j Mol Cell Cardiol 17,675-684 (1985) Involvement of Hydrogen Peroxide and Hydroxyl Radical in the 'Oxygen Paradox': Reduction of Creatine Kinase Release by Catalase, Allopurinol or Deferoxamine, but not by Superoxide Dismutase Christina L. Myers, Stephen J. Weiss, Marvin M. Kirsh and Marshal Shlafer Departments of Pharmacology, Internal Medicine and Surgery, University of Michigan Medical School, Ann Arbor, MI, USA (Received 20 March 1984, accepted in revised form 7 September 1984) C. L. MYERS, S. J. WEISS, M. M. KIRSH, M. SHLAFER. Involvement of Hydrogen Peroxide and Hydroxyl Radical in the 'Oxygen Paradox': Reduction of Creatine Kinase Release by Catalase, Allopurinol or Deferoxa- mine, but not by Superoxide Dismutase. Journal of Molecularand CellularCardiology (1985) 17, 675 684. The objective of this study was to test the hypothesis that cytotoxic oxygen metabolites participate in lytic cardiac cell damage, detected as creatine kinase release, upon reoxygenation of hypoxic, isolated buffer-perfused hearts (oxygen paradox). Perfusate additives included: superoxide dismutase (30 mg/1) ; catalase (2 rag/l) ; deferoxa- mine (0.5 mM) ; and allopurinol (1 mM). Creatine kinase release upon reoxygenation was reduced, to levels not significantly different from nonhypoxic controls, by adding either catalase, allopurinol or deferoxamine to the buffer during hypoxia. Reduced creatine kinase leakage was not accompanied by parallel preservation of ventricular function or coronary vascular resistance. Administration of catalase during hypoxia was superior to administering it only during reoxygenation. Treatment with catalase during both hypoxia and reoxygenation provided no more protection than administration only during hypoxia. The data suggest that an important component of hypoxia-indueed cardiac cell damage is due primarily to hydrogen peroxide, which may then form hydroxyl radical. Superoxide anion plays an important role as a precursor of these species, but added superoxide dismutase alone did not significantly reduce creatine kinase loss. The data also suggest that damage resulting in creatine kinase release upon reoxygenation occurs during oxygen deprivation, and it is mediated in part by cytotoxic oxygen metabolites. KEY WORDS: Allopurinol; Catalase; Deferoxamine; Hydrogen peroxide; Hypoxia; Oxygen; Reoxygenation; Superoxide ; Superoxide dismutase ; Radicals ; Free radicals. Introduction Cytotoxic oxygen metabolites [superoxide anion (0 2" -), hydrogen peroxide (H202) , hydroxyl radical (OH')] have been impli- cated as participants in ischemic cardiac damage [22, 24, 28, 34-36, 38]. This is sup- ported by observations that superoxide dis- mutase plus catalase significantly reduce functional and biochemical indices of damage to globally ischemic isolated buffer-perfused rabbit hearts [35] and blood-perfused cat hearts [36], or to dog hearts subjected to regional ischemia and reperfusion in situ [24]. Although those studies showed significant protection due to the enzyme additives, the combined use of two treatments, either of which might have been sufficient to reduce damage, did little to identify which oxygen metabolites might be responsible for damage. Cell damage due to oxygen radicals may also occur when the nonischemic perfused heart is deprived of oxygen and then reoxyge- nated [8-10, 16, 18, 19, 21]. This phenomenon Address correspondence to: Marshal Shlafer, Ph.D., Department of Pharmacology, University of Michigan Medical School, M-6322 Medical Sciences Bldg. I, Ann Arbor, MI 48109-0010, USA Supported by NIH Grant HL-29499. 0022 2828/85/070675+ 10 $03.00/0 9 1985 Academic Press Inc. (London) Limited