Increased carnitine-dependent fatty acid uptake into mitochondria of human colon cancer cells induces apoptosis.
Carnitine-dependent fatty acid import into mitochondria and beta-oxidation seem to be impaired in tumor cells. In the present study we show that a supply of palmitoylcarnitine together with L-carnitine potently induces apoptosis in HT-29 human colon cancer cells as a consequence of accelerated fatty acid oxidation. Caspase-3-like activities, measured by the cleavage rate of a fluorogenic tetrapeptide substrate and nuclear fragmentation determined after DNA labeling in fixed cells by fluorescence microscopy, served as indicators of apoptosis. Neither L-carnitine nor palmitoylcarnitine alone were able to increase caspase-3-like activities and DNA fragmentation, but when provided together, apoptosis occurred. That exogenous carnitine was indeed able to enhance fatty acid uptake into mitochondria was demonstrated by an increased influx of a fluorescent palmitic acid analog. Enhanced fatty acid availability in mitochondria led to an increased generation of O*2-, as detected by a O*2- -sensitive fluorogenic dye, indicating oxidation of delivered substrates. Benzoquinone, an O*2- scavenger, blocked O*2- generation and prevented apoptosis as initiated by the combination of palmitoylcarnitine and carnitine. The lack of effect of the ceramide synthesis inhibitor fumonisin on palmitoylcarnitine/carnitine-induced apoptosis further supports the notion that apoptotic cell death is specifically due to fatty acid oxidation. In contrast to HT-29 cells, nontransformed human colonocytes did not respond to exogenous palmitoylcarnitine/carnitine and no apoptosis was observed. In conclusion, our studies provide evidence that a limited mitochondrial fatty acid import in human colon cancer cells prevents high rates of mitochondrial O*2- production and protects colon cancer cells from apoptosis that can be overcome by an exogenous carnitine supply.
Wenzel
Uwe
U
Molecular Nutrition Unit, Department of Food and Nutrition, Technical University of Munich, Hochfeldweg 2, D-85350 Freising, Germany. uwenzel@wzw.tum.de
Nickel
Alexander
A
Daniel
Hannelore
H
D017209:Apoptosis; D002331:Carnitine / Q000378:metabolism* / Q000494:pharmacology; D002460:Cell Line; D002518:Ceramides / Q000096:biosynthesis; D003110:Colonic Neoplasms / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology*; D015536:Down-Regulation; D004338:Drug Combinations; D005227:Fatty Acids / Q000493:pharmacokinetics*; D019073:HT29 Cells; D006801:Humans; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D010169:Palmitic Acids / Q000493:pharmacokinetics; D010172:Palmitoylcarnitine / Q000494:pharmacology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000187:drug effects / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D051020:bcl-X Protein
C494811:BCL2L1 protein, human; D002518:Ceramides; D004338:Drug Combinations; D005227:Fatty Acids; D010169:Palmitic Acids; D019253:Proto-Oncogene Proteins c-bcl-2; D017382:Reactive Oxygen Species; D051020:bcl-X Protein; D010172:Palmitoylcarnitine; D002331:Carnitine