Airway resistance, inflammation and oxidative stress following exposure to diesel exhaust particle in angiotensin II-induced hypertension in mice

Exposure to particulate matter is a risk factor for respiratory and cardiovascular diseases. However, the mechanisms underlying these effects are not well understood. Here, we compared the impact of diesel exhaust particles (DEP) on airway resistance, inflammation and oxidative stress in normal mice, or mice made hypertensive by implanting osmotic minipump infusing angiotensin II. On day 13 after the onset of infusion, angiotensin II induced significant increase in heart rate (P<0.05) and systolic blood pressure (P<0.0001). On the same day, mice were intratracheally instilled with either DEP (15μg/mouse) or saline. Twenty-four hour later, the measurement of airway reactivity to methacholine (0-10. mg/ml) in vivo by a forced oscillation technique showed a significant and dose dependent increase in airway resistance in normotensive mice exposed to DEP compared to those exposed to saline. In hypertensive mice, there was no difference in airway resistance in DEP versus saline exposed mice. However, following exposure to DEP, airway resistance significantly increased in normotensive versus hypertensive mice. Bronchoalveolar lavage (BAL) fluid analysis showed a significant increase in macrophage numbers in normotensive mice exposed to DEP compared to those exposed to saline, and to hypertensive mice exposed to DEP. Neutrophil numbers were significantly increased in both normotensive and hypertensive mice exposed to DEP compared with their respective control groups. Superoxide dismutase activity was significantly decreased following DEP exposure in both normotensive and hypertensive mice compared to their respective controls. However, total proteins, a marker for increase of epithelial permeability, and malondialdehyde, a reflection of lipid peroxidation, were only increased in normotensive mice exposed to DEP. Therefore, our data suggest that DEP do not aggravate airway resistance and inflammation in angiotensin II-induced hypertensive mice. On the contrary, at the dose of DEP and time point investigated, airway resistance, inflammation and oxidative stress are increased in normotensive compared to hypertensive mice.