Strategies to minimize bone disease in renal failure

Calcium-Phosphate Metabolism Disorders in Patients with Renal Failure Clinical Significance, Diagnosis and Treatment

Chronic kidney diseases (CKD) are commonly associated with calcium and phosphorus metabolism disorders. The general term of “renal osteodystrophy” (ROD) encompasses a complex spectrum of abnormalities in bone and mineral metabolism in CKD. This is one of the most serious and debilitating complications of CKD. It is related to disproportionately high direct and indirect costs of healthcare, thus posing a major burden on society. The development of ROD begins too early in the course of CKD. Some mechanisms involved in the pathogenesis of ROD are reduced calciferol production, calcium deficiency and hyperphosphatemia. Clinically, ROD occurs with varied manifestations – osteomalacia, osteoporosis, adynamic bone disease. The diagnosis and the treatment are a challenge for the physician and effort should be made to prolong the duration and quality of life of the affected patients.

Secondary Hyperparathyroidism in Chronic Kidney Disease: Focus on Clinical Consequences and Vitamin D Therapies

Objective:

To assess vitamin D–based treatment approaches for secondary hyperparathyroidism and its complications.

Data Sources:

A literature search was performed using MEDLINE (1990–February 28, 2006). Key words used were chronic kidney disease and vitamin D to identify relevant papers published in English.

Study Selection and Data Extraction:

From the database of articles generated, 48 papers were identified. Titles and abstracts were examined to identify those directly related to the objective. Discussion was expanded through the bibliographies of cited articles.

Data Synthesis:

The increasing prevalence of chronic kidney disease (CKD) in the US indicates an urgent need for treatment strategies to delay or prevent disease progression. Abnormalities in phosphorus and calcium homeostasis, vitamin D levels, and the subsequent development of secondary hyperparathyroidism (SHPT) are secondary complications of CKD associated with increased morbidity and mortality. Management options include dietary phosphorus restriction, phosphate binders and/or calcium supplementation, vitamin D supplementation, and calcimimetics. Vitamin D supplementation has received increased attention given the prevalence of vitamin D deficiency in patients with CKD and the beneficial effect of correcting this deficiency.

Conclusions:

Early identification and intervention appropriate to the stage of CKD are likely to improve patient outcomes. Improved knowledge of interactions between vitamin D and vitamin D receptors has led to the development of vitamin D analogs and calcimimetics, which offer benefits in the management of SHPT. Integrating available treatment options into practice to achieve optimal therapeutic goals of SHPT based on the stage of CKD is a significant challenge for pharmacists managing patients with CKD.

Vitamin D Levels After Kidney Transplantation and the Risk of Cytomegalovirus Infection

Background:

Some studies reported an association between low levels of vitamin D and the risk of infections, especially viral infections. Kidney transplant patients are at risk of opportunistic infections; however, no study has been conducted on the association between vitamin D levels and the risk of CMV infection.

Objectives:

The aim of this study was to compare the level of vitamin D in two groups of patients with and without CMV infection within four months after the transplantation. Moreover, we aimed to find a relation between vitamin D level, before and after transplantation in each group.

Patients and Methods:

This prospective cohort study was conducted in Baqiyatallah hospital in Tehran in 2013. A total of 82 kidney transplant patients were enrolled and vitamin D levels were measured in them before transplantation. The kidney transplant patients had been followed up for four months and monitored for the presence of cytomegalovirus antigen (CMV Ag) in their blood. In patients with positive CMV Ag, vitamin D level was measured again when they became positive but in other patients it was measured at the end of follow-up; at the end, characteristics of patients and vitamin D levels were compared between the two groups.

Results:

Of all, 40 patients were CMV Ag positive and 42 patients were negative. In most patients transplanted organs were taken from cadaver (66%) and the most common type of dialysis was hemodialysis (92%). Most participants did not undergo antithymocyte globulin therapy (69%) and pulse corticosteroid therapy (83%). Vitamin D level before transplantation was 17.2 ± 11.6 ng/mL. In patients with positive results or at the end of follow-up in patients without CMV Ag, vitamin D level was 16.3 ± 11.4 ng/mL. Only 11% of kidney transplant patients, within four months after transplantation, had a normal level of vitamin D (> 30 ng/mL). There was no significant difference between the two groups for patients’ characteristics (P > 0.05). Vitamin D levels, before transplantation and at the time of detecting CMV Ag or at the end of follow-up period in patients without CMV, were not significantly different between the two groups (P > 0.05). However, vitamin D levels decreased in patients with CMV, while it increased in CMV Ag negative patients, which was statistically significant (P = 0.037).

Conclusions:

Only 11% of kidney transplant patients, even with a successful transplantation of the kidney and with an acceptable performance of the transplanted kidney, had an adequate level of vitamin D. Although, we did not find any significant association between vitamin D levels and CMV infection during a 4-month follow-up after kidney transplantation. It was observed that, compared with the time before transplantation, vitamin D levels decreased in patients with CMV, while it increased in CMV negative patients.

The effect of vitamin C on parathyroid hormone in patients on hemodialysis with secondary hyperparathyroidism: a double blind, placebo-controlled study

BACKGROUND

Secondary hyperparathyroidism (SHPT) is a prevalent disorder in patients with chronic kidney disease. It is proffered that there is a contradictory relation between serum level of vitamin C and parathyroid hormone (PTH) in hemodialysis patients with secondary hyperparathyroidism.

OBJECTIVES

The goal of this study was to assess the effects of the supplemental vitamin C on parathyroid hormone among hemodialysis patients with secondary hyperparathyroidism.

PATIENTS AND METHODS

This randomized, placebo-controlled, double-blind and parallel-group trial was conducted on 82 hemodialysis patients with serum levels of PTH more than 200 pg/mL. In intervention group, 250 mg vitamin C was injected three times a week for 8 weeks in a row immediately at the end of each dialysis session via the intravenous route. In the control group, same term of placebo saline was injected.

RESULTS

The mean of serum PTH was 699.81 (± 318.8) and 596.03 (± 410.7) pg/mL in intervention and control groups respectively at baseline (reference range, 6 to 66 pg/mL), and at the end of study it changed to 441.4 and 424.6 in these groups. The values of serum Calcium and Phosphate did not significantly change during the study (8.4 ± 0.6 mg/dL versus 8.1 ± 0.8 mg/dL, P = 0.39; 5.89 ± 1.7 mg/dL versus 5.9 ± 1.9 mg/dL, P = 0.08, respectively).

CONCLUSIONS

This study finding does not warranted therapeutic effect of vitamin C on secondary hyperparathyroidism.

Differential effects of oral doxercalciferol (Hectorol) or paricalcitol (Zemplar) in the Cyp27b1-null mouse model of uremia

BACKGROUND/AIMS

Kidney disease patients experience declining calcitriol levels and develop secondary hyperparathyroidism (SHPT). Animal models of uremia based on 5/6 nephrectomy (NTX) do not consistently reproduce this calcitriol deficiency. We developed an animal model, the NTX Cyp27b1-null mouse, which completely lacks endogenous calcitriol, and examined the suitability of this model for evaluation of treatment with vitamin D analogs in uremia.

METHODS

NTX was performed at 2 months of age. One week post-NTX, animals were treated for 4 weeks with vehicle; doxercalciferol at 30, 100 or 300 pg/g body weight (b.w.); or paricalcitol at 100, 300 or 1,000 pg/g b.w. by gavage 3 times per week.

RESULTS

Serum blood urea nitrogen and creatinine were elevated. Vehicle-treated NTX null mice had hypocalcemia and SHPT. Doxercalciferol at 100 or 300 pg/g b.w. normalized serum calcium and parathyroid hormone (PTH) levels. Paricalcitol at 300 or 1,000 pg/g normalized serum calcium, but PTH levels remained elevated. Osteomalacia was corrected by 100 pg/g b.w. of doxercalciferol or 1,000 pg/g b.w. of paricalcitol. The highest dose of doxercalciferol, but not of paricalcitol, significantly reduced osteitis fibrosa.

CONCLUSION

Our results reveal the differential efficacy of doxercalciferol and paricalcitol in this novel animal model incorporating both calcitriol deficiency and renal insufficiency.

Comparative effects of doxercalciferol (1α-hydroxyvitamin D₂) versus calcitriol (1α,25-dihydroxyvitamin D₃) on the expression of transporters and enzymes in the rat in vivo

Effects of 1.28 nmol/kg doxercalciferol [1α(OH)D₂], a synthetic vitamin D₂ analog that undergoes metabolic activation to 1α,25-dihydroxyvitamin D₂, the naturally occurring, biologically active form of vitamin D₂, on rat transporters and enzymes were compared with those of 1α,25-dihydroxyvitamin D₃ [1,25(OH)₂D₃, active form of vitamin D₃; 4.8 and 6.4 nmol/kg] given on alternate days intraperitoneally for 8 days. Changes were mostly confined to the intestine and kidney where the vitamin D receptor (VDR) was highly expressed: increased intestinal Cyp24 and Cyp3a1 messenger RNA (mRNA) and a modest elevation of apical sodium-dependent bile salt transporter (Asbt) and P-glycoprotein (P-gp) protein; increased renal VDR, Cyp24, Cyp3a9, Mdr1a, and Asbt mRNA, as well as Asbt and P-gp protein expression; and decreased renal PepT1 and Oat1 mRNA expression. In comparison, 1α(OH)D₂ treatment exerted a greater effect than 1,25(OH)₂D₃ on Cyp3a and Cyp24 mRNA. However, the farnesoid X receptor -related repressive effects on liver Cyp7a1 were absent because intestinal Asbt, FGF15 and portal bile acid concentrations were unchanged. Rats on the alternate day regimen showed milder changes and lessened signs of hypercalcemia and weight loss compared with rats receiving daily injections (similar or greater amounts of 0.64-2.56 nmol/kg daily ×4) described in previous reports, showing that the protracted pretreatment regimen was associated with milder inductive and lesser toxic effects in vivo.

Low bone density in children with hypercalciuria and/or nephrolithiasis

The objective of this study was to identify how many children with hypercalciuria and/or nephrolithiasis have a low bone density and whether the risk of low bone density can be identified by 24-h urine stone-risk profiles and/or growth parameters. A retrospective chart review was performed on 110 idiopathic hypercalciuria and/or kidney stone patients who received both a 24-h urine for stone-risk profile and a dual-energy X-ray densitometry scan. Patients were divided into low bone density vs. normal bone density groups and hypercalcuria verus nephrolithiasis groups and analyzed for differences in growth parameters, urine stone-risk profiles, and bone densities. Overall, 47% had a bone density z score < -1, and 26% had a bone density z score < -2. Patients with a low bone density had a higher body mass index and lower urine creatinine and ammonium than those with a normal bone density. Patients with nephrolithiasis had a lower bone density z score than patients with hypercalcuria and no nephrolithiasis. Clinicians should be aware of the increased incidence of low bone density in children with hypercalciuria and nephrolithiasis. The effect of hypercalciuria and nephrolithiasis treatment on bone density and the natural progression of the bone density in the studied patient population warrants further investigation.

Impact of treatment with calcimimetics on hyperparathyroidism and vascular mineralization

Soft tissue calcification that involves primarily the medial portion of the arterial vasculature is a widely recognized and common complication of chronic kidney disease Vascular calcification (VC) causes increased arterial stiffness and contributes to the high cardiovascular mortality and morbidity in dialysis patients. The pathogenesis of VC is complex and includes factors that promote calcification and others that inhibit calcification. Studies in dialysis patients have shown a correlation between VC and a number of uremia-related factors. Overall, abnormalities in calcium and phosphate metabolism, such as hyperphosphatemia and a raised serum calcium-phosphorus product traditionally have been thought of as important determinants in patients with chronic renal failure. Common therapeutic interventions in secondary hyperparathyroidism have come under scrutiny for associations with the development of VC. Calcimimetics provide a means of controlling serum levels of parathyroid hormone in secondary hyperparathyroidism without increasing the calcium-phosphorus product and, more important, may lower the risk for VC in these patients.

Bone health and vascular calcification relationships in chronic kidney disease

Abnormal bone in chronic kidney disease (CKD) may adversely affect vascular calcification via disordered calcium and phosphate metabolism. In this context, bone health should be viewed as a prerequisite for the successful prevention/treatment of vascular calcification (VC) along with controlled parathyroid hormone (PTH) secretion, the use of calcium-based phosphate binders and vitamin D therapy. In CKD patients, VC occurs more frequently and progresses more rapidly than in the general population, and is associated with increased cardiovascular disease (CVD) morbidity and mortality. A number of therapies aimed at reducing PTH concentration are associated with an increase of calcaemia and Ca x P product, e.g. calcium-containing phosphate binders or active vitamin D. The introduction of calcium-free phosphate binders has reduced calcium load, attenuating VC and improving trabecular bone content. In addition, a major breakthrough has been achieved through the use of calcimimetics, as first agents which lower PTH without increasing the concentrations of serum calcium and phosphate. Nowadays, it is becoming evident that even early stage CKD is recognised as an independent CVD risk factor. Moreover, the excess of CVD among dialysis patients cannot be explained entirely on the basis of abnormal mineral and bone metabolism. Hence, much controversy has surrounded the cost-effectiveness of treatment with the new phosphate-binding drugs as well as new vitamin D analogs and calcimimetics. Thus, it seems prudent and reasonable that maintaining bone health and mineral homeostasis should rely on some modifications of standard phosphate binding and calcitriol therapy. Hypophosphataemia and hypercalcaemia in adynamic bone disease (ABD) might be treated by reducing the number of calcium carbonate/acetate tablets in order to increase serum phosphate and decrease serum calcium, which, in turn, might positively stimulate PTH secretion. The same rationale is assumed for the use of a low calcium dialysate. On the other hand, secondary hyperparathyroidism with hyperphosphataemia and hypocalcaemia should be treated with a substantial number of calcium carbonate/acetate tablets in combination with calcitriol and low calcium dialysate in order to decrease serum phosphate and maintain the Ca x P product within K/DOQI guidelines (<4.4 mmol l(-1)). Finally, it becomes apparent that prevention, with judicious use of calcium-based binders, vitamin D and a low calcium dialysate without adverse effects on Ca x P or oversuppression of PTH, provides the best management of VC and mineral and bone disorder in CKD patients.

Vitamin D Deficiency and Secondary Hyperparathyroidism Among Patients with Chronic Kidney Disease

BACKGROUND

Chronic kidney disease (CKD) is associated with morbid complications that lead to high mortality and costs. Vitamin D deficiency and secondary hyperparathyroidism (SHPT) are frequent complications of CKD.

METHODS

We reviewed the current literature regarding the prevalence, diagnosis, complications, and management of vitamin D deficiency and SHPT among patients with CKD.

RESULTS

There is a high prevalence of vitamin D deficiency among adolescents and adults in the United States (age and gender dependent). Patients with CKD or those who are dialysis-dependent are much more likely to have low levels of vitamin D in comparison to those without kidney disease. In order to avoid significant complications including SHPT and musculoskelatal diseases, vitamin D needs to be measured routinely by primary care physicians and nephrologists. In the majority of CKD patients, SHPT is not diagnosed until late, leading to advanced cardiovascular and bone diseases.

CONCLUSIONS

In conclusion, current management of vitamin D deficiency and SHPT is suboptimal. Early diagnosis of vitamin D deficiency and SHPT are integral to optimal management of CKD, and additional research is needed in this area.

Influence of the parathyroid glands on bone metabolism

Bone is a classic target tissue for parathyroid hormone (PTH), whose calciotropic effect is mediated largely via catabolic actions on this tissue. Paradoxically, PTH also exerts anabolic actions, with intermittent injections of PTH or its amino-terminal fragments causing an increase in bone formation and bone mass, actions that form the basis for the use of PTH in the treatment of osteoporosis. Besides vitamin D, PTH is the only other known bone anabolic agent. High-affinity PTH receptors (PTH-1R) have been detected on osteoblasts and osteoclasts (albeit in lower numbers). Bone turnover, which includes activation of osteoclasts and osteoblasts, appears to be best reflected not by absolute concentrations of PTH (which can vary based on the assay and antibody used) but by a balance of circulating full-length PTH-(1-84) and amino-terminally truncated C-PTH fragments. When PTH-(1-84) is predominant, bone turnover is promoted. Among PTH fragments, PTH-(7-84) appears to be the most potent antagonist of PTH-(1-84). The mechanisms involved in these effects are unclear although mediation via unique C-terminal receptors has been suggested. We propose that, within the range of total PTH (100-1000 pg mL(-1)), the ratio of PTH-(1-84)/C-PTH fragment is a valuable tool for diagnosis of bone turnover. Data indicate that at PTH levels < 100-150 pg mL(-1) and > 1000 pg mL(-1), the ratio looses its predictive power. Assay type, patient characteristics (race, underlying renal disease) and treatment attributes (vitamin D, corticosteroids, phosphate binders) have an impact on the PTH ratio, and care should be used in interpreting assay results and making subsequent treatment decisions.

Lanthanum carbonate

OBJECTIVE

To review the pharmacology, pharmacokinetics, clinical efficacy, and safety profile of lanthanum carbonate, a phosphate binder for chronic kidney disease (CKD).

DATA SOURCES

Information was selected from PubMed (1965-October 2005). All studies presented as scientific posters and abstracts from nephrology meetings from 1999 to 2005 were also included.

STUDY SELECTION AND DATA EXTRACTION

All published articles regarding lanthanum carbonate were included. In addition, abstracts and presentations from scientific meeting symposia were also considered for inclusion.

DATA SYNTHESIS

Lanthanum carbonate has been recently approved as non-calcium-based therapy for phosphate reduction in patients with stage 5 CKD requiring dialysis. The recommended dose is 250-500 mg with meals, for a maximum of 1500 mg daily. Clinical studies have shown short- and long-term safety with lanthanum carbonate administration. Adverse effects were primarily gastrointestinal in nature. Clinical trials have also shown reductions in serum phosphorus to target concentrations, reductions in associated calcium-phosphorus product, and minimal effects on serum calcium and parathyroid hormone concentrations.

CONCLUSIONS

Lanthanum carbonate is an effective phosphate-binding agent without significant risk of hypercalcemia or worsening metabolic acidosis. Lanthanum carbonate is a safe and effective drug for reduction of elevated serum phosphorus levels associated with stage 5 CKD. The role of lanthanum carbonate relative to other phosphate-binding drugs, such as calcium salts and sevelamer, remains to be determined.

Long-Term Efficacy and Tolerability of Lanthanum Carbonate: Results from a 3-Year Study

BACKGROUND

Control of serum phosphate over the long term is essential in patients with end-stage renal disease. Six-month and 2-year extensions to a 6-month study evaluated the long-term safety, tolerability and efficacy of the new phosphate binder lanthanum carbonate.

METHODS

Patients who participated in a 6-month, randomized trial comparing lanthanum carbonate with calcium carbonate were eligible for a 24-week, open-label extension. Lanthanum carbonate-treated patients continued taking their established maintenance dose ('continued-lanthanum group') and calcium carbonate-treated patients switched to lanthanum carbonate, 375-3,000 mg/day ('switch group'). Patients could also enter a further 2-year extension. Efficacy parameters, including serum phosphate, were monitored.

RESULTS

Mean serum phosphate was approximately 1.80 mmol/l throughout the trial. The percentage of patients with controlled serum phosphate (< or =1.80 mmol/l) after the 6-month extension was 63.3 and 58.4% in the continued-lanthanum and switch groups, respectively; after the 2-year extension, 54.4% of patients had controlled serum phosphate. After discontinuation of calcium carbonate and initiation of lanthanum carbonate, the hypercalcemia incidence was 2.7%, compared with 20.2% during the double-blind phase. Calcium x phosphate product was maintained at an acceptable level. Lanthanum carbonate was well tolerated; adverse events were mild/moderate and mainly gastrointestinal.

CONCLUSIONS

Lanthanum carbonate maintains effectiveness with continued tolerability for up to 3 years.

Risk factors associated with incident clinical vertebral and nonvertebral fractures in postmenopausal women: the Canadian Multicentre Osteoporosis Study (CaMos)

Utilizing data from the Canadian Multicentre Osteoporosis Study (CaMos), we examined the association between potential risk factors and incident vertebral and nonvertebral fractures. A total of 5,143 postmenopausal women were enrolled. Information collected during the study included data from the CaMos baseline and annually mailed fracture questionnaires, the Short Form 36 (SF-36), the Health Utilities Index, and physical measurements. Participants were followed for 3 years. Postmenopausal women were classified into four groups according to their incident fracture status since baseline: those without a new fracture; those with a new clinically recognized vertebral fracture; those with an incident nonvertebral fracture at the wrist, hip, humerus, pelvis, or ribs (main nonvertebral fracture group); and those with any new nonvertebral fracture (any-nonvertebral-fracture group). We performed multivariate Cox proportional hazard analysis using all possible risk factors to determine the association between risk factors and the time to the first minimal trauma fracture. Best predictive models were also determined using variables that were included in the full models. The Bayesian information criterion was used for model selection. For all analyses, relative risks and associated 95% confidence intervals were calculated. During the follow-up period, 34, 163, and 280 women developed a vertebral, a main nonvertebral, or any nonvertebral fracture, respectively. The best predictive models indicated that a five point lower quality of life as measured by the SF-36 physical component summary score was associated with relative risks of 1.21 (95% CI, 1.02 to 1.44), 1.17 (95% CI, 1.07 to 1.28), and 1.19 (95% CI, 1.11 to 1.27) for incident vertebral, main nonvertebral, and all nonvertebral fractures, respectively. In addition, for a one standard deviation (SD=0.12) lower femoral neck BMD, the relative risks for incident vertebral, main nonvertebral, and any nonvertebral fractures increased by 2.73 (95% CI, 1.74 to 4.28), 1.39 (95% CI, 1.06 to 1.82), and 1.34 (95% CI, 1.09 to 1.65), respectively. Furthermore, various anthropometric measures, disease conditions, and medications are associated with a new fracture. Identifying postmenopausal women at risk is important given that fracture prevention therapies are now available.

1,25-Dihydroxyvitamin D3 but not cinacalcet HCl (Sensipar/Mimpara) treatment mediates aortic calcification in a rat model of secondary hyperparathyroidism

BACKGROUND

Calcitriol treatment of secondary hyperparathyroidism (HPT) in chronic kidney disease (CKD) patients can lead to increased serum calcium and phosphorus, which have been associated as risk factors for vascular calcification. Cinacalcet HCl (Sensipar/Mimpara) {(alphaR)-(-)-alpha-methyl-N-[3-[3-(trifluoromethylphenyl)propyl]-1-napthalenemethanamine hydrochloride} lowers serum parathyroid hormone (PTH), calcium, phosphorus and calcium-phosphorous (CaxP) product in stage 5 CKD dialysis patients; however, its effects on vascular calcification are unknown.

METHODS

Cinacalcet HCl (10 or 1 mg/kg, p.o. gavage), 1,25-dihydroxyvitamin D(3) (0.1 microg, s.c, calcitriol) or the combination was administered daily for 26 days in a rat model of secondary HPT [5/6 nephrectomy]. After dosing, aortic calcification was determined using the von Kossa staining method. Serum PTH and blood chemistries were determined on days 0, 26 and 0, 14, 26, respectively, prior to and after dosing.

RESULTS

Calcitriol-treated rats had moderate to marked aortic calcification, whereas no significant calcification was observed in vehicle- or cinacalcet HCl-only treated groups. Co-administration of cinacalcet HCl with calcitriol did not attenuate the calcitriol-mediated increase in CaxP product or calcitriol-mediated aortic calcification. Both calcitriol and cinacalcet HCl therapy significantly reduced serum PTH levels. Calcitriol significantly elevated serum calcium, serum phosphorous and CaxP product above pretreatment levels, or those seen with vehicle or cinacalcet HCl. Cinacalcet HCl (10 or 1 mg/kg) decreased serum ionized calcium and decreased calcitriol-induced hypercalcaemia.

CONCLUSION

Cinacalcet HCl and calcitriol both effectively reduce PTH, albeit via different mechanisms, but unlike calcitriol, cinacalcet HCl did not produce hypercalcaemia, an increased CaxP product or vascular calcification.

Efficacy, Tolerability, and Safety of Lanthanum Carbonate in Hyperphosphatemia: A 6-Month, Randomized, Comparative Trial versus Calcium Carbonate

BACKGROUND/AIMS

Hyperphosphatemia is an important clinical consequence of renal failure, and its multiple adverse systemic effects are associated with significantly increased risks of morbidity and mortality in dialysis patients. Existing oral phosphate binders have not permitted control of serum phosphate within currently accepted guidelines. This study compares lanthanum carbonate with calcium carbonate for control of serum phosphate in hemodialysis patients.

METHODS

In this European multicentre study, 800 patients were randomised to receive either lanthanum or calcium carbonate and the dose titrated over 5 weeks to achieve control of serum phosphate. Serum levels of phosphate, calcium and parathryoid hormone were followed over the following 20 weeks.

RESULTS

Around 65% of patients in each group achieved phosphate control, but in the calcium carbonate group this was at the expense of significant hypercalcemia (20.2% of patients vs. 0.4%). Consequently, calcium x phosphate product tended to be better controlled in the lanthanum group.

CONCLUSION

This 6-month study demonstrates that serum phosphate control with lanthanum carbonate (750-3,000 mg/day) is similar to that seen with calcium carbonate (1,500-9,000 mg/day), but with a significantly reduced incidence of hypercalcemia. Lanthanum carbonate is well tolerated and may be more effective in reducing calcium x phosphate product than calcium carbonate.

Paricalcitol

Paricalcitol (Zemplar) is a synthetic vitamin D(2) analogue that inhibits the secretion of parathyroid hormone (PTH) through binding to the vitamin D receptor. It is approved in the US and in most European nations for intravenous use in the prevention and treatment of secondary hyperparathyroidism associated with chronic renal failure in adult, and in the US paediatric, patients. Paricalcitol effectively reduced elevated serum PTH levels and was generally well tolerated in children and adults with secondary hyperparathyroidism associated with chronic renal failure. In well designed clinical trials, paricalcitol was as effective as calcitriol and as well tolerated in terms of the incidence of prolonged hypercalcaemia and/or elevated calcium-phosphorus product (Ca x P). Thus, paricalcitol is a useful option for the management of secondary hyperparathyroidism in adults and children with chronic renal failure.

Parathyroid hormone secretion during citrate anticoagulated hemodialysis in acutely ill maintenance hemodialysis patients

Regional citrate anticoagulation during extracorporeal treatment is used in patients at risk for hemorrhage. We conducted a prospective clinical trial on the effect of large- versus small-dose calcium supplementation during citrate anticoagulated hemodialysis on ionized calcium and intact parathyroid hormone (iPTH). Twenty-five treatments were studied in 25 patients with active bleeding or at risk for hemorrhage. Sixteen patients received large-dose calcium (15 mmol/h), and 9 received small-dose calcium (5 mmol/h) substitution during treatment. Ionized calcium increased in 13 of 16 patients in the large-dose calcium group and decreased in 8 of 9 patients in the small-dose calcium group. Intact PTH decreased by 25% in the large-dose group and increased by 121% in the small-dose group (P = 0.0007 for Delta; P = 0.007 for Delta%). In the 14 patients in whom ionized calcium increased, iPTH decreased. In 10 of 11 patients in whom ionized calcium decreased, iPTH increased. The increase or decrease of ionized calcium was more predictive for changes in iPTH than was the calcium-substitution rate (R(2) = 0.5526 versus 0.3962, respectively). We conclude that the behavior of iPTH can be influenced in a predictive manner by adjusting the calcium-substitution rate during treatment.

The Consequences of Uncontrolled Secondary Hyperparathyroidism and Its Treatment in Chronic Kidney Disease

Secondary hyperparathyroidism (HPT) is a common complication of chronic kidney disease (CKD) and a frequent cause of clinically significant bone disease. Soft-tissue and vascular calcification, cardiovascular disease, and calcific uremic arteriolopathy (CUA) are additional serious consequences of the disorder that may contribute directly to cardiovascular morbidity and mortality in patients with CKD. Less widely appreciated manifestations include neurological disturbances, hematological abnormalities, and endocrine dysfunction. Secondary HPT arises from alterations in calcium, phosphorus, and vitamin D metabolism that develop early in the course of CKD and become more pronounced as kidney function declines. Treatment is often delayed, however, until the disease is well established. Current therapeutic strategies rely largely on the use of vitamin D sterols to diminish excess parathyroid hormone (PTH) synthesis and to lower serum or plasma PTH levels, but their use is often confounded by increases in serum calcium and phosphorus concentrations, changes that can aggravate soft-tissue and vascular calcification. As such, there is a need for new therapeutic interventions that can effectively lower serum or plasma PTH levels without producing untoward side effects. The current review summarizes the diverse manifestations of secondary HPT in patients with CKD. The consequences of inadequately controlled secondary HPT and the adverse effects of selected therapeutic interventions for the disorder on vascular calcification and cardiovascular disease in those with CKD are discussed.

Efficacy of 19-Nor-1,25-(OH)2D2 in the prevention and treatment of hyperparathyroid bone disease in experimental uremia

BACKGROUND

The control of parathyroid hyperplasia and high circulating parathyroid hormone (PTH) levels is crucial in preventing secondary hyperparathyroidism (SH) in renal failure. Parathyroid gland enlargement and elevated levels of PTH are major contributors to increase bone resorption, a feature of renal osteodystrophy.

METHODS

These studies assessed the efficacy of the 1,25(OH)2D3 analog, 19-Nor-1,25(OH)2D2 (19-Nor), in the prevention (protocol I) and treatment (protocol II) of SH and renal osteodystrophy in uremic rats. In protocol I, normal and uremic rats were fed a high phosphorus diet for 2 months; uremic rats were administered intraperitoneal injections of either vehicle or 19-Nor (200 ng three times a week). In protocol II, normal and uremic rats were fed a high phosphorus diet for 4 months; 2 months after the onset of uremia, rats were administered either intraperitoneal vehicle or 19-Nor (200 ng three times a week). Serum PTH and bone histology were used to assess the degree of SH.

RESULTS

19-Nor was effective in preventing (protocol I) and suppressing (protocol II) the significant SH induced by uremia and further enhanced by a high phosphorus diet. In protocol I, bone histology in uremic controls showed a threefold increase in the cancellous bone mass compared to normal rats. This expansion in unmineralized bone was accompanied by 5-, 1.5-, and 7-fold increases in eroded surface, mineralization lag time (MLT), and bone formation rate (BFR/BS), respectively. Moreover, cortical bone porosity in untreated uremic rats increased 267-fold compared to normal animals. 19-Nor ameliorated these changes in cancellous and cortical bone. In protocol II, the reported indices worsened even further. In contrast, 2 months of 19-Nor treatment improved bone histology by reducing cortical bone porosity, woven bone formation, MLT, and BFR/BS.

CONCLUSION

In an experimental model of chronic renal failure (CRF), 19-Nor prevents SH and ameliorates the histomorphometric changes induced by uremia and high phosphorus diet. In addition, 19-Nor suppresses serum PTH and improves bone histology in uremic rats with established severe SH. Further studies in patients with CRF are necessary to define the clinical applicability of 19-Nor on bone histology in humans.

Advantages of adjusting the initial dose of intravenous calcitriol according to PTH levels

BACKGROUND

To assess the usefulness of starting calcitriol therapy with a dose proportional to the degree of hyperparathyroidism, 141 patients from 28 centers were treated with intravenous calcitriol for 6 months. The aim was to achieve a final PTH between 125 and 250 pg/mL. Patients with serum PTH>250 pg/mL were included in the study and divided into 4 groups according to baseline PTH levels.

METHODS

The study was completed by 100 patients, a third of which were treated strictly according to the protocol, labeled "compliants"; thus, calcitriol was started according to baseline PTH levels. Two thirds of patients, labeled "noncompliants," showed one or more violation in the dosage regimen.

RESULTS

After 2 months of treatment with calcitriol, 59% of the "compliants" and 35% of the "noncompliants" decreased their PTH levels>40% (P = 0.022), 70%, and 49%, respectively after 3 months of treatment. After 3 months of treatment, 67% of the "compliants" reached the target (PTH 125 to 250 pg/mL) in contrast with 23% of the "noncompliants" (P < 0.001). The number of hypercalcemic and hyperphosphatemic episodes was significantly lower in the "compliants" group (P < 0.006).

CONCLUSION

These results demonstrate several advantages when calcitriol therapy is started with a dose proportional to the severity of hyperparathyroidism.

Higher impact of mineral metabolism on cardiovascular mortality in a European hemodialysis population

BACKGROUND

Cardiovascular disease is the main cause of morbidity and mortality among hemodialysis patients. Chronic renal failure influences a number of factors that cause accelerated atherogenesis, with calcium, phosphorus, and PTH playing key roles. Several studies have demonstrated the influence of these factors on all-cause and cardiovascular mortality in the American hemodialysis population. In the present study we evaluated the variables that influence long-term cardiovascular mortality in a European hemodialysis population.

METHODS

One hundred and forty-three hemodialysis patients were followed for six years. Several Cox models were used to study the influence of demographic and biochemical data, and comorbid conditions in cardiovascular survival, with a particular interest in mineral metabolism.

RESULTS

There was an increased risk of cardiovascular death in patients with serum P>6.5 mg/dL (risk ratio [RR], 2.5), PTH>50 pmol/L (RR, 3.9), Ca x P>52 (RR, 2.8), BB or Bb genotype (RR, 3.8), and in diabetics.

CONCLUSION

There is a stronger influence of mineral metabolism on cardiovascular death among European patients when compared to the American population.

Musculoskeletal manifestations of chronic renal failure

Musculoskeletal problems remain among the main limitations of the quality of life of renal failure patients, in particular of those treated with long-term maintenance dialysis. Renal osteodystrophy continues to receive great attention. The mechanisms of uremic skeletal resistance to parathormone (PTH) are further investigated. The assay used for the dosage of "intact PTH" has been found to detect 7-84 fragments with an inhibitory effect on the action of the whole hormone. A decrease in the density of PTH receptor on osteoblasts is another recently evidenced factor. Investigations of the recently described RANK-RANKL system have demonstrated an increase in serum osteprotegerin levels, which, together with the two above-mentioned abnormalities, may explain bone resistance to PTH. These are important advances in the understanding of renal osteodystrophy as skeletal resistance to PTH appears to play an important part in the pathophysiology of secondary hyperparathyroidism and of adynamic bone disease. Because of this skeletal resistance, it has been recommended for several years that serum PTH level be monitored and kept twofold to threefold above the upper value of the normal level to maintain normal bone turnover in dialysis patients. Relative hypoparathyroidism has recently been found to be associated with increased spontaneous fracture rate and mortality, so this recommendation appears to hold adequate, despite the demonstration that serum PTH levels in this range are a poor predictor of bone turnover and that chronic parathyroid gland hyperplasia is likely to favor parathyroid gland autonomization. Recent publications have insisted on the role that hyperphosphatemia plays not only in the development of secondary hyperparathyroidism, but also of vascular, especially coronary, calcification and as a predictor of mortality. This "silent killer" of uremic patients is one of the main targets for therapeutic intervention. Extensive use of calcium-containing phosphate binders has been recently criticized as calcium overload appears to favor vascular calcification. Sevelaner (RenaGel) is a calcium- and aluminum-free phosphate binder that is an important advance in the management of renal osteodystrophy, especially in patients with extraskeletal calcification and hypercalcemia. The use of vitamin D derivatives has also raised concern because they enhance calcium and phosphorus absorption and reduce bone turnover. New metabolites with fewer hypercalcemic effects have been developed. Calcium-sensing receptor agonists are stimulating interest and are likely to take an important place in the future management of renal osteodystrophy. Uremic myopathy has received recent attention. Impaired muscle capillary oxygen transfer has been identified as a pathophysiologic factor, and progressive resistance training has been shown to improve the condition. Finally, a new entity, nephrogenic fibrosing dermopathy, has been described, which must be distinguished from calciphylaxis and scleromyxedema.

Moderate cholecalciferol supplementation depresses intestinal calcium absorption in growing dogs

Hormonal regulation of calcium (Ca) absorption was investigated in a cholecalciferol (vitamin D(3))-supplemented group (hVitD) vs. a control group (cVitD) of growing Great Danes (100 vs. 12.5 micro g vitamin D(3)/kg diet). Although Ca intakes did not differ, fractional Ca absorption was significantly lower in the hVitD group than in the cVitD group. There were no differences in plasma concentrations of Ca, inorganic phosphate, parathyroid hormone, growth hormone or insulin-like growth factor I between groups. Plasma 25-hydroxycholecalciferol [25(OH)D(3)] concentrations were maintained in the hVitD dogs at the same levels as in the cVitD dogs due to increased turnover of 25(OH)D(3) into 24,25-dihydroxycholecalciferol [24,25(OH)(2)D(3)] and 1,25-dihydroxycholecalciferol [1,25(OH)(2)D(3)]. In hVitD dogs, the greater plasma 24,25(OH)(2)D(3) concentration and the enhanced metabolic clearance rate (MCR) of 1,25(OH)(2)D(3) indicated upregulated 24-hydroxylase activity. The increased MCR of 1,25(OH)(2)D(3) decreased plasma 1,25(OH)(2)D(3) concentrations. In hVitD dogs, the greater production rate of 1,25(OH)(2)D(3) was consistent with the 12.9-fold greater renal 1alpha-hydroxylase gene expression compared with cVitD dogs and compensated to a certain extent for the accelerated MCR of 1,25(OH)(2)D(3). The moderately decreased plasma 1,25(OH)(2)D(3) concentration can only partially explain the decreased Ca absorption in the hVitD dogs. Intestinal vitamin D receptor concentrations did not differ between groups and did not account for the decreased Ca absorption. We suggest that 24,25(OH)(2)D(3) may downregulate Ca absorption.