Ameliorative effects of Glycyrrhiza glabra L. (licorice) on animal and human pulmonary fibrosis: A review of current knowledge

Air-borne inflammation plays an essential role in the pathogenesis of acute respiratory distress syndrome (ARDS), asthma, and chronic obstructive pulmonary disease (COPD). Anti-inflammatory therapy effectively improves the symptoms of these diseases. There are more than 30 species of the genus Glycyrrhiza, which are widely distributed worldwide. Licorice root extracts have beneficial effects on the treatment of throat infections, tuberculosis, respiratory and liver diseases, as well as antibacterial, anti-inflammatory, and immunodeficiency impacts. Therefore, the focus of this article is a review of the molecular mechanism of licorice extracts and its four flavonoids (isolycoirithigenin, licoirithigenin, lycalocone, and guanidine) and their therapeutic effects on respiratory distress syndrome and fibrosis caused by this disease. By its combination of flavonoid, triterpenoid, saponin, and isoflavones, licorice is essential in reducing inflammation, strengthening the immune system and antioxidant properties. Licorice can be a natural alternative to current treatment to eliminate new emerging pathogens, such as viral diseases with side effects. Based on this systematic review article, it is suggested that licorice effectively reduces lung inflammation caused by viral pathogens by inhibiting the infiltration of inflammatory cells and the release of inflammatory mediators, which subsequently results in neutrophil recruitment in the lung and neutrophil-mediated oxidative damage, edema and reducing congestion. Therefore, products that target transforming growth factor (TGF)-β1 signaling proteins, Smads, and phosphorylated Smads (p-Smads), with the ability of epithelial cells to adopt mesenchymal phenotypes, may be helpful in the development of therapies. New pulmonary fibrosis should be followed by respiratory distress syndrome.