Fenofibrate inhibits TGF-β-induced myofibroblast differentiation and activation in human lung fibroblasts in vitro

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.

Promising small molecule anti-fibrotic agents: Newly developed or repositioned drugs targeting myofibroblast transdifferentiation

Fibrosis occurs in all organs and tissues except the brain, and its progression leads to dysfunction of affected organs. Fibrosis-induced organ dysfunction results from the loss of elasticity, strength, and functionality of tissues due to the extracellular matrix secreted by myofibroblasts that express smooth muscle-type actin as a marker. Myofibroblasts, which play a major role in fibrosis, were once thought to originate exclusively from activated fibroblasts; however, it is now clear that myofibroblasts are diverse in origin, from epithelial cells, endothelial cells, adipocytes, macrophages, and other cells. Fibrosis of vital organs, such as the heart, lungs, kidneys, and liver, is a serious chronic disease that ultimately leads to death. Currently, anti-cancer drugs have made remarkable progress, as evidenced by the development of many molecular-targeted drugs, and are making a significant contribution to improving the prognosis of cancer treatment. However, the development of anti-fibrotic agents, which also play an important role in prognosis, has lagged. In this review, the current knowledge regarding myofibroblasts is summarized, with particular attention given to their origin and transdifferentiation signaling pathways (e.g., TGF-β, Wnt/β-catenin, YAP/TAZ and AMPK signaling pathways). The development of new small molecule anti-fibrotic agents and the repositioning of existing drugs targeting myofibroblast transdifferentiation are discussed.

Fenofibrate attenuates the cytotoxic effect of cisplatin on lung cancer cells by enhancing the antioxidant defense system in vitro

Fenofibrate (FF) is a peroxisome proliferator- activated receptor (PPAR)-α agonist that is widely used for the treatment of hyperlipidemia. It has been shown to have pleiotropic actions beyond its hypolipidemic effect. FF has been shown to exert a cytotoxic effect on some cancer cells when used at higher than clinically relevant concentrations; on the other hand, its cytoprotective effect on normal cells has also been reported. The present study assessed the effect of FF on cisplatin (CDDP) cytotoxicity to lung cancer cells in vitro. The results demonstrated that the effect of FF on lung cancer cells depends on its concentration. FF at ≤50 µM, which is a clinically achievable blood concentration, attenuated CDDP cytotoxicity to lung cancer cells, whereas FF at ≥100 µM, albeit clinically unachievable, had an anticancer effect. The mechanism of FF attenuation of CDDP cytotoxicity involved PPAR-α-dependent aryl hydrocarbon receptor (AhR) expression, which in turn stimulated nuclear factor erythroid 2-related factor 2 (Nrf2) expression and antioxidant production, resulting in lung cancer cell protection from CDDP-evoked oxidative damage. In conclusion, the present study revealed that FF, at clinically relevant concentrations, attenuated CDDP cytotoxicity to lung cancer cells by enhancing the antioxidant defense system through activation of a pathway that involves the PPAR-α-PPAR response element-AhR xenobiotic response element-Nrf2-antioxidant response element. These findings suggested that concomitant use of FF with CDDP may compromise the efficacy of chemotherapy. Although the anticancer property of FF has recently attracted much attention, concentrations that exceed clinically relevant concentrations are required.

PPARδ Agonist GW501516 Suppresses the TGF-β-Induced Profibrotic Response of Human Bronchial Fibroblasts from Asthmatic Patients

The airway wall remodeling observed in asthma is associated with subepithelial fibrosis and enhanced activation of human bronchial fibroblasts (HBFs) in the fibroblast to myofibroblast transition (FMT), induced mainly by transforming growth factor-β (TGF-β). The relationships between asthma severity, obesity, and hyperlipidemia suggest the involvement of peroxisome proliferator-activated receptors (PPARs) in the remodeling of asthmatic bronchi. In this study, we investigated the effect of PPARδ ligands (GW501516 as an agonist, and GSK0660 as an antagonist) on the FMT potential of HBFs derived from asthmatic patients cultured in vitro. This report shows, for the first time, the inhibitory effect of a PPARδ agonist on the number of myofibroblasts and the expression of myofibroblast-related markers-α-smooth muscle actin, collagen 1, tenascin C, and connexin 43-in asthma-related TGF-β-treated HBF populations. We suggest that actin cytoskeleton reorganization and Smad2 transcriptional activity altered by GW501516 lead to the attenuation of the FMT in HBF populations derived from asthmatics. In conclusion, our data demonstrate that a PPARδ agonist stimulates antifibrotic effects in an in vitro model of bronchial subepithelial fibrosis. This suggests its potential role in the development of a possible novel therapeutic approach for the treatment of subepithelial fibrosis during asthma.

Drugs against metabolic diseases as potential senotherapeutics for aging-related respiratory diseases

Recent advances in aging research have provided novel insights for the development of senotherapy, which utilizes cellular senescence as a therapeutic target. Cellular senescence is involved in the pathogenesis of various chronic diseases, including metabolic and respiratory diseases. Senotherapy is a potential therapeutic strategy for aging-related pathologies. Senotherapy can be classified into senolytics (induce cell death in senescent cells) and senomorphics (ameliorate the adverse effects of senescent cells represented by the senescence-associated secretory phenotype). Although the precise mechanism has not been elucidated, various drugs against metabolic diseases may function as senotherapeutics, which has piqued the interest of the scientific community. Cellular senescence is involved in the pathogenesis of chronic obstructive pulmonary disease (COPD) and idiopathic pulmonary fibrosis (IPF), which are aging-related respiratory diseases. Large-scale observational studies have reported that several drugs, such as metformin and statins, may ameliorate the progression of COPD and IPF. Recent studies have reported that drugs against metabolic diseases may exert a pharmacological effect on aging-related respiratory diseases that can be different from their original effect on metabolic diseases. However, high non-physiological concentrations are needed to determine the efficacy of these drugs under experimental conditions. Inhalation therapy may increase the local concentration of drugs in the lungs without exerting systemic adverse effects. Thus, the clinical application of drugs against metabolic diseases, especially through an inhalation treatment modality, can be a novel therapeutic approach for aging-related respiratory diseases. This review summarizes and discusses accumulating evidence on the mechanisms of aging, as well as on cellular senescence and senotherapeutics, including drugs against metabolic diseases. We propose a developmental strategy for a senotherapeutic approach for aging-related respiratory diseases with a special focus on COPD and IPF.