Electrokinetic, analytical and functional heterogeneity of circulating human platelets: separation of subpopulations by continuous flow electrophoresis after taxol stabilization

Sialic Acid: its importance to platelet function in health and disease

Platelets are known to contain sialic acid, most of which resides on glycoprotein carbohydrate side-chains. A large proportion of the platelet sialic acid is neuraminidase-labile. The sialic acid of human platelets is of the N-acetyl neuramininic acid type and is implicated in platelet functional events, such as aggregation and adhesion as well as contributing to the platelet's electrophoretic mobility. In this respect the platelet has an overall electronegative charge which is predominately the result of the carboxyl group of the sialic acid moiety. Platelet subpopulations have been isolated with differing amounts of sialic acid and cleavage of platelet sialic acid by neuraminidase is associated with loss of platelets from the circulation. This has relevance to platelet aging in vivo where removal of platelet sialic acid may reveal 'senescence antigens' which could facilitate platelet 'uptake' by the reticuloendothelial system. The importance of platelet sialic acid status has been described in certain platelet disorders such as some thrombocytopenias as well as particular disease states including malignancies and atherosclerosis.

An experience of oseltamivir phosphate (tamiflu™) in a pediatric patient with chronic idiopathic thrombocytopenic purpura: a case report

We report a pediatric patient with chronic idiopathic thrombocytopenic purpura who suffered from an influenza A (H1N1) virus infection. A 13-year-old girl presented with fever, coughing, and generalized petechiae. The influenza A antigen was positive in her pharyngeal aspirate. She was successfully treated with neuraminidase inhibitor oseltamivir phosphate. Her platelet counts progressively increased with oseltamivir phosphate without another blood product or agent. We suggest that oseltamivir phosphate can be used in patients with immune thrombocytopenic purpura who present with influenza virus A infection. We also suggest that oseltamivir phosphate can be effective in patients with immune thrombocytopenic purpura. Large study groups are needed to confirm the relationship between idiopathic thrombocytopenic purpura and neurominidase inhibitors.

In vitro hemocompatibility studies of drug-loaded poly-(L-lactic acid) fibers

Our objective was to evaluate the hemocompatibility of biodegradable stent fibers, employing a closed-loop circulation system filled with human blood. We also investigated the effects of the anti-inflammatory and anti-proliferative drugs curcumin and paclitaxel, incorporated into stent fibers. Fresh whole blood was circulated in four parallel closed-loop systems: the empty tube circuit (control) and tubes containing either a PLLA fiber coil (PLLA), a curcumin-loaded PLLA coil (C-PLLA) or a paclitaxel-loaded PLLA coil (P-PLLA). The influence of PLLA fiber, alone or loaded with drug incorporated during melt-extrusion, on leukocyte and platelet adhesion and activation was determined by flow cytometry. The effects of blood flow and fiber properties on cell deposition were assessed by scanning electron microscopy (SEM). The flow cytometry results clearly demonstrated that PLLA triggers blood cell activation at the site of deployment, as shown by increases in CD11b, CD62P and leukocyte-platelet aggregates, compared to controls. Curcumin and paclitaxel treatments both significantly reduced leukocyte and platelet activation and adhesion to PLLA fibers, as shown by flow cytometry and SEM. Activated leukocytes and platelets revealed significantly lower CD11b and CD62P receptor binding for C-PLLA compared with PLLA alone, and slightly lower for P-PLLA. Reductions in platelet-leukocyte aggregates were observed as well. In addition, there was less leukocyte and platelet adhesion to C-PLLA, compared with PLLA fiber controls, as shown by SEM. A continuous linear thrombus, composed of platelets, leukocytes, red blood cells and fibrin was occasionally detected along the line of tangency between the coil and the tube wall. Flow separation and eddying, proximal and distal to the line of tangency of coil and tube, is thought to contribute to this deposit. Curcumin was more effective than paclitaxel in reducing leukocyte and platelet activation and adhesion to PLLA stent fibers in this setting. However there was evidence of paclitaxel degeneration during melt extrusion that may have inhibited its effectiveness. Incorporation of the anti-inflammatory and anti-proliferative drug curcumin into bioresorbable stent fibers is proposed to prevent thrombosis and in-stent restenosis.

A clinical and pharmacokinetic study of the combination of carboplatin and paclitaxel for epithelial ovarian cancer

The aim of this phase I study was to determine the maximum tolerated dose of a 3-h infusion of paclitaxel, combined with carboplatin at a fixed AUC of 7 mg ml-1 min every 4 weeks for up to six cycles and to evaluate any possible pharmacokinetic interaction. Twelve chemonaive patients with ovarian cancer were treated with paclitaxel followed by a 30-min infusion of carboplatin. Paclitaxel dose was escalated from 150 mg m-2 to 225 mg m-2 in cohorts of three patients. Carboplatin dose was based on renal function. Pharmacokinetic studies were performed in nine patients (at least two at each dose level). A total of 66 courses were evaluable for assessment. Grade 3 or 4 neutropenia was seen in 70% of the courses, however hospitalization was not required. Grade 3 or 4 thrombocytopenia occurred in 24% of the courses. Alopecia, myalgia and peripheral neuropathy were common but rarely severe. The pharmacokinetics of paclitaxel was non-linear and did not appear to be influenced by co-administration of carboplatin. The AUC of carboplatin was 7.0 +/- 1.4 mg ml-1 min, indicating that there was no pharmacokinetic interaction. The combination of carboplatin and paclitaxel may be administered as first-line treatment for advanced ovarian cancer. Although myelosuppression is the dose-limiting toxicity of the component drugs, the severity of thrombocytopenia was less than anticipated. The results of this study, with only a small number of patients, need to be confirmed in future investigations.

Blood platelet heterogeneity: a functional hierarchy in the platelet population

The platelet population in man and rat can be divided into two classes of about equal size based on the presence/absence of a p-nitrophenylphosphatase, which probably is a phosphotyrosine phosphatase (PTPase). Phosphorylation of tyrosines on several platelet proteins is implicated in platelet activation, and I carried out in vitro and in vivo experiments on rats to determine whether PTPase positive and negative platelets differed in their reaction time. I used adhesion to collagen in vitro and in vivo (longitudinal slits in aorta and vena portae) and platelet aggregates in clots formed in vivo. I present evidence that PTPase negative platelets react the fastest, most conspicuously seen in the arterial bleeding under high flow conditions, where the first platelets to respond and adhere are predominantly PTPase negative.

Electrokinetic properties of human cryopreserved platelets

A method for the cryopreservation of human platelets with glycerol/glucose is described which was a simplified modification of the method of Dayian and Pert (1979). The effect of cryoinjury of the platelet surface membrane was investigated by studying the surface electrokinetic properties of the platelet. A significant increase in platelet electrophoretic mobility was found after cryopreservation. The fresh platelets had a mean electrophoretic mobility of 1.04 +/- 0.05 microns s-1 V-1 cm-1 and cryopreserved platelets 1.18 +/- 0.05 microns s-1 V-1 cm-1, P < 0.05. However, the total platelet sialic acid of fresh platelets was 62.5 +/- 5.6 nmol 10(-9) platelets compared to 47.2 +/- 4.6 nmol 10(-9) platelets after cryopreservation, P < 0.001. Similarly, the neuraminidase-labile sialic acid was 26.4 +/- 4.3 nmol 10(-9) platelets for fresh platelets and 17.6 +/- 4.0 nmol 10(-9) platelets after cryopreservation, P < 0.001. Using polyacrylamide gel electrophoresis with Western blotting, we showed a reduction in the platelet glycoprotein Gp Ib after cryopreservation, this was confirmed by using crossed immunoelectrophoresis. Electron microscopy revealed a significant change in platelet morphology after the cryopreservation procedure with disruption of the platelet membrane and also platelet shape change. These features may explain the changes in platelet electrokinetic properties.

Electrokinetic behaviour and surface sialic acid status of blood platelets in essential thrombocythaemia (ET)

We have previously reported, for platelets from patients with idiopathic thrombocytopenic purpura, that there was in increased electrophoretic mobility that was related to their increased sialic acid content. Heterogeneity in the circulating platelet pool of patients with essential thrombocythaemia (platelet counts 600-1000 x 10(9)/l) has also been investigated by preparative continuous flow electrophoresis (CFE). The surface charge-dependent separation profiles of all the patients' platelets showed marked anodal shifts compared with the profiles of platelets from age- and sex-matched control subjects separated under identical conditions. The increase above normal in the net electronegativity of the patients' platelets could not be accounted for by differences in surface neuraminidase-labile or total platelet sialic acid content.

Electrokinetic properties and surface membrane sialic acid status of platelets in idiopathic thrombocytopenic purpura (ITP)

Continuous flow electrophoresis has been used to investigate heterogeneity in the circulating platelets from patients with idiopathic thrombocytopenia (ITP) and from age- and sex-matched control donors. The ITP patients' platelet counts ranged from 15 to 80 X 10(9)/l and they had much higher mean volumes and significantly higher (two-fold) total cell and neuraminidase-labile surface sialic acid contents expressed per unit cell than normal. After volume normalization the mean difference between the two groups was not statistically significant. The relationships of these findings to abnormal thrombopoiesis and to molecular recognition for reticuloendothelial system (RES) removal are discussed.