Dr Michael Emerson from Imperial College London has received two NC3Rs project grants to develop a refined mouse model of pulmonary embolism which avoids the severe suffering associated with the use of death as an endpoint.
Principal Investigator: Michael Emerson, Senior Lecturer in Molecular Medicine
Organisation: Imperial College London
Awards: £149,180, in 2007, over 18 months; £204,442, in 2010, over 18 months
Title: Refinement of a mouse model of pulmonary embolism
Read more about Dr Emerson's research.
New medicines are required to treat pulmonary embolism
Blood clot formation in the large veins of the legs and pelvic region is common in hospitalised patients, the elderly and occasionally following a long haul flight. These so-called deep vein thrombi can become dislodged and enter the circulation, leading to pulmonary embolism. Pulmonary embolism is caused when the thrombi become trapped in the pulmonary vessels which carry blood between the lungs and the heart, leading to vascular obstruction, cardiac dysfunction and even death. In developed countries it is estimated to affect one in 1,000 people annually with a mortality rate of one in 25,000.
Clinically, only massive (that is, obstruction of a main pulmonary artery causing systemic hypotension and decreased cardiac output) or submassive (that is an obstruction which does not cause hypotension but produces changes on echocardiography) pulmonary embolism are treated. Treatment options are limited to thrombolysis which dissolves the clots. Although thrombolysis can be effective in treating massive pulmonary embolism there is controversy over its usefulness as a therapy for submassive pulmonary embolism because of the risk of bleeding. Greater understanding of the cellular and molecular mechanisms that lead to pulmonary embolism is central to the design of better treatment strategies and improved survival rates.
Mouse models of pulmonary embolism involve paralysis and death
Traditionally, the most commonly used mouse model of pulmonary embolism involves the intravenous administration of a lethal dose of clotting agents such as collagen or thrombin, which causes massive pulmonary embolism. The agent is injected into conscious mice and paralysis or death is observed in 90% of the mice within 15 minutes. This procedure is classified as substantial severity under the Animals (Scientific Procedures) Act 1986 because of the suffering caused to the animals.
The effects of drugs and genetic modifications are studied by measuring their ability to significantly change the proportion of mice that develop paralysis or die. The model has provided information on cellular pathways involved in thrombosis and the effects of various compounds as treatments for pulmonary embolism. Nevertheless, the ability to study massive pulmonary embolism only, which is usually fatal in humans, limits the usefulness of the model since it cannot be used to study earlier stages of the disease and particularly those which are more amenable to therapeutic intervention. Moreover, the model is also limited by the reliance on non-specific clinical signs such as paralysis and death, which can also be caused by other factors such as shock.
With NC3Rs funding, Dr Michael Emerson, Imperial College London, has refined and reduced the use of mice in pulmonary embolism research, providing an in vivo model which better mimics the physiology and biochemistry of the condition in man and models the earlier stages of the disease.
A new approach to studying pulmonary embolism using anaesthetised mice
In the first grant, Dr Emerson developed a model which allows thrombus formation to be tracked in vivo using radiolabelled platelets isolated from the blood of donor mice. The radiolabelled platelets are injected into a recipient mouse, under terminal anaesthesia, and a sublethal dose of the clotting agent is administered. Platelet accumulation can then be measured non-invasively using a spectrometer connected to a gamma scintillation probe. This is a major refinement which avoids paralysis and death and has allowed the procedure to be unclassified (rather than classified as substantial severity) under the Animals (Scientific Procedures) Act 1986. The model also has a number of other advantages in that it allows measurement of platelet aggregation and disaggregation directly in real-time and takes into account non-platelet factors such as endothelial status and blood flow.
Using human instead of mouse platelets
In the second grant, Dr Emerson has further evolved the new model by using radiolabelled human platelets. The human platelets are then injected into NOD-SCID mice which lack T and B lymphocytes and are therefore amenable for transplantation studies. The human platelets remain viable and can be tracked in the mouse. The humanised mouse model is currently being validated by studying the anti-thrombotic effect of aspirin administered to human volunteers.
The number of mice has been reduced from 200 to 15 per study
The traditional mouse model of pulmonary embolism typically uses 200 animals per study. The refined model allows a significant reduction in animal use. By optimising the procedures for repeat administration of clotting agents, one mouse can be used several times whilst under terminal anaesthesia. This has enabled the number of animals used to be reduced to 30 per study where mice are used as platelet donors and to 15 per study where human platelets are used.
New research funding has been awarded on the basis of the refined model
Based on the development of this refined model, Dr Emerson has also received grants from the Wellcome Trust and British Heart Foundation to support more basic mechanistic studies of pulmonary embolism.
The refined mouse model of pulmonary embolism has also been adopted elsewhere in the UK through collaborations Dr Emerson has established with groups at the Universities of Reading and Leicester, and the William Harvey Research Institute at Barts and The London School of Medicine and Dentistry.
This case study was published in a review of our research portfolio in September 2011.