Rationale and Approaches to Phosphate and Fibroblast Growth Factor 23 Reduction in CKD

Effect of Lanthanum Carbonate on Serum Phosphate, Oxidative Stress, and Vascular Dysfunction in CKD: A Mechanistic Randomized Controlled Trial

Key Points

A key mechanism contributing to vascular dysfunction in CKD is increased oxidative stress. Lanthanum carbonate did not discernibly affect vascular endothelial function, arterial stiffness, or markers of endothelial oxidative stress.

Background

Vascular endothelial dysfunction and arterial stiffness are common in CKD and independently predict cardiovascular disease. Elevated serum phosphorus, even within the normal range, associates with cardiovascular disease and mortality in CKD. Excess phosphorus may increase oxidative stress leading to vascular dysfunction.

Methods

This is a randomized double-blind trial in which we compared lanthanum carbonate, a noncalcium phosphate binder, with placebo on vascular function and endothelial and circulating measures of oxidative stress and inflammation in 54 participants with CKD 3b–4 and normal phosphorus levels. Primary end points were change in brachial artery flow-mediated dilation (FMDBA) and carotid-to-femoral pulse-wave velocity (cfPWV) at 12 weeks. Mechanistic end points were changes from baseline in FMDBA after ascorbic acid infusion and circulating and endothelial markers of oxidative stress and inflammation.

Results

The age was 65±8 years and eGFR was 38±14 ml/min per 1.73 m2. At 12 weeks, serum phosphorus did not change with lanthanum (3.44±0.47 versus 3.44±0.52 mg/dl; P = 0.94) but tended to increase with placebo (3.42±0.80 versus 3.74±1.26 mg/dl; P = 0.09). FMDBA and cfPWV did not change from baseline in either group: FMDBA lanthanum 3.13%±2.87% to 2.73%±2.48% versus placebo 3.74%±2.86% to 3.09%±2.49% (P = 0.67); CfPWV lanthanum 1214±394 to 1216±322 cm/s versus placebo 993±289 to 977±254 cm/s (P = 0.77). Ascorbic acid infusion to inhibit oxidative stress did not differentially affect FMDBA. Circulating and endothelial markers of oxidative stress and inflammation did not differ between groups.

Conclusions

Lanthanum carbonate did not discernibly affect vascular endothelial function, arterial stiffness, or markers of endothelial oxidative stress among participants with CKD 3b–4 and normophosphatemia.

Determinants of circulating calcitriol in cardiovascular disease

Circulating calcitriol may contribute to the risk of cardiovascular disease (CVD), but its regulation in patients with CVD is poorly characterized. We therefore aimed to assess determinants of circulating calcitriol in these patients. We analyzed 2183 independent samples from a large cohort of patients scheduled for coronary angiography and 1727 independent samples from different other cohorts from patients with a wide range of CVDs, including heart transplant candidates, to quantify the association of different parameters with circulating calcitriol. We performed univariable and multivariable linear regression analyses using the mathematical function that fitted best with circulating calcitriol. In the multivariable analysis of the large single cohort, nine parameters remained significant, explaining 30.0 % (32.4 % after exclusion of 22 potential outliers) of the variation in circulating calcitriol (r=0.548). Log-transformed 25-hydroxyvitamin D [25(OH)D] and log-transformed glomerular filtration rate were the strongest predictors, explaining 17.6 % and 6.6 %, respectively, of the variation in calcitriol. In the analysis of the combined other cohorts, including heart transplant candidates, the multivariable model explained a total of 42.6 % (46.1 % after exclusion of 21 potential outliers) of the variation in calcitriol (r=0.653) with log-transformed fibroblast growth factor-23 and log-transformed 25(OH)D explaining 29.0 % and 6.2 %, respectively. Circulating 25(OH)D was positively and FGF-23 inversely associated with circulating calcitriol. Although significant, PTH was only a weak predictor of calcitriol in both analyses (<2.5 %). In patients with CVD, FGF-23 and 25(OH)D are important independent determinants of circulating calcitriol. The relative importance of these two parameters may vary according to CVD severity. Future studies should focus on the clinical importance of regulating circulating calcitriol by different parameters.

Associations of Kidney Functional Magnetic Resonance Imaging Biomarkers with Markers of Inflammation in Individuals with CKD

Key Points

Lower baseline apparent diffusion coefficient, indicative of greater cortical fibrosis, correlated with higher baseline concentrations of serum markers of inflammation. No association between baseline cortical R2* and baseline serum markers of inflammation were found. Baseline kidney functional magnetic resonance imaging biomarkers of fibrosis and oxygenation were not associated with changes in inflammatory markers over time, which may be due to small changes in kidney function in the study.

Background

Greater fibrosis and decreased oxygenation may amplify systemic inflammation, but data on the associations of kidney functional magnetic resonance imaging (fMRI) measurements of fibrosis (apparent diffusion coefficient [ADC]) and oxygenation (relaxation rate [R2*]) with systemic markers of inflammation are limited.

Methods

We evaluated associations of baseline kidney fMRI-derived ADC and R2* with baseline and follow-up serum IL-6 and C-reactive protein (CRP) in 127 participants from the CKD Optimal Management with Binders and NicotinamidE trial, a randomized, 12-month trial of nicotinamide and lanthanum carbonate versus placebo in individuals with CKD stages 3–4. Cross-sectional analyses of baseline kidney fMRI biomarkers and markers of inflammation used multivariable linear regression. Longitudinal analyses of baseline kidney fMRI biomarkers and change in markers of inflammation over time used linear mixed-effects models.

Results

Mean±SD eGFR, ADC, and R2* were 32.2±8.7 ml/min per 1.73 m2, 1.46±0.17×10−3 mm2/s, and 20.3±3.1 s−1, respectively. Median (interquartile range) IL-6 and CRP were 3.7 (2.4–4.9) pg/ml and 2.8 (1.2–6.3) mg/L, respectively. After multivariable adjustment, IL-6 and CRP were 13.1% and 27.3% higher per 1 SD decrease in baseline cortical ADC, respectively. Baseline cortical R2* did not have a significant association with IL-6 or CRP. Mean annual IL-6 and CRP slopes were 0.98 pg/ml per year and 0.91 mg/L per year, respectively. Baseline cortical ADC and R2* did not have significant associations with change in IL-6 or CRP over time.

Conclusions

Lower cortical ADC, suggestive of greater fibrosis, was associated with higher systemic inflammation. Baseline kidney fMRI biomarkers did not associate with changes in systemic markers of inflammation over time.

The rationale for intermittent administration of PTH in the management of mineral and bone disorder of chronic kidney disease

A major complication of chronic kidney disease is the derangement of mineral metabolism, leading to increased risk of fractures and cardiovascular mortality. Current therapeutic regimens are focused on reducing parathyroid hormone levels caused by secondary hyperparathyroidism, and the active vitamin D metabolite l,25(OH)2D, with limited success. It may be a more effective approach, however, if we could target the delayed response of parathyroid hormone in the early retention of phosphate following loss of renal function.We propose intermittent administration (even in stage 2 chronic kidney disease) of parathyroid hormone, known for its bone anabolic effects compared to the catabolic effects of the continuously elevated parathyroid hormone associated with the hyperparathyroid state, to mitigate the retention of phosphate. This approach may prevent the compensatory responses of the other two major calcium- and phosphate-regulating hormones (FGF-23 and l,25(OH)2D) that lead to further worsening of the derangement of mineral metabolism.In addition to its strong theoretical basis, there are data supporting the need for further research focused on the use of intermittent parathyroid hormone in the management of chronic kidney disease-mineral bone disorder.

FGF23 and klotho at the intersection of kidney and cardiovascular disease

Cardiovascular disease is the leading cause of death in patients with chronic kidney disease (CKD). As CKD progresses, CKD-specific risk factors, such as disordered mineral homeostasis, amplify traditional cardiovascular risk factors. Fibroblast growth factor 23 (FGF23) regulates mineral homeostasis by activating complexes of FGF receptors and transmembrane klotho co-receptors. A soluble form of klotho also acts as a 'portable' FGF23 co-receptor in tissues that do not express klotho. In progressive CKD, rising circulating FGF23 levels in combination with decreasing kidney expression of klotho results in klotho-independent effects of FGF23 on the heart that promote left ventricular hypertrophy, heart failure, atrial fibrillation and death. Emerging data suggest that soluble klotho might mitigate some of these effects via several candidate mechanisms. More research is needed to investigate FGF23 excess and klotho deficiency in specific cardiovascular complications of CKD, but the pathophysiological primacy of FGF23 excess versus klotho deficiency might never be precisely resolved, given the entangled feedback loops that they share. Therefore, randomized trials should prioritize clinical practicality over scientific certainty by targeting disordered mineral homeostasis holistically in an effort to improve cardiovascular outcomes in patients with CKD.

Inositol 1,4,5-trisphosphate receptor type 2 is associated with the bone-vessel axis in chronic kidney disease-mineral bone disorder

Objective: The pathogenesis of renal osteopathy and cardiovascular disease suggests the disordered bone-vessel axis in chronic kidney disease-mineral bone disorder (CKD-MBD). However, the mechanism of the bone-vessel axis in CKD-MBD remains unclear.Methods: We established a CKD-MBD rat model to observe the pathophysiological phenotype of the bone-vessel axis and performed RNA sequencing of aortas to identify novel targets of the bone-vessel axis in CKD-MBD.Results: The microarchitecture of the femoral trabecular bone deteriorated and alveolar bone loss was aggravated in CKD-MBD rats. The intact parathyroid hormone and alkaline phosphatase levels increased, 1,25-dihydroxyvitamin D3 levels decreased, and intact fibroblast growth factor-23 levels did not increase in CKD-MBD rats at 16 weeks; other bone metabolic parameters in the serum demonstrated dynamic characteristics. With calcium deposition in the abdominal aortas of CKD-MBD rats, RNA sequencing of the aortas revealed a significant decrease in inositol 1,4,5-trisphosphate receptor type 2 (ITPR2) gene levels in CKD-MBD rats. A similar trend was observed in rat aortic smooth muscle cells. As a secretory protein, ITPR2 serum levels decreased at 4 weeks and slightly increased without statistical differences at 16 weeks in CKD-MBD rats. ITPR2 serum levels were significantly increased in patients with vascular calcification, negatively correlated with blood urea nitrogen levels, and positively correlated with serum tartrate-resistant acid phosphatase 5b levels.Conclusion: These findings provide preliminary insights into the role of ITPR2 in the bone-vessel axis in CKD-MBD. Thus, ITPR2 may be a potential target of the bone-vessel axis in CKD-MBD.

The open system of FGF-23 at the crossroad between additional P-lowering therapy, anemia and inflammation: how to deal with the intact and the C-terminal assays?

Fibroblast growth factor 23 (FGF-23) has been associated with increased cardiovascular risk and poor survival in dialysis patients. It is well established that FGF-23 synthesis is directly induced by positive phosphate (P) balance. On the other hand, P-lowering treatments such as nutritional P restriction, P binders and dialysis are capable of reducing FGF-23 levels. However, there are many uncertainties regarding the possibility of adopting FGF-23 to guide the clinical decision-making process in the context of chronic kidney disease-mineral bone disorder (CKD-MBD). Furthermore, the best assay to adopt for measurement of FGF-23 levels (namely the intact vs the C-terminal one) remains to be determined, especially in conditions capable of altering the synthesis as well as the cleavage of the intact and biologically active molecule, as occurs in the presence of CKD and its complications. This Editorial discusses the main insights provided by the post hoc analysis of the NOPHOS trial, with particular attention given to evidence-based peculiarities of the intact and the C-terminal assays available for measuring FGF-23 levels, especially in patients receiving additive P-lowering therapy in the presence of inflammation, anemia and iron deficiency.

Experimental heart failure models in small animals

Heart failure (HF) is one of the most critical health and economic burdens worldwide, and its prevalence is continuously increasing. HF is a disease that occurs due to a pathological change arising from the function or structure of the heart tissue and usually progresses. Numerous experimental HF models have been created to elucidate the pathophysiological mechanisms that cause HF. An understanding of the pathophysiology of HF is essential for the development of novel efficient therapies. During the past few decades, animal models have provided new insights into the complex pathogenesis of HF. Success in the pathophysiology and treatment of HF has been achieved by using animal models of HF. The development of new in vivo models is critical for evaluating treatments such as gene therapy, mechanical devices, and new surgical approaches. However, each animal model has advantages and limitations, and none of these models is suitable for studying all aspects of HF. Therefore, the researchers have to choose an appropriate experimental model that will fully reflect HF. Despite some limitations, these animal models provided a significant advance in the etiology and pathogenesis of HF. Also, experimental HF models have led to the development of new treatments. In this review, we discussed widely used experimental HF models that continue to provide critical information for HF patients and facilitate the development of new treatment strategies.

Focusing on Phosphorus Loads: From Healthy People to Chronic Kidney Disease

Phosphorus is an essential micromineral with a key role in cellular metabolism and tissue structure. Serum phosphorus is maintained in a homeostatic range by the intestines, bones, and kidneys. This process is coordinated by the endocrine system through the highly integrated actions of several hormones, including FGF23, PTH, Klotho, and 1,25D. The excretion kinetics of the kidney after diet phosphorus load or the serum phosphorus kinetics during hemodialysis support that there is a "pool" for temporary phosphorus storage, leading to the maintenance of stable serum phosphorus levels. Phosphorus overload refers to a state where the phosphorus load is higher than is physiologically necessary. It can be caused by a persistently high-phosphorus diet, renal function decline, bone disease, insufficient dialysis, and inappropriate medications, and includes but is not limited to hyperphosphatemia. Serum phosphorus is still the most commonly used indicator of phosphorus overload. Trending phosphorus levels to see if they are chronically elevated is recommended instead of a single test when judging phosphorus overload. Future studies are needed to validate the prognostic role of a new marker or markers of phosphorus overload.

The Dietary Fermentable Fiber Inulin Alters the Intestinal Microbiome and Improves Chronic Kidney Disease Mineral-Bone Disorder in a Rat Model of CKD

Background

Dietary fiber is important for a healthy diet, but intake is low in CKD patients and the impact this has on the manifestations of CKD-Mineral Bone Disorder (MBD) is unknown.

Methods

The Cy/+ rat with progressive CKD was fed a casein-based diet of 0.7% phosphate with 10% inulin (fermentable fiber) or cellulose (non-fermentable fiber) from 22 weeks to either 30 or 32 weeks of age (~30 and ~15 % of normal kidney function). We assessed CKD-MBD, cecal microbiota, and serum gut-derived uremic toxins. Two-way ANOVA was used to evaluate the effect of age and inulin diet, and their interaction.

Results

In CKD animals, dietary inulin led to changes in microbiota alpha and beta diversity at 30 and 32 weeks, with higher relative abundance of several taxa, including Bifidobacterium and Bacteroides , and lower Lactobacillus . Inulin reduced serum levels of gut-derived uremic toxins, phosphate, and parathyroid hormone, but not fibroblast growth factor-23. Dietary inulin decreased aorta and cardiac calcification and reduced left ventricular mass index and cardiac fibrosis. Bone turnover and cortical bone parameters were improved with inulin; however, bone mechanical properties were not altered.

Conclusions

The addition of the fermentable fiber inulin to the diet of CKD rats led to changes in the gut microbiota composition, lowered gut-derived uremic toxins, and improved most parameters of CKD-MBD. Future studies should assess this fiber as an additive therapy to other pharmacologic and diet interventions in CKD.

Significance Statement

Dietary fiber has well established beneficial health effects. However, the impact of fermentable dietary fiber on the intestinal microbiome and CKD-MBD is poorly understood. We used an animal model of progressive CKD and demonstrated that the addition of 10% of the fermentable fiber inulin to the diet altered the intestinal microbiota and lowered circulating gut-derived uremic toxins, phosphorus, and parathyroid hormone. These changes were associated with improved cortical bone parameters, lower vascular calcification, and reduced cardiac hypertrophy, fibrosis and calcification. Taken together, dietary fermentable fiber may be a novel additive intervention to traditional therapies of CKD-MBD.

Strategies to lower fibroblast growth factor 23 bioactivity

Fibroblast growth factor 23 (FGF23) is a circulating hormone derived from the bone whose release is controlled by many factors and exerts a multitude of systemic actions. There are congenital and acquired disorders of increased and decreased FGF23 levels. In chronic kidney disease (CKD), elevations of FGF23 levels can be 1000-fold above the upper physiological limit. It is still debated whether this high FGF23 in CKD is a biomarker or causally related to morbidity and mortality. Data from human association studies support pathogenicity, while experimental data are less robust. Knowledge of the biology and pathobiology of FGF23 has generated a plethora of means to reduce FGF23 bioactivity at many levels that will be useful for therapeutic translations. This article summarizes these approaches and addresses several critical questions that still need to be answered.

Targeted Disruption of a Proximal Tubule-Specific TMEM174 Gene in Mice Causes Hyperphosphatemia and Vascular Calcification

BACKGROUND

The proximal tubules play a critical role in phosphate (Pi) homeostasis by reabsorbing Pi via sodium-dependent Pi cotransporters. NPT2A is a major proximal-specific Pi cotransporter, whose expression is regulated by circulating hormones, such as parathyroid hormone (PTH) and fibroblast growth factor 23 (FGF23). In this study, we aimed to find a novel regulator in Pi homeostasis.

METHODS

Using RNA-seq and RT-qPCR analysis, we identified proximal tubule cell-enriched genes. We next used RNAi screening of the identified proximal tubular cell-enriched genes to identify a novel proximal tubule-specific gene that contributes to FGF23- and PTH-mediated inhibition of Pi uptake and NPT2 reduction. We created mice lacking this novel regulator of Pi homeostasis to examine whether the novel regulator contributes to Pi homeostasis in vivo.

RESULTS

We identified 54 kidney-enriched genes, 19 of which are expressed in renal primary proximal tubule cells. One of the proximal tubule-specific genes, TMEM174, interacted with NPT2A, and its knockdown blocked the reduction of NPT2A protein by FGF23 and PTH treatments in human and opossum proximal tubule cells. TMEM174 KO mice had significantly increased levels of serum Pi, FGF23, and PTH, resulting in vascular calcification.

CONCLUSIONS

TMEM174 is a novel regulator of Pi homeostasis that interacts with NPT2A.

The American Association of Endocrine Surgeons Guidelines for the Definitive Surgical Management of Secondary and Tertiary Renal Hyperparathyroidism

OBJECTIVE

To develop evidence-based recommendations for safe, effective, and appropriate treatment of secondary (SHPT) and tertiary (THPT) renal hyperparathyroidism.

BACKGROUND

Hyperparathyroidism is common among patients with chronic kidney disease, end-stage kidney disease, and kidney transplant. The surgical management of SHPT and THPT is nuanced and requires a multidisciplinary approach. There are currently no clinical practice guidelines that address the surgical treatment of SHPT and THPT.

METHODS

Medical literature was reviewed from January 1, 1985 to present January 1, 2021 by a panel of 10 experts in SHPT and THPT. Recommendations using the best available evidence was constructed. The American College of Physicians grading system was used to determine levels of evidence. Recommendations were discussed to consensus. The American Association of Endocrine Surgeons membership reviewed and commented on preliminary drafts of the content.

RESULTS

These clinical guidelines present the epidemiology and pathophysiology of SHPT and THPT and provide recommendations for work-up and management of SHPT and THPT for all involved clinicians. It outlines the preoperative, intraoperative, and postoperative management of SHPT and THPT, as well as related definitions, operative techniques, morbidity, and outcomes. Specific topics include Pathogenesis and Epidemiology, Initial Evaluation, Imaging, Preoperative and Perioperative Care, Surgical Planning and Parathyroidectomy, Adjuncts and Approaches, Outcomes, and Reoperation.

CONCLUSIONS

Evidence-based guidelines were created to assist clinicians in the optimal management of secondary and tertiary renal hyperparathyroidism.

Fibroblast Growth Factor 23 and Cardiovascular Risk in Diabetes Patients-Cardiologists Be Aware

Numerous clinical studies have indicated that elevated FGF23 (fibroblast growth factor 23) levels may be associated with cardiovascular (CV) mortality, especially in patients with chronic kidney disease. The purpose of this study was to examine the hypothesis that FGF23 may be a potent CV risk factor among patients with long-standing type 2 diabetes mellitus (T2DM). Research was performed utilizing patients with T2DM and regular outpatient follow-up care. Baseline characteristics determined by laboratory tests were recorded. Serum FGF23 levels were detected using a sandwich enzyme-linked immunosorbent assay. All patients underwent echocardiograms and 12-lead electrocardiograms. Data records of 102 patients (males: 57%) with a median age of 69 years (interquartile range (IQR) 66.0-74.0) were analyzed. Baseline characteristics indicated that one-third (33%) of patients suffered from ischemic heart disease (IHD), and the median time elapsed since diagnosis with T2DM was 19 years (IQR 14.0-25.0). The hemoglobin A1c, estimated glomerular filtration rate, and FGF23 values were, respectively, as follows: 6.85% (IQR 6.5-7.7), 80 mL/min/1.73 m2 (IQR 70.0-94.0), and 253.0 pg/mL (IQR 218.0-531.0). The study revealed that FGF23 was elevated in all patients, regardless of IHD status. Thus, the role of FGF23 as a CV risk factor should not be overestimated among patients with T2DM and good glycemic control.

Lung-kidney interactions and their role in chronic kidney disease-associated pulmonary diseases

Chronic illnesses rarely present in a vacuum, devoid of other complications, and chronic kidney disease is hardly an exception. Comorbidities associated with chronic kidney disease lead to faster disease progression, expedited dialysis dependency, and a higher mortality rate. Although chronic kidney disease is most commonly accompanied by cardiovascular diseases and diabetes, there is clear cross talk between the lungs and kidneys pH balance, phosphate metabolism, and immune system regulation. Our present understanding of the exact underlying mechanisms that contribute to chronic kidney disease-related pulmonary disease is poor. This review summarizes the current research on kidney-pulmonary interorgan cross talk in the context of chronic kidney disease, highlighting various acute and chronic pulmonary diseases that lead to further complications in patient care. Treatment options for patients presenting with chronic kidney disease and lung disease are explored by assessing activated molecular pathways and the body's compensatory response mechanisms following homeostatic imbalance. Understanding the link between the lungs and kidneys will potentially improve health outcomes for patients and guide healthcare professionals to better understand how and when to treat each of the pulmonary comorbidities that can present with chronic kidney disease.

Interplay between mineral bone disorder and cardiac damage in acute kidney injury: from Ca2+ mishandling and preventive role of Klotho in mice to its potential mortality prediction in human

Biomarkers of mineral bone disorders (MBD) including phosphorus, fibroblast growth factor (FGF)-23 and Klotho are strongly altered in patients with acute kidney injury (AKI) who have high cardiac outcomes and mortality rates. However, the crosslink between MBD and cardiac damage after an AKI episode still remains unclear. We tested MBD and cardiac biomarkers in an experimental AKI model after 24 or 72 hours of folic acid injection and we analyzed structural cardiac remodeling, intracellular calcium (Ca²⁺) dynamics in cardiomyocytes and cardiac rhythm. AKI mice presented high levels of FGF-23, phosphorus and cardiac troponin T and exhibited a cardiac hypertrophy phenotype accompanied by an increase in systolic Ca²⁺ release 24 hours after AKI. Ca²⁺ transients and contractile dysfunction were reduced 72 hours after AKI while diastolic sarcoplasmic reticulum Ca²⁺ leak, pro-arrhythmogenic Ca²⁺ events and ventricular arrhythmias were increased. These cardiac events were linked to the activation of the calcium/calmodulin-dependent kinase II pathway through the increased phosphorylation of ryanodine receptors and phospholamban specific sites after AKI. Cardiac hypertrophy and the altered intracellular Ca²⁺ dynamics were prevented in transgenic mice overexpressing Klotho after AKI induction. In a translational retrospective longitudinal clinical study, we determined that combining FGF-23 and phosphorus with cardiac troponin T levels achieved a better prediction of mortality in AKI patients at hospital admission. Thus, monitoring MBD and cardiac damage biomarkers could be crucial to prevent mortality in AKI patients. In this setting, Klotho might be considered as a new cardioprotective therapeutic tool to prevent deleterious cardiac events in AKI conditions.

Cardiac Calcifications: Phenotypes, Mechanisms, Clinical and Prognostic Implications

There is a growing interest in arterial and heart valve calcifications, as these contribute to cardiovascular outcome, and are leading predictors of cardiovascular and kidney diseases. Cardiovascular calcifications are often considered as one disease, but, in effect, they represent multifaced disorders, occurring in different milieus and biological phenotypes, following different pathways. Herein, we explore each different molecular process, its relative link with the specific clinical condition, and the current therapeutic approaches to counteract calcifications. Thus, first, we explore the peculiarities between vascular and valvular calcium deposition, as this occurs in different tissues, responds differently to shear stress, has specific etiology and time courses to calcification. Then, we differentiate the mechanisms and pathways leading to hyperphosphatemic calcification, typical of the media layer of the vessel and mainly related to chronic kidney diseases, to those of inflammation, typical of the intima vascular calcification, which predominantly occur in atherosclerotic vascular diseases. Finally, we examine calcifications secondary to rheumatic valve disease or other bacterial lesions and those occurring in autoimmune diseases. The underlying clinical conditions of each of the biological calcification phenotypes and the specific opportunities of therapeutic intervention are also considered and discussed.

Abnormalities in Cardiac Structure and Function among Individuals with CKD: The COMBINE Trial

Background

Individuals with CKD have a high burden of cardiovascular disease (CVD). Abnormalities in cardiac structure and function represent subclinical CVD and can be assessed by cardiac magnetic resonance imaging (cMRI).

Methods

We investigated differences in cMRI parameters in 140 individuals with CKD stages 3b-4 who participated in the CKD Optimal Management with BInders and NicotinamidE (COMBINE) trial and in 24 age- and sex-matched healthy volunteers. Among COMBINE participants, we examined the associations of eGFR, urine albumin-creatinine ratio (UACR), phosphate, fibroblast growth factor 23 (FGF23), and parathyroid hormone (PTH) with baseline (N=140) and 12-month change (N=112) in cMRI parameters.

Results

Mean (SD) ages of the COMBINE participants and healthy volunteers were 64.9 (11.9) and 60.4 (7.3) years, respectively. The mean (SD) baseline eGFR values in COMBINE participants were 32.1 (8.0) and 85.9 (16.0) ml/min per 1.73 m² in healthy volunteers. The median (interquartile range [IQR]) UACR in COMBINE participants was 154 (20.3-540.0) mg/g. Individuals with CKD had lower mitral valve E/A ratio compared with healthy volunteers (for CKD versus non-CKD, β estimate, -0.13; 95% CI, -0.24 to -0.012). Among COMBINE participants, multivariable linear regression analyses showed that higher UACR was significantly associated with lower mitral valve E/A ratio (β estimate per 1 unit increase in natural-log UACR, -0.06; 95% CI, -0.09 to -0.03). This finding was preserved among individuals without baseline CVD. UACR was not associated with 12-month change in any cMRI parameter. eGFR, phosphate, FGF23, and PTH were not associated with any cMRI parameter in cross-sectional or change analyses.

Conclusions

Individuals with CKD stages 3b-4 have evidence of cMRI abnormalities. Albuminuria was independently associated with diastolic dysfunction, as assessed by mitral valve E/A ratio, in individuals with CKD with and without clinical CVD. Albuminuria was not associated with change in any cMRI parameter.

Association of central arterial blood pressure and left ventricular hypertrophy in patients with chronic kidney disease

AIMS

In the general population, central arterial blood pressure has proved to be more closely related to left ventricular hypertrophy (LVH) than brachial arterial blood pressure. We aimed to investigate whether this relationship was true in patients with chronic kidney disease (CKD).

METHODS

In this retrospective study, we reviewed the medical records of 289 adult patients with CKD from the Zhejiang Provincial People's Hospital in Zhejiang, China. Demographic, echocardiographic and brachial and central blood pressure parameters were retrieved from medical records. Central blood pressure was measured using the SphygmoCor® CvMS (AtCor, Australia) device and its corresponding software. Multivariate logistic regression analyses were performed to identify independent predictors of LVH. Receiver operating characteristic curves were used to determine the ability of central and brachial blood pressure to predict LVH.

RESULTS

The left ventricular mass index was positively associated with both central and brachial blood pressures. However, multiple logistic regression analysis demonstrated that a central pulse pressure (CPP) ≥ 58 mm Hg was an independent risk factor for LVH (OR = 5.597, 95%CI 2.363-13.259, p < .001). Brachial pulse pressure is not superior to CPP in predicting LVH (area under the curve [AUC] = 0.695, 95%CI 0.634-0.756, p < .001 vs. AUC = 0.687, 95%CI: 0.626-0.748, p < .001, respectively; p = .4824).

CONCLUSION

Our results suggested that, similarly to the general population, CPP is a better parameter for predicting the occurrence of LVH in patients with CKD.

Effectiveness of fibroblast growth factor 23 lowering modalities in chronic kidney disease: a systematic review and meta-analysis

INTRODUCTION

The heightened fibroblast growth factor 23 (FGF23) level in patients with chronic kidney disease (CKD) is associated with increased cardiovascular disease and mortality. We performed a systematic review and meta-analysis to synthesize the available strategies to reduce FGF23 in CKD patients.

METHODS

We conducted a meta-analysis by searching the databases of MEDLINE, Scopus, and Cochrane Central Register of Controlled Trials for randomized controlled trials (RCTs) and single-arm studies that examined the effects of dietary phosphate restriction, phosphate binders, iron supplements, calcimimetics, parathyroidectomy, dialysis techniques, and the outcome of preservation of residual renal function (RRF) on FGF23 levels in CKD patients. Random-effects model meta-analyses were used to compute changes in the outcome of interests.

RESULTS

A total of 41 articles (7590 patients), comprising 36 RCTs, 5 prospective studies were included in this meta-analysis. Dietary phosphate restriction less than 800 mg per day yielded insignificant effect on FGF23 reduction. Interestingly sevelamer, lanthanum, iron-based phosphate binders, and iron supplement significantly lowered FGF23 levels. In CKD patients with secondary hyperparathyroidism, calcimimetics prescription could significantly reduce FGF23 levels, while surgical parathyroidectomy had no significant effect. In dialysis patients, preservation of RRF and hemoperfusion as well as hemodiafiltration provided a significant decrease in FGF23 levels.

CONCLUSIONS

The present meta-analysis demonstrated that non-calcium-based phosphate binders including sevelamer, lanthanum, and iron-based phosphate binders, iron supplements, calcimimetics, hemoperfusion, and preservation of RRF could effectively reduce FGF23 in CKD patients.

Osteoporosis and Chronic Kidney Disease-Mineral and Bone Disorder (CKD-MBD): Back to Basics

Osteoporosis is defined as a skeletal disorder of compromised bone strength predisposing those affected to an elevated risk of fracture. However, based on bone histology, osteoporosis is only part of a spectrum of skeletal complications that includes osteomalacia and the various forms of renal osteodystrophy of chronic kidney disease-mineral and bone disorder (CKD-MBD). In addition, the label "kidney-induced osteoporosis" has been proposed, even though the changes caused by CKD do not qualify as osteoporosis by the histological diagnosis. It is clear, therefore, that such terminology may not be helpful diagnostically or in making treatment decisions. A new label, "CKD-MBD/osteoporosis" could be a more appropriate term because it brings osteoporosis under the official label of CKD-MBD. Neither laboratory nor noninvasive diagnostic investigations can discriminate osteoporosis from the several forms of renal osteodystrophy. Transiliac crest bone biopsy can make the diagnosis of osteoporosis by exclusion of other kidney-associated bone diseases, but its availability is limited. Recently, a classification of metabolic bone diseases based on bone turnover, from low to high, together with mineralization and bone volume, has been proposed. Therapeutically, no antifracture treatments have been approved by the US Food and Drug Administration for patients with kidney-associated bone disease. Agents that suppress parathyroid hormone (vitamin D analogues and calcimimetics) are used to treat hyperparathyroid bone disease. Antiresorptive and osteoanabolic agents approved for osteoporosis are being used off-label to treat CKD stages 3b-5 in high-risk patients. It has now been suggested that intermittent administration of parathyroid hormone as early as CKD stage 2 could be an effective management strategy. If confirmed in clinical trials, it could mitigate the retention of phosphorus and subsequently the rise in fibroblast growth factor 23 and may be beneficial for coexisting osteoporosis.

Hyperphosphatemia and Cardiovascular Disease

Hyperphosphatemia or even serum phosphate levels within the “normal laboratory range” are highly associated with increased cardiovascular disease risk and mortality in the general population and patients suffering from chronic kidney disease (CKD). As the kidney function declines, serum phosphate levels rise and subsequently induce the development of hypertension, vascular calcification, cardiac valvular calcification, atherosclerosis, left ventricular hypertrophy and myocardial fibrosis by distinct mechanisms. Therefore, phosphate is considered as a promising therapeutic target to improve the cardiovascular outcome in CKD patients. The current therapeutic strategies are based on dietary and pharmacological reduction of serum phosphate levels to prevent hyperphosphatemia in CKD patients. Large randomized clinical trials with hard endpoints are urgently needed to establish a causal relationship between phosphate excess and cardiovascular disease (CVD) and to determine if lowering serum phosphate constitutes an effective intervention for the prevention and treatment of CVD.

Efficacy and Safety of a Novel Nicotinamide Modified-Release Formulation in the Treatment of Refractory Hyperphosphatemia in Patients Receiving Hemodialysis-A Randomized Clinical Trial

INTRODUCTION

Despite widespread use of phosphate binders (PBs), phosphate control is insufficient in many hemodialysis patients. Preliminary clinical observations suggest that nicotinamide may act synergistically with PBs to improve phosphate control.

METHODS

This multinational, randomized, double-blind, placebo-controlled study evaluated the efficacy and safety of nicotinamide modified release (NAMR) in combination with oral PB in a large cohort of hemodialysis patients with abnormal serum phosphate concentration (>4.5 mg/dl) despite treatment with PB. Patients entered a proof-of-efficacy phase (12 weeks [W12]) in which adjustments of relevant comedication were not permitted, followed by a safety extension phase for up to 52 weeks. Here, we report the results of the first phase.

RESULTS

The intention-to-treat (ITT) population consisted of 539 patients in the NAMR and 183 patients in the placebo group. NAMR and placebo were orally administered once daily (250-1500 mg/d). Mean age of patients was 61.8 years, and 63.0% were men. In the confirmatory analysis that estimated the difference in serum phosphate concentration after 12 weeks, NAMR proved superior over placebo with a significant difference of -0.51 mg/dl (95% confidence interval [CI] -0.72, -0.29; P < 0.0001). This effect was associated with significantly lower intact parathyroid hormone (iPTH) values (NAMR: 292.4±300.4 pg/ml vs. placebo: 337.0±302.7 pg/ml; P = 0.04) and an improved calcification propensity (T50 time; NAMR: 23.8±97.1 minutes vs. placebo: 2.3±100.7 minutes; P = 0.02). Diarrhea and pruritus were more frequent in the NAMR group.

CONCLUSION

NAMR combined with oral PB significantly improved phosphate control in hemodialysis patients.

Efficacy and safety of calcium carbonate in normophosphataemic patients with chronic kidney disease Stages 3 and 4

BACKGROUND

Disordered bone and mineral metabolism are a common complication of chronic kidney disease (CKD). Phosphate binders are often prescribed in advanced CKD, when hyperphosphataemia develops. Little is known about the role of these drugs in earlier stages, when serum phosphorus levels are kept in the normal range by increased urinary excretion.

METHODS

A retrospective, controlled observational study was conducted on a cohort of 78 pre-dialysis patients. Subjects had CKD Stage 3 or 4, normal serum phosphorus levels and increased urinary fractional excretion of phosphate. Thirty-eight patients receiving calcium carbonate for 24 months were compared with 40 patients under no phosphate binders, regarding mineral metabolism parameters and vascular calcification scores.

RESULTS

Calcium carbonate decreased mean urinary fractional excretion of phosphate and median 24-h urine phosphorus, whereas no significant change was seen in the control group. Mean serum phosphorus and median serum intact parathyroid hormone (iPTH) remained stable in treated patients but increased in the control group. Vascular calcification, assessed by Kauppila and Adragão scores, worsened under calcium carbonate with no significant change in the control group.

CONCLUSIONS

Calcium carbonate reduced urinary phosphate excretion and prevented the rise in phosphorus and iPTH serum levels in a cohort of normophosphataemic pre-dialysis patients. However, treatment was associated with increased vascular calcification, suggesting that calcium-based phosphate binders are not a safe option for CKD patients.

Consensus Recommendations for the Diagnosis and Management of X-Linked Hypophosphatemia in Belgium

X-linked hypophosphatemia (XLH) is the most common genetic form of hypophosphatemic rickets and osteomalacia. In this disease, mutations in the PHEX gene lead to elevated levels of the hormone fibroblast growth factor 23 (FGF23), resulting in renal phosphate wasting and impaired skeletal and dental mineralization. Recently, international guidelines for the diagnosis and treatment of this condition have been published. However, more specific recommendations are needed to provide guidance at the national level, considering resource availability and health economic aspects. A national multidisciplinary group of Belgian experts convened to discuss translation of international best available evidence into locally feasible consensus recommendations. Patients with XLH may present to a wide array of primary, secondary and tertiary care physicians, among whom awareness of the disease should be raised. XLH has a very broad differential-diagnosis for which clinical features, biochemical and genetic testing in centers of expertise are recommended. Optimal care requires a multidisciplinary approach, guided by an expert in metabolic bone diseases and involving (according to the individual patient's needs) pediatric and adult medical specialties and paramedical caregivers, including but not limited to general practitioners, dentists, radiologists and orthopedic surgeons. In children with severe or refractory symptoms, FGF23 inhibition using burosumab may provide superior outcomes compared to conventional medical therapy with phosphate supplements and active vitamin D analogues. Burosumab has also demonstrated promising results in adults on certain clinical outcomes such as pseudofractures. In summary, this work outlines recommendations for clinicians and policymakers, with a vision for improving the diagnostic and therapeutic landscape for XLH patients in Belgium.

A Randomized Trial on the Effect of Phosphate Reduction on Vascular End Points in CKD (IMPROVE-CKD)

BACKGROUND

Hyperphosphatemia is associated with increased fibroblast growth factor 23 (FGF23), arterial calcification, and cardiovascular mortality. Effects of phosphate-lowering medication on vascular calcification and arterial stiffness in CKD remain uncertain.

METHODS

To assess the effects of non-calcium-based phosphate binders on intermediate cardiovascular markers, we conducted a multicenter, double-blind trial, randomizing 278 participants with stage 3b or 4 CKD and serum phosphate >1.00 mmol/L (3.10 mg/dl) to 500 mg lanthanum carbonate or matched placebo thrice daily for 96 weeks. We analyzed the primary outcome, carotid-femoral pulse wave velocity, using a linear mixed effects model for repeated measures. Secondary outcomes included abdominal aortic calcification and serum and urine markers of mineral metabolism.

RESULTS

A total of 138 participants received lanthanum and 140 received placebo (mean age 63.1 years; 69% male, 64% White). Mean eGFR was 26.6 ml/min per 1.73 m2; 45% of participants had diabetes and 32% had cardiovascular disease. Mean serum phosphate was 1.25 mmol/L (3.87 mg/dl), mean pulse wave velocity was 10.8 m/s, and 81.3% had abdominal aortic calcification at baseline. At 96 weeks, pulse wave velocity did not differ significantly between groups, nor did abdominal aortic calcification, serum phosphate, parathyroid hormone, FGF23, and 24-hour urinary phosphate. Serious adverse events occurred in 63 (46%) participants prescribed lanthanum and 66 (47%) prescribed placebo. Although recruitment to target was not achieved, additional analysis suggested this was unlikely to have significantly affected the principle findings.

CONCLUSIONS

In patients with stage 3b/4 CKD, treatment with lanthanum over 96 weeks did not affect arterial stiffness or aortic calcification compared with placebo. These findings do not support the role of intestinal phosphate binders to reduce cardiovascular risk in patients with CKD who have normophosphatemia.

CLINICAL TRIAL REGISTRY NAME AND REGISTRATION NUMBER

Australian Clinical Trials Registry, ACTRN12610000650099.

Hyperphosphatemia Drives Procoagulant Microvesicle Generation in the Rat Partial Nephrectomy Model of CKD

Hyperphosphatemia has been proposed as a cardiovascular risk factor, contributing to long-term vascular calcification in hyperphosphatemic Chronic Kidney Disease (CKD) patients. However, more recent studies have also demonstrated acute effects of inorganic phosphate (Pi) on endothelial cells in vitro, especially generation of pro-coagulant endothelial microvesicles (MV). Hitherto, such direct effects of hyperphosphatemia have not been reported in vivo. Thirty-six male Sprague-Dawley rats were randomly allocated to three experimental groups: (1) CKD induced by partial nephrectomy receiving high (1.2%) dietary phosphorus; (2) CKD receiving low (0.2%) dietary phosphorus; and (3) sham-operated controls receiving 1.2% phosphorus. After 14 days the animals were sacrificed and plasma MVs counted by nanoparticle tracking analysis. MVs isolated by centrifugation were assayed for pro-coagulant activity by calibrated automated thrombography, and relative content of endothelium-derived MVs was assessed by anti-CD144 immunoblotting. When compared with sham controls, high phosphorus CKD rats were shown to be hyperphosphatemic (4.11 ± 0.23 versus 2.41 ± 0.22 mM Pi, p < 0.0001) with elevated total plasma MVs (2.24 ± 0.37 versus 1.31 ± 0.24 × 10⁸ per ml, p < 0.01), showing increased CD144 expression (145 ± 25% of control value, p < 0.0001), and enhanced procoagulant activity (18.06 ± 1.75 versus 4.99 ± 1.77 nM peak thrombin, p < 0.0001). These effects were abolished in the low phosphorus CKD group. In this rat model, hyperphosphatemia (or a Pi-dependent hormonal response derived from it) is sufficient to induce a marked increase in circulating pro-coagulant MVs, demonstrating an important link between hyperphosphatemia and thrombotic risk in CKD.

Fibroblast Growth Factor 23 and Adverse Clinical Outcomes in Type 2 Diabetes: a Bitter-Sweet Symphony

PURPOSE OF REVIEW

Fibroblast growth factor 23 (FGF23) is a key phosphate-regulating hormone that has been associated with adverse outcomes in patients with chronic kidney disease (CKD). Emerging data suggest that FGF23 plays a specific role in type 2 diabetes, partly independent of kidney function. We aimed to summarize current literature on the associations between FGF23 and outcomes in patients with type 2 diabetes with or without CKD.

RECENT FINDINGS

Several cohort studies have shown strong associations between plasma FGF23 and cardiovascular outcomes in diabetic CKD. Moreover, recent data suggest that FGF23 are elevated and may also be a risk factor for cardiovascular disease and mortality in type 2 diabetes patients without CKD, although the magnitude of the association is smaller than in CKD patients. Diabetes-related factors may influence plasma FGF23 levels, and a higher FGF23 levels seem to contribute to a higher cardiovascular and mortality risk in patients with type 2 diabetes. Although this risk may be relevant in diabetic individuals with preserved kidney function, it is strongly accentuated in diabetic nephropathy. Future studies should clarify if FGF23 is merely a disease severity marker or a contributor to adverse outcomes in type 2 diabetes and establish if antidiabetic medication can modify FGF23 levels.

Kidney Functional Magnetic Resonance Imaging and Change in eGFR in Individuals with CKD

BACKGROUND AND OBJECTIVES

Kidney functional magnetic resonance imaging (MRI) requires further investigation to enhance the noninvasive identification of patients at high risk of CKD progression.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In this exploratory study, we obtained baseline diffusion-weighted and blood oxygen level-dependent MRI in 122 participants of the CKD Optimal Management with Binders and Nicotinamide trial, which was a multicenter, randomized, double-blinded, 12-month, four-group parallel trial of nicotinamide and lanthanum carbonate versus placebo conducted in individuals with eGFR 20-45 ml/min per 1.73 m². Lower values of apparent diffusion coefficient (ADC) on diffusion-weighted MRI may indicate increased fibrosis, and higher values of relaxation rate (R2*) on blood oxygen level-dependent MRI may represent decreased oxygenation. Because there was no effect of active treatment on eGFR over 12 months, we tested whether baseline kidney functional MRI biomarkers were associated with eGFR decline in all 122 participants. In a subset of 87 participants with 12-month follow-up MRI data, we evaluated whether kidney functional MRI biomarkers change over time.

RESULTS

Mean baseline eGFR was 32±9 ml/min per 1.73 m², and mean annual eGFR slope was -2.3 (95% confidence interval [95% CI], -3.4 to -1.1) ml/min per 1.73 m² per year. After adjustment for baseline covariates, baseline ADC was associated with change in eGFR over time (difference in annual eGFR slope per 1 SD increase in ADC: 1.3 [95% CI, 0.1 to 2.5] ml/min per 1.73 m² per year, ADC×time interaction P=0.04). This association was no longer significant after further adjustment for albuminuria (difference in annual eGFR slope per 1 SD increase in ADC: 1.0 (95% CI, -0.1 to 2.2) ml/min per 1.73 m² per year, ADC×time interaction P=0.08). There was no significant association between baseline R2* and change in eGFR over time. In 87 participants with follow-up functional MRI, ADC and R2* values remained stable over 12 months (intraclass correlation: 0.71 and 0.68, respectively).

CONCLUSIONS

Baseline cortical ADC was associated with change in eGFR over time, but this association was not independent of albuminuria. Kidney functional MRI biomarkers remained stable over 1 year.

CLINICAL TRIAL REGISTRY NAME AND REGISTRATION NUMBER

CKD Optimal Management with Binders and Nicotinamide (COMBINE), NCT02258074.

Short-term effect of the New Nordic Renal Diet on phosphorus homoeostasis in chronic kidney disease Stages 3 and 4

BACKGROUND

The New Nordic Diet is a food concept favouring organically produced food items, fruits, vegetables, whole grains and fish. We investigated the short-term effects of a modified phosphorus-reduced New Nordic Renal Diet (NNRD) in chronic kidney disease (CKD) patients on important parameters of phosphorus homoeostasis.

METHODS

The NNRD contained a total of 850 mg phosphorus/day. A total of 18 patients, CKD Stages 3 and 4 were studied in a randomized crossover trial comparing a 1-week control period of the habitual diet with a 1-week period of the NNRD. Data were obtained at baseline and during 1 week of dietary intervention (habitual diet versus NNRD) by collecting fasting blood samples and 24-h urine collections. The primary outcome was the difference in the change in 24-h urine phosphorus excretion from baseline to Day 7 between the NNRD and habitual diet periods. Secondary outcomes were changes in the fractional excretion of phosphorus, fibroblast growth factor 23 (FGF23) and plasma phosphate.

RESULTS

As compared with the habitual diet, 24-h urine phosphorus excretion was reduced in the NNRD by 313 mg/day (P < 0.001). The mean baseline phosphorus was 875 ± 346 mg/day and was decreased by 400 ± 256 mg/day in the NNRD and 87 ± 266 mg/day in the habitual diet. The 24-h urine fractional excretion of phosphorus decreased by 11% (P < 0.001) and FGF23 decreased by 30 pg/mL (P = 0.03) with the NNRD compared with the habitual diet. Plasma phosphate did not change.

CONCLUSION

This study demonstrates that dietary phosphorus restriction in the context of the NNRD is feasible and has positive effects on phosphorus homeostasis in CKD patients.

Targeting Vascular Calcification in Chronic Kidney Disease

Cardiovascular (CV) disease remains an important cause of morbidity and mortality for patients with chronic kidney disease (CKD). Although clustering of traditional risk factors with CKD is well recognized, kidney-specific mechanisms are believed to drive the disproportionate burden of CV disease. One perturbation that is frequently observed at high rates in patients with CKD is vascular calcification, which may be a central mediator for an array of CV sequelae. This review summarizes the pathophysiological bases of intimal and medial vascular calcification in CKD, current strategies for diagnosis and management, and posits vascular calcification as a risk marker and therapeutic target.

A Simple Equation to Estimate Urinary Flow Rate Using Urine Creatinine

BACKGROUND

Accurate assessment of urine flow remains challenging in both inpatient and outpatient settings. We hypothesized we could derive an equation that would accurately estimate urine flow rate (eV) through derivation from other existing equations commonly used in nephrology clinical practice.

METHODS

The eV equation was derived using the Cockcroft-Gault and the measured creatinine clearance (CrCl = UCrV/PCr) equations. Within the African American Study of Kidney Disease and Hypertension (AASK; n = 570) and COMBINE (n = 133) clinical trials, we identified participants with concordant estimated and measured creatinine excretion rates to define a subset with highly accurate 24-h urine collections, to assure a reliable gold standard. We then compared eV to measured 24-h urine flow rates in these trials.

RESULTS

In AASK, we found a high correlation between eV and measured urine flow rate (V; r = 0.91, p < 0.001); however, Bland-Altman plots showed that eV was 9.5 mL/h lower than V, on average. Thus, we added a correction factor to the eV equation and externally validated the new equation in COMBINE. eV and V were again highly correlated (r = 0.91, p < 0.001), and bias was improved (mean difference 5.3 mL/h). Overall, 80% of individuals had eV that was within 20% of V.

CONCLUSIONS

A simple equation using urine creatinine, demographics, and body weight can accurately predict urine flow rate and may have clinical utility in situations where it is difficult to accurately measure the urine flow rate.

Current Understanding of Mineral and Bone Disorders of Chronic Kidney Disease and the Scientific Grounds on the Use of Exogenous Parathyroid Hormone in Its Management

Chronic Kidney disease (CKD) disturbs mineral homeostasis leading to mineral and bone disorders (MBD). Serum calcium and phosphate (Pi) remain normal until the late stages of CKD at the expense of elevate fibroblast growth factor-23 (FGF-23), a phosphaturic hormone, followed by reduced 1,25-dihydroxy-vitamin D (1,25[OH]₂D) and finally elevated parathyroid hormone (PTH). Pi retention is thought to be the initial cause of CKD-MBD. The management of MBD is a huge clinical challenge because the effectiveness of current therapeutic regimens to prevent and treat MBD is limited. An intermittent regimen of PTH, when administered at the early stages of CKD, through its phosphaturic action, could prevent FGF-23 increases, the drop of 1,25(OH)₂D, and the development of renal osteodystrophy, including secondary hyperparathyroidism (HPT) and its catabolic effects on the skeleton. Even in more advanced stages of CKD that have not progressed to tertiary HPT, could be beneficial. Therapeutic effects could be achieved in vascular calcification as well. Limited experimental/clinical data support the effectiveness of PTH in CKD-MBD. Its safety, has been established only when it is used for the treatment of osteoporosis, including patients with CKD. The proposed intermittent PTH administration is biologically plausible but its effectiveness and safety has to be critically assessed in long term prospective studies in patients with CKD-MBD.

The effects of tenapanor on serum fibroblast growth factor 23 in patients receiving hemodialysis with hyperphosphatemia

Background

Elevated serum fibroblast growth factor 23 (FGF23) is strongly associated with cardiovascular risk and mortality. Tenapanor, an inhibitor of gastrointestinal sodium/hydrogen exchanger isoform 3, decreased serum phosphate in a randomized, double-blind, placebo-controlled Phase 2 trial (ClinicalTrials.gov identifier NCT02081534) of patients receiving hemodialysis with hyperphosphatemia. Here, we report a secondary analysis of effects on serum FGF23 during that study.

Methods

After 1–3 weeks of washout of phosphate binders, 162 patients were randomized to receive 4 weeks of treatment with placebo or one of six tenapanor regimens (3 or 30 mg once daily, or 1, 3, 10 or 30 mg twice daily). Intact FGF23 concentrations were determined from serum samples collected at screening, post-washout and end of treatment, assayed in duplicate in a single batch at the end of the study.

Results

After phosphate-binder washout, serum FGF23 concentrations increased in all groups [range of geometric means: 1430–2605 pg/mL before, to 2601–6294 pg/mL after washout (P < 0.001 for all patients analyzed as a single group)]. Serum FGF23 concentrations subsequently decreased in tenapanor-treated patients (2030–3563 pg/mL), whereas they increased further in placebo-treated patients (6930 pg/mL). In an analysis of covariance, FGF23 decreased by 9.1–27.9% in tenapanor-treated patients and increased by 21.9% in placebo-treated patients (P ≤ 0.001–0.04).

Conclusions

Following a marked increase in serum FGF23 in response to withdrawal of phosphate binders, tenapanor significantly decreased serum FGF23 in patients receiving hemodialysis with hyperphosphatemia. Further studies are required to explore the long-term effects of controlling FGF23 with tenapanor.

Regulation and Effects of FGF23 in Chronic Kidney Disease

Chronic kidney disease (CKD) is a global health epidemic that accelerates cardiovascular disease, increases risk of infection, and causes anemia and bone disease, among other complications that collectively increase risk of premature death. Alterations in calcium and phosphate homeostasis have long been considered nontraditional risk factors for many of the most morbid outcomes of CKD. The discovery of fibroblast growth factor 23 (FGF23), which revolutionized the diagnosis and treatment of rare hereditary disorders of FGF23 excess that cause hypophosphatemic rickets, has also driven major paradigm shifts in our understanding of the pathophysiology and downstream end-organ complications of disordered mineral metabolism in CKD. As research of FGF23 in CKD has rapidly advanced, major new questions about its regulation and effects continuously emerge. These are promoting exciting innovations in laboratory, patient-oriented, and epidemiological research and stimulating clinical trials of new therapies and repurposing of existing ones to target FGF23.

From old uraemic toxins to new uraemic toxins: place of 'omics'

Uraemic toxins seem to play an important role in the genesis of cardiovascular and renal damage in chronic kidney disease patients. This short article is divided into two thematic sections. The first part focuses on a selection of ‘old’ toxins for which recent data (published between 2016 and 2018) have provided a better understanding of the associated harmful mechanisms and which, in our opinion, nephrologists should be more aware of. The second part highlights new perspectives for identifying and quantifying these compounds using ‘omics’ techniques.

Serum Phosphorus as a Risk Factor of Metabolic Syndrome in the Elderly in Taiwan: A Large-Population Cohort Study

Background: The impact of serum phosphorus concentration on metabolic syndrome were limited. Therefore, this study aimed to explore the association between the serum phosphorus and incident metabolic syndrome in the elderly in Taiwan. Methods: We included 1491 participants who had health check-ups in the Tri-Service General Hospital for the period 2007 to 2015 and divided them based on age to assess the incidence of metabolic syndrome. We performed the COX regression model to explore the impact of serum phosphorus for metabolic syndrome, diabetes mellitus, and hypertension by an age-specific group. Results: Our result showed that higher serum phosphorus concentration was noted in the elderly in the baseline characteristics. In the group older than 60 years, serum phosphorus concentration was correlated with the incidence of metabolic syndrome (hazard ratios (HR) = 1.39, 95% CI 1.11–1.74) and diabetes mellitus (HR = 1.49, 95% CI 1.15–1.92) after adjustment. We further found the relationship between serum phosphorus and incidence of the components of metabolic syndrome, including higher waist circumference, high-density lipoprotein (HDL), serum triglyceride, and fast glucose. Conclusions: Our study might provide an epidemiological evidence that serum phosphorus was related with the incidence of metabolic syndrome in the elderly in Taiwan.

Ferric citrate reduces fibroblast growth factor 23 levels and improves renal and cardiac function in a mouse model of chronic kidney disease

Iron deficiency, anemia, hyperphosphatemia, and increased fibroblast growth factor 23 (FGF23) are common and interrelated complications of chronic kidney disease (CKD) that are linked to CKD progression, cardiovascular disease and death. Ferric citrate is an oral phosphate binder that decreases dietary phosphate absorption and serum FGF23 concentrations while increasing iron stores and hemoglobin in patients with CKD. Here we compared the effects of ferric citrate administration versus a mineral sufficient control diet using the Col4a3 knockout mouse model of progressive CKD and age-matched wild-type mice. Ferric citrate was given to knockout mice for four weeks beginning at six weeks of age when they had overt CKD, or for six weeks beginning at four weeks of age when they had early CKD. Ten-week-old knockout mice on the control diet showed overt iron deficiency, anemia, hyperphosphatemia, increased serum FGF23, hypertension, decreased kidney function, and left ventricular systolic dysfunction. Ferric citrate rescued iron deficiency and anemia in knockout mice regardless of the timing of treatment initiation. Circulating levels and bone expression of FGF23 were reduced in knockout mice given ferric citrate with more pronounced reductions observed when ferric citrate was initiated in early CKD. Ferric citrate decreased serum phosphate only when it was initiated in early CKD. While ferric citrate mitigated systolic dysfunction in knockout mice regardless of timing of treatment initiation, early initiation of ferric citrate also reduced renal fibrosis and proteinuria, improved kidney function, and prolonged life span. Thus, initiation of ferric citrate treatment early in the course of murine CKD lowered FGF23, slowed CKD progression, improved cardiac function and significantly improved survival.

Impact of Abdominal Aortic Calcification on Central Haemodynamics and Decline of Glomerular Filtration Rate in Patients with Chronic Kidney Disease Stages 3 and 4

BACKGROUND/AIM

Calcifications of large arteries are frequent in chronic kidney disease (CKD) and may contribute to the high cardiovascular risk in this population. The aim of this study was to examine whether abdominal aortic calcification volume (AACV) was a predictor of the rate of decline in glomerular filtration rate (GFR) in a cohort of patients with CKD stages 3 and 4.

METHODS

Eighty-four patients with CKD stages 3 and 4 were enrolled in this prospective observational study. At study entry, and annually, GFR was measured by plasma 51Cr-EDTA clearance. At baseline, haemodynamics was assessed and AACV was determined by computer tomography.

RESULTS

The mean follow-up time was 3.4 years and mean decline in GFR was -2.69 mL/min/1.73 m2 per year. At baseline, abdominal aortic calcification (AAC) was detected in 66 patients (79%). A binary logistic regression analysis revealed that age was the only statistically significant independent predictor of AAC. In patients with AAC, male gender (B = 0.413, p = 0.030), aortic diastolic blood pressure (B = -0.025, p = 0.001) and ankle-brachial index (B = -1.666, p = 0.002) were independently associated with AACV using a multiple linear regression analysis. Neither the presence nor the extent of AAC was significantly associated with the rate of change in GFR during follow-up.

CONCLUSION

In this cohort of patients with CKD stages 3 and 4, only age was an independent predictor of the presence of AAC. AACV was not associated with the rate of decline in GFR.

Effects of Nicotinamide and Lanthanum Carbonate on Serum Phosphate and Fibroblast Growth Factor-23 in CKD: The COMBINE Trial

BACKGROUND

Higher serum phosphate and fibroblast growth factor-23 (FGF23) levels may be modifiable to prevent cardiovascular disease in CKD. Short-term studies have reported modest efficacy in phosphate and FGF23 reduction with intestinal phosphate binders in CKD.

METHODS

To investigate effects of lanthanum carbonate (LC; a phosphate binder) and/or nicotinamide (NAM; an inhibitor of active intestinal phosphate transport) on serum phosphate and FGF23 in stage 3b/4 CKD, we conducted a randomized trial among individuals with eGFR 20-45 ml/min per 1.73 m² to NAM (750 mg twice daily) plus LC (1000 mg thrice daily), NAM plus LC placebo, LC plus NAM placebo, or double placebo for 12 months. Dual primary end points were change from baseline in serum phosphate and intact FGF23 concentrations.

RESULTS

Mean eGFR for the 205 participants was 32ml/min per 1.73 m². At baseline, serum phosphate was 3.7 mg/dl and median FGF23 was 99 pg/ml (10th, 90th percentiles: 59, 205). Mean rates of change in phosphate increased slightly over 12 months in all groups and did not differ significantly across arms. Similarly, percent changes in FGF23 per 12 months increased for all arms except LC plus placebo, and did not differ significantly across arms. Gastrointestinal symptoms limited adherence. Adverse events rates were similar across arms.

CONCLUSIONS

LC and/or NAM treatment did not significantly lower serum phosphate or FGF23 in stage 3b/4 CKD over 12 months. Although these agents appeared safe, intestinal symptoms limited adherence. Reducing phosphate and FGF23 in nondialysis CKD will require new approaches.

FGF23, Biomarker or Target?

Fibroblast growth factor 23 (FGF23) plays a key role in the complex network between the bones and other organs. Initially, it was thought that FGF23 exclusively regulated phosphate and vitamin D metabolism; however, recent research has demonstrated that an excess of FGF23 has other effects that may be detrimental in some cases. The understanding of the signaling pathways through which FGF23 acts in different organs is crucial to develop strategies aiming to prevent the negative effects associated with high FGF23 levels. FGF23 has been described to have effects on the heart, promoting left ventricular hypertrophy (LVH); the liver, leading to production of inflammatory cytokines; the bones, inhibiting mineralization; and the bone marrow, by reducing the production of erythropoietin (EPO). The identification of FGF23 receptors will play a remarkable role in future research since its selective blockade might reduce the adverse effects of FGF23. Patients with chronic kidney disease (CKD) have very high levels of FGF23 and may be the population suffering from the most adverse FGF23-related effects. The general population, as well as kidney transplant recipients, may also be affected by high FGF23. Whether the association between FGF23 and clinical events is causal or casual remains controversial. The hypothesis that FGF23 could be considered a therapeutic target is gaining relevance and may become a promising field of investigation in the future.

Fibroblast growth factor 23: fueling the fire

In chronic kidney disease, systemic inflammation is common and associated with mortality. The present study demonstrates that fibroblast growth factor 23 (FGF23) contributes to uremic inflammation by increasing hepatic expression and secretion of inflammatory cytokines. FGF23 binds to hepatic FGFR4, inducing calcineurin/nuclear factor of activated T-cell signaling, resulting in increased expression of interleukin 6 and C-reactive protein. The proinflammatory effects of FGF23 are inhibited by an isoform-specific FGFR4 blocking antibody and by cyclosporine, a calcineurin inhibitor.

Can we IMPROVE cardiovascular outcomes through phosphate lowering in CKD? Rationale and protocol for the IMpact of Phosphate Reduction On Vascular End-points in Chronic Kidney Disease (IMPROVE-CKD) study

INTRODUCTION

Patients with chronic kidney disease (CKD) are at heightened cardiovascular risk, which has been associated with abnormalities of bone and mineral metabolism. A deeper understanding of these abnormalities should facilitate improved treatment strategies and patient-level outcomes, but at present there are few large, randomised controlled clinical trials to guide management. Positive associations between serum phosphate and fibroblast growth factor 23 (FGF-23) and cardiovascular morbidity and mortality in both the general and CKD populations have resulted in clinical guidelines suggesting that serum phosphate be targeted towards the normal range, although few randomised and placebo-controlled studies have addressed clinical outcomes using interventions to improve phosphate control. Early preventive measures to reduce the development and progression of vascular calcification, left ventricular hypertrophy and arterial stiffness are crucial in patients with CKD.

METHODS AND ANALYSIS

We outline the rationale and protocol for an international, multicentre, randomised parallel-group trial assessing the impact of the non-calcium-based phosphate binder, lanthanum carbonate, compared with placebo on surrogate markers of cardiovascular disease in a predialysis CKD population-the IM pact of P hosphate R eduction O n V ascular E nd-points (IMPROVE)-CKD study. The primary objective of the IMPROVE-CKD study is to determine if the use of lanthanum carbonate reduces the burden of cardiovascular disease in patients with CKD stages 3b and 4 when compared with placebo. The primary end-point of the study is change in arterial compliance measured by pulse wave velocity over a 96-week period. Secondary outcomes include change in aortic calcification and biochemical parameters of serum phosphate, parathyroid hormone and FGF-23 levels.

ETHICS AND DISSEMINATION

Ethical approval for the IMPROVE-CKD trial was obtained by each local Institutional Ethics Committee for all 17 participating sites in Australia, New Zealand and Malaysia prior to study commencement. Results of this clinical trial will be published in peer-reviewed journals and presented at conferences.

TRIAL REGISTRATION NUMBER

ACTRN12610000650099.

Drug Targets for Heart Failure with Preserved Ejection Fraction: A Mechanistic Approach and Review of Contemporary Clinical Trials

Heart failure with preserved ejection fraction (HFpEF) accounts for over half of prevalent heart failure (HF) worldwide, and prognosis after hospitalization for HFpEF remains poor. Due, at least in part, to the heterogeneous nature of HFpEF, drug development has proved immensely challenging. Currently, there are no universally accepted therapies that alter the clinical course of HFpEF. Despite these challenges, important mechanistic understandings of the disease have revealed that the pathophysiology of HFpEF is distinct from that of HF with reduced ejection fraction and have also highlighted potential new therapeutic targets for HFpEF. Of note, HFpEF is a systemic syndrome affecting multiple organ systems. Depending on the organ systems involved, certain novel therapies offer promise in reducing the morbidity of the HFpEF syndrome. In this review, we aim to discuss novel pharmacotherapies for HFpEF based on its unique pathophysiology and identify key research strategies to further elucidate mechanistic pathways to develop novel therapeutics in the future.

Update on Chronic Kidney Disease Mineral and Bone Disorder in Cardiovascular Disease

Chronic kidney disease mineral and bone disorder (MBD) encompasses changes in mineral ion and vitamin D metabolism that are widespread in the setting of chronic kidney disease and end-stage renal disease. MBD components associate with cardiovascular disease in many epidemiologic studies. Through impacts on hypertension, activation of the renin-angiotensin-aldosterone system, vascular calcification, endothelial function, and cardiac remodeling and conduction, MBD may be a direct and targetable cause of cardiovascular disease. However, assessment and treatment of MBD is rife with challenges owing to biological tensions between its many components, such as calcium and phosphorus with their regulatory hormones fibroblast growth factor 23 and parathyroid hormone; fibroblast growth factor 23 with its co-receptor klotho; and vitamin D with control of calcium and phosphorus. These complex interactions between MBD components hinder the simple translation to clinical trials, which ultimately are needed to prove the benefits of treating MBD. Deeper investigation using precision medicine tools and principles, including genomics and individualized risk assessment and therapy, may help move the field closer toward clinical applications. This review provides a high-level overview of conventional and precision epidemiology in MBD, potential mechanisms of cardiovascular disease pathogenesis, and guiding therapeutic principles for established and emerging treatments.