title: Pyridoxal isonicotinoyl hydrazone inhibits iron-induced ascorbate oxidation and ascorbyl radical formation.
abstract: Previous work from our laboratory demonstrated that pyridoxal isonicotinoyl hydrazone (PIH) has in vitro antioxidant activity against iron plus ascorbate-induced 2-deoxyribose degradation due to its ability to chelate iron; the resulting Fe(III)-PIH(2) complex is supposedly unable to catalyze oxyradical formation. A putative step in the antioxidant action of PIH is the inhibition of Fe(III)-mediated ascorbate oxidation, which yields the Fenton reagent Fe(II) [Biochim. Biophys. Acta 1523 (2000) 154]. In this work, we demonstrate that PIH inhibits Fe(III)-EDTA-mediated ascorbate oxidation (measured at 265 nm) and the formation of ascorbyl radical (in electron paramagnetic resonance (EPR) studies). The efficiency of PIH against ascorbate oxidation, ascorbyl radical formation and 2-deoxyribose degradation was dose dependent and directly proportional to the period of preincubation of PIH with Fe(III)-EDTA. The efficiency of PIH in inhibiting ascorbate oxidation and ascorbyl radical formation was also inversely proportional to the Fe(III)-EDTA concentration in the media. When EDTA was replaced by the weaker iron ligand nitrilotriacetic acid (NTA), PIH was much more effective in preventing ascorbate oxidation, ascorbyl radical formation and 2-deoxyribose degradation. Moreover, the replacement of EDTA with citrate, a physiological chelator with a low affinity for iron, also resulted in PIH having a higher efficiency in inhibiting iron-mediated ascorbate oxidation and 2-deoxyribose degradation. These results demonstrate that PIH removes iron from EDTA (or from either NTA or citrate), forming an iron-PIH complex that cannot induce ascorbate oxidation effectively, thus inhibiting iron-mediated oxyradical formation. These results are of pharmacological relevance because PIH has been considered for experimental chelating therapy in iron-overload diseases.
authors.affiliation: Oxyradical Research Group, Departamento de Biologia Celular, Universidade de Brasília, Brazil.
authors.forename: Angelo Q
authors.initials: AQ
authors.lastname: Maurício
authors.forename: George K B
authors.initials: GK
authors.lastname: Lopes
authors.forename: Cezar S
authors.initials: CS
authors.lastname: Gomes
authors.forename: Ricardo G
authors.initials: RG
authors.lastname: Oliveira
authors.forename: Antonio
authors.initials: A
authors.lastname: Alonso
authors.forename: Marcelo
authors.initials: M
authors.lastname: Hermes-Lima
mesh_terms: D001205:Ascorbic Acid / Q000737:chemistry*; D002614:Chelating Agents / Q000494:pharmacology*; D003855:Deoxyribose / Q000737:chemistry; D004492:Edetic Acid / Q000037:antagonists & inhibitors; D004578:Electron Spin Resonance Spectroscopy; D005290:Ferric Compounds / Q000037:antagonists & inhibitors*; D005609:Free Radicals / Q000737:chemistry; D017665:Hydroxyl Radical / Q000737:chemistry; D007538:Isoniazid / Q000031:analogs & derivatives* / Q000494:pharmacology*; D009571:Nitrilotriacetic Acid / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors; D010084:Oxidation-Reduction / Q000187:drug effects; D018384:Oxidative Stress; D011730:Pyridoxal / Q000031:analogs & derivatives* / Q000494:pharmacology*
chemical_list: D002614:Chelating Agents; D005290:Ferric Compounds; D005609:Free Radicals; D017665:Hydroxyl Radical; D011730:Pyridoxal; D003855:Deoxyribose; C025314:ferric citrate; C021079:pyridoxal isonicotinoyl hydrazone; D004492:Edetic Acid; D009571:Nitrilotriacetic Acid; C019179:Fe(III)-EDTA; D001205:Ascorbic Acid; D007538:Isoniazid; C020326:ferric nitrilotriacetate