Full-length Parathyroid Hormone Research Articles

A-042 Comparison of the Second-Generation Parathyroid Hormone Assays: ELSA-PTH and Alinity i Intact PTH

Abstract Background Measurement of parathyroid hormone (PTH) level is essential in diagnosing and treating hyper- and hypoparathyroidism. Because of the various presenting forms of PTH (biologically active full-length PTH and also PTH fragments) in the blood and the lack of standardization, there can be a difference in results between the assays even when the same assay generation is used. We compared the two second-generation PTH assays, ELSA-PTH and Alinity i Intact PTH, and evaluated the analytical performance of Alinity i Intact PTH, newly adopted in the laboratory. Methods For method comparison, 56 remnant samples of routinely ordered sera for the PTH test were collected. ESLA-PTH assay tested on Gamma-10 contains the anti-[39-84, amino acids] PTH antibody coated on the tube, which captures PTH in the sample and is measured by the radioactivity through the bound I125-labelled anti-[1-34] PTH antibody. Alinity i Intact PTH assay performed on Alinity i system uses the anti-[39-84] PTH antibody coated on a paramagnetic microparticle and is analyzed by the emitted light through the captured acridinium-labeled anti-[1-34] PTH antibody. The correlation between the two tests was evaluated. Additionally, precision, linearity, and reference range verification were analyzed to investigate the performance of the Alinity i Intact PTH assay. Results Of the 56 samples, 35 (62.5%) were requested by the Nephrology department for evaluating chronic kidney disease, 16 (28.6%) by the General surgery department during and after parathyroid and thyroid surgery, and 5 (8.9%) by other departments. 52.3% of the patients were female, and the median age was 61.5 years (interquartile range: 45.3–71). The median values of ELSA-PTH and Alinity i Intact PTH were 69.0 pg/mL and 101.9 pg/mL, respectively, and the PTH values of Alinity i Intact PTH were significantly higher (P < 0.0001) by the Wilcoxon test. The Pearson correlation coefficient (r) was 0.959, and the average difference between the two tests was 78.57 pg/mL. In Alinity i Intact PTH, the coefficient of variation obtained at each low (10.5 pg/mL), medium (66.6 pg/mL), high (254.6 pg/mL) levels were 1.9%, 2.4%, and 1.8% for repeatability, and 2.03%, 2.71%, and 2.65% for within-laboratory precision, respectively. Linearity was observed within the analytical measuring range of 3–3000 pg/mL. The reference range (15–68.3 pg/mL) recommended by the manufacturer was validated with 20 normal sera. Conclusion The PTH values of Alinity i Intact PTH were significantly higher than those of the ELSA-PTH, and both assays showed a strong correlation. Additionally, the Alinity i Intact PTH assay demonstrated acceptable analytical performance.

Full-length versus intact PTH concentrations in pseudohypoparathyroidism type 1 and primary hyperparathyroidism: clinical evaluation of immunoassays in individuals from China.

PurposeThe application of the third-generation parathyroid hormone (PTH) assay [PTH(1–84) assay] for evaluating PTH levels in patients with pseudohypoparathyroidism type-1 (PHP1) is less popular than the second-generation assay. Therefore, we aimed at examining the conformity between the PTH(1–84) assay and the intact PTH (iPTH) assay, specifically examining their performance in individuals with PHP1 versus individuals with primary hyperparathyroidism (PHPT), compared to healthy controls.MethodsPTH(1–84) and iPTH assay were performed in patients with PHP1, patients with PHPT, and healthy volunteers. ∆PTH%, PTH(1–84)/iPTH (3rd/2nd ratio), iPTH/upper limit of normal (ULN), and PTH (1–84)/ULN of each group were calculated for comparison. Linear regression, Kappa conformity test, and Bland–Altman analysis of ∆PTH/mean of iPTH and PTH(1–84) (percent bias) plotted against the mean of iPTH and PTH(1–84) were performed to determine the conformance of PTH(1–84) assay with iPTH assay.ResultsA total of 54 patients with PHP1, 127 patients with PHPT, and 65 healthy volunteers were enrolled in this study. All the three groups showed strong linear relationship between iPTH and PTH (1–84) (r2 = 0.9661, 0.7733, and 0.9575, respectively). No significant differences were noted in 3rd/2nd ratio (median 0.76 vs. 0.72) between the PHP1 and PHPT groups (p > 0.05). Conformity examination showed the Kappa value was 0.778 and 0.395 for PHP1 and PHPT groups respectively. No difference in the Kappa values was found between PHP1A and PHP1B subgroups. Bland–Altman plot demonstrated that the proportion of data points that were plotted within mean ± 1.96 SD in PHP1, PHPT and normal control groups were 96.3%, 93.7%, and 98.5%, respectively. The mean percent bias of the three groups were 26.1%, 31.2%, and 17.0%, respectively. The range of mean ± 1.96 SD of percent bias of the three groups were 2.2%–50.0%, −14.3%–76.6%, and 6.7%–27.2%, respectively.ConclusionAlthough iPTH and PTH(1–84) values were both lower in the present PHP1 cohort than in the PHPT cohort, there appear to be differences in the relative agreement between both immunoassays, and in the relationship between the two values, especially in comparison to healthy controls. Whether these differences are due to differential accumulation of C-terminal fragments or other factors requires further study.

High-Resolution Mass Spectrometry for the Measurement of PTH and PTH Fragments: Insights into PTH Physiology and Bioactivity.

Full-length parathyroid hormone (PTH 1-84) is crucial for the regulation of calcium and phosphate homeostasis and bone remodeling. PTH 1-84 is metabolized into various PTH fragments, which are measured with varying levels of efficiency by PTH immunoassays. These PTH fragments, which increase in serum as CKD progresses, could potentially modulate the effects of PTH 1-84 and contribute to CKD-associated bone disorders. To obtain a true biologic representation of total PTH bioactivity, it is necessary to measure not only PTH 1-84 but also PTH fragments that are present in circulation. Traditional second-generation PTH immunoassays collectively measure PTH 1-84, PTH fragments, and post-translationally modified PTH 1-84, making it difficult to accurately predict the character of underlying renal osteodystrophy. This review highlights current advances in methods available for PTH measurement and the clinical relevance of PTH fragments in CKD. We emphasize the usefulness of mass spectrometry as a potential reference method for PTH measurement.

Bioactive, full-length parathyroid hormone delivered using an adeno-associated viral vector.

Delivering the parathyroid hormone (PTH) gene has been attempted preclinically in a handful of studies, but delivering full-length PTH (1-84) using adeno-associated viral (AAV) vectors has not. Given the difficulty in achieving therapeutic levels of secreted proteins using gene therapy, this study seeks to determine the feasibility of doing so with PTH. An AAV vector was used to deliver human PTH driven by a strong promoter. We demonstrate the ability to secrete full-length PTH from various cell types in vitro. PTH secretion from hepatocytes was measured over time and a fluorescent marker was used to compare the secretion rate of PTH in various cell types. Potency was measured by the ability of PTH to act on the PTH receptors of osteosarcoma cells and induced proliferation. PTH showed potency in vitro by inducing proliferation in two osteosarcoma cell lines. In vivo, AAV was administered systemically in immunocompromised mice which received xenografts of osteosarcoma cells. Animals that received the highest dose of AAV-PTH had higher liver and plasma concentrations of PTH. All dosing groups achieved measurable plasma concentrations of human PTH that were above the normal range. The high-dose group also had significantly larger tumors compared to control groups on the final day of the study. The tumors also showed dose-dependent differences in morphology. When looking at endocrine signaling and endogenous bone turnover, we observed a significant difference in tibial growth plate width in animals that received the high-dose AAV as well as dose-dependent changes in blood biomarkers related to PTH. This proof-of-concept study shows promise for further exploration of an AAV gene therapy to deliver full-length PTH for hypoparathyroidism. Additional investigation will determine efficacy in a disease model, but data shown establish bioactivity in well-established models of osteosarcoma.

Effect of Recombinant Human Parathyroid Hormone (1-84) on Resolution of Active Charcot Neuro-osteoarthropathy in Diabetes: A Randomized, Double-Blind, Placebo-Controlled Study

OBJECTIVEFractures in Charcot neuro-osteoarthropathy (CN) often fail to heal despite prolonged immobilization with below-knee casting. The aim of the study was to assess the efficacy of recombinant human parathyroid hormone (PTH) in reducing time to resolution of CN and healing of fractures.RESEARCH DESIGN AND METHODSPeople with diabetes and acute (active) Charcot foot were randomized (double-blind) to either full-length PTH (1-84) or placebo therapy, both in addition to below-knee casting and calcium and vitamin D3 supplementation. The primary outcome was resolution of CN, defined as a skin foot temperature difference >2°C at two consecutive monthly visits.RESULTSMedian time to resolution was 5 months (95% CI 4, 12) in intervention and 6 months (95% CI 2, 9) in control. There was no significant difference in time to resolution between the groups (mixed-effects logistic regression; P = 0.64). The hazard ratio of resolution was 0.84 (95% CI 0.41, 1.74; P = 0.64), and the odds ratio of resolution by 12 months was 1.22 (0.90, 1.67; P = 0.20) (intervention vs. control). On linear regression analysis, there were no significant differences in the effect of treatment on fracture scores quantitated on MRI scans (coefficient 0.13 [95% CI −0.62, 0.88]; P = 0.73) and on foot and ankle X-rays (coefficient 0.30 [95% CI −0.03, 0.63]; P = 0.07).CONCLUSIONSThis double-blind placebo-controlled trial did not reduce time to resolution or enhance fracture healing of CN. There was no added benefit of daily intervention with PTH (1-84) to below-knee casting in achieving earlier resolution of CN.

FC 076DIAGNOSTIC ACCURACY OF BONE TURNOVER MARKERS IN RENAL OSTEODYSTROPHY

Abstract Background and Aims A transiliac bone biopsy is the gold standard for diagnosing renal osteodystrophy, but is not recommended as part of routine clinical workup due to its invasive nature. Suitable non-invasive alternatives have yet to be established. The aim of this study was to investigate the diagnostic accuracy novel biochemical markers of bone remodeling compared to that of biointact parathyroid hormone (PTH) for bone turnover as evaluated by histomorphometry. Method Protocolled bone biopsies were performed in end-stage kidney disease patients (ESKD, n = 80) and kidney transplant recipients (n = 119). Full-length (1-84) PTH, bone-specific alkaline phosphatase (BsAP), intact N-terminal propeptide of type I collagen (P1NP), and tartrate-resistant acid phosphatase isoform 5b (TRAP5b) were measured. Diagnostic performance was evaluated by area under the receiver operator characteristics curve (AUC). Optimal diagnostic cutoffs were established in an exploration cohort (n=100), and subsequently validated in a separate subset of patients (n=99). Results Mean age was 55±13 years, two-thirds were men (67%), and 23% had diabetes mellitus. Post-transplant eGFR was 49 [IQR 39, 59] ml/min/1.73m². Bone turnover was low in 47 (24%), normal in 119 (60%), and high in 33 (17%) patients. All biomarkers differed significantly across categories of bone turnover (p < 0.001). The AUC of biointact PTH for high turnover was 0.82 (0.73, 0.91), which was not significantly different from AUC values for BsAP, Intact P1NP, and TRAP5b (0.87, 0.90, and 0.86, respectively). AUC of biointact PTH for low turnover was 0.71 (0.63, 0.78), which was significantly lower than the values for BsAP, Intact P1NP, and TRAP5b (0.79, 0.83, and 0.79, respectively; p < 0.05, all). Calculated optimal diagnostic cutoffs in the exploration cohort are shown in Table 1. Applying these cutoffs in the validation cohort revealed high negative predictive values for both high (92 - 96%) and low (82 - 90%) bone turnover. Positive predictive values were consistently low. Conclusion The diagnostic accuracies of BsAP, Intact P1NP and TRAP5b are sufficient to rule out both high and low bone turnover in CKD. Biointact PTH shows inferior performance, particularly in kidney transplant recipients.

Improving the Accuracy and Reliability of Parathyroid Hormone Levels Through the Mass-Spectrometric Measurement of Full-length PTH and C-Terminal PTH Fragments

Parathyroid hormone (PTH) is a key biomarker for hypo/hyperparathyrioidism as well as chronic kidney disease, one of the leading health conditions in the USA. As a result, the most recent update of the Kidney Disease Improving Global Outcomes (KDIGO) guideline for CKD-MBD management emphasized the role of PTH as one of the key biomarkers of this disorder. The earlier stages of CKD generate few symptoms and only until the kidney is significantly impaired do patients begin experiencing signs of renal failure. Therefore, the measurement of parathyroid hormone (PTH) in serum and/or plasma is critical not only for the correct detection, diagnosis, and prevention of renal failure, but also calcium, phosphate, and vitamin D disorders. Current laboratory methods for PTH show high variability and inaccuracy, thus creating the need for a reference measurement procedure that can help laboratories and assay manufacturers improve their measurement accuracy and reliability to avoid the misclassification of patients. Due to the short half-life of PTH, this 84 amino-acid polypeptide hormone is produced at low circulating levels in normal conditions ranging from 10 - 65 pg/mL. In addition, N-terminal and C-terminal peptides, which have shown to interfere with clinical analyzer platforms, account for over 80% of all circulating PTH levels. Therefore, a highly specific and sensitive method is needed for the accurate detection of full-length PTH and these PTH fragments. There is clinical relevancy in the ability to measure C-terminal PTH fragments as the ratio of these PTH fragments to full-length PTH has been diagnostic for severe or end-stage renal disease, non-dynamic bone disease, and hyperparathyroid-associated bone loss. Bottom-up proteomics approaches that incorporate enzymatic digestion steps during sample preparation will result in the loss of information for the fragments. Therefore, a new, innovative, top-down proteomics method was developed to measure full-length PTH and its breakdown products (fragments) by mass spectrometry (UHPLC-HRMS). This method enabled, for the first time, the detection of full-length PTH at very low concentrations typically observed in patients with hypoparathyroidism as well as C-terminal fragments that may interfere with regular immunoassays typically used in patient care. The highly specific and sensitive method for PTH and related peptides in CKD patient sera demonstrated no interference from the internal standards and other PTH fragments. Therefore, the optimized method was applied for the screening of normal and CKD serum at various stages of disease progression. Preliminary results demonstrated that certain PTH fragments are correlated with eGFR and different stages of chronic kidney diseases (CKD). This method along with the respective findings from this study will help to improve the diagnosis, treatment, and prevention of CKD-MBD.

Chemical Characterization and Quantification of Circulating Intact PTH and PTH Fragments by High-Resolution Mass Spectrometry in Chronic Renal Failure.

BACKGROUND:The precise concentrations of full-length parathyroid hormone (PTH1–84) and the identity and concentrations of PTH fragments in patients with various stages of chronic renal failure are unknown.METHODS:We developed a liquid chromatography-high resolution mass spectrometry (LC-HRMS) method to characterize and quantify PTH1–84 and PTH fragments in serum of 221 patients with progressive renal dysfunction. Following capture by matrix-bound amino-terminal or carboxyl-terminal region-specific antibodies and elution from matrix, PTH1–84 and PTH fragments were identified and quantitated using LC-HRMS. PTH was simultaneously measured using an intact PTH (iPTH) immunoassay.RESULTS:Full-length PTH1–84 and 8 PTH fragments (PTH28–84, 34–77, 34–84, 37–77, 37–84, 38–77, 38–84, and 45–84) were unequivocally identified and were shown to increase significantly when an eGFR declined to ≤17–23 mL/min/1.73m2. Serum concentrations of PTH1–84 were similar when measured by LC-HRMS following capture by amino-terminal or carboxyl-terminal immunocapture methods. In patients with an eGFR of <30 mL/min/1.73 m2, serum PTH concentrations measured using LC-HRMS were significantly lower than PTH measured using an iPTH immunoassay. PTH7–84 and oxidized forms of PTH1–84 were below the limit of detection (30 and 50 pg/mL, respectively).CONCLUSIONS:LC-HRMS identifies circulating PTH1–84, carboxyl-terminal PTH fragments, and mid-region PTH fragments, in patients with progressive renal failure. Serum PTH1–84 and its fragments markedly rise when an eGFR decreases to ≤17–23 mL/min/1.73 m2. PTH concentrations measured using LC-HRMS tend to be lower than those measured using an iPTH immunoassay, particularly in severe chronic renal failure. Our data do not support the existence of circulating PTH7–84 and oxidized PTH1–84.

Parathyroid Hormone-Related Protein Negatively Regulates Tumor Cell Dormancy Genes in a PTHR1/Cyclic AMP-Independent Manner.

Parathyroid hormone-related protein (PTHrP) expression in breast cancer is enriched in bone metastases compared to primary tumors. Human MCF7 breast cancer cells “home” to the bones of immune deficient mice following intracardiac inoculation, but do not grow well and stain negatively for Ki67, thus serving as a model of breast cancer dormancy in vivo. We have previously shown that PTHrP overexpression in MCF7 cells overcomes this dormant phenotype, causing them to grow as osteolytic deposits, and that PTHrP-overexpressing MCF7 cells showed significantly lower expression of genes associated with dormancy compared to vector controls. Since early work showed a lack of cyclic AMP (cAMP) response to parathyroid hormone (PTH) in MCF7 cells, and cAMP is activated by PTH/PTHrP receptor (PTHR1) signaling, we hypothesized that the effects of PTHrP on dormancy in MCF7 cells occur through non-canonical (i.e., PTHR1/cAMP-independent) signaling. The data presented here demonstrate the lack of cAMP response in MCF7 cells to full length PTHrP(1–141) and PTH(1–34) in a wide range of doses, while maintaining a response to three known activators of adenylyl cyclase: calcitonin, prostaglandin E2 (PGE2), and forskolin. PTHR1 mRNA was detectable in MCF7 cells and was found in eight other human breast and murine mammary carcinoma cell lines. Although PTHrP overexpression in MCF7 cells changed expression levels of many genes, RNAseq analysis revealed that PTHR1 was unaltered, and only 2/32 previous PTHR1/cAMP responsive genes were significantly upregulated. Instead, PTHrP overexpression in MCF7 cells resulted in significant enrichment of the calcium signaling pathway. We conclude that PTHR1 in MCF7 breast cancer cells is not functionally linked to activation of the cAMP pathway. Gene expression responses to PTHrP overexpression must, therefore, result from autocrine or intracrine actions of PTHrP independent of PTHR1, through signals emanating from other domains within the PTHrP molecule.

Repurposing a novel parathyroid hormone analogue to treat hypoparathyroidism.

Human parathyroid hormone (PTH) is critical for maintaining physiological calcium homeostasis and plays an important role in the formation and maintenance of the bone. Full-length PTH and a truncated peptide form are approved for treatment of hypoparathyroidism and osteoporosis respectively. Our initial goal was to develop an improved PTH therapy for osteoporosis, but clinical development was halted. The novel compound was then repurposed as an improved therapy for hypoparathyroidism. A longer-acting form of PTH was synthesised by altering the peptide to increase cell surface residence time of the bound ligand to its receptor. In vitro screening identified a compound, which was tested in an animal model of osteoporosis before entering human trials. This compound was subsequently tested in two independent animal models of hypoparathyroidism. The peptide identified, LY627-2K, exhibited delayed internalization kinetics. In an ovariectomy-induced bone loss rat model, LY627-2K demonstrated improved vertebral bone mineral density and biomechanical properties at skeletal sites and a modest increase in serum calcium. In a Phase I clinical study, dose-dependent increases in serum calcium were reproduced. These observations prompted us to explore a second indication, hypoparathyroidism. In animal models of this disease, LY627-2K restored serum calcium, comparing favourably to treatment with wild-type PTH. We summarize the repositioning of a therapeutic candidate with substantial preclinical and clinical data. Our results support its repurposing and continued development, from a common indication (osteoporosis) to a rare disease (hypoparathyroidism) by exploiting a shared molecular target. This article is part of a themed section on Inventing New Therapies Without Reinventing the Wheel: The Power of Drug Repurposing. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.2/issuetoc.

Recombinant human parathyroid hormone in the therapy of hypoparathyroidism

Hypoparathyroidism is an endocrine disease that results from deficiency or complete absence of parathyroid hormone (PTH), a biologically active 84-amino acid polypeptide. Standard therapy for chronic hypoparathyroidism includes oral calcium salts and active vitamin D metabolites and is aimed at maintaining a balance between optimal near-normal serum calcium concentration and normocalcuria. Traditional treatment regimens not always lead to the compensation for calcium and phosphorus metabolism. Until recently, hypoparathyroidism is the only endocrine disorder that has not been treated with the recombinant hormone. To date, two recombinant PTH forms have been synthesized, which can be used as pathogenetic therapy for hypoparathyroidism. This review is dedicated to replacement therapy for hypoparathyroidism, by using both the full-length PTH molecule (1-84) and its shorter, but fully active, PTH form (1-34). This review considers stages in the developmental of hormone replacement therapy for hypoparathyroidism, discusses the most rational dosing regimens, and compares their efficacy and safety, as well as prospects for the development of this area.

Review of Hypoparathyroidism.

Hypoparathyroidism is a rare endocrine disorder in which parathyroid hormone (PTH) production is abnormally low or absent, resulting in low serum calcium and increased serum phosphorus. The most common cause of hypoparathyroidism is parathyroid gland injury or inadvertent removal during thyroid surgery. Current treatments include supplementation with calcium and active vitamin D, with goal albumin-corrected serum calcium level in the low-normal range of 8–9 mg/dl. Complications of the disease include renal dysfunction, nephrocalcinosis, kidney stones, extracellular calcifications of the basal ganglia, and posterior subcapsular cataracts, as well as low bone turnover and increased bone density. Until January 2015, hypoparathyroidism was the only classic endocrine disease without an available hormone replacement. Recombinant human PTH 1-84, full-length PTH, is now available for a selected group of patients with the disease who are not well controlled on the current standard therapy of calcium and active vitamin D. In addition, the role of PTH replacement on quality of life, intracerebral calcifications, cataracts, improving bone turnover, and reduction of renal complications of the disease remains to be further investigated.

Pharmacokinetics and Pharmacodynamics of Subcutaneous Recombinant Parathyroid Hormone (1–84) in Patients With Hypoparathyroidism: An Open-Label, Single-Dose, Phase I Study

BackgroundImpaired mineral homeostasis affecting calcium, phosphate, and magnesium is a result of parathyroid hormone (PTH) deficiency in hypoparathyroidism. The current standard of treatment with active vitamin D and oral calcium does not control levels of these major minerals. Recombinant full-length human PTH 1–84 (rhPTH[1–84]) is being developed for the treatment of hypoparathyroidism. ObjectiveThe goal of this study was to investigate the pharmacokinetics and pharmacodynamics of a single subcutaneous injection of rhPTH(1–84) in patients with hypoparathyroidism. MethodsThis was an open-label, dose-escalating study of single subcutaneous administration of 50 µg and then 100 µg of rhPTH(1–84). Enrolled patients (age range, 25–85 years) had ≥12 months of diagnosed hypoparathyroidism defined according to biochemical evidence of hypocalcemia with concomitant low-serum intact PTH and were taking doses ≥1000 mg/d of oral calcium and ≥0.25 µg/d of active vitamin D (oral calcitriol). The patient’s prescribed dose of calcitriol was taken the day preceding but not on the day of or during the 24 hours after rhPTH(1–84) administration. Each patient received a single 50-µg rhPTH(1–84) dose, had at least a 7-day washout interval, and then received a single 100-µg rhPTH(1–84) dose. The following parameters were assessed: plasma PTH; serum and urine total calcium, magnesium, phosphate, and creatinine; and urine cyclic adenosine monophosphate. ResultsAfter administration of rhPTH(1–84) 50 µg (n = 6) and 100 µg (n = 7), the approximate t½ was 2.5 to 3 hours. Plasma PTH levels increased rapidly, then declined gradually back to predose levels at ~12 hours. The median AUC was similar with calcitriol and rhPTH(1–84) for serum 1,25-dihydroxyvitamin D (calcitriol, 123–227 pg · h/mL; rhPTH[1–84], 101–276 pg · h/mL), calcium (calcitriol, 3.3–3.7 mg · h/dL; rhPTH[1–84], 3.3–7.6 mg · h/dL), and magnesium (calcitriol, 0.7–0.9 mg · h/dL; rhPTH[1–84], 1.3–2.8 mg · h/dL). In contrast, the median AUC for phosphate was strongly negative with rhPTH(1–84) (calcitriol, −1.0 to 0.8 mg · h/dL; rhPTH[1–84], −21.3 to −26.5 mg · h/dL). Compared with calcitriol, rhPTH(1–84) 50 µg reduced 24-hour calcium excretion and calcium-to-creatinine ratios by 12% and 23%, respectively, and rhPTH(1–84) 100 µg reduced them by 26% and 27%. There was little overall impact on urine magnesium levels. Compared with calcitriol, rhPTH(1–84) 50 µg increased urinary phosphate excretion and phosphate-to-creatinine ratios by 53% and 54%, respectively, and rhPTH(1–84) 100 µg increased them by 45% and 42%. Urine cyclic adenosine monophosphate–to–creatinine ratio increased with rhPTH(1–84) by 2.3-fold (50 µg) and 4.4-fold (100 µg) compared with calcitriol. ConclusionsPTH replacement therapy with rhPTH(1–84) regulated mineral homeostasis of calcium, magnesium, phosphate, and vitamin D metabolism toward normal in these study patients with hypoparathyroidism.

Comparison of the Elecsys PTH(1–84) assay with four contemporary second generation intact PTH assays and association with other biomarkers in chronic kidney disease patients

ObjectivesThe COBAS Elecsys PTH(1–84) assay is a novel, electro-chemiluminescence immunoassay that exclusively measures full-length parathyroid hormone (PTH). The aim of this study is to compare the automated biointact Elecsys PTH(1–84) assay with four contemporary, iPTH assays in chronic kidney disease (CKD) patients. Design and methodsWe compared the Elecsys PTH(1–84) assay with four iPTH assays (Siemens ADVIA Centaur, Ortho Clinical Diagnostics (OCD) VITROS, Beckman Access2, Abbott ARCHITECT) in the measurement of PTH in 83 local CKD patients. Majority of the patients (44) had CKD but were not on dialysis, 15 were on hemodialysis, 15 were on peritoneal dialysis, and 9 were post-renal transplant. The precision performance and correlation of the assays were determined. PTH(1–84) concentrations were correlated with calcium, phosphate, alkaline phosphatase, hemoglobin, HbA1c and lipid concentrations. ResultsThe Elecsys PTH(1–84) assay showed comparable precision and good correlation with the iPTH assays. Although the four different iPTH assays correlated well with each other, there was significant discrepancy among assays. The discrepancy among assays increased with increasing PTH concentrations. The ADVIA Centaur and ARCHITECT assays measured significantly higher PTH concentrations than the VITROS and Access2 assays. PTH(1–84) showed a positive association with phosphate and alkaline phosphatase and an inverse association with HbA1c. There was no significant association with lipid concentrations. ConclusionsThe third generation Elecsys PTH(1–84) assay had comparable precision performance and correlated well with second generation iPTH assays. However, significant discrepancy was found among the four iPTH assays in measuring iPTH in CKD patients.

Teriparatide - Indications beyond osteoporosis

Osteoporosis is a condition of impaired bone strength that results in an increased risk of fracture. The current and most popular pharmacological options for the treatment of osteoporosis include antiresorptive therapy, in particular, oral bisphosphonates (alendronate, risedronate, ibandronate). Anabolic agents like teriparatide have widened our therapeutic options. They act by directly stimulating bone formation and improving bone mass quantity and quality. Two forms of recombinant human parathyroid hormone (PTH) are available : full-length PTH (PTH 1–84; approved in the EU only) and the 1–34 N-terminal active fragment of PTH (teriparatide, US FDA approved). This review aims to discuss the benefits of teriparatide beyond the currently licensed indications like fracture healing, dental stability, osteonecrosis of jaw, hypoparathyroidism, and hypocalcemia.

Parathyroid hormone analogues in the treatment of osteoporosis

Osteoporosis is characterized by the occurrence of fragility fractures. Over the past years, various treatment options have become available, mostly antiresorptive agents such as bisphosphonates. However, antiresorptive therapy cannot restore bone mass and structure that has been lost due to increased remodeling. In this case, recombinant human parathyroid hormone (PTH) analogues-the full-length PTH(1-84) or the shortened molecule PTH(1-34), which is also known as teriparatide-present the possibility of increasing the formation of new bone substance by virtue of their anabolic effects. The bone formation induced by PTH analogues not only increases BMD or bone mass but also improves the microarchitecture of the skeleton, thereby leading to improved strength of bone and increased mechanical resistance. Controlled trials have shown that both analogues significantly reduce the incidence of vertebral fractures, and PTH(1-34) also reduces the risk of nonvertebral fractures. The need for daily self-injection and the higher cost compared with other forms of treatment limit the widespread use of PTH analogues. Nevertheless, treatment with PTH analogues should be considered in postmenopausal women and men with severe osteoporosis, as well as in patients on established glucocorticoid treatment with a high fracture risk. Concurrent therapy with antiresorptive agents should be avoided, but sequential therapy with these agents might consolidate the beneficial effects on the skeleton.

Novel Electrochemiluminescence Immunoassay Exclusively for Full‐length Parathyroid Hormone during Treatment with Cinacalcet for Secondary Hyperparathyroidism

A novel, electrochemiluminescence immunoassay that exclusively measures full-length parathyroid hormone (PTH), called Elecsys PTH (1-84) assay, is currently under development for clinical use. We measured serum PTH levels using this novel assay, as well as the Elecsys Intact PTH assay and the Whole PTH immunoradiometric assay, in 53 hemodialysis patients who participated in a 52-week clinical trial of cinacalcet. At baseline, serum PTH (1-84) levels measured with the Elecsys PTH (1-84) assay and those with the Whole PTH assay were comparable, and both values were significantly lower than Elecsys Intact PTH levels. After 52 weeks of cinacalcet treatment, Elecsys PTH (1-84) levels and Whole PTH levels decreased significantly by 56% and 60% from baseline, respectively. These results indicate that the Elecsys PTH (1-84) assay provides comparable data to the Whole PTH assay for monitoring parathyroid function in patients receiving hemodialysis. Introduction of this novel automated immunoassay would provide more widespread measurements of full-length PTH (1-84) in clinical practice.

Treatment of postmenopausal women with osteoporosis with PTH(1–84) for 36 months: treatment extension study

Objective:To determine the safety and efficacy of full-length parathyroid hormone, PTH(1–84), treatment for up to 36 months by evaluating bone mineral density (BMD) changes, bone histomorphometric indices, and clinical fracture incidence in postmenopausal women with osteoporosis.Background:The TOP trial demonstrated increased lumbar spine BMD (6.9%) versus placebo after 18 months of PTH(1–84) treatment and reduced the incidence of new vertebral fractures (61%; p = 0.001). The therapeutic benefits of long-term treatment of postmenopausal women with PTH(1–84) are unknown.Methods:The safety and efficacy of 36 months of once-daily dosing with 100 µg PTH(1–84) in postmenopausal women with osteoporosis were assessed. Women receiving placebo during the TOP trial were eligible for PTH(1–84) in the extension study.Clinical trial registration:NCT00172120.Results:Lumbar spine BMD increased by 8.5% above baseline (p < 0.001) at 36 months of PTH(1–84) treatment, remaining stable during the last 12 months of treatment. Increases in total hip and femoral neck BMD occurred more slowly, reaching 3.2% and 3.4%, respectively above baseline at 36 months (p < 0.001). The total hip BMD showed no signs of reaching a limiting value although the femoral neck plateaued from months 24 to 36. Seven patients had vertebral fractures during the placebo phase of the TOP trial and before entering the extension study, but this rate decreased with the introduction of PTH(1–84) therapy, resulting in a single worsened vertebral fracture in the first 6 months and no further vertebral fractures from months 6 to 36. Treatment over 36 months with PTH(1–84) was well-tolerated and iliac crest biopsies showed no adverse effects on bone.Limitations:There was no placebo group for BMD comparisons. The number of patients assessed for fracture incidence was small.Conclusions:PTH(1–84) treatment for 36 months resulted in significant increases in BMD at the lumbar spine and hip, was associated with a lower incidence of vertebral fracture when compared to before therapy initiation, and was well-tolerated. The continuous increases in total hip BMD suggest that prolonged PTH(1–84) treatment may be beneficial for postmenopausal osteoporosis. Increased BMD at the femoral neck and lumbar spine also showed favourable changes but plateaued between 24 and 36 months. Long-term treatment was not associated with abnormalities in bone biopsies.

The Calcemic Response to Continuous Parathyroid Hormone (PTH)(1-34) Infusion in End-Stage Kidney Disease Varies According to Bone Turnover: A Potential Role for PTH(7-84)

Factors contributing to PTH resistance in dialysis patients remain elusive. The study assessed the skeletal and biochemical response to 46 h of PTH(1-34) infusion in dialysis patients. The study was a prospective, controlled assessment of response to PTH(1-34). The study was performed at the University of California, Los Angeles, General Clinical Research Center. Nineteen dialysis patients and 17 healthy volunteers were studied. PTH(1-34) was infused at a rate of 8 pmol/kg x h for 46 h. Bone biopsy was performed in all dialysis patients. Serum calcium, phosphorus, 1,25-dihydroxyvitamin D, PTH (four separate assays), and FGF-23 were determined at baseline and h 7, 23, 35, and 46 of the infusion. Serum calcium levels rose in healthy volunteers (9.2 +/- 0.1 to 11.9 +/- 0.3 mg/dl; P < 0.01) and in dialysis patients with adynamic/normal bone turnover (9.0 +/- 0.3 to 10.7 +/- 0.7 mg/dl; P < 0.05) but did not change in dialysis patients with high bone turnover. Serum phosphorus levels declined in healthy volunteers (3.9 +/- 0.1 to 3.5 +/- 0.1 mg/dl; P < 0.05) but increased in all dialysis patients (6.7 +/- 0.4 to 8.0 +/- 0.3 mg/dl; P < 0.05). Full-length PTH(1-84) declined in all subjects; however, PTH(7-84) fragments declined only in healthy subjects and in dialysis patients with normal/adynamic bone but remained unchanged in dialysis patients with high bone turnover. The skeleton of dialysis patients with high bone turnover is resistant to the calcemic actions of PTH. PTH(7-84) may contribute to this phenomenon.

Amino terminal cleavage of PTH(1–84) to PTH(7–84) is regulated by serum calcium concentration via calcium-sensing receptor in hemodialysis patients

Secondary hyperparathyroidism is one of the critical complications of end-stage renal disease patients. Conventionally intact parathyroid hormone (iPTH) was used to assess secondary hyperparathyroidism, but this assay measures both PTH(1-84) (full-length parathyroid hormone) and PTH(7-84) (amino (N)-terminal-cleaved parathyroid hormone). PTH(7-84) is biologically inactive or antagonistic for PTH. In this study, we examined the relationship between serum calcium concentration and PTH(7-84)/PTH(1-84) ratio and the effect of calcimimetics on the ratio in hemodialysis (HD) patients. Ionized-calcium (iCa), iPTH, and whole PTH (wPTH) were measured at the start of HD sessions on HD patients. Patients were divided into four groups by presence (+) or absence (-) of vitamin D (VD) and calcimimetics (CM). PTH(7-84)/PTH(1-84) ratios of the four groups [VD(-)CM(-), VD(+)CM(-), VD(-)CM(+) and VD(+)CM(+)] were 0.735, 0.799, 0.844, and 1.156, respectively. In VD(-)CM(-) and VD(+)CM(-) groups, iCa and PTH(7-84)/PTH(1-84) ratio showed equilateral correlation (r = 0.634, p < 0.001 and r = 0.360, p < 0.01, respectively). In calcimimetics-treated group, iCa and PTH(7-84)/PTH(1-84) ratio did not show correlation. Whereas in the absence of calcimimetics cleavage of N-terminal PTH was regulated by serum calcium concentration, this regulation was abolished in the presence of calcimimetics. This suggests that cleavage of N-terminal PTH is regulated by calcium concentration via a calcium-sensing receptor and that calcimimetics may have a novel effect to reduce PTH level.