11.    A continuous exposure to urban air pollution aggravates myocardial infarction in               mice: the role of lung oxidative stress and inflammation

The exposure to air pollution leads to increased morbidity and mortality rates from cardiorespiratory diseases, largely due to myocardial infarction (MI). It has been suggested that pulmonary and systemic oxidative stress and inflammation play a central role in this scenario. In order to address this hypothesis, the aim of this work was to characterize a mice model of continuous exposure to urban air pollution by the assessment of different markers of lung, blood, and cardiac oxygen metabolism and inflammation, and to study its contribution over experimental MI. 8-week-old BALB/c male mice were exposed to filtered air (control) or urban air in whole-body inhalation chambers located in a highly populated area of Buenos Aires City. Animals were exposed during 8 hours/day, 5 days/week, for up to 3 months. After 2 months, mice breathing urban air showed a 53% increase in total leucocyte count in bronchoalveolar lavage (BAL) samples in comparison with the control group (control: 1.0±0.2 x105 cells, p<0.001), together with a 104% increase in BAL protein concentration (control: 0.15±0.03 mg/mL, p<0.05). Both BAL leucocyte count and protein concentration were still significantly increased after 3 months. At this time point, a 4-fold increase in MCP-1 was found in BAL samples from exposed mice in comparison with the control group. Consistently, lung histology showed inflammatory leukocyte recruitment, edema, and thickening of the alveolar wall. Moreover, BAL analysis by flow cytometry showed increased alveolar macrophage activation and nitric oxide production in exposed mice. In lung homogenates, a significant increase in phospholipids oxidation together with a decrease in SOD activity was observed after 1 and 2 months in exposed mice, followed by a later
increase in NADPH oxidase activity in this group. While no differences were observed in lung oxygen consumption at any evaluated time point, cardiac oxygen consumption was significantly decreased by 32% after 3 months in exposed mice (control: 1100±90 nmol O2/min g tissue, p<0.01). Interestingly, impaired cardiac mitochondrial function was observed in this group, due to a decrease in active state respiration rate. However, no changes were observed in mitochondrial H2O2 or ATP production rates. In plasma, the exposure to urban air led to a significant increase in TNF-α and IL-6 levels after 3 months. At this time point, the exposure to air pollution aggravated MI as indicated by a 53% increase in ischaemia/reperfusion injury when compared to the control group (control: 43±4 % risk area, p<0.01). Diastolic function was also compromised in exposed mice, as shown by a sustained increase in LVEDP during reperfusion. In conclusion, in the present animal model we were able to reproduce some of the main features of the adverse health effects of air pollution exposure reported in human populations, highlighting the importance of considering them during the development of cardiovascular diseases in urban areas.