Mayo Clinic Researchers Discover a Hidden Kidney Pathway for Water Regulation, Opening New Avenues for PKD Treatment
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Mayo Clinic scientists led by Dr. Fouad Chebib have identified a previously unknown vasopressin-independent pathway through which the kidneys regulate water balance, published in the Journal of Clinical Investigation.
The discovery emerged unexpectedly when the decades-old drug probenecid slowed cyst growth in PKD cell models, contrary to researchers' predictions that it would worsen the disease.
In a small clinical trial, adding probenecid to tolvaptan reduced patients' urine volume by approximately 30% and cut nighttime urination from multiple episodes to about once per night.
Mayo Clinic researchers have uncovered a previously unrecognized biological pathway that allows the kidneys to conserve water independently of vasopressin, the hormone long considered the master regulator of urine concentration. The discovery, published in the Journal of Clinical Investigation, carries immediate implications for patients with polycystic kidney disease (search) (PKD) and could reshape the therapeutic landscape for a condition affecting millions worldwide.
The study was led by Fouad Chebib, M.D., a nephrologist at Mayo Clinic whose interest in kidney disease was sparked after his own father was diagnosed with PKD.
"The kidney's ability to regulate water is one of the most fundamental processes in the body," Dr. Chebib said. "It's not every day that you uncover a new way it carries out that function."
A Serendipitous Finding in the Lab
The discovery originated from experiments that were designed to go in a different direction entirely. Dr. Chebib's team uses laboratory-grown cell models to study how kidney cysts develop and grow in PKD. During one set of experiments, researchers tested compounds they expected would worsen the disease by increasing cellular activity linked to cyst growth.
One of those compounds was probenecid, a medication first introduced in the 1940s to help conserve scarce supplies of penicillin by reducing how much of the antibiotic was excreted in urine.
"We thought this drug would make the disease process worse," Dr. Chebib said. "Instead, it did the opposite."
Rather than accelerating cyst growth, probenecid slowed it down. After repeating the experiments several times and obtaining the same result, the researchers realized they had uncovered something unexpected.
Urate as a Signaling Molecule
The team then investigated why probenecid was producing this effect. Their research revealed that the drug alters how kidney cells handle urate, a molecule most commonly associated with gout.
Inside kidney cells, urate acts as a signaling molecule. It sets off a series of cellular events that move water channels to the cell surface, allowing the kidneys to reabsorb water and concentrate urine. Critically, this process can occur without relying on vasopressin, which has traditionally been viewed as the primary regulator of urine concentration.
"This represents a distinct pathway from what is described in traditional physiology models," Dr. Chebib said. "It demonstrates that the kidney has an additional mechanism to preserve water."
Addressing a Major Treatment Limitation in PKD
The finding could help address one of the most significant drawbacks of current PKD treatment. Polycystic kidney disease (search) is a genetic disorder that causes fluid-filled cysts to develop in the kidneys, gradually impairing function and often leading to kidney failure. In the United States, approximately 140,000 people have the most common form, autosomal dominant PKD (search) (ADPKD). Many patients ultimately require dialysis or a kidney transplant.
The only approved medication for slowing PKD progression is tolvaptan. The drug works by blocking vasopressin, which helps reduce cyst growth. However, it also causes patients to produce very large amounts of urine—often 6 to 7 liters per day. For many people, that side effect can be difficult to manage and may lead them to discontinue treatment.
In preclinical studies and a small clinical trial, researchers found that adding probenecid reduced both urine volume and nighttime urination while maintaining the effectiveness of treatment. On average, patients experienced about a 30% reduction in urine volume after taking probenecid. Many went from waking up multiple times each night to urinate to waking only about once per night. Participants also reported improvements in their quality of life.
"The goal is to preserve the therapeutic benefit of tolvaptan while reducing its burden," Dr. Chebib said.
Beyond Probenecid: Toward Targeted Therapies
Despite the encouraging results, the researchers do not view probenecid itself as a long-term answer. The medication is several decades old, affects multiple biological systems, and is not widely available today. Instead, the team hopes to use what they learned from the drug to create new therapies that specifically target the newly identified pathway.
"Probenecid helped us uncover the mechanism," Dr. Chebib said. "Our goal is to take this insight and develop therapies designed specifically for this pathway."
For Dr. Chebib, the research carries deep personal significance. "This has been a long and deeply purposeful journey," he said. "It started with a personal motivation and led to something that could ultimately benefit patients."