Targeting reprogrammed metabolism as a therapeutic approach for respiratory diseases

Metabolic reprogramming underlies the etiology and pathophysiology of respiratory diseases such as asthma, idiopathic pulmonary fibrosis (IPF), and chronic obstructive pulmonary disease (COPD). The dysregulated cellular activities driving airway inflammation and remodelling in these diseases have reportedly been linked to aberrant shifts in energy-producing metabolic pathways: glycolysis and oxidative phosphorylation (OXPHOS). The rewiring of glycolysis and OXPHOS accompanying the therapeutic effects of many clinical compounds and natural products in asthma, IPF, and COPD, supports targeting metabolism as a therapeutic approach for respiratory diseases. Correspondingly, inhibiting glycolysis has largely attested effective against experimental asthma, IPF, and COPD. However, modulating OXPHOS and its supporting catabolic pathways like mitochondrial pyruvate catabolism, fatty acid β-oxidation (FAO), and glutaminolysis for these respiratory diseases remain inconclusive. An emerging repertoire of metabolic enzymes are also interconnected to these canonical metabolic pathways that similarly possess therapeutic potential for respiratory diseases. Taken together, this review highlights the urgent demand for future studies to ascertain the role of OXPHOS in different respiratory diseases, under different stimulatory conditions, and in different cell types. While this review provides strong experimental evidence in support of the inhibition of glycolysis for asthma, IPF, and COPD, further verification by clinical trials is definitely required.

Dexamethasone protects against Aspergillus fumigatus-induced severe asthma via modulating pulmonary immunometabolism

Severe asthma is a difficult-to-treat chronic airway inflammatory disease requiring systemic corticosteroids to achieve asthma control. It has recently been shown that drugs targeting immunometabolism have elicited anti-inflammatory effects. The purpose of this study was to investigate potential immunometabolic modulatory actions of systemic dexamethasone (Dex) in an Aspergillus fumigatus (Af)-induced severe asthma model. Mice were repeatedly exposed to the Af aeroallergen before systemic treatment with Dex. Simultaneous measurements of airway inflammation, real-time glycolytic and oxidative phosphorylation (OXPHOS) activities, expression levels of key metabolic enzymes, and amounts of metabolites were studied in lung tissues, and in primary alveolar macrophages (AMs) and eosinophils. Dex markedly reduced Af-induced eosinophilic airway inflammation, which was coupled with an overall reduction in lung glycolysis, glutaminolysis, and fatty acid synthesis. The anti-inflammatory effects of Dex may stem from its immunometabolic actions by downregulating key metabolic enzymes including pyruvate dehydrogenase kinase, glutaminase, and fatty acid synthase. Substantial suppression of eosinophilic airway inflammation by Dex coincided with a specific escalation of mitochondrial proton leak in primary lung eosinophils. Besides, while our findings confirmed that inflammation corresponds with an upregulation of glycolysis, it was accompanied with an unexpectedly stable or elevated OXPHOS in the lungs and activated immune cells, respectively. Our findings reveal that the anti-inflammatory effects of Dex in severe asthma are associated with downregulation of pyruvate dehydrogenase kinase, glutaminase, and fatty acid synthase, and the augmentation of mitochondrial proton leak in lung eosinophils. These enzymes and biological processes may be valuable targets for therapeutic interventions against severe asthma.

Degradation of MK2 with natural compound andrographolide: A new modality for anti-inflammatory therapy

The p38MAPK-MK2 signaling axis functions as an initiator of inflammation. Targeting the p38MAPK-MK2 signaling axis represents a direct therapeutic intervention of inflammatory diseases. We described here a novel role of andrographolide (AG), a small-molecule ent-labdane natural compound, as an inhibitor of p38MAPK-MK2 axis via MK2 degradation. AG was found to bind to the activation loop of MK2, located at the interface of the p38MAPK-MK2 biomolecular complex. This interaction disrupted the complex formation and predisposed MK2 to proteasome-mediated degradation. We showed that AG induced MK2 degradation in a concentration- and time-dependent manner and exerted its anti-inflammatory effects by enhancing the mRNA-destabilizing activity of tristetraprolin, thereby inhibiting pro-inflammatory mediator production (e.g., TNF-α, MCP-1). Administration of AG via intratracheal (i.t.) route to mice induced MK2 downregulation in lung alveolar macrophages, but not lung tissues, and prevented macrophage activation. Our study also demonstrated that the anti-inflammatory effects achieved by AG via MK2 degradation were more durable and sustained than that achieved by the conventional MK2 kinase inhibitors (e.g., PF-3644022). Taken together, our findings illustrated a novel mode of action of AG by modulating the p38MAPK-MK2 signaling axis and would pave the way for the development of a novel class of anti-inflammatory agents targeting MK2 for degradation by harnessing the privileged scaffold of AG.

Targeting the renin angiotensin system for respiratory diseases

Renin-angiotensin system (RAS) plays an indispensable role in regulating blood pressure through its effects on fluid and electrolyte balance. As an aside, cumulative evidence from experimental to clinical studies supports the notion that dysregulation of RAS contributes to the pro-inflammatory, pro-oxidative, and pro-fibrotic processes that occur in pulmonary diseases like asthma, chronic obstructive pulmonary disease (COPD), idiopathic pulmonary fibrosis (IPF), and acute lung injury (ALI). Pharmacological intervention of the various RAS components can be a novel therapeutic strategy for the treatment of these respiratory diseases. In this chapter, we first give a recent update on the RAS, and then compile, review, and analyse recent reports on targeting RAS components as treatments for respiratory diseases. Inhibition of the pro-inflammatory renin, angiotensin-converting enzyme (ACE), angiotensin (Ang) II, and Ang II type 1 receptor (AT1R) axis, and activation of the protective ACE2, AT2R, Ang (1-7), and Mas receptor axis have demonstrated varying degrees of efficacies in experimental respiratory disease models or in human trials. The newly identified alamandine/Mas-related G-protein-coupled receptor member D pathway has shown some therapeutic promise as well. However, our understanding of the RAS ligand-and-receptor interactions is still inconclusive, and the modes of action and signaling cascade mediating the newly identified RAS receptors remain to be better characterized. Clinical data are obviously lacking behind the promising pre-clinical findings of certain well-established molecules targeting at different pathways of the RAS in respiratory diseases. Translational human studies should be the focus for RAS drug development in lung diseases in the next decade.