Genes up- or down-regulated by high calcium medium in parathyroid tissue explants from patients with primary hyperparathyroidism

Computational drug repurposing for primary hyperparathyroidism

In hyperparathyroidism (hyperPTH), excessive amounts of PTH are secreted, interfering with calcium regulation in the body. Several drugs can control the disease's side effects, but none of them is an alternative treatment to surgery. Therefore, new drug candidates are necessary. In this study, three computationally repositioned drugs, DG 041, IMD 0354, and cucurbitacin I, are evaluated in an in vitro model of hyperPTH. First, we integrated publicly available transcriptomics datasets to propose drug candidates. Using 3D spheroids derived from a single primary hyperPTH patient, we assessed their in vitro efficacy. None of the proposed drugs affected the viability of healthy cell control (HEK293) or overactive parathyroid cells at the level of toxicity. This behavior was attributed to the non-cancerous nature of the parathyroid cells, establishing the hyperPTH disease model. Cucurbitacin I and IMD 0354 exhibited a slight inverse relationship between increased drug concentrations and cell viability, whereas DG 041 increased viability. Based on these results, further studies are needed on the mechanism of action of the repurposed drugs, including determining the effects of these drugs on cellular PTH synthesis and secretion and on the metabolic pathways that regulate PTH secretion.

Assessment of Clinical Utility of Assaying FGF-23, Klotho Protein, Osteocalcin, NTX, and Sclerostin in Patients with Primary Hyperparathyroidism

The purpose of this study was to assess the clinical usefulness of assaying the fibroblast growth factor (FGF-23), Klotho, osteocalcin, N-terminal telopeptide of type I collagen (NTX), and sclerostin levels in patients with primary hyperparathyroidism (PHPT) as markers of bone damage as well as for surgical treatment success. Seventeen patients with hypercalcemic PHPT and normal kidney function were studied. In all patients, PTH (parathormone), serum calcium, and creatinine were performed before and six months after parathyroidectomy (PTX). The studied group included patients whose PTH and calcium concentrations normalized post-operatively and with confirmed histopathological diagnosis. The control group consisted of nine age-matched healthy volunteers. The PHPT patients had elevated concentrations of FGF-23, osteocalcin, and NTX and reduced levels of sclerostin, as compared to the control group. After PTX, osteocalcin, NTX, and sclerostin levels normalized. The plasma values of FGF-23 decreased significantly, but remained higher than in healthy subjects. Serum Klotho protein levels did not differ significantly in the two groups. These results suggest that osteocalcin and NTX may potentially be considered as markers of PHPT progression. Additionally, serum normalization of osteocalcin, NTX, and sclerostin might be considered as indicators of PTX success. On the other hand, FGF-23 can represent a parameter reflecting the degree of calcium–phosphate imbalance in PHPT patients, but its usefulness in monitoring the effects of PTX requires further research. The clinical utility of assaying Klotho in PHPT remains to be confirmed.

Tissue expression and source of circulating αKlotho

αKlotho (Klotho), a type I transmembrane protein and a coreceptor for Fibroblast Growth Factor-23, was initially thought to be expressed only in a limited number of tissues, most importantly the kidney, parathyroid gland and choroid plexus. Emerging data may suggest a more ubiquitous Klotho expression pattern which has prompted reevaluation of the restricted Klotho paradigm. Herein we systematically review the evidence for Klotho expression in various tissues and cell types in humans and other mammals, and discuss potential reasons behind existing conflicting data. Based on current literature and tissue expression atlases, we propose a classification of tissues into high, intermediate and low/absent Klotho expression. The functional relevance of Klotho in organs with low expression levels remain uncertain and there is currently limited data on a role for membrane-bound Klotho outside the kidney. Finally, we review the evidence for the tissue source of soluble Klotho, and conclude that the kidney is likely to be the principal source of circulating Klotho in physiology.

Fluoride Modulates Parathyroid Hormone Secretion in vivo and in vitro

The study objective was to investigate the effects of fluoride on intact parathyroid hormone (iPTH) secretion. Thyro-parathyroid complexes (TPC) from C3H (n = 18) and B6 (n = 18) mice were cultured in Ca²⁺-optimized medium. TPC were treated with 0, 250, or 500 µM NaF for 24 h and secreted iPTH assayed by ELISA. C3H (n = 78) and B6 (n = 78) mice were gavaged once with distilled or fluoride (0.001 mg [F⁻]/g of body weight) water. At serial time points (0.5-96 h) serum iPTH, fluoride, total calcium, phosphorus, and magnesium levels were determined. Expression of genes involved in mineral regulation via the bone-parathyroid-kidney (BPK) axis, such as parathyroid hormone (Pth), calcium-sensing receptor (Casr), vitamin D receptor (Vdr), parathyroid hormone-like hormone (Pthlh), fibroblast growth factor 23 (Fgf23), α-Klotho (αKlotho), fibroblast growth factor receptor 1c (Fgf1rc), tumor necrosis factor 11 (Tnfs11), parathyroid hormone receptor 1 (Pth1r), solute carrier family 34 member 1 (Slc34a1), solute carrier 9 member 3 regulator 1 (Slc9a3r1), chloride channel 5 (Clcn5), and PDZ domain-containing 1 (Pdzk1), was determined in TPC, humeri, and kidneys at 24 h. An in vitro decrease in iPTH was seen in C3H and B6 TPC at 500 µM (p < 0.001). In vivo levels of serum fluoride peaked at 0.5 h in both C3H (p = 0.002) and B6 (p = 0.01). In C3H, iPTH decreased at 24 h (p < 0.0001), returning to baseline at 48 h. In B6, iPTH increased at 12 h (p < 0.001), returning to baseline at 24 h. Serum total calcium, phosphorus, and magnesium levels did not change significantly. Pth, Casr,αKlotho,Fgf1rc,Vdr, and Pthlh were significantly upregulated in C3H TPC compared to B6. In conclusion, the effects of fluoride on TPC in vitro were equivalent between the 2 mouse strains. However, fluoride demonstrated an early strain-dependent effect on iPTH secretion in vivo. Both strains demonstrated differences in the expression of genes involved in the BPK axis, suggesting a possible role in the physiologic handling of fluoride.

Bone development and mineral homeostasis in the fetus and neonate: roles of the calciotropic and phosphotropic hormones

Mineral and bone metabolism are regulated differently in utero compared with the adult. The fetal kidneys, intestines, and skeleton are not dominant sources of mineral supply for the fetus. Instead, the placenta meets the fetal need for mineral by actively transporting calcium, phosphorus, and magnesium from the maternal circulation. These minerals are maintained in the fetal circulation at higher concentrations than in the mother and normal adult, and such high levels appear necessary for the developing skeleton to accrete a normal amount of mineral by term. Parathyroid hormone (PTH) and calcitriol circulate at low concentrations in the fetal circulation. Fetal bone development and the regulation of serum minerals are critically dependent on PTH and PTH-related protein, but not vitamin D/calcitriol, fibroblast growth factor-23, calcitonin, or the sex steroids. After birth, the serum calcium falls and phosphorus rises before gradually reaching adult values over the subsequent 24-48 h. The intestines are the main source of mineral for the neonate, while the kidneys reabsorb mineral, and bone turnover contributes mineral to the circulation. This switch in the regulation of mineral homeostasis is triggered by loss of the placenta and a postnatal fall in serum calcium, and is followed in sequence by a rise in PTH and then an increase in calcitriol. Intestinal calcium absorption is initially a passive process facilitated by lactose, but later becomes active and calcitriol-dependent. However, calcitriol's role can be bypassed by increasing the calcium content of the diet, or by parenteral administration of calcium.

Involvement of α-klotho, fibroblast growth factor-, vitamin-D- and calcium-sensing receptor in 53 patients with primary hyperparathyroidism

The presentation of patients with primary hyperparathyroidism is often atypical and ranges from normocalcemic, primary hyperparathyroidism to severe, symptomatic hypercalcemia. G-protein-coupled, calcium-sensing receptor (CaSR), vitamin D receptor (VDR), and fibroblast growth factor receptor (FGFR)/klotho complexes seem to be involved in the development of pHPT. Parathyroid glands from 53 patients with pHPT and normal parathyroid tissue from 7 patients were obtained during parathyroidectomy. Conventional detailed morphological and immunohistochemical analyses of parathyroid glands were performed after dividing each slide in a 3 × 3 array. From morphology, the number of lipocytes was significantly lower in parathyroid tissue glands in the pHPT group (p < 0.001). Protein expressions of klotho, CaSR, and VDR were significantly reduced in the pHPT compared with the control group (p = 0.004, p = 0.007, p < 0.001). No differences were seen between the two groups (p = 0.35) regarding expression of FGFR. Correlations between expression showed significant positively correlations between klotho and CaSR and FGFR and VDR. No correlations between klotho expression and serum calcium levels could be detected (R = -0.13, p = 0.66), but there were positive correlations between expressions of CaSR/serum phosphate and klotho/serum phosphate. Impaired protein expression of CaSR and VDR seem to be involved in the development of pHPT. The role of the FGFR/klotho-axis remains still unclear. Correlations between protein expression of CaSR and serum phosphate and klotho and serum phosphate levels could be detected. Whether these findings give new insights into the pathogenesis of the disease is yet unknown and has to be elucidated.

Primary hyperparathyroidism influences the expression of inflammatory and metabolic genes in adipose tissue

Background

Primary hyperparathyroidism (PHPT) is characterised by increased production of parathyroid hormone (PTH) resulting in elevated serum calcium levels. The influence on bone metabolism with altered bone resorption is the most studied clinical condition in PHPT. In addition to this, patients with PHPT are at increased risk of non-skeletal diseases, such as impaired insulin sensitivity, arterial hypertension and increased risk of death by cardiovascular diseases (CVD), possibly mediated by a chronic low-grade inflammation. The aim of this study was to investigate whether adipose tissue reflects the low-grade inflammation observed in PHPT patients.

Methodology/Principal Findings

Subcutaneous fat tissue from the neck was sampled from 16 non-obese patients with PHPT and from 16 patients operated for benign thyroid diseases, serving as weight-matched controls. RNA was extracted and global gene expression was analysed with Illumina BeadArray Technology. We found 608 differentially expressed genes (q-value<0.05), of which 347 were up-regulated and 261 were down-regulated. Gene ontology analysis showed that PHPT patients expressed increased levels of genes involved in immunity and defense (e.g. matrix metallopeptidase 9, S100 calcium binding protein A8 and A9, CD14, folate receptor 2), and reduced levels of genes involved in metabolic processes. Analysis of transcription factor binding sites present in the differentially expressed genes corroborated the up-regulation of inflammatory processes.

Conclusions/Significance

Our findings demonstrate that PHPT strongly influences gene regulation in fat tissue, which may result in altered adipose tissue function and release of pathogenic factors that increase the risk of CVD.

A proteomic approach to study parathyroid glands

Parathyroid tumours are heterogeneous and in some cases the diagnosis may be difficult using histological features. In this study we used a two-dimensional electrophoresis (2D)/mass spectrometry (MS)-based approach to examine the global changes of parathyroid adenoma tissues protein profile compared to the parathyroid normal tissues. Validation of protein expression was performed by immunoblotting using specific antibodies. Ingenuity software was used to identify the biological processes to which these proteins belong and to construct a potential network. A total of 30 proteins were found to be differentially expressed, of which 22 resulted in being over-expressed. Proteins identified by 2D/MS/MS proteomics were classified into functional categories and a major change (≥ 2-fold) in terms of expression was found in proteins involved in response to biotic stimuli, cell organization and signal transduction. After Ingenuity analysis, 14-3-3 ζ/δ appears to be a key protein in the network of parathyroid adenoma, where it is linked to other proteins such as annexin A2, B box and SPRY domain-containing protein (BSPRY), p53 and epidermal growth factor receptor (EGFR). Our results suggest that the proteomic approach was able to differentiate the protein profiles of normal parathyroid and parathyroid adenoma and identify a panel of proteins which are differentially expressed. The functional role of these proteins in the network of intracellular pathways is discussed.