Vascular calcification and renal osteodystrophy relationship in chronic kidney disease

Bone and bone derived factors in kidney disease

Purpose of review: Mineral and bone disorder (MBD) is a prevalent complication in chronic kidney disease (CKD), significantly impacting overall health with multifaceted implications including fractures, cardiovascular events, and mortality. Despite its pervasive nature, effective treatments for CKD-MBD are lacking, emphasizing the urgency to advance understanding and therapeutic interventions. Bone metabolism intricacies, influenced by factors like 1,25 dihydroxy vitamin D, parathyroid hormone (PTH), and fibroblast growth factor 23 (FGF23), along with intrinsic osseous mechanisms, play pivotal roles in CKD. Skeletal abnormalities precede hormonal changes, persisting even with normalized systemic mineral parameters, necessitating a comprehensive approach to address both aspects. Recent findings: In this review, we explore novel pathways involved in the regulation of systemic mineral bone disease factors, specifically examining anemia, inflammation, and metabolic pathways. Special emphasis is placed on internal bone mechanisms, such as hepatocyte nuclear factor 4α, transforming growth factor-β1, and sclerostin, which play crucial roles in the progression of renal osteodystrophy. Summary: Despite advancements, effective treatments addressing CKD-MBD morbidity and mortality are lacking, necessitating ongoing research for novel therapeutic targets.

Postoperative Outcomes Among Dialysis Patients Undergoing Hip Fracture Repair

Background

Geriatric hip fractures are strongly correlated with increased morbidity. Even so, postoperative outcomes following surgical repair of hip fractures for patients with end stage renal disease lack extensive investigation. Chronic kidney disease (CKD) poses unique risks for surgical procedures as it has been associated with several complications. Little information is available regarding the outcomes of patients whose renal function decline necessitates dialysis usage. The purpose of this study was to compare post-surgical outcomes based on dialysis usage among CKD patients requiring hip fracture repair.

Materials and Methods

We used the PearlDiver database to identify hip fracture repair patients diagnosed with stages 3, 4, and 5 CKD. We matched the populations according to patient characteristics and comorbidities. We then compared patient complication rates among dialyzed and non-dialyzed CKD patients following hip fracture repair at 30 days, 90 days, and 1 year following the procedure.

Results

Dialyzed patients were more likely to experience myocardial infarction within 30 days (P = .02) and 90 days (P = .002). Dialyzed patients suffered cardiac arrest at higher rates within the same time intervals (P = .02; P = .002). Furthermore, dialysis patients developed sepsis (P = .005) and pneumonia (P = .005) at higher rates within 30 days of operation. Dialysis patients did not have increased risk of blood transfusion within 30 days of the operation (P = .07).

Discussion

We found significant increases in myocardial infarction, cardiac arrest, pneumonia, and sepsis risk among dialyzed CKD patients. Blood transfusion risk failed to reach statistical significance. Our findings are consistent with previous research regarding CKD pathophysiology and associated perioperative outcomes.

Conclusion

Given the drastic decline of renal function among patients on dialysis, our findings may be attributable to decreased glomerular filtration rate in CKD as well as dialysis itself. Regardless, multidisciplinary collaboration should be employed when performing hip fracture repair on a patient who is actively undergoing hemodialysis.

The Dark Side of Ultrasound Imaging in Parathyroid Disease

The diagnosis of parathyroid diseases by imaging still has some intrinsic technical limitations due to the differential diagnosis of different structures of the neck that mimic the parathyroid glands. In this view, ultrasound (US) is an established, low-cost, and non-invasive imaging technique that still represents the first-line approach for evaluating patients with parathyroid disease. The objective of this article is to provide a comprehensive review of the applications of USs in clinical practice, discussing the histopathological and US characteristics of the parathyroid glands in normal and pathological conditions, the advantages of preoperative imaging, and novel updates on the most useful and currently available multiparameter US techniques.

Low bone turnover is associated with plain X-ray vascular calcification in predialysis patients

Background

Vascular calcification (VC) is a common finding in chronic kidney disease (CKD) patients and predicts subsequent cardiovascular morbidity and mortality in this population. Vascular calcification is linked to disordered mineral metabolism and has been associated with bone histomorphometry changes in CKD. However, data on predialysis patients is scarce.

Methods

A cross-sectional study was conducted on a cohort of 56 CKD patients not yet on dialysis, who underwent a transiliac bone biopsy for histomorphometric evaluation after double tetracycline labeling. Patients had no previous exposure to calcium salts, vitamin D agents, steroids or bisphosphonates. Vascular calcification was assessed at the time of biopsy, using Kauppila (plain X-ray of the lateral lumbar spine) and Adragão (plain X-ray of the pelvis and hands) scores.

Results

Vascular calcification was seen in two-thirds of the cohort. Subjects with VC were more likely to be male and have diabetes, and had significantly higher sclerostin and osteoprotegerin circulating levels than those without VC. The histomorphometric analysis showed that bone formation rate was significantly lower in VC compared to non-VC patients. In the multivariable logistic regression analysis, bone formation rate was independently associated with the presence of VC.

Conclusions

Vascular calcification is highly prevalent in predialysis patients, especially in those with diabetes. The independent association between bone formation rate and VC provides evidence of an important interaction between bone and vessel in CKD. Our results suggest that low bone turnover is a non-traditional risk factor for cardiovascular disease in predialysis patients.

Bone Mineral Density and Aortic Calcification: Evidence for a Bone-vascular Axis After Kidney Transplantation

BACKGROUND

Chronic kidney disease mineral and bone disorders (CKD-MBD) and vascular calcification are often seen in kidney transplantation recipients (KTR). This study focused on the bone-vascular axis hypothesis, the pathophysiological mechanisms driving both bone loss and vascular calcification, supported by an association between lower bone mineral density (BMD) and higher risk of vascular calcification.

METHODS

KTR referred for a dual-energy X-ray absorptiometry procedure within 6 mo after transplantation were included in a cross-sectional study (2004-2014). Areal BMD was measured at the proximal femur, and abdominal aortic calcification (AAC) was quantified (8-points score) from lateral single-energy images of the lumbar spine. Patients were divided into 3 AAC categories (negative-AAC: AAC 0; low-AAC: AAC 1-3; and high-AAC: AAC 4-8). Multivariable-adjusted multinomial logistic regression models were performed to study the association between BMD and AAC.

RESULTS

We included 678 KTR (51 ± 13 y old, 58% males), 366 (54%) had BMD disorders, and 266 (39%) had detectable calcification. High-AAC was observed in 9%, 11%, and 25% of KTR with normal BMD, osteopenia, and osteoporosis, respectively (P < 0.001). Higher BMD (T-score, continuous) was associated with a lower risk of high-AAC (odds ratio 0.61, 95% confidence interval 0.42-0.88; P = 0.008), independent of age, sex, body mass index, estimated glomerular filtration rate, and immunosuppressive therapy. KTR with normal BMD were less likely to have high-AAC (odds ratio 0.24, 95% confidence interval 0.08-0.72; P = 0.01).

CONCLUSIONS

BMD disorders are highly prevalent in KTR. The independent inverse association between BMD and AAC may provide evidence to point toward the existence, while highlighting the clinical and epidemiological relevance, of a bone-vascular axis after kidney transplantation.

Fortified phosphorus‑lowering treatment through administration of lanthanum protects against vascular calcification via regulation of FGF23 in chronic kidney disease

Phosphorus reduction can prevent against vascular calcification (VC) in chronic kidney disease (CKD), but the mechanisms underlying its actions remain unclear. The aim of the present study was to determine the effect of a fortified phosphorus-lowing treatment on VC in CKD. Serum levels of creatinine, blood urea nitrogen (BUN), fibroblast growth factor 23 (FGF23), calcium and phosphorus, and the plasma levels of parathyroid hormone (PTH) were determined in an animal model of CKD treated with or without lanthanum. Haematoxylin and eosin (H&E) staining was performed to examine the structure of kidney tissues. Western blot analysis was performed to compare the levels of total- (t-) extracellular signal-related kinase (ERK) and phospho- (p-)ERK among the different experimental groups to investigate the effect of FGF23 on p-ERK expression. In the animal model, administration of adenine increased the serum levels of creatinine, BUN, FGF23 and phosphorus but decreased the serum levels of calcium. In addition, adenine treatment increased the plasma levels of PTH. H&E staining showed that lanthanum treatment did not alter the severity of renal cortex injury. Furthermore, the levels of t-ERK levels did not notably differ between the Adenine-free, Adenine-vehicle and Adenine-lanthanum groups, whereas the levels of p-ERK and aortic calcium in the Adenine-vehicle group were significantly upregulated. In addition, ectopic overexpression of FGF23 increased the levels of p-ERK, Msx2 and Osx in a dose-dependent manner. Furthermore, a total of 48 patients were enrolled in the present study. In the fortified group, the serum levels of FGF23, phosphorus and PTH were significantly reduced, whereas the serum levels of calcium were significantly increased, indicating an enhanced preventative effect in the fortified group. The results of the present study suggest that FGF23 may be used as a therapeutic target in the management and prevention of VC in CKD.

Lifestyle, Inflammation, and Vascular Calcification in Kidney Transplant Recipients: Perspectives on Long-Term Outcomes

After decades of pioneering and improvement, kidney transplantation is now the renal replacement therapy of choice for most patients with end-stage kidney disease (ESKD). Where focus has traditionally been on surgical techniques and immunosuppressive treatment with prevention of rejection and infection in relation to short-term outcomes, nowadays, so many people are long-living with a transplanted kidney that lifestyle, including diet and exposure to toxic contaminants, also becomes of importance for the kidney transplantation field. Beyond hazards of immunological nature, a systematic assessment of potentially modifiable-yet rather overlooked-risk factors for late graft failure and excess cardiovascular risk may reveal novel targets for clinical intervention to optimize long-term health and downturn current rates of premature death of kidney transplant recipients (KTR). It should also be realized that while kidney transplantation aims to restore kidney function, it incompletely mitigates mechanisms of disease such as chronic low-grade inflammation with persistent redox imbalance and deregulated mineral and bone metabolism. While the vicious circle between inflammation and oxidative stress as common final pathway of a multitude of insults plays an established pathological role in native chronic kidney disease, its characterization post-kidney transplant remains less than satisfactory. Next to chronic inflammatory status, markedly accelerated vascular calcification persists after kidney transplantation and is likewise suggested a major independent mechanism, whose mitigation may counterbalance the excess risk of cardiovascular disease post-kidney transplant. Hereby, we first discuss modifiable dietary elements and toxic environmental contaminants that may explain increased risk of cardiovascular mortality and late graft failure in KTR. Next, we specify laboratory and clinical readouts, with a postulated role within persisting mechanisms of disease post-kidney transplantation (i.e., inflammation and redox imbalance and vascular calcification), as potential non-traditional risk factors for adverse long-term outcomes in KTR. Reflection on these current research opportunities is warranted among the research and clinical kidney transplantation community.

Cortical unlike trabecular bone loss is not associated with vascular calcification progression in CKD patients

Background

Vascular calcification progression has been associated with the loss of trabecular bone in chronic kidney disease (CKD) patients. There are few data evaluating the relationship between cortical bone loss and vascular calcification in this population. The aim of this study was to prospectively evaluate the association between changes in cortical bone density and coronary artery calcification (CAC) progression in non-dialyzed CKD patients.

Methods

Changes of cortical and trabecular bone, and changes of calcium score, were analyzed using vertebral tomographic images from a prospective study. Automatic delineation of the cortical bone layer was performed by Image J software, and trabecular bone was determined by selecting a region of interest using Vitrea 2® software. Cortical and trabecular bone density (BD) were expressed in Hounsfield Units (HU), and coronary artery calcium score in Agatston Units (AU).

Results

Seventy asymptomatic patients [57.8 ± 10.2 years, 63% males, 20% diabetic, estimated glomerular filtration rate (eGFR) = 37.3 (24.8–51.3) mL/min/1.73m²] were followed for 24 months. The mean cortical and trabecular BD did not change over time. While 49 patients lost either bone, 29 (41%) patients lost cortical [− 4.4%/year (ranging from − 7.15 to − 0.5)] and 39 (56%) lost trabecular bone [− 3.15%/year (− 13.7 to − 0.25)]. There was no association between cortical and trabecular BD changes (p = 0.12). CAC was observed in 33 (46%) patients at baseline, and 30 (91%) of them showed CAC progression. While an inverse correlation between trabecular bone and calcium score changes was observed (p = 0.001), there was no correlation between cortical bone and calcium score changes (p = 0.34).

Conclusion

CKD patients experience either cortical or trabecular bone loss over time, but these changes do not take place simultaneously in all patients. Cortical, unlike trabecular bone loss, is not associated with vascular calcification progression in these patients.

Abdominal aortic calcification in predialysis patients: Contribution of traditional and uremia-related risk factors

Cardiovascular disease is the main cause of morbidity and mortality in end-stage renal disease (ESRD) patients. Recent population based epidemiological studies demonstrated a correlation between reduced renal function and risk for all causes and cardiovascular mortality, 50% of patients dying before the commencement of renal replacement therapy. Vascular calcifications (VC) and arterial stiffness are major contributors to cardiovascular disease and are independent predictors of cardiovascular mortality in ESRD patients. Scarce information is available on the risk factors and prognosis of predialysis patients with VC. The aim of this study was to evaluate the contribution of traditional and uremia related risk factors to abdominal aortic calcification in predialysis patients. A single center, retrospective study was performed on 305 adult patients monitored at the Bucharest University Emergency Hospital for at least 6 months. Our study reports an increased incidence of VC in predialysis chronic kidney disease (CKD) patients, higher in those with advanced age, history of cardiovascular disease, osteoporosis, and declining renal function.

The effectiveness of cinacalcet: a randomized, open label study in chronic hemodialysis patients with severe secondary hyperparathyroidism

Background: Secondary hyperparathyroidism (SHPT) is associated with high incidences of cardiovascular disease, bone fracture, and mortality. This study was conducted to demonstrate the effectiveness of cinacalcet treatment on chronic kidney disease-mineral bone disorder (CKD-MBD) markers in chronic hemodialysis patients with severe SHPT.

Methods: In phase 1, 30 adult HD patients were randomized to cinacalcet or control groups for 12 weeks to explore the achievement of >30% reduction of iPTH. In phase 2, 45 patients were participated to further explore the effect of cinacalcet on CKD-MBD parameters for 24-week follow up and 12 additional weeks after cinacalcet discontinuation.

Results: In phase 1, the baseline serum iPTH levels were not different [1374 (955, 1639) pg/mL in the control group vs. 1191 (1005, 1884) pg/mL in the cinacalcet group], the percentage of patients achieving iPTH target were significantly higher in the treatment group [80% vs. 13%, p = .001]. In phase 2, the significant reductions of iPTH, FGF-23, tartrate-resistant acid phosphatase 5b, and slightly decreased size of parathyroid gland and stabilized vascular calcification were observed at 24-week follow up and markedly rebounded after discontinuation of cinacalcet.

Conclusions: The effectiveness of cinacalcet were still obviously demonstrated even in chronic HD patients with severe SHPT. In addition, the improvements of bone markers and FGF-23, and stabilization of vascular calcification were observed. Therefore, cinacalcet can provide salutary effects on CKD-MBD in severe SHPT and might be an initially effective PTH-lowering therapy prior to surgical parathyroidectomy as well as an alternative treatment in the patients unsuitable for surgery.

Clinical trial registration: ClinicalTrials.gov: NCT02056730. Date of registration: February 4, 2014.

Associations of plasma fibroblast growth factor 23 and other markers of chronic kidney disease-Mineral and bone disorder with all-cause mortality in South African patients on maintenance dialysis: A 3-year prospective cohort study

INTRODUCTION

Few studies have linked high levels of plasma C-terminal fibroblast growth factor 23 (FGF23) with poor clinical outcomes in patients on maintenance haemodialysis (MHD), while the association between intact FGF23 and mortality in this group of patients remains inconclusive. Therefore, the aim of this study was to evaluate the association between plasma levels of intact FGF23 and mortality in dialysis patients.

METHODS

A prospective multicenter study involving patients undergoing dialysis at three dialysis centers in Johannesburg was undertaken between 1st October 2014 and 31st December 2017.

RESULTS

The study comprised 165 chronic dialysis patients (111 blacks, 54 whites) with a mean age of 46.6 ±14.2 years. During a three year follow up period, there were 46 deaths (1.03 per 100 person-years). The median plasma FGF 23 level was 382 pg/ml (interquartile range [IQR], 145-2977). In adjusted multivariable analyses, there was a non-statistically significant increase in the risk of mortality with higher quartiles of FGF 23 levels: the adjusted hazard ratios (HR) for the second, third and fourth quantiles were HR 3.20 (95% CI, 0.99-10.35; P = 0.052), HR 2.43(95% CI,0.65-9.09; P = 0.19), and HR 2.09 (95% CI, 0.66-7.32; P = 0.25),respectively. Corrected serum calcium 2.38-2.5 mmol/l [HR 2.98 (95% CI, 1.07-8.29; P = 0.04] and > 2.50 mmol/l [HR 5.50 (95% CI, 1.84-16.48; P = 0.002] were independently associated with increased risk of death. Likewise, patients with intact parathyroid hormone > 600 pg/ml had a 3.46-fold higher risk of death (HR 3.46, 95% CI, 1.22-9.82 P = 0.019). These findings persisted in time -dependent analyses.

CONCLUSION

Higher levels of intact FGF 23 appear not to be independently associated with all-cause mortality in our dialysis patients, while hypercalcaemia and severe hyperparathyroidism were found to be independent predictors of mortality in this cohort of patients.

Factors and Outcome of Renal Osteodystrophy-Associated Initial Fragility Fracture in End-Stage Renal Disease Patients

Background

Renal osteodystrophy has caused increased risk of fragility fracture in end-stage renal disease (ESRD) patients. However, risk factors and outcome of ESRD patients with fragility fracture remain uncharacterized. We aimed to assess these parameters in ESRD patients.

Summary

This retrospective case-control study analyzed 354 ESRD patients (initial fragility fracture [FF] group, n = 59; control group, n = 295). Pre-dialysis blood hemoglobin, serum albumin, lipid, calcium, phosphorus, alkaline phosphatase (ALP), and intact parathyroid hormone (iPTH) were collected. All procedures performed involving human participants were in accordance with the ethical standards of the institutional committee of The First Affiliated Hospital of Chongqing Medical University (IRB approval number 216-82), and informed consent was obtained from all participants. There were higher prevalence rates of primary hypertension and diabetes, higher serum ALP, corrected calcium, and lower serum total cholesterol, low-density lipoprotein, lipoprotein-α, and iPTH in the FF group. Fractures were more likely to occur in the higher level of corrected calcium as well as in the lower iPTH group. High corrected calcium (p = 0.010, OR = 11.308, 95% CI: 1.770-72.242) and serum ALP (p = 0.000, OR = 1.007, 95% CI: 1.004-1.011) were independent risk factors of fragility fracture. The incidence of all-cause mortality and cardiovascular (CV) events in ESRD patients with fragility fracture was higher than in those without fracture.

Key Messages

Patients with hypertension, diabetes, excessive suppression of PTH, and poor nutritional status are more prone to fractures. Serum corrected calcium and ALP were independent risk factors of fragility fracture. Patients with initial fragility fracture had more CV events and higher mortality.

High calcium, phosphate and calcitriol supplementation leads to an osteocyte-like phenotype in calcified vessels and bone mineralisation defect in uremic rats

A link between vascular calcification and bone anomalies has been suggested in chronic kidney disease (CKD) patients with low bone turnover disease. We investigated the vascular expression of osteocyte markers in relation to bone microarchitecture and mineralization defects in a model of low bone turnover CKD rats with vascular calcification. CKD with vascular calcification was induced by 5/6 nephrectomy followed by high calcium and phosphate diet, and vitamin D supplementation (Ca/P/VitD). CKD + Ca/P/VitD group (n = 12) was compared to CKD + normal diet (n = 12), control + normal diet (n = 8) and control + Ca/P/VitD supplementation (n = 8). At week 6, tibia, femurs and the thoracic aorta were analysed by Micro-Ct, histomorphometry and for expression of osteocyte markers. High Ca/P/VitD treatment induced vascular calcification only in CKD rats, suppressed serum parathyroid hormone levels and led to higher sclerostin, DKK1 and FGF23 serum levels. Expression of sclerostin, DKK1 and DMP1 but not FGF23 were increased in calcified vessels from CKD + Ca/P/VitD rats. Despite low parathyroid hormone levels, tibia bone cortical thickness was significantly lower in CKD + Ca/P/VitD rats as compared to control rats fed a normal diet, which is likely the result of radial growth impairment. Finally, Ca/P/VitD treatment in CKD rats induced a bone mineralization defect, which is likely explained by the high calcitriol dose. In conclusion, Ca/P/VitD supplementation in CKD rats induces expression of osteocyte markers in vessels and bone mineralisation anomalies. Further studies should evaluate the mechanisms of high dose calcitriol-induced bone mineralisation defects in CKD.

Prognostic importance of plasma total magnesium in a cohort of cats with azotemic chronic kidney disease

Background

Hypomagnesemia is associated with increased mortality and renal function decline in humans with chronic kidney disease (CKD). Magnesium is furthermore inversely associated with fibroblast growth factor 23 (FGF23), an important prognostic factor in CKD in cats. However, the prognostic significance of plasma magnesium in cats with CKD is unknown.

Objectives

To explore associations of plasma total magnesium concentration (tMg) with plasma FGF23 concentration, all‐cause mortality, and disease progression in cats with azotemic CKD.

Animals

Records of 174 client‐owned cats with IRIS stage 2‐4 CKD.

Methods

Cohort study. Cats with azotemic CKD were identified from the records of two London‐based first opinion practices (1999–2013). Possible associations of baseline plasma tMg with FGF23 concentration and risks of death and progression were explored using, respectively, linear, Cox, and logistic regression.

Results

Plasma tMg (reference interval, 1.73–2.57 mg/dL) was inversely associated with plasma FGF23 when controlling for plasma creatinine and phosphate concentrations (partial correlation coefficient, −0.50; P < .001). Hypomagnesemia was observed in 12% (20/174) of cats, and independently associated with increased risk of death (adjusted hazard ratio, 2.74; 95% confidence interval [CI], 1.35–5.55; P = .005). The unadjusted associations of hypermagnesemia (prevalence, 6%; 11/174 cats) with survival (hazard ratio, 2.88; 95% CI, 1.54–5.38; P = .001), and hypomagnesemia with progressive CKD (odds ratio, 17.7; 95% CI, 2.04–154; P = .009) lost significance in multivariable analysis.

Conclusions and Clinical Importance

Hypomagnesemia was associated with higher plasma FGF23 concentrations and increased risk of death. Measurement of plasma tMg augments prognostic information in cats with CKD, but whether these observations are associations or causations warrants further investigation.

Parathyroid Nodular Hyperplasia and Responsiveness to Drug Therapy in Renal Secondary Hyperparathyroidism: An Open Question

The goal of the pharmacological therapy in secondary hyperparathyroidism (SHPT) is to reduce serum levels of parathyroid hormone and phosphorus, to correct those of calcium and vitamin D, to arrest or reverse the parathyroid hyperplasia. However, when nodular hyperplasia or an autonomous adenoma develops, surgery may be indicated. We reviewed the literature with the aim of defining if the echographic criteria predictive of unresponsiveness of SHPT to calcitriol therapy are valid also in the cinacalcet era and if drug therapy may reverse nodular hyperplasia of parathyroid gland (PTG). The responsiveness to therapy and regression of the nodular hyperplasia of PTG remains an open question in the calcimimetic era as well as the cutoff between medical and surgical therapy. Prospective studies are needed in order to clarify if an earlier use of cinacalcet in moderate SHPT might arrest the progression of parathyroid growth and stabilize SHPT.

Prospective cohort study: Cinacalcet-mediated lowering of PTH level and cardiovascular disease mortality in younger Korean patients with stage 5 CKD at a Korean secondary hospital

WHAT IS KNOWN AND OBJECTIVES

Cinacalcet may reduce cardiovascular disease (CVD) mortality in elderly patients with chronic kidney disease (CKD). However, previous studies of the clinical responses to cinacalcet have exhibited discrepancies due to highly variable baseline levels of parathyroid hormone (PTH), kidney function and age. Little is known about the true effect of cinacalcet on stage 5 CKD. The objective of the current observational study was to evaluate whether cinacalcet-mediated lowering of PTH levels improves all-cause mortality and cardiovascular disease mortality in younger stage 5 CKD patients (mean age <55 years).

METHODS

This prospective, cohort study reviewed the electronic medical records (EMRs) of CKD patients (n=540) with secondary hyperparathyroidism (SHPT) for a period of 36 months. Of 540 patients, 104 subjects met the inclusion criteria and were included in the final evaluation (mean serum iPTH 688.7 pg/mL). Patients were divided into a cinacalcet group (n=43) and a non-cinacalcet group (n=61).

RESULTS AND DISCUSSION

Comparing the cinacalcet group to the non-cinacalcet group, Cox proportional hazard modelling found that all-cause mortality was five (31.3%) in the cinacalcet group and three (15.8%) in the non-cinacalcet group for patients with serum levels of PTH>600 pg/mL [P=.277, hazard ratio 2.213, 95% confidence interval (CI): 0.529-9.262]. Cardiovascular disease mortality (CVD: heart disease) occurred in two (5.3%) in the cinacalcet group and one (2.1%) in the non-cinacalcet group [P=.425, HR 2.611, 95% CI: 0.228-9.939]. Overall, there were no significant differences in CVD mortality between the two groups.

WHAT IS NEW AND CONCLUSION

Cinacalcet was not associated with decreases in all-cause mortality or CVD mortality in younger stage 5 CKD patients with high PTH levels (>600 pg/mL). This could be explained by the diversity of the population in terms of the patient's age, health insurance policies, target serum level of biochemical and PTH, and glomerular filtration rate (GFR) at admission. These data, although based on an observational study, indicate that adding cinacalcet to the current standard care for younger stage 5 CKD patients should be re-evaluated.

Effects of different phosphate lowering strategies in patients with CKD on laboratory outcomes: A systematic review and NMA

BACKGROUND

Chronic kidney disease-mineral and bone disorder (CKD-MBD), a complication of chronic kidney disease, has been linked to reduced quality and length of life. High serum phosphate levels that result from CKD-MBD require phosphate-lowering agents, also known as phosphate binders. The objective of this systematic review is to compare the effects of available phosphate binders on laboratory outcomes in patients with CKD-MBD.

METHODS

Data sources included MEDLINE and EMBASE from January 1996 to April 2016, and the Cochrane Register of Controlled Trials up to April 2016. Teams of two reviewers, independently and in duplicate, screened titles and abstracts and potentially eligible full text reports to determine eligibility, and subsequently abstracted data and assessed risk of bias in eligible randomized controlled trials (RCTs). Eligible trials enrolled patients with CKD-MBD and randomized them to receive calcium-based phosphate binders (delivered as calcium acetate, calcium citrate or calcium carbonate), non-calcium-based phosphate binders (NCBPB) (sevelamer hydrochloride, sevelamer carbonate, lanthanum carbonate, sucroferric oxyhydroxide and ferric citrate), phosphorus restricted diet (diet), placebo or no treatment and reported effects on serum levels of phosphate, calcium and parathyroid hormone. We performed Bayesian network meta-analyses (NMA) to calculate the effect estimates (mean differences) and 95% credible intervals for serum levels of phosphate, calcium and parathyroid hormone. We calculated direct, indirect and network meta-analysis estimates using random-effects models. We applied the GRADE (Grading of Recommendations, Assessment, Development and Evaluation) approach to rate the quality of evidence for each pairwise comparison.

RESULTS

Our search yielded 1108 citations; 71 RCTs were retrieved for full review and 16 proved eligible. Including an additional 13 studies from a previous review, 29 studies that enrolled 8335 participants proved eligible; 26 trials provided data for quantitative synthesis. Sevelamer, lanthanum, calcium, iron, diet and combinations of active treatments (calcium or sevelamer or lanthanum and combination of calcium and sevelamer) resulted in significantly lower serum phosphate as compared to placebo (moderate to very low quality of evidence). We found no statistically significant differences between active treatment categories in lowering serum phosphate. Sevelamer, lanthanum and diet resulted in lower serum calcium compared to calcium (moderate quality evidence for lanthanum and diet; low quality evidence for Sevelamer). Iron, sevelamer and calcium yielded lower parathyroid hormone levels as compared to lanthanum. Meta-regression analyses did not yield a statistically significant association between treatment effect and trial duration.

DISCUSSION/CONCLUSIONS

We found few differences between treatments in impact on phosphate and differences in parathyroid hormone. Relative to calcium, sevelamer, lanthanum and diet showed significant reduction in serum calcium from baseline. Treatment recommendations should be based on impact on patient-important outcomes rather than on surrogate outcomes. Systematic review registration: PROSPERO CRD-42016032945.

MicroRNAs 223-3p and 93-5p in patients with chronic kidney disease before and after renal transplantation

Chronic kidney disease (CKD) is associated with a multifactorial dysregulation of bone and vascular calcification and closely linked to increased cardiovascular mortality and concomitant bone disease. We aimed to investigate specific microRNA (miRNA) signatures in CKD patients to find indicators for vascular calcification and/or bone mineralization changes during CKD and after kidney transplantation (KT). A miRNA array was used to investigate serum miRNA profiles in CKD patients, then selected miRNAs were quantified in a validation cohort comprising 73 patients in CKD stages 3 to 5, 67 CKD patients after KT, and 36 healthy controls. A spectrum of biochemical parameters including markers for kidney function, inflammation, glucose, and mineral metabolism was determined. The relative expression of miR-223-3p and miR-93-5p was down-regulated in patients with CKD stage 4 and 5 compared to healthy controls. This down-regulation disappeared after kidney transplantation even when lower glomerular filtration rates (eGFR) persisted. MiR-223-3p and miR-93-5p were associated with interleukin-6 (IL-6) and eGFR levels, and by trend with interleukin-8 (IL-8), C-peptide, hematocrit, and parathyroid hormone (PTH). This study contributes new knowledge of serum miRNA expression profiles in CKD, potentially reflecting pathophysiological changes of bone and calcification pathways associated with inflammation, vascular calcification, mineral and glucose metabolism. Identified miRNA signatures can contribute to future risk markers or future therapeutic targets in bone and kidney disease.

A critical appraisal of chronic kidney disease mineral and bone disorders clinical practice guidelines using the AGREE II instrument

BACKGROUND

Patients with chronic kidney disease mineral and bone disorders (CKD-MBD) suffer high rates of morbidity and mortality, in particular related to bone and cardiovascular outcomes. The management of CKD-MBD remains challenging. The objective of this systematic survey is to critically appraise clinical practice guidelines (CPGs) addressing CKD-MBD.

METHODS/DESIGN

Data sources included MEDLINE, EMBASE, the National Guideline Clearinghouse, Guideline International Network and Turning Research into Practice up to May 2016. Teams of two reviewers, independently and in duplicate, screened titles and abstracts and potentially eligible full text reports to determine eligibility and subsequently appraised the guidelines using the Advancing Guideline Development, Reporting and Evaluation in Health Care instrument II (AGREE).

RESULTS

Sixteen CPGs published from 2003 to 2015 addressing the diagnosis and management of CKD-MBD in adult patients (11 English, two Spanish, one Italian, one Portuguese and one Slovak) proved eligible. The National Institute for Health and Care Excellence guideline performed best with respect to AGREE II criteria; only three other CPGs warranted high scores on all domains. All other guidelines received scores of under 60% on one or more domains. Major discrepancies in recommendations were not, however, present, and we found no association between quality of CPGs which was not associated with resulting recommendations.

CONCLUSIONS

Most guidelines assessing CKD-MBD suffer from serious shortcomings using AGREE criteria although limitations with respect to AGREE criteria do not necessarily lead to inappropriate recommendations.

Parathyroid Ultrasonography in Renal Secondary Hyperparathyroidism: An Overlooked and Useful Procedure

In secondary hyperparathyroidism (SHPT), ultrasonography (US) can accurately define the size and structure of parathyroid glands as well as differentiate diffuse and nodular hyperplasia. US may be also useful to predict the response of SHPT to vitamin D analogs and cinacalcet and to assess for regression of parathyroid glands hyperplasia by measurement of parathyroid gland volume. There is increasing evidence that US can potentially identify patients who will benefit from prompt surgical intervention. Therefore, US should be part of the diagnostic armamentarium in the treatment of SHPT in the daily clinical practice.

Comparative Effectiveness of Phosphate Binders in Patients with Chronic Kidney Disease: A Systematic Review and Network Meta-Analysis

BACKGROUND

Chronic kidney disease-mineral and bone disorder (CKD-MBD) has been linked to poor health outcomes, including diminished quality and length of life. This condition is characterized by high phosphate levels and requires phosphate-lowering agents-phosphate binders. The objective of this systematic review is to compare the effects of available phosphate binders on patient-important outcomes in patients with CKD-MBD.

METHODS

Data sources included MEDLINE and EMBASE Trials from 1996 to February 2016. We also searched the Cochrane Register of Controlled Trials up to April 2016. Teams of two reviewers, independently and in duplicate, screened titles and abstracts and potentially eligible full text reports to determine eligibility, and subsequently abstracted data and assessed risk of bias in eligible randomized controlled trials (RCTs). Eligible trials enrolled patients with CKD-MBD, randomized them to receive calcium (delivered as calcium acetate, calcium citrate or calcium carbonate), non-calcium-based phosphate binders (NCBPB) (sevelamer hydrochloride, sevelamer carbonate, lanthanum carbonate, sucroferric oxyhydroxide and ferric citrate), phosphorus restricted diet, placebo or no treatment, and reported effects on all-cause mortality, cardiovascular mortality or hospitalization at ≥4 weeks follow-up. We performed network meta-analyses (NMA) for all cause-mortality for individual agents (seven-node analysis) and conventional meta-analysis of calcium vs. NCBPBs for all-cause mortality, cardiovascular mortality and hospitalization. In the NMAs, we calculated the effect estimates for direct, indirect and network meta-analysis estimates; for both NMA and conventional meta-analysis, we pooled treatment effects as risk ratios (RR) and calculated 95% confidence intervals (CIs) using random effect models. We used the GRADE (Grading of Recommendations, Assessment, Development and Evaluation) approach to rate the quality of evidence for each paired comparison.

RESULTS

Our search yielded 1190 citations, of which 71 RCTs were retrieved for full review and 15 proved eligible. With 13 eligible studies from a prior review, we included 28 studies with 8335 participants; 25 trials provided data for our quantitative synthesis. Results suggest higher mortality with calcium than either sevelamer (NMA RR, 1.89 [95% CI, 1.02 to 3.50], moderate quality evidence) or NCBPBs (conventional meta-analysis RR, 1.76 [95% CI, 1.21 to 2.56, moderate quality evidence). Conventional meta-analysis suggested no difference in cardiovascular mortality between calcium and NCBPBs (RR, 2.54 [95% CI, 0.67 to 9.62 low quality evidence). Our results suggest higher hospitalization, although non-significant, with calcium than NCBPBs (RR, 1.293 [95% CI, 0.94 to 1.74, moderate quality evidence).

DISCUSSION/CONCLUSIONS

Use of calcium results in higher mortality than either sevelamer in particular and NCBPBs in general (moderate quality evidence). Our results raise questions about whether administration of calcium as an intervention for CKD- MBD remains ethical. Further research is needed to explore the effects of different types of phosphate binders, including novel agents such as iron, on quality and quantity of life.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD-42016032945.

The FRAX ® as a predictor of mortality in Japanese incident hemodialysis patients: an observational, follow-up study

The World Health Organization Fracture Risk Assessment Tool (FRAX(®)) was recently developed to estimate the 10-year absolute risk of osteoporotic fracture among the general population. However, the evidence for its use in chronic kidney disease patients has been lacking, and the association between the FRAX(®) and mortality is unknown. Therefore, a hospital-based, prospective, cohort study was conducted to evaluate the predictive ability of the FRAX(®) for mortality in hemodialysis patients. A total of 252 patients who had been started on maintenance hemodialysis, 171 men and 81 women, with a mean age of 67 ± 14 years, was studied. The endpoint was defined as all-cause death. The Cox proportional hazards model was used to calculate hazard ratios and 95 % confidence intervals. During the mean follow-up period of 3.4 ± 2.7 years, 61 deaths occurred. The median (interquartile range) of the FRAX(®) for major osteoporotic fracture was 6.9 (4.6-12.0) % in men and 19.0 (7.6-33.0) % in women. Cumulative survival rates at 5 years after starting dialysis, with the FRAX(®) levels above and below the median, were 51.9 and 87.9 %, respectively, in men and 67.4 and 83.7 %, respectively, in women. Overall, in men, the multivariate Cox regression analyses revealed that the log-transformed FRAX(®) remained an independent predictor of death after adjusting by confounding variables. However, in women, the significant association between the FRAX(®) value and the outcome was eliminated if age was put into these models. Among Japanese hemodialysis patients, the FRAX(®) seems to be useful for predicting death, especially in men.

Molecular Mechanisms of Vascular Calcification in Chronic Kidney Disease: The Link between Bone and the Vasculature

Vascular calcification is highly prevalent in patients with chronic kidney disease (CKD) and increases mortality in those patients. Impaired calcium and phosphate homeostasis, increased oxidative stress, and loss of calcification inhibitors have been linked to vascular calcification in CKD. Additionally, impaired bone may perturb serum calcium/phosphate and their key regulator, parathyroid hormone, thus contributing to increased vascular calcification in CKD. Therapeutic approaches for CKD, such as phosphate binders and bisphosphonates, have been shown to ameliorate bone loss as well as vascular calcification. The precise mechanisms responsible for vascular calcification in CKD and the contribution of bone metabolism to vascular calcification have not been elucidated. This review discusses the role of systemic uremic factors and impaired bone metabolism in the pathogenesis of vascular calcification in CKD. The regulation of the key osteogenic transcription factor Runt-related transcription factor 2 (Runx2) and the emerging role of Runx2-dependent receptor activator of nuclear factor kappa-B ligand (RANKL) in vascular calcification of CKD are emphasized.

Pathogenesis of drug-resistant hypertension

More is known about the epidemiology of drug-resistant hypertension than particular pathogenic factors and pathways. Several recurring themes, however, seem evident on using insight from epidemiology and general knowledge of the pathophysiology of hypertension. Specifically, 4 main pathways converge on drug resistance including sodium handling, sympathetic nervous system activation, endothelial dysfunction, and arterial stiffness. These factors, and the various pathways and elements contributing to them, are reviewed. In addition to describing how these factors exert their individual influences on resistant hypertension, several examples of how interactions between these factors, particularly in the case of chronic kidney disease, are included. At the conclusion of this review some thoughts are offered on additional mechanisms and areas for potential research.

Arterial stiffness and chronic kidney disease: lessons from the Chronic Renal Insufficiency Cohort study

PURPOSE OF REVIEW

The purpose of this review is to highlight what the Chronic Renal Insufficiency Cohort (CRIC) study has taught us regarding arterial stiffness in chronic kidney disease. The CRIC study began in mid-2003 and enrolled more than 3900 people with chronic kidney disease.

RECENT FINDINGS

The recent findings from the CRIC study are covered in 10 lessons. Within the CRIC study, we enrolled about 2800 participants who underwent a pulse wave velocity measurement. At the time of initial funding, very little was known about the role of arterial stiffness in chronic, nondialyzed, kidney disease. The lessons span the gamut from simple correlations to measures such as central arterial pressure profiles and reproducibility of pulse wave velocity measurements between operators, to relationships of pulse wave velocity to kidney function, protein excretion, cardiovascular disease prevalence, and incident cardiovascular events such as heart failure.

SUMMARY

The implications from these lessons are that pulse wave velocity is a robust, reproducible measure of arterial stiffness which adds important information to standard clinical assessments such as SBP and DBP in a population with chronic kidney disease, a disorder with high likelihood of progressive kidney function loss, and a substantial predisposition to cardiovascular disease.

[Pharmaceutical therapy of bone metabolism disorders in chronic kidney disease mineral bone disorder (CKD-MBD) with special respect to antiresorptive substances]

Disturbances in bone and mineral turnover are common complications in patients with impaired renal function. Besides an increased risk for cardiovascular events they promote skeletal events, such as bone pain and fractures. Evidence for the antifracture efficacy of antiresorptive and osteoanabolic treatment strategies has only been demonstrated for patients with osteoporosis. The use of osteotropic drugs in patients with impaired renal function requires large randomized placebo-controlled trials.

A comparison of calcium to zoledronic acid for improvement of cortical bone in an animal model of CKD

Patients with chronic kidney disease (CKD) have increased risk of fractures, yet the optimal treatment is unknown. In secondary analyses of large randomized trials, bisphosphonates have been shown to improve bone mineral density and reduce fractures. However, bisphosphonates are currently not recommended in patients with advanced kidney disease due to concern about oversuppressing bone remodeling, which may increase the risk of developing arterial calcification. In the present study we used a naturally occurring rat model of CKD with secondary hyperparathyroidism, the Cy/+ rat, and compared the efficacy of treatment with zoledronic acid, calcium given in water to simulate a phosphate binder, and the combination of calcium and zoledronic acid. Animals were treated beginning at 25 weeks of age (approximately 30% of normal renal function) and followed for 10 weeks. The results demonstrate that both zoledronic acid and calcium improved bone volume by micro-computed tomography (µCT) and both equally suppressed the mineral apposition rate, bone formation rate, and mineralizing surface of trabecular bone. In contrast, only calcium treatment with or without zoledronic acid improved cortical porosity and cortical biomechanical properties (ultimate load and stiffness) and lowered parathyroid hormone (PTH). However, only calcium treatment led to the adverse effects of increased arterial calcification and fibroblast growth factor 23 (FGF23). These results suggest zoledronic acid may improve trabecular bone volume in CKD in the presence of secondary hyperparathyroidism, but does not benefit extraskeletal calcification or cortical biomechanical properties. Calcium effectively reduces PTH and benefits both cortical and trabecular bone yet increases the degree of extra skeletal calcification. © 2014 American Society for Bone and Mineral Research.

Parathyroid hormone and clinical outcome in kidney transplant patients with optimal transplant function

BACKGROUND

The aim of the study was to investigate whether serum levels of intact parathyroid hormone (iPTH) are associated with an increased risk of cardiovascular events, graft loss, or mortality in kidney transplant patients with optimal transplant function.

METHODS

From the Norwegian Renal Registry, we identified 522 patients who received a first kidney transplant from 2001 to 2008 with optimal transplant function defined as an estimated glomerular filtration rate (eGFR)≥60 mL/min/1.73 m2, more than one yr after transplantation. Cox's proportional hazard models were used to assess the association between iPTH measured 10 wk after transplantation and the composite endpoint. The estimates were adjusted for age, gender, serum calcium, serum phosphate, diabetes mellitus, cardiovascular disease, and time on dialysis prior to transplantation.

RESULTS

Median follow-up time was 3.9 yr (interquartile range, IQR: 2.0-6.0 yr). Patients in the third iPTH quartile (9.3-14.4 pM) had the lowest risk for reaching the composite endpoint. Patients in the fourth iPTH quartile (>14.4 pM) had an increased risk compared to those in the third quartile (HR: 2.60, 95% CI: 1.10-6.16, p=0.03).

CONCLUSION

In patients with optimal transplant function, iPTH levels are associated with a clinical outcome consisting of cardiovascular events, graft loss, and all-cause mortality.

Effects of dietary phosphate on adynamic bone disease in rats with chronic kidney disease--role of sclerostin?

High phosphate intake is known to aggravate renal osteodystrophy along various pathogenetic pathways. Recent studies have raised the possibility that dysregulation of the osteocyte Wnt/β-catenin signaling pathway is also involved in chronic kidney disease (CKD)-related bone disease. We investigated the role of dietary phosphate and its possible interaction with this pathway in an experimental model of adynamic bone disease (ABD) in association with CKD and hypoparathyroidism. Partial nephrectomy (Nx) and total parathyroidectomy (PTx) were performed in male Wistar rats. Control rats with normal kidney and parathyroid function underwent sham operations. Rats were divided into three groups and underwent pair-feeding for 8 weeks with diets containing either 0.6% or 1.2% phosphate: sham 0.6%, Nx+PTx 0.6%, and Nx+PTx 1.2%. In the two Nx+PTx groups, serum creatinine increased and blood ionized calcium decreased compared with sham control group. They also presented hyperphosphatemia and reduced serum parathyroid hormone (PTH) and fibroblast growth factor 23 (FGF23) levels. Fractional urinary excretion of phosphate increased in Nx+PTx 1.2% rats despite lower PTH and FGF23 levels than in sham group. These biochemical changes were accompanied by a decrease in bone formation rates. The Nx+PTx 1.2% group had lower bone volume (BV/TV), higher osteoblast and osteocyte apoptosis, and higher SOST and Dickkopf-1 gene expression than the Nx+PTx 0.6% group. Nx+PTx 0.6% rat had very low serum sclerostin levels, and Nx+PTx 1.2% had intermediate sclerostin levels compared with sham group. Finally, there was a negative correlation between BV/TV and serum sclerostin. These results suggest that high dietary phosphate intake decreases bone volume in an experimental model of CKD-ABD, possibly via changes in SOST expression through a PTH-independent mechanism. These findings could have relevance for the clinical setting of CKD-ABD in patients who low turnover bone disease might be attenuated by optimal control of phosphate intake and/or absorption.

Impact of age on survival predictability of bone turnover markers in hemodialysis patients

BACKGROUND

Abnormalities in serum alkaline phosphatase (ALP) and intact parathyroid hormone (PTH) concentrations, as biochemical markers of bone turnover in dialysis patients, correlate with increased mortality in maintenance hemodialysis (MHD) patients. Changes in bone turnover rate vary with age. The mortality predictability of serum ALP and PTH levels in MHD patients may be different across ages.

METHODS

We examined differences across four age groups (18 to <45, 45 to <65, 65 to <75 and ≥ 75 years) in the mortality predictability of serum ALP and PTH in 102 149 MHD patients using Cox models.

RESULTS

Higher serum ALP levels were associated with higher mortality across all ages; however, the ALP-mortality association was much stronger in young patients (<45 years) compared with older patients. The association between higher serum PTH levels and mortality was stronger in older patients compared with the younger groups. Serum PTH levels were incrementally associated with mortality only in middle-aged and elderly patients (≥ 45 years). Compared with patients with serum PTH 150 to <300 pg/mL, the death risks were higher in patients with serum PTH 300 to <600 pg/mL [HRs (95% CI): 1.05 (1.01-1.10), 1.15 (1.10-1.21) and 1.25 (1.19-1.31) for patients 45 to <65, 65 to <75 and ≥ 75 years, respectively], and ≥ 600 pg/mL [HRs(95% CI): 1.07 (1.01-1.14), 1.31(1.21-1.42) and 1.45(1.33-1.59) for age categories 45 to <65, 65 to <75 and ≥ 75 years, respectively]. However, no significant association between higher serum PTH levels and mortality was observed in patients <45 years.

CONCLUSIONS

There are important differences in mortality-predictability of serum ALP and PTH in older MHD patients compared with their younger counterparts. The effect of age needs to be considered when interpreting the prognostic implications of serum ALP and PTH levels.

Potential beneficial role of sevelamer hydrochloride in diabetic retinopathy

Patients with chronic kidney disease (CKD) experience co-morbid illnesses, including cardiovascular disease and retinopathy. Sevelamer hydrochloride (Renagel®); a non-calcium phosphate binder reduces coronary artery and aortic calcification as compared to calcium containing phosphate binders and additionally effects inflammatory biomarkers such as C-reactive protein (CRP), and lowers LDL cholesterol in patients with CKD. Since retinopathy is proven to be associated with increased coronary calcification, shared pathophysiological processes may contribute to both microvascular and macrovascular disease. We here suggest three different mechanisms of possible sevelamer's influence on the retinopathy: (1) by direct effect on the microvasculature through lowering CRP and LDL, involved in endothelial dysfunction and atherogenesis, (2) indirectly by attenuation of vascular calcification of aorta and carotid internal artery, it reduces ischaemia and improves circulation in the opthalmic artery and hence postponing retinopathy, (3) through hypertension by reducing atherosclerosis and calcification of carotid arteries, sevelamer decreases stiffness and intima-media wall thickness, therefore lowering blood pressure, which is well known to increase progression of diabetic retinopathy. So far no studies have yet been published on the direct influence of sevelamer on the retinopathy which we believe has good theoretical background. With its combined macrovascular and microvascular effect, sevelamer could potentially postpone and/or decrease retinopathy in diabetic patients with hypertension, and that are on hemodialysis or even predialysis patients.

FGF23 neutralization improves chronic kidney disease-associated hyperparathyroidism yet increases mortality

Chronic kidney disease-mineral and bone disorder (CKD-MBD) is associated with secondary hyperparathyroidism (HPT) and serum elevations in the phosphaturic hormone FGF23, which may be maladaptive and lead to increased morbidity and mortality. To determine the role of FGF23 in the pathogenesis of CKD-MBD and development of secondary HPT, we developed a monoclonal FGF23 antibody to evaluate the impact of chronic FGF23 neutralization on CKD-MBD, secondary HPT, and associated comorbidities in a rat model of CKD-MBD. CKD-MBD rats fed a high-phosphate diet were treated with low or high doses of FGF23-Ab or an isotype control antibody. Neutralization of FGF23 led to sustained reductions in secondary HPT, including decreased parathyroid hormone, increased vitamin D, increased serum calcium, and normalization of bone markers such as cancellous bone volume, trabecular number, osteoblast surface, osteoid surface, and bone-formation rate. In addition, we observed dose-dependent increases in serum phosphate and aortic calcification associated with increased risk of mortality in CKD-MBD rats treated with FGF23-Ab. Thus, mineral disturbances caused by neutralization of FGF23 limited the efficacy of FGF23-Ab and likely contributed to the increased mortality observed in this CKD-MBD rat model.

Aortic calcification and femoral bone density are independently associated with left ventricular mass in patients with chronic kidney disease

Background

Vascular calcification and reduced bone density are prevalent in chronic kidney disease and linked to increased cardiovascular risk. The mechanism is unknown. We assessed the relationship between vascular calcification, femoral bone density and left ventricular mass in patients with stage 3 non-diabetic chronic kidney disease in a cross-sectional observational study.

Methodology and Principal Findings

A total of 120 patients were recruited (54% male, mean age 55±14 years, mean glomerular filtration rate 50±13 ml/min/1.73 m²). Abdominal aortic calcification was assessed using lateral lumbar spine radiography and was present in 48%. Mean femoral Z-score measured using dual energy x-ray absorptiometry was 0.60±1.06. Cardiovascular magnetic resonance imaging was used to determine left ventricular mass. One patient had left ventricular hypertrophy. Subjects with aortic calcification had higher left ventricular mass compared to those without (56±16 vs. 48±12 g/m², P = 0.002), as did patients with femoral Z-scores below zero (56±15 vs. 49±13 g/m², P = 0.01). In univariate analysis presence of aortic calcification correlated with left ventricular mass (r = 0.32, P = 0.001); mean femoral Z-score inversely correlated with left ventricular mass (r = −0.28, P = 0.004). In a multivariate regression model that included presence of aortic calcification, mean femoral Z-score, gender and 24-hour systolic blood pressure, 46% of the variability in left ventricular mass was explained (P<0.001).

Conclusions

In patients with stage 3 non-diabetic chronic kidney disease, lower mean femoral Z-score and presence of aortic calcification are independently associated with increased left ventricular mass. Further research exploring the pathophysiology that underlies these relationships is warranted.

Vitamin D in kidney disease: pathophysiology and the utility of treatment

CKD is associated with decreased vitamin D metabolites, both the storage form 25(OH)D and the active form 1,25-dihydroxyvitamin D. This contributes to hyperparathyroidism, and increased levels of PTH mobilize minerals from the skeleton and increase the risk for fractures. Treatment with vitamin D sterols efficiently reduces secondary hyperparathyroidism of CKD. Observational studies suggest survival and other potential benefits of vitamin D treatment in the CKD population. These observations need to be verified with controlled prospective trials.

Phosphate: a stealthier killer than previously thought?

The kidneys excrete excess dietary phosphate, and patients with chronic kidney disease may suffer from phosphate overload and hyperphosphatemia. In chronic kidney disease, hyperphosphatemia has emerged as a risk factor for vascular calcification, cardiovascular mortality, left ventricular hypertrophy, and progression of chronic kidney disease. Serum phosphate at the upper limits of normal has also been associated with adverse outcomes in patients with relatively preserved kidney function. Of note, hyperphosphatemia is not a sensitive indicator of phosphate overload. In this regard, increased circulating fibroblast growth factor-23, a phosphatonin that is released in response to phosphate overload, is independently associated with adverse outcomes in patients with and without chronic kidney disease. Direct effects of extracellular phosphate on vascular calcification or cardiovascular cell biology; adverse consequences of adaptive mechanisms activated to limit phosphate overload, such as left ventricular hypertrophy induced by fibroblast growth factor-23; or epidemiological associations of additional cardiovascular risk factors with chronic kidney disease may underlie these observations. We now review the pathophysiology of phosphate, its relationship with cardiovascular outcomes, the potential consequences for patient care related to dietary phosphate and phosphate binders, and the clinical relevance for patients without overt chronic kidney disease.

Fibroblast growth factor 23 (FGF23) and alpha-klotho stimulate osteoblastic MC3T3.E1 cell proliferation and inhibit mineralization

Elevated serum levels of the phosphate-regulating hormone fibroblast growth factor 23 (FGF23) are found in patients with phosphate wasting diseases and chronic kidney disease-mineral and bone disorder (CKD-MBD). These diseases are associated with rickets and renal osteodystrophy, respectively. FGF23 is secreted from osteoblastic cells and signals through FGFRs, membrane coreceptor alpha-Klotho (Klotho), and, possibly, a circulating form of Klotho. Despite the absence of detectable Klotho on osteoblastic cells, studies have suggested that forced FGF23 expression in osteoblasts inhibited mineralization. Thus, we examined the effects of exogenously applied FGF23 on osteoblastic MC3T3.E1 cell proliferation and differentiation, with and without soluble Klotho. MC3T3.E1 cells were cultured in osteoblast differentiation medium, supplemented with FGF23 (0.1-1,000 ng/mL), Klotho (50 ng/mL), the combination FGF23 + Klotho, and FGF2 (100 ng/mL) as a control. Neither FGF23 nor Klotho exposure affected proliferation of day 4 growth phase cells or mineralization of day 14 cultures. In contrast, FGF23 + Klotho resulted in inhibition of mineralization and osteoblast activity markers at day 14, and a slight, reproducible induction of proliferation. Inhibition of FGFR1, but not FGFR2 or FGFR3, completely restored FGF23 + Klotho-induced inhibition of alkaline phosphatase (ALP) activity at day 7. ALP activity was partially restored by the MAPK inhibitor U0126 but not inhibitors p38 and P13K. Thus, soluble Klotho enables FGF23 signaling in MC3T3.E1 cells, likely through FGFR 1(IIIc). Elevated FGF23 actions, in part, appear to parallel FGF2 with lower potency. In addition to affecting bone via indirect phosphate wasting pathways, supraphysiological FGF23 and soluble Klotho may directly impact bone in diseases with elevated FGF23 levels.

Endothelin but Not Angiotensin II May Mediate Hypertension-Induced Coronary Vascular Calcification in Chronic Kidney Disease

To understand the relationship between putative neurohormonal factors operative in hypertension and coronary artery calcification (CAC), the relevant cellular actions of angiotensin (Ang II) and endothelin-1 (ET-1) are reviewed. There is compelling evidence to implicate ET-1 in CAC. ET-1 increases phosphate transport with a 42 to 73% increase in V_max. Increased cellular phosphate may induce CAC through increased Ca x phosphate product, transformation of vascular smooth muscle cells into a bone-producing phenotype or cell apoptosis that releases procalcific substances. ET-1 is increased in several models of vascular calcification. ET-1 inhibits inhibitors of calcification, matrix Gla and osteoprotegerin, while enhancing pro-calcific factors such as BMP-2 and osteopontin. In contrast, Ang II inhibits phosphate transport decreasing V_max by 38% and increases matrix Gla. Ang II also stimulates bone resorption. Vascular calcification is reduced by ET-1 A receptor antagonists and to a greater extent than angiotensin receptor blockade although both agents reduce blood pressure.

Is coronary artery calcification associated with vertebral bone density in nondialyzed chronic kidney disease patients?

BACKGROUND AND OBJECTIVES

Low bone mineral density and coronary artery calcification (CAC) are highly prevalent among chronic kidney disease (CKD) patients, and both conditions are strongly associated with higher mortality. The study presented here aimed to investigate whether reduced vertebral bone density (VBD) was associated with the presence of CAC in the earlier stages of CKD.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Seventy-two nondialyzed CKD patients (age 52 ± 11.7 years, 70% male, 42% diabetics, creatinine clearance 40.4 ± 18.2 ml/min per 1.73 m(2)) were studied. VBD and CAC were quantified by computed tomography.

RESULTS

CAC > 10 Agatston units (AU) was observed in 50% of the patients (median 120 AU [interquartile range 32 to 584 AU]), and a calcification score ≥ 400 AU was found in 19% (736 [527 to 1012] AU). VBD (190 ± 52 Hounsfield units) correlated inversely with age (r = -0.41, P < 0.001) and calcium score (r = -0.31, P = 0.01), and no correlation was found with gender, creatinine clearance, proteinuria, lipid profile, mineral parameters, body mass index, and diabetes. Patients in the lowest tertile of VBD had expressively increased calcium score in comparison to the middle and highest tertile groups. In the multiple logistic regression analysis adjusting for confounding variables, low VBD was independently associated with the presence of CAC.

CONCLUSIONS

Low VBD was associated with CAC in nondialyzed CKD patients. The authors suggest that low VBD might constitute another nontraditional risk factor for cardiovascular disease in CKD.

Cardiovascular and Renal Links along the Cardiorenal Continuum

The cardiorenal syndrome includes the widely known relationship between kidney function and cardiovascular disease. A large number of patients have various degrees of heart and kidney dysfunction worldwide, both in developed and developing countries. Disorders affecting one of them mostly involve the other. Such interactions represent the pathogenesis for a clinical condition called cardiorenal syndrome. Renal and cardiovascular disease shares similar etiologic risk factors. The majority of vascular events are caused by accelerated atherosclerosis. Moreover, cardiovascular events rarely occur in patients without underlying disease; rather, they typically take place as the final stage of a pathophysiological process that results in progressive vascular damage, including vital organ damage, specifically the kidney and the heart if these factors are uncontrolled. Chronic kidney disease is a novel risk factor included at this stage that accelerates both vascular and cardiac damage.

Confusion on the complexity of calcium balance

Calcium balance is an overall assessment of the net calcium taken in minus the net calcium taken out. It can only be assessed when patients are in steady state and requires complicated isotope methods that can simultaneously assess intestinal absorption and endogenous secretion, urinary and stool excretion, bone calcium uptake and removal, and dialysate calcium removal. By virtue of the need for steady state, formal balance studies cannot be accurately carried out in patients on dialysis. However, many of the components of calcium balance have been assessed. Importantly, because 99% of calcium is in bone, studies must accurately assess both the rapidly exchangeable calcium from the bone surface and the net bone calcium balance that results from the difference in bone formation minus resorption. While it is tempting to adjust the dialysate calcium concentration to correct the net positive calcium balance that is likely present in patients who receive calcium-based phosphate binders, the reality is that the highly variable, yet important, role of bone cannot be easily assessed at the bedside. Thus, it is best to prevent the calcium overload in the first place by avoiding high-dose calcium-based phosphate binders and optimizing bone remodeling.

Surrogate markers of cardiovascular disease in CKD: what's under the hood?

Although clinical cardiovascular outcomes, such as heart attack, stroke, and sudden cardiac death, have a dramatic onset, they result from prolonged exposure to an ever-growing array of risk factors. Several noninvasive procedures are available to assess the cumulative effect of these exposures with the goal of more precisely estimating a person's cardiovascular risk. These include ankle-brachial index, which provides an estimation of obstruction in major-vessel lumen caliber; carotid ultrasound, which evaluates carotid intima-media thickness and plaque, visibly quantifying atherosclerotic burden; aortic pulse wave velocity, which provides a measure of large-artery stiffness; and echocardiography, which measures left ventricular mass, providing a measure of subclinical hypertensive heart disease. In this narrative review, we discuss the role of each of these measures, with a particular emphasis on patients with chronic kidney disease.

Using vertebral bone densitometry to determine aortic calcification in patients with chronic kidney disease

BACKGROUND

Vascular calcification (VC) is a major contributor to increased cardiovascular (CV) disease in chronic kidney disease (CKD) and an independent predictor of mortality. VC is inversely correlated with bone mineral density (BMD). Screening for VC may be useful to determine those at greater CV risk and dual-energy X-ray absorptiometry (DXA) may have a dual role in providing VC measurement as well as BMD.

METHODS

We report cross-sectional data on 44 patients with CKD stages 3-4 and aim to determine and validate measurement of VC using DXA. Patients had computed tomography (CT) of abdominal aorta and DXA of lateral lumbar spine, to determine both aortic VC and BMD. Semi-quantitative measurement of VC from DXA was determined (blinded) using previously validated 8- and 24-point scales, and compared with VC from CT. BMD determination from L2 to L4 vertebrae on CT was compared with DXA-reported BMD.

RESULTS

Patients 66% male, 57% diabetic, had mean age 63.4 years and mean estimated glomerular filtration rate 31.4 +/- 12 mL/min. Aortic VC was present in 95% on CT, mean 564.9 +/- 304 Hounsfield units (HU). Aortic VC was seen in 68% on lateral DXA, mean scores 5.1 +/- 5.9 and 1.9 +/- 1.9 using 24- and 8-point scales, respectively. Strong correlation of VC measurement was present between CT and DXA (r 0.52, P < 0.001). For DXA VC 24-point score, intraclass correlations for intra-rater and inter-rater agreement were 0.91 and 0.64, respectively (8-point scale, intraclass correlations 0.90 and 0.69). Vertebral BMD measured by CT (mean 469.3 HU L2-4) also significantly correlated with lateral DXA-reported BMD (mean spine T-score -0.67 +/- 1.6) (r 0.56, P < 0.001).

CONCLUSION

Despite limitations in CKD, DXA may be useful as lateral DXA images provide concurrent assessment of aortic calcification as well as lumbar spine BMD, both correlating significantly with CT measurements. Lateral DXA may provide VC screening to determine patients at greater CV risk although more studies are needed to evaluate their potential role.

Fibroblast growth factor (FGF)-23 and fetuin-A in calcified carotid atheroma

AIMS

Human atheroma calcification occurs secondary to repetitive injury/remodelling of the vessel wall and might be initiated by adherence of mineral-loaded fetuin-A whether or not professional matrix mineralizing cells are present. The aim was to investigate the contribution of fibroblast growth factor (FGF)-23 to ectopic mineralization.

METHODS AND RESULTS

Serial sections of formalin-fixed paraffin-embedded human carotid atheroma (n = 54) were investigated with respect to (i) size and distribution of calcific deposits, (ii) indicators of chondrogenic/osteogenic transformation, and (iii) expression of fetuin-A and FGF-23. All specimens were calcified and SOX-9, collagen type II, cathepsin-K, fetuin-A and FGF-23 expression was seen in 46, 53, 53, 54 and 48 specimens, respectively. The intracellular detection of FGF-23 (45/48) indicates local synthesis. Whereas fetuin-A expression was seen also within areas of vascular smooth muscle actin-positive cells adjacent to calcific deposits, FGF-23 expression was apparently restricted to the mineralization-prone areas. Both local expression and FGF-23 serum concentrations were significantly associated with the degree of atheroma calcification.

CONCLUSIONS

Besides the induction of bone islets and subsequent mineral deposition, severe remodelling of the vessel wall is sufficient to create a mineralizable fetuin-A-attracting microenvironment. FGF-23 might contribute to the formation of proper mineral, i.e. control local phosphate concentration.

The bone-vascular axis in chronic kidney disease

PURPOSE

This review highlights the most recent publications addressing the relationship between bone and vascular calcification in patients with chronic and end-stage kidney disease.

RECENT FINDINGS

The relatively new term 'chronic kidney disease-mineral bone disorder' reflects the growing reach of chronic kidney disease research into the realm of systems physiology, involving a triad of renal, skeletal, and vascular tissues. Recent studies address underlying mechanisms of the bone and vascular complications of chronic kidney disease and point to a variety of biochemical factors, including phosphatonins (fibroblast growth factor-23, matrix extracellular phosphoglycoprotein), bone morphogenetic protein 7, osteoprotegerin, matrix GLA protein, ectonucleotide pyrophosphatase/phosphodiesterase 1, alkaline phosphatase, and lipid oxidation products. Studies also demonstrate that agents used for treatment of one component of the triad often act on the other components of the triad - beneficially or adversely. These findings emphasize the importance of avoiding the subspecialty, single organ viewpoint when treating individual components of chronic kidney disease-mineral bone disorder.

SUMMARY

The consistent synchrony among chronic kidney disease, aortic calcification, and bone loss offers clues to underlying mechanisms for the systemic abnormalities.

Vascular calcifications and renal osteodystrophy in chronic hemodialysis patients: what is the relationship between them?

INTRODUCTION

Vascular calcifications (VCs) and renal osteodystrophy (ROD) are frequently seen together and represent the major causes of morbidity and mortality in hemodialysis (HD) patients. Some studies suggest a pathogenic link between them, but there is no consensus as yet regarding this issue. The main objective of our study was to establish whether there is any relation between VCs and ROD in our HD patients. We evaluated the prevalence of VCs and ROD and the relationship between VCs and some clinical and biochemical characteristics of HD patients.

METHODS

We examined radiological signs of VCs and ROD on hands and pelvis bone radiographs in 81 chronic HD patients, and we calculated a VC score on this basis.

RESULTS

We found a significant relation between radiological signs of ROD and those of VC (P = 0.019). The patients with ROD had a higher mean VC score (P = 0.02). By linear regression, the VC score correlated directly with serum calcium (Ca), phosphorus (P), intact parathyroid hormone (iPTH) and CaxP product and inversely with serum albumin. The logistic regression model revealed that ROD, male gender and treatment with calcium salts were predictive of VCs development. There were no associations between VCs and age, HD vintage, diabetes, dialysate Ca concentration, vitamin D treatment, spKt/V, URR and C-reactive protein (CRP) levels.

CONCLUSION

There seems to be a pathogenetic link between bone and artery diseases in chronic HD patients. Both VCs and ROD have a high prevalence. ROD, male gender and treatment with calcium salts are risk factors for VCs.