1,721,188 research outputs found
Megathrombocytes, platelet regeneration time and platelet associated IgG in idiopathic thrombocytopenic purpura and in thrombocytopenia associated with chronic liver disease.
No full textPercentage of megathrombocytes, platelet regeneration time (PRT) and platelet-Associated IgG (Pl-A-IgG) were investigated in 12 patients with clinical features consistent with idiopathic thrombocytopenic purpura and in 11 patients with thrombocytopenia associated with chronic liver disease. Bone marrow smears were also examined and megakaryocytes classified into stages I-III according to the current principle. Of 12 patients with idiopathic thrombocytopenic purpura the percentage of megathrombocytes was increased in 9, PRT reduced in 10, and Pl-A-IgG increased in 8 patients. A statistically significant correlation was found between the percentage of megathrombocytes and the level of Pl-A-IgG. A slight correlation was also found between PRT and the percentage of megathrombocytes, while a significant correlation was found between megakaryocytes in stage I and the percentage of megathrombocytes, suggesting that growth of megakaryocytes probably contributes to platelet heterogeneity. In patients with thrombocytopenia and chronic liver disease, the percentage of megathrombocytes was in the normal range. A moderately increased level of Pl-A-IgG was found only in patients with active chronic hepatitis, PRT was reduced only in a few patients, while most of them also showed an increase of Pl-A-IgG
Amidolytic assay of thrombin bound to alpha2-macroglobulin in plasma.
No full textA method for the determination in plasma of alpha2-macroglogulin-bound thrombin is described. Alpha2-Macroglobulin-bound thrombin is precipitated from plasma by 13% polyethyleneglycol, and its amidolytic activity is assayed by using the chromogenic substrate benzoyl-Phe-Val-Arg-p-nitroanilide (S 2160). After thrombin addition to plasma, only about 1.7% of the added thrombin activity was recovered in the alpha2-macro-globulin precipitate. It is suggested that the contribution of alpha2-macroglobulin to anti-thrombin activity of normal plasma is of little relevance
Multimorbidity and polypharmacy in the elderly: lessons from REPOSI
No full textMultimorbidity and polypharmacy in the elderly: lessons from REPOS
The linkage between binding of the C-terminal domain of hirudin and amidase activity in human alpha-thrombin.
No full textA method derived from the analysis of viscosity effects on the hydrolysis of the amide substrates D-phenylalanylpipecolyl-arginine-p-nitroaniline, tosylglycylprolylarginine-p-nitroanaline and cyclohexylglycylalanylarginine-p-nitroalanine by human alpha-thrombin was developed to dissect the Michaelis-Menten parameters Km and kcat into the individual rate constants of the binding, acylation and deacylation reactions. This method was used to analyse the effect of the C-terminal hirudin (residues 54-65) [hir-(54-65)] domain on the binding and hydrolysis of the three substrates. The results showed that the C-terminal hir-(54-65) fragment affects only the acylation rate, which is increased approx. 1.2-fold for all the substrates. Analysis of the dependence of acylation rate constants on hirudin-fragment concentration, allowed the determination of the equilibrium binding constant of C-terminal hir-(54-65) (Kd approximately 0.7 microM). In addition this peptide was found to competitively inhibit thrombin-fibrinogen interaction with a Ki which is in excellent agreement with the equilibrium constant derived from viscosity experiments. These results demonstrate that binding of hir-(54-65) to the fibrinogen recognition site of thrombin does not affect the equilibrium binding of amide substrates, but induces only a small increase in the acylation rate of the hydrolysis reaction
Feasibility of randomised clinical trials in rare diseases: the case of polycythemia vera.
No full textAlthough it has long been recognised as the only reliable instrument for producing scientific evidence on the benefit/risk profile of therapeutic interventions, the technology of randomised clinical trials (RCT) is far from being the backbone of medical knowledge. Randomised clinical trials in polycythemia vera have been carried out when their methodology was being built up and, therefore, was rather unsatisfactory. Now we have aggressive cytoreductive treatments with chemotherapeutic agents loaded with doubts on long-term safety, while phlebotomy and preventive antiplatelet therapy are left to personal preferences because of debatable results of old, low-power clinical trials. A complex profile of uncertainties requires a simple, but articulated strategy of care and research to allow at the same time a reasonable transfer of the best available validated knowledge and a timely investigation of the most relevant questions. Without doubts, multi-country, collaborative RCTs is the key (not isolated or abstract) element of the current scenario. The declared background hypothesis is the willingness of a medical caring community of being, at the same time and with the same patients, a research community. The trial design comes in as the simplest technical way to deal with uncertainty. Data to be collected, criteria, contents, intensity of follow-up, and documentation of the events are exactly the same as those which are planned and adopted in routine care. One of the greatest achievements of the multicenter trials with this orientation has been to produce a "core" of data and practices, on which the main analyses will be made, but which at the same time reflect an optimal level of assistance to the majority of patients. The purpose of this paper is therefore twofold: a) to provide a brief methodological review of the controlled evidence available for the direction of therapeutic practice for PV: b) to outline and discuss the opportunity, general design, and feasibility of research strategies where a comparative large-scale trial between therapeutic alternatives could play a central role
Aspirin in polycythemia vera and essential thrombocythemia: current facts and perspectives.
No full textThe role of aspirin in the antithrombotic strategy of patients with polycythemia vera (PV) and essential thrombocythemia (ET) is highly controversial. Long considered unsafe on the basis of a single clinical trial testing very high doses in PV patients, aspirin is being increasingly used at lower dosage. The rationale for the use of aspirin in patients with PV and ET is provided by the efficacy of this agent in the treatment of microcirculatory disturbances of thrombocythemic states associated with myeloproliferative disorders and by recent evidence that asymptomatic PV and ET patients have persistently increased thromboxane (TX) A2-biosynthesis. This increase, which most likely reflects enhanced platelet activation in vivo, is independent of the platelet mass and blood viscosity and largely supressed by a short term low-dose aspirin regimen (50 mg/day for 7 days). Since enhanced TXA2 biosynthesis may play a role in transducing the increased thrombotic risk associated with PV and ET, long-term low-dose aspirin administration has been proposed as a possible antithombotic strategy in these subjects. The safety of this treatment in PV patients has been recently reassessed by the Gruppo Italiano per lo Studio della Policitemia Vera (GISP) which has followed for over one year 112 patients randomized to receive 40 mg/day aspirin or placebo. In the same study, serum TXB2 measurements provided evidence that the low-dose aspirin regimen tested was fully effective in inhibiting platelet cyclooxygenase activity. On this basis, a large scale trial aimed at assessing the antithrombotic efficacy of this approach is currently being organized. In patients with ET both the minimal aspirin dose required for complete inhibition of platelet cyclooxygenase and the safety of long-term aspirin administration need to be established prior to extensive clinical evaluation of this strategy
'Monolateral' superior vena cava syndrome: right internal jugular vein occlusion
No full textSuperior vena cava syndrome is characterised by dyspnoea, headache, facial oedema, and venous distention in the neck, upper chest and arms. These symptoms are bilateral.
A 47-year-old woman reported the appearance of venous ectasias in the right side of her chest, face and neck. The patient was affected by systemic lupus erythematous with antiphospholipid syndrome and end-stage renal disease. She was on haemodialysis via a right subclavian central venous silicone, double-lumen, tunnelled catheter (central venous catheter, CVC) because of a previous thrombosis of arteriovenous fistula. Although this type of CVC has a higher risk of complications (ie, thrombosis), the reason of this choice was not clear, since the patient was treated at another haemodialysis service.
At physical examination, the patient's clinical condition was discrete; right side of the face appeared slightly swollen; distension of the right external jugular vein and superficial ectasic veins of the right hemithorax were present (figure 1). Ultrasound scan showed a fibrotic right internal jugular vein, without Doppler signal. Neck and chest CT confirmed the lack of contrast enhancement of the right internal jugular vein in its distal tract (5.5 cm) until the confluence with the subclavian vein (figures 2A, B) and the presence of multiple ectasic veins of the subcutaneous tissue of the right anterior chest wall and neck (figures 3 and 4). The CVC was passing through the brachiocephalic vein to the right atrium
Prophylaxis against venous thromboembolism in patients with cancer
No full textProphylaxis against venous thromboembolism in patients with cancer
Allosteric modulation of BPTI interaction with human alpha- and zeta-thrombin.
No full textIn this study, thrombin interaction with the basic pancreatic trypsin inhibitor (BPTI) was investigated in the presence of different allosteric modulators of thrombin, that is the C-terminal hirudin peptide 54-65 (Hir54-65), a recombinant thrombomodulin form (TMEGF4-6) and Na+. BPTI binding to alpha-thrombin is positively linked to Na+. Under low sodium concentration (5 mM Na+) the BPTI affinity for alpha-thrombin was roughly threefold lower than in the presence of 150 mM sodium (Ki = 320 microM vs. 100 microM). The hirudin fragment, which binds to the fibrinogen recognition site (FRS) of thrombin, induced a progressive and saturable decrease (3.6-fold) of alpha-thrombin affinity for BPTI, whereas the thrombomodulin peptide, which binds to a more extended region of FRS, caused a 5.5-fold increase of the enzyme affinity for the inhibitor. The opposite effect exerted by Hir54-65 and TMEGF4-6 was also observed for BPTI interaction with zeta-thrombin, in which the amidic bond between W148 and T149 is cleaved. However, in this case the effect by Hir54-65 and TMEGF4-6, although qualitatively similar to that observed with alpha-thrombin, had a smaller magnitude. Thrombin hydrolysis of Protein C was also differently affected by Hir54-65 and TMEGF4-6 peptides. While the latter enhanced the Protein C activation, the former caused a reduction of both alpha- and zeta-thrombin kcat/K(m)' for Protein C cleavage. These results showed that (a) Na+ facilitates BPTI interaction with thrombin; (b) Hir54-65 and TMEGF4-6, though sharing in part the same binding site at the thrombin FRS, can affect in opposite way thrombin's interaction with BPTI and Protein C; (c) such findings along with the results obtained with zeta-thrombin might be explained by admitting that the thermodynamic linkage between FRS and the critical W60-loop is also controlled by ligation and/or conformational state of the W148 insertion loop
Thermodynamics of substrates and reversible inhibitors binding to the active site cleft of human alpha-thrombin.
No full textThe study of the temperature effect on the binding to the active site of human alpha-thrombin for ten different ligands, i.e. nine peptide substrates and the tight binding inhibitor N alpha -(naphthalene-sulphonyl-glycyl)-4-amidino-DL-phenyl-alanine-piperidine (alpha-NAPAP), showed that the enthalpy is constant over the temperature range spanning from 10 to 40 degrees C. It was found that the values of the binding enthalpy are linearly correlated to those of entropy, and that this correlation arises from a real phenomenon of chemical compensation. On the other hand, no compensatory chemical effect was found for the process of thrombin acylation. Additional experiments showed that binding to thrombin of two competitive thrombin inhibitors, i.e. proflavin and p-aminobenzamidine, is characterized by a change in the standard heat capacity change (delta Cp), approximately equal to -1 kcal/mol K. By analogy with model compound transfer studies and protein folding investigations, it is proposed that a burial of a large surface area of non-polar residues, roughly equal to 3000 A2, brings about the observed heat capacity change. Altogether, the observed phenomena of the chemical compensation and heat capacity change, although qualitatively different, are interpreted as expressions of the same property of the enzyme, i.e. the capacity to undergo conformational transitions upon ligation of the catalytic domain. These structural transitions are strictly ligand-linked and could play a central role for setting the rules which regulate the specificity of substrates and inhibitors binding to the catalytic groove of human alpha-thrombin
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