leukotriene-e4 and arachidonic-acid-5-hydroperoxide

The family of eicasanoids, biologically active metabolites of polyunsaturated C20 fatty acids such as arachidonic acid, has recently been enlarged by the recognition of a new biosynthetic pathway leading to the leukotrienes, including the compounds described two decades ago as 'slow reacting substances'. These biologically potent substances are involved in regulation of the immune response and also as mediators in various disease states. This account presents a brief history of this field, an overview of the biological relevance of leukotrienes, and a discussion of the investigations which led to the clarification of the molecular structures, pathway of biosynthesis and total chemical synthesis of the leukotrienes, including leukotrienes A, B, C, D and E (LTA-LTE). As a result of the synthetic work these rare substances are available for the first time in pure form and in quantities sufficient for biological and medical studies. Also reviewed are recent discoveries with regard to the development of inhibitors of leukotriene biosynthesis and anti-leukotrienes.

Topics: Animals; Arachidonic Acids; Asthma; Autacoids; Chemical Phenomena; Chemistry; Humans; Hydroxyeicosatetraenoic Acids; Hypersensitivity; Leukotriene A4; Leukotriene B4; Leukotriene E4; Leukotrienes; Lipoxygenase Inhibitors; Macrophages; Mast Cells; Molecular Conformation; Neutrophils; SRS-A; Stereoisomerism; Structure-Activity Relationship

The aim of this work was to study the effect of high concentrations of leukotrienes on luteinizing hormone (LH) secretion in rat anterior pituitary cells. We also investigated the effect of leukotrienes in parallel with gonadotropin-releasing hormone (GnRH) action. Experiments were on cells gained from trypsinized pituitaries of female rats. Tests were performed by superfusion of the cells attached to cytodex-1 carrier beads. The LH content in samples of perfusate was estimated by radioimmunoassay. This work reports 48% inhibition of basic LH release by action of leukotriene C4 in superfused cells when applied continuously at a concentration of 100 nmol/l. Moreover, we have shown that leukotrienes suppressed GnRH-induced LH secretion in rat pituitary cells when applied in parallel to GnRH (1 nmol/l) as a 4-min pulse at a concentration of 0.1 nmol/l. GnRH-induced LH release was reduced to 66% of its value by leukotriene (LT) B4 (0.1 nmol/l) action; also to 54% by LTC4, 66% by LTD4 and 74% by LTE4 action. In contrast, arachidonic acid (50 pmol/l) and its other 5-lipoxygenase metabolites: 5-hydroperoxyeicosatetraenoic acid (5-HPETE) (50 pmol/l), or 5-hydroxyeicosatetraenoic acid (5-HETE) (50 pmol/l), had no inhibitory effect on GnRH-induced LH release. Arachidonic acid and 5-HETE potentiated GnRH-induced LH release up to 249% and 429%, respectively, when applied in parallel with GnRH (1 nmol/l) as a 4-min pulse at a concentration of 10 pmol/l. In our earlier work we have shown that several leukotrienes are potent stimulants of LH release. The present report documents the finding that the 5-lipoxygenase pathway is also involved in the inhibitory regulation of hormone release in anterior pituitary cells.

Topics: Animals; Arachidonic Acid; Cells, Cultured; Female; Gonadotropin-Releasing Hormone; Hydroxyeicosatetraenoic Acids; Leukotriene B4; Leukotriene C4; Leukotriene D4; Leukotriene E4; Leukotrienes; Luteinizing Hormone; Perfusion; Pituitary Gland, Anterior; Rats; Rats, Sprague-Dawley; Time Factors

Omega-oxidation of leukotrienes is the initial step of hepatic degradation and thus inactivation of these proinflammatory mediators. Omega-oxidation is followed by beta-oxidation of leukotrienes from the omega-end. After exposure of rats to a single dose of the anesthetic agent halothane, a transient decrease in leukotriene omega-oxidation was induced both in vivo and in vitro. In untreated rats, 44.1 +/- 6.0% of N-[3H]acetylleukotriene E4 injected intravenously was recovered unchanged in bile collected for 60 min in vivo; 46.5 +/- 3.0% was recovered as omega-/beta-oxidation products, of which 24.7 +/- 4.5% were associated with beta-oxidation products only (mean +/- SEM; n = 5). In rats receiving a single dose of halothane 18 h before the experiment, recovery of unchanged N-[3H]acetylleukotriene E4 was significantly increased to 79.8 +/- 4.8%, while the fraction of omega-/beta-oxidation products decreased to 9.0 +/- 1.7% (n = 5); 90 h after exposure to halothane, N-[3H]acetylleukotriene E4 recovery decreased to 30.0 +/- 3.0% and omega-/beta-oxidation products amounted to 49.1 +/- 3.8%; the fraction of beta-oxidation products was significantly increased to 43.1 +/- 3.4% (n = 5). Ten days after exposure of rats to halothane, the recoveries of N-[3H]acetylleukotriene E4, of omega-/beta-oxidation products, and of beta-oxidation products alone, returned to almost normal values. Microsomal fractions obtained from rat hepatocytes catalyzed the NADPH- and O2-dependent leukotriene omega-oxidation in vitro. The formation of omega-hydroxy-metabolites of leukotriene B4, leukotriene E4, and N-acetylleukotriene E4 was decreased by 50% in microsomal fractions obtained from rats 18 h and 90 h after halothane treatment, and returned back to control levels in microsomal fractions obtained 10 days after halothane treatment. The Km value of leukotriene B4 omega-oxidation revealed no significant change in enzyme affinity towards leukotriene B4; in contrast, as reflected by the reduction of the Vmax value by 65%, a decrease in the amount of the active enzyme in microsomes obtained from rats 18 h after halothane treatment was observed. Halothane-metabolism-dependent trifluoroacetylation of hepatic proteins may mediate this process. Thus, the time course of the density on immunoblots of trifluoroacetylated protein adducts paralleled that of the transient decrease in leukotriene omega-oxidation. In contrast to its omega-oxidation, leukotriene B4 synthesis from 5-hydroperoxyeicosa

Topics: Animals; Cytochrome P-450 Enzyme System; Halothane; Isoenzymes; Kinetics; Leukotriene B4; Leukotriene E4; Leukotrienes; Liver; Male; Microsomes, Liver; Oxidation-Reduction; Rats; Rats, Inbred Strains; SRS-A; Trifluoroacetic Acid