3-Hydroxyanthranilic Acid Is an Efficient, Cell-derived Co-antioxidant for α-Tocopherol, Inhibiting Human Low Density Lipoprotein and Plasma Lipid Peroxidation

Abstract

␣-Tocopherol (␣-TOH) can promote lipid peroxidation in human low density lipoprotein (LDL) unless co-antioxidants are present that eliminate the chain-carrying ␣-tocopheroxyl radical (␣-TO ⅐ ) (Bowry, V. W., Mohr, D., Cleary, J., and Stocker, R. (1995) J. Biol. Chem. 270, 5756 -5763). Interferon-␥ inhibits human monocyte/ macrophage-facilitated LDL lipid peroxidation via induction of cellular tryptophan degradation and production and release of 3-hydroxyanthranilic acid (3HAA) (Christen, S., Thomas, S. R., Garner, B., and Stocker, R. (1994) J. Clin. Invest. 93, 2149 -2158). We now report on the mechanism of antioxidant action of 3HAA. 3HAA directly reduced ␣-TO ⅐ in UV-exposed micellar dispersions of ␣-TOH or in LDL incubated with soybean 15-lipoxygenase (SLO), as assessed by electron paramagnetic resonance spectroscopy. 3HAA did not inhibit SLO enzyme activity. Anthranilic acid, which lacks the phenoxyl group, was incapable of reducing ␣-TO ⅐ . 3HAA dose-dependently inhibited the peroxidation of surface phospholipids and core cholesteryl esters in LDL exposed to SLO, peroxyl radicals (ROO ⅐ ), or Cu 2؉ ; oxidants that convert ␣-TOH to ␣-TO ⅐ . In all cases, sparing of LDL's ␣-TOH, but not ubiquinol-10 (CoQ 10 H 2 ), was observed until the majority of 3HAA was consumed. Addition of 3HAA or ascorbate prevented further consumption of ␣-TOH and accumulation of lipid hydroperoxides when added to aqueous or lipophilic ROO ⅐ -oxidizing LDL after complete and partial consumption of CoQ 10 H 2 and ␣-TOH, respectively. In contrast, addition of urate, an efficient ROO ⅐ scavenger incapable of scavenging ␣-TO ⅐ , did not efficiently inhibit ongoing lipid peroxidation. Oxidation of 3HAA-supplemented human plasma by aqueous ROO ⅐ resulted in the successive consumption of ascorbate, CoQ 10 H 2 , 3HAA, bilirubin, ␣-TOH, and urate. Lipid peroxidation was prevented as long as ascorbate, CoQ 10 H 2 , and 3HAA were present, but subsequently proceeded as a free-radical chain reaction concomitant with ␣-TOH, bilirubin, and urate consumption. Addition of 3HAA to aqueous ROO ⅐ -oxidizing plasma, after complete consumption of ascorbate and CoQ 10 H 2 , strongly inhibited ongoing lipid peroxidation and consumption of ␣-TOH, bilirubin, and urate immediately and as efficiently as did ascorbate. These findings demonstrate that 3HAA is a highly efficient co-antioxidant for plasma lipid peroxidation by virtue of its ability to interact with ␣-TO ⅐ in lipoproteins. Since interferon-␥ is the principal inducer of tryptophan degradation and release of 3HAA by monocytes/macrophages, this may represent a localized extracellular antioxidant defense against LDL oxidation in inflammation.

Role of indoleamine 2,3-dioxygenase in health and disease

“…Our subsequent studies reported that 3-HAA is an efficient antioxidant capable of inhibiting LDL oxidation induced by a variety of oxidants, involving the ability of 3-HAA to scavenge oxidants (e.g. peroxynitrite) or act as a co-antioxidant, referring to its ability to efficiently reduce the vitamin E radical, ensuring the reduced and antioxidant form of vitamin E is maintained within LDL [345,346].…”

Role of Oxidative Modifications in Atherosclerosis

“…Most studies of LDL lipid peroxidation in vitro utilize lipoproteins removed from native environments, although it is now recognized that such environs play an important role in the antioxidant function of vitamin E. For example, a number of endogenous reducing agents, termed "coantioxidants," can impede the pro-oxidant activity of ␣-TOH (79,666,949,1059). As depicted in Figure 9, coantioxidants (denoted as XH) reduce the ␣-TO⅐ and eliminate the radical character from the LDL particle, thereby inhibiting tocopherol-mediated peroxidation.…”

Implications for the Kynurenine Pathway and Quinolinic Acid in Amyotrophic Lateral Sclerosis

“…3-Hydroxyanthranilic acid (3-HAA) is a further KP product that is a potent free radical scavenger [103] , which may have some neuroprotective effects. In IFN-␥ -stimulated macrophages, 3-HAA inhibits peroxidation of LDL by acting in synergy with ␣ -tocopherol [104] . It remains to be seen whether enough 3-HAA is produced in vivo to have these benefi cial effects.…”