Differential effects of short- and long-term hyperhomocysteinaemia on cholinergic neurons, spatial memory and microbleedings in vivo in rats

Pannexin1 Mediates Early-Life Seizure-Induced Social Behavior Deficits

There is a high co-morbidity between childhood epilepsy and autism spectrum disorder (ASD), with age of seizure onset being a critical determinant of behavioral outcomes. The interplay between these comorbidities has been investigated in animal models with results showing that the induction of seizures at early post-natal ages leads to learning and memory deficits and to autistic-like behavior in adulthood. Modifications of the excitation/inhibition (glutamate/GABA, ATP/adenosine) balance that follows early-life seizures (ELS) are thought to be the physiological events that underlie neuropsychiatric and neurodevelopmental disorders. Although alterations in purinergic/adenosinergic signaling have been implicated in seizures and ASD, it is unknown whether the ATP release channels, Pannexin1 (Panx1), contribute to ELS-induced behavior changes. To tackle this question, we used the ELS-kainic acid model in transgenic mice with global and cell type specific deletion of Panx1 to evaluate whether these channels were involved in behavioral deficits that occur later in life. Our studies show that ELS results in Panx1 dependent social behavior deficits and also in poor performance in a spatial memory test that does not involve Panx1. These findings provide support for a link between ELS and adult behavioral deficits. Moreover, we identify neuronal and not astrocyte Panx1 as a potential target to specifically limit astrogliosis and social behavioral deficits resultant from early-life seizures.

Astrocyte and Neuronal Panx1 Support Long-Term Reference Memory in Mice

Pannexin 1 (Panx1) is an ubiquitously expressed protein that forms plasma membrane channels permeable to anions and moderate-sized signaling molecules (e.g., ATP, glutamate). In the nervous system, activation of Panx1 channels has been extensively shown to contribute to distinct neurological disorders (epilepsy, chronic pain, migraine, neuroAIDS, etc.), but knowledge of the extent to which these channels have a physiological role remains restricted to three studies supporting their involvement in hippocampus dependent learning. Given that Panx1 channels may provide an important mechanism for activity-dependent neuron-glia interaction, we used Panx1 transgenic mice with global and cell-type specific deletions of Panx1 to interrogate their participation in working and reference memory. Using the eight-arm radial maze, we show that long-term spatial reference memory, but not spatial working memory, is deficient in Panx1-null mice and that both astrocyte and neuronal Panx1 contribute to the consolidation of long-term spatial memory. Field potential recordings in hippocampal slices of Panx1-null mice revealed an attenuation of both long-term potentiation (LTP) of synaptic strength and long-term depression (LTD) at Schaffer collateral-CA1 synapses without alterations of basal synaptic transmission or pre-synaptic paired-pulse facilitation. Our results implicate both neuronal and astrocyte Panx1 channels as critical players for the development and maintenance of long-term spatial reference memory in mice.

The Role of Organosulfur Compounds as Nrf2 Activators and Their Antioxidant Effects

Nuclear factor erythroid 2-related factor 2 (Nrf2) signaling has become a key pathway for cellular regulation against oxidative stress and inflammation, and therefore an attractive therapeutic target. Several organosulfur compounds are reportedly activators of the Nrf2 pathway. Organosulfur compounds constitute an important class of therapeutic agents in medicinal chemistry due to their ability to participate in biosynthesis, metabolism, cellular functions, and protection of cells from oxidative damage. Sulfur has distinctive chemical properties such as a large number of oxidation states and versatility of reactions that promote fundamental biological reactions and redox biochemistry. The presence of sulfur is responsible for the peculiar features of organosulfur compounds which have been utilized against oxidative stress-mediated diseases. Nrf2 activation being a key therapeutic strategy for oxidative stress is closely tied to sulfur-based chemistry since the ability of compounds to react with sulfhydryl (-SH) groups is a common property of Nrf2 inducers. Although some individual organosulfur compounds have been reported as Nrf2 activators, there are no papers with a collective analysis of these Nrf2-activating organosulfur compounds which may help to broaden the knowledge of their therapeutic potentials and motivate further research. In line with this fact, for the first time, this review article provides collective and comprehensive information on Nrf2-activating organosulfur compounds and their therapeutic effects against oxidative stress, thereby enriching the chemical and pharmacological diversity of Nrf2 activators.

Serum Vitamins and Homocysteine Levels in Obsessive-Compulsive Disorder: A Systematic Review and Meta-Analysis

Vitamin and homocysteine (Hcy) alternations have been associated with psychiatric disorders. The aim of this meta-analysis was to assess the association of serum vitamin and Hcy levels with obsessive-compulsive disorder (OCD). Following PRISMA protocol, we used the databases including Scopus, PubMed, Google Scholar, and Web of Science with no time restriction. Data were pooled using a random-effects model and/or fixed-effects model to estimate the standard mean difference (SMD) for evaluation of the strength of association analyses. Our data showed a significant reduction in vitamin B12 (SMD = -0.58, 95% CI = -1.08 to -0.08, p = 0.02, I2 = 65%; pheterogeneity = 0.06), vitamin E (SMD = -0.89, 95% CI = -1.23 to -0.56, p < 0.00001, I2 = 23%; pheterogeneity = 0.26), and vitamin C (SMD = -1.40, 95% CI = -2.44 to -0.36, p = 0.008, I2 = 92%; pheterogeneity < 0.0001) in OCD patients. In addition, the findings showed significantly higher levels of Hcy (SMD = 1.11, 95% CI = [0.48, 1.75], p = 0.0006, I2 = 73%; ph = 0.02) in patients compared to controls. Also, our data showed that vitamin B9 and D levels are not associated with OCD (vitamin B9: SMD = -0.23, 95% CI = -1.01 to 0.55, p = 0.56, I2 = 88%; pheterogeneity < 0.0001; vitamin D: SMD = -0.63, 95% CI = -1.41 to 0.15, p = 0.11, I2 = 88%; pheterogeneity = 0.0002). Our findings support significant impacts of Hcy and vitamin B12, E, and C levels in OCD pathogenesis. This will be important for prevention and treatment of OCD. However, further studies are recommended to elucidate more accurate conclusions.

Hyperhomocysteinemia: Metabolic Role and Animal Studies with a Focus on Cognitive Performance and Decline-A Review

Disturbances in the one-carbon metabolism are often indicated by altered levels of the endogenous amino acid homocysteine (HCys), which is additionally discussed to causally contribute to diverse pathologies. In the first part of the present review, we profoundly and critically discuss the metabolic role and pathomechanisms of HCys, as well as its potential impact on different human disorders. The use of adequate animal models can aid in unravelling the complex pathological processes underlying the role of hyperhomocysteinemia (HHCys). Therefore, in the second part, we systematically searched PubMed/Medline for animal studies regarding HHCys and focused on the potential impact on cognitive performance and decline. The majority of reviewed studies reported a significant effect of HHCys on the investigated behavioral outcomes. Despite of persistent controversial discussions about equivocal findings, especially in clinical studies, the present evaluation of preclinical evidence indicates a causal link between HHCys and cognition-related- especially dementia-like disorders, and points out the further urge for large-scale, well-designed clinical studies in order to elucidate the normalization of HCys levels as a potential preventative or therapeutic approach in human pathologies.

Mild hyperhomocysteinemia induces blood-brain barrier dysfunction but not neuroinflammation in the cerebral cortex and hippocampus of wild-type mice

This study explored the potential effects of mild hyperhomocysteinemia (HHcy) on the blood-brain barrier (BBB) and neuroinflammation. Seven-week-old male wild-type C57BL/6 mice were fed normal mouse chow (the control group) or a methionine-enriched diet (the HHcy group) for 14 weeks. Mice in the HHcy group exhibited a slight increase in serum Hcy levels (13.56 ± 0.61 μmol/L). Activation of the ERK signaling pathway, up-regulation of matrix metalloproteinase-9 (MMP-9), and degradation of tight junction proteins (occludin and claudin-5) were observed in both the cerebral cortex and hippocampus of mice with mild HHcy. However, microglia were not activated and the levels of tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) were not changed in either the cerebral cortex or hippocampus of mice with mild HHcy. Moreover, the signaling activity of STAT3 also did not differ significantly between the two groups. These findings demonstrate that the BBB is highly vulnerable to homocysteine insult. Even a slight increase in serum homocysteine levels up-regulates MMP-9 expression and disrupts the BBB integrity. Meanwhile, microglia activation or the STAT3 pathway might not contribute to the effects of mild HHcy on the brain.

Hyperhomocysteinemia-Induced Oxidative Stress Exacerbates Cortical Traumatic Brain Injury Outcomes in Rats

Traumatic brain injury (TBI) is a leading cause of morbidity and mortality among military service members and civilians in the United States. Despite significant advances in the understanding of TBI pathophysiology, several clinical reports indicate that multiple genetic and epigenetic factors can influence outcome. Homocysteine (HCY) is a non-proteinogenic amino acid, the catabolism of which can be dysregulated by stress, lifestyle, aging, or genetic abnormalities leading to hyperhomocysteinemia (HHCY). HHCY is a neurotoxic condition and a risk factor for multiple neurological and cardiovascular disorders that occurs when HCY levels is clinically > 15 µM. Although the deleterious impact of HHCY has been studied in human and animal models of neurological disorders such as stroke, Alzheimer's disease and Parkinson's disease, it has not been addressed in TBI models. This study tested the hypothesis that HHCY has detrimental effects on TBI pathophysiology. Moderate HHCY was induced in adult male Sprague Dawley rats via daily administration of methionine followed by impact-induced traumatic brain injury. In this model, HHCY increased oxidative stress, upregulated expression of proteins that promote blood coagulation, exacerbated TBI-associated blood-brain barrier dysfunction and promoted the infiltration of inflammatory cells into the cortex. We also observed an increase of brain injury-induced lesion size and aggravated anxiety-like behavior. These findings show that moderate HHCY exacerbates TBI outcomes and suggest that HCY catabolic dysregulation may be a significant biological variable that could contribute to TBI pathophysiology heterogeneity.

Effects of Alzheimer-Like Pathology on Homocysteine and Homocysteic Acid Levels-An Exploratory In Vivo Kinetic Study

Hyperhomocysteinemia has been suggested potentially to contribute to a variety of pathologies, such as Alzheimer’s disease (AD). While the impact of hyperhomocysteinemia on AD has been investigated extensively, there are scarce data on the effect of AD on hyperhomocysteinemia. The aim of this in vivo study was to investigate the kinetics of homocysteine (HCys) and homocysteic acid (HCA) and effects of AD-like pathology on the endogenous levels. The mice received a B-vitamin deficient diet for eight weeks, followed by the return to a balanced control diet for another eight weeks. Serum, urine, and brain tissues of App^NL-G-F knock-in and C57BL/6J wild type mice were analyzed for HCys and HCA using LC-MS/MS methods. Hyperhomocysteinemic levels were found in wild type and knock-in mice due to the consumption of the deficient diet for eight weeks, followed by a rapid normalization of the levels after the return to control chow. Hyperhomocysteinemic App^NL-G-F mice had significantly higher HCys in all matrices, but not HCA, compared to wild type control. Higher serum concentrations were associated with elevated levels in both the brain and in urine. Our findings confirm a significant impact of AD-like pathology on hyperhomocysteinemia in the App^NL-G-F mouse model. The immediate normalization of HCys and HCA after the supply of B-vitamins strengthens the idea of a B-vitamin intervention as a potentially preventive treatment option for HCys-related disorders such as AD.

Abnormal Homocysteine Metabolism: An Insight of Alzheimer's Disease from DNA Methylation

Alzheimer's disease (AD) is a chronic neurodegenerative disease in the central nervous system that has complex pathogenesis in the elderly. The current review focuses on the epigenetic mechanisms of AD, according to the latest findings. One of the best-characterized chromatin modifications in epigenetic mechanisms is DNA methylation. Highly replicable data shows that AD occurrence is often accompanied by methylation level changes of the AD-related gene. Homocysteine (Hcy) is not only an intermediate product of one-carbon metabolism but also an important independent risk factor of AD; it can affect the cognitive function of the brain by changing the one-carbon metabolism and interfering with the DNA methylation process, resulting in cerebrovascular disease. In general, Hcy may be an environmental factor that affects AD via the DNA methylation pathway with a series of changes in AD-related substance. This review will concentrate on the relation between DNA methylation and Hcy and try to figure out their rule in the pathophysiology of AD.

Homocysteine as a peripheral biomarker in bipolar disorder: A meta-analysis

Background:

Bipolar disorder (BD) is a psychiatric disorder with an uncertain aetiology. Recently, special attention has been given to homocysteine (Hcy), as it has been suggested that alterations in 1-carbon metabolism might be implicated in diverse psychiatric disorders. However, there is uncertainty regarding possible alterations in peripheral Hcy levels in BD.

Methods:

This study comprises a meta-analysis comparing serum and plasma Hcy levels in persons with BD and healthy controls. We conducted a systematic search for all eligible English and non-English peer-reviewed articles.

Results:

Nine cross-sectional studies were included in the meta-analyses, providing data on 1547 participants. Random-effects meta-analysis showed that serum and plasma levels of Hcy were increased in subjects with BD in either mania or euthymia when compared to healthy controls, with a large effect size in the mania group (g= 0.98, 95% CI: 0.8–1.17,P< 0.001,n= 495) and a small effect in the euthymia group (g= 0.3, 95% CI: 0.11–0.48,P= 0.002,n= 1052).

Conclusions:

Our meta-analysis provides evidence that Hcy levels are elevated in persons with BD during mania and euthymia. Peripheral Hcy could be considered as a potential biomarker in BD, both of trait (since it is increased in euthymia), and also of state (since its increase is more accentuated in mania). Longitudinal studies are needed to clarify the relationship between bipolar disorder and Hcy, as well as the usefulness of peripheral Hcy as both a trait and state biomarker in BD.

Can mouse models mimic sporadic Alzheimer's disease?

Alzheimer's disease (AD) is a progressive neurodegenerative disorder and the most common form of dementia worldwide. As age is the main risk factor, > 97% of all AD cases are of sporadic origin, potentiated by various risk factors associated with life style and starting at an age > 60 years. Only < 3% of AD cases are of genetic origin caused by mutations in the amyloid precursor protein or Presenilins 1 or 2, and symptoms already start at an age < 30 years. In order to study progression of AD, as well as therapeutic strategies, mouse models are state-of-the-art. So far many transgenic mouse models have been developed and used, with mutations in the APP or presenilin or combinations (3×Tg, 5×Tg). However, such transgenic mouse models more likely mimic the genetic form of AD and no information can be given how sporadic forms develop. Several risk genes, such as Apolipoprotein E4 and TREM-2 enhance the risk of sporadic AD, but also many risk factors associated with life style (e.g., diabetes, hypercholesterolemia, stress) may play a role. In this review we discuss the current situation regarding AD mouse models, and the problems to develop a sporadic mouse model of AD.

Evaluation of hyperhomocysteinemia prevalence and its influence on the selected cognitive functions in patients with schizophrenia

There is evidence that hyperhomocysteinemia may be associated with the development of schizophrenia and cognitive impairment. Therefore, the aim of this study was to analyze the relationship between cognitive functions and normal homocysteine concentrations vs. hyperhomocysteinemia in schizophrenia patients before and after supplementation with vitamins B6, B12 and folate. An 8-week prospective, non-randomized study enrolled 122 adult patients with schizophrenia (67F/55M, mean age 43.54 ± 11.94 years). Homocysteine concentrations were measured in all individuals and afterwards hyperhomocysteinemia patients (n = 42) were divided into two subgroups: treated with oral vitamins supplementation (B6 - 25 mg/d, B12 - 20 μg/d, folate - 2,5 mg/d) (n = 22) and without supplementation (n = 20). The assessment of schizophrenia symptoms severity in study group was performed using the Positive and Negative Syndrome Scale (PANSS). Cognitive functions were evaluated using the Stroop test and the Trail Making Test (TMT). We observed a higher prevalence of hyperhomocysteinemia in schizophrenia patients (34.4%) in comparison to the general population. Individuals with schizophrenia and coexisting hyperhomocysteinemia had worse performance on the Stroop and the TMT tests as well as higher PANSS scores. In these patients, supplementation with vitamins effectively decreased the homocysteine concentrations to the normal values, however there was no statistically significant improvement in the PANSS and cognitive test scores, except a significant decrease in the number of the Stroop test errors. We conclude that significant results obtained in this study show that there is a relationship between homocysteine blood concentration and schizophrenia severity. Moreover, homocysteine concentration lowering might be beneficial in schizophrenia patients with hyperhomocysteinemia in terms of cognitive functions improvement.

Homocysteine, rather than age of onset, is a better predictor for cognitive function in older adults with bipolar disorder

OBJECTIVES

The association between older-age bipolar disorder and cognitive impairments may be mediated by vascular burden. The aim of the study was to examine the difference of cognitive function between older people with late-onset bipolar disorder (LOBD) and early-onset bipolar disorder (EOBD) by considering rigorous vascular risk burden evaluation, comprehensive cognitive tests, and relevant biochemistry data.

METHODS

We recruited 95 outpatients aged over 55 with a DSM-IV-TR diagnosis of bipolar I disorder. Fifty had LOBD, defined by age of onset after 40. Cognitive function was evaluated through a battery of tests assessing verbal memory, attention/speed, visuospatial function, verbal fluency, and cognitive flexibility. Vascular risk assessments included individual disorders, 10-year Framingham cardiovascular risk scores, and serum levels of homocysteine, vitamin B12, folate, and triiodothyronine.

RESULTS

No differences were observed between LOBD and EOBD on any cognitive test after adjusting for potential confounders. In addition to age and educational years, multiple linear regression analyses indicated significantly negative associations between serum homocysteine levels and cognitive performances in attention, psychomotor speed, verbal memory, and executive function.

CONCLUSIONS

Among older people with bipolar disorder, LOBD is not associated with more cognitive dysfunction in this study. However, higher serum homocysteine levels were significantly associated with worse cognitive performance in this particular group. Clinicians therefore have to pay attention to the cognitive function in older bipolar patients with higher levels of homocysteine.

Chronic treatment with five vascular risk factors causes cerebral amyloid angiopathy but no Alzheimer pathology in C57BL6 mice

Alzheimer's disease (AD) is a progressive neurodegenerative brain disorder and the most common form of dementia coming along with cerebral amyloid angiopathy (CAA) in more than 70% of all cases. However, CAA occurs also in pure form without AD pathology. Vascular life style risk factors such as obesity, hypertension, hypercholesterolemia, diabetes, stress or an old age play an important role in the progression of CAA. So far, no animal model for sporadic CAA has been reported, thus the aim of the present study was to create and characterize a new mouse model for sporadic CAA by treatment with different vascular risk factors. Healthy C57BL6 mice were treated with lifestyle vascular risk factors for 35 or 56 weeks: lipopolysaccharide, social stress, streptozotozin, high cholesterol diet and copper in the drinking water. Four behavioral tests (black-white box, classical maze, cheeseboard maze and plus-maze discriminative avoidance task) showed impaired learning, memory and executive functions as well as anxiety with increased age. The treated animals exhibited increased plasma levels of cortisol, insulin, interleukin-1ß, glucose and cholesterol, confirming the effectiveness of the treatment. Confocal microscopy analysis displayed severe vessel damage already after 35 weeks of treatment. IgG positive staining points to a severe blood-brain barrier (BBB) disruption and furthermore, cerebral bleedings were observed in a much higher amount in the treatment group. Importantly, inclusions of beta-amyloid in the vessels indicated the development of CAA, but no deposition of beta-amyloid plaques and tau pathology in the brains were seen. Taken together, we characterized a novel sporadic CAA mouse model, which offers a strategy to study the progression of the disease and therapeutic and diagnostic interventions.

Hyperhomocysteinemia as a Risk Factor for Vascular Contributions to Cognitive Impairment and Dementia

Behind only Alzheimer's disease, vascular contributions to cognitive impairment and dementia (VCID) is the second most common cause of dementia, affecting roughly 10-40% of dementia patients. While there is no cure for VCID, several risk factors for VCID, such as diabetes, hypertension, and stroke, have been identified. Elevated plasma levels of homocysteine, termed hyperhomocysteinemia (HHcy), are a major, yet underrecognized, risk factor for VCID. B vitamin deficiency, which is the most common cause of HHcy, is common in the elderly. With B vitamin supplementation being a relatively safe and inexpensive therapeutic, the treatment of HHcy-induced VCID would seem straightforward; however, preclinical and clinical data shows it is not. Clinical trials using B vitamin supplementation have shown conflicting results about the benefits of lowering homocysteine and issues have arisen over proper study design within the trials. Studies using cell culture and animal models have proposed several mechanisms for homocysteine-induced cognitive decline, providing other targets for therapeutics. For this review, we will focus on HHcy as a risk factor for VCID, specifically, the different mechanisms proposed for homocysteine-induced cognitive decline and the clinical trials aimed at lowering plasma homocysteine.

Homocysteine and Real-Space Navigation Performance among Non-Demented Older Adults

BACKGROUND

High plasma homocysteine (Hcy) level is related to higher risk of Alzheimer's disease (AD) and lower cognitive performance in older adults.

OBJECTIVE

To assess the association between plasma Hcy level and real-space navigation performance and the role of vascular risk and protective factors, APOE status, and white matter lesions (WML) on this association.

METHODS

Ninety-two non-demented older adults (29 with amnestic mild cognitive impairment, 46 with subjective cognitive decline, and 17 cognitively normal older adults) underwent spatial navigation testing of egocentric, allocentric, and mixed navigation in a real-space analogue of the Morris water maze, neuropsychological examination, blood collection, and MRI brain scan with evaluation of WML.

RESULTS

In the regression analyses controlling for age, gender, education, and depressive symptoms, higher plasma Hcy level was related to worse mixed and egocentric (β= 0.31; p = 0.003 and β= 0.23; p = 0.017) but not allocentric (p > 0.05) navigation performance. Additional controlling for vascular risk and protective factors, WML, and APOE status did not modify the results. High total cholesterol and low vitamin B12 and folate levels increased the adverse effect of Hcy on egocentric and mixed navigation. WML did not explain the association between plasma Hcy level and navigation performance.

CONCLUSION

Elevated plasma Hcy level may affect real-space navigation performance above and beyond vascular brain changes. This association may be magnified in the presence of high total cholesterol and low folate or vitamin B12 levels. Attention to the level of plasma Hcy may be a viable intervention strategy to prevent decline in spatial navigation in non-demented older adults.

Hyperhomocysteinemia-induced autophagy and apoptosis with downregulation of hairy enhancer of split 1/5 in cortical neurons in mice

It has been reported that hyperhomocysteinemia (HHcy) is associated with neurodegenerative and cardiovascular diseases. However, little is known about brain histomorphology, neuronal organelles, and hairy enhancer of split (hes) expression under HHcy. In this study, non-HHcy and HHcy induced by high-methionine diet in apolipoprotein E–deficient (Apo E^−/−) mice were comparatively investigated. The histomorphology, ultrastructure, autophagosomes, apoptosis, and expression of proteins, HES1, HES5 and P62, were designed to assess the effects of HHcy on brain. The results showed that compared to the non-HHcy mice, the HHcy group had an increase in autophagosomes, vacuolization in mitochondria, and neuron apoptosis; treatment with folate and vitamin B₁₂ reduced the extent of these lesions. However, the elementary histomorphology, the numbers of cortical neurons, and Nissl bodies had no significant difference between the HHcy and the non-HHcy groups or the group treated with folate and vitamin B₁₂. Immunohistochemistry and immunofluorescence demonstrated a decrease in HES1- or HES5-positive neurons in the HHcy group when compared to the non-HHcy groups, wild-type, and Apo E^−/− controls, or the HHcy mice with folate and vitamin B₁₂ supplement. Western blots showed that HHcy induced a decreased expression of HES1 and HES5, or P62, in which the expression of HES1 and P62 was elevated by treating with folate and vitamin B₁₂ supplement. These results suggest that HHcy-enhanced brain damage is associated with increased autophagy and neuronal apoptosis in Apo E^−/− mice, in which downregulation of hes1 and hes5 is involved.

Homocysteine, hyperhomocysteinemia and vascular contributions to cognitive impairment and dementia (VCID)

Homocysteine is produced physiologically in all cells, and is present in plasma of healthy individuals (plasma [HCy]: 3-10μM). While rare genetic mutations (CBS, MTHFR) cause severe hyperhomocysteinemia ([HCy]: 100-200μM), mild-moderate hyperhomocysteinemia ([HCy]: 10-100μM) is common in older people, and is an independent risk factor for stroke and cognitive impairment. As B-vitamin supplementation (B6, B12 and folate) has well-validated homocysteine-lowering efficacy, this may be a readily-modifiable risk factor in vascular contributions to cognitive impairment and dementia (VCID). Here we review the biochemical and cellular actions of HCy related to VCID. Neuronal actions of HCy were at concentrations above the clinically-relevant range. Effects of HCy <100μM were primarily vascular, including myocyte proliferation, vessel wall fibrosis, impaired nitric oxide signalling, superoxide generation and pro-coagulant actions. HCy-lowering clinical trials relevant to VCID are discussed. Extensive clinical and preclinical data support HCy as a mediator for VCID. In our view further trials of combined B-vitamin supplementation are called for, incorporating lessons from previous trials and from recent experimental work. To maximise likelihood of treatment effect, a future trial should: supply a high-dose, combination supplement (B6, B12 and folate); target the at-risk age range; and target cohorts with low baseline B-vitamin status. This article is part of a Special Issue entitled: Vascular Contributions to Cognitive Impairment and Dementia edited by M. Paul Murphy, Roderick A. Corriveau and Donna M. Wilcock.

Vascular pathology of 20-month-old hypercholesterolemia mice in comparison to triple-transgenic and APPSwDI Alzheimer's disease mouse models

Several studies have shown that elevated plasma cholesterol levels (i.e. hypercholesterolemia) serve as a risk factor for late-onset Alzheimer's disease (AD). However, it remains unclear how hypercholesterolemia may contribute to the onset and progression of AD pathology. In order to determine the role of hypercholesterolemia at various stages of AD, we evaluated the effects of high cholesterol diet (5% cholesterol) in wild-type (WT; C57BL6) and triple-transgenic AD (3xTg-AD; Psen1, APPSwe, tauB301L) mice at 7, 14, and 20 months. The transgenic APP-Swedish/Dutch/Iowa AD mouse model (APPSwDI) was used as a control since these animals are more pathologically-accelerated and are known to exhibit extensive plaque deposition and cerebral amyloid angiopathy. Here, we describe the effects of high cholesterol diet on: (1) cognitive function and stress, (2) AD-associated pathologies, (3) neuroinflammation, (4) blood–brain barrier disruption and ventricle size, and (5) vascular dysfunction. Our data show that high dietary cholesterol increases weight, slightly impairs cognitive function, promotes glial cell activation and complement-related pathways, enhances the infiltration of blood-derived proteins and alters vascular integrity, however, it does not induce AD-related pathologies. While normal-fed 3xTg-AD mice display a typical AD-like pathology in addition to severe cognitive impairment and neuroinflammation at 20 months of age, vascular alterations are less pronounced. No microbleedings were seen by MRI, however, the ventricle size was enlarged. Triple-transgenic AD mice, on the other hand, fed a high cholesterol diet do not survive past 14 months of age. Our data indicates that cholesterol does not markedly potentiate AD-related pathology, nor does it cause significant impairments in cognition. However, it appears that high cholesterol diet markedly increases stress-related plasma corticosterone levels as well as some vessel pathologies. Together, our findings represent the first demonstration of prolonged high cholesterol diet and the examination of its effects at various stages of cerebrovascular- and AD-related disease.

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.

Intravenous infusion of monocytes isolated from 2-week-old mice enhances clearance of Beta-amyloid plaques in an Alzheimer mouse model

Alzheimer's disease (AD) is characterized by the deposition of β-amyloid (Aβ) senile plaques and tau-associated neurofibrillary tangles. Other disease features include neuroinflammation and cholinergic neurodegeneration, indicating their possible importance in disease propagation. Recent studies have shown that monocytic cells can migrate into the AD brain toward Aβ plaques and reduce plaque burden. The purpose of this study was to evaluate whether the administration of intravenous infusions of 'young' CD11b-positive (+) monocytes into an AD mouse model can enhance Aβ plaque clearance and attenuate cognitive deficits. Peripheral monocytes were isolated from two-week-old wildtype mice using the Pluriselect CD11b+ isolation method and characterized by FACS analysis for surface marker expression and effective phagocytosis of 1 μm fluorescent microspheres, FITC-Dextran or FITC-Aβ1-42. The isolated monocytes were infused via the tail vein into a transgenic AD mouse model, which expresses the Swedish, Dutch/Iowa APP mutations (APPSwDI). The infusions began when animals reached 5 months of age, when little plaque deposition is apparent and were repeated again at 6 and 7 months of age. At 8 months of age, brains were analyzed for Aβ+ plaques, inflammatory processes and microglial (Iba1) activation. Our data show that infusions of two-week-old CD11b+ monocytes into adult APPSwDI mice results in a transient improvement of memory function, a reduction (30%) in Aβ plaque load and significantly in small (<20 μm) and large (>40 μm) plaques. In addition, we observe a reduction in Iba1+ cells, as well as no marked elevations in cytokine levels or other indicators of inflammation. Taken together, our findings indicate that young CD11b+ monocytes may serve as therapeutic candidates for improved Aβ clearance in AD.

Homocysteine levels in schizophrenia and affective disorders-focus on cognition

Although homocysteine (Hcy) has been widely implicated in the etiology of various physical health impairments, especially cardiovascular diseases, overwhelming evidence indicates that Hcy is also involved in the pathophysiology of schizophrenia and affective disorders. There are several mechanisms linking Hcy to biological underpinnings of psychiatric disorders. It has been found that Hcy interacts with NMDA receptors, initiates oxidative stress, induces apoptosis, triggers mitochondrial dysfunction and leads to vascular damage. Elevated Hcy levels might also contribute to cognitive impairment that is widely observed among patients with affective disorders and schizophrenia. Supplementation of vitamins B and folic acid has been proved to be effective in lowering Hcy levels. There are also studies showing that this supplementation strategy might be beneficial for schizophrenia patients with respect to alleviating negative symptoms. However, there are no studies addressing the influence of add-on therapies with folate and vitamins B on cognitive performance of patients with schizophrenia and affective disorders. In this article, we provide an overview of Hcy metabolism in psychiatric disorders focusing on cognitive correlates and indicating future directions and perspectives.

β-amyloid deposition is shifted to the vasculature and memory impairment is exacerbated when hyperhomocysteinemia is induced in APP/PS1 transgenic mice

Introduction

Vascular dementia is the second most common cause of dementia after Alzheimer’s disease (AD). In addition, it is estimated that almost half of all AD patients have significant cerebrovascular disease comorbid with their AD pathology. We hypothesized that cerebrovascular disease significantly impacts AD pathological progression.

Methods

We used a dietary model of cerebrovascular disease that relies on the induction of hyperhomocysteinemia (HHcy). HHcy is a significant clinical risk factor for stroke, cardiovascular disease and type 2 diabetes. In the present study, we induced HHcy in APP/PS1 transgenic mice.

Results

While total β-amyloid (Aβ) load is unchanged across groups, Congophilic amyloid deposition was decreased in the parenchyma and significantly increased in the vasculature as cerebral amyloid angiopathy (CAA; vascular amyloid deposition) in HHcy APP/PS1 mice. We also found that HHcy induced more microhemorrhages in the APP/PS1 mice than in the wild-type mice and that it switched the neuroinflammatory phenotype from an M2a biased state to an M1 biased state. Associated with these changes was an induction of the matrix metalloproteinase protein 2 (MMP2) and MMP9 systems. Interestingly, after 6 months of HHcy, the APP/PS1 mice were cognitively worse than wild-type HHcy mice or APP/PS1 mice, indicative of an additive effect of the cerebrovascular pathology and amyloid deposition.

Conclusions

These data show that cerebrovascular disease can significantly impact Aβ distribution in the brain, favoring vascular deposition. We predict that the presence of cerebrovascular disease with AD will have a significant impact on AD progression and the efficacy of therapeutics.

Intravenous infusion of nerve growth factor-secreting monocytes supports the survival of cholinergic neurons in the nucleus basalis of Meynert in hypercholesterolemia Brown-Norway rats

The recruitment of monocytes into the brain has been implicated in Alzheimer's disease and recent studies have indicated that monocytes can reduce amyloid plaque burden. Our previous investigations have shown that hypercholesterolemic rats develop cognitive, cholinergic, and blood-brain barrier dysfunction, but do not develop amyloid plaques. This study was designed to evaluate the effects of repeated intravenous (i.v.) infusion (via the dorsal penile vein) of primary monocytes on cognition, the cholinergic system, and cortical cytokine levels in hypercholesterolemia Brown-Norway rats. In addition, we also transduced the monocytes with nerve growth factor (NGF) to evaluate whether these cells could be used to deliver a neuroprotective agent to the brain. Our results indicate that repeated i.v. infused monocytes migrate into the brains of hypercholesterolemic rats; however, this migration does not translate into marked effects on learning. Animals receiving NGF-loaded monocytes demonstrate slightly improved learning and significantly elevated cholinergic neuron staining compared to treatment with monocytes alone. Furthermore, our data indicate that repeated infusion of monocytes does not lead to elevated cytokine secretion, indicating that no inflammatory response is induced. This study provides an experimental attempt to evaluate the effects of blood-derived primary monocytes in hypercholesterolemia rats.

Cholesterol diet counteracts repeated anesthesia/infusion-induced cognitive deficits in male Brown Norway rats

A variety of cardiovascular and cerebrovascular diseases are associated with alterations in cholesterol levels and metabolism. Moreover, convincing evidence shows that high cholesterol diet can lead to learning and memory impairments. On the other hand, a significant body of research has also demonstrated that learning is improved by elevated dietary cholesterol. Despite these conflicting findings, it is clear that cholesterol plays an important role in these cognitive properties. However, it remains unclear how this blood-brain barrier (BBB)-impenetrable molecule affects the brain and under what circumstances it provides either detrimental or beneficial effects to learning and memory. The aim of this study was to characterize the effects of 5% cholesterol diet on six-month-old inbred Brown Norway rats. More important, we sought to examine the role that cholesterol can play when repeated anesthesia and intravenous infusion disrupts cognitive function. This present study supports previous work showing that enriched cholesterol diet leads to significant alterations in neuroinflammation and BBB disruption. Following repeated anesthesia and intravenous infusion of saline we observe that animals under normal diet conditions exhibit significant deficiencies in spatial learning and cholinergic neuron populations compared to animals under enriched cholesterol diet, which do not show such deficiencies. These findings indicate that cholesterol diet can protect against or counteract anesthesia/infusion-induced cognitive deficits. Ultimately, these results suggest that cholesterol homeostasis serves an important functional role in the brain and that altering this homeostasis can either exert positive or negative effects on cognitive properties.

Induction of hyperhomocysteinemia models vascular dementia by induction of cerebral microhemorrhages and neuroinflammation

Vascular dementia (VaD) is the second leading cause of dementia behind Alzheimer's disease (AD) and is a frequent comorbidity with AD, estimated to occur in as many as 40% of AD patients. The causes of VaD are varied and include chronic cerebral hypoperfusion, microhemorrhages, hemorrhagic infarcts, or ischemic infarcts. We have developed a model of VaD by inducing hyperhomocysteinemia (HHcy) in wild-type mice. By placing wild-type mice on a diet deficient in folate, B6, and B12 and supplemented with excess methionine, we induced a moderate HHcy (plasma level homocysteine 82.93 ± 3.561 μmol). After 11 weeks on the diet, the hyperhomocysteinemic mice showed a spatial memory deficit as assessed by the 2-day radial-arm water maze. Also, magnetic resonance imaging and subsequent histology revealed significant microhemorrhage occurrence. We found neuroinflammation induced in the hyperhomocysteinemic mice as determined by elevated interleukin (IL)-1β, tumor necrosis factor (TNF)α, and IL-6 in brain tissue. Finally, we found increased expression and increased activity of the matrix metalloproteinase 2 (MMP2) and MMP9 systems that are heavily implicated in the pathogenesis of cerebral hemorrhage. Overall, we have developed a dietary model of VaD that will be valuable for studying the pathophysiology of VaD and also for studying the comorbidity of VaD with other dementias and other neurodegenerative disorders.

Inflammatory status of transmigrating primary rat monocytes in a novel perfusion model simulating blood flow

It remains unclear whether monocyte infiltration plays a protective or detrimental role in neurodegenerative disease. The present study characterizes the inflammatory status of primary monocytes in a novel in vitro perfusion model. Monocytes under perfusion do not undergo elevated cell death. However, perfusion does lead to altered morphology, which can be counteracted by anti-inflammatory drugs. Functional studies indicate that cytokine levels are significantly reduced in perfusion compared to stationary conditions and enhanced with brain slices or capillary endothelial cells. Understanding monocyte properties could lead to refined treatment and new ways to interfere with inflammation in diseased brains.

The relationship between associative learning, transfer generalization, and homocysteine levels in mild cognitive impairment

Previous studies have shown that high total homocysteine levels are associated with Alzheimer's disease (AD) and mild cognitive impairment (MCI). In this study, we test the relationship between cognitive function and total homocysteine levels in healthy subjects (Global Dementia Rating, CDR = 0) and individuals with MCI (CDR = 0.5). We have used a cognitive task that tests learning and generalization of rules, processes that have been previously shown to rely on the integrity of the striatal and hippocampal regions, respectively. We found that total homocysteine levels are higher in MCI individuals than in healthy controls. Unlike what we expected, we found no difference between MCI subjects and healthy controls in learning and generalization. We conducted further analysis after diving MCI subjects in two groups, depending on their Global Deterioration Scale (GDS) scores: individuals with very mild cognitive decline (vMCD, GDS = 2) and mild cognitive decline (MCD, GDS = 3). There was no difference among the two MCI and healthy control groups in learning performance. However, we found that individuals with MCD make more generalization errors than healthy controls and individuals with vMCD. We found no difference in the number of generalization errors between healthy controls and MCI individuals with vMCD. In addition, interestingly, we found that total homocysteine levels correlate positively with generalization errors, but not with learning errors. Our results are in agreement with prior results showing a link between hippocampal function, generalization performance, and total homocysteine levels. Importantly, our study is perhaps among the first to test the relationship between learning (and generalization) of rules and homocysteine levels in healthy controls and individuals with MCI.

GE-25-like immunoreactivity in the rat eye

This study aimed to investigate the presence and distribution of the chromogranin A-derived peptide GE-25 in the rat eye. The molecular form detected by the GE-25 antiserum was evaluated in the rat trigeminal ganglion, retina and remaining tissues of the rat eye by means of Western blots and the distribution pattern of GE-25-like immunoreactivity was studied in the rat eye and rat trigeminal ganglion by immunofluorescence. One single band of approximately 70kDa was stained in the trigeminal ganglion and retina which represents the uncleaved intact chromogranin A indicating that the proteolytic processing of chromogranin A to GE-25 is limited in these tissues. Sparse GE-25-like immunoreactive nerve fibers were visualized in the corneal stroma, at the limbus around blood vessels, in the sphincter and dilator muscle and stroma of the iris, in the stroma of the ciliary body and ciliary processes and in the stroma and around blood vessels in the choroid. This distribution pattern is characteristic for neuropeptides whereas the presence of immunoreactivity in the corneal endothelium and in Müller glia in the retina is atypical. GE-25-like immunoreactivity was found in small to medium-sized ganglion cells in the rat trigeminal ganglion clearly indicating that the nerve fibers in the rat eye are of sensory origin. The colocalization of GE-25-immunoreactivity with SP-immunoreactivity in the rat ciliary body is in agreement with the presumption of the sensory nature of the innervation of the anterior segment of the eye by GE-25.

Chronic vascular risk factors (cholesterol, homocysteine, ethanol) impair spatial memory, decline cholinergic neurons and induce blood-brain barrier leakage in rats in vivo

Epidemiological studies show that vascular risk factors (e.g. atherosclerosis, diabetes, homocysteine, hypertension or cholesterol) may play a role in the development of Alzheimer's disease. Animal models may help to discover the role of vascular risk factors on cognition. In the present project we treated male Sprague Dawley rats with a diet containing homocysteine (hyperhomocysteinemia) or cholesterol (hypercholesterolemia) for 5 months or exposed the rats to ethanol (20% in drinking water) or a combination of cholesterol + ethanol (mix) for 12 months. Our experiments show that all 3 treatments (homocysteine, cholesterol, ethanol) declined spatial memory in the 8-arm radial maze, reduced the number of cholinergic neurons and induced blood–brain barrier leakage in the cortex. Rats treated with cholesterol also displayed markedly enhanced inflammation in the cortex. Levels of amyloid precursor protein, beta-amyloid_(1–42), as well as tau and phospho-tau 181 were significantly enhanced in the cortex of cholesterol-fed rats. A combination of ethanol and cholesterol did not further potentiate the effects on spatial memory, cholinergic neurons and blood–brain barrier leakage. The data suggest that chronic mild vascular risk factors over months induce small lesions of the brain capillaries in the cortex, which may contribute to the development of vascular dementia or also Alzheimer's disease.

Ethanol transiently suppresses choline-acetyltransferase in basal nucleus of Meynert slices

The cholinergic system plays a major role in learning and cognition and cholinergic neurons appear to be particularly vulnerable to ethanol (EtOH) exposure. There are conflicting results if EtOH directly damages cholinergic neurons. Thus, the aims of the present study were (1) to investigate the effect of different EtOH concentrations on cholinergic neurons in organotypic brain slices of the nucleus basalis of Meynert (nbM) and (2) to study if the most potent cholinotrophic substance nerve growth factor (NGF) or inhibitors of mitogen activated kinase (MAPK) p38- and nitric-oxide synthase (NOS)-pathways may counteract any EtOH effect. Two-week old organotypic rat brain slices of the nbM were exposed to 1–100 mM EtOH for 7 days with or without drugs and the number of choline-acetyltransferase (ChAT)-positive neurons was counted. Our data show that EtOH significantly reduced the number of ChAT-positive neurons with the most potent effect at a concentration of 50 mM EtOH (54 ± 5 neurons per slice, p < 0.001), compared to control slices (120 ± 13 neurons per slice). Inhibition of MAPK p38 (SB 203580, 10 μM) and NOS (L-thiocitrulline, 10 μM) counteracted the EtOH-induced decline of cholinergic neurons and NGF protected cholinergic neurons against the EtOH-induced effect. Withdrawal of EtOH resulted in a reversal of cholinergic neurons to nearly controls. In conclusion, EtOH caused a transient decline of cholinergic neurons, possibly involving MAPK p38- and NOS-pathways suggesting that EtOH does not induce direct cell death, but causes a transient downregulation of the cholinergic key enzyme, possibly reflecting a form of EtOH-associated plasticity.

Homocysteine has anti-inflammatory properties in a hypercholesterolemic rat model in vivo

Inflammation is a hallmark in many neurodegenerative diseases like Alzheimer's disease or vascular dementia. Cholesterol and homocysteine are both vascular risk factors which have been associated with dementia, inflammation and blood–brain barrier dysfunction. In previous studies we found that hypercholesterolemia but not hyperhomocysteinemia induced inflammation in rats in vivo. The aim of the present study was to investigate the effect of a combined treatment of Sprague Dawley rats with cholesterol and homocysteine for 5 months on spatial learning and memory, blood–brain barrier integrity and inflammation. Cholesterol treated rats showed severe learning deficits, while rats treated with cholesterol and homocysteine (Mix) counteracted the cholesterol-induced inflammation and partly the cortical blood–brain barrier disruptions, although cognition was still impaired. To study the potential protective effect of homocysteine, inflammation was induced in organotypic rat brain cortex slices and primary microglial cells by treatment with different inflammatory stimuli (e.g. lipopolysaccharide or tissue plasminogen activator). Tissue plasminogen activator-induced inflammation was counteracted by homocysteine. In conclusion, our data demonstrate that homocysteine significantly ameliorates cholesterol-induced inflammation and blood–brain barrier disruption but not the memory impairment, possibly involving a tissue plasminogen activator-related mechanism.

Effects of oxidative stress on amyloid precursor protein processing in rat and human platelets

Alzheimer's disease (AD) is the most common neurodegenerative illness affecting the elderly and is characterized by beta-amyloid (Aβ) deposition in the brain (plaques) and in microvessels (Aβ-angiopathy). The reasons for Aβ deposition are not clear, but an impaired clearance of Aβ at the blood-brain barrier may be implicated and oxidative stress possibly plays a major role in this process. Platelets are of particular interest, because they contain high levels of the amyloid precursor protein (APP) and in AD an abnormal expression of platelets APP fragments was found. The aim of the present study was to investigate (1) if oxidative stress induced by hydrogen peroxide (H(2)O(2)) affects APP expression in rat and human platelets and (2) to compare the APP changes with platelets of AD patients. In rat platelets, all three fragments of APP (130-110-106 kilo Dalton, kDa) were found. H(2)O(2) (10 mM, 20 minutes) significantly reduced all three fragments in rat platelets, did not affect CD62P-staining and slightly increased the size of actin as seen in the Western blot. The effect was not seen at 1 mM H(2)O(2) and was counteracted by glutathione. Immunohistochemistry for CD62P, CD61, APP and Annexin-V was used to verify the changes at the cellular level. In platelets of young volunteers (age = 33 ± 4 years), 10 mM H(2)O(2) markedly reduced the smaller APP 110 and 106 kDa fragments after 20 minutes. Our data show that platelets of AD patients (age = 80 ± 1 years) had a significant reduced 130 kDa fragment compared to controls (age = 70 ± 2 years). In summary, oxidative stress may account for a dysfunctional processing of APP in rat and human control platelets and possibly in AD patients.

Effects of long-term moderate ethanol and cholesterol on cognition, cholinergic neurons, inflammation, and vascular impairment in rats

There is strong evidence that vascular risk factors play a role in the development of Alzheimer's disease (AD) or vascular dementia (vaD). Ethanol (EtOH) and cholesterol are such vascular risk factors, and we recently showed that hypercholesterolemia causes pathologies similar to AD [Ullrich et al. (2010) Mol Cell Neurosci 45, 408–417]. The aim of this study was to investigate the effects of long-term (12 months) EtOH treatment (20% v/v in drinking water) alone or long-term 5% cholesterol diet alone or a combination (mix) in adult Sprague–Dawley rats. Long-term EtOH treatment (plasma EtOH levels 58±23 mg/dl) caused significant impairment of spatial memory, reduced the number of choline acetyltransferase- and p75 neurotrophin receptor-positive nucleus basalis of Meynert neurons, decreased cortical acetylcholine, elevated cortical monocyte chemoattractant protein-1 and tissue-type plasminogen activator, enhanced microglia, and markedly induced anti-rat immunoglobulin G-positive blood–brain barrier leakage. The effect of long-term hypercholesterolemia was similar. Combined long-term treatment of rats with 20% EtOH and 5% cholesterol (mix) did not potentiate treatment with EtOH alone, but instead counteracted some of the EtOH-associated effects. In conclusion, our data show that vascular risk factors EtOH and cholesterol play a role in cognitive impairment and possibly vaD.