Reversal of adynamic bone disease by lowering of dialysate calcium

The Molecular Mechanisms Underlying the Systemic Effects Mediated by Parathormone in the Context of Chronic Kidney Disease

Chronic kidney disease (CKD) stands as a prominent non-communicable ailment, significantly impacting life expectancy. Physiopathology stands mainly upon the triangle represented by parathormone-Vitamin D-Fibroblast Growth Factor-23. Parathormone (PTH), the key hormone in mineral homeostasis, is one of the less easily modifiable parameters in CKD; however, it stands as a significant marker for assessing the risk of complications. The updated "trade-off hypothesis" reveals that levels of PTH spike out of the normal range as early as stage G2 CKD, advancing it as a possible determinant of systemic damage. The present review aims to review the effects exhibited by PTH on several organs while linking the molecular mechanisms to the observed actions in the context of CKD. From a diagnostic perspective, PTH is the most reliable and accessible biochemical marker in CKD, but its trend bears a higher significance on a patient's prognosis rather than the absolute value. Classically, PTH acts in a dichotomous manner on bone tissue, maintaining a balance between formation and resorption. Under the uremic conditions of advanced CKD, the altered intestinal microbiota majorly tips the balance towards bone lysis. Probiotic treatment has proven reliable in animal models, but in humans, data are limited. Regarding bone status, persistently high levels of PTH determine a reduction in mineral density and a concurrent increase in fracture risk. Pharmacological manipulation of serum PTH requires appropriate patient selection and monitoring since dangerously low levels of PTH may completely inhibit bone turnover. Moreover, the altered mineral balance extends to the cardiovascular system, promoting vascular calcifications. Lastly, the involvement of PTH in the Renin-Angiotensin-Aldosterone axis highlights the importance of opting for the appropriate pharmacological agent should hypertension develop.

Peritoneal dialysis fluids

There have been significant advances in the understanding of peritoneal dialysis (PD) in the last 40 years, and uptake of PD as a modality of kidney replacement therapy is increasing worldwide. PD fluids, therefore, remains the lifeline for patients on this treatment. Developing these fluids to be efficacious in solute clearance and ultrafiltration, with minimal adverse consequences to peritoneal membrane health and systemic effects is a key requirement. Since the first PD fluid produced in 1959, modifications to PD fluids have been made. Nonetheless, the search for that ideal PD fluid remains elusive. Understanding the components of PD fluids is a key aspect of optimizing the successful delivery of PD, allowing for individualized PD prescription. Glucose remains an integral component of PD fluids; however, its deleterious effects continue to be the impetus for the search of an alternative osmotic agent, and icodextrin remains the main alternative. More biocompatible PD fluids have been developed and have shown benefits in preserving residual kidney function. However, high cost and reduced accessibility remain deterrents to its widespread clinical use in many countries. Large-scale clinical trials are necessary and very much awaited to improve the narrow spectrum of PD fluids available for clinical use.

Study on the Effect of Low Calcium Dialysate on Biochemical Profile of Adynamic Bone Disease in Patients on Maintenance Hemodialysis

In recent years, adynamic bone disease (ABD) has become a common skeletal lesion in adult patients with chronic kidney disease. We aimed to compare the effects of low calcium dialysate (LCD) and standard calcium dialysate of our facility [high calcium dialysate (HCD)] on the evolution of bone and mineral parameter related to ABD in dialysis patients. Forty patients with predialysis intact parathyroid hormone (iPTH) <100 pg/mL and/or bone-specific alkaline phosphatase (BAP) <27 U/L were included in this study and were equally distributed over LCD (1.25 mmol/L) or HCD (1.75 mmol/L) treatment. The duration of the study was 6 months. There was no significant difference in baseline characters and biochemical parameters related to chronic kidney disease-mineral and bone disorder in both the groups. The groups did not differ in the mean tCa before dialysis, but this parameter was significantly lower in the LCD group versus HCD at the end of the study. The mean serum levels of iPTH, total alkaline phosphatase, and BAP in the LCD group were increased at 3 months and at the end of the study compared with the baseline levels. The bone markers in the HCD group did not change significantly. At the end of the study, all bone parameters in the LCD group were significantly higher than in the HCD group. Development of measures indicating increased bone turnover in patients receiving 1.25 mmol/L of dialysate calcium, most likely as a result of inhibiting a positive calcium balance and allowing for long-term PTH secretion stimulation. Hence, LCD might be considered a valuable therapeutic option for ABD patients.

A feasibility study of avoiding positive calcium balance and parathyroid hormone increase in patients on peritoneal dialysis

Background

The effect of the dialysate calcium concentration (D[Ca]) on mineral and bone metabolism in patients on peritoneal dialysis (PD) is overlooked. D[Ca] of 1.75 mmol/L is still prescribed to many patients on PD around the world. Previous studies on the effects of reducing D[Ca] have been carried out before the incorporation of calcimimetics in clinical practice. We hypothesized that a reduction in D[Ca] is safe and without the risk of a rise in serum parathyroid hormone (PTH).

Methods

In this non-randomized clinical trial, the D[Ca] was reduced from 1.75 mmol/L to 1.25 mmol/L for one year in prevalent patients on PD. Demographic, clinical, and CKD-MBD-related biomarkers were evaluated at baseline, 3, 6, and 12 months of follow-up.

Results

20 patients completed 1-year follow-up (56 ± 16 years, 50 % male, 25 % diabetic, 55 % with baseline parathyroid hormone – PTH >300 pg/mL). Over time, there was no significant change in calcium, phosphate, total alkaline phosphatase, 25(OH)-vitamin D or PTH, although adjustments in calcitriol and sevelamer prescription were required. After 1 year, absolute and percentual change in PTH levels were 36 (−58, 139) pg/mL, and 20 % (−28, 45) respectively. The proportion of patients with PTH > 300 pg/mL did not change during the follow-up (p = 0.173).

Conclusion

Knowing the risk of a positive calcium balance in patients on PD, reducing the D[Ca] concentration is a safe and valuable option, although medication adjustments are needed to detain PTH rising.

Is Adynamic Bone Always a Disease? Lessons from Patients with Chronic Kidney Disease

Renal osteodystrophy (ROD) is a common complication of end-stage kidney disease that often starts early with loss of kidney function, and it is considered an integral part in management of patients with chronic kidney disease (CKD). Adynamic bone (ADB) is characterized by suppressed bone formation, low cellularity, and thin osteoid seams. There is accumulating evidence supporting increasing prevalence of ADB, particularly in early CKD. Contemporarily, it is not very clear whether it represents a true disease, an adaptive mechanism to prevent bone resorption, or just a transitional stage. Several co-players are incriminated in its pathogenesis, such as age, diabetes mellitus, malnutrition, uremic milieu, and iatrogenic factors. In the present review, we will discuss the up-to-date knowledge of the ADB and focus on its impact on bone health, fracture risk, vascular calcification, and long-term survival. Moreover, we will emphasize the proper preventive and management strategies of ADB that are pivotal issues in managing patients with CKD. It is still unclear whether ADB is always a pathologic condition or whether it can represent an adaptive process to suppress bone resorption and further bone loss. In this article, we tried to discuss this hard topic based on the available limited information in patients with CKD. More studies are needed to be able to clearly address this frequent ROD finding.

Evaluation of Renal Osteodystrophy and Serum Bone-Related Biomarkers in a Peritoneal Dialysis Population

The spectrum of renal osteodystrophy (ROD) in peritoneal dialysis (PD) patients remains to be clarified. Ideal intact parathormone (iPTH) levels range is still not defined. The role of sclerostin, dickkopf-related protein 1, osteoprotegerin, and receptor activator for nuclear factor κB ligand for the diagnosis of ROD needs to be elucidated. In this cross-sectional study, tetracycline double-labeled bone biopsy was performed in 49 patients with histomorphometric analysis according Kidney Disease Improving Global Outcomes (KDIGO) guidelines. All patients were treated with biocompatible PD solutions, with calcium concentration of 1.25 mmol/L. Adynamic bone was the most frequent diagnosed pattern (42.9%) followed by hyperparathyroid-related bone disease (28.6%). Twenty-two percent of patients had normal bone. In patients with iPTH within the KDIGO recommended range for dialysis patients, adynamic bone was found in 59% of cases. Median (range) iPTH in patients with adynamic bone was 312 (60-631) pg/mL. Median (range) levels of sclerostin varied from 1511.64 (458.84-6387.70) pg/mL in patients with hyperparathyroid bone disease to 2433.1 (1049.59-11354.52) pg/mL in patients with adynamic bone. Sclerostin/iPTH ratio was the best marker of low turnover disease but iPTH performed best in the diagnosis of high turnover disease. Calcium mass transfer was positive in patients with low bone volume. Adynamic bone is the most frequent ROD pattern in contemporary PD. Our results suggest the need to review the iPTH target range for this population. The sclerostin/iPTH ratio showed improved performance compared to iPTH for the diagnosis of low turnover bone. © 2022 American Society for Bone and Mineral Research (ASBMR).

Adynamic bone disease: Revisited

The bone and mineral disorders form an integral part of the management of a chronic kidney disease (CKD) patient. Amongst various types of bone pathologies in chronic kidney disease-mineral bone disorder (CKD-MBD), the prevalence of adynamic bone disease (ABD) is increasing. The present review discusses the updated pathophysiology, risk factors, and management of this disorder.

Adynamic bone disease: Revisited

The bone and mineral disorders form an integral part of the management of a chronic kidney disease (CKD) patient. Amongst various types of bone pathologies in chronic kidney disease-mineral bone disorder (CKD-MBD), the prevalence of adynamic bone disease (ABD) is increasing. The present review discusses the updated pathophysiology, risk factors, and management of this disorder.

Osteoporosis in Patients with Chronic Kidney Diseases: A Systemic Review

Chronic kidney disease (CKD) is associated with the development of mineral bone disorder (MBD), osteoporosis, and fragility fractures. Among CKD patients, adynamic bone disease or low bone turnover is the most common type of renal osteodystrophy. The consequences of CKD-MBD include increased fracture risk, greater morbidity, and mortality. Thus, the goal is to prevent the occurrences of fractures by means of alleviating CKD-induced MBD and treating subsequent osteoporosis. Changes in mineral and humoral metabolism as well as bone structure develop early in the course of CKD. CKD-MBD includes abnormalities of calcium, phosphorus, PTH, and/or vitamin D; abnormalities in bone turnover, mineralization, volume, linear growth, or strength; and/or vascular or other soft tissue calcification. In patients with CKD-MBD, using either DXA or FRAX to screen fracture risk should be considered. Biomarkers such as bALP and iPTH may assist to assess bone turnover. Before initiating an antiresorptive or anabolic agent to treat osteoporosis in CKD patients, lifestyle modifications, such as exercise, calcium, and vitamin D supplementation, smoking cessation, and avoidance of excessive alcohol intake are important. Managing hyperphosphatemia and SHPT are also crucial. Understanding the complex pathogenesis of CKD-MBD is crucial in improving one's short- and long-term outcomes. Treatment strategies for CKD-associated osteoporosis should be patient-centered to determine the type of renal osteodystrophy. This review focuses on the mechanism, evaluation and management of patients with CKD-MBD. However, further studies are needed to explore more details regarding the underlying pathophysiology and to assess the safety and efficacy of agents for treating CKD-MBD.

Strategies for Phosphate Control in Patients With CKD

Hyperphosphatemia is a common complication in patients with chronic kidney disease (CKD), particularly in those requiring renal replacement therapy. The importance of controlling serum phosphate has long been recognized based on observational epidemiological studies that linked increased phosphate levels to adverse outcomes and higher mortality risk. Experimental data further supported the role of phosphate in the development of bone and cardiovascular diseases. Recent advances in our understanding of the mechanisms involved in phosphate homeostasis have made it clear that the serum phosphate concentration depends on a complex interplay among the kidneys, intestinal tract, and bone, and is tightly regulated by a complex endocrine system. Moreover, the source of dietary phosphate and the use of phosphate-based additives in industrialized foods are additional factors that are of particular importance in CKD. Not surprisingly, the management of hyperphosphatemia is difficult, and, despite a multifaceted approach, it remains unsuccessful in many patients. An additional issue is the fact that the supposedly beneficial effect of phosphate lowering on hard clinical outcomes in interventional trials is a matter of ongoing debate. In this review, we discuss currently available treatment approaches for controlling hyperphosphatemia, including dietary phosphate restriction, reduction of intestinal phosphate absorption, phosphate removal by dialysis, and management of renal osteodystrophy, with particular focus on practical challenges and limitations, and on potential benefits and harms.

Higher Proportion of Non-1-84 PTH Fragments in Peritoneal Dialysis Patients Compared to Hemodialysis Patients Using Solutions Containing 1.75 mmol/l Calcium

Background: The prevalence of low- turnover bone disease (LTBD) in peritoneal dialysis (PD) patients is higher than in hemodialysis (HD) patients. LTBD patients may be at risk for vascular calcification, and cardiovascular disease. Current therapy for chronic kidney disease metabolic bone disorders (CKD-MBD) is guided by biochemical parameters, as bone biopsy is not used in routine clinical care. Methods: We assessed intact PTH (iPTH: 1-84PTH plus non-1-84PTH), 1-84PTH, and the 1-84PTH/non-1-84PTH ratio in 129 hemodialysis and 73 PD prevalent patients dialyzed with solutions containing 1.75 mmol/L calcium. Results: Hemodialysis and PD patients presented similar iPTH and tCa values and prevalence of putative LTBD as defined according to KDOQI iPTH cut-off levels or 1-84 PTH levels. However, iCa accounted for a higher percentage of tCa in PD (53%) than in hemodialysis (39%) p < 0.001, and the 1-84PTH/non-1-84PTH ratio was lower in PD than in hemodialysis patients (0.44 ± 0.12) vs. (0.60 ± 0.10), p < 0.001. The prevalence of putative LTBD when using the coexistence of 1-84PTH/non-1-84PTH ratio < 1.0 and iPTH < 420 pg/m, was higher in PD than in hemodialysis patients (73 vs. 16% respectively, p < 0.001). In a multivariate logistic regression analysis, dialysis modality was the main determinant of the 1-84PTH/non-1-84PTH ratio. Conclusion: Solutions containing 1.75 mmol/L calciums are associated to a higher proportion of non-1-84PTH fragments in PD than in HD patients. Different analytical criteria result in widely different estimates of LTBD prevalence, thus impairing the ability of clinicians to optimize therapy for CKD-MBD.

Long-term effects of low calcium dialysates on the serum calcium levels during maintenance hemodialysis treatments: A systematic review and meta-analysis

Hypercalcemia and hyperparathyroidism in patients receiving maintenance hemodialysis (MHD) can cause the progression of cardiovascular diseases (CVD) and mineral bone disorders (MBD). The KDIGO recommends the dialysates with a calcium (Ca) concentration of 1.25–1.5 mmol/L for MHD treatments, but the optimal concentration remains controversial. Here, we conducted a systematic review and a meta-analysis of seven randomized controlled trials examining a total of 622 patients to investigate the optimal concentration for MHD for 6 months or longer. The dialysates with a low Ca concentration (1.125 or 1.25 mmol/L) significantly lowered the serum Ca and raised the intact parathyroid hormone levels by 0.52 mg/dL (95% confidence interval, 0.20–0.85) and 39.59 pg/mL (14.80–64.38), respectively, compared with a high Ca concentration (1.50 or 1.75 mmol/L). Three studies showed that a low concentration was preferred for lowering arterial calcifications or atherosclerosis in different arteries, but one study showed that coronary arterial calcifications increased with a low concentration. Two studies showed contradictory outcomes in terms of MBD. Our meta-analysis showed that a dialysate with a low Ca concentration lowered the serum Ca levels in patients receiving long-term MHD, but further studies are needed to determine the optimal Ca concentration in terms of CVD and MBD.

Dialysate Composition for Hemodialysis: Changes and Changing Risk

Dialysate composition is a critical aspect of the hemodialysis prescription. Despite this, trial data are almost entirely lacking to help guide the optimal dialysate composition. Often, the concentrations of key components are chosen intuitively, and dialysate composition may be determined by default based on dialysate manufacturer specifications or hemodialysis facility practices. In this review, we examine the current epidemiological evidence guiding selection of dialysate bicarbonate, calcium, magnesium, and potassium, and identify unresolved issues for which pragmatic clinical trials are needed.

Changing bone patterns with progression of chronic kidney disease

It is commonly held that osteitis fibrosa and mixed uremic osteodystrophy are the predominant forms of renal osteodystrophy in patients with chronic kidney disease. Osteitis fibrosa is a high-turnover bone disease resulting mainly from secondary hyperparathyroidism, and mixed uremic osteodystrophy is in addition characterized by a mineralization defect most often attributed to vitamin D deficiency. However, there is ancient and more recent evidence that in early chronic kidney disease stages adynamic bone disease characterized by low bone turnover occurs first, at least in a significant proportion of patients. This could be due to the initial predominance of bone turnover-inhibitory conditions such as resistance to the action of parathyroid hormone (PTH), reduced calcitriol levels, sex hormone deficiency, diabetes, and, last but not least, uremic toxins leading to repression of osteocyte Wnt/β-catenin signaling and increased expression of Wnt antagonists such as sclerostin, Dickkopf-1, and sFRP4. The development of high-turnover bone disease would occur only later on, when serum PTH levels are able to overcome peripheral PTH resistance and the other inhibitory factors of bone formation. Whether FGF23 and Klotho play a direct role in the transition from low- to high-turnover bone disease or participate only indirectly via regulating PTH secretion remains to be seen.

Calcium Mass Balance during Citrate Hemodialysis: A Randomized Controlled Trial Comparing Normal and Low Ionized Calcium Target Ranges

BACKGROUND

Regional citrate anticoagulation (RCA) during hemodialysis interferes with calcium homeostasis. Optimal ionized calcium (iCa) target range during RCA and consequent calcium balance are unknown.

METHODS

In a randomized controlled trial (ACTRN12613001029785) 30 chronic hemodialysis patients were assigned to normal (1.1-1.2 mmol/) or low (0.95-1.05 mmol/l) iCa target range during a single hemodialysis with RCA. The primary outcome was calcium mass balance during the procedure, using a partial spent dialysate collection method; magnesium mass balance was also measured. Intact parathormone (iPTH), total calcium (tCa) and magnesium were measured before and after procedures.

RESULTS

Mean iCa during procedures was significantly different in the two groups (1.12±0.06 in normal and 1.06±0.07 mmol/l in low iCa group, p <0.001), resulting in different tCa (2.18±0.22 vs. 1.95±0.17, p = 0.003) after the procedure. Mean delivered calcium during the procedure was 58.3±4.8 mmol in the normal and 51.5±8.2 mmol in the low iCa group (p = 0.010), which resulted in a significantly higher mean positive calcium mass balance of 14.6±8.3 mmol (584±333 mg) per procedure in normal as compared to 7.2±8.5 mmol (290±341 mg) in low iCa group (p = 0.024). Linear mixed effects model showed a significant interaction effect of time and iCa target range group on iPTH, i.e. a significant increase in iPTH in the low as compared to normal iCa target group (p = 0.008). Magnesium mass balance was mildly negative and comparable in both groups.

CONCLUSIONS

Low iCa target range resulted in a significantly less positive calcium mass balance, but in a significant increase in iPTH. To achieve a more neutral calcium balance, we recommend allowing a mild hypocalcemia during hemodialysis with RCA, especially when it is used for prolonged periods.

Management of adynamic bone disease in chronic kidney disease: A brief review

The Kidney Disease: Improving Global Outcomes (KDIGO) work group released recommendations in 2006 to define the bone-related pathology associated with chronic kidney disease as renal osteodystrophy. In 2009, KDIGO released revised clinical practice guidelines which redefined systemic disorders of bone and mineral metabolism due to chronic kidney disease as chronic kidney disease-mineral and bone disorders. Conditions under this overarching term include osteitis fibrosa cystica, osteomalacia, and adynamic bone disease. We aim to provide a brief review of the histopathology, pathophysiology, epidemiology, and diagnostic features of adynamic bone disease, focusing on current trends in the management of this complex bone disorder.

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.

Reduction of Dialysate Calcium Level Reduces Progression of Coronary Artery Calcification and Improves Low Bone Turnover in Patients on Hemodialysis

Exposure to high Ca concentrations may influence the development of low-turnover bone disease and coronary artery calcification (CAC) in patients on hemodialysis (HD). In this randomized, controlled study, we investigated the effects of lowering dialysate Ca level on progression of CAC and histologic bone abnormalities in patients on HD. Patients on HD with intact parathyroid hormone levels ≤300 pg/ml receiving dialysate containing 1.75 or 1.50 mmol/L Ca (n=425) were randomized to the 1.25-mmol/L Ca (1.25 Ca; n=212) or the 1.75-mmol/L Ca (1.75 Ca; n=213) dialysate arm. Primary outcome was a change in CAC score measured by multislice computerized tomography; main secondary outcome was a change in bone histomorphometric parameters determined by analysis of bone biopsy specimens. CAC scores increased from 452±869 (mean±SD) in the 1.25 Ca group and 500±909 in the 1.75 Ca group (P=0.68) at baseline to 616±1086 and 803±1412, respectively, at 24 months (P=0.25). Progression rate was significantly lower in the 1.25 Ca group than in the 1.75 Ca group (P=0.03). The prevalence of histologically diagnosed low bone turnover decreased from 85.0% to 41.8% in the 1.25 Ca group (P=0.001) and did not change in the 1.75 Ca group. At 24 months, bone formation rate, trabecular thickness, and bone volume were higher in the 1.25 Ca group than in the 1.75 Ca group. Thus, lowering dialysate Ca levels slowed the progression of CAC and improved bone turnover in patients on HD with baseline intact parathyroid hormone levels ≤300 pg/ml.

Adynamic bone disease: from bone to vessels in chronic kidney disease

Adynamic bone disease (ABD) is a well-recognized clinical entity in the complex chronic kidney disease (CKD)-mineral and bone disorder. Although the combination of low intact parathyroid hormone (PTH) and low bone alkaline phosphatase levels may be suggestive of ABD, the gold standard for precise diagnosis is histomorphometric analysis of tetracycline double-labeled bone biopsies. ABD essentially is characterized by low bone turnover, low bone volume, normal mineralization, and markedly decreased cellularity with minimal or no fibrosis. ABD is increasing in prevalence relative to other forms of renal osteodystrophy, and is becoming the most frequent type of bone lesion in some series. ABD develops in situations with reduced osteoanabolic stimulation caused by oversuppression of PTH, multifactorial skeletal resistance to PTH actions in uremia, and/or dysregulation of Wnt signaling. All may contribute not only to bone disease but also to the early vascular calcification processes observed in CKD. Various risk factors have been linked to ABD, including calcium loading, ageing, diabetes, hypogonadism, parathyroidectomy, peritoneal dialysis, and antiresorptive therapies, among others. The relationship between low PTH level, ABD, increased risk fracture, and vascular calcifications may at least partially explain the association of ABD with increased mortality rates. To achieve optimal bone and cardiovascular health, attention should be focused not only on classic control of secondary hyperparathyroidism but also on prevention of ABD, especially in the steadily growing proportions of diabetic, white, and elderly patients. Overcoming the insufficient osteoanabolic stimulation in ABD is the ultimate treatment goal.

Peritoneal dialysis per se is a risk factor for sclerostin-associated adynamic bone disease

Chronic kidney disease--mineral bone disorder (CKD-MBD) is a complex syndrome influenced by various factors, such as age, CKD etiology, uremic toxins, and dialysis modality. Although extensively studied in hemodialysis (HD) patients, only a few studies exist for peritoneal dialysis (PD) patients. Since most of these older studies contain no bone biopsy data, we studied the pattern of renal osteodystrophy in 41 prevalent PD patients. The most common presentation was adynamic bone disease (49%). There was a significant inverse association between serum sclerostin (a Wnt/β-catenin pathway inhibitor that decreases osteoblast action and bone formation) and the bone formation rate. Bone alkaline phosphatase had the best sensitivity and specificity to detect both high- and low-turnover diseases. The comparison between nondiabetic PD and HD patients, matched by age, gender, parathyroid hormone level, and length of dialysis, revealed low 25-hydroxyvitamin D levels, worse bone mineralization, and low bone turnover in the nondiabetic PD group. Thus, adynamic bone disease was the most frequent type of renal osteodystrophy in PD patients. Sclerostin seems to participate in the pathophysiology of adynamic bone disease and bone alkaline phosphatase was the best serum marker of bone turnover in these patients.

Bone histomorphometry before and after long-term treatment with cinacalcet in dialysis patients with secondary hyperparathyroidism

The multicenter, single-arm BONAFIDE study characterized the skeletal response to cinacalcet in adult dialysis patients with plasma parathyroid hormone (PTH) levels of 300 pg/ml or more, serum calcium of 8.4 mg/dl or more, bone-specific alkaline phosphatase over 20.9 ng/ml and biopsy-proven high-turnover bone disease. Of 110 enrolled patients, 77 underwent a second bone biopsy with quantitative histomorphometry after 6-12 months of cinacalcet treatment. The median PTH decreased from 985 pg/ml at baseline to 480 pg/ml at the end of study (weeks 44-52). Bone formation rate/tissue area decreased from 728 to 336 μm(2)/mm(2)/day, osteoblast perimeter/osteoid perimeter decreased from 17.4 to 13.9%, and eroded perimeter/bone perimeter decreased from 12.7 to 8.3%. The number of patients with normal bone histology increased from none at baseline to 20 at 12 months. Two patients had adynamic bone at the end of study with a PTH under 150 pg/ml, and one patient with overt hypophosphatemia at baseline that reoccurred during follow-up developed osteomalacia. Thus, long-term treatment with cinacalcet substantially reduced PTH, diminished the elevated bone formation rate/tissue area, lowered several biochemical markers of high-turnover bone disease toward normal, and generally improved bone histology. Twenty patients had normal bone histology at follow-up, whereas most had mild hyperparathyroidism or mixed uremic osteodystrophy.

Low calcium dialysate combined with CaCO3 in hyperphosphatemia in hemodialysis patients

This aim of this study was to observe the effects of the application of low calcium dialysate (LCD) combined with oral administration of CaCO3 in the treatment of hyperphosphatemia, as well as blood Ca2+, calcium-phosphate product (CPP), parathyroid hormone (PTH) and blood pressure in patients undergoing hemodialysis. Thirty-one maintenance hemodialysis (MHD) patients with hyperphosphatemia, but normal blood Ca2+, underwent dialysis with an initial dialy-sate Ca2+ concentration (DCa) of 1.50 mmol/l for six months and then with 1.25 mmol/l for six months. The patients who underwent dialysis with a DCa of 1.25 mmol/l were treated orally with 0.3 g CaCO3 tablets three times a day. In the third and sixth months [observation end point (OEP)] of the dialysis, the concentrations of Ca2+, phosphorus and intact PTH (iPTH) were measured; blood pressure and side-effects prior to and following dialysis were also observed. The Ca2+, CPP and iPTH levels increased (P<0.05) in the sixth month of treatment with a DCa of 1.50 mmol/l. However, the Ca2+ concentration declined to a certain degree, CPPs decreased significantly (P<0.05) and the iPTH concentration increased following treatment with a DCa of 1.25 mmol/l for six months. The incidence rate of adverse effects of LCD was 12.9% (4/31); the effects were mainly muscle spasms, hypotension and elevated PTH. The periodic application of LCD combined with the oral administration of CaCO3 effectively reduced serum phosphorus and CPPs among MHD patients with hyperphosphatemia, indicating that the treatment may be used clinically.

Insights into nutritional and inflammatory aspects of low parathyroid hormone in dialysis patients

In individuals with advanced chronic kidney disease, secondary hyperparathyroidism is known to be associated with high turnover bone disease. Low serum parathyroid hormone (PTH) levels may not necessarily be because of hypodynamic bone, but could be another facet of the malnutrition-inflammation-cachexia syndrome (MICS). A recent 5-year cohort study in 748 stable hemodialysis outpatients showed that after the confounding effect by the MICS was removed, the moderately low levels of PTH in the 100 to 150 pg/mL range was associated with the greatest survival rate. Data from Japanese dialysis patients show similar survival advantages of having a lower PTH range. Low levels of serum PTH seem to be associated with markers of protein-energy wasting and inflammation, and this association may confound the relationship between serum PTH and alkaline phosphatase. PTH stimulates lipogenesis through influx of calcium into the adipocytes. PTH secretion is suppressed by interleukin-1 beta and interleukin-6, which are proinflammatory cytokines that are associated with poor outcome in dialysis patients. These cytokines inhibits PTH secretion in cultured parathyroid tissue slices. In this article, we review the association of a low serum PTH level with the MICS in patients with chronic kidney disease and suggest avoiding over-interpretation of low serum PTH level as an indicator of low turnover bone disease.

Association of relatively low serum parathyroid hormone with malnutrition-inflammation complex and survival in maintenance hemodialysis patients

BACKGROUND

Low serum parathyroid hormone (PTH) has been implicated as a primary biochemical marker of adynamic bone disease in individuals with chronic kidney disease (CKD) who undergo maintenance hemodialysis (MHD) treatment. We hypothesized that the malnutrition-inflammation complex is associated with low PTH levels in these patients and confounds the PTH-survival association.

METHODS

We examined 748 stable MHD outpatients in southern California and followed them for up to 5 years (October 2001-December 2006).

RESULTS

In 748 MHD patients, serum PTH <150pg/mL was more prevalent among non-blacks and diabetics. There was no association between serum PTH and coronary artery calcification score, bone mineral density, or dietary protein or calorie intake. Low serum PTH was associated with markers of protein-energy wasting and inflammation, and this association confounded the relationship between serum PTH and alkaline phosphatase. Although 5-year crude mortality rates were similar across PTH increments, after adjustment for the case-mix and surrogates of malnutrition and inflammation, a moderately low serum PTH in 100-150pg/mL range was associated with the greatest survival compared to other serum PTH levels, i.e., a death hazard ratio of 0.52 (95% confidence interval: 0.29-0.92, p<0.001) compared to PTH of 300-600pg/mL (reference).

CONCLUSIONS

Low serum PTH may be another facet of the malnutrition-inflammation complex in CKD, and after controlling for this confounder, a moderately low PTH in 100-150pg/mL range appears associated with the greatest survival. Limitations of observational studies should be considered.

Can the combination of calcium and parathormone levels above K/DOQI guidelines be used as a marker of adynamic bone disease in African Americans?

BACKGROUND

Patients of African American descent are at risk for the development of adynamic bone disease at parathyroid hormone levels 50% above the K/DOQI guidelines. Since a low bone formation rate is associated with hypercalcemia, attempts to reach one K/DOQI guideline may result in serum calcium levels above another K/DOQI guideline. Calcium levels above K/DOQI guidelines therefore may signal a need to stop parathyroid suppression.

STUDY DESIGN

SETTING AND PARTICIPANTS

Bone biopsies were performed at the East Alabama Medical Center, in Opelika AL, USA on eight patients (four Caucasians, four African Americans) whose parathormone levels and serum calcium levels both exceeded K/DOQI guideline recommendations.

RESULTS

All patients had mild to severe hyperparathyroid bone disease. No variable studied was predictive of the finding.

LIMITATIONS

Small sample size and the unavailability of the original Nichols Diagnostic Institute radioimmunoassay for parathormone.

CONCLUSION

We did not find hypercalcemia predictive of adynamic bone in patients of African American descent at levels of parathormone where low bone formation rates have been documented to occur. Since no parameter predicted bone histology, perhaps bone biopsies will be necessary to distinguish hyperparathyroidism from adynamic bone disease in African Americans with ESRD, hypercalcemia, and moderately elevated levels of PTH. Further studies are needed to determine appropriate therapy.

Sevelamer and the bone-vascular axis in chronic kidney disease: bone turnover, inflammation, and calcification regulation

Hyperphosphatemia is a central characteristic feature of chronic kidney disease-mineral and bone disorder (CKD-MBD). Phosphorus excess is an independent cardiovascular risk factor for morbidity and mortality in patients with advanced CKD. Over the past 40 years, hyperphosphatemia has been a central therapeutic issue in advanced CKD. Mainstays of hyperphosphatemia treatment are reduction of dietary phosphorus, use of phosphate binders, and optimized phosphorus removal via dialysis. Currently, several phosphate binders are approved for use (aluminum, calcium, lanthanum, sevelamer); all share a common functionality in that they bind phosphorus and reduce the amount absorbed in the gastrointestinal lumen. Over the last decade, nephrologists have debated the relative tolerability and efficacy of these agents, especially the potential for vascular calcification and cardiovascular risk reduction. Recent research has focused on the question of whether a metal-free, calcium-free, and non-absorbed binder, such as sevelamer, offers advantages over other binder types. Most notable may be the potential benefit of reducing calcium load. In addition, sevelamer has several additional pleiotropic effects that may extend its basic indication, some of which may help attenuate vascular calcification. These include effects on bone turnover and the link between abnormal vascular processes and bone metabolism (the so-called 'bone-vascular axis'), as well as lipid metabolism, and systemic inflammatory mediators such as fetuin-A. We review the evidence for these pleiotropic effects, and suggest these may help in some way to improve the substantial disease burden in the CKD-MBD population.

Kidney disease outcomes quality initiative guidelines for bone and mineral metabolism: emerging questions

Since their initial publication in 2003, the National Kidney Foundation Kidney Disease Outcomes Quality Initiative clinical practice guidelines for bone and mineral metabolism have transformed the clinical approach to the management of metabolic bone disease in both dialysis and nondialysis chronic kidney disease patients. These guidelines largely were based on expert opinion rather than evidence. In the past 5 years, with the publication of several randomized controlled trials, large observational studies, and smaller clinical series, significant progress has been made in our understanding of mineral metabolism, calcium and phosphorus management, and the use of activated vitamin D irrespective of parathyroid hormone level in chronic kidney disease. More recently, fibroblast growth factor-23 and serum alkaline phosphatase have been shown to predict mortality in dialysis patients, making these attractive markers to monitor. In the wake of this progress, the bone Kidney Disease Outcomes Quality Initiative guidelines will need to be revised. Here, we review some of the issues and controversies that likely will form the basis of these revised guidelines.

Calcium metabolism in the early posttransplantation period

BACKGROUND AND OBJECTIVES

Information on the time course of serum calcium levels after renal transplantation is scanty, especially in the early posttransplantation period. Both the abrupt cessation of calcium-containing phosphorus binders and vitamin D (analogs) at the time of surgery and the recovery of renal function may be hypothesized to affect serum calcium levels in this period.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In this prospective observational study, biointact parathyroid hormone, calcidiol, calcitriol, calcium, and phosphorus levels were monitored in 201 renal transplant recipients at the time of transplantation and 3 mo thereafter. In addition, the serum calcium nadir and peak in each individual patient within this time frame were identified and the urinary fractional calcium excretion was determined at month 3.

RESULTS

Serum calcium levels followed a biphasic pattern with a significant decline during the first postoperative week, followed by a significant increase. High pretransplantation parathyroid hormone levels protect against hypocalcemia within the first postoperative week but put patients at risk for hypercalcemia later. These complications, occurring in 41 and 14% of the patients, respectively, most probably reflect inappropriate calcium release from the skeleton, rather than inappropriate renal calcium handling.

CONCLUSIONS

Our data indicate that both hypo- and hypercalcemia are prevalent in the early posttransplantation period. Pretransplantation parathyroid function is an important predictor of posttransplantation calcium levels.

Better preservation of residual renal function in peritoneal dialysis patients treated with a low-protein diet supplemented with keto acids: a prospective, randomized trial

BACKGROUND

While a low-protein diet may preserve residual renal function (RRF) in chronic kidney disease (CKD) patients before the start of dialysis, a high-protein intake is usually recommended in dialysis patients to prevent protein-energy wasting. Keto acids, which were often recommended to pre-dialysis CKD patients treated with a low-protein diet, had also been reported to be associated with both RRF and nutrition maintenance. We conducted a randomized trial to test whether a low-protein diet with or without keto acids would be safe and associated with a preserved RRF during peritoneal dialysis (PD).

METHODS

To assess the safety of low protein, we first conducted a nitrogen balance study in 34 incident PD patients randomized to receive in-centre diets containing 1.2, 0.9 or 0.6 g of protein/kg ideal body weight (IBW)/day for 10 days. Second, 60 stable PD patients [RRF 4.04 +/- 2.30 ml/ min/1.73 m(2), urine output 1226 +/- 449 ml/day, aged 53.6 +/- 12.8 years, PD duration 8.8 (1.5-17.8) months] were randomized to receive either a low- (LP: 0.6-0.8 g/kg IBW/day), keto acid-supplemented low- (sLP: 0.6-0.8 g/kg IBW/day with 0.12 g/kg IBW/day of keto acids) or high-protein (HP: 1.0-1.2 g/kg IBW/day) diet. The groups were followed for 1 year and RRF as well as nutritional status was evaluated serially.

RESULTS

A neutral or positive nitrogen balance was achieved in all three groups. RRF remained stable in group sLP (3.84 +/- 2.17 to 3.39 +/- 3.23 ml/min/1.73 m(2), P = ns) while it decreased in group LP (4.02 +/- 2.49 to 2.29 +/- 1.72 ml/min/1.73 m(2), P < 0.05) and HP (4.25 +/- 2.34 to 2.55 +/- 2.29 ml/min/1.73 m(2), P < 0.05). There was no change from baseline on nutritional status in any of the groups during follow-up.

CONCLUSIONS

A diet containing 0.6-0.8 g of protein/kg IBW/day is safe and, when combined with keto acids, is associated with an improved preservation of RRF in relatively new PD patients without significant malnutrition or inflammation.

Hypophosphatemic encephalopathy in a CAPD patient

Severe refeeding hypophosphatemia has been reported in infants and adults on continuous ambulatory peritoneal dialysis. We report an episode of transient encephalopathy and cardiac suppression in a diabetic, malnourished end-stage renal disease patient undergoing peritoneal dialysis with a glucose-based solution, which was associated with severe hypophosphatemia. Further investigation revealed an adynamic bone disease. The potential factors precipitating this episode of hypophosphatemia are discussed.

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.

Renal Osteodystrophy in Peritoneal Dialysis: Special Considerations

Bone disease is one of the most challenging complications in patients with chronic kidney disease. Today, it is considered to be part of a complex systemic disorder manifested by disturbances of mineral metabolism and vascular calcifications called chronic kidney disease – mineral bone disorder (CKD-MBD).

The term renal osteodystrophy is reserved to define the specific bone lesion in CKD-MBD, whose spectrum ranges from high turnover to low turnover disease. Phosphate retention, decreased serum calcium, and 1,25-dihydroxy vitamin D synthesis are involved in the pathogenesis of high bone turnover. However, the various therapeutic approaches (calcium supplements, phosphate binders, and vitamin D metabolites, among others), the renal replacement modality (hemodialysis or continuous ambulatory peritoneal dialysis), and the types of patients to whom dialysis is offered (more patients who are diabetic or older, or both) may influence the evolution of the bone disorder. As a result, recent studies have reported a greater prevalence of adynamic forms of renal osteodystrophy, especially in diabetic and peritoneal dialysis patients.

The present article reviews, for patients treated with peritoneal dialysis, the pathophysiologic mechanisms involved in the evolution and perpetuation of this bone disease and the therapeutic modalities for treating and preventing adynamic bone.

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.

Improvement of bone and mineral parameters related to adynamic bone disease by diminishing dialysate calcium

BACKGROUND

The existence of adynamic bone disease (ABD) as most prevalent form of renal osteodystrophy in recent years and its reduced ability to handle an exogenous calcium load has implied a higher risk for vascular and soft-tissue calcifications. The effect of low dialysate calcium (LCD) on parathyroid hormone (PTH) secretion in ABD patients has not yet sufficiently been clarified. This randomized, prospective study aimed to compare the effects of LCD and high calcium dialysate (HCD) on the evolution of bone and mineral parameters related to ABD in dialysis patients.

METHODS

52 out of 60 patients with predialysis intact PTH<100 pg/ml completed this study and were equally distributed over LCD (1.25 mmol/l) or HCD (1.75 mmol/l) treatment. The duration of the study was 6 months and the only peroral phosphate binder administered was calcium carbonate. Total and ionised calcium were measured monthly in serum before and after dialysis while serum parameters relevant to bone were measured at the enrollment and at 3-month intervals.

RESULTS

There were no differences in predialysis mean phosphate or calcium x phosphorus product (Ca x P). The most common side effects of both treatments were comparable. Hypotension occurred in 16% and 17% and cramps in 6% and 8% of the dialysis sessions, in the HCD and LCD group, respectively. The groups did not differ in the mean tCa before dialysis, but this parameter was significantly higher in the HCD group vs. LCD at the end of dialysis (2.59+/-0.18 vs. 2.44+/-0.19 mmol/l; p<0.01). The patients of the HCD group also had a significantly higher mean iCa both before (1.08+/-0.05 vs. 1.04+/-0.06 mmol/l; p=0.02) and at the end of dialysis (1.18+/-0.04 vs. 1.48+/-0.04 mmol/l; p<0.01). There were no differences within the LCD group between baseline and end of dialysis treatment values of tCa and iCa. However, the mean tCa and iCa were markedly increased at the end of dialysis in the HDC group [2.40+/-0.21 vs. 2.59+/-0.18 mmol/l (p<0.01); 1.08+/-0.05 vs. 1.18+/-0.04 mmol/l (p<0.01)]. Mean serum levels of iPTH and total alkaline phosphatase in the LCD group were increased at 3 months and at the end of the study compared with the baseline levels [(38.6+/-22.9 vs. 63.3+/-46.0 vs. 78.6+/-44.7 pg/ml); (59.5+/-18.7 vs. 75.9+/-26.7 vs. 84.0+/-35.4 U/l)], respectively, and bone alkaline phosphatase increased also only after 6 months of treatment (23.4+/-7.3 U/l vs. 35.6+/-22.3). The bone markers in the HCD group did not change. At the end of the study all bone parameters in the LCD group were significantly higher than in the HCD group.

CONCLUSION

There was an evolution towards parameters reflecting higher bone turnover in patients treated with dialysate calcium of 1.25 mmol/l, probably by prevention of a positive calcium balance and enabling sustained stimulation of PTH secretion. Hence, LCD might be considered a valuable therapeutic option for ABD 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.