Modification of the fatty acid composition of L1210 leukemia subcellular organelles

Differential Alteration of Cellular Lipids in Drug Sensitive and Resistant P388 Leukemia Cells by Clofibrate: Effects on Mitoxantrone Cytotoxicity

Earlier Investigations have Indicated a difference in the lipid profiles of drug-sensitive and drug-resistant tumor cells. This study was undertaken to evaluate the effect of alterations in the cellular lipid compositions by clofibrate (CPIB), an anti-hyperlipidemic agent, on mitoxantrone (Mtn) cytotoxicity in murine P388 leukemia cells sensitive (P388/S) and resistant (P388/Adr) to adriamycin and in human chronic myeloid leukemia (CML) cells. CPIB did not elicit any significant alterations in the lipid levels of P388/S cells, whereas in the P388/Adr cells it brought about a 14% and 49% decrease in the levels of cholesterol and triglyceride respectively. Inhibition of 3H-thymidine incorporation was utilized as a measure of cellular cytotoxicity. CPIB caused a dose dependent inhibition of DNA and RNA biosynthesis in P388/S, P388/Adr and CML cells. The combination of CPIB and Mtn induced a greater cytotoxicity in P388/Adr cells as compared to P388/S cells, as shown by enhanced inhibition of 3H-thymidine incorporation in P388/Adr cells. Similar results were observed when 3H-uridine was used as a measure of cellular cytotoxicity. These observations were further confirmed in fresh CML cell samples, in which the combination of CPIB with Mtn induced an irreversible and synergistic Inhibition of DNA biosynthesis. Results warrant extensive studies on CPIB as a clinical modulator to enhance the antiproliferative activity of Mtn.

Effects of Lipids on Cancer Therapy

The fatty acid composition of cancer cell membranes can change substantially when the cells are exposed to different types of fat. Such change occurs when tumors are grown in animals fed high-fat diets that differ in degree of unsaturation or during culture in media supplemented with various fatty acids. Certain physical and functional properties of the membrane are modified when the polyunsaturated fatty acid content is increased, and the cells become more sensitive to hyperthermia or treatment with doxorubicin. These findings suggest a potential role for lipid nutrition in cancer therapy. By altering the properties of the membrane lipids, changes in the dietary fat intake may provide a new approach for enhancing the effectiveness of certain antineoplastic therapies.

Free radical-mediated lipid peroxidation in cells: oxidizability is a function of cell lipid bis-allylic hydrogen content

Oxidizability of lipids in homogeneous solution varies linearly with the extent of their unsaturation. In vitro cellular, as well as in vivo, studies of oxidizability have generally relied upon chemical indicators of peroxidation such as thiobarbituric acid-reactive substances. To examine the oxidizability of lipids in cells, we have measured oxygen uptake and, using electron paramagnetic resonance spin trapping with alpha-(1-oxo-4-pyridyl)-N-tert-butylnitrone (POBN), the real time generation of lipid-derived free radicals. We have used our experimental in vitro cellular lipid modification model to examine the rate and extent of lipid peroxidation versus the degree of lipid unsaturation in L1210 murine leukemia cells. Lipid peroxidation was stimulated using the prooxidants iron, ascorbate, and the ether lipid compound 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine. We did a total cellular lipid analysis to determine the number of lipid carbon-carbon double bonds contained in L1210 cells enriched with eight fatty acids of different degrees of unsaturation. We found in cellular lipids that (i) lipid chain length had no apparent effect on the rate or extent of radical formation; (ii) the maximum amount of lipid radical generated increases with the total number of bis-allylic positions in the cellular lipids; and, most importantly, (iii) the rate of cellular lipid peroxidation increases exponentially with the number of bis-allylic positions. Our quantitative results clearly demonstrate, for the first time, that the number of bis-allylic positions contained in the cellular lipids of intact cells determines their susceptibility, i.e., oxidizability, to free radical-mediated peroxidative events.

Effect of dietary modulation of membrane lipid composition on the thermostability of HTC cells and of a membrane enzyme

Growth of hepatoma tissue culture (HTC) cells in the presence of linoleic (18:2) or arachidonic (20:4) acids for 36 h caused an increased cell thermosensitivity. Plasma membrane-rich fractions were purified (15-20-fold) with high yield (30%) from control and fatty acid-supplemented cells. Contamination with membranes from mitochondria, lysosomes and endoplasmic reticulum was low. Supplementation significantly increased the level of the supplemented fatty acid and decreased the level of oleic acid (18:1) in plasma membrane phospholipids (PL), causing a significant decrease in the oleic acid:PUFA (polyunsaturated fatty acid) ratio. No significant changes occurred in other parameters such as cholesterol:PL, cholesterol:protein or PL:protein ratios. Plasma membranes from PUFA-supplemented cells exhibited a lower membrane order, compared with control cell membranes, as determined by DPH fluorescence polarization over the temperature range 4-40 degrees C. Isothermal inactivation of alkaline phosphodiesterase I in plasma membranes from control and supplemented cells showed curvilinear kinetics. The change in membrane composition and order following supplementation with arachidonic acid was associated with increased thermosensitivity of this enzyme. These data are discussed with respect to the suggestion that the plasma membrane may be a target for cellular thermal injury and death.

Cholesterol content but not plasma membrane fluidity influences the susceptibility of L1210 leukemia cells to merocyanine 540-sensitized irradiation

This paper examines the relationship between lipid composition, plasma membrane fluidity, expression of dye binding sites, and susceptibility to merocyanine 540 (MC540)-sensitized irradiation in L1210 leukemia cells. Reducing the cells' cholesterol content by exchange diffusion with phosphatidylcholine liposomes or by inhibiting its biosynthesis with 25-hydroxycholesterol enhanced plasma membrane fluidity, the expression of dye binding sites, and the cells' susceptibility to MC540-sensitized irradiation. Conversely, if the cholesterol content was enhanced by exchange diffusion with cholesterol:phosphatidylcholine liposomes, the cells' susceptibility to MC540-sensitized irradiation was decreased. However, contrary to expectations, dye-binding was slightly enhanced and plasma membrane fluidity remained unchanged. Growing the cells in fatty acid-supplemented medium had profound effects on their lipid composition. Cells enriched in polyunsaturated fatty acids had more fluid plasma membranes. However, dye-binding was not significantly affected and photosensitivity was slightly reduced. These results suggest that cholesterol is one, but probably not the only, determinant of the expression of cellular dye binding sites and, consequently, the cell's susceptibility to MC540-sensitized irradiation. By contrast, plasma membrane fluidity does not appear to play a major role in the regulation of dye-binding site expression.

Incorporation of arachidonic, dihomogamma linolenic and eicosapentaenoic acids into cultured V79 cells

The uptake and distribution of three common dietary polyunsaturated fatty acids was studied using Chinese hamster lung fibroblasts (V79 cells). Treatment of V79 cells with arachidonic (20:4), eicosapentaenoic (20:5) and dihomogammalinolenic (20.3) acids for 24 hr produced a marked uptake of 20:3 and 20:4, both of which were assimilated to a considerably greater degree than 20:5. All polyunsaturated fatty acids were incorporated primarily into phospholipids; however, there were considerable differences in their distribution into individual phospholipid species. Although 20:4 was incorporated primarily into phosphatidylcholine, 20:3 entered largely into phosphatidylethanolamine and phosphatidylglycerol, and 20:5 was distributed about equally between phosphatidylcholine, phosphatidylethanolamine and phosphatidylinositol. A marked conversion of 20:3 to 20:4 was found after 24 hr and, in several phospholipids, there was as much derived-radiolabeled 20:4 as there was radiolabeled 20:3. There was little evidence of 20:4 and 20:5 metabolism. V79 cells undergo substantial changes in phospholipid fatty acid composition following supplementation with these polyunsaturated fatty acids; however, these fatty acids are assimilated to different degrees and their distribution among cellular phospholipids is distinct, suggesting incorporation via independent mechanisms.