Alzheimer's disease and malnutrition: a new etiological hypothesis

Gastrointestinal Dysfunction and Low-Grade Inflammation Associate With Enteric Neuronal Amyloid-β in a Model for Amyloid Pathology

BACKGROUND

Patients suffering from Alzheimer's disease, a progressive neurodegenerative disorder involving cognitive decline and memory impairment, often present with gastrointestinal comorbidities. Accumulating data also indicate that alterations in the gut can modulate Alzheimer's disease pathology, highlighting the need to better understand the link between gastrointestinal abnormalities and neurodegeneration in the brain.

METHODS

To disentangle the pathophysiology of gastrointestinal dysfunction in Alzheimer's disease, we conducted a detailed pathological characterization of the gastrointestinal tract of 5xFAD mice by performing histological analyses, gene expression studies, immunofluorescence labeling and gut function assays.

RESULTS

We found that 5xFAD mice have elevated levels of intestinal amyloid precursor protein and accumulate amyloid-β in enteric neurons. Histopathology revealed that this is associated with mild intestinal inflammation and fibrosis and accompanied by increased expression of proinflammatory cytokines. While overall enteric nervous system composition and organization appeared unaffected, 5xFAD mice have faster gastrointestinal transit.

CONCLUSION

Our findings indicate that amyloid-β accumulation in enteric neurons is associated with low-grade intestinal inflammation and altered motility and suggest that peripheral pathology may cause gastrointestinal dysfunction in Alzheimer's disease patients.

Multi-omics analysis reveals the key factors involved in the severity of the Alzheimer's disease

Alzheimer's disease (AD) is a debilitating neurodegenerative disorder with a global impact, yet its pathogenesis remains poorly understood. While age, metabolic abnormalities, and accumulation of neurotoxic substances are potential risk factors for AD, their effects are confounded by other factors. To address this challenge, we first utilized multi-omics data from 87 well phenotyped AD patients and generated plasma proteomics and metabolomics data, as well as gut and saliva metagenomics data to investigate the molecular-level alterations accounting the host-microbiome interactions. Second, we analyzed individual omics data and identified the key parameters involved in the severity of the dementia in AD patients. Next, we employed Artificial Intelligence (AI) based models to predict AD severity based on the significantly altered features identified in each omics analysis. Based on our integrative analysis, we found the clinical relevance of plasma proteins, including SKAP1 and NEFL, plasma metabolites including homovanillate and glutamate, and Paraprevotella clara in gut microbiome in predicting the AD severity. Finally, we validated the predictive power of our AI based models by generating additional multi-omics data from the same group of AD patients by following up for 3 months. Hence, we observed that these results may have important implications for the development of potential diagnostic and therapeutic approaches for AD patients.

miRNAs and Stem Cells as Promising Diagnostic and Therapeutic Targets for Alzheimer's Disease

Alzheimer's disease (AD) is a cumulative progressive neurodegenerative disease characterized mainly by impairment in cognitive functions accompanied by memory loss, disturbance in behavior and personality, and difficulties in learning. Although the main causes of AD pathogenesis are not fully understood yet, amyloid-β peptides and tau proteins are supposed to be responsible for AD onset and pathogenesis. Various demographic, genetic, and environmental risk factors are involved in AD onset and pathogenesis such as age, gender, several genes, lipids, malnutrition, and poor diet. Significant changes were observed in microRNA (miRNA) levels between normal and AD cases giving hope for a diagnostic procedure for AD through a simple blood test. As yet, only two classes of AD therapeutic drugs are approved by FDA. They are classified as acetylcholinesterase inhibitors and N-methyl-D-aspartate antagonists (NMDA). Unfortunately, they can only treat the symptoms but cannot cure AD or stop its progression. New therapeutic approaches were developed for AD treatment including acitretin due to its ability to cross blood-brain barrier in the brain of rats and mice and induce the expression of ADAM 10 gene, the α-secretase of human amyloid-β protein precursor, stimulating the non-amyloidogenic pathway for amyloid-β protein precursor processing resulting in amyloid-β reduction. Also stem cells may have a crucial role in AD treatment as they can improve cognitive functions and memory in AD rats through regeneration of damaged neurons. This review spotlights on promising diagnostic techniques such as miRNAs and therapeutic approaches such as acitretin and/or stem cells keeping in consideration AD pathogenesis, stages, symptoms, and risk factors.

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.

Dissecting Complex and Multifactorial Nature of Alzheimer's Disease Pathogenesis: a Clinical, Genomic, and Systems Biology Perspective

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by loss of memory and other cognitive functions. AD can be classified into familial AD (FAD) and sporadic AD (SAD) based on heritability and into early onset AD (EOAD) and late onset AD (LOAD) based on age of onset. LOAD cases are more prevalent with genetically complex architecture. In spite of significant research focused on understanding the etiological mechanisms, search for diagnostic biomarker(s) and disease-modifying therapy is still on. In this article, we aim to comprehensively review AD literature on established etiological mechanisms including role of beta-amyloid and apolipoprotein E (APOE) along with promising newer etiological factors such as epigenetic modifications that have been associated with AD suggesting its multifactorial nature. As genomic studies have recently played a significant role in elucidating AD pathophysiology, a systematic review of findings from genome-wide linkage (GWL), genome-wide association (GWA), genome-wide expression (GWE), and epigenome-wide association studies (EWAS) was conducted. The availability of multi-dimensional genomic data has further coincided with the advent of computational and network biology approaches in recent years. Our review highlights the importance of integrative approaches involving genomics and systems biology perspective in elucidating AD pathophysiology. The promising newer approaches may provide reliable means of early and more specific diagnosis and help identify therapeutic interventions for LOAD.

Disability and cognitive impairment in the elderly

Disability and cognitive impairment show similar patterns of increasing frequency with ageing. A review of the published literature shows that there is a cross-sectional relationship between cognitive impairment and disability, independent of demographic, medical, and lifestyle factors. Some instrumental activities of daily living (IADL) items appear more specifically related to cognitive impairment, but cognition and functional impairment are distinct concepts requiring separate assessments. Subjects with low cognitive performances are at higher risk of functional impairment in the following years. Cognitive impairment as well as disability increase the risk of death and institutionalization. Preventive strategies could be directed against the risk factors of cognitive impairment and disability, and would aim to delay the onset of dementia. Prevention of disability associated with cognitive impairment needs further assessment in elderly community-dwellers. Further research is needed to better identify the specific areas cognition involved in the disablement process.

Weight loss precedes dementia in community-dwelling older adults

OBJECTIVE

To determine whether the weight loss associated with Alzheimer's disease precedes or follows the dementia.

DESIGN

Older community-dwelling men (n = 134) and women (n = 165) were followed for 20 years before they were diagnosed as cognitively intact or demented. A repeated measures analysis was used to compare weight change in those who developed Alzheimer's Disease (AD) with those who remained cognitively intact.

MEASUREMENTS

Weight was measured at three clinic visits between 1972-74, 1984-87, and 1990-93. Participants were classified as having probable or possible AD or being cognitively intact at the 1990-93 evaluation. Diagnoses were made by two neurologists and a neuropsychometrist, based on neuropsychological tests and physical examination, using NINCDS-ADRDA criteria.

RESULTS

There were 36 men and 24 women diagnosed with probable or possible AD; they were considered to have mild to moderate dementia based on their test scores and community-dwelling status. Those who developed dementia were older than those diagnosed as cognitively intact. In age-adjusted analyses, both men and women who were later diagnosed with AD had a significant decrease in weight after the baseline visit (P < .001 and P < .003, respectively), but there was no significant weight loss in the men and women who remained cognitively intact. These differences were not explained by lifestyle, depression, or other illness.

CONCLUSION

Weight loss precedes mild to moderate dementia; early weight loss is, therefore, unlikely to be a consequence of AD patients being unable or unwilling to eat.

Deleterious network hypothesis of Alzheimer's disease

Numerous studies indicate that aberrant amyloid precursor protein metabolism, elevated peroxidative damage, depressed energy metabolism and altered calcium homeostasis are four pivotal deleterious factors in the pathogenesis of Alzheimer's disease. Cumulative evidence further suggests that these four factors are intimately interrelated, forming a deleterious network. Based on this new concept of 'deleterious network', a unifying hypothesis-the deleterious network hypothesis of Alzheimer's disease-is proposed. The main ideas of the hypothesis are delineated as follows: increases in free radical damage, alterations in amyloid precursor protein metabolism, impairment of energy metabolism and abnormalities of calcium homeostasis are four cornerstones of a deleterious network. Various risk factors of Alzheimer's disease can triger the network by promoting the occurrence of one of these key components, resulting in the biological abnormalities of Alzheimer's disease. Based on this new theory, a majority of the important observations about Alzheimer's disease can be explained consistently and succinctly.

[Erythrocyte transketolases and Alzheimer disease]

Abnormalities of thiamin metabolism have been reported in senile dementia of Alzheimer's type (SDAT). Transketolases (TK) were studied in 21 patients with SDAT, 24 age-matched controls and 12 chronic alcoholics. Erythrocytes were assessed for their TK activity coefficient (TK-AC, normal value 8.4 +/- 12.6%) and affinity for thaimin pyrophosphate (Km TPP, normal value 17.8 +/- 8.3 mumol). Comparison between study groups and controls demonstrated increased TK-AC in SDAT (16.6 +/- 15.7%, P < 0.05) and chronic alcoholism (43.4 +/- 40.6%, P < 0.05), and increased Km TPP (38.3 +/- 25.2 mumol, P < 0.01) in SDAT only. These findings suggest structural abnormalities of TK rather than vitamin B1 deficiency in SDAT.

Regulation of energy expenditure in aging humans

The regulation of daily energy expenditure and its components in aging humans in considered in this review. Specifically, the effects of age on resting metabolic rate (RMR), the thermic effect of a meal, body composition, and the interaction of these variables with physical activity in both men and women are considered. The possible modulators of the age-related decline in RMR are examined by exploring the influence of alterations in body composition, physical activity, and the sodium-potassium pump. Thereafter, the status of energy requirements in healthy and diseased individuals is examined. New information is presented regarding the use of the doubly-labeled water technique to measure daily energy expenditure and its applicability to the determination of daily energy requirements in free-living older persons.

Environmental risk factors for Alzheimer's disease: their relationship to age of onset and to familial or sporadic types

Data from a case-control study of Alzheimer's disease (AD) were analysed in relation to age of onset and familial/sporadic status. The analyses were restricted to environmental exposures which might injure the brain. Later-onset AD was found to be positively associated with starvation/malnutrition and with nose-picking and negatively with analgesics, while earlier-onset was associated with physical underactivity and nervous breakdown more than 10 years before. Sporadic AD was associated with starvation/malnutrition and with head injury. These analyses merit replication in other large case-control studies of AD.

Oxidative damage in Alzheimer's dementia, and the potential etiopathogenic role of aluminosilicates, microglia and micronutrient interactions

While evidence implicating free radical oxidative processes in the etiopathogenesis of Alzheimer's dementia is accumulating, the specific cellular and biochemical mechanisms involved remain to be identified. The potential pathogenic role of microglial cells in neurodegenerative processes is indicated by the finding that purified murine microglial cells exposed in vitro to various model aluminosilicate particles stimulate the generation of tissue-injurious free radical reactive oxygen metabolites. Analogous inorganic aluminosilicate deposits have been reported to occur in the core of the characteristic senile plaques found in the brains of Alzheimer disease subjects. The possible modulation of free radical oxidative activity by antioxidant micronutrients and pharmacological agents, provides a rational basis for further preventative and therapeutic clinical investigations.

Cephaloconiosis: a free radical perspective on the proposed particulate-induced etiopathogenesis of Alzheimer's dementia and related disorders

By analogy to the etiology of the pneumoconioses, exogenous dust-induced diseases of the lung, and endogenous crystal-induced arthropathies such as gout, it is proposed that Alzheimer's dementia and allied disorders are causally related to the accumulation of fibriform inorganic deposits within the brain. Hence the neonosological term 'Cephaloconiosis'. It is proposed that: 1) either by the extrinsic migration or intrinsic formation and deposition of insoluble and persistent inorganic reactive nidi, the particle-induced generation of tissue-damaging free-radical oxygen metabolites by stimulated brain glial macrophage-type and allied phagocytic cells, provides a rationale for the etiopathogenesis of neurodegenerative processes; 2) the modulation of the injurious oxidative metabolic reaction by micronutrient and pharmacological antioxidant agents is a rational and potentially feasible strategy for future therapeutic clinical investigations.

A study of digestive absorption in four cases of Down's syndrome. Down's syndrome, malnutrition, malabsorption, and Alzheimer's disease

Many data suggest that patients with Down's syndrome (DS) suffer from digestive malabsorption. A fecal test of absorption (search for undigested meat fibers following the ingestion of a measured diet) was conducted in 4 patients with DS. The results point to malabsorption in these patients and support the hypothesis of malabsorption in DS. The etiology of probable malabsorption in DS is discussed. Data are presented suggesting that chronic malnutrition caused by malabsorption could be the cause of the neuropathologic signs of Alzheimer's disease occurring at or slightly before the fourth decade in all patients with DS.

Eating habits in dementia. A descriptive study

The eating habits of 33 patients with dementia were studied. They were assessed by semistructured interview with a relative who was able to act as an informant for the whole period of the dementia. Changes in eating were found to be common and included both increased and decreased food intake, altered food choice, the consumption of inedible substances and disturbances in the process of eating. The clinical significance of these changes and some likely underlying mechanisms are discussed.

Dietary intake and clinical, anthropometric and biochemical indices of malnutrition in elderly demented patients and non-demented subjects

Anthropometric and biochemical indices of nutritional status and weighed dietary intake have been studied in hospitalized patients with senile dementia, demented patients living in the community and age-matched control subjects who were not cognitively impaired. Demented patients were lighter than control subjects, and had a lower body mass index, skinfold thickness, mid-arm circumference and arm muscle bulk. The hospitalized patients were more seriously affected than those living in the community, and body weight was significantly negatively correlated with duration of hospitalization. Over a 6-month period the hospitalized patients showed a further weight loss, while those living in the community did not. Both groups of demented patients had higher intakes of energy, protein, vitamins and minerals than the control subjects. The diet of the hospitalized patients was slightly, but not significantly, superior to that of the patients living in the community. Biochemical evidence of specific vitamin inadequacy was equally prevalent in all three groups of subjects, and there were no significant correlations between the degree of cognitive impairment or behavioural disorder and any of the indices of nutritional state. Clinical signs suggestive of malnutrition were not correlated with either biochemical evidence of deficiency or cognitive impairment and behavioural disturbance.

The risk factors for Alzheimer's disease: a review and a hypothesis

More than 20 risk factors for Alzheimer's disease (AD) have been proposed in the literature. The evidence for them is examined in this review. Amongst those that appear likely to be true risk factors, an attempt is made to identify a common mechanism to which they might contribute. There is some support for a hypothesis that the formation of amyloid plaques is due to the activity of free oxygen radicals. This would be consistent with the association between AD and late age, a family history of Down's syndrome, vascular dementia, head injury, and exposure to phenacetin, organic solvents or vibrating tools. This hypothesis provides a theory-driven lead in the search for further risk factors; if upheld, it would suggest a strategy for treatment and for prevention.

Risk factors and genetic background for Alzheimer's disease

Analytic epidemiology has contributed significantly to the generation and testing of hypotheses of the causes of AD. Several case-control studies have indicated risk factors related to the genetic hypothesis, such as: the presence of cases of either AD or Down's syndrome in other family members and the advanced age of the mother at subject's birth. In this respect recent molecular biology studies on DNA from patients affected by the familial form of AD, have demonstrated a genetic polymorphism localized on chromosome 21. On the same chromosome, the gene coding for beta-amyloid has been also recently localized. Immune, viral and toxic factors, thought to cause AD, have been also investigated in case-control studies, none of them has been found consistently associated with the disease, with the only exception of the head trauma. On the other hand most case-control studies have been carried out in younger cases and no large studies are yet available for late onset patients.

Changes in eating in dementia

Changes in eating and weight are not uncommon in dementia although they have yet to be systematically studied. These changes are of clinical importance since they can seriously affect patients' physical health and they are often a major problem for carers. These changes are also of theoretical interest since certain abnormalities may be a direct expression of specific brain pathology. Studying these changes in eating and weight may therefore further our understanding of certain of the pathological processes underlying dementia and suggest new approaches to the management of these problems.

Effect of aging on the blood-brain barrier

Aging is commonly associated with progressive deterioration in central nervous system (CNS) function. Nutritional factors or environmental toxins have important effects on CNS degenerative changes. The blood-brain barrier (BBB) is a major modulator of nutrient delivery to the CNS. The tight junctions and the paucity of pinocytosis or fenestrations in brain capillary endothelium act as an effective barrier between the CNS and the circulating toxic agents. Senescence is associated with significant, though often subtle, changes in BBB. Conditions which are commonly associated with aging, such as hypertension and cerebrovascular ischemia, aggravate the age-related alterations in BBB function. The histologic changes in brain vasculature with aging is region selective and species specific. The common age-related histologic changes include loss of capillary endothelial cells, elongation of the remaining endothelial cells, and decreased capillary diameter in rat cortex, but not in the monkey or human cortex, and a decrease in the number of mitochondria in endothelial cells of the brain capillaries in the monkey but not in the rat. The age-related alterations in BBB transport function include a decrease in BBB choline transport with aging and decreased brain glucose influx. The BBB neutral amino acid transport appears to be unaltered in the aged mice. Most of the studies reported so far have failed to show a significant age-related alteration in BBB permeability to water-soluble substances and high molecular weight solutes in the absence of neurological disease. A more profound change in BBB permeability appears to be associated with Alzheimer's disease. Immunohistological studies have demonstrated the presence of serum proteins in the cerebrovascular amyloid in patients with Alzheimer's disease.(ABSTRACT TRUNCATED AT 250 WORDS)

Nutrients, brain biochemistry, and behavior: a possible role for the neuronal membrane

Nutrients can modify brain biochemistry and behavior. Many studies indicate that one possible mode of action of nutrients is to induce alterations in the bioavailability of neurotransmitter precursors within the brain. However, a series of studies has also indicated that: (a) learning induces a decrease in the level of cholesterol in specific brain regions; (b) an iron-deficient diet induces changes in dopaminergic D receptor activity and in dopamine-associated behaviors (thermoregulation and motor activity) as well as in learning and memory capacities; and (c) dietary manipulation of a specific type of fatty acid resulted in an improved learning capacity, modification of the pain threshold level, and in thermoregulatory response. The most parsimonious explanation for these results seems to be that the treatments (learning, iron-deficient and fatty acid diets) induced changes in the lipid composition of the neuronal membrane. Such changes, in turn, resulted in changes in the membrane functions. Supportive evidence for this hypothesis is presented in this review. The "neuronal membrane functional modification hypothesis" should not be considered as contradictory to the accepted "brain neurotransmitter precursors bioavailability rates model" of nutrient effects, but as a complementary hypothesis.