A mitochondria-targeted fatty acid analogue influences hepatic glucose metabolism and reduces the plasma insulin/glucose ratio in male Wistar rats

PLoS One. 2019 Sep 24;14(9):e0222558. doi: 10.1371/journal.pone.0222558. eCollection 2019.

Abstract

A fatty acid analogue, 2-(tridec-12-yn-1-ylthio)acetic acid (1-triple TTA), was previously shown to have hypolipidemic effects in rats by targeting mitochondrial activity predominantly in liver. This study aimed to determine if 1-triple TTA could influence carbohydrate metabolism. Male Wistar rats were treated for three weeks with oral supplementation of 100 mg/kg body weight 1-triple TTA. Blood glucose and insulin levels, and liver carbohydrate metabolism gene expression and enzyme activities were determined. In addition, human myotubes and Huh7 liver cells were treated with 1-triple TTA, and glucose and fatty acid oxidation were determined. The level of plasma insulin was significantly reduced in 1-triple TTA-treated rats, resulting in a 32% reduction in the insulin/glucose ratio. The hepatic glucose and glycogen levels were lowered by 22% and 49%, respectively, compared to control. This was accompanied by lower hepatic gene expression of phosphenolpyruvate carboxykinase, the rate-limiting enzyme in gluconeogenesis, and Hnf4A, a regulator of gluconeogenesis. Gene expression of pyruvate kinase, catalysing the final step of glycolysis, was also reduced by 1-triple TTA. In addition, pyruvate dehydrogenase activity was reduced, accompanied by 10-15-fold increased gene expression of its regulator pyruvate dehydrogenase kinase 4 compared to control, suggesting reduced entry of pyruvate into the TCA cycle. Indeed, the NADPH-generating enzyme malic enzyme 1 (ME1) catalysing production of pyruvate from malate, was increased 13-fold at the gene expression level. Despite the decreased glycogen level, genes involved in glycogen synthesis were not affected in livers of 1-triple TTA treated rats. In contrast, the pentose phosphate pathway seemed to be increased as the hepatic gene expression of glucose-6-phosphate dehydrogenase (G6PD) was higher in 1-triple TTA treated rats compared to controls. In human Huh7 liver cells, but not in myotubes, 1-triple-TTA reduced glucose oxidation and induced fatty acid oxidation, in line with previous observations of increased hepatic mitochondrial palmitoyl-CoA oxidation in rats. Importantly, this work recognizes the liver as an important organ in glucose homeostasis. The mitochondrially targeted fatty acid analogue 1-triple TTA seemed to lower hepatic glucose and glycogen levels by inhibition of gluconeogenesis. This was also linked to a reduction in glucose oxidation accompanied by reduced PHD activity and stimulation of ME1 and G6PD, favouring a shift from glucose- to fatty acid oxidation. The reduced plasma insulin/glucose ratio indicate that 1-triple TTA may improve glucose tolerance in rats.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acetates / pharmacology*
  • Animals
  • Blood Glucose / analysis*
  • Cell Line
  • Fructosephosphates / metabolism
  • Glucose / metabolism*
  • Humans
  • Hypoglycemic Agents / pharmacology*
  • Insulin / blood*
  • Liver / drug effects*
  • Liver / metabolism
  • Liver Glycogen / metabolism
  • Male
  • Metabolic Networks and Pathways / drug effects
  • Mitochondria, Liver / drug effects*
  • Muscle Fibers, Skeletal / metabolism
  • NADP / metabolism
  • Palmitoyl Coenzyme A / metabolism
  • Pyruvate Dehydrogenase Complex / metabolism
  • Rats
  • Rats, Wistar

Substances

  • 2-(tridec-12-yn-1-ylthio)acetic acid
  • Acetates
  • Blood Glucose
  • Fructosephosphates
  • Hypoglycemic Agents
  • Insulin
  • Liver Glycogen
  • Pyruvate Dehydrogenase Complex
  • Palmitoyl Coenzyme A
  • NADP
  • fructose-6-phosphate
  • Glucose

Grants and funding

Funded by BB - Bergen Research Foundation; CL - Western Norway Regional Health Authority. The study sponsor was not involved in the design of the study; the collection, analysis, and interpretation of data; writing the report; or the decision to submit the report for publication.