Occurrence of intramitochondrial Ca2+ granules in a hypertrophied heart exposed to adriamycin

Toxic Mechanisms of the Heart: A Review*

Toxic injury is one of the many ways by which the functional integrity of the heart may become compromised. Any of the subcellular elements may be the target of toxic injury, including all of the various membranes and organelles. Understanding the mechanisms underlying cardiotoxicity may lead to treatment of the toxicity or to its prevention. Doxorubicin and its analogs are very important cancer chemotherapeutic agents that can cause cardiotoxicity. Other agents which are cardiotoxic and which have profound public health implications include the alkaloid emetine in ipecac syrup, cocaine, and ethyl alcohol. The most important cardiotoxic mechanisms proposed for doxorubicin include oxidative stress with its resultant damage to myocardial elements, changes in calcium homeostasis, decreased ability to produce ATP, and systemic release of cardiotoxic humoral mediators from tissue mast cells. Each of the first 3 mechanisms can lead to each of the other 2, and the causal relationships between all of these mechanisms are not clear. New evidence suggests that doxorubicinol, one of the metabolites of doxorubicin may be the moiety responsible for cardiotoxicity. Several other potential mechanisms also have been proposed for doxorubicin. Emetine in ipecac syrup is the first aid treatment of choice for many acute toxic oral ingestions and the alkaloid, itself, is used to treat amebiasis. Cardiotoxicity occurs following chronic exposure, such as occurs therapeutically in amebiasis and with ipecac abuse by bulemics. A number of mechanisms are proposed for emetine cardiotoxicity, but the current mechanistic literature is quite scarce. Cocaine abuse recently has caught the public interest, in particular because of the drug-related sudden deaths of certain athletes. Cocaine can cause hypertension, arrhythmias, and reduced coronary blood flow, each of which can contribute to its lethality. However, it may be possible that cocaine sudden death episodes are more related to hyperthermia and convulsive seizures, rather than to cardiovascular toxicity. Chronic alcohol use leads to dilated cardiomyopathy and failure as part of the general physical degeneration that occurs with alcoholism. Several mechanisms are proposed for the cardiomyopathy, but only 2 things seem clear. The cardiotoxicity is due to an intrinsic effect of alcohol, rather than to malnutrition or co-toxicity, and abstinence is the only effective treatment for the cardiomyopathy. Recent articles indicate that very moderate use of alcohol may be beneficial and protect against cardiovascular-related morbidity. One explanation for these findings seems to be that the non-drinking groups, against whom the moderate drinking comparisons were made, were enriched in former drinkers with significant alcohol-related cardiovascular pathology.

Dexrazoxane for the prevention of cardiac toxicity and treatment of extravasation injury from the anthracycline antibiotics

The cumulative cardiac toxicity of the anthracycline antibiotics and their propensity to produce severe tissue injury following extravasation from a peripheral vein during intravenous administration remain significant problems in clinical oncologic practice. Understanding of the free radical metabolism of these drugs and their interactions with iron proteins led to the development of dexrazoxane, an analogue of EDTA with intrinsic antineoplastic activity as well as strong iron binding properties, as both a prospective cardioprotective therapy for patients receiving anthracyclines and as an effective treatment for anthracycline extravasations. In this review, the molecular mechanisms by which the anthracyclines generate reactive oxygen species and interact with intracellular iron are examined to understand the cardioprotective mechanism of action of dexrazoxane and its ability to protect the subcutaneous tissues from anthracycline-induced tissue necrosis.

Disturbances in calcium metabolism and cardiomyocyte necrosis: the role of calcitropic hormones

A synchronized dyshomeostasis of extra- and intracellular Ca(2+), expressed as plasma ionized hypocalcemia and excessive intracellular Ca(2+) accumulation, respectively, represents a common pathophysiologic scenario that accompanies several diverse disorders. These include low-renin and salt-sensitive hypertension, primary aldosteronism and hyperparathyroidism, congestive heart failure, acute and chronic hyperadrenergic stressor states, high dietary Na(+), and low dietary Ca(2+) with hypovitaminosis D. Homeostatic responses are invoked to restore normal extracellular [Ca(2+)](o), including increased plasma levels of parathyroid hormone and 1,25(OH)(2)D(3). However, in cardiomyocytes these calcitropic hormones concurrently promote cytosolic free [Ca(2+)](i) and mitochondrial [Ca(2+)](m) overloading. The latter sets into motion organellar-based oxidative stress, in which the rate of reactive oxygen species generation overwhelms their detoxification by endogenous antioxidant defenses, including those related to intrinsically coupled increments in intracellular Zn(2+). In turn, the opening potential of the mitochondrial permeability transition pore increases, allowing for osmotic swelling and ensuing organellar degeneration. Collectively, these pathophysiologic events represent the major components to a mitochondriocentric signal-transducer-effector pathway to cardiomyocyte necrosis. From necrotic cells, there follows a spillage of intracellular contents, including troponins, and a subsequent wound healing response with reparative fibrosis or scarring. Taken together, the loss of terminally differentiated cardiomyocytes from this postmitotic organ and the ensuing replacement fibrosis each contribute to the adverse structural remodeling of myocardium and progressive nature of heart failure. In conclusion, hormone-induced ionized hypocalcemia and intracellular Ca(2+) overloading comprise a pathophysiologic cascade common to diverse disorders and that initiates a mitochondriocentric pathway to nonischemic cardiomyocyte necrosis.

Cation dyshomeostasis and cardiomyocyte necrosis: the Fleckenstein hypothesis revisited

An ongoing loss of cardiomyocytes to apoptotic and necrotic cell death pathways contributes to the progressive nature of heart failure. The pathophysiological origins of necrotic cell loss relate to the neurohormonal activation that accompanies acute and chronic stressor states and which includes effector hormones of the adrenergic nervous system. Fifty years ago, Albrecht Fleckenstein and coworkers hypothesized the hyperadrenergic state, which accompanies such stressors, causes cardiomyocyte necrosis based on catecholamine-initiated excessive intracellular Ca(2+) accumulation (EICA), and mitochondrial Ca(2+) overloading in particular, in which the ensuing dysfunction and structural degeneration of these organelles leads to necrosis. In recent years, two downstream factors have been identified which, together with EICA, constitute a signal-transducer-effector pathway: (i) mitochondria-based induction of oxidative stress, in which the rate of reactive oxygen metabolite generation exceeds their rate of detoxification by endogenous antioxidant defences; and (ii) the opening of the mitochondrial inner membrane permeability transition pore (mPTP) followed by organellar swelling and degeneration. The pathogenesis of stress-related cardiomyopathy syndromes is likely related to this pathway. Other factors which can account for cytotoxicity in stressor states include: hypokalaemia; ionized hypocalcaemia and hypomagnesaemia with resultant elevations in parathyroid hormone serving as a potent mediator of EICA; and hypozincaemia with hyposelenaemia, which compromise antioxidant defences. Herein, we revisit the Fleckenstein hypothesis of EICA in leading to cardiomyocyte necrosis and the central role played by mitochondria.

Doxorubicin increases the susceptibility of brain mitochondria to Ca(2+)-induced permeability transition and oxidative damage

This study was aimed at investigating the effects of subchronic administration of doxorubicin (DOX) on brain mitochondrial bioenergetics and oxidative status. Rats were treated with seven weekly injections of vehicle (sc, saline solution) or DOX (sc, 2 mg kg(-1)), and 1 week after the last administration of the drug the animals were sacrificed and brain mitochondrial fractions were obtained. Several parameters were analyzed: respiratory chain, phosphorylation system, induction of the permeability transition pore (PTP), mitochondrial aconitase activity, lipid peroxidation markers, and nonenzymatic antioxidant defenses. DOX treatment induced an increase in thiobarbituric acid-reactive substances and vitamin E levels and a decrease in reduced glutathione content and aconitase activity. Furthermore, DOX potentiated PTP induced by Ca2+. No statistical differences were observed in the other parameters analyzed. Altogether our results show that DOX treatment increases the susceptibility of brain mitochondria to Ca(2+)-induced PTP opening and oxidative stress, predisposing brain cells to degeneration and death.

Adriamycin-induced interference with cardiac mitochondrial calcium homeostasis

Adriamycin (doxorubicin) is a potent and broad-spectrum antineoplastic agent, the clinical utility of which is limited by the development of a cumulative and irreversible cardiomyopathy. Although the drug affects numerous structures in different cell types, the mitochondrion appears to a principal subcellular target for the development of cardiomyopathy. This review describes evidence demonstrating that adriamycin redox cycles on complex I of the mitochondrial electron transport chain to liberate highly reactive free radical species of molecular oxygen. The primary effect of adriamycin on mitochondrial performance is the interference with oxidative phosphorylation and inhibition of ATP synthesis. Free radicals liberated from adriamycin redox cycling are thought to be responsible for many of the secondary effects of adriamycin, including lipid peroxidation, the oxidation of both proteins and DNA, and the depletion of glutathione and pyridine nucleotide reducing equivalents in the cell. It is this altered redox status that is believed to cause assorted changes in intracellular regulation, including the induction of the mitochondrial permeability transition and complete loss of mitochondrial integrity and function. Associated with this is the interference with mitochondrial-mediated cell calcium signaling, which is implicated as essential to the capacity of mitochondria to participate in bioenergetic regulation in response to external signals reflecting changes in metabolic demand. If taken to an extreme, this loss of mitochondrial plasticity may manifest in the liberation of signals mediating either oncotic or necrotic cell death, further perpetuating the cardiac failure associated with adriamycin-induced mitochondrial cardiomyopathy.

Doxorubicin-induced cardiac mitochondrionopathy

Doxorubicin (Adriamycin) is a potent and broad-spectrum antineoplastic agent prescribed for the treatment of a variety of cancers, including both solid tumours and leukaemias. Unfortunately, despite its broad effectiveness, long-term therapy with doxorubicin is associated with a high incidence of a cumulative and irreversible dilated cardiomyopathy. Numerous mechanisms have been proposed to account for this toxicity. Although there is general consensus that doxorubicin undergoes redox cycling to generate free radicals that are responsible for mediating the various cytopathologies associated with drug exposure, the source and subcellular targets continue to be debated. This short review provides a synopsis of the evidence implicating cardiac mitochondria as key intracellular targets, both as sites of generation of highly reactive free radical intermediates as well as targets for the interference with cell calcium regulation and bioenergetic failure that are hallmarks of doxorubicin-induced cardiac failure.

Apoptosis in adriamycin cardiomyopathy and its modulation by probucol

The dose-dependent cardiomyopathy and heart failure due to adriamycin have been shown to be due to increased oxidative stress and loss of myocytes. We examined the incidence of myocardial apoptosis as well as changes in the expression of apoptotic regulatory gene products in an established animal model of adriamycin cardiomyopathy. Rats were treated with adriamycin (cumulative dose, 15 mg/kg), and the hearts were examined for apoptosis as well as expression of Bax, caspase 3, and Bcl-2 at 0, 4, 10, 16, and 21 days after the treatment. A significant increase in the incidence of apoptosis was seen at 4 days, followed by a decline at 10 and 16 days of posttreatment. At 21 days, the number of apoptotic cells increased again and included cells of the conducting system. Expression of Bax corresponded to these biphasic changes, whereas the converse was true for the expression of Bcl-2. The latter peaked at 10 days followed by a decline at 16 and 21 days. The Bax/Bcl-2 ratio also correlated with the incidence of apoptosis. Expression of caspase 3 correlated with increased apoptosis, but only at early time points. Probucol (cumulative dose, 120 mg/kg), a known antioxidant as well as promoter of endogenous antioxidants, significantly reduced the incidence of apoptosis as well as expression of Bax. Adriamycin-induced hemodynamic changes were also prevented by probucol. These data suggest that adriamycin-induced apoptosis is mediated by oxidative stress and may play a role in the development of heart failure.

Molecular mechanisms of doxorubicin-induced cardiomyopathy. Selective suppression of Reiske iron-sulfur protein, ADP/ATP translocase, and phosphofructokinase genes is associated with ATP depletion in rat cardiomyocytes

Doxorubicin, a cardiotoxic antineoplastic, disrupts the cardiac-specific program of gene expression (Kurabayashi, M., Dutta, S., Jeyaseelan, R., and Kedes, L. (1995) Mol. Cell. Biol. 15, 6386-6397). We have now identified neonatal rat cardiomyocyte mRNAs rapidly sensitive to doxorubicin, or its congener daunomycin, including transcripts of nuclear genes encoding enzymes critical in production of energy in cardiomyocytes: ADP/ATP translocase, a heart- and muscle-specific isoform; Reiske iron-sulfur protein (RISP), a ubiquitously expressed electron transport chain component; and a muscle isozyme of phosphofructokinase. Loss of these mRNAs following doxorubicin or daunomycin is evident as early as 2 h and precedes significant reduction of intracellular ATP. ATP levels in control cardiomyocytes (17.9 +/- 2.9 nM/mg of protein) fall only after 14 h and reach residual levels of 10.4 +/- 0.9 nM (doxorubicin; p = <0.006) and 6.7 +/- 1.9 nM (daunomycin; p = <0. 001) by 24 h. Loss of mRNAs generating ATP was highly selective since mRNAs for other energy production enzymes, (cytochrome c, cytochrome b, and malate dehydrogenase), and genes important in glycolysis (pyruvate kinase and glyceraldehyde-3-phosphate dehydrogenase) were unaffected even at 24 and 48 h. The drugs had no effect on levels of ubiquitously expressed RISP mRNA in fibroblasts. These findings could link doxorubicin-induced damage to membranes and signaling pathways with 1) suppression of transcripts encoding myofibrillar proteins and proteins of energy production pathways and 2) depletion of intracellular ATP stores, myofibrillar degeneration, and related cardiotoxic effects.

Probucol protects against adriamycin cardiomyopathy without interfering with its antitumor effect

BACKGROUND

The usefulness of adriamycin (ADR), a potent antitumor antibiotic, is limited by the development of life-threatening cardiomyopathy and congestive heart failure. Subcellular changes leading to heart failure are suggested to be mediated by a drug-induced increase in free radicals and lipid peroxidation. In an earlier study, concurrent treatment with probucol (PROB), a lipid-lowering drug with strong antioxidant properties, was shown to offer only partial protection against ADR cardiomyopathy. The present study had two aims: to determine whether this protective effect can be improved further by extended treatment with PROB, and to determine whether PROB affects the antitumor properties of ADR.

METHODS AND RESULTS

ADR (cumulative dose, 15 mg/kg body wt) was administered in rats in six equal injections (IP) over a period of 2 weeks. Three weeks after the end treatment, cardiomyopathy and congestive heart failure were characterized by ascites, congested liver, depressed cardiac function, elevated left ventricular end-diastolic pressure, and myocardial cell damage. Myocardial glutathione peroxidase (GSHPx) activity was decreased and lipid peroxidation was increased. Administration of PROB (cumulative dose, 120 mg/kg body wt) in 12 equal injections (IP), before and concurrent with ADR, completely prevented these cardiomyopathic changes, normalized left ventricular function, lowered mortality, and eliminated ascites. Treatment with PROB was also accompanied by an increase in myocardial GSHPx and superoxide dismutase activities with a concomitant decrease in lipid peroxidation. Tumor regression in syngeneic DBA/2 mice inoculated with L5178Y-F9 lymphoma cells in the ADR+PROB group was significant and comparable to the ADR group.

CONCLUSIONS

These data show for the first time that PROB can provide complete protection against ADR cardiomyopathy without interfering with antitumor properties of the drug. This protective effect of PROB may be related to the maintenance of the antioxidant status of the heart.

Probucol promotes endogenous antioxidants and provides protection against adriamycin-induced cardiomyopathy in rats

BACKGROUND

The potential usefulness of adriamycin (ADR) is restricted because of its cardiotoxic side effects. Since free radicals and lipid peroxidation are suggested to be involved in ADR cardiomyopathy, we examined the beneficial effects of probucol, a lipid-lowering drug with strong antioxidant properties.

METHODS AND RESULTS

ADR was administered to rats in six equal intraperitoneal injections over a period of 2 weeks (cumulative dose of 15 mg/kg). After a 3-week posttreatment period, cardiomyopathy and congestive heart failure were characterized by ascites, congested liver, depressed cardiac function, elevated left ventricular end-diastolic pressure, and myocardial cell damage. Myocardial glutathione peroxidase (GSHPx) activity was decreased, and lipid peroxidation was increased. Probucol (cumulative dose, 60 mg/kg IP) was administered in six equal injections over a 2-week period on days alternating with ADR treatment. Probucol significantly attenuated the myocardial effects of ADR, improved left ventricular function, and lowered mortality as well as the amount of ascites. Treatment with probucol was also accompanied by an increase in myocardial GSHPx and superoxide dismutase activities, with a concomitant decrease in lipid peroxidation.

CONCLUSIONS

These data provide evidence that ADR cardiomyopathy is associated with an antioxidant deficit. Improved cardiac function resulting from treatment with probucol may be related to the maintenance of the antioxidant status of the heart. The study suggests potential usefulness of antioxidant (probucol) therapy in ADR cardiomyopathy.

Altered glucose metabolism in adriamycin-induced heart failure

Spontaneously hypertensive rats received 1 mg/kg of Adriamycin intravenously once a week for up to 12 weeks; their hearts were excised and perfused with buffer containing 5 mM [1-13C]glucose. Histological evidence of Adriamycin cardiotoxicity was evident after 8 and 12 weeks of treatment and was accompanied by a significant decrease in cardiac function. There were only minor changes in the 31P-NMR spectra in hearts following treatment; however, 13C-NMR spectra revealed decreased incorporation of label into the lactate, alanine and glutamate pools in hearts with severe tissue damage compared to hearts from untreated animals.

Cardiac mitochondrial calcium content during fatal doxorubicin toxicity

The purpose of this study was to determine whether abnormalities of mitochondrial divalent cation metabolism are early, causative events in doxorubicin (DXR, Adriamycin) cardiotoxicity. We used electron probe microanalysis (EPMA) to examine the calcium (Ca) and magensium (Mg) content of in situ mitochondria in cryosections of rat hearts, rapidly frozen at 6 hr and 1, 3, and 5 days after a single iv injection of 20 mg/kg DXR. This dose produced 100% mortality in 7 days, with a mean survival of 5.8 days. Mean control mitochondrial Ca and Mg was 0.7 and 28 mmol/kg dry wt, respectively (+/- SEM), and did not change in the DXR-injected animals, even in severely symptomatic rats 5 days after DXR. This suggests that an alteration in mitochondrial divalent cation metabolism is unlikely to be a primary event in the pathogenesis of DXR-induced cardiotoxicity, and that the mitochondrial Ca accumulation demonstrated in previous studies represents a secondary event in cells damaged by another mechanism.