Stem cells from fat tissue may help prevent kidney dialysis access failure

To undergo kidney dialysis, doctors must first surgically create an access route—an arteriovenous fistula—usually in an arm, a conduit that will accommodate hemodialysis treatments. It is a routine outpatient procedure performed for years worldwide.

But it is a procedure beset by problems.

An arteriovenous fistula must first “mature,” a process in which the newly established connection between an artery and a vein becomes large enough to support the turbulent flow of blood in hemodialysis. For many patients, this artificially created channel tends to narrow, leaving it useless as a conduit.

Doctors at the Mayo Clinic in Rochester, Minnesota are investigating a possible way to prevent problematic narrowing—a condition called stenosis—with a procedure that relies on the use of stem cells.

The study, researchers asserted, is a crucial step toward improving a necessary treatment for patients with kidney failure by tapping into a population of cells that are essentially blank slates. The investigation is reported in the journal Science Translational Medicine.

The phase 1 randomized trial involved patients undergoing an arteriovenous fistula (AVF) placement in an arm. Some of the patients in the small trial also received autologous adipose-derived mesenchymal stem cells. The cells were delivered at the time of the AVF procedure.

“The stem cells were placed along the AVF starting at the distal artery, one centimeter upstream to the anastomosis [the surgical connection between adjacent blood vessels] and extending to the first four centimeters of the vein just distal to the anastomosis by dripping them onto the adventitia of the vessels slowly over five minutes,” wrote Dr. Sreenivasulu Kilari, lead author of the research. The adventitia is the outermost layer of a blood vessel.

Mesenchymal stem cells are a form of somatic, or adult stem cells, which can be found in a variety of tissues throughout the body, including adipose (fat) tissue, which is an abundant source.

The stem cells are aimed at improving AVF function by preventing vascular narrowing. The cells were also a site-specific treatment for another problem tied to arteriovenous fistulas: inflammation, a hallmark of AVFs. Fortunately, anti-inflammatory activity is a function of mesenchymal stem cells.

Side-by-side images in the study show the vascular opening to be wide and capable of handling the turbulence of hemodialysis among patients who received mesenchymal stem cells. Patients who did not receive the stem cell treatment suffered vascular narrowing.

The Mayo Clinic team sees promise in their unique approach, which is producing positive results at a critical time. The population requiring kidney dialysis—and a need for the AVF procedure—is expected to rise dramatically in the not-too-distant future, data in the study showed.

“Chronic kidney disease affects more than 800 million people worldwide,” Kilari, a researcher in the Vascular and Interventional Radiology Translational Laboratory at the Mayo Clinic, wrote in the study.

Chronic kidney disease, he added, morphs into end-stage kidney disease, a condition in which the twin purplish-colored organs can no longer adequately filter wastes or remove excess fluid from the body.

“It is estimated that there are more than 4 million people worldwide with end-stage kidney disease, and most will receive hemodialysis for their mode of renal replacement therapy,” Kilari continued. The population of end-stage kidney disease patients is expected to double over the next decade.

Numerous studies have confirmed that poor AVF outcomes affect vast numbers of end-stage kidney disease patients. Most studies estimate that approximately 60% of AVFs fail to mature because of venous stenosis caused by excessive growth of the inner layer of the outflow vein needed in hemodialysis. Overgrowth of the vein’s inner layer is technically known as neointimal hyperplasia.

Kilari and colleagues theorize that infusing mesenchymal stem cells not only helps prevent the major problems associated with AVFs—narrowing and inflammation—but additionally assists with fistula maturation.

The team’s phase 1 clinical trial involved 21 patients who received arteriovenous fistulas in the arm; 11 of the 21 patients also received mesenchymal stem cells derived from their own fat tissue. After 42 months, fistulas had matured faster in patients who received stem cells. Additional study and approval by the U.S. Food and Drug Administration are required before the treatment can become available.

Also, among patients who received stem cells, researchers noticed wider vascular openings compared with patients who received the placebo treatment, which was simply the AVF procedure alone. The stem-cell treated patients also exhibited less activity of inflammatory genes and proteins linked to cell aging.

“The mechanism of action by which mesenchymal stem cells exert their beneficial effects was first investigated using AVFs created in mice and pigs treated with allogenic mesenchymal stem cells,” Kilari explained in the study.

The animal studies had similar outcomes to the human clinical trial, confirming that mesenchymal stem cells produce a beneficial effect when introduced at the time of the AVF surgical procedure, Kilari and the Mayo Clinic team concluded.

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