The leukocyte-stiffening property of plasma in early acute respiratory distress syndrome (ARDS) revealed by a microfluidic single-cell study: the role of cytokines and protection with antibodies

Background

Leukocyte-mediated pulmonary inflammation is a key pathophysiological mechanism involved in acute respiratory distress syndrome (ARDS). Massive sequestration of leukocytes in the pulmonary microvasculature is a major triggering event of the syndrome. We therefore investigated the potential role of leukocyte stiffness and adhesiveness in the sequestration of leukocytes in microvessels. 

Methods

This study was based on in vitro microfluidic assays using patient sera. Cell stiffness was assessed by measuring the entry time (ET) of a single cell into a microchannel with a 6 × 9–μm cross-section under a constant pressure drop (ΔP = 160 Pa). Primary neutrophils and monocytes, as well as the monocytic THP-1 cell line, were used. Cellular adhesiveness to human umbilical vein endothelial cells was examined using the laminar flow chamber method. We compared the properties of cells incubated with the sera of healthy volunteers (n = 5), patients presenting with acute cardiogenic pulmonary edema (ACPE; n = 6), and patients with ARDS (n = 22), of whom 13 were classified as having moderate to severe disease and the remaining 9 as having mild disease. 

Results

Rapid and strong stiffening of primary neutrophils and monocytes was induced within 30 minutes (mean ET >50 seconds) by sera from the ARDS group compared with both the healthy subjects and the ACPE groups (mean ET <1 second) (p < 0.05). Systematic measurements with the THP-1 cell line allowed for the establishment of a strong correlation between stiffening and the severity of respiratory status (mean ET 0.82 ± 0.08 seconds for healthy subjects, 1.6 ± 1.0 seconds for ACPE groups, 10.5 ± 6.1 seconds for mild ARDS, and 20.0 ± 8.1 seconds for moderate to severe ARDS; p < 0.05). Stiffening correlated with the cytokines interleukin IL-1β, IL-8, tumor necrosis factor TNF-α, and IL-10 but not with interferon-γ, transforming growth factor-β, IL-6, or IL-17. Strong stiffening was induced by IL-1β, IL-8, and TNF-α but not by IL-10, and incubations with sera and blocking antibodies against IL-1β, IL-8, or TNF-α significantly diminished the stiffening effect of serum. In contrast, the measurements of integrin expression (CD11b, CD11a, CD18, CD49d) and leukocyte–endothelium adhesion showed a weak and slow response after incubation with the sera of patients with ARDS (several hours), suggesting a lesser role of leukocyte adhesiveness compared with leukocyte stiffness in early ARDS. 

Conclusions

The leukocyte stiffening induced by cytokines in the sera of patients might play a role in the sequestration of leukocytes in the lung capillary beds during early ARDS. The inhibition of leukocyte stiffening with blocking antibodies might inspire future therapeutic strategies.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-015-1157-5) contains supplementary material, which is available to authorized users.

Activation of nicotinic cholinergic receptors prevents ventilator-induced lung injury in rats

Respiratory distress syndrome is responsible for 40 to 60 percent mortality. An over mortality of about 10 percent could result from additional lung injury and inflammation due to the life-support mechanical ventilation, which stretches the lung. It has been recently demonstrated, in vitro, that pharmacological activation of the alpha 7 nicotinic receptors (α7-nAChR) could down regulate intracellular mediators involved in lung cell inflammatory response to stretch. Our aim was to test in vivo the protective effect of the pharmacological activation of the α7-nAChR against ventilator-induced lung injury (VILI). Anesthetized rats were ventilated for two hours with a high stretch ventilation mode delivering a stroke volume large enough to generate 25-cmH₂O airway pressure, and randomly assigned to four groups: pretreated with parenteral injection of saline or specific agonist of the α7-nAChR (PNU-282987), or submitted to bilateral vagus nerve electrostimulation while pre-treated or not with the α7-nAChR antagonist methyllycaconitine (MLA). Controls ventilated with a conventional stroke volume of 10 mL/kg gave reference data. Physiological indices (compliance of the respiratory system, lung weight, blood oxygenation, arterial blood pressure) and lung contents of inflammatory mediators (IL-6 measured by ELISA, substance P assessed using HPLC) were severely impaired after two hours of high stretch ventilation (sham group). Vagal stimulation was able to maintain the respiratory parameters close to those obtained in Controls and reduced lung inflammation except when associated to nicotinic receptor blockade (MLA), suggesting the involvement of α7-nAChR in vagally-mediated protection against VILI. Pharmacological pre-treatment with PNU-282987 strongly decreased lung injury and lung IL-6 and substance P contents, and nearly abolished the increase in plasmatic IL-6 levels. Pathological examination of the lungs confirmed the physiological differences observed between the groups. In conclusion, these data suggest that the stimulation of α7-nAChR is able to attenuate VILI in rats.

[Lemierre's syndrome from necrotizing pneumonia treated with extracorporeal CO2 removal]

We report a case of Lemierre's syndrome complicated with pulmonary septic abscesses, leading to necrotizing pneumonia. In spite of administration of appropriate antibiotics and a protective ventilation strategy, the patient had several bilateral pneumothoraces. In this setting, the mechanical ventilation was unsuccessful leading to two hypoxia-related cardiac arrests. An extracorporeal CO(2) removal was then carried out for 34-days duration. The patient was weaned from mechanical ventilation on day 68. He was then transferred to the chest surgery unit on day 83.

Prone positioning during veno-venous extracorporeal membrane oxygenation for severe acute respiratory distress syndrome in adults

BACKGROUND

Veno-venous extracorporeal membrane oxygenation (VV-ECMO) is an effective rescue therapy for improving oxygenation in selected severe acute respiratory distress syndrome (ARDS). Prone position (PP) is usually considered before vvECMO and few data are available on the association of PP during VV-ECMO. Thus, we investigated the effect on oxygenation and the safety of PP during vvECMO.

METHODS

During a two-year period, 15 patients with severe ARDS were turned into PP during VV-ECMO therapy for at least one of the three following conditions: severe hypoxemia (PaO2/FiO2 ratio below 70) despite maximal oxygenation, injurious ventilation parameters with plateau pressure exceeding 32 cmH2O or failure of attempt to wean ECMO after at least 10 days on ECMO support.

RESULTS

PP was considered after a median of 9 days of ECMO and applied for a median of 12 hours and an average of 1.4 sessions per patient resulting in a total of 21 procedures. We found significant improvement in PaO2/FiO2 ratio at 6 hours (P=0.03) and 12 hours (P=0.007) after reversal. The improvement in oxygenation has still persisted 1hour (P=0.017) and 6 hours (P=0.013) after back to the supine position. No change in PaCO2, respiratory system (RS) compliance was observed. ECMO flow was maintained constant during the procedure. No complication related to PP was detected.

CONCLUSION

PP may be considered in selected patients difficult to wean or remaining very hypoxemic despite VV-ECMO support.