Cardioprotective effects of ghrh agonists

Abstract

Disclosed herein are methods demonstrating that growth-hormone releasing hormone (GHRH) directly activates cellular reparative mechanisms within the injured heart, in a GH / IGF-I independent fashion. Following experimental myocardial infarction (MI), rats were randomly assigned to receive, during a 4 week period, either placebo (n=14), rat recombinant GH (rrGH, n=8) or JI-38 (n=8; 50 μg / Kg / day), a potent GHRH-agonist. JI-38 did not elevate serum levels of GH or IGF-I, but markedly attenuated the degree of cardiac functional decline and remodeling after injury. In contrast, GH administration markedly elevated body weight, heart weight, circulating GH and IGF-I, but did not offset the decline in cardiac structure and function. Whereas, both JI-38 and GH augmented levels of cardiac precursor cell proliferation, only JI-38 increased anti-apoptotic gene expression. Collectively, these findings demonstrate that within the heart, GHRH-agonists can activate cardiac repair following MI.

Description

RELATED APPLICATIONS[0001]This application is a divisional application of U.S. application Ser. No. 12 / 914,023 filed on Oct. 28, 2010, which claims priority to U.S. Provisional Application No. 61 / 289,949 filed Dec. 23, 2009, the contents of each of the foregoing applications are incorporated by reference herein.GOVERNMENT INTEREST[0002]This work was supported by NIH grant R01-AG025017, RO1-HL084275, RO1-HL65455, RO1-HL094848 and by National Heart, Lung, and Blood Institute Grants U54-HL081028. The studies in the laboratory of AVS were supported in part by The Medical Research Service of the Veterans Affairs Department and South Florida Veterans Affairs Foundation for Research and Education and University of Miami, Miller School of Medicine, Departments of Pathology and Medicine, Division of Hematology / Oncology.FIELD OF THE INVENTION[0003]Cardioprotective Effects of GHRH AgonistsSequence Listing[0004]The instant application contains a Sequence Listing which was submitted in ASCII for...

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Benefits of technology

[0008]The main finding of the present study is that GHRH-A has a cardioprotective role in vivo following acute MI. Animals receiving GHRH-A had improved cardiac structure and function and reduced infarct size. In addition, cardiac fibrosis, which is one of the main biological determinants of poor prognosis in heart failure, and strongly associated with severe arrhythmias, diastolic dysfunction and sudden death (14), was markedly reduced in the GHRH-A group but not in the rrGH group. The cardiac effects of GHRH-agonist appear to be direct, not involving the GH / IGF-I axis, since the circulating levels of these hormones were not increased by GHRH-A treatment.

[0010]Our findings demonstrate that rrGH markedly increases body weight (BW), heart weight (HW) and circulating levels of GH and IGF-I, but does not improve cardiac function or prevent remodeling; on the contrary, rats treated with rrGH exhibited larger chambers and worse ejection fraction (EF). These results are in agreement with a study which showed that GH caused adverse effects on the process of LV remodeling (18).

[0013]Traditionally, the adult heart has been considered a post-mitotic organ where the cardiac myocytes were terminally differentiated without ability to divide. However, several investigators (33-35) have suggested that at least a subpopulation of myocytes re-enter the cell cycle and divide, and also that a pool of cardiac stem cells may reside in the myocardium. In the present study, the expression of Ki67 positive cells was significantly higher at the remote zone but only in the rrGH group and this was accompanied by an increase in capillary density in the same group. Previous study has documented that GH is able to stimulate mature cardiac myocytes to re-enter the cell cycle, divide and thereby increase their number in rat myocardium (36). A reduction in apoptosis would also lead to an increased number of cardiac myocytes but in our study, surprisingly, the reduction in apoptosis in both treated groups was lower and not statistically significant when assessed by TUNEL assay; however, at the molecular level, changes in the expression of Bax and Bc12 supported an anti-apoptotic effect of GHRH-A.

[0014]We also examined the abundance of cardiac precursor cells which showed increased c-kit positive cells expression (clusters) in the infarct zone in both treated groups; recruitment of c-kit positive stem cells is associated with improvement in cardiac performance (37). Bru'el et al (36) also reported that the number of c-kit positive cells in a GH treated group was 31% higher than that of the control group, but it was not statistically significant. Given the observation of similar increases in c-kit cells with GH and GHRH, yet greater reverse remodeling with GHRH, it is attractive to speculate that GHRH may stimulate cardiopoiesis to a greater extent. An alternate explanation is that the c-kit cells may traffic and / or proliferate to a greater or earlier extent. Finally, the findings of an anti-apoptotic milieu might suggest improved survival of differentiation cardiac precursor cells (CPCs). Future work is required to evaluate the direct effects of GHRH on CPC). Besides CPCs possess the IGF-I / IGF-I receptor system (38) which potentiates their survival and growth (39). Further studies are needed to ascertain whether GHRH-A or rrGH stimulated existing cardiac stem cells to differentiate into mature cardiac myocytes.

Problems solved by technology

Congestive heart failure remains a leading cause of morbidity and mortality in developed countries.

Despite major therapeutic advances, current therapies fail to fully reverse heart failure and / or left ventricular (LV) dysfunction.

Moreover, several clinical studies have tested the impact of GH replacement on the failing human heart, with controversial results (3,4).

Ghrelin and other GH secretagogues may have pharmacological potential (10), but also have pleiotropic actions with a high possibility of unexpected side effects and potentially serious disadvantages.

Similarly, treatments with rat recombinant GH did not show beneficial effect in rats with large MI (19).

Importantly, all treatments with recombinant human GH in rats had a clear limitation due perhaps to the production of anti-GH antibodies after 2 weeks of treatment (23).

Our findings demonstrate that rrGH markedly increases body weight (BW), heart weight (HW) and circulating levels of GH and IGF-I, but does not improve cardiac function or prevent remodeling; on the contrary, rats treated with rrGH exhibited larger chambers and worse ejection fraction (EF).

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