Plasma amino acid profiles in relation to clinical response to moclobemide in patients with major depression. Danish University Antidepressant Group.

With the aim of identifying predictors of treatment response, plasma levels of tryptophan (Trp) and tyrosine (Tyr) pretreatment and during treatment, and their ratios in plasma to the sum of the other large neutral amino acids (LNAA), were determined in 26 inpatients with major depression. The subjects were treated double-blind on a fixed-dose schedule for 4 weeks with the monoamine oxidase (MAO) inhibitor moclobemide. The study took place at 4 clinical centers. Endogenous and nonendogenous depressives were comparable in all biochemical variables and were therefore analysed together. The levels of plasma Trp/LNAA were decreased pretreatment and during treatment in the depressives compared with healthy controls. No significant correlation between plasma amino acid levels or ratios, or plasma moclobemide level, and clinical improvement was found, and there were no indications of a specific plasma amino acid profile associating with a favourable clinical response. Endogenous depressives showed significantly greater improvement than nonendogenous depressives; however, neither subgroup showed significant correlations between biochemical and clinical variables. The findings are at variance with a series of studies, which showed significant correlations between plasma amino acid ratios and clinical improvement on a variety of antidepressant treatments.