Development and Evaluation of a Glucagon Sensitivity Test in Individuals With and Without Hepatic Steatosis
Condition: Non-Alcoholic Fatty Liver Disease; Glucagon Resistance; Type 1 Diabetes; Obesity
MeSH terms: Liver Diseases; Fatty Liver; Non-alcoholic Fatty Liver Disease
Study type: Interventional

Summary: 
      Glucagon is secreted from pancreatic alpha-cells in response to protein-rich meals and during
      hypoglycemia. A physiological feedback system exists between the liver and the pancreatic
      alpha cells termed the liver-alpha cell axis and signifies the role between amino
      acid-stimulated glucagon secretion and glucagon-stimulated amino acid metabolism.

      Individuals with non-alcoholic fatty liver disease have increased levels of glucagon
      (hyperglucagonemia) and amino acids (hyperaminoacidemia), which suggests that hepatic
      steatosis may uncouple glucagon's effect on amino acid metabolism (i.e. reduced glucagon
      sensitivity). Since hyperglucagonemia contributes to diabetes progression - due to its
      potentiating effects on hepatic glucose production - hepatic steatosis may create a
      diabetogenic circle. This study aims to develop and evaluate a test for measuring glucagon
      sensitivity in humans.

      The investigators (Associate Prof. Nicolai J Wewer Albrechtsen and Prof. Jørgen Rungby) will
      investigate whether amino acid metabolism is attenuated in individuals with hepatic steatosis
      (assessed by magnetic resonance imaging) due to impaired hepatic glucagon sensitivity and if
      glucagon's effect on hepatic glucose production is intact compared to individuals without
      hepatic steatosis suggestive of biased signaling.
    

Detailed description: 
      Amino acids administered orally or intravenously stimulate glucagon secretion from the
      pancreas and in turn, glucagon is a powerful stimulus for hepatic amino acid turnover through
      transcriptional (long-term) and non- transcriptional (acute) mechanisms. Several groups
      including the investigators have linked glucagon secretion to hepatic amino acid metabolism
      suggesting a mutual feedback cycle, termed the liver-alpha cell axis. A disruption of this
      axis, which has been shown both pharmacologically using glucagon receptor antagonists and
      genetically in glucagon receptor knockout mouse models, leads to increased glucagon
      (hyperglucagonemia) and amino acid (hyperaminoacidemia) concentrations. This phenotype is
      also evident in subjects with biopsy-verified metabolic dysfunction-associated steatotic
      liver disease (MASLD) independent of type 2 diabetes suggesting reduced hepatic glucagon
      sensitivity in the presence of hepatic steatosis. Glucagon increases amino acid catabolism by
      potentiating ureagenesis, a pathway exclusive to the liver, and hepatic accumulation of
      triglycerides may reduce glucagon's ability to augment amino acid turnover. Some amino acids
      are more potent in stimulating glucagon secretion (glucagonotropic amino acids), including
      alanine, and the glucagon-alanine index is currently used as a surrogate marker for the
      hepatic actions of glucagon on ureagenesis. The fate of amino acid turnover depends on both
      glucagon and insulin dynamics by stimulating amino acid catabolism and synthesis,
      respectively. Studying the effects of glucagon in individuals with type 1 diabetes will allow
      one to differentiate between the combined effects of glucagon and insulin compared to the
      effects of glucagon alone.

      This study aims to explore hepatic glucagon sensitivity towards amino acid metabolism in
      individuals with and without hepatic steatosis (based on magnetic resonance imaging (MRI)).

      The investigators hypothesize that the effect of endogenous and exogenous glucagon on plasma
      amino acid levels are impaired in individuals with MASLD (based on hepatic steatosis measured
      by MRI) compared to controls.

      The nomenclature for MASLD has recently been updated from non-alcoholic fatty liver disease
      (NAFLD) (https://pubmed.ncbi.nlm.nih.gov/37363821/).
    

Intervention name(s): Glucagon Sensitivity test consisting of an amino acid tolerance test and a bolus infusion of glucagon
Intervention type(s): Diagnostic Test
Intervention description(s): The test consists of two experimental study days:
Day 1: intravenous bolus-injection of glucagon (0.2 mg at time 0 minutes) evaluating the effect of exogenous glucagon on amino acid disappearance. Blood samples will be obtained from time -10 to 120 minutes.
Day 2: 45-minute intravenous infusion of mixed amino acids (331 mg/min/kg body weight from time 0-45 minutes) to evaluate the effect of endogenous glucagon on amino acid metabolism. Blood samples will be obtained from time -10 to 180 minutes.
All participants will be subjected to a magnetic resonance imaging scan to assess whole-liver steatosis, and a bioelectrical impedance analysis to assess body composition.
Following study inclusion and the magnetic resonance imaging scan, participants will be stratified into groups based on hepatic steatosis. Individuals with <5.6 % hepatic steatosis will be classified as controls and individuals with ≥5.6 % hepatic steatosis will be classified as MASLD.
Intervention MeSH terms: Glucagon; Glucagon-Like Peptide 1
Intervention model: Single Group Assignment
Masking: None (Open Label)
Primary purpose: Basic Science