Inhibition by interferon-gamma of human mononuclear cell-mediated low density lipoprotein oxidation. Participation of tryptophan metabolism along the kynurenine pathway.

Abstract

In this study we examined the potential inhibition by interferon-y (IFN'y) of the early stages of low density lipoprotein (LDL) oxidation mediated by human peripheral blood mononuclear cells (PBMC) and monocyte-derived macrophages (NMDMN) in Ham's F-10 medium supplemented with physiological amounts of L-tryptophan (Trp). We assessed LDL oxidation by measuring the consumption of LDL's major antioxidant (i.e., a-tocopherol) and targets for oxidation (cholesteryllinoleate and cholesterylarachidonate), together with the accumulation of cholesterylester hydroperoxides and the increase in relative electrophoretic mobility of the lipoprotein particle. Exposure of PBMC or MDM to IFNy induced the degradation of extracellular Trp with concomitant accumulation of kynurenine, anthranilic and 3-hydroxyanthranilic acid (3HAA) in the culture medium. Formation of 3HAA, but neither Trp degradation nor formation ofkynurenine and anthranilic acid, was inhibited by low amounts of diphenylene iodonium (DPI) in a concentration-dependent manner. In contrast to oxidative Trp metabolism, exposure of human PBMC or MDM to IFN-y failed to induce degradation ofarginine, and nitrite was not detected in the cell supernatant, indicating that nitric oxide synthase was not induced under these conditions. Incubation of LDL in Trpsupplemented F-10 medium resulted in a time-dependent oxidation of the lipoprotein that was accelerated in the presence of PBMC or MDM but inhibited strongly in the presence of both cells and IFNy, i.e., when Trp degradation and formation of 3HAA were induced. In contrast, when IFNy was added to PBMC or MDM in F-10 medium that was virtually devoid of Trp, inhibition of cell-accelerated LDL oxidation was not observed. Exogenous 3HAA added to PBMC or purified monocytes in the absence of IFNy also strongly and in a concentration-dependent manner inhibited LDL oxidation. Selective inhibition of IFNy-induced formation of 3HAA by DPI caused reversion of the inhibitory action of this cytokiine on both PBMC-and MDM-mediated LDL oxidation. These results show that IFN'y treatment of human PBMC or MDM in vitro attenuates the extent of LDL oxidation caused by these cells,

Cytochrome b5, Not Superoxide Anion Radical, Is a Major Reductant of Indoleamine 2,3-Dioxygenase in Human Cells

“…7B, such treatment did not decrease IDO activity. Similar results were observed with rhIFN␥-primed human monocyte-derived macrophages (data not shown) and peripheral blood mononuclear cells (18), where diphenyleneiodonium at concentrations up to 20 M did not modulate IDO activity.…”

“…to reductively activate purified rabbit IDO such that L-Trp and O 2 can bind tightly (9). Furthermore, using 18 O 2 -labeled potassium superoxide, these authors showed O 2 .…”

Laccase‐mediated formation of the phenoxazinone derivative, cinnabarinic acid

“…Laccase and ceruloplasmin have previously been shown to oxidize many of the same substrates [22]. Because 3-HAA oxidation has been reported to play an important physiological role in mammals [1,5], we tested the ability of ceruloplasmin to catalyze CA formation. Oxidation of 3-HAA by ceruloplasmin was slower than for the laccase-mediated reaction.…”

“…The conversion of 3-HAA to CA has received considerable attention in clinical studies because 3-HAA is produced in relatively large amounts by interferon-y-primed mononuclear phagocytes [5] and has been shown to act as a powerful scavenger of reactive oxygen species [1]. CA is one of the major products of the peroxyl radical-mediated oxidation of 3-HAA suggested to prevent oxidative damage in mammalian tissues [6].…”

Thematic review series: The Immune System and Atherogenesis. Cytokine regulation of macrophage functions in atherogenesis

“…Oxidation of LDL by cultured mouse peritoneal macrophages, as defined by the content of thiobarbituric acid-reacting substances, is decreased by incubating cells with interferon (IFN)-␥ (15). One potential mechanism of IFN-␥ -induced reduction of LDL oxidation is an acceleration of extracellular tryptophan degradation (16). Several reports have demonstrated a role of IFN-␥ via a lipoxygenase pathway that is also thought to involve oxidation (17).…”