Design and Preclinical Development of TransCon PTH,an Investigational Sustained-Release PTH Replacement Therapy for Hypoparathyroidism

Hypoparathyroidism (HP) is a condition of parathyroid hormone (PTH) deficiency leading to abnormal calcium and phosphate metabolism. The mainstay of therapy consists of vitamin D and calcium supplements, as well as adjunct Natpara (PTH(1-84)). However, neither therapy optimally controls urinary calcium (uCa) or significantly reduces the incidence of hypercalcemia and hypocalcemia. TransCon PTH, a sustained-release prodrug of PTH(1-34) in development for the treatment of HP, was designed to overcome these limitations. To determine the pharmacokinetics and pharmacodynamics of TransCon PTH, single and repeat s.c. dose studies were performed in rats and monkeys. TransCon PTH demonstrated a half-life of 28 and 34 hours in rats and monkeys, respectively. After repeated dosing, an infusion-like profile of the released PTH, characterized by low peak-to-trough levels, was obtained in both species. In intact rats and monkeys, daily subcutaneous administration of TransCon PTH was associated with increases in serum calcium (sCa) levels and decreases in serum phosphate levels (sP). In monkeys, at a single dose of TransCon PTH that increased sCa levels within the normal range, a concurrent decrease in uCa excretion was observed. In 4-week repeat-dose studies in intact rats and monkeys, uCa excretion was comparable to controls across all dose levels despite increases in sCa levels. Further, in a rat model of HP, TransCon PTH normalized sCa and sP levels 24 hours per day. This was in contrast to only transient trends toward normalization of sCa and sP levels with an up to 6-fold higher molar dose of PTH(1-84). After repeated dosing to HP rats, uCa excretion transiently increased, corresponding to increases in sCa above normal range, but at the end of the treatment period, uCa excretion was generally comparable to sham controls. TransCon PTH was well tolerated and the observed pharmacokinetics and pharmacodynamics were in line with the expected action of physiological replacement of PTH. © 2019 American Society for Bone and Mineral Research.     

Pharmacodynamic Actions of a Long‐Acting PTH Analog (LA‐PTH) in Thyroparathyroidectomized (TPTX) Rats and Normal Monkeys

Hypoparathyroidism is a disease of chronic hypocalcemia and hyperphosphatemia due to a deficiency of parathyroid hormone (PTH). PTH and analogs of the hormone are of interest as potential therapies. Accordingly, we examined the pharmacological properties of a long‐acting PTH analog, [Ala^1,3,12,18,22, Gln¹⁰,Arg¹¹,Trp¹⁴,Lys²⁶]‐PTH(1‐14)/PTHrP(15‐36) (LA–PTH) in thyroparathyroidectomized (TPTX) rats, a model of HP, as well as in normal monkeys. In TPTX rats, a single intravenous administration of LA‐PTH at a dose of 0.9 nmol/kg increased serum calcium (sCa) and decreased serum phosphate (sPi) to near‐normal levels for longer than 48 hours, whereas PTH(1‐34) and PTH(1‐84), each injected at a dose 80‐fold higher than that used for LA‐PTH, increased sCa and decreased sPi only modestly and transiently (<6 hours). LA‐PTH also exhibited enhanced and prolonged efficacy versus PTH(1‐34) and PTH(1‐84) for elevating sCa when administered subcutaneously (s.c.) into monkeys. Daily s.c. administration of LA‐PTH (1.8 nmol/kg) into TPTX rats for 28 days elevated sCa to near normal levels without causing hypercalciuria or increasing bone resorption markers, a desirable goal in the treatment of hypoparathyroidism. The results are supportive of further study of long‐acting PTH analogs as potential therapies for patients with hypoparathyroidism. © 2016 American Society for Bone and Mineral Research.     

Efficacy and Safety of Parathyroid Hormone Replacement With TransCon PTH in Hypoparathyroidism: 26-Week Results From the Phase 3 PaTHway Trial

Conventional therapy for hypoparathyroidism consisting of active vitamin D and calcium aims to alleviate hypocalcemia but fails to restore normal parathyroid hormone (PTH) physiology. PTH replacement therapy is the ideal physiologic treatment for hypoparathyroidism. The double-blind, placebo-controlled, 26-week, phase 3 PaTHway trial assessed the efficacy and safety of PTH replacement therapy for hypoparathyroidism individuals with the investigational drug TransCon PTH (palopegteriparatide). Participants (n = 84) were randomized 3:1 to once-daily TransCon PTH (initially 18 μg/d) or placebo, both co-administered with conventional therapy. The study drug and conventional therapy were titrated according to a dosing algorithm guided by serum calcium. The composite primary efficacy endpoint was the proportion of participants at week 26 who achieved normal albumin-adjusted serum calcium levels (8.3–10.6 mg/dL), independence from conventional therapy (requiring no active vitamin D and ≤600 mg/d of calcium), and no increase in study drug over 4 weeks before week 26. Other outcomes of interest included health-related quality of life measured by the 36-Item Short Form Survey (SF-36), hypoparathyroidism-related symptoms, functioning, and well-being measured by the Hypoparathyroidism Patient Experience Scale (HPES), and urinary calcium excretion. At week 26, 79% (48/61) of participants treated with TransCon PTH versus 5% (1/21) wiplacebo met the composite primary efficacy endpoint (p < 0.0001). TransCon PTH treatment demonstrated a significant improvement in all key secondary endpoint HPES domain scores (all p < 0.01) and the SF-36 Physical Functioning subscale score (p = 0.0347) compared with placebo. Additionally, 93% (57/61) of participants treated with TransCon PTH achieved independence from conventional therapy. TransCon PTH treatment normalized mean 24-hour urine calcium. Overall, 82% (50/61) treated with TransCon PTH and 100% (21/21) wiplacebo experienced adverse events; most were mild (46%) or moderate (46%). No study drug-related withdrawals occurred. In conclusion, TransCon PTH maintained normocalcemia while permitting independence from conventional therapy and was well-tolerated in individuals with hypoparathyroidism. © 2022 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).     

Calcemic and phosphaturic response to parathyroid hormone in normal and chronically uremic dogs

It is well established that the calcemic response to parathyroid hormone (PTH) is blunted in chronic uremia and is corrected partially by 1,25(OH)2D treatment. Recent evidence suggests that PTH(1-34) and not PTH(1-84) may be the actual calcemic fragment. Equivalent doses of both peptides were infused into five normal dogs (GFR = 51 ml/min) and eight dogs with a remnant kidney and chronic renal insufficiency (GFR = 15 ml/min). Both the calcemic and phosphaturic responses were studied. Remnant dogs had a blunted calcemic response to bPTH(1-84). The increase in fractional phosphate excretion was similar. In contrast, the calcemic response to bPTH(1-34) was equivalent in remnant and normal dogs. Treatment of uremic dogs with 400 ng 1,25(OH)2D daily for 3 days restored the effect of bPTH(1-84) on serum calcium and increased the control value for tubular phosphate reabsorption from 28 +/- 3 micrograms/ml GFR to 37 +/- 4 micrograms/ml GFR (P less than 0.01). These results suggest that there is an impaired conversion of PTH(1-84) to PTH(1-34) in chronic renal insufficiency and that 1,25 (OH)2D may be involved in metabolism of PTH(1-84). In addition, the effect of PTH on fractional phosphate excretion is not magnified in nonparathyroidectomized uremic dogs.     

PTH and FGF23 Exert Interdependent Effects on Renal Phosphate Handling: Evidence From Patients With Hypoparathyroidism and Hyperphosphatemic Familial Tumoral Calcinosis Treated With Synthetic Human PTH 1–34

Parathyroid hormone (PTH) and fibroblast growth factor 23 (FGF23) both influence blood phosphate levels by regulating urinary phosphate reabsorption. Clinical data suggest that adequate renal phosphate handling requires the presence of both FGF23 and PTH, but robust evidence is lacking. To investigate whether the phosphaturic effects of PTH and FGF23 are interdependent, 11 patients with hypoparathyroidism, which features high blood phosphate in spite of concomitant FGF23 elevation, and 1 patient with hyperphosphatemic familial tumoral calcinosis (HFTC), characterized by deficient intact FGF23 action and resulting hyperphosphatemia, were treated with synthetic human PTH 1–34 (hPTH 1–34). Biochemical parameters, including blood phosphate, calcium, intact FGF23 (iFGF23), nephrogenic cAMP, 1,25(OH)₂ vitamin D (1,25D), and tubular reabsorption of phosphate (TRP), were measured at baseline and after hPTH 1–34 treatment. In patients with hypoparathyroidism, administration of hPTH 1–34 increased nephrogenic cAMP, which resulted in serum phosphate normalization followed by a significant decrease in iFGF23. TRP initially decreased and returned to baseline. In the patient with HFTC, hPTH 1–34 administration also increased nephrogenic cAMP, but this did not produce changes in phosphate or TRP. No changes in calcium were observed in any of the studied patients, although prolonged hPTH 1–34 treatment did induce supraphysiologic 1,25D levels in the patient with HFTC. Our results indicate that PTH and FGF23 effects on phosphate regulation are interdependent and both are required to adequately regulate renal phosphate handling. Published 2021. This article is a U.S. Government work and is in the public domain in the USA.     

Increased Serum 1,25-Dihydroxyvitamin D after Growth Hormone Administration is not Parathyroid Hormone-Mediated

To assess the effects of growth hormone (GH) on serum 1,25-dihydroxyvitamin D [1,25(OH)₂D], we performed the following prospective crossover study in six healthy, young, adult, white men. During each of two admissions for 2? days to a general clinical research center, subjects were placed on a daily dietary calcium intake of 400 mg. Serum calcium, phosphorus, 1,25(OH)₂D, immunoreactive intact parathyroid hormone (PTH), insulin-like growth factor I (IGF-I), IGF binding protein 3 (IGFBP3), tubular reabsorption of phosphate (TRP), and maximum tubular reabsorption of phosphate (TMP/GFR) were measured. Recombinant human GH (rhGH, Humatrope) (25 μg/kg/day subcutaneously for 1 week) was administered prior to and during one of the admissions. Results are expressed as mean ± SEM. Whereas serum 1,25(OH)₂D (58.9 ± 7.7 versus 51.6 ± 7.4 pg/ml, P < 0.01), serum phosphorus (4.5 ± 0.1 versus 3.7 ± 0.1 mg/dl, P < 0.01), TRP (92.0 ± 0.5 versus 87.8 ± 0.7 mg/dl, P < 0.005), TMP/GFR (4.6 ± 0.1 versus 3.5 ± 0.2, P < 0.005), and urinary calcium (602 ± 49 versus 346 ± 25 mg/day, P < 0.001) increased significantly, serum PTH decreased significantly (19.9 ± 1.9 versus 26.8 ± 4.0 pg/ml, P < 0.05) and serum calcium did not change when subjects received rhGH. These findings indicate that in humans, GH affects serum 1,25(OH)₂D independently of circulating PTH and that this effect is mediated by IGF-I. We propose, therefore, that one potential mechanism by which GH stimulates increases in bone mass is via modest increases in serum 1,25(OH)₂D. Received: 2 May 1996 / Accepted: 18 October 1996     

Diphtheria Toxin‐ and GFP‐Based Mouse Models of Acquired Hypoparathyroidism and Treatment With a Long‐Acting Parathyroid Hormone Analog

Hypoparathyroidism (HP) arises most commonly from parathyroid (PT) gland damage associated with neck surgery, and is typically treated with oral calcium and active vitamin D. Such treatment effectively increases levels of serum calcium (sCa), but also brings risk of hypercalciuria and renal damage. There is thus considerable interest in using PTH or PTH analogs to treat HP. To facilitate study of this disease and the assessment of new treatment options, we developed two mouse models of acquired HP, and used them to assess efficacy of PTH(1–34) as well as a long‐acting PTH analog (LA‐PTH) in regulating blood calcium levels. In one model, we used PTHcre‐iDTR mice in which the diphtheria toxin (DT) receptor (DTR) is selectively expressed in PT glands, such that systemic DT administration selectively ablates parathyroid cells. For the second model, we generated GFP‐PT mice in which green fluorescent protein (GFP) is selectively expressed in PT cells, such that parathyroidectomy (PTX) is facilitated by green fluorescence of the PT glands. In the PTHcre‐iDTR mice, DT injection (2 × 5 μg/kg, i.p.) resulted in moderate yet consistent reductions in serum PTH and sCa levels. The more severe hypoparathyroid phenotype was observed in GFP‐PT mice following GFP‐guided PTX surgery. In each model, a single subcutaneous injection of LA‐PTH increased sCa levels more effectively and for a longer duration (>24 hours) than did a 10‐fold higher dose of PTH(1–34), without causing excessive urinary calcium excretion. These new mouse models thus faithfully replicate two degrees of acquired HP, moderate and severe, and may be useful for assessing potential new modes of therapy. © 2015 American Society for Bone and Mineral Research.     

Association of increased active PTH(1–84) fraction with decreased GFR and serum Ca in predialysis CRF patients: modulation by serum 25-OH-D

Summary As the serum calcium and glomerular filtration rate decreased, the proportion of active PTH(1–84) molecules in PTH immunoreactivity increased in serum from predialysis uremic patients, particularly those with vitamin D insufficiency. Introduction The PTH(1–84) fraction was altered in predialysis patients with chronic renal failure (CRF). Methods Serum PTH in predialysis CRF patients without any medication was measured by PTH(1–84)-specific whole PTH assay and intact PTH assay cross-reacting with N-truncated PTH. Results In CRF patients, the glomerular filtration rate (GFR) correlated positively with serum Ca and 1,25-dihydroxyvitamin D (1,25(OH)₂D), and inversely with serum Pi, log intact PTH, and log whole PTH. In multiple regression analysis, including age, gender, body mass index, GFR, Ca, and Pi and 1,25(OH)₂D as independent variables, serum Ca and GFR associated significantly with serum log whole PTH and intact PTH. Serum log whole PTH/intact PTH ratio, which increased as serum Ca and GFR decreased, retained a negative correlation in those with serum 25-hydroxyvitamin D levels below 20 ng/ml, but not in those above 20 ng/ml. The ratio also correlated positively with serum log tartrate-resistant acid-phosphatase-5b, log cross-linked N-telopeptide of type-I collagen, and log bone alkaline-phosphatase. Conclusion As GFR declined with suppression of serum Ca, the proportion of active PTH molecules increased in predialysis CRF patients, particularly those with vitamin D insufficiency.     

A 7‐day continuous infusion of PTH or PTHrP suppresses bone formation and uncouples bone turnover

Human in vivo models of primary hyperparathyroidism (HPT), humoral hypercalcemia of malignancy (HHM), or lactational bone mobilization for more than 48 hours have not been described previously. We therefore developed 7‐day continuous‐infusion models using human parathyroid hormone(1–34) [hPTH(1–34)] and human parathyroid hormone–related protein(1–36) [hPTHrP(1–36)] in healthy human adult volunteers. Study subjects developed sustained mild increases in serum calcium (10.0 mg/dL), with marked suppression of endogenous PTH(1–84). The maximal tolerated infused doses over a 7‐day period (2 and 4 pmol/kg/h for PTH and PTHrP, respectively) were far lower than in prior, briefer human studies (8 to 28 pmol/kg/h). In contrast to prior reports using higher PTH and PTHrP doses, both 1,25‐dihydroxyvitamin D₃ [1,25(OH)₂D₃] and tubular maximum for phosphorus (TmP/GFR) remained unaltered with these low doses despite achievement of hypercalcemia and hypercalciuria. As expected, bone resorption increased rapidly and reversed promptly with cessation of the infusion. However, in contrast to events in primary HPT, bone formation was suppressed by 30% to 40% for the 7 days of the infusions. With cessation of PTH and PTHrP infusion, bone‐formation markers abruptly rebounded upward, confirming that bone formation is suppressed by continuous PTH or PTHrP infusion. These studies demonstrate that continuous exposure of the human skeleton to PTH or PTHrP in vivo recruits and activates the bone‐resorption program but causes sustained arrest in the osteoblast maturation program. These events would most closely mimic and model events in HHM. Although not a perfect model for lactation, the increase in resorption and the rebound increase in formation with cessation of the infusions are reminiscent of the maternal skeletal calcium mobilization and reversal that occur following lactation. The findings also highlight similarities and differences between the model and HPT. © 2011 American Society for Bone and Mineral Research     

Impaired Phosphate Tolerance Revealed With an Acute Oral Challenge

Elevated serum phosphate is consistently linked with cardiovascular disease (CVD) events and mortality in the setting of normal and impaired kidney function. However, serum phosphate does not often exceed the upper limit of normal until glomerular filtration rate (GFR) falls below 30 mL/min/m². It was hypothesized that the response to an oral, bioavailable phosphate load will unmask impaired phosphate tolerance, a maladaptation not revealed by baseline serum phosphate concentrations. In this study, rats with varying kidney function as well as normo‐phosphatemic human subjects, with inulin‐measured GFR (13.2 to 128.3mL/min), received an oral phosphate load. Hormonal and urinary responses were evaluated over 2 hours. Results revealed that the more rapid elevation of serum phosphate was associated with subjects and rats with higher levels of kidney function, greater responsiveness to acute changes in parathyroid hormone (PTH), and significantly more urinary phosphate at 2 hours. In humans, increases in urinary phosphate to creatinine ratio did not correlate with baseline serum phosphate concentrations but did correlate strongly to early increase of serum phosphate. The blunted rise in serum phosphate in rats with CKD was not the result of altered absorption. This result suggests acute tissue deposition may be altered in the setting of kidney function impairment. Early recognition of impaired phosphate tolerance could translate to important interventions, such as dietary phosphate restriction or phosphate binders, being initiated at much higher levels of kidney function than is current practice. © 2017 American Society for Bone and Mineral Research.     

Safety and Efficacy of PTH 1-34 and 1-84 Therapy in Chronic Hypoparathyroidism: A Meta-Analysis of Prospective Trials

Hypoparathyroidism is the only endocrine deficiency for which hormone replacement therapy is not the standard of care. Although conventional treatments may control hypocalcaemia, other complications such as hyperphosphatemia, kidney stones, peripheral calcifications, and bone disease remain unmet needs. This meta-analysis (PROSPERO registration number CRD42019126881) aims to evaluate and compare the efficacy and safety of PTH₁₋₃₄ and PTH₁₋₈₄ in restoring calcium metabolism in chronic hypoparathyroidism. EMBASE, PubMed, and CENTRAL databases were searched for randomized clinical trials or prospective studies published between January 1996 and March 2021. English-language trials reporting data on replacement with PTH₁₋₃₄ or PTH₁₋₈₄ in chronic hypoparathyroidism were selected. Three authors extracted outcomes, one author performed quality control, all assessed the risk of biases. Overall, data from 25 studies on 588 patients were analyzed. PTH therapy had a neutral effect on calcium levels, while lowering serum phosphate (−0.21 mmol/L; 95% confidence interval [CI], −0.31 to −0.11 mmol/L; p < 0.001) and urinary calcium excretion (−1.21 mmol/24 h; 95% CI, −2.03 to −0.41 mmol/24 h; p = 0.003). Calcium phosphate product decreased under PTH₁₋₈₄ therapy only. Both treatments enabled a significant reduction in calcium and calcitriol supplementation. PTH therapy increased bone turnover markers and lumbar spine mineral density. Quality of life improved and there was no difference in the safety profile between PTH and conventionally treated patients. Results for most outcomes were similar for the two treatments. Limitations of the study included considerable population overlap between the reports, incomplete data, and heterogeneity in the protocol design. In conclusion, the meta-analysis of data from the largest collection to date of hypoparathyroid patients shows that PTH therapy is safe, well-tolerated, and effective in normalizing serum phosphate and urinary calcium excretion, as well as enabling a reduction in calcium and vitamin D use and improving quality of life. © 2022 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).     

Vitamin D independent anabolic action of PTHin vivo

We examined the involvement of endogenous calcium-regulating hormones in the anabolic action of PTH, especially in relation to vitamin D. When normal rats (4 weeks old) were given a subcutaneous injection of hPTH(1-34) everyday or one, two or three times a week for 4 weeks adjusting the total weekly dose to 350μg/kg, femoral dry weight increased in an injection frequency-dependent manner. Daily injection of hPTH(1-34) into normal rats for 12 days caused a dose-dependent increase in serum concentration of 1,25(OH)₂D but not calcitonin, associated with a dose-dependent increase in femoral dry weight. Therefore, the effect of hPTH(1-34) was examined under the condition of vitamin D (VD)-deficiency. In VD-deficient rats (13 weeks old), the change in serum immunoreactive PTH after the injection of hPTH(1-34) was the same as that observed in normal rats, although the basal level of serum PTH was significantly higher. Furthermore, VD-deficient rats treated with hPTH(1-34) for 4 weeks showed a dose-dependent increase in femoral dry weight without affecting circulating 1,25(OH)₂D. These results suggest the involvement of systemic or local factor(s) independent of the action of VD in the anabolic action of daily PTH treatment.     

Daily parathyroid hormone 1-34 replacement therapy for hypoparathyroidism induces marked changes in bone turnover and structure

Parathyroid hormone (PTH) has variable actions on bone. Chronically increased PTH is catabolic and leads to osteoporosis; yet intermittent administration is anabolic and increases bone mass. PTH deficiency is associated with decreased bone remodeling and increased bone mass. However, the effects of PTH replacement therapy on bone in hypoparathyroidism are not well known. We discontinued calcitriol therapy and treated 5 hypoparathyroid subjects (2 adults and 3 adolescents) with synthetic human PTH 1‐34 (hPTH 1‐34), injected two to three times daily for 18 months, with doses individualized to maintain serum calcium at 1.9 to 2.25 mmol/L. Biochemical markers and bone mineral density (BMD) were assessed every 6 months; iliac‐crest biopsies were performed before and after 1 year of treatment. hPTH 1‐34 therapy significantly increased bone markers to supranormal levels. Histomorphometry revealed that treatment dramatically increased cancellous bone volume and trabecular number and decreased trabecular separation. Changes in trabecular width were variable, suggesting that the increase in trabecular number was due to the observed intratrabecular tunneling. Cortical width remained unchanged; however, hPTH 1‐34 treatment increased cortical porosity. Cancellous bone remodeling was also stimulated, inducing significant changes in osteoid, mineralizing surface, and bone formation rate. Similar changes were seen in endocortical and intracortical remodeling. BMD Z‐scores were unchanged at the spine and femoral neck. Total hip Z‐scores increased; however, total body BMD Z‐scores decreased during the first 6 months of treatment and then stabilized, remaining significantly decreased compared to baseline. Radial Z‐scores also decreased with treatment; this was most pronounced in the growing adolescent. Daily hPTH 1‐34 therapy for hypoparathyroidism stimulated bone turnover, increased bone volume, and altered bone structure in the iliac crest. These findings suggest that treatment with hPTH 1‐34 in hypoparathyroid adults and adolescents has varying effects in the different skeletal compartments, leading to an increase in trabecular bone and an apparent trabecularization of cortical bone. Published 2012 American Society for Bone and Mineral Research. This article is a US Government work and, as such, is in the public domain in the United States of America.     

Effects of Strontium Ranelate Administration on Calcium Metabolism in Female Patients with Postmenopausal Osteoporosis and Primary Hyperparathyroidism

We investigated possible changes of parameters of calcium metabolism induced by strontium ranelate (SR). Twenty-three patients with postmenopausal osteoporosis (PO) and 14 with primary hyperparathyroidism (PHPT) were studied while taking 2 g/day of SR. Women with PO and 10 healthy age-matched control women were also daily supplemented with 1,000 mg calcium and 800 IU vitamin D. All subjects were studied at baseline and after 7 and 30 days; PO women and controls were also investigated at 180 and 360 days of treatment. Serum ionized calcium (iCa), phosphate (sP), magnesium, creatinine, 25-hydroxycholecalciferol (25[OH]D), 1,25-dihydroxycholecalciferol (1,25[OH]₂D), serum parathyroid hormone (PTH) were measured. In spot urine, we assessed calcium and phosphate over creatinine ratios (uCa/Cr, uP/Cr), calcium excretion (Ca ex) and renal phosphate threshold (TmP/GFR); in 24-h urine, calcium and magnesium over creatinine clearance ratios (CaCl/CrCl and MgCl/CrCl). In PO, SR administration was associated with a significant decrease of PTH and 1,25(OH)₂D levels but an increase of sP (p < 0.001). SR also significantly increased Ca/Cr, Ca ex, and TmP/GFR in spot urine and CaCl/CrCl in both spot and 24-h urine (p = 0.004 to <0.001). In PHPT, SR significantly decreased iCa and increased sP, slightly modifying PTH, 25(OH)D, and 1,25(OH)₂D values. Also in PHPT, Ca ex and CaCl/CrCl of spot and 24-h urine, as TmP/GFR, significantly increased (all p < 0.02). SR influenced the main parameters of calcium homeostasis, probably through the calcium-sensing receptor.     

A comparison of parathyroid hormone‐related protein (1‐36) and parathyroid hormone (1‐34) on markers of bone turnover and bone density in postmenopausal women: The PrOP study

Parathyroid hormone‐related protein (PTHrP)(1‐36) increases lumbar spine (LS) bone mineral density (BMD), acting as an anabolic agent when injected intermittently, but it has not been directly compared with parathyroid hormone (PTH)(1‐34). We performed a 3‐month randomized, prospective study in 105 postmenopausal women with low bone density or osteoporosis, comparing daily subcutaneous injections of PTHrP(1‐36) to PTH(1‐34). Thirty‐five women were randomized to each of three groups: PTHrP(1‐36) 400 µg/day; PTHrP(1‐36) 600 µg/day; and PTH(1‐34) 20 µg/day. The primary outcome measures were changes in amino‐terminal telopeptides of procollagen 1 (PINP) and carboxy‐terminal telopeptides of collagen 1 (CTX). Secondary measures included safety parameters, 1,25(OH)₂ vitamin D, and BMD. The increase in bone resorption (CTX) by PTH(1‐34) (92%) (p < 0.005) was greater than for PTHrP(1‐36) (30%) (p < 0.05). PTH(1‐34) also increased bone formation (PINP) (171%) (p < 0.0005) more than either dose of PTHrP(1‐36) (46% and 87%). The increase in PINP was earlier (day 15) and greater than the increase in CTX for all three groups. LS BMD increased equivalently in each group (p < 0.05 for all). Total hip (TH) and femoral neck (FN) BMD increased equivalently in each group but were only significant for the two doses of PTHrP(1‐36) (p < 0.05) at the TH and for PTHrP(1‐36) 400 (p < 0.05) at the FN. PTHrP(1‐36) 400 induced mild, transient (day 15) hypercalcemia. PTHrP(1‐36) 600 required a dose reduction for hypercalcemia in three subjects. PTH(1‐34) was not associated with hypercalcemia. Each peptide induced a marked biphasic increase in 1,25(OH)₂D. Adverse events (AE) were similar among the three groups. This study demonstrates that PTHrP(1‐36) and PTH(1‐34) cause similar increases in LS BMD. PTHrP(1‐36) also increased hip BMD. PTH(1‐34) induced greater changes in bone turnover than PTHrP(1‐36). PTHrP(1‐36) was associated with mild transient hypercalcemia. Longer‐term studies using lower doses of PTHrP(1‐36) are needed to define both the optimal dose and full clinical benefits of PTHrP. © 2013 American Society for Bone and Mineral Research. © 2013 American Society for Bone and Mineral Research.     

The effect of adding PTH(1–84) to conventional treatment of hypoparathyroidism: A randomized,placebo‐controlled study

In hypoparathyroidism, plasma parathyroid hormone (PTH) levels are inadequate to maintain plasma calcium concentration within the reference range. On conventional treatment with calcium supplements and active vitamin D analogues, bone turnover is abnormally low, and BMD is markedly increased. We aimed to study the effects of PTH‐replacement therapy (PTH‐RT) on calcium‐phosphate homeostasis and BMD. In a double‐blind design, we randomized 62 patients with hypoparathyroidism to daily treatment with PTH(1–84) 100 µg or similar placebo for 24 weeks as add‐on therapy to conventional treatment. Compared with placebo, patients on PTH(1–84) reduced their daily dose of calcium and active vitamin D significantly by 75% and 73%, respectively, without developing hypocalcemia. However, hypercalcemia occurred frequently during the downtitration of calcium and active vitamin D. Plasma phosphate and renal calcium and phosphate excretion did not change. Compared with placebo, PTH(1–84) treatment significantly increased plasma levels of bone‐specific alkaline phosphatase (+226% ± 36%), osteocalcin (+807% ± 186%), N‐terminal propeptide of procollagen 1 (P1NP; +1315% ± 330%), cross‐linked C‐telopeptide of type 1 collagen (CTX; +1209% ± 459%), and urinary cross‐linked N‐telopeptide of type 1 collagen (NTX; (+830% ± 165%), whereas BMD decreased at the hip (?1.59% ± 0.57%), lumbar spine (?1.76% ± 1.03%), and whole body (?1.26% ± 0.49%) but not at the forearm. In conclusion, the need for calcium and active vitamin D is reduced significantly during PTH‐RT, whereas plasma calcium and phosphate levels are maintained within the physiologic range. In contrast to the effect of PTH(1–84) treatment in patients with osteoporosis, PTH‐RT in hypoparathyroidism causes a decrease in BMD. This is most likely due to the marked increased bone turnover. Accordingly, PTH‐RT counteracts the state of overmineralized bone and, during long‐term treatment, may cause a more physiologic bone metabolism. © 2011 American Society for Bone and Mineral Research     

Abaloparatide at the Same Dose Has the Same Effects on Bone as PTH (1-34) in Mice

Abaloparatide, a novel analog of parathyroid hormone-related protein (PTHrP 1–34), became in 2017 the second osteoanabolic therapy for the treatment of osteoporosis. This study aims to compare the effects of PTH (1-34), PTHrP (1-36), and abaloparatide on bone remodeling in male mice. Intermittent daily subcutaneous injections of 80 μg/kg/d were administered to 4-month-old C57Bl/6J male mice for 6 weeks. During treatment, mice were followed by DXA-Piximus to assess changes in bone mineral density (BMD) in the whole body, femur, and tibia. At either 4 or 18 hours after the final injection, femurs were harvested for μCT analyses and histomorphometry, sera were assayed for bone turnover marker levels, and tibias were separated into cortical, trabecular, and bone marrow fractions for gene expression analyses. Our results showed that, compared with PTH (1-34), abaloparatide resulted in a similar increase in BMD at all sites, whereas no changes were found with PTHrP (1-36). With both PTH (1-34) and abaloparatide, μCT and histomorphometry analyses revealed similar increases in bone volume associated with an increased trabecular thickness, in bone formation rate as shown by P1NP serum level and in vivo double labeling, and in bone resorption as shown by CTX levels and osteoclast number. Gene expression analyses of trabecular and cortical bone showed that PTH (1-34) and abaloparatide led to different actions in osteoblast differentiation and activity, with increased Runx2, Col1A1, Alpl, Bsp, Ocn, Sost, Rankl/Opg, and c-fos at different time points. Abaloparatide seems to generate a faster response on osteoblastic gene expression than PTH (1-34). Taken together, abaloparatide at the same dose is as effective as PTH (1-34) as an osteoanabolic, with an increase in bone formation but also an increase in bone resorption in male mice. © 2019 American Society for Bone and Mineral Research.     

Treatment of Autosomal Dominant Hypocalcemia Type 1 With the Calcilytic NPSP795 (SHP635)

Autosomal dominant hypocalcemia type 1 (ADH1) is a rare form of hypoparathyroidism caused by heterozygous, gain-of-function mutations of the calcium-sensing receptor gene (CAR). Individuals are hypocalcemic with inappropriately low parathyroid hormone (PTH) secretion and relative hypercalciuria. Calcilytics are negative allosteric modulators of the extracellular calcium receptor (CaR) and therefore may have therapeutic benefits in ADH1. Five adults with ADH1 due to four distinct CAR mutations received escalating doses of the calcilytic compound NPSP795 (SHP635) on 3 consecutive days. Pharmacokinetics, pharmacodynamics, efficacy, and safety were assessed. Parallel in vitro testing with subject CaR mutations assessed the effects of NPSP795 on cytoplasmic calcium concentrations (Ca²⁺_i), and ERK and p38^MAPK phosphorylation. These effects were correlated with clinical responses to administration of NPSP795. NPSP795 increased plasma PTH levels in a concentration-dependent manner up to 129% above baseline (p = 0.013) at the highest exposure levels. Fractional excretion of calcium (FECa) trended down but not significantly so. Blood ionized calcium levels remained stable during NPSP795 infusion despite fasting, no calcitriol supplementation, and little calcium supplementation. NPSP795 was generally safe and well-tolerated. There was significant variability in response clinically across genotypes. In vitro, all mutant CaRs were half-maximally activated (EC₅₀) at lower concentrations of extracellular calcium (Ca²⁺_o) compared to wild-type (WT) CaR; NPSP795 exposure increased the EC₅₀ for all CaR activity readouts. However, the in vitro responses to NPSP795 did not correlate with any clinical parameters. NPSP795 increased plasma PTH levels in subjects with ADH1 in a dose-dependent manner, and thus, serves as proof-of-concept that calcilytics could be an effective treatment for ADH1. Albeit all mutations appear to be activating at the CaR, in vitro observations were not predictive of the in vivo phenotype or the response to calcilytics, suggesting that other parameters impact the response to the drug. © 2019 American Society for Bone and Mineral Research.     

Parathyroid hormone increases the expression level of matrix metalloproteinase-13 in vivo

Parathyroid hormone (PTH) increases serum calcium (Ca) by enhancing bone resorption and renal Ca reabsorption. However, detailed mechanisms of enhanced bone resorption by PTH remain to be elucidated. Although PTH has been shown to increase the expression level of osteoblastic matrix metalloproteinase (MMP)-13 in vitro, only limited results are available regarding the in vivo regulation of MMP expression. In the present study, we have examined expression levels of MMPs in PTH-infused rats. Infusion of 1.5 or 2.0 nmol/kg/day rat PTH(1–34) for 3 days resulted in a dose-dependent increase in serum Ca. PTH infusion also decreased serum phosphate levels and increased urinary excretion of Ca and phosphate. Infusion of PTH for 7 days resulted in less severe hypercalcemia and hypophosphatemia. Urinary Ca and phosphate excretion in rats infused for 7 days was less than that in rats infused for 3 days. Northern blot analysis showed that PTH infusion increased the expression level of MMP-13 in calvaria, although it did not affect MMP-2 expression. Furthermore, the time-course and severity of hypercalcemia and hypercalciuria correlated with the expression level of MMP-13. In situ hybridization also showed that PTH infusion increased the expression level of MMP-13 in femora. These results indicate that PTH enhances MMP-13 expression in vivo and suggest that PTH stimulates bone resorption at least partly by enhancing MMP-13 expression. Received: June 5, 2000 / Accepted: January 12, 2001     

Defect in parathyroid-hormone-induced luminal calcium absorption in connecting tubules of Klotho mice.

BACKGROUND: Homozygous Klotho mutant mice (KL(-/-) mice) exhibit multiple phenotypes resembling human ageing. Increases in the ratio of urinary calcium to urinary creatinine (uCa/uCr) and in serum Ca concentration and decreases in urinary Cr excretion and serum parathyroid hormone (PTH) concentration were reported; however, precise information about renal Ca handling was not reported in these animals. METHODS: We evaluated the PTH-induced increase in intracellular Ca(2+) concentration ([Ca(2+)]i) in cells of isolated perfused connecting tubules (CNTs) of KL(-/-) mice. We also determined fractional excretion of Ca from the urine and serum samples of the same animals (n = 7), and compared them with KL(+/+) mice and hemi-nephrectomized KL(-+/+) mice (n = 10 in each) as controls. RESULTS: FECa was significantly higher in KL(-/-) mice than in controls (0.67 +/- 0.13 vs 0.20 +/- 0.04%). The PTH (10 nM)-induced increase in [Ca(2+)]i was diminished in KL(-/-) mice (58 +/- 5 vs 231 +/- 15 nM). Addition of 10 nM of 8-(4-chlorophenylthio)-cyclic adenosine 3',5'-monophosphate had a similar effect. The PTH-induced increase had completely disappeared by the removal of Ca from lumen and bath in both groups of animals. Removal of sodium (Na) from the solution increased [Ca(2+)]i to a similar extent in both groups. Conclusion. We conclude that renal Ca excretion estimated by determining FECa was defective in the KL(-/-) mice. Impairment of Ca absorption from the lumen by stimulation of PTH in CNTs is one of the mechanisms of this defect. Activity of the basolateral Na/Ca exchanger was preserved in this strain. Therefore, the pathway downstream after generation of second messengers following stimulation of PTH (such as the sorting of transporters of Ca absorption) might be impaired by disruption of the Klotho gene.