Tryptophan as a help in depression

Alteration of tryptophan metabolism elicited by inflammation has been recently gaining some medical attention as a novel concept to explain the pathophysiology of depression. The kynurenine pathway is one of the tryptophan metabolic pathways, and it is an alternative pathway to tryptophan being metabolized into the “calming” neurotransmitter serotonin. Pro-inflammatory cytokines strengthen the kynurenin pathway, deprive the serotoninergic neurons of tryptophan source and thus reduce serotonin synthesis. The resultant decrease in serotonin production in the specific regions of the brain relates to the prevailing monoamine hypothesis of depression.

In addition, the above changes could decently explain the hippocampal atrophy that appears in chronic depression and which is probably also associated with decreases of serotonin. Because pro-inflammatory cytokines also activate the endocrine (HPA) axis, these imbalances may inhibit the hippocampal negative feedback system. In that way, changes in the tryptophan metabolism or decreases in dietary intake of tryptophan itself, may also relate to the HPA axis-hyperactivity hypothesis of major depression Taken all together, inflammation shifting tryptophan away from the serotonin production in the brain may contribute to depression in a powerful double pathway. Watch your dietary tryptophan …