Fermented Platycodon grandiflorum Extracts Relieve Airway Inflammation and Cough Reflex Sensitivity In Vivo

Platycodon grandiflorum (PG) has been extensively utilized as an herb to relieve phlegm. In this study, the effects of PG root extracts on airway inflammation and cough reflex were investigated, especially using fermented PG extracts (FPE) to increase an active compound, platycodin D by fermentation. FPE significantly reduced the numbers of eosinophils and total cells in the bronchoalveolar lavage fluid (BALF) obtained from lipopolysaccharide/ovalbumin (LPS/OVA)-induced asthma mice versus those of vehicle control. Moreover, in the BALF and the serum, FPE significantly reduced the concentration of IL-17E, a proinflammatory cytokine that causes T_H2 immunity, including eosinophil amplification. It was also demonstrated that FPE might relieve inflammations through histological analysis of the lung separated from each mouse. Furthermore, in cough reflex guinea pigs induced by citric acid treatment, FPE treatment significantly reduced the number of coughs versus that of vehicle control, and consequently decreased cough reflex sensitivity. In addition, the total cell number and eosinophils significantly decreased in the BALF obtained from each guinea pig versus that of vehicle control. In in vitro study, pretreatment with FPE in LPS-stimulated RAW264.7 cells significantly reduced the levels of proinflammatory cytokines such as TNF-α, IL-6, and IL-1β, and inducible nitric oxide synthases (iNOS). Therefore, we demonstrated that FPE relieved airway inflammation and cough reflex sensitivity in vivo, and exhibited anti-inflammatory effects through suppression of iNOS and several proinflammatory cytokines. These findings suggest that FPE might have a beneficial effect on respiratory health, and may be useful as a functional food to prevent respiratory diseases.

Keywords: • Platycodon grandiflorum; • asthma; • cough reflex; • fermentation.