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Soluble klotho may be a marker of phosphate reabsorption.

ABSTRACT: Background: Membrane-bound ?-klotho functions as a co-receptor with fibroblast growth factor receptor at the renal tubule conferring specificity to fibroblast growth factor-23 (FGF-23), allowing it to inhibit tubular phosphate reabsorption at physiological concentrations. ?-klotho also exists as a soluble protein. However, the complex interrelationships between soluble ?-klotho (sKl), FGF-23 and phosphate reabsorption are poorly understood, with little known about the links between sKl, FGF-23 and phosphate reabsorption in chronic kidney disease (CKD). This study addresses this issue in a cohort of patients with and without CKD. Methods: We conducted a single-centre, cross-sectional study of contemporaneously obtained samples of blood and 24-h urine biochemistry along with sKl and intact FGF-23 (iFGF-23) from non-dialysis-dependent CKD patients and healthy volunteers. Pearson's correlation coefficients were used to determine correlations between natural log-transformed (Ln) sKl and iFGF-23 with other parameters of interest. Backward multivariate analysis was undertaken to evaluate the relationship between mineral parameters. Results: One hundred and sixteen participants (77 with CKD and 39 healthy volunteers) were studied, of which 74 (63.8%) were male. The median age was 61 (interquartile range 49-71) years. Those with CKD had lower sKl (408 versus 542?pg/mL), higher iFGF-23 (94 versus 41?pg/mL), higher fractional excretion of phosphate (25.05 versus 10.98%) and lower daily urinary phosphate excretion (UPE) (24.8 versus 32.3?mmol/L) compared with healthy volunteers (all P ?? 0.002). Age correlated inversely and estimated glomerular filtration rate (eGFR) correlated positively with phosphate reabsorption and Ln(sKl), while the opposite was seen with Ln(iFGF23). Upon multivariate analysis, eGFR, Ln(sKl) and parathyroid hormone were independently associated with phosphate reabsorption, whereas Ln(iFGF-23) was not, after adjustment for age. Conclusions: Abnormalities in phosphate regulatory pathways are disturbed early in CKD. While iFGF-23 is associated with phosphate excretion on univariate analyses, sKl demonstrates a significant association with phosphate reabsorption independent of iFGF-23, and this relationship deserves further exploration.

SUBMITTER: Tan SJ

PROVIDER: S-EPMC5466110 | biostudies-literature | 2017 Jun

REPOSITORIES: biostudies-literature

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Soluble klotho may be a marker of phosphate reabsorption.

Tan Sven-Jean SJ Smith Edward R ER Holt Stephen G SG Hewitson Tim D TD Toussaint Nigel D ND

Clinical kidney journal 20170228 3

<b>Background:</b> Membrane-bound α-klotho functions as a co-receptor with fibroblast growth factor receptor at the renal tubule conferring specificity to fibroblast growth factor-23 (FGF-23), allowing it to inhibit tubular phosphate reabsorption at physiological concentrations. α-klotho also exists as a soluble protein. However, the complex interrelationships between soluble α-klotho (sKl), FGF-23 and phosphate reabsorption are poorly understood, with little known about the links between sKl, F ...[more]

PMID: 28616218

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Project description:Alpha-Klotho (alphaKl) regulates mineral metabolism such as calcium ion (Ca(2+)) and inorganic phosphate (Pi) in circulation. Defects in mice result in clinical features resembling disorders found in human aging. Although the importance of transmembrane-type alphaKl has been demonstrated, less is known regarding the physiological importance of soluble-type alphaKl (salphaKl) in circulation.The aims of this study were: (1) to establish a sandwich ELISA system enabling detection of circulating serum salphaKl, and (2) to determine reference values for salphaKl serum levels and relationship to indices of renal function, mineral metabolism, age and sex in healthy subjects.We successively developed an ELISA to measure serum salphaKl in healthy volunteers (n=142, males 66) of ages (61.1+/-18.5year). The levels (mean+/-SD) in these healthy control adults were as follows: total calcium (Ca; 9.46+/-0.41mg/dL), Pi (3.63+/-0.51mg/dL), blood urea nitrogen (BUN; 15.7+/-4.3mg/dL), creatinine (Cre; 0.69+/-0.14mg/dL), 1,25 dihydroxyvitamin D (1,25(OH)(2)D; 54.8+/-17.7pg/mL), intact parathyroid hormone (iPTH; 49.2+/-20.6pg/mL), calcitonin (26.0+/-12.3pg/mL) and intact fibroblast growth factor (FGF23; 43.8+/-17.6pg/mL). Serum levels of salphaKl ranged from 239 to 1266pg/mL (mean+/-SD; 562+/-146pg/mL) in normal adults. Although salphaKl levels were not modified by gender or indices of mineral metabolism, salphaKl levels were inversely related to Cre and age. However, salphaKl levels in normal children (n=39, males 23, mean+/-SD; 7.1+/-4.8years) were significantly higher (mean+/-SD; 952+/-282pg/mL) than those in adults (mean+/-SD; 562+/-146, P<0.001). A multivariate linear regression analysis including children and adults in this study demonstrated that salphaKl correlated negatively with age and Ca, and positively with Pi. Finally, we measured a serum salphaKl from a patient with severe tumoral calcinosis derived from a homozygous missense mutation of alpha-klotho gene. In this patient, salphaKl level was notably lower than those of age-matched controls.We established a detection system to measure human serum salphaKl for the first time. Age, Ca and Pi seem to influence serum salphaKl levels in a normal population. This detection system should be an excellent tool for investigating salphaKl functions in mineral metabolism.

Project description:Background:Soluble Klotho has multiple systemic salutary effects. In animals, both acute and chronic kidney disease models display systemic Klotho deficiency. As such, there is considerable interest in investigating soluble Klotho as a biomarker in patients with different types and severity of kidney diseases. Unfortunately, there remains uncertainty regarding the best method to measure soluble Klotho in human serum samples. Methods:Using human serum samples obtained from several clinical cohorts with a wide range of kidney function, we measured soluble Klotho using a commercial enzyme-linked immunosorbent assay (ELISA) as well as with an immunoprecipitation-immunoblot (IP-IB) assay utilizing a synthetic antibody with high affinity and specificity for Klotho. Recovery of spiking with a known amount of exogenous Klotho was tested. A subset of samples was analyzed with and without the addition of a protease inhibitor cocktail at the time of collection or after the first freeze-thaw cycle to determine if these maneuvers influenced performance. Results:The IP-IB assay was superior to the ELISA at recovery of exogenous Klotho (81-115% versus 60-81%) across the spectrum of kidney function. Klotho measurements by IP-IB were highly correlated with estimated glomerular filtration rate (eGFR) (R?=?0.80, P?<?0.001) in comparison with the commercial ELISA, which exhibited minimal correlation with eGFR (R?=?0.18, P?=?0.12). Use of a protease inhibitor cocktail neither improved nor impaired performance of the IP-IB assay; however, subsequent freeze-thaw cycle resulted in a significant reduction in Klotho recovery and dissipated the correlation between Klotho levels and eGFR. With the ELISA, the use of protease inhibitor cocktail resulted in an increase in intrasubject variability. Conclusions:The IP-IB assay is preferable to the commercial ELISA to measure soluble Klotho concentrations in never-thawed serum samples of humans with varying severity of kidney disease. However, due to the labor-intensive nature of the IP-IB assay, further research is needed to secure an assay suitable for high-throughput work.

Project description:Cellular senescence is an irreversible cell growth arrest and is associated with aging and age-related diseases. High plasma phosphate (Pi) and deficiency of Klotho contribute to aging and kidney fibrosis, a pathological feature in the aging kidney and chronic kidney disease. This study examined the interactive role of Pi and Klotho in kidney senescence and fibrosis. Homozygous Klotho hypomorphic mice had high plasma Pi, undetectable Klotho in plasma and kidney, high senescence with massive collagen accumulation in kidney tubules, and fibrin deposits in peritubular capillaries. To examine the Pi effect on kidney senescence, a high (2%) Pi diet was given to wild-type mice. One week of high dietary Pi mildly increased plasma Pi, and upregulated kidney p16/p21 expression, but did not significantly decrease Klotho. Two weeks of high Pi intake led to increase in plasminogen activator inhibitor (PAI)-1, and decrease in kidney Klotho, but still without detectable increase in kidney fibrosis. More prolonged dietary Pi for 12 weeks exacerbated kidney senescence and fibrosis; more so in heterozygous Klotho hypomorphic mice compared to wild-type mice, and in mice with chronic kidney disease (CKD) on high Pi diet compared to CKD mice fed a normal Pi diet. In cultured kidney tubular cells, high Pi directly induced cellular senescence, injury and epithelial-mesenchymal transition, and enhanced H2O2-induced cellular senescence and injury, which were abrogated by Klotho. Fucoidan, a bioactive molecule with multiple biologic functions including senescence inhibition, blunted Pi-induced cellular senescence, oxidation, injury, epithelial-mesenchymal transition, and senescence-associated secretary phenotype. In conclusion, high Pi activates senescence through distinct but interconnected mechanisms: upregulating p16/p21 (early), and elevating plasminogen activator inhibitor-1 and downregulating Klotho (late). Klotho may be a promising agent to attenuate senescence and ameliorate age-associated, and Pi-induced kidney degeneration such as kidney fibrosis.

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Soluble klotho may be a marker of phosphate reabsorption.

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Soluble klotho may be a marker of phosphate reabsorption.

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