Kiat Tsong Tan

Platelet microparticles and soluble P selectin in peripheral artery disease: relationship to extent of disease and platelet activation markers.

Background. There is increased platelet activation in many cardiovascular diseases. This observation may explain the presence of increased levels of platelet microparticles (PMP) in these diseases. However, whether or not levels of PMPs inter‐relate with other markers of platelet activation, such as soluble P‐selectin, or with disease severity, is unknown. We therefore hypothesized raised PMP levels in stable peripheral artery disease (PAD) intermittent claudication (IC), with an additional increase in severe PAD critical limb ischaemia (CLI). Furthermore, we tested the hypothesis that PMP levels are correlated with other markers of platelet activation, such as soluble P‐selectin, membrane bound P‐selectin (CD62P) and CD63. Methods. Patients with PAD were recruited from the vascular outpatient and inpatient facilities at a teaching hospital. Age‐ and sex‐matched controls were also recruited from healthy volunteers. Venous blood was obtained from 23 patients with severe disease (CLI), 36 with moderate disease (IC), and from 30 healthy controls. The percentage of platelets positive for CD62P and CD63, as well as the numbers of PMPs were defined by flow cytometry. Plasma soluble P selectin was measured by enzyme‐linked immunosorbent assay (ELISA). Results. PMPs were increased relative to healthy controls in patients with IC, with a further increase in CLI (P<0.001). Soluble P selectin and CD62+ve platelets were raised in both patient groups, but there was no difference amongst the two patient groups. CD63+ve cells were raised only in CLI compared to healthy controls. In multivariate analysis, only PMP and soluble P selectin independently predicted disease severity, and the two markers correlated modestly (r = 0.345, P<0.001). Conclusion. Increased PMP and soluble P selectin are both related to the severity of symptomatic PAD. However, it is uncertain if this relationship is a cause or effect of atherosclerosis. This finding may have clinical implications as PMPs have the potential to influence the progression of atheroma as well as promote thrombosis.

Clinically apparent atherosclerotic disease in diabetes is associated with an increase in platelet microparticle levels.

Background  The commonest cause of mortality in patients with Type 2 diabetes is atherothrombosis, which can be related to abnormalities in the coagulation and fibrinolytic pathways, as well as in platelet function. Platelet microparticles (PMPs) may contribute to the prothrombotic state and may promote the progression of atherosclerosis. We hypothesized that PMPs are elevated in Type 2 diabetes and that patients with Type 2 diabetes and clinically apparent atherosclerosis would have the highest levels. Similarly, we hypothesized that soluble plasma P‐selectin (sPsel) and CD40L (both molecules which are released by activated platelets), as well as %CD62P (P‐selectin) and %CD63 positivity on platelets quantified by flow cytometry, would be highest in patients with Type 2 diabetes and clinically apparent atherosclerotic disease, and might be correlated to PMP levels.

Elevated platelet microparticles in stable coronary artery disease are unrelated to disease severity or to indices of inflammation.

Platelet microparticles (PMPs), procoagulant membrane vesicles derived from activated platelets, are elevated in acute myocardial infarction and unstable angina but their relationship to inflammation and indices of coronary artery disease are unclear. We therefore hypothesised that PMPs are related to scores of coronary atheroma and/or coronary stenosis. Our study was completed by comparing PMP data with other platelet markers and with hs-CRP, marking inflammation. We recruited 54 patients attending for coronary angiography, comparing them to 35 age- and sex-matched controls. Peripheral blood was analysed for PMPs, percent platelets positive for CD62P and CD63 (all flow cytometry), soluble P selectin and hsCRP (both immunoassay). Patients exhibited higher PMPs, increased platelet %CD62P, %CD63 and soluble P selectin (all P < 0.01) and hs-CRP (P = 0.0167) than healthy controls. However, analysing only patients with an unequivocal classification, there were no significant (P ≤ 0.01) correlations with coronary atheroma or coronary stenosis. These findings provide no support for the hypothesis that PMPs are related to the degree of coronary artery disease and therefore may simply be a marker of widespread inappropriate platelet activity.

Soluble CD40L in peripheral artery disease Relationship with disease severity, platelet markers and the effects of angioplasty

Although soluble CD40L (sCD40L, possibly derived from platelets and pro-inflammatory in vitro) may be implicated in thrombosis and haemostasis, there are little data in peripheral artery disease (PAD). We hypothesised the following: (a) that sCD40L relates to the clinical severity of PAD; and (b) that peripheral artery angioplasty acutely raises sCD40L levels. sCD40L was compared to established platelet markers soluble P selectin, platelet microparticles and platelet surface expression of CD62 and CD63. We recruited 36 healthy controls, 33 patients with intermittent claudication (IC), and 33 with symptomatically more severe critical limb ischaemia (CLI), measuring plasma markers by ELISA and membrane markers by flow cytometry. Eleven patients with CLI subsequently underwent peripheral artery angioplasty: blood was taken before and 10 minutes after the intervention. Results show that sCD40L was raised in IC at median 68 (IQR 28-333) pg/ml and in CLI at 64 (34-282) pg/mL compared to 35 (IQR 28-55) pg/ml in the healthy controls (p=0.009). Levels were no different between IC and CLI. The same distribution pattern was present for soluble P selectin, %platelets CD62+ve and CD63+ve. sCD40L failed to correlate significantly with ABPI (p=0.264), unlike %platelets CD62+ve (p=0.0032) and CD63+ve (p=0.009). Pre-angioplasty sCD40L level of 72 (35-610) ng/ml rose to 100 ng/ml (IQR=60-237)(p=0.018) post-angioplasty. Plasma sCD40L, in addition to other platelet indices, is raised in peripheral atherosclerosis and is increased by peripheral artery angioplasty, although levels seem unrelated to clinical severity. Failure to correlate with other markers suggest the platelet may not be the sole source of sCD40L, and that other cells may contribute to plasma levels.

Factor X inhibitors

Factor X plays a central role in coagulation, being the point of convergence of the extrinsic and intrinsic pathways of blood clotting. It may also act as one of the links between the coagulation and inflammatory pathways. These findings suggest that factor X may represent an attractive target for a new antithrombotic drug. Indeed, a factor X inhibitor, fondaparinux, has already been approved for clinical use to prevent post-operative deep vein thrombosis. Factor X inhibitors are also being evaluated for use in the treatment of the acute coronary syndromes, pulmonary embolism and deep vein thrombosis. Oral factor X inhibitors are also being developed, which may be of use in the outpatient prevention and/or treatment of stroke and thromboembolism.

Platelets, atherosclerosis and the endothelium: new therapeutic targets?

One of the major causes of morbidity and mortality in the developed world is atherosclerosis. Recent research has suggested that the interaction of platelets with the endothelium is important in both the progression of atherosclerosis and the development of the acute complications of the disease. Both of these cells secrete various signalling molecules and express adhesion molecules, which can influence the development of pathological states. Certainly, there may be a vicious cycle in which platelet activation promotes atherosclerosis; a process involving inflammation and the activation of many other cell types (for example, leukocytes and smooth muscle cells), which causes further platelet activation. Therefore, intense effort has been made to develop therapeutic agents that can modulate the function of these cells, with the ultimate aim to retard (or even reverse) the progression of atheroma growth.

To stroke or not to stroke: Is ICAM-1 or CRP the answer?

Surgical treatment of asymptomatic severe (>70%) carotid stenosis is controversial. Although recent data suggest that there may be a benefit of carotid endarterectomy (CEA) in asymptomatic patients with severe stenosis, this reduction in risk is dependent on a low rate of surgical complications. In addition, the number of patients needed to treat to prevent a stroke has been estimated to be 83, a figure that could hardly be used confidently to recommend major surgery to a person who otherwise seems well.1 As the main benefit of CEA is to prevent disabling symptomatic events (i.e., stroke), the discovery of a marker that could reliably predict future onset of symptoms could direct surgery towards those most likely to benefit while avoiding unnecessary iatrogenic morbidity. Indeed, this statement not only is true for CEA but could be generalized to include the whole spectrum of atherosclerotic disease. The realization that atherosclerosis is an inflammatory disease, at least in its later …

Giant right coronary artery aneurysm on 64-MDCT.

An 81-year-old woman was referred for cardiac computed tomography-angiography (CCTA) after an extracardiac mass was found on echocardiography. CCTA found a giant atherosclerotic right coronary artery aneurysm with a maximal diameter of 80 mm, which was compressing the right atrium and right appendage, proximal superior vena cava, right ventricle inlet and tricuspid annulus.