Homocysteine, another risk factor for Alzheimer disease, impairs apolipoprotein E3 function

Homocysteine, neurodegenerative biomarkers, and APOE ε4 in neurodegenerative diseases

INTRODUCTION

Elevated plasma homocysteine (Hcy) is associated with an increased risk of developing neurodegenerative diseases; however, its relationship with the apolipoprotein E (APOE) ε4 allele has not been well characterized.

METHODS

Participants clinically diagnosed with Alzheimer's disease or mild cognitive impairment (AD/MCI), frontotemporal dementia, Parkinson's disease, or cerebrovascular disease were stratified by the presence of the APOE ε4 allele. Volumetric magnetic resonance imaging, plasma amyloid/tau/neurodegeneration biomarkers, and cognitive performance were quantified.

RESULTS

Across all diagnostic groups, Hcy was associated with lower brain parenchymal fraction and greater neurofilament light chain in APOE ε4 non-carriers only. In AD/MCI, Hcy was associated with phosphorylated tau 217 in APOE ε4 non-carriers, but not in carriers. Exploratory analyses revealed interactions between Hcy and APOE ε4 on memory and visuospatial function.

DISCUSSION

Hcy may contribute to neurodegeneration depending on the presence of the APOE ε4 allele and specific disease processes. Trials on vitamin B12 supplementation may consider stratifying by APOE genotype. Highlights Homocysteine (Hcy) was associated with neurodegenerative biomarkers across disease groups. Relationships with Hcy were predominantly found in apolipoprotein E (APOE) ε4 non-carriers. In Alzheimer's disease, associations between Hcy and phosphorylated tau 217 were found in APOE ε4 non-carriers only. Significant interactions existed between Hcy and APOE ε4 status on cognition.

A review of dementia, focusing on the distinct roles of viral protein corona and MMP9 in dementia: Potential pharmacotherapeutic priorities

Dementia, in particular, is a defining feature of Alzheimer's and Parkinson's diseases. Because of the combination of motor and cognitive impairments, Parkinson's disease dementia (PDD) has a greater impact on affected people than Alzheimer's disease dementia (ADD) and others. If one family member develops dementia, the other members will suffer greatly in terms of social and occupational functioning. Currently, no relevant treatment is available based on an examination of the absolute pathophysiology of dementia. As a result, our objective of current review encouraged to look for dementia pharmacotherapy based on their pathogenesis. We systematically searched electronic databases such as PubMed, Scopus, and ESCI for information on the pathophysiology of demetia, as well as their treatment with allopathic and herbal medications. By modulating intermediate proteins, oxidative stress, viral protein corona, and MMP9 are etiological factors that cause dementia. The pathophysiology of ADD was described by two hypotheses: the amyloid cascade hypothesis and the tau and tangle hypothesis. ADD is caused by an increase in amyloid-beta (Aβ) and neurofibrillary tangles in the cerebrum. The viral protein corona (VPC) is more contagious and helps to form amyloid-beta (Aβ) plaques and neurofibrillary tangles in the cerebrum. Thioredoxin interacting protein (TXNIP) inside the BBB encourages Aβ to become more engaged. PDD is caused by decreased or absent dopamine secretion from nerve cells in the substantia nigra, as well as PRKN gene deletion/duplication mutations, and shift in the PRKN-PACRG organisation, all of which are linked to ageing. This article discussed the pathophysiology of dementia, as well as a list of herbal medications that can easily cross the BBB and have a therapeutic effect on dementia.

Cholesterol Regulates Exosome Release in Cultured Astrocytes

Exosomes are vesicles secreted by various kinds of cells, and they are rich in cholesterol, sphingomyelin (SM), phosphatidylcholine, and phosphatidylserine. Although cellular sphingolipid-mediated exosome release has been reported, the involvement of other lipid components of cell membranes in the regulation of exosome release is poorly understood. Here, we show that the level of exosome release into conditioned media is significantly reduced in cultured astrocytes prepared from apolipoprotein E (ApoE) knock-out mice when compared to those prepared from wild-type (WT) mice. The reduced level of exosome release was accompanied by elevated levels of cellular cholesterol. The addition of cholesterol to WT astrocytes significantly increased the cellular cholesterol levels and reduced exosome release. PI3K/Akt phosphorylation was enhanced in ApoE-deficient and cholesterol-treated WT astrocytes. In contrast, the depletion of cholesterol in ApoE-deficient astrocytes due to treatment with β-cyclodextrin recovered the exosome release level to a level similar to that in WT astrocytes. In addition, the reduced levels of exosome release due to the addition of cholesterol recovered to the control levels after treatment with a PI3K inhibitor (LY294002). The cholesterol-dependent regulation of exosome release was also confirmed by in vivo experiments; that is, exosome levels were significantly reduced in the CSF and blood serum of WT mice that were fed a high-fat diet and had increased cholesterol levels when compared to those in WT mice that were fed a normal diet. These results suggest that exosome release is regulated by cellular cholesterol via stimulation of the PI3K/Akt signal pathway.

Mild Hyperhomocysteinemia Causes Anxiety-like Behavior and Brain Hyperactivity in Rodents: Are ATPase and Excitotoxicity by NMDA Receptor Overstimulation Involved in this Effect?

Mild hyperhomocysteinemia is a risk factor for psychiatric and neurodegenerative diseases, whose mechanisms between them are not well-known. In the present study, we evaluated the emotional behavior and neurochemical pathways (ATPases, glutamate homeostasis, and cell viability) in amygdala and prefrontal cortex rats subjected to mild hyperhomocysteinemia (in vivo studies). The ex vivo effect of homocysteine on ATPases and redox status, as well as on NMDAR antagonism by MK-801 in same structures slices were also performed. Wistar male rats received a subcutaneous injection of 0.03 µmol Homocysteine/g of body weight or saline, twice a day from 30 to 60th-67th days of life. Hyperhomocysteinemia increased anxiety-like behavior and tended to alter locomotion/exploration of rats, whereas sucrose preference and forced swimming tests were not altered. Glutamate uptake was not changed, but the activities of glutamine synthetase and ATPases were increased. Cell viability was not altered. Ex vivo studies (slices) showed that homocysteine altered ATPases and redox status and that MK801, an NMDAR antagonist, protected amygdala (partially) and prefrontal cortex (totally) effects. Taken together, data showed that mild hyperhomocysteinemia impairs the emotional behavior, which may be associated with changes in ATPase and glutamate homeostasis, including glutamine synthetase and NMDAR overstimulation that could lead to excitotoxicity. These findings may be associated with the homocysteine risk factor on psychiatric disorders development and neurodegeneration.

Characteristics of TCM Constitution and Related Biomarkers for Mild Cognitive Impairment

INTRODUCTION

The incidence of Alzheimer's disease is on the rise, early detection of cognitive impairment of the elderly is very important. In traditional Chinese medicine, constitution is related to the susceptibility of the human body to diseases. Based on the theory of constitution of traditional Chinese medicine (TCM), the human population can be classified into 9 constitutions. However, little is known about the characteristics of medical constitution and related biomarkers in subjects with mild cognitive impairment (MCI).

METHODS

We measured the TCM Constitution of 214 subjects by using the Constitution in Chinese Medicine Questionnaire (CCMQ). MMSE and MoCA were used to assess cognitive function. The subjects were divided into mild cognitive impairment group (MCI, n = 152) and normal control group (NC, n = 62). The levels of serum Hcy and serum/urine 8-iso-PGF 2α were determined.

RESULTS

1) It was found that there was a significant difference in constitution types between MCI and NC. There were significant differences in MMSE and MoCA score, serum Hcy and serum/urine 8-iso-PGF 2a levels between the two groups. 2) In logistic regression analysis, the variables with statistical significance were TCM Constitution of Yang-Deficient, Phlegm-Dampness, Blood-Stasis and abnormal increase of Hcy (OR>1). 3) The MoCA scores had a positive correlation with the MMSE. A statistically significant inverse association was found between serum Hcy, blood and urine 8-iso-PGF 2a and scores of cognitive assessment in MCI.

CONCLUSION

Constitution types (Yang-Deficient, Phlegm-Dampness and Blood-Stasis) and abnormal serum Hcy elevation can be used as risk factors for MCI. MoCA scores can serve to detect MCI at early stage. Serum/urine 8-iso-PGF 2α has a certain relationship with MCI. Higher levels of serum/urine 8-iso-PGF 2α are more likely to be associated with MCI risk.

Expression of miR-28-3p in patients with Alzheimer's disease before and after treatment and its clinical value

Expression of miR-28-3p in patients with Alzheimer's disease (AD) before and after treatment and clinical value of miR-28-3p were determined. There were three groups: 68 AD patients treated with donepezil combined with basic therapy in The People's Hospital of Shouguang collected as an AD group, 70 patients with mild cognitive impairment (MCI) as an MCI group, and 75 healthy people as a normal group. Serum miR-28-3p was detected by qRT-PCR. The Montreal cognitive assessment scale (MoCA), mini mental state examination scale (MMSE), activities of daily living scale (ADL) and homocysteine (Hcy) were adopted to assess patients before and after treatment. miR-28-3p in normal group was significantly lower than that in other two groups, and miR-28-3p in MCI group was significantly lower than that in AD group (P<0.001). miR-28-3p correlated with the course and severity of patients. miR-28-3p in AD group after treatment was significantly lower than that before treatment (P<0.001). ADL and Hcy of AD patients after treatment were significantly lower than before treatment (P<0.05), and MMSE and MoCA after treatment were significantly higher than before treatment (P<0.05). Before and after treatment, miR-28-3p was significantly positively correlated with ADL score and Hcy level, but negatively correlated with MMSE score and MoCA score. Analysis of the working characteristic curve of the patients indicated that miR-28-3p can be used for diagnosis of AD patients. Donepezil therapy may reduce miR-28-3p level to alleviate the symptoms of AD patients, and miR-28-3p level can be used as an early diagnosis and prognosis evaluation of AD patients.

Homocysteine Induces Inflammation in Retina and Brain

Homocysteine (Hcy) is an amino acid that requires vitamins B₁₂ and folic acid for its metabolism. Vitamins B₁₂ and folic acid deficiencies lead to hyperhomocysteinemia (HHcy, elevated Hcy), which is linked to the development of diabetic retinopathy (DR), age-related macular degeneration (AMD), and Alzheimer’s disease (AD). The goal of the current study was to explore inflammation as an underlying mechanism of HHcy-induced pathology in age related diseases such as AMD, DR, and AD. Mice with HHcy due to a lack of the enzyme cystathionine-β-synthase (CBS) and wild-type mice were evaluated for microglia activation and inflammatory markers using immuno-fluorescence (IF). Tissue lysates isolated from the brain hippocampal area from mice with HHcy were evaluated for inflammatory cytokines using the multiplex assay. Human retinal endothelial cells, retinal pigment epithelial cells, and monocyte cell lines treated with/without Hcy were evaluated for inflammatory cytokines and NFκB activation using the multiplex assay, western blot analysis, and IF. HHcy induced inflammatory responses in mouse brain, retina, cultured retinal, and microglial cells. NFκB was activated and cytokine array analysis showed marked increase in pro-inflammatory cytokines and downregulation of anti-inflammatory cytokines. Therefore, elimination of excess Hcy or reduction of inflammation is a promising intervention for mitigating damage associated with HHcy in aging diseases such as DR, AMD, and AD.

Plasma Apolipoprotein E Monomer and Dimer Profile and Relevance to Alzheimer's Disease

The APOEɛ4 gene variant is the strongest genetic risk factor for Alzheimer's disease (AD), whereas APOEɛ3 conventionally is considered as 'risk neutral' although APOEɛ3-carriers also develop AD. Previous studies have shown that the apolipoprotein E3 (apoE3) isoform occurs as monomers, homodimers and heterodimers with apolipoprotein A-II in human body fluids and brain tissue, but the relevance of a plasma apoE3 monomer/dimer profile to AD is unknown. Here we assessed the distribution of monomers, homodimers and heterodimers in plasma from control subjects and patients with mild cognitive impairment (MCI) and AD with either a homozygous APOEɛ3 (n = 31 control subjects, and n = 14 MCI versus n = 5 AD patients) or APOEɛ4 genotype (n = 1 control subject, n = 21 MCI and n = 7 AD patients). Total plasma apoE levels were lower in APOEɛ4-carriers and overall correlated significantly to CSF Aβ42, p(Thr181)-tau and t-tau levels. Apolipoprotein E dimers were only observed in the APOEɛ3-carriers and associated with total plasma apoE levels, negatively correlated to apoE monomers, but were unrelated to plasma homocysteine levels. Importantly, the APOEɛ3-carrying AD patients versus controls exhibited a significant decrease in apoE homodimers (17.8±9.6% versus 26.7±6.3%, p = 0.025) paralleled by an increase in apoE monomers (67.8±18.3% versus 48.5±11.2%, p = 0.008). In the controls, apoE monomers and heterodimers were significantly associated with plasma triglycerides; the apoE heterodimers were also associated with levels of high-density lipoprotein cholesterol. The physiological relevance of apoE dimer formation needs to be further investigated, though the distribution of apoE in monomers and dimers appears to be of relevance to AD in APOEɛ3 subjects.

Deciphering the Link Between Hyperhomocysteinemia and Ceramide Metabolism in Alzheimer-Type Neurodegeneration

Aging is one of the strongest risk factor for Alzheimer's disease (AD). However, several data suggest that dyslipidemia can either contribute or serve as co-factors in AD appearance. AD could be examined as a metabolic disorder mediated by peripheral insulin resistance. Insulin resistance is associated with dyslipidemia, which results in increased hepatic ceramide generation. Hepatic steatosis induces pro-inflammatory cytokine activation which is mediated by the increased ceramides production. Ceramides levels increased in cells due to perturbation in sphingolipid metabolism and upregulated expression of enzymes involved in ceramide synthesis. Cytotoxic ceramides and related molecules generated in liver promote insulin resistance, traffic through the circulation due to injury or cell death caused by local liver inflammation, and because of their hydrophobic nature, they can cross the blood-brain barrier and thereby exert neurotoxic responses as reducing insulin signaling and increasing pro-inflammatory cytokines. These abnormalities propagate a cascade of neurodegeneration associated with oxidative stress and ceramide generation, which potentiate brain insulin resistance, apoptosis, myelin degeneration, and neuro-inflammation. Therefore, excess of toxic lipids generated in liver can cause neurodegeneration. Elevated homocysteine level is also a risk factor for AD pathology and is narrowly associated with metabolic diseases and non-alcoholic fatty liver disease. The existence of a homocysteine/ceramides signaling pathway suggests that homocysteine toxicity could be partly mediated by intracellular ceramide accumulation due to stimulation of ceramide synthase. In this article, we briefly examined the role of homocysteine and ceramide metabolism linking metabolic diseases and non-alcoholic fatty liver disease to AD. We therefore analyzed the expression of mainly enzymes implicated in ceramide and sphingolipid metabolism and demonstrated deregulation of de novo ceramide biosynthesis and S1P metabolism in liver and brain of hyperhomocysteinemic mice.

Chronic mild Hyperhomocysteinemia impairs energy metabolism, promotes DNA damage and induces a Nrf2 response to oxidative stress in rats brain

Homocysteine (HCY) has been linked to oxidative stress and varied metabolic changes that are dependent on its concentration and affected tissues. In the present study we evaluate parameters of energy metabolism [succinate dehydrogenase (SDH), complex II and IV (cytochrome c oxidase), and ATP levels] and oxidative stress [DCFH oxidation, nitrite levels, antioxidant enzymes and lipid, protein and DNA damages, as well as nuclear factor erythroid 2-related (Nrf2) protein abundance] in amygdala and prefrontal cortex of HCY-treated rats. Wistar male rats were treated with a subcutaneous injection of HCY (0.03 µmol/g of body weight) from the 30th to 60th post-natal day, twice a day, to induce mild hyperhomocysteinemia (HHCY). The rats were euthanatized without anesthesia at 12 h after the last injection, and amygdala and prefrontal cortex were dissected for biochemical analyses. In the amygdala, mild HHCY increased activities of SDH and complex II and decreased complex IV and ATP level, as well as increased antioxidant enzymes activities (glutathione peroxidase and superoxide dismutase), nitrite levels, DNA damage, and Nrf 2 protein abundance. In the prefrontal cortex, mild HHCY did not alter energy metabolism, but increased glutathione peroxidase, catalase and DNA damage. Other analyzed parameters were not altered by HCY-treatment. Our findings suggested that chronic mild HHCY changes each brain structure, particularly and specifically. These changes may be associated with the mechanisms by which chronic mild HHCY has been linked to the risk factor of fear, mood disorders and depression, as well as in neurodegenerative diseases.

Relationship Between B-Vitamin Biomarkers and Dietary Intake with Apolipoprotein E є4 in Alzheimer's Disease

The potential for B-vitamins to reduce plasma homocysteine (Hcy) and reduce the risk of Alzheimer's disease (AD) has been described previously. However, the role of Apolipoprotein E є4 (APOE4) in this relationship has not been adequately addressed. This case-control study explored APOE4 genotype in an Australian sample of 63 healthy individuals (female = 38; age = 76.9 ± 4.7 y) and 63 individuals with AD (female = 35, age = 77.1 ± 5.3 y). Findings revealed 55 of 126 participants expressed the APOE4 genotype with 37 of 126 having both AD and the APOE4 genotype. Analysis revealed an increased likelihood of AD when Hcy levels are >11.0 µmol/L (p = 0.012), cysteine levels were <255 µmol/L (p = 0.033) and serum folate was <22.0 nmol/L (p = 0.003; in males only). In females, dietary intake of total folate <336 µg/day (p=0.001), natural folate <270 µg/day (p = 0.011), and vitamin B2 < 1.12 mg/day (p = 0.028) was associated with an increased AD risk. These results support Hcy, Cys, and SF as useful biomarkers for AD, irrespective of APOE4 genotype and as such should be considered as part of screening and managing risk of AD.

Homocysteine Modification in Protein Structure/Function and Human Disease

Epidemiological studies established that elevated homocysteine, an important intermediate in folate, vitamin B₁₂, and one carbon metabolism, is associated with poor health, including heart and brain diseases. Earlier studies show that patients with severe hyperhomocysteinemia, first identified in the 1960s, exhibit neurological and cardiovascular abnormalities and premature death due to vascular complications. Although homocysteine is considered to be a nonprotein amino acid, studies over the past 2 decades have led to discoveries of protein-related homocysteine metabolism and mechanisms by which homocysteine can become a component of proteins. Homocysteine-containing proteins lose their biological function and acquire cytotoxic, proinflammatory, proatherothrombotic, and proneuropathic properties, which can account for the various disease phenotypes associated with hyperhomocysteinemia. This review describes mechanisms by which hyperhomocysteinemia affects cellular proteostasis, provides a comprehensive account of the biological chemistry of homocysteine-containing proteins, and discusses pathophysiological consequences and clinical implications of their formation.

Epigenetic Factors in Late-Onset Alzheimer's Disease: MTHFR and CTH Gene Polymorphisms, Metabolic Transsulfuration and Methylation Pathways, and B Vitamins

DNA methylation and other epigenetic factors are important in the pathogenesis of late-onset Alzheimer's disease (LOAD). Methylenetetrahydrofolate reductase (MTHFR) gene mutations occur in most elderly patients with memory loss. MTHFR is critical for production of S-adenosyl-l-methionine (SAM), the principal methyl donor. A common mutation (1364T/T) of the cystathionine-γ-lyase (CTH) gene affects the enzyme that converts cystathionine to cysteine in the transsulfuration pathway causing plasma elevation of total homocysteine (tHcy) or hyperhomocysteinemia-a strong and independent risk factor for cognitive loss and AD. Other causes of hyperhomocysteinemia include aging, nutritional factors, and deficiencies of B vitamins. We emphasize the importance of supplementing vitamin B12 (methylcobalamin), vitamin B₉ (folic acid), vitamin B₆ (pyridoxine), and SAM to patients in early stages of LOAD.

Redox status of serum apolipoprotein E and its impact on HDL cholesterol levels

BACKGROUND

Apolipoprotein E (apoE) is closely involved in the pathogenesis of apoE-related diseases, such as Alzheimer's disease and cardiovascular disease. The redox modulation of cysteine-thiols in a protein is involved in various pathophysiological regulations; however, that of apoE has not been studied in detail. Herein, we devised an analytical method to determine the redox status of serum apoE and assessed its relation to serum cholesterol levels and apoE phenotype.

METHODS

The present method was based on a band shift assay, using a photocleavable maleimide-conjugated polyethylene glycol.

RESULTS

The basic characteristics of the present method were found to be satisfactory to determine the redox status of serum apoE quantitatively. Serum apoE was separated into its reduced-form (r-), non-reduced-form (nr-), apoE-AII complex, and homodimer using this method. R-apoE could be detected as a 40-kDa band, whereas nr-apoE remained as monomeric apoE. R-apoE displayed a preference for VLDL; however, the levels showed the correlation with HDL-cholesterol levels (p<0.005). Redox status of serum apoE was significantly different among apoE phenotypes. The quantitative ratios of nr-apoE to total apoE in serum from subjects with apoE4/E3 were higher than in serum from subjects with apoE3/E3 (p<0.0001) and apoE3/E2 (p<0.001).

CONCLUSION

The redox status of serum apoE might be related to the synthesis of HDL. The information concerning the redox status of serum apoE provided by the present method may be a potent indicator to evaluate various apoE-related diseases.

Low-Dose Homocystine Enhances Proliferation and Migration of Bv2 Microglia Cells

Homocysteine (Hcy) is a non-essential amino acid that is derived from the breakdown of dietary methionine. Hyperhomocysteinemia (HHcy) is an independent risk factor for a variety of chronic diseases, especially neurodegenerative conditions. To better understand the role of HHcy in the pathogenesis of neurodegenerative disorders, we investigated the effect of Hcy on the proliferation and activation of microglia Bv2 cells. Cells were treated with six different Hcy concentrations: 0, 50, 100, 300, 500, and 1000 µM for different time periods (8, 12, 16, 24, and 48 h). The morphology of Bv2 cells was observed, and cell activity and proliferation were detected. Cell migration and secretion of pro-inflammatory cytokines were detected by the scratch wound assay, the transwell assay, and ELISA, respectively. The effect of Hcy on Bv2 proliferation occurred earlier (<24 h, especially 16 h) after treatment with concentrations between 100 and 300 μM, and there was no cytotoxicity to Bv2 cells. Meanwhile, functional assays suggested that Hcy not only promoted Bv2 secretion of the pro-inflammatory cytokines IL-1β, TNF-α, and IL-6, but also enhanced Bv2 migration and invasion, with 100 μM being the most effective concentration. In summary, Bv2 proliferation and activation can be promoted by short-term treatment with low-dose Hcy.

High levels of homocysteine downregulate apolipoprotein E expression via nuclear factor kappa B

AIM: To investigate the effect of high homocysteine (Hcy) levels on apolipoprotein E (apoE) expression and the signaling pathways involved in this gene regulation.

METHODS: Reverse transcriptase polymerase chain reaction (RT-PCR) and Western blot were used to assess apoE expression in cells treated with various concentrations (50-500 μmol/L) of Hcy. Calcium phosphate-transient transfections were performed in HEK-293 and RAW 264.7 cells to evaluate the effect of Hcy on apoE regulatory elements [promoter and distal multienhancer 2 (ME2)]. To this aim, plasmids containing the proximal apoE promoter [(-500/+73)apoE construct] alone or in the presence of ME2 [ME2/(-500/+73)apoE construct] to drive the expression of the reporter luciferase gene were used. Co-transfection experiments were carried out to investigate the downstream effectors of Hcy-mediated regulation of apoE promoter by using specific inhibitors or a dominant negative form of IKβ. In other co-transfections, the luciferase reporter was under the control of synthetic promoters containing multiple specific binding sites for nuclear factor kappa B (NF-κB), activator protein-1 (AP-1) or nuclear factor of activated T cells (NFAT). Chromatin immunoprecipitation (ChIP) assay was accomplished to detect the binding of NF-κB p65 subunit to the apoE promoter in HEK-293 treated with 500 μmol/L Hcy. As control, cells were incubated with similar concentration of cysteine. NF-κB p65 proteins bound to DNA were immunoprecipitated with anti-p65 antibodies and DNA was identified by PCR using primers amplifying the region -100/+4 of the apoE gene.

RESULTS: RT-PCR revealed that high levels of Hcy (250-750 μmol/L) induced a 2-3 fold decrease in apoE mRNA levels in HEK-293 cells, while apoE gene expression was not significantly affected by treatment with lower concentrations of Hcy (100 μmol/L). Immunoblotting data provided additional evidence for the negative role of Hcy in apoE expression. Hcy decreased apoE promoter activity, in the presence or absence of ME2, in a dose dependent manner, in both RAW 264.7 and HEK-293 cells, as revealed by transient transfection experiments. The downstream effectors of the signaling pathways of Hcy were also investigated. The inhibitory effect of Hcy on the apoE promoter activity was counteracted by MAPK/ERK kinase 1/2 (MEK1/2) inhibitor U0126, suggesting that MEK1/2 is involved in the downregulation of apoE promoter activity by Hcy. Our data demonstrated that Hcy-induced inhibition of apoE took place through activation of NF-κB. Moreover, we demonstrated that Hcy activated a synthetic promoter containing three NF-κB binding sites, but did not affect promoters containing AP-1 or NFAT binding sites. ChIP experiments revealed that NF-κB p65 subunit is recruited to the apoE promoter following Hcy treatment of cells.

CONCLUSION: Hcy-induced stress negatively modulates apoE expression via MEK1/2 and NF-κB activation. The decreased apoE expression in peripheral tissues may aggravate atherosclerosis, neurodegenerative diseases and renal dysfunctions.

Can APOE and MTHFR polymorphisms have an influence on the severity of cardiovascular manifestations in Italian Pseudoxanthoma elasticum affected patients?

Background

The clinical phenotype of Pseudoxanthoma elasticum (PXE) affected patients, although progressive with age, is very heterogeneous, even in the presence of identical ABCC6 mutations, thus suggesting the occurrence of modifier genes. Beside typical skin manifestations, the cardiovascular (CV) system, and especially the peripheral vasculature, is frequently and prematurely compromised.

Methods and results

A cohort of 119 Italian PXE patients has been characterized for apolipoprotein E (APOE) and methylenetetrahydrofolate reductase (MTHFR) gene polymorphisms by PCR. The severity of the clinical phenotype has been quantified according to the Phenodex PXE International score system. Statistical analysis (chi² test, odd ratio, regression analysis, analysis of variance) were done by GraphPad. Data demonstrate that the frequency of APOE alleles is similar in PXE patients and in healthy subjects and that the allelic variant E2 confers a protection against the age-related increase of CV manifestations. By contrast, PXE patients are characterized by high frequency of the MTHFR-T677T polymorphism. With age, CV manifestations in T677T, but also in C677T, patients are more severe than those associated with the C677C genotype. Interestingly, compound heterozygosity for C677T and A1298C polymorphisms is present in 70% of PXE patients.

Conclusions

PXE patients may be screened for these polymorphisms in order to support clinicians for a better management of disease-associated CV complications.

Hyperhomocysteinemia and methylenetetrahydrofolate reductase polymorphism in cervical artery dissection: a meta-analysis

BACKGROUND

Cervical artery dissection (CAD) is a recognized cause of ischemic stroke. Hyperhomocysteinemia (HHcy), i.e. an elevated concentration of plasma homocysteine, is identified as an independent risk factor for stroke prevalence. However, an association between HHcy and CAD has so far remained unknown.

METHODS

A meta-analysis was performed to analyze the association between HHcy and CAD as well as the relevance of the C677T polymorphism of methylenetetrahydrofolate reductase (MTHFR), the key enzyme in homocysteine metabolism during CAD. We searched PubMed and Embase for studies reporting homocysteine concentrations or MTHFR genotype frequencies in CAD patients from 1990 to 2013. Outcomes were extracted from studies meeting the inclusion criteria and were subjected to a meta-analysis by the random-effect model. Heterogeneity was assessed by the I(2) test.

RESULTS

Eight case-control studies with 2,146 individuals fulfilled the required criteria and were included in the meta-analysis. HHcy was found to be significantly associated with CAD (pooled standardized mean difference: 0.96; 95% confidence interval, CI: 0.42-1.49; p < 0.01). We also found a significantly increased risk of CAD in individuals with the MTHFR C677T polymorphism by both the recessive model (TT vs. CT+CC; odds ratio, OR = 1.81; 95% CI: 1.22-2.67; p = 0.003) and the dominant model (TT+CT vs. CC; OR = 1.47; 95% CI: 1.08-1.99; p = 0.014).

CONCLUSION

Our data suggest positive correlations between HHcy and CAD and between the C677T polymorphism of MTHFR and CAD.

Lowering homocysteine levels with folic acid and B-vitamins do not reduce early atherosclerosis, but could interfere with cognitive decline and Alzheimer's disease

Inheired or acquired hyperhomocysteinemia (HHcy) is associated with several impairments, as certain tumors, deep venous thrombosis, tube neural defects, osteoporosis, early atherosclerosis and vascular acute events (IMA, stroke, PVD), mild cognitive impairments till Alzheimer's disease (AD). But, vascular and neuronal derangements are the most frequent HHcy-manifestations. As far as early atherosclerosis, some clinical trials demonstrated that folates and B6-12 vitamins supplementation is unable to reduce atherosclerotic lesions and cardiovascular events, even if it lowers HHcy levels. Thus, for atherosclerosis and its acute events (IMA, stroke, PVD) HHcy acts as a powerful biomarker rather than a risk factor. For that, the supplementation with folates and B vitamins to lower atherosclerotic lesions-events in hyperhomocysteinemic patients is not recommended. On the contrary, several clinical investigations demonstrated that folates and vitamins administration is able to reduce Hcy serum levels and antagonize some mechanisms favouring neurodegenerative impairments, as mild cognitive impairment, AD and dementia. Thus, contrarily to the atherosclerotic manifestations in hyperhomocysteinemic patients, preventive treatment with folates and B6-12 vitamins reduces Hcy concentration and could prevent or delay cognitive decline and AD.

KIF6 719Arg Carrier Status Association with Homocysteine and C-Reactive Protein in Amnestic Mild Cognitive Impairment and Alzheimer's Disease Patients

Recent research has demonstrated associations between statin use, KIF6 719Arg carrier status, and cholesterol levels and amnestic mild cognitive impairment (aMCI) and Alzheimer's disease (AD) patients. The association between 719Arg carrier status with homocysteine (tHcy) and c-reactive protein (CRP) levels in aMCI and AD has not been previously investigated. Data from 175 aMCI and AD patients were used for the analysis. 719Arg carriers had significantly lower levels of tHcy than noncarriers (P = 0.02). No significant difference in CRP levels between 719Arg carriers and noncarriers was present (P = 0.37). Logistic regression yielded no significant effect for 719Arg status on CRP [OR = 1.79 (0.85, 3.83), P = 0.13] but did demonstrate a significant effect for tHcy [OR = 0.44 (0.23, 0.83), P = 0.01] after adjusting for ApoE ε4 carrier status, age, gender, and statin use. This study is the first to explore the relationship between KIF6 719Arg carrier status with tHcy and CRP levels. 719Arg carriers were more likely to have normal tHcy levels after adjusting for ApoE ε4 status, age, gender, and statin use. These results suggest that the KIF6 gene might influence cardiovascular pathways associated with AD.

Effects of homocysteine on ERK signaling and cell proliferation in fetal neural stem cells in vitro

The aim of the present study was to determine if the excitatory amino acid homocysteine (Hcy) alters ERK signaling and cell proliferation in fetal neural stem cells (NSCs) in vitro. NSCs were isolated from fetal rats and grown in serum-free suspension medium. The cells were identified as NSCs by their expression of immunoreactive Sox2. NSCs were assigned to one of four treatment groups: vehicle control, low-dose Hcy group (Hcy-L, medium contained 30 μmol/L Hcy), middle-dose Hcy group (Hcy-M, 100 μmol/L Hcy) and high-dose Hcy group (Hcy-H, 300 μmol/L Hcy). Cell proliferation was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Protein expression levels of ERK1/2 and phosphorylated ERK1/2 were detected by Western blot. The effects of Hcy on NSC death, including apoptosis, were assessed by using flow cytometry and trypan blue exclusion. The results showed that NSCs grew as neurospheres in the serum-free medium. Hcy decreased ERK1/2 protein phosphorylation and NSC proliferation, but it did not induce cell death or apoptosis within the concentration from 30 to 300 μmol/L. The above results are consistent with the hypothesis that Hcy decreases fetal NSC proliferation by inhibiting ERK signaling.

DNA methylation, a hand behind neurodegenerative diseases

Epigenetic alterations represent a sort of functional modifications related to the genome that are not responsible for changes in the nucleotide sequence. DNA methylation is one of such epigenetic modifications that have been studied intensively for the past several decades. The transfer of a methyl group to the 5 position of a cytosine is the key feature of DNA methylation. A simple change as such can be caused by a variety of factors, which can be the cause of many serious diseases including several neurodegenerative diseases. In this review, we have reviewed and summarized recent progress regarding DNA methylation in four major neurodegenerative diseases: Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), and amyotrophic lateral sclerosis (ALS). The studies of these four major neurodegenerative diseases conclude the strong suggestion of the important role DNA methylation plays in these diseases. However, each of these diseases has not yet been understood completely as details in some areas remain unclear, and will be investigated in future studies. We hope this review can provide new insights into the understanding of neurodegenerative diseases from the epigenetic perspective.

S-linked protein homocysteinylation: identifying targets based on structural, physicochemical and protein-protein interactions of homocysteinylated proteins

An elevated level of homocysteine, a thiol-containing amino acid is associated with a wide spectrum of disease conditions. A majority (>80 %) of the circulating homocysteine exist in protein-bound form. Homocysteine can bind to free cysteine residues in the protein or could cleave accessible cysteine disulfide bonds via thiol disulfide exchange reaction. Binding of homocysteine to proteins could potentially alter the structure and/or function of the protein. To date only 21 proteins have been experimentally shown to bind homocysteine. In this study we attempted to identify other proteins that could potentially bind to homocysteine based on the criteria that such proteins will have significant 3D structural homology with the proteins that have been experimentally validated and have solvent accessible cysteine residues either with high dihedral strain energy (for cysteine-cysteine disulfide bonds) or low pKa (for free cysteine residues). This analysis led us to the identification of 78 such proteins of which 68 proteins had 154 solvent accessible disulfide cysteine pairs with high dihedral strain energy and 10 proteins had free cysteine residues with low pKa that could potentially bind to homocysteine. Further, protein-protein interaction network was built to identify the interacting partners of these putative homocysteine binding proteins. We found that the 21 experimentally validated proteins had 174 interacting partners while the 78 proteins identified in our analysis had 445 first interacting partners. These proteins are mainly involved in biological activities such as complement and coagulation pathway, focal adhesion, ECM-receptor, ErbB signalling and cancer pathways, etc. paralleling the disease-specific attributes associated with hyperhomocysteinemia.

Association of COMT, MTHFR, and SLC19A1(RFC-1) polymorphisms with homocysteine blood levels and cognitive impairment in Parkinson's disease

INTRODUCTION

Elevated plasma homocysteine (Hcy) concentration is an independent risk factor for cardiovascular disease, and its involvement in endothelial cell dysfunction is well established. However, the role of Hcy and folate in the pathogenesis of Parkinson's disease (PD) remains controversial.

OBJECTIVES

The study was aimed at evaluating the relationships between Hcy, vitamin B12, and folic acid levels in the blood and cognitive status in PD patients with the genetic polymorphisms of MTHFR (rs1801133: C>T-677C>T, rs1801131: A>C-1298A>C), COMT (rs4680: A>G-Val158Met, rs6269: A>G, rs4633: C>T, rs4818: C>G), or SLC19A1 (rs1051266: G>A-80G>A).

METHODS

A total of 502 participants (248 with PD and 254 age-matched and sex-matched controls) were included in the study. The Unified Parkinson's Disease Rating Scale score, Hoehn-Yahr staging, and the Schwab-England scale were used to assess motor abilities and activity during daily life. Complex psychological examination with a battery of tests was used to classify patients into groups with (PDD) and without (nPDD) dementia. Blood samples were examined for Hcy, vitamin B12, and folic acid levels, as well as polymorphisms in genes related to Hcy metabolism, such as COMT, MTHFR, and SLC19A1(RFC-1).

RESULTS

The frequency of homozygous COMT rs4680G and rs4633C allele carriers was significantly decreased in PD patients in comparison with the controls (P=0.015; odds ratio=0.60; 95% confidence interval 0.41-0.90 and P=0.020; odds ratio=0.619; 95% confidence interval 0.42-0.92, respectively). No significant differences in the distribution of MTHFR 677C>T, 1298A>C, and SLC19A1 80G>A alleles and genotypes between PD patients and the controls were found. Hcy levels were significantly increased in PD patients (18±7.8 μmol/l) as compared with the controls (14.0±9.6 μmol/l, P=10(-8)) and were significantly associated with the MTHFR 677C>T polymorphism both in PD patients and controls, in which T allele carriers were characterized by markedly elevated Hcy plasma concentrations. No association was observed between Hcy plasma level and COMT and SLC19A polymorphisms. The results of multivariate logistic regression analysis revealed age (P=0.0003) and Hcy plasma levels (P=0.07) as independent risk factors predisposing individuals to PD dementia. The studied polymorphisms were not associated with cognitive status in PD patients.

CONCLUSION

The genetic factors studied were not associated with cognitive status in PD patients. Only age and Hcy plasma levels were found to be independent risk factors predisposing individuals to PD dementia. However, COMT: rs4680: A>G and rs4633: C>T polymorphisms were found to significantly affect PD risk, and the MTHFR 677C>T polymorphism helped determine plasma Hcy concentrations.

Homocysteine induces energy imbalance in rat skeletal muscle: is creatine a protector?

Homocystinuria is a neurometabolic disease caused by a severe deficiency of cystathionine beta-synthase activity, resulting in severe hyperhomocysteinemia. Affected patients present several symptoms including a variable degree of motor dysfunction. In this study, we investigated the effect of chronic hyperhomocysteinemia on the cell viability of the mitochondrion, as well as on some parameters of energy metabolism, such as glucose oxidation and activities of pyruvate kinase, citrate synthase, isocitrate dehydrogenase, malate dehydrogenase, respiratory chain complexes and creatine kinase in gastrocnemius rat skeletal muscle. We also evaluated the effect of creatine on biochemical alterations elicited by hyperhomocysteinemia. Wistar rats received daily subcutaneous injections of homocysteine (0.3-0.6 µmol/g body weight) and/or creatine (50 mg/kg body weight) from the 6th to the 28th days of age. The animals were decapitated 12 h after the last injection. Homocysteine decreased the cell viability of the mitochondrion and the activities of pyruvate kinase and creatine kinase. Succinate dehydrogenase was increased other evaluated parameters were not changed by this amino acid. Creatine, when combined with homocysteine, prevented or caused a synergistic effect on some changes provoked by this amino acid. Creatine per se or creatine plus homocysteine altered glucose oxidation. These findings provide insights into the mechanisms by which homocysteine exerts its effects on skeletal muscle function, more studies are needed to elucidate them. Although creatine prevents some alterations caused by homocysteine, it should be used with caution, mainly in healthy individuals because it could change the homeostasis of normal physiological functions.

Association studies of several cholesterol-related genes (ABCA1, CETP and LIPC) with serum lipids and risk of Alzheimer's disease

Objectives

Accumulating evidence suggested that dysregulation of cholesterol homeostasis might be a major etiologic factor in initiating and promoting neurodegeneration in Alzheimer’s disease (AD). ATP-binding cassette transporter A1 (ABCA1), hepatic lipase (HL, coding genes named LIPC) and cholesteryl ester transfer protein (CETP) are important components of high-density lipoprotein (HDL) metabolism and reverse cholesterol transport (RCT) implicated in atherosclerosis and neurodegenerative diseases. In the present study, we will investigate the possible association of several common polymorphisms (ABCA1R219K, CETPTaqIB and LIPC-250 G/A) with susceptibility to AD and plasma lipid levels.

Methods

Case–control study of 208 Han Chinese (104 AD patients and 104 non-demented controls) from Changsha area in Hunan Province was performed using the PCR-RFLP analysis. Cognitive decline was assessed using Mini Mental State Examination (MMSE) as a standardized method. Additionally, fasting lipid profile and the cognitive testing scores including Wechsler Memory Scale (WMS) and Wisconsin Card Sorting Test (WCST) were recorded.

Results and conclusions

We found significant differences among the genotype distributions of these three genes in AD patients when compared with controls. But after adjusting other factors, multivariate logistic regression analysis showed only ABCA1R219K (B = −0.903, P = 0.005, OR = 0.405, 95%CI:0.217-0.758) and LIPC-250 G/A variants(B = −0.905, P = 0.018, OR = 0.405, 95%CI:0.191-0.858) were associated with decreased AD risk. There were significantly higher levels of high-density lipoprotein cholesterol (HDL-C) and apolipoproteinA-I in the carriers of KK genotype and K allele (P < 0.05), and B2B2 genotype of CETP Taq1B showed significant association with higher HDL-C levels than other genotypes (F = 5.598, P = 0.004), while -250 G/A polymorphisms had no significant effect on HDL-C. In total population, subjects carrying ABCA1219K allele or LIPC-250A allele obtained higher MMSE or WMS scores than non-carriers, however, no significant association was observed in AD group or controls. Therefore, this preliminary study showed that the gene variants of ABCA1R219K and LIPC-250 G/A might influence AD susceptibility in South Chinese Han population, but the polymorphism of CETPTaq1B didn't show any association in despite of being a significant determinant of HDL-C.

Mild hyperhomocysteinemia alters extracellular adenine metabolism in rat brain

Since homocysteine (Hcy) is considered a risk factor to cerebral diseases and adenine nucleotides are important molecules to brain normal function, in the present study we investigated the effect of chronic mild hyperhomocysteinemia on ectonucleotidase activities and expression in rat cerebral cortex. The levels of ATP, ADP, AMP and adenosine (Ado) in cerebrospinal fluid (CSF) of adult rats also were evaluated by high-performance liquid chromatography. For the chronic chemically induced mild hyperhomocysteinemia, Hcy (0.03 μmol/g of body weight) was administered subcutaneously from the 30th to the 60th day of life. Control rats received saline solution in the same volumes. Results showed that Hcy significantly decreased nucleotide hydrolysis in the synaptosomal fraction and increased E-NTPDase1 and ecto-5'-nucleotidase transcripts in rat cerebral cortex. ATP levels were significantly increased, while Ado decreased in CSF of Hcy-treated rats. These findings suggest that the unbalance in ATP and Ado levels may be, at last in part, involved in the cerebral toxicity of mild hyperhomocysteinemia.

Homocysteine metabolism in peripheral blood mononuclear cells: evidence for cystathionine beta-synthase activity in resting state

Activated peripheral blood mononuclear cells (PBMC) release homocysteine and possess cystathionine β-synthase (CBS) activity; however, it was thought that there is no CBS in resting state. Previously, we found that nickel decreased intracellular homocysteine concentration in un-stimulated (e.g. resting) PBMC, suggesting that resting PBMC might also have active homocysteine metabolism. Here, we demonstrated that un-stimulated PBMC synthesize (incorporate L-[methyl-14C]methionine to DNA, lipids and proteins), release (increase extracellular homocysteine), and metabolize homocysteine. Intracellular homocysteine concentration varied with incubation time, depending on extracellular concentrations of methionine, homocysteine, and glutathione. Methionine synthase activity was constant and independent of thiol concentrations. In Western blot, CBS protein was clearly identified in freshly isolated PBMC. CBS protein level and activity increased with incubation time, upon stimulation, and similar to intracellular homocysteine, depending on intra- and extracellular homocysteine and glutathione concentrations. According to our knowledge, this is the first evidence that certifies homocysteine metabolism and regulatory role of CBS activity to keep balanced intracellular homocysteine level in resting PBMC. Homocysteine, released by PBMC, in turn can modulate its functions contributing to the development of hyperhomocysteinemia-induced diseases.

DNA methylation in neurodegenerative disorders: a missing link between genome and environment?

The risk of developing neurodegenerative disorders such as Alzheimer's disease or Parkinson's disease is influenced by genetic and environmental factors. Environmental events occurring during development or later in life can be related to disease susceptibility. One way by which the environment may exert its effect is through epigenetic modifications, which might affect the functioning of genes. These include nucleosome positioning, post-translational histone modifications, and DNA methylation. In this review we will focus in the potential role of DNA methylation in neurodegenerative disorders and in the approaches to explore such epigenetic changes. Advances in deciphering the role of epigenetic modifications in phenotype are being uncovered for a variety of diseases, including cancer, autoimmune, neurodevelopmental and cognitive disorders. Epigenetic modifications are now being also associated with cardiovascular and metabolic traits, and they are expected to be especially involved in learning and memory processes, as well as in neurodegenerative disease. The study of the role of methylation and other epigenetic modifications in disease development will provide new insights in the etiopathogenesis of neurodegenerative disorders, and should hopefully shape new avenues in the development of therapeutic strategies.

Apolipoprotein E regulates the integrity of tight junctions in an isoform-dependent manner in an in vitro blood-brain barrier model

Apolipoprotein E (apoE) is a major apolipoprotein in the brain. The ε4 allele of apoE is a major risk factor for Alzheimer disease, and apoE deficiency in mice leads to blood-brain barrier (BBB) leakage. However, the effect of apoE isoforms on BBB properties are as yet unknown. Here, using an in vitro BBB model consisting of brain endothelial cells and pericytes prepared from wild-type (WT) mice, and primary astrocytes prepared from human apoE3- and apoE4-knock-in mice, we show that the barrier function of tight junctions (TJs) was impaired when the BBB was reconstituted with primary astrocytes from apoE4-knock-in mice (apoE4-BBB model). The phosphorylation of occludin at Thr residues and the activation of protein kinase C (PKC)η in mBECs were attenuated in the apoE4-BBB model compared with those in the apoE3-BBB model. The differential effects of apoE isoforms on the activation of PKCη, the phosphorylation of occludin at Thr residues, and TJ integrity were abolished following the treatment with an anti-low density lipoprotein receptor-related protein 1 (LRP1) antibody or a LRP1 antagonist receptor-associated protein. Consistent with the results of in vitro studies, BBB permeability was higher in apoE4-knock-in mice than in apoE3-knock-in mice. Our studies provide evidence that TJ integrity in BBB is regulated by apoE in an isoform-dependent manner.