title: Selective modulation of the human platelet thromboxane A2/prostaglandin H2 receptor by eicosapentaenoic and docosahexaenoic acids in intact platelets and solubilized platelet membranes.
abstract: We previously demonstrated that nonesterified as well as esterified eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3) inhibit U46619-induced platelet aggregation and [3H]U46619 specific binding to washed human platelets. It was also demonstrated that esterification of these fatty acids resulted in a decrease in the affinity of [3H]U46619 for the thromboxane A2/prostaglandin H2 (TXA2/PGH2) receptor. In order to investigate the specificity of this inhibition, the effects of 20:5n-3 and 22:6n-3 on the function and binding of the platelet alpha 2-adrenergic receptor were studied. It was found that neither 20:5n-3 nor 22:6n-3 (nonesterified or esterified) altered epinephrine-induced aggregation or [3H]yohimbine specific binding. Moreover, Scatchard analysis revealed that esterification with either 20:5n-3 or 22:6n-3 did not alter the dissociation constant for [3H]yohimbine binding. Modulation of the TXA2/PGH2 receptor by 20:5n-3 and 22:6n-3 was next evaluated using CHAPS- and digitonin-solubilized platelet membranes. [3H]SQ29,548 dissociation constants of 26.5 nM and 20.8 nM were measured for CHAPS and digitonin-solubilized membranes, respectively. Competitive binding experiments in these solubilized preparations revealed that 20:5n-3 or 22:6n-3 blocked [3H] SQ29,548 binding with IC50 values in the range of 6-15 microM, while concentrations of these fatty acids of up to 100 microM showed no effect on [3H]yohimbine binding. On the other hand, the IC50 values for inhibition of [3H] SQ29,548 binding by linoleic acid (18:2n-6) and gamma-linolenic acid (18:3n-6) were in the range of 150 microM. Furthermore, 18:2n-6 and 18:3n-6 showed similar inhibitory effects on [3H]yohimbine binding. Finally, competition binding studies performed in a partially purified TXA2/PGH2 receptor preparation also demonstrated inhibition of [3H]SQ29,548 binding by 20:5n-3 and 22:6n-3. Collectively, these findings support the notion that 20:5n-3 and 22:6n-3 can selectively and directly modulate TXA2/PGH2 receptor function, and that this mechanism of action may contribute to the antiplatelet activity associated with diets rich in these fatty acids.
authors.affiliation: Department of Pharmacology, University of Illinois, Chicago 60612.
authors.forename: C A
authors.initials: CA
authors.lastname: Parent
authors.forename: M
authors.initials: M
authors.lastname: Lagarde
authors.forename: D L
authors.initials: DL
authors.lastname: Venton
authors.forename: G C
authors.initials: GC
authors.lastname: Le Breton
mesh_terms: D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D019086:Bridged Bicyclo Compounds, Heterocyclic; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002793:Cholic Acids; D003902:Detergents; D004072:Digitonin / Q000494:pharmacology; D004281:Docosahexaenoic Acids / Q000494:pharmacology*; D015118:Eicosapentaenoic Acid / Q000494:pharmacology*; D005231:Fatty Acids, Unsaturated; D006801:Humans; D006834:Hydrazines / Q000378:metabolism / Q000494:pharmacology; D010974:Platelet Aggregation / Q000187:drug effects; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology; D011450:Prostaglandin Endoperoxides, Synthetic / Q000494:pharmacology; D011463:Prostaglandins H / Q000378:metabolism; D011982:Receptors, Prostaglandin / Q000187:drug effects* / Q000378:metabolism; D017482:Receptors, Thromboxane; D044244:Receptors, Thromboxane A2, Prostaglandin H2; D013928:Thromboxane A2 / Q000037:antagonists & inhibitors / Q000378:metabolism
chemical_list: D019086:Bridged Bicyclo Compounds, Heterocyclic; D002793:Cholic Acids; D003902:Detergents; D005231:Fatty Acids, Unsaturated; D006834:Hydrazines; D010975:Platelet Aggregation Inhibitors; D011450:Prostaglandin Endoperoxides, Synthetic; D011463:Prostaglandins H; D011982:Receptors, Prostaglandin; D017482:Receptors, Thromboxane; D044244:Receptors, Thromboxane A2, Prostaglandin H2; D004281:Docosahexaenoic Acids; D013928:Thromboxane A2; C045749:SQ 29548; D015118:Eicosapentaenoic Acid; D004072:Digitonin; C028213:3-((3-cholamidopropyl)dimethylammonium)-1-propanesulfonate