Effects of Thymus vulgaris L., Cinnamomum verum J.Presl and Cymbopogon nardus (L.) Rendle Essential Oils in the Endotoxin-induced Acute Airway Inflammation Mouse Model

Abstract

Thyme (TO), cinnamon (CO), and Ceylon type lemongrass (LO) essential oils (EOs) are commonly used for inhalation. However, their effects and mechanisms on inflammatory processes are not well-documented, and the number of in vivo data that would be important to determine their potential benefits or risks is low. Therefore, we analyzed the chemical composition and investigated the activity of TO, CO, and LO on airway functions and inflammatory parameters in an acute pneumonitis mouse model. The components of commercially available EOs were measured by gas chromatography-mass spectrometry. Airway inflammation was induced by intratracheal endotoxin administration in mice. EOs were inhaled during the experiments. Airway function and hyperresponsiveness were determined by unrestrained whole-body plethysmography on conscious animals. Myeloperoxidase (MPO) activity was measured by spectrophotometry from lung tissue homogenates, from which semiquantitative histopathological scores were assessed. The main components of TO, CO, and LO were thymol, cinnamaldehyde, and citronellal, respectively. We provide here the first evidence that TO and CO reduce inflammatory airway hyperresponsiveness and certain cellular inflammatory parameters, so they can potentially be considered as adjuvant treatments in respiratory inflammatory conditions. In contrast, Ceylon type LO inhalation might have an irritant effect (e.g., increased airway hyperresponsiveness and MPO activity) on the inflamed airways, and therefore should be avoided.

Keywords: airway hyperresponsiveness; airway inflammation; cinnamon; endotoxin; essential oil; lemongrass; mouse model; myeloperoxidase activity; perivascular edema; thyme.

Figure 1

Effects of thyme (TO), cinnamon (CO) and lemongrass (LO) essential oils on (A) breathing frequency, (B) tidal volume, (C) minute ventilation, (D) time of inspiration, (E) time of expiration, (F) peak inspiratory flow, (G) peak expiratory flow, (H) relaxation time and (I) Penh compared to the negative control paraffin oil (PO), after lipopolysaccharide (LPS - black columns)/phosphate-buffered saline (PBS - white columns) treatment. (n = 8–10/group, # p < 0.05, ## p < 0.005, ### p < 0.0005, #### p < 0.0001 vs. respective PBS-treated group, *p < 0.05, ** p < 0.005, *** p < 0.0005, **** p < 0.0001 vs. LPS-PO-treated mice).

Figure 1

Effects of thyme (TO), cinnamon (CO) and lemongrass (LO) essential oils on (A) breathing frequency, (B) tidal volume, (C) minute ventilation, (D) time of inspiration, (E) time of expiration, (F) peak inspiratory flow, (G) peak expiratory flow, (H) relaxation time and (I) Penh compared to the negative control paraffin oil (PO), after lipopolysaccharide (LPS - black columns)/phosphate-buffered saline (PBS - white columns) treatment. (n = 8–10/group, # p < 0.05, ## p < 0.005, ### p < 0.0005, #### p < 0.0001 vs. respective PBS-treated group, *p < 0.05, ** p < 0.005, *** p < 0.0005, **** p < 0.0001 vs. LPS-PO-treated mice).

Figure 2

Histopathological alterations in the lung. Representative pictures of lung parenchyma after (A) PBS and PO treatment, (B) LPS and PO treatment, (C) PBS and TO treatment, (D) LPS and TO treatment, (E) PBS and CO treatment, (F) LPS and CO treatment, (G) PBS and LO treatment, and (H) LPS and LO treatment. (Hematoxylin–eosin staining, 200 × magnification; a: alveolus, b: bronchiole, v: vessel, ed: edema).

Figure 3

Semiquantitative evaluation of (A) perivascular and peribronchial edema, (B) accumulation of neutrophil granulocytes, (C) macrophages and (D) total score of lung histopathological alterations (n = 8–10/group, # p < 0.05, ## p < 0.005, #### p < 0.000 vs. respective PBS-treated group) are demonstrated in box plots showing the median, upper/lower quartile, and maximum/minimum values.

Figure 4

Results of myeloperoxidase (MPO) activity measurements. (n = 8–10/group, ## p < 0.005, ### p < 0.0005, #### p < 0.0001 vs. respective PBS-treated group, * p < 0.05, **** p < 0.0001 vs. LPS-PO-treated).