Outcomes associated with phosphorus binders in men with non-dialysis-dependent CKD

Update on current and emerging treatment paradigms for hyperphosphatemia in chronic kidney disease

INTRODUCTION

Hyperphosphatemia in advanced CKD often accompanies high PTH and FGF23 levels, impaired bone mineralization, ectopic calcifications, and increased cardiovascular risks. Novel treatments are now available to lower serum phosphorus effectively. However, safety, tolerability, and patient adherence must be evaluated to determine the best therapeutic option for hyperphosphatemia.

AREAS COVERED

This review examines available treatment strategies for hyperphosphatemia in CKD patients and new emerging treatments, emphasizing the latest inhibitors of active phosphate absorption.

EXPERT OPINION

Despite the numerous compounds available, managing hyperphosphatemia in CKD remains challenging. While many phosphate binders exist, they often have limitations and side effects. Aluminum carries significant toxicity risks. Calcium-based binders are effective but can cause hypercalcemia and vascular calcification. Lanthanum is absorbed in the gut, but its long-term tissue deposition appears clinically irrelevant. Sevelamer reduces vascular calcification but has inconclusive data and gastrointestinal side effects. Iron-based binders are effective but may cause gastrointestinal discomfort and lack long-term outcome data. New inhibitors of intestinal phosphate absorption show promise with low pill burden but need more clinical validation. Although these newer compounds might eventually improve phosphate management in CKD patients, enhancing adherence and reducing pill burden, future studies are required to elucidate the best treatment for hyperphosphatemia.

Risk improvement and adverse kidney outcomes in patients with chronic kidney disease: findings from KNOW-CKD

BACKGROUND

Many trials have attempted to slow the progression of chronic kidney disease (CKD) by modifying specific risk factors, but without achieving satisfactory results. We aimed to evaluate the association between the degree of improvement in multiple risk factors and adverse kidney outcomes.

METHODS

This was a prospective observational study of 839 patients with CKD G3-G4. The main predictors were the number of improved risk factors between baseline and year one as follows: a decrease in proteinuria, systolic blood pressure, phosphate, and uric acid, and an increase in hemoglobin and bicarbonate from the baseline status to out of the target range. The primary outcome was a composite one, including CKD progression (50% decline in eGFR or kidney replacement therapy) and all-cause death.

RESULTS

Patients whose risk factors eventually improved had more unfavorable baseline profiles of the six considered factors. During 3097.8 person-years of follow-up (median 3.5 years per patient), the composite outcome occurred in 48.0% of patients (incidence rate, 13.0 per 100 person-years). Compared with an improvement of no risk factors, the adjusted HRs (95% CI) for improvement of 1 and ≥ 2 risk factors were 0.96 (0.76-1.22) and 0.53 (0.37-0.75), respectively. The association was not affected by diabetic status or CKD severity. Among the risk factors, proteinuria accounted for the greatest contribution to CKD progression.

CONCLUSIONS

In patients with CKD G3-G4, improvement in multiple factors was associated with a decreased risk of CKD progression, suggesting the importance of multifactorial risk management.

Real-World Phosphate Binder Use among Dialysis-Dependent Patients with CKD

INTRODUCTION

For patients with chronic kidney disease (CKD), the need for phosphate binder (PB) treatment peaks at onset of dialysis. This real-world study assessed rates of PB utilization and switching in patients with dialysis-dependent CKD (DD-CKD).

METHODS

We identified patients with PB utilization among those with prevalent DD-CKD using 2018-2019 Medicare Parts A/B/D data. Patients were assigned to cohorts based on primary (most frequently used) PB among calcium acetate, ferric citrate, lanthanum carbonate, sevelamer (hydrochloride and carbonate), sucroferric oxyhydroxide. We measured proportion of patients who were adherent (proportion of days covered >80%) and persistent (patients whose last 90 days of outpatient dialysis reported PB use). Net switching rates were calculated as the difference between switches to and from the primary agent.

RESULTS

We identified 136,912 patients with PB use. Proportion of patients adherent ranged from 63.8% (lanthanum carbonate) to 67.7% (sevelamer) and persistent from 85.1% (calcium acetate) to 89.5% (ferric citrate). Most patients (73%) used the same PB throughout the study. Overall, 20.5% of patients experienced one switch and 2.3% two or more. Positive net switching rates were observed for ferric citrate, sucroferric oxyhydroxide, and lanthanum carbonate (2-10%) but negative for sevelamer and calcium acetate (-2% to -7%).

CONCLUSION

Adherence and persistence rates were low with slight variation across PBs. Net positive switching occurred for ferric citrate, sucroferric oxyhydroxide, and lanthanum carbonate. Further studies are needed to determine the reasons for these findings and could identify opportunities for better control of phosphate levels among patients with CKD.

Association between Serum Inorganic Phosphorus Levels and Adverse Outcomes in Chronic Kidney Disease: The Fukushima CKD Cohort Study

Objective Although an association between serum inorganic phosphorus levels and a poor prognosis has been noted in dialysis patients, these associations have been insufficiently reported in non-dialysis-dependent chronic kidney disease (NDD-CKD) patients. This study attempted to determine the association between serum inorganic phosphorus levels and adverse outcomes in Japanese NDD-CKD patients. Methods We investigated the relationships between serum inorganic phosphorus levels and adverse outcomes, such as kidney events, cardiovascular events, and all-cause death, in Japanese NDD-CKD patients using longitudinal data from the Fukushima CKD Cohort Study with a median follow-up period of 2.8 years. The study evaluated 822 patients with NDD-CKD enrolled between June 2012 and July 2014. A kidney event was defined as a combination of doubling of the baseline serum creatinine or end-stage renal disease. Cox regression was performed to analyze the relationships of the quartile of the serum inorganic phosphorus with kidney events, cardiovascular events, and all-cause death. Results The frequency of kidney events per 1,000 person-years exhibited a U-shaped distribution based on serum inorganic phosphorus levels, with these levels not significantly associated with an increased risk of cardiovascular events and all-cause death. A multivariable Cox regression analysis showed an increased risk of kidney events for the highest quartile of the serum inorganic phosphorus levels (≥3.7 mg/dL) versus the second quartile (2.9-3.2 mg/dL, hazard ratio, 3.30; 95% confidence interval, 1.50-7.28; p=0.003). There were no significant associations between the serum calcium levels and adverse outcomes. Conclusion Serum inorganic phosphorus levels were associated with an increased risk of CKD progression in Japanese NDD-CKD patients.

Non calcium phosphate binders - Is there any evidence of benefit

PURPOSE OF REVIEW

Low-level evidence and opinion-based clinical practice guidelines highlight the substantial uncertainty in the practice patterns of hyperphosphatemia management in patients with chronic kidney disease (CKD). This manuscript reviews the evidence for the choice of phosphate binders and its impact on clinical outcomes.

RECENT FINDINGS

Phosphate binders are among the most common medications prescribed for patients on dialysis. Clinical practice guidelines recommend lowering phosphate levels toward normal range and restricting calcium-based binders in all CKD patients. There is substantial gap in the evidence underlying these recommendations with lack of any placebo-controlled, randomized trials showing survival benefits for any class of phosphate-binders. Despite the lack of evidence for specific phosphate target or if lowering phosphate improves survival, use of phosphate binders has remained central strategy in approach to hyperphosphatemia. Use of binders has added to the cost and contributed significant pill burden. Restriction of calcium-based binders to avoid positive calcium balance and consequent vascular calcification risk has a physiological rationale and weight of observational studies.

SUMMARY

There is currently no conclusive evidence that definitively guides the choice of any specific binders for management of hyperphosphatemia in patients with CKD. Use of noncalcium-based binders has a theoretical advantage in restricting total calcium intake to decrease the risk of vascular calcification but no proven benefits for mortality.

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 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.

High Dietary Phosphate Exacerbates and Acts Independently of Low Autophagy Activity in Pathological Cardiac Remodeling and Dysfunction

High phosphate contributes to uremic cardiomyopathy. Abnormal autophagy is associated with the development and progression of heart disease. What is unknown is the effects of phosphate on autophagy and whether the ill effects of phosphate on cardiomyocytes are mediated by low autophagy. High (2.0% w/w)-phosphate diet reduced LC3 puncta in cardiomyocytes and ratio of LC3 II/I and increased p62 protein, indicating that autophagy activity was suppressed. Mice with cardiomyocyte-specific deletion of autophagy-related protein 5 (H-atg5-/-) had reduced autophagy only in the heart, developed cardiac dysfunction with hypertrophy and fibrosis, and had a short lifespan. When H-atg5-/- mice were fed a high-phosphate diet, they developed more apoptosis in cardiomyocytes, more severe cardiac remodeling, and shorter lifespan than normal phosphate-fed H-atg5-/- mice, indicating that cardiac phosphotoxicity is imparted independently of atg5. In conclusion, although high phosphate suppresses autophagy, high phosphate and low autophagy independently trigger and additionally amplify cardiac remodeling and dysfunction.

A chronic high phosphate intake in mice is detrimental for bone health without major renal alterations

BACKGROUND

Phosphate intake has increased in the last decades due to a higher consumption of processed foods. This higher intake is detrimental for patients with chronic kidney disease, increasing mortality and cardiovascular disease risk and accelerating kidney dysfunction. Whether a chronic high phosphate diet is also detrimental for the healthy population is still under debate.

METHODS

We fed healthy mature adult mice over a period of one year with either a high (1.2% w/w) or a standard (0.6% w/w) phosphate diet, and investigated the impact of a high phosphate diet on mineral homeostasis, kidney function and bone health.

RESULTS

The high phosphate diet increased plasma phosphate, parathyroid hormone (PTH) and calcitriol levels, with no change in fibroblast growth factor 23 levels. Urinary phosphate, calcium and ammonium excretion were increased. Measured glomerular filtration rate was apparently unaffected, while blood urea was lower and urea clearance was higher in animals fed the high phosphate diet. No change was observed in plasma creatinine levels. Blood and urinary pH were more acidic paralleled by higher bone resorption observed in animals fed a high phosphate diet. Total and cortical bone mineral density was lower in animals fed a high phosphate diet and this effect is independent of the higher PTH levels observed.

CONCLUSIONS

A chronic high phosphate intake did not cause major renal alterations, but affected negatively bone health, increasing bone resorption and decreasing bone mineral density.

Effects of calcium-containing phosphate binders on cardiovascular events and mortality in predialysis CKD stage 5 patients

Background

Hyperphosphatemia and calcium load were associated with vascular calcification. The role of calcium-containing phosphate binders (CCPBs) use as important determinants of death and cardiovascular events in predialysis hyperphosphatemic chronic kidney disease (CKD) patients remain unclear due to the absence of evidence for reduced mortality with CCPB use compared with placebo. We aimed to investigate the effect of using CCPBs or nonuse in all-cause mortality rates and cardiovascular events in CKD stage 5 patients between 2000 and 2005 in the Taiwanese National Health Insurance Research Database.

Methods

Patients with known coronary heart disease and those who had undergone dialysis or renal transplantation were excluded. The CCPB users were matched with nonusers by the propensity score model. Multivariable Cox proportional hazards model was used to estimate hazard ratios (HRs) of all-cause mortality and cardiovascular events.

Results

During a mean follow-up of 4.58 years, 879 CCPB users were matched with 3516 nonusers. CCPB use was an independent risk factor for cardiovascular events [adjusted hazard ratio (HR) 1.583, 95% confidence interval (CI) 1.393–1.799]. The increased cardiovascular risk was dose-dependent and consistent across all subgroup analyses. Compared with no use, CCPB use was associated with no significant all-cause mortality risk (1.74 vs. 1.75 events per 100 person-years, adjusted HR 0.964, 95% CI 0.692–1.310).

Conclusions

CCPB use in CKD stage 5 patients was associated with a significantly increased cardiovascular event risk compared with the nonusers, whereas the all-cause mortality risk was similar between the two groups. Whether these relationships are causal require further randomized controlled trials.

Lithocholic acid increases intestinal phosphate and calcium absorption in a vitamin D receptor dependent but transcellular pathway independent manner

Phosphate/calcium homeostasis is crucial for health maintenance. Lithocholic acid, a bile acid produced by intestinal bacteria, is an agonist of vitamin D receptor. However, its effects on phosphate/calcium homeostasis remain unclear. Here, we demonstrated that lithocholic acid increases intestinal phosphate/calcium absorption in an enterocyte vitamin D receptor-dependent manner. Lithocholic acid was found to increase serum phosphate/calcium levels and thus to exacerbate vascular calcification in animals with chronic kidney disease. Lithocholic acid did not affect levels of intestinal sodium-dependent phosphate transport protein 2b, Pi transporter-1, -2, or transient receptor potential vanilloid subfamily member 6. Everted gut sac analyses demonstrated that lithocholic acid increased phosphate/calcium absorption in a transcellular pathway-independent manner. Lithocholic acid suppressed intestinal mucosal claudin 3 and occludin in wild-type mice, but not in vitamin D receptor knockout mice. Everted gut sacs of claudin 3 knockout mice showed an increased permeability for phosphate, but not calcium. In patients with chronic kidney disease, serum 1,25(OH)₂ vitamin D levels are decreased, probably as an intrinsic adjustment to reduce phosphate/calcium burden. In contrast, serum and fecal lithocholic acid levels and fecal levels of bile acid 7α-dehydratase, a rate-limiting enzyme involved in lithocholic acid production, were not downregulated. The effects of lithocholic acid were eliminated by bile acid adsorptive resin in mice. Thus, lithocholic acid and claudin 3 may represent novel therapeutic targets for reducing phosphate burden.

Inhibition of tissue-nonspecific alkaline phosphatase protects against medial arterial calcification and improves survival probability in the CKD-MBD mouse model

Medial arterial calcification (MAC) is a major complication of chronic kidney disease (CKD) and an indicator of poor prognosis. Aortic overexpression of tissue-nonspecific alkaline phosphatase (TNAP) accelerates MAC formation. The present study aimed to assess whether a TNAP inhibitor, SBI-425, protects against MAC and improves survival probability in a CKD-mineral and bone disorder (MBD) mouse model. CKD-MBD mice were divided in three groups: vehicle, SBI-10, and SBI-30. They were fed a 0.2% adenine and 0.8% phosphorus diet from 14 to 20 weeks of age to induce CKD, followed by a high-phosphorus (0.2% adenine and 1.8% phosphorus) diet for another 6 weeks. At 14-20 weeks of age, mice in the SBI-10 and SBI-30 groups were given 10 and 30 mg/kg SBI-425 by gavage once a day, respectively, while vehicle-group mice were given distilled water as vehicle. Control mice were fed a standard chow (0.8% phosphorus) between the ages of 8 and 20 weeks. Computed tomography imaging, histology, and aortic tissue calcium content revealed that, compared to vehicle animals, SBI-425 nearly halted the formation of MAC. Mice in the control, SBI-10 and SBI-30 groups exhibited 100% survival, which was significantly better than vehicle-treated mice (57.1%). Aortic mRNA expression of Alpl, encoding TNAP, as well as plasma and aortic tissue TNAP activity, were suppressed by SBI-425 administration, whereas plasma pyrophosphate increased. We conclude that a TNAP inhibitor successfully protected the vasculature from MAC and improved survival rate in a mouse CKD-MBD model, without causing any adverse effects on normal skeletal formation and residual renal function. © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

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.

Dietary phosphate toxicity: an emerging global health concern

Phosphate is a common ingredient in many healthy foods but, it is also present in foods containing additives and preservatives. When found in foods, phosphate is absorbed in the intestines and filtered from the blood by the kidneys. Generally, any excess is excreted in the urine. In renal pathologies, however, such as chronic kidney disease, a reduced renal ability to excrete phosphate can result in excess accumulation in the body. This accumulation can be a catalyst for widespread damage to the cellular components, bones, and cardiovascular structures. This in turn can reduce mortality. Because of an incomplete understanding of the mechanism for phosphate homeostasis, and the multiple organ systems that can modulate it, treatment strategies designed to minimize phosphate burden are limited. The Recommended Dietary Allowance (RDA) for phosphorous is around 700 mg/day for adults, but the majority of healthy adult individuals consume far more phosphate (almost double) than the RDA. Studies suggest that low-income populations are particularly at risk for dietary phosphate overload because of the higher amounts of phosphate found in inexpensive, processed foods. Education in nutrition, as well as access to inexpensive healthy food options may reduce risks for excess consumption as well as a wide-range of disorders, ranging from cardiovascular diseases to kidney diseases to tumor formation. Pre-clinical and clinical studies suggest that dietary phosphate overload has toxic and prolonged adverse health effects. Improved regulations for reporting of phosphate concentrations on food labels are necessary so that people can make more informed choices about their diets and phosphate consumption. This is especially the case given the lack of treatments available to mitigate the short and long-term effects of dietary phosphate overload-related toxicity. Phosphate toxicity is quickly becoming a global health concern. Without measures in place to reduce dietary phosphate intake, the conditions associated with phosphate toxicity will likely to cause untold damage to the wellbeing of individuals around the world.

Changes With Lanthanum Carbonate, Calcium Acetate, and Phosphorus Restriction in CKD: A Randomized Controlled Trial

INTRODUCTION

Abnormal phosphorus homeostasis develops early in chronic kidney disease (CKD). It is unclear if its correction results in improved clinical outcomes in non-dialysis dependent CKD.

METHODS

We conducted a randomized controlled, parallel design clinical trial in 120 patients with estimated glomerular filtration rate 15 to 59 ml/min per 1.73 m2 and abnormal phosphorus homeostasis (serum phosphorus >4.6 mg/dl, parathyroid hormone [PTH] >70 pg/ml or tubular reabsorption of phosphorus [TRP] <80%). Patients were randomized to open-label lanthanum carbonate versus calcium acetate versus dietary intervention over 1 year. The co-primary outcomes were month 12 (vs. baseline) biochemical (serum phosphorus, TRP, PTH, calcium, bone-specific alkaline phosphatase [bALP], and fibroblast growth factor 23 [FGF23]) and vascular parameters (coronary artery calcium score, pulse wave velocity, and endothelial dysfunction) in all patients. Secondary outcomes were between-treatment differences in change for each parameter between month 12 and baseline. All analyses were intention to treat.

RESULTS

Baseline characteristics were similar in the 3 groups. A total of 107 patients (89%) completed 12 months of follow-up. Differences were not significant at month 12 (vs. baseline) for any of the outcomes except bALP (median [25th, 75th] percentile at month 12 versus baseline: 13.8 [10.6, 17.6] vs. 15.8 [12.1, 21.1], P < .001) and FGF23 (132 [99, 216] vs. 133 [86, 189], P = .002). Changes for all outcomes were similar in the 3 arms except for PTH, which was suppressed more effectively by calcium acetate (P < .001).

CONCLUSION

A 1-year intervention to limit phosphorus absorption using dietary restriction or 2 different phosphorus binders resulted in decreased bALP suggesting improved bone turnover, but no other significant changes in biochemical or vascular parameters in patients with CKD stage 3/4. (ClinicalTrials.gov: NCT01357317).

Deleting Death and Dialysis: Conservative Care of Cardio-Vascular Risk and Kidney Function Loss in Chronic Kidney Disease (CKD)

The uremic syndrome, which is the clinical expression of chronic kidney disease (CKD), is a complex amalgam of accelerated aging and organ dysfunctions, whereby cardio-vascular disease plays a capital role. In this narrative review, we offer a summary of the current conservative (medical) treatment options for cardio-vascular and overall morbidity and mortality risk in CKD. Since the progression of CKD is also associated with a higher cardio-vascular risk, we summarize the interventions that may prevent the progression of CKD as well. We pay attention to established therapies, as well as to novel promising options. Approaches that have been considered are not limited to pharmacological approaches but take into account lifestyle measures and diet as well. We took as many randomized controlled hard endpoint outcome trials as possible into account, although observational studies and post hoc analyses were included where appropriate. We also considered health economic aspects. Based on this information, we constructed comprehensive tables summarizing the available therapeutic options and the number and kind of studies (controlled or not, contradictory outcomes or not) with regard to each approach. Our review underscores the scarcity of well-designed large controlled trials in CKD. Nevertheless, based on the controlled and observational data, a therapeutic algorithm can be developed for this complex and multifactorial condition. It is likely that interventions should be aimed at targeting several modifiable factors simultaneously.

[Management of bone and mineral metabolism disorders before the dialysis stage remains still perfectible. Data from the French Phosphorus and Calcium Survey Photo-Graphe]

Only limited data is available on the management of the chronic kidney disease-associated bone and mineral metabolism disorder (CKD-MBD) in the pre-dialysis stages of CKD in France. A better knowledge of current management habits could lead to an improvement in the implementation of international recommendations (KDIGO). The 3rd version of the French Phosphorus and Calcium Survey Photo-Graphe (Sanofi) included a cohort of CKD stages 4 and 5 patients, whose aim was to examine the prevalence of CKD-MBD and the quality of its management in patients under the care of 62 nephrologists from over 20 geographical regions in France. The study started in October 2011, i.e. one year after patient enrollment. We examined in particular the percentage of patients presenting with laboratory parameter abnormalities indicative of CKD-MBD who were not receiving adequate treatment. A total of 456 patients with CKD stage 4 and 154 with CKD stage 5 were studied. Their mean age was 72.9±14.2 years, and male/female ratio was 58/42. KDIGO targets of serum PTH for CKD stages 4 and 5 were not achieved in respectively 80 and 84% of the patients, for serum calcium in 8 and 22% and for serum phosphate in 12 and 46%. As a potential explanation, insufficient therapy was estimated to account for respectively 45 and 60% of insufficiently controlled secondary hyperparathyroidism, and for 36% of persistent hyperphosphatemia in stage 5. It should be noted that 55.5 and 57.5% of patients were receiving native vitamin D. In this national observatory, the management of CKD-MBD stages 4 and 5 appears suboptimal, especially as regards the control of secondary hyperparathyroidism, which remained untreated in nearly 50% of the patients. Hyperphosphatemia was also common and inadequately controlled in CKD stage 5. To improve the management of CKD-MBD, nephrologists need to be more aware of the importance of aiming for recommended laboratory targets and how this can be achieved.

A novel fluorescent probe-based flow cytometric assay for mineral-containing nanoparticles in serum

Calciprotein particles, nanoscale aggregates of insoluble mineral and binding proteins, have emerged as potential mediators of phosphate toxicity in patients with Chronic Kidney Disease. Although existing immunochemical methods for their detection have provided compelling data, these approaches are indirect, lack specificity and are subject to a number of other technical and theoretical shortcomings. Here we have developed a rapid homogeneous fluorescent probe-based flow cytometric method for the detection and quantitation of individual mineral-containing nanoparticles in human and animal serum. This method allows the discrimination of membrane-bound from membrane-free particles and different mineral phases (amorphous vs. crystalline). Critically, the method has been optimised for use on a conventional instrument, without the need for manual hardware adjustments. Using this method, we demonstrate a consistency in findings across studies of Chronic Kidney Disease patients and commonly used uraemic animal models. These studies demonstrate that renal dysfunction is associated with the ripening of calciprotein particles to the crystalline state and reveal bone metabolism and dietary mineral as important modulators of circulating levels. Flow cytometric analysis of calciprotein particles may enhance our understanding of mineral handling in kidney disease and provide a novel indicator of therapeutic efficacy for interventions targeting Chronic Kidney Disease-Mineral Bone Disorder.

Use of Phosphorus Binders among Non-Dialysis Chronic Kidney Disease Patients and Mortality Outcomes

BACKGROUND

Whether the benefits of phosphorus binders extend to those without end stage renal disease is uncertain. Among a large diverse non-dialysis chronic kidney disease (CKD) population with hyperphosphatemia, we sought to evaluate phosphorus binder use and compare mortality risk between patients prescribed and not prescribed binders.

METHODS

A retrospective cohort study within an integrated health system (January 1, 1998 - December 31, 2012) among CKD patients (age ≥18) was performed. Non-dialysis CKD patients with 2 separate estimated glomerular filtrate rate (eGFR) <30 mL/min/1.73 m2 and serum phosphorus ≥5.0 mg/dL within 180 days of eGFR were included. Multivariable cox proportional hazards and inverse probability of treatment-weighted models were used to estimate mortality hazard ratios (HRs) for patients who received phosphorus binders compared to no binders.

RESULTS

Among 10,165 study patients, 2,733 subjects (27%) received phosphorus binders. Compared to the no-phosphorus-binder group, the binder group had mortality HRs (95% CI) of 0.86 (0.79-0.94) and 0.86 (0.80-0.93) using traditional multivariable and inverse probability of treatment-weighted models respectively. Sensitivity analyses removing patients who were prescribed binders >180 days after index date revealed no difference in mortality between those with binders and with no binders.

CONCLUSION

Our findings from a real-world clinical environment revealed that 27% of hyperphosphatemic non-dialysis CKD patients were prescribed binders. They also had lower risk of mortality compared to those not prescribed phosphorus binders. However, the lower mortality risk was not observed when we accounted for immortal time bias. Whether phosphorus binder use in CKD improves survival remains to be determined.

Preclinical and Healthy Volunteer Studies of Potential Drug-Drug Interactions Between Tenapanor and Phosphate Binders

Tenapanor (RDX5791, AZD1722), a first‐in‐class small molecule with minimal systemic availability, is an inhibitor of the sodium/hydrogen exchanger isoform 3. Tenapanor acts locally in the gut, where it reduces absorption of sodium and phosphate. It is being studied in patients with chronic kidney disease requiring dialysis, who are often administered phosphate binders such as sevelamer to help control hyperphosphatemia. We investigated whether coadministration of tenapanor with phosphate binders (sevelamer or calcium‐based binders) impacts the pharmacodynamic effects of tenapanor. In vitro studies suggested a binding interaction between tenapanor and sevelamer, but this did not translate into altered pharmacodynamic effects in rats. An open‐label, 2‐way crossover study was then conducted in healthy volunteers (NCT02346890). This showed that 4 days’ treatment with tenapanor hydrochloride (15 mg twice daily) with or without sevelamer carbonate (800 mg 3 times daily) resulted in comparable 24‐hour stool and urinary sodium and phosphorus levels. Stool frequency, consistency, and weight were also comparable between the treatments. These results suggest that the binding between sevelamer and tenapanor observed in vitro does not translate into altered pharmacodynamic effects in humans.

Analysis of the kinetics of the parathyroid hormone, and of associated patient outcomes, in a cohort of haemodialysis patients

Background

Observational studies have recently associated a decrease in serum parathyroid hormone (PTH) level with a higher rate of mortality among hemodialysis (HD) patients. Decreases in PTH level can result from medical intervention (MPD) and surgical parathyroidectomy (PTX), or may occur spontaneously, usually associated with an underlying malnutrition-inflammation syndrome (SPD). The aim of our study was to prospectively identify the incidence of decreases in PTH level in a cohort of HD patients and the frequency distribution of the different causes (MPD, PTX and SPD), as well as to evaluate the survival outcomes for each PTH group (MPD, PTX and SPD) compared to patients who did not experience a PTH decrease over the first 36 months of the study (NPD).

Methods

The 197 patients receiving HD at our center in January 2010, and meeting our eligibility criteria, were enrolled in our prospective study, and were observed for a period of 60 months. A decrease in PTH level >50 % between two successive PTH measurements obtained within an interval <3 months was defined as a significant event. MPD referred to a decrease in PTH due to an increased oral calcium intake, increased dialysate calcium concentration (DCC), increased alfacalcidol use, or use of cinacalcet therapy. A surgical 7/8 PTX was performed in young patients or in patients in whom cinacalcet therapy failed. SPD referred to a decrease in PTH related to a medical or surgical event. Baseline characteristics among patients in each group (MPD, PTX, SPD, and NPD) were evaluated using Fisher’s exact test. The 60-month survival was evaluated using Kaplan-Meier and Cox multivariable proportional hazards models. Univariate and multivariate Cox analyzes were used identify variables with mortality. The relative risk of mortality was expressed as a hazard ratio (HR).

Results

The distribution of the 197 patients forming our four study groups was 34 % in the NPD group, 35 % in the SPD group, 25 % in the MSD group and 6 % in the PTX group. Among patients in the SPD group, the main acute comorbid conditions were peripheral vascular and cardiac complications, sepsis, fractures, and cancers with an increase in serum CRP level (from 14.3 ± 18 to 132 ± 90 mg/L) and a decrease in serum albumin (from 33 ± 4.5 to 28.6 ± 4 g/L). In the MPD group, the main therapeutic change was an increase in DCC, either independently or in association with cinacalcet therapy. The median survival rate among patients was 10 months for SPD, compared to 22 months among patients in the MPD group (p < 0.001). Using multivariable Cox model and taking the NPD group as reference, the risk of mortality was lower among patients in the MPD group (HR, 0.42[0.2-0.87] p = 0.01), with survival being comparable for the SPD and NPD groups (HR, 1.3 [0.75-2.2]). No mortality was observed in the PTX group.

Conclusion

The poor outcomes associated with SPD, related to acute comorbid conditions, should not lead to undertreat secondary hyperparathyroidism whose appropriate medical or surgical therapies are associated with better outcomes.

Chronic Kidney Disease-Mineral and Bone Disorders (CKD-MBDs): What the Endocrinologist Needs to Know

OBJECTIVE

Chronic kidney disease-mineral and bone disorders (CKD-MBDs) are a spectrum of abnormalities involving skeletal hormones, minerals, and bone turnover and mineralization. This paper focuses on what the endocrinologist should know about the assessment and management of skeletal and metabolic disorders in CKD-MBDs.

METHODS

Relevant literature was reviewed to (1) define disturbances of minerals and hormones in the course of CKD; (2) identify the variable radiographic and histomorphometric changes of CKD-MBDs; (3) review the association among CKD-MBDs, vascular calcification, cardiovascular disease (CVD), and mortality; and (4) clarify issues in CKD-MBDs therapy.

RESULTS

Assessment and treatment of CKD-MBDs is complicated by progressive changes in bone minerals and skeletal regulatory hormones as kidney function declines. CKD-MBDs are associated with fracture risk, and studies demonstrate that bone mineral density can be used to assess bone loss and fracture risk in these patients. Treatment of CKD-MBDs continues to evolve. Use of calcium, phosphate binders, vitamin D, vitamin D-receptor analogs, and drugs for osteoporosis and CKD-MBDs treatment are discussed in the context of safety and efficacy for patients with CKD.

CONCLUSION

The association of CKD with bone disease, vascular calcification, CVD, and mortality mandates earlier recognition and treatment of CKD-MBDs. Osteoporosis as a distinct entity can be diagnosed and managed in CKD, although assessment of osteoporosis becomes challenging in late (stage 4 to 5) CKD. Diabetes is common in early (stage 1 to 3) CKD. In addition, 96% of all individuals identified as having CKD have early CKD. The endocrinologist is uniquely positioned to address and treat both diabetes and many of the metabolic and skeletal disorders associated with early CKD-MBDs, including osteoporosis.

Con: Phosphate binders in chronic kidney disease

Phosphate binders are prescribed to chronic kidney disease (CKD) patients based on associations of serum phosphate concentrations with mortality and calcification, experimental evidence for direct calcifying effects of phosphate on vascular smooth muscle tissue and the central importance of phosphate retention in CKD-mineral and bone disorder (CKD-MBD). Current knowledge regarding phosphate metabolism in CKD provides important insight into disease mechanisms and supports future clinical trials of phosphate binders in CKD patients to determine the impact of these medications on clinically relevant outcomes. The risks and benefits of phosphate binders cannot be inferred from association studies of serum phosphate concentrations, which are inconsistent and subject to confounding, animal-experimental data, which are based on conditions that differ from human disease, or physiological arguments, which are limited to known regulatory factors. Many interventions that targeted biochemical pathways suggested by association studies and suspected biological importance have yielded null or harmful results. Clinical trials of phosphate binders are of high clinical and scientific importance to nephrology. Demonstration of reduced rates of clinical disease in such trials could lead to important health benefits for CKD patients, whereas negative results would refocus efforts to understand and treat CKD-MBD. Clinical trials that employ highly practical or 'pragmatic' designs represent an optimal approach for determining the safety and effectiveness of phosphate binders in real-world settings. Absent clinical trial data, observational studies of phosphate binders in large CKD populations could provide important information regarding the benefits, risks and/or unintended side effects of these medications.

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

Patients with CKD often progress to ESRD and develop cardiovascular disease (CVD), yet available therapies only modestly improve clinical outcomes. Observational studies report independent associations between elevated serum phosphate and fibroblast growth factor 23 (FGF23) levels and risks of ESRD, CVD, and death. Phosphate excess induces arterial calcification, and although elevated FGF23 helps maintain serum phosphate levels in the normal range in CKD, it may contribute mechanistically to left ventricular hypertrophy (LVH). Consistent epidemiologic and experimental findings suggest the need to test therapeutic approaches that lower phosphate and FGF23 in CKD. Dietary phosphate absorption is one modifiable determinant of serum phosphate and FGF23 levels. Limited data from pilot studies in patients with CKD stages 3-4 suggest that phosphate binders, low phosphate diets, or vitamin B3 derivatives, such as niacin or nicotinamide, may reduce dietary phosphate absorption and serum phosphate and FGF23 levels. This review summarizes current knowledge regarding the deleterious systemic effects of phosphate and FGF23 excess, identifies questions that must be addressed before advancing to a full-scale clinical outcomes trial, and presents a novel therapeutic approach to lower serum phosphate and FGF23 levels that will be tested in the COMBINE Study: The CKD Optimal Management With BInders and NicotinamidE study.

Sevalamer Hydrochloride, Sevelamer Carbonate and Lanthanum Carbonate: In Vitro and In Vivo Effects on Gastric Environment

Hyperphosphatemia is common in patients with chronic renal failure. Phosphate binders are associated with gastric intolerance, representing the main reason of drug discontinuation. The aim of this study was to compare the effects in vitro and in vivo of sevelamer hydrochloride (SH), sevelamer carbonate (SC) and lanthanum carbonate (LC) on gastric microenvironment. We have also evaluated the efficacy and tolerability of these drugs in hemodialysis (HD) patients. In vitro analysis: Dissolution time, ability to uptake phosphorus, changes in pH starting from gastric milieu and the amount of carbon dioxide (CO(2)) produced were the variables analyzed. In vivo analysis: 24-h esophago-gastric pH measurement was evaluated in 24 HD patients treated with phosphate binders and proton pump inhibitor (PPI). In vitro: LC dissolved over a longer time compared with SC (58 ± 2.4 vs. 12 ± 0.6 min; P < 0.001) and SH (58 ± 2.4 vs. 10.3 ± 0.8 min; P < 0.001), determining the most alkaline pH. SC had the highest chelation power, binding 4.00 × 10(-9)  mol/L of phosphoric acid. CO2 volume released was increased in LC solution (53.2 ± 7.8) compared to SC (33.9 ± 6.2; P < 0.001) and SH (2.3 ± 1.8; P < 0.001). In vivo: gastric pH increased after administration of phosphate binder. The most alkaline pH was recorded in patients treated with SC. The alkalinization of the gastric environment was not prevented by PPI therapy. 424 episodes of esophageal reflux were registered, 74% of them were alkaline. The LC group was characterized by the highest number of episodes. Sevelamer carbonate had a greater capacity and rapidity to chelate phosphorus, with a mild tolerability, due to its low CO(2) production. Sevelamer HCl was the most tolerated chelator because it did not produce CO(2), while lanthanum carbonate was the least soluble.

A pharmacoeconomic analysis of phosphate binders cost-effectiveness in the RISCAVID study

BACKGROUND

A pharmacoeconomic analysis of the RISCAVID database aimed at assessing the cost effectiveness of phosphate binders in preventing CV mortality and morbidity over 7 years was performed.

METHODS

Morbid or fatal events occurring in 750 chronic HD patients were recorded. Statistical analysis evaluated the distribution of variables and the effect of sevelamer on survival. A cost-effectiveness evaluation was performed using a probabilistic model based on a Markov chain.

RESULTS

Multivariate analysis showed that treatment with sevelamer was associated with a reduced stroke incidence by 52% (p = 0.04) and reduced levels of C-reactive protein (p < 0.01). Cost-effectiveness evaluation evidenced a 33% decrease in hospital-days for patients treated with sevelamer, with and without comorbidities compared to patients undergoing calcium binders treatment.

CONCLUSION

Treatment with sevelamer was associated with a reduced risk of stroke in HD patients, with a clear saving on disease-related costs for the Italian National Healthcare System.

Phosphate management in chronic kidney disease

PURPOSE OF REVIEW

The review focuses on the rationale and evidence behind management strategies for hyperphosphatemia in patients with chronic kidney disease (CKD).

RECENT FINDINGS

Optimal management of phosphate in CKD remains an area of uncertainty, but multiple studies now point to a clinical benefit from the use of phosphate binders. Evidence of improved survival is particularly strong with sevelamer, though it remains unclear whether the absence of calcium or other properties of sevelamer are responsible for this relationship. Newer agents, such as iron-based binders or niacin compounds to inhibit phosphorus absorption, may have additional benefits which will be better defined with additional experience. A reduced pill count may be a particularly beneficial characteristic of newer agents, and has been associated with improved response to therapy. Increased use of frequent, nocturnal hemodialysis is an additional tool to help ameliorate phosphate control. Data on the reduction of fibroblast growth factor 23 through use of phosphate binders remain weak.

SUMMARY

An improved understanding of phosphate regulation and the development of new therapeutic agents have reinvigorated a once stagnant field, but significant changes to practice cannot yet be justified. There is increasing support for using sevelamer in place of calcium-based binders, though economic practicability remains challenging.

Sevelamer is cost-saving vs. calcium carbonate in non-dialysis-dependent CKD patients in italy: a patient-level cost-effectiveness analysis of the INDEPENDENT study

OBJECTIVES

To conduct a cost-effectiveness analysis of sevelamer versus calcium carbonate in patients with non-dialysis-dependent CKD (NDD-CKD) from the Italian NHS perspective using patient-level data from the INDEPENDENT-CKD study.

METHODS

Patient-level data on all-cause mortality, dialysis inception and phosphate binder dose were obtained for all 107 sevelamer and 105 calcium carbonate patients from the INDEPENDENT-CKD study. Hospitalization and frequency of dialysis data were collected post hoc for all patients via a retrospective chart review. Phosphate binder, hospitalization, and dialysis costs were expressed in 2012 euros using hospital pharmacy, Italian diagnosis-related group and ambulatory tariffs, respectively. Total life years (LYs) and costs per treatment group were calculated for the 3-year period of the study. Bootstrapping was used to estimate confidence intervals around outcomes, costs, and cost-effectiveness and to calculate the cost-effectiveness acceptability curve. A subgroup analysis of patients who did not initiate dialysis during the INDEPENDENT-CKD study was also conducted.

RESULTS

Sevelamer was associated with 0.06 additional LYs (95% CI -0.04 to 0.16) and cost savings of EUR -5,615 (95% CI -10,066 to -1,164) per patient compared with calcium carbonate. On the basis of the bootstrap analysis, sevelamer was dominant compared to calcium carbonate in 87.1% of 10,000 bootstrap replicates. Similar results were observed in the subgroup analysis. RESULTS were driven by a significant reduction in all-cause mortality and significantly fewer hospitalizations in the sevelamer group, which offset the higher acquisition cost for sevelamer.

CONCLUSIONS

Sevelamer provides more LYs and is less costly than calcium carbonate in patients with NDD-CKD in Italy.

Effect of niacin on FGF23 concentration in chronic kidney disease

BACKGROUND

Elevated serum phosphorus and FGF23 are independent cardiovascular risk factors in patients with chronic kidney disease. In a randomized controlled trial of patients with dyslipidemia assigned to either extended release niacin (ERN) alone, ERN combined with the selective prostaglandin D2 receptor subtype 1 inhibitor laropiprant (ERN-L) or placebo, niacin lowered serum phosphorus; however, it is not known if it lowers FGF23 concentrations.

METHODS

This is an ancillary study to a multicenter, randomized, double-blind, placebo-controlled trial among patients with dyslipidemia and an estimated glomerular filtration rate (eGFR) of 30-74 ml/min/1.73 m(2). Participants were randomized to ERN-L (n = 162), ERN (n = 97), or placebo (n = 68) in a 3:2:1 ratio for 24 weeks. The primary outcome was a change in serum FGF23 concentrations, and secondary outcomes were changes in other mineral metabolism parameters.

RESULTS

Both the ERN and ERN-L groups showed significant declines in serum phosphorus, calcium and calcium·phosphorus product at 24 weeks compared to placebo. A significant decline from baseline (10.9%, p < 0.01) in the serum FGF23 concentration was observed in the ERN group compared to placebo, but not in the ERN-L group compared to placebo (p = 0.36 and 0.97 for ERN-L and placebo, respectively), despite equivalent declines in serum phosphorus. Similarly, the most marked declines in PTH occurred in the ERN-only group versus placebo; no change in PTH was observed in the ERN-L group.

CONCLUSIONS

In this ancillary study of hyperlipidemic patients with an eGFR of 30-74 ml/min/1.73 m(2), ERN alone but not in combination with laropiprant lowered FGF23 and PTH concentrations. If confirmed, niacin may provide a novel strategy to decrease phosphorus, FGF23, and PTH concentrations in patients with chronic kidney disease.

The role of the gastrointestinal tract in phosphate homeostasis in health and chronic kidney disease

Purpose of review

For a number of years, there has been increasing interest in the concept of directly targeting intestinal phosphate transport to control hyperphosphatemia in chronic kidney disease. However, progress has been slow due to the paucity of information on the mechanisms involved in intestinal phosphate absorption. This editorial highlights the most recent developments in our understanding of this process and the role of the intestine in the maintenance of phosphate balance.

Recent findings

Recent studies in NaPi-IIb knockout mice have confirmed that this transport protein plays a significant role in intestinal phosphate absorption and is critical in the proposed feed-forward mechanism between the small intestine and kidney, which helps to maintain normal phosphate balance and steady-state plasma phosphate concentrations. In addition, renal failure-induced hyperphosphatemia is attenuated in NaPi-IIb knockout mice, confirming that NaPi-IIb is a suitable target in the prevention and treatment of hyperphosphatemia.

Summary

Recent findings suggest that consumption of processed foods containing phosphate preservatives may lead to excessive phosphate exposure (if not overload), toxicity, and cardiovascular disease in the general population, as well as in patients with declining renal function. Therefore, establishing more effective ways of targeting the intestine to limit dietary phosphate absorption could have wide-reaching health benefits.

Traditional and novel dietary interventions for preventing progression of chronic kidney disease

Treatment of chronic kidney disease (CKD) and its complications remain largely unresolved. Currently used treatments include blood pressure control and the use of angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs), which can slow down the progression of CKD but are unable to halt or reverse it. Dietary protein restriction represents an additional therapeutic measure used to slow the progression of CKD. The putative mechanisms of action responsible for its therapeutic effects include beneficial hemodynamic effects and the limitation of absorbable protein breakdown products that could lead to the accumulation of uremic waste and consequent various deleterious effects. The practical implementation of protein restriction through dietary intervention has been hindered on multiple levels, including patient nonadherence, lack of health care resources, and concerns related to adverse effects associated with the development of protein-energy wasting (PEW). As a result, alternative interventions have been designed to address some or all of these shortcomings and concerns. One such intervention is the administration of medications that prevent the absorption of protein catabolic products from the gut. This article reviews the various interventions using such a strategy to prevent or slow the progression of CKD, with special focus on recent advances in this field.

Optimal use of phosphate binders in chronic kidney disease

INTRODUCTION

Hyperphosphatemia is one of the major factors associated with the development of vascular calcification in patients with chronic kidney disease (CKD). Since phosphate is retained in such patients, pharmacological treatment and other measures are necessary to control hyperphosphatemia. Several phosphate binders (calcium salts, magnesium salts, non-calcium-based binders and aluminium) are available for the treatment of hyperphosphatemia. Nevertheless, none of the above mentioned agents has shown an overall superiority over others, while potency and side effects are quite variable among them creating difficulties in choosing the optimal drug for each patient.

AREAS COVERED

The authors discuss the disturbed phosphate metabolism, the available phosphate binders, as well as the general therapeutic principles of treating hyperphosphatemia in CKD patients. The literature used for this review had been retrieved from PubMed and covers a large number of original and retrospective studies as well as prospective cohort studies, meta-analyses and international clinical guidelines.

EXPERT OPINION

Lowering serum phosphate levels in CKD patients may potentially have a positive impact on cardiovascular morbidity and mortality. Factors that should be taken into consideration when selecting a specific drug include CKD stage, cardiovascular disease, severity of secondary hyperparathyroidism, concomitant medications, life expectancy and patient compliance. Therefore, when selecting a specific phosphate binder, individualisation is mandatory.

Dietary and pharmacological modification of fibroblast growth factor-23 in chronic kidney disease

Increased levels of phosphorus and fibroblast growth factor-23 (FGF-23) are strong predictors of cardiovascular morbidity and mortality. From a physiological perspective and supported by some data, phosphorus is the main driver for FGF-23 secretion. Therefore, it is conceivable that interventions aiming at restriction of phosphorus uptake from the gastrointestinal tract may lower serum FGF-23 levels and improve cardiovascular risk and subsequently survival. It is not currently known to what extend phosphorus and FGF-23 are independent risk factors, and therefore both need to be targeted. However, their respective metabolisms are tightly connected. Control of phosphorus levels in chronic kidney disease (CKD) patients is attempted mainly by restriction of dietary intake and the use of phosphorus binders. In this review, it is outlined that not just the amount of dietary phosphorus intake is important but also its type (organic vs. inorganic), its source (animal vs. plant derived), and the protein-to-phosphorus ratio in the bioavailability of phosphorus from food. This qualitative aspect of diet is likely a neglected aspect of dietary counseling in CKD. However, in more advanced stages of CKD, dietary restriction of phosphorus alone is usually not sufficient to control hyperphosphatemia, and phosphorus binders are indicated. The inexpensive, calcium-containing dietary phosphorus binders are used commonly worldwide. However, they are not suitable for every patient because of the association with elevated serum calcium, increase in vascular and valvular calcification scores, and cardiovascular and all-cause mortality. The calcium content itself in these binders has recently been implicated to upregulate FGF-23. For that reason, the noncalcium, aluminum-free agents such as sevelamer and lanthanum are being advocated. However, these drugs do not have a clearly defined effect on circulating levels of FGF-23. Although it is conceivable that targeting FGF-23 may lead to improved clinical outcomes, this remains speculative. Therefore, more studies are needed to answer the question if this can be achieved with any of the phosphorus binders, or by another (additional) pharmacological intervention.

Comparison of mineral metabolites as risk factors for adverse clinical outcomes in CKD

Patients with chronic kidney disease are at increased risk for progressing to end-stage renal disease, developing cardiovascular disease, and dying prematurely. Recent evidence has suggested that disordered mineral metabolism, which includes hyperphosphatemia, secondary hyperparathyroidism, vitamin D deficiency, and fibroblast growth factor 23 excess, may contribute to the high rates of adverse outcomes in this population. However, marked within-subject variability for some of these biochemical parameters exists, potentially detracting from the utility of certain metabolites as prognostic tools. This review summarizes the available data on the epidemiology of phosphate, parathyroid hormone, vitamin D, and fibroblast growth factor 23, and their relationships with adverse clinical outcomes in chronic kidney disease, compares the performance of each as a biomarker of risk and introduces recent insights into the pathophysiology behind some of the observed relationships.

Hyperphosphatemia in patients with ESRD: assessing the current evidence linking outcomes with treatment adherence

In recent years, the imbalance in phosphate homeostasis in patients with end-stage renal disease (ESRD) has been the subject of much research. It appears that, while hyperphosphatemia may be a tangible indicator of deteriorating kidney function, lack of phosphate homeostasis may also be associated with the increased risk of cardiovascular events and mortality that has become a hallmark of ESRD. The need to maintain phosphorus concentrations within a recommended range is reflected in evidence-based guidelines. However, these do not reflect serum phosphorus concentrations achieved by most patients in clinical practice. Given this discrepancy, it is important to consider ways in which dietary restriction of phosphorus intake and, in particular, use of phosphate binders in patients with ESRD can be made more effective. Poor adherence is common in patients with ESRD and has been associated with inadequate control of serum phosphorus concentrations. Studies indicate that, among other factors, major reasons for poor adherence to phosphate binder therapy include high pill burden and patients’ lack of understanding of their condition and its treatment. This review examines available evidence, seeking to understand fully the reasons underlying poor adherence in patients with ESRD and consider possible strategies for improving adherence in clinical practice.

Patient education for phosphorus management in chronic kidney disease

OBJECTIVES

This review explores the challenges and solutions in educating patients with chronic kidney disease (CKD) to lower serum phosphorus while avoiding protein insufficiency and hypercalcemia.

METHODS

A literature search including terms "hyperphosphatemia," "patient education," "food fatigue," "hypercalcemia," and "phosphorus-protein ratio" was undertaken using PubMed.

RESULTS

Hyperphosphatemia is a strong predictor of mortality in advanced CKD and is remediated via diet, phosphorus binders, and dialysis. Dietary counseling should encourage the consumption of foods with the least amount of inorganic or absorbable phosphorus, low phosphorus-to-protein ratios, and adequate protein content, and discourage excessive calcium intake in high-risk patients. Emerging educational initiatives include food labeling using a "traffic light" scheme, motivational interviewing techniques, and the Phosphate Education Program - whereby patients no longer have to memorize the phosphorus content of each individual food component, but only a "phosphorus unit" value for a limited number of food groups. Phosphorus binders are associated with a clear survival advantage in CKD patients, overcome the limitations associated with dietary phosphorus restriction, and permit a more flexible approach to achieving normalization of phosphorus levels.

CONCLUSION

Patient education on phosphorus and calcium management can improve concordance and adherence and empower patients to collaborate actively for optimal control of mineral metabolism.

Re-evaluating the predictive roles of metabolic complications and clinical outcome according to eGFR levels--a four-years prospective cohort study in Taiwan

Background

Metabolic complications are associated with clinical outcomes in patients with chronic kidney disease (CKD). These outcomes differ among patients according to the different stages of disease. The prevalence and association of type and number of metabolic complications with renal progression and death in patients having different eGFR levels has high clinical value, but this fact has been rarely evaluated in prospective studies.

Methods

We prospectively followed a cohort of 1157 CKD patients from 2006 to death or until 2010, and evaluated the prevalence of CKD-related complications and their association with renal progression (defined as a decline in eGFR by > 50% from baseline, or end-stage renal disease requiring dialysis) and death in patients with eGFRs above and below 45 mL/min/1.73 m² using Cox-proportional hazard models.

Results

The estimated rate (per 100 patient-years) of renal progression and death were 11.9 and 4.9, respectively. The eGFR thresholds determined by ROC analysis with a sensitivity of 90% for any metabolic complication were 60.8 mL/min/1.73 m² and 74.3 mL/min/1.73 m² using the MDRD and CKD Epidemiology Collaboration equations, respectively. CKD-related complications associated with renal progression in patients having eGFR < 45 mL/min/1.73 m² were hyperphosphatemia, anemia, microinflammation and hypoalbuminemia. Those CKD-related complications associated with death were hypoalbuminemia and hyperuricemia. Hypoalbuminemia predicted renal progression, and, hypoalbuminemia and microinflammation predicted death in patients with eGFR ≥ 45 mL/min/1.73 m². The number of complications (≥ 3) independently predicted both endpoints in patients with eGFR < 45 mL/min/1.73 m².

Conclusions

Hypoalbuminemia was a unique and strong predictor of renal progression and all-cause mortality in CKD patients, independent of their demographic characteristics, traditional risk factors, renal function severity, the presence of cardiovascular disease and other metabolic abnormalities. Most other metabolic complications and the number of complications (≥3) were associated with the clinical outcomes of patients with eGFR < 45 mL/min/1.73 m² rather than in those with higher eGFRs. The findings from the present study offer a novel insight into the association between metabolic complications and patient outcomes and may help to refine risk stratification according to disease stage.

Effects of phosphate binders in moderate CKD

Some propose using phosphate binders in the CKD population given the association between higher levels of phosphorus and mortality, but their safety and efficacy in this population are not well understood. Here, we aimed to determine the effects of phosphate binders on parameters of mineral metabolism and vascular calcification among patients with moderate to advanced CKD. We randomly assigned 148 patients with estimated GFR=20-45 ml/min per 1.73 m(2) to calcium acetate, lanthanum carbonate, sevelamer carbonate, or placebo. The primary endpoint was change in mean serum phosphorus from baseline to the average of months 3, 6, and 9. Serum phosphorus decreased from a baseline mean of 4.2 mg/dl in both active and placebo arms to 3.9 mg/dl with active therapy and 4.1 mg/dl with placebo (P=0.03). Phosphate binders, but not placebo, decreased mean 24-hour urine phosphorus by 22%. Median serum intact parathyroid hormone remained stable with active therapy and increased with placebo (P=0.002). Active therapy did not significantly affect plasma C-terminal fibroblast growth factor 23 levels. Active therapy did, however, significantly increase calcification of the coronary arteries and abdominal aorta (coronary: median increases of 18.1% versus 0.6%, P=0.05; abdominal aorta: median increases of 15.4% versus 3.4%, P=0.03). In conclusion, phosphate binders significantly lower serum and urinary phosphorus and attenuate progression of secondary hyperparathyroidism among patients with CKD who have normal or near-normal levels of serum phosphorus; however, they also promote the progression of vascular calcification. The safety and efficacy of phosphate binders in CKD remain uncertain.