Abstract 26: 12-Lipoxygenase is an Essential Regulator of Fatty Acid Protection Against Platelet Activation and Thrombosis
Introduction Human platelet-type 12-lipoxygenase (12-LOX) has recently been shown to play an important role in regulation of platelet function by reacting with arachidonic acid (AA). It is possible that a number of other fatty acids present on the platelet surface are oxidized by 12-LOX. Identifying novel bioactive metabolites which regulate platelet function are essential for understanding the role of 12-LOX in regulation of thrombosis, vessel occlusion, and stroke.
Objectives We sought to characterize the substrate specificity of 12-LOX against several polyunsaturated fatty acids (PUFAs) in vitro, ex vivo, and in vivo and determine if PUFA metabolites act as endogenous regulators of platelet activation.
Methods Metabolite production was measured in vitro by assessing which PUFAs are oxidized by 12-LOX to form bioactive metabolites. These metabolites were further characterized for anti-platelet properties in platelets ex vivo. Finally, using wild-type and 12-LOX-deficient mouse models, the importance of 12-LOX in regulating the protective effects of these PUFAs was assessed in vivo.
Results A number of PUFAs were found to be oxidized by 12-LOX in vitro. The bioactive lipid products resulting from 12-LOX oxidation of DGLA in particular, 12-(S)-hydroperoxy-8- Z, 10E, 14Z-eicosatrienoic acid [12(S)-HPETrE], and its reduced product, 12(S)-HETrE, resulted in significant attenuation of agonist-mediated platelet aggregation, granule secretion, α IIbβ3 activation, Rap1 activation, and clot retraction. Treatment with DGLA similarly inhibited platelet activation as well as platelet clot retraction. Blocking 12-LOX rescued normal platelet activity. Finally, mice fed a DGLA-enriched diet showed increased bleeding and decreased platelet activity. However, mice deficient in 12-LOX were resistant to DGLA-induced attenuation of platelet activation but not direct application of 12-HETrE.
Conclusions These observations support our hypothesis that the overall effect of 12-LOX oxidation of fatty acids in the platelet is dependent on the fatty acid substrates available at the platelet membrane. DGLA and its metabolite 12-HETrE may help explain the protective effect of PUFAs on cardiovascular function.
- © 2013 by American Heart Association, Inc.