Plasma total versus bone alkaline phosphatase as markers of bone turnover in hemodialysis patients

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.

In Hemodialysis Patients, Intradialytic Resistance Exercise Improves Osteoblast Function: A Pilot Study

OBJECTIVE

Abnormalities in mineral and bone metabolism are frequent in chronic kidney disease patients. Physical exercise can improve many indicators of physical functioning, and recent studies showed beneficial effects on bone mineral density in the general population. The aim of this study was to evaluate the effects of resistance exercise training on bone markers and body composition in hemodialysis (HD) patients.

DESIGN

This was a randomized controlled trial.

SUBJECTS

The study included 13 HD patients (46.2% men).

INTERVENTION

Patients were divided into a control group and an exercise group, which performed 8 weeks of intradialytic resistance exercise. Serum sclerostin, bone alkaline phosphatase (BAP), insulin, leptin, 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D, and body composition were measured before and after the exercise period.

RESULTS

In the exercise group, BAP levels increased from 11.4 ± 6.5 to 14.6 ± 6.4 U/L (P < .05) and serum 1,25-dihydroxyvitamin D levels from 46.0 ± 23.5 to 87.2 ± 31.8 ng/mL (P < .05). After exercise, serum BAP levels were inversely correlated with serum sclerostin (r = -0.96, P < .05). There was no change in body composition in either group.

CONCLUSION

Resistance exercise training appears to be an interesting approach for stimulating BAP production in HD patients and may prevent bone loss and stimulate bone formation.

Total and bone-specific alkaline phosphatase are associated with bone mineral density over time in end-stage renal disease patients starting dialysis

BACKGROUND

Alkaline phosphatase (ALP) and bone-specific ALP (BALP) are implicated in the abnormal skeletal mineralization and accelerated vascular calcification in chronic kidney disease (CKD) patients. Whereas ALP and BALP may predict mortality in CKD, BALP is reported to have higher sensitivity and specificity than total ALP in reflecting histological alterations in bone; however, results on their associations with bone mineral density (BMD) are inconsistent. Here we evaluated associations of total ALP and BALP with BMD during up to 24 months in end-stage renal disease (ESRD) patients.

METHODS

In this longitudinal study, 194 ESRD patients (median age 57 years, 66 % male, 32 % diabetes mellitus, mean body mass index 24.8 kg/m²) underwent measurements of total ALP and BALP and total and regional body BMD (by dual-energy X-ray absorptiometry) at dialysis initiation (n = 194), and after 12 (n = 98) and 24 months (n = 40) on dialysis.

RESULTS

At baseline, patients had median total ALP 65.4 (43.3-126.4) U/l, BALP 13.5 (7.1-27.3) µg/l and BMD 1.14 (0.97-1.31) g/cm². During the study period, serum concentrations of ALP and BALP increased significantly (p < 0.001), whereas total and regional BMD remained stable. BMD correlated inversely with total ALP (rho = -0.20, p = 0.005) and BALP (rho = -0.30, p < 0.001) at baseline, and correlations were similar also at 12 and 24 months.

CONCLUSION

ALP and BALP are equally accurate albeit weak predictors of BMD in ESRD patients, both at baseline and longitudinally. The dissociation between stable BMD and increasing ALP and BALP may possibly reflect increased soft tissue calcifications with time on dialysis.

Serum Parathyroid Hormone Concentrations and Clinical Outcomes in ESRD: A Call for Targeted Clinical Trials

Secondary hyperparathyroidism almost universally accompanies end-stage renal disease (ESRD). In some, but not all studies, elevated serum parathyroid hormone (PTH) concentrations are associated with increased fracture rates, cardiovascular disease, and mortality in ESRD. The serum concentration of PTH required for optimal bone health and reduced cardiovascular risk in such patients remains elusive. Recent clinical trials have failed to show substantial changes in morbidity and mortality following reductions of elevated serum PTH concentrations. In this review, we will assess some of the difficulties in evaluating elevated serum PTH concentrations, and their association with skeletal fractures and mortality in ESRD patients. We are of the opinion that in the context of ESRD, elevated PTH concentrations occur in conjunction with other comorbid conditions such as diabetes mellitus, malnutrition, hypertension, volume excess, preexisting heart disease, all of which have prevented establishing a precise association between elevated serum PTH concentrations and global or skeletal outcomes. Age, gender, and racial variability among groups make interpretation exceptionally difficult. Analysis of prevalent ESRD populations with secondary hyperparathyroidism should take all these factors into account. We suggest that future clinical trials which examine the usefulness of reductions in serum PTH concentrations be conducted in age, sex, and racially balanced groups, without or with minimal coexisting confounding disease. Furthermore, trials in such populations should have as their primary outcome a reduction in fractures rather than an alteration in mortality.

Fifty shades of gray: Bone disease in renal transplantation

Kidney transplantation is the renal replacement therapy of choice for patients with end stage renal disease. Advances in technology, surgical techniques and pharmacotherapy have improved renal allograft survival. Increasingly, we are seeing long term side effects related to renal transplantation, bone disease being a major one amongst them. Renal transplant patients have a higher risk of fragility fractures even when compared to those who remain on dialysis. This is likely to be related to pre-existing underlying bone disease and the emergence of new metabolic bone problems post-transplant. Conditions such as persistent hyperparathyroidism and the use of certain immunosuppressive agents have a deleterious effect on the post renal transplant bone.

Remarkable advances in the field of metabolic bone research have been made in the last decade and newer imaging techniques, biomarkers and therapeutic options are now available for osteoporosis in the general population. Interest is being focused on attempting to extrapolate these new discoveries to the management of bone disease post renal transplant. This review will briefly describe the metabolic bone changes that occur after transplantation and will provide an update on the currently available investigative options and therapeutic strategies for the management of post renal transplant bone disease.

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.

Bone alkaline phosphatase isoforms in hemodialysis patients with low versus non-low bone turnover: a diagnostic test study

BACKGROUND

Renal osteodystrophy encompasses the bone histologic abnormalities seen in patients with chronic kidney disease (CKD). The bone-specific alkaline phosphatase (bALP) isoform B1x is exclusively found in serum of some patients with CKD.

STUDY DESIGN

The aim of this cross-sectional diagnostic test study was to examine the relationship between serum bALP isoform activity and histomorphometric parameters of bone in patients with CKD receiving maintenance hemodialysis.

SETTINGS & PARTICIPANTS

Anterior iliac crest bone biopsy samples from 40 patients with CKD were selected on the basis of bone turnover for histomorphometric analysis. There were samples from 20 patients with low and 20 with non-low bone turnover.

INDEX TEST

In serum, bALP, bALP isoforms (B/I, B1x, B1, and B2), and parathyroid hormone (PTH) were measured.

REFERENCE TEST

Low bone turnover was defined by mineral apposition rate < 0.36μm/d. Non-low bone turnover was defined by mineral apposition rate ≥ 0.36μm/d.

OTHER MEASUREMENTS

PTH.

RESULTS

B1x was found in 21 patients (53%) who had lower median levels of bALP, 18.6 versus 46.9U/L; B/I, 0.10 versus 0.22 μkat/L; B1, 0.40 versus 0.88 μkat/L; B2, 1.21 versus 2.66 μkat/L; and PTH, 49 versus 287pg/mL, compared with patients without B1x (P<0.001). 13 patients (65%) with low bone turnover and 8 patients (40%) with non-low bone turnover (P<0.2) had detectable B1x. B1x correlated inversely with histomorphometric parameters of bone turnover. Receiver operating characteristic curves showed that B1x can be used for the diagnosis of low bone turnover (area under the curve [AUC], 0.83), whereas bALP (AUC, 0.89) and PTH (AUC, 0.85) are useful for the diagnosis of non-low bone turnover.

LIMITATIONS

Small number of study participants. Requirement of high-performance liquid chromatography methods for measurement of B1x.

CONCLUSIONS

B1x, PTH, and bALP have similar diagnostic accuracy in distinguishing low from non-low bone turnover. The presence of B1x is diagnostic of low bone turnover, whereas elevated bALP and PTH levels are useful for the diagnosis of non-low bone turnover.

Markers of bone metabolism are affected by renal function and growth hormone therapy in children with chronic kidney disease

Objectives

The extent and relevance of altered bone metabolism for statural growth in children with chronic kidney disease is controversial. We analyzed the impact of renal dysfunction and recombinant growth hormone therapy on a panel of serum markers of bone metabolism in a large pediatric chronic kidney disease cohort.

Methods

Bone alkaline phosphatase (BAP), tartrate-resistant acid phosphatase 5b (TRAP5b), sclerostin and C-terminal FGF-23 (cFGF23) normalized for age and sex were analyzed in 556 children aged 6–18 years with an estimated glomerular filtration rate (eGFR) of 10–60 ml/min/1.73m². 41 children receiving recombinant growth hormone therapy were compared to an untreated matched control group.

Results

Standardized levels of BAP, TRAP5b and cFGF-23 were increased whereas sclerostin was reduced. BAP was correlated positively and cFGF-23 inversely with eGFR. Intact serum parathormone was an independent positive predictor of BAP and TRAP5b and negatively associated with sclerostin. BAP and TRAP5B were negatively affected by increased C-reactive protein levels. In children receiving recombinant growth hormone, BAP was higher and TRAP5b lower than in untreated controls. Sclerostin levels were in the normal range and higher than in untreated controls. Serum sclerostin and cFGF-23 independently predicted height standard deviation score, and BAP and TRAP5b the prospective change in height standard deviation score.

Conclusion

Markers of bone metabolism indicate a high-bone turnover state in children with chronic kidney disease. Growth hormone induces an osteoanabolic pattern and normalizes osteocyte activity. The osteocyte markers cFGF23 and sclerostin are associated with standardized height, and the markers of bone turnover predict height velocity.

Impact of the uremic milieu on the osteogenic potential of mesenchymal stem cells

Human mesenchymal stem cells (hMSCs), the precursors of osteoblasts during osteogenesis, play a role in the balance of bone formation and resorption, but their functioning in uremia has not been well defined. To study the effects of the uremic milieu on osteogenic properties, we applied an in vitro assay culturing hMSCs in osteogenic medium supplemented with serum from healthy donors and from uremic patients on hemodialysis. Compared to control, serum from uremic patients induces, in hMSC cultures, a modification of several key regulators of bone remodeling, in particular a reduction of the ratio Receptor Activator of Nuclear factor Kappa B Receptor (RANKL) over osteoprotegerin, indicating an adaptive response of the system to favor osteogenesis over osteoclastosis. However, the levels of osteopontin, osteocalcin, and collagen type I, are increased in cell medium, while BMP-2, and alizarin red staining were decreased, pointing to a reduction of bone formation favoring resorption. Selected uremic toxins, such as p-cresylsulfate, p-cresylglucuronide, parathyroid hormone, indoxyl sulfate, asymmetric dimethylarginine, homocysteine, were able to mimic some of the effects of whole serum from uremic patients. Serum from cinacalcet-treated patients antagonizes these effects. Hydrogen sulfide (H2S) donors as well as hemodialysis treatment are able to induce beneficial effects. In conclusion, bone modifications in uremia are influenced by the capability of the uremic milieu to alter hMSC osteogenic differentiation. Cinacalcet, H2S donors and a hemodialysis session can ameliorate the hampered calcium deposition.

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.

News on biomarkers in CKD-MBD

The increased awareness of the potential role played by mineral and bone disorder in the appearance of cardiovascular disease in renal patients has produced research efforts aimed at discovering possible pathogenic links. Accordingly, the diagnostic significance of the classic bone markers of mineral disorders and of the new markers in the setting of chronic kidney disease-mineral and bone disorders (CKD-MBD) needs to be re-evaluated along with increasing information. In this article we include classic markers of bone metabolism and some of the noncollagenous bone proteins that are gaining experimental and clinical significance in CKD-MBD. Among classic markers of secondary hyperparathyroidism and of renal osteodystrophy, we analyzed parathyroid hormone, alkaline phosphatase, tartrate-resistant acid phosphatase, and bone collagen-derived peptides. We underlined, for each, the relevance of parent proteins (peptides or isoforms) that affect assay methods and, eventually, the diagnostic or prognostic significance. Also, we considered their relationship with cardiovascular mortality. Among the numerous noncollagenous bone proteins, we examined matrix Gla protein (MGP), osteocalcin (OC), osteoprotegerin, and the small integrin-binding ligand N-linked glycoprotein family. For MGP and OC we report the relevant involvement with the process of calcification (MGP) and with glucose and energy metabolism (OC). Both of these proteins require vitamin K to become active and this is a specific problem in renal patients who frequently are deficient of this vitamin. Finally, recent acquisitions on the fascinating family of the small integrin-binding ligand N-linked glycoprotein proteins are recapitulated briefly to underline their potential clinical interest and their complex involvement with all aspects of CKD-MBD. Their diagnostic role in clinical practice awaits further studies.

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.

Effect of zinc supplementation on bone formation in hemodialysis patients with normal or low turnover bone

Zinc (Zn) is an essential trace element, which has been shown to stimulate osteoblastic bone formation and to inhibit osteoclastic bone resorption in vitro. In thalassemia, major patients Zn supplementation was reported to increase whole-body bone mineral content and areal bone mineral density. Therefore, we investigated the effect of Zn supplementation on bone formation in hemodialysis (HD) patients. Nine male patients with age of 66 (35-78) years indicated by median (range), HD vintage of 57 (4-97) months and serum intact parathyroid hormone (PTH) of 113 (6-310) pg/mL were supplemented with polaprezinc containing 34 mg Zn/day for 18 months. Doses of vitamin D were not changed during supplementation. Blood was collected at baseline, 3, 6, 12 and 18 months. Serum Zn increased significantly from 58 (52-65) μg/dL to 71 (57-93) μg/dL at three months and remained unchanged until 18 months. No changes were observed in serum intact PTH during supplementation. Although we found no changes in serum bone alkaline phosphatase (BAP) during Zn supplementation analyzed by Friedman test and Scheffe post hoc test, a significant trend of increase in serum BAP was verified by Jonckheere-Terpstra test (p = 0.0409). On the contrary, there was no trend in serum TRACP5b by Jonckheere-Terpstra test. Therefore, we suggested the effect of Zn supplementation on promoting bone formation, not affected by the status of PTH and vitamin D, in HD patients with normal or low turnover bone.

Inter-method variability in bone alkaline phosphatase measurement: clinical impact on the management of dialysis patients

BACKGROUND

Bone-specific alkaline phosphatase (BAP) is now recommended to assess bone turnover in hemodialysis (HD) patients. However, little is known about potential variability between methods available to measure BAP.

METHODS

We measured BAP in 76 HD patients with six different assays (Beckman-Coulter Ostase IRMA, Beckman-Coulter Ostase Access, IDS iSYS Ostase, IDS Ostase enzyme immunoassay, DiaSorin Liaison Ostase and Quidel MicroVue BAP).

RESULTS

We observed a high correlation between all the assays ranging from 0.9948 (IDS iSYS vs. IDS EIA) to 0.9215 (DiaSorin Liaison vs. Quidel MicroVue). However, using the regression equations, the equivalent concentration of a Beckman-Coulter Access value of 10 μg/L can range from 7.7 to 14.4 μg/L and of 20 μg/L can range from 16.9 to 27.9 μg/L with other assays. According to Beckman-Coulter Access, 13%, 50% and 37% of the patients presented BAP values ≤10, between 10 and 20 and ≥20 μg/L, respectively. Discrepancies are observed when other assays are used (concordance from 10 to 100%).

CONCLUSIONS

Analytical problems leading to inter-method variation should be overcome to improve the usefulness of this marker in clinical practice. According to correlation results, recalibration of BAP assays is necessary but should not be a major issue.

Calcitriol resistance in hemodialysis patients with secondary hyperparathyroidism

Nonselective vitamin D receptor activators (VDRA), such as calcitriol and alfacalcidol, have been successfully used in the treatment of secondary hyperparathyroidism (SHPT) in hemodialysis. Despite their beneficial effects on the control of serum PTH levels, their use has been limited by intolerance (development of hypercalcemia and hyperphosphatemia with consecutive cardiovascular toxicity). Apart from becoming intolerant, in 20-30 % of patients who use nonselective VDRA, serum PTH levels do not decrease appropriately despite increasing doses of these agents. These patients are considered calcitriol-resistant patients. Thus, calcitriol resistance and intolerance are two sides of the same coin: active vitamin D failure. Despite the clinical relevance of active vitamin D failure, definitions of resistance and intolerance are imprecise and have varied over time. More selective VDRA claim to produce less hypercalcemia and hyperphosphatemia and could help clinicians to overcome intolerance. Also, some studies have also shown that paricalcitol can be even useful in resistant patients. Significant limitations of iPTH as a reliable and useful clinical biomarker have been increasingly appreciated. There is evidence that intact PTH concentration must differ by 72 % between any two measurements before it can be considered a significant change. VDR polymorphisms could be involved in the development of SHPT in CKD patients. Interestingly, a higher incidence of the b allele of the VDR BsmI gene variant has been shown to be present in SHPT. The BsmI genotype can also affect the response of hemodialysis to IV calcitriol. A challenge for the future will be to establish biomarkers such as laboratory determinations or ultrasound findings that can help us to early identify those patients who will not respond appropriately to calcitriol or exhibit intolerable side effects .

Comparative mortality-predictability using alkaline phosphatase and parathyroid hormone in patients on peritoneal dialysis and hemodialysis

BACKGROUND

In hemodialysis (HD) patients, serum alkaline phosphatase (ALP) and parathyroid hormone (PTH) derangements are associated with mortality, but outcome-predictability using ALP and PTH in peritoneal dialysis (PD) patients remains uncertain.

METHODS

In a cohort of 9244 adult PD patients from a large national dialysis organization (entry period 2001 - 2006, with follow-up through 2009), we used multivariable Cox models adjusted for case-mix and laboratory covariates to examine the associations of time-averaged ALP and PTH with all-cause mortality. We then compared mortality-predictability using ALP and PTH in 9244 PD and 99 323 HD patients.

RESULTS

In PD patients, ALP concentrations exceeding 150 U/L were associated with increased mortality (reference ALP: 70 to <90 U/L). Hazard ratios (HRs) and 95% confidence intervals (CIs) were 1.18 (1.03 to 1.36), 1.27 (1.08 to 1.50), 1.49 (1.23 to 1.79), and 1.35 (1.19 to 1.53) for ALP concentrations of 150 to <170 U/L, 170 to <190 U/L, 190 to <210 U/L, and ≥210 U/L respectively. In contrast, we observed a U-shaped association between PTH concentration and death risk in PD patients, with PTH concentrations of less than 200 pg/mL and 700 pg/mL or more associated with increased mortality (reference PTH: 200 to <300 pg/mL). Hazard ratios and 95% CIs were 1.25 (1.12 to 1.41), 1.12 (1.02 to 1.23), 1.06 (0.96 to 1.18), 1.09 (0.97 to 1.24), 1.12 (0.97 to 1.29), 1.18 (0.99 to 1.40), and 1.23 (1.09 to 1.38) for PTH concentrations of <100 pg/mL, 100 to <200 pg/mL, 300 to <400 pg/mL, 400 to <500 pg/mL, 500 to <600 pg/mL, 600 to <700 pg/mL, and ≥700 pg/mL respectively. Compared with PD patients having serum concentrations of ALP and PTH within reference ranges, patients on HD experienced increased mortality across all ALP and PTH concentrations, particularly those in the lowest and highest categories.

CONCLUSIONS

In summary, higher ALP concentrations are associated with increased mortality, and lower and higher PTH concentrations are both associated with death risk in PD patients. The utility of ALP in the management of chronic kidney disease mineral bone disorders in PD patients warrants further study.

Bisphophonates in CKD patients with low bone mineral density

Patients with chronic kidney disease-mineral and bone disorder (CKD-MBD) have a high risk of bone fracture because of low bone mineral density and poor bone quality. Osteoporosis also features low bone mass, disarranged microarchitecture, and skeletal fragility, and differentiating between osteoporosis and CKD-MBD in low bone mineral density is a challenge and usually achieved by bone biopsy. Bisphosphonates can be safe and beneficial for patients with a glomerular filtration rate of 30 mL/min or higher, but prescribing bisphosphonates in advanced CKD requires caution because of the increased possibility of low bone turnover disorders such as osteomalacia, mixed uremic osteodystrophy, and adynamic bone, even aggravating hyperparathyroidism. Therefore, bone biopsy in advanced CKD is an important consideration before prescribing bisphosphonates. Treatment also may induce hypocalcemia in CKD patients with secondary hyperparathyroidism, but vitamin D supplementation may ameliorate this effect. Bisphosphonate treatment can improve both bone mineral density and vascular calcification, but the latter becomes more unlikely in patients with stage 3-4 CKD with vascular calcification but no decreased bone mineral density. Using bisphosphonates requires considerable caution in advanced CKD, and the lack of adequate clinical investigation necessitates more studies regarding its effects on these patients.

Elevation in Serum Concentration of Bone-Specific Alkaline Phosphatase without Elevation in Serum Creatinine Concentration Secondary to Adefovir Dipivoxil Therapy in Chronic Hepatitis B Virus Infection

Of 168 patients with chronic hepatitis B virus (HBV) infection-related liver disease, 20 patients who had received 100 mg of lamivudine plus 10 mg/day of adefovir dipivoxil (ADV) (ADV group) and 124 patients who had received 0.5 mg/day of entecavir or 100 mg/day of lamivudine (non-ADV group) for >1 year were enrolled. For comparative analyses, 19 well-matched pairs were obtained from the groups by propensity scores. At the time of enrollment, serum creatinine and phosphate concentrations were similar between the ADV and non-ADV groups; however, urinary phosphate (P = 0.0424) and serum bone-specific alkaline phosphatase (BAP) (P = 0.0228) concentrations were significantly higher in the ADV group than in the non-ADV group. Serum BAP was significantly higher at the time of enrollment than before ADV administration in the ADV group (P = 0.0001), although there was no significant change in serum BAP concentration in the non-ADV group. There was a significant positive correlation between the period of ADV therapy and ΔBAP (R (2) = 0.2959, P = 0.0160). Serum BAP concentration increased before increase in serum creatinine concentration and was useful for early detection of adverse events and for developing adequate measures for continuing ADV for chronic HBV infection-related liver disease.

Women and CKD-mineral and bone disorder

Development of CKD-mineral and bone disorder (MBD) increases morbidity and mortality in men and women with CKD. The corresponding link among bone disease, fracture, and extraskeletal calcifications has been the subject of much focus. In the general population, the incidence of cardiovascular disease is higher in men than women, and this gender differences in degree of calcification and morbidity is maintained in kidney disease. Gender differences in phosphorus and fibroblast growth factor-23 (FGF-23) have been described. Increases in both have been linked with increasing likelihood of death in the CKD population as a whole; however, this link is not as well described when looking at women alone. The clinical significance of these differences, and the potential associated outcomes, are poorly understood. Traditional understanding of bone disease in women without kidney disease may not be fully applicable in women with CKD. Use of bone densitometry is limited in this population, and the traditional preventative interventions may not be fully transferrable to women with CKD.

Recent advances in the noninvasive diagnosis of renal osteodystrophy

Chronic kidney disease-mineral and bone disorder (CKD-MBD) is the term used to describe a constellation of biochemical abnormalities, bone disturbances that may lead to fractures, and extraskeletal calcification in soft tissues and arteries seen in CKD. This review focuses on the noninvasive diagnosis of renal osteodystrophy, the term used exclusively to define the bone pathology associated with CKD. Transiliac bone biopsy and histomorphometry with double-labeled tetracycline or its derivatives remains the gold standard for diagnosis of renal osteodystrophy. However, histomorphometry provides a 'window' into bone only at a single point in time, and is not clinically practical for studying continuous changes in bone morphology. Furthermore, the etiology of fractures in CKD is multifactorial and not fully explained by histomorphometry findings alone. The propensity of a bone to fracture is determined by bone strength, which is affected by bone mass and bone quality; the latter is a term used to describe the structure and composition of bone. Bone quantity is traditionally assessed by dual X-ray absorptiometry (DXA) and CT-based methods. Bone quality is more difficult to assess noninvasively, but newer techniques are emerging and are described in this review. Ultimately, the optimal diagnostic strategy for renal osteodystrophy may be a combination of multiple imaging techniques and biomarkers that are specific to each gender and race in CKD, with a goal of predicting fracture risk and optimizing therapy.

A comparison of calcium acetate/magnesium carbonate and sevelamer-hydrochloride effects on fibroblast growth factor-23 and bone markers: post hoc evaluation from a controlled, randomized study

BACKGROUND

Different phosphate binders exert differing effects on bone mineral metabolism and levels of regulating hormones. The objective of this post hoc evaluation of the CALcium acetate MAGnesium carbonate (CALMAG) study was to compare the effects of calcium acetate/magnesium carbonate (CaMg) and a calcium-free phosphate binder, sevelamer-hydrochloride (HCl), on serum levels of fibroblast growth factor-23 (FGF-23) and markers of bone turnover.

METHODS

This secondary analysis of the controlled, randomized CALMAG study, comparing the effect of CaMg and sevelamer-HCl on serum phosphorus (P), aimed to investigate the parameters described above. The analysis included 204 patients who completed the initial study per protocol (CaMg, n = 105; sevelamer-HCl, n = 99).

RESULTS

The study showed that serum levels of FGF-23 were significantly reduced with CaMg and sevelamer-HCl, with no difference between groups at Week 25 [analysis of covariance (ANCOVA); log-intact FGF-23 (iFGF-23), P = 0.1573]. FGF-23 levels strongly correlated with serum P levels at all time points in both groups. The bone turnover parameters alkaline phosphatase (AP), bone AP (BAP), procollagen type 1 amino-terminal propeptide 1 (P1NP), osteoprotegerin (OPG), beta-crosslaps (β-CTX) and tartrate-resistant acid phosphatase 5b (TRAP 5b) increased significantly in the sevelamer-HCl group; they remained almost unchanged in the CaMg group, after the initial phase of P lowering (ANCOVA, P < 0.0001 for all except OPG, P = 0.1718).

CONCLUSIONS

CaMg and sevelamer-HCl comparably lower serum levels of iFGF-23. Changes in bone parameters were dependent on characteristics of the phosphate binder; in contrast with sevelamer-HCl, CaMg had no influence on bone turnover markers.

Bone alkaline phosphatase in CKD-mineral bone disorder

Overall and cardiovascular mortality in patients with chronic kidney disease (CKD) is greatly increased, without obvious current effective treatments. Mineral and bone disorder (MBD) is a common manifestation of CKD and contributes to the high risk of fracture and cardiovascular mortality in these patients. Traditionally, clinical management of CKD-MBD focused on attenuation of secondary hyperparathyroidism due to impaired renal activation of vitamin D and phosphate retention, although recently, adynamic forms of renal bone disease have become more prevalent. Definitive diagnosis was based on histologic (histomorphometric) analysis of bone biopsy material supported by radiologic changes and changes in levels of surrogate laboratory markers. Of these various markers, parathyroid hormone (PTH) has been considered to be the most sensitive and currently is the most frequently used; however, the many pitfalls of measuring PTH in patients with CKD increasingly are appreciated. We propose an alternative or complementary approach using bone alkaline phosphatase (ALP), which is directly related to bone turnover, reflects bone histomorphometry, and predicts outcomes in hemodialysis patients. Here, we consider the overall merits of bone ALP as a marker of bone turnover in adults with CKD-MBD, examine published bone histomorphometric data comparing bone ALP to PTH, and discuss possible pathogenic mechanisms by which bone ALP may be linked to outcomes in patients with CKD.

Risk factors for diminished bone mineral density among male hemodialysis patients--a cross-sectional study

This cross-sectional study was performed to characterize the factors affecting bone mass in male hemodialysis subjects. We found that of all the factors analyzed, the strongest correlation was with body mass index. In fact, after adjusting for body weight, the correlations with bone turnover markers and sex hormones were no longer significant.

PURPOSE

Abnormalities in bone and mineral metabolism are commonly seen in patients with end-stage renal disease, reducing bone quality and raising the risk of fracture. This cross-sectional study was performed to characterize risk factors affecting bone mass among male hemodialysis subjects.

METHODS

For this cross-sectional study, we recruited 66 men from three local hemodialysis units. Subjects received dual emission X-ray absorptiometry assessment of three sites (lumbar spine, hip, and distal radius) and the values were correlated with the levels of sex hormones, non-renally excreted bone turnover markers, and mineral metabolism markers.

RESULTS

Subjects were found to have bone mineral density (BMD) reduced predominantly at the distal radius, with Z score < −2 seen in 15.4 % and T score < −2.5 in 21 % of men. Independent predictors of bone density included levels of bone-specific alkaline phosphatase and tartrate-resistant acid phosphatase 5b, which were inversely correlated with the femoral neck Z score. Factors positively associated with an increased Z score included body mass index at all sites and free estradiol levels at the hip and distal radius. Markers of mineral metabolism (e.g., calcium, phosphate, and 25-hydroxyvitamin D) were not correlated with Z scores of any site or with bone turnover markers. After adjusting for body weight, the associations between BMD, sex hormones, and bone turnover markers were no longer significant.

CONCLUSION

We recommend that future studies seeking to assess the factors affecting bone strength among male hemodialysis subjects incorporate a weight-adjusted analysis. Additionally, dialysis-dependent men receiving dual emission X-ray absorptiometry should have the distal radius site added to the standard assessment.

Effects and safety of calcimimetics in end stage renal disease patients with secondary hyperparathyroidism: a meta-analysis

Purpose

Secondary hyperparathyroidism (SHPT) is one of the most common abnormalities of mineral metabolism in patients with chronic kidney disease. We performed a meta-analysis to determine the effect and safety of cinacalcet in SHPT patients receiving dialysis.

Methods

The meta-analysis was performed to determine the effect and safety of cinacalcet in SHPT patients receiving dialysis by using the search terms ‘cinacalcet’ or ‘mimpara’ or ‘sensipar’ or ‘calcimimetic’ or ‘R586’ on MEDLINE and EMBASE (January 1990 to February 2012).

Results

Fifteen trials were included, all of which were performed between 2000 and 2011 enrolling a total of 3387 dialysis patients. Our study showed that calcimimetic agents effectively ameliorated iPTH levels(WMD, −294.36 pg/mL; 95% CI, −322.76 to −265.95, P<0.001) in SHPT patients and reduced serum calcium (WMD, −0.81 mg/dL; 95% CI, −0.89 to −0.72, P<0.001) and phosphorus disturbances(WMD, −0.29 mg/dL; 95% CI, −0.41 to −0.17, P<0.001). The percentage of patients in whom there was a 30% decrease in serum iPTH levels by the end of the dosing was higher in cinacalcet group than that in control group(OR = 10.75, 95% CI: 6.65–17.37, P<0.001). However, no significant difference was found in all-cause mortality and all adverse events between calcimimetics and control groups(OR = 0.86, 95% CI: 0.46–1.60, P = 0.630; OR = 1.30, 95% CI: 0.78–2.18, P = 0.320, respectively). Compared with the control therapy, there was a significant increase in the episodes of hypocalcemia (OR = 2.46, 95% CI: 1.58–3.82, P<0.001), nausea (OR = 2.45, 95% CI: 1.29–4.66, P = 0.006), vomiting(OR = 2.78, 95% CI: 2.14–3.62, P<0.001), diarrhea(OR = 1.51, 95% CI: 1.04–2.20, P = 0.030) and upper respiratory tract infection (OR = 1.79, 95% CI: 1.20–2.66, P = 0.004)in calcimimetics group.

Conclusions

Calcimimetic treatment effectively improved biochemical parameters of SHPT patients receiving dialysis without increasing all-cause mortality and all adverse events.

Bone-specific alkaline phosphatase concentrations are less variable than those of parathyroid hormone in stable hemodialysis patients

Abnormalities of bone mineral metabolism and vascular calcification are prevalent in patients with kidney failure. Clinical management is based on biochemical targets, in particular parathyroid hormone (PTH) concentrations, but this has many limitations including high biological variation. A possible alternative is bone-specific alkaline phosphatase (ALP); therefore, we evaluated the biological variation of this marker in patients undergoing hemodialysis. Bone ALP was measured in non-fasting serum samples taken twice a week over a 6-week period in 22 stable hemodialysis patients and 12 healthy volunteers. The within-individual coefficients of variance were calculated and used to derive the critical difference required to be certain that an observed change was significant. The coefficient of variance for bone ALP was significantly higher in hemodialysis patients compared to healthy individuals. Seven samples were required to estimate the homeostatic set point of bone ALP, within 10%, in a hemodialysis patient. The concentration of serial bone ALP measurements would need to change by 36% between any two measurements before it can be considered a significant change. Since the biological variation of bone ALP is less than half that reported for PTH, our study provides further support for the use of bone ALP as an alternative marker of bone mineral metabolism in the setting of chronic kidney disease–mineral and bone disorder.

PTH--a particularly tricky hormone: why measure it at all in kidney patients?

Plasma parathyroid hormone (PTH) concentrations are commonly measured in the context of CKD, as PTH concentration elevation is typical in this clinical context. Much has been inferred from this raised PTH concentration tendency, both about the state of skeletal integrity and health and also about the potential clinical outcomes for patients. However, we feel that reliance on PTH concentrations alone is a dangerous substitute for the search for, and use of, more precise and reliable biomarkers. In this article, we rehearse these arguments, bringing together patient-level and analytical considerations for the first time.

The role of bone turnover markers in monitoring treatment in postmenopausal osteoporosis

Bone metabolism is assessed using biochemical bone turnover markers (BTM). BTM reflect the metabolic effect of drugs on bone turnover, help to establish the lowest dose inducing the largest change in the BTM, predict treatment-related reduction in fracture risk, and are helpful in bridging studies. Changes in BTM during anti-osteoporotic therapy depend on the cellular mechanism of action of the drug, degree of change in bone turnover rate and route of administration. BTM help to establish the optimal dose of anti-osteoporotic drugs because treatment-related changes in BTM are more rapid compared with change in BMD. A greater decrease in BTM levels during the first year of tantiresorptive treatment is associated with greater antifracture efficacy over 3 years. According to preliminary data, measurement of BTM can improve persistence with anti-resorptive treatment. The use of BTM to monitor anti-osteoporotic therapy in "real life" is limited at this stage.

Mineral and bone disorders in chronic kidney disease and end-stage renal disease patients: new insights into vitamin D receptor activation

Progressive loss of kidney function leads to reduced production of calcitriol (1,25-dihydroxyvitamin D; active vitamin D) and an imbalance in serum calcium (Ca) and phosphorus (P) levels, which are associated with progression of renal failure as well as increased rates of cardiovascular (CV) events and mortality. In addition, multifactorial hypocalcemia and resistance to parathyroid hormone (PTH) can lead to prolonged and excessive synthesis and secretion of PTH, eventually leading to development of secondary hyperparathyroidism and renal osteodystrophy. These changes associated with chronic kidney disease (CKD), extending beyond bone and related biochemical abnormalities, have prompted the development of the term CKD–mineral and bone disorder to describe its systemic nature. Excessive P loading, among other factors, will promote vascular calcification (VC), and PTH production will affect bone remodeling. Although administration of calcitriol increases serum Ca levels and decreases PTH, it is also associated with elevated Ca × P product. Therefore, compounds that selectively activate vitamin D receptors (VDR activators), potentially reducing Ca–P toxicity and distinctly affecting pathogenic mechanisms of VC, might enhance CV and renal protection, increase the vitamin D therapeutic window, and thus provide a significant clinical benefit. Moreover, selective VDR activators have been associated with improvement in survival, at least among dialysis patients. Thus, selective VDR activators should be considered a novel and interesting approach to enhance the standard of care in CKD patients.

[Clinical and biological forms of secondary hyperparathyroidism in dialysis patients]

The diagnosis and treatment of hyperparathyroidism (HPT) are not yet well standardized in chronic renal failure patients. The aim of this study was to identify the main types of HPT on the basis of clinical and biological findings in a haemodialysis population. Between 2004 and 2010, all patients undergoing haemodialysis were observed and treated using the same strategy: conventional therapy with vitamin D supplements, phosphate binders, dialysate calcium adjusted to serum parathyroid hormone (PTH) level and calcitriol analogues (CA), along with regular bone marker analysis. Wherever required, cinacalcet (CC) was administered and parathyroidectomy (PTX) was performed. Of the 520 patients, 158 were classified as having HPT (30%) with a serum PTH level greater than 300 pg/mL. From this population, we identified five main types of HPT: (1) HPT with 'no bone impact' had normal or low bone marker levels (n=28, 17.7%); (2) 'secondary' HPT had elevated bone marker levels, but showed favorable response to CT (n=59, 37.7%); (3) 'tertiary' HPT was accompanied with hypercalcemia and required CC or PTX in case of CT failure (n=11, 6.9%); (4) 'mixed' HPT could not be completely treated with CT and required CC or PTX (n=57, 36%); (5) 'resistant' HPT did not show hypercalcemia, but required PTX after CT and CC failure (n=3, 1.8%). CC was prescribed in 51% cases, CA in 76%, and PTX in 7% of cases. We typified HPT on the basis of physiopathology and stages of HPT progression. Further studies on HPT that focus on bone marker levels are required to establish well-defined treatment strategies. In our study, HPT cases did not show uniform findings in Hémodialyse (HD) patients because of the variation in the stages of the disease at the time of diagnosis.

Diagnostic usefulness of bone mineral density and biochemical markers of bone turnover in predicting fracture in CKD stage 5D patients--a single-center cohort study

BACKGROUND

In chronic kidney disease stage 5D, diagnostic usefulness of bone mineral density (BMD) in predicting fracture has not been established because of variable results in previous studies. The reason for this may be the heterogeneity of underlying pathogenesis of the fracture.

METHODS

BMD was measured annually and serum biochemistry monthly for 485 hemodialyzed patients from April 2003 to March 2008, and all fractures were recorded.

RESULTS

Forty-six new episodes of any type of fracture and 29 cases of prevalent spine fracture were recorded. Serum bone-specific alkaline phosphatase (b-AP) was a very useful surrogate marker for any type of incident fracture risk [area under curve (AUC) = 0.766, P < 0.0001]. A significantly greater risk of any type of incident fracture was associated with parathyroid hormone (PTH) levels either <150 pg/mL [hazard ratio (HR) = 3.47, P < 0.01] or >300 pg/mL (HR = 5.88, P < 0.0001) compared with 150-300 pg/mL. Receiver-operating characteristic analysis demonstrated a significant predictive power for incident of any type of fracture by BMD at the total hip (AUC = 0.760, P < 0.0001) and other hip regions in females in the lower PTH group (PTH < 204 pg/mL). BMDs at every site but whole body or lumbar spine had significant power to discriminate prevalent spine fracture regardless of gender or PTH.

CONCLUSIONS

Hemodialyzed patients with low or high PTH or increased b-AP had a high fracture risk. BMD by Dual Energy X-ray Absorptiometry (DEXA), especially at the total hip region, was useful to predict any type of incident of fracture for females with low PTH or to discriminate prevalent spine fracture for every patient.