Association of hyperphosphataemia with haemodynamic disturbances in end-stage renal disease

Effect of 2′-phosphophloretin on renal function in chronic renal failure rats

Hyperhosphatemia and secondary hyperparathyroidism are common and severe complications of chronic renal failure. Therapies to reduce serum phosphate have been shown to reduce serum parathyroid hormone (PTH) and slow the progression of renal failure. The effect of the inhibitor of intestinal phosphate absorption, 2′-phosphophloretin (2′-PP), on serum and urine chemistry, renal histology, and cardiac structure in the uremic rat model of renal failure, 5/6 nephrectomy (5/6 NX), was examined. The effect of 2′-PP on serum phosphate, serum PTH, serum total Ca2+, and ionized Ca2+, Ca2+ × Pi product, urine protein, urine osmolality, and creatinine clearance in 5/6 NX rats was examined. Uremic rats in chronic renal failure were gavaged daily with 25 μM 2′-PP. Over the course of a 5-wk experiment, serum chemistry in untreated uremic rats, 2′-PP-treated uremic rats, and age-matched control rats with normal renal function was determined twice a week. Urine creatinine, urine osmolality, urine phosphate, and urine protein were determined once a week from 24-h collections. 2′-PP reduced serum phosphate 40 ± 3% compared with a 17% increase in untreated uremic control rats. 2′-PP did not alter total serum Ca2+. During 5-wk experiments, serum PTH increased 65 ± 25% in untreated uremic rats and decreased 70 ± 7% in uremic rats treated with 25 μM 2′-PP. Creatinine clearance decreased 20% in untreated uremic rats compared with a 100% increase in 2′-PP-treated uremic rats. Urine protein decreased and urine osmolality increased in uremic rats treated with 2′-PP. The mechanism of the effect of 2′-PP on serum phosphate was inhibition of intestinal phosphate absorption. 2-PP inhibited intestinal phosphate absorption 50% without altering dietary protein absorption or intestinal Ca2+ absorption. Over the course of the 5-wk treatment with 2′-PP, uremic animals treated with 2′-PP had a 2–4% weight gain/wk, similar to the weight gain seen in age-matched control rats with normal renal function.

Vascular calcification in chronic kidney disease

Dialysis patients have increased cardiovascular morbidity, mortality, and vascular calcification, and the latter appears to impact the former. Recent evidence indicates that vascular calcification is an active, cell-mediated process. Osteoblast differentiation factor Cbfa1 and several bone-associated proteins (osteopontin, bone sialoprotein, alkaline phosphatase, type I collagen) are present in histologic sections of arteries obtained from patients with end-stage renal disease (chronic kidney disease stage V [CKD-V]). This supports the theory that vascular smooth muscle cells can dedifferentiate or transform to osteoblast-like cells, possibly by up-regulation of Cbfa1. In in vitro experiments, addition of pooled serum from dialysis patients (versus normal healthy controls) accelerated mineralization and increased expression of Cbfa1, osteopontin, and alkaline phosphatase in cultured vascular smooth muscle cells. Clinically, the pathogenesis of vascular calcification is not completely understood, although increased levels of phosphorus and/or other potential uremic toxins may play an important role by transforming vascular smooth muscle cells into osteoblast-like cells. Presumably, once this process begins, increased serum calcium X phosphorus product, or calcium load from binders, accelerates this process. In addition, it is likely that circulating inhibitors of calcification are also important. Further understanding of the pathophysiology of vascular calcification is needed to intervene appropriately.

An update on vitamin D as related to nephrology practice: 2003

In this article, an up-to-date consideration of vitamin D therapeutics in nephrology is reviewed. The condition of vitamin D insufficiency is defined as the level of serum 25(OH)vitamin D at which vitamin D2 or D3 supplementation leads to a reduction of levels of parathyroid hormone (PTH). The risks of such vitamin D insufficiency in the normal population and likely risks in individuals with chronic kidney disease (CKD) stages 3 and 4 are reviewed. The potential for its safe treatment and prevention using moderate supplements of vitamin D2 or vitamin D3 are outlined. The role of altered "vitamin D nutrition" in leading to the observed greater incidence of secondary hyperparathyroidism in African Americans with ESRD compared to other racial groups is considered. The actions of active vitamin D sterols to augment intestinal absorption of both calcium and phosphorus, the effect to reduce levels of PTH, and to be a factor contributing to the rising incidence of low bone turnover (adynamic bone) are discussed. Growing evidence for contributions of elevated levels of serum calcium, serum phosphorus, and the calcium x phosphorus product as factors contributing to vascular and cardiac calcification in ESRD patients are cited. Questions are raised about whether the current practice of vitamin D usage in ESRD patients might be a contributing factor to such vascular abnormalities. The economic factors that likely affect the usage of intravenous vitamin D sterols in the United States are reviewed. It is recommended that potential adverse vascular effects of vitamin D sterols related to the increments of serum Ca and P be carefully evaluated.

Time and exercise improve phosphate removal in hemodialysis patients

BACKGROUND

Control of serum phosphate remains a difficult clinical issue in most hemodialysis (HD) patients. This study examines 2 nonpharmacological approaches to improving phosphate control in HD patients.

METHODS

First, 9 stable HD patients underwent dialysis in random fashion for either 4 hours 3 times weekly or 5 hours 3 times weekly. Adjustments were made to blood flow rates such that Kt/V was the same for all sessions, thus allowing independent assessment of the influence of time. The primary end point was weekly dialysate phosphate removal. In the second study, 12 different patients underwent an exercise program in which they pedaled a bicycle ergometer either immediately before or during dialysis. Again, weekly dialysate phosphate removal was measured.

RESULTS

In the time study, urea reduction ratio (69% +/- 0.02% versus 68% +/- 0.07, 4 versus 5 hours) and weekly urea removal were no different between the 2 groups. However, weekly phosphate removal (3,007 +/- 641 versus 3,400 +/- 647 mg; P < 0.02) significantly improved with longer dialysis duration. Serum phosphate levels improved, but did not reach statistical significance in this short-term study. In the exercise study, weekly phosphate removal improved with exercise, but did not reach significance (2,741 +/- 715 [no exercise] versus 2,917 +/- 833 [exercise predialysis] versus 2,992 +/- 852 mg [exercise during dialysis]; P = 0.055), although comparing only exercise during dialysis with no exercise reached significance (P = 0.02). There was no significant difference in serum phosphate levels.

CONCLUSION

Both increased dialysis time and exercise result in increased dialytic removal of phosphate and could be expected in the long term to improve phosphate control.

Left Ventricular Geometry and Hypotension in End-Stage Renal Disease: A Mechanical Perspective

ABSTRACT. Hemodynamic and nonhemodynamic factors are implicated in the maintenance and aggravation of left ventricular (LV) hypertrophy in ESRD. Functional consequences of LV geometry are of substantial importance in patients who undergo dialysis and may contribute to explain the negative outcome related to LV hypertrophy, also in patients without overt coronary heart disease (CHD). Whereas most patients with eccentric LV hypertrophy have systolic dysfunction and the underlying CHD imposes progression of their disease, when overt CHD does not occur to remodel left ventricle, concentric LV geometry is more prevalent in ESRD and functional consequences are different. Concentric LV geometry is very sensitive to abrupt changes of cardiac loading conditions because of increased LV stiffness. Dialysis-related decrease in LV filling pressure reduces Starling forces recruitment and causes a fall in stroke volume as a result of reduced preload. This fall cannot be compensated by increased contractility, as myocardial mechanics is impaired in concentric LV geometry and no functional reserve can be used. When adequate increase in heart rate is not achieved to compensate reduced stroke volume, cardiac output substantially decreases and hypotension occurs. Occurrence of hypotension in the context of concentric LV geometry might contribute to reduce repeatedly coronary blood flow supply in the stiff and thick myocardium and might accelerate myocardial structural deterioration seen in ESRD. E-mail: simogi@unina.it

Hyperphosphatemia aggravates cardiac fibrosis and microvascular disease in experimental uremia

BACKGROUND

Hyperphosphatemia is a known predictor of cardiovascular death and specifically of cardiac death in hemodialysis patients. The pathomechanisms involved have not been completely clarified. While a number of observations suggest an important role of hyperphosphatemia and positive calcium balance on atherosclerosis and calcification of the coronary conduit arteries, independent effects on postcoronary microvessels and on cardiac fibrosis have not been excluded.

METHODS

Male Sprague-Dawley rats were sham operated (N = 14) or subtotally nephrectomized (SNX, N = 17) and subsequently placed on low phosphorus (0.08% w/w) and high phosphorus (1.2% w/w) diet under pair-feeding conditions. After 8 weeks, serum chemistry and inhibitory parathyroid hormone (iPTH) were measured, and the hearts were harvested using perfusion fixation. Arteriolar thickness and volume density of the interstitium (excluding vessels) were quantitated using stereologic techniques.

RESULTS

In SNX animals with moderate renal failure serum phosphorus concentrations were higher than in sham-operated controls on low phosphorus diet (1.7 +/- 0.37 mmol/L) and were significantly higher in SNX + high phosphorus diet (2.33 +/- 0.23 mmol/L) compared to SNX + low phosphorus diet (1.95 +/- 0.32 mmol/L; P < 0.05). In sham-operated controls, dietary phosphorus content had no effect on cardiac morphologic indices. In contrast, in SNX + high phosphorus diet the index of interstitial cardiac fibrosis was significantly higher (3.22 +/- 0.44%) than in SNX + low phosphorus (2.75 +/- 0.46%) or in sham-operated controls (2.5 +/- 0.05% on high phosphorus and 2.4 +/- 0.89 on low phosphorus, respectively). In SNX + high phosphorus (14.0 +/- 9.0 microm), but not in SNX + low phosphorus (9.2 +/- 4.5 microm), arterial wall thickness was significantly higher compared to sham-operated controls (10.2 +/- 5.1 on high phosphorus and 9.8 +/- 5.0 micro;m on low phosphorus, respectively). The data were confirmed in an independent repeat experiment.

CONCLUSION

High dietary phosphorus and hyperphosphatemia have significant effects on cardiac fibrosis and arterial wall thickening. Such abnormalities of cardiac architecture may be relevant for the increased cardiac risk in hyperphosphatemic uremic patients.

Uremia induces the osteoblast differentiation factor Cbfa1 in human blood vessels

BACKGROUND

Bone matrix proteins are expressed in calcified arteries from dialysis patients, suggesting that vascular smooth muscle cells (VSMCs) may transform to osteoblast-like cells. One of the key transcriptional regulators of osteoblast differentiation is Cbfa1. Thus, we hypothesized that this may be a key factor in arterial calcification.

METHODS

To test this hypothesis, we examined sections of the inferior epigastric artery from uremic patients for the presence of Cbfa1 and type I collagen and osteopontin by in situ hybridization and immunostaining. We also examined the effect of pooled uremic sera from dialysis patients on the expression of Cbfa1 by reverse transcription-polymerase chain reaction (RT-PCR) in bovine VSMCs in vitro.

RESULTS

Cbfa1 and osteopontin were expressed in both the media and the intima in vessels that were calcified, but there was only minimal staining in non-calcified vessels. In vitro studies demonstrated that pooled uremic serum, compared to pooled control human serum induced the expression of Cbfa1 by RT-PCR in bovine VSMCs in a time-dependent, nonphosphorus-mediated mechanism.

CONCLUSION

These results support that Cbfa1 is a key regulatory factor in the vascular calcification observed in dialysis patients and is up-regulated in response to many uremic toxins.

Improvement in lower-extremity peripheral arterial disease by nocturnal hemodialysis

A 42-year-old man with end-stage renal disease (ESRD) was referred for conversion to nocturnal hemodialysis (NHD) therapy from conventional hemodialysis (CHD) therapy because of refractory intermittent claudication secondary to peripheral arterial disease (PAD). The patient was initiated on CHD therapy in 1976 and subsequently had undergone two unsuccessful renal transplantations. While on CHD therapy, his clinical course was complicated by worsening vascular and soft-tissue calcification. Extensive dystrophic soft-tissue calcification was noted bilaterally in his hands, lower extremities, and sacral region, requiring surgical excision. Lower-extremity arterial Doppler scans documented vascular calcification and a pronounced decrease in peripheral arterial flow bilaterally. After conversion to NHD therapy (7.5 h/session five times weekly), the patient became symptom free and had significant clinical improvements in (1) hemodynamics, measured by clinic blood pressure and two-dimensional echocardiography, (2) biochemical profile, and (3) a sustained improvement in arterial Doppler flow measured by duplex Doppler ultrasound. We conclude that NHD was able to improve lower-extremity PAD in our patient. Further observational and interventional studies are required to investigate the therapeutic potential of NHD for the treatment of PAD in patients with ESRD.

Phosphorus and uremic serum up-regulate osteopontin expression in vascular smooth muscle cells

BACKGROUND

Dialysis patients have accelerated atherosclerosis, with extensive calcification of both the intima and media. Cross-sectional studies have implicated hyperphosphatemia in this process, but the mechanism is unclear.

METHODS

To test the hypothesis that hyperphosphatemia and/or uremia induces vascular calcification, bovine vascular smooth muscle cells (BVSMC) were treated with increasing concentrations of beta-glycerophosphate, a phosphate donor, in the presence or absence of inhibitors for sodium/phosphate (Na/Pi) co-transport (foscarnet) or alkaline phosphatase (levamisole) for 48 hours. BVSMC also were incubated for various times with DMEM plus 15% pooled uremic sera from patients with low (LP) or high serum phosphorus (HP), or from pooled healthy control serum. Calcification in BVSMC was examined by quantitation of calcium deposition. Osteopontin expression and alkaline phosphatase activity were assessed by Western blotting and a colorimetric assay.

RESULTS

beta-glycerophosphate increased osteopontin expression and alkaline phosphatase activity in BVSMC. Inhibition of either alkaline phosphatase activity or Na/Pi co-transport abolished this effect. Compared to incubation with control human serum, BVSMC cultured with uremic sera had increased mineral deposition. Uremic sera also increased alkaline phosphatase activity and osteopontin expression in BVSMC. The addition of beta-glycerophosphate to uremic HP or LP sera did not further augment osteopontin expression. Blocking Na/Pi co-transport or alkaline phosphatase activity only partially inhibited uremic sera-induced osteopontin expression, indicating that other non-Na/Pi co-transport dependent mechanisms also are involved.

CONCLUSION

beta-glycerophosphate and uremic sera induce calcification and osteopontin expression in BVSMC. The uremic sera-induced osteopontin expression in BVSMC is partially mediated through alkaline phosphatase activity and a Na/Pi co-transporter dependent mechanism. However, other non-Na/Pi dependent mechanisms also contribute to accelerated vascular calcification in patients with ESRD.

Cardiovascular disease in patients with chronic kidney disease

Cardiovascular disease (CVD) is the major cause of morbidity and mortality in patients with renal failure. Patients with chronic kidney disease have significant CVD, and carry a high cardiovascular burden by the time they commence renal replacement therapy (RRT). The severity of CVD that has been observed in dialysis patients lead to a growing body of research examining the pathogenesis and progression of CVD during the progression of chronic kidney disease (CKD) to end-stage renal disease (ESRD) (ie, predialysis phase). Multiple factors are involved in the development of CVD in CKD. More importantly, critical and key factors seem to develop early in the course of CKD, and result in preventable worsening of CVD in this patient population. Anemia is common in patients with CKD, and has been shown to have an independent role in the genesis of left ventricular hypertrophy (LVH) and subsequent CVD. Unfortunately, it is underdiagnosed and undertreated in patients with CKD. Early intervention, and better correction of anemia, seems to gain a great momentum in the prevention and management of CVD in CKD. Hypertension is another risk factor that has been targeted by the National Kidney Foundation Task Force on CVD in chronic kidney disease. This article reviews the different factors involved in the pathogenesis of CVD in CKD and the evidence supporting early and aggressive intervention.

Pseudohyperphosphatemia in a hyperphosphatemic hemodialysis patient

Hyperphosphatemia is a predictable consequence of end-stage renal disease. Pseudohyperphosphatemia is a spurious elevation of serum phosphate in samples containing a substance that interferes with the laboratory assay for phosphate. The most common cause is a paraprotein in disorders such as Waldenström's macroglobulinemia and multiple myeloma. We report here a case of pseudohyperphosphatemia in a hyperphosphatemic patient with end-stage renal disease on long-term hemodialysis caused by a saline solution containing phosphorus used to dilute the patient's serum sample in the clinical chemistry laboratory. Investigations showed that the phosphorus most likely was introduced at the time of saline manufacture. Pseudohyperphosphatemia resulting from the manufacture and distribution of saline-containing phosphorus could be a cause of abnormally high serum phosphate measurements in hyperphosphatemic dialysis patients whose serum samples must be diluted in the laboratory. Such spuriously elevated results can lead to inappropriate changes in medications and subject patients to additional hemodialysis treatments.

Update on vitamin D and its newer analogues: actions and rationale for treatment in chronic renal failure

Vitamin D is an important hormone for mineral homeostasis and the proper formation and maintenance of bone. In addition, vitamin D has broader functions in the body that expand its traditionally known role in mineral balance. In chronic renal failure, calcitriol deficiency contributes to the development and progression of secondary hyperparathyroidism, bone disorders, and altered mineral metabolism. Recent revelations of the broader role of vitamin D also suggest calcitriol deficiency may contribute to decreased cardiac and immune function in chronic renal failure patients. Research on vitamin D has led to a more complete understanding of the actions of vitamin D at the transcriptional level and with respect to the clinical use of vitamin D and its analogs to control parathyroid hormone overactivity and to replace the other D hormone-dependent actions in patients with renal failure. Limitations of vitamin D and its metabolites include hypercalcemia, hyperphosphatemia and suppression of bone turnover with the risk of adynamic bone disease. Vitamin D analogs may offer greater selectivity and potentially greater safety as compared to calcitriol because of their altered relative potency on calcium and phosphorus metabolism. This review focuses on the current understanding of the biological actions of vitamin D and its analogs and the rationale for treating patients with chronic renal failure.

Future role of calcimimetics in end-stage renal disease

Calcimimetic agents are small organic molecules that act as allosteric activators of the calcium-sensing receptor. In parathyroid cells, they lower the threshold for receptor activation by extracellular calcium ions and diminish parathyroid hormone (PTH) secretion. These compounds offer a novel way of controlling excess PTH secretion in clinical disorders associated with excess PTH secretion, including secondary hyperparathyroidism due to chronic renal failure. The first calcimimetic agent to be evaluated in clinical trials was R-568, but studies were discontinued because of its limited bioavailability and inconsistent pharmacokinetic profile. Extensive assessments are currently underway by using a second-generation calcimimetic compound, AMG 073, to treat secondary hyperparathyroidism. Work completed thus far has shown that AMG 073 effectively lowers plasma PTH, without increasing values for the calcium-phosphorus ion product in serum in patients with end-stage renal disease. Indeed, serum phosphorus levels often decline as plasma PTH levels fall during treatment. Recent experimental evidence also suggests that calcimimetic agents may impede the development of parathyroid gland hyperplasia, an integral component of secondary hyperparathyroidism due to chronic renal failure. Calcimimetics agents have considerable potential therefore as a new approach to the medical management secondary hyperparathyroidism.

The Calcimimetic agent AMG 073 lowers plasma parathyroid hormone levels in hemodialysis patients with secondary hyperparathyroidism

Treatment with vitamin D sterols can lower plasma parathyroid hormone (PTH) in many patients with secondary hyperparathyroidism due to end-stage renal disease, but hypercalcemia, hyperphosphatemia, or both often develop during treatment. As such, alternative therapeutic approaches to managing excess PTH secretion are needed. Calcimimetic agents directly inhibit PTH secretion by activating the calcium-sensing receptor in the parathyroid glands, but clinical experience with them is limited. Fifty-two hemodialysis patients with secondary hyperparathyroidism were given single orally administered doses of the calcimimetic agent AMG 073 ranging from 5 to 100 mg, or placebo. Plasma PTH levels decreased 2 h after 25-, 50-, 75-, or 100-mg doses, falling by a maximum of 43 +/- 29%, 40 +/- 36%, 54 +/- 28%, or 55 +/- 39%, respectively. Plasma PTH levels decreased in all patients given doses of > or =25 mg but did not change in those who received placebo. In patients treated with daily doses of 25 or 50 mg of AMG 073 for 8 d, plasma PTH levels declined for the first 3 to 4 d and remained below baseline values after 8 d of treatment. Serum calcium concentrations also decreased by 5 to 10% from pretreatment levels in patients given 50 mg of AMG 073 for 8 d, but values were unchanged in those who received lower doses. Serum phosphorus levels and values for the calcium-phosphorus ion product both decreased after treatment with AMG 073. Thus, 8 d of treatment with AMG 073 effectively lowers plasma PTH levels and improves several disturbances in mineral metabolism that have been associated with soft tissue and vascular calcification and with adverse cardiovascular outcomes in patients with end-stage renal disease.

Medial artery calcification in ESRD patients is associated with deposition of bone matrix proteins

BACKGROUND

In non-ESRD patients, recent studies have demonstrated that the process of vascular calcification resembles developmental osteogenesis. Patients with ESRD are known to have excessive vascular calcification, but this has previously been attributed to the non-cell-mediated process of metastatic calcification.

METHODS

To determine if the calcification observed in patients with ESRD is related to a cell-mediated process, we removed a piece of inferior epigastric artery at the time of renal transplant. Calcium content of the entire vessel was quantified with spiral computed tomography (CT). The vessel was then examined histologically for calcification and the presence of bone matrix proteins by immunohistochemistry, and medial and intimal thickness quantified by histomorphometry. These findings were correlated with demographic, clinical and laboratory values.

RESULTS

The proximal inferior epigastric artery was obtained from 41 patients undergoing renal transplantation, but two were inadequate for histologic examination. Twenty-seven of the remaining vessels had no evidence of calcification by MacNeal's or Alizarin red pH 4.2 staining, five vessels had mild/moderate calcification, and seven had severe calcification, all in the medial layer. Calcification assessed histologically was closely correlated with calcification score as assessed by spiral CT, normalized for vessel weight (P=0.027). Positive immunostaining for the bone matrix proteins osteopontin, type I collagen, bone sialoprotein, and alkaline phosphatase was strongly correlated with calcification (all P < or = 0.001), as was a history of coronary artery disease (P < 0.001), and diabetes (P=0.034). The calcification score by spiral CT correlated with these same factors and the serum phosphorus and calcium x phosphorus product (P=0.032 and 0.037). The location of immunostaining for the bone proteins was strongly associated with the presence of calcification. However, positive immunostaining also was observed in association with disorganization of the vascular smooth muscle cells in the medial layer due to deposition of a matrix-like substance, prior to overt calcification.

CONCLUSIONS

In patients with ESRD undergoing renal transplantation, vascular calcification of the medial layer of the inferior epigastric artery is common (44%), can be detected by spiral CT, and is associated with deposition of bone matrix proteins. This implies an active cell-mediated process, raising hope that directed intervention can arrest this process.

Compounds in development to combat hyperphosphataemia

Hyperphosphataemia in haemodialysis patients is associated with secondary hyperparathyroidism and more importantly with an increased cardiovascular mortality in dialysed patients. Removal of phosphate during dialysis is less than net intestinal uptake. This imbalance results in a positive phosphate balance. To control serum phosphate concentration oral phosphate binders have to be taken to reduce net intestinal uptake. The use of classical phosphate binders such as calcium carbonate, calcium acetate and aluminium-containing phosphate binders is limited by their side effects. Hypercalcaemia aggravates vascular calcification and cardiovascular risk. Aluminium intoxication causes aluminium osteopathy, anaemia and encephalopathy. Therefore, the development of calcium- and aluminium free phosphate binders has become a challenge to clinical nephrology. Polyallylamine hydrochloride (sevelamer) is one of the new alternative compounds which has been shown to effectively bind phosphate in dialysis patients. A promising approach in the development of alternative phophate binders are trivalent-iron (Fe(III)) containing phosphate binders. They were not only successfully tested in experimental animals but have also been shown to reduce urinary phosphate excretion and serum phosphate concentrations in patients with preterminal failure and those on maintenance haemodialysis. This review outlines the experimental and clinical data on Fe-III based phosphate binders providing evidence that they will be as effective and safe as phosphate binders without the major side effects of classical phosphate-binding compounds.

Consequences of hyperphosphatemia and elevated levels of the calcium-phosphorus product in dialysis patients

Control of serum phosphorus levels is a central goal in the management of patients with chronic renal failure. Inadequate control of serum phosphorus leads to elevated levels of the calcium-phosphorus product. This plays a pivotal role in vascular calcification, cardiovascular disease, calciphylaxis, and death. Elevated phosphorus and elevated levels of the calcium-phosphorus product are both significant predictors of cardiovascular mortality, at phosphorus and calcium-phosphorus product levels that were considered safe until recently. A lowering of levels such that phosphorus is maintained between 2.2 and 5.5 mg/dl, calcium-phosphorus product is below 55 mg(2)/dl(2), and serum calcium is at 9.2-9.6 mg/dl, respectively, might well be the goal of therapeutic management strategies.

Non-invasive assessments of cardiovascular disease in patients with renal failure

Vascular calcification is common in patients with chronic renal failure, and it may contribute to the very high mortality rate from cardiovascular causes in the end-stage renal disease population. Vascular calcification in chronic renal failure can arise from the calcification of the intimal layer of arteries as a result of atherosclerosis or from medial wall calcification due largely to alterations in mineral metabolism. Although several reports indicate that coronary artery calcification, as measured by electron-beam computed tomography, is quite common in patients with end-stage renal disease who are treated with dialysis, the clinical significance of these findings remain uncertain. In the general population, electron-beam computed tomography evidence of coronary calcification serves as a useful index of atherosclerotic burden and has value as a predictor of adverse coronary events. The relationship between coronary artery calcification and atherosclerotic cardiovascular disease has not been adequately studied, however, in patients with end-stage renal disease, and calcification scores in this population may reflect both intimal and medial wall calcification. Assessments using coronary angiography are needed to determine the diagnostic value of electron-beam computed tomography as a predictor of atherosclerotic cardiovascular disease in patients with chronic renal failure. Nevertheless, electron-beam computed tomography makes it possible to detect the presence and monitor the progression of coronary calcification in those undergoing long-term dialysis. The technique may provide important information about the impact of new therapeutic strategies aimed at reducing the risks of vascular calcification in those with chronic renal failure.

Phosphate removal and hemodialysis conditions

Hyperphosphatemia is frequently found in hemodialysis patients, and the association with an increased risk of mortality has been demonstrated. Other authors have linked hyperphosphatemia to increased cardiovascular mortality. The normalization of phosphate plasma levels is therefore an important goal in the treatment of end-stage renal disease patients. Absorption of phosphate from the food exceeds the elimination through a hemodialysis treatment, and this leads to a chronic phosphate load for the majority of hemodialysis patients. This imbalance should be improved by either a reduction of phosphate absorption or an increased removal of phosphate. A reduction of phosphate absorption can be achieved by reducing the amount of phosphate in the diet or by the administration of phosphate binders. Unfortunately, these measures imply practical difficulties, for example, a lack of patient compliance or other side effects. When considering modifications of the hemodialysis treatment, an essential understanding of the kinetics of dialytic phosphate removal is mandatory. Phosphate is unevenly distributed in different compartments of the body. Only a very small amount of phosphate is present in the easily accessible plasma compartment. The major part of phosphate removed during hemodialysis originates from the cytoplasm of cells. A transfer from intracellular space to the plasma and further from the plasma to the dialysate is necessary. However, if we consider improvement to phosphate removal by dialysis procedures, full dialyzer clearance is effective in only the initial phase of the dialysis treatment. After this initial phase, the transfer rate for phosphate from the intracellular space to the plasma becomes the rate-limiting step for phosphate transport. Attempts to improve this transfer rate have recently been investigated by acidosis correction, but turned out not to be consistently successful. Furthermore, modifications of the treatment schedule have been described in the literature as measures to influence the phosphate balance consistently. Successful improvements of the phosphate balance can be achieved specifically through increasing the frequency of the dialysis treatments.

Parathormon, calcium, phosphorus, and left ventricular structure and function in normotensive hemodialysis patients

Clinical and experimental data suggest that Parathormon (PTH), calcium, and phosphorus participate in left ventricular hypertrophy (LVH) and affect myocardial contractility in end-stage renal disease. Cellular calcium overload and interstitial fibrosis induced by PTH may lead to impairment of left ventricular diastolic function. Hyperphosphatemia is an independent risk of cardiovascular mortality in dialysis patients. The aim of the study was to estimate the influence of PTH and calcium-phosphorus metabolism on left ventricular structure and function in hemodialysis patients, without hypertension and antihypertensive drug therapy (SBP = 126.2 +/- 11.1 DBP = 75.8 +/- 6.5 mmHg). Echocardiographic findings in a group of 22 normotensive HD patients had been compared to 43 hypertensive HD patients. Relationships between PTH, calcium-phosphorus metabolism and echocardiography in normotensive group were then evaluated. Left ventricular mass index (LVMI) was lower in normotensive patients: 128.3 +/- 46.2 versus 165.8 +/- 46.7 (p < 0.01). The prevalence of LVH was 55% in normotensive HD patients compared to 86% in hypertensive group (p < 0.01). In normotensive group we found correlation between PTH and LVMI (r = 0.44; p < 0.05). There were also significant relationships between calcium and posterior wall thickness (r = -0.44; p < 0.05), phosphorus and LVMI (r = 0.47; p < 0.05). A significant correlation was observed between both phosphorus, calcium x phosphorus product and E/A ratio: r = -0.47 and r = -0.43, respectively (p < 0.05 both). Disturbances of calcium-phosphorus metabolism and secondary hyperparathyroidism contributes to left ventricular hypertrophy, and impaired left ventricular diastolic function in normotensive hemodialysis patients.

Vitamin D therapy in patients with chronic renal disease: the role of the renal dietitian

Chronic renal failure causes decreased vitamin D production, which profoundly alters parathyroid hormone (PTH) metabolism, and calcium and phosphorus balance. Correcting this deficiency is an important strategy in managing secondary hyperparathyroidism (SHPT) and helping to restore mineral balance. However, hypercalcemia and hyperphosphatemia are common side effects that hamper vitamin D hormone therapy by increasing dietary calcium and phosphorus absorption. This limitation has led to the development of D-hormone analogs that retain the ability to suppress PTH levels without causing drastic changes in calcium and phosphorus metabolism. These analogs have the potential to advance the management of SHPT. Renal dietitians can play a leading role in ensuring successful management of SHPT by participating in early patient intervention for abnormal mineral and vitamin D metabolism, by encouraging long-term phosphorus control, and by updating and implementing clinical protocols that promote optimal hormone levels (D and PTH), mineral levels (phosphorus and calcium), and nutritional factors.

Intermittent doxercalciferol (1alpha-hydroxyvitamin D(2)) therapy for secondary hyperparathyroidism

Hypercalcemia and hyperphosphatemia frequently necessitate vitamin D withdrawal in hemodialysis patients with secondary hyperparathyroidism. In short-term trials, doxercalciferol (1alpha-hydroxyvitamin D(2) [1alphaD(2)]) suppressed intact parathyroid hormone (iPTH) effectively with minimal increases in serum calcium and phosphorus (P) levels. This modified, double-blinded, controlled trial examined the efficacy and safety of 1alphaD(2) use in 138 hemodialysis patients with moderate to severe secondary hyperparathyroidism by using novel dose titration; 99 patients completed the study. Hemodialysis patients with secondary hyperparathyroidism were enrolled onto this study, consisting of washout (8 weeks), open-label 1alphaD(2) treatment (16 weeks), and randomized, double-blinded treatment with 1alphaD(2) or placebo (8 weeks). Oral 1alphaD(2) was administered at each hemodialysis session, with doses titrated to achieve target iPTH levels of 150 to 300 pg/mL. Baseline iPTH levels (897 +/- 52 [SE] pg/mL) decreased by 20% +/- 3.4% by week 1 (P: < 0.001) and by 55% +/- 2.9% at week 16; iPTH levels returned to baseline during placebo treatment but remained suppressed with 1alphaD(2) treatment. In 80% of the patients, iPTH level decreased by 70%, reaching the target level in 83% of the patients. Grouping patients by entry iPTH level (<600, 600 to 1,200, and >1,200 pg/mL) showed rapid iPTH suppression in the group with the lowest level; greater doses and longer treatment were required in the group with the highest level. During open-label treatment, serum calcium and P levels were 9.2 +/- 0.84 (SD) to 9.7 +/- 1.05 mg/dL and 5.4 +/- 1.10 to 5.9 +/- 1.55 mg/dL, respectively. During double-blinded treatment, serum calcium levels were slightly greater with 1alphaD(2) than placebo, but P levels did not differ. During double-blinded treatment, 3.26% and 0.46% of serum calcium measurements exceeded 11.2 mg/dL with 1alphaD(2) and placebo, respectively (P: < 0.01); median level was 11.6 mg/dL during hypercalcemia. Intermittent oral 1alphaD(2) therapy effectively suppresses iPTH in hemodialysis patients with secondary hyperparathyroidism, with acceptable mild hypercalcemia and hyperphosphatemia.

Calcimimetic agents and the calcium-sensing receptor

Blood ionized extracellular calcium is closely regulated. To accomplish this, a hormone-like receptor that is responsive to extracellular ionized calcium regulates both the secretion of parathyroid hormone and the excretion of urinary calcium (as well as other cellular processes). Several hereditary disorders have mutations that cause either loss or gain of function of the calcium-sensing receptor, and alterations of the calcium-sensing receptor may play a role in both primary and secondary hyperparathyroidism. Calcimimetics are agents that act to make the calcium-sensing receptor more sensitive to extracellular ionized calcium; thereby they suppress the secretion of parathyroid hormone. Early trials in animal models of secondary hyperparathyroidism and in patients with primary hyperparathyroidism or with uremic secondary hyperparathyroidism have shown that the first generation calcimimetic, R-568, effectively lowers parathyroid hormone levels and is well tolerated.