Fibroblast growth factor‐23 (FGF23) is a bone‐derived hormone regulating renal phosphate reabsorption and vitamin D synthesis in renal proximal tubules. Here, we show that FGF23 directly regulates ...the membrane abundance of the Na+:Cl− co‐transporter NCC in distal renal tubules by a signaling mechanism involving the FGF receptor/αKlotho complex, extracellular signal‐regulated kinase 1/2 (ERK1/2), serum/glucocorticoid‐regulated kinase 1 (SGK1), and with‐no lysine kinase‐4 (WNK4). Renal sodium (Na+) reabsorption and distal tubular membrane expression of NCC are reduced in mouse models of Fgf23 and αKlotho deficiency. Conversely, gain of FGF23 function by injection of wild‐type mice with recombinant FGF23 or by elevated circulating levels of endogenous Fgf23 in Hyp mice increases distal tubular Na+ uptake and membrane abundance of NCC, leading to volume expansion, hypertension, and heart hypertrophy in a αKlotho and dietary Na+‐dependent fashion. The NCC inhibitor chlorothiazide abrogates FGF23‐induced volume expansion and heart hypertrophy. Our findings suggest that FGF23 is a key regulator of renal Na+ reabsorption and plasma volume, and may explain the association of FGF23 with cardiovascular risk in chronic kidney disease patients.
Synopsis
FGF23 serum levels are elevated in chronic kidney disease patients. FGF23 is here shown to be a regulator of the sodium‐chloride channel NCC in distal renal tubules, thus affecting renal sodium retention, plasma expansion, hypertension, and heart hypertrophy.
FGF23 regulates membrane abundance and activity of the renal sodium‐chloride channel NCC through the ERK1/2‐SGK1‐WNK4 signaling pathway.
FGF23 is a sodium‐conserving hormone.
Elevated circulating FGF23 leads to volume expansion, hypertension, and cardiac hypertrophy in a Klotho‐dependent fashion.
The NCC inhibitor chlorothiazide blunts FGF23‐induced hypertension.
A low sodium diet aggravates the hypertensive action of FGF23 through crosstalk with aldosterone signaling at the level of SGK1.
FGF23 serum levels are elevated in chronic kidney disease patients. FGF23 is here shown to be a regulator of the sodium‐chloride channel NCC in distal renal tubules, thus affecting renal sodium retention, plasma expansion, hypertension, and heart hypertrophy.
The development of bone‐rebuilding anabolic agents for potential use in the treatment of bone loss conditions, such as osteoporosis, has been a long‐standing goal. Genetic studies in humans and mice ...have shown that the secreted protein sclerostin is a key negative regulator of bone formation, although the magnitude and extent of sclerostin's role in the control of bone formation in the aging skeleton is still unclear. To study this unexplored area of sclerostin biology and to assess the pharmacologic effects of sclerostin inhibition, we used a cell culture model of bone formation to identify a sclerostin neutralizing monoclonal antibody (Scl‐AbII) for testing in an aged ovariectomized rat model of postmenopausal osteoporosis. Six‐month‐old female rats were ovariectomized and left untreated for 1 yr to allow for significant estrogen deficiency‐induced bone loss, at which point Scl‐AbII was administered for 5 wk. Scl‐AbII treatment in these animals had robust anabolic effects, with marked increases in bone formation on trabecular, periosteal, endocortical, and intracortical surfaces. This not only resulted in complete reversal, at several skeletal sites, of the 1 yr of estrogen deficiency‐induced bone loss, but also further increased bone mass and bone strength to levels greater than those found in non‐ovariectomized control rats. Taken together, these preclinical results establish sclerostin's role as a pivotal negative regulator of bone formation in the aging skeleton and, furthermore, suggest that antibody‐mediated inhibition of sclerostin represents a promising new therapeutic approach for the anabolic treatment of bone‐related disorders, such as postmenopausal osteoporosis.
The ability of current immunoassays to accurately measure equimolar amounts of 25(OH)D2 and 25(OH)D3 has been recently questioned. This study determined serum 25(OH)D2, 25(OH)D3 and total serum ...25(OH)D concentrations in healthy vitamin D2-supplemented subjects by isotope dilution liquid chromatography mass spectrometry (ID-LC-MS/MS); and, evaluated the ability of the Siemens, DiaSorin, Roche, and Abbott Vitamin D Total assays to monitor total serum 25(OH)D concentrations compared to an ID-LC-MS/MS method traceable to the National Institute of Standards and Technology (NIST), and that has achieved certification from the Centers for Disease Control and Prevention (CDC) Vitamin D Standardization Certification Program (VDSCP).
Twenty (20) healthy adults, with no history of prior vitamin D supplementation were administered oral vitamin D2 (2400IU/day for 6months). Serum samples (140) from baseline and monthly blood draws were tested.
After one month, the mean serum 25(OH)D2 concentrations rose from 0.8 to 43.6nmol/L, whereas 25(OH)D3 concentrations declined from 84.0 to 63.4nmol/L; total serum 25(OH)D concentrations rose from 86.6 to 107.0nmol/L. The overall mean bias to ID-LC-MS/MS was −7.1% for the Siemens ADVIA Centaur assay, −15.3% for the DiaSorin LIAISON assay; −8.4% for the Roche ELECSYS assay and −16.3% for the Abbott ARCHITECT assay. Correlation coefficients (r) were 0.94, 0.79, 0.74, and 0.73; the mean bias for baseline 25(OH) D3-containing versus six-month 25(OH)D2- and 25(OH)D3-containing samples was −13.4% and −5.7%; −3.5% and 20.3%, 9.6% and −12.1%, and 0.2% and −17.8%, respectively.
The bias results obtained for the Siemens ADVIA Centaur assay and Roche ELECSYS assay were slightly lower than those for the DiaSorin LIAISON assay and the Abbott ARCHITECT assay, but all 25(OH)D assays demonstrated acceptable performance.
•Six month supplementation with 25(OH)D2 led to 25(OH)D2/25(OH)D3 ratio of 1:1.•We evaluated four immunoassays to measure equimolar 25(OH)D2 and 25(OH)D3.•Siemens, DiaSorin, Roche and Abbott immunoassays show acceptable bias to LC-MS/MS.
FGF23 Fails to Inhibit Uremic Parathyroid Glands CANALEJO, Rocío; CANALEJO, Antonio; MARTINEZ-MORENO, Julio Manuel ...
Journal of the American Society of Nephrology,
07/2010, Letnik:
21, Številka:
7
Journal Article
Recenzirano
Odprti dostop
Fibroblast growth factor 23 (FGF23) modulates mineral metabolism by promoting phosphaturia and decreasing the production of 1,25-dihydroxyvitamin D(3). FGF23 decreases parathyroid hormone (PTH) mRNA ...and secretion, but despite a marked elevation in FGF23 in uremia, PTH production increases. Here, we investigated the effect of FGF23 on parathyroid function in normal and uremic hyperplastic parathyroid glands in rats. In normal parathyroid glands, FGF23 decreased PTH production, increased expression of both the parathyroid calcium-sensing receptor and the vitamin D receptor, and reduced cell proliferation. Furthermore, FGF23 induced phosphorylation of extracellular signal-regulated kinase 1/2, which mediates the action of FGF23. In contrast, in hyperplastic parathyroid glands, FGF23 did not reduce PTH production, did not affect expression of the calcium-sensing receptor or vitamin D receptor, and did not affect cell proliferation. In addition, FGF23 failed to activate the extracellular signal-regulated kinase 1/2-mitogen-activated protein kinase pathway in hyperplastic parathyroid glands. We observed very low expression of the FGF23 receptor 1 and the co-receptor Klotho in uremic hyperplastic parathyroid glands, which may explain the lack of response to FGF23 in this tissue. In conclusion, in hyperparathyroidism secondary to renal failure, the parathyroid cells resist the inhibitory effects of FGF23, perhaps as a result of the low expression of FGF23 receptor 1 and Klotho in this condition.
OPG is a new member of the tumor necrosis factor (TNF) receptor family which plays a key role in the physiological regulation of osteoclastic bone resorption. The protein, which is produced by ...osteoblasts and marrow stromal cells, lacks a transmembrane domain and acts as a secreted decoy receptor which has no direct signaling capacity. OPG acts by binding to its natural ligand OPGL, which is also known as RANKL (receptor activator of NF-kappaB ligand). This binding prevents OPGL from activating its cognate receptor RANK, which is the osteoclast receptor vital for osteoclast differentiation, activation and survival. Overexpression of OPG in transgenic mice leads to profound osteopetrosis secondary to a near total lack of osteoclasts. Conversely, ablation of the OPG gene causes severe osteoporosis in mice. Ablation of OPGL or RANK also produces profound osteopetrosis, indicating the important physiological role of these proteins in regulating bone resorption. The secretion of OPG and OPGL from osteoblasts and stromal cells is regulated by numerous hormones and cytokines, often in a reciprocal manner. The relative levels of OPG and OPGL production are thought to ultimately dictate the extent of bone resorption. Excess OPGL increases bone resorption, whereas excess OPG inhibits resorption. Recombinant OPG blocks the effects of virtually all factors which stimulate osteoclasts, in vitro and in vivo. OPG also inhibits bone resorption in a variety of animal disease models, including ovariectomy-induced osteoporosis, humoral hypercalcemia of malignancy, and experimental bone metastasis. OPG might represent an effective therapeutic option for diseases associated with excessive osteoclast activity.
Calcimimetics and vitamin D sterols reduce serum parathyroid hormone (PTH) in patients with secondary hyperparathyroidism receiving dialysis, a disease state associated with parathyroid hyperplasia, ...vascular calcification, bone disease, and increased mortality. The aim of this study was to determine the effects of the research calcimimetic AMG 641 (Amgen, Inc., Thousand Oaks, CA) or calcitriol (Sigma Aldrich Corporation, St. Louis, MO) on vascular calcification in a rodent model of progressive uremia with accompanying secondary hyperparathyroidism induced by dietary adenine. Treatment effects on parathyroid gland hyperplasia and bone loss were also investigated. Rats were treated daily with vehicle, calcitriol (10 ng), AMG 641 (3 mg/kg), or no treatment during the 4 week period the animals were fed adenine. The uremia-induced increases in serum PTH levels were significantly attenuated by both AMG 641 (>
90%) and calcitriol (~
50%). AMG 641 significantly reduced calcium–phosphorus product (Ca
×
P) and significantly attenuated the development of both parathyroid hyperplasia and vascular calcification. In addition, AMG 641 prevented the defects in trabecular bone volume, trabecular number, and bone mineralization, as well as increases in trabecular spacing in this rodent model of secondary hyperparathyroidism. Calcitriol (10 ng/rat) decreased osteoid surface/bone surface, but had no effects on other bone parameters, or parathyroid hyperplasia (likely due to the lower PTH suppressive effect of calcitriol at the dose used in this study). However, this dose of calcitriol significantly exacerbated vascular calcification. These results suggest that calcimimetics can reduce the development of vascular calcification, parathyroid hyperplasia and bone abnormalities associated with secondary hyperparathyroidism.
Vitamin D status in different populations relies on accurate measurement of total serum 25-hydroxyvitamin D 25(OH)D concentrations i.e., 25(OH)D3 and 25(OH)D2. This study evaluated agreement between ...the ADVIA Centaur Vitamin D Total assay for 25(OH)D testing (traceable to the NIST-Ghent reference method procedure) and a liquid chromatography tandem mass spectrometry (LC-MS/MS) method for various populations with different levels of vitamin D binding protein (DBP). Total serum 25(OH)D concentrations were measured for 36 pregnant women, 40 hemodialysis patients, and 30 samples (DBP-spiked or not) from healthy subjects. ELISA measured DBP levels. The mean serum DBP concentrations were higher for pregnancy (415 μg/mL) and lower for hemodialysis subjects (198 μg/mL) than for healthy subjects and were highest for spiked serum (545 μg/mL). The average bias between the ADVIA Centaur assay and the LC-MS/MS method was −1.4% (healthy), −6.1% (pregnancy), and 4.4% (hemodialysis). The slightly greater bias for samples from some pregnancy and hemodialysis subjects with serum DBP levels outside of the normal healthy range fell within a clinically acceptable range—reflected by analysis of their low-range (≤136 μg/mL), medium-range (137–559 μg/mL), and high-range (≥560 μg/mL) DBP groups. Thus, the ADVIA Centaur Vitamin D Total assay demonstrates acceptable performance compared with an LC-MS/MS method for populations containing different amounts of DBP.
•ELFTM aids prognostic evaluation in patients with advanced liver fibrosis in NASH.•The ELF score comprises results of 3 fibrosis markers, HA, PIIINP, and TIMP-1.•The Atellica IM Analyzer was used ...for analytical performance of 3 analytes and ELF.•Detection capability, precision, interference, linearity, hook effect, were studied.•All predetermined requirements were met making the assay fit for clinical use.
The Enhanced Liver Fibrosis (ELFTM) Test comprises 3 direct serum markers of fibrosis—hyaluronic acid (HA), amino-terminal pro-peptide of type III procollagen (PIIINP), and tissue inhibitor of matrix metalloproteinase 1 (TIMP-1)—whose results are combined in an algorithm to generate the ELF score. Outside the U.S., the ELF Test and score are CE marked for assessment of liver fibrosis severity in patients with signs, symptoms, or risk factors of chronic liver disease to support diagnosis of fibrosis staging or prognosis for likelihood of progression to cirrhosis and liver-related clinical events. In the U.S., the FDA granted de novo marketing authorization to aid prognostic evaluation of disease progression (to cirrhosis and liver-related clinical events) in nonalcoholic steatohepatitis patients with advanced liver fibrosis. We describe the analytical performance of the ELF analytes and score on the Atellica® IM Analyzer.
Clinical and Laboratory Standards Institute protocols were followed for detection capability (limits of blank LoB, detection LoD, and quantitation LoQ), precision, interference, linearity, hook effect, and ELF reference interval.
All parameters met predetermined requirements: HA (LoB 1.00 ng/mL, LoD 2.00 ng/mL, LoQ 3.00 ng/mL); PIIINP (LoB 0.50 ng/mL, LoD 0.75 ng/mL, LoQ 1.00 ng/mL); TIMP-1 (LoB 3.0 ng/mL, LoD 4.0 ng/mL, LoQ 5.0 ng/mL). Across the 3 assays, repeatability was ≤5.4% CV; within-lab precision was ≤8.5% CV. ELF score repeatability was ≤0.6% CV, within-lab precision ≤1.3% CV, and reproducibility ≤1.1% CV. Good correlation was obtained between the Atellica IM ELF and ADVIA Centaur ELF Tests (y = 1.01x − 0.22, r = 0.997). Assays were linear across analytical measuring ranges.
Analytical performance validation results for the ELF Test and ELF score were excellent making the test acceptable for routine clinical use.
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