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D L Amrani

Publications and source records attributed to D L Amrani.

At least 37 records · Page 2Linked to original sources
PubMed1988

The role of fibrinogen A alpha chains in ADP-induced platelet aggregation in the presence of fibrinogen molecules containing gamma' chains.

Human plasma fibrinogen (Fgn) is heterogenous with respect to the size of its gamma chains, which differ in that residues 408 to 411 of gammaA chains (93% of total) are replaced in gamma' chains by a unique 20 amino acid sequence (gamma408 to gamma427). In this study, we compared the contribution to adenosine diphosphate (ADP)-induced platelet aggregation of the A alpha chains in Fgn molecules containing predominantly (fraction 1-2) or exclusively (peak 1 Fgn) gammaA chains with that of molecules containing approximately 50% gamma' chains (peak 2 Fgn). Using washed human platelets, we confirmed that the number of peak 2 Fgn molecules binding to platelets in the presence of ADP was about half the number of peak 1 Fgn molecules (18,962 +/- 2,298 v 44,366 +/- 16,096 molecules per platelet), and that isolated S-carboxymethylated (SCM) gammaA chains supported ADP-induced platelet aggregation nearly as well as peak 1 Fgn. In contrast, SCM-gamma' chains alone supported aggregation poorly, whereas a mixture of SCM-gammaA and gamma' chains (1:1 ratio) gave intermediate results. Despite the findings with isolated SCM-gamma' chains, we found that peak 2 Fgn supported platelet aggregation nearly as well as peak 1 Fgn. However, peak 2 Fgn from which carboxy (COOH)-terminal A alpha chain segments had been removed by digestion with plasmin showed a markedly decreased platelet aggregation potential. Peak 1 Fgn core fraction from an 88% to 90% coagulable plasmin digest, or Fgn fraction 1-9, which has a high gammaA/gamma' chain ratio (93:7), but lacks COOH-terminal regions of A alpha chains, supported platelet aggregation to the same extent as did intact peak 2 Fgn. These findings indicate that Fgn molecules containing gamma' chains can approach the aggregation potential of Fgn molecules containing predominantly or exclusively gammaA chains only if intact A alpha chains are also present.

Adenosine Diphosphate↗
PubMed1987

Regulation of plasma fibronectin biosynthesis by glucocorticoids in chick hepatocyte cultures.

Plasma fibronectin is an acute-phase reactant synthesized by hepatocytes. Glucocorticoids are one of the major factors implicated in controlling the hepatic acute-phase response. To study the regulatory effects of glucocorticoids on plasma fibronectin biosynthesis, a model chick hepatocyte culture system under serum- and hormone-free conditions was used. In the presence of either dexamethasone or corticosterone, secreted plasma fibronectin increased maximally to 2.8-fold above basal levels. The stimulatory effect of the hormones was maintained only in their continuous presence, since plasma fibronectin production dropped to near basal levels within 16 h of glucocorticoid withdrawal. Pulse-chase studies indicated that pretreatment of cells with dexamethasone stimulated the level of secreted plasma fibronectin but had no effect on its rate of secretion. The increase in plasma fibronectin production by dexamethasone was abolished in a dose-dependent manner by the addition of progestin, an antagonist of dexamethasone known to compete specifically for the liver glucocorticoid receptor. Actinomycin D and alpha-amanitin, which are inhibitors of transcription, also blocked the early dexamethasone effect on plasma fibronectin synthesis. Slot blot hybridization of total RNA samples from dexamethasone-treated cultures revealed a 6-fold stimulatory rise in fibronectin mRNA during the first 6 h of treatment, which later declined and was no longer evident at 48 and 72 h. However, fibronectin mRNA levels were elevated to about the same extent in control and dexamethasone-treated cells at the later time points. During the same time period (0 to 72 h), plasma fibronectin protein levels rose and remained elevated. Evaluation of pulse-chase experiments following pretreatment with hormone for 48 h demonstrated that equal amounts of plasma fibronectin were translated by dexamethasone-treated and control cells, but only 42% of labeled plasma fibronectin was secreted by control cells compared with 93% for dexamethasone-treated cells. These findings suggest that the early phase of glucocorticoid regulation of plasma fibronectin biosynthesis occurs at the transcriptional level and is mediated through the specific action of the glucocorticoid receptor. A later phase of glucocorticoid-stimulated plasma fibronectin biosynthesis results from modulation of post-translational processing events leading to secretion of an increased amount of newly translated plasma fibronectin polypeptides.

Animals↗
PubMed1987

Studies on the ultrastructure of fibrin lacking fibrinopeptide B (beta-fibrin).

Release of fibrinopeptide B from fibrinogen by copperhead venom procoagulant enzyme results in a form of fibrin (beta-fibrin) with weaker self-aggregation characteristics than the normal product (alpha beta-fibrin) produced by release of fibrinopeptides A (FPA) and B (FPB) by thrombin. We investigated the ultrastructure of these two types of fibrin as well as that of beta-fibrin prepared from fibrinogen Metz (A alpha 16 Arg----Cys), a homozygous dysfibrinogenemic mutant that does not release FPA. At 14 degrees C and physiologic solvent conditions (0.15 mol/L of NaCl, 0.015 mol/L of Tris buffer pH 7.4), the turbidity (350 nm) of rapidly polymerizing alpha beta-fibrin (thrombin 1 to 2 U/mL) plateaued in less than 6 min and formed a "coarse" matrix consisting of anastomosing fiber bundles (mean diameter 92 nm). More slowly polymerizing alpha beta-fibrin (thrombin 0.01 and 0.001 U/mL) surpassed this turbidity after greater than or equal to 60 minutes and concomitantly developed a network of thicker fiber bundles (mean diameters 118 and 186 nm, respectively). Such matrices also contained networks of highly branched, twisting, "fine" fibrils (fiber diameters 7 to 30 nm) that are usually characteristic of matrices formed at high ionic strength and pH. Slowly polymerizing beta-fibrin, like slowly polymerizing alpha beta-fibrin, displayed considerable quantities of fine matrix in addition to an underlying thick cable network (mean fiber diameter 135 nm), whereas rapidly polymerizing beta-fibrin monomer was comprised almost exclusively of wide, poorly anastomosed, striated cables (mean diameter 212 nm). Metz beta-fibrin clots were more fragile than those of normal beta-fibrin and were comprised almost entirely of a fine network. Metz fibrin could be induced, however, to form thick fiber bundles (mean diameter 76 nm) in the presence of albumin at a concentration (500 mumol/L) in the physiologic range and resembled a Metz plasma fibrin clot in that regard. The diminished capacity of Metz beta-fibrin to form thick fiber bundles may be due to impaired use or occupancy of a polymerization site exposed by FPB release. Our results indicate that twisting fibrils are an inherent structural feature of all forms of assembling fibrin, and suggest that mature beta-fibrin or alpha beta-fibrin clots develop from networks of thin fibrils that have the ability to coalesce to form thicker fiber bundles.

Blood Coagulation↗
PubMed1986

Effect of hepatocyte-stimulating factor and glucocorticoids on plasma fibronectin levels.

We evaluated the effects of hepatocyte-stimulating factor (HSF) and a glucocorticoid (dexamethasone) on changes in the levels, in vivo and in vitro, of plasma fibronectin (Fn), a glycoprotein that is synthesized and secreted by hepatocytes. In turpentine-treated chickens, plasma levels of Fn, which peaked at 48 h (whereas fibrinogen levels were maximum at 72 h) rose 200-250% over basal levels, whereas albumin levels decreased by 20-40%. Corticosterone levels in serum samples taken between 5 and 48 h after injection revealed a 124% increase in hormone levels at 24 h in turpentine-treated chickens. We also showed that circulating HSF levels were maximal 8 to 12 h after injection and that HSF activity, as assessed by molecular-exclusion chromatography, was eluted in the 30-45 kDa range. Addition of either serum-derived HSF or dexamethasone (2 nM) to chick hepatocyte cultures resulted in a 130-150% increase in secreted Fn as well as in fibrinogen. When HSF and dexamethasone were added together, a 360-489% increase in the secreted levels of both proteins was found. Chicken mononuclear phagocytic cells treated with lipopolysaccharide secreted an HSF activity that was eluted in two peaks, a minor peak at approximately 70 kDa and a major peak in the 25-40 kDa range. Addition of mononuclear-cell-derived HSF resulted in a greater increase in Fn levels than did the addition of serum HSF. These findings indicate that Fn, like fibrinogen, is an acute-phase protein, the production of which, at least in chickens, is stimulated by HSF and glucocorticoids in an additive manner.

Acute-Phase Reaction↗
PubMed1985

Evidence that chicken antithrombin III is a developmentally regulated glycoprotein synthesized by hepatocytes.

Antithrombin III is the principal circulating active-site inhibitor of thrombin and other serine proteinases. We studied a protein synthesized and secreted by cultured chick embryo hepatocytes that has very similar immunological, structural and functional properties to adult antithrombin III. Its presence was demonstrated by; immunodiffusion analysis of a 100-fold concentrate of culture medium, which produced a single precipitin line of identity with adult and 1-day-old hatchling plasma antithrombin III; immunoprecipitation of a metabolically labelled protein from culture medium, having the same molecular size as adult chicken antithrombin III; conversion of antithrombin activity in culture medium to a faster acting thrombin inhibitory activity in the presence of heparin. Antithrombin III antigen levels were increased 3- to 4-fold in the presence of dexamethasone (2 nM) during a 3-day culture period. Plasma antithrombin III antigen levels from unhatched chicks increased from 26 +/- 6 micrograms/ml at 16 days of development to 104 /+- 6 micrograms/ml at 20 days, whereas 1-day-old hatchlings (21 days) had levels similar to that in adults (135 +/- 7 micrograms/ml vs. 143 +/- 24 micrograms/ml). In contrast to immunodiffusion and immunoelectrophoretic analysis of hepatocyte or hatchling plasma antithrombin III, which showed lines of identity with adult antithrombin III, 16- and 20-day-old embryonic plasma antithrombin III yielded lines of partial identity and migrated less anodally than adult antithrombin III. Consistent with this finding, embryonic plasma antithrombin III had no sialic acid (less than 0.01 residue/mol) in contrast with the adult form (3.5 residues/mol). These studies show that the increase in adult antigen levels and sialation of antithrombin III occurs rapidly after hatchling, suggesting developmental changes in expression at the transcriptional and translational levels in addition to post-translational carbohydrate processing.

Animals↗
PubMed1985

Preparation of functionally intact monomers by limited disulfide reduction of human plasma fibronectin dimers.

Most (90 to 95%) human plasma fibronectin (PFn) molecules exist as 450-kDa disulfide-rich dimers comprised of two major types of subunits (A, 220 kDa; B, 215 kDa) that are joined near the COOH terminus by two disulfide bonds. Smaller PFn species (Zone II; 190-235 kDa) consist mainly of monomers and/or a monomeric subunit joined covalently to a smaller peptide remnant presumably derived by proteolysis of a parent 450-kDa molecule. A relatively simple and selective method for preparing functionally active, partially reduced monomeric fibronectin subunits (PR-PFn) by limited and selective reduction of dimeric plasma fibronectin (PFn) has been developed. PR-PFn was prepared by incubating PFn in phosphate-buffered saline, pH 7.4, for 2 h at room temperature in the presence of 17 mM dithiothreitol (DTT). Following S-carboxymethylation or S-carboxyamidomethylation, the material was passed through a gelatin-Sepharose column and nonbinding material was discarded; gelatin-bound material was eluted using a 0 to 2 M KSCN gradient. Residual dimeric species (10-20%) could be separated from monomers in high yield by gel-sieving chromatography on a Sepharose 6B-Cl in the presence of a chaotropic salt, 0.3 M KSCN. Most new SH groups (74-81%) in that fraction of PR-PFn binding to gelatin were localized in proteolytic fragments containing the COOH terminus, thus suggesting that selective cleavage of the interchain disulfide bridges had taken place. The binding affinity of PR-PFn to gelatin- and fibrin-Sepharose was lower than that of dimeric PFn, but the same as that of Zone II PFn and other monomeric gelatin-binding proteolytic derivatives. PR-PFn also bound to heparin-Sepharose and promoted cell attachment and spreading. We conclude that PR-PFn monomers possess the same functional activities as those of the parent chains.

Chromatography, Affinity↗
PubMed1985

Studies of fibronectin synthesized by cultured chick hepatocytes.

We have adapted a chick embryo liver cell system for studying the synthesis of proteins secreted by hepatocytes. In primary liver cell cultures maintained for several days in arginine-deficient medium containing ornithine (0.7 mM) and carbamyl phosphate (1 mM), only hepatocytes demonstrated normal morphological and biosynthetic characteristics, indicating that they possessed a functional ornithine cycle as a source of arginine production. Non-parenchymal liver cells, such as fibroblasts, which lack the ornithine cycle were excluded. Hepatocytes in arginine-deficient or arginine-containing medium synthesized fibronectin (Fn) over several days at a constant rate of 3 micrograms +/- 1 microgram/mg cell protein per day, with fibronectin representing approximately 3% of the total secreted hepatocyte proteins during any culture period after the first 24 h. Pulse-chase experiments indicated that Fn synthesis and secretion was relatively rapid (t1/2 = 45 min) and represented approximately 95% of the intracellularly labelled Fn. This Fn is secreted predominantly as a 450 kD dimer with a subunit size that is indistinguishable from the plasma form as assessed by one-dimensional electrophoretic analysis. Continuous exposure of hepatocytes to insulin caused a moderate decrease (26%) in Fn synthesis, whereas there was no effect of short-term exposure. In contrast, dexamethasone stimulated Fn production 2-3-fold, consistent with its known ability to stimulate hepatocyte production of acute phase proteins. Under these conditions, electrophoretic analyses showed that an increased quantity of intact hepatocyte Fn was produced having the same molecular size of plasma Fn.

Animals↗
PubMed1985

Human platelet fibrinogen: purification and hemostatic properties.

Conditions were developed in which 80% to 90% of platelet fibrinogen could be routinely purified in nondegraded form from the fluid phase of platelet suspensions stimulated with the calcium ionophore, A23187, in the presence of calcium, leupeptin, and prostaglandin E1. Fibrinogen was separated from other released proteins by chromatography on diethylaminoethanol (DEAE)-cellulose using a continuous pH and ionic strength gradient. Purified platelet fibrinogen, greater than 98% homogeneous by immunoelectrophoresis and sodium-dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), consisted of intact A alpha, B beta and gamma A chains, but not gamma' chains, and was 95% to 96% clottable. Platelet fibrinogen was shown to compete for the binding of radiolabeled plasma fibrinogen to ADP-activated platelets in a manner identical to that of unlabeled plasma fibrinogen itself. Also, at equivalent protein concentrations, platelet and plasma fibrinogens supported platelet aggregation to an equivalent extent. Based upon these results, we conclude that there is no significant difference between platelet and plasma fibrinogen with respect to their size, their clottability, their affinity for the activated platelet fibrinogen receptor, or their capacity to support subsequent platelet aggregation.

Adenosine Diphosphate↗
PubMed1984

Human platelet fibrinogen gamma chain structure.

Human plasma fibrinogen is produced by liver parenchymal cells. Such molecules contain two classes of gamma-chains (gamma A, gamma'), which differ with respect to their COOH-terminal sequences. When fibrin is crosslinked in the presence of factor XIIIa and Ca2+, three types of gamma-dimer are formed (gamma A-gamma A; gamma A-gamma'; gamma'-gamma'). A separate fibrinogen pool is located in platelet alpha-granules. We analyzed this fibrinogen to determine whether gamma'-chains were present to the same extent (7%) that they are found in plasma fibrinogen. Electrophoretic analysis (Laemmli system) of reduced samples of the clot that formed subsequent to release of fibrinogen from thrombin-stimulated washed platelets, revealed a single crosslinked gamma-dimer band in the gamma A-gamma A position. Material collected into EDTA-containing buffer and subsequently crosslinked in the presence of added factor XIII and Ca2+ also revealed a gamma A-gamma A dimer band. This finding was further investigated by Western blotting of reduced gel specimens that had been reacted with an anti-gamma-chain antibody followed by 125I-labeled protein A. A single type of gamma-chain, gamma A, was present in the fibrinogen from a Triton X-100 or 10 M urea platelet lysate, or in noncrosslinked fibrin obtained from thrombin-treated platelets. Crosslinked reduced fibrin from thrombin-treated platelets or that prepared from the Triton lysate revealed a single type of gamma-dimer, gamma A-gamma A. We conclude that there are no gamma'-chains (less than 1%) in platelet fibrinogen. This structural difference from hepatic fibrinogen probably results from differences in the processing and/or regulation of the fibrinogen gamma-chain gene in megakaryocytes.

Afibrinogenemia↗
PubMed1983

Separation and analysis of the major forms of plasma fibronectin.

Human plasma fibronectin exists in circulation in multiple molecular forms that are distinguishable by SDS-polyacrylamide gel electrophoresis (zone I, approx. 450 kDa dimers; zone II, 190-235 kDa; Zone III, 146-175 kDa). (Chen, A.B., Amrani, D.L. and Mosesson, M.W. (1977) Biochim. Biophys. Acta 493, 310-322). We report here on investigations of plasma fibronectin that had been purified from the 'heparin-precipitable fraction' of plasma by DEAE-cellulose chromatography using buffers containing a chaotropic salt (KSCN). Zone I fibronectin and zone II fibronectin were subsequently separated by Sepharose CL-6B chromatography in the presence of 0.3 M KSCN. Electrophoresis of reduced zone I fibronectin dimers showed the presence of three types of subunits (i.e., 220 kDa, 215 kDa, 207 kDa), evidently all having the same NH2-terminal sequence. Subunits of this size were also found in reduced zone II fibronectin, as well as another polypeptide of 190 kDa, the latter amounting to under 5% of the total. Unreduced zone I fibronectin was resolved by gel electrophoresis into a doublet. The upper component amounted to approx. 90% of the total and was comprised of 220 kDa and/or 215 kDa subunits; the lower component contained 207 kDa plus a 220 kDa or 215 kDa subunit. Scanning transmission electron microscopy indicated that under physiologic conditions zone II fibronectin molecules, like those in zone I, exist as pleiomorphic, loosely folded structures (approx. 16 X 8-12 nm) that are somewhat smaller than dimeric zone I molecules (approx. 24 X 16 nm). Circular dichroic spectral analyses suggests that both types have similarly folded local domains. Affinity chromatography experiments revealed a relative decrease in the binding of zone II fibronectin to gelatin but no difference from zone I fibronectin with respect to heparin or fibrin binding.

Amino Acids↗
PubMed1983

Structural analysis of fibrinogen synthesized by cultured chicken hepatocytes in the presence or absence of dexamethasone.

Hepatocyte monolayers, derived from chick embryos and cultured in chemically defined medium without hormones, synthesize and secrete fibrinogen that resembles chicken plasma fibrinogen immunochemically and structurally. Addition of a synthetic glucocorticoid, dexamethasone, to the cultured cells resulted in an appreciable and relatively selective increase in fibrinogen synthesis. Autoradiography of fibrinogen that had been metabolically labelled with [35S]methionine and then subjected to SDS-polyacrylamide gel electrophoresis, unreduced or under disulfide-reducing conditions, revealed that only dimeric forms of fibrinogen, containing undegraded A alpha, B beta, and gamma chains, were secreted under stimulated and unstimulated culture conditions.

Animals↗
PubMed1983

Solution and surface effects on plasma fibronectin structure.

As assessed by electron microscopy, the reported shape of the plasma fibronectin molecule ranges from that of a compact particle to an elongated, rod-like structure. In this study, we evaluated the effects of solution and surface conditions on fibronectin shape. Freeze-dried, unstained human plasma fibronectin molecules deposited at pH 7.0-7.4 onto carbon films and examined by scanning transmission electron microscopy appeared relatively compact and pleiomorphic, with approximate average dimensions of 24 nm X 16 nm. Negatively stained molecules also had a similar shape but revealed greater detail in that we observed irregular, yarn-like structures. Glutaraldehyde-induced intramolecular cross-linking did not alter the appearance of plasma fibronectin. Molecules deposited at pH 2.8, pH 9.3, or after succinylation were less compact than those deposited at neutral pH. In contrast, fibronectin molecules sprayed onto mica surfaces at pH 7, rotary shadowed, and examined by transmission electron microscopy were elongated and nodular with a contour length of 120-130 nm. Sedimentation velocity experiments and electron microscopic observations indicate that fibronectin unfolds when it is succinylated, when the ionic strength is raised at pH 7, or when the pH is adjusted to 9.3 or 2.8. Greater unfolding is observed at pH 2.8 at low ionic strength (less than 0.01) compared with material at that pH in 0.15 M NaCl solution. We conclude that (a) the shape assumed by the fibronectin molecule can be strongly affected by solution conditions and by deposition onto certain surfaces; and that (b) the images of fibronectin seen by scanning transmission electron microscopy at neutral pH on carbon film are representative of molecules in physiologic solution.

Electrophoresis, Polyacrylamide Gel↗
PubMed1982

Distribution of plasma fibronectin (cold-insoluble globulin) and components of the factor VIII complex after heparin-induced precipitation of plasma.

Factor VIII procoagulant (VIII:C) activity, factor VIII coagulant antigen (VIII:CAg), von Willebrand ristocetin cofactor (VIIIR:RC) activity, factor VIII-related antigen (VIIIR:Ag), and plasma fibronectin (CIg; cold-insoluble globulin) were measured in the heparin precipitable fraction (HPF) and heparin supernatant fraction (HS) of normal human plasma. Following heparin induced precipitation, most measurable VIII:C activity (77% +/- 24%) was recovered in the HS. Although there was little VIII:C activity (less than 1%) in the HPF, 20% +/- 6.5% VIII:CAg was present as well as CIg (81% +/- 5.6%). VIIIR:RC activity (72% +/- 12%), and VIIIR:Ag (34 +/- 5.2%). As assessed by Na dodecyl SO4 glyoxyl agarose electrophoresis, the multimeric forms of plasma VIIIR:Ag could be resolved into a series of bands. Larger multimers tended to precipitate with the HPF whereas the smaller multimers tended to remain supernatant. Plasma from a subject with congenital afibrinogenemia was also studied. Although the afibrinogenemic HPF contained CIg, neither VIIIR:RC activity nor VIIIR:Ag was precipitated. However, both were present in the HPF from afibrinogenemic plasma to which fibrinogen had been added, suggesting that they are incorporated in this precipitate because of an affinity for fibrinogen. The ability of heparin to induce precipitation of CIg while leaving most VIII:C activity in the supernatant plasma may be useful in the preparation of procoagulant-rich plasma subfractions, since VIII:C can subsequently be recovered in good yield by cryoprecipitation.

Afibrinogenemia↗
PubMed1982

Evidence for circulating fibrin in familial Mediterranean fever.

Cryofibrinogenemia was found in 10 of 24 plasma samples (42%) from subjects with FMF. This precipitate was found during active disease as well as during intervals between crises. We found a higher incidence of cryofibrinogenemia in subjects with mild to moderately severe disease not being treated with colchicine (six of eight) as compared with colchicine-treated subjects who were in partial or complete clinical remission (four or 16; p less than 0.02). All cryofibrinogen precipitates contained fibrin, as assessed by electrophoretic analyses showing the presence of multimeric crosslinked forms of fibrin(ogen) linked by gamma-dimers. This finding in clinical specimens supports the hypothesis that fibrin in an obligatory component of cryofibrinogen. Fibrin was also found in HPF (two of six specimens) prepared from cryofibrinogen-negative FMF plasmas, thus showing that soluble forms of fibrin are even more prevalent in this disorder than is indicated by the frequent finding of cryofibrinogenemia.

Adolescent↗
PubMed1977

Heterogeneity of the cold-insoluble globulin of human plasma (CIg), a circulating cell surface protein.

The cold-insoluble globulin of human plasma (CIg), a circulating cell surface protein, exists in multiple molecular forms. Most molecules are found as two chain (MR approximately 220 000 per chain) disulfide-bridged dimeric units but several minor components of smaller size have also been identified; based upon their migration rates in dodecyl sulfate gel electrophoretic experiments, the smaller molecules characterized in this study range in molecular size from 235 000 to 146 000. The component of molecular weight 235 000 apparently represents a two chain disulfide-bridged derivative of larger parent molecules (one chain of 220 000 plus a smaller remnant), whereas smaller CIg components appear to be single chain proteins. These observations plus electrophoretic analyses of samples of plasmic digests of CIg indicate that the interchain disulfide bridging in the two chain molecule is located in a segment within approx. 175 residues of the NH2- or COOH-terminus.

Dithiothreitol↗