From the Guidelines
Impaired tryptophan metabolism can be diagnosed through tests that assess amino acid metabolism, particularly those that measure tryptophan and its related pathways.
Key Tests
- Metabolomics analysis: This involves the use of techniques such as high-resolution metabolomics to identify and quantify metabolites in biological samples, including those related to tryptophan metabolism 1.
- Urine and serum samples analysis: Analyzing urine and serum samples can help identify changes in tryptophan metabolism, as seen in studies where tryptophan and phenylalanine metabolism were identified as age-dependent biological pathways in children exposed to air pollution 1.
Relevant Pathways
- Tryptophan metabolism: This pathway is involved in the breakdown and synthesis of tryptophan, and changes in this pathway have been associated with air pollution exposure 1.
- Amino acid metabolism: This broader pathway includes tryptophan metabolism and has been identified as a key area of change in response to air pollution exposure 1.
Laboratory Information
- Metabolon, Inc.: This laboratory has been involved in several studies analyzing metabolomics data, including those related to tryptophan metabolism and air pollution exposure 1.
- Emory Clinical Laboratory, Emory University: This laboratory has also been involved in studies analyzing metabolomics data, including those related to tryptophan metabolism and air pollution exposure 1.
From the Research
Diagnostic Tests for Impaired Tryptophan Metabolism
The following tests can be used to diagnose impaired tryptophan metabolism:
- Tryptophan depletion test, which induces a rapid and substantial lowering of both total and free plasma tryptophan, consequently decreasing brain serotonin content and cerebral serotonin function 2
- High-performance liquid chromatography (HPLC) for the simultaneous analysis of tryptophan and its metabolites, involving in-line pre-column derivatization with o-phthaldialdehyde (OPA) and dual-channel fluorescence detection 3
- (13)C-tryptophan breath test ((13)C-TBT), a noninvasive, stable-isotope tracer method that measures exhaled (13)CO2 attributable to tryptophan catabolism via the kynurenine pathway 4
Key Findings
- The tryptophan depletion test has been used to study the role of serotonin in the pathobiology of depressive disorders and their treatment modalities 2
- HPLC analysis can detect tryptophan and its metabolites in biological samples, with a detection limit of 30 pmol/mL or 150 fmol/injection 3
- The (13)C-TBT has been shown to detect increased catabolic turnover of tryptophan along the kynurenine pathway in patients with major depressive disorder 4
Tryptophan Metabolism
- Tryptophan metabolism is involved in the development and progression of immune, nervous, and digestive system diseases 5
- The kynurenine pathway, activated by indoleamine-2,3-dioxygenase (IDO) and tryptophan 2,3-dioxygenase, affects the migration and invasion of glioma cells and the development of COVID-19 and depression 5
- Tryptophan metabolites can serve as potential markers for disease therapy and guide clinical decision-making 5, 6