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Biomedical subjects

R Landolfi

Publications and source records attributed to R Landolfi.

At least 19 recordsLinked to original sources
PubMed1992

Increased thromboxane biosynthesis in patients with polycythemia vera: evidence for aspirin-suppressible platelet activation in vivo.

Increased thromboxane (TX) production and modified aspirin sensitivity has been detected in vitro in platelets isolated from patients with polycythemia vera. To verify the relevance of these capacity-related measurements to the actual rate of TXA2 biosynthesis in vivo and its suppression by oral aspirin, we have investigated the urinary excretion of major enzymatic metabolites of TXB2 in 17 patients with polycythemia vera and 23 gender- and age-matched controls. Urinary 11-dehydro-TXB2 and 2,3-dinor-TXB2 were measured by previously validated radioimmunoassays. In addition, urinary immunoreactive leukotriene (LT) E4 was measured to explore the 5-lipoxygenase pathway of arachidonate metabolism. Polycythemic patients had significantly (P < .001) higher excretion rates of both 11-dehydro-TXB2 (1,033 +/- 1,050 v 117 +/- 45 pmol/mmol creatinine; mean +/- SD) and 2,3-dinor-TXB2 (725 +/- 676 v 82 +/- 43 pmol/mmol creatinine) than controls. In contrast, urinary LTE4 was not significantly different. Enhanced metabolite excretion did not correlate with the platelet count or with the hematocrit value, and was not related to the current treatment or to a clinical history of thrombotic complications. Platelet TX receptor studies did not show any significant changes in the binding characteristics of two different ligands. A platelet-selective regimen of aspirin therapy (50 mg/d for 7 to 14 days) was associated with greater than 80% suppression in metabolite excretion in nine patients. These results are consistent with abnormal stimuli operating in polycythemia vera to induce a selective enhancement in the platelet biosynthesis of TXA2 without changes in receptor binding. This in vivo abnormality in platelet biochemistry can be largely suppressed by low doses of aspirin.

Adult↗
PubMed1991

Effect of fibrinogen concentration on the velocity of platelet aggregation.

The relationship between fibrinogen binding to its receptor and platelet aggregation has been investigated by comparing 125I-fibrinogen binding and aggregation velocities of gel-filtered platelets in the presence of adenosine diphosphate (ADP). Aggregometric responses at various fibrinogen concentrations are found to be bell-shaped and show a maximum at fibrinogen concentrations (Fmax) similar to the 125I-fibrinogen hemisaturating doses. At higher and lower fibrinogen concentrations, platelet aggregation velocities decrease in a parallel manner. Lowering ADP concentration increases Fmax, in agreement with the modulatory effect of ADP on fibrinogen binding to platelets. Variations of fibrinogen in the range of physiopathologic plasma concentrations affect platelet aggregation induced by any ADP dose. These results clarify the relationship between the fibrinogen binding process and aggregation and demonstrate that plasma fibrinogen concentration has a major influence on the velocity of platelet aggregation.

Adenosine Diphosphate↗
PubMed1990

The linkage between adenosine nucleotide binding and amidase activity in human alpha-thrombin.

The amidase activity of human alpha-thrombin has been studied in the presence of the adenosine nucleotides AMP, ADP and ATP. At low concentrations, adenosine nucleotides increase thrombin activity up to 30%, while at high concentrations (greater than 5 mM) inhibition takes place up to 20%. Inhibition is progressively reduced by increasing substrate concentration. A simple, phenomenological description of the linkage between adenosine nucleotide binding and amidase activity of human alpha-thrombin is proposed and the free energy changes for the underlying reactions involved in the linkage scheme are resolved by global analysis of the experimental data. The linkage scheme assumes that thrombin activation is determined by a conformational transition due to binding of adenosine nucleotides to a regulatory site. Inhibition, on the other hand, would be a consequence of competitive binding to the catalytic site.

Adenosine Diphosphate↗
PubMed1989

Inhibition of fibrinogen binding to human platelets by blockage of Na+/H+ exchange.

Binding of ADP to platelets enhances the binding of fibrinogen to Gp IIb-IIIa, the specific platelet receptor for adhesive proteins. The linkage between ADP and fibrinogen binding is indirect since ADP does not bind to the same receptor as fibrinogen. We have recently proposed that a third component, once affected by ADP binding, induces a conformational transition of the fibrinogen receptor from the low to the high affinity state, which is responsible for platelet aggregation [De Cristofaro, R., Landolfi, R., Castagnola, M., De Candia, E., Di Cera, E., & Wyman, J. (1988) Proc. Natl. Acad. Sci. USA 85, 8473-8476]. In the present study we provide evidence that this component should be identified with the platelet Na+/H+ antiport. Inhibition of the antiport by pharmacological agents such as amiloride, or else by decreasing extracellular Na+, results in a marked decrease of fibrinogen binding to platelets.

Adenosine Diphosphate↗
PubMed1989

Carbon monoxide and oxygen binding to human hemoglobin F0.

Differential binding curve measurements of carbon monoxide and oxygen binding to human hemoglobin F0 under near-physiological conditions (0.1 M NaCl and 15 mM 2,3-diphosphoglyceric acid, pH 7.35, and 37 degrees C) have allowed a detailed description of the binding and linkage between these two gaseous ligands. Comparison with human hemoglobin A0 under identical solution conditions shows that fetal hemoglobin F0 binds oxygen and carbon monoxide with higher affinity than human hemoglobin A0, but with the same cooperativity. Construction of the partition coefficient surface for carbon monoxide and oxygen binding reveals a failure of Haldane's laws for both hemoglobins. Linkage graphs are used to explore the phenomenological properties of the system. The graphs provide a quantitative description of the mechanism of carbon monoxide toxicity on oxygen transport by hemoglobin in vivo and demonstrate striking similarities between the functional properties of fetal and adult hemoglobins.

Carbon Monoxide↗
PubMed1988

Meningeal hematopoiesis causing exophthalmus and hemiparesis in myelofibrosis: effect of radiotherapy. A case report.

Meningeal myeloid metaplasia (MM) is very rarely observed in patients with myelofibrosis. We report the occurrence of meningeal MM causing exophthalmus and fever in a patient with myelofibrosis secondary to polycythemia vera. A computerized tomography (CT) scan showed multiple intracranial and intraorbital enhancing masses. A needle aspirate of retrobulbar space confirmed the diagnosis of extramedullary hematopoiesis. The patient subsequently developed a rapidly worsening tumor-like syndrome with hemiparesis, aphasia, and loss of sphinteric control. The administration of radiotherapy caused a complete and stable regression of clinical symptoms and a marked reduction of MM masses.

Adult↗
PubMed1988

High-performance liquid chromatography in protein sequence determinations.

The use of reversed-phase high-performance liquid chromatography (RP-HPLC) for the determination of protein sequences is reported. Topics considered include the peptide separation of endoprotease digestion mixtures, the application of HPLC peptide mapping as an efficient system to check the accuracy of an assumed protein sequence, obtained indirectly by DNA sequencing and the use of HPLC for amino acid analysis in the Edman sequence strategy. The use of RP-HPLC for an unconventional sequence strategy is demonstrated; HPLC exopeptidase mapping appears to be particularly useful as a future technique for small terminal sequence analysis. Finally, the coupling of HPLC with fast atom bombardment mass spectrometry is discussed.

Acetates↗
PubMed1988

Allosteric equilibria in the binding of fibrinogen to platelets.

The binding of fibrinogen to platelets occurs according to the law of mass action. The platelet receptor binds reversibly a single fibrinogen molecule and undergoes a conformational transition between two allosteric states, T and R, that differ in their affinity for fibrinogen. The equilibrium between the two forms is shifted by ADP toward the R (high-affinity) state, thus promoting the aggregation process. This model opens the way to consideration of allosteric modulation of the binding of fibrinogen to its platelet receptor.

Adenosine Diphosphate↗
PubMed1988

Determination of neutral haemoglobin variants by immobilized pH gradient, reversed-phase high-performance liquid chromatography and fast-atom bombardment mass spectrometry: the case of a Hb Torino alpha 43 (CE1) Phe----Val.

A neutral haemoglobin variant was identified by the combined use of different analytical methods. Isoelectric focusing on immobilized pH gradients (under denaturing conditions) allowed to detect and alpha chain variant. HPLC of tryptic digest showed that its amino-acid variation resided on T alpha 6 peptide (position 41-56). In the fast-atom bombardment (FAB) positive mass spectrum of the tryptic digest, the protonated molecular ion of the T alpha 6 peptide occurred 48 mass units lower than the normal T alpha 6 fragment, corresponding to a Phe----Val substitution. To a partial sequence determination (aminopeptidase digestion of the T alpha 6 peptide, followed by amino acid determination and FAB-MS analysis of the digestion-generated mixture) the substitution appeared to be on Phe43 (CE1). This variant is already known as Hb Torino. The procedure here described proved to be fast and simple, and feasible whenever neutral variants are supposed to occur.

Child, Preschool↗
PubMed1988

Increased platelet-fibrinogen affinity in patients with myeloproliferative disorders.

Patients with myeloproliferative disorders (MPD) are known to have some abnormalities of platelet glycoproteins (Gp). Quantitative changes of the Gp Ib, IIb-IIIa, and/or their glucidic content have been reported. Since the Gp IIb-IIIa complex plays a major role in fibrinogen binding by activated platelets, we measured the platelet fibrinogen affinity in nine patients with polycythemia vera (PV) and one subject with chronic myeloid leukemia (CML) by the aggregometric method of Marguerie. In all patients the Kd of the platelet fibrinogen reaction was significantly decreased as compared to controls, with evidence in two cases with PV of a heterogeneity of platelet-fibrinogen receptor sites. The measurement of 125I-labeled fibrinogen-platelet binding, performed in seven patients (five PV and two CML), showed receptor populations with increased (Kd1 = 0.58 + 0.3 X 10(7) mol/L) and normal affinity (Kd2 = 5.12 + 3.1 X 10(7) mol/L). These results demonstrate a heterogeneity of platelet-fibrinogen receptors in these patients and may explain the thrombotic diathesis of MPD subjects.

Adult↗
PubMed1986

T lymphocyte subsets and platelet-associated IgG in idiopathic thrombocytopenic purpura: effect of splenectomy.

The modifications of cell-mediated immunity in idiopathic thrombocytopenic purpura (ITP) were investigated using the technique of Moretta et al. [J. exp. Med. 151: 969-974, 1980] to study T lymphocyte subsets in 35 ITP subjects at various clinical stages. In all these patients, platelet-associated IgG (PAIgG) were measured by a complement lysis inhibition technique. Untreated ITP patients did not show significant modifications of T lymphocyte subsets. Patients with thrombocytopenia not responsive to corticoids or splenectomy and increased PAIgG levels showed significant reduction of Fc-gamma-bearing T lymphocytes (T-gamma). Patients 'cured' by splenectomy (12 out of 17) showed a normal PAIgG level, a marked increase of T-gamma cells and a reduction of T-mu cells; patients 'not cured' by splenectomy showed an increased PAIgG level and a reduction of T-gamma cells. An increase of PAIgG levels and a reduction of T-gamma cells were found in 2 splenectomized patients after relapse. An association between chronic nonresponsive ITP and decrease of T-gamma cells was established.

Adolescent↗
PubMed1979

Human platelet aggregation by thimerosal. Functional and ultrastructural studies.

Thimerosal, a sulfhydryl group inhibitor, produces in an aggregometer a decrease in optical density of normal platelet-rich plasma over a wide range of concentrations. Ultrastructural study shows that the decrease of optical density produced by thimerosal at low doses is due to a true platelet aggregation preceded by a release reaction, whereas the aggregometric curves recorded after addition of thimerosal at high doses can be attributed to marked alterations of platelet morphology. Electron microscopic study shows the presence of electron-dense material between plasma membranes after addition of a low dose, and the early rupture of membranes after a high dose. These findings support previous conclusions that thimerosal binds to plasma membranes. Thimerosal induces a release reaction, seen in ultrastructural study and revealed by measurement of 14C-serotonin release. Moreover, thimerosal-induced aggregation is independent of released ADP and of formation of intermediates of the arachidonate pathway. Thimerosal-induced platelet aggregation is inhibited neither by ADP removal nor by aspirin addition.

Adenosine Diphosphate↗