Abstract WP225: Rapid Complement Activation Induced By Acute Hyperglycemia Worsens Ischemic Stroke Outcome

Background: Acute hyperglycemia, which occurs in over 40% of ischemic stroke patients regardless of pre-existing diabetes, increases brain edema, hemorrhagic transformation (HT) and worsens stroke outcome. Understanding the mechanisms of hyperglycemia-exacerbated stroke injury will be vital for developing novel treatments. Here we identify systemic complement activation as a novel contributor to hyperglycemic-exacerbated damage in rodent stroke. Method: Male C57/BL6 mice (10-11 weeks) were subjected to middle cerebral artery occlusion (MCAO) for 30 min, followed by reperfusion to mimic ischemic stroke. Acute hyperglycemia was induced by glucose injection 10 min before MCAO. To assess the effect of hyperglycemia on stroke outcomes, mice were sacrificed at 4.5 and 24 hr post-stroke to analyze brain edema, blood-brain barrier (BBB) leakage, and HT; or allowed to survive 14 days to examine mortality rate, neurological deficit, and motor-sensory dysfunction using the horizontal rotating beam test. Complement activation was evaluated at 1, 2, 4.5 hr post-stroke. To inhibit C3 activation, the targeted complement inhibitor CR2-Crry fusion protein, or PBS control, was injected via femoral vein 15 min after reperfusion. Result: Hyperglycemia worsens stroke outcomes in our mouse model, with rapid increased BBB leakage (p<0.0001), brain swelling (p<0.001) and HT at (p<0.0001) 4.5 and 24 hr after stroke compared to normoglycemia; and poorer prognosis including higher mortality (100% VS 25%, p=0.0008), body weight loss, and impaired behavioral performance by day 14. Interestingly, acute hyperglycemia rapidly increased plasma complement C3 levels at 1 and 2 hr after stroke (p<0.01 compared to normoglycemic mice), accompanied by activation of C3 in ischemic brain vessels as indicated by elevated levels of vascular C3d. Vascular C3d colocalized with IgM/IgG, suggesting the involvement of classical pathway in C3 activation. Notably, activated C3 levels positively correlated with brain swelling and HT (p<0.01). Inhibition of C3 by CR2-Crry markedly reduced brain swelling (p<0.05) and HT in hyperglycemic stroke. Conclusion: Rapid activation of complement C3 by acute hyperglycemia may be an important contributor to BBB leakage, brain swelling and HT.