Novel multipotent AChEI-CCB attenuates hyperhomocysteinemia-induced memory deficits and Neuropathologies in rats

Polyherbal and Multimodal Treatments: Kaempferol- and Quercetin-Rich Herbs Alleviate Symptoms of Alzheimer's Disease

Alzheimer's Disease (AD) is a progressive neurodegenerative disorder impairing cognition and memory in the elderly. This disorder has a complex etiology, including senile plaque and neurofibrillary tangle formation, neuroinflammation, oxidative stress, and damaged neuroplasticity. Current treatment options are limited, so alternative treatments such as herbal medicine could suppress symptoms while slowing cognitive decline. We followed PRISMA guidelines to identify potential herbal treatments, their associated medicinal phytochemicals, and the potential mechanisms of these treatments. Common herbs, including Ginkgo biloba, Camellia sinensis, Glycyrrhiza uralensis, Cyperus rotundus, and Buplerum falcatum, produced promising pre-clinical results. These herbs are rich in kaempferol and quercetin, flavonoids with a polyphenolic structure that facilitate multiple mechanisms of action. These mechanisms include the inhibition of Aβ plaque formation, a reduction in tau hyperphosphorylation, the suppression of oxidative stress, and the modulation of BDNF and PI3K/AKT pathways. Using pre-clinical findings from quercetin research and the comparatively limited data on kaempferol, we proposed that kaempferol ameliorates the neuroinflammatory state, maintains proper cellular function, and restores pro-neuroplastic signaling. In this review, we discuss the anti-AD mechanisms of quercetin and kaempferol and their limitations, and we suggest a potential alternative treatment for AD. Our findings lead us to conclude that a polyherbal kaempferol- and quercetin-rich cocktail could treat AD-related brain damage.

Hyperhomocysteinemia: Metabolic Role and Animal Studies with a Focus on Cognitive Performance and Decline-A Review

Disturbances in the one-carbon metabolism are often indicated by altered levels of the endogenous amino acid homocysteine (HCys), which is additionally discussed to causally contribute to diverse pathologies. In the first part of the present review, we profoundly and critically discuss the metabolic role and pathomechanisms of HCys, as well as its potential impact on different human disorders. The use of adequate animal models can aid in unravelling the complex pathological processes underlying the role of hyperhomocysteinemia (HHCys). Therefore, in the second part, we systematically searched PubMed/Medline for animal studies regarding HHCys and focused on the potential impact on cognitive performance and decline. The majority of reviewed studies reported a significant effect of HHCys on the investigated behavioral outcomes. Despite of persistent controversial discussions about equivocal findings, especially in clinical studies, the present evaluation of preclinical evidence indicates a causal link between HHCys and cognition-related- especially dementia-like disorders, and points out the further urge for large-scale, well-designed clinical studies in order to elucidate the normalization of HCys levels as a potential preventative or therapeutic approach in human pathologies.

Unprecedented polycyclic polyprenylated acylphloroglucinols with anti-Alzheimer's activity from St. John's wort

Hyperforones A–J (1–10), ten degraded and reconstructed polycyclic polyprenylated acylphloroglucinols (PPAPs) with six different types of unusual architectures, were isolated from Hypericum perforatum (St. John's wort). Compound 1 is characterized by an unprecedented 1,5-epoxyfuro[3′,4′:1,5]cyclopenta[1,2-c]oxecine ring system; compounds 2 and 3 represent the first PPAPs with a contracted B-ring leading to the unique 5/5 core skeletons; compound 4, a proposed biosynthetic precursor of 2, is defined by an oxonane-2,7-dione architecture; compound 5 features an unusual spiro[furo[3′,4′:1,5]cyclopenta[1,2-b]oxepine-3,2′-oxetane] ring system; compounds 6–8 possess a rare macrocyclic lactone ring in addition to the newly formed C-ring; and compounds 9 and 10 contain a newly formed six-membered C-ring, which constructed the unexpected 6/6 scaffold with the B-ring. Hypothetic biosynthetic pathways to generate these scaffolds starting from the classic [3.3.1]-type PPAPs helped to elucidate their origins and validate their structural assignments. Compounds 4 and 6 simultaneously displayed notable activation of PP2A (EC₅₀: 258.8 and 199.0 nM, respectively) and inhibition of BACE1 in cells (IC₅₀: 136.2 and 98.6 nM, respectively), and showed better activities than the positive controls SCR1693 (a PP2A activator, EC₅₀: 413.9 nM) and LY2811376 (a BACE1 inhibitor, IC₅₀: 260.2 nM). Furthermore, compound 6 showed better therapeutic effects with respect to the reduction of pathological and cognitive impairments in 3 × Tg AD mice than LY2811376. Compound 6 represents the first multitargeted natural product that could activate PP2A and simultaneously inhibit BACE1, which highlights compound 6 as a promising lead compound and a versatile scaffold in AD drug development.

Ten PPAPs with unusual skeletons were isolated from H. perforatum. 6 represents the first multitargeted natural product that could activate PP2A and simultaneously inhibit BACE1, which highlights 6 as a promising lead compound in AD drug development.

Direct Activation of Protein Phosphatase 2A (PP2A) by Tricyclic Sulfonamides Ameliorates Alzheimer's Disease Pathogenesis in Cell and Animal Models

Alzheimer's disease (AD) is a multifactorial neurodegenerative disease for which there are limited therapeutic strategies. Protein phosphatase 2A (PP2A) activity is decreased in AD brains, which promotes the hyperphosphorylation of Tau and APP, thus participate in the formation of neurofibrillary tangles (NFTs) and β-amyloid (Aβ) overproduction. In this study, the effect of synthetic tricyclic sulfonamide PP2A activators (aka SMAPs) on reducing AD-like pathogenesis was evaluated in AD cell models and AD-like hyperhomocysteinemia (HHcy) rat models. SMAPs effectively increased PP2A activity, and decreased tau phosphorylation and Aβ40/42 levels in AD cell models. In HHcy-AD rat models, cognitive impairments induced by HHcy were rescued by SMAP administration. HHcy-induced tau hyperphosphorylation and Aβ overproduction were ameliorated through increasing PP2A activity on compound treatment. Importantly, SMAP therapy also prevented neuronal cell spine loss and neuronal synapse impairment in the hippocampus of HHcy-AD rats. In summary, our data reveal that pharmacological PP2A reactivation may be a novel therapeutic strategy for AD treatment, and that the tricyclic sulfonamides constitute a novel candidate class of AD therapeutic.

Preventive Electroacupuncture Ameliorates D-Galactose-Induced Alzheimer's Disease-Like Pathology and Memory Deficits Probably via Inhibition of GSK3β/mTOR Signaling Pathway

Acupuncture has been practiced to treat neuropsychiatric disorders for a thousand years in China. Prevention of disease by acupuncture and moxibustion treatment, guided by the theory of Chinese acupuncture, gradually draws growing attention nowadays and has been investigated in the role of the prevention and treatment of mental disorders such as AD. Despite its well-documented efficacy, its biological action remains greatly invalidated. Here, we sought to observe whether preventive electroacupuncture during the aging process could alleviate learning and memory deficits in D-galactose-induced aged rats. We found that preventive electroacupuncture at GV20-BL23 acupoints during aging attenuated the hippocampal loss of dendritic spines, ameliorated neuronal microtubule injuries, and increased the expressions of postsynaptic PSD95 and presynaptic SYN, two important synapse-associated proteins involved in synaptic plasticity. Furthermore, we observed an inhibition of GSK3β/mTOR pathway activity accompanied by a decrease in tau phosphorylation level and prompted autophagy activity induced by preventive electroacupuncture. Our results suggested that preventive electroacupuncture can prevent and alleviate memory deficits and ameliorate synapse and neuronal microtubule damage in aging rats, which was probably via the inhibition of GSK3β/mTOR signaling pathway. It may provide new insights for the identification of prevention strategies of AD.

Protein Phosphatase 2A as a Drug Target in the Treatment of Cancer and Alzheimer's Disease

Protein phosphatase 2A (PP2A) is a major serine/threonine phosphatase which participates in the regulation of multiple cellular processes. As a confirmed tumor suppressor, PP2A activity is downregulated in tumors and its re-activation can induce apoptosis of cancer cells. In the brains of Alzheimer's disease (AD) patients, decreased PP2A activity also plays a key role in promoting tau hyperphosphorylation and Aβ generation. In this review, we discussed compounds aiming at modulating PP2A activity in the treatment of cancer or AD. The upstream factors that inactivate PP2A in diseases have not been fully elucidated and further studies are needed. It will help for the refinement and development of novel and clinically tractable PP2A-targeted compounds or therapies for the treatment of tumor and AD.

Methanolic extract of Tamarix Gallica attenuates hyperhomocysteinemia induced AD-like pathology and cognitive impairments in rats

Although few drugs are available today for the management of Alzheimer’s disease (AD) and many plants and their extracts are extensively employed in animals’ studies and AD patients, yet no drug or plant extract is able to reverse AD symptoms adequately. In the present study, Tamarix gallica (TG), a naturally occurring plant known for its strong antioxidative, anti-inflammatory and anti-amyloidogenic properties, was evaluated on homocysteine (Hcy) induced AD-like pathology and cognitive impairments in rats. We found that TG attenuated Hcy-induced oxidative stress and memory deficits. TG also improved neurodegeneration and neuroinflammation by upregulating synaptic proteins such as PSD95 and synapsin 1 and downregulating inflammatory markers including CD68 and GFAP with concomitant decrease in proinflammatory mediators interlukin-1β (IL1β) and tumor necrosis factor α (TNFα). TG attenuated tau hyperphosphorylation at multiple AD-related sites through decreasing some kinases and increasing phosphatase activities. Moreover, TG rescued amyloid-β (Aβ) pathology through downregulating BACE1. Our data for the first time provide evidence that TG attenuates Hcy-induced AD-like pathological changes and cognitive impairments, making TG a promising candidate for the treatment of AD-associated pathological changes.

Moringa Oleifera Alleviates Homocysteine-Induced Alzheimer's Disease-Like Pathology and Cognitive Impairments

Alzheimer’s disease (AD) is multifactorial with unclear etiopathology. Due to the complexity of AD, many attempted single therapy treatments, like Aβ immunization, have generally failed. Therefore, there is a need for drugs with multiple benefits. Naturally occurring phytochemicals with neuroprotective, anti-amyloidogenic, antioxidative, and anti-inflammatory properties could be a possible way out. In this study, the effect of Moringa oleifera (MO), a naturally occurring plant with high antioxidative, anti-inflammatory, and neuroprotective effects, was evaluated on hyperhomocysteinemia (HHcy) induced AD-like pathology in rats. Homocysteine (Hcy) injection for 14 days was used to induce AD-like pathology. Simultaneous MO extract gavage followed the injection as a preventive treatment or, after injection completion, MO gavage was performed for another 14 days as a curative treatment. MO was found to not only prevent but also rescue the oxidative stress and cognitive impairments induced by Hcy treatment. Moreover, MO recovered the decreased synaptic proteins PSD93, PSD95, Synapsin 1 and Synaptophysin, and improved neurodegeneration. Interestingly, MO decreased the Hyc-induced tau hyperphosphorylation at different sites including S-199, T-231, S-396, and S-404, and at the same time decreased Aβ production through downregulation of BACE1. These effects in HHcy rats were accompanied by a decrease in calpain activity under MO treatment, supporting that calpain activation might be involved in AD pathogenesis in HHcy rats. Taken together, our data, for the first time, provided evidence that MO alleviates tau hyperphosphorylation and Aβ pathology in a HHcy AD rat model. This and previous other studies support MO as a good candidate for, and could provide new insights into, the treatment of AD and other tauopathies.

Nature of Tau-Associated Neurodegeneration and the Molecular Mechanisms

Neurodegeneration is defined as the progressive loss of structure or function of the neurons. As the nature of degenerative cell loss is currently not clear, there is no specific molecular marker to measure neurodegeneration. Therefore, researchers have been using apoptotic markers to measure neurodegeneration. However, neurodegeneration is completely different from apoptosis by morphology and time course. Lacking specific molecular marker has been the major hindrance in research of neurodegenerative disorders. Alzheimer's disease (AD) is the most common neurodegenerative disorder, and tau accumulation forming neurofibrillary tangles is a hallmark pathology in the AD brains, suggesting that tau must play a critical role in AD neurodegeneration. Here we review part of our published papers on tau-related studies, and share our thoughts on the nature of tau-associated neurodegeneration in AD.

Trillium tschonoskii maxim extract attenuates abnormal Tau phosphorylation

Large-scale epidemiological studies have found that hyperhomocysteinemia is a powerful, independent risk factor for Alzheimer’s disease. Trillium tschonoskii maxim is a traditional Chinese medicine that is used to promote memory. However, scientific understanding of its mechanism of action is limited. This report studied the potential neuroprotective effects of Trillium tschonoskii maxim extract against homocysteine-induced cognitive deficits. Rats were intravenously injected with homocysteine (400 μg/kg) for 14 days to induce a model of Alzheimer’s disease. These rats were then intragastrically treated with Trillium tschonoskii maxim extract (0.125 or 0.25 g/kg) for 7 consecutive days. Open field test and Morris water maze test were conducted to measure spontaneous activity and learning and memory abilities. Western blot assay was used to detect the levels of Tau protein and other factors involved in Tau phosphorylation in the hippocampus. Immunohistochemical staining was used to examine Tau protein in the hippocampus. Golgi staining was applied to measure hippocampal dendritic spines. Our results demonstrated that homocysteine produced learning and memory deficits and increased levels of Tau phosphorylation, and diminished the activity of catalytic protein phosphatase 2A. The total number of hippocampal dendritic spines was also decreased. Trillium tschonoskii maxim extract treatment reversed the homocysteine-induced changes. The above results suggest that Trillium tschonoskii maxim extract can lessen homocysteine-induced abnormal Tau phosphorylation and improve cognitive deterioration such as that present in Alzheimer’s disease.

A novel acetylcholinesterase inhibitor and calcium channel blocker SCR-1693 improves Aβ25-35-impaired mouse cognitive function

RATIONALE

The mechanism involved in AD is complex, which has prompted to develop compounds that could simultaneously interact with several potential targets. Here, we report a new synthesized compound SCR-1693 which is designed to target both AChE and calcium channels that are potential for AD therapy.

OBJECTIVES

We investigated the effects of SCR-1693 on AChE and calcium channels, the effects of neuroprotection and anti-amnesia in icv-Aβ25-35-injected mice, and the potential mechanisms.

METHODS

AChE activity assay, intracellular Ca(2+) content and calcium currents measurement, and Aβ25-35-induced cellular death determine were performed for validation of designed targets and neuroprotection of SCR-1693. Mice were orally administrated with SCR-1693 once daily after an Aβ25-35 injection. The Morris water maze and Y-maze test, and hippocampal protein detection were conducted on days 5-10, day 11, and day 8. The pyramidal neuron number, hippocampal AChE activity, and synaptic transmission were measured on day 12.

RESULTS

SCR-1693 acted as a selective, reversible, and noncompetitive inhibitor of AChE, and a nonselective voltage-gated calcium channel blocker. SCR-1693 also inhibited the increase of AChE activity in the mouse hippocampus. SCR-1693 was more effective than donepezil and memantine in preventing Aβ25-35-induced long-term and short-term memory impairment, maintaining the basal transmission of Schaffer collateral-CA1 synapses, and sustaining LTP in mouse hippocampus. SCR-1693 attenuated Aβ25-35-induced death of SH-SY5Y cell and the loss of hippocampal pyramidal neurons, and regulated Aβ25-35-induced signal cascade in neurons.

CONCLUSIONS

All these findings indicated that SCR-1693, as a double-target-direction agent, is a considerable candidate for AD therapy.

Senescence may mediate conversion of tau phosphorylation-induced apoptotic escape to neurodegeneration

Neurodegeneration is the characteristic pathology in the brains of Alzheimer's disease (AD). However, the nature and molecular mechanism leading to the degeneration are not clarified. Given that only the neurons filled with neurofibrillary tangles survive to the end stage of the disease and the major component of the tangles is the hyperphosphorylated tau proteins, it is conceivable that tau hyperphosphorylation must play a crucial role in AD neurodegeneration. We have demonstrated that tau hyperphosphorylation renders the cells more resistant to the acute apoptosis. The molecular mechanisms involve substrate competition of tau and β-catenin for glycogen synthase kinase 3β (GSK-3β); activation of Akt; preservation of Bcl-2 and suppression of Bax, cytosolic cytochrome-c, and caspase-3 activity; and upregulation of unfolded protein response (UPR), i.e., up-regulating phosphorylation of PERK, eIF2 and IRE1 with an increased cleavage of ATF6 and ATF4. On the other hand, tau hyperphosphorylation promotes its intracellular accumulation and disrupts axonal transport; hyperphosphorylated tau also impairs cholinergic function and inhibits proteasome activity. These findings indicate that tau hyperphosphorylation and its intracellular accumulation play dual role in the evolution of AD. We speculate that transient tau phosphorylation helps cells abort from an acute apoptosis, while persistent tau hyperphosphorylation/accumulation may trigger cell senescence that eventually causes a chronic neurodegeneration. Therefore, the nature of "AD neurodegeneration" may represent a new type of tau-regulated chronic neuron death; and the stage of cell senescence may provide a broad window for the intervention of AD.

A novel tacrine-dihydropyridine hybrid (-)SCR1693 induces tau dephosphorylation and inhibits Aβ generation in cells

AChE inhibitors are the first choice for the treatment of Alzheimer׳s disease (AD), but they could only delay the progression of cognitive and behavioral dysfunction, and fail to reverse neuronal damage. Calcium channel blockers have been identified to have protective effect on neurons. Thus, therapy targeting both AChE and calcium channels is supposed to be more effective in AD treatment. In the present study, we explored the effect of a synthesized juxtaposition of an AChE inhibitor and a Calcium channel blocker (named (-)SCR1693) on tau phosphophorylation and Aβ generation. The results showed that: (1) Compared with higher concentrations, (-)SCR1693 incubation in low concentrations such as 0.4, 2, 4μM for 24h did not affect the cell viability of HEK293/tau (HEK293 cells stably transfected with human tau40) and N2a/APP (N2a cells stably transfected with human APP) cells; (2) long-term treatment of cells with (-)SCR1693 (0.4, 2, 5μM) (24h) induced tau dephosphorylation and reduced the total tau level in HEK293/tau cells. Short-term treatment (6h) also resulted in tau dephosphorylation, but did not reduce the total tau level; and (3) (-)SCR1693 (0.4, 2, 4μM) incubation inhibited Aβ generation and release dramatically in N2a/APP cells. We conclude that the novel tacrine-dihydropyridine hybrid (-)SCR1693 in low concentrations could reduce total and phosphorylated tau levels, inhibit the generation and release of Aβ in cells. Thus, (-)SCR1693 may be a potential candidate for effectively treating AD.