The fatty acid oxidation enzyme long-chain acyl-CoA dehydrogenase can be a source of mitochondrial hydrogen peroxide

Fatty acid oxidation (FAO)-driven H₂O₂ has been shown to be a major source of oxidative stress in several tissues and disease states. Here, we established that the mitochondrial flavoprotein long-chain acyl-CoA dehydrogenase (LCAD), which catalyzes a key step in mitochondrial FAO, directly produces H₂O₂in vitro by leaking electrons to oxygen. Kinetic analysis of recombinant human LCAD showed that it produces H₂O₂ 15-fold faster than the related mitochondrial enzyme very long-chain acyl-CoA dehydrogenase (VLCAD), but 50-fold slower than a bona fide peroxisomal acyl-CoA oxidase. The rate of H₂O₂ formation by human LCAD is slow compared to its activity as a dehydrogenase (about 1%). However, expression of hLCAD in HepG2 cells is sufficient to significantly increase H₂O₂ in the presence of fatty acids. Liver mitochondria from LCAD-/- mice, but not VLCAD-/- mice, produce significantly less H₂O₂ during incubation with fatty acids. Finally, we observe highest LCAD expression in human liver, followed by kidney, lung, and pancreas. Based on our data, we propose that the presence of LCAD drives H₂O₂ formation in response to fatty acids in these tissues.