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ABSTRACTIntroductionChronic obstructive pulmonary disease (COPD) is a lung disease characterized by chronic bronchitis, emphysema, and remodeling. Its prevalence is increasing worldwide; however, there are few effective therapies, and none of the treatments currently available prevent the progression of the disease or target all of the hallmark features. The development and progression of COPD are heterogeneous, which has hampered the development of new therapies.Areas coveredIn this review, we cover the emergence of the improvement of existing classes of drugs including glucocorticoids, β2-adrenoceptor agonists, phosphodiesterase inhibitors, PDE4 selective inhibitors, PDE3/PDE4 inhibitors, protease inhibitors, recombinant α1-antitrypsin and neutrophil elastase inhibitors. We also highlight new compounds that target recently identified mechanisms of COPD, new dual-action muscarinic antagonists, and β2-agonists, kinase inhibitors, cytokine modifiers, chemokines modifiers, NF-κB inhibitors, senolytics, antioxidants, inhaled antiviral agents, anti-fibrotic compounds, and compounds stimulating lung regeneration.Expert opinionGiven the myriad of potential therapeutic avenues that can be pursued, careful consideration of the phenotypes/endotypes of COPD patients will be important for personalized treatment options in the future, and a full understanding of disease mechanisms in patient subsets will ensure these emerging therapies are targeted appropriately.

Lung innate immunity is the first line of defence against inhaled allergens, pathogens and environmental pollutants. Cellular metabolism plays a key role in innate immunity. Catabolic pathways, including glycolysis and fatty acid oxidation (FAO), are interconnected with biosynthetic and redox pathways. Innate immune cell activation and differentiation trigger extensive metabolic changes that are required to support their function. Pro-inflammatory polarisation of macrophages and activation of dendritic cells, mast cells and neutrophils are associated with increased glycolysis and a shift towards the pentose phosphate pathway and fatty acid synthesis. These changes provide the macromolecules required for proliferation and inflammatory mediator production and reactive oxygen species for anti-microbial effects. Conversely, anti-inflammatory macrophages use primarily FAO and oxidative phosphorylation to ensure efficient energy production and redox balance required for prolonged survival. Deregulation of metabolic reprogramming in lung diseases, such as asthma and chronic obstructive pulmonary disease, may contribute to impaired innate immune cell function. Understanding how innate immune cell metabolism is altered in lung disease may lead to identification of new therapeutic targets. This is important as drugs targeting a number of metabolic pathways are already in clinical development for the treatment of other diseases such as cancer.

ABSTRACTIntroduction: COPD and lung cancer are leading causes of morbidity and mortality worldwide, and they share a common environmental risk factor in cigarette smoke exposure and a genetic predisposition represented by their incidence in only a fraction of smokers. This reflects the ability of cigarette smoke to induce an inflammatory response in the airways of susceptible smokers. Moreover, COPD could be a driving factor in lung cancer, by increasing oxidative stress and the resulting DNA damage and repression of the DNA repair mechanisms, chronic exposure to pro-inflammatory cytokines, repression of innate immunity and increased cellular proliferation.Areas covered: We have focused our review on the potential pathogenic molecular links between tobacco smoking-related COPD and lung cancer and the potential molecular targets for new drug development by understanding the common signaling pathways involved in COPD and lung cancer.Expert commentary: Research in this field is mostly limited to animal models or small clinical trials. Large clinical trials are needed but mostly combined models of COPD and lung cancer are necessary to investigate the processes caused by chronic inflammation, including genetic and epigenetic alteration, and the expression of inflammatory mediators that link COPD and lung cancer, to identify new molecular therapeutic targets.

COPD is a leading cause of morbidity and mortality worldwide. Long-term cigarette smoking is the cause of > 90% of COPD cases in Westernized countries. However, only a fraction of chronic heavy smokers develop symptomatic COPD by age 80. COPD is characterized by an abnormal immune response in the lower airways, and its progression is associated with infiltration of the lung by innate and adaptive inflammatory immune cells that form lymphoid follicles. There is growing evidence that both cellular- and antibody-mediated autoimmunity has a fundamental role in the pathogenesis of stable COPD. In particular, carbonyl-modified proteins may help to drive autoimmunity in COPD and cause the characteristic small airways abnormalities and even contribute to the pathogenesis of pulmonary emphysema. Although direct, indirect, and circumstantial evidence of a role for autoimmunity in stable patients with COPD has been identified, no cause-and-effect relationship between autoimmunity and the mechanisms of COPD has been firmly established in man. As such, the potential contribution of an autoimmune response to the pathogenesis of COPD exacerbation is still being investigated and represents an area of active research. Many drugs targeting autoimmune responses are already available, and the results of controlled clinical trials are awaited with great interest. The potential for measuring specific serum autoantibodies as biomarkers to predict clinical phenotypes or progression of stable COPD is promising.

Abnormal plasma and lung iron mobilization is associated with the onset and progression of ARDS and is detectable in specific at-risk populations. Patients with ARDS also have pronounced oxidative and nitrosative stress that can be catalyzed and thereby aggravated by the bioavailability of redox active iron. ARDS of pulmonary and extrapulmonary origin may differ pathophysiologically and require different ventilatory strategies. Evidence suggests that genetic predisposition is relevant to the pathogenesis of ARDS. We therefore explored the hypothesis that polymorphisms from a panel of genes encoding iron-metabolizing proteins determine susceptibility to ARDS.

The neutrophil enzyme myeloperoxidase (MPO) purposefully makes hypochlorous acid (HOCl) as part of the cells defence against microbial infections. During cell lysis, however, MPO will be released into the extracellular environment where production of HOCl, a powerful oxidant, will lead to molecular damage. Extracellular MPO binds to the copper-containing protein caeruloplasmin (Cp) and prevents MPO making HOCl. Cp has several important antioxidant functions in extracellular fluids associated with its ability to catalyse oxidation of ferrous ions and to remove peroxides. The binding of MPO to Cp did not inhibit these important extracellular antioxidant activities of Cp, but in so doing it provided additional antioxidant protection against formation of HOCl.

Haem oxygenase-1 (HO-1) is a highly inducible stress protein that removes haem from cells with the release of biliverdin, carbon monoxide and low-molecular-mass iron (LMrFe). Several antioxidant functions have been ascribed to HO; its induction is considered to be a protective event. However, LMrFe produced during haem catabolism might elicit a pro-oxidant response, with deleterious consequences. We therefore investigated the delicate balance between pro-oxidant and antioxidant events with the use of a microsomal lipid peroxidation (LPO) system. By using microsomal-bound HO in an NADPH-dependent LPO system, we assessed the pro-oxidant nature of the released LMrFe and the antioxidant effect of the released bilirubin. Hb, a biologically relevant substrate for HO, was included with the microsomes to supplement the source of haem iron and to promote LPO. We found significant increases in microsomal LPO, by using the thiobarbituric acid (TBA) test, after incubation with Hb. This Hb-stimulated peroxidation was inhibited by HO inhibitors and by iron chelators, suggesting a HO-driven, iron-dependent mechanism. GLC-MS was employed to measure the specific LPO product 4-hydroxy-2-nonenal and to confirm our TBA test results. A HO inhibitor attenuated an increase in intracellular LMrFe that occurred after treatment of rat pulmonary artery smooth-muscle cells with Hb. Additionally, exogenously added bilirubin at an equimolar concentration to the LMrFe present in both microsomal and liposomal systems was unable to prevent the pro-oxidant effect of the iron. Under certain circumstances HO can act as a pro-oxidant and seems to have a role in stimulating microsomal LPO.

Haem oxygenase‐1 is upregulated by numerous insults, including oxidative stress, and under such circumstances it is considered to be a protective stratagem. We have measured the haem oxygenase‐1 expression in heart, lung and liver tissues of control and iron‐overloaded rats. Lung tissue from iron‐overloaded rats displayed a significant increase in the haem oxygenase‐1 protein but no changes in haem oxygenase‐1 mRNA. Conversely, heart tissue showed a significant increase in haem oxygenase‐1 mRNA but no changes in haem oxygenase‐1 protein. We conclude that during oxidative stress caused by iron overload, lung tissue responds with a rapid upregulation of haem oxygenase‐1 levels.

Cardiopulmonary bypass surgery is associated with the release of low molecular mass iron, which increases the saturation of plasma transferrin to over 50% in all adult patients treated. In a significant minority, however plasma transferrin becomes 100% iron saturated and non-transferrin bound iron can be detected in the plasma. An iron-saturated transferrin is also a common physiological finding in normal term and pre-term infants at a time when their plasma antioxidants, which protect against iron toxicity and radical scavening, are profoundly different from those seen in adults. This study was conducted to assess the extent to which antioxidants, which protect against iron toxicity, are altered in neonates, infants, and children undergoing cardiopulmonary bypass surgery.

1.Albumin is often administered intravenously to critically ill patients as a volume expander, to combat hypoalbuminaemia, and to decrease hyperbilirubinaemia. There is, however, an ongoing debate concerning the therapeutic benefit of the former which is an expensive form of treatment. 2.Albumin has several biological functions, in particular as a ligand binder. It also acts as an extracellular transition metal ion-binding and radical-scavenging antioxidant. These functions are influenced by the presence of an exposed thiol group (cys 34) on the surface of the albumin molecule. 3.The ability of infused albumin to influence the plasma thiol pool, and hence antioxidant potential, was investigated in patients with sepsis syndrome. 4.Plasma thiol levels rose rapidly after albumin infusion and remained elevated even after plasma albumin levels had declined significantly, due to interstitial leakage. Data are suggestive of some form of thiol exchange in the plasma of these patients between albumin and molecules containing oxidized thiol groups. 5.Administration of albumin to patients with sepsis syndrome leads to a sustained increase in plasma thiols. Thiols have several important antioxidant functions, and thiol repletion in these patients, who are known to suffer from oxidative stress, may have beneficial antioxidant effects. Antioxidant repletion may represent an important facet of clinically administered albumin.

Extracorporeal circulation of blood during cardiopulmonary bypass surgery exposes cells to non-physiological surfaces and shear stress which can activate several regulatory cascades, and neutrophils to release superoxide and hydrogen peroxide. Shear stresses generated by pumps and suction systems cause lysis of red blood cells and the release of haemoglobin. Together the release of reactive forms of oxygen and haemoglobin can lead to the appearance of low molecular mass chelatable iron (bleomycin-detectable iron). All patients undergoing open heart surgery appear to release iron to plasma transferrin, increasing its iron saturation. In 13% of patients, however, the transferrin became fully iron-saturated, and by the end of open-heart surgery we could detect bleomycin-chelatable iron in the plasma. Saturation of transferrin with iron eliminates its iron-binding antioxidant properties, which can result in a stimulation of iron-dependent radical damage to selected detector molecules.

Ferric ions bind to citrate and undergo an autoreduction to form a ferrous-citrate complex, greatly increasing the redox activity of the iron complex. Ferrous ions and citrate are also essential for the enzymic activity of aconitase. Aconitase, with its iron-sulphur cluster has a versatile structure which allows it to act as an iron regulatory protein (IW-1). The purpose of this study was to see whether iron binding, and its autoreduction by citrate, could play a physiological signalling role in iron regulation. Significant amounts of ferrous ions were associated with citrate, when measured using ferrozine, however, these did not appear to activate iron-requiring aconitase.

Redox active iron chelatable to bleomycin is often present in the plasma of cord blood samples taken from preterm and term babies. The low caeruloplasmin and high ascorbate levels in plasma at birth may allow this iron to exist in the reduced ferrous state. In support of this postulate thirteen cord blood samples showing the presence of low molecular mass iron were able to degrade DNA in the presence of bleomycin and plasma.

Cardiopulmonary bypass patients undergoing heart valve replacement surgery appear to be under oxidative stress, when compared with normal healthy controls, by showing increased levels of protein and lipid damage. During bypass surgery two further episodes of oxidative stress occur. The first is seen when patients are placed on extracorporeal blood circulation and oxygenation which results in a rise in lipid peroxides and thiobarbituric acid-reactive substances. The second phase of oxidative stress occurs during reperfusion of the myocardium following removal of the aortic cross clamp. Coincident with evidence of increased oxidative damage to lipids during these latter phases of oxidative stress were decreases in plasma iron-binding and iron-oxidising antioxidant activities.

Pulmonary arterial hypertension describes a group of diseases characterised by raised pulmonary vascular resistance, resulting from vascular remodelling in the pre-capillary resistance arterioles. Left untreated, patients die from right heart failure. Pulmonary vascular remodelling involves all cell types but to date the precise roles of the different cells is unknown. This study investigated differences in basal gene expression between pulmonary arterial hypertension and controls using both human pulmonary microvascular endothelial cells and human pulmonary artery smooth muscle cells. Human pulmonary microvascular endothelial cells and human pulmonary artery smooth muscle cells from pulmonary arterial hypertension patients and controls were cultured to confluence, harvested and RNA extracted. Whole genome sequencing was performed and after transcript quantification and normalisation, we examined differentially expressed genes and applied gene set enrichment analysis to the differentially expressed genes to identify putative activated pathways. Human pulmonary microvascular endothelial cells displayed 1008 significant (p≤ 0.0001) differentially expressed genes in pulmonary arterial hypertension samples compared to controls. In human pulmonary artery smooth muscle cells, there were 229 significant (p≤ 0.0001) differentially expressed genes between pulmonary arterial hypertension and controls. Pathway analysis revealed distinctive differences: human pulmonary microvascular endothelial cells display down-regulation of extracellular matrix organisation, collagen formation and biosynthesis, focal- and cell-adhesion molecules suggesting severe endothelial barrier dysfunction and vascular permeability in pulmonary arterial hypertension pathogenesis. In contrast, pathways in human pulmonary artery smooth muscle cells were mainly up-regulated, including those for fatty acid metabolism, biosynthesis of unsaturated fatty acids, cell–cell and adherens junction interactions suggesting a more energy-driven proliferative phenotype. This suggests that the two cell types play different mechanistic roles in pulmonary arterial hypertension pathogenesis and further studies are required to fully elucidate the role each plays and the interactions between these cell types in vascular remodelling in disease progression.