gamma-linolenic acid and eicosapentaenoic acid induce modifications in mitochondrial metabolism, reactive oxygen species generation, lipid peroxidation and apoptosis in Walker 256 rat carcinosarcoma cells

The polyunsaturated fatty acids gamma -linolenic acid (GLA) and eicosapenta enoic acid (EPA) are cytotoxic to tumour cells. GLA inhibits Walker 256 tum our growth in vivo, causing alterations in mitochondrial ultrastructure and cellular metabolism. The objective of the present study was to investigate the mechanisms behind fatty acid inhibition of Walker 256 tumour growth un der controlled in vitro conditions, At a concentration of 150 muM, both GLA and EPA caused a decrease in cell proliferation and an increase in apoptot ic index. Increases in reactive oxygen species (ROS) and lipid peroxide pro duction were identified, as well as alterations in energy metabolism and th e deposition of large amounts of triacylglycerol in the form of lipid dropl ets. Mitochondrial respiratory chain complexes I+III and IV had significant ly decreased activity and mitochondrial membrane potential was greatly dimi nished. Intracellular ATP concentrations were maintained at 70-80% of contr ol values despite the decreased mitochondrial function, which may be in par t due to increased utilisation of glucose for ATP generation. Cytochrome c release from mitochondria was found, as was caspase-3-like activation. DNA fragmentation in situ revealed many apoptotic events within the cell popula tion. The mechanism(s) by which ROS and lipid peroxides induce apoptosis re mains unclear, but the effects of GLA and EPA appear to involve the mitocho ndrial pathway of apoptosis induction leading to cytochrome c release, casp ase activation, loss of mitochondrial membrane potential and DNA fragmentat ion. (C) 2001 Elsevier Science B.V. All rights reserved.