title: Cardiac tissue iron: effects on post-ischemic function and free radical production, and its possible role during preconditioning.
abstract: We determined whether prior treatment of rats (study 1) with subthreshold doses of iron (no evidence of cardiac tissue overload), or in vitro ischemic pre-conditioning (IP: 5 min. Ischemia (I)/5 min. Reperfusion (R) x 2 cycles) of hearts from untreated rats (study 2), can modulate redox-active cardiac tissue iron levels or distribution, leading to alterations in post-ischemic lipid peroxidation-derived free radical (FR) production and severity of reperfusion injury. In study 1, rats received biweekly i.p. injections of 0 (saline=S), 3, 6, or 12 mg FeCl3/ml for 3-wks prior to imposing 30 min. I/15 min. R in vitro. The highest dose caused no elevations in plasma or heart tissue Fe levels, but did further reduce post-ischemic recoveries of left ventricular developed pressure (17% lower), cardiac work (57%) and output (54%), and increased effluent lipid hydroperoxides (2.1-fold) compared to the S-group. Post-ischemic FR production was assessed in toluene-extracted effluent by ESR spectroscopy and alpha-phenyl-N-tert butylnitrone (PBN=2.5 mM perfusate) spin trapping. PBN/alkoxyl (alphaH=1.90 G, alphaN=13.63 G) was the dominant signal detected in all groups; however, Fe-treated groups displayed significant dose-dependent increases in total alkoxyl content (3, 6, 12 mg/ml: 1.8-, 2.3-, 2.7-fold higher) compared to the S-group. These data suggest that even mild, non-overloading doses of iron can be functionally and oxidatively detrimental to hearts when an I/R stress is imposed. In study 2, isolated hearts from untreated rats were exposed to two-IP cycles: during IP, total effluent iron content (atomic absorption) increased 11.4-fold compared to control and analysis of cardiovascular tissue iron distribution (X-ray microanalysis) suggested that iron loss from capillary endothelium was far greater than from tissue myocytes. Moreover, iron-catalyzed production of alkoxyl radicals following severe I/R stress (40 min. I/15 min. R) was substantially lower (73%) in IP hearts compared to the non-IP counterparts. These preliminary findings suggest that cardioprotection resulting from IP may, in part, be related to IP-induced release of cardiovascular endothelial iron (redox-active) prior to imposing severe I/R stress.
authors.affiliation: Department of Physiology and Experimental Medicine, The George Washington University Medical Center, Washington, DC 20037, USA. phyjhk@gwumc.edu
authors.forename: J H
authors.initials: JH
authors.lastname: Kramer
authors.forename: F G
authors.initials: FG
authors.lastname: Lightfoot
authors.forename: W B
authors.initials: WB
authors.lastname: Weglicki
mesh_terms: D000818:Animals; D003497:Cyclic N-Oxides; D004305:Dose-Response Relationship, Drug; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals; D006321:Heart / Q000187:drug effects* / Q000502:physiology; D007501:Iron / Q000097:blood / Q000378:metabolism / Q000494:pharmacology / Q000627:therapeutic use*; D007511:Ischemia; D019157:Ischemic Preconditioning, Myocardial; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D009589:Nitrogen Oxides / Q000627:therapeutic use; D010084:Oxidation-Reduction; D051381:Rats; D017207:Rats, Sprague-Dawley; D013054:Spectrophotometry, Atomic; D019097:Spin Trapping; D013997:Time Factors
chemical_list: D003497:Cyclic N-Oxides; D005609:Free Radicals; D009589:Nitrogen Oxides; C029217:phenyl-N-tert-butylnitrone; D007501:Iron