thromboxane-b2 and 9-11-linoleic-acid

The effects of four conjugated linoleic acid (CLA) isomers on in vitro collagen-induced human platelet aggregation and thromboxane (TXB(2), the inactive metabolite of the proaggregatory TXA(2)) production were examined. As the free fatty acid (FFA), 9t, 11t-CLA was the most effective inhibitor of these two processes (I(50)s of 2.2 and 4 microM, respectively) and the 9c, 11c-CLA was the least effective (I(50)s of 8.3 and 37 microM) of the isomers tested. When platelets were preesterified with either 25 microM 9t, 11t-CLA or 9c, 11c-CLA, CLA incorporation in total platelet lipids increased from 0.24% to 0.31% and 0.38%, and most of this increase was found to be in the phosphatidyl choline and phosphatidyl ethanolamine subclasses. The decrease in arachidonic acid (AA) content in total fatty acids or phospholipids was an order of magnitude greater. Furthermore, no significant differences between platelets prelabeled with either 9t, 11t- or 9c, 11c-CLA in the inhibition of collagen-induced aggregation and TXB(2) formation were observed. However, platelets prelabeled with 9c, 11c-CLA stimulated basal TXB(2) production (4-fold) which was not observed with platelets pretreated with either 9t, 11t-CLA, linoleic acid or stearic acid. This enhancement was associated with a 2.4-5-fold increase in the release of endogenous AA. Our results suggest that the presence of a conjugated cis, cis double bond appears to change the lipid environment sufficiently to stimulate the basal platelet phospholipase activity, which in turn increases the formation of TXB(2).

Topics: Arachidonic Acid; Blood Platelets; Collagen; Enzyme Activation; Humans; Isomerism; Linoleic Acids; Linoleic Acids, Conjugated; Phospholipases; Platelet Aggregation; Platelet Aggregation Inhibitors; Thromboxane B2

Conjugated diene isomers of linoleic acid (CLA) are normal constituents of certain foods and exhibit anticarcinogenic and antiatherogenic properties. In the present study, the effects of several CLA isomers on human platelet aggregation and arachidonic acid metabolism were examined. It was found that 9c,11t-CLA, 10t, 12c-CLA and 13-hydroxy-9c,11t-octadecadienoic acid (13-HODE) inhibited arachidonic acid- and collagen-induced platelet aggregation with I50s in the 5-7 microM range. The nonconjugated 9c, 12c-LA was about 300% and 50%, respectively, less potent an inhibitor with these aggregating agents. Using either thrombin or the calcium ionophore A23187 as aggregating agents, a CLA isomer mix was also found to be more inhibitory than 9c,12c-LA. The 9c,11t- and 10t,12c-CLA isomers as well as the CLA isomer mix inhibited formation of the proaggregatory cyclooxygenase-catalyzed product TXA2, as measured by decreased production of its inactive metabolite [14C]TXB2 from exogenously added [14C]arachidonic acid (I50s=9-16 microM). None of the CLA isomers tested inhibited production of the platelet lipoxygenase metabolite [14C]12-HETE. The additional presence of a hydroxyl group gave opposite results: 13-HODE (I50=3 microM) was about 4-fold more potent a cyclooxygenase inhibitor than the 9c,11t-CLA isomer but 9-HODE was 2- to 3-fold less effective an inhibitor (I50=34 microM) of [14C]TXB2 formation than the corresponding 10t,12c-CLA. In both the aggregation and arachidonic acid metabolism experiments, the inhibitory effects of CLA on platelets were reversible and dependent on the time of addition of either the aggregating agent or the [14C]arachidonic acid substrate. These studies suggest that CLA isomers may also possess antithrombotic properties.

Topics: 12-Hydroxy-5,8,10,14-eicosatetraenoic Acid; Arachidonic Acid; Blood Platelets; Dietary Fats, Unsaturated; Humans; Isomerism; Linoleic Acids; Linoleic Acids, Conjugated; Platelet Aggregation Inhibitors; Thromboxane B2