The Importance of Phosphate Control in Chronic Kidney Disease

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.

Iron Deficiency and Renal Phosphate Handling: The Role of Maximal Tubular Reabsorption of Phosphate Normalized to Glomerular Filtration Rate (TmP/GFR) in Proximal Tubular Dysfunction

BACKGROUND AND AIM

Phosphate dysregulation is often associated with chronic kidney disease (CKD), and recent studies suggest that it may also be present in non-CKD patients with systemic conditions including iron deficiency anemia. This study aimed to evaluate the relationship between iron deficiency parameters (total iron-binding capacity {TIBC}, hemoglobin, and serum ferritin) and markers of proximal tubular dysfunction (the maximal tubular reabsorption of phosphate normalized to glomerular filtration rate {TmP/GFR} and tubular reabsorption of phosphate {TRP}) in non-CKD patients with iron deficiency anemia.

METHODS

This was a hospital-based analytical cross-sectional study conducted in the outpatient department and/or inpatient wards of the Department of Internal Medicine, Swaroop Rani Nehru (SRN) Hospital associated with Moti Lal Nehru (MLN) Medical College, Prayagraj, Uttar Pradesh, India, between July 2023 and August 2024.

RESULTS

This study analyzed 40 anemic patients without CKD, with a mean age of 33.9 years. Most participants (n=24, 60%) were aged 18-35 years, and the majority (n=27, 67.5%) were female. Peripheral smear analysis revealed that 72.5% (n=29) had microcytic hypochromic anemia. Hemoglobin levels averaged 7.7 g/dL, serum iron was 91.0 µg/dL, total iron-binding capacity (TIBC) was 316.3 µg/dL, and serum ferritin was 199.7 ng/mL. Phosphate handling was assessed with TmP/GFR and tubular reabsorption of phosphate (TRP) showing mean values of 4.1 mg/dL and 99.2%, respectively. This study found that TmP/GFR had a significant positive correlation with TIBC (r=0.402, p=0.010), but non-significant negative correlations with hemoglobin and serum iron. TRP was negatively correlated with hemoglobin and serum ferritin, but not significantly. Among patients with microcytic hypochromic anemia, 55.2% (n=16) had increased TmP/GFR, and 61.1% (n=20) of patients with iron deficiency anemia exhibited increased TmP/GFR. Regression analysis revealed that TIBC significantly predicted TmP/GFR (p=0.022), indicating that higher TIBC values are associated with increased TmP/GFR, suggesting a potential link between iron metabolism and renal phosphate handling.

CONCLUSION

Higher TIBC levels were associated with increased TmP/GFR, suggesting that iron deficiency anemia may influence proximal tubular function. The findings emphasize the importance of considering renal phosphate handling in patients with iron deficiency anemia.

Effectivity and safety profile of tenapanor, a sodium-hydrogen exchanger isoform 3 inhibitor, as an innovative treatment for hyperphosphatemia in chronic kidney disease: A systematic review of clinical studies

BACKGROUND

Chronic kidney disease (CKD) is a major global health problem. Hyperphosphatemia is frequent in CKD and a reason for increased morbidity and mortality as it generates hyperparathyroidism, high fibroblast growth factor 23 (FGF23), and hypocalcemia. Available hyperphosphatemia therapies still have limitations, including risk of metal overload, cardiovascular calcification, and systemic adverse effects (AEs). Tenapanor is a new hyperphosphatemia treatment in CKD with sodium-hydrogen exchanger isoform 3 (NHE3) inhibition mechanism and low systemic AEs.

OBJECTIVES

Discovering the effectivity and safety of tenapanor as hyperphosphatemia management in CKD.

METHOD

Literature searching is performed by using "pubmed" and "science direct" with "tenapanor", "chronic kidney disease", and "hyperphosphatemia" as keywords. The literatures were selected using PRISMA algorithm version 2020. Literature was screened based on Population, Intervention, Comparison, and Outcome (PICO) criteria which are: CKD patients requiring dialysis as population, tenapanor or its combination with dialysis or phosphate binders as intervention, placebo or other phosphate binders without tenapanor as comparison, and serum phosphate, safety profile, and other pleiotropic benefits related to hyperphosphatemia management as the outcome. The included studies then assessed for risk of bias and qualitatively reviewed.

OUTCOME

Tenapanor was able to reduce serum phosphate, generally in a dose-dependent manner. Tenapanor also suppressed FGF23 and parathyroid hormone, probably due to decreased serum phosphate. The frequent AEs were transient mild-to-moderate diarrhea in a dose-dependent manner. Tenapanor was generally well-tolerated with low systemic AEs due to its non-calcium, metal-free, and low-absorbed properties.

CONCLUSION

Tenapanor is an effective and safe option for hyperphosphatemia management in CKD.

Tolerability, safety and efficacy of a novel phosphate binder VS-505 (AP301): a Phase 2 dose-escalation and dose-ranging study in patients undergoing maintenance hemodialysis

BACKGROUND

VS-505 (AP301), an acacia and ferric oxyhydroxide polymer, is a novel fiber-iron-based phosphate binder. This two-part Phase 2 study evaluated the tolerability, safety and efficacy of oral VS-505 administered three times daily with meals in treating hyperphosphatemia in chronic kidney disease (CKD) patients receiving maintenance hemodialysis (MHD).

METHODS

In Part 1, patients received dose-escalated treatment with VS-505 2.25, 4.50 and 9.00 g/day for 2 weeks each, guided by serum phosphorus levels. In Part 2, patients received randomized, open-label, fixed-dosage treatment with VS-505 (1.50, 2.25, 4.50 or 6.75 g/day) or sevelamer carbonate 4.80 g/day for 6 weeks. The primary efficacy endpoint was the change in serum phosphorus.

RESULTS

The study enrolled 158 patients (Part 1: 25; Part 2: 133), with 130 exposed to VS-505 in total. VS-505 was well tolerated. The most common adverse events were gastrointestinal disorders, mainly feces discolored (56%) and diarrhea (15%; generally during Weeks 1-2 of treatment). Most gastrointestinal disorders resolved without intervention, and none was serious. In Part 1, serum phosphorus significantly improved (mean change -2.0 mg/dL; 95% confidence interval -2.7, -1.4) after VS-505 dose escalation. In Part 2, serum phosphorus significantly and dose-dependently improved in all VS-505 arms, with clinically meaningful reductions with VS-505 4.50 and 6.75 g/day, and sevelamer carbonate 4.80 g/day [mean change -1.6 (-2.2, -1.0), -1.8 (-2.4, -1.2) and -1.4 (-2.2, -0.5) mg/dL, respectively]. In both parts, serum phosphorus reductions occurred within 1 week of VS-505 initiation, returning to baseline within 2 weeks of VS-505 discontinuation.

CONCLUSION

VS-505, a novel phosphate binder, was well tolerated with a manageable safety profile, and effectively and dose-dependently reduced serum phosphorus in CKD patients with hyperphosphatemia receiving MHD.

CLINICAL TRIAL REGISTRATION NUMBER

NCT04551300 .

Disturbed Dynamic Brain Activity and Neurovascular Coupling in End-Stage Renal Disease Assessed With MRI

BACKGROUND

Pathophysiological mechanisms underlying cognitive impairment in end-stage renal disease (ESRD) remain unclear, with limited studies on the temporal variability of neural activity and its coupling with regional perfusion.

PURPOSE

To assess neural activity and neurovascular coupling (NVC) in ESRD patients, evaluate the classification performance of these abnormalities, and explore their relationships with cognitive function.

STUDY TYPE

Prospective.

POPULATION

Exactly 33 ESRD patients and 35 age, sex, and education matched healthy controls (HCs).

FIELD STRENGTH/SEQUENCE

The 3.0T/3D pseudo-continuous arterial spin labeling, resting-state functional MRI, and 3D-T1 weighted structural imaging.

ASSESSMENT

Dynamic (dfALFF) and static (sfALFF) fractional amplitude of low-frequency fluctuations and cerebral blood flow (CBF) were assessed. CBF-fALFF correlation coefficients and CBF/fALFF ratio were determined for ESRD patients and HCs. Their ability to distinguish ESRD patients from HCs was evaluated, alongside assessment of cerebral small vessel disease (CSVD) MRI features. All participants underwent blood biochemical and neuropsychological tests to evaluate cognitive decline.

STATISTICAL TESTS

Chi-squared test, two-sample t-test, Mann-Whitney U tests, covariance analysis, partial correlation analysis, family-wise error, false discovery rate, Bonferroni correction, area under the receiver operating characteristic curve (AUC) and multivariate pattern analysis. P < 0.05 denoted statistical significance.

RESULTS

ESRD patients exhibited higher dfALFF in triangular part of left inferior frontal gyrus (IFGtriang) and left middle temporal gyrus, lower CBF/dfALFF ratio in multiple brain regions, and decreased CBF/sfALFF ratio in bilateral superior temporal gyrus (STG). Compared with CBF/sfALFF ratio, dfALFF, and sfALFF, CBF/dfALFF ratio (AUC = 0.916) achieved the most powerful classification performance in distinguishing ESRD patients from HCs. In ESRD patients, decreased CBF/fALFF ratio correlated with more severe renal impairment, increased CSVD burden, and cognitive decline (0.4 < |r| < 0.6).

DATA CONCLUSION

ESRD patients exhibited abnormal dynamic brain activity and impaired NVC, with dynamic features demonstrating superior discriminative capacity and CBF/dfALFF ratio showing powerful classification performance.

LEVEL OF EVIDENCE

1 TECHNICAL EFFICACY: Stage 1.

Serum phosphorus concentration and its association with the degree and pattern of intracranial arterial calcification

BACKGROUND AND AIM

The aim of this study was to determine whether the serum phosphorus concentrations (SPC) are associated with the degree and pattern of intracranial arterial calcification (IAC) in patients with normal renal function or mild-moderate renal impairment.

METHODS AND RESULTS

A total of 513 patients were enrolled in this study. The degree of IAC measured by IAC scores was evaluated on non-contrast head computed tomography (CT) images and IAC was classified as intimal or medial calcification. Study participants were classified according to IAC degrees (mild, moderate and severe) and patterns (intimal and medial calcification). A multivariate regression model was used to assess the independent relationship of SPC with IAC scores and patterns. Of 513 study participants (mean [SD] age, 68.3 [10.3] years; 246 females [48%]), the mean SPC was 1.07 ± 0.17 mmol/L and IAC scores was 4.0 (3.0-5.0). Multivariate analysis showed that higher serum phosphorus was a significant risk factor for moderate/severe IAC in both patients with eGFR ≥60 ml/min/1.73 m2 (odds ratio [OR], 1.27; 95% confidence interval [CI], 1.01-1.59; P < 0.05) and eGFR <60 ml/min/1.73 m2 (OR, 1.92; 95% CI, 1.04-3.57; P < 0.05), when those with mild IAC were considered as the reference group. However, higher SPC was associated with an increased odds of medial calcification only in patients with eGFR <60 ml/min/1.73 m2 (OR, 1.67; 95% CI, 1.08 to 2.61).

CONCLUSIONS

High levels of serum phosphorus were positively correlated with the degree of IAC, and this significant effect on medial IAC was only present in patients with impaired renal function (eGFR <60 ml/min/1.73 m2).

Brown Tumors: The Hidden Face of Primary and Renal Hyperparathyroidism Amid Real-Life Settings

Brown tumors, an exceptional bone complication of severe primary (PHP) or renal (secondary) hyperparathyroidism (RHP), are caused by long-standing, elevated parathormone (PTH)-induced osteoclast activation causing multinucleated giant cell conglomerates with hemosiderin deposits in addition to the local production of cytokines and growth factors. We aim to present an adult case series including two females displaying this complication as part of a multidisciplinary complex panel in high PTH-related ailments. The approach was different since they had distinct medical backgrounds and posed a wide area of challenges amid real-life settings, namely, a 38-year-old lady with PHP and long-term uncontrolled hypercalcemia (with a history of pregnancy-associated PHP, the removal of a cystic jaw tumor, as well as a family and personal positive diagnosis of polycystic kidney disease, probably a PHP-jaw tumor syndrome), as well as, a 26-year-old woman with congenital single kidney and chronic renal disease-associated RHP who was poorly controlled under dialysis and developed severe anemia and episodes of metabolic acidosis (including one presentation that required emergency hemodialysis and was complicated with convulsive seizures, followed by resuscitated respiratory arrest). Both subjects displayed a severe picture of PHP/RHP with PTH levels of >1000 pg/mL and >2000 pg/mL and elevated serum bone turnover markers. Additionally, they had multiple brown tumors at the level of the ribs and pelvis (asymptomatically) and the spine, skull, and pelvis (complicated with a spontaneous cervical fracture). As an endocrine approach, the control of the underlying parathyroid disease was provided via surgery in PHP (for the postparathyroidectomy hungry bone syndrome) via medical intervention (with vitamin D analogs) in RHP. Additionally, in this case, since the diagnosis was not clear, a multidisciplinary decision to perform a biopsy was taken (which proved inconclusive), and the resection of the skull tumor to confirm the histological traits. This series highlights the importance of addressing the entire multidisciplinary panel of co-morbidities for a better outcome in patients with PHP/RHP-related brown tumors. However, in the instance of real-life medicine, poor compliance and reduced adherence to recommendations might impair the overall health status. Thus, sometimes, a direct approach at the level of cystic lesion is taken into consideration; this stands for a narrow frame of decision, and it is a matter of personalized decision. As seen here, brown tumors represent the hidden face of PHP/RHP, primarily the complex and severe forms, and awareness is essential even in the modern era.

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.

SNF472: a novel therapeutic agent for vascular calcification and calciphylaxis

Vascular calcification is a common complication in patients with chronic kidney disease (CKD) and is strongly associated with an increased risk of cardiovascular events and all-cause mortality. Calciphylaxis is a specific and life-threatening manifestation of vascular calcifications that usually affects individuals with advanced kidney function impairment or those undergoing dialysis. Currently, the treatment of vascular calcification and calciphylaxis in CKD lacks approved treatments and focuses on controlling risk factors. SNF472, the intravenous formulation of myo-inositol hexaphosphate, is a novel vascular calcification inhibitor currently undergoing phase 3 clinical trials, demonstrating its ability to directly inhibit the formation of calcium and phosphorus crystals, thereby blocking the production and deposition of ectopic calcium. The efficacy and safety of SNF472 in inhibiting vascular calcification have been confirmed in recent clinical studies. This review summarizes the results of studies related to SNF472 to provide a comprehensive overview of its mechanism of action, efficacy, safety, and ongoing clinical studies.

A novel consensus bacterial 6-phytase variant improves the responses of laying hens fed an inorganic phosphorus-free diet with reduced energy and nutrients from 23 to 72 wk of age

The objective of this study was to evaluate the effect of a novel consensus bacterial 6-phytase variant (PhyG) on egg productivity, eggshell quality, and body composition of laying hens fed inorganic phosphate-free diets with reduced energy and nutrients from 23 to 72 wk of age. Five treatments were randomly assigned, performing 28 replicates per treatment with 4 hens each, totaling 560 Hy-Line W80 birds. A positive control (PC) feed was formulated to contain adequate levels of energy and nutrients. A negative control (NC) feed was formulated without added inorganic phosphate (0.12% nonphytic phosphorus [nPP]) and reduced in Ca, Na, dig AA, and metabolizable energy in comparison with PC feed. Phytase was supplemented in the NC feed at 0, 300, 600, and 900 FTU/kg of feed. The responses evaluated were performance, egg quality, economic analysis, body composition, and tibia composition. Data were analyzed by a 2-factor (diet and age) repeated measure analysis. Overall, the feed intake, hen-day egg production, egg mass, and egg revenue were reduced by the complete removal of dicalcium phosphate (DCP) (P < 0.05). Supplement phytase in the NC diet elicits a positive response on each one of those variables. Laying hens consuming the NC feed with 900 FTU/kg of phytase produced more eggs per hen-housed compared with the phytase dosages of 300 and 600 FTU/kg. Body composition was not affected by dietary nPP, Ca, Na, dig AA, and energy reductions (P > 0.05). At 72-wk-old, tibia ash was reduced in hens consuming the NC diet vs. PC (P < 0.05) and no difference was observed between hens supplemented with phytase and the PC feed. Margin over feeding cost increased in a dose-dependent manner with phytase supplementation. Supplementation with 900 FTU/kg of phytase is recommended to improve the number of eggs produced per hen-housed and the number of marketable eggs produced through 23 to 72 wk of age, under this dietary setting.

Progress in pharmacotherapy for the treatment of hyperphosphatemia in renal failure

INTRODUCTION

Among the clinical and metabolic complications of progressive chronic kidney disease (CKD), CKD-mineral bone disorder (CKD-MBD) significantly contributes to morbidity and mortality. While overt and persistent hyperphosphatemia is typical of advanced CKD and requires treatment, other abnormalities of calcium/phosphate metabolism begin to occur since the early stages of the disease.

AREAS COVERED

We searched on the PubMed database, without restrictions for language or time range, for randomized clinical trials and meta-analyses investigating phosphate-lowering therapies. The various phosphate binders show different safety profiles and diverse effects on calcium/phosphate metabolism and vascular calcification. The in-depth knowledge of the characteristics of these drugs is crucial to ensure adequate treatment to CKD patients.

EXPERT OPINION

A proper control of serum phosphate can be achieved using phosphate binders. These medications may induce side effects. Moreover, data on their impact on clinical outcomes are partly controversial or scarce, especially for the new generation drugs. Hyperphosphatemia favors cardiovascular disease and increases the risk for CKD progression. These effects are partially mediated by fibroblast growth factor 23 (FGF23), a phosphaturic hormone that raises to maintain normal serum phosphate. Since there are no data supporting the use of phosphate-lowering agents when phosphataemia is normal, a key role is played by reducing dietary phosphate intake with the aim to control serum phosphate and the compensatory FGF23 and parathyroid hormone (PTH) increase.

Targeting aging with the healthy skeletal system: The endocrine role of bone

Aging is an inevitable biological process, and longevity may be related to bone health. Maintaining strong bone health can extend one's lifespan, but the exact mechanism is unclear. Bone and extraosseous organs, including the heart and brain, have complex and precise communication mechanisms. In addition to its load bearing capacity, the skeletal system secretes cytokines, which play a role in bone regulation of extraosseous organs. FGF23, OCN, and LCN2 are three representative bone-derived cytokines involved in energy metabolism, endocrine homeostasis and systemic chronic inflammation levels. Today, advanced research methods provide new understandings of bone as a crucial endocrine organ. For example, gene editing technology enables bone-specific conditional gene knockout models, which allows the study of bone-derived cytokines to be more precise. We systematically evaluated the various effects of bone-derived cytokines on extraosseous organs and their possible antiaging mechanism. Targeting aging with the current knowledge of the healthy skeletal system is a potential therapeutic strategy. Therefore, we present a comprehensive review that summarizes the current knowledge and provides insights for futures studies.

Phosphate Control in Peritoneal Dialysis Patients: Issues, Solutions, and Open Questions

Hyperphosphatemia is a common complication in advanced chronic kidney disease and contributes to cardiovascular morbidity and mortality. The present narrative review focuses on the management of phosphatemia in uremic patients receiving peritoneal dialysis. These patients frequently develop hyperphosphatemia since phosphate anion behaves as a middle-size molecule despite its low molecular weight. Accordingly, patient transporter characteristics and peritoneal dialysis modalities and prescriptions remarkably influence serum phosphate control. Given that phosphate peritoneal removal is often insufficient, especially in lower transporters, patients are often prescribed phosphate binders whose use in peritoneal dialysis is primarily based on clinical trials conducted in hemodialysis because very few studies have been performed solely in peritoneal dialysis populations. A crucial role in phosphate control among peritoneal dialysis patients is played by diet, which must help in reducing phosphorous intake while preventing malnutrition. Moreover, residual renal function, which is preserved in most peritoneal dialysis patients, significantly contributes to maintaining phosphate balance. The inadequate serum phosphate control observed in many patients on peritoneal dialysis highlights the need for large and well-designed clinical trials including exclusively peritoneal dialysis patients to evaluate the effects of a multiple therapeutic approach on serum phosphate control and on hard clinical outcomes in this high-risk population.

Fibroblast Growth Factor 23 and Muscle Wasting: A Metabolic Point of View

Protein energy wasting (PEW), mostly characterized by decreased body stores of protein and energy sources, particularly in the skeletal muscle compartment, is highly prevalent in patients with moderate to advanced chronic kidney disease (CKD). Fibroblast growth factor 23 (FGF23) is an endocrine hormone secreted from bone and has systemic actions on skeletal muscle. In CKD, FGF23 is elevated and its coreceptor α-klotho is suppressed. Multiple lines of evidence suggest that FGF23 is interconnected with various mechanisms of skeletal muscle wasting in CKD, including systemic and local inflammation, exaggerated oxidative stress, insulin resistance (IR), and abnormalities in adipocytokine metabolism. Investigation of metabolic actions of FGF23 on muscle tissue could provide new insights into metabolic and nutritional abnormalities observed in patients with CKD.

Chronic Kidney Disease-State of Either "Too Much" or "Too Little"

Chronic kidney disease (CKD) is a world-wide phenomenon with an increasing incidence and prevalence [...].

Evocalcet Rescues Secondary Hyperparathyroidism-driven Cortical Porosity in CKD Male Rats

To elucidate the effect of evocalcet, a new oral calcimimetic to bone of secondary hyperparathyroidism (SHPT) with chronic kidney disease (CKD), the rats were 5/6 nephrectomized and fed on a high-phosphate diet. The treated rats were then divided into vehicle groups and evocalcet administered groups. The rats in the vehicle groups exhibited increased levels of serum PTH and inorganic phosphate (Pi) levels, high bone turnover, and severe cortical porosity, mimicking SHPT (CKD-SHPT rats). The cortical bone of the CKD-SHPT rats showed broad demineralization around the osteocytes, suppression of Phex/small integrin-binding ligand N-linked glycoprotein-mediated mineralization in the periphery of the osteocytic lacunae, and increased levels of osteocytic cell death, all of which were considered as the first steps of cortical porosity. In contrast, evocalcet ameliorated the increased serum PTH levels, the enlarged osteocytic lacunae, and the cortical porosity of the CKD-SHPT rats. Osteocytes of CKD-SHPT rats strongly expressed PTH receptor and Pit1/Pit2, which sense extracellular Pi, indicating that PTH and Pi affected these osteocytes. Cell death of cultured osteocytes increased in a Pi concentration-dependent manner, and PTH administration rapidly elevated Pit1 expression and enhanced osteocytic death, indicating the possibility that the highly concentrated serum PTH and Pi cause severe perilacunar osteolysis and osteocytic cell death. It is likely therefore that evocalcet not only decreases serum PTH but also reduces the exacerbation combined with PTH and Pi to the demineralization of osteocytic lacunae and osteocytic cell death, thereby protecting cortical porosity in CKD-SHPT rats.

Caffeine intake improves the cognitive performance of patients with chronic kidney disease

Objective

Cognitive impairment is a common complication of chronic kidney disease (CKD). Caffeine intake has been reported to improve cognitive performance in several studies. However, whether the benefits of caffeine intake on cognitive function apply to patients with CKD remains unknown.

Methods

We performed a retrospective cross-sectional study based on the National Health and Nutrition Examination Survey (NHANES). The data of CKD subjects and non-CKD subjects from NHANES 2011−2014 were analyzed. Propensity score matching (PSM) was performed based on age, sex, diabetes, cancer, educational level, energy intake and protein intake to select subjects. The Consortium to Establish a Registry for Alzheimer’s Disease Word Learning Test (CERAD-WL), the CERAD Word List Recall Test (CERAD-DR), the Animal Fluency Test (AF) and the Digit Symbol Substitution Test (DSST) were used, whereby the occurrence of cognitive impairment was identified. Logistic regression models were performed to evaluate the association between caffeine intake and cognitive performance in CKD and non-CKD participants. Stratified analyses according to the stage of CKD and the urinary albumin/creatinine ratio levels were performed. Plot curves were then generalized to present a non-linear relationship, and the inflection point for each non-linear model was obtained by using a recursive algorithm.

Results

Cognitive impairment was more prevalent in CKD patients than in non-CKD subjects. For CKD patients, caffeine intake was associated with higher CERAD-WL, CERAD-DR, AF and DSST scores. For non-CKD subjects, caffeine intake was associated with higher DSST scores only. Subgroup analysis revealed that caffeine only benefited the cognitive function of patients with CKD stages 2 and 3. The analysis showed non-linear relationships of caffeine intake and cognitive function for both CKD and non-CKD subjects. The inflection point of caffeine intake for CKD patients was 279 mg/day.

Conclusion

The recommended dose of caffeine intake to improve the cognitive function of CKD patients is ≤279 mg/day.

Safety and Efficacy of PTH 1-34 and 1-84 Therapy in Chronic Hypoparathyroidism: A Meta-Analysis of Prospective Trials

Hypoparathyroidism is the only endocrine deficiency for which hormone replacement therapy is not the standard of care. Although conventional treatments may control hypocalcaemia, other complications such as hyperphosphatemia, kidney stones, peripheral calcifications, and bone disease remain unmet needs. This meta-analysis (PROSPERO registration number CRD42019126881) aims to evaluate and compare the efficacy and safety of PTH_1-34 and PTH_1-84 in restoring calcium metabolism in chronic hypoparathyroidism. EMBASE, PubMed, and CENTRAL databases were searched for randomized clinical trials or prospective studies published between January 1996 and March 2021. English-language trials reporting data on replacement with PTH_1-34 or PTH_1-84 in chronic hypoparathyroidism were selected. Three authors extracted outcomes, one author performed quality control, all assessed the risk of biases. Overall, data from 25 studies on 588 patients were analyzed. PTH therapy had a neutral effect on calcium levels, while lowering serum phosphate (-0.21 mmol/L; 95% confidence interval [CI], -0.31 to -0.11 mmol/L; p < 0.001) and urinary calcium excretion (-1.21 mmol/24 h; 95% CI, -2.03 to -0.41 mmol/24 h; p = 0.003). Calcium phosphate product decreased under PTH_1-84 therapy only. Both treatments enabled a significant reduction in calcium and calcitriol supplementation. PTH therapy increased bone turnover markers and lumbar spine mineral density. Quality of life improved and there was no difference in the safety profile between PTH and conventionally treated patients. Results for most outcomes were similar for the two treatments. Limitations of the study included considerable population overlap between the reports, incomplete data, and heterogeneity in the protocol design. In conclusion, the meta-analysis of data from the largest collection to date of hypoparathyroid patients shows that PTH therapy is safe, well-tolerated, and effective in normalizing serum phosphate and urinary calcium excretion, as well as enabling a reduction in calcium and vitamin D use and improving quality of life. © 2022 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Phosphate in the Context of Cognitive Impairment and Other Neurological Disorders Occurrence in Chronic Kidney Disease

The nervous system and the kidneys are linked under physiological states to maintain normal body homeostasis. In chronic kidney disease (CKD), damaged kidneys can impair the central nervous system, including cerebrovascular disease and cognitive impairment (CI). Recently, kidney disease has been proposed as a new modifiable risk factor for dementia. It is reported that uremic toxins may have direct neurotoxic (astrocyte activation and neuronal death) and/or indirect action through vascular effects (cerebral endothelial dysfunction, calcification, and inflammation). This review summarizes the evidence from research investigating the pathophysiological effects of phosphate toxicity in the nervous system, raising the question of whether the control of hyperphosphatemia in CKD would lower patients’ risk of developing cognitive impairment and dementia.

Unraveling the Metabolic Hallmarks for the Optimization of Protein Intake in Pre-Dialysis Chronic Kidney Disease Patients

The daily amount and quality of protein that should be administered by enteral nutrition in pre-dialysis chronic kidney disease (CKD) patients is a widely studied but still controversial issue. This is due to a compromise between the protein necessary to maintain muscular proteostasis avoiding sarcopenia, and the minimal amount required to prevent uremia and the accumulation of nitrogenous toxic substances in blood because of the renal function limitations. This review underlines some intracellular and extracellular features that should be considered to reconcile those two opposite factors. On one hand, the physiological conditions and usual side effects associated with CKD, mTOR and other proteins and nutrients involved in the regulation of protein synthesis in the muscular tissue are discussed. On the other hand, the main digestive features of the most common proteins used for enteral nutrition formulation (i.e., whey, casein and soy protein) are highlighted, due to the importance of supplying key amino acids to serum and tissues to maintain their concentration above the anabolic threshold needed for active protein synthesis, thereby minimizing the catabolic pathways leading to urea formation.

Salivary phosphate as a biomarker for human diseases

Phosphate is a common ingredient of the daily consumed foods and is absorbed in the intestine and is excreted in the urine through the kidney to maintain the homeostatic balance. For adults, the Recommended Dietary Allowance (RDA) for phosphorus is around 700 mg/day. The change in dietary habits resulted in far more phosphate consumption (almost double) than the RDA, contributing to increased cardiovascular diseases, kidney diseases, and tumor formation. Due to a lack of clinical appreciation for the long-term consequences of chronic phosphate burden on non-communicable disorders, it is rapidly becoming a global health concern. The possible association between dysregulated phosphate metabolism and obesity is not studied in-depth, mainly because such an association is believed to be nonexistent. However, in the animal model of obesity, serum phosphate level was higher than their non-obese controls. In a similar observation line, significantly higher salivary phosphate levels were detected in obese children compared to normal-weight children. Of clinical importance, despite the significant increase of salivary phosphate levels in obese children, the plasma phosphate levels did not change in samples collected from the same group of children. Such disparity between plasma and saliva raised the possibility that human salivary phosphate levels may be an early biomarker of childhood obesity.

Longitudinal Effects of Serum Calcium and Phosphate Levels and Their Ratio on Incident Ischemic Heart Disease among Korean Adults

Serum calcium and phosphate levels are controlled by a regulatory system, but their individual concentration tendencies and interactions may affect long-term vascular health. This study aimed to assess the effects of serum calcium and phosphate levels on incident ischemic heart disease (IHD) in a large-scale community-dwelling Korean cohort. We evaluated 15,259 non-diabetic individuals (median age, 45 years; range, 30–85) without previous IHD or ischemic stroke using the Korean National Health Insurance data. The study population was classified based on the calcium, phosphate, and calcium/phosphate ratios. Using Cox proportional hazards regression models, we estimated hazard ratios (HRs) with 95% confidence intervals (CIs) for IHD over 50 months after baseline enrolment. The age- and sex-adjusted incidence of IHD gradually increased with serum calcium and phosphate quartiles and decreased with calcium/phosphate ratio quartiles, with an overall crude rate of 2.1% (315/15,259). After setting the lowest calcium, phosphate, and calcium/phosphate ratio quartiles as a reference group, the HRs (95% CIs) of the highest calcium, phosphate, and calcium/phosphate ratio quartiles for IHD were 1.77 (1.15–2.72), 1.73 (1.18–2.55), and 0.58 (0.39–0.87), respectively, after adjusting for potential confounding variables. Serum calcium and phosphate levels were positively associated with IHD incidence, while the serum calcium/phosphate ratio exhibited an inverse relationship. Serum calcium and phosphate homeostasis may merit serious consideration to understand the pathogenesis of coronary atherosclerosis as a risk modifier for IHD.

Use of Micro-CT Imaging to Assess Ventral Mandibular Cortical Thickness and Volume in an Experimental Rodent Model With Chronic High-Phosphorus Intake

Adverse effects of high dietary phosphorus on bone health have been observed in both animal and human studies. The aim of the investigation was to examine chronic effects of high phosphorus diet on the apical mandibular cortical thickness and volume in a hystricomorph rodent (Octodon degus) using microcomputed tomography. Male degus were randomly divided into two groups fed by different mineral contents from the age of 12 weeks till the age of 17 months. The micro-CT scanning and wall thickness analysis were applied on the region of the mandible exactly under the apices of the 4th premolar tooth, first molar tooth, and second molar tooth in two animals from each group. General overview and mapping of the ventral mandibular bone thickness revealed pronounced bony mandibular protrusions in all the animals fed a high-phosphorus diet with obvious bone thinning apically to the 4th premolar and first and second molar tooth apices. Mandibular bone volume and thickness located apically to the premolar and molars were statistically significantly smaller/thinner in the group fed by a high phosphorus diet. The thinnest bone measured 0.004 mm, where the mandibular 4th premolar tooth almost perforated the mandibular cortex. Similar studies of metabolic bone disease and its influence on alveolar bone were also published in rats and mice. The influence of different environmental, infectious, or metabolic factors on the growing tooth, alveolar bone formation, and bone pathologies must be done experimentally on growing animals. In contrast, degus have continuously growing dentition, and the effect of any of the above listed factors can be studied in this animal model at any age and for longer time periods.

Reduced White Matter Integrity in Patients With End-Stage and Non-end-Stage Chronic Kidney Disease: A Tract-Based Spatial Statistics Study

Background and Purpose: Reduced white matter (WM) integrity has been implicated in chronic kidney disease (CKD), especially in end-stage renal disease (ESRD). However, whether the differences in WM abnormalities exist in ESRD and non-end-stage CKD (NES-CKD) remains unclear. Hence, this study aimed to investigate the WM microstructural changes between the two stages using diffusion tensor imaging (DTI) and explore the related influencing factors.

Methods: Diffusion tensor imaging’ images were prospectively acquired from 18 patients with ESRD, 22 patients with NES-CKD, and 19 healthy controls (HCs). Tract-based spatial statistics (TBSS) was performed to assess the voxel-wise differences in WM abnormalities among the three groups. The relationships between DTI parameters and biochemical data were also analyzed.

Results: Compared with NES-CKDs, FA value was significantly decreased, and AD value increased in ESRDs mainly in brain regions of bilateral anterior thalamic radiation (ATR), the genu and body of corpus callosum (CC), bilateral anterior corona radiata, superior corona radiata, and superior longitudinal fasciculus. Besides, extensive and symmetrical deep WM damages were observed in patients with ESRD, accompanied by increased MD and RD values. Multiple regression analysis revealed that uric acid and serum phosphorus level can be used as independent predictors of WM microstructural abnormalities in clusters with statistical differences in DTI parameters between ESRD and NES-CKD groups.

Conclusion: In the progression of CKD, patients with ESRD have more severe WM microstructural abnormalities than NES-CKDs, and this progressive deterioration may be related to uric acid and phosphate levels.

The Emerging Role of Nutraceuticals in Cardiovascular Calcification: Evidence from Preclinical and Clinical Studies

Cardiovascular calcification is the ectopic deposition of calcium-phosphate crystals within the arterial wall and the aortic valve leaflets. This pathological process leads to increased vascular stiffness, reduced arterial elasticity, and aortic valve stenosis, increasing the risk of cardiovascular diseases. Although cardiovascular calcification is an increasing health care burden, to date no medical therapies have been approved for treating or preventing it. Considering the current lack of therapeutic strategies and the increasing prevalence of cardiovascular calcification, the investigation of some nutraceuticals to prevent this pathological condition has become prevalent in recent years. Recent preclinical and clinical studies evaluated the potential anti-calcific role of nutraceuticals (including magnesium, zinc, iron, vitamin K, and phytate) in the progression of vascular calcification, providing evidence for their dietary supplementation, especially in high-risk populations. The present review summarizes the current knowledge and latest advances for nutraceuticals with the most relevant preclinical and clinical data, including magnesium, zinc, iron, vitamin K, and phytate. Their supplementation might be recommended as a cost-effective strategy to avoid nutritional deficiency and to prevent or treat cardiovascular calcification. However, the optimal dose of nutraceuticals has not been identified and large interventional trials are warranted to support their protective effects on cardiovascular disease.