Clinical concentrations of doxorubicin inhibit activity of myocardial membrane-associated, calcium-independent phospholipase A(2)

Use of the anticancer antibiotic doxorubicin continues to be limited by its cumulative dose-related cardiotoxicity, Our study reports inhibition of my ocardial intracellular calcium-independent phospholipase A(2) (iPLA(2)) act ivity by clinically relevant concentrations of the drug. The effect was fir st-shown in vitro using suspensions of freshly isolated rat and rabbit card iomyocytes, Addition of 0.1-10 muM doxorubicin to these cells led to a conc entration- and time-dependent inhibition of total iPLA(2), as measured usin g (16:0, [H-3]18:1) plasmenylcholine and phosphatidylcholine substrates in the presence or absence of calcium. Subcellular fractionation into cytosoli c and membrane fraction revealed that the drug selectively inhibits membran e-associated iPLA(2), activity, without altering activity of the cytosolic enzyme. Doxorubicin treatment of cells prelabeled with [H-3]arachidonic aci d led to a depression of baseline arachidonic acid release levels, corrobor ating iPLA(2) inhibition. Reducing agents blocked PLA(2), inhibition in car diomyocyte suspensions, suggesting that the doxorubicin effect is mediated by oxidation of susceptible cysteines, Iii vivo experiments, in which adult s rats were i.v. injected with a bolus dose of 4 mg/kg doxorubicin, confirm ed in vitro findings, revealing a 2-fold decrease in membrane-associated Ca 2+-independent iPLA(2), activity in the heart tissue of treated animals. Th e observed phenomenon has important implications for myocyte signaling casc ades and membrane remodeling.