Evaluation of Cardiac Mitochondrial Function in the Fructose-Fed Rat

  • Author / Creator
    Scott, Katrina Y
  • Multiple sources suggest that insulin resistance and derangements of cardiac metabolism are among the earliest signs of type-2 diabetes detected in the heart. Unfortunately, limited evidence reflects early changes in cardiac mitochondrial metabolism linked to the development of this disease. Thus, pinpointing the location of early alterations was the objective of this study. The fructose-fed insulin resistant rat at six weeks of fructose feeding was selected as an appropriate model for the characterization of early type-2 diabetes. The respiration of mitochondria isolated from the left ventricular wall of healthy and fructose-fed rats was measured in response to different substrate and/or inhibitor combinations using the Oroboros Oxygraph-2K high-resolution respirometry system. These measurements were supplemented with assessments of key metabolic protein levels by immunoblotting and enzymatic activities by biochemical assays. Respiratory state differences in the fructose-fed group consisted of the increased oxidative phosphorylation of certain fatty acids, i.e. palmitoyl-CoA and octanoylcarnitine, with malate. Increases in the uptake and the oxidation of fatty acids were suggested by: (i) the elevated sarcolemmal expression of cluster of differentiation 36 (CD36), (ii) the augmented expression of the primary cardiac isoform of carnitine palmitoyltransferase-I (CPT1), (iii) the increased mitochondrial expression of CD36, (iv) the reduced presence of CPT1’s inhibitor malonyl-CoA, (v) the reduced sensitivity of CPT1 to malonyl-CoA, and (vi) the enhanced activity of the fatty acid β-oxidation (FAO) enzyme β-hydroxyacyl-CoA dehydrogenase. Furthermore, the upregulated expressions of peroxisome proliferator-activated receptor-α (PPARα) and peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) indicate the heightened potential for PPARα/PGC-1α signaling, which is intimately involved in FAO. The decreased activity of the pyruvate dehydrogenase complex and the increased expression of pyruvate dehydrogenase kinase 4 revealed a less prominent glucose oxidation. Sirtuin 1 and sirtuin 3 were more abundantly expressed in hearts of fructose-fed rats. However, the extent of their activity is unclear. These changes were accompanied by indications of oxidative stress, i.e. increased hydroxynoneal Michael adducts and decreased aconitase activity, in the absence of major antioxidant responses. Diminished mitochondrial markers, i.e. citrate synthase activity and cytochrome c oxidase IV expression, were also observed. In conclusion, there are significant metabolic changes combined with signs of decompensation in the fructose-fed rat model of early type-2 diabetes.

  • Subjects / Keywords
  • Graduation date
    Fall 2016
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.