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

Parathyroid Hormone Gene and Genes Involved in the Maintenance of Vitamin D Levels Association with Mandibular Retrognathism

In this study we evaluated whether single nucleotide polymorphisms (SNPs) in the genes encoding PTH, VDR, CYP24A1, and CYP27B1 were associated with mandibular retrognathism (MR). Samples from biologically-unrelated Brazilian patients receiving orthodontic treatment were included in this study. Pre-orthodontic lateral cephalograms were used to determine the phenotype. Patients with a retrognathic mandible were selected as cases and those with an orthognathic mandible were selected as controls. Genomic DNA was used for genotyping analysis of SNPs in PTH (rs694, rs6256, and rs307247), VDR (rs7975232), CYP24A1 (rs464653), and CYP27B1 (rs927650). Chi-squared or Fisher’s tests were used to compare genotype and allele distribution among groups. Haplotype analysis was performed for the SNPs in PTH. The established alpha was p < 0.05. Multifactor dimensionality reduction (MDR) was used to identify SNP–SNP interactions. A total of 48 (22 males and 26 females) MR and 43 (17 males and 26 females) controls were included. The linear mandibular and the angular measurements were statistically different between MR and controls (p < 0.05). In the genotype and allele distribution analysis, the SNPs rs694, rs307247, and rs464653 were associated with MR (p < 0.05). MDR analyses predicted the best interaction model for MR was rs694–rs927650, followed by rs307247–rs464653–rs927650. Some haplotypes in the PTH gene presented statistical significance. Our results suggest that SNPs in PTH, VDR, CYP24A1, and CYP27B1 genes are associated with the presence of mandibular retrognathism.

Older Age Is Associated with Decreased Levels of VDR, CYP27B1, and CYP24A1 and Increased Levels of PTH in Human Parathyroid Glands

Parathyroid glands contain the vitamin D receptor (VDR) and 25-hydroxyvitamin D-1α-hydroxylase (CYP27B1) and 24-hydroxylase (CYP24A1), which catalyze the production and degradation of 1,25-dihydroxyvitamin D [1,25(OH)₂D], respectively. Previous studies have shown that the serum level of intact parathyroid hormone (iPTH) increases with age. We hypothesized that the expression of CYP27B1 or VDR in parathyroid glands decreases with age, which might account for the increased serum levels of iPTH due to decreased suppression of parathyroid hormone (PTH) secretion by 1,25(OH)₂D in older people. To test this hypothesis, we examined relative expression levels of VDR, CYP27B1, CYP24A1, and PTH in specimens from parathyroid glands unintentionally removed during thyroidectomy for 70 patients varying in age from 10 to 70 years. The results showed that there was an inverse correlation between age and VDR, CYP27B1, and CYP24A1 expression (p < 0.05). A significant positive correlation between PTH expression levels and age was also observed (p < 0.05). These data indicate that older age is associated with decreased levels of VDR, CYP27B1, and CYP24A1 and increased levels of PTH in human parathyroid glands.

Off‑target effect of imatinib and nilotinib on human vitamin D3 metabolism

Prolonged treatment with tyrosine kinase inhibitors (TKI) including imatinib (IMA) or nilotinib (NIL), induces severe disturbances of bone metabolism in patients with chronic myeloid leukaemia. As vitamin D3 (VD3) is involved in the complex cycle of bone remodelling, the present study investigated in vitro, the influence of IMA and NIL on VD3 metabolism i) in HaCaT cells and ii) in cultured outer root sheath keratinocytes (ORS‑KC) from hair follicles of IMA treated children. Cells were incubated in the presence of IMA or NIL. Concomitantly, specific inhibitors were applied to analyze the inhibition of the VD3 processing cytochrome P450 isoenzyme family by TKIs. In vitro, IMA and NIL significantly impaired the production of calcitriol in HaCaT and cultured ORS‑KC cells from hair follicles of IMA treated children. For NIL, this inhibitory effect demonstrated a 4‑fold increase. In HaCaT and ORS‑KC, application of specific CYP450 inhibitors revealed that CYP27B1 was impaired by IMA and NIL leading to an intracellular accumulation of calcidiol. However, during TKI treatment, KC of IMA treated children revealed no differences in calcidiol and calcitriol levels. In conclusion, IMA and NIL interfere with the vitamin D3 cascade due to their metabolism by CYP27B1.

Vitamin D metabolism and activity in the parathyroid gland

Parathormone (PTH) and vitamin D are two critical hormonal regulators of calcium homeostasis. An important cross-talk exists between the PTH and vitamin D hormonal systems. PTH enhances vitamin D hydroxylation on carbon 1 in kidney cells thereby allowing the systemic release of 1-25-dihydroxy-vitamin D, which represents the fully active hormone. Conversely, parathyroid gland represents a direct target for vitamin D. Parathyroid cells express the vitamin D receptor and the 1-α-hydroxylase enzyme, which allows the local formation of 1-25-dihydroxy-vitamin D. Because of its potential implication in several diseases, including osteoporosis or chronic kidney disease, the interplay between PTH and vitamin D has received considerable attention these last two decades. The aim of this review is to summarize our current understanding of the molecular basis of vitamin D action and metabolism in parathyroid cells. The potential clinical implications of the recent advances made in this field will also be discussed.

Aberrant WNT/β-catenin signaling in parathyroid carcinoma

Background

Parathyroid carcinoma (PC) is a very rare malignancy with a high tendency to recur locally, and recurrent disease is difficult to eradicate. In most western European countries and United States, these malignant neoplasms cause less than 1% of the cases with primary hyperparathyroidism, whereas incidence as high as 5% have been reported from Italy, Japan, and India. The molecular etiology of PC is poorly understood.

Results

The APC (adenomatous polyposis coli) tumor suppressor gene was inactivated by DNA methylation in five analyzed PCs, as determined by RT-PCR, Western blotting, and quantitative bisulfite pyrosequencing analyses. This was accompanied by accumulation of stabilized active nonphosphorylated β-catenin, strongly suggesting aberrant activation of the WNT/β-catenin signaling pathway in these tumors. Treatment of a primary PC cell culture with the DNA hypomethylating agent 5-aza-2'-deoxycytidine (decitabine, Dacogen(r)) induced APC expression, reduced active nonphosphorylated β-catenin, inhibited cell growth, and caused apoptosis.

Conclusion

Aberrant WNT/β-catenin signaling by lost expression and DNA methylation of APC, and accumulation of active nonphosphorylated β-catenin was observed in the analyzed PCs. We suggest that adjuvant epigenetic therapy should be considered as an additional option in the treatment of patients with recurrent or metastatic parathyroid carcinoma.

Parathyroid Klotho and FGF-receptor 1 expression decline with renal function in hyperparathyroid patients with chronic kidney disease and kidney transplant recipients

Current studies suggest that short-term exposure of parathyroid glands to fibroblast growth factor 23 (FGF23) reduces parathyroid hormone secretion. However, patients with chronic kidney disease (CKD) develop secondary hyperparathyroidism despite high levels of serum FGF23, indicating a parathyroid FGF23 'resistance'. Here we analyzed the expression of the FGF23 receptors Klotho and FGF receptor 1 (FGFR1) in 88 hyperplastic parathyroid glands from 31 patients with CKD (including 21 renal allograft recipients), and their regulation in isolated bovine and human hyperplastic parathyroid cells. Glandular expression was variable, yet the Klotho and FGFR1 mRNA levels declined in parallel with the decreasing glomerular filtration rate, significantly decreasing over CKD stages. We found no association between the expression of Klotho, FGFR1, and the proliferation marker Ki67. In vitro treatment of bovine cells with FGF23 or calcium reduced the Klotho level, whereas active vitamin D(3) compounds increased its expression. Phosphate and parathyroid hormone had no effect. Treatment had less impact on Klotho in cultured human cells than in the bovine healthy cell model, whereas FGFR1 expression was induced in the hyperplastic cells. Thus parathyroid Klotho and FGFR1 decrease with declining renal function, possibly because of alterations in mineral metabolism related to the failing kidney. This could explain the observed parathyroid resistance to FGF23 in late CKD.