Binding of iron and inhibition of iron-dependent oxidative cell injury by the "calcium chelator" 1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid (BAPTA).
A role for increases in intracellular calcium (Ca2+) has been suggested in the pathophysiology of various forms of oxidant-mediated cell injury. In recent studies, we found that iron bound to the Pseudomonas aeruginosa siderophore, pyochelin, augments oxidant-mediated endothelial cell injury by catalyzing the formation of hydroxyl radical (HO.). To investigate the role of Ca2+ in this process, the effects of two Ca2+ chelating agents, Fura-2 and 1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid (BAPTA), were assessed. BAPTA, but not Fura-2, was protective against H2O2/ferripyochelin-mediated injury. Subsequent data suggested that chelation of iron rather than Ca2+ by BAPTA was most likely responsible. Spectrophotometry demonstrated that both ferrous (Fe2+) and ferric (Fe3+) iron formed a complex with BAPTA. The affinity of BAPTA for the metals was Fe3+ > Ca2+ > Fe2+. BAPTA was found to decrease markedly iron-catalyzed production of HO. and/or ferryl species when analyzed by spin trapping. Although our results do not definitively prove that BAPTA protects endothelial cells from ferripyochelin-associated damage by chelating iron, these data indicate that caution must be exercised in utilizing protective effects of intracellular "Ca2+ chelating agents" as evidence for a role of alterations in cellular Ca2+ levels in experimental conditions in which iron-mediated oxidant production is also occurring.
Britigan
B E
BE
Research Service, VA Medical Center, Iowa City, IA 52246, USA. bradley-britigan@uiowa.edu
Rasmussen
G T
GT
Cox
C D
CD
D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D002614:Chelating Agents / Q000494:pharmacology*; D004533:Egtazic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D004730:Endothelium, Vascular / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D017665:Hydroxyl Radical; D007501:Iron / Q000378:metabolism*; D018384:Oxidative Stress; D010636:Phenols / Q000494:pharmacology; D013113:Spin Labels
D002614:Chelating Agents; D010636:Phenols; D013113:Spin Labels; C025315:ferripyochelin; D017665:Hydroxyl Radical; D004533:Egtazic Acid; D007501:Iron; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium