SUPPRESSION OF TCA CYCLE ACTIVITY IN THE CARDIAC-MUSCLE CELL BY HYDROPEROXIDE-INDUCED OXIDANT STRESS

Excess H2O2 contributes to myocardial reperfusion injury. We detail th e effect of H2O2-induced oxidant stress on the tricarboxylic acid (TCA ) cycle in isolated heart muscle cells. Cardiomyocyte exposure to bolu s H2O2 (>50 mu M) acutely suppressed TCA cycle activity. Loss of cardi omyocyte TCA cycle function on cellular H2O2 exposure was supported by the rapid in situ inactivation of aconitase along with cardiomyocyte membrane peroxidation. Without peroxidation, the loss of aconitase cat alysis was itself sufficient to jeopardize TCA cycle activity. Only H2 O2 dismutation completely preserved both cardiomyocyte aconitase activ ity and TCA cycle flux during H2O2 overload. Restoration of aconitase catalysis after alleviation of the oxidant insult was prohibited by ce ll-permeable metal chelators, and TCA cycle flux could not be reestabl ished in peroxidized cells, even if aconitase activity had recovered. The characteristics of aconitase inactivation-reactivation observed ar e consistent with adverse redox changes to the enzyme's (Fe-S) cluster . These data demonstrate that specific aspects of the TCA cycle in hea rt muscle are sensitive to H2O2-induced oxidative stress and identify a peroxidative component of the injury process.