Onset of obesity in carboxypeptidase E-deficient mice and effect on airway responsiveness and pulmonary responses to ozone

Abstract

When compared with lean, wild-type mice, obese Cpefat mice, 14 wk of age and older, manifest innate airway hyperresponsiveness (AHR) to intravenous methacholine and enhanced pulmonary inflammation following acute exposure to ozone (O3). The purpose of this study was to examine the onset of these augmented pulmonary responses during the onset of obesity. Thus airway responsiveness and O3-induced pulmonary inflammation and injury were examined in 7- and 10-wk-old Cpefat and age-matched, wild-type, C57BL/6 mice. Compared with age-matched controls, 7- and 10-wk-old Cpefat mice were approximately 25 and 61% heavier, respectively. Airway responsiveness to intravenous methacholine was assessed via forced oscillation in unexposed Cpefat and wild-type mice. The 10- but not 7-wk-old Cpefat mice exhibited innate AHR. O3 exposure (2 ppm for 3 h) increased markers of pulmonary inflammation and injury in the bronchoalveolar lavage fluid of all mice. However, most markers were greater in Cpefat vs. wild-type mice, regardless of age. Serum levels of leptin, a satiety hormone and proinflammatory cytokine, were increased in Cpefat vs. wild-type mice of both age groups, but the serum levels of other systemic inflammatory markers were greater only in 10-wk-old Cpefat vs. wild-type mice. These results demonstrate that a 25% increase in body weight is sufficient to augment pulmonary responses to O3, but innate AHR is not manifest until the mice become much heavier. These results suggest that the mechanistic bases for these responses are different and may develop according to the nature and degree of the chronic systemic inflammation that is present.

Fig. 1.

Total body masses of male and female wild-type and Cpe^fat mice at 7 or 10 wk of age. Values are means ± standard error of the means (SE); n = 6−16 mice for each group. *P < 0.05 compared with age- and sex-matched, wild-type mice.

Fig. 2.

Serum concentrations of soluble tumor necrosis factor receptor 1 (sTNFR1) (A), sTNFR2 (B), IL-6 (C), monocyte chemotactic protein (MCP)-1 (D), leptin (E), and adiponectin (F), as well as the number of blood leukocytes (G) from room air-exposed wild-type and Cpe^fat mice, which are 7 or 10 wk of age. Values are means ± SE; n = 6−9 mice for each group. *P < 0.05 compared with age-matched, wild-type mice.

Fig. 3.

Changes in pulmonary resistance (Rl) induced by intravenous methacholine in unexposed 7-wk-old (A) or 10-wk-old (B) wild-type and Cpe^fat mice. Values are means ± SE; n = 5−6 mice for each group. *P < 0.05 compared with age-matched, wild-type mice.

Fig. 4.

Responses to intravenous methacholine for airway resistance (Raw) (A), coefficient of lung tissue damping (G) (B), and coefficient of lung tissue elastance (H) (C) in unexposed 10-wk-old wild-type and Cpe^fat mice. Values are means ± SE; n = 6 mice for each group. *P < 0.05 compared with age-matched, wild-type mice.

Fig. 5.

Concentrations of protein (A), IL-6 (B), KC (C), macrophage inflammatory protein (MIP)-2 (D), and eotaxin (E), as well as the number of macrophages (F), neutrophils (G), and epithelial cells (H) in the bronchoalveolar lavage (BAL) fluid (BALF) of wild-type and Cpe^fat mice, which are 7 or 10 wk of age. BAL was performed on each animal 4 h following the cessation of a 3-h exposure to either room air or 2 ppm ozone (O₃). Values are means ± SE; n = 7−9 mice for each group. *P < 0.05 compared with age- and genotype-matched, room air-exposed mice. #P < 0.05 compared with age-matched, wild-type mice exposed to O₃.