Phthalide derivative CD21 regulates the platelet- neutrophil extracellular trap-thrombin axis and protects against ischemic brain injury in rodents

Prothrombotic and proinflammatory properties of neutrophil extracellular traps (NETs) contribute to brain damage after ischemic stroke. CD21 is a novel phthalide neuroprotectant against cerebral ischemia in rodents. This study investigated effects of CD21 on the platelet-NET-thrombin axis and ischemic brain injury and the underlying mechanism. CD21 exerteddose-dependent neuroprotectionin rats that were subjected to2 h middle cerebral artery occlusion,dose-dependentlyinhibited adenosine diphosphate-mediatedplatelet aggregationin rats, and dose-dependentlyexertedanti-thrombotic activityin rodents that received a collagen-epinephrine combination, ferric chloride, or an arteriovenous shunt. Equimolar CD21 doses exerted stronger efficacy than 3-N-butylphthalide (NBP, natural phthalide for the treatment of ischemic stroke). CD21 dose-dependently improved regional cerebral blood flow, neurobehavioral deficits, and infarct volume in mice that were subjected to photothrombotic stroke (PTS). CD21 (13.79 mg/kg, i.v.) significantly decreased NET components (plasma dsDNA concentrations; mRNA levels of elastase, myeloperoxidase, and neutrophil gelatinase-associated lipocalin and protein level of citrullinated histone H3 in ischemic brain tissues), mRNA and protein levels of peptidyl-arginine deiminase 4 (PDA4, NET formation enzyme), and mRNA levels of NET-related inflammatory mediators (interleukin-1β, interleukin-17A, matrix metalloproteinase 8, and matrix metalloproteinase 9) in ischemic brain tissues, despite no effect on mRNA levels of deoxyribonuclease I (NET elimination enzyme). Pretreatment with compound C (inhibitor of adenosine monophosphate-activated protein kinase [AMPK]) significantly reversed the inhibitory effects of CD21 on NETs, PDA4, and inflammatory mediators in PTS mice. These results suggest that CD21 might regulate the platelet-NET-thrombin axis and protect against ischemic brain injury partly through the induction of AMPK activation.