Affective disorders and S-adenosylmethionine: a new hypothesis

Endogenous hydrogen sulphide attenuates NLRP3 inflammasome-mediated neuroinflammation by suppressing the P2X7 receptor after intracerebral haemorrhage in rats

Background

Emerging studies have demonstrated the important physiological and pathophysiological roles of hydrogen sulphide (H₂S) as a gasotransmitter for NOD-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome-associated neuroinflammation in the central nervous system. However, the effects of H₂S on neuroinflammation after intracerebral haemorrhage (ICH), especially on the NLRP3 inflammasome, remain unknown.

Methods

We employed a Sprague–Dawley rat of collagenase-induced ICH in the present study. The time course of H₂S content and the spatial expression of cystathionine-β-synthase (CBS) after ICH, the effects of endogenous and exogenous H₂S after ICH, the effects of endogenous and exogenous H₂S on NLRP3 inflammasome activation under P2X7 receptor (P2X7R) overexpression after ICH, and the involvement of the P2X7R in the mechanism by which microglia-derived H₂S prevented NLRP3 inflammasome activation were investigated.

Results

We found ICH induced significant downregulation of endogenous H₂S production in the brain, which may be the result of decreasing in CBS, the predominant cerebral H₂S-generating enzyme. Administration of S-adenosyl-l-methionine (SAM), a CBS-specific agonist, or sodium hydrosulfide (NaHS), a classical exogenous H₂S donor, not only restored brain and plasma H₂S content but also attenuated brain oedema, microglial accumulation and neurological deficits at 1 day post-ICH by inhibiting the P2X7R/NLRP3 inflammasome cascade. Endogenous H₂S production, which was derived mainly by microglia and above treatments, was verified by adenovirus-overexpressed P2X7R and in vitro primary microglia studies.

Conclusions

These results indicated endogenous H₂S synthesis was impaired after ICH, which plays a pivotal role in the P2X7R/NLRP3 inflammasome-associated neuroinflammatory response in the pathogenesis of secondary brain injury. Maintaining appropriate H₂S concentrations in the central nervous system may represent a potential therapeutic strategy for managing post-ICH secondary brain injury and associated neurological deficits.

Adenosinergic signaling in epilepsy

Despite the introduction of at least 20 new antiepileptic drugs (AEDs) into clinical practice over the past decades, about one third of all epilepsies remain refractory to conventional forms of treatment. In addition, currently used AEDs have been developed to suppress neuronal hyperexcitability, but not necessarily to address pathogenic mechanisms involved in epilepsy development or progression (epileptogenesis). For those reasons endogenous seizure control mechanisms of the brain may provide alternative therapeutic opportunities. Adenosine is a well characterized endogenous anticonvulsant and seizure terminator of the brain. Several lines of evidence suggest that endogenous adenosine-mediated seizure control mechanisms fail in chronic epilepsy, whereas therapeutic adenosine augmentation effectively prevents epileptic seizures, even those that are refractory to conventional AEDs. New findings demonstrate that dysregulation of adenosinergic mechanisms are intricately involved in the development of epilepsy and its comorbidities, whereas adenosine-associated epigenetic mechanisms may play a role in epileptogenesis. The first goal of this review is to discuss how maladaptive changes of adenosinergic mechanisms contribute to the expression of seizures (ictogenesis) and the development of epilepsy (epileptogenesis) by focusing on pharmacological (adenosine receptor dependent) and biochemical (adenosine receptor independent) mechanisms as well as on enzymatic and transport based mechanisms that control the availability (homeostasis) of adenosine. The second goal of this review is to highlight innovative adenosine-based opportunities for therapeutic intervention aimed at reconstructing normal adenosine function and signaling for improved seizure control in chronic epilepsy. New findings suggest that transient adenosine augmentation can have lasting epigenetic effects with disease modifying and antiepileptogenic outcome. This article is part of the Special Issue entitled 'Purines in Neurodegeneration and Neuroregeneration'.

Metabolomics analysis reveals insights into biochemical mechanisms of mental stress-induced left ventricular dysfunction

Mental stress induced left ventricular dysfunction (LVD) has been associated with a greater risk of adverse events in coronary heart disease (CHD) patients independent of conventional risk indicators. The underlying biochemical mechanisms of this cardiovascular condition are poorly understood. Our objective was to use metabolomics technology to identify biochemical changes that co-occur with mental stress-induced LVD in patients with clinically stable CHD. Participants were adult CHD patients who were recruited for mental stress-induced myocardial ischemia screening. For this study, we randomly selected 30 patients representing the extremes of the mental stress-induced left ventricular ejection fraction (LVEF) change distribution; 15 who showed LVD (i.e. LVEF reduction ≥5) and 15 who showed a normal left ventricular response (NLVR; i.e. a LVEF increase of ≥5) to three mental stressors. An electrochemistry based metabolomics platform was used to profile pre- and post-stress serum samples yielding data for 22 known compounds, primarily within the tyrosine, tryptophan, purine and methionine pathways. There were significant stress-induced changes in several compounds. A comparison between the NLVR and LVD groups showed significant effects for kynurenine (p = .036, N-acetylserotonin (p = .054), uric acid (p = .015), tyrosine (p = .019) and a trend for methionine (p = .065); the NLVR group showed a significantly greater stress-induced reduction in all of those compounds compared to the LVD group. Many of these biochemicals have been implicated in other stress-related phenomena and are plausible candidates for mechanisms underlying LVD in response to mental stress.

Cerebrospinal fluid metabolome in mood disorders-remission state has a unique metabolic profile

Targeted metabolomics provides an approach to quantify metabolites involved in specific molecular pathways. We applied an electrochemistry-based, targeted metabolomics platform to define changes in tryptophan, tyrosine, purine and related pathways in the depressed and remitted phases of major depressive disorder (MDD). Biochemical profiles in the cerebrospinal fluid of unmedicated depressed (n = 14; dMDD) or remitted MDD subjects (n = 14; rMDD) were compared against those in healthy controls (n = 18; HC). The rMDD group showed differences in tryptophan and tyrosine metabolism relative to the other groups. The rMDD group also had higher methionine levels and larger methionine-to-glutathione ratios than the other groups, implicating methylation and oxidative stress pathways. The dMDD sample showed nonsignificant differences in the same direction in several of the metabolic branches assessed. The reductions in metabolites associated with tryptophan and tyrosine pathways in rMDD may relate to the vulnerability this population shows for developing depressive symptoms under tryptophan or catecholamine depletion.

Influence of the MTHFR C677T polymorphism on magnetic resonance imaging hyperintensity volume and cognition in geriatric depression

OBJECTIVE

The 5,10-methylenetetrahydrofolate reductase gene (MTHFR) has been linked to unipolar major depressive disorder (MDD) and magnetic resonance imaging (MRI) hyperintensities. The authors examined the relationship between the MTHFR C677T polymorphism (C677T) and a) geriatric depression, b) MRI hyperintense lesion volume, and c) neurocognitive test performance.

DESIGN

Cross-sectional.

SETTING

Duke University Medical Center.

PARTICIPANTS

Depressed (N = 178) and comparison (N = 85) elderly subjects.

MEASUREMENTS

Subjects had blood drawn to assess MTHFR genotype, were imaged by MRI to determine their white matter hyperintense lesion (WML) and gray matter hyperintense lesion (GML) volume, and assessed using a comprehensive neurocognitive battery evaluating multiple domains of function. Linear regression models were fit to test the effect of genotype, a depression by genotype interaction, and an age by genotype interaction on both hyperintense lesion volume measures and neurocognitive task performance.

RESULTS

The MTHFR C677T genotype by age interaction term was significantly associated with MRI WML volume (p = 0.0175); however, this relationship was no longer statistically significant when WML volumes underwent a log transformation to produce a more normal distribution. The 677T allele was neither more frequent in depressed subjects nor associated with either gray matter hyperintensity volume or neurocognitive test performance.

CONCLUSIONS

MTHFR genotype affects the relationship between age and WML volume where individuals who carry the 677T allele exhibit greater WML volume by age, although this relationship should be verified given the failure to replicate the finding using transformed WML volumes. Genotype was not related to GML volume, cognitive function, or presence of depression, although demographic differences could account for this negative finding.

Hydrogen sulphide in the hypothalamus causes an ATP-sensitive K+ channel-dependent decrease in blood pressure in freely moving rats

Hydrogen sulfide (H2S) is a naturally occurring gas that may act as an endogenous signaling molecule. In the brain, H2S is mainly produced by cystathionine beta-synthase (CBS) and its cellular effects have been attributed to interactions with N-methyl-D-aspartate (NMDA) receptors and cyclic adenosine 3',5'-monophosphate (cAMP). In contrast, direct vasodilator actions of H2S are most probably mediated by opening smooth muscle ATP-sensitive K+ (K(ATP)) channels. In the hypothalamus, K(ATP) channel-dependent mechanisms are involved in CNS-mediated regulation of blood pressure. In this report, we investigated the hypothesis that H2S may act via K(ATP) channels in the hypothalamus to regulate blood pressure. Mean arterial blood pressure (MAP) and heart rate were monitored in freely moving rats via a pressure transducer placed in the femoral artery. Drugs were infused via a cannula placed in the posterior hypothalamus. Infusion of 200 microM sodium hydrogen sulfide (NaHS), an H2S donor, into the hypothalamus of freely moving rats reduced MAP and heart rate. Infusion of 300 nM to 3 microM gliclazide dose-dependently blocked the effect of 200 microM NaHS. Infusion of the CBS activator, s-adenosyl-L-methionine (0.1 mM and 1 mM), likewise decreased MAP. Infusion of the CBS inhibitors aminooxyacetic acid (10 mM) and hydroxylamine (20 mM) increased MAP but did not block the effects of infusion of 200 microM NaHS. These data indicate that actions of H2S in the hypothalamus decrease blood pressure and heart rate in freely moving rats. This effect appears to be mediated by a K(ATP) channel-dependent mechanism and mimicked by endogenous H2S.

Methylation and acetylation in nervous system development and neurodegenerative disorders

The cytoarchitecture and cellular signaling mechanisms of the nervous system are complex, and this complexity is reflected at the molecular level with more genes being expressed in the nervous system than in any other tissue. Gene expression and protein function in neural cells can be regulated by methylation and acetylation. Studies of mice deficient in enzymes that control DNA methylation and of animals with a dietary deficiency of folate have established critical roles for methylation in development of the nervous system. Various neuronal proteins including histones and tubulin are regulated by acetylation which appears to serve important functions in the development, stability and plasticity of neuronal networks. Some inherited neurological disorders have recently been linked to mutations in genes that regulate DNA methylation, and alterations in DNA and protein methylation and/or acetylation have been documented in studies of age-related neurodegenerative disorders including Alzheimer's disease (AD), Parkinson's disease (PD) and Huntington's disease (HD). Manipulations of methylation and acetylation can affect the vulnerability of neurons to degeneration and apoptosis in experimental models of neurodegenerative disorders, suggesting a contribution to altered methylation and acetylation to the disease processes. Interestingly, dietary factors that influence DNA methylation may affect the risk of neurodegenerative disorders, for example, individuals with low dietary folate intake are at increased risk of Alzheimer's and Parkinson's diseases.

Improving mental health through nutrition: the future

Tell me what you eat, and I will tell you what you are (Anthelme Brillat-Savarin). When I behold a fashionable table set out in all its magnificence, I fancy that I see gouts and dropsies, fever and lethargies, with other innumerable distempers, lying in ambuscade among the dishes. Nature delights in the most plain and simple diet. Every animal, but man, keeps to one dish. Herbs are the food of this species, fish of that, and flesh of a third. Man falls upon everything that comes in his way; not the smallest fruit or excrescence of the earth, scarce a berry or a mushroom can escape him (Joseph Addison). The pleasures of the palate deal with us like the Egyptians thieves, who strangle those whom they embrace (Seneca). Let food be your medicine and medicine be your food (Hippocrates).

Evidence that hydrogen sulphide can modulate hypothalamo-pituitary-adrenal axis function: in vitro and in vivo studies in the rat

The gas hydrogen sulphide (H2S) is normally produced in large amounts in the central nervous system during the metabolism of sulphur-containing aminoacids. H2S was recently shown to influence long-term potentiation in the rat hippocampus; this finding suggested that the gas may act as a neuromodulator in the brain. We therefore tested the effect of the gas on the release of corticotropin-releasing hormone (CRH) from rat hypothalamic explants. CRH immunoreactivity in the incubation media was taken as a marker of peptide release. We found that the addition of NaHS to incubation media was consistently associated with a concentration-dependent decrease in KCl-stimulated CRH release, whereas basal secretion was unaffected. Increased endogenous H2S production may be also obtained using an indirect precursor of H2S formation, S-adenosyl-L-methionine (SAMe). The latter mimicked the effects of NaHS, since it reduced potassium-stimulated CRH release. In vivo, SAMe showed no effect on hypothalamo-pituitary-adrenal (HPA) function under resting conditions, but inhibited stress-related glucocorticoid increase.

Cobalamin level is related to self-reported and clinically rated mood and to syndromal depression in bereaved HIV-1(+) and HIV-1(-) homosexual men

OBJECTIVE

An examination of the relationship of plasma cobalamin (vitamin B(12)) level to overall psychological distress, specific mood states, and major depressive disorder was conducted in 159 bereaved men (90 HIV-1(+) and 69 HIV-1(-)).

METHODS

The relationship of a continuous measure of cobalamin level to psychological distress was examined, while controlling for HIV-1 serostatus, life stressors, social support, and coping styles.

RESULTS

Of this sample, 23.9% were either overtly or marginally cobalamin deficient; however, the deficiency rate was not significantly different by HIV-1 serostatus. Cobalamin level was inversely related to self-reported overall distress level and specifically to depression, anxiety, and confusion subscale scores, as well as to clinically rated depressed and anxious mood. Lower plasma cobalamin levels also were associated with the presence of symptoms consistent with major depressive disorder.

CONCLUSION

These findings suggest that cobalamin level may be physiologically related to depressed and anxious mood level, as well as to syndromal depression.

Methionine enhances alcohol-induced narcosis in mice

Methionine is an essential amino acid that has been used as a therapeutic drug in some disorders. In this study we questioned whether methionine affects ethanol-induced loss of righting reflex (narcosis). One hour after IP methionine administration (60, 120, 240, 480, 720, 960, and 1280 mg/kg), mice were injected with ethanol (4.0 g/kg), and the duration of loss of righting reflex was recorded. Methionine, at the higher doses (960 and 1280 mg/ kg), significantly increased this effect on ethanol-treated animals. A time-course study revealed that methionine increased the duration of the loss of righting reflex induced by ethanol until 4 h after being injected. Because methionine did not affect blood ethanol levels, no change in peripheral alcohol can explain the observed effects. This potentiation was not specific for ethanol because methionine increased 3-methyl-1-butanol (0.6 g/kg) and 1-propanol (2.4 g/kg)-induced loss of righting reflex as well. Therefore, the results obtained in this study suggest the need for further investigation into methionine-ethanol interactions prior to the use of methionine as an agent that can be used as an antidepressant and to prevent damage to organic tissue in alcoholism.

Brain ATP:L-methionine S-adenosyltransferase (MAT), S-adenosylmethionine (SAM) and S-adenosylhomocysteine (SAH): regional distribution and age-related changes

The distribution of the activity of the enzyme methionine adenosyltransferase (ATP:L-methionine S-adenosyltransferase, EC 2.5.1.6, MAT) was investigated in human postmortem brains of individuals without a known history of neuropsychiatric disorders. The brain regions were the frontal, temporal, parietal and occipital cortices, nucleus caudatus, putamen, globus pallidus, thalamus and white matter. The activities in the nucleus caudatus and putamen were approximately 25% higher than the activities in the seven other brain regions, however, not on a statistically significant level. The apparent values of MAT Km and Vmax in the parietal cortex were 11.41 +/- 3.51 microM methionine and 25.72 +/- 3.90 nmol/mg protein/h, respectively. In the frontal cortex, a significant positive correlation between age and the activity of MAT was found (r = 0.997, P < 0.01). Concerning MAT stability in the rat brain, there was a steady decrease in the activity with postmortem time in the brains kept for 0-72 h at room temperature (23 degrees C), which reached the level of significance at 24 h. The activity did not change significantly when the brains were kept for 120 h at 4 degrees C, or by freezing and thawing the tissue before analysis. In a parallel study in rats of different ages (2-22 months), a homogeneous distribution of SAM and SAH was observed in the cortex, striatum, midbrain, hypothalamus, brainstem and cerebellum. The lowest levels of SAM and the highest levels of SAH observed in the striatum gave the lowest SAM/SAH ratio. The SAH content of rat cerebral cortex was highest in the oldest group.(ABSTRACT TRUNCATED AT 250 WORDS)

S-adenosylmethionine levels in psychiatric and neurological disorders: a review

INTRODUCTION

S-adenosylmethionine (SAMe) is an important methyl donor in over 35 methylation reactions involving DNA, proteins, phospholipids and catechol- and indole- amines.

MATERIAL AND METHODS

This article reviews the studies that have examined brain and blood levels of SAMe in several psychological, neurological and metabolic disorders.

RESULTS

Although studies have found no consistent changes in whole blood SAMe levels in psychiatric patients, other investigators have found low cerebrospinal fluid (CSF) SAMe levels in patients with neurological disorders such as Alzheimer's dementia, subacute combined degeneration of the spinal cord (SACD), and HIV-related neuropathies, as well as in patients with metabolic disorders such as 5, 10-CH2-H4 folate reductase deficiency.

CONCLUSION

Intravenous or oral administration of SAMe thus represents a possible treatment for these neurological and metabolic disorders.

Methionine adenosyltransferase: structure and function

Methionine adenosyltransferase (MAT), a key enzyme in metabolism, catalyzes the synthesis of one of the most important and pivotal biological molecules, S-adenosyl-methionine. In every organism studied thus far, MAT exists in multiple forms; most are encoded by related, but distinct genes. Molecular and immunological studies revealed the presence of considerable conservation in the structure of MAT from different species; however, the various MAT isozymes differ in their physical and kinetic properties in ways that allow them to be regulated differently. Recent studies suggest that human MAT is composed of nonidentical subunits that can assume multiple states of aggregation, each with different kinetic characteristics. The tissue distribution of MAT isozymes and the ability of cells within the same tissue to switch between the different forms of MAT suggest that this mode of regulation is important for cellular function and differentiation. Therefore, understanding the regulation and structure-function relationship of this fascinating enzyme should help us clarify its role in biology and may provide us with tools to effectively manipulate its activity in clinical situations such as cancer, autoimmunity and organ transplantation.

Effect of S-adenosyl-L-methionine on brain muscarinic receptors of aged rats

The number of muscarinic receptors in the striatum and hippocampus of aged rats is significantly lower than the number measured in young animals. The treatment of aged rats for 30 days with S-adenosyl-L-methionine (SAM) restored the number of muscarinic receptors to levels found in the striatum and hippocampus from young animals. We did not observe a clear-cut difference between the dissociation constants of untreated young and untreated or SAM-treated aged rats, whereas the binding capacity varied. Moreover, in vitro addition of SAM to hippocampal membranes from aged rats resulted in a significant increase in the number of binding sites. This in vitro effect was antagonized by S-adenosyl-L-homocysteine, a specific in vitro inhibitor of methyltransferase activity. The reduction in the muscarinic receptor density could be related to a decrease in neuronal membrane fluidity induced by aging, while its increase after SAM treatment might be ascribed to the ability of this methyl donor to increase the fluidity of cell membranes by stimulating phospholipid synthesis.

Quantification of erythrocyte S-adenosyl-L-methionine levels and its application in enzyme studies

A highly selective high-performance liquid chromatographic method for the quantification of human erythrocyte S-adenosyl-L-methionine levels is described. A strong cation-exchange sorbent with propylsulphonic acid functional groups was used to extract S-adenosyl-L-methionine and S-adenosylethionine (internal standard) from erythrocytes. Quantification of erythrocyte S-adenosyl-L-methionine levels was achieved by using reversed-phase high-performance liquid chromatography and ultraviolet detection at 254 nm. This method was adapted to measure methionine-adenosyltransferase activity in erythrocytes, which enables us to study the possible role of altered methylation in different diseases.