Polyunsaturated fatty acids (PUFA) may reduce cell multiplication in cultures of normal, as well as transformed, white blood cells. We assessed the sensitivity of 14 different leukemia cell lines to PUFA by measuring cell number after 3 days of incubation. Ten of the examined cell lines were sensitive to 30, 60 and/or 120 M of arachidonic, eicosapentaenoic and docosahexaenoic acid, whereas four cell lines were resistant. The sensitivity to PUFA was not associated with any particular cell lineage, clinical origin or specific mRNA pattern of bcl-2 and c-myc. Effects on cell viability were assessed by studying cell membrane integrity, DNA fragmentation and cell morphology. The sensitive cell lines Raji and Ramos died by necrosis and apoptosis, respectively, during incubation with eicosapentaenoic acid, whereas the viability of the resistant U-698 cell line was unaffected. The effects of EPA on Raji cells, was counteracted by vitamin E, indicating that lipid peroxidation was involved. However, apoptosis induced by eicosapentaenoic acid in Ramos cells, was unaffected by vitamin E, as well as eicosanoid synthesis inhibitors. In conclusion, our results indicate that a majority of leukemia cell lines are sensitive to PUFA. This sensitivity may be caused by induction of apoptosis or necrosis by very long-chain polyunsaturated fatty acids.

No abstract

Recently, we showed that levels of circulating free fatty acids are increased in women who later develop pre-eclampsia long before the clinical onset of the disease. Among the serum free fatty acids, oleic-, linoleic-, and palmitic acid were found to be increased by 37, 25 and 25%, respectively. In the present study we asked if these free fatty acids can interfere with endothelial cell functions. Cultured endothelial cells were exposed to linoleic-, oleic- and palmitic acid in concentrations ranging from 0.016 to 0.133 mumol ml-1, resulting in molar ratios of free fatty acids to albumin of 0.2-1.6. We found that among these fatty acids, linoleic acid reduced the thrombin-stimulated prostacyclin release by 30-60%, oleic acid by 10-30%, whereas palmitic acid had no effect. Endothelial cells incubated in presence of linoleic acid showed a concentration-dependent reduction in prostacyclin release in response to thrombin, and cells incubated with linoleic acid for up to 28 h, showed a reduced thrombin-induced prostacyclin release at every time point. Endothelial level of cGMP mainly reflected the synthesis of endothelium-derived relaxing factor/nitrogen monoxide (EDRF/NO), since blocking of the endogenous production of EDRF/NO with N-omega-nitro-L-arginine, resulted in about 90% reduction in cGMP-content of the endothelial cells. Incubation with linoleic acid reduced the endothelial cGMP level by 70%. Linoleic acid reduced the endothelial cells ability to inhibit platelet aggregation by 10-45%, (p = 0.0019). It was concluded that linoleic acid impedes the ability of the endothelial cells to produce prostacyclin and cGMP, and to inhibit platelet aggregation.

Eicosapentaenoic acid (EPA; 20:5n-3) may reduce the cell number in cultured leukemia/lymphoma cells owing to reduced cell proliferation, induction of cell death, or a combination of these processes. EPA has been shown to promote apoptosis in Ramos cells, and our present study was focused on a possible cell cycle arrest and the pathways by which the apoptotic process is induced. Apoptosis may proceed along the intrinsic (mitochondrial) or the extrinsic (death receptor) pathway, which are mediated via different caspases. Caspases are a class of homologous cysteine proteases recognized as pivotal mediators of apoptosis. We investigated whether EPA affects progression of the cell cycle or promotes apoptosis directly. By incorporation of [3H]thymidine and [3H]valine, we showed that DNA, as well as protein synthesis, was reduced after incubation of Ramos cells with EPA for 6 h. We monitored cell cycle distribution by 5-bromo-2'-deoxyuridine staining and observed no cell cycle arrest in the EPA-incubated cells. Incubation of cells with EPA caused PS-flipping, as demonstrated by annexin V-binding (flow cytometry), and cleavage of poly(ADP-ribose) polymerase measured by Western blot analysis. Furthermore, we observed increased activity of caspase-3 and -9, but not of caspase-8. Whereas inhibitors of caspase-3 and -9 reduced EPA-induced apoptosis, inhibition of caspase-8 did not. This suggests that EPA may promote apoptosis via the intrinsic pathway in Ramos cells. Thus, the reduction in cell number can be explained by a direct apoptotic effect of EPA rather than via cell cycle arrest.