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Fibroblast growth factor-23 (FGF23) is a hormone indispensable for maintaining phosphate homeostasis. In response to phosphate intake, FGF23 is secreted from osteocytes/osteoblasts and acts on the kidney to increase urinary phosphate excretion. However, the mechanism by which these cells sense phosphate intake remains elusive. Calciprotein particles are nanoparticles of calcium-phosphate precipitates bound to serum protein fetuin-A and are generated spontaneously in solution containing calcium, phosphate, and fetuin-A to be dispersed as colloids. In cultured osteoblastic cells, increase in either calcium or phosphate concentration in the medium induced FGF23 expression, which was dependent on calciprotein particle formation. When transition of calcium-phosphate precipitates from the amorphous phase to the crystalline phase was blocked by bisphosphonate, the calciprotein particle size was reduced and FGF23 expression was augmented, suggesting that small calciprotein particles containing amorphous calcium-phosphate precipitates function as a more potent FGF23 inducer than larger calciprotein particles containing crystalline calcium-phosphate precipitates. In mice, bolus phosphate administration by oral gavage transiently increased circulating calciprotein particle levels followed by a modest increase in FGF23 expression and serum FGF23 levels. However, continuous dietary phosphate load induced robust and persistent increase in circulating calciprotein particles and FGF23 levels. We confirmed by in vivo imaging that calciprotein particles injected intravenously extravasated into the bone marrow and were deposited on the inner surface of the bone, indicating that these particles have direct access to osteoblasts. Thus, we propose that osteoblasts induce FGF23 expression and secretion when they sense an increase in extracellular calciprotein particles following phosphate ingestion., (Copyright © 2019 International Society of Nephrology. Published by Elsevier Inc. All rights reserved.)

Introduction: The glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) are members of the nuclear receptor superfamily and ligand-dependent transcription factors, whose major ligands are glucocorticoid and mineralocorticoid, so-called corticosteroids. The corticosteroids are a class of substances that include steroid hormones naturally produced in the adrenal cortex of vertebrates and analogues of these hormones that are synthesized in industry. They are involved in a wide range of physiological processes including stress and immune responses, and the regulation of carbohydrate metabolism, protein catabolism, sodium homeostasis, and inflammation. These substances are potential environmental contaminants because they are clinically consumed in large amounts worldwide. To develop a simple and sensitive bioassay to detect corticosteroids, we newly established reporter assay yeasts expressing human GR and MR., Methods: Ligand responses of the established assay yeasts were improved by forced expression of a human transcription coactivator SRC-1e. Further enhancement of the responses was achieved by inactivating the CWP and PDR genes that encode cell wall mannoproteins and plasma membrane efflux pumps, respectively, which may be attributable to an increased intracellular concentration of ligands., Results: These new assay yeasts were more responsive to both natural and synthetic agonist ligands than the conventional assay yeasts. They detected both agonistic and antagonistic activities of mifepristone, spironolactone, and eplerenone in a receptor-selective manner. They also detected ligand activities contained in oral pharmaceutical tablets and human urine., Discussion: This assay system will be a valuable tool to detect agonists as well as antagonists of corticosteroid receptors, in the fields of drug discovery and the assessment of environmental pollutants., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Introduction: Retinoic acids are essential for embryonic development, tissue organization, and homeostasis and act via retinoic acid receptors (RARs) that form heterodimers with retinoid X receptors (RXRs). Human RARs and RXRs include the three subtypes α, β, and γ, which have varying distributions and physiological functions among human tissues. Recent reports show that subtype-specific binding of several chemicals to RARs or RXRs may lead to endocrine disruption. To evaluate these ligand-like chemicals, convenient assay systems for each receptor subtype are required., Methods: We developed reporter assay yeasts to screen ligands for RXR subtype receptor homodimers. To screen RAR ligands, yeasts were engineered to express RAR subtypes with defective RXRα, which fails to bind to coactivators because of its shortened c-terminus., Results: These assay yeasts were validated using known RXR- and RAR-specific ligands and subtype-specific responses were clearly shown. Subtype-specific ligand activities of the suspected chemical RAR or RXR ligands o-t-butylphenol, triphenyltin chloride, tributyltin chloride, and 4-nonylphenol were determined., Discussion: The present assay yeasts may be valuable tools for subtype-specific assessments of unidentified environmental ligand chemicals and receptor-specific pharmaceuticals., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Benzo[a]pyrene (BaP) is metabolically activated by cytochrome P450 enzymes, and forms DNA adduct leading to mutations. Cytochrome P450 1A1 plays a central role in this activation step, and this enzyme is strongly induced by chemical agents that bind to the aryl hydrocarbon receptor (AhR), which is also known as a dioxin receptor. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), a potent AhR ligand has not been shown to form any DNA adduct, but has a possibility to aggravate the toxicity of precarcinogenic polycyclic hydrocarbons through the induction of metabolic enzymes. We treated human hepatoma cells (HepG2) with TCDD, and subsequently exposed them to BaP to elucidate the synergistic effects on mutations. Surprisingly, mutant frequency induced by BaP at the hypoxanthine-guanine phosphribosyltransferase (HPRT) locus was decreased by pretreatment with TCDD. In correlation with decrease in the mutant frequencies, BaP-DNA adduct formation was also decreased by TCDD pretreatment. This suppressive effect of TCDD was more potent when the cells were exposed to (±)-anti-benzo[a]pyrene-7,8-diol-9,10-epoxide (BPDE), a reactive metabolic intermediate of BaP. Among the enzymes catalyzing BaP oxidation and conjugation, cytochrome P450 1A1, 1A2, 3A4 and UDP-glucuronosyltransferase 1A1 mRNAs were induced by the exposure to TCDD. In cytochrome P450 1A1-deficient murine cells and cytochrome P450 1A1-uninducible human cells, TCDD could not suppress BPDE-DNA adduct formation. Further experiments using "Tet-On" cytochrome P450 1A1-overexpressing cells and a recombinant cytochrome P450 1A1 enzyme demonstrated that this is the key enzyme involved in the biotransformation of BaP, that is, both production and inactivation of BPDE. We conclude that TCDD-induced cytochrome P450 catalyzes the metabolism of BPDE to as yet-unidentified products that are not apparently DNA-reactive, thereby reducing mutations in hepatoma cells., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Direct maxacalcitol (OCT) injection into a parathyroid gland (PTG) ameliorates several important etiologic factors of resistance to medical treatments for secondary hyperparathyroidism (s-HPT): the upregulations of vitamin D receptor (VDR) and Ca-sensing receptor (CaSR) in PTGs and the regression of PTG hyperplasia by the induction of apoptosis. In this study, we evaluated the bone histomorphology on the basis of maintaining these effects in advanced s-HPT. Five/six nephrectomized Sprague-Dawley rats were fed a high-phosphorus and low-calcium diet for 8 weeks. These rats were divided into four treatment groups: (1) basic uremic (at the baseline), (2) direct OCT single injection into PTGs (DI-OCT) followed by OCT intravenous administration for 4 weeks (IV-OCT), (3) direct vehicle injection and IV-OCT, and (4) no treatment for an additional 4 weeks. The effects of these treatments on serum intact-parathyroid hormone (PTH) level, PTG weight, VDR and CaSR expression levels in PTGs, and bone histomorphometric parameters were investigated. In the DI-OCT+IV-OCT group, the significant decrease in serum intact-PTH level was maintained by the following IV-OCT. A significant decrease in PTG weight and the upregulations of VDR and CaSR expression levels in PTGs were also observed. Bone histomorphometric analysis showed significant improvements in osteitis fibrosa in both cancellous and cortical bones. However, these findings were not observed in the other groups. These results suggest that osteitis fibrosa caused by advanced s-HPT can be successfully reversed by a control of PTH at an appropriate level through the improvement of PTG hyperplasia as induced by DI-OCT+IV-OCT.

The aryl hydrocarbon receptor (AhR) mediates a wide variety of toxic effects due to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The human hepatoma cell line SK-HEP-1 expresses AhR and ARNT. However, TCDD failed to induce CYP1A1 and XRE-dependent reporter genes in these cells. Although CYP1A1 was not induced by TCDD exposure, both CYP1B1 and AhR repressor (AhRR) were constitutively expressed. The AhR antagonist alpha-naphthoflavone altered the basal level of XRE-dependent reporter gene expression dose-dependently. As our results suggested the activation of AhR signals by putative endogenous ligands, we established SK-HEP-1-derived cell lines that stably expressed CYP1A1. The inducibility of XRE-dependent reporter genes and CYP1B1 by TCDD was restored in these cells. Our findings demonstrated the presence of endogenous ligands in SK-HEP-1 cells due to the absence of the metabolizing enzyme CYP1A1, but not CYP1B1, which allowed the constitutive expression of AhR target genes.

Background: A high level of parathyroid hormone (PTH) is considered to be an indicator of poor prognosis and a poor quality of life of dialysis patients; therefore, an effective and safe therapy for secondary hyperparathyroidism (SHPT) has been developed., Methods: In 20 patients with SHPT resistant to maxacalcitol (OCT) intravenously administered, all detectably enlarged parathyroid glands were treated by percutaneous maxacalcitol injection therapy (PMIT) under ultrasonographic guidance consecutively 6 times, which was followed by OCT that was intravenously administered. The clinical effects of PMIT were evaluated based on the changes in the serum intact-PTH, adjusted Ca, phosphorus, and bone marker levels, and the parathyroid gland volume determined by ultrasonography. Morphologic examination, apoptosis analysis, and PTH mRNA expression level determination by reverse transcription-polymerase chain reaction (RT-PCR) using parathyroid tissues obtained by a biopsy technique were performed., Results: PMIT and subsequent intravenous OCT administrations significantly decreased the serum intact-PTH level and parathyroid gland volume for at least 12 weeks after PMIT without major complications. Parathyroid tissues obtained after PMIT exhibited some partial defects of parathyroid cells, a marked increase in the number of the terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL)-positive cells, the ladder formation determined by DNA electrophoresis, and the decrease in the PTH mRNA expression level., Conclusion: PMIT is effective and safe for the treatment of refractory SHPT, and a locally high level of OCT suppresses PTH secretion and regresses parathyroid hyperplasia, which is involved in the induction of apoptosis of parathyroid cells.

Acute coronary occlusion after percutaneous transluminal coronary angioplasty is one of the major problems in coronary intervention. This study evaluated the hydrogel-coated balloon delivery of argatroban to the arterial wall and argatroban persistence after angioplasty in 17 rabbits. A hydrogel-coated balloon was immersed three times in argatroban/saline solution (1 mg/ml) and inflated at 6 atm pressure for 1 min in the common carotid artery. The transfer of argatroban to the vascular wall was measured by high-performance liquid chromatography. The concentrations of argatroban at 0, 5, and 15 min after deflation were 14.8, 4.2, and 3.9 nmole/g.wet weight. The hydrogel-coated balloon catheter can deliver argatroban to the local arterial wall during balloon inflation.