Evidence of a cyclooxygenase-related prostaglandin synthesis in coral. The allene oxide pathway is not involved in prostaglandin biosynthesis.
(17/3278)
Certain corals are rich natural sources of prostaglandins, the metabolic origin of which has remained undefined. By analogy with the lipoxygenase/allene oxide synthase pathway to jasmonic acid in plants, the presence of (8R)-lipoxygenase and allene oxide synthase in the coral Plexaura homomalla suggested a potential metabolic route to prostaglandins (Brash, A. R., Baertshi, S. W., Ingram, C.D., and Harris, T. M. (1987) J. Biol. Chem. 262, 15829-15839). Other evidence, from the Arctic coral Gersemia fruticosa, has indicated a cyclooxygenase intermediate in the biosynthesis (Varvas, K., Koljak, R., Jarving, I., Pehk, T., and Samel, N. (1994) Tetrahedron Lett. 35, 8267-8270). In the present study, active preparations of G. fruticosa have been used to identify both types of arachidonic acid metabolism and specific inhibitors were used to establish the enzyme type involved in the prostaglandin biosynthesis. The synthesis of prostaglandins and (11R)-hydroxyeicosatetraenoic acid was inhibited by mammalian cyclooxygenase inhibitors (indomethacin, aspirin, and tolfenamic acid), while the formation of the products of the 8-lipoxygenase/allene oxide pathway was not affected or was increased. The specific cyclooxygenase-2 inhibitor, nimesulide, did not inhibit the synthesis of prostaglandins in coral. We conclude that coral uses two parallel routes for the initial oxidation of polyenoic acids: the cyclooxygenase route, which leads to optically active prostaglandins, and the lipoxygenase/allene oxide synthase metabolism, the role of which remains to be established. An enzyme related to mammalian cyclooxygenases is the key to prostaglandin synthesis in coral. Based on our inhibitor data, the catalytic site of this evolutionary early cyclooxygenase appears to differ significantly from both known mammalian cyclooxygenases. (+info)
Expression of cyclo-oxygenase types-1 and -2 in human fetal membranes throughout pregnancy.
(18/3278)
Human labour is associated with increased prostaglandin synthesis within the fetal membranes. We have studied the expression of the two isoforms of the central prostaglandin synthetic enzyme, cyclo-oxygenase (COX-1 and COX-2), in human fetal membranes throughout pregnancy, at mRNA, protein and activity levels. COX-1 mRNA expression was low in human amnion and chorion-decidua and did not change with gestational age. COX-2 mRNA expression in fetal membranes increased with gestational age, with significant up-regulation prior to the onset of labour and in association with labour. Protein concentrations of COX-1 did not change, whilst concentrations of COX-2 increased from the first to the third trimester. COX activity increased with gestational age and in association with labour, although prostaglandin production in fetal membranes collected after labour was reduced, suggesting reduced substrate supply. These data suggest that it is up-regulation of COX-2, rather than of COX-1, which mediates increased prostaglandin synthesis within the fetal membranes at term. Much of the increase in COX-2 expression precedes the onset of labour, suggesting that it is a cause, rather than a consequence, of labour. (+info)
Aspects of the involvement of interleukin-1 and nitric oxide in the pathogenesis of insulin-dependent diabetes mellitus.
(19/3278)
The possible involvement of the cytokine interleukin-1 (IL-1) and nitric oxide (NO) in the pathogenesis of insulin-dependent diabetes mellitus (IDDM) is reviewed and current and potential therapies are discussed. IDDM is a common disorder in the Western world and it is rising in incidence. In IDDM, islet-infiltrating macrophages produce IL-1 which is cytotoxic specifically to beta-cells in vitro. IL-1 increases beta-cell formation of NO, ceramide, prostaglandins, heat-shock proteins, and activates a protease. Additionally, IL-1 depresses beta-cell energy production, insulin gene expression and cyclic AMP synthesis, and impacts negatively on different parts of the insulin stimulus-secretion coupling, actions mimicked by NO. Conversely, blocking NO formation prevented many of these effects in most reports published. Also, changes in cyclic AMP and prostaglandins seem unlikely events in mediating the cytotoxicity of IL-1, while the role of ceramide remains less clear. Peptides capable of blocking beta-cell IL-1 receptors, and agents blocking NO synthesis may prove valuable in preserving beta-cell function in IDDM. Although IDDM causes immense morbidity and expense, uniformly effective preventive or beta-cell protective therapy is not currently available. If IL-1 is causing beta-cell dysfunction in human IDDM through NO production, several processes in the IL-1-NO connection are appropriate targets for agents protecting beta-cells from destruction and functional inhibition in IDDM. (+info)
Limited anti-inflammatory efficacy of cyclo-oxygenase-2 inhibition in carrageenan-airpouch inflammation.
(20/3278)
1. Cyclo-oxygenase-2 (COX-2) is expressed at sites of inflammation and is believed to be the major source of inflammation-associated prostaglandin synthesis. Selective inhibition of COX-2 has been suggested to produce anti-inflammatory effects with reduced toxicity in the gastrointestinal tract. We examined the extent to which suppression of COX-2 led to inhibition of various components of inflammation in the carrageenan-airpouch model in the rat. 2. Indomethacin (> or =0.3 mg kg(-1)), nimesulide (> or =3 mg kg(-1)) and the selective COX-2 inhibitor, SC-58125 (> or =0.3 mg kg(-1)), significantly suppressed the production of prostaglandin E2 at the site of inflammation. At higher doses, indomethacin (> or =1 mg kg(-1)) and nimesulide (30 mg kg(-1)), but not SC-58125 (up to 10 mg kg(-1)), significantly inhibited COX-1 activity (as measured by whole blood thromboxane synthesis). 3. All three test drugs significantly reduced the volume of exudate in the airpouch, but only at doses greater than those required for substantial (>90%) suppression of COX-2 activity. Similarly, reduction of leukocyte infiltration was only observed with the doses of indomethacin and nimesulide that caused significant suppression of COX-1 activity. 4. SC-58125 did not significantly affect leukocyte infiltration into the airpouch at any dose tested (up to 10 mg kg(-1)). A second selective COX-2 inhibitor, Dup-697, was also found to suppress exudate PGE2 levels without significant effects on leukocyte infiltration. 5. These results indicate that selective inhibition of COX-2 results in profound suppression of PGE2 synthesis in the carrageenan-airpouch, but does not affect leukocyte infiltration. Exudate volume was only reduced with the highly selective COX-2 inhibitor when a dose far above that necessary for suppression of COX-2 activity was used. Inhibition of leukocyte infiltration was observed with indomethacin and nimesulide, but only at doses that inhibited both COX-1 and COX-2. (+info)
Pro- and anti-inflammatory actions of thrombin: a distinct role for proteinase-activated receptor-1 (PAR1).
(21/3278)
1. Thrombin has well characterized pro-inflammatory actions that have recently been suggested to occur via activation of its receptor, proteinase-activated receptor-1 (PAR1). 2. In the present study, we have compared the effects of thrombin to those of two peptides that selectively activate the PAR1 receptor, in a rat hindpaw oedema model. We have also examined whether or not thrombin can exert anti-inflammatory activity in this model. 3. Both thrombin and the two PAR1 activating peptides induced significant oedema in the rat hindpaw following subplantar injection. 4. The oedema induced by thrombin was abolished by pre-incubation with hirudin, and was markedly reduced in rats in which mast cells were depleted through treatment with compound 48/80 and in rats pretreated with indomethacin. In contrast, administration of the PAR1 activating peptides produced an oedema response that was not reduced by indomethacin and was only slightly reduced in rats pretreated with compound 48/80. 5. Co-administration of thrombin together with a PAR1 activating receptor resulted in a significantly smaller oedema response than that seen with the PAR1 activating peptide alone. This anti-inflammatory effect of thrombin was abolished by pre-incubation with hirudin. 6. These results demonstrate that the pro-inflammatory effects of thrombin occur through a mast-cell dependent mechanism that is, at least in part, independent of activation of the PAR1 receptor. Moreover, thrombin is able to exert anti-inflammatory effects that are also unrelated to the activation of PAR1. (+info)
Regulation of delayed prostaglandin production in activated P388D1 macrophages by group IV cytosolic and group V secretory phospholipase A2s.
(22/3278)
Group V secretory phospholipase A2 (sPLA2) rather than Group IIA sPLA2 is involved in short term, immediate arachidonic acid mobilization and prostaglandin E2 (PGE2) production in the macrophage-like cell line P388D1. When a new clone of these cells, P388D1/MAB, selected on the basis of high responsivity to lipopolysaccharide plus platelet-activating factor, was studied, delayed PGE2 production (6-24 h) in response to lipopolysaccharide alone occurred in parallel with the induction of Group V sPLA2 and cyclooxygenase-2 (COX-2). No changes in the level of cytosolic phospholipase A2 (cPLA2) or COX-1 were observed, and Group IIA sPLA2 was not detectable. Use of a potent and selective sPLA2 inhibitor, 3-(3-acetamide 1-benzyl-2-ethylindolyl-5-oxy)propanesulfonic acid (LY311727), and an antisense oligonucleotide specific for Group V sPLA2 revealed that delayed PGE2 was largely dependent on the induction of Group V sPLA2. Also, COX-2, not COX-1, was found to mediate delayed PGE2 production because the response was completely blocked by the specific COX-2 inhibitor NS-398. Delayed PGE2 production and Group V sPLA2 expression were also found to be blunted by the inhibitor methylarachidonyl fluorophosphonate. Because inhibition of Ca2+-independent PLA2 by an antisense technique did not have any effect on the arachidonic acid release, the data using methylarachidonyl fluorophosphonate suggest a key role for the cPLA2 in the response as well. Collectively, the results suggest a model whereby cPLA2 activation regulates Group V sPLA2 expression, which in turn is responsible for delayed PGE2 production via COX-2. (+info)
Prostaglandin endoperoxide-dependent vasospasm in bovine coronary arteries after nitration of prostacyclin synthase.
(23/3278)
In the present study we used a bioassay to study the effects of peroxynitrite (ONOO-) on angiotensin II (A-II)-triggered tension in isolated bovine coronary arteries in order to show the consequences of the previously reported PGI2-synthase inhibition by ONOO- in this model. The following results were obtained: 1. 1 micromol L(-1) ONOO- impaired A-II-induced vasorelaxation and caused a second long lasting constriction phase. Indomethacin (10(-5)M) prevented both effects. U51605, a dual blocker of PGI2-synthase and thromboxane (TX)A2-synthase mimicked the effects of ONOO-. 2. The selective TXA2/prostaglandin endoperoxide (PGH2) receptor antagonist SQ29548 antagonized the second vasoconstriction phase after ONOO- -treatment. Since a generation of TXA2 and 8-iso-prostaglandin F2alpha could be excluded a direct action of unmetabolized PGH2 on the TXA2/PGH2 receptor was postulated. 3. ONOO- dose-dependently inhibited the conversion of 14C-PGH2 into 6-keto-PGF1alpha in isolated bovine coronary arteries with an IC50-value of 100 nM. 4. Immunoprecipitation of 3-nitrotyrosine-containing proteins with a monoclonal antibody revealed PGI2-synthase as the only nitrated protein in bovine coronary arteries treated with 1 micromol 1(-1) ONOO-. 5. Using immunohistochemistry a co-localization of PGI2-synthase and nitrotyrosine-containing proteins was clearly visible in both endothelial and vascular smooth muscle cells. We concluded that ONOO- not only eliminated the vasodilatory, growth-inhibiting, antithrombotic and antiadhesive effects of PGI2 but also allowed and promoted an action of the potent vasoconstrictor, prothrombotic agent, growth promoter, and leukocyte adherer, PGH2. (+info)
In vitro prostanoid release from spinal cord following peripheral inflammation: effects of substance P, NMDA and capsaicin.
(24/3278)
1. Spinal prostanoids are implicated in the development of thermal hyperalgesia after peripheral injury, but the specific prostanoid species that are involved are presently unknown. The current study used an in vitro spinal superfusion model to investigate the effect of substance P (SP), N-methyl-d-aspartate (NMDA), and capsaicin on multiple prostanoid release from dorsal spinal cord of naive rats as well as rats that underwent peripheral injury and inflammation (knee joint kaolin/carrageenan). 2. In naive rat spinal cords, PGE2 and 6-keto-PGF1alpha, but not TxB2, levels were increased after inclusion of SP, NMDA, or capsaicin in the perfusion medium. 3. Basal PGE2 levels from spinal cords of animals that underwent 5-72 h of peripheral inflammation were elevated relative to age-matched naive cohorts. The time course of this increase in basal PGE2 levels coincided with peripheral inflammation, as assessed by knee joint circumference. Basal 6-keto-PGF1alpha levels were not elevated after injury. 4. From this inflammation-evoked increase in basal PGE2 levels, SP and capsaicin significantly increased spinal PGE2 release in a dose-dependent fashion. Capsaicin-evoked increases were blocked dose-dependently by inclusion of S(+) ibuprofen in the capsaicin-containing perfusate. 5. These data suggest a role for spinal PGE2 and NK-1 receptor activation in the development of hyperalgesia after injury and demonstrate that this relationship is upregulated in response to peripheral tissue injury and inflammation. (+info)