Longitudinal FGF23 and Klotho axis characterization in children treated with chronic peritoneal dialysis

Involvement of α-klotho in growth hormone (GH) signaling

Growth hormone (GH) exerts multiple effects on different organs directly or via its main mediator, insulin-like growth factor1 (IGF1). In this study, we focused on the novel relationship between GH action and the antiaging hormone α-klotho. Immunofluorescent staining of α-klotho was observed in the renal distal tubules and pituitary glands of somatostatin- and GH-positive cells in wild-type (WT) mice. Treatment of 4-week-old WT mice with GH increased IGF1 mRNA expression in the pituitary gland, liver, heart, kidney, and bone but increased α-klotho mRNA expression only in the pituitary gland, kidney, and bone. Increased α-klotho protein levels were observed in the kidney but not in the pituitary gland. No induction of α-klotho RNA expression by GH was observed in juvenile mice with kidney disease, indicating GH resistance. Furthermore, GH and α-klotho supplementation in HEK293 cells transfected with GHR increased Janus kinase 2 mRNA (a GH downstream signal) expression compared to supplementation with GH alone. In conclusion, we suggest that 1) the kidney is the main source of secreted α-klotho, which is detected in blood by the downstream action of GH, 2) α-klotho induction by GH is resistant in kidney disease, and 3) α-klotho might be an enhanced regulator of GH signaling.

Soluble Klotho, a Potential Biomarker of Chronic Kidney Disease-Mineral Bone Disorders Involved in Healthy Ageing: Lights and Shadows

Shortly after the discovery of Klotho, interest grew in its potential role in chronic kidney disease (CKD). There are three isoforms of the Klotho protein: αKlotho, βKlotho and γKlotho. This review will focus on αKlotho due to its relevance as a biomarker in CKD. αKlotho is synthesized mainly in the kidneys, but it can be released into the bloodstream and urine as soluble Klotho (sKlotho), which undertakes systemic actions, independently or in combination with FGF23. It is usually accepted that sKlotho levels are reduced early in CKD and that lower levels of sKlotho might be associated with the main chronic kidney disease-mineral bone disorders (CKD-MBDs): cardiovascular and bone disease. However, as results are inconsistent, the applicability of sKlotho as a CKD-MBD biomarker is still a matter of controversy. Much of the inconsistency can be explained due to low sample numbers, the low quality of clinical studies, the lack of standardized assays to assess sKlotho and a lack of consensus on sample processing, especially in urine. In recent decades, because of our longer life expectancies, the prevalence of accelerated-ageing diseases, such as CKD, has increased. Exercise, social interaction and caloric restriction are considered key factors for healthy ageing. While exercise and social interaction seem to be related to higher serum sKlotho levels, it is not clear whether serum sKlotho might be influenced by caloric restriction. This review focuses on the possible role of sKlotho as a biomarker in CKD-MBD, highlighting the difference between solid knowledge and areas requiring further research, including the role of sKlotho in healthy ageing.

Klotho and Fibroblast Growth Factor 23 Are Independent of Vitamin D, and Unlike Vitamin D, Are Not Associated With Graft- and Patient Survival After Kidney Transplantation

Short-term survival after kidney transplantation is excellent but long-term survival remains suboptimal. The aim of the study was to explore the relationship between soluble α-Klotho (sKlotho) and intact fibroblast growth factor 23 (iFGF23) measured 8 wk and 1 y posttransplant with long-term graft- and patient survival in a cohort of kidney transplant recipients with deficient and nondeficient vitamin D (25[OH]D) levels.

Methods

Vitamin D, sKlotho, and iFGF23 were measured 8 wk and 1 y posttransplant in 132 recipients transplanted between November 2012 and October 2013.

Results

Of the 132 kidney transplant recipients, 49 had deficient vitamin D levels (<30 nmol/L) and 83 had nondeficient vitamin D levels (≥30 nmol/L) at 8 wk posttransplant. The mean age was 51 y and the median follow-up was 7.4 y. At 1 y posttransplant, vitamin D increased significantly. There were no significant differences in sKlotho or iFGF23 levels between the 2 vitamin D groups neither at 8 wk nor 1 y. sKlotho increased significantly and iFGF23 decreased significantly in the whole cohort. During the follow-up, there were 36 graft losses (27%) and 27 deaths (20%). Ninety-four percent of the transplant recipients with nondeficient vitamin D levels were alive with a well-functioning graft after 5 y using Kaplan-Meier survival estimates, compared with 84% of the patients with deficient vitamin D levels (P = 0.014). Klotho and FGF23 levels did not influence graft- and patient survival.

Conclusions

In this nationwide cohort of kidney transplant recipients, long-term graft- and patient survival were significantly better in patients with vitamin D ≥30 nmol/L 8 wk posttransplant compared with those with vitamin D <30 nmol/L. sKlotho levels increased and iFGF23 levels decreased from 8 wk to 1 y posttransplant. Klotho and FGF23 levels were not associated with graft- and patient survival.

Mineral Metabolism in Children: Interrelation between Vitamin D and FGF23

Fibroblast growth factor 23 (FGF23) was identified at the turn of the century as the long-sought circulating phosphatonin in human pathology. Since then, several clinical and experimental studies have investigated the metabolism of FGF23 and revealed its relevant pathogenic role in various diseases. Most of these studies have been performed in adult individuals. However, the mineral metabolism of the child is, to a large extent, different from that of the adult because, in addition to bone remodeling, the child undergoes a specific process of endochondral ossification responsible for adequate mineralization of long bones’ metaphysis and growth in height. Vitamin D metabolism is known to be deeply involved in these processes. FGF23 might have an influence on bones’ growth as well as on the high and age-dependent serum phosphate concentrations found in infancy and childhood. However, the interaction between FGF23 and vitamin D in children is largely unknown. Thus, this review focuses on the following aspects of FGF23 metabolism in the pediatric age: circulating concentrations’ reference values, as well as those of other major variables involved in mineral homeostasis, and the relationship with vitamin D metabolism in the neonatal period, in vitamin D deficiency, in chronic kidney disease (CKD) and in hypophosphatemic disorders.

Factors associated with 1-year changes in serum fibroblast growth factor 23 levels in pediatric patients with chronic kidney disease

BACKGROUND

Fibroblast growth factor 23 (FGF23) levels increase as kidney function decreases and are associated with increased mortality in patients with chronic kidney disease (CKD). Inflammation has also been shown to increase FGF23 production in adults; however, this has not been validated in pediatric patients with CKD. Furthermore, previous studies on children involved a single measurement of FGF23 without a follow-up, and a few studies have examined changes in FGF23 levels.

METHODS

We measured the levels of serum intact FGF23, tumor necrosis factor-α (TNF-α), and interleukin-6 as parameters of inflammation and other variables related to bone metabolism at baseline and after 1 year in 62 pediatric patients with CKD (stages 2-5D, 1-16 years old). Factors related to changes in FGF23 levels were investigated.

RESULTS

The median age of patients at the evaluation was 10.5 years (interquartile range 6.0-14.0), and the estimated glomerular filtration rate (eGFR) was 59.0 mL/min/1.73 m2 (45.1-69.3). Primary diseases included congenital anomalies of the kidney and urinary tract, ischemic kidney, and glomerulonephritis. The baseline value of FGF23 was 66.5 pg/mL (48.3-96.4), and percent change in FGF23 levels after 1 year was 8.5% (- 29.9-74.7). The percent change in FGF23 levels showed a negative correlation with that in eGFR (P = 0.010), and a positive correlation with that in TNF-α levels (P = 0.035). A multivariate linear regression analysis identified TNF-α as an independent factor increasing FGF23 levels.

CONCLUSIONS

An increase in TNF-α levels is associated with elevation of FGF23 levels in pediatric patients with CKD.

Fibroblast growth factor 23-Klotho and hypertension: experimental and clinical mechanisms

Hypertension (HTN) and chronic kidney disease (CKD) are increasingly recognized in pediatric patients and represent risk factors for cardiovascular morbidity and mortality later in life. In CKD, enhanced tubular sodium reabsorption is a leading cause of HTN due to augmented extracellular fluid volume expansion. The renin-angiotensin-aldosterone system (RAAS) upregulates various tubular sodium cotransporters that are also targets of the hormone fibroblast growth factor 23 (FGF23) and its co-receptor Klotho. FGF23 inhibits the activation of 1,25-dihydroxyvitamin D that is a potent suppressor of renin biosynthesis. Here we review the complex interactions and disturbances of the FGF23-Klotho axis, vitamin D, and the RAAS relevant to blood pressure regulation and discuss the therapeutic strategies aimed at mitigating their pathophysiologic contributions to HTN.

The intersection of Mineralocorticoid Receptor (MR) activation and the FGF23 - Klotho cascade. A Duopoly that promotes renal and cardiovascular injury

The nexus of CKD and cardiovascular disease (CVD) amplifies the morbidity and mortality of CKD, emphasizing the need for defining and establishing therapeutic initiatives to modify and abrogate the progression of CKD and concomitant CV risks. In addition to the traditional CV risk factors, disturbances of mineral metabolism are specific risk factors that contribute to the excessive CV mortality in patients with CKD. These risk factors include dysregulations of circulating factors that modulate phosphate metabolism including fibroblast growth factor 23 (FGF23) and soluble Klotho. Reduced circulating levels and suppressed renal klotho expression may be associated with adverse outcomes in CKD patients. While elevated circulating concentrations or locally produced FGF23 in the strained heart exert pro-hypertrophic mechanisms on the myocardium, Klotho attenuates tissue fibrosis, progression of CKD, cardiomyopathy, endothelial dysfunction, vascular stiffness, and vascular calcification. Mineralocorticoid receptor (MR) activation in non-classical targets, mediated by aldosterone and other ligands, amplifies CVD in CKD. In concert, we detail how the interplay of elevated FGF23, activation of the MR, and concomitant reductions of circulating Klotho in CKD, may potentiate each other's deleterious effects on kidney and the heart, thereby contributing to the initiation and progression of kidney and cardiac functional deterioration, acting through multipronged albeit complementary mechanistic pathways.

Klotho in Clinical Nephrology: Diagnostic and Therapeutic Implications

αKlotho (called Klotho here) is a membrane protein that serves as the coreceptor for the circulating hormone fibroblast growth factor 23 (FGF23). Klotho is also cleaved and released as a circulating substance originating primarily from the kidney and exerts a myriad of housekeeping functions in just about every organ. The vital role of Klotho is shown by the multiorgan failure with genetic deletion in rodents, with certain features reminiscent of human disease. The most common causes of systemic Klotho deficiency are AKI and CKD. Preclinical data on Klotho biology have advanced considerably and demonstrated its potential diagnostic and therapeutic value; however, multiple knowledge gaps exist in the regulation of Klotho expression, release, and metabolism; its target organs; and mechanisms of action. In the translational and clinical fronts, progress has been more modest. Nonetheless, Klotho has potential clinical applications in the diagnosis of AKI and CKD, in prognosis of progression and extrarenal complications, and finally, as replacement therapy for systemic Klotho deficiency. The overall effect of Klotho in clinical nephrology requires further technical advances and additional large prospective human studies.

Cardioprotective Effects of Paricalcitol Alone and in Combination With FGF23 Receptor Inhibition in Chronic Renal Failure: Experimental and Clinical Studies

BACKGROUND

In uremic animals, vitamin D receptor (VDR) agonists like paricalcitol (Pc) attenuate cardiac hypertrophy, but this effect has not been replicated consistently in humans with chronic kidney disease. Elevated fibroblast growth factor 23 (FGF23) levels cause cardiac hypertrophy with activation of the myocardial calcineurin/nuclear factor of activated T cell (NFAT) axis and may antagonize the cardioprotective effects of VDR agonist therapy. We hypothesized that the effectiveness of Pc may depend on the prevailing circulating levels of FGF23 and could be potentiated by the combined administration of a pan-FGF23 receptor (FGFR) blocker agent (PD173074).

METHODS

In rats with 5/6 nephrectomy treated with Pc or PD173074 or both agents concurrently, myocardial mRNA expression of renin-angiotensin system, VDR, FGFR4, and calcineurin/NFAT target genes was determined. In adolescents on hemodialysis, we analyzed sequential echocardiograms, blood pressures and serial FGF23 measurements, and their relations to the cumulative administered dose of parenteral Pc.

RESULTS

The ratio of Pc dose/plasma levels of FGF23 correlated inversely (P < 0.005) with the cardiac mass in uremic rats and in hemodialysis patients, independently of hypertension. Despite persistently elevated FGF23 levels and myocardial FGFR4 activation, Pc suppressed upregulated myocardial calcineurin/NFAT target genes, and the effects were amplified by coadministration of PD173074.

CONCLUSIONS

The beneficial effects of Pc on uremic cardiac hypertrophy are counterbalanced by the increased FGF23 levels. Blockade of FGF23-mediated signaling increased the Pc-induced suppression of the myocardial calcineurin/NFAT system. Higher doses of Pc should be considered in the treatment of patients with uremic cardiomyopathy.

The importance of cardiovascular disease in pediatric transplantation and its link to the kidneys

Cardiovascular disease is a frequent cause of morbidity and mortality in pediatric patients following solid organ transplant. CKD is also common in pediatric patients after a solid organ transplant, and the link between CKD and cardiovascular morbidity is strong. In this review, we examine potential etiologies to explain the risk of cardiovascular morbidity and mortality in pediatric solid organ recipients and identify targets for improving outcomes.

The FGF23-Klotho axis and cardiac tissue Doppler imaging in pediatric chronic kidney disease-a prospective cohort study

BACKGROUND

Chronic kidney disease-associated mineral bone disorder (CKD-MBD) is common in pediatric kidney disease patients and a risk factor for future cardiovascular disease (CVD). Fibroblast growth factor-23 (FGF23) and Klotho are novel key players in CKD-MBD, and has been suggested to be involved in the development of CVD.

METHODS

This prospective cohort study included 74 pediatric patients; 31 with CKD (age range 0.8-18.8 years, glomerular filtration rate (GFR) range 9-68 mL/min/1.73 m²) and 43 transplanted patients (CKD-T; age range 3.3-17.7 years, GFR range 10-99 mL/min/1.73 m²) examined annually for 3 years. We assessed longitudinal patterns and predictors of FGF23 and soluble Klotho, as well as associations to cardiac remodeling and function using echocardiographic pulse wave Doppler (PWD) and color-coded tissue Doppler imaging (cc-TDI).

RESULTS

The prevalence of high FGF23 levels (≥95th percentile) was 60% in CKD and 42% in CKD-T patients, despite a low prevalence of hyperphosphatemia and normal Klotho levels. Low GFR at baseline was a predictor for high mean log FGF23 during follow-up in CKD and CKD-T patients (β = -0.2, p < 0.001). A high log FGF23 z-score longitudinally was borderline significantly associated with elevated left ventricular mass index (LVMI) in CKD patients (β = 1.8, p = 0.06). In addition, high log FGF23 (β = -0.43, p = 0.01) and low log Klotho (β = 0.44, p = 0.006) over time were associated with a worse left ventricular diastolic function (cc-TDI e'/a') in CKD-T patients.

CONCLUSIONS

In pediatric CKD and CKD-T patients, the FGF23 level increase and Klotho level decrease with progressing renal failure, despite well-controlled phosphate levels. Following adjustments, both high FGF23 and low Klotho levels were strongly associated with a worse left ventricular diastolic function longitudinally. The potential role of FGF23 and Klotho in cardiac morbidity in pediatric CKD requires further investigation.

Potential application of klotho in human chronic kidney disease

The extracellular domain of transmembrane alpha-Klotho (αKlotho, hereinafter simply called Klotho) is cleaved by secretases and released into the circulation as soluble Klotho. Soluble Klotho in the circulation starts to decline early in chronic kidney disease (CKD) stage 2 and urinary Klotho possibly even earlier in CKD stage 1. Therefore soluble Klotho could serve as an early and sensitive marker of kidney function decline. Moreover, preclinical animal data support Klotho deficiency is not just merely a biomarker, but a pathogenic factor for CKD progression and extrarenal CKD complications including cardiovascular disease and disturbed mineral metabolism. Prevention of Klotho decline, re-activation of endogenous Klotho production or supplementation of exogenous Klotho are all associated with attenuation of renal fibrosis, retardation of CKD progression, improvement of mineral metabolism, amelioration of cardiomyopathy, and alleviation of vascular calcification in CKD. Therefore Klotho is not only a diagnostic and/or prognostic marker for CKD, but the treatment of Klotho deficiency may be a promising strategy to prevent, retard, and decrease the burden of comorbidity in CKD.

Soluble klotho may be a marker of phosphate reabsorption

Background: 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, 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.

Association between Soluble Klotho and Change in Kidney Function: The Health Aging and Body Composition Study

CKD appears to be a condition of soluble klotho deficiency. Despite known associations between low soluble klotho levels and conditions that promote kidney damage, such as oxidative stress and fibrosis, little information exists regarding the longitudinal association between soluble klotho levels and change in kidney function. We assayed serum soluble α-klotho in 2496 participants within the Health Aging and Body Composition study, a cohort of older adults. The associations between soluble klotho levels and decline in kidney function (relative decline: eGFR decline ≥30%; absolute decline: eGFR decline >3 ml/min per year) and incident CKD (incident eGFR <60 ml/min per 1.73 m2 and >1 ml/min per year decline) were evaluated. We adjusted models for demographics, baseline eGFR, urine albumin-to-creatinine ratio, comorbidity, and measures of mineral metabolism. Among participants, the mean (SD) age was 75 (3) years, 52% were women, and 38% were black. Median (25th, 75th percentiles) klotho level was 630 (477, 817) pg/ml. In fully adjusted models, each two-fold higher level of klotho associated with lower odds of decline in kidney function (odds ratio, 0.78 [95% confidence interval, 0.66 to 0.93] for 30% decline in eGFR, and 0.85 [95% confidence interval, 0.73 to 0.98] for >3 ml/min per year decline in eGFR), but not of incident CKD (incident rate ratio, 0.90 [95% confidence interval, 0.78 to 1.04]). Overall, a higher soluble klotho level independently associated with a lower risk of decline in kidney function. Future studies should attempt to replicate these results in other cohorts and evaluate the underlying mechanism.

Total Phosphate Elimination is Negatively Associated With Increased Serum Fibroblast Growth Factor 23 Levels in Patients who Undergo Peritoneal Dialysis

As fibroblast growth factor 23 (FGF23) has been shown to induce cardiovascular disease directly in patients with chronic kidney disease, identification of factors and treatments that can modulate serum FGF23 (sFGF23) level is clinically important. This retrospective longitudinal study investigated factors that modulate sFGF23 in 49 patients who underwent peritoneal dialysis (PD). sFGF23 ratio (sFGF23 at 18 months/baseline sFGF23) was used as an indicator of changes in sFGF23 level. Total phosphate elimination was the sum of both renal phosphate excretion and dialysate phosphate elimination. In multivariate analysis, log sFGF23 ratio was associated negatively with total phosphate elimination and the use of cinacalcet at baseline, and positively with the use of vitamin D receptor activators at baseline, even after adjusting for potential confounding factors. Our study indicates that maintaining phosphate elimination can prevent increased sFGF23_, thereby preventing cardiovascular events in patients who undergo PD.

Klotho/FGF23 Axis in Chronic Kidney Disease and Cardiovascular Disease

BACKGROUND

Membrane αKlotho (hereinafter called Klotho) is highly expressed in the kidney and functions as a coreceptor of FGF receptors (FGFRs) to activate specific fibroblast growth factor 23 (FGF23) signal pathway. FGF23 is produced in bones and participates in the maintenance of mineral homeostasis. The extracellular domain of transmembrane Klotho can be cleaved by secretases and released into the circulation as soluble Klotho. Soluble Klotho does not only weakly activate FGFRs to transduce the FGF23 signaling pathway, but also functions as an enzyme and hormonal substance to play a variety of biological functions. FGF23 exerts its biological effects through activation of FGFRs in a Klotho-dependent manner. However, extremely high FGF23 can exert its pathological action in a Klotho-independent manner.

SUMMARY

The decline in serum and urinary Klotho followed by a rise in serum FGF23 at an early stage of chronic kidney disease (CKD) functions as an early biomarker for kidney dysfunction and can also serve as a predictor for risk of cardiovascular disease (CVD) and mortality in both CKD patients and the general population. Moreover, Klotho deficiency is a pathogenic factor for CKD progression and CVD. FGF23 may also contribute to CVD. Prevention of Klotho decline, reactivation of endogenous Klotho production, or supplementation of exogenous Klotho attenuate renal fibrosis, retard CKD progression, improve mineral metabolism, ameliorate cardiomyopathy, and alleviate vascular calcification in CKD. However, the poor CVD outcome after depletion of FGF23 with FGF23 antibody stimulates the generation of a more specific inhibitor of FGF23 for CKD treatment.

KEY MESSAGE

Klotho/FGF23 may not only be diagnostic and/or prognostic biomarkers for CKD and CVD, but are also pathogenic contributors to CKD progression and CVD development. The Klotho/FGF23 axis should be a novel target for renal clinics.

Fibroblast growth factor-23 and renin-angiotensin system levels in vitamin-D-dependent rickets type I

BACKGROUND

As 1,25(OH)2D3 vitamin D3 induces fibroblast growth factor-23 (FGF-23) production and suppresses the renin-angiotensin-aldosterone system (RAAS), its absence in vitamin-D-dependent rickets type I (VDDR-I) may have adverse health consequences.

CASE DESCRIPTION

An infant presented at age 8 months with hypocalcemia and rickets and very low 1,25(OH)2D3 levels. Genetic analysis confirmed VDRR-I, and calcitriol therapy was initiated. During periods of nonadherence to therapy, chemical measurements revealed detectable FGF-23 levels, with undetectable 1,25(OH)2D3, hypophosphatemia, low tubular reabsorption of phosphate, hypocalcemia, and very elevated parathyroid hormone (PTH) levels. These changes, in addition to elevated RAAS levels, normalized during calcitriol therapy despite elevated FGF-23 levels. At age 12 years, all rachitic manifestations were absent, and bone mineral density (BMD) and the echocardiogram were normal.

CONCLUSIONS

Whereas 1,25(OH)2D3 is not indispensable for FGF-23 production, PTH in the absence of vitamin D may maintain FGF-23 secretion despite hypocalcemia. Normalization of urinary phosphate losses despite elevated FGF-23 during calcitriol-mediated suppression of secondary hyperparathyroidism points to a cardinal role of PTH as a cause of the phosphaturia in VDRR-I. Normalization of RAAS by calcitriol may conceivably prevent adverse cardiovascular outcomes.

Sclerostin, TNF-alpha and Interleukin-18 Correlate and are Together with Klotho Related to Other Growth Factors and Cytokines in Haemodialysis Patients

Patients with chronic renal failure are known to have renal osteodystrophy (bone disease) and increased calcification of vessels. A new marker of bone disease, sclerostin, the two pro-inflammatory cytokines tumour necrosis factor-alpha (TNF-alpha) and interleukin-18 (IL-18), and the fibroblast growth factor-23 (FGF-23) receptor-associated marker Klotho were tested in 84 haemodialysis (HD) patients and in healthy controls. The patients had significantly higher levels of the three former markers than of the controls while Klotho was significantly higher in the controls. Low level, but significant, correlations were observed in the patient group when the levels of these four markers were compared to each other and to those of 5 cytokines and growth factors tested earlier; high-sensitive CRP (hsCRP), interleukin-6 (IL-6), hepatocyte growth factor (HGF), fibroblast growth factor-23 (FGF-23) and soluble urokinase plasminogen activator (suPAR). Ln sclerostin correlated positively to Ln hsTNF-alpha, Ln HGF and Ln suPAR. Ln hsTNF-alpha correlated positively to Ln sclerostin, Ln hsCRP, Ln IL-6, Ln FGF-23, Ln suPAR and Ln IL-18. Ln IL-18 correlated positively to Ln suPAR and Ln TNF-alpha. Ln Klotho correlated negatively to Ln hsCRP but did not correlate to Ln FGF-23. The markers studied here may be involved in the calcification of vessels seen in HD patients due to a combination of inflammation and bone disease. The mechanisms are still not fully known but may be of importance for future therapeutic possibilities in this group of patients.

αKlotho and Chronic Kidney Disease

Alpha-Klotho (αKlotho) protein is encoded by the gene, Klotho, and functions as a coreceptor for endocrine fibroblast growth factor-23. The extracellular domain of αKlotho is cleaved by secretases and released into the circulation where it is called soluble αKlotho. Soluble αKlotho in the circulation starts to decline in chronic kidney disease (CKD) stage 2 and urinary αKlotho in even earlier CKD stage 1. Therefore soluble αKlotho is an early and sensitive marker of decline in kidney function. Preclinical data from numerous animal experiments support αKlotho deficiency as a pathogenic factor for CKD progression and extrarenal CKD complications including cardiac and vascular disease, hyperparathyroidism, and disturbed mineral metabolism. αKlotho deficiency induces cell senescence and renders cells susceptible to apoptosis induced by a variety of cellular insults including oxidative stress. αKlotho deficiency also leads to defective autophagy and angiogenesis and promotes fibrosis in the kidney and heart. Most importantly, prevention of αKlotho decline, upregulation of endogenous αKlotho production, or direct supplementation of soluble αKlotho are all associated with attenuation of renal fibrosis, retardation of CKD progression, improvement of mineral metabolism, amelioration of cardiac function and morphometry, and alleviation of vascular calcification in CKD. Therefore in rodents, αKlotho is not only a diagnostic and prognostic marker for CKD but the enhancement of endogenous or supplement of exogenous αKlotho are promising therapeutic strategies to prevent, retard, and decrease the comorbidity burden of CKD.