L-Tryptophan & Serotonin Metabolism - IDO Activity

Regulation of L-Tryptophan, Kynurenine and Serotonin Balance by IDO Activity

L-Tryptophan & Serotonin Synthesis - Depression

Unlike some time ago, it is now clear that conditions in the depressive spectrum are not purely psychological in nature but are often also triggered in part by biological factors. Identifying these allows the therapist to recognize new starting points and to treat more individually. A clinically relevant, well-studied marker is a particular enzyme, indoleamine 2,3-dioxygenase, or IDO for short. Depressive symptoms are often accompanied by increased IDO activity. This increased IDO activity is an expression of neuro-/endocrine-immunological dysregulation. IDO inhibits serotonin synthesis in two ways: on the one hand, by promoting the breakdown of tryptophan. On the other hand, IDO produces kynurenines (which are also active in the nervous system) from tryptophan. This inhibits serotonin synthesis, which can cause depressive symptoms in the CNS. Kynurenines include, among others, quinolinic acid and 3-OH-kynurenine, which have neurotoxic effects and promote depressive symptoms.

When Is Tryptophan Supplementation Appropriate?

Tryptophan supplementation is discussed in connection with serotonin synthesis. However, it is only considered if no increased IDO activity can be detected and the tryptophan level is low. For patients with fructose malabsorption, a fructose-reduced diet is described in this context, because fructose remaining in the intestine inhibits the absorption of tryptophan.

When Is Anti-Inflammatory Therapy Considered?

If TNF-alpha and IFN-gamma are elevated, this increases IDO activity and indicates a systemic inflammatory process. In this case, an anti-inflammatory therapy (causal if possible, or at least general) can be discussed in consultation with your treating physicians.

Diagnostics - L-Tryptophan and Serotonin

Serotonin in the blood. Melatonin in saliva. IDO activity: tryptophan level, kynurenine in the blood