Effects of mitochondria and o-methoxybenzoylalanine on 3-hydroxyanthranilic acid dioxygenase activity and quinolinic acid synthesis.
The use of o-methoxybenzoylalanine, a selective kynureninase inhibitor, has been proposed with the aim of reducing brain synthesis of quinolinic acid, an excitotoxic tryptophan metabolite. In liver homogenates, however, this compound caused unexpected accumulation of 3-hydroxyanthranilic acid, the product of kynureninase activity and the precursor of quinolinic acid. To explain this observation, we investigated the interaction(s) of o-methoxybenzoylalanine with 3-hydroxyanthranilic acid dioxygenase, the enzyme responsible for quinolinic acid formation. When the purified enzyme or partially purified cytosol preparations were used, o-methoxybenzoylalanine did not affect 3-hydroxyanthranilic acid dioxygenase activity. However, a significant reduction of this enzymatic activity did occur when o-methoxybenzoylalanine was tested in the presence of mitochondria. It is interesting that addition of purified mitochondria to 3-hydroxyanthranilic acid dioxygenase preparations reduced the enzymatic activity and the synthesis of quinolinic acid. In vivo, administration of o-methoxybenzoylalanine significantly reduced quinolinic acid synthesis and content in both blood and brain of mice. Our results suggest that mitochondrial protein(s) interact(s) with soluble 3-hydroxyanthranilic acid dioxygenase and cause(s) modifications in the enzyme resulting in a decrease in its activity. These modifications also allow the enzyme to interact with o-methoxybenzoylalanine, thus leading to a further reduction in quinolinic acid synthesis.
Chiarugi
A
A
Department of Preclinical and Clinical Pharmacology, University of Florence, Italy.
Moroni
F
F
D050561:3-Hydroxyanthranilate 3,4-Dioxygenase; D015095:3-Hydroxyanthranilic Acid / Q000378:metabolism; D000409:Alanine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D001921:Brain / Q000378:metabolism / Q000648:ultrastructure; D049308:Dioxygenases; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006867:Hydrolases / Q000037:antagonists & inhibitors / Q000378:metabolism; D066298:In Vitro Techniques; D007737:Kynurenine / Q000378:metabolism; D008099:Liver / Q000201:enzymology / Q000378:metabolism; D051379:Mice; D008928:Mitochondria / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D008930:Mitochondria, Liver / Q000201:enzymology / Q000378:metabolism; D016202:N-Methylaspartate / Q000378:metabolism; D010105:Oxygenases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D017378:Quinolinic Acid / Q000097:blood / Q000378:metabolism*
C095159:2-methoxybenzoylalanine; D004791:Enzyme Inhibitors; D015095:3-Hydroxyanthranilic Acid; D007737:Kynurenine; D016202:N-Methylaspartate; D010105:Oxygenases; D049308:Dioxygenases; D050561:3-Hydroxyanthranilate 3,4-Dioxygenase; D006867:Hydrolases; C021480:kynureninase; D017378:Quinolinic Acid; D000409:Alanine