Hyperhomocysteinemia increases beta-amyloid by enhancing expression of gamma-secretase and phosphorylation of amyloid precursor protein in rat brain

Seeding of proteins into amyloid structures by metabolite assemblies may clarify certain unexplained epidemiological associations

The accumulation of various metabolites appears to be associated with diverse human diseases. However, the aetiological link between metabolic alteration and the observed diseases is still elusive. This includes the correlation between the abnormally high levels of homocysteine and quinolinic acid in Alzheimer's disease, as well as the accumulation of oncometabolites in malignant processes. Here, we suggest and discuss a possible mechanistic insight into metabolite accumulation in conditions such as neurodegenerative diseases and cancer. Our hypothesis is based on the demonstrated ability of metabolites to form amyloid-like structures in inborn error of metabolism disorders and the potential of such metabolite amyloids to promote protein aggregation. This notion can provide a new paradigm for neurodegeneration and cancer, as both conditions were linked to loss of function due to protein aggregation. Similar to the well-established observation of amyloid formation in many degenerative disorders, the formation of amyloids by tumour-suppressor proteins, including p53, was demonstrated in malignant states. Moreover, this new paradigm could fill the gap in understanding the high occurrence of specific types of cancer among genetic error of metabolism patients. This hypothesis offers a fresh view on the aetiology of some of the most abundant human maladies and may redirect the efforts towards new therapeutic developments.

An appraisal of folates as key factors in cognition and ageing-related diseases

Folic acid (FA) is often consumed as a food supplement and can be found in fortified staple foods in various western countries. Even though FA supplementation during pregnancy is known to prevent severe congenital anomalies in the developing child (e.g., neural tube defects), much less is known about its influence on cognition and neurological functioning. In this review, we address the advances in this field and situate how folate intake during pregnancy, postnatal life, adulthood and in the elderly affects cognition. In addition, an association between folate status and ageing, dementia and other neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis is discussed. While its role in the incidence and severity of these diseases is becoming apparent, the underlying action of folates and related metabolites remains elusive. Finally, the potential of FA as a nutraceutical has been proposed, although the efficacy will highly depend on the interplay with other micronutrients, the disease stage and the duration of supplementation. Hence, the lack of consistent data urges for more animal studies and (pre)clinical trials in humans to ascertain a potential beneficial role for folates in the treatment or amelioration of cognitive decline and ageing-related disorders.

Liraglutide Ameliorates Hyperhomocysteinemia-Induced Alzheimer-Like Pathology and Memory Deficits in Rats via Multi-molecular Targeting

Hyperhomocysteinemia (Hhcy) is an independent risk factor for Alzheimer's disease (AD), and insulin-resistance is commonly seen in patients with Hhcy. Liraglutide (Lir), a glucagon-like peptide that increases the secretion and sensitivity of insulin, has a neurotrophic or neuroprotective effect. However, it is not known whether Lir ameliorates the AD-like pathology and memory deficit induced by Hhcy. By vena caudalis injection of homocysteine to produce the Hhcy model in rats, we found here that simultaneous administration of Lir for 2 weeks ameliorated the Hhcy-induced memory deficit, along with increased density of dendritic spines and up-regulation of synaptic proteins. Lir also attenuated the Hhcy-induced tau hyperphosphorylation and Aβ overproduction, and the molecular mechanisms involved the restoration of protein phosphatase-2A activity and inhibition of β- and γ-secretases. Phosphorylated insulin receptor substrate-1 also decreased after treatment with Lir. Our data reveal that Lir improves the Hhcy-induced AD-like spatial memory deficit and the mechanisms involve the modulation of insulin-resistance and the pathways generating abnormal tau and Aβ.

Serum homocysteine level is related to cerebral small vessel disease in a healthy population

OBJECTIVE

To evaluate the relationship between serum total homocysteine (tHcy) levels and cerebral small vessel disease (cSVD) in a healthy population.

METHODS

We included consecutive participants who visited our department for health checkups between 2006 and 2013. We rated white matter hyperintensity volumes using both the Fazekas score and semiautomated quantitative methods. We also evaluated lacunes, cerebral microbleeds, and enlarged perivascular spaces (EPVS), which are involved in cSVD. To assess the dose-dependent relationship between tHcy and cSVD parameters, we scored the burdens of each radiologic marker of cSVD.

RESULTS

A total of 1,578 participants were included (age 55 ± 8 years, male sex 57%). In the multivariable analysis, tHcy remained an independent predictor of the white matter hyperintensity volume (B = 0.209; 95% confidence interval [CI] = 0.033-0.385, p = 0.020), presence of cerebral microbleeds (adjusted odds ratio = 2.800; 95% CI = 1.104-7.105, p = 0.030), and moderate to severe EPVS (adjusted odds ratio = 5.906; 95% CI = 3.523-9.901, p < 0.001) after adjusting for confounders. Furthermore, tHcy had positive associations with periventricular Fazekas score (p = 0.001, p for trend <0.001), subcortical Fazekas score (p = 0.003, p for trend = 0.005), and moderate to severe EPVS lesion burden (p < 0.001, p for trend <0.001) in a dose-dependent manner.

CONCLUSIONS

Serum tHcy level is correlated with cSVD development in a dose-dependent manner. These findings provide us with clues for further studies of the pathophysiology of cSVD.

Emodin Rescued Hyperhomocysteinemia-Induced Dementia and Alzheimer's Disease-Like Features in Rats

BACKGROUND

Hyperhomocysteinemia is an independent risk factor for dementia, including Alzheimer's disease. Lowering homocysteine levels with folic acid treatment with or without vitamin B12 has shown few clinical benefits on cognition.

METHODS

To verify the effect of emodin, a naturally active compound from Rheum officinale, on hyperhomocysteinemia-induced dementia, rats were treated with homocysteine injection (HCY, 400 μg/kg/d, 2 weeks) via vena caudalis. Afterwards, HCY rats with cognitive deficits were administered intragastric emodin at different concentrations for 2 weeks: 0 (HCY-E0), 20 (HCY-E20), 40 (HCY-E40), and 80 mg/kg/d (HCY-E80).

RESULTS

β-Amyloid overproduction, tau hyperphosphorylation, and losses of neuron and synaptic proteins were detected in the hippocampi of HCY-E0 rats with cognitive deficits. HCY-E40 and HCY-E80 rats had better behavioral performance. Although it did not reduce the plasma homocysteine level, emodin (especially 80 mg/kg/d) reduced the levels of β-amyloid and tau phosphorylation, decreased the levels of β-site amyloid precursor protein-cleaving enzyme 1, and improved the activity of protein phosphatase 2A. In the hippocampi of HCY-E40 and HCY-E80 rats, the neuron numbers, levels of synaptic proteins, and phosphorylation of the cAMP responsive element-binding protein at Ser133 were increased. In addition, depressed microglial activation and reduced levels of 5-lipoxygenase, interleukin-6, and tumor necrosis factor α were also observed. Lastly, hyperhomocysteinemia-induced microangiopathic alterations, oxidative stress, and elevated DNA methyltransferases 1 and 3β were rescued by emodin.

CONCLUSIONS

Emodin represents a novel potential candidate agent for hyperhomocysteinemia-induced dementia and Alzheimer's disease-like features.

Neuroprotective Effect of Hydrogen Sulfide in Hyperhomocysteinemia Is Mediated Through Antioxidant Action Involving Nrf2

Homocysteine (Hcy) is a sulfur-containing amino acid derived from methionine metabolism. Elevated plasma Hcy levels (> 15 µM) result in a condition called hyperhomocysteinemia (HHcy), which is an independent risk factor in the development of various neurodegenerative disorders. Reactive oxygen species (ROS) produced by auto-oxidation of Hcy have been implicated in HHcy-associated neurological conditions. Hydrogen sulfide (H₂S) is emerging as a potent neuroprotective and neuromodulator molecule. The present study was aimed to evaluate the ability of NaHS (a source of H₂S) to attenuate Hcy-induced oxidative stress and altered antioxidant status in animals subjected to HHcy. Impaired cognitive functions assessed by Y-maze and elevated plus maze in Hcy-treated animals were reversed on NaHS administration. Increased levels of ROS, lipid peroxidation, protein carbonyls, and 4-hydroxynonenal (4-HNE)-modified proteins were observed in the cortex and hippocampus of Hcy-treated animals suggesting accentuated oxidative stress. This increase in Hcy-induced oxidative stress was reversed following NaHS supplementation. GSH/GSSG ratio, activity of antioxidant enzymes viz; superoxide dismutase, glutathione peroxidase, glutathione reductase, and glutathione-S-transferase were decreased in Hcy-treated animals. NaHS supplementation, on the otherhand, restored redox ratio and activity of antioxidant enzymes in the brains of animals with HHcy. Further, NaHS administration normalized nuclear factor erythroid 2-related factor 2 expression and acetylcholinesterase (AChE) activity in the brain of Hcy-treated animals. Histopathological studies using cresyl violet indicated higher number of pyknotic neurons in the cortex and hippocampus of HHcy animals, which were reversed by NaHS administration. The results clearly demonstrate that NaHS treatment significantly ameliorates Hcy-induced cognitive impairment by attenuating oxidative stress, improving antioxidant status, and modulating AChE activity thereby suggesting potential of H₂S as a therapeutic molecule.

The protective mechanism of Nigella sativa against diethylnitrosamine-induced hepatocellular carcinoma through its antioxidant effect and EGFR/ERK1/2 signaling

A wide variety of natural products have powerful chemopreventive effects due to their antioxidant, antimutagenic, and anti-inflammatory activities that enable them to arrest cell proliferation in several cancer models. In the present study, we shed light on the protective mechanism of Nigella sativa extract against diethylnitrosamine (DENA)-induced preneoplastic stage of hepatocellular carcinoma (HCC) in rats. We studied the extract effect on EGFR/ERK1/2 signaling pathway as one of the major signaling pathways controlling cell proliferation during hepatocarcinogenesis as well as the investigation of its antioxidant activity. The study also compared the effects of NSEE to those of (thymoquinone) TQ and silymarin as hepatoprotective substances. Rats received daily doses of NSEE (150, 250, 350 mg/kg BW), a dose per three alternative days/week of TQ (20 mg/kg BW) and a daily dose of silymarin (100 mg/kg BW). The doses were administered orally by gavage for 12 days before DENA and CCl4 administration, and then the supply of NSEE, TQ or silymarin was continued until the end of the experiment (16 weeks). DENA administration activated EGFR/ERK1/2 signaling and caused a significant increase in P-EGFR and P-ERK1/2 as well as a significant up-regulation of expression of target genes such as PCNA, c-fos and Bcl2, which indicated the increase in cell proliferation. Furthermore, a significant elevation in alpha-fetoprotein (AFP) and hepatic enzymes was observed in DENA-treated rats in addition to a decrease in the antioxidant status. The protection with NSEE, TQ, or silymarin has the potential to inhibit the EGFR/ERK1/2 activation and improve the antioxidant status. Moreover, the action of NSEE against the hepatocarcinogenesis was supported by high antioxidant activity and the histopathological observations of the liver. These data suggest that NSEE has a chemopreventive role in DENA-induced HCC through the inhibition of the EGFR/ERK1/2 signaling pathway and their target genes in addition to its role as an antioxidant.

Proton Pump Inhibitors and Dementia: Physiopathological Mechanisms and Clinical Consequences

Alzheimer's disease (AD) is the most common type of dementia, mainly encompassing cognitive decline in subjects aged ≥65 years. Further, AD is characterized by selective synaptic and neuronal degeneration, vascular dysfunction, and two histopathological features: extracellular amyloid plaques composed of amyloid beta peptide (Aβ) and neurofibrillary tangles formed by hyperphosphorylated tau protein. Dementia and AD are chronic neurodegenerative conditions with a complex physiopathology involving both genetic and environmental factors. Recent clinical studies have shown that proton pump inhibitors (PPIs) are associated with risk of dementia, including AD. However, a recent case-control study reported decreased risk of dementia. PPIs are a widely indicated class of drugs for gastric acid-related disorders, although most older adult users are not treated for the correct indication. Although neurological side effects secondary to PPIs are rare, several preclinical reports indicate that PPIs might increase Aβ levels, interact with tau protein, and affect the neuronal microenvironment through several mechanisms. Considering the controversy between PPI use and dementia risk, as well as both cognitive and neuroprotective effects, the aim of this review is to examine the relationship between PPI use and brain effects from a neurobiological and clinical perspective.

Genetic influence of plasma homocysteine on Alzheimer's disease

Observational studies have consistently reported elevated plasma homocysteine as a risk factor for Alzheimer's disease (AD). However, results from clinical trials of homocysteine-lowering treatments are inconsistent. This discrepancy may be explained by a lack of causal association between homocysteine and AD. Mendelian randomization studies have the potential to provide insight into the causality of this association through studying the effect of genetic predisposition to high homocysteine on AD. Our analyses using summarized (n = 54,162) and individual participant (n = 6987) data from Caucasian participants did not show an effect of plasma homocysteine genetic risk on susceptibility to AD. Although with smaller sample sizes, further subanalyses also did not support an effect of genetically determined plasma homocysteine on cognitive impairment and decline, beta-amyloid and tau pathology and gray matter atrophy in AD. However, we found associations with tau tangle burden (n = 251) and gray matter atrophy (n = 605) in cognitively normal elderly. Our results do not support a causal association between elevated homocysteine and risk, severity, and progression of AD. However, the relationship between genetically determined homocysteine and brain pathology in cognitively normal elderly requires further exploration.

Hydrogen sulfide attenuates homocysteine-induced cognitive deficits and neurochemical alterations by improving endogenous hydrogen sulfide levels

Hyperomocysteinemia (HHcy) has been associated with mild cognitive impairment and dementia. Hydrogen sulfide (H₂ S) has been suggested to be an endogenous modulator of neuronal functions. However, the effect and mechanisms involved in beneficial effect of H₂ S has not been investigated in homocysteine (Hcy)-induced cognitive deficits. This study has been designed to evaluate the effect of exogenous H₂ S on behavioral deficits and neurochemical alterations in HHcy animals. Hcy levels were significantly elevated in plasma, cortex, and hippocampus of Hcy administered animals. A progressive decline in memory functions and increased anxiolytic behavior was observed in HHcy animals. This was accompanied by decrease in endogenous H₂ S levels along with decreased activity of cystathionase (CSE) and cystathionine β-synthase (CBS). However, a significant increase in CSE and CBS mRNAs was observed. In addition, the catecholamine and serotonin levels were reduced and the activity of monoamine oxidase A and B were increased in brain regions of HHcy animals. Haematoxylin and eosin staining revealed higher number of pyknotic cells in brain regions of HHcy animals. H₂ S administration was found to lower elevated plasma and brain Hcy levels. The activities of CBS, CSE, and levels of H₂ S were restored in HHcy animals administered H₂ S. Exogenous H₂ S also ameliorated behavioral deficits accompanied by significant increase in catecholamines. Histological analysis revealed normal cell morphology in Hcy-treated animals supplemented with H₂ S. These results clearly demonstrate that the protective effect of H₂ S on Hcy-induced cognitive deficits is mediated through increased catecholamine and H₂ S levels thereby suggesting its beneficial role in preventing HHcy-induced neurodegeneration. © 2016 BioFactors, 43(3):434-450, 2017.

Downregulating ANP32A rescues synapse and memory loss via chromatin remodeling in Alzheimer model

Background

The impairment of histone acetylation is causally linked to the cognitive decline in Alzheimer’s disease (AD). In addition to histone acetyltransferases (HATs) and histone deacetylases (HDACs), inhibitor of acetyltransferases (INHAT) can also regulate histone acetylation. As a key component of INHAT, level of ANP32A is selectively upregulated in the brain of AD patients. Here we investigated whether downregulating ANP32A can rescue AD-like synapse and memory deficits.

Methods

RFP-labeled lentiviral ANP32A-shRNA was infused stereotaxically into the hippocampal CA3 region of the human tau transgenic mice (termed htau). The spatial learning and memory were assessed by Morris water maze (MWM). The synaptic function was measured by electrophysiological recording and the spine density was detected by Golgi staining. RT-PCR and Western blotting were used to detect the mRNA and protein levels.

Results

Elevation of ANP32 in htau transgenic mice was correlated with learning deficits, while the hippocampal infusion of lenti-siANP32A to downregulate ANP32A in 12 m-old htau mice could rescue memory loss. Further studies demonstrated that downregulating ANP32A restored synapse morphology and the function. In the brain of htau mice, the acetylated histone decreased while knockdown ANP32A unmasked histone for a robust acetylation with reduced INHAT complex formation. Downregulating of ANP32A also attenuated AD-like tau hyperphosphorylation. Finally, several AD-associated risk factors, including tau accumulation, β-amyloid and H₂O₂ exposure, increased ANP32A by activating CCAAT/enhancer binding protein-β (C/EBPβ).

Conclusion

We conclude that downregulating ANP32A rescues synaptic plasticity and memory ability by reducing INHAT formation and unmasking histone for hyperacetylation. Our findings reveal novel mechanisms for AD memory loss and potential molecular markers for protection.

Electronic supplementary material

The online version of this article (doi:10.1186/s13024-017-0178-8) contains supplementary material, which is available to authorized users.

Tautomeric Effect of Histidine on the Monomeric Structure of Amyloid β-Peptide(1-42)

Tautomeric state of histidine is one of the factors that influence the structural and aggregation properties of amyloid β (Aβ)-peptide in neutral state. It is worth it to uncover the monomeric properties of Aβ(1-42) peptide in comparison with Aβ(1-40) peptide. Our replica-exchange molecular dynamics simulations results show that the sheet content of each tautomeric isomer in Aβ(1-42) monomer is slightly higher than that in Aβ(1-40) monomer except His6(δ)-His13(δ)-His14(δ) (δδδ) isomer, implying higher aggregation tendency in Aβ(1-42), which is in agreement with previous experimental and theoretical studies. Further analysis indicates that (εεε), (εδε), (εδδ), and (δδε) isomers prefer sheet conformation although they are in nondominating states. Particularly, it is confirmed that antiparallel β-sheets of (εδδ) were formed at K16-E22 (22.0-43.9%), N27-A30 except G29 (21.9-40.2%), and M35-I41 except G37 (24.1-43.4%). Furthermore, (εδδ) may be the easiest one to overcome structural transformation due to nonobstructing interactions between K16 and/or L17 and histidine residues. The current study will help to understand the tautomeric effect of Aβ(1-42) peptide to overcome Alzheimer's disease.

Possible role of endothelin receptor against hyperhomocysteinemia and β-amyloid induced AD type of vascular dementia in rats

Vascular dementia (VaD) is considered as the second commonest form of dementia after Alzheimer's disease (AD). The study was designed to investigate the effect of endothelin receptor against β-amyloid induced AD type of vascular dementia. This disease was induced by combine administration of single ICV (intracerebroventricle) infusion of β-amyloid (Aβ) once and chronic oral administration of l-Methionine for 21 days. Bosentan (dual endothelin receptor antagonist) was administered for 21 days. Behavioral alterations were observed during different time interval of the study. Animals were killed immediately following the last behavior session. Oxidative parameters, acetylcholinesterase activity, neuro-inflammatory markers, amyloid beta levels were determined in hippocampus and cortex while serum homocysteine, serum nitrite carotid artery superoxide anion level were also determined. Endothelial function was measured on isolated carotid artery using myograph instrument. Aβ+l-Methionine showed more significant development of cognitive and vascular endothelial deficits, manifested in terms of increase in serum homocysteine level, endothelial dysfunction, impairment of learning and memory, enhanced brain acetylcholinesterase activity, marked mito-oxidative damage in rats. We have observed that l-Methionine and combination of Aβ+l-Methionine significantly enhanced Aβ level both in cortex as well as hippocampus. Treatment of bosentan attenuated Aβ+l-Methionine induced impairment of learning and memory, enhanced Aβ level, mitochondrial and endothelial dysfunction. The results of present study concluded that bosentan offers protection against β-amyloid-induced vascular dementia in rats. Endothelin receptor may be considered as a potential pharmacological target for the management of AD type of vascular dementia.

Association between C677T polymorphism of MTHFR gene and risk of amyotrophic lateral sclerosis: Polish population study and a meta-analysis

OBJECTIVE

Genetic factors play a role in pathogenesis of amyotrophic lateral sclerosis (ALS). A few studies demonstrated that the TT genotype of C677T polymorphism of the 5,10-methylenetetrahydrofolate reductase (MTHFR) gene can increase the risk of sporadic ALS. The aim of our study was to determine the relationship between C677T polymorphism of MTHFR gene and the risk of sporadic ALS in Polish population and to perform the meta-analysis assessing the significance this polymorphism for the risk of ALS in Caucasian population.

METHODS

We included 251 patients with ALS and 500 control subjects recruited from Polish population and performed the meta-analysis of published data from Caucasian population. MTHFR C677T polymorphism was genotyped using a TaqMan assay and 7900HT Fast real Time PCR System.

RESULTS

The frequency of genotypes did not differ significantly between Polish ALS patients and control subjects (CC: 45.0 vs 45.8%, CT: 48.2 vs 45.0%, TT: 6.8 vs 9.2%, P=0.46). The meta-analysis including 863 ALS patients and 1362 controls revealed that TT genotype increases the risk of sporadic ALS in Caucasian population.

CONCLUSION

Although we did not find the association between C677T polymorphism of MTHRF gene and risk of ALS in Polish population, the results of meta-analysis suggest that the TT genotype can be a genetic risk factor for ALS in Caucasian population.

Cross-Sectional Associations of Total Plasma Homocysteine with Cortical β-Amyloid Independently and as a Function of Omega 3 Polyunsaturated Fatty Acid Status in Older Adults at Risk of Dementia

OBJECTIVES

Elevated total plasma homocysteine is a risk factor for Alzheimer's disease (AD) and there is some evidence that omega-3 polyunsaturated fatty acids (n-3 PUFAs) can modulate the effects of homocysteine-lowering B vitamins on AD related pathologies. Hence we investigated the relationship between total plasma homocysteine and cortical β-amyloid (Aβ) in older adults at risk of dementia. The role of erythrocyte membrane n-3 PUFAs (omega 3 index) on this relationship was also explored.

DESIGN

This is a cross-sectional study using data from the Multidomain Alzheimer Preventive Trial (MAPT); a randomised controlled trial.

SETTING

French community dwellers aged 70 or over reporting subjective memory complaints, but free from a diagnosis of clinical dementia.

PARTICIPANTS

Individuals were from the MAPT trial (n = 177) with data on total plasma homocysteine at baseline and cortical Aβ load.

MEASUREMENTS

Cortical-to-cerebellar standard uptake value ratios were assessed using [18F] florbetapir positron emission tomography (PET). Total baseline plasma homocysteine was measured using an enzymatic cycling assay. Baseline omega 3 index was measured using gas chromatography. Cross-sectional associations were explored using adjusted multiple linear regression models.

RESULTS

We found that total baseline plasma homocysteine was not significantly associated with cortical Aβ as demonstrated using multiple linear regression models adjusted for age, sex, education, cognitive status, time interval between baseline and PET-scan, omega-3 index, MAPT group allocation and Apolipoprotein E ε4 status (B-coefficient -0.001, 95 % CI: -0.008,0.006, p = 0.838). Exploratory analysis showed that homocysteine was however significantly associated with cortical Aβ in subjects with low baseline omega-3 index (< 4.72 %) after adjustment for Apolipoprotein E ε4 status (B-coefficient 0.041, 95 % CI: 0.017,0.066, p = 0.005, n = 10), but not in subjects with a high baseline omega-3 index (B-coefficient -0.010, 95 % CI: -0.023,0.003, p = 0.132, n = 66).

CONCLUSIONS

The role of n-3 PUFAs on the relationship between homocysteine and cerebral Aβ warrants further investigation.

Hydrogen Sulfide Ameliorates Homocysteine-Induced Cognitive Dysfunction by Inhibition of Reactive Aldehydes Involving Upregulation of ALDH2

BACKGROUND

Homocysteine, a risk factor for Alzheimer's disease, induces cognitive dysfunction. Reactive aldehydes play an important role in cognitive dysfunction. Aldehyde-dehydrogenase 2 detoxifies reactive aldehydes. Hydrogen sulfide, a novel neuromodulator, has neuroprotective effects and regulates learning and memory. Our previous work confirmed that the disturbance of hydrogen sulfide synthesis is invovled in homocysteine-induced defects in learning and memory. Therefore, the present work was to explore whether hydrogen sulfide ameliorates homocysteine-generated cognitive dysfunction and to investigate whether its underlying mechanism is related to attenuating accumulation of reactive aldehydes by upregulation of aldehyde-dehydrogenase 2.

METHODS

The cognitive function of rats was assessed by the Morris water maze test and the novel object recognition test. The levels of malondialdehyde, 4-hydroxynonenal, and glutathione as well as the activity of aldehyde-dehydrogenase 2 were determined by enzyme linked immunosorbent assay; the expression of aldehyde-dehydrogenase 2 was detected by western blot.

RESULTS

The behavior experiments, Morris water maze test and novel objects recognition test, showed that homocysteine induced deficiency in learning and memory in rats, and this deficiency was reversed by treatment of NaHS (a donor of hydrogen sulfide). We demonstrated that NaHS inhibited homocysteine-induced increases in generations of MDA and 4-HNE in the hippocampus of rats and that hydrogen sulfide reversed homocysteine-induced decreases in the level of glutathione as well as the activity and expression of aldehyde-dehydrogenase 2 in the hippocampus of rats.

CONCLUSION

Hydrogen sulfide ameliorates homocysteine-induced impairment in cognitive function by decreasing accumulation of reactive aldehydes as a result of upregulations of glutathione and aldehyde-dehydrogenase 2.

Potential Links between Impaired One-Carbon Metabolism Due to Polymorphisms, Inadequate B-Vitamin Status, and the Development of Alzheimer's Disease

Alzheimer's disease (AD) is the major cause of dementia and no preventive or effective treatment has been established to date. The etiology of AD is poorly understood, but genetic and environmental factors seem to play a role in its onset and progression. In particular, factors affecting the one-carbon metabolism (OCM) are thought to be important and elevated homocysteine (Hcy) levels, indicating impaired OCM, have been associated with AD. We aimed at evaluating the role of polymorphisms of key OCM enzymes in the etiology of AD, particularly when intakes of relevant B-vitamins are inadequate. Our review indicates that a range of compensatory mechanisms exist to maintain a metabolic balance. However, these become overwhelmed if the activity of more than one enzyme is reduced due to genetic factors or insufficient folate, riboflavin, vitamin B6 and/or vitamin B12 levels. Consequences include increased Hcy levels and reduced capacity to synthetize, methylate and repair DNA, and/or modulated neurotransmission. This seems to favor the development of hallmarks of AD particularly when combined with increased oxidative stress e.g., in apolipoprotein E (ApoE) ε4 carriers. However, as these effects can be compensated at least partially by adequate intakes of B-vitamins, achieving optimal B-vitamin status for the general population should be a public health priority.

The Protective Effects of Icariin against the Homocysteine-Induced Neurotoxicity in the Primary Embryonic Cultures of Rat Cortical Neurons

Icariin, an ingredient in the medicinal herb Epimedium brevicornum Maxim (EbM), has been considered as a potential therapeutic agent for neurodegenerative diseases such as Alzheimer’s disease (AD). Hyperhomocysteinaemia is a risk factor for AD and other associated neurological diseases. In this study we aim to investigate whether icariin can reverse homocysteine (Hcy)-induced neurotoxicity in primary embryonic cultures of rat cortical neurons. Our findings demonstrated that icariin might be able restore the cytoskeleton network damaged by Hcy through the modulation of acetyl-α-tubulin, tyrosinated-α-tubulin, and phosphorylation of the tubulin-binding protein Tau. In addition, icariin downregulated p-extracellular signal-regulated kinase (ERK) which is a kinase targeting tau protein. Furthermore, icariin effectively restored the neuroprotective protein p-Akt that was downregulated by Hcy. We also applied RT² Profiler PCR Arrays focused on genes related to AD and neurotoxicity to examine genes differentially altered by Hcy or icariin. Among the altered genes from the arrays, ADAM9 was downregulated 15 folds in cells treated with Hcy, but markedly restored by icariin. ADAM family, encoded α-secreatase, plays a protective role in AD. Overall, our findings demonstrated that icariin exhibits a strong neuroprotective function and have potential for future development for drug treating neurological disorders, such as AD.

Homocysteine metabolism is associated with cerebrospinal fluid levels of soluble amyloid precursor protein and amyloid beta

Disturbed homocysteine metabolism may contribute to amyloidogenesis by modulating the amyloid precursor protein (APP) production and processing. The objective of this study was to investigate the relationships between cerebral amyloid production and both blood and cerebrospinal fluid (CSF) markers of the homocysteine metabolism. We assessed CSF concentrations of soluble APPα, soluble APPβ, and amyloid β1-42 (Aβ1-42), as well as plasma levels of homocysteine (Hcys), total vitamin B12, and folate, and CSF concentrations of homocysteine (Hcys-CSF), 5-methyltetrahydrofolate (5-MTHF), S-adenosylmethionine (SAM), and S-adenosylhomocysteine (SAH) in 59 subjects with normal cognition. Linear regression analyses were performed to assess associations between homocysteine metabolism parameters and amyloid production. The study was approved by the Ethical Committee of the University of Bonn. After controlling for age, gender, APOEe4 status, and albumin ratio (Qalb), higher Aβ1-42 CSF levels were associated with high Hcys and low vitamin B12 plasma levels as well as with high Hcys, high SAH, and low 5-MTHF CSF levels. Higher CSF concentrations of sAPPα and sAPPβ were associated with high SAH levels. The results suggest that disturbed homocysteine metabolism is related to increased CSF levels of sAPP forms and Aβ1-42, and may contribute to the accumulation of amyloid pathology in the brain. Disturbed homocysteine metabolism may contribute to amyloidogenesis by modulating the amyloid precursor protein (APP) production and processing. We found associations between CSF levels of soluble APP forms and Aβ1-42, and markers of the homocysteine metabolism in both plasma and CSF in adults with normal cognition. Disturbed homocysteine metabolism may represent a target for preventive and early disease-modifying interventions in Alzheimer's disease.

The involvement of homocysteine in stress-induced Aβ precursor protein misprocessing and related cognitive decline in rats

Chronic stress is a risk factor in the development of cognitive decline and even Alzheimer's disease (AD), although its underlying mechanism is not fully understood. Our previous data demonstrated that the level of homocysteine (Hcy) was significantly elevated in the plasma of stressed animals, which suggests the possibility that Hcy is a link between stress and cognitive decline. To test this hypothesis, we compared the cognitive function, plasma concentrations of Hcy, and the brain beta-amyloid (Aβ) level between rats with or without chronic unexpected mild stress (CUMS). A lower performance by rats in behavioral tests indicated that a significant cognitive decline was induced by CUMS. Stress also disturbed the normal processing of Aβ precursor protein (APP) and resulted in the accumulation of Aβ in the brains of rats, which showed a positive correlation with the hyperhomocysteinemia (HHcy) that appeared in stressed rats. Hcy-targeting intervention experiments were used to verify further the involvement of Hcy in stress-induced APP misprocessing and related cognitive decline. The results showed that diet-induced HHcy could mimic the cognitive impairment and APP misprocessing in the same manner as CUMS, while Hcy reduction by means of vitamin B complex supplements and betaine could alleviate the cognitive deficits and dysregulation of Aβ metabolism in CUMS rats. Taken together, the novel evidence from our present study suggests that Hcy is likely to be involved in chronic stress-evoked APP misprocessing and related cognitive deficits. Our results also suggested the possibility of Hcy as a target for therapy and the potential value of vitamin B and betaine intake in the prevention of stress-induced cognitive decline.

Associations between Homocysteine, Folic Acid, Vitamin B12 and Alzheimer's Disease: Insights from Meta-Analyses

The associations between homocysteine (Hcy), folic acid, and vitamin B12 and Alzheimer's disease (AD) have gained much interest, while remaining controversial. We aim to perform meta-analyses to evaluate comprehensively: i) Hcy, folic acid, and vitamin B12 levels in AD patients in comparison with controls; and ii) the association between Hcy, folic acid, and vitamin B12 levels and risk of AD. A literature search was performed using Medline and Scopus databases. A total of 68 studies were identified and included in the meta-analyses. Stata 12.0 statistical software was used to perform the meta-analyses. First, AD patients may have higher level of Hcy, and lower levels of folate and vitamin B12 in plasma than controls. Further age-subgroup analysis showed no age effect for Hcy levels in plasma between AD patients and matched controls, while the differences in folate and vitamin B12 levels further enlarged with increased age. Second, data suggests that high Hcy and low folate levels may correlate with increased risk of AD occurrence. The comprehensive meta-analyses not only confirmed higher Hcy, lower folic acid, and vitamin B12 levels in AD patients than controls, but also implicated that high Hcy and low folic acid levels may be risk factors of AD. Further studies are encouraged to elucidate mechanisms linking these conditions.

Lipoprotein-associated phospholipase A2, homocysteine, and Alzheimer's disease

INTRODUCTION

Lipoprotein-associated phospholipase A2 (Lp-PLA2) and homocysteine (Hcy) have been linked to inflammation and Alzheimer's disease (AD). Using a case-control design, we examined their independent effects and interactions with cardiovascular disease equivalent (CVDE), on AD risk.

METHODS

AD cases and controls were from the Texas Alzheimer's Research and Care Consortium study. Lp-PLA2 was determined using the PLAC test (diaDexus, Inc), and Hcy by recombinant cycling assay (Roche Hitachi 911). Logistic regression was used to predict AD case status. We assayed for Lp-PLA2 in the brain tissue of cases and controls.

RESULTS

AD case status was independently associated with Lp-PLA2 and Hcy above the median (odds ratio [OR] = 1.91; 95% confidence interval [CI] = 1.22-2.97; P < .001 and OR = 1.81; 95% CI = 1.16-2.82; P = .009, respectively). Lp-PLA2, but not Hcy, interacted with CVDE to increase risk. Lp-PLA2 was absent from the brain tissue in both groups.

DISCUSSION

Higher Lp-PLA2 and Hcy are independently associated with AD. The association of Lp-PLA2 with AD may be mediated through vascular damage.

Is L-methionine a trigger factor for Alzheimer's-like neurodegeneration?: Changes in Aβ oligomers, tau phosphorylation, synaptic proteins, Wnt signaling and behavioral impairment in wild-type mice

BACKGROUND

L-methionine, the principal sulfur-containing amino acid in proteins, plays critical roles in cell physiology as an antioxidant and in the breakdown of fats and heavy metals. Previous studies suggesting the use of L-methionine as a treatment for depression and other diseases indicate that it might also improve memory and propose a role in brain function. However, some evidence indicates that an excess of methionine can be harmful and can increase the risk of developing Type-2 diabetes, heart diseases, certain types of cancer, brain alterations such as schizophrenia, and memory impairment.

RESULTS

Here, we report the effects of an L-methionine-enriched diet in wild-type mice and emphasize changes in brain structure and function. The animals in our study presented 1) higher levels of phosphorylated tau protein, 2) increased levels of amyloid-β (Aβ)-peptides, including the formation of Aβ oligomers, 3) increased levels of inflammatory response,4) increased oxidative stress, 5) decreased level of synaptic proteins, and 6) memory impairment and loss. We also observed dysfunction of the Wnt signaling pathway.

CONCLUSION

Taken together, the results of our study indicate that an L-methionine-enriched diet causes neurotoxic effects in vivo and might contribute to the appearance of Alzheimer's-like neurodegeneration.

[A modern concept of mixed dementia]

Cognitive impairment is currently one of the most urgent problems. A number of newly registered cases of dementia in the world approaches to 7,7 millions that means that a new case of dementia arises every four seconds. According to WHO data, Western Europe is in the first place (appr. 7,0 millions of patients). In 2010, Russia was among 9 countries with the highest number of patients with dementia. Mixed dementia is characterized by the presence of one or several pathogenetic mechanisms of cognitive impairment. Its prevalence is about 45%. Neurodegenerative and vascular processes underlying dementia are mutually potentiated. An analysis of the majority of characteristics demonstrates that mixed dementia has characteristics of both Alzheimer's disease and vascular dementia. Disturbances of neurotransmitter systems are caused by cholinergic deficit. Galantamine (reminil) is the drug that has demonstrated its efficacy in the treatment of dementia of Alzheimer's type including dementia with chronic disturbances of cerebral blood circulation.

Selected Micronutrients in Cognitive Decline Prevention and Therapy

Population aging is a worldwide demographic trend. Consequently, the prevalence of chronic age-related conditions such as clinically diagnosed neurological diseases, cognitive decline, and dementia will significantly increase in the near future. The important role of diets and healthy lifestyle as preventative of neurodegenerative diseases is widely accepted nowadays, and it may provide preventive strategies in very early, non-symptomatic phases of dementia well, especially because there are still no effective treatments for it. In this article, we review the known effects of selected micronutrients on the aging brain and we propose strategies for dietary improvements.

Homocysteine Induced Cerebrovascular Dysfunction: A Link to Alzheimer's Disease Etiology

A high serum level of homocysteine, known as hyperhomocystenemia (HHcy) is associated with vascular dysfunction such as altered angiogenesis and increased membrane permeability. Epidemiological studies have found associations between HHcy and Alzheimer’s disease (AD) progression that eventually leads to vascular dementia (VaD). VaD is the second most common cause of dementia in people older than 65, the first being AD. VaD affects the quality of life for those suffering by drastically decreasing their cognitive function. VaD, a cerebrovascular disease, generally occurs due to cerebral ischemic events from either decreased perfusion or hemorrhagic lesions. HHcy is associated with the hallmarks of dementia such as tau phosphorylation, Aβ aggregation, neurofibrillary tangle (NFT) formation, neuroinflammation, and neurodegeneration. Previous reports also suggest HHcy may promote AD like pathology by more than one mechanism, including cerebral microangiopathy, endothelial dysfunction, oxidative stress, neurotoxicity and apoptosis. Despite the corelations presented above, the question still exists – does homocysteine have a causal connection to AD? In this review, we highlight the role of HHcy in relation to AD by discussing its neurovascular effects and amelioration with dietary supplements. Moreover, we consider the studies using animal models to unravel the connection of Hcy to AD.

Correlations between homocysteine and grey matter volume in patients with Alzheimer's disease

BACKGROUND

Previous studies have reported that elevated total homocysteine levels are associated with cognitive dysfunction. However, few studies have examined the radiological markers of associated neuropathology in Alzheimer's disease (AD). We hypothesized that elevated levels of homocysteine are associated with cerebral grey matter volume loss. We compared the grey matter in a high homocysteine group and a normal homocysteine group using an optimized voxel-based morphometry.

METHODS

The study included 79 patients with AD who were divided into two groups: a high homocysteine group and a normal homocysteine group. The participants underwent brain magnetic resonance imaging using a standardized protocol and neurocognitive evaluation. Homocysteine tests and other routine laboratory examinations for dementia assessment were carried out in all patients.

RESULTS

There was no significant difference in grey matter volume between the patients with high homocysteine levels and those with normal homocysteine levels. A multiple regression analysis also revealed that the levels of homocysteine were not associated with the grey matter volume in patients with AD. Homocysteine levels were not correlated significantly with Mini-Mental State Examination, Global Deterioration Scale, or Clinical Dementia Rating.

CONCLUSION

Our results showed that elevated homocysteine levels are not associated with reduced cerebral grey matter volume in AD. Larger samples will be needed to assess potential correlations between homocysteine and neuroanatomical pathology in the future.

Senescence may mediate conversion of tau phosphorylation-induced apoptotic escape to neurodegeneration

Neurodegeneration is the characteristic pathology in the brains of Alzheimer's disease (AD). However, the nature and molecular mechanism leading to the degeneration are not clarified. Given that only the neurons filled with neurofibrillary tangles survive to the end stage of the disease and the major component of the tangles is the hyperphosphorylated tau proteins, it is conceivable that tau hyperphosphorylation must play a crucial role in AD neurodegeneration. We have demonstrated that tau hyperphosphorylation renders the cells more resistant to the acute apoptosis. The molecular mechanisms involve substrate competition of tau and β-catenin for glycogen synthase kinase 3β (GSK-3β); activation of Akt; preservation of Bcl-2 and suppression of Bax, cytosolic cytochrome-c, and caspase-3 activity; and upregulation of unfolded protein response (UPR), i.e., up-regulating phosphorylation of PERK, eIF2 and IRE1 with an increased cleavage of ATF6 and ATF4. On the other hand, tau hyperphosphorylation promotes its intracellular accumulation and disrupts axonal transport; hyperphosphorylated tau also impairs cholinergic function and inhibits proteasome activity. These findings indicate that tau hyperphosphorylation and its intracellular accumulation play dual role in the evolution of AD. We speculate that transient tau phosphorylation helps cells abort from an acute apoptosis, while persistent tau hyperphosphorylation/accumulation may trigger cell senescence that eventually causes a chronic neurodegeneration. Therefore, the nature of "AD neurodegeneration" may represent a new type of tau-regulated chronic neuron death; and the stage of cell senescence may provide a broad window for the intervention of AD.

CaMKII-dependent dendrite ramification and spine generation promote spatial training-induced memory improvement in a rat model of sporadic Alzheimer's disease

Participation in cognitively stimulating activities can preserve memory capacities in patients with Alzheimer's disease (AD), but the mechanism is not fully understood. Here, we used a rat model with hyperhomocysteinemia, an independent risk factor of AD, to study whether spatial training could remodel the synaptic and/or dendritic plasticity and the key molecular target(s) involved. We found that spatial training in water maze remarkably improved the subsequent short-term and long-term memory performance in contextual fear conditioning and Barnes maze. The trained rats showed an enhanced dendrite ramification, spine generation and plasticity in dentate gyrus (DG) neurons, and stimulation of long-term potentiation between perforant path and DG circuit. Spatial training also increased the levels of postsynaptic GluA1, GluN2A, GluN2B, and PSD93 with selective activation of calcium/calmodulin-dependent protein kinase II (CaMKII), although inhibition of CaMKII by stereotaxic injection of KN93 into hippocampal DG, abolished the training-induced cognitive improvement, dendrite ramification, and spine generation. We conclude that spatial training can preserve the cognitive function by CaMKII-dependent remodeling of dendritic plasticity in hyperhomocysteinemia-induced sporadic AD-like rats.

Reciprocal modulation of Aβ42 aggregation by copper and homocysteine

Hyperhomocysteinemia is a risk factor for Alzheimer’s disease (AD). Both homocysteine (Hcy) and amyloid β (Aβ), which accumulates in the brain of AD patients, bind copper. Aim of this study was to test the hypothesis that the association of Hcy and AD results from a molecular interaction between Hcy and Aβ that is mediated by copper. We established a microtiter plate format thioflavin T aggregation assay to monitor Aβ42 fibrillization. Copper (5 μM) completely prevented Aβ42 (5 μM) fibrillization. Homocysteine in the absence of copper did not impact Aβ42 fibrillization, but physiological concentrations of Hcy (10–100 μM) attenuated the inhibitory effect of copper on Aβ42 fibril formation. These results were qualitatively confirmed by electron microscopy, which did not reveal morphological differences. To compare the toxicity of fibrillar and non-fibrillar Aβ42 exposed to copper or Hcy, rat primary cortical neurons were treated in vitro with 5 μM Aβ42 for 72 h. After incubation with 5 μM Aβ42 that had been aggregating in the absence of Hcy or copper, cell viability was reduced to 40%. Incubation with 5 μM Aβ42, in which fibril formation had been prevented or reverted by the addition of 5 μM copper, resulted in cell viability of approximately 25%. Accordingly, viability was reduced to 25% after incubation with 5 μM monomeric, i.e., non-fibrillized, Aβ42. The addition of Hcy plus copper to 5 μM Aβ42 yielded 50% viability. In conclusion, copper prevents and reverts Aβ fibril formation leading rather to formation of lower order oligomers or amorphous aggregates, and Hcy reduces these effects. Such mechanisms may explain the association of hyperhomocysteinemia and AD, leading to novel therapeutic strategies in the prevention and treatment of this disease.

Hypoxia-induced tau phosphorylation and memory deficit in rats

Hypoxia was shown to be associated with an increased risk of Alzheimer's disease (AD). The effects of hypoxia on the development of AD pathology and spatial memory ability and the possible molecular mechanisms remain poorly understood. In this study, we demonstrate that rats exposed to a hypoxic condition (10% oxygen concentration) for 1, 2, 4 and 8 weeks (6 h each day) displayed spatial memory impairment and increased tau phosphorylation at Ser198/199/202, Thr205, Ser262, Ser396 and Ser404 in the hippocampus. Concomitantly, the levels of Tyr216-phosphorylated glycogen synthase kinase (GSK)-3β (activated form of GSK-3β) and Tyr307-phosphorylated protein phosphatase 2A (inactivated form of PP2A) were significantly increased in the hippocampus of the rats with 1, 2, 4 and 8 weeks of hypoxia exposure, while the levels of methylated PP2A (activated form of PP2A) were significantly decreased in the hippocampus of the rats with 4 and 8 weeks of hypoxia exposure. In addition, the content of malondialdehyde, an indicator of oxidative stress, was elevated, whereas the activity of superoxide dismutase was not significantly changed in the hippocampus of the rats exposed to hypoxia. Taken together, these data demonstrated that hypoxia induced tau hyperphosphorylation and memory impairment in rats, and that the increased tau phosphorylation could be attributed to activation of GSK-3β and inactivation of PP2A. These data suggest that interventions to improve hypoxia may be helpful to prevent the development of AD pathology and cognitive impairment.

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.

Protein phosphatase 2A dysfunction in Alzheimer's disease

Protein phosphatase 2A (PP2A) is a large family of enzymes that account for the majority of brain Ser/Thr phosphatase activity. While PP2A enzymes collectively modulate most cellular processes, sophisticated regulatory mechanisms are ultimately responsible for ensuring isoform-specific substrate specificity. Of particular interest to the Alzheimer’s disease (AD) field, alterations in PP2A regulators and PP2A catalytic activity, subunit expression, methylation and/or phosphorylation, have been reported in AD-affected brain regions. “PP2A” dysfunction has been linked to tau hyperphosphorylation, amyloidogenesis and synaptic deficits that are pathological hallmarks of this neurodegenerative disorder. Deregulation of PP2A enzymes also affects the activity of many Ser/Thr protein kinases implicated in AD. This review will more specifically discuss the role of the PP2A/Bα holoenzyme and PP2A methylation in AD pathogenesis. The PP2A/Bα isoform binds to tau and is the primary tau phosphatase. Its deregulation correlates with increased tau phosphorylation in vivo and in AD. Disruption of PP2A/Bα-tau protein interactions likely contribute to tau deregulation in AD. Significantly, alterations in one-carbon metabolism that impair PP2A methylation are associated with increased risk for sporadic AD, and enhanced AD-like pathology in animal models. Experimental studies have linked deregulation of PP2A methylation with down-regulation of PP2A/Bα, enhanced phosphorylation of tau and amyloid precursor protein, tau mislocalization, microtubule destabilization and neuritic defects. While it remains unclear what are the primary events that underlie “PP2A” dysfunction in AD, deregulation of PP2A enzymes definitely affects key players in the pathogenic process. As such, there is growing interest in developing PP2A-centric therapies for AD, but this may be a daunting task without a better understanding of the regulation and function of specific PP2A enzymes.

Disturbance of endogenous hydrogen sulfide generation and endoplasmic reticulum stress in hippocampus are involved in homocysteine-induced defect in learning and memory of rats

Homocysteine (Hcy) is a risk factor for Alzheimer's disease (AD). Hydrogen sulfide (H2S) acts as an endogenous neuromodulator and neuroprotectant. It has been shown that endoplasmic reticulum (ER) stress is involved in the pathological mechanisms of the learning and memory dysfunctions and that H2S exerts its neuroprotective role via suppressing ER stress. In the present work, we explored the effects of intracerebroventricular injection of Hcy on the formation of learning and memory, the generation of endogenous H2S, and the expression of ER stress in the hippocampus of rats. We found that intracerebroventricular injection of Hcy in rats leads to learning and memory dysfunctions in the Morris water maze and novel of object recognition test and decreases in the expression of cystathionine-β-synthase, the major enzyme responsible for endogenous H2S generation, and the generation of endogenous H2S in the hippocampus of rats. We also showed that exposure of Hcy could up-regulate the expressions of glucose-regulated protein 78 (GRP78), CHOP, and cleaved caspase-12, which are the major mark proteins of ER stress, in the hippocampus of rats. Taken together, these results suggest that the disturbance of hippocampal endogenous H2S generation and the increase in ER stress in the hippocampus are related to Hcy-induced defect in learning and memory.

Mice deficient in cystathionine beta synthase display increased Dyrk1A and SAHH activities in brain

Hyperhomocysteinemia is associated with brain disease. However, biological actions linking hyperhomocysteinemia to neuronal abnormalities are not well understood. We recently found a relationship between Dyrk1A protein expression, a serine/threonine kinase that might be responsible for cognitive functions in Down's syndrome, and hepatic S-adenosylhomocysteine hydrolase (SAHH) activity, which plays a key role in S-adenosylmethionine-dependent methylation reactions. Considering the role of methylation and Dyrk1A in cognitive functions, the aim of this study was to investigate the relationship between Dyrk1A and SAHH activity in brain of hyperhomocysteinemic mice. We found an increase in Dyrk1A protein expression and activity in brain of hyperhomocysteinemic mice, concomitant with an increased SAHH activity. The effect of overexpression of protein Dyrk1A on SAHH activity was confirmed in brain of Dyrk1A transgenic mice, and additionally we found a positive correlation between Dyrk1A and SAHH activity. These observations suggest a potential effect of Dyrk1A on brain phenotypes linked to hyperhomocysteinemia.

Betaine attenuates Alzheimer-like pathological changes and memory deficits induced by homocysteine

Hyperhomocysteinemia (Hhcy) may induce memory deficits with β-amyloid (Aβ) accumulation and tau hyperphosphorylation. Simultaneous supplement of folate and vitamin B12 partially restored the plasma homocysteine level and attenuated tau hyperphosphorylation, Aβ accumulation and memory impairments induced by Hhcy. However, folate and vitamin B12 treatment have no effects on Hhcy which has the methylenetetrahydrofolate reductase genotype mutation. In this study, we investigated the effects of simultaneous supplement of betaine on Alzheimer-like pathological changes and memory deficits in hyperhomocysteinemic rats after a 2-week induction by vena caudalis injection of homocysteine (Hcy). We found that supplementation of betaine could ameliorate the Hcy-induced memory deficits, enhance long-term potentiation (LTP) and increase dendritic branches numbers and the density of the dendritic spines, with up-regulation of NR1, NR2A, synaptotagmin, synaptophysin, and phosphorylated synapsin I protein levels. Supplementation of betaine also attenuated the Hcy-induced tau hyperphosphorylation at multiple AD-related sites through activation protein phosphatase-2A (PP2A) with decreased inhibitory demethylated PP2A(C) at Leu309 and phosphorylated PP2A(C) at Tyr307. In addition, supplementation of betaine also decreased Aβ production with decreased presenilin-1 protein levels. Our data suggest that betaine could be a promising candidate for arresting Hcy-induced AD-like pathological changes and memory deficits.

Associations between elevated homocysteine, cognitive impairment, and reduced white matter volume in healthy old adults

OBJECTIVES

Elevated homocysteine has emerged as a risk factor for cognitive impairment even in healthy elderly persons. Reduced brain volume and white matter hyperintensities also occur in healthy elderly as well, but the interrelationships between these have not been well studied. We report these interrelationships in non demented, relatively healthy, community-dwelling older adults from a single East Asian population.

METHODS

Two hundred twenty-eight right-handed participants age 55 years and above were evaluated. Persons with medical conditions or neurological diseases other than well-controlled diabetes mellitus and hypertension were excluded. Participants underwent quantitative magnetic resonance imaging of the brain using a standardized protocol and neuropsychological evaluation. Plasma homocysteine, folate, vitamin B(12), and markers for cardiovascular risk: blood pressure, body mass index, fasting blood glucose, and lipid profile were measured.

RESULTS

Elevated homocysteine was associated with reduced global cerebral volume, larger ventricles, reduced cerebral white matter volume, and lower cognitive performance in several domains. Elevated homocysteine was associated with reduced white matter volume (β = -20.80, t = -2.9, df = 223, p = 0.004) and lower speed of processing (β = -0.38, t = -2.1, df = 223, p = 0.03), even after controlling for age, gender, and education. However, the association between homocysteine and lower speed of processing disappeared after controlling for white matter volume. Elevated homocysteine was not associated with white matter hyperintensity volume or with hippocampal volume. Although homocysteine and folate levels were correlated, their effects on white matter volume were dissociated.

CONCLUSION

In non demented, relatively healthy adults, elevated homocysteine is associated with lower cognitive scores and reduced cerebral white matter volume. These effects can be dissociated from those related to white matter hyperintensities or reduced folate level.

Potential therapeutic effect of nanobased formulation of rivastigmine on rat model of Alzheimer's disease

Background

To sustain the effect of rivastigmine, a hydrophilic cholinesterase inhibitor, nanobased formulations were prepared. The efficacy of the prepared rivastigmine liposomes (RLs) in comparison to rivastigmine solution (RS) was assessed in an aluminium chloride (AlCl₃)-induced Alzheimer’s model.

Methods

Liposomes were prepared by lipid hydration (F1) and heating (F2) methods. Rats were treated with either RS or RLs (1 mg/kg/day) concomitantly with AlCl₃ (50 mg/kg/day).

Results

The study showed that the F1 method produced smaller liposomes (67.51 ± 14.2 nm) than F2 (528.7 ± 15.5 nm), but both entrapped the same amount of the drug (92.1% ± 1.4%). After 6 hours, 74.2% ± 1.5% and 60.8% ± 2.3% of rivastigmine were released from F1 and F2, respectively. Both RLs and RS improved the deterioration of spatial memory induced by AlCl₃, with RLs having a superior effect. Further biochemical measurements proved that RS and RLs were able to lower plasma C-reactive protein, homocysteine and asymmetric dimethy-larginine levels. RS significantly attenuated acetylcholinesterase (AChE) activity, whereas Na⁺/K⁺-adenosine triphosphatase (ATPase) activity was enhanced compared to the AlCl₃-treated animals; however, RLs succeeded in normalization of AChE and Na⁺/K⁺ ATPase activities. Gene-expression profile showed that cotreatment with RS to AlCl₃-treated rats succeeded in exerting significant decreases in BACE1, AChE, and IL1B gene expression. Normalization of the expression of the aforementioned genes was achieved by coadministration of RLs to AlCl₃-treated rats. The profound therapeutic effect of RLs over RS was evidenced by nearly preventing amyloid plaque formation, as shown in the histopathological examination of rat brain.

Conclusion

RLs could be a potential drug-delivery system for ameliorating Alzheimer’s disease.

Age-related lysosomal dysfunction: an unrecognized roadblock for cobalamin trafficking?

Vitamin-B(12) is a generic term for corrinoid compounds that exhibit the biological activity of cyanocobalamin and are collectively referred to as cobalamins. Methylcobalamin and 5-deoxyadenosylcobalamin are the active cobalamins in human metabolism. Cobalamin plays a crucial role in the maintenance of homocysteine and methylmalonyl-CoA homeostasis and is required for erythrocyte formation and DNA synthesis. Data from human and animal studies indicate that cobalamin deficiency impairs neuronal function; a process that is thought to contribute to age-related cognitive decline and dementia. Cobalamin deficiency also results in dysfunction of the peripheral nervous system; among other disorders. Although there is a detailed understanding of the biochemical pathways that are perturbed in cobalamin deficiency, the mechanisms underlying age-related dyshomeostasis in such pathways remain to be addressed. Because cobalamin utilization is dependent on its efficient transit through lysosomes, and mounting evidence indicates that lysosomal function deteriorates in aging long-lived post-mitotic cells such as neurons, in the present article we review published data that supports the proposition that impaired lysosomal processing of cobalamin may play a significant role in age-related (neuro) degenerative diseases.

Acetyl-L-carnitine attenuates homocysteine-induced Alzheimer-like histopathological and behavioral abnormalities

Hyperhomocystinemia could induce tau protein hyperphosphorylation, β-amyloid (Aβ) accumulation, and memory deficits as seen in Alzheimer disease (AD), the most common cause of senile dementia with no effective cure currently. To search for possible treatment for AD, we produced a hyperhomocysteinemia model by vena caudalis injection of homocystine (Hcy) for 2 weeks and studied the effects of acetyl-L-carnitine (ALC) in rats. We found that simultaneous supplement of ALC could improve the Hcy-induced memory deficits remarkably, with attenuation of tau hyperphosphorylation and Aβ accumulation. Supplement of ALC almost abolished the Hcy-induced tau hyperphosphorylation at multiple AD-related sites. Supplementation of ALC also suppressed the phosphorylation of β-amyloid precursor proteins (APP), which may underlie the reduction of Aβ. Our data suggest that ALC could be a promising candidate for arresting Hcy-induced AD-like pathological and behavioral impairments.

Acid sphingomyelinase gene deficiency ameliorates the hyperhomocysteinemia-induced glomerular injury in mice

Hyperhomocysteinemia (hHcys) enhances ceramide production, leading to the activation of NADPH oxidase and consequent glomerular oxidative stress and sclerosis. The present study was performed to determine whether acid sphingomyelinase (Asm), a ceramide-producing enzyme, is implicated in the development of hHcys-induced glomerular oxidative stress and injury. Uninephrectomized Asm-knockout (Asm(-/-)) and wild-type (Asm(+/+)) mice, with or without Asm short hairpin RNA (shRNA) transfection, were fed a folate-free (FF) diet for 8 weeks, which significantly elevated the plasma Hcys level compared with mice fed normal chow. By using in vivo molecular imaging, we found that transfected shRNAs were expressed in the renal cortex starting on day 3 and continued for 24 days. The FF diet significantly increased renal ceramide production, Asm mRNA and activity, urinary total protein and albumin excretion, glomerular damage index, and NADPH-dependent superoxide production in the renal cortex from Asm(+/+) mice compared with that from Asm(-/-) or Asm shRNA-transfected wild-type mice. Immunofluorescence analysis showed that the FF diet decreased the expression of podocin but increased desmin and ceramide levels in glomeruli from Asm(+/+) mice but not in those from Asm(-/-) and Asm shRNA-transfected wild-type mice. In conclusion, our observations reveal that Asm plays a pivotal role in mediating podocyte injury and glomerular sclerosis associated with NADPH oxidase-associated local oxidative stress during hHcys.