Nutritional status of selenium in Alzheimer's disease patients

Insights into cancer and neurodegenerative diseases through selenoproteins and the connection with gut microbiota - current analytical methodologies

Introduction: Selenium plays many key roles in health especially in connection with cancer and neurodegenerative diseases. However, it needs to be appreciated that the essentiality/toxicity of selenium depends on both, a narrow range of concentration and the chemical specie involved. In this context, selenoproteins are essential biomolecules against these disorders, mainly due to its antioxidant action. To this end, analytical methodologies may allow identifying and quantifying individual selenospecies in human biofluids and tissues. Areas covered: This review focus on the role of selenoproteins in medicine, with special emphasis in cancer and neurodegenerative diseases, considering the possible link with gut microbiota. In particular, this article reviews the analytical techniques and procedures recently developed for the absolute quantification of selenoproteins and selenometabolites in human biofluids and tissues. Expert commentary: The beneficial role of selenium in human health has been extensively studied and reviewed. However, several challenges remain unsolved as discussed in this article: (i) speciation of selenium (especially selenoproteins) in cancer and neurodegenerative disease patients; (ii) supplementation of selenium in humans using functional foods and nutraceuticals; (iii) the link between selenium and selenoproteins expression and the gut microbiota and (iv) analytical methods and pitfalls for the absolute quantification of selenoproteins and selenometabolites.

Selenium and selenium species in the etiology of Alzheimer's dementia: The potential for bias of the case-control study design

Several human studies imply that the trace element selenium and its species may influence the onset of neurological disease, including Alzheimer's dementia (AD). Nevertheless, the literature is conflicting, with reported associations between exposure and risk in opposite direction, possibly due to biases in exposure assessment. After conducting a cohort study that detected an excess AD risk associated with higher levels of inorganic-hexavalent selenium in subjects with mild cognitive impairment (MCI), we investigated the relation between selenium and AD using a case-control study design. We determined cerebrospinal fluid levels of selenium species in 56 MCI participants already included in the cohort study, considered as referents, and in 33 patients with established AD. AD risk was inversely correlated with inorganic selenium species and with the organic form bound to selenoprotein P. Selenium bound to other organo-selenium species was positively correlated with AD risk, suggesting compensatory selenoprotein upregulation following increased oxidative stress. The finding of an increased AD risk associated with inorganic-hexavalent selenium from the cohort study was not replicated. This case-control study yielded entirely different results than those generated by a cohort study with a partially overlapping participant population, suggesting that case-control design does not allow to reliably assess the role of selenium exposure in AD etiology. This inability appears to be due to exposure misclassification, falsely indicating an etiologic role of selenium deficiency likely due to reverse causation, and involving most selenium species. The case-control design may instead lend insights into the pathologic process underlying disease progression.

Identification of FAM96B as a novel selenoprotein W binding partner in the brain

Selenoprotien W (SelW) plays a key role in brain development, although the exact biological function and mechanisms remain unclear. We performed a yeast two-hybrid screen on a human fetal brain cDNA library and identified FAM96B as a novel binding partner of SelW. FRET analyses confirmed the interaction between SelW' and FAM96B. The mutated SelW' construct was cloned and overexpressed in E. coli, and a pull-down assay verified a direct interaction between SelW' and FAM96B. Finally, Co-Immunoprecipitation on murine brain tissue proteins demonstrated an endogenous interaction between the two proteins in the brain. Taken together, our findings prove a direct interaction between SelW and FAM96B, which may provide new insights into the role of SelW in brain development and neurodegenerative diseases.

The redox balance of healthy Brazilian adults is associated with GPX1 Pro198Leu and -602A/G polymorphisms, selenium status, and anthropometric and lifestyle parameters

PURPOSE

Considering that oxidative stress is implicated in the pathogenesis and progression of different health conditions, we aimed to evaluate whether the redox balance of a healthy Brazilian population is associated with GPX1 polymorphisms, selenium status, lipid profile, and anthropometric and lifestyle parameters.

METHODS

343 healthy adults were assessed for redox balance markers [glutathione peroxidase (GPx) and superoxide dismutase (SOD) activity; malondialdehyde (MDA) and oxygen radical absorption capacity (ORAC)]; genotyped for the polymorphisms GPX1 Pro198Leu (rs1050450), -602A/G (rs3811699) and Arg5Pro (rs8179169); evaluated for selenium biomarkers (plasma, erythrocyte, and urine) and intake; and assessed for lipid profile. Anthropometric (BMI) and lifestyle data (physical activity, current smoking habit and alcohol consumption) were collected. Multivariable regression models were applied to investigate the possible associations.

RESULTS

Although there were no differences in GPx activity according to GPX1 Pro198Leu and -602A/G polymorphisms, this redox balance marker was positively associated with erythrocyte selenium and negatively associated with the presence of a minor allele of Pro198Leu. SOD activity was positively associated with the presence of a minor allele for these polymorphisms. ORAC showed the same pattern among Leu and G carriers and was positively associated with Leu allele presence, BMI and alcohol intake. MDA was only associated negatively with the male sex and plasma selenium.

CONCLUSIONS

Our findings suggest that the redox balance of a Brazilian healthy population is associated with GPX1 polymorphisms (Pro198Leu and -602A/G), selenium status, BMI, sex, smoking habit and alcohol consumption.

Supranutritional Sodium Selenate Supplementation Delivers Selenium to the Central Nervous System: Results from a Randomized Controlled Pilot Trial in Alzheimer's Disease

Insufficient supply of selenium to antioxidant enzymes in the brain may contribute to Alzheimer's disease (AD) pathophysiology; therefore, oral supplementation may potentially slow neurodegeneration. We examined selenium and selenoproteins in serum and cerebrospinal fluid (CSF) from a dual-dose 24-week randomized controlled trial of sodium selenate in AD patients, to assess tolerability, and efficacy of selenate in modulating selenium concentration in the central nervous system (CNS). A pilot study of 40 AD cases was randomized to placebo, nutritional (0.32 mg sodium selenate, 3 times daily), or supranutritional (10 mg, 3 times daily) groups. We measured total selenium, selenoproteins, and inorganic selenium levels, in serum and CSF, and compared against cognitive outcomes. Supranutritional selenium supplementation was well tolerated and yielded a significant (p < 0.001) but variable (95% CI = 13.4-24.8 μg/L) increase in CSF selenium, distributed across selenoproteins and inorganic species. Reclassifying subjects as either responsive or non-responsive based on elevation in CSF selenium concentrations revealed that responsive group did not deteriorate in Mini-Mental Status Examination (MMSE) as non-responsive group (p = 0.03). Pooled analysis of all samples revealed that CSF selenium could predict change in MMSE performance (Spearman's rho = 0.403; p = 0.023). High-dose sodium selenate supplementation is well tolerated and can modulate CNS selenium concentration, although individual variation in selenium metabolism must be considered to optimize potential benefits in AD. The Vel002 study is listed on the Australian and New Zealand Clinical Trials Registry ( http://www.anzctr.org.au /), ID: ACTRN12611001200976.

Sodium selenite protects from 3-nitropropionic acid-induced oxidative stress in cultured primary cortical neurons

Selenium (Se) is an essential trace element for humans; its intake is needed to allow the proper synthesis of 25 different selenoproteins that are necessary to the normal functioning of several organs, including the brain. Accordingly, decreased Se levels have been associated with neurological disorders. In the present study, we investigated the potential beneficial effects of Se, as sodium selenite, against 3-nitropropionic acid (3-NP)-induced oxidative stress in primary cultures of mouse cortical neurons. 3-NP treatment caused a significant decrease in cellular viability, which was accompanied by decreases in mitochondrial complex II activity and reduced glutathione (GSH) content, as well as increases in reactive oxygen species (ROS) generation and oxidized glutathione (GSSG) levels. Sodium selenite pretreatment (6 days) attenuated 3-NP-induced decrease in cell viability. In addition, sodium selenite pretreatment significantly protected against 3-NP-induced increase in ROS generation and decrease in GSH/GSSG ratio. Of note, sodium selenite pretreatment did not change 3-NP-induced decrease of mitochondrial complex II activity, suggesting that Se modulates secondary events resultant from 3-NP-induced mitochondrial dyshomeostasis. In addition, sodium selenite pretreatment significantly increased glutathione peroxidase (GPx) activity. Our data provide insights into the mechanism of protection by sodium selenite, which is related, at least in part, to GPx induction.

Selenium, selenoprotein P, and Alzheimer's disease: is there a link?

The essential trace element, selenium (Se), is crucial to the brain but it may be potentially neurotoxic, depending on dosage and speciation; Se has been discussed for decades in relation to Alzheimer's disease (AD). Selenoprotein P (SELENOP) is a secreted heparin-binding glycoprotein which serves as the main Se transport protein in mammals. In vivo studies showed that this protein might have additional functions such as a contribution to redox regulation. The current review focuses on recent research on the possible role of SELENOP in AD pathology, based on model and human studies. The review also briefly summarizes results of epidemiological studies on Se supplementation in relation to brain diseases, including PREADViSE, EVA, and AIBL. Although mainly positive effects of Se are assessed in this review, possible detrimental effects of Se supplementation or exposure, including potential neurotoxicity, are also mentioned. In relation to AD, various roles of SELENOP are discussed, i.e. as the means of Se delivery to neurons, as an antioxidant, in cytoskeleton assembly, in interaction with redox-active metals (copper, iron, and mercury) and with misfolded proteins (amyloid-beta and hyperphosphorylated tau-protein).

Dietary supplementation with Allium hirtifolium and/or Astragalus hamosus improved memory and reduced neuro-inflammation in the rat model of Alzheimer’s disease

Allium hirtifolium Boiss and Astragalus hamosus L. are mentioned in Iranian traditional medicine documentation as therapy for a kind of dementia with the features and symptoms similar to those of Alzheimer’s disease (AD). In the present study, the effects of these herbs on neuro-inflammation and memory have been evaluated as new therapies in amyloid beta (Aβ)-induced memory impairment model. Separate groups of rats were fed with A. hirtifolium or A. hamosus extract (both 100 mg/(kg·day)−1) started 1 week before stereotaxic surgery to 24 h before behavioral testing (totally, for 16 successive days). The effects of oral administration of mentioned extracts on the memory and neuro-inflammation were assessed in the Aβ-injected rats. The results of this study showed that oral administration of both A. hirtifolium and A. hamosus improved the memory, examined by using Y-maze test and shuttle box apparatus. Also, Western blotting analysis of cyclooxygenase-2, interleukin-1β, and tumor necrosis factor-α showed that these herbs have ameliorating effects against the neuro-inflammation caused by Aβ. These findings suggest that the use of A. hirtifolium and A. hamosus as herbal therapy may be suitable for decreasing AD-related symptoms and treatment of other neurodegenerative disorders.

Brain, immune system and selenium: a starting point for a new diagnostic marker for Alzheimer's disease?

The clinical diagnosis of Alzheimer's disease (AD) is based primarily on neuropsychological tests, which assess the involutive damage, and imaging techniques that evaluate morphologic changes in the brain. Currently available diagnostic tests do not show complete specificity and do not permit accurate differentiation between AD and other forms of senile dementia. The correlation of these tests with laboratory investigations based on biochemical parameters could increase the certainty of diagnosis. In recent years, several biochemical markers for the diagnosis of AD have been proposed, but in most cases they show a limited specificity and their application is invasive, requiring, in general, sampling of cerebrospinal fluid. Thus, the use of a peripheral biochemical marker could represent a valuable complement for the diagnosis of this disease. Several studies have shown a relationship between neurodegenerative disorders typical of the ageing process, weakening of the immune system and alterations in the levels of selenium and of the antioxidant selenoenzymes in brain tissues and blood cells. Among blood cells, neutrophil granulocytes uniquely express the selenoenzyme methionine sulfoxide reductase B1 (MsrB1). In a preliminary analysis carried out on neutrophils from subjects affected by AD, we observed a significant decline in MsrB1 activity compared to normal subjects. Therefore, we deem it of particular interest to explore the potential use of MsrB1 as a selective peripheral marker for the diagnosis of AD.

Se-Methylselenocysteine Ameliorates Neuropathology and Cognitive Deficits by Attenuating Oxidative Stress and Metal Dyshomeostasis in Alzheimer Model Mice

SCOPE

Se-methylselenocysteine (SMC) is a major selenocompound in selenium (Se)-enriched plants. Se is vital for proper brain function, and Se-deficient is considered to be related with cognitive impairment and Alzheimer's disease (AD). The potential of SMC in intervening cognitive deficits and neuropathology of triple transgenic AD (3 × Tg-AD) mice is evaluated for the first time.

METHODS AND RESULTS

AD mice are treated with SMC (0.75 mg kg^-1 BW per day) in their drinking water for 10 months. Results reveal that SMC 1) reduces oxidative stress and neuro-inflammation; 2) modulates the distribution and levels of several metal ions; 3) decreases amyloid-β peptide (Aβ) generation by inhibiting the expression of its precursor protein APP and β-secretase (BACE1); and 4) attenuates tau hyperphosphorylation and neurofibrillary tangles (NFT) formation via promoting protein phosphatase 2A (PP2A) activity, thereby preserving synaptic proteins and neuron activities and finally improving spatial learning and memory deficits in AD model mice. The authors suggest that the inhibitory effect of SMC on MEK/ERK activation may play a critical role in intervening AD progression.

CONCLUSIONS

These results reveal that SMC is powerful in ameliorating AD-related neuropathology and cognitive deficits via modulating oxidative stress, metal homeostasis, and extracellular signal-regulated kinase (ERK) activation.

Reversal of memory and neuropsychiatric symptoms and reduced tau pathology by selenium in 3xTg-AD mice

Accumulation of amyloid-β plaques and tau contribute to the pathogenesis of Alzheimer’s disease (AD), but it is unclear whether targeting tau pathology by antioxidants independently of amyloid-β causes beneficial effects on memory and neuropsychiatric symptoms. Selenium, an essential antioxidant element reduced in the aging brain, prevents development of neuropathology in AD transgenic mice at early disease stages. The therapeutic potential of selenium for ameliorating or reversing neuropsychiatric and cognitive behavioral symptoms at late AD stages is largely unknown. Here, we evaluated the effects of chronic dietary sodium selenate supplementation for 4 months in female 3xTg-AD mice at 12–14 months of age. Chronic sodium selenate treatment efficiently reversed hippocampal-dependent learning and memory impairments, and behavior- and neuropsychiatric-like symptoms in old female 3xTg-AD mice. Selenium significantly decreased the number of aggregated tau-positive neurons and astrogliosis, without globally affecting amyloid plaques, in the hippocampus of 3xTg-AD mice. These results indicate that selenium treatment reverses AD-like memory and neuropsychiatric symptoms by a mechanism involving reduction of aggregated tau and/or reactive astrocytes but not amyloid pathology. These results suggest that sodium selenate could be part of a combined therapeutic approach for the treatment of memory and neuropsychiatric symptoms in advanced AD stages.

Selenium Levels in Serum, Red Blood Cells, and Cerebrospinal Fluid of Alzheimer's Disease Patients: A Report from the Australian Imaging, Biomarker & Lifestyle Flagship Study of Ageing (AIBL)

Selenium (Se) protects cells against oxidative stress damage through a range of bioactive selenoproteins. Increased oxidative stress is a prominent feature of Alzheimer's disease (AD), and previous studies have shown that Se deficiency is associated with age-related cognitive decline. In this study, we assessed Se status in different biofluids from a subgroup of participants in the Australian Imaging, Biomarkers and Lifestyle Flagship Study of Ageing. As Se in humans can either be an active component of selenoproteins or inactive via non-specific incorporation into other proteins, we used both size exclusion chromatography-inductively coupled plasma-mass spectrometry (SEC-ICP-MS) and tandem mass spectrometry to characterize selenoproteins in serum. We observed no differences in total Se concentration in serum or cerebrospinal fluid of AD subjects compared to mildly cognitively impairment patients and healthy controls. However, Se levels in erythrocytes were decreased in AD compared to controls. SEC-ICP-MS analysis revealed a dominant Se-containing fraction. This fraction was subjected to standard protein purification and a bottom-up proteomics approach to confirm that the abundant Se in the fraction was due, in part, to selenoprotein P. The lack of change in the Se level is at odds with our previous observations in a Brazilian population deficient in Se, and we attribute this to the Australian cohort being Se-replete.

The Relationship Between Copper, Iron, and Selenium Levels and Alzheimer Disease

This study aimed to evaluate the concentrations of copper, iron, and selenium in elderly people with Alzheimer disease (AD), comparing the same parameters in a paired group of healthy people, in order to verify if the amount of these metals may influence the cognitive impairment progression. Patients' cognitive impairment was evaluated by Clinical Dementia Rating (CDR). The elementary quantification of erythrocytes was performed by inductively coupled plasma mass spectrometry technique. The statistical analyses were carried out by SPSS software 20.0 version, employing Shapiro-Wilk, Wilcoxon, Kruskall-Wallis, and Spearman correlation tests, considering significant results of p < 0.05. The sample was composed of 34% (n = 11) of women and 66% (n = 21) of men in each group. The AD group was characterized by a higher concentration of copper (p < 0.0001) and iron (p < 0.0001); however, there is no significant difference in selenium level. The analyses of the metal levels in different stages of AD were not significant in CDR-1, however in CDR-2 and CDR-3, elevated levels of copper and iron were observed; in CDR-3 patients, the level of selenium was lower (p < 0.008) compared to that of healthy controls. Patients with Alzheimer disease studied present increase in biometal blood levels, especially of copper and iron, and such increase can be different according to the disease stage and can cause more impairment cognitive functions in AD.

Evidence for widespread, severe brain copper deficiency in Alzheimer's dementia

Datasets comprising simultaneous measurements of many essential metals in Alzheimer's disease (AD) brain are sparse, and available studies are not entirely in agreement. To further elucidate this matter, we employed inductively-coupled-plasma mass spectrometry to measure post-mortem levels of 8 essential metals and selenium, in 7 brain regions from 9 cases with AD (neuropathological severity Braak IV-VI), and 13 controls who had normal ante-mortem mental function and no evidence of brain disease. Of the regions studied, three undergo severe neuronal damage in AD (hippocampus, entorhinal cortex and middle-temporal gyrus); three are less-severely affected (sensory cortex, motor cortex and cingulate gyrus); and one (cerebellum) is relatively spared. Metal concentrations in the controls differed among brain regions, and AD-associated perturbations in most metals occurred in only a few: regions more severely affected by neurodegeneration generally showed alterations in more metals, and cerebellum displayed a distinctive pattern. By contrast, copper levels were substantively decreased in all AD-brain regions, to 52.8-70.2% of corresponding control values, consistent with pan-cerebral copper deficiency. This copper deficiency could be pathogenic in AD, since levels are lowered to values approximating those in Menkes' disease, an X-linked recessive disorder where brain-copper deficiency is the accepted cause of severe brain damage. Our study reinforces others reporting deficient brain copper in AD, and indicates that interventions aimed at safely and effectively elevating brain copper could provide a new experimental-therapeutic approach.

Metals and neurodegenerative diseases. A systematic review

Neurodegenerative processes encompass a large variety of diseases with different pathological patterns and clinical presentation such as Amyotrophic Lateral Sclerosis (ALS), Alzheimer Disease (AD) and Parkinson's disease (PD). Genetic mutations have a known causative role, but the majority of cases are likely to be probably caused by a complex gene-environment interaction. Exposure to metals has been hypothesized to increase oxidative stress in brain cells leading to cell death and neurodegeneration. Neurotoxicity of metals has been demonstrated by several in vitro and in vivo experimental studies and it is likely that each metal could be toxic through specific pathways. The possible pathogenic role of different metals has been supported by some epidemiological evidences coming from occupational and ecological studies. In order to assess the possible association between metals and neurodegenerative disorders, several case-control studies have also been carried out evaluating the metals concentration in different biological specimens such as blood/serum/plasma, cerebrospinal fluid (CSF), nail and hair, often reporting conflicting results. This review provides an overview of our current knowledge on the possible association between metals and ALS, AD and PD as main neurodegenerative disorders.

Relation of plasma selenium and lipid peroxidation end products in patients with Alzheimer's disease

Increased oxidative stress in the brain during the course of Alzheimer's disease (AD) leads to an imbalance of antioxidants and formation of free radical reaction end-products which may be detected in blood as fluorescent lipofuscin-like pigments (LFPs). The aim of this study was to evaluate and compare LFPs with plasma selenium concentrations representing an integral part of the antioxidant system. Plasma samples from subjects with AD dementia (ADD; n=11), mild cognitive impairment (MCI; n=17) and controls (n=12), were collected. The concentration of selenium was measured using atomic absorption spectroscopy. LFPs were analyzed by fluorescence spectroscopy and quantified for different fluorescent maxima and then correlated with plasma selenium. Lower levels of selenium were detected in MCI and ADD patients than in controls (P=0.003 and P=0.049, respectively). Additionally, higher fluorescence intensities of LFPs were observed in MCI patients than in controls in four fluorescence maxima and higher fluorescence intensities were also observed in MCI patients than in ADD patients in three fluorescence maxima, respectively. A negative correlation between selenium concentrations and LFPs fluorescence was observed in the three fluorescence maxima. This is the first study focused on correlation of plasma selenium with specific lipofuscin-like products of oxidative stress in plasma of patients with Alzheimer´s disease and mild cognitive impairment.

Lower brain and blood nutrient status in Alzheimer's disease: Results from meta-analyses

INTRODUCTION

Alzheimer's disease (AD) patients are at risk of nutritional insufficiencies because of physiological and psychological factors. Recently, we showed the results of the meta-analyses indicating lower plasma levels of vitamins A, B12, C, E, and folate in AD patients compared with cognitively intact elderly controls (controls). Now, additional and more extensive literature searches were performed selecting studies which compare blood and brain/cerebrospinal fluid (CSF) levels of vitamins, minerals, trace elements, micronutrients, and fatty acids in AD patients versus controls.

METHODS

The literature published after 1980 in Cochrane Central Register of Controlled Trials, Medline, and Embase electronic databases was systematically analyzed using Preferred Reporting Items for Systematic reviews and Meta-Analyses guidelines to detect studies meeting the selection criteria. Search terms used are as follows: AD patients, Controls, vitamins, minerals, trace elements, micronutrients, and fatty acids. Random-effects meta-analyses using a linear mixed model with correction for age differences between AD patients and controls were performed when four or more publications were retrieved for a specific nutrient.

RESULTS

Random-effects meta-analyses of 116 selected publications showed significant lower CSF/brain levels of docosahexaenoic acid (DHA), choline-containing lipids, folate, vitamin B12, vitamin C, and vitamin E. In addition, AD patients showed lower circulatory levels of DHA, eicosapentaenoic acid, choline as phosphatidylcholine, and selenium.

CONCLUSION

The current data show that patients with AD have lower CSF/brain availability of DHA, choline, vitamin B12, folate, vitamin C, and vitamin E. Directionally, brain nutrient status appears to parallel the lower circulatory nutrient status; however, more studies are required measuring simultaneously circulatory and central nutrient status to obtain better insight in this observation. The brain is dependent on nutrient supply from the circulation, which in combination with nutrient involvement in AD-pathophysiological mechanisms suggests that patients with AD may have specific nutritional requirements. This hypothesis could be tested using a multicomponent nutritional intervention.

Brazil nuts: Nutritional composition, health benefits and safety aspects

Brazil nuts are among the richest selenium food sources, and studies have considered this Amazonian nut as an alternative for selenium supplementation. Besides selenium, Brazil nuts present relevant content of other micronutrients such as magnesium, copper, and zinc. The nutritional composition of nuts, also characterized by adequate fatty acid profile and high content of protein and bioactive compounds, has many health benefits. In the present review, we examine the nutritional composition of Brazil nuts, comparing it with other nuts, and describe the relevance of possible contaminants and metal toxicants observed in this nut for human health. Furthermore, we report different trials available in the literature, which demonstrate positive outcomes such as modulation of the lipid serum profile, enhancement of the antioxidant system and improvement of anti-inflammatory response. These effects have been assessed under different conditions, such as cognitive impairment, dyslipidemia, cancer, and renal failure.

Zinc and selenium status in critically ill patients according to severity stratification

OBJECTIVE

The aim of this study was to evaluate the concentrations of zinc and selenium in different biological materials and to associate them with the clinical severity score according to the Simplified Acute Physiology Score (SAPS) III.

METHODS

The study was conducted in a 10-bed general intensive care unit of the Américo Brasiliense State Hospital/SP, with 95 patients stratified by the SAPS III score cutoff points (63.5 points) as less or more severe and by the diagnosis of sepsis. Analyses of zinc and selenium concentrations in plasma, erythrocytes, and urine were conducted.

RESULTS

Plasma concentrations were found to be lower than the reference values for both micronutrients (8.4 ± 4 and 0.18 ± 0.06 μmol/L, respectively, for zinc and selenium), and urinary zinc concentration was higher than the reference (38.6 ± 35.8 μmol/24 h). The mean selenium plasma concentration was significantly lower in patients with greater severity, which was not observed for zinc (P > 0.05). The mean selenium plasma and erythrocyte concentrations were significantly different between the groups diagnosed with sepsis, which was not observed in the analysis of zinc. Albumin levels (r = -0.26; P = 0.01) and C-reactive protein (r = 0.40; P < 0.001) correlated with the SAPS III severity score.

CONCLUSION

Plasma concentrations of zinc and selenium are low in critically ill patients upon admission to the intensive care unit and may make these patients more susceptible to oxidative stress. The low concentration of erythrocyte selenium may represent an inadequate intake by this population. Additional studies using new biomarkers should be performed with the objective of identifying values for the local population.

The APOE ε4 Allele Is Associated with Lower Selenium Levels in the Brain: Implications for Alzheimer's Disease

The antioxidant activity of selenium, which is mainly conferred by its incorporation into dedicated selenoproteins, has been suggested as a possible neuroprotective approach for mitigating neuronal loss in Alzheimer's disease. However, there is inconsistent information with respect to selenium levels in the Alzheimer's disease brain. We examined the concentration and cellular compartmentalization of selenium in the temporal cortex of Alzheimer's disease and control brain tissue. We found that Alzheimer's disease was associated with decreased selenium concentration in both soluble (i.e., cytosolic) and insoluble (i.e., plaques and tangles) fractions of brain homogenates. The presence of the APOE ε4 allele correlated with lower total selenium levels in the temporal cortex and a higher concentration of soluble selenium. Additionally, we found that age significantly contributed to lower selenium concentrations in the peripheral membrane-bound and vesicular fractions. Our findings suggest a relevant interaction between APOE ε4 and selenium delivery into brain, and show changes in cellular selenium distribution in the Alzheimer's disease brain.

A systematic review and meta-analysis of the circulatory, erythrocellular and CSF selenium levels in Alzheimer's disease: A metal meta-analysis (AMMA study-I)

BACKGROUND

Available studies in the literature on the selenium levels in Alzheimer's disease (AD) are inconsistent with some studies reporting its decrease in the circulation, while others reported an increase or no change as compared to controls.

AIM

The objective of this study was to perform a meta-analysis of circulatory (plasma/serum and blood), erythrocyte and cerebrospinal fluid (CSF) selenium levels in AD compared controls. We also performed a meta-analysis of the correlation coefficients (r) to demonstrate the associations between selenium and glutathione peroxidase (GPx) in AD patients.

METHODS

All major databases were searched for eligible studies. We included 12 case-control/observational studies reporting selenium concentrations in AD and controls. Pooled-overall effect size as standardized mean difference (SMD) and pooled r-values were generated using Review Manager 5.3 and MedCalc 15.8 software.

RESULTS

Random-effects meta-analysis indicated a decrease in circulatory (SMD=-0.44), erythrocellular (SMD=-0.52) and CSF (SMD=-0.14) selenium levels in AD patients compared to controls. Stratified meta-analysis demonstrated that the selenium levels were decreased in both the subgroups with (SMD=-0.55) and without (SMD=-0.37) age matching between AD and controls. Our results also demonstrated a direct association between decreased selenium levels and GPx in AD.

CONCLUSION

This meta-analysis suggests that circulatory selenium concentration is significantly lower in AD patients compared to controls and this decrease in selenium is directly correlated with an important antioxidant enzyme, the GPx, in AD.

Selenoprotein S is required for clearance of C99 through endoplasmic reticulum-associated degradation

Amyloid beta precursor protein (APP) is normally cleaved by α-secretase, but can also be cleaved by β-secretase (BACE1) to produce C99 fragments in the endoplasmic reticulum (ER) membrane. C99 is subsequently cleaved to amyloid β (Aβ), the aggregation of which is known to cause Alzheimer's disease. Therefore, C99 removing is for preventing the disease. Selenoprotein S (SelS) is an ER membrane protein participating in endoplasmic reticulum-associated degradation (ERAD), one of the stages in resolving ER stress of misfolded proteins accumulated in the ER. ERAD has been postulated as one of the processes to degrade C99; however, it remains unclear if the degradation depends on SelS. In this study, we investigated the effect of SelS on C99 degradation. We observed that both SelS and C99 were colocalized in the membrane fraction of mouse neuroblastoma Neuro2a (N2a) cells. While the level of SelS was increased by ER stress, the level of C99 was decreased. However, despite the induction of ER stress, there was no change in the amount of C99 in SelS knock-down cells. The interaction of C99 with p97(VCP), an essential component of the ERAD complex, did not occur in SelS knock-down cells. The ubiquitination of C99 was decreased in SelS knock-down cells. We also found that the extracellular amount of Aβ^1-42 was relatively higher in SelS knock-down cells than in control cells. These results suggest that SelS is required for C99 degradation through ERAD, resulting in inhibition of Aβ production.

Sodium selenate treatment improves symptoms and seizure susceptibility in a malin-deficient mouse model of Lafora disease

OBJECTIVE

To search for new therapies aimed at ameliorating the neurologic symptoms and epilepsy developing in patients with Lafora disease.

METHODS

Lafora disease is caused by loss-of-function mutations in either the EPM2A or EPM2B genes. Epm2a^-/- and Epm2b^-/- mice display neurologic and behavioral abnormalities similar to those found in patients. Selenium is a potent antioxidant and its deficiency has been related to the development of certain diseases, including epilepsy. In this study, we investigated whether sodium selenate treatment improved the neurologic alterations and the hyperexcitability present in the Epm2b^-/- mouse model.

RESULTS

Sodium selenate ameliorates some of the motor and memory deficits and the sensitivity observed with pentylenetetrazol (PTZ) treatments in Epm2b^-/- mice. Neuronal degeneration and gliosis were also diminished after sodium selenate treatment.

SIGNIFICANCE

Sodium selenate could be beneficial for ameliorating some symptoms that present in patients with Lafora disease.

Sodium selenate regulates the brain ionome in a transgenic mouse model of Alzheimer's disease

Many studies have shown that imbalance of mineral metabolism may play an important role in Alzheimer's disease (AD) progression. It was recently reported that selenium could reverse memory deficits in AD mouse model. We carried out multi-time-point ionome analysis to investigate the interactions among 15 elements in the brain by using a triple-transgenic mouse model of AD with/without high-dose sodium selenate supplementation. Except selenium, the majority of significantly changed elements showed a reduced level after 6-month selenate supplementation, especially iron whose levels were completely reversed to normal state at almost all examined time points. We then built the elemental correlation network for each time point. Significant and specific elemental correlations and correlation changes were identified, implying a highly complex and dynamic crosstalk between selenium and other elements during long-term supplementation with selenate. Finally, we measured the activities of two important anti-oxidative selenoenzymes, glutathione peroxidase and thioredoxin reductase, and found that they were remarkably increased in the cerebrum of selenate-treated mice, suggesting that selenoenzyme-mediated protection against oxidative stress might also be involved in the therapeutic effect of selenate in AD. Overall, this study should contribute to our understanding of the mechanism related to the potential use of selenate in AD treatment.

Selenium in the Therapy of Neurological Diseases. Where is it Going?

Selenium (₃₄Se), an antioxidant trace element, is an important regulator of brain function. These beneficial properties that Se possesses are attributed to its ability to be incorporated into selenoproteins as an amino acid. Several selenoproteins are expressed in the brain, in which some of them, e.g. glutathione peroxidases (GPxs), thioredoxin reductases (TrxRs) or selenoprotein P (SelP), are strongly involved in antioxidant defence and in maintaining intercellular reducing conditions. Since increased oxidative stress has been implicated in neurological disorders, including Parkinson’s disease, Alzheimer’s disease, stroke, epilepsy and others, a growing body of evidence suggests that Se depletion followed by decreased activity of Se-dependent enzymes may be important factors connected with those pathologies. Undoubtedly, the remarkable progress that has been made in understanding the biological function of Se in the brain has opened up new potential possibilities for the treatment of neurological diseases by using Se as a potential drug. However, further research in the search for optimal Se donors is necessary in order to achieve an effective and safe therapeutic income.

GPX1 Pro198Leu polymorphism and GSTM1 deletion do not affect selenium and mercury status in mildly exposed Amazonian women in an urban population

Mercury is potent toxicant element, but its toxicity can be reduced by forming a complex with selenium for safe excretion. Considering the impact of mercury exposure in the Amazon region and the possible interaction between these two elements, we aimed to assess the effects of Pro198Leu polymorphism to GPX1 and GSTM1 deletion, on mercury levels in a population from Porto Velho, an urban locality in the Brazilian Amazon region. Two hundred women from the capital city of Rondônia state were recruited for this study with 149 deemed suitable to participate. We assessed dietary intake using 24-hour recall. Selenium levels in plasma and erythrocytes were measured using hydride generation quartz tube atomic absorption spectroscopy and total hair mercury using cold vapor atomic absorption spectrometry. Oxidative stress parameters (GPx activity, oxygen radical absorbency capacity [ORAC] and malondialdehyde [MDA]) were also analyzed. All participants were genotyped for Pro198Leu polymorphism and GSTM1 deletion. We observed that this population presented high prevalence of selenium deficiency, and also low levels of mercury, likely due to food habits that did not include selenium-rich food sources or significant consumption of fish (mercury biomagnifiers) regularly. Univariate statistical analysis showed that Pro198Leu and GSTM1 genotypes did not affect selenium and mercury levels in this population. Pro198Leu polymorphism and GSTM1 deletion had no effect on mercury levels in mildly exposed people, suggesting these genetic variants impact mercury levels only in highly exposed populations.

Protective Effects of Selol Against Sodium Nitroprusside-Induced Cell Death and Oxidative Stress in PC12 Cells

Selol is an organic selenitetriglyceride formulation containing selenium at +4 oxidation level that can be effectively incorporated into catalytic sites of of Se-dependent antioxidants. In the present study, the potential antioxidative and cytoprotective effects of Selol against sodium nitroprusside (SNP)-evoked oxidative/nitrosative stress were investigated in PC12 cells and the underlying mechanisms analyzed. Spectrophoto- and spectrofluorimetic methods as well as fluorescence microscopy were used in this study; mRNA expression was quantified by real-time PCR. Selol dose-dependently improved the survival and decreased the percentage of apoptosis in PC12 cells exposed to SNP. To determine the mechanism of this protective action, the effect of Selol on free radical generation and on antioxidative potential was evaluated. Selol offered significant protection against the elevation of reactive oxidative species (ROS) evoked by SNP. Moreover, this compound restored glutathione homeostasis by ameliorating the SNP-evoked disturbance of GSH/GSSG ratio. The protective effect exerted by Selol was associated with the prevention of SNP-mediated down-regulation of antioxidative enzymes: glutathione peroxidase (Se-GPx), glutathione reductase (GR), and thioredoxin reductase (TrxR). Finally, GPx inhibition significantly abolished the cytoprotective effect of Selol. In conclusion, these results suggest that Selol effectively protected PC12 cells against SNP-induced oxidative damage and death by adjusting free radical levels and antioxidant system, and suppressing apoptosis. Selol could be successfully used in the treatments of diseases that involve oxidative stress and resulting apoptosis.

Treatment strategies in Alzheimer's disease: a review with focus on selenium supplementation

Alzheimer's disease (AD) is a neurodegenerative disorder presenting one of the biggest healthcare challenges in developed countries. No effective treatment exists. In recent years the main focus of AD research has been on the amyloid hypothesis, which postulates that extracellular precipitates of beta amyloid (Aβ) derived from amyloid precursor protein (APP) are responsible for the cognitive impairment seen in AD. Treatment strategies have been to reduce Aβ production through inhibition of enzymes responsible for its formation, or to promote resolution of existing cerebral Aβ plaques. However, these approaches have failed to demonstrate significant cognitive improvements. Intracellular rather than extracellular events may be fundamental in AD pathogenesis. Selenate is a potent inhibitor of tau hyperphosphorylation, a critical step in the formation of neurofibrillary tangles. Some selenium (Se) compounds e.g. selenoprotein P also appear to protect APP against excessive copper and iron deposition. Selenoproteins show anti-inflammatory properties, and protect microtubules in the neuronal cytoskeleton. Optimal function of these selenoenzymes requires higher Se intake than what is common in Europe and also higher intake than traditionally recommended. Supplementary treatment with N-acetylcysteine increases levels of the antioxidative cofactor glutathione and can mediate adjuvant protection. The present review discusses the role of Se in AD treatment and suggests strategies for AD prevention by optimizing selenium intake, in accordance with the metal dysregulation hypothesis. This includes in particular secondary prevention by selenium supplementation to elderly with mild cognitive impairment.

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.

Pro198Leu polymorphism affects the selenium status and GPx activity in response to Brazil nut intake

Selenoproteins play important roles in antioxidant mechanisms, but it is hypothesised that single polymorphism nucleotides (SNPs) may affect their function.

Selenomethionine reduces the deposition of beta-amyloid plaques by modulating β-secretase and enhancing selenoenzymatic activity in a mouse model of Alzheimer's disease

Effects on Aβ production and the probable connection among selenoenzymes, GSK3β and Aβ pathology by selenomethionine treatment in AD mice.

Effects of Souvenaid on plasma micronutrient levels and fatty acid profiles in mild and mild-to-moderate Alzheimer's disease

INTRODUCTION

Circulating levels of uridine, selenium, vitamins B12, E and C, folate, docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) have been shown to be lower in patients with Alzheimer's disease (AD) than in healthy individuals. These low levels may affect disease pathways involved in synapse formation and neural functioning. Here, we investigated whether, and to what extent, circulating levels of micronutrients and fatty acids can be affected by oral supplementation with Souvenaid (containing a specific nutrient combination), using data derived from three randomized clinical trials (RCT) and an open-label extension (OLE) study with follow-up data from 12 to 48 weeks.

METHODS

Subjects with mild (RCT1, RCT2) or mild-to-moderate AD (RCT3) received active or control product once daily for 12-24 weeks or active product during the 24-week OLE following RCT2 (n = 212-527). Measurements included plasma levels of B vitamins, choline, vitamin E, selenium, uridine and homocysteine and proportions of DHA, EPA and total n-3 long-chain polyunsaturated fatty acids in plasma and erythrocytes. Between-group comparisons were made using t tests or non-parametric alternatives.

RESULTS

We found that 12-24-week active product intake increased plasma and/or erythrocyte micronutrients: uridine; choline; selenium; folate; vitamins B6, B12 and E; and fatty acid levels of DHA and EPA (all p < 0.001). In the OLE study, similar levels were reached in former control product/initial active product users, whereas 24-week continued active product intake showed no suggestion of a further increase in nutrient levels.

CONCLUSIONS

These data show that circulating levels of nutrients known to be decreased in the AD population can be increased in patients with mild and mild-tomoderate AD by 24-48-week oral supplementation with Souvenaid. In addition, to our knowledge, this is the first report of the effects of sustained dietary intake of uridine monophosphate on plasma uridine levels in humans. Uptake of nutrients is observed within 6 weeks, and a plateau phase is reached for most nutrients during prolonged intake, thus increasing the availability of precursors and cofactors in the circulation that may be used for the formation and function of neuronal membranes and synapses in the brain.

Role of environmental contaminants in the etiology of Alzheimer's disease: a review

Alzheimer's dis ease (AD) is a leading cause of mortality in the developed world with 70% risk attributable to genetics. The remaining 30% of AD risk is hypothesized to include environmental factors and human lifestyle patterns. Environmental factors possibly include inorganic and organic hazards, exposure to toxic metals (aluminium, copper), pesticides (organochlorine and organophosphate insecticides), industrial chemicals (flame retardants) and air pollutants (particulate matter). Long term exposures to these environmental contaminants together with bioaccumulation over an individual's life-time are speculated to induce neuroinflammation and neuropathology paving the way for developing AD. Epidemiologic associations between environmental contaminant exposures and AD are still limited. However, many in vitro and animal studies have identified toxic effects of environmental contaminants at the cellular level, revealing alterations of pathways and metabolisms associated with AD that warrant further investigations. This review provides an overview of in vitro, animal and epidemiological studies on the etiology of AD, highlighting available data supportive of the long hypothesized link between toxic environmental exposures and development of AD pathology.

Tricyclic phenothiazine and phenoselenazine derivatives as potential multi-targeting agents to treat Alzheimer's disease

A group of tricyclic phenothiazines (6a, 6b and 7a–l) and phenoselenazines (12a, 12b and 13a–l) was designed, synthesized and evaluated as multi-targeting ligands aimed at the cholinergic, amyloid and oxidative stress pathways of Alzheimer's disease.

Selenium, selenoproteins and neurodegenerative diseases

A review of selenium's essential role in normal brain function and its potential involvement in neurodegenerative diseases.

Sulfur and selenium antioxidants: challenging radical scavenging mechanisms and developing structure-activity relationships based on metal binding

Because sulfur and selenium antioxidants can prevent oxidative damage, numerous animal and clinical trials have investigated the ability of these compounds to prevent the oxidative stress that is an underlying cause of cardiovascular disease, Alzheimer's disease, and cancer, among others. One of the most common sources of oxidative damage is metal-generated hydroxyl radical; however, very little research has focused on determining the metal-binding abilities and structural attributes that affect oxidative damage prevention by sulfur and selenium compounds. In this review, we describe our ongoing investigations into sulfur and selenium antioxidant prevention of iron- and copper-mediated oxidative DNA damage. We determined that many sulfur and selenium compounds inhibit Cu(I)-mediated DNA damage and that DNA damage prevention varies dramatically when Fe(II) is used in place of Cu(I) to generate hydroxyl radical. Oxidation potentials of the sulfur or selenium compounds do not correlate with their ability to prevent DNA damage, highlighting the importance of metal coordination rather than reactive oxygen species scavenging as an antioxidant mechanism. Additional gel electrophoresis, mass spectrometry, and UV-visible studies confirmed sulfur and selenium antioxidant binding to Cu(I) and Fe(II). Ultimately, our studies established that both the hydroxyl-radical-generating metal ion and the chemical environment of the sulfur or selenium significantly affect DNA damage prevention and that metal coordination is an essential mechanism for these antioxidants.

Selenium status in elderly: relation to cognitive decline

Studies show that decreased antioxidant system is related to cognitive decline. Thus we aimed to measure selenium (Se) status in Alzheimer's disease (AD) and mild cognitive impairment (MCI) elderly and compared them with a control group (CG). 27 AD, 17 MCI and 28 control elderly were evaluated. Se concentration was determined in plasma and erythrocyte by using hydride generation atomic absorption spectroscopy. Erythrocyte Se concentration in AD group was lower than CG (43.73±23.02μg/L and 79.15±46.37μg/L; p=0.001), but not statistically different from MCI group (63.97±18.26μg/L; p=0.156). AD group exhibited the lowest plasma Se level (34.49±19.94μg/L) when compared to MCI (61.36±16.08μg/L; p=0.000) and to CG (50.99±21.06μg/L; p=0.010). It is observed that erythrocyte Se decreases as cognition function does. Since erythrocyte reflects longer-term nutritional status, the data point to the importance of the relation between Se exposure and cognitive function. Our findings suggest that the deficiency of Se may contribute to cognitive decline among aging people.

Study of selenium intake and disposition in various matrices based on mathematical algorithms derived from pooled biomonitoring data

Biomonitoring is increasingly used to assess exposure to selenium (Se) in the population. However, there is little harmonization among protocols used in the different studies (varying biological matrices, differences in expression of results (concentrations versus amounts, units)). This makes inter-comparison of biomonitoring results across studies difficult. From a public health risk perspective, it also becomes challenging to estimate baseline levels in biological matrices for populations exposed by various sources. The aim of this study was thus to perform a systematic analysis of the relationship between Se intakes and biological concentrations based on published data. Inclusion and exclusion criteria were used and led to select 75 published biomonitoring data in humans from an extended review of Se biomonitoring studies. This represents 8 628 individuals who provided biological samples aiming at documenting Se exposure and/or Se concentrations in two or more biological matrices. Mathematical algorithms that relate Se intakes to biological concentrations and establish matrix-to-matrix associations were derived from these pooled biomonitoring data. Logarithmic regressions showed good correlations between Se intakes and whole blood concentrations (R(2)=0.884), plasma concentrations (R(2)=0.863) and urinary excretion rates (R(2)=0.958). Blood and plasma concentrations were also strongly related (R(2)=0.874), as were whole blood concentrations and urinary excretion rates (R(2)=0.953). The interpretation of the log-regression coefficients allowed illustrating Se physiology. Se concentrations in plasma tend to plateau when daily intake exceed 150 μg/d, whereas Se in urine increases rapidly above this threshold. The application of the algorithms to other independent data sets in order to reconstruct past Se intakes confirmed that interpretation of results on the basis of Se in integuments may be misleading if external contamination is not avoided. This approach based on pooled data covered a wide range of exposure and the large number of data integrated increased the level of confidence of results.

Selenium and selenoprotein function in brain disorders

Selenoproteins are important for normal brain function, and decreased function of selenoproteins can lead to impaired cognitive function and neurological disorders. This review examines the possible roles of selenoproteins in Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), and epilepsy. Selenium deficiency is associated with cognitive decline, and selenoproteins may be helpful in preventing neurodegeneration in AD. PD is associated with impaired function of glutathione peroxidase selenoenzymes. In HD, selenium deters lipid peroxidation by increasing specific glutathione peroxidases. Selenium deficiency increases risk of seizures in epilepsy, whereas supplementation may help to alleviate seizures. Further studies on the mechanisms of selenoprotein function will increase our understanding of how selenium and selenoproteins can be used in treatment and prevention of brain disorders.

Selenium inadequacy is not associated with oxidative stress in child and adolescent acute lymphocytic leukemia survivors

OBJECTIVE

Acute lymphocytic leukemia (ALL) and its subsequent treatment may provoke increased oxidative stress. The aim of this study was to investigate the antioxidant status of children and adolescents who had received ALL therapy, and to test the hypothesis that selenium (Se) inadequacy is correlated with reduced defenses against oxidative stress in this population.

METHODS

This case-control study involved 24 patients between ages 5 and 13 y who had been treated successfully for ALL (ALL group) and 60 children of similar age and socioeconomic background with no clinical history of leukemia (control group). Dietary intake of Se was evaluated by the 24-h recall method, and the concentrations of Se in plasma, erythrocytes, and urine determined. Antioxidant status was assessed by analysis of the oxidative stress markers, namely, superoxide dismutase (SOD), glutathione peroxidase (GPx), malondialdehyde (MDA), α-tocopherol, and 8-oxo-deoxyguanosine (8-oxo-dG).

RESULTS

There were no between-group differences with respect to plasma (P = 0.122), erythrocyte (P = 0.202), urinary (P = 0.608), or dietary (P = 0.757) levels of Se. GPx activity was significantly (P < 0.001) reduced in the ALL group compared with the control group, whereas SOD activity and MDA concentrations were similar. The concentrations of α-tocopherol and 8-oxo-dG were significantly increased in the ALL group compared with the control group (P < 0.001 and P = 0.031, respectively).

CONCLUSION

All participants were Se inadequate, but such inadequacy was not correlated with reduced defenses against oxidative stress. However, individuals of the ALL group were with increased oxidative stress compared with the control group, possibly due to previous disease and to intensive polychemotherapy.

Plasma nutrient status of patients with Alzheimer's disease: Systematic review and meta-analysis

BACKGROUND

Alzheimer disease (AD) patients are at risk of nutritional insufficiencies because of physiological and psychological factors. Nutritional compounds are postulated to play a role in the pathophysiological processes that are affected in AD. We here provide the first systematic review and meta-analysis that compares plasma levels of micronutrients and fatty acids in AD patients to those in cognitively intact elderly controls. A secondary objective was to explore the presence of different plasma nutrient levels between AD and control populations that did not differ in measures of protein/energy nourishment.

METHODS

We screened literature published after 1990 in the Cochrane Central Register of Controlled Trials, Medline, and Embase electronic databases using Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines for AD patients, controls, micronutrient, vitamins, and fatty acids, resulting in 3397 publications, of which 80 met all inclusion criteria. Status of protein/energy malnutrition was assessed by body mass index, mini nutritional assessment score, or plasma albumin. Meta-analysis, with correction for differences in mean age between AD patients and controls, was performed when more than five publications were retrieved for a specific nutrient.

RESULTS

We identified five or more studies for folate, vitamin A, vitamin B12, vitamin C, vitamin D, vitamin E, copper, iron, and zinc but fewer than five studies for vitamins B1 and B6, long-chain omega-3 fatty acids, calcium, magnesium, manganese, and selenium (the results of the individual publications are discussed). Meta-analysis showed significantly lower plasma levels of folate and vitamin A, vitamin B12, vitamin C, and vitamin E (P < .001), whereas nonsignificantly lower levels of zinc (P = .050) and vitamin D (P = .075) were found in AD patients. No significant differences were observed for plasma levels of copper and iron. A meta-analysis that was limited to studies reporting no differences in protein/energy malnourishment between AD and control populations yielded similar significantly lower plasma levels of folate and vitamin B12, vitamin C, and vitamin E in AD.

CONCLUSIONS

The lower plasma nutrient levels indicate that patients with AD have impaired systemic availability of several nutrients. This difference appears to be unrelated to the classic malnourishment that is well known to be common in AD, suggesting that compromised micronutrient status may precede protein and energy malnutrition. Contributing factors might be AD-related alterations in feeding behavior and intake, nutrient absorption, alterations in metabolism, and increased utilization of nutrients for AD pathology-related processes. Given the potential role of nutrients in the pathophysiological processes of AD, the utility of nutrition may currently be underappreciated and offer potential in AD management.

Nutrition and the risk of Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that accounts for the major cause of dementia, and the increasing worldwide prevalence of AD is a major public health concern. Increasing epidemiological studies suggest that diet and nutrition might be important modifiable risk factors for AD. Dietary supplementation of antioxidants, B vitamins, polyphenols, and polyunsaturated fatty acids are beneficial to AD, and consumptions of fish, fruits, vegetables, coffee, and light-to-moderate alcohol reduce the risk of AD. However, many of the results from randomized controlled trials are contradictory to that of epidemiological studies. Dietary patterns summarizing an overall diet are gaining momentum in recent years. Adherence to a healthy diet, the Japanese diet, and the Mediterranean diet is associated with a lower risk of AD. This paper will focus on the evidence linking many nutrients, foods, and dietary patterns to AD.