PROTECTIVE EFFECTS OF ICARIIN AGAINST LEARNING AND MEMORY DEFICITS INDUCED BY ALUMINIUM IN RATS

Icariin inhibits hydrogen peroxide-induced toxicity through inhibition of phosphorylation of JNK/p38 MAPK and p53 activity

Oxidative stress caused by hydrogen peroxide (H(2)O(2)) plays an important role in the pathogenesis of Alzheimer's disease (AD). The prominent damages caused by H(2)O(2) include the ruin of membrane integrity, loss of intracellular neuronal glutathione (GSH), oxidative damage to DNA as well as the subsequent caspase-3 and p53 activation. Icariin is a flavonoid extracted from the traditional Chinese herb Epimedium brevicornum Maxim. We have previously reported that icariin has a good curative effect on patients with mild cognitive impairment (MCI), AD animal and cell models. However, the molecular mechanism of how icariin exerts neuroprotective effects is still not well understood. To address this question, we exposed undifferentiated neuronal cell lines (PC12 cells) to hydrogen peroxide (H(2)O(2)) and investigated the possible neuroprotective mechanisms of icariin. Vitamin E was used as a positive control. We observed that H(2)O(2) activated the JNK/p38 mitogen-activated protein kinase (MAPK) and induced PC12 cells apoptosis in a concentration-dependent manner. More over, we demonstrated that icariin protected PC12 cells by attenuating LDH leakage, reducing GSH depletion, preventing DNA oxidation damage and inhibiting subsequent activation of caspase-3 and p53, which are the main targets of H(2)O(2)-induced cell damage. In addition, we also found that icariin's neuroprotective effect may partly correlate with its inhibitory effect on JNK/p38 MAPK pathways. Therefore, our findings suggest that icariin is a candidate for a novel neuroprotective drug to against oxidative-stress induced neurodegeneration.

Protective effects of icariin on brain dysfunction induced by lipopolysaccharide in rats

In this study we examined the protective effects of icariin, a flavonol isolated from Herba epimedii, on learning and memory in a rat model with brain inflammation induced by lipopolysaccharide (LPS). Injecting LPS into the lateral ventricle caused rat brain dysfunction, as evidenced by deficits of spatial learning and memory in the Morris water maze. With administration of icariin (30, 60, 120mg/kg body wt./day) for 17 consecutive days, spatial learning and memory abilities were markedly altered. Escape latency and searching distance decreased, and the expressions of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and cyclooxygenase-2 (COX-2) of brain were significantly reduced as observed by real-time RT-PCR and immunohistochemistry. This study used ibuprofen (40mg/kg body wt./day) as positive control. In conclusion, this study suggested that icariin can improve spatial learning and memory abilities in rats with brain dysfunction induced by LPS, an effect which may be due to decreased expressions of TNF-α, IL-1β and COX-2 in the hippocampus.

Retrospect and prospect of active principles from Chinese herbs in the treatment of dementia

With an ageing population, dementia has become one of the world's primary health challenges. However, existing remedies offer limited benefits with certain side effects, which has prompted researchers to seek complementary and alternative therapies. China has long been known for abundant usage of various herbs. Some of these herbal decoctions are effective in stimulating blood circulation, supplementing vital energy and resisting aging, the lack of which are believed to underlie dementia. These herbs are regarded as new and promising sources of potential anti-dementia drugs. With the rapid evolution of life science and technology, numerous active components have been identified that are highly potent and multi-targeted with low toxicity, and therefore meet the requirements for dementia therapy. This review updates the research progress of Chinese herbs in the treatment of dementia, focusing on their effective principles.

Icariin inhibits the increased inward calcium currents induced by amyloid-beta(25-35) peptide in CA1 pyramidal neurons of neonatal rat hippocampal slice

Overload of intracellular calcium caused by amyloid-beta peptide has been implicated in the pathogenesis of neuronal damage in Alzheimer's disease. Voltage-gated calcium channels (VGCCs) provide one of the major sources of Ca(2+) entry into cells. Here, we investigated whether icariin had effect on the changes of calcium currents induced by Abeta(25-35) in hippocampal pyramidal neurons. Using whole-cell patch-clamp, we showed that Abeta(25-35) enhanced the inward Ba(2+) and Ca(2+) currents. The currents were partially inhibited by Ni(2+) and completely suppressed by Cd(2+), indicating that Abeta(25-35) disrupts intracellular calcium homeostasis via the modulation of both L- and T-type channels. Furthermore, icariin nearly complete suppressed the abnormal inward calcium currents induced by Abeta(25-35) in a dose-dependant manner. Our findings suggest that the potential neuroprotective effect of icariin on Abeta(25-35)-induced neurotoxicity via the balance intracelluar calcium homeostasis.

Icariin attenuates lipopolysaccharide-induced microglial activation and resultant death of neurons by inhibiting TAK1/IKK/NF-kappaB and JNK/p38 MAPK pathways

Microglia in the central nervous system (CNS) play an important role in the initiation of neuroinflammatory response. Icariin, a compound from Epimedium brevicornum Maxim, has been reported to have anti-inflammatory effect on the macrophage cell line RAW264.7. However, it is currently unknown what anti-inflammatory role icariin may play in the CNS. Here, we reported the discovery that icariin significantly inhibited the release of nitric oxide (NO), prostaglandin E (PGE)-2, reactive oxygen species (ROS) and mRNA expression of proinflammatory cytokines such as tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta and IL-6 in lipopolysaccharide (LPS)-activated microglia. Icariin also inhibited the protein expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX)-2 in a dose-dependent manner. Further mechanism studies revealed that icariin blocked TAK1/IKK/NF-kappaB and JNK/p38 MAPK pathways. It was also found that icariin reduced the degeneration of cortical neurons induced by LPS-activated microglia in neuron-microglia co-culture system. Taken together these findings provide mechanistic insights into the suppressive effect of icariin on LPS-induced neuroinflammatory response in microglia, and emphasize the neuroprotective effect and therapeutic potential of icariin in neuroinflammatory diseases.

Oxidative stress status and RNA expression in hippocampus of an animal model of Alzheimer's disease after chronic exposure to aluminum

It is well established that aluminum (Al) is a neurotoxic agent that induces the production of free radicals in brain. Accumulation of free radicals may cause degenerative events of aging such as Alzheimer's disease. On the other hand, melatonin (Mel) is a known antioxidant, which can directly act as free radical scavenger, or indirectly by inducing the expression of some genes linked to the antioxidant defense. In this study, AbetaPP female transgenic (Tg2576) (Tg) and wild-type mice (5 months of age) were fed with Al lactate supplemented in the diet (1 mg Al/g diet). Simultaneously, animals received oral Mel (10 mg/kg) dissolved in tap water until the end of the study at 11 months of age. Four treatment groups were included for both Tg and wild-type mice: control, Al only, Mel only, and Al+Mel. At the end of the period of treatment, hippocampus was removed and processed to examine the following oxidative stress markers: reduced glutathione (GSH), oxidized glutathione (GSSG), superoxide dismutase (SOD), glutathione reductase (GR), glutathione peroxidase (GPx), catalase (CAT), and thiobarbituric acid reactive substances (TBARS). Moreover, the gene expression of Cu-ZnSOD, GR, and CAT was evaluated by real-time RT-PCR. Aluminum concentration in hippocampus was also determined. The biochemical changes observed in this tissue suggest that Al acts as a pro-oxidant agent. Melatonin exerts an antioxidant action by increasing the mRNA levels of the antioxidant enzymes SOD, CAT, and GR evaluated in presence of Al and Mel, with independence of the animal model.

Icariin inhibits beta-amyloid peptide segment 25-35 induced expression of beta-secretase in rat hippocampus

The present study was undertaken to investigate the protective effects of icariin on the learning and memory abilities in Alzheimer's disease model rats and explore its protection mechanisms. Beta-amyloid peptide (Abeta) is a key etiology in Alzheimer's disease and targeting on Abeta production and assembly is a new therapeutic strategy. Six-month (400-600 g) Wistar rats were unilaterally injected with amyloid beta-protein fragment 25-35 (Abeta(25-35)) 10 microg (5 g/l, 2 microl) into the right hippocampus. The day following Abeta injection, icariin 30, 60 or 120 mg/kg was administered by gavage for 14 days. The ability of spatial learning and memory of the animals was tested by the Morris water maze. In place navigation test, icariin significantly decreased the mean escape latency and searching distance. In the space probing test, icariin increased remarkably the searching time and searching distance in the quadrant where the platform was originally located. All tests indicated icariin improved the ability of spatial learning and memory in Alzheimer's disease model rats. Furthermore, immunohistochemistry and real time RT-PCR analysis showed that icariin significantly reduced the contents of Abeta(1-40) and the mRNA levels of beta-secretase in the hippocampus and increased the mRNA level of superoxide dismutase-2, but it had no apparent effects on the immunostain and mRNA level of amyloid protein precursor. These results demonstrate that icariin can improve the learning and memory abilities in Abeta(25-35)-induced Alzheimer's disease rats. The mechanisms appear to be due to the decreased production of insoluble fragments of Abeta through suppression of beta-secretase expression.

Effect of intrahippocampal injection of aluminum on active avoidance learning in adult male rats

Aim of this research was to study the effect of intrahippocampal injection of different doses of AlCl3 in adult male rats on active avoidance learning. Thirty five adult male Wistar rats (250-300 g) were used into five groups: (1) Control, (2) Test-I received daily 1 microL AlCl3 1%, pH = 7.2, 3); Test-II received daily 1 microL AlCl3 0.5%, pH = 3.4, 4); Sham-I received daily 1 microL aCSF, pH = 7.2, 5); Sham-II received daily 1 microL aCSF, pH = 3.4. All rats in test and sham groups treated 10 min before training. Animals were anaesthetized with ketamine HCl/xylazine (90/10 mg kg(-1) b.wt.(-1), i.p.) and underwent a stereotaxic surgery for implant of two stainless steel guide cannula into the hippocampus bilaterally. Every day 10 min after above treatments all rats were used to assess the spatial learning performing using Y-maze. Criterion Correct Response (CCR) was 90% in last session of training. There were no significant differences between training sessions to receiving CCR in control, Sham-I and Sham-II groups. Cognition in animals received AlCl3 1%, pH = 7.2 was impaired significantly with compare to other groups (*p<0.0001). Present results show that intrahippocampal injection of AlCl3 1%, causes active avoidance learning impairment significantly. The exact mechanism of Al3 effect on brain and cognition is remains unknown.