Effects of dietary phosphorus concentration and phosphate salt form on renal tubule function in unilateral nephrectomized rats

Abstract

Background: Excessive consumption of phosphorus (P) impairs renal tubule function; however, the effects of different dietary phosphate salts on chronic kidney disease (CKD) are unclear. Aim: To examine the effects of potassium dihydrogen phosphate (KH₂PO₄) and potassium tripolyphosphate (K₅P₃O₁₀) and P concentration on renal function in a rat model of early CKD. Methods: Male sham-operated Sprague-Dawley rats were fed a diet containing KH₂PO₄ with a normal P level. Kidney injury was induced by unilateral nephrectomy (UNx), and the rats were divided into four groups fed dietary KH₂PO₄ or K₅P₃O₁₀ with a normal (UNx-NKH, UNx-NKP) or high (UNx-HKH, UNx-HKP) P concentration, respectively, for 21 days. Results: UNx-NKH rats showed significantly lower creatinine clearance (CCr) and higher albumin (ALB) compared with those of sham rats, confirming UNx-induced kidney injury. The urinary levels of liver-type fatty acid-binding protein (L-FABP) and ALB were significantly higher in UNx-HKP rats than in UNx-HKH rats. However, other markers of renal tubule function, such as CCr, serum creatinine (CRE), calcium (Ca), and hormones, only differed among groups according to the P concentration and not the dietary phosphate salt form. Histological examination showed higher incidence and severity of tubulointerstitial lesions, tubule regeneration, tubule dilation, and calcification in the high-phosphorus than in the normal-phosphorus UNx groups. These changes were more severe in the UNx-HKP group compared with the UNx-HKH group. Conclusion: This study highlights the importance of controlling dietary P intake in terms of both concentration and source to prevent the progression of CKD.