Eucalyptol promotes lung repair in mice following cigarette smoke-induced emphysema

Background: Eucalyptol is a monoterpenoid oil present in many plants, principally the Eucalyptus species, and has been reported to have anti-inflammatory and antioxidative effects. Hypothesis/purpose: Since the potential effect of eucalyptol on mouse lung repair has not yet been studied, and considering that chronic obstructive pulmonary disease (COPD) is the fourth leading cause of death worldwide, the aim of this study was to investigate eucalyptol treatment in emphysematous mice. Study design: Male mice (C57BL/6) were divided into the following groups: control (sham-exposed), cigarette smoke (CS) (mice exposed to 12 cigarettes a day for 60 days), CS+1 mg/ml (CS mice treated with 1 mg/ml eucalyptol for 60 days), and CS+ 10 mg/ml (CS mice treated with 10 mg/ml eucalyptol for 60 days). Mice in the CS and control groups received vehicle for 60 days. Eucalyptol (or the vehicle) was administered via inhalation (15 min/daily). Mice were sacrificed 24 h after the completion of the 120-day experimental procedure. Methods: Histology and additional lung morphometric analyses, including analysis of mean linear intercept (Lm) and volume density of alveolar septa (Vv[alveolar septa]) were performed. Biochemical analyses were also performed using colorimetric assays for myeloperoxidase (MPO), malondialdehyde (MDA), and superoxide dismutase (SOD) activity, in addition to using ELISA kits for the determination of inflammatory marker levels (tumor necrosis factor alpha [TNF-alpha], interleukin-1 beta [IL-1 beta], interleukin 6 [IL-6], keratinocyte chemoattractant [KC], and tumor growth factor beta 1 [TGF-beta 1]). Finally, we investigated protein levels by western blotting (nuclear factor (erythroid-derived 2)-like 2 [Nrf2], nuclear factor kappa B [NF-kappa B], matrix metalloproteinase 12 [MMP-12], tissue inhibitor of matrix metalloproteinase 1 [TIMP-1], neutrophil elastase [NE], and elastin). Results: Eucalyptol promoted lung repair at the higher dose (10 mg/ml), with de novo formation of alveoli, when compared to the CS group. This result was confirmed with Lm and Vv[alveolar septa] morphometric analyses. Moreover, collagen deposit around the peribronchiolar area was reduced with eucalyptol treatment when compared to the CS group. Eucalyptol also reduced all inflammatory (MPO, TNF-alpha, IL-1 beta, IL-6, KC, and TGF-beta 1) and redox marker levels (MDA) when compared to the CS group (at least p < 0.05). In general, 10 mg/ml eucalyptol was more effective than 1 mg/ml and, at both doses, we observed an upregulation of SOD activity when compared to the CS group (p < 0.001). Eucalyptol upregulated elastin and TIMP-1 levels, and reduced neutrophil elastase (NE) levels, when compared to the CS group. Conclusion: In summary, eucalyptol promoted lung repair in emphysematous mice and represents a potential therapeutic phytomedicine in the treatment of COPD.