Why is this work important? Kidney disease is a pressing global health problem, affecting approximately 10% of the world’s population, or roughly 850 million people 1. As the disease progresses to its final stage, known as kidney failure or end stage renal disease (ESRD), the condition becomes irreversible and fatal without kidney replacement therapy. Among the life-saving treatment options are kidney transplants, peritoneal dialysis, and hemodialysis, with the latter being the most common modality in the U.S., where more than 60% of ESRD patients receive hemodialysis 2. During hemodialysis, the patient’s blood is passed through a filter by a pump to remove accumulated waste products. Typically, patients undergo hemodialysis in an outpatient setting several times a week.
What are the challenges? The process of hemodialysis triggers blood clotting that traps some blood in the hemodialyzer machine. Therefore, the blood-thinner “anticoagulant” heparin is commonly added to the blood that passes through the filter to reduce clotting in the device. However, using heparin to prevent blood clot accumulation in the dialyzer is not suitable for everyone. Exposure to heparin in some patients may cause severe complications. A small proportion of patients may experience a life-threatening allergic complication called heparin-induced thrombocytopenia. Heparin in the circulating blood may also put some patients at an elevated risk for bleeding. In the U.S., an estimated 10% of hemodialysis sessions are performed without the use of heparin 3.
While heparin-free hemodialysis is considered reasonably safe, it is associated with increased clotting in the dialyzer. This issue is compounded by the high incidence of anemia among ESRD patients, with about 85% requiring erythropoiesis-stimulating agents (ESA) 4. Unfortunately, many of these patients are hyporesponsive to ESA due to anemia of inflammation, rendering them especially vulnerable to additional blood loss during hemodialysis. Accordingly, patients unable to tolerate heparin have limited options to prevent dialyzer clotting and blood loss during hemodialysis.
How can this be addressed? In response to this challenge, we have been investigating the potential of using a recombinant enzyme, AB002, for hemodialyzer clot prevention in heparin-intolerant patients. The enzyme’s principal action is to bind a cofactor in blood vessels and produce a controlled, localized burst of activated protein C (APC), a natural antithrombotic and cytoprotective enzyme. In experimental disease models, increasing endogenous APC generation with AB002 has been shown to limit inflammation, reduce clot formation, and promote clot lysis without increased bleeding 5,6.
Several key features of AB002 make it suitable for use in hemodialyzers, including its rapid onset of action, compatibility with direct infusion into the extracorporeal hemodialysis circuit, non-renal metabolism, favorable safety profile, and short half-life.
How did we innovate? One of the principal challenges of our study was characterizing the degree of clotting in each patient’s hemodialysis circuit without heparin administration. To establish a baseline, we gathered and averaged data from four hemodialysis sessions conducted in the absence of heparin, which enabled us to compare each patient’s individual response when they received AB002 during hemodialysis. We then developed quantitative methods to reliably measure the degree of clotting in the patients’ hemodialysis circuits. Treatment-blinded hemodialysis providers were asked to score the circuit at the end of each session using an adapted scoring algorithm, focusing on areas prone to clot accumulation such as the exterior surface of the dialyzer filter and the venous drip chamber.
However, this method only assessed visible clots, so we devised a supplementary method to detect and quantify clots trapped within the interior fibers of the dialyzer. This secondary method relies upon measuring masses of potassium and iron ions released from red blood cells trapped inside the filter. Using both approaches, we found evidence that AB002 reduces clotting in the hemodialysis circuit and limits blood entrapment within the filter.
A visual scoring scale was used determine whether AB002 reduced clotting severity within the dialyzer circuit. This photograph of an intact dialyzer circuit shows the tubing, venous chamber and dialyzer filter that comprise the circuit. At the end of each hemodialysis session, the circuit was inspected by a trained medical aide and assigned a numerical score to categorize the degree of clotting within the venous chamber. After the circuit was scored, the filter was processed to quantify blood entrapment within the filter itself. Shown is a representative photograph of this circuit during a hemodialysis session.
What is the broader impact and future potential? Our study reveals that AB002, which acts via a fundamentally new pharmacologic mechanism, was well tolerated by the 24 patients who received the drug, and we further show that AB002 reduces dialyzer clotting during hemodialysis. The trial participants had complex medical backgrounds, including hypertension, diabetes and history of cardiovascular disease, underscoring the robust safety and exploratory efficacy of AB002.
The next steps involve establishing the safety and efficacy of AB002 in a larger, more diverse cohort of patients over multiple hemodialysis sessions. Moreover, AB002’s favorable safety and tolerability profile in this study suggest it could be useful in other clinical applications beyond hemodialysis, such as acute ischemic stroke or heart attack, where there is a need for safe alternatives to existing treatments.
What are our conclusions? Patients undergoing heparin-free hemodialysis face challenges due to the lack of FDA-approved safe and effective alternatives to heparin for preventing hemodialyzer clotting and blood loss. Our study suggests that using AB002 to prevent clots could be a viable solution. Further, the potential clinical applications of AB002 extend beyond hemodialysis, offering hope for safer antithrombotic and/or clot busting treatments in various clinical scenarios, where the risk of bleeding limits treatment options.
References
1 KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney Int 105, S117-S314 (2024).
2 System, U. S. R. D. (National Institutes of Health, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD, 2022).
3 Kato, C. et al. Anticoagulation strategies in extracorporeal circulatory devices in adult populations. Eur J Haematol 106, 19-31, doi:10.1111/ejh.13520 (2021).
4 Sibbel, S. P., Koro, C. E., Brunelli, S. M. & Cobitz, A. R. Characterization of chronic and acute ESA hyporesponse: a retrospective cohort study of hemodialysis patients. BMC Nephrol 16, 144, doi:10.1186/s12882-015-0138-x (2015).
5 Tucker, E. I. et al. The protein C activator AB002 rapidly interrupts thrombus development in baboons. Blood 135, 689-699, doi:10.1182/blood.2019002771 (2020).
6 Verbout, N. G. et al. Cytoprotective E-WE thrombin reduces disease severity in a murine model of relapsing-remitting multiple sclerosis. Am J Physiol Cell Physiol 326, C40-C49, doi:10.1152/ajpcell.00377.2023 (2024).