Differential expression of caveolin-1 and caveolin-3: potential marker for cardiac toxicity subsequent to chronic ozone inhalation.

Earlier studies from our laboratory have shown myocardial dysfunction subsequent to chronic O(3) exposure in rats may be associated with a decrease in antioxidant reserve and increased activity of inflammatory mediators. The present study tested the hypothesis that O(3)-induced cardiac dysfunction in healthy adult rats may be due to changes in caveolin-1 and caveolin-3 levels. Sprague-Dawley rats were exposed 8 h/day for 28 and 56 days to filtered air or 0.8 ppm O(3). In order to assess the chronic effects to O(3), in vivo cardiac function was assessed by measuring LVDP, 24 h after termination of O(3) exposure. Compared to rats exposed to filtered air, LVDP values significantly decreased in all O(3)-exposed animals. This attenuation of cardiac function was associated with increased myocardial TNF-α levels and decreased myocardial activities of superoxidase dismutase. Progressive increases in the expression of myocardial TNF-α in 28 days and 56 days O(3)-exposed animals were followed by decreases in cardiac caveolin-1 levels. On the other hand, differential changes in the expression of caveolin-3 in hearts from 28 and 56 days O(3)-exposed animals were independent of intra-cardiac TNF-α levels. These novel findings suggest the interesting possibility that a balance between caveolin-1 and caveolin-3 may be involved in O(3)-mediated cardiac toxicity.

Cardiac dysfunction subsequent to chronic ozone exposure in rats.

A number of advancements have been made toward identifying the risk factors associated with cardiovascular disease (CVD) and have resulted in a decline in mortality. However, many patients with cardiac disease show no established previous risk. Thus, it appears that other unknown factors contribute to the pathophysiology of CVD. Out of 350,000 sudden cardiac deaths each year in the United States, 60,000 deaths have been linked to air pollution, suggesting a detrimental role of environmental pollutants in the development of CVD. This study tested the hypothesis that chronic ozone (O(3)) exposure diminishes myocardial function in healthy population. Male Sprague-Dawley rats were exposed 8 h/day for 28 and 56 days to filtered air or 0.8 ppm O(3). In vivo cardiac function was assessed by measuring LVDP, +dP/dt, -dP/dt, and LVEDP 24 h after termination of the O(3) exposure. Compared to rats exposed to filtered air, LVDP, +dP/dt, and -dP/dt were significantly decreased, and LVEDP was significantly increased in O(3) exposed animals. This attenuation of cardiac function was associated with increased myocardial TNF-alpha levels and lipid peroxidation as well as decreased myocardial activities of superoxidase dismutase and interleukin-10 levels. These novel findings suggest myocardial dysfunction subsequent to chronic O(3) exposure in normal adult rats may be associated with a decrease in antioxidant reserve and with an increased production of inflammatory mediators.

Enhanced death signaling in ozone-exposed ischemic-reperfused hearts.

Although numerous advancements made in the field of human health have resulted in reduced deaths due to cardiovascular diseases (CVD), many patients with cardiac disease show no established risk. Therefore, other unknown factors may be responsible for the pathophysiology of CVD. Out of 350,000 sudden cardiac deaths each year in the United States, 60,000 deaths have been related to air pollution, suggesting a detrimental role of environmental pollutants in the development of CVD. The present study tested our hypothesis that chronic ozone exposure enhances the sensitivity to ischemia-reperfusion (I/R) injury in isolated perfused hearts. Sprague-Dawley rats were continuously exposed for 8 h/day for 28 and 56 days to filtered air or 0.8 ppm ozone. Isolated hearts were subjected to 30 min of global ischemia followed by 60 min of reperfusion. Cardiac function after I/R measured as left ventricular developed pressure (LVDP), +dP/dt, -dP/dt, and left ventricular end diastolic pressure (LVEDP) was significantly decreased and increased respectively in ozone-exposed I/R hearts compared to I/R hearts exposed to filtered air. The enhanced sensitivity to I/R injury upon ozone exposure was associated with increased myocardial TNF-alpha levels and lipid peroxidation and decreased myocardial activities of superoxidase dismutase (SOD) and IL-10. These data suggest that ozone-induced sensitivity to myocardial I/R injury may be due to promoting levels of oxidative stress as well as inflammatory mediators.

Antiarrhythmic effects of some antioxidant vitamins in rats injected with epinephrine.

Since excessive amounts of catecholamines are known to produce arrhythmias and increase the plasma level of aminochrome, an oxidation product of catecholamines, we tested the hypothesis that antioxidants may reduce the formation of aminochrome and prevent the catecholamine-induced arrhythmias. For this purpose, Sprague-Dawley rats were pretreated orally, with vitamin A or vitamin C for 21 days, and their effects on ventricular arrhythmias induced by a bolus dose or cumulative doses of intravenous epinephrine were examined. Electrocardiogram recording of these animals revealed that pretreatment with either of these vitamins increased the time of onset and decreased the duration of the epinephrine-induced ventricular arrhythmias. Ventricular fibrillations due to high doses of epinephrine were also prevented by the antioxidant pretreatment. Although pretreatment with either vitamin A or vitamin C did not affect the basal malondialdehyde level in control animals, the increase in malondialdehyde level caused by epinephrine administration was significantly reduced by these agents. The elevated level of plasma aminochrome due to epinephrine was also decreased by vitamins A and C treatments. The results indicate that antioxidant may prevent catecholamine-induced arrhythmias by reducing the formation of aminochrome and thus may provide a new strategy for the management of stress-related heart disease.

Modification of epinephrine-induced arrhythmias by N-acetyl-L-cysteine and vitamin E.

Sprague-Dawley rats were pretreated for 21 days with N-acetyl-L-cysteine (NAC) or vitamin E to investigate their influence on arrhythmias induced by a bolus injection or by cumulative doses of epinephrine. Electrocardiographic analysis revealed that both NAC and vitamin E decreased the duration and increased the time of onset of epinephrine-induced arrhythmias in a dose-dependent manner. The antiarrhythmic effects of NAC were comparable with those seen in the vitamin E-pretreated animals. The lipid peroxidation due to cumulative doses of epinephrine was reduced in both pretreated groups; however, NAC, unlike vitamin E, failed to decrease the basal level of malondialdehyde. Although the plasma concentrations of both norepinephrine and epinephrine were markedly increased, the level of aminochromes on epinephrine administration was decreased by both NAC and vitamin E pretreatments. The results support the view that antioxidants may prevent the catecholamine-induced heart rhythm disorders by reducing the formation of oxidized catecholamines.

Potential role and mechanisms of subcellular remodeling in cardiac dysfunction due to ischemic heart disease.

Several studies have revealed varying degrees of changes in sarcoplasmic reticular and myofibrillar activities, protein content, gene expression and intracellular Ca-handling during cardiac dysfunction due to ischemia-reperfusion (I/R); however, relatively little is known about the sarcolemmal and mitochondrial alterations, as well as their mechanisms in the I/R hearts. Because I/R is associated with oxidative stress and intracellular Ca-overload, it has been indicated that changes in subcellular activities, protein content and gene expression due to I/R are related to both oxidative stress and Ca-overload. Intracellular Ca-overload appears to induce changes in subcellular activities, protein contents and gene expression (subcellular remodeling) by activation of proteases and phospholipases, as well as by affecting the genetic apparatus, whereas oxidative stress is considered to cause oxidation of functional groups of different subcellular proteins in addition to modifying the genetic machinery. Ischemic preconditioning, which is known to depress the development of both intracellular Ca-overload and oxidative stress due to I/R, was observed to attenuate the I/R-induced subcellular remodeling and improve cardiac performance. It is suggested that a combination therapy with antioxidants and interventions, which reduce the development of intracellular Ca-overload, may improve cardiac function by preventing or attenuating the occurrence of subcellular remodeling due to ischemic heart disease. It is proposed that defects in the activities of subcellular organelles may serve as underlying mechanisms for I/R-induced cardiac dysfunction under acute conditions, whereas subcellular remodeling due to alterations in gene expression may explain the impaired cardiac performance under chronic conditions of I/R.

Dependence of changes in beta-adrenoceptor signal transduction on type and stage of cardiac hypertrophy.

To examine whether cardiac hypertrophy is associated with changes in beta-adrenoceptor signal transduction mechanisms, pressure overload (PO) was induced by occlusion of the abdominal aorta and volume overload (VO) by creation of an aortocaval shunt for 4 and 24 wk in rats. After hemodynamic assessment of the animals, the left ventricular (LV) particulate fraction was isolated for measurement of beta(1)-adrenoceptors and adenylyl cyclase activity, and cardiomyocytes were isolated for monitoring of the intracellular Ca(2+) concentration. Although PO and VO produced cardiac hypertrophy and increased LV end-diastolic pressure at 4 wk, cardiac function was increased in animals subjected to PO but remained unaltered in animals subjected to VO. Cardiac hypertrophy and increased LV end-diastolic pressure were associated with depressed cardiac function at 24 wk of PO or VO, but clinical signs of congestive heart failure were evident only in animals subjected to VO. Isoproterenol-induced increases in cardiac function, activation of adenylyl cyclase activity, and increase in intracellular Ca(2+) concentration, as well as beta(1)-adrenoceptor density, were unaltered by PO at 4 wk, augmented by VO at 4 wk, and attenuated by PO and VO at 24 wk. These results suggest that alterations in beta(1)-adrenoceptor signal transduction are dependent on the type and stage of cardiac hypertrophy.

Blockade of the renin-angiotensin system attenuates sarcolemma and sarcoplasmic reticulum remodeling in chronic diabetes.

Although the defects in the sarcolemma (SL) and sarcoplasmic reticulum (SR) membranes are known to be associated with cardiac dysfunction in chronic diabetes, very little information regarding the mechanisms of these membrane abnormalities is available in the literature. For this reason, rats were treated daily for 8 weeks with and without enalapril, an angiotensin-converting enzyme inhibitor, or losartan, an angiotensin receptor antagonist, 3 days after inducing diabetes with an injection of streptozocin. Treatment of diabetic animals with both enalapril and losartan attenuated alterations in cardiac function and the left ventricular redox potential without any changes in the increased plasma glucose or reduced plasma insulin levels. The SL Na+-K+ ATPase, Ca2+ pump, Na+-dependent Ca2+-uptake, Ca2+-channel density, and low-affinity Ca2+-binding activities were depressed whereas Ca2+ ecto-ATPase activity was increased in the diabetic heart. Furthermore, the SR Ca2+-release and Ca2+-pump activities in the diabetic hearts were decreased without any changes in the Mg2+-ATPase activity. These alterations in SL and SR membranes in diabetic animals were partly prevented by treatments with enalapril and losartan. The results suggest that the activation of the renin-angiotensin system plays an important role in diabetes-induced changes in SL and SR membranes as well as cardiac function.

Differential changes in beta-adrenoceptor signal transduction in left and right ventricles of infarcted rats.

Although different experimental and clinical studies have revealed varying degrees of defects in beta-adrenoceptors (beta-ARs) during the development of heart failure, the mechanisms for differences in beta-AR signal transduction between the left (LV) and right ventricle (RV) are not understood. Because biochemical alterations in the myocardium depend on the stage of heart disease, this study was undertaken to assess the status of beta-ARs in the LV and RV at different stages of heart failure. Myocardial infarction was induced in rats by occluding the left coronary artery for 8 and 24 weeks. The beta-AR signal transduction was monitored by measuring beta1-AR density, the isoproterenol-induced positive inotropic effect, the increase in [Ca2+]i in cardiomyocytes, and the activation of adenylyl cyclase. The beta-AR signal transduction parameters in the 8- and 24-week failing LV were depressed, whereas the RV showed upregulation at 8 weeks and downregulation at 24 weeks of these mechanisms. These results suggest that beta-AR-mediated signal transduction in the LV and RV are differentially regulated and are dependent upon the stage of development of congestive heart failure due to myocardial infarction.

Subcellular remodeling as a viable target for the treatment of congestive heart failure.

It is now well known that congestive heart failure (CHF) is invariably associated with cardiac hypertrophy, and changes in the shape and size of cardiomyocytes (cardiac remodeling) are considered to explain cardiac dysfunction in CHF. However, the mechanisms responsible for the transition of cardiac hypertrophy to heart failure are poorly understood. Several lines of evidence both from various experimental models of CHF and from patients with different types of CHF have indicated that the functions of different subcellular organelles such as extracellular matrix, sarcolemma, sarcoplasmic reticulum, myofibrils, mitochondria, and nucleus are defective. Subcellular abnormalities for protein contents, gene expression, and enzyme activities in the failing heart become evident as a consequence of prolonged hormonal imbalance, metabolic derangements, and cation maldistribution. In particular, the occurrence of oxidative stress, development of intracellular Ca2+ overload, activation of proteases and phospholipases, and alterations in cardiac gene expression result in changes in the biochemical composition, molecular structure, and function of different subcellular organelles (subcellular remodeling). Not only does subcellular remodeling appear to be intimately involved in the transition of cardiac hypertrophy to heart failure, the mismatching of the function of different subcellular organelles leads to the development of cardiac dysfunction. Although blockade of the renin-angiotensin system, sympathetic nervous system, and various other hormonal actions have been reported to produce beneficial effects on cardiac remodeling and heart dysfunction in CHF, the actions of various cardiac drugs on subcellular remodeling have not been examined extensively. Some recent studies have indicated that both the angiotensin-converting enzyme inhibitors and angiotensin receptor antagonists attenuate changes in sarcolemma, sarcoplasmic reticulum, and myofibril enzyme activities, protein contents, and gene expression, and partly improve cardiac function in the failing hearts. It is suggested that subcellular remodeling is an excellent target for the development of improved drug therapy for CHF. Furthermore, extensive studies should investigate the effects of different agents individually or in combination on reverse subcellular remodeling, cardiac remodeling, and cardiac dysfunction in various experimental models of CHF.

Changes in beta-adrenoceptors in heart failure due to myocardial infarction are attenuated by blockade of renin-angiotensin system.

Earlier studies have revealed an improvement of cardiac function in animals with congestive heart failure (CHF) due to myocardial infarction (MI) by treatment with angiotensin converting enzyme (ACE) inhibitors. Since heart failure is also associated with attenuated responses to catecholamines, we examined the effects of imidapril, an ACE inhibitor, on the beta-adrenoceptor (beta-AR) signal transduction in the failing heart. Heart failure in rats was induced by occluding the coronary artery, and 3 weeks later the animals were treated with g/(kg x day) (orally) imidapril for 4 weeks. The animals were assessed for their left ventricular function and inotropic responses to isoproterenol. Cardiomyocytes and crude membranes were isolated from the non-ischemic viable left ventricle and examined for the intracellular concentration of Ca2+ [Ca2+]i and beta-ARs as well as adenylyl cyclase (AC) activity, respectively. Animals with heart failure exhibited depressions in ventricular function and positive inotropic response to isoproterenol as well as isoproterenol-induced increase in [Ca2+]i in cardiomyocytes; these changes were attenuated by imidapril treatment. Both beta1-AR receptor density and isoproterenol-stimulated AC activity were decreased in the failing heart and these alterations were prevented by imidapril treatment. Alterations in cardiac function, positive inotropic effect of isoproterenol, beta1-AR density and isoproterenol-stimulated AC activity in the failing heart were also attenuated by treatment with another ACE inhibitor, enalapril and an angiotensin II receptor antagonist, losartan. The results indicate that imidapril not only attenuates cardiac dysfunction but also prevents changes in beta-AR signal transduction in CHF due to MI. These beneficial effects are similar to those of enalapril or losartan and thus appear to be due to blockade of the renin-angiotensin system.

Improvement of cardiac function and beta-adrenergic signal transduction by propionyl L-carnitine in congestive heart failure due to myocardial infarction.

OBJECTIVES: Earlier studies have revealed beneficial effects of metabolic therapy in animals with congestive heart failure (CHF) due to myocardial infarction. Because heart failure is also associated with attenuated response to catecholamines, we examined the effects of propionyl L-carnitine (PLC) (a carnitine derivative) therapy on the beta-adrenoceptor (beta-AR) signal transduction in the failing heart. METHODS: Heart failure in rats was induced by occluding the coronary artery and 3 weeks later the animals were treated with or without 100 mg/kg (intraperitoneally, daily) PLC for 5 weeks. The animals were assessed for their left ventricular function and inotropic responses to isoproterenol. Crude membranes were isolated from the remote, nonischemic (viable) left ventricle and examined for changes in beta-AR and adenylyl cyclase (AC) activity. RESULTS: Animals with heart failure exhibited depressions in ventricular function, positive inotropic response to isoproterenol, beta-AR receptor density and basal AC activity; these changes were also attenuated by PLC treatment. The stimulation of AC activities with isoproterenol, 5'-guanyl imidodiphosphate, forskolin and sodium fluoride was decreased in the failing hearts and these changes were also prevented by PLC treatment. CONCLUSION: The results indicate that metabolic therapy with PLC not only attenuates the defects in heart function but also prevents changes in the beta-AR signal transduction in CHF due to myocardial infarction.

Changes in ß-adrenoceptors in heart failure due to myocardial infarction are attenuated by blockade of renin-angiotensin system.

Earlier studies have revealed an improvement of cardiac function in animals with congestive heart failure (CHF) due to myocardial infarction (MI) by treatment with angiotensin converting enzyme (ACE) inhibitors. Since heart failure is also associated with attenuated responses to catecholamines, we examined the effects of imidapril, an ACE inhibitor, on the ß-adrenoceptor (ß-AR) signal transduction in the failing heart. Heart failure in rats was induced by occluding the coronary artery, and 3 weeks later the animals were treated with 1 mg/(kg·day) (orally) imidapril for 4 weeks. The animals were assessed for their left ventricular function and inotropic responses to isoproterenol. Cardiomyocytes and crude membranes were isolated from the non-ischemic viable left ventricle and examined for the intracellular concentration of Ca(2+) [Ca(2+)]i and ß-ARs as well as adenylyl cyclase (AC) activity, respectively. Animals with heart failure exhibited depressions in ventricular function and positive inotropic response to isoproterenol as well as isoproterenol-induced increase in [Ca(2+)]i in cardiomyocytes; these changes were attenuated by imidapril treatment. Both ß1-AR receptor density and isoproterenol-stimulated AC activity were decreased in the failing heart and these alterations were prevented by imidapril treatment. Alterations in cardiac function, positive inotropic effect of isoproterenol, ß1-AR density and isoproterenol-stimulated AC activity in the failing heart were also attenuated by treatment with another ACE inhibitor, enalapril and an angiotensin II receptor antagonist, losartan. The results indicate that imidapril not only attenuates cardiac dysfunction but also prevents changes in ß-AR signal transduction in CHF due to MI. These beneficial effects are similar to those of enalapril or losartan and thus appear to be due to blockade of the renin-angiotensin system. (Mol Cell Biochem 263: 11-20, 2004).