Long-term exposure to urban particulate matter exacerbates mortality after ischemic stroke in mice

Exposure to fine particulate matter (PM_2.5) has been epidemiologically reported to worsen the prognosis of ischemic stroke; however, the details have not been investigated. One of the major toxic mechanisms of PM_2.5 inhalation is oxidative stress, which is mediated by reactive oxygen species generated by PM_2.5 components such as metals and polycyclic aromatic hydrocarbons. In this study, we examined the effects of long-term exposure to urban particulate matter, focusing on oxidative stress, on prognosis after ischemic stroke in mice. When mice were intranasally exposed for 28 days to an urban aerosol collected in Beijing, China (CRM28), microglial activation was observed in the cerebral cortex, indicating that CRM28 induced neuroinflammation. CRM28 exposure resulted in increased serum levels of brain natriuretic peptide and troponin I, suggesting that cardiac injury was elicited by CRM28. Lung inflammation was also observed following CRM28 exposure; however, systemic inflammation was not detected. Mice exposed to CRM28 showed an exacerbation of mortality after ischemic stroke induction compared with vehicle mice. A vitamin E-rich diet suppressed CRM28-induced lipid peroxidation in the heart and lungs but not in the brain. A vitamin E-rich diet also attenuated cardiac injury and lung inflammation induced by CRM28 exposure, whereas neuroinflammation was not affected. Mortality after ischemic stroke improved with the administration of a vitamin E-rich diet. Considering that systemic inflammation did not occur, cardiac injury induced by oxidative stress under exposure to urban particulate matter may be involved in increased mortality after ischemic stroke. Antioxidation under air pollution is fundamental for protection against ischemic stroke.