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Arachidonic Acid Release (arachidonic + acid_release)
Selected AbstractsDifferential effects of arachidonoyl trifluoromethyl ketone on arachidonic acid release and lipid mediator biosynthesis by human neutrophilsFEBS JOURNAL, Issue 15 2002Evidence for different arachidonate pools The goal of this study was to determine the effects of a putative specific cytosolic phospholipase A2 inhibitor, arachidonyl trifluoromethyl ketone (AACOCF3), on arachidonic acid (AA) release and lipid mediator biosynthesis by ionophore-stimulated human neutrophils. Initial studies indicated that AACOCF3 at concentrations 0,10 µm did not affect AA release from neutrophils. In contrast, AACOCF3 potently inhibited leukotriene B4 formation by ionophore-stimulated neutrophils (IC50 , 2.5 µm). Likewise, AACOCF3 significantly inhibited the biosynthesis of platelet activating factor. In cell-free assay systems, 10 µm AACOCF3 inhibited 5-lipoxygenase and CoA-independent transacylase activities. [3H]AA labeling studies indicated thatthe specific activities of cell-associated AA mimicked that of leukotriene B4 and PtdCho/PtdIns, while the specific activities of AA released into the supernatant fluid closely mimicked that of PtdEtn. Taken together, these data argue for the existence of segregated pools of arachidonate in human neutrophils. One pool of AA is linked to lipid mediator biosynthesis while another pool provides free AA that is released from cells. Additionally, the data suggest that AACOCF3 is also an inhibitor of CoA-independent transacylase and 5-lipoxygenase. Thus, caution should be exercised in using AACOCF3 as an inhibitor of cytosolic phospholipase A2 in whole cell assays because of the complexity of AA metabolism. [source] Lead-dependent effects on arachidonic acid accumulation and the proliferation of vascular smooth muscleJOURNAL OF BIOCHEMICAL AND MOLECULAR TOXICOLOGY, Issue 5 2002Robert V. Dorman Abstract Lead (Pb2+) has been implicated in the development of hypertension and atherosclerosis. The proliferation of vascular smooth muscle cells (VSMC) is a central feature of both conditions and there is evidence that Pb2+ potentiates serum-dependent cell growth. The aim of this work was to examine the role of phospholipase A2 in mitogen-dependent VSMC proliferation and determine if Pb2+ interacts with this system in order to potentiate mitotic events. It was observed that cell proliferation induced by angiotensin II, or fetal bovine serum, required the activation of a Ca2+ -dependent cytosolic phospholipase A2 and the subsequent release of unesterified arachidonic acid. This path was affected by Pb2+ as the metal increased the amount of arachidonic acid accumulation induced by either mitogen. In addition, Pb2+ potentiated mitogen-induced DNA synthesis when present at lower doses (0.02 or 0.2 mg%), but had no effect on DNA synthesis, or cell numbers, in unstimulated cells. However, a high dose (2 mg%) of Pb2+ attenuated the DNA synthesis stimulated by angiotensin II, or serum, but induced the accumulation of unesterified arachidonic acid in unstimulated cells. A biphasic effect of Pb2+ on cell numbers and viability was also observed as 0.02 or 0.2 mg% Pb2+ did not affect cell numbers or trypan blue exclusion in unstimulated cells, while 2 mg% Pb2+ reduced cell numbers and viability. It appeared, therefore, that the lower concentrations of Pb2+ increased arachidonic acid release and DNA synthesis only in stimulated VSMC, perhaps due to further activation of a Ca2+ -dependent processes. In contrast, the high dose of Pb2+ reduced DNA synthesis in stimulated cells and reduced cell numbers and viability in unstimulated cells, which may relate to the noted increase in unesterified arachidonic acid. © 2002 Wiley Periodicals, Inc. J Biochem Mol Toxicol 16:245,253, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jbt.10045 [source] Altered arachidonic acid biosynthesis and antioxidant protection mechanisms in Schwann cells grown in elevated glucoseJOURNAL OF NEUROCHEMISTRY, Issue 6 2002Cristinel Mîinea Abstract In cultured Schwann cells, elevated glucose induces alterations in arachidonic acid metabolism that cause a decrease in the content of glycerophospholipid arachidonoyl-containing molecular species (ACMS). This could result from decreased de novo arachidonic acid biosynthesis, or increased arachidonic acid release from phospholipids. Incorporation of radioactive 8,11,14-eicosatrienoic acid into ACMS was lower for cells grown in 30 mm versus 5 mm glucose, consistent with a decrease in ,5 desaturase activity. However, neither basal arachidonic acid release from prelabeled cells nor stimulated generation of arachidonic acid in the presence of the reacylation inhibitor, thimerosal, the phosphotyrosine phosphatase inhibitor, bipyridyl peroxovanadium, or both together, were altered by varying the glucose concentrations, indicating that arachidonic acid turnover did not contribute to ACMS depletion. Free cytosolic NAD+/NADH decreased, whereas NADP+/NADPH remained unchanged for cells grown in elevated glucose, implying that decreased desaturase activity is a result of metabolic changes other than cofactor availability. Schwann cells in elevated glucose were susceptible to oxidative stress, as shown by increased malondialdehyde, depleted glutathione levels, and reduced cytosolic superoxide dismutase activity. Glutathione-altering compounds had no effect on ACMS levels, in contrast to N -acetylcysteine and ,-lipoic acid, which partly corrected ACMS depletion in phosphatidylcholine. These findings suggest that in the Schwann cell cultures, a high glucose level elicits oxidative stress and weakens antioxidant protection mechanisms which could decrease arachidonic acid biosynthesis and that this deficit can be partly corrected by treatment with exogenous antioxidants. [source] Lipid signaling changes in smooth muscle remodeling associated with partial urinary bladder outlet obstructionNEUROUROLOGY AND URODYNAMICS, Issue 2 2006Edward LaBelle Abstract Aims Hypertrophy of the urinary bladder smooth muscle (detrusor) is associated with partial bladder outlet obstruction (PBOO). Hypertrophied detrusor smooth muscle (DSM) reveals altered contractile characteristics. In this study, we analyzed the lipid-dependent signaling system that includes phospholipase A2 in PBOO-induced DSM remodeling and hypertrophy to determine whether the release of arachidonic acid (AA) from phospholipid is altered in the detrusor. Methods Partial bladder outlet obstruction (PBOO) was produced by partial ligation of the urethra in New Zealand white rabbits. Two weeks after the surgery, the bladder function was studied by keeping the rabbits in metabolic cages for 24 hr. Bladders were removed from rabbits that had bladder dysfunction (increased urinary frequency and decreased void volume) and the DSM separated from mucosa and serosa. The isolated smooth muscle was incubated with [3H] AA to equilibrate the cytoplasmic AA. The level of AA release was compared with the level obtained with 2-week sham-operated rabbits. Results The rate of AA release was high in DSM from bladders with PBOO-induced hypertrophy. Carbachol stimulated AA release in control DSM but DSM from obstructed rabbits revealed no further increase from the elevated basal AA release. The half-maximal concentration of carbachol that was required to stimulate AA release from control samples of detrusor was 35 µM. Conclusions The increased levels of AA release that are observed in this tissue after PBOO indicate the activation of phospholipase A2. The finding that carbachol could induce contraction, but not an increase in AA, indicates that the carbachol-induced contraction in the obstructed bladders is independent of lipid signaling pathways that involve AA. It is possible that the increased rate of arachidonic acid release from obstructed bladders correlates with the enhanced rates of prostaglandin production reported by other investigators from the same tissue. Neurourol. Urodynam. © 2006 Wiley-Liss, Inc. [source] Histamine H3 -receptor-mediated [35S]GTP,[S] binding: evidence for constitutive activity of the recombinant and native rat and human H3 receptorsBRITISH JOURNAL OF PHARMACOLOGY, Issue 2 2002A Rouleau Constitutive activity of the recombinant and native rat and human H3 receptors (H3Rs) was studied using H3R-mediated [35S]GTP,[S] binding and [3H]-arachidonic acid release. Ciproxifan, an inverse agonist at the rat H3R (rH3R), decreased [3H]arachidonic acid release from CHO cells expressing moderate densities (,200,300 fmol mg,1 protein) of the human H3R (hH3R). This effect occurred with the same magnitude than at the rH3R. The expression of the hH3R was associated with an increase in [35S]GTP,[S] binding to membranes of CHO cells. Ciproxifan decreased [35S]GTP,[S] binding to membranes of CHO (hH3R) cells. Both effects were correlated to receptor density and revealed that constitutive activity of the hH3R, although lower than that of the rH3R in this assay, was again observed at physiological densities (<500 fmol mg,1 protein). Ciproxifan was less potent at the human than the rat receptor, not only as an antagonist (Ki=45 nM), but also as an inverse agonist (EC50=15 nM). Constitutive activity of the hH3R was also evidenced using inhibition of [35S]GTP,[S] binding by unlabelled GTP,S. The expression of the hH3R generated a high affinity binding for GTP,S which was increased by imetit, but partially decreased by ciproxifan, therefore acting as a partial inverse agonist. [35S]GTP,[S] binding to rat brain membranes was decreased in several regions by thioperamide, ciproxifan and FUB 465, three inverse agonists at the H3R, whose effects were blocked by proxyfan, a neutral antagonist. [35S]GTP,[S] binding was also decreased by an A1 -adenosine receptor inverse agonist, but remained unchanged in the presence of inverse agonists at D2/D3 dopamine, H1 and H2 histamine, ,2 -adrenergic and , opioid receptors. In conclusion, the present study shows that the recombinant rat and human H3 receptors expressed at physiological densities display constitutive activity and suggests that constitutive activity of native H3Rs is one of the highest among G-protein-coupled receptors present in rat brain. British Journal of Pharmacology (2002) 135, 383,392; doi:10.1038/sj.bjp.0704490 [source] Inhibition by troglitazone of the antigen-induced production of leukotrienes in immunoglobulin E-sensitized RBL-2H3 cellsBRITISH JOURNAL OF PHARMACOLOGY, Issue 2 2000Masamichi Yamashita The effect of troglitazone, an anti-diabetic drug with insulin-sensitizing action, on antigen-induced production of leukotriene (LT) B4, C4 and E4 and prostaglandin D2 (PGD2) was examined in dinitrophenol (DNP)-specific immunoglobulin E (IgE)-sensitized RBL-2H3 mast cells following stimulation by the antigen, DNP-conjugated human serum albumin. Levels of LTB4, C4 and E4 and PGD2 in the conditioned medium were enzyme-immunoassayed. Troglitazone inhibited the antigen-induced production of LTB4, C4 and E4 and the potency of the inhibition was comparable to that of zileuton, a specific inhibitor of 5-lipoxygenase (5-LOX) and a clinically used anti-asthmatic drug. Neither troglitazone nor zileuton affected antigen-induced production of PGD2, arachidonic acid release from membrane phospholipids and degranulation. Troglitazone inhibited LTB4 production by the supernatant fraction of RBL-2H3 cell lysate with similar potency to zileuton, suggesting that troglitazone inhibits LT production by direct inhibition of 5-LOX activity. Furthermore, it was shown that troglitazone as well as zileuton inhibited LTB4 production in A23187-stimulated rat peritoneal neutrophils. These findings suggest that troglitazone inhibits antigen-induced LT production in the IgE-sensitized RBL-2H3 cells and A23187-stimulated rat peritoneal neutrophils by direct inhibition of 5-LOX activity. British Journal of Pharmacology (2000) 129, 367,373; doi:10.1038/sj.bjp.0703044 [source] Short-period hypoxia increases mouse embryonic stem cell proliferation through cooperation of arachidonic acid and PI3K/Akt signalling pathwaysCELL PROLIFERATION, Issue 2 2008S. H. Lee Hypoxia plays important roles in some early stages of mammalian embryonic development and in various physiological functions. This study examined the effect of arachidonic acid on short-period hypoxia-induced regulation of G1 phase cell-cycle progression and inter-relationships among possible signalling molecules in mouse embryonic stem cells. Hypoxia increased the level of hypoxia-inducible factor-1, (HIF-1,) expression and H2O2 generation in a time-dependent manner. In addition, hypoxia increased the levels of cell-cycle regulatory proteins (cyclin D1, cyclin E, cyclin-dependent kinase 2 (CDK2) and CDK4). Maximum increases in the level of these proteins and retinoblastoma phosphorylation were observed after 12,24 h of exposure to hypoxic conditions, and then decreased. Alternatively, the level of the CDK inhibitors, p21Cip1 and p27Kip1 were decreased. These results were consistent with the results of [3H]-thymidine incorporation and cell counting. Hypoxia also increased the level of [3H]-arachidonic acid release and inhibition of cPLA2 reduced hypoxia-induced increase in levels of the cell-cycle regulatory proteins and [3H]-thymidine incorporation. The level of cyclooxygenase-2 (COX-2) was also increased by hypoxia and inhibition of COX-2 decreased the levels of cell-cycle regulatory proteins and [3H]-thymidine incorporation. Indeed, the percentage of cells in S phase, levels of cell cycle regulatory proteins, and [3H]-thymidine incorporation were further increased in hypoxic conditions with arachidonic acid treatment compared to normoxic conditions. Hypoxia-induced Akt and mitogen-activated protein kinase (MAPK) phosphorylation was inhibited by vitamin C (antioxidant, 10,3 M). In addition, hypoxia-induced increase of cell-cycle regulatory protein expression and [3H]-thymidine incorporation were attenuated by LY294002 (PI3K inhibitor, 10,6 M), Akt inhibitor (10,6 M), rapamycin (mTOR inhibitor, 10,9 M), PD98059 (p44/42 inhibitor, 10,5 M), and SB203580 (p38 MAPK inhibitor, 10,6 M). Furthermore, hypoxia-induced increase of [3H]-arachidonic acid release was blocked by PD98059 or SB203580, but not by LY294002 or Akt inhibitor. In conclusion, arachidonic acid up-regulates short time-period hypoxia-induced G1 phase cyclins D1 and E, and CDK 2 and 4, in mouse embryonic stem cells through the cooperation of PI3K/Akt/mTOR, MAPK and cPLA2 -mediated signal pathways. [source] | ||||||||||||||||