IDO1 (indoleamine 2,3-dioxygenase 1) is a member of a unique class of mammalian haem dioxygenases that catalyse the oxidative catabolism of the least-abundant essential amino acid, L-Trp (L-tryptophan), along the kynurenine pathway. Significant increases in knowledge have been recently gained with respect to understanding the fundamental biochemistry of IDO1 including its catalytic reaction mechanism, the scope of enzyme reactions it catalyses, the biochemical mechanisms controlling IDO1 expression and enzyme activity, and the discovery of enzyme inhibitors. Major advances in understanding the roles of IDO1 in physiology and disease have also been realised. IDO1 is recognised as a prominent immune regulatory enzyme capable of modulating immune cell activation status and phenotype via several molecular mechanisms including enzyme-dependent deprivation of L-Trp and its conversion into the aryl hydrocarbon receptor ligand kynurenine and other bioactive kynurenine pathway metabolites, or non-enzymatic cell signalling actions involving tyrosine phosphorylation of IDO1. Through these different modes of biochemical signalling, IDO1 regulates certain physiological functions (e.g. pregnancy) and modulates the pathogenesis and severity of diverse conditions including chronic inflammation, infectious disease, allergic and autoimmune disorders, transplantation, neuropathology and cancer. In the present review, we detail the current understanding of IDO1's catalytic actions and the biochemical mechanisms regulating IDO1 expression and activity. We also discuss the biological functions of IDO1 with a focus on the enzyme's immune-modulatory function, its medical implications in diverse pathological settings and its utility as a therapeutic target.

Indoleamine 2,3-dioxygenase is a heme enzyme that catalyzes the oxidative degradation of L-Trp and other indoleamines. We have used resonance Raman spectroscopy to characterize the heme environment of purified recombinant human indoleamine 2,3-dioxygenase (hIDO). In the absence of L-Trp, the spectrum of the Fe

The 'oxidation theory' of atherosclerosis proposes that oxidation of low density lipoprotein (LDL) contributes to atherogenesis. Although little direct evidence for a causative role of 'oxidized LDL' in atherogenesis exists, several studies show that, in vitro, oxidized LDL exhibits potentially proatherogenic activities and lipoproteins isolated from atherosclerotic lesions are oxidized. As a consequence, the molecular mechanisms of LDL oxidation and the actions of alpha-tocopherol (alpha-TOH, vitamin E), the major lipid-soluble lipoprotein antioxidant, have been studied in detail. Based on the known antioxidant action of alpha-TOH and epidemiological evidence, vitamin E is generally considered to be beneficial in coronary artery disease. However, intervention studies overall show a null effect of vitamin E on atherosclerosis. This confounding outcome can be rationalized by the recently discovered diverse role for alpha-TOH in lipoprotein oxidation; that is, alpha-TOH displays neutral, anti-, or, indeed, pro-oxidant activity under various conditions. This review describes the latter, novel action of alpha-TOH, termed tocopherol-mediated peroxidation, and discusses the benefits of vitamin E supplementation alone or together with other antioxidants that work in concert with alpha-TOH in ameliorating lipoprotein lipid peroxidation in the artery wall and, hence, atherosclerosis.

Indoleamine 2,3-dioxygenase (IDO) 4 is an intracellular heme enzyme that catalyzes the initial and rate-limiting step of L-tryptophan (L-Trp) metabolism along the kynurenine pathway (reviewed in Refs.1-4). IDO catalyzes the oxidative cleavage of the pyrrole ring of L-Trp by insertion of molecular oxygen (O 2 ) to generate N-formyl-kynurenine, which is hydrolyzed to kynurenine and formate (Fig.

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Abstract-Oxidation of low-density lipoproteins (LDL) is a key process in atherogenesis, and vitamin E (␣-tocopherol, TOH) has received attention for its potential to attenuate the disease. Despite this, the type and extent of TOH oxidation and its relationship to lipid oxidation in the vessel wall where lesions develop remain unknown. Therefore, we measured oxidized lipids, TOH, and its oxidation products, ␣-tocopherylquinone (TQ), 2,3-and 5,6-epoxy-␣-tocopherylquinones by gas chromatography-mass spectrometry analysis in human lesions representing different stages of atherosclerosis. We also oxidized LDL in vitro to establish "footprints" of TOH oxidation product for different oxidants. The in vitro studies demonstrated that tocopherylquinone epoxides are the major products when LDL is exposed to the one-electron (ie, radical) oxidants, peroxyl radicals, and copper ions, whereas TQ preferentially accumulates with the two-electron (nonradical) oxidants, hypochlorite, and peroxynitrite. In human lesions, the relative extent of TOH oxidation was maximal early in the disease where it exceeded lipid oxidation. Independent of the disease stage, TQ was always the major oxidation product with all products together representing Ͻ20% of the total TOH present, and the oxidation product profile mirroring that formed during LDL oxidation by activated monocytes in the presence of nitrite. In contrast, oxidized lipid increased with increasing disease severity. These results suggest that two-electron oxidants are primarily responsible for TOH oxidation in the artery wall, and that the extent of TOH oxidation is limited yet substantial lipid oxidation takes place. This study may have important implications regarding antioxidant supplements aimed at preventing LDL oxidation and hence atherogenesis. Key Words: tocopherol Ⅲ LDL oxidation Ⅲ atherogenesis Ⅲ hypochlorous acid T he oxidation of low-density lipoproteins (LDL) in the artery wall is considered to be a key contributor to atherogenesis. 1 In support of this, a wide variety of markers of oxidized lipid and protein have been detected in human atherosclerotic lesions, including F 2 -isoprostanes, 2 cholesteryl ester hydro(pero)xides (CE-O(O)H), 3,4 and chloroand nitrotyrosine. 5,6 The exact identity of the oxidant(s) responsible for LDL oxidation in vivo remains undetermined although several oxidants have been implicated, including transition metals, 15-lipoxygenase, myeloperoxidasegenerated hypochlorous acid (HOCl), and reactive nitrogen species such as peroxynitrite (ONOO Ϫ ). 7 Antioxidants are potential antiatherogenic agents because they can inhibit LDL oxidation. Most attention has focused on vitamin E (␣-tocopherol, TOH), as it is the major lipid-soluble antioxidant in LDL, yet the outcome of interventions with TOH supplements has been overall disappointing. 8 Also, in vitro mechanistic studies have revealed a complex role for TOH during lipoprotein lipid oxidation. Thus, in the absence of compounds capable of reducing the ␣-tocopheroxyl radical (TO·) and exporting the...

The heme enzyme indoleamine 2,3-dioxygenase (IDO) plays an important immune regulatory role by catalyzing the oxidative degradation of l-tryptophan. Here we show that the selenezal drug ebselen is a potent IDO inhibitor. Exposure of human macrophages to ebselen inhibited IDO activity in a manner independent of changes in protein expression. Ebselen inhibited the activity of recombinant human IDO (rIDO) with an apparent inhibition constant of 94 +/- 17 nM. Optical and resonance Raman spectroscopy showed that ebselen altered the active site heme of rIDO by inducing a transition of the ferric heme iron from the predominantly high- to low-spin form and by lowering the vibrational frequency of the Fe-CO stretch of the CO complex, indicating an opening of the distal heme pocket. Substrate binding studies showed that ebselen enhanced nonproductive l-tryptophan binding, while circular dichroism indicated that the drug reduced the helical content and protein stability of rIDO. Thiol labeling and mass spectrometry revealed that ebselen reacted with multiple cysteine residues of IDO. Removal of cysteine-bound ebselen with dithiothreitol reversed the effects of the drug on the heme environment and significantly restored enzyme activity. These findings indicate that ebselen inhibits IDO activity by reacting with the enzyme's cysteine residues that result in changes to protein conformation and active site heme, leading to an increase in the level of nonproductive substrate binding. This study highlights that modification of cysteine residues is a novel and effective means of inhibiting IDO activity. It also suggests that IDO is under redox control and that the enzyme represents a previously unrecognized in vivo target of ebselen.

Rate coefficients for reaction and for rotational energy transfer in collisions between CN in selected rotational levels ( X Σ + 2 , v = 2 , N = 0 , 1, 6, 10, 15, and 20) and C 2 H 2The dynamics of the reaction H 2 COϩh(Ϸ330 nm͒→HϩHCO have been studied following excitation of formaldehyde into the Ã( 1 A 2 ) state, just above the dissociation threshold of the X( 1 A 1 ) state. Formaldehyde was excited via specific J, K a , K c rotational states and the ensuing rotational distribution of HCO measured by fully resolving N, K a , K c , and JϭNϮS of the fragment. When only the N and K a quantum numbers of both formaldehyde and the formyl radical are considered, the distributions are generally modeled well by phase space theory ͑PST͒. Within Ϸ10 cm Ϫ1 of the threshold, however, the PST predictions consistently exceed the experimental populations. This was accounted for by the inclusion of a centrifugal barrier in the PST model. The attractive part of the effective centrifugal potential was modeled by a dipole-induced dipole plus dispersion interaction. The barrier is weak and long range ͑Ͼ5 Å͒. Resolution of K c in the reaction, in both parent and product, gave large deviations from the PST model. The HCO population distributions separate according to whether K c was the upper-or lower-energy state. Additionally, the upper/lower preference was sensitive to the choice of K c in the parent. Insufficient data are currently available to quantify this observation. The product state distribution was also found to be independent of the spin-rotation state of HCO.