2013 New Treatments, Target Identification
Molecular Basis and Novel Therapy of Systemic Lupus-Associated Thrombosis
The Study and What It Means to Patients
"Blood clots triggered by autoantibodies that stick to blood cells are a major complication of lupus. We are seeking to discover how lupus blood clots occur and testing whether a natural chemical found in certain foods, rutin, may be able to prevent clots in lupus mice. If so, we will start testing in humans as rutin is already approved as a food supplement by the FDA."
Why lupus autoantibodies stick to blood cells causing potentially fatal blood clots is not known. As a hematologist and new to lupus, I am working with my brother, a leading rheumatologist to combine my experience in clotting disorders with his expertise in lupus, to discover how blood clots occur in lupus patients and how to prevent them. First, we are using cutting-edge imaging techniques to visualize the formation of clots in the blood vessels of live mice to work out which blood cell type and which protein on the surface of blood cells is targeted by the clot-causing autoantibodies. Second, we recently found that a chemical (rutin) that occurs naturally in certain fruits and vegetables can prevent clots forming in mice with lupus autoantibodies. We are testing rutin in mouse models of lupus thrombosis. If it proves to be effective we anticipate moving quickly to clinical trials in patients, as the drug has already been deemed safe as a food supplement by the US Food and Drug Administration.
Intravital videomicroscopy and our thrombosis model will be used in mice to determine the target cell and receptor of beta2GP1 human autoantibodies important in lupus-associated thrombosis and the anti-phospholipid syndrome. These autoantibodies enhance thrombus size by over 100-fold (Arad, 2011), but the mechanism by which the anti-beta2GP1 autoantibody-beta2GP1 complex activates vascular cells is unknown. Using fluorescent anti-beta2GP1 autoantibodies and beta2GP1, we will identify the cells targeted by these antibodies during thrombus formation. Knockout mice lacking specific receptors will be used to identify the receptors required for thrombus enhancement by anti-beta2GP1 autoantibodies. We discovered the requirement for protein disulfide isomerase (PDI) during thrombus formation. Inhibition of PDI activity blocks thrombus development. Therefore, PDI represents a novel antithrombotic target in lupus. By high throughput screening, we identified a natural product (quercetin-3-rutinoside) that inhibits PDI activity and is approved by the FDA as safe. We will perform pre-clinical studies with this agent using our mouse model to evaluate whether this agent, used prophylactically, will prevent thrombosis induced by beta2GP1 autoantibodies. These are novel approaches to lupus-associated thrombosis, and have never been applied to explore the mechanism of thrombus formation in lupus. Furthermore, quercetin-3-rutinoside offers a new therapeutic approach to the prophylaxis of thrombosis in lupus.
Subsequent Publication 2014
Platelets are blood cells that are the first responders to an injury. When someone gets a cut, platelets arrive at the scene and help form a clot to stop the bleeding.
A person with lupus is at risk for APS, a potentially life-threatening complication where the body makes antibodies that interact with blood cells to trigger blood clots when there is no injury. These clots can cause strokes, heart attacks and other dangerous conditions. APS also has a significant impact on the health and safety of pregnant women because these antibodies can cause miscarriages and pre-eclampsia (high blood pressure during pregnancy).
Previous research identified autoantibodies that attach to a protein called beta2-glycoprotein-1 as a biomarker for predicting and monitoring APS. Beta2-glycoprotein-1 circulates through the bloodstream and when the autoantibodies come into contact with it they fuse together into a complex that mistakenly triggers clotting. Until this recent discovery the exact kind of cell the complex acts on to promote clotting was a mystery..
Accurately identifying the target of the beta2-glycoprotein-1 autoantibody complex was challenging. Researchers have thought that the autoantibodies could be activating any of the different types of cells integral to the clotting process.
With his 2013 LRI Novel Research Grant, Dr. Furie used cutting-edge imaging techniques in live mice to show that it is the beta2-glycoprotein-1 autoantibody complex that activates platelets to form clots. Dr. Furie’s study also showed that when platelets are not switched on, clotting stopped even in the presence of APS autoantibodies.
Treatment options for people with lupus and APS are limited. If we can understand the pathway by which APS antibodies cause harm, therapies can be developed to block these mechanisms. The ultimate goal is an oral medication that prevents these deadly blood clots.
Building on the new discovery described here, Dr. Furie’s next step is to narrow down what the autoandibody complexes are attaching to on the platelet. Once the receptor on platelets is located and characterized, researchers may be able to create targeted treatments that stop the autoantibody complexes from attaching to platelets to trigger clotting.