Role of group I metabotropic glutamate receptors and NMDA receptors in homocysteine-evoked acute neurodegeneration of cultured cerebellar granule neurones

Visual Evoked Potentials in Patients With Vitamin B12 Deficiency

PURPOSE

The aim of this study was to investigate the subclinical involvement of the optic nerve in asymptomatic patients with vitamin B12 deficiency using visual evoked potentials.

METHODS

This study included 40 asymptomatic patients diagnosed with vitamin B12 deficiency (considered as serum levels below 150 pg/mL) and a control group of 40 healthy individuals. All participants underwent a visual evoked potential examination. Routine screening for homocysteine was performed for patients with vitamin B12 deficiency. The levels of vitamin B12 and homocysteine and the presence of megaloblastic anemia were analyzed statistically compared with P100, N75, and N135 latencies and amplitudes.

RESULTS

The mean vitamin B12 level was 96 pg/mL in the patient group and 374 pg/mL in the control group. In the patient group, 24 (60%) patients had hyperhomocysteinemia and 8 (20%) patients had megaloblastic anemia. The P100 wave latency of patients with vitamin B12 deficiency was significantly prolonged compared with the control group ( P < 0.01). There was no significant difference in the P100 amplitude between the patient group and the control group. P100 latencies were significantly longer in patients with hyperhomocysteinemia ( P = 0.002).

CONCLUSIONS

Our study showed that patients with vitamin B12 deficiency may have visual evoked potential abnormalities without visual symptoms or examination findings. In addition, high homocysteine levels led to a prolonged P100 latency in the patient group independent of vitamin B12 levels.

A factor analytic comparison of three commonly used depression scales (HAMD, MADRS, BDI) in a large sample of depressed inpatients

BACKGROUND

Quantifying depression mainly relies on the use of depression scales, and understanding their factor structure is crucial for evaluating their validity.

METHODS

This post-hoc analysis utilized prospectively collected data from a naturalistic study of 1014 inpatients with major depression. Confirmatory and exploratory factor analyses were performed to test the psychometric abilities of the Hamilton Depression Rating Scale, the Montgomery Asberg Depression Rating Scale, and the self-rated Beck Depression Inventory. A combined factor analysis was also conducted including all items of all scales.

RESULTS

All three scales showed good to very good internal consistency. The HAMD-17 had four factors: an "anxiety" factor, a "depression" factor, an "insomnia" factor, and a "somatic" factor. The MADRS also had four factors: a "sadness" factor, a neurovegetative factor, a "detachment" factor and a "negative thoughts" factor, while the BDI had three factors: a "negative attitude towards self" factor, a "performance impairment" factor, and a "somatic" factor. The combined factor analysis suggested that self-ratings might reflect a distinct illness dimension within major depression.

CONCLUSIONS

The factors obtained in this study are comparable to those found in previous research. Self and clinician ratings are complementary and not redundant, highlighting the importance of using multiple measures to quantify depression.

The role of homocysteine levels as a risk factor of ischemic stroke events: a systematic review and meta-analysis

Introduction

Among numerous risk factors, homocysteine (Hcy) has been linked to cerebral infarction; however, results have been inconsistent. This review aimed to conduct a meta-analysis of published studies to investigate the relationship between plasma Hcy levels and the risk of ischemic stroke.

Methods

A systematic literature search was conducted until November 2022 to obtain articles reporting Hcy levels in ischemic stroke patients. Review Manager software was used to perform all statistical analyses (version 5.3).

Results

Initial investigation yielded 283 articles. The final evaluation included 21 articles, including two prospective studies, one retrospective cohort, and 18 case-control studies. These studies included 9888 participants, of which 5031 were admitted patients with ischemic stroke. An integrated analysis revealed that ischemic stroke patients had significantly higher levels of Hcy than controls (mean difference (MD) = +3.70, 95% confidence interval (CI) = 2.42-5.81, p < 0.001).

Conclusion

This meta-analysis and systematic review indicate that ischemic stroke patients have significantly higher homocysteine levels than controls. Detecting hyperhomocysteinemia and reducing homocysteine levels should be explored among individuals at increased risk for ischemic stroke.

Association of serum homocysteine levels with intestinal flora and cognitive function in schizophrenia

Some studies have indicated that elevated homocysteine (Hcy) levels and intestinal flora may be involved in schizophrenia (SZ) cognition pathophysiology. This study was the first to investigate the association among Hcy, intestinal flora and schizophrenia cognition. Here, 140 individuals were divided into two groups: SZ patients (N = 68) and healthy controls (HCs, N = 72). Participant data on serum Hcy levels, intestinal flora and cognitive function evaluation using the MATRICS Consensus Cognitive Battery (MCCB) were collected. Clinical symptoms of patients were evaluated using the Positive and Negative Syndrome Scale. Serum Hcy levels and the incidence of hyperhomocysteinaemia were considerably increased in SZ patients compared with HCs. Hcy levels were significantly negatively associated with verbal learning index scores (r = -0.425, p < 0.001) but positively associated with Eubacterium (r = 0.32, p = 0.007), Lactobacillus (r = 0.32, p = 0.008), Corynebacterium (r = 0.26, p = 0.035), Mogibacterium (r = 0.31, p = 0.01), and Bulleidia (r = 0.31, p = 0.01) in SZ patients. Our findings suggest that serum Hcy levels are associated with cognitive function and intestinal flora in SZ patients. However, the mechanism of the interaction between Hcy and intestinal flora and its effects on cognitive function in SZ patients requires further investigation.

Diet's Role in Modifying Risk of Alzheimer's Disease: History and Present Understanding

Diet is an important nonpharmacological risk-modifying factor for Alzheimer's disease (AD). The approaches used here to assess diet's role in the risk of AD include multi-country ecological studies, prospective and cross-sectional observational studies, and laboratory studies. Ecological studies have identified fat, meat, and obesity from high-energy diets as important risk factors for AD and reported that AD rates peak about 15-20 years after national dietary changes. Observational studies have compared the Western dietary pattern with those of the Dietary Approaches to Stop Hypertension (DASH), Mediterranean (MedDi), and Mediterranean-DASH Intervention for Neurodegenerative Delay (MIND) diets. Those studies identified AD risk factors including higher consumption of saturated and total fats, meat, and ultraprocessed foods and a lower risk of AD with higher consumption of fruits, legumes, nuts, omega-3 fatty acids, vegetables, and whole grains. Diet-induced factors associated with a significant risk of AD include inflammation, insulin resistance, oxidative stress, elevated homocysteine, dietary advanced glycation end products, and trimethylamine N-oxide. The molecular mechanisms by which dietary bioactive components and specific foods affect risk of AD are discussed. Given most countries' entrenched food supply systems, the upward trends of AD rates would be hard to reverse. However, for people willing and able, a low-animal product diet with plenty of anti-inflammatory, low-glycemic load foods may be helpful.

Homocysteine, Cognitive Functions, and Degenerative Dementias: State of the Art

There is strong evidence that homocysteine is a risk factor not only for cerebrovascular diseases but also for degenerative dementias. A recent consensus statement renewed the importance and the role of high levels of homocysteine in cognitive decline in several forms of degenerative dementia, such as Alzheimer's disease. Although the molecular mechanisms by which homocysteine causes cell dysfunction are known, both the impact of homocysteine on specific cognitive functions and the relationship between homocysteine level and non-Alzheimer dementias have been poorly investigated. Most of the studies addressing the impact of hyperhomocysteinemia on dementias have not examined the profile of performance across different cognitive domains, and have only relied on screening tests, which provide a very general and coarse-grained picture of the cognitive status of the patients. Yet, trying to understand whether hyperhomocysteinemia is associated with the impairment of specific cognitive functions would be crucial, as it would be, in parallel, learning whether some brain circuits are particularly susceptible to the damage caused by hyperhomocysteinemia. These steps would allow one to (i) understand the actual role of homocysteine in the pathogenesis of cognitive decline and (ii) improve the diagnostic accuracy, differential diagnosis and prognostic implications. This review is aimed at exploring and revising the state of the art of these two strictly related domains. Suggestions for future research are provided.

Predicting target-ligand interactions with graph convolutional networks for interpretable pharmaceutical discovery

Drug Discovery is an active research area that demands great investments and generates low returns due to its inherent complexity and great costs. To identify potential therapeutic candidates more effectively, we propose protein–ligand with adversarial augmentations network (PLA-Net), a deep learning-based approach to predict target–ligand interactions. PLA-Net consists of a two-module deep graph convolutional network that considers ligands’ and targets’ most relevant chemical information, successfully combining them to find their binding capability. Moreover, we generate adversarial data augmentations that preserve relevant biological backgrounds and improve the interpretability of our model, highlighting the relevant substructures of the ligands reported to interact with the protein targets. Our experiments demonstrate that the joint ligand–target information and the adversarial augmentations significantly increase the interaction prediction performance. PLA-Net achieves 86.52% in mean average precision for 102 target proteins with perfect performance for 30 of them, in a curated version of actives as decoys dataset. Lastly, we accurately predict pharmacologically-relevant molecules when screening the ligands of ChEMBL and drug repurposing Hub datasets with the perfect-scoring targets.

Gut dysbiosis and homocysteine: a couple for boosting neurotoxicity in Huntington disease

Huntington's disease (HD), a neurodegenerative disorder caused by an expansion of the huntingtin triplet (Htt), is clinically characterized by cognitive and neuropsychiatric alterations. Although these alterations appear to be related to mutant Htt (mHtt)-induced neurotoxicity, several other factors are involved. The gut microbiota is a known modulator of brain-gut communication and when altered (dysbiosis), several complaints can be developed including gastrointestinal dysfunction which may have a negative impact on cognition, behavior, and other mental functions in HD through several mechanisms, including increased levels of lipopolysaccharide, proinflammatory cytokines and immune cell response, as well as alterations in Ca²⁺ signaling, resulting in both increased intestinal and blood-brain barrier (BBB) permeability. Recently, the presence of dysbiosis has been described in both transgenic mouse models and HD patients. A bidirectional influence between host brain tissues and the gut microbiota has been observed. On the one hand, the host diet influences the composition and function of microbiota; and on the other hand, microbiota products can affect BBB permeability, synaptogenesis, and the regulation of neurotransmitters and neurotrophic factors, which has a direct effect on host metabolism and brain function. This review summarizes the available evidence on the pathogenic synergism of dysbiosis and homocysteine, and their role in the transgression of BBB integrity and their potential neurotoxicity of HD.

Association between Homocysteine, Frailty and Biomechanical Response of the CNS in NPH-suspected Patients

Frailty is a geriatric syndrome that combines physiological decline, disruptions of homeostatic mechanisms across multiple physiologic systems and thus, strong vulnerability to further pathological stress. Previously, we provided the first evidence that increased risk of poor health outcomes, as quantified by a frailty index, is associated with an alteration of the central nervous system (CNS) biomechanical response to blood pulsatility. In this study, we explored correlation between fourteen biological parameters, the CNS elastance coefficient and frailty index. We included 60 adults (52-92 years) suspected of normal pressure hydrocephalus (NPH) and presenting with markers of multiple co-existing brain pathologies, including Parkinson disease (PD), Alzheimer disease (AD) and vascular dementia. We showed that the homocysteine (Hcy) level was independently and positively associated with both frailty index and the CNS elastance coefficient (adjusted R² of 10% and 6%). We also demonstrated that creatinine clearance and folate level were independently associated with Hcy level. Based on previous literature results describing the involvement of Hcy in endothelial dysfunction, glial activation and neurodegeneration, we discuss how Hcy could contribute to the altered biomechanical response of the CNS and frailty.

Homocysteine and Age-Related Central Nervous System Diseases: Role of Inflammation

Hyperhomocysteinemia (HHcy) is remarkably common among the aging population. The relation between HHcy and the development of neurodegenerative diseases, such as Alzheimer's disease (AD) and eye diseases, and age-related macular degeneration (AMD) and diabetic retinopathy (DR) in elderly people, has been established. Disruption of the blood barrier function of the brain and retina is one of the most important underlying mechanisms associated with HHcy-induced neurodegenerative and retinal disorders. Impairment of the barrier function triggers inflammatory events that worsen disease pathology. Studies have shown that AD patients also suffer from visual impairments. As an extension of the central nervous system, the retina has been suggested as a prominent site of AD pathology. This review highlights inflammation as a possible underlying mechanism of HHcy-induced barrier dysfunction and neurovascular injury in aging diseases accompanied by HHcy, focusing on AD.

Homocysteine in Neurology: A Possible Contributing Factor to Small Vessel Disease

Homocysteine (Hcy) is a sulfur-containing amino acid generated during methionine metabolism, accumulation of which may be caused by genetic defects or the deficit of vitamin B12 and folate. A serum level greater than 15 micro-mols/L is defined as hyperhomocysteinemia (HHcy). Hcy has many roles, the most important being the active participation in the transmethylation reactions, fundamental for the brain. Many studies focused on the role of homocysteine accumulation in vascular or degenerative neurological diseases, but the results are still undefined. More is known in cardiovascular disease. HHcy is a determinant for the development and progression of inflammation, atherosclerotic plaque formation, endothelium, arteriolar damage, smooth muscle cell proliferation, and altered-oxidative stress response. Conversely, few studies focused on the relationship between HHcy and small vessel disease (SVD), despite the evidence that mice with HHcy showed a significant end-feet disruption of astrocytes with a diffuse SVD. A severe reduction of vascular aquaporin-4-water channels, lower levels of high-functioning potassium channels, and higher metalloproteinases are also observed. HHcy modulates the N-homocysteinylation process, promoting a pro-coagulative state and damage of the cellular protein integrity. This altered process could be directly involved in the altered endothelium activation, typical of SVD and protein quality, inhibiting the ubiquitin-proteasome system control. HHcy also promotes a constant enhancement of microglia activation, inducing the sustained pro-inflammatory status observed in SVD. This review article addresses the possible role of HHcy in small-vessel disease and understands its pathogenic impact.

GluN2 Subunit-Dependent Redox Modulation of NMDA Receptor Activation by Homocysteine

Homocysteine (HCY) molecule combines distinct pharmacological properties as an agonist of N-methyl-d-aspartate receptors (NMDARs) and a reducing agent. Whereas NMDAR activation by HCY was elucidated, whether the redox modulation contributes to its action is unclear. Here, using patch-clamp recording and imaging of intracellular Ca²⁺, we study dithiothreitol (DTT) effects on currents and Ca²⁺ responses activated by HCY through native NMDARs and recombinant diheteromeric GluN1/2A, GluN1/2B, and GluN1/2C receptors. Within a wide range (1–800 μM) of [HCY]s, the concentration–activation relationships for recombinant NMDARs revealed a biphasicness. The high-affinity component obtained between 1 and 100 µM [HCY]s corresponding to the NMDAR activation was not affected by 1 mM DTT. The low-affinity phase observed at [HCY]s above 200 μM probably originated from thiol-dependent redox modulation of NMDARs. The reduction of NMDAR disulfide bonds by either 1 mM DTT or 1 mM HCY decreased GluN1/2A currents activated by HCY. In contrast, HCY-elicited GluN1/2B currents were enhanced due to the remarkable weakening of GluN1/2B desensitization. In fact, cleaving NMDAR disulfide bonds in neurons reversed the HCY-induced Ca²⁺ accumulation, making it dependent on GluN2B- rather than GluN2A-containing NMDARs. Thus, estimated concentrations for the HCY redox effects exceed those in the plasma during intermediate hyperhomocysteinemia but may occur during severe hyperhomocysteinemia.

Hormetic-Like Effects of L-Homocysteine on Synaptic Structure, Function, and Aβ Aggregation

Alzheimer’s Disease (AD) is the primary cause of dementia among the elderly population. Elevated plasma levels of homocysteine (HCy), an amino acid derived from methionine metabolism, are considered a risk factor and biomarker of AD and other types of dementia. An increase in HCy is mostly a consequence of high methionine and/or low vitamin B intake in the diet. Here, we studied the effects of physiological and pathophysiological HCy concentrations on oxidative stress, synaptic protein levels, and synaptic activity in mice hippocampal slices. We also studied the in vitro effects of HCy on the aggregation kinetics of Aβ₄₀. We found that physiological cerebrospinal concentrations of HCy (0.5 µM) induce an increase in synaptic proteins, whereas higher doses of HCy (30–100 µM) decrease their levels, thereby increasing oxidative stress and causing excitatory transmission hyperactivity, which are all considered to be neurotoxic effects. We also observed that normal cerebrospinal concentrations of HCy slow the aggregation kinetic of Aβ₄₀, whereas high concentrations accelerate its aggregation. Finally, we studied the effects of HCy and HCy + Aβ₄₂ over long-term potentiation. Altogether, by studying an ample range of effects under different HCy concentrations, we report, for the first time, that HCy can exert beneficial or toxic effects over neurons, evidencing a hormetic-like effect. Therefore, we further encourage the use of HCy as a biomarker and modifiable risk factor with therapeutic use against AD and other types of dementia.

B Vitamins and Fatty Acids: What Do They Share with Small Vessel Disease-Related Dementia?

Many studies have been written on vitamin supplementation, fatty acid, and dementia, but results are still under debate, and no definite conclusion has yet been drawn. Nevertheless, a significant amount of lab evidence confirms that vitamins of the B group are tightly related to gene control for endothelium protection, act as antioxidants, play a co-enzymatic role in the most critical biochemical reactions inside the brain, and cooperate with many other elements, such as choline, for the synthesis of polyunsaturated phosphatidylcholine, through S-adenosyl-methionine (SAM) methyl donation. B-vitamins have anti-inflammatory properties and act in protective roles against neurodegenerative mechanisms, for example, through modulation of the glutamate currents and a reduction of the calcium currents. In addition, they also have extraordinary antioxidant properties. However, laboratory data are far from clinical practice. Many studies have tried to apply these results in everyday clinical activity, but results have been discouraging and far from a possible resolution of the associated mysteries, like those represented by Alzheimer's disease (AD) or small vessel disease dementia. Above all, two significant problems emerge from the research: No consensus exists on general diagnostic criteria-MCI or AD? Which diagnostic criteria should be applied for small vessel disease-related dementia? In addition, no general schema exists for determining a possible correct time of implementation to have effective results. Here we present an up-to-date review of the literature on such topics, shedding some light on the possible interaction of vitamins and phosphatidylcholine, and their role in brain metabolism and catabolism. Further studies should take into account all of these questions, with well-designed and world-homogeneous trials.

GluN2A-NMDA receptor-mediated sustained Ca2+ influx leads to homocysteine-induced neuronal cell death

Homocysteine, a metabolite of the methionine cycle, is a known agonist of N-methyl-d-aspartate receptor (NMDAR), a glutamate receptor subtype and is involved in NMDAR-mediated neurotoxicity. Our previous findings have shown that homocysteine-induced, NMDAR-mediated neurotoxicity is facilitated by a sustained increase in phosphorylation and activation of extracellular signal-regulated kinase/mitogen-activated protein kinase (ERK MAPK). In the current study, we investigated the role GluN1/GluN2A-containing functional NMDAR (GluN2A-NMDAR) and GluN1/GluN2B-containing functional NMDAR (GluN2B-NMDAR) in homocysteine-induced neurotoxicity. Our findings revealed that exposing primary cortical neuronal cultures to homocysteine leads to a sustained low-level increase in intracellular Ca²⁺ We also showed that pharmacological inhibition of GluN2A-NMDAR or genetic deletion of the GluN2A subunit attenuates homocysteine-induced increase in intracellular Ca²⁺ Our results further established the role of GluN2A-NMDAR in homocysteine-mediated sustained ERK MAPK phosphorylation and neuronal cell death. Of note, the preferential role of GluN2A-NMDAR in homocysteine-induced neurotoxicity was distinctly different from glutamate-NMDAR-induced excitotoxic cell death that involves overactivation of GluN2B-NMDAR and is independent of ERK MAPK activation. These findings indicate a critical role of GluN2A-NMDAR-mediated signaling in homocysteine-induced neurotoxicity.

The Controversial Role of Homocysteine in Neurology: From Labs to Clinical Practice

Homocysteine (Hcy) is a sulfur-containing amino acid that is generated during methionine metabolism. Physiologic Hcy levels are determined primarily by dietary intake and vitamin status. Elevated plasma levels of Hcy can be caused by deficiency of either vitamin B12 or folate. Hyperhomocysteinemia (HHcy) can be responsible of different systemic and neurological disease. Actually, HHcy has been considered as a risk factor for systemic atherosclerosis and cardiovascular disease (CVD) and HHcy has been reported in many neurologic disorders including cognitive impairment and stroke, independent of long-recognized factors such as hyperlipidemia, hypertension, diabetes mellitus, and smoking. HHcy is typically defined as levels >15 micromol/L. Treatment of hyperhomocysteinemia with folic acid and B vitamins seems to be effective in the prevention of the development of atherosclerosis, CVD, and strokes. However, data from literature show controversial results regarding the significance of homocysteine as a risk factor for CVD and stroke and whether patients should be routinely screened for homocysteine. HHcy-induced oxidative stress, endothelial dysfunction, inflammation, smooth muscle cell proliferation, and endoplasmic reticulum (ER) stress have been considered to play an important role in the pathogenesis of several diseases including atherosclerosis and stroke. The aim of our research is to review the possible role of HHcy in neurodegenerative disease and stroke and to understand its pathogenesis.

The Effect of Electrospun Fiber Diameter on Astrocyte-Mediated Neurite Guidance and Protection

The topography of electrospun fiber scaffolds modifies astrocytes toward in vivo-like morphologies and behaviors. However, little is known about how electrospun fiber diameter influences astrocyte behavior. In this work, aligned fibers with two distinct nanoscale fiber diameters (808 and 386 nm) were prepared, and the astrocyte response was measured over time. Astrocytes on the large diameter fibers showed significantly increased elongation as early as 2 h after seeding and remained significantly more elongated for up to 4 days compared to those on small diameter fibers. Astrocytes extending along larger diameter fibers were better equipped to support long neurite outgrowth from dorsal root ganglia neurons, and neurite outgrowth along these astrocytes was less branched than outgrowth along astrocytes cultured on small diameter fibers. The differences in astrocyte shape observed on the small or large diameter fibers did not translate into differences in GLT-1, GFAP, or GLAST protein expression. Thus, different fiber diameters were unable to influence astrocyte protein expression uniquely. Nevertheless, astrocytes cultured in either small or large fibers significantly increased their expression of GLT-1 compared to astrocytes cultured on nonfiber (film) controls. Fibrous-induced increases in astrocyte GLT-1 expression protected astrocyte/neuron cocultures from toxicity generated by high extracellular glutamate. Alternatively, astrocytes/neurons cultured on films were less able to protect these cells from culture conditions consisting of high glutamate levels. Biomaterials, such as the fibrous materials presented here, may help stimulate astrocytes to increase GLT-1 expression and uptake more glutamate, since astrocytes are less likely to uptake glutamate in neurodegenerative pathologies or following central nervous system injury.

High sensitivity of cerebellar neurons to homocysteine is determined by expression of GluN2C and GluN2D subunits of NMDA receptors

Homocysteine (HCY) induced neurotoxicity largely depends on interaction of this endogenous amino acid with glutamate NMDA receptors (NMDARs). This receptor type is composed by GluN1 and different GluN2 (A, B, C or D) subunits. However, the receptor activity of HCY in brain regions which differ in relative contribution of GluN2 subunits was not tested so far. In the current study, we explored the action of HCY on cerebellar neurons which natively express GluN2C and GluN2D subunits of NMDARs and compared this with the action of HCY on cortical neurons which are mainly composed by GluN2A and GluN2B subunits. To validate obtained results, we also studied the responses to HCY in recombinant GluN1/2C and GluN1/2D NMDARs expressed in HEK293T cells. Responses to HCY were compared to membrane currents evoked by glutamate or by the specific agonist NMDA. First, we found that on HEK cells expressing GluN1/2C or GluN1/2D NMDARs, HCY was full agonist producing membrane currents similar in amplitude to currents induced by glutamate. The EC₅₀ values for these particular receptor subtype activation were 80 μM and 31 μM, respectively. Then, we found that HCY similarly to NMDA, evoked large slightly desensitizing membrane currents in native NMDARs of cerebellar and cortical neurons. In cortical neurons, the ratio of the respective currents (I_HCY/I_NMDA) was 0.16 and did not significantly change during in vitro maturation. In sharp contrast, in cerebellar neurons, the ratio of currents evoked by HCY and NMDA was dramatically increased from 0.31 to 0.72 from 7 to 21 day in culture. We show that least 75% of HCY-induced currents in cerebellum were mediated by GluN2C- or GluN2D-containing NMDARs. Thus, our data revealed a large population of cerebellar NMDA receptors highly sensitive to HCY which suggest potential vulnerability of this brain region to pathological conditions associated with enhanced levels of this neurotoxic amino acid.

Role of Homocysteine in the Ischemic Stroke and Development of Ischemic Tolerance

Homocysteine (Hcy) is a toxic, sulfur-containing intermediate of methionine metabolism. Hyperhomocysteinemia (hHcy), as a consequence of impaired Hcy metabolism or defects in crucial co-factors that participate in its recycling, is assumed as an independent human stroke risk factor. Neural cells are sensitive to prolonged hHcy treatment, because Hcy cannot be metabolized either by the transsulfuration pathway or by the folate/vitamin B12 independent remethylation pathway. Its detrimental effect after ischemia-induced damage includes accumulation of reactive oxygen species (ROS) and posttranslational modifications of proteins via homocysteinylation and thiolation. Ischemic preconditioning (IPC) is an adaptive response of the CNS to sub-lethal ischemia, which elevates tissues tolerance to subsequent ischemia. The main focus of this review is on the recent data on homocysteine metabolism and mechanisms of its neurotoxicity. In this context, the review documents an increased oxidative stress and functional modification of enzymes involved in redox balance in experimentally induced hyperhomocysteinemia. It also gives an interpretation whether hyperhomocysteinemia alone or in combination with IPC affects the ischemia-induced neurodegenerative changes as well as intracellular signaling. Studies document that hHcy alone significantly increased Fluoro-Jade C- and TUNEL-positive cell neurodegeneration in the rat hippocampus as well as in the cortex. IPC, even if combined with hHcy, could still preserve the neuronal tissue from the lethal ischemic effects. This review also describes the changes in the mitogen-activated protein kinase (MAPK) protein pathways following ischemic injury and IPC. These studies provide evidence for the interplay and tight integration between ERK and p38 MAPK signaling mechanisms in response to the hHcy and also in association of hHcy with ischemia/IPC challenge in the rat brain. Further investigations of the protective factors leading to ischemic tolerance and recognition of the co-morbid risk factors would result in development of new avenues for exploration of novel therapeutics against ischemia and stroke.

Inhibition of glutamate receptors reduces the homocysteine-induced whole blood platelet aggregation but does not affect superoxide anion generation or platelet membrane fluidization

Homocysteine (Hcy) is an excitotoxic amino acid. It is potentially possible to prevent Hcy-induced toxicity, including haemostatic impairments, by antagonizing glutaminergic receptors. Using impedance aggregometry with arachidonate and collagen as platelet agonists, we tested whether the blockade of platelet NMDA (N-methyl-D-aspartate), AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) and kainate receptors with their inhibitors: MK-801 (dizocilpine hydrogen maleate, [5R,10S]-[+]-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine), CNQX (7-nitro-2,3-dioxo-1,4-dihydroquinoxaline-6-carbonitrile) and UBP-302 (2-{[3-[(2S)-2-amino-2-carboxyethyl]-2,6-dioxo-3,6-dihydropyrimidin 1(2H)-yl]methyl}benzoic acid) may hamper Hcy-dependent platelet aggregation. All the tested compounds significantly inhibited Hcy-augmented aggregation of blood platelets stimulated either with arachidonate or collagen. Hcy stimulated the generation of superoxide anion in whole blood samples in a concentration-dependent manner; however, this process appeared as independent on ionotropic glutamate receptors, as well as on NADPH oxidase and protein kinase C, and was not apparently associated with the extent of either arachidonate- or collagen-dependent platelet aggregation. Moreover, Hcy acted as a significant fluidizer of surface (more hydrophilic) and inner (more hydrophobic) regions of platelet membrane lipid bilayer, when used at the concentration range from 10 to 50 µmol/l. However, this effect was independent on the Hcy action through glutamate ionotropic receptors, since there was no effects of MK-801, CNQX or UBP-302 on Hcy-mediated membrane fluidization. In conclusion, Hcy-induced changes in whole blood platelet aggregation are mediated through the ionotopic excitotoxic receptors, although the detailed mechanisms underlying such interactions remain to be elucidated.

Homocysteine and Mild Cognitive Impairment: Are These the Tools for Early Intervention in the Dementia Spectrum?

Dementia, being a neurodegenerative disease, has devastating consequences not just for the ailing but also for the carers as it has a tremendous negative impact on the quality of life. The pathophysiology of dementia commences far earlier than its diagnosis. Mild cognitive impairment (MCI) is a stage prior to definite dementia. The progression from MCI to dementia is insidious with no definite demarcation, thus making diagnosis clinically difficult at an early stage. This paper attempts to throw light on the epidemiology, risk factors and the aetiopathogenesis of MCI. It further attempts to elaborate on the rate of conversion of MCI to definite dementia and the factors influencing the same. Many established as well as probable, modifiable as well as non-modifiable risk factors influence the progress of MCI to definite dementia. Homocysteine, a sulphur containing amino-acid has been identified as a probable risk factor for the dementia spectrum. Various existing clinical evidences and biological plausibility towards probable link between homocysteine and dementia are discussed in this paper. B vitamin mediated homocysteine reduction and cognitive outcomes demonstrate mixed results. This review attempts to evaluate hyperhomocysteinaemia and MCI as a brain risk marker and assess their potential for future research with a view to attempt early intervention.

Novel insights into the effect of vitamin B₁₂ and omega-3 fatty acids on brain function

The prevalence of psychiatric disorders which are characterized by cognitive decline is increasing at an alarming rate and account for a significant proportion of the global disease burden. Evidences from human and animal studies indicate that neurocognitive development is influenced by various environmental factors including nutrition. It has been established that nutrition affects the brain throughout life. However, the mechanisms through which nutrition modulates mental health are still not well understood. It has been suggested that the deficiencies of both vitamin B12 and omega-3 fatty acids can have adverse effects on cognition and synaptic plasticity. Studies indicate a need for supplementation of vitamin B12 and omega-3 fatty acids to reduce the risk of cognitive decline, although the results of intervention trials using these nutrients in isolation are inconclusive. In the present article, we provide an overview of vitamin B12 and omega-3 fatty acids, the possible mechanisms and the evidences through which vitamin B12 and omega-3 fatty acids modulate mental health and cognition. Understanding the role of vitamin B12 and omega-3 fatty acids on brain functioning may provide important clues to prevent early cognitive deficits and later neurobehavioral disorders.

A quantitative proteomic approach for unveiling novel mechanisms associated with MeHg-induced toxicity: effects on the methylation cycle

Methylmercury (MeHg) is still a major threat for human health and the environment due to its extremely high toxicity that mainly affects the nervous system. Despite the great efforts made during the last few decades, the specific molecular mechanisms involved in MeHg-induced toxicity are still not completely unveiled. In this work we explored such mechanisms using neuroblastoma cells (Neuro-2a) and SILAC as a quantitative proteomic approach. We found that exposure of Neuro-2a cells to 2 mg L-1 MeHg for 8 h decreased the cell viability to 70% and caused significant changes in the morphology of the cells, specially regarding neurite development. Our proteomic results showed different proteins altered upon MeHg exposure that helped to identify pathways related to the toxicity exerted by MeHg. Specifically, we have found that MeHg affects the methylation cycle by inhibiting the expression of key enzymes including MTHFD1 and MTR. Moreover, we demonstrate that inhibition of MTHFD1 is not observed when exposing the cells to inorganic Hg and other heavy metals such as Pb or Cu. Thus, this work sets the stage for dissecting a specific molecular mechanism for MeHg-induced toxicity.

Effect of Homocysteine on Survival of Human Glial Cells

Several neurodegenerative conditions, such as Alzheimer’s disease and Parkinson’s disease, or vascular dementia and cognitive impairment, are associated with mild hyperhomocysteinemia. Hyperhomocysteinemia is defined as an increase of the homocysteine (Hcy) level beyond 10 μM. Although the adverse effect of Hcy on neurons is well documented, knowledge about the impact of this amino acid on glial cells is missing. Therefore, with the aim to evaluate the neurotoxic properties of Hcy on glial cells, we used a glioblastoma cell line as a study model. The viability of cells was assayed biochemically and cytologically. At a concentration around 50 μM in the culture medium D,L-Hcy induced cell death. It is noteworthy that Hcy induces cell death of human glial cells at concentrations encountered during mild hyperhomocysteinemia. Therefore, we propose that Hcy-induced impairment of neuronal functions along with damage of glial cells may contribute to the etiopathogenesis of neurodegenerative diseases associated with hyperhomocysteinemia.

The potential physiological crosstalk and interrelationship between two sovereign endogenous amines, melatonin and homocysteine

The antioxidant melatonin and the non-proteinogenic excitotoxic amino acid homocysteine (Hcy) are very distinct but related reciprocally to each other in their mode of action. The elevated Hcy level has been implicated in several disease pathologies ranging from cardio- and cerebro-vascular diseases to neurodegeneration owing largely to its free radical generating potency. Interestingly, melatonin administration potentially normalizes the elevated Hcy level, thereby protecting the cells from the undesired Hcy-induced excitotoxicity and cell death. However, the exact mechanism and between them remain obscure. Through literature survey we have found an indistinct but a vital link between melatonin and Hcy i.e., the existence of reciprocal regulation between them, and this aspect has been thoroughly described herein. In this review, we focus on all the possibilities of co-regulation of melatonin and Hcy at the level of their production and metabolism both in basal and in pathological conditions, and appraised the potential of melatonin in ameliorating homocysteinemia-induced cellular stresses. Also, we have summarized the differential mode of action of melatonin and Hcy on health and disease states.

Stereoselective synthesis of activated 2-arylazetidines via imino-aldol reaction

A highly stereoselective synthesis ofN-sulfinyl andN-sulfonyl azetidines have been developed involving imino-aldol reaction of ester enolates with aldimines.

Modulation of glutamate transport and receptor binding by glutamate receptor antagonists in EAE rat brain

The etiology of multiple sclerosis (MS) is currently unknown. However, one potential mechanism involved in the disease may be excitotoxicity. The elevation of glutamate in cerebrospinal fluid, as well as changes in the expression of glutamate receptors (iGluRs and mGluRs) and excitatory amino acid transporters (EAATs), have been observed in the brains of MS patients and animals subjected to experimental autoimmune encephalomyelitis (EAE), which is the predominant animal model used to investigate the pathophysiology of MS. In the present paper, the effects of glutamatergic receptor antagonists, including amantadine, memantine, LY 367583, and MPEP, on glutamate transport, the expression of mRNA of glutamate transporters (EAATs), the kinetic parameters of ligand binding to N-methyl-D-aspartate (NMDA) receptors, and the morphology of nerve endings in EAE rat brains were investigated. The extracellular level of glutamate in the brain is primarily regulated by astrocytic glutamate transporter 1 (GLT-1) and glutamate-aspartate transporter (GLAST). Excess glutamate is taken up from the synaptic space and metabolized by astrocytes. Thus, the extracellular level of glutamate decreases, which protects neurons from excitotoxicity. Our investigations showed changes in the expression of EAAT mRNA, glutamate transport (uptake and release) by synaptosomal and glial plasmalemmal vesicle fractions, and ligand binding to NMDA receptors; these effects were partially reversed after the treatment of EAE rats with the NMDA antagonists amantadine and memantine. The antagonists of group I metabotropic glutamate receptors (mGluRs), including LY 367385 and MPEP, did not exert any effect on the examined parameters. These results suggest that disturbances in these mechanisms may play a role in the processes associated with glutamate excitotoxicity and the progressive brain damage in EAE.

Mechanisms involved in the ischemic tolerance in brain: effect of the homocysteine

Hyperhomocysteinemia (hHCy) is recognized as a co-morbid risk factor of human stroke. It also aggravates the ischemia-induced injury by increased production of reactive oxygen species, and by the homocysteinylation and thiolation of functional proteins. Ischemic preconditioning represents adaptation of the CNS to sub-lethal ischemia, resulting in increased brain tolerance to subsequent ischemia. We present here an overview of recent data on the homocysteine (Hcy) metabolism and on the genetic and metabolic causes of hHCy-related neuropathologies in humans. In this context, the review documents for an increased oxidative stress and for the functional modifications of enzymes involved in the redox balance in experimentally induced hHCy. Hcy metabolism leads also to the redox imbalance and increased oxidative stress resulting in elevated lipoperoxidation and protein oxidation, the products known to be included in the neuronal degeneration. Additionally, we examine the effect of the experimental hHCy in combination with ischemic insult, and/or with the preischemic challenge on the extent of neuronal degeneration as well as the intracellular signaling and the regulation of DNA methylation. The review also highlights that identification of the effects of co-morbid factors in the mechanisms of ischemic tolerance mechanisms would lead to improved therapeutics, especially the brain tissue.

Activation of mGluR5 attenuates NMDA-induced neurotoxicity through disruption of the NMDAR-PSD-95 complex and preservation of mitochondrial function in differentiated PC12 cells

Glutamate-mediated toxicity is implicated in various neuropathologic conditions, and activation of ionotropic and metabotropic glutamate receptors is considered to be the most important mechanism. It has been reported that pharmacological saturation of metabotropic glutamate receptors (mGluRs) can facilitate N-methyl-d-aspartate receptor (NMDAR) related signaling cascades, but the mechanism leading to mGluR-NMDAR interactions in excitotoxic neuronal injury has remained unidentified. In the present study, we investigated the role of mGluR5 in the regulation of N-methyl-d-aspartate (NMDA)-induced excitotoxicity in differentiated PC12 cells. We found that activation of mGluR5 with the specific agonist R,S-2-chloro-5-hydroxyphenylglycine (CHPG) increased cell viability and inhibited lactate dehydrogenase (LDH) release in a dose-dependent manner. CHPG also inhibited an increase in the Bax/Bcl-2 ratio, attenuated cleavage of caspase-9 and caspase-3, and reduced apoptotic cell death after NMDA treatment. The NMDA-induced mitochondrial dysfunction, as indicated by mitochondrial reactive oxygen species (ROS) generation, collapse of mitochondrial membrane potential (MMP), and cytochrome c release, was also partly prevented by CHPG treatment. Furthermore, CHPG blocked the NMDA-induced interaction of NMDAR with postsynaptic density protein-95 (PSD-95), but had no effects on intracellular calcium concentrations. All these results indicated that activation of mGluR5 protects differentiated PC12 cells from NMDA-induced neuronal excitotoxicity by disrupting NMDAR-PSD-95 interaction, which might be an ideal target for investigating therapeutic strategies in various neurological diseases where excitotoxicity may contribute to their pathology.

Review of dextromethorphan administration in 18 patients with subacute methotrexate central nervous system toxicity

BACKGROUND

The pathogenesis of methotrexate central nervous system toxicity is multifactorial, but it is likely related to central nervous system folate homeostasis. The use of folinate rescue has been described to decrease toxicity in patients who had received intrathecal methotrexate. It has also been described in previous studies that there is an elevated level of homocysteine in plasma and cerebrospinal fluid of patients who had received intrathecal methotrexate. Homocysteine is an N-methyl-D-aspartate receptor agonist. The use of dextromethorphan, noncompetitive N-methyl-D-aspartate receptor receptor antagonist, has been used in the treatment of sudden onset of neurological dysfunction associated with methotrexate toxicity. It remains unclear whether the dextromethorphan impacted the speed of recovery, and its use remains controversial. This study reviews the use of dextromethorphan in the setting of subacute methotrexate central nervous system toxicity.

METHODS

Charts of 18 patients who had sudden onset of neurological impairments after receiving methotrexate and were treated with dextromethorphan were reviewed.

RESULT

The use of dextromethorphan in most of our patients resulted in symptomatic improvement. In this patient population, earlier administration of dextromethorphan resulted in faster improvement of impairments and led to prevention of recurrence of seizure activity induced by methotrexate central nervous system toxicity.

CONCLUSIONS

Our study provides support for the use of dextromethorphan in patients with subacute methotrexate central nervous system toxicity.

Neurotoxic effects of indocyanine green -cerebellar granule cell culture viability study

The aim of this study was to examine neurotoxicity indocyanine green (ICG). We assessed viability of primary cerebellar granule cell culture (CGC) exposed to ICG to test two mechanisms that could be the first triggers causing neuronal toxicity: imbalance in calcium homeostasis and the degree of oligomerization of ICG molecules. We have observed this imbalance in CGC after exposure to 75-125μΜ ICG and dose and application sequence dependent protective effect of Gadovist on surviving neurons in vitro when used with ICG. Spectroscopic studies suggest the major cause of toxicity of the ICG is connected with oligomers formation. ICG at concentration of 25 μM (which is about 4 times higher than the highest concentration of ICG in the brain applied in in-vivo human studies) is not neurotoxic in the cell culture.

Behavioral and neurochemical effects of dietary methyl donor deficiency combined with unpredictable chronic mild stress in rats

Methyl donor deficiencies and chronic stress cause depression independently, but their interaction has never been thoroughly evaluated. In our study, methyl donor deficient diet and chronic stress condition consisted respectively of a B2, B9, B12, and choline-free diet and a chronic mild stress procedure. Rats were randomly assigned to six groups with three "diet" conditions (free-feeding, pair-fed and methyl donor deficient diet) and two "stress" conditions (no-stress and stress) and were evaluated in the open-field, the elevated plus-maze and the forced swimming test. After the behavioral evaluation, corticosterone and homocysteine plasma levels were measured and dopamine, DOPAC, serotonin, 5HIAA concentrations were evaluated in several brain areas. Rats given a methyl donor deficient diet for 11 weeks causing elevated plasma homocysteine levels were compared to pair-fed and free-feeding rats with or without unpredictable chronic mild stress. Regardless of stress environmental conditions, the methyl donor deficient diet decreased plasma corticosterone levels and caused disinhibition in the elevated plus-maze condition relative to both control groups. However, stress potentiated the effects of the deficient regimen on rearing in the open-field and climbing in the forced swim test. The dietary changes involved in behavior and plasma corticosterone could be caused by homocysteine-induced decreases in dopamine and 5-hydroxytryptamine metabolites in selective brain regions and it can be noted that regardless of stress-conditions, methyl donor deficient diet decreases DOPAC/dopamine and 5HIAA/serotonin ratios in striatum and hypothalamus and selectively 5HIAA/serotonin ratio in the sensorimotor cortex. Our experimental data is particularly relevant in the context of neuropsychiatric disorders frequently associated with folate deficiency and hyperhomocysteinemia.

Synergistic neurotoxicity of oxygen-glucose deprivation and tetrabromobisphenol A in vitro: role of oxidative stress

BACKGROUND

Tetrabromobisphenol A (TBBPA) is a toxic brominated flame retardant. Previous studies have demonstrated that exposure of primary cultures of rat cerebellar granule cells (CGC) to ≥ 10 μM TBBPA induces toxicity and excitotoxicity, and the underlying mechanism may involve calcium imbalance and oxidative stress. Here we examined whether the application of TBBPA at subtoxic concentrations may exacerbate acute damage of CGC challenged with oxygen-glucose deprivation (OGD), and evaluated with fluorescent indicators the involvement of calcium imbalance, mitochondrial depolarization and oxidative stress.

METHODS

Survival of CGC was assessed 24 h after OGD/TBBPA using fluorescent dyes. An OGD challenge lasting for 45, 60 or 75 min induced a duration-dependent injury to the neurons.

RESULTS

Application of 2.5, 5 or 7.5 μM TBBPA for 45 min to normoxic and glucose-containing incubation medium did not reduce the viability of cultured CGC, but this compound exacerbated the toxic effects of OGD in a concentration-dependent way. Moreover, TBBPA had a slight effect on calcium homeostasis and mitochondrial membrane potential, but significantly activated the production of reactive oxygen species in CGC. The application of H(2)O(2) at 5, 10 and 25 μM mimicked the effects of TBBPA on OGD toxicity, while 0.1 mM ascorbic acid or 1 mM glutathione ameliorated this toxicity.

CONCLUSION

These results suggest the involvement of oxidative stress in the synergistic neurotoxic effects of TBBPA and OGD.

Modulation of neurological deficits and expression of glutamate receptors during experimental autoimmune encephalomyelitis after treatment with selected antagonists of glutamate receptors

The aim of our investigation was to characterize the role of group I mGluRs and NMDA receptors in pathomechanisms of experimental autoimmune encephalomyelitis (EAE), the rodent model of MS. We tested the effects of LY 367385 (S-2-methyl-4-carboxyphenylglycine, a competitive antagonist of mGluR1), MPEP (2-methyl-6-(phenylethynyl)-pyridine, an antagonist of mGluR5), and the uncompetitive NMDA receptor antagonists amantadine and memantine on modulation of neurological deficits observed in rats with EAE. The neurological symptoms of EAE started at 10-11 days post-injection (d.p.i.) and peaked after 12-13 d.p.i. The protein levels of mGluRs and NMDA did not increase in early phases of EAE (4 d.p.i.), but starting from 8 d.p.i. to 25 d.p.i., we observed a significant elevation of mGluR1 and mGluR5 protein expression by about 20% and NMDA protein expression by about 10% over the control at 25 d.p.i. The changes in protein levels were accompanied by changes in mRNA expression of group I mGluRs and NMDARs. During the late disease phase (20–25 d.p.i.), the mRNA expression levels reached 300% of control values. In contrast, treatment with individual receptor antagonists resulted in a reduction of mRNA levels relative to untreated animals.

Homocysteine thiolactone-induced seizures in adult rats are aggravated by inhibition of inducible nitric oxide synthase

Homocysteine and its metabolites (homocysteine thiolactone (HT)) induce seizures via different but still not well-known mechanisms. The role of nitric oxide (NO) in epileptogenesis is highly contradictory and depends on, among other factors, the source of NO production. The aim of the present study was to examine the effects of aminoguanidine, selective inhibitor of inducible NO synthase (iNOS), on HT-induced seizures. Aminoguanidine (50, 75, and 100 mg/kg, intraperitoneally (i.p.)) was injected to rats 30 min prior to inducing HT (5.5 mmol/kg, i.p.). Seizure behavior was assessed by seizure incidence, latency time to first seizure onset, number of seizure episodes, and their severity during observational period of 90 min. Number and duration of spike and wave discharges (SWDs) were determined in electroencephalogram (EEG). Seizure latency time was significantly shortened, while seizure incidence, number, and duration of HT-induced SWD in EEG significantly increased in rats receiving aminoguanidine 100 mg/kg before subconvulsive dose of HT. Aminoguanidine in a dose-dependent manner also significantly increased the number of seizure episodes induced by HT and their severity. It could be concluded that iNOS inhibitor (aminoguanidine) markedly aggravates behavioral and EEG manifestations of HT-induced seizures in rats, showing functional involvement of iNOS in homocysteine convulsive mechanisms.

Neurodegeneration and neuroprotection in diabetic retinopathy

Diabetic retinopathy is widely considered to be a neurovascular disease. This is in contrast to its previous identity as solely a vascular disease. Early in the disease progression of diabetes, the major cells in the neuronal component of the retina consist of retinal ganglion cells and glial cells, both of which have been found to be compromised. A number of retinal function tests also indicated a functional deficit in diabetic retina, which further supports dysfunction of neuronal cells. As an endocrinological disorder, diabetes alters metabolism both systemically and locally in several body organs, including the retina. A growing body of evidences indicates increased levels of excitotoxic metabolites, including glutamate, branched chain amino acids and homocysteine in cases of diabetic retinopathy. Also present, early in the disease, are decreased levels of folic acid and vitamin-B12, which are potential metabolites capable of damaging neurons. These altered levels of metabolites are found to activate several metabolic pathways, leading to increases in oxidative stress and decreases in the level of neurotrophic factors. As a consequence, they may damage retinal neurons in diabetic patients. In this review, we have discussed those potential excitotoxic metabolites and their implications in neuronal damage. Possible therapeutic targets to protect neurons are also discussed. However, further research is needed to understand the exact molecular mechanism of neurodegeneration so that effective neuroprotection strategies can be developed. By protecting retinal neurons early in diabetic retinopathy cases, damage of retinal vessels can be protected, thereby helping to ameliorate the progression of diabetic retinopathy, a leading cause of blindness worldwide.

Homocysteine induces apoptosis of rat hippocampal neurons by inhibiting 14-3-3ε expression and activating calcineurin

A high level of plasma homocysteine (Hcy) increases the risk for neurodegenerative diseases. One such disorder is Alzheimer's disease, which involves marked neuronal apoptosis of unknown etiology. This study shows that Hcy inhibits expression of 14-3-3ε and activates calcineurin in rat hippocampal neurons in a dose-dependent manner. Calcineurin-mediated Bad dephosphorylation, which is blocked by calcineurin inhibition and Ca(2+) chelation, causes mitochondrial translocation of Bad and apoptosis; this step in the apoptotic pathway is synergistically blocked by calcineurin inhibition and overexpression of 14-3-3ε. These findings demonstrated that calcineurin activation and downregulation of 14-3-3ε may be one of the mechanisms of Hcy-induced apoptosis of hippocampal neurons.

Mild hyperhomocysteinemia alters extracellular adenine metabolism in rat brain

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

[Homocysteine, vitamin B-12, folic acid and the cognitive decline in the elderly]

Hyperhomocysteinemia is a risk factor for neurological diseases, but the underlying pathophysiology has not been adequately explained. Mild hyperhomocysteinemia, which is sometimes associated with a low plasma level of vitamin B9, B12 and folic acid, is responsible in the toxicity in neural cell by activating NMDA receptor. Indeed, even if vitamin supplementation has clearly proven its efficiency on lowering plasma levels of homocysteine, recent studies do not show any positive effect of vitamin therapy on cognitive function. The hypothesis that this therapy is inefficient has been recently reinforced by two randomized trials on the effects of vitamin supplementation. Several hypotheses still need to be explored: Mechanisms of homocysteine toxicity and that of total uselessness of vitamin supplementation; the possible need to complete the actual data with further, more powerful studies in order to prove the role of homocysteine in the development of neurodegenerative diseases and a clinical effect of vitamin therapy.