Saturated Fatty Acid Increases Lung Macrophages and Augments House Dust Mite-Induced Airway Inflammation in Mice Fed with High-Fat Diet

Abstract

Obesity is one of the phenotypes of severe asthma, which is considered to be a heterogeneous syndrome; however, its interaction with airway inflammation is not fully understood. The aim of this study was to clarify the role of saturated fatty acids in augmenting airway inflammation induced by house dust mite (HDM) in obesity. Subjects were Balb/c mice fed a high-fat diet (HFD) for 10 weeks, followed by sensitization and exposure to HDM. Subjects were also administered palmitic acid (PA) for 4 weeks with concurrent sensitization and exposure to HDM. Airway inflammation was assessed by quantifying the amount of inflammatory cells in bronchoalveolar lavage (BAL) and airway resistance was measured. In vitro, lipopolysaccharide (LPS)-primed macrophages were stimulated by PA. The amount of monocyte chemoattractant protein-1 (MCP-1), interleukin-1β (IL-1β), and tumor necrosis factor α (TNF-α) was examined in the supernatant. Compared to normal chow mice, HFD mice underwent significant increases in body weight; increases in number of lung macrophages, including circulating monocytes and alveolar macrophages; and increases in bronchoalveolar lavage fluid (BALF) total cell count, including neutrophils but not eosinophils, after HDM sensitization and exposure. In vitro, PA induced MCP-1 and augmented LPS-primed production of IL-1β and TNF-α in macrophages. Among HDM mice that were administered PA, there was an increase BALF total cell count, including neutrophils but not eosinophils, compared to vehicle mice. In conclusion, saturated fatty acid increased the number of lung macrophages and augmented HDM-induced neutrophilic airway inflammation in a HFD mouse model.

Keywords: bronchial asthma; high-fat diet; house dust mite; macrophages; obesity; saturated fatty acid.

Fig. 2

HFD augments HDM-induced neutrophilic airway inflammation, airway hyperresponsiveness, and cytokine production in the lungs. a Protocol of HDM-induced airway inflammation in normal chow or HFD mouse model. b Body weight gain is compared among PBS-chow, HDM-chow, PBS-HFD, and HDM-HFD mice (n = 6 in each group). c Bronchoalveolar lavage fluid analysis for total and differential cell counts among PBS-chow, HDM-chow, PBS-HFD, and HDM-HFD mice (n = 6 in each group). The HDM-HFD group is compared with the HDM-chow group. d Airway hyperresponsiveness is measured through assessment of airway resistance according to graded concentrations of methacholine in PBS-chow, HDM-chow, PBS-HFD, and HDM-HFD mice (n = 6 in each group). The HDM-chow group is compared with the PBS-chow group, while the HDM-HFD group is compared with HDM-chow mice. e Histologic examination for airway inflammation. Sections are stained with H & E (upper panels) and PAS (lower panels). Original magnification was × 200. Concentrations of f IL-13, g IL-17A, h IL-1β, and i MIP2 in lung tissue are measured by ELISA (n = 6 in each group). *P < 0.05, **P < 0.01. HFD, high-fat diet; HDM, house dust mite; PBS, phosphate-buffered saline; H & E, hematoxylin and eosin; PAS, periodic acid-Schiff; MIP2, macrophage inflammatory protein 2; ELISA, enzyme-linked immunosorbent assay.

Fig. 2

HFD augments HDM-induced neutrophilic airway inflammation, airway hyperresponsiveness, and cytokine production in the lungs. a Protocol of HDM-induced airway inflammation in normal chow or HFD mouse model. b Body weight gain is compared among PBS-chow, HDM-chow, PBS-HFD, and HDM-HFD mice (n = 6 in each group). c Bronchoalveolar lavage fluid analysis for total and differential cell counts among PBS-chow, HDM-chow, PBS-HFD, and HDM-HFD mice (n = 6 in each group). The HDM-HFD group is compared with the HDM-chow group. d Airway hyperresponsiveness is measured through assessment of airway resistance according to graded concentrations of methacholine in PBS-chow, HDM-chow, PBS-HFD, and HDM-HFD mice (n = 6 in each group). The HDM-chow group is compared with the PBS-chow group, while the HDM-HFD group is compared with HDM-chow mice. e Histologic examination for airway inflammation. Sections are stained with H & E (upper panels) and PAS (lower panels). Original magnification was × 200. Concentrations of f IL-13, g IL-17A, h IL-1β, and i MIP2 in lung tissue are measured by ELISA (n = 6 in each group). *P < 0.05, **P < 0.01. HFD, high-fat diet; HDM, house dust mite; PBS, phosphate-buffered saline; H & E, hematoxylin and eosin; PAS, periodic acid-Schiff; MIP2, macrophage inflammatory protein 2; ELISA, enzyme-linked immunosorbent assay.

Fig. 5

PA arguments HDM-induced neutrophilic airway inflammation, airway hyperresponsiveness, and cytokine production in the lungs. a Protocol of HDM-induced airway inflammation mouse model administered with vehicle or PA. b Bronchoalveolar lavage fluid total and differential cell counts is compared among PBS-vehicle, HDM-vehicle, PBS-PA, and HDM-PA mice (n = 6 in each group). The HDM-vehicle group is compared with the HDM-PA group. c Airway hyperreactivity is assessed by measuring airway resistance according to graded concentrations of methacholine in PBS-vehicle, HDM-vehicle, PBS-PA, and HDM-PA mice (n = 6 in each group). The HDM-vehicle group is compared with the PBS-vehicle group, while the HDM-PA group is compared with the HDM-vehicle mice. d Histologic examination for airway inflammation. Sections are stained with H & E (upper panels) and PAS (lower panels). Original magnification was ×200. Concentrations of e IL-13, f IL-17A, g IL-1β, and h MIP2 in the lung tissue were measured by ELISA (n = 6 in each group). *P < 0.05, **P < 0.01. HDM, house dust mite; PA, palmitic acid; PBS, phosphate-buffered saline; H & E, hematoxylin and eosin; PAS, periodic acid-Schiff; MIP2, macrophage inflammatory protein 2; ELISA, enzyme-linked immunosorbent assay.

Fig. 5

PA arguments HDM-induced neutrophilic airway inflammation, airway hyperresponsiveness, and cytokine production in the lungs. a Protocol of HDM-induced airway inflammation mouse model administered with vehicle or PA. b Bronchoalveolar lavage fluid total and differential cell counts is compared among PBS-vehicle, HDM-vehicle, PBS-PA, and HDM-PA mice (n = 6 in each group). The HDM-vehicle group is compared with the HDM-PA group. c Airway hyperreactivity is assessed by measuring airway resistance according to graded concentrations of methacholine in PBS-vehicle, HDM-vehicle, PBS-PA, and HDM-PA mice (n = 6 in each group). The HDM-vehicle group is compared with the PBS-vehicle group, while the HDM-PA group is compared with the HDM-vehicle mice. d Histologic examination for airway inflammation. Sections are stained with H & E (upper panels) and PAS (lower panels). Original magnification was ×200. Concentrations of e IL-13, f IL-17A, g IL-1β, and h MIP2 in the lung tissue were measured by ELISA (n = 6 in each group). *P < 0.05, **P < 0.01. HDM, house dust mite; PA, palmitic acid; PBS, phosphate-buffered saline; H & E, hematoxylin and eosin; PAS, periodic acid-Schiff; MIP2, macrophage inflammatory protein 2; ELISA, enzyme-linked immunosorbent assay.