Division of Biological Chemistry, Biocenter, Innsbruck Medical University, Innsbruck, Austria.
Transpl Immunol. 2011 Sep;25(2-3):119-23. doi: 10.1016/j.trim.2011.06.005. Epub 2011 Jul 1.
The anti-proliferative and immunomodulatory enzyme indoleamine 2,3-dioxygenase (IDO) degrades the essential amino acid tryptophan via the kynurenine pathway. IDO is stimulated during cellular immune responses preferentially by Th1-type cytokine interferon-γ (IFN-γ). IDO activity is estimated by calculating the kynurenine to tryptophan ratio (Kyn/Trp). In human monocyte-derived macrophages and dendritic cells, GTP-cyclohydrolase I is induced in parallel to IDO and produces neopterin. This study investigated the effects of common immunosuppressants on freshly isolated human peripheral blood mononuclear cells (PBMC) in vitro. PBMC were incubated with compounds for 30 min and then either left unstimulated or stimulated with mitogen phytohaemagglutinin (PHA). Concentrations of tryptophan, kynurenine and neopterin were measured in supernatants after 48 h. Kyn/Trp, neopterin and IFN-γ concentrations were significantly higher in PHA-stimulated vs. unstimulated PBMC. Tacrolimus (FK506), cyclosporine A (CsA), sirolimus and methylprednisolone dose-dependently inhibited tryptophan degradation and neopterin production. FK506, CsA and sirolimus showed significant inhibition at concentrations as low as 0.1 μg/ml, whereas prednisolone and methylprednisolone required higher doses to suppress tryptophan degradation. Mycophenolate-mofetil suppressed neopterin formation more efficiently than Kyn/Trp. All tested drugs also strongly decreased mitogen-induced IFN-γ concentrations. Overall the investigated immunosuppressants are effective to inhibit IDO activity and neopterin production in a similar and dose-dependent manner, however with some differences in IC50s when comparing individual compounds. The corresponding changes of IFN-γ concentrations are in line with its role as a trigger of both biochemical changes.
色氨酸分解代谢酶吲哚胺 2,3-双加氧酶（IDO）通过犬尿氨酸途径降解必需氨基酸色氨酸。细胞免疫反应会优先刺激 IDO，其刺激物为 Th1 型细胞因子干扰素-γ（IFN-γ）。IDO 活性通过计算犬尿氨酸与色氨酸的比值（Kyn/Trp）来估计。在人单核细胞衍生的巨噬细胞和树突状细胞中，与 IDO 平行诱导 GTP 环化水解酶 I，并产生新蝶呤。本研究在体外研究了常用免疫抑制剂对新鲜分离的人外周血单核细胞（PBMC）的影响。将 PBMC 与化合物孵育 30 分钟，然后用有丝分裂原植物血凝素（PHA）刺激或不刺激。孵育 48 小时后，测量上清液中色氨酸、犬尿氨酸和新蝶呤的浓度。与未刺激的 PBMC 相比，PHA 刺激的 PBMC 中 Kyn/Trp、新蝶呤和 IFN-γ浓度显著升高。他克莫司（FK506）、环孢素 A（CsA）、西罗莫司和甲泼尼龙剂量依赖性地抑制色氨酸降解和新蝶呤生成。FK506、CsA 和西罗莫司在低至 0.1μg/ml 的浓度下即显示出显著抑制作用，而泼尼松龙和甲泼尼龙需要更高剂量才能抑制色氨酸降解。霉酚酸酯比 Kyn/Trp 更有效地抑制新蝶呤的形成。所有测试药物也强烈降低有丝分裂原诱导的 IFN-γ 浓度。总的来说，研究中的免疫抑制剂以相似且剂量依赖性的方式有效抑制 IDO 活性和新蝶呤的产生，但在比较单个化合物时，IC50 存在一些差异。IFN-γ 浓度的相应变化与其作为生化变化触发因素的作用一致。
