Effects of lipids and aging on the neurotoxicity and neuronal loss caused by intracerebral injections of the amyloid-β peptide in the rat

Administering crocin ameliorates anxiety-like behaviours and reduces the inflammatory response in amyloid-beta induced neurotoxicity in rat

Anxiety, hippocampus synaptic plasticity deficit, as well as pro-inflammatory cytokines, are involved in Alzheimer's disease (AD). The present study is designed to evaluate the possible therapeutic effect of crocin on anxiety-like behaviours, hippocampal synaptic plasticity and neuronal shape, as well as pro-inflammatory cytokines in the hippocampus using in vivo amyloid-beta (Aβ) models of AD. The Aβ peptide (1-42) was bilaterally injected into the frontal-cortex. Five hours after the surgery, the rats were given intraperitoneal (IP) crocin (30 mg/kg) daily up to 12 days. Elevated plus maze results showed that crocin treatment after bilateral Aβ injection significantly increased the percentage of spent time into open arms, frequency of entries, and percentage of entries into open arms as compared with the Aβ group. In the open field test, the Aβ+crocin group showed a higher percentage of spent time in the centre and frequency of entries into central zone as compare with the Aβ treated animals. Administering crocin increased the number of soma, dendrites and axonal arbores in the CA1 neurons among the rats with Aβ neurotoxicity. Cresyl violet (CV) staining showed that crocin increased the number of CV-positive cells in the CA1 region of the hippocampus compared with the Aβ group. Silver-nitrate staining indicated that crocin reduced neurofibrillary tangle formation induced by Aβ. Crocin treatment attenuated the expression of TNF-α and IL-1β mRNA in the hippocampus compared with the Aβ group. Our results suggest that crocin attenuated Aβ-induced anxiety-like behaviours and neuronal damage, and synaptic plasticity loss in hippocampal CA1 neurons may via its anti-inflammatory effects.

Crocin attenuates the granular cells damages on the dentate gyrus and pyramidal neurons in the CA3 regions of the hippocampus and frontal cortex in the rat model of Alzheimer's disease

Amyloid β-peptides (Aβ) are considered as a major hallmark of Alzheimer's disease (AD) that can induce synaptic loss and apoptosis in brain regions, particularly in the cortex and the hippocampus. Evidence suggests that crocin, as the major component of saffron, can exhibit neuromodulatory effects in AD. However, specific data related to their efficacy to attenuate the synaptic loss and neuronal death in animal models of AD are limited. Hence, we investigated the efficacy of crocin in the CA3 and dentate gyrus (DG) regions of the hippocampus and also in frontal cortex neurons employing a rat model of AD. Male Wistar rats were randomly divided into control, sham, AD model, crocin, and AD model + crocin groups, with 8 rats per group. AD model was established by injecting Aβ1-42 into the frontal cortex rats, and thereafter the rats were administrated by crocin (30 mg/kg) for a duration of 12-day. The number of live cells, neuronal arborization and apoptosis were measured using a Cresyl violet, Golgi-Cox and TUNEL staining, respectively. Results showed that, the number of live cells in the hippocampus pyramidal neurons in the CA3 and granular cells in the DG regions of the AD rats significantly decreased, which was significantly rescued by crocin. Compared with the control group, the axonal, spine and dendrites arborization in the frontal cortex and CA3 region of the AD model group significantly decreased. The crocin could significantly reverse this arborization loss in the AD rats (P < 0.05). The apoptotic cell number in the CA3 and DG regions in the AD model group was significantly higher than that of the control group (P < 0.05), while crocin significantly decreased the apoptotic cell number in the AD group (P < 0.05). Conclusion. Crocin can improve the synaptic loss and neuronal death of the AD rats possibly by reducing the neuronal apoptosis.

Diffusion spectrum imaging in white matter microstructure in subjects with type 2 diabetes

This study aimed to investigate the feasibility and clinical applicability of Diffusion Spectrum Imaging (DSI) for quantitative detection of white matter microstructural integrity. Twenty-seven patients with type 2 diabetes mellitus (T2DM; aged 60.6±7.6 years) and 21 healthy controls (HC; aged 56.1±7.8 years) underwent high-resolution T1-weighted imaging and DSI scanning. Cognitive function scores were obtained using such instruments as the Montreal Cognitive Assessment (MoCA). The fasting blood glucose, glycated hemoglobin, and total cholesterol (CHO) of T2DM were measured. The bilateral uncinate fasciculus and superior cingulum bundle were reconstructed by DSI tractography. Statistical analysis was performed using SPSS 21.0 software and P<0.05 was considered significant. Generalized fractional anisotropy (GFA) values were significantly decreased in the left uncinate fasciculus (t = −2.915, p = 0.005) and right superior cingulum bundle (t = −2.604, p = 0.012) in T2DM patients compared with the healthy controls (p<0.05). The MoCA (t = −3.339, p = 0.002) and CDT (t = −3.039, p = 0.004) scores of T2DM were significantly lower than those of healthy controls. Meanwhile, the GFA value of the right superior cingulum bundle was negatively associated with VFT score (r = −0.475, p = 0.012), and that of the right superior cingulum bundle was negatively associated with blood CHO level (r = −0.458, p = 0.016). DSI tractography is capable of evaluating the microstructural integrity of the white matter bundle in T2DM and is related to clinical cognitive scores and related biochemical indices; therefore, it can help to predict early white matter abnormalities in T2DM.

Royal Jelly Reduces Cholesterol Levels, Ameliorates Aβ Pathology and Enhances Neuronal Metabolic Activities in a Rabbit Model of Alzheimer's Disease

Alzheimer's disease (AD) is the most common form of dementia characterized by aggregation of amyloid β (Aβ) and neuronal loss. One of the risk factors for AD is high cholesterol levels, which are known to promote Aβ deposition. Previous studies have shown that royal jelly (RJ), a product of worker bees, has potential neuroprotective effects and can attenuate Aβ toxicity. However, little is known about how RJ regulates Aβ formation and its effects on cholesterol levels and neuronal metabolic activities. Here, we investigated whether RJ can reduce cholesterol levels, regulate Aβ levels and enhance neuronal metabolic activities in an AD rabbit model induced by 2% cholesterol diet plus copper drinking water. Our results suggest that RJ significantly reduced the levels of plasma total cholesterol (TC) and low density lipoprotein-cholesterol (LDL-C), and decreased the level of Aβ in rabbit brains. RJ was also shown to markedly ameliorate amyloid deposition in AD rabbits from Aβ immunohistochemistry and thioflavin-T staining. Furthermore, our study suggests that RJ can reduce the expression levels of β-site APP cleaving enzyme-1 (BACE1) and receptor for advanced glycation end products (RAGE), and increase the expression levels of low density lipoprotein receptor-related protein 1 (LRP-1) and insulin degrading enzyme (IDE). In addition, we found that RJ remarkably increased the number of neurons, enhanced antioxidant capacities, inhibited activated-capase-3 protein expression, and enhanced neuronal metabolic activities by increasing N-acetyl aspartate (NAA) and glutamate and by reducing choline and myo-inositol in AD rabbits. Taken together, our data demonstrated that RJ could reduce cholesterol levels, regulate Aβ levels and enhance neuronal metabolic activities in AD rabbits, providing preclinical evidence that RJ treatment has the potential to protect neurons and prevent AD.

Alterations in CA1 pyramidal neuronal intrinsic excitability mediated by Ih channel currents in a rat model of amyloid beta pathology

Amyloid beta (Aβ) accumulation plays an important role in the pathogenesis of Alzheimer's disease (AD) by changing the neuronal excitability. However, the cellular mechanisms by which accumulation of Aβ affects intrinsic neuronal properties are not well understood. The effect of bilateral intra-frontal cortex Aβ (1-42) peptide injection on the intrinsic excitability of hippocampal CA1 pyramidal neurons with particular focus on the contribution of hyperpolarization-activated (Ih) channel currents was examined using whole-cell patch-clamp recording. Passive avoidance memory impairment and morphological changes in rats receiving intra-frontal Aβ treatment were observed, which was associated with significant changes both in passive and active intrinsic electrical membrane properties of CA1 pyramidal neurons. Electrophysiological recording showed a significant decrease in neuronal excitability associated with an augmentation in the first spike after-hyperpolarization (AHP) amplitude. In addition, the depolarizing sag voltage was altered in neurons recorded from Aβ-treated group. In voltage-clamp condition, a hyperpolarizing activated inward current sensitive to ZD7288 and capsaicin was significantly increased in neurons from Aβ-treated rats. The Ih current density was increased and the activation curve was shifted toward less negative potential in the Aβ-treated group as compared to control group. The enhancing effect of Aβ treatment on Ih current was confirmed by showing upregulation of the mRNA of HCN1 channel in the CA1 pyramidal layer of hippocampi. These findings suggest the contribution of Ih and possibly TRPV1 channel currents to the changes induced by Aβ treatment in the intrinsic membrane properties, which, in turn, may provide therapeutic targets for treatment of AD.

Characterization of the APP/PS1 mouse model of Alzheimer's disease in senescence accelerated background

The APP/PS1 mouse model of Alzheimer's disease (AD) exhibits remarkable elevation of β-amyloid production associated with certain behavioral abnormalities, while the senescence accelerated mouse prone 8 (SAMP8) is characterized by early and age-related deterioration of learning and memory. In order to obtain an AD model that develops earlier pathological changes and cognitive impairment, we generated SAMP8-APP/PS1, a novel senescence accelerated APP/PS1 transgenic mouse model of AD. Standard histological staining and immunohistochemistry using an amyloid beta (Aβ) antibody showed an age, genotype and strain-dependent progression of amyloid deposition and neuron loss in the cerebral cortex and hippocampus of SAMP8-APP/PS1 mice. Results from the cognitive behavioral tests revealed early deficits in learning and memory in SAMP8-APP/PS1 mice in the two way active avoidance and Morris water maze tests compared with C57-APP/PS1, SAMP8 wild-type and control mice. These results suggest that accelerated senescence exacerbates amyloid deposition and cognitive dysfunction in APP/PS1 mice and the senescence accelerated-APP/PS1 (SAMP8-APP/PS1) mouse model might be a valuable tool to study AD progression and to evaluate the effect of drugs on AD.

The amyloid-cell membrane system. The interplay between the biophysical features of oligomers/fibrils and cell membrane defines amyloid toxicity

Amyloid cytotoxicity, structure and polymorphisms are themes of increasing importance. Present knowledge considers any peptide/protein able to undergo misfolding and aggregation generating intrinsically cytotoxic amyloids. It also describes growth and structure of amyloid fibrils and their possible disassembly, whereas reduced information is available on oligomer structure. Recent research has highlighted the importance of the environmental conditions as determinants of the amyloid polymorphisms and cytotoxicity. Another body of evidence describes chemical or biological surfaces as key sites of protein misfolding and aggregation or of interaction with amyloids and the resulting biochemical modifications inducing cell functional/viability impairment. In particular, the membrane lipid composition appears to modulate cell response to toxic amyloids, thus contributing to explain the variable vulnerability to the same amyloids of different cell types. Finally, a recent view describes amyloid toxicity as an emerging property dependent on a complex interplay between the biophysical features of early aggregates and the interacting cell membranes taken as a whole system.

Octodon degus: a model for the cognitive impairment associated with Alzheimer's disease

Octodon degus (O. degus) is a diurnal rodent that spontaneously develops several physiopathological conditions, analogous in many cases to those experienced by humans. In light of this, O. degus has recently been identified as a very valuable animal model for research in several medical fields, especially those concerned with neurodegenerative diseases in which risk is associated with aging. Octodon degus spontaneously develops β-amyloid deposits analogous to those observed in some cases of Alzheimer's disease (AD). Moreover, these deposits are thought to be the key feature for AD diagnosis, and one of the suggested causes of cell loss and cognitive deficit. This review aims to bring together information to support O. degus as a valuable model for the study of AD.

Role of cholesterol in APP metabolism and its significance in Alzheimer's disease pathogenesis

Alzheimer's disease (AD) is a complex multifactorial neurodegenerative disorder believed to be initiated by accumulation of amyloid β (Aβ)-related peptides derived from proteolytic processing of amyloid precursor protein (APP). Research over the past two decades provided a mechanistic link between cholesterol and AD pathogenesis. Genetic polymorphisms in genes regulating the pivotal points in cholesterol metabolism have been suggested to enhance the risk of developing AD. Altered neuronal membrane cholesterol level and/or subcellular distribution have been implicated in aberrant formation, aggregation, toxicity, and degradation of Aβ-related peptides. However, the results are somewhat contradictory and we still do not have a complete understanding on how cholesterol can influence AD pathogenesis. In this review, we summarize our current understanding on the role of cholesterol in regulating the production/function of Aβ-related peptides and also examine the therapeutic potential of regulating cholesterol homeostasis in the treatment of AD pathology.

Soluble oligomeric forms of beta-amyloid (Abeta) peptide stimulate Abeta production via astrogliosis in the rat brain

The aim of this study was to investigate the interaction between beta-amyloid (Abeta) peptide and astrogliosis in early stages of Abeta toxicity. In Wistar rats, anaesthetised with equitesine, a single microinjection of Abeta1-42 oligomers was placed into the retrosplenial cortex. Control animals were injected with Abeta42-1 peptide into the corresponding regions of cerebral cortex. Immunocytochemical analysis revealed an intense Abeta immunoreactivity (IR) at the level of Abeta1-42 injection site, increasing from the first 24 h to later (72 h) time point. Control injection showed a light staining surrounding the injection site. In Abeta oligomers-treated animals, Abeta-immunopositive product also accumulates in cortical cells, particularly in frontal and temporal cortices at an early (24 h) time point. Abeta-IR structures-like diffuse aggregates forms were also observed in hippocampus and in several cortical areas, increasing from the first 24 h to later (72 h) time point. In control animals no specific staining was seen neither in cortical cells nor in structures-like diffuse aggregates forms. Injections of Abeta oligomers also induce activation of astrocytes surrounding and infiltrating the injection site. Astrocyte activation is evidenced by morphological changes and upregulation of glial fibrillary acidic protein (GFAP). By GFAP immunoblotting we detected two immunopositive protein bands, at 50 and 48 kDa molecular mass. Confocal analysis also showed that GFAP co-localized with Abeta-IR material in a time-dependent manner. In conclusion, our results indicate that astrocyte activation might have a critical role in the mechanisms of Abeta-induced neurodegeneration, and that should be further studied as possible targets for therapeutic intervention in AD.

Soluble aggregates of the amyloid-beta peptide are trapped by serum albumin to enhance amyloid-beta activation of endothelial cells

Background

Self-assembly of the amyloid-β peptide (Aβ) has been implicated in the pathogenesis of Alzheimer's disease (AD). As a result, synthetic molecules capable of inhibiting Aβ self-assembly could serve as therapeutic agents and endogenous molecules that modulate Aβ self-assembly may influence disease progression. However, increasing evidence implicating a principal pathogenic role for small soluble Aβ aggregates warns that inhibition at intermediate stages of Aβ self-assembly may prove detrimental. Here, we explore the inhibition of Aβ_1–40 self-assembly by serum albumin, the most abundant plasma protein, and the influence of this inhibition on Aβ_1–40 activation of endothelial cells for monocyte adhesion.

Results

It is demonstrated that serum albumin is capable of inhibiting in a dose-dependent manner both the formation of Aβ_1–40 aggregates from monomeric peptide and the ongoing growth of Aβ_1–40 fibrils. Inhibition of fibrillar Aβ_1–40 aggregate growth is observed at substoichiometric concentrations, suggesting that serum albumin recognizes aggregated forms of the peptide to prevent monomer addition. Inhibition of Aβ_1–40 monomer aggregation is observed down to stoichiometric ratios with partial inhibition leading to an increase in the population of small soluble aggregates. Such partial inhibition of Aβ_1–40 aggregation leads to an increase in the ability of resulting aggregates to activate endothelial cells for adhesion of monocytes. In contrast, Aβ_1–40 activation of endothelial cells for monocyte adhesion is reduced when more complete inhibition is observed.

Conclusion

These results demonstrate that inhibitors of Aβ self-assembly have the potential to trap small soluble aggregates resulting in an elevation rather than a reduction of cellular responses. These findings provide further support that small soluble aggregates possess high levels of physiological activity and underscore the importance of resolving the effect of Aβ aggregation inhibitors on aggregate size.

Medial septal beta-amyloid 1-40 injections alter septo-hippocampal anatomy and function

Degeneration of septal neurons in Alzheimer's disease (AD) results in abnormal information processing at cortical circuits and consequent brain dysfunction. The septum modulates the activity of hippocampal and cortical circuits and is crucial to the initiation and occurrence of oscillatory activities such as the hippocampal theta rhythm. Previous studies suggest that amyloid beta peptide (Abeta) accumulation may trigger degeneration in AD. This study evaluates the effects of single injections of Abeta 1-40 into the medial septum. Immunohistochemistry revealed a decrease in septal cholinergic (57%) and glutamatergic (53%) neurons in Abeta 1-40 treated tissue. Additionally, glutamatergic terminals were significantly less in Abeta treated tissue. In contrast, septal GABAergic neurons were spared. Unitary recordings from septal neurons and hippocampal field potentials revealed an approximately 50% increase in firing rates of slow firing septal neurons during theta rhythm and large irregular amplitude (LIA) hippocampal activities and a significantly reduced hippocampal theta rhythm power (49%) in Abeta 1-40 treated tissue. Abeta also markedly reduced the proportion of slow firing septal neurons correlated to the hippocampal theta rhythm by 96%. These results confirm that Abeta alters the anatomy and physiology of the medial septum contributing to septo-hippocampal dysfunction. The Abeta induced injury of septal cholinergic and glutamatergic networks may contribute to an altered hippocampal theta rhythm which may underlie the memory loss typically observed in AD patients.

Decreased nicotinic receptors and cognitive deficit in rats intracerebroventricularly injected with beta-amyloid peptide(1-42) and fed a high-cholesterol diet

To investigate whether the changes in nicotinic receptors (nAChRs) and in learning and memory associated with Alzheimer's disease (AD) are influenced by both beta-amyloid peptide (Abeta) and cholesterol in vivo, we examined the effects of intracerebroventricular injection of Abeta(1-42) and/or a high-cholesterol diet on brain levels of nAChRs and learning and memory in rats. The levels of nAChR subunit proteins and the corresponding mRNA were measured by Western blotting and RT-PCR, respectively; and learning and memory were evaluated with the Morris Water Maze examination. Injection of Abeta(1-42) resulted in deposition of this peptide, activation of astrocytes, decreased levels of the alpha7 and alpha4 protein subunits of the nAChR, and elevated expression of alpha7 mRNA, as well as impaired learning and spatial memory. A high-cholesterol diet activated astrocytes and, more importantly, potentiated the toxic effects of Abeta on nAChR subunit levels and on learning and memory. These findings may be highly relevant to the mechanisms underlying the cognitive deficits associated with AD.

Beta-amyloid peptide-induced modifications in alpha7 nicotinic acetylcholine receptor immunoreactivity in the hippocampus of the rat: relationship with GABAergic and calcium-binding proteins perikarya

The effects of the injected beta-amyloid (Abeta) protein on the alpha7 subtype of nicotinic acetylcholine receptor protein (alpha7nAChR) in the hippocampus were studied in rats. Injections of Abeta into the retrosplenial cortex resulted in a decrease in alpha7nAChR-immunoreactivity in the hippocampus. Quantitative analysis revealed a significant reduction in alpha7nAChR-immunoreactivity in the dorsal part of the CA1 ipsilateral to the Abeta-injected side as compared to the corresponding hemisphere of non-treated control animals and with that seen in the contralateral hemisphere, which corresponds to the control (PBS)-injected side. A significant decrease in alpha7nAChR-immunoreactivity was also found in the dorsal part of the ipsilateral CA1 as compared with that in the ventral part of the CA1, in CA2, and in CA3 ipsilateral to the Abeta-injected side. The analysis also revealed a significant decrease in alpha7nAChR-immunoreactivity in the dentate gyrus ipsilateral to the Abeta-injected side as compared to the corresponding hemisphere of non-treated control animals and with that in the PBS-injected side co-localization studies showed that the alpha7nAChR protein is highly localized in GABA- and Parv-immunoreactive cells, while only few Calb-positive cells expressed immunoreactivity for alpha7nAChR. In addition, injections of Abeta protein resulted in a significant reduction in the number of GABA- and Parv-immunoreactive cells in the dorsal part of the ipsilateral CA1 as compared to the corresponding region of non-treated control animals and with that in the corresponding region of the PBS-injected side. Our findings suggest that Abeta induces a reduction in alpha7nAChR-containing cells, which may contribute to impairment of GABAergic synaptic transmission in the hippocampus.

Effects of beta-amyloid protein on M1 and M2 subtypes of muscarinic acetylcholine receptors in the medial septum-diagonal band complex of the rat: relationship with cholinergic, GABAergic, and calcium-binding protein perikarya

Cortical cholinergic dysfunction has been correlated with the expression and processing of beta-amyloid precursor protein. However, it remains unclear as to how cholinergic dysfunction and beta-amyloid (Abeta) formation and deposition might be related to one another. Since the M1- and M2 subtypes of muscarinic acetylcholine receptors (mAChRs) are considered key molecules that transduce the cholinergic message, the purpose of the present study was to assess the effects of the injected Abeta peptide on the number of M1mAchR- and M2mAChR-immunoreactive cells in the medial septum-diagonal band (MS-nDBB) complex of the rat. Injections of Abeta protein into the retrosplenial cortex resulted in a decrease in M1mAChR and M2mAChR immunoreactivity in the MS-nDBB complex. Quantitative analysis revealed a significant reduction in the number of M1mAChR- and M2mAChR-immunoreactive cells in the medial septum nucleus (MS) and in the horizontal nucleus of the diagonal band of Broca (HDB) as compared to the corresponding hemisphere in control animals and with that seen in the contralateral hemisphere, which corresponds to the PBS-injected side. Co-localization studies showed that the M1mAChR protein is localized in GABA-immunoreactive cells of the MS-nDBB complex, in particular those of the MS nucleus, while M2mAChR protein is localized in both the cholinergic and GABAergic cells. Moreover, GABAergic cells containing M2mAChR are mainly localized in the MS nucleus, while cholinergic cells containing M2mAChR are localized in the MS and the HDB nuclei. Our findings suggest that Abeta induces a reduction in M1mAChR- and M2mAChR-containing cells, which may contribute to impairments of cholinergic and GABAergic transmission in the MS-nDBB complex.