Effect of electroconvulsive therapy on biopterin and large neutral amino acids in severe, medication-resistant depression.

Biopterin, neopterin and the large neutral amino acids (LNAA), i.e. phenylalanine, tyrosine, tryptophan, isoleucine, leucine and valine were measured in plasma of 20 severely depressed inpatients before and after a course of electroconvulsive therapy (ECT). These patients showed a significantly lower plasma biopterin concentration at baseline in comparison with healthy controls. After treatment an increase in biopterin was found, which was statistically significant in the depressed patients with psychotic features. The plasma phenylalanine-tyrosine ratio, which previously increased, normalised after ECT. Mean tryptophan concentration was lower in depressed patients than in normal controls. The patients who responded to ECT showed an increase in the tryptophan concentration and its ratio (tryptophan/LNAA) after treatment. Our results suggest that ECT increases biopterin, which probably results in synthesis of amino acids, especially tyrosine. Furthermore, ECT seems to increase cerebral tryptophan availability because of less tryptophan catabolism parallel with biopterin activation. More research is required to see if biopterin could be useful as a biological marker for the depressive state in this subgroup of patients, because this compound seems to play an important role in the etiology and treatment of depression.