Parathyroid Hormone Release Research Articles

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 (>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

Mechanism of calcitriol regulating parathyroid cells in secondary hyperparathyroidism.

A common consequence of chronic renal disease is secondary hyperparathyroidism (SHPT) and is closely related to the mortality and morbidity of uremia patients. Secondary hyperparathyroidism (SHPT) is caused by excessive PTH production and release, as well as parathyroid enlargement. At present, the mechanism of cell proliferation in secondary hyperparathyroidism (SHPT) is not completely clear. Decreased expression of the vitamin D receptor (VDR) and calcium-sensing receptor (CaSR), and 1,25(OH)2D3 insufficiency all lead to a decrease in cell proliferation suppression, and activation of multiple pathways is also involved in cell proliferation in renal hyperparathyroidism. The interaction between the parathormone (PTH) and parathyroid hyperplasia and 1,25(OH)2D3 has received considerable attention. 1,25(OH)2D3 is commonly applied in the therapy of renal hyperparathyroidism. It regulates the production of parathormone (PTH) and parathyroid cell proliferation through transcription and post-transcription mechanisms. This article reviews the role of 1,25(OH)2D3 in parathyroid cells in secondary hyperparathyroidism and its current understanding and potential molecular mechanism.

Enhanced bone tissue regeneration with hydrogel-based scaffolds by embedding parathyroid hormone in mesoporous bioactive glass.

To evaluate hydrogel-based scaffolds embedded with parathyroid hormone (PTH)-loaded mesoporous bioactive glass (MBG) on the enhancement of bone tissue regeneration in vitro. MBG was produced via sol-gel technique followed by PTH solution imbibition. PTH-loaded MBG was blended into the hydrogels and submitted to a lyophilisation process associated with a chemical crosslinking reaction to the production of the scaffolds. Characterisation of the MBG and PTH-loaded MBG scaffolds, including the scanning electron microscope (SEM) connected with an X-ray detector (EDX), Fourier transform infrared (FTIR), compression strength, rheological measurements, swelling and degradation rates, and PTH release analysis, were performed. Also, bioactivity using simulated-body fluid (SBF), biocompatibility (MTT), and osteogenic differentiation analyses (von Kossa and Alizarin Red stainings, and μ-computed tomography, μCT) of the scaffolds were carried out. SEM images demonstrated MBG particles dispersed into the hydrogel-based scaffold structure, which was homogeneously porous and well interconnected. EDX and FTIR revealed large amounts of carbon, oxygen, sodium, and silica in the scaffold composition. Bioactivity experiments revealed changes on sample surfaces over the analysed period, indicating the formation of carbonated hydroxyapatite; however, the chemical composition remained stable. PTH-loaded hydrogel-based scaffolds were biocompatible for stem cells from human-exfoliated deciduous teeth (SHED). A high quantity of calcium deposits on the extracellular matrix of SHED was found for PTH-loaded hydrogel-based scaffolds. μCT images showed MBG particles dispersed into the scaffolds' structure, and a porous, lamellar, and interconnected hydrogel architecture. PTH-loaded hydrogel-based scaffolds demonstrated consistent morphology and physicochemical properties for bone tissue regeneration, as well as bioactivity, biocompatibility, and osteoinductivity in vitro. Thus, the scaffolds presented here are recommended for future studies on 3D printing. Bone tissue regeneration is still a challenge for several approaches to oral and maxillofacial surgeries, though tissue engineering applying SHED, scaffolds, and osteoinductive mediators might help to overcome this clinical issue.

Mathematical Models of Parathyroid Gland Biology: Complexity and Clinical Use.

Altered parathyroid gland biology is a major driver of chronic kidney disease-mineral bone disorder (CKD-MBD) in patients with chronic kidney disease. CKD-MBD is associated with a high risk of vascular calcification and cardiovascular events. A hallmark of CKD-MBD is secondary hyperparathyroidism with increased parathyroid hormone (PTH) synthesis and release and reduced expression of calcium-sensing receptors on the surface of parathyroid cells and eventually hyperplasia of parathyroid gland cells. The KDIGO guidelines strongly recommend the control of PTH in hemodialysis patients. Due to the complexity of parathyroid gland biology, mathematical models have been employed to study the interaction of PTH regulators and PTH plasma concentrations. Here, we present an overview of various model approaches and discuss the impact of different model structures and complexities on the clinical use of these models.

Aspects of Psychological Stress in Success of Parathyroid Allotransplantation

Parathyroid auto/allotransplant (PA) may be a valuable alternative in the treatment of permanent hypoparathyroidism which is defined by insufficient levels of parathyroid hormone (PTH). Here, we aimed to investigate a possible association between the PTH levels of the patients who had undergone PA and their psychological stress conditions. The three patients with hypoparathyroidism were reported before and after PA for three-month-follow-up period. The examinations of patients were assessed by biochemical parameters [intact PTH (iPTH), Ca, and P]. The anxiety and stress levels of patients were assessed by self-report measures: State-Trait Anxiety Inventory (STAI-S/T) and Perceived Stress Scale (PSS). Although iPTH levels of all patients had a tendency to increase after PA, one of the patients with a low level of anxiety and stress only reached the normal range of PTH levels. The recovery of the serum iPTH levels at month 1 post-PA was negatively correlated with PSS scores of patients (r =-0.999, p=0.028). The outcomes of this report showed for the first time that insufficient PTH release, even after PA, might be related to the stress level of patients. By taking all results into consideration, PTH could be speculated as a stress biomarker.

A Patient With Polyuria and Hypercalcemia

A Patient With Polyuria and Hypercalcemia

Differential parathyroid and kidney Ca2+-sensing receptor activation in autosomal dominant hypocalcemia 1.

SummaryBackgroundParathyroid Ca2+-sensing receptor (CaSR) activation inhibits parathyroid hormone (PTH) release, while activation of renal CaSRs attenuates Ca2+ transport and increases expression of the pore-blocking claudin-14. Patients with autosomal dominant hypocalcemia 1 (ADH1), due to activating CASR mutations, exhibit hypocalcemia but not always hypercalciuria (elevated Ca2+ in urine). The latter promotes nephrocalcinosis and renal insufficiency. Although CaSRs throughout the body including the kidney harbor activating CASR mutations, it is not understood why only some ADH1 patients display hypercalciuria.MethodsActivation of the CaSR was studied in mouse models and a ADH1 patient. In vitro CaSR activation was studied in HEK293 cells.FindingsCldn14 showed blood Ca2+ concentration-dependent regulation, which was absent in mice with kidney-specific Casr deletion, indicating Cldn14 is a suitable marker for chronic CaSR activation in the kidney. Mice with a gain-of-function mutation in the Casr (Nuf) were hypocalcemic with low plasma PTH levels. However, renal CaSRs were not activated at baseline but only after normalizing blood Ca2+ levels. Similarly, significant hypercalciuria was not observed in a ADH1 patient until blood Ca2+ was normalized. In vitro experiments indicate that increased CaSR expression in the parathyroid relative to the kidney could contribute to tissue-specific CaSR activation thresholds.InterpretationOur findings suggest that parathyroid CaSR overactivity can reduce plasma Ca2+ to levels insufficient to activate renal CaSRs, even when an activating mutation is present. These findings identify a conceptually new mechanism of CaSR-dependent Ca2+ balance regulation that aid in explaining the spectrum of hypercalciuria in ADH1 patients.FundingErasmus+ 2018/E+/4458087, the Canadian Institutes for Health research, the Novo Nordisk Foundation, the Beckett Foundation, the Carlsberg Foundation and Independent Research Fund Denmark.

An optogenetic approach for regulating human parathyroid hormone secretion

Parathyroid hormone (PTH) plays crucial role in maintaining calcium and phosphorus homeostasis. In the progression of secondary hyperparathyroidism (SHPT), expression of calcium-sensing receptors (CaSR) in the parathyroid gland decreases, which leads to persistent hypersecretion of PTH. How to precisely manipulate PTH secretion in parathyroid tissue and underlying molecular mechanism is not clear. Here, we establish an optogenetic approach that bypasses CaSR to inhibit PTH secretion in human hyperplastic parathyroid cells. We found that optogenetic stimulation elevates intracellular calcium, inhibits both PTH synthesis and secretion in human parathyroid cells. Long-term pulsatile PTH secretion induced by light stimulation prevented hyperplastic parathyroid tissue-induced bone loss by influencing the bone remodeling in mice. The effects are mediated by light stimulation of opsin expressing parathyroid cells and other type of cells in parathyroid tissue. Our study provides a strategy to regulate release of PTH and associated bone loss of SHPT through an optogenetic approach.

Вплив альтерації гомеостазу глюкози на водно-електролітний баланс та кислотно-основний стан у пацієнтів із цукровим діабетом

Незважаючи на успіхи в терапії цукрового діабету, частота виникнення ускладнень, зокрема порушення водно-електролітного та кислотно-основного стану, останніми роками не зменшилась. Цікаво відмітити той факт, що клінічні прояви такого грізного ускладнення, як діабетичний кетоацидоз, уперше описав Дрешфельд у 1886 році. Відтоді і до початку застосування інсуліну (в 1922 р.) смертність від цього ускладнення сягала 100 %. Широке впровадження в практику інсулінотерапії знизило смертність до 30 %, а з удосконаленням методів лікування, зокрема інфузійної терапії, відбулось подальше її зниження. На сьогодні рівень летальності пацієнтів із порушеннями водно-електролітного та кислотно-основного стану залишається високим (близько 5 % у спеціалізованих центрах). Тільки в США щорічно від цього ускладнення помирає близько 4000 хворих на цукровий діабет. Прогноз перебігу захворювання значно погіршується з віком, при розвитку коми та артеріальної гіпотензії. Поширеність цукрового діабету стрімко зростає і на сьогодні становить від 20 до 50 % випадків вперше виявленого захворювання в молодих людей. Порушення електролітів є частими в пацієнтів із даною патологією і можуть бути результатом зміненого розподілу електролітів, пов’язаного з індукованою гіперглікемією осмотичних зрушень рідини, або загального дефіциту, спричиненого осмотичним діурезом. Ускладнення від пошкодження органів-мішеней і методи лікування цукрового діабету можуть також сприяти електролітним порушенням. Порушення регуляції гомеостазу глюкози призводить до великої кількості прямих і непрямих впливів на електролітний і кислотно-основний баланс, оскільки велика поширеність діабету гарантує, що лікарі практично кожної спеціальності мають справу з пацієнтами, хворими на цукровий діабет, а знання, пов’язані зі змінами електролітів, є необхідними. У статті розглянуто, як впливають зміни гомеостазу глюкози при цукровому діабеті на водно-електролітний баланс та кислотно-основний стан пацієнта.

Вітамін D у пародонтології

Генералізований пародонтит є одним із найчастіших стоматологічних захворювань, що може призвести до рухомості та втрати зубів. Основним його етіологічним чинником є зубний наліт, однак генералізований пародонтит є мультифакторним захворюванням. Наявні дані про вплив рівня вітаміну D на генералізований пародонтит. Вітамін D справляє плейотропну дію, впливаючи на різні ланки патогенезу генералізованого пародонтита. Стимулюючи секрецію антимікробних пептидів, вітамін D підвищує місцевий імунітет та негативно впливає на пародонтопатогени; модулюючи імунну систему, впливає на перебіг запалення в тканинах пародонта та імунну відповідь; підвищуючи всмоктування кальцію та зменшуючи виділення паратгормона, стимулює мінералізацію кісткової тканини. Висока поширеність дефіциту та недостатності вітаміну D у всьому світі говорить про актуальність вивчення його впливу на організм людини загалом та ротової порожнини зокрема.

Activation of the Calcium Receptor by Calcimimetic Agents Is Preserved Despite Modest Attenuating Effects of Hyperphosphatemia.

Phosphorus levels in the range seen clinically among patients undergoing dialysis have been reported to attenuate calcium receptor activation and modify parathyroid hormone (PTH) release from isolated parathyroid glands in vitro. Some clinicians and providers of dialysis thus have suggested that calcimimetic agents are ineffective and should not be used to manage secondary hyperparathyroidism among those undergoing dialysis when serum phosphorus concentrations exceed certain threshold levels. To determine whether hyperphosphatemia diminishes the therapeutic response to calcimimetic agents, we used data from large clinical trials to analyze the effects of etelcalcetide and cinacalcet to lower plasma PTH levels in individuals on hemodialysis who had secondary hyperparathyroidism and varying degrees of hyperphosphatemia. Plasma PTH levels declined progressively during 26 weeks of treatment with either etelcalcetide or cinacalcet without regard to the degree of hyperphosphatemia at baseline. However, with each calcimimetic agent, the decreases in PTH from baseline were less at each interval of follow-up during the trials among participants with serum phosphorus levels above one of three prespecified threshold values compared with those with serum phosphorus levels below these thresholds. These in vivo findings are the first in humans to support the idea that hyperphosphatemia attenuates calcium receptor activation by calcium ions and by calcimimetic agents. The effect of hyperphosphatemia on the responsiveness to calcimimetic agents appears relatively modest, however, and unlikely to be significant therapeutically. The efficacy of treatment with calcimimetic agents for lowering plasma PTH levels among those with secondary hyperparathyroidism remains robust despite substantial elevations in serum phosphorus.

Vitamin D and Phosphate Interactions in Health and Disease.

Vitamin D plays an essential role in calcium and inorganic phosphate (Pi) homeostasis, maintaining their optimal levels to assure adequate bone mineralization. Vitamin D, as calcitriol (1,25(OH)2D), not only increases intestinal calcium and phosphate absorption but also facilitates their renal reabsorption, leading to elevated serum calcium and phosphate levels. The interaction of 1,25(OH)2D with its receptor (VDR) increases the efficiency of intestinal absorption of calcium to 30-40% and phosphate to nearly 80%. Serum phosphate levels can also influence 1,25(OH)2D and fibroblast growth factor 23 (FGF23) levels, i.e., higher phosphate concentrations suppress vitamin D activation and stimulate parathyroid hormone (PTH) release, while a high FGF23 serum level leads to reduced vitamin D synthesis. In the vitamin D-deficient state, the intestinal calcium absorption decreases and the secretion of PTH increases, which in turn causes the stimulation of 1,25(OH)2D production, resulting in excessive urinary phosphate loss. Maintenance of phosphate homeostasis is essential as hyperphosphatemia is a risk factor of cardiovascular calcification, chronic kidney diseases (CKD), and premature aging, while hypophosphatemia is usually associated with rickets and osteomalacia. This chapter elaborates on the possible interactions between vitamin D and phosphate in health and disease.

Acute Effects of an Inorganic Phosphorus Additive on Mineral Metabolism and Cardiometabolic Risk Factors in Healthy Subjects.

Hyperphosphatemia and high levels of fibroblast growth factor 23 (FGF23) are risk factors for cardiovascular events in patients with chronic kidney diseases. However, the impact of an inorganic phosphorus additive in healthy people is largely unknown. We aimed to investigate the acute effect of excessive dietary phosphorus administered as sodium dihydrogen phosphate on the postprandial levels of Pi and FGF23 and the response to food. This study was a double-blind placebo-controlled crossover study with 29 healthy male and female participants from the general community who were administered a single dose of either 700 mg phosphorus (NaH2PO4) or a sodium-adjusted placebo in combination with a test meal. Postprandial plasma levels of Pi and FGF23 were measured. Compared with placebo, oral phosphorus increased the plasma Pi level, which remained elevated during the ensuing 8 hours (at 480 minutes: 1.31 vs 1.16 mmol/l; P < 0.001), increased urinary Pi (iAUC0-480 789 vs 95 mmol/mmol; P < 0.001), reduced tubular Pi reabsorption (iAUC0-480 -31.5 vs -6.2; P < 0.001), decreased urinary calcium (iAUC0-240 30.6 vs 53.0 mmol/mmol; P = 0.009), and stimulated the release of parathyroid hormone (iAUC0-480 2212 vs 768 ng/l; P < 0.001). However, the FGF23 levels did not change. Postprandial levels of glucose, insulin, and lipids were not substantially affected by phosphorus vs placebo. An oral phosphorus load can induce elevated postprandial levels of circulating Pi for hours in healthy subjects, despite rapid homeostatic counterreactions. FGF23 levels and the postprandial response to food were not affected.

Injectable Hydrogel with NIR Light‐Responsive, Dual‐Mode PTH Release for Osteoregeneration in Osteoporosis

AbstractEffective treatments to overcome osteoblast/osteoclast imbalance are the key to achieving desirable bone regeneration for osteoporosis patients. When used for local bone repair, parathyroid hormone (PTH) often leads to either excessive osteoclasts under continuous exposure or insufficient osteoclasts with pulsatile release of PTH. Herein, an injectable multifunctional in situ‐generated calcium phosphate nanoparticle (ICPN)‐coordinated poly(dimethylaminoethyl methacrylate‐co‐2‐hydroxyethyl methacrylate) (DHCP) hydrogel loaded with PTH for near‐infrared (NIR)‐stimulated release is developed to achieve bone regeneration in an ovariectomized (OVX) model. Photothermal‐responsive poly(N‐acryloyl glycinamide‐co‐acrylamide) PNAm‐indocyanine green ICG‐PTH microspheres (PIP MSs) endow a dual‐mode release system with a sustained release at low concentrations, a pulse release of PTH, and in situ pore formation properties. The PIP MS‐encapsulated DHCP hydrogel (DHCP‐10PIP/d) is injected into the bone defects of OVX rats. Under NIR irradiation, the localized photothermal effects trigger on‐demand PTH release and in situ micropores formation through the gel–sol transition of PIP MSs, and the repeated treatment is harmless to the bioactivity of PTH. This platform can enhance osteoblast and osteoclast activity at the same time both in vitro and in vivo and repair the cranial defects of OVX rats successfully. Overall, this work provides a promising strategy for PTH delivery to repair osteoporotic bone defects.

Quantitative Detection of Parathyroid Hormone Using Europium Complex Doped Silica Nanoparticles.

Parathyroid hormone (PTH) is a hormone that plays a critical role in bone remodeling because it regulates the calcium levels. Either higher or lower than normal range of PTH release can cause serious metabolic disorders such as hyperparathyroidism or hypoparathyroidism. Therefore, the demand of highly sensitive monitoring sensor of PTH is on the rise. However, due to its presence of small size and low concentration in serum, the monitoring of a small change of PTH level is extremely difficult. In this article, we suggested the fabrication of europium complex doped nanoparticles conjugated with PTH antibodies for the sensitive fluorescence monitoring of PTH. For the synthesis of europium complex, 4,4,4-trifluoro-1-(2-naphthyl)-1,3-butanedione (NTA) and trioctylphosphine oxide (TOPO) are used to encapsulate europium. The amphiphilic polymer, polyvinylpyrrolidone (PVP), was applied to hydrophobic europium complex, and then silica shell was synthesized on the complex. Using the europium complex doped silica nanoparticles, we could obtain approximately 4.24-fold enhanced fluorescence in low levels of PTH in PBS, when compared to the conventional enzyme-linked immunosorbent assay (ELISA). In addition, we could obtain the sensitive PTH immunoassay in PTH spiked serum with high selectivity.

Development of AC265347-Inspired Calcium-Sensing Receptor Ago-Positive Allosteric Modulators.

The calcium-sensing receptor (CaSR) is a clinical target in the treatment of hyperparathyroidism and related diseases. However, clinical use of approved CaSR-targeting drugs such as cinacalcet is limited due to adverse side effects including hypocalcaemia, nausea and vomiting, and in some instances, a lack of efficacy. The CaSR agonist and positive allosteric modulator (ago-PAM), AC265347, is chemically distinct from clinically-approved CaSR PAMs. AC265347 potently suppressed parathyroid hormone (PTH) release in rats with a lower propensity to cause hypocalcaemia compared to cinacalcet and may therefore offer benefits over current CaSR PAMs. Here we report a structure activity relationship (SAR) study seeking to optimise AC265347 as a drug candidate and disclose the discovery of AC265347-like compounds with diverse pharmacology and improved physicochemical and drug-like properties.

Secondary Hyperparathyroidism in Chronic Kidney Disease: Pathophysiology and Management

Serum calcium concentration is the main determinant of parathyroid hormone (PTH) release. Defect in the activation of vitamin D in the kidneys due to chronic kidney disease (CKD) leads to hypocalcemia and hyperphosphatemia, resulting in a compensatory increase in parathyroid gland cellularity and parathyroid hormone production and causing secondary hyperparathyroidism (SHP). Correction and maintenance of normal serum calcium and phosphate are essential to preventing SHP, hungry bone disease, cardiovascular events, and anemia development. Understanding the pathophysiology of PTH and possible therapeutic agents can reduce the development and associated complications of SHP in patients with CKD. Medical interventions to control serum calcium, phosphate, and PTH such as vitamin D analogs, calcium receptor blockers, and parathyroidectomy are needed in some CKD patients. In this review, we discuss the pathophysiology, clinical presentation, and management of SHP in CKD patients.

Heterogeneity of G protein activation by the calcium-sensing receptor.

The calcium-sensing receptor (CaSR) is a G protein-coupled receptor that plays a fundamental role in extracellular calcium (Ca2+e) homeostasis by regulating parathyroid hormone release and urinary calcium excretion. The CaSR has been described to activate all four G protein subfamilies (Gαq/11, Gαi/o, Gα12/13, Gαs), and mutations in the receptor that cause hyper/hypocalcaemia, have been described to bias receptor signalling. However, many of these studies are based on measurements of second messengers or gene transcription that occurs many steps downstream of receptor activation and can represent convergence points of several signalling pathways. Therefore, to assess CaSR-mediated G protein activation directly, we took advantage of a recently described NanoBiT G protein dissociation assay system. Our studies, performed in HEK293 cells stably expressing CaSR, demonstrate that Ca2+e stimulation activates all Gαq/11 family and several Gαi/o family proteins, although Gαz was not activated. CaSR stimulated dissociation of Gα12/13 and Gαs from Gβ-subunits, but this occurred at a slower rate than that of other Gα-subunits. Investigation of cDNA expression of G proteins in three tissues abundantly expressing CaSR, the parathyroids, kidneys and pancreas, showed Gα11, Gαz, Gαi1 and Gα13 genes were highly expressed in parathyroid tissue, indicating CaSR most likely activates Gα11 and Gαi1 in parathyroids. In kidney and pancreas, the majority of G proteins were similarly expressed, suggesting CaSR may activate multiple G proteins in these cells. Thus, these studies validate a single assay system that can be used to robustly assess CaSR variants and biased signalling and could be utilised in the development of new pharmacological compounds targeting CaSR.

Differential activation of parathyroid and renal Ca 2+ ‐sensing receptors underlies the renal phenotype in autosomal dominant hypocalcemia 1

Parathyroid Ca2+-sensing receptor (CaSR) activation inhibits parathyroid hormone (PTH) release, while activation of CaSRs in kidneys and intestine attenuates local transepithelial Ca2+ transport. In patients with autosomal dominant hypocalcemia 1 (ADH1) due to activating CASR mutations, treatment of symptomatic hypocalcemia can be complicated by treatment-induced hypercalciuria, resulting in nephrocalcinosis and renal insufficiency. Although CaSRs throughout the body are activated by increased extracellular Ca2+ concentrations, it is not understood why some ADH1 patients have reduced PTH, but not hypercalciuria at presentation, despite CaSR expression in both kidney and parathyroid. Activation of the CaSR was studied in mouse models and a ADH1 patient. In vitro CaSR activation was studied in HEK293 cells. Mice with a gain-of-function mutation in Casr are hypocalcemic with reduced plasma PTH levels. However, renal CaSRs are not activated as indicated by normal urinary calcium handling and unaltered renal Cldn14 expression. Activation of renal CaSRs only occurred after increasing plasma Ca2+ levels. Similarly, calcimimetic administration to wildtype mice induced hypocalcemia without activating renal CaSRs. Moreover, significant hypercalciuria was not observed in an ADH1 patient until blood Ca2+ was normalized. In vitro experiments suggest that increased CaSR levels in the parathyroid relative to the kidney contribute tissue-specific CaSR activation thresholds. Here we delineate tissue-specific CaSR activation thresholds, where parathyroid CaSR overactivity can reduce plasma Ca2+ to levels insufficient to activate renal CaSRs, even with overactivating mutations. These findings may aid in the management of ADH1 patients.

PTH/PTHrP in controlled release hydrogel enhances orthodontic tooth movement by regulating periodontal bone remodaling.

This study aimed to evaluate the effects of local application of parathyroid hormone (PTH) or parathyroid hormone-related protein (PTHrP) on osteogenesis and osteoclastogenesis during orthodontic tooth movement (OTM). Periodontal bone remodeling is the crucial biological process in the OTM that involves both bone resorption and formation, with the former more important as the initiator. PTH or PTHrP both play dual roles in bone remodeling regulation, and the balance may shift to the bone resorption side when they are given continuously, suggesting them as potential candidate medicine for OTM acceleration. A total of 40 rats underwent orthodontic mesialization of the maxillary first molars and received no micro-perforation (MOP), or MOP followed by injection of temperature-sensitive hydrogel containing PTH, PTHrP, or normal saline. The rats were sacrificed after 2-week OTM, except for the relapse groups, which had one more week of observation after removal of the force appliances. The amount of tooth movement, rate of relapse after OTM, and effects on the bone remodeling were assessed through micro-computed tomography (μCT) analysis, alkaline phosphatase (ALP) assay, alizarin red staining, tartrate-resistant acid phosphatase (TRAP) staining, immunohistochemistry (IHC) analysis, Western blot (WB), and quantitative real-time polymerase chain reaction (qRT-PCR). The effects of PTHrP on the osteogenic differentiation of human periodontal ligament cells (hPDLCs) were explored in vitro. The cumulative release of PTH or PTHrP from PECE hydrogels was beyond 75% at 14days in a sustained manner. After the intervention in vivo, the distance of OTM in the PTH (0.78±0.06mm) or PTHrP (0.81±0.04mm) group was significantly larger than that of the MOP only (0.51±0.04mm) or the no MOP (0.46±0.05mm) group. Moreover, PTH injection significantly reduced the rate of relapse after OTM (25.7±4.3%) compared to the control (69.6±6.1%). μCT analysis showed decreased BV/TV, BS/BV, and Tb.N, while increased Tb.Sp of alveolar bone in the PTH or PTHrP group. There were also more TRAP-positive osteoclasts in the PTH or PTHrP group with a significantly enhanced ratio of receptor activator of nuclear factor-κB ligand (RANKL)/osteoprotegerin (OPG). The protein expressions of PTH/PTHrP type 1 receptor (PTHR1), alkaline phosphatase (ALP), osteocalcin (OCN), runt-related transcription factor 2 (RUNX2), and β-catenin were significantly increased in the PTH or PTHrP group, as well as the gene expressions of Pth1r, Bglap, and Alpl. There was no significant difference between the effects of PTH and PTHrP. Nevertheless, inhibition of PTHrP on the osteogenic differentiation of hPDLCs was detected in vitro with decreased expression of OCN, RUNX2, COL-1, and ALP. Local injection of either PTH or PTHrP carried by controlled release PECE hydrogel similarly enhances OTM in rats through regulating periodontal bone remodeling, which deserves further study for potential clinical application.