Baicalin attenuates proinflammatory cytokine production in oxygen-glucose deprived challenged rat microglial cells by inhibiting TLR4 signaling pathway

Baicalin, a flavonoid compound isolated from Scutellariae radix, has been shown to possess a number of pharmacological effects. The aim of the present study was to observe the inhibitory effects of baicalin on the activation of microglial cells induced by oxygen–glucose deprivation (OGD) and the specific mechanisms by which these effects are mediated. Cultured rat primary microglial cells were exposed to baicalin at final concentrations of 10 μg/ml, 20 μg/ml and 40 μg/ml during 4 h of OGD. The effects of baicalin on (i) cell viability; (ii) secretion of proinflammatory cytokines; (iii) Tlr4 mRNA expression; (iv) p-c-jun, p-ERK1/2, p-JNK, p-p38, TRAF6 and p-IκB-α levels; and (v) co-localization of TLR4 and MyD88 were evaluated using the Cell Counting Kit-8 (CCK-8), enzyme-linked immunosorbent assays (ELISA), reverse transcription-polymerase chain reaction (RT-PCR), western blot and double-labeled immunofluorescence staining, respectively. OGD increased cell viability and release of TNF-α, IL-1β, IL-6 and IL-8, these effects were suppressed by baicalin. Baicalin also attenuated the OGD-induced increases in Tlr4 mRNA expression. In addition, high dose of baicalin reduced TRAF6 levels remarkably. Furthermore, baicalin also downregulated phosphorylation of IκB-α, c-jun, ERK1/2, JNK, p38 and inhibited the OGD-induced transfer of MyD88 from cytoplasm to membrane in microglial cells. The results show that baicalin can inhibit OGD-induced production of inflammatory factors in microglial cells by attenuating inflammatory factors and regulating the TLR4 signaling pathways.