The transmethylation and one-carbon cycle hypotheses of schizophrenia

Reduced folic acid, vitamin B12 and docosahexaenoic acid and increased homocysteine and cortisol in never-medicated schizophrenia patients: implications for altered one-carbon metabolism

Abnormal one-carbon metabolism has long been suggested as one of the mechanisms for neuropathology and psychopathology of schizophrenia. Variable levels of components of one-carbon metabolism (folic acid and vitamin B12) and consequent altered levels of homocysteine and phospholipid docosahexaenoic acid (DHA) have been independently reported, mostly in medicated patients. This study examined the simultaneous levels of these key components of one-carbon metabolism and its consequences in unique, medication-naïve first-episode psychotic patients (FEP, n=31) and healthy controls (HC, n=48) matched for confounds such as race, diet and lifestyle to reduce the variability. Significantly lower levels of folate and vitamin B12 in plasma and folate in red blood cells were observed in FEP compared to HC. These reductions paralleled the significant increase in plasma homocysteine and cortisol levels. Significantly reduced levels of membrane DHA were also observed in FEP compared to HC. This study, using a unique cohort, provided a broader mechanism (disturbed folic acid-vitamin B12-DHA balance) of altered one-carbon metabolism and one of its key consequential components, an increased homocysteine level that together with cortisol, can contribute to the neuropathology of psychosis. These data may have important implications for the amelioration of psychopathology in schizophrenia.

Ayahoasca: an experimental psychosis that mirrors the transmethylation hypothesis of schizophrenia

The experimental psychosis observed after drinking Ayahoasca, a South American hallucinogenic beverage from the Amazon Indians, reproduces the pathologic transmethylation theory of schizophrenia. This theory postulates a decrease in the monoamine oxidase (MAO) activity, which results in the accumulation of methylated indolealkylamines, such as bufotenin (5-hydroxy-N,N-dimethyltryptamine), N,N-dimethyltryptamine (DMT) and 5-methoxy-N,N-dimethyltryptamine. These substances are strong hallucinogens as has been previously confirmed experimentally. On the other hand, it is known that Ayahoasca is a beverage usually prepared by boiling two plants, one of them rich in beta-carbolines, which are naturally occurring strong inhibitors of MAO, and the other with high quantities of DMT. This particular combination reproduces what is supposed to occur under pathologic conditions of different psychoses. The effects of Ayahoasca were studied in subjects, assessing urine levels of DMT by gas chromatography-mass spectrometry (GC-MS) before and after the intake of the beverage. The results of this study confirm that the hallucinogenic compounds detected in the healthy subjects' (post-Hoasca, but not before) urine samples are the same as those found in samples from acute psychotic unmedicated patients. The chemical composition of the Ayahoasca beverage, and of the plant material used for its preparation are also reported as well as psychometric and neuroendocrine subject parameters.

Altered consciousness states and endogenous psychoses: a common molecular pathway?

Interest in the role of indolamines in the pathogenesis of psychoses has been renewed in recent years by the development of atypical antipsychotic drugs such as clozapine, olanzapine, and risperidone, which act on serotonin receptors. Discovery of the hallucinogenic compounds called methylated indolealkyalamines (MIAs) (e.g. N,N-dimethylserotonin, or bufotenin, and N,N-dimethyltryptamine, or DMT) led proponents of the transmethylation hypothesis of schizophrenia to theorize that through some inborn error of metabolism, serotonin or tryptamine might undergo the addition of extra methyl radicals, thereby forming MIAs with hallucinogenic properties. Various studies have attempted to detect the excretion of MIAs, especially DMT, in the body fluids of psychotic patients and normal controls. Some of these studies have demonstrated elevated MIA concentrations in psychotic patients, including those with schizophrenia, compared with normal persons, and others have not. A number of variables may account for these contradictory findings. The mechanism whereby the beverage ayahuasca, which is used in certain cure and divination rituals in the Amazon Basin, exerts its hallucinogenic effects may serve as a model to explain the mechanism underlying hallucinogenic symptoms in schizophrenia and may lend support to the transmethylation hypothesis. Certain studies suggest that specific perceptual disturbances manifested by schizophrenic patients could contribute to progressive deterioration and negative symptomatology. All these findings point to the need for further study of the neurophysiology of MIAs and their pathogenetic role in endogenous psychoses.

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.

Tracer kinetic evidence for abnormal methyl metabolism in schizophrenia

The original transmethylation hypothesis of schizophrenia has evolved with time and experiment to the present concept that a defect in the methyl-carbon metabolic pathway may be causative in this illness. Various researchers have proposed that specific steps in the methyl-carbon pathway may be defective, and have presented evidence to support these possibilities. We have tested the general concept of the hypothesis by administering methionine labeled with 11C or 14C in the S-methyl carbon to patients with schizophrenia and to controls and measured the expiration of 11CO2 and 14CO2. We found that the rate and total expiration of labeled CO2 were three times less in the patients than in the controls, with no overlap of data points in the two groups. Specific steps in the methylcarbon pathway that might be defective and produce the results seen here are discussed in light of this and other researchers' findings.

Formation and metabolism of catecholestrogens in depressed patients

The evidence that catecholestrogens are formed in the brain and exert behavioral effects in animal models suggest that these steroids might have psychotropic activities. In the present investigation, the formation and metabolism of catecholestrogens were studied in depressed patients. Twenty-four-hr urine samples were collected from 6 male patients (59 +/- 8 years) with endogenous retarded depression (subtype primary, endogenous, and recurrent according to Research Diagnostic Criteria) and from 12 male control subjects (51 +/- 4 years). The patients were treated with the monoamine oxidase inhibitor tranylcypromine (10-40 mg/day for 3-4 weeks). The concentrations of primary estrogens, 4- and 2-hydroxyestrogens and 2-methoxyestrogens, were measured in the urine samples after multiple chromatographic separation steps by radioimmunoassay. In the depressed patients, the excretion rates of 4-hydroxyestrogens were significantly lower than in control subjects. The ratio 2-methoxyestrogens:2-hydroxyestrogens as an index for 2-O-methylation was 3.8 +/- 1.6 in patients and 1.8 +/- 0.7 in controls. The increased methylation and reduced 4-hydroxylation rates of patients were not affected by treatment with tranylcypromine though the psychopathological state was improved by 46%. Therefore, it seemed unlikely that the observed alterations were pathognomonically relevant in these depressed patients. The alterations in the formation and methylation of catecholestrogens show that the depressed patients exhibited remarkable metabolic disturbances. The functional role of these disturbances remains to be clarified.

One-carbon metabolism disturbances in affective disorders. A preliminary report

Methionine adenosyltransferase (MAT) activity (Vmax) and the relative amount of phosphatidylcholine (% PC) were measured in erythrocytes of up to 30 DSM-III diagnosed manic, 17 unipolar depressed patients, and 28 normal controls. Manic subjects had significantly higher and depressed subjects significantly lower MAT Vmax than normals. The relative amount of PC was in the low range for the depressives, and in the high range for the manics. Depressive patients present, in these tests, similar abnormalities to those seen previously in schizophrenic patients. Clinical and diagnostic implications of these findings are discussed.