Dietary Phosphorus Differentially Alters Uremic Toxin Production in a Rat Model of Chronic Kidney Disease

Abstract

ObjectivesChronic kidney disease (CKD) is characterized by declining kidney function, limiting the kidney’s ability to efficiently remove metabolic waste products from circulation. Byproducts of gut microbial protein metabolism, termed uremic retention solutes (URS), accumulate in CKD patients and are associated with accelerating kidney decline. The gut microbes responsible for generating URS are dependent upon phosphorus (P) for growth and survival. As dietary P restriction is a cornerstone of CKD treatment, we hypothesized that changes in dietary P loads would alter URS production. MethodsTo evaluate this, 8-week-old male Sprague Dawley rats underwent 5/6th nephrectomy (Nx, n = 24) or sham operation (n = 20) and were maintained on a 0.6% P diet (w/w) for three weeks. Animals were then randomized to receive either low (0.1% (w/w)) or high (1.2% (w/w)) P diets for 4h/d for 7d. Blood was collected at the start and end of the 7d diet (baseline and sacrifice, respectively). Serum was analyzed for blood urea nitrogen (BUN) and URS, including trimethylamine oxide (TMAO), indoxyl sulfate (IS), and p-cresol sulfate (pCS), via LC-MS. ResultsNx rats had significantly elevated BUN compared to sham controls (38.9 ± 5.9 vs 23.1 ± 5.1 mg/dL, p < 0.0001). Additionally, the presence of significantly enlarged kidney tissue in Nx animals verified the progression of kidney decline. At sacrifice, all URS were elevated in Nx animals as compared to sham controls (p < 0.0001), though changes in dietary P loads only affected IS production (low vs. high, p = 0.0003). When comparing baseline to sacrifice, TMAO decreased, IS remained consistent, and pCS increased in all rats. ConclusionsOur results indicate that dietary P loads may differentially affect the production of some URS in a rat model of CKD. As dietary P restriction is one of the cornerstones of CKD treatment, we posit that this dietary strategy influences URS production, CKD progression, and, ultimately, health outcomes. Funding SourcesASBMR, NIH K01.