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Biomedical subjects

E Sigal

Publications and source records attributed to E Sigal.

50 records · Page 3Linked to original sources
PubMed1990

Colocalization of 15-lipoxygenase mRNA and protein with epitopes of oxidized low density lipoprotein in macrophage-rich areas of atherosclerotic lesions.

Oxidation of low density lipoprotein (LDL) enhances its atherogenicity, and inhibition of such oxidation decreases the rate of progression of atherosclerotic lesions. The mechanism of LDL oxidation in vivo remains uncertain, but in vitro studies have suggested that cellular lipoxygenases may play a role by initiating lipid peroxidation in LDL. In situ hybridization studies using a 15-lipoxygenase riboprobe and immunostaining using antibodies against 15-lipoxygenase showed strongly positive reactivity largely confined to macrophage-rich areas of atherosclerotic lesions. Polymerase chain reaction with 15-lipoxygenase-specific oligonucleotides and restriction enzyme digestions of the amplified fragment were used to confirm the presence of 15-lipoxygenase message in the reverse-transcribed lesion mRNA. Immunostaining with antibodies reactive with oxidized LDL (but not with native LDL) indicated that the lipoxygenase colocalizes with epitopes of oxidized LDL, compatible with a role for macrophage lipoxygenase in the oxidation of LDL in vivo. Since oxidized LDL is chemotactic for blood monocytes, early lesions might progress at a markedly accelerated rate because of further recruitment of more monocytes which, in turn, would increase further the rate of oxidation of LDL. These data suggest that therapy targeted to block macrophage lipoxygenase activity might decrease the rate of development of atherosclerotic lesions.

Animals↗
PubMed1990

The expression of active human reticulocyte 15-lipoxygenase in bacteria.

A cloned cDNA that encodes human reticulocyte 15-lipoxygenase was characterized by Northern blot analysis and heterologous expression in bacteria. The 2.7 kb cDNA specifically hybridizes to reticulocyte RNA from anemic rabbits. The RNA levels correlate with the appearance of enzymatic activity in anemia. The cDNA was subcloned into an inducible bacterial expression vector in frame with the amino terminal ten amino acids of beta-galactosidase (pUCLOX). The soluble fraction of the cell lysate of E. coli transformed with pUCLOX contained a protein that has the same catalytic and antigenic characteristics as reticulocyte 15-lipoxygenase.

Anemia↗
PubMed1989

Cloning and expression of human arachidonate 15-lipoxygenase.

Because of the predominance of 15-lipoxygenase activity in airway epithelium and because of the known biological activities of 15-lipoxygenase metabolites, we have initiated detailed studies of this enzyme. The enzyme was isolated to homogeneity from eosinophil-enriched leukocytes. Using oligonucleotide probes, we isolated a full-length cDNA encoding 15-lipoxygenase from a human reticulocyte cDNA library. The clone is immunologically related to leukocyte 15-lipoxygenase and has been expressed in mammalian cells. Demonstration of active catalytic function is further proof of the authenticity of the isolated clone. The predicted amino acid structure shares significant sequence similarity with other lipoxygenases in certain regions. This extends our earlier observation that the lipoxygenases form a family of enzymes. Furthermore, the conservation of amino acid residues in select regions suggests a role in enzymatic activity. The availability of a clone for 15-lipoxygenase should prove useful in studying the structure and function of the enzyme, the regulation of 15-lipoxygenase gene expression, and the comparison of 15-lipoxygenases from various cells and tissues.

Amino Acid Sequence↗
PubMed1988

Molecular cloning and primary structure of human 15-lipoxygenase.

A full-length cDNA encoding 15-lipoxygenase has been isolated from a human reticulocyte cDNA library. The predicted primary structure of the enzyme exhibits a sequence similarity of 61% and 45% with human 5-lipoxygenase and the soybean lipoxygenase isoenzyme I, respectively. When all three lipoxygenases are aligned, there are two distinct regions of significant sequence identity including a cluster of five histidine residues conserved in all three lipoxygenases. Because histidines can serve as ligands for the enzymatically active iron, this region may be critical to enzymatic function. These results provide a basis for exploring functional domains of lipoxygenases.

Amino Acid Sequence↗
PubMed1988

Inhibition of human leukocyte 5-lipoxygenase by 15-HPETE and related eicosanoids.

The inhibition of human leukocyte 5-lipoxygenase by 15-hydroperoxyeicosatetraenoic acid and its chemical or enzymatic rearrangement products was investigated. 15-Hydroperoxyeicosatetraenoic acid was the most potent inhibitor tested. The inhibition was found to be time dependent and is not due to chemical or enzymatic decomposition products nor metabolism of 15-hydroperoxyeicosatetraenoic acid to 5,15-dihydroperoxyeicosatetraenoic acid.

Arachidonate Lipoxygenases↗
PubMed1988

Arachidonate 15-lipoxygenase (omega-6 lipoxygenase) from human leukocytes. Purification and structural homology to other mammalian lipoxygenases.

The enzyme responsible for 15-lipoxygenation of arachidonic acid was purified to homogeneity from human eosinophil-enriched leukocytes using a combination of ammonium sulfate precipitation, hydrophobic interaction chromatography, and high pressure liquid chromatography on hydroxyapatite and cation-exchange columns. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the purified protein revealed a single major band (apparent Mr 70,000). Amino acid sequence analysis yielded a single N-terminal sequence. Comparison of the N-terminal 15 residues reveals 71% sequence identity to the rabbit reticulocyte lipoxygenase and 36% sequence identity to the rat basophilic leukemia 5-lipoxygenase. In contrast, sequence identity to the soybean lipoxygenase-1 is not observed. These results demonstrate that human 15-lipoxygenase can be isolated from eosinophil-enriched leukocytes and is accessible for direct sequence analysis. Furthermore, we present initial evidence that the mammalian lipoxygenases constitute an homologous family of enzymes. The availability of homogeneous human 15-lipoxygenase will play a key role in elucidating other relationships in this family of enzymes.

Amino Acid Sequence↗
PubMed1988

Arachidonate 15-lipoxygenase from human eosinophil-enriched leukocytes: partial purification and properties.

Arachidonate 15-lipoxygenase was purified from human eosinophil-enriched leukocytes after showing that 15-lipoxygenase activity was 100-fold greater in eosinophils than in neutrophils. Partial purification was achieved using ammonium sulfate precipitation, cation-exchange and hydrophobic-interaction chromatography. New evidence is presented suggesting that 15-lipoxygenase has electrostatic and hydrophobic properties distinct from 5-lipoxygenase. In addition, ATP is shown to inhibit, and phosphatidylcholine is shown to stimulate, 15-lipoxygenase, suggesting a regulatory role for these compounds in the lipoxygenation of arachidonic acid.

Adenosine Triphosphate↗
PubMed1988

An in vivo chemotaxis assay in the dog trachea: evidence for chemotactic activity of 8,15-diHETE.

We describe a new in vivo chemotaxis assay in the dog trachea using a double-balloon endotracheal catheter. When inflated, the two balloons isolate a segment of trachea, which is perfused through Silastic tubes using a peristaltic pump. After instilling a chemotactic agent, the perfusate is sampled periodically to permit characterization of the chemotactic response. We anesthetized four mongrel dogs and ventilated them mechanically through the double-balloon catheter. Two mediators, leukotriene B4 (LTB4) and 8S,15S-dihydroxyeicosatetraenoic acid (8,15-diHETE) were tested in each dog by perfusing the trachea with each mediator in Hanks' balanced salt solution (HBSS) containing ethanol and antibiotics. Aliquots were removed for differential cell counts at fixed time intervals over a 4-h period. Control experiments performed in each dog with the identical concentrations of ethanol and antibiotics in HBSS showed no cellular response before 180 min. At 240 min, the cell counts were 86 +/- 28 (SE) granulocytes/microliter (n = 4). In contrast, both LTB4 and 8,15-diHETE gave a significant cellular response at 120 min (309 +/- 125 and 141 +/- 41 granulocytes/microliter, respectively; P less than 0.05) but did not differ significantly from each other. These results suggest that both LTB4 and 8,15-diHETE can incite inflammatory responses in the dog trachea in vivo. Furthermore, the double-balloon catheter technique promises to be a useful in vivo chemotaxis assay.

Animals↗
PubMed1988

Arachidonic acid 15-lipoxygenase and airway epithelium. Biologic effects and enzyme purification.

Pulmonary epithelial cells may be primarily responsible for initiating or regulating inflammatory responses in the airways, in part by releasing chemical mediators. Among the most potent mediators of inflammation are the lipoxygenase metabolites of arachidonic acid, including the leukotrienes and the other mono- and dihydroxyeicosatetraenoic acids (HETEs). The human airway epithelium contains significant 15-lipoxygenase activity. Although some biologic functions of 15-lipoxygenase metabolites are known, further understanding of the role of this enzyme in the airway requires localization in tissue and studies of expression, regulation, and biologic activity. Towards these aims, we purified and characterized 15-lipoxygenase from eosinophil-enriched leukocytes. First, we studied cofactors that may be involved in regulating enzymatic activity. We discovered that calcium and phosphatidylcholine both enhanced, but ATP inhibited, the 15-lipoxygenase activity of highly enriched enzyme. Second, we isolated to homeogeneity, for the first time, human 15-lipoxygenase. This led to the determination of the N-terminal amino acid sequence and the discovery of homology among various mammalian lipoxygenases. Further research using purified lipoxygenase is expected to increase our understanding of the biologic roles and biochemical features of 15-lipoxygenation of arachidonic acid.

Arachidonate 15-Lipoxygenase↗
PubMed1984

Marked hepatic congestion caused by a thoracoabdominal aneurysm.

A 70-yr-old man with a large thoracoabdominal aortic aneurysm developed marked congestive hepatomegaly. Evaluation by arteriography, venography, and computed tomography revealed compression and venous obstruction at the confluence of the hepatic veins and inferior vena cava. Although obstruction of the inferior vena cava caused by rupture of an abdominal aortic aneurysm is known to occur, obstruction without rupture and involving the hepatic veins has not been previously reported.

Aged↗
PubMedDate not supplied

Human 15-lipoxygenase: induction by interleukin-4 and insights into positional specificity.

Arachidonate 15-lipoxygenase (15-lipoxygenase) is a lipid-peroxidizing enzyme associated with specific inflammatory cells seen in asthma and atherosclerosis. In atherosclerosis, 15-lipoxygenase is induced in the macrophages of human and rabbit lesions and has been implicated in foam cell formation. In human lung, 15-lipoxygenase is preferentially expressed in airway epithelial cells and eosinophils. Our studies have focused both on the regulation of expression and on the structure-function relationships of the enzyme. To determine factors that could regulate expression, peripheral blood monocytes were purified and cultured with combinations of 18 factors. Only interleukin-4 (60 pM) induced 15-lipoxygenase mRNA, protein and enzymatic activity. Interferon-gamma (100 pM) inhibited the interleukin-4 dependent induction of 15-lipoxygenase. Results with cultured human airway cells were similar. These data suggest that expression of 15-lipoxygenase is regulated by interleukin-4, and that 15-lipoxygenase is a potential downstream effector molecule for this potent cytokine. In parallel studies, we have investigated determinants of positional specificity using site-directed mutagenesis and bacterial expression of human 15-lipoxygenase. Hypotheses for mutagenesis were derived from an analysis of conserved differences among multiple lipoxygenase sequences. Switching four amino acids in 15-lipoxygenase to their counterparts in 12-lipoxygenase resulted in a variant enzyme that produced equal 12- and 15-lipoxygenation. Further analysis has identified two amino acids that completely control the positional specificity of 15-lipoxygenase. These data have led to a preliminary model of the enzyme's active site region.

Amino Acid Sequence↗