Cyclooxygenase Pathway Of Arachidonic Acid Metabolism Research Articles

Effect of glycine on the cyclooxygenase pathway of the kidney arachidonic acid metabolism in a rat model of metabolic syndrome

The kidneys are organs that can be severely impaired by metabolic syndrome (MS). This is characterized by the association of various pathologies such as hypertension, dyslipidemia, and type-2 diabetes. Glycine, a nonessential amino acid, is known to possess various protective effects in the kidney, such as a decrease in the deterioration of renal function and a reduction of the damage caused by hypoxia. In a rat model of MS, the effect of glycine on the cyclooxygenase (COX) pathway of arachidonic acid (AA) metabolism was studied in isolated perfused kidney. MS was induced in Wistar rats by feeding them a 30% sucrose solution for 16weeks. The addition of 1% glycine to their drinking water containing 30% sucrose, for 8weeks, reduced high blood pressure, triglyceride levels, insulin concentration, homeostatis model assessment (HOMA) index, albuminuria, AA concentration in kidney homogenate, renal perfusion pressure, prostaglandin levels, PLA2 expression, and COX isoform expression, compared with MS rats that did not receive the glycine supplement. Glycine receptor expression decreased significantly with MS, but glycine treatment increased it. The results suggest that in the MS model, 1% glycine treatment protects the kidney from damage provoked by the high sucrose consumption, by acting as an anti-inflammatory on the COX pathway of AA metabolism in kidney.

Actions of general anaesthetics and arachidonic acid pathway inhibitors on K+ currents activated by volatile anaesthetics and FMRFamide in molluscan neurones

1. K+ currents activated by volatile general anaesthetics (IK(An)) and by the neuropeptide FMRFamide (IK(FMRFa)) were studied under voltage clamp in isolated identified neurones from the pond snail Lymnaea stagnalis. 2. IK(An) was activated by all the volatile anaesthetics studied. The maximal responses varied from agent to agent, with halothane sevoflurane > isoflurane > enflurane approximately chloroform. 3. IK(An) was inhibited rather than activated by the n-alcohols from hexanol to dodecanol and by the 6- and 8-carbon cycloalcohols. The n-alcohols exhibited a cutoff effect, with dodecanol being unable to half-inhibit IK(An). 4. Unlike IK(An) which did not desensitize at reasonable halothane concentrations, IK(FMRFa) desensitized at most FMRFamide concentrations studied. This desensitization could be substantially removed by halothane. Nonetheless, both IK(An) and IK(FMRFa) had similar sensitivities to the potassium channel blockers tetraethylammonium and 4-aminopyridine, consistent with both currents flowing through the same channels. Responses to low concentrations of halothane and FMRFamide showed synergy. 5. The phospholipase A2 inhibitor aristolochic acid inhibited IK(An), consistent with a role for arachidonic acid (AA). The lipoxygenase and cyclooxygenase inhibitor nordihydroguaiaretic acid blocked IK(FMRFa) but did not affect IK(An). IK(An) and IK(FMRFa) were little affected by the cyclooxygenase inhibitor indomethacin. These findings suggest that neither lipoxygenase nor cyclooxygenase pathways of AA metabolism are involved in the anaesthetic activation of IK(An. 6. Inhibitors of a third, cytochrome P450-mediated, pathway of AA metabolism (clotrimazole and econazole) potently blocked IK(An), suggesting possible roles for certain cytochrome P450 isoforms in the activation of IK(An).

Inhibition by fatty acids of cyclic AMP‐dependent protein kinase activity in brush border membranes isolated from human placental vesicles

1. The inhibitory effects of arachidonic acid (AA) and a number of structurally related fatty acids on cyclic AMP-dependent protein kinase activity have been investigated in brush border membranes (BBM) prepared from human placental vesicles. 2. BBM vesicles were characterized by electron microscopy and displayed enrichment of the appropriate marker enzymes, alkaline phosphatase and gamma-glutamyltranspeptidase; BBM were prepared by vesicles lysis in hypotonic medium. 3. Cyclic AMP-dependent protein kinase (PKA) activity was measured in BBM. At 1 microM, cyclic AMP stimulated a 4.2 +/- 0.06 fold increase over basal levels of [32P]-phosphate incorporation into the synthetic substrate kemptide and this effect was abolished by a selective PKA inhibitor. By use of synergistic pairs of site-selective cyclic AMP analogues, the kinase was identified as the type II enzyme. 4. Cyclic AMP-stimulated PKA activity was inhibited by 10 microM AA and this effect was significantly enhanced by nordihydroguaiaretic acid (NDGA) + indomethacin (Indo), inhibitors of the lipoxygenase and cyclo-oxygenase pathways of AA metabolism respectively. 5. Oleic acid, elaidic acid, but not caprylic or palmitic acids, also significantly inhibited PKA activity and this effect was again enhanced by NDGA + Indo. While arachidonyl alcohol alone was not inhibitory, in the presence of the metabolic inhibitors a significant reduction in stimulated activity was observed. 6. The commercially available PKA type II holoenzyme (activated by cyclic AMP), but not the free catalytic subunit, was inhibitable by AA, oleic or elaidic acids. 7. These results suggest that PKA localized to the brush border membrane of human placental vesicles is inhibited by fatty acids which may compete with cyclic AMP for binding to the kinase regulatory subunit. The reported inhibition by fatty acids of cyclic AMP-dependent Cl- secretion in epithelial cells may therefore be due in part to negative regulation of a Cl- channel-associated PKA.

Analysis of Relaxin Release by Cultured Porcine Luteal Cells Using a Reverse Hemolytic Plaque Assay: Effects of Arachidonic Acid, Cyclo- and Lipooxygenase Blockers, Phospholipase A2, and Melittin*

The effect of the obligatory precursor of prostaglandin biosynthesis, arachidonic acid, on the release of relaxin by porcine luteal cells was examined by use of a reverse hemolytic plaque assay. In this assay, luteal cells were cocultured in monolayers with protein-A-coupled ovine erythrocytes. In the presence of porcine relaxin antiserum and complement, a zone of hemolysis, a plaque, developed around relaxin-releasing luteal cells, identified as large luteal cells (LLCs). The rate of development of plaques in time-course studies and the area of plaques were then used as an index of the rate of relaxin release and cumulative amount of hormone released, respectively. Incubation of collagenase-dispersed luteal cells derived from early pregnant pigs with 0.1-100 microM arachidonic acid (AA) resulted in dose-dependent increases in the rate of plaque formation. Despite AA stimulation, however, only 55-65% of all LLCs formed plaques during the experimental incubation period (up to 12 h). Minimally and maximally effective doses were about 1 and 10 microM, respectively. In the presence of 10 microM AA, maximal plaque formation occurred significantly faster (1-2 h) than in controls (4-8 h; P less than 0.05). The percentage of plaque-forming cells (plaque-forming LLCs) was, likewise, significantly greater in 10 microM AA-treated monolayers than in controls during the first 3-4 h of incubation. Similarly, agents that liberate endogenous AA (phospholipase A2 and melittin) also stimulated relaxin release. The stimulatory effect of AA (10 microM) on relaxin release was almost wholly blocked by a cyclooxygenase inhibitor (ibuprofen; 20 microM); but not by a lipooxygenase inhibitor (nordihydroguaretic acid; 20 microM). However, the same dose of ibuprofen (20 microM) failed to modulate the stimulatory effect of prostaglandin E2 (1 microM) or phorbol diester (4 beta-phorbol 12 beta-myristate 13 alpha-acetate; 50 nM) on the rate of relaxin release. These results indicate that a product(s) of the cyclooxygenase pathway of AA metabolism participates in the control of relaxin release, but that this metabolite(s) is not essential to the biological action of at least one stimulatory secretagogue. Moreover, this metabolite failed to influence a subpopulation of nonresponsive LLCs. These data taken in association with our previous demonstration that the pathways of both calcium mobilization and protein kinase-C activation are implicated in the regulation of relaxin release, are consistent with the view that AA liberation may amplify the actions of other signalling mechanisms.

Perfused and ventilated guinea-pig lung: a method for evaluating xenobiotic effects on arachidonic acid using formaldehyde.

Lipoxygenase as well as cyclooxygenase pathways of arachidonic acid (AA) metabolism are involved in antigen-induced bronchoconstriction in ovalbumin-sensitized guinea-pig lungs. Chemical lung challenge induced by aerosol containing formaldehyde (5 ppm up to 20 ppm) was effective in increasing thromboxane (TX) B2 release in a dose-dependent manner, without affecting leukotriene (LT) release. This suggests that xenobiotics acting by non-immunologic mechanisms on bronchial mucosa may stimulate the cyclooxygenase pathway of AA metabolism, which, in turn, might cause bronchial and/or lung parenchymal effects of pathophysiological relevance.

Effects of Arachidonic Acid and Its Metabolites on Antigen-Induced Histamine Release from Human Basophils in Vitro

Abstract We have studied the role of arachidonic acid (AA) metabolism in immediate hypersensitivity reactions. The AA analog, eicosa-5,8,11,14-tetraynoic acid (ETYA), which inhibits both the cyclo-oxygenase and lipoxygenase pathways of AA metabolism, was found to cause a dose-dependent inhibition of antigen-induced histamine release from human basophils; complete inhibition occurred at 10-4 M. In contrast, nonsteroidal anti-inflammatory drugs (NSAID) including indomethacin (10-9 to 10-6 M), meclofenamic acid (10-6 to 10-4 M), and aspirin (10-5 to 10-3 M), which block the cyclo-oxygenase pathway of AA metabolism, enhanced mediator release. AA (10-7 to 10-5 M) also enhanced basophil mediator release, an effect that was not affected by preincubation with indomethacin. Other fatty acids including linoleic, linolenic, and stearic acids were without effect. Indomethacin (and the other NSAID studied) reversed the inhibition caused by the AA metabolite, prostaglandin (PG) E2, in a dose-dependent fashion. This reversal of inhibition was not unique to PG, but was observed with all inhibitors of histamine release studied that act via activation of adenylate cyclase including isoproterenol and the H2 agonist, dimaprit. NSAID, however, did not reverse the inhibition caused by drugs that do not act on adenylate cyclase, i.e., dibutyryl cAMP, isobutylmethylxanthine, and 2-deoxyglucose. In the leukocyte preparations studied, the NSAID did not block the increase in the intracellular cAMP levels caused by agonists that act via adenylate cyclase. It appears that a product(s) of AA metabolism, generated via the lipoxygenase pathway, is involved in IgE-mediated histamine release and that the same or a different product(s) modulates the control mechanisms that are linked to adenylate cyclase.