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Biomedical subjects

B Samuelsson

Publications and source records attributed to B Samuelsson.

At least 163 records · Page 9Linked to original sources
PubMed1986

Comparison of the Microtox test with the 96-hr LC50 test for the harpacticoid Nitocra spinipes.

A comparison between the static 96-hr LC50 test with the brackish water harpacticoid Nitocra spinipes and the Microtox (Beckman Instruments, Inc.) screening method has been done. The relationship between the two bioassays were evaluated for 16 pure and technical chemicals and 11 complex effluents from different types of industries. The correlation between the 96-hr LC50 values for Nitocra and the 5-, 15-, and 30-min effective concentration (EC50) for pure and technical chemicals had R2 values ranging between 0.751 and 0.796. A somewhat better correlation was shown between the two test methods for the complex effluents with R2 values ranging from 0.903 to 0.927. The sensitivity of the two tests for the actual types of samples were found to be in the same order of magnitude. Investigations concerning pretreatments of three chemicals (dibutyl phthalate, 1-octanol, and pentachlorophenol) fairly insoluble in water (less than 1000 mg/liter) have been done. Three solvents, acetone, dimethyl sulfoxide (DMSO), and propylene glycol, were studied with the Microtox system in a low concentration (500 mg/liter). Acetone exerted a slightly stimulatory effect and propylene glycol a slight reduction effect on bacterial luminescence.

Acetone↗
PubMed1986

Characterization of leukotriene A4 synthase from murine mast cells: evidence for its identity to arachidonate 5-lipoxygenase.

Leukotriene A4 synthase was purified from the cytosolic fraction of murine mast cells. The enzyme converted 5-hydroperoxy-6-trans-8,11,14-cis-icosatetraenoic acid (5-HPETE) to leukotriene A4. This unstable product was identified by demonstration of two epimers of 6-transleukotriene B4, methanol trapping, as well as further transformation to leukotriene B4 by leukotriene A4 hydrolase. Leukotriene A4 synthase stereospecifically eliminated the D-hydrogen at C-10 (pro-R) in the synthesis of leukotriene A4 when incubated with [10D-3H;3-(14)C]5-HPETE. The purified enzyme also exhibited 5-lipoxygenase activity toward arachidonic acid and 8-lipoxygenase activity towards 8,11,14-cisicosatrienoic acid. All of these activities required Ca2+ and ATP for their maximal velocities. The effects of heat treatment and of several lipoxygenase inhibitors on these enzyme activities as well as coelution in various chromatographic systems strongly suggest that lipoxygenase and leukotriene A4 synthase activities reside in the same enzyme molecule.

Animals↗
PubMed1986

Single protein from human leukocytes possesses 5-lipoxygenase and leukotriene A4 synthase activities.

The activity of leukotriene A4 (LTA4) synthase in crude human leukocyte homogenates was found to have a similar requirement for Ca2+ and ATP as had been noted previously for 5-lipoxygenase activity. Purification of the 5-lipoxygenase using ammonium sulfate fractionation, AcA 44 gel-filtration chromatography, and HPLC on anion-exchange and hydroxyapatite columns demonstrated that LTA4 synthase activity copurified with the 5-lipoxygenase with similar recoveries and increases in specific activity. Furthermore, the two enzymatic activities coeluted exactly on three different HPLC systems. Maximal activity of purified LTA4 synthase required the addition of three nondialyzable stimulatory factors, two of which were cytosolic and one of which was membrane-bound. These findings were identical for 5-lipoxygenase activity. When incubated with arachidonic acid, the purified 5-lipoxygenase converted approximately equal to 15% of its endogenously generated 5-hydroperoxyicosatetraenoic acid (5-HPETE) to LTA4. LTA4 production was more efficient when the enzyme utilized 5-HPETE generated from arachidonic acid than when 5-HPETE was exogenously supplied as substrate. These findings suggest that a single protein from human leukocytes possesses 5-lipoxygenase and LTA4 synthase activities and that the synthesis of LTA4 from 5-HPETE is controlled by the same complex multicomponent system that regulates the 5-lipoxygenase reaction.

Adenosine Triphosphate↗
PubMed1986

On the stereochemistry and biosynthesis of lipoxin B.

Lipoxin B (LXB) was prepared by incubation of (15S)-15-hydroperoxy-5,8,11-cis-13-trans-icosatetraenoic acid (15-HPETE) with human leukocytes. Comparison with a number of trihydroxyicosatetraenes prepared by total synthesis showed that biologically derived LXB is (5S,14R,15S)-5,14,15-trihydroxy-6,10,12-trans-8-cis-icosatetraenoi c acid. Two isomers of LXB were identified by using an improved isolation procedure. These compounds were shown to be (5S,14R,15S)-5,14,15-trihydroxy-6,8,10,12-trans-icosatetraenoic acid (8-trans-LXB) and (5S,14S,15S)-5,14,15-trihydroxy-6,8,10,12-trans-icosatetraenoic acid [(14S)-8-trans-LXB]. Experiments with 18O2 showed that formation of LXB and its two isomers occurred with incorporation of molecular oxygen at C-5 but not at C-14. These results together with the finding that (15S)-hydroxy-5,8,11-cis-13-trans-icosatetraenoic acid (15-HETE) is a precursor of LXB compounds in activated leukocytes suggest that 15-hydroxy-5,6-epoxy-7,9,13-trans-11-cis-icosatetraenoic acid or its equivalent is a common intermediate in the biosynthesis of LXB and its two isomers.

Arachidonic Acids↗
PubMed1985

15-Lipoxygenase in human platelets.

The metabolism of arachidonic acid by washed human platelets was investigated. [1-14C]Arachidonic acid was extensively converted to [1-14C]12-hydroxyeicosatetraenoic acid. In addition, several minor labeled products were formed with a considerably lower specific activity, indicating their preferential formation from endogenous substrate. These were dihydroxy metabolites of arachidonic acid with conjugated triene structures and were identified as 14,15-dihydroxyeicosatetraenoic acid (three isomers) and 8,15-dihydroxyeicosatetraenoic acid (three isomers). The identification was based on comparison with reference compounds with respect to chromatographic properties, characteristic UV spectra, and mass spectrometry of several derivatives. Bradykinin (10(-8)-10(-5) M) was found to enhance the formation of all these compounds. In addition, the monohydroxy acid fraction was found to contain 15-hydroxyeicosatetraenoic acid. The present investigation thus demonstrates the occurrence of a 15-lipoxygenase in human platelets in addition to the previously known 12-lipoxygenase.

Arachidonate Lipoxygenases↗
PubMed1985

Appearance of an arachidonic acid 15-lipoxygenase pathway upon differentiation of the human promyelocytic cell-line HL-60.

The metabolism of arachidonic acid and 15-HPETE was studied in a human promyelocytic cell line (HL-60). Upon exposure to DMSO, HL-60 cells undergo differentiation and acquire a 15-lipoxygenase activity while undifferentiated cells challenged with either arachidonic acid or 15-HPETE did not enzymatically transform these precursors. Products of the arachidonic acid 15-lipoxygenase pathway were identified by HPLC. UV-absorption and gas chromatography-mass spectrometry. Results indicate that upon differentiation HL-60 cells express a 15-lipoxygenase activity as well as the ability to transform 15-HPETE to 8,15-DHETEs and 14,15-DHETE. Moreover, these findings suggest that products of the 15-lipoxygenase cascade may be generated by a single cell system.

Arachidonate Lipoxygenases↗
PubMed1985

Leukotriene C4 as a mediator of luteinizing hormone release from rat anterior pituitary cells.

This study demonstrates that leukotriene C4, at concentrations in the picomolar range, released luteinizing hormone (LH) but not growth hormone (GH) from dispersed rat anterior pituitary cells. Leukotriene B4, another lipoxygenase pathway product of arachidonic acid, had no effect on LH or GH release. The stimulatory effect of leukotriene C4 could be seen after 0.5 but not after 3 hr of incubation. This was in contrast to the dose-dependent LH-releasing hormone (LHRH)-induced LH release that was not measurable after 0.5 hr but was fully established after incubation for 3 hr. Furthermore, the LH-releasing ability of leukotriene C4 was blocked in the presence of high doses of LHRH. The immunohistochemical analysis revealed leukotriene C4-immunoreactive fibers at all levels of the median eminence, mainly in the lateral parts. These fibers exhibited a marked overlap distribution with LHRH-immunoreactive fibers and elution-restaining experiments revealed identity of at least a large proportion of the leukotriene C4- and LHRH-immunoreactive fibers. Furthermore, cell bodies in the preoptic area contained both leukotriene C4- and LHRH-like immunoreactivities, suggesting localization of these two compounds in the same neurons.

Animals↗
PubMed1985

On the nature of the 5-lipoxygenase reaction in human leukocytes: enzyme purification and requirement for multiple stimulatory factors.

Arachidonate 5-lipoxygenase was purified 400-fold from homogenates of human peripheral blood leukocytes by a combination of ammonium sulfate fractionation, gel filtration chromatography, and HPLC on anion exchange and hydroxylapatite columns. NaDodSO4/polyacrylamide gel electrophoresis of the purified protein revealed the presence of a single major band (apparent Mr, 80,000). Densitometric analysis of the Coomassie blue staining pattern of the gels revealed that a 90-97% purity had been achieved. As has been reported for the 5-lipoxygenase from other mammalian sources, the human leukocyte enzyme required Ca2+ and ATP for maximal activity. In addition, a number of factors were isolated during the course of the purification, which possessed significant 5-lipoxygenase stimulatory activities. These were obtained in a high-speed pellet of leukocyte homogenate, a 60-90% ammonium sulfate precipitate fraction, and the unabsorbed protein from the first anion exchange HPLC step. In the absence of stimulatory factors, little activity was detected in the purified enzyme, even in the presence of Ca2+ and ATP. The specific function of these various factors is unknown, but their existence suggests that the human leukocyte 5-lipoxygenase is regulated by a complex mechanism that is likely to play an important role in the control of leukotriene and lipoxin biosynthesis.

Arachidonate Lipoxygenases↗
PubMed1985

On the nature of the 5-lipoxygenase reaction in human leukocytes: characterization of a membrane-associated stimulatory factor.

When 10,000 X g supernatants of human leukocyte homogenates were subjected to centrifugation at 100,000 X g for 75 min, the activity of 5-lipoxygenase decreased by 30-60%, even though no enzyme was detectable in the resuspended 100,000 X g pellet. Recombination of the 100,000 X g supernatant and pellet resulted in a restoration of the lost enzymatic activity, indicating the presence of a 5-lipoxygenase stimulatory factor in the microsomal membrane preparation. Dialysis of human leukocyte supernatants resulted in an apparent decrease in 5-lipoxygenase activity, but only in samples that contained the membrane-associated stimulatory factor, suggesting that the factor required a small molecular weight component for optimal function. The 5-lipoxygenase stimulatory activity was highly unstable to washing of the 100,000 X g pellet or to incubation (16-20 hr) at 4 degrees C. In contrast, the activity was remarkably stable to heat (100 degrees C for 40 min). The responses of the 12- and 15-lipoxygenases in human leukocyte homogenates to the membrane-associated factor and to dialysis were notably different from that of the 5-lipoxygenase. These results demonstrate, therefore, that the 5-lipoxygenase is unique among the human lipoxygenases, not only in its requirement for Ca2+ and ATP but also in its regulation by a membrane-associated stimulatory factor. The mechanism of action of this regulatory factor is of obvious interest for the understanding of the control of leukotriene and lipoxin biosynthesis.

Adenosine Triphosphate↗
PubMed1985

Circulating hydroxy fatty acids in familial Mediterranean fever.

Episodes of fever, serositis, and arthritis in familial Mediterranean fever (FMF) suggested circulating mediators of acute inflammation (e.g., neutrophil activation). The mean serum neutrophil-aggregating activity of 51 FMF patients was 2.5 +/- 0.2 cm2/min, compared to 1.0 +/- 0.1 cm2/min in 20 normal controls (P less than 0.0002). Lipid extracts of FMF sera retained neutrophil-aggregating activity and had UV absorbance peaks at 269 and 279 nm, indicating the presence of lipids with a conjugated triene structure. Chromatography of extracts yielded peaks that were coeluted with reference dihydroxyicosatetraenoic acids, had UV absorbance peaks at 259, 269, and 279 nm, and possessed neutrophil-aggregating activity. The presence of leukotriene B4 was excluded by chromatography following methyl-esterification. Monohydroxy compounds identified in FMF extracts by gas chromatography/mass spectrometry included 5-hydroxyicosatetraenoic acid, and 9- and 13-hydroxyoctadecadienoic acids. Hydroxy acids were present in 19 of 31 FMF sera and absent in extracts of sera from 8 patients with active systemic lupus erythematosus, 7 with fever from infection, and 12 normal controls. The finding of circulating mono- and dihydroxy fatty acids in FMF suggests that defects in the formation or elimination of these compounds might play a role in the pathogenesis of FMF.

Cell Aggregation↗
PubMed1985

Action of novel eicosanoids lipoxin A and B on human natural killer cell cytotoxicity: effects on intracellular cAMP and target cell binding.

Lipoxin A (5,6,15L-trihydroxy-7,9,11,13-eicosatetraenoic acid) and lipoxin B (5D,14,15-trihydroxy-6,8,10,12-eicosatetraenoic acid), two newly isolated compounds derived from the oxygenation of arachidonic acid in human leukocytes, inhibit the cytotoxic activity of human natural killer (NK) cells. Dose-response studies showed that both lipoxin A and lipoxin B inhibit, at submicromolar concentrations (ID50 10(-7) M), NK cell activity assayed against K562 target cells. Prostaglandin E2 (PGE2) also inhibited cytotoxicity, whereas both 15-HETE (5(S)-hydroxy-5,8,11,13-eicosatetraenoic acid) and leukotriene B4 (synthetic and biologically derived) were ineffective. PGE2 stimulated a time- and dose-dependent increase in intracellular cAMP, which was accompanied by a decrease in NK target cell binding. Lipoxin A and lipoxin B did not elevate intracellular cAMP, nor did they inhibit target cell binding. Together these findings suggest that lipoxin A and lipoxin B abrogate NK cell cytotoxicity at a step distal to target effector cell recognition. In contrast, PGE2 appears to exert its effect, at least in part, on cytotoxicity indirectly by decreasing the binding between target and effector cells (in vitro). Moreover, they suggest that novel oxygenated derivatives of arachidonic acid (i.e., lipoxin A, lipoxin B) may regulate the activities of NK cells.

Binding Sites↗