SO2 Inhalation Contributes to the Development and Progression of Ischemic Stroke in the Brain

Epidemiological literatures show an association between air pollution and ischemic stroke, and effective pollutants may include SO2, NOx, O-3, CO, and particulates. However, existing experimental studies lack evidence as to the presence of effects for SO2, which has been the focus in developing countries with increasing use of coal as the main resource. In the present study, we treated Wistar rats with SO2 at various concentrations and determined endothelin-1 (ET-1), inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), and intercellular adhesion molecule 1 (ICAM-1) messenger RNA (mRNA) and protein expression in the cortex. The results show that SO2 elevated the levels of ET-1, iNOS, COX-2, and ICAM-1 mRNA and protein in a concentration-dependent manner. Then, we set up rat model of ischemic stroke using middle cerebral artery occlusion (MCAO) and further treated the model rats with filtered air and lower concentration SO2 for the same period. As expected, elevated expression of ET-1 iNOS, COX-2, and ICAM-1 occurred in the cortex of MCAO model rats exposed to filtered air, followed by increased activation of caspase-3 and cerebral infarct volume. Interestingly, SO2 inhalation after MCAO significantly amplified above effects. It implies that SO2 inhalation caused brain injuries similar to that of cerebral ischemia, and its exposure in atmospheric environment contributed to the development and progression of ischemic stroke.