Exogenous PTH and endogenous 1,25-dihydroxyvitamin D are complementary in inducing an anabolic effect on bone

Abaloparatide Maintains Normal Rat Blood Calcium Level in Part Via 1,25-Dihydroxyvitamin D/osteocalcin Signaling Pathway

The PTH-related peptide(1-34) analog, abaloparatide (ABL), is the second anabolic drug available for the treatment of osteoporosis. Previous research demonstrated that ABL had a potent anabolic effect but caused hypercalcemia at a significantly lower rate. However, the mechanism by which ABL maintains the stability of blood calcium levels remains poorly understood. Our in vivo data showed that ABL treatment (40 µg/kg/day for 7 days) significantly increased rat blood level of 1,25-dihydroxyvitamin D [1,25-(OH)2D] without raising the blood calcium value. ABL also significantly augmented the carboxylated osteocalcin (Gla-Ocn) in the blood and bone that is synthesized by osteoblasts, and increased noncarboxylated Ocn, which is released from the bone matrix to the circulation because of osteoclast activation. The in vitro data showed that ABL (10 nM for 24 hours) had little direct effects on 1,25-(OH)2D synthesis and Gla-Ocn formation in nonrenal cells (rat osteoblast-like cells). However, ABL significantly promoted both 1,25-(OH)2D and Gla-Ocn formation when 25-hydroxyvitamin D, the substrate of 1α-hydroxylase, was added to the cells. Thus, the increased 1,25-(OH)2D levels in rats treated by ABL result in high levels of Gla-Ocn and transient calcium increase in the circulation. Gla-Ocn then mediates calcium ions in the extracellular fluid at bone sites to bind to hydroxyapatite at bone surfaces. This regulation by Gla-Ocn at least, in part, maintains the stability of blood calcium levels during ABL treatment. We conclude that the signaling pathway of ABL/1,25-(OH)2D/Gla-Ocn contributes to calcium homeostasis and may help understand the mechanism of ABL for osteoporosis therapy.

Parathyroid hormone alleviates non-alcoholic liver steatosis via activating the hepatic cAMP/PKA/CREB pathway

Non-alcoholic fatty liver disease (NAFLD), hallmarked by liver steatosis, is becoming a global concern, but effective and safe drugs for NAFLD are still lacking at present. Parathyroid hormone (PTH), the only FDA-approved anabolic treatment for osteoporosis, is important in calcium-phosphate homeostasis. However, little is known about its potential therapeutic effects on other diseases. Here, we report that intermittent administration of PTH ameliorated non-alcoholic liver steatosis in diet-induced obese (DIO) mice and db/db mice, as well as fasting-induced hepatic steatosis. In vitro, PTH inhibits palmitic acid-induced intracellular lipid accumulation in a parathyroid hormone 1 receptor (PTH1R)-dependent manner. Mechanistically, PTH upregulates the expression of genes involved in lipid β-oxidation and suppresses the expression of genes related to lipid uptake and de novo lipogenesis by activating the cAMP/PKA/CREB pathway. Taken together, our current finding proposes a new therapeutic role of PTH on NAFLD.

Anabolic actions of PTH in murine models: two decades of insights

Parathyroid hormone (PTH) is produced by the parathyroid glands in response to low serum calcium concentrations where it targets bones, kidneys, and indirectly, intestines. The N-terminus of PTH has been investigated for decades for its ability to stimulate bone formation when administered intermittently (iPTH) and is used clinically as an effective anabolic agent for the treatment of osteoporosis. Despite great interest in iPTH and its clinical use, the mechanisms of PTH action remain complicated and not fully defined. More than 70 gene targets in more than 90 murine models have been utilized to better understand PTH anabolic actions. Because murine studies utilized wild-type mice as positive controls, a variety of variables were analyzed to better understand the optimal conditions under which iPTH functions. The greatest responses to iPTH were in male mice, with treatment starting later than 12 weeks of age, a treatment duration lasting 5-6 weeks, and a PTH dose of 30-60 μg/kg/day. This comprehensive study also evaluated these genetic models relative to the bone formative actions with a primary focus on the trabecular compartment revealing trends in critical genes and gene families relevant for PTH anabolic actions. The summation of these data revealed the gene deletions with the greatest increase in trabecular bone volume in response to iPTH. These included PTH and 1-α-hydroxylase (Pth;1α(OH)ase, 62-fold), amphiregulin (Areg, 15.8-fold), and PTH related protein (Pthrp, 10.2-fold). The deletions with the greatest inhibition of the anabolic response include deletions of: proteoglycan 4 (Prg4, -9.7-fold), low-density lipoprotein receptor-related protein 6 (Lrp6, 1.3-fold), and low-density lipoprotein receptor-related protein 5 (Lrp5, -1.0-fold). Anabolic actions of iPTH were broadly affected via multiple and diverse genes. This data provides critical insight for future research and development, as well as application to human therapeutics. © 2021 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Intermittent administration of parathyroid hormone ameliorates periapical lesions in mice

INTRODUCTION

Intermittent administration of parathyroid hormone (PTH) promotes oral osseous wound healing and protects against ligature-induced alveolar bone loss. However, its therapeutic value on periapical periodontitis is unknown. The goal of this study was to determine the effect of intermittent PTH administration on the progression of periapical periodontitis.

METHODS

Seven lymphotoxin alpha-deficient mice received pulp exposures of mandibular first and second molars. Exposed pulp in the right mandible was covered with plaque-contaminated fibrin, whereas exposed pulp in the left mandible was left open. After 4 weeks, the periapical tissues were examined to determine the effect of plaque-contaminated fibrin to induce periapical lesions. Fourteen mice received pulp exposure covered with plaque-contaminated fibrin. PTH (40 μg/kg/d) was administered intermittently to half of the mice for 3 weeks beginning 1 week after pulp exposure. The remaining half received saline injections as the vehicle control. At sacrifice, mandibles and tibiae were harvested and processed for histologic examination. Evaluation of neutrophils and blood vessels was performed after staining with immunofluorescence, and periradicular bone was histomorphometrically analyzed.

RESULTS

The exposed pulp covered with plaque-contaminated fibrin resulted in significantly larger periapical lesions compared with the control. Intermittent PTH administration reduced the size of periapical lesions significantly. Significantly less neutrophil infiltration around the root apex was found in PTH-treated animals compared with the control.

CONCLUSIONS

PTH treatment suppressed periapical inflammation by reducing neutrophil infiltration and protected against tissue destruction by periapical periodontitis.

Vitamin D and its receptor during late development

Expression of the vitamin D receptor (VDR) is widespread but may vary depending on the developmental stage of the animal, and therefore may differentially influence phenotypic function. Thus, the major role of the 1,25-dihydroxyvitamin D [1,25(OH)2D]/VDR system is to regulate mineral and skeletal homeostasis, although mainly after birth. Post-natally, under conditions of low dietary calcium, the 1,25(OH)2D/VDR system enhances intestinal transcellular transport of calcium and possibly paracellular calcium entry by regulating genes that are critical for these functions. This process, by providing adequate calcium, is essential for normal development of the skeletal growth plate and mineralization of bone. Furthermore, blood calcium and phosphorus homeostasis is maintained by an interplay between feedback loops of the 1,25(OH)2D/VDR system with parathyroid hormone and with fibroblast-growth factor (FGF) 23 respectively. The 1,25(OH)2D/VDR system can also modulate the expression of genes involved in both bone formation and resorption post-natally. Ligand independent activity of the VDR normally influences mammalian hair cycling after birth by potentiating Wnt and bone morphogenetic protein (BMP) signaling. Nevertheless ligand bound VDR may also modulate epidermal cell proliferation/differentiation by regulating the balance in function of c-MYC and its antagonist the transcriptional repressor MAD1/MXD1 in skin epithelia. The 1,25(OH)2D/VDR system can also modulate innate immune cells and promote a more tolerogenic immunological status and may therefore influence inflammation and the development of autoimmunity; whether this impacts the fetus is uncertain. This article is part of a Special Issue entitled: Nuclear receptors in animal development.

Histone deacetylation mediates the rejuvenation of osteoblastogenesis by the combination of 25(OH)D3 and parathyroid hormone in MSCs from elders

Vitamin D metabolites are important effectors of bone and mineral homeostasis. Human bone marrow stromal cells (hMSCs) are targets of 1α,25-dihydroxyvitamin D [1α,25(OH)2D] action to promote their differentiation to osteoblasts. Osteoblastogenesis is also stimulated by 25-hydroxyvitamin D [25(OH)D], an effect that requires conversion to 1α,25(OH)2D3 by 25-hydroxyvitamin D3 1α-hydroxylase (CYP27B1). These findings support an autocrine/paracrine role of vitamin D metabolism in osteoblastogenesis of hMSCs. In this study, we assessed whether and by what mechanisms osteoblastogenesis could be rejuvenated with hMSCs from elders. First, knockdown studies with VDR-siRNA showed that both the pro-differentiation and anti-proliferative effects of 1α,25(OH)2D3 required VDR. Second, 100nM 25(OH)D3 (p<0.01 vs. control, ANOVA) and 100nM PTH1-34 (p<0.05) significantly stimulated alkaline phosphatase (ALP) activity (a measure of osteoblastogenesis), with a synergistic effect when combined (p<0.001). Scriptaid, an inhibitor of histone deacetylase, blocked the effect of 25(OH)D3 and PTH on osteoblastogenesis. Scriptaid alone downregulated VDR in hMSCs. These data demonstrate that histone deacetylation is required for the synergistic effect of 25(OH)D3 and PTH on osteoblastogenesis in hMSCs. Both VDR siRNA and Scriptaid dowregulated VDR mRNA and inhibited osteoblastogenesis. Thus, epigenetic regulation of the VDR may be central to rejuvenating osteoblastogenesis in hMSCs from elders. This article is part of a Special Issue entitled 'Vitamin D Workshop'.

Vitamin D metabolism in human bone marrow stromal (mesenchymal stem) cells

There are many human extra-renal tissues and cells that biosynthesize 1α,25-dihydroxyvitamin D (1α,25(OH)(2)D) by the action of CYP27B1/1α-hydroxylase. Human marrow stromal cells (hMSCs), also known as mesenchymal stem cells, were isolated from marrow discarded from well-characterized, consented subjects during common orthopedic procedures. Human MSCs can give rise to osteoblasts, chondrocytes, adipocytes, and other lineages. Their in vitro differentiation to osteoblasts is stimulated by 1α,25(OH)(2)D, and recent evidence indicates that they have the capacity to metabolize vitamin D in a regulated manner. Human MSCs express the vitamin D receptor, 25-hydroxylases, 1α-hydroxylase, and 24-hydroxylase; stimulation of in vitro osteoblastogenesis by 25(OH)D depends on the activity of CYP27B1/1α-hydroxylase. The finding that hMSCs are a both a producer and target of 1α,25(OH)(2)D suggests a potential autocrine/paracrine role of vitamin D metabolism in osteoblast differentiation. Expression and enzyme activity of CYP27B1/1α-hydroxylase are upregulated by substrate 25(OH)D and Parathyroid Hormone (PTH) and are downregulated by 1α,25(OH)(2)D. With subject age, there are decreases in basal osteoblast potential and in stimulation of osteoblastogenesis by 1α,25(OH)(2)D, 25(OH)D, and PTH. In vitro treatment with a combination of 25(OH)D and PTH rejuvenated osteoblastogenesis with hMSCs from elders; this was attributable to increases in CYP27B1/1α-hydroxylase and in receptor for each hormone by the reciprocal factor. Other clinical variables beside age, i.e. low serum 25(OH)D or low estimated glomerular filtration rate, are correlated with reduced osteoblastogenesis. These studies suggest that osteoblastogenesis may not be optimal unless there is sufficient serum 25(OH)D substrate for hMSCs to synthesize and respond to local 1α,25(OH)(2)D.

Time course of 25(OH)D3 vitamin D3 as well as PTH (parathyroid hormone) during fracture healing of patients with normal and low bone mineral density (BMD)

BACKGROUND

Until now the exact biochemical processes during healing of metaphyseal fractures of healthy and osteoporotic bone remain unclear. Especially the physiological time courses of 25(OH)D(3) (Vitamin D) as well as PTH (Parathyroid Hormone) the most important modulators of calcium and bone homeostasis are not yet examined sufficiently. The purpose of this study was to focus on the time course of these parameters during fracture healing.

METHODS

In the presented study, we analyse the time course of 25(OH)D3 and PTH during fracture healing of low BMD level fractures versus normal BMD level fractures in a matched pair analysis. Between March 2007 and February 2009 30 patients older than 50 years of age who had suffered a metaphyseal fracture of the proximal humerus, the distal radius or the proximal femur were included in our study. Osteoporosis was verified by DEXA measuring. The time courses of 25(OH)D(3) and PTH were examined over an eight week period. Friedmann test, the Wilcoxon signed rank test and the Mann-Withney U test were used as post-hoc tests. A p-value ≤ 0.05 was considered significant.

RESULTS

Serum levels of 25(OH)D(3) showed no differences in both groups. In the first phase of fracture healing PTH levels in the low BMD level group remained below those of the normal BMD group in absolute figures. Over all no significant differences between low BMD level bone and normal BMD level bone could be detected in our study.

CONCLUSIONS

The time course of 25(OH)D(3) and PTH during fracture healing of patients with normal and low bone mineral density were examined for the first time in humans in this setting and allowing molecular biological insights into fracture healing in metaphyseal bones on a molecural level. There were no significant differences between patients with normal and low BMD levels. Hence further studies will be necessary to obtain more detailed insight into fracture healing in order to provide reliable decision criteria for therapy and the monitoring of fracture healing.

Time course of 25(OH)D3 vitamin D3 as well as PTH (parathyroid hormone) during fracture healing of patients with normal and low bone mineral density (BMD)

BACKGROUND

Until now the exact biochemical processes during healing of metaphyseal fractures of healthy and osteoporotic bone remain unclear. Especially the physiological time courses of 25(OH)D(3) (Vitamin D) as well as PTH (Parathyroid Hormone) the most important modulators of calcium and bone homeostasis are not yet examined sufficiently. The purpose of this study was to focus on the time course of these parameters during fracture healing.

METHODS

In the presented study, we analyse the time course of 25(OH)D3 and PTH during fracture healing of low BMD level fractures versus normal BMD level fractures in a matched pair analysis. Between March 2007 and February 2009 30 patients older than 50 years of age who had suffered a metaphyseal fracture of the proximal humerus, the distal radius or the proximal femur were included in our study. Osteoporosis was verified by DEXA measuring. The time courses of 25(OH)D(3) and PTH were examined over an eight week period. Friedmann test, the Wilcoxon signed rank test and the Mann-Withney U test were used as post-hoc tests. A p-value ≤ 0.05 was considered significant.

RESULTS

Serum levels of 25(OH)D(3) showed no differences in both groups. In the first phase of fracture healing PTH levels in the low BMD level group remained below those of the normal BMD group in absolute figures. Over all no significant differences between low BMD level bone and normal BMD level bone could be detected in our study.

CONCLUSIONS

The time course of 25(OH)D(3) and PTH during fracture healing of patients with normal and low bone mineral density were examined for the first time in humans in this setting and allowing molecular biological insights into fracture healing in metaphyseal bones on a molecural level. There were no significant differences between patients with normal and low BMD levels. Hence further studies will be necessary to obtain more detailed insight into fracture healing in order to provide reliable decision criteria for therapy and the monitoring of fracture healing.

The calcium-sensing receptor complements parathyroid hormone-induced bone turnover in discrete skeletal compartments in mice

Although the calcium-sensing receptor (CaSR) and parathyroid hormone (PTH) may each exert skeletal effects, it is uncertain how CaSR and PTH interact at the level of bone in primary hyperparathyroidism (PHPT). Therefore, we simulated PHPT with 2 wk of continuous PTH infusion in adult mice with deletion of the PTH gene (Pth(-/-) mice) and with deletion of both PTH and CaSR genes (Pth(-/-)-Casr (-/-) mice) and compared skeletal phenotypes. PTH infusion in Pth(-/-) mice increased cortical bone turnover, augmented cortical porosity, and reduced cortical bone volume, femoral bone mineral density (BMD), and bone mineral content (BMC); these effects were markedly attenuated in PTH-infused Pth(-/-)-Casr(-/-) mice. In the absence of CaSR, the PTH-stimulated expression of receptor activator of nuclear factor-κB ligand and tartrate-resistant acid phosphatase and PTH-stimulated osteoclastogenesis was also reduced. In trabecular bone, PTH-induced increases in bone turnover, trabecular bone volume, and trabecular number were lower in Pth(-/-)-Casr(-/-) mice than in Pth(-/-) mice. PTH-stimulated genetic markers of osteoblast activity were also lower. These results are consistent with a role for CaSR in modulating both PTH-induced bone resorption and PTH-induced bone formation in discrete skeletal compartments.

Age-related decline in osteoblastogenesis and 1α-hydroxylase/CYP27B1 in human mesenchymal stem cells: stimulation by parathyroid hormone

With aging, there is a decline in bone mass and in osteoblast differentiation of human mesenchymal stem cells (hMSCs) in vitro. Osteoblastogenesis can be stimulated with 1,25-dihydroxyvitamin D(3) [1,25(OH)(2) D(3) ] and, in some hMSCs, by the precursor 25-hydroxyvitamin D(3) (25OHD(3) ). CYP27B1/1α-hydroxylase activates 25OHD(3) and, to a variable degree, hMSCs express CYP27B1. In this study, we tested the hypotheses (i) that age affects responsiveness to 25OHD(3) and expression/activity of CYP27B1 in hMSCs and (ii) that parathyroid hormone (PTH) upregulates CYP27B1 in hMSCs, as it does in renal cells. There were age-related declines in osteoblastogenesis (n=8, P=0.0286) and in CYP27B1 gene expression (n=27, r= -0.498; P=0.008) in hMSCs. Unlike hMSCs from young subjects (≤50 years), hMSCs from older subjects (≥55 years) were resistant to 25OHD(3) stimulation of osteoblastogenesis. PTH1-34 (100 nm) provided hMSCs with responsiveness to 25OHD(3) (P=0.0313, Wilcoxon matched pairs test) and with two episodes of increased 1,25(OH)(2) D(3) synthesis, of cAMP response element binding protein (CREB) activation, and of CYP27B1 upregulation. Both increases in CYP27B1 expression by PTH were obliterated by CREB-siRNA or KG-501 (which specifically inhibits the downstream binding of activated CREB). Only the second period of CREB signaling was diminished by AG1024, an inhibitor of insulin-like growth factor-I receptor kinase. Thus, PTH stimulated hMSCs from elders with responsiveness to 25OHD(3) by upregulating expression/activity of CYP27B1 and did so through CREB and IGF-I pathways.

Parathyroid hormone regulates osteoblast differentiation in a Wnt/β-catenin-dependent manner

Intermittent parathyroid hormone (PTH) administration shows an anabolic effect on bone. However, the mechanisms are not fully studied. Recent studies suggest that Wnt signaling is involved in PTH-induced bone formation. The current study was to examine if Wnt/β-catenin pathway is required during PTH-induced osteoblast differentiation. Osteoblastic MC3T3-E1 cells were treated with human PTH (1-34) (hPTH [1-34]) and expression levels of osteoblast differentiation markers were detected by real-time PCR. RNA levels of β-catenin, Runx2, Osteocalcin, Alkaline phosphatase, and Bone sialoprotein were significantly up-regulated after treatment with 10(-8) M of hPTH (1-34) for 6 h. Alkaline phosphatase activity and protein expression of β-catenin were also increased after 6 days of intermittent treatment with hPTH (1-34) in MC3T3-E1 cells. hPTH (1-34) significantly enhanced Topflash Luciferase activity after 6 h of treatment. More important, PTH-induced Alkaline phosphatase activity was significantly inhibited by knocking down β-catenin expression in cells using siRNA. Real-time RT-PCR results further showed down regulation of Runx2, Osteocalcin, Alkaline phosphatase, Bone sialoprotein gene expression in β-catenin siRNA transfected cells with/without PTH treatment. These results clearly indicate that PTH stimulates Wnt/β-catenin pathway in MC3T3-E1 cells and osteoblast differentiation markers expression was up-regulated by activation of Wnt/β-catenin signaling. Our study demonstrated that PTH-induced osteoblast differentiation mainly through activation of Wnt/β-catenin pathway in osteoblastic MC3T3-E1 cells.

Emerging roles for calcium-regulating hormones beyond osteolysis

Parathyroid hormone (PTH), the active form of vitamin D, 1,25-dihydroxyvitamin D [1,25(OH)2D], and PTH-related peptide (PTHrP), the mediator of hypercalcemia of malignancy, are all osteolytic hormones. Recent studies have demonstrated that endogenous PTH and PTHrP also exert bone anabolic activity and that PTHrP is a crucial modulator of growth plate development. At least part of these PTHrP functions can be mediated by intracrine effects, involving a unique interplay of cell surface membrane and intracellular signaling. 1,25(OH)2D also exerts bone anabolic effects and, as with PTHrP, acts on multiple extraskeletal tissues. The skeletal functions of these hormones now extend beyond modulating bone resorption, and important extraskeletal activities have been discovered which involve unique local modes of action.

Parathyroid hormone-related protein for the treatment of postmenopausal osteoporosis: defining the maximal tolerable dose

CONTEXT

PTH is the only approved skeletal anabolic agent for the treatment of human osteoporosis. Unlike PTH, which is a mixed anabolic and catabolic agent, PTHrP displays features suggesting that it may be a pure anabolic agent when intermittently administered. The full dose range of PTHrP is unknown.

OBJECTIVES

The primary objective of the study was to define the complete therapeutic window and dose-limiting toxicities of PTHrP. The secondary objective was to determine whether PTHrP retains a pure anabolic profile at the highest usable doses.

DESIGN

This was a single-blinded, two-part, dose-escalating clinical trial.

SETTING

The study was conducted in a university academic setting.

PATIENTS OR OTHER PARTICIPANTS

Participants included 41 healthy postmenopausal women between the ages of 45 and 75 yr.

INTERVENTION

INTERVENTIONs included PTHrP(1-36) or placebo in a dose-escalating design for 3 wk.

MAIN OUTCOME MEASURES

Safety measures (hypercalcemia, nausea, vomiting, hemodynamics, flushing, miscellaneous) and bone turnover markers were measured.

RESULTS

Intermittent PTHrP was administered safely and without serious adverse events in subjects receiving 500 and 625 microg/d for 3 wk. Subjects receiving 750 microg/d developed mild hypercalcemia. Bone turnover markers suggested that even at the highest doses, daily sc PTHrP may not activate bone resorption, i.e. may be purely anabolic. Interestingly, when hypercalcemia occurred, it may have resulted not from bone resorption but from activation of intestinal calcium absorption by 1,25 dihydroxyvitamin D.

CONCLUSIONS

In doses as high as 750 microg/d, in contrast to PTH, intermittently administered PTHrP appears to act as a pure skeletal anabolic agent. Surprisingly, PTHrP in the high doses studied activates 1,25 dihydroxyvitamin D production. Dosing information obtained herein can be used to design a longer term head-to-head comparative efficacy trial of PTHrP vs. PTH.

Short-term intermittent PTH 1-34 administration enhances bone formation in SCID/Beige mice

The anabolic effect of intermittent PTH on bone is variable depending on the species studied, duration/mode of administration, and location of skeletal response investigated. We tested the hypothesis low dose, short term, intermittent PTH 1-34 administration is sufficient to enhance bone formation without altering bone resorption. To test our hypothesis, mice were treated intermittently with one of three concentrations of PTH 1-34 (1 microg/kg; low, 10 microg/kg, or 20 microg/kg; high) for three weeks. The skeletal response was identified by quantifying: serum markers of bone turnover, cancellous bone parameters in distal femur, proximal tibia, and lumbar vertebrae by microCT, and number of osteoblasts and osteoclasts in distal femur. Mice receiving 20 microg/kg of PTH 1-34 demonstrated a 30% increase in serum osteocalcin, but no differences in serum calcium, type I collagen teleopeptides, or TRACP 5b. For all bones, microCT analysis suggested mice receiving 20 microg/kg of PTH 1-34 had increased cancellous bone mineral density, trabecular thickness and spacing, but decreased trabecular number. A 60% increase in the number of alkaline phosphatase positive osteoblasts in the distal femur was also observed in tissue sections; however, the number of TRAP positive osteoclasts was not different between test and control groups. While animals administered 10 microg/kg demonstrated similar trends for all bone turnover indices, such alterations were not observed in animals administered PTH 1-34 at 1 microg/kg per day. Thus, PTH 1-34, administered intermittently for three weeks at 20 microg/kg is sufficient to enhance bone formation without enhancing resorption.

The effect of recombinant PTH(1-34) and PTH(1-84) on serum ionized calcium, 1,25-dihydroxyvitamin D, and urinary calcium excretion: a pilot study

We investigated the frequency of hypercalcemia and/or hypercalciuria following parathyroid hormone (PTH) 1-34 and 1-84 administration in a crossover trial. Ten postmenopausal osteoporotic women previously treated with bisphosphonates were subdivided into two groups of five patients each. A 24-h urine collection to determine baseline calcium (Ca) and creatinine (Cr) the day before administration of PTH was followed by determination of serum ionized Ca (Ca(2+)), Cr, 25(OH)D, and 1,25(OH)(2)D at baseline. Thereafter, 100 mcg of PTH(1-84) or 20 mcg of PTH(1-34) was administered. A 24-h urinary collection and blood samples 2, 4, and 24-h after each PTH administration were again taken. One week after the first PTH administration patients were rechallenged with the second PTH. The PTH peptides did not differ with respect to changes in Ca(2+) at 2, 4, and 24 h postinjection; at the last time point the values were virtually identical to the initial values. There was no difference in urinary Ca on the day following PTH injection compared to baseline, in terms both of Ca/Cr and of Ca excretion. The two PTH peptides did not differ with respect to changes in 1,25(OH)(2)D at 2, 4, and 24 h considering both the absolute values and the percent changes with respect to baseline (24-h 1-84 = 125.6 + or - 58.6 pg/ml, 153% increase; 1-34 = 124.1 + or - 64.7, 130%). Our results indicate no difference in postinjection serum Ca(2+), 1,25(OH)(2)D, or urinary Ca excretion after a single dose of either PTH(1-84) or PTH(1-34) in patients previously treated with bisphosphonates.