Clinical Trial Details
— Status: Recruiting
Administrative data
| NCT number |
NCT00407368 |
| Other study ID # |
75/06 |
| Secondary ID |
|
| Status |
Recruiting |
| Phase |
N/A
|
| First received |
December 4, 2006 |
| Last updated |
December 4, 2006 |
| Start date |
September 2006 |
| Est. completion date |
December 2007 |
Study information
| Verified date |
November 2006 |
| Source |
Assaf-Harofeh Medical Center |
| Contact |
Shai Efrati, MD |
| Phone |
+972-577-346364 |
| Email |
efratishai[@]013.net |
| Is FDA regulated |
No |
| Health authority |
Israel: Israeli Health Ministry Pharmaceutical Administration |
| Study type |
Observational
|
Clinical Trial Summary
The purpose of this study is to perform a prospective evaluation regarding the relationship
between platelets function and cardiovascular events in patients with ESRD.
The study will include 100-200 patients with ESRD, age 18 years or older, treated in the
nephrology division of Assaf Harofeh medical center.
The primary end points of the study are cardiovascular events including acute myocardial
infarction (defined as symptoms + acute elevation of TnI), need for coronary artery disease
revascularization, or acute cerebrovascular event (TIA or CVA) and mortality. The secondary
end points are any hospitalization due to acute coronary syndrome, active bleeding with the
need for blood transfusion and dialysis access graft thrombosis (time to thrombosis).
Blood will be taken for complete blood count including platelets count and mean platelets
volume, serum electrolytes, albumin, blood lipids, Kt/V, troponin and two 5 ml aliquots from
each blood collection will be separated and stored at -70co until analyzed for oxidative
stress, homocysteine and highly sensitive CRP will be performed. Five mL of blood will be
sent for platelets function assessment.
During the follow up period the correlation between platelets function an cardiovascular
events will be assessed.
Description:
Background Platelets play an important role in cardiovascular disease both in the
pathogenesis of atherosclerosis and in the development of acute thrombotic events. Their
importance in coronary disease and in acute coronary syndromes is indirectly confirmed by
the benefit of antiplatelet agents (particularly aspirin, clopidogrel, ticlopidine, and the
glycoprotein IIb/IIIa inhibitors) in these disorders. Cardiovascular disease is the single
best predictor of mortality in patients with end-stage renal disease, as it accounts for
almost 50 percent of deaths. Patients with end stage renal disease (ESRD) have an increased
tendency to bleeding due to platelet dysfunction that can be partly corrected by either
hemodialysis or peritoneal dialysis in approximately two-thirds of cases. Currently there is
only scant data concerning the relations between platelet function and cardiovascular risk
in patients with ESRD.
Platelets, platelet products, and thrombosis play important and proximate causal roles in
the occurrence of acute occlusive vascular events such as MI and ischemic stroke. The
disruption of platelet and fibrin rich atherosclerotic plaques may lead to enhanced platelet
deposition, and ultimately the formation of a thrombus that can precipitate an acute
clinical event. The following observations are compatible with the importance of platelet
thrombus formation in acute ischemic syndromes:
- Thrombus formation within a coronary vessel is the acute precipitating event in most
unstable ischemic coronary syndromes, as documented by angiographic and pathologic
studies . Among patients with sudden death due to coronary thrombosis, the thrombi
typically have a layered appearance indicative of episodic growth. Episodic growth may
alternate with intermittent fragmentation of the thrombus, leading to distal
embolization of both thrombus and platelet aggregates and microinfarction.
- Increased platelet-derived thromboxane A2 and other prostaglandin metabolites have been
found in patients with acute myocardial infarction and unstable angina, providing
biochemical support for platelet activation as the cause of these events.
- Patients with unstable angina have elevated levels of P-selectin, an integral membrane
protein involved in platelet adhesion. Pulsatile shear stress, as occurs in stenotic
arteries, can cause platelet aggregation via an increased expression of P-selectin.
Hydrodynamic shear stress, resulting from plaque rupture, can activate platelets and
cause both platelet aggregation (via glycoprotein IIb/IIIa and von Willebrand factor)
and platelet-mediated neutrophil aggregation via upregulation of P-selectin. Although
levels of P-selectin decrease during the first month after treatment, levels remain
higher than normal even with therapy with glycoprotein IIb/IIIa inhibitors, suggesting
continued platelet activation.
- Aggregating platelets from patients with acute coronary syndromes produce less nitric
oxide than those from patients with stable or no angina. Why this might occur is not
known, but impaired nitric oxide production can enhance platelet aggregation and
thrombus formation.
Another platelet-related factor believed to contribute to cardiovascular thrombosis is the
presence of larger, more reactive platelets in patients with acute ischemic events (19-21).
The increase in platelet size, which is in compensation for a persistent decrease in
platelet count, results from the ongoing consumption of platelets in unstable angina; this
is not seen in an acute myocardial infarction. In addition, platelets from patients with
unstable angina, as determined by studying platelet aggregability ex vivo, are
hyperaggregable. These effects promote thrombus growth, limitation of blood flow, and acute
ischemia.
Except for the important of platelets in occlusive vascular events several studies suggests
that they may also have a role in the evolutionary phase of the atherosclerotic plaque.
After adhesion to exposed subendothelium following endothelial injury they release
vasoactive substances that induce smooth muscle cell migration and proliferation. Platelets
may serve as a lipid source in the development of the fatty streak and can promote foam cell
formation even in the absence of hyperlipidemia. However, currently there is no clear
clinical evidence that platelets contribute to coronary atherosclerosis. In addition,
prophylactic therapy with aspirin has not been clearly shown to decrease the atherosclerotic
burden.
ESRD is associated with prolongation of the bleeding time due primarily impaired platelet
function. It is likely that multiple factors are responsible for the platelet dysfunction in
uremia. Three of the factors that may contribute are the retention of uremic toxins, anemia,
and nitric oxide.
- Uremic toxins – The importance of circulating toxins is suggested by the often
beneficial effect of acute dialysis on platelet dysfunction, although the bleeding time
is rarely normalized. In addition, raising the BUN to 60 to 120 mg/dL by dietary
manipulation can diminish platelet adhesiveness and prolong the bleeding time in some
normal subjects. Urea alone, however, is probably not the major platelet toxin and
there is no predictable correlation between the BUN and the bleeding time in patients
with renal failure. Other potential toxins include guanidinosuccinic acid, phenolic
acid, and middle molecules (mol wt 500 to 3000 daltons). In vitro studies in which
normal platelets are incubated with uremic serum suggest that a dialyzable factor
interferes with the binding of fibrinogen to the platelet glycoprotein (GP) IIb/IIIa
receptor. In addition, uremic platelets are unable to adequately increase the
expression of GP IIb/IIIa and P-selectin in response to stimulation.
- Anemia – Previously, anemia was a common finding in chronic renal failure. The degree
of anemia appears to correlate relatively closely with the degree of prolongation of
the bleeding time. Furthermore, correction of anemia with blood transfusions or
erythropoietin often improves platelet function. It has been proposed that the
rheologic factors play an important role in the relationship between anemia and
platelet dysfunction. At a hematocrit above 30 percent, the red cells primarily occupy
the center of the vessel, while the platelets are in a skimming layer at the
endothelial surface. This close proximity allows the platelets to adhere and then form
a platelet plug when there is endothelial injury. With anemia, on the other hand, the
platelets are more dispersed, thereby impairing adherence to the endothelium.
- Nitric oxide – Nitric oxide (NO; endothelium-derived relaxing factor) is an inhibitor
of platelet aggregation that is produced by endothelial cells and platelets. Studies in
uremic patients have shown that platelet NO synthesis is increased and that uremic
plasma stimulates NO production by cultured endothelial cells. The increase in NO
synthesis may be due to elevated levels of guanidinosuccinic acid, a uremic toxin that
may be a precursor for nitric oxide in this setting.
Although patients with ESRD are at increase risk for cardiovascular disease there are only
scant data concerning the cardioprotective effect of antiplatelets drugs for primary or
secondary prevention in this population. In a retrospective evaluation of patients with ESRD
after acute myocardial infarction, Berger et al. have found that aspirin is underused in
this population (67.0%) and Similar results were found by McCullough et al., . Balanced
against the potential, but unproven benefit of aspirin in patients with ESRD are its
potential risks, including bleeding and a possible acceleration of access thrombosis. The
evidence for accelerate dialysis access graft thrombosis is based on the work of Himmelfarb
and colleagues. In their trial aspirin appeared to increase the relative risk (RR=1.99) of
graft thrombosis. They subsequently demonstrated that, in vitro, aspirin enhanced
platelet-derived growth factor-induced vascular smooth muscle proliferation. Adding
clopidogrel to aspirin in hemodialysis patients was associated with a significantly
increased risk of bleeding and probably would not result in a reduced frequency of graft
thrombosis. Although data concerning aspirin for primary or secondary prevention of
cardiovascular disease in ESRD patients is not sufficient its efficacy is well proven in the
general population. Currently, it seems not ethical to perform a randomized placebo
controlled trial to evaluate the antiplatelet protective effect in these patients. The
purpose of this study is to perform a prospective evaluation regarding the relationship
between platelets function and cardiovascular events in patients with ESRD.
Methods The study will include 100-200 patients with ESRD, age 18 years or older, treated in
the nephrology division of Assaf Harofeh medical center. Patients will be excluded if their
platelets count will be lower then 50,000 cu/mm, if they have known hematologic
malignancies, other solid malignancy with life expectancy of less then 1 year or if they are
treated with Warfarin (Comadin). Patients will sign a written informed consent before their
inclusion in the study.
The primary end points of the study are cardiovascular events including acute myocardial
infarction (defined as symptoms + acute elevation of TnI), need for coronary artery disease
revascularization, or acute cerebrovascular event (TIA or CVA) and mortality. The secondary
end points are any hospitalization due to acute coronary syndrome, active bleeding with the
need for blood transfusion and dialysis access graft thrombosis (time to thrombosis).
At the beginning of the study, blood will be taken for complete blood count including
platelets count and mean platelets volume, serum electrolytes, albumin, blood lipids, Kt/V,
troponin and two 5 ml aliquots from each blood collection will be separated and stored at
-70co until analyzed for oxidative stress, homocysteine and highly sensitive CRP will be
performed. Five mL of blood will be sent for platelets function assessment (described
below).
The follow up period will be up to 2 years. During the follow up period, treatment with
aspirin or clopidogrel will be given as needed and platelet function will be assessed after
any change in the antiplatelets therapy. Patients who are being treated with aspirin, will
continue to take the medication with no dose change unless they will have acute
cardiovascular event or active bleeding. Patients will be treated with antihypertensive
therapy, erythropoietin, calcium, vitamin D and other medications as needed.
Platelet Function Tests Cone-and-Platelet Analyzer This technology has been described
elsewhere (40). Briefly, 200 µL of citrated blood was placed in a polystyrene well and
subjected to a shear rate of 1300 sec-1 using a rotating conical disk for 2 minutes. The
well was washed and stained by May-Gruenwald stain. Platelet adhesion was evaluated as the
percentage of total area covered with platelets designated as surface coverage (%) and
aggregation as the mean size of the surface-bound aggregates designated as average size
(µ`m2) by use of an image analysis system (Galai).
Aspirin Response Assay 3.6µl Arachidonic Acid and 0.2ml blood will be added into a micro
tube (2ml), (final Arachidonic Acid concentration 0.275 mM). The tube will be rotated on the
tube mixer at 10rpm for 1 minute. 130µl will be placed in a well and tested with the cone
and platelet analyzer.
Clopidogrel Response Assay 5µl ADP and 0.2ml blood will be added into a micro tube (2ml)
(final ADP concentration 1.25µM). The tube will be rotated on the tube mixer at 10rpm for 1
minute. 130µl will be placed in a well and tested with the cone and platelet analyzer.
