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L B Safier

Publications and source records attributed to L B Safier.

32 records · Page 2Linked to original sources
PubMed1984

Production of metabolic products of arachidonic acid during cell-cell interactions.

We studied interactions of human platelets and neutrophils with particular reference to the arachidonic acid pathway. Suspensions of [3H]arachidonate-labeled platelets and unlabeled neutrophils were stimulated with ionophore A23187. We detected several radioactive arachidonate metabolites, which are not produced by platelets alone. These included [3H]-labeled leukotriene B4 (LTB4), dihydroxy-eicosatetraeonic acid (DiHETE), and 5-hydroxy-eicosatetraenoic acid (5-HETE). DiHETE was formed when the platelet product [3H]12-HETE was added to ionophore-stimulated neutrophils. In addition, DiHETE was the major metabolite when [3H]5-HETE, a neutrophil arachidonate product, was added to stimulated platelets. We therefore suggest that upon stimulation, platelet-derived arachidonate can serve as precursor for the neutrophil-derived eicosanoids LTB4 and 5-HETE, and the platelet-derived product 12-HETE can be metabolized to DiHETE by stimulated human neutrophils. More recently we have shown that 12-HETE from thrombin-stimulated platelets can also be metabolized to a new product, 12,20-DiHETE, by unstimulated human neutrophils. It would appear that the platelet and neutrophil lipoxygenase pathways take part in cell-cell interactions--an observation that suggests a role for the neutrophils that are present in hemostatic plugs, thrombi, and inflammatory processes.

Arachidonate Lipoxygenases↗
PubMed1984

12S,20-dihydroxyicosatetraenoic acid: a new icosanoid synthesized by neutrophils from 12S-hydroxyicosatetraenoic acid produced by thrombin- or collagen-stimulated platelets.

A new metabolite of arachidonic acid, formed during interaction between thrombin- or collagen-stimulated platelets and unstimulated neutrophils, has been demonstrated by both thin-layer radiochromatography and high-performance liquid chromatography. Production of the 3H-labeled metabolite in combined suspensions containing [3H]arachidonate-labeled platelets and unlabeled neutrophils from aspirin-treated donors suggested that platelet 3H-labeled 12S-hydroxy-5,8-cis,10-trans,14-cis-icosatetraenoic acid (12-HETE) was the precursor. This was confirmed by identification of the same product when purified 12-[3H]HETE was added directly to unstimulated neutrophils. Hydrogenation and oxidation of the isolated product, followed by gas chromatography-mass spectrometry showed the structure to be 12S,20-dihydroxyicosatetraenoic acid. These experiments further show that platelet stimuli known to occur in vivo may initiate metabolic interactions between different cell types via the arachidonic acid pathway.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗
PubMed1984

Production of arachidonic acid lipoxygenase products during platelet-neutrophil interactions.

We studied interactions of human platelets and neutrophils with particular reference to the arachidonic acid pathway. Suspensions of [3H]-arachidonate-labeled platelets and unlabeled neutrophils were stimulated with ionophore A23187. We detected several radioactive arachidonate metabolites, which are not produced by platelets alone. This included [3H]-labeled leukotriene B4 (LTB4), dihydroxyeicosatetraenoic acid (DHETE) and 5-hydroxyeicosatetraenoic acid (5-HETE). When the platelet product, [3H]12-HETE, was added to ionophore-stimulated neutrophils, DHETE was formed. In addition, when [3H]5-HETE, a neutrophil arachidonate product, was added to stimulated platelets, DHETE was the major metabolite. We, therefore, suggest that upon stimulation, the platelet derived arachidonate can serve as precursor for the neutrophil-derived eicosanoids LTB4 and 5-HETE and that the platelet-derived product 12-HETE can be metabolized to DHETE by stimulated human neutrophils. It would appear that the platelet and neutrophil lipoxygenase pathways take part in cell-cell interactions - an observation which suggests a role for the neutrophils which are present in hemostatic plugs, thrombi and inflammatory processes.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗
PubMed1981

Interactions between stimulated platelets and endothelial cells in vitro.

Prostaglandins and hydroxy acids are synthesized mainly from the essential polyunsaturated fatty acid arachidonate, and these substances have been identified in almost all mammalian tissues. Prostaglandins, thromboxane A2 (TXA2) and prostacyclin (PGI2) are autocoids that appear to function in the regulation of vascular tone, cell secretion and contractile processes. So far, hydroxy acids have been found to function as chemotactic agents and in the formation of slow-reacting substances. Other actions of hydroxy acids will certainly be defined in future research. The endoperoxides PGG2 and PGH2 represent common precursors of all prostaglandin end-products. In studying the prostaglandin metabolism of a specific tissue, the total profile of endoperoxide transformation should be determined. In platelets the endoperoxides are transformed mainly into TXA2, a potent vasoconstrictor and inducer of platelet aggregation. Endothelial cells convert endoperoxides to PGI2, a vasodilator and inhibitor of platelet aggregation. In addition, endothelial cells can utilize endoperoxides from stimulated plates to form PGI2. The concept that platelets and endothelial cells can share common precursors for the production of modulating substances may be applicable to other cell types.

Arachidonic Acids↗
PubMed1981

Effects of acetyl glyceryl ether phosphorylcholine on human platelet function in vitro.

AGEPC (PAF), at 1.9 x 10(-8) M or higher, induced concentration-dependent aggregation and release in human platelet-rich plasma. Comparative studies with arachidonate, collagen, ionophore, and ADP suggested that AGEPC was a strong stimulus for platelet aggregation and probably a moderate agonist for release, as well as a relatively weak inducer of TXA2 production. The initial phase of AGEPC-induced aggregation was independent of ADP release and TXA2 formation, since it was not inhibited by ASA, apyrase, or CP/CPK. Whereas irreversible aggregation always required ADP release, TXA2 formation was not essential in each instance. Thus, in several experiments, full aggregation responses took place in AGEPC-stimulated platelets that had been pretreated with ASA. AGEPC-induced release of 5-HT, beta -thromboglobulin and PF-4 occurred in parallel and were inhibited by both apyrase and ASA. Washed human platelets did not respond to exogenous AGEPC in the absence of ADP and did not appear to generate significant quantities of AGEPC upon stimulation with thrombin or ionophore.

Adenosine Diphosphate↗
PubMed1977

Superoxide production and reducing activity in human platelets.

Human platelets contain the cuprozinc (cytoplasmic) and manganese (mitochondrial) forms of superoxide dismutase. Nevertheless, superoxide radicals were detectable in the surrounding medium of metabolically viable platelet suspensions by using two assay systems: cytochrome c and nitroblue tetrazolium. The quantity of superoxide generated by platelets (5 X 10(5) superoxide radicals/platelet per 10 min) was constant and did not increase after aggregation by agents such as collagen and thrombin. The superoxide-generating system was present in the supernate of both aggregated and resting platelets and therefore was not platelet-bound. Platelet superoxide production was unaffected by prior ingestion of aspirin, indicating that the prostaglandin and thromboxane pathways were not involved. Both resting and aggregated platelets exhibited a reductive capacity toward cytochrome c and nitroblue tetrazolium which was unrelated to superoxide production. Furthermore, the aggregation process always resulted in a marked increase in this reduction. The nonsuperoxide reduction associated with aggregation was found to be membrane bound and to decrease with an apparent first order reaction rate (k1 = 0.067 min-1). In addition, accumulative, time-dependent nonsuperoxide-related cytochrome c reduction was also detected. Since there is no superoxide dismutase in plasma, the presence of superoxide radicals in the surrounding medium of platelets may have in vitro significance for platelet and leukocyte concentration and storage and in vivo significance for hemostasis, coagulation, and thrombosis. The nonsuperoxide-related reducing activities may represent a biochemical basis for platelet-blood vessel interactions, with particular reference to blood vessel integrity.

Aspirin↗
PubMed1972

Studies on human platelet gangliosides.

Gangliosides, glycosphingolipids which contain sialic acid, were studied in human platelets. They represented 0.5% of the platelet lipids and accounted for 6% of the total neuraminic acid content of platelets. Three major ganglioside fractions were identified and characterized. Ganglioside I was hematoside (G(6)) and comprised 92% of the platelet gangliosides. It contained glucose, galactose, and sialic acid in molar ratios of 1:1:1 and no hexosamine. The major fatty acid was behenate (22:0). Ganglioside I was also identified in isolated platelet granules and membranes. Ganglioside II (5%) contained glucose, galactose, sialic acid, and hexosamines (molar ratios 1:2:1:1). The hexosamines were glucosamine (72%) and galactosamine (28%). It was therefore designated as ganglioside lacto-N-neotetraose. Ganglioside III (2%) contained disialosyllactosyl ceramide (G(3A)) as well as two other gangliosides which could not be precisely characterized. Gangliosides I, II, and III were susceptible to the action of Clostridium perfringens neuraminidase as evidenced by full recovery of sialic acid in its free form after incubation. Neutral platelet glycolipids were qualitatively examined by thin-layer chromatography. The major component was lactosyl ceramide. Interactions of gangliosides I and III and serotonin-(14)C were examined in an equilibrium dialysis system at 4 degrees C. The gangliosides bound serotonin-(14)C in relatively small quantities, whereas control lipids were negative. The binding was essentially unchanged by reverse dialysis, ultracentrifugation and subsequent thin-layer chromatography. The results are comparable to the previously observed nonmetabolic interactions between whole platelets and serotonin in the cold. It is suggested that the orientation and specific distribution of platelet membrane glycolipids may be important determinants of the unique surface properties of platelets.

Blood Platelets↗
PubMed1969

Lipid composition of subcellular particles of human blood platelets.

Human platelets can be fractionated into three main subcellular components: granules, membranes, and a soluble fraction. In this study we determined the phospholipid and neutral lipid content of the granules and membranes. Quantitative relationships between lipids and protein were examined. The fatty acid and aldehyde composition of individual phospholipids and neutral lipids was also determined. Whole platelets had a lower lipid to protein ratio than did the subcellular particles, but the basic lipid composition of the granules, membranes, and platelets was similar. The phospholipid composition of platelets and subcellular fractions was found to differ only in that granules had a lower percentage of lecithin. Each of the phospholipid classes displayed a distinctive fatty acid pattern which was the same in all fractions and in whole platelets. The major neutral lipid was free cholesterol. Cholesteryl esters, triglycerides, and free fatty acids were minor components. The molar ratio of cholesterol to phospholipid in the platelet membranes was lower than that of brain myelin and erythrocyte ghosts. Some differences in fatty acid composition of the neutral lipids of platelet fractions were found. A special lipid composition or constituent that would correlate with platelet function has not been found.

Aldehydes↗
PubMed1967

Platelet thrombosthenin: subcellular localization and function.

Thrombosthenin, an immunologically distinct contractile protein was isolated in relatively pure form from human platelets. The protein, which was of high molecular weight appeared to be composed of multiple polypeptide subunits, probably polymeric in nature.Thrombosthenin had magnesium-dependent ATPase activisty, releasing an average of 3 mug phosphorus per mg protein in 30 min. After the addition of ATP, there was a reversible alteration in viscosity with calculated ATP sensitivity ranging from 64 to 90%. These biochemical properties of thrombosthenin resemble those of smooth muscle.Specific antisera to thrombosthenin significantly inhibited the ATPase activity of the protein. Clot retraction of recalcified platelet-rich plasma and clot retraction of clotted fibrinogen-platelet mixtures were also inhibited by the antisera. The findings suggest that thrombosthenin is an important component of the clot retraction system.Thrombosthenin was extracted from isolated platelet granule and membrane fractions. The contractile protein derived from the membrane compartment was more active as an ATPase and appeared to be more homogeneous on immunologic analysis.

Journal Article↗