Host immune response in sepsis due to ventilator-associated pneumonia: how is it different?

Sepsis-Related Lung Injury and the Complication of Extrapulmonary Pneumococcal Pneumonia

Globally, sepsis and pneumonia account for significant mortality and morbidity. A complex interplay of immune-molecular pathways underlies both sepsis and pneumonia, resulting in similar and overlapping disease characteristics. Sepsis could result from unmanaged pneumonia. Similarly, sepsis patients have pneumonia as a common complication in the intensive care unit. A significant percentage of pneumonia is misdiagnosed as septic shock. Therefore, our knowledge of the clinical relationship between pneumonia and sepsis is imperative to the proper management of these syndromes. Regarding pathogenesis and etiology, pneumococcus is one of the leading pathogens implicated in both pneumonia and sepsis syndromes. Growing evidence suggests that pneumococcal pneumonia can potentially disseminate and consequently induce systemic inflammation and severe sepsis. Streptococcus pneumoniae could potentially exploit the function of dendritic cells (DCs) to facilitate bacterial dissemination. This highlights the importance of pathogen-immune cell crosstalk in the pathophysiology of sepsis and pneumonia. The role of DCs in pneumococcal infections and sepsis is not well understood. Therefore, studying the immunologic crosstalk between pneumococcus and host immune mediators is crucial to elucidating the pathophysiology of pneumonia-induced lung injury and sepsis. This knowledge would help mitigate clinical diagnosis and management challenges.

The Susceptibility of MDR-K. Pneumoniae To Polymyxin B Plus Its Nebulised Form Versus Polymyxin B Alone in Critically Ill South Asian Patients

Introduction

Critically ill patients in intensive care units are at high risk of dying not only from the severity of their illness but also from secondary causes such as hospital-acquired infections. USA national medical record-data show that approximately 10% of patients on mechanical ventilation in an intensive care unit developed ventilator-associated pneumonia. Polymyxin B has been used intravenously in the treatment of multi-drug resistant gram-negative infections, either as a monotherapy or with other potentially effective antibiotics, and the recent international guidelines have emphasised the use of nebulised polymyxin B together with intravenous polymyxin B to gain the optimum clinical outcome in ventilator-associated pneumonia cases caused by multi-drug resistant gram-negative infections.

Methods

One hundred and seventy-eight patients with ventilator-associated pneumonia due to multi-drug resistant K. pneumoniae were identified during the study period. Following the inclusion and exclusion criteria, 121 patients were enrolled in the study and randomly allocated to two study groups. Group 1 patients were treated with intravenous Polymyxin B plus nebulised polymyxin B (n=64) and Group 2 patients with intravenous Polymyxin B alone (n=57). The study aimed to compare the use of Polymyxin B plus its nebulised form to polymyxin B alone, in the treatment of MDR-K. pneumoniae associated ventilator-associated pneumonia in critically ill patients.

Results

In Group 1, a complete clearance of K. pneumoniae was found in fifty-nine patients (92.1%; n=64) compared to forty patients (70.1%, n=57) in the Group 2 (P<0.003). The average time till extubation was significantly higher in Group 2 compared to Group 1 (P<0.05). The total length-of-stay in the ICU was significantly higher in Group 2 compared to Group 1. (P<0.05). These results support the view that the Polymyxin B dual-route regime may be considered as an appropriate antibiotic therapy, in critically ill South Asian patients with ventilator-associated pneumonia.

Mitophagy-Mediated mtDNA Release Aggravates Stretching-Induced Inflammation and Lung Epithelial Cell Injury via the TLR9/MyD88/NF-κB Pathway

Background

In animal models of ventilation-induced lung injury, mitophagy triggers mitochondria damage and the release of mitochondrial (mt) DNA, which activates inflammation. However, the mechanism of this process is unclear.

Methods

A model of cyclic stretching (CS)-induced lung epithelial cell injury was established. The genetic intervention of phosphatase and tensin homolog-induced kinase 1 (PINK1) expression via lentivirus transfection was used to identify the relationship between PINK1-mediated mitophagy and mtDNA release in stretching-induced inflammatory response and injury. Pharmacological inhabitation of Toll-like receptor 9 (TLR9) and myeloid differentiation factor 88 (MyD88) expression was performed via their related inhibitors, while pre-treatment of exogenous mtDNA was used to verify the role of mtDNA in stretching-induced inflammatory response and injury.

Results

Using a cell culture model of CS, we found that knocking down PINK1 in lung epithelial cells reduced mitophagy activation and mtDNA release, leading to milder inflammatory response and injury; conversely, up-regulating PINK1 exacerbated stretching-induced inflammation and injury, and similar effects were observed by upregulating TLR9 to induce expression of MyD88 and nuclear factor-κB (NF-κB)/p65. Down-regulating MyD88 protected lung epithelial cells from stretching injury and decreased NF-κB/p65 expression.

Conclusion

These findings suggest that PINK1-dependent mitophagy and associated TLR9 activation is indeed a major factor in stretch-induced cell injury via a mechanism in which released mtDNA activates TLR9 and thereby the MyD88/NF-κB pathway. Inhibiting this process may be a therapeutic approach to prevent inflammation and cell injury in patients on mechanical ventilation.

Changes in immune indicators and bacteriologic profile were associated with patients with ventilator-associated pneumonia

The aim of this study is to explore and identify ventilator-associated pneumonia (VAP)-related prognostic immune factors and further detect the drug-resistant pathogens to establish the theoretical guidance for clinical prevention and treatment strategies of VAP. A total of 478 patients using ventilator who were hospitalized in July 2014 to November 2016 in our hospital were enrolled in this study. About 103 patients with VAP (21.5%, 103/478) among 478 cases of patients using ventilator. Among the 103 patients with VAP, the distribution of pathogenic bacteria and drug resistance in patients with VAP were detected and analyzed. In the VAP group, 35 patients died and 43 patients had simultaneous sepsis. Compared with those of non-VAP group, the proportion of CD3 (P = .012), CD3CD4 (P = .024) and CD8CD28 ( P = .017) T cells in VAP group increased significantly, which indicated more severe immune response. Multivariate regression model analysis revealed that tracheotomy of mechanical ventilation (P = .013), mechanical ventilation time ≥7 days (P = .02) and aspiration and reflux (P = .011) were independent risk factors associated with VAP. According to the results of bacterial culture and drug sensitivity test, rational selection of antibiotics and monitoring of patients within intensive care unit can effectively control the incidence of VAP and improve the prognosis of patients.

High Tidal Volume Induces Mitochondria Damage and Releases Mitochondrial DNA to Aggravate the Ventilator-Induced Lung Injury

Objective

This study aimed to determine whether high tidal volume (HTV) induce mitochondria damage and mitophagy, contributing to the release of mitochondrial DNA (mtDNA). Another aim of the present study was to investigate the role and mechanism of mtDNA in ventilator-induced lung injury (VILI) in rats.

Methods

Rats were tracheotomized and allowed to breathe spontaneously or mechanically ventilated for 4 h. After that, lung injury was assessed. Inhibition of toll-like receptor 9 (TLR9), named ODN2088, was used to determine the involvement of TLR9/myeloid differentiation factor 88 (MyD88)/nuclear factor-κB (NF-κB) signaling pathway in VILI. The mitochondrial damage and release of mtDNA were assessed. Pharmacological inhibition of mtDNA (chloroquine) was used to determine whether mtDNA trigger inflammation via TLR9 in VILI. EDU-labeled mtDNA deriving from mitophagy was assessed by immunofluorescence. The role of mitophagy in VILI was shown by administration of antimycin A and cyclosporine A.

Main results

Rats subjected to HTV showed more severe pulmonary edema and inflammation than the other rats. The decreased expression of TLR9, MyD88, and NF-κB were observed following the use of ODN2088. Mechanical ventilation (MV) with HTV damaged mitochondria which resulted in dysfunctional ATP synthesis, accumulation of reactive oxygen species, and loss of mitochondrial membrane potential. Moreover, the results of distribution of fluorescence in rats upon HTV stimulation indicated that mtDNA cleavage was associated with mitophagy. The expression levels of mitophagy related genes (LC3B-II/LC3B-I, PINK1, Parkin, and mitofusin 1) in animals ventilated with HTV were significantly upregulated. Administration of antimycin A aggregated the histological changes and inflammation after MV, but these effects were attenuated when administered in the presence of cyclosporine A.

Conclusion

MV with HTV induces mitochondrial damage and mitophagy, contributing to the release of mtDNA, which may be induced VILI in rat via TLR9/MyD88/NF-κB signaling pathway.