The Protective Effects Of Icariin On 6-OHDA-induced Dopaminergic Neuronal Lesion

Objective: To illustrate the protective effects and mechanisms of icariin(ICA)on dopaminergic(DA)neuronal lesion induced by 6-hydroxydopamine(6-OHDA).Methods:(1)The in vivo DA neuronal injury model was induced by a single injection of 6-OHDA(8 μg)into the substantia nigra(SN)on one side of rat brain.Rats were randomly divided into control,ICA(20 mg/kg),6-OHDA(8 μg),6-OHDA+ICA(10 mg/kg)and 6-OHDA+ICA(20 mg/kg)groups.After 14 daily oral administration of ICA,rat behavioral activity was observed by rotarod test.Immunohistochemical staining was used to detect the morphological and quantitative changes of DA neurons and the activation of microglia.(2)Primary neuron-glia co-cultures were performed from the ventral midbrain tissues of embryonic day 14 and 15 rats.The cultures were randomly divided into control,ICA(0.1 μM),6-OHDA(40 μM),6-OHDA+ICA(0.01 μM)and 6-OHDA+ICA(0.1 μM)groups.DA neuronal lesion and microglial activation were tested by immunocytochemical staining.The levels of TNF-α,IL-1β and NO in the culture supernatant were measured with Griess reagent and enzyme linked immunosorbent assay(ELISA),respectively.The protein expressions of tyrosine hydroxylase(TH),ionized calcium-binding adapter molecule-1(Iba1),and phosphorylated-IκBα(p-IκBα)and phosphorylated-p65(p-p65)were detected by western blotting assay.Results:(1)In vivo study: Compared with the control group,6-OHDA significantly induced rat behavioral activity lesion,decreased the number of DA neurons in SN and elicited microglia activation.Compared with 6-OHDA group,the impaired behavioral activity was recovered,the number of DA neurons was increased and microglia activation was attenuated after ICA treatment.(2)In primary rat midbrain neuron-glia co-cultures,ICA protected 6-OHDA-induced DA neuronal damage and inhibited6-OHDA-induced microglial activation and decreased release of NO,TNF-α and IL-1β in the culture medium.Moreover,ICA suppressed 6-OHDA-induced activation of NF-κB signaling pathway.Conclusion: ICA protects 6-OHDA-induced DA neuronal damage both in vivo and in vitro.The underlying mechanisms are at least related to the inhibition of microglia-mediated neuroinflammation.