Iron laden macrophages in idiopathic pulmonary fibrosis: the telltale of occult alveolar hemorrhage?

Down-regulation of CYTL1 attenuates bleomycin-induced pulmonary fibrosis in mice by inhibiting M2 macrophage polarization via the TGF-β/CCN2 axis

Idiopathic pulmonary fibrosis (IPF) is an interstitial lung disease characterized by chronic inflammation, lung tissue fibrotic changes and impaired lung function. Pulmonary fibrosis 's pathological process is thought to be influenced by macrophage-associated phenotypes. IPF treatment requires specific targets that target macrophage polarization. Cytokine-like 1(CYTL1) is a secreted protein with multiple biological functions first discovered in CD34+ haematopoietic cells. However, its possible effects on IPF progression remain unclear. This study investigated the role of CYTL1 in IPF progression in a bleomycin-induced lung injury and fibrosis model. In bleomycin-induced mice, CYTL1 is highly expressed. Moreover, CYTL1 ablation alleviates lung injury and fibrosis in vivo. Further, downregulating CYTL1 reduces macrophage M2 polarization. Mechanically, CYTL1 regulates transforming growth factor β (TGF-β)/connective tissue growth factor (CCN2) axis and inhibition of TGF-β pathway alleviates bleomycin-induced lung injury and fibrosis. In conclusion, highly expressed CYTL1 inhibits macrophage M2 polarization by regulating TGF-β/CCN2 expression, alleviating bleomycin-induced lung injury and fibrosis. CYTL1 could, therefore, serve as a promising IPF target.

Dihydroartemisinin (DHA) inhibits myofibroblast differentiation through inducing ferroptosis mediated by ferritinophagy

Idiopathic pulmonary fibrosis (IPF) is caused by persistent micro-injuries and aberrant repair processes. Myofibroblast differentiation in lung is a key event for abnormal repair. Dihydroartemisinin(DHA), a well-known anti-malarial drug, have been shown to alleviate pulmonary fibrosis, but its mechanism is not clear. Ferroptosis is involved in the pathgenesis of many diseases, including IPF. Ferritinophagy is a form of cellular autophagy which regulates intracellular iron homeostasis. The function of DHA on myofibroblasts differentiation of pulmonary and whether related with ferroptosis and ferritinophagy are unknown now. Using human fetal lung fibroblast 1(HFL1) cell line and the qRT-PCR, immunofluorescent and Western blotting techniques, we found that after TGF-β1 treatment, the levels of ɑ-SMA expression and ROS increased; the mRNA and protein levels of FTH1 and NCOA4, the content of Fe2+ and 4-HNE increased significantly at 6h, then gradually reduced with time. After DHA treatment, FHL1 cells appeared ferroptosis; the levels of α-SMA mRNA and protein reduced and the levels of ROS and 4-HNE increased; the Fe2+ levels decreased sharply at 6h, then increased with time, and were higher than normal since 24h; the mRNA and protein levels of FTH1 and NCOA4 decreased, exhibited a downward trend. These results show that Fe2+, ROS and lipid peroxidation are involved in and ferritinophagy is inhibited during fibroblast-to-myofibroblast differentiation; The depletion of Fe2+ at early stage induced by DHA treatment triggers the ferritinophagy in HFL1 cells, leading to degradation of FTH1 and NCOA4 and following increase of Fe2+ levels. DHA may inhibit the fibroblast-to-myofibroblast differentiation through inducing ferroptosis mediated by ferritinophagy.

Identification of Hub Genes in Idiopathic Pulmonary Fibrosis and Their Association with Lung Cancer by Bioinformatics Analysis

BACKGROUND

Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive, and irreversible disease with a high mortality rate worldwide. However, the etiology and pathogenesis of IPF have not yet been fully described. Moreover, lung cancer is a significant complication of IPF and is associated with increased mortality. Nevertheless, identifying common genes involved in developing IPF and its progression to lung cancer remains an unmet need. The present study aimed to identify hub genes related to the development of IPF by meta-analysis. In addition, we analyzed their expression and their relationship with patients' progression in lung cancer.

METHOD

Microarray datasets GSE24206, GSE21369, GSE110147, GSE72073, and GSE32539 were downloaded from Gene Expression Omnibus (GEO). Next, we conducted a series of bioinformatics analysis to explore possible hub genes in IPF and evaluated the expression of hub genes in lung cancer and their relationship with the progression of different stages of cancer.

RESULTS

A total of 1888 differentially expressed genes (DEGs) were identified, including 1105 upregulated and 783 downregulated genes. The 10 hub genes that exhibited a high degree of connectivity from the PPI network were identified. Analysis of the KEGG pathways showed that hub genes correlate with pathways such as the ECM-receptor interaction. Finally, we found that these hub genes are expressed in lung cancer and are associated with the progression of different stages of lung cancer.

CONCLUSIONS

Based on the integration of GEO microarray datasets, the present study identified DEGs and hub genes that could play an essential role in the pathogenesis of IPF and its association with the development of lung cancer in these patients, which could be considered potential diagnostic biomarkers or therapeutic targets for the disease.

Monocytes and macrophages: emerging mechanisms and novel therapeutic targets in pulmonary fibrosis

Pulmonary fibrosis results from a plethora of abnormal pathogenetic events. In idiopathic pulmonary fibrosis (IPF), inhalational, environmental, or occupational exposures in genetically and epigenetically predisposed individuals trigger recurrent cycles of alveolar epithelial cell injury, activation of coagulation pathways, chemoattraction, and differentiation of monocytes into monocyte-derived alveolar macrophages (Mo-AMs). When these events happen intermittently and repeatedly throughout the individual's life cycle, the wound repair process becomes aberrant leading to bronchiolization of distal air spaces, fibroblast accumulation, extracellular matrix deposition, and loss of the alveolar-capillary architecture. The role of immune dysregulation in IPF pathogenesis and progression has been underscored in the past mainly after the disappointing results of immunosuppressant use in IPF patients; however, recent reports highlighting the prognostic and mechanistic roles of monocytes and Mo-AMs revived the interest in immune dysregulation in IPF. In this review, we will discuss the role of these cells in the onset and progression of IPF, as well as potential targeted therapies.

Metabolism of tissue macrophages in homeostasis and pathology

Cellular metabolism orchestrates the intricate use of tissue fuels for catabolism and anabolism to generate cellular energy and structural components. The emerging field of immunometabolism highlights the importance of cellular metabolism for the maintenance and activities of immune cells. Macrophages are embryo- or adult bone marrow-derived leukocytes that are key for healthy tissue homeostasis but can also contribute to pathologies such as metabolic syndrome, atherosclerosis, fibrosis or cancer. Macrophage metabolism has largely been studied in vitro. However, different organs contain diverse macrophage populations that specialize in distinct and often tissue-specific functions. This context specificity creates diverging metabolic challenges for tissue macrophage populations to fulfill their homeostatic roles in their particular microenvironment and conditions their response in pathological conditions. Here, we outline current knowledge on the metabolic requirements and adaptations of macrophages located in tissues during homeostasis and selected diseases.

Cigarette Smoke Particle-Induced Lung Injury and Iron Homeostasis

It is proposed that the mechanistic basis for non-neoplastic lung injury with cigarette smoking is a disruption of iron homeostasis in cells after exposure to cigarette smoke particle (CSP). Following the complexation and sequestration of intracellular iron by CSP, the host response (eg, inflammation, mucus production, and fibrosis) attempts to reverse a functional metal deficiency. Clinical manifestations of this response can present as respiratory bronchiolitis, desquamative interstitial pneumonitis, pulmonary Langerhans’ cell histiocytosis, asthma, pulmonary hypertension, chronic bronchitis, and pulmonary fibrosis. If the response is unsuccessful, the functional deficiency of iron progresses to irreversible cell death evident in emphysema and bronchiectasis. The subsequent clinical and pathological presentation is a continuum of lung injuries, which overlap and coexist with one another. Designating these non-neoplastic lung injuries after smoking as distinct disease processes fails to recognize shared relationships to each other and ultimately to CSP, as well as the common mechanistic pathway (ie, disruption of iron homeostasis).

Hemosiderin-Laden Macrophages in Bronchoalveolar Lavage: Predictive Role for Acute Exacerbation of Idiopathic Interstitial Pneumonias

Background

Hemosiderin-laden macrophages (HLMs) have been identified in the bronchoalveolar lavage fluid (BALF) of patients with idiopathic pulmonary fibrosis (IPF). This retrospective study examined the ability of HLMs in BALF to predict the acute exacerbation (AE) of chronic idiopathic interstitial pneumonias (IIPs).

Methods

Two hundred and twenty-one patients with IIP diagnosed by bronchoscopy were enrolled in the study (IPF, n = 87; IIPs other than IPF, n = 134). Giemsa stain was used to detect HLMs in BALF specimens. Prussian blue stain was used to quantify HLMs in BALF, and a hemosiderin score (HS) was given to the specimens containing HLMs.

Results

Twenty-four patients had a positive HS (range: 7‒132). The receiver-operating characteristic curve analysis identified the cutoff HS value for predicting the AE of IIPs to be 61.5. Seven cases had a higher HS (≥61.5) and 214 had a lower HS. AE occurred significantly earlier in the higher HS group (4/7 cases) than in the lower HS group (41/214 cases) during a median observation period of 1239 days (log-rank test, p = 0.026). Multivariate Cox proportional hazard regression analysis showed that a higher HS was a significant predictor of AE in addition to IPF, percent predicted forced vital capacity, and modified Medical Research Council score. The C-statistics for the prediction of AE did not significantly improve by all the above parameters with HS as compared without HS.

Conclusions

A higher HS was a significant predictor of AE in IIPs but did not significantly improve the predictive ability of other parameters.

Red Blood Cell-Derived Iron Alters Macrophage Function in COPD

Lung macrophage iron levels are increased in COPD patients. Lung macrophage iron levels are thought to be increased by cigarette smoke, but the role of red blood cells (RBCs) as a source of iron has not been investigated. We investigate RBCs as a potential source of alveolar iron in COPD, and determine the effect of RBC-derived iron on macrophage function. We used lung tissue sections to assess RBC coverage of the alveolar space, iron and ferritin levels in 11 non-smokers (NS), 15 smokers (S) and 32 COPD patients. Lung macrophages were isolated from lung resections (n = 68) and treated with hemin or ferric ammonium citrate (50, 100 or 200 μM). Lung macrophage phenotype marker gene expression was measured by qPCR. The phagocytosis of Non-typeable Haemophilus influenzae (NTHi) was measured by flow cytometry. Cytokine production in response to NTHi in iron-treated macrophages was measured by ELISA. Lung macrophage iron levels were significantly correlated with RBC coverage of the alveolar space (r = 0.31, p = 0.02). Furthermore, RBC coverage and lung macrophage iron were significantly increased in COPD patients and correlated with airflow obstruction. Hemin treatment downregulated CD36, CD163, HLA-DR, CD38, TLR4, CD14 and MARCO gene expression. Hemin-treated macrophages also impaired production of pro-inflammatory cytokines in response to NTHi exposure, and decreased phagocytosis of NTHi (200 μM: 35% decrease; p = 0.03). RBCs are a plausible source of pulmonary iron overload in COPD. RBC-derived iron dysregulates macrophage phenotype and function.

Iron overload and mitochondrial dysfunction orchestrate pulmonary fibrosis

Pulmonary fibrosis (PF) is a chronic, progressive heterogeneous disease of lung tissues with poor lung function caused by scar tissue. Due to our limited understanding of its mechanism, there is currently no treatment strategy that can prevent the development of PF. In recent years, iron accumulation and mitochondrial damage have been reported to participate in PF, and drugs that reduce iron content and improve mitochondrial function have shown significant efficacy in animal experimental models. Excessive iron leads to mitochondrial impairment, which may be the key cause that results in the dysfunction of various kinds of pulmonary cells and further promotes PF. As an emerging research hotspot, there are few targeted effective therapeutic strategies at present due to limited mechanistic understanding. In this review, the roles of iron homeostasis imbalance and mitochondrial damage in PF are summarized and discussed, highlighting a promising direction for finding truly effective therapeutics for PF.

Anticoagulant Use as an Independent Risk Factor and Higher In-Hospital Mortality in Patients Showing Alveolar Hemorrhage in Diffuse Lung Disease

Background and objectives: Bronchoalveolar lavage (BAL) is commonly performed to evaluate diffuse lung disease and occasionally to identify alveolar hemorrhage. However, the clinical impact of alveolar hemorrhage and its risk factors in patients with diffuse lung disease have not been clarified. Materials and Methods: We retrospectively analyzed the medical records of all patients who underwent BAL to evaluate diffuse lung disease from January 2017 to December 2020. Alveolar hemorrhage was defined as progressive hemorrhagic BAL fluid or the presence of ≥20% hemosiderin-laden macrophages in the BAL fluid. Logistic regression analysis was performed to assess the association between alveolar hemorrhage and other factors. Results: Sixty subjects were enrolled in this study. Alveolar hemorrhage was observed in 19 subjects (31.7%) with idiopathic interstitial pneumonia, acute respiratory distress syndrome, interstitial pneumonia with autoimmune features, drug-induced lung injury, eosinophilic pneumonia, adenocarcinoma, and systemic lupus erythematosus. The use of anticoagulants was a significant risk factor for alveolar hemorrhage (odds ratio 7.57, p = 0.049). Patients with alveolar hemorrhage required intubated mechanical ventilation more frequently (63.2% vs. 24.4%, p = 0.005) and had higher in-hospital mortality rates (26.3% vs. 4.9%, p = 0.028) than those without alveolar hemorrhage. Conclusions: Alveolar hemorrhage was observed in various etiologies. The use of anticoagulants was a significant risk factor for alveolar hemorrhage. Patients with alveolar hemorrhage showed more severe respiratory failure and had higher in-hospital mortality than those without alveolar hemorrhage.

Nutritional immunity: the impact of metals on lung immune cells and the airway microbiome during chronic respiratory disease

Nutritional immunity is the sequestration of bioavailable trace metals such as iron, zinc and copper by the host to limit pathogenicity by invading microorganisms. As one of the most conserved activities of the innate immune system, limiting the availability of free trace metals by cells of the immune system serves not only to conceal these vital nutrients from invading bacteria but also operates to tightly regulate host immune cell responses and function. In the setting of chronic lung disease, the regulation of trace metals by the host is often disrupted, leading to the altered availability of these nutrients to commensal and invading opportunistic pathogenic microbes. Similarly, alterations in the uptake, secretion, turnover and redox activity of these vitally important metals has significant repercussions for immune cell function including the response to and resolution of infection. This review will discuss the intricate role of nutritional immunity in host immune cells of the lung and how changes in this fundamental process as a result of chronic lung disease may alter the airway microbiome, disease progression and the response to infection.

Clioquinol Attenuates Pulmonary Fibrosis through Inactivation of Fibroblasts via Iron Chelation

Strict control of iron homeostasis is critical for the maintenance of normal lung function. Iron accumulates in the lungs of patients with idiopathic pulmonary fibrosis (PF), but the characteristics of iron metabolism in the pathogenesis of PF and related targeting therapeutics are not well studied. In this study, we investigated the cellular and molecular characteristics of iron metabolism in fibrotic lungs and further explored the efficacy of clioquinol (CQ) for the treatment of PF as well as its functional mechanism. Iron aggregates accumulated in the lungs of patients with idiopathic PF, and FTL (ferritin light chain) transcripts were increased in their pulmonary fibroblasts. In the bleomycin (BLM)-induced PF (BLM-PF) mouse model, pulmonary iron accumulation is a very early and concomitant event of PF. Labile iron pool levels in both fibroblasts and macrophages from the BLM-PF model were elevated, and iron metabolism was dysregulated. CQ attenuated PF induced by BLM and FITC, and iron-saturated CQ did not alleviate BLM-PF. Furthermore, CQ inhibited the activation of fibroblasts, including proliferation, fibrotic differentiation, proinflammatory cytokine secretion, and migration. In conclusion, our study demonstrated that CQ, acting as an iron chelator, attenuates experimental PF through inactivation of fibroblasts, providing support for targeting iron metabolism as a basis for PF treatment.

Macrophage metabolic reprogramming during chronic lung disease

Airway macrophages (AMs) play key roles in the maintenance of lung immune tolerance. Tissue tailored, highly specialised and strategically positioned, AMs are critical sentinels of lung homoeostasis. In the last decade, there has been a revolution in our understanding of how metabolism underlies key macrophage functions. While these initial observations were made during steady state or using in vitro polarised macrophages, recent studies have indicated that during many chronic lung diseases (CLDs), AMs adapt their metabolic profile to fit their local niche. By generating reactive oxygen species (ROS) for pathogen defence, utilising aerobic glycolysis to rapidly generate cytokines, and employing mitochondrial respiration to fuel inflammatory responses, AMs utilise metabolic reprogramming for host defence, although these changes may also support chronic pathology. This review focuses on how metabolic alterations underlie AM phenotype and function during CLDs. Particular emphasis is given to how our new understanding of AM metabolic plasticity may be exploited to develop AM-focused therapies.

Insights into the Role of Bioactive Food Ingredients and the Microbiome in Idiopathic Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic disease mainly associated with aging and, to date, its causes are still largely unknown. It has been shown that dietary habits can accelerate or delay the occurrence of aging-related diseases; however, their potential role in IPF development has been underestimated so far. The present review summarizes the evidence regarding the relationship between diet and IPF in humans, and in animal models of pulmonary fibrosis, in which we discuss the bioactivity of specific dietary food ingredients, including fatty acids, peptides, amino acids, carbohydrates, vitamins, minerals and phytochemicals. Interestingly, many animal studies reveal preventive and therapeutic effects of particular compounds. Furthermore, it has been recently suggested that the lung and gut microbiota could be involved in IPF, a relationship which may be linked to changes in immunological and inflammatory factors. Thus, all the evidence so far puts forward the idea that the gut-lung axis could be modulated by dietary factors, which in turn have an influence on IPF development. Overall, the data reviewed here support the notion of identifying food ingredients with potential benefits in IPF, with the ultimate aim of designing nutritional approaches as an adjuvant therapeutic strategy.

Lung fibrosis enters the iron age†

Iron is an essential nutrient for numerous cellular processes. However, excess iron in the lung (e.g. inhaled in pollution/cigarette smoke) can be harmful, acting as a catalyst in the formation of free radicals. Pulmonary iron content is therefore tightly regulated and alterations in iron metabolism have been associated with chronic lung disease. In particular, patients with idiopathic pulmonary fibrosis have been reported to have numerous aspects of dysfunctional iron metabolism in the lung, including increased iron levels, presence of iron-laden macrophages and iron-induced oxidative stress. In a recent issue of The Journal of Pathology, Ali et al showed a mechanistic link between iron accumulation and pulmonary fibrosis pathology. Using mouse models of iron overload, the authors showed that increased iron levels resulted in reduced lung function and worse pulmonary fibrosis upon lung injury by bleomycin. Treatment with inhaled iron chelator deferoxamine ameliorated pulmonary fibrosis and prevented lung function decline in vivo. This study highlights the importance of iron homeostasis in the lung and provides evidence of pulmonary iron overload contributing to the development and progression of pulmonary fibrosis. © 2020 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Highlights of high-resolution computed tomography imaging in evaluation of complications and co-morbidities in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) represents a condition included in the heterogeneous group of interstitial lung diseases without known causes. The recent ATS/ERS/JRS/ALAT guidelines and the white paper published by the Fleischner Society have well-defined diagnosis and management of idiopathic pulmonary fibrosis. Idiopathic pulmonary fibrosis management is complex because it is also influenced by several co-morbidities and complications. The new frontier in idiopathic pulmonary fibrosis is represented by the effort to understand the complex mechanism of the pathogenesis and progression of disease in order to predict several consequences and co-morbidities. In our review, we tried to distinguish co-morbidities from complications of idiopathic pulmonary fibrosis. In each complication, we have reviewed the existing literature and we have emphasized the complex pathobiological pathway which links the progression of idiopathic pulmonary fibrosis to the development of the complication itself. For every co-morbidity, we tried to identify share common risk factors which explain the coexistence of idiopathic pulmonary fibrosis with its co-morbidities. We then analyzed high-resolution computed tomography (CT) aspects of co-morbidities and complications of idiopathic pulmonary fibrosis that the radiologist should be aware of. In this review, we focused on the role of high-resolution CT imaging in the evaluation of co-morbidities and complications in idiopathic pulmonary fibrosis because their early diagnosis and treatment could change the prognosis in patients with idiopathic pulmonary fibrosis. We have also pointed out that in some cases the final combined quantitative CT tools and conventional visual CT score would allow to get an accurate analysis and quantification of disease progression, co-morbidities, and complications of idiopathic pulmonary fibrosis in order to improve staging systems in idiopathic pulmonary fibrosis.

The Transferrin Receptor CD71 Delineates Functionally Distinct Airway Macrophage Subsets during Idiopathic Pulmonary Fibrosis

Rationale: Idiopathic pulmonary fibrosis (IPF) is a devastating progressive disease with limited therapeutic options. Airway macrophages (AMs) are key components of the defense of the airways and are implicated in the pathogenesis of IPF. Alterations in iron metabolism have been described during fibrotic lung disease and in murine models of lung fibrosis. However, the role of transferrin receptor 1 (CD71)-expressing AMs in IPF is not known. Objectives: To assess the role of CD71-expressing AMs in the IPF lung. Methods: We used multiparametric flow cytometry, gene expression analysis, and phagocytosis/transferrin uptake assays to delineate the role of AMs expressing or lacking CD71 in the BAL of patients with IPF and of healthy control subjects. Measurements and Main Results: There was a distinct increase in proportions of AMs lacking CD71 in patients with IPF compared with healthy control subjects. Concentrations of BAL transferrin were enhanced in IPF-BAL, and furthermore, CD71- AMs had an impaired ability to sequester transferrin. CD71+ and CD71- AMs were phenotypically, functionally, and transcriptionally distinct, with CD71- AMs characterized by reduced expression of markers of macrophage maturity, impaired phagocytosis, and enhanced expression of profibrotic genes. Importantly, proportions of AMs lacking CD71 were independently associated with worse survival, underlining the importance of this population in IPF and as a potential therapeutic target. Conclusions: Taken together, these data highlight how CD71 delineates AM subsets that play distinct roles in IPF and furthermore show that CD71- AMs may be an important pathogenic component of fibrotic lung disease.

ToF-SIMS mediated analysis of human lung tissue reveals increased iron deposition in COPD (GOLD IV) patients

Chronic obstructive pulmonary disease (COPD) is a debilitating lung disease that is currently the third leading cause of death worldwide. Recent reports have indicated that dysfunctional iron handling in the lungs of COPD patients may be one contributing factor. However, a number of these studies have been limited to the qualitative assessment of iron levels through histochemical staining or to the expression levels of iron-carrier proteins in cells or bronchoalveolar lavage fluid. In this study, we have used time of flight secondary ion mass spectrometry (ToF-SIMS) to visualize and relatively quantify iron accumulation in lung tissue sections of healthy donors versus severe COPD patients. An IONTOF 5 instrument was used to perform the analysis, and further multivariate analysis was used to analyze the data. An orthogonal partial least squares discriminant analysis (OPLS-DA) score plot revealed good separation between the two groups. This separation was primarily attributed to differences in iron content, as well as differences in other chemical signals possibly associated with lipid species. Further, relative quantitative analysis revealed twelve times higher iron levels in lung tissue sections of COPD patients when compared to healthy donors. In addition, iron accumulation observed within the cells was heterogeneously distributed, indicating cellular compartmentalization.

Smoking-induced iron dysregulation in the lung

Iron is one of the most abundant transition elements and is indispensable for almost all organisms. While the ability of iron to participate in redox chemistry is an essential requirement for participation in a range of vital enzymatic reactions, this same feature of iron also makes it dangerous in the generation of hydroxyl radicals and superoxide anions. Given the high local oxygen tensions in the lung, the regulation of iron acquisition, utilization, and storage therefore becomes vitally important, perhaps more so than in any other biological system. Iron plays a critical role in the biology of essentially every cell type in the lung, and in particular, changes in iron levels have important ramifications on immune function and the local lung microenvironment. There is substantial evidence that cigarette smoke causes iron dysregulation, with the implication that iron may be the link between smoking and smoking-related lung diseases. A better understanding of the connection between cigarette smoke, iron, and respiratory diseases will help to elucidate pathogenic mechanisms and aid in the identification of novel therapeutic targets.

Ferritin H Deficiency in Myeloid Compartments Dysregulates Host Energy Metabolism and Increases Susceptibility to Mycobacterium tuberculosis Infection

Iron is an essential factor for the growth and virulence of Mycobacterium tuberculosis (Mtb). However, little is known about the mechanisms by which the host controls iron availability during infection. Since ferritin heavy chain (FtH) is a major intracellular source of reserve iron in the host, we hypothesized that the lack of FtH would cause dysregulated iron homeostasis to exacerbate TB disease. Therefore, we used knockout mice lacking FtH in myeloid-derived cell populations to study Mtb disease progression. We found that FtH plays a critical role in protecting mice against Mtb, as evidenced by increased organ burden, extrapulmonary dissemination, and decreased survival in Fth-/- mice. Flow cytometry analysis showed that reduced levels of FtH contribute to an excessive inflammatory response to exacerbate disease. Extracellular flux analysis showed that FtH is essential for maintaining bioenergetic homeostasis through oxidative phosphorylation. In support of these findings, RNAseq and mass spectrometry analyses demonstrated an essential role for FtH in mitochondrial function and maintenance of central intermediary metabolism in vivo. Further, we show that FtH deficiency leads to iron dysregulation through the hepcidin-ferroportin axis during infection. To assess the clinical significance of our animal studies, we performed a clinicopathological analysis of iron distribution within human TB lung tissue and showed that Mtb severely disrupts iron homeostasis in distinct microanatomic locations of the human lung. We identified hemorrhage as a major source of metabolically inert iron deposition. Importantly, we observed increased iron levels in human TB lung tissue compared to healthy tissue. Overall, these findings advance our understanding of the link between iron-dependent energy metabolism and immunity and provide new insight into iron distribution within the spectrum of human pulmonary TB. These metabolic mechanisms could serve as the foundation for novel host-directed strategies.

Bronchoalveolar lavage (BAL) cells in idiopathic pulmonary fibrosis express a complex pro-inflammatory, pro-repair, angiogenic activation pattern, likely associated with macrophage iron accumulation

Idiopathic pulmonary fibrosis (IPF) is a chronic lung disease of unknown cause characterized by alveolar epithelial damage, patchy interstitial fibrosis and diffuse microvascular abnormalities. In IPF, alveolar clustering of iron-laden alveolar macrophages—a common sign of microhemorrhage, has been associated with vascular abnormalities and worsening of pulmonary hypertension. As iron-dependent ROS generation has been shown to induce unrestrained macrophage activation in disease models of vascular damage, we explored alveolar macrophage activation phenotype in IPF patients (n = 16) and healthy controls (CTR, n = 7) by RNA sequencing of bronchoalveolar lavage (BAL) cells. The frequencies of macrophages in BAL cells were 86+4% and 83.4+8% in IPF and CTR groups, respectively (p-value = 0.41). In IPF patients, BAL cells showed increased iron-dependent ROS generation (p-value<0.05 vs CTR). Gene expression analysis showed overrepresentation of Gene Ontology processes/functions and KEGG pathways enriched in upregulated M1-type inflammatory (p-value<0.01), M2-type anti-inflammatory/tissue remodeling (p-value<0.0001), and MTPP-type chronic inflammatory/angiogenic (p-value<0.0001) chemokine and cytokine genes. The ex vivo finding was confirmed by the induction of iron-dependent ROS generation and chemokine/cytokine overexpression of Ccl4, Cxcl10 (M1), Il1rn (M2), Cxcl2, and Cxcl7 (MTPP) in MH-S murine immortalized alveolar macrophages exposed to ferric ammonium citrate in culture (p-value<0.05 vs CTR). The data show alveolar macrophage expression of a pro-inflammatory, tissue remodeling and angiogenic complex activation pattern, suggesting that iron accumulation may play a role in macrophage activation.

Pulmonary hypertension in patients with interstitial lung disease

Interstitial lung diseases (ILDs) comprise a broad and heterogeneous group of more than two hundred diseases with common functional characteristics. Their diagnosis and management require a multidisciplinary approach. This multidisciplinary approach involves the assessment of comorbid conditions including pulmonary hypertension (PH) that exerts a dramatic impact on survival. The current World Health Organization (WHO) classification of PH encompasses many of the interstitial lung diseases into WHO Group 3, while sarcoidosis, Pulmonary Langerhans Cell Histiocytosis and lymphangioleiomyomatosis are placed into WHO Group 5 as diseases with unclear or multifactorial mechanisms. Connective tissue diseases could span any of the 5 WHO groups based on the primary phenotype into which they manifest. Interestingly, several challenging phenotypes present with features that overlap between two or more WHO PH groups. Currently, PH-specific treatment is recommended only for patients classified into WHO Group 1 PH. The lack of specific treatment for other groups, including PH in the setting of ILD, reflects the poor outcomes of these patients. Thus, identification of the optimal strategy for ILD patients with PH remains an amenable need. This review article provides a brief overview of biomarkers indicative of vascular remodeling in interstitial lung disease, summarizes the current state of knowledge regarding patients with PH and ILD and highlights future perspectives that remain to be addressed.

Transition and post-transition metals in exhaled breath condensate

Water vapor in expired air, as well as dispersed non-volatile components, condense onto a cooler surface after exiting the respiratory tract. This exhaled breath condensate (EBC) provides a dilute sampling of the epithelial lining fluid. Accordingly, the collection of EBC imparts a capacity to provide biomarkers of injury preceding clinical disease. Concentrations of transition and post-transition metals in EBC are included among these endpoints. Iron and zinc are the metals with the highest concentration and are measurable in all EBC samples from healthy subjects; other metals are most frequently either at or below the level of detection in this group. Gender, age, and smoking can impact EBC metal concentrations in healthy subjects. EBC metal concentrations among patients diagnosed with particular lung diseases (e.g. asthma, chronic obstructive disease, and interstitial lung disease) have been of research interest but no definite pattern of involvement has been delineated. Studies of occupationally exposed workers confirm significant exposure to specific metals, but such EBC metal measurements frequently provide evidence redundant with environmental sampling. Measurements of metal concentrations in EBC remain a research tool into metal homeostasis in the respiratory tract and participation of metals in disease pathogenesis. The quantification of metal concentrations in EBC is currently not reliable for clinical use in either supporting or determining any diagnosis. Issues that must be addressed prior to the use of EBC metal measurements include the establishment of both standardized collection and measurement techniques.

Iron accumulation in senescent cells is coupled with impaired ferritinophagy and inhibition of ferroptosis

Cellular senescence is characterised by the irreversible arrest of proliferation, a pro-inflammatory secretory phenotype and evasion of programmed cell death mechanisms. We report that senescence alters cellular iron acquisition and storage and also impedes iron-mediated cell death pathways. Senescent cells, regardless of stimuli (irradiation, replicative or oncogenic), accumulate vast amounts of intracellular iron (up to 30-fold) with concomitant changes in the levels of iron homeostasis proteins. For instance, ferritin (iron storage) levels provided a robust biomarker of cellular senescence, for associated iron accumulation and for resistance to iron-induced toxicity. Cellular senescence preceded iron accumulation and was not perturbed by sustained iron chelation (deferiprone). Iron accumulation in senescent cells was driven by impaired ferritinophagy, a lysosomal process that promotes ferritin degradation and ferroptosis. Lysosomal dysfunction in senescent cells was confirmed through several markers, including the build-up of microtubule-associated protein light chain 3 (LC3-II) in autophagosomes. Impaired ferritin degradation explains the iron accumulation phenotype of senescent cells, whereby iron is effectively trapped in ferritin creating a perceived cellular deficiency. Accordingly, senescent cells were highly resistant to ferroptosis. Promoting ferritin degradation by using the autophagy activator rapamycin averted the iron accumulation phenotype of senescent cells, preventing the increase of TfR1, ferritin and intracellular iron, but failed to re-sensitize these cells to ferroptosis. Finally, the enrichment of senescent cells in mouse ageing hepatic tissue was found to accompany iron accumulation, an elevation in ferritin and mirrored our observations using cultured senescent cells.

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Altered iron homeostasis in senescent cells is driven by impaired ferritinophagy.

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Impaired ferritinophagy causes functional cellular iron deficiency.

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senescent cells are resistant to iron mediated cell death including ferroptosis.

Trace metals in fluids lining the respiratory system of patients with idiopathic pulmonary fibrosis and diffuse lung diseases

Idiopathic pulmonary fibrosis (IPF) is an interstitial lung disease with a poor prognosis and an undefined etiopathogenesis. Oxidative stress contributes to alveolar injury and fibrosis development and, because transition metals are essential to the functioning of most proteins involved in redox reactions, a better knowledge of metal concentrations and metabolism in the respiratory system of IPF patients may provide a valuable complementary approach to prevent and manage a disease which is often misdiagnosed or diagnosed in later stages. The present review summarizes and discusses literature data on the elemental composition of bronchoalveolar lavage (BAL), induced sputum and exhaled breath condensate (EBC) from patients affected by IPF and healthy subjects. Available data are scanty and the lack of consistent methods for the collection and analysis of lung and airways lining fluids makes it difficult to compare the results of different studies. However, the elemental composition of BAL samples from IPF patients seems to have a specific profile that can be distinguished from that of patients with other interstitial lung diseases (ILD) or control subjects. Suggestions are given towards standard sampling and analytical procedures of BAL samples, in the aim to assess typical element concentration patterns and their potential role as biomarkers of IPF.

Role of iron in the pathogenesis of respiratory disease

Iron is essential for many biological processes, however, too much or too little iron can result in a wide variety of pathological consequences, depending on the organ system, tissue or cell type affected. In order to reduce pathogenesis, iron levels are tightly controlled in throughout the body by regulatory systems that control iron absorption, systemic transport and cellular uptake and storage. Altered iron levels and/or dysregulated homeostasis have been associated with several lung diseases, including chronic obstructive pulmonary disease, lung cancer, cystic fibrosis, idiopathic pulmonary fibrosis and asthma. However, the mechanisms that underpin these associations and whether iron plays a key role in the pathogenesis of lung disease are yet to be fully elucidated. Furthermore, in order to survive and replicate, pathogenic micro-organisms have evolved strategies to source host iron, including freeing iron from cells and proteins that store and transport iron. To counter these microbial strategies, mammals have evolved immune-mediated defence mechanisms that reduce iron availability to pathogens. This interplay between iron, infection and immunity has important ramifications for the pathogenesis and management of human respiratory infections and diseases. An increased understanding of the role that iron plays in the pathogenesis of lung disease and respiratory infections may help inform novel therapeutic strategies. Here we review the clinical and experimental evidence that highlights the potential importance of iron in respiratory diseases and infections.

Hemosiderin-laden macrophages are an independent factor correlated with pulmonary vascular resistance in idiopathic pulmonary fibrosis: a case control study

BACKGROUND

Increases in hemosiderin-laden macrophages (HLM) are reported to be observed in idiopathic pulmonary fibrosis (IPF). According to a recent study, significant correlation between hemosiderin deposition in the lung tissue of IPF and pulmonary hypertension evaluated by echocardiography has been suspected. In this study, we aimed to evaluate whether HLM in bronchoalveolar lavage fluid (BALF) is a factor correlated with pulmonary hemodynamic parameters evaluated by right heart catheterization in patients with IPF.

METHODS

Initial data from 103 consecutive patients with IPF who underwent surgical lung biopsy between November 2007 and March 2014 were retrospectively analyzed. The "HLM score" of BALF was established by dividing the number of Perls' Prussian blue stain positive macrophages by the total number of macrophages counted.

RESULTS

BALF showed an elevated HLM score (38.2%). Right heart catheterization revealed mean pulmonary arterial pressure (mPAP) of 16.3 mmHg and pulmonary vascular resistance (PVR) of 1.55 Wood units. HLM score was positively correlated with mPAP (ρ = 0.204; p = 0.038) and PVR (ρ = 0.349, p < 0.001). In multivariate analysis, 6-min walk distance (standardized partial regression coefficient [β], -0.391; p < 0.001), minimum oxygen saturation during 6-min walk distance (β, -0.294; p = 0.001) and HLM score (β, 0.265; p = 0.002) were independently correlated with PVR.

CONCLUSIONS

HLM score in BALF is an independent factor correlated with PVR in patients with IPF.

Prognostic scoring systems for clinical course and survival in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is the most common and rapidly fatal among idiopathic interstitial pneumonias. Its clinical course is variable. A significant fraction of the population of patients display a slow disease course and can remain stable for years, while other patients show a rapid progressive course and may die within few months from diagnosis. For these reasons estimating prognosis of IPF patients is extremely difficult and has important clinical repercussions on optimal patients management including patients referral for lung transplantation. Several studies have tried to address this key point in the course of the two last decades analyzing different clinical, functional, radiological and biological variables. The purpose of this review is to assess relevant studies published on this subject and to examine the variety of prognostic predictors proposed along with staging systems.

Change in serum marker of oxidative stress in the progression of idiopathic pulmonary fibrosis

BACKGROUND

Increased oxidative stress is supposed to be involved in the etiology of idiopathic pulmonary fibrosis (IPF). It was reported that oxidative stress values measured by a spectrophotometric technique (d-ROMs test) were significantly higher in IPF patients than in controls, and were negatively correlated with Forced Vital Capacity (FVC) and Carbon Monoxide Diffusing Capacity (DLCO). However, the relationship between progression of IPF over time and change in serum oxidative stress marker remains unclarified.

AIMS

This study aimed to investigate the change in serum oxidative stress marker during progression of IPF.

SUBJECTS AND METHODS

The levels of oxidative stress in blood samples of 43 treatment-naïve IPF patients were measured by the d-ROMs test. FVC and DLCO were measured concurrently. The changes in oxidative stress and pulmonary function were evaluated in 27 untreated patients 6 months later. Oxidative stress levels of 13 patients with acute exacerbation of IPF (AE-IPF) and 30 healthy controls were also evaluated.

RESULTS

Oxidative stress values [median, interquartile range (IQR); Carratelli units (U.CARR)] were significantly higher in 43 IPF patients than in controls (366, 339-443 vs. 289, 257-329, p < 0.01) and were significantly increased 6 months later in 27 untreated patients (353, 311-398 at baseline to 385, 345-417 at follow-up, p < 0.01). The increase in oxidative stress values (24.0, 6.0-49.0 U.CARR/6 months) was negatively correlated with baseline DLCO (rs = -0.44, p < 0.05) and FVC changes after 6 months (rs = -0.54, p < 0.01). Oxidative stress values were significantly higher in IPF patients with acute exacerbation than in those with stable disease (587, 523-667 vs. 366, 339-443 U.CARR, respectively; p < 0.01).

CONCLUSIONS

Serum oxidative stress values increased with disease progression in IPF patients.

HFE gene variants and iron-induced oxygen radical generation in idiopathic pulmonary fibrosis

In idiopathic pulmonary fibrosis (IPF), lung accumulation of excessive extracellular iron and macrophage haemosiderin may suggest disordered iron homeostasis leading to recurring microscopic injury and fibrosing damage. The current study population comprised 89 consistent IPF patients and 107 controls. 54 patients and 11 controls underwent bronchoalveolar lavage (BAL). Haemosiderin was assessed by Perls' stain, BAL fluid malondialdehyde (MDA) by high-performance liquid chromatography, BAL cell iron-dependent oxygen radical generation by fluorimetry and the frequency of hereditary haemochromatosis HFE gene variants by reverse dot blot hybridisation. Macrophage haemosiderin, BAL fluid MDA and BAL cell unstimulated iron-dependent oxygen radical generation were all significantly increased above controls (p<0.05). The frequency of C282Y, S65C and H63D HFE allelic variants was markedly higher in IPF compared with controls (40.4% versus 22.4%, OR 2.35, p=0.008) and was associated with higher iron-dependent oxygen radical generation (HFE variant 107.4±56.0, HFE wild type (wt) 59.4±36.4 and controls 16.7±11.8 fluorescence units per 10(5) BAL cells; p=0.028 HFE variant versus HFE wt, p=0.006 HFE wt versus controls). The data suggest iron dysregulation associated with HFE allelic variants may play an important role in increasing susceptibility to environmental exposures, leading to recurring injury and fibrosis in IPF.

Protein and microRNA biomarkers from lavage, urine, and serum in military personnel evaluated for dyspnea

Background

We have identified candidate protein and microRNA (miRNA) biomarkers for dyspnea by studying serum, lavage fluid, and urine from military personnel who reported serious respiratory symptoms after they were deployed to Iraq or Afghanistan.

Methods

Forty-seven soldiers with the complaint of dyspnea who enrolled in the STudy of Active Duty Military Personnel for Environmental Dust Exposure (STAMPEDE) underwent comprehensive pulmonary evaluations at the San Antonio Military Medical Center. The evaluation included fiber-optic bronchoscopy with bronchoalveolar lavage. The clinical findings from the STAMPEDE subjects pointed to seven general underlying diagnoses or findings including airway hyperreactivity, asthma, low diffusivity of carbon monoxide, and abnormal cell counts. The largest category was undiagnosed. As an exploratory study, not a classification study, we profiled proteins or miRNAs in lavage fluid, serum, or urine in this group to look for any underlying molecular patterns that might lead to biomarkers. Proteins in lavage fluid and urine were identified by accurate mass tag (database-driven) proteomics methods while miRNAs were profiled by a hybridization assay applied to serum, urine, and lavage fluid.

Results

Over seventy differentially expressed proteins were reliably identified both from lavage and from urine in forty-eight dyspnea subjects compared to fifteen controls with no known lung disorder. Six of these proteins were detected both in urine and lavage. One group of subjects was distinguished from controls by expressing a characteristic group of proteins. A related group of dyspnea subjects expressed a unique group of miRNAs that included one miRNA that was differentially overexpressed in all three fluids studied. The levels of several miRNAs also showed modest but direct associations with several standard clinical measures of lung health such as forced vital capacity or gas exchange efficiency.

Conclusions

Candidate proteins and miRNAs associated with the general diagnosis of dyspnea have been identified in subjects with differing medical diagnoses. Since these markers can be measured in readily obtained clinical samples, further studies are possible that test the value of these findings in more formal classification or case–control studies in much larger cohorts of subjects with specific lung diseases such as asthma, emphysema, or some other well-defined lung disease.