The Interplay between Dietary Phosphorous, Protein Intake, and Mortality in a Prospective Hemodialysis Cohort

Hyperphosphatemia in Chronic Kidney Disease: The Search for New Treatment Paradigms and the Role of Tenapanor

Hyperphosphataemia represents a significant challenge in the management of chronic kidney disease, exerting a pronounced influence on the pathogenesis of cardiovascular complications and mineral bone disorders. Traditional approaches to address hyperphosphataemia involve implementing dietary phosphate restrictions, administering phosphate binders, and, in cases of end-stage renal disease, resorting to dialysis. Unfortunately, these interventions frequently prove inadequate in maintaining phosphate levels within recommended ranges. Additionally, commonly employed pharmacological agents are not immune to eliciting adverse events, thereby limiting their prescription and therapeutic adherence. There is a growing focus on exploring novel therapeutic strategies in this context. The current discussion centres on tenapanor, a pharmacological agent predominantly acting as a selective inhibitor of sodium/hydrogen exchanger isoform 3 (NHE3). Its mechanism of action involves modulating tight junctions, resulting in reduced sodium absorption and intestinal paracellular permeability to phosphate. Furthermore, tenapanor downregulates sodium-dependent phosphate 2b transport protein (NaPi2b) expression, thereby impeding active transcellular phosphate transport. Clinical trials have elucidated the efficacy and safety profile of tenapanor. This evidence hints at a potential paradigm shift in the management of hyperphosphataemia. However, the burgeoning optimism surrounding tenapanor warrants tempered enthusiasm, as further research remains indispensable. The imperative lies in meticulously delineating its efficacy and safety contours within the crucible of clinical practice. In this review, we synthesize the intricate interplay between hyperphosphataemia and Chronic Kidney Disease-Mineral Bone Disorder, and we discuss the existing pharmacological interventions for hyperphosphataemia and explore emerging treatment paradigms that offer novel perspectives in managing elevated phosphate levels in CKD patients.

Phosphate in Cardiovascular Disease: From New Insights Into Molecular Mechanisms to Clinical Implications

Hyperphosphatemia is a common feature in patients with impaired kidney function and is associated with increased risk of cardiovascular disease. This phenomenon extends to the general population, whereby elevations of serum phosphate within the normal range increase risk; however, the mechanism by which this occurs is multifaceted, and many aspects are poorly understood. Less than 1% of total body phosphate is found in the circulation and extracellular space, and its regulation involves multiple organ cross talk and hormones to coordinate absorption from the small intestine and excretion by the kidneys. For phosphate to be regulated, it must be sensed. While mostly enigmatic, various phosphate sensors have been elucidated in recent years. Phosphate in the circulation can be buffered, either through regulated exchange between extracellular and cellular spaces or through chelation by circulating proteins (ie, fetuin-A) to form calciprotein particles, which in themselves serve a function for bulk mineral transport and signaling. Either through direct signaling or through mediators like hormones, calciprotein particles, or calcifying extracellular vesicles, phosphate can induce various cardiovascular disease pathologies: most notably, ectopic cardiovascular calcification but also left ventricular hypertrophy, as well as bone and kidney diseases, which then propagate phosphate dysregulation further. Therapies targeting phosphate have mostly focused on intestinal binding, of which appreciation and understanding of paracellular transport has greatly advanced the field. However, pharmacotherapies that target cardiovascular consequences of phosphate directly, such as vascular calcification, are still an area of great unmet medical need.

Association between phosphate binder pill burden and mortality risk in patients on maintenance hemodialysis: a single-center cohort study with 7-year follow-up of 513 patients

BACKGROUND

Dialysis patients often take multiple oral medications, leading to a high pill burden. Phosphate binders (PBs) account for a large proportion of this daily pill burden (DPB). The relationship between DPB and mortality risk remains unclear, and we hypothesized that this relationship might be influenced by the proportion of PBs to all medications.

METHODS

We divided DPB into those derived from PBs and non-PB drugs and analyzed the association with mortality risk over a 7-year period in 513 chronic hemodialysis patients using a baseline model.

RESULTS

The median (interquartile range) DPB from all drugs was 15.8 (11.2-21.0) pills/day/patient, and the median ratio of PB pills to all drug pills was 29.3 (13.7-45.9)% at baseline. During a median observation period of 5.2 years, 161 patients (31.4%) died. Kaplan-Meier analysis showed no significant difference in all-cause mortality between PB users and non-users. However, a significant survival advantage was observed in the highest tertile of DPB from PBs compared to the lowest tertile. Conversely, the highest tertile of DPB from non-PB drugs was associated with worse survival. Consequently, the highest tertile of the ratio of PBs to all pills was associated with better survival. This association remained significant even after adjusting for patient characteristics in the Cox proportional hazards model. However, when serum nutritional parameters were included as covariates, the significant association disappeared.

CONCLUSIONS

Dialysis patients prescribed a higher rate of PB pills to all medications exhibited a lower mortality risk, possibly due to their better nutritional status.

Nutritional and Dietary Management of Chronic Kidney Disease Under Conservative and Preservative Kidney Care Without Dialysis

While dialysis has been the prevailing treatment paradigm for patients with advanced chronic kidney disease (CKD), emphasis on conservative and preservative management in which dietary interventions are a major cornerstone have emerged. Based on high-quality evidence, international guidelines support the utilization of low-protein diets as an intervention to reduce CKD progression and mortality risk, although the precise thresholds (if any) for dietary protein intake vary across recommendations. There is also increasing evidence demonstrating that plant-dominant low-protein diets reduce the risk of developing incident CKD, CKD progression, and its related complications including cardiometabolic disease, metabolic acidosis, mineral and bone disorders, and uremic toxin generation. In this review, we discuss the premise for conservative and preservative dietary interventions, specific dietary approaches used in conservative and preservative care, potential benefits of a plant-dominant low-protein diet, and practical implementation of these nutritional strategies without dialysis.

Association between annual variability of potassium levels and prognosis in patients undergoing hemodialysis

BACKGROUND

Hyperkalemia and hypokalemia are associated with mortality in patients undergoing hemodialysis. However, there are few reports on the association between potassium level fluctuations and mortality. We retrospectively investigated the association between serum potassium level variability and mortality in patients undergoing hemodialysis.

METHODS

This study was conducted at a single center. Variability in serum potassium levels was evaluated using the standard deviation of potassium level from July 2011 to June 2012, and its association with prognosis was examined by following up the patients for 5 years. Serum potassium variability was assessed as the coefficient of variation, and the statistical analysis was performed after log transformation.

RESULTS

Among 302 patients (mean age 64.9 ± 13.3; 57.9% male; and median dialysis vintage 70.5 months [interquartile range, IQR 34-138.3]), 135 died during the observation period (median observation period 5.0 years [2.3-5.0]). Although the mean potassium level was not associated with prognosis, serum potassium level variability was associated with prognosis, even after adjustments for confounding factors such as age and dialysis time (hazard ratio: 6.93, 95% confidence interval [Cl] 1.98-25.00, p = 0.001). After the adjustments, the coefficient of variation of potassium level in the highest tertile (T3) showed a higher relative risk for prognosis than that in T1 (relative risk: 1.98, 95% CI 1.19-3.29, p = 0.01).

CONCLUSIONS

Variability in serum potassium levels was associated with mortality in patients undergoing hemodialysis. Careful monitoring of potassium levels and their fluctuations is necessary for this patient population.

The efficacy and safety of cuttlebone for lowering serum phosphate in patients with end-stage renal disease: a meta-analysis of randomized controlled trials

Background: The efficacy of cuttlebone for treating hyperphosphatemia in patients with end-stage renal disease and its safety remained unclear. Methods: Randomized controlled trials comparing the efficacy of cuttlebone with conventional interventions were retrieved from MEDLINE, EMBASE, Cochrane Library, Airiti Library, and other major Chinese databases until 1 February 2023. The primary outcome was circulating phosphate concentration, while secondary outcomes included circulating calcium and intact parathyroid hormone levels, calcium-phosphorus product, and treatment-related side-effects. Results: Analysis of nine studies published between 2000 and 2019 including 726 participants showed a lower circulating phosphate concentration in the cuttlebone group than in controls [mean difference (MD) = -0.23, 95% CI: -0.39 to -0.06, p = 0.006, I2 = 94%, 726 patients] and a dose-dependent effect of cuttlebone against hyperphosphatemia. Therapeutic benefits were noted after both short-term (1-2 months) and long-term (3-6 months) treatments. Besides, patients receiving hemodialysis showed a better response to cuttlebone than those receiving peritoneal dialysis. There was no difference in circulating calcium level (mean difference = 0.03, 95% CI: -0.01 to 0.07, p = 0.17, I2 = 34%, 654 patients), while patients receiving cuttlebone showed lower circulating iPTH level and calcium-phosphorus product (MD = -43.63, 95% CI: -74.1 to -13.16, p = 0.005, I2 = 76%, 654 patients), (MD = -0.38, 95% CI: -0.38 to -0.01, p = 0.04, I2 = 83%, 520 patients). No difference in the risks of constipation, gastrointestinal discomfort, and elevated blood calcium was noted between the two groups. Conclusion: Compared with conventional phosphate-binding agents, cuttlebone more efficiently suppressed hyperphosphatemia with a dose-dependent effect. The limited number of included studies warrants further clinical investigations to verify our findings. Systematic Review Registration: https://www.crd.york.ac.uk/prospero/, identifier CRD42023396300.