Mechanical ventilation in the management of acute respiratory distress syndrome

Effect and Mechanism Study of Sodium Houttuyfonate on Ventilator-Induced Lung Injury by Inhibiting ROS and Inflammation

PURPOSE

Ventilator-induced lung injury (VILI) is a serious complication of mechanical ventilation (MV) that increases morbidity and mortality of patients receiving ventilator treatment. This study aimed to reveal the molecular mechanism of sodium houttuyfonate (SH) on VILI.

MATERIALS AND METHODS

The male mice VILI model was established by high tidal volume ventilation. The cell model was established by performing cell stretch (CS) experiments on murine respiratory epithelial cells MLE-15. In addition, the JNK activator Anisomycin and JNK inhibitor SP600125 were used on VILI mice and CS-treated cells.

RESULTS

VILI modeling damaged the structural integrity, increased apoptosis and wet-to-dry (W/D) ratio, enhanced the levels of inflammatory factors, reactive oxygen species (ROS) and malonaldehyde (MDA), and activated JNK pathway in lung tissues. SH gavage alleviated lung injury, decreased apoptosis and W/D ratio, and reduced levels of inflammatory factors, ROS and MDA, and p-JNK/JNK expression of lung tissues in VILI mice. However, activation of JNK wiped the protective effect of SH on VILI. Contrary results were found in experiments with JNK inhibitor SP600125.

CONCLUSION

SH relieved VILI by inhibiting the ROS-mediated JNK pathway.

Mitochondrial Coenzyme Q Protects Sepsis-Induced Acute Lung Injury by Activating PI3K/Akt/GSK-3β/mTOR Pathway in Rats

The aim of our study was to assess the effects of mitochondrial coenzyme Q (MitoQ) on sepsis-induced acute lung injury (ALI) and investigate its possible mechanisms. The cecal ligation and puncture (CLP) method was used to establish a septic ALI model. Rats were randomly divided into Con group, CLP group, MitoQ group, and MitoQ + LY294002 group. The survival rate of the rats was recorded, and the survival rate curve was plotted. Moreover, the ratio of wet/dry weight (W/D) in lung tissue was measured. The activity of myeloperoxidase (MPO) was measured by using the MPO colorimetric activity assay kit. The levels of high-mobility group box 1 (HMGB1) and interleukin-6 (IL-6), macrophage inflammatory protein 2 (MIP2), and keratinocyte chemoattractant (KC) were analyzed by ELISA. The histopathological changes were measured by HE staining, and the lung injury was scored. TUNEL assay was applied to detect the apoptotic cells in lung tissue. The protein expressions were detected by western blot. MitoQ increased the survival rate and alleviated pulmonary edema in septic ALI rats. In addition, MitoQ inhibited the MPO activity and decreased the levels of HMGB1 and IL-6. After treatment with MitoQ, alveolar wall edema, inflammatory cell infiltration, and red blood cell exudation were relieved. MitoQ inhibited cell apoptosis in lung tissue of septic ALI rats. Meanwhile, MitoQ treatment remarkedly increased the expression of p-Akt, p-GSK-3β, and p-mTOR but decreased Bax, caspase-3, caspase-9, Beclin-1, and LC-3II/LC-3I. The effects of MitoQ were significantly reversed by the PI3K inhibitor (LY294002). Our study demonstrated that MitoQ could protect sepsis-induced acute lung injury by activating the PI3K/Akt/GSK-3β/mTOR pathway in rats.

Effects of cisatracurium in combination with ventilation on inflammatory factors and immune variations in sepsis rats

The effects of cisatracurium in combination with ventilation on inflammatory factors and immune variations in sepsis rats were investigated. A total of 54 male Sprague-Dawley rats were selected and divided randomly into three groups: Sham group (n=6), model group (n=24) and experiment group (n=24). Rats in the model and experiment groups underwent cecal ligation and puncture (CLP) for establishment of sepsis model. Rats in experiment group additionally received cisatracurium medication in combination with ventilation for treatment. At 6, 12 and 24 h after CLP, the levels of tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6 and procalcitonin (PCT) in serum and the ratio of leukocyte to neutrophil in peripheral blood was also detected. Twenty-four hours later, the expression of high mobility group box 1 (HMGB1) in lung tissues and cluster of differentiation (CD) 4⁺ and CD8⁺ in T-lymphocyte subsets were also detected, and the wet/dry (W/D) ratio of lung was measured. Compared with that in model group, the levels of inflammatory factors in the experiment group were significantly decreased, while the indicators in assays of cellular immunity were obviously elevated. Ratio of leukocyte to neutrophil in peripheral blood was significantly decreased after treatment. Cisatracurium in combination with ventilation can alleviate the inflammatory injury to organs in sepsis rats through inhibiting the inflammatory responses and regulating the immune functions, which manifests a new significance in guiding the clinical diagnosis and treatment.

Hyperoxia treatment of TREK-1/TREK-2/TRAAK-deficient mice is associated with a reduction in surfactant proteins

We previously proposed a role for the two-pore domain potassium (K2P) channel TREK-1 in hyperoxia (HO)-induced lung injury. To determine whether redundancy among the three TREK isoforms (TREK-1, TREK-2, and TRAAK) could protect from HO-induced injury, we now examined the effect of deletion of all three TREK isoforms in a clinically relevant scenario of prolonged HO exposure and mechanical ventilation (MV). We exposed WT and TREK-1/TREK-2/TRAAK-deficient [triple knockout (KO)] mice to either room air, 72-h HO, MV [high and low tidal volume (TV)], or a combination of HO + MV and measured quasistatic lung compliance, bronchoalveolar lavage (BAL) protein concentration, histologic lung injury scores (LIS), cellular apoptosis, and cytokine levels. We determined surfactant gene and protein expression and attempted to prevent HO-induced lung injury by prophylactically administering an exogenous surfactant (Curosurf). HO treatment increased lung injury in triple KO but not WT mice, including an elevated LIS, BAL protein concentration, and markers of apoptosis, decreased lung compliance, and a more proinflammatory cytokine phenotype. MV alone had no effect on lung injury markers. Exposure to HO + MV (low TV) further decreased lung compliance in triple KO but not WT mice, and HO + MV (high TV) was lethal for triple KO mice. In triple KO mice, the HO-induced lung injury was associated with decreased surfactant protein (SP) A and SPC but not SPB and SPD expression. However, these changes could not be explained by alterations in the transcription factors nuclear factor-1 (NF-1), NKX2.1/thyroid transcription factor-1 (TTF-1) or c-jun, or lamellar body levels. Prophylactic Curosurf administration did not improve lung injury scores or compliance in triple KO mice.

Astragalus polysaccharides combined with ibuprofen exhibit a therapeutic effect on septic rats via an anti-inflammatory cholinergic pathway

The aim of the present study was to investigate the effects of Astragalus polysaccharides (APS) in combination with ibuprofen (IBU) in the treatment of sepsis and the underlying mechanism. The combined drug treatment was evaluated in a rat model of cecal ligation and puncture (CLP). The serum concentrations of tumor necrosis factor (TNF)-α, interleukin (IL)-6 and acetylcholine (ACh) were determined. Nicotinic acetylcholine (nAChR) α7 receptor expression and histopathological changes in the lung tissue were also observed. When compared with untreated rats and rats treated with either component alone, the combined treatment significantly decreased the production of TNF-α and IL-6 (P<0.05), and increased nAChR α7 receptor mRNA expression and the release of ACh in the serum (P<0.05). These results demonstrated that APS combined with IBU can effectively reduce the generation of inflammatory mediators in the serum of CLP-induced septic rats. These effects may be mediated via a cholinergic anti-inflammatory pathway involving nAChR α7.

The role of stretch-activated ion channels in acute respiratory distress syndrome: finally a new target?

Mechanical ventilation (MV) and oxygen therapy (hyperoxia; HO) comprise the cornerstones of life-saving interventions for patients with acute respiratory distress syndrome (ARDS). Unfortunately, the side effects of MV and HO include exacerbation of lung injury by barotrauma, volutrauma, and propagation of lung inflammation. Despite significant improvements in ventilator technologies and a heightened awareness of oxygen toxicity, besides low tidal volume ventilation few if any medical interventions have improved ARDS outcomes over the past two decades. We are lacking a comprehensive understanding of mechanotransduction processes in the healthy lung and know little about the interactions between simultaneously activated stretch-, HO-, and cytokine-induced signaling cascades in ARDS. Nevertheless, as we are unraveling these mechanisms we are gathering increasing evidence for the importance of stretch-activated ion channels (SACs) in the activation of lung-resident and inflammatory cells. In addition to the discovery of new SAC families in the lung, e.g., two-pore domain potassium channels, we are increasingly assigning mechanosensing properties to already known Na(+), Ca(2+), K(+), and Cl(-) channels. Better insights into the mechanotransduction mechanisms of SACs will improve our understanding of the pathways leading to ventilator-induced lung injury and lead to much needed novel therapeutic approaches against ARDS by specifically targeting SACs. This review 1) summarizes the reasons why the time has come to seriously consider SACs as new therapeutic targets against ARDS, 2) critically analyzes the physiological and experimental factors that currently limit our knowledge about SACs, and 3) outlines the most important questions future research studies need to address.

Auricularia auricular-judae polysaccharide attenuates lipopolysaccharide-induced acute lung injury by inhibiting oxidative stress and inflammation

Auricularia auricular-judae polysaccharide (AAP) has shown a variety of pharmacological properties. In the present study, the role of AAP in acute lung injury (ALI) induced by lipopolysaccharide (LPS) was analyzed in rats to further explore the possible underlying mechanisms. Adult Sprague-Dawley rats were randomly assigned into the control, AAP, LPS and LPS plus AAP groups. Rats were injected with LPS (10 mg/kg, intraperitoneal) to induce ALI. Rats in the LPS plus AAP group were treated with AAP for 7 days before the induction of ALI. The protein concentration in the bronchoalveolar lavage fluid (BALF) was measured. The animal lung edema degree was evaluated by the wet/dry (W/D) weight ratio. The myeloperoxidase (MPO) activity and malondialdehyde (MDA) level were assayed by MPO and MDA kits, respectively. The levels of inflammatory mediators, tumor necrosis factor-α (TNF-α) and interleukin (IL)-6, were assayed by the enzyme-linked immunosorbent assay method. Pathological changes of lung tissues were observed by hematoxylin and eosin staining. The data showed that treatment with AAP significantly improved LPS-induced lung pathological changes, attenuated protein concentration in the BALF, inhibited MPO activity and reduced the MDA level and lung W/D weight ratio. AAP also inhibited the release of TNF-α and IL-6 in blood. The results indicated that AAP has a protective effect on LPS-induced ALI in rats.

The effect of dexmedetomidine on inflammatory response of septic rats

Background

Some studies have demonstrated dexmedetomidine has anti-inflammatory effect on septic rats. However, the mechanism of how dexmedetomidine exerts these effects is still remained unknown. This study was designed to investigate the mechanism of how dexmedetomidine inhibits the production of inflammatory mediators in cecal ligation and puncturinduced septic rats.

Methods

48 Sprague-Dawley rats were randomly divided into six groups: sham-operated (sham) group, cecal ligation and puncture (CLP) group, dexmedetomidine 5 μg/kg (DEX5) group, dexmedetomidine 10 μg/kg (DEX10) group,dexmedetomidine + yohimbine (DEX10 + Yoh) group and yohimibine group (Yoh). Blood, bronchoalveolarlavage fluid (BALF) and lung tissues in each group were collected at six hours after dexmedetomidine or yohimbine treatment,. Tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in BALF and plasma were measured by enzyme-linked immunosorbent assay (ELISA). Toll-like receptor-4(TLR4) and myeloid differerntiation factor(MyD88) expression were measuredby quantitative PCR, and extracellular signal-regulated kinase (ERK) 1/2 phosphorylation were determined by western blott.

Results

Compared with CLP group, dexmedetomidine significantly decreased not only the production of TNF-α and IL-6 both in plasma and BALF, but also inhibited the expression of TLR4 and MyD88 in mRNA level and the activation of ERK1/2 and NF-κB in the lung tissues of CLP-induced septic rats. All these effects could not be reversed by yohimibine.

Conclusions

Dexmedetomidine treatment can effectively reduce the generation of inflammatory mediators in the plasma and BALF of CLP-induced septic rats. These effects of dexmedetomidine rely on TLR4/MyD88/MAPK/ NF-κB signaling pathway and are independent of α₂-adrenoceptor.

The 2-pore domain potassium channel TREK-1 regulates stretch-induced detachment of alveolar epithelial cells

Acute Respiratory Distress Syndrome remains challenging partially because the underlying mechanisms are poorly understood. While inflammation and loss of barrier function are associated with disease progression, our understanding of the biophysical mechanisms associated with ventilator-associated lung injury is incomplete. In this line of thinking, we recently showed that changes in the F-actin content and deformability of AECs lead to cell detachment with mechanical stretch. Elsewhere, we discovered that cytokine secretion and proliferation were regulated in part by the stretch-activated 2-pore domain K⁺ (K2P) channel TREK-1 in alveolar epithelial cells (AECs). As such, the aim of the current study was to determine whether TREK-1 regulated the mechanobiology of AECs through cytoskeletal remodeling and cell detachment. Using a TREK-1-deficient human AEC line (A549), we examined the cytoskeleton by confocal microscopy and quantified differences in the F-actin content. We used nano-indentation with an atomic force microscope to measure the deformability of cells and detachment assays to quantify the level of injury in our monolayers. We found a decrease in F-actin and an increase in deformability in TREK-1 deficient cells compared to control cells. Although total vinculin and focal adhesion kinase (FAK) levels remained unchanged, focal adhesions appeared to be less prominent and phosphorylation of FAK at the Tyr⁹²⁵ residue was greater in TREK-1 deficient cells. TREK-1 deficient cells have less F-actin and are more deformable making them more resistant to stretch-induced injury.

Dexmedetomidine inhibits inflammatory reaction in lung tissues of septic rats by suppressing TLR4/NF-κB pathway

Dexmedetomidine has been reported to reduce mortality in septic rats. This study was designed to investigate the effects of dexmedetomidine on inflammatory reaction in lung tissues of septic rats induced by CLP. After induction of sepsis, the rats were treated with normal saline or dexmedetomidine (5, 10, or 20 μg/kg). The survival rate of septic rats in 24 h was recorded. The inflammation of lung tissues was evaluated by HE stain. The concentrations of IL-6 and TNF-α in BALF and plasma were measured by ELISA. The expressions of TLR4 and MyD88 were measured by western blotting. The activation of NF-κB in rat lung tissues was assessed by western blotting and immunohistochemistry. It was found that the mortality rate and pulmonary inflammation were significantly increased in septic rats. IL-6 and TNF-α levels in BALF and plasma, NF-κB activity, and TLR4/MyD88 expression in rat lung tissues were markedly enhanced after CLP. Dexmedetomidine (10 and 20 μg/kg) significantly decreased mortality and pulmonary inflammation of septic rats, as well as suppressed CLP-induced elevation of TNF-α and IL-6 and inhibited TLR4/MyD88 expression and NF-κB activation. These results suggest that dexmedetomidine may decrease mortality and inhibit inflammatory reaction in lung tissues of septic rats by suppressing TLR4/MyD88/NF-κB pathway.

The effect of positive-end expiratory pressure on oxygenation during high frequency jet ventilation and conventional mechanical ventilation in the rabbit model of acute lung injury

BACKGROUND

The use of positive end expiratory pressure (PEEP) in patients with acute lung injury (ALI) improves arterial oxygenation by alleviating pulmonary shunting, helping the respiratory muscles to decrease the work of breathing, decreasing the rate of infiltrated and atelectatic tissues, and increasing functional residual capacity. In a rabbit model of saline lavage-induced ALI, we examined the effects of PEEP on gas exchange, hemodynamics, and oxygenation during high frequency jet ventilation (HFJV), and then compared these parameters with those during conventional mechanical ventilation (CMV).

METHODS

Twelve rabbits underwent repeated saline lavage to create ALI. The animals were divided in 2 groups: 1) Group CMV (n = 6), and 2) Group HFJV (n = 6). In both groups, we applied 2 levels of PEEP (5 cmH(2)O and 10 cmH(2)O) and then measured the arterial blood gas, mixed venous blood gas, and hemodynamic parameters.

RESULTS

With administration of PEEP of either 5 cmH(2)O or 10 cmH(2)O, the arterial oxygen content of both groups was increased, although without statistically significant differences between groups. On the contrary, the arterial carbon dioxide content was significantly decreased in the HFJV group, as compared with the CMV group, during the entire experiment. Furthermore, there was significant decreases in mean arterial pressures in both groups with a PEEP of 10 cmH(2)O.

CONCLUSIONS

The application of PEEP in rabbits with ALI effectively improves oxygenation in either HFJV or CMV.

Tracheal gas insufflation with partial liquid ventilation to treat LPS-induced acute lung injury in juvenile piglets

OBJECTIVES

Partial liquid ventilation (PLV) with perfluorocarbons (PFC) seems not superior to conventional ventilation clinically. We hypothesized that a combination of continuous tracheal gas insufflation (TGI) with protective strategy of PLV (low dose of PFC, low inflation pressure, moderate inhalation of oxygen and moderate anesthesia) would improve cardiopulmonary function in acute lung injury.

METHODS

Twenty-four healthy juvenile piglets were anesthetized and mechanically ventilated at PEEP of 2 cmH(2)O with a peak inspiratory pressure of 10 cmH(2)O and FIO(2) of 0.4. The piglets were challenged with lipopolysaccharide and randomly assigned to four groups (n = 6 each): (1) mechanical ventilation alone (MV); (2) PLV with perfluorodecalin (10 ml/kg); (3) TGI with continuous airway flow 2 L/min; and (4) combination of PLV and TGI. The outcome was assessed functionally and histologically.

RESULTS

All treatments except MV improved pH, PaO(2)/FIO(2), PaCO(2), ventilation efficacy index (VEI) and tidal volume. Both PLV-associated treatments also improved heart rate, respiratory rate, pulse contour cardiac output, systemic vascular resistance, dynamic lung compliance, mean airway resistance and mean airway pressure. The combination group resulted in higher PaO(2)/FIO(2), VEI and a better lung histology score than any other treatments.

CONCLUSIONS

The new protective strategy may provide a better treatment for sepsis-induced acute lung injury.

Protective effects of dexmedetomidine-ketamine combination against ventilator-induced lung injury in endotoxemia rats

BACKGROUND

Pulmonary inflammatory response is crucial in mediating the development of ventilator-induced lung injury (VILI) in animals experiencing endotoxemia. Dexmedetomidine and ketamine are two sedative agents with potent anti-inflammatory capacity. We sought to elucidate the anti-inflammatory effects of dexmedetomidine-ketamine combination against VILI in endotoxemia rats.

MATERIALS AND METHODS

Eighty-four adult male rats were allocated to receive normal saline, VILI, VILI plus dexmedetomidine-ketamine combination (D+K), lipopolysaccharide (LPS), LPS plus D+K, LPS plus VILI, or LPS plus VILI plus D+K (designated as the NS, V, V-D+K, LPS, LPS-D+K, LPS/V, and LPS/V-D+K group, respectively; n = 12 in each group). VILI was induced by high-tidal volume ventilation (tidal volume 20 mL/kg; respiratory rate 50 breath/min; FiO(2) 21%). After being mechanically ventilated for 4 h, rats were sacrificed and the levels of pulmonary inflammatory response were evaluated.

RESULTS

Histologic findings revealed severe, moderate, and mild inflammation in lung tissues of the LPS/V, LPS, and V groups, respectively, whereas those of the LPS/V-D+K, LPS-D+K, and V-D+K groups revealed moderate, mild, and normal to minimal inflammation, respectively. Moreover, the total cell number and the concentrations of macrophage inflammatory protein-2 and interleukin-1β in bronchoalveolar lavage fluid as well as the lung water content, leukocyte infiltration, myeloperoxidase activity, and the concentrations of inducible nitric oxide synthase/nitric oxide, and cyclooxygenase 2/prostaglandin E(2) in lung tissues of the LPS/V, LPS, and V groups were significantly higher than those of the LPS/V-D+K, LPS-D+K, and V-D+K groups, respectively.

CONCLUSIONS

Dexmedetomidine-ketamine combination could mitigate pulmonary inflammatory response induced by VILI in endotoxemia rats.

Partial liquid ventilation confers protection against acute lung injury induced by endotoxin in juvenile piglets

To investigate the effect of partial liquid ventilation (PLV) at low inflation pressures on acute lung injury (ALI), endotoxin was administered to healthy anesthetized juvenile piglets. The animals were randomly assigned to two groups, n=6 each: (1) conventional mechanical ventilation (MV) and (2) PLV with perfluorodecalin (10 mL kg(-1)). Compared with MV, PLV improved each cardiopulmonary variable measured. These variables included pulse contour cardiac output, heart rate, blood pH, breathing rate, both partial pressure of arterial oxygen (PaO2) and PaO2/FIO2 (fraction of inspired oxygen), partial pressure of arterial carbon dioxide (PaCO2), dynamic lung compliance, tidal volume, and ventilation efficacy index. Lung morphology also showed less damage in the PLV group, even in non-dependent regions (P<0.05). Our data support the hypothesis that PLV can decrease pulmonary damage, improve gas exchange and cardiac output, and may lead to a better prognosis in endotoxin-induced ALI.