The broad objective of this program is to perform preclinical experimentation on animal models of myocardial ischemia and subsequent chronic heart failure (CHF) to elucidate the mechanisms of its development and to evaluate the potential of different therapeutic modalities to limit the extent of myocardial damage and to prevent or attenuate the development of CHF. I. Beta-2 adrenergic receptors in treatment of CHF. The role of beta-adrenergic receptors (AR) subtype signaling in development of CHF is clearly important. It is widely accepted now that beta-1 AR activation is associated with development of CHF. Recent data indicate that stimulation of beta-1 AR is proapoptotic, thus, the use of beta-1 AR antagonists became a recommended therapy for HF. The possible role of beta-2 AR agonists remains debatable;however, the consensus is that similar to beta-1 AR, activation of beta-2 AR during CHF is harmful. Recent research in LCS using single myocytes indicated that beta-2 AR agonist, fenoterol, possesses a unique cardioprotective property, and, in fact, is antiapoptotic. Capitalizing on this finding, we studied the effects of chronic treatment with beta-2 AR agonist, fenoterol, and beta-1 AR blocker, metaprolol, in rats starting 2 weeks after ligation of a coronary artery. Our results indicated that both beta-2 AR agonist and beta-1 AR blocker reduced the apoptosis in myocardium, but beta-2 AR agonist was superior to beta-2 AR blocker in attenuation of left ventricular remodeling and functional decline. Moreover, beta-2 agonist treatment arrested the infarct expansion, resulting in actual decrease of the relative infarct size. These two therapies affected different aspects of cardiac function: metaprolol improved systolic cardiac performance by increasing left ventricular elastance, while fenoterol achieved the same result by reducing the arterial elastance (after-load). Metaprolol did not improve diastolic function, while fenoterol normalized it. Combined treatment with beta-1 blocker and beta-2 agonist resulted in morphometric and functional improvements similar to a treatment with beta-2 agonist alone. In additional experiments we showed that a treatment with a combination of beta-1 blocker, metaprolol, and beta-2 agonist, fenoterol, is clearly superior to a single therapy with beta1-blocker in reduction of cardio myocyte apoptosis, attenuation of LV remodeling, and it actually improves the LV function. In a yearlong experiment, we demonstrated a significant survival benefit of combined therapy with beta-2 agonist and beta-1 blocker compared with any single therapy alone. Moreover, a therapeutic benefit of beta-2 agonist lasted only 2 months after coronary ligation, while the effect of combined therapy lasted six months. In the latest study, we compared the effects of the beta-1 AR blocker-beta-2 AR agonist combination with a combination of beta-1 AR blocker and angiotensin converting enzyme inhibitor (ACEi), i.e., the current therapy of choice for CHF. Two weeks after coronary artery ligation, rats were divided into groups of similar average myocardial infarct (MI) size measured by echocardiography, and the following 12-mo treatments were initiated: fenoterol, a beta-2 AR agonist, and metoprolol, a beta-1 AR blocker;metaprolol and enalapril an ACEi;and a combination of all three compounds. These treatment groups were compared to a non-treated (nT) and sham groups. The 12-mo mortality was significantly reduced in all treatment groups (44% in beta1-beta2+, 56% in beta 1-beta 2+ACEi, 59% in beta 1-ACEi vs 81% in nT). Bi-monthly Echo revealed significant attenuation of the left ventricular (LV) chamber remodeling, LV functional deterioration, and MI expansion in all three treatment groups, but effects were significantly more pronounced when treatment included a beta 2AR agonist. We concluded that the combination of 1AR blocker and 2AR agonist is equipotent with a combination of beta 1AR blocker and ACEi in the treatment of CHF with the respect to mortality and exceeds the later with respect to cardiac remodeling and MI expansion. Thus, this novel therapeutic regimen for CHF merits clinical trial consideration. Fenoterol exists as four stereoisomers. Combination of two of enantiomers, RR and SS are a racemic mixture, which represents an actual drug that had been used clinically for treatment of asthma and for our experiments cited above. In order to refine the therapeutic effectiveness of fenoterol in the CHF model, its stereoisomers have been synthesized and tested with respect to their binding ability to beta2 AR, selectivity, and functional activity. It has been reported that in experiments in isolated rat cardiomyocytes the R-enantiomer of fenoterol exhibits more potent effects on cardiomyocyte contractility and better Gs protein selectivity than other stereoisomers. Thus the R-enantiomer of fenoterol might be a promising new drug. In the present study we used the rat experimental model of post MI DCM to compare the efficacy of the R- and L-enantiomers of fenoterol with its racemic mixture, whose efficacy had been demonstrated in our previous experiments. Racemic mixture of fenoterol (F) and one of its enantiomers, right (RF) or left (LF) were given to rats in drinking water as described above, starting 2 weeks after induction of MI. The LV remodeling and function were assessed during the next 5 months via serial echocardiograaphy. All the effects of fenoterol described above, attenuation of LV remodeling and functional decline and arrest of MI expansion were replicated in the present experiment, including the loss of effectiveness after 3 months as a monotherapy. Both groups treated with right or left enantiomers of fenoterol were undistinguishable from the untreated group. Thus, the therapeutic potential of the R-enantiomer of fenoterolreported on the basis of experiment on single cardiomyocyte level was not confirmed in our whole animal experiments. II. Blueberry-enriched diet in treatment of chronic heart failure. We have reported that blueberry-enriched diet (BD) attenuates necro-apoptosis and inflammation in peri-infarct area in experiments on rats and thus reduces surgically induced myocardial infarction. Since it is now generally accepted that a major factor leading to progression of CHF is cumulative cell loss in myocardium, we tested the hypothesis that BD would attenuate the course of CHF, including mortality and cardiac remodeling during the first year after induction of myocardial infarction in rats. Two weeks after coronary artery ligation, rats were divided into two groups of similar average MI size, measured by echocardiography, and the following 12-mo dietary regimens were initiated: ad libitum regular diet (control, CD, n=27) and isocaloric food with 2% blueberry supplement (BD, n=27) also available ad libitum. These dietary groups were compared to each other and to sham group (SH). The 12-mo mortality was reduced by 22% in BD compared with CD (p<0.01). In the course of developing CHF, BD had no effect on the body weight, heart rate or blood pressure. Bi-monthly Echo revealed significant attenuation of the LV chamber remodeling, LV posterior wall thinning, and MI expansion in BD compared with CD. In fact, BD arrested the MI expansion. This is the first experimental evidence that a blueberry-enriched diet has positive effects on the course of CHF and thus warrants consideration for clinical testing.
