Search

The kynurenine pathway (KP) and one of its end-products, the excitotoxin quinolinic acid (QUIN), are involved in the pathogenesis of several major neuroinflammatory brain diseases. A relevant animal model to study KP metabolism is now needed to assess whether intervention in this pathway may improve the outcome of such diseases. Humans and macaques share a very similar genetic makeup. In this study, we characterized the KP metabolism in macaque primary macrophages of three different species in comparison to human cells. We found that the KP profiles in simian macrophages were very similar to those in humans when challenged with inflammatory cytokines. Further, we found that macaque macrophages are capable of producing a pathophysiological concentration of QUIN. Our data validate the simian model as a relevant model to study the human cellular KP metabolism in the context of inflammation.

Evidence for an immunosuppressive function of indoleamine 2,3-dioxygenase (IDO) has been accumulating. However, the unusual distribution of IDO1 in gynecologic cancer cells suggests that modulating immunity may not its only function. To clarify the physiological importance of IDO1 in endometriosis, a tumor-like benign disease, we have investigated the potential mechanism by which IDO1 modulated endometrial stromal cells (ESCs) proliferation and invasion. ESCs were obtained from 16 control women (normal) and 14 patients with ovarian endometrioma, then the normal ESCs were treated with plasmid pEGFP-N1-IDO1 or SD11-IDO1 short hairpin RNA (shRNA) alone, or in combination with c-Jun N-terminal kinase (JNK) inhibitor (SP600125), and subjected to cell viability, proliferation, apoptosis assay and Matrigel invasion assay. IDO1 mRNA expression was evaluated by quantitative real-time reverse transcription-polymerase chain reaction (real-time PCR), and protein levels of IDO1, survivin, protein 53 (p53), matrix metalloproteinase (MMP)-2, MMP-9, tissue-inhibitor of metalloproteinase-1 (TIMP-1) and cyclooxygenase-2 (COX-2) in IDO1-overexpressing and IDO1-deficiency ESCs were analyzed by in-cell Western. We found that IDO1 expression was higher in endometriosis-derived eutopic and ectopic ESCs, compared with endometriosis-free normal ESCs. As a result, IDO1-overexpression in ESCs was markedly linked to reduction of apoptosis and p53 expression, and upregulation of survival, proliferation, invasion, as well as expression of MMP-9, COX-2 expression, rather than expression of survivin, MMP-2 and TIMP-1. Reversely, JNK blockage could abrogate these alterations of ESCs in IDO1-overexpressing milieu, suggesting that JNK signaling pathway was indispensable for ESCs survival, proliferation and invasion enhanced by IDO1, which may contribute to the pathophysiology of endometriosis.

Immune escape, the ability of tumor cells to avoid tumor-specific immune responses, occurs during the development and progression of several types of human malignancies, including colorectal cancer (CRC). Indoleamine 2,3-dioxygenase (IDO), the tryptophan catabolic enzyme, plays a significant role in regulating the immune response and provides tumor cells with a potent tool to evade the immune system. In the present study, we examined the effects of (-)-epigallocatechin gallate (EGCG), the major catechin in green tea, on the inhibition of IDO expression induced by interferon (IFN)-γ in human CRC cells. We found that IFN-γ increased the expression levels of IDO protein and mRNA in HT29 and SW837 CRC cell lines. Treatment of SW837 cells with EGCG significantly decreased IFN-γ-induced expression of IDO protein and mRNA in a dose-dependent manner. Enzymatic activity of IDO, determined by the concentration of L-kynurenine in the culture medium, was also significantly inhibited by EGCG treatment. Phosphorylation of signal transducer and activator of transcription 1 (STAT1) induced by IFN-γ was also significantly inhibited by EGCG. Reporter assays indicated that EGCG inhibited the transcriptional activities of IDO promoters, IFN-stimulated response element and IFN-γ activation sequence, activated by STAT1 phosphorylation. These findings suggest that EGCG may exert antitumor effects on CRC, at least in part, by inhibiting the expression and function of IDO through the suppression of STAT1 activation. EGCG may, thus, serve as a potential agent for antitumor immunotherapy and be useful in the chemoprevention and/or treatment of CRC.

Aim: Exposure to UV light is the major risk factor in the development of age-related cataract (ARC). UV filters produced during tryptophan catabolism maintain the transparency of the lens and protect retina from photo damage. Indoleamine 2, 3-dioxygenase (IDO), the first rate-limiting enzyme in the tryptophan catabolism, is up regulated by interferon-gamma (IFN-g) which harbors single nucleotide polymorphisms (SNPs). The T allele of SNP at +874 position of the IFN-g is known to be associated with the up regulation of IDO than the allele A. Hence, we attempted to study the IFN-g+874(T/A) polymorphism for its association with ARCs., Materials and Methods: A total of 680 cataract cases [199 nuclear (NC), 175 cortical (CC), 174 posterior subcapsular (PSC), and 132 mixed types (MT)] and 210 healthy controls were genotyped for +874(T/A) polymorphism using amplification refractory mutation system-polymerase chain reaction on 2% agarose gel stained with ethidium bromide., Results: There was increased risk for CC and PSC when the patients happened to be females, with low body mass index and with early onset. Considering the IFN-g polymorphism, a high risk was observed for CC and PSC in female patients of AA genotype with significant protection for those with TT genotypes., Conclusion: Present results indicate that +874(T/A) polymorphism may be considered as one of the biomarkers to distinguish between the CC and PSC types of cataracts for risk estimations. The study appears to be the first of its kind reporting an association of IFN-g+874(T/A) polymorphism with ARCs.

This article highlights the evidence linking depression to increased inflammatory drive and explores putative mechanisms for the association by reviewing both preclinical and clinical literature. The enzyme indoleamine 2,3-dioxygenase is induced by proinflammatory cytokines and may form a link between immune functioning and altered neurotransmission, which results in depression. Increased indoleamine 2,3-dioxygenase activity may cause both tryptophan depletion and increased neurotoxic metabolites of the kynurenine pathway, two alterations which have been hypothesized to cause depression. The tryptophan-kynurenine pathway is comprehensively described with a focus on the evidence linking metabolite alterations to depression. The use of immune-activated groups at high risk of depression have been used to explore these hypotheses; we focus on the studies involving chronic hepatitis C patients receiving interferon-alpha, an immune activating cytokine. Findings from this work have led to novel strategies for the future development of antidepressants including inhibition of indoleamine 2,3-dioxygenase, moderating the cytokines which activate it, or addressing other targets in the kynurenine pathway.

This paper examines the role of selective serotonin reuptake inhibitors (SSRIs) in the treatment of hepatitis-C virus (HCV) patients who have developed interferon-alpha induced depression. A 2-year data analysis of HCV psychiatric liaison clinic has been undertaken. The diagnosis, treatment, and progress of those patients who were treated with interferon-alpha (INF-alpha) are reported. 53 of the 78 patients enrolled at the HCV Clinic and treated with INF-alpha were referred for psychiatric consultation. Six patients developed major depressive illness following INF therapy. They were all treated with SSRIs and they made full recovery. This is a significant observation and is concordant with other studies. Its biochemical ramifications are presented. It is concluded that INF-induced depression is fully reversible. A hypothesis is proposed that SSRIs modulate the neuro-protective neurotoxic ratio by possibly inhibiting the indole-2,3-dioxygenase induction of the kynurenine pathway.