High in comparison with low tidal volume ventilation aggravates oxidative stress-induced lung injury

Ventilator-induced lung injury results in oxidative stress response and mitochondrial swelling in a mouse model

Background

Mechanical ventilation is a life-saving therapy for critically ill patients, providing rest to the respiratory muscles and facilitating gas exchange in the lungs. Ventilator-induced lung injury (VILI) is an unfortunate side effect of mechanical ventilation that may lead to serious consequences for the patient and increase mortality. The four main injury mechanisms associated with VILI are: baro/volutrauma caused by overstretching the lung tissues; atelectrauma, caused by repeated opening and closing of the alveoli resulting in shear stress; oxygen toxicity due to use of high ratio of oxygen in inspired air, causing formation of free radicals; and biotrauma, the resulting biological response to tissue injury, that leads to a cascade of events due to excessive inflammatory reactions and may cause multi-organ failure. An often-overlooked part of the inflammatory reaction is oxidative stress. In this research, a mouse model of VILI was set up with three tidal volume settings (10, 20 and 30 mL/kg) at atmospheric oxygen level. Airway pressures and heart rate were monitored and bronchoalveolar lavage fluid (BALF) and lung tissue samples were taken.

Results

We show a correlation between increased inflammation and barrier failure, and higher tidal volumes, evidenced by increased IL-6 expression, high concentration of proteins in BALF along with changes in expression of adhesion molecules. Furthermore, swelling of mitochondria in alveolar type II cells was seen indicating their dysfunction and senescence-like state. RNA sequencing data present clear increases in inflammation, mitochondrial biogenesis and oxidative stress as tidal volume is increased, supported by degradation of Keap1, a redox-regulated substrate adaptor protein.

Conclusions

Oxidative stress seems to be a more prominent mechanism of VILI than previously considered, indicating that possible treatment methods against VILI might be identified by impeding oxidative pathways.

Dexmedetomidine attenuates oxidative stress induced lung alveolar epithelial cell apoptosis in vitro

Background. Oxidative stress plays a pivotal role in the lung injuries of critical ill patients. This study investigates the protection conferred by α₂ adrenoceptor agonist dexmedetomidine (Dex) from lung alveolar epithelial cell injury induced by hydrogen peroxide (H₂O₂) and the underlying mechanisms. Methods. The lung alveolar epithelial cell line, A549, was cultured and then treated with 500 μM H₂O₂ with or without Dex (1 nM) or Dex in combination with atipamezole (10 nM), an antagonist of α₂ receptors. Their effect on mitochondrial membrane potential (Δψ_m), reactive oxygen species (ROS), and the cell cycle was assessed by flow cytometry. Cleaved-caspases 3 and 9, BAX, Bcl-2, phospho-mTOR (p-mTOR), ERK1/2, and E-cadherin expression were also determined with immunocytochemistry. Results. Upregulation of cleaved-caspases 3 and 9 and BAX and downregulation of Bcl-2, p-mTOR, and E-cadherin were found following H₂O₂ treatment, and all of these were reversed by Dex. Dex also prevented the ROS generation, cytochrome C release, and cell cycle arrest induced by H₂O₂. The effects of Dex were partially reversed by atipamezole. Conclusion. Our study demonstrated that Dex protected lung alveolar epithelial cells from apoptotic injury, cell cycle arrest, and loss of cell adhesion induced by H₂O₂ through enhancing the cell survival and proliferation.

Ventilation-induced lung injury

Mechanical ventilation (MV) is, by definition, the application of external forces to the lungs. Depending on their magnitude, these forces can cause a continuum of pathophysiological alterations ranging from the stimulation of inflammation to the disruption of cell-cell contacts and cell membranes. These side effects of MV are particularly relevant for patients with inhomogeneously injured lungs such as in acute lung injury (ALI). These patients require supraphysiological ventilation pressures to guarantee even the most modest gas exchange. In this situation, ventilation causes additional strain by overdistension of the yet non-injured region, and additional stress that forms because of the interdependence between intact and atelectatic areas. Cells are equipped with elaborate mechanotransduction machineries that respond to strain and stress by the activation of inflammation and repair mechanisms. Inflammation is the fundamental response of the host to external assaults, be they of mechanical or of microbial origin and can, if excessive, injure the parenchymal tissue leading to ALI. Here, we will discuss the forces generated by MV and how they may injure the lungs mechanically and through inflammation. We will give an overview of the mechanotransduction and how it leads to inflammation and review studies demonstrating that ventilator-induced lung injury can be prevented by blocking pathways of mechanotransduction or inflammation.

Renal hypoperfusion and impaired endothelium-dependent vasodilation in an animal model of VILI: the role of the peroxynitrite-PARP pathway

Introduction

Mechanical ventilation (MV) can injure the lungs and contribute to an overwhelming inflammatory response, leading to acute renal failure (ARF). We previously showed that poly(adenosine diphosphate-ribose) polymerase (PARP) is involved in the development of ventilator-induced lung injury (VILI) and the related ARF, but the mechanisms underneath remain unclear. In the current study we therefore tested the hypothesis that renal blood flow and endothelial, functional and tissue changes in the kidney of rats with lipopolysaccharide (LPS)-induced lung injury aggravated by MV, is caused, in part, by activation of PARP by peroxynitrite.

Methods

Anesthetized Sprague Dawley rats (n = 31), were subjected to intratracheal instillation of lipopolysaccharide at 10 mg/kg followed by 210 min of mechanical ventilation at either low tidal volume (6 mL/kg) with 5 cm H₂O positive end-expiratory pressure or high tidal volume (19 mL/kg) with zero positive end-expiratory pressure in the presence or absence of a peroxynitrite decomposition catalyst, WW85 or a PARP inhibitor, PJ-34. During the experiment, hemodynamics and blood gas variables were monitored. At time (t) t = 0 and t = 180 min, renal blood flow was measured. Blood and urine were collected for creatinine clearance measurement. Arcuate renal arteries were isolated for vasoreactivity experiment and kidneys snap frozen for staining.

Results

High tidal volume ventilation resulted in lung injury, hypotension, renal hypoperfusion and impaired renal endothelium-dependent vasodilation, associated with renal dysfunction and tissue changes (leukocyte accumulation and increased expression of neutrophil gelatinase-associated lipocalin). Both WW85 and PJ-34 treatments attenuated lung injury, preserved blood pressure, attenuated renal endothelial dysfunction and maintained renal blood flow. In multivariable analysis, renal blood flow improvement was, independently from each other, associated with both maintained blood pressure and endothelium-dependent vasodilation by drug treatment. Finally, drug treatment improved renal function and reduced tissue changes.

Conclusions

The peroxynitrite-induced PARP activation is involved in renal hypoperfusion, impaired endothelium-dependent vasodilation and resultant dysfunction, and injury, in a model of lung injury.

Protein kinase C inhibition attenuates hypochlorite-induced acute lung injury

Neutrophil-derived oxidative stress plays a crucial role in acute lung injury. Hypochlorite/hypochlorous acid (HOCl) is a major oxidant of neutrophils. Protein kinase C (PKC) may be an appropriate target for HOCl due to its functionally important thiols. This study investigates the role of PKC in HOCl-induced acute lung injury. Isolated lung preparations were from 30 rabbits. HOCl (1000 nmol min(-1)) or buffer (control) were infused into isolated rabbit lungs. Pulmonary artery pressure (PAP [Torr]) and lung weight were continuously measured. Capillary filtration coefficient (K(f,c)), was measured at baseline and at 30, 60, 90 min. Experiments were terminated at 105 min or when fluid retention exceeded 50 g. The non-selective protein kinase inhibitor staurosporin (100 nM) or the selective PKC inhibitor bisindolylmaleimide I (GF109203X, 10nM) were added to the perfusate 5 min prior to the start of the experiments. Staurosporin completely prevented the HOCl-induced increase in PAP (no change versus DeltaPAP(max) 5.2+/-0.78) but did not influence the increase in vascular permeability. GF109203X delayed the HOCl-induced increase in PAP and vascular permeability. PAP(max) was observed significantly later in the HOCl-GF109203X group (84.4+/-4.0 min) in comparison with the HOCl group (52.1+/-3.5 min). Termination of the experiments due to edema formation occurred significantly later in experiments with GF109203X (91.8+/-1.9 versus 79.2+/-4.1 min). Protein kinases are involved in HOCl-induced acute lung injury. Specifically PKC inhibition delayed HOCl-induced increases in PAP and vascular permeability.

Role of oxidative stress in experimental sepsis and multisystem organ dysfunction

Massive increase in radical species can lead to oxidative stress, promoting cell injury and death. This review focuses on experimental evidence of oxidative stress in critical illnesses, sepsis and multisystem organ dysfunction. Oxidative stress could negatively affect organ injury and thus overall survival of experimental models. Based on this experimental evidence, we could improve the rationale of supplementation of antioxidants alone or in combination with standard therapies aimed to reduce oxidative stress as novel adjunct treatment in critical care.