Protective Effects and Mechanism of Icariin on LPS-induced Dopaminergic Neuronal Damage

Objective:To observe the protective effects of Icariin（ICA） on lipopolysaccharide（LPS）-induced dopaminergic（DA） neuronal damage and explore the possible mechanisms. Methods:Thirty SD rats were randomly divided into control,ICA(20 mg·kg-1) alone,model（LPS,5μg）,LPS+ICA(10 mg·kg-1) and LPS+ICA(20 mg·kg-1).The DA neuronal damage was induced by injecting LPS into one side of rat midbrain substantia nigra（SN）. After seven daily intragastric administration of ICA,rat behavior changes were analyzed by the rotarod test and then brains were collected to detect the expression of tyrosine hydroxylase（TH,a marker of DA neuron） and OX-42（a marker of microglia activation） by double-labelimmunofluorescent analysis. Primary rat midbrain neuron-glia co-cultures were applied to further elucidate the ICA-exerted neuroprotection in vitro. The cultures were randomly divided into control,ICA(0.1 μmol·L-1) alone,LPS(10 ng·mL-1),LPS+ICA(0.01 μmol·L-1) and LPS+ICA(0.1 μmol·L-1). LPS-induced DA neuronal damage and microglia activation were evaluated by immunofluorescent analysis and western blot analysis. The levels of NO,TNF-α and IL-1β in the culture supernatantwere measured with Griess reagent and ELISA,respectively. In addition,BV2 cell lines were prepared to investigate the effects of ICA on LPS-induced protein expressions of TLR4,MyD88,p65 and phosphorylated-p65（p-p65）. Results:ICA attenuated the loss of DA neurons and microglia activation induced by LPS-injected SN in vivo.Inneuron-glia co-cultures,ICA ameliorated LPS-induced DA neuronal damage and microglia activation. Moreover,ICA reduced LPS-elevated NO,TNF-α and IL-1β production in the culture supernatant. In addition,ICA suppressed LPS-induced activation of TLR4,MyD88 and NF-κBpathways. Conclusion:ICA could afford neuroprotection against LPS-induced DA neurotoxicity both in vivo and in vitro through the inhibition of microglia activation and the subsequent production of neuroinfl ammatory factors.