Potential of tocotrienols in the prevention and therapy of Alzheimer's disease

Metabolite-derived damage-associated molecular patterns in immunological diseases

Damage-associated molecular patterns (DAMPs) are typically derived from the endogenous elements of necrosis cells and can trigger inflammatory responses by activating DAMPs-sensing receptors on immune cells. Failure to clear DAMPs may lead to persistent inflammation, thereby contributing to the pathogenesis of immunological diseases. This review focuses on a newly recognized class of DAMPs derived from lipid, glucose, nucleotide, and amino acid metabolic pathways, which are then termed as metabolite-derived DAMPs. This review summarizes the reported molecular mechanisms of these metabolite-derived DAMPs in exacerbating inflammation responses, which may attribute to the pathology of certain types of immunological diseases. Additionally, this review also highlights both direct and indirect clinical interventions that have been explored to mitigate the pathological effects of these DAMPs. By summarizing our current understanding of metabolite-derived DAMPs, this review aims to inspire future thoughts and endeavors on targeted medicinal interventions and the development of therapies for immunological diseases.

Regulation of cholesterol metabolism: New players for an old physiological process

Identified more than two centuries ago, cholesterol plays a pivotal role in human physiology. Since cholesterol metabolism is a physiologically significant process, it is not surprising that its alterations are associated with several pathologies. The discovery of new molecular targets or compounds able to modulate this sophisticated metabolism has been capturing the attention of research groups worldwide since many years. Endogenous and exogenous compounds are known to regulate cellular cholesterol synthesis and uptake, or reduce cholesterol absorption at the intestinal level, thereby regulating cholesterol homeostasis. However, there is a great need of new modulators and diverse new pathways have been uncovered. Here, after illustrating cholesterol metabolism and its well-known regulators, some new players of this important physiological process are also described.

The emerging relationship between vitamin K and neurodegenerative diseases: a review of current evidence

Neurodegenerative disease refers to a group of disorders that predominantly damage the neurons in the brain. Despite significant progress in the knowledge of neurodegenerative diseases, there is currently no disease-modifying drug available. Vitamin K was first established for its involvement in blood clotting, but there is now compelling evidence indicating its role in the neurological system. In particular, the results of recent studies on the effects of vitamin K2 on preventing apoptosis, oxidative stress, and microglial activation in neuron cells through its role in electron transport are very promising against Alzheimer's disease. In addition to its protective effect on cognitive functions, its inhibitory effects on inflammation and α-synuclein fibrillization in Parkinson's disease, which has been revealed in recent years, are remarkable. Although there are many studies on the mechanism and possible treatment methods of neurodegenerative diseases, especially Parkinson's and Alzheimer's disease, studies on the relationship between vitamin K and neurodegenerative diseases are very limited, yet have promising findings. Vitamin K has also been proposed for therapeutic use in multiple sclerosis patients to lower the intensity or to slow down the progression of the disease. Accordingly, the aim of this study is to review the current evidence for the use of vitamin K supplementation in neurodegenerative diseases, in particular Alzheimer's disease, Parkinson's disease, and multiple sclerosis.

The mevalonate suppressor δ-tocotrienol increases AMPA receptor-mediated neurotransmission

Synaptic dysfunction is a hallmark of aging and is found in several neurological disorders such as Alzheimer's disease. A common mechanism related to synaptic dysfunction is dysregulation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, which mediate excitatory neurotransmission and synaptic plasticity. Accumulating evidence suggests that tocotrienols, vitamin E molecules that contain an isoprenoid side chain, may promote cognitive improvement in hippocampal-dependent learning tasks. Tocotrienols have also been shown to reduce the secretion of β-amyloid (Aβ) and cholesterol biosynthesis in part by downregulating 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, the rate-limiting enzyme that controls flux of the mevalonate pathway and cholesterol biosynthesis. We hypothesized that tocotrienols might promote cognitive improvement by increasing AMPA receptor-mediated synaptic transmission. Here, we found that δ-tocotrienol increased surface levels of GluA1 but not the GluA2 AMPA receptor subunit in primary hippocampal neurons. Unexpectedly, δ-tocotrienol treatment caused a decrease in the phosphorylation of GluA1 at Serine 845 with no significant changes in GluA1 at Serine 831. Moreover, δ-tocotrienol increased spontaneous excitatory postsynaptic current (sEPSC) amplitude and reduced the secretion of Aβ₄₀ in primary hippocampal neurons. Taken together, our findings suggest that δ-tocotrienol increases AMPA receptor-mediated neurotransmission via noncanonical changes in GluA1 phosphorylation status. These findings suggest that δ-tocotrienol may be beneficial in ameliorating synaptic dysfunction found in aging and neurological disease.

Progress in the development of naturally derived active metabolites-based drugs: Potential therapeutics for Alzheimer's disease

Alzheimer's disease (AD) is an extensive age-associated neurodegenerative disorder. In spite of wide-ranging progress in understanding the AD pathology for the past 50 years, clinical trials based on the hypothesis of amyloid-beta (Aβ) have reserved worsening particularly at late-stage human trials. Consequently, very few old drugs are presently used for AD with inadequate clinical consequences and various side effects. We focus on widespread pharmacological and beneficial principles for existing as well as future drugs. Multitargeting approaches by means of general antioxidant and anti-inflammatory mechanisms allied with particular receptor and/or enzyme-mediated actions in neuroprotection and neurodegeneration. The plant kingdom comprises a vast range of species with an incredible diversity of bioactive metabolites with diverse chemical scaffolds. In recent times, an increasing body of facts recommended the use of phytochemicals to decelerate AD's onset and progression. The definitive goal of AD investigation is to avert the onset of neurodegeneration, thereby allowing successful aging devoid of cognitive decline. At this point, we discussed the neurological protective role of natural products and naturally derived therapeutic agents for AD from various natural polyphenolic compounds and medicinal plants. In conclusion, medicinal plants act as a chief source of different bioactive constituents.

Tocotrienol in the Treatment of Topical Wounds: Recent Updates

Healing wounds is an important attempt to keep the internal higher organs safe. Complications in topical wound healing may lead to the formation of scars, which can affect the patient's quality of life. Although several approaches are ongoing in parallel in the exploration of natural compounds via advanced delivery, in this article, an attempt has been made to highlight tocotrienol. Tocotrienol is a natural form of vitamin E and has shown its potential in certain pharmacological activities better than tocopherol. Its antioxidant, anti-inflammatory, cell signal-mediating effects, angiogenic properties, management of scar, and promotion of wound environment with essential factors have shown potential in the management of topical wound healing. Therefore, this review has aimed to focus on recent advances in topical wound healing through the application of tocotrienols. Challenges in delivering tocotrienols to the topical wound due to its large molecular weight and higher logP have also been explored using nanotechnological-based carriers, which has made tocotrienol a potential tool to facilitate the closure of wounds. Exploration of tocotrienol has also been made in human volunteers for biopsy wounds; however, the results are yet to be reported. Overall, based on the current findings in the literature, it could be inferred that tocotrienol would be a viable alternative to the existing wound dressing components for the management of topical wounds.

An Interactive Review on the Role of Tocotrienols in the Neurodegenerative Disorders

Neurodegenerative disorders, such as Parkinson's and Alzheimer's disease, are claimed to be of major concern causing a significant disease burden worldwide. Oxidative stress, mitochondrial dysfunction and nerve damage are the main reasons for the emergence of these diseases. The formation of reactive oxygen species (ROS) is the common chemical molecule that is formed from all these three interdependent mechanisms which is highly reactive toward the neuronal cells. For these reasons, the administration of tocotrienols (T3s), which is a potent antioxidant, is proven to cater to this problem, through in vitro and in vivo investigations. Interestingly, their therapeutic potentials are not only limited to antioxidant property but also to being able to reverse the neuronal damage and act as a shield for mitochondria dysfunction. Thereby, T3s prevents the damage to the neurons. In regards to this statement, in this review, we focused on summarizing and discussing the potential therapeutic role of T3s on Alzheimer's and Parkinson's diseases, and their protective mechanisms based on evidence from the in vitro and in vivo studies. However, there is no clinical trial conducted to prove the efficacy of T3s for Alzheimer's and Parkinson's subjects. As such, the therapeutic role of T3s for these neurodegenerative disorders is still under debate.

Tocotrienols: Dietary Supplements for Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is one of the leading causes of death worldwide. Emphysema and chronic bronchitis are the two major phenotypes of COPD, which have many symptoms, such as dyspnea, chronic cough, and mucus overproduction. Emphysema is characterized by the destruction of the alveolar wall, while chronic bronchitis is characterized by limitations in expiratory airflow. Cigarette smoking is the most significant risk factor for the pathogenesis of COPD in the developed world. Chronic inflammation contributes to the onset and progression of the disease and furthers the risk of comorbidities. Current treatment options and prevention strategies for COPD are very limited. Tocotrienols are a group of vitamin E molecules with antioxidant and anti-inflammatory properties. Individual tocotrienols (α, γ, and δ) have shown their ability to attenuate inflammation specifically via suppressing nuclear factor-κB-mediated cytokine production. The δ- and γ-forms of tocotrienols have been indicated as the most effective in the prevention of macrophage infiltration, production of reactive oxygen species, and cytokine secretion. This review briefly discusses the pathogenesis of COPD and the role of inflammation therein. Furthermore, we summarize the in vitro and in vivo evidence for the anti-inflammatory activity of tocotrienols and their potential application to COPD management. Coupled with the bioavailability and safety profile of tocotrienols, the ability of these compounds to modulate COPD progression by targeting the inflammation pathways renders them potential candidates for novel therapeutic approaches in the treatment of COPD patients.

Effects of vitamin E on neurodegenerative diseases: an update

Vitamin E deficiency is associated with many neurological problems. Although the mechanisms of vitamin E action in neurodegenerative diseases are not clear, there are many possible mechanisms. Examples of such mechanisms are the protective effects of vitamin E against oxidative stress damage and its suppressive role in the expression of many genes involved in the development of neurodegeneration. Many studies have evaluated the relationship between vitamin E intake or vitamin E levels in body fluids and neurodegenerative diseases. Some studies concluded that vitamin E can play a protective role in neurodegeneration with respect to diseases such as Alzheimer's disease (AD), Parkinson's disease (PD), stroke and amyotrophic lateral sclerosis (ALS). Vitamin E supplementation was also associated with risk factors for some neurodegenerative diseases. In this review, we discuss the possible effects of vitamin E on the development and course of AD, PD, stroke and ALS, and the potential mechanisms involved.

Vitamin E deficiency is associated with many neurological problems. Although the mechanisms of vitamin E action in neurodegenerative diseases are not clear, there are many possible mechanisms. Examples of such mechanisms are the protective effects of vitamin E against oxidative stress damage and its suppressive role in the expression of many genes involved in the development of neurodegeneration. Many studies have evaluated the relationship between vitamin E intake or vitamin E levels in body fluids and neurodegenerative diseases. Some studies concluded that vitamin E can play a protective role in neurodegeneration with respect to diseases such as Alzheimer’s disease (AD), Parkinson’s disease (PD), stroke and amyotrophic lateral sclerosis (ALS). Vitamin E supplementation was also associated with risk factors for some neurodegenerative diseases. In this review, we discuss the possible effects of vitamin E on the development and course of AD, PD, stroke and ALS, and the potential mechanisms involved.

Regulation of Small GTPase Prenylation in the Nervous System

Mevalonate pathway inhibitors have been extensively studied for their roles in cholesterol depletion and for inhibiting the prenylation and activation of various proteins. Inhibition of protein prenylation has potential therapeutic uses against neurological disorders, like neural cancers, neurodegeneration, and neurotramatic lesions. Protection against neurodegeneration and promotion of neuronal regeneration is regulated in large part by Ras superfamily small guanosine triphosphatases (GTPases), particularly the Ras, Rho, and Rab subfamilies. These proteins are prenylated to target them to cellular membranes. Prenylation can be specifically inhibited through altering the function of enzymes of the mevalonate pathway necessary for isoprenoid production and attachment to target proteins to elicit a variety of effects on neural cells. However, this approach does not address how prenylation affects a specific protein. This review focuses on the regulation of small GTPase prenylation, the different techniques to inhibit prenylation, and how this inhibition has affected neural cell processes.

Destabilization potential of phenolics on Aβ fibrils: mechanistic insights from molecular dynamics simulation

Ellagic acid from pomegranate and walnuts is found to destabilize Aβ fibrils. It can be a potential drug to treat AD.

Vitamin E and Alzheimer's disease: what do we know so far?

Vitamin E has been proposed as a potential clinical intervention for Alzheimer's disease (AD) given the plausibility of its various biological functions in influencing the neurodegenerative processes associated with the condition. The tocopherol and tocotrienol isoforms of vitamin E have multiple properties including potent antioxidant and anti-inflammatory characteristics, in addition to influences on immune function, cellular signalling and lowering cholesterol. Several of these roles offer a theoretical rationale for providing benefit for the treatment of AD-associated pathology. Diminished circulating concentrations of vitamin E have been demonstrated in individuals with AD. Reduced plasma levels have furthermore been associated with an increased risk of AD development while intake, particularly from dietary sources, may limit or reduce the rate of disease progression. This benefit may be linked to synergistic actions between vitamin E isoforms and other micronutrients. Nevertheless, randomised trials have found limited and inconsistent evidence of vitamin E supplementation as an effective clinical intervention. Thus, despite a strong rationale in support of a beneficial role for vitamin E for the treatment of AD, the evidence remains inconclusive. Several factors may partly explain this discrepancy and represent the difficulties of translating complex laboratory evidence and dietary interactions into clinical interventions. Methodological design limitations of existing randomised trials and restrictions to supplementation with a single vitamin E isoform may also limit the influence of effect. Moreover, several factors influence individual responsiveness to vitamin E intake and recent findings suggest variation in the underlying genetic architecture attenuates vitamin E biological availability and activity which likely contributes to the variation in clinical responsiveness and the failure of randomised trials to date. Importantly, the clinical safety of vitamin E remains controversial and warrants further investigation.

Anti-inflammatory Activity of Tocotrienols in Age-related Pathologies: A SASPected Involvement of Cellular Senescence

Tocotrienols (T3) have been shown to represent a very important part of the vitamin E family since they have opened new opportunities to prevent or treat a multitude of age-related chronic diseases. The beneficial effects of T3 include the amelioration of lipid profile, the promotion of Nrf2 mediated cytoprotective activity and the suppression of inflammation. All these effects may be the consequence of the ability of T3 to target multiple pathways. We here propose that these effects may be the result of a single target of T3, namely senescent cells. Indeed, T3 may act by a direct suppression of the senescence-associated secretory phenotype (SASP) produced by senescent cells, mediated by inhibition of NF-kB and mTOR, or may potentially remove the origin of the SASP trough senolysis (selective death of senescent cells). Further studies addressed to investigate the impact of T3 on cellular senescence “in vitro” as well as in experimental models of age-related diseases “in vivo” are clearly encouraged.

Induction of peroxisomal changes in oligodendrocytes treated with 7-ketocholesterol: Attenuation by α-tocopherol

The involvement of organelles in cell death is well established especially for endoplasmic reticulum, lysosomes and mitochondria. However, the role of the peroxisome is not well known, though peroxisomal dysfunction favors a rupture of redox equilibrium. To study the role of peroxisomes in cell death, 158 N murine oligodendrocytes were treated with 7-ketocholesterol (7 KC: 25-50 μM, 24 h). The highest concentration is known to induce oxiapoptophagy (OXIdative stress + APOPTOsis + autoPHAGY), whereas the lowest concentration does not induce cell death. In those conditions (with 7 KC: 50 μM) morphological, topographical and functional peroxisome alterations associated with modifications of the cytoplasmic distribution of mitochondria, with mitochondrial dysfunction (loss of transmembrane mitochondrial potential, decreased level of cardiolipins) and oxidative stress were observed: presence of peroxisomes with abnormal sizes and shapes similar to those observed in Zellweger fibroblasts, lower cellular level of ABCD3, used as a marker of peroxisomal mass, measured by flow cytometry, lower mRNA and protein levels (measured by RT-qPCR and western blotting) of ABCD1 and ABCD3 (two ATP-dependent peroxisomal transporters), and of ACOX1 and MFP2 enzymes, and lower mRNA level of DHAPAT, involved in peroxisomal β-oxidation and plasmalogen synthesis, respectively, and increased levels of very long chain fatty acids (VLCFA: C24:0, C24:1, C26:0 and C26:1, quantified by gas chromatography coupled with mass spectrometry) metabolized by peroxisomal β-oxidation. In the presence of 7 KC (25 μM), slight mitochondrial dysfunction and oxidative stress were found, and no induction of apoptosis was detected; however, modifications of the cytoplasmic distribution of mitochondria and clusters of mitochondria were detected. The peroxisomal alterations observed with 7 KC (25 μM) were similar to those with 7 KC (50 μM). In addition, data obtained by transmission electron microcopy and immunofluorescence microscopy by dual staining with antibodies raised against p62, involved in autophagy, and ABCD3, support that 7 KC (25-50 μM) induces pexophagy. 7 KC (25-50 μM)-induced side effects were attenuated by α-tocopherol but not by α-tocotrienol, whereas the anti-oxidant properties of these molecules determined with the FRAP assay were in the same range. These data provide evidences that 7 KC, at concentrations inducing or not cell death, triggers morphological, topographical and functional peroxisomal alterations associated with minor or major mitochondrial changes.

A Review on the Relationship between Tocotrienol and Alzheimer Disease

Alzheimer’s disease (AD) is plaguing the aging population worldwide due to its tremendous health care and socioeconomic burden. Current treatment of AD only offers symptomatic relief to patients. Development of agents targeting specific pathologies of AD is very slow. Tocotrienol, a member of the vitamin E family, can tackle many aspects of AD, such as oxidative stress, mitochondrial dysfunction and abnormal cholesterol synthesis. This review summarizes the current evidence on the role of tocotrienol as a neuroprotective agent. Preclinical studies showed that tocotrienol could reduce oxidative stress by acting as a free-radical scavenger and promoter of mitochondrial function and cellular repair. It also prevented glutamate-induced neurotoxicity in the cells. Human epidemiological studies showed a significant inverse relationship between tocotrienol levels and the occurrence of AD. However, there is no clinical trial to support the claim that tocotrienol can delay or prevent the onset of AD. As a conclusion, tocotrienol has the potential to be developed as an AD-preventing agent but further studies are required to validate its efficacy in humans.

Essential Dietary Bioactive Lipids in Neuroinflammatory Diseases

SIGNIFICANCE

Under physiological conditions, neurons and glia are in a healthy, redox-balanced environment; when injury perturbs this equilibrium, a neuroinflammatory state is established by activated microglia that triggers pro-inflammatory responses and alters the oxidant/antioxidant balance, thus leading to neuronal loss and neurodegeneration. In neurodegenerative diseases (such as Alzheimer's disease, Parkinson's disease, amyothrophic lateral sclerosis, and multiple sclerosis), the brain is in a constitutively self-sustaining cycle of inflammation and oxidative stress that prompts and amplifies brain damage. Recent Advances: Recently, an increasing amount of scientific data highlight the ability of specific nutrients to cross the blood-brain barrier, and to modulate inflammatory and oxidative pathways. Therefore, nutritional approaches may contribute to restore the lost equilibrium among factors accounting for neurodegeneration.

CRITICAL ISSUES

Herein, we critically examine how essential lipids (including fatty acids, liposoluble vitamins and phytosterols) might contribute to accelerate or prevent the onset and progression of such pathologies. In particular, we highlight that experimental and clinical findings, although promising, are still inadequate to draw definitive conclusions.

FUTURE DIRECTIONS

More research is warranted in order to establish the real impact of lipid intake on brain health, especially when redox balance and inflammatory responses have been already compromised. In the future, it would be hoped to gain a detailed knowledge of chemical modifications and dynamic properties of such nutrients, before planning to exploit them as potential therapeutics. Antioxid. Redox Signal. 29, 37-60.

Almond, hazelnut and walnut, three nuts for neuroprotection in Alzheimer's disease: A neuropharmacological review of their bioactive constituents

An increase in the prevalence of Alzheimer's disease (AD) as a multifactorial neurodegenerative disorder is an almost obvious issue in the world. Researches on natural products for finding effective drugs to prevent the disease are in progress. There is special attention to the three types of nuts including almond, hazelnut and walnut in manuscripts of traditional Persian medicine (PM) as the preventive agents against brainatrophy and memory loss. The purpose of this study is a pharmacological review of their bioactive constituents and introducing the value of these nuts as the effective supplements and natural medicinal foods in AD patients. Databases including PubMed and ScienceDirect were searched in title, abstract and keywords from year 2000 to present for AD-related researches on these tree nuts, their major phytochemicals and their mechanisms of action. As result, almond, hazelnut and walnut provide macronutrients, micronutrients, and phytochemicals which affect several pathways in AD pathogenesis such as amyloidogenesis, tau phosphorylation, oxidative stress, cholinergic pathways, and some non-target mechanisms including cholesterol lowering and anti-inflammatory properties, as well as effect on neurogenesis. These nuts are recommended in PM for their brain-protective activity and particularly reversing brain atrophy in case of hazelnut. The therapeutical statements of PM scholars mentioned in their books are based on their clinical observations with support of a long history of experiences. Beyond the molecular activities attributed to the phytochemicals, the use of these tree nuts could be more considered in scientific researches as the effective nutrients for prevention or even management of AD.

Effects of nutrient and bioactive food components on Alzheimer's disease and epigenetic

Alzheimer's disease (AD) is the most common form of dementia in the elderly and is a chronic neurodegenerative disease that is becoming widespread. For this reason, in recent years factors affecting the development, progression and cognitive function of the AD have been emphasized. Nutrients and other bioactive nutrients are among the factors that are effective in AD. In particular, vitamins A, C and E, vitamins B₁, B₆ and B₁₂, folate, magnesium, choline, inositol, anthocyanins, isoflavones etc. nutrients and bioactive nutrients are known to be effective in the development of AD. Nutrients and nutrient components may also have an epigenetic effect on AD. At the same time, nutrients and bioactive food components slow down the progression of the disease. For this reason, the effect of nutrients and food components on AD was examined in this review.

In Vivo Biosynthesized Zinc and Iron Oxide Nanoclusters for High Spatiotemporal Dual-Modality Bioimaging of Alzheimer's Disease

Alzheimer's disease is still incurable and neurodegenerative, and there is a lack of detection methods with high sensitivity and specificity. In this study, by taking different month old Alzheimer's mice as models, we have explored the possibility of the target bioimaging of diseased sites through the initial injection of zinc gluconate solution into Alzheimer's model mice post-tail vein and then the combination of another injection of ferrous chloride (FeCl₂) solution into the same Alzheimer's model mice post-stomach. Our observations indicate that both zinc gluconate solution and FeCl₂ solution could cross the blood-brain barrier (BBB) to biosynthesize the fluorescent zinc oxide nanoclusters and magnetic iron oxide nanoclusters, respectively, in the lesion areas of the AD model mice, thus enabling high spatiotemporal dual-modality bioimaging (i.e., including fluorescence bioimaging (FL) and magnetic resonance imaging (MRI)) of Alzheimer's disease for the first time. The result presents a novel promising strategy for the rapid and early diagnosis of Alzheimer's disease.

Tocotrienol Affects Oxidative Stress, Cholesterol Homeostasis and the Amyloidogenic Pathway in Neuroblastoma Cells: Consequences for Alzheimer's Disease

One of the characteristics of Alzheimer´s disease (AD) is an increased amyloid load and an enhanced level of reactive oxidative species (ROS). Vitamin E has known beneficial neuroprotective effects, and previously, some studies suggested that vitamin E is associated with a reduced risk of AD due to its antioxidative properties. However, epidemiological studies and nutritional approaches of vitamin E treatment are controversial. Here, we investigate the effect of α-tocotrienol, which belongs to the group of vitamin E, on AD-relevant processes in neuronal cell lines. In line with the literature, α-tocotrienol reduced the ROS level in SH-SY5Y cells. In the presence of tocotrienols, cholesterol and cholesterol esters, which have been shown to be risk factors in AD, were decreased. Besides the unambiguous positive effects of tocotrienol, amyloid-β (Aβ) levels were increased accompanied by an increase in the activity of enzymes responsible for Aβ production. Proteins and gene expression of the secretases and their components remained unchanged, whereas tocotrienol accelerates enzyme activity in cell-free assays. Besides enhanced Aβ production, tocotrienols inhibited Aβ degradation in neuro 2a (N2a)-cells. Our results might help to understand the controversial findings of vitamin E studies and demonstrate that besides the known positive neuroprotective properties, tocotrienols also have negative characteristics with respect to AD.