Clenbuterol, a Selective β2-Adrenergic Receptor Agonist, Inhibits or Limits Post-Stroke Pneumonia, but Increases Infarct Volume in MCAO Mice

Younian Xu,1 Yangyang Ge,1 Miaomiao Zhou,2 Zongze Zhang2 1Anesthesiology Department, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, People’s Republic of China; 2Anesthesiology Department, Zhongnan Hospital of Wuhan University, Wuhan, People’s Republic of ChinaCorrespondence: Miaomiao ZhouAnesthesiology Department, Zhongnan Hospital of Wuhan University, No. 169 Donghu Road, Wuchang District, Wuhan, 430071, Hubei Province, People’s Republic of ChinaTel/Fax +86 027-67812903Email 879475227@qq.comBackground: Large ischemic stroke provokes an inflammatory response, promoting the release of norepinephrine (NE) by intensifying the sympathetic nervous system. This augmented sympathetic outflow was deemed to act on β 2-adrenergic receptors (β 2-ARs) expressed by immune cells, rendering organisms to post-stroke infections, like pneumonia. To clarify this issue, we introduced selective β 2-ARs agonist clenbuterol (CLEN) to stroke mice to investigate how β 2-adrenergic signaling augmentation after stroke affects immune response and post-stroke outcomes, including central and peripheral.Methods: We developed a middle cerebral artery occlusion (MCAO) stroke model in mice to induce large ischemic stroke and administered CLEN 24 h after the onset of MCAO stroke. First, we assessed infarct volume and NE levels in plasma and spleen 3ds later. Next, the immune state was identified by analyzing the spleen index, immune cell populations, and immune cytokines. Finally, peripheral outcomes were assessed by measuring signs of pneumonia, such as pathology, bacterial burden, and lung cytokines.Results: We report that CLEN treatment 24 h after MCAO stroke causes an enlarged infarct volume and a decrease in NE levels at 3ds after stroke. Consistent with a reduction of total T cells, T helper cells, and increase of cytotoxic T cells, the immune milieu after CLEN treatment presents an anti-inflammatory landscape, showing raised expression of anti-inflammatory cytokines: IL-4, IL-10, and TGF-β 1, and decreased expression of pro-inflammatory cytokines, such as TNF-α, IL-1β, and IFN-γ, with a dramatically reduced percentage of Gr-1+ neutrophils and B cells but an increased percentage of NK cells. In our study, CLEN treatment results in no higher risk of pneumonia but relieves bacterial burden, inhibits or limits pneumonia, and diminishes TNF-α expression in lung tissues after MCAO.Conclusion: We identified increased β 2-adrenergic signaling after MCAO stroke, inhibits or limits post-stroke pneumonia but enlarges stroke volume in MCAO mice. Thus, careful consideration must be taken to improve post-stroke outcomes by manipulation over β 2-adrenergic receptors.Keywords: ischemic stroke, β 2-adrenergic receptor, infarct, pneumonia, immunity, sympathetic