Michael F. Hill

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.

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.

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.

Mobilization of Antioxidant Vitamin Pools and Hemodynamic Function After Myocardial Infarction

BACKGROUND Although most previous studies have attempted to correlate plasma concentrations of vitamins with specific cardiovascular end points, metabolic considerations suggest that changes in myocardial tissue and storage organs may be better indicators of myocardial oxidative stress. METHODS AND RESULTS Rats fed commercial chow or a diet enriched with vitamin E for 2 weeks were subjected to either a surgical myocardial infarction (MI) or a sham procedure. Rats were hemodynamically assessed 16 weeks after surgery, and their heart, liver, kidney, and plasma were analyzed for antioxidant vitamins E (tocopherol) and A (retinol and total retinyl esters). At 16 weeks, MI rats on a control diet showed depressed peak systolic and elevated diastolic pressures in both right and left ventricles compared with their sham controls. Plasma concentrations of vitamins E and A in MI rats were not different from sham controls fed the same diet. However, concentrations of vitamin E in left ventricle and liver and of vitamin A in liver (retinol) and kidney (retinyl esters) were decreased in rats with MI compared with the sham controls. Vitamin E supplementation improved hemodynamic function in rats with MI and increased plasma, myocardial, liver, and kidney concentrations of vitamin E. The vitamin E diet also prevented the loss of total retinyl esters from the kidney but not of retinol from the liver in MI rats. CONCLUSIONS Dietary supplements of vitamin E can sustain better cardiac function subsequent to MI. Antioxidant vitamin levels in the myocardium or in storage organs and not in plasma may be better indicators of myocardial oxidative stress.

Bifunctional Role of Protein Tyrosine Kinases in Late Preconditioning Against Myocardial Stunning in Conscious Rabbits

Although protein tyrosine kinases (PTKs) have been implicated in late preconditioning (PC) against infarction, their role in late PC against stunning is unknown. Furthermore, it is unknown whether PTK signaling is necessary only to trigger late PC on day 1 or also to mediate it on day 2. Thus, conscious rabbits underwent a sequence of six 4-minute coronary occlusion/4-minute reperfusion cycles for 3 consecutive days (days 1, 2, and 3). In the control group (group I, n=7), the recovery of systolic wall thickening after the 6 occlusion/reperfusion cycles was markedly improved on days 2 and 3 compared with day 1, indicating the development of late PC against stunning. Administration of the PTK inhibitor lavendustin-A (LD-A, 1 mg/kg IV) before the first occlusion on day 1 (group II, n=7) completely prevented the late PC effect against stunning on day 2. Late PC against stunning was also abrogated when LD-A was given before the first occlusion on day 2 (group III, n=7); however, in these rabbits, the late PC effect became apparent on day 3, indicating that LD-A itself did not have any delayed deleterious actions on myocardial stunning. In group V (n=5), the sequence of 6 occlusion/reperfusion cycles resulted in a robust increase in the activity of inducible NO synthase (iNOS [assessed as Ca(2+)-independent L-citrulline formation]) and nitrite+nitrate (NO(x)) tissue levels 24 hours later (on day 2), with no concomitant change in Ca(2+)-dependent NO synthase (endothelial NO synthase and/or neuronal NO synthase) activity. Similar results were obtained on day 3 (group VIII, n=6), indicating sustained upregulation of iNOS. Administration of LD-A either on day 1 (group VI, n=5) or on day 2 (group VII, n=6) abrogated the increase in iNOS activity and NO(x) levels on day 2. LD-A had no effect on iNOS activity or NO(x) levels in the absence of PC (group X, n=5). This study demonstrates that in conscious rabbits, PTK activity is necessary not only to trigger late PC against stunning on day 1 but also to mediate the protection on day 2. This investigation also provides the first direct evidence that cardiac iNOS activity is upregulated during the late phase of ischemic PC in rabbits. Furthermore, the data indicate that PTK signaling is essential for the augmentation of iNOS activity and that PTKs modulate this enzyme at two distinct levels: at an early stage on day 1 and at a late stage on day 2. This bifunctional role of PTKs in late PC has broad implications for the signaling mechanisms that underlie the response of the heart to ischemic stress and, possibly, other stresses.

Nitric oxide donors attenuate myocardial stunning in conscious rabbits

Although previous studies suggested that the protection of late preconditioning (PC) against myocardial stunning is mediated by nitric oxide (NO), direct evidence that exogenous administration of NO attenuates myocardial stunning is lacking. Furthermore, although exogenous NO administration was shown to elicit a late PC phase, it is unknown whether NO donors also induce an early PC phase. Therefore, conscious rabbits underwent two experimental stages (3 days of six 4-min occlusion/4-min reperfusion cycles each) 2 wk apart. In study I, both stages were control stages ( n = 7). In studies II and III, stage I was the control stage. On day 1of stage II, seven rabbits received infusion of nitroglycerin (NTG; 2 μg ⋅ kg-1 ⋅ min-1iv) during the ischemia-reperfusion sequence, starting 30 min before the 1st occlusion and ending 10 min after the 6th reperfusion ( study II). Another seven rabbits received infusion of NTG (2 μg ⋅ kg-1 ⋅ min-1iv) for 1 h followed by a 30-min washout interval and then underwent six 4-min occlusion/4-min reperfusion cycles ( study III). In the control stage of all three studies, recovery of wall thickening (WTh) after occlusion/reperfusion cycles was markedly enhanced on days 2 and 3 compared with day 1, indicating late PC. In study II, infusion of NTG during the occlusion/reperfusion cycles on day 1 resulted in significant and sustained enhancement in WTh recovery. A similar attenuation of stunning was observed in study IV in six rabbits given intravenous infusion of S-nitroso- N-acetylpenicillamine (SNAP) during occlusion/reperfusion cycles. The magnitude of the protection afforded by NTG and SNAP was comparable to that afforded by the late ischemic PC phase. In contrast, in study III infusion of NTG before occlusion/reperfusion cycles did not enhance WTh recovery, indicating that NTG failed to induce an early PC effect against stunning. This study demonstrates that administration of hemodynamically inactive doses of two unrelated NO donors alleviates myocardial stunning in conscious rabbits, providing direct evidence for a protective action of NO in this setting.Although previous studies suggested that the protection of late preconditioning (PC) against myocardial stunning is mediated by nitric oxide (NO), direct evidence that exogenous administration of NO attenuates myocardial stunning is lacking. Furthermore, although exogenous NO administration was shown to elicit a late PC phase, it is unknown whether NO donors also induce an early PC phase. Therefore, conscious rabbits underwent two experimental stages (3 days of six 4-min occlusion/4-min reperfusion cycles each) 2 wk apart. In study I, both stages were control stages (n = 7). In studies II and III, stage I was the control stage. On day 1 of stage II, seven rabbits received infusion of nitroglycerin (NTG; 2 microg. kg(-1). min(-1) iv) during the ischemia-reperfusion sequence, starting 30 min before the 1st occlusion and ending 10 min after the 6th reperfusion (study II). Another seven rabbits received infusion of NTG (2 microg. kg(-1). min(-1) iv) for 1 h followed by a 30-min washout interval and then underwent six 4-min occlusion/4-min reperfusion cycles (study III). In the control stage of all three studies, recovery of wall thickening (WTh) after occlusion/reperfusion cycles was markedly enhanced on days 2 and 3 compared with day 1, indicating late PC. In study II, infusion of NTG during the occlusion/reperfusion cycles on day 1 resulted in significant and sustained enhancement in WTh recovery. A similar attenuation of stunning was observed in study IV in six rabbits given intravenous infusion of S-nitroso-N-acetylpenicillamine (SNAP) during occlusion/reperfusion cycles. The magnitude of the protection afforded by NTG and SNAP was comparable to that afforded by the late ischemic PC phase. In contrast, in study III infusion of NTG before occlusion/reperfusion cycles did not enhance WTh recovery, indicating that NTG failed to induce an early PC effect against stunning. This study demonstrates that administration of hemodynamically inactive doses of two unrelated NO donors alleviates myocardial stunning in conscious rabbits, providing direct evidence for a protective action of NO in this setting.

Endogenous antioxidants in isolated hypertrophied cardiac myocytes and hypoxia-reoxygenation injury

Effects of hypoxia-reoxygenation (H-R) on myocytes isolated from 10 week hypertrophied and sham control rat hearts were studied. Myocyte hypertrophy was indicated by an increase in cell size. Superoxide dismutase (SOD) and glutathione peroxidase (GSHPx) enzyme activities were significantly higher and lipid peroxidation (TBARS) was lower in hypertrophied myocytes prior to any H-R. Hypertrophied myocyte population showed significantly less damage to cell morphology due to H-R. In sham as well as hypertrophied myocytes, Na+ and Ca2+ contents were increased by H-R, but Ca2+ accumulation was significantly less in the hypertrophied myocytes. Both SOD and GSHPx activities were depressed by the oxidative stress in the sham myocytes whereas these activities were not significantly changed in the hypertrophied myocytes. Catalase activity in the prehypoxic sham and hypertrophied myocytes was comparable and this activity did not change during H-R. There was a significant increase in lipid peroxidation due to H-R but this change was less in hypertrophied myocytes. This study shows less vulnerability of hypertrophied myocytes to oxidative stress and an increase in endogenous antioxidant reserve may have an important role in mediating this protection.

EFFECTS OF CAPTOPRIL ON MYOCARDIAL OXIDATIVE STRESS CHANGES IN POST-MI RATS

Changes in oxidative stress as indicated by the redox ratio as well as lipid peroxidation were characterized in rat hearts at different time points, subsequent to myocardial infarction (MI). In the severe heart failure stage at 16 weeks of post-MI, oxidative stress was significantly increased. Treatment with afterload reducing drugs, captopril or prazosin, started at 4 weeks post-MI and continued up to 16 weeks, resulted in a significant modulation of the oxidative stress changes with an improved hemodynamic function. It is suggested that the improved prognosis in MI patients with afterload reduction reported earlier may involve an improvement of the antioxidant reserve coupled with a reduction in the oxidative stress in the infarcted heart.

Chronic Neuregulin-1β Treatment Mitigates the Progression of Postmyocardial Infarction Heart Failure in the Setting of Type 1 Diabetes Mellitus by Suppressing Myocardial Apoptosis, Fibrosis, and Key Oxidant-Producing Enzymes

BACKGROUND Type 1 diabetes mellitus (DM) patients surviving myocardial infarction (MI) have substantially higher cardiovascular morbidity and mortality compared to their nondiabetic counterparts owing to the more frequent development of subsequent heart failure (HF). Neuregulin (NRG)-1β is released from cardiac microvascular endothelial cells and acts as a paracrine factor via the ErbB family of tyrosine kinase receptors expressed in cardiac myocytes to regulate cardiac development and stress responses. Because myocardial NRG-1/ErbB signaling has been documented to be impaired during HF associated with type 1 DM, we examined whether enhancement of NRG-1β signaling via exogenous administration of recombinant NRG-1β could exert beneficial effects against post-MI HF in the type 1 diabetic heart. METHODS AND RESULTS Type 1 DM was induced in male Sprague Dawley rats by a single injection of streptozotocin (STZ) (65 mg/kg). Two weeks after induction of type 1 DM, rats underwent left coronary artery ligation to induce MI. STZ-diabetic rats were treated with saline or NRG-1β (100 µg/kg) twice per week for 7 weeks, starting 2 weeks before experimental MI. Residual left ventricular function was significantly greater in the NRG-1β-treated STZ-diabetic MI group compared with the vehicle-treated STZ-diabetic MI group 5 weeks after MI as assessed by high-resolution echocardiography. NRG-1β treatment of STZ-diabetic MI rats was associated with reduced myocardial fibrosis and apoptosis as well as decreased gene expression of key oxidant-producing enzymes. CONCLUSIONS These results suggest that recombinant NRG-1β may be a promising therapeutic for HF post-MI in the setting of type 1 DM.