Exploring the Potential Effects and Mechanisms of Asarum sieboldii Radix Essential Oil for Treatment of Asthma

Abstract

Asthma, a common chronic pulmonary disorder characterized by airway remodeling, hyperresponsiveness and obstruction, can be aggravated by repeated exposure to particulate matter (PM). The potential effect and mechanisms of Asarum sieboldii Radix essential oil (AEO) against asthma were explored based on network pharmacology. AEO was pre-treated using a nebulizer for 3 weeks and the mice were sensitized to ovalbumin (OVA) and PM₁₀ with the co-treatment of AEO for 4 weeks. In addition, A549 lung epithelial cells were sensitized with PM₁₀ to investigate the underlying mechanisms of AEO regarding the lung-fibrosis-related mediators. The target genes of methyl eugenol, a main compound of AEO, were highly matched by 48% with the gene set of asthma. AEO markedly inhibited the increase in epithelial thickness through the accumulation of goblet cells in the airways. Collagen deposition in the lung tissues of OVA+PM₁₀-challenged asthmatic mice was significantly decreased by AEO. AEO also inhibited the influx of inflammatory cells in the bronchoalveolar lavage fluid, as well as the increases in serum IgE and IgG_2a and cytokines in the lung tissues. Furthermore, AEO regulated the expressions of fibrotic mediators, especially POSTN and TGF-β. In conclusion, we expect that AEO can be one of the effective alternative therapeutics to relieve asthma.

Keywords: Asarum sieboldii; air pollution; asthma; essential oil; particulate matter.

Figure 1

Network pharmacological analysis of AEO. (A) Network of AEO with 106 nodes and 968 edges. The nodes and edges indicate the targeted genes of AEO and their relationships, respectively. The black nodes present seed nodes and the gray ones are nodes that interact with the seed nodes. Yellow, predicted; purple, co-expression; pink, physical interactions; blue, co-localization; light green, shared protein domains; sky, pathways; green, genetic interactions. (B) Veen diagram of intersection targets between AEO network and the gene sets of asthma disease. (C) Common genes of AEO and asthma.

Figure 2

Histological structural changes in lung and trachea tissues stained by hematoxylin and eosin. Magnification is ×400. Blue bars indicate the epithelial thicknesses of lung and trachea tissues, respectively. Results are presented as mean ± standard error of the mean. ### p < 0.001 vs. NOR group; * p < 0.05 and *** p < 0.001 vs. OVA+PM₁₀ group.

Figure 3

Goblet cell population per area of lung and trachea tissues stained by PAS. Magnification is ×400. Red arrowheads indicate PAS-positive purpled goblet cells. Results are presented as mean ± standard error of the mean. ### p < 0.001 vs. NOR group; * p < 0.05, ** p < 0.01 and *** p < 0.001 vs. OVA+PM₁₀ group.

Figure 4

Collagen deposition % of area of lung tissues. (A) Lung tissues stained by Masson’s trichrome. Blue-stained area of lung tissues indicates collagen accumulation. Magnification is ×100. Results are presented as mean ± standard error of the mean. ### p < 0.001 vs. NOR group; ** p < 0.01 and *** p < 0.001 vs. OVA+PM₁₀ group. (B) Expressions of COL1A1, COL3A1 mRNA levels in lung tissues. Results are presented as mean ± standard error of the mean. ### p < 0.001 vs. NOR group; *** p < 0.001 vs. OVA+PM₁₀ group.

Figure 5

Number of inflammatory cells, including macrophages, neutrophils, eosinophils, lymphocytes and total cells, in BALF (A) and serum IgE and IgG2a levels (B). Results are presented as mean ± standard error of the mean. # p < 0.05, ## p < 0.01 and ### p < 0.001 vs. NOR group; * p < 0.05, ** p < 0.01 and *** p < 0.001 vs. OVA+PM₁₀ group.

Figure 6

Expressions of pro-inflammatory and Th2-specific cytokines in lung tissues. (A) mRNA levels of TNF-α, IL-1β and IL-6 in lung tissues. Results are presented as mean ± standard error of the mean. ### p < 0.001 vs. NOR group; ** p < 0.01 and *** p < 0.001 vs. OVA+PM₁₀ group. (B) mRNA levels of IL-4 and IL-13 in lung tissues. Results are presented as mean ± standard error of the mean. ### p < 0.001 vs. NOR group; ** p < 0.01 and *** p < 0.001 vs. OVA+PM₁₀ group.

Figure 7

Expressions of MMPs, including MMP-1, -2 and -9, in lung tissues. Results are presented as mean ± standard error of the mean. ### p < 0.001 vs. NOR group; ** p < 0.01 and *** p < 0.001 vs. OVA+PM₁₀ group.

Figure 8

Expressions of fibrotic mediators including POSTN and TGF-β. (A) mRNA levels of POSTN and TGF-β in lung tissues. Results are presented as mean ± standard error of the mean. ### p < 0.001 vs. NOR group; * p < 0.05, ** p < 0.01 and *** p < 0.001 vs. OVA+PM₁₀ group. (B) mRNA levels of POSTN and TGF-β in A549 lung epithelial cells. Results are presented as mean ± standard error of the mean. ### p < 0.001 vs. non-treated cells; *** p < 0.001 vs. PM₁₀-stimulated cells.

Figure 9

Expressions of epithelial–mesenchymal transition markers including snail, vimentin, E-cadherin, N-cadherin and fibronectin. (A) Protein levels of snail, vimentin, E-cadherin, N-cadherin and fibronectin with quantified values in lung tissues. Results are presented as mean ± standard error of the mean. ### p < 0.001 vs. NOR group; ** p < 0.01 and *** p < 0.001 vs. OVA+PM₁₀ group. (B) Protein levels of snail, vimentin, E-cadherin, N-cadherin and fibronectin with quantified values in A549 lung epithelial cells. Results are presented as mean ± standard error of the mean. ### p < 0.001 vs. non-treated cells; *** p < 0.001 vs. PM₁₀-stimulated cells.

Figure 10

STRING network representing the predicted functional partners of POSTN. Predicted functional partners with POSTN (A). Network of POSTN and functional partners (B).