Soluble α-Klotho Research Articles

Deficiency of Soluble α-Klotho as an Independent Cause of Uremic Cardiomyopathy.

Cardiovascular disease (CVD) is the major cause of mortality for patients with chronic kidney disease (CKD). Cardiac hypertrophy, occurring in up to 95% patients with CKD (also known as uremic cardiomyopathy), increases their risk for cardiovascular death. Many CKD-specific risk factors of uremic cardiomyopathy have been recognized, such as secondary hyperparathyroidism, indoxyl sulfate (IS)/p-cresyl, and vitamin D deficiency. However, several randomized controlled trials have recently shown that these risk factors have little impact on the mortality of CVD. Klotho is a type 1 membrane protein predominantly produced in the kidney, and CKD is known to be a Klotho-deficient state. Because of its important role in FGF23 and phosphate metabolism, Klotho is believed to affect cardiac growth and function indirectly through FGF23 and phosphate. Recent studies showed that soluble Klotho protects the heart against stress-induced cardiac hypertrophy by inhibiting TRPC6 channel-mediated abnormal Ca(2+) signaling in the heart, and the decreased level of circulating soluble Klotho in CKD is an important cause of uremic cardiomyopathy independent of FGF23 and phosphate. These new evidence suggested that Klotho is an independent contributing factor for uremic cardiomyopathy and a possible new target for treatment of this disease.

Soluble Serum αKlotho Is a Potential Predictive Marker of Disease Progression in Clear Cell Renal Cell Carcinoma.

Renal cell carcinoma (RCC) accounts for approximately 3% of adult malignancies, and clear cell RCC (ccRCC), that has a high metastatic index and high relapse rate, is the most common histological subtype. The identification of new biomarkers in ccRCC is fundamental for stratifying patients into prognostic risk groups and to guide therapy. The renoprotective antiaging gene, αKlotho, has recently been found to work as a tumor suppressor in different human cancers. Here, we evaluated αKlotho expression in tissue and serum of ccRCC patients and correlated it with disease progression. Tissue αKlotho expression was studied by quantitative RT-PCR and immunohistochemistry. In addition, soluble serum αKlotho levels were preoperatively measured in 160 patients who underwent nephrectomy for RCC with ELISA. Estimates of cancer-specific (CSS) and progression-free survival (PFS) were calculated according to the Kaplan–Meier method. Multivariate analysis was performed to identify the most significant variables for predicting CSS and PFS. αKlotho protein levels were significantly decreased in RCC tissues compared with normal tissues (P < 0.01) and the more advanced the disease, the more evident the down-regulation. This trend was also observed in serum samples. Statistically significant differences resulted between serum αKlotho levels and tumor size (P = 0.003), Fuhrman grade (P = 0.007), and clinical stage (P = 0.0004). CSS and PFS were significantly shorter in patients with lower levels of αKlotho (P < 0.0001 and P = 0.0004, respectively). At multivariate analysis low serum levels of αKlotho were independent adverse prognostic factors for CSS (HR = 2.11; P = 0.03) and PFS (HR = 2.18; P = 0.03).These results indicate that a decreased αKlotho expression is correlated with RCC progression, and suggest a key role of declining αKlotho in the onset of cancer metastasis.

Where is the link between mineral bone markers and cardiovascular disease in CKD?

Where is the link between mineral bone markers and cardiovascular disease in CKD?

Soluble αKlotho as a candidate for the biomarker of aging

Although the Klotho gene has been recognized as an aging-suppressor gene, the significance of its soluble product, soluble αKlotho (sKlotho), in aging remains to be elucidated. To address this issue, we conducted a single-centered cross-sectional study in a region with a high prevalence of aging. We compared sKlotho levels with the patient characteristics from medical records and laboratory measurements, including fibroblast growth factor 23 (FGF23), intact parathyroid hormone, activated vitamin D3 and factors associated with mineral bone metabolism, in 52 outpatients with a mean age of 78.2 years. Serum sKlotho levels significantly decreased with age, but were not associated with the stage of chronic kidney disease (CKD). Serum FGF23 levels increased as CKD stages advanced, but were not associated with aging. Univariate analyses revealed that sKlotho levels positively correlated with glomerular filtration rate, and negatively with age and serum levels of FGF23 and phosphorus. In a multivariable linear regression analysis, sKlotho significantly correlated with aging and lower FGF23 levels. Only osteoporosis affected sKlotho and FGF23 levels among the various complications and patient status including medication. In summary, serum sKlotho levels inversely correlated with age and FGF23, and were significantly reduced in patients with osteoporosis. sKlotho may serve as a biomarker of aging independent of renal function.

Renal Production, Uptake, and Handling of Circulating αKlotho.

αKlotho is a multifunctional protein highly expressed in the kidney. Soluble αKlotho is released through cleavage of the extracellular domain from membrane αKlotho by secretases to function as an endocrine/paracrine substance. The role of the kidney in circulating αKlotho production and handling is incompletely understood, however. Here, we found higher αKlotho concentration in suprarenal compared with infrarenal inferior vena cava in both rats and humans. In rats, serum αKlotho concentration dropped precipitously after bilateral nephrectomy or upon treatment with inhibitors of αKlotho extracellular domain shedding. Furthermore, the serum half-life of exogenous αKlotho in anephric rats was four- to five-fold longer than that in normal rats, and exogenously injected labeled recombinant αKlotho was detected in the kidney and in urine of rats. Both in vivo (micropuncture) and in vitro (proximal tubule cell line) studies showed that αKlotho traffics from the basal to the apical side of the proximal tubule via transcytosis. Thus, we conclude that the kidney has dual roles in αKlotho homeostasis, producing and releasing αKlotho into the circulation and clearing αKlotho from the blood into the urinary lumen.

Interrelated aldosterone and parathyroid hormone mutually modify cardiovascular mortality risk

BackgroundInappropriate aldosterone and parathyroid hormone (PTH) secretion is associated with increased cardiovascular risk. Accumulating evidence suggests bidirectional interplay between aldosterone and PTH. MethodsWe evaluated the cross-sectional relationship between plasma aldosterone concentration (PAC), aldosterone to renin ratio (ARR) and PTH and subsequently tested whether the interaction between PAC and PTH modified the risk of cardiovascular death.PAC [78.0 (48.0–123.0) pg/mL], ARR [6.4 (2.9–12.9) pg/mL/pg/mL] and PTH concentration [median: 29.0 (22.0–40.0) pg/mL] were measured in 3074 patients (mean age: 62.5±10.6years; 30.3% women) referred to coronary angiography in a tertiary care center in Southwest Germany. ResultsUsing multiple linear regression analysis, PAC and ARR emerged as an independent predictor of higher PTH concentrations (β=0.12 and 0.21, P<0.001 for both) irrespective of intake of antihypertensive treatment, 25(OH)D, kidney function, serum calcium, phosphate, magnesium, cortisol, NT-pro-BNP, soluble α-klotho and FGF-23 concentration. After a median follow-up of 9.9years, 512 (16.7%) participants had died due to fatal cardiovascular events. Multivariate Cox proportional hazard analysis revealed that both PAC and PTH were independently associated with cardiovascular mortality, with a potential synergistic interaction (P=0.028). PAC and PTH are exclusively associated with cardiovascular death in subjects with PTH and PAC concentrations above the median, respectively (PAC: HR per log SD: 1.14; 95% CI 1.02–1.29; P=0.026; PTH: HR per log SD: 1.18; 95% CI 1.02–1.37; P=0.031). ConclusionsHigher PAC and ARR were independently associated with PTH. PAC was independently related to incident cardiovascular mortality exclusively in patients with elevated PTH and vice versa.

Molecular basis of Klotho: from gene to function in aging.

The discovery of the Klotho (KL) gene, which was originally identified as a putative aging-suppressor gene, has generated tremendous interest and has advanced understanding of the aging process. In mice, the overexpression of the KL gene extends the life span, whereas mutations to the KL gene shorten the life span. The human KL gene encodes the α-Klotho protein, which is a multifunctional protein that regulates the metabolism of phosphate, calcium, and vitamin D. α-Klotho also may function as a hormone, although the α-Klotho receptor(s) has not been found. Point mutations of the KL gene in humans are associated with hypertension and kidney disease, which suggests that α-Klotho may be essential to the maintenance of normal renal function. Three α-Klotho protein types with potentially different functions have been identified: a full-length transmembrane α-Klotho, a truncated soluble α-Klotho, and a secreted α-Klotho. Recent evidence suggests that α-Klotho suppresses the insulin and Wnt signaling pathways, inhibits oxidative stress, and regulates phosphatase and calcium absorption. In this review, we provide an update on recent advances in the understanding of the molecular, genetic, biochemical, and physiological properties of the KL gene. Specifically, this review focuses on the structure of the KL gene and the factors that regulate KL gene transcription, the key sites in the regulation of α-Klotho enzyme activity, the α-Klotho signaling pathways, and the molecular mechanisms that underlie α-Klotho function. This current understanding of the molecular biology of the α-Klotho protein may offer new insights into its function and role in aging.

Diurnal variation and short-term pre-analytical stability of serum soluble α-klotho in healthy volunteers: a pilot study.

To investigate the diurnal variability and pre-analytical stability of soluble α-klotho in serum. Recent evidence suggests that the cleaved extracellular domain of the α-klotho receptor, soluble α-klotho, affects phosphate homeostasis, ion channel regulation and antifibrotic/antioxidant pathways. However, soluble α-klotho measurements have yielded inconsistent results when related to renal function, markers of mineral metabolism and patient outcomes. Pre-analytical factors such as biological variation and analyte stability may affect the interpretation of soluble α-klotho results but are yet to be formally assessed. Clotted blood samples were collected from 10 healthy adult volunteers at three time-points during the day to assess diurnal change. Additional samples were collected and allowed to stand at room temperature for 30, 60 and 120 min, prior to centrifugation and analysis to evaluate analyte stability. Serum soluble α-klotho was measured using a validated commercial enzyme-linked immunosorbent assay. Delayed processing of samples had no significant effect on serum soluble α-klotho concentrations over a 2-h period. Serum soluble α-klotho concentrations remained stable over morning, midday and afternoon time-points in this pilot study. Serum soluble α-klotho demonstrates short-term pre-analytical stability and minimal diurnal variability in this pilot study. Larger studies are warranted to confirm these findings.

Soluble α-klotho as a novel biomarker in the early stage of nephropathy in patients with type 2 diabetes.

ObjectiveAlthough α-klotho is known as an anti-aging, antioxidant, and cardio-renal protective protein, the clinical implications of soluble α-klotho levels in patients with diabetes have not been evaluated. Therefore, this study evaluated whether plasma and urinary α-klotho levels are associated with albuminuria in kidney disease in diabetes.Research Design and MethodsA total of 147 patients with type 2 diabetes and 25 healthy control subjects were enrolled. The plasma and urine concentrations of α-klotho were analyzed by enzyme-linked immunosorbent assay.ResultsPlasma α-klotho (572.4 pg/mL [95% CI, 541.9–604.6 pg/mL] vs. 476.9 pg/mL [95% CI, 416.9–545.5 pg/mL]) and urinary α-klotho levels (59.8 pg/mg creatinine [95% CI, 43.6–82.0 pg/mg creatinine] vs. 21.0 pg/mg creatinine [95% CI, 9.7–45.6 pg/mg creatinine]) were significantly higher in diabetic patients than non-diabetic controls. Among diabetic patients, plasma α-klotho concentration was inversely associated with albuminuria stages (normoalbuminuria, 612.6 pg/mL [95% CI, 568.9–659.6 pg/mL], microalbuminuria, 551.8 pg/mL [95% CI, 500.5–608.3 pg/mL], and macroalbuminuria, 505.7 pg/mL [95% CI, 439.7–581.7 pg/mL] (p for trend = 0.0081), while urinary α-klotho levels were remained constantly high with increasing urinary albumin excretion.ConclusionsSoluble α-klotho levels in plasma and urine may be novel and useful early markers of diabetic renal injury.

α-Klotho protects against oxidative damage in pulmonary epithelia.

α-Klotho exerts pleiotropic biological actions. Heterozygous α-Klotho haplo-insufficient mice (kl/+) appear normal at baseline except for age-related changes in the lung, suggesting heightened pulmonary susceptibility to α-Klotho deficiency. We used in vivo and in vitro models to test whether α-Klotho protects lung epithelia against injury. Normally, α-Klotho is not expressed in the lung, but circulating α-Klotho levels are reduced -40% in kl/+ mice and undetectable in homozygous α-Klotho-deficient mice (kl/kl). kl/+ mice show distal air space enlargement at a given airway pressure, with elevated lung oxidative damage marker (8-hydroxydeoxyguanosine; 8-OHdG); these abnormalities are exacerbated in kl/kl mice. Studies were performed in A549 lung epithelial cells and/or primary culture of alveolar epithelial cells. Hyperoxia (95% O2) and high inorganic phosphate concentrations (Pi, 3-5 mM) additively caused cell injury (lactate dehydrogenase release), oxidative DNA damage (8-OHdG), lipid oxidation (8-isoprostane), protein oxidation (carbonyl), and apoptosis (caspase-8 activity and TUNEL stain). Transfection of transmembrane or soluble α-Klotho, or addition of soluble α-Klotho-containing conditioned media, increased cellular antioxidant capacity (Cu- and Fe-based assays) via increased nuclear factor erythroid-derived 2-related factors 1 and 2 (Nrf1/2) transcriptional activity and ameliorated hyperoxic and phosphotoxic injury. To validate the findings in vivo, we injected α-Klotho-containing conditioned media into rat peritoneum before and during hyperoxia exposure and found reduced alveolar interstitial edema and oxidative damage. We conclude that circulating α-Klotho protects the lung against oxidative damage and apoptosis partly via increasing endogenous antioxidative capacity in pulmonary epithelia. Cytoprotection by α-Klotho may play an important role in degenerative diseases of the lung.

Assessment of tubular reabsorption of phosphate as a surrogate marker for phosphate regulation in chronic kidney disease

Fibroblast growth factor 23 (FGF23) and soluble α-Klotho are emerging potential biomarkers of phosphorus and vitamin D metabolism which change in concentration in early chronic kidney disease (CKD) in order to maintain normal phosphorus levels. Tubular reabsorption of phosphate (TRP) has been commonly used to assess renal tubular phosphate transport. The aim of this study was to evaluate the usefulness of TRP as a surrogate marker of parameters of CKD-mineral bone disease (CKD-MBD) in CKD. A cross-sectional study was performed in 93 stable patients with predialysis CKD stage 1-5. In all patients, TRP, estimated glomerular filtration rate (eGFR), calcium, phosphate, intact parathyroid hormone (iPTH), 25-hydroxyvitamin D, serum FGF23 and urine soluble α-Klotho levels were measured. As renal function declined, TRP significantly decreased (P < 0.001; r = 0.763) and both iPTH and serum FGF23 increased (P < 0.001; r = -0.598, P < 0.001; r = -0.453, respectively). The prevalence of hyperphosphatemia, secondary hyperparathyroidism, FGF23 excess and abnormal TRP increased progressively with declining eGFR. Although TRP level changed later than FGF23, abnormal levels of both TRP and FGF23 were observed earlier than changes in iPTH and serum phosphate. Decreased TRP was found to be independently associated with decreased eGFR and increased iPTH but was not associated with urine soluble α-Klotho or serum FGF23 level in multiple linear regression analysis. TRP is a simple, useful and cost-saving surrogate marker of the assessment of altered mineral metabolism in CKD patients and can be used as an alternative to serum FGF23, especially for mild to moderate renal insufficiency.

Soluble α-Klotho and Its Relation to Kidney Function and Fibroblast Growth Factor-23

Relations between fibroblast growth factor-23 (FGF-23), soluble α-klotho (s-α-klotho), and kidney function in chronic kidney disease (CKD) are still unclear. Especially the role of s-α-klotho requires further study. Our objectives were to analyze the relation of s-α-klotho to estimated glomerular filtration rate (eGFR), FGF-23, and other parameters of calcium-phosphate metabolism and to investigate the response of s-α-klotho to cholecalciferol. Twenty-four CKD (stage 1-5) patients participated in this 8-week randomized controlled trial (vitamin D and chronic renal insufficiency). Interventions included 40 000 IU cholecalciferol or placebo weekly. S-α-klotho was determined by ELISA with antihuman klotho antibodies 67G3 and 91F1. For all patients, s-α-klotho concentrations did not differ between CKD stages. When patients were subdivided based on FGF-23 concentrations, a positive association of s-α-klotho with eGFR became apparent in patients with lower than median FGF-23 concentrations but not in those above median value. Patients with s-α-klotho below 204 pg/mL showed higher age, lower phosphate clearance, and lower bone-specific alkaline phosphatase compared with patients with higher s-α-klotho. Treatment with cholecalciferol significantly increased 1,25-dihydroxyvitamin D. The increase of FGF-23 had only borderline significance. There was no significant effect of high-dose cholecalciferol administration for 8 weeks on plasma s-α-klotho. CKD patients with s-α-klotho below 204 pg/mL had higher age, lower phosphate clearance, and lower bone-specific alkaline phosphatase. An association of s-α-klotho with eGFR was observed only in the presence of close to normal, but not high, FGF-23 concentrations. Cholecalciferol treatment did not change s-α-klotho concentrations.

Association of plasma soluble α-klotho with pro-endothelin-1 in patients with type 2 diabetes

ObjectivesTo study the relationship between plasma soluble klotho (sKlotho) and pro-endothelin-1 (proET-1) in patients with type 2 diabetes (T2DM). Subjects and methodsIn this cross-sectional study, we recruited 175 T2DM subjects and 56 non-diabetic controls. Plasma sKlotho, proET-1 and extracellular superoxide dismutase (SOD) were measured by ELISA and ILMA, respectively. ResultsPlasma sKlotho level in patients with T2DM was lower compared to that in non-diabetic controls (416.8 ± 148.1 vs. 494.6 ± 134.3 pg/ml, p = 0.001) and showed significant interaction with diabetes status in its association with proET-1. Plasma sKlotho was inversely correlated with proET-1 in T2DM (Rho = −0.410, p < 0.0001) but not in non-diabetic controls (Rho = 0.091, p = 0.505). Multivariable linear regression models revealed that sKlotho was independently associated with proET-1 after adjustment for renal filtration function, albuminuria, diabetes duration, HbA1c, systolic and diastolic blood pressure. ConclusionsPlasma sKlotho was associated with proET-1 independent of renal function in patients with T2DM.

Infection and smoking are associated with decreased plasma concentration of the anti-aging protein, α-klotho.

The objective of this study was to determine whether maternal plasma concentrations of soluble α-klotho are different between women with microbial invasion of the intra-amniotic cavity (MIAC) and those without MIAC among preterm labor and intact membranes (PTL) or preterm prelabor rupture of membranes (pPROM). A cross-sectional study was conducted to include women in the following groups: i) PTL with MIAC (n=14); ii) PTL without MIAC (n=79); iii) pPROM with MIAC (n=30); and iv) pPROM without MIAC (n=33). MIAC was defined as a positive amniotic fluid culture for microorganisms (aerobic/anaerobic bacteria or genital mycoplasmas). Amniotic fluid samples were obtained within 48 h of maternal blood collection. Plasma concentration of soluble α-klotho was determined by ELISA. i) The median plasma concentration (pg/mL) of soluble α-klotho was significantly lower in patients with MIAC than in those without MIAC (787.0 vs. 1117.8; P<0.001). ii) Among patients with PTL, those with MIAC had a lower median plasma concentration (pg/mL) of soluble α-klotho than those without MIAC (787.0 vs. 1138.9; P=0.007). iii) Among patients with pPROM, those with MIAC had a lower median plasma concentration (pg/mL) of soluble α-klotho than those without MIAC (766.4 vs. 1001.6; P=0.045). iv) There was no significant difference in the median plasma concentration of soluble α-klotho between PPROM without MIAC and PTL without MIAC (1001.6 pg/mL vs. 1138.9 pg/mL, respectively; P=0.5). v) After adjustment for potential confounders (maternal age, tobacco use, gestational age at venipuncture), soluble α-klotho remained significantly associated with MIAC (P=0.02); and vi) Among patients without MIAC, smoking was significantly associated with a lower median plasma concentration soluble α-klotho than in non-smokers (794.2 pg/mL vs. 1382.0 pg/mL, respectively; P<0.001); however, this difference was not observed in patients with MIAC. Intra-amniotic infection occurring at preterm gestations (regardless of membrane status) was associated with a decrease in maternal plasma concentrations of soluble α-klotho. Moreover, among patients without infection, the plasma concentration of α-klotho was lower in smokers.

Soluble α-Klotho: a novel serum biomarker for the activity of GH-producing pituitary adenomas

Klotho is a lifespan-influencing gene expressed mainly in the kidneys. Soluble α-Klotho (αKL) is released into the circulation. In this study, we present baseline αKL serum levels of patients with acromegaly compared with controls with other pituitary adenomas and assess changes following transsphenoidal surgery. Prospective controlled study. We measured soluble αKL (sandwich ELISA) and IGF1 (RIA) in sera of 14 patients (eight females and six males) with active acromegaly and in 22 control patients (13 females and nine males) operated for non-GH-producing pituitary adenomas. Immunohistochemical staining for Klotho was performed in resected adenomas and in normal pituitary tissue samples. Soluble αKL was high in the acromegaly group preoperatively (median 4217 pg/ml, interquartile range (IQR) 1812-6623 pg/ml) and declined after surgery during early follow-up (2-6 days; median 645 pg/ml, IQR 550-1303 pg/ml) (P<0.001) and during late follow-up (2-3 months post-operatively; median 902 pg/ml, IQR 497-1340 pg/ml; P<0.001). In controls, preoperative soluble αKL was significantly lower than in acromegalics, 532 pg/ml (400-677 pg/ml; P<0.001). Following surgery, soluble αKL remained low during early and late follow-up - changes over time within the control group were not statistically significant. These results were independent of age, sex and kidney function. Klotho staining was equal or slightly decreased in GH-positive adenomas compared with controls. High soluble αKL serum levels were specific to GH-producing adenomas and decreased rapidly following adenoma removal. Thus, soluble αKL appears to be a new specific and sensitive biomarker reflecting disease activity in acromegaly. Similar Klotho staining patterns in controls and acromegalics suggest that the rise in serum αKL is caused by systemic actions of pituitary GH rather than due to increased expression of Klotho by the pituitary (adenoma).

FGF23 Suppresses Chondrocyte Proliferation in the Presence of Soluble α-Klotho both in Vitro and in Vivo

Fibroblast growth factor-23 (FGF23) is well established to play crucial roles in the regulation of phosphate homeostasis. X-linked hypophosphatemic rickets (XLH) is characterized by impaired mineralization and growth retardation associated with elevated circulating FGF23 levels. Administration of phosphate and calcitriol is effective in improving growth retardation, but is not sufficient to fully reverse impaired growth, suggesting the existence of a disease-specific mechanism in the development of growth retardation in addition to dysregulated phosphate metabolism. However, the precise mechanisms of growth retardation in XLH remain elusive. Here, we postulated that FGF23 suppressed chondrocyte proliferation in the presence of soluble α-Klotho (sKL). In vitro and ex vivo studies revealed that FGF23 formed a protein complex with sKL through KL1 internal repeat and suppressed the linear growth of metatarsals in the presence of sKL, which was antagonized by co-incubation with neutralizing antibodies against FGF23 or by knocking-down FGFR3 expression. Additionally, FGF23 binding to FGFR3 was enhanced in the presence of sKL. Histologically, the length of the proliferating zone was diminished and was associated with decreased chondrocyte proliferation. FGF23/sKL suppressed Indian hedgehog (Ihh) expression and administration of Ihh protein partially rescued the suppressive effect of FGF23/sKL on metatarsal growth. Intraperitoneal administration of sKL in Hyp mice, a murine model for XLH, caused a decrease in the length of the proliferating zone associated with decreased chondrocyte proliferation without altering circulating phosphate levels. These findings suggest that suppression of chondrocyte proliferation by FGF23 could have a causative role in the development of growth retardation in XLH.

823: Soluble α-klotho, an anti-aging protein, is reduced in patients with intra-amniotic infection

823: Soluble α-klotho, an anti-aging protein, is reduced in patients with intra-amniotic infection

Plasma soluble α-klotho protein levels in premature and term neonates: correlations with growth and metabolic parameters

α-Klotho (α-KL), a protein with antiaging properties, regulates phosphate, calcium, and bone metabolism, induces resistance to oxidative stress, and may participate in insulin signaling. The role of α-KL in neonates, known to be prone to metabolic disturbances and oxidative stress, is not known. The aim of this study was to evaluate circulating soluble α-KL concentrations in preterm and full-term neonates and unravel possible correlations with growth, metabolism, and indices of oxidative stress. Prospective study. Plasma-soluble α-KL levels were determined by specific ELISA in 50 healthy neonates (25 preterm, mean (s.d.) gestational age (GA) 33.7 (1.1) weeks, and 25 full-term infants) at days 14 and 28 of life. Associations of α-KL with anthropometric, metabolic parameters, and indices of oxidative stress were examined. α-KL levels were significantly higher in full-term than in preterm infants at both days 14 (1099 (480) pg/ml vs 884 (239) pg/ml respectively; P<0.05) and 28 (1277 (444) pg/ml vs 983 (264) pg/ml respectively; P<0.01). In both preterm and full-term infants, α-KL levels increased significantly from day 14 to 28 of life (P<0.001). Circulating α-KL concentrations correlated with GA (β=0.32, P=0.001), body weight (β=0.34, P=0.001), body length (β=0.33, P=0.001), 1,25-dihydroxy-vitamin D level (β=0.24, P<0.05), and malondialdehyde level (β=0.20, P<0.05) but not with glucose, insulin, or homeostasis model assessment index of insulin resistance values. Soluble α-KL levels rise as GA and postnatal age advance in neonates and may have an impact on vitamin D metabolism and oxidative stress. Whether α-KL may have a role in the regulation of infants' growth should be further studied.

Serum soluble ?-Klotho in hemodialysis patients

The extracellular domain of klotho is cleaved and released into various extracellular fluids, such as blood, urine, and cerebrospinal fluid, as soluble α-klotho (sαKl). We measured sαKl in 53 hemodialysis patients and 20 healthy controls to examine its role in mineral metabolism. The sαKl level of the hemodialysis patients was 430 pg/ml (386 - 540 pg/ml, which was lower than that of healthy controls 740 pg/ml (550 - 913 pg/ml, p < 0.01). The serum sαKl level showed a positive correlation with serum phosphorus (P) (σ = 0.33, p = 0.014), while serum corrected Ca tended to be negatively correlated with sαKl (σ = -0.26, p = 0.06). Both parameters showed the same trends in healthy subjects. However, there was no significant association between serum sαKl and age (σ= 0.21, p = 0.14), intact PTH (σ = -0.08, p= 0.55), whole PTH (σ = -0.08, p = 0.59), or FGF23 (σ = -0.07, p = 0.62). Multiple regression analysis showed that P was independently associated with the serum sαKl levels (total adjusted R2 = 0.18, p = 0.02). The sαKl level was lower in hemodialysis patients than in healthy persons. Serum P level was independently associated with the serum sαKl level.

Serum levels of soluble secreted α-Klotho are decreased in the early stages of chronic kidney disease, making it a probable novel biomarker for early diagnosis

α-Klotho was first identified as an aging gene and was later shown to be a regulator of phosphate metabolism. Fibroblast growth factor 23 (FGF23) is the key regulator of phosphate metabolism. Serum levels of soluble α-Klotho in chronic kidney disease (CKD) patients have not previously been determined, especially in relation with FGF23 and creatinine levels. This study was designed to investigate whether serum soluble α-Klotho levels are modulated by renal function, age, and FGF23 level in CKD patients. This study is the first report on the utility of measuring soluble α-Klotho levels in human CKD. A total of 292 CKD patients were enrolled. Serum samples were collected, and FGF23 and soluble α-Klotho levels were measured using enzyme-linked immunosorbent assay kits. In addition, serum creatinine, hemoglobin, albumin, calcium, and phosphate levels were measured. Serum soluble α-Klotho levels were associated positively with estimated glomerular filtration rate (eGFR) (P < 0.0001) and inversely with serum creatinine level (P < 0.01). Interestingly, α-Klotho levels were significantly decreased in stage 2 CKD compared with stage 1 (P = 0.0001). Serum FGF23 levels were associated positively with serum creatinine and negatively with eGFR. FGF23 levels were significantly increased in stage 5 compared with stage 1 CKD. Soluble α-Klotho was associated inversely with log-transformed FGF23 level (P < 0.01). Our data indicate that soluble α-Klotho levels are significantly decreased in stage 2 CKD compared to stage 1, and not only in the advanced stages of the disease. Soluble α-Klotho may thus represent a new biomarker for the diagnosis of CKD, especially in the early stage.