Altered pain perception and inflammatory response in mice lacking prostacyclin receptor

Mitochondrial coupling factor 6 as a potent endogenous vasoconstrictor

We demonstrated recently that coupling factor 6, an essential component of the energy-transducing stalk of mitochondrial ATP synthase, suppresses the synthesis of prostacyclin in vascular endothelial cells. Here, we tested the hypothesis that coupling factor 6 is present on the cell surface and is involved in the regulation of systemic circulation. This peptide is present on the surface of CRL-2222 vascular endothelial cells and is released by these cells into the medium. In vivo, the peptide circulates in the vascular system of the rat, and its gene expression and plasma concentration are higher in spontaneously hypertensive rats (SHRs) than in normotensive controls. Elevation of blood pressure with norepinephrine did not affect the plasma concentration of coupling factor 6. Intravenous injection of recombinant peptide increased blood pressure, apparently by suppressing prostacyclin synthesis, whereas a specific Ab to coupling factor 6 decreased systemic blood pressure concomitantly with an increase in plasma prostacyclin. Interestingly, the antibody's hypotensive effect could be abolished by treating with the cyclooxygenase inhibitor indomethacin. These findings indicate that mitochondrial coupling factor 6 functions as a potent endogenous vasoconstrictor in the fashion of a circulating hormone and may suggest a new mechanism for hypertension.

Potential adverse effects of cyclooxygenase-2 inhibition: evidence from animal models of inflammation

Cyclooxygenase (COX; prostaglandin H synthase, prostaglandin endoperoxidase) is the key enzyme in the synthesis of the prostaglandin and thromboxane families of eicosanoid mediators, and is the target for the nonsteroidal anti-inflammatory drugs (NSAIDs). The identification of an inducible COX isoform, COX-2, and the demonstration of its specific expression at sites of inflammation suggested that it may provide a useful therapeutic target for novel anti-inflammatory drugs. Inhibition of an enzyme that is not expressed in most healthy tissues would potentially avoid most of the adverse effects associated with NSAIDs, which target a constitutively expressed isoform, COX-1. The development of novel 'super aspirins' with high selectivity towards the inhibition of COX-2 showed that this hypothesis was well-founded and that high levels of these drugs could be tolerated without these serious adverse effects. The first two of these new generation NSAIDs, celecoxib and rofecoxib, are now in clinical use. More recently, however, concern has been expressed that COX-2 inhibition may in fact have a number of potential, previously hidden, pitfalls. These have arisen from the demonstration that COX-2 induction is not exclusively associated with the onset of an inflammatory reaction, with expression limited to inflammatory sites. In fact, COX-2 is expressed more chronically, and is also seen during the resolution of inflammation and in areas of wound-healing. The application of COX-2-selective inhibitors during these periods has been shown to be deleterious in that resolution of inflammation is delayed, gastric ulcer healing is delayed and, in some patients, ulcers have been shown to progress further to perforation. The suggestion has now been made that, in these situations, COX-2 may help resolve the pathology, perhaps by generating alternative series of prostaglandins such as the cyclopentenone prostaglandins. The finding that these prostaglandins can affect proteins by direct chemical modifications as well as having their own receptor families has rekindled debate on the deleterious and beneficial effects of prostanoids, and the implications of inhibiting the production of these mediators, in the body. Therefore, in this review we discuss the role of COX-2 in inflammation and the potential adverse effects of its inhibition.

Protein kinase A-mediated phosphorylation of serine 357 of the mouse prostacyclin receptor regulates its coupling to G(s)-, to G(i)-, and to G(q)-coupled effector signaling

The prostacyclin receptor (IP) is primarily coupled to G alpha(s)-dependent activation of adenylyl cyclase; however, a number of studies indicate that the IP may couple to other secondary effector systems perhaps in a species-specific manner. In the current study, we investigated the specificity of G protein:effector coupling by the mouse (m) IP overexpressed in human embryonic kidney 293 cells and endogenously expressed in murine erythroleukemia cells. The mIP exhibited efficient G alpha(s) coupling and concentration-dependent increases in cAMP generation in response to the IP agonist cicaprost; however, mIP also coupled to G alpha(i) decreasing the levels of cAMP in forskolin-treated cells. mIP coupling to G alpha(i) was pertussis toxin-sensitive and was dependent on protein kinase (PK) A activation status. In addition, the mIP coupled to phospholipase C (PLC) activation in a pertussis toxin-insensitive, G alpha(i)-, G beta gamma-, and PKC-independent but in a G alpha(q)- and PKA-dependent manner. Whole cell phosphorylation assays demonstrated that the mIP undergoes cicaprost-induced PKA phosphorylation. mIP(S357A), a site-directed mutant of mIP, efficiently coupled to G alpha(s) but failed to couple to G alpha(i) or to efficiently couple to G alpha(q):PLC. Moreover, mIP(S357A) did not undergo cicaprost-induced phosphorylation confirming that Ser(357) is the target residue for PKA-dependent phosphorylation. Finally, co-precipitation experiments permitted the detection of G alpha(s), G alpha(i), and G alpha(q) in the immunoprecipitates of mIP, whereas only G alpha(s) was co-precipitated with mIP(S357A) indicating that Ser(357) of mIP is essential for G alpha(i) and G alpha(q) interaction. Moreover, inhibition of PKA blocked co-precipitation of mIP with G alpha(i) or G alpha(q). Taken together our data indicate that the mIP, in addition to coupling to G alpha(s), couples to G alpha(i) and G alpha(q); however, G alpha(i) and G alpha(q) coupling is dependent on initial cicaprost-induced mIP:G alpha(s) coupling and phosphorylation of mIP by cAMP-dependent PKA where Ser(357) was identified as the target residue for PKA phosphorylation.

Characterization of EP receptor subtypes responsible for prostaglandin E2-induced pain responses by use of EP1 and EP3 receptor knockout mice

Prostaglandin E2 (PGE2) is known to be the principal pro-inflammatory prostanoid and play an important role in nociception. To identify PGE receptor (EP) subtypes that mediate pain responses to noxious and innocuous stimuli, we studied them by use of EP1 and EP3 knockout (EP1(-/-) and EP3(-/-)) mice. PGE2 could induce mechanical allodynia in EP1(+/+), EP3(+/+) and EP3(-/-) mice, but not in EP1(-/-) mice. N-methyl-D-aspartate (NMDA), the substrate of nitric oxide (NO) synthase L-arginine, or the NO donor sodium nitroprusside administered intrathecal (i.t.) could induce allodynia in EP3(-/-) and EP1(-/-) mice. Activation of EP1 receptors appears to be upstream, rather than downstream, of NMDA receptor activation and NO production in the PGE2-induced allodynia. Although PGE2 produced thermal hyperalgesia over a wide range of dosages from 50 pg to 0.5 microg kg(-1) in EP3(+/+) mice, it showed a monophasic hyperalgesic action at 5 ng kg(-1) or higher doses in EP3(-/-) mice. The selective EP3 agonist, ONO-AE-248, induced hyperalgesia at 500 pg kg(-1) in EP3(+/+) mice, but not in EP3(-/-) mice. Saline-injected EP1(-/-) mice showed hyperalgesia, which was reversed by i.t. PGE2 in a dose-dependent manner. There was no significant difference in the formalin-induced behaviours between EP1(-/-) or EP3(-/-) mice and the cognate wild-type mice. These results demonstrate that spinal EP1 receptors are involved in the PGE2-induced allodynia and that spinal EP3 receptors are involved in the hyperalgesia induced by low doses of PGE2. However, the formalin-induced pain cannot be ascribed to a single EP receptor subtype EP1 or EP3.

Anandamide activates vanilloid receptor 1 (VR1) at acidic pH in dorsal root ganglia neurons and cells ectopically expressing VR1

The vanilloid receptor type 1 (VR1) is a heat-activated ionophore preferentially expressed in nociceptive neurons of trigeminal and dorsal root ganglia (DRG). VR1, which binds and is activated by capsaicin and other vanilloid compounds, was noted to interact with the endocannabinoid anandamide (ANA) and certain inflammatory metabolites of arachidonic acid in a pH-dependent manner. At pH < or = 6.5 ANA induced (45)Ca(2+) uptake either in primary cultures of DRG neurons or cells ectopically expressing C-terminally tagged recombinant forms of VR1 with an EC(50) = approximately 10 microm at pH 5.5. Capsazepine, a potent antagonist of vanilloids, inhibited ANA-induced Ca(2+) transport in both cell systems. Vanilloids displaced [(3)H]ANA in VR1-expressing cells, suggesting competition for binding to VR1. Ratiometric determination of intracellular free calcium and confocal imaging of the VR1-green fluorescent fusion protein revealed that, at low pH (< or =6.5), ANA could induce an elevation of intracellular free Ca(2+) and consequent intracellular membrane changes in DRG neurons or transfected cells expressing VR1. These actions of ANA were similar to the effects determined previously for vanilloids. The ligand-induced changes in Ca(2+) at pH < or = 6.5 are consistent with the idea that ANA and other eicosanoids act as endogenous ligands of VR1 in a conditional fashion in vivo. The pH dependence suggests that tissue acidification in inflammation, ischemia, or traumatic injury can sensitize VR1 to eicosanoids and transduce pain from the periphery.

Effects of selective cyclooxygenase-2 inhibition on vascular responses and thrombosis in canine coronary arteries

BACKGROUND

Prostanoid synthesis via the action of cyclooxygenase-2 (COX-2) is a component of the inflammatory response. Prostacyclin, a product of COX-2 in vascular endothelium, has important physiological roles, such as increasing blood flow to injured tissues, reducing leukocyte adherence, and inhibiting platelet aggregation. We examined the possibility that selective COX-2 inhibition could suppress the protective effects of prostacyclin, resulting in an alteration of the hemostatic balance and vascular tone.

METHODS AND RESULTS

Circumflex coronary artery thrombosis was induced in dogs by vascular electrolytic injury. Orally administered celecoxib (COX-2 inhibition) or high-dose aspirin (HDA) (COX-1 and COX-2 inhibition) did not alter time to occlusive thrombus formation compared with controls (celecoxib 77.7+/-7.2 minutes, HDA 72.0+/-18.5 minutes, control 93.0+/-21.8 minutes). Oral HDA with an endothelial recovery period (HDA-ER) (COX-1 inhibition) produced a significant increase in time to vessel occlusion (257.0+/-41.6 minutes). The observed increase in time to occlusion was abolished when celecoxib was administered to animals dosed with HDA-ER (80.7+/-20.6 minutes). The vasomotor effect of endothelium-derived prostacyclin was examined by monitoring coronary flow during intracoronary administration of arachidonic acid or acetylcholine. In celecoxib-treated animals, vasodilation in response to arachidonic acid was reduced significantly compared with controls.

CONCLUSIONS

The results indicate important physiological roles for COX-2-derived prostacyclin and raise concerns regarding an increased risk of acute vascular events in patients receiving COX-2 inhibitors. The risk may be increased in individuals with underlying inflammatory disorders, including coronary artery disease.

Proinflammatory characteristics of a nonpeptide bradykinin mimic, FR190997, in vivo

1. Proinflammatory potency of the nonpeptide bradykinin (BK) B(2) receptor agonist FR190997 (8-[2,6-dichloro-3-[N-[(E)-4-(N-methylcarbamoyl)cinnamidoacetyl]-N-methylamino]benzyloxy]-2-methyl-4-(2-pyridylmethoxy)quinoline) was investigated. 2. Intradermal injection of FR190997 (0.03 - 3 nmol site(-1)) into dorsal skin of rats increased vascular permeability in a dose-dependent manner. The effect was less than that of BK, but it was long-acting and was inhibited by treatment with FR173657 (3 mg kg(-1), p.o.). Captopril (10 mg kg(-1), i.p.) did not enhance the plasma extravasation by FR190997 (0.3 nmol site(-1)) in the presence of soybean trypsin inhibitor (SBTI, 30 microg site(-1)). 3. Subcutaneous injection of FR190997 (3 nmol site(-1)) into the hindpaw of mice markedly induced paw swelling. The oedema lasted up to 3 h after the injection. Administration of indomethacin or NS-398 (10 mg kg(-1), i.p.) significantly reduced it at 3 h after the injection. 4. Simultaneous i.p. injection of prostaglandin (PG) E(2) (1 nmol site(-1)) or beraprost sodium (0.5 nmol site(-1)) with FR190997 (5 nmol site(-1)) greatly enhanced frequency of writhing reactions in mice. 5. FR190997 (0.3 - 30 nmol kg(-1), i.v.) showed less increase in airway opening pressure (Pao) in the guinea-pig after i.v. injection. Furthermore, FR190997 (0.03 - 30 nmol) resulted in a very weak contraction of tracheal ring strips and lung parenchymal sections in vitro. 6. In mice sponge implants, topical application of FR190997 increased angiogenesis and granulation with enhanced expressions of basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF) mRNAs. 7. These results indicate that FR190997 has proinflammatory long-lasting characteristics and it might be 'a stable tool' for studying the role of BK B(2) receptor in vivo.

Analysis of urinary prostacyclin and thromboxane/prostacyclin ratio in patients with rheumatoid arthritis using gas chromatography/selected ion monitoring

We investigated production of prostacyclin and the urinary ratio of thromboxane and prostacyclin in patients with rheumatoid arthritis. The prostacyclin production level was assessed according to the level of urinary 2,3-dinor-6-keto-prostaglandin F(1 alpha)measuring by gas chromatography/selected ion monitoring. In patients receiving medication, the prostacyclin level was lower and the thromboxane/prostacyclin ratio was greater compare with that of healthy volunteers. The prostacyclin level in patients without medication was approximately 4-fold higher than that of healthy volunteers and 8-fold higher than those of medicated groups. Although the ratio of the group without medication was similar to that of healthy volunteers, the urinary levels of each prostanoid were higher than those of other groups. Then, the ratios of groups receiving steroids were higher than that of other groups owing to high TX level. The present findings demonstrated that endogenous prostacyclin and thromboxane production increased in patients without medication, and prostacyclin production decreased with medication.

Major roles of prostanoid receptors IP and EP(3) in endotoxin-induced enhancement of pain perception

To know the roles of prostaglandin I (IP) and prostaglandin E (EP) receptors in pain perception, we compared the acetic acid-induced writhing response in mice deficient in prostaglandin receptors, i.e. IP, EP(1,) EP(2,) EP(3,) or EP(4,) with or without lipopolysaccharide (LPS) pretreatment. Without LPS pretreatment, IP-receptor deficient mice showed a significantly smaller number of responses, as previously reported, whereas mice deficient in any of the EP-receptor subtypes showed a number of writhings similar to those of wild-type mice. When mice were pretreated with LPS for 24 hr to induce cyclooxygenase-2 expression, the wild-type as well as EP(1)-, EP(2)-, or EP(4)-receptor-deficient mice showed a similar enhanced writhing response, whereas IP- and EP(3)-receptor-deficient mice had a significantly less enhanced number of writhings. These results indicate that IP and EP(3) are the major prostaglandin receptors mediating the enhanced acetic acid-induced writhing response in mice pre-exposed to LPS, i.e. in endotoxin-enhanced inflammatory nociception.

Microsomal prostaglandin E synthase is regulated by proinflammatory cytokines and glucocorticoids in primary rheumatoid synovial cells

The selective induction of PGE(2) synthesis in inflammation suggests that a PGE synthase may be linked to an inducible pathway for PG synthesis. We examined the expression of the recently cloned inducible microsomal PGE synthase (mPGES) in synoviocytes from patients with rheumatoid arthritis, its modulation by cytokines and dexamethasone, and its linkage to the inducible cyclooxygenase-2. Northern blot analysis showed that IL-1beta or TNF-alpha treatment induces mPGES mRNA from very low levels at baseline to maximum levels at 24 h. IL-1beta-induced mPGES mRNA was inhibited by dexamethasone in a dose-dependent fashion. Western blot analysis demonstrated that mPGES protein was induced by IL-1beta, and maximum expression was sustained for up to 72 h. There was a coordinated up-regulation of cyclooxygenase-2 protein, although peak expression was earlier. Differential Western blot analysis of the microsomal and the cytosolic fractions revealed that the induced expression of mPGES protein was limited to the microsomal fraction. The detected mPGES protein was catalytically functional as indicated by a 3-fold increase of PGES activity in synoviocytes following treatment with IL-1beta; this increased synthase activity was limited to the microsomal fraction. In summary, these data demonstrate an induction of mPGES in rheumatoid synoviocytes by proinflammatory cytokines. This novel pathway may be a target for therapeutic intervention for patients with arthritis.

Cross talk between prostacyclin and nitric oxide under shear in smooth muscle cell: role in monocyte adhesion

We tested the hypothesis that at sites of vascular damage, vessel homeostasis is maintained through the cross talk of shear-induced production of prostacyclin and nitric oxide (NO) in vascular smooth muscle cells (VSMC). Confluent A7r5 cells derived from rat aortic VSMC and mesenteric VSMC were exposed to shear stress at 15 dyn/cm(2) for 90 min with the use of a cone-plate device, and productions of prostacyclin and NO were examined. Shear stress increased cumulative production of prostacyclin by 3- to 3.5-fold and that of NO by 6- to 7.5-fold. Western blot analysis showed that inducible NO synthase protein was expressed after shear stress in both types of VSMC. Inhibition of NO synthase enhanced the shear-induced production of prostacyclin from 40 to 60%. Shear-induced production of NO was suppressed by 70% after treatment with 10(-4) M of indomethacin. A7r5 cells adhesiveness for monocytes was suppressed by 50% after shear stress. This suppression was abolished by pretreatment with 10(-4) M of indomethacin, whereas inhibition of NO synthase only minimally inhibited it. We conclude that there is a cross talk of shear-induced production of prostacyclin and NO in VSMC. At sites of vascular damage, prostacyclin synthesis may prevent monocyte adhesiveness for VSMC through the concomitant enhancement of NO production.

G protein-coupled prostanoid receptors and the kidney

Renal cyclooxygenase 1 and 2 activity produces five primary prostanoids: prostaglandin E2, prostaglandin F2alpha, prostaglandin I2, thromboxane A2, and prostaglandin D2. These lipid mediators interact with a family of distinct G protein-coupled prostanoid receptors designated EP, FP, IP, TP, and DP, respectively, which exert important regulatory effects on renal function. The intrarenal distribution of these prostanoid receptors has been mapped, and the consequences of their activation have been partially characterized. FP, TP, and EP1 receptors preferentially couple to an increase in cell calcium. EP2, EP4, DP, and IP receptors stimulate cyclic AMP, whereas the EP3 receptor preferentially couples to Gi, inhibiting cyclic AMP generation. EP1 and EP3 mRNA expression predominates in the collecting duct and thick limb, respectively, where their stimulation reduces NaCl and water absorption, promoting natriuresis and diuresis. The FP receptor is highly expressed in the distal convoluted tubule, where it may have a distinct effect on renal salt transport. Although only low levels of EP2 receptor mRNA are detected in the kidney and its precise intrarenal localization is uncertain, mice with targeted disruption of the EP2 receptor exhibit salt-sensitive hypertension, suggesting that this receptor may also play an important role in salt excretion. In contrast, EP4 receptor mRNA is predominantly expressed in the glomerulus, where it may contribute to the regulation of glomerular hemodynamics and renin release. The IP receptor mRNA is highly expressed near the glomerulus, in the afferent arteriole, where it may also dilate renal arterioles and stimulate renin release. Conversely, TP receptors in the glomerulus may counteract the effects of these dilator prostanoids and increase glomerular resistance. At present there is little evidence for DP receptor expression in the kidney. These receptors act in a concerted fashion as physiological buffers, protecting the kidney from excessive functional changes during periods of physiological stress. Nonsteroidal anti-inflammatory drug (NSAID)-mediated cyclooxygenase inhibition results in the loss of these combined effects, which contributes to their renal effects. Selective prostanoid receptor antagonists may provide new therapeutic approaches for specific disease states.

Prostanoid receptors: subtypes and signaling

Cyclooxygenases metabolize arachidonate to five primary prostanoids: PGE(2), PGF(2 alpha), PGI(2), TxA(2), and PGD(2). These autacrine lipid mediators interact with specific members of a family of distinct G-protein-coupled prostanoid receptors, designated EP, FP, IP, TP, and DP, respectively. Each of these receptors has been cloned, expressed, and characterized. This family of eight prostanoid receptor complementary DNAs encodes seven transmembrane proteins which are typical of G-protein-coupled receptors and these receptors are distinguished by their ligand-binding profiles and the signal transduction pathways activated on ligand binding. Ligand-binding selectivity of these receptors is determined by both the transmembrane sequences and amino acid residues in the putative extracellular-loop regions. The selectivity of interaction between the receptors and G proteins appears to be mediated at least in part by the C-terminal tail region. Each of the EP(1), EP(3), FP, and TP receptors has alternative splice variants described that alter the coding sequence in the C-terminal intracellular tail region. The C-terminal variants modulate signal transduction, phosphorylation, and desensitization of these receptors, as well as altering agonist-independent constitutive activity.

A stable prostacyclin analog enhances ectopic activity in rat sensory neurons following neuropathic injury

Prostanoids sensitize sensory afferents during inflammation. However, their role in neuropathic pain is still unclear. We analyzed the actions of prostanoids, non-selective (indomethacin) or selective (celecoxib and NS-398) cyclooxygenase-2 (COX or COX-2) inhibitors, on the ectopic activity of dorsal root ganglia (DRG) and dorsal horn (DH) neurons in a model of neuropathic injury. Extracellular recordings of DRG and DH neurons and cardiovascular measurements were performed on anesthetized, paralyzed and artificially ventilated adult male Sprague-Dawley rats whose sciatic nerve had been transected. PGD(2), PGE(2), PGF(2alpha), carbaprostacyclin (cPGI(2); a stable prostacyclin analog), and carbocyclic thromboxane (cTXA(2)) were administered at cumulative doses (0.0001-5 mg/kg, i.p.) at 5 or 10 min intervals. Only cPGI(2) significantly increased the DRG and DH activity in a dose-dependent manner, with ED(50) values of 0.05 (0.01-0.96) and 0.69 (0.11-1.04) mg/kg, respectively. The other prostanoids did not significantly increase activity, although they reduced heart rate for up to 5 min following administration. Time course experiments with single doses of cPGI(2) (1 mg/kg, i.v.) increased DH discharge rate 3-17 min after injection. Indomethacin (3 mg/kg, s.c.), but not celecoxib or NS-398 (both at 6 mg/kg, s.c.), reduced both DRG and DH activity. Our results indicate that cPGI(2) excites DRG and DH neurons of neuropathic rats, and may suggest a role for IP prostanoid receptors in pain episodes associated with nerve injury. The inhibitory effect of indomethacin, but not celecoxib or NS-398, on ectopic activity may suggest that a tonic generation of PGI(2) by COX-1 could contribute to neuropathic pain.

Roles of prostaglandins and leukotrienes in acute inflammation caused by bacterial infection

Prostanoids, including prostaglandins and thromboxanes, are generated by the phospholipase A2/cyclooxygenase pathway, and leukotrienes are generated by the 5-lipoxygenase pathway from arachidonic acid. At physiological concentrations, vasodilator prostaglandins enhance the vascular permeability effects of histamine and bradykinin, and leukotrienes are important mediators of leukocyte accumulation during acute inflammation. On the other hand, prostaglandin metabolites such as cyclopentenone prostaglandins contribute to the resolution of acute inflammation through inhibition of nuclear factor-kappaB activation. Thus, arachidonic acid oxygenation products mediate diverse effects that induce and resolve acute inflammation caused by bacterial infection.

Potentiation of Ibudilast Inhibition of Platelet Aggregation in the Presence of Endothelial Cells

Although communications between platelets and endothelial cells or other blood cells are important in in vivo thrombus formation, laboratory platelet function tests are usually performed in isolation from these surrounding cells. In this study, we evaluated the effect of an antiplatelet drug, ibudilast (3-isobutyryl-2-isopropylpyrazolo[1,5-a]pyridine), on platelet aggregation in the presence and absence of human umbilical vein endothelial cells (HUVECs) and with the use of platelet-rich plasma (PRP) or whole blood as platelet samples. Stimulation-dependent platelet aggregation was weakened in the presence of HUVECs, which was especially prominent when the thrombin receptor-activating peptide SFLL (compared with ADP and epinephrine) was used as an aggregating agent. Ibudilast hardly affected SFLL-induced platelet aggregation (in PRP), while this antiplatelet agent was found to clearly inhibit this SFLL-induced response in a concentration-dependent manner, in the presence of HUVECs. Ibudilast tended to inhibit ADP- or epinephrine-induced platelet aggregation in the presence of HUVECs, but the effects were not statistically significant. Enhanced inhibition by ibudilast of SFLL-induced platelet aggregation (in the presence of HUVECs) was reproduced with the use of whole blood samples when a screen filtration pressure method was employed. It is suggested that the platelet aggregation studies in the presence of endothelial cells and/or other blood cells provide us with valuable information on platelet reactivity in vivo and improvement of antiplatelet therapy.

Regulation of TNFalpha and interleukin-10 production by prostaglandins I(2) and E(2): studies with prostaglandin receptor-deficient mice and prostaglandin E-receptor subtype-selective synthetic agonists

To know which receptors of prostaglandins are involved in the regulation of TNFalpha and interleukin 10 (IL-10) production, we examined the production of these cytokines in murine peritoneal macrophages stimulated with zymosan. The presence of PGE(2) or the PGI(2) analog carbacyclin in the medium reduced the TNFalpha production to one-half, whereas IL-10 production increased several fold; and indomethacin caused the reverse effects, suggesting that endogenous prostaglandins may have a regulatory effect on the cytokine production. Among prostaglandin E (EP) receptor-selective synthetic agonists, EP2 and EP4 agonists caused down-regulation of the zymosan-induced TNFalpha production, but up-regulation on the IL-10 production; while EP1 and EP3 agonists showed no effect. Macrophages harvested from prostaglandin I (IP) receptor-deficient mice showed the up- and down-regulatory effects on the cytokine production by the EP2 and EP4 agonists or PGE(2), but no effect was obtained by carbacyclin. On the contrary, macrophages from EP2-deficient mice showed the effect by PGE(2), carbacyclin, and the EP4 agonist, but not by the EP2 agonist; and the cells from EP4-deficient mice showed the effect by PGE(2), carbacyclin, and EP2 agonist, but not by the EP4 agonist. These functional effects of prostaglandins well accorded with the mRNA expression of TNFalpha and IL-10 when such expression was examined by the RT-PCR method. The peritoneal macrophages from normal mice expressed IP, EP2, and EP4 receptors, but not EP1 and EP3, when examined by RT-PCR. Thus the results suggest that PGI(2) and PGE(2) generated simultaneously with cytokines by macrophages treated with zymosan may influence the cytokine production through IP, EP2, and EP4 receptors.

Regulation of prostacyclin and prostaglandin E(2) receptor mediated responses in adult rat dorsal root ganglion cells, in vitro

1. Primary cultures of adult rat dorsal root ganglia (DRG) were prepared to examine the properties of prostacyclin (IP) receptors and prostaglandin E(2) (EP) receptors in sensory neurones. 2. IP receptor agonists, cicaprost and iloprost, stimulated adenylyl cyclase activity with EC(50) values of 22 and 28 nM, respectively. Prostaglandin E(1) (PGE(1)) and prostaglandin E(2) (PGE(2)) were 7 fold less potent than cicaprost and iloprost, with PGE(2) displaying a lower maximal response. 3. Adenylyl cyclase activation by iloprost, PGE(1) and PGE(2), but not by forskolin, was highly dependent on DRG cell density. Although the potency of iloprost and PGE(2) for stimulating adenylyl cyclase was unchanged, their maximal responses were significantly increased at low cell density. 4. Both IP and EP(2/4) receptors could be down-regulated by agonist pretreatment, however the presence of cyclo-oxygenase (COX) inhibitors did not prevent this apparent down-regulation of IP and EP(2/4) receptors at high DRG cell densities. 5. Stimulation of adenylyl cyclase by the neuropeptide calcitonin gene-related peptide was also decreased at high DRG cell density, whereas the responses to beta-adrenoceptor agonists were increased at high DRG cell density. 6. Addition of nerve growth factor (NGF), or the addition of anti-neurotrophin antibodies during the 5-day culture of DRG cells, had no effect on IP receptor-mediated responses. 7. These results indicate that G(s)-coupled receptors involved in nociception are regulated in a variable manner in adult rat sensory neurones, and that this cell density-dependent regulation may be agonist-independent for IP and EP(2/4) receptors.

[Pain, fever and prostanoids]

Although it has been known that prostanoids are involved in pain regulation and fever, the precise roles of their receptors and receptor subtypes are unclear. All prostanoid receptors have been cloned and mice deficient in each receptor have been developed. Recent studies using prostanoid-receptor-knockout mice are shedding some light on these issues. Nociceptive responses to an intraperitoneal injection of acetic acid and hyperalgesia induced by carrageenan were abolished by IP-receptor deficiency. In addition, the use of mice lacking prostanoid receptor is revealing an interesting role of prostanoid in neuropathic as well as inflammatory pain. With regard to pyrexia, PGE2 injected intracerebroventricularly induced the febrile response in wild-type mice, but it was without effect in mice lacking the EP3 receptor. Furthermore, febrile responses induced by IL-1 beta, an endogenous pyrogen, and LPS, an exogenous pyrogen, were specifically suppressed in mice lacking the EP3 receptor. These results indicate that PGE2 works as a common final mediator of the febrile response and that this action of PGE2 is mediated by the EP3 receptor. The determination of precise roles of prostanoids in pain and fever may provide novel targets for antipyretic analgesics with fewer side effects.

Angiogenesis stimulation in explanted hearts from patients pre-treated with intravenous prostaglandin E(1)

BACKGROUND

Prostaglandin E(1) (PGE(1)) is a potent vasodilator and induces angiogenesis in animal tissues. Previous clinical studies demonstrated that PGE(1) improves hemodynamic parameters in patients with heart failure listed for heart transplantation (HTX). Therefore, we designed a retrospective immunohistochemistry study to investigate various markers of angiogenesis using hearts explanted from PGE(1)-treated patients with idiopathic dilated cardiomyopathy (IDCM).

METHODS AND RESULTS

We investigated neovascularization in 18 hearts explanted from patients with IDCM: 9 patients received treatment with chronic infusions of PGE(1) for end-stage heart failure before HTX, whereas the remaining patients with IDCM did not receive PGE(1) and served as controls. We used immunoreactivity against CD34, von Willebrand factor (vWf), vascular endothelial growth factor (VEGF), and MIB-1 (Ki-67) to quantify angiogenesis, and used sirius red staining to determine the degree of fibrosis. Compared with the control group, PGE(1)-treated patients had significantly more CD34-, vWf- and MIB-1-positive cells in the sub-endocardium, myocardium and sub-epicardium (p < 0.01). The degree of fibrosis in the hearts of PGE(1)-treated patients was significantly lower than in control patients (p < 0.05), but we did not see any difference in the percentage of muscle mass. Finally, throughout the ventricles, we found significantly more VEGF-positive capillaries in the PGE(1) group (p < 0.0001).

CONCLUSIONS

The data suggest that PGE(1) could be a potent inducer of angiogenesis and the angiogenic factor VEGF, and could cause reduced fibrosis in the failing human heart.

[Inflammation-allergy and prostanoids. (1). Prostanoids in experimental inflammatory reaction]

It is known that prostaglandins (PGs) modify the inflammatory reaction in concert with other biologically active mediators. However, characteristics of these interactions or modulating actions have not yet been clarified well. Recently, the production of mice with specific receptor deficiencies by using the gene targeting procedure for PG receptors has accelerated elucidation of the roles of PGs through correlation of their phenotypes and experimental features. Here I discuss roles of PGs in experimental paw edema, the writhing reaction of a pain model, and regulation of cytokine production, as determined using some PG-receptor-deficient mice. From the experiment of carrageenin-induced paw edema in IP receptor-deficient mice, with an indomethacin or bradykinin antagonist, we conclude that bradykinin initially induces paw swelling and then stimulates the release PGI2, which in turn enhances the swelling with bradykinin. By comparing the writhing responses in IP-deficient and wild-type mice, we found that PGI2 is a main mediator for this pain reaction. However, in the LPS-pretreated mice, not only PGI2 but also other PGs produced by COX-2 may be involved in pain induction. Production of TNF alpha and IL-10 was modified with PGI2 or PGE2; the production of TNF alpha was down-regulated by the stimulation via IP-, EP2- or EP4 receptor, but that of IL-10 was up-regulated by these receptors, resulting in an anti-inflammatory effect.

Acceleration of atherogenesis by COX-1-dependent prostanoid formation in low density lipoprotein receptor knockout mice

The cyclooxygenase (COX) product, prostacyclin (PGI(2)), inhibits platelet activation and vascular smooth-muscle cell migration and proliferation. Biochemically selective inhibition of COX-2 reduces PGI(2) biosynthesis substantially in humans. Because deletion of the PGI(2) receptor accelerates atherogenesis in the fat-fed low density lipoprotein receptor knockout mouse, we wished to determine whether selective inhibition of COX-2 would accelerate atherogenesis in this model. To address this hypothesis, we used dosing with nimesulide, which inhibited COX-2 ex vivo, depressed urinary 2,3 dinor 6-keto PGF(1alpha) by approximately 60% but had no effect on thromboxane formation by platelets, which only express COX-1. By contrast, the isoform nonspecific inhibitor, indomethacin, suppressed platelet function and thromboxane formation ex vivo and in vivo, coincident with effects on PGI(2) biosynthesis indistinguishable from nimesulide. Indomethacin reduced the extent of atherosclerosis by 55 +/- 4%, whereas nimesulide failed to increase the rate of atherogenesis. Despite their divergent effects on atherogenesis, both drugs depressed two indices of systemic inflammation, soluble intracellular adhesion molecule-1, and monocyte chemoattractant protein-1 to a similar but incomplete degree. Neither drug altered serum lipids and the marked increase in vascular expression of COX-2 during atherogenesis. Accelerated progression of atherosclerosis is unlikely during chronic intake of specific COX-2 inhibitors. Furthermore, evidence that COX-1-derived prostanoids contribute to atherogenesis suggests that controlled evaluation of the effects of nonsteroidal anti-inflammatory drugs and/or aspirin on plaque progression in humans is timely.

Activation of the murine EP3 receptor for PGE2 inhibits cAMP production and promotes platelet aggregation

The importance of arachidonic acid metabolites (termed eicosanoids), particularly those derived from the COX-1 and COX-2 pathways (termed prostanoids), in platelet homeostasis has long been recognized. Thromboxane is a potent agonist, whereas prostacyclin is an inhibitor of platelet aggregation. In contrast, the effect of prostaglandin E2 (PGE2) on platelet aggregation varies significantly depending on its concentration. Low concentrations of PGE2 enhance platelet aggregation, whereas high PGE2 levels inhibit aggregation. The mechanism for this dual action of PGE2 is not clear. This study shows that among the four PGE2 receptors (EP1-EP4), activation of EP3 is sufficient to mediate the proaggregatory actions of low PGE2 concentration. In contrast, the prostacyclin receptor (IP) mediates the inhibitory effect of higher PGE2 concentrations. Furthermore, the relative activation of these two receptors, EP3 and IP, regulates the intracellular level of cAMP and in this way conditions the response of the platelet to aggregating agents. Consistent with these findings, loss of the EP3 receptor in a model of venous inflammation protects against formation of intravascular clots. Our results suggest that local production of PGE2 during an inflammatory process can modulate ensuing platelet responses.

Cyclooxygenases: structural, cellular, and molecular biology

The prostaglandin endoperoxide H synthases-1 and 2 (PGHS-1 and PGHS-2; also cyclooxygenases-1 and 2, COX-1 and COX-2) catalyze the committed step in prostaglandin synthesis. PGHS-1 and 2 are of particular interest because they are the major targets of nonsteroidal anti-inflammatory drugs (NSAIDs) including aspirin, ibuprofen, and the new COX-2 inhibitors. Inhibition of the PGHSs with NSAIDs acutely reduces inflammation, pain, and fever, and long-term use of these drugs reduces fatal thrombotic events, as well as the development of colon cancer and Alzheimer's disease. In this review, we examine how the structures of these enzymes relate mechanistically to cyclooxygenase and peroxidase catalysis, and how differences in the structure of PGHS-2 confer on this isozyme differential sensitivity to COX-2 inhibitors. We further examine the evidence for independent signaling by PGHS-1 and PGHS-2, and the complex mechanisms for regulation of PGHS-2 gene expression.

Cyclooxygenase inhibition and thrombogenicity

Cyclooxygenase (COX)-1 and COX-2 catalyze the formation of prothrombotic and antithrombotic eicosanoids, respectively. Aspirin, conventional nonsteroidal anti-inflammatory drugs (NSAIDs), and COX-2-specific inhibitors exhibit different patterns of inhibition of COX-1-mediated thromboxane biosynthesis and COX-2-mediated prostacyclin biosynthesis. The relationship between the pharmacologic inhibition of these vasoactive eicosanoids and the thromboprophylaxis or thrombogenicity exhibited by different therapeutic agents is currently unclear. Future studies are needed to assess the antithrombotic properties of commonly used NSAIDs, the hypothetical thrombogenicity of COX-2-specific inhibitors in high-risk patients, the need for concomitant aspirin with selective versus nonselective COX inhibitors, and the antiplatelet and gastric toxicity of the aspirin/COX-2-specific inhibitor combination in comparison with the aspirin/conventional NSAID combination.

Cloning, expression, and up-regulation of inducible rat prostaglandin e synthase during lipopolysaccharide-induced pyresis and adjuvant-induced arthritis

We have cloned and expressed the inducible form of prostaglandin (PG) E synthase from rat and characterized its regulation of expression in several tissues after in vivo lipopoylsaccharide (LPS) challenge. The rat PGE synthase is 80% identical to the human enzyme at the amino acid level and catalyzes the conversion of PGH(2) to PGE(2) when overexpressed in Chinese hamster ovary K1 (CHO-K1) cells. PGE synthase activity was measured using [(3)H]PGH(2) as substrate and stannous chloride to terminate the reaction and convert all unreacted unstable PGH(2) to PGF(2alpha) before high pressure liquid chromatography analysis. We assessed the induction of PGE synthase in tissues from Harlan Sprague-Dawley rats after LPS-induced pyresis in vivo. Rat PGE synthase was up-regulated at the mRNA level in lung, colon, brain, heart, testis, spleen, and seminal vesicles. Cyclooxygenase (COX)-2 and interleukin 1beta were also up-regulated in these tissues, although to different extents than PGE synthase. PGE synthase and COX-2 were also up-regulated to the greatest extent in a rat model of adjuvant-induced arthritis. The RNA induction of PGE synthase in lung and the adjuvant-treated paw correlated with a 3.8- and 16-fold induction of protein seen in these tissues by immunoblot analysis. Because PGE synthase is a member of the membrane-associated proteins in eicosanoid and glutathione metabolism (MAPEG) family, of which leukotriene (LT) C(4) synthase and 5-lipoxygenase-activating protein are also members, we tested the effect of LTC(4) and the 5-lipoxygenase-activating protein inhibitor MK-886 on PGE synthase activity. LTC(4) and MK-886 were found to inhibit the activity with IC(50) values of 1.2 and 3.2 microm, respectively. The results demonstrate that PGE synthase is up-regulated in vivo after LPS or adjuvant administration and suggest that this is a key enzyme involved in the formation of PGE(2) in COX-2-mediated inflammatory and pyretic responses.

Modulation of rat platelet activation by vessel wall-derived prostaglandin and platelet-derived thromboxane: effects of dietary fish oil on thromboxane-prostaglandin balance

By dietary manipulation of rats with n-3 polyunsaturated fatty acids (PUFAs), platelets and endothelium-containing aortic tissue were obtained with decreased levels of arachidonate and increased levels of eicosapentaenoate and docosahexaenoate. These diet-induced changes were accompanied by a reduced formation of thromboxane A(2) (TXA(2)) and prostaglandin I(2) (PGI(2)) in platelets and aortic tissue, respectively. When platelets were incubated with autologous, aorta-derived PGI(2), the dietary modulation of PGI(2) generation had a stronger effect on the activation process than the dietary effect on TXA(2) generation. The platelet-inhibiting effect of PGI(2) was independent of the type of agonist and involved both TXA(2)-dependent and -independent activation responses. PGI(2) also inhibited the agonist-induced formation of TXA(2). In addition, the platelet-inhibitory effect of PGI(2) was more prolonged in time than the brief, stimulatory effect of TXA(2). We conclude that, in the thromboxane-prostaglandin balance of platelet activation, PGI(2) plays a more prominent role than TXA(2). Furthermore, dietary n-3 PUFAs appear to influence platelet activation more by reducing formation of endothelial PGI(2) than by decreasing autocrine-produced TXA(2). Thus, in rats, the proposed antithrombotic effect of fish oil is unlikely to be caused by an altered thromboxane-prostaglandin balance.

The prostaglandin E2 EP1 receptor mediates pain perception and regulates blood pressure

The lipid mediator prostaglandin E2 (PGE2) has diverse biological activity in a variety of tissues. Four different receptor subtypes (EP1-4) mediate these wide-ranging effects. The EP-receptor subtypes differ in tissue distribution, ligand-binding affinity, and coupling to intracellular signaling pathways. To identify the physiological roles for one of these receptors, the EP1 receptor, we generated EP1-deficient (EP1-/-) mice using homologous recombination in embryonic stem cells derived from the DBA/1lacJ strain of mice. The EP1-/- mice are healthy and fertile, without any overt physical defects. However, their pain-sensitivity responses, tested in two acute prostaglandin-dependent models, were reduced by approximately 50%. This reduction in the perception of pain was virtually identical to that achieved through pharmacological inhibition of prostaglandin synthesis in wild-type mice using a cyclooxygenase inhibitor. In addition, systolic blood pressure is significantly reduced in EP1 receptor-deficient mice and accompanied by increased renin-angiotensin activity, especially in males, suggesting a role for this receptor in cardiovascular homeostasis. Thus, the EP1 receptor for PGE2 plays a direct role in mediating algesia and in regulation of blood pressure.

A novel 7-transmembrane receptor expressed in nerve growth factor-dependent sensory neurons

This study reports on the full-length cDNA cloning of a gene identified on the basis of its preferential expression in nerve growth factor, compared with neurotrophin-3-dependent neurons. It encodes a putative 7-transmembrane polypeptide that is distantly related to other members of the G protein-coupled receptor superfamily. Unique features of this receptor include a very long carboxy-terminal tail of 360 amino acids and a specific expression pattern in the chick peripheral nervous system, including nerve growth factor-dependent sensory and sympathetic neurons, as well as enteric neurons. In the central nervous system, the receptor is strongly developmentally regulated and is expressed at high levels in the external granule cell layer of the cerebellum, as well as in motoneurons of the spinal cord, and in retinal ganglion cells.

Adaptive cytoprotection mediated by prostaglandin I(2) is attributable to sensitization of CRGP-containing sensory nerves

BACKGROUND & AIMS

The phenomenon by which the gastric mucosa is protected in response to mild irritants has been called adaptive cytoprotection, a mechanism believed to be related to production of endogenous prostaglandins (PGs). We tested whether PGs generated by mild irritant prevent injury through the release of calcitonin gene-related peptide (CGRP) from the sensory nerves using prostanoid receptor-knockout mice.

METHODS

The stomach was doubly cannulated and perfused with 1 mol/L NaCl or 50% ethanol. CGRP levels in the perfusate were determined by enzyme immunoassay, and the injured area was estimated at the end of perfusion.

RESULTS

Preperfusion with mildly hypertonic saline (1 mol/L NaCl) increased generation of gastric PGE(2) and PGI(2) and reduced ethanol-induced mucosal damage. Exposure of ethanol after 1 mol/L NaCl increased intragastric CGRP levels from 166 +/- 27 to 713 +/- 55 pg/2 min (n = 4, P < 0.05), and the protective action of 1 mol/L NaCl was inhibited by indomethacin treatment. CGRP antagonist blocked 1 mol/L NaCl-induced protective effect. Intragastric perfusion of 50% ethanol after administration of PGI(2), but not of PGE(2), increased CGRP levels. Application of 1 mol/L NaCl to IP receptor-knockout mice (IP(-/-)) did not elicit the protective effects seen in the wild-type on ethanol-induced gastric mucosal lesions. Protective effect of 1 mol/L NaCl was observed in EP3 receptor-knockout mice (EP3(-/-)). CGRP level during ethanol perfusion was not increased in IP(-/-) but was increased in EP3(-/-) and wild-type counterparts after preperfusion of 1 mol/L NaCl.

CONCLUSIONS

These results indicate that the endogenous PGI(2) generated by 1 mol/L NaCl may have a protective role in gastric mucosal injury through enhancement of CGRP release from gastric mucosa. This mechanism may explain the adaptive cytoprotection observed after treatment with mild irritants.

Importance of quantitative genetic variations in the etiology of hypertension

Recent progress has been remarkable in identifying mutations which cause diseases (mostly uncommon) that are inherited simply. Unfortunately, the common diseases of humankind with a strong genetic component, such as those affecting cardiovascular function, have proved less tractable. Their etiology is complex with substantial environmental components and strong indications that multiple genes are implicated. In this article, we consider the genetic etiology of essential hypertension. After presenting the distribution of blood pressures in the population, we propose the hypothesis that essential hypertension is the consequence of different combinations of genetic variations that are individually of little consequence. The candidate gene approach to finding relevant genes is exemplified by studies that identified potentially causative variations associated with quantitative differences in the expression of the angiotensinogen gene (AGT). Experiments to test causation directly are possible in mice, and we describe their use to establish that blood pressures are indeed altered by genetic changes in AGT expression. Tests of differences in expression of the genes coding for the angiotensin-converting enzyme (ACE) and for the natriuretic peptide receptor A are also considered, and we provide a tabulation of all comparable experiments in mice. Computer simulations are presented that resolve the paradoxical finding that while ACE inhibitors are effective, genetic variations in the expression of the ACE gene do not affect blood pressure. We emphasize the usefulness of studying animals heterozygous for an inactivating mutation and a wild-type allele, and briefly discuss a way of establishing causative links between complex phenotypes and single nucleotide polymorphisms.

Meloxicam inhibits prostaglandin E(2) generation via cyclooxygenase 2 in the inflammatory site but not that via cyclooxygenase 1 in the stomach

We studied the effects of meloxicam on prostanoid levels, both in the inflammatory site in rat carrageenin-induced pleurisy and in the rat stomach injected with 1 mol/l NaCl solution, to clarify the relationship between its low gastric toxicity and its relative cyclooxygenase (COX) 2 selectivity. NS-398 (3 mg/kg), a highly selective COX-2 inhibitor, and meloxicam (3 mg/kg) exhibited anti-inflammatory effects in the pleurisy model. Prostaglandin (PG) E(2) thromboxane (TX) B(2) and 6-keto-PGF(1alpha) were detectable in the inflammatory site. Anti-inflammatory doses of NS-398 and meloxicam each suppressed the intrapleural PGE(2) level at 5 h as potently as piroxicam (3 mg/kg) as aspirin (100 mg/kg), both of which are nonselective COX inhibitors. NS-398 was much less potent than the other three in suppressing the levels of TXB(2) and 6-keto-PGF(1alpha). These results suggest that PGE(2) may be produced mainly via COX-2 in this model and that meloxicam may inhibit COX-2 in the inflammatory site. Piroxicam completely inhibited the increase in gastric PGE(2) induced by administering 1 mol/l NaCl solution into the rat stomach. Nimesulide (3 mg/kg), another selective COX-2 inhibitor, however, never affected this increase, suggesting that the gastric PGE(2) may be produced via COX-1. The anti-inflammatory dose of meloxicam caused statistically nonsignificant suppression of the PGE(2) level, by approximately 50%. These results suggest that the potent anti-inflammatory effect of meloxicam, accompanied with low gastric toxicity, may be related to its relative selectivity for COX-2 over COX-1.

Internalization and sequestration of the human prostacyclin receptor

Prostacyclin (PGI(2)), the major product of cyclooxygenase in macrovascular endothelium, mediates its biological effects through its cell surface G protein-coupled receptor, the IP. PKC-mediated phosphorylation of human (h) IP is a critical determinant of agonist-induced desensitization (Smyth, E. M., Hong Li, W., and FitzGerald, G. A. (1998) J. Biol. Chem. 273, 23258-23266). The regulatory events that follow desensitization are unclear. We have examined agonist-induced sequestration of hIP. Human IP, tagged at the N terminus with hemagglutinin (HA) and fused at the C terminus to the green fluorescent protein (GFP), was coupled to increased cAMP (EC(50) = 0.39 +/- 0.09 nm) and inositol phosphate (EC(50) = 86. 6 +/- 18.3 nm) generation when overexpressed in HEK 293 cells. Iloprost-induced sequestration of HAhIP-GFP, followed in real time by confocal microscopy, was partially colocalized to clathrin-coated vesicles. Iloprost induced a time- and concentration-dependent loss of cell surface HA, indicating receptor internalization, which was prevented by inhibitors of clathrin-mediated trafficking and partially reduced by cotransfection of cells with a dynamin dominant negative mutant. Sequestration (EC(50) = 27.6 +/- 5.7 nm) was evident at those concentrations of iloprost that induce PKC-dependent desensitization. Neither the PKC inhibitor GF109203X nor mutation of Ser-328, the site for PKC phosphorylation, altered receptor sequestration indicating that, unlike desensitization, internalization is PKC-independent. Deletion of the C terminus prevented iloprost-induced internalization, demonstrating the critical nature of this region for sequestration. Internalization was unaltered by cotransfection of cells with G protein-coupled receptor kinases (GRK)-2, -3, -5, -6, arrestin-2, or an arrestin-2 dominant negative mutant, indicating that GRKs and arrestins do not play a role in hIP trafficking. The hIP is sequestered in response to agonist activation via a PKC-independent pathway that is distinct from desensitization. Trafficking is dependent on determinants located in the C terminus, is GRK/arrestin-independent, and proceeds in part via a dynamin-dependent clathrin-coated vesicular endocytotic pathway although other dynamin-independent pathways may also be involved.

Biochemistry of cyclooxygenase (COX)-2 inhibitors and molecular pathology of COX-2 in neoplasia

Several types of human tumors overexpress cyclooxygenase (COX) -2 but not COX-1, and gene knockout transfection experiments demonstrate a central role of COX-2 in experimental tumorigenesis. COX-2 produces prostaglandins that inhibit apoptosis and stimulate angiogenesis and invasiveness. Selective COX-2 inhibitors reduce prostaglandin synthesis, restore apoptosis, and inhibit cancer cell proliferation. In animal studies they limit carcinogen-induced tumorigenesis. In contrast, aspirin-like nonselective NSAIDs such as sulindac and indomethacin inhibit not only the enzymatic action of the highly inducible, proinflammatory COX-2 but the constitutively expressed, cytoprotective COX-1 as well. Consequently, nonselective NSAIDs can cause platelet dysfunction, gastrointestinal ulceration, and kidney damage. For that reason, selective inhibition of COX-2 to treat neoplastic proliferation is preferable to nonselective inhibition. Selective COX-2 inhibitors, such as meloxicam, celecoxib (SC-58635), and rofecoxib (MK-0966), are NSAIDs that have been modified chemically to preferentially inhibit COX-2 but not COX-1. For instance, meloxicam inhibits the growth of cultured colon cancer cells (HCA-7 and Moser-S) that express COX-2 but has no effect on HCT-116 tumor cells that do not express COX-2. NS-398 induces apoptosis in COX-2 expressing LNCaP prostate cancer cells and, surprisingly, in colon cancer S/KS cells that does not express COX-2. This effect may due to induction of apoptosis through uncoupling of oxidative phosphorylation and down-regulation of Bcl-2, as has been demonstrated for some nonselective NSAIDs, for instance, flurbiprofen. COX-2 mRNA and COX-2 protein is constitutively expressed in the kidney, brain, spinal cord, and ductus deferens, and in the uterus during implantation. In addition, COX-2 is constitutively and dominantly expressed in the pancreatic islet cells. These findings might somewhat limit the use of presently available selective COX-2 inhibitors in cancer prevention but will probably not deter their successful application for the treatment of human cancers.

Characterization of prostanoid receptors mediating contraction of the gastric fundus and ileum: studies using mice deficient in prostanoid receptors

Receptors mediating prostanoid-induced contractions of longitudinal sections of gastric fundus and ileum were characterized by using tissues obtained from mice deficient in each type and subtype of prostanoid receptors. The fundus and ileum from mice deficient in either EP(3) (EP(3)(-/-) mice), EP(1) (EP(1)(-/-) mice) and FP (FP(-/-) mice) all showed decreased contraction to PGE(2) compared to the tissues from wild-type mice, whereas contraction of the fundus slightly increased in EP(4)(-/-) mice. 17-phenyl-PGE(2) also showed decreased contraction of the fundus from EP(3)(-/-), EP(1)(-/-) and FP(-/-) mice. Sulprostone showed decreased contraction of the fundus from EP(3)(-/-) and FP(-/-) mice, and decreased contraction of the ileum to this compound was seen in tissues from EP(3)(-/-), EP(1)(-/-) and FP(-/-) mice. In DP(-/-) mice, sulprostone showed increased contraction. DI-004 and AE-248 caused the small but concentration-dependent contraction of both tissues, and these contractions were abolished in tissues obtained from EP(1)(-/-) and EP(3)(-/-) mice, respectively, but not affected in other mice. Contractions of both fundus and ileum to PGF(2)alpha was absent at lower concentrations (10(-9) to 10(-7) M), and suppressed at higher concentrations (10(-6) to 10(-5) M) of the agonist in the FP(-/-) mice. Suppression of the contractions at the higher PGF(2)alpha concentrations was also seen in the fundus from EP(3)(-/-), EP(1)(-/-) and TP(-/-) mice and in the ileum from EP(3)(-/-) and TP(-/-) mice. Contraction of the fundus to PGD(2) was significantly enhanced in DP(-/-) mice, and contractions of the fundus and ileum to this PG decreased in FP(-/-) and EP(3)(-/-) mice. Contractions of both tissues to I-BOP was absent at 10(-9) to 10(-7) M and much suppressed at higher concentrations in TP(-/-) mice. Slight suppression to this agonist was also observed in the tissues from EP(3)(-/-) mice. PGI(2) induced small relaxation of both tissues from wild-type mice. These relaxation reactions were much potentiated in EP(3)(-/-) mice. On the other hand, significant contraction to PGI(2) was observed in both tissues obtained from IP(-/-) mice. These results show that contractions of the fundus and ileum induced by each prostanoid agonist are mediated by actions of this agonist on multiple types of prostanoid receptors and in some cases modified by its action on relaxant receptors.

Prostaglandins E2 and I2 downregulate tumor necrosis factor alpha-induced intercellular adhesion molecule-1 expression in human oral gingival epithelial cells

In the present study, we examined whether prostaglandin (PG) E2 and PGI2 regulated intercellular adhesion molecule-1 (ICAM-1) expression in human oral gingival epithelial cells stimulated with tumor necrosis factor alpha (TNF alpha). TNF alpha potently induced ICAM-1 expression in a dose- and time-dependent fashion. PGE2 and carbacyclin (a stable analogue of PGI2) significantly decreased ICAM-1 expression in TNF alpha-challenged oral gingival epithelial cells. Next, of the four subtypes of PGE2 receptors (EP1, EP2, EP3 and EP4), we examined which subtype(s) mediated inhibition of TNF alpha-induced ICAM-1 expression by PGE2. 11-deoxy-PGE2, an EP2/EP4 agonist, significantly suppressed TNF alpha-induced ICAM-1 expression, whereas butaprost, an EP2 agonist, sulprostone, an EP1/EP3 agonist, and ONO-AP-324, an EP3 agonist, caused no effect on it. By reverse transcriptase-polymerase chain reaction, expression of EP4 mRNA was detected in oral gingival epithelial cells. Dibutyryl cAMP, a cAMP analogue, and forskolin, a direct activator of adenylate cyclase, significantly inhibited TNF alpha-induced ICAM-1 expression in oral gingival epithelial cells. From these results, we suggest that PGE2 and PGI2 inhibit TNF alpha-elicited ICAM-1 expression by cAMP-dependent pathways via EP4 receptors and IP receptors, respectively.

Expression of cyclooxygenase-2 and prostanoid receptors by human myometrium

Prostanoids play an important role in the regulation of parturition. All reproductive tissues, including fetal membranes, decidua, and myometrium, have the capacity to synthesize prostanoids, and fetal membranes have been shown to express elevated levels of cyclooxygenase-2 (Cox-2) at the onset of labor. We have now investigated the expression of Cox-2 in human myometrium. Myometrial samples collected from women in labor during lower segment cesarean section expressed 15-fold higher levels of Cox-2 messenger ribonucleic acid (mRNA) compared to myometrial specimens collected from women not in labor, as detected by Northern blot analysis. Immunohistochemical detection of Cox-2 protein showed cytoplasmic staining in the smooth muscle cells of the myometrium. Cultured myometrial cells expressed low levels of Cox-2 mRNA under baseline conditions, but interleukin-1beta (IL-1beta) caused a 17-fold induction of expression of the Cox-2 transcript after incubation for 6 h. IL-1beta also induced expression of biologically active Cox-2 protein, as detected by immunofluorescence, Western blot analysis, and measuring the conversion of arachidonic acid to prostanoids in the presence and absence of a Cox-2-selective inhibitor, NS-398. PGE2 receptor subtype EP2 mRNA was expressed in cultured myometrial smooth muscle cells, whereas transcripts for EP1, EP3, EP4, FP, and IP were low or below the detection limit as measured by Northern blot analysis. However, IL-1beta stimulated expression of EP4 receptor mRNA. Our data suggest that expression of Cox-2 transcript is elevated at the onset of labor in myometrial smooth muscle cells, which may depend on induction by cytokines. As, in addition to Cox-2, the expression of prostanoid receptors is regulated, not only the production of prostanoids, but also responsiveness to them, may be modulated.

Identifying pain genes: Bottom-up and top-down approaches

A major goal of pain research at the present time is the identification of pain genes. Such genes have been informally defined in a number of ways, including the deletion or transcriptional inhibition of which produces alterations in behavioral responses on nociceptive assays; those the transcription of which is selective to pain-relevant anatomic loci (eg, small-diameter cells of the dorsal root ganglion); those the transcription of which is enhanced in animals experiencing tonic nociception or hypersensitivity states; and, finally, those existing in polymorphic forms relevant to interindividual variability. The purpose of this review is to compare the utility of various bottom-up and top-down approaches in defining, identifying, and studying pain genes. We will focus on 4 major techniques: transgenic knockouts, antisense knockdowns, gene expression assays (including DNA microarray-based expression profiling), and linkage mapping.

Cyclooxygenase-1 and -2-dependent prostacyclin formation in patients with atherosclerosis

BACKGROUND

The formation of prostacyclin (PGI(2)), thromboxane (TX) A(2), and isoprostanes is markedly enhanced in atherosclerosis. We examined the relative contribution of cyclooxygenase (COX)-1 and -2 to the generation of these eicosanoids in patients with atherosclerosis.

METHODS AND RESULTS

The study population consisted of 42 patients with atherosclerosis who were undergoing surgical revascularization. COX-2 mRNA was detected in areas of atherosclerosis but not in normal blood vessel walls, and there was evidence of COX-1 induction. The use of immunohistochemical studies localized the COX-2 to proliferating vascular smooth muscle cells and macrophages. Twenty-four patients who did not previously receive aspirin were randomized to receive either no treatment or nimesulide at 24 hours before surgery and then for 3 days. Eighteen patients who were receiving aspirin were continued on a protocol of either aspirin alone or a combination of aspirin and nimesulide. Urinary levels of 11-dehydro-TXB(2) and 2,3-dinor-6-keto-PGF(1alpha), metabolites of TXA(2) and PGI(2), respectively, were elevated in patients with atherosclerosis compared with normal subjects (3211+/-533 versus 679+/-63 pg/mg creatinine, P<0.001; 594+/-156 versus 130+/-22 pg/mg creatinine, P<0.05, respectively), as was the level of the isoprostane 8-iso-PGF(2alpha). Nimesulide reduced 2, 3-dinor-6-keto-PGF(1alpha) excretion by 46+/-5% (378.3+/-103 to 167+/-37 pg/mg creatinine, P<0.01) preoperatively and blunted the increase after surgery. Nimesulide had no significant effect on 11-dehydro-TXB(2) before (2678+/-694 to 2110+/-282 pg/mg creatinine) or after surgery. The levels of both products were lower in patients who were taking aspirin, and no further reduction was seen with the addition of nimesulide. None of the treatments influenced urinary 8-iso-PGF(2alpha) excretion.

CONCLUSIONS

Both COX-1 and -2 are expressed and contribute to the increase in PGI(2) in patients with atherosclerosis, whereas TXA(2) is generated by COX-1.

Therapeutic inhibition of platelet function in stroke

Platelet-dependent thrombotic- and thromboembolic-occlusive events are the usual cause of ischemic strokes. Antiplatelet strategies target one of the three platelet recruitment pathways (thromboxane A2, adenosine diphosphate, or thrombin) or the common cohesion pathway involving integrin alphaIIbbeta3 fibrinogen receptors. Aspirin selectively and irreversibly interrupts TxA2 and decreases events by 20-25%. Clopidogrel selectively and irreversibly inactivates platelet-ADP receptors and reduces events by 30-35%. Additive effects are produced by combining aspirin and clopidogrel. Integrin alphaIIbbeta3 fibrinogen receptor antagonists, such as abciximab, produce dose-dependent inhibition of platelet recruitment and thrombo-occlusive events, regardless of the agonist(s) initiating platelet activation, but correspondingly impair platelet hemostatic function. Because chronic antiplatelet therapy has the potential for producing abnormal bleeding it is important for current clinical trials to evaluate the benefit risk relationship.

Coordinated regulation of fetal and maternal prostaglandins directs successful birth and postnatal adaptation in the mouse

Cyclooxygenase (COX)-derived prostaglandins (PGs) regulate numerous maternal-fetal interactions during pregnancy. PGs stimulate uterine contractions and prepare the cervix for parturition, whereas in the fetus, PGs maintain patency of the ductus arteriosus (DA), a vascular shunt that transmits oxygenated placental blood to the fetal systemic circulation. However, the origin and site of action of these PGs remain undefined. To address this, we analyzed mice lacking COX-1 (null mutation) or COX-2 (pharmacologic inhibition) or pups with a double null mutation. Our results show that COX-1 in the uterine epithelium is the major source of PGs during labor and that COX-1(-/-) females experience parturition failure that is reversible by exogenous PGs. Using embryo transfer experiments, we also show that successful delivery occurs in COX-1(-/-) recipient mothers carrying wild-type pups, establishing the sufficiency of fetal PGs for parturition. Although patency of the DA is PG dependent, neither COX-1 nor COX-2 expression was detected in the fetal or postnatal DA, and offspring with a double null mutation died shortly after birth with open DAs. These results suggest that DA patency depends on circulating PGs acting on specific PG receptors within the DA. Collectively, these findings demonstrate the coordinated regulation of fetal and maternal PGs at the time of birth but raise concern regarding the use of selective COX inhibitors for the management of preterm labor.

Complete inhibition of purinoceptor agonist-induced nociception by spinorphin, but not by morphine

We found that spinorphin, a novel neuropeptide showed analgesia in a different manner compared with morphine. By measuring flexor responses induced by the intraplanter injection of substances, the presence of three different types of sensory neurons were demonstrated. Although spinorphin completely blocked 2-metylthioadenosine (2-MeS ATP, a P2X(3) agonist)-induced responses, morphine did not. On the other hand, morphine-induced blockade of bradykinin (BK, a B(2)-receptor agonist)-responses was attenuated by pertussis toxin (PTX) treatment, whereas that of spinorphin was not. Thus it is suggested that spinorphin has a spectrum of analgesia which covers the blockade of nociception insensitive to morphine.

Dysregulation of EGF family of growth factors and COX-2 in the uterus during the preattachment and attachment reactions of the blastocyst with the luminal epithelium correlates with implantation failure in LIF-deficient mice

Various mediators, including cytokines, growth factors, homeotic gene products, and prostaglandins (PGs), participate in the implantation process in an autocrine, paracrine, or juxtacrine manner. However, interactions among these factors that result in successful implantation are not clearly understood. Leukemia inhibitory factor (LIF), a pleiotropic cytokine, was shown to be expressed in uterine glands on day 4 morning before implantation and is critical to this process in mice. However, the mechanism by which LIF executes its effects in implantation remains unknown. Moreover, interactions of LIF with other implantation-specific molecules have not yet been defined. Using normal and delayed implantation models, we herein show that LIF is not only expressed in progesterone (P4)-primed uterine glands before implantation in response to nidatory estrogen, it is also induced in stromal cells surrounding the active blastocyst at the time of the attachment reaction. This suggests that LIF has biphasic effects: first in the preparation of the receptive uterus and subsequently in the attachment reaction. The mechanism by which LIF participates in these events was addressed using LIF-deficient mice. We observed that while uterine cell-specific proliferation, steroid hormone responsiveness, and expression patterns of several genes are normal, specific members of the EGF family of growth factors, such as amphiregulin (Ar), heparin-binding EGF-like growth factor (HB-EGF), and epiregulin, are not expressed in LIF(-/-) uteri before and during the anticipated time of implantation, although EGF receptor family members (erbBs) are expressed correctly. Furthermore, cyclooxygenase-2 (COX-2), an inducible rate-limiting enzyme for PG synthesis and essential for implantation, is aberrantly expressed in the uterus surrounding the blastocyst in LIF(-/-) mice. These results suggest that dysregulation of specific EGF-like growth factors and COX-2 in the uterus contributes, at least partially, to implantation failure in LIF(-/-) mice. Since estrogen is essential for uterine receptivity, LIF induction, and blastocyst activation, it is possible that the nidatory estrogen effects in the P4-primed uterus for implantation are mediated via LIF signaling. However, we observed that LIF can only partially resume implantation in P4-primed, delayed implanting mice in the absence of estrogen, suggesting LIF induction is one of many functions that are executed by estrogen for implantation.