Isoliensinine ameliorates cognitive dysfunction in AlCl/D-gal-induced Alzheimer's disease-like mice by inhibiting the calcium signaling pathway.

ETHNOPHARMACOLOGICAL RELEVANCE

The embryos of lotus (Nelumbo nucifera Gaertn.) is a famous traditional Chinese medicine used to treat insomnia, memory decline, and dementia for a long time. However, the underlying material basis and mechanisms of this medicine are still unclear. Isoliensinine (IL) is a major alkaloid derived from lotus embryos. Our previous research has demonstrated that IL can exert strong anti-inflammatory and neuroprotective effects in vitro.

AIM OF THE STUDY

To reveal the underlying therapeutic effect and mechanism of IL on Alzheimer's disease (AD)-like mice induced by AlCl and D-galactose (D-gal) in vivo.

MATERIALS AND METHODS

The AD-like mice were modeled by intragastric injection (i.g.) of AlCl (20 mg/kg/day) and intraperitoneal injection (i.p.) of D-gal (120 mg/kg/day) for 8 weeks. Starting from the third week, AD-like mice were treated with IL (1, 3, or 10 mg/kg/day; i.p.) for 6 weeks. Cognitive impairment in AD-like mice was evaluated through some behavioral experiments including nest building, open field, novel object recognition, Y maze, and Morris water maze tests. The cortex and hippocampus (DG, CA1, and CA3) regions were analyzed as follows: Neuronal pathological changes and neurofibrillary tangles (NFTs) formation were observed by hematoxylin-eosin (HE) and silver staining, respectively; The production of Aβ plaques and the activation of microglia and astrocytes were detected by immunohistochemistry; The levels of Ca levels were determined by the ortho-cresolphtalein complexone method. The levels of inflammatory cytokines (TNF-α, IL-6, and IL-1β) were analyzed using the ELISA kits. The expression of CaM, p-CaMKII, Calpain, CDK5, p35/p25, p-Tau, ADAM10, BACE1, PSEN1, APP, Aβ, p-IκBα, and IκBα were evaluated by western blotting.

RESULTS

IL (1, 3, and 10 mg/kg) treatment effectively ameliorated cognitive impairment in AD-like model mice. IL inhibited the decrease of brain index and body weight in AD-like mice and alleviated neuronal damage in the cortex and hippocampus (DG, CA1, and CA3). IL decreased the levels of Ca and reduce high expression of CaM and Calpain in the cortex and hippocampus of AD-like mice. IL treatment did not affect the expression of CDK5 but inhibited the expression of p-CaMKII and p25/p35, and reduced Tau phosphorylation and NFTs formation. IL also down-regulated the high expression of Aβ and APP and regulated the expression of APP-cleavage secretase (reducing the expression of BACE1 and PSEN1, while increasing the expression of ADAM10), thereby inhibited the production of Aβ plaques in AD-like mouse brain. Moreover, IL inhibited the phosphorylation and degradation of IκBα, as well as the production of inflammatory cytokines (TNF-α, IL-6, and IL-1β), and prevented the activation of microglia and astrocytes in AD-like mice.

CONCLUSIONS

IL has a significant therapeutic effect on pathological alterations and cognitive impairment in AlCl and D-gal-induced AD-like mice, indicating that IL may have the potential to treat AD. The anti-AD activity of IL may be associated with its regulation of the Ca homeostasis and downstream signaling molecules such as CaM and Calpain.