S-adenosyl-methionine in depression: a comprehensive review of the literature

Epigenetics in mood disorders

Depression develops as an interaction between stress and an individual's vulnerability to stress. The effect of early life stress and a gene-environment interaction may play a role in the development of stress vulnerability as a risk factor for depression. The epigenetic regulation of the promoter of the glucocorticoid receptor gene has been suggested as a molecular basis of such stress vulnerability. It has also been suggested that antidepressive treatment, such as antidepressant medication and electroconvulsive therapy, may be mediated by histone modification on the promoter of the brain-derived neurotrophic factor gene. Clinical genetic studies in bipolar disorder suggest the role of genomic imprinting, although no direct molecular evidence of this has been reported. The role of DNA methylation in mood regulation is indicated by the antimanic effect of valproate, a histone deacetylase inhibitor, and the antidepressive effect of S-adenosyl methionine, a methyl donor in DNA methylation. Studies of postmortem brains of patients have implicated altered DNA meA methylation of the promoter region of membrane-bound catechol-O-methyltransferase in bipolar disorder. An altered DNA methylation status of PPIEL (peptidylprolyl isomerase E-like) was found in a pair of monozygotic twins discordant for bipolar disorder. Hypomethylation of PPIEL was also found in patients with bipolar II disorder in a case control analysis. These fragmentary findings suggest the possible role of epigenetics in mood disorders. Further studies of epigenetics in mood disorders are warranted.

The role of one-carbon metabolism in schizophrenia and depression

OBJECTIVE

Physicians often check folate and cobalamin levels in patients with schizophrenia and depression. The reasons for this practice are reviewed, as well as implications for treatment.

METHOD

The physiology of the one-carbon cycle, involving folate, cobalamin, homocysteine, S-adenosyl-methionine, and methylene tetrahydrofolate reductase (MTHFR) is first reviewed, and then the particular contributions of folate and B12 are reviewed. PubMed was searched for studies of the association between folate, cobalamin, homocysteine, and MTHFR polymorphisms and schizophrenia and depression.

RESULTS

The recent key studies from the large literature addressing these topics are summarized. Treatment implications are discussed.

CONCLUSION

It is important to check folate and B12 levels in certain situations, such as alcoholism, malnutrition, malabsorption, and the concurrent use of some medications. Checking homocysteine and methylmalonic levels might be useful. With respect to treatment, folate and cobalamin deficiencies should be corrected. Cobalamin supplementation is probably not helpful. Folate supplementation is indicated in pregnancy but may exacerbate the effects of cobalamin deficiency. SAMe may prove to be a useful antidepressant. In the future, screening for MTHFR polymorphisms might be useful.

16 Inhibition of mammalian protein methyltransferases by 5'-methylthioadenosine (MTA): A mechanism of action of dietary same?

5'-deoxy-5'-methylthioadenosine (5'-methylthioadenosine, MTA) is a naturally occurring metabolite. As an experimental reagent, it has proved useful in providing investigators a window onto the role of protein methylation reactions in intact cells, although its mode of action is poorly understood in most cases. This chapter reevaluates its utility as a reagent. It appears now that MTA is at best a poor direct inhibitor of methyltransferases and that its effectiveness in intact cells may depend on its ability to inhibit S-adenosyl-l-homocysteine hydrolase. This chapter reviews recent evidence that points to an important role for MTA as an intermediary in the beneficial pharmaceutical action of orally ingested S-adenosyl-l-methionine (AdoMet, SAMe). These new results suggest that oral AdoMet may function not by enhancing the activity of cellular methyltransferases, as has been previously surmised, but by inhibiting their action. Such inhibition, particularly of protein methyltransferases involved in intracellular communication, may attenuate signal transduction pathways otherwise leading to inflammatory damage to tissues.

Update and critique of natural remedies as antidepressant treatments

Natural medications such as St. John's Wort, SAMe, and omega-3 fatty acids eventually may prove to be valuable additions to the psychiatrist's pharmacologic armamentarium, both as monotherapy and as adjunctive therapy for mood disorders. Current research data are compelling, from a standpoint of both efficacy and safety, but before clinicians can recommend these as first-line treatments, more well-designed controlled studies in large patient populations are needed. During the past decade, the National Institutes of Health, the National Institute for Mental Health, and the National Center for Complementary and Alternative Medicine have widened their support for research on the efficacy and safety of alternative treatments, and increasing numbers of academic institutions are undertaking large-scale, multicenter studies on the natural medications reviewed here, as well as others. These studies should help answer some of the yet-unsettled questions about natural medications. Psychiatrists who are considering recommending natural antidepressants to their patients should emphasize that these treatments are relatively unproven and that it remains to be seen whether they would be appropriate or preferable to the conventional psychotropic agents. in the absence of more conclusive data, the best candidates for alternative treatments may be patients for whom a delay in adequate treatment would not be devastating(eg, the mildly symptomatic patient who has a strong interest in natural remedies). Other good candidates may include patients who have been unresponsive to conventional antidepressants or particularly intolerant of side effects; these patients, however, often are the most difficult to treat, and alternative agents seem best suited for the mildly ill. Care should be taken with patients who are taking multiple medications, in view of adverse drug-drug interactions that have emerged with increased use of alternative treatments. Finally, as with all psychotropic agents, natural medications should be used preferably under the supervision of a physician.

A general liquid chromatography/mass spectroscopy-based assay for detection and quantitation of methyltransferase activity

Methyltransferases form a large class of enzymes, most of which use S-adenosylmethionine as the methyl donor. In fact, S-adenosylmethionine is second only to ATP in the variety of reactions for which it serves as a cofactor. Several methods to measure methyltransferase activity have been described, most of which are applicable only to specific enzymes and/or substrates. In this work we describe a sensitive liquid chromatography/mass spectroscopy-based methyltransferase assay. The assay monitors the conversion of S-adenosylmethionine to S-adenosylhomocysteine and can be applied to any methyltransferase and substrate of interest. We used the well-characterized enzyme catechol O-methyltransferase to demonstrate that the assay can monitor activity with a variety of substrates, can identify new substrates, and can be used even with crude preparation of enzyme. Furthermore, we demonstrate the utility of the assay for kinetic characterization of enzymatic activity.

Brain MRI white matter hyperintensities and one-carbon cycle metabolism in non-geriatric outpatients with major depressive disorder (Part II)

The objective of this study was to investigate the relative impact of brain white matter hyperintensities (WMHs), cardiovascular risk factors and elements of the one-carbon cycle metabolism (including serum folate, vitamin B12 and homocysteine levels) on the outcome of antidepressant treatment in non-elderly subjects with major depressive disorder (MDD). Fifty MDD subjects were administered brain magnetic resonance imaging (MRI) scans at 1.5 T to detect T2 WMHs. The severity of brain WMHs was classified with the Fazekas scale (range=0-3). We assessed cardiovascular risk factors in all MDD subjects (age, gender, smoking, diabetes, family history, hypertension, cholesterol). MDD patients also had serum folate, vitamin B12 and homocysteine levels measured. All MDD subjects received treatment with fluoxetine 20 mg/day for 8 weeks. In a logistic regression, the severity of subcortical WMHs and the presence of hypofolatemia were independent predictors of lack of clinical response to antidepressant treatment. Separately, hypofolatemia also predicted lack of remission to antidepressant treatment. These associations were independent of the presence of smoking, diabetes, family history, hypercholesterolemia, hyperhomocysteinemia and low B12 levels. Although preliminary, the results of the present work suggest that subcortical brain WMHs and hypofolatemia may have an independent negative impact on the likelihood of responding to antidepressant treatment in non-geriatric subjects with MDD.

Brain MRI white matter hyperintensities and one-carbon cycle metabolism in non-geriatric outpatients with major depressive disorder (Part I)

The objective of the present work was to study the interrelationship between white matter hyperintensities (WMHs), cardiovascular risk factors and elements of the one-carbon cycle including serum folate, vitamin B12, and homocysteine levels in a relatively young sample of outpatients with major depressive disorder (MDD), and to compare the severity of white matter hyperintensities in MDD patients and healthy volunteers. Fifty MDD outpatients (34% women, age 40.6+/-10.3 years), free of psychotropic medications for at least 2 weeks before enrollment, underwent magnetic resonance imaging (MRI) scans of the brain to detect T2 WMHs and also had (1) serum folate, vitamin B12, homocysteine and cholesterol levels measured, and (2) cardiovascular risk factors assessed during the same study visit. Thirty-five healthy comparison subjects (40% women, age 39.2+/-9.8 years) also underwent brain MRI scans. Hypofolatemia, hypertension and age independently predicted a greater severity of total brain WMHs. Separately, the same factors also predicted a greater severity of subcortical WMHs. Hypofolatemic and hypertensive patients had more severe WMHs than normal controls. In light of the adverse impact of WMHs on a number of health-related outcomes later in life, hypofolatemia and hypertension may represent modifiable risk factors to prevent the occurrence of such adverse outcomes.

Treatment of depression: time to consider folic acid and vitamin B12

We review the findings in major depression of a low plasma and particularly red cell folate, but also of low vitamin B12 status. Both low folate and low vitamin B12 status have been found in studies of depressive patients, and an association between depression and low levels of the two vitamins is found in studies of the general population. Low plasma or serum folate has also been found in patients with recurrent mood disorders treated by lithium. A link between depression and low folate has similarly been found in patients with alcoholism. It is interesting to note that Hong Kong and Taiwan populations with traditional Chinese diets (rich in folate), including patients with major depression, have high serum folate concentrations. However, these countries have very low life time rates of major depression. Low folate levels are furthermore linked to a poor response to antidepressants, and treatment with folic acid is shown to improve response to antidepressants. A recent study also suggests that high vitamin B12 status may be associated with better treatment outcome. Folate and vitamin B12 are major determinants of one-carbon metabolism, in which S-adenosylmethionine (SAM) is formed. SAM donates methyl groups that are crucial for neurological function. Increased plasma homocysteine is a functional marker of both folate and vitamin B12 deficiency. Increased homocysteine levels are found in depressive patients. In a large population study from Norway increased plasma homocysteine was associated with increased risk of depression but not anxiety. There is now substantial evidence of a common decrease in serum/red blood cell folate, serum vitamin B12 and an increase in plasma homocysteine in depression. Furthermore, the MTHFR C677T polymorphism that impairs the homocysteine metabolism is shown to be overrepresented among depressive patients, which strengthens the association. On the basis of current data, we suggest that oral doses of both folic acid (800 microg daily) and vitamin B12 (1 mg daily) should be tried to improve treatment outcome in depression.