Frontline Science: Two flavonoid compounds attenuate allergic asthma by regulating epithelial barrier via G protein-coupled estrogen receptor: Probing a possible target for allergic inflammation.

Allergic asthma is a common chronic lung inflammatory disease and seriously influences public health. We aim to investigate the effects of formononetin (FMN) and calycosin (CAL), 2 flavonoids in Radix Astragali, on allergic asthma and elucidate possible therapeutic targets. A house dust mite (HDM)-induced allergic asthma mouse model and TNF-α and Poly(I:C) co-stimulated human bronchial epithelial cell line (16HBE) were performed respectively in vivo and in vitro. The role of G protein-coupled estrogen receptor (GPER) was explored by its agonist, antagonist, or GPER small interfering RNA (siGPER). E-cadherin, occludin, and GPER were detected by western blotting, immunohistochemistry, or immunofluorescence. The epithelial barrier integrity was assessed by trans-epithelial electric resistance (TEER). Cytokines were examined by enzyme-linked immunosorbent assay (ELISA). The results showed that flavonoids attenuated pulmonary inflammation and hyperresponsiveness in asthmatic mice. These flavonoids significantly inhibited thymic stromal lymphopoietin (TSLP), increased occludin and restored E-cadherin in vivo and in vitro. The effects of flavonoids on occludin and TSLP were not interfered by ICI182780 (estrogen receptor antagonist), while blocked by G15 (GPER antagonist). Furthermore, compared with PPT (ERα agonist) and DPN (ERß agonist), G1 (GPER agonist) significantly inhibited TSLP, up-regulated occludin, and restored E-cadherin. siGPER and TEER assays suggested that GPER was pivotal for the flavonoids on the epithelial barrier integrity. Finally, G1 attenuated allergic lung inflammation, which could be abolished by G15. Our data demonstrated that 2 flavonoids in Radix Astragali could alleviate allergic asthma by protecting epithelial integrity via regulating GPER, and activating GPER might be a possible therapeutic strategy against allergic inflammation.

Astragaloside IV ameliorates allergic inflammation by inhibiting key initiating factors in the initial stage of sensitization.

To illuminate the anti-allergy mechanism of astragaloside IV (AS-IV), we assessed its effects in a murine model of allergic contact dermatitis (ACD). AS-IV administered in the sensitization phase, rather than in the elicitation phase, dramatically alleviated the symptoms of allergic inflammation. We hypothesized that AS-IV exerts its anti-allergy effects by regulating the production of key pro-allergic cytokines based on the fact that interleukin (IL)-33 and thymic stromal lymphopoietin (TSLP) levels increase significantly in the initial stage of the sensitization phase. AS-IV administered in the initial stage of ACD inhibited TSLP and IL-33 expression and reduced the proportion of type-2 innate lymphoid cells (ILC2s). An in vitro study showed that the production of pro-allergic cytokines was significantly inhibited in AS-IV presenting HaCaT cells. We also verified that AS-IV administered only in the initial stage markedly alleviated inflammation, including ear swelling, Th2 cytokine expression, and histological changes. Taken together, these results suggest that AS-IV effectively ameliorates the progression of allergic inflammation by inhibiting key initiating factors, including TSLP and IL-33, and can be used to prevent and/or treat patients with ACD. Our data also suggest that these key pro-allergic cytokines are potential therapeutic targets for allergic diseases.