PTH Fragments Research Articles

The secretion of parathyroid hormone and its fragments from dispersed cells of adenomatous parathyroid tissue at different calcium concentrations.

The effect of varying calcium concentrations on PTH release from dispersed cells of adenomatous parathyroid tissues (n = 15) was studied. During high calcium concentrations PTH secretion was inhibited up to 62.5% as compared to low calcium concentrations. There was no correlation between iPTH secretion rate and suppressibility. Each adenoma had a different iPTH secretion rate. Three adenomas showed a high suppressibility (28.0%, 53.8%, and 62.5%). The supernates of their media were chromatographed and examined by midregion and C-terminal specific PTH-RIAs. Carboxyl-terminal PTH fragments were found to be released by two adenomas. There was no evidence for the release of midregion PTH fragments. Comparison of incubation media revealed that the adenoma with the lowest suppressibility released the highest amount of intact PTH (per 100,000 cells/ml). This adenoma exclusively secreted intact PTH, whereas PTH fragments were only released from two adenomas with higher suppressibility. In these media the ratio of PTH fragments to intact PTH increased with the calcium content of the media. The ratio was also dependent on the suppressibility of the adenomas; i.e. the ratio was greater when the suppressibility was higher. This suggests that in adenomas the intracellular hormone degradation is responsible for the degree of PTH suppression. As the suppressibility of PTH secretion is reduced in hyperfunctioning parathyroid tissue, diminished intracellular hormone degradation seems to be involved in the pathogenesis of primary hyperparathyroidism.

The Influence of Parathyroid Hormone and Its Fragments on Results from Midregion and C-Terminal Specific Radioimmunoassays*)

We compared a midregion (44-68) human parathyroid hormone (hPTH) specific radioimmunoassay (M-RIA) with a C-terminal (65-84) hPTH specific radioimmunoassay (C-RIA). The M-RIA discriminated 21 of 23 patients with primary hyperparathyroidism from 95 normals (normal range: 22.4-106.5 pmol/l). With the C-RIA 12 patients including the 2 patients not discriminated by the M-RIA had immunoreactive PTH (iPTH) values within the normal range of this assay (normal range: undetectable to 88.6 pmol/l). To investigate the reasons for these different abilities of separation, hyperparathyroid sera were subjected to gel-filtration and analyzed using the two assays. Intact PTH appeared to have a major influence on the immunoreactivity of circulating PTH in the M-RIA. In contrast, the C-RIA showed the highest immunoreactivity with midregion-C-terminal PTH fragments. Hyperparathyroid sera not discriminated by the C-RIA but with elevated iPTH in the M-RIA showed decreased amounts of midregion-C-terminal PTH fragments, while intact PTH comprised the highest amount of total circulating PTH immunoreactivity in the M-RIA. From the present results we conclude that the superiority of the M-RIA is due to the determination of intact PTH which is preferable for clinical measurements with relation to the diagnosis of primary hyperparathyroidism.

PROGRESS IN UREMIC TOXIN RESEARCH: Parathyroid Hormone, A Uremic Toxin

Despite the innovations in the treatment of secondary hyperparathyroidism, there are uremic patients with marked elevation in PTH levels. Uremic toxicity is in part attributable to the excess of circulating PTH. It has been known for many years that PTH may induce changes in cell calcium, a key intracellular signal required for normal cell function. The effect of PTH in dialysis patients is not limited to bone; the diversity of biologic effects of PTH is summarized in this review. In addition, the present review addresses other issues: (i) the presence of different circulating PTH fragments in uremic patients, (ii) the PTH assays currently utilized to measure circulating PTH, and (iii) the fact that some of the PTH effects seen in uremic patients may be due to the interaction of C-terminal PTH fragment with putative C-terminal PTH receptors.

Connexin43 Modulation of Osteoblast/Osteocyte Apoptosis: A Potential Therapeutic Target?

Connexin43 Modulation of Osteoblast/Osteocyte Apoptosis: A Potential Therapeutic Target?

On the Interpretation of Rat Carcinogenicity Studies for Human PTH(1-34) and Human PTH(1-84)

On the Interpretation of Rat Carcinogenicity Studies for Human PTH(1-34) and Human PTH(1-84)

Fracture repair: Modulation of fracture-callus and mechanical properties by sequential application of IL-6 following PTH 1–34 or PTH 28–48

Fracture healing presents a sequence of three major stages: inflammation and granulation tissue formation, callus formation and remodeling. Our working hypothesis was that fracture-repair might be enhanced by stimulating proliferation of chondrocytes and osteoblasts in the early stages of fracture healing followed by sequential acceleration of the remodeling process. In the present study we employed a novel device developed by us implementing a standardized fracture in rat tibiae. We investigated the effect of PTH 28–48 or PTH 1–34 alone or in sequence combination with IL-6 together with its soluble receptor (IL-6sR) on fracture repair. PTH 28–48 or PTH 1–34 was applied locally into the hematoma of fractures on days 4, 5 and 6 and IL-6+ its soluble receptor on days 7, 9, and 11. Post-fracture callus volume as measured 14 days post-fracture was increased significantly only by PTH 1–34 (20%; P<0.01). When one of the PTH fragments and IL-6+IL-6sR were applied sequentially callus volume was increased significantly (33%; P<0.01). X-rays radiography at 5 weeks post-fracture showed enlarged callus volume following treatment by either PTH fragments alone, and complete union following the sequential injection of both PTH fragments and IL-6+IL-6sR, only. Only the combination of one of the PTH fragments with IL-6+IL-6sR, as measured 6 weeks post-fracture by three point bending, changed dramatically the quality of the regenerating bone as presented by a 300% increase in mechanical resistance when PTH 1–34 was combined and 200% when PTH 28–48 was combined relative to vehicle-treated fractured bones. We conclude that the sequential application of IL-6+IL-6sR with both PTH fragments has the potential of enhancing fracture healing in long bones and should be further explored in preclinical and in clinical studies.

The Role of Quick Bio-Intact PTH(1-84) Assay During Parathyroidectomy for Secondary Hyperparathyroidism

The role of the quick PTH assay in surgery for secondary HPT is unclear because of overestimation of intact PTH(1-84) values due to the cross-reactivity of currently available first-generation PTH assays with non-PTH(1-84) fragments that accumulate in renal failure. In this study, we used a second-generation quick PTH immunometric assay that are claimed to detect the biologically active PTH(1-84) molecule with no cross-reactivity with PTH fragments to investigate the potential utility of the assay during parathyroidectomy for secondary HPT. The study was performed on 18 patients (12 women, 6 men) between October 2004 and March 2005. EDTA serum samples were drawn via a peripheral venous catheter after induction of anesthesia (basal), and at 5, 10, and 30 min after excision of diseased parathyroid glands. Serum active PTH(1-84) was measured by the quick Bio-Intact PTH(1-84) assay, which is a two-site chemiluminometric assay. At 30 min the quick Bio-PTH(1-84) level of 16 patients was under 45 pg/mL. Four parathyroid glands were removed macroscopically from 12 of the 16 patients, and three glands were removed from the other four patients. All patients were cured of their HPT. Four enlarged parathyroid glands were removed from a patient whose Bio-Intact PTH(1-84) at 30 min had not fallen below 45 pg/mL, and no other glands were found by further exploration. At the 6 mo follow-up examination, the first-generation intact PTH level of this patient was over 45 pg/mL, but several diagnostic imaging methods did not reveal any enlarged parathyroid glands. Three enlarged parathyroid glands from the other patient, and exploration led to the identification of an ectopic parathyroid gland at the carotid bifurcation. The results of this prospective study show that quick Bio-Intact PTH(1-84) monitoring is a valuable new tool for use in the surgical treatment of secondary HPT. An intraoperative, quick Bio-Intact PTH(1-84) assay will be of value for the adequate prediction of surgical cure.

Effect of haemodialysis on markers of bone turnover in children

'Intact' parathyroid hormone (iPTH) assays are used to measure serum PTH levels in haemodialysis patients to diagnose and monitor secondary hyperparathyroidism and consequent renal osteodystrophy (ROD); these assays exhibit cross-reactivity with long carboxyl-terminal PTH fragments (C-PTH) that accumulate in end stage renal failure (ESRF) and antagonise the biological activity of the whole molecule, 1-84 PTH. The effects of haemodialysis on C-PTH are not known. We investigated how haemodialysis affects serum concentrations of calcium, iPTH, 1-84 PTH, C-PTH, and other markers of bone turnover; bone-specific alkaline phosphatase (BALP) and type 1 collagen cross-linked telopeptide (CTx). Fifteen patients, mean (range) age 13.9 (4.3-17.6) years, haemodialysed for a median of 16.3 (4-41) months, had pre- and post-dialysis serum samples collected for routine biochemistry, BALP, CTx, iPTH and 1-84 PTH assays. Changes to serum concentrations and relationships between these biochemical surrogate markers of ROD were investigated. Serum phosphate and PTH levels (measured by both assays) fell significantly during dialysis, whereas serum calcium, C-PTH, the 1-84 PTH: C-PTH ratio and BALP and CTx concentrations were not significantly changed. 1-84 PTH levels were related to pre but not post dialysis serum calcium levels and changes to 1-84 PTH levels during dialysis were related to changes in serum calcium levels. 1-84 PTH and iPTH were reduced by haemodialysis, whereas levels of BALP and CTx remained stable post-dialysis. The relationship between BALP and CTx and bone histology requires investigation to determine whether they are more useful markers of bone turnover in this patient group.

Study on preparation and activity of a novel recombinant human parathyroid hormone(1–34) analog with N-terminal Pro–Pro extension

A recombinant human parathyroid hormone fragment, Pro–Pro–hPTH(1–34), with molecular weight of 4311.46 was acquired through gene engineering. It was then isolated and purified. The homogeneity of this fragment was characterized by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), high performance liquid chromatography(HPLC), isoelectronic focusing (IEF) electrophoresis and mass spectrometry(MS) methods. Its isoelectric point is 8.0 which was determined by IEF. It was found that the hormone fragment significantly induced calcium increment as compared to the control group ( P < 0.001) in Parsons's Chicken Assay, an established bioassay for the evaluation of the PTH effect. After the 3-month-old ovariectomized (OVXed) rats, the OVXed rat is one of the two models required by the U.S. Food and Drug Administration for the preclinical assessment of drugs for treating osteoporosis [DeLuca PP, Dani BA. Skeletal effects of parathyroid hormone (1–34) in ovariectomized rats with or without concurrent administration of salmon calcitonin. Am Assoc Pharm Sci 2001;3(4):E27 [1]]. Sprague–Dawley rats were fed for 14 weeks, daily subcutaneous injections of Pro–Pro–hPTH(1–34) for 16 weeks (0.4, 0.6 or 0.9 nmol/100 g body weight), reduced the ovariectomy (OVX)-triggered mass loss of vertebral trabecular bone. The mean Bone Material Density (BMD) increased to 29.2–34.5% in 3-month-old OVXed rats compared to control-vehicle group ( P < 0.001) and increased to 17.5–22.3% compared to sham-operated groups ( P < 0.01). In short, A recombinant Pro–Pro–hPTH(1–34) was harvested in purified form and its physico-chemical characterization was determined. It showed significantly enhanced activity upon two typical models for PTH fragments. It can increase the mineral density of vertebral trabecular bone just as synthetic hPTH(1–34), and the functional activity of Pro–Pro–hPTH(1–34) should be due to the removing of Pro–Pro- by Dipeptidyl peptidase IV (DPPIV). This study opened out a simplified method which was cheaper, faster than the conventional one for producing active hPTH fragment, and its applied prospect would be good; Furthermore, it may open up our own path in finding new methods for post-processing of gene-engineering product.

Mutation of phenylalanine-34 of parathyroid hormone disrupts NHERF1 regulation of PTH type I receptor signaling

Internalization of the PTH type I receptor (PTH1R) is regulated in a cell- and ligand-specific manner. We previously demonstrated that the sodium/proton exchanger regulatory factor type 1 (NHERF1; EBP50) is pivotal in determining the range of peptides that internalize the PTH1R. Antagonist PTH fragments can internalize the PTH1R in some kidney and bone cell models. PTH(7-34), which binds to, but does not activate, the PTH1R, internalizes the PTH1R in kidney distal tubule (DT) cells, where NHERF1 is not expressed. The effect of antagonist PTHrP peptides has not, to this point, been assessed. PTH1R internalization was measured by real-time confocal fluorescence microscopy of DT cells stably expressing 105 EGFP-tagged PTH1R/cell. PTHrP(7-34) internalized the PTH1R in a manner indistinguishable from PTH(7-34). Introduction of NHERF1 into DT cells, however, blocked PTH(7-34)-, but not PTHrP(7-34)-, induced PTH1R internalization. To delineate the sequences within PTHrP that determine whether PTH1R internalization is affected by NHERF1, chimeric PTH/PTHrP fragments were tested for their ability to induce PTH1R internalization. PTH(7-21)/PTHrP (22-34), PTH(7-32)/PTHrP(33-34), and PTH(7-33)/PTHrP(34) at 1 microM each internalized the PTH1R 50-70% in a NHERF1-independent manner. When the C terminus of PTHrP was replaced with homologous amino acids from PTH, NHERF1 inhibited PTH1R internalization. It was determined that simply mutating F34 to A in PTH induced PTH1R internalization in a NHERF1-independent manner. None of the chimeric peptides activated the PTH1R but all effectively competed for 1 nM PTH(1-34) in cyclic AMP assays. In addition, all chimeric peptides competed for radiolabeled PTH(1-34) in binding assays in DT cells. PTH(1- 34) and PTHrP(7-34), but not PTH(7-34), efficiently recruited beta-arrestin1 to plasma membrane PTH1Rs. We, therefore, conclude that PTH(1-34) and PTHrP(7-34) induce a conformational change in the PTH1R that promotes arrestin binding and dissociates NHERF1 from PTH1R internalization.

Daily Treatment of Aged Ovariectomized Rats with Human Parathyroid Hormone (1-84) for 12 Months Reverses Bone Loss and Enhances Trabecular and Cortical Bone Strength

Most studies that have investigated the anabolic effects of parathyroid hormone (1-84) (PTH) or PTH fragments on the skeleton of ovariectomized (OVX) rats have evaluated the short-term effects of high-dose PTH(1-34) in young animals. This study used densitometry, histomorphometry, and biomechanical testing to evaluate the effects of 12-month daily treatment with low-dose PTH (15 or 30 microg/kg) in rats that were 10 months old at baseline, 4 months after OVX. Bone mineral density (BMD) and bone strength were reduced substantially in control OVX rats. The 15 microg/kg dose of PTH restored BMD to levels similar to those in sham animals within 6 months at the lumbar spine, distal and central femur, and whole body and maintained the BMD gain from 6 to 12 months. The 30 microg/kg dose produced greater effects. Both PTH doses normalized the trabecular bone volume-to-total volume ratio (BV/TV) at lumbar vertebra 3 but not at the proximal tibia (where baseline BV/TV was very low), solely by increasing trabecular thickness. PTH dose-dependently increased bone formation by increasing the mineralizing surface, but only the 30 microg/kg dose increased resorption. PTH increased cortical BMD, area, and thickness, primarily by increasing endocortical bone formation, and restored all measures of bone strength to levels similar to those in sham animals at all skeletal sites. PTH increased bone mass safely; there was no osteoid accumulation, mineralization defect, or marrow fibrosis and there were no abnormal cells. Thus, long-term PTH therapy normalized bone strength in the aged OVX rat, a model of postmenopausal osteoporosis, through increased bone turnover and enhanced formation of both trabecular and cortical bone.

Evolution of PTH assays

PTH metabolism is complex and the circulating forms include the intact 1-84 molecule as well as several carboxyl-terminal fragments. The first generation of PTH assays included several types of competitive assays, with specificities that spanned carboxyl, mid-region and amino-terminal portions of the molecule. The limitations of these assays and the methodological evolution led to the description of 2nd generation non-competitive immunometric assays for PTH in the late 80's, based on the recognition of the PTH molecule by two different antibodies, one directed against de amino-terminal and other against the carboxyl-terminal segments. The observation that in some circumstances "long" carboxyl-terminal segments were also measured by 2nd generation assays led to the development of 3rd generation assays based on amino-terminal specific antibodies that are specific for the first amino acids, measuring only the molecular forms that activate PTH1R. The practical and cost-benefit advantages of these assays are still debatable. The recent observation that carboxyl-terminal fragments of PTH have biological activity via a distinct receptor than PTH1R, points to the future need of more than one assay in order to evaluate parathyroid hormone function.

Aspects pratiques des dosages de PTH

New knowledge concerning PTH biology was accumulated during the past few years. The finding that the so-called “intact” PTH assays measure a “non 1-84” PTH fragment in addition to full-length PTH has led to the development of new assays. These new assays, which were initially thought to measure 1-84 PTH only, have been shown to recognize also another PTH species called “amino-PTH”. As the various names given to the different assay methods are highly confusing, there is a need for a simplified nomenclature. A simple way would be to identify the older “intact” PTH assays as second-generation assays and the new assays (Whole, CAP, BioIntact) as third-generation assays. Although of considerable potential interest for the comprehension of PTH physiology, the third-generation PTH assays have not yet proved to be superior to the second-generation assays in clinical practice. There is thus currently no recommendation to switch from the second-generation to the third-generation assays in clinical practice, or to use a ratio derived from the concomitant measurement of PTH with both assay-generation. Because second- and third-generation PTH assays are usually highly correlated, significant differences in the clinical information provided by these methods are unlikely. However, our opinion is that more definitive bone biopsy studies in dialyzed patients selected according to their bone- and calcium-related treatment are still needed to reach a consensus. Finally, we have proposed that PTH reference values should be established in healthy subjects with a normal vitamin D status. This supposes that 25OHD is measured in the reference population beforehand, and that the subjects with vitamin D insufficiency are eliminated from the reference group. Although more complicated than the usual way to establish normative data, we have shown that it decreases the upper limit of normal by 25–35%, enhancing thus the diagnostic sensitivity for hyperparathyroidism without a decrease in specificity.

The present conditions and problems for PTH assay

The common clinical diagnostic kits for intact PTH assay detected not only PTH (1-84) but also PTH (7-84) fragment. Recently, it is reported that PTH (1-84) fragment is the antagonist to PTH (7-84) biological action. Now, PTH assays of whole PTH for IRMA method and bio-intact PTH for CLIA method respectively, which detect only (1-84) fragment may be useful for more precise measurement of PTH activity in diagnosis of bone metabolic disease and uremic patient.

Exogenous PTH-Related Protein and PTH Improve Mineral and Skeletal Status in 25-Hydroxyvitamin D-1α-Hydroxylase and PTH Double Knockout Mice

We examined the effect of NH2-terminal fragments of PTHrP and PTH in young mutant mice deficient in both PTH and 1,25-dihydroxyvitamin D. Both proteins prolonged murine survival by increasing serum calcium, apparently by enhancing renal calcium transporter expression. The dominant effect on the skeleton was an increase in both endochondral bone and appositional formation without increased bone resorption. PTH-related protein (PTHrP) was discovered as a hypercalcemic agent responsible for the syndrome of humeral hypercalcemia of malignancy, and PTH is the major protein hormone regulating calcium homeostasis. Both proteins have skeletal anabolic actions when administered intermittently. We examined effects of exogenous PTHrP(1-86) and PTH(1-34) in double null mutant mice deficient in both PTH and 25-hydroxyvitamin D-1alpha-hydroxylase [1alpha(OH)ase] to determine the action of these proteins in the absence of the two major regulators of calcium and skeletal homeostasis. Mice heterozygous for the PTH null allele and for the 1alpha(OH)ase null allele were mated to generate pups homozygous for both null alleles. PTHrP(1-86) and PTH(1-34) were administered subcutaneously starting 4 days after birth. Serum biochemistry and skeletal radiology, histology, and histomorphometry were performed, and indices of bone formation, resorption, and renal calcium transport were determined by real time RT-PCR, Western blot, and immunohistochemical approaches. In the double mutant mice, which die within 3 weeks after birth with severe hypocalcemia, tetany, and skeletal defects, exogenous PTHrP and PTH enhanced survival of the animals by improving serum calcium. Both proteins increased renal calcium transporter expression and long bone length and augmented growth plate chondrocyte proliferation, differentiation, and cartilage matrix mineralization. Cortical and trabecular bone mass was increased with augmented osteoblast number and activity; however, bone resorption was not increased. PTHrP and PTH reduced hypocalcemia by enhancing renal calcium reabsorption but not by increasing bone resorption. The major skeletal effects of exogenous PTHrP and PTH were to increase bone anabolism.

Third- or Second-Generation Parathyroid Hormone Assays: A Remaining Debate in the Diagnosis of Primary Hyperparathyroidism

Since the demonstration that the second-generation PTH assays, also called intact PTH assays, recognize a non-1-84 PTH fragment in addition to the intact 1-84 PTH, new PTH assays defined as third-generation assays have been commercialized. Two previous studies aimed at evaluating whether these third-generation PTH assays improved the diagnostic sensitivity for primary hyperparathyroidism (PHPT), but they yielded opposite results. In the present study we compared two second-generation PTH assays (the total intact PTH assay from Scantibodies Laboratory, Inc., and the intact PTH assay from Nichols Institute Diagnostics) with two third-generation assays (the cyclase-activating PTH assay also from Scantibodies Laboratory and the bio-intact PTH assay from Nichols Institute) in a series of 145 consecutive PHPT patients operated in our endocrine surgery department over a 10-month period. A group of 74 healthy subjects served as controls. The diagnostic sensitivities for PHPT of the total intact, the intact, the cyclase-activating, and the bio-intact assays were 93.8%, 97.3%, 84.2%, and 89.0%, respectively, with 95% confidence intervals in the control groups of 10-46, 11-60, 8.4-34, and 9-41 ng/liter, respectively. Our findings demonstrate that the diagnostic sensitivities of second- and third-generation PTH assays are similar. Third-generation PTH assays do not therefore improve the diagnosis of elevated serum PTH levels in PHPT, although there are numerical differences among the values.

First- and second-generation immunometric PTH assays during treatment of hyperparathyroidism with cinacalcet HCl

First-generation immunometric assays for "intact" parathyroid hormone (iPTH) also measure large N-terminally truncated PTH fragments, whereas second-generation assays, such as the "bio-intact" PTH (biPTH) assay, measure only full-length biologically active PTH(1-84). This study compared iPTH and biPTH assays during cinacalcet treatment in subjects with secondary HPT receiving dialysis. Four hundred and ten subjects were enrolled in a 26-week randomized, double-blind, placebo-controlled trial of oral cinacalcet (or placebo), 30 to 180 mg once daily, and efficacy was assessed using biPTH and iPTH assays. Compared with control treatment, cinacalcet improved the management of secondary HPT. Both biPTH and iPTH decreased by 38%+/- 3% during weeks 13 to 26 in the cinacalcet group; biPTH increased by 23%+/- 4% and iPTH increased by 9.5%+/- 3% in the control group (P < 0.001). Fifty-six percent of cinacalcet subjects and 10% of control subjects had a > or = 30% reduction in biPTH, and 61% and 11%, respectively, had a > or = 30% reduction in iPTH. Significant correlations between biPTH and iPTH levels were observed throughout the study. Both assays correlated similarly with bone-specific alkaline phosphatase levels. The ratio of biPTH to iPTH was maintained at 56% +/- 1% after treatment in both treatment groups. Increasing serum calcium levels were associated with a decreasing ratio of biPTH to (iPTH-biPTH). These data show that PTH can be monitored with either iPTH or biPTH assays during therapy with cinacalcet, and that cinacalcet therapy does not exert a major influence on the ratio between PTH(1-84) and large, N-terminally truncated PTH fragments.

Normalization of reversed bio-intact-PTH(1-84)/intact- PTH ratio after parathyroidectomy in a patient with severe secondary hyperparathyroidism

The conventional intact-PTH assay detects both (1-84)-PTH and C-terminal fragments. The newer PTH assays, bio-intact-PTH assay and whole-PTH assay, use an antibody that binds only if the first amino acid is present, making it specific for the complete molecule, (1-84)-PTH. Thus, the intact-PTH concentrations are theoretically higher than bio-intact-PTH concentrations, and the ratio of bio-intact-PTH/intact-PTH is usually less than 1. These findings are observed in normal subjects and patients with primary and secondary hyperparathyroidism. Here we present a hemodialysis patient with severe secondary hyperparathyroidism who was found to have abnormally higher plasma bio-intact-PTH concentrations than intact-PTH concentrations, and the abnormally high biointact-PTH/intact-PTH ratio improved after parathyroidectomy (PTx). The patient was a 67-year-old man on maintenance hemodialysis since 1995. Since 2003, he was found to have high plasma intact-PTH concentrations and two swollen parathyroid glands in the neck. PTx with forearm autograft was performed in October 2003. Before PTx, an abnormally high ratio of bio-intact-PTH/intact-PTH was detected (840 pg/ml/770 pg/ml, > 1), while the same ratio was improved to normal range (100 pg/ml/200 pg/ml, < 1). Recently, a few patients with parathyroid carcinoma have been found to have higher (1-84)-PTH concentrations than intact-PTH concentrations with abnormally high (1-84)-PTH/intact-PTH ratio. Moreover, a new molecular form of PTH distinct from (1-84)-PTH was detected in these patients. We speculate that the resected parathyroid gland in our patient might have produced a new molecular form of PTH that was less well detected by the conventional intact-PTH assay.

7-84 parathyroid hormone fragments are proportionally increased with the severity of uremic hyperparathyroidism

Recent progress in PTH assay has revealed that the intact PTH assay kit in current use does not differentiate between the truncated 7-84 PTH molecule and the 1-84 PTH molecule. In our series, we examined the effectiveness of a new PTH assay as a noninvasive method of evaluating severity of uremic hyperparathyroidism. Two hundred and seventy hemodialysis (HD) patients recruited from three HD centers were included and divided into subgroups according to the conventional iPTH assay results. Pre-dialysis blood samples were collected and subjected to two different PTH assays: "intact" PTH assay (iPTH) and "whole" PTH (wPTH) assay. Two biochemical markers of bone remodeling were also examined. In all cases, PTH levels determined by the wPTH assay were in the average 32.3% lower than those determined by the iPTH assay. The difference of the results of the two PTH assay methods, which indicated the portion of 7-84 PTH fragments of the total PTH molecules measured with the iPTH assay, was gradually increased while the severity of uremic hyperparathyroidism increased. Biochemical markers of bone formation/resorption showed a similar change. The portion of the 7-84 PTH fragments and markers of increased bone turnover increased in proportion to the severity of uremic hyperparathyroidism. This finding disproves the hypothetical role of 7-84 PTH fragments alone as the noninvasive marker of low-turnover bone disease in HD patients.

Pharmacokinetic and pharmacodynamic characteristics of subcutaneously applied PTH-1–37

Exogeneous delivery of parathyroid hormone fragments has become a novel treatment moiety for osteopenic conditions. The presented study was performed to assess the pharmacokinetic and pharmacodynamic properties of subcutaneously applied human hPTH-1–37 in comparison to hPTH-1–34 in healthy postmenopausal women. In total, 33 subjects participated in the study (age range: 57, 41–71 years, duration of postmenopausal state: 10, 2–28 years, BMI (mean±STD): 27.0±2.8kg/m2). The volunteers were randomized to either receive 10µg, 20µg, or 40µg of hPTH-1–37, 20µg hPTH-1–34, or placebo. Observation parameters were: adverse events and serum concentrations of hPTH-1–37, hPTH-1–34, hPTH-1–84, calcium, and cAMP. Both investigated PTH fragments showed fast absorption from the subcutaneous tissue. Tmax following hPTH-1–37 application was reached 44±3min after dosing hPTH-1–34 50±9min (p<0.05) and both PTH fragments had receded to baseline levels within 360min after administration (T1/2: hPTH-1–37: 63±5min; hPTH-1–34: 50±8min, p<0.05). The bioavailability of hPTH-1–37 relative to hPTH-1–34 as calculated from the AUC values was 68%. The Cmax values increased in a dose dependent manner (hPTH-1–37: 10µg: 27±7 pg/ml; 20µg: 71±25 pg/ml; 40µg: 127±37 pg/ml; hPTH-1–34, 20µg: 104±12 pg/ml). A dose response relationship was also seen for the increase in calcium after 6 hrs, while hPTH-1–84 was almost equally suppressed by all active PTH fragment concentrations. Only few and minor adverse events were reported that are known side effects from PTH treatment (headache, nausea etc.). In conclusion, in comparison to hPTH-1–34, hPTH-1–37 shows the same pharmacokinetic and pharmacodynamic properties and an acceptable relative bioavailability. hPTH-1–37 is an adequate future candidate for treatment of osteoporosis and other osteopenic conditions.