Pawan K. Singal

Role of oxidative stress in transition of hypertrophy to heart failure

OBJECTIVES In an attempt to define the role of increased oxidative stress in the transition from compensatory hypertrophy to heart failure, this study examined the effects of long-term vitamin E therapy on the occurrence of heart failure subsequent to chronic pressure overload in guinea pigs. BACKGROUND Hyperfunctional heart hypertrophy has been shown to be accompanied by an increase in the endogenous antioxidant reserve, whereas congestive heart failure is accompanied by a decrease in this reserve. The effects of vitamin E, a naturally occurring antioxidant, on the development of heart failure from a hypertrophic stage were examined. METHODS The ascending aorta in guinea pigs was coarcted. For vitamin treatment, slow-release pellets were implanted at the time of the operation. The animals were assessed at 10 and 20 weeks for hemodynamic function, myocardial structure, antioxidant agents and oxidative stress. RESULTS Banding of the ascending aorta in guinea pigs resulted in hyperfunctional hypertrophy at 10 weeks, which was followed by congestive heart failure at 20 weeks. Hypertrophied hearts showed decreased oxidative stress, as evidenced by a higher oxidation-reduction (redox) state and less lipid peroxidation, whereas the failure stage was characterized by increased oxidative stress. Supplementation of animals with timed-release vitamin E tablets resulted in an increased myocardial content of the vitamin, and the banded animals did not develop any signs of heart failure at 20 weeks. Hemodynamic function at 20 weeks in these vitamin E-treated animals was also better maintained. The myocardial reduced glutathione/oxidized glutathione ratio of vitamin E-treated animals at 20 weeks was higher and lipid peroxidation was less compared with the untreated animals. Ultrastructural abnormalities were significantly less in the vitamin E-treated hearts compared with the untreated failing hearts at 20 weeks. CONCLUSIONS An improved myocardial redox state with vitamin E therapy, coupled with the modulation of the development of heart failure, may indicate a pathophysiologic role for increased oxidative stress in the pathogenesis of heart failure. This study suggests the potential therapeutic value of long-term antioxidant treatment in modulating or preventing the pathogenesis of heart failure.

Adriamycin-induced heart failure: mechanisms and modulation

Adriamycin (doxorubicin) is one of the most effective chemotherapeutic agents against a variety of cancers, but its usefulness is seriously curtailed by the risk of developing heart failure. Available laboratory evidence suggests that an increase in oxidative stress, brought about by increased free radical production and decreased myocardial endogenous antioxidants, plays an important role in the pathogenesis of heart failure. Adriamycin-induced apoptosis and hyperlipidemia may also be involved in the process. Probucol, a lipid-lowering drug and an antioxidant, completely prevents the occurrence of heart failure by reducing oxidative stress as well as by the modulation of apoptis and high lipid concentrations. Thus, combined therapy with adriamycin and probucol has a high potential for optimizing the treatment of cancer patients.

The role of oxidative stress in the genesis of heart disease

Although researchers in radiation and cancer biology have known about the existence of free radicals and their potential role in pathobiology for several decades, cardiac biologists only began to take notice of these noxious species in the 1970s. Exponential growth of free radical research occurred after the discovery of superoxide dismutase in 1969. This antioxidant enzyme is responsible for the dismutation of superoxide radical--a free radical chain initiator. A fine balance between free radicals and a variety of endogenous antioxidants is believed to exist. Any disturbance in this equilibrium in favour of free radicals causes an increase in oxidative stress and initiates subcellular changes leading to cardiomyopathy and heart failure. Our knowledge about the role of free radicals in the pathogenesis of cardiac dysfunction is fast approaching the point where newer therapies employing antioxidants are in sight.

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.

Right and Left Myocardial Antioxidant Responses During Heart Failure Subsequent to Myocardial Infarction

BACKGROUND Heart failure subsequent to myocardial infarction (MI) is accompanied by depressed antioxidants and increased oxidative stress in the myocardium. Antioxidant enzyme activities and oxidative stress were examined in the viable left (LV) and right (RV) ventricles in relation to their hemodynamic function. METHODS AND RESULTS The left coronary artery in rats was ligated. At 1 week after MI, LV systolic pressure (LVSP), LV end-diastolic pressure (LVEDP), and RV end-diastolic pressure (RVEDP) remained near control values, whereas RV systolic pressure (RVSP) was significantly elevated. In the 4, 8, and 16 week post-MI animals, LVSP was significantly reduced, with values of 112.0+/-1.57, 99.9+/-0.52, and 89.2+/-1.4 mm Hg, whereas LVEDP was significantly elevated, with values of 8.2+/-0.52, 17.4+/-1.7, and 31.4+/-1.5 mm Hg, respectively. RVEDP was higher at 8 and 16 weeks, and RVSP was significantly reduced at 16 weeks. At 1 week after MI, myocardial catalase activity in the LV was maintained near control levels, whereas in the RV, it was 134% compared with its control value. At 4, 8, and 16 weeks, catalase activity in the LV was 71%, 48%, and 28% of respective controls. Catalase activity in the RV was significantly reduced only at 16 weeks. A similar trend was seen with respect to glutathione peroxidase activity. Reduced/oxidized glutathione ratio was significantly depressed in the LV at 1, 4, 8, and 16 weeks, whereas in the RV, this ratio was significantly reduced only at 8 and 16 weeks. Myocardial lipid peroxidation in the LV at 4, 8, and 16 weeks was elevated by approximately 40%, 51%, and 100%, respectively, whereas in the RV, an increase of approximately 50% was seen only at 16 weeks. CONCLUSIONS These data show that heart failure subsequent to MI is associated with an antioxidant deficit as well as increased oxidative stress, first in the LV, followed by the RV. Furthermore, these changes correlated with the hemodynamic function in each of the ventricles, suggesting their role in the pathogenesis of ventricular dysfunction.

Calcium movements in relation to heart function

SummaryIt is widely recognized that calcium is of singular importance in the viability of the myocardial cell, nonetheless little is known concerning the precise nature of the action of calcium in myocardium as to how it maintains the life of the cell and how it may dictate the death of the cell. However, recent advances in research involved with the study of calcium movement in the heart have been highly valuable for the formulation of new concepts with respect to the physiological and pathological aspects of calcium metabolism in the myocardium. It is becoming clear that calcium movements are closely related to cardiac electrophysiological events, contractile function, membrane integrity and energy metabolism. In particular, a novel theory involving phosphatidylinositol turnover and Ca2+-dependent ATPase activation has been advanced regarding the mechanism and control of calcium entry into the cardiac cell upon excitation. Alterations in the regulation of calcium metabolism through the interaction of a number of separate, elements may affect calcium distribution in the cell and thereby may change cardiac function and metabolism. The part calcium plays in the genesis of pathological states in the myocardium is discussed in the light of research employing various experimental protocols. Intracellular calcium overload and deficiency are postulated to contribute to cardiac contractile failure and cell death through a number of distinct mechanisms. It is now a real challenge to understand the precise nature of processes associated with the occurrence of intracellular calcium overload or intracellular calcium deficiency in order to achieve proper management of cardiac disorders.ZusammenfassungEs ist allgemein anerkannt, daß Calcium von besonderer Bedeutung für die Funktion der Myokardzelle ist. Trotzdem ist über die genaue Natur der Calcium-Wirkung sowie auch über die mögliche Bedeutung von Calcium für das Absterben einer Myokardzelle wenig bekannt. Fortschritte in der Erforschung der Calcium-Bewegungen im Herzen ermöglichen neue Vorstellungen über die Rolle des Calciums unter physiologischen und pathophysiologischen Bedingungen. Offensichtlich bestehen enge Beziehungen zwischen Calcium-Bewegungen und elektrophysiologischen Abläufen, kontraktiler Funktion, Membranintegrität und Energiemetabolismus. Insbesondere wurde eine neue Theorie entwickelt, die den giemetabolismus. Insbesondere wurde eine neue Theorie entwickelt, die den Inositphosphatid-Umsatz und die Aktivierung der Ca-abhängigen ATPase berücksichtigt im Hinblick auf die Mechanismen und die Kontrolle des Calcium-Eintritts in die Zelle bei Erregung. Änderungen in der Regulierung des Calcium-Stoffwechsels können die Ca-Verteilung in der Zelle beeinflussen und dadruch Herzfunktion und Stoffwechsel verändern. Die Rolle, die Calcium bei der Entwicklung pathologischer Zustände im Myokard spielt, wird im Lichte der Forschungsergebnisse bei Verwendung unterschiedlicher experimenteller Ansätze diskutiert. Es wird postuliert, daß Überladung der Zelle mit Calcium und Calcium-Mangel der Zelle zum kontraktilen Versagen des Herzens und zum Zelltod beitragen durch eine Anzahl definierter Mechanismen. Im Hinblick auf eine sachgerechte Behandlung kardialer Störungen stellt sich daher die Aufgabe, die genaue Natur der Prozesse zu klären, die mit Calcium-Überbeladung oder Calcium-Mangel einhergehen.

Free radicals and the heart

Because of the molecular configuration, most free radicals are highly reactive and can cause cell injury. Protective mechanisms have evolved to provide defense against free-radical injury. Any time these defense systems are overwhelmed, such as during disease states, cell dysfunction may occur. In this review we discuss cellular sources as well as the significance of free radicals, oxidative stress, and antioxidants. A probable role of oxidative stress in various cardiac pathologies has been also analyzed. Although some methods for the detection of free radicals as well as oxidative stress have been cited, better methods to study the quantity as well as subcellular distribution of free radicals are needed in order to understand fully the role of free radicals in both health and disease.

Potential oxidative pathways of catecholamines in the formation of lipid peroxides and genesis of heart disease.

Effects of vitamin E, a fat soluble antioxidant, on the isoproterenol-induced changes in the lipid peroxide activity as determined by a quantitation of malondialdehyde (MDA) content in the myocardium were examined. Isoproterenol treatment (80 mg/kg given over two days in two equal doses) caused more than 100 percent increase in the MDA content which was prevented by pretreatment of the animals with vitamin E (alpha-tocopherol acetate, 10 mg/kg) for two weeks. Animals maintained on vitamin E deficient diet for 8 weeks were found to be more sensitive to isoproterenol-induced increase in the MDA content. A small increase in MDA content was also seen due to vitamin E deficiency alone. These changes were found to be reversible upon a 2 week feeding of the animals on the normal diet coupled with vitamin E treatment. Based on these data it is proposed that free radical mediated increase in lipid peroxide activity may have a role in catecholamine-induced heart disease.

Cardiac alpha- and beta-adrenergic receptor alterations in diabetic cardiomyopathy

SummaryThe effect of chronic experimental diabetes on the adrenergic receptors in the rat heart was investigated. Diabetes was induced by streptozotocin (65 mg/kg; i.v.) administration, animals were sacrificed 8 weeks later, and positive as well as negative dF/dt values were determined in isolated papillary muscle preparations. Stimulation of the contractile force generation by isoproterenol and methoxamine was attenuated in diabetic preparations. Beta-and alpha-adrenergic receptor bindings were determined in cardiac membranes by employing3H-dihydroalprenolol and3H-dihydroergocryptine respectively. Reduced number of beta- and alpha-receptor binding sites without changes in the affinity constants were observed in diabetic myocardium. Such a decrease in alpha- and beta-receptor density in the heart may account for the depressed contractile responsiveness to adrenergic stimuli in diabetic cardiomyopathy.ZusammenfassungEs wurde der Einfluß eines chronischen, experimentellen Diabetes auf die adrenergen Rezeptoren des Rattenherzens untersucht. Diabetes wurde durch Streptozotocin (65 mg/kg i.v.) erzeugt. Die Untersuchungen wurden 8 Wochen nach Verabreichung durchgeführt. Es wurden positive und negative dF/dt-Werte (Geschwindigkeit der Kraftentwicklung) von isolierten Papillarmuskeln bestimmt. Die durch Isoproterenol und Methoxamin gesteigerte Kraftentwicklung war bei Ratten mit Diabetes vermindert. Die Bindungseigenschaften von Beta-und Alpha-rezeptoren in den Membranen des Herzens wurden mit Hilfe von3H-dihydroalprenolol und3H-dihydroergocryptin bestimmt. Im diabetischen Myokard war die Zahl der Beta- und Alpharezeptor-Bindungsstellen vermindert, nicht jedoch die Affinitätskonstanten. Die verringerte Beta- und Alpharezeptoren-Dichte im Herz könnte für die verminderte Ansprechbarkeit der Mechanik auf adrenerge Reize bei der diabetischen Kardiomyopathie verantwortlich sein.

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.