Increased plasma homocysteine levels in multiple sclerosis

Plasma lipid profiles and homocysteine levels in anti-N-methyl-D-aspartate receptor encephalitis

Introduction

We aimed to investigate whether lipid profiles and homocysteine levels in patients with anti-N-methyl-D-aspartate receptor encephalitis are related to clinical presentation and prognosis, which may contribute to further research on the pathogenesis and treatment of this disease.

Methods

This study included a total of 43 patients with anti-N-methyl-D-aspartate receptor encephalitis and 43 sex-age-matched healthy controls. Baseline demography, clinical data, patient outcomes, and ancillary examination results were recorded. Patients were followed up every 2-3 months during the first year. The modified Rankin Scale score was used to evaluate the therapeutic effect and clinical outcome.

Results

Among the 43 patients included in this study, 55.81% were male, the mean age of onset was 27 years old, and the median modified Rankin Scale score on admission was 3.0. Apolipoprotein A-1 was significantly lower in patients with anti-N-methyl-D-aspartate receptor encephalitis compared with healthy controls (p = 0.004). Compared with healthy controls, homocysteine (p = 0.002), apolipoprotein B (p = 0.004), Lpa (p = 0.045), and apolipoprotein B/apolipoprotein A-1 (p = 0.001) were significantly increased in patients with anti-N-methyl-D-aspartate receptor encephalitis. According to the modified Rankin Scale scores, 6 months after discharge, 72.09% of patients had a good prognosis and 27.91% had a poor prognosis. In the good prognosis group, age (p = 0.031), lipoprotein a (p = 0.023), apolipoprotein A-1 (p = 0.027) at baseline, and the modified Rankin Scale score on admission (p = 0.019) were significantly higher than those in the poor prognosis group.

Conclusion

This study suggests the possibility that serum lipid profile and homocysteine play an important role in the pathogenesis of anti-N-methyl-D-aspartate receptor encephalitis, providing support for lipid-lowering treatment of anti-N-methyl-D-aspartate receptor encephalitis patients.

Quantification of individual remyelination during short-term disease course by synthetic magnetic resonance imaging

MRI is an important diagnostic tool for evaluation of myelin content in multiple sclerosis and other CNS diseases, being especially relevant for studies investigating remyelinating pharmacotherapies. In this study, we evaluated a new synthetic MRI–based myelin estimation in methylenetetrahydrofolate reductase deficiency as a treatable primary demyelinating disorder and compared this method with established diffusion tensor imaging in both methylenetetrahydrofolate reductase deficiency patients and healthy controls. This is the first synthetic MRI–based in vivo evaluation of treatment-associated remyelination. 1.5 T synthetic MRI and 3 T diffusion MRI were obtained from three methylenetetrahydrofolate reductase deficiency patients at baseline and 6 months after therapy initiation, as well as from age-matched healthy controls (diffusion tensor imaging: n = 14, synthetic MRI: n = 9). Global and regional synthetic MRI parameters (myelin volume fraction, proton density, and relaxation rates) were compared with diffusion metrics (fractional anisotropy, mean/radial/axial diffusivity) and related to healthy controls by calculating z-scores and z-deviation maps. Whole-brain myelin (% of intracranial volume) of the index patient was reduced to 6 versus 10% in healthy controls, which recovered to a nonetheless subnormal level of 6.6% following initiation of high-dosage betaine. Radial diffusivity was higher at baseline compared with healthy controls (1.34 versus 0.79 × 10⁻³ mm²/s), recovering at follow-up (1.19 × 10⁻³ mm²/s). The index patient’s lesion volume diminished by 58% under treatment. Regional analysis within lesion area and atlas-based regions revealed lower mean myelin volume fraction (12.7_Baseline/14.71_Follow-up%) and relaxation rates, higher proton density, as well as lower fractional anisotropy and higher radial diffusivity (1.08 × 10⁻³_Baseline/0.94 × 10⁻³_Follow-up) compared with healthy controls. The highest z-scores were observed for myelin volume fraction in the posterior thalamic radiation, with greater deviation from controls at baseline and reduced deviation at follow-up. Z-deviations of diffusion metrics were less pronounced for radial and mean diffusivity than for myelin volume fraction. Z-maps for myelin volume fraction of the index patient demonstrated high deviation within and beyond lesion areas, among others in the precentral and postcentral gyrus, as well as in the cerebellum, and partial remission of these alterations at follow-up, while radial diffusivity demonstrated more widespread deviations in supra- and infratentorial regions. Concordant changes of myelin volume fraction and radial diffusivity after treatment initiation, accompanied by dramatic clinical and paraclinical improvement, indicate the consistency of the methods, while myelin volume fraction seems to characterize remyelinated regions more specifically. Synthetic MRI–based myelin volume fraction provides myelin estimation consistent with changes of diffusion metrics to monitor short-term myelin changes on individual patient level.

Identify the report as a systematic review

Background: To examine the relationship of vitamin B12 and folate concentrations to cognitive function, fatigue measures, physical function, quality of life (patient-centred outcomes) and homocysteine plasma concentrations (intermediate marker of cobalamin and folate deficiency) for patients with Multiple Sclerosis (MS). Methods: Systematic searches for eligible articles of MEDLINE, CINAHL, EMBASE, Scopus, Web of Science and OpenGray databases were conducted from 1983 in March 2021. Heterogeneity, Weighted Mean Difference (WMD) and Confidence Intervals (CI) calculated using Random Effects Model. Results: Sixteen studies were included involving; 616 MS patients and 655 healthy controls. 14 of these had acceptable or better quality but there was high heterogeneity. No difference was found between MS, healthy controls for folate and cobalamin concentrations; WMD 0.00ug/L (95% CI: -0.01, 0.01) and WMD 7.01pmol/L (95% CI: -25.54, 39.55) respectively. MS group showed mild-to-moderate disability WMD was 2.78 (95% CI: 2.00, 3.56). MS may be associated with elevated plasma homocysteine concentrations on average 2.47µmol/L more than healthy controls. Discussion: Physical ability of MS group was worse than healthy controls, but there was no difference in folate and cobalamin concentrations. This suggests folate and cobalamin are not influential factors in worsening physical function. There may be an association between worse cognitive function, and increased homocysteine concentrations. Results were inconclusive due to high heterogeneity and limited number of studies. A core outcome set would enable easier synthesis of future results.

Vascular and immunopathological role of Asymmetric Dimethylarginine (ADMA) in Experimental Autoimmune Encephalomyelitis

Asymmetric dimethylarginine (ADMA) is an endogenous nitric oxide synthase (NOS) inhibitor/uncoupler inducing vascular pathology. Vascular pathology is an important factor for the development and progression of CNS pathology of MS, yet the role of ADMA in MS remains elusive. Patients with multiple sclerosis (MS) are reported to have elevated blood levels of ADMA, and mice with experimental autoimmune encephalomyelitis (EAE, an animal model of MS) generated by auto-immunization of myelin oligodendrocyte glycoprotein (MOG) and blood-brain barrier (BBB) disruption by pertussis toxin also had increased blood ADMA levels in parallel with induction of clinical disease. To explore the role of ADMA in EAE pathogenesis, EAE mice were treated with a daily dose of ADMA. It is of special interest that ADMA treatment enhanced the BBB disruption in EAE mice and exacerbated the clinical and CNS disease of EAE. ADMA treatment also induced the BBB disruption and EAE disease in MOG-immunized mice even without pertussis toxin treatment, suggesting the role of ADMA in BBB dysfunction in EAE. T-cell polarization studies also documented that ADMA treatment promotes T_H 1- and T_H 17-mediated immune responses but without affecting Treg-mediated immune response in EAE mice as well as in in vitro T-cell culture. Taken together, these data, for the first time, document the vascular and immunopathogenic roles of ADMA in EAE, thus pointing to the potential of ADMA-mediated mechanism as a new target of potential therapy for MS.

Involvements of Hyperhomocysteinemia in Neurological Disorders

Homocysteine (HCY), a physiological amino acid formed when proteins break down, leads to a pathological condition called hyperhomocysteinemia (HHCY), when it is over a definite limit. It is well known that an increase in HCY levels in blood, can contribute to arterial damage and several cardiovascular disease, but the knowledge about the relationship between HCY and brain disorders is very poor. Recent studies demonstrated that an alteration in HCY metabolism or a deficiency in folate or vitamin B12 can cause altered methylation and/or redox potentials, that leads to a modification on calcium influx in cells, or into an accumulation in amyloid and/or tau protein involving a cascade of events that culminate in apoptosis, and, in the worst conditions, neuronal death. The present review will thus summarize how much is known about the possible role of HHCY in neurodegenerative disease.

Hyperhomocysteinemia and Endothelial Dysfunction in Multiple Sclerosis

Endothelial dysfunction is recognized as one of the leading factors in the pathogenesis of diseases of the central nervous system of various etiologies. Numerous studies have shown the role of hyperhomocysteinemia in the development of endothelial dysfunction and the prothrombogenic state. The most important condition in the development of multiple sclerosis (MS) is a dysregulation of the blood-brain barrier (BBB) and transendothelial leukocyte migration. It has been proven that homocysteine also contributes to the damage of neurons by the mechanism of excitotoxicity and the induction of the apoptosis of neurons. These processes can be one of the factors of neurodegenerative brain damage, which plays a leading role in the progression of MS. This review describes the pleiotropic effect of homocysteine on these processes and its role in MS pathogenesis.

Multiple Sclerosis: Lipids, Lymphocytes, and Vitamin D

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system. We review the two core MS features, myelin instability, fragmentation, and remyelination failure, and dominance of pathogenic CD4⁺ Th17 cells over protective CD4⁺ Treg cells. To better understand myelin pathology, we describe myelin biosynthesis, structure, and function, then highlight stearoyl-CoA desaturase (SCD) in nervonic acid biosynthesis and nervonic acid's contribution to myelin stability. Noting that vitamin D deficiency decreases SCD in the periphery, we propose it also decreases SCD in oligodendrocytes, disrupting the nervonic acid supply and causing myelin instability and fragmentation. To better understand the distorted Th17/Treg cell balance, we summarize Th17 cell contributions to MS pathogenesis, then highlight how 1,25-dihydroxyvitamin D₃ signaling from microglia to CD4⁺ T cells restores Treg cell dominance. This signaling rapidly increases flux through the methionine cycle, removing homocysteine, replenishing S-adenosyl-methionine, and improving epigenetic marking. Noting that DNA hypomethylation and inappropriate DRB1*1501 expression were observed in MS patient CD4⁺ T cells, we propose that vitamin D deficiency thwarts epigenetic downregulation of DRB1*1501 and Th17 cell signature genes, and upregulation of Treg cell signature genes, causing dysregulation within the CD4⁺ T cell compartment. We explain how obesity reduces vitamin D status, and how estrogen and vitamin D collaborate to promote Treg cell dominance in females. Finally, we discuss the implications of this new knowledge concerning myelin and the Th17/Treg cell balance, and advocate for efforts to address the global epidemics of obesity and vitamin D deficiency in the expectation of reducing the impact of MS.

Homocysteine, vitamin B12, and folate levels in patients with multiple sclerosis in Chinese population: A case-control study and meta-analysis

BACKGROUND

Current studies suggested discrepancies on the correlations between multiple sclerosis (MS) and blood levels of homocysteine (Hcy), vitamin B12 (VB12), and folate. We performed a case-control study and meta-analysis to help resolve the controversy of these lab values in Chinese patients with MS.

METHODS

We recruited 80 Chinese MS patients, 86 age/sex matched neurological controls (patients with peripheral vertigo or sleep disorders), and 80 age- and sex-matched healthy controls. Serum Hcy levels were measured using flourimetric high-performance liquid chromatography, serum levels of VB12 and folate using immune assay. A literature search of PubMed, Embase, Web of Science, Chinese National Knowledge Infrastructure, Wanfang, and SinoMed was conducted for case-control studies with pure Chinese populations published up to March 16, 2019. The effective size was estimated by the pooled standardized mean difference (SMD) and associated 95% confidence interval (CI).

RESULTS

The case-control study results suggest higher Hcy levels (mean ± SD) and frequency of hyperhomocysteinemia in the Chinese MS cases than control groups (all p < 0.001), lower for VB12 levels (mean ± SD, p = 0.043 or 0.039). No significant difference was observed for levels of folate (mean ± SD, both p > 0.05), and for frequency of folate or VB12 deficiency (all p > 0.05). Analysis of pooled SMDs and 95% CIs suggested increased Hcy levels in Chinese MS patients (SMD: 2.31, 95% CI: 1.33-3.28, p < 0.001), and in relapsing or remitting cases relative to controls (SMD: 0.94 or 0.85, 95% CI: 0.49-1.39 or 0.35-1.34, both p < 0.001). The meta-analysis results also suggested reduced VB12 levels in Chinese MS patients (SMD: -0.30, 95% CI: -0.46-0.14, p < 0.001), and in relapsing MS patients compared to controls (SMD: -0.31, 95% CI: -0.47-0.15, p < 0.001), while no statistical difference for cases in remission. No significant difference was observed for levels folate in all comparisons.

CONCLUSION

Patients with MS tend to have increased blood Hcy levels compared to controls. MS patients of Chinese origin and those in relapse may have decreased levels of VB12. Hcy and VB12 may contribute to pathogenesis of the disease, and VB12 may correlate with MS relapse.

Elevated Plasma Homocysteine Levels in Anti-N-methyl-D-aspartate Receptor Encephalitis

Objective: Homocysteine (Hcy) levels have been investigated in many diseases, such as neurodegenerative and autoimmune diseases. However, changes in Hcy levels in anti-N-Methyl-D-aspartate receptor (anti-NMDAR) encephalitis have not been investigated thus far.

Methods: Case data were collected from 45 patients with anti-NMDAR encephalitis and 179 age- and sex-matched healthy controls (HCs). Clinical characteristics, Hcy levels, C reactive protein (CRP) levels, and cerebrospinal fluid (CSF) parameters were determined. Association of Hcy and clinical parameters were evaluated in these patients. Among these 45 patients, 15 had a follow-up evaluation at 3 months after treatment.

Results: Hcy levels (p < 0.001) and CRP levels (p = 0.005) from the patients with anti-NMDAR encephalitis were significantly higher than those from HCs. Hcy levels from male patients were significantly lower than those from male HCs (p < 0.001). Comparing anti-NMDAR encephalitis patients after treatment with before treatment, the former has significantly higher Hcy levels (p = 0.004), CRP levels (p = 0.041) and mRS scores (p = 0.002). Furthermore, a significant negative correlation between the changes in Hcy levels and the changes in mRS scores (r = −0.534, p = 0.040) was observed.

Conclusion: Elevated plasma homocysteine occurs in anti-NMDAR encephalitis, and seems associated with male sex.

Plasma Homocysteine Level Is Associated with the Expanded Disability Status Scale in Neuromyelitis Optica Spectrum Disorder

BACKGROUND AND OBJECTIVE

Plasma homocysteine (Hcy) levels have been investigated among patients with multiple sclerosis (MS). However, the changes in Hcy levels and the association between Hcy levels and inflammatory/immune/cerebrospinal fluid (CSF) parameters in neuromyelitis optica spectrum disorder (NMOSD) patients have not been investigated yet.

METHODS

Case data were collected from 97 acute-phase NMOSD patients and 39 stable-phase NMOSD patients. Patients in the acute phase were divided into 2 groups based on the EDSS score with cutoff equal to 4. Hcy levels, immunoglobulins (Ig) A, G, and M, complement 3 and 4, CH50, C-reactive protein, erythrocyte sedimentation rate (ESR), and CSF examination including white blood cells and total protein were determined.

RESULTS

No significant differences in Hcy levels are observed between acute-phase and stable-phase NMOSD patients. Hcy and ESR levels were significantly higher in acute-phase NMOSD patients with EDSS score ≥4. Besides, EDSS is positively correlated with Hcy level, ESR, 1/aquaporin-4 titer and Hcy level is negatively correlated with IgM in acute-phase NMOSD patients.

CONCLUSION

Elevated plasma Hcy has the potential to affect the pathogenesis or progression of NMOSD.

1,25-Dihydroxyvitamin D3 increases the methionine cycle, CD4+ T cell DNA methylation and Helios+Foxp3+ T regulatory cells to reverse autoimmune neurodegenerative disease

We investigated how one calcitriol dose plus vitamin D₃ reverses experimental autoimmune encephalomyelitis (EAE), a multiple sclerosis model. This protocol rapidly increased CD4⁺ T cell Ikzf2 transcripts, Helios protein, and CD4⁺Helios⁺FoxP3⁺ T regulatory cells. It also rapidly increased CD4⁺ T cell Bhmt1 transcripts, betaine:homocysteine methyltransferase-1 (BHMT1) enzyme activity, and global DNA methylation. BHMT1 transmethylates homocysteine to replenish methionine. Targeting the Vdr gene in T cells decreased Ikzf2 and Bhmt1 gene expression, reduced DNA methylation, and elevated systemic homocysteine in mice with EAE. We hypothesize that calcitriol drives a transition from encephalitogenic CD4⁺ T cell to Treg cell dominance by upregulating Ikzf2 and Bhmt1, recycling homocysteine to methionine, reducing homocysteine toxicity, maintaining DNA methylation, and stabilizing CD4⁺Helios⁺FoxP3⁺Tregulatory cells. Conserved vitamin D-responsive element (VDRE)-type sequences in the Bhmt1 and Ikzf2 promoters, the universal need for methionine in epigenetic regulation, and betaine's protective effects in MTHFR-deficiency suggest similar regulatory mechanisms exist in humans.

Emerging Role for Methylation in Multiple Sclerosis: Beyond DNA

Multiple Sclerosis (MS) is a chronic inflammatory disease of the central nervous system. The inflammatory and neurodegenerative pathways driving MS are modulated by DNA, lysine, and arginine methylation, as evidenced by studies made possible by novel tools for methylation detection or loss of function. We present evidence that MS is associated with genetic variants and metabolic changes that impact on methylation. Further, we comprehensively review current understanding of how methylation can impact on central nervous system (CNS) resilience and neuroregenerative potential, as well as inflammatory versus regulatory T helper (Th) cell balance. These findings are discussed in the context of therapeutic relevance for MS, with broad implications in other neurologic and immune-mediated diseases.

Secondary Progressive Multiple Sclerosis: Definition and Measurement

Secondary progressive multiple sclerosis (SPMS) is diagnosed retrospectively and involves a clinical course characterized by a progressive accumulation of neurological disability, independent of relapses, following an initial relapsing-remitting (RR) phase. Our incomplete understanding of the pathological mechanisms underlying neurodegeneration in multiple sclerosis (MS) may explain why, to date, there is no definitive imaging or laboratory test that is able to inform us when the disease is clearly entering into a progressive phase and why the vast majority of clinical trials testing immunosuppressant and immunomodulating drugs in SPMS patients has so far yielded disappointing or mixed results. Here we discuss the definition(s) of SPMS and how it may vary, outcome measurements (current and emerging) and modern trial design.

Hyperhomocysteinemia and neurologic disorders: a review

Homocysteine (Hcy) is a sulfur-containing amino acid that is generated during methionine metabolism. It has a physiologic role in DNA metabolism via methylation, a process governed by the presentation of folate, and vitamins B6 and B12. Physiologic Hcy levels are determined primarily by dietary intake and vitamin status. Elevated plasma levels of Hcy (eHcy) can be caused by deficiency of either vitamin B12 or folate, or a combination thereof. Certain genetic factors also cause eHcy, such as C667T substitution of the gene encoding methylenetetrahydrofolate reductase. eHcy has been observed in several medical conditions, such as cardiovascular disorders, atherosclerosis, myocardial infarction, stroke, minimal cognitive impairment, dementia, Parkinson's disease, multiple sclerosis, epilepsy, and eclampsia. There is evidence from laboratory and clinical studies that Hcy, and especially eHcy, exerts direct toxic effects on both the vascular and nervous systems. This article provides a review of the current literature on the possible roles of eHcy relevant to various neurologic disorders.

Neurodegeneration in multiple sclerosis involves multiple pathogenic mechanisms

Multiple sclerosis (MS) is a complex autoimmune disease that impairs the central nervous system (CNS). The neurological disability and clinical course of the disease is highly variable and unpredictable from one patient to another. The cause of MS is still unknown, but it is thought to occur in genetically susceptible individuals who develop disease due to a nongenetic trigger, such as altered metabolism, a virus, or other environmental factors. MS patients develop progressive, irreversible, neurological disability associated with neuronal and axonal damage, collectively known as neurodegeneration. Neurodegeneration was traditionally considered as a secondary phenomenon to inflammation and demyelination. However, recent data indicate that neurodegeneration develops along with inflammation and demyelination. Thus, MS is increasingly recognized as a neurodegenerative disease triggered by an inflammatory attack of the CNS. While both inflammation and demyelination are well described and understood cellular processes, neurodegeneration might be defined by a diverse pool of any of the following: neuronal cell death, apoptosis, necrosis, and virtual hypoxia. In this review, we present multiple theories and supporting evidence that identify common biological processes that contribute to neurodegeneration in MS.

LC-MS/MS identification of the one-carbon cycle metabolites in human plasma

The one-carbon cycle is composed of four major biologically important molecules: methionine (L-Met), S-adenosylmethionine (SAM), S-adenosylhomocysteine (SAH), and homocysteine (Hcy). In addition to these key metabolites, there are multiple enzymes, vitamins, and cofactors that play essential roles in the cascade of the biochemical reactions that convert one metabolite into another in the cycle. Simultaneous quantitative measurement of four major metabolites can be used to detect possible aberrations in this vital cycle. Abnormalities in the one-carbon cycle might lead to hyper- or hypomethylation, homocystinemia, liver dysfunction, and accumulation of white-matter hyperintensities in the human brain. Previously published methods describe evaluation of several components of the one-carbon cycle, but none to our knowledge demonstrated simultaneous measurement of all four key molecules (L-Met, SAM, SAH, and Hcy). We describe a novel analytical method suitable for simultaneous identification and quantification of L-Met, SAM, SAH, and Hcy with LC-MS/MS. Moreover, we tested this method to identify these metabolites in human plasma collected from patients with multiple sclerosis and healthy individuals. In a pilot feasibility study, our results indicate that patients with multiple sclerosis showed abnormalities in the one-carbon cycle.

Elevated plasma homocysteine levels in patients with multiple sclerosis are associated with male gender

Elevated homocysteine (Hcy) levels exert several neurotoxic actions and vascular dysfunctions that may be involved in pathogenesis and progression of multiple sclerosis (MS). The effective role of Hcy in MS however remains to be determined. The aim of this work was to compare plasma Hcy levels in MS patients and neurological disease controls (NDC) and to evaluate their relationships with clinical and demographic variables. In this cross-sectional study, we examined plasma Hcy levels in 217 patients with MS [53 clinically isolated syndromes (CIS) suggestive of MS, 134 relapsing remitting (RR), 23 secondary progressive (SP) and seven primary progressive (PP) MS], recruited among patients attending a tertiary clinical center in southern Italy and in 219 age/sex-matched controls. Median Hcy levels were slightly higher in MS patients compared to NDC (9.1 μmol/l; range, 3.4-35.9 vs. 8.6, range 3.5-27.4; p = 0.02). Median Hcy concentrations were increased in males more than in females in the MS population (10.4 vs. 8.4; p < 0.0001), whereas no differences across genders were found in NDC (9.1 vs. 8.5). Hcy levels were higher in male MS patients compared to the male NDC patients (p = 0.001). Patients with CIS had lower Hcy (7.5 μmol/l; p = 0.004) compared to patients with RR (9.5 μmol/l), SP (10.1 μmol/l) and PP (9.9 μmol/l). Median Hcy concentration was higher in patients with disease duration longer than 22 months (9.7 vs. 8.6 μmol/l; p = 0.02). Plasma Hcy levels are increased in patients with definite MS. Higher Hcy levels are associated with male sex, suggesting a role of Hcy in neurodegenerative processes of MS, which are prominent in male patients.

Vascular aspects of multiple sclerosis

Three types of vascular dysfunction have been described in multiple sclerosis (MS). First, findings from epidemiological studies suggest that patients with MS have a higher risk for ischaemic stroke than people who do not have MS. The underlying mechanism is unknown, but might involve endothelial dysfunction secondary to inflammatory disease activity and increased plasma homocysteine concentrations. Second, patients with MS have global cerebral hypoperfusion, which might predispose them to the development of ischaemic stroke. The widespread decrease in perfusion in normal-appearing white matter and grey matter in MS seems not to be secondary to axonal degeneration, but might be a result of reduced axonal activity, reduced astrocyte energy metabolism, and perhaps increased blood concentrations of endothelin-1. Data suggest that a subtype of focal MS lesions might have an ischaemic origin, and there seems to be a link between reduced white matter perfusion and cognitive dysfunction in MS. Third, the pathology of MS might be the consequence of a chronic state of impaired venous drainage from the CNS, for which the term chronic cerebrospinal venous insufficiency (CCSVI) has been coined. A number of recent vascular studies do not support the CCSVI theory, but some elements of CCSVI might be explained by slower cerebral venous blood flow secondary to the reduced cerebral perfusion in patients with MS compared with healthy individuals.

Vascular complications of cystathionine β-synthase deficiency: future directions for homocysteine-to-hydrogen sulfide research

Homocysteine (Hcy), a cardiovascular and neurovascular disease risk factor, is converted to hydrogen sulfide (H(2)S) through the transsulfuration pathway. H(2)S has attracted considerable attention in recent years for many positive effects on vascular health and homeostasis. Cystathionine β-synthase (CBS) is the first, and rate-limiting, enzyme in the transsulfuration pathway. Mutations in the CBS gene decrease enzymatic activity, which increases the plasma Hcy concentration, a condition called hyperhomocysteinemia (HHcy). Animal models of CBS deficiency have provided invaluable insights into the pathological effects of transsulfuration impairment and of both mild and severe HHcy. However, studies have also highlighted the complexity of HHcy and the need to explore the specific details of Hcy metabolism in addition to Hcy levels per se. There has been a relative paucity of work addressing the dysfunctional H(2)S production in CBS deficiency that may contribute to, or even create, HHcy-associated pathologies. Experiments using CBS knockout mice, both homozygous (-/-) and heterozygous (+/-), have provided 15 years of new knowledge and are the focus of this review. These murine models present the opportunity to study a specific mechanism for HHcy that matches one of the etiologies in many human patients. Therefore, the goal of this review was to integrate and highlight the critical information gained thus far from models of CBS deficiency and draw attention to critical gaps in knowledge, with particular emphasis on the modulation of H(2)S metabolism. We include findings from human and animal studies to identify important opportunities for future investigation that should be aimed at generating new basic and clinical understanding of the role of CBS and transsulfuration in cardiovascular and neurovascular disease.