Finding New Ways to Control Phosphorus

Dr. Christov’s NKF-funded research initiative to discover alternative ways to remove phosphorus from the body

Early in her career, Marta Christov, MD, watched a dialysis patient develop significant bone loss and blood vessel calcification in a short period of time.

Seeing the effects of kidney failure on the skeletal and vascular systems pushed her to become an expert in renal bone disease. She spends her days tackling the mysteries of how calcium and phosphorus are regulated normally and what drives their abnormal levels when patients' kidneys fail.

“Abnormal mineral metabolism and bone dysfunction contribute to significant cardiovascular disease in kidney patients,” Dr. Christov said. “By understanding phosphorus metabolism, we can better control phosphorus and the hormones that regulate it. There is a huge opportunity here to decrease suffering and save lives.”

Originally from Bulgaria, the 42-year-old Christov attended medical school at Dartmouth’s Geisel School of Medicine. She is now a researcher at Massachusetts General Hospital and a practicing nephrologist at Beth Israel Deaconess Medical Center in Boston. Her current research project, Use of PTH to Lower Phosphorus and FGF23 in CKD, is supported by a Young Investigator Grant from the National Kidney Foundation.

The research initiative is focused on discovering alternative ways to remove phosphorus from the body.

“Lowering phosphorus levels in patients with chronic kidney disease (CKD) may have beneficial effects on their hearts and blood vessels, but practically, it is very hard to do,” said Dr. Christov. “Patients can reduce the amount of phosphorus they eat, but that is difficult because a lot of foods contain hidden phosphorus. Patients can also take phosphorus binders, which try to prevent the dietary phosphorus from being absorbed from the gut. But the pills are big, and patients need to take a lot of pills with each meal, which can be hard.”

One of the hormones that increases phosphorus excretion by the kidneys is parathyroid hormone, or PTH. Dr. Christov is investigating whether the use of PTH in the early to moderate stages of CKD can enhance phosphorus excretion by the kidneys. PTH is already an approved drug used by some patients for osteoporosis treatment, so it would be available to patients quickly if Dr. Christov’s hypothesis is correct. Results are expected to be published by early 2015.

On the horizon, Dr. Christov sees advances in the therapies available to practitioners to lower serum phosphorus in patients, while she will continue to focus on understanding how kidneys communicate and interact with our skeletal systems.

“We know that virtually all patients with advanced and end-stage kidney disease have bone dysfunction, but it is not clear if there are direct ways via which the kidneys "signal" the bone, or if the effects are merely a consequence of an inability to excrete phosphorus, for example,” she said. “Ultimately, I'd like to be able to prevent the problems patients with CKD have such as phosphorus elevation, bone fractures, and vascular calcifications.”