A Comparative Study of Lung Host Defense in Murine Obesity Models. Insights into Neutrophil Function

Diabetes impairs IFNγ-dependent antibacterial defense in the lungs

Diabetes mellitus is associated with an increased risk of pneumonia, often caused by so-called typical and atypical pathogens including Streptoccocus pneumoniae and Legionella pneumophila, respectively. Here, we employed a variety of mouse models to investigate how diabetes influences pulmonary antibacterial immunity. Following intranasal infection with S. pneumoniae or L. pneumophila, type 2 diabetic and prediabetic mice exhibited higher bacterial loads in their lungs compared to control animals. Single cell RNA sequencing, flow cytometry, and functional analyses revealed a compromised IFNγ production by natural killer cells in diabetic and prediabetic mice, which was associated with reduced IL-12 production by CD103+ dendritic cells. Blocking IFNγ enhanced susceptibility of non-diabetic mice to L. pneumophila, while IFNγ treatment restored defense against this intracellular pathogen in diabetic animals. In contrast, IFNγ treatment did not increase resistance of diabetic mice to S. pneumoniae, suggesting that impaired IFNγ production is not the sole mechanism underlying the heightened susceptibility of these animals to pneumococcal infection. Thus, our findings uncover a mechanism that could help to explain how type 2 diabetes predisposes to pneumonia. We establish proof of concept for host-directed treatment strategies to reinforce compromised IFNγ-mediated antibacterial defense against atypical lung pathogens.

Obstructive Sleep Apnea Effects on Chronic Airway Disease Exacerbations-Missed Opportunities for Improving Outcomes in Chronic Obstructive Pulmonary Disease and Asthma

In patients with chronic obstructive pulmonary disease (COPD) and asthma, exacerbations determine the natural history of both diseases. Patients with both respiratory diseases who suffer from obstructive sleep apnea (OSA) as a comorbidity (overlap syndromes) have a higher risk of exacerbations and hospitalization. In cases of OSA/COPD and OSA/asthma, continuous positive airway pressure treatment is indicated. Adequate adherence to therapy appears to reduce exacerbations and their severity, especially in OSA/COPD overlap. However, there is a lack of randomized trials that definitively demonstrate this evidence.

Obesity Paradox in Lung Diseases: What Explains It?

BACKGROUND

Obesity is a globally increasing health problem that impacts multiple organ systems and a potentially modifiable risk factor for many diseases. Obesity has a significant impact on lung function and is strongly linked to the pathophysiology that contributes to lung diseases. On the other hand, reports have emerged that obesity is associated with a better prognosis than for normal weight individuals in some lung diseases, including pneumonia, acute lung injury/acute respiratory distress syndrome, chronic obstructive pulmonary disease, and lung cancer. The lesser mortality and better prognosis in patients with obesity is known as obesity paradox. While obesity paradox is both recognized and disputed in epidemiological studies, recent research has suggested possible mechanisms.

SUMMARY

In this review, we attempted to explain and summarize these factors and mechanisms, including immune response, pulmonary fibrosis, lung function, microbiota, fat and muscle reserves, which are significantly altered by obesity and may contribute to the obesity paradox in lung diseases. We also discuss contrary literature that attributes the "obesity paradox" to confounding.

KEY MESSAGES

The review will illustrate the possible role of obesity in the prognosis or course of lung diseases, leading to a better understanding of the obesity paradox and provide hints for further basic and clinical research in lung diseases.

Diabetes and obesity and risk of pyogenic liver abscess

Few literatures discussed the relationship of glycemic control and body mass index (BMI) with the risk of pyogenic liver abscess. We conducted a population-based cohort study using participants of a community-based health screening program in Taiwan from 2005 to 2008 (n = 125,865). Information on fasting plasma glucose (FPG), BMI, and other potential risk factors of liver abscess were collected at baseline. Incidence of pyogenic liver abscess was ascertained using inpatient records from the National Health Insurance database. During a median 8.6 years of followed up, 192 incident cases of pyogenic liver abscess were reported. The incidence rate of pyogenic liver abscess was 70.2 and 14.7 per 100,000 in the diabetic and non-diabetic population respectively. In multivariable Cox regression analysis, the adjusted hazard ratio (HR) was 2.18 (95% confidence interval (CI) 1.22-3.90) in patients with diabetes with good glycemic control (FPG ≤ 130 mg/dl) and 3.34 (95% CI 2.37-4.72) in those with poor glycemic control (FPG > 130 mg/dl), when compared with non-diabetics. In the dose-response analysis, the risk of liver abscess increased monotonically with increasing FPG. After adjusting for diabetes and other comorbidities, overweight (25 ≤ BMI < 30) (adjusted HR: 1.43, 95% CI 1.05-1.95) and obese (BMI ≥ 30) (adjusted HR: 1.75, 95% CI 1.09-2.81) populations had a higher risk of liver abscess when compared to people with normal weight. Diabetes, especially poorly controlled disease, and high BMI were associated with higher risk of pyogenic liver abscess. Improving glycemic control and weight reduction may reduce the risk of developing pyogenic liver abscess.

A role of STING signaling in obesity-induced lung inflammation

BACKGROUND

It is established that pulmonary disorders are comorbid with metabolic disorders such as obesity. Previous studies show that the stimulator of interferon genes (STING) signaling plays crucial roles in obesity-induced chronic inflammation via TANK-binding kinase 1 (TBK1) pathways. However, it remains unknown whether and how the STING signaling is implicated in the inflammatory processes in the lung in obesity.

METHODS

Human lung tissues were obtained from obese patients (n = 3) and controls (n = 3). Mice were fed with the high-fat diet or regular control diet to establish the diet-induced obese (DIO) and lean mice, and were treated with C-176 (a specific STING inhibitor) or vehicle respectively. The lung macrophages were exposed to palmitic acid (PA) in vitro. The levels of STING singaling and metabolic inflammation factors were detected and anlyzed.

RESULTS

We find that STING+/CD68+ macrophages are increased in lung tissues in patients with obesity. Our data also show that the expressions of STING and the levels of proinflammatory cytokines are increased both in lung tissues and bronchoalveolar lavage fluid (BALF) in obesity compared to controls, and inhibition of the STING blunted the obesity-induced lung inflammation. Mechanistically, our data demonstrate that the STING signaling pathway is involved in the PA-induced inflammation through the STING-TBK1-IRF3 (interferon regulatory factor 3)/NF-κB (nuclear factor kappa B) pathways in the lung macrophages.

CONCLUSIONS

Our results collectively suggest that the STING signaling contributes to obesity-associated inflammation by stimulating proinflammatory processes in lung macrophages, one that may serve as a therapeutic target in ameliorating obesity-related lung dysfunctions.

Therapeutic ketosis decreases methacholine hyperresponsiveness in mouse models of inherent obese asthma

Obese asthmatics tend to have severe, poorly controlled disease and exhibit methacholine hyperresponsiveness manifesting in proximal airway narrowing and distal lung tissue collapsibility. Substantial weight loss in obese asthmatics or in mouse models of the condition decreases methacholine hyperresponsiveness. Ketone bodies are rapidly elevated during weight loss, coinciding with or preceding relief from asthma-related comorbidities. As ketone bodies may exert numerous potentially therapeutic effects, augmenting their systemic concentrations is being targeted for the treatment of several conditions. Circulating ketone body levels can be increased by feeding a ketogenic diet or by providing a ketone ester dietary supplement, which we hypothesized would exert protective effects in mouse models of inherent obese asthma. Weight loss induced by feeding a low-fat diet to mice previously fed a high-fat diet was preceded by increased urine and blood levels of the ketone body β-hydroxybutyrate (BHB). Feeding a ketogenic diet for 3 wk to high-fat diet-fed obese mice or genetically obese db/db mice increased BHB concentrations and decreased methacholine hyperresponsiveness without substantially decreasing body weight. Acute ketone ester administration decreased methacholine responsiveness of normal mice, and dietary ketone ester supplementation of high-fat diet-fed mice decreased methacholine hyperresponsiveness. Ketone ester supplementation also transiently induced an "antiobesogenic" gut microbiome with a decreased Fermicutes/Bacteroidetes ratio. Dietary interventions to increase systemic BHB concentrations could provide symptom relief for obese asthmatics without the need for the substantial weight loss required of patients to elicit benefits to their asthma through bariatric surgery or other diet or lifestyle alterations.

Diet-induced obesity in mice impairs host defense against Klebsiella pneumonia in vivo and glucose transport and bactericidal functions in neutrophils in vitro

Obesity impairs host defense against Klebsiella pneumoniae, but responsible mechanisms are incompletely understood. To determine the impact of diet-induced obesity on pulmonary host defense against K. pneumoniae, we fed 6-wk-old male C57BL/6j mice a normal diet (ND) or high-fat diet (HFD) (13% vs. 60% fat, respectively) for 16 wk. Mice were intratracheally infected with Klebsiella, assayed at 24 or 48 h for bacterial colony-forming units, lung cytokines, and leukocytes from alveolar spaces, lung parenchyma, and gonadal adipose tissue were assessed using flow cytometry. Neutrophils from uninfected mice were cultured with and without 2-deoxy-d-glucose (2-DG) and assessed for phagocytosis, killing, reactive oxygen intermediates (ROI), transport of 2-DG, and glucose transporter (GLUT1-4) transcripts, and protein expression of GLUT1 and GLUT3. HFD mice had higher lung and splenic bacterial burdens. In HFD mice, baseline lung homogenate concentrations of IL-1β, IL-6, IL-17, IFN-γ, CXCL2, and TNF-α were reduced relative to ND mice, but following infection were greater for IL-6, CCL2, CXCL2, and IL-1β (24 h only). Despite equivalent lung homogenate leukocytes, HFD mice had fewer intraalveolar neutrophils. HFD neutrophils exhibited decreased Klebsiella phagocytosis and killing and reduced ROI to heat-killed Klebsiella in vitro. 2-DG transport was lower in HFD neutrophils, with reduced GLUT1 and GLUT3 transcripts and protein (GLUT3 only). Blocking glycolysis with 2-DG impaired bacterial killing and ROI production in neutrophils from mice fed ND but not HFD. Diet-induced obesity impairs pulmonary Klebsiella clearance and augments blood dissemination by reducing neutrophil killing and ROI due to impaired glucose transport.

Neutrophils and their role in the aetiopathogenesis of type 1 and type 2 diabetes

Multiple and complex aetiological processes underlie diabetes mellitus, which invariably result in the development of hyperglycaemia. Although there are two prevalent distinct forms of the disease, that is, type 1 and type 2 diabetes, accumulating evidence indicates that these syndromes share more aetiopathological mechanisms than originally thought. This compels a rethinking of the approaches to prevent and treat the different manifestations of what eventually becomes a hyperglycaemic state. This review aims to address the involvement of neutrophils, the most abundant type of granulocytes involved in the initiation of the acute phase of inflammation, in the aetiopathogenesis of diabetes mellitus, with a focus on type 1 and type 2 diabetes. We review the evidence that neutrophils are the first leucocytes to react to and accumulate inside target tissues of diabetes, such as the pancreas and insulin-sensitive tissues. We then review available data on the role of neutrophils and their functional alteration, with a focus on NETosis, in the progression towards clinical disease. Finally, we review potential approaches as secondary and adjunctive treatments to limit neutrophil-mediated damage in the prevention of the progression of subclinical disease to clinical hyperglycaemia.

Storage conditions of high-fat diets affect pulmonary inflammation

Obesity alters the risks and outcomes of inflammatory lung diseases. It is important to accurately recapitulate the obese state in animal models to understand these effects on the pathogenesis of disease. Diet-induced obesity is a commonly used model of obesity, but when applied to other disease models like acute respiratory distress syndrome, pneumonia, and asthma, it yields widely divergent. We hypothesized high-fat chow storage conditions would affect lipid oxidation and inflammatory response in the lungs of lipopolysaccharide (LPS)-challenged mice. For 6 weeks, C57BL/6crl mice were fed either a 10% (low-fat diet, LFD) or 60% (high-fat diet, HFD) stored at room temperature (RT, 23°C) for up to 7, 14, 21, or 42 days. Mice were treated with nebulized LPS to induce lung inflammation, and neutrophil levels in bronchoalveolar lavage were determined 24 h later. Lipid oxidation (malondialdehyde, MDA) was assayed by thiobarbituric acid reactive substances in chow and mouse plasma. Concentrations of MDA in chow and plasma rose in proportion to the duration of RT chow storage. Mice fed a HFD stored <2 weeks at RT had an attenuated response 24 h after LPS compared with mice fed an LFD. This effect was reversed after 2 weeks of chow storage at RT. Chow stored above freezing underwent lipid oxidation associated with significant alterations in the LPS-induced pulmonary inflammatory response. Our data show that storage conditions affect lipid peroxidation, which in turn affects pulmonary inflammatory responses in a mouse model of disease. It also suggests changes in the microbiome, although not significantly different suggests decreased variety and richness of bacteria in the gut, a large aspect of the immune system. Dietary composition and storage of chow may also affect pulmonary inflammation and the gut microbiome in humans.

Effects of propofol and its formulation components on macrophages and neutrophils in obese and lean animals

We hypothesized whether propofol or active propofol component (2,6-diisopropylphenol [DIPPH] and lipid excipient [LIP-EXC]) separately may alter inflammatory mediators expressed by macrophages and neutrophils in lean and obese rats. Male Wistar rats (n = 10) were randomly assigned to receive a standard (lean) or obesity-inducing diet (obese) for 12 weeks. Animals were euthanized, and alveolar macrophages and neutrophils from lean and obese animals were exposed to propofol (50 µM), active propofol component (50 µM, 2,6-DIPPH), and lipid excipient (soybean oil, purified egg phospholipid, and glycerol) for 1 h. The primary outcome was IL-6 expression after propofol and its components exposure by alveolar macrophages extracted from bronchoalveolar lavage fluid. The secondary outcomes were the production of mediators released by macrophages from adipose tissue, and neutrophils from lung and adipose tissues, and neutrophil migration. IL-6 increased after the exposure to both propofol (median [interquartile range] 4.14[1.95-5.20]; p = .04) and its active component (2,6-DIPPH) (4.09[1.67-5.91]; p = .04) in alveolar macrophages from obese animals. However, only 2,6-DIPPH increased IL-10 expression (7.59[6.28-12.95]; p = .001) in adipose tissue-derived macrophages. Additionally, 2,6-DIPPH increased C-X-C chemokine receptor 2 and 4 (CXCR2 and CXCR4, respectively) in lung (10.08[8.23-29.01]; p = .02; 1.55[1.49-3.43]; p = .02) and adipose tissues (8.78[4.15-11.57]; p = .03; 2.86[2.17-3.71]; p = .01), as well as improved lung-derived neutrophil migration (28.00[-3.42 to 45.07]; p = .001). In obesity, the active component of propofol affected both the M1 and M2 markers as well as neutrophils in both alveolar and adipose tissue cells, suggesting that lipid excipient may hinder the effects of active propofol.

The Role of Obesity in the Immunopathogenesis of COVID-19 Respiratory Disease and Critical Illness

Coronavirus disease (COVID-19), the clinical syndrome caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is currently a global health pandemic with substantial morbidity and mortality. COVID-19 has cast a shadow on nearly every aspect of society, straining health systems and economies across the world. Although it is widely accepted that a close relationship exists between obesity, cardiovascular disease, and metabolic disorders on infection, we are only beginning to understand ways in which the immunological sequelae of obesity functions as a predisposing factor related to poor clinical outcomes in COVID-19. As both the innate and adaptive immune systems are each primed by obesity, the alteration of key pathways results in both an immunosuppressed and hyperinflammatory state. The present review will discuss the cellular and molecular immunology of obesity in the context of its role as a risk factor for severe COVID-19, discuss the role of cytokine storm, and draw parallels to prior viral epidemics such as severe acute respiratory syndrome (SARS), Middle East respiratory syndrome (MERS), and 2009 H1N1.

The Inflammatory Profile of Obesity and the Role on Pulmonary Bacterial and Viral Infections

Obesity is a globally increasing health problem, entailing diverse comorbidities such as infectious diseases. An obese weight status has marked effects on lung function that can be attributed to mechanical dysfunctions. Moreover, the alterations of adipocyte-derived signal mediators strongly influence the regulation of inflammation, resulting in chronic low-grade inflammation. Our review summarizes the known effects regarding pulmonary bacterial and viral infections. For this, we discuss model systems that allow mechanistic investigation of the interplay between obesity and lung infections. Overall, obesity gives rise to a higher susceptibility to infectious pathogens, but the pathogenetic process is not clearly defined. Whereas, viral infections often show a more severe course in obese patients, the same patients seem to have a survival benefit during bacterial infections. In particular, we summarize the main mechanical impairments in the pulmonary tract caused by obesity. Moreover, we outline the main secretory changes within the expanded adipose tissue mass, resulting in chronic low-grade inflammation. Finally, we connect these altered host factors to the influence of obesity on the development of lung infection by summarizing observations from clinical and experimental data.

Mortality association between obesity and pneumonia using a dual restricted cohort model

BACKGROUND

An obesity survival paradox has been reported among obese patients with pneumonia.

AIMS

To determine the impact of obesity on pneumonia outcomes and analyze the correlation between in-hospital all-cause mortality and obesity among patients with pneumonia.

METHODS

The United States Nationwide Readmissions Database (NRD) was retrospectively analyzed for patients with pneumonia from 2013 to 2014. We used a step-wise restricted and propensity score matching cohort model (dual model) to compare mortality rates and other outcomes among pneumonia patients based on BMI. Mortality was calculated by a Cox proportional hazard model, adjusted for potential confounders with propensity score matched analysis.

RESULTS

A total of 70,886,775 patients were registered in NRD during the study period. Of these, 7,786,913 patients (11.0%) were considered obese and 1,652,456 patients (2.3%) were admitted to the hospital with pneumonia. Based on the step-wise restricted cohort model, the hazard ratio comparing the mortality rates among obese pneumonia patients to mortality rates among normal BMI pneumonia patients was 0.75 (95% CI 0.60-0.94). The propensity score matched analysis estimated a hazard rate of 0.84 (95% CI 0.79-0.90) and the hazard ratio estimated from the dual model was 0.82 (95% CI 0.63-1.07).

CONCLUSIONS

With the application of a dual model, there appears to be no significant difference in mortality of obese patients with pneumonia compared to normal BMI patients with pneumonia.

IL-33, diet-induced obesity, and pulmonary responses to ozone

Background

Obesity augments pulmonary responses to ozone. We have reported that IL-33 contributes to these effects of obesity in db/db mice. The purpose of this study was to determine whether IL-33 also contributes to obesity-related changes in the response to ozone in mice with diet-induced obesity.

Methods

Male wildtype C57BL/6 mice and mice deficient in ST2, the IL-33 receptor, were placed on chow or high fat diets for 12 weeks from weaning. Because the microbiome has been implicated in obesity-related changes in the pulmonary response to ozone, mice were either housed with other mice of the same genotype (same housed) or with mice of the opposite genotype (cohoused). Cohousing transfers the gut microbiome from one mouse to its cagemates.

Results

Diet-induced increases in body mass were not affected by ST2 deficiency or cohousing. In same housed mice, ST2 deficiency reduced ozone-induced airway hyperresponsiveness and neutrophil recruitment in chow-fed but not HFD-fed mice even though ST2 deficiency reduced bronchoalveolar lavage IL-5 in both diet groups. In chow-fed mice, cohousing abolished ST2-related reductions in ozone-induced airway hyperresponsiveness and neutrophil recruitment, but in HFD-fed mice, no effect of cohousing on these responses to ozone was observed. In chow-fed mice, ST2 deficiency and cohousing caused changes in the gut microbiome. High fat diet-feeding caused marked changes in the gut microbiome and overrode both ST2-related and cohousing-related differences in the gut microbiome observed in chow-fed mice.

Conclusion

Our data indicate a role for IL-33 in pulmonary responses to ozone in chow-fed but not high fat diet-fed mice and are consistent with the hypothesis that these diet-related differences in the role of IL-33 are the result of changes in the gut microbiome.

Mortality association between obesity and pneumonia using a dual restricted cohort model

BACKGROUND

An obesity survival paradox has been reported among obese patients with pneumonia.

AIMS

To determine the impact of obesity on pneumonia outcomes and analyze the correlation between in-hospital all-cause mortality and obesity among patients with pneumonia.

METHODS

The United States Nationwide Readmissions Database (NRD) was retrospectively analyzed for patients with pneumonia from 2013 to 2014. We used a step-wise restricted and propensity score matching cohort model (dual model) to compare mortality rates and other outcomes among pneumonia patients based on BMI. Mortality was calculated by a Cox proportional hazard model, adjusted for potential confounders with propensity score matched analysis.

RESULTS

A total of 70,886,775 patients were registered in NRD during the study period. Of these, 7,786,913 patients (11.0%) were considered obese and 1,652,456 patients (2.3%) were admitted to the hospital with pneumonia. Based on the step-wise restricted cohort model, the hazard ratio comparing the mortality rates among obese pneumonia patients to mortality rates among normal BMI pneumonia patients was 0.75 (95% CI 0.60-0.94). The propensity score matched analysis estimated a hazard rate of 0.84 (95% CI 0.79-0.90) and the hazard ratio estimated from the dual model was 0.82 (95% CI 0.63-1.07).

CONCLUSIONS

With the application of a dual model, there appears to be no significant difference in mortality of obese patients with pneumonia compared to normal BMI patients with pneumonia.

Short-term high-fat diet feeding protects from the development of experimental allergic asthma in mice

BACKGROUND

A close association between obesity and asthma has been described. The nature of this association remains elusive, especially with respect to allergic asthma. Controversial findings exist regarding the impact of short-term high-fat diet (HFD) feeding on the development of allergic asthma.

OBJECTIVE

To delineate the impact of short-term HFD feeding on the development of experimental allergic asthma.

METHODS

Female C57BL/6JRJ mice were fed with a short-term HFD or chow diet (CD) for 12 weeks. Allergic asthma was induced by intraperitoneal OVA/alum sensitization followed by repeated OVA airway challenges. We determined airway hyperresponsiveness (AHR) and pulmonary inflammation by histologic and flow cytometric analysis of immune cells. Furthermore, we assessed the impact of HFD on dendritic cell (DC)-mediated activation of T cells.

RESULTS

Female mice showed a mild increase in body weight accompanied by mild metabolic alterations. Upon OVA challenge, CD-fed mice developed strong AHR and airway inflammation, which were markedly reduced in HFD-fed mice. Mucus production was similar in both treatment groups. OVA-induced increases in DC and CD4⁺ T-cell recruitment to the lungs were significantly attenuated in HFD-fed mice. MHC-II expression and CD40 expression in pulmonary CD11b⁺ DCs were markedly lower in HFD-fed compared to CD-fed mice, which was associated in vivo with a decreased T helper (Th) 1/17 differentiation and Treg formation without impacting Th2 differentiation.

CONCLUSIONS/CLINICAL RELEVANCE

These findings suggest that short-term HFD feeding attenuates the development of AHR, airway inflammation, pulmonary DC recruitment and MHC-II/CD40 expression leading to diminished Th1/17 but unchanged Th2 differentiation. Thus, short-term HFD feeding and associated metabolic alterations may have protective effects in allergic asthma development.

Effects of Obesity on Pulmonary Inflammation and Remodeling in Experimental Moderate Acute Lung Injury

Obese patients are at higher risk of developing acute respiratory distress syndrome (ARDS); however, their survival rates are also higher compared to those of similarly ill non-obese patients. We hypothesized that obesity would not only prevent lung inflammation, but also reduce remodeling in moderate endotoxin-induced acute lung injury (ALI). Obesity was induced by early postnatal overfeeding in Wistar rats in which the litter size was reduced to 3 pups/litter (Obese, n = 18); Control animals (n = 18) were obtained from unculled litters. On postnatal day 150, Control, and Obese animals randomly received E. coli lipopolysaccharide (ALI) or saline (SAL) intratracheally. After 24 h, echocardiography, lung function and morphometry, and biological markers in lung tissue were evaluated. Additionally, mediator expression in neutrophils and macrophages obtained from blood and bronchoalveolar lavage fluid (BALF) was analyzed. Compared to Control-SAL animals, Control-ALI rats showed no changes in echocardiographic parameters, increased lung elastance and resistance, higher monocyte phagocytic capacity, collagen fiber content, myeloperoxidase (MPO) activity, and levels of interleukin (IL-6), tumor necrosis factor (TNF)-α, transforming growth factor (TGF)-β, and type III (PCIII), and I (PCI) procollagen in lung tissue, as well as increased expressions of TNF-α and monocyte chemoattractant protein (MCP)-1 in blood and BALF neutrophils. Monocyte (blood) and macrophage (adipose tissue) phagocytic capacities were lower in Obese-ALI compared to Control-ALI animals, and Obese animals exhibited reduced neutrophil migration compared to Control. Obese-ALI animals, compared to Obese-SAL, exhibited increased interventricular septum thickness (p = 0.003) and posterior wall thickness (p = 0.003) and decreased pulmonary acceleration time to pulmonary ejection time ratio (p = 0.005); no changes in lung mechanics, IL-6, TNF-α, TGF-β, PCIII, and PCI in lung tissue; increased IL-10 levels in lung homogenate (p = 0.007); reduced MCP-1 expression in blood neutrophils (p = 0.009); decreased TNF-α expression in blood (p = 0.02) and BALF (p = 0.008) neutrophils; and increased IL-10 expression in monocytes (p = 0.004). In conclusion, after endotoxin challenge, obese rats showed less deterioration of lung function, secondary to anti-inflammatory and anti-fibrotic effects, as well as changes in neutrophil and monocyte/macrophage phenotype in blood and BALF compared to Control rats.

Controversies when using mechanical ventilation in obese patients with and without acute distress respiratory syndrome

INTRODUCTION

As the prevalence of obesity increases, so does the number of obese patients undergoing surgical procedures and being admitted into intensive care units. Obesity per se is associated with reduced lung volume. The combination of general anaesthesia and supine positioning involved in most surgeries causes further reductions in lung volumes, thus resulting in alveolar collapse, decreased lung compliance, increased airway resistance, and hypoxemia. These complications can be amplified by common obesity-related comorbidities. In otherwise healthy obese patients, mechanical ventilation strategies should be optimised to prevent lung damage; in those with acute distress respiratory syndrome (ARDS), strategies should seek to mitigate further lung damage. Areas covered: This review discusses non-invasive and invasive mechanical ventilation strategies for surgical and critically ill adult obese patients with and without ARDS and proposes practical clinical insights to be implemented at bedside both in the operating theatre and in intensive care units. Expert opinion: Large multicentre trials on respiratory management of obese patients are required. Although the indication of lung protective ventilation with low tidal volume is apparently translated to obese patients, optimal PEEP level and recruitment manoeuvres remain controversial. The use of non-invasive respiratory support after extubation must be considered in individual cases.

Obesity and Type 2 Diabetes mellitus induce lipopolysaccharide tolerance in rat neutrophils

Obesity and diabetes implicate in various health complications and increased mortality caused by infection. Innate immune system is broadly affected by these diseases, leading the patients to an immunosuppressive state. A mechanism that leads innate immune cells to a less capacity of killing microorganism is the impaired TLR4 activation. TLR4 recognizes a component of the outer membrane of Gram-negative bacteria, lipopolysaccharide (LPS), and when activated increases the production of inflammatory substances. Neutrophils are components of the innate immune system and are the first responders to an invading agent. The correct activation of TLR4 in these cells is required for the initiation of the inflammatory process and elimination of the microorganisms. The aim of this study was to evaluate the influence of type 2 diabetes and obesity in the TLR4 pathway in rat neutrophils. Two experimental models were used: Goto-Kakizaki rats and high-fat-diet induced obese Wistar rats. To evaluate neutrophil response to LPS, intratracheal LPS instillation was used. Neutrophils from obese and diabetic animals exhibited tolerance to LPS, mainly by the impaired production of cytokines and chemokines and the low content of phospho-NFκB and phospho-IKBα. Neutrophils from both experimental models had increased cell death, impaired in vivo migration and myeloperoxidase activity.

The effect of obesity on lung function

INTRODUCTION

There is a major epidemic of obesity, and many obese patients suffer with respiratory symptoms and disease. The overall impact of obesity on lung function is multifactorial, related to mechanical and inflammatory aspects of obesity. Areas covered: Obesity causes substantial changes to the mechanics of the lungs and chest wall, and these mechanical changes cause asthma and asthma-like symptoms such as dyspnea, wheeze, and airway hyperresponsiveness. Excess adiposity is also associated with increased production of inflammatory cytokines and immune cells that may also lead to disease. This article reviews the literature addressing the relationship between obesity and lung function, and studies addressing how the mechanical and inflammatory effects of obesity might lead to changes in lung mechanics and pulmonary function in obese adults and children. Expert commentary: Obesity has significant effects on respiratory function, which contribute significantly to the burden of respiratory disease. These mechanical effects are not readily quantified with conventional pulmonary function testing and measurement of body mass index. Changes in mediators produced by adipose tissue likely also contribute to altered lung function, though as of yet this is poorly understood.

The Impact of Diet on Immunity and Respiratory Diseases

The Western world has witnessed a tremendous increase in the occurrence of allergy and autoimmunity in the second half of the 20th century. Extensive efforts have been made to explain this phenomenon and various hypotheses have been formulated. Among them, two concepts have attracted the most attention: the "hygiene hypothesis," identifying the reduced exposure to environmental microorganisms as a driving force behind the observed epidemiological trends; and the "diet hypotheses," pointing to the importance of changes in our dietary habits. In this review, we discuss the interplay between the Western diet, microbiota, and inflammatory conditions, with particular emphasis on respiratory diseases. This is followed by an in-depth overview of the immunomodulatory potential of different dietary fatty acids. We conclude by identifying the outstanding questions, which, if answered, could shed further light on the impact of dietary habits on immunity and interconnect it with postulates proposed by the hygiene hypothesis. Linking these two concepts will be an important step towards understanding how Western lifestyle shapes disease susceptibility.

Phosphatidylinositol-(3,4,5)-Trisphosphate Induces Phagocytosis of Nonmotile Pseudomonas aeruginosa

Pathogenic bacteria that establish chronic infections in immunocompromised patients frequently undergo adaptation or selection for traits that are advantageous for their growth and survival. Clinical isolates of Pseudomonas aeruginosa, a Gram-negative, opportunistic bacterial pathogen, exhibit a temporal transition from a motile to a nonmotile phenotype through loss of flagellar motility during the course of chronic infection. This progressive loss of motility is associated with increased resistance to both antibiotic and immune clearance. We have previously shown that loss of bacterial motility enables P. aeruginosa to evade phagocytic clearance both in vitro and in vivo and fails to activate the phosphatidylinositol 3-kinase (PI3K)/Akt-dependent phagocytic pathway. Therefore, we tested the hypothesis that clearance of phagocytosis-resistant bacteria could be induced by exogenously pretreating innate immune cells with the Akt-activating molecule phosphatidylinositol-(3,4,5)-trisphosphate (PIP₃). Here, we demonstrate that PIP₃ induces the uptake of nonmotile P. aeruginosa by primary human neutrophils >25-fold, and this effect is phenocopied with the use of murine phagocytes. However, surprisingly, mechanistic studies revealed that the induction of phagocytosis by PIP₃ occurs because polyphosphoinositides promote bacterial binding by the phagocytes rather than bypassing the requirement for PI3K. Moreover, this induction was selective since the uptake of other nonmotile Gram-negative, but not Gram-positive, bacteria can also be induced by PIP₃ Since there is currently no treatment that effectively eradicates chronic P. aeruginosa infections, these findings provide novel insights into a potential methodology by which to induce clearance of nonmotile pathogenic bacteria and into the endogenous determinants of phagocytic recognition of P. aeruginosa.

Pulmonary Surfactant Promotes Virulence Gene Expression and Biofilm Formation in Klebsiella pneumoniae

The interactions between Klebsiella pneumoniae and the host environment at the site of infection are largely unknown. Pulmonary surfactant serves as an initial point of contact for inhaled bacteria entering the lung and is thought to contain molecular cues that aid colonization and pathogenesis. To gain insight into this ecological transition, we characterized the transcriptional response of K. pneumoniae MGH 78578 to purified pulmonary surfactant. This work revealed changes within the K. pneumoniae transcriptome that likely contribute to host colonization, adaptation, and virulence in vivo Notable transcripts expressed under these conditions include genes involved in capsule synthesis, lipopolysaccharide modification, antibiotic resistance, biofilm formation, and metabolism. In addition, we tested the contributions of other surfactant-induced transcripts to K. pneumoniae survival using engineered isogenic KPPR1 deletion strains in a murine model of acute pneumonia. In these infection studies, we identified the MdtJI polyamine efflux pump and the ProU glycine betaine ABC transporter to be significant mediators of K. pneumoniae survival within the lung and confirmed previous evidence for the importance of de novo leucine synthesis to bacterial survival during infection. Finally, we determined that pulmonary surfactant promoted type 3 fimbria-mediated biofilm formation in K. pneumoniae and identified two surfactant constituents, phosphatidylcholine and cholesterol, that drive this response. This study provides novel insight into the interactions occurring between K. pneumoniae and the host at an important infection site and demonstrates the utility of purified lung surfactant preparations for dissecting host-lung pathogen interactions in vitro.

Ablation of the leptin receptor in myeloid cells impairs pulmonary clearance of Streptococcus pneumoniae and alveolar macrophage bactericidal function

Leptin is a pleiotropic hormone produced by white adipose tissue that regulates appetite and many physiological functions, including the immune response to infection. Genetic leptin deficiency in humans and mice impairs host defenses against respiratory tract infections. Since leptin deficiency is associated with obesity and other metabolic abnormalities, we generated mice that lack the leptin receptor (LepRb) in cells of the myeloid linage (LysM-LepRb-KO) to evaluate its impact in lean metabolically normal mice in a murine model of pneumococcal pneumonia. We observed higher lung and spleen bacterial burdens in LysM-LepRb-KO mice following an intratracheal challenge with Streptococcus pneumoniae. Although numbers of leukocytes recovered from bronchoalveolar lavage fluid did not differ between groups, we did observe higher levels of pulmonary IL-13 and TNFα in LysM-LepRb-KO mice 48 h post infection. Phagocytosis and killing of ingested S. pneumoniae were also impaired in alveolar macrophages (AMs) from LysM-LepRb-KO mice in vitro and were associated with reduced LTB₄ and enhanced PGE₂ synthesis in vitro. Pretreatment of AMs with LTB₄ and the cyclooxygenase inhibitor, indomethacin, restored phagocytosis but not bacterial killing in vitro. These results confirm our previous observations in leptin-deficient ( ob/ob) and fasted mice and demonstrate that decreased leptin action, as opposed to metabolic irregularities associated with obesity or starvation, is responsible for the defective host defense against pneumococcal pneumonia. They also provide novel targets for therapeutic intervention in humans with bacterial pneumonia.

Isolation and Characterization of Mouse Neutrophils

Isolation of murine neutrophils from several anatomical compartments allows for functional characterization and analysis of these cells. Here we describe the isolation of bone marrow, peripheral blood, and lung airspace and interstitial neutrophil populations, using density gradient separation, lavage, and flow cytometry techniques.

High-Fat Feeding Protects Mice From Ventilator-Induced Lung Injury, Via Neutrophil-Independent Mechanisms

OBJECTIVE

Obesity has a complex impact on acute respiratory distress syndrome patients, being associated with increased likelihood of developing the syndrome but reduced likelihood of dying. We propose that such observations are potentially explained by a model in which obesity influences the iatrogenic injury that occurs subsequent to intensive care admission. This study therefore investigated whether fat feeding protected mice from ventilator-induced lung injury.

DESIGN

In vivo study.

SETTING

University research laboratory.

SUBJECTS

Wild-type C57Bl/6 mice or tumor necrosis factor receptor 2 knockout mice, either fed a high-fat diet for 12-14 weeks, or age-matched lean controls.

INTERVENTIONS

Anesthetized mice were ventilated with injurious high tidal volume ventilation for periods up to 180 minutes.

MEASUREMENTS AND MAIN RESULTS

Fat-fed mice showed clear attenuation of ventilator-induced lung injury in terms of respiratory mechanics, blood gases, and pulmonary edema. Leukocyte recruitment and activation within the lungs were not significantly attenuated nor were a host of circulating or intra-alveolar inflammatory cytokines. However, intra-alveolar matrix metalloproteinase activity and levels of the matrix metalloproteinase cleavage product soluble receptor for advanced glycation end products were significantly attenuated in fat-fed mice. This was associated with reduced stretch-induced CD147 expression on lung epithelial cells.

CONCLUSIONS

Consumption of a high-fat diet protects mice from ventilator-induced lung injury in a manner independent of neutrophil recruitment, which we postulate instead arises through blunted up-regulation of CD147 expression and subsequent activation of intra-alveolar matrix metalloproteinases. These findings may open avenues for therapeutic manipulation in acute respiratory distress syndrome and could have implications for understanding the pathogenesis of lung disease in obese patients.

Beyond BMI: Obesity and Lung Disease

The worldwide prevalence of obesity has increased rapidly in the last 3 decades, and this increase has led to important changes in the pathogenesis and clinical presentation of many common diseases. This review article examines the relationship between obesity and lung disease, highlighting some of the major findings that have advanced our understanding of the mechanisms contributing to this relationship. Changes in pulmonary function related to fat mass are important, but obesity is much more than simply a state of mass loading, and BMI is only a very indirect measure of metabolic health. The obese state is associated with changes in the gut microbiome, cellular metabolism, lipid handling, immune function, insulin resistance, and circulating factors produced by adipose tissue. Together, these factors can fundamentally alter the pathogenesis and pathophysiology of lung health and disease.

Mouse Modeling of Obese Lung Disease. Insights and Caveats

As the obesity epidemic has worsened, its impact on lung health and disease has become progressively evident. The interactions between obesity and the accompanying metabolic syndrome and diseases such as asthma, pneumonia, and acute respiratory distress syndrome (ARDS) have proven complex and often counterintuitive in human studies. Hence, there is a growing need for relevant experimental approaches to understand the interactions between obesity and the lung. To this end, researchers have increasingly exploited mouse models combining both obesity and lung diseases, including ARDS, pneumonia, and asthma. Such models have both complemented and advanced the understanding we have gained from clinical studies and have allowed elegant dissections of obesity's effects on the pathogenesis of lung disease. Yet these models come with several critically important caveats that we must reflect on when interpreting their results.

Effect of Obesity on Perioperative Outcomes After Robotic-Assisted Pulmonary Lobectomy

OBJECTIVE

We investigated whether higher body mass index (BMI) affects perioperative and postoperative outcomes after robotic-assisted video-thoracoscopic pulmonary lobectomy.

METHODS

We retrospectively studied all patients who underwent robotic-assisted pulmonary lobectomy by one surgeon between September 2010 and January 2015. Patients were grouped according to the World Health Organization's definition of obesity, with "obese" being defined as BMI >30.0 kg/m². Perioperative outcomes, including intraoperative estimated blood loss (EBL) and postoperative complication rates, were compared.

RESULTS

Over 53 months, 287 patients underwent robotic-assisted pulmonary lobectomy, with 7 patients categorized as "underweight," 94 patients categorized as "normal weight," 106 patients categorized as "overweight," and 80 patients categorized as "obese." Because of the relatively low sample size, "underweight" patients were excluded from this study, leaving a total cohort of 280 patients. There was no significant difference in intraoperative complication rates, conversion rates, perioperative outcomes, or postoperative complication rates among the 3 groups, except for lower risk of prolonged air leaks ≥7 days and higher risk of pneumonia in patients with obesity.

CONCLUSIONS

Patients with obesity do not have increased risk of intraoperative or postoperative complications, except for pneumonia, compared with "normal weight" and "overweight" patients. Robotic-assisted pulmonary lobectomy is safe and effective for patients with high BMI.

Early local immune defences in the respiratory tract

The respiratory immune response consists of multiple tiers of cellular responses that are engaged in a sequential manner in order to control infections. The stepwise engagement of effector functions with progressively increasing host fitness costs limits tissue damage. In addition, specific mechanisms are in place to promote disease tolerance in response to respiratory infections. Environmental factors, obesity and the ageing process can alter the efficiency and regulation of this tiered response, increasing pathology and mortality as a result. In this Review, we describe the cell types that coordinate pathogen clearance and tissue repair through the serial secretion of cytokines, and discuss how the environment and comorbidity influence this response.

"Obesity Paradox" in Acute Respiratory Distress Syndrome: Asystematic Review and Meta-Analysis

Background

It is unclear whether an “obesity paradox” exists in the respiratory system, especially in acute respiratory distress syndrome (ARDS) and acute lung injury (ALI). Previous studies have postulated a causal relation between obesity and ARDS/ALI but have lacked power to form a definitive conclusion.

Objective

To investigate the relationships between obesity, ARDS/ALIrisk, and mortality.

Methods

A systematic search current to April 2016 was performed in Pubmed, EMBASE, Medline, Cochrane databases to find relevant studies. All studies that estimate the effect of obesity in the morbidity and mortality of ARDS/ALI were included.

Results

A total of 24 studies including 9,187,248 subjects were analyzed. The combined results from 16 studies that examined the effect of obesity in morbidity of ARDS/ALI showed an89% increase in odds ratio(pooled odds ratios (OR) 1.89, 95% confidence intervals (CI) 1.45 to 2.47). In subgroup analysis, compared to normal weight, obesity was associated with an increased risk of ARDS/ALI (OR1.57, 95% CI 1.30–1.90 for obese (BMI30-39.9kg/m²); OR1.75, 95% CI 1.42–2.15 for obese(BMI≥30kg/m²); OR1.67, 95% CI 1.04–2.68 for morbid obese(BMI≥40kg/m²)). The combined results from 9 studies that examined the effect of obesity in mortality of ARDS/ALI had a pooled odds ratio(pooled OR 0.63, 95% CI 0.41 to 0.98). Inversely, obesity was significantly associated with reduced risk of ARDS/ALI mortality(OR0.88, 95% CI 0.78–1.00 for overweight(BMI≤18.5m²); OR0.74, 95% CI 0.64–0.84 for obese (BMI30-39.9kg/m²);OR0.84, 95% CI 0.75–0.94 for 60days mortality; OR0.38, 95% CI 0.22–0.66 for 90days mortality).

Conclusions

Our data identify obesity as an important risk factor for the development of ARDS/ALI; however, ARDS/ALI outcomes are improved in this population when compared to individuals with a normal body mass index. This meta-analysis results supported ‘‘obesity paradox” in ARDS/ALI.

Hyperleptinemia is associated with impaired pulmonary host defense

We have previously reported that obesity attenuates pulmonary inflammation in both patients with acute respiratory distress syndrome (ARDS) and in mouse models of the disease. We hypothesized that obesity-associated hyperleptinemia, and not body mass per se, drives attenuation of the pulmonary inflammatory response and that this e_ect could also impair the host response to pneumonia. We examined the correlation between circulating leptin levels and risk, severity, and outcome of pneumonia in 2 patient cohorts (NHANES III and ARDSNet-ALVEOLI) and in mouse models of diet-induced obesity and lean hyperleptinemia. Plasma leptin levels in ambulatory subjects (NHANES) correlated positively with annual risk of respiratory infection independent of BMI. In patients with severe pneumonia resulting in ARDS (ARDSNet-ALVEOLI), plasma leptin levels were found to correlate positively with subsequent mortality. In obese mice with pneumonia, plasma leptin levels were associated with pneumonia severity, and in obese mice with sterile lung injury, leptin levels were inversely related to bronchoalveolar lavage neutrophilia, as well as to plasma IL-6 and G-CSF levels. These results were recapitulated in lean mice with experimentally induced hyperleptinemia. Our findings suggest that the association between obesity and elevated risk of pulmonary infection may be driven by hyperleptinemia.