Red Blood Cell-Derived Iron Alters Macrophage Function in COPD

Iron-laden macrophage-mediated paracrine profibrotic signaling induces lung fibroblast activation

Idiopathic pulmonary fibrosis (IPF) is a devastating condition characterized by progressive lung scarring and uncontrolled fibroblast proliferation, inevitably leading to organ dysfunction and mortality. Although elevated iron levels have been observed in patients and animal models of lung fibrosis, the mechanisms linking iron dysregulation to lung fibrosis pathogenesis, particularly the role of macrophages in orchestrating this process, remain poorly elucidated. Here we evaluate iron metabolism in macrophages during pulmonary fibrosis using both in vivo and in vitro approaches. In murine bleomycin- and amiodarone-induced pulmonary fibrosis models, we observed significant iron deposition and lipid peroxidation in pulmonary macrophages. Intriguingly, the ferroptosis regulator glutathione peroxidase 4 (GPX4) was upregulated in pulmonary macrophages following bleomycin instillation, a finding corroborated by single-cell RNA sequencing analysis. Moreover, macrophages isolated from fibrotic mouse lungs exhibited increased transforming growth factor (TGF)-β1 expression that correlated with lipid peroxidation. In vitro, iron overload in bone marrow-derived macrophages triggered lipid peroxidation and TGF-β1 upregulation, which was effectively suppressed by ferroptosis inhibitors. When cocultured with iron-overloaded macrophages, lung fibroblasts exhibited heightened activation, evidenced by increased α-smooth muscle actin and fibronectin expression. Importantly, this profibrotic effect was attenuated by treating macrophages with a ferroptosis inhibitor or blocking TGF-β receptor signaling in fibroblasts. Collectively, our study elucidates a novel mechanistic paradigm in which the accumulation of iron within macrophages initiates lipid peroxidation, thereby amplifying TGF-β1 production, subsequently instigating fibroblast activation through paracrine signaling. Thus, inhibiting iron overload and lipid peroxidation warrants further exploration as a strategy to suppress fibrotic stimulation by disease-associated macrophages. NEW & NOTEWORTHY This study investigates the role of iron in pulmonary fibrosis, specifically focusing on macrophage-mediated mechanisms. Iron accumulation in fibrotic lung macrophages triggers lipid peroxidation and an upregulation of transforming growth factor (TGF)-β1 expression. Coculturing iron-laden macrophages activates lung fibroblasts in a TGF-β1-dependent manner, which can be mitigated by ferroptosis inhibitors. These findings underscore the potential of targeting iron overload and lipid peroxidation as a promising strategy to alleviate fibrotic stimulation provoked by disease-associated macrophages.

Effect of the Lipoxin Receptor Agonist BML-111 on Cigarette Smoke Extract-Induced Macrophage Polarization and Inflammation in RAW264.7 Cells

Background

Macrophages are known to play a crucial role in the chronic inflammation associated with Chronic Obstructive Pulmonary Disease (COPD). BML-111, acting as a lipoxin A4 (LXA4) receptor agonist, has shown to be effective in protecting against COPD. However, the precise mechanism by which BML-111 exerts its protective effect remains unclear.

Methods

In order to establish a cell model of inflammation, cigarette smoke extract (CSE) was used on the RAW264.7 cell line. Afterwards, an Enzyme-linked immunosorbent assay (ELISA) kit was employed to measure concentrations of tumor necrosis factor-α (TNF-α), interleukin-1beta (IL-1β), interleukin-18 (IL-18), and interleukin-10 (IL-10) in the cell supernatants of the RAW264.7 cells.In this study, we examined the markers of macrophage polarization using two methods: quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot analysis. Additionally, we detected the expression of Notch-1 and Hes-1 through Western blotting.

Results

BML-111 effectively suppressed the expression of pro-inflammatory cytokines TNF-α, IL-1β, and IL-18, as well as inflammasome factors NLRP3 and Caspase-1, while simultaneously up-regulating the expression of the anti-inflammatory cytokine IL-10 induced by CSE. Moreover, BML-111 reduced the expression of iNOS, which is associated with M1 macrophage polarization, and increased the expression of Arg-1, which is associated with M2 phenotype. Additionally, BML-111 downregulated the expression of Hes-1 and the ratio of activated Notch-1 to Notch-1 induced by CSE. The effect of BML-111 on inflammation and macrophage polarization was reversed upon administration of the Notch-1 signaling pathway agonist Jagged1.

Conclusion

BML-111 has the potential to suppress inflammation and modulate M1/M2 macrophage polarization in RAW264.7 cells. The underlying mechanism may involve the Notch-1 signaling pathway.

Iron and mitochondria in the susceptibility, pathogenesis and progression of COPD

Chronic obstructive pulmonary disease (COPD) is a debilitating lung disease characterised by airflow limitation, chronic bronchitis, emphysema and airway remodelling. Cigarette smoke is considered the primary risk factor for the development of COPD; however, genetic factors, host responses and infection also play an important role. Accumulating evidence highlights a role for iron dyshomeostasis and cellular iron accumulation in the lung as a key contributing factor in the development and pathogenesis of COPD. Recent studies have also shown that mitochondria, the central players in cellular iron utilisation, are dysfunctional in respiratory cells in individuals with COPD, with alterations in mitochondrial bioenergetics and dynamics driving disease progression. Understanding the molecular mechanisms underlying the dysfunction of mitochondria and cellular iron metabolism in the lung may unveil potential novel investigational avenues and therapeutic targets to aid in the treatment of COPD.

Protective Effects of Chestnut (Castanea crenata) Inner Shell Extract in Macrophage-Driven Emphysematous Lesion Induced by Cigarette Smoke Condensate

Chestnut (Castanea crenata) inner shell extract (CIE), a curative herb in Korea, has diverse pharmacological effects against various diseases including pulmonary fibrosis, asthma, and chronic obstructive pulmonary disease (COPD). However, its molecular mechanisms of anti-emphysematous effects are still not fully elucidated. In the present study, we elucidate the efficacy of CIE against emphysematous lesion progression in a cigarette smoke condensate (CSC)-instilled mice and CSC-stimulated H292 cell line. The mice are administered CSC via intranasal instillation at 7-day intervals for 1 month after 1 week of pretreatment with CIE. CIE (100 or 300 mg/kg) is administered by oral gavage for 1 month. CIE decreased the macrophage count in bronchoalveolar lavage fluid and the severity of emphysematous lesions in lung tissue. Additionally, CIE suppressed the phosphatidylinositol 3-kinase/protein kinase B/nuclear factor kappa B signal pathway and thereby downregulated matrix metalloprotease-9 expression, which was confirmed in CSC-stimulated H292 cells. Thus, CIE effectively inhibited CSC-induced macrophage-driven emphysema progression in airways; this inhibition was associated with the suppression of protease-antiprotease imbalance. Our results propose that CIE has the potential for the alleviation of COPD.

Non-heme iron overload impairs monocyte to macrophage differentiation via mitochondrial oxidative stress

Iron is a key element for systemic oxygen delivery and cellular energy metabolism. Thus regulation of systemic and local iron metabolism is key for maintaining energy homeostasis. Significant changes in iron levels due to malnutrition or hemorrhage, have been associated with several diseases such as hemochromatosis, liver cirrhosis and COPD. Macrophages are key cells in regulating iron levels in tissues as they sequester excess iron. How iron overload affects macrophage differentiation and function remains a subject of debate. Here we used an in vitro model of monocyte-to-macrophage differentiation to study the effect of iron overload on macrophage function. We found that providing excess iron as soluble ferric ammonium citrate (FAC) rather than as heme-iron complexes derived from stressed red blood cells (sRBC) interferes with macrophage differentiation and phagocytosis. Impaired macrophage differentiation coincided with increased expression of oxidative stress-related genes. Addition of FAC also led to increased levels of cellular and mitochondrial reactive oxygen species (ROS) and interfered with mitochondrial function and ATP generation. The effects of iron overload were reproduced by the mitochondrial ROS-inducer rotenone while treatment with the ROS-scavenger N-Acetylcysteine partially reversed FAC-induced effects. Finally, we found that iron-induced oxidative stress interfered with upregulation of M-CSFR and MAFB, two crucial determinants of macrophage differentiation and function. In summary, our findings suggest that high levels of non-heme iron interfere with macrophage differentiation by inducing mitochondrial oxidative stress. These findings might be important to consider in the context of diseases like chronic obstructive pulmonary disease (COPD) where both iron overload and defective macrophage function have been suggested to play a role in disease pathogenesis.

Gallium protoporphyrin as an antimicrobial for non-typeable Haemophilus influenzae in COPD patients

AIMS

Colonisation with non-typeable Haemophilus influenzae (NTHi) is common in COPD. Iron is required by bacteria for nutrition. Gallium is imported into bacteria using iron import proteins. Gallium cannot fulfill key metabolic functions, causing bactericidal effects. We tested the efficacy of gallium compounds as antimicrobials against NTHi in hemin rich conditions, and their ability to reduce NTHi induced pro-inflammatory responses in macrophages.

MAIN METHODS

NTHi was cultured with the free iron analogue gallium nitrate (GaN) and heme iron analogue gallium protoporphyrin (GaPP) (0.5-4 μM; 24 h). Growth of NTHi reference strain (NCTC 12699) and 6 clinical isolates from COPD patients (including antibiotic resistant isolates) was assessed by optical density, and viability by Miles Misra. Monocyte derived macrophages (MDMs) were treated with GaPP before/after NTHi exposure. Viable intracellular NTHi was assessed by gentamicin protection assay. GaN or GaPP was added to NTHi cultures prior to culture with MDMs. Cytokine gene expression (qPCR) and protein secretion (ELISA) were measured.

KEY FINDINGS

NTHi growth and viability were reduced by GaPP but not GaN. GaPP inhibited growth of COPD isolates (4 μM: 87 % reduction). GaPP reduced intracellular viability of NTHi in macrophage infection models. MDM cytokine gene expression and protein secretion (TNF-α, IL-6 and CXCL8) in response to NTHi was reduced (82, 66 and 86 % for gene expression) when cultured with GaPP 4 μM.

SIGNIFICANCE

GaPP is an effective antimicrobial for NTHi while GaN showed no effect on growth or viability. Culture of NTHi with GaPP also reduced the pro-inflammatory cytokine response in MDMs.

COPD lung studies of Nrf2 expression and the effects of Nrf2 activators

BACKGROUND

Nrf2 regulates cellular antioxidant defence in lung cells, including epithelial cells and alveolar macrophages (AM). The Nrf2/Keap-1 pathway can be modulated by activators with different modes of action; electrophilic compounds and protein-protein interaction (PPI) inhibitors. We assessed Nrf2 and Keap-1 protein and gene levels in COPD compared to controls and the effect of Nrf2 activators on COPD AM.

METHODS

Lung resected tissue from non-smokers, smokers and COPD patients were analysed for epithelial and AM expression of Nrf2 and Keap-1 by imunoshistochemistry and by qPCR in isolated AM. AM were cultured with Nrf2 activators CDDO, C4X_6665, GSK7, MMF and Sulforaphane. Expression of Nrf2 target genes NQO1, HMOX1 SOD1 and TXNRD1 and NQO1 activity were assessed.

RESULTS

Nrf2 and Keap-1 expression was not altered in the epithelium or AM of COPD patients compared to controls. NQO1 activity was downregulated, while NQO1, HMOX1, SOD1 and TXNRD1 gene expression increased in COPD patients. All Nrf2 activators increased NQO1 activity, and NQO1, HMOX1, SOD1 and TXNRD1 expression in AMs from both COPD and smokers. The potency of C4X_6665 on NQO1 activity and regulation of Nrf2 target gene expression was higher than other compounds.

CONCLUSION

There is evidence of dysregulation of the Nrf2 signalling pathway in AM from COPD patients. The higher potency of the novel PPI Nrf2 compound C4X_6665 for inducing antioxidant activity and gene expression compared to electrophilic and other PPI Nrf2 activators highlights the therapeutic potential of this compound to address Nrf2 pathway dysregulation in COPD AM.