Albiglutide, a long lasting glucagon-like peptide-1 analog, protects the rat heart against ischemia/reperfusion injury: evidence for improving cardiac metabolic efficiency

Abstract

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.

Figure 1. Infarct size following myocardial ischemia/reperfusion injury.

Sprague-Dawley rats were subjected to 30 min LAD coronary artery occlusion followed by 24 h reperfusion. Hearts were harvested and analyzed for area at risk and infarct size. Representative photographs of heart sections from vehicle, 1, 3, and 10 mg/kg albiglutide-treated animals stained with 2,3,5-triphenyltetrazolium chloride (TTC) and Evans blue dye illustrate myocardial infarct (white), area at risk (white and red) and area not at risk (dark blue) (A). Myocardial infarct size was assessed as a percentage of area at risk in the left ventricle (B). The area at risk was assessed as a percentage of the left ventricle area is shown in (C). Cardiac cAMP was measured in both ischemic and non-ischemic areas (D). Values are presented as mean ± SEM. *p<0.01 and ^†p<0.001 vs. vehicle.

Figure 2. Cardiac glucose metabolism in vivo and ex vivo.

Cardiac [³H]-2-deoxyglucose uptake was examined in vivo over a 30 min period (A). Additionally, cardiac glucose uptake (B), lactate production (C) and tissue lactate concentration (D) were measured directly in the Langendorff perfused hearts. Values are presented as mean ± SEM. *p<0.05 vs. vehicle.

Figure 3. In vivo intermediary glucose metabolism in normal rat hearts.

A euinsulinemic-hyperglycemic clamp was performed for 2 h using 1-¹³C glucose as the exogenous precursor. LV intermediary metabolite ¹³C enrichments of alanine, lactate, and glutamate are presented as atom percent excess (APE) (A). The intermediary metabolite enrichments were used to indirectly assess the relative metabolic flux through carbohydrate versus fat oxidation as a percentage of flux through acetyl-CoA (B). Values are presented as mean ± SEM. *p<0.05 vs. vehicle.

Figure 4. Lactate disposition ex vivo.

Net lactate efflux across the heart during a 30 min perfusion period using a 1 mM 3-¹³C lactate precursor (A), cardiac tissue lactate concentration (B), and relative lactate oxidation as reflected by increased glutamate labeling (C). Values are presented as mean ± SEM. *p<0.05 vs. vehicle.

Figure 5. Principal Component Analysis of metabolic genes.

Principal Component Analysis of the gene expression data collected from normal and ischemia injured heart samples was performed and presented for normal hearts (A) and area at risk hearts following 30 min myocardial ischemia and 24 h reperfusion (B) and area not at risk hearts from the same animals (C).

Figure 6. Cardiac function and high energy metabolites following myocardial ischemia/reperfusion injury.

LV ejection fraction (A) and LV end systolic volume (B) were assessed by MRI immediately following the ³¹P MRS measurement at 24 h post-reperfusion. A voxel (15.8×11×17 mm) was orthogonally positioned in all 3 scout image planes of the heart and representative ³¹P MRS spectra from sham, vehicle- and albiglutide-treated hearts are presented with the prominent high-energy phosphate peaks visible (i.e., γ-ATP at −2.4 ppm, α-ATP at −7.5 ppm, β-ATP at −16 ppm, PCr at 0 ppm, intracellular inorganic phosphate (P_i(in)) at 4.9 ppm, and extracellular inorganic phosphate (P_i(ex)) at 5.1 ppm) (C). The resulting PCr/ATP ratio (D) PCr/Pi ratio (E) and cellular pH (F) are shown. Absolute whole heart ATP and PCr concentrations are shown in (G) and (H). Values are presented as mean ± SEM. *p<0.001, ^‡p<0.01 and ^§p<0.05 vs. sham; ^†p<0.01 and ^IIp<0.05 vs. vehicle.