ABSTRACT
Enhanced mitochondrial generation of oxidants, including hydrogen peroxide (H2O2), is related to a large number of pathological conditions, including diet-induced obesity and steatohepatosis. Indeed, we have previously shown that high fat diets increase the generation of H2O2 in liver mitochondria energized by activated fatty acids. Here, we further study fatty-acid induced H2O2 release in liver mitochondria, and determine the characteristics that regulate it. We find that this production of H2O2 is independent of mitochondrial inner membrane integrity and insensitive to purine nucleotides. On the other hand, palmitate-induced H2O2 production is strongly enhanced by high fat diets and is pH-sensitive, with a peak at a matrix pH of ~8.5. Using recombinantly expressed human very long chain acyl-CoA dehydrogenase, we are able to demonstrate that palmitate-induced H2O2 release may be ascribed to the activity of this enzyme alone, acting as an oxidase. Our results add to a number of findings indicating that sources outside of the electron transport chain can generate significant, physiopathologically relevant, amounts of oxidants in mitochondria.
Subject(s)
Acyl-CoA Dehydrogenase, Long-Chain/metabolism , Diet, High-Fat , Hydrogen Peroxide/metabolism , Mitochondria, Liver/metabolism , Acyl-CoA Dehydrogenase, Long-Chain/genetics , Adenosine Diphosphate/pharmacology , Adenosine Monophosphate/pharmacology , Adenosine Triphosphate/pharmacology , Animals , Enzyme Assays , Female , Guanosine Diphosphate/pharmacology , Guanosine Triphosphate/pharmacology , Hydrogen-Ion Concentration , Kinetics , Mice , Mitochondria, Liver/drug effects , Oxidation-Reduction , Palmitic Acid/pharmacology , Recombinant Proteins/genetics , Recombinant Proteins/metabolismABSTRACT
High fat diets and accompanying hepatic steatosis are highly prevalent conditions. Previous work has shown that steatosis is accompanied by enhanced generation of reactive oxygen species (ROS), which may mediate further liver damage. Here we investigated mechanisms leading to enhanced ROS generation following high fat diets (HFD). We found that mitochondria from HFD livers present no differences in maximal respiratory rates and coupling, but generate more ROS specifically when fatty acids are used as substrates. Indeed, many acyl-CoA dehydrogenase isoforms were found to be more highly expressed in HFD livers, although only the very long chain acyl-CoA dehydrogenase (VLCAD) was more functionally active. Studies conducted with permeabilized mitochondria and different chain length acyl-CoA derivatives suggest that VLCAD is also a source of ROS production in mitochondria of HFD animals. This production is stimulated by the lack of NAD(+). Overall, our studies uncover VLCAD as a novel, diet-sensitive, source of mitochondrial ROS.
