| Chronic heart failure is a common clinical syndrome with a high morbidity and mortality rate. Chronic beta-adrenergic receptor blockade is effective in treating heart failure. The beta-adrenergic receptor-selective blockers, metoprolol and bisoprolol, as well as carvedilol, a nonselective beta-adrenergic receptor antagonist with alpha1adrenergic receptor blocking and potent antioxidant activities, not only increase left ventricular systolic function but also reduce cardiac mortality and morbidity in patients with chronic heart failure. However, the extent of improvements produced by these agents varies. In a direct comparison study, carvedilol was shown to produce a greater survival benefit in patients with chronic heart failure when compared to metoprolol. There is broad consensus that these three drugs are effective in treating chronic heart failure. However, we do not know if one of them is superior to the others. There has not been a direct comparison of the three beta-blockers now widely used in clinical practice.Chromogranin A (CgA) is a49-kDa protein with439amino acids, and it has been identified as playing a role in the endocrine and nervous systems. Circulating CgA has been shown to increase in proportion to clinical severity and to be associated with prognosis in patients with chronic or postinfarction heart failure. It has been widely accepted that ventricle remodeling plays an important part in the development of heart failure. The overactivation of neuroendocrine system plays a detrimental role in ventricle remodeling. The overactivation of the sympathetic nerves in chronic heart failure results in the progression of the disease and poor progonosis. Markedly elevated plasma levels of CgA have been observed in patients with neuroendocrine tumors. Many scientists believe that circulating CgA may integrate neuroendocrine signals from various sources and thus represent an index of overall neuroendocrine activity. If beta-blockers influence the expression of CgA in the circulation and myocardium, circulating CgA may be a good marker for heart failure and may be used to adjust beta-blocker doses to achieve the best beta-blockade.In this study, we sought to explore the therapeutic effects of carvedilol, metoprolol and bisoprolol on doxorubicin-induced chronic heart failure in mice. Meanwhile, we examined their influence on the CgA expression in the myocardium and circulation. PART1:The induction of chronic heart failure in miceObjective:To develop an appropriate method to induce the model of chronic heart failure in mice with doxorubicin.Methods:Twenty C57BL/6mice and twenty BALB/C mice were divided into four groups. GROUP A:C57BL/6(n=10), long-term method; GROUP B:C57BL/6(n=10), short-term method; GROUP C:BALB/C (n=10), short-term method; GROUP D: BALB/C (n=10), long-term method. The long-term method:doxorubicin2.0mg/kg, every other day for4times, then once a week for6times, for a total cumulative dose of20mg/kg, total time is8weeks; the short-term method:doxorubicin2.5mg/kg, every other day for6times for a total cumulative dose of15mg/kg, then observe for another4weeks after the last injection, total time is6weeks. Record every death of the mouse in each group. Echocardiography was done before and after the study. Results:In the long-term method groups (GROUP A and GROUP D), chronic heart failure was successfully induced in C57BL/6mice and with a low death rate (30%).Though BALB/C mice also presented with chronic heart failure, the death rate (70%) was too high to accept. In the short-term method groups (GROUP B and GROUP C), there is no significant difference in survival rate between GROUP B and GROUP C (90%vs80%). But there were no obvious changes in efection fraction and left ventricular internal diameter during diastole after the doxorubicin injection in BALB/C mice, which mean the failure to induce heart failure. As far as C57BL/6was concerned, the short term method shared similar death rate, ejection fraction and left ventricular internal diameter during diastole with the long term method. Meanwhile, the short term method saved2weeks than the long-term method. Conclusions:C57BL/6mice are more appropriate than BALB/C mice to be used to induce chronic heart failure with doxorubicin.Intraperitoneal injection of doxorubicin in C57BL/6mice (2.5mg/kg, every other day for6times for a total cumulative dose of15mg/kg, then another4weeks) is a reliable method to induce chronic heart failure. PART2:Comparison of different beta-blockers on the therapeutic effects in chronic heart failure miceObjective:To compare the therapeutic effects of carvedilol, metoprolol and bisoprolol in mice with chronic heart failure.Methods:Seven mice were kept as controls (CON group) out of82C57BL/6mice. Seventy-five were injected intraperitoneally with doxorubicin,2.5mg/kg every other day6total times for a cumulative dose of15mg/kg. Before the first injection and4weeks after the last injection, echocardiography was performed to evaluate for systolic heart failure. Then, the mice with systolic heart failure were randomly assigned to one of the following groups:CAR, MET, PED, BIS and DOX. For the CAR group, carvedilol was administered twice a day at a target dose of8mg/kg/d. For the MET group, metoprolol was administered twice a day at a target dose of20mg/kg/d. For the PER group, perindopril was administered daily with a target dose of1.5mg/kg/d. For the BIS group, bisoprolol was administered daily with a target dose of1.5mg/kg/d. The DOX group did not receive any additional treatment. All drugs were dissolved in CMC (carboxymethyl cellulose) and administered intragastrically each day. The mice in the DOX and CON groups were given CMC daily. All drugs were initially given low doses, titrated to the target doses within a week, and then maintained at this dose for6weeks. At the end of the study, echocardiography, noninvasive measurement of the tail blood pressure and rate and histological analyses were done.Results:Two mice in the DOX group died, the others survived. Carvedilol, metoprolol and bisoprolol shared the same ability in improving the left ventricle ejection fraction and decreasing the enlarged left ventricular internal diameter during diastole and ameliorating the extent of injury of the heart.Conclusions:Our study suggests that carvedilol, metoprolol and bisoprolol share the same therapeutic ability. PART3:Comparison of different beta-blockers on the expression of chromogranin A in chronic heart failure miceObjective:To compare influences of carvedilol, metoprolol and bisoprolol on the expression of chromogranin A both in circulation and myocardium in mice with chronic heart failure.Methods:Animal study was the same as was shown in the second part of the study. Serum chromogranin A (CgA) concentrations were detected by enzyme-linked immunosorbent assay. Myocardial expressions of CgA were detected by Immunohistochemistry and Western Blot.Results:Although circulating CgA was elevated in heart failure mice, the three beta-blockers failed to lower it and circulating CgA failed to show a good correlation with ejection fraction. The myocardial expression of CgA was elevated about50%percent in the DOX group compared to the CON group. Carvedilol was the only drug among the four that was successful in lowering the myocardial expression of CgA.Conclusion:Circulating CgA may not be a good marker for heart failure or the best choice in adjusting beta-blocker doses to achieve the best beta-blockade. |
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