Smoke/burn injury-induced respiratory failure elicits apoptosis in ovine lungs and cultured lung cells, ameliorated with arteriovenous CO2 removal

SOCS-1 ameliorates smoke inhalation-induced acute lung injury through inhibition of ASK-1 activity and DISC formation

Smoke inhalation leads to acute lung injury (ALI), a devastating clinical problem associated with high mortality. Suppressor of cytokine signaling-1 (SOCS-1) is a negative regulator of apoptosis and pro-inflammatory cytokine signaling, two major contributors to the pathogenesis of ALI. We have found that SOCS-1 protects lung epithelial cells from smoke-induced apoptosis through two mechanisms. One is that SOCS-1 enhances degradation of ASK-1 and diminishes cleavage of pro-caspase-3 to repress smoke-triggered apoptosis in lung epithelial cells. The other is that SOCS-1 represses smoke-triggered DISC formation through altering TRADD-caspase-8 interaction rather than TNFR-1-TRADD interaction or TNFR-1-TRAF-2 interaction. In conclusion, SOCS-1 relieves smoke inhalation-induced lung injury by repressing ASK-1 and DISC-mediated epithelium apoptosis.

Inflammatory Mediators in Tracheal Aspirates of Preterm Infants Participating in a Randomized Trial of Permissive Hypercapnia

BACKGROUND

Ventilator-induced lung injury is considered to be a main factor in the pathogenesis of bronchopulmonary dysplasia (BPD). Optimizing ventilator strategies may reduce respiratory morbidities in preterm infants. Permissive hypercapnia has been suggested to attenuate lung injury. We aimed to determine if a higher PCO₂ target range results in less lung injury compared to the control target range and possibly reduces pro-inflammatory cytokines and acid sphingomyelinase (ASM) in tracheal aspirates (TA), which has not been addressed before.

METHODS

During a multicenter trial of permissive hypercapnia in extremely low birthweight infants (PHELBI), preterm infants (birthweight 400-1,000 g, gestational age 23 0/7-28 6/7 weeks) requiring mechanical ventilation within 24 h of birth were randomly assigned to a high PCO₂ target or a control group. The high target group aimed at PCO₂ values of 55-65, 60-70, and 65-75 mmHg and the control group at PCO₂ values of 40-50, 45-55 and 50-60 mmHg on postnatal days 1-3, 4-6, and 7-14, respectively. TA was analyzed for pro-inflammatory cytokines from postnatal day 2-21. BPD was determined at a postmenstrual age of 36 weeks ± 2 days.

MAIN FINDINGS

Levels of inflammatory cytokines and ASM were similar in both groups: interleukin (IL)-6 (p = 0.14), IL-8 (p = 0.43), IL-10 (p = 0.24), IL-1β (p = 0.11), macrophage inflammatory protein 1α (p = 0.44), albumin (p = 0.41), neuropeptide Y (p = 0.52), leukotriene B₄ (p = 0.11), transforming growth factor-β₁ (p = 0.68), nitrite (p = 0.15), and ASM (p = 0.94). Furthermore, most inflammatory mediators were strongly affected by the age of the infants and increased from postnatal day 2 to 21. BPD or death was observed in 14 out of 62 infants, who were distributed evenly between both groups.

CONCLUSION

The results suggest that high PCO₂ target levels did not result in lower pulmonary inflammatory activity and thus reflect clinical results. This indicates that high PCO₂ target ranges are not effective in reducing ventilator-induced lung injury in preterm infants, as compared to control targets.

TRIAL REGISTRATION

ISRCTN56143743.

Seventy-two hour gas exchange performance and hemodynamic properties of NOVALUNG®iLA as a gas exchanger for arteriovenous carbon dioxide removal

Objective: Acute respiratory failure is complicated by acidosis and altered end-organ perfusion. NOVA-LUNG®iLA is an interventional lung assist (ILA) device for arteriovenous carbon dioxide removal (AVCO2R). The present study was conducted to evaluate the device for short-term CO2 removal performance and hemodynamic response.

Methods: Six adult sheep received cannulation of the jugular vein and carotid artery. The ILA-AVCO2R circuit was placed on the sheep for 72 hours. Hemodynamics and PaCO2 were measured; CO2 removal was calculated while varying sweep gas flow rates (Qg), device blood flow rates (Qb), and PaCO2.

Results: Hemo-dynamic variables remained normal throughout the 72 hour study. CO2 removal increased with increases in Qgor Qb. Mean CO2 removal was 119.3 ml/min for Qb 1L/min, Qg 5 L/min, and PaCO2 40 - 50 mmHg.PaCO2 was directly proportional to CO2 clearance (R-0.72, p B/0.001).

Conclusion: NOVALUNG®iLA can provide near total CO2 removal with Qb 1 - 2 L/min,Qg 5 L/min, and minimal flow resistance (3.889/0.82 mmHg/L/min). PaCO2 correlates with CO2 removal and is dependent on Qb and Qg.

Immobilized Carbonic Anhydrase on Hollow Fiber Membranes Accelerates CO(2) Removal from Blood

Current artificial lungs and respiratory assist devices designed for carbon dioxide removal (CO(2)R) are limited in their efficiency due to the relatively small partial pressure difference across gas exchange membranes. To offset this underlying diffusional challenge, bioactive hollow fiber membranes (HFMs) increase the carbon dioxide diffusional gradient through the immobilized enzyme carbonic anhydrase (CA), which converts bicarbonate to CO(2) directly at the HFM surface. In this study, we tested the impact of CA-immobilization on HFM CO(2) removal efficiency and thromboresistance in blood. Fiber surface modification with radio frequency glow discharge (RFGD) introduced hydroxyl groups, which were activated by 1M CNBr while 1.5M TEA was added drop wise over the activation time course, then incubation with a CA solution covalently linked the enzyme to the surface. The bioactive HFMs were then potted in a model gas exchange device (0.0084 m(2)) and tested in a recirculation loop with a CO(2) inlet of 50mmHg under steady blood flow. Using an esterase activity assay, CNBr chemistry with TEA resulted in 0.99U of enzyme activity, a 3.3 fold increase in immobilized CA activity compared to our previous method. These bioactive HFMs demonstrated 108 ml/min/m(2) CO(2) removal rate, marking a 36% increase compared to unmodified HFMs (p < 0.001). Thromboresistance of CA-modified HFMs was assessed in terms of adherent platelets on surfaces by using lactate dehydrogenase (LDH) assay as well as scanning electron microscopy (SEM) analysis. Results indicated HFMs with CA modification had 95% less platelet deposition compared to unmodified HFM (p < 0.01). Overall these findings revealed increased CO(2) removal can be realized through bioactive HFMs, enabling a next generation of more efficient CO(2) removal intravascular and paracorporeal respiratory assist devices.

[Permissive and non-permissive hypercapnia: mechanisms of action and consequences of high carbon dioxide levels]

Acute lung injury is a disease with high incidence of mortality and its treatment is still controversial. Increasing the levels of CO2 beyond the physiological range has been proposed as a potential protective strategy for patients on mechanical ventilation, as it could moderate the inflammatory response. In this article we review the published evidence on the role of CO2 during acute lung injury. We conclude that although there are reports suggesting benefits from hypercapnia, more recent evidence suggests that hypercapnia could be deleterious, contributing to worsening of the lung injury.

Sensing, physiological effects and molecular response to elevated CO2 levels in eukaryotes

Carbon dioxide (CO₂) is an important gaseous molecule that maintains biosphere homeostasis and is an important cellular signalling molecule in all organisms. The transport of CO₂ through membranes has fundamental roles in most basic aspects of life in both plants and animals. There is a growing interest in understanding how CO₂ is transported into cells, how it is sensed by neurons and other cell types and in understanding the physiological and molecular consequences of elevated CO₂ levels (hypercapnia) at the cell and organism levels. Human pulmonary diseases and model organisms such as fungi, C. elegans, Drosophila and mice have been proven to be important in understanding of the mechanisms of CO₂ sensing and response.

High CO2 levels impair alveolar epithelial function independently of pH

Background

In patients with acute respiratory failure, gas exchange is impaired due to the accumulation of fluid in the lung airspaces. This life-threatening syndrome is treated with mechanical ventilation, which is adjusted to maintain gas exchange, but can be associated with the accumulation of carbon dioxide in the lung. Carbon dioxide (CO₂) is a by-product of cellular energy utilization and its elimination is affected via alveolar epithelial cells. Signaling pathways sensitive to changes in CO₂ levels were described in plants and neuronal mammalian cells. However, it has not been fully elucidated whether non-neuronal cells sense and respond to CO₂. The Na,K-ATPase consumes ∼40% of the cellular metabolism to maintain cell homeostasis. Our study examines the effects of increased pCO₂ on the epithelial Na,K-ATPase a major contributor to alveolar fluid reabsorption which is a marker of alveolar epithelial function.

Principal Findings

We found that short-term increases in pCO₂ impaired alveolar fluid reabsorption in rats. Also, we provide evidence that non-excitable, alveolar epithelial cells sense and respond to high levels of CO₂, independently of extracellular and intracellular pH, by inhibiting Na,K-ATPase function, via activation of PKCζ which phosphorylates the Na,K-ATPase, causing it to endocytose from the plasma membrane into intracellular pools.

Conclusions

Our data suggest that alveolar epithelial cells, through which CO₂ is eliminated in mammals, are highly sensitive to hypercapnia. Elevated CO₂ levels impair alveolar epithelial function, independently of pH, which is relevant in patients with lung diseases and altered alveolar gas exchange.

Inhibition of JNK activation prolongs survival after smoke inhalation from fires

Initial injury from smoke inhalation is mainly to the trachea and bronchi and is characterized by mucosal hyperemia and increased microvascular permeability, exfoliation of epithelial lining, mucous secretion, mucous plugging, and an acute inflammatory cell influx. In this study, we explore the role of the c-Jun N-terminal protein kinase (JNK) pathway in smoke inhalation lung injury using a rat model of exposure to smoke from burning cotton. Male Sprague-Dawley rats were exposed to smoke from burning cotton for 15 min, and 1 h after injury a JNK inhibitor (SP-600125) or vehicle was injected. We measured neutrophil influx, cytokine release, percent of apoptotic cells, airway plugging, and survival. Administration of a JNK inhibitor 1 h after smoke inhalation decreased airway apoptosis, mucous plugging, influx of inflammatory cells, and the release of cytokines and significantly prolonged animal survival (P < 0.05). These in vivo data show that the JNK pathway plays a critical role in smoke-induced lung injury and offer an attractive therapeutic approach for this injury.

Efficacy and safety of a low-flow veno-venous carbon dioxide removal device: results of an experimental study in adult sheep

Introduction

Extracorporeal lung assist, an extreme resource in patients with acute respiratory failure (ARF), is expanding its indications since knowledge about ventilator-induced lung injury has increased and protective ventilation has become the standard in ARF.

Methods

A prospective study on seven adult sheep was conducted to quantify carbon dioxide (CO₂) removal and evaluate the safety of an extracorporeal membrane gas exchanger placed in a veno-venous pump-driven bypass. Animals were anaesthetised, intubated, ventilated in order to reach hypercapnia, and then connected to the CO₂ removal device. Five animals were treated for three hours, one for nine hours, and one for 12 hours. At the end of the experiment, general anaesthesia was discontinued and animals were extubated. All of them survived.

Results

No significant haemodynamic variations occurred during the experiment. Maintaining an extracorporeal blood flow of 300 ml/minute (4.5% to 5.3% of the mean cardiac output), a constant removal of arterial CO₂, with an average reduction of 17% to 22%, was observed. Arterial partial pressure of carbon dioxide (PaCO₂) returned to baseline after treatment discontinuation. No adverse events were observed.

Conclusion

We obtained a significant reduction of PaCO₂ using low blood flow rates, if compared with other techniques. Percutaneous venous access, simplicity of circuit, minimal anticoagulation requirements, blood flow rate, and haemodynamic impact of this device are more similar to renal replacement therapy than to common extracorporeal respiratory assistance, making it feasible not only in just a few dedicated centres but in a large number of intensive care units as well.

“Systemic apoptotic response” after thermal burns

The systemic pathophysiologic changes following thermal injuries affect multiple organs and body systems leading to clinical manifestations including shock, intestinal alterations, respiratory and renal failure, immunosuppression and others. Recent advances in the comprehension of mechanisms underlying systemic complications of thermal injuries have contributed to uncover part of the cellular and molecular basis that underlie such changes. Recently, programmed cell death (apoptosis) has been considered playing an important role in the development of such pathological events. Therefore, investigators utilizing animal models and clinical studies involving human primates have produced a large body of information suggesting that apoptosis is associated with most of the tissue damages triggered by severe thermal injuries. In order to draw the attention on the important role of apoptosis on systemic complications of thermal injuries, in this review we describe most of these studies, discuss possible cellular and molecular mechanisms and indicate ways to utilize them for the development of therapeutic strategies by which apoptosis may be prevented or counteracted.