Exosomes derived from baicalin-pretreated bone marrow mesenchymal stem cells inactivate the TLR4/MyD88/NF-kB pathway to improve asthma

Background: Baicalin, a natural compound isolated from the root of Scutellaria baicalensis Georgi, has been shown to have various pharmacological effects on lung diseases including asthma. Recently, research has suggested that baicalin combined with exosomes may have significant potential against disease development. The present work analyzes the effects of exosomes derived from baicalin-pretreated bone marrow mesenchymal stem cells (BMSCs) on asthma and the underlying mechanism.

Methods: BALB/c mice were sensitized with ovalbumin (OVA) through intraperitoneal injection to establish an animal model of asthma. Human bronchial epithelial cells (16HBE) were exposed to lipopolysaccharide to mimic a cell model of asthma. The pathological conditions of lung tissues in OVA-induced mice were analyzed by haematoxylin and eosin staining assays. Masson staining and quantification analysis were conducted to analyze percentage of Collagen fibers in lung tissues of OVA-induced mice. The Wright-Giemsa assay was used to determine the number of eosinophils, neutrophils, lymphocytes and macrophages. Enzyme-linked immunosorbent assays were performed to analyze expression levels of inflammatory factors including IL-4, IL-5, IL-13 and TNF-α levels. The values of airway resistance (Rrs), elastance (Ers) and compliance (Crs) were recorded for analyzing airway hyperresponsiveness through the FlexiVent system. Protein expression was analyzed by immunohistochemistry (IHC) and/or western blotting assay.

Results: Ovalbumin (OVA) pretreatment increased airway inflammation, airway hyperresponsiveness, Collagen deposition and epithelial-mesenchymal transition (EMT) in mice, however, these phenomena were significantly improved after treatment with baicalin-pretreated BMSC exosomes. Lipopolysaccharide (LPS)-induced 16HBE cells showed increased levels of interleukin-4 (IL-4), interleukin-5 (IL-5), interleukin-13 (IL-13) and tumor necrosis factor-α (TNF-α), elevated N-Cadherin and Vimentin protein expression, and decreased E-cadherin protein expression, whereas these LPS-induced effects were relieved after treatment with baicalin-pretreated BMSC exosomes. Additionally, protein expression of Toll-like Receptor 4 (TLR4), myeloid differentiation primary response protein 88 (MyD88) and phosphor p65 (p-p65) was upregulated in lung tissues of OVA-induced mice and LPS-stimulated 16HBE cells, but these phenomena were counteracted following exosomes treatment from baicalin-pretreated BMSCs.

Conclusion: Exosomes derived from baicalin-pretreated BMSCs ameliorated airway inflammation, airway hyperresponsiveness and airway remodeling after asthma by inactivating the TLR4/MyD88/nuclear factor kappa B pathway, providing a therapeutic strategy for asthma.

Asthma; Baicalin; Bone marrow mesenchymal stem cells; Exosomes.