The skin bleeding time test as a predictor of brain bleeding time in a rat model

PFA-100 System: A New Method for Assessment of Platelet Dysfunction

This is a celebratory reprint of a historical paper published in STH in 1998. The original Abstract follows.The PFA-100 system is a platelet function analyzer designed to measure platelet-related primary hemostasis. The instrument uses two disposable cartridges: a collagen/epinephrine (CEPI) and a collagen/ADP (CADP) cartridge. Previous experience has shown that CEPI cartridges detect qualitative platelet defects, including acetylsalicylic acid (ASA)-induced abnormalities, while CADP cartridges detect only thrombocytopathies and not ASA use. In this seven-center trial, 206 healthy subjects and 176 persons with various platelet-related defects, including 127 ASA users, were studied. The platelet function status was determined by a platelet function test panel. Comparisons were made as to how well the defects were identified by the PFA-100 system and by platelet aggregometry. The reference intervals for both cartridges, testing the 206 healthy subjects, were similar to values described in smaller studies in the literature (mean closure time [CT] of 132 seconds for CEPI and 93 seconds for CADP). The use of different lot numbers of cartridges or duplicate versus singleton testing revealed no differences. Compared with the platelet function status, the PFA-100 system had a clinical sensitivity of 94.9% and a specificity of 88.8%. For aggregometry, a sensitivity of 94.3% and a specificity of 88.3% were obtained. These values are based on all 382 specimens. A separate analysis of sensitivity by type of platelet defect, ASA use versus congenital thrombocytopathies, revealed for the PFA-100 system a 94.5% sensitivity in identifying ASA users and a 95.9% sensitivity in identifying the other defects. For aggregometry, the values were 100% for ASA users and 79.6% for congenital defects. Analysis of concordance between the PFA-100 system and aggregometry revealed no difference in clinical sensitivity and specificity between the systems (p > 0.9999). The overall agreement was 87.5%, with a Kappa index of 0.751. The two tests are thus equivalent in their ability to identify normal and abnormal platelet defects. Testing 126 subjects who took 325 mg ASA revealed that the PFA-100 system (CEPI) was able to detect 71.7% of ASA-induced defects with a positive predictive value of 97.8%. The overall clinical accuracy of the system, calculated from the area under the receiver operating characteristic curve, was 0.977. The data suggest that the PFA-100 system is highly accurate in discriminating normal from abnormal platelet function. The ease of operation of the instrument makes it a useful tool to use in screening patients for platelet-related hemostasis defects.

Prohemorrhagic and bleeding time activities of recombinant tissue plasminogen activator, heparin, aspirin, and a glycoprotein IIb/IIIa antagonist

Intracerebral hemorrhage (ICH) is the most serious side effect of antithrombotic agents, especially in cases of cerebrovascular disease. In the present study, we compared the exacerbation of ICH and prolongation of bleeding time (BT) in guinea pigs with recombinant tissue plasminogen activator (rt-PA), heparin, aspirin, and FK419, a novel nonpeptide platelet glycoprotein (GP) IIb/IIIa receptor antagonist. ICH was induced by injection of bacterial collagenase into the caudate nucleus; BT was measured with a Simplate R device. Neither heparin nor aspirin prolonged BT. In contrast, rt-PA at the highest dose used in the study did prolong BT, and FK419 caused a dose-dependent prolongation of BT. Moreover, rt-PA and heparin increased the degree of ICH in a dose-dependent manner, leading to death in more than half of the animals treated with higher doses of these drugs. These findings show that the prohemorrhagic mechanisms underlying the prolongation of BT differ from those in collagenase-induced ICH, and that the risk of an agent with antithrombotic effects potentiating hemorrhage in the collagenase-induced model of ICH more closely parallels that in stroke patients than does the effect of the agent on BT. The findings also suggest that antiplatelet agents, including FK419, may be safer than thrombolytic or anticoagulant agents for use in patients at risk for ICH, such as those with stroke or cerebral aneurysm.

Pharmacological properties of YM-57029, a novel platelet glycoprotein IIb/IIIa antagonist

The pharmacological properties of YM-57029 [4-[4-(4-carbamimidoylphenyl)-3-oxopiperazin-1-yl]piperidino]acetic acid monohydrochloride trihydrate), a novel glycoprotein IIb/IIIa antagonist were examined in this study. YM-57029 inhibited fibrinogen binding to purified glycoprotein IIb/IIIa, 1000-fold more potently than the tetrapeptide arginine-glycine-aspartic acid-serine (RGDS). YM-57029 concentration-dependently inhibited ADP-, collagen- and high shear stress-induced platelet aggregation, strongly inhibited ATP release from platelets activated by ADP, and enhanced deaggregation of ADP-induced platelet aggregates. In a pro-aggregatory activity study, RGDS or SC-54701A ((S)-3-[3-[(4-amidinophenyl)carbamoyl]propionamido]-4-pentynoic acid monohydrochloride) caused prominent small aggregate formation. At a higher concentration, RGDS induced medium and large size aggregates, and SC-54701A induced medium aggregates. In contrast, YM-57029 produced only a few small and no larger size aggregates. Ex vivo ADP-induced platelet aggregation and platelet retention to collagen-coated plastic beads were dose-dependently inhibited by YM-57029 after intravenous bolus injection in guinea pigs. YM-57029 produced dose-dependent antithrombotic effects in carotid artery thrombosis and arterio-venous shunt thrombosis models in guinea pigs at 10 and 30 microg/kg, respectively. At these doses, YM-57029 prolonged template bleeding time. These results suggest that YM-57029 is a potent glycoprotein IIb/IIIa antagonist which has less pro-aggregatory effect. It may be a promising antiplatelet agent for thromboembolic diseases, and a good prototype for developing an orally active compound.

Discontinuation of the Bleeding Time Test without Detectable Adverse Clinical Impact

Background: The bleeding time (BT) test predicts a higher bleeding complication rate in populations at risk for inherited or acquired platelet dysfunction, but it is of limited assistance in evaluating individual patients. There are no reports of clinical outcomes after discontinuation of the BT test.

Methods: Interviews with a subset of the physicians who had ordered the BT test before discontinuation of the test were conducted. The total number of platelet-aggregation tests, the mean number of monthly, unmodified platelet units transfused, the incidence of kidney biopsy complications, and the number of doses of 1-deamino-8-d-arginine vasopressin (DDAVP) administered 5 months before and after discontinuation of the BT test were compared. We recorded the rates of bleeding complications in the Major Surgery Risk Pool during the 12 months before and the 5 months after the discontinuation of the BT test.

Results: Clinicians reported they did not significantly change their preprocedural work-ups, postpone an invasive procedure, experience an increase in bleeding complications, or increase their use of blood products after discontinuation of the BT test. Platelet-aggregation tests (n = 9, before and after), platelet transfusions (P = 0.958), and DDAVP administration (before = 24; after = 10) did not increase after discontinuation of the BT test. The rate of postprocedural bleeding complications did not increase significantly in either Major Surgery Risk Pool cases (<3ς deviation from the mean rate) or in patients undergoing renal biopsies (P = 0.225 for decrease in hematocrit; P = 1.000 for the percentage of patients transfused) after discontinuation of the BT test.

Conclusions: Our study failed to identify a clinically significant, negative impact of discontinuing the BT test.

Thromboxane A(2) synthase inhibitor enhanced antithrombotic efficacy of GPIIb-IIIa receptor antagonist without increasing bleeding

The advantage of platelet integrin GPIIb-IIIa receptor antagonists in the prevention of thrombotic occlusion was clearly proven in patients who underwent interventional treatment of the coronary artery, but its value in cerebral ischemia is still under investigation. The expectation of intracranial hemorrhage on strong inhibition of platelet function restricts its application in cerebral ischemia. To minimize bleeding while keeping antithrombotic activity, we have tried to find an appropriate approach using a combination of platelet integrin GPIIb-IIIa receptor antagonist and some other antithrombotic agents. The time to thrombotic occlusion was measured using a photothrombotic occlusion model of guinea pig middle cerebral artery. A platelet integrin GPIIb-IIIa receptor antagonist, ME3277 (sodium hydrogen [4-[(4,5,6,7-tetrahydrothieno [3,2-c] pyridin-2-yl) carbonylamino] acetyl-o-phenylene] dioxydiacetate), delayed occlusion time from 7.3 min in vehicle to 15.0, 20.6 and 25.9 min (P<0.05) at 0.1, 0.3 and 1 mg/kg, respectively. ME3277 profoundly inhibited ex vivo platelet aggregation and the highest dose of ME3277 prolonged (3.5 folds, P<0.01) the bleeding time measured in the hind paw. A thromboxane A(2) synthase inhibitor, sodium ozagrel, significantly delayed occlusion time to 19.5 min at 30 mg/kg (P<0.05) while it did not affect bleeding time or platelet aggregation. ME3277 (0.1 mg/kg) in combination with 10 mg/kg sodium ozagrel synergistically delayed occlusion time (sodium ozagrel alone; 7.9 min, combination; 26.1 min, P<0.05 vs. ME3277 alone). Sodium ozagrel did not affect ex vivo platelet aggregation or bleeding time when combined with 0.1 mg/kg of ME3277. This synergy was cancelled by combination with 30 mg/kg aspirin (14.7 min). A thromboxane A(2) receptor antagonist, vapiprost (0.1 mg/kg), did not enhance the antithrombotic efficacy of ME3277. These results imply that local prostacyclin production enhances the in vivo antithrombotic effect of the platelet integrin GPIIb-IIIa receptor antagonist. Therefore, the thromboxane A(2) synthase inhibitor allowed a reduction in the dose level of the platelet integrin GPIIb-IIIa receptor antagonist for cerebral thrombosis, which resulted in a reduced risk of bleeding.

ME3277, a GPIIb/IIIa antagonist reduces cerebral infarction without enhancing intracranial hemorrhage in photothrombotic occlusion of rabbit middle cerebral artery

GPIIb/IIIa antagonists are expected to have a beneficial effect on acute cerebral infarction, however, the occurrence of intracranial hemorrhage has not been as widely investigated. A rabbit focal thrombotic occlusion model of the middle cerebral artery was established by creating a photochemical reaction between green light and Rose Bengal. Hemorrhagic transformation was common in the area of cerebral infarction. Using this model, the effect of a GPIIb/IIIa antagonist, ME3277 (low dose, (L); 0.15 mg/kg + 0.125 mg/kg x h, middle dose, (M); 0.3 mg/kg + 0.25 mg/kg x h and high dose, (H); 0.6 mg/kg + 0.5 mg/kg x h), aspirin (20 mg/kg) and sodium ozagrel (thromboxane A2 synthase inhibitor, 1 mg/kg + 2 mg/ kg x h) were evaluated. Drugs were intravenously administrated 30 minutes after the photochemical reaction for 24 hours. Aspirin inhibited the ex vivo platelet aggregation induced by arachidonic acid and collagen but not by adenosine diphosphate (ADP), while sodium ozagrel only inhibited the arachidonic acid-induced aggregation. ME3277 dose-dependently inhibited the platelet aggregation induced by all the inducers (approximately 60% in L, 80% in M, and 90% in H). At 24 hours of middle cerebral artery (MCA) occlusion, infarct volume was significantly reduced by aspirin and each dose of ME3277. These agents improved neurologic deficits, with ME3277 being more potent than aspirin. Sodium ozagrel did not alter the infarct volume nor neurologic deficits. No drug was found to worsen hemorrhage volume despite increasing bleeding time (2-3 fold) in the skin. In this model, the occluded artery was spontaneously recanalized and re-thrombosed frequently. One mechanism by which antiplatelet agents reduced infarct volume was inhibition of rethrombosis of the MCA. These results suggest that treatment with a GPIIb/IIIa antagonist is a useful intervention for acute cerebral infarction prolonging dose bleeding time to 3 times the basal value.

Overview of platelet physiology and laboratory evaluation of platelet function

Appropriate laboratory testing for the platelet-type bleeding disorders hinges on an adequate assessment in the history and physical examination. Patients with histories and screening laboratory results consistent with coagulation disorders (hemophilia, disseminated intravascular coagulation) are not appropriate candidates for platelet function testing. In contrast, patients with a lifelong history of platelet-type bleeding symptoms and perhaps a positive family history of bleeding would be appropriate for testing. Figure 6 depicts one strategy to evaluate these patients. Platelet morphology can easily be evaluated to screen for two uncommon qualitative platelet disorders: Bernard-Soulier syndrome (associated with giant platelets) and gray platelet syndrome, a subtype of storage pool disorder in which platelet granulation is morphologically abnormal by light microscopy. If the bleeding disorder occurred later in life (no bleeding with surgery or trauma early in life), the focus should be on acquired disorders of platelet function. For those patients thought to have an inherited disorder, testing for vWD should be done initially because approximately 1% of the population has vWD. The complete vWD panel (factor VIII coagulant activity, vWf antigen, ristocetin cofactor activity) should be performed because many patients will have abnormalities of only one particular panel component. Patients diagnosed with vWD should be classified using multimeric analysis to identify the type 1 vWD patients likely to respond to DDAVP. If vWD studies are normal, platelet aggregation testing should be performed, ensuring that no antiplatelet medications have been ingested at least 1 week before testing. If platelet aggregation tests are normal and if suspicion for an inherited disorder remains high, vWD testing should be repeated. The evaluation of thrombocytopenia may require bone marrow examination to exclude primary hematologic disorders. If future studies with thrombopoietin assays confirm preliminary results, however, the bone marrow examination of certain patients may be replaced by a thrombopoietin level.

Antithrombotic effects of YM-60828 in three thrombosis models in guinea pigs

The antithrombotic effects of a novel factor Xa inhibitor, YM-60828 ([N-[4-[(1-acetimidoyl-4-piperidyl)oxy]phenyl]-N-[(7-amidino-2-nap hthyl)methyl]sulfamoyl]acetic acid dihydrochloride), in three thrombosis models in guinea pigs were studied in comparison with its effect on bleeding time. The antithrombotic effects of YM-60828 were most pronounced in the venous thrombosis and the arterio-venous shunt models but YM-60828 showed 10-fold weaker effects in the carotid thrombosis model. However, YM-60828 prolonged bleeding time at a much higher dose than that required in all thrombosis models. In conclusion, YM-60828 exerted its antithrombotic effects without prolonging bleeding time in all thrombosis models and may be of clinical value not only in venous thrombosis but also in arterial thrombosis.

Antithrombotic effects of YM-60828, a newly synthesized factor Xa inhibitor, in rat thrombosis models and its effects on bleeding time

1. The effects of YM-60828, a newly synthesized factor Xa inhibitor, were investigated to analyse the relationship between its antithrombotic effects and its prolongation of template bleeding time in rats. YM-60828 was compared with argatroban, heparin and dalteparin. All agents were intravenously administered as a bolus. 2. In ex vivo studies, YM-60828 and argatroban prolonged both prothrombin time and activated partial thromboplastin time in a dose-dependent manner, while heparin and dalteparin prolonged only activated partial thromboplastin time. 3. In a venous thrombosis model, all agents exerted antithrombotic effects in a dose-dependent manner. The ID50 values of YM-60828, argatroban, heparin and dalteparin were 0.0081 mg kg(-1), 0.011 mg kg(-1), 6.3 iu kg(-1) and 4.7 iu kg(-1), respectively. 4. In an arterio-venous shunt model, all agents exerted antithrombotic effects in a dose-dependent manner. The ID50 values of YM-60828, argatroban, heparin and dalteparin were 0.010 mg kg(-1), 0.011 mg kg(-1), 10 iu kg(-1) and 4.2 iu kg(-1), respectively. 5. In bleeding time studies, all agents prolonged template bleeding time in a dose-dependent manner. ED2 values, the doses causing a 2 fold prolongation of bleeding time in the saline group, of YM-60828, argatroban, heparin and dalteparin were 0.76 mg kg(-1), 0.081 mg kg(-1), 18 iu kg(-1) and 25 iu kg(-1), respectively. 6. The ratio (ED2/ID50) of YM-60828 was more than 30 fold greater than that of heparin and more than 10 fold greater than those of argatroban and dalteparin. 7. These data show that YM-60828 can exert its antithrombotic effects with little prolongation of bleeding time compared with the other currently used anticoagulant agents.

Enhancement of platelet deposition by cross-linked hemoglobin in a rat carotid endarterectomy model

BACKGROUND

Purified human cross-linked hemoglobin, which is now being used in clinical trials, increases mean arterial pressure through binding of nitric oxide (NO). We postulated that binding of NO by cross-linked hemoglobin (alpha alpha Hb) could also increase platelet deposition at sites of subintimal injury.

METHODS AND RESULTS

Male Sprague-Dawley rats were infused with alpha alpha Hb (0.88 g/kg, n = 8) or with the NO synthase inhibitor NG-monomethyl-L-arginine (L-NMMA, 30 mg/kg, n = 7) before undergoing microsurgical carotid endarterectomy. 111In-labeled platelets were infused after endarterectomy, and platelet deposition was measured 20 minutes later. In control endarterectomized rats (n = 8), mean platelet deposition was 7.7 +/- 0.7 x 10(6)/mm2. Platelet deposition was significantly increased above controls in rats that received alpha alpha Hb (13.2 +/- 0.9 x 10(6)/mm2, P = .0004) and in rats infused with L-NMMA (13.9 +/- 1.0 x 10(6)/mm2, P = .0002). The increase was prevented by infusion of L-arginine (150 mg/kg) immediately after alpha alpha Hb or L-NMMA. To determine whether aspirin (ASA) blocked the increased deposition induced by alpha alpha Hb, rats received oral ASA (10 mg/kg) 18 hours before endarterectomy. Platelet deposition in animals receiving ASA alone was 6.4 +/- 0.9 x 10(6)/mm2 (n = 8). This was significantly increased to 10.8 +/- 0.8 x 10(6)/mm2 (P = .002) for the ASA-treated group that received alpha alpha Hb at the time of endarterectomy (n = 8). The prolonged bleeding times induced by ASA were unaffected by the infusion of alpha alpha Hb.

CONCLUSIONS

These data suggest that in a rat endarterectomy model, alpha alpha Hb increases platelet deposition at sites of subintimal injury by binding NO. Increased deposition induced by alpha alpha Hb can be prevented by administration of L-arginine but not by pretreatment with aspirin.

A monoclonal antibody that recognizes the GPIIb/IIIa antagonist DMP 728. Reversal of the effects of DMP 728 on platelet aggregation and bleeding time in the dog

Since hemorrhagic events represent a major safety concern associated with the use of new antithrombotic therapies such as glycoprotein (GP) IIb/IIIa receptor blockade, we evaluated the ability of a monoclonal antibody recognizing DMP 728 (cyclic [D-2-aminobutyryl-N2-methyl-L-argininyl-glycyl-L-aspartyl-3- aminomethyl-benzoic acid] methanesulfonic acid salt), a potent GPIIb/IIIa receptor antagonist, to reverse the pharmacological actions of DMP 728 in the dog. DC11 was chosen for in vivo evaluation based on its ability to inhibit the binding of [3H]DMP 728 to activated platelets and to attenuate the inhibition of ADP-induced aggregation on platelet-rich plasma ex vivo by DMP 728. After anesthesia mongrel dogs were given DMP 728 (20 micrograms/kg body wt IV) infused into the femoral vein, bleeding times were determined using a Simplate device from incisions on the backside of the tongue, and platelet aggregation was determined ex vivo. Nearly complete inhibition of platelet aggregation was observed for the dogs treated with DMP 728 (20 ug/kg IV) for up to 210 minutes, and bleeding times were prolonged > 15 minutes for 2 hours and remained elevated for more than 4 hours. DC11 (0.2 or 1.0 mg/kg body wt IV) given to dogs 10 minutes after DMP 728 resulted in 50% attenuation of the effect of DMP 728 on aggregation at 3 hours. Approximately 34% inhibition of the DMP 728-mediated bleeding time was achieved at 1 hour with the 0.2 mg/kg dose, whereas approximately 50% inhibition of the bleeding time was observed for the 1 mg/kg dose at 1 hour.(ABSTRACT TRUNCATED AT 250 WORDS)