Resolvin D1 prevents smoking-induced emphysema and promotes lung tissue regeneration

Abstract

Purpose: Emphysema is an irreversible disease that is characterized by destruction of lung tissue as a result of inflammation caused by smoking. Resolvin D1 (RvD1), derived from docosahexaenoic acid, is a novel lipid that resolves inflammation. The present study tested whether RvD1 prevents smoking-induced emphysema and promotes lung tissue regeneration.

Materials and methods: C57BL/6 mice, 8 weeks of age, were randomly divided into four groups: control, RvD1 only, smoking only, and smoking with RvD1 administration. Four different protocols were used to induce emphysema and administer RvD1: mice were exposed to smoking for 4 weeks with poly(I:C) or to smoking only for 24 weeks, and RvD1 was injected within the smoking exposure period to prevent regeneration or after completion of smoking exposure to assess regeneration. The mean linear intercept and inflammation scores were measured in the lung tissue, and inflammatory cells and cytokines were measured in the bronchoalveolar lavage fluid.

Results: Measurements of mean linear intercept showed that RvD1 significantly attenuated smoking-induced lung destruction in all emphysema models. RvD1 also reduced smoking-induced inflammatory cell infiltration, which causes the structural derangements observed in emphysema. In the 4-week prevention model, RvD1 reduced the smoking-induced increase in eosinophils and interleukin-6 in the bronchoalveolar lavage fluid. In the 24-week prevention model, RvD1 also reduced the increased neutrophils and total cell counts induced by smoking.

Conclusion: RvD1 attenuated smoking-induced emphysema in vivo by reducing inflammation and promoting tissue regeneration. This result suggests that RvD1 may be useful in the prevention and treatment of emphysema.

Keywords: COPD; emphysema; resolvin D1.

Figure 1

Experimental design. Notes: (A) 4-week prevention model. (B) 4-week regeneration model. (C) 24-week prevention model. (D) 24-week regeneration model. Abbreviations: PBS, phosphate buffered saline; w, weeks; D, day.

Figure 2

Measurements of emphysema assessed by MLI. Notes: RvD1 reduced smoking-induced increase in MLI in all four models: (A) 4-week prevention, (B) 4-week regeneration, (C) 24-week prevention, and (D) 24-week regeneration models. *P<0.05, **P<0.01, and ***P<0.001 (one-way ANOVA with Tukey’s post tests). The scale bars indicate 100 μm. The results are presented as the mean of the mice included in all experiments. Abbreviations: MLI, mean linear intercept; RvD1, resolvin D1; ANOVA, analysis of variance; CTL, control; RE, RvD1 only; SM, smoking; SR, smoking + RvD1.

Figure 3

Degree of inflammatory cell infiltration. Notes: Histologic scoring indicates that smoking significantly increased peribronchial and perivascular inflammatory cell infiltrations and that infiltration was reduced by resolvin D1 in the (A) 4-week prevention, (B) 4-week regeneration, (C) 24-week prevention, and (D) 24-week regeneration models. **P<0.01 and ***P<0.001 (one-way ANOVA with Tukey’s post tests). The scale bars indicate 100 μm. Abbreviations: ANOVA, analysis of variance; CTL, control; RE, RvD1 only; RvD1, resolvin D1; SM, smoking; SR, smoking + RvD1.

Figure 4

BAL fluid analysis in the 4-week prevention model. Notes: RvD1 significantly reduced the smoking-induced increase in (A) total cell counts, (B) eosinophil counts, and (C) IL-6 levels in the BAL fluid. *P<0.05, **P<0.01, and ***P<0.001 (one-way ANOVA with Tukey’s post tests). Abbreviations: BAL, bronchoalveolar lavage; RvD1, resolvin D1; IL6, interleukin-6; ANOVA, analysis of variance; CTL, control; RE, RvD1 only; SM, smoking; SR, smoking + RvD1; Mac, macrophage; Lym, lymphocyte; Eos, eosinophil; Neu, neutrophil.

Figure 5

BAL fluid analysis in the 24 week prevention model. Notes: RvD1 significantly reduced the smoking-induced increase in (A) total cell counts and (B) neutrophil counts. (C) The IL-6 level in the BAL fluid also decreased, but statistical significance was not reached because the basal level was too low. *P<0.05, **P<0.01, and ***P<0.001 (one-way ANOVA with Tukey’s post tests). Abbreviations: BAL, bronchoalveolar lavage; RvD1, resolvin D1; IL6, interleukin-6; ANOVA, analysis of variance; CTL, control; RE, RvD1 only; SM, smoking; SR, smoking + RvD1; Mac, macrophage; Lym, lymphocyte; Eos, eosinophil; Neu, neutrophil.