Effects of beta-amyloid on behavioral and amino acids spectrum in rats' brain and their modulation by embryonic proteins

Effects of β-amyloid (1-42) Administration on the Main Neurogenic Niches of the Adult Brain: Amyloid-Induced Neurodegeneration Influences Neurogenesis

Alzheimer's disease (AD) is the most prevalent neurodegenerative disorder and warrants further study as well as timely treatment. Additionally, the mechanisms of the brain's intrinsic defense against chronic injury are not yet fully understood. Herein, we examined the response of the main neurogenic niches to amyloid exposure and the associated changes in structure and synaptic activity. Flow cytometry of Nestin-, Vimentin-, Nestin/Vimentin-, NeuN-, GFAP-, NeuN/GFAP-, NSE-, BrdU-, Wnt-, BrdU/Wnt-, VEGF-, Sox14-, VEGF/Sox14-, Sox10-, Sox2-, Sox10/Sox2-, Bax-, and Bcl-xL-positive cells was performed in the subventricular zone (SVZ), hippocampus, and cerebral cortex of rat brains on 90th day after intracerebroventricular (i.c.v.) single injection of a fraction of β-amyloid (Aβ) (1-42). The relative structural changes in these areas and disruptions to synaptic activity in the entorhinal cortex-hippocampus circuit were also evaluated. Our flow analyses revealed a reduction in the numbers of Nestin-, Vimentin-, and Nestin/Vimentin-positive cells in neurogenic niches and the olfactory bulb. These changes were accompanied by an increased number of BrdU-positive cells in the hippocampus and SVZ. The latter changes were strongly correlated with changes in the numbers of VEGF- and VEGF/Sox14-positive cells. The morphological changes were characterized by significant neural loss, a characteristic shift in entorhinal cortex-hippocampus circuit activity, and decreased spontaneous alternation in a behavioral test. We conclude that although an injection of Aβ (1-42) induced stem cell proliferation and triggered neurogenesis at a certain stage, this process was incomplete and led to neural stem cell immaturity. We propose the idea of enhancing adult neurogenesis as a promising strategy for preventing dementia at healthy elderly people andpeople at high risk for developing AD, or treating patients diagnosed with AD.

The Involvement of Insulin-Like Growth Factor 1 and Nerve Growth Factor in Alzheimer's Disease-Like Pathology and Survival Role of the Mix of Embryonic Proteoglycans: Electrophysiological Fingerprint, Structural Changes and Regulatory Effects on Neurotrophins

Alzheimer’s disease (AD)-associated neurodegeneration is triggered by different fragments of amyloid beta (Aβ). Among them, Aβ (25–35) fragment plays a critical role in the development of neurodegeneration—it reduces synaptic integrity by disruption of excitatory/inhibitory ratio across networks and alters the growth factors synthesis. Thus, in this study, we aimed to identify the involvement of neurotrophic factors—the insulin-like growth factor 1 (IGF-1) and nerve growth factor (NGF)—of AD-like neurodegeneration induced by Aβ (25–35). Taking into account our previous findings on the neuroprotective effects of the mix of proteoglycans of embryonic genesis (PEG), it was suggested to test its regulatory effect on IGF-1 and NGF levels. To evaluate the progress of neurodegeneration, in vivo electrophysiological investigation of synaptic activity disruption of the entorhinal cortex–hippocampus circuit at AD was performed and the potential recovery effects of PEG with relative structural changes were provided. To reveal the direct effects of PEG on brain functional activity, the electrophysiological pattern of the single cells from nucleus supraopticus, sensomotor cortex and hippocampus after acute injection of PEG was examined. Our results demonstrated that after i.c.v. injection of Aβ (25–35), the level of NGF decreased in cerebral cortex and hypothalamus, and, in contrast, increased in hippocampus, prompting its multidirectional role in case of brain damage. The concentration of IGF-1 significantly increased in all investigated brain structures. The administration of PEG balanced the growth factor levels accompanied by substantial restoration of neural tissue architecture and synaptic activity. Acute injection of PEG activated the hypothalamic nucleus supraopticus and hippocampal neurons. IGF-1 and NGF levels were found to be elevated in animals receiving PEG in an absence of amyloid exposure. We suggest that IGF-1 and NGF play a critical role in the development of AD. At the same time, it becomes clear that the neuroprotective effects of PEG are likely mediated via the regulation of neurotrophins.

Disruption of Cholinergic Circuits as an Area for Targeted Drug Treatment of Alzheimer's Disease: In Vivo Assessment of Short-Term Plasticity in Rat Brain

The search for new therapeutics for the treatment of Alzheimer’s disease (AD) is still in progress. Aberrant pathways of synaptic transmission in basal forebrain cholinergic neural circuits are thought to be associated with the progression of AD. However, the effect of amyloid-beta (Aβ) on short-term plasticity (STP) of cholinergic circuits in the nucleus basalis magnocellularis (NBM) is largely unknown. STP assessment in rat brain cholinergic circuitry may indicate a new target for AD cholinergic therapeutics. Thus, we aimed to study in vivo electrophysiological patterns of synaptic activity in NBM-hippocampus and NBM-basolateral amygdala circuits associated with AD-like neurodegeneration. The extracellular single-unit recordings of responses from the hippocampal and basolateral amygdala neurons to high-frequency stimulation (HFS) of the NBM were performed after intracerebroventricular injection of Aβ 25–35. We found that after Aβ 25–35 exposure the number of hippocampal neurons exhibiting inhibitory responses to HFS of NBM is decreased. The reverse tendency was seen in the basolateral amygdala inhibitory neural populations, whereas the number of amygdala neurons with excitatory responses decreased. The low intensity of inhibitory and excitatory responses during HFS and post-stimulus period is probably due to the anomalous basal synaptic transmission and excitability of hippocampal and amygdala neurons. These functional changes were accompanied by structural alteration of hippocampal, amygdala, and NBM neurons. We have thus demonstrated that Aβ 25–35 induces STP disruption in NBM-hippocampus and NBM-basolateral amygdala circuits as manifested by unbalanced excitatory/inhibitory responses and their frequency. The results of this study may contribute to a better understanding of synaptic integrity. We believe that advancing our understanding of in vivo mechanisms of synaptic plasticity disruption in specific neural circuits could lead to effective drug searches for AD treatment.

Embryonic proteoglycans regulate monoamines in the rat frontal cortex and hippocampus in Alzheimer's disease-like pathology

Using the rat Alzheimer's disease (AD)-like model we have analyzed the hippocampal short-term potentiation, levels of monoamines, and morphological changes in the hippocampal and cortical neurons after the administration of proteoglycans of embryonic origin (PEG). Results showed that the levels of monoamines and especially norepinephrine in the target AD brain structures were found elevated, except serotonin, which was unaffected in the hippocampus, but decreased in the frontal cortex. These changes were accompanied by the substantial structural damage of cortical and hippocampal neurons. PEG was able to reverse most of these changes. In addition, PEG administration had regime-dependent effects on a short-term potentiation pattern of hippocampal neurons. The elevated levels of key elements of brain monoaminergic system in the model of AD support the hypothesis of the important role of monoamines in the excessive synaptic excitation resulting in cognitive dysfunction in AD brain. The neuroprotective effect of PEG, as manifested by the recovery of the monoaminergic system, suggests this bioactive substance as a perspective therapeutic agent for the treatment of AD.

Alzheimer's disease-like pathology-triggered oxidative stress, alterations in monoamines levels, and structural damage of locus coeruleus neurons are partially recovered by a mix of proteoglycans of embryonic genesis

Alzheimer's disease (AD) pathogenesis includes oxidative damage and perturbations of monoamines. However, as many details of these alterations are not known, we have investigated the changes in monoamine levels as well as the free radical oxidation processes (FRO) in the brainstem of rats that were administered i.c.v. Aβ (25-35) (rat model of AD-like pathology). The level of oxidative stress was found elevated in the brainstem along with the increased concentrations of monoamines, especially norepinephrine in the locus coeruleus (LC) area of the brainstem. This was accompanied by the substantial structural damage of monoaminergic neurons of LC. In addition, we have tested the ability of proteoglycans of embryonic genesis (PEG) that were shown previously to act as neuroprotectors, to restore the AD-triggered alterations in monoaminergic system and FRO. Indeed, PEG reduced the increased FRO and upregulated monoamines in the brainstem of Aβ (25-35) treated animals. Administration of PEG to control animals led to the increase of the antioxidant capacity as well as the intensity of free radical oxidation processes. Our study confirms the important role of the brainstem FRO and monoamine shifts in AD development along with the known aggregation of Ab peptide and Tau hyperphosphorylation. We suggest that at the early stages of AD development, with still functional neurons, regulation of monoamine levels via stabilizing FRO processes can be beneficial. Our data demonstrate the regulatory action of PEG on the monoamine disturbances and the level of oxidative stress in the AD damaged structures, suggesting its possible therapeutic application in AD.

The role of monoamines in the development of Alzheimer's disease and neuroprotective effect of a proline rich polypeptide

INTRODUCTION

We have analyzed the alterations in the brain monoaminergic system using the rat model of AD-like pathology. In addition, we have investigated potential neuroprotective effects of the hypothalamic proline-rich polypeptide (PRP-1).

METHODS

Histochemical staining, HPLC, chemiluminescent and bioluminescence assays.

RESULTS

The levels of monoamines in the target AD brain structures were found elevated, except serotonin, which was unaffected in both hippocampus and brainstem and decreased in frontal cortex. This was accompanied by the substantial structural damage of cortical, hippocampal, as well as the monoaminergic neurons of locus coeruleus and oxidative stress. PRP-1 was able to reverse most of these changes.

DISCUSSION

The increased levels of major brain monoamines in the model of AD supports the hypothesis of the important role of monoamines in the excessive synaptic excitation resulting in cognitive dysfunction in AD brain. The neuroprotective effect of PRP-1 as manifested by the recovery of monoaminergic system suggests this bioactive compound as a perspective therapeutic agent for the treatment of AD.

Neuromodulatory Effect of Thymoquinone in Attenuating Glutamate-Mediated Neurotoxicity Targeting the Amyloidogenic and Apoptotic Pathways

Overexposure of the glutamatergic N-methyl-d-aspartate (NMDA) receptor to the excitatory neurotransmitter l-glutamic acid leads to neuronal cell death by excitotoxicity as a result of increased intracellular Ca²⁺, mitochondrial dysfunction, and apoptosis. Moreover, it was previously reported that prolonged activation of the NMDA receptor increased beta-amyloid (Aβ) levels in the brain. Thymoquinone (TQ), the active constituent of Nigella sativa seeds, has been shown to have potent antioxidant and antiapoptotic effects. The aim of the present study was to explore the neuromodulatory effects of different doses of TQ (2.5 and 10 mg/kg) against apoptotic cell death and Aβ formation resulting from glutamate administration in rats using vitamin E as a positive control. Behavioral changes were assessed using Y-maze and Morris water maze tests for evaluating spatial memory and cognitive functions. Caspase-3, Lactate dehydrogenase, Aβ-42, and cytochrome c gene expression were determined. TQ-treated groups showed significant decreases in the levels of all tested biochemical and behavioral parameters compared with the glutamate-treated group. These findings demonstrated that TQ has a promising neuroprotective activity against glutamate-induced neurotoxicity and this effect is mediated through its anti-amyloidogenic, antioxidant, and antiapoptotic activities.

Exendin-4, a glucagon-like peptide 1 receptor agonist, protects against amyloid-β peptide-induced impairment of spatial learning and memory in rats

Type 2 diabetes mellitus (T2DM) and Alzheimer's disease (AD) share specific molecular mechanisms, and agents with proven efficacy in one may be useful against the other. The glucagon-like peptide-1 (GLP-1) receptor agonist exendin-4 has similar properties to GLP-1 and is currently in clinical use for T2DM treatment. Thus, this study was designed to characterize the effects of exendin-4 on the impairment of learning and memory induced by amyloid protein (Aβ) and its probable molecular underlying mechanisms. The results showed that (1) intracerebroventricular (i.c.v.) injection of Aβ1-42 resulted in a significant decline of spatial learning and memory of rats in water maze tests; (2) pretreatment with exendin-4 effectively and dose-dependently protected against the Aβ1-42-induced impairment of spatial learning and memory; (3) exendin-4 treatment significantly decreased the expression of Bax and cleaved caspase-3 and increased the expression of Bcl2 in Aβ1-42-induced Alzheimer's rats. The vision and swimming speed of the rats among all groups in the visible platform tests did not show any difference. These findings indicate that systemic pretreatment with exendin-4 can effectively prevent the behavioral impairment induced by neurotoxic Aβ1-42, and the underlying protective mechanism of exendin-4 may be involved in the Bcl2, Bax and caspase-3 pathways. Thus, the application of exendin-4 or the activation of its signaling pathways may be a promising strategy to ameliorate the degenerative processes observed in AD.

The neuroprotection of Rattin against amyloid β peptide in spatial memory and synaptic plasticity of rats

Rattin, a specific derivative of humanin in rats, shares the ability with HN to protect neurons against amyloid β (Aβ) peptide-induced cellular toxicity. However, it is still unclear whether Rattin can protect against Aβ-induced deficits in cognition and synaptic plasticity in rats. In the present study, we observed the effects of Rattin and Aβ31-35 on the spatial reference memory and in vivo hippocampal Long-term potentiation of rats by using Morris water maze test and hippocampal field potential recording. Furthermore, the probable molecular mechanism underlying the neuroprotective roles of Rattin was investigated. We showed that intra-hippocampal injection of Rattin effectively prevented the Aβ31-35-induced spatial memory deficits and hippocampal LTP suppression in rats; the Aβ31-35-induced activation of Caspase-3 and inhibition of STAT3 in the hippocampus were also prevented by Rattin treatment. These findings indicate that Rattin treatment can protect spatial memory and synaptic plasticity of rats against Aβ31-35-induced impairments, and the underlying protective mechanism of Rattin may be involved in STAT3 and Caspases-3 pathways. Therefore, application of Rattin or activation of its signaling pathways in the brain might be beneficial to the prevention of Aβ-related cognitive deficits.

Neuroprotective action of proline-rich polypeptide-1 in β-amyloid induced neurodegeneration in rats

It is recognized that the main trigger of Alzheimer disease related neurodegeneration is β-amyloid peptide, which subsequently generates different metabolic disorders in neuron and finally leads to neuronal death. Several biologically active products were tested as neuroprotectors, but only few of them demonstrated any efficiency. Proline-rich polypeptide-1 was tested as a neuroprotective agent on Aβ25-35 animal model of Alzheimer disease. Biochemical analysis (determination of spectrum of neuroactive amino acids, such as glutamate, gamma-aminobutyric acid, glycine, aspartate and taurine), as well as behavioral, electrophysiological and morphological studies were performed to reveal the neuroprotective potential of proline-rich polypeptide in rats. Based on the results of our study it can be concluded that proline-rich polypeptide-1 has a potential to be one of the effective preventive or therapeutic agents against neurodegenerative disorders, such as Alzheimer disease.

Comparative protective action of curcumin, memantine and diclofenac against scopolamine-induced memory dysfunction

The comparative preventive effect of curcumin, memantine, and diclofenac on scopolamine-induced memory dysfunction was investigated in a controlled study. A group of male and female rats was treated with one of these compounds for 15 days, after which a single dosage of scopolamine was administered. The preventive activity of curcumin on memory dysfunction was higher than that of diclofenac or memantine, that was, however, administered at lower dosages. Gender differences were observed.

N-iminoethyl-L-lysine improves memory and reduces amyloid pathology in a transgenic mouse model of amyloid deposition

A large body of evidence suggests the importance of inflammation and oxidative or nitrosative stress in Alzheimer's disease (AD) pathogenesis. Inflammatory stimuli upregulate transcription of inducible nitric oxide synthase (iNOS), which can lead to the production of nitric oxide and other reactive nitrogen species. We previously found that genetic deletion of iNOS in mice overexpressing the amyloid precursor protein (APP) and presenilin-1 (PS1) reduced mortality, nitrosative stress, amyloid plaque burden, microgliosis, astrocytosis, and peri-plaque tau phosphorylation. We therefore examined the effects of N6-(1-iminoethyl)-L-lysine (L-NIL), a pharmacological iNOS inhibitor, or d-NIL, its enantiomeric control, in a transgenic mouse model of amyloid deposition. Tg19959 mice carry human APP with two mutations and develop amyloid plaques and memory impairment starting at 3-4 months of age. Mice were given L-NIL or D-NIL in the drinking water from 1 month of age and assessed behaviorally and histopathologically at 8 months of age. We found that L-NIL administration reduced disinhibition in the elevated plus maze, improved spatial memory performance in the Morris water maze, and decreased cortical amyloid deposition as well as microglial activation in 8-month-old Tg19959 mice. These findings are consistent with previous reports demonstrating that iNOS inhibition ameliorates AD pathogenesis.