J. Mchowat et al., Clinical concentrations of doxorubicin inhibit activity of myocardial membrane-associated, calcium-independent phospholipase A(2), CANCER RES, 61(10), 2001, pp. 4024-4029
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.