Impaired cardiovascular responses to glucagon-like peptide 1 in metabolic syndrome and type 2 diabetes mellitus

Abstract

Recent advancements in the management of systemic glucose regulation in obesity/T2DM include drug therapies designed to utilize components of the incretin system specifically related to glucagon-like peptide 1 (GLP-1). More recently, GLP-1 has been investigated for potential cardioprotective effects. Several investigations have revealed that acute/sub-acute intravenous administration of GLP-1 significantly reduces myocardial infarct size following ischemia/reperfusion injury and improves cardiac contractile function in the settings of coronary artery disease, myocardial ischemia/reperfusion injury, and heart failure. Despite an abundance of data indicating that intravenous infusion of GLP-1 is cardioprotective, information has been lacking on the cardiac effects of iv GLP-1 in the MetS or T2DM population. Some important questions this study aimed to address are 1) what are the direct, dose-dependent cardiac effects of GLP-1 in-vivo 2) are the cardiac effects influenced by cardiac demand (MVO2) and/or ischemia, 3) does GLP-1 effect myocardial blood flow, glucose uptake or total oxidative metabolism in human subjects, and 4) are the cardiac effects of GLP-1 treatment impaired in the settings of obesity/MetS and T2DM. Initial studies conducted in canines demonstrated that GLP-1 had no direct effect on coronary blood flow in-vivo or vasomotor tone in-vitro, but preferentially increased myocardial glucose uptake in ischemic myocardium independent of effects on cardiac contractile function or coronary blood flow. Parallel translational studies conducted in the humans and Ossabaw swine demonstrate that iv GLP-1 significantly increases myocardial glucose uptake at rest and in response to increases in cardiac demand (MVO2) in lean subjects, but not in the settings of obesity/MetS and T2DM. Further investigation in isolated cardiac tissue from lean and obese/MetS swine indicate that this impairment in GLP-1 responsiveness is related to attenuated activation of p38-MAPK, independent of alterations in GLP-1 receptor expression or PKA-dependent signaling. Our results indicate that the affects of GLP-1 to reduce cardiac damage and increase left ventricular performance may be impaired by obesity/MetS and T2DM.