Effect Of Parathyroid Hormone Research Articles

Biological changes in human B-cell line Ramos (RA.1) related to increasing doses of human parathyroid hormone

BackgroundThe etiopathogenesis of autoimmune diseases is multifactorial, including hormonal factors. Remission of autoimmunity has been observed following treatment for concomitant hyperparathyroidism. Additionally, patients with autoimmune diseases have shown increased expression of parathyroid hormone receptor (PTH1R) and altered distribution of B cells subsets. Hence, this study aims to evaluate potential mechanisms and in vitro effects of PTH stimulation on B lymphocytes. MethodsUsing the human B-cell line Ramos (RA.1), various biological effects were evaluated with and without parathyroid hormone (PTH) stimulation at varying concentrations. Flow cytometry was employed to evaluate the phenotype of B lymphocytes based on IgD and CD38 expression, apoptosis induction via Annexin V and proliferation using CFSE. IgM production was quantified through ELISA, and Western blot analysis was performed to assess syk protein phosphorylation as an indicator of cell activation. ResultsRamos cells (RA.1) evidenced a statistically significant change in the phenotype under human PTH stimulation, demonstrating an increased proportion of germinal centre cells (Bm3-Bm4) when stimulated with high concentrations of PTH. ConclusionsThe in vitro effects of PTH in B cells subsets align with previous findings of an altered phenotype in B lymphocytes expressing PTH1R among autoimmune disease patients, suggesting a potential role of this hormone in the pathophysiology of autoimmune diseases. However, further studies are necessary to elucidate the mechanisms by which PTH generates observed effects in B lymphocytes and to determine if PTH plays a role in autoimmunity.

EXPLORING THE IMPACT OF PTH THERAPY ON BONE REMODELING: A MATHEMATICAL INVESTIGATION

The regulatory influence of the parathyroid hormone (PTH) is exerted on bone, which serves as a vital reservoir of calcium within the body. While various aspects of bone growth, turnover, and mechanisms operate independently of gonadal hormones, a crucial role is assumed by sex steroids, particularly estrogen, in maintaining bone equilibrium in adults. In order to unravel the underlying mechanisms of bone remodeling mediated by PTH, a distinguished mathematical model of this intricate process is presented. Subsequently, the temporal effects of Plasma PTH and PTH external dosages are investigated using the proposed mathematical model. Among the limited repertoire of approved and accessible anabolic treatments for severe osteoporosis, daily injections of PTH stand out. This pharmaceutical marvel possesses a unique dual action, capable of acting either anabolically or catabolically, contingent upon the mode of administration. The study aims to accurately predict osteogenic responses to introduced and endogenous PTH, incorporating factors such as [Formula: see text]-[Formula: see text], [Formula: see text], and bisphosphonates in osteoblast–osteoclast signaling, as well as considering PTH’s influence on the gland and the regulatory roles of [Formula: see text], [Formula: see text], and [Formula: see text] in osteoblast apoptosis and bone volume effects. Through diverse methods including illustrative depictions, numerical simulations, sensitivity analysis, and stability analysis, this work seeks to comprehend how PTH therapy impacts bone volume, enhancing its therapeutic relevance.

Interactions between PTH and adiposity: appetizing possibilities.

Although parathyroid hormone (PTH) is best known for its role as a regulator of skeletal remodelling and calcium homeostasis, more recent evidence supports a role for it in energy metabolism and other non-classical targets. In this report, we summarize evidence for an effect of PTH on adipocytes. This review is based upon all peer-reviewed papers, published in the English language with PubMed as the primary search engine. Recent preclinical studies have documented an effect of PTH to stimulate lipolysis in both adipocytes and liver cells and to cause browning of adipocytes. PTH also reduces bone marrow adiposity and hepatic steatosis. Although clinical studies are limited, disease models of PTH excess and PTH deficiency lend support to these preclinical findings. This review supports the concept of PTH as a polyfunctional hormone that influences energy metabolism as well as bone metabolism.

β-Receptor blocker enhances the anabolic effect of PTH after osteoporotic fracture

The autonomic nervous system plays a crucial role in regulating bone metabolism, with sympathetic activation stimulating bone resorption and inhibiting bone formation. We found that fractures lead to increased sympathetic tone, enhanced osteoclast resorption, decreased osteoblast formation, and thus hastened systemic bone loss in ovariectomized (OVX) mice. However, the combined administration of parathyroid hormone (PTH) and the β-receptor blocker propranolol dramatically promoted systemic bone formation and osteoporotic fracture healing in OVX mice. The effect of this treatment is superior to that of treatment with PTH or propranolol alone. In vitro, the sympathetic neurotransmitter norepinephrine (NE) suppressed PTH-induced osteoblast differentiation and mineralization, which was rescued by propranolol. Moreover, NE decreased the PTH-induced expression of Runx2 but enhanced the expression of Rankl and the effect of PTH-stimulated osteoblasts on osteoclastic differentiation, whereas these effects were reversed by propranolol. Furthermore, PTH increased the expression of the circadian clock gene Bmal1, which was inhibited by NE-βAR signaling. Bmal1 knockdown blocked the rescue effect of propranolol on the NE-induced decrease in PTH-stimulated osteoblast differentiation. Taken together, these results suggest that propranolol enhances the anabolic effect of PTH in preventing systemic bone loss following osteoporotic fracture by blocking the negative effects of sympathetic signaling on PTH anabolism.

Tmem119 is involved in bone anabolic effects of PTH through enhanced osteoblastic bone formation in mice

The intermittent administration of parathyroid hormone (PTH) exerts potent bone anabolic effects, which increase bone mineral density (BMD) and reduce fracture risk in osteoporotic patients. However, the underlying mechanisms remain unclear. Tmem119 has been proposed as a factor that is closely linked to the osteoblast phenotype, and we previously reported that PTH enhanced the expression of Tmem119 in mouse osteoblastic cells. However, roles of Tmem119 in the bone anabolic effects of PTH in vivo remain unknown. We herein investigated the roles of Tmem119 in bone anabolic effects of PTH using Tmem119-deficient mice. Tmem119 deficiency significantly reduced PTH-induced increases in trabecular bone volume and cortical BMD of femurs. Effects of Tmem119 deficiency on bone mass seemed predominant in female mice. Histomorphometric analyses with calcein labeling showed that Tmem119 deficiency significantly attenuated PTH-induced increases in the rates of bone formation and mineralization as well as numbers of osteoblasts. Moreover, Tmem119 deficiency significantly blunted PTH-induced decreases in phosphorylation of β-catenin and increases in alkaline phosphatase activity in osteoblasts. In conclusion, the present results indicate that Tmem119 is involved in bone anabolic effects of PTH through osteoblastic bone formation partly related to canonical Wnt-β-catenin signaling in mice.

Effect of intraoral administration of parathyroid hormone on osseous and soft tissue healing around implants in ovariectomized rat maxillae.

Intermittent administration of parathyroid hormone (PTH) increases systemic bone mass. However, the effect of PTH on osseous and soft tissue healing around implants in osteoporosis patients remains unclear. This study aimed to investigate the effects of PTH on tissue healing around implants in ovariectomized rats and to compare systemic and intraoral administration routes. Implants were placed at the healed sites of ovariectomized rats 3 weeks after maxillary first molar extraction. Rats were randomly divided into two groups that received either daily systemic subcutaneous or local intraoral PTH administration. Maxillae were dissected to examine bone architectures with micro-computed tomography images. Histomorphometric and immunohistochemical analyses were performed to evaluate osseous and soft tissue healing around the implants. Regardless of the administration route, PTH significantly increased bone area and the numbers of osteoblasts, osteoclasts, and osteocytes in the first and second inside and outside areas of implant threads, in addition to decreasing the number of sclerostin+ osteocytes. However, the intraoral PTH administration route was superior to the systemic route by significantly improving bone quality and promoting collagen production in the connective tissue around implants. Parathyroid hormone administration promoted both osseous and soft tissue healing around implants, irrespective of administration route. Interestingly, intraoral administration improved the evaluated parameters more than systemic administration. Thus, the intraoral route could become a useful treatment strategy for implant treatment in osteoporosis patients.

Parathyroid hormone stimulates bone regeneration in an atrophic non-union model in aged mice

BackgroundNon-union formation still represents a major burden in trauma and orthopedic surgery. Moreover, aged patients are at an increased risk for bone healing failure. Parathyroid hormone (PTH) has been shown to accelerate fracture healing in young adult animals. However, there is no information whether PTH also stimulates bone regeneration in atrophic non-unions in the aged. Therefore, the aim of the present study was to analyze the effect of PTH on bone regeneration in an atrophic non-union model in aged CD-1 mice.MethodsAfter creation of a 1.8 mm segmental defect, mice femora were stabilized by pin-clip fixation. The animals were treated daily with either 200 mg/kg body weight PTH 1–34 (n = 17) or saline (control; n = 17) subcutaneously. Bone regeneration was analyzed by means of X-ray, biomechanics, micro-computed tomography (µCT) imaging as well as histological, immunohistochemical and Western blot analyses.ResultsIn PTH-treated animals bone formation was markedly improved when compared to controls. This was associated with an increased bending stiffness as well as a higher number of tartrate-resistant acid phosphatase (TRAP)-positive osteoclasts and CD31-positive microvessels within the callus tissue. Furthermore, PTH-treated aged animals showed a decreased inflammatory response, characterized by a lower number of MPO-positive granulocytes and CD68-positive macrophages within the bone defects when compared to controls. Additional Western blot analyses demonstrated a significantly higher expression of cyclooxygenase (COX)-2 and phosphoinositide 3-kinase (PI3K) in PTH-treated mice.ConclusionTaken together, these findings indicate that PTH is an effective pharmacological compound for the treatment of non-union formation in aged animals.

SAT182 Effects Of An Orally Bioavailable Nonpeptide Parathyroid Hormone Receptor Type 1 (PTH1R) Antagonist In Rodent Models Of Primary Hyperparathyroidism (PHPT)

Abstract Disclosure: A.S. Antwan: Employee; Self; Crinetics Pharmaceuticals. E. Rico-Bautista: Employee; Self; Crinetics Pharmaceuticals. J. Pontillo: Employee; Self; Crinetics Pharmaceuticals. S. Wang: Employee; Self; Crinetics Pharmaceuticals. M. Johns: Employee; Self; Crinetics Pharmaceuticals. B. Ramms: Employee; Self; Crinetics Pharmaceuticals. M.A. Fowler: Employee; Self; Crinetics Pharmaceuticals. J.B. Nguyen: Employee; Self; Crinetics. A.A. Castellanos Gonzalez: Employee; Self; Crinetics. B. Fleck: Employee; Self; Crinetics Pharmaceuticals. K. Retting: Employee; Self; Crinetics Pharmaceuticals. D. Dalvie: Employee; Self; Crinetics Pharmaceuticals. S.F. Betz: Employee; Self; Crinetics Pharmaceuticals. S. Markison: Employee; Self; Crinetics Pharmaceuticals. Primary hyperparathyroidism (PHPT) is a condition resulting from an over-secretion of parathyroid hormone (PTH) from one or more overactive parathyroid glands. PTH is a peptide hormone that regulates blood calcium concentrations through effects on bone, intestines, and kidney. PTH acts on parathyroid hormone receptor type 1 (PTH1R) in the kidney to increase calcium reabsorption and block phosphate reabsorption. The loss of phosphate ions then causes an increase in ionized calcium in the blood and cAMP in the urine. At the bone, continuous PTH infusion stimulates osteoclast activity while inhibiting osteoblast activity, leading to breakdown of bone and release of calcium into the extracellular fluid. Conditions that cause excess PTH, such as PHPT, result in elevated concentrations of plasma calcium, increased bone loss, increased fracture risk, and higher susceptibility to kidney stone development. PHPT affects approximately 100,000 patients per year, but many patients are asymptomatic and remain undiagnosed. While a partial or total parathyroidectomy may be suitable for patients diagnosed with severe cases of PHPT, there are limited treatment options for those who do not meet the criteria or do not wish to undergo surgery. The goals for medicinal treatment are to normalize blood calcium levels and urinary calcium excretion, as well as increase bone mineral density to reduce fracture risk. Blocking PTH action directly via a potent PTH1R antagonist may provide an important new therapeutic mechanism to treat patients with PHPT. Using iterative medicinal chemistry and pharmacology, Crinetics has identified several potent and orally bioavailable PTH1R antagonists with good drug-like properties. Lead molecules were evaluated in vivo in preclinical rodent models for their ability to suppress the effects of excess PTH on serum calcium, bone turnover, and cAMP levels in the kidney. One of these compounds, ANT-5, was characterized as a potent negative allosteric modulator of both human and rat PTH1R. In rats, oral administration of ANT-5 dose-dependently suppressed PTH-induced hypercalcemia. ANT-5 also suppressed PTH-stimulated urinary cAMP in rats, indicating its ability to inhibit the actions of PTH in the kidney. We further evaluated the effect of ANT-5 in a rodent model of continuous PTH infusion-induced bone turnover. Once-daily oral administration of ANT-5 mitigated PTH-induced bone resorption, suggesting that inhibiting PTH1R may have beneficial clinical effects on bone density. The culmination of these studies has led to a subset of candidate molecules that are being evaluated in safety studies to identify the compound(s) suitable for evaluation in human clinical trials. Support: Crinetics Pharmaceuticals. Presentation: Saturday, June 17, 2023

Normocalcemic Primary Hyperparathyroidism. A Case Report and Literature Review

Normocalcemic primary hyperparathyroidism (PHP) has been proposed to be a new phenotype of the disease. It is characterized by persistently high levels of parathyroid hormone (PTH) and normal calcium levels. Since there are no known causes of secondary hyperparathyroidism or PTH elevation, the exact biological mechanism is not known. It could be the first stage of the disease or a unique situation marked by resistance of the kidneys and bones to the effects of PTH. This is a disease that is getting more and more common. It is often found when evaluating perimenopausal women with low bone mass or when evaluating or following up on patients with osteoporosis. Normocalcemic PHP has a diverse and varied phenotype that ranges from cases with no usual PHP symptoms to cases with symptoms and specific complications. The method to diagnosing secondary hyperparathyroidism should focus on ruling out all possible causes, especially vitamin D deficiency (25-OH vitamin D levels less than 30ng/mL) and kidney function impairment (glomerular filtration rate less than 60 mL/min, as measured by CKD- EPI). Not much is known about its past in the wild. Some people get hypercalcemia, but more than 75% of them don't. There don't seem to be any ways to predict who will get hypercalcemia, so measuring total and adjusted calcium levels once a year is recommended. Even though measuring ionic calcium is a part of what it means to have Normocalcemic PHP and is recommended by some writers during follow-up, there are a number of real problems with it that should be kept in mind.

Parathyroid Hormone Inhibits Fatty Infiltration and Muscle Atrophy After Rotator Cuff Tear by Browning of Fibroadipogenic Progenitors in a Rodent Model

Background: Progressive fatty infiltration and muscle atrophy after rotator cuff tears lead to tendon repair failure and poor outcomes. Fibro-adipogenic progenitors (FAPs) are involved in fatty infiltration and muscle homeostasis of skeletal muscle. Inducing FAP differentiation into brown adipocyte–like “beige adipocytes” suppresses fatty infiltration and muscle atrophy. Hypothesis: Parathyroid hormone (PTH) suppresses fatty infiltration and muscle atrophy after rotator cuff tears in a rat model by browning of FAPs. Study Design: Controlled laboratory study. Methods: PTH was administered subcutaneously for 4 or 8 weeks to a rotator cuff tear model in rats. After treatment, fatty infiltration of supraspinatus muscles was assessed using Oil Red O staining and muscle atrophy using wet muscle weight and muscle fiber cross-sectional area. Costaining of platelet-derived growth factor receptor α (FAP marker) and uncoupling protein 1 (browning marker) was performed to confirm FAP browning by PTH. Mouse-isolated FAPs were cultured with PTH and evaluated for browning-related gene expression and adipogenic differentiation using BODIPY staining. Myogenic differentiation of C2C12 myoblasts was evaluated using coculture of PTH-treated browning FAPs with C2C12. Results: PTH inhibited fatty infiltration after rotator cuff tear at 8 weeks. Rotator cuff wet muscle loss of PTH-treated rats was inhibited at 4 and 8 weeks. Furthermore, PTH-treated rats demonstrated larger myofiber cross-sectional area than did untreated rats at 4 and 8 weeks. Costaining indicated colocalization of platelet-derived growth factor receptor α and uncoupling protein 1 and promoted PTH-induced FAP browning. PTH increased the expression of browning-related genes in FAPs and suppressed fat droplet accumulation in vitro. Coculture with PTH-treated FAPs promoted C2C12 cell differentiation into myotubes. Conclusion: PTH induced FAP-derived beige adipocytes by upregulating browning-related gene expression, and the browning effect of PTH on FAPs inhibited fatty infiltration and muscle atrophy in the rat rotator cuff tear model. PTH might have potential as a therapeutic drug for fatty infiltration and muscle atrophy after rotator cuff tears. Clinical Relevance: PTH may expand treatment options for rotator cuff tears by reducing fatty infiltration and muscle atrophy after rotator cuff tears by browning of FAPs.

LITTIP/Lgr6/HnRNPK complex regulates cementogenesis via Wnt signaling

Orthodontically induced tooth root resorption (OIRR) is a serious complication during orthodontic treatment. Stimulating cementum repair is the fundamental approach for the treatment of OIRR. Parathyroid hormone (PTH) might be a potential therapeutic agent for OIRR, but its effects still lack direct evidence, and the underlying mechanisms remain unclear. This study aims to explore the potential involvement of long noncoding RNAs (lncRNAs) in mediating the anabolic effects of intermittent PTH and contributing to cementum repair, as identifying lncRNA-disease associations can provide valuable insights for disease diagnosis and treatment. Here, we showed that intermittent PTH regulates cell proliferation and mineralization in immortalized murine cementoblast OCCM-30 via the regulation of the Wnt pathway. In vivo, daily administration of PTH is sufficient to accelerate root regeneration by locally inhibiting Wnt/β-catenin signaling. Through RNA microarray analysis, lncRNA LITTIP (LGR6 intergenic transcript under intermittent PTH) is identified as a key regulator of cementogenesis under intermittent PTH. Chromatin isolation by RNA purification (ChIRP) and RNA immunoprecipitation (RIP) assays revealed that LITTIP binds to mRNA of leucine-rich repeat-containing G-protein coupled receptor 6 (LGR6) and heterogeneous nuclear ribonucleoprotein K (HnRNPK) protein. Further co-transfection experiments confirmed that LITTIP plays a structural role in the formation of the LITTIP/Lgr6/HnRNPK complex. Moreover, LITTIP is able to promote the expression of LGR6 via the RNA-binding protein HnRNPK. Collectively, our results indicate that the intermittent PTH administration accelerates root regeneration via inhibiting Wnt pathway. The lncRNA LITTIP is identified to negatively regulate cementogenesis, which activates Wnt/β-catenin signaling via high expression of LGR6 promoted by HnRNPK.

Relation of parathyroid hormone with malnutrition in peritoneal dialysis patients

Aims: Protein-energy wasting syndrome is a risk factor specific to ESRD is protein-energy wasting (PEW) syndrome. Clinical and experimental studies have suggested that secondary hyperparathyroidism plays a vital role in increasing energy expenditure in patients with ESRD. The geriatric nutritional risk index (GNRI) is used to evaluate nutritional status in various pathological conditions. Considering the effect of parathormone on malnutrition and studies indicating that parathyroid hormone causes weight loss, we aimed to investigate the relationship between malnutrition and parathyroid hormone (PTH) in our patients using GNRI.
 Methods: Forty-nine patients without known malignancy, liver disease, or chronic inflammatory disease who underwent peritoneal dialysis were included in the study. Patient data were recorded from these files. Height and weight were measured. GNRI was calculated by the formula 14.89 × serum albumin (g/dL) + [41.7 × bodyweight/ideal body weight
 Results: Forty-nine patients (29 females, 59.2%) were included in the study. Three (6.1%), seven (14.3%), and seven (14.3%) patients had severe, moderate, and mild malnutrition, respectively. GNRI was positively correlated with albumin, hematocrit, and calcium levels (r=0.757, r=0.355, r=0.423; p

The effect of intermittent parathyroid hormone on bone lengthening: current evidence to inform future effective interventions.

Recent studies have demonstrated the positive effects of parathyroid hormone (PTH) on bone healing, and findings support the use of PTH to accelerate bone healing following distraction osteogenesis. The goal of this review was to compile and discuss the mechanisms potentially underlying the effects of PTH on newly formed bone following a bone-lengthening procedure incorporating all relevant evidence in both animal and clinical studies. This review summarized all evidence from in vivo to clinical studies regarding the effects of PTH administration on a bone-lengthening model. In addition, a comprehensive evaluation of what is currently known regarding the potential mechanisms underlying the potential benefits of PTH in bone lengthening was presented. Some controversial findings regarding the optimal dosage and timing of administration of PTH in this model were also discussed. The findings demonstrated that the potential mechanisms associated with the action of PTH on the acceleration of bone regeneration after distraction osteogenesis are involvement in mesenchymal cell proliferation and differentiation, endochondral bone formation, membranous bone formation, and callus remodeling. In the last 20 years, a number of animal and clinical studies have indicated that there is a prospective role for PTH treatment in human bone lengthening as an anabolic agent that accelerates the mineralization and strength of the regenerated bone. Therefore, PTH treatment can be viewed as a potential treatment to increase the amount of new calcified bone and the mechanical strength of the bone in order to shorten the consolidation stage after bone lengthening.

Oncostatin M is a regulator of fibroblast growth factor 23 (FGF23) in UMR106 osteoblast-like cells

Renal phosphate and vitamin D metabolism is under the control of fibroblast growth factor 23 (FGF23), an endocrine and paracrine factor predominantly produced in bone. FGF23 formation is stimulated by active vitamin D, or parathyroid hormone (PTH), which are further regulators of phosphate homeostasis. In renal, inflammatory, and other diseases, plasma FGF23 reflects disease stage and correlates with outcome. Oncostatin M is part of the interleukin-6 (IL-6) family and regulates remodeling and PTH effects in bone as well as cardiac FGF23 production in heart failure via glycoprotein gp130. Here, we studied whether oncostatin M is a regulator of FGF23 in bone cells. Experiments were performed in UMR106 osteoblast-like cells, Fgf23 mRNA was determined by qRT-PCR, FGF23 protein by Western Blotting and ELISA, and oncostatin M receptor and leukemia inhibitory factor (LIF) receptor gene knockout accomplished by siRNA. As a result, oncostatin M dose-dependently up-regulated Fgf23 expression and protein secretion. The oncostatin M effect on FGF23 was mediated by oncostatin M receptor and gp130 and involved, at least in part, STAT3 and MEK1/2. Taken together, oncostatin M is a regulator of FGF23 through oncostatin M receptor, gp130, as well as STAT3 and MEK1/2 in UMR106 osteoblasts.

Regional modular responses in different bone compartments to the anabolic effect of PTH (1-34) and axial loading in mice.

Beneficial effects of intermittent parathyroid hormone (PTH) on bone mass and architecture are described to either simply add to, or to synergise with those of mechanical loading. We evaluate whether interaction with in vivo loading is reinforced by PTH dosing regimen and exhibits compartment-specific sensitivities. Female 12-week-old C57Bl6 mice received daily (7/7) or interrupted 5day/week (5/7) PTH for 3weeks (two vehicle groups). All mice had six loading episodes (12N) applied to right tibia (left, non-loaded) for the last 2weeks. Micro-CT scans were used to evaluate mass and architecture in almost the entire cortical and proximal trabecular regions. Epiphyseal cortical, trabecular and marrow space volumes, and bony growth-plate bridge incidence were evaluated. Statistical analyses employed a linear mixed-effects model at each percentile and 2-way ANOVA with post-hoc test for epiphyses and bridging. We found that daily PTH enhances cortical mass and modifies shape along almost the entire tibia and that these effects are partly mitigated by brief interruption in treatment. Mechanical loading alone augments cortical mass and modifies shape but only in a region proximal to the tibiofibular junction. The effect of combining load and daily PTH dosing is solely additive for cortical bone mass with no significant load: PTH interaction, but exhibits clear synergy with interrupted PTH treatment. Daily, not interrupted PTH stimulates trabecular bone gains, yet load:PTH interaction is present at limited regions with both daily and interrupted treatment. PTH treatment, but not loading, modifies epiphyseal bone but, in contrast, only loading modifies bridge number and areal density. Our findings demonstrate impressive local effects on tibial mass and shape of combined loading and PTH that are sensitive to dosing regimen and exert their effects modularly. These findings emphasise a need to clarify PTH dosing regimens and that advantages could be accrued by aligning treatment accordingly to patient requirements and life-style.

β-Arrestin 2 knockout prevents bone loss in response to continuous parathyroid hormone stimulation in male and female mice

ABSTRACT Background β-Arrestin 2 (β-arr2) binds activated parathyroid hormone (PTH) receptors stimulating internalization. PTH stimulates both anabolic and catabolic effect on bone depending on the way it is administered. Intermittent PTH stimulation increases trabecular bone formation in mice, but this is decreased in mice lacking β-arr 2, suggesting a role for β-arr 2 in the anabolic effects of PTH. The role of β-arr 2 in the catabolic effects of continuous PTH (cPTH) treatment is not known. Objective To assess the effects of cPTH administration on bone in mice lacking β-arr 2 compared to wild-type (WT). Methods Groups of male and female WT or β-arr2 knockout (KO) mice were administered either PTH or phosphate-buffered saline by osmotic pumps for 2 weeks. Following treatment, serum calcium and phosphate levels were measured, bone structure and mineral density were measured by microcomputed tomography, and bone cells measured by static and dynamic histomorphometry. Results β-arr2 KO had no effects on skeletal development in mice of either sex. PTH treatment caused hypercalcemia and hypophosphatemia and decreased trabecular and cortical bone only in male WT mice. β-arr2 KO in male mice completely abrogated the effects of PTH on bone, while in female β-arr2 KO mice, PTH treatment increased trabecular bone with no effects on cortical bone. Conclusions These results demonstrate a profound sex effect on skeletal responses to cPTH treatment, suggesting a protective effect of estrogen on bone loss. β-arr2 plays a role in restraining the anabolic effects of PTH in both male and female mice.

In Vitro Effects of PTH (1-84) on Human Skeletal Muscle-Derived Satellite Cells.

Parathyroid hormone (PTH) is a hormone secreted by the parathyroid glands. Despite its well-known characterized anabolic and catabolic actions on the skeleton, the in vitro effects of PTH on skeletal muscle cells are limited and generally performed on animal models. The aim of this study was to evaluate the effects of a short impulse of PTH (1-84) on the proliferation and the differentiation of skeletal muscle satellite cells isolated from human biopsies. The cells were exposed for 30 min to different concentrations of PTH (1-84), from 10-6 mol/L to 10-12 mol/L. ELISA was used to assay cAMP and the myosin heavy-chain (MHC) protein. The proliferation was assayed by BrdU and the differentiation by RealTime-qPCR. A statistical analysis was performed by ANOVA followed by Bonferroni's test. No significant variations in cAMP and the proliferation were detected in the isolated cells treated with PTH. On the other hand, 10-7 mol/L PTH on differentiated myotubes has shown significant increases in cAMP (p ≤ 0.05), in the expression of myogenic differentiation genes (p ≤ 0.001), and in the MHC protein (p ≤ 0.01) vs. untreated controls. This work demonstrates for the first time the in vitro effects of PTH (1-84) on human skeletal muscle cells and it opens new fields of investigation in muscle pathophysiology.

Differential effects of parathyroid hormone, parathyroid hormone-related protein, and abaloparatide on collagen 1 expression by mouse cementoblasts and mouse tooth root density

Parathyroid hormone (PTH) plays an important role in maintaining mineral homeostasis by regulating calcium and phosphate levels. Clinical trials have shown that peptides of PTH (1-34), PTH-related protein (PTHrP 1-36), and the new peptide modeled on PTHrP, abaloparatide, can have different anabolic effects on osteoporotic subjects, but the underlying mechanisms are still unclear. The prevalence of moderate and major gingival recession has been shown to be higher in postmenopausal women with osteoporosis. In addition, there is a significant association between osteoporosis and tooth loss. We investigated the actions of these peptides on the cementoblasts and teeth of mice. The murine cementoblast line, OCCM-30, known to express collagen I (Col1a1), was treated with intermittent PTH (1-34), PTHrP (1-36), or abaloparatide for 6 h/d for 3 days. Microcomputed tomography was performed on the teeth of mice receiving daily injections of phosphate-buffered saline, PTH (1-34), or abaloparatide. Statistical differences were analyzed by a 2-way or 1-way analysis of variance followed by a Tukey's post-hoc test. Results are expressed as mean ± standard deviation, and P<0.05 was considered significant. Gene expression showed regulation of Bsp, Col1a1, Opg, Rankl, and Mmp13 by the 3 peptides in these cells. Western blots revealed that after intermittent treatment for 3 days, PTH (1-34) caused an increase in COL1A1 protein immediately after treatment. In contrast, abaloparatide showed a latent effect in increasing COL1A1 protein 18 hours after treatment. PTHrP had no effect on COL1A1 expression. Immunofluorescence confirmed the same result as the Western blots. Microcomputed tomography of teeth showed PTH (1-34) injections increased molar root mineral density in mice, whereas abaloparatide increased density in roots of incisors and molars. This study reveals the differential anabolic effects of intermittent PTH (1-34), PTHrP (1-36), and abaloparatide on cementoblasts, as revealed by COL1A1 expression and root mineral density. Abaloparatide may be a potential therapeutic approach for achieving improved cementogenesis.

Dynamic Balance between PTH1R-Dependent Signal Cascades Determines Its Pro- or Anti-Osteogenic Effects on MSC.

Parathyroid hormone (PTH) is one of the key regulators of calcium and phosphate metabolism in the body, controlling bone metabolism and ion excretion by the kidneys. At present, attempts to use PTH as a therapeutic agent have been associated with side-effects, the nature of which is not always clear and predictable. In addition, it is known that in vivo impairment of PTH post-receptor signaling is associated with atypical differentiation behavior not only of bone cells, but also of connective tissues, including adipose tissue. In this work, we studied the functional responses of multipotent mesenchymal stromal cells (MSCs) to the action of PTH at the level of single cells. We used MSCs isolated from the periosteum and subcutaneous adipose tissue to compare characteristics of cell responses to PTH. We found that the hormone can activate three key responses via its receptor located on the surface of MSCs: single transients of calcium, calcium oscillations, and hormone-activated smooth increase in intracellular calcium. These types of calcium responses led to principally different cellular responses of MSCs. The cAMP-dependent smooth increase of intracellular calcium was associated with pro-osteogenic action of PTH, whereas phospholipase C dependent calcium oscillations led to a decrease in osteogenic differentiation intensity. Different variants of calcium responses are in dynamic equilibrium. Suppression of one type of response leads to increased activation of another type and, accordingly, to a change in the effect of PTH on cell differentiation.

ODP076 A Unique Case of Iatrogenic Hypermagnesemia Induced Symptomatic Hypocalcemia

Abstract Introduction Magnesium plays a role in production, release, and end-organ responsiveness of parathyroid hormone (PTH) and calcium homeostasis. Hypomagnesemia has been well documented to cause hypocalcemia by impaired secretion of PTH or PTH resistance. Iatrogenic hypermagnesemia in pregnant patients receiving intravenous magnesium for suppression of premature labor and pre-eclampsia is an uncommon cause of hypocalcemia. We are reporting a case of symptomatic hypocalcemia caused by iatrogenic hypermagnesemia in post-partum mother, who had high PTH in contrast to previous case reports. CaseA 28-year-old G4P1122 female, postpartum day 16 was admitted for headache, slurred speech, and vomiting. She was found to have elevated blood pressures and was started on IV magnesium for postpartum preeclampsia. On her first day, she received a 4g bolus of magnesium sulfate followed by 2g as maintenance for seizure prophylaxis. The following morning, the patient awoke complaining of numbness/tingling in both arms and twitching in her face and eyelids. Later that day, she had developed bilateral spontaneous carpopedal spasm as well. Labs drawn at that time revealed ionized calcium 0.78mmol/L (1.18-1.32 mmol/L), corrected calcium 7.42mg/dL (8.5-10.1), vitamin D 25-OH 45ng/mL (30-100), PTH 149.1pg/mL (18.5-88), phosphorus 2.9mg/dL (2.3-4.6), GFR116mL/min (&amp;gt;60) and magnesium 3.5mg/dL (1.4-2.2). Patient was started on IV calcium gluconate infusion along with calcium carbonate 1g QID and vitamin D3 5000 units daily. By the evening of the second day, patient's carpopedal spasm and paresthesia completely resolved. Repeat labs demonstrated improved ionized calcium of 1.17mmol/L (1.18-1.32), corrected calcium of 9.78mg/dL (8.5-10.1), and magnesium of 1.5mg/dL (1.4-2.2). Patient was discharged on calcium carbonate 1g TID and Vitamin D3 5000 units daily. Patient self-discontinued calcium and vitamin D supplementation a week after discharge. Repeat labs one week later showed normal corrected calcium, magnesium, and PTH levels. Conclusion Our patient developed transient, symptomatic hypocalcemia with elevated PTH secondary to iatrogenic hypermagnesemia, which improved with intravenous calcium. Hypomagnesemia is a known cause of hypocalcemia, but hypermagnesemia is a significantly less recognized etiology. Hypermagnesemia can cause low PTH due to activation of calcium sensing receptors resulting in inhibition of PTH secretion. Hypermagnesemia can also blunt the peripheral effect of PTH and promote hypercalciuria. Previous studies showed PTH can peak by the end of magnesium infusion but still result in hypocalcemia, although this is an uncommon clinical presentation. Our case highlights this aspect of elevated PTH after the completion of IV Magnesium infusion but still unable to correct hypocalcemia due to PTH resistance from hypermagnesemia. This calls attention to another underrecognized sequalae of hypermagnesemia: blunting of peripheral tissues response to PTH. Clinicians should be aware of development of hypocalcemia with both hypo- and hypermagnesemia as well as the underlying pathophysiology. Presentation: No date and time listed