Terminal Parathyroid Hormone Research Articles

Hypokinetic azotemic osteodystrophy

CASE PRESENTATION A 61-year-old male dialysis patient was referred from another center to the Bone and Mineral Research Unit of the Hospital Central de Asturias for evaluation. At age 24, renal tuberculosis had necessitated a left nephrectomy; at age 42 nephrolithiasis in the right kidney had prompted surgical intervention. Four years later, moderate renal failure presumably due to chronic interstitial nephritis was diagnosed; 7 years later, at age 53, he entered the dialysis program. He received treatment in a dialysis unit equipped with a reverse osmosis (RO) system for water treatment. Renal osteodystrophy had been present since the beginning of dialysis, and the thoracic and lumbar spine showed demineralization. During the first 5 years of hemodialysis, symptoms and radiologic signs of hyperparathyroidism, including multiple vascular calcifications, worsened. The serum calcium (Ca+) level progressively increased, reaching 10.5 mg/dl. The serum phosphorus (P) level was high, although the patient had received long-term treatment with aluminum hydroxide. During that period, parathyroid hormone (PTH) levels (carboxy terminal) had remained 40 to 50 times higher than the upper limit of normal. Total alkaline phosphatase measurements had stayed in the low-normal range. The patient needed frequent red cell transfusions to avoid symptoms of anemia. Five years after beginning dialysis, he had a non-traumatic radial fracture coincident with worsening of the radiologic signs and his symptoms. A subtotal parathyroidectomy was performed. During the 2 years after the subtotal parathyroidectomy, his symptoms mildly improved, and the carboxy terminal PTH level decreased, stabilizing in the upper limit of normal. Total alkaline phosphatase fell to lower than normal, and the serum P was kept at acceptable values by aluminum hydroxide and calcium carbonate. Oral calcitriol (1.5–3.5 μg/week) maintained serum Ca+ levels in the range of 10.0 mg/dl–10.5 mg/dl. Two years after the parathyroidectomy, bilateral carpal tunnel syndrome was detected and surgically relieved. Amyloid was detected in the surrounding fat tissue, serum beta-2 microglobulin was elevated; dialysis with highly permeable membranes (PAN) was prescribed. Three years after the parathyroidectomy, PTH levels, measured several times using a PTH intact assay, revealed very low values (from undetectable to 13.5 pg/ml) and total alkaline phosphatase had returned to pre-surgery values (in the low-normal range). Basal serum aluminum (Al) was 96 μg/liter, increasing to 234 μg/liter after the infusion of 40 mg/kg of deferoxamine. Because Al-induced bone disease was suspected, a bone biopsy with tetracycline labeling was performed. The main histologic and histomorphometric findings of the bone biopsy were reduction in trabecular bone volume (11%), a slight increase in relative osteoid surface (20%), a decrease in osteoid volume (1.3%), low osteoblast surface (0.12%), low osteoclast surface (0.59%), positive Al surface staining (aluminum 16%; solochrome of azurine, 47%), and negative iron (Fe) staining (Perls). Bone Al and Fe concentration, measured by atomic absorption spectrometry, were 28 μg/g and 405 μg/g, respectively (normal, 3 μg/g and 300 μg/g, respectively). The tetracycline study showed only a single and diffuse labeling. Aluminum-induced adynamic bone disease was diagnosed. After the bone biopsy, therapy with deferoxamine (40 mg/kg/week) was prescribed (18 months of intermittent treatment over 3 years). During deferoxamine therapy, repeated basal serum Al levels were 50–85 μg/liter; these values doubled after the deferoxamine tests performed during that period. At the end of deferoxamine treatment, the serum Al remained at the same level, but intact PTH and alkaline phosphatase levels progressively increased, reaching 150 pg/ml and 219 U/liter, respectively (normal, 10–65 pg/ml and 70–280 U/liter). Before and after the deferoxamine treatment, serum transferrin, serum Fe, and Fe-transferrin saturation were always in the normal range. Two years after the bone biopsy, when the patient was 62 years old, he suffered a fracture of the right femoral neck; one year later, he fractured the left femoral neck. Both were treated with standard surgical techniques. During the following 4 years, the patient was admitted to the hospital several times with diagnoses of diabetes mellitus type II, diverticulitis, ventricular tachycardia, and congestive cardiac failure. Also, severe vascular obstruction of the left leg necessitated amputation of the second toe of the left foot. During the last year (7 years after the bone biopsy), he has maintained a serum calcium ranging between 9.0–9.5 mg/dl; serum phosphorus, 4.7–6.5 mg/dl; serum aluminum, 73.0–90.8 μg/liter; normal serum iron parameters; intact PTH levels of 314–415 pg/ml; and an alkaline phosphatase of 125–139 U/liter.

Controlled trial of falecalcitriol versus alfacalcidol in suppression of parathyroid hormone in hemodialysis patients with secondary hyperparathyroidism

Active vitamin D3 is extensively used for the treatment of secondary hyperparathyroidism in hemodialysis patients. But it is often impossible to administer enough dose to suppress parathyroid hormone (PTH) level, because of hypercalcemia and hyperphosphatemia. New modalities with higher specificity for PTH suppression are desirable. We conducted a crossover comparative study of falecalcitriol, an active vitamin D3 analog, and alfacalcidol (1alpha[OH]D3). In this study, 25 hemodialysis patients with moderate to severe secondary hyperparathyroidism who had normal serum calcium levels were enrolled. They received daily oral doses of alfacalcidol during an 8-week observation period. Based on serum calcium levels and intact PTH, the subjects were allocated into two groups, and a comparative study was conducted using unmasked crossover design of two drugs x two periods. The dosage of both drugs was adjusted to maintain the initial serum calcium levels, and the relative change (%change) of serum biochemical parameters were compared. Comparison of two drugs in period 1 was taken as primary efficacy evaluation. Reproducibility of drug action was confirmed by comparing the effect of falecalcitriol between period 1 and 2. The percent change of PTH of falecalcitriol was lower than that of alfacalcidol: Those were, respectively, -7.89% and +30.42% for c- terminal PTH (P = 0.022), -4.39% and +38.88% for i-PTH (P = 0.077), and +3.68% and +30.52% for midregion PTH (P = 0.099). The similar changes were observed in the falecalcitriol group during period 2, confirming the reproducibility. Falecalcitriol was found to be superior to alfacalcidol in suppression of PTH levels in patients with moderate to severe secondary hyperparathyroidism when it is administered in equivalent doses that might maintain similar serum calcium levels. (Am J Kidney Dis 1998 Aug;32(2):238-46)

Stimulatory effect of carboxyl-terminal parathyroid hormone fragments on osteoclast-like cell formation and osteoclastic activity

The controversy exists about the biological activity of carboxyl (C)-terminal parathyroid hormone (PTH) fragments. The present study was performed to examine the effect of C-terminal PTH fragments on osteoclast-like cell formation and bone-resorbing activity. Human (h) PTH-(1-84) caused a stimulation of osteoclast-like cell formation in osteoblast-containing mouse bone cell cultures more effectively than hPTH-(1-34). All of the C-terminal fragments examined [hPTH-(35-84), hPTH-(53-84) and hPTH-(69-84)] significantly stimulated osteoclast-like cell formation. The conditioned medium from osteoblastic UMR-106 cells pretreated with C-terminal PTH as well as amino-terminal PTH significantly stimulated osteoclast-like cell formation from mouse hemopoietic blast cells supported by granulocyte-macrophage colony stimulating factor. Moreover, all of the C-terminal fragments also caused a stimulation of osteoclast-like cell formation from hemopoietic blast cells even in the absence of osteoblasts. As for bone-resorbing activity of mature osteoclasts, all of the C-terminal fragments stimulated bone-resorbing activity in osteoblast-containing mouse bone cell cultures, while these fragments did not affect bone-resorbing activity of isolated rabbit osteoclasts. The present study indicates that C-terminal PTH fragments stimulate osteoclast-like cell formation as well as bone-resorbing activity of mature osteoclasts in the presence of osteoblast and also accelerate osteoclast-like cell formation from hemopoietic blast cells in the absence of osteoblasts.

Dialysis membranes and PTH changes during hemodialysis in patients with secondary hyperparathyroidism.

Changes in parathyroid hormone (PTH) during hemodialysis have been explained by the influence of ionized calcium changes on PTH secretion. In this study we have investigated the influence of dialysis membranes of different permeability on PTH changes during hemodialysis. Five chronic renal failure patients underwent three consecutive hemodialysis sessions with cuprophane (CUP) polysulfone (PS) and polyacrylonitrile (PAN). Two hours of isolated ultrafiltration were followed by 3 h dialysis. A significant decrease in carboxy terminal PTH (COOH PTH) was observed with PAN (p < 0.05) but not with CUP or PS. Intact PTH decreased (p < 0.001) with all three membranes, following a significant increase in ionized calcium (p < 0.001). Sieving coefficients for COOH PTH were significantly lower with CUP than with PS (p < 0.05) or PAN (p < 0.001). Intact PTH sieving coefficients were near zero for all three membranes. COOH PTH and intact PTH clearance rates were significantly higher with PAN (p < 0.001) than with PS or CUP, either in isolated ultrafiltration or with dialysis fluid. Thus PTH changes during hemodialysis do not only depend on the increase in calcium but also on the nature of the dialysis membrane. Adsorption of PTH to the PAN membrane surface explain the high PTH clearance rates achieved with this filter.

Measurement of feline intact parathyroid hormone: Assay validation and sample handling studies

ABSTRACTA two‐site intact immunoradiometric assay was validated for the measurement of parathyroid hormone (PTH) in the cat, by assessment of precision, sensitivity and specificity. The mean intra‐ and interassay coefficients of variation were 12·7 and 12·8 per cent, respectively. The sensitivity of the assay was 3·90 pgl/ml. The presence of carboxyl fragment interference was suspected from the non‐parallel dilution of two of seven feline samples and the decreased recovery of PTH on addition of carboxyl terminal fragment PTH to samples. The plasma PTH concentration, measured using this assay, in 40 clinically healthy cats was 10·9 ± 5·3 pg/ml (mean ± SD). The assay demonstrated appropriate responses in cases of secondary renal hyperparathyroidism, hypercalcaemia of malignancy and iatrogenic hypoparathyroidism. Storage characteristics would permit posting of samples. This assay will therefore provide a useful non‐invasive tool for the diagnosis of disorders of calcium metabolism in the cat.

Production and characterisation of monoclonal antibodies to parathyroid hormone (1–34)

Monoclonal antibodies to the biologically active N terminal region of parathyroid hormone (PTH) suitable for use in the measurement of circulating PTH concentrations have proved difficult to produce. In this study, no serum PTH antibody titres could be detected in mice using synthetic human PTH (1–34) (free or coupled to albumin) or PTH (1–10) (coupled to keyhole limpet haemocyanin) as immunogen. A consistent response to PTH (1–34) peptide was obtained in DA rats. We have produced five monoclonal antibodies to PTH (1–34) derived from the fusion of DA rat spleen cells and the mouse myeloma line X63 Ag.8.653. Bulk production of the antibodies was achieved using congenitally athymic mice for ascites production. Antibody assessment studies revealed the antibodies to be sensitive to the oxidation state of the methionine residues in PTH (1–34). Two of the antibodies, 3B3 and 6E3, were shown to be of potential use in measuring circulating PTH (1–84) when used in combination with available antibodies to C terminal PTH. A third antibody, 4G3, which failed to recognise PTH (1–84) when used in combination with 3B3, formed the basis of a specific assay for PTH (1–34).

Absence of hyperparathyroidism in severe liver disease

Elevated serum levels of intact parathyroid hormone (PTH) have been reported in severe versus mild biliary cirrhosis. The aim of this study was to determine whether hyperparathyroidism was present in severe liver disease on the basis of the inability of the liver to catabolize the hormone. Because biologic activity resides in the amino terminal, and amino terminal PTH determinations have not been routinely made in liver disease, it is possible that hyperparathyroidism was previously missed in these patients. Accordingly, we obtained fasting blood from 11 patients with severe liver disease and 8 age-matched controls. We measured intact, amino terminal, and mid-region PTH, vitamin D metabolites, bone gamma carboxyglutamic acid protein (BGP), ionized calcium, phosphorus, magnesium, and liver function tests. Serum levels of PTH were normal with all assays and 1,25(OH)2D levels were not elevated. These findings argue against the possibility that hyperparathyroidism plays a role in the pathogenesis of hepatic osteodystrophy.

Peripheral metabolism of PTH: fate of biologically active amino terminus in vivo.

Clearance of intact parathyroid hormone (PTH) from blood is associated with rapid uptake by liver and kidney, limited proteolysis by tissue endopeptidases and, within minutes, appearance of circulating carboxyl-(COOH)-terminal PTH fragments. The fate of the corresponding amino(NH2)-terminal portion of the hormone during this peripheral metabolism is still unknown, however. To determine this, we have employed [35S]bovine PTH (bPTH) labeled to high specific activity at NH2-terminal methionines, which permits direct monitoring of the fate of the PTH NH2-terminus during metabolism in vivo. The [35S]PTH was administered by bolus or continuous intravenous infusion to anesthetized normal rats, to rats subjected to acute ablation of the liver, the kidneys, or both, and to rats receiving co-infusions of excess synthetic bPTH(1-34) NH2-terminal fragments. Analysis by high-resolution chromatographic techniques sensitive to 10(-13) M [35S]PTH peptides in plasma yields no evidence that peripheral metabolism of PTH generates circulating NH2-terminal fragments, even when special measures are taken to block clearance of such putative fragments from blood. We find that the NH2-terminus of PTH is rapidly degraded in situ by the liver but that both liver and especially kidney nevertheless contain low levels of NH2-terminal PTH fragments that, although not released into the blood, are large enough to be potentially active. Thus, the peripheral metabolism of PTH in normal animals does not normally lead to the formation of circulating amino terminal fragments of the hormone that might act independently of intact PTH on peripheral target tissues.

The value to the surgeon of parathyroid hormone assays in primary hyperparathyroidism.

The role of various parathyroid hormone (PTH) radio-immunoassays in the diagnosis of primary hyperparathyroidism (PHP) is controversial. A series of 204 patients with surgically proven PHP was studied. Serum total calcium, serum ionized calcium, amino (N)-terminal PTH and carboxyl(C)-terminal PTH were assessed in relation to the volume and weight of adenomatous or hyperplastic parathyroid tissue excised at operation. N-terminal PTH was elevated above the normal laboratory range in only 24% of patients and correlated relatively poorly with the volume of abnormal parathyroid tissue (r = 0.20, P = 0.05). C-terminal PTH was elevated above the normal range in 91% of patients and had a strong correlation with the volume of abnormal parathyroid tissue (r = 0.63, P less than 0.001). The correlation coefficients between C-terminal PTH and serum total calcium and serum ionized calcium were both 0.63 (P less than 0.001). In contrast, there was no correlation between N-terminal PTH and serum total calcium (r = -0.02), serum ionized calcium (r = -0.04) or C-terminal PTH (r = 0.09). A combination of hypercalcaemia and elevated C-terminal PTH can be regarded as strong diagnostic evidence of PHP. Furthermore, the level of C-terminal PTH can assist the surgeon by approximately predicting the amount of adenomatous or hyperplastic parathyroid tissue that may be expected at surgical exploration.

Comparison of poly- and monoclonal antibodies as labels in a two-site immunochemiluminometric assay for intact parathyroid hormone

We have evaluated the potential of monoclonal antibodies in the development of a non-isotopic immunometric assay for intact human parathyroid hormone (PTH). The assay has been designed to utilise a chemiluminescent acridinium ester labelled anti-aminoterminal (anti-N) antibody and a solid-phase anti-carboxyterminal antibody in order to measure specifically the intact hormone. In this system the characteristics of the labelled antibody proved crucial to the performance of the assay. A low affinity monoclonal reagent yielded insufficient analytical sensitivity, while a higher affinity monoclonal reagent cross-reacted poorly with the intact molecule relative to the amino terminal PTH fragment to which it was raised. Neither antibody could therefore match the performance of an affinity-purified polyclonal anti-N PTH reagent. These results highlight the problems to be addressed in the selection of suitable reagents for immunometric assay development when specificity and sensitivity are crucial requirements.

Parathyroid hormone and bone histology: Response to hypocalcemia in osteitis fibrosa

AbstractParathyroid hormone and bone histology: Response to hypocalcemia in osteitis fibrosa. The parathyroid hormone (PTH) response to hypocalcemia was studied in 18 hemodialysis patients with osteitis fibrosa, and the relationship with PTH and bone histology in 26 hemodialysis patients. Hypocalcemia was produced during hemodialysis by the use of a dialysate devoid of calcium. Both amino (N) (P < 0.05) and carboxy (C) (P < 0.005) terminal PTH attained maximum levels by 15min despite only a minimal decline in plasma calcium. Throughout the remainder of the study, C and N-PTH levels remained elevated but did not increase despite a further decline in plasma calcium. Five patients increased both C and N-PTH to maximum or near maximum levels by the first sampling, although plasma calcium remained above 9 mg/dl. Basal C and N-PTH correlated with the maximum levels of each induced by hypocalcemia (P < 0.005). Both basal N-PTH and the maximum change in C-PTH produced by hypocalcemia correlated with osteoblastic osteoid, active resorption, osteoclasts/mm2, and endosteal fibrosis (P < 0.005). In conclusion, (1) a minimal decline in plasma calcium produces a maximum C and N-PTH response; (2) an altered PTH set point may be present in some hemodialysis patients; (3) the correlation between basal and maximally stimulated PTH levels suggests that basal PTH levels may reflect parathyroid gland mass; and (4) a correlation with basal and stimulated PTH and bone histology is present.Hormone parathyroïdienne et histologie osseuse: Réponse a l'hypocalcémie dans l'ostéïte fibreuse. La réponse de l'hormone parathyroïdienne (PTH) a l'hypocalcémie a été étudiée chez 18 malades hémodialysés avec une ostéïte fibreuse, et la relation entre la PTH et l'histologie osseuse chez 26 malades hémodialysés. L'hypocalcémie était produite pendant l'hémodialyse par l'emploi d'un dialysat dépouvu de calcium. Les PTH amino (N) (P < 0.05) et carboxy (C) (P < 0.005) terminales atteignaient des niveaux maximum en 15 min, malgré une diminution seulement minime du calcium plasmatique. Pendant le reste de l'étude, les niveaux de C et N-PTH sont restés élevés mais n'ont pas augmenté malgré une diminution supplémentaire du calcium plasmatique. Cinq malades ont augmenté C et N-PTH à des niveaux maximaux ou voisins du maximum lors du premier recueil plasmatique, bien que le calcium plasmatique soit resté au-dessus de 9 mg/dl. C et N-PTH de base étaient corrélées avec les niveaux maximum de chacune lors d'une hypocalcémie (P < 0.005). N-PTH basale et la modification maximale de C-PTH entraînée par l'hypocalcémie étaient corrélées avec l'ostéoïde ostéoblastique, la résorption active, les ostéoclastes/mm2, et la fibrose endostéale (P < 0.005). En conclusion, (1) une diminution minime de la calcémie entraîne une réponse maximale de C et N-PTH; (2) une altération du niveau de régulation de la PTH peut être présente chez certains malades hémodialysés; (3) la corrélation entre le niveau de PTH de base et après stimulation maximale suggère que les niveaux de PTH de base pourraient réfléter la masse glandulaire parathyroidïenne; enfin (4) une corrélation entre la PTH de base et après stimulation et l'histologie osseuse est présente.

Effect of Intact Parathyroid Hormone on Hepatic Glucose Release in the Dog

The liver has been shown to remove parathyroid hormone (PTH) from its arterial circulation by a mechanism that is selective for the intact form of the peptide (PTH 1-84). The present studies demonstrate that PTH has biologic effects on the liver in vivo. Bovine PTH 1-84 stimulated hepatic glucose release in dogs with indwelling hepatic vein catheters from basal values of 31+/-8 to 68+/-9 mg/min per kg after bolus injections of PTH. The effect on hepatic glucose release was apparent by 5 min and persisted for the 80 min of observation. The NH(2)-terminal PTH fragment (syn b-PTH 1-34) had no effect. Bovine PTH 1-84 administered in doses designed to produce circulating levels of immunoreactive PTH similar to the endogenous levels observed in uremic dogs also increased the incorporation of (14)C from infused [(14)C]alanine into glucose, and increased estimated hepatic uptake of both chemical and [(14)C]alanine, while increasing hepatic glucose release. Thus, administration of "physiologic levels" of b-PTH 1-84 stimulated hepatic glucose release in part through increased gluconeogenesis in vivo, whereas syn b-PTH 1-34 had no demonstrable effect. Circulating levels of insulin rose after PTH administration, an increase which presumably represents a secondary response to the rise in glucose release. These results suggest that the liver is a target organ of PTH, and that PTH might potentially alter carbohydrate metabolism during hypersecretion. They also suggest that hepatic uptake of PTH may be related in part to production of a specific biologic effect rather than just simple peptide degradation.

The renal handling of parathyroid hormone. Role of peritubular uptake and glomerular filtration.

The mechanisms of uptake of parathyroid hormone (PTH) by the kidney was studied in anesthetized dogs before and after ureteral ligation. During constant infusion of bovine PTH (b-PTH 1-84), the renal arteriovenous (A-V) difference for immunoreactive PTH (i-PTH) was 22+/-2%. After ureteral ligation and no change in renal plasma flow, A-V i-PTH fell to 15+/-1% (P < 0.01), indicating continued and significant uptake of i-PTH at peritubular sites and a lesser role of glomerular filtration (GF) in the renal uptake of i-PTH. Since, under normal conditions, minimal i-PTH appears in the final urine, the contribution of GF and subsequent tubular reabsorption was further examined in isolated perfused dog kidneys before and after inhibition of tubular reabsorption by potassium cyanide. Urinary i-PTH per 100 ml GF rose from 8+/-4 ng/min (control) to 170+/-45 ng/min after potassium cyanide. Thus, i-PTH is normally filtered and reabsorbed by the tubular cells. The physiological role of these two mechanisms of renal PTH uptake was examined by giving single injections of b-PTH 1-84 or synthetic b-PTH 1-34 in the presence of established ureteral ligation. After injection of b-PTH 1-84, renal A-V i-PTH was 20% only while biologically active intact PTH was present (15-20 min). No peritubular uptake of carboxyl terminal PTH fragments was demonstrable. In contrast, after injection of synthetic b-PTH 1-34, renal extraction of N-terminal i-PTH after ureteral ligation (which was 13.4+/-0.6% vs. 19.6+/-0.9% in controls) continued for as long as i-PTH persisted in the circulation. These studies indicate that both GF and peritubular uptake are important mechanisms for renal PTH uptake. Renal uptake of carboxyl terminal fragments of PTH is dependent exclusively upon GF and tubular reabsorption, whereas peritubular uptake can only be demonstrated for biologically active b-PTH 1-84 and synthetic b-PTH 1-34.

Degradation of parathyroid hormone and fragment production by the isolated perfused dog kidney. The effect of glomerular filtration rate and perfusate CA++ concentrations.

The renal degradation of intact bovine parathyroid hormone (b-PTH 1-84) was studied with the isolated perfused dog kidney. Disappearance of b-PTH 1-84 from the perfusate occurred concomitantly with the appearance of smaller molecular weight forms of immunoreactive parathyroid hormone (PTH). These smaller molecular weight PTH fragments included both carboxyl and amino terminal regions of the PTH peptide. Perfusate from kidneys with lower glomerular filtration rates (GFR) contained b-PTH 1-84 for longer periods of time than kidneys with higher GFRs, and perfusate from kidneys with lower GFRs demonstrated greater accumulation of carboxyl terminal PTH fragments. Perfusate containing high Ca++ concentrations retarded, and perfusate with low Ca++ concentrations accelerated the rate of degradation of b-PTH 1-84 by the kidney. These studies, therefore document the production of PTH fragments during the course of intact hormone degradation by the kidney. They also demonstrate renal clearance of the PTH fragments produced and define the effects of glomerular filtration rate and calcium concentrations on degradation of intact hormone and the clearance of PTH fragments.