Journal of lipid mediators最新文献

The pathophysiologic role of thromboxane and of arachidonate 5-lipoxygenation products in mediating changes in glomerular filtration rate (GFR) and renal blood flow (RBF) was investigated in a rat model of mesangial cell immune injury induced by a monoclonal antibody (ER4) directed against the mesangial cell membrane antigen, Thy 1. Following a single intravenous dose of the ER4 antibody acute decrements in GFR and RBF occurred at 1 h and were associated with enhanced glomerular leukocyte infiltration and synthesis of thromboxane A2, 12-HETE and LTB4. Pretreatment of animals with the thromboxane synthase inhibitor, Furegrelate, or the thromboxane receptor antagonist SQ-29,548 ameliorated or completely abolished the decrements in GFR and RBF without reducing glomerular leukocyte infiltration. Pretreatment with the arachidonate 5-lipoxygenase inhibitor MK-886 partially ameliorated the decrements in GFR and RBF, reduced the glomerular leukocyte infiltration and completely inhibited the glomerular LTB4 synthesis. Combined treatment with Furegrelate and MK-886 completely abolished the decrements in GFR and RBF as well as the glomerular synthesis of thromboxane, LTB4 and 12-HETE without altering glomerular leukocyte infiltration. These observations indicate that in mesangial cell immune injury thromboxane A2 and arachidonate 5-lipoxygenation products originating from infiltrating inflammatory cells mediate the decrements in GFR and RBF. Selective inhibition of these eicosanoids could be of benefit in clinical forms of mesangial nephritis.

Reaction of ovine PGH synthase with arachidonic acid or hydroperoxides produces several tyrosine radical species that can be distinguished by electron paramagnetic resonance (EPR) spectroscopy. We have correlated the temporal sequence of the EPR signals with optical changes of the heme center, and with product formation. The synthase was reconstituted with either heme (Fe-PGHS) or Mn protoporphyrin IX (Mn-PGHS). Incubation of Fe-PGHS with equimolar arachidonate resulted in rapid appearance of a wide doublet tyrosyl radical EPR signal (34 G peak-to-trough); the intensity was near maximal by 7 s. The doublet gave way over the next 10 s to a wide singlet (32 G peak-to-trough) which peaked at 46 s and then decayed slowly. Electronic absorbance spectra indicated that formation of peroxidase Compound I was complete within 1 s; accumulation of peroxidase Compound II paralleled accumulation of the wide doublet tyrosyl radical. PGG2 and PGH2 accumulated rapidly during the first 5 s of reaction; little arachidonate remained after 12 s. The tyrosyl radical giving the wide doublet EPR signal is thus the best candidate for the oxidizing species postulated to abstract the 13S hydrogen atom from arachidonate during cyclooxygenase catalysis by Fe-PGHS. Incubation of Mn-PGHS with arachidonate also led to rapid generation of an oxidized peroxidase cycle intermediate, a protein-linked free radical, and prostaglandins. The radical signal seen with Mn-PGHS (singlet, 36 G peak-to-trough) was distinct from those observed with Fe-PGHS, but the kinetics of the Mn-PGHS radical were consistent with participation in cyclooxygenase catalysis.

Structure and activity relationships of (methoxyalkyl)thiazole and 4-methoxytetrahydropyran series of 5-lipoxygenase inhibitors are reviewed. One member of the 4-methoxytetrahydropyran series, 6-([fluoro-5-(4-methoxy-3,4,5,6-tetrahydro-2H-pyran-4-yl)phenoxy]methyl) -1- methylquinol-2-one (ICI D2138), is undergoing clinical evaluation.

Seizures promote PLA2 activation which is selectively detectable in isolated synaptosomes by an increased free arachidonic acid (AA) and docosahexaenoic acid (DHA) pool size. During long-term potentiation, a role of AA and its oxygenated metabolites has been explored in several laboratories. We have studied another PLA2 product, platelet-activating factor (PAF, 1-O-alkyl-2-acetyl-glycerophosphocholine) that is also generated during intense synaptic activity such as seizures. We found specific PAF binding sites in both synaptic and intracellular membranes. Using rat postnatal hippocampal synaptic pairs we have shown that PAF specifically increases the release of excitatory neurotransmitter. This effect is elicited through the synaptic binding site since an antagonist selective for this site blocks the PAF-mediated increase in excitatory neurotransmitter release. Although PAF augments evoked excitatory synaptic currents, it does not alter GABA-mediated inhibitory currents. PAF increases the frequency but not the amplitude of spontaneous excitatory synaptic minis. At present it is not known if the phospholipase A2 that accumulates free polyunsaturated fatty acids is the same as the one that gives rise to PAF. This lipid mediator effect on excitatory synaptic transmission may be a critical step in long term potentiation, synaptic plasticity, memory formation and epileptogenesis.

Recent studies have shown that, in Chinese hamster ovary cells transfected with D2-receptor cDNA, CHO(D2) cells, D2 agonists are potent in enhancing the release of [3H]arachidonic acid (AA) induced by stimulation of constitutive purinergic receptors or by application of Ca2+ ionophores. This facilitatory action is further amplified by the concomitant activation of D1 receptors, which per se have no effect on evoked [3H]AA release. Here, we review a series of experiments aimed at examining the molecular mechanism of this synergistic interaction. The results show that, in CHO(D2) cells: (a) application of 8-Br-cAMP or stimulation of constitutive prostaglandin (PG)E2 receptors augment the AA response produced by D2 agonists; (b) in CHO(D2) cells transfected with human beta 2-receptor cDNA, the beta-agonist, isoproterenol, produces a similar effect; (c) the potentiation of [3H]AA release produced by PGE2 and 8-Br-cAMP is prevented by overexpressing either a protein inhibitor of cAMP-dependent protein kinase (PKA) or a mutated form of pKA regulatory subunit incapable of binding cAMP; (d) mock-synergism is obtained in CHO(D2) cells overexpressing the catalytic subunit of PKA; (e) PGE2 is a major AA metabolite in stimulated CHO(D2) cells and its formation may contribute to the effect of D2 agonists on AA release. The results indicate that cAMP-induced activation of PKA represents a likely molecular basis for D1/D2 receptor synergism on AA release. They also suggest that additional membrane receptors, colocalized with D2 and positively linked to adenylyl cyclase, may exert a similar action. Furthermore, stimulation of PGE2 receptors by endogenously produced prostaglandin may participate in AA signaling at the D2 receptor, by providing a paracrine positive feedback loop.

Prostaglandin (PG) D2 and PGE2 receptor binding activities are regulated in various fashions. The protein phosphorylation by exogenous cAMP-dependent protein kinase or calmodulin-dependent protein kinase II significantly increased PGE2 binding activity through an increase in the apparent amount of the maximal binding, suggesting that the PGE2 receptor may be regulated through protein phosphorylation-dephosphorylation. Other possible regulatory mechanisms were found as the result of studies on functional modification of glycoconjugates. Pretreatment with glycoprotein-specific endoglycosidases (peptide N-glycohydrolase F, endo-alpha-N-acetylgalactosaminidase) decreased both PGD2 and PGE2 receptor binding activities and consequently these activities became nonspecific ones. In addition, these binding activities were increased by the addition of a ganglioside or cerebroside mixture, but not ceramide. The addition of separate purified glycolipids showed more specifically their effect on each PG binding. PGD2 binding activity was increased by GD1a and GQ1b and decreased by GM1 and GT1a, while PGE2 binding activity was increased by GQ1b and galactocerebroside. In such a way, PG receptors may require some specific microenvironment for their maximal binding activity.

The enantiomer BAY X1005 [(R)-2-[4-(quinolin-2-yl-methoxy)phenyl]-2-cyclopentyl acetic acid] potently inhibits LTB4 synthesis in isolated PMNL of various species (IC50 mumol/l, human 0.22, rat 0.026, mouse 0.039) and LTC4 synthesis in mouse macrophages (IC50 0.021 mumol/l). Due to high protein binding the in vitro potency for LTB4 synthesis inhibition in whole blood is lowered to 17 mumol/l as determined by RIA. BAY X1005 is selective for the 5-lipoxygenase pathway leaving 12-HETE and HHT unaltered, as determined in human whole blood. After oral application BAY X1005 inhibits edema formation and myeloperoxidase activity in the arachidonate-induced mouse ear inflammation test (ED50 48.7 and 7.9, respectively). Oral activity in the rat ex vivo is found in whole blood for LTB4 synthesis inhibition (ED50 11.8 mg/kg p.o.). BAY X1005 demonstrates a high bioavailability (f 86%) with a Cmax of 13 mg/l and t1/2 of 3.5 h in the rat at 10 mg/kg p.o. Thus, the pharmacodynamic, pharmacokinetic profile and safety aspects of the leukotriene synthesis inhibitor BAY X1005 allow testing in man for its therapeutic potential in inflammatory and allergic diseases.

Prostacyclin and nitric oxide (NO) are two labile vasorelaxant and anti-aggregatory substances which are released by receptor activation and in response to shear forces acting on endothelial cells, whereas the potent constrictor peptide, endothelin-1 (ET-1) is probably slowly released and exerts long-term control over the cardiovascular system. This review deals with the synthesis, release and pharmacological actions of prostacyclin, NO and ET-1, as well as the diseases which might result from their under- or over-production.