Acute effects of doxorubicin (adriamycin) on left ventricular function in dogs

The Effects of Repeat-Dose Doxorubicin on Cardiovascular Functional Endpoints and Biomarkers in the Telemetry-Equipped Cynomolgus Monkey

Purpose: Doxorubicin-related heart failure has been recognized as a serious complication of cancer chemotherapy. This paper describes a cardiovascular safety pharmacology study with chronic dosing of doxorubicin in a non-human primate model designed to characterize the onset and magnitude of left ventricular dysfunction (LVD) using invasive and non-invasive methods.

Methods: Cynomolgus monkeys (N = 12) were given repeated intravenous injections of doxorubicin over 135 days (19 weeks) with dosing holidays when there was evidence of significantly decreased hematopoiesis; a separate group (N = 12) received vehicle. Arterial and left ventricular pressure telemetry and cardiac imaging by echocardiography allowed regular hemodynamic assessments and determination of LVD. Blood samples were collected for hematology, clinical chemistry, and assessment of cardiac troponin (cTnI) and N-terminal pro b-type natriuretic peptide (NT-proBNP). Myocardial histopathology was a terminal endpoint.

Results: There was variable sensitivity to the onset of treatment effects, for example 25% of doxorubicin-treated animals exhibited LVD (e.g., decreases in ejection fraction) following 50–63 days (cumulative dose: 8–9 mg/kg) on study. All animals deteriorated into heart failure with additional dosing 135 days (total cumulative dose: 11–17 mg/kg). Reductions in arterial pressure and cardiac contractility, as well as QTc interval prolongation, was evident following doxorubicin-treatment. Both cTnI and NT-proBNP were inconsistently higher at the end of the study in animals with LVD. Measurements collected from control animals were consistent and stable over the same time frame. Minimal to mild, multifocal, vacuolar degeneration of cardiomyocytes was observed in 7 of 12 animals receiving doxorubicin and 0 of 12 animals receiving vehicle.

Conclusions: This repeat-dose study of doxorubicin treatment in the cynomolgus monkey demonstrated a clinically relevant pattern of progressive heart failure. Importantly, the study revealed how both telemetry and non-invasive echocardiography measurements could track the gradual onset of LVD.

Assessment of cardiac troponin I (cTnI) and tissue velocity imaging (TVI) in 14 dogs with malignant lymphoma undergoing chemotherapy treatment with doxorubicin

Doxorubicin has been shown to be cardiotoxic at high doses but is an efficacious chemotherapeutic agent in the treatment of canine lymphoma. Echocardiographic measurements and serum ultrasensitive cardiac troponin I (cTnI) levels were obtained before and after doxorubicin administration in 14 dogs diagnosed with lymphoma. The aim of this prospective study was to evaluate changes in cTnI concentrations and tissue velocity imaging (TVI) values in dogs with lymphoma undergoing chemotherapy with doxorubicin. A total of 182 cTnI and 1017 TVI measurements were performed. Standard echocardiographic parameters, tissue Doppler indices and cTnI concentrations did not differ at any time point within a 12-week cyclic combination protocol. In conclusion, the use of doxorubicin at standard doses in the treatment of canine lymphoma may not be associated with significant myocardial damage.

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.

Adriamycin-induced cardiomyopathy in the dog--an appropriate model for research on partial left ventriculectomy?

OBJECTIVE

To evaluate the adriamycin-induced cardiomyopathy in the dog for research on partial left ventriculectomy (PLV).

METHODS

An intracoronary catheter was introduced into the left main stem via the first diagonal branch in a retrograde fashion in 6 adult FBI (Foxhound Boehringer Ingelheim) dogs weighing 30 to 35 kg. The catheter was connected to a percutaneous access port that was used for weekly adriamycin administration (10 mg over a 1-hour period for 5 times). Follow-up examinations (transthoracic echocardiography, hemodynamic parameters, cardiopulmonary status, and neurohormones) were done before, 1 week after the last adriamycin administration, and 6 weeks later. After the last measurements, all dogs were euthanized with saturated potassium chloride under general anesthesia and the hearts were excised for histologic examinations. All data were calculated as mean values and standard error of the mean. Differences were calculated by the Wilcoxon signed rank test for paired and unpaired data. p values less than 0.05 were considered significant.

RESULTS

Central venous pressure (2.2 +/- 0.8 vs 5.2 +/- 0.4 mm Hg, p = 0.03), mean pulmonary artery pressure (8.6 +/- 1.1 vs 12.4 +/- 0.5 mm Hg, p = 0.03), pulmonary wedge pressure (2.6 +/- 0.9 vs 7.0 +/- 0 mm Hg, p = 0.03), left ventricular endsystolic diameter (2.5 +/- 0.2 vs 3.1 +/- 0.4 cm, p = 0.03), and enddiastolic (4.5 +/- 0.2 vs 4.9 +/- 0.2 cm, p = 0.03) diameter increased significantly after adriamycin administration, whereas cardiac output (4.0 +/- 0.3 vs 3.3 +/- 0.1 liter/min, p = 0.03), stroke volume index (66.0 +/- 7.4 vs 54.0 +/- 3.9 ml/beat/m(2), p = 0.03), and ejection fraction (61.1 +/- 5.1 vs 37.7 +/- 5.7%, p = 0.03) decreased markedly. These changes were accompanied by a significant decline of oxygen delivery (1130 +/- 170 vs 790 +/- 65 ml/min, p = 0.03), which led to an enhanced oxygen extraction (0.12 +/- 0.01 vs 0.24 +/- 0.01, p = 0.03). Consequently, venous oxygen saturation (82.7 +/- 4.1 vs 71.3 +/- 2.5%, p = 0.03) decreased. Troponin I (0.02 +/- 0.025 vs 1.7 +/- 0.6 ng/ml, p = 0.03) and the anti-diuretic hormone (1.9 +/- 0.9 vs 20.0 +/- 1.9 pg/ml, p = 0.03) increased significantly after adriamycin administration. Deterioration of cardiac function continued after termination of adriamycin administration, albeit slower than during adriamycin administration. All hearts had severe histologic alterations, which were characteristic of adriamycin-induced toxicity: cytoplasmic vacuolation, myocyte degeneration, and increased fibrosis.

CONCLUSIONS

The adriamycin-induced cardiomyopathy in the dog is similar to the dilated cardiomyopathy in humans and may be an appropriate model for PLV.

Acute presynaptic inhibition by doxorubicin of negative chrono- and inotropic responses to parasympathetic nerve stimulation in isolated, blood-perfused dog atrium

The clinical use of doxorubicin, an anthracycline antineoplastic agent, is limited by its cardiotoxicity. Although several previous reports have shown neurotoxic effects of doxorubicin, there is little information about the acute effects of doxorubicin on the autonomic nerve functions in the heart. Accordingly, to evaluate the effects of doxorubicin on the cardiac responses to autonomic nerve activation, we studied the effects of doxorubicin on the negative chrono- and inotropic responses to intracardiac parasympathetic nerve stimulation and acetylcholine (ACh), and the positive chrono- and inotropic responses to norepinephrine (NE) in the isolated, blood-perfused dog atrium. Doxorubicin (0.01-3 mumol), injected into the sinus node artery of the isolated atrium, induced negative inotropic effects dose dependently and weak negative chronotropic effects. Doxorubicin inhibited the negative chrono- and inotropic responses to parasympathetic nerve stimulation dose dependently. However, doxorubicin affected neither the negative chrono- and inotropic responses to ACh nor the positive chrono- and inotropic responses to NE. These results indicate that doxorubicin interacts with neither muscarinic receptors nor beta-adrenoceptors and suggest that doxorubicin inhibits the negative cardiac responses to parasympathetic nerve activation due to the inhibition of ACh release from nerve varicosities in the heart.

A model of left ventricular dysfunction caused by intracoronary adriamycin

Experimental evaluation of new therapy for congestive heart failure has been hampered by the lack of a simple and reliable animal model of heart failure. This study was undertaken to develop a canine model of chronic left ventricular dysfunction. A left thoracotomy was performed in 9 adult mongrel dogs. A 1.5-mm Silastic (Dow Corning) catheter with an attached subcutaneous access port was positioned in the left main coronary artery. Six animals received five weekly infusions of Adriamycin (doxorubicin hydrochloride) (10 mg/wk), and 3 received saline solution. Hemodynamic studies were performed before insertion of the catheter and 2 weeks after completion of the infusions. In animals that received Adriamycin, rest ejection fraction declined from 0.54 +/- 0.03 to 0.35 +/- 0.03, cardiac output fell from 5.6 +/- 0.6 to 3.9 +/- 0.5 L/min, and left ventricular end-diastolic volume increased from 76 +/- 9 to 99 +/- 12 mL (p less than 0.05). There was a small increase in right atrial pressure (2.7 +/- 1 versus 5.7 +/- 1 mm Hg) but no change in right ventricular ejection fraction (0.31 +/- 0.04 versus 0.30 +/- 0.03). In no animal did alopecia, weight loss, neutropenia, or anemia develop. Histological changes consistent with Adriamycin-induced cardiac toxicity were found in each dog. No significant hemodynamic or histological changes occurred in the control animals. Administration of Adriamycin into the left main coronary artery causes left ventricular dysfunction without resulting in systemic side effects or compromising right ventricular function. This animal model could be used to evaluate the effects of new possible therapy, such as cardiomyoplasty, on left ventricular failure.

Reducing doxorubicin cardiotoxicity in the rat using deferred treatment with ADR-529

The purpose of this study was to evaluate the optimal timing of ADR-529 administration to protect rats treated with doxorubicin (DXR) against drug-induced cardiotoxicity. Complete electrocardiographic monitoring (QRS complex, S alpha T segment and T wave) and the histopathological analysis of cardiac tissue were used to assess the degree of heart damage produced in female rats treated with ten i.v. doses of 1 mg/kg DXR over a period of 15 weeks; body-weight increase and survival were also analyzed to evaluate the toxicity of treatments. Cardiac alterations induced by DXR were compared with those occurring in animals receiving 20 mg/kg i.v. ADR-529 at 30 min prior to DXR administration, starting at the first, third, or sixth DXR dose and given until the end of the study (15th week). Rats treated with DXR were severely cardiomyopathic, showing progressive and irreversible ECG alterations (QRS-complex and S alpha T-segment widening and T-wave flattening) and marked degeneration of the myocardium (myocyte vacuolation, myofibrillar loss, and endomyocardial fibrosis). The most effective cardiac protection was provided by the administration of ADR-529 beginning with the first or third DXR dose. Delaying treatment with ADR-529 until the sixth DXR dose resulted in a significant reduction in its therapeutic action on heart damage. A significant difference in body-weight increase and survival was observed between the treatment groups: ADR-529 injected prior to the first DXR dose significantly protected animals from DXR toxicity, but this schedule was significantly more toxic than the administration of ADR-529 beginning with the third or sixth DXR dose. Taking into account the degree of cardiac protection and the toxicity of combination treatments, the results of the present study demonstrate the superiority of ADR-529 given prior to the third DXR dose over the other schedules tested. This finding suggests that significant protection against DXR-induced chronic cardiotoxicity in the rat can be obtained using deferred treatment with ADR-529.

Anthracycline gels

Gels have been prepared from aqueous solutions of anthracyclines by addition of salts. The gels are thixotropic and thermally reversible. They are stable for several months in the refrigerator and for long times even at room temperature. The gel-solution transition (melting) temperature depends on the concentration of the anthracycline and on the concentration and nature of the added salt. The melting has been followed by 1H-NMR. Only weak intermolecular interactions (stacking and hydrogen bonds) originate the drug network, within which the solvent is entrapped. 1H-NMR and polarimetric data suggest a stacked helical arrangement of the anthracycline molecules. The gelation process is cooperative.

A simple, non-invasive method of assessing the acute hemodynamic effects of doxorubicin

Left ventricular stroke distance was measured by Doppler ultrasound in 10 doxorubicin-treated and 10 control patients. Measurements were made 10 min, 2 h and 4 h after drug administration. Stroke distance (a linear analogue of stroke volume) increased significantly from 12.6 cm (S.D. 2.7) before and 12.5 cm (S.D. 2.7) 10 min after, to 13.6 cm (S.D. 2.8) 2 h after and 13.7 cm (S.D. 2.7) 4 h after doxorubicin (p less than 0.05). Throughout the study period there were no significant changes in stroke distance in the control patients who were infused with similar fluid volumes, and no significant changes in heart rate or blood pressure in either group. These observations confirm previous findings made by radionuclide ventriculography, a much more complex, expensive and hazardous technique, not amenable to repetition at short time intervals. The measurement of stroke distance by Doppler ultrasound is a convenient bedside method of assessing acute hemodynamic changes after doxorubicin or any drug affecting cardiac function. The method we describe is eminently suitable for investigating the cardiotoxicity of chemotherapeutic agents.

31P NMR spectroscopy in chronic adriamycin cardiotoxicity

Abnormal cardiac energy metabolism has been postulated as a mechanism for adriamycin induced cardiotoxicity. This study was designed to determine high energy phosphate stores at rest and with hemodynamic stress in perfused rat hearts after animals had been chronically exposed to adriamycin (2 mg/kg weekly for 14 weeks). Morphologic and hemodynamic changes were mild in this model. Phosphorus-31 NMR determined intracellular pH and levels of inorganic phosphate (Pi) and ATP were comparable in treated and control hearts. Phosphocreatine (PCr) levels were markedly decreased in treated hearts (0.89 +/- 0.07 units/g versus 1.7 +/- 0.13 units/g, p less than 0.001). The PCr/Pi ratio decreased in both groups during hemodynamic stress. It recovered earlier in controls and there was a marked over-shoot after cessation of rapid pacing in this group which was not present in adriamycin treated hearts. These results suggest that metabolic regulation in response to hemodynamic stress is impaired after chronic adriamycin exposure. PCr depletion and delayed metabolic recovery after hemodynamic stress appear to be potentially useful markers for the effect of adriamycin on the heart.

Pharmacokinetics and central haemodynamic effects of doxorubicin and 4'epi-doxorubicin in the pig

The relationship between the cardiotoxicity and the haemodynamics/pharmacokinetics of clinical concentrations of doxorubicin and 4'epi-doxorubicin was studied. Twelve pigs were randomized to receive i.v. infusions of either drug of 50 mg/m2 over 3.0 min. Aortic, pulmonary arterial, coronary sinus and central venous plasma concentrations of the agents were determined until 180 min after the infusion. The V5 ECG, left ventricular dP/dT, aortic, pulmonary arterial and right atrial pressures were recorded continuously, cardiac output and coronary sinus blood flow were recorded intermittently. No haemodynamic changes were recorded after administration of either drug. Pharmacokinetic data indicated myocardial extraction, followed by myocardial release of both drugs. This release was higher after administration of 4'epi-doxorubicin than after doxorubicin, within the range 2-4 min and 20-40 min after the infusion. The tendency of greater myocardial release of 4'epi-doxorubicin may explain its lower cardiotoxicity.

The role of lipid peroxidation in acute doxorubicin-induced cardiotoxicity as studied in rat isolated heart

Doxorubicin induces an acute cardiotoxicity that becomes manifest in isolated hearts as a deterioration in mechanical function. The oxidative component in this myocardial damage has been investigated. The effects of doxorubicin on the activity of superoxide dismutase and the capacity of the glutathione system, factors of the cellular protective mechanism against free radicals, were examined in rat isolated heart. Doxorubicin was found to reduce the capacity of the protective mechanisms. Whether oxidative membrane damage due to excessive free radical formation plays a role in the pathogenesis of the acute cardiotoxic action of doxorubicin was also examined. Its acute effect on myocardial contraction amplitude, frequency of beating, coronary flow and on the above mentioned biochemical parameters was compared in rat hearts sufficient or deficient in vitamin E. Peroxidation of lipids was measured as the formation of malondialdehyde, one of the final products of this process. Vitamin E deficiency neither aggravated the decrease in the capacity of the cellular protective factors nor worsened the reduction in myocardial function. Nor did induction of lipid peroxidation by doxorubicin occur in vitamin E-deficient hearts. It was concluded that lipid peroxidative damage most probably is not decisive in the development of the acute cardiomyopathy in rats.

Acute circulatory effects of doxorubicin in the conscious dog

Experimental work on the mechanisms of acute doxorubicin-induced cardiotoxicity may contribute to a better understanding of the clinical problem of cardiac failure after treatment with anthracycline derivatives. We studied aortic pressure and heart rate continuously for 1 h following a bolus injection of doxorubicin (1 mg/kg) in 7 dogs. In contrast with previous studies in intact animals, no anesthesia was used in order to eliminate possible interactions of doxorubicin with other drugs. One minute after doxorubicin injection a severe hypotension was observed, the average nadir in systolic and diastolic pressure being 62% and 42% of initial values. Surprisingly, the decrease in arterial blood pressure was not accompanied by cardiac acceleration. Doxorubicin, apparently interferes with the normal regulation of heart rate through the baroreceptor control system. Although several theories have been put forward regarding the mechanisms governing acute anthracycline cardiotoxicity, our knowledge of the phenomenon is still incomplete.