Myocardial contractility and heart pharmacokinetics of adriamycin following a single administration in rat

The Rat Model in the Comparative Evaluation of Anthracyclines Cardiotoxicity

In the present investigation, the cardiotoxic effects of three anthracycline analogs (doxorubicin, 4′-epi-doxorubicin and 4′-deoxy-doxorubicin) were compared. For this purpose, 9.0 mg/kg of doxorubicin, divided into three closely spaced sub-doses, were injected intravenously in rats. The two derivatives were administered according to the same time schedule and their doses were chosen on the basis of the clinically adopted ratio, doxorubicin : 4′-epidoxorubicin : 4′-deoxy-doxorubicin = 1:1: 0.5. The degree of cardiomyopathy induced by the three anthracyclines was evaluated by ECG changes and morphological alterations. Doxorubicin was found to produce a significant degree of cardiotoxicity, thus confirming the validity of the experimental model adopted. Both 4′-substituted derivatives proved to be less cardiotoxic than the parent compound, although not completely devoid of this side effect.

Doxorubicin induced heart failure: Phenotype and molecular mechanisms

Long term survival of childhood cancers is now more than 70%. Anthracyclines, including doxorubicin, are some of the most efficacious anticancer drugs available. However, its use as a chemotherapeutic agent is severely hindered by its dose-limiting toxicities. Most notably observed is cardiotoxicity, but other organ systems are also degraded by doxorubicin use. Despite the years of its use and the amount of information written about this drug, an understanding of its cellular mechanisms is not fully appreciated. The mechanisms by which doxorubicin induces cytotoxicity in target cancer cells have given insight about how the drug damages cardiomyocytes. The major mechanisms of doxorubicin actions are thought to be as an oxidant generator and as an inhibitor of topoisomerase 2. However, other signaling pathways are also invoked with significant consequences for the cardiomyocyte. Further the interaction between oxidant generation and topoisomerase function has only recently been appreciated and the consequences of this interaction are still not fully understood. The unfortunate consequences of doxorubicin within cardiomyocytes have promoted the search for new drugs and methods that can prevent or reverse the damage caused to the heart after treatment in cancer patients. Alternative protocols have lessened the impact on newly diagnosed cancer patients. However the years of doxorubicin use have generated a need for monitoring the onset of cardiotoxicity as well as understanding its potential long-term consequences. Although a fairly clear understanding of the short-term pathologic mechanisms of doxorubicin actions has been achieved, the long-term mechanisms of doxorubicin induced heart failure remain to be carefully delineated.

Telemetrically monitored arrhythmogenic effects of doxorubicin in a dog model of heart failure

A model of chronic heart failure has been induced in dogs by repeated intracoronary infusion of doxorubicin, which is an antineoplastic medication that has dose-limiting cardiotoxic side effects. Although many of the dogs receiving doxorubicin develop typical signs of dilated cardiomypathy over 4-6 weeks, some of them suddenly die before completing the four weekly infusions of the drug. The present study was undertaken to determine whether such sudden death may be caused by the development of fatal arrhythmias during doxorubicin treatment. This was assessed by telemetrically monitoring the EKG of seven dogs, which received intracoronary infusion of 1 mg/kg doxorubicin given in four divided weekly doses. The recordings were obtained for 8-10 h on alternate days up to 4 weeks. Echo-cardiographic recordings were obtained once a week. The acute effects with each infusion of doxorubicin included a significant increase in heart rate, and no significant change in QRS complex. The cumulative prolonged effects of doxorubicin included slight reduction in QRS amplitude and duration, and marked arrhythmic changes. Four out of seven dogs showed a spectrum of arrhythmic events such as single or groups of premature ventricular complexes (PVCs), bigeminy, ventricular tachycardia (VTAC), ventricular fibrillations (VFIB), and asystole. All dogs did not show each of the events listed above and the same dog did not show all the events all the time. One of these four dogs developed VFIB for 25 min and then asystole leading to sudden death. These studies conclusively showed that fatal arrhythmias develop in some of the dogs receiving doxorubicin treatment accounting for the sporadic incidence of sudden death. Prophylactic treatment with antiarrhythmic agents may prevent such adverse events.

Doxorubicin induces early lipid peroxidation associated with changes in glucose transport in cultured cardiomyocytes

Doxorubicin (DOX) has not only chronic, but also acute toxic effects in the heart, ascribed to the generation of reactive oxygen species (ROS). Focusing on the DOX-induced early biochemical changes in rat cardiomyocytes, we demonstrated that lipid peroxidation is an early event, in fact conjugated diene production increased after 1-h DOX exposure, while cell damage, evaluated as lactate dehydrogenase (LDH) release, was observed only later, when at least one third of the cell antioxidant defences were consumed. Cell pre-treatment with alpha-tocopherol (TC) inhibited both conjugated diene production and LDH release. In cardiomyocytes, DOX treatment caused a maximal increase in glucose uptake at 1 h, demonstrating that glucose transport may represent an early target for DOX. At longer times, as the cell damage become significant, the glucose uptake stimulation diminished. Immunoblotting of glucose transporter isoform GLUT1 in membranes after 1-h DOX exposure revealed an increase in GLUT1 amount similar to the increase in transport activity; both effects were inhibited by alpha TC. Early lipid peroxidation evokes an adaptive response resulting in an increased glucose uptake, presumably to restore cellular energy. The regulation of nutrient transport mechanisms in cardiomyocytes may be considered an early event in the development of the cardiotoxic effects of the anthracycline.

The action of 2,4-Dichlorophenoxyacetic acid on the isolated heart of insect and amphibia

The action of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) on the isolated heart of the frog (Rana ridibunda) and two insects, the honeybee (Apis mellifera macedonica) and the beetle (Tenebrio molitor), was investigated using basic electrophysiological methods. The results of this study showed that a concentration of 1 μM 2,4-D was required to reduce the force and the frequency of the isolated heart of the honeybee to about 70% of the initial contraction in less than 20 min. To cause the same effects on the atria of the frog, 45 μM 2,4-D was required and on the isolated heart of the beetle, over 1000 μM of 2,4-D. The presence of an extensive system of gap junctions found in the honeybee is most probably the cause of the unusual sensitivity of its heart to 2,4-D, compared with the heart of the beetle, where no gap junctions were identified.

Adriamycin-induced changes of creatine kinase activity in vivo and in cardiomyocyte culture

Adriamycin (ADM) is an anthracycline anti-neoplastic agent, whose clinical effectiveness is limited by severe side effects, including cardiotoxicity. The toxic effects of ADM are likely to be the consequence of the generation of free radicals. This study demonstrates that ADM induces significant changes in the activity of the oxidative sensitive enzyme creatine kinase (CK) in the heart in vivo and in a cardiomyocyte culture model. The changes observed are likely to reflect the ability of ADM to damage the plasma membrane of cardiac cells and to induce the direct inactivation of CK. The role for ADM-derived free radicals is one of the possible mechanisms for the CK inactivation observed during the ADM treatment.

Effects of combined irradiation and doxorubicin treatment on cardiac function and antioxidant defenses in the rat

Combined radiotherapy and chemotherapy have represented a major advance in the therapeutic management of cancer therapy. However, the combination of doxorubicin (DXR) and cardiac irradiation (IRR) could precipitate the unexpected expression of congestive heart failure. Oxidative lesions induced by IRR and DXR could represent one of the pathogenic factors of myocardial dysfunction. Our investigations were performed to evaluate in the rat: 1) cardiac functional changes, 2) cardiac and plasma peroxidative damage and antioxidant defenses variations, that occur 24 h (acute effects) and 30 d (middle term effects) following DXR treatment 1 mg/kg(-1)/day(-1) IP for 10 d and a 1 x 20 Gy cardiac gamma-irradiation. Our results showed that DXR affected heart reactivity as early as the end of its administration, although irradiation exerted no detectable effect. Antioxidant defenses disturbances in hearts of DXR treated rats were characterized by vitamins C and E decreases, catalase activity induction and an increase in lipid peroxidation. Moreover, plasma vitamin C consumption and the lower level of plasma lipid peroxidation attested to the efficient solicitation of antioxidant defenses that probably contributed to the preservation of cardiac function at 24 h. After 30 d, cardiac dysfunction became symptomatic at rest, resulting from DXR cardiac toxicity. In spite of the persistent activation of cardiac catalase activity, antioxidant deficiency and increased plasma and cardiac lipid peroxidation highlighted defenses overtaken. Thus, different physiopathological mechanisms are involved in heart disturbance at acute and middle terms, IRR and DXR acting on distinct targets without disclosing synergistic effects. After 30 d, cardiac and plasma biochemical abnormalities were emphasized by the combined DXR+IRR therapy, pointing out the severity of the damage. Oxidative damage to the heart induced both by irradiation and DXR, may be one of the pathogenic factors of myocardial dysfunction. There is the possibility that the deleterious effects might be limited by the use of pharmacologic antioxidant agents.

Adriamycin induces protein oxidation in erythrocyte membranes

Adriamycin is an anthracycline antineoplastic agent whose clinical effectiveness is limited by severe side effects, including cardiotoxicity. A current hypothesis for adriamycin cardiotoxicity involves free radical oxidative stress. To investigate this hypothesis in a model system, we applied the technique of immunochemical detection of protein carbonyls, known to be increased in oxidized proteins, to study the effect of adriamycin on rat erythrocyte membranes. Erythrocytes obtained from adriamycin-treated rats demonstrated an increase of carbonyl formation in their membrane proteins. Yet, in separate experiments when adriamycin was incubated with rat erythrocyte ghosts, there was no significant increase of membrane protein carbonyls detected. In contrast, isolated erythrocytes incubated with an adriamycin-Fe3+ complex exhibited a robust carbonyl incorporation into their membrane proteins in a time-dependent manner. The level of carbonyl formation was dependent upon the concentration of Fe3+ known to form the adriamycin-Fe3+ complex. When the time course between protein carbonyl formation and lipid peroxidation was compared, protein carbonyl detection occurred earlier than lipid peroxidation as assayed by thiobarbituric acid reactive substances formation. These results are consistent with the notion that oxidative modification of membrane proteins may contribute to the development of the acute adriamycin-mediated toxicity.

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.

Development of the model of rat isolated perfused heart for the evaluation of anthracycline cardiotoxicity and its circumvention

1. In order to develop a predictive model for the preclinical evaluation of anthracycline cardiotoxicity and the means of preventing it, we have studied the functional parameters of perfused hearts isolated from rats receiving repeated doses of several anthracyclines. 2. The anthracyclines studied were doxorubicin, epirubicin, pirarubicin and daunorubicin, and we also studied a liposomal formulation of daunorubicin (DaunoXome) and the co-administration of dexrazoxane (ICRF-187) and doxorubicin. 3. Anthracyclines were administered i.p. at equimolar doses corresponding to 3 mg kg-1 per injection of doxorubicin, every other day for a total of six doses. Dexrazoxane was used at the dose of 30 mg kg-1 per injection and was administered either 30 min before or 30 min after doxorubicin. We evaluated any general toxicity towards the animals as well as alterations of left ventricular contractility and relaxation ex vivo. 4. Epirubicin and daunorubicin were significantly less cardiotoxic than doxorubicin, and neither pirarubicin nor DaunoXome caused significant alterations in cardiac function. There was a direct relationship between the decrease in cardiac contractility or relaxation and anthracycline accumulation in the heart, evaluated after the same treatment schedule. 5. Dexrazoxane induced a significant protection against doxorubicin-induced cardiac toxicity when administered 30 min before doxorubicin, whereas this protection was ineffective when administered 30 min after doxorubicin. Direct perfusion of DaunoXome in isolated hearts of untreated animals resulted in a 12-fold reduction of the accumulation of daunorubicin in heart tissue as compared to the perfusion of free daunorubicin, and did not cause alterations in cardiac function at a dosage for which free daunorubicin induced major alterations. 6. The isolated perfused rat heart appears to be a valuable model for screening of new anthracyclines and of strategies for circumventing anthracycline cardiotoxicity.

Pharmacological action of a new spin trapping compound, 2-phenyl DMPO, in the adriamycin-induced cardiotoxicity

Adriamycin (ADR)-induced cardiotoxicity was adopted in this investigation as a reliable model of radical-dependent myocardial pathology allowing both quantitative studies of drug activity in the isolated organ and in vivo comparison of the cardio-protection vs. general toxicity. Since commercially available lipophilic spin trapping compounds were shown to develop significant protective activity, in this investigation a newly synthesized spin trap (2-phenyl-DMPO) was studied. In Langendorff rat heart, 200 microM ADR induced a significant impairment of contractile performance, while 2-phenyl-DMPO was not cardiotoxic up to the 5 mM concentration. By this dose, 2-phenyl-DMPO induced a significant protection against the ADR-induced contractile impairment. In in vivo experiments, ADR (9 mg/kg i.v.) produced a significant impairment of ECG, coronary flow and contractility. The continuous administration of 2-phenyl-DMPO i.p. by osmotic pump delivering 0.3 mumol/hr was unable to protect the animals against the cardiotoxic signs. Seven days after ADR administration, severe general toxicity (arrest of body weight increase) and myelotoxicity were also observed. 2-phenyl-DMPO was unable to protect the animals from these toxic signs. The present results confirm that lipophilic spin traps can be a new class of antiradical drugs, as confirmed by the experiments performed in the isolated heart with the 2-phenyl-DMPO; however, this last compound is probably metabolized in vivo to inactivate derivatives.

Timing of treatment with ICRF-187 and its effect on chronic doxorubicin cardiotoxicity

Studies were conducted to evaluate whether the timing of administration of ICRF-187 [(+)-1,2-bis(3,5 dioxopiperazinyl-1-yl)propane] would influence the degree of cardioprotection provided by this agent against the development of doxorubicin-induced chronic cardiomyopathy. Beagle dogs (8.5-14 kg) received either doxorubicin alone (1.75 mg/kg, i.v., n = 8), doxorubicin (1.75 mg/kg) simultaneously with ICRF-187 (35 mg/kg, i.v., n = 8), or doxorubicin (1.75 mg/kg) followed 2 h later by ICRF-187 (35 mg/kg, n = 8). Control animals received ICRF-187 (35 mg/kg, n = 4) or saline (n = 4). All animals received a course of seven treatments, each given 3 weeks apart, and were killed 3 weeks after the last treatment. Semiquantitative grading of histologic sections of myocardium showed that as compared with animals treated with doxorubicin alone, the incidence and the severity of the doxorubicin-induced myocardial lesions were reduced in the two groups of animals given doxorubicin plus ICRF-187. However, protection was significantly better in dogs receiving ICRF-187 and doxorubicin simultaneously than in those given ICRF-187 2 h after doxorubicin. These observations were interpreted as indicating that the timing of administration of ICRF-187 with respect to that of doxorubicin is an important factor in determining the degree of cardioprotection and that there is a "time window" in which ICRF-187 exerts optimal effects.

Cardiotoxicity induced by doxorubicin in vivo: protective activity of the spin trap alpha-phenyl-tert-butyl nitrone

The role of free radical generation in the development of the acute cardiotoxicity induced by doxorubicin (DXR) in the rat and the protective activity of anti-radical drugs were investigated in in vivo experiments by evaluating the body weight curve, ECG, contractile performance and coronary flow up to 10 days after DXR. A lipophilic spin trap (alpha-phenyl-tert-butyl nitrone, PBN) was continuously administered at a dose of 0.65 mg/kg every hour for 2 weeks by an intraperitoneal osmotic pump. DXR was administered i.v. at a dose of 9 mg/kg 3 days after beginning the PBN infusion. DXR impaired ECG and body weight gain after 3 days (partly reversible at later times), while contractility and coronary flow were significantly impaired throughout the experimental time. PBN was shown to prevent the DXR-induced alterations of contractility and coronary flow, while ECG was non-significantly improved. The body weight curve was not affected. Since the dose of PBN used does not produce pharmacological effects, the protective activity in rats receiving DXR indicates that free radicals may play a causal role in the acute cardiotoxicity in vivo. The use of suitable spin traps and administration schedules seems to be an interesting approach for the prevention of radical-dependent pathologies.

Effect of flunarizine on the delayed cardiotoxicity of doxorubicin in rats

The calcium antagonist flunarizine (FLN) was tested for its ability to prevent doxorubicin (DXR)-induced cardiotoxicity in the rat. A cumulative dose of 9.0 mg/kg of DXR was administered i.v. over a period of 1 week. FLN (10 mg/kg/day i.p., 6 days/week) was administered according to two different time schedules, covering respectively the first and last 4 weeks after the beginning of DXR treatment. The two schedules were adopted to assess whether early and/or delayed DXR-induced cardiotoxic effects were affected by FLN. The development of cardiac toxicity was monitored by ECG recordings. The animals were sacrificed 8 weeks after the beginning of DXR treatment. The contractile performance of isolated atria and the morphological pattern of left ventricular fragments were subsequently evaluated. The early administration schedule of FLN was shown to be ineffective in preventing DXR-induced cardiotoxicity and in some cases was actually found to potentiate the effects of DXR. In contrast, the histological evaluation of ventricular preparations from rats treated with DXR and FLN according to the delayed time schedule showed a significant improvement with respect to hearts from animals treated with DXR alone. An inhibition of the delayed calcium overload occurring after DXR administration has been proposed as a possible mechanism for this protective action.

Doxorubicin cardiotoxicity may be caused by its metabolite, doxorubicinol

Doxorubicin (former generic name, adriamycin), a highly effective anticancer drug, produces cardiotoxicity, which limits its therapeutic potential. The mechanism of this cardiotoxicity has remained elusive. Our data suggest that this toxicity could involve doxorubicinol, the primary circulating metabolite of doxorubicin. Doxorubicinol was markedly more potent than doxorubicin at compromising both systolic and diastolic cardiac function. Similarly, doxorubicinol was much more potent than doxorubicin at inhibiting the calcium pump of sarcoplasmic reticulum [ATP phosphohydrolase (Ca2+-transporting), EC 3.6.1.38], the Na+/K+ pump of sarcolemma [ATP phosphohydrolase (Na+/K+-transporting), EC 3.6.1.37], and the F0F1 proton pump of mitochondria [ATP phosphohydrolase (H+-transporting, EC 3.6.1.34]. Our finding that this highly toxic metabolite was produced by cardiac tissue exposed to doxorubicin suggests that doxorubicinol could accumulate in the heart and contribute significantly to the chronic cumulative cardiotoxicity of doxorubicin therapy. Our observation that doxorubicin was more potent than doxorubicinol in inhibiting tumor cell growth in vitro suggests that the cardiotoxicity of doxorubicin is dissociable from its anticancer activity.