Investigation Of The Relationship Between Plasma Tryptophan Metabolite
Levels And Lithium Treatment Response In Euthymic Bipolar Patients
Abstract
Objective: Lithium is a cornerstone treatment option in bipolar
disorder. Currently, only clinical findings are used to predict the
response of lithium treatment but reliable biological marker has not yet
been identified. With this background, it was aimed to compare
tryptophan metabolite levels between bipolar patients and healthy
control group and to investigate the relationship between lithium
treatment response and tryptophan metabolite levels of euthymic bipolar
patients(BP). Materials and Methods: 52 euthymic BP patients on lithium
were included in the study. Sociodemographic and clinical information
were recorded and lithium treatment response status was determined
according to the Alda scale. Age and gender matched Healthy controls(HC)
were selected from the people who admitted to Selcuk University Medical
Faculty Hospital Health Board. Plasma tryptophan metabolite levels were
compared between BP and HC. The correlation and association between the
lithium response levels of the patients and the plasma tryptophan
metabolites were evaluated. Results: Plasma tryptophan(TRP),
kynurenine(KYN), kynurenine/tryptophan ratio(KYN/TRP),
3-hydroxy-kynurenine(3-HK) and kynurenic acid(KYNA) levels were
significantly lower in BP than HC. In the regression analysis, only
plasma KYNA concentrations were found to be significantly lower in the
responding well to lithium treatment and TRP levels. None of the
tryptophan metabolites were found to be associated well response to
lithium treatment after the logistic regression analysis. Conclusion:
Our findings indicate that KYNA levels might be used as a screening test
for discriminating bipolar patients from the HC. TRP levels might be
used to predict lithium treatment response in spite of low specifity and
low sensitivity levels. Key words: Tryptophan metabolites, lithium
treatment response, bipolar disorder