Regulation of Intestinal Phosphate Transport in Humans and in a Rat Model of Chronic Kidney Disease

Abstract

In chronic kidney disease (CKD) hyperphosphatemia is a common occurrence and plays important roles in cardiovascular and bone disease. The mechanisms however still remain unknown and the role of intestinal phosphate (Pi) transport is subject of ongoing debate. We have determined that Na/Pi cotransport activity and NaPi‐2b protein is expressed in the duodenum, jejunum, and ileum of human intestinal samples. We further studied regulation of intestinal phosphate transport in a model of 5/6 nephrectomy (Nx) induced CKD in the rat fed a relatively high Pi diet (1.5% Pi, 0.6% Ca). Male rats with 5/6 Nx had a marked increase in serum BUN (37.7 ± 2.0 vs. 150.5 ± 29.8 mg/dl in sham control, p<0.02), serum creatinine (0.5 ± 0.06 vs. 1.65 ± 0.23 mg/dl in sham control, p<0.008), and serum Pi (7.48 ± 0.85 vs. 18.19 ± 1.84 mg/dl in sham control, p<0.001). We isolated apical brush border membrane vesicles (BBMV) from the duodenum and the jejunum and studied sodium gradient dependent Pi (Na+/Pi) cotransport as a function of pH. Across every single pH studied, including 5.5, 6.0, 6.5, 7.0, and 7.5 Na+/Pi transport activity was increased in BBM from 5/6 Nx rats. This was associated with a 2‐fold increase in NaPi‐2b protein abundance in the duodenum and a1.4‐fold increase in NaPi‐2b protein abundance in the jejunum. To determine if there are sex‐dependent differences in CKD and intestinal Na+/Pi transport, we also studied in parallel female rats with 5/6 Nx. We found that female rats with 5/6 Nx also had a marked increase in serum Pi (4.75 ± 0.39 vs. 10.7 ± 1.24 mg/dl in sham control, p<0.003). In addition, there were marked increases in intestinal Na+/Pi transport activity paralleled by increases in NaPi‐2b protein abundance.Our study therefore indicates that in both male and female rats with CKD, increased intestinal Na+/Pi transport activity and increased NaPi‐2b protein expression mediate the hyperphosphatemiaThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.