Increased kynurenine concentration attenuates serotonergic neurotoxicity induced by 3,4-methylenedioxymethamphetamine (MDMA) in rats through activation of aryl hydrocarbon receptor.

3,4-Methylenedioxymethamphetamine (MDMA) is an amphetamine derivative that has been shown to produce serotonergic damage in the brains of primates, including humans, and of rats. Tryptophan, the precursor of serotonin, is primarily degraded through the kynurenine (KYN) pathway, producing among others KYN, the main metabolite of this route. KYN has been reported as an endogenous agonist of the aryl hydrocarbon receptor (AhR), a transcription factor involved in several neurological functions. This study aims to determine the effect of MDMA on the KYN pathway and on AhR activity and to establish their role in the long-term serotonergic neurotoxicity induced by the drug in rats. Our results show that MDMA induces the activation of the KYN pathway, mediated by hepatic tryptophan 2,3-dioxygenase (TDO). MDMA also activated AhR as evidenced by increased AhR nuclear translocation and CYP1B1 mRNA expression. Autoradiographic quantification of serotonin transporters showed that both the TDO inhibitor 680C91 and the AhR antagonist CH-223191 potentiated the neurotoxicity induced by MDMA, while administration of exogenous l-kynurenine or of the AhR positive modulator 3,3'-diindolylmethane (DIM) partially prevented the serotonergic damage induced by the drug. The results demonstrate for the first time that MDMA increases KYN levels and AhR activity, and these changes appear to play a role in limiting the neurotoxicity induced by the drug. This work provides a better understanding of the physiological mechanisms that attenuate the brain damage induced by MDMA and identify modulation of the KYN pathway and of AhR as potential therapeutic strategies to limit the negative effects of MDMA.

Indoleamine and tryptophan 2,3-dioxygenases as important future therapeutic targets.

Conversion of tryptophan to N-formylkynurenine is the first and rate-limiting step of the tryptophan metabolic pathway (i.e., the kynurenine pathway). This conversion is catalyzed by three enzyme isoforms: indoleamine 2,3-dioxygenase 1 (IDO1), indoleamine 2,3-dioxygenase 2 (IDO2), and tryptophan 2,3-dioxygenase (TDO). As this pathway generates numerous metabolites that are involved in various pathological conditions, IDOs and TDO represent important targets for therapeutic intervention. This pathway has especially drawn attention due to its importance in tumor resistance. Over the last decade, a large number of IDO and TDO inhibitors have been developed, many of which have entered clinical trials. Here, detailed structural comparisons of these three enzymes (with emphasis on their active sites), their involvement in cellular signaling, and their role(s) in pathological conditions are discussed. Furthermore, the most important recent inhibitors described in papers and patents and involved in clinical trials are reviewed, with a focus on both selective and multiple inhibitors. A short overview of the biochemical and cellular assays used for inhibitory potency evaluation is also presented. This review summarizes recent advances on IDO and TDO as potential drug targets, and provides the key features and perspectives for further research and development of potent inhibitors of the kynurenine pathway.

Cyclooxygenase inhibition targets neurons to prevent early behavioural decline in Alzheimer's disease model mice.

Identifying preventive targets for Alzheimer's disease is a central challenge of modern medicine. Non-steroidal anti-inflammatory drugs, which inhibit the cyclooxygenase enzymes COX-1 and COX-2, reduce the risk of developing Alzheimer's disease in normal ageing populations. This preventive effect coincides with an extended preclinical phase that spans years to decades before onset of cognitive decline. In the brain, COX-2 is induced in neurons in response to excitatory synaptic activity and in glial cells in response to inflammation. To identify mechanisms underlying prevention of cognitive decline by anti-inflammatory drugs, we first identified an early object memory deficit in APPSwe-PS1ΔE9 mice that preceded previously identified spatial memory deficits in this model. We modelled prevention of this memory deficit with ibuprofen, and found that ibuprofen prevented memory impairment without producing any measurable changes in amyloid-ß accumulation or glial inflammation. Instead, ibuprofen modulated hippocampal gene expression in pathways involved in neuronal plasticity and increased levels of norepinephrine and dopamine. The gene most highly downregulated by ibuprofen was neuronal tryptophan 2,3-dioxygenase (Tdo2), which encodes an enzyme that metabolizes tryptophan to kynurenine. TDO2 expression was increased by neuronal COX-2 activity, and overexpression of hippocampal TDO2 produced behavioural deficits. Moreover, pharmacological TDO2 inhibition prevented behavioural deficits in APPSwe-PS1ΔE9 mice. Taken together, these data demonstrate broad effects of cyclooxygenase inhibition on multiple neuronal pathways that counteract the neurotoxic effects of early accumulating amyloid-ß oligomers.

Inhibition of indoleamine 2,3-dioxygenase suppresses NK cell activity and accelerates tumor growth.

Indoleamine 2,3-dioxygenase (IDO), a tryptophan catabolizing enzyme, is induced under various pathological conditions, including viral and bacterial infection, allograft rejection, cerebral ischemia, and tumor growth. We have previously reported that the expression of IDO mRNA was increased in some clinical cases of hepatocellular carcinoma in which the recurrence-free survival rate in these IDO-positive patients was significantly higher than that in patients without IDO mRNA induction in tumors. Additionally, IDO expressed in tumors was localized not to the tumor cells but instead to tumor-infiltrating cells by immunohistochemistry. In this study, in order to elucidate the mechanisms underlying anti-tumor effect of IDO, we investigated whether IDO inhibitor (1-methyl-dl-tryptophan, 1MT) affects the growth of subcutaneous B16 tumors in mice. Subsequently, the activity of natural killer (NK) cells was investigated under the conditions of inhibited IDO activity in vivo and in vitro. IDO mRNA expression of B16 cells, B16 subcutaneous tumor, sprenocytes of mice, and human NK cells were studied by reverse transcription-polymerase chain reaction. B16 subcutaneous tumor growth with or without IDO inhibition was observed and cytotoxic activity of NK cells were investigated under the conditions of inhibited IDO activity in vivo and in vitro. IDO mRNA was expressed in B16 subcutaneous tumor, splenocytes of tumor bearing mice, co-cultured splenocytes with B16, and human NK cells. On day 14, after injection of B16 melanoma cells, the sizes of tumors in IDO-inhibited mice were significantly larger than those in control mice. The cytotoxic activity of mice NK cells was reduced by IDO inhibition in vivo. In vitro inhibition of IDO, NK activity was reduced in dose-dependent manner of 1MT. In conclusion, these results indicated that IDO plays an important role in anti-tumor immunity by regulating cytotoxic activity of NK cells.

Tryptophan availability selectively limits NO-synthase induction in macrophages.

We studied the effects of tryptophan (TRP) availability on the synthesis and release of nitric oxide (NO) and tumor necrosis factor alpha (TNF-alpha) in interferon-gamma (IFN-gamma)-activated murine macrophages of the BAC1.2F5 cell line. IFN-gamma (100 U/ml) not only increased the synthesis and release of NO and TNF-alpha from these cells but also induced indoleamine-2,3-dioxygenase, the rate-limiting enzyme of TRP catabolism. This led to an increased metabolic flow through the kynurenine pathway and significantly decreased TRP levels in macrophage incubation media. Low TRP concentrations in the media, however, modified IFN-gamma effects. In TRP-"starved" cultures, in fact, the IFN-gamma-mediated NO synthase induction was significantly reduced, and the increased TNF-alpha synthesis and release were not affected. Our results suggest that a reduced local TRP availability may modify macrophage function and possibly the outcome of immune responses.

The enzyme indoleamine 2,3-dioxygenase is induced in the mouse brain in response to peripheral administration of lipopolysaccharide and superantigen.

The essential amino-acid, L-tryptophan, is the precursor of serotonin. Its availability in the brain is controlled by indoleamine 2,3-dioxygenase (IDO). This enzyme is inducible by cytokines such as interferon-gamma (IFN-gamma) and is the first and rate-limiting enzyme of the catabolism pathway of tryptophan. Since induction of IDO has been proposed to mediate the influence of cytokines on mood in patients with various somatic disorders, the present study aimed at analyzing the relationships between changes in brain IDO activity and serum IFN-gamma levels in response to peripheral immune stimulation by lipopolysaccharide (LPS) and superantigen in mice. Each of these treatments induced an increase in serum IFN-gamma at 6 h post-treatment followed 24 h later by a two-fold increase in IDO activity in the brain. These results support the involvement of peripheral IFN-gamma in the control of L-tryptophan catabolism in the brain.

Interleukin-1 enhances indoleamine 2,3-dioxygenase activity by increasing specific mRNA expression in human mononuclear phagocytes.

The objective of this study was to determine the utility of the THP-1 monocytic leukemia cell line as a model for analyzing molecular mechanisms involved in enhancement of interferon (IFN)-gamma-induced indoleamine dioxygenase (IDO) activity by interleukin-1 (IL-1). Following treatment of THP-1 cells with combinations of IFN-gamma and IL-1, IDO activity and IDO mRNA were quantified by HPLC and radioanalytic imaging of RT-PCR products, respectively. IL-1 increased the amount of IDO activity and the expression of IDO mRNA in IFN-treated cells; IL-1 alone had no effect on untreated THP-1 cells. Because IDO gene regulation might differ between immature THP-1 cells and mature macrophages, experiments were repeated using primary macrophage cultures. IFN-gamma induced IDO activity, and IDO mRNA was expressed in a dose-dependent manner. In the presence of IL-1, 10 times less IFN was required to obtain the same amount of IDO mRNA and IDO activity. Furthermore, IL-1 alone increased IDO mRNA expression. It appears that unlike what was observed in THP-1 cells, IL-1 transcriptionally activates the IDO gene in primary macrophages. However, increases in IDO activity were not observed following treatment with IL-1 alone. Although the THP-1 cell may be used to model cytokine potentiation of IFN-induced IDO activity, some differences in regulation between THP-1 cells and primary macrophage cultures may exist.

Operative deliveries induce a significant activation of indoleamine 2,3-dioxygenase in human placenta: existence of a new mechanism for activating the enzyme.

The physiological activating mechanism for human placental indoleamine 2,3-dioxygenase was investigated. No cell fractions of the placental homogenate were found to replace the electron-mediation activity of methylene blue from a reductant to the enzyme in the exogenous enzyme-activating system with L-ascorbic acid, B-NADPH, or B-NADH as a reductant. However, the preincubation at 37 degrees C of the supernatant fraction (10,000 x g, 30 min) prior to starting the indoleamine 2,3-dioxygenase reaction drastically caused the activation of the enzyme without added reductants and methylene blue, which suggests the existence of an endogenous indoleamine 2,3-dioxygenase-activating system. The endogenous enzyme activation was induced in the placentas delivered operatively by vacuum extraction or cesarean section much more significant degree than in those delivered normally.

Correlation between toxicity and effects on intermediary metabolism in 2,3,7,8-tetrachlorodibenzo-p-dioxin-treated male C57BL/6J and DBA/2J mice.

Male mice were treated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) by gavage. C57BL/6J (C57) mice received 0.03 to 235 micrograms/kg, DBA/2J (DBA) mice 1 to 3295 micrograms/kg. On Day 8 after dosing blood was collected, and livers and kidneys were removed. Body weights and feed intake were not much affected until Day 8 after exposure. Hepatomegaly developed at doses above 3 and 97.5 micrograms/kg in C57 and DBA mice, respectively. Ethoxyresorufin O-deethylase activity was induced in liver with an ED50 of 1.1 and 16 micrograms/kg and in kidney with an ED50 of 65 and 380 micrograms/kg in C57 and DBA mice, respectively. The activity of phosphoenolpyruvate carboxykinase (PEPCK) in livers of both mouse strains was reduced over the entire dose range, displaying a plateau in the dose response at the onset of acute toxicity of TCDD. This enzyme activity was decreased by as much as 80% at the respective lethal doses. PEPCK activity in kidney was not affected. Glucose-6-phosphatase activity (G-6-Pase) in liver was altered only in the lethal dose range with a maximum reduction of about 50%. Serum glucose concentration was reduced over the entire dose range, but the reduction was significant only at doses in which G-6-Pase activity was affected, reaching levels as low as 3 mmol/liter in DBA mice. Tryptophan 2,3-dioxygenase activity was not lowered at any dose of TCDD in either mouse strain, and no increase in serum tryptophan levels was observed. Serum levels of thyroxine (T4) and triiodothyronine (T3) were dose dependently decreased over most of the dose range administered, with T3 levels exactly paralleling T4 levels in both mouse strains. It is concluded that TCDD causes acute toxicity in male C57 and DBA mice by a severe reduction of gluconeogenesis, but, in contrast to rats, it does not affect tryptophan homeostasis. Following administration of TCDD serum T3 levels in the mouse appear to correlate with T4 levels, whereas in the rat they are independent of each other.

Heparin inhibits the antiparasitic and immune modulatory effects of human recombinant interferon-gamma.

Interferon-gamma (IFN-gamma) is a potent immune regulatory cytokine and is, in addition, involved in the induction of antiparasitic effector mechanisms in different cell types. The first step of IFN-gamma action is its binding to a specific receptor. Furthermore, it has been shown that IFN-gamma binds with a great affinity to the heparin-like structure of heparan sulfate, which is localized in basement membranes and on cell surfaces. In this study, we analyze the effect of heparin and heparan sulfate on three different IFN-gamma-mediated activities inducible in human glioblastoma cells (87HG31 and 86HG39). We find firstly that heparin is able to inhibit IFN-gamma-mediated induction of major histocompatibility complex (MHC) class II antigen expression on 87HG31 cells, an effect which can be abrogated by protamine. Secondly, we show that heparin inhibits the IFN-gamma-induced toxoplasmostasis within 86HG39 cells in a dose-dependent fashion, and thirdly that heparin inhibits the IFN-gamma-mediated induction of the tryptophan-degrading enzyme indoleamine 2,3-dioxygenase. In contrast to IFN-gamma-induced effects, the activity of other cytokines, such as interleukin (IL)-1, IL-2 and IL-6, is not influenced by heparin. The possible mechanism of heparin-induced inhibition of IFN-gamma is discussed.

Human indoleamine 2,3-dioxygenase inhibits Toxoplasma gondii growth in fibroblast cells.

Interferon-gamma (IFN-gamma) is known to inhibit the growth of Toxoplasma gondii both in vivo and in vitro. The IFN-gamma induced anti-toxoplasma activity in human cells is strongly correlated with the degradation of the essential amino acid L-tryptophan in vitro. Destruction of L-tryptophan is due to an increased activity of indoleamine 2,3-dioxygenase (IDO), which is transcriptionally activated by IFN-gamma. To determine if indoleamine 2,3-dioxygenase alone is sufficient to block the T. gondii growth, we transfected human fibroblast cells with an IDO cDNA expression plasmid using a metallothionein-inducible promoter. We showed that IDO mRNA and its enzymatic activity are inducible in fibroblast cells transfected with right-orientation IDO cDNA upon addition of CdCl2 to culture medium. The elevated IDO enzyme activity is strongly correlated with an inhibition of T. gondii growth. No IDO mRNA nor enzyme activity is induced by CdCl2 in reverse orientation transfected cells, and no adverse effects were observed on T. gondii growth in cells transfected with the reverse IDO-construct or in control parent cells with or without supplementation of CdCl2. Our observations along with the recent report by Habara-Ohkubo et al. (Infect. Immun. 61, 1810-1813, 1993) suggest that IFN-gamma-induced antitoxoplasma activity is due at least in part to the activation of IDO gene.

Reduction of hepatic phosphoenolpyruvate carboxykinase (PEPCK) activity by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is due to decreased mRNA levels.

We have previously shown that the rate of hepatic gluconeogenesis is reduced in TCDD-treated rats and that this decrease in carbohydrate production is associated with a dose-dependent reduction of the activity of PEPCK, the rate limiting enzyme of gluconeogenesis. This derailment of glucose metabolism has been suggested to be the critical lesion in acute TCDD toxicity. To further elucidate the mechanism of decreased PEPCK activity we performed Northern blot analyses using a cDNA probe complementary to a portion of the mRNA coding for PEPCK. We have demonstrated that 4 and 8 days after TCDD treatment (125 micrograms/kg, p.o.) liver PEPCK mRNA in Sprague-Dawley rats was decreased to very low levels as compared to vehicle-treated and pair-fed control animals. This decline of PEPCK mRNA was paralleled by decreased levels of PEPCK protein, as revealed by Western blot analyses and was accompanied by a reduction in the enzymatic activity of PEPCK. These results indicate that the decrease of PEPCK activity by TCDD is most likely the result of decreased expression of the PEPCK gene. These together with previous results also suggest that many of the physiological responses occurring in TCDD-treated animals (reduced feed intake, decreased insulin, increased corticosterone, increased glucagon and cAMP levels) which would normally stimulate PEPCK gene expression, are ineffective. Furthermore tryptophan 2,3-dioxygenase (TdO) activity, which is regulated in a very similar fashion to PEPCK activity, is also reduced after TCDD treatment, suggesting a common mechanism by which TCDD alters the regulation of these enzymes. P-450 1A1 mRNA and related EROD activity were maximally induced under the conditions of these experiments and represent a positive control for TCDD-related alterations of gene expression. However, because of differences in the dose-response characteristics of TCDD-induced reduction of PEPCK activity and induction of EROD activity an involvement of the Ah receptor in the reduction of PEPCK activity cannot be postulated.

Hydroquinone simultaneously induces indole amine 2,3 dioxygenase (IOD) and inhibits tyrosinase in Bufo melanostictus.

Hydroquinone administration in Bufo melanostictus causes an induction of indole amine 2,3-dioxygenase in skin and liver while simultaneously inhibiting tyrosinase in these organs. The result is discussed with the reports of higher urinary excretion of abnormal indole metabolites including derivatives of anthranilic acid in vitiliginous subjects (Roychoudhury and Chakraborty, Clinica. Chim. Acta 22, 298, 1968; Kurbanov and Berezov, Vopr. Med. Khim. 22, 683, 1976).

Differential induction of indoleamine-2,3-dioxygenase (IDO) by interferon-gamma in human gynecologic cancer cells.

Induction of indoleamine-2,3-dioxygenase (IDO) by interferon-gamma (IFN-gamma) is thought to be one mechanism underlying IFN-gamma's antineoplastic properties. Since clinical trials with IFN-gamma have yielded variable efficacy in treating cancers of gynecological origin, we tested the effects of IFN-gamma on cell growth and IDO activity in cell lines from seven gynecologic and five breast cancers. At a dose of 250 IU/ml, IFN-gamma suppressed cell growth and induced IDO activity in one cervical (C41), one vulva (A431), one breast (HS578T) and two ovarian (OVCAR-3, CAOV-3) cancer cell lines. Differing inhibition of cell growth, but with no induction of IDO activity, was found with IFN-gamma treatment of the other cell lines.

Involvement of lysosomes in substrate stabilization of tryptophan-2,3-dioxygenase in rat liver.

Administration of tryptophan or hydrocortisone to rats caused a several-fold increase in tryptophan-2,3-dioxygenase activity in the liver. Highly purified lysosomes were isolated from livers of tryptophan- or hydrocortisone-treated animals as well as the control rats. Immunoblotting of lysosomal proteins with anti-tryptophan-2,3-dioxygenase showed 48 kDa band, corresponding to the subunit molecular weight of the enzyme. The relative amount of the immuno-reactive substance in the lysosomes from hydrocortisone-treated rats was 3 times higher than the control while the value in the lysosomes from tryptophan-treated rats was essentially the same as in the control. These results indicate that administration of tryptophan renders cytosolic tryptophan-2,3-dioxygenase less vulnerable to lysosomal uptake and causes an accumulation of the enzyme in the cytosol.

Clinical and biologic effects of combination therapy with gamma-interferon and tumor necrosis factor.

Tumor necrosis factor (TNF) and gamma-interferon (gamma-IFN) are cytokines with synergistic biologic and antiproliferative effects in vitro and in mouse models. The biologic effects of the combination of TNF and gamma-IFN, however, have not been studied well in humans. A Phase I trial was conducted of TNF and gamma-IFN therapy in 24 patients with advanced malignancies to determine the tolerability of the combination and the biologic effects of TNF and gamma-IFN in vivo. Both TNF and gamma-IFN were administered as 30-minute intravenous infusions three times per week. Doses of TNF ranged from 25 to 100 micrograms/m2; all patients received 100 micrograms/m2 of gamma-IFN. Dose-limiting toxicity consisted primarily of orthostatic hypotension and constitutional symptoms. The maximum tolerated dose level (MTDL) of 50 micrograms/m2 of TNF and 100 micrograms/m2 of IFN-gamma was less than the maximum tolerated dose (MTD) observed in previous Phase I trials of gamma-IFN and TNF alone. Biologic responses were studied in seven patients treated at the MTDL. Serum interleukin-2 receptor levels and neopterin secretion were enhanced significantly 24 hours after therapy (P = 0.002); enhancement of monocyte Fc receptor levels had borderline statistical significance (P = 0.07). With the exception of the mean fluorescent intensity on monocytes positive for histocompatibility antigen HLA-DR (P = 0.03), HLA Class I and II cell surface protein expression was not increased. The combination significantly enhanced indoleamine dioxygenase activity and serum beta 2-microglobulin expression (P less than 0.04) but not 2',5'-oligoadenylate synthetase activity, bactericidal function, or chemiluminescence. These results were compared retrospectively with those observed in previous Phase I trials of gamma-IFN and TNF alone. The combination of TNF and gamma-IFN significantly increased urinary kynurenine levels more than either TNF alone or gamma-IFN alone. Given the limitations inherent in any retrospective analysis, however, the enhancement in the other biologic parameters measured at the MTDL during this trial did not differ significantly from the changes observed at the MTD of either TNF or gamma-IFN alone. It was concluded that the combination of TNF and gamma-IFN, when administered at the MTDL of the combination, does not offer any enhancement in biologic responses over either agent alone.

The effects of lofepramine and desmethylimipramine on tryptophan metabolism and disposition in the rat.

Acute and chronic administration of lofepramine and its major metabolite desmethylimipramine (DMI) to rats elevates brain tryptophan concentration, thereby enhancing cerebral 5-hydroxytryptamine (5-HT) synthesis, by increasing the availability of circulating tryptophan to the brain, secondarily to inhibition of liver tryptophan pyrrolase (tryptophan 2,3-dioxygenase, L-tryptophan:O2 oxidoreductase, decyclizing; EC 1.13.11.11) activity. The pyrrolase inhibition by lofepramine occurs independently of metabolism to DMI, because it can be demonstrated directly in vitro. Lofepramine also differs from DMI in its action profile on the above and related aspects of tryptophan metabolism and disposition. These results demonstrate that lofepramine influences tryptophan and 5-HT metabolism and disposition independently of its major metabolite DMI, and are discussed briefly in relation to the mechanism of action of antidepressants.

The effect of inhibitors of transcription and translation on basal and haem-induced tryptophan-2,3-dioxygenase activity in the rat liver.

The effect of actinomycin D and cycloheximide on basal tryptophan-2,3-dioxygenase (EC 1.13.11.11) activity in Wistar rat liver and on the enzyme activity induced by pretreatment with haemin was studied. Inhibition of either transcription or translation was accompanied by a reduction in tryptophan oxygenase activity, and this occurred more rapidly in the case of inhibition of translation. A 40% and 45% reduction in holoenzyme activity was found 2.5 and 6.5 h after introduction of cycloheximide and actinomycin D, respectively. Pretreatment with the antibiotics did not impair saturation of the apoenzyme by exogenous haem but haem induced tryptophan oxygenase activity was affected in various ways. Introduction of cycloheximide after haemin was accompanied by a rapid fall in the activity of both forms of the enzyme, but when transcription was inhibited under these conditions there was a subsequent increase in both holoenzyme activity and overall tryptophan oxygenase activity. The results support the concept that a regulatory pool of haem exists in hepatocytes and that haem is involved in both the activation and the degradation of tryptophan oxygenase.