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

Assessing the effects of LXR agonists in cholesterol handling: stable isotope tracer studies

The liver X receptors α and β (LXR) are responsible for transcriptional regulation of a number of genes involved in cholesterol efflux from cells and therefore may be molecular target for the treatment of cardiovascular disease. However, the effects of LXR ligands on cholesterol turnover in cells and in animals have not been examined comprehensively. Here we examined the effects of LXR agonists on cholesterol handling in both in-vitro (HepG2 cells) and in-vivo (Golden Syrian hamsters) models using stable isotope probes and corresponding multi-compartmental mathematical modeling. A two compartmental analysis of 1-13C sodium acetate tracer in combination with Mass Isotopomer Distribution Analysis (MIDA) revealed varying responses to cholesterol handling (e.g. synthesis, catabolism, influx and efflux) in cultured HepG2 cells following treatment with synthetic non-steroidal LXR agonists (GW3965, T0901317, SB742881) and steroidal LXR agonists (22(R)-hydroxycholesterol, 24(S),25-epoxycholesterol, Dimethyl-3β-hydroxy-cholenamide). Unlike the steroidal LXR agonists, non-steroidal LXR agonists increased cholesterol synthesis by 5 fold, decreased cholesterol influx by 70-80% and increased cholesterol efflux by 2 fold. For experiments assessing LXR effects on cholesterol handling in hamsters, six compartmental model was created to define free cholesterol and esterified cholesterol flux in three separate pools (plasma, liver, extrahepatic tissue). The six compartmental analysis of 3,4-13C cholesterol tracer in hamsters resulted in a slight, but non-significant increase in free cholesterol efflux from liver (60%) following treatment with LXR agonist: GW3965, consistent with in vitro observations. In summary, comprehensive mathematical models were developed in order to assess cholesterol handling in cells and in animals. For the first time, LXR perturbation of cholesterol handling in these in vivo systems was assessed.Ph.D., Physics -- Drexel University, 200

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