Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:1.13.11.12 (lipoxygenase)
 8,696 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Studying Swiss 3T3 fibroblasts, we report that arachidonic acid strongly stimulates mRNA levels of the growth-associated immediate early genes c-fos and Egr-1. Structurally related compounds like arachidonic acid methyl ester, arachidonyl alcohol, or eicosatetraynoic acid are ineffective, indicating a specific role of free unesterified arachidonic acid or an arachidonic acid metabolite in c-fos and Egr-1 mRNA accumulation. Blocking the conversion of arachidonic acid to prostaglandins by inhibiting cyclooxygenase abolishes arachidonic acid-induced accumulation of c-fos and Egr-1 mRNA. Inhibition of the lipoxygenase or cytochrome P-450 epoxygenase pathways has no significant effect on arachidonic acid-induced c-fos and Egr-1 mRNA levels, indicating that prostaglandin synthesis is necessary for the increase in c-fos and Egr-1 mRNA. Reversed phase high performance liquid chromatography revealed prostaglandin E2 (PGE2) as the major arachidonic acid metabolite in Swiss 3T3 fibroblasts. When added to the cells, PGE2 stimulates c-fos and Egr-1 mRNA levels to the same degree as arachidonic acid. Also, the inhibition of arachidonic acid-stimulated c-fos and Egr-1 mRNA accumulation by indomethacin is reversed by PGE2. Contrary to reports that PGE2 caused an increase in cAMP levels in Swiss 3T3 fibroblasts, we found that arachidonic acid and PGE2 only minimally increase cAMP levels as compared with untreated cells. In contrast, inhibition of protein kinase C by calphostin C and chelerythrine or down-regulation with phorbol 12-myristate 13-acetate drastically reduces PGE2 and arachidonic acid-induced c-fos and Egr-1 mRNA levels. These data indicate that arachidonic acid exerts its stimulatory effect on c-fos and Egr-1 mRNA via synthesis of PGE2 and subsequent activation of protein kinase C, probably through a PGE2 receptor coupled to phospholipase C.
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PMID:Arachidonic acid increases c-fos and Egr-1 mRNA in 3T3 fibroblasts by formation of prostaglandin E2 and activation of protein kinase C. 796 34

The clinical pharmacology of all-trans retinoic acid (RA) has distinct differences from that of its widely studied stereoisomer 13-cis retinoic acid (cRA). RA is much more rapidly cleared from plasma following oral administration; their respective half-lives are < 1 h and 13 h. There is extensive accumulation of the 4-oxo-cRA in plasma following repeated doses of cRA, while 4-oxo-RA is only a minor metabolite in plasma following RA administration. The extent of isomerization in vivo differs for the two retinoids. In contrast to cRA, where up to a 1:3 ratio of RA to cRA is observed in patient plasma following drug administration, cRA concentrations in excess of 10 ng/ml are rarely observed in plasma of patients receiving exogenous RA. RA administration produces autoinduction of its own oxidative catabolism; this effect does not occur with cRA. These pharmacokinetic differences have been observed in leukemia and solid tumor patients. Detailed analysis of the results of the population studied suggest that both constitutive and RA-induced hypercatabolism of RA occurs. Both of these hypercatabolic states can be modulated by concurrent administration of ketoconazole, an inhibitor of cytochrome P-450 and lipoxygenase-mediated oxidations.
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PMID:Clinical pharmacology of all-trans retinoic acid. 796 26

Stimulating rat thyroid FRTL-5 cells with agonists that activate the inositol phosphate cascade results in the release of sequestered calcium and influx of extracellular calcium. In addition, phospholipase A2 (PLA2) is activated. Since PLA2 is a calcium-dependent enzyme we wanted to investigate the interrelationships between PLA2 activity and the entry of calcium. Stimulating 3H-arachidonic acid (3H-AA)-labelled cells with thapsigargin resulted in a substantial release of 3H-AA. This release was totally abolished in a calcium-free buffer. Pretreatment of Fura 2 loaded cells with 4-bromophenacyl bromide, an inhibitor of PLA2 activity, decreased the thapsigargin-induced entry of calcium, suggesting a role for PLA2 in the regulation of calcium entry. In cells treated with nordihydroguaiaretic acid (NDGA), clotramizole, or econazole, compounds with lipoxygenase and cytochrome P-450 inhibitory actions, the thapsigargin-induced entry of calcium was decreased in a dose-dependent manner. However, treatment of the cells with indomethacin, a cyclooxygenase inhibitor, had no effect on the thapsigargin-induced calcium entry. We also showed that stimulation of the cells with arachidonic acid released sequestered calcium, apparently from the same intracellular pool as did thapsigargin. The results suggested that the calcium-induced PLA2 activation and the metabolism of the produced arachidonic acid by a noncyclooxygenase pathway may be of importance in maintaining calcium entry after releasing sequestered Ca2+ in FRTL-5 cells.
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PMID:Thapsigargin-induced calcium entry in FRTL-5 cells: possible dependence on phospholipase A2 activation. 802 Dec 98

Recent reports have shown the occurrence of regiospecific and enantioselective lipoxygenase-mediated metabolism of arachidonic acid (AA) in cytosolic extracts of marine and freshwater hydroids. Here we report that cytosolic extracts of Hydra magnipapillata are unique among hydrozoans for their capability of converting AA into two major metabolites which showed chromatographic, mass spectrometric and nuclear magnetic resonance properties identical to those of 11-R- and 12-S-hydroxyeicosatetraenoic acid (11-R-HETE and 12-S-HETE). The production of neither compound was affected by co-incubation of H. magnipapillata extracts with the cytochrome P-450 inhibitor proadifen. The 5- and 12-lipoxygenase inhibitor nordihydroguaiaretic acid (NDGA), while inhibiting 12-S-HETE formation at high concentrations, did not influence 11-R-HETE production, thus suggesting the co-localisation, unprecedented in hydroids, of two separate enantioselective lipoxygenase-like activities. The possible role of the two metabolites in the control of hydroid body pattern was investigated. At low micromolar concentrations, both enantiomers of 11-HETE inhibited diacylglycerol-induced ectopic head formation (EHF), while 12-S-HETE, and its likely precursor 12-S-hydroperoxy-eicosatetraenoic acid (12-S-HPETE), enhanced bud formation, thus providing the first example of endogenous metabolites controlling, respectively, hydroid 'head activation potential' and asexual reproduction.
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PMID:Enantiospecific synthesis of bioactive hydroxyeicosatetraenoic acids (HETEs) in Hydra magnipapillata. 802 33

The effect of 5,8,11,14-eicosatetraynoic acid (ETYA), an inhibitor of lipoxygenase and cytochrome P-450 epoxygenase enzymes, on calcium fluxes was investigated in Fura 2 loaded rat thyroid FRTL-5 cells. ETYA per se released sequestered calcium. ETYA also inhibited calcium influx in thapsigargin-stimulated cells in dose-dependent manner. Addition of calcium to cells treated with ETYA and stimulated with thapsigargin in a calcium-free buffer resulted in a blunted increase in intracellular free calcium compared with the response in control cells. In addition, ETYA per se acidified the cytosol in a dose-dependent manner. Acidification of the cytosol with the K+/H+ ionophore nigericin also decreased thapsigargin-induced calcium entry, but not to the same extent as that seen in cells treated with ETYA. The results suggest that ETYA is a potent modulator of calcium entry, and that part of the inhibitory effect of ETYA may be due to the ETYA-induced acidification of the cytosol.
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PMID:Effects of 5,8,11,14-eicosatetraynoic acid on thapsigargin-induced calcium entry, and intracellular pH in thyroid FRTL-5 cells. 808 99

Various reports have described that amino acid substitutions can alter substrate, positional, inhibitory, and target gene specificities of proteins. By using the method of Chou and Fasman, the present work predicts that critical amino acids for converting these substrate specificities of trypsin, L-lactate dehydrogenase, aspartate aminotransferase, beta-lactamase, and cytochrome P-450 are found to exist within regions predicted as beta-turns. The ratios of hydroxylation and oxygenation positions of substrates by cytochrome P-450 and lipoxygenase, respectively, are varied by changes of the protein structures, probably around turn conformations. Inhibitory specificities of bovine pancreatic trypsin inhibitor and alpha 1-antitrypsin and target gene specificity of glucocorticoid receptor are converted by changing turn structures. Occurrence of beta-turn probabilities can be predicted around the amino acid alteration positions of an evolutionally antecedent protein of a nylon degradation enzyme. These findings will have relevance to work on protein engineering and enzyme evolution.
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PMID:Critical amino acids responsible for converting specificities of proteins and for enhancing enzyme evolution are located around beta-turn potentials: data-based prediction. 813 29

Stimulating rat thyroid FRTL-5 cells with the purinergic agonist ATP activates both the inositol phosphate signal-transduction pathway and the phospholipase A2 pathway. In the present study we wanted to investigate the possible inter-relationships between these two systems during ATP-induced changes in intracellular free calcium ([Ca2+]i). Pretreatment of Fura-2 loaded cells with 4-bromophenylacyl, an inhibitor of phospholipase A2, had no effect on the ATP-induced entry of Ca2+ but inhibited the release of sequestered Ca2+. Nordihydroguaiaretic acid (NDGA), a lipoxygenase inhibitor, and 5,8,11,14-eicosatetraynoic acid (ETYA), an inhibitor of cytochrome P-450 enzymes, attenuated the ATP-evoked transient increase in [Ca2+]i. Furthermore, the capacitative entry of Ca2+ was also attenuated in NDGA- and ETYA-treated cells stimulated with ATP. Similar results were obtained using econazole, an inhibitor of cytochrome P-450 enzymes. However, treatment of the cells with indomethacin, a cyclooxygenase inhibitor, had no effect on the ATP-evoked response in [Ca2+]i. We also showed that stimulation of intact or permeabilized FRTL-5 cells with arachidonic acid released sequestered calcium. This calcium originated, at least in part, from an IP3 sensitive calcium pool. In addition, arachidonic acid rapidly acidified the cytosol. The results suggest that metabolism of arachidonic acid by a non-cyclooxygenase pathway is of importance in supporting agonist-induced calcium fluxes evoked via stimulation of the inositol phosphate pathway in FRTL-5 cells. Furthermore, arachidonic acid per se may modify agonist-induced calcium fluxes in these cells.
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PMID:Importance of arachidonic acid metabolites in regulating ATP-induced calcium fluxes in thyroid FRTL-5 cells. 814 15

Bradykinin-induced relaxation of precontracted, porcine coronary artery (PCA) rings is mediated by distinctly different endothelium-derived relaxing factors depending on the contractile agent used. Thus when contracted with KCl, bradykinin-induced relaxation of PCA rings is mediated solely by nitric oxide (NO), whereas when contracted with the thromboxane mimetic U46619, a small component of the relaxation is attributable to NO and a large component is attributable to a non-NO mechanism that is independent of cyclooxygenase activity. We hypothesized that the non-NO component was mediated by arachidonic acid (AA) or by a non-cyclooxygenase product of AA metabolism. Bradykinin-induced relaxations of PCA rings precontracted with U46619 in the presence of indomethacin (10 mumol/L) were moderately attenuated by the NO synthase inhibitor N omega-nitro-L-arginine methyl ester (L-NAME, 100 mumol/L), whereas when precontracted with KCl, L-NAME abolished the relaxations. AA produced endothelium-dependent relaxations of rings precontracted with U46619 that were unaffected by L-NAME, whereas AA did not relax rings precontracted with KCl. In rings precontracted with U46619, in the presence of L-NAME and indomethacin the phospholipase inhibitors quinacrine (50 mumol/L) and 4-bromophenacyl bromide (10 mumol/L) attenuated bradykinin- but not AA-induced relaxations. Inhibitors of both lipoxygenase (BW 755c [100 mumol/L] and nafazatrom [20 mumol/L]) and cytochrome P-450 (proadifen [10 mumol/L] and clotrimazole [10 mumol/L]) pathways did not eliminate bradykinin- or AA-induced relaxations, although clotrimazole partially attenuated AA-induced relaxations. These findings suggest that bradykinin-induced relaxation of PCA rings is mediated by AA through a mechanism that is not dependent on cyclooxygenase, lipoxygenase, or cytochrome P-450 pathways.
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PMID:Relaxation of porcine coronary artery to bradykinin. Role of arachidonic acid. 820 38

Recent reports have suggested the involvement of arachidonic acid (AA) and its metabolites in the control of body pattern, head and tentacle regeneration and bud formation in Hydra spp. Here we describe for the first time the biosynthesis of hydroxyeicosatetraenoic acids (HETEs) in vitro by hydroid cytosolic extracts. Incubation of both unlabelled and tritiated AA with homogenates of Hydra vulgaris led to the conversion of up to 11% of the exogenous fatty acid into mainly two metabolites. These were characterized as 11-hydroperoxyeicosatetraenoic acid (11-HPETE) and 11-HETE by means of a combination of chromatographic, chemical, 1H-n.m.r. and electron-impact m.s. techniques. Trace amounts of 9-HETE and 12-HETE were also found. Analysis of 11-HETE by chiral-phase h.p.l.c. revealed that this metabolite was composed mainly of the R enantiomer. The production of 11-HPETE and 11-HETE was found to be: (1) associated with the cytosolic fraction of Hydra homogenates; (2) dependent on AA concentration, incubation time and protein amount in the homogenates; (3) unaffected by co-incubation with the 5- and 12-lipoxygenase inhibitors, 5,8,11-eicosatriynoic acid and nordihydroguaiaretic acid, the cyclo-oxygenase inhibitor, indomethacin, or the cytochrome P-450 inhibitors, proadifen and methoxalen. These results strongly suggest the presence of a very active (R)-11-lipoxygenase in H. vulgaris. The activity of both R and S enantiomers of synthetic 9-, 11- and 12-HETE and of 'endogenous' 11-HETE was studied on tentacle regeneration and bud formation in decapitated Hydra. Although almost all compounds tested inhibited budding, only endogenous 11-HETE and synthetic (R)-11-HETE significantly enhanced the average number of tentacles, thus suggesting that this eicosanoid might be one of the cellular regulators of regeneration in H. vulgaris.
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PMID:Biosynthesis, structure and biological activity of hydroxyeicosatetraenoic acids in Hydra vulgaris. 821 22

We characterized cytochrome P-450-dependent arachidonate (P-450-AA) metabolism throughout the intestinal tract, since some metabolites derived via this pathway modify epithelial ion transport and regional blood flow. Microsomes (0.3 mg/ml) were prepared from each region of the intestines of anesthetized New Zealand White male rabbits and incubated with [14C]AA (7 microM) for 30 min at 37 degrees C. In the presence of NADPH (1 mM), ileal microsomes exhibited the greatest P-450-AA metabolism, whereas duodenal microsomes exhibited little or no activity. For jejunal, ileal, and cecal microsomes, AA metabolism was reduced in the absence of NADPH and by boiling microsomes, was unaffected by indomethacin (10 microM) and BW-755C (50 microM), but was significantly attenuated by the P-450 enzyme inhibitors, 7-ethoxyresorufin (1 microM) and SKF-525A (100 microM). However, colonic (ascending, transverse, and descending) microsomal activity was inhibited by both P-450 and lipoxygenase inhibitors. Analysis of ileal AA metabolites by high-pressure liquid chromatography and negative ion chemical ionization gas chromatography-mass spectrometry revealed products corresponding to monohydroxyeicosatetraenoic acids (HETEs). Semiquantitative analysis showed that 20-, 19-, 18-, 17-, and 16-HETEs were present in a ratio of 6.2:3.3:0.3:0.1:0.1, respectively. Furthermore, ileal P-450-HETEs dilated the isolated perfused mesenteric bed, as did 20-HETE, the predominant ileal AA metabolite. Because 20-HETE was also shown to affect epithelial ion transport, we suggest that P-450-AA metabolites may make important contributions to intestinal function.
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PMID:Characterization of cytochrome P-450-dependent arachidonic acid metabolism in rabbit intestine. 823 57


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