Lower doses of rFVIIa therapy are safe and effective for surgical interventions in patients with severe FXI deficiency and inhibitors.

Severe FXI deficiency is a rare injury-related bleeding disorder. In patients with FXI inhibitors, surgeries may be treated using recombinant activated factor VII; however, treatment safety is a major concern and the best dosing regimen as well as mode of administration is still to be defined. We describe four patients with severe factor XI deficiency and inhibitors to FXI, undergoing eight (four major) surgical procedures treated with continuous infusion of rFVIIa. Following acute MI that evolved after surgery of our first patient, all other patients were treated with low-dose bolus rFVIIa followed by low-dose continuous infusion of rFVIIa. Haemostasis was successfully achieved and no further thrombotic complications occurred. To support our clinical results ex-vivo thromboelastography studies were performed, demonstrating the differences of clot formation and lysis between patients with FXI deficiency and healthy controls and suggesting that low-dose rFVIIa corrects coagulation similarly to high-dose rFVIIa in FXI deficiency. Recombinant FVIIa at low doses may effectively induce haemostasis and seems to be a safe treatment mode in patients with FXI deficiency and inhibitors undergoing surgeries.

Impact of frailty on outcomes in surgical patients: A systematic review and meta-analysis.

IMPORTANCE: Age has historically been used to predict negative post-surgical outcomes. The concept of frailty was introduced to explain the discrepancies that exist between patients' chronological and physiological age. The efficacy of the modified frailty index (mFI) to predict surgical risk is not clear. OBJECTIVE: We sought to synthesize the current literature to quantify the impact of frailty as a prognostic indicator across all surgical specialties. DATA SOURCES: Pubmed and Cochrane databases were screened from inception to 1 January 2018. STUDY SELECTION: Studies utilizing the modified Frailty Index (mFI) as a post-operative indicator of any type of surgery. The mFI was selected based on a preliminary search showing it to be the most commonly applied index in surgical cohorts. DATA EXTRACTION AND SYNTHESIS: Articles were selected via a two-stage process undertaken by two reviewers (AP and DS). Statistical analysis was performed in Revman (Review manager V5.3). The random-effects model was used to calculate the Risk Ratios (RR). MAIN OUTCOME(S) AND MEASURE(S): The primary outcomes: post-operative complications, re-admission, re-operation, discharge to a skilled care facility, and mortality. RESULTS: This meta-analysis of 16 studies randomizes 683,487 patients, 444,885 frail, from gastrointestinal, vascular, orthopedic, urogenital, head and neck, emergency, neurological, oncological, cardiothoracic, as well as general surgery cohorts. Frail patients were more likely to experience complications (RR 1.48, 95%CI 1.35-1.61; p < 0.001), major complications (RR 2.03, 95%CI 1.26-3.29; p = 0.004), and wound complications (RR 1.52, 95%CI 1.47-1.57; p < 0.001). Furthermore, frail patients had higher risk of readmission (RR 1.61, 95%CI 1.44-1.80; p < 0.001) and discharge to skilled care (RR 2.15, 95%CI 1.92-2.40; p < 0.001). Notably, the risk of mortality was 4.19 times more likely in frail patients (95% CI 2.96-5.92; p < 0.001). CONCLUSIONS: and Relevance: This study is the first to synthesize the evidence across multiple surgical specialties and demonstrates that the mFI is an underappreciated prognostic indicator that strongly correlates with the risk of post-surgical morbidity and mortality. This supports that formal incorporation of pre-operative frailty assessment improves surgical decision-making.

Aspirin responsiveness in acute brain ischaemia: association with stroke severity and clinical outcome.

PURPOSE: Platelets play a critical role in the pathogenesis of acute brain ischaemia. We studied the association between the degree of inhibition of platelet function by aspirin (ASA) and the severity and outcome of acute brain ischaemia. METHODS: Platelet responsiveness to ASA was assessed in patients with acute brain ischaemia, treated with ASA since hospital admission. The degree of ASA responsiveness was assessed by optical aggregometry and categorized into patients with good response, partial response and complete unresponsiveness to ASA (good responders, partial responders and non-responders, respectively). An additional evaluation of responsiveness to ASA was performed by Impact-R (cone and platelet analyzer). Patients underwent serial clinical assessment during hospitalization, at discharge and during follow-up. RESULTS: Among 105 patients (mean age 63 +/- 12 years; 66% men), impaired ASA responsiveness at baseline as assessed by aggregometry was associated with increased stroke severity at baseline, unfavourable clinical course, and poor functional outcome during follow-up (p < 0.05 for all). Age-adjusted odds ratios in non-responders compared to good responders were 9.8 for severe stroke on admission (95% CI 2.8-34.9), 3.1 for lack of early clinical improvement (95% CI 1.1-8.8) and 8.6 for poor functional outcome during follow-up (95% CI 2.4-30.4). Less robust trends were observed with the Impact-R. CONCLUSIONS: Impaired responsiveness to ASA in acute brain ischaemia is common and is associated with worse neurological deficits at stroke onset, early clinical deterioration and poorer functional outcome. The clinical significance of these findings requires further evaluation in larger longitudinal studies.

Testing agonist-induced platelet aggregation by the Impact-R [Cone and plate(let) analyzer (CPA)].

The Impact-R [Cone and plate(let) analyzer (CPA)] is useful to assess platelet adhesion in different diseases and to monitor antiplatelet therapy. The purpose of the present study was to adapt this system to test agonist-induced platelet aggregation. Blood samples were tested by light transmission platelet aggregometry (LTA), Impact-R regular test and Impact-R agonist-response test. In the latter, samples were pre-incubated for 1 min with an agonist leading to platelet activation, micro-aggregates formation and reduced adhesion. Impact-R regular test of ten healthy volunteers demonstrated platelet adhesion (surface coverage, SC) of 11.2 +/- 2.6% while LTA induced by ADP, ristocetin, epinephrine, collagen and arachidonic acid (AA) yielded maximal aggregation (81% to 93%). In the Impact-R agonist-response test, SC was reduced to 2.2 +/- 1.0%, 1.2 +/- 0.9%, 2.3 +/- 1.0%, 2.2 +/- 0.8% and 2.4 +/- 0.4%, respectively. Prostaglandin E(1) treatment weakened SC reduction in response to ADP and epinephrine (SC of 8.8 +/- 1.8% and 9.5 +/- 2.0%, respectively). Inhibition of P2Y(12) receptor with 2MeSAMP resulted in a dose-dependent decrease in maximal aggregation in the ADP-induced test, which inversely correlated to SC in the Impact-R ADP-response test. The Impact-R agonist-response tests detected aggregation defects in patients with storage pool disease, severe von Willebrand disease and epinephrine response deficiency, and may be useful to assess the effect of different agonists on platelet aggregation.

[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.

Factors related to the development of acquired von Willebrand syndrome in patients with essential thrombocythemia and polycythemia vera.

OBJECTIVE: We characterized acquired von Willebrand syndrome (AVWS) among essential thrombocythemia (ET) and polycythemia vera (PV) patients. METHODS: A review of patients with ET or PV evaluated for AVWS. RESULTS: Of 116 patients with ET, 64 (55%) developed AVWS; of 57 with PV, 28 (49%) developed AVWS. Median platelet counts of ET and PV patients who developed AVWS were 920×109/L and 679×109/L, respectively (P=0.01). Of patients who developed AVWS, 69.5% had platelet counts below 1000×109/L. Bleeding was more common in patients with AVWS, among both ET and PV patients (P<0.001). VWF:RCo levels and VWF:RCo/VWF:Ag ratio were lower among JAK2 V617F positive- vs. JAK2 V617F negative- ET patients (P=0.02 and P=0.002, respectively); whereas VWF:Ag levels were comparable (P=0.96). ET patients harboring the JAK2 V617F mutation were more likely to develop AVWS than were calreticulin-positive patients (70.3% vs. 45.7%, P=0.02), despite lower platelet counts (median 773 vs. 920×109/L, P=0.05). In multivariable analysis, younger age (P=0.002), platelet count (P<0.001), hemoglobin level (P=0.01) and JAK2 V617F mutation (P=0.01) independently predicted the development of AVWS among ET patients; whereas only platelet count predicted its development among PV patients (P<0.001). CONCLUSION: Among ET and PV patients, AVWS was common and associated with higher bleeding rates and higher platelet count; nonetheless, most AVWS patients had platelet counts under 1000×109/L. Thus, AVWS screening should be included in routine assessment of ET and PV patients. Among ET patients, JAK2 V617F was a main driver for the development of AVWS.

Telomerase activity in the normal and neoplastic rat mammary gland.

The 1-methyl-1-nitrosourea-induced rat mammary tumor model system is well studied, reproducible, and widely used. We have investigated whether these tumors possess higher telomerase activity than normal mammary tissue. Using the telomeric repeat amplification protocol assay, we found significantly higher telomerase activity in 36 mammary carcinomas than in 72 mammary glands of virgin rats. The level of telomerase activity in virgin rats was unaffected by strain, age, stage of the estrous cycle, or ovariectomy. However, mammary glands obtained from pregnant rats exhibited telomerase activity comparable to that found in the tumors, possibly reflecting the high epithelial content of these tissues. Indeed, isolated epithelial cells from virgin and pregnant mammary glands and from carcinomas had similar telomerase activities. Thus, telomerase activity is constitutive in the rat mammary epithelium and is not a unique characteristic of malignant transformation in this tissue. These results underscore the importance of attributing biochemical properties to specific cell types in a tissue, a situation not paralleled in the interpretation of data from in vitro models.

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.

Careful histological confirmation and microdissection reveal telomerase activity in otherwise telomerase-negative breast cancers.

Studies of invasive breast cancers consistently identify a subset of tumors without telomerase activity, compromising its utility as a tumor marker. Telomerase-negative tumors may represent a biologically different subset, or the result could be attributed to assay imperfections. To resolve this issue, we tested 105 invasive breast cancers for telomerase activity and found that 23 (22%) tumors were telomerase negative. Careful histological confirmation of an adjacent cryosection and/or microdissection of pure tumor cells reduced this number to 5 (5%). Thus, truly telomerase-negative invasive breast cancers are rare, making this enzyme a potentially very useful tumor marker in breast cancer.

Hypereosinophilic syndrome associated with polycythemia vera.

A 60-year-old woman presented with relapse of polycythemia vera associated with hypereosinophilic syndrome (HES) with abnormal immunologic measures, including increased serum IgE and IgG levels, high levels of circulating immune complexes, rheumatoid factor, and antinuclear antibodies. Treatment with hydroxyurea was followed by a dramatic response of both the polycythemia vera and the HES, with return to normal of the abnormal immunologic measures. This case report documents that evidence of immunologic and myeloproliferative causes of HES may coexist in the same patient.

Platelets and their microparticles as key players in pathophysiological responses.

Platelets are known to play a central role in primary hemostasis as well as in the pathophysiology of thrombotic disorders. However, in addition to hemostasis, platelets are involved in a variety of pathophysiological responses including immune responses, inflammation, angiogenesis, tissue regeneration, and cancer metastasis. Recent studies revealed a significant role for platelet-derived microparticles (PMP), in these responses. PMP communicate with, and deliver signals to, other cells, induce signals, and change their phenotype during inflammation, angiogenesis, and tumor metastasis. The current report describes the recent development in this field with a focus on the role of platelets and PMP in all of the above responses.

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.

The combining ability of glycoproteins IIb, IIIa and Ca2+ in EDTA-treated nonaggregable platelets.

Platelets deprived of calcium and incubated at 37 degrees C for 10 min lose their ability to bind fibrinogen or aggregate with ADP when adequate concentrations of calcium are restored. Since the calcium complex of glycoproteins (GP) IIb and IIIa is the presumed receptor for fibrinogen, it seemed appropriate to examine the behavior of these glycoproteins in incubated nonaggregable platelets. No differences were noted in the electrophoretic pattern of nonaggregable EDTA-treated and aggregable control CaEDTA-treated platelets when SDS gels of Triton X-114 fractions were stained with silver. GP IIb and IIIa were extracted from either nonaggregable EDTA-treated platelets or aggregable control platelets with calcium-Tris-Triton buffer and subjected to sucrose density gradient centrifugation or crossed immunoelectrophoresis. With both types of platelets, these glycoproteins formed a complex in the presence of calcium. If the glycoproteins were extracted with EDTA-Tris-Triton buffer, or if Triton-solubilized platelet membranes were incubated with EGTA at 37 degrees C for 30 min, GP IIb and IIIa were unable to form a complex in the presence of calcium. We conclude that inability of extracted GP IIb and IIIa to combine in the presence of calcium is not responsible for the irreversible loss of aggregability that occurs when whole platelets are incubated with EDTA at 37 degrees C.

Monoclonal purified F VIII for continuous infusion: stability, microbiological safety and clinical experience.

Replacement therapy for patients with hemophilia A postoperatively or for major hemorrhage, administered as a continuous infusion, is efficient and reduces the requirement for factor VIII (F VIII). The convenience of the method is increased by using a minipump and not diluting the concentrate further after reconstitution. A monoclonally purified F VIII concentrate (Monoclate-P), was evaluated for its stability after reconstitution in different infusion systems, for its microbiological safety as well as clinical safety and efficacy in continuous infusion. The F VIII activity was unaffected by 2 of the 3 infusion systems at room temperature during 15 days, whereas in the third (CADD-1) it decreased below 80% of initial value after 3-7 days. Addition of heparin (1 U/ml) or low molecular weight heparin (1 anti-Xa U/ml), which are used to prevent thrombophlebitis at the site of infusion, did not affect the stability. Nine out of 9 samples taken from the infusion systems after 3 days and again after 7 days were sterile. After inoculation with Staphylococcus aureus or Escherichia coli the bacterial growth in samples of the reconstituted concentrate was not different from that in lidocaine in saline or heparin in saline. F VIII was given in continuous infusion with a minipump (Infu-Med) to 12 patients undergoing major surgery and 8 patients with major hemorrhage for a total of 157 days. A progressive decrease of the clearance was seen during the first 5 days of infusion from 3.0 to 1.7 ml/kg/h. Hemostasis was effectively achieved, and no infectious complications were registered.(ABSTRACT TRUNCATED AT 250 WORDS)

Cyclosporine therapy for acquired factor VIII inhibitor in a patient with systemic lupus erythematosus.

The case of a 27-year-old woman with systemic lupus erythematosus and development of an autoantibody against factor VIII during an exacerbation of her underlying disorder is described. Attempts to eliminate the antibody with high dose gammaglobulin and repeated courses of cyclophosphamide failed, whereafter she received cyclosporine in increasing doses. When therapeutic serum levels of cyclosporine were achieved (150-350 ng/ml) the inhibitor rapidly decreased and disappeared with a concomitant normalization of the factor VIII levels. Treatment with cyclosporine was subsequently reduced and discontinued after one year, and at present no inhibitor is detectable. In view of the successful results with cyclosporine treatment in 4 of 6 previous cases and in all 3 previous cases with autoimmune disorders, this regimen should be evaluated in a systematic manner as a potential first line drug in patients with acquired hemophilia and an underlying autoimmune disorder.

Platelet aggregation on extracellular matrix: effect of a recombinant GPIb-binding fragment of von Willebrand factor.

Platelets in whole blood incubated on extracellular matrix (ECM) produced by bovine corneal endothelial cells under oscillatory flow conditions demonstrate extensive aggregate formation. Since both platelet-subendothelium and platelet-platelet interactions are mediated by von Willebrand factor (vWF), we used this system to examine the effect of a recombinant GPIb-binding fragment of vWF (designated RG12986), comprising residues 445-733 of the native vWF subunit, on platelet reactivity with ECM. The seven cysteines present in the RG12986 fragment were reduced and alkylated in order to achieve a monomeric conformation. The recombinant vWF fragment binds to unstimulated platelets in the absence of exogenous modulators. When added to platelet-rich plasma, it inhibits ristocetin-induced platelet agglutination. Binding of 51Cr-labeled platelets in reconstituted whole blood to ECM was inhibited by RG12986 in a dose dependent and saturable manner, with IC50 of 4 microM and maximal inhibition (about 70%) at 6 microM. Scanning electron microscope (SEM) analysis showed that addition of RG12986 to whole blood significantly inhibited platelet aggregation on ECM. The extent of inhibition observed with RG12986 at a final concentration of 4 microM was similar to that obtained with the cell adhesion peptide RGDS at the concentration of 0.1 mM. The ability of the RG12986 fragment to inhibit platelet aggregation on ECM is in agreement with the concept that blockade of vWF-GPIb interaction may inhibit further events leading to activation of the glycoprotein IIb/IIIa (GPIIb/IIIa) complex and subsequent thrombus formation.

High versus ultra-high purity factor VIII concentrate therapy: prospective evaluation of immunological and clinical parameters in HIV seronegative and seropositive hemophiliacs.

This study aimed at evaluation of the immunological status and the clinical course of both HIV seronegative and seropositive hemophiliacs treated with either an ultra-pure factor VIII product (UP-F VIII), or a high-purity F VIII (HP-F VIII) concentrate. Eighteen HIV seronegative patients were divided into two groups of therapy and their immune status was followed for 2 years. During the second year of the study 8 patients of the HP-F VIII and 6 from the UP-F VIII therapy groups were switched to the alternative F VIII concentrates. Eighteen asymptomatic HIV seropositive patients were also divided into therapy groups and their immune status and any development of HIV-related symptoms were followed for 4 years. Evaluation of the HIV seronegative patients during the first year did not reveal any differences between the groups in the CD4 or CD8 cell counts, in natural killer cell (NK) activity, or in the mitogenic responses of T lymphocytes to Phytohemagglutinin (PHA), and of B lymphocytes to Pokeweed mitogen (PWM). The switch of 8 patients from the HP-F VIII and 6 from the UP-F VIII groups to the alternative concentrate did not yield any changes in their immune profile during the second year of the study. The HIV seropositive groups differed in the initial CD4 count, with a lower CD4 count (193 +/- 126 vs 437 +/- 142) and a higher F VIII consumption (63,000 +/- 17,000 vs 26,000 +/- 10,000) in the UP-F VIII group.(ABSTRACT TRUNCATED AT 250 WORDS)

Safety and efficacy of continuous infusion of a combined factor VIII-von Willebrand factor (vWF) concentrate (Haemate-P) in patients with von Willebrand disease.

We studied the safety and efficacy of treatment with continuous infusion of a von Willebrand factor (vWF) concentrate Haemate-P in patients with von Willebrand disease (vWD). Three patients with mild and 5 patients with severe forms of vWD, were treated with continuous infusion of Haemate-P by minipump. The indications for treatment were: to prevent bleeding during 9 surgical procedures or 1 vaginal delivery in 6 patients and to treat 2 bleeding episodes in 2 patients. The patients were monitored daily for factor VIII (FVIII:C) and ristocetin cofactor (vWF: RCo) levels and the infusion rate was adjusted to maintain the desired therapeutic level of vWF:RCo. The treatment was effective in preventing surgical bleeding and controlling bleeding episodes. All factor VIII:C and most of the vWF:RCo levels measured during the study period were above the target therapeutic levels. A significant decrease in clearance of FVIII:C and vWF:RCo was observed over the treatment period. Haemate-P consumption averaged 24.3+/-7.9 vWF:RCo U/kg/day which is approximately half the expected dose had intermittent bolus injections been used. We suggest that continuous Haemate-P infusion is superior to intermittent bolus injections for the treatment of vWD patients by virtue of its efficiency, simplicity and considerable savings.

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.

Inhibition of integrin-mediated platelet aggregation, fibrinogen-binding, and interactions with extracellular matrix by nonpeptidic mimetics of Arg-Gly-Asp.

The interaction of the activated platelet integrin, glycoprotein IIb-IIIa (GPIIb-IIIa) with fibrinogen and von-Willebrand factor (vWF) is essential for platelet aggregation. The minimal structure required for this integrin's binding to fibrinogen is the Arg-Gly-Asp (RGD) sequence. Inasmuch as normal level of GPIIb-IIIa-RGD interactions are required for maintaining hemostasis, elevated platelet aggregation can cause adverse pathological effects. We have previously reported that nonpeptidic mimetics of RGD, consisting of carboxylate and guanidinium groups of Asp and Arg divided by a linear 11-atom spacer, acquired a significant affinity for the GPIIb-IIIa integrin and inhibited platelet aggregation. The structural requirements for the interactions of the RGD sequence with GPIIb-IIIa and the inhibitory potential of a newly designed series of mimetics on platelet aggregation and interactions with extracellular matrix (ECM) were assayed herein. Adenosine-diphosphate (ADP)-induced platelet aggregation was inhibited in a dose-dependent manner by various RGD mimetics, with a maximal inhibition of 80-100% with an IC50 of 3 microM for the most potent inhibitor, NS-11, in which a six-membered ring was introduced into the spacer chain, which exceeded the IC50 attained with the original RGDS peptide. The inhibitory effect of the RGD mimetics was attributed to their specific interaction with the GPIIb-IIIa integrin, since these mimetics inhibited the binding of the PAC-1 mAb to GPIIb-IIIA. Furthermore, the binding of 125I-labeled fibrinogen to platelets was inhibited by the RGD surrogates in a dose-dependent and saturable manner. The RGD-mimetics also inhibited up to 70% the adhesion, aggregation, and deposition of platelets onto ECM.(ABSTRACT TRUNCATED AT 250 WORDS)