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The role of anabolic agents
Published in Peter V. Giannoudis, Thomas A. Einhorn, Surgical and Medical Treatment of Osteoporosis, 2020
Nifon K. Gkekas, Eustathios Kenanidis, Panagiotis Anagnostis, Michael Potoupnis, Dimitrios G. Goulis, Eleftherios Tsiridis
PTH is an 84 and PTHrP a 36 amino acid polypeptide encoded by interrelated genes that bind to the same PTH 1 receptor (PTH1R). PTH is secreted by the parathyroid glands and plays a crucial role in the regulation of calcium and phosphate metabolism. PTH increases serum calcium concentrations via promotion of an osteoclast-mediated calcium release from the bone, proximal renal tubular calcium reabsorption, and indirectly, by intestinal calcium and phosphorus absorption via an increase in calcitriol formation in the kidney (9).
Individual conditions grouped according to the international nosology and classification of genetic skeletal disorders*
Published in Christine M Hall, Amaka C Offiah, Francesca Forzano, Mario Lituania, Michelle Fink, Deborah Krakow, Fetal and Perinatal Skeletal Dysplasias, 2012
Christine M Hall, Amaka C Offiah, Francesca Forzano, Mario Lituania, Michelle Fink, Deborah Krakow
Genetics: autosomal recessive, caused by loss-of-function mutations of the gene PTHR1 (parathyroid hormone receptor-1). Activating dominant mutations of the same gene can cause metaphyseal chondrodysplasia Jansen type and a small proportion of cases of Ollier enchondromatosis. PTHR1 binds PTH and PTHrP. PTH signalling through PTHRP delays the hypertrophic differentiation of proliferating chondrocytes in normal growth plates; PTHrP signalling through PTHR1 regulates endochondral bone development and epithelial-mesenchymal interactions in the formation of the mammary glands and teeth.
Laboratory evaluation of parathyroid gland function
Published in Pallavi Iyer, Herbert Chen, Thyroid and Parathyroid Disorders in Children, 2020
Parathyroid hormone is synthesized and secreted by the chief cells of the four paired parathyroid glands that embryologically originate in the dorsal portions of the third (paired inferior glands) and fourth (paired superior glands) pharyngeal pouches; on occasion, a fifth parathyroid gland may be located within the thyroid gland or in the mediastinum. PTH is an 84 amino acid (aa) peptide derived from its 115 aa precursor—preproPTH (3). In serum PTH circulates in the intact bioactive 84 aa form, as an amino terminal fragment that may or may not be bioactive, and as a carboxyl terminal bioinactive fragment. Depending upon the characteristics of the immunoassay, normal serum concentrations of intact PTH range between 10 and 55 pg/mL, amino terminal PTH 8 and 24 pg/mL, and carboxyl terminal PTH 50 and 330 pg/mL. The intracellular signal of PTH is transmitted through its seven transmembrane G-protein coupled PTH receptor encoded by PTH1R. PTH mobilizes calcium from bone, facilitates its reabsorption by the renal tubule, and inhibits renal tubular reabsorption of phosphate thereby increasing its urinary excretion. PTH increases urinary excretion of cyclic adenosine monophosphate (cyclic AMP). (The Ellsworth–Howard test employs biosynthetic PTH1-34 to determine renal tubular responsiveness to PTH: the urinary excretion of phosphate and cyclic AMP increase after administration of PTH1-34 to the subject with intact renal tubular function.) PTH stimulates synthesis of the bioactive metabolite of vitamin D (calcitriol) (vide infra). Parathyroid hormone-like hormone (PTHLH) is a 141 aa peptide whose activity is also mediated by the PTH1R that has many biologic activities in common with PTH; serum concentrations of PTHrP are usually <2 pmol/L. When enlarged, the parathyroid glands may be visualized by ultrasonography, technetium99m-labeled sestamibi scintigraphy with/without co-administration of iodine123, computed tomography (CT), and magnetic resonance imaging (MRI). Hybrid technologies for visualization of the enlarged parathyroid gland include 11C-methionine positron-emission tomography (PET), 11C-choline PET/CT, and 3-tesla simultaneous PET/MRI (4,5). Intraoperative identification of PTH-secreting parathyroid tissue may be accomplished by serial measurements of serum PTH concentrations before and after removal of the suspicious mass, an expensive and time-consuming procedure, and near-infrared autofluorescence possibly with superimposition of the image upon the surgical field of vision (6).
Abaloparatide: an anabolic treatment to reduce fracture risk in postmenopausal women with osteoporosis
Published in Current Medical Research and Opinion, 2020
Paul D. Miller, John P. Bilezikian, Lorraine A. Fitzpatrick, Bruce Mitlak, Eugene V. McCloskey, Felicia Cosman, Henry G. Bone
Parathyroid hormone (PTH) and parathyroid hormone-related protein (PTHrP) both signal through the PTH receptor type 1 (PTHR1) with important, but different, effects on bone development and remodeling21–23. Studies have demonstrated that PTH and PTHrP bind to different conformations of the PTHR1 receptor with differing affinities22. PTH binds with greater affinity than PTHrP22 to the G-protein uncoupled conformation, R0, which is associated with prolonged cyclic AMP signaling, while PTHrP and PTH bind with similar affinities to the G protein-coupled RG conformation, which results in shorter duration of cyclic AMP response22. Therefore, only PTH results in sustained cyclic AMP production, which involves receptor internalization and positive calcium allostery23–26. Studies have shown that continuous cyclic AMP signaling favors osteoclast formation and bone resorption while intermittent signaling favors a net anabolic effect21,27–29; however, whether this translates to clinically relevant difference with PTH and PTHrP ligands on bone resorption remains to be determined.
Experiences with measuring parathyroid hormone 1-34 in patients with chronic kidney disease
Published in Scandinavian Journal of Clinical and Laboratory Investigation, 2023
Sabina Chaudhary Hauge, Niklas Rye Jørgensen, Ditte Hansen
PTH is an 84-amino acid peptide hormone synthesized in the parathyroid glands, regulating both calcium and phosphate homeostasis. PTH 1-84 is cleaved from pre-pro-PTH (115 amino acids) inside the parathyroid gland chief cell, and its secretion is regulated by extracellular ionized calcium. PTH 1-84 exerts its biological effects through the binding of its amino-terminal structure (1–34) to the PTH1R receptor. The PTH1R receptor is a G-protein-coupled receptor expressed on the surface of osteoblasts and osteocytes in bone, leading to both catabolic and anabolic actions, and the receptor is also located on the tubular cells in the kidney, stimulating calcium reabsorption and urinary phosphate excretion [3,4].
Parathyroid hormone-related protein activates HSCs via hedgehog signalling during liver fibrosis development
Published in Artificial Cells, Nanomedicine, and Biotechnology, 2019
Shuying He, Jing Tang, Na Diao, Yan Liao, Jie Shi, Xiaoping Xu, Fang Xie, Lan Bai
Parathyroid hormone-like hormone (PTHLH), also referred to as parathyroid hormone-related protein (PTHrP) [8], is widely distributed in many organs, including the liver [8–10]. The secretory N-terminal PTHLH(1–40) fragment shares homology with parathyroid hormone (PTH) and is referred to as the common PTH/PTHLH type 1 receptor (PTH1R) ligand, and PTH1R usually participates in the protein kinase A (PKA) intracellular signalling pathway [11]. Through an autocrine or paracrine mechanism, PTHLH suppresses the growth of HepG2 cells, and during endotoxaemia, PTHLH levels increase and can potentially cause an acute hepatic response [12,13]. Recently, PTHLH has been reported to be involved in renal fibrogenesis in cooperation with transforming growth factor-β1(TGF-β1) [14–16]. Our previous results showed that PTHLH(1–40) activates HSCs and promotes ECM deposition [17]. In addition, we found that PTHLH promotes intestinal fibrosis by activating the transcription factor Runx2 [18]. These results suggest that PTHLH is involved in liver fibrosis progression; however, the exact effects of PTHLH on hepatic fibrosis and its molecular mechanism are poorly understood. The Hedgehog (Hh) signalling pathway plays a vital role in orchestrating wound healing responses [19,20]. HSCs are a type of Hh-responsive cell involved in liver fibrosis progression, and HSCs express the Hh-receptor Patched. Under normal circumstances, Hh ligands in cooperation with Patched liberate Smo signalling, resulting in a cascade that ultimately activates members of the Gli transcription factor family [21–24]. Thus, we further reasoned that the liver repair process might be regulated by PTHLH and Hh pathways because there is obvious evidence that PTHLH and Hh pathways are important regulators of cartilage development [25,26].