Tryptophan is also metabolized by a separate pathway to
kynurenine by the enzyme, indoleamine 2,3-dioxygenase (IDO).
When you exercise, the levels of an enzyme called
kynurenine aminotransferase build up in your muscles.
Also, the fact that alterations have been observed in the
kynurenine pathway in tyrosine metabolism in parkinsonian fly, it can be concluded that
kynurenine pathway which is a metabolic pathway leading to the production of nicotinamide adenine dinucleotide (NAD +) from the degradation of the essential amino tryptophan acid, may be associated with Parkinson's disease.
Inflammation-associated depression: from serotonin to
kynurenine. Psychoneuroendocrinology 2011;36:426-36.
In a randomized, crossover feeding study including 11 obese nondiabetic participants, plasma concentrations of tryptophan, phenylalanine, and
kynurenine were increased after a high-fat meal with whey protein isolate (35).
Stroup et al., "Metabolomic changes demonstrate reduced bioavailability of tyrosine and altered metabolism of tryptophan via the
kynurenine pathway with ingestion of medical foods in phenylketonuria," Molecular Genetics and Metabolism, vol.
Kelley, "Inflammation-associated depression: from serotonin to
kynurenine," Psychoneuroendocrinology, vol.
Additionally, CTLA-4 induces the expression of the enzyme indoleamine 2,3-dioxygenase (IDO) by DCs, which catalyzes degradation of the essential amino acid tryptophan to
kynurenine, leading to effector T cell starvation [25].
Orhan et al., "Erratum:Skeletal muscle PGC-1a1 modulates
kynurenine metabolism and mediates resilience to stress-induced depression (Cell (2014) 159 (3345))," Cell, vol.
Indoleamine-2,3-dioxygenase, which catalyzes the oxidative breakdown of the essential amino acid tryptophan, via the
kynurenine pathway, is an inhibitor of T-cell proliferation that has been implicated in immune resistance in several cancers, including soft tissue sarcoma [45].
[33] reported that
kynurenine 3-monooxygenase (KMO), an enzyme playing a critical role in Huntington's and Alzheimer's diseases, exhibits tumor-promoting effects towards HCC.
They also have immunomodulatory and immunosuppressive properties through the direct interaction between cells and secretion of prostaglandin E2 (PGE2), leukaemia-inhibiting factor (LIF), and
kynurenine [11, 62].