Involucrasin B suppresses airway inflammation in obese asthma by inhibiting the TLR4-NF-κB-NLRP3 pathway.

BACKGROUND: Obese asthma is an asthma phenotype that causes more severe lung inflammation and airway hyperresponsiveness than allergic asthma and it is resistant to conventional therapy. Involucrasin B (IB) is a dihydroflavonoid isolated from Shuteria involucrata (Wall.) Wight & Arn., a traditional "Dai" and "Wa" medicine was used in southern China to treat the "phlegm and wetness of sputum" (obesity disease) as well as lung inflammation. However, whether IB can ameliorate obese asthma remains unclear, and the underlying mechanisms and molecular expression in obese asthma specifically targeted by IB are still not fully understood. METHODS: An in vivo C57BL/6 J mouse model of obese asthma was established using house dust mites (HDMs) and high-fat diet (HFD) as inducers to evaluate the therapeutic effect of IB. An in vitro cell culture of human THP-1 monocytic cell culture was used to investigate the effect of IB after the treatment with lipopolysaccharide (LPS) and palmitic acid (PA). RESULTS: In vivo, we found that intervention with IB improved airway hyperresponsiveness and lung histopathology and significantly inhibited the secretion of relevant inflammatory factors, such as interleukin (IL)-1ß, IL-17A, and IL-22 in bronchoalveolar lavage fluid, and total-IgE and HDM-IgE in serum compared with the model group (HFD+HDM). The findings indicate that IB could decrease the expression of granulocyte receptor 1 (Gr-1) and neutrophil extracellular traps (NETs) in lung tissue, as well as the expression of NLR family pyrin domain containing 3 (NLRP3) and inducible nitric oxide synthase in M1 macrophages (M1). IB also reduced the population of ILC3/Th17 cells, which are responsible for producing IL-17A, a crucial mediator of neutrophil-mediated inflammation, confirming that the therapeutic effect of IB in obesity-related asthma was related to neutrophils and M1 cells. In addition, IB regulated lipid metabolism and inhibited the production of macrophages in adipose tissue. The in vitro results revealed that IB inhibited the secretion of IL-1ß, IL-18, and tumor necrosis factor-α (TNF-α) from THP-1 cells, and the expression of NLRP3-related protein in THP-1 cells compared with the model groups (LPS, PA, and LPS+PA), confirming that the action of IB involved the TLR4-NF-κB-NLRP3 pathway. CONCLUSION: This study demonstrated the therapeutic effect of IB in obese asthma for the first time and further clarified its mechanistic pathway as the TLR4-NF-κB-NLRP3 pathway.

(±)-Involucrasin D, a pair of enantiomeric bisflavonoid from the roots of Shuteria involucrata and its anti-inflammatory activity.

An undescribed bisflavonoid, named involucrasin D (1), along with two known flavonoids, 2(S)7,3',5'-trihydroxydihydroflavone (2) and sigmone (3) were isolated from the roots of Shuteria involucrata. A further chiral separation of 1 to yielded a pair of enantiomers (+)-1 and (-)-1. The structures were elucidated based on spectroscopic analyses and electron circular dichroism (ECD) calculations. Among them, bisflavonoid 1 and its enantiomers displayed remarkable anti-inflammatory effects by inhibiting the production of TNF-α and IL-6 in a dose-dependent manner.