Received for publication March 6, 2008.
Revised April 18, 2008.
Accepted for publication April 18, 2008.

Protection Against Hydrogen Peroxide-Mediated Cytotoxicity in Friedreich's Ataxia Fibroblasts using Novel Iron Chelators of the PCIH Class

Abstract

Iron (Fe)-loading diseases remain an important problem due to the toxicity of Fe-catalyzed redox reactions. Iron-loading occurs in the mitochondria of Friedreich's ataxia (FA) patients and may play a role in its pathogenesis. This suggests that Fe chelation therapy could be useful. Previously, we developed lipophilic Fe chelators known as the 2-pyridylcarboxaldehyde isonicotinoyl hydrazone (PCIH) ligands and identified 2-pyridylcarboxaldehyde 2-thiophenecarboxyl hydrazone (PCTH) as the most promising analog. Hence, this study assessed the efficacy of PCTH and other PCIH analogs in comparison to various chelators including deferiprone and desferrioxamine (DFO). Age- and sex-matched control and FA fibroblasts were pre-incubated with Fe chelators and subsequently challenged with hydrogen peroxide (H₂O₂; 50 µM) for up to 24 h. The current study demonstrates an interesting structure-activity relationship amongst the closely related PCIH series of ligands, with only PCTH being highly effective at preventing H₂O₂-induced cytotoxicity. PCTH increased FA fibroblast cell viability by up to 70%, while DFO rescued viability by 1-5% only. Hence, PCTH, which was well-tolerated by cells was far more effective than DFO at preventing oxidative stress. Significantly, kinetic studies demonstrated that PCTH rapidly penetrated cells to induce ⁵⁹Fe efflux, while DFO, PCIH, PCBH and PCBBH were far slower, indicating it is the rate of chelator permeation that is crucial for protection against H₂O₂. Additionally, PCTH was found to be as, or more effective, than classical radical scavengers or the clinically-trialed anti-oxidant, idebenone, at protecting cells against H₂O₂-mediated cytotoxicity. These findings further indicate the potential of PCTH for treatment of Fe-overload.

Key words: Structure-activity relationships and modeling, Metals and chelators, Oxidative stress/antioxidants