Liebau Christian, Baltzer Axel W A, Schmidt Sebastian, Roesel Christian, Karreman Christiaan, Prisack Johannes Bernd, Bojar Hans, Merk Harry
Department of Orthopaedic Surgery, Ernst-Moritz-Arndt-University of Greifswald, Germany.
Anticancer Res. 2002 Mar-Apr;22(2A):931-6.
In this study we evaluated the ability of inducing activation of the enzyme indoleamine 2,3-dioxygenase (IDO) for the development of a new adjuvant therapy of osteosarcomas. The pathway that has described in the literature states that IDO activity is elevated by IFN-gamma. This mechanism is important because the increased IDO activation induces an intracellular degradation of the essential amino acid tryptophan and thereby activates apoptosis in human osteosarcoma cells.
Four different well-established human osteosarcoma cell lines (MNNG/HOS, KHOS-240, HOS and MG-63) were investigated in vitro. Several cytokines were tested for their ability to induce IDO activity. However special emphasis was placed to evaluate the synergistic effects of Interleukin-12 (IL-12) in combination with Interleukin-18 (IL-18). In the first series of experiments IDO induction was investigated by direct application of the cytokines IFN-gamma, TNF-alpha, IL-12 and IL-18 in different concentrations. Secondly, the increase of IDO expression from osteosarcoma cell lines was analysed in the presence of activated lymphocytes with or without cytokine application.
Our results demonstrated that the combined application of IL-12 and IL-18 enhanced IDO activity in the human osteosarcoma cell lines HOS and MG-63, in the presence of activated lymphocytes. In the absence of activated lymphocytes, no significant enhancement could be detected. In all our experiments the increase in IDO expression was only partly inhibited by blocking INF-gamma.
The presented study demonstrates that IL-12 and IL-18, or even more a combined application of both cytokines, induce IDO expression besides the known pathway via IFN-gamma. These mechanisms have been shown herein for the first time in human osteosacoma cell lines. Since IDO expression could still be shown after complete blocking of IFN-gamma, we conclude that at least a second pathway is responsible for inducing IDO activity. This is in contrast to the present knowledge about IDO activation.
在本研究中，我们评估了诱导吲哚胺2,3-双加氧酶（IDO）激活的能力，以开发骨肉瘤的新型辅助治疗方法。文献中描述的途径表明，IDO活性可被干扰素-γ（IFN-γ）提高。这一机制很重要，因为IDO激活增加会诱导必需氨基酸色氨酸的细胞内降解，从而激活人骨肉瘤细胞中的凋亡。
对四种不同的成熟人骨肉瘤细胞系（MNNG/HOS、KHOS-240、HOS和MG-63）进行体外研究。测试了几种细胞因子诱导IDO活性的能力。然而，特别强调评估白细胞介素-12（IL-12）与白细胞介素-18（IL-18）联合应用的协同效应。在第一系列实验中，通过直接应用不同浓度的细胞因子IFN-γ、肿瘤坏死因子-α（TNF-α）、IL-12和IL-18来研究IDO诱导情况。其次，在有或无细胞因子应用的情况下，分析活化淋巴细胞存在时骨肉瘤细胞系中IDO表达的增加情况。
我们的结果表明，在活化淋巴细胞存在的情况下，IL-12和IL-18联合应用可增强人骨肉瘤细胞系HOS和MG-63中的IDO活性。在无活化淋巴细胞的情况下，未检测到显著增强。在我们所有的实验中，通过阻断INF-γ仅部分抑制了IDO表达的增加。
本研究表明，IL-12和IL-18，或甚至两种细胞因子的联合应用，除了通过IFN-γ的已知途径外，还可诱导IDO表达。这些机制首次在人骨肉瘤细胞系中得到证实。由于在完全阻断IFN-γ后仍可显示IDO表达，我们得出结论，至少第二条途径负责诱导IDO活性。这与目前关于IDO激活的认识相反。
