerated in vivo thrombosis in a FeCl3-injured mesenteric arteriole thrombosis mouse model. Platelet depletion and transfusion experiments confirmed that NOD2 from platelets contributes to the in vivo thrombosis in mice. NOD2 activation also accelerates platelet-dependent hemostasis. We further found that platelets express receptor-interacting protein 2, and provided evidence suggesting that mitogen activated-protein kinase and nitric oxide/soluble guanylyl cyclase/cGMP/protein kinase G pathways downstream of receptor-interacting protein mediate the role of NOD2 in platelets. Finally, muramyl dipeptide stimulates proinflammatory cytokine interleukin-1β maturation and accumulation in human and mouse platelets NOD2 dependently.. NOD2 is expressed in platelets and functions in platelet activation and arterial thrombosis, possibly during infection. To our knowledge, this is the first study on NOD-like receptors in platelets that link thrombotic events to inflammation.

Topics: Acetylmuramyl-Alanyl-Isoglutamine; Animals; Bacteremia; Blood Platelets; Clot Retraction; Cyclic GMP; Dimerization; Hemostasis; Humans; Inflammation; Interleukin-1beta; MAP Kinase Signaling System; Mice; Mice, Inbred NOD; Nitric Oxide; Nod2 Signaling Adaptor Protein; Platelet Activation; Receptor-Interacting Protein Serine-Threonine Kinase 2; Receptor-Interacting Protein Serine-Threonine Kinases; Signal Transduction; Thrombosis

Nitric oxide and vasoactive intestinal peptide (VIP) are potent vasodilators and postulated as inducers of hypotension. These mediators activate guanylate cyclase and adenylate cyclase, respectively, with subsequent biosynthesis of cyclic guanosine monophosphate (cGMP) and cyclic adenosine monophosphate (cAMP) producing vascular smooth muscle relaxation and vasodilatation. Cyclic nucleotides and VIP were evaluated during Escherichia coli septicemia in two groups of rabbits; 1) sepsis alone and 2) sepsis and a competitive inhibitor of nitric oxide synthase, NG-monomethyl-L-arginine. Arterial blood was obtained for determination of bacteremia, lactic acidemia, nucleotides, nitrites, and VIP levels. Significant bacteremia, endotoxemia, tachycardia, lactic acidosis, and hypotension occurred in all animals (P < 0.005). Circulating blood levels of cGMP, nitrites, cAMP, and VIP (P < 0.005) increased with development of shock. The NG-monomethyl-L-arginine treated animals had less cGMP, nitrites, cAMP, and VIP produced (P < 0.01). Plasma cGMP levels remained stable, suggesting that stimulated phagocytes in whole blood were responsible for increased cGMP levels. Infusion of VIP produced profound hypotension and lactic acidemia. Results of these experiments provide definitive evidence that nitric oxide and VIP are mediators during septic shock and their messengers are cGMP and cAMP, respectively. In addition, phagocytic stimulation with increased production of cGMP may initiate shock, with these mediators acting synergistically to prolong hypotension.

Topics: Amino Acid Oxidoreductases; Animals; Arginine; Bacteremia; Blood Pressure; Cyclic AMP; Cyclic GMP; Disease Models, Animal; Escherichia coli Infections; Heart Rate; Lactates; Nitric Oxide; Nitric Oxide Synthase; omega-N-Methylarginine; Rabbits; Reference Values; Vasoactive Intestinal Peptide

Endotoxin and other bacterial products induce the release of mediators which alter the circulation and cellular metabolism. Recent evidence suggests nitric oxide (NO) is one such mediator. The proposed mechanism by which NO produces hypotension is the activation of guanylate cyclase with subsequent biosynthesis of 3':5' cyclic guanosine monophosphate (cGMP). We studied the production of cGMP during Escherichia coli-induced septic shock in two experiments; the first with sepsis alone and the second using NG-monomethyl-L-arginine (L-NMMA), a competitive inhibitor of nitric oxide synthase. Animals in both experiments experienced significant bacteremia (P < 0.05), endotoxemia (P < 0.05), and lactic acidosis (P < 0.03). Mean arterial blood pressure decreased (P < 0.03) and heart rate increased (P < 0.05) within both groups but did not differ between groups. A significant increase in the production of circulating whole blood cGMP occurred at 3-5 h (P < 0.03). There was significantly less cGMP produced by the L-NMMA-treated animals (P < 0.01). These results demonstrate an elevation in cGMP during septic shock which is attenuated by the addition of L-NMMA. This suggests that NO may be present during gram-negative septic shock and its effects mediated through cGMP.

Topics: Animals; Arginine; Bacteremia; Carbon Dioxide; Cyclic GMP; Escherichia coli Infections; Lactates; Lactic Acid; Male; Nitric Oxide; omega-N-Methylarginine; Rabbits; Shock, Septic