Rhizophora mucronata attenuates beta-amyloid induced cognitive dysfunction, oxidative stress and cholinergic deficit in Alzheimer's disease animal model

Mechanistic insights and emerging therapeutic stratagems for Alzheimer's disease

Alzheimer's disease (AD), a multi-factorial neurodegenerative disorder has affected over 30 million individuals globally and these numbers are expected to increase in the coming decades. Current therapeutic interventions are largely ineffective as they focus on a single target. Development of an effective drug therapy requires a deep understanding of the various factors influencing the onset and progression of the disease. Aging and genetic factors exert a major influence on the development of AD. Other factors like post-viral infections, iron overload, gut dysbiosis, and vascular dysfunction also exacerbate the onset and progression of AD. Further, post-translational modifications in tau, DRP1, CREB, and p65 proteins increase the disease severity through triggering mitochondrial dysfunction, synaptic loss, and differential interaction of amyloid beta with different receptors leading to impaired intracellular signalling. With advancements in neuroscience tools, new inter-relations that aggravate AD are being discovered including pre-existing diseases and exposure to other pathogens. Simultaneously, new therapeutic strategies involving modulation of gene expression through targeted delivery or modulation with light, harnessing the immune response to promote clearance of amyloid deposits, introduction of stem cells and extracellular vesicles to replace the destroyed neurons, exploring new therapeutic molecules from plant, marine and biological sources delivered in the free state or through nanoparticles and use of non-pharmacological interventions like music, transcranial stimulation and yoga. Polypharmacology approaches involving combination of therapeutic agents are also under active investigation for superior therapeutic outcomes. This review elaborates on various disease-causing factors, their underlying mechanisms, the inter-play between different disease-causing players, and emerging therapeutic options including those under clinical trials, for treatment of AD. The challenges involved in AD therapy and the way forward have also been discussed.

Moringa oleifera-supplemented diet protect against cortico-hippocampal neuronal degeneration in scopolamine-induced spatial memory deficit in mice: role of oxido-inflammatory and cholinergic neurotransmission pathway

The therapeutic and pharmacological management of Alzheimer's disease (AD) is generally considered a major concern in ethnomedicine. Moreover, plant-based foods containing flavonoids were previously reported to show neuroprotective effects by modulating self-aggregation of amyloid-β (Aβ)/or tau peptide into oligomers and fibrils, associated with the pathogenesis of AD. This study investigated the impact of Moringa oleifera-supplemented diet (MO-SD) in scopolamine-induced spatial memory deficit in mice. Mice were partitioned into two phases with five groups each (n=6) and pretreated intraperitoneally with scopolamine (1 mg/kg) prior the daily oral administration of MO-SD (1 %, 5 % and 10 %) for 7 and 14 days. Spatial memory function was assessed using the Morris water maze (MWM) test. Thereafter, markers of cholinergic system inhibition (Acetylcholinesterase; AChE) and oxido-inflammatory stress (Malonaldehyde, MDA; Nitrite; Superoxide Dismutase, SOD; Tumor necrosis factor-alpha, TNF-α) and histo-morphology of the cortico-hippocampal neuron were measured. The scopolamine treatment led to loss of spatial memory function in mice spatial exploration of the escape platform in the MWM test. Meanwhile, treatment with MO-SD attenuated loss of spatial memory function via significant decrease in escape latency, significant increase in the frequency of cross with time spent in the platform quadrant. Furthermore, scopolamine treatment altered the endogenous antioxidants and pro-inflammatory mediators, elevated acetylcholinesterase activity and promoted chromatolysis of the cortico-hippocampal neuron. However, MO-SD significantly ameliorated oxido-inflammatory stress, restored cholinergic transmission via acetylcholinesterase inhibition and maintains neuronal integrity in the mice brain at both phases. These results suggest that Moringa oleifera-supplemented diet may serve a potential therapeutic and possible pharmacological macromolecule for preventing loss of neuronal cells and management of Alzheimer's disease.

Mixture of Phlorotannin and Fucoidan from Ecklonia cava Prevents the Aβ-Induced Cognitive Decline with Mitochondrial and Cholinergic Activation

The anti-amnesic effect of a mixture (4:6 = phlorotannin:fucoidan from Ecklonia cava, P4F6) was evaluated on amyloid-beta peptide (Aβ)-induced cognitive deficit mice. The cognitive function was examined by Y-maze, passive avoidance, and Morris water maze tests, and the intake of the mixture (P4F6) showed an ameliorating effect on Aβ-induced learning and memory impairment. After the behavioral tests, superoxide dismutase (SOD) activity and thiobarbituric acid-reactive substances (TBARS) contents were confirmed in brain tissue, and in the results, the mixture (P4F6) attenuated Aβ-induced oxidative stress. In addition, mitochondrial activity was evaluated by mitochondrial reactive oxygen species (ROS) content, mitochondrial membrane potential (MMP), adenosine triphosphate (ATP) content, and mitochondria-mediated apoptotic signaling pathway, and the mixture (P4F6) enhanced mitochondrial function. Furthermore, the mixture (P4F6) effectively regulated tau hyperphosphorylation by regulating the protein kinase B (Akt) pathway, and promoted brain-derived neurotrophic factor (BDNF) in brain tissue. Moreover, in the cholinergic system, the mixture (P4F6) ameliorated acetylcholine (ACh) content by regulating acetylcholinesterase (AChE) activity and choline acetyltransferase (ChAT) expression in brain tissue. Based on these results, we suggest that this mixture of phlorotannin and fucoidan (P4F6) might be a substance for improving cognitive function by effectively regulating cognition-related molecules.

Neuroprotective effects of the Chrysophyllum perpulchrum extract against an Alzheimer-like rat model of β amyloid1-40 intrahippocampal injection

Objective

Alzheimer’s disease (AD) is a threatening disease for African populations in the upcoming years because of the increase in their expectancy of life. Here, we investigated whether natural products from Chrysophyllum perpulchrum as catechin and two dimeric procyanidins (catechin + hexose) could prevent progression of oxidative stress and cognitive changes using an AD-like rat model induced by Aβ_1-40 injection into the hippocampal CA1 subfield.

Methodology

Adult male Wistar rats were either microinjected with 1% ammonia as a vehicle (10 µL) or aggregated Aβ_1-40 at 10 µg bilateral hippocampus. On the 14th day of post-surgery, some Aβ rats were treated with melatonin (10 mg/kg i.p.) or with the Chrysophyllum perpulchrum extract (300 mg/kg p.o.), and some sham-operated rats received the extract alone. Cognitive abilities were tested with Y-maze, object recognition test and Morris Water Maze. Oxidative stress markers as well as the level of activated microglial cells were assayed in the brain.

Results

Aβ rats exhibited significant deficits of recognition memory and spatial learning. This was associated with an increase of microglia Iba 1 immunoreactivity as well as nitric oxide (NO), malondialdehyde and superoxide dismutase levels but not to the thiol content in the hippocampus, prefrontal cortex and septum of AD-like rats. The Chrysophyllum perpulchrum extract treatment mitigated Aβ-induced cognitive impairments and reversed microglia overactivation and subsequent generation of oxidative stress markers. Interestingly, the neuroprotective actions of the Chrysophyllum perpulchrum extract seem to be comparable to the control drug melatonin used albeit with some more beneficial effects.

Conclusion

These findings are preliminary and should be strengthened by more pharmacological studies of bioactive compounds of Chrysophyllum perpulchrum before being proposed as a promising drug against AD.

Scrophularia buergeriana Extract Improves Memory Impairment via Inhibition of the Apoptosis Pathway in the Mouse Hippocampus

Scrophularia buergeriana (SB) Miq. (Scrophulariaceae) has been used to help cure swelling and fever and has reported antioxidant and neuro-protective effects. However, few mechanism–based studies have evaluated the memory-improving effects in a beta-amyloid induced memory loss model. As a result of Scrophularia buergeriana extract (SBE) administration (30 and 100 mg/kg) for 28 days significantly recovered beta-amyloid-induced amnesia in the passive avoidance test and improved the impairment of spatial memory in the Morris Water Maze (MWM) task. Furthermore, SBE up-regulated superoxide dismutase-1 (SOD)-1, SOD-2, glutathione peroxidase-1, and B-cell lymphoma (Bcl)-2 protein expression levels. Additionally, SBE downregulated Bcl-2-associated X protein, cleaved caspase-9, cleaved poly (adenosine diphosphate-ribose) polymerase, and Aβ protein expression levels and inhibited the phosphorylation of the tau protein of Aβ-treated mice hippocampus. These results demonstrate that SBE improved memory impairment by reducing beta-amyloid induced neurotoxicity and regulated oxidative stress, anti-apoptotic pathways.

Crocin Treatment after Maternal Hypoxia Attenuates Spatial Memory Impairment and Expression of BACE1 and HIF-1α in Rat Offspring Brain

Introduction

Hypoxia via expression of Hypoxia-Inducible Factor-1 (HIF-1) is an important and effective factor in the onset and progression of memory disorders, such as Alzheimer Disease (AD). The activity of β-secretase (BACE1) is increased in hypoxia conditions. BACE1 triggers a cascade of pathological events resulting in AD. Crocin acts as a memoryimproving agent but its molecular mechanism is not well-known. Therefore, in this study, the effect of crocin on spatial memory, HIF-1α, and BACE1 gene expression was investigated in rat offspring under maternal hypoxia.

Methods

Female pregnant rats on the 20th day of pregnancy were divided into 4 groups, including sham, crocin-treated, hypoxia, and hypoxia group treated with crocin. In the hypoxia groups, pregnant rats were exposed to 7% oxygen and 93% nitrogen intensity for 3 h. In the crocin-treated group, crocin (30 mg/kg) was injected at P14-28 (i.p). At the end, Morris water maze was used to assess spatial memory and real-time polymerase chain reaction was performed to measure the expression of BACE1 and HIF-1α genes in the brain of offspring.

Results

Maternal hypoxia impaired memory compared with the sham group. However, crocin treatment improved cognitive behavior. HIF-1α and BACE1 expressions were upregulated in the brain of offspring in the hypoxia group. Crocin treatment could attenuate the expression of both genes.

Conclusion

According to our results, down-regulation of HIF-1α and BACE1 gene expressions in the brain of rat offspring after crocin treatment can be suggested as a molecular mechanism for crocin to improve spatial memory.

Cortico-hippocampal memory enhancing activity of hesperetin on scopolamine-induced amnesia in mice: role of antioxidant defense system, cholinergic neurotransmission and expression of BDNF

Alzheimer disease (AD) is an age related neurodegenerative disease causing severe cognitive and memory decline in elderly people. Flavonoids play neuroprotective role by inhibiting and/or modifying the self-assembly of the amyloid-β (Aβ) or tau peptide into oligomers and fibrils. This study sought to investigate the effect of hesperetin (HPT) on scopolamine-induced memory impairments in mice. Mice were orally pretreated with HPT (1, 5 or 50 mg/kg) or vehicle (normal saline; 10 ml/kg) for 3 consecutive days. One hour post-treatment on day 3, scopolamine (3 mg/kg, i.p.) was administered 5 min before locomotor activity (open field test) and memory function (novel object recognition test (NORT) for 2 consecutive days and Morris water maze task (MWM) for 5 consecutive days). Levels of oxidative stress markers / brain derived neurotrophic factors (BDNF) and acetylcholinesterase activity were determined in the hippocampus and prefrontal cortex after completion of MWM task. Scopolamine caused no significant change in mice exploration of the familiar or novel object in the test session whereas the HPT-treated mice spent more time exploring the novel object more than familiar object in NORT. Scopolamine also increased the escape latency in acquisition phase and decreases time spent in target quadrant in probe phase which were ameliorated by the pretreatment with HPT. Scopolamine-induced alteration of oxidant-antioxidant balance, acetylcholinesterase activity and neurogenesis in the hippocampus and prefrontal cortex were attenuated by HPT treatment. This study showed that HPT ameliorated non-spatial/spatial learning and memory impairment by scopolamine possibly through enhancement of antioxidant defense, cholinergic and BDNF signaling.

Dexmedetomidine attenuates the toxicity of β‑amyloid on neurons and astrocytes by increasing BDNF production under the regulation of HDAC2 and HDAC5

Cytotoxicity of β-Amyloid (Aβ) is a major contributor to the pathogenesis of Alzheimer's disease. Dexmedetomidine (Dex) has been revealed to have multiple neuroprotective actions as a clinical anesthetic agent. The aim of the present study was to investigate the protection of Dex against Aβ in neurons and astrocytes, and the possible protective mechanisms. Primary neurons and astrocytes were isolated respectively from the hippocampus and cerebral cortex of neonatal Sprague Dawley rats. The neurons and astrocytes were incubated with Aβ in the presence or absence of Dex, which was followed by evaluation of the cell viability and apoptosis. Reverse transcription‑quantitative polymerase chain reaction, western blotting and ELISA assays were performed to assess the levels of specific genes or proteins. The results revealed that Aβ decreased the viabilities of neurons and astrocytes in a dose‑dependent manner, and elevated the rate of apoptosis. However, Dex attenuated the detrimental effects of Aβ. Aβ caused deacetylation of histone H3 by promoting the accumulation of histone deacetylase (HDAC)‑2 and HDAC5 in the cell nucleus, resulting in the reduced production of brain‑derived neurotrophic factor (BDNF). However, Dex reversed the Aβ‑induced deacetylation of histone H3 and thus, increased BDNF production. Using a HDAC inhibitor or recombinant BDNF protein also protected the neurons and astrocytes against Aβ cytotoxicity. These results suggested that the protective effect of Dex against Aβ is particularly relevant to BDNF. Thus, the present study provides a foundation for the further study of Dex protection against Aβ in animal models and pre‑clinical researches.

Protective Effects of Wogonin against Alzheimer's Disease by Inhibition of Amyloidogenic Pathway

One of the pathogenic systems of Alzheimer's disease (AD) is the formation of β-amyloid plaques in the brains of patients, and amyloidogenic activity becomes one of the therapeutic targets. Here, we report wogonin, one of the major active constituting components in Scutellaria baicalensis, which has the neuroprotective effects on amyloid-β peptides- (Aβ-) induced toxicity. Oral wogonin treatment improved the performance of triple transgenic AD mice (h-APPswe, h-Tau P301L, and h-PS1 M146V) on the Morris water maze, Y-maze, and novel object recognition. Furthermore, wogonin activated the neurite outgrowth of AD cells by increasing neurite length and complexity of Tet-On Aβ₄₂-GFP SH-SY5Y neuroblastoma cells (AD cells) and attenuated amyloidogenic pathway by decreasing the levels of β-secretase, APP β-C-terminal fragment, Aβ-aggregation, and phosphorylated Tau. Wogonin also increased mitochondrial membrane potential (∆ψm) and protected against apoptosis by reducing the expression of Bax and cleaved PARP. Collectively, these results conclude that wogonin may be a promising multifunctional drug candidate for AD.

In vitro antiaggregation and deaggregation potential of Rhizophora mucronata and its bioactive compound (+)- catechin against Alzheimer's beta amyloid peptide (25-35)

OBJECTIVE

Amyloid hypothesis states that endogenous β-amyloid peptides (Aβ), especially its aggregated oligomers and fibrils are the key pathogenic factors leading to Alzheimer's disease (AD). Therefore, inhibition of Aβ fibrillation rather than blocking its production is considered promising therapeutic intervention. Hence, the present study was carried out to assess the effect of methanolic leaf extract of R. mucronata (MERM) and its bioactive compound catechin on in vitro fibrillation of Aβ (25-35).

METHODOLOGY

Antiaggregation and disaggregation effect by MERM and (+)- catechin against Aβ (25-35) were assessed in three different phases by thioflavin T (ThT) fluorescence assay and confocal microscopic analysis. The conformational changes in the aggregated Aβ fibrils in the presence and absence of MERM and catechin were analysed by Fourier transform infrared (FTIR), transmission electron microscopy (TEM) and CD spectroscopy.

RESULTS

Results of ThT and confocal microscopic studies showed decrease in fluorescence intensity in MERM and catechin-treated groups illustrating that both MERM and catechin effectively inhibited fibril aggregation as well as destabilized preformed Aβ fibril. TEM revealed that MERM incubated samples were virtually devoid of structured fibrils but had an amorphous-like consistency, whereas the control contained structured fibrils of various width and length. FTIR analysis showed decrease in absorbance at 1630 cm^-1 (amide I region) in MERM-treated groups substantiating the results of ThT assay. Circular dichroism data indicate that catechin prevents the formation of β-structured aggregates of Aβ peptide.

CONCLUSION

Results suggest that MERM and catechin might have direct interaction with Aβ peptide preventing its fibrillation.