Introduction: In stroke patients higher plasma IL-6 levels are correlated with larger infarct volume, increased stroke severity and poor long term prognosis. IL-6 signaling may be detrimental in the periphery with high serum levels linked to detrimental outcomes. However, direct brain injection of IL-6 blocking antibodies increase deficits suggesting that therapeutic agents may need to block the peripheral rise in IL-6 without altering brain IL-6. This study sought to determine if Tocilizumab, an FDA approved drug that blocks IL-6 receptors and therefore inhibits the peripheral effects of IL-6, while having low blood brain barrier permeability; would result in reduced infarct and leukocyte infiltration after ischemic stroke.
Methods: Experiments utilized young (8 week; 20-25g) C57BL/6J male mice to examine neuroprotection, leukocyte infiltration and IL-6 activation post-ischemia. Stroke was induced by 60 min of transient right middle cerebral artery occlusion under anesthesia followed by reperfusion for 3 days. Four hours after the onset of ischemia all mice were randomly assigned into two groups and given an intraperitoneal injection of either Tocilizumab (13 day half-life) at a dose of 6 mg/kg body weight or saline vehicle as a control. The mice underwent behavioral testing to evaluate the effects of Tocilizumab on stroke recovery, testing evaluated motor/sensory deficits, anxiety and locomotor activity. Mice were sacrificed and used to either assess leukocyte infiltration and activation using IHC or infarct measurement using TTC staining.
Results: Tocilizumab not only ameliorated the severity of ischemic injury but also reduced behavioral deficits in mice after stroke. Treatment led to a significant reduction (p<0.05 vs saline) in infarct size. The results with the corner test, a sensorimotor function test, and neurological deficit scores further supported the beneficial effect of the drug. Immunohistochemical analysis displayed attenuated microglia activation in the tocilizumab treatment group suggesting that tocilizumab lowers immune system response to stroke by mediating the response of IL-6. This study demonstrates that inhibition of the IL-6 receptor with Tocilizumab may be a potential therapeutic approach for stroke treatment.