Amino acids, purines, and pyrimidines as potential biochemical markers of bipolar disorder – current state of knowledge

Purpose
The aim of the paper is to provide an overview of knowledge about changes in blood serum levels of amino acids, purines and pyrimidines in individuals with bipolar disorder, including suggestions for potential ways of modifying the course of the disease using these substances in the diet of people in this group.

Views
According to the majority of the papers in the literature, amino acids, which could possibly be used in tests for bipolar disorder, are closely related to the neurotransmitters considered to be involved in the pathogenesis of the disease. Among them the most important are phenylalanine, a substrate of tyrosine, and following this such neurotransmitters as dopamine, noradrenaline and adre­naline – which play a key role in the regulation of mood and cognitive functions – tryptophan, a precursor of 5-hydroxytryptamine (serotonin), then glycine, serine and threonine (connected with NMDA receptor). Reduced serum levels of branched-chain amino acids (leucine, isoleucine, and valine) are observed in bipolar patients, but some reports have proposed that the usage of them in diet to alleviate manic symptoms is more important clinically. Purines and pyrimidines also play important roles in neurotransmission and neuromodulation, influencing the activity of several neurotransmitters. The most promising data are those concerning adenosine and uric acid.

Conclusions
DAt the present stage of knowledge and time of writing there is some promising data suggesting directions for further investigation, but the evidentiary value of it remains weak. The problem requires further research, such as the full assessment of patients’ profiles for amino acids, purines and pyrimidines, and the confirmation of this approach needs to be established in larger numbers of patients.