Redox cycling of anthracyclines by cardiac mitochondria. I. Anthracycline radical formation by NADH dehydrogenase

Daunorubicin-induced apoptosis in rat cardiac myocytes is inhibited by dexrazoxane

-The clinical efficacy of anthracycline antineoplastic agents is limited by a high incidence of severe and usually irreversible cardiac toxicity, the cause of which remains controversial. In primary cultures of neonatal and adult rat ventricular myocytes, we found that daunorubicin, at concentrations </=1 micromol/L, induced myocyte programmed cell death within 24 hours, as defined by several complementary techniques. In contrast, daunorubicin concentrations >/=10 micromol/L induced necrotic cell death within 24 hours, with no changes characteristic of apoptosis. To determine whether reactive oxygen species play a role in daunorubicin-mediated apoptosis, we monitored the generation of hydrogen peroxide with dichlorofluorescein (DCF). However, daunorubicin (1 micromol/L) did not increase DCF fluorescence, nor were the antioxidants N-acetylcysteine or the combination of alpha-tocopherol and ascorbic acid able to prevent apoptosis. In contrast, dexrazoxane (10 micromol/L), known clinically to limit anthracycline cardiac toxicity, prevented daunorubicin-induced myocyte apoptosis, but not necrosis induced by higher anthracycline concentrations (>/=10 micromol/L). The antiapoptotic action of dexrazoxane was mimicked by the superoxide-dismutase mimetic porphyrin manganese(II/III)tetrakis(1-methyl-4-peridyl)porphyrin (50 micromol/L). The recognition that anthracycline-induced cardiac myocyte apoptosis, perhaps mediated by superoxide anion generation, occurs at concentrations well below those that result in myocyte necrosis, may aid in the design of new therapeutic strategies to limit the toxicity of these drugs.

Manganese superoxide dismutase protects mitochondrial complex I against adriamycin-induced cardiomyopathy in transgenic mice

Adriamycin (ADR) is a potent anticancer drug that causes severe cardiomyopathy. We have previously demonstrated that ADR-induced ultrastructural mitochondrial injury in the heart was attenuated in manganese superoxide dismutase (MnSOD) transgenic mice. To further investigate the biochemical mechanisms by which MnSOD protected mitochondria against ADR-induced damage, cardiac mitochondrial function and activities were evaluated. The results showed that ADR caused significant decrease in state 3 respiration and respiratory control ratio using both complex I and II substrates in nontransgenic mice. In transgenic mice, state 3 respiration for complex I substrates remained unaffected by ADR, but was reduced for complex II substrate. Complex I activity was significantly decreased in nontransgenic, but not in transgenic mice after ADR treatment, suggesting that mitochondrial complex I is sensitive to inactivation by superoxide radicals. The activities of complex II and mitochondrial creatine kinase were decreased by ADR in both nontransgenic and transgenic mice. These results support our previous observations on the protective role of MnSOD on the ultrastructural damage of the heart after ADR treatment and extend the understanding of its mechanisms in mitochondria.

Oxidative stress causes a general, calcium-dependent degradation of mitochondrial polynucleotides

Oxidative stress has many effects on biological cells, including the modulation of gene expression. Reactive oxygen species are known to up-regulate and down-regulate RNA expression in prokaryotic and eukaryotic cells. We have previously reported that a preferential and calcium-dependent down-regulation of mitochondrial RNAs occurs when HA-1 hamster fibroblasts are exposed to hydrogen peroxide. Here we extend these studies to determine whether this down-regulation is specific to mitochondria RNA or involves general polynucleotide degradation. Degradation and associated decreases in the levels of 16S mitochondrial rRNA following exposure of cells to 400 microM hydrogen peroxide were found to be dependent on calcium at 2 and 5 h. Degradation of mitochondrial genomic DNA was also observed following peroxide exposure, and occurred at similar time points as for mitochondrial RNA degradation. As with mitochondrial RNA degradation, this mitochondrial genomic DNA degradation was dependent on calcium. These results indicate that there is a general, calcium-dependent degradation of mitochondrial polynucleotides following exposure of HA-1 fibroblasts to oxidative stress, and suggest that a dramatic shut-down in mitochondrial biosynthesis is an early-stage response to oxidative stress.

Current issues in the enzymology of mitomycin C metabolic activation

1. Mitomycin C (MMC) is considered to be the prototype bioreductive drug undergoing activation to toxic species preferentially under hypoxic conditions. Therefore a proper understanding of the enzymology of bioreduction in tumor tissue is of great importance. 2. DT-diaphorase and NADPH:cytochrome P-450 reductase (quinone reductases) are believed to have established roles in this activation pathway, but these roles are now undergoing revision. 3. It is emerging, however, that different reductases prevail under different physiological conditions. Indeed, DT-diaphorase has been found to protect cells from the hypoxic cytotoxicity of MMC in cell lines expressing high levels of the enzyme. 4. A novel mitochondrial reductase(s) has been identified in solid tumor tissue and is active only under hypoxic conditions and is more efficient at metabolizing MMC than are the other reductases identified. 5. Thus, this newly identified mitochondrial reductase(s) is a potential new target for enzyme-directed bioreductive drug therapy if tumor hypoxia can be achieved. However, because most tumors overexpress DT-diaphorase, this enzyme may prove optimal for MMC drug therapy.

Role of mitochondria in oxidative stress and ageing

Mitochondria are deeply involved in the production of reactive oxygen species through one-electron carriers in the respiratory chain; mitochondrial structures are also very susceptible to oxidative stress as evidenced by massive information on lipid peroxidation, protein oxidation, and mitochondrial DNA (mtDNA) mutations. Oxidative stress can induce apoptotic death, and mitochondria have a central role in this and other types of apoptosis, since cytochrome c release in the cytoplasm and opening of the permeability transition pore are important events in the apoptotic cascade. The discovery that mtDNA mutations are at the basis of a number of human pathologies has profound implications: maternal inheritance of mtDNA is the basis of hereditary mitochondrial cytopathies; accumulation of somatic mutations of mtDNA with age has represented the basis of the mitochondrial theory of ageing, by which a vicious circle is established of mtDNA damage, altered oxidative phosphorylation and overproduction of reactive oxygen species. Experimental evidence of respiratory chain defects and of accumulation of multiple mtDNA deletions with ageing is in accordance with the mitochondrial theory, although some other experimental findings are not directly ascribable to its postulates.

Quinone specificity of complex I

This review considers the interaction of Complex I with different redox acceptors, mainly homologs and analogs of the physiological acceptor, hydrophobic Coenzyme Q. After examining the physical properties of the different quinones and their efficacy in restoring mitochondrial respiration, a survey ensues of the advantages and drawbacks of the quinones commonly used in Complex I activity determination and of their kinetic properties. The available evidence is then displayed on structure-activity relationships of various quinone compounds in terms of electron transfer activity and proton translocation, and the present knowledge is discussed in terms of the nature of multiple quinone-binding sites in the Complex.

Lipid peroxidation of rat myocardial tissue following daunomycin administration

Daunomycin-induced cardiotoxicity has been regarded to be the result of oxygen-mediated lipid peroxidation of cell membranes. The aim of the present work was to evaluate the extent of lipid peroxidation in rat heart after administration of this anticancer drug and, further, to examine possible activation of some endogenous antioxidant defense systems. Myocardial tissue from both control and drug-treated rats was tested for lipid peroxidation using a selective third-order derivative method that is based on the analysis of the free malondialdehyde produced. Determination of reduced/oxidized glutathione levels and measurement of the activity of DT-diaphorase, glutathione-S-transferase, glutathione reductase, glucose-6-phosphate dehydrogenase and NADPH-cytochrome P-450 reductase were also carried out using literature methods. Significant increase of malondialdehyde content, and DT-diaphorase and glutathione-S-transferase activities were found in myocardial tissue from daunomycin-treated rats. On the other hand, reduced and oxidized glutathione levels were significantly decreased while the activity of glutathione reductase, glucose-6-phosphate dehydrogenase and NADPH-cytochrome P-450 reductase remained unchanged after daunomycin administration. The results of the present study give further evidence that daunomycin can induce lipid peroxidation in heart. However, additional experimentation is needed in order to delineate the molecular details of this process as well as of the mechanisms evolved to limit it.

Oxidative stress, antioxidant defences and aging

Apoptosis and aging share common mechanisms in oxidative stress and mitochondrial involvement. Treatment of cultured neuroblastoma cells with a radical initiator induced apoptosis; raise in hydrogen peroxide and release of cytochrome c from mitochondria preceded collapse of mitochondrial potential and cell death. In rat hepatocytes treated with adriamycin incubation with exogenous Coenzyme Q10 counteracted the drug-induced increase of hydrogen peroxide and the fall of the mitochondrial potential, thus demonstrating the quinone antioxidant effect. Complex I activity and its rotenone sensitivity decreased in brain cortex non-synaptic mitochondria from old rats; a 5 kb mitochondrial DNA deletion was found only in the old rats. A similar behavior was found in human platelets from old individuals. The postulated energy decline was confirmed by the inhibitor sensitivities of platelet aggregation and lactate production. The lack of the 5 kb deletion in platelets throws doubts on mitochondrial DNA lesions as the only causes of mitochondrial dysfunction in aging.

Conformational and electrostatic properties of naphthazarin, juglone, and naphthoquinone: an ab initio theoretical study

Conformational features of naphthazarin, juglone, and naphthoquinone have been examined via ab initio (Hartree-Fock) SCF calculations at 3-21G level. The results suggest a planar structure for all the three molecules and internally hydrogen-bonded structure for naphthazarin and juglone to be their preferred conformation. The optimized structural features are essentially the same as their crystal geometries. Molecular electrostatic potential (MEP) calculations using ab initio SCF methods ranging from 3-21G to 6-31G levels have been performed to visualize their three-dimensional pharmacophoric patterns and topography. The results indicate that two factors--(i) the depth, extent, and relative location of negative potential around hydroxyl and quinonoid oxygens, and (ii) a gradual loss of negative potential over the molecular plane due to the presence and orientation of the hydroxyl groups in the phenolic part of the molecules--are crucial for recognition interaction of the compounds with their receptors. Aqueous solvation seems to have significant influence on the MEP profiles of the molecules. Although intrinsic nucleophilicity increases for all the compounds, including the different conformers, due to aqueous solvation, the intrinsic electrophilicity shows remarkable decrease for all. It appears that the acidic nature of the hydrogens in these compounds and conformers decreases sharply along with shifts of positions while going from the gas phase to the aqueous phase. These observations may help to explain the mechanism of action(s) of the anthracyclin family of cytotoxic antibiotics.

Enhanced resistance of adriamycin-treated MCR-5 lung fibroblasts by increased intracellular glutathione peroxidase and extracellular antioxidants

Considerable evidence indicates that reactive oxygen species play an etiological role in both cardiotoxicity and the skin necrosis induced by adriamycin (ADM). An increase in glutathione peroxidase activity on addition of selenium to cultured MCR-5 lung fibroblasts was observed; this increase was accompanied by enhanced cellular resistance to ADM toxicity. Moreover, the presence of exogenous antioxidant systems, such as superoxide dismutase, catalase, vitamin E, dimethylsulfoxide, and desferroxamine, an iron chelating agent, resulted in significant protection from ADM-mediated damage.

Effect of active oxygen radicals on protein and carbohydrate moieties of recombinant human erythropoietin

Our previous study showed that active oxygen radicals generated from a Fenton system and a xanthine plus xanthine oxidase system caused serious loss of in vivo bioactivity of recombinant human erythropoietin (EPO), a highly glycosylated protein. In the present study, we characterized the oxidative modifications to the protein and carbohydrate moiety of EPO, which lead to a reduction of its bioactivity. In vitro bioactivity was reduced when EPO was treated with oxygen radicals generated from a Fenton system in the presence of 0.016 mM H2O2, and the reduction was directly proportional to the loss of in vivo bioactivity. SDS-PAGE analysis showed that dimer formation and degradation was observed under more severe conditions (Fenton reaction with 0.16 mM H2O2). The tryptophan destruction was detected at 0.016 mM H2O2 and well correlated with the loss of in vitro bioactivity, whereas loss of other amino acids were occurred under more severe conditions. Treatment with the Fenton system did not result in any specific damage on the carbohydrate moiety of EPO, except a reduction of sialic acid content under severe condition. These results suggest that active oxygen radicals mainly react with the protein moiety rather than the carbohydrate moiety of EPO. Destruction of tryptophan residues is the most sensitive marker of oxidative damage to EPO, suggesting the importance of tryptophan in the active EPO structure. Deglycosylation of EPO caused an increased of susceptibility to oxygen radicals compared to intact EPO. The role of oligosaccharides in EPO may be to protect the protein structure from active oxygen radicals.

Localization of the Enzyme System Involved in Anaerobic Reduction of Azo Dyes by Sphingomonas sp. Strain BN6 and Effect of Artificial Redox Mediators on the Rate of Azo Dye Reduction

The effect of different artificial redox mediators on the anaerobic reduction of azo dyes by Sphingomonas sp. strain BN6 or activated sludge was investigated. Reduction rates were greatly enhanced in the presence of sulfonated anthraquinones. For strain BN6, the presence of both cytoplasmic and membrane-bound azo reductase activities was shown.

Oxidation of erythrocyte protein and lipid, and hemolysis in rabbit red blood cells treated with benzo[a]pyrene or adriamycin

A number of free-radical-generating carcinogens catalyze the oxidative modification of macromolecules. Malondialdehyde (MDA), carbonyl content, alanine formation, and hemolysis were used as biomarkers of oxidative stress, and were determined in rabbit erythrocytes treated in vitro with benzo[a]pyrene or adriamycin. MDA and carbonyl content were significantly increased in a concentration-dependent manner by carcinogens. Alanine formation was also increased in a concentration-dependent manner in rabbit erythrocytes treated with carcinogens. Hemolysis occurred in erythrocytes treated with benzo[a]pyrene (540 microM) or adriamycin (300 microM) between 4 and 8 h of incubation, respectively. The hemolysis pattern correlated with increases in MDA, carbonyl content, and alanine formation. These data indicate that lipid peroxidation as measured by MDA may be the most sensitive indicator for oxidative stress in erythrocytes. Hemolysis could thus be applicable to free-radical-induced cellular damage as an alternative biomarker of oxidative stress.

Preferential oxidation of cardiac mitochondrial DNA following acute intoxication with doxorubicin

The purpose of this investigation was to determine whether acute doxorubicin intoxication causes a preferential accumulation of 8-hydroxydeoxyguanosine (8OHdG) adducts to mitochondrial DNA (mtDNA) as opposed to nuclear DNA (nDNA), particularly in cardiac tissue. Adult male rats received a single i.p. bolus of doxorubicin (15 mg/kg) and were killed 1-14 days later. Acute intoxication with doxorubicin caused a 2-fold greater increase in 8OHdG adducts to mtDNA compared to nDNA, the concentration of adducts to both nDNA and mtDNA being 20%-40% greater for heart as opposed to liver. For both tissues, the relative abundance of adducts was highest at the earliest time-point examined (24 h) and decreased to control values by 2 weeks. The temporal dilution of 8OHdG adducts was not the result of cell hyperplasia and was only partially due to amplification of the mitochondrial genome, most probably via an increase in DNA copy number rather than a stimulation of mitochondrial biogenesis.

Enhancement of adriamycin toxicity by iron chelates is not a free radical mechanism

The possible involvement of metal ions and free radicals in the cytotoxic mechanism of Adriamycin (ADR) was investigated, using a model system of Escherichia coli cells. It is shown that E. coli mediated the production of free radicals under anaerobic (ADR-semiquinone) and aerobic (superoxide) conditions. ADR-induced loss of colony-forming ability was enhanced by the addition of iron (Fe) chelates. These observations suggested that a Fenton-type free radical mechanism was responsible for ADR toxicity. However, the mortality rate was essentially unchanged by the exclusion of oxygen. It was also unaffected by the addition of H2O2, catalase, or chelating agents. Cu(II), Zn(II) or Mg(II) had no effect on ADR toxicity. ADR and iron chelates did not induce measurable amounts of DNA strand-breaks. These observations suggest a mechanism of ADR-induced cell killing that is enhanced by Fe chelates, but does not directly involve oxygen-derived free radicals.

Cholesteryl hemisuccinate treatment protects rodents from the toxic effects of acetaminophen, adriamycin, carbon tetrachloride, chloroform and galactosamine

In addition to its use as a stabilizer/rigidifier of membranes, cholesteryl hemisuccinate, tris salt (CS) administration has also been shown to protect rats from the hepatotoxic effects of carbon tetrachloride (CCl4). To further our understanding of the mechanism of CS cytoprotection, we examined in rats and mice the protective abilities of CS and the non-hydrolyzable ether form of CS, gamma-cholesteryloxybutyric acid, tris salt (CSE) against acetaminophen-, adriamycin-, carbon tetrachloride-, chloroform- and galactosamine-induced toxicity. The results of these studies demonstrated that CS-mediated protection is not selective for a particular species, organ system or toxic chemical. A 24-h pretreatment of both rats and mice with a single dose of CS (100mg/kg, i.p.), resulted in significant protection against the hepatotoxic effects of CCl4, CHCl3, acetaminophen and galactosamine and against the lethal (and presumably cardiotoxic) effect of adriamycin administration. Maximal CS-mediated protection was observed in experimental animals pretreated 24 h prior to the toxic insult. These data suggest that CS intervenes in a critical cellular event that is an important common pathway to toxic cell death. The mechanism of CS protection does not appear to be dependent on the inhibition of chemical bioactivation to a toxic reactive intermediate (in light of the protection observed against galactosamine hepatotoxicity). However, based on the data presented, we can not exclude the possibility that CS administration inhibits chemical bioactivation. Our findings do suggest that CS-mediated protection is dependent on the action of the intact anionic CS molecule (non-hydrolyzable CSE was as protective as CS), whose mechanism has yet to be defined.

Roles of reactive oxygen species and antioxidant enzymes in murine daunomycin-induced nephropathy

We evaluated the roles of reactive oxygen species and intrinsic antioxidant enzymes in the development of daunomycin (DM)-induced nephropathy in mice. A single dose of DM (20 mg/kg intravenously) induced proteinuria by day 7 and the nephrotic syndrome by day 14 in DM-sensitive strain (A/J) but not in DM-resistant strain (C57BL/6J) (B6). Renal cortical lipid peroxide levels in the A/J mice significantly increased at days 2, 4, and 7 after DM injection, whereas no increase was observed in the B6 mice. The resistance to DM in B6 mice was associated with higher activities in renal cortical superoxide dismutase and glutathione peroxidase. The administration of superoxide dismutase or of dimethylthiourea significantly suppressed the DM-induced proteinuria in the A/J mice. Four days of superoxide dismutase or dimethylthiourea administration suppressed the proteinuria. These findings suggested that murine DM-nephropathy appeared to be mediated by reactive oxygen species and that intrinsic antioxidant enzyme activities may play an important role in the susceptibility to DM-induced nephropathy in mice.

Analyses of the molecular mechanism of adriamycin-induced cardiotoxicity

The molecular basis of the adriamycin (AQ)-dependent development of cardiotoxicity is still far from being clear. In contrast to our incomplete understanding of the organ-specific mechanism mitochondria are unequivocally accepted as the locus where the molecular disorder is triggered. A growing number of reports intimate the establishment of unbalanced oxygen activation through heart mitochondria in the presence of anthraquinones. In fact, in contrast to liver mitochondria, isolated heart mitochondria have been unequivocally shown to shuttle single electrons to AQ, giving rise to O2.- formation by autoxidizing AQ. semiquinones. Earlier we have demonstrated the involvement of the exogenous NADH dehydrogenase in this deleterious electron deviation from the respiratory chain. This enzyme that is associated with complex I of the respiratory chain catalyzes the oxidation of cytosolic NADH. AQ activation through isolated heart mitochondria was reported to require the external addition of NADH, suggesting a flux of reducing equivalents from NADH to AQ in the cytosol. Unlike heart mitochondria, intact liver mitochondria, which are lacking this NADH-related pathway of reducing equivalents from the cytosol to the respiratory chain, cannot be made to activate AQ to semiquinones by NADH or any other substrate of respiration. It appears, therefore, that the exogenous NADH dehydrogenase of heart mitochondria exerts a key function in the myocardial toxicogenesis of anthraquinones via oxygen activation through semireduced AQ. Assessing the toxicological significance of the exogenous NADH dehydrogenase in AQ-related heart injury requires analysis of reaction products and their impact on vital bioenergetic functions, such as energy gain from the oxidation of respiratory substrates. We have applied ESR technique to analyze the identity and possible interactions of radical species emerging from NADH-respiring heart mitochondria in the presence of AQ. The following metabolic steps occur causing depression of energy metabolism in the cardiac tissue. After one-electron transfer to the parent hydrophilic anthraquinone molecule destabilization of the radical formed causes cleavage of the sugar residue. Accumulation of the lipophilic aglycone metabolite in the inner mitochondrial membrane diverts electrons from the regular pathway to electron acceptors out of sequence such as H2O2. HO. radicals are formed and affect the functional integrity of energy-linked respiration. The key and possibly initiating role of the exogenous NADH dehydrogenase of cardiac mitochondria in this reaction pathway provides a rationale to explain the selective cardiotoxic potency of the cytostatic anthraquinone glycosides.

Lipid peroxidation and antioxidant defense mechanisms in rat renal tissue after daunorubicin administration

Redox cycling compounds such as daunorubicin have been assumed to be toxic because they stimulate reactive oxygen-mediated lipid peroxidation. Furthermore, both DT-diaphorase and glutathione (GSH) have been regarded as protective cellular compounds against daunorubicin cardiotoxicity, but their role in daunorubicin nephrotoxicity remains unclear. To investigate this issue, 10 adult Wistar rats were twice injected with a single dose of 20 mg/kg body weight daunorubicin into the tail vein; the interval between injections was 48 h. A control group of 10 rats were injected with normal saline. One day after the second injection, all the animals were sacrificed and their kidneys were analyzed for malondialdehyde (MDA) as an index of lipid peroxidation, DT-diaphorase activity, and GSH and glutathione disulphide (GSSG) content. A significant increase of MDA concentration (2.41 vs. 1.64 p < 0.001) and DT-diaphorase activity (0.2 vs. 0.12, p < 0.001) was found in the renal tissue of daunorubicin injected rats. In contrast, GSH and GSSG levels were decreased in those animals (566 vs. 1282, p < 0.001 and 115 vs 187, p < 0.01, respectively). The results of this study give evidence that a high dosage of daunorubicin induces lipid peroxidation in renal tissue of rats stimulating the activation of DT-diaphorase and the detoxificative depletion of GSH.

Long-lasting effect of dexrazoxane against anthracycline cardiotoxicity in rats

The long-lasting protective effect of dexrazoxane (ADR-529) against doxorubicin- and epirubicin-induced cardiotoxicity was evaluated in the multiple-dose 35-wk rat model. Groups of 36 male Sprague-Dawley rats were given ADR-529 30 min before administration of cardiotoxic doses of doxorubicin (1 mg/kg/wk) or epirubicin (1.13 mg/kg/wk). The compounds were intravenously injected once weekly for 7 consecutive wk at ADR-529; anthracycline ratios ranging from 5:1 to 20:1. These ratios covered the entire chemotherapeutic range in humans and allowed studying the chronic progressive cardiomyopathy in our rat model. Animals were observed for up to 35 wk to follow the time course of the well-characterized cardiomyopathy, which was evaluated through the well-established qualitative/quantitative morphological grading. It was clearly demonstrated in this rat model that ADR-529, at the ratios administered, provided ample cardioprotection for a duration of 35 wk, which corresponds to 25 yr of equivalent human time.

Enzymology of mitomycin C metabolic activation in tumour tissue. Characterization of a novel mitochondrial reductase

In this study, the enzymology of mitomycin C (MMC) bioactivation in two murine colon adenocarcinomas, MAC 16 and MAC 26, was examined. Subcellular quinone reductase assessment via cytochrome c reduction confirmed a number of active enzymes. MAC 16 exhibited 22-fold greater levels of cytosolic DT-diaphorase than MAC 26, while microsomal NADPH:cytochrome P-450 reductase levels were similar in both tumour types. Metabolism of MMC by subcellular fractions isolated from both MAC 16 and MAC 26 was quantitated by monitoring the formation of the principle metabolite 2,7-diaminomitosene (2,7-DM) via high-performance liquid chromatography (HPLC). In MAC 16 only, activity displaying the properties of cytosolic DT-diaphorase and microsomal NADPH:cytochrome P-450 reductase was detected and confirmed, using the enzyme inhibitors dicoumarol and cytochrome P-450 reductase antiserum, respectively. The highest level of MMC metabolism was associated with the mitochondrial fraction from both tumours and was the sole enzyme activity detected in MAC 26. The greatest mitochondrial drug metabolism was achieved in the presence of NADPH as cofactor and hypoxia (MAC 16-specific activity, 3.67 +/- 0.58 nmol/30 min/mg; MAC 26 specific-activity, 3.87 +/- 0.71 nmol/30 min/mg) and was unaffected by the addition of the inhibitors dicoumarol and cytochrome P-450 reductase antiserum. NADH-dependent mitochondrial activity was only observed in MAC 16 at approximately 4-fold less than that seen with NADPH. MAC 26 homogenate incubations displayed enhanced metabolism under hypoxia, presumably due to the presence of the identified mitochondrial enzyme. MAC 16 homogenates showed no increase in metabolism under hypoxia, suggesting that other enzyme(s) may be predominant. These data indicate the presence of a novel mitochondrial one-electron reductase capable of metabolising MMC in MAC 16 and MAC 26.

Inhibition of anthracycline semiquinone formation by ICRF-187 (dexrazoxane) in cells

The formation of semiquinone free radicals of doxorubicin, epirubicin, daunorubicin, and idarubicin was measured by electron paramagnetic resonance (EPR) spectroscopy in hypoxic suspensions of chinese hamster ovary (CHO) cells. The amount of semiquinone produced was in the order idarubicin >> doxorubicin > daunorubicin > epirubicin. The idarubicin semiquinone signal was both the fastest to be formed and to decay. Idarubicin, which was the most lipophilic of the anthracyclines studied, also displayed the fastest fluorescence-measured cellular uptake of drug. Thus, it was concluded that semiquinone formation was dependent upon the rate of cellular uptake. Lysed cell suspensions were also shown to be capable of producing the doxorubicin semiquinone in the presence of added NADPH. The cardioprotective agent dexrazoxane (ICRF-187) was observed to decrease the amount of doxorubicin semiquinone observed in cell suspensions. Dexrazoxane also decreased the amount of doxorubicin semiquinone observed in the NADPH-lysed cell suspension mixture. Neither bipyridine nor deferoxamine decreased NADPH-dependent doxorubicin semiquinone formation. These results suggest that dexrazoxane does not decrease doxorubicin semiquinone formation through an iron complex formed from hydrolyzed dexrazoxane. Dexrazoxane may be inhibiting an NADPH-dependent enzyme.

Semiquinone free radical formation by daunorubicin aglycone incorporated into the cellular membranes of intact Chinese hamster ovary cells

The production of semiquinone free radicals has been measured by electron paramagnetic resonance spectroscopy (EPR) in Chinese hamster ovary cells in which 7-hydroxy daunorubicin aglycone had been incorporated. The highly lipophilic daunorubicin aglycone was incorporated into the cellular membrane by swirling a cell suspension over a thin layer of daunorubicin aglycone. Thus, the observed semiquinone free radical was likely formed directly in the lipophilic environment of the cellular membrane. The linewidth of the observed EPR signal suggested that a neutral protonated semiquinone species was formed. In the presence of the cell-impermeant paramagnetic line broadening agent chromium(III) oxalate, no detectable signal was observed. This result indicates that even though the semiquinone is embedded in the membrane, it is still partly accessible to the external chromium(III) oxalate. Analysis of chloroform extracts of the cells after EPR experiments indicated that daunorubicin aglycone was extensively metabolized. The results of a growth inhibition assay carried out on cells into which daunorubicin aglycone had been incorporated showed almost no effect on cell growth. This result indicates that in spite of significant daunorubicin aglycone-induced radical formation taking place directly in the cell membrane, little cell damage results.

Irradiation increases manganese superoxide dismutase mRNA levels in human fibroblasts. Possible mechanisms for its accumulation

Irradiation induces the production of superoxide radicals (O2.-), which play an important causative role in radiation damage. Manganese superoxide dismutase (MnSOD) is a mitochondrial enzyme involved in scavenging O2..-. This study examined MnSOD gene regulation by irradiation in WI38 human fibroblasts. Unstimulated fibroblasts constitutively expressed MnSOD activity and mRNA; irradiation markedly increased MnSOD activity and mRNA levels. The increase in MnSOD transcripts by irradiation was both time- and dose-dependent. WI38 fibroblasts constitutively produce low levels of interleukin-1 (IL-1). The induction of MnSOD mRNA by irradiation was partially blocked by anti-IL-1 antibodies, and treatment of cells with IL-1 also increased MnSOD mRNA levels. Inhibition of the cyclo-oxygenase pathway with indomethacin augmented the induction MnSOD mRNA by irradiation and prostaglandin E2 inhibited the accumulation of MnSOD mRNA by irradiation. Transcriptional run-on analysis showed that irradiation increased the rate of MnSOD transcription 2-fold. Stability studies of MnSOD mRNA in these cells showed that the half-life increased from < 1.5 h in unirradiated cells to > 4 h in irradiated cells. These results suggest that induction of the MnSOD gene after irradiation is regulated, at least in part, by IL-1 production and that increased levels of MnSOD transcripts also occur through a pathway of endogenous prostaglandin E2 production. Our data indicate that the increase in MnSOD mRNA observed after irradiation occurs through both transcriptional and post-transcriptional mechanisms.

The loss of in vivo activity of recombinant human erythropoietin by active oxygen species

The effects of active oxygen species on the in vivo activity of recombinant human erythropoietin (EPO) treated by Fenton system, xanthine (X) plus xanthine oxidase (XO) system and hydrogen peroxide (H2O2) has been studied by means of counting the increase in number of hemolyser-resistant cells (HRCs) in EPO-injected mice. The results showed that both Fenton and X plus XO systems caused a significant reduction of the activity in proportion to the concentration of generated active oxygen species. Meanwhile, the treatment of EPO with H2O2 alone resulted in a relatively slight reduction of the activity. Electrophoretic studies on the structure of EPO revealed that its main protein band on sodium dodecyl sulfate-polyacrylamide gel (SDS-PAGE) disappeared in proportion with the extent of exposure to active oxygen generating systems. Both Fenton and X plus XO systems caused a significant loss of fluorescence in the pyridylamino (PA-) sugar chain in proportion to the concentration of generated active oxygen species, and no degradation products in the sugar chain part of the PA-sugar chain were detected. This showed that aromatic groups in EPO were sensitive to attack by active oxygen species. These results provide evidence that hydroxyl radical and other active oxygen species have a potential to react with EPO, leading to a reduction of its in vivo activity.

Fluorescent substances and high molecular weight protein aggregates formed in rat heart mitochondria upon doxorubicin-induced lipid peroxidation

A rat heart mitochondrial suspension was incubated with doxorubicin, FeCl3 and NADH. Fluorescent substances and high molecular weight protein aggregates were observed in the mitochondrial membranes upon the formation of thiobarbituric acid-reactive substances. Since both fluorescent substances and high molecular weight protein aggregates are retained in mitochondrial membranes, they can be of use in the clarification of the site of doxorubicin-induced lipid peroxidation.

Inhibition of doxorubicin-induced membrane damage by thiol compounds: toxicologic implications of a glutathione-dependent microsomal factor

The hypothesis was tested that glutathione exerts its protective actions against doxorubicin-induced oxidative stress through an enzyme-dependent mechanism. Glutathione at biological concentrations decreased doxorubicin-dependent rat hepatic microsomal lipid peroxidation, whereas N-acetylcysteine had no effect. Glutathione was utilized during this inhibition at a rate dependent on the concentration of both doxorubicin and the sulfhydryl. Increasing glutathione concentrations resulted in significant increases in utilization. N-acetylcysteine was also oxidized in the microsomal system; however, the rate of oxidation was not enhanced by doxorubicin. If bovine cardiac microsomes were substituted for the hepatic microsomes, no lipid peroxidation was detected in the presence of doxorubicin, yet significant utilization of glutathione was detected. Microsomes isolated from tocopherol-deficient rats utilized less glutathione in the presence of doxorubicin, and there was no inhibition of doxorubicin-dependent lipid peroxidation. These findings support the conclusion that glutathione inhibits hepatic microsomal lipid peroxidation initiated by the redox-cycling of doxorubicin. Inhibition of doxorubicin-dependent lipid peroxidation appears to be enzyme-mediated and to require tocopherol. A similar mechanism for protection against doxorubicin appears to be present in heart microsomal membranes.

Lipid peroxidation products, and vitamin and trace element status in patients with cancer before and after chemotherapy, including adriamycin. A preliminary study

Adriamycin is a potent chemotherapeutic agent used in the treatment of human neoplastic diseases. A major side effect limiting the use of this drug is its toxic effect on the heart. Several hypotheses have been proposed to explain the cardiotoxicity of Adriamycin. However, the most plausible hypothesis seems to be the reduction of Adriamycin and free radical production, which induces lipid peroxidation and oxidative damages in the heart. We have thus undertaken this preliminary study to investigate Adriamycin-induced lipid peroxidation by the measurement of plasma thiobarbituric acid reactant materials and antioxidant systems, namely glutathione content, glutathione peroxidase activity, and vitamin and trace element status, in patients with cancer before and after chemotherapy, including Adriamycin. The concentration of thiobarbituric acid reactant materials in plasma of patients with cancer was higher than in controls and was further increased after chemotherapy. Blood glutathione and plasma glutathione peroxidase activity, as well as plasma zinc and selenium in patients with cancer, were decreased, but not further modified by chemotherapy. However, only zinc and selenium levels reached a significant level. In contrast, plasma vitamin E and beta-carotene levels were not significantly increased in patients with cancer. Finally, plasma vitamin A and copper levels were not modified either in patients with cancer or by chemotherapy.

Interactions of adriamycin aglycones with mitochondria may mediate adriamycin cardiotoxicity

Adriamycin and related anthracyclines are potent oncolytic agents, the clinical utility of which is limited by severe cardiotoxicity. Aglycone metabolites of Adriamycin (5-20 microM) induce a Ca(2+)-dependent increase in the permeability of the inner mitochondrial membrane of both heart and liver mitochondria to small (< 1,500 Da) solutes; this phenomenon is accompanied by release of mitochondrial Ca2+, mitochondrial swelling, collapse of the membrane potential, oxidation of mitochondrial pyridine nucleotides [NAD(P)H], uncoupling, and a transition from the condensed to the orthodox conformation and is inhibited by ATP, dithiothreitol, the immunosuppressant cyclosporin A, and the ubiquitous polyamine spermine. Aglycones also modify mitochondrial sulfhydryl groups and induce a Ca2+ independent oxidation of mitochondrial NAD(P)H which appears to reflect electron transport from NADH to oxygen, mediated by the aglycones and resulting in the production of superoxide (O2-). Selenium deficiency and butylated hydroxytoluene inhibit aglycone-induced Ca2+ release from liver, but not heart, mitochondria, suggesting that the interactions of the aglycones with mitochondria differ in these two tissues. It can be proposed that the effects of Adriamycin aglycones on heart mitochondria are responsible for the cardiotoxicity of the parent drug.

Effects of Adriamycin on heart mitochondrial function in rested and exercised rats

The effect of Adriamycin (ADM) administration on heart mitochondria was investigated in rats at rest and after an acute bout of maximal exercise. ADM was given intravenously at a dosage of 8 mg/kg body weight 24 and 1 hr before rats were decapitated. Respiratory functions of the isolated heart mitochondria were measured polarographically with both site 1 (pyruvate-malate and 2-oxoglutarate) and site 2 (succinate) substrates. State 4 (basal) respiration was increased using all substrates in ADM-treated rat hearts compared with non-drug control hearts. The mitochondrial respiratory control index was decreased with ADM, but the reduction was due to an increase in state 4 rather than a decrease of state 3 (ADP-stimulated) respiration. ADM administration abolished an exercise-induced elevation of state 3 respiration using all substrates. There was no significant myocardial oxidative damage of dysfunction as evaluated by lipid peroxidation and antioxidant enzyme activity. Addition of exogenous free radicals to the respiratory medium using hypoxanthine and xanthine oxidase resulted in significant deterioration of mitochondrial function in all parameters measured, but no drug- or exercise-specific patterns of damage were revealed. It is concluded that the current dose of ADM (20% of the established cumulative toxic dose) administered within 24 hr can interfere with normal heart mitochondrial function both at rest and during heavy exercise, but does not elicit overwhelming oxidative damage to the myocardium.

Pharmacodynamics of the hydrolysis-activation of the cardioprotective agent (+)-1,2-bis(3,5-dioxopiperazinyl-1-yl)propane

The hydrolysis of the cardioprotective agent ICRF-187 [(+)-1,2-bis(3,5-dioxopiperazinyl-1-yl)propane] to its presumed active form under conditions of physiologic pH and temperature were followed by HPLC chromatography. Successful chromatography of all of the hydrolysis products required the use of EDTA in the aqueous eluant to prevent metals in the HPLC flow system from binding to the strongly metal ion-binding product ADR-925. The kinetics of the hydrolysis was followed to approximately 200 h. The ring closest to the methyl group on ICRF-187 was observed to open at about twice the rate of the other ring. This product accumulates in the reaction mixture not only because it is produced more quickly but also because it decays more slowly. ICRF-187 is lost from the reaction mixture with a half-life of 9.3 h, whereas the final hydrolysis product ADR-925 is produced with a half-life of 23.0 h. Rate constants for ring opening to one-ring and two-ring opened hydrolysis products were obtained with a reaction scheme that assumed parallel and consecutive first-order reactions for these steps.

In-vivo and in-vitro mitochondrial membrane damages induced in mice by adriamycin and derivatives

A major limitation to a prolonged use of adriamycin (ADM) during a clinical treatment is its dose-dependent cardiotoxicity. This toxicity has been related to a general disturbance of the inner mitochondrial membrane structure and its essential biological functions, associated to the production of free radicals by the anthracyclines. 4'-Epiadriamycin (4'-epiADM), 4'-deoxyadriamycin (4'-deoxyADM), 4'-deoxy-4'-iodoadriamycin (4'-deoxy-4'-iodoADM) and 4'-demethoxydaunorubicin (4-demethoxyDNR) are ADM and daunorubicin (DNR) derivatives differing from their parent compounds by minor structural modifications. They are nevertheless documented as less cardiotoxic. Our purpose was to establish whether mitochondrial membrane damages induced in vivo in mice heart by those compounds are correlated with the free radical formation. Heart mitochondria of treated mice were isolated 48 h after a single drug injection in order to measure the acute mitochondrial toxicity. Enzymatic activities of complex I-III and complex IV of the mitochondrial respiratory chain, mitochondrial membrane fluidity and lipid peroxidation were measured. None of the ADM and DNR derivatives displayed a significant acute mitochondrial toxicity. A mitochondrial toxicity was however detected for 4-deoxyADM and 4-demethoxyDNR when drugs were given chronically, but it was strongly reduced as compared with ADM and DNR. Electron transfer between NADH and cytochrome c, formation of superoxide radicals and lipid peroxidation were measured in vitro for the various drugs. Comparison of the in-vivo and in-vitro results provides evidence that free radical production explains only partly the in-vivo toxicities.

Comparison of adriamycin and derivatives uptake into large unilamellar lipid vesicles in response to a membrane potential

The uptake of adriamycin (ADM) and several derivatives into large unilamellar vesicles (LUV) displaying a transmembrane potential and having a lipid composition close to that of the inner mitochondrial membrane has been measured. Drug association to neutral liposomes, made of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) (70:30, w/w) was shown to be potential-dependent: in the absence of potential, accumulation of drug was almost undetectable, whereas between 11 and 50 nmol of drug/mumol phospholipid, depending on the anthracycline used, was associated to LUV exhibiting a membrane potential after 1 h incubation. Association of drugs to LUV with a lipid composition closer to that of the inner mitochondrial (cardiolipin, CL, 20%; PC 50%; PE, 30%, w/w) and displaying a membrane potential is higher than with neutral vesicles (between 40 and 76 nmol of anthracycline/mumol phospholipid after 1 h incubation). Since it is known that ADM and derivatives have a high affinity for CL, a fraction of the associated drug may bind to CL on the outer side of the vesicles. This was confirmed by the fact that, in the absence of potential, between 40 and 56 nmol of anthracycline/mumol phospholipid was still associated to LUV containing CL. In order to discriminate between drug adsorbed at the surface of the LUV and drug accumulated inside the LUV, an anthracycline fluorescence quencher (I-) was used. It was shown on neutral LUV displaying a membrane potential, that between 55 and 81% of the associated drug is actually entrapped inside the vesicles, inaccessible to the quencher. These percentages decreased to between 41 and 68%, respectively, in the presence of LUV containing CL and exhibiting a membrane potential, whereas for LUV of the same composition but displaying no membrane potential almost all the associated drug is adsorbed on the outer face of the LUV, accessible to the quencher, and likely bound to CL. This study brings evidence that antitumour anthracyclines despite important structural homologies do not accumulate to the same extent into vesicles mimicking the lipid composition and the membrane potential of mitoplasts. This ability to reach the matrix compartment of mitochondria could partly explain the differences of cardiotoxicities associated to anthracyclines with closely related molecular structure.

The removal of metal ions from transferrin, ferritin and ceruloplasmin by the cardioprotective agent ICRF-187 [(+)-1,2-bis(3,5-dioxopiperazinyl-1-yl)propane] and its hydrolysis product ADR-925

The ability of the metal ion binding rings-opened hydrolysis product of the anthracycline cardioprotective agent ICRF-187 [dexrazoxane; (+)-1,2-bis(3,5-dioxopiperazinyl-1-yl)propane] to remove iron from transferrin and ferritin, and copper from ceruloplasmin was examined. ADR-925 completely removed Fe3+ from transferrin at below physiological pH but was unreactive at pH 7.4. ADR-925 slowly removed copper from ceruloplasmin at physiological pH (68% removal after 4.8 days). ADR-925 was capable of removing 18% of the iron from ferritin in 7.0 days. All of the metalloproteins displayed saturation behavior in their initial rates of metal ion removal by ADR-925. ICRF-187 may be, in part, preventing doxorubicin-induced cardiotoxicity by depleting iron and copper from these storage and transport proteins or by scavenging metal ions released from these proteins, thus inhibiting hydroxyl radical production by iron-doxorubicin complexes.

Modulation of glutathione and glutathione dependent antioxidant enzymes in mouse heart following doxorubicin therapy

The toxicity of the antineoplastic agent doxorubicin (DOX) has been shown to be moderated by the antioxidant enzyme glutathione peroxidase. It has been reported that acute doses of DOX can cause an inhibition of glutathione peroxidase in cardiac tissue, that may render this tissue especially susceptible to further prooxidant damage. In this study, multiple DOX treatments at a therapeutic dose were assessed for their effect on the antioxidant enzyme status of cardiac and kidney tissue. DOX was administered i.p. (5 mg/kg) once a week for two weeks to male balb/c mice. The activities of the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPOX) and glutathione reductase (GR) were measured 1, 2 and 7 days following the second DOX treatment in both heart and kidney. Levels of reduced glutathione (GSH) were also measured in cardiac tissue at these same times. Cardiac levels of GPOX and GR showed a time-dependent decrease in activity, with 10% and 12% inhibition for GPOX and GR, respectively, at 7 days post second treatment. Cardiac levels of GSH also showed a significant decrease, approximately 15%, at 7 days post second treatment. Cardiac levels of SOD and CAT as well as kidney levels of all four antioxidant enzymes were not affected by DOX treatment. These data suggest that DOX given in a therapeutic regimen, at a therapeutic dose, can cause decreases in cardiac levels of GPOX, GR and GSH that could render the heart especially susceptible to further oxidative challenge.

Covalent modification of DNA by daunorubicin

Daunorubicin, a clinically useful antitumor agent, induces mammary adenocarcinoma in Sprague-Dawley rats. As part of an investigation of the mechanism of tumor induction by daunorubicin, the formation of daunorubicin-DNA adducts has been investigated by 32P-postlabeling assay. Rat-liver DNA incubated with either 0.05 or 0.1 mM daunorubicin, rat-liver microsomes, and 5 mM reduced nicotinamide adenine dinucleotide phosphate (NADPH) for 1 h contained covalent DNA adducts in addition to the endogenous adduct profile present in control DNA. With 1.5 mM cumene hydroperoxide serving as a cofactor, higher levels of these two adducts and two additional adducts were formed, all of which most likely were daunorubicin-DNA adducts. This latter treatment also resulted in an intensification of three endogenous DNA modifications over levels occurring in control DNA. Covalent DNA alterations in vivo were studied in rats treated with 20 mg/kg daunorubicin for 2 days and 200 mg/kg on the 3rd day. Daunorubicin-DNA adducts as observed in vitro could not be detected in DNA of liver or mammary epithelial cells. The levels of endogenous modifications in drug-treated rats were increased by 200% in mammary DNA and by 50% in hepatic DNA as compared with controls. It was concluded from these experiments that daunorubicin may be metabolically activated to a reactive metabolite that binds covalently to DNA. These daunorubicin-DNA adducts may not play a role in tumor induction because they were not detectable in vivo. However, the increase in levels of endogenous DNA modifications induced by daunorubicin both in vitro and in vivo is consistent with a role of this class of DNA modification in the carcinogenic process.

Fungal quinone pigments as oxidizers and inhibitors of mitochondrial NADH:ubiquinone reductase

The interaction of fungal quinone pigments bostricoidin, fusarubin, javanicin, and 2-oxyjuglone with mitochondrial NADH:ubiquinone reductase (complex I, EC 1.6.99.3) has been studied. The bimolecular rate constants (turnover number (TN)/Km) of rotenone-insensitive reduction of these compounds are in the range of 1.2 x 10(4)-1.6 x 10(5) M-1s-1. 2-Oxyjuglone acts as inhibitor of NADH:ferricyanide reductase reaction of complex I (KI = 30 microM). All quinone pigments, except javanicin, decrease the TN of reduction of 5,8-dioxy-1,4-naphtoquinone being reduced at its binding site but with significantly lower TN. They do not affect the rotenone-sensitive reduction of ubiquinone-1. The binding of quinone pigments close to the NADH and ferricyanide binding site is suggested. It seems that quinone pigments, especially 2-oxyjuglone, react with complex I faster than it follows from their approximate values of one-electron reduction potential calculated from their reactivities with flavocychrome b2 and adrenodoxin.

PZ-51 (Ebselen) in vivo protection against adriamycin-induced mouse cardiac and hepatic lipid peroxidation and toxicity

Adriamycin (Adr)-induced cardiotoxicity occurs most likely via an oxidative mechanism of action. Moderation of this activity may result in an improved therapeutic index for this compound. PZ-51, 2-phenyl-1,2-benzoisoselenazol-3(2H)-one, is a selenoorganic compound with thiol-dependent, peroxidase-like activity. We tested this compound alone and in combination with N-acetylcysteine (NAC) for its effect on Adr-induced in vivo toxicity in Balb/c mice. These studies demonstrated that PZ-51 protects against Adr-induced lipid peroxidation in heart and liver tissue and Adr-induced toxicity in general, as measured by total serum creatine kinase activity and body weight.

Subcellular distribution of two spin trapping agents in rat heart: possible explanation for their different protective effects against doxorubicin-induced cardiotoxicity

Previous investigations, performed on isolated rat atria, showed that the lipophylic spin-trapping agent N-tert-butyl- alpha-phenylnitrone (PBN) is able to prevent the acute cardiotoxic effects produced by doxorubicin (DXR), whereas the hydrophylic compound 5,5-dimethyl-pyrroline-N-oxide (DMPO) is inactive. The present study was designed to ascertain whether differences in the pharmacological effects of the two spin traps are related to their different subcellular distribution. Langendorff rat hearts were perfused for 60 minutes with [14C]-DXR and either PBN or DMPO. The subcellular mapping of the three compounds was performed by measuring DXR by liquid scintillation counting, PBN by GC/MS, and DMPO by HPLC in the following isolated fractions: nuclei, mitochondria, sarcoplasmic reticulum, sarcolemma, cytosol. DMPO was shown to accumulate in the cytosolic compartment; both PBM and DXR are taken up by nuclei and mitochondria, while only trace amounts of DXR were detected in the sarcoplasmic reticulum. These results suggest that mitochondrial (and not sarcoplasmic) enzymes are mainly involved in DXR-induced free radical production, which is thought to cause the acute cardiotoxic effects of DXR. An involvement of DXR-induced free radical generation in the nuclear compartment seems unlikely in the short-term "in vitro" effects observed with the experimental model adopted for these studies, although it may play a role in the delayed pathology.

Paraquat damage of rat liver mitochondria by superoxide production depends on extramitochondrial NADH

Pure rat liver heavy mitochondrial fractions, in which the absence of significant microsomal contamination was confirmed by electron microscopy and by the lack of glucose-6-phosphatase activity, were used to demonstrate the effect of paraquat on mitochondrial ultrastructure in the presence of external NADH. Starved mitochondria (orthodox conformation) did not show O2 uptake or structural injury from either paraquat alone or NADH alone. Marked O2 uptake and structural breakage occurred only when paraquat and NADH were added in combination. These alterations were resistant to rotenone and malate plus glutamate or NADPH could not substitute for NADH. Paraquat was reduced anaerobically by the mitochondria in the presence of NADH, but not of NADPH. The addition of superoxide dismutase, ferricytochrome c or p-benzoquinone protected against the breakage of mitochondria caused by paraquat plus NADH. These results demonstrate that mitochondria may produce paraquat radicals in the presence of extramitochondrial NADH and thus generate superoxide anion radicals, resulting in structural injury to the mitochondria, by mechanisms that may involve the mitochondrial outer membrane rather than the electron transfer chain. These mitochondrial mechanisms in paraquat toxicity seemed to be more probable in vivo than are microsomal mechanisms; the latter are postulated to function in detoxication because phenobarbital diminished paraquat toxicity and SKF 525-A or cobaltous ions enhanced the toxicity.

Protection by salvianolic acid A against adriamycin toxicity on rat heart mitochondria

It was found that salvianolic acid A (Sai A) has potent antioxidant activity. The effects of Sai A on adriamycin-induced heart mitochondrial toxicity of rats in vitro and on adriamycin antitumor activity are investigated in this article. Malondialdehyde (MDA) formation and membrane rigidification of rat heart mitochondria intoxicated with adriamycin were significantly reduced by Sai A. In the electron spin resonance (ESR) studies, Sai A has no significant effect on the formation of adriamycin semiquinone radicals (AQ.), while hydroxyl radicals generated by electron transfer from AQ. to H2O2 were scavenged by Sai A dose-dependently. On the other hand, Sai A was shown to have no effects on the antitumor activity of adriamycin in cultured L1210 ascitic tumor cells and in mice with P388 ascite tumor. These results indicate that Sai A protects against adriamycin induced heart mitochondrial toxicity of rats, while Sai A has no antagonizing effect on the antitumor activity of adriamycin.