Effects of oral calcitriol on bone mineral density in patients with end-stage renal failure

Calcium Kinetic Studies in Patients on Capd: Improvement of Secondary Hyperparathyroidism without Concomitant Improvement of Calcium Turnover

Objective

An association between the development of low turnover osteopathy and the form of dialysis treatment, that is, continuous ambulatory peritoneal dialysis (CAPD), has been described. To examine the effect of a year-long CAPD treatment on calcium (Ca) turnover, 12 patients were studied prior to and one year after initiation of CAPD treatment with a dialysate calcium of 1.75 mmol/L.

Design

A prospective analysis.

Setting

Academic teaching hospital dialysis unit.

Patients

Twelve patients with an average age of 54.8 years (range: 23 76 years) at commencement of dialysis and after 13 months of CAPD treatment.

Measurements

Calcium kinetic studies were performed using two calcium isotopes: 45Ca as an oral tracer and 47Ca as an intravenous tracer. Measurements of plasma and whole body activities were performed over a four week period. From these measurements, kinetic parameters describing calcium turnover in different compartments were studied. These measurements were repeated after a mean time of 13.4 months. Patients were not treated with vitamin D, but received aluminum and calcium -containing phosphate binders, in order to keep inorganic phosphate below 2.0 mmol/L and calcium within the normal range.

Results

After one year on CAPD, serum levels of calcium increased from 2.2 mmol/L to 2.35 mmol/L. Inorganic phosphate also increased from 1.4 mmol/L to 1.9 mmol/L, despite increased use of oral phosphate binders. Serum levels of intact parathyroid hormone (i PTH) decreased from 51.2 pmol/L to 28.3 pmol/L. Alkaline phosphatase did not change, nor did serum levels of vitamin D. Despite improvement of serum iPTH levels and better control of serum calcium, the kinetic parameters describing calcium turnover in the different calcium pools did not improve. In addition, the calcium retention of bone remained below normal range and did not rise. Perhaps more importantly, the relationship between Ca efflux and Ca retention did not change. While Ca retention remained low, plasma Ca efflux was normal. This imbalance was seen at the beginning of CAPD and did not change under CAPD.

Conclusion

These data demonstrate that, after one year of CAPD treatment without vitamin D treatment, calcium turnover did not improve, despite a significant fall in serum iPTH levels. Studies on a larger number of patients are warranted to verify these results.

Long Term Dialysis with Low-Calcium Solution (1.0 Mmol/L) in Capd: Effects on Bone Mineral Metabolism

Objective

Peritoneal dialysate solutions with conventionally high-calcium (Ca) concentrations (1.75 mmol/L) are now widely replaced by solutions with a lower, more physiological calcium content to prevent hypercalcemia in patients treated with oral calcium-containing phosphate binders and/or calcitriol. While there is still debate on how far the dialysate calcium should be lowered (1.25 mmol/L or less), little information is available concerning the effects of a long-term treatment with low-calcium solutions on secondary hyperparathyroidism and bone mineral metabolism in general.

Design

A prospective, randomized, controlled multicenter study to compare the effects of low-calcium (LCa, dialysate calcium 1.0 mmol/L) versus standard calcium dialysate solution (SCa, dialysate calcium 1.75 mmol/L)on bone mineral metabolism in continuous ambulatory peritoneal dialysis (CAPD) patients over 2 years of treatment.

Setting

Nephrology and dialysis units of primary and tertiary hospitals in Germany and Switzerland.

Patients

All CAPD patients in the participating centers between 18 and 80 years of age, stable on CAPD for at least 1 month, free of aluminum bone disease or prior parathyroidectomy were invited to enter the study. Sixty-four patients could be randomly allotted to LCa (n = 35) or SCa (n = 29) treatment in a 2-year protocol; 34 finished the study as planned.

Interventions

Calcium carbonate (CaCO3) was given as oral phosphate binder to maintain serum phosphate <2.0 mmol/L. If hypercalcemia supervened, CaCO3 was exchanged stepwise for aluminium hydroxide (AI(OH)3)’ until normocalcemia was obtained. Patients received calcitriol (0.25 μg/day per os) if parathyroid hormone (PTH) exceeded the upper limit of normal by a factor of 2 or more.

Main Outcome Measures

We assessed total and ionized serum calcium, phosphate, serum aluminum, alkaline phosphatase, osteocalcin, PTH (intact molecule), and phosphate binder intake at regular intervals. Measurements of bone mineral density and hand skeleton x-rays were obtained at the start and after 6 months and 2 years, respectively.

Results

With LCa, mean total and ionized serum calcium levels were within the normal range (total Ca: 2.0 2.6 mmol/L; ionized Ca: 1.19–1.32 mmol/L), but throughout the treatment period were significantly lower than with SCa. The incidence of hypercalcemia (>2.8 mmol/L) was three times higher in patients on SCa, despite the significantly higher amount of AI(OH)3 and less CaCO3 given in this group. In parallel, serum aluminum increased with SCa throughout the study, whereas it was slowly decreasing with LCa. Median PTH levels remained stable at about two times the upper limit of normal over the 2 years of study with LCa. However, 23% of the patients on LCa developed severe hyperparathyroidism, with PTH levels exceeding ten times the upper limit of normal compared to only 10.3% of the patients on SCa. With SCa, median PTH decreased towards near normal levels. Alkaline phosphatase and serum osteocalcin correlated positively with PTH levels. Bone mineral density was in the lower normal range in both groups a n d remained unchanged at the end of the study. Skeletal x-ray films showed only minor alterations in very few patients in both groups with no correlation to serum PTH or treatment modality.

Conclusion

In CAPD patients low-calcium dialysate solutions can be used successfully over prolonged periods of time with stable control of serum calcium. The risk of hypercalcemia resulting from calcium-containing phosphate binders and the need to use aluminum-containing phosphate binders is markedly diminished. However, there is a certain risk that severe secondary hyperparathyroidism with long-term LCa therapy will develop, even if normocalcemia is maintained. Thus, LCa dialysis requires closeand continuous monitoring of PTH and bone metabolism.

Chronic Kidney Disease-Mineral and Bone Disorders (CKD-MBDs): What the Endocrinologist Needs to Know

OBJECTIVE

Chronic kidney disease-mineral and bone disorders (CKD-MBDs) are a spectrum of abnormalities involving skeletal hormones, minerals, and bone turnover and mineralization. This paper focuses on what the endocrinologist should know about the assessment and management of skeletal and metabolic disorders in CKD-MBDs.

METHODS

Relevant literature was reviewed to (1) define disturbances of minerals and hormones in the course of CKD; (2) identify the variable radiographic and histomorphometric changes of CKD-MBDs; (3) review the association among CKD-MBDs, vascular calcification, cardiovascular disease (CVD), and mortality; and (4) clarify issues in CKD-MBDs therapy.

RESULTS

Assessment and treatment of CKD-MBDs is complicated by progressive changes in bone minerals and skeletal regulatory hormones as kidney function declines. CKD-MBDs are associated with fracture risk, and studies demonstrate that bone mineral density can be used to assess bone loss and fracture risk in these patients. Treatment of CKD-MBDs continues to evolve. Use of calcium, phosphate binders, vitamin D, vitamin D-receptor analogs, and drugs for osteoporosis and CKD-MBDs treatment are discussed in the context of safety and efficacy for patients with CKD.

CONCLUSION

The association of CKD with bone disease, vascular calcification, CVD, and mortality mandates earlier recognition and treatment of CKD-MBDs. Osteoporosis as a distinct entity can be diagnosed and managed in CKD, although assessment of osteoporosis becomes challenging in late (stage 4 to 5) CKD. Diabetes is common in early (stage 1 to 3) CKD. In addition, 96% of all individuals identified as having CKD have early CKD. The endocrinologist is uniquely positioned to address and treat both diabetes and many of the metabolic and skeletal disorders associated with early CKD-MBDs, including osteoporosis.

Calcitriol Suppression of Parathyroid Hormone Fails to Improve Skeletal Properties in an Animal Model of Chronic Kidney Disease

BACKGROUND

Chronic kidney disease (CKD) leads to complex metabolic changes and an increased risk of fracture. Currently, calcitriol is the standard of care as it effectively suppresses parathyroid hormone (PTH) levels in CKD patients. While calcitriol and its analogs improve BMD and reduce fractures in the general population, the extension of these benefits to patients with advanced kidney disease is unclear. Here, the impact of calcitriol on the skeleton was examined in the setting of reduction in PTH.

METHODS

Male Cy/+ rats, a PKD-like CKD model, were treated with either vehicle or calcitriol for 5 weeks. Their normal littermates served as controls. Animals were assessed for changes in mineral metabolism and skeletal parameters (microCT, histology, whole bone mechanics and bone quality).

RESULTS

PTH levels were significantly higher (12-fold) in animals with CKD compared to normal controls. CKD animals also exhibited negative changes in bone structural and mechanical properties. Calcitriol treatment resulted in a 60% suppression of PTH levels in animals with CKD. Despite these changes, it had no impact on bone volume (cortical or cancellous), bone turnover, osteoclast number or whole bone mechanical properties.

CONCLUSIONS

These data indicate that while calcitriol effectively lowered PTH in rats with CKD, it did little to prevent the negative effects of secondary hyperparathyroidism on the skeleton.

Adynamic bone in patients with chronic kidney disease

Adynamic bone in patients with chronic kidney disease (CKD) is a clinical concern because of its potential increased risk for fracture and cardiovascular disease (CVD). Prevalence rates for adynamic bone are reportedly increased, although the variance for its prevalence and incidence is large. Differences in its prevalence are largely attributed to classification and population differences, the latter of which constitutes divergent groups of elderly patients having diabetes and other comorbidities that are prone to low bone formation. Most patients have vitamin D deficiency and the active form, 1,25-dihydroxyvitamin D, invariably decreases to very low levels during CKD progression. Fortunately, therapy with vitamin D receptor activators (VDRAs) appears to be useful in preventing bone loss, in part, by its effect to stimulate bone formation and in decreasing CVD morbidity, and should be considered as essential therapy regardless of bone turnover status. Future studies will depend on assessing cardiovascular outcomes to determine whether the risk/reward profile for complications related to VDRA and CKD is tolerable.

Bone and mineral guidelines for patients with chronic kidney disease: a call for revision

Recent clinical studies of mineral metabolism in patients with chronic kidney disease have helped to verify and extend the Kidney Disease Outcomes Quality Initiative practice guidelines for bone metabolism and disease that were published in 2003. In particular, investigations that examined calcium loading, vitamin D therapy, and mortality risk associated with serum calcium and phosphate in dialysis patients have been the most helpful clinically. As a consequence, there is now a growing interest to have the previous guidelines amended accordingly, which will be performed through the Kidney Disease: Improving Global Outcomes working group after a debate within the nephrology community. The new data support this call for revision in an attempt to improve survival of the dialysis patient by emphasizing the importance of intravenous vitamin D therapy and of preventing excess calcium loading. These studies also suggest avenues for future investigation into nontraditional causes and treatments of cardiovascular disease in patients with chronic kidney disease.

Survival after Parathyroidectomy in Patients with End-stage Renal Disease and Severe Hyperparathyroidism

BACKGROUND

Patients with end-stage renal disease (ESRD) and secondary hyperparathyroidism (SHPT) are at high risk of mortality. Whether an increased risk of death persists after a parathyroidectomy (PTX) is not clearly established.

SUBJECTS AND METHODS

The survival of 40 patients with ESRD and SHPT who underwent PTX was compared with that of 664 ESRD patients.

RESULTS

From first dialysis, a lower mortality rate was found in the group of patients who underwent PTX than in the nonoperated ESRD group (hazard ratio: 0.23; 95% CI: 0.14-0.37). The patients who underwent PTX were younger, had a longer time on dialysis, and had a higher prevalence of kidney transplantation. The mean number of comorbidities was lower (Charlson score 4.2 +/- 2.1 versus 6.4 +/- 2.9, p < 0.001). Then, we randomly selected two matched controls for each PTX case (80 controls, 40 PTX) who had at least an equivalent mean duration of dialysis between the first dialysis and PTX of the PTX group. In a univariate model, there was a trend for PTX being associated with prolonged survival. The mortality was higher both among those at an advanced age and those with a high Charlson score. Adjustments for these covariates made the effect of PTX no more significant.

CONCLUSIONS

The risk of death of patients with severe SHPT leading to PTX differed from that of nonoperated subjects. The apparent differences in survival may be related to the number and severity of associated comorbidities. ESRD patients who undergo PTX may represent a subset of healthier subjects.

Minimizing bone abnormalities in children with renal failure

Renal osteodystrophy (ROD), a metabolic bone disease accompanying chronic renal failure (CRF), is a major clinical problem in pediatric nephrology. Growing and rapidly remodeling skeletal systems are particularly susceptible to the metabolic and endocrine disturbances in CRF. The pathogenesis of ROD is complex and multifactorial. Hypocalcemia, phosphate retention, and low levels of 1,25 dihydroxyvitamin D(3) related to CRF result in disturbances of bone metabolism and ROD. Delayed diagnosis and treatment of bone lesions might result in severe disability. Based on microscopic findings, renal bone disease is classified into two main categories: high- and low-turnover bone disease. High-turnover bone disease is associated with moderate and severe hyperparathyroidism. Low-turnover bone disease includes osteomalacia and adynamic bone disease. The treatment of ROD involves controlling serum calcium and phosphate levels, and preventing parathyroid gland hyperplasia and extraskeletal calcifications. Serum calcium and phosphorus levels should be kept within the normal range. The calcium-phosphorus product has to be <5 mmol(2)/L(2) (60 mg(2)/dL(2)). Parathyroid hormone (PTH) levels in children with CRF should be within the normal range, but in children with end-stage renal disease PTH levels should be two to three times the upper limit of the normal range. Drug treatment includes intestinal phosphate binding agents and active vitamin D metabolites. Phosphate binders should be administered with each meal. Calcium carbonate is the most widely used intestinal phosphate binder. In children with hypercalcemic episodes, sevelamer, a synthetic phosphate binder, should be introduced. In children with CRF, ergocalciferol (vitamin D(2)), colecalciferol (vitamin D(3)), and calcifediol (25-hydroxyvitamin D(3)) should be used as vitamin D analogs. In children undergoing dialysis, active vitamin D metabolites alfacalcidol (1alpha-hydroxy-vitamin D(3)) and calcitriol (1,25 dihydroxyvitamin D(3)) are applied. In recent years, a number of new drugs have emerged that hold promise for a more effective treatment of bone lesions in CRF. This review describes the current approach to the diagnosis and treament of ROD.

Bone mineral density and bone turnover markers in children with chronic renal failure

Bone mineral density (BMD) at lumbar spine (L2-L4) was measured by dual-energy X-ray absorptiometry (DEXA) in 21 children with predialysis chronic renal failure (CRF) and 44 children with end-stage renal failure (ESRF) on regular hemodialysis. BMD results were expressed as Z-scores. Osteopenia was documented in 13 predialysis patients (61.9%) and 26 patients (59.1%) with ESRF. No significant correlation was observed between Z-scores and the duration of CRF or estimated creatinine clearance. In osteopenic children there was a negative correlation between Z-scores and serum phosphorus (r=-0.61, P=0.004), intact parathyroid hormone (iPTH) (r=-0.47, P=0.03), and bone-specific alkaline phosphatase (r=-0.52, P=0.02) and a positive correlation with total calcium (r=0.41, P=0.07) and 25-hydroxycholecalciferol (r=0.53, P=0.02). Osteopenic children who had iPTH values > or = 200 pg/ml were more osteopenic than those who had lower iPTH levels (P=0.006). In conclusion, osteopenia, assessed by DEXA, is frequent in children with CRF. It occurs early irrespective of the duration or the severity of CRF. In children with ESRF the degree of osteopenia is correlated with laboratory markers of renal osteodystrophy and patients with biochemical findings of secondary hyperparathyroidism are more osteopenic than the others.

Prevalence and risk factors for osteopenia in dialysis patients

Dialysis patients are at risk for low bone mineral density (BMD) consequent of hyperparathyroidism, 1,25-dihydroxyvitamin D deficiency, previous immunosuppression, chronic acidosis, secondary amenorrhea, and chronic heparin and aluminum exposure. We wanted to determine the prevalence and distribution of osteopenia and the influence of risk factors for osteopenia in dialysis patients. Dual energy x-ray absorptiometry was used to record BMD at the lumbar spine (LS), hip, and nondominant forearm. Results were expressed as Z-scores (standard deviations from the mean of a healthy age- and gender-matched reference population). Osteopenia was defined as a Z-score worse than -2. In the 250 dialysis patients studied, the prevalence of osteopenia at the LS, femoral neck (FN) and ultradistal radius (UD) was 8%, 13% and 20%, respectively. The median Z-scores at these sites were all significantly different from the healthy reference population median of 0 and were 0.29 (P = 0.008), -0.67 (P < 0.001), and -1.01 (P < 0.001), respectively. Previous transplantation was associated with as much as a one Z-score lower BMD at the FN (P = 0.0069) and UD (P = 0.0011) and a marginally significant reduction at the LS (P = 0.0777). Previous parathyroidectomy was associated with a markedly higher LS BMD (P = 0.0001) and a higher BMD at the FN (P = 0.0017) but not the UD (P = 0.3691). A history of secondary amenorrhea was associated with a lower FN BMD (P = 0.0047) but not a significantly lower BMD at the LS (P = 0.0978) or UD (P = 0.2327). In hemodialysis patients without a history of transplantation, parathyroidectomy, or secondary amenorrhea, there was no correlation between Z-score at any site and duration of dialysis. Thus, osteopenia in dialysis patients occurs in both axial and appendicular sites and sites of compact and cancellous bone. It is more common with previous transplantation and secondary amenorrhea, whereas a history of parathyroidectomy is associated with increased BMD. No relationship was found between BMD and duration of hemodialysis, which suggests that important changes in BMD occur during the predialysis stage of chronic renal failure.