Calcium-based Binders Research Articles

Hypoxia regulates PDGF-B interactions between glomerular capillary endothelial and mesangial cells

Platelet-derived growth factor (PDGF)-B regulates mesangial cell and vessel development during embryogenesis, and contributes to the pathogenesis of adult renal and vascular diseases. Endothelial cell PDGF-B exerts paracrine effects on mesangial cells, but its regulation is not well defined. We examined the impact of hypoxia on PDGF-B-mediated interactions between glomerular endothelial and mesangial cells, a condition of potential relevance in developing, and diseased adult, kidneys. Glomerular endothelial or mesangial cells were subjected to hypoxia and responses compared to normoxic cells. Endothelial PDGF-B was studied by Northern and Western analysis. Mesangial proliferative responses to PDGF-B were assessed by (3)H-thymidine incorporation, and migration by a modified Boyden chamber assay. Hypoxia-induced changes in receptor specific binding capacity were studied by saturation binding assays. Hypoxia stimulated increases in endothelial PDGF-B mRNA and protein. In normoxic mesangial cells, PDGF-B stimulated dose-dependent proliferation, but the proliferative response of hypoxic cells was two to three times greater. Exogenous PDGF-B also caused prompter migration in hypoxic mesangial cells. Mesangial cells were treated with endothelial cell-conditioned medium. More cells migrated when hypoxic cells were stimulated with hypoxic conditioned medium, than when normoxic cells were stimulated with normoxic conditioned medium. Preincubating conditioned medium with PDGF-B neutralizing antibody greatly decreased the chemoattractant activity. Binding studies demonstrated increased specific binding capacity in hypoxic cells. Hypoxia enhances PDGF-B paracrine interactions between glomerular endothelial and mesangial cells. These hypoxia-regulated interactions may be important during glomerulogenesis in fetal life and during the pathogenesis of adult glomerular disease.

Phosphate binder therapy for attainment of K/DOQI™ bone metabolism guidelines

Phosphate binder therapy for attainment of K/DOQI™ bone metabolism guidelines

An introduction to phosphate binders for the treatment of hyperphosphatemia in patients with chronic kidney disease

An introduction to phosphate binders for the treatment of hyperphosphatemia in patients with chronic kidney disease. Chronic kidney disease has the potential to induce sequelae that can have severe and mortal outcomes. In particular, impaired glomerular filtration can cause a hyperphosphatemic state, which, if left unchecked, can lead to secondary hyperparathyroidism, vascular calcification, and renal osteodystrophy. Therapeutic management of hyperphosphatemia must maintain both phosphorus and calcium serum concentrations within the recommended guidelines. The balance of both minerals is regulated by parathyroid hormone; thus, an imbalance of one affects the other. In end-stage renal disease, patients often present with hypocalcemic levels due to the kidneys' inability to generate active vitamin D to promote calcium absorption in the intestine. Absorption of calcium can be increased by the administration of active vitamin D analogues. Minimizing phosphorus intake through a strict dietary regimen, combined with the use of phosphate binders to absorb excess ingested phosphate, can help to maintain serum phosphate levels near the recommended concentration of 5.5 mg/dL. Phosphate-binding compounds have evolved from the original aluminum-based binders pioneered in the 1970s to calcium-based binders such as calcium acetate, and more recently, to the following additions to the nephrologist's armamentarium: sevelamer—a polyhydrochloride polymer, and lanthanum carbonate. One of the top 2 common clinical treatments for hyperphosphatemia, calcium acetate, has an established history of efficacy since the 1980s, and has been shown to be cost effective and well tolerated, as well.

Treatment of hyperphosphatemia in patients with chronic kidney disease on maintenance hemodialysis

Treatment of hyperphosphatemia in patients with chronic kidney disease on maintenance hemodialysis. Hyperphosphatemia in patients with ESRD leads to secondary hyperparathyroidism, renal osteodystrophy, and is independently associated with mortality risk. The exact mechanism by which hyperphosphatemia increases mortality risk is unknown, but it may relate to enhanced cardiovascular calcification. National Kidney Foundation K/DOQI bone metabolism and disease guidelines recommend maintenance of serum phosphorus (P) below 5.5 mg/dL, and Ca x P product less than 55 mg(2)/dL(2). Although calcium-based phosphate binders (CBPB) are cost effective, long-term safety concerns relate to their postulated role in progression of cardiovascular calcification. Sevelamer hydrochloride has been recommended as an alternative noncalcium phosphate binder. Results from the Calcium Acetate Renagel Evaluation (CARE study) indicate that calcium acetate is more effective than sevelamer in controlling serum phosphorous and Ca x P product in hemodialysis patients. In the Treat-to-Goal study, dialysis patients treated with sevelamer had slower progression of coronary and aortic calcification than patients treated with CBPB. The mechanism underlying the beneficial effect of sevelamer is unknown, but may relate to decreased calcium loading or to dramatic reductions in LDL cholesterol in sevelamer-treated patients. At present, evidence incriminating CBPB in the progression of cardiovascular calcification in ESRD remains largely circumstantial. As calcium acetate is more efficacious and cost effective than sevelamer, it remains an accepted first-line phosphate binder. In this review, we will examine these issues and provide rational guidelines for the use of calcium-based phosphate binders in patients on maintenance hemodialysis.

Vascular Calcifications in Chronic Kidney Disease: Are There New Treatments?

Cardiovascular disease is extremely common in patients with end-stage renal disease (ESRD) and accounts for at least 50% of deaths among these patients. Vascular calcifications (VC) have been recently implicated as a possible cause of this excess cardiovascular mortality. Medial calcification is a striking feature of vascular disease in patients with ESRD. The traditional view that VC is a degenerative and passive process has been seriously challenged, based on strong evidence suggesting that VC is an active and highly regulated process similar to bone formation. Different data support the notion that elevated levels of phosphorus and/or other uremic toxins may play an important role by transforming vascular smooth muscle cells into osteoblast-like cells, which can produce bone matrix proteins. This nidus can then mineralize if the balance of pro-mineralizing factors outweighs inhibitory factors. The advent of newer noninvasive screening tests have generated great interest for screening patients with ESRD for vascular calcifications. Control of serum phosphorus with sevelamer, a recently developed non-calcium, non-aluminum phosphate binder, have attenuated or arrested progression of coronary artery and aortic calcifications compared to treatment with calcium-based binders. Amino bisphosphonates, have shown to completely inhibit soft tissue calcifications, calciphylaxis and prevent death in animal models. The first generation bisphosphonate, etidronate, reduces the progression of coronary artery calcifications patients receiving long-term hemodialysis and intravenous pamidronate has produced a rapid improvement of calciphylaxis. In conclusion, VC is a widespread phenomenon in patients with ESRD with important cardiovascular consequences. A better understanding of the processes of VC is leading to therapies to retard or improve this phenomenon and will probably have an important impact on patient mortality.

Plasma aluminium: a redundant test for patients on dialysis?

Aluminium toxicity as a cause of dementia, osteodystrophy and anaemia in patients receiving renal dialysis was first described in the 1970s and led to the regular monitoring of aluminium in plasma and dialysate water. However, aluminium phosphate binders have now been replaced by calcium-based binders or sevelamer and reverse osmosis (RO) water is used in the preparation of dialysate fluid. This has reduced the exposure of dialysis patients to aluminium and it is therefore opportune to review aluminium monitoring in patients undergoing regular renal dialysis. Plasma and water aluminium results were audited over the period January 2000-January 2004, with results obtained from nine renal dialysis units in the UK. Patients with a plasma aluminium concentration in the toxic range (>3.7 micromol/L) were followed up by contacting the relevant consultant. Plasma aluminium results were collected on 1626 patients over the four-year period (mean=0.47 micromol/L, median=0.3 micromol/L, range 0.07-30.26 micromol/L, n=5918). Forty-six patients had an aluminium concentration >3.7 micromol/L and nine were not retested. Only three patients had a repeat aluminium concentration >2.2 micromol/L, one being a result of desferrioxamine treatment, with no further clinical information available on the other two. All renal units are using RO water to prepare dialysate and aluminium-based phosphate binders are no longer prescribed. Only one of 212 RO water aluminium concentrations measured was >10 microg/L. Patients with clinical symptoms of overt aluminium toxicity were not identified in this population. The role of aluminium monitoring in long-term renal dialysis patients needs re-evaluation. Regular monitoring of plasma aluminium may not be required, but should be considered in any patient showing signs or symptoms of aluminium toxicity or exposed to a contaminated water supply. It is more important that RO water supplies are maintained and monitored. Environmental aluminium as a source of sample contamination should be considered and eliminated during blood collection and sample processing.

Management of hyperphosphataemia in dialysis patients: role of phosphate binders in the elderly.

Phosphorus control remains a relevant clinical problem in dialysis patients. With age, however, serum phosphorus level decreases significantly because of a spontaneous decrease in protein intake. Older patients usually need lower doses of phosphorus binders. Nevertheless, hyperphosphataemia is observed in a quarter of patients aged >65 years. Phosphorus retention is related to an imbalance between phosphorus intake and removal by dialysis, and is usually aggravated when vitamin D analogues are employed. Hyperphosphataemia induces secondary hyperparathyroidism and the development of osteitis fibrosa. Recent publications describe an association between phosphorus retention and increased calcium and phosphorus product (Ca2+ x P), with significant progression of tissue calcification and higher mortality risk. Dietary intervention, phosphorus removal during dialysis and phosphorus binders are current methods for the management of hyperphosphataemia. However, the phosphorus removed by standard haemodialysis is insufficient to achieve a neutral phosphorus balance when protein intake is >50 g/day. Additional protein restriction may impose the risk of a negative protein balance. More frequent dialysis may help to control resistant hyperphosphataemia. Phosphorus binders constitute the mainstay of serum phosphorus level control in end-stage renal disease patients. Aluminium-based phosphorus binders, associated with toxic effects, have largely been substituted by calcium-based phosphorus binders. However, widespread use of calcium-based phosphorus binders has evidenced the frequent appearance of hypercalcaemia and long-term progressive cardiovascular calcification. Sevelamer, a relatively new phosphorus binder, has proved efficacious in lowering serum phosphorus and parathyroid hormone (PTH) levels without inducing hypercalcaemia. Furthermore, several investigators have reported that sevelamer may prevent progression of coronary calcification. However, its efficacy in severe cases of hyperphosphataemia remains to be confirmed in large series. There are no specific guidelines for phosphorus control in the elderly. Until more information is available, levels of mineral metabolites should be targeted in the same range as those recommended for the general population on dialysis (calcium 8.7-10.2 mg/dL, phosphorus 3.5-5.5 mg/dL and Ca2+ x P 50-55 mg2/dL2). PTH values over 120 ng/L help to avoid adynamic bone disease. Since elderly patients have a higher incidence of adynamic bone (which buffers less calcium) and vascular calcification, sevelamer should be the phosphorus binder of choice in this population; but sevelamer is costly and its long-term efficacy has not been definitively validated. Patients with low normal levels of calcium may receive calcium-based phosphorus binders with little risk. Patients with low values of PTH and high normal calcium should receive sevelamer. Tailored combinations of calcium-based phosphorus binders and sevelamer should be considered, and calcium dialysate concentration adjusted accordingly.

Slowing the progression of vascular calcification in hemodialysis.

Hyperphosphatemia and secondary hyperparathyroidism are common complications of ESRD (chronic kidney disease stage 5) that, when untreated, may result in increased morbidity and mortality. Hyperphosphatemia and hypercalcemia have been associated with increased coronary artery calcification. Achieving control of serum phosphorus without increasing serum calcium is an important goal for patients with ESRD. Although calcium-based phosphate binders effectively reduce serum phosphorus and parathyroid hormone concentrations, these agents can lead to hypercalcemia and have been associated with increased vascular calcification. The phosphorus binder sevelamer was developed to overcome the limitations associated with the usual management of hyperphosphatemia and secondary hyperparathyroidism (i.e., mineral salts). Sevelamer, a nonabsorbable hydrogel, is as efficacious as calcium-based phosphate binders for reducing serum phosphorus but does not cause hypercalcemia or other adverse metabolic effects. Sevelamer also exhibits beneficial effects on lipids, consistently and significantly decreasing LDL cholesterol and increasing HDL cholesterol in most studies. In a head-to-head randomized clinical trial, sevelamer and calcium-based binders achieved similarly excellent phosphorus control, but the use of calcium-based binders led to significantly higher serum calcium concentrations and an increased incidence of hypercalcemia and unintended suppression of parathyroid hormone. Treatment with calcium-based binders also led to the progression of coronary artery and aortic calcification, whereas sevelamer attenuated or arrested progression. Strategies that use oral calcium and vitamin D in patients with ESRD should be reexamined, and the potential advantages of sevelamer should be considered when selecting a primary agent to reduce serum phosphorus in hemodialysis patients.

Calcium salts in the treatment of hyperphosphatemia in hemodialysis patients.

Hyperphosphatemia in patients with end-stage renal disease leads to secondary hyperparathyroidism and renal osteodystrophy, and is independently associated with mortality risk. How hyperphosphatemia increases mortality risk is unknown but it may promote cardiovascular calcification. It is recommended that dialysis patients be treated to maintain normal serum phosphorus. Although calcium-based phosphate binders are cost-effective, their long-term safety has been questioned because of their postulated role in progression of cardiovascular calcification. In this regard, sevelamer hydrochloride has been recommended as an alternative phosphate binder. In this review, we will examine these issues and provide rational guidelines for the use of calcium-based phosphate binders. Results from the calcium acetate Renagel evaluation study indicate that calcium acetate is more effective than sevelamer in controlling serum phosphorus and calcium x phosphorus product in hemodialysis patients. However, in the Treat-to-Goal study dialysis patients treated with sevelamer had less progression of coronary and aortic calcification than patients treated with calcium-containing binders. The mechanism underlying the slower rate of progression of cardiovascular calcification in sevelamer-treated patients remains uncertain but may relate to decreased calcium loading or to dramatic reductions in LDL cholesterol. At present, evidence incriminating calcium-containing phosphate binders in the progression of cardiovascular calcification in end-stage renal disease remains largely circumstantial. As calcium acetate is more efficacious and cost-effective than sevelamer, it remains an accepted first-line drug. Treatment with sevelamer hydrochloride should be considered for patients with persistent hypercalcemia during calcium-based binder therapy despite appropriate adjustment of vitamin D therapy.

Phosphate binder usage in kidney failure patients

Phosphorus binders are used in patients with kidney failure becuase of the incomplete removal of phosphorus with dialysis and the inability to exclude phosphorus from the diet. Aluminium was the initial phosphorus binder used, but was replaced by calcium-containing binders becuase of the development of aluminium toxicity. Calcium-based binders have been the mainstay of therapy for many years, but recent investigations have pointed to increased rates of vascular calcification in patients taking calcium-containing binders. For this reason, alternative agents have been developed. Sevelamer (Renagel®, GelTex Pharmaceuticals Inc.) is a polymer which has been found to effectively bind phosphorus. It has resulted in a decreased rate of vascular calcification compared to calcium-containing binders. Other agents under development include lanthanum carbonate and iron-complex preparations. Further research will likely concentrate on identifying binders that bind phosphate more efficiently, have minimal gastrointestinal side effects and provide other benefits to dialysis patients.

High frequency of marked hyperphosphatemia during intravenous calcitriol therapy in hemodialysis patients with refractory hyperparathyroidism.

Efficacy and safety of intermittent intravenous calcitriol therapy were studied in 8 chronic hemodialysis patients with marked hyperparathyroidism refractory to oral therapy with calcium salts and daily vitamin D. They were followed for 20 weeks (32 weeks for 2 patients). At the start of the study, serum calcium was < 2.65 mmol/l and phosphate levels were controlled with calcium-based binders only. The phosphate content of the prescribed diet (< 1 g/day) remained unchanged during the study, and a low-calcium dialysate was used (1.38 mmol/l). The initial postdialysis calcitriol dose was 1 microgram and was increased to 2 micrograms in 6 patients. Intravenous calcitriol effectively improved hyperparathyroidism in 7 patients, with a significant decrease of the intact parathyroid hormone level from 650 +/- 433 to 195 +/- 208 pg/ml (p < 0.05). Hypercalcemia > 2.7 mmol/l occurring in 3 patients was observed in only 11% of the weekly laboratory controls and always resolved rapidly. In contrast, hyperphosphatemia > or = 2.0 mmol/l was observed in 7 patients and in 40% of the weekly laboratory controls. In 15% of the cases the phosphate values even exceeded 2.4 mmol/l. The phosphate binder therapy had to be intensified accordingly, not only by increasing the dose of calcium-based binders, but also by introducing aluminum salts in 6 patients. In summary, our data show that intravenously administered calcitriol is effective in the treatment of severe hyperparathyroidism in most hemodialysis patients resistant to oral therapy. However, its usefulness seems to be limited by frequency and severity of hyperphosphatemia, frequently necessitating additional prescription of aluminum-based binders. These undesirable secondary events may thus limit the long-term utility of intravenously administered calcitriol.