Platelet-endothelial interactions in atherothrombotic disease: therapeutic implications

Endothelial dysfunction in Marfan syndrome mice is restored by resveratrol

Patients with Marfan syndrome (MFS) develop thoracic aortic aneurysms as the aorta presents excessive elastin breaks, fibrosis, and vascular smooth muscle cell (vSMC) death due to mutations in the FBN1 gene. Despite elaborate vSMC to aortic endothelial cell (EC) signaling, the contribution of ECs to the development of aortic pathology remains largely unresolved. The aim of this study is to investigate the EC properties in Fbn1^C1041G/+ MFS mice. Using en face immunofluorescence confocal microscopy, we showed that EC alignment with blood flow was reduced, EC roundness was increased, individual EC surface area was larger, and EC junctional linearity was decreased in aortae of Fbn1^C1041G/+ MFS mice. This modified EC phenotype was most prominent in the ascending aorta and occurred before aortic dilatation. To reverse EC morphology, we performed treatment with resveratrol. This restored EC blood flow alignment, junctional linearity, phospho-eNOS expression, and improved the structural integrity of the internal elastic lamina of Fbn1^C1041G/+ mice. In conclusion, these experiments identify the involvement of ECs and underlying internal elastic lamina in MFS aortic pathology, which could act as potential target for future MFS pharmacotherapies.

Cell Type-Specific Mechanisms in the Pathogenesis of Ischemic Stroke: The Role of Apoptosis Signal-Regulating Kinase 1

Stroke has become a more common disease worldwide. Despite great efforts to develop treatment, little is known about ischemic stroke. Cerebral ischemia activates multiple cascades of cell type-specific pathomechanisms. Ischemic brain injury consists of a complex series of cellular reactions in various cell types within the central nervous system (CNS) including platelets, endothelial cells, astrocytes, neutrophils, microglia/macrophages, and neurons. Diverse cellular changes after ischemic injury are likely to induce cell death and tissue damage in the brain. Since cells in the brain exhibit different functional roles at distinct time points after injury (acute/subacute/chronic phases), it is difficult to pinpoint genuine roles of cell types after brain injury. Many experimental studies have shown the association of apoptosis signal-regulating kinase 1 (ASK1) with cellular pathomechanisms after cerebral ischemia. Blockade of ASK1, by either pharmacological or genetic manipulation, leads to reduced ischemic brain injury and subsequent neuroprotective effects. In this review, we present the cell type-specific pathophysiology of the early phase of ischemic stroke, the role of ASK1 suggested by preclinical studies, and the potential use of ASK suppression, either by pharmacologic or genetic suppression, as a promising therapeutic option for ischemic stroke recovery.

Parsley extract inhibits in vitro and ex vivo platelet aggregation and prolongs bleeding time in rats

Many cardiovascular diseases are associated with an increase in blood platelet activity. In Morocco, parsley (Petroselinum crispum, Apiaceae) is one of the medicinal herbs used to treat cardiovascular diseases such as arterial hypertension. In this study, crude aqueous extract (CAE) of parsley was evaluated for its anti-platelet activity in experimental animals on platelet aggregation in vitro and ex vivo; and on bleeding time in vivo. The in vitro aggregation was monitored after pre-incubation of platelets with CAE. The bleeding time and ex vivo aggregation were performed after oral treatment. CAE inhibited dose dependently platelet aggregation in vitro induced by thrombin, ADP, collagen and epinephrine. The oral administration of CAE (3g/kg) inhibited significantly (p<0.001) platelet aggregation ex vivo and prolonged bleeding time (p<0.001) without changes in the platelet amount. The prolongation of bleeding time by CAE may be attributed to the observed inhibition of platelet aggregation. These effects could be related in part to the polyphenolic compounds present in the extract. These results support the hypothesis that the dietary intake of parsley may be benefit in the normalization of platelet hyperactivation, in the nutritional prevention of cardiovascular diseases and are potentially interesting in the development of new prevention strategies.

Clopidogrel

Clopidogrel (Plavix), Iscover) selectively and irreversibly inhibits adenosine diphosphate (ADP)-induced platelet aggregation. Long-term administration of clopidogrel was associated with a modest but statistically significant advantage over aspirin in reducing adverse cardiovascular outcomes in patients with established cardiovascular disease in the CAPRIE trial. In other large well designed multicentre trials, such as CURE, COMMIT and CLARITY-TIMI 28, the addition of clopidogrel to aspirin therapy improved outcomes in patients with acute coronary syndromes. However, some issues regarding the use of clopidogrel remain unresolved, such as the optimal loading dose in patients undergoing percutaneous coronary interventions (PCI) and the optimal treatment duration following drug-eluting intracoronary stent placement. Results of several large randomised trials, therefore, have established clopidogrel as an effective and well tolerated antiplatelet agent for the secondary prevention of ischaemic events in patients with various cardiovascular conditions, including those with ischaemic stroke or acute coronary syndromes. In addition, treatment guidelines from the US and Europe acknowledge the importance of clopidogrel in contemporary cardiovascular medicine.

Fixed combination isosorbide dinitrate–hydralazine for nitric-oxide-enhancing therapy in heart failure

The major advances in our understanding and management of heart failure (HF) in recent decades have not fully benefited all segments of our population. HF still represents a growing epidemic, especially for African-Americans, in whom the burden of HF is even greater. The recently reported beneficial effects of the fixed combination of isosorbide dinitrate and hydralazine (ISDN+HYD) in the African-American Heart Failure Trial (A-HeFT), has led to both the FDA approval of this agent and its endorsement by the latest HF guidelines. The properties of ISDN+HYD are well known as its components are mature agents, readily available in generic formulations that have been used for decades in other indications. However, fixed-dose ISDN+HYD represents the first drug to undergo targeted clinical development and to be approved for use in a specific ethnic group. As such, A-HeFT and the approval of ISDN+HYD represent landmark events that merit further scrutiny.

Recombinant factor VIIa reverses the inhibitory effect of aspirin or aspirin plus clopidogrel on in vitro thrombin generation

BACKGROUND

Antiplatelet drugs constitute the therapy of choice for acute coronary syndromes, but bleeding can be a side-effect requiring treatment. Restoration of normal platelet activity is also mandatory before urgent surgery. This study investigated: (a) whether a regimen of aspirin or clopidogrel plus aspirin significantly inhibited platelet thrombin generation (TG); and (b) the reversal of this inhibition by recombinant activated factor VII (rFVIIa).

METHODS AND RESULTS

TG was evaluated by the lag time, time to peak, peak of TG, and area under the curve after 35 min of assay (AUC(0 --> 35 min)). These measures were examined by the calibrated automated thrombography method in 22 healthy volunteers, 22 volunteers after a 100 mg day(-1) aspirin intake (200 mg first day) for 5-7 days, and 22 healthy volunteers after aspirin 100 mg day(-1) (200 mg first day) plus clopidogrel 75 mg day(-1) (300 mg first day) for 4-7 days. The TG parameters were measured under basal conditions and after platelet stimulation by sodium arachidonate (AA), adenosine 5'-diphosphate (ADP), collagen and rFVIIa in normal non-aspirinated as well as in vivo aspirinated platelet-rich plasma (PRP) or aspirin plus clopidogrel PRP. Lag time was shorter (P < 0.05), and peak of TG and AUC(0 --> 35 min) were significantly greater (P < 0.01 for both), in PRP activated with ADP, collagen, AA or FVIIa than in non-activated PRP from normal subjects. Both non-activated PRP and activated PRP prepared from platelets obtained from volunteers after aspirin intake showed significant prolongation of the time parameters but there was less effect on peak of TG and AUC(0 --> 35 min). For most parameters, aspirin plus clopidogrel administration showed to be more effective compared with the effect obtained by aspirin alone. When rFVIIa was added to ASA-PRP or ASA + Clop PRP, lag time (P < 0.001 for all) and time to peak (P < 0.001-0.017) were significantly shortened, indicating that rFVIIa reverses the inhibitory effect of these anti-aggregating agents.

CONCLUSION

Platelets activated by AA, ADP, collagen or FVIIa triggered TG. This effect was inhibited by aspirin plus clopidogrel, suggesting an additional benefit of this drug combination for preventing thrombosis. rFVIIa reverses the inhibitory effect of aspirin or aspirin plus clopidogrel, and could be useful for bleeding complications or when acute surgery is needed during treatment with these antiplatelet drugs.

Endothelial microparticles induce formation of platelet aggregates via a von Willebrand factor/ristocetin dependent pathway, rendering them resistant to dissociation

Endothelial microparticles (EMP) released from activated or apoptotic endothelial cells (EC) are emerging as useful markers for detection of EC dysfunction. Our recent observation that EMP carry von Willebrand factor (vWf) led us to investigate their interaction with platelets. EMP were incubated with normal washed platelets in the presence or absence of ristocetin, then platelet aggregates were measured by flow cytometry. In the absence of ristocetin, negligible EMP conjugated with platelets (< 5%) but in the presence of ristocetin (1 mg mL(-1)), EMP induced up to 95% of platelets to aggregate. EMP-platelet interaction was 80% blocked by anti-CD42b, or by 0.1 microm filtration to remove EMP. Platelet aggregates induced by normal plasma or high molecular weight vWf (Humate-P) dissociated 50% within 15-25 min following 1:20 dilution. In contrast, aggregates formed with EMP persisted two- to threefold longer with the same treatment, indicating greater stability. A similar degree of prolongation of dissociation was observed using plasma from thrombotic thrombocytopenic purpura (TTP) patients compared with normal plasma. Addition of EMP to plasma from severe von Willebrand disease restored his ristocetin-induced platelet aggregation. Multimer analysis of vWf on EMP showed unusually large vWf (ULvWf). In summary, EMP carries ULvWf multimers, promote platelet aggregates, and increase the stability of the aggregates thus formed.

Antithrombotic Properties of the Thromboxane A2/Prostaglandin H2 Receptor Antagonist S18886 on Prevention of Platelet-Dependent Cyclic Flow Reductions in Dogs

A potent thromboxane A2/PGH2 (TP)-receptor antagonist, S18886, was evaluated for its antithrombotic property in a dog model of acute periodic platelet-mediated thrombosis in stenosed coronary arteries with endothelial damage. After thrombosis had been obtained in 11 dogs, S18886 (300 microg/kg bolus) was administered IV. Heart rate, systemic blood pressure, and coronary blood flow were continuously recorded. Ex vivo whole blood platelet aggregation (PA), blood pH, hematocrit, platelet count, PO2, PCO2, and bleeding times were measured before and 30 minutes after administration of S18886. S18886 completely inhibited thrombosis in all dogs in approximately 5-10 minutes. No change in heart rate, blood pressure, pH, PO2, PCO2, platelet count, or bleeding time and a slight but significant elevation in hematocrit occurred. Infusion of epinephrine IV after complete inhibition of thrombosis by S18886 partially restored thrombosis in 3 of the 11 dogs. PA induced by collagen (4 microg/mL), collagen (0.25 microg/mL) plus epinephrine (1 microg/mL), collagen (1 microg/mL) plus epinephrine (1 microg/mL), ADP (40 microM) plus epinephrine (1 microg/mL), and phorbol 12-myristate 13-acetate (0.5 nM) were attenuated by 90 +/- 8% (P < 0.005), 98 +/- 2% (P < 0.05), 78 +/- 6% (P < 0.005), 70 +/- 10% (P < 0.005), and 28 +/- 8% (P < 0.05), respectively. In conclusion, S18886 is a potent platelet inhibitor that attenuates in vivo platelet-dependent thrombosis in the experimental dog model and reduces ex vivo platelet aggregation.

D-003 and warfarin interaction on the bleeding time and venous thrombosis experimentally induced in rats

D-003 is a mixture of higher aliphatic primary acids isolated and purified from sugarcane wax, the main component of which is octacosanoic acid. D-003 exhibits a cholesterol-lowering effect as well as antiplatelet and antithrombotic effects in experimental models. Warfarin is a coumarin derivative with anticoagulant activity that acts as a vitamin K antagonist. Since in clinical practice warfarin and D-003 could be administered together, the objective of this study was to evaluate the effects of the simultaneous administration of both drugs on the bleeding time and the venous thrombosis experimentally induced in rats. The combined therapy of minimally effective doses of D-003 and warfarin produced an antithrombotic effect significantly higher than those produced by each monotherapy. Likewise, the prolongation of bleeding time induced by warfarin was increased by the simultaneous administration with D-003, showing a synergistic effect between both drugs.

Brain (B-type) Natriuretic Peptide

Heart failure is the leading cause for hospitalization in the United States, resulting in over $8 billion in costs annually. Over 4.8 million Americans are afflicted with the disease and the number is increasing as the baby boomer generation continues to age. It is imperative that new and innovative modalities of therapy and diagnosis evolve as we continue to redefine the nature of heart failure and discover more about this debilitating disease. This article addresses the implications for endogenous brain (B-type) natriuretic peptide (BNP) testing in patients diagnosed with heart failure as well as the implications for the first available form of exogenous BNP, nesiritide. In addition, the pathophysiology of heart failure and traditional treatment modalities are discussed.

Demographics, Treatment Regimens and the Use of Angiotensin-Receptor Blockers in Heart Failure: Findings from the Valsartan Heart Failure Trial

Heart failure is the only major cardiovascular disease with an incidence and prevalence that continue to increase in the developed world. Early identification and correct treatment of the condition are of paramount importance. In recent years, there has been growing interest in identifying the differences between patients in terms of their risk of heart failure and response to treatment. Differences between men and women, different age groups, patients with varying aetiologies or co-morbidities and differences between ethnic groups are only some of the factors that have been identified. This review surveys the available data on differences in responses to treatment, and discusses the use of angiotensin-receptor blockers in heart failure in light of the recent Valsartan Heart Failure Trial (Val-HeFT).

Conclusion: Heart failure is a complex syndrome, a fact that is reflected in the wide spectrum of patient characteristics and breadth of treatments available to physicians. Recommendations will keep evolving as we learn more about the changing aetiology and manifestations of the disease, and as new data become available on old and emerging treatments. The recent addition of ARBs (or at least valsartan) to the list of drugs of benefit in HF is a welcome development. Perhaps the most important message from Val-HeFT is that valsartan significantly reduced the risk of a first morbid event, irrespective of most underlying physiological and demographic parameters. This implies that valsartan will be beneficial in most patients, whether they are old or young, male or female and whatever the aetiology of their HF. As polypharmacy will continue to be the therapy of choice in HF and as no wonder-drug seems to be on the horizon to make the concept obsolete, further blocking the RAS by adding a well-tolerated agent would seem a very welcome expansion of our current treatment options.

The HEDIS performance NAVIGATOR for controlling high blood pressure: a resource to assist health plans improve patient adherence

This article describes how the resources in the Health Plan Employer and Data Information Set (HEDIS; a registered trademark of the National Committee for Quality Assurance) Performance NAVIGATOR for Controlling High Blood Pressure (HEDIS NAVIGATOR) developed by Merck & Co., Inc. assist managed care organizations in understanding and encouraging the active involvement of their members in adhering to a treatment plan developed in partnership by physicians and patients. (HEDIS is a set of standardized performance measures that enable purchasers and consumers to make informed decisions regarding the quality of managed care organizations.) The discussion uses the Health Belief and Transtheoretical Models as a framework to better understand patient behavior change. Targeted strategies to facilitate adherence are also addressed. Examples of structured programs using nationally recommended guidelines and HEDIS NAVIGATOR resources are included to illustrate coordinated efforts to assist patients with high blood pressure adhere to their treatment plan and help managed care organizations improve patient outcomes and HEDIS scores.

Assessment of the effects of D-003, a new antiplatelet and lipid-lowering compound, in healthy volunteers. A phase I clinical study

OBJECTIVE

To investigate the effects of D-003 on the bleeding time (BT) and lipid profile of healthy human volunteers.

METHODS

This single-blind, randomised, placebo-controlled, parallel-group study was conducted in healthy volunteers. Step 1 investigated the effects of single doses of D-003 5, 25 or 50 mg on BT in comparison with placebo. Step 2 investigated the effects of 30 days of D-003 5, 25 or 50 mg/day compared with placebo on lipid profile with an interim assessment at 14 days. BT, lipid profile, physical and haematological safety indicators were measured and adverse events (AEs) recorded. Both steps were followed by a 14- or 30-day washout period.

RESULTS

Step 1: D-003 25 and 50 mg significantly increased mean BT 2 hours after administration compared with baseline, but a significant difference versus placebo occurred only with the 50 mg dose. Individual values from participants taking this dose, however, remained within normal limits. This effect was reversible. BT values obtained 2 hours after drug administration showed a moderate dose-dependent relationship. No drug-related changes in safety indicators were found with D-003. Step 2: After 7 days on D-003 50 mg/day, BT was significantly increased compared with baseline and placebo up to the end of the active treatment period. However, all individual values for participants taking this dosage remained within the normal range. This effect was reversible by the end of the washout period. After 30 days, D-003 (5, 25 and 50 mg/day) significantly reduced serum TC (by 13.3 to 17.4%) and LDL-C (by 11.6 to 22.6%) levels, and raised HDL-C levels (by 14.6 to 29.7%), but did not affect triglyceride levels. The significant increase in HDL-C was observed after 14 days on treatment. The effects on the lipid profile were reversible by the end of the 30-day washout period, although after 14 days of washout the effects on HDL-C and LDL-C still remained significant, revealing a certain persistence of effect. Eight participants (four receiving placebo and four receiving D-003 5, 25 or 50 mg/day) reported a total of nine AEs, none of which were drug-related. Of these patients, only two treated with D-003 25 and 50 mg/day discontinued treatment.

CONCLUSIONS

D-003 in single or repeated doses (50 mg) induced significant and reversible increases in BT. In addition, repeated doses (5, 25 and 50 mg/day) significantly and reversibly lowered serum LDL-C and TC levels and significantly raised serum HDL-C levels. These effects were reversible by 30 days after the end of treatment.

Synergistic effect of D-003 and aspirin on experimental thrombosis models

D-003 is a mixture of higher primary aliphatic saturated acids purified from sugarcane wax, with antiplatelet and antithrombotic effects experimentally demonstrated. Octacosanoic acid is the main component of D-003, followed by triacontanoic, dotriacontanoic, and tetracontanoic acids, while other acids are minor components. This work investigates the effects of combination therapy D-003+aspirin (ASA) on arachidonic acid (AA)-induced sudden death in mice and bleeding time in rats. In addition, the effects of D-003 on serum levels of two metabolites of AA: thromboxane A(2) and prostacyclin, assessed through the measurement of their stable metabolites: thromboxane B(2) (TxB(2)) and 6 keto PgF1alpha by radioimmunoassay kits, were also investigated. Combination therapy of D-003 (50mg/kg) and ASA (3mg/kg) significantly increased bleeding time in rats in a synergistic manner compared with D-003 or ASA alone. Moreover, the combined treatment of D-003 (200mg/kg) and ASA (5mg/kg) in mice protected against AA-induced sudden death (83% survivors) in a synergistic manner which was compared with each treatment alone (33% survivors). These results indicate that antiplatelet effects of D-003 are not mediated by a cyclooxygenase inhibition. D-003 and ASA monotherapies reduced serum TxB(2) levels, whereas D-003, but not ASA, significantly increased 6 keto PgF1alpha levels.

Antiplatelet effects of policosanol (20 and 40 mg/day) in healthy volunteers and dyslipidaemic patients

1. The present study was undertaken to compare the effects of a higher dose of policosanol, a cholesterol-lowering drug, (40 mg/day) with the effects of 20 mg/day policosanol on platelet aggregation in healthy volunteers and type II hypercholesterolaemic patients. 2. Study subjects were randomized to receive, under double-blind conditions, placebo or policosanol (20 or 40 mg/day) for 30 days once a day. Blood sampling was performed at baseline and after 30 days on therapy. 3. Platelet aggregation was induced with three aggregating agents: arachidonic acid (AA), collagen and low doses of ADP. 4. Policosanol (20 and 40 mg/day) moderately yet significantly reduced platelet aggregation, but no differences were observed in the effects produced by either dose of policosanol. In healthy volunteers, policosanol at 20 and 40 mg/day inhibited aggregation induced by 2 mmol/L AA (28.2 and 24.9%, respectively), 1 micro g/mL collagen (21.1 and 20.2%) and 1 micro mol/L ADP (30.9 and 29.1%). Changes that occurred following the administration of placebo were not significant, although an upward trend for collagen- and ADP-induced aggregation occurred in normal and hypercholesterolaemic subjects, respectively, thus partially masking the effects of policosanol on these responses. 5. The antiplatelet effects of policosanol at 20 and 40 mg/day in hypercholesterolaemic patients were also similar, so that both doses inhibited aggregation induced by 1.5 mmol/L AA (20.1 and 33.0%, respectively), 0.5 micro g/mL collagen (22.7 and 21.1%) and 1 micro mol/L ADP (40.5 and 34.7%). 6. In addition, after 30 days of therapy, 20 and 40 mg/day policosanol significantly (P < 0.01) reduced low-density lipoprotein-cholesterol (15.9 and 17.0%, respectively) and total cholesterol (12.4 and 12.3%, respectively; P < 0.05), yet increased high-density lipoprotein-cholesterol values by 5% in both groups (P < 0.05). 7. Triglycerides were decreased compared with baseline, but not with respect to the placebo. 8. We conclude that the antiplatelet effects induced by 40 mg/day policosanol administered for 30 days to healthy volunteers and to hypercholesterolaemic patients were similar to the effects induced by 20 mg/day policosanol. Thus, no enhancement of the response was achieved with the use of a higher dose of policosanol in study patients.

Effect of a potent cyclooxygenase inhibitor, 5-ethyl-4-methoxy-2-phenylquinoline (KTC-5), on human platelets

Because the metabolites of arachidonic acid participate in many physiopathological responses, including inflammation and platelet aggregation, cyclooxygenase inhibitors are important in the treatment of associated diseases. A biologically active compound, 5-ethyl-4-methoxy-2-phenylquinoline (KTC-5), selectively and concentration dependently inhibited aggregation of platelets from man and ATP release caused by arachidonic acid (200 microM) and collagen (10 microg mL(-1)) without affecting the aggregation caused by thrombin (0.1 U mL(-1)) and U46619 (2 microM). The IC50 value (drug concentration inhibiting maximum response by 50%) of KTC-5 for aggregation induced by arachidonic acid and collagen was 0.11+/-0.04 microM and 0.20+/-0.03 microM, respectively. This inhibitory effect of KTC-5 was reversible and time dependent. KTC-5 specifically inhibited intracellular calcium mobilization initiated by arachidonic acid or collagen without affecting that caused by thrombin or U46619 in human platelets. Furthermore, KTC-5 inhibited thromboxane B2 and prostaglandin D2 formation provoked by arachidonic acid. The IC50 value of KTC-5 for arachidonic-acid-induced thromboxane B2 formation was 0.07+/-0.02 microM. Based on these observations, the data indicated that KTC-5 potently inhibited human platelet aggregation and ATP release mainly via the inhibition of the cyclooxygenase-1 activity. Moreover, KTC-5 inhibited lipopolysaccharide-induced prostaglandin E2 formation in RAW264.7 cells in the presence of external arachidonic acid with an IC50 value of 0.17+/-0.06 microM. Immunoblot analysis showed that KTC-5 did not affect the cyclooxygenase-2 expression in the presence of lipopolysaccharide on RAW264.7 cells. This result indicated that KTC-5 affects the activity of cyclooxygenase-2. According to these data, we concluded that KTC-5 is a cyclooxygenase inhibitor for both subtypes.

D-003, a potential antithrombotic compound isolated from sugar cane wax with effects on arachidonic acid metabolites

D-003 is a natural mixture of higher primary saturated aliphatic acids purified from sugar cane wax, whose main component is octacosanoic acid followed by triacontanoic, dotriacontanoic, and tetratriacontanoic acids. D-003 inhibits platelet aggregation and arterial thrombosis experimentally induced in a dose-dependent fashion. This study was undertaken to investigate the effects of D-003 (25 and 200 mg/kg) in experimental models of venous thrombosis and on plasma levels of two metabolites from arachidonic acid (AA) : thromboxane A(2) (TxA(2)) and prostacyclin (PgI(2)). D-003 orally administered as single doses of 200 mg/kg, but not at 25 mg/kg, significantly increased plasma levels of 6 keto PgF1alpha levels, a stable metabolite of PgI(2) in PPP obtained from collagen-stimulated blood (4 microg/ml) compared with control group. Nevertheless, levels of 6 keto PgF1alpha levels determined after 10 days of oral treatment with both doses of D-003 were significantly larger than those of the controls. Likewise, single and repeated oral doses of D-003 (25 and 200 g/kg) significantly reduced the TxB(2) and MDA plasma levels obtained from whole blood stimulated by collagen. Hence, TxB(2)/6 keto PgF1alpha ratio significantly decreased in animals treated with D-003. Single and repeated oral doses of D-003 (25 and 200 mg/kg) significantly reduced the weight of venous thrombus experimentally induced in rats. D-003 at single doses (400 mg/kg but not 200 mg/kg) significantly protected from death induced by endovenous infusion of collagen plus epinephrine in mice. The present results support that these effects of D-003 on AA metabolites could explain, at least partially, its antiplatelet and antithrombotic effects.

Endogenous heparin activity deficiency: the 'missing link' in atherogenesis?

This paper reviews published studies since 1995 dealing with many atherogenic mechanisms where exogenous heparin was beneficial. In these areas endogenous heparin deficiency is likely to be harmful. Mechanisms included inflammatory factors, lower endogenous plasma heparin levels, lipoprotein lipase, chemokines, APOE e4, lipoprotein(a), among others. Demonstrated reduction of heparan sulfate proteoglycans (HSPG) and of endogenous plasma heparin was reviewed.

Indobufen: an updated review of its use in the management of atherothrombosis

Indobufen inhibits platelet aggregation by reversibly inhibiting the platelet cyclooxygenase enzyme thereby suppressing thromboxane synthesis. Clinical trials have evaluated the efficacy of oral indobufen in the secondary prevention of thromboembolic complications in patients with or without atrial fibrillation, in the prevention of graft occlusion after coronary artery bypass graft (CABG) surgery and in the treatment of intermittent claudication. In the secondary prevention of thromboembolic events indobufen 200 mg once or twice daily was significantly more effective than no treatment although not as effective as ticlopidine 250 mg once or twice daily, during 1-year nonblind clinical trials. Compared with placebo, indobufen 100 mg twice daily significantly reduced the risk of stroke in a small 28-month trial of patients at increased risk of systemic embolism (50% had atrial fibrillation). Furthermore, in patients with nonrheumatic atrial fibrillation and a recent cerebrovascular event enrolled in the 1-year Studio Italiano Fibrillazione Atriale (SIFA) trial, indobufen 100 or 200 mg twice daily was as effective as warfarin (titrated to produce an international normalised ratio of 2.0 to 3.5) in the secondary prevention of thromboembolic events; the incidences of the composite end-point of major vascular events (10.6 vs 9.0%) and recurrent stroke (5 vs 4%) were similar between treatments. In 2 large 12-month trials, the Studio Indobufene nel Bypass Aortocoronarico (SINBA) and the UK study, indobufen 200 mg twice daily was as effective as aspirin (acetylsalicylic acid) 300 or 325 mg plus dipyridamole 75 mg 3 times daily in the prevention of early and late occlusion of saphenous grafts in patients after CABG surgery. Indobufen 200 mg twice daily for 6 months significantly improved walking capacity compared with placebo, and caused a more pronounced improvement in both pain-free and total walking distance than either pentoxifylline 300 mg or aspirin 500 mg twice daily in separate 6- and 12-month studies of patients with intermittent claudication. Oral indobufen up to 200 mg twice daily was generally well tolerated in >5000 patients with atherosclerotic disease. Adverse events (predominantly gastrointestinal), reported by 3.9% of patients, rarely required withdrawal from treatment. In the SINBA and UK studies, fewer adverse events and less gastrointestinal bleeding were seen with indobufen than with aspirin plus dipyridamole treatment, while in the SIFA trial, noncerebral bleeding events occurred significantly less frequently in indobufen than warfarin recipients (0.6 vs 5.1%) and major bleeding events occurred only in the warfarin group.

CONCLUSION

Indobufen is as effective as warfarin in the prophylaxis of thromboembolic events in at risk patients with nonrheumatic atrial fibrillation, as aspirin plus dipyridamole in the prevention of CABG occlusion and may be more effective than aspirin or pentoxifylline in improving walking capacity in patients with intermittent claudication. The improved tolerability profile of indobufen (favourable gastric tolerance and reduced haemorrhagic complications) compared with aspirin 300 to 325 mg 3 times daily or warfarin, in addition to a similar antiplatelet effect, suggests indobufen can be considered a drug with a definite role in the management of atherothrombotic events. In particular, indobufen may be an effective alternative for at risk patients with nonrheumatic atrial fibrillation in whom anticoagulant therapy is contraindicated or who are at higher risk of bleeding.

Choice of drug treatment for obesity-related hypertension: where is the evidence?

Hypertension and obesity are common medical conditions independently associated with increased cardiovascular risk. Many large epidemiological studies have demonstrated associations between body mass index and blood pressure, and there is evidence to suggest that obesity is a causal factor in the development of hypertension in obese individuals. Consequently, all hypertension management guidelines consider weight reduction as a first step in the management of increased blood pressure in obese individuals. Weight reduction may be achieved by behaviour modification, diet and exercise, or by the use of anti-obesity medications. However, the long-term outcomes of weight management programmes for obesity are generally poor, and most hypertensive patients will require antihypertensive drug treatment. Some classes of antihypertensive agents may have potentially unwanted effects on some of the metabolic and haemodynamic abnormalities that link obesity and hypertension, yet most hypertension guidelines fail to provide specific advice on the pharmacological management of obese patients. This may be because there are currently no studies examining the efficacy of specific antihypertensive agents in reducing mortality in obese hypertensive patients. This paper reviews the theoretical reasons for the differential use of the major classes of antihypertensive agents in the pharmacological management of obesity-related hypertension and also considers the potential role of anti-obesity agents.

Platelets adhere to and translocate on von Willebrand factor presented by endothelium in stimulated veins

With the use of intravital microscopy, a new type of platelet–endothelial interaction in mouse mesenteric venules at low shear (80-100 seconds−1) is described. Stimulation of these vessels with calcium ionophore A23187, a known secretagogue of Weibel-Palade bodies, induced immediate platelet adhesion (within 15 seconds) and translocation without the formation of aggregates. This stop-and-go process reached a maximum in approximately 1 minute, when approximately 25 000 platelets adhered/mm2·s, and then adhesion progressively decreased. This adhesion process was dependent on von Willebrand factor (vWF) and independent of P-selectin. Immunohistologic analysis showed that the venules were not denuded withA23187 treatment, suggesting that platelets adhered to vWF secreted on the luminal face of the endothelial cells. Histamine treatment induced a similar adhesion phenomenon. Platelet adhesion was not abolished in β3-deficient mice or when the platelets were treated with inhibitory antibodies to PECAM-1 or PSGL-1, indicating that these molecules are not required for platelet–endothelium interaction at low shear. The adhesion was mediated by platelet glycoprotein Ibα (GPIbα) because the adhesion of murine platelets expressing exclusively the human GPIbα could be prevented by a pretreatment with mocarhagin, a snake venom protease that cleaves human GPIbα. The results indicate that vWF released from Weibel-Palade bodies can dramatically increase the concentration of platelets along the vessel wall through an interaction with GPIbα. It is proposed that this process may rapidly recruit platelets to sites of injury or inflammation in veins.

Platelets adhere to and translocate on von Willebrand factor presented by endothelium in stimulated veins

With the use of intravital microscopy, a new type of platelet–endothelial interaction in mouse mesenteric venules at low shear (80-100 seconds−1) is described. Stimulation of these vessels with calcium ionophore A23187, a known secretagogue of Weibel-Palade bodies, induced immediate platelet adhesion (within 15 seconds) and translocation without the formation of aggregates. This stop-and-go process reached a maximum in approximately 1 minute, when approximately 25 000 platelets adhered/mm2·s, and then adhesion progressively decreased. This adhesion process was dependent on von Willebrand factor (vWF) and independent of P-selectin. Immunohistologic analysis showed that the venules were not denuded withA23187 treatment, suggesting that platelets adhered to vWF secreted on the luminal face of the endothelial cells. Histamine treatment induced a similar adhesion phenomenon. Platelet adhesion was not abolished in β3-deficient mice or when the platelets were treated with inhibitory antibodies to PECAM-1 or PSGL-1, indicating that these molecules are not required for platelet–endothelium interaction at low shear. The adhesion was mediated by platelet glycoprotein Ibα (GPIbα) because the adhesion of murine platelets expressing exclusively the human GPIbα could be prevented by a pretreatment with mocarhagin, a snake venom protease that cleaves human GPIbα. The results indicate that vWF released from Weibel-Palade bodies can dramatically increase the concentration of platelets along the vessel wall through an interaction with GPIbα. It is proposed that this process may rapidly recruit platelets to sites of injury or inflammation in veins.

Vasoregulation by the beta1 subunit of the calcium-activated potassium channel

Small arteries exhibit tone, a partially contracted state that is an important determinant of blood pressure. In arterial smooth muscle cells, intracellular calcium paradoxically controls both contraction and relaxation. The mechanisms by which calcium can differentially regulate diverse physiological responses within a single cell remain unresolved. Calcium-dependent relaxation is mediated by local calcium release from the sarcoplasmic reticulum. These 'calcium sparks' activate calcium-dependent potassium (BK) channels comprised of alpha and beta1 subunits. Here we show that targeted deletion of the gene for the beta1 subunit leads to a decrease in the calcium sensitivity of BK channels, a reduction in functional coupling of calcium sparks to BK channel activation, and increases in arterial tone and blood pressure. The beta1 subunit of the BK channel, by tuning the channel's calcium sensitivity, is a key molecular component in translating calcium signals to the central physiological function of vasoregulation.

Clopidogrel: a review of its use in the prevention of atherothrombosis

Clopidogrel is an ADP receptor antagonist that is indicated for the reduction of atherosclerotic events including myocardial infarction, ischaemic stroke and vascular death in patients with atherosclerosis manifested by recent stroke, myocardial infarction or established peripheral vascular disease. In the 19 185 patients enrolled in the multicentre, randomised double-blind CAPRIE study, the annual risk of the combined end-point of ischaemic stroke, myocardial infarction and death from vascular disease (vascular death) was significantly lower during treatment with clopidogrel 75 mg/day than aspirin 325 mg/day [5.3 vs 5.8%/year, respectively; relative risk reduction (RRR) 8.7%, p = 0.043] after a mean follow-up of 1.9 years. Clopidogrel provided even greater reductions in the risk of recurrent ischaemic events than aspirin in patients with a history of coronary artery bypass surgery, diabetes mellitus and in those receiving concomitant lipid-lowering therapy. Moreover there was a significant reduction in the incidence of hospitalisation in patients treated with clopidogrel. In a patient population (Saskatchewan, Canada) with a greater risk of ischaemic events than the CAPRIE study population, the number of patients needed to be treated with clopidogrel to prevent 1 ischaemic event was estimated to be 70 (vs 200 in the CAPRIE study). In randomised trials and registry surveys, clopidogrel 75 mg/day plus aspirin had similar efficacy (as measured by adverse cardiac outcomes) to ticlopidine 250mg twice daily plus aspirin during the 30 days after placement of intracoronary stents. Tolerability of clopidogrel was significantly better than ticlopidine in the randomised, double-blind CLASSICS study. Among patients treated with clopidogrel or aspirin in the CAPRIE study, the overall gastrointestinal tolerability of clopidogrel was generally better than that of aspirin; the frequency of gastrointestinal haemorrhage was significantly lower among patients treated with clopidogrel than aspirin. Diarrhoea, rash and pruritus were significantly more common with clopidogrel than aspirin.

CONCLUSION

Clopidogrel was significantly more effective than aspirin in the prevention of vascular events (ischaemic stroke, myocardial infarction or vascular death) [corrected] in patients with atherothrombotic disease manifested by recent myocardial infarction, recent ischaemic stroke or symptomatic peripheral arterial occlusive disease [corrected] in the CAPRIE study. The overall tolerability profile of the drug was similar to that of aspirin, although gastrointestinal haemorrhage occurred significantly less often in clopidogrel recipients. The drug is widely used in combination with aspirin for the prevention of atherothrombosis after placement of intravascular stents, and available data suggest that this combination is as effective as ticlopidine plus aspirin for this indication.