Decreased Serum Tryptophan in Patients with Cancer Cachexia Correlates with Increased Serum Neopterin

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Abstract
We investigated serum tryptophan (Trp), neopterin (NPT) and immunosuppressive acidic protein (IAP), one of tumor-associated tumor marker, concentrations in 28 patients with gastrointestinal tumors representing cancer cachexia and 10 healthy controls. NPT comes from activated macrophages presumably activated by tumor-sensitized T cells via gamma-interferon (IFN-γ) excitation of the macrophages. We found that the NPT level was significantly higher than the control value. The negative correlation of NPT and Trp concentrations indicates activity of indoleamine 2,3-dioxygenase(IDO), a Trp degradating enzyme, in cancer-burden patients. The activity of IDO can be induced by cytokines such as IFN-γ, and therefore low Trp levels may result from endogenous IFN-γ production due to immune activation against tumors. We also found a positive correlation between NPT and IAP levels, suggesting that host immune activation against tumors played a role in the immunosuppression of cancer-burden states, followed by cancer-cachexia.