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Biomedical subjects

S Menashi

Publications and source records attributed to S Menashi.

At least 37 records · Page 2Linked to original sources
PubMed1991

Modulation of endothelial cells fibrinolytic activity by platelets.

Interaction between endothelial cells (EC) and platelets in culture was shown to regulate the fibrinolytic system of the aortic EC. Untreated porcine EC from aorta exhibited almost no net fibrinolytic activity and zymographic assay have shown a single fibrin lysis band of 105 kDa corresponding to a tPA-PAI complex. Incubation of aortic EC with intact platelets stimulated a cell-associated fibrinolytic activity of the urokinase type as evidenced by a plasminogen-dependent fibrin independent amidolytic activity, and the appearance of a new 48 kDa lysis band on zymography. However, in the culture medium of platelet-treated aortic EC, a new lysis band of 92 kDa appeared with no associated amidolytic activity suggesting that the 48 kDa plasminogen activator secreted by the aortic EC after treatment with platelets is complexed to the inhibitor PAI1. This modulation of fibrinolytic activity depends on the EC origin since it is not observed with pulmonary artery EC, and represents a new concept in fibrinolysis regulation by cell-cell interaction.

Animals↗
PubMed1990

Endothelial proteases stimulated by blood platelets.

Endothelial cells secrete a protease which is activated in the extracellular medium by platelets. This protease PECAP, degrades casein and fibrinogen, and its characteristics differentiate it from the other known blood and vascular proteases.

Blood Platelets↗
PubMed1990

[Endothelial cell proteases and their modulation by platelets].

Endothelial cells produce and secrete a large number of proteases which are implicated in various disease states. These proteases fall into two classes: serine proteases include plasminogen activators (t-PA) and urokinase (u-PA) and play a major role in fibrinolysis, tissue repair and carcinogenesis; and metalloproteases include collagenases and stromelysine, two enzymes involved in the tissue remodelling that occurs during angiogenesis and tumor growth. The authors have recently identified two other proteases in porcine aortic endothelial cell culture medium. One is an elastase-like enzyme of the metalloprotease group, whereas the other is a new protease whose molecular weight is 85 Kd and whose activity becomes apparent only after exposure of the endothelial cells to platelets. The term Platelet Endothelial Cell Activated Protease accurately describes this enzyme. PECAP degrades casein and fibrinogen. Because PECAP is not inhibited by the usual inhibitors of the various classes of proteases, it remains at present unclassified.

Blood Platelets↗
PubMed1989

Elastase-like activity in cultured aortic endothelial cells.

Cultured porcine aortic endothelial cells were studied for cellular and secreted elastase activity. We describe an activity hydrolyzing the synthetic elastase substrate, succinyl(alanine)3 nitroanilide, but not elastin, which was shown to be membrane located and was not secreted to the culture medium. A different neutral proteinase activity degrading insoluble elastin was demonstrated in the culture medium following its fractionation by gel filtration high performance liquid chromatography (HPLC). Since no elastinolytic activity could be directly detected in the conditioned medium, it is likely that the chromatographic separation removed an endogenous inhibitor.

Animals↗
PubMed1989

Interaction of platelets with endothelial cells: activation of a novel neutral protease.

The activation of a new neutral protease of MW 85,000 was demonstrated on interaction between porcine aortic endothelial cells and human and porcine platelets in culture. The activity of this enzyme, PECAP (platelet endothelial cell activated protease), was detected by electrophoresis on polyacrylamide gels impregnated with the substrate casein. Our results showed that the platelet-endothelial cell interaction did not involve induction of synthesis of de novo enzyme, but rather an activation of a latent enzyme. PECAP cleaved casein and fibrinogen, but had no activity against gelatin or elastin. It was not inhibited by inhibitors of metalloproteases (EDTA, 1.10 phenanthroline), serine proteases (phenylmethylsulfonyl fluoride, elastatinal), or cysteine proteases (iodoacetate, N-ethylmaleimide) and it seems to be unrelated to the previously known proteases of mesenchymal and hematopoietic cells.

Animals↗
PubMed1987

Collagen in abdominal aortic aneurysm: typing, content, and degradation.

The collagen content of the media of infrarenal aorta has been compared in age- and sex-matched normal aorta and dilated and nondilated atherosclerotic aorta. The proportion of collagen was increased in aneurysmal aorta from 62% to 84% and appears to be the result of preferential elastin degradation. The ratio of type I to type III collagen, estimated from sodium dodecyl sulfate-polyacrylamide gel electrophoresis of specific cyanogenbromide peptides, did not vary significantly from 2:1 in any of the three groups of aortas. There was no evidence of increased collagenase activity in unruptured aneurysmal aorta. Collagenase activity was increased in ruptured aneurysmal aorta but could only be satisfactorily measured after resolution from the endogenous tissue inhibitor of metalloproteinases. We suggest that only limited collagen turnover occurs in the media of abdominal aortic aneurysms before rupture. A subgroup of three patients with a significant family history of aneurysm had lower amounts of type III collagen in the aortic media, suggesting that abnormalities in type III collagen may be one of the genetic factors contributing to familial clustering of aneurysms.

Aorta, Abdominal↗
PubMed1987

Whole blood clotting tests: an evaluation of five methods.

Five different methods of measuring the clotting time of fresh whole blood have been compared. The Biobridge was the best instrument, and was able to measure both anticoagulation and hypercoagulation accurately and reproducibly.

Blood Coagulation Tests↗
PubMed1986

Pepsinogen--an immunoglobulin binding artefact in 'collagen' preparations.

It has previously been shown that extracts of human articular cartilage, many many of which contain type II collagen, react with heat-aggregated immunoglobulin and artificially prepared immune complexes. Sera from patients with rheumatoid arthritis and psoriatic arthritis, but not from patients with inflammatory bowel disease, react with these extracts. There are two distinct patterns of binding, either as low molecular weight immune complexes or as free antibody directed against collagen. Aggregate-binding activity identified in extracts of human articular cartilage following pepsin digestion was found to be distinct from collagen in its salt solubility. Further purification of this aggregate-binding factor by SDS gel electrophoresis has shown it to be an artefact resulting from the binding of small immune complexes to pepsinogen present in the pepsin preparation used to digest the cartilage.

Antigen-Antibody Complex↗
PubMed1984

Characterization of the calcium-sequestering process associated with human platelet intracellular membranes isolated by free-flow electrophoresis.

By using density-gradient fractionation and high-voltage free-flow electrophoresis, human platelet membranes were separated into highly purified subfractions of surface (SM) and intracellular (IM) origin. Associated exclusively with the IM fraction is an ATP-dependent Ca2+ uptake that, in the absence of oxalate, reaches steady-state levels in 5-10 min. When Ca2+-EGTA buffers were used to control the external Ca2+ concentrations (range 0.1-50 microM) there was an increase in the intravesicle steady-state level of Ca2+ up to 10 microM external Ca2+ concentration. Above this level the intravesicle space becomes saturated at a concentration between 10 and 20 nmol of Ca2+ X (mg of protein)-1. The ionophore A23187 promotes a rapid and almost total release of the sequestered Ca2+ (greater than 90%, t1/2 1-2 min). The presence of oxalate in the external medium greatly enhances the Ca2+ accumulation to levels as high as 200 nmol X (mg of protein)-1, but the uptake process is more variable and rarely reaches steady-state level even after 2 h incubation. Moreover, accumulation in the presence of oxalate effects ionophore release with less than 80% depletion in 45-60 min. These findings, taken together with the known presence in the platelet of a wide variety of functional and metabolic processes triggered by this cation, suggest that the platelet IM has a key role in controlling cytosolic Ca2+ concentrations.

Adenosine Triphosphate↗
PubMed1982

Localization of cyclo-oxygenase and thromboxane synthetase in human platelet intracellular membranes.

Platelet mixed membrane fractions can be separated into discrete vesicle subpopulations of surface and intracellular origin. Intracellular membrane vesicles are the predominant site of phospholipid-modifying enzymes that liberate arachidonic acid. We report the selective enrichment in intracellular membranes of cyclo-oxygenase and thromboxane synthetase activities. Surface membrane fractions show no such enrichment. These results suggest that a sequence of activities leading to the biosynthesis of thromboxane from arachidonate is associated with the intracellular membrane elements known as dense tubular membranes.

Arachidonic Acid↗
PubMed1982

The phospholipid and fatty acid composition of human platelet surface and intracellular membranes isolated by high voltage free flow electrophoresis.

Human platelets were labeled with tracer doses of [14C]arachidonic acid, then fractionated into mixed membranes which are separated into intracellular membranes and two different domains of surface membranes by high voltage free flow electrophoresis. Each subfraction was analyzed for its phospholipid content. Glycerophospholipids were separated by high performance liquid chromatography and their fatty acids analyzed by glass capillary gas chromatography. Intracellular membranes appeared substantially depleted in sphingomyelin, while enrichment of this phospholipid was seen in surface membranes. PC and PI were more enriched in intracellular membranes than in the surface membranes and the contrary was observed for PE. On the other hand, the pattern of the phospholipid labeling by [14C]arachidonate followed closely the glycerophospholipid profiles of the membrane subfractions, but the specific radioactivity of PI was higher than of PC, which itself was higher than that of PE. Moreover, the endogenous content of arachidonic acid accentuates these tendencies. The percentage of arachidonate in PE was higher in the surface membranes than in the intracellular membranes and the contrary was observed for arachidonyl-PC and PI. These differences were compensated for by certain saturated and monounsaturated fatty acids present in the composition profiles. These findings are discussed in relation to the membrane localization of lipases involved in the liberation of arachidonic acid for prostanoid synthesis.

Blood Platelets↗
PubMed1981

Characterization of human platelet surface and intracellular membranes isolated by free flow electrophoresis.

High voltage free flow electrophoresis has been applied to the separation of human platelet membranes. After short treatment with neuraminidase at the whole cell level, three membrane vesicle subpopulations have been isolated. Using a surface label (125I-labeled Lens culinaris lectin), the marker enzyme NADH-cytochrome c reductase, and lipid analysis, two of the fractions have been identified as of surface origin and the other consists of intracellular membrane elements. The distribution of adenylate cyclase, leucyl aminopeptidase, 5'-nucleotidase and Ca2+-ATPase has also been investigated, and their usefulness as markers for the different membrane fractions has been evaluated. All three fractions are vesicular but differ in size and character. Their phospholipid and cholesterol contents have been determined, and the cholesterol/phospholipid ratios of the two surface fractions are over twice that of the intracellular membrane, which also has a significantly lower microviscosity as determined by fluorescence polarization using diphenyl hexatriene. The polypeptide profiles from sodium dodecyl sulfate-polyacrylamide gel electrophoresis are particularly distinctive, with actin present in the two surface membrane fractions and absent from the intracellular membranes. Myosin, confirmed by its ATPase characteristics, is almost exclusively localized in one of the surface membrane fractions, and actin-binding protein is a prominent feature of the other.

5'-Nucleotidase↗
PubMed1981

Influence of streptozitocin-induced diabetes on glycosyltransferase activities in plasma and renal cortex.

The collagen glucosyltransferase of renal cortex is increased in experimental diabetes and this increased may be partially reversed or prevented by insulin treatment. The absence of any consistent increase in the plasma collagen glucosyltransferase level in diabetes argues against the enzyme's having a significant role in the pathological thickening of capillary basement membranes. The biological significance of the increased renal glucosyltransferase activity in chemically-induced diabetes must therefore remain in doubt but it is possible that the high glucose concentration in the blood simply stimulates the synthesis of new enzyme protein in the kidney.

Animals↗
PubMed1979

Studies on the collagen glucosyltransferase activity present in platelets and plasma.

1. Collagen glucosyltransferase was demonstrated to be associated with pig platelets by using a specific assay for the synthesis of [(14)C]glucosylgalactosylhydroxylysine. 2. This enzyme from pig platelets required denatured collagen as substrate and the reaction was not inhibited by the presence of triple-helical collagen. These observations indicate that the platelet enzyme cannot form either an enzyme-substrate complex or an enzyme-inhibitor complex with triple-helical collagen. 3. Platelets were fractionated by sucrose-density-gradient centrifugation after either lysis by a glycerol-loading technique or homogenization. Assays of subcellular fractions for collagen glucosyltransferase activity indicated that the enzyme was localized predominantly in the cytosolic fraction and less than 5% of the activity was associated with the membrane fractions. 4. Enzyme assays were carried out on platelet-rich plasma and platelet-poor plasma prepared from pig and human blood. These analyses indicated that most of the collagen glucosyltransferase activity of platelet-rich plasma was in a soluble form and only about 10% was associated with platelets. 5. Comparative studies on the enzyme activity in plasma and platelets of various animal species revealed marked variation, with the guinea pig exhibiting the highest activity. In most cases there was a correlation between the activity found in platelets and plasma, but little species variation was noted in enzyme amounts detected in bone-marrow preparations. 6. The results described here are discussed in the context of the proposal that collagen glucosyltransferase might play a role in mediating collagen-platelet adhesion.

Animals↗