Inhibition of inflammatory responses by ambroxol, a mucolytic agent, in a murine model of acute lung injury induced by lipopolysaccharide

Abstract

Objective: The aim of this study is to investigate whether ambroxol inhibits inflammatory responses in a murine model of lipopolysaccharide-induced acute lung injury (ALI).

Methods: Mice (n=295) were first intratracheally instilled with lipopolysaccharide (LPS) to induce ALI and then received an intraperitoneal (i.p.) injection of either normal saline (NS), ambroxol (30 or 90 mg/kg per day) or dexamethasone (2.5 or 5 mg/kg per day) for 7 days. Metabolism (n=10, each), lung morphology (n=5, each) and wet-to-dry lung weight ratio (n=10, each) were studied. The levels of tumor necrosis factor (TNF-alpha), interleukin-6 (IL-6) and transforming growth factor (TGF-beta1) and the protein concentration (n=5 or 7, each) in bronchoalveolar lavage (BAL) were measured.

Results: Mice with LPS-induced ALI that were treated with ambroxol at a dosage of 90 mg/kg per day significantly gained weight compared to the control and dexamethasone-treated groups. Ambroxol and dexamethasone significantly reduced the lung hemorrhage, edema, exudation, neutrophil infiltration and total lung injury histology score at 24 and 48 h. In addition, ambroxol and dexamethasone significantly attenuated the lung wet-to-dry weight ratio at 24 and 48 h (p<0.05). Compared to the control group, TNF-alpha, IL-6 and TGF-beta1 levels in the BAL in both ambroxol- and dexamethasone-treated groups were significantly reduced at 24 and 48 h. The protein in BAL, an index of vascular permeability, was also significantly decreased in the ambroxol- and dexamethasone-treated groups (p<0.05).

Conclusion: Ambroxol inhibited proinflammatory cytokines, reduced lung inflammation and accelerated recovery from LPS-induced ALI.

Figures

Fig. 1.

The influence of ambroxol on metabolism in the mice with LPS-induced ALI. (A) Water intake; (B) Food consumption (C) The changes of body weight. *p<0.05, for ambroxol 90 mg/kg vs control at 72, 96 120 and 168 h; §p<0.01, for the dexamethasone-treated group vs ambroxol 90 mg/kg group at 72, 96 120 and 168 h; #p<0.01, for dexamethasone 2.5 and 5 mg/kg vs control at 96, 120 and 168 h. Values are presented as means ± SD, n=10 in each group

Fig. 2.

( A) Changes of histology and lung injury scores of lung at 24 h after LPS instillation in the NS-, ambroxol- and dexamethasone-treated groups. a representative of histological change at 0 h in the NS-treated group; b-d represent histological changes at 24 h in the NS-, ambroxol (90 mg/kg)- and dexamethasone (5 mg/kg)-treated groups, respectively. *p<0.05, **p<0.01 at 24 h in the ambroxol-treated group vs in the NS-treated group; #p<0.05, ##p<0.01 at 24 h in the dexamethasone-treated group vs in the NS-treated group. (B) Changes of histology and lung injury scores of lung at 48 h after LPS instillation in the NS-, ambroxol- and dexamethasone-treated groups. a representative of histological change at 0 h in the NS-treated group. b-d represent histological change at 48 h in the NS-, ambroxol- and dexamethasone-treated groups. *p<0.05, **p<0.01 at 48 h in the ambroxol-treated group vs in the NS-treated group. #p<0.05, ##p<0.01 at 48 h in the dexamethasone-treated group vs in the NS-treated group (Magnification ×100, bar =50 μm)

Fig. 3

. Lung wet-to-dry weight ratios were significantly decreased at 24 and 48 h after LPS instillation. *p<0.05 24 h vs 0 h in the NS-treated group; **p<0.01 24 h vs 0 h in the NS-treated group; #p<0.05 the ambroxol-treated group vs the NS-treated group at 24 h and 48 h; §p<0.05 the dexamethasone-treated group vs the NS-treated group at 24 h and 48 h. Values are presented as means ± SD

Fig. 4.

(A) Ambroxol reduced the level of TNF-α in BAL at 24 h after intratracheal instillation of LPS. **p<0.01 24 h vs 0 h in the NS-treated group; *p<0.05 the ambroxol-treated group vs the NS-treated group at 24 h; #p<0.01 the dexamethasone-treated group vs the NS-treated group at 24 h and 48 h. (B) Ambroxol inhibited the level of IL-6 in BAL at 48 h after intratracheal instillation of LPS. **p<0.01 48 h vs 0 h in the NS-treated group; ##p<0.01 the ambroxol-treated group vs the NS-treated group at 48 h; §§p<0.01 the dexamethasone-treated group vs the NS-treated group at 48 h. (C) Ambroxol delayed the occurrence of the peak value and reduced the level of TGF-β1 in BAL in LPS induced ALI. *p<0.05 24 h vs 0 h in the NS-treated group; #p<0.05 the ambroxol-treated group vs the NS-treated group at 24 h; §p<0.05 the dexamethasone-treated group vs the NS-treated group at 24 h. (D) Ambroxol decreased the protein concentration in BAL at 24 h after instillation of LPS. *p<0.05 24 h vs 0 h in the NS-treated group; #p<0.05 the ambroxol-treated group vs the NS-treated group at 24 h; §p<0.05 the dexamethasone-treated group vs the NS-treated group at 24 h. Values are presented as means ± SD