Li-Bo Zou

Silibinin prevents amyloid β peptide‐induced memory impairment and oxidative stress in mice

Background and purpose:  Accumulated evidence suggests that oxidative stress is involved in amyloid β (Aβ)‐induced cognitive dysfunction. Silibinin (silybin), a flavonoid derived from the herb milk thistle (Silybum marianum), has been shown to have antioxidative properties; however, it remains unclear whether silibinin improves Aβ‐induced neurotoxicity. In the present study, we examined the effect of silibinin on the memory impairment and accumulation of oxidative stress induced by Aβ25–35 in mice.

Silibinin Attenuates Amyloid β25–35 Peptide-Induced Memory Impairments: Implication of Inducible Nitric-Oxide Synthase and Tumor Necrosis Factor-α in Mice

In Alzheimer’s disease (AD), the deposition of amyloid peptides is invariably associated with oxidative stress and inflammatory responses. Silibinin (silybin), a flavonoid derived from the herb milk thistle, has potent anti-inflammatory and antioxidant activities. However, it remains unclear whether silibinin improves amyloid β (Aβ) peptide-induced neurotoxicity. In this study, we examined the effect of silibinin on the fear-conditioning memory deficits, inflammatory response, and oxidative stress induced by the intracerebroventricular injection of Aβ peptide25–35 (Aβ25–35) in mice. Mice were treated with silibinin (2, 20, and 200 mg/kg p.o., once a day for 8 days) from the day of the Aβ25–35 injection (day 0). Memory function was evaluated in cued and contextual fear-conditioning tests (day 6). Nitrotyrosine levels in the hippocampus and amygdala were examined (day 8). The mRNA expression of inducible nitric-oxide synthase (iNOS) and tumor necrosis factor-α (TNF-α) in the hippocampus and amygdala was measured 2 h after the Aβ25–35 injection. We found that silibinin significantly attenuated memory deficits caused by Aβ25–35 in the cued and contextual fear-conditioning test. Silibinin significantly inhibited the increase in nitrotyrosine levels in the hippocampus and amygdala induced by Aβ25–35. Nitrotyrosine levels in these regions were negatively correlated with memory performance. Moreover, real-time RT-PCR revealed that silibinin inhibited the overexpression of iNOS and TNF-α mRNA in the hippocampus and amygdala induced by Aβ25–35. These findings suggest that silibinin (i) attenuates memory impairment through amelioration of oxidative stress and inflammatory response induced by Aβ25–35 and (ii) may be a potential candidate for an AD medication.

Inhibition of neprilysin by thiorphan (i.c.v.) causes an accumulation of amyloid β and impairment of learning and memory

An accumulation of amyloid beta peptide (Abeta) due to an imbalance between anabolism and catabolism triggers Alzheimers disease (AD). Neprilysin is a rate-limiting peptidase, which participates in the catabolism of Abeta in brain. We investigated whether rats continuously infused with thiorphan, a specific inhibitor for neprilysin, into the cerebral ventricle cause cognitive dysfunction, with an accumulation of Abeta in the brain. Thiorphan-infused rats displayed significant cognitive dysfunction in the ability to discriminate in the object recognition test and spatial memory in the water maze test, but not in other hippocampus-dependent learning and memory tasks. Thiorphan infusion also elevated the Abeta40 level in the insoluble fraction of the cerebral cortex, but not that of the hippocampus. There was no significant difference in the nicotine-stimulated release of acetylcholine in the hippocampus between vehicle- and thiorphan-infused rats. These results indicate that continuous infusion of thiorphan into the cerebral ventricle causes cognitive dysfunction by raising the level of Abeta in the cerebral cortex, and suggest that a reduction of neprilysin activity contribute to the deposition of Abeta and development of AD.

Prenatal exposure to PCP produces behavioral deficits accompanied by the overexpression of GLAST in the prefrontal cortex of postpubertal mice.

Altered glutamatergic neurotransmission in the prefrontal cortex (PFC) has been implicated in a myriad of neuropsychiatric disorders. We previously reported that prenatal exposure to PCP produced long-lasting behavioral deficits, accompanied by the abnormal expression and dysfunction of NMDA receptors. In addition, these behavioral changes were attenuated by clozapine treatment. However, whether the prenatal exposure adversely affects pre-synaptic glutamatergic neurotransmission in postpubertal mice remains unknown. In the present study, we investigated the involvement of prefrontal glutamatergic neurotransmission in the impairment of cognitive and emotional behavior after prenatal PCP treatment (5mg/kg/day) from E6 to E18 in mice. The PCP-treated mice showed an impairment of recognition memory in a novel object recognition test and enhancement of immobility in a forced swimming test at 8 weeks of age. Moreover, the prenatal treatment reduced the extracellular glutamate level, but increased the expression of a glial glutamate transporter (GLAST) in the PFC. The microinjection of DL-threo-β-benzyloxyaspartate (DL-TBOA, 10 nmol/site/bilaterally), a potent blocker of glutamate transporters, reversed these behavioral deficits by enhancing the prefrontal glutamatergic neurotransmission. Taken together, prenatal exposure to PCP produced impairments of long-term memory and emotional function which are associated with abnormalities of pre-synaptic glutamate transmission in the PFC of postpubertal mice. These findings suggest the prenatal inhibition of NMDA receptor function to contribute partly to the pathophysiology of neurodevelopment-related disorders, such as schizophrenia.

Prenatal exposure to phencyclidine produces abnormal behaviour and NMDA receptor expression in postpubertal mice

Several studies have shown the disruptive effects of non-competitive N-methyl-d-aspartate (NMDA) receptor antagonists on neurobehavioural development. Based on the neurodevelopment hypothesis of schizophrenia, there is growing interest in animal models treated with NMDA antagonists at developing stages to investigate the pathogenesis of psychological disturbances in humans. Previous studies have reported that perinatal treatment with phencyclidine (PCP) impairs the development of neuronal systems and induces schizophrenia-like behaviour. However, the adverse effects of prenatal exposure to PCP on behaviour and the function of NMDA receptors are not well understood. This study investigated the long-term effects of prenatal exposure to PCP in mice. The prenatal PCP-treated mice showed hypersensitivity to a low dose of PCP in locomotor activity and impairment of recognition memory in the novel object recognition test at age 7 wk. Meanwhile, the prenatal exposure reduced the phosphorylation of NR1, although it increased the expression of NR1 itself. Furthermore, these behavioural changes were attenuated by atypical antipsychotic treatment. Taken together, prenatal exposure to PCP produced long-lasting behavioural deficits, accompanied by the abnormal expression and dysfunction of NMDA receptors in postpubertal mice. It is worth investigating the influences of disrupted NMDA receptors during the prenatal period on behaviour in later life.

Xanthoceras sorbifolia extracts ameliorate dendritic spine deficiency and cognitive decline via upregulation of BDNF expression in a rat model of Alzheimer's disease

Xanthoceras sorbifolia, a traditional Chinese folk medicine with anti-inflammatory effects, has been used for a long time in China, especially in the Inner Mongolian area for the treatment of rheumatism. Inflammation is one of the main causes of Alzheimers disease (AD). AD is characterized by aggregation of amyloid β-peptide (Aβ) plaques, neurofibrillary tangle formation, synaptic dysfunction and neuronal loss. To investigate whether Xanthoceras sorbifolia extracts (XSE) improve cognition and protect dendritic spines, we performed behavioral tests to investigate learning and memory in an Aβ25-35-induced dementia animal model of AD as well as Golgi staining to observe dendritic spine formation in CA1 pyramidal neurons and western blots to test the expression levels of PSD95, BDNF and downstream signaling pathways. Our results indicated that oral treatment with XSE significantly reduced cognitive impairments in behavioral tests (passive avoidance test, novel object recognition test, Y-maze test and Morris water maze test). Golgi staining results revealed that XSE ameliorated dendritic spine density deficits in CA1 pyramidal neurons in the hippocampus. Western blot analysis suggested that XSE upregulated PSD95, which is the major scaffolding protein in synapses. BDNF levels and the ratio of p-TrkB/TrkB increased, and the expression of the RhoA, a member of the Rho-GTPase family, and its downstream target protein ROCK2 decreased in the dementia animal model following treatment with XSE. Therefore, the cognition-improving effects of XSE probably resulted from dendritic spine protection effects through regulation of BDNF signaling pathways.

Sigma-1 receptor in brain ischemia/reperfusion: Possible role in the NR2A-induced pathway to regulate brain-derived neurotrophic factor

Sigma-1 receptor (σ1r) activation could attenuate the learning and memory deficits in the AD model, ischemia model and others. In our previous study, the activation of σ1r increased the expression of brain-derived neurotrophic factor (BDNF), possibly through the NR2A-induced pathway, and σ1r agonists might function as neuroprotectant agents in vascular dementia. Here, we used σ1r knockout mice to confirm the role of σ1r. Furthermore, an antagonist of NR2A was first used to investigate whether the NR2A-induced pathway is the necessary link between σ1r and BDNF. The operation of brain ischemia/reperfusion was induced by bilateral common carotid artery occlusion for 20min in C57BL/6 and σ1r knockout mice as the ischemic group. A σ1r agonist, PRE084 (1mg/kg, i.p.), and NR2A antagonist, PEAQX (10mg/kg, i.p.), were administered once daily throughout the experiment. Behavioral tests were performed starting on day 8. On day 22 after brain ischemia/reperfusion, mice were sacrificed and brains were immediately collected and the injured and the hippocampus was isolated and stored at -80°C for western blot analysis. After ischemic operation, contrast with the σ1r knockout mice, PRE084 significantly ameliorated learning and memory impairments in the behavioral evaluation, and prevented the protein decline of BDNF, NR2A, CaMKIV and TORC1 expression in wild-type mice. However, the effects of PRE084 on CaMKIV-TORC1-CREB and BDNF, even for learning and memory impairment, were antagonized by the co-administration of PEAQX, an antagonist of NR2A. The activation of σ1r improves the impairment of learning and memory in the ischemia/reperfusion model, and the expression of BDNF, which may have been achieved through the NR2A-CaMKIV-TORC1 pathway.

Xanthoceraside modulates neurogenesis to ameliorate cognitive impairment in APP/PS1 transgenic mice

Neuronal loss is reported to be an important pathological process in Alzheimer’s disease (AD). Neurogenesis is a process of generation of new neurons to fill the neuronal loss. Xanthoceraside has been shown to attenuate the cognitive deficits in several AD animal models. However, little is known about the effect of xanthoceraside on neurogenesis in APP/PS1 transgenic mice. Thus, in this study, we investigated whether xanthoceraside can ameliorate learning and memory impairment by promoting NSCs proliferation and neuronal differentiation. The results suggested that xanthoceraside significantly ameliorated the cognitive impairment and induced NSCs proliferation and neuronal differentiation in APP/PS1 transgenic mice. Meanwhile, in vitro study revealed that xanthoceraside increased the size of NSCs and induced NSCs differentiation into neurons compared with amyloid beta-peptide (25–35) (Aβ25–35) treatment. Furthermore, we found that xanthoceraside significantly increased the expression of Wnt3a and p-GSK3β, decreased the expression of p-β-catenin, and induced nuclear translocation of β-catenin in APP/PS1 transgenic mice. Furthermore, in vitro study found that the effect of xanthoceraside on inducing NSCs proliferation and neuronal differentiation were inhibited by Wnt pathway inhibitor Dickkopf-1 (Dkk-1). Our data demonstrated that xanthoceraside may promote the proliferation and differentiation of NSCs into neurons by up-regulating the Wnt/β-catenin pathway to fill the neuronal loss, thereby improving learning and memory impairment in APP/PS1 transgenic mice.

The total triterpenoid saponins of Xanthoceras sorbifolia improve learning and memory impairments through against oxidative stress and synaptic damage

BACKGROUND X. sorbifolia is a widely cultivated ecologicalcrop in the north of China which is used to produce biodiesel fuel. It also possesses special medicinal value and has attracted keen interests of researchers to explore its bioactivity. PURPOSE To extract the total triterpenoid saponins from the husk of X. sorbifolia (TSX) and investigate its effects on Alzheimers disease (AD). STUDY DESIGN TSX was prepared via modern extraction techniques. Its effects on two AD animal models, as well as the preliminary mechanism were investigated comprehensively. METHODS The behavioral experiments including Y maze test, Morris water maze test and passive avoidance test were performed to observe the learning and memory abilities of the animals. ELISA assays, transmission electron microscope observation and Western blotting were employed in mechanism study. RESULTS TSX, the main composition of X. sorbifolia, accounted for 88.77% in the plant material. It could significantly increase the spontaneous alternation in Y maze test (F (6, 65)=3.209, P<0.01), prolong the swimming time in the fourth quadrant in probe test of Morris water maze test (F (6, 71)=4.019, P<0.01), and increase the escape latency in passive avoidance test (F (6, 65)=3.684, P<0.01) in AD model animals. The preliminary mechanism research revealed that TSX could significantly increase the contents of hippocampal Ach and ChAT, and enhance activity of ChAT in hippocampus of quinolinic acid injected rats (F (5, 61)=3.915, P 0.01; F (5, 61)=3.623, P<0.01, F (5, 61)=4.344, P<0.01, respectively). It could also increase the activities of T-AOC and T-SOD, and decrease the content of MDA in hippocampus of Aβ1-42 injected mice (F (5, 30)=5.193, P<0.01, F (5, 30)=2.865, P<0.05, F (5, 30)=4.735, P<0.01, respectively). Moreover, it significantly increased the expressions of SYP, PSD-95 and GAP-43 in hippocampus (F (4, 27)=3.495, P<0.05; F (4, 27)=2.965, P<0.05; F (4, 27)=4.365, P<0.01, respectively), and improved the synaptic ultra-structure damage in model rats. CONCLUSION TSX could significantly improve the impairments of learning and memory. The preliminary mechanism might associate with its protection effects against oxidative stress damage, cholinergic system deficiency and synaptic damage. TSX are perfectly suitable for AD patients as medicine or functional food, which would be a new candidate to treat AD.

Xanthoceraside attenuates amyloid β peptide1-42-induced memory impairments by reducing neuroinflammatory responses in mice

ABSTRACT Xanthoceraside, a novel triterpenoid saponin extracted from the husks of Xanthoceras sorbifolia Bunge, has neuroprotective effects in vivo and anti‐inflammatory properties in vitro. However, the exact mechanism of xanthoceraside on anti‐amyloid beta (A&bgr;)‐induced neuroinflammatory responses has not been elucidated. Therefore, we used intracerebroventricular injection of amyloid 1–42 (A&bgr;1–42) to establish a mouse model to test the effects of xanthoceraside on A&bgr;‐induced cognitive impairments and the TLR2/NF‐&kgr;B and MAPK pathways. The mice received xanthoceraside (0.02, 0.08 or 0.32 mg/kg) or vehicle from the day of A&bgr;1–42 injection. The Morris water maze test was performed 4 days after A&bgr;1–42 injection. The levels of inflammatory cytokines (interleukin (IL)−6 and IL‐4) were measured by enzyme‐linked immunosorbent assay (ELISA). The expression levels of glial fibrillary acidic protein (GFAP) and cluster of differentiation 11b (CD11b) in the hippocampus were determined with an immunohistochemistry assay. Inducible nitric oxide synthase (iNOS), cyclooxygenase‐2 (COX‐2), nuclear factor &kgr;B (NF‐&kgr;B) and mitogen‐activated protein kinase (MAPK) were analysed by Western blotting; iNOS, COX‐2 and Toll‐like receptor 2 (TLR2) mRNA expression levels were measured by reverse transcription‐polymerase chain reaction (RT‐PCR). Here, we observed that xanthoceraside at doses of 0.08 and 0.32 mg/kg significantly improved learning and memory impairments and significantly inhibited GFAP and CD11b overexpression induced by A&bgr;1–42 in mice. ELISA results revealed that xanthoceraside suppressed IL‐6 release and increased IL‐4 levels. Western blotting results showed that xanthoceraside reduced iNOS and COX‐2 protein levels in hippocampus; xanthoceraside also inhibited translocation of NF‐&kgr;B p50 and p65 into the nucleus and phosphorylation of extracellular signal‐regulated kinase (ERK), Jun N‐terminal kinase (JNK) and p38. RT‐PCR confirmed that xanthoceraside decreased iNOS, COX‐2 and TLR2 mRNA levels. These results suggest that xanthoceraside inhibition of the TLR2 pathway and down‐regulation of MAPK and NF‐&kgr;B activities may be related to the improvement in learning and memory impairments.