Icariside II attenuates lipopolysaccharide-induced neuroinflammation through inhibiting TLR4/MyD88/NF-κB pathway in rats

Inflammation in central nervous system (CNS) plays a vital role in neurodegenerative diseases such as Alzheimer's disease (AD), Parkinson's disease (PD), Lewy body dementia (DLB), HIV-related dementia and traumatic brain injury. Icariside II (ICS II), an active flavonoid compound derived from a Chinese herbal medicine Epimedium brevicornum Maxim, has been shown to possess a neuroprotective effect on AD model. However, whether ICS II has a directly protective effect on acute neuroinflammation remains still unclear. Therefore, the current study was designed to investigate the possible protective effect of ICS II on acute neuroinflammation induced by intracerebroventricular (ICV) injection of lipopolysaccharide (LPS), and further to explore its possible mechanism. After ICS II was prophylactically administered for 7 days before LPS injection, the rats were randomly divided into five groups as follows: sham group (n = 9), sham + ICS II-H (10 mg/kg) (n = 9), LPS (n = 14), LPS + ICS II-L (3 mg/kg) (n = 14), LPS + ICS II-H (10 mg/kg) (n = 14) groups, respectively. As expected, LPS injection exhibited neuronal morphological damage, and ionized calcium binding adapter molecule 1 (IBA-1) of microglia and glial fibrillary acidic protein (GFAP) of astrocyte were activated. However, pre-treatment with ICS II not only inhibited the activation of microglia and astrocyte, but also significantly reversed the expressions of inflammatory factors such as interleukin-1β (IL-1β), tumor necrosis factor (TNF-α), cyclooxygenase-2 (COX-2), as well as the expressions of Toll-Like receptor 4 (TLR4), myeloid differentiation factor 88 (MyD88) and TNF receptor associated factor 6 (TRAF6). Furthermore, ICS II inhibited the degradation of IκB and the following activation of NF-κB. Hence it is concluded that ICS II attenuates LPS-induced neuroinflammation through inhibiting TLR4/MyD88/NF-κB pathway in rats, and it has potential value as a new therapeutic agent to treat neuroinflammation-related diseases, such as AD.