Increased pulmonary responses to acute ozone exposure in obese db/db mice

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Abstract
Epidemiological studies indicate the incidence of asthma is increased in obese and overweight humans. Responses to ozone (O3), an asthma trigger, are increased in obese ( ob/ob) mice lacking the satiety hormone leptin. The long form of leptin receptor (Ob-Rb) is required for satiety; mice lacking this receptor ( db/db mice) are also substantially obese. Here, wild-type (WT) and db/ db mice were exposed to air or O3 (2 ppm) for 3 h. Airway responsiveness, measured by the forced oscillation technique, was greater in db/db than WT mice after air exposure. O3-induced increases in pulmonary resistance and airway responsiveness were also greater in db/ db mice. BALF eotaxin, IL-6, KC, and MIP-2 increased 4 h after O3 exposure and subsided by 24 h, whereas protein and neutrophils continued to increase through 24 h. For each outcome, the effect of O3 was significantly greater in db/ db than WT mice. Previously published results obtained in ob/ob mice were similar except for O3-induced neutrophils and MIP-2, which were not different from WT mice. O3 also induced pulmonary IL-1β and TNF-α mRNA expression in db/db but not ob/ob mice. Leptin was increased in serum of db/db mice, and pulmonary mRNA expression of short form of leptin receptor (Ob-Ra) was similar in db/db and WT mice. These data confirm obese mice have innate airway hyperresponsiveness and increased pulmonary responses to O3. Differences between ob/ob mice, which lack leptin, and db/db mice, which lack Ob-Rb but not Ob-Ra, suggest leptin, acting through Ob-Ra, can modify some pulmonary responses to O3.