[Influence of laser radiation of the whole blood in vitro on adhesion and aggregation of blood platelets]

The authors revealed dependence of reaction blood plates to photoeffect on the dose and rate of blood movement at laser radiation of donor blood in vitro. The red light decreases adhesion and aggregation of blood plates both at high and low rate of shift. Infrared laser radiation is effective only at high rate of shift leading to increase of adhesion and decrease of aggregation of blood plates. Blue laser is effective in small doses only and at low rate of sift it leads to decrease of adhesion and at high rate it provokes increase of adhesion. Blue laser do not have a significant influence on aggregation of blood plates. These results make possible to suppose ambiguity of biological response of venous and arterial blood to radiation.

Prevention of perioperative venous thromboembolism and coronary events: differential responsiveness to an intervention program to improve guidelines adherence

INTRODUCTION

Prevention of venous thromboembolism and coronary events (with beta-blockers) during and after surgery is at the top of a list of safety practices for hospitalized patients, recommended by the Agency for Health Care Research and Quality (AHRQ). We wished to determine and improve adherence to clinical guidelines for these topics in our institution. PATIENTS, MATERIAL, AND METHODS: A prospective survey was conducted over several weeks on operated patients in a 1200-beds medical center (a teaching, community and referral hospital in Jerusalem, Israel). Eligibility for and actual administration of prophylactic treatment with anticoagulant and beta-blockers were determined. Following an intervention program, which included staff meetings, development of local protocols, and academic detailing by a nurse, the survey was repeated.

RESULTS

In general, adherence to recommended anticoagulation prophylaxis was low, found in only 29% [95% confidence interval (CI) = 23-36] of eligible patients. After the intervention, adequate anticoagulation increased to 50% (95% CI = 40-59) of eligible patients (P < 0.001). Initiation of beta-blockers in preventing perioperative cardiac events was very low (0%, 95% CI = 0-5%) and did not increase after intervention.

CONCLUSIONS

Adherence to guidelines for prevention of surgical complications was found to be low in our institution. A multifaceted intervention significantly increased use of prophylaxis for venous thromboembolism but not for coronary events. This differential response suggests that the success of a quality improvement project strongly depends on topic content and its phase of acceptance.

Differential response of platelets to chemokines: RANTES non-competitively inhibits stimulatory effect of SDF-1 alpha

BACKGROUND

Among the chemokines related to CXC and CC receptor groups and released from platelets, leukocytes and endothelial cells, SDF-1, TARC and MDC have been found to be platelet agonists. Platelets do not contain SDF-1 alpha. In contrast, RANTES is constitutively present in platelet alpha-granules and released upon platelet activation.

OBJECTIVES

To study a possible role of RANTES as a modulator of SDF-1 alpha effect on platelets, in relation to CXCR4 and various CC receptors.

METHODS

CXCR-4 (CXCL12) receptor expression and platelet activation were evaluated by flow cytometry, platelet deposition was studied by cone and plate(let) analyzer, and platelet aggregation by turbidometric aggregometry.

RESULTS

Flow cytometry studies revealed similar expression of CXCR-4, the specific receptor of SDF-1 alpha on intact, inactivated, and activated platelets. Preincubation of platelets with RANTES affected neither CXCR-4 expression, nor SDF-1 alpha binding to the platelet membrane. In the presence of fibrinogen, SDF-1 alpha activated gel-filtered platelets. RANTES did not activate platelets, but substantially (by 70%) inhibited SDF-1 alpha-induced fibrinogen binding. Similarly, RANTES abrogated the promoting effect of SDF-1 alpha on whole blood platelet adhesion to endothelial cell monolayer under venous flow conditions. In platelet-rich plasma, RANTES moderately inhibited SDF-1 alpha-induced platelet aggregation, while it did not affect aggregation induced by thrombin-receptor activation peptide, adenosine diphosphate, or phorbol 12-myristate 13-acetate. A synergistic inhibitory effect of RANTES and prostaglandin E1 used at subthreshold concentrations, on SDF-1 alpha-induced aggregation and SDF-1 alpha-induced fibrinogen binding to platelets was observed, which may suggest involvement of RANTES in a cAMP-dependent signal transduction pathway.

CONCLUSIONS

RANTES non-competitively inhibits activation of platelets by SDF-1 alpha, and thus may play a regulatory role in platelet response to inflammation.

Deposition of whole blood platelets on extracellular matrix under flow conditions in preterm infants

BACKGROUND

A previous study showed greater adhesion by platelets of healthy full term infants to subendothelial extracellular matrix (ECM) under flow conditions compared with healthy adult platelets.

AIM

To investigate the adhesion and aggregation of platelets from preterm infants on ECM under defined shear conditions.

METHODS

In vitro platelet function was investigated in 106 preterm infants, 74 full term infants, and 26 healthy adults. Blood samples were obtained from all infants within 24 hours of birth, and weekly until discharge from preterm infants only. Citrated whole blood was placed in ECM precoated tissue culture plates and subjected to shear stress (1300 s-1) for two minutes using a rotating Teflon cone. Platelet adhesion (surface coverage) and aggregation (average size) to ECM were assayed using an image analyser. Assays for von Willebrand factor (vWF) antigen, ristocetin cofactor, and vWF collagen-binding activity were performed on samples from an additional 70 preterm infants, 23 healthy full term infants, and 24 healthy adults. Preterm infants with hyaline membrane disease (HMD) were analysed separately in both cohorts.

RESULTS

Platelets from preterm infants displayed significantly less platelet adhesion than those from full term infants but similar aggregation and levels of vWF antigen, ristocetin cofactor, and collagen binding activity. Mean surface coverage was 22.0 (8.4)% for preterm infants with HMD, 28.7 (8.0)% for healthy preterm infants, and 35.7 (7.9)% for full term infants. Surface coverage in the preterm infants correlated with gestational age during the first 24 hours only, and did not reach full term levels during 10 weeks of follow up.

CONCLUSION

Platelet adhesion to ECM is significantly poorer in preterm than in full term infants, and poorer in preterm infants with HMD than in healthy preterm infants. Intrinsic platelet properties rather than the concentration or activity of vWF may be responsible for this difference.

Factor XIII mediates adhesion of platelets to endothelial cells through alpha(v)beta(3) and glycoprotein IIb/IIIa integrins

Coagulation factor XIII (FXIII) is a transglutaminase that catalyzes crosslink formation in fibrin clots. Endothelial cells (EC) were demonstrated to bind FXIII via their alpha(v)beta3 integrin receptor. FXIII was also shown to bind platelet glycoprotein IIb/IIIa receptor. In the present study, we analyzed if FXIII can mediate platelet-EC interaction. Both FXIII and activated FXIII (FXIIIa) bound to EC monolayers; this binding was enhanced by the addition of Mn2+ and was inhibited by the monoclonal antibody L609 against alpha(v)beta3 integrin. Normal washed platelets also bound surface-immobilized or soluble FXIII and FXIIIa, and the binding was GPIIb/IIIa dependent. The effect of FXIII concentrate (Fibrogammin-P) treatment on the interaction of ECs with platelets from six FXIII-deficient patients was studied. Patients' platelets were radiolabeled with 3H-Adenine, washed, resuspended in autologous plasma and allowed to adhere to immortalized EC line EAhy926. Adhesion of platelets from FXIII-deficient patients to ECs increased 1.7+/-0.4-fold (P=.01) following intravenous infusion of FXIII concentrate. Similarly, addition of 1 U/ml of FXIII concentrate to the patients' PRP in vitro increased the adhesion 1.8+/-0.5-fold (P=.008). Preincubation of the EC monolayers with increasing concentrations of either FXIII or FXIIIa augmented the adhesion of normal washed platelets to ECs in a dose-dependent manner. At 10 U/ml of EC-bound FXIII or FXIIIa, platelet adhesion enhanced 1.7+/-0.25-fold (P=.03) and 2.5+/-0.5-fold (P=.02), respectively. The increase in platelet adhesion was completely abolished by pretreatment of ECs with the anti-alpha(v)beta3 antibody L609 or by preincubation of the platelets with the GPIIb/IIIa inhibitor Abciximab. Taken together, our data indicate that FXIII mediates the interaction of platelets with ECs by bridging between endothelial alpha(v)beta3 and platelet GPIIb/IIIa integrins. This interaction may be relevant for tissue remodeling and wound repair after vascular injury in FXIII-deficient patients.

Dispersion of cell-to-cell uncoupling precedes low K+-induced ventricular fibrillation

We hypothesize that hypokalemia-related electrolyte imbalance linked with abnormal elevation of intracellular free Ca2+ concentration can cause metabolic disturbances and subcellular alterations resulting in intercellular uncoupling, which favor the occurrence of malignant arrhythmias. Langendorff-perfused guinea pig heart (n = 44) was subjected to a standard Tyrode solution (2.8 mmol/l K+) followed by a K+-deficient solution (1.4 mmol/l K+). Bipolar ECG of the left atria and ventricle was continuously monitored and the incidence of ventricular fibrillation was evaluated. Myocardial tissue sampling was performed during stabilization, hypokalemia and at the onset of fibrillation. Enzyme activities of succinic dehydrogenase, glycogen phosphorylase and 5-nucleotidase were determined using in situ catalytic histochemistry. The main gap junction protein, connexin-43, was labeled using mouse monoclonal antibody and FITC conjugated goat antimouse antibody. Ultrastructure was examined by transmission electron microscopy. The free Ca2+ concentration was measured by the indo-1 method in ventricular cell cultures exposed to a K+-free medium. The results showed that sustained ventricular fibrillation appeared within 15-30 min of low K+ perfusion. This was preceded by ectopic activity, episodes of bigeminy and tachycardia. Hypokalemia induced moderate reversible and sporadically irreversible subcellular alterations of cardiomyocytes and impairment of intercellular junctions, which were heterogeneously distributed throughout myocardium. Patchy areas with decreased enzyme activities and diminished immunoreactivity of connexin-43 were found. Furthermore, lack of external K+ was accompanied by an increase of intracellular Ca2+. The prevention of Ca2+ overload by either 1 mmol/l Ni2+ (Na+/Ca2+ inhibitor), 2.5 micromol/l verapamil, 10 micromol/l d-sotalol or 10 micromol/l tedisamil was associated with the protection against fibrillation. The results indicate that hypokalemia induces Ca2+ overload injury and disturbances in intercellular coupling. Dispersion of these changes throughout the myocardium may serve as the basis for microreentry circuits and thus favor fibrillation occurrence.

Synthesis of Mannosyl and Oligomannosyl Threonine Building Blocks found on the Mycobacterium tuberculosis 45 kDa MPT 32 Glycoprotein

Mycobacterium tuberculosis secretes a 45 kDa glycoprotein (MPT 32) carrying mannosylated threonine residues. A general strategy was developed to couple peracetylated mannose, α -(1,2)-linked mannobiose or mannotriose to Fmoc-threonine-benzyl ester. Activation of mannosyl acetates or fluorides by borontrifluoride etherate gave the desired Fmoc-glycosyl amino acid building blocks in good yields. The synthesis leads to stable compounds and can easily be scaled up.

A new class of antiarrhythmic-defibrillatory agents

Novel dibenzoazepine and 11-oxo-dibenzodiazepine derivatives are shown to be effective ventricular defibrillating drug candidates. They exhibit significant in vivo defibrillatory activity with no observed changes in ECG either before or after the VF event. These compounds also exhibit antifibrillatory activity by elevating the fibrillation threshold potential, all suggesting that such drugs could be used to treat VF either by themselves or together with electrical defibrillators.

Mechanisms of action of the anti-atherogenic effect of magnesium: lessons from a mouse model

Magnesium (Mg) fortification of drinking water succeeded in inhibition of atherogenesis development in a transgenic model of atherosclerosis-prone mice fed a high-cholesterol content diet. In order to delineate possible mechanisms of action of the anti-atherogenic effect of Mg, the involvement of LDL oxidation was studied. We determined the susceptibility of LDL to Cu+2 oxidation, anti-oxidized LDL antibody levels, and liver content of retinol and retinyl-palmitate. In order to study another possible mechanism we tested platelets interaction with extracellular matrix in both male and female mice with or without Mg fortification of drinking water. No difference was found in susceptibility of LDL to undergo oxidation. Female mice that received Mg had decreased anti-oxidized LDL antibody levels compared with control female mice, while there was no significant difference among male groups. On the other hand, only in the male group with Mg was a higher content of retinol and retinyl-palmitate found in the livers. Platelets coverage area on extracellular matrix was similar between groups. These results suggest that Mg might affect LDL oxidation, and thus atherogenesis.

Adherence properties of Staphylococcus aureus under static and flow conditions: roles of agr and sar loci, platelets, and plasma ligands

Global regulatory genes in Staphylococcus aureus, including agr and sar, are known to regulate the expression of multiple virulence factors, including cell wall adhesins. In the present study, the adherence of S. aureus RN6390 (wild type), RN6911 (agr), ALC136 (sar), and ALC135 (agr sar) to immobilized fibrinogen, fibronectin, von Willebrand factor (vWF), extracellular matrix (ECM), and human endothelial cells (EC) EAhy.926 was studied. Bacteria grown to postexponential phase were subjected to light oscillation (static condition) or to shear stress at 200 s(-1) (flow condition) on tissue culture polystyrene plates coated with either protein ligands, ECM, or EC. Adherence of nonlabeled bacteria to immobilized ligands was measured by an image analysis system, while adherence of [(3)H]thymidine-labeled S. aureus to ECM and EC was measured by a beta-scintillation counter. The results showed increased adherence of agr and agr sar mutants to immobilized fibrinogen and higher potential of these mutants to induce platelet aggregation in suspension, decreased adherence of sar and agr sar mutants to immobilized fibronectin and vWF as well as to ECM and EC, increased adherence of both S. aureus wild type and sar mutant to EC treated with platelet-rich plasma (PRP) compared to platelet-poor plasma (PPP) and to EC treated with PPP compared to the control, and increased adherence of S. aureus wild type to EC coated with PRP in which platelets were activated with phorbol 12-myristate 13-acetate compared to intact PRP. This finding paralleled the increased adherence to EC of activated compared to intact platelets. It is suggested that platelet-mediated S. aureus adherence to EC depends on platelet activation and the number of adherent platelets and available receptors on the platelet membrane. In conclusion, the agr locus downregulates S. aureus adherence to fibrinogen, while the sar locus upregulates S. aureus adherence to fibronectin, vWF, ECM, and EC. The effect of both agr and sar on S. aureus adherence properties develops primarily under flow conditions, which suggests different adhesion mechanisms in static and flow conditions.

Testing platelet activation with a shear-dependent platelet function test versus aggregation-based tests: relevance for monitoring long-term glycoprotein IIb/IIIa inhibition

BACKGROUND

Tests developed to monitor glycoprotein (GP) IIb/IIIa blockade do not properly reflect platelet function in vivo and need a baseline (pretreatment) value. Because GP IIb/IIIa is essential in platelet aggregation and thrombosis under shear conditions, a flow-dependent approach to monitor its inhibition can be used.

METHODS AND RESULTS

We compared a test based on flow-dependent platelet deposition, the Cone and Platelet Analyzer (CPA), with in vitro platelet aggregometry and the Rapid Platelet Function Assay (RPFA) on platelet function after GP IIb/IIIa inhibition. In vitro, increasing concentrations of abciximab (0% to 100% receptor occupancy) were tested. Ex vivo, platelet function was monitored with the CPA and with aggregometry for up to 1 week after abciximab administration. The CPA was better correlated with the percentage of free GP IIb/IIIa receptors than was aggregometry or the RPFA. Only the RPFA, when expressed as a ratio over baseline (pretreatment), was comparable to the CPA. Ex vivo, the CPA, but not aggregometry, showed prolonged platelet inhibition with gradual recovery from GP IIb/IIIa receptor blockade in the first week after abciximab administration.

CONCLUSIONS

Platelet function assessment by shear-induced deposition is a reliable test to monitor a wide range of GP IIb/IIIa inhibition. Its accuracy does not require a baseline reference. The effects of GP IIb/IIIa blockade on platelet function should be examined under high shear conditions.

Transient adhesion refractoriness of circulating platelets under shear stress: the role of partial activation and microaggregate formation by suboptimal ADP concentration

Exposure of whole blood (WB) to subendothelial extracellular matrix (ECM) under shear stress in the cone and plate(let) analyser (CPA) results in platelet adhesion, followed by release reaction and aggregation of circulating platelets on the adherent platelets. The properties of circulating non-adhered platelets in the CPA was studied by exposure of WB to ECM at a high shear rate (1300/s) for 2 min (1st run), followed by transfer of the suspension to a new ECM-coated well for a second run (2nd run) under similar conditions. The results of the 2nd run demonstrated transient adhesion refractoriness associated with platelet microaggregate formation in the suspension. The adhesion refractoriness was dependent on platelet activation during the 1st run and was prevented by addition of apyrase (ADP scavenger) or ADP receptor inhibitor, suggesting a role for ADP in mediating this response. Furthermore, exposure of WB samples to suboptimal concentrations of ADP (0.4-1 micromol/l) or a thrombin receptor activating peptide (TRAP) (5 micromol/l) for 2 min resulted in a similar transient platelet adhesion refractoriness to ECM under flow conditions. The transient platelet refractoriness and microaggregate formation induced by ADP was associated with a transient reduction in glycoprotein (GP)Ib, increased P-selectin expression and increased fibrinogen binding by circulating platelets. These data suggest a role for platelet agonists at suboptimal concentrations in modulating platelet function and limiting the expansion of the thrombus.

Testing of platelet deposition on polystyrene surface under flow conditions by the cone and plate(let) analyzer: role of platelet activation, fibrinogen and von Willebrand factor

Recently, we described a method of testing platelet deposition on extracellular matrix under flow conditions. The method was used for assessment of platelet function in various platelet disorders, for monitoring of replacement and anti-platelet therapy. In the present study, we investigated platelet deposition on a polystyrene surface compared with that on extracellular matrix, under defined shear rates, using the original Cone and Plate(let) Analyzer. A correlation of adhesion rate (surface coverage) and aggregate formation (average size) of platelets from normal citrated blood between polystyrene and extracellular matrix was observed. Blocking of von Willebrand factor binding to glycoprotein Ib by a recombinant von Willebrand factor fragment substantially decreased platelet adhesion to both surfaces. Blocking of GPIIb-IIIa by Arg-Gly-Asp-Ser peptide prevented platelet adhesion to the polystyrene while an extensive adhesion of single platelets to extracellular matrix was observed. Furthermore, platelet adhesion to polystyrene but not to extracellular matrix was completely inhibited by platelet inactivation with prostaglandin E(1). Platelets from patients with severe von Willebrand disease yielded very low adhesion to both polystyrene and extracellular matrix. The addition of von Willebrand factor to the blood of these patients or pre-coating of polystyrene surface with von Willebrand factor restored the ability of platelets to adhere and aggregate on the surface. Platelets from patients with Glanzmann's thrombasthenia and afibrinogenemia adhered to extracellular matrix (with defective aggregate formation), while they failed to adhere to the polystyrene. Fibrinogen added to afibrinogenemia blood or pre-coating of the polystyrene with fibrinogen restored the ability of platelets to adhere and aggregate on the surface. In conclusion, the polystyrene surface, like extracellular matrix, can be used to assess platelet function disorders taking in account that platelet deposition on polystyrene under flow is absolutely dependent on platelet activation and on the presence of fibrinogen, von Willebrand factor, and their receptors.

Abciximab in carotid stenting for postsurgical carotid restenosis: intermediate results

PURPOSE

To report intermediate results of a pilot study in which the glycoprotein IIb/IIIa receptor antagonist abciximab was given to patients during percutaneous carotid stenting for recurrent internal carotid artery (ICA) stenosis. The objective was to prevent procedure-related cerebral embolic events and decrease the incidence of recurrent stenosis.

METHODS

Sixteen patients (9 women; mean age 66.5 years, range 39-78) with severe ICA recurrent stenosis (>80%) underwent balloon angioplasty and stenting. Before the procedure, abciximab was administered intravenously as a bolus (0.25 mg/kg) followed by a 12-hour continuous infusion (10 microg/min).

RESULTS

Fifteen patients received stents (14 Wallstent and 1 Strecker); 1 vessel was dilated with only 50% improvement in luminal diameter. Two stented arteries had residual stenosis (<30%) but satisfactory luminal diameter was achieved in the remaining 13 (81%) arteries. There were no neurological ischemic events during or following the procedure, nor were there any bleeding or peripheral vascular complications. Duplex surveillance studies up to 12 months revealed no significant recurrent stenosis in the treated vessels.

CONCLUSIONS

The administration of abciximab in conjunction with percutaneous revascularization procedures for postsurgical carotid artery stenosis may reduce cerebral ischemic episodes. It may also attenuate restenosis in the treated artery.

Induction of interactions between CD44 and hyaluronic acid by a short exposure of human T cells to diverse pro-inflammatory mediators

Migration of T cells into extravascular sites of inflammation is mediated by cell-cell and cell-matrix adhesion receptors, including the hyaluronan-binding glycoprotein, CD44. The biochemical nature of CD44 variants and the ligand specificity, function and the regulation of activation of CD44 expressed on various cell types have been extensively studied. However, little is still known about the short-term influence of cytokines and chemokines on the activation of CD44 on human T cells. Therefore, we studied the role of inflammatory mediators in regulating the adhesion of T cells from human peripheral blood to immobilized hyaluronan under static or shear stress conditions. We found that the CD44-dependent adhesion, under static and shear stress (i.e. relative gradual resistance to flow of 150 and 1500 s-1) conditions, of T cells to hyaluronan requires a T-cell activation of 2-3 hr and is regulated by the cross-linking of CD3, cytokines (e.g. interleukin-2 and tumour necrosis factor-alpha), and chemokines (e.g. MIP-1beta, interleukin-8, and RANTES). This T-cell adhesion was manifested by polarization, spreading and co-localization of cell surface CD44 with a rearranged actin cytoskeleton in hyaluronan-bound T cells. Thus, cytokines and chemokines present in the vicinities of blood vessel walls or present intravascularly in tissues where immune reactions take place, can rapidly activate the CD44 molecules expressed on T cells.

Recombinant fragment of von Willebrand factor AR545C inhibits platelet binding to thrombin and platelet adhesion to thrombin-treated endothelial cells

Activated, but not resting, platelets are capable of adhering to intact endothelial cells (ECs). We evaluated the effect of a recombinant von Willebrand factor (VWF) fragment AR545C, which inhibits glycoprotein Ib (GPIb)/VWF binding, on platelet adhesion to human ECs under static or flow conditions. Incubation of resting platelets with intact endothelium under flow conditions (350/s) resulted in minimal platelet adhesion. The adhesion was enhanced two- to threefold after either platelet activation by thrombin receptor agonist peptide (TRAP) or EC pretreatment with thrombin. The enhancing effect of thrombin was abolished by addition of either hirudin (10 u/ml) or PGE1 (1 microg/ml). Preincubation of resting platelets with increasing concentrations of AR545C under static or flow conditions resulted in a dose-dependent inhibition of thrombin-induced enhanced adhesion to ECs. AR545C (0.3 microM) completely abolished the effect of thrombin, reducing platelet adhesion to the control level observed with non-treated ECs. In contrast, the same concentration of AR545C had no effect on the adhesion of TRAP-activated platelets to ECs. AR545C also inhibited thrombin-induced platelet aggregation and binding in a dose-dependent manner. In addition, 0.3 microM of AR545C reduced thrombin-induced serotonin release by 57%, whereas monoclonal antibody AN51, which inhibits ristocetin-induced platelet aggregation, had no effect on either thrombin-induced platelet aggregation or binding or on serotonin release. Similarly, AR545C had no effect on TRAP-induced serotonin release. These findings suggest that (i) AR545C inhibits platelet activation mediated by thrombin and this inhibition occurs through blocking the high-affinity thrombin binding sites on the GPIb/IX complex and (ii) AR545C has no effect on the moderate affinity thrombin receptor (seven transmembrane domain thrombin receptor; STDR).

Treatment of bleeding episodes in patients with hemophilia and an inhibitor: comparison of two treatment protocols with recombinant activated factor VII

Six hemophilia A patients with inhibitors were treated with a continuous infusion of recombinant activated factor VII (rFVIIa) for various bleeding episodes. Bleeding episodes (n = 101) were treated according to a 12 h regular dose protocol or a shortened (6 h) augmented dose protocol. Patient response to therapy was assessed by symptomatic improvement within predefined timeframes. Although patient number was limited, both protocols appeared similar with respect to the proportion of patients responding to therapy; however, the augmented dose protocol appeared to be superior to the regular dose protocol with shorter response time, shorter duration of therapy and possibly lower rFVIIa requirements. Further studies are needed to define the efficacy of rFVIIa augmented dose administered as continuous infusion in treating hemophilia patients with inhibitors during major bleeding episodes, trauma and surgery.

Acquired hemophilia masked by warfarin therapy

People without hemophilia but with autoantibodies specifically directed against the procoagulant activity of factor VIII are known to have acquired hemophilia. The bleeding diathesis in these patients is often severe and life-threatening. The definite laboratory diagnosis of this disorder includes demonstration of low factor VIII levels in plasma with a high titer of factor VIII inhibitors, but the initial suspicion for its presence should rise in view of a prolonged partial thromboblastin time (PTT) and a normal prothrombin time associated with an acquired bleeding disorder. Oral anticoagulant treatment is known to prolong PTT as well, and the merger of these 2 situations may cause delayed diagnosis of acquired hemophilia with devastating consequences. We describe here the first reported case of acquired hemophilia diagnosed in a patient treated with warfarin. In such patients prolonged PTT may be ascribed to warfarin therapy rather than to acquired hemophilia, thus causing a dangerous delay in diagnosis.

Blood irradiation by He-Ne laser induces a decrease in platelet responses to physiological agonists and an increase in platelet cyclic GMP

The effect of He-Ne laser irradiation on platelet adhesion, activation and aggregation was investigated. Citrated whole blood was irradiated in vitro by He-Ne laser (632.8 nm, 7 mW) and then subjected to shear stress (1300 s-1) on subendothelial extracellular matrix (ECM)-coated plates. Laser irradiation was followed by a decrease in platelet adhesion and aggregation on ECM under flow conditions in a time exposure-dependent manner (by 30-40%). The inhibiting effect of laser light on platelets was detectable up to 1 h after the termination of irradiation. Laser irradiation of either platelet-rich plasma, gel-filtered platelets, platelet-poor plasma, or packed blood cells followed by whole blood reconstitution revealed a marked decrease in platelet deposition on ECM only in the cases of platelet-rich plasma or gel filtered platelets. In conventional aggregometry, laser-treated platelet-rich plasma demonstrated a diminished platelet response to both thrombin receptor-activating peptide (TRAP), converting a two-wave aggregation curve to reversible, and to the protein kinase C activator PMA (by 45%). In flow cytometry analysis, irradiated platelets presented lower fibrinogen binding and P-selectin expression in response to TRAP. Laser irradiation had no additional inhibitory effect on dibutyryl cGMP- and dibutyryl cAMP-pretreated platelets. A 50% increase in cGMP level was observed in laser-treated gel filtered platelets, both in the presence and in absence of the phosphodiesterase inhibitor, isobuthylmethylxanthine. The results suggest that guanylate cyclase is one of the primary mediators of the laser effect on platelet function.

Homocysteine and oxidized low density lipoprotein enhanced platelet adhesion to endothelial cells under flow conditions: distinct mechanisms of thrombogenic modulation

We investigated the effects of two well established risk factors for cardiovascular disease, homocysteine and oxidized low density lipoprotein (ox-LDL), on endothelial cell thrombogenicity. For this purpose we studied platelet adhesion to human endothelial cells (EC) under flow conditions at a shear rate of 350 s(-1) following EC treatment with either homocysteine or ox-LDL. Treatment of EC with either homocysteine (1 or 10 mmol/L for 16 h) or ox-LDL (100 microg/ml for 16 h) resulted in a 2-3 fold enhancement in platelet adhesion. The enhancement in platelet adhesion induced by 1 mmol/L homocysteine, but not that induced by 10 mmol/L homocysteine, was absolutely dependent on fibrin formation. Homocysteine treatment has significantly increased the cell surface tissue factor (TF) activity and slightly reduced the expression of the intercellular adhesion molecule I (ICAM-1). In contrast, ox-LDL treatment upregulated ICAM-1 expression and had no significant effect on endothelial TF activity. Neither homocysteine nor Ox-LDL affected surface expression of the alpha(v)beta3 integrin. The homocysteine-induced enhancement in platelet adhesion was almost completely abolished by blockade of the EC TF activity by a polyclonal antibody. The enhancing effect of homocysteine was also greatly reduced by inhibition of the EC alpha(v)beta3 integrin, but was not affected by blockade of EC ICAM-1. On the other hand, ox-LDL-induced enhancement in platelet - EC adhesion was greatly inhibited by blocking ICAM-1 or alpha(v)beta3, but remained unaffected by inhibition of TF activity. Preincubation of platelets with the glycoprotein IIb-IIIa (GPIIb-IIIa) antagonist Reo-Pro has virtually abolished the enhancing effect of both homocysteine and ox-LDL. Our results suggest that homocysteine and ox-LDL might increase endothelial thrombogenicity by distinct mechanisms: homocysteine - by inducing TF activity, and ox-LDL - by upregulating ICAM-1, both of which enhance GPIIb-IIIa/fibrinogen dependent platelet adhesion to EC. The alpha(v)beta3 integrin, although not affected by EC stimulation, seems to play a crucial role in platelet-EC interaction regardless of the mechanism of EC perturbation.

Staphylococcus aureus adherence to thrombin-treated endothelial cells is mediated by fibrinogen but not by platelets

Recent studies emphasize the role of blood constituents in Staphylococcus aureus (S. aureus) adherence to subendothelial extracellular matrix. In the present study, the adherence of two strains of S. aureus (ATCC 29213 and RN 6390) grown to a postexponential phase to cultured human umbilical vein endothelial cells (EC-304) was examined. Under flow conditions (600 s(-1)), pretreatment of endothelial cells (ECs) with human alpha-thrombin (2 U/mL) significantly (2- to 4-fold) increased bacterial adherence to ECs. Adherence of both S. aureus strains to thrombin-treated ECs was similarly higher in the presence of whole blood, platelet-rich plasma, or platelet-poor plasma when compared with Tris-buffered saline solution (TBS). Platelet inactivation in whole blood by prostaglandin E1 did not reduce the adherence rate. When ATCC 29213 bacteria were suspended in TBS containing increasing concentrations of fibrinogen at near-physiologic ranges (0.25 to 2 mg/mL), a dose-dependent increase in S. aureus adherence to thrombin-activated ECs was observed that reached a maximum level of about 12-fold. Fibronectin used at the above physiologic concentrations (12.5 to 100 microg/mL) enhanced bacterial adherence up to 2-fold. Von Willebrand factor (1 IU/mL) did not support bacterial adherence to ECs, either alone or in combination with fibrinogen. Inhibition of fibrin formation either by the Gly-Pro-Arg-Pro peptide or by hirudin increased bacterial adherence by 50% and 90%, respectively. Blockage of either ICAM-I, alpha5beta1, or alphavbeta3 receptors on ECs by appropriate monoclonal antibodies resulted in substantial inhibition of bacterial adherence (by 42%, 65%, and 72%, respectively). Preincubation of S. aureus with a fibrinogen gamma-chain binding domain peptide led to 65% inhibition of adherence to ECs in the presence of fibrinogen. In contrast, preincubation of bacteria with the Arg-Gly-Asp-Ser peptide failed to affect their adherence. The data suggest that S. aureus adherence to the EC surface was (1) significantly enhanced by thrombin treatment of ECs, (2) not mediated by platelets, and (3) mediated by plasma fibrinogen, which binds to the bacteria via the C-terminus gamma-chain binding domain but not via the Arg-Gly-Asp sequence.