Suppression of TCA cycle activity in the cardiac muscle cell by hydroperoxide-induced oxidant stress.

Excess H2O2 contributes to myocardial reperfusion injury. We detail the effect of H2O2-induced oxidant stress on the tricarboxylic acid (TCA) cycle in isolated heart muscle cells. Cardiomyocyte exposure to bolus H2O2 ( > 50 microM) acutely suppressed TCA cycle activity. Loss of cardiomyocyte 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 catalysis was itself sufficient to jeopardize TCA cycle activity. 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 reestablished 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. These data demonstrate that specific aspects of the TCA cycle in heart muscle are sensitive to H2O2-induced oxidative stress and identify a peroxidative component of the injury process.