Thomas S R, Mohr D, Stocker R
Biochemistry Group, Heart Research Institute, Sydney, New South Wales, Australia.
J Biol Chem. 1994 May 20;269(20):14457-64.
Indoleamine 2,3-dioxygenase (IDO) and nitric oxide synthase are part of the anti-tumor and antimicrobial activities of mononuclear phagocytes induced by interferon-gamma (IFN gamma). As IDO is a heme-containing enzyme and NO, the product of nitric oxide synthase-initiated arginine degradation, is a regulator of heme enzymes, we investigated whether NO is capable of modulating IDO activity in IFN gamma-primed mononuclear phagocytes. Authentic NO gas or the NO-generating compound, diethylamine dinitric oxide adduct, dose-dependently inhibited IDO activity in cell lysates prepared from IFN gamma-primed human peripheral blood mononuclear cells, as assessed by the ascorbate/methylene blue assay for IDO. In contrast, neither nitrite nor nitrate affected IDO activity. Exposure of intact IFN gamma-primed human peripheral blood mononuclear cells or monocyte-derived macrophages to any of the NO-generating compounds, sodium nitroprusside, glyceryl trinitrate, S-nitroso-N-acetylpenicillamine, or diethylamine dinitric oxide adduct, resulted in inhibition of both the consumption of tryptophan from and formation of its metabolite, kynurenine, in the culture medium. The observed inhibition of IDO activity was not due to toxicity of the NO generators and was abrogated by the co-addition of oxyhemoglobin, an antagonist of NO function. Comparable concentrations of nitrite or nitrate did not inhibit IDO activity in intact cells. In contrast to human cells, addition of IFN gamma to murine macrophages, cultured in complete RPMI 1640 medium, readily induced nitric oxide synthase. Others have reported that such treatment does not induce IDO activity in these cells. However, induction of IDO activity was observed in murine macrophages when the synthesis of reactive nitrogen species was inhibited, by using arginine-free medium and/or the nitric oxide synthesis inhibitor, NG-monomethyl-L-arginine. Together, these results demonstrate that both exogenous and endogenous NO inhibit IDO activity and that oxidative arginine and tryptophan metabolism in IFN gamma-primed mononuclear phagocytes are functionally related. Our study thereby provides an insight into how these cells may regulate some of their antimicrobial and anti-tumor activities.
吲哚胺2,3-双加氧酶（IDO）和一氧化氮合酶是干扰素-γ（IFNγ）诱导的单核吞噬细胞抗肿瘤和抗菌活性的一部分。由于IDO是一种含血红素的酶，而一氧化氮合酶启动的精氨酸降解产物NO是血红素酶的调节剂，我们研究了NO是否能够调节IFNγ预处理的单核吞噬细胞中的IDO活性。通过用于IDO的抗坏血酸/亚甲蓝测定法评估，纯NO气体或产生NO的化合物二乙胺二硝基氧化物加合物剂量依赖性地抑制从IFNγ预处理的人外周血单核细胞制备的细胞裂解物中的IDO活性。相反，亚硝酸盐和硝酸盐均不影响IDO活性。将完整的IFNγ预处理的人外周血单核细胞或单核细胞衍生的巨噬细胞暴露于任何产生NO的化合物，硝普钠、三硝酸甘油酯、S-亚硝基-N-乙酰青霉胺或二乙胺二硝基氧化物加合物，导致培养基中色氨酸的消耗及其代谢产物犬尿氨酸的形成均受到抑制。观察到的IDO活性抑制不是由于NO生成剂的毒性，并且通过共同添加血红蛋白（一种NO功能拮抗剂）而消除。相当浓度的亚硝酸盐或硝酸盐在完整细胞中不抑制IDO活性。与人类细胞相反，向在完全RPMI 1640培养基中培养的小鼠巨噬细胞中添加IFNγ很容易诱导一氧化氮合酶。其他人报道这种处理在这些细胞中不会诱导IDO活性。然而，当使用无精氨酸培养基和/或一氧化氮合成抑制剂NG-单甲基-L-精氨酸抑制活性氮物质的合成时，在小鼠巨噬细胞中观察到IDO活性的诱导。总之，这些结果表明外源性和内源性NO均抑制IDO活性，并且IFNγ预处理的单核吞噬细胞中的氧化精氨酸和色氨酸代谢在功能上相关。因此，我们的研究深入了解了这些细胞如何调节其一些抗菌和抗肿瘤活性。
