A Pilot Randomized Trial of Ferric Citrate Coordination Complex for the Treatment of Advanced CKD

Guidelines for clinical evaluation of chronic kidney disease in early stages : AMED research on regulatory science of pharmaceuticals and medical devices

BACKGROUND

For the development of pharmaceutical products in kidney field, appropriate surrogate endpoints which can predict long-term prognosis are needed as an alternative to hard endpoints, such as end-stage kidney disease. Though international workshop has proposed estimated glomerular filtration rate (GFR) slope reduction of 0.5-1.0 mL/min/1.73 m /year and 30% decrease in albuminuria/proteinuria as surrogate endpoints in early and advanced chronic kidney disease (CKD), it was not clear whether these are applicable to Japanese patients.

METHODS

We analyzed J-CKD-DB and CKD-JAC, Japanese databases/cohorts of CKD patients, and J-DREAMS, a Japanese database of patients with diabetes mellitus to investigate the applicability of eGFR slope and albuminuria/proteinuria to the Japanese population. Systematic review on those endpoints was also conducted including the results of clinical trials published after the above proposal.

RESULTS

Our analysis showed an association between eGFR slope and the risk of end-stage kidney disease. A 30% decrease in albuminuria/proteinuria over 2 years corresponded to a 20% decrease in the risk of end-stage kidney disease patients with baseline UACR ≥ 30 mg/gCre or UPCR ≥ 0.15 g/gCre in the analysis of CKD-JAC, though this analysis was not performed on the other database/cohort. Those results suggested similar trends to those of the systematic review.

CONCLUSION

The results suggested that eGFR slope and decreased albuminuria/proteinuria may be used as a surrogate endpoint in clinical trials for early CKD (including diabetic kidney disease) in Japanese population, though its validity and cutoff values must be carefully considered based on the latest evidence and other factors.

Impact of transferrin saturation on cardiovascular events in non-dialysis-dependent chronic kidney disease patients treated with darbepoetin alfa

BACKGROUND

Although the widespread use of long-acting erythropoiesis-stimulating agents (ESAs) has facilitated the improvement of anemia in patients with chronic kidney disease (CKD), the improvement in prognosis has not been fully demonstrated. Iron deficiency is associated with the development of cardiovascular diseases (CVDs), and the relative iron deficiency induced by erythropoiesis-stimulating agents may prevent the improvement of prognosis. Therefore, we investigated the association between iron deficiency and cardiovascular events during long-acting erythropoiesis-stimulating agent therapy using transferrin saturation (TSAT), which is less susceptible to inflammation than ferritin.

METHODS

This study included 1040 patients with non-dialysis-dependent CKD, aged ≥ 20 years, with a glomerular filtration rate < 60 mL/min/1.73 m2 and hemoglobin < 11 g/dL, who were treated with darbepoetin alfa for 96 weeks. The patients were recruited in the BRIGHTEN Trial, a multicenter, prospective, observational study conducted to evaluate erythropoiesis-stimulating agent resistance to darbepoetin alfa in treating anemia in non-dialysis-dependent CKD in a clinical setting. The association between transferrin saturation and the cumulative incidence of cardiovascular events was evaluated using the Kaplan-Meier method. To calculate the hazard ratio (HR), 95% confidence intervals (CI) and the Cox proportional hazards model were used.

RESULTS

Survival curve analysis for cardiovascular events indicated that patients with transferrin saturation ≥ 30% had a significantly better prognosis, with an adjusted hazard ratio of 0.34 (95% confidence interval 0.22-0.52). Stratified analysis revealed that patients with transferrin saturation of 30-40% had a significantly lower risk of cardiovascular events than those with transferrin saturation of 20-30%, even after a multivariate-adjusted hazard ratio of 0.33 (95% confidence interval 0.21-0.54).

CONCLUSION

Patients with CKD and transferrin saturation of 30-40% had significantly fewer cardiovascular events than those with transferrin saturation of 20-30% among patients treated with long-acting erythropoiesis-stimulating agents. Therefore, it may be useful to maintain higher transferrin saturation from the viewpoint of erythropoiesis-stimulating agent responsiveness and the reduction of cardiovascular events.

Iron Metabolism and Inflammatory Mediators in Patients with Renal Dysfunction

Chronic kidney disease (CKD) affects around 850 million people worldwide, posing significant challenges in healthcare due to complications like renal anemia, end-stage kidney disease, and cardiovascular diseases. This review focuses on the intricate interplay between iron metabolism, inflammation, and renal dysfunction in CKD. Renal anemia, prevalent in CKD, arises primarily from diminished erythropoietin (EPO) production and iron dysregulation, which worsens with disease progression. Functional and absolute iron deficiencies due to impaired absorption and chronic inflammation are key factors exacerbating erythropoiesis. A notable aspect of CKD is the accumulation of uremic toxins, such as indoxyl sulfate (IS), which hinder iron metabolism and worsen anemia. These toxins directly affect renal EPO synthesis and contribute to renal hypoxia, thus playing a critical role in the pathophysiology of renal anemia. Inflammatory cytokines, especially TNF-α and IL-6, further exacerbate CKD progression and disrupt iron homeostasis, thereby influencing anemia severity. Treatment approaches have evolved to address both iron and EPO deficiencies, with emerging therapies targeting hepcidin and employing hypoxia-inducible factor (HIF) stabilizers showing potential. This review underscores the importance of integrated treatment strategies in CKD, focusing on the complex relationship between iron metabolism, inflammation, and renal dysfunction to improve patient outcomes.

Ferric citrate for the treatment of hyperphosphatemia and iron deficiency anaemia in patients with NDD-CKD: a systematic review and meta-analysis

Background: The application of ferric citrate therapy has yielded unexpected benefits in recent years for Chronic kidney disease patients suffering from hyperphosphatemia and iron deficiency -anaemia. Despite this, earlier research on the impact of ferric citrate on NDD-CKD has been contentious. Objective: The goal of the meta-analysis is to evaluate the evidence regarding the advantages and dangers of ferric citrate for the treatment of hyperphosphatemia and iron deficiency anaemia in NDD-CKD patients. Methods: Between the start of the study and June 2022, we searched PubMed, Embase, Cochrane, EBSCO, Scopus, Web of Science, Wan Fang Data, CNKI, and VIP databases for randomised controlled trials of iron citrate for hyperphosphatemia and anaemia in patients with NDD-CKD. For binary categorical data, risk ratios (OR) were employed, and for continuous variables, weighted mean differences The effect sizes for both count and measurement data were expressed using 95% confidence intervals Results: The meta-analysis includes eight trials with a total of 1281 NDD-CKD patients. The phosphorus-lowering effect of ferric citrate was greater compared to the control group (WMD, -0.55, 95% CI, -0.81 to -0.28; I2 = 86%, p < 0.001). Calcium (WMD, 0.092; 95% CI, -0.051 to 0.234; p > 0.05; I2 = 61.9%), PTH (WMD, -0.10; 95% CI, -0.44 to 0.23; I2 = 75%, p > 0.05) and iFGF23 (WMD, -7.62; 95% CI, -21.18 to 5.94; I2 = 20%, p > 0.05) levels were not statistically different after ferric citrate treatment compared to control treatment. Furthermore, ferric citrate increased iron reserves and haemoglobin. The ferric citrate group had considerably greater levels than the controls. Ferric citrate, on the other hand, may raise the risk of constipation, diarrhoea, and nausea. Conclusion: This meta-analysis found that ferric citrate had a beneficial effect in the treatment of NDD-CKD, particularly in reducing blood phosphorus levels when compared to a control intervention. It also shown that ferric citrate has a favourable effect on iron intake and anaemia management. In terms of safety, ferric citrate may increase the likelihood of gastrointestinal side effects.

Association between serum iron markers, iron supplementation and cardiovascular morbidity in pre-dialysis chronic kidney disease

BACKGROUND

The optimal range of serum iron markers and usefulness of iron supplementation are uncertain in patients with pre-dialysis chronic kidney disease (CKD). We investigated the association between serum iron indices and risk of cardiovascular disease (CVD) events and the effectiveness of iron supplementation using Chronic Kidney Disease Japan Cohort data.

METHODS

We included 1416 patients ages 20-75 years with pre-dialysis CKD. The tested exposures were serum transferrin saturation and serum ferritin levels and the outcome measures were any cardiovascular event. Fine-Gray subdistribution hazard models were used to examine the association between serum iron indices and time to events. The multivariable fractional polynomial interaction approach was used to evaluate whether serum iron indices were effect modifiers of the association between iron supplementation and cardiovascular events.

RESULTS

The overall incidence rate of CVD events for a median of 4.12 years was 26.7 events/1000 person-years. Patients with serum transferrin saturation <20% demonstrated an increased risk of CVD [subdistribution hazard ratio (HR) 2.13] and congestive heart failure (subdistribution HR 2.42). The magnitude of reduction in CVD risk with iron supplementation was greater in patients with lower transferrin saturations (P = .042).

CONCLUSIONS

Maintaining transferrin saturation >20% and adequate iron supplementation may effectively reduce the risk of CVD events in patients with pre-dialysis CKD.

Efficacy and Safety of Ferric Citrate on Hyperphosphatemia among Chinese Patients with Chronic Kidney Disease Undergoing Hemodialysis: A Phase III Multicenter Randomized Open-Label Active-Drug-Controlled Study

INTRODUCTION

Hyperphosphatemia in chronic kidney disease (CKD) patients is positively associated with mortality. Ferric citrate is a potent phosphorus binder that lowers serum phosphorus level and improves iron metabolism. We compared its efficacy and safety with active drugs in Chinese CKD patients with hemodialysis.

METHODS

Chinese patients undergoing hemodialysis were randomized into two treatment groups in a 1:1 ratio, receiving either ferric citrate or sevelamer carbonate, respectively, for 12 weeks. Serum phosphorus levels, calcium concentration, and iron metabolism parameters were evaluated every 2 weeks. Frequency and severity of adverse events were recorded.

RESULTS

217 (90.4%) patients completed the study with balanced demographic and baseline characteristics between two groups. Ferric citrate decreased the serum phosphorus level to 0.59 ± 0.54 mmol/L, comparable to 0.56 ± 0.62 mmol/L by sevelamer carbonate. There was no significant difference between two groups (p > 0.05) in the proportion of patients with serum phosphorus levels reaching the target range, the response rate to the study drug, and the changes of corrected serum calcium concentrations, and intact-PTH levels at the end of treatment. The change of iron metabolism indicators in the ferric citrate group was significantly higher than those in the sevelamer carbonate group. There are 47 (40.5%) patients in the ferric citrate group, and 26 (21.3%) patients in the sevelamer carbonate group experienced drug-related treatment emergent adverse events (TEAEs); most were mild and tolerable. Common drug-related TEAEs were gastrointestinal disorders, including diarrhea (12.9 vs. 2.5%), fecal discoloration (14.7 vs. 0%), and constipation (1.7 vs. 7.4%) in ferric citrate and sevelamer carbonate group.

CONCLUSION

Ferric citrate capsules have good efficacy and safety in the control of hyperphosphatemia in adult patients with CKD undergoing hemodialysis. Efficacy is not inferior to sevelamer carbonate. The TEAEs were mostly mild and tolerated by the patients.

Unresolved aspects in the management of renal anemia, a Delphi consensus of the Anemia Group of the S.E.N

Anemia is a common complication of chronic kidney disease (CKD) and is associated with a decrease in quality of life and an increased risk of transfusions, morbidity and mortality, and progression of CKD. The Anemia Working Group of the Sociedad Española de Nefrología conducted a Delphi study among experts in anemia in CKD to agree on relevant unanswered questions by existing evidence. The RAND/UCLA consensus methodology was used. We defined 15 questions with a PICO structure, followed by a review in scientific literature databases. Statements to each question were developed based on that literature review. Nineteen experts evaluated them using an iterative Two-Round Delphi-like process. Sixteen statements were agreed in response to 8 questions related to iron deficiency and supplementation with Fe (impact and management of iron deficiency with or without anemia, iron deficiency markers, safety of i.v. iron) and 7 related to erythropoiesis stimulating agents (ESAs) and/or hypoxia-inducible factor stabilizers (HIF), reaching consensus on all of them (individualization of the Hb objective, impact and management of resistance to ESA, ESA in the immediate post-transplant period and HIF stabilizers: impact on ferrokinetics, interaction with inflammation and cardiovascular safety). There is a need for clinical studies addressing the effects of correction of iron deficiency independently of anemia and the impact of anemia treatment with various ESA on quality of life, progression of CKD and cardiovascular events.

Role of Chronic Kidney Disease (CKD)-Mineral and Bone Disorder (MBD) in the Pathogenesis of Cardiovascular Disease in CKD

Cardiovascular disease (CVD) is the leading cause of death in patients with chronic kidney disease (CKD). Multiple factors account for the increased incidence of cardiovascular morbidity and mortality in patients with CKD. Traditional risk factors for atherosclerosis and arteriosclerosis, including age, hypertension, dyslipidemia, diabetes mellitus, and smoking, are also risk factors for CKD. Non-traditional risk factors specific for CKD are also involved in CVD pathogenesis in patients with CKD. Recently, CKD-mineral and bone disorder (CKD-MBD) has emerged as a key player in CVD pathogenesis in the context of CKD. CKD-MBD manifests as hypocalcemia and hyperphosphatemia in the later stages of CKD; however, it initially develops much earlier in disease course. The initial step in CKD-MBD involves decreased phosphate excretion in the urine, followed by increased circulating concentrations of fibroblast growth factor 23 (FGF23) and parathyroid hormone (PTH), which increase urinary phosphate excretion. Simultaneously, the serum calcitriol concentration decreases as a result of FGF23 elevation. Importantly, FGF23 and PTH cause left ventricular hypertrophy, arrhythmia, and cardiovascular calcification. More recently, calciprotein particles, which are nanoparticles composed of calcium, phosphate, and fetuin-A, among other components, have been reported to cause inflammation, cardiovascular calcification, and other clinically relevant outcomes. CKD-MBD has become one of the critical therapeutic targets for the prevention of cardiovascular events and is another link between cardiology and nephrology. In this review, we describe the role of CKD-MBD in the pathogenesis of cardiovascular disorders and present the current treatment strategies for CKD-MBD.

Osteocyte Egln1/Phd2 links oxygen sensing and biomineralization via FGF23

Osteocytes act within a hypoxic environment to control key steps in bone formation. FGF23, a critical phosphate-regulating hormone, is stimulated by low oxygen/iron in acute and chronic diseases, however the molecular mechanisms directing this process remain unclear. Our goal was to identify the osteocyte factors responsible for FGF23 production driven by changes in oxygen/iron utilization. Hypoxia-inducible factor-prolyl hydroxylase inhibitors (HIF-PHI) which stabilize HIF transcription factors, increased Fgf23 in normal mice, as well as in osteocyte-like cells; in mice with conditional osteocyte Fgf23 deletion, circulating iFGF23 was suppressed. An inducible MSC cell line ('MPC2') underwent FG-4592 treatment and ATACseq/RNAseq, and demonstrated that differentiated osteocytes significantly increased HIF genomic accessibility versus progenitor cells. Integrative genomics also revealed increased prolyl hydroxylase Egln1 (Phd2) chromatin accessibility and expression, which was positively associated with osteocyte differentiation. In mice with chronic kidney disease (CKD), Phd1-3 enzymes were suppressed, consistent with FGF23 upregulation in this model. Conditional loss of Phd2 from osteocytes in vivo resulted in upregulated Fgf23, in line with our findings that the MPC2 cell line lacking Phd2 (CRISPR Phd2-KO cells) constitutively activated Fgf23 that was abolished by HIF1α blockade. In vitro, Phd2-KO cells lost iron-mediated suppression of Fgf23 and this activity was not compensated for by Phd1 or -3. In sum, osteocytes become adapted to oxygen/iron sensing during differentiation and are directly sensitive to bioavailable iron. Further, Phd2 is a critical mediator of osteocyte FGF23 production, thus our collective studies may provide new therapeutic targets for skeletal diseases involving disturbed oxygen/iron sensing.

Ferric citrate for the treatment of hyperphosphatemia and anemia in patients with chronic kidney disease: a meta-analysis of randomized clinical trials

BACKGROUND

Hyperphosphatemia and anemia, which are common complications of chronic kidney disease (CKD), can independently contribute to cardiovascular events. Several previous studies have found that the iron-based phosphate binder, ferric citrate (FC), could be beneficial to both hyperphosphatemia and anemia.

METHODS

Relevant literature from PUBMED, EMBASE, the Cochrane Central Register of Controlled Trials (CCRCT) and MEDLINE databases were searched up to 21 February 2022, in order to conduct a meta-analysis to investigate the efficacy, safety and economic benefits of ferric citrate treatment in CKD patients with hyperphosphatemia and anemia. The meta-analysis was conducted independently by two reviewers using the RevMan software (version 5.3).

RESULTS

In total, this study included 16 randomized clinical trials (RCT) involving 1754 participants. The meta-analysis showed that ferric citrate could significantly reduce the serum phosphorus in CKD patients compared to the placebo control groups (MD -1.76 mg/dL, 95% CI (-2.78, -0.75); p = 0.0007). In contrast, the difference between ferric citrate treatment and active controls, such as non-iron-based phosphate binders, sevelamer, calcium carbonate, lanthanum carbonate and sodium ferrous citrate, was not statistically significant (MD - 0.09 mg/dL, 95% CI (-0.35, 0.17); p = 0.51). However, ferric citrate could effectively improve hemoglobin levels when compared to the active drug (MD 0.43 g/dL, 95% CI (0.04, 0.82); p = 0.03) and placebo groups (MD 0.39 g/dL, 95% CI (0.04, 0.73); p = 0.03). According to eight studies, ferric citrate was found to be cost-effective treatment in comparison to control drugs. Most of the adverse events (AE) following ferric citrate treatment were mild at most.

CONCLUSION

Collectively, our review suggests that iron-based phosphate binder, ferric citrate is an effective and safe treatment option for CKD patients with hyperphosphatemia and anemia. More importantly, this alternative treatment may also less expensive. Nevertheless, more scientific studies are warranted to validate our findings.

A review of ferric citrate clinical studies, and the rationale and design of the Ferric Citrate and Chronic Kidney Disease in Children (FIT4KiD) trial

Pediatric chronic kidney disease (CKD) is characterized by many co-morbidities, including impaired growth and development, CKD-mineral and bone disorder, anemia, dysregulated iron metabolism, and cardiovascular disease. In pediatric CKD cohorts, higher circulating concentrations of fibroblast growth factor 23 (FGF23) are associated with some of these adverse clinical outcomes, including CKD progression and left ventricular hypertrophy. It is hypothesized that lowering FGF23 levels will reduce the risk of these events and improve clinical outcomes. Reducing FGF23 levels in CKD may be accomplished by targeting two key stimuli of FGF23 production-dietary phosphate absorption and iron deficiency. Ferric citrate is approved for use as an enteral phosphate binder and iron replacement product in adults with CKD. Clinical trials in adult CKD cohorts have also demonstrated that ferric citrate decreases circulating FGF23 concentrations. This review outlines the possible deleterious effects of excess FGF23 in CKD, summarizes data from the adult CKD clinical trials of ferric citrate, and presents the Ferric Citrate and Chronic Kidney Disease in Children (FIT4KiD) study, a randomized, placebo-controlled trial to evaluate the effects of ferric citrate on FGF23 in pediatric patients with CKD stages 3-4 (ClinicalTrials.gov Identifier NCT04741646).

Effects of ferric citrate and intravenous iron sucrose on markers of mineral, bone, and iron homeostasis in a rat model of CKD-MBD

BACKGROUND

Anemia and chronic kidney disease-mineral and bone disorder (CKD-MBD) are common and begin early in CKD. Limited studies have concurrently compared the effects of ferric citrate (FC) versus intravenous (IV) iron on CKD-MBD and iron homeostasis in moderate CKD.

METHODS

We tested the effects of 10 weeks of 2% FC versus IV iron sucrose in rats with moderate CKD (Cy/+ male rat) and untreated normal (NL) littermates. Outcomes included a comprehensive assessment of CKD-MBD, iron homeostasis and oxidative stress.

RESULTS

CKD rats had azotemia, elevated phosphorus, parathyroid hormone and fibroblast growth factor-23 (FGF23). Compared with untreated CKD rats, treatment with FC led to lower plasma phosphorus, intact FGF23 and a trend (P = 0.07) toward lower C-terminal FGF23. FC and IV iron equally reduced aorta and heart calcifications to levels similar to NL animals. Compared with NL animals, CKD animals had higher bone turnover, lower trabecular volume and no difference in mineralization; these were unaffected by either iron treatment. Rats treated with IV iron had cortical and bone mechanical properties similar to NL animals. FC increased the transferrin saturation rate compared with untreated CKD and NL rats. Neither iron treatment increased oxidative stress above that of untreated CKD.

CONCLUSIONS

Oral FC improved phosphorus homeostasis, some iron-related parameters and the production and cleavage of FGF23. The intermittent effect of low-dose IV iron sucrose on cardiovascular calcification and bone should be further explored in moderate-advanced CKD.

Anemia and fibroblast growth factor 23 elevation in chronic kidney disease: homeostatic interactions and emerging therapeutics

PURPOSE OF REVIEW

Chronic kidney disease (CKD) is a progressive disorder that is associated with development of elevated fibroblast growth factor 23 (FGF23) levels and anemia. Here, we review recent literature that extends our current knowledge on the interactions between FGF23 and anemia in CKD and the impact of anemia-targeting therapeutics on FGF23 elevation in CKD.

RECENT FINDINGS

The anemia of CKD is primarily driven by a lack of erythropoietin (EPO) and iron deficiency. In addition to EPO and iron replacement, novel drug classes to treat anemia have been approved or are in clinical development. A recent observational study provides supportive evidence for the hypothesis that FGF23 elevation in CKD mediates adverse effects of iron deficiency on the cardiovascular system in patients with CKD. Preclinical and clinical studies revealed that ferric citrate (FC), and hypoxia-induced factor-prolyl hydroxylase inhibitor (HIF-PHI) treatment may reduce elevated FGF23 levels in CKD, suggesting that correcting anemia in CKD could potentially lower FGF23 levels. However, as we describe, HIF-PHI have context-dependent effects. Moreover, whether a reduction in FGF23 will improve patient outcomes in patients with CKD remains to be determined.

SUMMARY

With the emergence of novel therapeutics to treat oxygen and iron utilization deficits in CKD, studies have investigated the impact of these new drugs on FGF23. Several of these drugs, including FC and HIF-PHIs, alleviate iron homeostasis alterations in CKD and are associated with FGF23 reduction. Herein, we review the relationships between oxygen/iron sensing and FGF23 in CKD, recent findings which link FGF23 with cardiac dysfunction, as well as future translational and clinical avenues.

Segregating the effects of ferric citrate-mediated iron utilization and FGF23 in a mouse model of CKD

Ferric citrate (FC) is an approved therapy for chronic kidney disease (CKD) patients as a phosphate (Pi) binder for dialysis-dependent CKD, and for iron deficiency anemia (IDA) in non-dialysis CKD. Elevated Pi and IDA both lead to increased FGF23, however, the roles of iron and FGF23 during CKD remain unclear. To this end, iron and Pi metabolism were tested in a mouse model of CKD (0.2% adenine) ± 0.5% FC for 6 weeks, with and without osteocyte deletion of Fgf23 (flox-Fgf23/Dmp1-Cre). Intact FGF23 (iFGF23) increased in all CKD mice but was lower in Cre+ mice with or without FC, thus the Dmp1-Cre effectively reduced FGF23. Cre+ mice fed AD-only had higher serum Pi than Cre- pre- and post-diet, and the Cre+ mice had higher BUN regardless of FC treatment. Total serum iron was higher in all mice receiving FC, and liver Tfrc, Bmp6, and hepcidin mRNAs were increased regardless of genotype; liver IL-6 showed decreased mRNA in FC-fed mice. The renal 1,25-dihydroxyvitamin D (1,25D) anabolic enzyme Cyp27b1 had higher mRNA and the catabolic Cyp24a1 showed lower mRNA in FC-fed mice. Finally, mice with loss of FGF23 had higher bone cortical porosity, whereas Raman spectroscopy showed no changes in matrix mineral parameters. Thus, FC- and FGF23-dependent and -independent actions were identified in CKD; loss of FGF23 was associated with higher serum Pi and BUN, demonstrating that FGF23 was protective of mineral metabolism. In contrast, FC maintained serum iron and corrected inflammation mediators, potentially providing ancillary benefit.

Renoprotective effects of ferric citrate in a mouse model of chronic kidney disease

In chronic kidney disease, ferric citrate has been shown to be an effective phosphate binder and source of enteral iron; however, the effects of ferric citrate on the kidney have been less well-studied. Here, in Col4α3 knockout mice—a murine model of progressive chronic kidney disease, we evaluated the effects of five weeks of 1% ferric citrate dietary supplementation. As expected, ferric citrate lowered serum phosphate concentrations and increased serum iron levels in the Col4α3 knockout mice. Consistent with decreased enteral phosphate absorption and possibly improved iron status, ferric citrate greatly reduced circulating fibroblast growth factor 23 levels. Interestingly, ferric citrate also lessened systemic inflammation, improved kidney function, reduced albuminuria, and decreased kidney inflammation and fibrosis, suggesting renoprotective effects of ferric citrate in the setting of chronic kidney disease. The factors mediating possible ferric citrate renoprotection, the mechanisms by which they may act, and whether ferric citrate affects chronic kidney disease progression in humans deserves further study.

Erythropoiesis-independent effects of iron in chronic kidney disease

Chronic kidney disease (CKD) leads to alterations of iron metabolism, which contribute to the development of anemia and necessitates iron supplementation in patients with CKD. Elevated hepcidin accounts for a significant iron redistribution in CKD. Recent data indicate that these alterations in iron homeostasis coupled with therapeutic iron supplementation have pleiotropic effects on many organ systems in patients with CKD, far beyond the traditional hematologic effects of iron; these include effects of iron on inflammation, oxidative stress, kidney fibrosis, cardiovascular disease, CKD-mineral and bone disorder, and skeletal growth in children. The effects of iron supplementation appear to be largely dependent on the route of administration and on the specific iron preparation. Iron-based phosphate binders exemplify the opportunity for using iron for both traditional (anemia) and novel (hyperphosphatemia) indications. Further optimization of iron therapy in patients with CKD may inform new approaches to the treatment of CKD complications and potentially allow modification of disease progression.

Emerging cross-talks between chronic kidney disease-mineral and bone disorder (CKD-MBD) and malnutrition-inflammation complex syndrome (MICS) in patients receiving dialysis

Chronic kidney disease–mineral and bone disorder (CKD–MBD) is a systemic disorder that affects multiple organs and systems and increases the risk of morbidity and mortality in patients with CKD, especially those receiving dialysis therapy. CKD–MBD is highly prevalent in CKD patients, and its treatment is gaining attention from healthcare providers who manage these patients. Additional important pathologies often observed in CKD patients are chronic inflammation and malnutrition/protein-energy wasting (PEW). These two pathologies coexist to form a vicious cycle that accelerates the progression of various other pathologies in CKD patients. This concept is integrated into the term “malnutrition–inflammation–atherosclerosis syndrome” or “malnutrition–inflammation complex syndrome (MICS)”. Recent basic and clinical studies have shown that CKD–MBD directly induces inflammation as well as malnutrition/PEW. Indeed, higher circulating levels of inorganic phosphate, fibroblast growth factor 23, parathyroid hormone, and calciprotein particles, as markers for critical components and effectors of CKD–MBD, were shown to directly induce inflammatory responses, thereby leading to malnutrition/PEW, cardiovascular diseases, and clinically relevant complications. In this short review, we discuss the close interplay between CKD–MBD and MICS and emphasize the significance of simultaneous control of these two seemingly distinct pathologies in patients with CKD, especially those receiving dialysis therapy, for better management of the CKD/hemodialysis population.

An update on phosphate binders for the treatment of hyperphosphatemia in chronic kidney disease patients on dialysis: a review of safety profiles

INTRODUCTION

Hyperphosphatemia is an inevitable complication for patients undergoing dialysis, as is the resulting need for treatment with phosphate binders. Currently, various phosphate binders are clinically available. In addition to their phosphate-lowering activity, individual phosphate binders have differing safety profiles and off-target actions.

AREAS COVERED

This paper reviews the safety of phosphate binders and issues to be resolved.

EXPERT OPINION

Calcium-based phosphate binders are well tolerated but may increase calcium overload risk. Sevelamer reduces serum cholesterol levels and exerts anti-inflammatory effects. Compared to sevelamer, bixalomer is associated with fewer gastrointestinal symptoms. Aluminum-containing binders, lanthanum carbonate, and sucroferric oxyhydroxide exhibit strong phosphate-lowering activity. Although ferric citrate reduces erythropoiesis-stimulating agents and intravenous iron doses, its use requires monitoring of iron metabolic markers to avoid overload. Occasionally, combined use of multiple phosphate binders can offer the advantages of each phosphate binder while minimizing their drawbacks; thus, this may be desirable according to individual patients' conditions and comorbidities. However, increased pill burden and nonadherence to phosphate binders emerge as new problems. We expect that novel therapeutic strategies will be developed to resolve these issues.

Ferric citrate hydrate is associated with a reduced cost of drugs and a smaller change in red blood cell distribution width

The ASTRIO study was a randomised, multicentre, 24-week study that compared the effects of ferric citrate hydrate (FC) and non-iron-based phosphate binders (control) on anaemia management in haemodialysis (HD) patients receiving erythropoiesis-stimulating agents (ESAs). In that study, FC reduced the doses of ESAs and intravenous iron without affecting haemoglobin (Hb); however, the cost-effectiveness of FC was unclear. We retrospectively implemented a cost-effectiveness analysis comparing the incremental cost-effectiveness ratios (ICERs) in FC (n = 42) and control (n = 40) groups in patients with serum phosphate and Hb controlled within the ranges of 3.5–6.0 mg/dL and 10–12 g/dL, respectively. Costs included drug costs of phosphate binders, ESAs, and intravenous iron. Elevated red cell distribution width (RDW) has been reported to be associated with mortality in HD patients and was therefore used as an effectiveness index. The mean (95% confidence interval) differences in drug costs and RDW between the FC and control groups were US$ − 421.36 (− 778.94 to − 63.78, p = 0.02) and − 0.83% (− 1.61 to – 0.05, p = 0.04), respectively. ICER indicated a decrease of US$ 507.66 per 1% decrease in RDW. FC was more cost-effective than non-iron-based phosphate binders. Iron absorbed via FC could promote erythropoiesis and contribute to renal anaemia treatment.

Iron deficiency anaemia: pathophysiology, assessment, practical management

The WHO has recognised iron deficiency anaemia (IDA) as the most common nutritional deficiency in the world, with 30% of the population being affected with this condition. Although the most common causes of IDA are gastrointestinal bleeding and menstruation in women, decreased dietary iron and decreased iron absorption are also culpable causes. Patients with IDA should be treated with the aim of replenishing iron stores and returning the haemoglobin to a normal level. This has shown to improve quality of life, morbidity, prognosis in chronic disease and outcomes in pregnancy. Iron deficiency occurs in many chronic inflammatory conditions, including congestive cardiac failure, chronic kidney disease and inflammatory bowel disease. This article will provide an updated overview on diagnosis and management of IDA in patients with chronic conditions, preoperative and in pregnancy. We will discuss the benefits and limitations of oral versus intravenous iron replacement in each cohort, with an overview on cost analysis between the different iron formulations currently on the market.

Systematic Review and Meta-Analyses of the Effects of Phosphate-Lowering Agents in Nondialysis CKD

BACKGROUND

Benefits of phosphate-lowering interventions on clinical outcomes in patients with CKD are unclear; systematic reviews have predominantly involved patients on dialysis. This study aimed to summarize evidence from randomized controlled trials (RCTs) concerning benefits and risks of noncalcium-based phosphate-lowering treatment in nondialysis CKD.

METHODS

We conducted a systematic review and meta-analyses of RCTs involving noncalcium-based phosphate-lowering therapy compared with placebo, calcium-based binders, or no study medication, in adults with CKD not on dialysis or post-transplant. RCTs had ≥3 months follow-up and outcomes included biomarkers of mineral metabolism, cardiovascular parameters, and adverse events. Outcomes were meta-analyzed using the Sidik-Jonkman method for random effects. Unstandardized mean differences were used as effect sizes for continuous outcomes with common measurement units and Hedge's g standardized mean differences (SMD) otherwise. Odds ratios were used for binary outcomes. Cochrane risk of bias and GRADE assessment determined the certainty of evidence.

RESULTS

In total, 20 trials involving 2498 participants (median sample size 120, median follow-up 9 months) were eligible for inclusion. Overall, risk of bias was low. Compared with placebo, noncalcium-based phosphate binders reduced serum phosphate (12 trials, weighted mean difference -0.37; 95% CI, -0.58 to -0.15 mg/dl, low certainty evidence) and urinary phosphate excretion (eight trials, SMD -0.61; 95% CI, -0.90 to -0.31, low certainty evidence), but resulted in increased constipation (nine trials, log odds ratio [OR] 0.93; 95% CI, 0.02 to 1.83, low certainty evidence) and greater vascular calcification score (three trials, SMD, 0.47; 95% CI, 0.17 to 0.77, very low certainty evidence). Data for effects of phosphate-lowering therapy on cardiovascular events (log OR, 0.51; 95% CI, -0.51 to 1.17) and death were scant.

CONCLUSIONS

Noncalcium-based phosphate-lowering therapy reduced serum phosphate and urinary phosphate excretion, but there was an unclear effect on clinical outcomes and intermediate cardiovascular end points. Adequately powered RCTs are required to evaluate benefits and risks of phosphate-lowering therapy on patient-centered outcomes.

The Effect of Iron Supplementation on FGF23 in Chronic Kidney Disease Patients: a Systematic Review and Time-Response Meta-Analysis

Fibroblast growth factor 23 (FGF23) gene is found to be responsible for autosomal dominant hypophosphatemic rickets, and is highly expressed in chronic kidney disease (CKD) and end-stage renal disease patients with iron deficiency anemia (IDA). We evaluated the efficacy of different iron treatments on FGF23 levels in dialysis-dependent and non-dialysis-dependent CKD patients with IDA. We performed a systematic review and meta-analysis of randomized controlled trials (RCTs) comparing different types of iron treatment versus placebo in CKD patients up to May 2020. We investigated the efficacy of iron treatment on the levels of FGF23 and C-terminal FGF23 (cFGF23) in CKD patients. We estimated weighted mean differences (WMDs) and 95% confidence intervals (CIs) using the random-effects model. Nine studies with 11 arms were included in the meta-analysis. Overall, iron treatment showed a significant reduction in FGF23 levels compared to control group (WMD: - 60.56 pg/ml, 95% CI: - 92.17, - 28.95). Compared to placebo, subgroup analysis showed that oral iron therapy (WMD: - 6.98 pg/ml, 95% CI: - 10.66, - 3.31) was more effective than intravenous (IV) iron therapy (WMD: 4.90 pg/ml, 95% CI: - 12.03, 21.83) on FGF23 levels. There was no significant change in cFGF23 levels between iron treatment and control group (WMD: - 64.72 Ru/ml, 95% CI: - 147.69, 18.25). Subgroup analysis showed that oral iron therapy resulted in a significant reduction in cFGF23 levels compared to control group (WMD: - 150.48 RU/ml, 95% CI: - 151.31, - 149.65). In conclusion, iron treatment was associated with a significant decrease in FGF23 levels in CKD patients.

Regulation of FGF23: Beyond Bone

PURPOSE OF REVIEW

Fibroblast growth factor 23 (FGF23) is a bone- and bone marrow-derived hormone that is critical to maintain phosphate homeostasis. The principal actions of FGF23 are to reduce serum phosphate levels by decreasing kidney phosphate reabsorption and 1,25-dihydroxyvitamin D synthesis. FGF23 deficiency causes hyperphosphatemia and ectopic calcifications, while FGF23 excess causes hypophosphatemia and skeletal defects. Excess FGF23 also correlates with kidney disease, where it is associated with increased morbidity and mortality. Accordingly, FGF23 levels are tightly regulated, but the mechanisms remain incompletely understood.

RECENT FINDINGS

In addition to bone mineral factors, additional factors including iron, erythropoietin, inflammation, energy, and metabolism regulate FGF23. All these factors affect Fgf23 expression, while some also regulate FGF23 protein cleavage. Conversely, FGF23 may have a functional role in regulating these biologic processes. Understanding the bi-directional relationship between FGF23 and non-bone mineral factors is providing new insights into FGF23 regulation and function.

Current Status of Renal Anemia Pharmacotherapy-What Can We Offer Today

Chronic kidney disease (CKD) is one of the fastest-growing major causes of death internationally. Better treatment of CKD and its complications is crucial to reverse this negative trend. Anemia is a frequent complication of CKD and is associated with unfavorable clinical outcomes. It is a devastating complication of progressive kidney disease, that negatively affects also the quality of life. The prevalence of anemia increases in parallel with CKD progression. The aim of this review is to summarize the current knowledge on therapy of renal anemia. Iron therapy, blood transfusions, and erythropoietin stimulating agents are still the mainstay of renal anemia treatment. There are several novel agents on the horizon that might provide therapeutic opportunities in CKD. The potential therapeutic options target the hepcidin–ferroportin axis, which is the master regulator of iron homeostasis, and the BMP-SMAD pathway, which regulates hepcidin expression in the liver. An inhibition of prolyl hydroxylase is a new therapeutic option becoming available for the treatment of anemia in CKD patients. This new class of drugs stimulates the synthesis of endogenous erythropoietin and increases iron availability. We also summarized the effects of prolyl hydroxylase inhibitors on iron parameters, including hepcidin, as their action on the hematological parameters. They could be of particular interest in the out-patient population with CKD and patients with ESA hyporesponsiveness. However, current knowledge is limited and still awaits clinical validation. One should be aware of the potential risks and benefits of novel, sophisticated therapies.

Preexisting comorbidities are associated with the mortality rate as well as the predialysis adverse events in incident dialysis patients

Background

Optimal estimated glomerular filtration rate (eGFR) to start maintenance dialysis is controversial. Observational studies have reported that initiation of dialysis at high eGFRs is associated with worse postdialysis survival.

Methods

We retrospectively investigated 1,038 incident dialysis patients who started maintenance dialysis during 2010–2015. Patients were assessed for comorbidities and adverse events during the transitional period of dialysis initiation. Patients were classified as planned dialysis (PD) vs. unplanned dialysis (UD) according to indications for dialysis initiation.

Results

UD group comprised 352 patients (33.9%). Mean eGFR at dialysis initiation was higher in UD patients than PD patients (7.9 ± 5.1 vs. 5.9 ± 3.4 mL/min/1.73 m², p < 0.001). Mean Davies comorbidity index in the UD group was higher (vs. PD group, 1.3 ± 1.0 vs. 0.9 ± 1.0, p < 0.001). Patients with more comorbidities experienced more ischemic heart disease (hazard ratio [HR], 4.36; 95% confidence interval [CI], 1.71–11.14) in the medium-risk group and HR of 8.84 (95% CI, 3.06–25.55) in the high-risk group (vs. low-risk group, p < 0.001)) during the predialysis period. High-risk group had increased postdialysis mortality (HR, 2.48; 95% CI, 1.46–4.20; p = 0.001). Adjusted HR of mortality was higher in the medium-risk group of UD patients (HR, 1.72; 95% CI, 1.16–2.56; p = 0.007).

Conclusion

Patients with more comorbidities were at increased risk of predialysis ischemic heart disease and postdialysis mortality. UD patients in the medium-risk population had increased risk of postdialysis mortality. Dialysis start should be individualized by considering comorbidities.

Treatment of Iron Deficiency Anemia in CKD and End-Stage Kidney Disease

Iron deficiency is common in individuals with chronic kidney disease and plays a major role in the development of anemia. Oral and intravenous iron agents are both available to replete iron in patients with chronic kidney disease diagnosed with iron deficiency. The choice of which agent to use is most often dictated by goals of therapy, tolerability, convenience, and response to prior therapy. Diminished absorption of iron in the gastrointestinal tract and a high incidence of gastrointestinal adverse effects can reduce the efficacy of oral iron agents, necessitating the use of i.v. iron formulations to treat iron deficiency anemia, particularly in patients requiring kidney replacement therapy. Newer oral agents may help to overcome these limitations and help treat iron deficiency in those not requiring kidney replacement therapy. Recent studies have provided new evidence that more aggressive repletion of iron in patients with chronic kidney disease requiring kidney replacement therapy may provide benefits with respect to anemia management and hard clinical outcomes such as cardiovascular disease and survival.

Iron status, fibroblast growth factor 23 and cardiovascular and kidney outcomes in chronic kidney disease

Disordered iron and mineral homeostasis are interrelated complications of chronic kidney disease that may influence cardiovascular and kidney outcomes. In a prospective analysis of 3747 participants in the Chronic Renal Insufficiency Cohort Study, we investigated risks of mortality, heart failure, end-stage kidney disease (ESKD), and atherosclerotic cardiovascular disease according to iron status, and tested for mediation by C-terminal fibroblast growth factor 23 (FGF23), hemoglobin and parathyroid hormone. Study participants were agnostically categorized based on quartiles of transferrin saturation and ferritin as: "Iron Replete" (27.1% of participants; referent group for all outcomes analyses), "Iron Deficiency" (11.1%), "Functional Iron Deficiency" (7.6%), "Mixed Iron Deficiency" (iron indices between the Iron Deficiency and Functional Iron Deficiency groups; 6.3%), "High Iron" (9.2%), or "Non-Classified" (the remaining 38.8% of participants). In multivariable-adjusted Cox models, Iron Deficiency independently associated with mortality (hazard ratio 1.28, 95% confidence interval 1.04-1.58) and heart failure (1.34, 1.05- 1.72). Mixed Iron Deficiency associated with mortality (1.61, 1.27-2.04) and ESKD (1.33, 1.02-1.73). High Iron associated with mortality (1.54, 1.24-1.91), heart failure (1.58, 1.21-2.05), and ESKD (1.41, 1.13-1.77). Functional Iron Deficiency did not significantly associate with any outcome, and no iron group significantly associated with atherosclerotic cardiovascular disease. Among the candidate facilitators, FGF23 most significantly mediated the risks of mortality and heart failure conferred by Iron Deficiency. Thus, alterations in iron homeostasis associated with adverse cardiovascular and kidney outcomes in patients with chronic kidney disease.

Controversies in optimal anemia management: conclusions from a Kidney Disease: Improving Global Outcomes (KDIGO) Conference

In chronic kidney disease, anemia and disordered iron homeostasis are prevalent and associated with significant adverse consequences. In 2012, Kidney Disease: Improving Global Outcomes (KDIGO) issued an anemia guideline for managing the diagnosis, evaluation, and treatment of anemia in chronic kidney disease. Since then, new data have accrued from basic research, epidemiological studies, and randomized trials that warrant a re-examination of previous recommendations. Therefore, in 2019, KDIGO decided to convene 2 Controversies Conferences to review the latest evidence, explore new and ongoing controversies, assess change implications for the current KDIGO anemia guideline, and propose a research agenda. The first conference, described here, focused mainly on iron-related issues, including the contribution of disordered iron homeostasis to the anemia of chronic kidney disease, diagnostic challenges, available and emerging iron therapies, treatment targets, and patient outcomes. The second conference will discuss issues more specifically related to erythropoiesis-stimulating agents, including epoetins, and hypoxia-inducible factor-prolyl hydroxylase inhibitors. Here we provide a concise overview of the consensus points and controversies resulting from the first conference and prioritize key questions that need to be answered by future research.

Hospitalization Trajectories and Risks of ESKD and Death in Individuals With CKD

INTRODUCTION

Management of chronic kidney disease (CKD) entails high medical complexity and often results in high hospitalization burden. There are limited data on the associations of longitudinal hospital utilization patterns with adverse clinical outcomes in individuals with CKD.

METHODS

We derived cumulative all-cause hospitalization trajectory groups using latent class trajectory analysis in 3012 participants of the Chronic Renal Insufficiency Cohort (CRIC) Study who were alive and did not reach end-stage kidney disease (ESKD) within 4 years of study entry. Cox proportional hazards models tested the associations between hospitalization trajectory groups and risks of ESKD and death prior to the onset of ESKD (ESKD-censored death).

RESULTS

Within 4 years of study entry, there were 5658 hospitalizations among 3012 participants. We identified 3 distinct subgroups of individuals with CKD based on cumulative all-cause hospitalization trajectories over 4 years: low-utilizer (n = 1066), intermediate-utilizer (n = 1802), and high-utilizer (n = 144). High-utilizers represented a patient population of lower socioeconomic status who had a greater prevalence of comorbid conditions and lower kidney function compared with intermediate- and low-utilizers. After the 4-year ascertainment period to form the trajectory subgroups, there were 544 ESKD events and 437 ESKD-censored deaths during a median follow-up time of 5.1 years. Compared with low-utilizers, intermediate-utilizers and high-utilizers were at 1.49-fold (95% confidence interval [CI] 1.22-1.84) and 1.75-fold (95% CI 1.20-2.56) higher risk of ESKD in adjusted analyses, respectively. Compared with low-utilizers, intermediate-utilizers and high-utilizers were at 1.48-fold (95% CI 1.17-1.87) and 2.58-fold (95% CI 1.74-3.83) higher risk of ESKD-censored death in adjusted analyses, respectively.

CONCLUSIONS

Trajectories of cumulative all-cause hospitalization identify subgroups of individuals with CKD who are at high risk of ESKD and death.

Clinical Approach to Vascular Calcification in Patients With Non-dialysis Dependent Chronic Kidney Disease: Mineral-Bone Disorder-Related Aspects

Chronic kidney disease (CKD) is associated with a very high morbimortality, mainly from cardiovascular origin, and CKD is currently considered in the high- or very high risk- cardiovascular risk category. CKD-mineral and bone disorders (CKD-MBDs), including vascular and/or valvular calcifications, are also associated with these poor outcomes. Vascular calcification (VC) is very prevalent (both intimal and medial), even in non-dialysis dependent patients, with a greater severity and more rapid progression. Simple X-ray based-scores such as Adragão's (AS) are useful prognostic tools and AS (even AS based on hand-X-ray only) may be superior to the classic Kauppila's score when evaluating non-dialysis CKD patients. Thus, in this mini-review, we briefly review CKD-MBD-related aspects of VC and its complex pathophysiology including the vast array of contributors and inhibitors. Furthermore, although VC is a surrogate marker and is not yet considered a treatment target, we consider that the presence of VC may be relevant in guiding therapeutic interventions, unless all patients are treated with the mindset of reducing the incidence or progression of VC with the currently available armamentarium. Avoiding phosphate loading, restricting calcium-based phosphate binders and high doses of vitamin D, and avoiding normalizing (within the normal limits for the assay) parathyroid hormone levels seem logical approaches. The availability of new drugs and future studies, including patients in early stages of CKD, may lead to significant improvements not only in patient risk stratification but also in attenuating the accelerated progression of VC in CKD.

The Importance of Phosphate Control in Chronic Kidney Disease

A series of problems including osteopathy, abnormal serum data, and vascular calcification associated with chronic kidney disease (CKD) are now collectively called CKD-mineral bone disease (CKD-MBD). The pathophysiology of CKD-MBD is becoming clear with the emerging of αKlotho, originally identified as a progeria-causing protein, and bone-derived phosphaturic fibroblast growth factor 23 (FGF23) as associated factors. Meanwhile, compared with calcium and parathyroid hormone, which have long been linked with CKD-MBD, phosphate is now attracting more attention because of its association with complications and outcomes. Incidentally, as the pivotal roles of FGF23 and αKlotho in phosphate metabolism have been unveiled, how phosphate metabolism and hyperphosphatemia are involved in CKD-MBD and how they can be clinically treated have become of great interest. Thus, the aim of this review is reconsider CKD-MBD from the viewpoint of phosphorus, its involvement in the pathophysiology, causing complications, therapeutic approach based on the clinical evidence, and clarifying the importance of phosphorus management.

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.

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.

Simultaneous management of disordered phosphate and iron homeostasis to correct fibroblast growth factor 23 and associated outcomes in chronic kidney disease

PURPOSE OF REVIEW

Hyperphosphatemia, iron deficiency, and anemia are powerful stimuli of fibroblast growth factor 23 (FGF23) production and are highly prevalent complications of chronic kidney disease (CKD). In this manuscript, we put in perspective the newest insights on FGF23 regulation by iron and phosphate and their effects on CKD progression and associated outcomes. We especially focus on new studies aiming to reduce FGF23 levels, and we present new data that suggest major benefits of combined corrections of iron, phosphate, and FGF23 in CKD.

RECENT FINDINGS

New studies show that simultaneously correcting iron deficiency and hyperphosphatemia in CKD reduces the magnitude of FGF23 increase. Promising therapies using iron-based phosphate binders in CKD might mitigate cardiac and renal injury and improve survival.

SUMMARY

New strategies to lower FGF23 have emerged, and we discuss their benefits and risks in the context of CKD. Novel clinical and preclinical studies highlight the effects of phosphate restriction and iron repletion on FGF23 regulation.

State-of-the-Art Management of Hyperphosphatemia in Patients With CKD: An NKF-KDOQI Controversies Perspective

Phosphate binders are among the most common medications prescribed to patients with kidney failure receiving dialysis and are often used in advanced chronic kidney disease (CKD). In patients with CKD glomerular filtration rate category 3a (G3a) or worse, including those with kidney failure who are receiving dialysis, clinical practice guidelines suggest "lowering elevated phosphate levels towards the normal range" with possible strategies including dietary phosphate restriction or use of binders. Additionally, guidelines suggest restricting the use of oral elemental calcium often contained in phosphate binders. Nutrition guidelines in CKD suggest<800-1,000mg of calcium daily, whereas CKD bone and mineral disorder guidelines do not provide clear targets, but<1,500mg in maintenance dialysis patients has been previously recommended. Many different classes of phosphate binders are now available and clinical trials have not definitively demonstrated the superiority of any class of phosphate binders over another with regard to clinical outcomes. Use of phosphate binders contributes substantially to patients' pill burden and out-of-pocket costs, and many have side effects. This has led to uncertainty regarding the use and best choice of phosphate binders for patients with CKD or kidney failure. In this controversies perspective, we discuss the evidence base around binder use in CKD and kidney failure with a focus on comparisons of available binders.

Anemia and Diabetic Kidney Disease Had Joint Effect on Diabetic Retinopathy Among Patients With Type 2 Diabetes

Purpose

Whether the association between diabetic kidney disease (DKD) and diabetic retinopathy (DR) in patients with type 2 diabetes mellitus (T2DM) is leveraged by anemia remains unclear. This study is to evaluate the joint effect of DKD and anemia on DR.

Methods

Data were collected from electronic medical records of 1389 patients with T2DM in the Yiwu Central Hospital of Zhejiang Province from 2018 to 2019. Based on retinal examination findings, patients were classified as without diabetic retinopathy (non-DR), non-proliferative diabetic retinopathy (NPDR), and proliferative diabetic retinopathy (PDR). Odds ratio (OR) from multinomial logistic regression models adjusting for potential risk factors of DR were used to evaluate associations of DKD, renal function measures, and anemia with risk of NPDR and PDR. Path analysis was performed to help understand the association of DKD and hemoglobin (Hb) with DR.

Results

The study included 901 patients with non-DR, 367 patients with NPDR and 121 patients with PDR. Both high DKD risk and abnormal renal function measures were significantly associated with PDR. Anemia was associated with increased risk of NPDR (OR = 1.75, 95% confidence interval [CI] = 1.18–2.58) and PDR (OR = 3.71, 95% CI = 2.23–6.18). DKD severity and anemia had joint effect on NPDR (OR = 2.29, 95% CI = 1.32–3.96) and PDR (OR = 11.31, 95% CI = 5.95–21.51). These associations were supported by path analysis.

Conclusions

DKD severity, abnormal estimated glomerular filtration rate (eGFR), and urinary albumin/creatinine ratio (UACR) were associated with increased risk of DR in patients with T2DM, and anemia had joint effect on these associations. Improving Hb level may decrease the risk of DR in patients with T2DM.

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.

The emerging role of iron in heart failure and vascular calcification in CKD

Iron deficiency is a frequent comorbidity of cardiovascular (CV) diseases and nearly 50% of patients with heart failure (HF) with or without anaemia have low levels of available iron. There is a strong association between anaemia and the increase in mortality and hospitalizations in patients with CV disease and HF. Moreover, anaemia and chronic kidney disease (CKD) often coexist in patients with HF, with anaemia increasing the risk of death in these subjects and with a further increased risk in CKD population. The evidence that the treatment of iron deficiency and the increase in haemoglobin are associated with a better prognosis in HF patients has elicited new interest in the utilization of iron in HF and CKD patients. One of the central players in CV disease is vascular calcification (VC), which has been recognized as a major independent risk factor for incident CV disease and overall mortality in chronic disease patients. In this review, we summarize the evidences generated by clinical trials aimed to study the effect of iron deficiency correction, the effect of iron-based phosphate binder in in vivo models of kidney failure and the effect of iron in in vitro models of VC, trying to give an overview of the present knowledge on iron effect and its mechanisms of action.

Nephropathic Cystinosis: A Distinct Form of CKD-Mineral and Bone Disorder that Provides Novel Insights into the Regulation of FGF23

BACKGROUND

The rare lysosomal storage disease nephropathic cystinosis presents with renal Fanconi syndrome that evolves in time to CKD. Although biochemical abnormalities in common causes of CKD-mineral and bone disorder have been defined, it is unknown if persistent phosphate wasting in nephropathic cystinosis is associated with a biochemical mineral pattern distinct from that typically observed in CKD-mineral and bone disorder.

METHODS

We assessed and compared determinants of mineral homeostasis in patients with nephropathic cystinosis across the predialysis CKD spectrum to these determinants in age- and CKD stage-matched patients, with causes of CKD other than nephropathic cystinosis.

RESULTS

The study included 50 patients with nephropathic cystinosis-related CDK and 97 with CKD from other causes. All major aspects of mineral homeostasis were differentially effected in patients with CKD stemming from nephropathic cystinosis versus other causes. Patients with nephropathic cystinosis had significantly lower percent tubular reabsorption of phosphate and fibroblast growth factor-23 (FGF23) at all CKD stages, and lower blood phosphate in CKD stages 3-5. Linear regression analyses demonstrated lower FGF23 levels in nephropathic cystinosis participants at all CKD stages when corrected for eGFR and age, but not when adjusted for serum phosphate.

CONCLUSIONS

Nephropathic cystinosis CKD patients have mineral abnormalities that are distinct from those in CKD stemming from other causes. Persistently increased urinary phosphate excretion maintains serum phosphate levels within the normal range, thus protecting patients with nephropathic cystinosis from elevations of FGF23 during early CKD stages. These findings support the notion that phosphate is a significant driver of increased FGF23 levels in CKD and that mineral abnormalities associated with CKD are likely to vary depending on the underlying renal disease.

Route of intestinal absorption and tissue distribution of iron contained in the novel phosphate binder ferric citrate

BACKGROUND

Anemia of chronic kidney disease (CKD) is, in part, caused by hepcidin-mediated impaired iron absorption. However, phosphate binder, ferric citrate (FC) overcomes the CKD-induced impairment of iron absorption and increases serum iron, transferrin saturation, and iron stores and reduces erythropoietin requirements in CKD/ESRD patients. The mechanism and sites of intestinal absorption of iron contained in FC were explored here.

METHODS

Eight-week old rats were randomized to sham-operated or 5/6 nephrectomized (CKD) groups and fed either regular rat chow or rat chow containing 4% FC for 6 weeks. They were then euthanized, and tissues were processed for histological and biochemical analysis using Prussian blue staining, Western blot analysis to quantify intestinal epithelial tight junction proteins and real-time PCR to measure Fatty Acid receptors 2 (FFA2) and 3 (FFA3) expressions.

RESULTS

CKD rats exhibited hypertension, anemia, azotemia, and hyperphosphatemia. FC-treated CKD rats showed significant reductions in blood pressure, serum urea, phosphate and creatinine levels and higher serum iron and blood hemoglobin levels. This was associated with marked increase in iron content of the epithelial and subepithelial wall of the descending colon and modest iron deposits in the proximal tubular epithelial cells of their remnant kidneys. No significant difference was found in hepatic tissue iron content between untreated and FC-treated CKD or control groups. Distal colon's epithelial tight Junction proteins, Occludin, JAM-1 and ZO-1 were markedly reduced in the CKD groups. The FFA2 expression in the jejunum and FFA3 expression in the distal colon were significantly reduced in the CKD rats and markedly increased with FC administration.

CONCLUSION

Iron contained in the phosphate binder, FC, is absorbed by the distal colon of the CKD animals via disrupted colonic epithelial barrier and upregulation of short chain fatty acid transporters.

Carbonyl iron and iron dextran therapies cause adverse effects on bone health in juveniles with chronic kidney disease

Anemia is a frequent complication of chronic kidney disease (CKD), related in part to the disruption of iron metabolism. Iron therapy is very common in children with CKD and excess iron has been shown to induce bone loss in non-CKD settings, but the impact of iron on bone health in CKD remains poorly understood. Here, we evaluated the effect of oral and parenteral iron therapy on bone transcriptome, bone histology and morphometry in two mouse models of juvenile CKD (adenine-induced and 5/6-nephrectomy). Both modalities of iron therapy effectively improved anemia in the mice with CKD, and lowered bone Fgf23 expression. At the same time, iron therapy suppressed genes implicated in bone formation and resulted in the loss of cortical and trabecular bone in the mice with CKD. Bone resorption was activated in untreated CKD, but iron therapy had no additional effect on this. Furthermore, we assessed the relationship between biomarkers of bone turnover and iron status in a cohort of children with CKD. Children treated with iron had lower levels of circulating biomarkers of bone formation (bone-specific alkaline phosphatase and the amino-terminal propeptide of type 1 procollagen), as well as fewer circulating osteoblast precursors, compared to children not treated with iron. These differences were independent of age, sex, and glomerular filtration rate. Thus, iron therapy adversely affected bone health in juvenile mice with CKD and was associated with low levels of bone formation biomarkers in children with CKD.

Ferric citrate in the management of hyperphosphataemia and iron deficiency anaemia: A meta-analysis in patients with chronic kidney disease

AIMS

Phosphate-lowering effects of ferric citrate were reported in several clinical trials, but mostly in small-scale studies. The aim of this meta-analysis was to investigate the efficacy and safety of ferric citrate in controlling hyperphosphataemia and iron-deficiency anaemia in chronic kidney disease (CKD) patients.

METHODS

PubMed, Embase and Cochrane Library were searched for clinical trials that enrolled CKD patients receiving ferric citrate for hyperphosphataemia. Two investigators performed systematic literature search to identify eligible studies, evaluated risk of bias and extracted relevant data.

RESULTS

Sixteen studies were included in the meta-analysis. Phosphate-lowering effects of ferric citrate were greater compared to no active treatment (standardized mean difference [SMD] = -1.15; P < 0.001) and comparable to other phosphate binders (SMD = 0.03; P = 0.61). Calcium concentrations post ferric citrate treatment did not differ compared to no active treatment (SMD = 0.15; P = 0.21) but were significantly lower compared to other phosphate binders (SMD = -0.14; P = 0.01). These led to significant reductions in calcium-phosphorus product with ferric citrate versus no active control (SMD = -1.02; P < 0.001) but no difference versus active control (SMD = -0.01; P = 0.93). Intact parathyroid hormone showed no substantial between-group difference in both comparison against no active and active controls. Ferric citrate improved iron stores and anaemia parameters, but increased risk of diarrhoea, abdominal pain and discoloured faeces.

CONCLUSION

Ferric citrate was effective in lowering phosphorus and phosphorus-calcium product versus no active treatment and had comparable effects versus other phosphate binders. Calcium levels were significantly lower with ferric citrate than with other phosphate-lowering treatment. Ferric citrate had additive effects on iron repletion and anaemia control and was associated with mostly gastrointestinal side effects.

Conventional and novel impacts of ferric citrate on iron deficiency anemia and phosphorus metabolism in rats

Ferric citrate is an oral iron-based phosphate binder, being known to affect iron status and improve iron deficiency anemia (IDA) in chronic kidney disease (CKD) patients. We examined whether oral administration of ferric citrate could change iron status and improve anemia without affecting phosphorus metabolism in iron deficiency anemia rats. In Normal rat study, normal rats were fed a diet containing 0.3 or 3% ferric citrate for 11 days for setting the dose and administration period of ferric citrate. The effects of ferric citrate on iron status- and phosphorus metabolism-related parameters were evaluated using blood and urine samples. Next, an iron deficiency anemia was induced by feeding iron-depleted diet in rats. After 7 days of starting the iron-depleted diet, 0.3% ferric citrate was administered for 7 days by dietary admixture. Iron status- and phosphorus metabolism-related parameters were evaluated with blood and urine samples. In Normal rat study, 3% ferric citrate treatment increased serum iron level and transferrin saturation (TSAT), and decreased serum phosphorus level, intact fibroblast growth factor 23 (iFGF23) level, and urinary phosphorus excretion, but 0.3% ferric citrate treatment showed no effects. On the other hand, in Iron deficiency anemia rat study, 0.3% ferric citrate treatment increased iron status-related parameters and improved anemia, but did not show any apparent changes in phosphorus metabolism-related parameters. In conclusion, ferric citrate could have hematopoietic effects without affecting phosphorus metabolism, and could be a potential option for the treatment of IDA in patients without CKD.

Phosphate binders in chronic kidney disease: an updated narrative review of recent data

Chronic kidney disease (CKD) is frequently accompanied by hyperphosphatemia. High serum phosphate usually requires dietary measures, adequate dialysis prescription and/or phosphate binders. For this narrative review a PubMed searched was undertaken to identify new publications on phosphate binders that had been published between January 2015 and July 2019. The present review summarizes this most recent information on dietary measures and their problems in treating hyperphosphatemia in CKD patients, overall effects of phosphate binders on cardiovascular mortality and morbidity, adherence to phosphate binder therapy as well as new data on specific aspects of the various phosphate binders on the market: calcium-containing phosphate binders, polymeric phosphate binders (sevelamer, bixalomer, colestilan), magnesium-containing phosphate binders, lanthanum carbonate, ferric citrate, sucroferric oxyhydroxide, and new compounds in development, in particular drugs targeting intestinal phosphate transporters.

Ferric citrate: cardio- and renoprotective in chronic kidney disease?

Ferric citrate is a phosphate binder that may also be used to treat iron-deficiency anemia. In human studies, ferric citrate treatment in the setting of chronic kidney disease has been associated with effective phosphate control, improved iron and hematologic parameters, and decreased fibroblast growth factor 23 levels. In the present study, mice with chronic kidney disease treated with ferric citrate have similarly improved biochemical profiles, but also have improved cardiac and renal function and prolonged survival.

FGF23 and Phosphate-Cardiovascular Toxins in CKD

Elevated levels of fibroblast growth factor 23 (FGF23) and phosphate are highly associated with increased cardiovascular disease and mortality in patients suffering from chronic kidney disease (CKD). As the kidney function declines, serum phosphate levels rise and subsequently induce the secretion of the phosphaturic hormone FGF23. In early stages of CKD, FGF23 prevents the increase of serum phosphate levels and thereby attenuates phosphate-induced vascular calcification, whereas in end-stage kidney disease, FGF23 fails to maintain phosphate homeostasis. Both hyperphosphatemia and elevated FGF23 levels promote the development of hypertension, vascular calcification, and left ventricular hypertrophy by distinct mechanisms. Therefore, FGF23 and phosphate are considered promising therapeutic targets to improve the cardiovascular outcome in CKD patients. Previous therapeutic strategies are based on dietary and pharmacological reduction of serum phosphate, and consequently FGF23 levels. However, clinical trials proving the effects on the cardiovascular outcome are lacking. Recent publications provide evidence for new promising therapeutic interventions, such as magnesium supplementation and direct targeting of phosphate and FGF receptors to prevent toxicity of FGF23 and hyperphosphatemia in CKD patients.