Isomers of trans fatty acids modify the activity of platelet 12-P lipoxygenase and cyclooxygenase/thromboxane synthase*1

Abstract

Trans isomers of fatty acids (TFA) have been implicated in the initiation and progression of atherosclerosis. Previous studies have shown that trans-unsaturated fatty acids like their cis-unsaturated counterparts exert a modifying effect on platelet aggregation. The aim of this work was to determine the influence of TFA on the aforementioned enzymes: lipoxygenase and cycloxygenase/thromboxane synthase. Two C18 cis–trans fatty acid pairs: oleic/elaidic and linoleic/linolelaidic were chosen. Fasting blood was sampled from 30 healthy volunteers without any lipid abnormalities and not on medication for at least 7 days prior to sampling. Platelet-rich plasma (PRP) was prepared and the platelet count was adjusted to 310 8 cellsml −1 . Fatty acids in hexane were added to a final concentration of 7 μM and evaporated to dryness under nitrogen, 500 μl of PRP was pipetted into each tube, thoroughly mixed and incubated at 37°C for 60 min. 12-P LOX activity was measured with a spectrophotometric method and expressed per mg protein. Cycloxygenase/thromboxane synthase activity was determined by TXB 2 production with an ELISA-based assay. Statistics were done with the Kruskal-Wallis test and Statistica software package. We have found that the activity of 12-P LOX was suppressed by all cis–trans fatty acids used by us. Cycloxygenase/thromboxane synthase activity was significantly inhibited by polyunsaturated fatty acids only. Linolelaidic acid was more potent in comparison to its monounsaturated (elaidic acid) counterpart. We believe that the effects of fatty acids are demonstrated at the membrane level where fatty acids may produce a perturbation in specific lipid domains. TFA are able to interact with the platelet membrane and transmembrane proteins just as the cis isomers. By interacting with proteins exposed on the cytoplasmic membrane, TFA may modify the activity of receptors and other membrane proteins. In this way, changes on the membrane surface are propagated into the cell affecting the activity of cytoplasmic enzymes like 12-P LOX and cycloxygenase/thromboxane synthase.