Stereochemistry and biosynthesis of lipoxins.
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Humans↗
Biomedical subjects
S E Webber
Publications and source records attributed to S E Webber.
Lipoxin A. Stereochemistry and biosynthesis.
Lipoxin A (LXA) was prepared by incubation of either (15S)-15-hydroxy-5,8,11-cis-13-trans-eicosatetraenoic acid (15-HETE) or (15S)-15-hydroperoxy-5,8,11-cis-13-trans-eicosatetraenoic (15-HPETE) with human leukocytes stimulated by either the ionophore A23187 or the chemotactic peptide fMet-Leu-Phe. Comparison with four trihydroxyeicosatetraenoic acids prepared by total synthesis showed that biologically derived LXA is 5S,6R,15S)-5,6,15-trihydroxy-7,9,13-trans-11-cis-eicosatetraenoic acid. Three isomers of LXA were also identified in extracts of leukocytes utilizing an improved isolation procedure. These were (5S,6S,15S)-5,6,15-trihydroxy-7,9,13-trans-11-cis-eicosatetraenoic acid (6S-LXA), (5S,6R,15S)-5,6,15-trihydroxy-7,9,11,13-trans-eicosatetraenoic acid (11-trans-LXA), and (5S,6S,15S)-5,6,15-trihydroxy-7,9,11,13-trans-eicosatetraenoic acid (6S-11-trans-LXA). 18O2-labeling studies indicated that formation of LXA and its isomers occurred with incorporation of 18O at their C-5 but not C-6 positions. These results suggest that 15-hydroxy-5,6-epoxy-7,9,13-trans-11-cis-eicosatetraenoic acid or its equivalent may serve as one intermediate in the biosynthesis of LXA and 6S-LXA. When added to guinea pig lung strips LXA provoked contractions which were slow in onset and long lasting. In addition, dose response studies showed that biologically derived LXA and synthetic LXA were indistinguishable in this bioassay whereas synthetic 6S-LXA and biologically derived 6S-LXA did not share this activity. Taken together, these results suggest that activated leukocytes utilize exogenous 15-HETE to generate lipoxins which in turn can modulate cellular responses.
Calcimycin↗
Evidence for a 5(6)-epoxytetraene intermediate in the biosynthesis of lipoxins in human leukocytes. Conversion into lipoxin A by cytosolic epoxide hydrolase.
The existence of a 15(S)-hydroxy-5,6-oxido-7,9,13-trans-11-cis-eicosatetraenoic acid intermediate in the biosynthesis of lipoxins A and B has recently been proposed. In the present study, human leukocytes were exposed to 15-HETE and the divalent cation ionophore A23187 and alcohol trapping studies were performed. The products containing alkyltetraenes were isolated and characterized. HPLC analysis, UV spectroscopy and GC/MS of the products showed that 5,15-dihydroxy-14-O-alkyleicosatetraenoic acids were formed, indicating that 5(6)-epoxytetraenes (precursor of the trapping product) were formed in human leukocytes. To gain further evidence for the role of 5(6)-epoxytetraene intermediate in the biosynthesis of lipoxins, (15)-hydroxy-5,6-oxido-7,9,13-trans-11-cis-eicosatetraenoic acid was prepared by total chemical synthesis. When added to purified human liver cytosolic epoxide hydrolase, the epoxide was rapidly and quantitatively converted into LXA. The results provide further evidence for the role of a 5(6)epoxytetraene intermediate in the biosynthesis of lipoxins.
Arachidonic Acids↗
Some studies of the action of betahistine at H1 and H2 receptors for histamine.
Betahistine produced a concentration-dependent contraction of the guinea-pig ileum and was about 27 times less active than histamine in this respect. Betahistine induced desensitization of contractile responses to histamine in the guinea-pig ileum. The H1 histamine receptor antagonist mepyramine was a competitive antagonist of the action of betahistine on the guinea-pig ileum. Betahistine caused relaxation of the rat uterus contracted by acetylcholine, and this action of betahistine was blocked by the H2 receptor antagonist cimetidine. Betahistine had a concentration-dependent positive chronotropic action on isolated guinea-pig atria, and in this respect was tenfold less potent than histamine. The action of betahistine on the atria was blocked by the H2 receptor antagonist YM11170. Betahistine caused a concentration-related contraction of the isolated lung parenchymal strip of the guinea-pig, and YM11170 potentiated this effect. Betahistine failed to release histamine from rat peritoneal mast cells at concentrations up to 100 microM and it did not prevent histamine release induced by either substance P or anti-IgE. Betahistine produced a dose-related flare and wheal reaction when injected intradermally into human skin. It is concluded that betahistine has agonist activity at both H1 and H2 receptors for histamine.
Animals↗
Coronary vasoactivity of four 7,13-bridged analogs of arachidonic acid.
Four newly synthesized 7,13-bridged arachidonic acid analogs which have been shown to exert 5-lipoxygenase inhibitory activity were studied in isolated perfused cat coronary arteries. The two dehydro analogs constricted and the two non-dehydro analogs dilated the coronary arteries. None antagonized LTD4 induced constriction. Thus there is no direct connection between lipoxygenase inhibition and leukotriene inhibition or vasoactivity.
Animals↗
A study of the H2-receptor for histamine stimulating adenylate cyclase in homogenates of guinea-pig lung parenchyma.
The effect of forskolin and several H2-agonists was investigated on the activity of adenylate cyclase in homogenates of guinea-pig lung parenchyma. Histamine, 0.1 microM to 1 mM, dimaprit, 1 microM to 10 mM, 4-methyl histamine, 0.1 microM to 10 mM, impromidine, 10 nM to 10 microM and forskolin, 1 nM to 100 microM, all produced a dose-dependent stimulation of adenylate cyclase activity above the basal level. The histamine H1-receptor antagonist mepyramine, 10 microM, and beta-adrenoceptor antagonist propranolol, 10 microM, had no effect on the stimulation by histamine of adenylate cyclase. The dose-response curve for stimulation by histamine of adenylate cyclase was shifted to the right in a dose-dependent manner by increasing concentrations of several H2-antagonists. Schild plots constructed for each H2-antagonist produced straight lines with slopes not significantly different from unity. The equilibrium dissociation constants obtained for the H2-antagonists in this study were similar to those previously reported for inhibition of dimaprit-induced relaxation of the pre-contracted lung strip, inhibition of [3H]-tiotidine binding to homogenates of guinea-pig lung parenchyma and inhibition of histamine-stimulated adenylate cyclase in guinea-pig gastric mucosa.
Adenylyl Cyclases↗
A study of the histamine H2-receptor mediating relaxation of the parenchymal lung strip preparation of the guinea-pig.
The relaxation produced by several H2-receptor agonists and forskolin was investigated on strips of guinea-pig lung parenchyma. Dimparit, 1 microM to 10 mM, 4-methyl histamine, 0.5 microM to 100 microM and impromidine, 10 nM to 1 microM, had no effect on the tone of the unstimulated strips of lung parenchyma but caused a dose-dependent relaxation of strips that were contracted by 2-pyridylethylamine (2-PEA), 15 microM. Forskolin, 10 nM to 4 microM, produced a dose-dependent relaxation of both the stimulated and unstimulated lung strips. The muscarinic antagonist atropine, 1 microM, and the beta 2-adrenoceptor antagonist propranolol, 10 microM, had no effect on the dose-response curve for dimaprit-induced relaxation of the lung strip. The dose-response curve for dimaprit was shifted to the right in a dose-dependent manner by increasing concentrations of a variety of H2-antagonists. Schild plots produced a straight line for all the H2-antagonists with slopes not significantly different from unity. The equilibrium dissociation constants for the H2-antagonists on the lung strip preparation were similar to those previously reported for inhibition of the chronotropic activity of histamine on guinea-pig right atria and inhibition of [3H]-tiotidine binding to homogenates of guinea-pig lung parenchyma.
Animals↗
The binding of [3H]-tiotidine to homogenates of guinea-pig lung parenchyma.
By use of a rapid filtration assay, the binding of [3H]-tiotidine to homogenates of guinea-pig lung parenchyma was found to be saturable and of a high affinity. Mean values for the KD and Bmax were calculated as 8.5 +/- 1.5 nM and 28 +/- 5 fmol mg-1 protein respectively. The association and dissociation rate constants for [3H]-tiotidine binding at 4 degrees C were calculated to be 0.81 +/- 0.06 microM min-1 and 0.063 +/- 0.005 min-1 respectively, yielding a kinetically derived KD of 7.8 nM. A wide range of H2-receptor agonist and antagonists displaced [3H]-tiotidine binding from lung parenchyma homogenates in a biphasic manner. Examination of the first phase of the displacement of [3H]-tiotidine yielded Ki values for the antagonists tested similar to those found in other binding studies using this ligand and similar to KB values calculated for the antagonists in pharmacological studies.
Animals↗
Contraction of guinea-pig lung parenchymal strips by substance P and related peptides.
A dose-response relationship for substance P and contraction of the lung parenchyma strip of the guinea-pig could only be obtained in the presence of a mixture of bacitracin, 1,4 dithio-L-threitol and ethylenediamine tetracetic acid, all at 100 microM, or in the presence of captopril, 1.8 mM. Substance P (50 nM) caused no contraction by itself but produced a shift to the left of the dose-response curve for histamine with a mean dose-ratio of 1.4 +/- 0.2 (S.E. of mean). The peptides physalaemin, eledoisin and kassinin were all approximately equipotent with substance P on the lung strip, in the presence of peptides inhibitors. [D-Pro4, D-Trp7,9,10]-SP4-11, produced dose-related inhibition of the contraction induced by substance P. Substance P activity in guinea-pig lung declined exponentially with a half-time of 2.3 min: bacitracin, dithiothreitol and EDTA (all 100 microM) increased this to 7.2 min and captopril (1.8 mM) to 5.1 min.
Animals↗
The effect of substance P and related peptides on the guinea-pig lung strip.
Substance P is present in sensory nerves in the lung and we report here its actions on the lung strip. Substance P was shown to produce rapid, small contractions of trhe lung strip at doses from 10(-9) to 10(-5) M, and there was no apparent dose-response relationship. In the presence of a mixture of three inhibitors of substance P breakdown: bacitracin, 1,4-dithio-L- threitol and ethylenediaminetetra-acetic acid all at 10(-4) M, the responses to substance P were greatly increased and dose-response curves could be established. The concentrations producing half maximal effect in the presence of these inhibitors were 6 X 10(-6) M +/- 4 X 10(-6) M. The inhibitors of substance P breakdown were found to have no effect on the histamine dose-response curve: any small shifts obtained were not significant. Chlorpheniramine 10(-6) M and 10(-5) M shifted the histamine dose-response curve to the right producing dose ratios of 100 and 900 respectively. At these doses chlorpheniramine had no effect on the dose-response curve to substance P. A dose of substance P not itself producing a response (5 X 10(-8) M) caused an increase in the size of the responses to histamine. The histamine dose-response curve was shifted to the left in the presence of substance P producing an average dose ratio of 1.4 +/- 0.2. In the presence of the peptidase inhibitors, dose-response curves have also been produced for physalaemin (10(-7) - 10(-5) M) and eledoisin (10(-7) - 10(-5) M).
Animals↗
Nonadrenergic, noncholinergic control of mucus secretion in the airways.
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Animals↗