Characterization of whole blood aggregation with a new type of aggregometer by a screen filtration pressure method

The Inhibitory Effect of Platelet Aggregation Ability Assessed by the Platelet Aggregatory Threshold Index in a Patient with Recurrent Stent Thrombosis

An 86-year-old man successfully underwent percutaneous coronary intervention (PCI), in which a drug-coated stent (DCS) was placed in the left anterior descending coronary artery. However, stent thrombosis occurred twice after eight and two months. After the second admission, the patient was tested for platelet aggregation activity using the platelet aggregation threshold index (PATI), and insufficient inhibition of platelet aggregation was observed. The patient's PATI improved to a satisfactory level using oral anticoagulants. At the six-month follow-up, clinical events were observed. Measuring the platelet aggregation ability can help clinicians understand the pathology of patients and determine treatment choices.

Myocardial salvage after ST-segment-elevation myocardial infarction: comparison between prasugrel and clopidogrel in the presence or absence of high-residual platelet reactivity

BACKGROUND

The effect of prasugrel over clopidogrel on myocardial salvage in ST-segment-elevation myocardial infarction (STEMI) patients undergoing primary percutaneous coronary intervention (p-PCI) is not fully elucidated.

METHODS

Among 854 consecutive STEMI patients who underwent p-PCI, 446 patients were evaluated by two-phase (7 days and 3 months) single-photo emission computed tomography (SPECT). Patients were divided into two groups based on the loading P2Y12 inhibitor. The clopidogrel group was further divided based on the result of platelet function testing. Thus, the prasugrel group included 227 patients; the clopidogrel without high-residual platelet reactivity (HRPR) group, 109 patients; and the clopidogrel with HRPR group, 107 patients. The primary endpoint was the Myocardial Salvage Index (MSI), determined by SPECT.

RESULTS

The incidence of final TIMI 0/1 and TIMI myocardial perfusion grade 0/1 was higher in the clopidogrel with HRPR group (0.9%, 1.8%, and 7.5%, P =  .002; 19.8%, 29.4%, and 41.1%, P = .0002, in the prasugrel, clopidogrel without HRPR, and clopidogrel with HRPR groups, respectively). The MSI was significantly lower in the clopidogrel with HRPR group (48% [27-66], 44% [30-72], and 36% [15-55], P =  .006, respectively).

CONCLUSIONS

Prasugrel in STEMI patients was associated with an increased MSI compared with clopidogrel in the presence of HRPR.

Keishibukuryogan, a Traditional Japanese Medicine, Inhibits Platelet Aggregation in Guinea Pig Whole Blood

Effects of keishibukuryogan (KBG) on platelet aggregation were investigated. To ensure the specificity of KBG, tokishakuyakusan (TSS) and kamisyoyosan (KSS), which are known to have platelet aggregation-inhibiting effects, and rikkunshito (RKT) and shakuyakukanzoto (SKT), which are considered to be devoid of such effects, were used for comparison. The platelet aggregation of each test drug was measured by the screen filtration pressure method using whole blood of guinea pigs and expressed as a collagen-induced pressure rate (%) or a collagen concentration required for 50% increase in the pressure rate (PATI value). KBG suppressed the collagen-induced whole blood pressure rate increase and increased the PATI value, like TSS and KSS. Neither RKT nor SKT showed these effects. The Moutan cortex and Cinnamomi cortex, the constituent crude drugs of KBG, showed KBG-like pressure rate suppression and PATI-increasing effects. Furthermore, paeonol, a representative component of Moutan cortex, and aspirin which is known to have platelet aggregation-inhibiting activity (COX-1 inhibitor) also showed similar effects. These results suggest that the platelet aggregation-inhibiting activity of the constituent crude drugs Moutan cortex and Cinnamomi cortex is involved in the improving effects of KBG on impaired microcirculation and that paeonol plays a role in these effects.

Endothelial progenitor cells inhibit platelet function in a P-selectin-dependent manner

Background

The role of endothelial progenitor cells (EPCs) in vascular repair is related to their recruitment at the sites of injury and their interaction with different components of the circulatory system. We have previously shown that EPCs bind and inhibit platelet function and impair thrombus formation via prostacyclin secretion, but the role of EPC binding to platelet P-selectin in this process has not been fully characterized. In the present study, we assessed the impact of EPCs on thrombus formation and we addressed the implication of P-selectin in this process.

Methods

EPCs were generated from human peripheral blood mononuclear cells cultured on fibronectin in conditioned media. The impact of EPCs on platelet aggregation and thrombus formation was investigated in P-selectin deficient (P-sel^−/−) mice and their wild-type (WT) counterparts.

Results

EPCs significantly and dose-dependently impaired collagen-induced whole blood platelet aggregation in WT mice, whereas no effects were observed in P-sel^−/− mice. Moreover, in a ferric chloride-induced arterial thrombosis model, infusion of EPCs significantly reduced thrombus formation in WT, but not in P-sel^−/− mice. Furthermore, the relative mass of thrombi generated in EPC-treated P-sel^−/− mice were significantly larger than those in EPC-treated WT mice, and the number of EPCs recruited within the thrombi and along the arterial wall was reduced in P-sel^−/− mice as compared to WT mice.

Conclusion

This study shows that EPCs impair platelet aggregation and reduce thrombus formation via a cellular mechanism involving binding to platelet P-selectin. These findings add new insights into the role of EPC-platelet interactions in the regulation of thrombotic events during vascular repair.

Utility of whole-blood aggregometry for evaluating anti-platelet therapy for Kawasaki disease

BACKGROUND

Anti-platelet therapy for Kawasaki disease (KD) is often done without monitoring drug efficacy. The aim of this study was to investigate the utility of whole-blood aggregometry to evaluate the efficacy of anti-platelet therapy for KD.

METHODS

Of 37 late-phase KD patients included in the present study, 20 were prescribed anti-platelet drugs. Platelet-rich plasma (PRP) aggregation with collagen as the stimulus was measured using an optical aggregometer. The area under the curve of small and large size aggregations was calculated, and categorized into five classes: -2, -1, 0, 1, and 2. Whole-blood aggregation with collagen or adenosine 5'-diphosphate (ADP) as stimulus was evaluated using the platelet aggregation threshold index (PATI), which is the concentration of stimulus that induces a whole-blood aggregation rate of 50%.

RESULTS

In both collagen- and ADP-induced aggregation, there was a negative correlation between PATI and class determination using the PRP technique (collagen, rs = -0.870, P < 0.0001; ADP, rs = -0.620, P < 0.0001). Moreover, the PATI in collagen- and ADP-induced aggregation was significantly higher in the anti-platelet drug therapy group than in the untreated group (collagen, P < 0.0001; ADP, P = 0.0002). The serum thromboxane B2 level in the anti-platelet drug therapy group was also significantly lower than that in the untreated group (P < 0.0001). PATI was significantly higher in those treated with thienopyridine drug combinations than those without drug therapy (P = 0.0036).

CONCLUSIONS

Whole-blood aggregometry is useful for monitoring the efficacy of anti-platelet therapy for KD.

Identification of the active region responsible for the anti-thrombotic activity of anopheline anti-platelet protein from a malaria vector mosquito

We previously identified an anti-platelet protein, anopheline anti-platelet protein (AAPP), from the salivary gland of female Anopheles stephensi (a mosquito vector of human malaria). AAPP specifically blocks platelet adhesion to collagen by binding directly to collagen and subsequently causing platelet aggregation. The aim of this study was to identify the active region of AAPP responsible for the anti-thrombotic activity because we hypothesized that AAPP could be used as a candidate anti-platelet drug. Various truncated forms of AAPP were produced using an Escherichia coli expression system. Each protein was examined for binding activities to soluble/fibrillar collagen and anti-thrombotic activity using a plate assay and platelet/whole blood aggregation study, respectively. Among the truncated forms examined, only a protein encoded by exon 3-4 (rAAPPex3-4) effectively bound to soluble/fibrillar collagen in a concentration-dependent and saturable manner. The EC50 values of full-length AAPP and rAAPPex3-4 for soluble collagen binding were 35 nM and 36 nM, respectively. In contrast to soluble collagen, there was a difference in binding affinity to fibrillar collagen between full-length AAPP and rAAPPex3-4, with EC50 values of 31 nM and 51 nM, respectively. rAAPPex3-4 also inhibited aggregation of platelets/whole blood, and the IC50 values of full-length AAPP and rAAPPex3-4 for platelet aggregation were 35 nM and 93 nM, respectively. These results indicated that the essential moiety of AAPP for collagen binding and anti-thrombotic activity was in the region encoded by exon 3-4, which is highly conserved among the counterpart regions of other mosquito species.

Cilostazol inhibits accumulation of triglyceride in aorta and platelet aggregation in cholesterol-fed rabbits

Cilostazol is clinically used for the treatment of ischemic symptoms in patients with chronic peripheral arterial obstruction and for the secondary prevention of brain infarction. Recently, it has been reported that cilostazol has preventive effects on atherogenesis and decreased serum triglyceride in rodent models. There are, however, few reports on the evaluation of cilostazol using atherosclerotic rabbits, which have similar lipid metabolism to humans, and are used for investigating the lipid content in aorta and platelet aggregation under conditions of hyperlipidemia. Therefore, we evaluated the effect of cilostazol on the atherosclerosis and platelet aggregation in rabbits fed a normal diet or a cholesterol-containing diet supplemented with or without cilostazol. We evaluated the effects of cilostazol on the atherogenesis by measuring serum and aortic lipid content, and the lesion area after a 10-week treatment and the effect on platelet aggregation after 1- and 10-week treatment. From the lipid analyses, cilostazol significantly reduced the total cholesterol, triglyceride and phospholipids in serum, and moreover, the triglyceride content in the atherosclerotic aorta. Cilostazol significantly reduced the intimal atherosclerotic area. Platelet aggregation was enhanced in cholesterol-fed rabbits. Cilostazol significantly inhibited the platelet aggregation in rabbits fed both a normal diet and a high cholesterol diet. Cilostazol showed anti-atherosclerotic and anti-platelet effects in cholesterol-fed rabbits possibly due to the improvement of lipid metabolism and the attenuation of platelet activation. The results suggest that cilostazol is useful for prevention and treatment of atherothrombotic diseases with the lipid abnormalities.

Impact of platelet reactivity to adenosine diphosphate before implantation of drug-eluting stents on subsequent adverse cardiac events in patients with stable angina

BACKGROUND

Diverse pharmacological effects of anti-platelet thienopyridines due to individual differences in metabolism have been reported. However, an association between on-treatment platelet reactivity and adverse ischemic events after drug-eluting stent (DES) implantation in Japanese patients has not been fully elucidated.

METHODS AND RESULTS

A total of 450 consecutive patients on dual anti-platelet therapy (aspirin and ticlopidine) with stable angina who underwent DES implantation were enrolled. Adenosine diphosphate (ADP)-induced platelet aggregation was measured before DES implantation using the screen filtration pressure method. The ADP concentration necessary for 50% aggregation was designated as the platelet aggregation threshold index (PATI). A composite primary endpoint of cardiac death, myocardial infarction, target lesion revascularization (TLR), and stent thrombosis occurring within 1 year after stenting, was evaluated. A PATI value <4.8 µmol/L was defined as high on-treatment reactivity to ADP. The composite primary endpoint occurred in 55 patients (12.2%) in the 1-year-period after DES implantation, and the prevalence was 19.0% and 5.1% in groups with high and low on-treatment reactivity to ADP, respectively, showing a significantly higher prevalence in the high reactivity group (P<0.001). The main event was TLR (18.1% vs. 5.1%, P<0.001).

CONCLUSIONS

These data suggested that high on-treatment platelet reactivity to ADP and subsequent occurrence of adverse ischemic events (particularly TLR) were correlated in patients with stable angina who underwent DES implantation.

Enhanced platelet responsiveness due to chilling and its relation to CD40 ligand level and platelet-leukocyte aggregate formation

To investigate platelet responsiveness during cold storage of whole blood, we examined platelet aggregation, expression of CD40 ligand (CD40L) on platelets, the plasma levels of soluble form of CD40L (sCD40L) as well as platelet-leukocyte aggregates. Flow cytometry analysis was performed to investigate platelet-leukocyte aggregate formation using antibodies against CD42b and CD45 and platelet activation using antibodies against P-selectin and PAC-1. Blood samples were collected from healthy volunteers, patients with cardiovascular diseases, or both. In the healthy volunteers' blood samples stored at 4 degrees C for 6 h, platelet aggregation in response to 1 micromol/l ADP was enhanced, and released levels of soluble form of P-selectin and thromboxane B2 in response to 1 micromol/l ADP markedly increased. In the samples stored at 4 degrees C for 6 h but not stimulated by any agonists, CD40L expression on the platelets was increased, and plasma levels of sCD40L were also elevated. Under the same condition, the increase in simultaneous expression of CD45 and CD42b was observed. In patients with cardiovascular diseases, the platelet aggregability, coexpression of P-selectin and PAC-1, expression of CD40L on platelets and both CD45-bound and CD42b-bound subsets were all comparable to those of healthy volunteers' samples stored at 4 degrees C for 6 h. Plasma levels of sCD40L in patients were higher than those in healthy volunteers' control. Taken together, storage of whole blood at 4 degrees C for 6 h caused platelet activation comparable to that of patients with cardiovascular diseases, and enhanced platelet activity in such patients may be involved in increased risk for thromboembolic events.

Low responsiveness to thienopyridine in hemodialysis patients

We sought to evaluate whether thienopyridine low responsiveness, a predictor of stent thrombosis, is found in hemodialysis patients. We measured platelet aggregation at the site of implantation of drug-eluting stents in 333 patients with angina pectoris undergoing dual anti-platelet therapy. Thirty-one patients were on hemodialysis (HD group), and 302 were not (N-HD group). We used a novel whole-blood aggregometer. The aggregometer used the screen filtration method, with adenosine diphosphate as an agonist. The concentration of agonist required to induce 50% of the maximum pressure rate was calculated and indicated as the platelet aggregatory threshold index (PATI). Low responsiveness for thienopyridine was defined if the PATI levels were <4 μmol/l. PATI levels (μmol/l) were significantly lower in the HD group than in the N-HD group (6.8 ± 4.8 vs. 9.1 ± 5.4, P = 0.023), and the rate of low responsiveness for thienopyridine was significantly higher in the HD group than in the N-HD group (45.7 vs. 26.8%, P = 0.019). Non-fatal myocardial infarction and stent thrombosis occurred in three of the HD group and in nine of the N-HD group (P = 0.122). Late stent thrombosis occurred at a significantly higher rate in the HD group than in the N-HD group (P = 0.002). The rate of target lesion revascularization was significantly higher in the HD group than in the N-HD group (38 vs. 11.8%, P = 0.0001). In conclusion, low responsiveness to thienopyridine, as an indicator of platelet reactivity, is found more frequently in hemodialysis patients.

Action of aspirin on whole blood-aggregation evaluated by the screen filtration pressure method

BACKGROUND

There are few monitoring systems widely used in clinical practice for evaluating the effectiveness of aspirin therapy, so in the present study aspirin's antiplatelet effects we investigated with a whole blood aggregometer using a screen filtration pressure (SFP) method.

METHODS AND RESULTS

Thirty-five healthy male volunteers took 100 mg/day aspirin for 14 days. Whole-blood aggregation was analyzed at baseline and on days 7 and 14, using collagen and adenosine diphosphate as the stimuli, and compared with the platelet-rich plasma (PRP) aggregation measured by optical aggregometer. The platelet-aggregation threshold index (PATI) for both methods, which was defined as the putative agonist-concentration giving half-maximal aggregation, and the PRP-maximal aggregation rate were analyzed. The maximal aggregation rate induced by 1.6 mg/L collagen decreased from 85.5% (80.8-92.8) [median (interquartile range)] at baseline to 51.5% (39-63.8) on day 14 (p<0.0001). The PRP-PATI and whole-blood PATI for collagen increased from 0.32 (0.28-0.70) to 1.82 mg/L (1.25-2.89) (p<0.0001) and from 0.28 (0.22-0.3) to 1.06 mg/L (1.01-1.29) (p<0.0001) respectively.

CONCLUSIONS

The whole-blood PATI and PRP-PATI for collagen, as well as the maximal PRP aggregation rate, clearly distinguish platelet aggregability before and after aspirin intake. However, whole-blood analysis by the SFP-method is easier to perform, and is a promising method of monitoring aspirin's effects.

Nanomaterials induce oxidized low-density lipoprotein cellular uptake in macrophages and platelet aggregation

BACKGROUND

Nanomaterials have numerous potential benefits for society, but the potential hazards of nanomaterials on human health are poorly understood. Nanomaterials are known to pass into the circulatory system in humans, causing vascular injuries that might play a role in the development of atherosclerosis. The present study aimed to determine the effects of chronic exposure to nanomaterials on macrophage phenotype and platelet aggregation.

METHODS AND RESULTS

Cultured macrophages (RAW264.7) were treated with carbon black (CB) and water-soluble fullerene (C60(OH)24) from 7 to 50 days. Individually, CB had no significant effects on RAW264.7 cell growth, whereas C60(OH)24 alone or CB and C60(OH)24 together with oxidized low-density lipoprotein (Ox-LDL) (100 microg/ml) induced cytotoxic morphological changes, such as Ox-LDL uptake-induced foam cell-like formation and decreased cell growth, in a dose-dependent manner. C60(OH)24 induced LOX-1 protein expression, pro-matrix metalloprotease-9 protein secretion, and tissue factor mRNA expression in lipid-laden macrophages. Although CB or C60(OH)24 alone did not induce platelet aggregation, C60(OH)24 facilitated adenosine diphosphate (ADP)-induced platelet aggregation. Furthermore, C60(OH)24 acted as a competitive inhibitor of ADP receptor antagonists in ADP-mediated platelet aggregation.

CONCLUSIONS

The present study confirmed novel effects of nanomaterials in macrophages and platelets. These effects suggest that exposure to nanomaterials might be a risk for atherothrombotic diseases.

Impaired blood rheology in critically ill patients in an intensive care unit

Critically ill patients are at increased risk of thromboembolic complications. Japanese patients admitted to the intensive care unit of Gunma University Hospital were divided into critically ill (high score) and moderately ill (low score) groups according to mean Acute Physiology and Chronic Health Evaluation (APACHE) II score. White blood cell count, potassium, creatinine, immunoglobulin G and blood passage time, measured using the microchannel method, were significantly higher and the platelet aggregation score and platelet count were significantly lower in the high-score group than in the low-score group, but other haemorheological parameters did not differ significantly between the two groups. White blood cell count, potassium, creatinine, APACHE II score and levels of immunoglobulins G, A and M were positively correlated with blood passage time in all patients. Critically ill patients had impaired blood rheology, which could result from increased white blood cell count, potassium, creatinine and immunoglobulins and may be associated with the pathophysiology of the thromboembolic process.

Distribution and metabolism of dihomo-gamma-linolenic acid (DGLA, 20:3n-6) by oral supplementation in rats

We compared the dietary effects of dihomo-gamma-linolenic acid (DGLA) contained in the DGLA oil produced by a fungus with gamma-linolenic acid (GLA) on the fatty acid composition. Wistar rats were fed with three kinds of oil for two weeks as follows: (i) control group: corn oil; (ii) GLA group: borage oil; (iii) DGLA group: DGLA oil/safflower oil = 55:45. The DGLA concentrations in the liver, serum, and brain of the DGLA group were higher than those of the GLA oil group. We also examined the dose effect of DGLA. The DGLA levels in the liver, serum, and brain significantly increased with increasing dosage of DGLA in the diet. DGLA administration significantly increased the ratio of PGE1/PGE2 in the rat plasma. The mechanism for GLA administration to improve atopic eczema is thought to involve an increase in the concentration of DGLA metabolized from GLA, so these results suggest that the dietary effect of DGLA would be more dominant than GLA.

Platelet dysfunction during cardiopulmonary bypass assessed by a novel whole-blood aggregometer

OBJECTIVE

The purpose of this study was to assess perioperative platelet function with 2 types of monitors (a whole-blood aggregometer [WBA analyzer; Mebanix, Tokyo, Japan]) and the Sonoclot monitor [Sienco, Wheat Ridge, CO]) in patients undergoing hypothermic cardiopulmonary bypass (CPB).

DESIGN

Prospective, observational study.

SETTING

Single-center study at a university hospital.

PARTICIPANTS

Twenty-six patients who underwent coronary artery bypass grafting or valve replacement under hypothermic CPB without platelet transfusion or fresh frozen plasma administration.

INTERVENTIONS

Blood sampling was performed at the following time periods: after anesthetic induction, after CPB, and on the first postoperative day. These samples were assessed with the WBA analyzer and the Sonoclot.

MEASUREMENTS AND MAIN RESULTS

Significant attenuation of adenosine diphosphate-induced platelet aggregation was detected shortly after CPB by 2 WBA analyzer-derived parameters: a decrease in the filtration pressure rate and an increase in the platelet aggregatory threshold index. Platelet aggregation returned to the preoperative level on the next day. There was no correlation between the amount of postoperative mediastinal drainage and defects in platelet aggregation. On the other hand, time to peak obtained by the Sonoclot did not show any significant changes.

CONCLUSIONS

Whole-blood aggregation measured with the WBA analyzer detected transient platelet dysfunction shortly after CPB, whereas the Sonoclot was less sensitive to this change.

Significance of alpha(IIb)beta(3) in subacute stent thrombosis after percutaneous coronary intervention

SUMMARY

Soluble P-selectin and whole blood aggregation (WBA) were measured after percutaneous coronary intervention in patients who then received antiplatelet therapy. One had subacute thrombosis on day 7. This patient's WBA exhibited time-dependent enhancement. In addition, the accentuation of WBA on day 3 was observed when anti-alpha(IIb)beta(3) antibody was added. The remaining 22 patients were divided according to WBA results on day 3 with anti-alpha(IIb)beta(3) antibody added (A group, WBA enhanced; B group, WBA did not enhance). WBA on day 3 was similar in the two groups. The ratio of WBA with and without anti-alpha(IIb)beta(3) antibody was higher in group A than in group B. A significant time-dependent increase of soluble P-selectin was observed in the A group. These results suggest that enhancement of WBA with anti-alpha(IIb)beta(3) antibody after percutaneous coronary intervention predicts subacute thrombosis.

Platelet P-selectin plays an important role in arterial thrombogenesis by forming large stable platelet-leukocyte aggregates

OBJECTIVES

We investigated the role of P-selectin in arterial thrombogenesis by forming large stable platelet-leukocyte aggregates.

BACKGROUND

Plaque rupture followed by thrombus formation is a fundamental pathophysiology of acute coronary syndromes. Although the adhesive interaction between platelets and leukocytes via P-selectin is known to mediate platelet-rich thrombi, the true function of P-selectin in thrombus formation in vivo is unknown.

METHODS

In wild-type (P(+/+)) and P-selectin-deficient (P(-/-)) mice with ferric chloride (FeCl(3))-induced carotid arterial thrombosis model, we measured in vivo platelet P-selectin expression and adenosine diphosphate (ADP)-induced ex vivo platelet aggregation. We also measured ex vivo ADP-induced whole blood aggregations and their size distribution by flow cytometry.

RESULTS

Time to thrombotic occlusion was longer in P(-/-) mice than in P(+/+) mice. Spontaneous reflow after total thrombotic occlusion was observed in 8 of 10 P(-/-) mice but not in any P(+/+) mice. ADP-induced ex vivo platelet aggregation was not different between the two groups. However, ADP-induced ex vivo whole blood aggregation was inhibited in P(-/-) mice compared to P(+/+) mice. FeCl(3) application increased in vivo expressions of platelet P-selectin in P(+/+) mice but not in P(-/-) mice. The number of leukocytes within thrombi was less in P(-/-) mice than in P(+/+) mice. In flow cytometric analysis of size distribution of ADP-induced whole blood aggregates, the number of large aggregates was less in P(-/-) mice than in P(+/+) mice. Using platelet and leukocyte fluorescence makers, the large aggregates were confirmed as platelet-leukocyte aggregates.

CONCLUSIONS

Platelet P-selectin plays an important role in arterial thrombogenesis by forming large stable platelet-leukocyte aggregates.

Intermittent pneumatic foot compression can activate blood fibrinolysis without changes in blood coagulability and platelet activation

BACKGROUND

Intermittent pneumatic foot compression (IPC) is a useful technique for prophylaxis of peri-operative venous thromboembolism. The aim of this study was to determine the effect of IPC on blood coagulation/fibrinolysis and platelet function using a blood viscometer (Sonoclot) and a platelet aggregation monitor (WBA analyzer(TM)), respectively. Using the same blood samples, serum levels of tissue-type plasminogen activator (t-PA), thrombomodulin (TM) and activated protein C (APC) were also measured.

METHODS

The soles and legs of each subject (n = 8) were compressed for 3 s (130 mmHg) at a 0.3-Hz interval using an IPC device. Parameters were measured 2 min before and at the end of 60-min compression.

RESULTS

Parameters of the Sonoclot time-to-peak were shortened and clot retraction rate was increased significantly by IPC, whereas the other parameters did not change. These results indicate that IPC can activate blood fibrinolysis but not coagulability. A parameter of the WBA analyzer PATI (platelet aggregatory threshold index) did not change, indicating that IPC cannot activate platelet function per se. The concentration of t-PA decreased slightly but significantly. A decrease in the concentration of t-PA can lead to activation of fibrinolysis. Other humoral parameters did not change, indicating that IPC has no effect on endothelial function. Although neither blood coagulability nor platelet function were affected by IPC, fibrinolytic activity increased slightly, probably by activation of t-PA function.

CONCLUSION

IPC is useful for prophylaxis for thromboembolism by activation of blood fibrinolysis as well as inhibition of blood stasis.

Measuring platelet aggregation to estimate small intestinal ischemia-reperfusion injury

BACKGROUND

The success of intestinal transplantation is affected by the extreme susceptibility of the small bowel to ischemia-reperfusion (I/R) injury. Currently, there is no quick, convenient method to estimate the extent of small bowel I/R injury. Although histological evaluation is reliable and accurate, it takes too long to allow favorable intervention in I/R injury. I/R causes the production of arachidonic acid products, oxygen free radicals, cytokines, and nitric oxide, which affect platelet function.

OBJECTIVE

This study determined whether measuring platelet aggregation is useful for evaluating small bowel I/R injury.

METHODS

Eighteen mongrel dogs were divided into three groups. In group A both the superior mesenteric artery (SMA) and vein (SMV) were occluded for 120 min. In group B the SMA was occluded for 60 min. Group C underwent a sham operation. Platelet aggregation was measured using a whole blood aggregometer (WBA analyzer), which readily handles small samples. Histological examination was performed. The correlation between platelet aggregation and histology was analyzed.

RESULTS

Platelet aggregation was similar in all groups before reperfusion. After reperfusion, platelet aggregation was significantly lower in group A than in groups B and C (P < 0.05), and mucosal damage was most severe in group A (P < 0.05). After 1 and 3 h of reperfusion, there was a significant negative correlation between platelet aggregation and histological damage.

CONCLUSIONS

Measuring platelet aggregation is rapid, easy, and useful for evaluating small bowel I/R injury.

Disruption of Nuclear Vitamin D Receptor Gene Causes Enhanced Thrombogenicity in Mice

Vitamin D metabolites influence the expression of various genes involved in calcium homeostasis, cell differentiation, and regulation of the immune system. Expression of these genes is mediated by the activation of the nuclear vitamin D receptor (VDR). Previous studies have shown that a hormonally active form of vitamin D, 1alpha,25-dihydroxyvitamin D3, exerts anticoagulant effects in cultured monocytic cells. To clarify whether activation of VDR plays any antithrombotic actions in vivo, hemostatic/thrombogenic systems were examined in normocalcemic VDR knock-out (KO) mice on a high calcium diet and compared with wild type and hypocalcemic VDRKO mice that were fed a regular diet. Platelet aggregation was enhanced significantly in normocalcemic VDRKO mice compared with wild type and hypocalcemic VDRKO mice. Aortic endothelial nitric-oxide (NO) synthase expression and urinary NOx excretions were reduced in hypocalcemic VDRKO mice, but not in normocalcemic VDRKO mice. Northern blot and RT-PCR analyses revealed that the gene expression of antithrombin in the liver as well as that of thrombomodulin in the aorta, liver and kidney was down-regulated in hypo- and normocalcemic VDRKO mice. Whereas tissue factor mRNA expression in the liver and kidney was up-regulated in VDRKO mice regardless of plasma calcium level. Furthermore, VDRKO mice manifested an exacerbated multi-organ thrombus formation after exogenous lipopolysaccharide injection regardless of the calcemic conditions. These results demonstrate that activation of nuclear VDR elicits antithrombotic effects in vivo, and suggest that the VDR system may play a physiological role in the maintenance of antithrombotic homeostasis.

Evaluation of anti-platelet aggregatory effects of aspirin, cilostazol and ramatroban on platelet-rich plasma and whole blood

To compare property in anti-platelet effects of aspirin (a cyclooxygenase inhibitor), cilostazol (a phosphodiesterase III inhibitor) and ramatroban (a specific thromboxane A2 receptor antagonist), we measured human platelet-rich plasma (PRP) aggregation induced by adenosine diphosphate (ADP), collagen and arachidonic acid, and whole blood (WB) aggregation induced by ADP. The release of P-selectin, transforming growth factor-beta 1, and the formation of thromboxane A2 in response to agonists were also investigated. Inhibitory effects of 100 micromol/l aspirin, 10 micromol/l cilostazol and 1 micromol/l ramatroban on 5 micromol/l ADP-induced PRP aggregation were similar. However, aspirin strongly inhibited thromboxane A2 formation in response to 5 micromol/l ADP compared with other drugs. Inhibitory effects of 10 micromol/l cilostazol on PRP aggregation and the release of molecules were quite similar in responsiveness induced by the three agonists. Aspirin and cilostazol inhibited platelet aggregation in a concentration-dependent, non-linear fashion, while ramatroban inhibited linearly with increasing concentration. Anti-platelet effects of drugs having different pharmacological mechanisms were demonstrated clearly by measuring PRP aggregation induced by the three agonists, and by measuring WB aggregation that most probably reflects not only platelet-platelet interactions, but also platelet-leukocyte interactions, as well as the release of intraplatelet molecules.

Characterization of platelet aggregation in whole blood of laboratory animals by a screen filtration pressure method

The characteristics of platelet aggregation of laboratory animals were investigated with whole blood and platelet-rich plasma (PRP). We measured the platelet aggregation threshold index (PATI) of whole blood and PRP aggregations induced by ADP or collagen, using a novel whole blood aggregometer, the WBA analyzer, with a screen filtration pressure (SFP) method. At 60 min after blood collection, PATI values of guinea pig, mouse, rat, dog and rabbit were 0.83, 1.78, 46.48, 49.85 and 53.42 microM for ADP-induced whole blood aggregation, respectively, whereas their PATI values for ADP-induced PRP aggregation were 1.16, 2.77, 2.65, 10.81 and 18.77 microM, respectively. These suggest that ADP-induced platelet aggregations of rat, dog and rabbit are suppressed in whole blood. PATI values of guinea pig, mouse, rat, dog and rabbit were 1.84, 0.62, 11.90, 2.34, 12.32 microg/ml for the collagen-induced whole blood aggregation, respectively, whereas their PATI values for the collagen-induced PRP aggregation were 4.21, 1.50, 5.36, 11.31, 13.30 microg/ml, respectively. Collagen-induced aggregation activity of the guinea pig, mouse and dog was significantly higher in whole blood than in the PRP. These results demonstrated that species differences in laboratory animals exist for whole blood aggregation, and that the SFP aggregometer may be useful to evaluate platelet function in various animal species.

Estimation of anti-platelet drugs on human platelet aggregation with a novel whole blood aggregometer by a screen filtration pressure method

1. The effects of anti-platelet drugs on human whole blood aggregation were evaluated using a novel whole blood aggregometer by a screen filtration pressure (SFP) method. 2. The SFP whole blood aggregometer was found to successfully detect whole blood aggregation induced by ADP, collagen and TRAP by measuring the SFP of blood samples. The platelet aggregation threshold index (PATI), the concentration of agonist required with an inducing pressure rate of 50%, varied time-dependently after collection of blood. High values for ADP and collagen were noted immediately after blood collection, suggesting low aggregation activity of platelets, and gradually increase thereafter. 3. Cilostazol (phosphodiesterase 3 inhibitor), dipyridamole, aspirin and tirofiban all inhibited whole blood aggregation in vitro. Inhibitory effects of cilostazol and dipyridamole, but not tirofiban, were markedly enhanced 6 or 7 fold by long pre-incubation (60 min), compared with short pre-incubation (2 min). Such enhancement was only observed with ADP- and not collagen-induced whole blood aggregation. A similar phenomenon was also observed for aggregation with platelet rich plasma (PRP). Cilostazol inhibition of ADP-induced platelet aggregation was more potent with PRP than whole blood (PATI(200)=3.80+/-0.95 microM for whole blood; 2.04+/-0.61 microM for PRP). Inhibitory effects of dipyridamole were attenuated in PRP without erythrocytes. 4. These results demonstrate that the SFP aggregometer can sensitively detect anti-platelet aggregatory effects of various kinds of drugs. So that it is a useful tool for evaluation of anti-platelet drugs.