Altered Tryptophan and Neopterin Metabolism In Cancer Patients

Summary Plasma 5-hydroxytryptamine (serotonin), tryptophan and neopterin levels were measured in patients with depressive cancer cachexia and in healthy controls during the same time period. Patients with advanced cancers had significantly raised neopterin, a marker of endogenous gamma-interferon (IFN-γ) production, but decreased serotonin and tryptophan levels. IFN-γ induces a high level of indoleamine dioxvgenase (IDO), a tryptophan degrading enzyme, which in turn increases metabolism along the tryptophan- nicotinic acid pathway, resulting in decreased synthesis of serotonin. These results suggest that persistent immune activation occur in patients with cancer cachexia, resulting in disorders involving tryptophan metabolism.