The case for routine parathyroid hormone monitoring

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

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

Non-Additive Effects of Combined NOX1/4 Inhibition and Calcimimetic Treatment on a Rat Model of Chronic Kidney Disease-Mineral and Bone Disorder (CKD-MBD)

Chronic kidney disease-mineral and bone disorder (CKD-MBD) increases cardiovascular calcification and skeletal fragility in part by increasing systemic oxidative stress and disrupting mineral homeostasis through secondary hyperparathyroidism. We hypothesized that treatments to reduce reactive oxygen species formation and reduce parathyroid hormone (PTH) levels would have additive beneficial effects to prevent cardiovascular calcification and deleterious bone architecture and mechanics before end-stage kidney disease. To test this hypothesis, we treated a naturally progressive model of CKD-MBD, the Cy/+ rat, beginning early in CKD with the NADPH oxidase (NOX1/4) inhibitor GKT-137831 (GKT), the preclinical analogue of the calcimimetic etelcalcetide, KP-2326 (KP), and their combination. The results demonstrated that CKD animals had elevated blood urea nitrogen, PTH, fibroblast growth factor 23 (FGF23), and phosphorus. Treatment with KP reduced PTH levels compared with CKD animals, whereas GKT treatment increased C-terminal FGF23 levels without altering intact FGF23. GKT treatment alone reduced aortic calcification and NOX4 expression but did not alter the oxidative stress marker 8-OHdG in the serum or aorta. KP treatment reduced aortic 8-OHdG and inhibited the ability for GKT to reduce aortic calcification. Treatments did not alter heart calcification or left ventricular mass. In the skeleton, CKD animals had reduced trabecular bone volume fraction and trabecular number with increased trabecular spacing that were not improved with either treatment. The cortical bone was not altered by CKD or by treatments at this early stage of CKD. These results suggest that GKT reduces aortic calcification while KP reduces aortic oxidative stress and reduces PTH, but the combination was not additive. © 2022 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Is it True Hypoparathyroidism? A Root Cause Analysis of Unusually Low Intact Parathyroid Hormone (iPTH) at a Clinical Laboratory

INTRODUCTION

Intact Parathyroid Hormone (iPTH) has a short half-life i.e. two to four minutes therefore the sampling regimen has to pass through a stringent pre-analytical process control. The aim of this study was to identify the causes of apparently falsely low iPTH encountered while signing out Laboratory reports by the Clinical Chemistry professionals.

MATERIAL AND METHODS

This report was conducted at the section of Clinical Chemistry, The Aga Khan University Hospital (AKUH) Karachi Pakistan from July to December 2017. Audit tool utilized was Plan-Do-Check-Act Cycle. After correlating with available clinical details and lab parameters, all low iPTH values (<16 pg/ml) were investigated by phone interview. A fresh sample was requested for non-correlating cases.Appropriate interventions were undertaken and a re-assessment was done from January to March 2018.

RESULTS

During the audit, 2559 iPTH samples were analyzed. 110 (4.3%) were identified as apparently falsely low. After recollection, the above 110 samples were immediately centrifuged, and cold chain maintained until re-analysis. 60 (2.4%) resulted with normal or elevated levels. The causes identified were poor compliance of staff with pre-analytical steps including delayed sample separation and unfavorable temperature chain maintenance. Interventions included online meetings with the staff country-wide and circulation of flyers detailing the pre-analytical steps via emails and hard copies. Re-audit showed reduction in number of apparently falsely low results to 30 out of a total of 1448 samples and 14 (0.96%) were investigated to be falsely low.

CONCLUSION

Stringent pre-analytical process control is vital for quality reporting and patient safety.

The Non-invasive Diagnosis of Bone Disorders in CKD

Abnormal bone metabolism is an integral part of the chronic kidney disease-mineral bone disorder (CKD-MBD). For several reasons, the difficult bone compartment was neglected for some time, but there has been renewed interest as a result of the conception of bone as a new endocrine organ, the increasing recognition of the cross-talk between bone and vessels, and, especially, the very high risk of osteoporotic fractures (and associated mortality) demonstrated in patients with CKD. Therefore, it has been acknowledged in different guidelines that action is needed in respect of fracture risk assessment and the diagnosis and treatment of osteoporosis in the context of CKD and CKD-MBD, even beyond renal osteodystrophy. These updated guidelines clearly underline the need to improve a non-invasive approach to these bone disorders in order to guide treatment decisions aimed at not only controlling CKD-MBD but also decreasing the risk of fracture. In this report, we review the current role of the most often clinically used or promising biochemical circulating biomarkers such as parathyroid hormone, alkaline phosphatases, and other biochemical markers of bone activity as alternatives to some aspects of bone histomorphometry. We also mention the potential role of classic and new imaging techniques for CKD patients. Information on many aspects is still scarce and heterogeneous, but many of us consider that it is indeed time for action, recognizing our definitely limited ability to base certain treatment decisions only on our current non-comprehensive knowledge.

Effect of Advanced Glycation End-Products (AGE) Lowering Drug ALT-711 on Biochemical, Vascular, and Bone Parameters in a Rat Model of CKD-MBD

Chronic kidney disease-mineral bone disorder (CKD-MBD) is a systemic disorder that affects blood measures of bone and mineral homeostasis, vascular calcification, and bone. We hypothesized that the accumulation of advanced glycation end-products (AGEs) in CKD may be responsible for the vascular and bone pathologies via alteration of collagen. We treated a naturally occurring model of CKD-MBD, the Cy/+ rat, with a normal and high dose of the AGE crosslink breaker alagebrium (ALT-711), or with calcium in the drinking water to mimic calcium phosphate binders for 10 weeks. These animals were compared to normal (NL) untreated animals. The results showed that CKD animals, compared to normal animals, had elevated blood urea nitrogen (BUN), PTH, FGF23 and phosphorus. Treatment with ALT-711 had no effect on kidney function or PTH, but 3 mg/kg lowered FGF23 whereas calcium lowered PTH. Vascular calcification of the aorta assessed biochemically was increased in CKD animals compared to NL, and decreased by the normal, but not high dose of ALT-711, with parallel decreases in left ventricular hypertrophy. ALT-711 (3 mg/kg) did not alter aorta AGE content, but reduced aorta expression of receptor for advanced glycation end products (RAGE) and NADPH oxidase 2 (NOX2), suggesting effects related to decreased oxidative stress at the cellular level. The elevated total bone AGE was decreased by 3 mg/kg ALT-711 and both bone AGE and cortical porosity were decreased by calcium treatment, but only calcium improved bone properties. In summary, treatment of CKD-MBD with an AGE breaker ALT-711, decreased FGF23, reduced aorta calcification, and reduced total bone AGE without improvement of bone mechanics. These results suggest little effect of ALT-711 on collagen, but potential cellular effects. The data also highlights the need to better measure specific types of AGE proteins at the tissue level in order to fully elucidate the impact of AGEs on CKD-MBD. © 2019 American Society for Bone and Mineral Research.

Chronic kidney disease and peripheral nerve function in the Health, Aging and Body Composition Study

BACKGROUND

Chronic kidney disease (CKD) is associated with poor mobility. Peripheral nerve function alterations play a significant role in low mobility. We tested the hypothesis that early CKD is associated with altered sensory, motor and autonomic nerve function.

METHODS

Participants in the Health, Aging and Body Composition cohort who had kidney function measures in Year 3 (1999-2000) and nerve function measurements at Year 4 (2000-01) were analyzed (n = 2290). Sensory (vibration threshold, monofilament insensitivity to light and standard touch), motor [compound motor action potentials (CMAPs), nerve conduction velocities (NCVs)] and autonomic (heart rate response and recovery after a 400-m walk test) nerve function as well as participant characteristics were compared across cystatin C- and creatinine-based estimated glomerular filtration rate categorized as ≤60 (CKD) or >60 mL/min/1.73 m2 (non-CKD). The association between CKD and nerve function was examined with logistic regression adjusted for covariates.

RESULTS

Participants with CKD (n = 476) were older (77 ± 3 versus 75 ± 3 years; P < 0.05) and had a higher prevalence of diabetes (20.6% versus 13.1%; P < 0.001). CKD was associated with higher odds for vibration detection threshold {odds ratio [OR] 1.7 [95% confidence interval (CI) 1.1-2.7]} and light touch insensitivity [OR 1.4 (95% CI 1.1-1.7)]. CMAPs and NCVs were not significantly different between CKD and non-CKD patients. In adjusted analyses, participants with CKD had higher odds of an abnormal heart rate response [OR 1.6 (95% CI 1.1-2.2)] and poor heart rate recovery [OR 1.5 (95% CI 1.1-2.0)].

CONCLUSIONS

CKD is associated with changes in sensory and autonomic nerve function, even after adjustment for demographics and comorbidities, including diabetes. Longitudinal studies in CKD are needed to determine the contribution of nerve impairments to clinically important outcomes.

Chronic Kidney Disease-Mineral and Bone Disorder (CKD-MBD): Current Perspectives

Despite the availability of global and regional guidelines to curtail the adverse clinical outcomes associated with chronic kidney disease–mineral and bone disorder (CKD-MBD), most CKD patients are still affected by the consequences of abnormalities of CKD-MBD. This important clinical complication of CKD continues to be studied, in order to improve the understanding and management of CKD-MBD. Some notable discoveries include the role of fibroblast growth factor 23 (FGF23) in the pathogenesis of CKD-MBD, leading to a shift from the previous well-established classic trade-off hypothesis to the updated trade-off hypothesis. More recently, there has been a shift from the treatment of CKD-MBD based on a single level of biomarkers to serial measurements of calcium, phosphate and parathyroid hormone (PTH). Furthermore, some clinical trials have emerged after the 2009 Kidney Disease-Improving Global Outcomes (KDIGO) Guidelines, leading to the 2017 KDIGO updated recommendations. Hence, this review gives an overview of the rapidly evolving trends in CKD-MBD, linking the past and current concepts of CKD-MBD.

Chronic Kidney Disease-Associated Pruritus and Quality of Life in Malaysian Patients Undergoing Hemodialysis

CKD-associated pruritus is one of the common symptoms in patients undergoing dialysis, thus contributing to the diminished and compromised quality of life. This study aimed to explore the association between the CKD-associated pruritus on quality of life of patients undergoing hemodialysis in Malaysia. A cross-sectional multicenter study, carried out from February to September 2017 at tertiary care settings in Kuala Lumpur, Malaysia. Patients aged 18 years and above, undergoing hemodialysis, understanding Malay language and willing to participate were included. The CKD-associated pruritus was assessed by using Malay 5D-itch scale and Malay FANLTC questionaiare. To determine the factors associated with pruritus and quality of life, multivariate logistic regression analysis was used having P value < 0.05 as statistically significant. Among n = 334 recruited patients with a response rate of 100%, 59.6% were males and total of 61.3% were having CKD-associated pruritus. The results showed a statistically significant weak negative correlation between CKD-associated pruritus and quality of life. Multivariate linear regression revealed none of these factors were found to be associated with pruritus; however, CKD-associated prurtius was found to be associated with quality of life score. CKD-associated pruritus is have a negative impact on the patient's quality of life including physical, social, mental/emotional, and functional well-being. Despite the high prevalence and negative impact of CKD-associated pruritus on quality of life, it is disregarded by most health care professionals. It is thus pertinent to monitor the potential risk factors and consider providing timely treatment implications for CKD-associated pruritus in hemodialysis patients, in order to improve their quality of life.

Alkaline Phosphatases in the Complex Chronic Kidney Disease-Mineral and Bone Disorders

Alkaline phosphatases (APs) remove the phosphate (dephosphorylation) needed in multiple metabolic processes (from many molecules such as proteins, nucleotides, or pyrophosphate). Therefore, APs are important for bone mineralization but paradoxically they can also be deleterious for other processes, such as vascular calcification and the increasingly known cross-talk between bone and vessels. A proper balance between beneficial and harmful activities is further complicated in the context of chronic kidney disease (CKD). In this narrative review, we will briefly update the complexity of the enzyme, including its different isoforms such as the bone-specific alkaline phosphatase or the most recently discovered B1x. We will also analyze the correlations and potential discrepancies with parathyroid hormone and bone turnover and, most importantly, the valuable recent associations of AP's with cardiovascular disease and/or vascular calcification, and survival. Finally, a basic knowledge of the synthetic and degradation pathways of APs promises to open new therapeutic strategies for the treatment of the CKD-Mineral and Bone Disorder (CKD-MBD) in the near future, as well as for other processes such as sepsis, acute kidney injury, inflammation, endothelial dysfunction, metabolic syndrome or, in diabetes, cardiovascular complications. However, no studies have been done using APs as a primary therapeutic target for clinical outcomes, and therefore, AP's levels cannot yet be used alone as an isolated primary target in the treatment of CKD-MBD. Nonetheless, its diagnostic and prognostic potential should be underlined.

Calcium-Sensing Receptor Genotype and Response to Cinacalcet in Patients Undergoing Hemodialysis

BACKGROUND AND OBJECTIVES

We tested the hypothesis that single nucleotide polymorphisms (SNPs) in the calcium-sensing receptor (CASR) alter the response to the calcimimetic cinacalcet.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We analyzed DNA samples in the Evaluation of Cinacalcet HCl Therapy to Lower Cardiovascular Events (EVOLVE) trial, a randomized trial comparing cinacalcet to placebo on a background of usual care. Of the 3883 patients randomized, 1919 (49%) consented to DNA collection, and samples from 1852 participants were genotyped for 18 CASR polymorphisms. The European ancestry (EA; n=1067) and African ancestry (AfAn; n=405) groups were assessed separately. SNPs in CASR were tested for their association with biochemical measures of mineral metabolism at baseline, percent change from baseline to 20 weeks, and risk of clinical fracture as dependent variables.

RESULTS

There were modest associations of CASR SNPs with increased baseline serum parathyroid hormone and bone alkaline phosphatase primarily with the minor allele in the EA group (all P≤0.03), but not in the AfAn sample. In contrast, there was a modest association of decreased baseline serum calcium and FGF23 with CASR SNPs (P=0.04) primarily with the minor allele in the AfAn but not in the EA sample. The minor allele of two SNPs was associated with decreased percent reduction in parathyroid hormone from baseline to 20 weeks in the EA population (P<0.04) and this was not altered with cinacalcet. In both EA and AfAn, the same SNP (rs9740) was associated with decreased calcium with cinacalcet treatment (EA and AfAn P≤0.03). Three SNPs in high linkage disequilibrium were associated with a higher risk of clinical fracture that was attenuated by cinacalcet treatment in the EA sample (P<0.04).

CONCLUSIONS

These modest associations, if validated, may provide explanations for differences in CKD-mineral bone disorder observed in EA and AfAn populations, and for differential biochemical responses to calcimimetics.

The Strategy to Prevent and Regress the Vascular Calcification in Dialysis Patients

The high prevalence of arterial calcification in end-stage renal disease (ESRD) is far beyond the explanation by common cardiovascular risk factors such as aging, diabetes, hypertension, and dyslipidemia. The finding relies on the fact that vascular and valvular calcifications are predictors of cardiovascular diseases and mortality in persons with chronic renal failure. In addition to traditional cardiovascular risk factors such as diabetes mellitus and blood pressure control, other ESRD-related risks such as phosphate retention, excess calcium, and prolonged dialysis time also contribute to the development of vascular calcification. The strategies are to reverse "calcium paradox" and lower vascular calcification by decreasing procalcific factors including minimization of inflammation (through adequate dialysis and by avoiding malnutrition, intravenous labile iron, and positive calcium and phosphate balance), correction of high and low bone turnover, and restoration of anticalcification factor balance such as correction of vitamin D and K deficiency; parathyroid intervention is reserved for severe hyperparathyroidism. The role of bone antiresorption therapy such as bisphosphonates and denosumab in vascular calcification in high-bone-turnover disease remains unclear. The limited data on sodium thiosulfate are promising. However, if calcification is to be targeted, ensure that bone health is not compromised by the treatments.

Perspective and priorities for improvement of parathyroid hormone (PTH) measurement - A view from the IFCC Working Group for PTH

Parathyroid hormone (PTH) measurement in serum or plasma is a necessary tool for the exploration of calcium/phosphate disorders, and is widely used as a surrogate marker to assess skeletal and mineral disorders associated with chronic kidney disease (CKD), referred to as CKD-bone mineral disorders (CKD-MBD). CKD currently affects >10% of the adult population in the United States and represents a major health issue worldwide. Disturbances in mineral metabolism and fractures in CKD patients are associated with increased morbidity and mortality. Appropriate identification and management of CKD-MBD is therefore critical to improving clinical outcome. Recent increases in understanding of the complex pathophysiology of CKD, which involves calcium, phosphate and magnesium balance, and is also influenced by vitamin D status and fibroblast growth factor (FGF)-23 production, should facilitate such improvement. Development of evidence-based recommendations about how best to use PTH is limited by considerable method-related variation in results, of up to 5-fold, as well as by lack of clarity about which PTH metabolites these methods recognise. This makes it difficult to compare PTH results from different studies and to develop common reference intervals and/or decision levels for treatment. The implications of these method-related differences for current clinical practice are reviewed here. Work being undertaken by the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) to improve the comparability of PTH measurements worldwide is also described.

Calcium Homeostasis in Health and in Kidney Disease

Calcium is an important ion in cell signaling, hormone regulation, and bone health. Its regulation is complex and intimately connected to that of phosphate homeostasis. Both ions are maintained at appropriate levels to maintain the extracellular to intracellular gradients, allow for mineralization of bone, and to prevent extra skeletal and urinary calcification. The homeostasis involves the target organs intestine, parathyroid glands, kidney, and bone. Multiple hormones converge to regulate the extracellular calcium level: parathyroid hormone, vitamin D (principally 25(OH)D or 1,25(OH)2D), fibroblast growth factor 23, and α-klotho. Fine regulation of calcium homeostasis occurs in the thick ascending limb and collecting tubule segments via actions of the calcium sensing receptor and several channels/transporters. The kidney participates in homeostatic loops with bone, intestine, and parathyroid glands. Initially in the course of progressive kidney disease, the homeostatic response maintains serum levels of calcium and phosphorus in the desired range, and maintains neutral balance. However, once the kidneys are no longer able to appropriately respond to hormones and excrete calcium and phosphate, positive balance ensues leading to adverse cardiac and skeletal abnormalities. © 2016 American Physiological Society. Compr Physiol 6:1781-1800, 2016.

Clinical and Practical Use of Calcimimetics in Dialysis Patients With Secondary Hyperparathyroidism

CKD and CKD-related mineral and bone disorders (CKD-MBDs) are associated with high cardiovascular and mortality risks. In randomized clinical trials (RCTs), no single drug intervention has been shown to reduce the high mortality risk in dialysis patients, but several robust secondary analyses point toward important potential beneficial effects of controlling CKD-MBD-related factors and secondary hyperparathyroidism. The advent of cinacalcet, which has a unique mode of action at the calcium-sensing receptor, represented an important step forward in controlling CKD-MBD. In addition, new RCTs have conclusively shown that cinacalcet improves achievement of target levels for all of the metabolic abnormalities associated with CKD-MBD and may also attenuate the progression of vascular and valvular calcifications in dialysis patients. However, a final conclusion on the effect of cinacalcet on hard outcomes remains elusive. Tolerance of cinacalcet is limited by frequent secondary side effects such as nausea, vomiting, hypocalcemia and oversuppression of parathyroid hormone, which may cause some management difficulties, especially for those lacking experience with the drug. Against this background, this review aims to summarize the results of studies on cinacalcet, up to and including the publication of the recent ADVANCE and EVOLVE RCTs, as well as recent post hoc analyses, and to offer practical guidance on how to improve the clinical management of the most frequent adverse events associated with cinacalcet, based on both currently available information and personal experience. In addition, attention is drawn to less common secondary effects of cinacalcet treatment and advisable precautions.

A new player in chronic kidney disease mineral and bone disorder: tenascin-C

AIMS

Chronic kidney disease-mineral and bone disorder (CKD-MBD) is a condition frequently observed in CKD. The search for a reliable and easy to use biomarker in the diagnosis of CKD-MBD is continuing. Tenascin-C (TN-C) is an important extracellular (ECM) protein synthesized by osteoblasts during bone growth and morphogenesis. The purpose of this study was to assess the relation between inflammation and MBD and TN-C in HD patients and to identify a new marker that can be used to help diagnose CKD-MBD.

MATERIALS AND METHODS

136 HD patients and 22 healthy controls were enrolled in this cross-sectional, observational multicenter study. Once patients' demographic and biochemical parameters had been recorded, peripheral blood samples were collected for TN-C measurement before the mid-week HD session. The relationship between TN-C levels and demographic and biochemical parameters was then assessed.

RESULTS

TN-C levels were significantly higher in the HD patient than in the control group (P&lt;.001). Intact parathormone (iPTH) affected TN-C levels in the HD patient group. TN-C levels was significantly higher in both the high (&gt;300 pg/ml) and low iPTH groups (&lt;150 pg/ml) compared to the 150-300 pg/ml iPTH group (P&lt;.001, &lt;.001 respectively).

CONCLUSIONS

This study showed, for the first time in the literature, high levels of TN-C in the low and high iPTH groups and that this elevation was associated with iPTH. We think that if our study is supported by further research, TN-C can be a biomarker capable of use in diagnosing CKD-MBD.

Calcium-phosphate and parathyroid intradialytic profiles: A potential aid for tailoring the dialysate calcium content of patients on different hemodialysis schedules

Severe hyperparathyroidism is a challenge on hemodialysis. The definition of dialysate calcium (Ca) is a pending issue with renewed importance in cases of individualized dialysis schedules and of portable home dialysis machines with low-flow dialysate. Direct measurement of calcium mass transfer is complex and is imprecisely reflected by differences in start-to-end of dialysis Ca levels. The study was performed in a dialysis unit dedicated to home hemodialysis and to critical patients with wide use of daily and tailored schedules. The Ca-phosphate (P)-parathyroid hormone (PTH) profile includes creatinine, urea, total and ionized Ca, albumin, sodium, potassium, P, PTH levels at start, mid, and end of dialysis. "Severe" secondary hyperparathyroidism was defined as PTH > 300 pg/mL for ≥3 months. Four schedules were tested: conventional dialysis (polysulfone dialyzer 1.8-2.1 m(2) ), with dialysate Ca 1.5 or 1.75 mmol/L, NxStage (Ca 1.5 mmol/L), and NxStage plus intradialytic Ca infusion. Dosages of vitamin D, calcium, phosphate binders, and Ca mimetic agents were adjusted monthly. Eighty Ca-P-PTH profiles were collected in 12 patients. Serum phosphate was efficiently reduced by all techniques. No differences in start-to-end PTH and Ca levels on dialysis were observed in patients with PTH levels < 300 pg/mL. Conversely, Ca levels in "severe" secondary hyperparathyroid patients significantly increased and PTH decreased during dialysis on all schedules except on Nxstage (P < 0.05). Our data support the need for tailored dialysate Ca content, even on "low-flow" daily home dialysis, in "severe" secondary hyperparathyroid patients in order to increase the therapeutic potentials of the new dialysis techniques.

News on biomarkers in CKD-MBD

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

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 heart rate variability in haemodialysis patients

BACKGROUND

Depressed heart rate variability (HRV) reflects abnormal cardiac autonomic regulation and has been linked with increased cardiovascular risk and sudden cardiac death. High parathyroid hormone (PTH) levels have also been associated with an increased risk of sudden cardiac death in haemodialysis (HD) patients. Our aim was to investigate the association between HRV indices and PTH in HD patients.

METHODS

Continuous intradialytic electrocardiograms were repeated in stable HD patients 5 times every 2 weeks. The absolute values of high-frequency (HF) and low-frequency (LF) HRV components were calculated every 5 min and averaged during the first and last hour of each recording (distinguished by subscripts F and L, respectively). Pre-HD PTH, corrected calcium, and phosphate levels were measured before the first recording.

RESULTS

Data were analysed for 75 subjects aged 60 ± 15, 32% females, 37% diabetics. Baseline biochemical parameters were PTH 44 ± 32 pmol/l, calcium 2.3 ± 0.2 mmol/l, and phosphate 1.6 ± 0.4 mmol/l. All HRV indices showed intra-subject stability over the 5 recordings. Diabetics had lower LFL compared to non-diabetics (-5.5 ± 0.5 vs. -5.2 ± 0.5 after logarithmic transformation, p = 0.012). In non-diabetics, PTH correlated negatively with LFL and HFL (LFL r = -0.340, p = 0.020, HFL r = -0.325, p = 0.026) and phosphate correlated negatively with LFF (r = -0.427, p = 0.003), HFF (r = -0.442, p = 0.002) and HFL (r = -0.307, p = 0.040).

CONCLUSION

High PTH and phosphate are associated with depressed HRV in non-diabetic dialysis patients. Prospective studies are needed to evaluate the role of mineral abnormalities in autonomic imbalance and arrhythmic risk in HD patients.

The relationship between secondary hyperparathyroidism and thyroid cancer in end stage renal disease: a population based cohort study

OBJECTIVES

We conducted a retrospective cohort study to investigate the risk of cancer in end stage renal disease (ESRD) patients with secondary hyperparathyroidism (HPT).

PATIENTS AND METHODS

This study investigated the elevated overall cancer risk in ESRD patients with secondary HPT in Taiwan. We used a population-based retrospective cohort consisting of original claims data of 1 million beneficiaries randomly sampled from the Taiwan National Health Insurance Research Database (NHIRD). We calculated the hazard ratios (HRs) and 95% confidence intervals (CIs) of cancer in the ESRD with secondary HPT and comparison cohorts, using the Cox proportional hazards regression model.

RESULTS

We observed that ESRD patients with secondary HPT exhibited a 10.1-fold increased risk of thyroid cancer than did ESRD patients without this parathyroid complication, after adjusting for comorbidities (95% confidence interval=1.12-91.0).

CONCLUSION

These phenomena indicate that ESRD patients with secondary HPT are at greater risk of thyroid cancer. Physicians should be alert for occult thyroid cancer in ESRD patients with secondary HPT.