High-affinity uptake of kynurenine and nitric oxide-mediated inhibition of indoleamine 2,3-dioxygenase in bone marrow-derived myeloid dendritic cells

Department of Medical Technology, Nagoya University School of Health Sciences, 1-20 Daikominami-1-chome, Higashi-ku, Nagoya, Aichi, 461-8673, Japan.
Immunology Letters (Impact Factor: 2.51). 03/2008; 116(1):95-102. DOI: 10.1016/j.imlet.2007.11.016
Source: PubMed

ABSTRACT Indoleamine 2,3-dioxygenase (IDO)-initiated tryptophan metabolism along the kynurenine (Kyn) pathway in some dendritic cells (DC) such as plasmacytoid DC (pDC) regulates T-cell responses. It is unclear whether bone marrow-derived myeloid DC (BMDC) express functional IDO. The IDO expression was examined in CD11c(+)CD11b(+) BMDC differentiated from mouse bone marrow cells using GM-CSF. CpG oligodeoxynucleotides (CpG) induced the expression of IDO protein with the production of nitric oxide (NO) in BMDC in cultures for 24h. In the enzyme assay using cellular extracts of BMDC, the IDO activity of BMDC stimulated with CpG was enhanced by the addition of a NO synthase (NOS) inhibitor, suggesting that IDO activity was suppressed by NO production. On the other hand, the concentration of Kyn in the culture supernatant of BMDC was not increased by stimulation with CpG. Exogenously added Kyn was taken up by BMDC independently of CpG stimulation and NO production, and the uptake of Kyn was inhibited by a transport system L-specific inhibitor or high concentrations of tryptophan. The uptake of tryptophan by BMDC was markedly lower than that of Kyn. In conclusion, IDO activity in BMDC is down-regulated by NO production, whereas BMDC strongly take up exogenous Kyn.

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Available from: Osamu Takikawa, Sep 26, 2015
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    • "IDO activation can down-regulate the expression and activity of iNOS. Conversely, induction of NO by activation of iNOS down-regulates IDO activity in cell types as diverse as human uroepithelial transformed cells (Daubener et al., 1999), murine bone marrow-derived myeloid dendritic cells (Hara et al., 2008), human transformed and primary macrophages (Thomas et al., 1994) and mouse peritoneal cells (Ohtaki et al., 2009). "
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    ABSTRACT: Indoleamine 2,3-dioxygenase (IDO) is an intracellular heme-containing enzyme that is activated by proinflammatory cytokines, including interferon-γ (IFNγ), and metabolizes tryptophan along the kynurenine pathway. Activation of murine macrophages induces not only IDO but also nitric oxide synthase (iNOS), and the ensuing production of nitric oxide (NO) inhibits IDO. To determine the sensitivity of primary cultures of murine microglia to NO, microglia were stimulated with recombinant murine IFNγ (1 ng/ml) and lipopolysaccharide (LPS) (10 ng/ml). This combination of IFNγ+LPS synergized to produce maximal amounts of nitrite as early as 16h. Steady-state mRNAs for both iNOS and IDO were significantly increased by IFNγ+LPS at 4h post-treatment, followed by an increase in IDO enzymatic activity at 24h. Murine microglia (>95% CD11b(+)) were pretreated with the iNOS inhibitor, L-NIL hydrochloride, at a dose (30 μM) that completely abrogated production of nitrite. L-NIL had no effect on IDO mRNA at 4h or IDO enzymatic activity at 24h following stimulation with IFNγ+LPS. These data establish that IDO regulation in murine microglia is not restrained by NO, thereby permitting the accumulation of kynurenine and its downstream metabolites in the central nervous system.
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    ABSTRACT: Expression of tryptophan-catabolizing enzyme indoleamine-pyrrole 2,3-dioxygenase (IDO) has been associated with the regulatory phenotype of tumor-associated dendritic cells, along with other tolerogenic mechanisms, including production of immunomodulatory cytokines and expression of immune-inhibitory receptors. IDO activation in dendritic cells leads to tryptophan depletion and accumulation of its toxic downstream metabolites which in concert directly suppress proliferation of T cells and induce T-cell apoptosis. Furthermore, IDO-positive dendritic cells promote the induction of regulatory T cells, which further impair protective immunity against tumors. In the context of cancer, IDO induction in dendritic cells can be triggered by receptors expressed by regulatory T cells, such as CTLA4 and GITR, and by soluble tumor-associated factors, such as prostaglandin E2, in close alliance with TNF signaling. Immunosuppressive effects of enzymatically active IDO can be overcome by specific inhibitors such as 1-methyl-tryptophan which can be used for therapeutic purposes.
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