Curcumin ameliorates scopolamine-induced mice memory retrieval deficit and restores hippocampal p-Akt and p-GSK-3β

Nanocurcumin prevents memory impairment, hippocampal apoptosis, Akt and CaMKII-α signaling disruption in the central STZ model of Alzheimer's disease in rat

The central route of streptozotocin (STZ) administration has been introduced as a rat model of sporadic Alzheimer's disease (AD). Curcumin was suggested to possess possible neuroprotective effects, which may be profitable in AD. However, the low bioavailability of curcumin hinders its beneficial effects in clinical studies. Earlier studies suggested that a bovine serum albumin-based nanocurcumin, produces superior neuroprotective effects compared to natural curcumin. In the present study, the protective effect of nanocurcumin in rat model of central STZ induced memory impairment was assessed. In addition, due to the importance of the hippocampus in memory, the amounts of hippocampal active caspase-3, Akt, and CaMKII-α were evaluated. Adult male Wistar rats weighing 250-300 g were used. STZ (icv) was injected during days 1 and 3 (3 mg/kg in divided), and nanocurcumin or curcumin 50 mg/kg/oral gavage was administered daily during days 4-14. Morris water maze training was performed on days 15-17, and the retention memory test was achieved on the 18th day. Following memory assessment, the rats were sacrificed and the hippocampi were used to assess caspase-3 cleavage, Akt, and CaMKII-α signaling. The findings revealed that nanocurcumin ingestion (but not natural curcumin) in the dose of 50 mg/kg was capable to prevent the impairment of water maze learning and memory induced by central STZ. Molecular assessments indicated that STZ treatment increased the caspase-3 cleavage in the hippocampus while deactivating Akt and CaMKII-α. Nanocurcumin reduced caspase-3 cleavage to a non-significant level compared to control group and restored Akt and CaMKII-α within the hippocampus while natural curcumin exerted no significant effect. These findings might suggest that nanocurcumin can restore memory deficit, hippocampal apoptosis as well as Akt and CaMKII-α signaling disruption associated with brain insulin resistance.

New curcumin-loaded nanocapsules as a therapeutic alternative in an amnesia model

This study aimed to investigate the action of two different formulations of curcumin (Cur)-loaded nanocapsules (Nc) (Eudragit [EUD] and poly (ɛ-caprolactone) [PCL]) in an amnesia mice model. We also investigated the formulations' effects on scopolamine-induced (SCO) depressive- and anxiety-like comorbidities, the cholinergic system, oxidative parameters, and inflammatory markers. Male Swiss mice were randomly divided into five groups (n = 8): group I (control), group II (Cur PCL Nc 10 mg/kg), group III (Cur EUD Nc 10 mg/kg), group IV (free Cur 10 mg/kg), and group V (SCO). Treatments with Nc or Cur (free) were performed daily or on alternate days. After 30 min of treatment, the animals received the SCO and were subjected to behavioral tests 30 min later (Barnes maze, open-field, object recognition, elevated plus maze, tail suspension tests, and step-down inhibitory avoidance tasks). The animals were then euthanized and tissue was removed for biochemical assays. Our results demonstrated that Cur treatment (Nc or free) protected against SCO-induced amnesia and depressive-like behavior. The ex vivo assays revealed lower acetylcholinesterase (AChE) and catalase (CAT) activity, reduced thiobarbituric species (TBARS), reactive species (RS), and non-protein thiols (NSPH) levels, and reduced interleukin-6 (IL-6) and tumor necrosis factor (TNF) expression. The treatments did not change hepatic markers in the plasma of mice. After treatments on alternate days, Cur Nc had a more significant effect than the free Cur protocol, implying that Cur may have prolonged action in Nc. This finding supports the concept that it is possible to achieve beneficial effects in nanoformulations, and treatment on alternate days differs from the free Cur protocol regarding anti-amnesic effects in mice.

Cholinergic deficit induced memory retrieval impairment and hippocampal CaMKII-alpha deregulation is counteracted by sub-chronic agmatine treatment in mice

Alzheimer's disease (AD) is one of the most prevalent neurodegenerative disease characterized by brain cholinergic dysfunction. Evidence suggests the impairment of memory retrieval phase in AD. It has been shown that CaMKII-α expressing neurons are selectively reduced in the hippocampus in AD brains. The present study aimed to investigate the effect of scopolamine on the memory retrieval phase and the hippocampal CaMKII-α signaling. In addition, the effect of sub-chronic administration of agmatine against scopolamine induced memory and possible hippocampal CaMKII-α deregulation was investigated in mice. Adult male NMRI mice were administered with agmatine at the doses of 5, 10, 20, 30 and 40 mg/kg/i.p. or saline for 11 days. Acquisition and retrieval tests of passive avoidance task were performed on days 10 and 11, respectively (30 Min following agmatine treatment). Scopolamine (1 mg/kg/i.p.) was administered once, 30 Min before retrieval test. Upon completion of the behavioral tasks, the hippocampi were isolated for western blot analysis to detect the phosphorylated and total levels of CaMKII-α and beta actin proteins. The results showed that scopolamine induced memory retrieval deficit and decreased the phosphorylated level of hippocampal CaMKII-α. Sub-chronic agmatine treatment at the dose of 40 mg/kg prevented scopolamine induced memory retrieval deficit and restored the level of hippocampal phosphorylated CaMKII-α. This study suggests that hippocampal CaMKII-α might play a role in scopolamine induced amnesia and sub-chronic agmatine prevents the impairing effect of scopolamine on the retrieval phase of memory and the phosphorylation of hippocampal CaMKII-α protein.

Evidence of disturbed insulin signaling in animal models of Alzheimer's disease

Since glucose reuptake by neurons is mostly independent of insulin, it has been an intriguing question whether insulin has or not any roles in the brain. Consequently, the identification of insulin receptors in the central nervous system has fueled investigations of insulin functions in the brain. It is also already known that insulin can influence glucose reuptake by neurons, mostly during activities that have the highest energy demand. The identification of high density of insulin receptors in the hippocampus also suggests that insulin may present important roles related to memory. In this context, studies have reported worse performance in cognitive tests among diabetic patients. In addition, alterations in the regulation of central insulin pathways have been observed in the brains of Alzheimer's disease (AD) patients. In fact, some authors have proposed AD as a third type of diabetes and recently, our group proposed insulin resistance as a common link between different AD hypotheses. Therefore, in the present narrative review, we intend to revise and gather the evidence of disturbed insulin signaling in experimental animal models of AD.

Design, synthesis and evaluation of monoketene compounds as novel potential Parkinson's disease agents by suppressing ER stress via AKT

Curcumin is identified that it has the potential to treat Parkinson's disease (PD), but its instability limits its further application in clinic. The mono-carbonyl analogs of curcumin (MACs) with diketene structure can effectively improve its stability, but it is highly toxic. In the present study, a less cytotoxic and more stable monoketene MACs skeleton S2 was obtained, and a series of monoketene MACs were synthesized by combining 4-hydroxy-3‑methoxy groups of curcumin. In the 6-OHDA-induced PD's model in-vitro, some compounds exhibited significant neurotherapeutic effect. The quantitative structure-activity relationship (QSAR) model established by the random forest algorithm (RF) for the cell viability rate of above compounds showed that the statistical results are good (R² = 0.883507), with strong reliability. Among all compounds, the most active compound A4 played an important role in neuroprotection in the PD models both in vitro and in vivo by activating AKT pathway, and then inhibiting the apoptosis of cells caused by endoplasmic reticulum (ER) stress. In the PD model in-vivo, compound A4 significantly improved survival of dopaminergic neurons and the contents of neurotransmitters. It also enhanced the retention of nigrostriatal function which was better than the effect in the mice treated by Madopar, a classical clinical drug for PD. In summary, we screened out the compound A4 with high stability, less cytotoxic monoketene compounds. And these founding provide evidence that the compound A4 can protect dopaminergic neurons via activating AKT and subsequently suppressing ER stress in PD.

The effect of curcumin on blood pressure and cognitive impairment in spontaneously hypertensive rats

BACKGROUND/OBJECTIVES

It is known that the renin-angiotensin system (RAS) in the brain could regulate cognitive functions as well as blood pressure. Inhibition of RAS for the improvement of cognitive function may be a new strategy, but studies so far have mostly reported on the effects of RAS inhibition by drugs, and there is no research on cognitive improvement through RAS inhibition of food ingredients. Therefore, this study investigated the effect of curcumin on blood pressure and cognitive function and its related mechanism in spontaneously hypertensive rat/Izm (SHR/Izm).

MATERIALS/METHODS

Six-week-old SHR/Izm rats were divided into 5 groups: control group (CON), scopolamine group (SCO, drug for inducing cognitive deficits), positive control (SCO and tacrine [TAC]), curcumin 100 group (CUR100, SCO + Cur 100 mg/kg), and curcumin 200 group (CUR200, SCO + Cur 200 mg/kg). Changes in blood pressure, RAS, cholinergic system, and cognitive function were compared before and after cognitive impairment.

RESULTS

The SCO group showed increased blood pressure and significantly reduced cognitive function based on the y-maze and passive avoidance test. Curcumin treatments significantly improved blood pressure and cognitive function compared with the SCO group. In both the CUR100 and CUR200 groups, the mRNA expressions of angiotensin-converting enzyme (ACE) and angiotensin II receptor type1 (AT1), as well as the concentrations of angiotensin II (Ang II) in brain tissue were significantly decreased. The mRNA expression of the muscarinic acetylcholine receptors (mAChRs) and acetylcholine (ACh) content was significantly increased, compared with the SCO group.

CONCLUSIONS

The administration of curcumin improved blood pressure and cognitive function in SCO-induced hypertensive mice, indicating that the cholinergic system was improved by suppressing RAS and AT1 receptor expression and increasing the mAChR expression.

The effects of curcumin in learning and memory impairment associated with hypothyroidism in juvenile rats: the role of nitric oxide, oxidative stress, and brain-derived neurotrophic factor

The effect of curcumin (Cur) on cognitive impairment and the possible role of brain tissue oxidative stress, nitric oxide (NO) levels, and brain-derived neurotrophic factor (BDNF) were investigated in juvenile hypothyroid rats. The juvenile rats (21 days old) were allocated into the following groups: (1) control; (2) hypothyroid (0.05% propylthiouracil (PTU) in drinking water); (3-5) hypothyroid-Cur 50, 100, and 150, which in these groups 50, 100, or 150 mg/kg, Cur was orally administered by gavage during 6 weeks. In the hypothyroid rats, the time elapsed and the traveled distance to locate the hidden platform in the learning trials of Morris water maze (MWM) increased, and on the probe day, the amount of time spent in the target quadrant and the distance traveled in there was decreased. Hypothyroidism also decreased the latency and increased the time spent in the darkroom of the passive avoidance (PA) test. Compared with the hypothyroid group, Cur enhanced the performance of the rats in both MWM and PA tests. In addition, Cur reduced malondialdehyde concentration and NO metabolites; however, it increased thiol content as well as the activity of catalase (CAT) and superoxide dismutase enzymes in both the cortex and hippocampus. Cur also increased hippocampal synthesis of BDNF in hypothyroid rats. The beneficial effects of Cur cognitive function in juvenile hypothyroid rats might be attributed to its protective effect against oxidative stress and potentiation of BDNF production.

Targeting Impaired Nutrient Sensing via the Glycogen Synthase Kinase-3 Pathway With Therapeutic Compounds to Prevent or Treat Dementia: A Systematic Review

Background: Dementia is a global challenge with 10 million individuals being diagnosed every year. Currently, there are no established disease-modifying treatments for dementia. Impaired nutrient sensing has been implicated in the pathogenesis of dementia. Compounds that inhibit the glycogen synthase kinase-3 (GSK3) pathway have been investigated as a possible treatment to attenuate the progression of the disease, particularly the suppression of the hyper-phosphorylation process of the tau protein.

Aims: Systematically summarizing compounds which have been tested to inhibit the GSK3 pathway to treat cognitive impairment and dementia.

Methods: PubMed, Embase and Web of Science databases were searched from inception until 28 July 2021 for articles published in English. Interventional animal studies inhibiting the GSK3 pathway in Alzheimer’s disease (AD), Parkinson’s dementia, Lewy body dementia, vascular dementia, mild cognitive impairment (MCI) and normal cognitive ageing investigating the change in cognition as the outcome were included. The Systematic Review Centre for Laboratory animal Experimentation’s risk of bias tool for animal studies was applied.

Results: Out of 4,154 articles, 29 described compounds inhibiting the GSK3 pathway. All studies were based on animal models of MCI, AD or normal cognitive ageing. Thirteen out of 21 natural compounds and five out of nine synthetic compounds tested in MCI and dementia animal models showed an overall positive effect on cognition. No articles reported human studies. The risk of bias was largely unclear.

Conclusion: Novel therapeutics involved in the modulation of the GSK3 nutrient sensing pathway have the potential to improve cognitive function. Overall, there is a clear lack of translation from animal models to humans.

Action Mechanisms of Curcumin in Alzheimer's Disease and Its Brain Targeted Delivery

AD is a chronic neurodegenerative disease. Many different signaling pathways, such as Wnt/β-catenin, Notch, ROS/JNK, and PI3K/Akt/mTOR are involved in Alzheimer’s disease and crosstalk between themselves. A promising treatment involves the uses of flavonoids, and one of the most promising is curcumin; however, because it has difficulty permeating the blood–brain barrier (BBB), it must be encapsulated by a drug carrier. Some of the most frequently studied are lipid nanocarriers, liposomes, micelles and PLGA. These carriers are further conjugated with brain-targeting agents such as lactoferrin and transferrin. In this review paper, curcumin and its therapeutic effects, which have been examined in vivo, are analyzed and then the delivery systems to the brain are addressed. Overall, the analysis of the literature revealed great potential for curcumin in treating AD and indicated the challenges that require further research.

Role of phytochemicals as nutraceuticals for cognitive functions affected in ageing

Cognitive decline can occur with normal ageing and in age-related brain disorders, such as mild cognitive impairment and dementia, including Alzheimer's disease, with limited pharmacological therapies available. Other approaches to reduce cognitive decline are urgently needed, and so, the role of dietary interventions or nutraceuticals has received much attention in this respect. In this review, we examine the evidence for dietary plants and their chemical constituents as nutraceuticals, relevant to both cognitive decline in normal ageing and in dementia. Pharmacological (in vitro and in vivo), clinical and epidemiological evidence is assessed for both frequently consumed plants and their dietary forms, including tea, coffee, cocoa (chocolate), red wine, grapes, citrus and other fruits; in addition to plants used less frequently in certain diets and those that cross the blurred boundaries between foods, nutraceuticals and medicinal plants. For the latter, turmeric, saffron, sage, rosemary and lemon balm are examples of those discussed. LINKED ARTICLES: This article is part of a themed section on The Pharmacology of Nutraceuticals. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.6/issuetoc.

Clinical Chemistry Route for Investigation of Alzheimer's Disease: A Label-Free Electrochemiluminescent Biosensor for Glycogen Synthase Kinase-3 Beta

Herein, we report a novel label-free electrochemiluminescent (ECL) biosensor for the detection of glycogen synthase kinase-3 beta (GSK-3β). A simple and feasible sensor was prepared by a two-step process. A polymeric coordination layer of phosphorylated poly vinyl with Zr⁴⁺ was used as the sensory hosting matrix because it efficiently formed a complex. The exterior Zr⁴⁺ can further combine with another phosphate through coordination, and GSK-3β catalyzes the phosphorylation of protein molecules. Thus, the biosensor can detect GSK-3β using luminol as an ECL probe. The ECL intensity of the proposed sensor responded proportionally to the concentration of GSK-3β under direct immersion mode with a linear response in a logarithmic scale over the wide range from 0.5 to 91.5 ng L^-1 and a detection limit of 0.055 ng L^-1. Excellent selectivity, stability, and reproducibility were achieved using the prepared biosensor, which has a simple preparation, low cost, and disposable suitability. This work aims to provide a novel tool for early diagnosis and pathological mechanism exploration about AD by detecting inchoate change of GSK-3β content in body fluid, thus to precaution the risk of Alzheimer's disease. It is of great importance for clinical chemistry for the investigation of Alzheimer's disease.