Urine Protein Predictors of Nephrolithiasis

DESCRIPTION (provided by applicant): The scientific and commercial objective of the proposed research is to improve the medical prevention of nephrolithiasis by developing a new clinical assay that can predict the recurrence of kidney stones in patients with this chronic and costly disease. Currently available technology, consisting of routine urine chemistry measurements, is a poor predictor of a patient's risk for developing recurrent stones. Those patients destined to recur would benefit from tests that could identify them in advance so that therapy or prevention could be implemented early. We have found three proteins that are known inhibitors of calcium oxalate crystal growth to be significantly altered in the urine of stone formers. Preliminary studies of family members of calcium stone formers have shown that measurements of these proteins combined with standard urine chemistry risk factors vastly improved the discrimination of stone formers from non stone formers compared to standard urine chemistries alone. Our hypothesis is that alterations in these proteins in the urine of kidney stone patients may serve as a marker of stone disease activity or vulnerability to recurrence. We propose to develop improved western blotting and ELISA methods to measure the most highly discriminating forms of these proteins. We will validate these assays by determining intraassay and interassay variability through multiple measurements of urine samples from a small set of stone forming and non stone forming men and women. We will also use these samples to evaluate the stability of the proteins under different storage conditions that approximate the way urine is currently collected and shipped to our laboratory. In Phase II, we will use these assays and conditions to prospectively test whether these protein measurements improve the identification of kidney stone patients compared to conventional urine chemistry stone risk factors in people within and outside of stone forming families, and in people with different types of stones.