Allergic airway responses in obese mice

Abstract

Rationale: Epidemiologic data indicate an increased incidence of asthma in the obese.

Objectives: To determine whether obese mice exhibit augmented pulmonary responses after allergen sensitization and challenge.

Methods: Lean, wild-type (C57BL/6), obese ob/ob, and obese db/db mice were sensitized to ovalbumin (OVA), and then challenged with aerosolized OVA or phosphate-buffered saline (PBS). Changes in total pulmonary resistance (Rl) induced by intravenous methacholine were measured by forced oscillation. Blood was collected, bronchoalveolar lavage (BAL) was performed, and lungs were harvested for measurement of cytokine expression by real-time reverse transcription-polymerase chain reaction.

Measurements and main results: OVA challenge increased baseline Rl in ob/ob, but not wild-type, mice, and airway responsiveness was greater in ob/ob than wild-type mice, regardless of the challenge. Compared with PBS, OVA challenge caused an increase in the number of BAL fluid (BALF) cells, an increase in lung Th2 cytokine expression, and an increase in serum IgE. Significantly fewer BALF cells were recovered from OVA-challenged ob/ob versus wild-type mice, whereas serum IgE levels were elevated significantly more in ob/ob versus wild-type mice. BALF and lung Th2 cytokine expression was not different in ob/ob versus wild-type mice. Airway responsiveness was greater in db/db versus wild-type mice, regardless of the challenge, and OVA caused airway hyperresponsiveness in db/db but not wild-type mice, despite reduced BALF cells in OVA-challenged db/db versus wild-type mice.

Conclusions: These results demonstrate that obesity enhances OVA-induced changes in pulmonary resistance and serum IgE and that these changes are not the result of increased Th2 type airway inflammation.

Figure 1.

Changes in pulmonary resistance (Rl) induced by intravenous methacholine in ovalbumin (OVA)-sensitized wild-type (C57BL/6) and ob/ob mice challenged with aerosols of either phosphate-buffered saline (PBS) or OVA once per day for 7 consecutive days. Responses were measured 24 hours after the cessation of the final aerosol challenge. n = 9–10 mice for each group. Solid circles, wild-type (PBS); solid squares, wild-type (OVA); open circles, ob/ob (PBS); open squares, ob/ob (OVA). *P < 0.05 compared with wild-type (C57BL/6) mice with an identical exposure; ^#P < 0.05 compared with genotype-matched, PBS-challenged controls.

Figure 2.

Concentration of total IgE in the serum of ovalbumin (OVA)-sensitized wild-type (C57BL/6) and ob/ob mice challenged with aerosols of either phosphate-buffered saline (PBS) or OVA once per day for 7 consecutive days. Blood was collected and serum was isolated 24 hours after the cessation of the final aerosol challenge. n = 6–10 mice for each group. Solid bars, wild-type; open bars, ob/ob. *P < 0.05 compared with genotype-matched, PBS-challenged controls. ^#P < 0.05 compared with wild-type (C57BL/6) mice with an identical exposure.

Figure 3.

Total number of (A) macrophages, (B) eosinophils, (C) lymphocytes, and (D) neutrophils in the bronchoalveolar lavage fluid (BALF) of ovalbumin (OVA)-sensitized wild-type (C57BL/6) and ob/ob mice challenged with aerosols of either phosphate-buffered saline (PBS) or OVA once per day for 7 consecutive days. BALF was collected 24 hours after the cessation of the final aerosol challenge. n = 10–14 mice for each group. Solid bars, wild-type; open bars, ob/ob. *P < 0.05 compared with genotype-matched, PBS-challenged controls; ^#P < 0.05 compared with wild-type (C57BL/6) mice with an identical exposure.

Figure 4.

(A–D) Representative hematoxylin-and-eosin–stained histologic sections, (E) inflammation score, and (F) periodic acid-Schiff (PAS) reaction prevalence of carbohydrates and mucoproteins from the lungs of ovalbumin (OVA)-sensitized wild-type (C57BL/6) and ob/ob mice challenged with aerosols of either phosphate-buffered saline (PBS) or OVA once per day for 7 consecutive days. A and B are sections from PBS-challenged wild-type and ob/ob mice, respectively. C and D are sections from OVA-challenged wild-type and ob/ob mice, respectively. Lungs were fixed in situ with 10% formalin 24 hours after the cessation of the final aerosol challenge. n = 6–7 mice for each group. Solid bars, wild-type; open bars, ob/ob. *P < 0.05 compared with genotype-matched, PBS-challenged controls; ^#P < 0.05 compared with wild-type (C57BL/6) mice with an identical exposure.

Figure 5.

Concentration of total (A) IL-4, (B) IL-13, and (C) eotaxin in the bronchoalveolar lavage fluid (BALF) of ovalbumin (OVA)-sensitized wild-type (C57BL/6) and ob/ob mice challenged with aerosols of either phosphate-buffered saline (PBS) or OVA once per day for 7 consecutive days. BALF was collected 24 hours after the cessation of the final aerosol challenge. n = 4–10 mice for each group. Solid bars, wild-type; open bars, ob/ob. *P < 0.05 compared with genotype-matched, PBS-challenged controls; ^#P < 0.05 compared with wild-type (C57BL/6) mice with an identical exposure.

Figure 6.

mRNA expression of (A) IL-4, (B) IL-5, (C) IL-13, (D) IFN-γ, and (E) acidic mammalian chitinase (AMCase) in the lung tissue of ovalbumin (OVA)-sensitized wild-type (C57BL/6) and ob/ob mice challenged with aerosols of either phosphate-buffered saline (PBS) or OVA once per day for 7 consecutive days. Lung tissue was collected 24 hours after the cessation of the final aerosol challenge. mRNA transcript copy number was normalized to β-actin transcript copy number. n = 4–10 mice for each group. Solid bars, wild-type; open bars, ob/ob. *P < 0.05 compared with genotype-matched, PBS-challenged controls.

Figure 7.

Concentrations of total serum (A) soluble tumor necrosis factor receptor 1 (sTNFR1), (B) sTNFR2, (C) eotaxin, as well as (D) total number of blood leukocytes from ovalbumin (OVA)-sensitized wild-type (C57BL/6) and ob/ob mice challenged with aerosols of phosphate-buffered saline (PBS) once per day for 7 consecutive days. Blood was collected and serum was isolated 24 hours after the cessation of the final aerosol challenge. n = 5–14 for each group. Solid bars, wild-type; open bars, ob/ob. *P < 0.05 compared with wild-type (C57BL/6) mice.

Figure 8.

Changes in (A) pulmonary resistance (Rl) and (B) dynamic compliance (Cdyn) induced by intravenous methacholine in ovalbumin (OVA)-sensitized wild-type (C57BL/6) and db/db mice challenged with aerosols of either phosphate-buffered saline (PBS) or OVA once per day for 3 consecutive days. Responses were measured 48 hours after the cessation of the final aerosol challenge. n = 6–7 mice for each group. Solid circles, wild-type (PBS); solid squares, wild-type (OVA); open circles, db/db (PBS); open squares, db/db (OVA). *P < 0.05 compared with wild-type (C57BL/6) mice with an identical exposure; ^#P < 0.05 compared with genotype-matched, PBS-challenged controls.

Figure 9.

Total number of (A) macrophages, (B) eosinophils, (C) lymphocytes, and (D) neutrophils in the bronchoalveolar lavage fluid (BALF) of ovalbumin (OVA)-sensitized wild-type (C57BL/6) and db/db mice challenged with aerosols of either phosphate-buffered saline (PBS) or OVA once per day for 3 consecutive days. BALF was collected 48 hours after the cessation of the final aerosol challenge. n = 4–5 mice for each group. Solid bars, wild-type; open bars, db/db. *P < 0.05 compared with genotype-matched, PBS-challenged controls; ^#P < 0.05 compared with wild-type (C57BL/6) mice with an identical exposure.