title: GLP-1 receptor agonism ameliorates hepatic VLDL overproduction and de novo lipogenesis in insulin resistance.
abstract: OBJECTIVE
  Fasting dyslipidemia is commonly observed in insulin resistant states and mechanistically linked to hepatic overproduction of very low density lipoprotein (VLDL). Recently, the incretin hormone glucagon-like peptide-1 (GLP-1) has been implicated in ameliorating dyslipidemia associated with insulin resistance and reducing hepatic lipid stores. Given that hepatic VLDL production is a key determinant of circulating lipid levels, we investigated the role of both peripheral and central GLP-1 receptor (GLP-1R) agonism in regulation of VLDL production.
  
  
  METHODS
  The fructose-fed Syrian golden hamster was employed as a model of diet-induced insulin resistance and VLDL overproduction. Hamsters were treated with the GLP-1R agonist exendin-4 by intraperitoneal (ip) injection for peripheral studies or by intracerebroventricular (ICV) administration into the 3rd ventricle for central studies. Peripheral studies were repeated in vagotomised hamsters.
  
  
  RESULTS
  Short term (7-10 day) peripheral exendin-4 enhanced satiety and also prevented fructose-induced fasting dyslipidemia and hyperinsulinemia. These changes were accompanied by decreased fasting plasma glucose levels, reduced hepatic lipid content and decreased levels of VLDL-TG and -apoB100 in plasma. The observed changes in fasting dyslipidemia could be partially explained by reduced respiratory exchange ratio (RER) thereby indicating a switch in energy utilization from carbohydrate to lipid. Additionally, exendin-4 reduced mRNA markers associated with hepatic de novo lipogenesis and inflammation. Despite these observations, GLP-1R activity could not be detected in primary hamster hepatocytes, thus leading to the investigation of a potential brain-liver axis functioning to regulate lipid metabolism. Short term (4 day) central administration of exendin-4 decreased body weight and food consumption and further prevented fructose-induced hypertriglyceridemia. Additionally, the peripheral lipid-lowering effects of exendin-4 were negated in vagotomised hamsters implicating the involvement of parasympathetic signaling.
  
  
  CONCLUSIONS
  Exendin-4 prevents fructose-induced dyslipidemia and hepatic VLDL overproduction in insulin resistance through an indirect mechanism involving altered energy utilization, decreased hepatic lipid synthesis and also requires an intact parasympathetic signaling pathway.
authors.affiliation: Molecular Structure and Function, Research Institute, The Hospital for Sick Children, Toronto, ON, Canada ; Department of Laboratory Medicine and Pathobiology, University of Toronto, ON, Canada.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Taher
authors.affiliation: Molecular Structure and Function, Research Institute, The Hospital for Sick Children, Toronto, ON, Canada.
authors.forename: Christopher L
authors.initials: CL
authors.lastname: Baker
authors.affiliation: Molecular Structure and Function, Research Institute, The Hospital for Sick Children, Toronto, ON, Canada.
authors.forename: Carmelle
authors.initials: C
authors.lastname: Cuizon
authors.affiliation: Molecular Structure and Function, Research Institute, The Hospital for Sick Children, Toronto, ON, Canada.
authors.forename: Hassan
authors.initials: H
authors.lastname: Masoudpour
authors.affiliation: Molecular Structure and Function, Research Institute, The Hospital for Sick Children, Toronto, ON, Canada.
authors.forename: Rianna
authors.initials: R
authors.lastname: Zhang
authors.affiliation: Molecular Structure and Function, Research Institute, The Hospital for Sick Children, Toronto, ON, Canada ; Department of Laboratory Medicine and Pathobiology, University of Toronto, ON, Canada.
authors.forename: Sarah
authors.initials: S
authors.lastname: Farr
authors.affiliation: Molecular Structure and Function, Research Institute, The Hospital for Sick Children, Toronto, ON, Canada.
authors.forename: Mark
authors.initials: M
authors.lastname: Naples
authors.affiliation: Physiology and Experimental Medicine, Research Institute, The Hospital for Sick Children, Toronto, ON, Canada.
authors.forename: Celine
authors.initials: C
authors.lastname: Bourdon
authors.affiliation: Physiology and Experimental Medicine, Research Institute, The Hospital for Sick Children, Toronto, ON, Canada.
authors.forename: Zdenka
authors.initials: Z
authors.lastname: Pausova
authors.affiliation: Molecular Structure and Function, Research Institute, The Hospital for Sick Children, Toronto, ON, Canada ; Department of Laboratory Medicine and Pathobiology, University of Toronto, ON, Canada.
authors.forename: Khosrow
authors.initials: K
authors.lastname: Adeli
keywords: FFA, free fatty acid; Fasting dyslipidemia; GLP-1, glucagon-like peptide-1; GLP-1R, GLP-1 receptor; Glucagon-like peptide-1 (GLP-1); Hepatic steatosis; ICV, intracerebroventricular; Incretin; Insulin resistance; RER, respiratory exchange ratio; T2D, type 2 diabetes; VLDL, very low density lipoprotein; Very low density lipoprotein (VLDL); apoB100, apolipoproteinB100; ip, intraperitoneal