Dynamic microstructure and hydration of peroxidized membrane of rat cardiac mitochondria and effects of adriamycin

Acute doxorubicin (adriamycin) dosage does not reduce cardiac protein synthesis in vivo, but decreases diaminopeptidase I and proline endopeptidase activities

Anthracycline antibiotics are effective anticancer agents but their use is limited due to unwanted adverse side effects. The toxic effects of doxorubicin (adriamycin) include the development of defined cardiac lesions leading to cardiomyopathy in some patients. This has been reported to be due to reductions in cardiac protein synthesis. However, virtually all of these previous studies have failed to consider the specific radioactivity of the precursor pool in their measurements or have carried out their studies in vitro. To further resolve the above we measured fractional rates of cardiac protein synthesis using the "flooding dose" method in rats treated with adriamycin (5 mg/kg body wt). Controls were identically treated and injected with saline. At 2.5 or 24 h after adriamycin injection, rates of protein synthesis were measured with a flooding dose of l-[4-(3)H]phenylalanine. Measurements included free (S(i)) and protein-bound (S(b)) phenylalanine-specific radioactivities, the protein synthetic capacity (RNA/protein ratio; C(s)), the fractional rates of protein synthesis calculated from the ratio S(b)/S(i), and the protein synthetic efficiency calculated from the ratio k(s)/C(s). Complementary analyses included assays of lysosomal (cathepsins B, D, H, and L and diaminopeptidases I and II) and cytoplasmic proteases (alanyl aminopeptidase, arginyl aminopeptidase, leucyl aminopeptidase, diaminopeptidase IV, tripeptidyl aminopeptidase, and proline endopeptidase). These enzymes constitute the most active proteases in this tissue and represent an index of protein degradation capacity in cardiac muscle. The results showed that in 2.5-h dosed rats, adriamycin had no effect on S(i), S(b), C(s), k(s), or k(RNA) (P > 0.05, not significant (NS) in all instances). In 2.5-h dosed rats, levels of diaminopeptidase I activity were reduced (P < 0.05), whereas the activities of other proteases were not significantly altered (NS in all instances). In 24-h dosed rats, adriamycin reduced cardiac S(b) (P < 0.001), which would normally be interpreted as a reduction in protein synthesis. However, S(i) was also decreased in 24-h adriamycin-injected rats (P < 0.025%). C(s) was not changed (NS). Consequently, the calculated k(s) and k(RNA) values were not significantly affected in 24-h adriamycin-dosed rats (NS). There were also significant reductions in proline endopeptidase activities in rats exposed for 24 h to adriamycin. The activities of other proteases were not significantly affected at this time point (NS in all instances). In conclusion, adriamycin reduces amino acid labeling of cardiac proteins, an effect that is a consequence of altered free phenylalanine-specific radioactivities. There was some evidence of limited altered intracellular proteolysis.

Triggered release of hydrophilic agents from plasmalogen liposomes using visible light or acid

Triggered release from liposomes composed of semi-synthetic 1-alk-1'-enyl-2-acyl-sn-glycero-3-phosphocholine (plasmalogen) lipids has been demonstrated using either aerobic visible illumination or low pH to induce leakage. The photodynamic release system consists of three functional components: (1) small (less than 1000 A) unilamellar plasmalogen vesicles (SUVs) containing encapsulated glucose, (2) oxygen and (3) zinc phthalocyanine (ZnPc) incorporated within the hydrophobic region of the SUV membrane. Irradiation (lambda greater than 640 nm) at 37 degrees C of air-saturated 1-alk-1'-enyl-2-palmitoyl-sn-glycero-3-phosphocholine (PlasPPC)/1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) (8:1, mol/mol) liposomes at physiologically relevant temperatures results in glucose release rates that are twice those of the corresponding dark control. Photolysis of argon-saturated PlasPPC/DPPC liposomes or of identical vesicles lacking either ZnPc or the plasmalogen vinyl ether bond exhibit glucose release curves which are indistinguishable from the dark control. Irradiation under identical conditions, but in the presence of 100 mM sodium azide, also results in no increased rate of glucose release above that of the dark control. TLC analysis indicates that oxidized lipid species are produced only in air-saturated, irradiated plasmalogen liposomes. The acid lability of the plasmalogen vinyl ether linkage has also been used to trigger release of entrapped calcein. At pH 4.2, the release rate at 37 degrees C is increased 4-fold over rates observed at pH 8. TLC analysis indicates formation of a lysoplasmalogen product. Taken together, these results indicate that both photodynamic and acid triggering can be used to increase plasmalogen liposome permeability and suggest that these liposomes are potentially useful for drug delivery applications.

Estimation of the oxygen gradient across phospholipid bilayers of mitochondria from reperfused rabbit hearts after ischemia

Mitochondria isolated from myocardium exposed to 30 minute ischemia followed by 30 minute reperfusion showed an increase in membrane viscosity and a decrease in wobbling angle of phospholipids, compared with those from the normally perfused myocardium in anesthetized open-chest rabbits. The values for the membrane viscosity were used to estimate the oxygen gradient across the lipid bilayers of mitochondrial membranes with a model of cylindrical diffusion. The effective diffusion coefficient for oxygen, DO2, was approximated to be 6.5 and 6.3 x 10(-5) cm2/sec in the control and ischemic-reperfused area, respectively, by comparing reported DO2 values with values for membrane viscosity. For the surface area of the inner mitochondrial membrane including cristae and for the oxygen consumption rate of the myocardium, reported values for rats and cats, respectively, were employed. Using these values, oxygen gradients across the lipid bilayers of mitochondrial lipid membranes were estimated to be only 0.055 and 0.057 nM in the control and 30 minute ischemic-reperfused myocardium, respectively. If the mitochondrial membranes are hydrated because of the ischemia-reperfusion, the absorption coefficient of the membrane to oxygen will decrease and the oxygen gradient will be increased. In the present study, however, the fluorescence life time of DPH, the hydrophobic fluorophore, showed no shortening despite the ischemia-reperfusion. Hence, no indication of membrane hydration was obtained.