In-vitro evidence of enhanced breast cancer resistance protein-mediated intestinal urate secretion by uremic toxins in Caco-2 cells.

Abstract

It has been reported that intestinal urate excretion is increased at chronic kidney disease (CKD) state. In this report, whether uremic toxins are involved in the upregulation of intestinal breast cancer resistance protein (BCRP), an intestinal urate exporter, was examined. Uremic toxins that were increased at least 15-fold at CKD state were selected for investigation. Caco-2 cells were exposed to these uremic toxins at clinically relevant concentrations. mRNA was quantified by real-time PCR, and flow cytometry was utilized to measure BCRP protein and function in Caco-2 cells. Transcellular secretory transport of [(14) C]urate was determined utilizing Transwell studies after uremic toxin exposure. Indoxyl sulfate (IS) treatment alone resulted in ∼ 3-fold increase in BCRP mRNA in Caco-2 cells. Membrane protein expression of BCRP in Caco-2 cells also was increased by 1.8-fold after treatment with IS. Intracellular accumulation of pheophorbide A, a selective BCRP substrate, was decreased by 22% after IS treatment for 3 days. Consistent with these findings, transcellular secretory transport of urate across Caco-2 cell monolayers was increased by 22%. Intestinal urate secretion may be increased at CKD state partially by upregulation of intestinal BCRP by uremic toxins such as IS.