Alveolar macrophages from overweight/obese subjects with asthma demonstrate a proinflammatory phenotype

Abstract

Rationale: Obesity is associated with increased prevalence and severity of asthma. Adipose tissue macrophages can contribute to the systemic proinflammatory state associated with obesity. However, it remains unknown whether alveolar macrophages have a unique phenotype in overweight/obese patients with asthma.

Objectives: We hypothesized that leptin levels would be increased in the bronchoalveolar lavage fluid from overweight/obese subjects and, furthermore, that leptin would alter the response of alveolar macrophages to bacterial LPS.

Methods: Forty-two subjects with asthma and 46 healthy control subjects underwent research bronchoscopy. Bronchoalveolar lavage fluid from 66 was analyzed for the level of cellular inflammation, cytokines, and soluble leptin. Cultured primary macrophages from 22 subjects were exposed to LPS, leptin, or leptin plus LPS. Cytokines were measured in the supernatants.

Measurements and main results: Leptin levels were increased in overweight/obese subjects, regardless of asthma status (P = 0.013), but were significantly higher in overweight/obese subjects with asthma. Observed levels of tumor necrosis factor-α were highest in overweight/obese subjects with asthma. Ex vivo studies of primary alveolar macrophages indicated that the response to LPS was most robust in alveolar macrophages from overweight/obese subjects with asthma and that preexposure to high-dose leptin enhanced the proinflammatory response. Leptin alone was sufficient to induce production of proinflammatory cytokines from macrophages derived from overweight/obese subjects with asthma.

Conclusions: Ex vivo studies indicate that alveolar macrophages derived from overweight/obese subjects with asthma are uniquely sensitive to leptin. This macrophage phenotype, in the context of higher levels of soluble leptin, may contribute to the pathogenesis of airway disease associated with obesity.

Figure 1.

Log-normalized bronchoalveolar lavage fluid (BALF) leptin levels in four groups, divided by sex. (A) BAL leptin levels were significantly higher in overweight/obese subjects with asthma and in (B) overweight/obese females with asthma. (C) BALF leptin levels do not differ in males. LA = lean subjects with asthma; LN = lean normal subjects; OA = overweight/obese subjects with asthma; ON = overweight/obese normal subjects. **P < 0.001; *P < 0.01; ^#P < 0.05.

Figure 2.

Log-normalized bronchoalveolar lavage fluid (BALF) tumor necrosis factor (TNF)-α levels in four groups, divided by sex. (A) BALF TNF-α levels were significantly higher in overweight/obese subjects with asthma and in (B) overweight/obese females with asthma. (C) BALF leptin and TNF-α levels do not differ in males. LA = lean subjects with asthma; LN = lean normal subjects; OA = overweight/obese subjects with asthma; ON = overweight/obese normal subjects. *P < 0.01; ^#P < 0.05.

Figure 3.

Correlation between bronchoalveolar lavage (BAL) leptin and tumor necrosis factor (TNF)-α in four groups and based on sex. (A) BAL TNF-α levels are correlated with BAL leptin levels overall (R² = 0.15, *P = 0.014). (B) There is a significant correlation between BAL TNF-α and leptin in female subjects (R² = 0.36, *P = 0.0008). (C) There is no correlation of these two cytokines in male subjects (P = 0.053).

Figure 4.

Effect of leptin, LPS, and leptin plus LPS on cytokine production by macrophages from subjects with asthma and normal control subjects. Data are reported as fold change = postexposure cytokine production/negative control. (A) Leptin results in higher IL-5 levels in subjects with asthma regardless of weight status. Fold changes in IL-5 levels are higher in overweight/obese subjects with asthma in response to LPS and leptin plus LPS exposure. (B and C) Tumor necrosis factor (TNF)-α and IFN-γ levels are higher in overweight/obese subjects with asthma in response to leptin. There is no differential response to LPS. Leptin plus LPS results in significantly higher fold changes in IFN-γ and TNF-α levels in overweight/obese subjects with asthma. (D) IL-8 levels are higher in overweight/obese subjects with asthma in response to leptin, LPS, and leptin plus LPS. LA = lean subjects with asthma; LN = lean normal subjects; OA = overweight/obese subjects with asthma; ON = overweight/obese normal subjects. **P < 0.001; *P < 0.01; ^#P < 0.05.