Effect of folic acid by mouth on cerebrospinal fluid homovanillic acid and 5-hydroxyindoleacetic acid concentration

Folic acid and psychopathology

1. The incidence of folic acid deficiency is high in patients with various psychiatric disorders including depression, dementia and schizophrenia. 2. In epileptics on anticonvulsants, folate deficiency often occurs because anticonvulsants inhibit folate absorption. In these patients folate deficiency is often associated with psychiatric symptoms. 3. In medical patients psychiatric symptoms occur more frequently, and in psychiatric patients symptoms are more severe, in those with folate deficiency than in those with normal levels. 4. Many open studies have demonstrated therapeutic effects of folate administration on psychiatric symptoms in folate deficient patients. 5. Several placebo-controlled studies have not demonstrated therapeutic effects, possibly because the doses they used (15-20 mg/day) are known to be toxic and to cause mental symptoms. 6. Two placebo-controlled studies have demonstrated beneficial effects of folic acid administration, one in patients with a syndrome of psychiatric and neuropsychological changes associated with folate deficiency and the other in patients on long-term lithium therapy. In the latter study the dose was only 0.2 mg/day. 7. Folic acid deficiency is known to lower brain S-adenosylmethionine and 5-hydroxytryptamine. S-Adenosylmethionine, which has antidepressant properties, raises brain 5-hydroxytryptamine. Thus, depression associated with folate deficiency is probably related to low brain 5HT. 8. S-Adenosylmethionine is involved in many methylation reactions, including methylation of membrane phospholipids, which influences membrane properties. This may explain the wide variety of symptoms associated with folate deficiency. 9. Because the costs and risks associated with low doses of folic acid (up to 0.5 mg/day) are small, folic acid should be given as an adjunct in the treatment of patients with unipolar or bipolar affective disorders and anorexia, epileptics on anticonvulsants, geriatric patients with mental symptoms and patients with gastrointestinal disorders who exhibit psychiatric symptoms. 10. Although the majority of the patients listed above will probably not be helped by folic acid therapy, a significant minority are likely to have folate-responsive symptoms.

Drugs and folate metabolism

Folates are a group of compounds which are required in the diet and are important in DNA, amino acids and possibly also amine metabolism. The biologically active folates are in the tetrahydro form. Tetrahydrofolates are produced from unreduced dietary folates by the enzyme dihydrofolate reductase. A number of drugs such as aminopterin, methotrexate (amethopterin), pyrimethamine, trimethoprim and triamterene act as folate antagonists and produce folate deficiency by inhibiting this enzyme. With other drugs which produce low serum and tissue concentrations of folate such as anticonvulsants, antituberculosis drugs, alcohol and oral contraceptives, the mechanism of this effect is uncertain. Possible mechanism include reduced absorption, prevention of release of folate from tissue stores, altered plasma protein binding, or increased folate metabolism in the liver. Treatment with folic acid antagonists such as methotrexate readily causes megaloblastic anaemia; this can be prevented by therapy with folinic acid (5-formyltetrahydrofolate). The role of other drugs in producing megaloblastic anaemia is less certain, e.g. it occurs in less than 0.75% of patients receiving anticonvulsants. The possible neurological and psychiatric effects of folate deficiency are also uncertain. However, in patients with folate deficiency who have neuropsychiatric symptoms, neuropathy or myelopathy, and normal vitamin B12 levels, it may be of value to try therapy with folic or folinic acid.

Folate and monoamine metabolism in epilepsy

In 27 drug-treated epileptics there was a significant fall in serum, red cell and CSF folate levels compared with 15 untreated epileptics and 22 neurological controls. The 3 folate parameters were positively correlated with each other and negatively correlated with serum phenobarbitone, diphenylhydantoin and primidone. There was also a significant elevation of CSF 5-hydroxyindoleacetic acid (5HIAA) in the drug-treated epileptics; but this was not seen until "therapeutic" serum levels of phenobarbitone and diphenylhydantoin had been achieved and was most marked in clinically intoxicated patients. Similar trends were observed in CSF homovanillic acid (HVA). CSF 5HIAA and HVA were positively correlated with each other, especially in the drug-treated patients, in whom both amine metabolites were also negatively correlated with CSF folate. A possible relationship between folate and monoamine metabolism is discussed with particular reference to the antiepileptic and toxic effects of phenobarbitone, diphenylhydantoin and primidone.