The Effects of Sevelamer Hydrochloride and Calcium Carbonate on Kidney Calcification in Uremic Rats

Abstract

Abstract. The control of serum phosphorus (P) and calciumphosphate (Ca ϫ P) product is critical to the prevention of ectopic calcification in chronic renal failure (CRF). Whereas calcium (Ca) salts, the most commonly used phosphate binders, markedly increase serum Ca and positive Ca balance, the new calcium-and aluminum-free phosphate binder, sevelamer hydrochloride (RenaGel), reduces serum P without altering serum Ca in hemodialysis patients. Using an experimental model of CRF, these studies compare sevelamer and calcium carbonate (CaCO 3 ) in the control of serum P, secondary hyperparathyroidism (SH), and ectopic calcifications. 5/6 nephrectomized rats underwent one of the following treatments for 3 mo: uremic ϩ high-P diet (U-HP); UHP ϩ 3% CaCO 3 (U-HPϩC); UHP ϩ 3% sevelamer (U-HPϩS). Sevelamer treatment controlled serum P independent of increases in serum Ca, thus reducing serum Ca ϫ P product and further deterioration of renal function, as indicated by the highest creatinine clearances. Sevelamer was as effective as CaCO 3 in the control of high-P-induced SH, as shown by similar serum PTH levels, parathyroid (PT) gland weight, and markers of PT hyperplasia.Also, both P binders elicited similar efficacy in reducing the myocardial and hepatic calcifications induced by uremia. However, sevelamer caused a dramatic reduction of renal Ca deposition (29.8 Ϯ 8.6 g/g wet tissue) compared with both U-HP (175.5 Ϯ 45.7 g/g wet tissue, P Ͻ 0.01) and the U-HPϩC (58.9 Ϯ 13.7 g/g wet tissue, P Ͻ 0.04). Histochemical analyses using Von Kossa and Alizarin red S staining of kidney sections confirmed these findings. The high number of foci of calcification in the kidney of uremic controls (108 Ϯ 25) was reduced to 33.0 Ϯ 11.3 by CaCO 3 and decreased even further with sevelamer (16.4 Ϯ 8.9, P Ͻ 0.02 versus CaCO 3 ). Importantly, the degree of tubulointerstitial fibrosis was also markedly lower in U-HPϩS (5%) compared with either U-HPϩC (30%) or U-HP (50%). It is concluded that in experimental CRF in rats, despite a similar control of serum P and SH, sevelamer is more effective than CaCO 3 in preventing renal Ca deposition and tubulointerstitial fibrosis, including better preservation of renal function. These findings cannot be extrapolated to human disease, and further studies in patients are necessary to determine the benefits of either P binder.In end-stage renal disease, hyperphosphatemia and elevated calcium-phosphate (Ca ϫ P) product associate with ectopic calcifications and increased risk of calciphylaxis, resulting in higher prevalence of morbidity and mortality from cardiovascular events (1-6). High serum phosphorus (P) levels worsen uremia-induced secondary hyperparathyroidism by enhancing parathyroid hyperplasia and parathyroid hormone (PTH) synthesis and secretion (7-8). Elevated PTH levels cause ectopic calcification not only by enhancing serum P and Ca ϫ P product through inducing high bone turnover, but also by increasing both serum and intracellular calcium (Ca) (9 -10). The control of serum P in patients with ch...

Risk of Kidney Injury Following Oral Phosphosoda Bowel Preparations

“…Moreover, data in rat models of CKD (remnant kidney and nephrotoxic serum nephritis) demonstrate that higher levels of dietary phosphate accelerate loss of kidney function 10,11 and that this effect is attenuated by administration of phosphate binders. 12,13 Despite this plausible link, our data do not support an association between receipt of OPS and kidney injury.…”

Vascular Calcification Mechanisms

“…Significantly, although both treatments controlled P levels equivalently, treatment with Ca containing binders led to an increased frequency of hypercalcemic episodes and greater suppression of serum parathyroid hormone (PTH) levels in hemodialysis patients (54,55). Similar effects of sevelamer were also noted in a rat uremia model, where renal calcification was greatly reduced compared to Ca carbonate treatment (56). Thus, decreasing Ca and P burdens appear to be beneficial in blocking vascular calcification.…”

Klotho Deficiency Causes Vascular Calcification in Chronic Kidney Disease

“…Kidney, heart, and aorta were stained with Von Kossa and counterstained with nuclear Fast Red for evaluation of calcium precipitation. 90 Positive signal for calcium precipitation would be seen in black or brown-black.…”