Cellular metabolism of substance P produces neurokinin-1 receptor peptide agonists with diminished cyclic AMP signaling.

Substance P (SP) is released from sensory nerves in the arteries and heart. It activates neurokinin-1 receptors (NK1Rs) causing vasodilation, immune modulation, and adverse cardiac remodeling. The hypothesis was tested: SP and SP metabolites activate different second messenger signaling pathways. Macrophages, endothelial cells, and fibroblasts metabolized SP to N- and C-terminal metabolites to varying extents. SP 5-11 was the most abundant metabolite followed by SP 1-4, SP 7-11, SP 6-11, SP 3-11, and SP 8-11. In NK1R-expressing human embryonic kidney 293 (HEK293) cells, SP and some C-terminal SP metabolites stimulate the NK1R, promoting the dissociation of several Gα proteins, including Gαs and Gαq from their ßγ subunits. SP increases intracellular calcium concentrations ([Ca]i) and cyclic 3',5'-adenosine monophosphate (cAMP) accumulation with similar -log EC50 values of 8.5 ± 0.3 and 7.8 ± 0.1 M, respectively. N-terminal metabolism of SP by up to five amino acids and C-terminal deamidation of SP produce peptides that retain activity to increase [Ca]i but not to increase cAMP. C-terminal metabolism results in the loss of both activities. Thus, [Ca]i and cAMP signaling are differentially affected by SP metabolism. To assess the role of N-terminal metabolism, SP and SP 6-11 were compared with cAMP-mediated activities in NK1R-expressing 3T3 fibroblasts. SP inhibits nuclear factor κB (NF-κB) activity, cell proliferation, and wound healing and stimulates collagen production. SP 6-11 had little or no activity. Cyclooxygenase-2 (COX-2) expression is increased by SP but not by SP 6-11. Thus, metabolism may select the cellular response to SP by inhibiting or redirecting the second messenger signaling pathway activated by the NK1R.NEW & NOTEWORTHY Endothelial cells, macrophages, and fibroblasts metabolize substance P (SP) to N- and C-terminal metabolites with SP 5-11 as the most abundant metabolite. SP activates neurokinin-1 receptors to increase intracellular calcium and cyclic AMP. In contrast, SP metabolites of N-terminal metabolism and C-terminal deamidation retain the ability to increase calcium but lose the ability to increase cyclic AMP. These new insights indicate that the metabolism of SP directs cellular functions by regulating specific signaling pathways.

Macrophage 12(S)-HETE Enhances Angiotensin II-Induced Contraction by a BLT2 (Leukotriene B4 Type-2 Receptor) and TP (Thromboxane Receptor)-Mediated Mechanism in Murine Arteries.

12/15-LO (12/15-lipoxygenase), encoded by Alox15 gene, metabolizes arachidonic acid to 12(S)-HETE (12-hydroxyeicosatetraenoic acid). Macrophages are the major source of 12/15-LO among immune cells, and 12/15-LO plays a crucial role in development of hypertension. Global Alox15- or macrophage-deficient mice are resistant to Ang II (angiotensin II)-induced hypertension. This study tests the hypothesis that macrophage 12(S)-HETE contributes to Ang II-mediated arterial constriction and thus to development of Ang II-induced hypertension. Ang II constricted isolated abdominal aortic and mesenteric arterial rings. 12(S)-HETE (100 nmol/L) alone was without effect; however, it significantly enhanced Ang II-induced constriction. The presence of wild-type macrophages also enhanced the Ang II-induced constriction, while Alox15-/- macrophages did not. Using this model, pretreatment of aortic rings with inhibitors, receptor agonists/antagonists, or removal of the endothelium, systematically uncovered an endothelium-mediated, Ang II receptor-2-mediated and superoxide-mediated enhancing effect of 12(S)-HETE on Ang II constrictions. The role of superoxide was confirmed using aortas from p47phox-/- mice where 12(S)-HETE failed to enhance constriction to Ang II. In cultured arterial endothelial cells, 12(S)-HETE increased the production of superoxide, and 12(S)-HETE or Ang II increased the production of an isothromboxane-like metabolite. A TP (thromboxane receptor) antagonist inhibited 12(S)-HETE enhancement of Ang II constriction. Both Ang II-induced hypertension and the enhancing effect of 12(S)-HETE on Ang II contractions were eliminated by a BLT2 (leukotriene B4 receptor-2) antagonist. These results outline a mechanism where the macrophage 12/15-LO pathway enhances the action of Ang II. 12(S)-HETE, acting on the BLT2, contributes to the hypertensive action of Ang II in part by promoting endothelial synthesis of a superoxide-derived TP agonist.

GPR40 is a low-affinity epoxyeicosatrienoic acid receptor in vascular cells.

Endothelium-derived epoxyeicosatrienoic acids (EETs) have numerous vascular activities mediated by G protein-coupled receptors. Long-chain free fatty acids and EETs activate GPR40, prompting us to investigate the role of GPR40 in some vascular EET activities. 14,15-EET, 11,12-EET, arachidonic acid, and the GPR40 agonist GW9508 increase intracellular calcium concentrations in human GPR40-overexpressing HEK293 cells (EC50 = 0.58 ± 0.08 µm, 0.91 ± 0.08 µm, 3.9 ± 0.06 µm, and 19 ± 0.37 nm, respectively). EETs with cis- and trans-epoxides had similar activities, whereas substitution of a thiirane sulfur for the epoxide oxygen decreased the activities. 8,9-EET, 5,6-EET, and the epoxide hydrolysis products 11,12- and 14,15-dihydroxyeicosatrienoic acids were less active than 11,12-EET. The GPR40 antagonist GW1100 and siRNA-mediated GPR40 silencing blocked the EET- and GW9508-induced calcium increases. EETs are weak GPR120 agonists. GPR40 expression was detected in human and bovine endothelial cells (ECs), smooth muscle cells, and arteries. 11,12-EET concentration-dependently relaxed preconstricted coronary arteries; however, these relaxations were not altered by GW1100. In human ECs, 11,12-EET increased MAP kinase (MAPK)-mediated ERK phosphorylation, phosphorylation and levels of connexin-43 (Cx43), and expression of cyclooxygenase-2 (COX-2), all of which were inhibited by GW1100 and the MAPK inhibitor U0126. Moreover, siRNA-mediated GPR40 silencing decreased 11,12-EET-induced ERK phosphorylation. These results indicated that GPR40 is a low-affinity EET receptor in vascular cells and arteries. We conclude that epoxidation of arachidonic acid to EETs enhances GPR40 agonist activity and that 11,12-EET stimulation of GPR40 increases Cx43 and COX-2 expression in ECs via ERK phosphorylation.

(5Z,11Z,15R)-15-Hydroxyeicosa-5,11-dien-13-ynoic acid: A stable isomer of 15(S)-HETE that retains key vasoconstrictive and antiproliferative activity.

15(S)-Hydroxyeicosa-(5Z,8Z,11Z,13E)-tetraenoic acid (15(S)-HETE) is a metabolite of arachidonic acid that elicits a number of biological effects including vasoconstriction and angiogenesis. (5Z,11Z,15R)-15-Hydroxyeicosa-5,11-dien-13-ynoic acid (HETE analog 1) is a synthetic isomer of 15(S)-HETE that is much more stable to autoxidation. Using isometric recording of isolated pulmonary arteries from male and female rabbits, HETE analog 1 and 15(S)-HETE were found to elicit concentration-dependent contractions that were slightly greater in females compared to males. The maximal response in females was greater with 15(S)-HETE. HETE analog 1 and 15(S)-HETE increased [(3)H]-thymidine incorporation in vascular smooth muscle cells cultured from male rabbit pulmonary arteries; both the maximal response and potency were greater with 15(S)-HETE. In contrast, HETE analog 1 produced a concentration-dependent inhibition in proliferation and migration of human hormone-independent prostate carcinoma PC-3 cells. The protocol for synthesis of HETE analog 1 is reported. The stability of this substance and its similar biological profile to 15(S)-HETE support future studies in eicosanoid research.

Tyrosine dephosphorylation enhances the therapeutic target activity of epidermal growth factor receptor (EGFR) by disrupting its interaction with estrogen receptor (ER).

Protein-protein interactions can increase or decrease its therapeutic target activity and the determining factors involved, however, are largely unknown. Here, we report that tyrosine-dephosphorylation of epidermal growth factor receptor (EGFR) increases its therapeutic target activity by disrupting its interaction with estrogen receptor (ER). Protein tyrosine phosphatase H1 (PTPH1) dephosphorylates the tyrosine kinase EGFR, disrupts its interaction with the nuclear receptor ER, and increases breast cancer sensitivity to small molecule tyrosine kinase inhibitors (TKIs). These effects require PTPH1 catalytic activity and its interaction with EGFR, suggesting that the phosphatase may increase the sensitivity by dephosphorylating EGFR leading to its dissociation with ER. Consistent with this notion, a nuclear-localization defective ER has a higher EGFR-binding activity and confers the resistance to TKI-induced growth inhibition. Additional analysis show that PTPH1 stabilizes EGFR, stimulates the membranous EGFR accumulation, and enhances the growth-inhibitory activity of a combination therapy of TKIs with an anti-estrogen. Since EGFR and ER both are substrates for PTPH1 in vitro and in intact cells, these results indicate that an inhibitory EGFR-ER protein complex can be switched off through a competitive enzyme-substrate binding. Our results would have important implications for the treatment of breast cancer with targeted therapeutics.

Endothelial 12(S)-HETE vasorelaxation is mediated by thromboxane receptor inhibition in mouse mesenteric arteries.

Arachidonic acid (AA) metabolites mediate endothelium-dependent relaxation in many vascular beds. Previously, we identified the major AA 12/15-lipoxygenase (12/15-LO) metabolite of mouse arteries as 12-hydroxyeicosatetraenoic acid (12-HETE). The goal was to determine the stereospecific configuration of mouse vascular 12-HETE and characterize the role of 12-HETE stereoisomers in the regulation of vascular tone. Using normal, reverse phase, and chiral HPLC, the stereospecific configuration was identified as 12(S)-HETE. 12(S)-HETE relaxed U46619-, carbocyclic thromboxane A(2)-, PGF(2α)-, and 8-iso PGF(2α)-preconstricted mesenteric arteries, but not phenylephrine-preconstricted arteries. 12(R)-HETE was more potent than 12(S)-HETE in relaxing U46619-preconstricted mouse arteries (maximum relaxations = 91.4 ± 2.7% and 71.8 ± 5.9%, respectively). Neither 12-HETE isomer caused constriction. Pretreatment with 12(S)- or 12(R)-HETE (1 µM) inhibited constrictions to U46619 but not phenylephrine. To investigate the role of thromboxane A(2) (TP) receptors in 12-HETE vascular actions, [(3)H]SQ29548 radioligand binding studies were performed in mouse platelets. U46619, 12(R)-HETE, and 12(S)-HETE displaced [(3)H]SQ29548 binding with IC(50)s of 0.07, 0.32, and 1.73 µM, respectively. Both 12(S)- and 12(R)-HETE inhibited intracellular calcium increases induced by U46619 (10 nM) in HEK293 cells overexpressing TP(α) receptor (65.5% and 45.1%, respectively) and coexpressing prostacyclin (IP) and TP(α) receptors (58.0% and 27.1%, respectively). The LO inhibitor NDGA (10 µM) reduced AA relaxations in arteries preconstricted with U46619 but not phenylephrine. These results indicate that exogenous and endogenous 12(S)-HETE relax mouse mesenteric arteries that are preconstricted with thromboxane agonists. These 12(S)-HETE relaxations are mediated by TP receptor competitive inhibition and inhibition of TP agonist-induced increases in intracellular calcium.

Pulmonary arterial responses to reactive oxygen species are altered in newborn piglets with chronic hypoxia-induced pulmonary hypertension.

Reactive oxygen species (ROS) have been implicated in the pathogenesis of pulmonary hypertension. ROS might mediate vascular responses, at least in part, by stimulating prostanoid production. Our goals were to determine whether the effect of ROS on vascular tone is altered in resistance pulmonary arteries (PRAs) of newborn piglets with chronic hypoxia-induced pulmonary hypertension and the role, if any, of prostanoids in ROS-mediated responses. In cannulated, pressurized PRA, ROS generated by xanthine (X) plus xanthine oxidase (XO) had minimal effect on vascular tone in control piglets but caused significant vasoconstriction in hypoxic piglets. Both cyclooxygenase inhibition with indomethacin and thromboxane synthase inhibition with dazoxiben significantly blunted constriction to X+XO in hypoxic PRA. X+XO increased prostacyclin production (70 ± 8%) by a greater degree than thromboxane production (50 ± 6%) in control PRA; this was not the case in hypoxic PRA where the increases in prostacyclin and thromboxane production were not statistically different (78 ± 13% versus 216 ± 93%, respectively). Thromboxane synthase expression was increased in PRA from hypoxic piglets, whereas prostacyclin synthase expression was similar in PRA from hypoxic and control piglets. Under conditions of chronic hypoxia, altered vascular responses to ROS may contribute to pulmonary hypertension by a mechanism that involves the prostanoid vasoconstrictor, thromboxane.

Role of superoxide and thromboxane receptors in acute angiotensin II-induced vasoconstriction of rabbit vessels.

This study explored the hypothesis that a portion of angiotensin II-induced contractions is dependent on superoxide generation and release of a previously unidentified arachidonic acid metabolite that activates vascular smooth muscle thromboxane receptors. Treatment of rabbit aorta or mesentery artery with the thromboxane receptor antagonist SQ29548 (10 µM) reduced angiotensin II-induced contractions (maximal contraction in aorta; control vs. SQ29548: 134 ± 16 vs. 93 ± 10%). A subset of rabbits deficient in vascular thromboxane receptors also displayed decreased contractions to angiotensin II. The superoxide dismutase mimetic Tiron (30 mM) attenuated angiotensin II-induced contractions only in rabbits with functional vascular thromboxane receptors (maximal contraction in aorta; control vs. Tiron: 105 ± 5 vs. 69 ± 11%). Removal of the endothelium or treatment with a nitric oxide synthase inhibitor, nitro-l-arginine (30 µM) did not alter angiotensin II-induced contractions. Tiron and SQ29548 decreased angiotensin II-induced contractions in the denuded aortas by a similar percentage as that observed in intact vessels. The cyclooxygenase inhibitor indomethacin (10 µM) or thromboxane synthase inhibitor dazoxiben (10 µM) had no effect on angiotensin II-induced contractions indicating that the vasoconstrictor was not thromboxane. Angiotensin II increased the formation of a 15-series isoprostane. Isoprostanes are free radical-derived products of arachidonic acid. The unidentified isoprostane increased when vessels were incubated with the superoxide-generating system xanthine/xanthine oxidase. Pretreatment of rabbit aorta with the isoprostane isolated from aortic incubations enhanced angiotensin II-induced contractions. Results suggest the factor activating thromboxane receptors and contributing to angiotensin II vasoconstriction involves the superoxide-mediated generation of a 15-series isoprostane.

Role of lipoxygenase metabolites of arachidonic acid in enhanced pulmonary artery contractions of female rabbits.

Pulmonary arterial hypertension is characterized by elevated pulmonary artery pressure and vascular resistance. In women the incidence is 4-fold greater than that in men. Studies suggest that sustained vasoconstriction is a factor in increased vascular resistance. Possible vasoconstrictor mediators include arachidonic acid-derived lipoxygenase (LO) metabolites. Our studies in rabbits showed enhanced endothelium-dependent contractions to arachidonic acid in pulmonary arteries from females compared with males. Because treatment with a nonspecific LO inhibitor reduced contractions in females but not males, the present study identified which LO isoform contributes to sex-specific pulmonary artery vasoconstriction. The 15- and 5- but not 12-LO protein expressions were greater in females. Basal and A23187-stimulated release of 15-, 5-, and 12-hydroxyeicosatetraenoic acids (HETEs) from females and males were measured by liquid chromatography/mass spectrometry. Only 15-HETE synthesis was greater in females compared with males under both basal and stimulated conditions. Vascular contractions to 15-HETE were enhanced in females compared with males (maximal contraction: 44±6%versus 25±3%). The specific 15-LO inhibitor PD146176 (12 µmol/L) decreased arachidonic acid-induced contractions in females (maximal contraction: 93±4% versus 57±10%). If male pulmonary arteries were incubated with estrogen (1 µmol/L, 18 hours), protein expression of 15-LO and 15-HETE production increased. Mechanisms to explain the increased incidence of pulmonary hypertension in women are not known. Results suggest that the 15-LO pathway is different between females and males and is regulated by estrogen. Understanding this novel sex-specific mechanism may provide insight into the increased incidence of pulmonary hypertension in females.

Vascular pharmacology of epoxyeicosatrienoic acids.

Epoxyeicosatrienoic acids (EETs) are cytochrome P450 metabolites of arachidonic acid that are produced by the vascular endothelium in responses to various stimuli such as the agonists acetylcholine (ACH) or bradykinin or by shear stress which activates phospholipase A(2) to release arachidonic acid. EETs are important regulators of vascular tone and homeostasis. In the modulation of vascular tone, EETs function as endothelium-derived hyperpolarizing factors (EDHFs). In models of vascular inflammation, EETs attenuate inflammatory signaling pathways in both the endothelium and vascular smooth muscle. Likewise, EETs regulate blood vessel formation or angiogenesis by mechanisms that are still not completely understood. Soluble epoxide hydrolase (sEH) converts EETs to dihydroxyeicosatrienoic acids (DHETs) and this metabolism limits many of the biological actions of EETs. The recent development of inhibitors of sEH provides an emerging target for pharmacological manipulation of EETs. Additionally, EETs may initiate their biological effects by interacting with a cell surface protein that is a G protein-coupled receptor (GPCR). Since GPCRs represent a common target of most drugs, further characterization of the EET receptor and synthesis of specific EET agonists and antagonist can be used to exploit many of the beneficial effects of EETs in vascular diseases, such as hypertension and atherosclerosis. This review will focus on the current understanding of the contribution of EETs to the regulation of vascular tone, inflammation, and angiogenesis. Furthermore, the therapeutic potential of targeting the EET pathway in vascular disease will be highlighted.

Protein complex formation with heat shock protein 90 in chronic hypoxia-induced pulmonary hypertension in newborn piglets.

Aberrant interactions between heat shock protein (Hsp)90 and its client proteins could contribute to pulmonary hypertension. We tested the hypotheses that 1) the interaction between Hsp90 and its known client protein, endothelial nitric oxide synthase (eNOS), is impaired in pulmonary resistance arteries (PRAs) from piglets with pulmonary hypertension caused by exposure to 3 or 10 days of hypoxia and 2) Hsp90 interacts with the prostanoid pathway proteins prostacyclin synthase (PGIS) and/or thromboxane synthase (TXAS). We also determined whether Hsp90 antagonism with geldanamycin alters the agonist-induced synthesis of prostacyclin and thromboxane or alters PRA responses to these prostaglandin metabolites. Compared with normoxic piglets, less eNOS coimmunoprecipitated with Hsp90 in PRAs from hypoxic piglets. Despite reduced Hsp90-eNOS interactions, dilation to ACh was enhanced in geldanamycin-treated PRAs from hypoxic, but not normoxic, piglets. In PRAs from all groups of piglets, PGIS and TXAS coimmunoprecipitated with Hsp90. Geldanamycin reduced the ACh-induced synthesis of prostacyclin and thromboxane and altered responses to the thromboxane mimetic U-46619 in PRAs from all groups. Although geldanamycin enhanced responses to prostacyclin in PRAs from both groups of hypoxic piglets, geldanamycin had no effect on prostacyclin responses in PRAs from either group of normoxic piglets. Our findings indicate that Hsp90 influences both prostanoid and eNOS signaling in the pulmonary circulation of newborn piglets and that the impact of pharmacological inhibition of Hsp90 on these signaling pathways is altered during exposure to chronic hypoxia.

Chronic hypoxia enhances 15-lipoxygenase-mediated vasorelaxation in rabbit arteries.

15-Lipoxygenase (15-LO-1) metabolizes arachidonic acid (AA) to 11,12,15-trihydroxyeicosatrienoic acids (THETAs) and 15-hydroxy-11,12-epoxyeicosatrienoic acids (HEETA) that dilate rabbit arteries. Increased endothelial 15-LO-1 expression enhances arterial relaxations to agonists. We tested the effect of hypoxia on 15-LO-1 expression, THETA and HEETA synthesis, and relaxations in rabbit arteries. The incubation of rabbit aortic endothelial cells and isolated aortas in 0.7% O(2) increased 15-LO-1 expression. Rabbits were housed in a hypoxic atmosphere of 12% O(2) for 5 days. 15-LO-1 expression increased in the endothelium of the arteries of rabbits in 12% O(2) compared with room air. THETA and HEETA synthesis was also enhanced in aortas and mesenteric arteries. AA hyperpolarized the smooth muscle cells in indomethacin- and phenylephrine-treated mesenteric arteries of hypoxic rabbits from -29.4 +/- 1 to -50.1 +/- 3 mV. The hyperpolarization to AA was less in arteries of normoxic rabbits (from -26.0 +/- 2 to -37 +/- 2 mV). This AA-induced hyperpolarization was inhibited by the 15-LO inhibitor BW-755C. Nitric oxide and prostaglandin-independent maximum relaxations to acetylcholine (79.7 +/- 2%) and AA (38.3 +/- 4%) were enhanced in mesenteric arteries from hypoxic rabbits compared with the normoxic rabbits (49.7 +/- 6% and 19.9 +/- 2%, respectively). These relaxations were inhibited by BW-755C and nordihydroguaiaretic acid. Therefore, hypoxia increased the relaxations to agonists in the rabbit mesenteric arteries by enhancing endothelial 15-LO-1 expression and synthesis of the hyperpolarizing factors THETA and HEETA.

Hypercholesterolemia enhances 15-lipoxygenase-mediated vasorelaxation and acetylcholine-induced hypotension.

OBJECTIVE: Arachidonic acid (AA) metabolites from 15-lipoxygenase-1 (15-LO-1), trihydroxyeicosatrienoic acid (THETA), and hydroxyepoxyeicosatrienoic acid (HEETA) relax arteries. We studied 15-LO-1 expression, THETA and HEETA synthesis, and their effect on arterial relaxations and blood pressure in hypercholesterolemic nonatherosclerotic rabbits. METHODS AND RESULTS: Immunoblots, RTPCR analysis, and (14)C-AA metabolism revealed that hypercholesterolemia increased 15-LO-1 expression in the endothelium and THETA and HEETA synthesis in the arteries. Isometric tension recording, in presence of nitric oxide synthase (NOS) and cyclooxygenase (COX) inhibitors, showed greater relaxations to acetylcholine (ACH) and AA (max 76.0+/-4.6% and 79.5+/-2.4%, respectively) in aortas from hypercholesterolemic rabbits compared with normal rabbits (max 39.1+/-2.8% and 39.9+/-2.2%, respectively). AA induced greater hyperpolarization in the smooth muscle cells of hypercholesterolemic aortas (-45.85+/-3.0 mV) compared with normal aortas (-31.45+/-1.9 mV). The ACH- and AA-relaxations were inhibited by 15-LO-1 inhibitors. ACH induced hypotensive responses were greater in hypercholesterolemic rabbits in absence (-54.9+/-3.3%) or presence (-48.5+/-3.2%) of NOS and COX-inhibitors compared with control rabbits (-31.6+/-3.3% and -24.3+/-1.6%, respectively). BW755C reduced these responses in hypercholesterolemic rabbits to -29.3+/-2.3%. CONCLUSIONS: Hypercholesterolemia increases endothelial 15-LO-1 expression, THETA and HEETA synthesis and enhances vasorelaxation.

Characterization of endothelial thromboxane receptors in rabbit aorta.

An increased synthesis of thromboxane (TX) A(2) is associated with a number of cardiovascular diseases including atherosclerosis, unstable angina and hypertension. We previously identified a subgroup of NZW rabbits in which isolated arteries failed to contract to the TX agonists, U46619 or I-BOP. In vascular smooth muscle membranes, there was a significant decrease in TX receptors, termed TP. These rabbits are referred to as vTP- and those with the TP receptor are called vTP+. Because TP receptors are expressed in some types of endothelial cells, the present study was designed to determine whether functional TP receptors are present in endothelial cells cultured from aortas of vTP+ and vTP- rabbits. Radioligand binding studies were performed with (125)I-BOP. Aortic endothelial cells from vTP+ rabbits exhibited specific and saturable binding. In contrast, in endothelial preparations from vTP- rabbit aortas, no measurable binding to (125)I-BOP was detected. Using an anti-TP receptor antibody, we compared the amount of receptor expressed in endothelial cell lysates obtained from vTP+ and vTP- rabbits. Consistent with the results observed radioligand binding assays, the expression of TP receptor protein was decreased in vTP- compared to vTP+ endothelial cells. An in vitro wound healing assay was used on confluent monolayers of endothelial cells. In the untreated vTP+ cells, the area of the scratch was completely closed by 30 h. In the vTP+ cells treated with U46619 (3 microM), the rate of closure of the scratch area was reduced with approximately 12% of the scratch area remaining at 30 h. Pretreatment with the TP receptor antagonist, SQ 29548 (10 microM) prevented the inhibitory effect of U46619. The rate of closure of the scratch in the vTP- was not altered by U46619. In a separate study, U46619 (3 microM) increased the release of 6-keto PGF(1alpha), the stable metabolite of prostacyclin, in vTP+ but not vTP- endothelial cells. Pretreatment with SQ29548 (10 microM) or the cyclooxygenase inhibitor, indomethacin (10 microM) blocked the increase in vTP+ endothelial cells. In vascular reactivity studies in aortas from vTP+ rabbits, removal of the endothelium enhanced the vasoconstrictor response to U46619 indicating that activation of endothelial TP receptors may modulate vascular tone via the release of the vasodilator, prostacyclin. The results of this study suggest an important role for endothelial TP receptors in modulating vascular function.

Aortic thromboxane receptor deficiency alters vascular reactivity in cholesterol-fed rabbits.

Hypercholesterolemia is considered a major risk factor in the development of atherosclerotic disease. The endothelium is the source of a number of vasoactive compounds which may be altered by the disease process. For example, synthesis of the arachidonic acid metabolite thromboxane A(2) (TXA(2)) increases in atherosclerosis. Non-selective blockade of vascular and platelet thromboxane (TP) receptors retards the progression of the disease in various animal models. We have previously identified a subset of NZW rabbits that lack only vascular (v) TP receptors, referred to as vTP-. These rabbits provide a unique model to elucidate the role of vascular TP receptors in hypercholesterolemia. Studies evaluated vascular responses to phenylephrine and acetylcholine in isolated aortic rings obtained from vTP- and vTP+ rabbits fed 0.5% cholesterol diet for a period of only 3 weeks. In the cholesterol-fed vTP- rabbits, contractions to phenylephrine were reduced compared to the vTP+ cholesterol-fed rabbits. Acetylcholine-induced relaxations were greater in cholesterol-fed vTP- rabbits compared to cholesterol-fed vTP+ rabbits. While the overall incidence of aortic lesions was small after only 3 weeks of cholesterol-feeding, results indicated a reduction in lesions in the vTP- compared to the vTP+ rabbits. In summary, these studies are the first to show that if rabbits lack only vascular TP receptors, impaired vascular reactivity responses normally associated with hypercholesterolemia are diminished.

Cyclooxygenase-2 and an early stage of chronic hypoxia-induced pulmonary hypertension in newborn pigs.

Our objective was to determine whether cyclooxygenase (COX)-2-dependent metabolites contribute to the altered pulmonary vascular responses that manifest in piglets with chronic hypoxia-induced pulmonary hypertension. Piglets were raised in either room air (control) or hypoxia for 3 days. The effect of the COX-2 selective inhibitor NS-398 on responses to arachidonic acid or acetylcholine (ACh) was measured in endothelium-intact and denuded pulmonary arteries (100- to 400-microm diameter). Pulmonary arterial production of the stable metabolites of thromboxane and prostacyclin was assessed in the presence and absence of NS-398. Dilation to arachidonic acid was greater for intact control than for intact hypoxic arteries, was unchanged by NS-398 in intact arteries of either group, and was augmented by NS-398 in denuded hypoxic arteries. ACh responses, which were dilation in intact control arteries but constriction in intact and denuded hypoxic arteries, were diminished by NS-398 treatment of all arteries. NS-398 reduced prostacyclin production by control pulmonary arteries and reduced thromboxane production by hypoxic pulmonary arteries. COX-2-dependent contracting factors, such as thromboxane, contribute to aberrant pulmonary arterial responses in piglets exposed to 3 days of hypoxia.

Glibenclamide inhibits thromboxane-mediated vasoconstriction by thromboxane receptor blockade.

Because sulfonylureas, such as glibenclamide, are used to treat Type 2 diabetes and because this disease is associated with various cardiovascular complications that may be mediated by thromboxane (TX), this study was designed to characterize the role of glibenclamide on TX-mediated contractions in isolated ring segments of bovine coronary arteries and rabbit aortas. A series of TXA(2) analogs [9,11 Dideoxy-9alpha, 11alpha-methanoepoxy prostaglandin F(2alpha) (U46619), [1S-(1alpha, 2beta(5Z),3alpha(1E, 3R*),4alpha)]-7-[3-(3-hydroxy-4-(4'-iodophenoxy)-1-butenyl)-7-oxabicyclo [2.2.1]heptan-2-yl]-5-heptenoic acid (I-BOP), carbocyclic TXA(2) (CTA(2)) and 9,11-dideoxy-9alpha,11alpha-epoxymethano prostaglandin F(2alpha) (U44069)], endothelin and phenylephrine contracted both types of blood vessels. Glibenclamide (10 microM) inhibited the contraction to each of the TX agonists but had no effect on endothelin- or phenylephrine-induced contractions. We hypothesized that this effect was due to a direct effect to block the vascular smooth muscle cell TX receptor. Receptor binding studies were performed in rabbit vascular smooth muscle cells and indicated that glibenclamide (10 microM) inhibited (125)I-BOP binding by more than 80%. The inhibition constants or K(i) for glibenclamide was 0.53 microM. These studies provide the first evidence that the ability of glibenclamide to inhibit TX-mediated contractions occurs independent of the vascular K(ATP) channel and is, instead, mediated by the blockade of the vascular TX receptor.

Cultured rat microglial cells synthesize the endocannabinoid 2-arachidonylglycerol, which increases proliferation via a CB2 receptor-dependent mechanism.

Microglia, as phagocytes and antigen-presenting cells in the central nervous system, are activated in such disease processes as stroke and multiple sclerosis. Because peripheral macrophages are capable of producing endocannabinoids, we have examined endocannabinoid production in a macrophage-colony stimulating factor (M-CSF)-dependent rat microglial cell line (RTMGL1) using reversed phase high-pressure liquid chromatography and liquid chromatography-mass spectroscopy. We determined that cultured microglial cells produce the endocannabinoid 2-arachidonylglycerol (2-AG) as well as anandamide in smaller quantities. When 2-AG, but not anandamide, is added exogenously, RTMGL1 microglia increase their proliferation. This increased proliferation is blocked by an antagonist of the CB(2) receptor N-[(1S)endo-1,3,3-trimethyl bicyclo heptan-2-yl]-5-(4-chloro-3-methylphenyl)-1-(4-methylbenzyl)-pyrazole-3-carboxamide (SR144528) and mimicked by the CB(2) receptor-specific agonist 1,1-dimethylbutyl-1-deoxy-Delta(9)-tetrahydrocannabinol (JWH133). Accompanying the increase in proliferation seen with 2-AG is an increase in active ERK1 that is also blocked with SR144528. The RTMGL1 microglial cells, which exist in a primed state, express the CB(1) and CB(2) receptors as demonstrated by reverse transcription-polymerase chain reaction and immunostaining. The CB(2) receptor in untreated cells is expressed both at the cell surface and internally, and exposure of the cells to 2-AG significantly increases receptor internalization. These data suggest that 2-AG activation of CB(2) receptors may contribute to the proliferative response of microglial cells, as occurs in neurodegenerative disorders.

Production of hydroxyeicosatetraenoic acids and prostaglandins by a novel rat microglial cell line.

We have established a clonal cell line derived from rat microglia that proliferates in response to macrophage-colony stimulating factor (CSF-1). Like primary neonatal microglia, these cells (named RTMGL1) exhibit a ramified morphology, bind isolectin B4, express CD68 and are weakly positive for CD11b and MHC class II. CSF-1-dependent proliferation requires intact signal transduction through several pathways. RTMGL1 synthesize multiple cyclooxygenase (COX) products including 11- and 15-hydroxyeicosatetraenoic acid (HETE) and express COX-2. RTMGL1 synthesize 5-HETE from arachidonic acid (AA) likely via a 5-lipoxygenase (LO). Thus, RTMGL1 have morphological and histological characteristics of primary microglia and metabolize AA via both COX and LO pathways.

Role of platelet microparticles in the production of thromboxane by rabbit pulmonary artery.

This study examined the role of platelet microparticles in thromboxane A2 (TXA2) production. Incubation of microparticles with [14C]arachidonic acid and A23187 produced 14C-labeled TXB2, the stable metabolite of TXA2. To investigate the possibility that endothelial cells (ECs) transfer arachidonic acid to platelet microparticles and promote TXB2 synthesis, ECs with their cellular lipids prelabeled with tritiated arachidonic acid were incubated with microparticles. In the absence of microparticles, there was no production of tritiated TXB2 by the ECs. However, when microparticles were coincubated with prelabeled ECs, tritiated arachidonic acid was metabolized to tritiated TXB2. Aspirin was then used to inhibit cyclooxygenase. ECs coincubated with aspirin-treated platelet microparticles did not produce TXB2, as measured by radioimmunoassay. In contrast, aspirin-treated ECs coincubated with microparticles produced TXB2, and its production was enhanced by methacholine (10(-4) mol/L), indicating that endothelially derived arachidonic acid, and not endothelially derived prostaglandin endoperoxide, was transferred to the microparticle and further metabolized to TXA2. Additional studies with rabbit aorta and pulmonary artery investigated whether microparticles contributed to vascular contractions. Preincubation with microparticles enhanced arachidonic acid-induced contractions in the aorta and methacholine-induced contractions in the pulmonary artery. The thromboxane receptor antagonist SQ29548 and the thromboxane synthase inhibitor dazoxiben blocked these effects. Because TXA2 is an important mediator in various pathophysiologic states, including hypertension, the ability of platelet microparticles to act as a cellular source of TXA2 might provide new insight into the role of platelets and platelet microparticles in the control of vascular tone.