Clinical Trial Details
— Status: Active, not recruiting
Administrative data
| NCT number |
NCT05607602 |
| Other study ID # |
301611 |
| Secondary ID |
|
| Status |
Active, not recruiting |
| Phase |
|
| First received |
|
| Last updated |
|
| Start date |
October 17, 2022 |
| Est. completion date |
December 31, 2024 |
Study information
| Verified date |
June 2024 |
| Source |
King's College Hospital NHS Trust |
| Contact |
n/a |
| Is FDA regulated |
No |
| Health authority |
|
| Study type |
Observational [Patient Registry]
|
Clinical Trial Summary
This study will investigate whether the presence of uterine fibroids is independently
associated with a laboratory defined pro-thrombotic phenotype. VTE is associated with
significant mortality and morbidity. In addition, treating patients with UF and thrombosis
represents a particular challenge as fibroids frequently cause menorrhagia, which is
exacerbated by anticoagulation. It is therefore important to recognise and detect risk
factors and prevent thrombosis wherever possible. If a pro-thrombotic phenotype is detected
in patients with UF as their sole risk factor, then this could justify a new approach to the
assessment and risk-management of a very large number of patients and could translate into a
reduction in both morbidity and mortality for affected patients.
Description:
Uterine Fibroids (UF) are benign uterine tumours, also known as leiomyomas. They are
estimated to affect up to 80% of women of reproductive age. UF more commonly occur in women
of Afro-Caribbean ethnicity. UF may be asymptomatic or associated with a range of symptoms
including menorrhagia, dysmenorrhea, sub-fertility, and pressure symptoms.
An association between Venous Thromboembolic disease and UF has been inferred in case
reports, series, and one population-based study. The true prevalence and the full scale of
the problem is unknown. As UF are so prevalent, in many women, the apparent association
reflects the presence of known risk factors for Venous Thromboembolism (VTE) such as
thrombophilia, smoking and significant co-morbidities such as cancer. Thrombosis and UF have
also been shown to have common risk factors, such as obesity and age. Hormonal therapies,
which are often used to treat the symptoms of UF, can also increase the risk of VTE.
However, in a subset of women with VTE and UF, no thrombophilia or acquired risk factors for
VTE can be identified. In most of the reported case studies, bulky tumours cause extrinsic
compression of pelvic vessels, venous stasis and thus thrombosis. A clinical case review
reported by our centre has identified women with thrombosis and UF that do not cause local
venous stasis and no additional risk factors for thrombosis. This suggests that there may be
additional pathogenic mechanisms underlying the development of thrombosis in individuals with
UF. A second centre has also published a case review, similarly identifying an apparent
association between UF and thrombosis in the absence of venous stasis.
Clot structure and function is dictated by the conditions present during fibrin generation.
Endogenous thrombin production, cellular components and fibrinogen structure are all
implicated in altering clot structure and function. There are several plausible mechanisms
via which UF may affect thrombin generation, clot formation and structure to generate a
pro-thrombotic state. The fibroid tumours may secrete Transforming Growth Factor ß3 (TGF- ß3)
and this appears to influence production of thrombomodulin, antithrombin III and plasminogen
activator inhibitor 1, all of which can modify the blood's haemostatic capacity and may
result in a pro-thrombotic phenotype.
Alternatively, fibroids may mediate an indirect pro-thrombotic effect by inducing iron
deficiency anaemia. Iron deficiency anaemia has been associated in numerous case studies and
series with thrombotic events, most commonly cerebral venous thrombosis, but also Pulmonary
Embolism (PE) and Deep Vein Thrombosis (DVT). Iron deficiency anaemia may also cause a
reactive elevation in erythropoietin thrombocytosis, thrombopoietin and FVIII resulting in
enhanced thrombin generation. In the proposed study we will exclude participants with
moderate and severe anaemia to identify whether any pro-thrombotic phenotype identified is
caused by a mechanism other than anaemia.
A pro-thrombotic phenotype can be identified by several laboratory studies that each assess
the quality and function of clots formed. In this study we will perform global haemostatic
assays such as activated partial thromboplastic time (APTT), and prothrombin time (PT).
However, these tests provide information about the haemostatic process until the point of
initial fibrin formation and ignore the procedure of thrombin generation. In this study we
will perform Thrombin Generation studies, Plasma clot Lysis, and RNA sequencing in addition
to standard laboratory tests (APTT, PT, FVIII:C, fibrinogen (using Clauss methods), platelet
count, liver and renal function tests.
2 METHODOLOGY Plasma clot lysis and thrombin generation studies will be carried out in
platelet poor plasma (PPP). Therefore, the part played by platelets and fibrinogen, it will
allow us to freeze and store the samples so that the tests can be done in batch once all the
samples have been collected. This allows for testing to be done homogenously under the same
conditions.
2.1 Plasma Clot lysis There is evidence that formation of compact clots, with increased
resistance to lysis, predisposes to thrombosis. A pro-thrombotic clot phenotype is
characterized by small pore size, low clot permeability, and increased resistance to
fibrinolysis. The plasma-based clot formation assay allows for a detailed assessment of
fibrin formation and breakdown capacity. The principle is that citrated, platelet-poor plasma
(PPP) is mixed with an activator of coagulation (recombinant tissue factor or thrombin), as
well as phospholipids and calcium to induce fibrin formation. Simultaneously, tPa or another
plasminogen activator is added to induce clot lysis. The assay employs a turbidimetric
principle, as the fibrin network is first formed and then lysed in the well, turbidity
increases and subsequently decreases. Absorbance is registered continuously over a specified
time period (e.g., 1.5 h), resulting in the formation of the clot-lysis curve (Figure 1),
from which the following parameters can be derived: time to initial fibrin formation (lag
phase), maximum absorbance (peak fibrin concentration in well), integral or area under the
clot lysis curve (AUC - net fibrin formation), and time from peak to 50% lysis of the clot
(50% lysis time).
Pro-thrombotic laboratory phenotypes detected by these assays have been associated with
unprovoked VTE, chronic thromboembolic pulmonary hypertension and post thrombotic syndrome.
It has been associated with recurrent PE and may be predictive of recurrent DVT.
2.2 Thrombin Generation Thrombin generation is an established tool for assessing the overall
function of the blood clotting system. The whole clotting system is engaged in the generation
and subsequent inactivation of thrombin and the sum of these actions results in either a
haemostatic or a pro-thrombotic event. The method selected for assessing thrombin generation
is Calibrated Automated Thrombography (CAT) which involves using a fluorescent substrate
containing calcium to trigger thrombin generation, whilst the software continuously monitors
and records thrombin concentration in time. Using the specialized software and calibrator,
the fluorescent signal can be visualized as a thrombogram. From this, parameters can be
calculated such as lag time, time to peak thrombin level, peak thrombin level, and endogenous
thrombin potential (ETP).
2.3 RNA sequencing There is evidence in vitro and in vivo that extracellular RNA, released
upon vascular injury, promotes thrombosis by augmenting proteases involved in the contact
phase of coagulation. This theory was further demonstrated by Kannemeier et al. (2007) who
proved that the administration of RNAase delayed thrombus formation and blood vessel
occlusion. Extracellular RNA can be directly quantified by a method known as RNA Sequencing.
A more robust, reproducible, and easy-to-use technique has been developed by NanoString
Technologies, Inc. called "nCounter". Compared to routine RNA Sequencing, nCounter can
quantify smaller amounts of starting RNA (1ng vs. 100ng of total RNA). Samples will be
analysed in a NanoString Laboratory as nCounter is a proprietary platform.
