Doxorubicin was shown to form metal complexes with both ferrous and ferric ions. Formation of the ferrous ion complex was characterized by a shift in the absorption maximum of doxorubicin from 479 to 508 nm. In the presence of air, this ferrous ion complex rapidly oxidized, resulting in a product with lowered absorption in the 470-510-nm range and development of an intense absorption band in the 580-610-nm range. A complex with spectral properties identical with those of this oxidized complex formed directly upon addition of ferric ion.' The ferric ion was shown to accommodate up to three doxorubicins and to be able to compete with iron bound to acetohydroxamic acid. The 3:1 doxorubicin-iron complex was shown to have a molar extinction coefficient of 11400 at 600 nm, pH 7.4. The doxorubicin-ferric ion complex catalyzed the reduction of oxygen by both cysteine and glutathione, producing Superoxide and hydrogen peroxide. This catalysis was shown to be consistent with Michaelis-Menten kinetics. The apparent Km for oxygen under these conditions with glutathione as a thiol was 280 μM as compared with 191 μM with cysteine as a thiol. Conversely, the apparent Km for glutathione was 20 mM as compared to 1 mM for cysteine. Analysis by high-pressure liquid chrcmatography showed no alteration in the doxorubicin where the reaction was allowed to proceed to completion. The doxorubicin-ferric ion complex was shown to bind to human erythrocyte ghost membranes and cause efficient destruction of these ghosts in the presence of glutathione. This damage was shown to depend upon the production of both Superoxide and hydrogen peroxide by the complex. Mannitol partially (50%) inhibited complex-mediated ghost destruction, suggesting a role for the hydroxyl radical. On the basis of these observations, a model is proposed in which the destruction of erythrocyte ghosts depends on the ability of the complex to first bind to the ghost membrane and then generate high local concentrations of reactive oxygen species.
|Number of pages||7|
|Publication status||Published - 1982|
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