Parathyroid glands in calcium regulation and human disease

Challenges in establishing animal models for studying osteoimmunology of hypoparathyroidism

Hypoparathyroidism is a relatively rare human and veterinary disease characterized by deficient or absent production of parathyroid hormone (PTH). PTH is known as a classical regulator of calcium and phosphorus homeostasis. Nevertheless, the hormone also appears to modulate immune functions. For example, increased CD4:CD8 T-cell ratios and elevated interleukin (IL)-6 and IL-17A levels were observed in patients with hyperparathyroidism, whereas gene expression of tumor necrosis factor-α (TNF-α) and granulocyte macrophage-colony stimulating factor (GM-CSF) was decreased in patients with chronic postsurgical hypoparathyroidism. Various immune cell populations are affected differently. So, there is a need for validated animal models for the further characterization of this disease for identifying targeted immune-modulatory therapies. In addition to genetically modified mouse models of hypoparathyroidism, there are surgical rodent models. Parathyroidectomy (PTX) can be well performed in rats-for pharmacological and associated osteoimmunological research and bone mechanical studies, a large animal model could be preferable, however. A major drawback for successfully performing total PTX in large animal species (pigs and sheep) is the presence of accessory glands, thus demanding to develop new approaches for real-time detection of all parathyroid tissues.

Endocrine Diagnostics for Exotic Animals

Endocrine disease in exotic species is less common than in small animals. Nevertheless, the diagnostic principles used in small animals can be adapted to evaluate endocrine disease in many of the exotic species although species-specific aspects need to be considered. This article covers important diseases such as thyroid dysfunction in reptiles and birds, hyperthyroidism in guinea pigs, and hyperadrenocorticism in ferrets. Glucose metabolism in neoplasms affecting normal physiology, such as insulinoma in ferrets and gastric neuroendocrine carcinoma in bearded dragons, is discussed. Calcium abnormalities, including metabolic bone disease in reptiles and hypocalcemia in birds, are also covered.

Three pediatric patients with primary hyperparathyroidism caused by parathyroid adenoma

Primary hyperparathyroidism (PHPT) is a hypercalcemia disorder with inappropriately normal or increased serum parathyroid hormone (PTH) levels resulting from excessive secretion of PTH from one or more of the parathyroid glands. PHPT is uncommon in infants and children, with an estimated incidence of 2-5 cases per 100,000 persons. Patients with PHPT usually present with bone pain, urolithiasis, or nephrolithiasis, as well as nonspecific symptoms such as fatigue and weakness. Asymptomatic hypercalcemia may also be detected incidentally. Only a few cases of pediatric PHPT have been reported in Korea. We present three patients (a 9-year-old girl, a 14-year-old boy, and a 14-year-old girl) with PHPT who manifested variable clinical features of hypercalcemia. The first and second patients each had a parathyroid adenoma and presented with abdominal pain caused by pancreatitis and a ureter stone, respectively. The third patient had an ectopic mediastinal parathyroid adenoma and presented with gait disturbance and weakness of the lower extremities. All of the patients underwent surgical resection of parathyroid adenoma, and their serum calcium levels subsequently normalized without medication.

Rapid progression of aortic stenosis after initiation of teriparatide treatment: a case report

Introduction

Teriparatide, a recombinant formulation of endogenous PTH, is indicated for the treatment of osteoporosis in patients at high risk for fracture including postmenopausal women, men with primary or hypogonadal osteoporosis and patients with glucocorticoid-induced osteoporosis.

Case report

A 64-year-old Jewish osteoporotic woman initiated use of Teriparatide (FORTEOTM, 250 µg per 1 ml subcutaneously per day) in April 2018. Prior to therapy initiation, the patient has undergone eight echocardiograms with an aortic valve pressure gradient ranging between 29 and 39 mmHg, defined as mild aortic stenosis (AS), with no clear trend of progression. In two subsequent echo tests conducted 4 and 7 months after treatment initiation, there was a rapid progression of AS with gradient pressures of 55 and 58 mmHg, respectively.

Conclusion

Intermittent exposure to PTH analogues may be one of the causes of rapid progression of AS. Studies with sizeable populations are required to assess causal relationship between PTH analogues use and progression of AS.

Endocrine myopathies: clinical and histopathological features of the major forms

Endocrinopathies, such as thyroid and parathyroid diseases, disorders of the adrenal axis, and acromegaly are included among the many causes of myopathy. Muscle disturbances caused by endocrine disorders are mainly due to alterations in the protein and carbohydrate metabolisms. Either a deficiency or excess of hormones produced by the glands can cause muscle dysfunction that can be reversed by starting hormone replacement therapy or acting on hormone dysfunction. The diagnosis is usually easy if a muscle disorder occurs in an overt endocrinopathy; however, in few patients, myopathy could be the first manifestation of the underlying endocrinopathy. In this article we discuss pathophysiology, clinical features and management of muscle involvement related to the major endocrine diseases.

Preoperative vitamin D levels do not relate with the risk of hypocalcemia following total thyroidectomy. A cohort study

BACKGROUND

Hypocalcemia is the most common complication following total thyroidectomy. Few factors may relate with increased risk of postoperative hypocalcemia. Preoperative vitamin D values have been evaluated in few studies, but reports present conflicting data. Aim of our study is to evaluate the association of preoperative vitamin D values and hypocalcemia following total thyroidectomy.

METHODS

A retrospective analysis of patients undergoing total thyroidectomy in our department of endocrine surgery between November 2012 and November 2015 was performed.

RESULTS

Mean age of patients was 56.2 years (±14.0) and sex ratio (F:M) was 4.3:1. Sixty-four patients (17.4%) had preoperative vitamin D insufficiency (x<25 nmol/L), 138 patients (37.5%) vitamin D deficiency (25<x<50 nmol/L) and 166 patients (45.1%) vitamin D sufficiency (x>50 nmol/L). Following total thyroidectomy for both benign and malignant pathology, 66 patients (17.9%) had symptomatic hypocalcemia (x<2.0 mmol/L) requiring medical treatment (group 1), 64 patients (17.4%) biochemical hypocalcemia (2<x<2.1 mmol/L) not requiring treatment (group 2) and 238 patients (64.7%) had normal levels (x>2.1 mmol/L, group 3). Mean postoperative PTH value was 25.4 pg/ml (range 2-61). No statistical correlation between postoperative serum calcium and preoperative vitamin D values (R=-0.001, P=0.9849) was found nor associations were found regarding age, sex, type of thyroid disease or BMI.

CONCLUSIONS

In our cohort of patients, preoperative vitamin D levels were not associated with a higher risk of hypocalcemia following total thyroidectomy. Postoperative PTH appears to be the most sensible item to predict the risk of postoperative symptomatic hypocalcemia.

New therapeutic targets for osteoporosis

New anti-osteoporotic agents have been developed, potentially enriching the therapeutic armamentarium. Currently available osteoanabolic therapies are the parathyroid hormone (PTH) and PTH-related peptide (PTHrP) synthetic analogues, teriparatide and abaloparatide. Daily administration at doses of 20 and 80 μg, respectively, in contrast to continuous PTH secretion, leads to increased bone formation and reduces vertebral and non-vertebral fracture risk. Teriparatide is more effective than bisphosphonates (alendronate, risedronate) in increasing bone mineral density (BMD), improving bone architecture and reducing fracture risk. Abaloparatide leads to greater BMD gain, has greater anti-fracture efficacy regarding major osteoporotic fractures (upper arm, wrist, hip or clinical spine) compared with teriparatide (without a difference in morphometric vertebral and non-vertebral fractures), and has a lower risk of hypercalcaemia. Romosozumab, a sclerostin inhibitor, both induces bone formation and suppresses bone resorption. Administered at monthly subcutaneous doses of 210 mg, it reduces vertebral, non-vertebral and hip fracture risk compared with either placebo or alendronate. However, concerns have arisen about increased cardiovascular risk, which has suspended its approval by the FDA. Anabolic therapy should always be followed by administration of an anti-resorptive agent, such as bisphosphonates or denosumab, which preserves and may further increase BMD gain. Denosumab provides the greatest benefit for BMD when administered sequentially after its combination with teriparatide for 24 months and constitutes a reasonable option for patients at high risk of fracture. However, longitudinal data are needed to confirm the efficacy and safety of these therapeutic interventions.

Primary Hyperparathyroidism is Underdiagnosed and Suboptimally Treated in the Clinical Setting

Purpose

To evaluate whether patients presenting with laboratory results consistent with primary hyperparathyroidism (pHPT) are managed in accordance with guidelines.

Methods

The laboratory database at a hospital in Sweden, serving 127,000 inhabitants, was searched for patients with biochemically determined pHPT. During 2014, a total of 365 patients with biochemical laboratory tests consistent with pHPT were identified. Patients with possible differential diagnoses or other reasons for not being investigated according to international guidelines were excluded after scrutinizing records, after new blood tests, and clinical assessments by endocrine surgeons.

Results

Altogether, 92 patients had been referred to specialists and 82 had not. The latter group had lower serum calcium (median 2.54 mmol/L) and PTH (5.7 pmol/L). Out of these 82 cases, 9 patients were diagnosed with pHPT or had some sort of long-term follow-up planned as outpatients.

Conclusion

Primary hyperparathyroidism is overlooked and underdiagnosed in a number of patients in the clinical setting. It is important to provide local guidelines for the management of patients presenting with mild pHPT to ensure that these patients receive proper evaluation and follow-up according to current research.

Letrozole induced low estrogen levels affected the expressions of duodenal and renal calcium-processing gene in laying hens

Estrogen regulates the calcium homeostasis in hens, but the mechanisms involved are still unclear fully. In this study, we investigated whether letrozole (LZ) induced low estrogen levels affected the calcium absorption and transport in layers. In the duodenum, we observed a significant decrease of mRNA expressions of Calbindin-28k (CaBP-28k) and plasma membrane Ca²⁺-ATPase (PMCA 1b) while CaBP-28k protein expression was declined in birds with LZ treatment, and the mRNA levels of duodenal transient receptor potential vanilloid 6 (TRPV6) and Na⁺/Ca²⁺ exchanger 1 (NCX1) were not affected. Interestingly, we observed the different changes in the kidney. The renal mRNA expressions of TRPV6 and NCX1 were unregulated while the PMCA1b was down-regulated in low estrogen layers, however, the CaBP-28k gene and protein expressions were no changed in the kidney. Furthermore, it showed that the duodenal estradiol receptor 2 (ESR2) transcripts rather than parathyroid hormone 1 receptor (PTH1R) and calcitonin receptor (CALCR) played key roles to down-regulate calcium transport in LZ-treated birds. In conclusion, CaBP-28k, PMCA 1b and ESR2 genes in the duodenum may be primary targets for estrogen regulation in order to control calcium homeostasis in hens.

Long-term clinical outcome and the identification of homozygous CYP27B1 gene mutations in a patient with vitamin D hydroxylation-deficient rickets type 1A

Vitamin D hydroxylation-deficient rickets type 1A (VDDR1A) is an autosomal recessively-inherited disorder caused by mutations in CYP27B1 encoding the 1α-hydroxylase enzyme. We report on a female patient with VDDR1A who presented with hypocalcemic seizure at the age of 13 months. The typical clinical and biochemical features of VDDR1A were found, such as hypocalcemia, increased alkaline phosphatase, secondary hyperparathyroidism and normal 25-hydroxyvitamin D3 (25(OH)D₃). Radiographic images of the wrist showed metaphyseal widening with cupping and fraying of the ulna and distal radius, suggesting rickets. A mutation analysis of the CYP27B1 gene identified a homozygous mutation of c.589+1G>A in the splice donor site in intron 3, which was known to be pathogenic. Since that time, the patient has been under calcitriol and calcium treatment, with normal growth and development. During the follow-up period, she did not develop genu valgum, scoliosis, or nephrocalcinosis.

PTH and Vitamin D

PTH and Vitamin D are two major regulators of mineral metabolism. They play critical roles in the maintenance of calcium and phosphate homeostasis as well as the development and maintenance of bone health. PTH and Vitamin D form a tightly controlled feedback cycle, PTH being a major stimulator of vitamin D synthesis in the kidney while vitamin D exerts negative feedback on PTH secretion. The major function of PTH and major physiologic regulator is circulating ionized calcium. The effects of PTH on gut, kidney, and bone serve to maintain serum calcium within a tight range. PTH has a reciprocal effect on phosphate metabolism. In contrast, vitamin D has a stimulatory effect on both calcium and phosphate homeostasis, playing a key role in providing adequate mineral for normal bone formation. Both hormones act in concert with the more recently discovered FGF23 and klotho, hormones involved predominantly in phosphate metabolism, which also participate in this closely knit feedback circuit. Of great interest are recent studies demonstrating effects of both PTH and vitamin D on the cardiovascular system. Hyperparathyroidism and vitamin D deficiency have been implicated in a variety of cardiovascular disorders including hypertension, atherosclerosis, vascular calcification, and kidney failure. Both hormones have direct effects on the endothelium, heart, and other vascular structures. How these effects of PTH and vitamin D interface with the regulation of bone formation are the subject of intense investigation.

Novel CYP27B1 Gene Mutations in Patients with Vitamin D-Dependent Rickets Type 1A

The CYP27B1 gene encodes 25-hydroxyvitamin D-1α-hydroxylase. Mutations of this gene cause vitamin D-dependent rickets type 1A (VDDR-IA, OMIM 264700), which is a rare autosomal recessive disorder. To investigate CYP27B1 mutations, we studied 8 patients from 7 unrelated families. All coding exons and intron-exon boundaries of CYP27B1 gene were amplified by PCR from peripheral leukocyte DNA and subsequently sequenced. Homozygous mutations in the CYP27B1 gene were found in all the patients and heterozygous mutations were present in their normal parents. One novel single nucleotide variation (SNV, c.1215 T>C, p.R379R in the last nucleotide of exon 7) and three novel mutations were identified:, a splice donor site mutation (c.1215+2T>A) in intron 7, a 16-bp deletion in exon 6 (c.1022-1037del16), and a 2-bp deletion in exon 5 (c.934_935delAC). Both c.1215 T>C and c.1215+2T>A were present together in homozygous form in two unrelated patients, and caused exon 7 skipping. However, c.1215 T>C alone has no effect on pre-mRNA splicing. The skipping of exon 7 resulted in a shift of downstream reading frame and a premature stop codon 57 amino acids from L380 (p.L380Afs*57). The intra-exon deletions of c.1022-1037del16 and c.934_935delAC also resulted in a frameshift and the creation of premature stop codons at p.T341Rfs*5, and p.T312Rfs*19, respectively, leading to the functional inactivation of the CYP27B1 gene. Clinically, all the patients required continued calcitriol treatment and the clinical presentations were consistent with the complete loss of vitamin D1α-hydroxylase activity. In conclusion, three novel mutations have been identified. All of them caused frameshift and truncated proteins. The silent c.1215 T>C SNV has no effect on pre-mRNA splicing and it is likely a novel SNP. The current study further expands the CYP27B1 mutation spectrum.

Usefulness and feasibility of measuring ionized calcium in haemodialysis patients

Background

Measuring blood calcium level is recommended in haemodialysis (HD) patients. The Kidney Disease Improving Global Outcomes position states that the measurement of ionized calcium (ICa) level is preferred, but in the clinical setting, due to technical difficulties, total calcium (tCa) level is preferred to ICa.

Aim

The aim of this study was to test the possibility of delayed ICa analysis using frozen serum, and so to identify the factors associated with predialysis ICa level and compare the ability of tCa and Alb-Ca to predict ICa level and finally to compare the survival rate according to the three calcium measurements.

Methods

All prevalent HD patients, dialysed by a native AV fistula in a 3 × 4 to 3 × 8 h schedule, had their predialysis ICa, tCa and Alb-Ca levels and usual mid-week biology recorded. Intergroup comparisons between ICa quartile were performed. Bland–Altman plots and linear regression were used to assess the differences between 30 fresh and frozen samples. Survival analyses were performed using ICa and tCa levels.

Results

Comparing fresh blood and frozen serum samples, linear regression (y = 0.98 + 0.02, r = 0.961) showed that the two methods were quite identical with the same mean ICa value (1.1 ± 0.1 mmol/L, P = 0.45). A total of 160 HD patients were included in the study. Hypocalcaemia, using ICa values, was highly prevalent in our population (40%) whereas hypercalcaemia was observed only in three cases (1.8%). In predicting ICa hypocalcaemia (<1.12 mmol/L, n = 64), the use of tCa was accurate in 48.4% of patients, and the use of Alb-Ca was accurate in only 17.2% of patients; tCa was not a predictive factor for hypercalcaemia (ICa > 1.32 mmol/L, n = 3); Alb-Ca value predicted hypercalcaemia in 2/3 of the patients. In predicting normocalcaemia, the use of tCa values was correct in 92.4% of patients and the use of Alb-Ca values in 88.1% of patients; only younger age (P = 0.03) and female sex (P = 0.01) were associated with higher ICa quartile. None of the three calcium measures was significantly associated with survival rate using log-rank and Cox models adjusted for age, dialysis vintage, diabetes and sex.

Conclusion

In the present study, we report that (1) delayed ICa measure is feasible in dialysis patients using a freezing technique, (2) hypocalcaemia is highly prevalent in HD patients and poorly predicted by Alb-Ca level, (3) the main factor associated with ICa level is sex of the individual and (4) calcaemia is not associated with survival rate using any of the three methods.

Serum 25-Hydroxyvitamin D and Parathyroid Hormone Levels in Non-Lactating Women with Post-Partum Thyroiditis: The Effect of L-Thyroxine Treatment

Vitamin D deficiency seems to be implicated in the onset and progression of some autoimmune disorders. No previous study has investigated vitamin D homeostasis in post-partum thyroiditis. We compared 25-hydroxyvitamin D and parathyroid hormone (PTH) levels between four groups of non-lactating women who gave birth within 12 months before the beginning of the study: hypothyroid women with post-partum thyroiditis (group A; n = 14), euthyroid females with post-partum thyroiditis (group B; n = 14), women with non-autoimmune hypothyroidism (group C; n = 16) and healthy euthyroid females without thyroid autoimmunity (group D; n = 15). In the second part of the study, groups A and C were treated for 6 months with L-thyroxine. Serum levels of 25-hydroxyvitamin D were lower, while PTH higher in patients with post-partum thyroiditis than in patients without thyroid autoimmunity. They were also lower (25-hydroxyvitamin D) or higher (PTH) in group A than in group B, as well as in group C in comparison with group D. L-thyroxine treatment increased 25-hydroxyvitamin D and reduced PTH levels only in hypothyroid women with post-partum thyroiditis. Baseline levels of 25-hydroxyvitamin D correlated with thyroid antibody titres, thyroid function and circulating PTH levels, while the effect of L-thyroxine on serum levels of this vitamin correlated with the changes in thyroid antibody titres and PTH levels. The results of our study suggest the association of vitamin D status with post-partum thyroiditis and L-thyroxine treatment of this disorder.

Clinical and genetic analysis of patients with vitamin D-dependent rickets type 1A

CONTEXT

Vitamin D-dependent rickets type 1A (VDDR-IA, OMIM 264700) is a rare autosomal recessive disorder and is caused by mutations in the CYP27B1 gene.

OBJECTIVES

We aim to investigate CYP27B1 mutation in seven patients from four separate families and characterize the genotype-phenotype correlation.

METHODS

The entire coding region of the CYP27B1 gene was sequenced, and genotype-phenotype correlation among patients was assessed.

RESULTS

Sequencing analysis identified biallelic CYP27B1 mutations in all patients and monoallelic mutations in their parents. One patient from the first family was compound heterozygous for c.1166G>A (p.Arg389His) and a novel nonsense mutation c.1079 C>A (p.Ser360*). Two patients from the second family were homozygous for a novel splice donor site mutation in intron 1 (c.195 + 2 T>G), causing partial retention of the intron and a shift in the reading frame. Both novel mutations lead to the complete loss of vitamin D1α-hydroxylase activity. Four patients from families 3 and 4 were homozygous for a previously reported duplication mutation in exon 8 (1319-1325dupCCCACCC, Phe443Profs*24). Interestingly, one patient who was presented with severe hypocalcaemia and seizures at 4 months of age as a result of Phe443Profs*24 has improved spontaneously since 11 years of age and does not need regular treatment. Her laboratory tests showed normal serum calcium and 1,25(OH)(2) D after refusing to take medication for 12 months.

CONCLUSIONS

There is a good genotype-phenotype correlation in VDDR-IA. However, some patients may recover from the loss of CYP27B1 function, probably due to 1α-hydroxylase activity exerted by a non-CYP27B1 enzyme.

Calcium: An Essential Mineral

This review of calcium discusses briefly the role of the parathyroid glands, the gastrointestinal system, and the renal system in maintaining calcium homeostasis that is required for normal bone health, nerve and muscle function, and blood coagulation in the human body. The new recommendations for calcium intake by the United States Institute of Medicine are discussed. The concerns by the Institute of Medicine regarding adverse effects from excess calcium intake, especially hypercalcemia, nephrolithiasis (kidney stones), milk alkali syndrome, prostate cancer, and coronary heart disease, are reviewed.

trpm7 regulation of in vivo cation homeostasis and kidney function involves stanniocalcin 1 and fgf23

The transient receptor potential melastatin 7 (trpm7) channel kinase is a primary regulator of magnesium homeostasis in vitro. Here we show that trpm7 is an important regulator of cation homeostasis as well as kidney function in vivo. Using zebrafish trpm7 mutants, we show that early larvae exhibit reduced levels of both total magnesium and total calcium. Accompanying these deficits, we show that trpm7 mutants express higher levels of stanniocalcin 1 (stc1), a potent regulator of calcium homeostasis. Using transgenic overexpression and morpholino oligonucleotide knockdown, we demonstrate that stc1 modulates both calcium and magnesium levels in trpm7 mutants and in the wild type and that levels of these cations are restored to normal in trpm7 mutants when stc1 activity is blocked. Consistent with defects in both calcium and phosphate homeostasis, we further show that trpm7 mutants develop kidney stones by early larval stages and exhibit increased levels of the anti-hyperphosphatemic factor, fibroblast growth factor 23 (fgf23). Finally, we demonstrate that elevated fgf23 expression contributes to kidney stone formation by morpholino knockdown of fgf23 in trpm7 mutants. Together, these analyses reveal roles for trpm7 in regulating cation homeostasis and kidney function in vivo and implicate both stc1 and fgf23 in these processes.

Correlation between plasma calcium, parathyroid hormone (PTH) and the metabolic syndrome (MetS) in a community-based cohort of men and women

CONTEXT

In recent years, an association has been noted between several abnormalities that characterize the metabolic syndrome (MetS) and primary hyperparathyroidism (pHPT). These abnormalities include dyslipidaemia, obesity, insulin resistance and hypertension. The correlations between plasma calcium, parathyroid hormone (PTH) and the variables in the MetS in a normal population are still unclear.

OBJECTIVE

To describe correlations between plasma calcium and PTH and the various abnormalities present in the MetS in a healthy population.

DESIGN

We studied 1016 healthy individuals from the Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) population of 70 years old, by means of plasma analyses of calcium, PTH, creatinine, lipids, insulin and glucose, as well as by standardized blood pressure measurements. Further, body mass index (BMI) and waist circumference were determined.

RESULTS

The more National Cholesterol Education Program (NCEP) criteria for the MetS that were met, the higher the s-PTH and albumin-corrected s-calcium. Further, positive correlations between plasma calcium and BMI (P = 0.0003), waist circumference (P = 0.0009) and insulin resistance (P = 0.079) were found. PTH and BMI (P < 0.0001), waist circumference (P < 0.0001), systolic blood pressure (P = 0.0034), diastolic blood pressure (P = 0.0008), serum triglycerides (P = 0.0003) and insulin resistance (P = 0.0003) were positively correlated, whereas serum high density lipoproteins (HDL) (P = 0.036) and PTH were negatively correlated.

CONCLUSIONS

We conclude that PTH correlates with several of the metabolic factors included in the MetS within a normocalcaemic population. In addition, individuals with mild pHPT present significantly more NCEP criteria for MetS. We postulate that increased levels of PTH in pHPT may be associated with the increased cardiovascular morbidity and mortality seen in pHPT.

Stabilizing mutation of CTNNB1/beta-catenin and protein accumulation analyzed in a large series of parathyroid tumors of Swedish patients

Background

Aberrant accumulation of β-catenin plays an important role in a variety of human neoplasms. We recently reported accumulation of β-catenin in parathyroid adenomas from patients with primary hyperparathyroidism (pHPT). In CTNNB1 exon 3, we detected a stabilizing mutation (S37A) in 3 out of 20 analyzed adenomas. The aim of the present study was to determine the frequency and zygosity of mutations in CTNNB1 exon 3, and β-catenin accumulation in a large series of parathyroid adenomas of Swedish patients.

Results

The mutation S37A (TCT > GCT) was detected by direct DNA sequencing of PCR fragments in 6 out of 104 sporadic parathyroid adenomas (5.8%). Taking our previous study into account, a total of 9 out of 124 (7.3%) adenomas displayed the same mutation. The mutations were homozygous by DNA sequencing, restriction enzyme cleavage, and gene copy number determination using the GeneChip 500 K Mapping Array Set. All tumors analyzed by immunohistochemistry, including those with mutation, displayed aberrant β-catenin accumulation. Western blotting revealed a slightly higher expression level of β-catenin and nonphosphorylated active β-catenin in tumors with mutation compared to those without. Presence of the mutation was not related to distinct clinical characteristics.

Conclusion

Aberrant accumulation of β-catenin is very common in parathyroid tumors, and is caused by stabilizing homozygous mutation in 7.3% of Swedish pHPT patients.

Extracellular calcium as an integrator of tissue function

The past several decades of research into calcium signaling have focused on intracellular calcium (Ca(i)(2+)), revealing both exquisite spatial and dynamic control of this potent second messenger. Our understanding of Ca(i)(2+) signaling has benefited from the evolution of cell culture methods, development of high affinity fluorescent calcium indicators (both membrane-permeant small molecules and genetically encoded proteins), and high-resolution fluorescence microscopy. As our understanding of single cell calcium dynamics has increased, translational efforts have attempted to push calcium signaling studies back into tissues, organs and whole animals. Emerging results from these more complicated, diffusion-limited systems have begun to define a role for extracellular calcium (Ca(o)(2+)) as an agonist, spurred by the cloning and characterization of a G protein-coupled receptor activated by Ca(o)(2+) (the calcium sensing receptor, CaR). Here, we review the current state-of-the art for measurement of Ca(o)(2+) fluctuations, and the evidence that fluctuations in Ca(o)(2+) can act as primary signals regulating cell function. Current results suggest that Ca(o)(2+) in bone and epidermis may act as a chemotactic homing signal, targeting cells to the appropriate tissue locations prior to initiation of the differentiation program. Ca(i)(2+) signaling-mediated Ca(o)(2+) fluctuations in interstitial spaces may integrate cell signaling responses in multicellular networks through activation of CaR. Appreciation of the importance of Ca(o)(2+) fluctuations in coordinating cell function will likely spur identification of additional, niche-specific Ca(2+) sensors, and provide unique insights into the regulation of multicellular signaling networks.

An LRP5 receptor with internal deletion in hyperparathyroid tumors with implications for deregulated WNT/beta-catenin signaling

BACKGROUND

Hyperparathyroidism (HPT) is a common endocrine disorder with incompletely understood etiology, characterized by enlarged hyperactive parathyroid glands and increased serum concentrations of parathyroid hormone and ionized calcium. We have recently reported activation of the Wnt signaling pathway by accumulation of beta-catenin in all analyzed parathyroid tumors from patients with primary HPT (pHPT) and in hyperplastic parathyroid glands from patients with uremia secondary to HPT (sHPT). Mechanisms that may account for this activation have not been identified, except for a few cases of beta-catenin (CTNNB1) stabilizing mutation in pHPT tumors.

METHODS AND FINDINGS

Reverse transcription PCR and Western blot analysis showed expression of an aberrantly spliced internally truncated WNT coreceptor low-density lipoprotein receptor-related protein 5 (LRP5) in 32 out of 37 pHPT tumors (86%) and 20 out of 20 sHPT tumors (100%). Stabilizing mutation of CTNNB1 and expression of the internally truncated LRP5 receptor was mutually exclusive. Expression of the truncated LRP5 receptor was required to maintain the nonphosphorylated active beta-catenin level, transcription activity of beta-catenin, MYC expression, parathyroid cell growth in vitro, and parathyroid tumor growth in a xenograft severe combined immunodeficiency (SCID) mouse model. WNT3 ligand and the internally truncated LRP5 receptor strongly activated transcription, and the internally truncated LRP5 receptor was insensitive to inhibition by DKK1.

CONCLUSIONS

The internally truncated LRP5 receptor is strongly implicated in deregulated activation of the WNT/beta-catenin signaling pathway in hyperparathyroid tumors, and presents a potential target for therapeutic intervention.

Mechanisms of transcriptional repression by 1,25(OH)2 vitamin D

PURPOSE OF REVIEW

Vitamin D has diverse biological actions, and consequently the mechanisms behind how it regulates gene transcription are diverse. Unlike its well described positive effects on gene transcription, little is known about how vitamin D induces transcriptional repression.

RECENT FINDINGS

Vitamin D-induced transcriptional repression of several negative vitamin D receptor target genes has been studied on a molecular level. A new class of negative vitamin D response elements, which are E-box-type motifs, bind the bHLH-type transcriptional activator (VDIR) together with a histone acetyltransferase coactivator. The vitamin D receptor, activated by vitamin D, does not directly bind to the negative vitamin D response elements, but instead associates with VDIR. This leads to the dissociation of the histone acetyltransferase coactivator and recruitment of a histone deacetylase corepressor to transrepress transcription of the target gene promoter.

SUMMARY

Histone inactivation induced by histone deacetylase co-repressors appears to facilitate vitamin D-induced transcriptional repression via the vitamin D receptor. Following vitamin D binding, structural alteration of the DNA-unbound vitamin D receptor triggers transcriptional repression. Given this, the mechanisms behind vitamin D-induced transcriptional repression are probably more complex than those of vitamin D-induced transactivation.

Potentiating effects of nonactive/active vitamin D analogues and ketoconazole in parathyroid cells

BACKGROUND AND OBJECTIVE

1,25-dihydroxyvitamin D(3)[1alpha,25(OH)(2)D(3), calcitriol], and its less calcaemic synthetic analogues have therapeutic potential in several diseases, including hyperparathyroidism (HPT). We have suggested that non-1alpha-hydroxylated (nonactive) vitamin D analogues may present an alternative in tumour cells expressing 25-hydroxyvitamin D(3) 1alpha-hydroxylase (1alpha-hydroxylase). The aim of this study was to investigate biological effects of a non-1alpha-hydroxylated vitamin D analogue in normal and tumour parathyroid cells.

PATIENTS AND METHODS

Effects of vitamin D analogues and ketoconazole on parathyroid hormone (PTH) secretion (radioimmunoassay) and PTH mRNA expression (reverse transcription-polymerase chain reaction) were studied in primary bovine parathyroid cells. Proliferation of tumour cells isolated from HPT patients was determined by thymidine incorporation.

RESULTS

EB1285, non-1alpha-hydroxylated precursor of the vitamin D analogue EB1089, suppressed PTH secretion and PTH mRNA level as well as increased expression of 25-hydroxyvitamin D(3)-24-hydroxylase (24-hydroxylase) in bovine parathyroid cells. EB1285 also inhibited cell proliferation of parathyroid tumour cells from primary (pHPT) and secondary HPT (sHPT) patients. Combined treatment with the cytochrome P450-dependent enzyme inhibitor ketoconazole and EB1285 or with active vitamin D compounds potentiated the suppressive effect on PTH secretion from bovine parathyroid cells. Ketaconazole alone displayed PTH suppression and increased 24-hydroxylase expression.

CONCLUSION

The results support the idea that a non-1alpha-hydroxylated vitamin D analogue may elicit vitamin D receptor (VDR) effects in 1alpha-hydroxylase expressing parathyroid tumour cells. Further studies are warranted to elucidate whether precursor vitamin D analogues as well as inhibitors of 24-hydroxylase present therapeutic alternatives in patients suffering from HPT.

Activated β-catenin in the novel human parathyroid tumor cell line sHPT-1

Misregulation of the Wnt/beta-catenin signalling pathway is involved in the development and progression of many cancers. Recently, we presented evidence for aberrant accumulation of non-phosphorylated (stabilized) beta-catenin in benign parathyroid tumors from patients with primary hyperparathyroidism (pHPT) or HPT secondary to uremia (sHPT). Here we have used a human parathyroid hormone (PTH)-producing cell line (sHPT-1), established from a hyperplastic parathyroid gland removed at operation of a patient with sHPT, to further investigate the potential importance of beta-catenin in parathyroid tumorigenesis. Our studies demonstrate that efficient and specific knockdown of beta-catenin by small interfering RNA (siRNA) markedly decreased endogenous beta-catenin transcriptional activity as well as expression of the Wnt/beta-catenin target genes cyclin D1 and c-myc, known to be overexpressed in a substantial fraction of parathyroid tumors. Furthermore, siRNA to beta-catenin inhibited cellular growth and induced cell death. Growth and survival of the parathyroid tumor cells are thus dependent on maintained expression level of beta-catenin. The Wnt/beta-catenin signalling pathway, and beta-catenin in particular, presents a potential therapeutic target for HPT.

Accumulation of nonphosphorylated beta-catenin and c-myc in primary and uremic secondary hyperparathyroid tumors

CONTEXT

Primary hyperparathyroidism (pHPT) resulting from parathyroid tumors is a common endocrine disorder with incompletely understood etiology, affecting about 1% of the adult population, with an even higher prevalence for elderly individuals. In renal failure, secondary hyperparathyroidism (sHPT) occurs with multiple tumor development as a result of calcium and vitamin D regulatory disturbance.

OBJECTIVE

Aberrant Wnt/beta-catenin signaling with accumulation of beta-catenin in the cytoplasm/nucleus is involved in the development of a variety of neoplasms. The aim of this study was to evaluate whether the Wnt/beta-catenin signaling pathway is activated in parathyroid adenomas of pHPT and in hyperplastic glands from uremic patients with sHPT.

DESIGN

Immunohistochemistry, Western blotting, real-time quantitative RT-PCR, and DNA sequencing were performed.

RESULTS

beta-Catenin was accumulated in all analyzed parathyroid tumors (n = 47) from patients with pHPT and from patients with HPT secondary to uremia. The accumulation included nonphosphorylated, stabilized (transcriptionally active) beta-catenin. The overexpression was not related to increased beta-catenin mRNA levels. A protein-stabilizing mutation in exon 3 of beta-catenin (S37A) was detected in three of 20 pHPT tumors (15%). No mutation was detected in secondary hyperplastic glands (n = 20), and no evidence for truncated adenomatosis polyposis coli proteins was found in adenomas and secondary hyperplastic glands. Mutations in other Wnt signaling components leading to beta-catenin accumulation, other than in beta-catenin itself, are therefore anticipated. The beta-catenin target gene c-myc was overexpressed in a substantial fraction of the parathyroid tumors.

CONCLUSION

Our results strongly suggest that modifications in the Wnt/beta-catenin signaling pathway may be involved in the development of hyperparathyroidism.