Cross-transfusion of postshock mesenteric lymph provokes acute lung injury

OBJECTIVE

Substantial investigation has implicated mesenteric lymph as the mechanistic link between gut ischemia/reperfusion (I/R) and distant organ injury. Specifically, lymph diversion prevents acute lung injury (ALI) in vitro, and bioactive lipids and proteins isolated from postshock mesenteric lymph (PSML) maintain bioactivity in vitro. However, Koch's postulates remain to be satisfied via direct cross-transfusion into a naïve animal. We therefore hypothesized that real time cross-transfusion of postshock mesenteric lymph provokes acute lung injury.

METHODS

One set of Sprague-Dawley rats (lymph donors) was anesthetized, with the mesenteric lymph ducts cannulated and exteriorized to drain freely into a siliconates plastic cup; concurrently, a second group of rats ( lymph recipients) was anesthetized, with a cannula inserted into the animal's right internal jugular vein. Blood was removed from the donor rats to induce hemorrhagic shock (MAP of 35 mmHg × 45 min). The recipient rats were positioned 10 cm below the plastic cup, which emptied into the jugular vein cannula. Thus, mesenteric lymph from the shocked donor rat was delivered to the recipient rat at the rate generated during shock and the subsequent 3 h of resuscitation.

RESULTS

Neutrophil (PMN) accumulation in the lungs was substantially elevated in the postshock lymph cross-transfusion group compared to both sham lymph cross-transfusion and instrumented control (MPO: 9.42 ± 1.55 versus 2.81 ± 0.82 U/mg lung tissue in postshock versus sham lymph cross-transfusion, n = 6 in each group, P = 0.02). Additionally, cross-transfusion of PSML induced oxidative stress in the lung (0.21 ± 0.03 versus 0.10 ± 0.01 micromoles MDA per mg lung tissue in lymph cross-transfusion versus instrumented control, n = 6 in each group, P = 0.046). Furthermore, transfusion of PSML provoked lung injury (BAL protein 0.77 ± 0.18 versus 0.15 ± 0.02 mg/mL protein in BALF, postshock versus sham lymph cross-transfusion, n = 6 in each group, P = 0.004).

CONCLUSION

Cross-transfusion of PSML into a naïve animal leads to PMN accumulation and provokes ALI. These data provide evidence that postshock agents released into mesenteric lymph are capable of provoking distant organ injury.

Pulmonary edema fluid from patients with early lung injury stimulates fibroblast proliferation through IL-1 beta-induced IL-6 expression

Although the fibroproliferative response to lung injury occurs with a high frequency in patients with clinical acute lung injury, the mechanisms that initiate this response are largely unknown. This study was undertaken first to identify fibroblast mitogenic factors in pulmonary edema fluid, and second to examine the human lung fibroblast's gene expression profile in response to pulmonary edema fluid. The edema fluid obtained from patients with early lung injury has an eightfold higher concentration of IL-1beta and a twofold greater IL-1beta-dependent mitogenic effect than does fluid obtained from control patients with hydrostatic pulmonary edema. Furthermore, fibroblasts responded to acute lung injury patient-derived edema fluid through production of soluble mediators that possess an autocrine mitogenic effect. Gene array analysis reveals that acute lung injury edema fluid induces several inflammation-modulating and proliferation-related genes in fibroblasts, whose inductions are similarly dependent on bioactive IL-1beta. Most notably, the 20-fold induction of IL-6 mRNA and protein was completely blocked by IL-1 receptor antagonist. The combined addition of IL-1beta and IL-6 was mitogenic, and the proliferative response to conditioned medium from IL-1beta-exposed cells was blocked by antagonistically acting Abs to IL-6 or to gp130. These novel findings indicate that soluble IL-1beta bioactivity and autocrine IL-1beta-dependent IL-6 up-regulation are critical initiators of fibroblast activation and proliferation and that they likely play a role in the fibroproliferative response seen in human acute lung injury.

Exhaled breath condensate in children: pearls and pitfalls

Exhaled breath condensate (EBC) is a rapidly growing field of research in respiratory medicine. Airway inflammation is a central feature of chronic lung diseases, like asthma, cystic fibrosis, bronchopulmonary dysplasia and primary ciliary dyskinesia. EBC may be a useful technique for non-invasive assessment of markers of airway inflammation. The non-invasive character of EBC "inflammometry" and the general lack of appropriate techniques makes it particularly interesting for paediatrics. We provide a detailed update on the methods currently used for EBC collection and measurement of mediators. We emphasize on paediatric data. The apparent simplicity of the EBC method must not be overstated, as numerous methodological pitfalls have yet to overcome. Comparison and interpretation of data on this rapidly growing field of research is mainly hampered by the lack of standardization and the lack of specific high-sensitivity immunochemical or colorimetric assays. The initiative of the European Respiratory Society to institute a task force on this topic is a first step towards a uniform technique of EBC. Meanwhile, when using this technique or when interpreting research data, one should be fully aware of the possible methodological pitfalls.

Proinflammatory activity of anti-IL-8 autoantibody:IL-8 complexes in alveolar edema fluid from patients with acute lung injury

A significant fraction of IL-8 in lung fluids from patients with the acute lung injury (ALI) is associated with anti-IL-8 autoantibodies (anti-IL-8:IL-8 complexes), and lung fluid concentrations of these complexes correlate with development and outcome of ALI. In this study, we examined whether anti-IL-8:IL-8 complexes exhibit proinflammatory activity in vitro. These complexes were purified from pulmonary edema fluid samples obtained from patients with ALI. First, we found that IL-8 bound to the autoantibody retained its ability to trigger chemotaxis of neutrophils, whereas control antibody did not have significant chemotactic activity. Next, we examined the ability of anti-IL-8:IL-8 complexes to induce neutrophil activation, i.e., neutrophil respiratory burst and degranulation. Anti-IL-8:IL-8 complexes triggered superoxide and myeloperoxidase release from human neutrophils, and in contrast, the control antibody had no effect. We also demonstrated that IgG receptor, FcgammaRIIa, is the receptor involved in cellular activation mediated by these complexes. Blockade of FcgammaRIIa completely reverses activity of the complexes with the exception of chemotaxis. Both FcgammaRIIa and IL-8 receptors mediate chemotactic activity of anti-IL-8:IL-8 complexes, with FcgammaRIIa being, however, a predominant receptor. Furthermore, activity of the complexes is partially dependent on the activation of the mitogen-activated protein kinases, i.e., ERK and p38, important components of the FcgammaRIIa signaling cascade. Anti-IL-8:IL-8 complexes may therefore be involved in the pathogenesis of lung inflammation in clinical acute lung injury.

Activity of pulmonary edema fluid interleukin-8 bound to alpha(2)-macroglobulin in patients with acute lung injury

The formation of alpha(2)-macroglobulin (alpha(2)-M)/interleukin-8 (IL-8) complexes may influence the biological activity of IL-8 and the quantitative assessment of IL-8 activity. Therefore, in this study, concentrations of free IL-8 and IL-8 complexes with alpha(2)-M were measured in pulmonary edema fluid samples from patients with acute lung injury/acute respiratory distress syndrome (ALI/ARDS) and compared with control patients with hydrostatic pulmonary edema. Patients with ALI/ARDS had significantly higher concentrations of alpha(2)-M (P < 0.01) as well as alpha(2)-M/IL-8 complexes (P < 0.05). Because a substantial amount of IL-8 is complexed to alpha(2)-M, standard assays of free IL-8 may significantly underestimate the concentration of biologically active IL-8 in the distal air spaces of patients with ALI/ARDS. Furthermore, IL-8 bound to alpha(2)-M retained its biological activity, and this fraction of IL-8 was protected from proteolytic degradation. Thus complex formation may modulate the acute inflammatory process in the lung.

Estimate of the subepithelial hydrostatic pressure that drives inflammatory transudate into the airway lumen

Inflammatory diseases of the upper respiratory tract are characterized by flow of plasma filtrate across the epithelium into the airway lumen ("transudation"). Elsewhere, we have proposed that extravasation from microvessels causes edema, and this is associated with elevated subepithelial hydrostatic pressure that drives transudation. To test this hypothesis, we have attempted to block transudation by elevating luminal hydrostatic pressure. We measured the appearance of plasma markers into the lumen of an isolated perfused segment of rat trachea in vivo and found that stimulation of one vagal nerve caused a rapid (half-time approximately 5 min) and nonselective increase in the flow of markers from blood to airway lumen. Leukocyte migration also caused transudation that developed much more slowly (half-time = 2-3 h). In both cases, transudation was blocked by application of luminal hydrostatic pressures. The critical luminal pressure needed to block vagally induced transudation was approximately 4.5 cmH2O, and, to block epithelial transudation induced by leukocyte traffic, it was 3 cmH2O, and we conclude that these are the subepithelial pressures that drive inflammatory transudation into the airway lumen.

Comparable effects of HOCl and of FMLP-stimulated PMN on the circulation in an isolated lung model

Polymorphonuclear leukocytes (PMN) are involved in acute lung injury during adult respiratory distress syndrome (ARDS) via several mechanisms. This study focuses on neutrophil-derived oxidative stress. The influence of (A), continuous hypochlorous acid (HOCl) infusion over 105 min and (B) stimulation of PMN having been delayed in the pulmonary microvasculature were studied. Therefore pulmonary artery pressure (PAP), capillary filtration coefficient (Kf,c), and fluid retention (delta W) were monitored using isolated rabbit lungs. These models (A/B) were compared with each other to assess the reproducibility of neutrophil-derived oxidative stress by HOCl. A: Infusion of 250/500/1,000/2,000 nmol/min HOCl (n = 6/group) evoked a delta PAPmax of 0.4 +/- 0.07/2.4 +/- 0.21/4.9 +/- 0.29/4.6 +/- 0.25 mm Hg at 105/105/56.4 +/- 5.6/21.5 +/- 0.8 min and a tenfold increase in Kf,c/delta W at 60 min. B: Stimulation of PMN (1,480 +/- 323/microliter, n = 8), which were added into the perfusate and sequestrated in the microvasculature, with 1 microM FMLP resulted in a delta PAPmax = 8.4 +/- 1.1 torr (t = 3.7 +/- 0.19 min) and a twofold increase in Kf,c/delta W (t = 60 min) that were accompanied by a myeloperoxidase (MPO)-release (MPOmax = 56.1 +/- 7.3 mU/l, after 1 to 3 min). There was a strong correlation between delta PAPmax and MPOmax (r = 0.97, p < 0.01). Both models of neutrophil-derived oxidative stress evoked changes in pulmonary circulation providing evidence for an involvement of PMN via their major oxidant HOCl in pulmonary hypertension and edema during ARDS.

Local Pseudomonas instillation induces contralateral lung injury and plasma cytokines

We investigated whether local bacterial instillation leads to lung injury in noninstilled lung regions and examined local and systemic cytokine accumulation. Rats were challenged by intrabroncheal instillation of Pseudomonas aeruginosa, 10(7) colony-forming units (CFU) (HD group, n = 11), 4 x 10(6) CFU (LD group, n = 10), or saline (control group, n = 12). 99mTc-labeled macroaggregated albumin was added to the P. aeruginosa or saline solution for later documentation of the instilled area. At 4 h the right lung, including instilled segment, and the left lung were sampled. Lung injury was assessed by lung tissue to plasma 125I-labeled albumin (T/P) and lung wet-dry (W/D) ratios. We measured plasma and bronchoalveolar lavage fluid (BALF) levels of tumor necrosis factor (TNF) and cytokine-induced neutrophil chemoattractant (CINC). HD bacterial instillation induced neutrophil recruitment and TNF and CINC elevation in BALF (p < 0.05) associated with increased T/P (p < 0.005) and W/D (p < 0.05) ratios in both instilled and the noninstilled lungs as compared with the saline-instilled and noninstilled controls. LD bacterial instillation induced neutrophil recruitment and TNF and CINC elevation only in the instilled lung (p < 0.05), and not in the noninstilled lung, and did not increase the T/P or W/D ratio. Plasma levels of TNF and CINC were increased in the HD, but not the LD, group when compared with the saline controls (p < 0.05). These data indicate that, when the dose is high enough to cause an excess inflammatory response, local bacterial instillation leads to neutrophil sequestration, lung injury, and cytokine elevation in the noninstilled lung associated with systemic cytokine release.