thromboxane-a2 and herbimycin

The present study was carried out to examine the mechanisms of the synergistic interaction of PAF and A23187 mediated platelet aggregation. We found that platelet aggregation mediated by subthreshold concentrations of PAF (5 nM) and A23187 (1 mM) was inhibited by PAF receptor blocker (WEB 2086, IC50 = 0.65 mM) and calcium channel blockers, diltiazem (IC50 = 13 mM) and verapamil (IC50 = 18 mM). Pretreatment of platelets with PAF and A23187 induced rise in intracellular calcium and this effect was also blocked by verapamil. While examining the role of the down stream signaling pathways, we found that platelet aggregation induced by the co-addition of PAF and A23187 was also inhibited by low concentrations of phospholipase C (PLC) inhibitor (U73122; IC50 = 10 mM), a cyclooxygenase inhibitor (indomethacin; IC50 = 0.2 mM) and inhibitor of TLCK, herbimycin A with IC50 value of 5 mM. The effect was also inhibited by a specific TXA2 receptor antagonist, SQ 29548 with very low IC50 value of 0.05 mM. However, the inhibitors of MAP kinase, PD98059 and protein kinase C, chelerythrine had no effect on PAF and A23187-induced platelet aggregation. These data suggest that the synergism between PAF and A23187 in platelet aggregation involves activation of thromboxane and tyrosine kinase pathways.

Topics: Benzoquinones; Blood Platelets; Calcimycin; Humans; Indomethacin; Ionophores; Lactams, Macrocyclic; Platelet Activating Factor; Platelet Aggregation; Protein-Tyrosine Kinases; Quinones; Rifabutin; Thromboxane A2; Verapamil

Prostacyclin (PGI(2)), a potent smooth muscle relaxant, is a major prostaglandin secreted from human myometrium. The concentrations of PGI(2) metabolites in the maternal plasma were reported to be elevated during pregnancy, especially in labor. To clarify the mechanism in PGI(2) secretion from the myometrium, we first investigated the protein expression of cytosolic phospholipase A(2), cyclooxygenase (COX)-1, COX-2, and prostacyclin synthase (PGIS) in the human uterine myometrium at various gestational ages before labor. To elucidate the involvement of labor in the increase in PGI(2) production during labor, we next examined the effect of labor-like cyclic mechanical stretch on PGI(2) production by cultured human myometrial cells. Pregnancy specifically increased COX-1 and PGIS protein expression in the myometrial tissues before labor (P < 0.01 for both). Cyclic mechanical stretch augmented PGIS promoter activity, via activation of activator protein-1 site, and PGIS mRNA and protein expression in cultured human myometrial cells and resulted in a 3.5-fold increase in the concentration of 6-keto-prostaglandin F(1alpha), the stable metabolite of PGI(2), in the culture medium (P < 0.05). However, stretch did not affect the levels of prostaglandin E(2), prostaglandin F(2alpha), or thromboxane A(2) secreted into the same culture media. These results suggest that cyclic mechanical stretch during labor may contribute to the increase in the PGI(2) concentration in the maternal plasma during parturition.

Topics: Benzoquinones; Biomechanical Phenomena; Blotting, Western; Cells, Cultured; Culture Media, Conditioned; Curcumin; Cyclooxygenase 1; Cyclooxygenase 2; Cytochrome P-450 Enzyme System; Dinoprost; Dinoprostone; Epoprostenol; Female; Gene Expression; Genistein; Gestational Age; Humans; Intramolecular Oxidoreductases; Isoenzymes; Labor, Obstetric; Lactams, Macrocyclic; Membrane Proteins; Muscle Spindles; Myometrium; Phospholipases A; Pregnancy; Promoter Regions, Genetic; Prostaglandin-Endoperoxide Synthases; Quinones; Reverse Transcriptase Polymerase Chain Reaction; Rifabutin; RNA, Messenger; Thromboxane A2

The formation and deposition of monosodium urate (MSU) microcrystals in articular and periarticular tissues is the causative agent of acute or chronic inflammatory responses known as gouty arthritis. Mononuclear phagocyte activation is involved in early triggering events of gout attacks. Because stimulated mononuclear phagocytes can constitute an important source of the inducible isoform of cyclooxygenase (COX-2), we evaluated the effects that proinflammatory microcrystals might have on COX-2 protein expression in crystal-stimulated monocytes. We found that MSU crystals, but not calcium pyrophosphate dihydrate (CPPD) crystals, induced COX-2, which correlated with the synthesis of prostaglandin E2 (PGE2) and thromboxane A2 (TXA2). Crystal-induced de novo synthesis of COX-2 was dependent on transcriptional and translational events. Inhibition of tyrosine phosphorylation, by herbimycin A, blocked crystal-induced COX-2. Similarly, an inhibitor of the p38 mitogen-activated protein kinase, SB 203580, inhibited the stimulation of COX-2. Colchicine inhibited crystal-induced COX-2. In all cases, prostanoid synthesis was concomitantly inhibited. Taken together, these results implicate COX-2 in the development of MSU-induced inflammation.

Topics: Benzoquinones; Colchicine; Crystallization; Cyclooxygenase 2; Dinoprostone; Enzyme Induction; Enzyme Inhibitors; Gout Suppressants; Humans; Isoenzymes; Kinetics; Lactams, Macrocyclic; Membrane Proteins; Monocytes; Phosphorylation; Phosphotyrosine; Prostaglandin-Endoperoxide Synthases; Protein-Tyrosine Kinases; Quinones; Rifabutin; Thromboxane A2; Uric Acid

In order to determine whether protein tyrosine kinase mechanisms are involved in pressure-induced contraction, we compared effects of three structurally unrelated tyrosine kinase inhibitors and orthovanadate, a tyrosine phosphatase inhibitor, on the pressure-induced contraction of the posterior cerebral artery isolated from rats. The change in vessel diameter was continuously measured with a width analyzer. Herbimycin A inhibited the pressure-induced contraction, while it only slightly inhibited contractions produced by potassium chloride or 9,11-dideoxy-11alpha,9alpha-epoxymethano prostaglandin F2alpha (U46619). Genistein inhibited not only the pressure-induced contraction but also the U46619-induced one. Tyrphostin 23 significantly attenuated contractions in response to three different stimuli, i.e., pressure, potassium chloride and U46619. Orthovanadate potentiated the pressure-induced contraction. These results suggest that herbimycin A is a specific and potent inhibitor of the pressure-induced contraction and that a protein tyrosine kinase mechanism may play an important role in the genesis of the pressure-induced contraction of the rat cerebral artery.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Benzoquinones; Catechols; Cerebral Arteries; Genistein; In Vitro Techniques; Isoflavones; Lactams, Macrocyclic; Male; Muscle Contraction; Muscle, Smooth, Vascular; Nitriles; Potassium Chloride; Pressure; Prostaglandin Endoperoxides, Synthetic; Protein-Tyrosine Kinases; Quinones; Rats; Rats, Sprague-Dawley; Rifabutin; Thromboxane A2; Tyrphostins; Vanadates; Vasoconstrictor Agents

We have shown previously that thromboxane A2 stimulates hypertrophy of cultured rat aortic smooth muscle cells defined as protooncogene expression and protein synthesis without DNA synthesis or cellular proliferation (Dorn, G.W., II, Becker, M.W., Davis, M.G. (1992) J. Biol. Chem. 267, 24897-24905). Since endogenous growth modulators could possibly regulate vascular smooth muscle growth to this vasoconstrictor, we tested the hypothesis that thromboxane-stimulated vascular smooth muscle hypertrophy was due to increased expression of endogenously produced basic fibroblast growth factor (bFGF). The thromboxane mimetic (15S)-hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5Z,13E-dienoic acid (U46619) (1 microM) increased cultured rat aorta derived smooth muscle cell immunoreactive bFGF content by 331 +/- 40% over untreated controls after 24 h. Co-incubation of vascular smooth muscle cells with a specific antisense oligodeoxynucleotide (AS) against codon 60 of bFGF coding sequence reduced thromboxane-stimulated bFGF expression by 72 +/- 5% and prevented thromboxane-stimulated hypertrophy (nonsense oligonucleotide had no effects). Addition of exogenous bFGF (20 ng/ml) restored growth to AS-treated/thromboxane-stimulated vascular smooth muscle cells. Furthermore, addition to the culture medium of neutralizing antibody against bFGF inhibited U46619-stimulated vascular smooth muscle hypertrophy by 69 +/- 17%, whereas nonimmune IgG had no effect. Since protein tyrosine phosphorylation is a cell signal associated with growth, thromboxane-stimulated tyrosine phosphorylation was also examined. Exposure to 1 microM U46619 for 10 min increased vascular smooth muscle immunoreactive phosphotyrosine content of 130-144-, 86-, 80-, 75-, and 58-kDa proteins. The tyrosine kinase inhibitor herbimycin A (5 microM) prevented thromboxane-stimulated tyrosine phosphorylation, but not thromboxane-stimulated hypertrophy, suggesting that tyrosine phosphorylation was not required for thromboxane-stimulated vascular smooth muscle growth. These results indicate that increased expression and release of endogenous bFGF, but not direct tyrosine phosphorylation, mediates the hypertrophic vascular smooth muscle response to thromboxane.

Topics: Animals; Base Sequence; Benzoquinones; DNA; Fibroblast Growth Factor 2; Humans; Hypertrophy; Lactams, Macrocyclic; Molecular Sequence Data; Muscle, Smooth, Vascular; Phosphorylation; Protein Kinase Inhibitors; Quinones; Rats; Rifabutin; Thromboxane A2; Tyrosine; Up-Regulation

An isoflavone compound, genistein, which is known as a protein tyrosine kinase inhibitor, concentration-dependently (0.1-30 micrograms/ml) suppressed human platelet aggregation, serotonin secretion, and protein tyrosine phosphorylation induced by collagen or stable thromboxane A2 analogs [U46619 and 9,11-epithio-11,12-methano-thromboxane A2 (STA2)]. However, genistein did not inhibit these thrombin (0.1 unit/ml)-induced platelet responses. Although thrombin induced an increase in the platelet phosphotyrosine content, genistein at 100 micrograms/ml only slightly attenuated thrombin-induced protein tyrosine phosphorylation. Genistein competitively inhibited [3H]U46619 binding to washed platelets, in a concentration-dependent fashion. Daidzein (another isoflavone compound), which does not have a hydroxyl group at the 5-position of genistein and lacks inhibitory activity for protein tyrosine kinase, was found to suppress [3H]U46619 binding, leading to the inhibition of collagen- or STA2-induced platelet responses. These results indicate that the blockage by genistein of platelet responses induced by collagen or thromboxane A2 is due to its preventive action on thromboxane A2 binding to the receptor, rather than via inhibition of protein tyrosine phosphorylation, and that the drug does not appear to be a particularly good inhibitor of tyrosine phosphorylation in intact platelets.

Topics: Anti-Bacterial Agents; Benzoquinones; Blood Platelets; Cinnamates; Genistein; Humans; Isoflavones; Lactams, Macrocyclic; Phospholipids; Phosphorylation; Platelet Activation; Platelet Aggregation; Platelet Aggregation Inhibitors; Protein-Tyrosine Kinases; Quinones; Rifabutin; Serotonin; Signal Transduction; Sulfides; Thromboxane A2; Tyrosine