title: Hazards of antioxidant combinations containing superoxide dismutase.
abstract: Oxygen free radical scavengers protect against ischemia/reperfusion injury of the kidney in vivo and against hypoxia/reoxygenation (H/R) injury of renal cells in several in vitro systems. In an attempt to maximize renal protection we tested several antioxidants in combination; the individual components had previously reduced reoxygenation injury of hypoxic renal epithelial cells. Both glutathione (GSH; 1 mM) and Cu,Zn-SOD provided significant protection against posthypoxic injury. Surprisingly, the combination of Cu,Zn-SOD plus GSH eliminated protection entirely and was highly toxic to normoxic cells. The toxicity of Cu,Zn-SOD+GSH was not prevented by the iron chelator deferoxamine and was only slightly reduced by the hydroxyl scavenger DMTU. Catalase reversed the toxicity of Cu,Zn-SOD+GSH and provided net protection. Direct measurement of intracellular peroxides using 2,7-dichlorofluorescein quantitated by laser cytometry also revealed enhanced generation of peroxides by cells during H/R when Cu,Zn-SOD+GSH was present. GSSG was less toxic than GSH when combined with Cu,Zn-SOD. Importantly, the combination of Mn-SOD+GSH provided superior protection to either agent alone. In the presence of added GSH, heated or autoclaved Cu,Zn-SOD was still toxic, whereas SOD free of chelatable Cu++ was benign. In the presence of GSH, Cu++ derived from SOD may promote the formation of toxic thionyl radicals, metal-centered radicals, and/or H2O2, thereby causing cell injury. Great care should be used in designing and interpreting studies employing combinations of antioxidants.
authors.affiliation: Department of Medicine, University of Minnesota, Minneapolis 55409-0392, USA.
authors.forename: M S
authors.initials: MS
authors.lastname: Paller
authors.forename: J W
authors.initials: JW
authors.lastname: Eaton
mesh_terms: D000332:Aerobiosis; D000818:Animals; D000975:Antioxidants / Q000494:pharmacology* / Q000633:toxicity; D015687:Cell Hypoxia / Q000187:drug effects; D002478:Cells, Cultured; D003300:Copper / Q000378:metabolism; D003545:Cysteine / Q000494:pharmacology*; D004347:Drug Interactions; D004848:Epithelium / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D018698:Glutamic Acid / Q000494:pharmacology; D005978:Glutathione / Q000031:analogs & derivatives / Q000494:pharmacology*; D019803:Glutathione Disulfide; D005998:Glycine / Q000494:pharmacology; D007687:Kidney Tubules, Proximal / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D015227:Lipid Peroxidation / Q000187:drug effects; D008054:Lipid Peroxides / Q000378:metabolism*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D015424:Reperfusion; D013482:Superoxide Dismutase / Q000494:pharmacology*
chemical_list: D000975:Antioxidants; D008054:Lipid Peroxides; D018698:Glutamic Acid; D003300:Copper; D013482:Superoxide Dismutase; D005978:Glutathione; D003545:Cysteine; D005998:Glycine; D019803:Glutathione Disulfide