Secretory interleukin-1 receptor antagonist gene expression requires both a PU.1 and a novel composite NF-kappaB/PU.1/ GA-binding protein binding site.

The human secretory interleukin-1 receptor antagonist (secretory IL-1Ra) gene is controlled through three lipopolysaccharide (LPS)-responsive promoter elements, one of which was identified as an NF-kappaB binding site. Sequence analysis of the secretory IL-1Ra promoter identified a potential PU.1 binding site located between positions -80 and -90 on the complementary strand overlapping the NF-kappaB site. Gel shift analysis using this potential binding site with nuclear extracts from RAW 264.7 macrophages demonstrated the formation of three complexes, one LPS-inducible and two constitutive. The inducible factor was identified as NF-kappaB, and the constitutive factors were identified as PU.1 and GA-binding protein. Site-directed mutagenesis of the -93 to -79 promoter region demonstrated that mutation of either the NF-kappaB 5'-half site or the PU.1/GA-binding protein half-site alone did not significantly decrease LPS responsiveness. However, a mutation that disrupted the binding of all three factors resulted in a 50% decrease in LPS responsiveness. A second PU.1 binding site centered at -230 was identified by gel shift and supershift assays. Mutation of the core GGAA region resulted in a 50% decrease in LPS-responsive promoter activity. Mutation of both the distal and proximal LPS response elements led to an almost complete loss of responsiveness. These data therefore suggest that the regulation of IL-1Ra gene expression is a complex event involving the interactions of three different transcription factors with a single cis-acting element and that the two PU.1 binding sites are the major response elements for LPS-induced IL-1Ra gene expression.

Involvement of bradykinin B1 and B2 receptors in human PMN elastase release and increase in endothelial cell monolayer permeability.

Bradykinin (BK) is a potent inflammatory mediator, which can release other inflammatory mediators by interacting with bradykinin B1 and B2 receptors. The role of kinins in regulating human PMN elastase release was studied. BK induced elastase release 5-fold over basal levels. Elastase release was inhibited by both B1 and B2 receptor antagonists. A specific B1 agonist des-Arg10-KD increased elastase release 4-fold. Since elastase has been implicated in vascular leak, the effect of BK on endothelial cell monolayer (EM) permeability was assessed. BK increased EM leak (I125 flux) across the EM, whereas des-Arg10-KD was inactive. When co-cultured with human umbilical vein endothelial cells, des-Arg10-KD-treated PMNs increased EM leak by 35%. The elastase inhibitor AAVPK blocked des-Arg10-KD-induced leak by 80% suggesting that elastase is responsible for the increase in permeability. It is concluded that BK causes increased leak by inducing PMN elastase release via activation of both B1 and B2 receptors. BK blockade and elastase inhibition may be beneficial in inflammatory diseases such as ARDS which is characterized by increased lung permeability and both kinin and PMN activation are thought to participate.

Soluble ICAM-1 (sICAM-1) provokes PMN elastase release.

Elevated levels of soluble intercellular adhesion molecule-1 have been shown predictive of post-injury multiple organ failure. We hypothesized that sICAM-1 augments distant organ injury via its affect on the PMN and; thus, have examined neutrophil elastase and superoxide production in response to sICAM-1. To obtain soluble ICAM-1, Chinese Hamster Ovarian (CHO) cells were transfected with human ICAM-1 (cDNA vector CD1.8), lysed and centrifuged at 150,000g for 1 hr; supernatant was passed over an ICAM-1 affinity gradient, eluted with 0.1 mM glycine x HCl, and concentrated using an Amicon Spin-X filter. PMNs were incubated for 1 hr with sICAM-1 at 37 degrees C. Quiescent and PMA-activated PMNs served as negative and positive controls respectively. Elastase activity was measured by the cleavage of methoxy-succinyl-alalyl-alalyl-prolyl-valyl-p-nitroanilide. Superoxide production was determined by superoxide dismutase inhibitive ferricytochrome C reduction over a 5-60 min incubation. PMN incubation with sICAM-1 provoked marked increase in elastase release 10.43 +/- 2.90 (10(-6) U/hr) compared to control 1.64 +/- 0.57, and was equivalent to PMA-activated PMN elastase release 11.60 +/- 1.50 (10(-6) U/hr). In contrast, sICAM-1 alone did not promote spontaneous PMN superoxide production beyond buffer treated PMNs (0.25 +/- 0.09 nmole/2.5 x 10(5) PMN/min). In sum, sICAM-1 stimulates PMN elastase release in vitro. Clinically, this may represent a mechanism by which sICAM-1 participates in the genesis of post-injury multiple organ failure.

Hypoxia/reoxygenation of human endothelium activates PMNs to detach endothelial cells via a PAF mechanism.

Our previous in vivo studies have implicated phospholipase A2 activation and platelet-activating factor (PAF) production as an important mediator of neutrophil (PMN) priming after mesenteric ischemia/reperfusion. Furthermore, our in vitro studies demonstrate that PAF priming of PMN enhances PMN respiratory burst and increases PMN adherence to human umbilical vein endothelial cell cultures (HUVEC). Others have shown that cytokine stimulated HUVEC can activate quiescent PMNs to provoke endothelial cell (EC) monolayer disruption via EC detachment by a noncytolytic PMN protease mechanism. Hypoxia and reoxygenation (H/R) of HUVEC can also directly stimulate PAF production. Consequently, we hypothesized that HUVEC H/R can activate quiescent PMNs to disrupt the EC monolayer (detachment) through a PAF mediated mechanism. HUVEC were labeled with 51 chromium (51Cr) and subjected to 45 min hypoxia (95% N2/5% CO2). PMNs freshly isolated by Percoll gradient centrifugation were added to HUVEC and reoxygenated for 120 min. Additionally, H/R HUVEC with PMN pretreated with WEB2170 (a PAF receptor antagonist) was compared to control (non-H/R HUVEC incubated with PMNs). Wells were washed at end incubation, and adherent ECs counted. Detachment = [total counts - sample counts]/total counts X 100. H/R HUVEC plus PMN provoked a 29.3 +/- 1.6% detachment of EC compared to 9.3 +/- 2.9% detachment in control (non-H/R HUVEC with PMNs). In contrast, H/R HUVEC with PMNs preincubated with WEB2170 had 9.9 +/- 3.8% detachment of EC. In summary, HUVEC H/R activated quiescent PMNs to disrupt an EC monolayer (detachment) via a PAF mechanism.

Interleukin-6 delays neutrophil apoptosis.

BACKGROUND: Neutrophil (PMN) apoptosis promotes the phagocytosis of PMNs without inciting an inflammatory response or local cytotoxic effect. This is important in the normal resolution of inflammatory processes and the control of tissue injury. Conversely, a delay in PMN apoptosis may facilitate PMN-mediated organ dysfunction by extending PMN functional integrity at an inflammatory site. Elevated circulating and tissue levels of interleukin-6 (IL-6) have been associated with postinjury organ dysfunction, and IL-6 appears to augment PMN cytotoxic functions. Therefore, we hypothesized that IL-6 delays PMN apoptosis, thereby enhancing PMN-mediated cytotoxicity. METHODS: Neutrophils isolated from healthy human donors were incubated for 24 hours in enriched RPMI 1640 cell culture medium at 37 degrees C in 5% carbon dioxide. Subgroups were incubated with IL-6, heat-denatured IL-6, or buffer alone. Apoptosis was assessed morphologically using acridine orange-ethidium bromide stain, and biochemically by DNA gel electrophoresis. Functional capacity of PMNs was assessed by superoxide generation after activation with phorbol myristate acetate or platelet-activating factor plus formyl-methionyl-leucyl-phenylalanine. RESULTS: Treatment with IL-6 resulted in a greater population of surviving (nonapopototic) PMNs after 24 hours. In addition, the IL-6-treated population produced more superoxide after 24 hours than did the untreated or heat-denature IL-6-treated groups, after either activating stimulus. CONCLUSIONS: Interleukin-6 delays PMN apoptosis, resulting in a larger population of surviving PMNs with a greater collective capacity for superoxide production. This could potentially facilitate PMN-mediated tissue injury and may be a mechanism whereby IL-6 contributes to organ dysfunction.

Intercellular adhesion molecule-1 promotes neutrophil-mediated cytotoxicity.

BACKGROUND: Interaction of the CD11/CD18 complex on polymorphonuclear neutrophils (PMNs) and intercellular adhesion molecule (ICAM)-1 on endothelium is a critical event in PMN-mediated tissue injury. In addition, increased expression of ICAM-1 on type I pneumocytes has been identified in a variety of pulmonary disorders associated with PMN-induced inflammation. We hypothesized that ICAM-1 up-regulation is sufficient to promote cytotoxicity via activated PMNs. METHODS: The complementary DNA for human ICAM-1 was transfected into Chinese hamster ovarian (CHO) cells, which do not inherently express this adhesion receptor, by using the expression vector CD1.8. Fluorescence-activated cell sorter analysis revealed 62% CHO cell surface expression of ICAM-1. Wild type and transfected CHO cells were labeled with chromium 51 and exposed to quiescent or activated (1 mumol/L phorbol myristate acetate) PMNs for 4 hours. Subsets were pretreated with a monoclonal antibody to ICAM-1. PMN cytotoxicity was determined by specific percent 51Cr release. RESULTS: Incubation of quiescent PMNs with wild type and transfected CHO cells produced nominal cell lysis, 0.5% +/- 0.3% and 0.2% +/- 0.2%, respectively. Activated PMNs produced 13.6% +/- 3.2% versus 1.4% +/- 0.7% cell lysis, comparing transfected with wild type CHO cells, and 0.5% +/- 0.2% cell lysis after pretreatment with a monoclonal antibody to ICAM-1, p < 0.01. CONCLUSIONS: ICAM-1 up-regulation is sufficient to promote cytotoxicity via activated PMNs. This may represent a potential target for attenuating PMN-mediated injury to endothelial and other cell lines, including parenchyma.

Interleukin-8 increases endothelial permeability independent of neutrophils.

Interleukin-8 (IL-8) has been associated with a variety of hyperinflammatory states and adverse clinical events. Circulating IL-8 levels correlate with the severity of tissue trauma, and excessive elevations of IL-8 are associated with postinjury adult respiratory distress syndrome and multiple organ failure. While IL-8 is a potent neutrophil (PMN) chemoattractant and activator and enhances PMN transendothelial migration, it also acts to inhibit PMN adhesion to stimulated endothelial cells (ECs). We hypothesized that IL-8 could interact directly with ECs to increase permeability independent of PMNs. Human umbilical vein ECs (HUVECs) were cultured on collagen-coated micropore filters, and integrity of the EC monolayer measured by albumin flux across the filter. Cytochalasin D was used as a positive control. IL-8 induced increased permeability at a concentration of 1000 ng/mL. This effect was abrogated by preincubation of HUVECs with a protein synthesis inhibitor (cycloheximide). These data suggest a role for IL-8 in promoting endothelial leak independent of PMNs, via a mechanism involving protein synthesis.

Gut phospholipase A2 mediates neutrophil priming and lung injury after mesenteric ischemia-reperfusion.

Intestinal ischemia-reperfusion (I/R) provokes polymorphonuclear neutrophil (PMN)-mediated lung injury via a process characterized by circulating PMN priming, pulmonary PMN sequestration, and increased microvascular leak in the lung. We found in rats subjected to intestinal I/R (ischemia 45 min and reperfusion 6 h) that 1) intestinal phospholipase A2 (PLA2) was activated during ischemia, 2) circulating PMN priming (assessed by superoxide production with N-formyl-Met-Leu-Phe) occurred after 1 h reperfusion, and 3) exaggerated 125I-labeled albumin lung leak occurred after 2 h reperfusion, compared with sham-treated animals (P < 0.05). Treatment with a PLA2 inhibitor, quinacrine, within 15 min of reperfusion reversed the exaggerated gut PLA2 activity and abrogated subsequent PMN priming and lung leak (P < 0.05). However, when quinacrine was administered after 2 h of reperfusion, circulating PMN priming and lung leak continued to evolve despite suppression of intestinal PLA2 activity. We conclude that intestinal PLA2 activation may be a prerequisite for the sequelae of circulating PMN priming and pulmonary microvascular leak observed after intestinal I/R.

Interleukin-6 potentiates neutrophil priming with platelet-activating factor.

BACKGROUND: Polymorphonuclear neutrophil (PMN) priming appears to be an important event in the pathogenesis of hyperinflammatory states, resulting in adult respiratory distress syndrome or multiple organ failure. Interleukin-6 (IL-6) is an integral mediator of the acute stress response to injury and infection, but excessive and prolonged systemic levels have been associated with morbidity and mortality following trauma, burns, and elective surgery. We hypothesized that IL-6 primed PMNs for exaggerated cytotoxicity. However, we have been unable to directly prime PMNs for superoxide release with IL-6. OBJECTIVE: To determine whether IL-6 acted in concert with another inflammatory mediator (platelet-activating factor [PAF]) to prime PMNs. METHODS: Polymorphonuclear neutrophils isolated from healthy human donors were incubated for varying times with IL-6 (0.01 to 100 ng/mL), PAF (0.01 to 100 ng/mL), or a combination of IL-6 and PAF. Superoxide production was then measured with and without the addition of the PMN-activating formylpeptide formyl-methionyleucylphenylalanine. RESULTS: Over the range of times (5 to 90 minutes) and doses tested, IL-6 did not prime PMNs, while PAF primed PMNs in a dose- and time-dependent manner. Interleukin 6 (10 ng/mL) combined with a nonpriming concentration of PAF (0.1 ng/mL) primed PMNs for superoxide production over a range of incubation times. CONCLUSION: The inflammatory mediators IL-6 and PAF act synergistically to prime PMNs in vitro. This observation may begin to elucidate the mechanistic role of IL-6 in pathologic clinical states.

Gut ischemia/reperfusion produces lung injury independent of endotoxin.

OBJECTIVE: Bacterial translocation from the gut has been invoked as a common inciting event for postinjury multiple organ failure. We previously showed that gut ischemia/reperfusion induces remote organ injury. The purpose of this study was to ascertain if endotoxin has a pivotal mechanistic role in this process. DESIGN: Prospective, randomized study. SETTING: Animal laboratory. SUBJECTS: Sprague-Dawley rats weighing 300 to 350 g. INTERVENTIONS: Anesthetized animals underwent 45 mins of superior mesenteric artery occlusion and 2 hrs of reperfusion; sham laparotomy served as controls. Endotoxin was eliminated with the murine immunoglobulin (Ig) M antibody E5, 3 mg/kg i.v. before the study. MEASUREMENTS AND MAIN RESULTS: Plasma endotoxin was measured by the limulus amebocyte lysate assay. At 2 hrs of reperfusion, circulating neutrophil priming was determined by the difference in superoxide generation with and without the activating stimulus, N-formyl-Met-Leu-Phe. Neutrophil sequestration in the lung was quantitated by myeloperoxidase activity, and by lung endothelial permeability by 125I albumin lung/blood ratio. Endotoxin concentrations were not significantly (significance determined as p < .05) different between the gut ischemia/reperfusion and laparotomy groups (n = > or = 5) during ischemia or reperfusion. Circulating neutrophil priming, neutrophil accumulation in the lung, and lung injury were provoked by gut ischemia/reperfusion, but not altered by endotoxin elimination. CONCLUSION: Gut ischemia/reperfusion primes circulating neutrophils and produces lung injury by a mechanism independent of endotoxin.

Disparate signal transduction in neutrophil CD18 adhesion receptor expression versus superoxide generation.

BACKGROUND: We have previously shown that platelet-activating factor (PAF) primes polymorphonuclear neutrophils (PMNs) for superoxide generation and, concurrently, increases CD11/CD18 receptor expression; both events appear central to the pathogenesis of postinjury multiple organ failure. Recently, the counterinflammatory role of the neuroendocrine response to trauma has been emphasized, and, specifically, beta-adrenergic stimulation has been found to inhibit PMN activation. METHODS: Normal human PMNs were primed with PAF (10(-9) mol/L for 5 minutes) or pretreated with beta-receptor stimulation (isoproterenol, 10(-7) mol/L) or adenylate cyclase (AC) activation (forskoklin, 10(-7) mol/L) for 5 minutes and then primed with PAF. Superoxide generation in response to N-formyl-methionyl-leucyl-phenylalanine (10(-6) mol/L) was measured by superoxide dismutase inhibitable reduction of cytochrome C and CD18 expression determined by flow cytometry. RESULTS: PAF primed PMNs for superoxide generation (229.5 +/- 42.3 nmol/10(6) cells/min versus 18.7 +/- 6.5), whereas pretreatment with beta-adrenoreceptor stimulation (112.9 +/- 20.6) or AC activation (115.3 +/- 12.6) dramatically attenuated this process (p < 0.0001). PAF also enhanced CD18 expression (6.1 +/- 1.1 mean fluorescence intensity versus 10.3 +/- 2.3), but beta-adrenoreceptor stimulation (10.1 +/- 2.1) and AC activation (9.7 +/- 1.9) had no discernible effect. CONCLUSIONS: PAF priming of PMNs for superoxide generation was inhibited by the beta-adrenergic signal transduction pathway, but CD18 expression was not regulated via this pathway.

Platelet-activating factor-induced polymorphonuclear neutrophil priming independent of CD11b adhesion.

BACKGROUND: Our previous studies have implicated phospholipase A2-dependent platelet-activating factor (PAF) production in the genesis of polymorphonuclear neutrophil (PMN)-mediated tissue injury after gut ischemia-reperfusion. Further, these studies have suggested a discordance of PMN sequestration and tissue injury. CD11B-dependent PMN-endothelial cell adhesion has been purported to play a dominant role in PMN-mediated tissue injury. We therefore undertook this study with the hypothesis that PAF-induced PMN superoxide production requires CD11B-mediated PMN-endothelial cell adherence. METHODS: Human PMNs, isolated by Percoll gradient centrifugation, were exposed to PAF (10 ng/ml). At fixed times of exposure during 120 minutes, (1) superoxide production, (2) CD11B receptor expression, and (3) PMN adhesion to unstimulated human umbilical vein endothelial cell cultures were assayed. RESULTS: PAF induced prompt changes in PMN priming (increased superoxide production after N-formyl-methyl-leucyl-phenylalanine activation), adhesion to unstimulated endothelial cells, and CD11B receptor expression. Priming was temporally concordant with the rise and fall of CD11B expression but appeared to precede adhesion. CD11B blockade (F(Ab') 2 anti-CD11B [60.1] antibodies), before or at maximal PAF priming, reduced PMN adhesion but had no effect on superoxide production. CONCLUSIONS: In summary, PAF-induced PMN priming occurs in temporal concordance with the expression of CD11B and subsequent endothelial cell adherence, but CD11B-mediated adherence is not essential for this process.

Gut ischemia mediates lung injury by a xanthine oxidase-dependent neutrophil mechanism.

Neutrophils (PMNs) are believed to play a key role in the pathogenesis of postinjury adult respiratory distress syndrome. We have previously shown that gut ischemia/reperfusion (I/R) produces lung injury by a process that requires PMNs. More recently, we have shown that xanthine oxidase (XO) plays a role. The purpose of this study was to characterize the mechanistic sequencing of XO activity versus the PMN in this model of gut I/R-induced lung injury. Normal and XO-inactivated (tungsten enriched, molybdenum depleted diet) rats underwent 45 min of superior mesenteric artery occlusion. After 6 hr reperfusion, blood was sampled and gut and lungs harvested. Myeloperoxidase (MPO) was used to quantitate PMN presence in the gut and lungs, while circulating PMN priming was measured as the difference in superoxide production with and without the activating stimulus, fMLP. 125I-labeled albumin leak was used as a marker for lung endothelial permeability. We observed that the gut I/R increased gut MPO levels, primed circulating PMNs, increased lung MPO levels, and provoked distant lung leak. XO inactivation abolished gut MPO activity, attenuated circulating PMN priming, and blocked lung leak. In conclusion, XO plays a proximal role in the pathogenesis of remote organ injury following splanchnic hypoperfusion.

Phospholipase A2 inhibition decouples lung injury from gut ischemia-reperfusion.

BACKGROUND: Phospholipase A2 (PLA2) has recently been implicated as a key enzyme of local inflammation after gut ischemia-reperfusion (I/R). The hypothesis of this study is that PLA2 inhibition decouples remote organ injury from gut I/R. METHODS: Sprague-Dawley rats were pretreated with a PLA2 inhibitor, quinacrine (10 mg/kg, intravenously), before the induction of gut ischemia (45 minutes of superior mesenteric artery occlusion) followed by 6 hours of reperfusion. 125I-labeled albumin leak was employed as a marker of pulmonary endothelial permeability and myeloperoxidase as a monitor of neutrophil (PMN) traffic in the gut and lung. To further characterize the impact of PLA2 inhibition, PMNs were harvested at 6 hours of reperfusion and superoxide production was measured in the presence or absence of an activating stimulus, N-formyl-methionyl-leucyl-phenylalanine. RESULTS: Gut I/R increased gut PLA2 activity, elicited gut PMN influx, and produced lung leak; these events were prevented by PLA2 blockade. Gut I/R also markedly enhanced PMN superoxide production with N-formyl-methionyl-leucyl-phenylalanine, and this priming was ablated by PLA2 inhibition. CONCLUSION: These data suggest that PLA2 activation is a proximal step in the pathogenesis of distant organ injury after splanchnic hypoperfusion, a process that appears to involve PMN priming in the gut bed.