Quercetin in COPD: A Multi-Target Approach to Modulate Inflammation, Oxidative Stress, and Epithelial Dysfunction.

Chronic obstructive pulmonary disease (COPD) is a progressive lung disorder that affects millions of people globally. Although the mechanisms of COPD pathogenesis are not completely known, oxidative stress and lung inflammation caused by chronic exposure to cigarette smoke, environmental or occupational pollutants, gas from burning biomass fuel are thought to contribute to development of COPD. Therefore, therapies aimed at reducing oxidative stress along with inflammation may be important in treating COPD. However, the current pharmacological therapies treat symptoms and reduce acute exacerbations, but do not treat the root cause of COPD. Quercetin is a plant polyphenol present in berries, apples and onions, and has potent antioxidant and anti-inflammatory properties. Quercetin inhibits oxidative stress by scavenging reactive oxidant species and promoting expression of antioxidant enzymes. It reduces inflammation by inhibiting various kinases that participate in the expression of pro-inflammatory cytokines. It also alters gene expression by functioning as an epigenetic modifier. Quercetin also acts as antiviral agent by attenuating viral entry and replication. In preclinical models of COPD, quercetin reduces oxidative stress, lung inflammation, goblet cell metaplasia, expression of matrix metalloprotease MMP-9 and MMP-12, and prevents rhinovirus-induced progression of emphysema. It also promotes normal regeneration of airway epithelium by improving cell polarization, reducing goblet cell hyperplasia and increasing number of ciliated cells. This review compiles the current understanding of the biological properties of quercetin and its potential therapeutic role in COPD. We also summarize its potential benefits over the current therapeutic drugs used to treat COPD.