Regulation of M1-receptor mRNA stability by smilagenin and its significance in improving memory of aged rats

Harpagoside ameliorates the amyloid-β-induced cognitive impairment in rats via up-regulating BDNF expression and MAPK/PI3K pathways

So far, no effective disease-modifying therapies for Alzheimer's disease (AD) aiming at protecting or reversing neurodegeneration of the disease have been established yet. The present work aims to elucidate the effect of Harpagoside (abbreviated HAR), an iridoid glycosides purified from the Chinese medicinal herb Scrophularia ningpoensis, on neurodegeneration induced by β-amyloid peptide (Aβ) and the underlying molecular mechanism. Here we show that HAR exerts neuroprotective effects against Aβ neurotoxicity. Rats injected aggregated Aβ₁₋₄₀ into the bilateral hippocampus displayed impaired spatial learning and memory ability in a Y-maze test and novel object recognition test, while HAR treatment ameliorated Aβ₁₋₄₀-induced behavioral deficits. Moreover, administration of HAR increased the expression levels of brain-derived neurotrophic factor (BDNF) and activated the extracellular-regulated protein kinase (ERK) and the phosphatidylinositol 3-kinase (PI3-kinase) pathways both in the cerebral cortex and hippocampus of the Aβ₁₋₄₀-insulted rat model. Furthermore, in cultured primary cortical neurons, Aβ₁₋₄₂ induced significant decrease of choline acetyltransferase (ChAT)-positive neuron number and neurite outgrowth length, both of which were dose dependently increased by HAR. In addition, HAR pretreatment also significantly attenuated the decrease of cell viability in Aβ₁₋₄₂-injured primary cortical neurons. Finally, when K252a, an inhibitor of Trk tyrosine kinases, and a BDNF neutralizing antibody were added to the culture medium 2 h prior to HAR addition, the protective effect of HAR on Aβ₁₋₄₂-induced neurodegeneration in the primary cortical neuron was almost inhibited. Taken together, HAR exerting neuroprotection effect and ameliorating learning and memory deficit appears to be associated, at least in part, with up-regulation of BDNF content as well as activating its downstream signaling pathways, e.g., MAPK/PI3K pathways. It raises the possibility that HAR has potential to be a therapeutic agent against AD.

Stereoisomerism metabolites found in rats after oral administration of timosaponin B-II using HPLC-Q-TOF-MS and NMR methods

Stereoisomerism metabolites found in rats after oral administration of timosaponin B-II.

Reversal of dopamine neurons and locomotor ability degeneration in aged rats with smilagenin

The purpose of this paper is to study the effect of smilagenin (SMI) (PYM50028), a sapogenin compound originally identified from Chinese medicinal herb, on dopamine neurons and locomotor ability in aged rats. Experiments were carried out on young and aged Sprague-Dawley rats, which were daily administered with either SMI (18mg/kg/day) or vehicle (0.5% sodium carboxymethycellulose [CMCNa]). Open-field and rotarod performance tests revealed that behavioral ability was impaired in aged rats and was improved by oral administration of smilagenin. Immunohistochemical data showed that tyrosine hydroxylase (TH)-positive neuron numbers in the substantia nigra pars compacta (unbiased stereological counting) were altered with aging and were increased by smilagenin treatment. Likewise, the dopamine receptor density and the striatal dopamine transporter (DAT) density ((125)I-2β-carbomethoxy-3β-(4-iodophenyl)-N-(3-fluoropropyl) nortropane [(125)I-FP-CIT] autoradiography) were significantly lowered in aged rats as compared to young rats, and treatment with smilagenin significantly elevated the dopamine receptor and DAT density in aged rats. Furthermore, smilagenin enhances glial cell-derived neurotrophic factor (GDNF) release both in the striatum and midbrain. These results indicate a possible role of smilagenin in the treatment of age-related extrapyramidal disorders.

Clinical utility of neuroprotective agents in neurodegenerative diseases: current status of drug development for Alzheimer's, Parkinson's and Huntington's diseases, and amyotrophic lateral sclerosis

INTRODUCTION

According to the definition of the Committee to Identify Neuroprotective Agents in Parkinson's Disease (CINAPS), "neuroprotection would be any intervention that favourably influences the disease process or underlying pathogenesis to produce enduring benefits for patients" [Meissner W, et al. Trends Pharmacol Sci 2004;25:249-253]. Preferably, neuroprotective agents should be used before or eventually during the prodromal phase of the diseases that could start decades before the appearance of symptoms. Although several symptomatic drugs are available, a disease-modifying agent is still elusive.

AREAS COVERED

The aim of the present review is to give an overview of neuroprotective agents being currently investigated for the treatment of AD, PD, HD and ALS in clinical phases.

EXPERT OPINION

Development of effective neuroprotective therapies resulting in clinically meaningful results is hampered by several factors in all research stages, both conceptual and methodological. Novel solutions might be offered by evaluation of new targets throughout clinical studies, therapies emerging from drug repositioning approaches, multi-target approaches and network pharmacology.

Smilagenin attenuates beta amyloid (25-35)-induced degeneration of neuronal cells via stimulating the gene expression of brain-derived neurotrophic factor

The development of drugs that attenuate neurodegeneration is important for the treatment of Alzheimer's disease (AD). We previously found that smilagenin (SMI), a steroidal sapogenin from traditional Chinese medicinal herbs improves memory in animal models, is neither a cholinesterase inhibitor nor a glutamate receptor antagonist, but can significantly elevate the declined muscarinic receptor (M receptor) density. In this article, to clarify whether SMI represents a new approach for treating neurodegeneration disease, we first demonstrate that SMI pretreatment significantly attenuates the neurodegenerative changes induced by beta amyloid 25-35 (Aβ(25-35)) in cultured rat cortical neurons, including decreased cholinergic neuron number, shortened neurite outgrowth length, and declined M receptor density. Brain-derived neurotrophic factor (BDNF) protein levels in the culture medium were also decreased by Aβ(25-35) and significantly elevated by SMI. Parallel experiments revealed that when the trk receptors were inhibited by K252a or the action of BDNF was inhibited by a neutralizing anti-BDNF antibody, the effects of SMI on the Aβ(25-35)-induced neurodegeneration in rat cortical neurons were almost completely abolished. In the all-trans retinoic acid (RA)-differentiated SH-SY5Y neuroblastoma cells, the BDNF transcription rate measured by a nuclear run-on assay was significantly suppressed by Aβ(25-35) and elevated by SMI, but the BDNF degradation rate measured by half-life determination was unchanged by Aβ(25-35) and SMI. Transcript analysis of the SH-SY5Y cells using quantitative RT-PCR (qRT-PCR) showed that the IV and VI transcripts of BDNF mRNA were significantly decreased by Aβ(25-35) and elevated by SMI. Taken together, we conclude that SMI attenuates Aβ(25-35)-induced neurodegeneration in cultured rat cortical neurons and SH-SY5Y cells mainly through stimulating BDNF mRNA transcription implicating that SMI may represent a novel therapeutic strategy for AD.

M1 receptors mediate cholinergic modulation of excitability in neocortical pyramidal neurons

ACh release into the rodent prefrontal cortex is predictive of successful performance of cue detection tasks, yet the cellular mechanisms underlying cholinergic modulation of cortical function are not fully understood. Prolonged ("tonic") muscarinic ACh receptor (mAChR) activation increases the excitability of cortical pyramidal neurons, whereas transient ("phasic") mAChR activation generates inhibitory and/or excitatory responses, depending on neuron subtype. These cholinergic effects result from activation of "M1-like" mAChRs (M1, M3, and M5 receptors), but the specific receptor subtypes involved are not known. We recorded from cortical pyramidal neurons from wild-type mice and mice lacking M1, M3, and/or M5 receptors to determine the relative contribution of M1-like mAChRs to cholinergic signaling in the mouse prefrontal cortex. Wild-type neurons in layer 5 were excited by tonic mAChR stimulation, and had biphasic inhibitory followed by excitatory, responses to phasic ACh application. Pyramidal neurons in layer 2/3 were substantially less responsive to tonic and phasic cholinergic input. Cholinergic effects were largely absent in neurons from mice lacking M1 receptors, but most were robust in neurons lacking M3, M5, or both M3 and M5 receptors. The exception was tonic cholinergic suppression of the afterhyperpolarization in layer 5 neurons, which was absent in cells lacking either M1 or M3 receptors. Finally, we confirm a role for M1 receptors in behavior by demonstrating cue detection deficits in M1-lacking mice. Together, our results demonstrate that M1 receptors facilitate cue detection behaviors and are both necessary and sufficient for most direct effects of ACh on pyramidal neuron excitability.