Cardioprotection by systemic dosing of thymosin beta four following ischemic myocardial injury

Thymosin beta 4 (Tβ4) was previously shown to reduce infarct size and improve contractile performance in chronic myocardial ischemic injury via two phases of action: an acute phase, just after injury, when Tβ4 preserves ischemic myocardium via antiapoptotic or anti-inflammatory mechanisms; and a chronic phase, when Tβ4 activates the growth of vascular or cardiac progenitor cells. In order to differentiate between the effects of Tβ4 during the acute and during the chronic phases, and also in order to obtain detailed hemodynamic and biomarker data on the effects of Tβ4 treatment suitable for use in clinical studies, we tested Tβ4 in a rat model of chronic myocardial ischemia using two dosing regimens: short term dosing (Tβ4 administered only during the first 3 days following injury), and long term dosing (Tβ4 administered during the first 3 days following injury and also every third day until the end of the study). Tβ4 administered throughout the study reduced infarct size and resulted in significant improvements in hemodynamic performance; however, chamber volumes and ejection fractions were not significantly improved. Tβ4 administered only during the first 3 days following injury tended to reduce infarct size, chamber volumes and improve hemodynamic performance. Plasma biomarkers of myocyte injury were significantly reduced by Tβ4 treatment during the acute injury period, and plasma ANP levels were significantly reduced in both dosing groups. Surprisingly, neither acute nor chronic Tβ4 treatment significantly increased blood vessel density in peri-infarct regions. These results suggest the following: repeated dosing may be required to achieve clinically measureable improvements in cardiac function post-myocardial infarction (MI); improvement in cardiac function may be observed in the absence of a high degree of angiogenesis; and that plasma biomarkers of cardiac function and myocardial injury are sensitive pharmacodynamic biomarkers of the effects of Tβ4

Albiglutide, a Long Lasting Glucagon-Like Peptide-1 Analog, Protects the Rat Heart against Ischemia/Reperfusion Injury: Evidence for Improving Cardiac Metabolic Efficiency

BACKGROUND: The cardioprotective effects of glucagon-like peptide-1 (GLP-1) and analogs have been previously reported. We tested the hypothesis that albiglutide, a novel long half-life analog of GLP-1, may protect the heart against I/R injury by increasing carbohydrate utilization and improving cardiac energetic efficiency. METHODS/PRINCIPAL FINDINGS: Sprague-Dawley rats were treated with albiglutide and subjected to 30 min myocardial ischemia followed by 24 h reperfusion. Left ventricle infarct size, hemodynamics, function and energetics were determined. In addition, cardiac glucose disposal, carbohydrate metabolism and metabolic gene expression were assessed. Albiglutide significantly reduced infarct size and concomitantly improved post-ischemic hemodynamics, cardiac function and energetic parameters. Albiglutide markedly increased both in vivo and ex vivo cardiac glucose uptake while reducing lactate efflux. Analysis of metabolic substrate utilization directly in the heart showed that albiglutide increased the relative carbohydrate versus fat oxidation which in part was due to an increase in both glucose and lactate oxidation. Metabolic gene expression analysis indicated upregulation of key glucose metabolism genes in the non-ischemic myocardium by albiglutide. CONCLUSION/SIGNIFICANCE: Albiglutide reduced myocardial infarct size and improved cardiac function and energetics following myocardial I/R injury. The observed benefits were associated with enhanced myocardial glucose uptake and a shift toward a more energetically favorable substrate metabolism by increasing both glucose and lactate oxidation. These findings suggest that albiglutide may have direct therapeutic potential for improving cardiac energetics and function

Examining the relationship between exercise tolerance and isoproterenol-based cardiac reserve in murine models of heart failure

The loss of cardiac reserve is, in part, responsible for exercise intolerance in late-stage heart failure (HF). Exercise tolerance testing (ETT) has been performed in mouse models of HF; however, treadmill performance and at-rest cardiac indexes determined by magnetic resonance imaging (MRI) rarely correlate. The present study adopted a stress-MRI technique for comparison with ETT in HF models, using isoproterenol (ISO) to evoke cardiac reserve responses. Male C57BL/6J mice were randomly subjected to myocardial infarction (MI), transverse aortic constriction (TAC), or sham surgery under general anesthesia. Mice underwent serial ETT on a graded treadmill with follow-up ISO stress-MRI. TAC mice showed consistent exercise intolerance, with a 16.2% reduction in peak oxygen consumption vs. sham at 15-wk postsurgery (WPS). MI and sham mice had similar peak oxygen consumption from 7 WPS onward. Time to a respiratory exchange ratio of 1.0 correlated with ETT distance ( r = 0.64; P &lt; 0.001). The change in ejection fraction under ISO stress was reduced in HF mice at 4 WPS [10.1 ± 3.9% change (Δ) and 8.9 ± 3.5%Δ in MI and TAC, respectively, compared with 32.0 ± 3.5%Δ in sham; P &lt; 0.001]. However, cardiac reserve differences between surgery groups were not observed at 16 WPS in terms of ejection fraction or cardiac output. In addition, ETT did not correlate with cardiac indexes under ISO stress. In conclusion, ISO stress was unable to reflect consistent differences in ETT between HF and healthy mice, suggesting cardiac-specific indexes are not the sole factors in defining exercise intolerance in mouse HF models. </jats:p

Glucose utilization and reserve capacity in cultured CMs.

<p>Glucose utilization was assessed by examining percent change in ECAR and the reserve capacity assessed as percent change in OCR following FCCP challenge in the presence of indicated concentrations of GLP-1 or insulin at 70 nM. A typical seahorse plot representing changes in ECAR over time following acute treatment with 100 nM GLP-1 (maximal effective dose) or insulin optimal media (A) or suboptimal media (B). Percentage change in ECAR, 10 min post injection of GLP-1 (1, 10, 100 nM) or insulin with optimal media (C) and suboptimal media (D). Typical seahorse plots representing changes in OCR over time following acute treatment with 100 nM GLP-1 or insulin with optimal (E) or suboptimal (F) media. Percentage change in OCR, 80 min post injection of GLP-1 (1, 10, 100 nM) or insulin in optimal (G) and suboptimal (H) media. ECAR, extracellular acidification rate; OCR, oxygen consumption rate. Data are presented as mean±SEM of 3–5 replicates per treatment from 2–4 individual experiments. ***p<0.001, *p<0.05, vs Control.</p

Infarct assessment following cardiac ischemia-reperfusion injury in rat.

<p>Sprague-Dawley rats (n = 5-6) were subjected to a 30 min LAD coronary artery occlusion followed by 24 hr period of reperfusion. Hearts were harvested for assessment of area at risk and infarct size. Representative photographs of heart sections stained with TTC and Evans Blue dye are shown for both Vehicle (A) and GLP-1 (B) groups. The areas of myocardial infarct are white, areas at risk (AAR) are the combined white and red regions, and area not at risk (ANAR) are dark blue. Infarct size and area at risk are presented as percentage of AAR and left ventricle, respectively (C). Data are presented as mean±SEM. *p<0.05 vs Vehicle.</p

Tissue cAMP levels in the right ventricle, AAR, and ANAR of left ventricle after myocardial ischemia/reperfusion injury.

<p>Tissues were harvested following a 30 min ischemia/24 h reperfusion period and extracted as described in the text for cAMP analysis. Data comparing Vehicle (n = 3-6) with GLP-1 (300 pmol/kg/min) (n = 3-6) treatment groups are shown, with mean ±SEM as indicated. ***p<0.001 vs ANAR *p<0.05 vs Vehicle.</p

<i>In vivo</i> [³H]-2-DG uptake in rat myocardium.

<p>Kinetics of [^<b>3</b>H]-2-DG clearance from plasma after a single bolus injection for Vehicle (, n = 8), GLP-1 (300 pmol/kg/min) (∆, n = 8), or insulin (3 U/kg) (▼, N = 5) (A). Myocardial glucose uptake measured at the end of study; i.e. 30 min following tracer administration (B). Data are presented as mean±SEM. *p<0.05, ***p<0.001 vs Vehicle.</p

<i>In vivo</i> intermediary glucose metabolism in AAR and ANAR of rat left ventricle following a euinsulinemic-hyperglycemic clamp over 2 hr with 1-[¹³C] glucose infusion.

<p>Left ventricle intermediary metabolite ^<b>13</b>C enrichments of alanine, lactate and glutamate are presented for AAR or ANAR myocardial tissue from Vehicle (n = 6) and GLP-1 (300 pmol/kg/min group, n = 6) treatment groups (A). Relative carbohydrate oxidation versus fat oxidation in Vehicle and GLP-1 treated AAR and ANAR myocardial tissue (B). The relative carbohydrate versus fat oxidation is calculated using isotopomer analysis of alanine and glutamate enrichments as described in the methods section. Data are presented as mean±SEM. *p<0.05 vs respective Vehicle.</p