Expression of PRAD1/cyclin D1, retinoblastoma gene products, and Ki67 in parathyroid hyperplasia caused by chronic renal failure versus primary adenoma

Specific genetic aberrations of parathyroid in Chinese patients with tertiary hyperparathyroidism using whole-exome sequencing

Background

Tertiary hyperparathyroidism (THPT) is a peculiar subtype of hyperparathyroidism that usually develops from chronic kidney disease (CKD) and persists even after kidney transplantation. Unlike its precursor, secondary hyperparathyroidism (SHPT), THPT is characterized by uncontrolled high levels of calcium in the blood, which suggests the monoclonal or oligoclonal proliferation of parathyroid cells. However, the molecular abnormalities leading to THPT have not yet been fully understood.

Methods

In this study, we analyzed DNA samples from hyperplastic parathyroid and corresponding blood cells of 11 patients with THPT using whole-exome sequencing (WES). We identified somatic single nucleotide variants (SNV) and insertions or deletions variants (INDEL) and performed driver mutation analysis, KEGG pathway, and GO functional enrichment analysis. To confirm the impact of selected driver mutated genes, we also tested their expression level in these samples using qRT-PCR.

Results

Following quality control and mutation filtering, we identified 17,401 mutations, comprising 6690 missense variants, 3078 frameshift variants, 2005 stop-gained variants, and 1630 synonymous variants. Copy number variants (CNV) analysis showed that chromosome 22 copy number deletion was frequently observed in 6 samples. Driver mutation analysis identified 179 statistically significant mutated genes, including recurrent missense mutations on TBX20, ATAD5, ZNF669, and NOX3 genes in 3 different patients. KEGG pathway analysis revealed two enriched pathways: non-homologous end-joining and cell cycle, with a sole gene, PRKDC, involved. GO analysis demonstrated significant enrichment of various cellular components and cytobiological processes associated with four genes, including GO items of positive regulation of developmental growth, protein ubiquitination, and positive regulation of the apoptotic process. Compared to blood samples, THPT samples exhibited lower expression levels of PRKDC, TBX20, ATAD5, and NOX3 genes. THPT samples with exon mutations had relatively lower expression levels of PRKDC, TBX20, and NOX3 genes compared to those without mutations, although the difference was not statistically significant.

Conclusion

This study provides a comprehensive landscape of the genetic characteristics of hyperplastic parathyroids in THPT, highlighting the involvement of multiple genes and pathways in the development and progression of this disease. The dominant mutations identified in our study depicted new insights into the pathogenesis and molecular characteristics of THPT.

Molecular and Clinical Spectrum of Primary Hyperparathyroidism

Recent data suggest an increase in the overall incidence of parathyroid disorders, with primary hyperparathyroidism (PHPT) being the most prevalent parathyroid disorder. PHPT is associated with morbidities (fractures, kidney stones, chronic kidney disease) and increased risk of death. The symptoms of PHPT can be nonspecific, potentially delaying the diagnosis. Approximately 15% of patients with PHPT have an underlying heritable form of PHPT that may be associated with extraparathyroidal manifestations, requiring active surveillance for these manifestations as seen in multiple endocrine neoplasia type 1 and 2A. Genetic testing for heritable forms should be offered to patients with multiglandular disease, recurrent PHPT, young onset PHPT (age ≤40 years), and those with a family history of parathyroid tumors. However, the underlying genetic cause for the majority of patients with heritable forms of PHPT remains unknown. Distinction between sporadic and heritable forms of PHPT is useful in surgical planning for parathyroidectomy and has implications for the family. The genes currently known to be associated with heritable forms of PHPT account for approximately half of sporadic parathyroid tumors. But the genetic cause in approximately half of the sporadic parathyroid tumors remains unknown. Furthermore, there is no systemic therapy for parathyroid carcinoma, a rare but potentially fatal cause of PHPT. Improved understanding of the molecular characteristics of parathyroid tumors will allow us to identify biomarkers for diagnosis and novel targets for therapy.

Advances and Updates in Parathyroid Pathology

Hyperparathyroidism is a common endocrine disorder characterized by elevated levels of parathyroid hormone and hypercalcemia and is divided into 3 types: primary, secondary, and tertiary. Distinction between these types is accomplished by correlation of clinical, radiologic, and laboratory findings with pathologic features. Primary hyperparathyroidism occurs sporadically in 85% of cases with the remaining cases associated with multiple familial syndromes. The pathologic manifestations of primary hyperparathyroidism include parathyroid adenoma, parathyroid hyperplasia, and parathyroid carcinoma. Recent advances in the understanding of the pathogenesis of parathyroid disease has helped to refine the diagnosis and classification of parathyroid lesions. The identification of multiple clonal proliferations in traditional multiglandular parathyroid hyperplasia has led to the adoption by the World Health Organization (WHO) of the alternate term of primary hyperparathyroidism-related multiglandular parathyroid disease. Additional nomenclature changes include the adoption of the term atypical parathyroid tumor in lieu of atypical parathyroid adenoma to reflect the uncertain malignant potential of these neoplasms. Clinical and morphologic features characteristic of familial disease have been described that can help the practicing pathologist identify underlying familial disease and provide appropriate management. Use of ancillary immunohistochemistry and molecular studies can be helpful in classifying parathyroid neoplasms. Parafibromin has proven useful as a diagnostic and prognostic marker in atypical parathyroid tumors and parathyroid carcinomas. This review provides an update on the diagnosis and classification of parathyroid lesions considering the recent advances in the understanding of the molecular and clinical features of parathyroid disease and highlights the use of ancillary studies (immunohistochemical, and molecular) to refine the diagnosis of parathyroid lesions.

Renal hyperparathyroidism

The number of the patients with chronic kidney disease is now increasing in the world. The pathophysiology of renal hyperparathyroidism is closely associated with Klotho-FGF-endocrine axes, which must be solved definitively as early as possible. It was revealed that the expression of fgf23 is activated by calciprotein particles, which induces vascular ossification. And it is well known that phosphorus overload directly increases parathyroid hormone and hyperparathyroid bone disease develops in those subjects. On the other hand, low turnover bone disease is often recently. Both the patients with chronic kidney disease suffering from hyperparathyroid bone disease or low turnover bone disease are associated with increased fracture risk. Micropetrosis may be one of the causes of increased fracture risk in the subjects with low turnover bone disease. In this chapter, we now describe the diagnosis, pathophysiology and treatments of renal hyperparathyroidism.

Histone Modification on Parathyroid Tumors: A Review of Epigenetics

Parathyroid tumors are very prevalent conditions among endocrine tumors, being the second most common behind thyroid tumors. Secondary hyperplasia can occur beyond benign and malignant neoplasia in parathyroid glands. Adenomas are the leading cause of hyperparathyroidism, while carcinomas represent less than 1% of the cases. Tumor suppressor gene mutations such as MEN1 and CDC73 were demonstrated to be involved in tumor development in both familiar and sporadic types; however, the epigenetic features of the parathyroid tumors are still a little-explored subject. We present a review of epigenetic mechanisms related to parathyroid tumors, emphasizing advances in histone modification and its perspective of becoming a promising area in parathyroid tumor research.

Excessive proliferation and apoptosis of parathyroid cells contribute to primary hyperparathyroidism in rabbit model

To explore the molecular pathogenesis of primary hyperparathyroidism (PHPT), we investigated the proliferation and apoptosis of parathyroid cells in a rabbit model of diet-induced PHPT. A total of 120 adult Chinese rabbits were randomly divided into normal diet (Ca:P, 1:0.7) group (control group) or a high-phosphate diet (Ca:P, 1:7) group (experimental group). The thyroid and parathyroid complexes were harvested for 1-month interval from month 1 to month 6. The expression of proliferation markers, including proliferating cell nuclear antigen (PCNA) and cyclin-D1, and B cell lymphoma-2 (Bcl-2), were evaluated by immunohistochemistry in thyroid and parathyroid tissues. Apoptosis was quantified by DNA-fragment terminal labeling. Our results demonstrated that parathyroid cells in the experimental group started proliferating from the end of the 2nd month, the expression of PCNA, Bcl-2, and cyclin-D1 were significantly higher in the PHPT group than those of the control group (p<0.05). Furthermore, the apoptosis index (AI) was positively correlated with the glandular cell count and expression of PCNA in the 6th month in the PHPT group. Overall, our results suggested that excessive proliferation and apoptosis of parathyroid cells may contribute to the pathogenesis of PHPT through PCNA-related, Bcl-2-related, and cyclin-D1-related pathways.

Molecular Mechanisms of Parathyroid Disorders in Chronic Kidney Disease

Secondary hyperparathyroidism (SHP) is a common complication of chronic kidney disease (CKD) that induces morbidity and mortality in patients. How CKD stimulates the parathyroid to increase parathyroid hormone (PTH) secretion, gene expression and cell proliferation remains an open question. In experimental SHP, the increased PTH gene expression is post-transcriptional and mediated by PTH mRNA–protein interactions that promote PTH mRNA stability. These interactions are orchestrated by the isomerase Pin1. Pin1 participates in conformational change-based regulation of target proteins, including mRNA-binding proteins. In SHP, Pin1 isomerase activity is decreased, and thus, the Pin1 target and PTH mRNA destabilizing protein KSRP fails to bind PTH mRNA, increasing PTH mRNA stability and levels. An additional level of post-transcriptional regulation is mediated by microRNA (miRNA). Mice with parathyroid-specific knockout of Dicer, which facilitates the final step in miRNA maturation, lack parathyroid miRNAs but have normal PTH and calcium levels. Surprisingly, these mice fail to increase serum PTH in response to hypocalcemia or uremia, indicating a role for miRNAs in parathyroid stimulation. SHP often leads to parathyroid hyperplasia. Reduced expressions of parathyroid regulating receptors, activation of transforming growth factor α-epidermal growth factor receptor, cyclooxygenase 2-prostaglandin E2 and mTOR signaling all contribute to the enhanced parathyroid cell proliferation. Inhibition of mTOR by rapamycin prevents and corrects the increased parathyroid cell proliferation of SHP. This review summarizes the current knowledge on the mechanisms that stimulate the parathyroid cell at multiple levels in SHP.

Germline Mutations Related to Primary Hyperparathyroidism Identified by Next-Generation Sequencing

Primary hyperparathyroidism (PHPT) is characterized by overproduction of parathyroid hormone and subsequent hypercalcemia. Approximately 10% of PHPT cases are hereditary, and several genes, such as MEN1, RET, CASR, and CDC73, are responsible for the familial forms of PHPT. However, other genetic mutations involved in the etiology of PHPT are largely unknown. In this study, we identified genetic variants that might be responsible for PHPT, including familial PHPT, benign sporadic PHPT, and sporadic parathyroid cancer, using next-generation sequencing (NGS). A total of 107 patients with PHPT who underwent NGS from 2017 to 2021 at Severance Hospital were enrolled. We reviewed the pathogenic variants, likely pathogenic variants, and variants of uncertain significance (VUS) according to the American College of Medical Genetics and Genomics and the Association for Molecular Pathology criteria. Of the 107 patients (mean age: 47.6 ± 16.1 years, women 73.8%), 12 patients were diagnosed with familial PHPT, 13 with parathyroid cancer, and 82 with benign sporadic PHPT. Using NGS, we identified three pathogenic variants in two genes (CDC73 and MEN1), 10 likely pathogenic variants in six genes (CASR, CDC73, LRP5, MEN1, SDHA, and VHL), and 39 non-synonymous VUS variants that could be related to parathyroid disease. Interestingly, we identified one GCM2 variant (c.1162A>G [p.Lys388Glu]) and five APC variants that were previously reported in familial isolated hyperparathyroidism, benign sporadic PHPT, and parathyroid cancer. We also analyzed the characteristics of subjects with positive genetic test results (pathogenic or likely pathogenic variants), and 76.9% of them had at least one of the following features: 1) age < 40 years, 2) family history of PHPT, 3) multiglandular PHPT, or 4) recurrent PHPT. In this study, we analyzed the NGS data of patients with PHPT and observed variants that could possibly be related to PHPT pathogenesis. NGS screening for selected patients with PHPT might help in the diagnosis and management of the disease.

Comparative analysis of clinicopathologic features between adenoma and hyperplasia in surgically treated patients for hyperparathyroidism: A retrospective study

BACKGROUND

Hyperparathyroidism (HPT) is a common endocrine disorder resulting from overproduction of parathyroid hormone (PTH). Usually HPT is caused by parathyroid adenoma (PA) or parathyroid hyperplasia (PH). Our aim is to assess clinicopathologic features associated with PA and PH in patients with HPT.

METHODS

We retrospectively collected 29 cases of HPT recorded at the Department of Pathology of Hassan II University Hospital of Fes, Morocco, from 2013 to 2016.

RESULTS

The mean age was 52.14 ± 15.7 years (range of 22-76 years), 13 patients (44.8%) had primary HPT, 16 (55.2%) had secondary HPT. The largest size of the resected parathyroid specimens ranged from 1 to 3.6 cm (mean of 2.26 ± 0.66 cm). Seventeen patients (58.6%) had PA, the remaining cases were diagnosed as PH. There were no significant statistical differences between PA and PH in age, sex, clinical presentation, preoperative serum PTH, or in parathyroid gland size (P > 0.05). However compared to PH, PA is more often a single-gland disease, found in primary HPT with higher preoperative calcium level (P ˂ 0.05).

CONCLUSIONS

In patients surgically treated for HPT, PA is associated with some distinctive clinicopathologic features. These findings could be helpful to pathologists and clinicians for appropriate clinicopathologic management.

Local NF-κB Activation Promotes Parathyroid Hormone Synthesis and Secretion in Uremic Patients

Secondary hyperparathyroidism (SHPT) in uremic patients is characterized by parathyroid gland (PTG) hyperplasia and parathyroid hormone (PTH) elevation. Previously, we demonstrated that NF-κB activation contributed to parathyroid cell proliferation in rats with chronic kidney disease. Although vitamin D inhibits inflammation and ameliorates SHPT, the contribution of vitamin D deficiency to SHPT via local NF-κB activation remains to be clarified. PTGs collected from 10 uremic patients with advanced SHPT were used to test the expressions of vitamin D receptor (VDR), NF-κB, and proliferating cell nuclear antigen (PCNA). Freshly excised PTG tissues were incubated for 24 hours in vitro with VDR activator (VDRA) calcitriol or NF-κB inhibitor pyrrolidine thiocarbamate (PDTC). Chromatin immunoprecipitation (ChIP) and luciferase reporter assays were performed to investigate the regulation of PTH transcription by NF-κB. We found higher levels of activated NF-κB and lower expression of VDR in nodular hyperplastic PTGs than in diffuse hyperplasia. In cultured PTG tissues, treatment with VDRA or PDTC inhibited NF-κB activation and PCNA expression, and downregulated preproPTH mRNA and intact PTH levels. ChIP assays demonstrated the presence of NF-κB binding sites in PTH promoter. Furthermore, in luciferase reporter assays, addition of exogenous p65 significantly increased PTH luciferase activity by 2.4-fold (P < 0.01), while mutation of NF-κB binding site at position -908 of the PTH promoter suppressed p65-induced PTH reporter activity (P < 0.01). In summary, local NF-κB activation contributes to SHPT and mediates the transcriptional activation of PTH directly in uremic patients. Vitamin D deficiency may be involved in SHPT via the activation of NF-κB pathway.

Molecular analysis of cyclin D1 modulators PRKN and FBX4 as candidate tumor suppressors in sporadic parathyroid adenomas

OBJECTIVE

Primary hyperparathyroidism is most often caused by a sporadic single-gland parathyroid adenoma (PTA), a tumor type for which cyclin D1 is the only known and experimentally validated oncoprotein. However, the molecular origins of its frequent overexpression have remained mostly elusive. In this study, we explored a potential tumorigenic mechanism that could increase cyclin D1 stability through a defect in molecules responsible for its degradation.

METHODS

We examined two tumor suppressor genes known to modulate cyclin D1 ubiquitination, PRKN and FBXO4 (FBX4), for evidence of classic two-hit tumor suppressor inactivation within a cohort of 82 PTA cases. We examined the cohort for intragenic inactivating and splice site mutations by Sanger sequencing and for locus-associated loss of heterozygosity (LOH) by microsatellite analysis.

RESULTS

We identified no evidence of bi-allelic tumor suppressor inactivation of PRKN or FBXO4 via inactivating mutation or splice site perturbation, neither in combination with nor independent of LOH. Among the 82 cases, we encountered previously documented benign single nucleotide polymorphisms (SNPs) in 35 tumors at frequencies similar to those reported in the germlines of the general population. Eight cases exhibited intragenic LOH at the PRKN locus, in some cases extending to cover at least an additional 1.7 Mb of chromosome 6q25-26. FBXO4 was not affected by LOH.

CONCLUSION

The absence of evidence for specific bi-allelic inactivation in PRKN and FBXO4 in this sizeable cohort suggests that these genes only rarely, if ever, serve as classic driver tumor suppressors responsible for the growth of PTAs.

CDK4/6 Dependence of Cyclin D1-Driven Parathyroid Neoplasia in Transgenic Mice

The protein product of the cyclin D1 oncogene functions by activating partner cyclin-dependent kinases (cdk)4 or cdk6 to phosphorylate, thereby inactivating, the retinoblastoma protein pRB. Nonclassical, cdk-independent, functions of cyclin D1 have been described but their role in cyclin D1-driven neoplasia, with attendant implications for recently approved cdk4/6 chemotherapeutic inhibitors, requires further examination. We investigated whether cyclin D1's role in parathyroid tumorigenesis in vivo is effected primarily through kinase-dependent or kinase-independent mechanisms. Using a mouse model of cyclin D1-driven parathyroid tumorigenesis (PTH-D1), we generated new transgenic lines harboring a mutant cyclin D1 (KE) that is unable to activate its partner kinases. While this kinase-dead KE mutant effectively drove mammary tumorigenesis in an analogous model, parathyroid-overexpressed cyclin D1 KE mice did not develop the characteristic biochemical hyperparathyroidism or parathyroid hypercellularity of PTH-D1 mice. These results strongly suggest that in parathyroid cells, cyclin D1 drives tumorigenesis predominantly through cdk-dependent mechanisms, in marked contrast with the cdk-independence of cyclin D1-driven mouse mammary cancer. These findings highlight crucial tissue-specific mechanistic differences in cyclin D1-driven tumorigenesis, suggest that parathyroid/endocrine cells may be more tumorigenically vulnerable to acquired genetic perturbations in cdk-mediated proliferative control than other tissues, and carry important considerations for therapeutic intervention.

Clinical and Molecular Genetics of Primary Hyperparathyroidism

Calcium homeostasis is maintained by the actions of the parathyroid glands, which release parathyroid hormone into the systemic circulation as necessary to maintain the serum calcium concentration within a tight physiologic range. Excessive secretion of parathyroid hormone from one or more neoplastic parathyroid glands, however, causes the metabolic disease primary hyperparathyroidism (HPT) typically associated with hypercalcemia. Although the majority of cases of HPT are sporadic, it can present in the context of a familial syndrome. Mutations in the tumor suppressor genes discovered by the study of such families are now recognized to be pathogenic for many sporadic parathyroid tumors. Inherited and somatic mutations of proto-oncogenes causing parathyroid neoplasia are also known. Future investigation of somatic changes in parathyroid tumor DNA and the study of kindreds with HPT yet lacking germline mutation in the set of genes known to predispose to HPT represent two avenues likely to unmask additional novel genes relevant to parathyroid neoplasia.

Parathyroid Cell Proliferation in Secondary Hyperparathyroidism of Chronic Kidney Disease

Secondary hyperparathyroidism (SHP) is a common complication of chronic kidney disease (CKD) that correlates with morbidity and mortality in uremic patients. It is characterized by high serum parathyroid hormone (PTH) levels and impaired bone and mineral metabolism. The main mechanisms underlying SHP are increased PTH biosynthesis and secretion as well as increased glandular mass. The mechanisms leading to parathyroid cell proliferation in SHP are not fully understood. Reduced expressions of the receptors for calcium and vitamin D contribute to the disinhibition of parathyroid cell proliferation. Activation of transforming growth factor-α-epidermal growth factor receptor (TGF-α-EGFR), nuclear factor kappa B (NF-kB), and cyclooxygenase 2- prostaglandin E2 (Cox2-PGE2) signaling all correlate with parathyroid cell proliferation, underlining their roles in the development of SHP. In addition, the mammalian target of rapamycin (mTOR) pathway is activated in parathyroid glands of experimental SHP rats. Inhibition of mTOR by rapamycin prevents and corrects the increased parathyroid cell proliferation of SHP. Mice with parathyroid-specific deletion of all miRNAs have a muted increase in serum PTH and fail to increase parathyroid cell proliferation when challenged by CKD, suggesting that miRNA is also necessary for the development of SHP. This review summarizes the current knowledge on the mechanisms of parathyroid cell proliferation in SHP.

Prostaglandin E2 receptor EP2 mediates the effect of cyclooxygenase 2 on secondary parathyroid hyperplasia in end-stage renal disease

BACKGROUND

Secondary hyperparathyroidism (SHPT) in patients with end-stage renal disease (ESRD) is characterized by hyperplasia of the parathyroid glands (PTGs), while the underlying mechanism is not completely understood. Previously we demonstrated a relationship between cyclooxygenase 2 (COX2) overexpression and parathyroid hyperplasia and here we investigate the role of COX2 downstream metabolic product prostaglandin E2 (PGE2) and its receptor EP2 in the pathogenesis of SHPT.

METHODS

PTGs isolated from ESRD patients with advanced SHPT were used to test the expression of COX2-microsomal prostaglandin E synthase-1 (mPGES-1)-EP2 pathway. A diffuse proliferative section of the PTGs was used for tissue culture and treated with high phosphate (HPi) medium, COX2-PGE2-EP2 pathway inhibitors or agonists. EP2 short hairpin RNA (shRNA) lentivirus was locally applied to treat an SHPT rat model.

RESULTS

In PTGs isolated from ESRD patients, enhanced immunoactivities of COX2, mPGES-1 and EP2 were observed. In primary cultured PTG tissues, HPi induced intact parathyroid hormone (iPTH) secretion, proliferating cell nuclear antigen (PCNA) expression and COX2 activity, while COX2 and EP2 inhibitors attenuated hyperparathyroidism promoted by HPi. Furthermore, PGE2 or EP2 agonist (butaprost) directly stimulated hyperparathyroidism, whereas EP2 receptor antagonist or cyclic adenosine monophosphate inhibitor attenuated the hyperparathyroidism promoted by PGE2 or butaprost. EP2 shRNA treatment significantly reduced excessive expressions of EP2 and PCNA in the PTGs of nephrectomy rats fed an HPi diet, diminished the size of PTGs and downregulated serum iPTH levels.

CONCLUSIONS

The COX2 downstream PGE2 and its receptor EP2 may play an important role in HPi-induced parathyroid hyperplasia and may serve as a potential therapeutic target for SHPT in ESRD.

Deficiency in the secreted protein Semaphorin3d causes abnormal parathyroid development in mice

Primary hyperparathyroidism (PHPT) is a common endocrinopathy characterized by hypercalcemia and elevated levels of parathyroid hormone. The primary cause of PHPT is a benign overgrowth of parathyroid tissue causing excessive secretion of parathyroid hormone. However, the molecular etiology of PHPT is incompletely defined. Here, we demonstrate that semaphorin3d (Sema3d), a secreted glycoprotein, is expressed in the developing parathyroid gland in mice. We also observed that genetic deletion of Sema3d leads to parathyroid hyperplasia, causing PHPT. In vivo and in vitro experiments using histology, immunohistochemistry, biochemical, RT-qPCR, and immunoblotting assays revealed that Sema3d inhibits parathyroid cell proliferation by decreasing the epidermal growth factor receptor (EGFR)/Erb-B2 receptor tyrosine kinase (ERBB) signaling pathway. We further demonstrate that EGFR signaling is elevated in Sema3d ^-/- parathyroid glands and that pharmacological inhibition of EGFR signaling can partially rescue the parathyroid hyperplasia phenotype. We propose that because Sema3d is a secreted protein, it may be possible to use recombinant Sema3d or derived peptides to inhibit parathyroid cell proliferation causing hyperplasia and hyperparathyroidism. Collectively, these findings identify Sema3d as a negative regulator of parathyroid growth.

Whole-Exome Sequencing Identifies Novel Recurrent Somatic Mutations in Sporadic Parathyroid Adenomas

Primary hyperparathyroidism is commonly caused by excess production of parathyroid hormone from sporadic parathyroid adenomas. However, the genetic architecture of sporadic primary hyperparathyroidism remains largely uncharacterized, especially in the Chinese population. To identify genetic abnormalities that may be involved in the etiology of sporadic parathyroid adenomas and to determine the mutation frequency of previously identified genes in the Chinese population, we performed whole-exome sequencing of 22 blood-tumor pairs from sporadic parathyroid adenomas. The most important finding is the recurrently mutated gene, ASXL3, which has never been reported in parathyroid tumors before. Moreover, we identified two different somatic mutations in the CDC73 gene and one somatic mutation in the EZH2 gene. The Y54X mutation in the CDC73 gene was previously identified in parathyroid carcinomas, which proved that parathyroid adenomas and carcinomas might possess similar molecular signatures. No mutations in the MEN1 or CCND1 genes were observed in our study. Thus, our data provide insights into the genetic pathogenesis of sporadic parathyroid adenomas and are valuable for the development of diagnostic and therapeutic approaches for sporadic primary hyperparathyroidism.

Genetics of Hyperparathyroidism, Including Parathyroid Cancer

Primary hyperparathyroidism (HPT) is a metabolic disease caused by the excessive secretion of parathyroid hormone from 1 or more neoplastic parathyroid glands. HPT is largely sporadic, but it can be associated with a familial syndrome. The study of such families led to the discovery of tumor suppressor genes whose loss of function is now recognized to underlie the development of many sporadic parathyroid tumors. Heritable and acquired oncogenes causing parathyroid neoplasia are also known. Studies of somatic changes in parathyroid tumor DNA and investigation of kindreds with unexplained familial HPT promise to unmask more genes relevant to parathyroid neoplasia.

Clinical significance of parathyroid intervention on CKD-MBD management

Recently published ‘Guidelines for the management of secondary hyperparathyroidism in chronic dialysis patients’ by the Japanese Society for Dialysis Therapy advocate that percutaneous ethanol injection into enlarged glands, which has been considered as the only alternative to parathyroidectomy (PTx), should be indicated in patients with a single enlarged parathyroid gland (estimated volume >500 mm³, or estimated major axis >10 mm), and that PTx should be recommended in patients with multiple enlarged glands. Cinacalcet cannot achieve optimal control of chronic kidney disease–mineral bone disorder in all patients, and parathyroid intervention will be required in a considerable number of patients with refractory secondary hyperparathyroidism.

Reversed whole PTH/intact PTH ratio as an indicator of marked parathyroid enlargement: five case studies and a literature review

Parathyroid hormone (PTH) levels detected by intact PTH assays are generally higher than those detected by the whole PTH assay because the latter does not detect non-(1–84) PTH fragments, mainly PTH (7–84). Rare exceptions to this rule have been reported in patients with severe primary or secondary hyperparathyroidism and parathyroid carcinoma. Overproduction of an N-form of PTH other than PTH (1–84) has been observed in the sera of these patients. We report five additional cases with the reversed whole PTH/intact PTH ratio associated with severe hyperparathyroidism in haemodialysis patients. Three patients demonstrated enlargement of a single hypervascular gland, whereas the other two had undergone surgical parathyroidectomy and later showed recurrent hyperparathyroidism due to progressive autograft hyperplasia. In the case of a single enlarged gland, the pathological pattern and heterogeneous expression of parathyroid adenomatosis 1/cyclin D1 suggested it to be a single nodule of uraemic hyperparathyroidism rather than sporadic primary adenoma. These cases suggested that the reversed whole PTH/intact PTH ratio could be an indicator of marked parathyroid enlargement. Further studies are required to elucidate the clinical significance of the reversed whole PTH/intact PTH ratio in haemodialysis patients.

Parathyroid: The Pathology of Hyperparathyroidism

This review focuses on the pathologic entities associated with hyperparathyroidism in humans. A discussion of the lesions, their embryology, and pathologic features is included. Immunohistology, cytopathology, and a brief overview of molecular aspects of the lesion are included.

PTH-C1: a rat continuous cell line expressing the parathyroid phenotype

The lack of a continuous cell line of epithelial parathyroid cells able to produce parathyroid hormone (PTH) has hampered the studies on in vitro evaluation of the mechanisms involved in the control of parathyroid cell function and proliferation. The PT-r cell line was first established from rat parathyroid tissue in 1987, but these cells were known to express the parathyroid hormone-related peptide (Pthrp) gene, but not the Pth gene. In an attempt to subclone the PT-r cell line, a rat parathyroid cell strain was isolated and named PTH-C1. During 3 years, in culture, PTH-C1 cells maintained an epithelioid morphology, displaying a diploid chromosome number, a doubling time around 15 h during the exponential phase of growth, and parathyroid functional features. PTH-C1 cell line produces PTH and expresses the calcium sensing receptor (Casr) gene and other genes known to be involved in parathyroid function. Most importantly, the PTH-C1 cells also exhibit an in vitro secretory response to calcium. Altogether these findings indicate the uniqueness of the PTH-C1 cell line as an in vitro model for cellular and molecular studies on parathyroid physiopathology.

Genetic and epigenetic changes in sporadic endocrine tumors: parathyroid tumors

Parathyroid neoplasia is most commonly due to benign parathyroid adenoma but rarely can be caused by malignant parathyroid carcinoma. Evidence suggests that parathyroid carcinomas rarely, if ever, evolve through an identifiable benign intermediate, with the notable exception of carcinomas associated with the familial hyperparathyroidism-jaw tumor syndrome. Several genes have been directly implicated in the pathogenesis of typical sporadic parathyroid adenoma; somatic mutations in the MEN1 tumor suppressor gene are the most frequent finding, and alterations in the cyclin D1/PRAD1 oncogene are also firmly established molecular drivers of sporadic adenomas. In addition, good evidence supports mutation in the CDKN1B/p27 cyclin-dependent kinase inhibitor (CDKI) gene, and in other CDKI genes as contributing to disease pathogenesis in this context. Somatic defects in additional genes, including β-catenin, POT1 and EZH2 may contribute to parathyroid adenoma formation but, for most, their ability to drive parathyroid tumorigenesis remains to be demonstrated experimentally. Further, genetic predisposition to sporadic presentations of parathyroid adenoma appears be conferred by rare, and probably low-penetrance, germline variants in CDKI genes and, perhaps, in other genes such as CASR and AIP. The HRPT2 tumor suppressor gene is commonly mutated in parathyroid carcinoma.

Simultaneous expression analysis of vitamin D receptor, calcium-sensing receptor, cyclin D1, and PTH in symptomatic primary hyperparathyroidism in Asian Indians

BACKGROUND

To explore underlying molecular mechanisms in the pathogenesis of symptomatic sporadic primary hyperparathyroidism (PHPT).

MATERIALS AND METHODS

Forty-one parathyroid adenomas from patients with symptomatic PHPT and ten normal parathyroid glands either from patients with PHPT (n=3) or from euthyroid patients without PHPT during thyroid surgery (n=7) were analyzed for vitamin D receptor (VDR), calcium-sensing receptor (CASR), cyclin D1 (CD1), and parathyroid hormone (PTH) expressions. The protein expressions were assessed semiquantitatively by immunohistochemistry, based on percentage of positive cells and staining intensity, and confirmed by quantitative real-time PCR.

RESULTS

Immunohistochemistry revealed significant reductions in VDR (both nuclear and cytoplasmic) and CASR expressions and significant increases in CD1 and PTH expressions in adenomatous compared with normal parathyroid tissue. Consistent with immunohistochemistry findings, both VDR and CASR mRNAs were reduced by 0.36- and 0.45-fold change (P<0.001) and CD1 and PTH mRNAs were increased by 9.4- and 17.4-fold change respectively (P<0.001) in adenomatous parathyroid tissue. PTH mRNA correlated with plasma PTH (r=0.864; P<0.001), but not with adenoma weight, while CD1 mRNA correlated with adenoma weight (r=0.715; P<0.001). There were no correlations between VDR and CASR mRNA levels and serum Ca, plasma intact PTH, or 25-hydroxyvitamin D levels. In addition, there was no relationship between the decreases in VDR and CASR mRNA expressions and the increases in PTH and CD1 mRNA expressions.

CONCLUSIONS

The expression of both VDR and CASR are reduced in symptomatic PHPT in Asian Indians. In addition, CD1 expression was greatly increased and correlated with adenoma weight, implying a potential role for CD1 in adenoma growth and differential clinical expression of PHPT.

Animal models of hyperfunctioning parathyroid diseases for drug development

BACKGROUND

Disorders of mineral and bone metabolism have been implicated as a risk factor in the high mortality in patients with chronic kidney disease (CKD). Hyperphosphatemia, disorders of vitamin D metabolism and secondary hyperparathyroidism of uremia (SHPT) are therapeutic targets in these patients to improve the mortality. Animal models for CKD are indispensable and uremic rats produced by 5/6-nephrectomies are one of the most useful animal models for the development of new therapeutic agents. As there are limitations of uremic rats such as short lifespan and less severity of secondary hyperparathyroidism distinct from CKD patients on maintenance hemodialysis, the development of new model animals is expected.

OBJECTIVE

This review discusses the molecular pathogenesis of hyperfunctioning parathyroid diseases and the applications of animal models exhibiting hyperparathyroidisms in the aspect of the development of new therapeutics.

CONCLUSION

PTH-cyclin D1 transgenic mice, with parathyroid-targeted overexpression of cyclin D1 oncogene, not only developed abnormal parathyroid cell proliferation but, notably, also developed biochemical hyperparathyroidism with characteristic abnormalities in bone. The mice exhibit age-dependent development of biochemical hyperparathyroidism, which enables testing of the drug precisely. In addition, the mice develop parathyroid cell hyperplasia, followed by monoclonal expansion, which is observed in refractory SHPT patients.

Increased protein kinase A type Iα regulatory subunit expression in parathyroid gland adenomas of patients with primary hyperparathyroidism

Protein kinase A (PKA) regulatory subunit type Iα (RIα) is a major regulatory subunit that functions as an inhibitor of PKA kinase activity. We have previously demonstrated that elevated RIα expression is associated with diffuse-to-nodular transformation of hyperplasia in parathyroid glands of renal hyperparathyroidism. The aim of the current study was to determine whether or not RIα expression is increased in adenomas of primary hyperparathyroidism (PHPT), because monoclonal proliferation has been demonstrated in both adenomas and nodular hyperplasia. Surgical specimens comprising 22 adenomas and 11 normal glands, obtained from 22 patients with PHPT, were analyzed. Western blot and immunohistochemical analyses were employed to evaluate RIα expression. PKA activities were determined in several adenomas highly expressing RIα. RIα expression was also separately evaluated in chief and oxyphilic cells using the "Allred score" system. Expression of proliferating cell nuclear antigen (PCNA), a proliferation marker, was also immunohistochemically examined. Western blot analysis revealed that 5 out of 8 adenomas highly expressed RIα, compared with normal glands. PKA activity in adenomas was significantly less than in normal glands. Immunohistochemical analysis further demonstrated high expression of RIα in 20 out of 22 adenomas. In adenomas, the greater RIα expression and more PCNA positive cells were observed in both chief and oxyphilic cells. The present study suggested that high RIα expression could contribute to monoclonal proliferation of parathyroid cells by impairing the cAMP/PKA signaling pathway.

Molecular alterations in sporadic primary hyperparathyroidism

Primary hyperparathyroidism (PHPT) is a frequent endocrine disorder characterized by an excessive autonomous production and release of parathyroid hormone (PTH) by the parathyroid glands. This endocrinopathy may result from the development of a benign lesion (adenoma or hyperplasia) or from a carcinoma. Most of the PHPT cases occur sporadically; however, approximately 10% of the patients present a familial form of the disease. The molecular mechanisms underlying the pathogenesis of sporadic PHPT are incompletely understood, even though somatic alterations in MEN1 gene and CCND1 protein overexpression are frequently observed. The MEN1 gene is mutated in about 30% of the parathyroid tumours and the protooncogene CCND1 is implicated in parathyroid neoplasia by rearrangements, leading to an overexpression of CCND1 protein in parathyroid cells. The aim of this work is to briefly update the molecular alterations underlying sporadic primary hyperparathyroidism.

Cyclooxygenase 2 promotes parathyroid hyperplasia in ESRD

Hyperplasia of the PTG underlies the secondary hyperparathyroidism (SHPT) observed in CKD, but the mechanism underlying this hyperplasia is incompletely understood. Because aberrant cyclooxygenase 2 (COX2) expression promotes epithelial cell proliferation, we examined the effects of COX2 on the parathyroid gland in uremia. In patients with ESRD who underwent parathyroidectomy, clusters of cells within the parathyroid glands had increased COX2 expression. Some COX2-positive cells exhibited two nuclei, consistent with proliferation. Furthermore, nearly 78% of COX2-positive cells expressed proliferating cell nuclear antigen (PCNA). In the 5/6-nephrectomy rat model, rats fed a high-phosphate diet had significantly higher serum PTH levels and larger parathyroid glands than sham-operated rats. Compared with controls, the parathyroid glands of uremic rats exhibited more PCNA-positive cells and greater COX2 expression in the chief cells. Treatment with COX2 inhibitor celecoxib significantly reduced PCNA expression, attenuated serum PTH levels, and reduced the size of the glands. In conclusion, COX2 promotes the pathogenesis of hyperparathyroidism in ESRD, suggesting that inhibiting the COX2 pathway could be a potential therapeutic target.

Tissue-specific regulatory regions of the PTH gene localized by novel chromosome 11 rearrangement breakpoints in a parathyroid adenoma

Parathyroid adenomas can contain clonal rearrangements of chromosome 11 that activate the cyclin D1 oncogene through juxtaposition with the PTH gene. Here we describe such a chromosomal rearrangement whose novel features provide clues to locating elusive cis-regulatory elements in the PTH gene and also expand the physical spectrum of pathogenetic breakpoints in the cyclin D1 gene region. Southern blot analyses of the parathyroid adenoma revealed rearrangement in the PTH gene locus. Analysis of rearranged DNA clones that contained the breakpoint, obtained by screening a tumor genomic library, pinpointed the breakpoint in the PTH locus 3.3 kb upstream of the first exon. Accordingly, highly conserved distal elements of the PTH 5' regulatory region were rearranged at the breakpoint approximately 450 kb upstream of the cyclin D1 oncogene, resulting in overexpression of cyclin D1 mRNA. Thus, PTH-cyclin D1 gene rearrangement breakpoints in parathyroid tumors can be located far from those previously recognized. In addition to expanding the molecular spectrum of pathogenetic chromosomal lesions in this disease, features of this specific rearrangement reinforce the existence of one or more novel cis-enhancer/regulatory elements for PTH gene expression and narrow their location to a 1.7-kb DNA segment in the distal PTH promoter.

Clinical and molecular genetics of parathyroid neoplasms

Primary hyperparathyroidism (HPT) results from the excessive secretion of parathyroid hormone from parathyroid tumours. While most HPT is sporadic, it is associated with a familial syndrome in a minority of cases. The study of these syndromes has helped define the pathophysiology of both familial and sporadic parathyroid neoplasms. Investigation of kindred with multiple endocrine neoplasia type 1 (MEN1) and the hyperparathyroidism-jaw tumour syndrome (HPT-JT) led to the discovery of the tumour suppressor genes MEN1 and HRPT2. We now recognise that somatic mutations in MEN1 and HRPT2 tumour suppressor genes are frequent events in sporadic parathyroid adenomas and carcinomas, respectively. Parathyroid tumours in the MEN2A syndrome result from mutational activation of the RET oncogene. The CCND1/PRAD1 oncogene was discovered by analysis of sporadic parathyroid tumours. Studies of familial isolated HPT and analysis of chromosomal loss and gain in parathyroid tumours suggest that other genes relevant to parathyroid neoplasia await identification.

Frequent promoter hypermethylation of the APC and RASSF1A tumour suppressors in parathyroid tumours

Background

Parathyroid adenomas constitute the most common entity in primary hyperparathyroidism, and although recent advances have been made regarding the underlying genetic cause of these lesions, very little data on epigenetic alterations in this tumour type exists. In this study, we have determined the levels of promoter methylation regarding the four tumour suppressor genes APC, RASSF1A, p16^INK4A and RAR-β in parathyroid adenomas. In addition, the levels of global methylation were assessed by analyzing LINE-1 repeats.

Methodology/Principal Findings

The sample collection consisted of 55 parathyroid tumours with known HRPT2 and/or MEN1 genotypes. Using Pyrosequencing analysis, we demonstrate APC promoter 1A and RASSF1A promoter hypermethylation in the majority of parathyroid tumours (71% and 98%, respectively). Using TaqMan qRT-PCR, all tumours analyzed displayed lower RASSF1A mRNA expression and higher levels of total APC mRNA than normal parathyroid, the latter of which was largely conferred by augmented APC 1B transcription levels. Hypermethylation of p16^INK4A was demonstrated in a single adenoma, whereas RAR-β hypermethylation was not observed in any sample. Moreover, based on LINE-1 analyses, parathyroid tumours exhibited global methylation levels within the range of non-neoplastic parathyroid tissues.

Conclusions/Significance

The results demonstrate that APC and RASSF1A promoter hypermethylation are common events in parathyroid tumours. While RASSF1A mRNA levels were found downregulated in all tumours investigated, APC gene expression was retained through APC 1B mRNA levels. These findings suggest the involvement of the Ras signaling pathway in parathyroid tumorigenesis. Additionally, in contrast to most other human cancers, parathyroid tumours were not characterized by global hypomethylation, as parathyroid tumours exhibited LINE-1 methylation levels similar to that of normal parathyroid tissues.

Overexpression of degenerative spermatocyte homolog 1 up-regulates the expression of cyclin D1 and enhances metastatic efficiency in esophageal carcinoma Eca109 cells

Cyclin D1 plays a pivotal role in cell-cycle transition through G1 phase. In this article, we found that Degenerative Spermatocyte Homolog 1 (DEGS1) up-regulated the expression of cyclin D1 and the activation of transcription factor NF-kappaB was essential for DEGS1-induced cyclin D1 production. Forced expression of DEGS1 in Esophageal carcinoma cell line Eca109 cells increased their ability of cell migration and significantly induced tumor metastasis in nude mice, whereas RNA interference-mediated knockdown of DEGS1 cells significantly inhibited cell migration in vitro, as well as tumor metastasis in vivo. Our results demonstrated that expression of DEGS1 up-regulated the expression of cyclin D1 and enhanced the efficiency of tumor metastasis.

Proliferating potential and apoptosis in the development of secondary hyperparathyroidism: a study based on Ki-67 immunohistochemical staining and the terminal dUTP nick-end labeling assay

Secondary hyperparathyroidism (SHPT) is a common complication in hemodialysis (HD) patients. SHPT progresses from initial diffuse hyperplasia (diffuse) to early nodularity (early), then to multinodular hyperplasia (nodular), and finally to a single nodule (single) consisting of uniform parenchymal cells. We analyzed the roles of proliferation and apoptosis in SHPT progression. Seventy-four parathyroid glands from 36 HD patients with SHPT, and 10 parathyroid glands from 10 non-HD patients without SHPT were used for analysis. The former were classified as diffuse (N = 17), early (N = 22), nodular (N = 20), and single (N = 15); the latter were classified as normal (N = 10). To analyze proliferating cells we used Ki-67, and to detect apoptotic cells, we used the terminal deoxynucleotidyl transferase (Tdt)-mediated dUTP nick-end labeling (TUNEL) assay. Concerning the Ki-67 labeling index (LI), the incremental order was single, nodular, early, diffuse, and normal. Oxyphilic cells and around the central portion of each lesion were distinctly stained by Ki-67. Concerning the TUNEL LI, the incremental order was early, diffuse, nodular, single, and normal. Chief cells and around the peripheral portion of each lesion were distinctly stained by TUNEL. In the progression from early to nodular, for oxyphilic cells, the Ki-67 LI increased and the TUNEL LI decreased; for chief cells, the Ki-67 LI decreased and the TUNEL LI showed no significant change. We considered that proliferative activity increases and that the apoptosis rate decreases as SHPT progresses from diffuse to single. Moreover, the specific differences in the rate of proliferation and apoptosis between oxyphilic and chief cells might be associated with SHPT progression.

Clinical and operative management of persistent hyperparathyroidism after renal transplantation: A single-center experience

BACKGROUND

Persistent (tertiary) hyperparathyroidism (TH) after renal transplantation may cause considerable morbidity and necessitate parathyroidectomy. This study investigated the characteristics of this patient subgroup.

METHODS

The medical data and pathology specimens of 20 kidney transplant recipients who underwent parathyroidectomy for TH in 2001 to 2004 were reviewed.

RESULTS

Treatment consisted of subtotal resection of 3.5 glands in 13 patients, resection of 3 to 3.5 glands under intraoperative parathyroid hormone monitoring (iPTH) in 5 patients, and selective resection in 2 patients with markedly asymmetric gland enlargement. Eighteen patients had hyperplasia-diffuse in 10, nodular in 4, or both in 2; 2 patients had 1 large nodule in every gland. Six patients had postoperative complications. Follow-up of 2 years revealed recurrent hypercalcemia in 1 patient and a high level of PTH (>60 pg/mL) in 12.

CONCLUSION

Subtotal resection for TH may be insufficient. The use of iPTH monitoring is recommended. Renal transplant recipients have distinctive characteristics and require special perioperative attention.

Clinical features and hyperplastic patterns of parathyroid glands in hemodialysis patients with advanced secondary hyperparathyroidism refractory to maxacalcitol treatment and required parathyroidectomy

We have previously suggested that when parathyroid glands progress to nodular hyperplasia, secondary hyperparathyroidism (2HPT) may be refractory to medical treatments, including treatment with Maxacalcitol (OCT). In the present study we evaluated the clinical features and hyperplastic patterns of parathyroid glands in patients who underwent parathyroidectomy (PTx) after being withdrawn from OCT. One hundred and eighty-seven advanced 2HPT patients who had been withdrawn from OCT and required PTx were enrolled. At the start of OCT treatment, the patients had a mean age of 55.3 years and had been receiving hemodialysis (HD) for a mean period of 149 months. At the start of OCT treatment and at PTx, the mean intact PTH (i-PTH) levels were 772.8 +/- 446.0 and 855.5 +/- 420.5 pg/mL, respectively. The main reasons for withdrawal of OCT treatment were persistently high PTH (n = 148), hypercalcemia (n = 79), hyperphosphatemia (n = 65), and progressive symptoms (n = 60). We classified the parathyroid glands by hyperplastic pattern into four categories: diffuse hyperplastic gland (D), early nodularity in diffuse hyperplastic gland (EN), nodular hyperplastic gland (N), and single nodular gland (SN). The mean total excised gland weight was 2592.6 mg. Out of a total of 706 glands, 118 were classified as D, 66 as EN, 436 as N, and 86 as SN. All patients had at least one nodular hyperplastic gland or single nodular gland. The mean number of nodular hyperplastic glands and/or single nodular glands was 2.9. All hemodialysis patients with advanced OCT-refractory 2HPT who underwent PTx had at least one nodular hyperplastic gland or single nodular gland.

Modulation of cyclin D1 expression in human tumoral parathyroid cells: effects of growth factors and calcium sensing receptor activation

The study investigated cyclin D1 regulation by growth factors and calcium sensing receptor (CaSR) in human tumoral parathyroid cells. Basic fibroblast and epidermal growth factors increased cyclin D1 and phosphorylated extracellular signal-regulated kinases (pERK1/2) levels that were both efficiently inhibited by CaSR agonists. By contrast, in growth factors-free medium cyclin D1 levels were either unaffected or stimulated by CaSR activation independently from ERK1/2 pathway. Transforming growth factor beta (TGFbeta) reduced cyclin D1 levels in the majority of tumors, this effect being not influenced by CaSR activation and menin expression levels. In conclusion, in parathyroid tumors cyclin D1 expression was modulated by growth factors and CaSR activation. These data further support the oncogenic role of cyclin D1, which resulted to be target for stimulation by bFGF and EGF and inhibition by CaSR and TGFbeta signalling in the parathyroid.

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.

Basic and clinical aspects of parathyroid hyperplasia in chronic kidney disease

Marked parathyroid hyperplasia develops in patients with chronic kidney disease, especially those with long dialysis vintage. Although progression of hyperplasia is associated with downregulation of vitamin D receptor and calcium-sensing receptor, initial abnormality that triggers and maintains parathyroid cell proliferation, as well the critical abnormality for the progression of diffuse hyperplasia to nodular hyperplasia, still remains to be elucidated. It is quite important for the optimal management of renal osteodystrophy to recognize the development of nodular hyperplasia, because the cells in nodular hyperplasia are usually resistant to medical therapy and further treatment of such patients often leads to vascular calcification. For this purpose, size and blood supply of enlarged parathyroid glands have been used as good clinical markers. Furthermore, we have recently shown that the serum fibroblast growth factor 23 level can be used for predicting refractory hyperparathyroidism. Once nodular hyperplasia develops in any of the enlarged parathyroid glands, such patients need to be treated by parathyroid intervention including percutaneous ethanol injection therapy. In addition, as direct vitamin D injection therapy has been shown to induce regression of hyperplasia, it may become possible to reverse or normalize established nodular hyperplasia if we can develop new agents with such effects in the near future.

Is the volume of the parathyroid gland a predictor of Maxacalcitol response in advanced secondary hyperparathyroidism?

We evaluated the relationship between the volume of parathyroid glands estimated by ultrasonography (US) and response of 22-oxa calcitriol (Maxacalcitol, OCT) in patients with secondary hyperparathyroidism (2HPT) to evaluate whether the volume can be a predictor of the OCT response. Eleven institutes participated in this study. Ninety-four patients with advanced 2HPT were enrolled. The volume of the parathyroid glands were estimated by US before and 6 months after OCT treatment. The response of OCT treatment was classified into three groups (Group A: i-PTH < 300 pg/mL; Group B: 300 pg/mL < or = i-PTH < 500 pg/mL; Group C: i-PTH > or = 500 pg/mL). Forty-eight patients were in Group A, 28 patients in Group B, and 18 patients in Group C. The PTH levels at the beginning and 6 months were 458.3-199.1 pg/mL (P < 0.0001) in Group A, 524.6-403.2 pg/mL (P = 0.007) in Group B and 736.7-613.6 pg/mL (ns) in Group C, respectively. The volume of the largest gland in Group B was significantly larger than that in Group A (96.2 vs. 343.2 mm3: P < 0.001). Clinical factors affecting response of OCT was evaluated by logistic regression analysis and only the volume of the largest gland was a significant factor. In the patients whose volume was less than 300 mm3, the OCT response was significantly effective. We conclude that the glandular volume of the largest parathyroid gland estimated by US can be a useful factor to predict the OCT response in patients with moderate or severe renal HPT.