Longitudinal analysis of vascular function and biomarkers of metabolic bone disorders before and after renal transplantation

Non-Classical Effects of FGF23: Molecular and Clinical Features

This article reviews the role of fibroblast growth factor 23 (FGF23) protein in phosphate metabolism, highlighting its regulation of vitamin D, parathyroid hormone, and bone metabolism. Although it was traditionally thought that phosphate-calcium homeostasis was controlled exclusively by parathyroid hormone (PTH) and calcitriol, pathophysiological studies revealed the influence of FGF23. This protein, expressed mainly in bone, inhibits the renal reabsorption of phosphate and calcitriol formation, mediated by the α-klotho co-receptor. In addition to its role in phosphate metabolism, FGF23 exhibits pleiotropic effects in non-renal systems such as the cardiovascular, immune, and metabolic systems, including the regulation of gene expression and cardiac fibrosis. Although it has been proposed as a biomarker and therapeutic target, the inhibition of FGF23 poses challenges due to its potential side effects. However, the approval of drugs such as burosumab represents a milestone in the treatment of FGF23-related diseases.

High pretransplant FGF23 level is associated with persistent vitamin D insufficiency and poor graft survival in kidney transplant patients

Vitamin D3 (25[OH]D3) insufficiency and fibroblast growth factor 23 (FGF23) elevation are usually attenuated after kidney transplantation (KT). However, elevated FGF23 may be associated with poor graft outcomes and vitamin D insufficiency after KT. This study investigated the effect of pretransplant FGF23 levels on post-KT 25(OH)D3 status and graft outcomes. Serum FGF23 levels from 400 participants of the KoreaN Cohort Study for Outcome in Patients With Kidney Transplantation were measured. Annual serum 25(OH)D3 levels, all-cause mortality, cardiovascular event, and graft survival were assessed according to baseline FGF23 levels. Serum 25(OH)D3 levels were initially increased 1 year after KT (12.6 ± 7.4 vs. 22.6 ± 6.4 ng/mL). However, the prevalence of post-KT vitamin D deficiency increased again after post-KT 3 years (79.1% at baseline, 30.8% and 37.8% at 3 and 6 years, respectively). Serum FGF23 level was decreased 3 years post-KT. When participants were categorized into tertiles according to baseline FGF23 level (low, middle, high), 25(OH)D3 level in the low FGF23 group was persistently low at a median follow-up of 8.3 years. Furthermore, high baseline FGF23 level was a risk factor for poor graft survival (HR 5.882, 95% C.I.; 1.443-23.976, P = 0.013). Elevated FGF23 levels are associated with persistently low post-transplant vitamin D levels and poor graft survival.

The Role of Alterations in Alpha-Klotho and FGF-23 in Kidney Transplantation and Kidney Donation

Cardiovascular disease and mineral bone disorders are major contributors to morbidity and mortality among patients with chronic kidney disease and often persist after renal transplantation. Ongoing hormonal imbalances after kidney transplant (KT) are associated with loss of graft function and poor outcomes. Fibroblast growth factor 23 (FGF-23) and its co-receptor, α-Klotho, are key factors in the underlying mechanisms that integrate accelerated atherosclerosis, vascular calcification, mineral disorders, and osteodystrophy. On the other hand, kidney donation is also associated with endocrine and metabolic adaptations that include transient increases in circulating FGF-23 and decreases in α-Klotho levels. However, the long-term impact of these alterations and their clinical relevance have not yet been determined. This manuscript aims to review and summarize current data on the role of FGF-23 and α-Klotho in the endocrine response to KT and living kidney donation, and importantly, underscore specific areas of research that may enhance diagnostics and therapeutics in the growing population of KT recipients and kidney donors.

Bone Mineral Density Changes in Long-Term Kidney Transplant Recipients: A Real-Life Cohort Study of Native Vitamin D Supplementation

Vitamin D insufficiency has been associated with reduced bone mineral density (BMD) in kidney transplant patients (KTRs). However, the efficacy of vitamin D supplementation on BMD remains poorly defined, especially for long-term KTRs. We aimed to investigate the effect of native vitamin D supplementation on the BMD of KTRs during a 2-year follow-up. Demographic, clinical, and laboratory data were collected. BMD was evaluated with standard DEXA that was performed at baseline (before vitamin D supplementation) and at the end of study period. BMD was assessed at lumbar vertebral bodies (LV) and right femoral neck (FN) by a single operator. According to WHO criteria, results were expressed as the T-score (standard deviation (SD) relative to young healthy adults) and Z-score (SD relative to age-matched controls). Osteoporosis and osteopenia were defined as a T-score ≤ -2.5 SD and a T-score < -1 and a > -2.5 SD, respectively. Based on plasma levels, 25-OH-vitamin D (25-OH-D) was supplemented as recommended for the general population. Data from 100 KTRs were analyzed. The mean study period was 27.7 ± 3.4 months. At study inception, 25-OH-D insufficiency and deficiency were recorded in 65 and 35 patients. At the basal DEXA, the percentage of osteopenia and osteoporosis was 43.3% and 18.6% at LV and 54.1% and 12.2% at FN, respectively. At the end of the study, no differences in the Z-score and T-score gains were observed. During linear mixed model analysis, native vitamin D supplementation was found to have a negative nitration with Z-score changes at the right femoral neck in KTRs (p < 0.05). The mean dose of administered cholecalciferol was 13.396 ± 7.537 UI per week; increased 25-OH-D levels were found (p < 0.0001). Either low BMD or 25-OH-vitamin D concentration was observed in long-term KTRs. Prolonged supplementation with 25-OH-D did not modify BMD, Z-score, or T-score.

Εndothelial and microvascular function in CKD: Evaluation methods and associations with outcomes

BACKGROUND

Cardiovascular disease is the major cause of morbidity and mortality in patients with chronic kidney disease (CKD). Endothelial dysfunction, the hallmark of atherosclerosis, is suggested to be involved pathogenetically in cardiovascular and renal disease progression in these patients.

METHODS

This is a narrative review presenting the techniques and markers used for assessment of microvascular and endothelial function in patients with CKD and discussing findings of the relevant studies on the associations of endothelial dysfunction with co-morbid conditions and outcomes in this population.

RESULTS

Venous Occlusion Plethysmography was the first method to evaluate microvascular function; subsequently, several relevant techniques have been developed and used in patients with CKD, including brachial Flow-Mediated Dilatation, and more recently, Near-Infrared Spectroscopy and Laser Speckle Contrast Analysis. Furthermore, several circulating biomarkers are commonly used in clinical research. Studies assessing endothelial function using the above techniques and biomarkers suggest that endothelial dysfunction occurs early in CKD and contributes to the target organ damage, cardiovascular events, death and progression towards end-stage kidney disease.

CONCLUSIONS

Older and newer functional methods and several biomarkers have assessed endothelial dysfunction in CKD; accumulated evidence supports an association of endothelial dysfunction with outcomes. Future research with new, non-invasive and easily applicable methods could further delineate the role of endothelial dysfunction on cardiovascular and renal disease progression in patients with CKD.

Assessment of Endothelial and Microvascular Function in CKD: Older and Newer Techniques, Associated Risk Factors, and Relations with Outcomes

BACKGROUND

Endothelium is the inner cellular lining of the vessels that modulates multiple biological processes including vasomotor tone, permeability, inflammatory responses, hemostasis, and angiogenesis. Endothelial dysfunction, the basis of atherosclerosis, is characterized by an imbalance between endothelium-derived relaxing factors and endothelium-derived contracting factors.

SUMMARY

Starting from the semi-invasive venous occlusion plethysmography, several functional techniques have been developed to evaluate microvascular function and subsequently used in patients with CKD. Flow-mediated dilatation of the forearm is considered to be the "gold standard," while in the last years, novel, noninvasive methods such as laser speckle contrast imaging and near-infrared spectroscopy are scarcely used. Moreover, several circulating biomarkers of endothelial function have been used in studies in CKD patients. This review summarizes available functional methods and biochemical markers for the assessment of endothelial and microvascular function in CKD and discusses existing evidence on their associations with comorbid conditions and outcomes in this population. Key Messages: Accumulated evidence suggests that endothelial dysfunction occurs early in CKD and is associated with target organ damage, progression of renal injury, cardiovascular events, and mortality. Novel methods evaluating microvascular function can offer a detailed, real-time assessment of underlying phenomena and should be increasingly used to shed more light on the role of endothelial dysfunction on cardiovascular and renal disease progression in CKD.

Arterial vessel reactivity in patients in the long term after kidney transplantation - preliminary study

INTRODUCTION

The aim of this study was to evaluate the endothelial-dependent and -independent arterial vessels' reactivity in patients in the long term after kidney transplantation (KTx).

MATERIAL AND METHODS

The study included 36 (15 females; 21 males) patients after KTx with good, stable graft function and 94 healthy individuals (51 males, 43 females). The endothelial-dependent dilatory capacity of the brachial artery was estimated by an ischemic test (flow-mediated dilation - FMD), and independent by nitroglycerin-mediated vasodilation (NMD). The results were shown for age-related groups and compared with age-related healthy people.

RESULTS

KTx patients were mean 5.1 ±2.3 years after transplantation with the mean estimated glomerular filtration rate (eGFR) 50.3 ±17.1 ml/min/1.73 m². The mean vessel diameter before tests was significantly larger in healthy people than in KTx patients. The FMD test showed vasodilation becoming weaker along with age in both groups, but in KTx patients this relationship was clearly enhanced. The NMD was delayed in relation to age, and in KTx patients was preserved, being only slightly weaker than in healthy people.

CONCLUSIONS

Both endothelium-dependent and -independent arterial wall reactions decrease with age. The endothelial-dependent vascular response is more attenuated in KTx patients than the independent one. The endothelium-independent vasodilation in KTx patients is comparable with that in healthy people.

The role of endothelial glycocalyx in health and disease

The endothelium is the largest organ in the body and recent studies have shown that the endothelial glycocalyx (eGCX) plays a major role in health and disease states. The integrity of eGCX is vital for homoeostasis and disruption of its structure and function plays a major role in several pathologic conditions. An increased understanding of the numerous pathophysiological roles of eGCX may lead to the development of potential surrogate markers for endothelial injury or novel therapeutic targets. This review provides a state-of-the-art update on the structure and function of the eGCX, emphasizing the current understanding of interorgan crosstalk between the eGCX and other organs that might also contribute to the pathogenesis of kidney diseases.

A Pilot Trial to Examine the Changes in Carotid Arterial Inflammation in Renal Transplant Recipients as Assessed by 18F-Fluorodeoxyglucose (18F-FDG) Positron Emission Tomography Computed Tomography (PET/CT)

BACKGROUND Inflammatory activity of the artery can be assessed by measuring 18F-fluorodeoxyglucose (18F-FDG) uptake with positron emission tomography computed tomography (PET/CT). Improvement in vascular function after renal transplantation has been reported, but no studies have used 18F-FDG PET/CT to examine the changes in vascular inflammation. This study investigated the changes in the inflammatory activity in the carotid artery after renal transplantation in patients with chronic kidney disease (CKD). MATERIAL AND METHODS 18F-FDG PET/CT was performed before and at 4 months after transplantation. We quantified 18F-FDG uptake as the target-to-background ratio (TBR) in the carotid artery in 10 CKD patients. TBR was evaluated in the whole carotid artery (WH) and most-diseased segment (MDS), and the mean and maximum values were analyzed. The concentrations of inflammatory cytokines, including tumor necrosis factor-alpha, interleukin-6, plasminogen activator inhibitor-1, and endothelin-1, were measured. RESULTS Eight patients showed a decrease in mean or maximum TBR. The average mean or maximum TBRs in the WH and MDS of the right and left arteries were all reduced after transplantation. The average mean TBR for the right WH decreased significantly (% reduction [95% CI]) by -5.74% [-15.37, -0.02] (p=0.047). TBRs did not correlate significantly with cytokine concentrations. The changes in cytokine concentrations after transplantation varied. CONCLUSIONS 18F-FDG uptake by the WH and MDS tended to reduce after renal transplantation. Therefore, renal transplantation may confer an anti-inflammatory effect on carotid atherosclerosis in patients with CKD; however, this effect is not large enough to be demonstrated in this study with small sample size.

Uremic Toxins and Clinical Outcomes: The Impact of Kidney Transplantation

Non-transplanted and transplanted patients with chronic kidney disease (CKD) differ in terms of mortality and the risk of clinical events. This difference is probably due to the difference of both traditional and non-traditional risk factors. Uremic retention solutes may constitute important non-traditional risk factors in this population. In the present review, we selected a set of uremic toxins that have been associated with harmful effects, and are an appealing target for adjuvant therapy in CKD. For each toxin reviewed here, relevant studies were selected and the relationship with hard clinical outcomes of uremic toxins were compared between non-transplanted CKD patients and transplanted patients taking into account the level of glomerular filtration rate in these two situations.

Fibroblast Growth Factor-23: A Novel Biomarker for Cardiovascular Disease in Chronic Kidney Disease Patients

Fibroblast Growth Factor (FGF)-23 increase is considered one of the earliest biochemical abnormalities in chronic kidney disease-mineral bone disorder (CKD-MBD). Furthermore, accumulating data have provided evidence of a link between increased FGF-23 levels and cardiovascular morbidity and mortality in CKD patients as well as in several other populations including cardiology patients and general population. The cellular and molecular mechanisms underlying the deleterious effect of FGF-23 on the cardiovascular system are not yet completely defined and are the focus of intense research. However, animal and human studies have demonstrated important actions of FGF-23 in the heart and vessels through which could promote the development of cardiovascular complications in uremia. Moreover, significant interactions have been reported between FGF-23 and other well recognized cardiovascular risk factors such as renin-angiotensin system and inflammation which could account, at least in part, for the observed associations between FGF-23 and adverse clinical outcomes. Further studies are needed to clarify the mechanisms responsible for the pleiotropic actions of FGF-23 and moreover to identify whether it is a modifiable risk factor and a potential target of therapeutic interventions which could probably help to reduce the unacceptably high cardiovascular morbidity and mortality of CKD patients.

Current evidence on vitamin D deficiency and kidney transplant: What's new?

Kidney transplant is the treatment of choice for end-stage chronic kidney disease. Kidneys generate 1,25-dihydroxyvitamin D (calcitriol) from 25-hydroxyvitamin D (calcidiol) for circulation in the blood to regulate calcium levels. Transplant patients with low calcidiol levels have an increased risk of metabolic and endocrine problems, cardiovascular disease, type 2 diabetes mellitus, poor graft survival, bone disorders, cancer, and mortality rate. The recommended calcidiol level after transplant is at least 30 ng/mL (75 nmol/L), which could require 1000-3000 IU/d vitamin D3 to achieve. Vitamin D3 supplementation studies have found improved endothelial function and acute rejection episodes. However, since kidney function may still be impaired, raising calcidiol levels may not lead to normal calcitriol levels. Thus, supplementation with calcitriol or an analog, alfacalcidiol, is often employed. Some beneficial effects found include possible improved bone health and reduced risk of chronic allograft nephropathy and cancer.

Extrarenal effects of FGF23

Chronic kidney disease (CKD) is associated with an increased risk of cardiovascular mortality, infections, and impaired cognitive function. It is characterized by excessively increased levels of the phosphaturic hormone fibroblast growth factor 23 (FGF23) and a deficiency of its co-receptor Klotho. Despite the important physiological effect of FGF23 in maintaining phosphate homeostasis, there is increasing evidence that higher FGF23 levels are a risk factor for mortality and cardiovascular disease. FGF23 directly induces left ventricular hypertrophy via activation of the FGF receptor 4/calcineurin/nuclear factor of activated T cells signaling pathway. By contrast, the impact of FGF23 on endothelial function and the development of atherosclerosis are poorly understood. The results of recent experimental studies indicate that FGF23 directly impacts on hippocampal neurons and may thereby impair learning and memory function in CKD patients. Finally, it has been shown that FGF23 interferes with the immune system by directly acting on polymorphonuclear leukocytes and macrophages. In this review, we discuss recent data from clinical and experimental studies on the extrarenal effects of FGF23 with respect to the cardiovascular, central nervous, and immune systems.

Phosphocalcic Markers and Calcification Propensity for Assessment of Interstitial Fibrosis and Vascular Lesions in Kidney Allograft Recipients

Renal interstitial fibrosis and arterial lesions predict loss of function in chronic kidney disease. Noninvasive estimation of interstitial fibrosis and vascular lesions is currently not available. The aim of the study was to determine whether phosphocalcic markers are associated with, and can predict, renal chronic histological changes. We included 129 kidney allograft recipients with an available transplant biopsy in a retrospective study. We analyzed the associations and predictive values of phosphocalcic markers and serum calcification propensity (T50) for chronic histological changes (interstitial fibrosis and vascular lesions). PTH, T50 and vitamin D levels were independently associated to interstitial fibrosis. PTH elevation was associated with increasing interstitial fibrosis severity (r = 0.29, p = 0.001), while T50 and vitamin D were protective (r = -0.20, p = 0.025 and r = -0.23, p = 0.009 respectively). On the contrary, fibroblast growth factor 23 (FGF23) and Klotho correlated only modestly with interstitial fibrosis (p = 0.045) whereas calcium and phosphate did not. PTH, vitamin D and T50 were predictors of extensive fibrosis (AUC: 0.73, 0.72 and 0.68 respectively), but did not add to renal function prediction. PTH, FGF23 and T50 were modestly predictive of low fibrosis (AUC: 0.63, 0.63 and 0.61) but did not add to renal function prediction. T50 decreased with increasing arterial lesions (r = -0.21, p = 0.038). The discriminative performance of T50 in predicting significant vascular lesions was modest (AUC 0.61). In summary, we demonstrated that PTH, vitamin D and T50 are associated to interstitial fibrosis and vascular lesions in kidney allograft recipients independently of renal function. Despite these associations, mineral metabolism indices do not show superiority or additive value to fibrosis prediction by eGFR and proteinuria in kidney allograft recipients, except for vascular lesions where T50 could be of relevance.

Long term evolution of endothelial function during kidney transplantation

Background

Endothelial dysfunction is an important precursor to the development of atherosclerosis, and has been suggested to play a role in the increased cardiovascular risk in patients with end stage renal disease. Endothelial function improves rapidly following post kidney transplantation, but the long term change remains unclear. Hypothesizing that endothelial function would remain improved long term post kidney transplantation, we evaluated the longitudinal change of endothelial function, measured by flow-mediated dilation (FMD) of the brachial artery, from months 1 to 24 post transplantation. Given the previously reported association of fibroblast growth factor 23 (FGF-23) with endothelial dysfunction, we also examined changes in the association between FGF-23 levels and the change in FMD following kidney transplantation.

Methods

We performed a prospective cohort study of 149 kidney transplant recipients, measuring endothelial function by FMD at months 1, 12, and 24 post-transplant. FGF-23 levels were measured at months 1 and 24 post-transplant. Linear mixed effects models were used to assess both the unadjusted and adjusted outcomes.

Results

The cohort (mean age 49 ± 13 years) was 74 % male and 75 % white. The median FMD was 6.3 % (IQR: 3.4, 10.2), 5.4 % (IQR: 3.1, 8.5), and 5.6 % (IQR: 3.5, 9.1) at 1, 12, and 24 months, respectively. After adjustment for covariates, compared to month 1, no change occurred in FMD at 12 months (−0.66 %; 95 % CI: −1.81 %, 0.49 %; P = 0.262) or 24 months (−0.25 %; 95%CI: −1.76 %, 1.26 %; P = 0.746). FGF-23 decreased significantly over time (P = 0.024), but there was no significant association between FGF-23 and FMD (P = 0.799).

Conclusion

Endothelial function remained stable at 12 and 24 months from 1 month post-kidney transplant, indicating that the improved endothelial function seen with transplant is maintained up to 2 years post transplantation. There was also no significant association between FGF-23 and endothelial function following kidney transplantation.

Vascular Function at Baseline in the Hemodialysis Fistula Maturation Study

Background

End‐stage renal disease is accompanied by functional and structural vascular abnormalities. The objective of this study was to characterize vascular function in a large cohort of patients with end‐stage renal disease, using noninvasive physiological measurements, and to correlate function with demographic and clinical factors.

Methods and Results

We analyzed cross‐sectional baseline data from the Hemodialysis Fistula Maturation Study, a multicenter prospective observational cohort study of 602 patients with end‐stage renal disease from 7 centers. Brachial artery flow‐ and nitroglycerin‐mediated dilation, carotid‐femoral and ‐radial pulse wave velocity, and venous occlusion plethysmography were performed prior to arteriovenous fistula creation. Relationships of these vascular function measures with demographic, clinical, and laboratory factors were evaluated using linear mixed‐effects models. Arterial function, as assessed by flow‐ and nitroglycerin‐mediated dilation and carotid‐femoral pulse wave velocity, worsened with increasing age and diabetes mellitus. Venous capacitance decreased with diabetes mellitus but not with age. Flow‐mediated dilation was higher among patients undergoing maintenance dialysis than for those at predialysis, and a U‐shaped relationship between serum phosphorus concentration and flow‐mediated dilation was evident. Partial correlations among different measures of vascular function, adjusting for demographic factors, diabetes mellitus, and clinical center, were modest or essentially nonexistent.

Conclusions

Multiple demographic and clinical factors were associated with the functions of vessels of different sizes and types in this large cohort of patients with end‐stage renal disease. Low correlations between the different measures, controlling for demographic factors, diabetes mellitus, and center, indicated that these different types of vascular function otherwise vary heterogeneously across patients.

Serum phosphate modifies the vascular response to vitamin D receptor activation in chronic kidney disease (CKD) patients

BACKGROUND AND AIMS

Vitamin D receptor activation (VDRA) ameliorates endothelial dysfunction in CKD patients but also increases phosphate and FGF-23, which may attenuate the beneficial effect of VDRA on endothelial function.

METHODS AND RESULTS

This is a pre-specified secondary analysis of the PENNY trial (NCT01680198) testing the effect of phosphate and FGF-23 on the flow mediated vasodilatory (FMD) response to paricalcitol (PCT, 2 μg/day) and placebo over a 12-weeks treatment period. Eighty-eight stage G3-4 CKD patients were randomized to PCT (n = 44) and Placebo (n = 44). Endothelial function was assessed by measuring endothelium dependent forearm blood flow (FBF) response to ischemia. The FMD response was by the 61% higher in PCT treated patients than in those on placebo (P = 0.01). Phosphate (+11%, P = 0.039), calcium (+3%, P = 0.01) and, particularly so, FGF23 (+164%, P < 0.001) increased in PCT treated patients. Changes in FMD by PCT associated inversely with phosphate (r = -0.37, P = 0.01) but were independent of FGF-23, calcium and PTH changes. The response to PCT was maximal in patients with no changes in phosphate (1st tertile), attenuated in those with mild-to-moderate rise in phosphate (2nd tertile) and abolished in those with the most pronounced phosphate increase (3rd tertile) (effect modification P = 0.009). No effect modification by FGF-23 and other variables was observed.

CONCLUSIONS

The beneficial effect of PCT on endothelial function in CKD is maximal in patients with no or minimal changes in phosphate and it is abolished in patients with a pronounced phosphate rise. These findings generate the hypothesis that the endothelium protective effect by VDRA may be potentiated by phosphate lowering interventions.

A Prospective Cohort Study of Mineral Metabolism After Kidney Transplantation

Kidney transplantation corrects or improves many complications of chronic kidney disease, but its impact on disordered mineral metabolism is incompletely understood.

The prevalence of posttransplant hyperparathyroidism was 86% at 12 months (PTH >65 pg/ml) but only 40% (PTH >130 mg/dL) in the absence of cinacalcet, vitamin D sterols, or parathyroidectomy. Intact fibroblast growth factor 23 decreased rapidly to G40 pg/ml by 3 months posttransplant. Supplemental digital content is available in the text.

Vitamin D in patients with chronic kidney disease: a position statement of the Working Group "Trace Elements and Mineral Metabolism" of the Italian Society of Nephrology

In the late 1970s, calcitriol was introduced into clinical practice for the management of secondary renal hyperparathyroidism in chronic kidney disease (CKD). Since then, the use of calcifediol or other native forms of vitamin D was largely ignored until the publication of the 2009 Kidney Disease Improving Global Outcomes (KDIGO) recommendations. The guidelines suggested that measurement of circulating levels of 25(OH)D (calcifediol) and its supplementation were to be performed on the same basis as for the general population. This indication was based on the fact that the precursors of active vitamin D had provided to CKD patients considerable benefits in survival, mainly due to their pleiotropic effects on the cardiovascular system. However, despite the long-term use of various classes of vitamin D in CKD, a clear definition is still lacking concerning the most appropriate time for initiation of therapy, the best compound to prescribe (active metabolites or analogs), the proper dosage, and the most suitable duration of therapy. The aim of this position statement is to provide and critically appraise the current plentiful evidence on vitamin D in different clinical settings related to CKD, particularly focusing on outcomes, monitoring and treatment-associated risks. However, it should be taken in account that position statements are meant to provide guidance; therefore, they are not to be considered prescriptive for all patients and, importantly, they cannot replace the judgment of clinicians.

Cardiac and vascular changes with kidney transplantation

Cardiovascular event rates are high in patients with chronic kidney disease (CKD), increasing with deteriorating kidney function, highest in CKD patients on dialysis, and improve with kidney transplantation (KTx). The cardiovascular events in CKD patients such as myocardial infarction and heart failure are related to abnormalities of vascular and cardiac structure and function. Many studies have investigated the structural and functional abnormalities of the heart and blood vessels in CKD, and the changes that occur with KTx, but the evidence is often sparse and occasionally contradictory. We have reviewed the available evidence and identified areas where more research is required to improve the understanding and mechanisms of these changes. There is enough evidence demonstrating improvement of left ventricular hypertrophy, except in children, and sufficient evidence of improvement of left ventricular function, with KTx. There is reasonable evidence of improvement in vascular function and stiffness. However, the evidence for improvement of vascular structure and atherosclerosis is insufficient. Further studies are necessary to establish the changes in vascular structure, and to understand the mechanisms of vascular and cardiac changes, following KTx.

FGF23 and Klotho in relation to markers of endothelial dysfunction in kidney transplant recipients

BACKGROUND

Fibroblast growth factor (FGF) 23 is a newly discovered member of the FGF family. Klotho is a cofactor of FGF23. Activation of the FGF23-Klotho system is responsible for negative phosphate balance. In addition, FGF23 appears to be a risk factor for cardiovascular complications. The aim of this study was to assess levels of FGF23 and Klotho in stable kidney transplant recipients on triple immunosuppressive therapy in relation to comorbidities and markers endothelial dysfunction. Healthy volunteers served as a control group.

METHODS

Hemoglobin, urea, and creatinine were studied with the use of standard laboratory methods in the hospital central laboratory. We assessed FGF23 and Klotho, markers of endothelial function/injury von Willebrand factor (vWF), intercellular adhesion molecule (ICAM), vascular cell adhesion molecule (VCAM), and interleukin (IL) 6, N-terminal pro-B-type natriuretic peptide (NT-proBNP) and copeptin with the use of commercially available assays.

RESULTS

FGF23 was significantly higher and Klotho significantly lower in kidney transplant recipients compared with healthy volunteers. FGF23 correlated with copeptin (r = 0.28; P < .05), IL-6 (r = 0.39; P < .01), VCAM (r = 0.36; P < .01), time after transplantation (r = 0.31; P < .05), platelet count (r = 0.31; P < .05), mean corpuscular volume (r = -0.40; P < .01), and phosphate (r = 0.31; P < .05). Klotho correlated with NT-proBNP (r = 0.38; P < .01), vWF (r = -0.26; P < .05), calcium (r = -0.39; P < .01), and age (r = 0.45; P < .001). FGF23 was significantly higher and Klotho significantly lower in patients with estimated glomerular filtration rate (eGFR) >60 mL/min compared with patients with eGFR <60 mL/min.

CONCLUSIONS

Disturbances in the FGF23-Klotho system appeared to be related to the endothelial cell injury. Thus they are involved not only in pathogenesis of the metabolic bone disease but also in cardiovascular complications, particularly in kidney disease.

Phosphate and FGF-23 homeostasis after kidney transplantation

Dysregulated phosphate metabolism is a common consequence of chronic kidney disease, and is characterized by a high circulating level of fibroblast growth factor (FGF)-23, hyperparathyroidism, and hyperphosphataemia. Kidney transplantation can elicit specific alterations to phosphate metabolism that evolve over time, ranging from severe hypophosphataemia (<0.5 mmol/l) to hyperphosphataemia (>1.50 mmol/l) and high FGF-23 levels. The majority of renal transplant recipients develop hypophosphataemia during the first 3 months after transplantation as a consequence of relatively slow adaptation of FGF-23 and parathyroid hormone levels to restored renal function, and the influence of immunosuppressive drugs. By 3-12 months after transplantation, phosphate homeostasis is at least partially restored in the majority of recipients, which is paralleled by a substantially reduced risk of cardiovascular-associated morbidity and mortality compared with the pre-transplantation setting. Many renal transplant recipients, however, exhibit persistent abnormalities in phosphate homeostasis, which is often due to multifactorial causes, and may contribute to adverse outcomes on the cardiovascular system, kidney, and bone. Dietary and pharmacologic interventions might improve phosphate homeostasis in renal transplant recipients, but additional insight into the pathophysiology of transplantation-associated abnormalities in phosphate homeostasis is needed to further optimize disease management and improve prognosis for renal transplant recipients.

Relation between Red Cell Distribution Width and Fibroblast Growth Factor 23 Cleaving in Patients with Chronic Kidney Disease and Heart Failure

OBJECTIVE

In chronic kidney disease (CKD), both anemia and deregulated phosphate metabolism are common and predictive of adverse outcome. Previous studies suggest that iron status influences phosphate metabolism by modulating proteolytic cleavage of FGF23 into C-terminal fragments. Red cell distribution width (RDW) was recently identified as a strong prognostic determinant for cardiovascular morbidity and mortality, independently of iron status. We assessed whether RDW is associated with FGF23 cleaving in CKD patients with heart failure.

MATERIALS AND METHODS

The associations between RDW and either intact FGF23 (iFGF23), C-terminal FGF23 (cFGF23, reflecting iFGF23 and C-terminal fragments together) and the iFGF23/cFGF23 ratio were analyzed in 52 patients with CKD (eGFR 34,9 ± 13.9 ml/min/1.73m2) and chronic heart failure (CHF). Associations between RDW and FGF23 forms were studied by linear regression analysis adjusted for parameters of renal function, iron metabolism, phosphate metabolism and inflammation.

RESULTS

Median cFGF23 levels were 197.5 [110-408.5] RU/ml, median iFGF23 levels were 107.3 [65.1-162.2] pg/ml and median FGF23 ratio was 0.80 [0.37-0.86]. Mean RDW was 14.1 ± 1.2%. cFGF23 and RDW were associated (β = 1.63 x 10(-3), P < 0.001), whereas iFGF23 and RDW were not (β = -1.38 x 10(-3), P = 0.336). The iFGF23/cFGF23 ratio was inversely associated with RDW. The difference between cFGF23 and iFGF23 (cFGF23- iFGF23) was positively associated with RDW (β = 1.74 x 10(-3), P < 0.001). The association between cFGF23 and RDW persisted upon multivariable linear regression analysis, adjusted for parameters of renal function, phosphate metabolism, iron metabolism and inflammation (β = 0.97 x 10(-3), P = 0.047).

CONCLUSION

RDW is associated with cFGF23 but not with iFGF23 levels in patients with CKD and CHF. This suggests a connection between RDW and FGF23 catabolism, independent of iron status and inflammation. Future studies are needed to unravel underlying mechanisms and whether these pertain to the link between RDW and outcome.

Endothelial dysfunction in renal transplant recipients: role of vitamin D and fibroblast growth factor-23

BACKGROUND

Endothelial dysfunction can be detected at early stages of chronic kidney disease. Although endothelial functions improve after successful renal transplantation, renal transplant recipients have still worse endothelial functions compared to healthy subjects. Vitamin D deficiency and high fibroblast growth factor-23 (FGF-23) levels may have a role on endothelial dysfunction in chronic kidney disease patients. The aim of this study is to investigate the association between endothelial functions, vitamin D, and FGF-23 levels in renal transplant recipients.

METHODS

One hundred nine renal transplant recipients (71 male, 38 female) underwent brachial flow-mediated dilatation (FMD), serum 25-OH vitamin D, and FGF-23 level measurements. Vitamin D and FGF-23 levels were compared between patients with normal and abnormal endothelial functions. Correlations between FMD, vitamin D, and FGF-23 were also investigated.

RESULTS

Endothelial functions were abnormal in 72.5% of the patients. Prevalence of vitamin D deficiency was 80.7%. Vitamin D levels were significantly lower in patients with endothelial dysfunction compared to patients with normal endothelial functions (12.6 ± 6.6 μg/L vs 17.3 ± 10.0 μg/L respectively, P = .02). FGF-23 levels were not different between the two groups. 25-OH vitamin D levels had a significant positive correlation with amount of FMD (r = 0.218 and P = .02) and were an independent predictor of FMD after adjusting for potential confounding factors including age, transplantation duration, body mass index, mean blood pressure, glomerular filtration rate, proteinuria, hemoglobin, and FGF-23 in multivariate regression analysis (beta = 0.194, P = .04). FGF-23 levels were not predictive of FMD in this model (beta: -0.125, P = .197) CONCLUSION: Vitamin D deficiency is associated with endothelial dysfunction in renal transplant recipients. Further clinical and experimental studies are necessary to define a causal relationship between the parameters, discover the potential mechanisms, and observe the effect of vitamin D replacement on endothelial functions in renal transplant recipients.

αKlotho and vascular calcification: an evolving paradigm

PURPOSE OF REVIEW

Cardiovascular disease remains the single most serious contributor to mortality in chronic kidney disease (CKD). Although conventional risk factors are prevalent in CKD, both cardiomyopathy and vasculopathy can be caused by pathophysiologic mechanisms specific to the uremic state. CKD is a state of systemic αKlotho deficiency. Although the molecular mechanism of action of αKlotho is not well understood, the downstream targets and biologic functions of αKlotho are astonishingly pleiotropic. An emerging body of literature links αKlotho to uremic vasculopathy.

RECENT FINDINGS

The expression of αKlotho in the vasculature is controversial because of conflicting data. Regardless of whether αKlotho acts as a circulating or resident protein, there are good data associating changes in αKlotho levels with vascular pathology including vascular calcification and in-vitro data of the direct action of αKlotho on both the endothelium and vascular smooth muscle cells in terms of cytoprotection and prevention of mineralization.

SUMMARY

It is critical to understand the pathogenic role of αKlotho on the integral endothelium-vascular smooth muscle network rather than each cell type in isolation in uremic vasculopathy, as αKlotho can serve as a potential prognostic biomarker and a biological therapeutic agent.

A longitudinal study of inflammation, CKD-mineral bone disorder, and carotid atherosclerosis after renal transplantation

BACKGROUND AND OBJECTIVES

The role of reversibility of nontraditional risk factors, like inflammation and CKD-mineral bone disorder, in the reduction of cardiovascular risk after renal transplantation is still scarcely defined.

DESIGN, SETTING, PARTICIPANTS, AND MEASUREMENTS

The longitudinal relationship between C-reactive protein, CKD-mineral bone disorder biomarkers, and intima media thickness was investigated in a series of 178 patients (age=32±10 years) with stage 5 CKD maintained on chronic dialysis who underwent echo-color Doppler studies of the carotid arteries before and after renal transplantation. Smokers and patients with diabetes were excluded from the study. In all patients, immunosuppression was performed by a standard regimen on the basis of calcineurin inhibitors. Healthy controls were specifically selected to match the age and sex distribution of the patients. Biochemical and intima media thickness assessments were repeated 6 months after transplantation.

RESULTS

Before transplantation, intima media thickness in patients with stage 5 CKD on dialysis (average=0.9±0.2 mm) was higher (P<0.001) than in well matched healthy controls (0.6±0.1 mm) and reduced substantially (-22%; 95% confidence interval, -24% to -20%) after transplantation (P=0.001). GFR (multivariable-adjusted β=0.23; P<0.001), C-reactive protein (β=0.15; P<0.001), and fibroblast growth factor 23 (β=0.28; P<0.001) were the strongest independent correlates of intima media thickness before transplantation. Similarly, longitudinal changes in the same biomarkers were the sole independent correlates of simultaneous changes in intima media thickness (C-reactive protein: β=0.25; fibroblast growth factor 23: β=0.26; P<0.001 for both) after renal transplantation. The evolution of intima media thickness after transplantation was largely independent of classic risk factors, including BP, LDL cholesterol, and insulin resistance, as measured by homeostatic model assessment.

CONCLUSIONS

Intima media thickness improves after renal transplantation. Such an improvement associates with parallel changes in serum C-reactive protein and fibroblast growth factor 23. These observations are in keeping with the hypothesis that the decline in cardiovascular risk after transplantation, in part, depends on partial resolution of nontraditional cardiovascular risk factors, like inflammation and CKD-mineral bone disorder.

Paricalcitol and endothelial function in chronic kidney disease trial

Altered vitamin D metabolism and low levels of the active form of this vitamin, 1,25-dihydroxy-vitamin D, is a hallmark of chronic kidney disease (CKD), but there is still no randomized controlled trial testing the effect of active forms of vitamin D on vascular function in patients with CKD. Paricalcitol and ENdothelial fuNction in chronic kidneY disease (PENNY) is a double-blinded randomized controlled trial (ClinicalTrials.gov, NCT01680198) testing the effect of an active form of vitamin D, paricalcitol (2 μg/d×12 weeks) on endothelium-dependent and endothelium-independent vasodilatation in 88 patients with stage 3 to 4 CKD and parathormone >65 pg/mL (paricalcitol, n=44; placebo, n=44). Paricalcitol treatment reduced parathormone (-75 pg/mL; 95% confidence interval, -90 to -60), whereas parathormone showed a small rise during placebo (21 pg/mL; 95% confidence interval, 5-36). Blood pressure did not change in both study arms. Baseline flow-mediated dilation was identical in patients on paricalcitol (3.6±2.9%) and placebo (3.6±2.9%) groups. After 12 weeks of treatment, flow-mediated dilation rose in the paricalcitol but not in the placebo group, and the between-group difference in flow-mediated dilation changes (the primary end point, 1.8%; 95% confidence interval, 0.3-3.1%) was significant (P=0.016), and the mean proportional change in flow-mediated dilation was 61% higher in paricalcitol-treated patients than in placebo-treated patients. Such an effect was abolished 2 weeks after stopping the treatment. No effect of paricalcitol on endothelium-independent vasodilatation was registered. Paricalcitol improves endothelium-dependent vasodilatation in patients with stage 3 to 4 CKD. Findings in this study support the hypothesis that vitamin D may exert favorable effects on the cardiovascular system in patients with CKD.

Relationship between aortic pulse wave velocity, selected proinflammatory cytokines, and vascular calcification parameters in peritoneal dialysis patients

INTRODUCTION

Vascular calcification and arterial stiffening are cardiovascular risk factors among chronic kidney disease patients. Elevated aortic pulse wave velocity (AoPWV) is an independent predictor of increased cardiovascular morbidity and mortality.

OBJECTIVES

The aim of the study was to analyze the relationships between inflammatory and vascular calcification parameters and arterial wall stiffness in chronic kidney disease (CKD) patients treated by peritoneal dialysis.

PATIENTS AND METHODS

The study included 57 patients (27 women and 30 men) aged from 19 to 75 years (mean age 53 ± 13), treated by peritoneal dialysis during 4-100 months (mean 30.4 months). The concentrations of albumin, lipids, interleukin-6 (IL-6), IL-18, high-sensitive C-reactive protein, transforming growth factor-β1 (TGF-β1), osteocalcin, osteoprotegerin (OPG), fibroblast growth factor 23, fetuin A, parathyroid hormone (iPTH), total calcium (Ca), and phosphates (Pi) were measured. AoPWV was performed using a tonometric method, common carotid artery intima-media thickness (CCA-IMT) by ultrasonography evaluation, and calcium scoring (CaSc) with multirow spiral computed tomography (MSCT).

RESULTS

In univariate analysis, AoPWV correlated negatively with osteocalcin (R = -0.37; P = 0.005) and positively with OPG (R = 0.41; P = 0.002). Additionally, AoPWV was significantly positively associated with inflammatory parameters: IL-6 (R = 0.35; P = 0.009), TGF-β1 (R = 0.27; P = 0.047), and white blood cell (WBC) count (R = 0.33; P = 0.01). There were also positive correlations between AoPWV and imaging data: CCA-IMT (R = 0.32; P = 0.02) and CaSc (R = 0.38; P = 0.004). AoPWV did not correlate with calcium, phosphate, Ca × Pi index, or iPTH concentration. After multiple adjustments, osteocalcin was the only significant predictor of AoPWV. In logistic regression adjusted for age, hypertension, and mean arterial pressure at AoPWV evaluation, only osteocalcin was significantly associated with high (above median) AoPWV values [odds ratio 0.96 (0.92-0.99) per unit increase in osteocalcin].

CONCLUSION

OPG concentration and some inflammatory markers (WBC count, IL-6, TGF-β1) influenced the severity of arterial wall stiffness in CKD patients. Measurement of osteocalcin seems to be the best predictor of AoPWV.

Assessment of endothelial dysfunction in Asian Indian patients with chronic kidney disease and changes following renal transplantation

BACKGROUND

Endothelial dysfunction may explain increased cardiovascular risk in patients with chronic kidney disease (CKD).

METHODS

Brachial artery was imaged during reactive hyperemia (endothelium-dependent, flow-mediated dilatation, FMD) and during glyceryl trinitrate-mediated dilatation (nitroglycerine-mediated dilatation, NMD, endothelium-independent) in 108 patients with CKD and three months following renal transplantation (RT) in 60 of them.

RESULTS

Patients with CKD had significantly lower FMD vs. controls (9.1% vs. 18.3%, p < 0.001) while NMD was comparable (19.8% vs. 21.8%, p = ns). Impaired FMD (<4.5%) was observed in 26.8% patients with CKD and was more common in those on hemodialysis (HD; 28.4% vs. 15.4%) vs. those not on dialysis. FMD for patients with glomerular filtration rate (GFR) 15-60 vs. <15 mL/min/1.73 m(2) was 12.9% and 8.8% (p = 0.05; respectively -29% and -52% lower vs. controls), indicating reduced FMD with increasing CKD severity. There was +72% increase in FMD following RT (9.1 to 15.7%, p < 0.001) while mean NMD was unchanged. Following RT, only 3.3% had impaired FMD.

CONCLUSIONS

Patients with CKD have endothelial dysfunction as evidenced by reduced FMD. Decreased FMD indicating worsening endothelial function was noted with increasing severity of CKD. Within three months of RT, there was significant improvement in FMD, while NMD values did not change.

Hemodynamics and function of resistance arteries in healthy persons and end stage renal disease patients

INTRODUCTION

Cardiovascular disease is the leading cause of death in patients with end stage renal disease (ESRD). The vasodilator mechanisms in small resistance arteries are in earlier studies shown to be reduced in patients with end stage renal disease. We studied whether endothelium dependent vasodilatation were diminished in ESRD patients and the interaction between the macro- and microcirculation.

METHODS

Eleven patients with ESRD had prior to renal transplant or insertion of peritoneal dialysis catheter measured pulse wave velocity. During surgery, a subcutaneous fat biopsy was extracted. Resistance arteries were then dissected and mounted on a wire myograph for measurements of dilator response to increasing concentrations of acetylcholine after preconstriction with noradrenaline. Twelve healthy kidney donors served as controls.

RESULTS

Systolic blood pressure was elevated in patients compared to the healthy controls; no difference in the concentration of asymmetric dimethyl arginine was seen. No significant difference in the endothelium dependent vasodilatation between patients and controls was found. Correlation of small artery properties showed an inverse relationship between diastolic blood pressure and nitric oxide dependent vasodilatation in controls. Pulse pressure was positively correlated to the total endothelial vasodilatation in patients. A negative association between S-phosphate and endothelial derived hyperpolarisation-like vasodilatation was seen in resistance arteries from controls.

CONCLUSION

This study finds similar vasodilator properties in kidney patients and controls. However, correlations of pulse pressure and diastolic blood pressure with resistance artery function indicate compensating measures in the microcirculation during end stage renal disease.

Plasma FGF23 and the risk of stroke: the Northern Manhattan Study (NOMAS)

OBJECTIVE

To examine fibroblast growth factor 23 (FGF23) as a risk factor for incident stroke in a racially/ethnically diverse population-based urban cohort.

METHODS

Stroke-free Northern Manhattan Study participants with FGF23 measurements (n = 2,525) were followed for a mean of 12 (±5) years to detect incident strokes. We used Cox proportional hazards models to estimate the association of baseline FGF23 with incident total, ischemic, and hemorrhagic stroke.

RESULTS

Median FGF23 was 57 relative units (RU)/mL (interquartile range = 44-81 RU/mL). Each unit increase of natural log-transformed FGF23 conferred a 40% greater overall stroke risk after adjusting for estimated glomerular filtration rate and sociodemographic and vascular risk factors (hazard ratio = 1.4, 95% confidence interval 1.1-1.6, p = 0.004). Penalized spline analysis revealed a linear association with overall stroke risk at ≥90 RU/mL FGF23, compared with <90 RU/mL (hazard ratio = 1.5, 95% confidence interval = 1.2-2.1, p = 0.004). Greater FGF23 conferred a doubling of intracerebral hemorrhage (ICH) risk but no significant increased risk of ischemic stroke. The associations of elevated FGF23 levels with greater risks of overall stroke and ICH events were independent of phosphate and parathyroid hormone levels and were similar among participants without chronic kidney disease.

CONCLUSIONS

Elevated FGF23 was a risk factor for overall stroke and ICH events, in particular in a racially and ethnically diverse urban community, independent of chronic kidney disease.

Roles of phosphate and fibroblast growth factor 23 in cardiovascular disease

Disturbances in phosphate homeostasis are common in patients with chronic kidney disease. As kidney function declines, circulating concentrations of phosphate and the phosphate-regulatory hormone, fibroblast growth factor (FGF)-23, rise progressively. Higher serum levels of phosphate and FGF-23 are associated with an increased risk of adverse outcomes, including all-cause mortality and cardiovascular events. The associations between higher FGF-23 levels and adverse cardiovascular outcomes are generally independent of serum phosphate levels, and might be strongest for congestive heart failure. Higher serum phosphate levels are also modestly associated with an increased risk of cardiovascular events even after accounting for FGF-23 levels. This observation suggests that FGF-23 and phosphate might promote distinct mechanisms of cardiovascular toxicity. Indeed, animal models implicate high serum phosphate as a mechanism of vascular calcification and endothelial dysfunction, whereas high levels of FGF-23 are implicated in left ventricular hypertrophy. These seemingly distinct, but perhaps additive, adverse effects of phosphate on the vasculature and FGF-23 on the heart suggest that future population-level and individual-level interventions will need to simultaneously target these molecules to reduce the risk of associated cardiovascular events.

Calcidiol deficiency in end-stage organ failure and after solid organ transplantation: status quo

Among patients with organ failure, vitamin D deficiency is extremely common and frequently does not resolve after transplantation. This review crystallizes and summarizes existing data on the status quo of vitamin D deficiency in patients with organ failure and in solid organ transplant recipients. Interventional studies evaluating different treatment strategies, as well as current clinical practice guidelines and recommendations on the management of low vitamin D status in these patients are also discussed.

FGF23: a mature renal and cardiovascular risk factor?

High FGF23 predicts renal function loss in chronic kidney disease (CKD) patients and graft failure in transplant patients. FGF23, parathyroid hormone and serum phosphate are all interrelated but among these CKD-MBD biomarkers only FGF23 is independently related with CKD progression. High FGF23 associates with endothelial dysfunction in CKD patients and in elderly individuals in the general population. Furthermore, independently of serum phosphate, high FGF23 associates with mortality and left ventricular hypertrophy in dialysis patients and with atherosclerosis in elderly individuals in the general population. FGF23 also predicts a high risk for death and cardiovascular events in predialysis CKD patients and in subjects with coronary artery disease. A recent trial in CKD patients showed that low phosphate intake associated with a phosphate binder produces a 35% decrease in plasma FGF23. Yet in this and in another trial testing several phosphate binders, FGF23 levels remained well beyond the upper limit of the normal range. Of note, in this latter study, calcification of the coronary arteries and abdominal aorta actually increased, rather than decreased, during treatment with these drugs in the face of evidence of negative phosphate balance and amelioration of hyperparathyroidism. Mechanistic studies are still needed before testing the hypothesis that FGF23 is implicated in a causal manner in cardiovascular and renal diseases. Given the modest effects of phosphate binders on serum FGF23 in CKD patients, pharmacologic interventions antagonizing the effects of this growth factor rather than phosphate-lowering interventions should be put in place to properly test this hypothesis in the clinical scenario in CKD.