The antidepressant effects of asperosaponin VI are mediated by the suppression of microglial activation and reduction of TLR4/NF-kB induced IDO expression

Abstract

AimIndoleamine 2, 3-dioxygenase (IDO) is responsible for the progression of the kynurenine pathway, which has been implicated in the pathophysiology of inflammation-induced depression. It has been reported that asperosaponin VI (ASA VI) could play a neuroprotective role through anti-inflammatory and antioxidant. In this study, we examined the antidepressant effect of ASA VI in LPS-treated mice and further explored its molecular mechanism by insight into the microglial kynurenine pathway. MethodsTo produce the model, lipopolysaccharide (LPS) (0.83 mg/kg) was administered intraperitoneally to mice. The mice received ASA VI (10 mg/kg, 20mg/kg, 40mg/kg and 80mg/kg, i.p.) thirty minutes prior to LPS injection. Depressive-like behaviors were evaluated based on the duration of immobility in the forced swim test. Microglial activation and inflammatory cytokines were detected by immunohistochemistry, real-time PCR and ELISA. The TLR4/NF-B signaling pathway and the expression of IDO, GluA2, and CamKII{beta} were measured by western blotting. ResultsASA VI demonstrated significant antidepressant activity in the presence of LPS on immobility and latency times in the forced swim test. The LPS-induced activation of microglia and inflammatory response were inhabited by ASA VI in a dose-dependent manner. TLR4/NF-{kappa}B signaling pathway also was suppressed by ASA VI in the hippocampus and prefrontal cortex of LPS-treated mice. Furthermore, ASA VI inhibited the increase in IDO protein expression and normalized the aberrant glutamate transmission in the hippocampus and prefrontal cortex as a result of LPS administration. ConclusionOur results propose a promising antidepressant effect for ASA VI possibly through the downregulation of IDO expression and normalization of the aberrant glutamate transmission. This remedying effect of ASA VI could be attributed to suppress microglia-mediated neuroinflammatory response via inhibiting the TLR4/NF-{kappa}B signaling pathway.