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L De Marco

Publications and source records attributed to L De Marco.

At least 91 records · Page 5Linked to original sources
PubMed1986

Bernard-Soulier syndrome: diagnosis by an ELISA method using monoclonal antibodies in 2 new unrelated patients.

Two unrelated patients with Bernard-Soulier syndrome and their relatives were studied. The patients demonstrated severe bleeding diathesis, the relatives were asymptomatic. The propositi showed the characteristic abnormalities of the syndrome: thrombocytopenia, a percentage of giant platelets higher than 65%, prolonged bleeding time and defective platelet aggregation to ristocetin and bovine plasma. On the contrary, in the heterozygotes, the typical abnormalities were not fully evident. We introduce a simple ELISA method for the precise definition of both homozygous and heterozygous states for the syndrome by the quantitation of platelet glycoprotein (GP) Ib. Specific binding of monoclonal antibodies anti-platelet GPIb was performed both by direct binding of radioiodinated antibody and by ELISA. Comparable results were obtained. In fact, we demonstrated near absence of GPIb in the 2 propositi and about half the amount in the heterozygotes studied compared to normal platelets.

Adolescent↗
PubMed1986

von Willebrand factor interaction with the glycoprotein IIb/IIa complex. Its role in platelet function as demonstrated in patients with congenital afibrinogenemia.

We have studied three afibrinogenemic patients, who had only trace amounts of plasma and platelet fibrinogen as measured by radioimmunoassay, and demonstrate here that the residual aggregation observed in their platelet-rich plasma is dependent upon von Willebrand factor (vWF) binding to the platelet membrane glycoprotein (GP)IIb/IIIa complex. The abnormality of aggregation was more pronounced when ADP, rather than thrombin, collagen, or the combination of ADP plus adrenaline was used to stimulate platelets. With all stimuli, nevertheless, the platelet response was completely inhibited by a monoclonal antibody (LJP5) that is known to block vWF, but not fibrinogen binding to GPIIb/IIIa. Addition of purified vWF to the afibrinogenemic plasma resulted in marked increase in the rate and extent of aggregation, particularly when platelets were stimulated with ADP. This response was also completely blocked by LJP5. Addition of fibrinogen, however, restored normal aggregation even in the presence of LJP5, a finding consistent with the knowledge that antibody LJP5 has no effect on platelet aggregation mediated by fibrinogen binding to GPIIb/IIIa. Two patients gave their informed consent to receiving infusion of 1-desamino-8-D-arginine vasopressin (DDAVP), a vasopressin analogue known to raise the vWF levels in plasma by two- to fourfold. The bleeding time, measured before and 45 min after infusion, shortened from greater than 24 min to 12 min and 50 s in one patient and from 16 min to 9 min and 30 s in the other. Concurrently, the rate and extent of ADP-induced platelet aggregation improved after DDAVP infusion. The pattern, however, reversed to baseline levels within 4 h. The concentration of plasma vWF increased after DDAVP infusion, but that of fibrinogen remained at trace levels. We conclude that vWF interaction with GPIIb/IIIa mediates platelet-platelet interaction and may play a role in primary hemostasis.

Adenosine Diphosphate↗
PubMed1985

Interaction of purified type IIB von Willebrand factor with the platelet membrane glycoprotein Ib induces fibrinogen binding to the glycoprotein IIb/IIIa complex and initiates aggregation.

Von Willebrand factor (vWF) was purified from the plasma of a patient with type IIB von Willebrand disease (vWF from such a patient, IIB vWF) who had a normal platelet count and showed no evidence of spontaneous platelet aggregation. Large multimers of IIB vWF were absent from purified preparations and from plasma. Ristocetin-induced platelet aggregation was enhanced by purified IIB vWF. The aggregation of washed normal platelets mixed with IIB vWF (0.4 microgram/ml) required lower amounts of ristocetin than the aggregation of normal platelets mixed with the same concentrations of normal vWF. Moreover, purified IIB vWF alone induced aggregation of platelet-rich plasma at concentrations as low as 10 micrograms of IIB vWF/ml in the absence of any other agonist. Aggregation was blocked by a monoclonal antibody against the platelet membrane glycoprotein, GPIb, as well as by an anti-GPIIb/IIIa antibody. Washed platelet suspensions were promptly aggregated by IIB vWF only when fibrinogen and CaCl2 were added to the mixture. Purified IIB vWF induces the binding of fibrinogen to platelets. Such binding was blocked by the anti-GPIb monoclonal antibody as well as by the anti-GPIIb/IIIa monoclonal antibody that inhibited aggregation. A second anti-GPIIb/IIIa antibody, which has the property of blocking vWF but not fibrinogen binding to platelets, blocked neither aggregation nor fibrinogen binding induced by IIB vWF. These studies demonstrate that platelet aggregation is triggered by the initial interaction of IIB vWF with GPIb which is followed by exposure of fibrinogen binding sites on GPIIb/IIIa. Fibrinogen binds to these sites and acts as a necessary cofactor for the aggregation response.

Antibodies, Monoclonal↗
PubMed1985

Interaction of asialo von Willebrand factor with glycoprotein Ib induces fibrinogen binding to the glycoprotein IIb/IIIa complex and mediates platelet aggregation.

von Willebrand factor (vWF) is necessary for the initial attachment of platelets to exposed subendothelium, particularly under flow conditions like those prevailing in the microcirculation. Little is known about its possible participation in subsequent events leading to formation of platelet thrombi at sites of vascular injury. We addressed this question by studying the mechanisms by which desialylated vWF induces platelet aggregation in the absence of any other stimulus. Asialo vWF, unlike the native molecule, does not require ristocetin to interact with platelets. Agglutination induced by ristocetin is largely independent of active platelet metabolism and only partially reflects physiological events. We have shown here that binding of asialo vWF to platelets was accompanied by release of dense granule content and subsequent ADP-dependent fibrinogen binding to receptors on the glycoprotein (GP) IIb/IIIa complex. The initial interaction of asialo vWF with platelets was mediated by GPIb, as shown by blocking obtained with monoclonal antibody. Inhibition of this initial interaction completely abolished platelet aggregation induced by asialo vWF. The same effect was obtained with a monoclonal anti-GPIIb/IIIa antibody. This, however, did not block asialo vWF binding to platelets, but rather inhibited subsequent fibrinogen binding induced by asialo vWF. Therefore, the latter process was also essential for platelet aggregation under the conditions described. At saturation, asialo vWF induced binding of between 3.2 and 27.7 X 10(3) fibrinogen molecules/platelet, with an apparent dissociation constant between 0.28 and 1.18 X 10(-6) M. This study shows that asialo, and possibly native, vWF acts as a platelet agonist after its binding to GPIb and induces aggregation through a pathway dependent on GPIIb/IIIa-related receptors.

Asialoglycoproteins↗
PubMed1984

Pulmonary rhabdomyosarcoma with isolated small bowel metastasis. A report of a case with immunohistochemical and ultrastructural studies.

A unique case of pulmonary rhabdomyosarcoma with an isolated, symptomatic small bowel metastasis is presented. The tumor affected the middle lobe, and was treated with a right pneumonectomy. Eleven months after the operation, an isolated small bowel metastasis, which produced intestinal obstruction, was resected. The patient is currently alive, 11 months after operation. The myogenous nature of the tumor was confirmed by the immunohistochemical demonstration of myoglobin in the pulmonary and enteric lesion by the ultrastructural findings of poorly developed sarcomeres.

Adult↗
PubMed1984

The levels and subcellular distribution of hormones and marker enzymes in pituitaries from control subjects and patients with prolactinomas, acromegaly or functionless pituitary tumours.

Pituitary homogenates were prepared from patients undergoing pituitary ablation for breast or prostatic carcinoma (controls) and from patients with either PRL- and GH-secreting pituitary adenomas or from patients with 'functionless' pituitary tumours. The principal subcellular organelles, plasma membrane, lysosomes, mitochondria, endoplasmic reticulum, cytosol and hormone-containing granules were characterized by sucrose density gradient centrifugation. Tissue from patients with prolactinomas showed hormone granules, lysosomes and endoplasmic reticulum of lighter density than controls; cytosol, mitochondria and plasma membrane were similar. PRL-secreting tumours showed a 2-fold increase in PRL content with significant reduction of LH, FSH and GH. Activities of various lysosomal enzymes, except for PRL proteolytic activity, were significantly reduced. Similar conclusions were found for GH-secreting pituitary adenomas with a striking reduction in PRL proteolytic activity. Functionless tumours showed significant amounts, though reduced compared to control tissue, of all hormones. In contrast to the hormone-secreting adenomas, the activity of the lysosomal enzyme N-acetyl-beta-glucosaminidase was significantly increased compared to control tissue.

Acetylglucosaminidase↗
PubMed1984

Carbohydrate moiety of von Willebrand factor is not necessary for maintaining multimeric structure and ristocetin cofactor activity but protects from proteolytic degradation.

To better define the role of carbohydrate in the structure and ristocetin cofactor activity of von Willebrand factor, we have removed up to 83% of total hexose by sequential treatment of the molecule with endo-beta-N-acetyl-glucosaminidase F (endo F), neuraminidase, and beta-galactosidase. Endo F alone removed 69% of total hexose and D-galactose, and 71% of sialic acid. However, there was no discernible loss of large multimers and the ristocetin cofactor activity was decreased by only 11%. The reduced von Willebrand factor subunit migrated more rapidly in polyacrylamide gels containing SDS, consistent with a 10% decrease of molecular mass. All multimers of unreduced carbohydrate-modified von Willebrand factor migrated more rapidly in SDS-agarose, but the triplet pattern of individual multimers was unchanged. This alteration in multimer migration rate did not resemble alterations found so far in von Willebrand disease variants. Further treatment of von Willebrand factor with neuraminidase and beta-galactosidase reduced the D-galactose to 15% and ristocetin cofactor activity to 57%. A similar decrease in ristocetin cofactor activity was seen if von Willebrand factor was treated only with neuraminidase and beta-galactosidase. In contrast, treating von Willebrand factor with neuraminidase and beta-galactosidase in the presence of protease inhibitors (20 mM benzamidine, 20 U/ml aprotonin, 15 micrograms/ml leupeptin) resulted in a comparable removal of carbohydrate with no change in ristocetin cofactor activity. Moreover, the multimeric structure remained intact in spite of 80% removal of D-galactose. This suggested that carbohydrate was protecting von Willebrand factor against traces of one or more protease contaminants. Evidence in support of this hypothesis was obtained by exposing von Willebrand factor to plasmin after pretreatment with neuraminidase alone or with neuraminidase and beta-galactosidase. A loss of large multimers was observed from von Willebrand factor that had been pretreated with neuraminidase, but this was even greater if pretreatment was also with beta-galactosidase. In contrast, the multimeric structure of von Willebrand factor with intact carbohydrate was not affected by plasmin under similar conditions. These studies suggest that carbohydrate protects von Willebrand factor from disaggregation occurring secondarily to proteolytic attack but does not play a direct role in maintaining its multimeric structure or ristocetin cofactor activity.

Acetylglucosaminidase↗
PubMed1984

Effects of bromocriptine on pituitary organelle marker enzyme activities in lactating and postlactating rats: selective activation of lysosomal prolactin proteolytic activity.

Effects of the dopamine agonist 2-bromo-alpha-ergocryptine (bromocriptine) on plasma and pituitary PRL and enzyme activities in lactating and postlactating rats have been investigated. Lactating rats which had been suckling their young for 3 days were given a single sc injection of bromocriptine or solvent. The treated and control animals were divided into 2 further groups. One group (lactating rats) was permitted to suckle their pups for a further 12 or 24 h; the young were removed from the other group (postlactating rats). Homogenates were prepared from the anterior pituitaries and assayed for organelle marker enzyme activities. When 0.5-500 micrograms bromocriptine were administered to lactating rats for 24 h, pituitary PRL was increased by all doses, but only the 500-micrograms dose significantly reduced plasma PRL. Total protein was unchanged, lysosomal acid PRL proteolytic activity increased 8-fold, N-acetyl-beta-glucosaminidase and beta-glucuronidase (lysosomes) were unchanged, acid phosphatase (lysosomes and endoplasmic reticulum) was increased by three of four doses, 5'-nucleotidase and alkaline phosphatase (plasma membrane) were increased 4-fold, neutral-alpha-glucosidase (endoplasmic reticulum) and malate dehydrogenase (mitochondria) were unchanged, and catalase (peroxisomes) was significantly increased. Bromocriptine (500 micrograms) administration to lactating and postlactating rats for 12 and 24 h significantly decreased the pituitary DNA but not the total protein content of the pituitaries in all animals. The lysosomal acid PRL proteolytic activity and the lysosomal enzyme activities, N-acetyl-beta-glucosaminidase and beta-glucuronidase, were increased by suckling withdrawal alone. Acid PRL proteolytic activity was further increased (to 18-fold) by coadministration of bromocriptine, whereas the increase in the activities of the other lysosomal marker enzymes was blocked. Malate dehydrogenase activity (mitochondria) was also increased by litter removal and blocked by bromocriptine. The activity of the plasma membrane markers 5'-nucleotidase and alkaline phosphatase were increased by litter removal, and bromocriptine further increased both enzyme activities. The activity of neutral-alpha-glucosidase (endoplasmic reticulum) was unchanged by any treatment. The results demonstrate that bromocriptine produces significant changes in the activities of lysosomal marker enzymes, particularly acid PRL proteolytic activity, as well as marker enzymes of plasma membranes and other organelles in pituitaries of lactating and postlactating rats.

5'-Nucleotidase↗
PubMed1983

Membrane proteins on human megakaryocytes and platelets identified by monoclonal antibodies.

We describe five monoclonal antibodies that react with four discrete antigens present on human platelets. Antibodies B2.12 and B59.2 precipitate the glycoprotein IIb-IIIa complex from radiolabeled platelet membrane extracts and inhibit platelet aggregation induced by adenosine diphosphate (ADP), collagen, or epinephrine. The antigen recognized by the two antibodies is present on megakaryocytes but either absent entirely or expressed in small amounts on platelets from Glanzmann's thrombasthenic patients. The antigen recognized by antibody B37.3 is absent from thrombasthenic platelets. Antibody B1.12 reacts with an antigen shared by platelets and 20% of peripheral blood lymphocytes and is a potent inducer of platelet aggregation. Antibody B2.10 reacts specifically with platelets and megakaryocytes but does not affect platelet functions. Thus, these reagents are useful tools in diagnostic and functional studies of both normal and abnormal platelets.

Antibodies, Monoclonal↗
PubMed1983

Platelets have more than one binding site for von Willebrand factor.

The binding of 125I-von Willebrand factor (125I-vWF) to platelets stimulated by thrombin, ADP, and a combination of ADP + epinephrine (EPI) is specific, saturable, and reversible. Active platelet metabolism and divalent cations are required for binding induced by these stimuli, but not by ristocetin, suggesting the existence of different mechanisms involved in the vWF-platelet interaction. A monoclonal antibody directed against an epitope of membrane glycoprotein (GP) Ib had no effect on the binding of 125I-vWF to normal platelets stimulated by thrombin or a combination of ADP + EPI, but completely blocked ristocetin-induced binding. Binding induced by thrombin to GPIb-blocked platelets was specific. Moreover, thrombin-induced binding of 125I-vWF was increased, rather than decreased, in two patients with the Bernard-Soulier syndrome whose platelets lacked GPIb. Conversely, monoclonal antibodies directed against the GPIIb/IIIa complex had no effect on ristocetin-induced binding of 125I-v-WF to normal platelets, but blocked thrombin- and ADP + EPI-induced binding. To exclude effects mediated by the platelet Fc receptor, a monoclonal IgG directed against an epitope present on human B cells and monocytes, but not expressed on resting or stimulated platelets, was used. It did not affect 125I-vWF binding induced by any of the stimuli. These studies show that platelets have more than one binding site for vWF, and that they may be exposed by different stimuli.

Adenosine Diphosphate↗
PubMed1983

The role of ADP secretion and thromboxane synthesis in factor VIII binding to platelets.

Following stimulation with arachidonic acid, collagen, U-46619 (a stable analogue of prostaglandin endoperoxide/thromboxane-A2), thrombin, or adenosine diphosphate (ADP), unstirred human platelet suspensions bound labeled factor VIII in a reaction that reached equilibrium within 10 min. Apyrase inhibited binding induced by arachidonic acid, collagen, U-46619, and thrombin by less than 40%, but inhibited ADP-induced binding by 95%. Binding to aspirin-treated platelets was normal in response to U-46619, reduced by 60%-70% in response to ADP, collagen, and thrombin, and absent in response to arachidonic acid. Binding in response to U-46619 was not altered by the combination of apyrase and aspirin. Binding of factor VIII was decreased by 90% when 10 mM EDTA was added before each agonist, but it was inhibited less than 30% when EDTA was added following platelet stimulation. We conclude that arachidonic acid, collagen, and thrombin can expose binding sites for factor VIII independently of released ADP; that Ca++ is required for activation but probably not for binding of factor VIII to platelets; and that platelet thromboxane synthesis plays a major role in the binding of factor VIII to platelets induced by thrombin, ADP, or collagen.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1982

Inappropriately low serum GH in an acromegalic: lysosomal involvement in intracellular hormone degradation.

A patient with galactorrhea, amenorrhae and severe acromegaly was found to have a large pituitary adenoma. In view of the severity of the disease the serum growth hormone (GH) level (22.5 mlU/liter) was considered inappropriately low. Tissue from the adenoma was obtained during successful treatment with interstitial irradiation. (90Yttrium). Trypsin-dispersed biopsy cells in culture for 12 days secreted low amounts of GH compared to the same number of adenoma cells from 5 other unselected acromegalics or a normal pituitary. No other hormones were secreted in culture. Immunocytochemical staining was positive only with GH antisera but showed low intracellular content. This was confirmed by direct analysis of the tumor tissue which showed the GH content to be only 20% of that found in 5 normal pituitaries and 4% of that found in 8 other adenomas from acromegalics. Electron microscopy showed a striking appearance, with GH secretory granules that were sparse in number, smaller than usual, and in the main arranged around numerous intracellular profiles with double membranes and low electron density that were tentatively identified as autophagic vacuoles (secondary lysosomes). Subcellular fractionation showed the distribution of the radioimmunoassayable GH in the gradient to be coincident with the peak of the lysosomes whereas in 2 other acromegalics the GH peak was clearly separated from the lysosomes. We conclude that the simultaneous appearance in our patient of the relatively low serum GH together with a large tumor and severe acromegaly can be explained biochemically by the striking finding of crinophagy - disposal of hormone secretory granules within the somatotroph cells themselves.

Acromegaly↗