Glucagon Resistance at the Level of Amino Acid Turnover in Obese Subjects with Hepatic Steatosis

Glucagon secretion is regulated by circulating glucose, but it has turned out that amino acids also play an important role, and that hepatic amino acid metabolism and glucagon are linked in a mutual feed-back cycle, the liver-alpha cell axis. On this background, we hypothesized that hepatic steatosis might impair glucagon’s action on hepatic amino acid metabolism and lead to hyperaminoacidemia and hyperglucagonemia. We subjected 15 healthy lean and 15 obese steatotic male participants to a pancreatic clamp with somatostatin and evaluated hepatic glucose and amino acid metabolism during basal and high physiological levels of glucagon. The degree of steatosis was evaluated from liver biopsies. Total RNA sequencing of liver biopsies revealed perturbations in the expression of genes predominantly involved in amino acid metabolism in the obese steatotic individuals. This group was also characterized by fasting hyperglucagonemia, hyperaminoacidemia and an absent lowering of amino acid levels in response to high levels of glucagon. Endogenous glucose production was similar between lean and obese individuals. Our results suggest that hepatic steatosis causes resistance to the effect of glucagon on amino acid metabolism resulting in increased amino acid concentrations as well as increased glucagon secretion providing a likely explanation of fatty liver-associated hyperglucagonemia.