Abstract 1489: Mechanisms Underlying Cardioprotective Effects Of Glucagon-like Peptide-1 In Ischemia-reperfusion Injury
Background: GLP-1 is a member of the gut incretin hormone family, and a GLP-1 receptor agonist (exendin-4) is approved for the treatment of Type-II diabetes. Studies in man post-MI, and in rat and dog models suggest that GLP-1 is cardioprotective. However, the mechanisms underlying the effects of structurally diverse GLP-1 peptides in the heart have not been fully elucidated.
Methods & Results: GLP-1(7–36) (i.e. GLP-1), its cleavage product GLP(9–36), and the degradation-resistant GLP-1R agonist exendin-4 were examined in 30 min of global ischemia followed by 40 min of reperfusion (I/R) in Langendorff isolated heart preparations from both wild-type (WT) and GLP-1 receptor knockout (GLP-1R−/−) mice. In WT mice, recovery of left ventricular developed pressure (LVDP) following I/R was higher in GLP-1 pre-infused hearts than in untreated controls (79±9 vs. 42±1%; p<0.01). Pre-treatment with 5 nM but not with 0.3~3 nM exendin-4 also protected the heart from I/R injury. Although pre-infusion of GLP(9–36) induced lower recovery than untreated controls (21.4±1%), post-infusion of either GLP(9–36) or GLP-1 augmented functional recovery to a similar extent (59.1±6% and 53.3±6%). Surprisingly, the cardioprotective effects of pre- and post-treatments with both molecular forms of GLP-1 were detected in studies with GLP-1R−/− hearts (80.1±6% and 55.8±8). Of note, both GLP-1 and GLP(9–36) treatments also demonstrated potent vasodilatory effects, as manifested by increased coronary flow rates in isolated hearts and increased diameters of pre-constricted mesenteric arteries isolated from both WT and GLP-1R−/− mice. The cardioprotective effects on isolated hearts and vasodilatory effects on isolated mesenteric arteries, induced by GLP-1 was blunted by co-treatment with a dipeptidyl peptidase-4 (DPP-4) enzyme inhibitor, that blocked conversion of GLP-1 to GLP(9–36). Increased cGMP release in the coronary effluents was also observed following addition of GLP-1 and GLP(9–36) to hearts isolated from WT and GLP-1R−/− mice.
Summary: These data expand the complexity of GLP-1 biology by illustrating that the beneficial effects of GLP-1 in I/R injury are mediated in part by GLP(9–36) via a NO/cGMP-dependent vasodilatory effect that is independent of the known GLP-1R.