Tryptophan metabolite 3-hydroxyanthranilic acid selectively induces activated T cell death via intracellular GSH depletion

Differential action of 3-hydroxyanthranilic acid on viability and activation of stimulated lymphocytes

Lymphocytes proliferation after antigen-driven activation leads to an increase in cell count, which could last some week, until apoptosis mechanisms allow the homeostatic control of the system. During the first days of this stimulation, activated lymphocytes display high resistance to apoptosis and to most immunosuppressive drugs. According to the literature, few compounds have been described to kill recently activated cells, by inhibiting metabolic processes fundamental to proliferation. The aim of our work was to evaluate comparatively these different compounds, in order to identify the best strategy to kill cells that have undergone proliferation, while sparing the repertoire of resting cells. After preliminary experiments, 3-HAA and bortezomib were selected as the most suitable compounds for our purposes. The possible synergic effect of 3-HAA with bortezomib or with manganese ions was also assessed. 3-HAA was confirmed to be the most reliable pharmacologic approach to inhibit proliferation with acceptable toxicity on resting cells. While in the case of PHA stimulation 3-HAA led to death of most lymphocytes, only a minor percentage of cells were killed after allo-stimulation, suggesting that the effect is proportional to the percentage of stimulated lymphocytes. Manganese ions further enhanced this effect, while results with bortezomib seemed to be less consistent. These results deserve further investigations to develop new procedures for targeting activated cells with pharmacological approaches.

Involvement of kynurenines in Huntington's disease and stroke-induced brain damage

Several components of the kynurenine pathway of tryptophan metabolism are now recognised to have actions of profound biological importance. These include the ability to modulate the activation of glutamate and nicotinic receptors, to modify the responsiveness of the immune system to inflammation and infection, and to modify the generation and removal of reactive oxygen species. As each of these factors is being recognised increasingly as contributing to major disorders of the central nervous system (CNS), so the potentially fundamental role of the kynurenine pathway in those disorders is presenting a valuable target both for understanding the progress of those disorders and for developing potential drug treatments. This review will summarise some of the evidence for an important contribution of the kynurenines to Huntington's disease and to stroke damage in the CNS. Together with preliminary evidence from a study of kynurenine metabolites after major surgery, an important conclusion is that kynurenine pathway activation closely reflects cognitive function, and may play a significant role in cognitive ability.

L-kynurenine-induced apoptosis in human NK cells is mediated by reactive oxygen species

Recent studies have shown that indoleamine 2,3-dioxygenase (IDO) plays a pivotal role in the modulation of immune response against tumor and virus infection. Here we demonstrate the pro-apoptotic effect of L-kynurenine, a tryptophan catabolite of IDO, on human NK cell line, NK92 MI. Treatment with L-kynurenine dose-dependently induced growth inhibition and apoptosis in NK92 MI cells. Treatment with the antioxidant NAC completely protected cells from L-kynurenine-induced apoptosis. Moreover, we found that treatment with Z-VAD-fmk and ZB4 slightly inhibited L-kynurenine-induced apoptosis, suggesting that L-kynurenine-induced apoptosis in NK cells occurs primarily through an ROS mediated pathway. We observed that the presence of NAC blocks cytochrome c release and activation of caspase-3 during L-kynurenine-induced apoptosis. Overall, we conclude that L-kynurenine resulting from IDO can cause cell death via ROS pathway in NK cells. Our findings provide a new insight into the interaction between NK cells and IDO positive cancer cells in regulating immune responses.

Kynurenine metabolism in health and disease

Kynurenine is a small molecule derived from tryptophan when this amino acid is metabolised via the kynurenine pathway. The biological activity of kynurenine and its metabolites (kynurenines) is well recognised. Therefore, understanding the regulation of the subsequent biochemical reactions is essential for the design of therapeutic strategies which aim to interfere with the kynurenine pathway. However, kynurenine concentration in the body may not only be determined by the efficiency of kynurenine synthesis but also by the rate of kynurenine clearance. In this review, current knowledge about the mechanisms of kynurenine production and routes of its clearance is presented. In addition, the involvement of kynurenine and its metabolites in the biology of different T cell subsets (including Th17 cells and regulatory T cells) and neuronal cells is discussed.