The role of vitamin D in Alzheimer's disease: possible genetic and cell signaling mechanisms

Gut microbiome and brain transcriptome analyses reveal the effect of walnut oil in preventing scopolamine-induced cognitive impairment

Walnut Oil (WO) is recognized for its potential to improve cognition, but the mechanisms of its action related to improving cognitive impairment are not yet clear. In this study, the components of walnut oil were measured, and it was found that WO supplementation for 8 weeks could significantly prevent cognitive behavioral deficits and synaptic dysfunction induced by intraperitoneal injection of scopolamine (SCOP) in mice. By comparing and analyzing the changes in the hippocampal synaptic structure, oxidative stress, neurotransmitter fluctuations, brain transcriptome, inflammatory factors and gut microbiota in mice from different treatment groups, we observed a significant correlation between synaptic transmission genes, gut microbiota and neurotransmission in the WO supplemented group. It was found that WO supplementation could influence the secretion of neurotransmitters Ach and 5-HT by modulating the gut microbiota in vivo, thereby improving cognitive impairment through the central nervous system and hypothalamic-pituitary-adrenal (HPA) axis regulation.

Angiogenin Levels and Their Association with Cardiometabolic Indices Following Vitamin D Status Correction in Saudi Adults

Simple Summary

Angiogenin (ANG) is a small 123 amino acid protein which in normal growth is associated with formation of new blood vessels in a process called angiogenesis; however, the abnormal levels of this protein in blood has been associated with diseases such as cancer, neurological disorders, and cardiovascular diseases. Vitamin D deficiency and elevated levels of blood lipids have also been associated with many diseases including cardiovascular diseases. In this study, the investigators tried to evaluate the relationship between the circulating levels of ANG, vitamin D, and lipids. The model used was vitamin D supplementation of deficient Saudi adults in order to find the effect of vitamin D correction on circulating levels of ANG and blood lipids. With vitamin D supplementation, modest but non-significant elevation in ANG was observed, as well as significant increase in apolipoproteins CIII and E and significant decrease in apo B. In addition, the correlation between circulating levels of ANG and apolipoproteins especially apo E observed in this study are interesting and should be investigated more as both are linked with neurologic disorders like Alzheimer’s and Parkinson’s diseases.

Abstract

Angiogenin (ANG), a multifunctional protein known to induce blood vessel formation, is a potential biomarker for cardiovascular diseases; however, whether it is affected by vitamin D supplementation is not known. This interventional study in vitamin D-deficient Saudi adults was designed to investigate it. A total of 100 vitamin D-deficient Saudi adults aged 30–50 years were randomly selected to undergo 6-month vitamin D supplementation. Circulating levels of fasting glucose, lipids, vitamin D, apolipoproteins (AI, AII, B, CI, CII, CIII, E, and H), and ANG were measured using commercially available assays at baseline and after six months. Overall, vitamin D levels increased significantly post intervention. With this, levels of apo-CIII and apo-E significantly increased (p-values of 0.001 and 0.009, respectively) with a significant parallel decrease in apo-B (p = 0.003). ANG levels were significantly positively associated with most apolipoproteins and inversely correlated with HDL-cholesterol. Post intervention, the changes in ANG levels were positively correlated with apo-E (r = 0.32; p < 0.01 in all subjects and r = 0.40; p < 0.05 in males). Vitamin D supplementation may modestly affect ANG levels. The association observed between ANG and apo-E is worthy of further investigation since both biomarkers have been linked to neurodegenerative disorders.

Genetic, environmental and biomarker considerations delineating the regulatory effects of vitamin D on central nervous system function

Studies show that vitamin D (vit-D) (25(OH)D), the bioactive metabolite (1,25(OH)2D3) and vit-D receptors (vit-D receptor; protein disulphide isomerase, family A member 3) are expressed throughout the brain, particularly in regions pivotal to learning and memory. This has led to the paradigm that avoiding vit-D deficiency is important to preserve cognitive function. However, presently, it is not clear if the common clinical measure of serum 25(OH)D serves as a robust surrogate marker for central nervous system (CNS) homeostasis or function. Indeed, recent studies report CNS biosynthesis of endogenous 25(OH)D, the CNS expression of the CYP group of enzymes which catalyse conversion to 1,25(OH)2D3 and thereafter, deactivation. Moreover, in the periphery, there is significant ethnic/genetic heterogeneity in vit-D conversion to 1,25(OH)2D3 and there is a paucity of studies which have actually investigated vit-D kinetics across the cerebrovasculature. Compared with peripheral organs, the CNS also has differential expression of receptors that trigger cellular response to 1,25(OH)2D3 metabolites. To holistically consider the putative association of peripheral (blood) abundance of 25(OH)D on cognitive function, herein, we have reviewed population and genetic studies, pre-clinical and clinical intervention studies and moreover have considered potential confounders of vit-D analysis.

No effects without causes: the Iron Dysregulation and Dormant Microbes hypothesis for chronic, inflammatory diseases

Since the successful conquest of many acute, communicable (infectious) diseases through the use of vaccines and antibiotics, the currently most prevalent diseases are chronic and progressive in nature, and are all accompanied by inflammation. These diseases include neurodegenerative (e.g. Alzheimer's, Parkinson's), vascular (e.g. atherosclerosis, pre-eclampsia, type 2 diabetes) and autoimmune (e.g. rheumatoid arthritis and multiple sclerosis) diseases that may appear to have little in common. In fact they all share significant features, in particular chronic inflammation and its attendant inflammatory cytokines. Such effects do not happen without underlying and initially 'external' causes, and it is of interest to seek these causes. Taking a systems approach, we argue that these causes include (i) stress-induced iron dysregulation, and (ii) its ability to awaken dormant, non-replicating microbes with which the host has become infected. Other external causes may be dietary. Such microbes are capable of shedding small, but functionally significant amounts of highly inflammagenic molecules such as lipopolysaccharide and lipoteichoic acid. Sequelae include significant coagulopathies, not least the recently discovered amyloidogenic clotting of blood, leading to cell death and the release of further inflammagens. The extensive evidence discussed here implies, as was found with ulcers, that almost all chronic, infectious diseases do in fact harbour a microbial component. What differs is simply the microbes and the anatomical location from and at which they exert damage. This analysis offers novel avenues for diagnosis and treatment.

A Bacterial Component to Alzheimer's-Type Dementia Seen via a Systems Biology Approach that Links Iron Dysregulation and Inflammagen Shedding to Disease

The progression of Alzheimer's disease (AD) is accompanied by a great many observable changes, both molecular and physiological. These include oxidative stress, neuroinflammation, and (more proximal to cognitive decline) the death of neuronal and other cells. A systems biology approach seeks to organize these observed variables into pathways that discriminate those that are highly involved (i.e., causative) from those that are more usefully recognized as bystander effects. We review the evidence that iron dysregulation is one of the central causative pathway elements here, as this can cause each of the above effects. In addition, we review the evidence that dormant, non-growing bacteria are a crucial feature of AD, that their growth in vivo is normally limited by a lack of free iron, and that it is this iron dysregulation that is an important factor in their resuscitation. Indeed, bacterial cells can be observed by ultrastructural microscopy in the blood of AD patients. A consequence of this is that the growing cells can shed highly inflammatory components such as lipopolysaccharides (LPS). These too are known to be able to induce (apoptotic and pyroptotic) neuronal cell death. There is also evidence that these systems interact with elements of vitamin D metabolism. This integrative systems approach has strong predictive power, indicating (as has indeed been shown) that both natural and pharmaceutical iron chelators might have useful protective roles in arresting cognitive decline, and that a further assessment of the role of microbes in AD development is more than highly warranted.

1α,25-Dihydroxyvitamin D3 up-regulates IL-34 expression in SH-SY5Y neural cells

Vitamin D supplementation is regarded as a novel approach to treat Alzheimer’s disease, but the underlying mechanism remains elusive. The cytokine IL-34 provides strong neuroprotective and survival signals in brain injury and neurodegeneration and could be an immunological mediator for the vitamin D-induced protection. The aim of this study was to investigate whether human IL-34 is up-regulated in neuronal cells by the hormonally active form of vitamin D, 1α,25-dihydroxyvitamin D3 [1α,25(OH)2D3]. We found that IL-34 was detectable in a variety of cell lines and its expression was strongly induced in SH-SY5Y neural cells in a dose- and time-dependent manner by 1α,25(OH)2D3 through the vitamin D receptor (VDR). Furthermore, we identified the core promoter of IL-34 gene and a VDR binding site (CGCCCT) that was required for 1α,25(OH)2D3-induced IL-34 expression. These findings suggest that the induction of IL-34 expression by 1α,25(OH)2D3 may constitute a mechanism that explains the protective function of vitamin D in Alzheimer’s disease.

Inferring new indications for approved drugs via random walk on drug-disease heterogenous networks

Background

Since traditional drug research and development is often time-consuming and high-risk, there is an increasing interest in establishing new medical indications for approved drugs, referred to as drug repositioning, which provides a relatively low-cost and high-efficiency approach for drug discovery. With the explosive growth of large-scale biochemical and phenotypic data, drug repositioning holds great potential for precision medicine in the post-genomic era. It is urgent to develop rational and systematic approaches to predict new indications for approved drugs on a large scale.

Results

In this paper, we propose the two-pass random walks with restart on a heterogenous network, TP-NRWRH for short, to predict new indications for approved drugs. Rather than random walk on bipartite network, we integrated the drug-drug similarity network, disease-disease similarity network and known drug-disease association network into one heterogenous network, on which the two-pass random walks with restart is implemented. We have conducted performance evaluation on two datasets of drug-disease associations, and the results show that our method has higher performance than six existing methods. A case study on the Alzheimer’s disease showed that nine of top 10 predicted drugs have been approved or investigational for neurodegenerative diseases. The experimental results show that our method achieves state-of-the-art performance in predicting new indications for approved drugs.

Conclusions

We proposed a two-pass random walk with restart on the drug-disease heterogeneous network, referred to as TP-NRWRH, to predict new indications for approved drugs. Performance evaluation on two independent datasets showed that TP-NRWRH achieved higher performance than six existing methods on 10-fold cross validations. The case study on the Alzheimer’s disease showed that nine of top 10 predicted drugs have been approved or are investigational for neurodegenerative diseases. The results show that our method achieves state-of-the-art performance in predicting new indications for approved drugs.

Current status of biomarker research in neurology

Neurology is one of the typical disciplines where personalized medicine has been recently becoming an important part of clinical practice. In this article, the brief overview and a number of examples of the use of biomarkers and personalized medicine in neurology are described. The various issues in neurology are described in relation to the personalized medicine and diagnostic, prognostic as well as predictive blood and cerebrospinal fluid biomarkers. Such neurological domains discussed in this work are neuro-oncology and primary brain tumors glioblastoma and oligodendroglioma, cerebrovascular diseases focusing on stroke, neurodegenerative disorders especially Alzheimer's and Parkinson's diseases and demyelinating diseases such as multiple sclerosis. Actual state of the art and future perspectives in diagnostics and personalized treatment in diverse domains of neurology are given.

Oxidant/Antioxidant imbalance and the risk of Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia characterized by progressive loss of memory and other cognitive functions among older people. Senile plaques and neurofibrillary tangles are the most hallmarks lesions in the brain of AD in addition to neurons loss. Accumulating evidence has shown that oxidative stress-induced damage may play an important role in the initiation and progression of AD pathogenesis. Redox impairment occurs when there is an imbalance between the production and quenching of free radicals from oxygen species. These reactive oxygen species augment the formation and aggregation of amyloid-β and tau protein hyperphosphorylation and vice versa. Currently, there is no available treatments can modify the disease. However, wide varieties of antioxidants show promise to delay or prevent the symptoms of AD and may help in treating the disease. In this review, the role of oxidative stress in AD pathogenesis and the common used antioxidant therapies for AD will summarize.

Vitamin D and cognition in older adults: an update of recent findings

PURPOSE OF REVIEW

Ageing is a generally known risk factor for cognitive decline and dementia. Underlying mechanisms are expected to be multifactorial, but the exact causes are still elusive. This article reviews the potential role of vitamin D in brain function by presenting an overview of recently published mechanistic, rodent as well as human studies.

RECENT FINDINGS

There is emerging evidence that suggests a beneficial role for vitamin D in brain physiology, for instance by the promotion of neurotransmission, neurogenesis, synaptogenesis, amyloid clearance and the prevention of neuronal death. In addition, several observational studies have shown associations between higher serum vitamin D concentrations and better cognitive performance. To date, imaging studies and randomized controlled trials are scarce, but these studies are expected to fulfil a crucial role towards a better understanding on vitamin D-mediated brain processes in the future.

SUMMARY

Despite accumulating evidence supporting a role of vitamin D in brain function, only a handful of human trials have been performed. Consequently, the question whether the association between vitamin D, cognitive decline and dementia is causal cannot be sufficiently answered yet.

Simultaneous Quantification of 25-Hydroxyvitamin D3 and 24,25-Dihydroxyvitamin D3 in Rats Shows Strong Correlations between Serum and Brain Tissue Levels

While vitamin D3 is recognized as a neuroactive steroid affecting both brain development and function, efficient analytical method in determining vitamin D3 metabolites in the brain tissue is still lacking, and the relationship of vitamin D3 status between serum and brain remains elusive. Therefore, we developed a novel analysis method by using high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) to simultaneously quantify the concentrations of 25-hydroxyvitamin D3 (25(OH)D3) and 24,25-dihydroxyvitamin D3 (24,25(OH)2D3) in the serum and brain of rats fed with different dose of vitamin D3. We further investigated whether variations of serum vitamin D3 metabolites could affect vitamin D3 metabolite levels in the brain. Serum and brain tissue were analyzed by HPLC-MS/MS with electrospray ionization following derivatization with 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD). The method is highly sensitive, specific, and accurate to quantify 25(OH)D3 and 24,25(OH)2D3 in animal brain tissue. Vitamin D3 metabolites in brain tissue were significantly lower in rats fed with a vitamin D deficiency diet than in rats fed with high vitamin D3 diet. There was also a strong correlation of vitamin D3 metabolites in serum and brain. These results indicate that vitamin D3 status in serum affects bioavailability of vitamin D3 metabolites in the brain.

Nutrition, the brain and cognitive decline: insights from epigenetics

Nutrition affects the brain throughout life, with profound implications for cognitive decline and dementia. These effects are mediated by changes in expression of multiple genes, and responses to nutrition are in turn affected by individual genetic variability. An important layer of regulation is provided by the epigenome: nutrition is one of the many epigenetic regulators that modify gene expression without changes in DNA sequence. Epigenetic mechanisms are central to brain development, structure and function, and include DNA methylation, histone modifications and non-protein-coding RNAs. They enable cell-specific and age-related gene expression. Although epigenetic events can be highly stable, they can also be reversible, highlighting a critical role for nutrition in prevention and treatment of disease. Moreover, they suggest key mechanisms by which nutrition is involved in the pathogenesis of age-related cognitive decline: many nutrients, foods and diets have both immediate and long-term effects on the epigenome, including energy status, that is, energy intake, physical activity, energy metabolism and related changes in body composition, and micronutrients involved in DNA methylation, for example, folate, vitamins B6 and B12, choline, methionine. Optimal brain function results from highly complex interactions between numerous genetic and environmental factors, including food intake, physical activity, age and stress. Future studies linking nutrition with advances in neuroscience, genomics and epigenomics should provide novel approaches to the prevention of cognitive decline, and treatment of dementia and Alzheimer's disease.

Regulation of neurotropic signaling by the inducible, NF-kB-sensitive miRNA-125b in Alzheimer's disease (AD) and in primary human neuronal-glial (HNG) cells

Inducible microRNAs (miRNAs) perform critical regulatory roles in central nervous system (CNS) development, aging, health, and disease. Using miRNA arrays, RNA sequencing, enhanced Northern dot blot hybridization technologies, Western immunoblot, and bioinformatics analysis, we have studied miRNA abundance and complexity in Alzheimer's disease (AD) brain tissues compared to age-matched controls. In both short post-mortem AD and in stressed primary human neuronal-glial (HNG) cells, we observe a consistent up-regulation of several brain-enriched miRNAs that are under transcriptional control by the pro-inflammatory transcription factor NF-kB. These include miRNA-9, miRNA-34a, miRNA-125b, miRNA-146a, and miRNA-155. Of the inducible miRNAs in this subfamily, miRNA-125b is among the most abundant and significantly induced miRNA species in human brain cells and tissues. Bioinformatics analysis indicated that an up-regulated miRNA-125b could potentially target the 3'untranslated region (3'-UTR) of the messenger RNA (mRNA) encoding (a) a 15-lipoxygenase (15-LOX; ALOX15; chr 17p13.3), utilized in the conversion of docosahexaneoic acid into neuroprotectin D1 (NPD1), and (b) the vitamin D3 receptor (VDR; VD3R; chr12q13.11) of the nuclear hormone receptor superfamily. 15-LOX and VDR are key neuromolecular factors essential in lipid-mediated signaling, neurotrophic support, defense against reactive oxygen and nitrogen species (reactive oxygen and nitrogen species), and neuroprotection in the CNS. Pathogenic effects appear to be mediated via specific interaction of miRNA-125b with the 3'-UTR region of the 15-LOX and VDR messenger RNAs (mRNAs). In AD hippocampal CA1 and in stressed HNG cells, 15-LOX and VDR down-regulation and a deficiency in neurotrophic support may therefore be explained by the actions of a single inducible, pro-inflammatory miRNA-125b. We will review the recent data on the pathogenic actions of this up-regulated miRNA-125b in AD and discuss potential therapeutic approaches using either anti-NF-kB or anti-miRNA-125b strategies. These may be of clinical relevance in the restoration of 15-LOX and VDR expression back to control levels and the re-establishment of homeostatic neurotrophic signaling in the CNS.

Nutrient intake and brain biomarkers of Alzheimer's disease in at-risk cognitively normal individuals: a cross-sectional neuroimaging pilot study

OBJECTIVE

There is increasing evidence to suggest that diet, one of the most important modifiable environmental factors, may play a role in preventing or delaying cognitive decline and Alzheimer's disease (AD). This study examines the relationship between dietary nutrients and brain biomarkers of AD in cognitively normal individuals (NL) with and without AD risk factors.

DESIGN

As part of an ongoing brain imaging study, participants received clinical and laboratory examinations, a neurocognitive test battery, positron emission tomography (PET) with (11)C-Pittsburgh Compound-B (PiB; a measure of amyloid-β (Aβ) load) and (18)F-fluorodeoxyglucose (FDG; a proxy of neuronal activity), and completed semiquantitative food frequency questionnaires.

SETTING

Research centre affiliated with the Alzheimer's disease Core Center at New York University School of Medicine.

PARTICIPANTS

49 NL individuals (age 25-72 years, 69% women) with dietary information, (11)C-PiB and (18)F-FDG PET scans were examined.

RESULTS

Controlling for age and total caloric intake, higher intake of vitamin B12, vitamin D and ω-3 polyunsaturated fatty acid (PUFA) was associated with lower Aβ load in AD regions on PiB-PET, while higher intake of β-carotene and folate was associated with higher glucose metabolism on FDG-PET. β-carotene and folate were associated with reduced glucose metabolism for women, apolipoprotein E epsilon 4 (APOE4) carriers and participants with positive AD family history, but not for their risk-free counterparts. The associations of vitamin B12, vitamin D and ω-3 PUFA with PiB retention were independent of gender, APOE and family history. The identified nutrient combination was associated with higher intake of vegetables, fruit, whole grains, fish and legumes, and lower intake of high-fat dairies, meat and sweets.

CONCLUSIONS

Our data provide a potential pathophysiological mechanism for epidemiological findings showing that dietary interventions may play a role in the prevention of AD. Longitudinal studies are needed to determine whether there is a direct link between nutrient intake, brain biomarkers and risk of AD.

Calcium regulation of neural rhythms, memory and Alzheimer's disease

Alzheimer's disease (AD) begins with a decline in cognition followed by neuronal cell death and dementia. These changes have been linked to a deregulation of Ca(2+) signalling caused by a progressive increase in the resting level of Ca(2+), which may influence cognition by interfering with the rhythm rheostat that controls the sleep/wake cycle. The rise in resting levels of Ca(2+) may not alter the processes of memory acquisition during consciousness (gamma and theta rhythms), but may duplicate some of the events that occur during the slow oscillations responsible for the twin processes of memory consolidation and memory erasure that occur during sleep. The persistent elevation in the resting level of Ca(2+) induced by an accumulation of amyloid β (Aβ) oligomers duplicates a similar small global elevation normally restricted to the period of slow oscillations when memories are erased during sleep. In AD, such a rapid erasure of memories soon after they are acquired during the wake period means that they are not retained for consolidation during sleep. The Aβ deregulates Ca(2+) signalling through direct effects on the neurons and indirectly by inducing inflammatory responses in the microglia and astrocytes. Some of these deleterious effects of Aβ may be alleviated by vitamin D.