Calcimimetics or vitamin D analogs for suppressing parathyroid hormone in end-stage renal disease: time for a paradigm shift?

Fragility Fractures in End-Stage Chronic Kidney Disease (CKD) Population: Patient-Related and CKD-Related Factor Analysis-A Single-Center Experience

Background: Chronic kidney disease (CKD) stands as a prevalent global health concern, and mineral and bone disease are among the most impactful consequences. A severe complication arising from mineral and bone disease is the occurrence of fragility fractures, which disproportionately affect individuals with CKD compared to the general population. The prevalence of these fractures impacts both survival rates and quality of life. The aims of this study are analyzing and identifying (i) patient-related risk factors and (ii) CKD-related risk factors to contribute to the development of preventive measures for fragility fractures for this population. Methods: A retrospective, single-center observational study was conducted, encompassing patient data from the years 2021 to 2023. Registry data were recorded, including patient-related and CKD-related data. Patients were interviewed about traumatological history, and their answers were recorded. Logistic regression analysis was employed to investigate the association between independent variables and dependent variables. Results: Eighty-four patients, with a mean age of 64.3 ± 15.2 years and a male percentage of 58.3%, were included in this study. Among them, 19.5% exhibited smoking habits. The mean Charlson Comorbidity Index was 3.06 ± 1.21. All patients were diagnosed with end-stage chronic kidney disease, with mean durations of 208 months from the diagnosis and 84.5 months from the beginning of dialysis. The logistic regression analysis, adjusted for age, sex, and CCI, revealed that smoking habits play a significant role as a risk factor for fragility fractures in lower limbs (p: 0.011 *). The incidence of fragility fractures increases directly proportionally to the time since diagnosis (p-value: 0.021 *) and the beginning of dialysis treatment (p-value: 0.001 *). Conclusions: Among patient-related factors, smoking habits seem to significantly affect lower-limb fracture rates (p < 0.05), whereas among CKD-related factors, time since CKD diagnosis and time since the beginning of dialysis treatment are directly related to higher risks of fragility fractures. No relevant correlations emerged in the studied treatments, except for a reduction in proximal femur fracture occurrence when patients underwent a combined treatment of a calcimimetic and a vitamin D analog.

Efficacy and safety of evocalcet in treatment of secondary hyperparathyroidism in chronic kidney disease on hemodialysis patients: A protocol for a systematic review and meta-analysis

BACKGROUND

Secondary hyperparathyroidism (SHPT) have been associated with poor health outcomes in hemodialysis patients. The cinacalcet has popularized in clinic which has efficacy but more adverse events; the novel oral calcimimetic agents evocalcet has appeared in recent years. However, it is currently unknown whether evocalcet produces more beneficial effects and fewer adverse events in patients with SHPT. The aim of this systematic review is to estimate the safety and efficacy of evocacelt.

METHODS

Only randomized controlled trials (RCT) will be included in MEDLINE, EMBASE, the Cochrane Register of Controlled Trials, and PUBMED from July 2010 to July 2020. Two reviewers will screen, select studies, extract data, and assess quality independently. The methodological quality including the risk of bias of the included studies will be evaluated using a modified assessment form, which is based on Cochrane assessment tool. Review Manager 5.3 software will be used for heterogeneity assessment, generating funnel-plots, data synthesis, subgroup analysis, and sensitivity analysis. We will use GRADE system to evaluate the quality of our evidence.

RESULTS

We will provide some more practical and targeted results investigating the effect and safety of evocalcet for SHPT on hemodialysis in the current meta-analysis.

CONCLUSION

The stronger evidence about evocalcet effect and safety will be provided for clinicians and policymakers.

ETHICS AND DISSEMINATION

Ethical approval will be unnecessary because the data being included in this systematic review come from published literature and there will be no concerns regarding privacy. Findings of this research will be disseminated in a peer-reviewed journal or conference presentations.

OSF REGISTRATION NUMBER

DOI 10.17605/OSF.IO/N59RB.

One-year safety and efficacy of intravenous etelcalcetide in patients on hemodialysis with secondary hyperparathyroidism

BACKGROUND

Secondary hyperparathyroidism (sHPT), a common complication of chronic kidney disease, is characterized by elevated serum parathyroid hormone (PTH). Etelcalcetide is an intravenous calcimimetic that increases sensitivity of the calcium-sensing receptor to calcium and decreases PTH secretion. This open-label extension (OLE) trial evaluated the long-term effects of etelcalcetide for sHPT treatment in patients receiving hemodialysis.

METHODS

This 52-week, multicenter, single-arm OLE enrolled patients from three parent trials: two randomized, double-blind, placebo-controlled trials and one open-label, single-arm, 'switch' study from cinacalcet to etelcalcetide. The primary endpoint was to investigate the nature, frequency, severity and relation to treatment of all adverse events (AEs) reported throughout the trial. Secondary endpoints included the proportion of patients with >30% reduction from baseline in PTH and the percentage change from baseline in PTH, albumin-corrected calcium (Ca), phosphate (P) and the calcium-phosphate product (Ca × P).ClinicalTrials.gov identifier: NCT01785875; Amgen study: 20120231.

RESULTS

Overall, 89.8% of the patients experienced one or more treatment-emergent AE. The most common were decreased blood Ca (43.3%), diarrhea (10.8%), vomiting (10.4%) and nausea (9.6%); symptomatic hypocalcemia occurred in 3.7% of the patients. Approximately 68% of patients achieved >30% reduction in PTH, and ∼56% achieved PTH ≤300 pg/mL. Mean percent changes from baseline ranged from -25.4% to -26.1% for PTH, -8.3% to -9.1% for Ca, -3.6% to -4.1% for P and -12.0% to -12.6% for Ca × P.

CONCLUSIONS

Etelcalcetide effectively lowered PTH and its effect was sustained, while no new safety concerns emerged over a 1-year treatment period.

Cinacalcet studies in pediatric subjects with secondary hyperparathyroidism receiving dialysis

BACKGROUND

Secondary hyperparathyroidism (sHPT), a complication of chronic kidney disease (CKD) characterized by persistently elevated parathyroid hormone (PTH), alterations in calcium-phosphorus homeostasis, and vitamin D metabolism, affects 50% of children receiving dialysis. A significant proportion of these children develop CKD-mineral and bone disorder (CKD-MBD), associated with an increased risk of fractures and vascular calcification. The standard of care for sHPT in children includes vitamin D sterols, calcium supplementation, and phosphate binders. Several agents are approved for sHPT treatment in adults undergoing dialysis, including vitamin D analogs and calcimimetics, with limited information on their safety and efficacy in children. The calcimimetic cinacalcet is approved for use in adults with sHPT on dialysis, but is not approved for pediatric use outside Europe.

METHODS

This review provides dosing, safety, and efficacy information from Amgen-sponsored cinacalcet pediatric trials and data from non-Amgen sponsored clinical studies.

RESULTS

The Amgen cinacalcet pediatric clinical development program consisted of two Phase 3 randomized studies, one Phase 3 single arm extension study, one open-label Phase 2 study, and two open-label Phase 1 studies. Effects of cinacalcet on PTH varied across studies. Overall, 7.4 to 57.1% of subjects who received cinacalcet in an Amgen clinical trial attained PTH levels within recommended target ranges and 22.2 to 70.6% observed a ≥ 30% reduction in PTH. In addition, significant reductions in PTH were demonstrated in all non-Amgen-supported studies.

CONCLUSIONS

To help inform the pediatric nephrology community, this manuscript contains the most comprehensive review of cinacalcet usage in pediatric CKD patients to date.

Refractory hypercalcemia due to an ectopic mediastinal parathyroid gland in a hemodialysis patient: a case report

BACKGROUND

Hypercalcemia crisis is a complex disorder rarely induced by tertiary hyperparathyroidism, which clinically presents as nonsuppressible parathyroid hyperplasia with persistent increased PTH levels and hypercalcemia. It is one of the major risk factors of morbidity and mortality in end-stage renal disease. Parathyroidectomy should be in consideration in dialysis patients with severe hyperparathyroidism who are refractory to medical therapy. The implications and consequences of it, however, are not fully understood.

CASE PRESENTATION

We present a case of a 70 year-old man disturbed by gastrointestinal manifestations due to hypercalcaemic crisis. The patient had longstanding hypercalcaemia and hyperparathyrodism refractory to calcimimetics, calcitonin, hormone and haemodialysis. A ectopic parathyroid gland in anterior mediastinum was found and elucidated by Tc-99 m scan. Futhermore, a video-assisted thoracoscopic parathyroidectomy was performed. Histologically, the tumour consisted of densely arranged chief cells immunohistochemically positive for PTH antigens. Consequently, calcium and parathormone were declining stably without any complications.

CONCLUSIONS

On account of refractory hypercalcemia and hyperparathyroidism, radionuclide scanning is useful in the diagnosis of ectopic parathyroid gland. it is of great significance for multidisciplinary therapy combing anesthesia, surgical, endocrinology and nephrology staff.

NUTRITIONAL OR ACTIVE VITAMIN D FOR THE CORRECTION OF MINERAL METABOLISM ABNORMALITIES IN NON-DIALYSIS CHRONIC KIDNEY DISEASE PATIENTS?

CONTEXT

Benefits of vitamin D therapies in chronic kidney disease (CKD) are debated.

OBJECTIVE

To compare the effects of medium-term native (VitD) and active (VDRA) vitamin D on parameters of mineral metabolism and arterial function in non-dialysis CKD.

DESIGN

Open-label, active comparator, randomized study.

SUBJECTS AND METHODS

Forty-eight adult patients, vitamin D naïve, CKD stage 3 to 5 with increased parathyroid hormone (iPTH) were randomized to receive either oral cholecalciferol 1000UI/day (n=24) or paricalcitol 1mcg/day (n=24) for 6 months. Median changes at end of study vs. baseline in serum calcidiol, iPTH, total alkaline phosphatase (ALP), and cardio-ankle vascular index (CAVI) were the efficacy parameters.

RESULTS

Higher increase in calcidiol (15.5 [95%CI 13.3; 17.2] vs. 0.4 [95%CI -6.1; 3.7]ng/mL, p<0.001) were found in VitD group. Conversely, the decline of iPTH (-35.2 [95%CI -83; 9] vs. 13.3 [95%CI -8.1; 35]pg/mL, p=0.008) and ALP (-34 [95%CI -58; -11] vs. -10 [95%CI -23; -2]U/L, p=0.02) were greater after paricalcitol. More subjects experienced iPTH decrease in VDRA group (71% vs. 39%, p=0.03). The variation in CAVI and the incidence of hypercalcemia and hyperphosphatemia were similar.

CONCLUSIONS

It seems that secondary hyperparathyroidism was more efficiently treated by VDRA, whereas cholecalciferol better corrected the calcidiol deficiency in non-dialysis CKD.

Overview of the 2017 KDIGO CKD-MBD Update: Practice Implications for Adult Hemodialysis Patients

Renal dietitians play a pivotal role in the ongoing management of chronic kidney disease in patients on hemodialysis. Awareness of changes to clinical practice guidelines that may impact laboratory parameters associated with chronic kidney disease-mineral and bone disorder is important for optimal patient care. In this article, the Kidney Disease: Improving Global Outcomes 2017 Clinical Practice Guideline Update recommendations related to the treatment of secondary hyperparathyroidism in adults on hemodialysis are reviewed and treatment implications for renal dietitians discussed. Specific attention is given to the integration of updated recommendations such as the use of calcimimetics as part of a combination approach to the existing treatment paradigm. Renal dietitians can directly apply the updated clinical recommendations in the evaluation of diet composition; food additives; medication adherence challenges with phosphate binder type and use and serial monitoring of phosphorus, calcium, and parathyroid hormone levels to inform clinical decisions on treatment options for patients.

Management and outcomes of hyperparathyroidism: a case series from a single institution over two decades

Background

Hyperparathyroidism is a frequent endocrine disorder with variable clinical manifestations and outcomes. We aimed to evaluate clinical presentations, management and outcomes of hyperparathyroidism.

Methods

A retrospective study was conducted to include all patients presented with hyperparathyroidism between 1995 and 2014 at a single tertiary hospital with an average follow-up period of 46 months. Data were reviewed for clinical presentations, diagnostic work-up, intraoperative findings, management, and outcomes.

Result

We identified 161 patients with hyperparathyroidism; 69% were females and the mean age was 49.4±15 years. Patients presented mainly with musculoskeletal (65.8%), renal (37.3%), gastrointestinal tract (53.8%) and neuropsychiatric (8.8%) manifestations. At presentation, mean serum calcium and parathyroid hormone levels were elevated while mean vitamin D level was lower. Sestamibi-^99mTc (MIBI) scintigraphy was done for 134 patients (83.2%) and was positive in 94 (70%). Primary hyperparathyroidism (67.7%) was the most frequent diagnosis followed by secondary (29.8%) and tertiary hyperparathyroidism (2.5%). The frequent indication for surgery was hypercalcemia (67.3%), bone disease (35.6%) and renal calculi (28.9%). The main postoperative pathology was parathyroid adenoma (63.1%) followed by hyperplasia (37.3%). Fourteen (8.9%) and 18 (11.4%) patients had persistent and recurrent hyperparathyroidism, respectively. Autotransplantation of parathyroid tissue was done in 36 cases.

Conclusion

Primary hyperparathyroidism is the most frequent cause of the parathyroid disease. Parathyroidectomy is the effective surgical approach in symptomatic patients. Further studies are needed to establish the association between vitamin D levels, renal disorders and persistent or recurrent hyperparathyroidism.

Management of secondary hyperparathyroidism: practice patterns and outcomes of cinacalcet treatment with or without active vitamin D in Austria and Switzerland - the observational TRANSIT Study

Secondary hyperparathyroidism is a complex disorder requiring an individualized multicomponent treatment approach. This study was conducted to identify treatment combinations used in clinical practice in Austria and Switzerland and the potential to control this disorder. A total of 333 adult hemodialysis and peritoneal dialysis patients were analyzed. All patients received conventional care prior to initiation of a cinacalcet-based regimen. During the study, treatment components, e.g. cinacalcet, active vitamin D analogues and phosphate binders, were adapted to individual patient requirements and treatment dynamics were documented. Overall, the mean intact parathyroid hormone (iPTH) increased from 64.2 pmol/l to 79.6 pmol/l under conventional therapy and decreased after cinacalcet initiation to 44.0 pmol/l after 12 months (mean decrease between baseline and 12 months −45%). Calcium remained within the normal range throughout the study and phosphorus ranged around the upper limit of normal. The Kidney Disease: Improving Global Outcomes (KDIGO) target achievement for iPTH increased from 44.5% of patients at baseline to 65.7% at 12 months, corrected calcium from 58.9% to 51.9% and phosphorus from 18.4% to 24.4%. On average, approximately 30% of patients adapted their regimen from one observation period to the next. The reasons for changing a given regimen were to attain or maintain any of the bone mineral markers within recommended targets and to avoid developments to extreme values. Some regional differences in practice patterns were identified. No new safety signals emerged. In conclusion, cinacalcet appears to be a necessary treatment component to achieve recommended targets. The detailed composition of the treatment mix should be adapted to patient requirements and reassessed on a regular basis.

A computationally identified compound antagonizes excess FGF-23 signaling in renal tubules and a mouse model of hypophosphatemia

Fibroblast growth factor-23 (FGF-23) interacts with a binary receptor complex composed of α-Klotho (α-KL) and FGF receptors (FGFRs) to regulate phosphate and vitamin D metabolism in the kidney. Excess FGF-23 production, which causes hypophosphatemia, is genetically inherited or occurs with chronic kidney disease. Among other symptoms, hypophosphatemia causes vitamin D deficiency and the bone-softening disorder rickets. Current therapeutics that target the receptor complex have limited utility clinically. Using a computationally driven, structure-based, ensemble docking and virtual high-throughput screening approach, we identified four novel compounds predicted to selectively inhibit FGF-23-induced activation of the FGFR/α-KL complex. Additional modeling and functional analysis found that Zinc13407541 bound to FGF-23 and disrupted its interaction with the FGFR1/α-KL complex; experiments in a heterologous cell expression system showed that Zinc13407541 selectivity inhibited α-KL-dependent FGF-23 signaling. Zinc13407541 also inhibited FGF-23 signaling in isolated renal tubules ex vivo and partially reversed the hypophosphatemic effects of excess FGF-23 in a mouse model. These chemical probes provide a platform to develop lead compounds to treat disorders caused by excess FGF-23.

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.

Cinacalcet versus standard treatment for chronic kidney disease: a protocol for a systematic review and meta-analysis

BACKGROUND

Chronic kidney disease-mineral and bone disorders (CKD-MBD) have been associated with poor health outcomes, including diminished quality and length of life. Standard management for CKD-MBD includes phosphate-restricted diet, active vitamin D, vitamin D analogs, and phosphate binders. Persistently elevated parathyroid hormone (PTH) levels may require the addition of Cinacalcet hydrochloride (cinacalcet) which sensitizes calcium receptors on the parathyroid glands. The objective of this systematic review is to compare the effect of cinacalcet versus standard treatment in patients with CKD-MBD.

METHODS/DESIGN

Data sources will include MEDLINE, EMBASE, the Cochrane Register of Controlled Trials, and Web of Science from 1996 to June 2015. Teams of two reviewers will, independently and in duplicate, screen titles and abstracts and potentially eligible full text reports to determine eligibility, and subsequently abstract data and assess risk of bias in eligible trials. We will calculate the effect estimates (risk ratios or mean differences) and 95 % confidence intervals, as well as statistical measures of variability in results across studies using random effect models for patient-important and intermediate outcomes. We will use the GRADE (Grading of Recommendations, Assessment, Development and Evaluation) approach to rate the quality of evidence about estimates of effect on an outcome-by-outcome basis. We will present our results with a GRADE summary table.

DISCUSSION

Our review will explore the effect of cinacalcet versus standard treatment in patients with CKD-MBD. The results of this systematic review will help guide management of this patient population, and identify targets for future research.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42015020318 http://www.crd.york.ac.uk/PROSPERO/display_record.asp?ID=CRD42015020318.

Molecular basis of Klotho: from gene to function in aging

The discovery of the Klotho (KL) gene, which was originally identified as a putative aging-suppressor gene, has generated tremendous interest and has advanced understanding of the aging process. In mice, the overexpression of the KL gene extends the life span, whereas mutations to the KL gene shorten the life span. The human KL gene encodes the α-Klotho protein, which is a multifunctional protein that regulates the metabolism of phosphate, calcium, and vitamin D. α-Klotho also may function as a hormone, although the α-Klotho receptor(s) has not been found. Point mutations of the KL gene in humans are associated with hypertension and kidney disease, which suggests that α-Klotho may be essential to the maintenance of normal renal function. Three α-Klotho protein types with potentially different functions have been identified: a full-length transmembrane α-Klotho, a truncated soluble α-Klotho, and a secreted α-Klotho. Recent evidence suggests that α-Klotho suppresses the insulin and Wnt signaling pathways, inhibits oxidative stress, and regulates phosphatase and calcium absorption. In this review, we provide an update on recent advances in the understanding of the molecular, genetic, biochemical, and physiological properties of the KL gene. Specifically, this review focuses on the structure of the KL gene and the factors that regulate KL gene transcription, the key sites in the regulation of α-Klotho enzyme activity, the α-Klotho signaling pathways, and the molecular mechanisms that underlie α-Klotho function. This current understanding of the molecular biology of the α-Klotho protein may offer new insights into its function and role in aging.

Treatment of phosphate retention: The earlier the better?

Over the last 15 years, our knowledge and understanding of the underlying mechanisms involved in the regulation of calcium and phosphate homeostasis in chronic kidney disease have advanced dramatically. Contrary to general opinion in the 20(th) century that moderate hypercalcemia and hyperphosphatemia were acceptable in treating secondary hyperparathyroidism, the calcium and phosphate load is increasingly perceived to be a major trigger of vascular and soft tissue calcification. The current treatment options are discussed in view of historical developments and the expectations of the foreseeable future, focusing on the early treatment of hyperphosphatemia. At present, we lack indisputable evidence that active intervention using currently available drugs is of benefit to patients in chronic kidney disease stages 3 and 4.

A systems biology preview of the relationships between mineral and metabolic complications in chronic kidney disease

There are emerging data that the skeleton is connected to systemic biological functions through the release of two osteoblast-/osteocyte-derived hormones, fibroblastic growth factor 23 (FGF23) and undercarboxylated osteocalcin (Ocn). FGF23 is important in the regulation of phosphate and vitamin D metabolism, whereas Ocn participates in endocrine networks, coordinating bone and fat mass, energy metabolism, and sex hormone production. Bone remodeling and mineralization per se, along with the hormones leptin, insulin, glucocorticoids, PTH, and 1,25(OH)2D, regulate the release of FGF23 and Ocn, leading to complex cross-talk and coordination between endocrine networks previously thought to be distinct. These pathways are particularly important in chronic kidney disease, in which both FGF23 and Ocn are increased. Although these hormones initially serve an adaptive role, with progressive loss of renal function they show maladaptive effects, particularly on the cardiovascular system, through multiple mechanisms, including possible cross-talk with the renin angiotensin system. The complex interconnections between the various endocrine networks in chronic kidney disease may account for the difficulty in treating the uremic state.

Management of natural and added dietary phosphorus burden in kidney disease

Phosphorus retention occurs from higher dietary phosphorus intake relative to its renal excretion or dialysis removal. In the gastrointestinal tract the naturally existing organic phosphorus is only partially (∼60%) absorbable; however, this absorption varies widely and is lower for plant-based phosphorus including phytate (<40%) and higher for foods enhanced with inorganic phosphorus-containing preservatives (>80%). The latter phosphorus often remains unrecognized by patients and health care professionals, even though it is widely used in contemporary diets, in particular, low-cost foods. In a nonenhanced mixed diet, digestible phosphorus correlates closely with total protein content, making protein-rich foods a main source of natural phosphorus. Phosphorus burden is limited more appropriately in predialysis patients who are on a low-protein diet (∼0.6 g/kg/d), whereas dialysis patients who require higher protein intake (∼1.2 g/kg/d) are subject to a higher dietary phosphorus load. An effective and patient-friendly approach to reduce phosphorus intake without depriving patients of adequate proteins is to educate patients to avoid foods with high phosphorus relative to protein such as egg yolk and those with high amounts of phosphorus-based preservatives such as certain soft drinks and enhanced cheese and meat. Phosphorus rich foods should be prepared by boiling, which reduces phosphorus as well as sodium and potassium content, or by other types of cooking-induced demineralization. The dose of phosphorus-binding therapy should be adjusted separately for the amount and absorbability of phosphorus in each meal. Dietician counseling to address the emerging aspects of dietary phosphorus management is instrumental for achieving a reduction of phosphorus load.

A comparative transcriptome analysis identifying FGF23 regulated genes in the kidney of a mouse CKD model

Elevations of circulating Fibroblast growth factor 23 (FGF23) are associated with adverse cardiovascular outcomes and progression of renal failure in chronic kidney disease (CKD). Efforts to identify gene products whose transcription is directly regulated by FGF23 stimulation of fibroblast growth factor receptors (FGFR)/α-Klotho complexes in the kidney is confounded by both systemic alterations in calcium, phosphorus and vitamin D metabolism and intrinsic alterations caused by the underlying renal pathology in CKD. To identify FGF23 responsive genes in the kidney that might explain the association between FGF23 and adverse outcomes in CKD, we performed comparative genome wide analysis of gene expression profiles in the kidney of the Collagen 4 alpha 3 null mice (Col4a3^−/−) model of progressive kidney disease with kidney expression profiles of Hypophosphatemic (Hyp) and FGF23 transgenic mouse models of elevated FGF23. The different complement of potentially confounding factors in these models allowed us to identify genes that are directly targeted by FGF23. This analysis found that α-Klotho, an anti-aging hormone and FGF23 co-receptor, was decreased by FGF23. We also identified additional FGF23-responsive transcripts and activation of networks associated with renal damage and chronic inflammation, including lipocalin 2 (Lcn2), transforming growth factor beta (TGF-β) and tumor necrosis factor-alpha (TNF-α) signaling pathways. Finally, we found that FGF23 suppresses angiotensin-converting enzyme 2 (ACE2) expression in the kidney, thereby providing a pathway for FGF23 regulation of the renin-angiotensin system. These gene products provide a possible mechanistic links between elevated FGF23 and pathways responsible for renal failure progression and cardiovascular diseases.

Assessment of 24,25(OH)2D levels does not support FGF23-mediated catabolism of vitamin D metabolites

Progressive elevations of fibroblastic growth factor 23 (FGF23) in chronic kidney disease may reduce serum 25-hydroxyvitamin D (25(OH)) and 1,25-dihydroxyvitamin D (1,25(OH)(2)D) levels, via stimulation of 24-hydroxylase (Cyp24a1)-mediated catabolism of these vitamin D metabolites. To test this possibility, we measured serum concentrations of 24,25-dihydroxyvitamin D (24,25(OH)(2)D), a product of Cyp24a1 hydroxylation of 25(OH)D, in the Col4a3 knockout mouse, a model of Alport syndrome-derived chronic kidney disease, and in patients with chronic kidney disease of variable severity. There was an inverse correlation between serum FGF23 and both 25(OH)D and 1,25(OH)(2)D in the mouse model, but no significant relationship was observed in the cross-sectional patient cohort. The FGF23-dependent increase in Cyp24a1 mRNA expression in the mouse kidneys was consistent with the possibility that FGF23 induces vitamin D catabolism. There was, however, a reduction in serum 24,25(OH)(2)D levels, rather than the expected elevation, in both the mice and patients with chronic kidney disease. Low 25(OH)D and elevated FGF23 and parathyroid hormone levels were correlated with the reduced serum 24,25(OH)(2)D concentrations of these patients. Thus, we failed to find support for FGF23-mediated catabolism of vitamin D metabolites in chronic kidney disease assessed by 24,25(OH)(2)D levels.

Phosphorus and nutrition in chronic kidney disease

Patients with renal impairment progressively lose the ability to excrete phosphorus. Decreased glomerular filtration of phosphorus is initially compensated by decreased tubular reabsorption, regulated by PTH and FGF23, maintaining normal serum phosphorus concentrations. There is a close relationship between protein and phosphorus intake. In chronic renal disease, a low dietary protein content slows the progression of kidney disease, especially in patients with proteinuria and decreases the supply of phosphorus, which has been directly related with progression of kidney disease and with patient survival. However, not all animal proteins and vegetables have the same proportion of phosphorus in their composition. Adequate labeling of food requires showing the phosphorus-to-protein ratio. The diet in patients with advanced-stage CKD has been controversial, because a diet with too low protein content can favor malnutrition and increase morbidity and mortality. Phosphorus binders lower serum phosphorus and also FGF23 levels, without decreasing diet protein content. But the interaction between intestinal dysbacteriosis in dialysis patients, phosphate binder efficacy, and patient tolerance to the binder could reduce their efficiency.

Role of FGF23 in vitamin D and phosphate metabolism: implications in chronic kidney disease

FGF23 is a bone-derived hormone that regulates systemic phosphate homeostasis, vitamin D metabolism and α-Klotho expression through a novel bone-kidney axis. FGF23 inhibits renal tubular reabsorption of phosphate through mechanisms independent of PTH as well as reduces circulating 1, 25(OH)(2)D through its dual effects to suppress Cyp27b1 production and to stimulate Cyp24 catabolism of 1,25(OH)(2)D. 1,25(OH)(2)D and other factors regulating bone remodeling/mineralization are the major physiological regulators of FGF23 expression. FGF23 also suppresses the gene transcription of α-klotho by the kidney, which exists as a membrane and soluble protein. Membrane Klotho acts as a coreceptor for and dictates organ specificity of FGF23, whereas soluble Klotho act as an endocrine factor that regulates activity of cell surface glycoproteins and receptors in multiple tissues. Elevated FGF23 levels are responsible for several hereditary and acquired hypophosphatemic rickets disorders. FGF23 and Klotho deficiency have similar phenotypes characterized by hyperphosphatemia, elevated 1,25(OH)(2)D and tumoral calcinosis. FGF23 levels progressively increase during chronic kidney disease (CKD). FGF23 has been proposed to be the initial adaptive response leading to reductions in 1,25(OH)(2)D and secondary hyperparathyroidism (HPT) in CKD. The overall biological effect of this initial step may be to orchestrate a coordinated adaptation to protect the organism from the adverse effects of excess phosphate retention. The second step involves the effects of PTH on bone remodeling that further stimulates FGF23 production through both direct and indirect mechanisms related to alterations in extracellular matrix factors. PTH further amplifies FGF23 expression in later stages of CKD to compensate for the increased phosphate efflux from bone caused by excessive bone turnover. While many aspects of the regulation and functions of FGF23 remain to be established, the idea that FGF23 hormone is the initial adaptive hormonal response in CKD that suppresses 1,25(OH)(2)D, reduces gastrointestinal calcium and phosphate absorption and leads to a secondary HPT represents a paradigm shift in the conceptualization of the pathogenesis of secondary hyperparathyroidism. In addition, the prevalent thought that CKD is a functional "vitamin D deficient state" requiring therapy with 1,25(OH)(2)D analogs is challenged by effects of FGF23 to potentially lower both 25(OH)D and 1,25(OH)D by induction of Cyp24-mediated degradation. Finally, increments in FGF23 are associated with increased cardiovascular mortality in CKD. Whether these effects represent direct effects of FGF23 or represent a marker of other abnormalities in CKD remains to be determined.

Phosphate additives in food--a health risk

BACKGROUND

Hyperphosphatemia has been identified in the past decade as a strong predictor of mortality in advanced chronic kidney disease (CKD). For example, a study of patients in stage CKD 5 (with an annual mortality of about 20%) revealed that 12% of all deaths in this group were attributable to an elevated serum phosphate concentration. Recently, a high-normal serum phosphate concentration has also been found to be an independent predictor of cardiovascular events and mortality in the general population. Therefore, phosphate additives in food are a matter of concern, and their potential impact on health may well have been underappreciated.

METHODS

We reviewed pertinent literature retrieved by a selective search of the PubMed and EU databases (www.zusatzstoffe-online.de, www.codexalimentarius.de), with the search terms "phosphate additives" and "hyperphosphatemia."

RESULTS

There is no need to lower the content of natural phosphate, i.e. organic esters, in food, because this type of phosphate is incompletely absorbed; restricting its intake might even lead to protein malnutrition. On the other hand, inorganic phosphate in food additives is effectively absorbed and can measurably elevate the serum phosphate concentration in patients with advanced CKD. Foods with added phosphate tend to be eaten by persons at the lower end of the socioeconomic scale, who consume more processed and "fast" food. The main pathophysiological effect of phosphate is vascular damage, e.g. endothelial dysfunction and vascular calcification. Aside from the quality of phosphate in the diet (which also requires attention), the quantity of phosphate consumed by patients with advanced renal failure should not exceed 1000 mg per day, according to the guidelines.

CONCLUSION

Prospective controlled trials are currently unavailable. In view of the high prevalence of CKD and the potential harm caused by phosphate additives to food, the public should be informed that added phosphate is damaging to health. Furthermore, calls for labeling the content of added phosphate in food are appropriate.

Skeletal secretion of FGF-23 regulates phosphate and vitamin D metabolism

The discovery of fibroblast growth factor 23 (FGF-23) has expanded our understanding of phosphate and vitamin D homeostasis and provided new insights into the pathogenesis of hereditary hypophosphatemic and hyperphosphatemic disorders, as well as acquired disorders of phosphate metabolism, such as chronic kidney disease. FGF-23 is secreted by osteoblasts and osteocytes in bone and principally targets the kidney to regulate the reabsorption of phosphate, the production and catabolism of 1,25-dihydroxyvitamin D and the expression of α-Klotho, an anti-ageing hormone. Secreted FGF-23 plays a central role in complex endocrine networks involving local bone-derived factors that regulate mineralization of extracellular matrix and systemic hormones involved in mineral metabolism. Inactivating mutations of PHEX, DMP1 and ENPP1, which cause hereditary hypophosphatemic disorders and primary defects in bone mineralization, stimulate FGF23 gene transcription in osteoblasts and osteocytes, at least in part, through canonical and intracrine FGF receptor pathways. These FGF-23 regulatory pathways may enable systemic phosphate and vitamin D homeostasis to be coordinated with bone mineralization. FGF-23 also functions as a counter-regulatory hormone for 1,25-dihydroxyvitamin D in a bone-kidney endocrine loop. FGF-23, through regulation of additional genes in the kidney and extrarenal tissues, probably has broader physiological functions beyond regulation of mineral metabolism that account for the association between FGF-23 and increased mortality and morbidity in chronic kidney disease.

Regulation and function of the FGF23/klotho endocrine pathways

Calcium (Ca(2+)) and phosphate (PO(4)(3-)) homeostasis are coordinated by systemic and local factors that regulate intestinal absorption, influx and efflux from bone, and kidney excretion and reabsorption of these ions through a complex hormonal network. Traditionally, the parathyroid hormone (PTH)/vitamin D axis provided the conceptual framework to understand mineral metabolism. PTH secreted by the parathyroid gland in response to hypocalcemia functions to maintain serum Ca(2+) levels by increasing Ca(2+) reabsorption and 1,25-dihydroxyvitamin D [1,25(OH)(2)D] production by the kidney, enhancing Ca(2+) and PO(4)(3-) intestinal absorption and increasing Ca(2+) and PO(4)(3-) efflux from bone, while maintaining neutral phosphate balance through phosphaturic effects. FGF23 is a recently discovered hormone, predominately produced by osteoblasts/osteocytes, whose major functions are to inhibit renal tubular phosphate reabsorption and suppress circulating 1,25(OH)(2)D levels by decreasing Cyp27b1-mediated formation and stimulating Cyp24-mediated catabolism of 1,25(OH)(2)D. FGF23 participates in a new bone/kidney axis that protects the organism from excess vitamin D and coordinates renal PO(4)(3-) handling with bone mineralization/turnover. Abnormalities of FGF23 production underlie many inherited and acquired disorders of phosphate homeostasis. This review discusses the known and emerging functions of FGF23, its regulation in response to systemic and local signals, as well as the implications of FGF23 in different pathological and physiological contexts.

Decreases in PTH in Japanese hemodialysis patients with secondary hyperparathyroidism: associations with changing practice patterns

BACKGROUND AND OBJECTIVES

Control of serum concentrations of calcium (Ca), phosphorus (P), and parathyroid hormone (PTH) is essential for management of secondary hyperparathyroidism (SHPT).

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This is a planned interim analysis of a longitudinal cohort study. The settings are dialysis facilities in Japan. Eligible patients comprise all those who were receiving hemodialysis at one of 86 participating facilities and who have SHPT. Using data from a random sample (n = 3276) of the participants from January 2008 through June 2009, we measured changes in the percentages of patients who were within the national guideline-specified target ranges of Ca (8.4 to 10 mg/dl), P (3.5 to 6.0 mg/dl), and intact PTH (iPTH) (60 to 180 pg/ml), and changes in prescriptions of drugs targeting SHPT. We used regression models to identify factors affecting the achievement of the guideline-specified targets.

RESULTS

There were no notable changes in the percentage of patients who were within the guideline for Ca, P, or both. The percentage who were within the iPTH guideline increased from 14.5% to 43.3% (P < 0.001). There were no remarkable changes in the percentage of patients receiving vitamin D or phosphate binders. The percentage who received cinacalcet increased from 0% to 29%. Prescription of cinacalcet was associated with improvement or target-achievement for iPTH and for Ca by 16.8 percentage points (95% CI: 8.1 to 17.0) and by 12.6 percentage points (13.7 to 19.9), respectively.

CONCLUSIONS

In the routine care of hemodialysis patients, increasing use of cinacalcet was associated with better control of SHPT.

The association of vitamin D use with hypercalcemia and hyperphosphatemia in hemodialysis patients: a case-crossover study

PURPOSE

Elevated levels of phosphorus (P) and calcium (Ca) have been shown in observational studies to be associated with an increased risk of adverse clinical outcomes including mortality. Vitamin D sterols have been shown to increase the risk of hypercalcemia and hyperphosphatemia in clinical trials. We sought to explore these risks in real-world clinical practice.

METHODS

We employed a case-crossover design, which eliminates confounding by non-time-varying patient characteristics by comparing, within each patient, vitamin D doses before the event with those at an earlier period. Using this method, we estimated the risk of hypercalcemic (Ca ≥ 11 g/dL) and hyperphosphatemic (P ≥ 8 g/dL) events for patients at different dose quartiles of vitamin D relative to patients not on a vitamin D sterol.

RESULTS

There was a dose-dependent association between vitamin D dose quartile and risk of hypercalcemia or hyperphosphatemia. In adjusted analyses, each increase in vitamin D quartile was associated with a multiple of hypercalcemia risk between 1.7 and 19 times compared with those not on vitamin D and a multiple of hyperphosphatemia risk between 1.8 and 4.

CONCLUSION

Use of vitamin D sterols is associated with an increased risk of hypercalcemic and hyperphosphatemic events in real-world clinical practice. Other potential predictors of these events, such as phosphate binder use and dialysate Ca levels, were not examined in this analysis.

Use of ultrasound to assess the response to therapy for secondary hyperparathyroidism

Secondary hyperparathyroidism (SHPT) is a common complication in patients with chronic kidney disease. In SHPT, the biology of parathyroid cells changes significantly toward diffuse nodular hyperplasia. Currently, diagnosis of SHPT is based on intact parathyroid hormone serum levels and parameters of mineral metabolism. The morphologic diagnosis of SHPT relies on high-resolution ultrasonography with color Doppler imaging. This report describes a maintenance hemodialysis patient with severe SHPT treated using conventional therapy (phosphate binders and oral/intravenous vitamin D or analogues) and the subsequent addition of a calcimimetic. The role of color Doppler ultrasonography in the diagnosis, clinical follow-up, and assessment of therapeutic response of SHPT is discussed. This case suggests that the availability of calcimimetics has changed the natural history of clinical SHPT and may change the therapeutic utility of parathyroidectomy. Use of color Doppler ultrasonography further supports these therapeutic advances, allowing evaluation of the morphologic and vascular changes in hyperplastic parathyroid glands and aiding clinical, pharmacologic, and surgical strategies.

Phosphate Metabolism in CKD Stages 3-5: Dietary and Pharmacological Control

When compared to the available information for patients on dialysis (CKD stage 5D), data on the epidemiology and appropriate treatment of calcium and phosphate metabolism in the predialysis stages of chronic kidney disease (CKD) are quite limited. Perceptible derangements of calcium and phosphate levels start to become apparent when GFR falls below 30 mL/min in some, but not all, patients. However, hyperphosphatemia may be a significant morbidity and mortality risk predictor in predialysis CKD stages. The RIND study, evaluating progression of coronary artery calcification in incident hemodialysis patients, indirectly demonstrated that vascular calcification processes start to manifest in CKD patients prior to the dialysis stage, which may be closely linked to early and invisible derangements in calcium and phosphate homeostasis. Novel insights into the pathophysiology of calcium and phosphate handling such as the discovery of FGF23 and other phosphatonins suggest that a more complex assessment of phosphate balance is warranted, possibly including measurements of fractional phosphate excretion and phosphatonin levels in order to appropriately evaluate disordered metabolism in earlier stages of kidney disease. As a consequence, early and preventive treatment approaches may have to be developed for patients in CKD stages 3-5 to halt progression of CKD-MBD.

Vitamin D deficiency and toxicity in chronic kidney disease: in search of the therapeutic window

Both vitamin D deficiency and vitamin D toxicity are associated with cardiovascular complications in chronic kidney disease (CKD). Clinical and experiment data indicate that the association of vitamin D levels with cardiovascular disease is best illustrated as a biphasic, or U-shaped, curve. Children and adolescents with CKD need vitamin D due to the demands of a growing skeleton, to prevent renal rickets. However, this therapy carries the risk of severe side effects and chronic toxicity. Observational studies show that vitamin D deficiency and toxicity are frequently present in patients with CKD. In view of the importance of cardiovascular complications for the long-term survival of young patients, these findings demand a judicious use of vitamin D preparations. In clinical practice, the therapeutic window is rather small, presenting a therapeutic challenge to avoid both vitamin D deficiency and toxicity.

Fibroblast growth factor-23 in early chronic kidney disease: additional support in favor of a phosphate-centric paradigm for the pathogenesis of secondary hyperparathyroidism

BACKGROUND AND OBJECTIVES

The discovery of fibroblast growth factor-23 (FGF-23) and the elucidation of its function as a phosphaturic and 1,25(OH)2VitD counter-regulatory hormone provides a new conceptual framework for the understanding of the pathogenesis of secondary hyperparathyroidism. This study aims to elucidate the complex associations between FGF-23, parathyroid hormone (PTH), 1,25(OH)2D, and phosphate in patients with early-stage chronic kidney disease (CKD) and to provide clinical evidence in favor of the new phosphate-centric paradigm for the pathogenesis of secondary hyperparathyroidism.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Serum biointact PTH and FGF-23, 25(OH)D, 1,25(OH)2D, calcium, phosphate, 24-hour urine excretion of phosphate and calcium, and urinary fractional excretion of phosphate were determined in a cross-sectional study including 125 patients with CKD stages 1 to 3.

RESULTS

Serum phosphate levels showed an inverse association with estimated GFR (eGFR), but were within the normal range in all but one patient. FGF-23 and PTH were inversely associated with eGFR, even in the subgroup of patients with CKD stages 1 and 2. High FGF-23 levels were significantly more prevalent than high PTH levels. The urinary fractional excretion of phosphate was highest in patients with both a high serum FGF-23 and PTH level. Increased FGF-23 and phosphate and decreased 25(OH)D were independently associated with decreased 1,25(OH)2D.

CONCLUSIONS

Our data are in favor of the new paradigm for the pathogenesis of secondary hyperparathyroidism according to which a reduced phosphate excretion capacity is the principal abnormality that initiates secondary hyperparathyroidism.

Vitamin D affects survival independently of vascular calcification in chronic kidney disease

BACKGROUND AND OBJECTIVES

Cardiovascular disease is the main cause of mortality in chronic kidney disease (CKD) patients. Vitamin D might have beneficial effects on vascular health. The aim of this study was to determine the prevalence of vitamin D deficiency (25-hydroxyvitamin D [25D] <or= 15 ng/ml) and insufficiency (25D levels between 16 and 30 ng/ml) in a cohort of patients at different CKD stages and the relationships between vitamin D serum levels, vascular calcification and stiffness, and the mortality risk.

DESIGN, SETTING, PARTICIPANTS & MEASUREMENTS

One hundred forty CKD patients (85 men, mean age 67 +/- 12 yr; CKD stages 2 [8%], 3 [26%], 4 [26%], 5 [7%], and 5D [(33%]) were allocated for a prospective study. Serum levels of 25D and 1,25-dihydroxyvitamin D, aortic calcification score, and pulse wave velocity (PWV) were evaluated.

RESULTS

There was a high prevalence of vitamin D deficiency (42%) and insufficiency (34%). Patients with 25D <or= 16.7 ng/ml (median) had a significantly lower survival rate than patients with 25D >16.7 ng/ml (mean follow-up, 605 +/- 217 d; range, 10 to 889; P = 0.05). Multivariate adjustments (included age, gender, diabetes, arterial pressure, CKD stage, phosphate, albumin, hemoglobin, aortic calcification score and PWV) confirmed 25D level as an independent predictor of all-cause mortality.

CONCLUSIONS

Vitamin D deficiency and insufficiency were highly prevalent in this CKD cohort. Low 25D levels affected mortality independently of vascular calcification and stiffness, suggesting that 25D may influence survival in CKD patients via additional pathways that need to be further explored.