Suppression Of Parathyroid Hormone Secretion Research Articles

Activation of the Calcium-Sensing Receptor by a Subfraction of Amino Acids Contained in Thyroid Drainage Fluid.

Hypoparathyroidism is a common sequela of thyroid surgery; in this study, we aimed at exploring the pathogenesis behind it. The following premises suggest that wound fluid might be a causative agent. (i) Parathyroid hormone secretion is under feedback control by the calcium-sensing receptor, which responds to a diverse array of activating ligands. (ii) Postoperative hypoparathyroidism arises from a secretory deficiency of the parathyroid glands. Even in patients later unaffected by hypoparathyroidism, parathyroid hormone levels drop within hours after surgery. (iii) Wound fluid is bound to enter the tissue around the thyroid bed, where the parathyroid glands are located. Its composition is shaped by a series of proteolytic reactions triggered by wounding. Using thyroid drainage as a surrogate, we addressed the possibility that wound fluid contains compounds activating the calcium-sensing receptor. Drainage fluid ultrafiltrate was found to be rich in amino acids, and on separation by HPLC, compounds activating the calcium-sensing receptor partitioned with hydrophilic matter that rendered buffer acidic. The data show that glutamate and aspartate at millimolar concentrations supported activation of the calcium-sensing receptor, an effect contingent on low pH. In the presence of glutamate/aspartate, protons activated the calcium-sensing receptor with a pH50 of 6.1, and at pH 5, produced maximal activation. This synergistic mode of action was exclusive; glutamine/asparagine did not substitute for the acidic amino acids, nor did Ca2+ substitute for protons. NPS-2143, a negative allosteric receptor modulator completely blocked receptor activation by glutamate/aspartate and by fractionated drainage fluid. Thus, wound fluid may be involved in suppressing parathyroid hormone secretion.

Disease-Modifying Adjunctive Therapy of Osteopenia and Osteoporosis with a Multimineral Marine Extract, LithoLexal® Bone

There is evidence to suggest that restoration of major/rare biominerals by supplementation can produce osteogenic and anti-resorptive effects in humans. LithoLexal® is a natural extract harvested from a marine alga, Lithothamnion sp., with a porous microstructure and multimolecular composition rich in calcium (32% w/w) and magnesium (2.2% w/w) together with ~72 trace bioelements. In vitro, LithoLexal® demonstrated cellular-level osteogenic efficacy through enhancing the maturation and activity of pre-osteoblasts. This extract also expressed the ability to suppress osteoclastogenesis by downregulating the pro-resorptive cytokines TNF-α and IL-1β and the master regulator of inflammation NF-κB. Parathyroid hormone inhibition of parathyroid hormone secretion is another bioactivity of LithoLexal® Bone reported with both short- and long-term administration at a longer duration and higher magnitude than what calcium carbonate could induce. Due to these bioactivities that affect pathogenetic factors of osteoporosis, LithoLexal® Bone is referred to as a disease-modifying adjunctive therapy (DMAT). In postmenopausal animal models, LithoLexal® monotherapy preserved bone mineral density, microarchitecture, and biomechanical properties, while calcium carbonate failed to produce significant outcomes. The pro-resorptive effect of a high-fat diet was also efficiently counteracted in vivo by supplementary LithoLexal®. A large clinical trial on postmenopausal women verified the mitigating effects of LithoLexal® Bone on bone resorption and turnover rate. The characteristic composition of LithoLexal® together with its lattice microstructure are suggested to underlie its in vivo bioactivities. In conclusion, adjunctive therapy with LithoLexal® Bone is an attractive option for clinical prevention and treatment of osteopenia/osteoporosis.

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

Effects of Multi-stage Procurement on the Viability and Function of Human Donor Parathyroid Glands.

Parathyroid allotransplantation is an emerging treatment for severe hypoparathyroidism. Ensuring the viability and functional integrity of donor parathyroid glands following procurement is essential for optimal transplantation outcomes. Cellular viability, calcium-responsive hormone secretion, and gland xenograft survival were assessed in a series of deceased donor parathyroid glands following a two-stage procurement procedure recently developed by our group (en bloc cadaveric dissection with subsequent gland isolation after transport to the laboratory). Parathyroid glands resected in this manner and stored up to 48h in 4°C University of Wisconsin (UW) media retained invitro viability with no induction of hypoxic stress (HIF-1α) or apoptotic (caspase-3) markers. Exvivo storage did not significantly affect parathyroid gland calcium sensing capacity, with comparable calcium EC50 values and suppression of parathyroid hormone secretion at high ambient calcium concentrations. The isolated glands engrafted readily, vascularizing rapidly invivo following transplantation into mice. Parathyroid tissue retains viability, calcium-sensing capacity, and invivo engraftment capability after en bloc cadaveric resection, exvivo dissection, and extended cold storage.

Anterior Cruciate Ligament Reconstruction Upregulates Vitamin D Activating Pathways within the Quadriceps

Anterior cruciate ligament (ACL) tears are prevalent sport‐related injuries that result in protracted quadriceps atrophy and weakness despite surgical reconstruction and physical therapy. Vitamin D and its receptor are integral for skeletal muscle development and homeostasis. In addition, vitamin D status is positively associated with muscle size and strength. If the vitamin D receptor and related enzymes are upregulated with ACL injury and reconstruction, then overall vitamin D status may be an important effector of recovery. Concentrations of vitamin D needed to support optimal recovery may differ from typical clinical cut points used to diagnose vitamin D deficiency, which could have powerful therapeutic implications following ACL injury and reconstruction. This is especially important given recent research showing over 50% of athletes have vitamin D inadequacy. We hypothesized that subjects with circulating vitamin D sufficient to suppress parathyroid hormone secretion (≥ 40 ng/mL) would be better protected against quadriceps atrophy at the conclusion of rehabilitation. Muscle biopsies (vastus lateralis) were obtained from ACL‐injured and Healthy limbs of 16 participants (6M,10F; 19±5yr, body mass index: 25.1±3.7kg/m2) prior to surgical reconstruction, 1 week following reconstruction (Recon), and following the completion of post‐surgical rehabilitation (6 months following surgery, Post‐Rehab). RNA was isolated from all quadriceps biopsies, followed by library construction, sequencing, and bioinformatics analysis. Transcript abundance of vitamin D activating pathway regulators (vitamin D receptor [VDR], and Cytochrome P450 2R1 [CYP2R1] and Family 27 Subfamily B Member 1 [CYP27B1]) was assessed following analysis using DESeq2 and false discovery rate (FDR) adjustment of p‐values. Additionally, 25‐hydroxy vitamin D (25(OH)D) was assessed in serum samples obtained at the time of reconstruction surgery. Quadriceps fiber cross‐sectional area was measured via laminin immunohistochemistry. Recon (1 week post‐surgery) muscle showed increased transcript abundance of the vitamin D receptor, VDR(elevated 7.8 fold, FDR<0.05), and vitamin D‐activating pathway regulators CYP2R1 (elevated 1.5 fold, FDR<0.05) and CYP27B1 (elevated 2.6 fold, FDR<0.05) when compared to the Healthy limb. Following the completion of rehabilitation at the 6‐month follow‐up, participants with 25(OH)D above 40 ng/mL showed 6.4% atrophy of quadriceps fiber size compared to 22.8% atrophy in participants with 25(OH)D below 40 ng/mL (p=0.06). These findings provide evidence for surgically induced elevations in the vitamin D activating pathway within skeletal muscle. Upregulation of the vitamin D activating pathway may support quadriceps mitochondrial health and satellite cell activity and self‐renewal capacity, both of which are compromised following ACL reconstruction. In addition, elevated vitamin D concentrations may protect against protracted quadriceps atrophy. Future research should investigate if manipulation of vitamin D concentrations can enhance quadriceps functional recovery following ACL reconstruction.

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.

Значение фактора роста Фибробластов 23 (FGF-23) в организме человека

Nowadays chronic kidney disease (CKD) is one of the leading chronic non-communicable diseases in terms of morbidity and mortality. One of the most serious complications is mineral-bone disorder, which worsen the clinical course and prognosis of patients. Fibroblast growth factor 23 (FGF-23) is a new biomarker that regulates phosphate metabolism and plays an important role in the pathogenesis of many complications in CKD. Purpose. To study the physiological role of FGF-23, as well as its potential clinical significance in the progression of CKD and its complications. Material and methods. A 20-year-deep literature search was conducted in the international scientific databases PubMed / Medline, Web of Science and Google Scholar for the following keywords: "Fibroblast growth factor 23", "FGF-23", "phosphate homeostasis", "chronic kidney disease", "Mineral and bone disorders", "left ventricular hypertrophy". Results and discussion. FGF-23 is a protein secreted by bone cells and its primary physiological role is to regulate urinary excretion of phosphate to maintain a stable level in serum. Moreover, FGF-23 decreases calcitriol levels and inhibits parathyroid hormone secretion. In CKD, there is a gradual increase in FGF-23 levels as renal function declines, which can be regarded as physiological compensation to stabilize serum phosphate levels. According to the several studies, FGF-23 might be associated with cardiovascular complications, such as left ventricular hypertrophy and heart failure. Conclusion. Thus, FGF-23 is not only a marker of mineral-bone disorders in CKD, but also a key link in the pathogenesis of the development of secondary hyperparathyroidism and cardiovascular complications. With this in mind, FGF-23 may represent a multifunctional therapeutic target that may improve the prognosis of patients with CKD. Keywords: fibroblast growth factor-23, phosphate, parathyroid hormone, left ventricular hypertrophy, mineral-bone disorder.

Effect of etelcalcetide on parathyroid hormone secretion by primary hyperparathyroidism patient-derived primary parathyroid cells.

Etelcalcetide (Parsabiv®, AMG 416/ONO-5163) is a novel allosteric modulator for the calcium-sensing receptor approved for hemodialysis patients with secondary hyperparathyroidism of uremia. Etelcalcetide reduced parathyroid hormone levels in hemodialysis patients with secondary hyperparathyroidism of uremia in clinical studies. However, its direct effect on parathyroid hormone secretion in human parathyroid cells remains unknown. This study aimed to determine if etelcalcetide suppresses parathyroid hormone secretion by human parathyroid cells in vitro. We prepared primary cell cultures from human parathyroid tissue and determined calcium-sensing receptor expression levels by immunohistochemistry. Pathyroid tumors were removed from fourteen patients with primary hyperparathyrodism. Parathyroid tissue was dispersed with collagenase, resuspended in culture medium, incubated for 2h with etelcalcetide and Ca2+, and the medium was then collected. Final etelcalcetide concentrations in the medium were 0.005-50µmol/L. Levels of human parathyroid hormone in the medium were determined by enzyme-linked immunosorbent assay. In eight of the fourteen parathyroid cell cultures, extracellular Ca2+ reduced parathyroid hormone levels. In four of the eight parathyroid cell cultures which responded extracellular Ca2+, etelcalcetide reduced hormone secretion with the 50% effective concentrations of 0.57, 20.8, 0.42, and 0.57µmol/L. Expression levels of the calcium-sensing receptor were significantly lower in primary hyperparathyroidism patient-derived parathyroid tissues compared with controls. This is the first report that etelcalcetide directly reduced parathyroid hormone secretion from the primary cultured human parathyroid cells from patients with primary hyperparathyroidism. To verify this conclusion, further studies are needed using secondary hyperparathyroidism patient-derived parathyroid cells.

Vitamin D supplementation: cholecalciferol, calcifediol, and calcitriol.

The specific compound that is meant for use in the context of vitamin D supplementation is often ambiguous. The term "supplementation" has been used in the context of cholecalciferol, ergocalciferol, calcidiol, and calcitriol. In nature, by far the major form of vitamin D that nurtures the body is cholecalciferol. In contrast, ergocalciferol is primarily a synthetic and less stable product which is less potent per microgram dose than is cholecalciferol. Calcidol is the major circulating metabolite of cholecalciferol, while calcitriol is the hormone that upregulates the active transport of calcium from the gut, and which suppresses parathyroid hormone secretion. Nutrition policy papers and guidelines leave unstated the obvious fact that calcidiol and calcitriol are not nutrients, and that those metabolites are not pertinent to food fortification or dietary supplementation. Recent evidence shows that ergocalciferol is not stable with storage, and it is far more susceptible to breakdown with cooking and baking than is cholecalciferol. Therefore, it must be concluded that cholecalciferol is the only form of vitamin D that should be considered in the context of the nutritional functions of fortification and supplementation.

Secretion of parathyroid hormone may be coupled to insulin secretion in humans.

Objective:Parathyroid hormone (PTH) is a key hormone in regulation of calcium homeostasis and its secretion is regulated by calcium. Secretion of PTH is attenuated during intake of nutrients, but the underlying mechanism(s) are unknown. We hypothesized that insulin acts as an acute regulator of PTH secretion.Methods:Intact PTH was measured in plasma from patients with T1D and matched healthy individuals during 4-h oral glucose tolerance tests (OGTT) and isoglycemic i.v. glucose infusions on 2 separate days. In addition, expression of insulin receptors on surgical specimens of parathyroid glands was assessed by immunochemistry (IHC) and quantitative PCR (qPCR).Results:The inhibition of PTH secretion was more pronounced in healthy individuals compared to patients with T1D during an OGTT (decrementalAUC0–240min: −5256 ± 3954 min × ng/L and −2408 ± 1435 min × ng/L, P = 0.030). Insulin levels correlated significantly and inversely with PTH levels, also after adjusting for levels of several gut hormones and BMI (P = 0.002). Expression of insulin receptors in human parathyroid glands was detected by both IHC and qPCR.Conclusion:Our study suggests that insulin may act as an acute regulator of PTH secretion in humans.

P0882STUDY ON MECHANISM OF PTH SECRETION IN SECONDARY HYPERPARATHYROIDISM BY OPTOGENECTICS

Abstract Background and Aims Hyperparathyroidism (SHPT) which caused by disorders of PTH metabolism is one of the most common complications in CKD patients. In the progression of SHPT, expression of CaSR in the parathyroid gland decreases, which impairs the regulation of PTH secretion. It is technically challenging to precisely manipulate PTH secretion in hyperplastic human parathyroid tissue. As an emerging technology, optogenetics allows the reversible control of neuronal activity and cellular precesses using lights. In this study, we establish an optogenetic approach that bypasses CaSR to regulate the level of PTH secretion in human parathyroid cells. It is hoped to provide a new idea for the prevention and treatment of SHPT. Method First, we isolated and identified human parathyroid gland by SHPT patients. The primary cell culture of chief cells were performed and identification. After that, the cells were transfected with the lentivirus carrying ChETA-eYFP or eYFP gene. Lights stimulation of the cultured human parathyroid cells was performed after ChETA expression. The PTH level was measured by ELISA before and after stimulation. Meanwhile, Fura-2/AM was loaded to normal or ChETA expressing chief cells for calcium imaging by microscope. Results The parathyroid glands of three SHPT patients were obtained after total parathyroidectomy (Fig.1A). Hematoxylin & Eosin (HE) staining was performed. The tissue showed typical histological characteristics of SHPT: asymmetric enlargement of the chief cells and the nodular distribution (Fig.1B). Parathyroid cells were cultured by primary culture method. By the 7th day of cultivation, the chief cells were grown in uniform size and aggregation state (Fig. 2A). The cells were stained with immunofluorescence, results showed that most of the isolated cells expressed parathyroid hormone (PTH), calcium-sensing receptors (CaSRs) and Vitamin D receptors (VDR) (Fig. 2B). We used lentivirus carrying the CMV-ChETA-eYFP construct to transfect cultured human parathyroid cells. Comparing with eYFP, most of the chief cells were labeled and expressed green fluorescence successfully after 48 hours (Fig.3). We constructed a blue light-emitting diode to stimulated the transfected human parathyroid chief cells for 0.5h (20 Hz with stimulus intervals of 50 ms). Culture medium was collected before and after stimulation for 1h and 6h, and PTH was determined by ELISA. The results showed that there was no significant difference in PTH level between ChETA group and eYFP group before stimulation, however, PTH decreased significantly after 1 hour of stimulation in ChETA group, and gradually returned to the control group after 6 hours (Fig.4). After that, we used a calcium fluorescence assay to reveal light-induced changes of intracellular Ca2+. In ChETA group, blue light stimulation led to a significant increase in fluorescent signals, but a significant decrease when turned off, and the signal strength increased again when it was turned on in a rhythmic manner. But the fluorescent signal of eYFP group remained stable throughout the whole process (Fig.5). Conclusion We used optogenetics to bypass CaSR rhythmic suppression of PTH secretion in human parathyroid cells. It is hoped that this study will provide new strategies for the treatment and prevention of SHPT

Analyses of risk factors for temporarily inhibited parathyroid hormone secretion of postoperative primary hyperparathyroidism

Objective: To study relative risk factors for temporarily inhibited parathyroid hormone (PTH) secretion after surgery of primary hyperparathyroidism (PHPT). Methods: Seventy-two cases with PHPT from October 2017 to March 2019 in Beijing Chaoyang Hospital were analyzed retrospectively, including 22 males and 50 females aged from 13 to 83 years old. They were reviewed and divided into a complete inhibition group (24 cases, PTH=0 pg/ml), an incomplete inhibition group (23 cases, 0<PTH<12.4 pg/ml), and a non-inhibition group (25 cases, PTH≥12.4 pg/ml) according to the PTH level on the first day after surgery of PHPT. With the Kruskal-Wallis multi-group rank sum test and the Nemenyi test, preoperative and postoperative biochemical parameters and endocrine indexes, including the preoperative serum levels of calcium, phosphorus, PTH, 25-hydroxyvitamin D, and alkaline phosphatase, as well as the levels of PTH 10 min after focal resection, calcium on the first day after surgery, and PTH on the third day after surgery, were compared among three groups to evaluate potential risk factor for postoperative temporary inhabitation of PTH secretion. The predictive values of various risk factors for postoperative temporary inhibition of PTH secretion were evaluated with ROC curve analysis. Results: Preoperative serum PTH, calcium levels, and serum calcium level on the first day after surgery in the complete inhibition group were higher than those in the non-inhibition group,respectively, with statically significant differences [256.5(141.6,585.3) pg/ml vs. 130.2(92.1,256.6) pg/ml, 2.90(2.69,3.22) mmol/L vs. 2.61(2.50,2.75) mmol/L, 2.23(2.08,2.41) mmol/L vs. 2.12(2.05,2.14) mmol/L, χ(2) were 7.17, 11.90, 8.32, respectively, all P<0.05]. When the preoperative serum calcium level was higher than 2.62 mmol/L (AUC=0.698, 95%CI: 0.57-0.83, P=0.006) or the preoperative PTH level was higher than 115.9 pg/ml (AUC=0.697, 95%CI: 0.58-0.82, P=0.007), patients tended to inhibit completely PTH secretion after operation. Conclusions: Preoperative serum calcium and PTH levels are risk factors for postoperative temporary PTH inhibition in PHPT.

Control of PTH secretion by the TRPC1 ion channel.

Familial hypocalciuric hypercalcemia (FHH) is a genetic condition associated with hypocalciuria, hypercalcemia, and, in some cases, inappropriately high levels of circulating parathyroid hormone (PTH). FHH is associated with inactivating mutations in the gene encoding the Ca2+-sensing receptor (CaSR), a GPCR, and GNA11 encoding G protein subunit α 11 (Gα11), implicating defective GPCR signaling as the root pathophysiology for FHH. However, the downstream mechanism by which CaSR activation inhibits PTH production/secretion is incompletely understood. Here, we show that mice lacking the transient receptor potential canonical channel 1 (TRPC1) develop chronic hypercalcemia, hypocalciuria, and elevated PTH levels, mimicking human FHH. Ex vivo and in vitro studies revealed that TRPC1 serves a necessary and sufficient mediator to suppress PTH secretion from parathyroid glands (PTGs) downstream of CaSR in response to high extracellular Ca2+ concentration. Gα11 physically interacted with both the N- and C-termini of TRPC1 and enhanced CaSR-induced TRPC1 activity in transfected cells. These data identify TRPC1-mediated Ca2+ signaling as an essential component of the cellular apparatus controlling PTH secretion in the PTG downstream of CaSR.

Unexpected complication of a common therapy in a pregnant patient

Background: Pre-eclampsia/eclampsia is a life-threatening disease with considerable risks on maternal and neonatal health. Globally, it affects between 2–8% of all pregnancies. Worldwide, approximately 63,000 pregnant women die each year due to pre-eclampsia/eclampsia. The MAGPIE (Magnesium sulphate for Prevention of Eclampsia) trial stated that the risk of developing convulsions was lowered significantly (58%) in severe pre-eclampsia patients who received magnesium sulfate in comparison to the placebo group.1 The exact mechanism of action of magnesium sulfate (MgSO4) is not completely understood, blocking calcium channels and decreasing availability of calcium for smooth muscle contractions has been suggested. Pritchard advocated that therapeutic concentration of MgSO4 should be between 2-4 mmol/l.2 Despite strong evidence of the effectiveness of MgSO4, concerns have been expressed about the risk of hypocalcemia to the patient when used alone or concomitantly with nifedipine as both of them affect calcium metabolism.3 Hypermagnesemia causes hypocalcemia by inhibiting parathyroid hormone secretion and increases urinary excretion of calcium. Severe hypocalcemia is a life-threatening condition and may lead to focal or generalized tonic muscle cramps, convulsions, arrhythmia, and laryngospasm and stridor which is common in the pediatric population but has also been reported in adults.4 A case of symptomatic hypocalcemia secondary to hypermagnesemia is extremely rare, and to the best of our knowledge, only a few cases have been reported.5 We believe this is the only case in the literature with stridor and potential airway obstruction. Case: A 30-year old black South African woman, gravida 5, para 3+1, presented with severe preeclampsia (BP 215/145 mmHg, proteinuria +2), and preterm premature rupture of membrane at 33 weeks of gestation. General and obstetric examinations were unremarkable. Laboratory parameters on admission showed acute kidney injury, anemia and elevated lactate dehydrogenase and alkaline phosphatase. Other investigations were normal (Table 1). She was admitted to the high dependent unit and received 10 grams of intramuscular MgSO4, followed by continuous intravenous infusion at a rate of 2 g/hour for 24 hours. Her blood pressure dropped to 145/95 mmHg. Three hours post-admission, her blood pressure raised to 186/124 mmHg and was controlled with a labetalol intravenous infusion and nifedipine 10 mg orally. Her blood pressure then dropped to 150/90 mmHg. Six hours post-admission, the patient had an uneventful emergency caesarean section under spinal anesthesia for fetal distress. Nine hours post-admission, the patient had dyspnea, respiratory distress, and inspiratory stridor, and chest examination was unremarkable. While checking her blood pressure, the patient had carpopedal spasm (Trousseau's sign) and masseter muscle spasm (Chvostek's sign). MgSO4 infusion was stopped. She received 10 ml of 10% calcium chloride over 10 minutes and responded dramatically to resuscitation and calcium chloride. Investigations (arterial blood gas, FBC, urea and electrolytes) were performed and showed low ionized calcium 0.89 mmol/l and her magnesium level was 2.74 mmol/l. Conclusion: Although MgSO4 is considered as the treatment of choice for the prevention of convulsions in pre-eclampsia/eclampsia patients, concerns have been raised regarding the risk of severe hypocalcemia, especially when used concomitantly with calcium channel blockers. Prospective studies designed in a controlled fashion are needed to assess the safe combination of magnesium sulfate and nifedipine.

Pharmacology of Parsabiv® (etelcalcetide, ONO-5163/AMG 416), a novel allosteric modulator of the calcium-sensing receptor, for secondary hyperparathyroidism in hemodialysis patients

Etelcalcetide hydrochloride (Parsabiv®, ONO-5163/AMG 416) is an allosteric modulator of the calcium (Ca)-sensing receptor that was originally produced by KAI Pharmaceuticals Inc. (now Amgen Inc.). It has recently been approved as the first intravenous calcimimetic agent for secondary hyperparathyroidism (SHPT) in many countries. Etelcalcetide is an intravenous injectable drug that can be administered and eliminated through the dialysis circuit in chronic kidney disease patients. In the present study, we evaluated the in vitro pharmacological profile and in vivo parathyroid hormone (PTH)- and Ca-lowering activities of etelcalcetide in a rat 5/6 nephrectomy model of chronic renal insufficiency with SHPT. Etelcalcetide increased the intracellular Ca concentration in HEK-293T cells expressing human Ca-sensing receptor with an EC50 value (95% confidence interval) of 0.53 μM (0.28–1.0 μM) and suppressed PTH secretion from rat parathyroid gland cells with 0.36 μM (0.24–0.54 μM) by activating Ca-sensing receptor. The specificity of etelcalcetide was evaluated by examining its ability to stimulate or inhibit radioligand binding to a panel of 34 off-target proteins. There were no significant changes in the presence of 10 μM etelcalcetide. Furthermore, in a rat 5/6 nephrectomy model of chronic renal insufficiency with SHPT, single intravenous administration of etelcalcetide at 0.3, 1.0, and 3.0 mg/kg decreased plasma PTH and serum Ca levels. Taken together, the present findings identify etelcalcetide as a calcimimetic with potent PTH- and Ca-lowering effects via Ca-sensing receptor agonist activity.

Fibroblast Growth Factor (FGF) 23 Regulates the Plasma Levels of Parathyroid Hormone In Vivo Through the FGF Receptor in Normocalcemia, But Not in Hypocalcemia

The calcium and phosphate homeostasis is regulated by a complex interplay between parathyroid hormone (PTH), fibroblast growth factor 23 (FGF23), and calcitriol. Experimental studies have demonstrated an inhibitory effect of FG23 on PTH production and secretion; the physiological role of this regulation is however not well understood. Surprisingly, in uremia, concomitantly elevated FGF23 and PTH levels are observed. The parathyroid gland rapidly loses its responsiveness to extracellular calcium in vitro and a functional parathyroid cell line has currently not been established. Therefore, the aim of the present investigation was to study the impact of FGF23 on the Ca2+/PTH relationship in vivo under conditions of normocalcemia and hypocalcemia. Wistar rats were allocated to treatment with intravenous recombinant FGF23 and inhibition of the FGF receptor in the setting of normocalcemia and acute hypocalcemia. We demonstrated that FGF23 rapidly inhibited PTH secretion and that this effect was completely blocked by inhibition of the FGF receptor. Furthermore, inhibition of the FGF receptor by itself significantly increased PTH levels, indicating that FGF23 has a suppressive tonus on the parathyroid gland’s PTH secretion. In acute hypocalcemia, there was no effect of either recombinant FGF23 or FGF receptor inhibition on the physiological response to the low ionized calcium levels. In conclusion, FGF23 has an inhibitory tonus on PTH secretion in normocalcemia and signals through the FGF receptor. In acute hypocalcemia, when increased PTH secretion is needed to restore the calcium homeostasis, this inhibitory effect of FGF23 is abolished.

USE OF TERIPARATIDE IN A FOUR YEAR OLD PATIENT WITH AUTOSOMAL DOMINANT HYPOCALCAEMIA

AimWe report the effective use of the synthetic parathyroid hormone (PTH) teriparatide to treat a 4 year old boy with autosomal dominant hypocalcaemia.BackgroundAutosomal Dominant hypocalcaemia is characterised by hypocalcaemia with...

Nonclinical Safety Profile of Etelcalcetide, a Novel Peptide Calcimimetic for the Treatment of Secondary Hyperparathyroidism.

Etelcalcetide is a novel d-amino acid peptide that functions as an allosteric activator of the calcium-sensing receptor and is being developed as an intravenous calcimimetic for the treatment of secondary hyperparathyroidism in patients with chronic kidney disease on hemodialysis. To support clinical development and marketing authorization, a comprehensive nonclinical safety package was generated. Primary adverse effects included hypocalcemia, tremoring, and convulsions. Other adverse effects were considered sequelae of stress associated with hypocalcemia. Cardiovascular safety evaluations in the dog revealed an anticipated prolongation of the corrected QT interval that was related to reductions in serum calcium. Etelcalcetide did not affect the human ether-a-go-go gene ion channel current. Etelcalcetide was mutagenic in some strains of Salmonella, however, based on the negative results in 2 in vitro and 2 in vivo mammalian genotoxicity assays, including a 28-day Muta mouse study, etelcalcetide is considered nongenotoxic. Further support for a lack of genotoxicity was provided due to the fact that etelcalcetide was not carcinogenic in a 6-month transgenic rasH2 mouse model or a 2-year study in rats. There were no effects on fertility, embryo-fetal development, and prenatal and postnatal development. All of the adverse effects observed in both rat and dog were considered directly or secondarily related to the pharmacologic activity of etelcalcetide and the expected sequelae associated with dose-related reductions in serum calcium due to suppression of parathyroid hormone secretion. These nonclinical data indicate no safety signal of concern for human risk beyond that associated with hypocalcemia and associated QT prolongation.

Vascular Calcification - Pathological Mechanism and Clinical Application - . The effect of cinacalcet on vascular calcification

Cinacalcet acts on calcium receptors (CaR) expressed on chief cells of the parathyroid gland to inhibit the secretion of parathyroid hormone (PTH) . This drug inhibits PTH secretion without causing an elevation of serum calcium and phosphorus, unlike active vitamin D. Several experimental studies demonstrated an inhibitory effect of calcimimetics on the progression of vascular calcification in animals with chronic kidney disease (CKD), in keeping with the expression of the calcium-sensing receptor (CaSR) in vascular tissue. The EVOLVE, evaluated in patients with CKD 5D the effects of the cinacalcet on the progression of vascular calcification and hard cardiovascular outcomes, respectively. The EVOLVE trials missed their respective primary end point by intent-to-treat analysis. However, recently, in order to define the frequency of fatal and nonfatal cardiovascular events attributable to atherosclerotic and nonatherosclerotic mechanisms, risk factors for these events, and the effects of cinacalcet, post hoc analysis using adjudicated data collected during the EVOLVE Trial were perfomed. In this trial, combining fatal and nonfatal cardiovascular events, randomization to cinacalcet reduced the rates of sudden death and heart failure. Patients randomized to cinacalcet experienced fewer nonatherosclerotic cardiovascular events, while the effect of cinacalcet on atherosclerotic events did not reach statistical significance.

Pathophysiologic Changes in Extracellular pH Modulate Parathyroid Calcium-Sensing Receptor Activity and Secretion via a Histidine-Independent Mechanism.

The calcium-sensing receptor (CaR) modulates renal calcium reabsorption and parathyroid hormone (PTH) secretion and is involved in the etiology of secondary hyperparathyroidism in CKD. Supraphysiologic changes in extracellular pH (pHo) modulate CaR responsiveness in HEK-293 (CaR-HEK) cells. Therefore, because acidosis and alkalosis are associated with altered PTH secretion in vivo, we examined whether pathophysiologic changes in pHo can significantly alter CaR responsiveness in both heterologous and endogenous expression systems and whether this affects PTH secretion. In both CaR-HEK and isolated bovine parathyroid cells, decreasing pHo from 7.4 to 7.2 rapidly inhibited CaR-induced intracellular calcium (Ca(2+)i) mobilization, whereas raising pHo to 7.6 potentiated responsiveness to extracellular calcium (Ca(2+)o). Similar pHo effects were observed for Ca(2+)o-induced extracellular signal-regulated kinase phosphorylation and actin polymerization and for L-Phe-induced Ca(2+)i mobilization. Intracellular pH was unaffected by acute 0.4-unit pHo changes, and the presence of physiologic albumin concentrations failed to attenuate the pHo-mediated effects. None of the individual point mutations created at histidine or cysteine residues in the extracellular domain of CaR attenuated pHo sensitivity. Finally, pathophysiologic pHo elevation reversibly suppressed PTH secretion from perifused human parathyroid cells, and acidosis transiently increased PTH secretion. Therefore, pathophysiologic pHo changes can modulate CaR responsiveness in HEK-293 and parathyroid cells independently of extracellular histidine residues. Specifically, pathophysiologic acidification inhibits CaR activity, thus permitting PTH secretion, whereas alkalinization potentiates CaR activity to suppress PTH secretion. These findings suggest that acid-base disturbances may affect the CaR-mediated control of parathyroid function and calcium metabolism in vivo.