vapiprost and 7-(3-(3-hydroxy-4-(4--iodophenoxy)-1-butenyl)-7-oxabicyclo(2.2.1)heptan-2-yl)-5-heptenoic-acid

A single gene encodes the human thromboxane receptor (TP), of which there are two identified splice variants, alpha and beta. Both isoforms are rapidly phosphorylated in response to thromboxane agonists when overexpressed in human embryonic kidney 293 cells; this phenomenon is only slightly altered by inhibitors of protein kinase C. Pharmacological studies have defined two classes of TP in human platelets; sites that bind the agonist I-BOP with high affinity support platelet shape change. Low affinity sites, which irreversibly bind the antagonist GR 32191, transduce platelet activation and aggregation. Isoform-specific antibodies permitted detection of TPalpha, but not TPbeta, from human platelets, although mRNA for both isoforms is present. A broad protein band of 50-60 kDa, reflecting the glycosylated receptor, was phosphorylated upon activation of platelets for 2 min with I-BOP. This was a rapid ( approximately 30 s) and transient (maximum, 2-4 min) event and was inhibited by TP antagonists. Both arachidonic acid and low concentrations of collagen stimulated TPalpha phosphorylation, which was blocked by cyclooxygenase inhibition or TP antagonism. Blockade of the low affinity TP sites with GR 32191 prevented I-BOP-induced TPalpha phosphorylation. This coincided with agonist-induced platelet aggregation and activation but not shape change. Also, activation of these sites with the isoprostane iPF2alpha-III induced platelet shape change but not TPalpha phosphorylation. Heterologous TP phosphorylation was observed in aspirin-treated platelets exposed to thrombin, high concentrations of collagen, and the calcium ionophore A 23187. Both homologous and heterologous agonist-induced phosphorylation of endogenous TPalpha was blocked by protein kinase C inhibitors. TPalpha was the only isoform detectably translated in human platelets. This appeared to correspond to the activation of the low affinity site defined by the antagonist GR 32191 and not activated by the high affinity agonist, iPF2alpha-III. Protein kinase C played a more important role in agonist-induced phosphorylation of native TPalpha in human platelets than in human embryonic kidney 293 cells overexpressing recombinant TPalpha.

Topics: Arachidonic Acid; Aspirin; Biphenyl Compounds; Blood Platelets; Bridged Bicyclo Compounds, Heterocyclic; Cell Line; Electrophoresis, Polyacrylamide Gel; Fatty Acids, Unsaturated; Heptanoic Acids; Humans; Hydrazines; Phosphorylation; Platelet Activation; Platelet Aggregation Inhibitors; Protein Kinase C; Receptors, Thromboxane; Thrombin; Thromboxane A2

1. 5-HT and the prostanoid TP receptor agonists, U46619 and I-BOP, constricted the human umbilical artery with pEC50 values of 7.3+/-0. 2, 6.7+/-0.1, and 7.3+/-0.2, respectively. The selective TP receptor antagonist, GR32191 (0.1 microM), shifted the concentration-effect curves to U46619 and I-BOP to the right, but had no effect on the response to 5-HT. 2. The natural prostaglandins, PGF2alpha and PGE2, caused concentration-dependent contraction with pEC50 values of 5.2+/-0.2 and 4.9+/-0.2, respectively. PGD2 was a partial agonist with a pEC50 of 5.24+/-0.03. GR32191 (0.1 microM) inhibited the responses to all of these compounds suggesting that they produce contraction by acting at TP receptors. 3. Sulprostone failed to elicit contraction in the human umbilical artery at concentrations up to 4.4 microM suggesting the absence of EP1 and EP3 receptors. Despite this, 17-phenyltrinor PGE2 and GR63799 both induced contraction at concentrations above 1 microM, but the effects were sensitive to GR32191 (0.1 microM). 4. Fluprostenol had no effect on the human umbilical artery at concentrations up to 17 microM suggesting the absence of FP receptors. Cloprostenol was ineffective in two tissues, but caused contraction in one tissue at the highest concentration tested (1.7 microM). However, this response was abolished in the presence of GR32191 (0.1 microM). 5. The effects of four TP receptor antagonists were assessed by global non-linear regression analysis. GR32191, SQ29548, SQ30741, and ICI192605 competitively inhibited responses to U46619 with pKb values of 8.0+/-0.1, 7.6+/-0.1, 7.0+/-0. 2 and 8.1+/-0.1, respectively. 6 These results suggest that the human umbilical artery functionally expresses TP receptors, but not EP1, EP2 or FP receptors.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Biphenyl Compounds; Bridged Bicyclo Compounds, Heterocyclic; Dinoprost; Dinoprostone; Fatty Acids, Unsaturated; Female; Heptanoic Acids; Humans; In Vitro Techniques; Isometric Contraction; Pregnancy; Prostaglandin Antagonists; Receptors, Prostaglandin; Serotonin; Umbilical Arteries; Vasoconstriction; Vasoconstrictor Agents

Thromboxane A2 (TxA2) stimulates contraction of glomerular mesangial cells. However, mesangial cell TxA2 receptors have not been previously characterized. We therefore investigated TxA2 binding and TxA2-associated signal transduction pathways in rat glomerular mesangial cells using the specific thromboxane receptor agonist (1S-[1 alpha,2 beta(5Z),3 alpha-(1E,3S)4 alpha])-7-(3-[3-hydroxy-4-(p- iodophenoxy)-1-butenyl]7-oxabicyclo[2.2.1]hept-2-yl)-5-heptenoic acid (IBOP). In these cells, [125I]BOP binding was saturable, displaceable, and of high affinity. Scatchard analysis revealed a single class of binding sites with a dissociation constant (Kd) of 293 pM and a maximal density of binding sites (Bmax) of 33 fmol/mg protein. Specific binding was inhibited by the thromboxane agonist (15S)-hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5Z,13E-dienoic acid (U-46619) [inhibitor dissociation constant (Ki) = 297 nM] and the TxA2 receptor antagonists SQ 29548 (Ki = 1 nM) and (1R-[1 alpha(Z),2 beta,3 beta,5 alpha])-(+)-7-(5-[(1,1'-biphenyl)- 4-yl-methoxy]-3-hydroxy-2-(1-piperidinyl)cyclopentyl]-4-heptenoic acid (GR 32191) (Ki = 92 nM). Binding was also highly specific for thromboxane because prostaglandin E2 (Ki = 16 microM) and the inactive thromboxane metabolite, TxB2 (Ki = 41 microM), were approximately 1,000-fold less potent at inhibiting binding. IBOP stimulated phosphatidylinositol hydrolysis with an effective concentration of drug that produces 50% of the maximal response of 229 pM, which correlated well with the equilibrium Kd and enhanced phosphorylation of an acidic 80-kDa protein substrate for protein kinase C.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Binding, Competitive; Biphenyl Compounds; Bridged Bicyclo Compounds; Bridged Bicyclo Compounds, Heterocyclic; Cells, Cultured; Dose-Response Relationship, Drug; Fatty Acids, Unsaturated; Heptanoic Acids; Hydrazines; Inositol Phosphates; Intracellular Signaling Peptides and Proteins; Kidney Glomerulus; Kinetics; Membrane Proteins; Myristoylated Alanine-Rich C Kinase Substrate; Phosphorylation; Protein Kinase C; Proteins; Rats; Signal Transduction; Thromboxanes

Binding and function of BMS 180,291 ([(+)1S-(1 alpha,2 alpha,3 alpha,4 alpha)]-2-[[3-[4-[(n-pentylamino)carbonyl]-2-oxazolyl]-7- oxabicyclo[2.2.1] hept-2-yl]methyl]benzenepropanoic acid]) in human platelets was examined. Kinetic determination of [3H]BMS 180,291 binding produced ligand-receptor association and dissociation rates of 1.4 x 10(7) +/- 0.2 M-1 x min-1 (n = 5) and 0.04 +/- 0.005 min-1 (n = 5), respectively. The resultant Kd was 3.1 +/- 1.1 nM (n = 5). Saturation binding analysis in platelet membranes was consistent with a single class of [3H]BMS 180,291 binding sites with a Kd of 3.6 +/- 0.19 nM (n = 4) and a binding site maxima (Bmax) of 2099.1 +/- 70.3 fmol/mg of protein (n = 4). Specific [3H]BMS 180,291 binding was inhibited by thromboxane A2/endoperoxide receptor antagonists and agonists with a rank order of potency of: BMS 180,291 > or = SQ 29,548 = I-BOP race 15-(1 alpha,2 beta(5Z), 3 alpha(1E,3S),4 alpha) d7-[3-(3-hydroxy-4-(p-iodophenoxy)-1-butenyl)-7- oxabicyclo[2.2.1]hept-2-yl]5-heptenoic acid) > or = BM 13,505 > or = SQ 30,741 = U 44,609 > U 46,619 >> BM 13,177. Prostaglandin E2 and prostacyclin did not appreciably inhibit the specific binding of [3H]BMS 180,291. BMS 180,291 (10 nM-5 microM) shifted the I-BOP-induced platelet shape change curve to the right in a parallel manner without reduction of the maximal response (KB = 13 +/- 3.5 nM; pA2 = 8 +/- 0.2; slope = -1.0 +/- 0.05), whereas 30 nM drug decreased the maximal I-BOP-induced platelet aggregation.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Biphenyl Compounds; Blood Platelets; Bridged Bicyclo Compounds; Bridged Bicyclo Compounds, Heterocyclic; Fatty Acids, Unsaturated; Heptanoic Acids; Humans; Hydrazines; In Vitro Techniques; Kinetics; Oxazoles; Platelet Aggregation; Propionates; Receptors, Thromboxane

The vasoconstrictor eicosanoid thromboxane plays an important role in the pathogenesis of several renal diseases. As an autacoid, its local release alters blood flow and induces platelet aggregation. We report a direct stimulatory effect of thromboxane on extracellular matrix protein production and gene expression in vitro. Treatment of two cell types, differentiated mouse teratocarcinoma cells (F9+) and human glomerular mesangial cells, with two different thromboxane analogues resulted in increased production of components of the extracellular matrix including fibronectin and the basement membrane proteins laminin and type IV collagen. These responses to thromboxane were not the result of a mitogenic effect of thromboxane nor the result of an increase in total cellular protein. The increased production of extracellular matrix proteins was, at least in part, due to an increase in the steady-state level of mRNA for these genes. Furthermore, the effect of thromboxane was markedly inhibited by cotreatment with a thromboxane-receptor antagonist. These results suggest a new potential role for thromboxane as a mediator of the sclerotic and fibrotic responses to injury.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Adult; Animals; Biphenyl Compounds; Bridged Bicyclo Compounds; Bridged Bicyclo Compounds, Heterocyclic; Cell Division; Cell Line; Cells, Cultured; Collagen; DNA Replication; Extracellular Matrix Proteins; Fatty Acids, Unsaturated; Fibronectins; Glomerular Mesangium; Heptanoic Acids; Humans; Kinetics; Laminin; Mice; Prostaglandin Endoperoxides, Synthetic; RNA, Messenger; Teratoma; Thromboxanes; Thymidine