Intestinal Phosphate Transporter Expression in CKD Patients

Elevated serum phosphate is a potent predictor of death and cardiovascular events in patients with renal disease. Control of serum-phosphate to desired target ranges is insufficient in many patients with advanced chronic kidney disease (CKD), in particular dialysis patients despite dietary restrictions, optimized dialysis regimens and the use of phosphate binders. One reason why for example, phosphate binders are insufficient to control phosphate uptake in the intestine or why they even loose efficacy, is a compensatory upregulation of phosphate transporters in the gut wall. Thus, several companies attempt to specifically interfere with intestinal phosphate transporters, in particular the NaPi-IIb transporter. However, recent Chugai data obtained in experimental CKD challenge the assumption that NaPi-IIb is the major therapeutic target in this situation. In addition to NaPi-IIb, PiT-1 and -2 also might contribute to phosphate transport. In normal human intestinal mucosa the most prominent expression of all 3 transporters is observed in the duodenum, i.e. an area, which can easily be assessed by endoscopy. During endoscopy a biopsy for research purposes will be obtained. Chugai will evaluate the expression level of NaPi-IIb, PiT-1, PiT-2, and villin1 at the mRNA and, if possible, the protein level.