BACKGROUND: Increasing evidence has shown that microglia-induced neuroinflammation is involved in the pathogenesis of ischemic stroke. Stepharine, one of the alkaloids extracted from Stephania japonica (Thunb.) Miers, exhibited strong inhibitory effect on microglial overactivation. However, it is not known whether it has the potential to prevent ischemic stroke. METHODS: The neuroprotective and anti-neuroinflammatory effects of stepharine were investigated in vivo and in vitro, using a rat model of middle cerebral artery occlusion (MCAO) and lipopolysaccharide (LPS)-stimulated BV-2 cells, respectively. RESULTS: In vivo, stepharine (500 mug/kg) suppressed neurological deficits scores, brain water content and cerebral infarct volume induced by MCAO. Moreover, stepharine (500 mug/kg) inhibited NeuN(+) cells loss and Iba-1(+) cells increase in the MCAO ischemic cortex. In vitro, stepharine (10, 30 muM) substantially inhibited nitric oxide release as well as the mRNA and protein expression of pro-inflammatory mediators [inducible nitric oxide synthase, interleukin (IL)-6, tumor necrosis factor (TNF)-alpha, IL-1beta] in LPS-activated BV-2 cells. LPS-induced increase of TLR4 expression, IkappaBalpha phosphorylation, and NF-kappaB p65 nuclear translocation was inhibited by stepharine (10, 30 muM). Molecular docking analysis showed that stepharine directly interacted with TLR4. SPR assay further confirmed that stepharine could bind to the TLR4/MD2 complex. Meanwhile, stepharine exhibited neuroprotective effects on SH-SY5Y cells cultured with LPS-treated conditioned medium. CONCLUSION: Our study demonstrated for the first time that stepharine improved the outcomes in MCAO rats, reduced neuronal loss, and suppressed microglial overactivation via the inhibition of TLR4/NF-kappaB pathway. These results suggest that stepharine might be a potential therapeutic agent for the treatment of ischemic stroke. CI - Copyright (c) 2020 Elsevier GmbH. All rights reserved.