Cardioprotective Potential of Iron Chelators and Prochelators

Heart is a particularly sensitive organ to iron overload and cardiomyopathy due to the excessive cardiac iron deposition causes most deaths in disorders such as beta-thalassemia major. Free or loosely bound iron ions readily cycle between ferrous and ferric states and catalyze Haber-Weiss reaction that yields highly reactive and toxic hydroxyl radicals. Treatment with iron chelators (desferrioxamine, deferiprone, and deferasirox) substantially improved cardiovascular morbidity and mortality in iron overloaded patients. Furthermore, iron chelators have been studied in various cardiovascular disorders with known or presumed oxidative stress roles (e.g., ischemia/reperfusion injury) also in patients with normal body iron contents. The pharmacodynamic and pharmacokinetic properties of these chelators are critical for effective therapy. For example, the widely clinically used but hydrophilic chelator desferrioxamine suffers from poor plasma membrane permeability, which means that high and clinically unachievable concentrations/doses must be employed to obtain cardioprotection. Therefore, small-molecular and lipophilic chelators with oral availability are more suitable for this purpose, particularly in states without systemic iron overload. Apart from agents that are already used in clinical practice, aroylhydrazone iron chelators, namely salicylaldehyde isonicotinoyl hydrazone (SIH), have provided promising results. However, the use of classical iron-chelating agents is associated with a risk of toxicity due to indiscriminate iron depletion. Recent studies have therefore focused on "masked" prochelators that have little or no affinity for iron until site-specific activation by reactive oxygen species.