Comparison of Clinically Used and Experimental Iron Chelators for Protection against Oxidative Stress-Induced Cellular Injury

Comparison of various iron chelators used in clinical practice as protecting agents against catecholamine-induced oxidative injury and cardiotoxicity

Catecholamines are stress hormones and sympathetic neurotransmitters essential for control of cardiac function and metabolism. However, pathologically increased catecholamine levels may be cardiotoxic by mechanism that includes iron-catalyzed formation of reactive oxygen species. In this study, five iron chelators used in clinical practice were examined for their potential to protect cardiomyoblast-derived cell line H9c2 from the oxidative stress and toxicity induced by catecholamines epinephrine and isoprenaline and their oxidation products. Hydroxamate iron chelator desferrioxamine (DFO) significantly reduced oxidation of catecholamines to more toxic products and abolished redox activity of the catecholamine-iron complex at pH 7.4. However, due to its hydrophilicity and large molecule, DFO was able to protects cells only at very high and clinically unachievable concentrations. Two newer chelators, deferiprone (L1) and deferasirox (ICL670A), showed much better protective potential and were effective at one or two orders of magnitude lower concentrations as compared to DFO that were within their clinically relevant plasma levels. Ethylenediaminetetraacetic acid (EDTA), dexrazoxane (ICRF-187, clinically approved cardioprotective agent against anthracycline-induced cardiotoxicity) as well as selected beta adrenoreceptor antagonists and calcium channel blockers exerted no effect. Hence, results of the present study indicate that small, lipophilic and iron-specific chelators L1 and ICL670A can provide significant protection against the oxidative stress and cardiomyocyte damage exerted by catecholamines and/or their reactive oxidation intermediates. This potential new application of the clinically approved drugs L1 and ICL670A warrants further investigation, preferably using more complex in vivo animal models.

Oxidative stress in sickle cell disease; pathophysiology and potential implications for disease management

Sickle cell disease (SCD) is a hemoglobinopathy characterized by hemolytic anemia, increased susceptibility to infections and vaso-occlusion leading to a reduced quality of life and life expectancy. Oxidative stress is an important feature of SCD and plays a significant role in the pathophysiology of hemolysis, vaso-occlusion and ensuing organ damage in sickle cell patients. Reactive oxygen species (ROS) and the (end-)products of their oxidative reactions are potential markers of disease severity and could be targets for antioxidant therapies. This review will summarize the role of ROS in SCD and their potential implication for SCD management.

Advances in iron chelation: an update

INTRODUCTION

Oxidative stress (caused by excess iron) can result in tissue damage, organ failure and finally death, unless treated by iron chelators. The causative factor in the etiology of a variety of disease states is the presence of iron-generated reactive oxygen species (ROS), which can result in cell damage or which can affect the signaling pathways involved in cell necrosis-apoptosis or organ fibrosis, cancer, neurodegeneration and cardiovascular, hepatic or renal dysfunctions. Iron chelators can reduce oxidative stress by the removal of iron from target tissues. Equally as important, removal of iron from the active site of enzymes that play key roles in various diseases can be of considerable benefit to the patients.

AREAS COVERED

This review focuses on iron chelators used as therapeutic agents. The importance of iron in oxidative damage is discussed, along with the three clinically approved iron chelators.

EXPERT OPINION

A number of iron chelators are used as approved therapeutic agents in the treatment of thalassemia major, asthma, fungal infections and cancer. However, as our knowledge about the biochemistry of iron and its role in etiologies of seemingly unrelated diseases increases, new applications of the approved iron chelators, as well as the development of new iron chelators, present challenging opportunities in the areas of drug discovery and development.

Iron chelation with salicylaldehyde isonicotinoyl hydrazone protects against catecholamine autoxidation and cardiotoxicity

Elevated catecholamine levels are known to induce damage of the cardiac tissue. This catecholamine cardiotoxicity may stem from their ability to undergo oxidative conversion to aminochromes and concomitant production of reactive oxygen species (ROS), which damage cardiomyocytes via the iron-catalyzed Fenton-type reaction. This suggests the possibility of cardioprotection by iron chelation. Our in vitro experiments have demonstrated a spontaneous decrease in the concentration of the catecholamines epinephrine and isoprenaline during their 24-h preincubation in buffered solution as well as their gradual conversion to oxidation products. These changes were significantly augmented by addition of iron ions and reduced by the iron-chelating agent salicylaldehyde isonicotinoyl hydrazone (SIH). Oxidized catecholamines were shown to form complexes with iron that had significant redox activity, which could be suppressed by SIH. Experiments using the H9c2 cardiomyoblast cell line revealed higher cytotoxicity of oxidized catecholamines than of the parent compounds, apparently through the induction of caspase-independent cell death, whereas co-incubation of cells with SIH was able to significantly preserve cell viability. A significant increase in intracellular ROS formation was observed after the incubation of cells with catecholamine oxidation products; this could be significantly reduced by SIH. In contrast, parent catecholamines did not increase, but rather decreased, cellular ROS production. Hence, our results demonstrate an important role for redox-active iron in catecholamine autoxidation and subsequent toxicity. The iron chelator SIH has shown considerable potential to protect cardiac cells by both inhibition of deleterious catecholamine oxidation to reactive intermediates and prevention of ROS-mediated cardiotoxicity.

Synthesis and initial in vitro evaluations of novel antioxidant aroylhydrazone iron chelators with increased stability against plasma hydrolysis

Oxidative stress is known to contribute to a number of cardiovascular pathologies. Free intracellular iron ions participate in the Fenton reaction and therefore substantially contribute to the formation of highly toxic hydroxyl radicals and cellular injury. Earlier work on the intracellular iron chelator salicylaldehyde isonicotinoyl hydrazone (SIH) has demonstrated its considerable promise as an agent to protect the heart against oxidative injury both in vitro and in vivo. However, the major limitation of SIH is represented by its labile hydrazone bond that makes it prone to plasma hydrolysis. Hence, in order to improve the hydrazone bond stability, nine compounds were prepared by a substitution of salicylaldehyde by the respective methyl- and ethylketone with various electron donors or acceptors in the phenyl ring. All the synthesized aroylhydrazones displayed significant iron-chelating activities and eight chelators showed significantly higher stability in rabbit plasma than SIH. Furthermore, some of these chelators were observed to possess higher cytoprotective activities against oxidative injury and/or lower toxicity as compared to SIH. The results of the present study therefore indicate the possible applicability of several of these novel agents in the prevention and/or treatment of cardiovascular disorders with a known (or presumed) role of oxidative stress. In particular, the methylketone HAPI and nitro group-containing NHAPI merit further in vivo investigations.