Cellular enrichment with polyunsaturated fatty acids induces an oxidative stress and activates the transcription factors AP1 and NFkappaB.

A 48-h incubation of cultured human fibroblasts with 5 x 10(-5) M oleic acid or polyunsaturated fatty acids (PUFA) from the (n-6) (linoleic, gamma-linolenic and arachidonic acids) or (n-3) (alpha-linolenic and eicosapentaenoic acids) series resulted in an enrichment of the cells with the introduced fatty acid. Cell enrichment with PUFA initiated a rise in the intracellular level of reactive oxygen species (ROS) and lipid peroxidation products (thiobarbituric reactive substances TBARS). Simultaneously, cell enrichment with all the studied PUFA induced an increase in AP1 and NFkappaB binding activity measured by electrophoretic mobility shift assay, whereas no significant effect was observed with the monounsaturated oleic acid. Furthermore, the antioxidants vitamin E (alpha-tocopherol) and N-acetyl cysteine prevented both the arachidonic acid-induced increase in intracellular ROS and TBARS, and the activation of AP1 and NFkappaB. These results indicate that the accumulation of PUFA from (n-6) and (n-3) series elicited an intracellular oxidative stress, resulting in the activation of oxidative stress-responsive transcription factors such as AP1 and NFkappaB.

Polyunsaturated fatty acid enrichment enhances endothelial cell-induced low-density-lipoprotein peroxidation.

Oxidative modification of low-density lipoprotein (LDL) is an important feature in the initiation and progression of atherosclerosis. LDL modification by endothelial cells was studied after supplementation of the cells with oleic acid and polyunsaturated fatty acids (PUFA) of the n-6 and n-3 series. In terms of the lipid peroxidation product [thiobarbituric acid reactive substances (TBARS)] content and diene level of the LDL particle, oleic acid had no significant effect, and linoleic acid was poorly effective. Gamma linolenic acid (C18:3,n-6) and arachidonic acid (C20:4,n-6) increased by about 1.6-1.9-fold the cell-mediated LDL modification. PUFA from the n-3 series, alpha linolenic acid (C18:3,n-3), eicosapentaenoic acid (C20:5,n-3) and docosahexaenoic acid (C22:6,n-3), induced a less marked effect (1. 3-1.6-fold increase). The relative electrophoretic mobility of the LDL particle and its degradation by macrophages were enhanced in parallel. Concomitantly, PUFA stimulated superoxide anion secretion by endothelial cells. The intracellular TBARS content was also increased by PUFA. Comparison of PUFA from the two series indicates a good correlation between LDL oxidative modification, superoxide anion secretion and intracellular lipid peroxidation. The lipophilic antioxidant vitamin E decreased the basal as well as the PUFA-stimulated LDL peroxidation. These results indicate that PUFAs with a high degree of unsaturation of the n-6 and n-3 series could accelerate cell-mediated LDL peroxidation and thus aggravate the atherosclerotic process.