A paradoxical protective role for the proinflammatory peptide substance P receptor (NK1R) in acute hyperoxic lung injury.

The neuropeptide substance P manifests its biological functions through ligation of a G protein-coupled receptor, the NK1R. Mice with targeted deletion of this receptor reveal a preponderance of proinflammatory properties resulting from ligand activation, demonstrating a neurogenic component to multiple forms of inflammation and injury. We hypothesized that NK1R deficiency would afford a similar protection from inflammation associated with hyperoxia. Counter to our expectations, however, NK1R-/- animals suffered significantly worse lung injury compared with wild-type mice following exposure to 90% oxygen. Median survival was shortened to 84 h for NK1R-/- mice from 120 h for wild-type animals. Infiltration of inflammatory cells into the lungs was significantly increased; NK1R-/- animals also exhibited increased pulmonary edema, hemorrhage, and bronchoalveolar lavage fluid protein levels. TdT-mediated dUTP nick end labeling (TUNEL) staining was significantly elevated in NK1R-/- animals following hyperoxia. Furthermore, induction of metallothionein and Na(+)-K(+)-ATPase was accelerated in NK1R-/- compared with wild-type mice, consistent with increased oxidative injury and edema. In cultured mouse lung epithelial cells in 95% O(2), however, addition of substance P promoted cell death, suggesting the neurogenic component of hyperoxic lung injury is mediated by additional mechanisms in vivo. Release of bioactive constituents including substance P from sensory neurons results from activation of the vanilloid receptor, TRPV1. In mice with targeted deletion of the TRPV1 gene, acute hyperoxic injury is attenuated relative to NK1R-/- animals. Our findings thus reveal a major neurogenic mechanism in acute hyperoxic lung injury and demonstrate concerted actions of sensory neurotransmitters revealing significant protection for NK1R-mediated functions.

Influence of mast cells on the expression of adhesion molecules on circulating and migrating leukocytes in acute pancreatitis-associated lung injury.

Pancreatitis-associated lung injury is an early-occurring and severe complication, still associated with substantial mortality. A number of inflammatory cells and their products are involved in the initiation and progress of the condition. In the present study, acute pancreatitis (AP) was induced by the intraductal infusion of 5% sodium taurodeoxycholate in the rat. Pulmonary endothelial barrier dysfunction was measured by plasma exudation of radiolabeled albumin. Expression of PECAM-1, ICAM-1, and L: -selectin on neutrophils (CD11b(+)) and monocytes/macrophages (CD11b/c(+)), obtained from circulation and lung tissue, was measured 1 and 6 hours after AP induction (n = 10 rats/time point/group). Plasma levels of histamine and serotonin were determined. The role of mast cells was evaluated by pretreatment with the mast cell stabilizer cromolyn. Intraperitoneal administration of cromolyn downregulated pancreatitis-induced systemic increase of histamine at 1 hour (513 +/- 82 vs. 309 +/- 50, p < 0.05). Cromolyn prevented a decreased expression of PECAM-1 on circulatory neutrophils and monocytes/macrophages and against an increased expression of ICAM-1 and PECAM-1 on pulmonary neutrophils and monocytes/macrophages 6 hours after AP induction (about 40% vs. 10%, p < 0.01). The mast cell stabilizer also prevented pancreatitis-induced pulmonary endothelial barrier dysfunction at 6 hours. Thus, our data indicate that mast cells may play a critical role in the activation of leukocytes during the initiation of pancreatitis-associated lung injury by altering phenotypes of adhesion molecules.

Alterations of adhesion molecule expression and inflammatory mediators in acute lung injury induced by septic and non-septic challenges.

The lung is frequently the first failing organ during the sequential development of multiple organ dysfunction under both septic or non-septic conditions. The present study compared polymorphisms of tumor necrosis factor (TNFalpha), monocyte chemoattractant protein-1 (MCP-1), and adhesion molecule (AM) expression on circulating, recruited, and migrating leukocytes in the development of lung injury after induction of acute pancreatitis (AP) or abdominal sepsis by cecal ligation and puncture (CLP). Pulmonary alveolar barrier and endothelial barrier permeability dysfunction were measured. The expression of AMs (CD11b, CD11b/c, CD31, CD54 and CD62L) on leukocytes isolated from blood, lung tissue, and bronchoalveolar space were measured by flowcytometry. Plasma exudation to the interstitial tissue and the bronchoalveolar space significantly increased 1 and 3 hours after induction of pancreatitis and to the bronchoalveolar space from 6 hours after sepsis. Bronchoalveolar levels of MCP-1 significantly increased earlier than plasma exudation to the alveoli in both pancreatitis and sepsis. Alterations in expression of adhesion molecules on bronchoalveolar lavage (BAL) leukocytes can represent a marker reflecting leukocyte activation in the lung tissue, since both BAL and lung tissue leukocytes showed similar patterns of changes. Expression of adhesion molecules on circulating leukocytes increased 1 hour after induction of pancreatitis. Activating phenotypes of circulating, lung tissue and bronchoalveolar leukocytes may thus be responsible for the-development and severity of secondary lung injury.

The effect of intestinal ischemia and reperfusion injury on ICAM-1 expression, endothelial barrier function, neutrophil tissue influx, and protease inhibitor levels in rats.

Multiple organ dysfunction syndrome (MODS) is mediated by complex mechanisms in which interactions between activated leukocytes and endothelial cells play a central role. ICAM-1 (intercellular adhesion molecule-1) mediates firm adhesion and transendothelial migration of activated leukocytes from postcapillary venules into the tissue. The present study evaluated the ICAM-1 expression in various organs after 40 min of intestinal ischemia and 1, 3, 6, 12 h of reperfusion (I/R) in the rat, using a dual monoclonal antibody technique (n = 36). Endothelial barrier permeability, using the vascular leakage of radiolabeled human serum albumin was also assessed (n = 12). Neutrophil sequestration in the lungs was quantitated by myeloperoxidase activity and plasma protease inhibitor levels were measured with electroimmunoassay. Significant regional differences were found in ICAM-1 expression between organs, both constitutively and after I/R-injury. The highest constitutive levels were observed in the liver and lungs, followed by the kidneys. The constitutive ICAM-1 expression in the intestines and in the heart was about 1/20 compared with that found in the liver and lungs. The brain and muscle had levels of about 1/150 of that in the liver and lungs. After intestinal I/R, significant increases (17-45%) were found in the lungs, intestines, brain, heart, and muscle. Albumin leakage index (ALI) in all examined organs and myeloperoxidase activity in the lungs increased after I/R-injury. Serum levels of albumin and most protease inhibitors decreased significantly after I/R challenge. Intestinal I/R results in an increase of systemic ICAM-1 expression with marked organ variability. The upregulation of ICAM-1 could represent a crucial step in the adherence- and migration process of activated leukocytes and potentially in the development of tissue injury.

Mast cells contribute to early pancreatitis-induced systemic endothelial barrier dysfunction.

BACKGROUND: Activated mast cells can produce and release a number of inflammatory mediators involved in the pathophysiological process of acute conditions. The aim of the study was to evaluate the effect of mast cell stimulation on the early development of multiple organ dysfunction (MODS) in acute pancreatitis (AP). METHODS: AP was induced by the intraductal infusion of 5% sodium taurodeoxycholate in the rat. Tissue endothelial barrier dysfunction (TEBD) was measured by plasma exudation of radiolabeled albumin. Activation of mast cells was estimated by measuring the release of histamine. Mast cell stimulation was achieved with compound 48/80 (C48/80) administered intravenously (i.v.) or intraperitoneally (i.p.) in different doses either as pretreatment (30 min prior to induction of AP) or treatment immediately after induction of AP. RESULTS: Administration of C48/80 both i.p. and i.v. demonstrated the same effects. A single pretreatment dose of C48/80 (0.5 mg/kg) significantly reduced AP-induced TEBD in the pancreas and gut. Administration of C48/80 immediately after sham operation or induction of AP resulted in a significant increase in pancreatic and intestinal TEBD (p < 0.05 vs. AP+saline). Plasma levels of histamine increased with increasing doses of C48/80. CONCLUSION: The results imply that mast cell activation could be involved in the initiation of AP and the early phase of AP-induced MODS. Mechanisms seem to be complex and are still to be elucidated.

Effective treatment of gut barrier dysfunction using an antioxidant, a PAF inhibitor, and monoclonal antibodies against the adhesion molecule PECAM-1.

BACKGROUND: Oxygen free radicals (OFRs), platelet activating factor (PAF), cell adhesion molecules, and transmigration of polymorphonuclear leukocytes through the gut barrier are probably all essential in the development of gut barrier dysfunction following intestinal ischemia and reperfusion (I/R). Pretreatment and early treatment of I/R with the OFRs-scavenger (NAC), the PAF inhibitor lexipafant, and monoclonal antibodies against the adhesion molecule PECAM-1 (anti-PECAM-1-Mab) have been reported to be effective in the prevention or recovery of gut barrier dysfunction and result in a decrease in cytokine levels. Less is known about the effect of treatment inserted during the late stage of I/R. The objective of this study was to evaluate the potential therapeutic value of single or combination therapy with NAC, lexipafant, and anti-PECAM-1-MAb administered late during intestinal I/R in the rat. METHODS: NAC, lexipafant, and anti-PECAM-1-MAb were administrated, alone or in combination, after 3 h of reperfusion following 40 min of superior mesenteric arterial ischemia in the rat. Intestinal endothelial and epithelial barrier permeability, myeloperoxidase (MPO) activity, interleukin-1 beta (IL-1 beta), and protease inhibitor levels were evaluated after 12 h of reperfusion. RESULTS: Intestinal endothelial and epithelial permeability significantly increased in rats with I/R and saline treatment. Proteolytic activity in plasma was indicated by low levels of the three measured plasma protease inhibitors. Intestinal mucosal MPO content increased significantly. These changes were, to different degrees, reduced by late inserted treatment with NAC, lexipafant, or anti-PECAM-1-MAb. Alterations in systemic levels of IL-1 beta paralleled the changes found in gut barrier permeability and leukocyte trapping. Systemic antithrombin III levels and increased barrier permeability in remote organs were partly restored, especially by multimodal therapy. CONCLUSION: Treatment with NAC, lexipafant, and/or monoclonal antibodies against PECAM-1, inserted at a later stage of I/R, reduced the severity of I/R-associated intestinal dysfunction and decreased the systemic concentrations of IL-1 beta, local leukocyte recruitment (MPO), and partly restored plasma protease inhibitor levels.