FGF23 is associated with early post-transplant hypophosphataemia and normalizes faster than iPTH in living donor renal transplant recipients: a longitudinal follow-up study

Autosomal dominant hypercalciuric hypocalcaemia: the calcium-sensing receptor in renal calcium homeostasis and the impact of renal transplantation

Calcium-sensing receptors (CaSRs) are G protein-coupled receptors that help maintain Ca2+ concentrations, modulating calciotropic hormone release (parathyroid hormone (PTH), calcitonin and 1,25-dihydroxyvitamin D) by direct actions in the kidneys, gastrointestinal tract and bone. Variability in population calcium levels has been attributed to single nucleotide polymorphisms in CaSR genes, and several conditions affecting calcium and phosphate homeostasis have been attributed to gain- or loss-of-function mutations. An example is autosomal dominant hypercalciuric hypocalcaemia, because of a missense mutation at codon 128 of chromosome 3, as reported in our specific case and her family. As a consequence of treating symptomatic hypocalcaemia as a child, this female subject slowly developed progressive end-stage kidney failure because of nephrocalcinosis and nephrolithiasis. After kidney transplantation, she remains asymptomatic, with decreased vitamin D and elemental calcium requirements, stable fluid and electrolyte homeostasis during intercurrent illnesses and has normalised urinary calcium and phosphate excretion, reducing the likelihood of hypercalciuria-induced graft impairment. We review the actions of the CaSR, its role in regulating renal Ca2+ homeostasis along with the impact of a proven gain-of-function mutation in the CaSR gene resulting in autosomal dominant hypercalciuric hypocalcaemia before and after kidney transplantation.

Fibroblast growth factor 23-Klotho and mineral metabolism in the first year after pediatric kidney transplantation: A single-center prospective study

BACKGROUND

The role of fibroblast growth factor 23 (FGF23) levels in mineral metabolism before and after kidney transplantation in pediatric patients is poorly understood.

METHODS

We prospectively evaluated 24 patients under 18 years of age (4.5 [3.3-9.8] years) who underwent living kidney transplantation between July 2016 and March 2018, and measured intact FGF23 and serum αKlotho levels, and other parameters of mineral metabolism before and after transplantation (Day 7, 1 and 4 months, and 1 year). Relationships between parameters were examined by linear analysis.

RESULTS

FGF23 level was 440.8 [63.4-5916.3] pg/ml pre-transplant and decreased significantly to 37.1 [16.0-71.5] pg/ml at Day 7 post-transplant (-91.6%, p < .001). Thereafter, it remained at normal levels until 1 year. αKlotho level was 785 [568-1292] pg/ml pre-transplant and remained low at Day 7 and 1 month post-transplant, with an increasing trend at 4 months. Post-transplant phosphorus levels were significantly decreased compared with pre-transplant, with a lowest level of 1.7 [1.3-2.9] mg/dl, -5.7 [-6.8, -3.8] SD at Day 4, followed by gradual recovery. Phosphorus levels and the ratio of tubular maximum phosphate reabsorption were significantly and negatively associated with pre-transplant FGF23 until 4 months of post-transplant. Pre-transplant αKlotho was negatively associated with pre-transplant FGF23 but not FGF23 or other parameters after transplantation.

CONCLUSION

FGF23 in pediatric kidney transplant patients decreased rapidly after transplantation and associated with post-transplant hypophosphatemia and increased phosphorus excretion. Post-transplant αKlotho was low early post-transplant but tended to increase subsequently. Post-transplant αKlotho was unaffected by pre-transplant FGF23 or other factors, suggesting pre-transplant chronic kidney disease status has no effect.

Wnt/β-catenin pathway inhibitors, bone metabolism and vascular health in kidney transplant patients

BACKGROUND AND OBJECTIVES

Sclerostin, dickkopf-related protein 1 (DKK1), fibroblast growth factor-23 (FGF23) and α-klotho have been shown to play an important role in bone and vascular disease of chronic kidney disease. We aimed to evaluate the evolution of these bone markers in newly kidney transplanted patients, and whether they are associated with bone metabolism and vascular stiffness.

DESIGN, SETTING, PARTICIPANTS AND MEASUREMENTS

This is a longitudinal single-center observational cohort study. Circulating levels of Wnt/β-catenin pathway inhibitors (sclerostin, DKK1, FGF23 and α-klotho), arterial stiffness (carotid-femoral pulse-wave velocity (PWV), carotid-radial PWV, PWV ratio, augmented index) and bone parameters were assessed before (M0), and at 3 (M3) and 6 months (M6) after transplantation. Generalized estimating equations were conducted for comparative analyses between the three time points. We used a marginal structural model for repeated measures for the impact of changes in bone markers on the evolution of arterial stiffness. Multivariate linear regression analyses were performed for the associations between Wnt/β-catenin pathway inhibitors and mineral metabolism parameters.

RESULTS

We included 79 patients (70% male; median age of 53 (44-60) years old). The levels of sclerostin (2.06 ± 1.18 ng/mL at M0 to 0.88 ± 0.29 ng/mL at M6, p ≤ 0.001), DKK1 (364.0 ± 266.7 pg/mL at M0 to 246.7 ± 149.1 pg/mL at M6, p ≤ 0.001), FGF23 (5595 ± 9603 RU/mL at M0 to 137 ± 215 RU/mL at M6, p ≤ 0.001) and α-klotho (457.6 ± 148.6 pg/mL at M0 to 109.8 ± 120.7 pg/mL at M6, p < 0.05) decreased significantly after kidney transplant. Sclerostin and FGF23 were positively associated with carotid-femoral (standardized β = 0.432, p = 0.037 and standardized β = 0.592, p = 0.005) and carotid-radial PWV (standardized β = 0.259, p = 0.029 and standardized β = 0.242, p = 0.006) throughout the 6 months of follow-up. The nature of the associations between bone markers and bone metabolism parameters varies after kidney transplant.

CONCLUSIONS

The circulating levels of Wnt/β-catenin pathway inhibitors and α-klotho significantly decrease after kidney transplantation, while sclerostin and FGF23 levels might be associated with improvement of vascular stiffness and blood pressure.

Mineral Bone Disorders in Kidney Disease Patients: The Ever-Current Topic

Chronic kidney disease (CKD) is a complex and multifactorial disease, and one of the most prevalent worldwide. Chronic kidney disease–mineral bone disorders (CKD–MBD) with biochemical and hormonal alterations are part of the complications associated with the progression of CKD. Pathophysiology of CKD–MBD focused on abnormalities in serum levels of several biomarkers (such as FGF-23, klotho, phosphate, calcium, vitamin D, and PTH) which are discussed in this review. We therefore examine the prognostic association between CKD–MBD and the increased risk for cardiovascular events, mortality, and CKD progression to end-stage kidney disease (ESKD). Lastly, we present specific treatments acting on CKD to prevent and treat the complications associated with secondary hyperparathyroidism (SHPT): control of hyperphosphatemia (with dietary restriction, intestinal phosphate binders, and adequate dialysis), the use of calcimimetic agents, vitamin D, and analogues, and the use of bisphosphonates or denosumab in patients with osteoporosis.

Fibroblast growth factor 23: translating analytical improvement into clinical effectiveness for tertiary prevention in chronic kidney disease

OBJECTIVES

Fibroblast growth factor 23 (FGF23) plays a key role in the pathophysiology of chronic kidney disease (CKD) and of the associated cardiovascular diseases, ranking on the crossroads of several evolving areas with a relevant impact on the health-care system (ageing, treatment of CKD and prevention from cardiovascular and renal events). In this review, we will critically appraise the overall issues concerning the clinical usefulness of FGF23 determination in CKD, focusing on the analytical performances of the methods, aiming to assess whether and how the clinical introduction of FGF23 may promote cost-effective health care policies in these patients.

CONTENT

Our comprehensive critical appraisal of the literature revealed that we are currently unable to establish the clinical usefulness of FGF23 measured by ELISA in CKD, as stability issues and suboptimal analytical performances are the major responsible for the release of misleading results. The meta-analytical approach has failed to report unambiguous evidence in face of the wide heterogeneity of the results from single studies.

SUMMARY AND OUTLOOK

Our review has largely demonstrated that the clinical usefulness depends on a thorough analytical validation of the assay. The recent introduction of chemiluminescent intact-FGF23 (iFGF23) assays licensed for clinical use, after passing a robust analytical validation, has allowed the actual assessment of preliminary risk thresholds for cardiovascular and renal events and is promising to capture the iFGF23 clinically relevant changes as a result of a therapeutic modulation. In this perspective, the analytical optimization of FGF23 determination may allow a marriage between physiology and epidemiology and a merging towards clinical outcomes.

Serum Phosphorus, Parathyroid Hormone, and Serum Fibroblast Growth Factor-23 in Egyptian Patients Six Months after Undergoing Living-donor Kidney Transplantation

End-stage renal disease is a major health problem with many complications. Previous studies emphasized the relationship of cardiovascular disease and mortality among these patients to dysregulated phosphate homeostasis. Even after successful renal transplantation, the risk is not eliminated. Several factors seem to interplay to regulate serum phosphorus levels after renal transplantation. Fibroblast growth factor-23 (FGF-23) is a hormone with the major function of inhibiting the reabsorption of phosphate by the renal tubules. Parathormone reduces the reabsorption of phosphate from the proximal tubule of the kidney. The aim of our study was to explore the changes that occurred in FGF-23 and intact parathyroid hormone (iPTH) levels in a cohort of Egyptian patients undergoing renal transplantation and to examine the effect of these factors on posttransplant serum phosphorus levels. The study was carried out prospectively on 37 candidates for live-donor renal transplantation. Serum levels of calcium, phosphorus, iPTH, and FGF-23 were measured before and 6 months after renal transplantation. Statistically significant differences were detected in serum calcium, phosphorus, FGF-23, and iPTH before and 6 months after transplantation (P < 0.001, P < 0.001, P < 0.001, and P < 0.001, respectively). The results also showed a statistically significant correlation between FGF-23 levels and phosphorus levels before transplantation. The interplay between FGF-23 and iPTH has an impact on posttransplant serum phosphorus levels.

Clinical factors associated with severe hypophosphataemia after kidney transplant

BACKGROUND

The mechanism by which hypophosphataemia develops following kidney transplantation remains debated, and limited research is available regarding risk factors. This study aimed to assess the association between recipient and donor variables, and the severity of post-transplantation hypophosphataemia.

METHODS

We performed a single-centre retrospective observational study. We assessed the association between demographic, clinical and biochemical variables and the development of hypophosphataemia. We used linear regression analysis to assess association between these variables and phosphate nadir.

RESULTS

87.6% of patients developed hypophosphataemia. Patients developing hypophosphataemia were younger, had a shorter time on renal replacement therapy, were less likely to have had a parathyroidectomy or to experience delayed graft function, were more likely to have received a living donor transplant, from a younger donor. They had higher pre-transplantation calcium levels, and lower alkaline phosphatase levels. Receipt of a living donor transplant, lower donor age, not having had a parathyroidectomy, receiving a transplant during the era of tacrolimus-based immunosuppression, not having delayed graft function, higher pre-transplantation calcium, and higher pre-transplantation phosphate were associated with lower phosphate nadir by multiple linear regression.

CONCLUSIONS

This analysis demonstrates an association between variables relating to better graft function and hypophosphataemia. The links with biochemical measures of mineral-bone disease remain less clear.

The inflammatory state is a risk factor for cardiovascular disease and graft fibrosis in kidney transplantation

Several factors, such as donor brain death, ischemia-reperfusion injury, rejection, infection, and chronic allograft dysfunction, may induce an inflammatory state in kidney transplantation. Furthermore, inflammatory cells, cytokines, growth factors, complement and coagulation cascade create an unbalanced interaction with innate and adaptive immunity, which are both heavily involved in atherogenesis. The crosstalk between inflammation and thrombosis may lead to a prothrombotic state and impaired fibrinolysis in kidney transplant recipients increasing the risk of cardiovascular disease. Inflammation is also associated with elevated levels of fibroblast growth factor 23 and low levels of Klotho, which contribute to major adverse cardiovascular events. Hyperuricemia, glucose intolerance, arterial hypertension, dyslipidemia, and physical inactivity may create a condition called metaflammation that concurs in atherogenesis. Another major consequence of the inflammatory state is the development of chronic hypoxia that through the mediation of interleukins 1 and 6, angiotensin II, and transforming growth factor beta can result in excessive accumulation of extracellular matrix, which can disrupt and replace functional parenchyma, leading to interstitial fibrosis and chronic allograft dysfunction. Lifestyle and regular physical activity may reduce inflammation. Several drugs have been proposed to control the graft inflammatory state, including low-dose aspirin, statins, renin-angiotensin inhibitors, xanthine-oxidase inhibitors, vitamin D supplements, and interleukin-6 blockade. However, no prospective controlled trial with these measures has been conducted in kidney transplantation.

Association between serum osteoprotegerin level and mortality in kidney transplant recipients - a prospective observational cohort study

Paradoxically, higher serum levels of osteoprotegerin (OPG: a vascular calcification inhibitor) have been associated with increased arterial stiffness, risk of cardiovascular disease and all-cause mortality. A few studies reported that post-transplant OPG levels are associated with mortality in kidney transplant (KT) recipients. In this study, this association was assessed in a cohort of prevalent KT recipients, adjusting for previously untested potential confounders, including fibroblast growth factor 23 (FGF23) and interleukin 6 (IL-6). Socio-demographic and clinical parameters, medical and transplant history, and laboratory data were collected from 982 prevalent KT recipients. The association between serum OPG and all-cause mortality over a 6-year follow-up period was examined using Kaplan-Meier survival curves and multivariable-adjusted Cox regression models. Participants with high serum OPG were more likely female, older, deceased donor KT recipients and have more comorbidity, lower eGFR, higher FGF23, higher IL-6, and longer dialysis vintage. Each 1 pmol/l higher serum OPG level was associated with a 49% higher risk of mortality (hazard ratio (HR) [95% confidence interval (CI)]: 1.49 [1.40-1.61]). This association persisted after adjusting for confounders (HR [95% CI]: 1.20 [1.10-1.30]). In conclusion, serum OPG was associated with all-cause mortality independent of several novel confounders in prevalent KT recipients.

Approach and Management of Hypertension After Kidney Transplantation

Hypertension is one of the most common cardiovascular co-morbidities after successful kidney transplantation. It commonly occurs in patients with other metabolic diseases, such as diabetes mellitus, hyperlipidemia, and obesity. The pathogenesis of post-transplant hypertension is complex and is a result of the interplay between immunological and non-immunological factors. Post-transplant hypertension can be divided into immediate, early, and late post-transplant periods. This classification can help clinicians determine the etiology and provide the appropriate management for these complex patients. Volume overload from intravenous fluid administration is common during the immediate post-transplant period and commonly contributes to hypertension seen early after transplantation. Immunosuppressive medications and donor kidneys are associated with post-transplant hypertension occurring at any time point after transplantation. Transplant renal artery stenosis (TRAS) and obstructive sleep apnea (OSA) are recognized but common and treatable causes of resistant hypertension post-transplantation. During late post-transplant period, chronic renal allograft dysfunction becomes an additional cause of hypertension. As these patients develop more substantial chronic kidney disease affecting their allografts, fibroblast growth factor 23 (FGF23) increases and is associated with increased cardiovascular and all-cause mortality in kidney transplant recipients. The exact relationship between increased FGF23 and post-transplant hypertension remains poorly understood. Blood pressure (BP) targets and management involve both non-pharmacologic and pharmacologic treatment and should be individualized. Until strong evidence in the kidney transplant population exists, a BP of <130/80 mmHg is a reasonable target. Similar to complete renal denervation in non-transplant patients, bilateral native nephrectomy is another treatment option for resistant post-transplant hypertension. Native renal denervation offers promising outcomes for controlling resistant hypertension with no significant procedure-related complications. This review addresses the epidemiology, pathogenesis, and specific etiologies of post-transplant hypertension including TRAS, calcineurin inhibitor effects, OSA, and failed native kidney. The cardiovascular and survival outcomes related to post-transplant hypertension and the utility of 24-h blood pressure monitoring will be briefly discussed. Antihypertensive medications and their mechanism of actions relevant to kidney transplantation will be highlighted. A summary of guidelines from different professional societies for BP targets and antihypertensive medications as well as non-pharmacological interventions, including bilateral native nephrectomy and native renal denervation, will be reviewed.

Fibroblast growth factor 23: are we ready to use it in clinical practice?

Patients with chronic kidney disease (CKD) have a greatly enhanced risk of cardiovascular morbidity and mortality. Over the past decade it has come clear that a disturbed calcium-phosphate metabolism, with Fibroblast Growth Factor-23 as a key hormone, is partly accountable for this enhanced risk. Numerous studies have been performed unravelling FGF23s actions and its association with clinical conditions. As FGF23 is strongly associated with adverse outcome it may be a promising biomarker for risk prediction or, even more important, targeting FGF23 may be a strategy to improve patient outcome. This review elaborates on the clinical usefulness of FGF23 measurement. Firstly it discusses the reliability of the FGF23 measurement. Secondly, it evaluates whether FGF23 measurement may lead to improved patient risk classification. Finally, and possibly most importantly, this review evaluates if lowering of FGF23 should be a target for therapy. For this, the review discusses the current evidence indicating that FGF23 may be in the causal pathway to cardiovascular pathology, provides an overview of strategies to lower FGF23 levels and discusses the current evidence concerning the benefit of lowering FGF23.

Early postkidney transplantation hypophosphatemia

Background:

As hypophosphatemia is a common multifactorial problem of kidney transplantation (Tx), this research aimed at studying the frequency of posttransparent hypophosphatemia in the early postkidney Tx period and investigating the risk components associated with the situation.

Materials and Methods:

In this study, 50 renal transplant recipients on the day before (−1) and on days 10 (+10) and 30 (+30) days after kidney Tx were examined for the levels of serum phosphate (Pi). Levels of serum creatinine (Cr), Pi, 25-hydroxyvitamin D (25[OH] D), intact parathyroid hormone (iPTH) and fibroblast growth factor 23 (FGF-23), the 24 h urinary excretion of Pi and Cr, estimated glomerular filtration rate (eGFR), and the ratio of transport maximum of Pi (TMP) to eGFR (TMP/GFR) were evaluated on the same days.

Results:

Hypophosphatemia (serum Pi <2.5 mg/dl) was seen in 0%, 40%, and 42% of the patients on days −1, +10, and +30, respectively. The levels of 25(OH)D and iPTH were not significantly different in patients with and without hypophosphatemia on days +10 and +30. Compared to those with normophosphatemia, pre-Tx FGF-23 level was significantly higher in patients with hypophosphatemia on days +10 and +30, respectively. The regression coefficient of TMP/GFR and Cr was positive on days −1, +10, and +30. The coefficient of pre-Tx FGF-23 on post-Tx serum Pi was negative on days +10 (P < 0.03) and +30 (P < 0.003), and the coefficient of post-Tx FGF-23 was negative just on day +10 with serum Pi (P < 0.008).

Conclusion:

The main causes of post-Tx hypophosphatemia in the multivariate linear analysis were pre-Tx FGF-23 and post-Tx FGF-23 levels on days +10, post-Tx Cr, and TMP/GFR.

Positive correlation of serum fibroblast growth factor 23 with peripheral arterial stiffness in kidney transplantation patients

BACKGROUND

Fibroblast growth factor 23 (FGF-23) has a role in arterial stiffness (AS) apart from regulating mineral metabolism. We investigated the association between FGF-23 concentration and peripheral AS in renal transplantation (RT) recipients.

METHODS

The fasting blood samples of RT recipients (n = 66) were collected and analyzed.

RESULTS

A total of 29 (43.9%) RT recipients were classified under the peripheral AS group. The RT recipients in this group had a higher prevalence of diabetes (P < 0.001), hypertension (P = 0.001), and metabolic syndrome (P = 0.023); longer post-RT duration (P = 0.006); higher systolic blood pressure (P < 0.001) and diastolic blood pressure (P = 0.024); and higher fasting glucose (P = 0.002), total cholesterol (P = 0.049), blood urea nitrogen (P = 0.027), phosphorus (P = 0.047), and FGF-23 concentrations (P = 0.003) and FGF-23/α-klotho ratio (P < 0.001) but lower klotho concentrations (P = 0.025) than those in the control group. Moreover, FGF-23 concentration (adjusted odds ratio: 1.057, 95% confidence interval: 1.011-1.105, P = 0.015) was found to be an independent predictor of peripheral AS in RT recipients.

CONCLUSIONS

Serum FGF-23 concentration was a significant predictor of peripheral AS in RT recipients.

Cardiovascular Disease After Kidney Transplant

Renal transplantation is the preferred treatment for patients with end-stage kidney disease. However, despite successful kidney transplantation, cardiovascular disease (CVD) remains one of the major causes of patient death and hence graft loss. The antecedents of this increased risk reside within the development of end-stage kidney disease and dialysis. Risk factors for the development of CVD include diabetes, hypertension, and dyslipidemia. Other transplant-specific factors include the presence of a patent arteriovenous fistula and immunosuppressive therapy. Efforts to modify these factors should be strongly encouraged to improve long-term outcomes of transplant patients and reduce death from CVD in this at-risk patient population.

Correlation of serum levels of fibroblast growth factor 23 and Klotho protein levels with bone mineral density in maintenance hemodialysis patients

Objective

The correlation of serum fibroblast growth factor 23 (FGF-23) and Klotho protein levels with bone mineral density (BMD) in maintenance hemodialysis (MHD) patients was analyzed.

Methods

Between January 2015 and November 2015, 125 MHD patients in our hospital were enrolled. Dual-energy X-ray absorptiometry was used to examine the BMD in the femoral neck and lumbar spine of MHD patients. The patients were divided into three groups: a normal bone mass group, an osteopenia group, and an osteoporosis group. An ELISA was performed to measure serum FGF-23, Klotho protein, and 1,25(OH)₂VitD₃ levels. Other parameters, including calcium (Ca), phosphorus (P), and parathyroid hormone, were also measured.

Results

Of the 125 MHD patients, 82.40% of patients had femoral neck osteopenia, and 56.00% of patients had lumbar spinal osteopenia. The serum FGF-23 level was highest in the osteoporosis group. However, there was no significant difference in serum FGF-23 levels among the three groups, depending on femoral neck and lumbar spinal BMD (P > 0.05). Spearman’s correlation analysis also pointed to a lack of correlation between serum FGF-23 levels and BMD. Among the three groups, there were significant differences in serum Klotho protein levels and femoral neck BMD (P < 0.05). Serum Klotho protein levels in the osteoporosis group were clearly lower than those in the normal bone mass group and osteopenia group (P < 0.05). Similarly, serum Klotho protein levels were significantly lower in those with lumbar spinal osteopenia as compared with those in the normal group. There was a positive correlation between serum Klotho protein levels and BMD and T values for the femoral neck and lumbar spine. The results of a multiple linear regression analysis revealed that the serum Klotho protein level was one of the main factors affecting BMD in MHD patients.

Conclusions

The serum level of FGF-23 was not correlated with a change in BMD of MHD patients, whereas the serum Klotho protein level was associated with the degree of BMD. A high Klotho protein level may decrease the severity of chronic kidney disease and mineral bone disorder (CKD-MBD) in MHD patients with low BMD.

FGF23 in kidney transplant: the strange case of Doctor Jekyll and Mister Hyde

During the last decade, a new view into the molecular mechanisms of chronic kidney disease-mineral bone disorder (CKD-MBD) has been proposed, with fibroblast growth factor 23 (FGF23) as a novel player in the field. Enhanced serum FGF23 levels cause a reduction in serum phosphate, together with calcitriol suppression and consequent hyperparathyroidism (HPT). In contrast, reduced serum FGF23 levels are associated with hyperphosphatemia, higher calcitriol levels and parathyroid hormone (PTH) suppression. In addition, serum FGF23 levels are greatly increased and positively correlated with serum phosphate levels in CKD patients. In this population, high serum FGF23 concentration seems to predict the occurrence of refractory secondary HPT and to be associated with higher mortality risk in incident haemodialysis patients. In living-donor kidney transplant recipients, a faster normalization of FGF23 and phosphate levels with a lower prevalence of HPT, may be considered a major pathway to investigate.