Supression of tricarboxylic acid cycle activity in the cardiac muscle cell by hydroperoxide-induced oxidant stress. Janero, David R., and David Hreniuk. Research Department, Ciba Pharmaceuticals, Summit, New Jersey 07901; and Department of Biochemistry and Molecular Biology, NitroMed, Inc., Boston, Massachusetts 02118
APStracts 2:0431C, 1995.
Excess hydrogen peroxide (H2O2) may contribute to myocardial reperfusion injury. We have examined the effect of H2O2-induced oxidant stress on the tricarboxylic acid (TCA) cycle in heart muscle by using isolated neonatal-rat cardiomyocytes. Cardiomyocyte exposure to bolus H2O2 (50 [mu]M-1.0 mM) acutely suppressed TCA-cycle activity, indexed as acetate oxidation. Neither acetate supply nor acetate activation to its CoA ester appeared responsible for the diminished TCA-cycle activity. Rather, loss of cardiomyocyte TCA -cycle function upon cellular H2O2 exposure was supported by the rapid, in situ inactivation of aconitase (EC 4.2.1.3) along with cardiomyocyte membrane peroxidation. Aconitase inactivation occurred independently of membrane peroxidation, and without peroxidation the loss of aconitase catalysis was itself sufficient to jeopardize TCA -cycle activity. The degrees of TCA-cycle suppression and aconitase inactivation correlated directly with the magnitude of the oxidant insult. Only H2O2 dismutation completely preserved both cardiomyocyte aconitase activity and TCA-cycle flux during H2O2 overload. Restoration of aconitase catalysis after alleviation of the oxidant insult was prohibited by cell-permeable metal chelators, and TCA -cycle flux could not be re-established in peroxidized cells, even if aconitase activity had recovered. The characteristics of aconitase inactivation-reactivation observed are consistent with adverse redox changes to the enzyme's [Fe-S] cluster without cluster breakdown during C319-5/rev. 1 3. cardiomyocyte hydroperoxide overload. These data demonstrate that specific aspects of the TCA cycle in heart muscle are injury targets sensitive to H2O2-induced oxidative stress and identify a peroxidation-sensitive component of the injury process. 

Received 7 June 1995; accepted in final form 22 November 1995.
APS Manuscript Number C319-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 8 December 95