RESUMO
A new series of iron chelators designed to protect tissues against iron-catalysed oxidative damage is described. These compounds are aminocarboxylate derivatives bearing pendant aromatic groups. They were designed to have a relatively low affinity for both ferrous and ferric iron and to be site-specifically oxidizable by hydrogen peroxide through intramolecular aromatic hydroxylation into species with strong iron binding capacity which do not catalyse hydroxyl radical formation. Thus, at the cellular level, oxidative injury is used to convert weak iron chelators into strong iron chelators in order to promote cell survival. The purpose of this local activation process is to minimise toxicity compared to strong iron chelators which may interfere with normal iron metabolism. Compounds within this series were evaluated in vitro in view of their capacity to undergo intramolecular hydroxylation and to protect cultured cells against oxidative injury. Results show that the intramolecular aromatic hydroxylation capacity is critically dependent upon the amino carboxylate chelating moieties and the substituents of the aromatic rings. Cell protection against oxidative injury is only observed with compounds possessing sufficient lipophilicity. The monohydroxylation product of N,N'-dibenzylethylenediamine N,N'-diacetic acid, protects cells against both H2O2 and tBuOOH toxicity with IC50's of 12 and 60 microM, respectively, in agreement with the oxidative activation concept. These results represent the first step toward the development of a new strategy to safe iron chelation for the prevention of oxidative damage.
Assuntos
Quelantes de Ferro/farmacologia , Estresse Oxidativo/efeitos dos fármacos , Ácido Ascórbico/química , Morte Celular , Estabilidade de Medicamentos , Compostos Férricos/química , Compostos Ferrosos/química , Radicais Livres , Humanos , Peróxido de Hidrogênio/química , Hidroxilação , Quelantes de Ferro/química , Modelos Moleculares , Oxirredução , Espectrofotometria , Relação Estrutura-Atividade , Células U937RESUMO
N,N'-bis-(3,4,5-trimethoxybenzyl) ethylenediamine N,N,-diacetic acid dihydrochloride (OR10141) is a member of a recently described series of "oxidative stress activatable iron chelators." These chelators have a relatively low affinity for iron but can be site-specifically oxidized, in situations mimicking oxidative stress in vitro, into species with strong iron-binding capacity. It is hoped that this local activation process will minimise toxicity compared to strong iron chelators that may interfere with iron metabolism. The present paper describes the results of experiments aimed at characterising oxidative reactions between iron-OR10141 complexes and hydrogen peroxide. Incubation of ascorbate and hydrogen peroxide with the ferric chelate of OR10141 in neutral aqueous solution yields a purple solution with a chromophore at 560 nm, which is consistent with an o-hydroxylation of one of the trimethoxybenzyl rings. Oxidation of OR10141 also takes place, although more slowly, by incubating hydrogen peroxide with ferric OR10141 complex in the absence of reductant. HPLC analysis shows that OR10141 is consumed during the reaction and transformed principally into N-(2-hydroxy 3,4,5-trimethoxybenzyl) N'-(3,4,5-trimethoxybenzyl) ethylenediamine N,N'-diacetic acid. Minor products are also formed, some of which were identified by mass spectrometry. The protective effect of OR10141 in vitro against DNA single strand breaks, protein damage, and lipid peroxidation induced by Fenton chemistry suggests that this compound is able to compete for iron with biological molecules and, thus, that this strategy of protection against oxidative stress is feasible. In addition, preliminary results showing protective effects of OR10141 dimethyl ester against toxicity induced by hydrogen peroxide in cell culture are described. It is concluded that OR10141 and related prodrugs might be useful in vivo in chronic situations involving oxidative stress.