Inhibition of fatty acid oxidation by etomoxir impairs NADPH production and increases reactive oxygen species resulting in ATP depletion and cell death in human glioblastoma cells

Normal differentiated cells rely primarily on mitochondrial oxidative phosphorylation to produce adenosine triphosphate (ATP) to maintain their viability and functions by using three major bioenergetic fuels: glucose, glutamine and fatty acids. Many cancer cells, however, rely on aerobic glycolysis for their growth and survival, and recent studies indicate that some cancer cells depend on glutamine as well. This altered metabolism in cancers occurs through oncogene activation or loss of tumor suppressor genes in multiple signaling pathways, including the phosphoinositide 3-kinase and Myc pathways. Relatively little is known, however, about the role of fatty acids as a bioenergetic fuel in growth and survival of cancer cells. Here, we report that human glioblastoma SF188 cells oxidize fatty acids and that inhibition of fatty acid beta-oxidation by etomoxir, a carnitine palmitoyltransferase 1 inhibitor, markedly reduces cellular ATP levels and viability. We also found that inhibition of fatty acid oxidation decreases nicotinamide adenine dinucleotide phosphate (NADPH) levels and the reduced glutathione (GSH) content and elevates intracellular reactive oxygen species. These results suggest that modulation of fatty acid oxidation controls the NADPH level. In the presence of reactive oxygen species scavenger tiron, however, ATP depletion is prevented without restoring fatty acid oxidation. This suggests that oxidative stress may lead to bioenergetic failure and cell death. Our work provides evidence that mitochondrial fatty acid oxidation may provide NADPH for defense against oxidative stress and prevent ATP loss and cell death. This article is part of a Special Issue entitled: Bioenergetics of Cancer. (C) 2010 Elsevier B.V. All rights reserved.