Phosphate: a stealthier killer than previously thought?

Obesity, Diabetes Mellitus, and Vascular Impediment as Consequences of Excess Processed Food Consumption

Regular intake of ready-to-eat meals is related to obesity and several noninfectious illnesses, such as cardiovascular diseases, hypertension, diabetes mellitus (DM), and tumors. Processed foods contain high calories and are often enhanced with excess refined sugar, saturated and trans fat, Na⁺ andphosphate-containing taste enhancers, and preservatives. Studies showed that monosodium glutamate (MSG) induces raised echelons of oxidative stress, and excessive hepatic lipogenesis is concomitant to obesity and type 2 diabetes mellitus (T2DM). Likewise, more than standard salt intake adversely affects the cardiovascular system, renal system, and central nervous system (CNS), especially the brain. Globally, excessive utilization of phosphate-containing preservatives and additives contributes unswervingly to excessive phosphate intake through food. In addition, communities and even health experts, including medical doctors, are not well-informed about the adverse effects of phosphate preservatives on human health. Dietary phosphate excess often leads to phosphate toxicity, ultimately potentiating kidney disease development. The mechanisms involved in phosphate-related adverse effects are not explainable. Study reports suggested that high blood level of phosphate causes vascular ossification through the deposition of Ca²⁺ and substantially alters fibroblast growth factor-23 (FGF23) and calcitriol.

Cellular abundance of sodium phosphate cotransporter SLC20A1/PiT1 and phosphate uptake are controlled post-transcriptionally by ESCRT

Inorganic phosphate is essential for human life. The widely expressed mammalian sodium/phosphate cotransporter SLC20A1/PiT1 mediates phosphate uptake into most cell types; however, while SLC20A1 is required for development, and elevated SLC20A1 expression is associated with vascular calcification and aggressive tumor growth, the mechanisms regulating SLC20A1 protein abundance are unknown. Here, we found that SLC20A1 protein expression is low in phosphate-replete cultured cells but is strikingly induced following phosphate starvation, whereas mRNA expression is high in phosphate-replete cells and only mildly increased by phosphate starvation. To identify regulators of SLC20A1 protein levels, we performed a genome-wide CRISPR-based loss-of-function genetic screen in phosphate-replete cells using SLC20A1 protein induction as readout. Our screen revealed that endosomal sorting complexes required for transport (ESCRT) machinery was essential for proper SLC20A1 protein downregulation in phosphate-replete cells. We show that SLC20A1 colocalizes with ESCRT and that ESCRT deficiency increases SLC20A1 protein and phosphate uptake into cells. We also found numerous additional candidate regulators of mammalian phosphate homeostasis, including genes modifying protein ubiquitination and the Krebs cycle and oxidative phosphorylation pathways. Many of these targets have not been previously implicated in this process. We present here a model in which SLC20A1 protein abundance and phosphate uptake are tonically negatively regulated post-transcriptionally in phosphate-replete cells through direct ESCRT-mediated SLC20A1 degradation. Moreover, our screening results provide a comprehensive resource for future studies to elucidate the mechanisms governing cellular phosphate homeostasis. We conclude that genome-wide CRISPR-based genetic screening is a powerful tool to discover proteins and pathways relevant to physiological processes.

Oxidative Stress Related to Plasmalemmal and Mitochondrial Phosphate Transporters in Vascular Calcification

Inorganic phosphate (Pi) is essential for maintaining cellular function but excess of Pi leads to serious complications, including vascular calcification. Accumulating evidence suggests that oxidative stress contributes to the pathogenic progression of calcific changes. However, the molecular mechanism underlying Pi-induced reactive oxygen species (ROS) generation and its detrimental consequences remain unclear. Type III Na⁺-dependent Pi cotransporter, PiT-1/-2, play a significant role in Pi uptake of vascular smooth muscle cells. Pi influx via PiT-1/-2 increases the abundance of PiT-1/-2 and depolarization-activated Ca²⁺ entry due to its electrogenic properties, which may lead to Ca²⁺ and Pi overload and oxidative stress. At least four mitochondrial Pi transporters are suggested, among which the phosphate carrier (PiC) is known to be mainly involved in mitochondrial Pi uptake. Pi transport via PiC may induce hyperpolarization and superoxide generation, which may lead to mitochondrial dysfunction and endoplasmic reticulum stress, together with generation of cytosolic ROS. Increase in net influx of Ca²⁺ and Pi and their accumulation in the cytosol and mitochondrial matrix synergistically increases oxidative stress and osteogenic differentiation, which could be prevented by suppressing either Ca²⁺ or Pi overload. Therapeutic strategies targeting plasmalemmal and mitochondrial Pi transports can protect against Pi-induced oxidative stress and vascular calcification.

The Influence of Sevelamer Hydrochloride and Calcium Carbonate on Markers of Inflammation and Oxidative Stress in Hemodialysis at Six Months of Follow-Up

Patients with end-stage renal disease (ESRD) present alterations in mineral and bone metabolism. Hyperphosphatemia in ESRD is considered an independent risk factor for cardiovascular disease (CVD), increasing morbidity, and mortality. Sevelamer hydrochloride is a calcium-free, non-absorbable phosphate-chelating polymer. Calcium carbonate chelator is helpful in controlling serum phosphate levels. There is insufficient information on the influence of sevelamer hydrochloride and calcium carbonate on the behavior of oxidative stress (OS) markers and inflammation in patients on hemodialysis (HD). A randomized open clinical trial was carried out on patients to evaluate sevelamer hydrochloride and calcium carbonate influence at 6 months of study follow-up. Levels of oxidants (LPO, NO, and 8-isoprostanes), antioxidants (SOD and TAC), oxidative DNA damage (8-OHdG and hOGG1), pro-inflammatory cytokines (IL-6 and TNF-α), and inflammation markers (ferritin and C-reactive protein) were measured with colorimetric and ELISA methods. We found a significant increase in oxidants LPO and NO, and antioxidants SOD and TAC, and downregulation of IL-6 and TNF-α. Ferritin decrease at 6 months follow-up in the sevelamer hydrochloride group. Increase in C-reactive protein was found in the group of patients treated with calcium carbonate. In conclusion, we found an oxidative state imbalance with increase in LPO and NO oxidants. The activity of the antioxidant enzymes (SOD and TAC) was also found to increase, suggesting a compensatory effect in the face of increase in oxidants. The same phenomenon was observed with increase in the oxidative damage marker to DNA and the increase in the DNA repair enzyme, suggesting a compensatory effect. Pro-inflammatory cytokines were predominantly downregulated by TNF-α in the group that ingested sevelamer hydrochloride in the final determination at 6 months of follow-up. Serum ferritin levels decreased significantly at the end of follow-up in patients on HD in the sevelamer hydrochloride group. The management of hyperphosphatemia with sevelamer hydrochloride appears to have obvious anti-inflammatory and antioxidant benefits.

Phosphate, Microbiota and CKD

Phosphate is a key uremic toxin associated with adverse outcomes. As chronic kidney disease (CKD) progresses, the kidney capacity to excrete excess dietary phosphate decreases, triggering compensatory endocrine responses that drive CKD-mineral and bone disorder (CKD-MBD). Eventually, hyperphosphatemia develops, and low phosphate diet and phosphate binders are prescribed. Recent data have identified a potential role of the gut microbiota in mineral bone disorders. Thus, parathyroid hormone (PTH) only caused bone loss in mice whose microbiota was enriched in the Th17 cell-inducing taxa segmented filamentous bacteria. Furthermore, the microbiota was required for PTH to stimulate bone formation and increase bone mass, and this was dependent on bacterial production of the short-chain fatty acid butyrate. We review current knowledge on the relationship between phosphate, microbiota and CKD-MBD. Topics include microbial bioactive compounds of special interest in CKD, the impact of dietary phosphate and phosphate binders on the gut microbiota, the modulation of CKD-MBD by the microbiota and the potential therapeutic use of microbiota to treat CKD-MBD through the clinical translation of concepts from other fields of science such as the optimization of phosphorus utilization and the use of phosphate-accumulating organisms.

Dietary Phosphorus as a Marker of Mineral Metabolism and Progression of Diabetic Kidney Disease

Phosphorus is an essential nutrient that is critically important in the control of cell and tissue function and body homeostasis. Phosphorus excess may result in severe adverse medical consequences. The most apparent is an impact on cardiovascular (CV) disease, mainly through the ability of phosphate to change the phenotype of vascular smooth muscle cells and its contribution to pathologic vascular, valvular and other soft tissue calcification. Chronic kidney disease (CKD) is the most prevalent chronic disease manifesting with the persistent derangement of phosphate homeostasis. Diabetes and resulting diabetic kidney disease (DKD) remain the leading causes of CKD and end-stage kidney disease (ESRD) worldwide. Mineral and bone disorders of CKD (CKD-MBD), profound derangement of mineral metabolism, develop in the course of the disease and adversely impact on bone health and the CV system. In this review we aimed to discuss the data concerning CKD-MBD in patients with diabetes and to analyze the possible link between hyperphosphatemia, certain biomarkers of CKD-MBD and high dietary phosphate intake on prognosis in patients with diabetes and DKD. We also attempted to clarify if hyperphosphatemia and high phosphorus intake may impact the onset and progression of DKD. Careful analysis of the available literature brings us to the conclusion that, as for today, no clear recommendations based on the firm clinical data can be provided in terms of phosphorus intake aiming to prevent the incidence or progression of diabetic kidney disease.

Control of phosphorus and prevention of fractures in the kidney patient

Patients with chronic kidney disease have a higher risk of fractures than the general population due to the added factor of uraemia. Although the mechanisms behind uraemia-associated fractures are not fully understood, it is widely accepted that the decrease in bone mineral content and alteration in bone architecture both increase bone fragility. As chronic kidney disease progresses, the risk of fracture increases, especially once the patient requires dialysis. Among the many causes of the increased risk are advanced age, amenorrhoea, steroid exposure, decreased vitamin D, increased PTH, malnutrition and chronic inflammation. Serum phosphorus, whether high or very low, seems to correlate with the risk of fracture. Moreover, increased serum phosphate is known to directly and indirectly affect bone metabolism through the development of adaptive hormonal mechanisms aimed at preventing hyperphosphataemia, such as the increase in PTH and FGF23 and the reduction in calcitriol. These adaptive mechanisms are less intense if the intestinal absorption of phosphorus is reduced with the use of phosphorus captors, which seem to have a positive impact in reducing the risk of fractures. We describe here the possible mechanisms associating serum phosphorus levels, the adaptive mechanisms typical in kidney disease and the use of drugs to control hyperphosphataemia with the risk of fractures. We found no studies in the literature providing evidence on the influence of different treatments on the risk of fractures in patients with chronic kidney disease. We suggest that control of phosphorus should be an objective to consider.

Oxidative stress by Ca2+ overload is critical for phosphate-induced vascular calcification

Hyperphosphatemia is the primary risk factor for vascular calcification, which is closely associated with cardiovascular morbidity and mortality. Recent evidence showed that oxidative stress by high inorganic phosphate (Pi) mediates calcific changes in vascular smooth muscle cells (VSMCs). However, intracellular signaling responsible for Pi-induced oxidative stress remains unclear. Here, we investigated molecular mechanisms of Pi-induced oxidative stress related with intracellular Ca²⁺ ([Ca²⁺]_i) disturbance, which is critical for calcification of VSMCs. VSMCs isolated from rat thoracic aorta or A7r5 cells were incubated with high Pi-containing medium. Extracellular signal-regulated kinase (ERK) and mammalian target of rapamycin were activated by high Pi that was required for vascular calcification. High Pi upregulated expressions of type III sodium-phosphate cotransporters PiT-1 and -2 and stimulated their trafficking to the plasma membrane. Interestingly, high Pi increased [Ca²⁺]_i exclusively dependent on extracellular Na⁺ and Ca²⁺ as well as PiT-1/2 abundance. Furthermore, high-Pi induced plasma membrane depolarization mediated by PiT-1/2. Pretreatment with verapamil, as a voltage-gated Ca²⁺ channel (VGCC) blocker, inhibited Pi-induced [Ca²⁺]_i elevation, oxidative stress, ERK activation, and osteogenic differentiation. These protective effects were reiterated by extracellular Ca²⁺-free condition, intracellular Ca²⁺ chelation, or suppression of oxidative stress. Mitochondrial superoxide scavenger also effectively abrogated ERK activation and osteogenic differentiation of VSMCs by high Pi. Taking all these together, we suggest that high Pi activates depolarization-triggered Ca²⁺ influx via VGCC, and subsequent [Ca²⁺]_i increase elicits oxidative stress and osteogenic differentiation. PiT-1/2 mediates Pi-induced [Ca²⁺]_i overload and oxidative stress but in turn, PiT-1/2 is upregulated by consequences of these alterations.NEW & NOTEWORTHY The novel findings of this study are type III sodium-phosphate cotransporters PiT-1 and -2-dependent depolarization by high Pi, leading to Ca²⁺ entry via voltage-gated Ca²⁺ channels in vascular smooth muscle cells. Cytosolic Ca²⁺ increase and subsequent oxidative stress are indispensable for osteogenic differentiation and calcification. In addition, plasmalemmal abundance of PiT-1/2 relies on Ca²⁺ overload and oxidative stress, establishing a positive feedback loop. Identification of mechanistic components of a vicious cycle could provide novel therapeutic strategies against vascular calcification in hyperphosphatemic patients.

Control of phosphorus and prevention of fractures in the kidney patient

Patients with chronic kidney disease have a higher risk of fractures than the general population due to the added factor of uraemia. Although the mechanisms behind uraemia-associated fractures are not fully understood, it is widely accepted that the decrease in bone mineral content and alteration in bone architecture both increase bone fragility. As chronic kidney disease progresses, the risk of fracture increases, especially once the patient requires dialysis. Among the many causes of the increased risk are advanced age, amenorrhoea, steroid exposure, decreased vitamin D, increased parathyroid hormone (PTH), malnutrition and chronic inflammation. Serum phosphorus, whether high or very low, seems to correlate with the risk of fracture. Moreover, increased serum phosphate is known to directly and indirectly affect bone metabolism through the development of adaptive hormonal mechanisms aimed at preventing hyperphosphataemia, such as the increase in PTH and fibroblast growth factor 23 (FGF23) and the reduction in calcitriol. These adaptive mechanisms are less intense if the intestinal absorption of phosphorus is reduced with the use of phosphorus captors, which seem to have a positive impact in reducing the risk of fractures. We describe here the possible mechanisms associating serum phosphorus levels, the adaptive mechanisms typical in kidney disease and the use of drugs to control hyperphosphataemia with the risk of fractures. We found no studies in the literature providing evidence on the influence of different treatments on the risk of fractures in patients with chronic kidney disease. We suggest that control of phosphorus should be an objective to consider.

Monocyte Chemoattractant Protein-1 Is an Independent Predictor of Coronary Artery Ectasia in Patients with Acute Coronary Syndrome

Our purpose was to assess a possible association of inflammatory, lipid and mineral metabolism biomarkers with coronary artery ectasia (CAE) and to determine a possible association of this with acute atherotrombotic events (AAT). We studied 270 patients who underwent coronary angiography during an acute coronary syndrome 6 months before. Plasma levels of several biomarkers were assessed, and patients were followed during a median of 5.35 (3.88–6.65) years. Two interventional cardiologists reviewed the coronary angiograms, diagnosing CAE according to previously published criteria in 23 patients (8.5%). Multivariate binary logistic regression analysis was used to search for independent predictors of CAE. Multivariate analysis revealed that, aside from gender and a diagnosis of dyslipidemia, only monocyte chemoattractant protein-1 (MCP-1) (OR = 2.25, 95%CI = (1.35–3.76) for each increase of 100 pg/mL, p = 0.001) was independent predictor of CAE, whereas mineral metabolism markers or proprotein convertase subtilisin/kexin type 9 were not. Moreover, CAE was a strong predictor of AAT during follow-up after adjustment for other clinically relevant variables (HR = 2.67, 95%CI = (1.22–5.82), p = 0.013). This is the first report showing that MCP-1 is an independent predictor of CAE, suggesting that CAE and coronary artery disease may share pathogenic mechanisms. Furthermore, CAE was associated with an increased incidence of AAT.

Sex Differences in Kidney Stone Disease in Chinese Patients with Type 2 Diabetes Mellitus

Objectives

To investigate the characteristics of kidney stone disease (KSD) among the Chinese population with type 2 diabetes mellitus (T2DM) and identify sex-specific factors associated with KSD.

Methods

A single-center, cross-sectional analysis was performed among Chinese patients with T2DM. KSD was identified by ultrasonography or computed tomography results. Demographic data, physical measurements, laboratory measurements, comorbidities, and related medication data were collected and analyzed. Binary logistic regression was used to explore the associated factors.

Results

A total of 7,257 patients with T2DM were included in the study, of which 56.1% were male and 15.0% were diagnosed with KSD. The male-to-female ratio for KSD among T2DM patients was 1.35. Among all the T2DM patients, male gender, HOMA2-IR, uric acid, and renal cysts were independent risk factors for KSD development, whereas serum phosphorus and the use of angiotensin-converting enzyme inhibitors (ACEIs) were independent protective factors for KSD. Among male diabetic patients, triglycerides, HOMA2-IR, renal cysts, and urinary tract infections were all associated with a greater risk of KSD. In contrast, serum phosphorus was associated with a lower risk of KSD. Among female diabetic patients, systolic blood pressure and HOMA2-B were both contributing factors, and ACEIs acted as a protective factor for KSD.

Conclusion

Among Chinese patients with T2DM, approximately 1 in 7 patients was affected by KSD, and the prevalence was twice as high as that in the general Chinese population. The factors associated with KSD varied by sex among T2DM patients. Focusing on these factors is beneficial for reducing the risk of KSD and delaying kidney damage in diabetic patients.

Dietary Care for ADPKD Patients: Current Status and Future Directions

Autosomal dominant polycystic kidney disease (ADPKD) is the most common genetic nephropathy, and tolvaptan is the only therapy available. However, tolvaptan slows but does not stop disease progression, is marred by polyuria, and most patients worldwide lack access. This and recent preclinical research findings on the glucose-dependency of cyst-lining cells have renewed interest in the dietary management of ADPKD. We now review the current dietary recommendations for ADPKD patients according to clinical guidelines, the evidence base for those, and the potential impact of preclinical studies addressing the impact of diet on ADPKD progression. The clinical efficacy of tolvaptan has put the focus on water intake and solute ingestion as modifiable factors that may impact tolvaptan tolerance and ADPKD progression. By contrast, dietary modifications suggested to ADPKD patients, such as avoiding caffeine, are not well supported and their impact is unknown. Recent studies have identified a chronic shift in energy production from mitochondrial oxidative phosphorylation to aerobic glycolysis (Warburg effect) as a contributor to cyst growth, rendering cyst cells exquisitely sensitive to glucose availability. Therefore, low calorie or ketogenic diets have delayed preclinical ADPKD progression. Additional preclinical data warn of potential negative impact of excess dietary phosphate or oxalate in ADPKD progression.

The role of phosphate-containing medications and low dietary phosphorus-protein ratio in reducing intestinal phosphorus load in patients with chronic kidney disease

Chronic kidney disease-mineral and bone disorder (CKD-MBD) is a common complication in patients experiencing end-stage renal disease (ESRD). It includes abnormalities in bone and mineral metabolism and vascular calcification. Hyperphosphatemia is a major risk factor leading to morbidity and mortality in patients with chronic kidney disease. Increased mortality has been observed in patients with ESRD, with serum phosphorus levels of >5.5 mg/dL. Therefore, control of hyperphosphatemia is a major therapeutic goal in the prevention and treatment of CKD-MBD. The treatment of hyperphosphatemia includes decreasing intestinal phosphorus load and increasing renal phosphorus removal. Decreasing the intestinal load of phosphorus plays a major role in the prevention and treatment of CKD-MBD. Among the dietary sources of phosphorus, some of the commonly prescribed medications have also been reported to contain phosphorus. However, drugs are often ignored even though they act as a potential source of phosphorus. Similarly, although proteins are the major source of dietary phosphorus, reducing protein intake can increase mortality in patients with CKD. Recently, the importance of phosphorus/protein ratio in food have been reported to be a sensitive marker for controlling dietary intake of phosphorus. This review summarizes the progress in the research on phosphate content in drugs as an excipient and the various aspects of dietary management of hyperphosphatemia in patients with CKD, with special emphasis on dietary restriction of phosphorus with low dietary phosphate/protein ratio.

Preparation, characterization and physicochemical properties of novel low-phosphorus egg yolk protein

BACKGROUND

In order to supply adequate dietary protein for chronic kidney disease (CKD) patients while simultaneously controlling phosphorus intake, a novel method was developed for the preparation of low-phosphorus egg yolk protein (LPYP) using alkaline protease auxiliary dephosphorization. In addition, the physicochemical properties of LPYP were studied.

RESULTS

In comparison with raw egg yolk protein (RYP) and defatted egg yolk protein (DFYP), LPYP was found to exhibit differences in amino acid (AA) composition, protein secondary structure, surface hydrophobicity, solubility and emulsion stability. It was observed that dephosphorization improved the AA composition, soluble protein content and dissolution stability of egg yolk protein. In addition, phosphate groups were found to impose a critical influence on the emulsion stability and particle size distribution. The final phosphorus to protein mass ratio (P/Pro) of LPYP was 5.64, which met the requirements of a protein diet for CKD patients. The FAO/WHO mode closeness and stability coefficient were 0.958 and 98.62% respectively.

CONCLUSION

LPYP can be effectively obtained by alkaline protease hydrolysis and subsequent alkali dephosphorization. The prepared LPYP can be considered to be a type of safe and suitable protein resource for CKD patients. © 2018 Society of Chemical Industry.

Molecular mechanisms underpinning phosphorus-use efficiency in rice

Orthophosphate (H₂ PO₄^- , Pi) is an essential macronutrient integral to energy metabolism as well as a component of membrane lipids, nucleic acids, including ribosomal RNA, and therefore essential for protein synthesis. The Pi concentration in the solution of most soils worldwide is usually far too low for maximum growth of crops, including rice. This has prompted the massive use of inefficient, polluting, and nonrenewable phosphorus (P) fertilizers in agriculture. We urgently need alternative and more sustainable approaches to decrease agriculture's dependence on Pi fertilizers. These include manipulating crops by (a) enhancing the ability of their roots to acquire limiting Pi from the soil (i.e. increased P-acquisition efficiency) and/or (b) increasing the total biomass/yield produced per molecule of Pi acquired from the soil (i.e. increased P-use efficiency). Improved P-use efficiency may be achieved by producing high-yielding plants with lower P concentrations or by improving the remobilization of acquired P within the plant so as to maximize growth and biomass allocation to developing organs. Membrane lipid remodelling coupled with hydrolysis of RNA and smaller P-esters in senescing organs fuels P remobilization in rice, the world's most important cereal crop.

High Circulatory Phosphate Level Is Associated with Cerebral Small-Vessel Diseases

High phosphate is linked to vascular calcification and endothelial dysfunction; however, its relationship with cerebral small-vessel diseases (CSVDs) is still unknown. Study subjects were prospectively recruited from the community-based I-Lan Longitudinal Aging Study. CSVDs including lacunes, white matter hyperintensities (WMHs), and cerebral microbleeds were evaluated using 3T magnetic resonance images. Multivariate analyses were performed to study the associations between circulatory phosphate level and the presence of CSVDs. In vitro experiments included human brain microvascular endothelial cell (HBMEC) studies and western blotting. The present study included 186 subjects (age [mean ± standard deviation, range] 64.7 ± 8.6, 50-86.8 years; 93 men). Multivariate analysis revealed that circulatory phosphate levels > 3.925 mg/dL were associated with severe WMH with an odds ratio of 3.7 (95% confidence interval = 1.3-10.6) independent of age, sex, traditional vascular risk factors, total cholesterol, renal function, or circulatory calcium level. The in vitro study revealed a downregulation of tight junction protein (zona occludens-1, occludin, and claudin-5) expression in HBMECs after 48 h of treatment with high phosphate (2.5/5 mM). We are the first to report a relationship between circulatory phosphate and CSVDs. Our results suggest that high circulatory phosphate level might be a novel risk factor for CSVD, possibly by impairing BBB structures.

U-shaped relationship between serum phosphate and cardiovascular risk: A retrospective cohort study

Background

High serum phosphate is associated with coronary artery disease in patients with normal and impaired renal function. We asked: Does the serum phosphate range provide prediction of primary cardiac events? We extracted coded primary care data for over 100,000 patients from a database of 135 primary medical practices. Patients aged between 18 and 90 years without pre-existing cardiovascular diagnoses were included from a potential sample of over 1·2 million individuals.

Methods and findings

Binary logistic regression models were used to evaluate the contribution of QRISK factors and electrolytes, including serum phosphate, to cardiac outcomes at five and nine years following an initial phosphate measurement. At five-year review (n = 113,993), low serum phosphate (OR 1·75, 95%CI 1·36–2·23, p<0·001), high-normal (OR 1·50, 95%CI 1·29–1·74, p<0·001), and high serum phosphate (OR 1·74, 95%CI 1·06–2·70, p = 0·02) were long-term risk factors for primary cardiac disease events after adjusting for confounding variables. A similar pattern was seen at our nine-year review.

Conclusions

The extremes of serum phosphate may confer cardiac event risk with a U-shaped trend. In particular, we raise new cardiac concerns for low serum phosphate in the general population. Also, the normal range for phosphate may require redefinition among healthy adults.

Nutrients Turned into Toxins: Microbiota Modulation of Nutrient Properties in Chronic Kidney Disease

In chronic kidney disease (CKD), accumulation of uremic toxins is associated with an increased risk of death. Some uremic toxins are ingested with the diet, such as phosphate and star fruit-derived caramboxin. Others result from nutrient processing by gut microbiota, yielding precursors of uremic toxins or uremic toxins themselves. These nutrients include l-carnitine, choline/phosphatidylcholine, tryptophan and tyrosine, which are also sold over-the-counter as nutritional supplements. Physicians and patients alike should be aware that, in CKD patients, the use of these supplements may lead to potentially toxic effects. Unfortunately, most patients with CKD are not aware of their condition. Some of the dietary components may modify the gut microbiota, increasing the number of bacteria that process them to yield uremic toxins, such as trimethylamine N-Oxide (TMAO), p-cresyl sulfate, indoxyl sulfate and indole-3 acetic acid. Circulating levels of nutrient-derived uremic toxins are associated to increased risk of death and cardiovascular disease and there is evidence that this association may be causal. Future developments may include maneuvers to modify gut processing or absorption of these nutrients or derivatives to improve CKD patient outcomes.

Circulating fibroblast growth factor-23 plasma levels predict adverse cardiovascular outcomes in patients with diabetes mellitus with coronary artery disease

BACKGROUND

Abnormalities of fibroblast growth factor-23 (FGF-23) plasma levels predict adverse outcomes in patients with coronary artery disease. However, FGF-23 has a different behaviour in the presence of type 2 diabetes mellitus (T2D). We explored whether the presence of T2D affects the predictive power of FGF-23.

METHODS

In 704 patients with stable coronary artery disease, FGF-23, calcidiol, parathormone (PTH) and phosphate plasma levels were prospectively assessed. The primary outcome was the development of acute ischemic events (acute coronary syndrome, stroke or transient ischemic attack), heart failure or death.

RESULTS

One hundred seventy-three (24.6%) patients had T2D, without differences in age, sex or estimated glomerular filtration rate as compared with non-diabetic patients. Serum PTH was lower and phosphate higher in T2D than in non-diabetic patients, without differences in FGF-23 or calcidiol levels. During follow-up (2.15 ± 0.99 years), 26 (15.2%) T2D and 51 (9.6%) non-diabetic patients developed the outcome (p = 0.048). T2D patients who developed the outcome had higher FGF-23 [112.0 (59.9, 167.6) vs 68.9 (54.2, 93.0) RU/mL; p = 0.002], PTH [71.3 (47.3, 106.6) vs 51.9 (40.8, 66.2) pg/mL; p = 0.004) and phosphate (3.53 ± 0.71 vs 3.25 ± 0.50 mg/dL; p = 0.017) levels than T2D subjects who remained stable. These differences were not significant in non-diabetic patients. By multivariable Cox proportional hazard model, FGF-23 predicted independently the outcome in T2D patients [hazard ratio = 1.277; 95% CI (1.132, 1.442)] but not in those without T2D.

CONCLUSIONS

FGF-23 plasma levels predict adverse cardiovascular outcomes in coronary artery disease patients who have T2D but not in those without T2D. This finding should be confirmed in larger studies. Copyright © 2016 John Wiley & Sons, Ltd.

Important abnormalities of bone mineral metabolism are present in patients with coronary artery disease with a mild decrease of the estimated glomerular filtration rate

Chronic kidney disease (CKD)-mineral and bone disorder (MBD) is characterized by increased circulating levels of parathormone (PTH) and fibroblast growth factor 23 (FGF23), bone disease, and vascular calcification, and is associated with adverse outcomes. We studied the prevalence of mineral metabolism disorders, and the potential relationship between decreased estimated glomerular filtration rate (eGFR) and CKD-MBD in coronary artery disease patients in a cross-sectional study of 704 outpatients 7.5 ± 3.0 months after an acute coronary syndrome. The mean eGFR (CKD Epidemiology Collaboration formula) was 75.8 ± 19.1 ml/min/1.73 m(2). Our patients showed lower calcidiol plasma levels than a healthy cohort from the same geographical area. In the case of men, this finding was present despite similar creatinine levels in both groups and older age of the healthy subjects. Most patients (75.6 %) had an eGFR below 90 ml/min/1.73 m(2) (eGFR categories G2-G5), with 55.3 % of patients exhibiting values of 60-89 ml/min/1.73 m(2) (G2). PTH (r = -0.3329, p < 0.0001) and FGF23 (r = -0.3641, p < 0.0001) levels inversely correlated with eGFR, whereas calcidiol levels and serum phosphate levels did not. Overall, PTH levels were above normal in 34.9 % of patients. This proportion increased from 19.4 % in G1 category patients, to 33.7 % in G2 category patients and 56.6 % in G3-G5 category patients (p < 0.001). In multivariate analysis, eGFR and calcidiol levels were the main independent determinants of serum PTH. The mean FGF23 levels were 69.9 (54.6-96.2) relative units (RU)/ml, and 33.2 % of patients had FGF23 levels above 85.5 RU/ml (18.4 % in G1 category patients, 30.0 % in G2 category patients, and 59.2 % in G3-G5 category patients; p < 0.001). In multivariate analysis, eGFR was the main predictor of FGF23 levels. Increased phosphate levels were present in 0.7 % of the whole sample: 0 % in G1 category patients, 0.3 % in G2 category patients, and 2.8 % in G3-G5 category patients (p = 0.011). Almost 90 % of patients had calcidiol insufficiency without significant differences among the different degrees of eGFR. In conclusion, in patients with coronary artery disease there is a large prevalence of increased FGF23 and PTH levels. These findings have an independent relationship with decreased eGFR, and are evident at an eGFR of 60-89 ml/min/1.73 m(2). Then, mild decreases in eGFR must be taken in consideration by the clinician because they are associated with progressive abnormalities of mineral metabolism.

Intracellular alkalinization by phosphate uptake via type III sodium-phosphate cotransporter participates in high-phosphate-induced mitochondrial oxidative stress and defective insulin secretion

Elevated plasma levels of inorganic phosphate (P_i) are harmful, causing, among other complications, vascular calcification and defective insulin secretion. The underlying molecular mechanisms of these complications remain poorly understood. We demonstrated the role of P_i transport across the plasmalemma on P_i toxicity in INS-1E rat clonal β cells and rat pancreatic islet cells. Type III sodium-phosphate cotransporters (NaP_is) are the predominant P_i transporters expressed in insulin-secreting cells. Transcript and protein levels of sodium-dependent phosphate transporter 1 and 2 (PiT-1 and -2), isotypes of type III NaP_i, were up-regulated by high-P_i incubation. In patch-clamp experiments, extracellular P_i elicited a Na⁺-dependent, inwardly rectifying current, which was markedly reduced under acidic extracellular conditions. Cellular uptake of P_i elicited cytosolic alkalinization; intriguingly, this pH change facilitated P_i transport into the mitochondrial matrix. Increased mitochondrial P_i uptake accelerated superoxide generation, mitochondrial permeability transition (mPT), and endoplasmic reticulum stress-mediated translational attenuation, leading to reduced insulin content and impaired glucose-stimulated insulin secretion. Silencing of PiT-1/2 prevented P_i-induced superoxide generation and mPT, and restored insulin secretion. We propose that P_i transport across the plasma membrane and consequent cytosolic alkalinization could be a therapeutic target for protection from P_i toxicity in insulin-secreting cells, as well as in other cell types.-Nguyen, T. T., Quan, X., Xu, S., Das, R., Cha, S.-K., Kong, I. D., Shong, M., Wollheim, C. B., Park, K.-S. Intracellular alkalinization by phosphate uptake via type III sodium-phosphate cotransporter participates in high-phosphate-induced mitochondrial oxidative stress and defective insulin secretion.

Design and rationale of a multicentre, randomised, double-blind, placebo-controlled clinical trial to evaluate the effect of vitamin D on ventricular remodelling in patients with anterior myocardial infarction: the VITamin D in Acute Myocardial Infarction (VITDAMI) trial

INTRODUCTION

Decreased plasma vitamin D (VD) levels are linked to cardiovascular damage. However, clinical trials have not demonstrated a benefit of VD supplements on left ventricular (LV) remodelling. Anterior ST-elevation acute myocardial infarction (STEMI) is the best human model to study the effect of treatments on LV remodelling. We present a proof-of-concept study that aims to investigate whether VD improves LV remodelling in patients with anterior STEMI.

METHODS AND ANALYSIS

The VITamin D in Acute Myocardial Infarction (VITDAMI) trial is a multicentre, randomised, double-blind, placebo-controlled trial. 144 patients with anterior STEMI will be assigned to receive calcifediol 0.266 mg capsules (Hidroferol SGC)/15 days or placebo on a 2:1 basis during 12 months.

PRIMARY OBJECTIVE

to evaluate the effect of calcifediol on LV remodelling defined as an increase in LV end-diastolic volume ≥10% (MRI).

SECONDARY OBJECTIVES

change in LV end-diastolic and end-systolic volumes, ejection fraction, LV mass, diastolic function, sphericity index and size of fibrotic area; endothelial function; plasma levels of aminoterminal fragment of B-type natriuretic peptide, galectin-3 and monocyte chemoattractant protein-1; levels of calcidiol (VD metabolite) and other components of mineral metabolism (fibroblast growth factor-23 (FGF-23), the soluble form of its receptor klotho, parathormone and phosphate). Differences in the effect of VD will be investigated according to the plasma levels of FGF-23 and klotho. Treatment safety and tolerability will be assessed. This is the first study to evaluate the effect of VD on cardiac remodelling in patients with STEMI.

ETHICS AND DISSEMINATION

This trial has been approved by the corresponding Institutional Review Board (IRB) and National Competent Authority (Agencia Española de Medicamentos y Productos Sanitarios (AEMPS)). It will be conducted in accordance with good clinical practice (International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use - Good Clinical Practice (ICH-GCP)) requirements, ethical principles of the Declaration of Helsinki and national laws. The results will be submitted to indexed medical journals and national and international meetings.

TRIAL REGISTRATION NUMBER

NCT02548364; Pre-results.

Serum phosphorus, cardiovascular and all-cause mortality in the general population: A meta-analysis

BACKGROUND

The association between elevated serum phosphorus concentration and cardiovascular or all-cause mortality yielded conflicting results.

OBJECTIVE

To assess the association between elevated serum phosphorus concentration and cardiovascular or all-cause mortality in the general population by conducting a meta-analysis.

METHODS

We systematically searched the Pubmed and Embase databases until March 2016 for the prospective studies investigating serum phosphorus concentration and cardiovascular or all-cause mortality in the general population. We pooled risk ratio (RR) and corresponding 95% confidence intervals (CI) for the highest versus the reference category of serum concentration of phosphorus.

RESULTS

Six prospective cohort studies involving 120,269 subjects were identified. When compared the highest with the reference concentration of serum phosphorus, the pooled RR of cardiovascular mortality and all-cause mortality were 1.36 (95% CI 1.07-1.72) and 1.35 for all-cause mortality (95% CI 1.15-1.58), respectively. Stratified analyses revealed that elevated serum phosphorus significantly increased all-cause mortality risk among men (RR 1.33; 95% CI 1.11-1.60), but not in women (RR 1.09; 95% CI 0.89-1.33).

CONCLUSIONS

Elevated serum phosphorus concentration is independently associated with excessive risk of cardiovascular and all-cause mortality in the general population without chronic kidney disease. Serum phosphorus on all-cause mortality risk appears to be pronounced in men but exhibits no clear effect on women. However, gender difference of elevated serum phosphorus on mortality risk should be verified by more prospective studies.

Plasma Levels of Monocyte Chemoattractant Protein-1, n-Terminal Fragment of Brain Natriuretic Peptide and Calcidiol Are Independently Associated with the Complexity of Coronary Artery Disease

Background and Objectives

We investigated the relationship of the Syntax Score (SS) and coronary artery calcification (CAC), with plasma levels of biomarkers related to cardiovascular damage and mineral metabolism, as there is sparse information in this field.

Methods

We studied 270 patients with coronary disease that had an acute coronary syndrome (ACS) six months before. Calcidiol, fibroblast growth factor-23, parathormone, phosphate and monocyte chemoattractant protein-1 [MCP-1], high-sensitivity C-reactive protein, galectin-3, and N-terminal pro-brain natriuretic peptide [NT-proBNP] levels, among other biomarkers, were determined. CAC was assessed by coronary angiogram as low-grade (0–1) and high-grade (2–3) calcification, measured with a semiquantitative scale ranging from 0 (none) to 3 (severe). For the SS study patients were divided in SS<14 and SS≥14. Multivariate linear and logistic regression analyses were performed.

Results

MCP-1 predicted independently the SS (RC = 1.73 [95%CI = 0.08–3.39]; p = 0.040), along with NT-proBNP (RC = 0.17 [95%CI = 0.05–0.28]; p = 0.004), male sex (RC = 4.15 [95%CI = 1.47–6.83]; p = 0.003), age (RC = 0.13 [95%CI = 0.02–0.24]; p = 0.020), hypertension (RC = 3.64, [95%CI = 0.77–6.50]; p = 0.013), hyperlipidemia (RC = 2.78, [95%CI = 0.28–5.29]; p = 0.030), and statins (RC = 6.12 [95%CI = 1.28–10.96]; p = 0.013). Low calcidiol predicted high-grade calcification independently (OR = 0.57 [95% CI = 0.36–0.90]; p = 0.013) along with ST-elevation myocardial infarction (OR = 0.38 [95%CI = 0.19–0.78]; p = 0.006), diabetes (OR = 2.35 [95%CI = 1.11–4.98]; p = 0.028) and age (OR = 1.37 [95%CI = 1.18–1.59]; p<0.001). During follow-up (1.79 [0.94–2.86] years), 27 patients developed ACS, stroke, or transient ischemic attack. A combined score using SS and CAC predicted independently the development of the outcome.

Conclusions

MCP-1 and NT-proBNP are independent predictors of SS, while low calcidiol plasma levels are associated with CAC. More studies are needed to confirm these data.

Targeting local vascular and systemic consequences of inflammation on vascular and cardiac valve calcification

INTRODUCTION

Cardiac valve calcification and vascular calcification (VC) are associated with cardiovascular mortality in the general population and in patients with chronic kidney disease (CKD). CKD, diabetes mellitus, and atherosclerosis are among the causes of systemic inflammation that are associated with VC.

AREAS COVERED

This review collates clinical and experimental evidence that inflammation accelerates VC progression. Specifically, we review the actions of key pro-inflammatory cytokines and inflammation-related transcription factors on VC, and the role played by senescence. Inflammatory cytokines, such as the TNF superfamily and IL-6 superfamily, and inflammation-related transcription factor NF-κB promote calcification in cultured vascular smooth muscle cells, valvular interstitial cells, or experimental animal models through direct effects, but also indirectly by decreasing circulating Fetuin A or Klotho levels.

EXPERT OPINION

Experimental evidence suggests a causal link between inflammation and VC that would change the clinical approach to prevention and treatment of VC. However, the molecular basis remains unclear and little is known about VC in humans treated with drugs targeting inflammatory cytokines. The effect of biologicals targeting TNF-α, RANKL, IL-6, and other inflammatory mediators on VC, in addition to the impact of dietary phosphate in patients with chronic systemic inflammation, requires study.

Use of sevelamer in chronic kidney disease: beyond phosphorus control

Sevelamer is a non-calcium phosphate binder used in advanced chronic kidney disease (CKD) and in dialysis for hyperphosphataemia control. Several experimental, observational studies and clinical trials have shown that sevelamer has pleiotropic effects, beyond hyperphosphataemia control, including actions on inflammation, oxidative stress, lipid profile and atherogenesis, vascular calcification, endothelial dysfunction and the reduction of several uremic toxins. This is the biological basis for its global effect on cardiovascular morbidity and mortality in patients with chronic kidney disease. This review focuses on these pleiotropic actions of sevelamer and their impact on cardiovascular health, with the experience published after more than ten years of clinical expertise.

Mitochondrial oxidative stress mediates high-phosphate-induced secretory defects and apoptosis in insulin-secreting cells

Inorganic phosphate (Pi) plays an important role in cell signaling and energy metabolism. In insulin-releasing cells, Pi transport into mitochondria is essential for the generation of ATP, a signaling factor in metabolism-secretion coupling. Elevated Pi concentrations, however, can have toxic effects in various cell types. The underlying molecular mechanisms are poorly understood. Here, we have investigated the effect of Pi on secretory function and apoptosis in INS-1E clonal β-cells and rat pancreatic islets. Elevated extracellular Pi (1~5 mM) increased the mitochondrial membrane potential (ΔΨm), superoxide generation, caspase activation, and cell death. Depolarization of the ΔΨm abolished Pi-induced superoxide generation. Butylmalonate, a nonselective blocker of mitochondrial phosphate transporters, prevented ΔΨm hyperpolarization, superoxide generation, and cytotoxicity caused by Pi. High Pi also promoted the opening of the mitochondrial permeability transition (PT) pore, leading to apoptosis, which was also prevented by butylmalonate. The mitochondrial antioxidants mitoTEMPO or MnTBAP prevented Pi-triggered PT pore opening and cytotoxicity. Elevated extracellular Pi diminished ATP synthesis, cytosolic Ca(2+) oscillations, and insulin content and secretion in INS-1E cells as well as in dispersed islet cells. These parameters were restored following preincubation with mitochondrial antioxidants. This treatment also prevented high-Pi-induced phosphorylation of ER stress proteins. We propose that elevated extracellular Pi causes mitochondrial oxidative stress linked to mitochondrial hyperpolarization. Such stress results in reduced insulin content and defective insulin secretion and cytotoxicity. Our data explain the decreased insulin content and secretion observed under hyperphosphatemic states.

Stewardship to tackle global phosphorus inefficiency: The case of Europe

The inefficient use of phosphorus (P) in the food chain is a threat to the global aquatic environment and the health and well-being of citizens, and it is depleting an essential finite natural resource critical for future food security and ecosystem function. We outline a strategic framework of 5R stewardship (Re-align P inputs, Reduce P losses, Recycle P in bioresources, Recover P in wastes, and Redefine P in food systems) to help identify and deliver a range of integrated, cost-effective, and feasible technological innovations to improve P use efficiency in society and reduce Europe's dependence on P imports. Their combined adoption facilitated by interactive policies, co-operation between upstream and downstream stakeholders (researchers, investors, producers, distributors, and consumers), and more harmonized approaches to P accounting would maximize the resource and environmental benefits and help deliver a more competitive, circular, and sustainable European economy. The case of Europe provides a blueprint for global P stewardship.

Gastrointestinal Inhibition of Sodium-Hydrogen Exchanger 3 Reduces Phosphorus Absorption and Protects against Vascular Calcification in CKD

In CKD, phosphate retention arising from diminished GFR is a key early step in a pathologic cascade leading to hyperthyroidism, metabolic bone disease, vascular calcification, and cardiovascular mortality. Tenapanor, a minimally systemically available inhibitor of the intestinal sodium-hydrogen exchanger 3, is being evaluated in clinical trials for its potential to (1) lower gastrointestinal sodium absorption, (2) improve fluid overload-related symptoms, such as hypertension and proteinuria, in patients with CKD, and (3) reduce interdialytic weight gain and intradialytic hypotension in ESRD. Here, we report the effects of tenapanor on dietary phosphorous absorption. Oral administration of tenapanor or other intestinal sodium-hydrogen exchanger 3 inhibitors increased fecal phosphorus, decreased urine phosphorus excretion, and reduced [(33)P]orthophosphate uptake in rats. In a rat model of CKD and vascular calcification, tenapanor reduced sodium and phosphorus absorption and significantly decreased ectopic calcification, serum creatinine and serum phosphorus levels, circulating phosphaturic hormone fibroblast growth factor-23 levels, and heart mass. These results indicate that tenapanor is an effective inhibitor of dietary phosphorus absorption and suggest a new approach to phosphate management in renal disease and associated mineral disorders.

Phosphate homeostasis and disorders

Recent studies of inherited disorders of phosphate metabolism have shed new light on the understanding of phosphate metabolism. Phosphate has important functions in the body and several mechanisms have evolved to regulate phosphate balance including vitamin D, parathyroid hormone and phosphatonins such as fibroblast growth factor-23 (FGF23). Disorders of phosphate homeostasis leading to hypo- and hyperphosphataemia are common and have clinical and biochemical consequences. Notably, recent studies have linked hyperphosphataemia with an increased risk of cardiovascular disease. This review outlines the recent advances in the understanding of phosphate homeostasis and describes the causes, investigation and management of hypo- and hyperphosphataemia.

Fibroblast growth factor 23 and left ventricular mass index in maintenance hemodialysis patients: standard versus long nocturnal hemodialysis

Elevated levels of fibroblast growth factor 23 (FGF23) and phosphorus (P) have been linked to greater risks of left ventricular hypertrophy (LVH) in patients with end stage renal disease (ESRD). The aim of this study was to test if differences exist in a long nocturnal HD group in comparison with a group treated with standard daily thrice weekly dialysis. The attempt was to evaluate if elevated FGF-23 levels, intact parathyroid hormone and P might be associated with left ventricular mass index (LVMI). Quantitative echocardiographic analyses were performed at baseline in 50 maintenance HD patients (17 women and 33 men, mean age: 56.4 ± 15.35 years, mean HD vintage: 9.06 ± 8.86 years, all patients are on HD thrice a week-median duration 15 h/week, 10 of them on long nocturnal HD, median duration 24 h/week). LVMIs were calculated. FGF23 was measured in duplicate using a second generation C-terminal enzyme-linked immunosorbent assay and log of FGF-23 values were computed. Mean LVMI was 136.44 ± 44.44 g/m(2) . Serum FGF-23 levels were elevated when compared to population data with preserved kidney function (median 1388.5 RU/mL, range 252 to 24 336 RU/mL). There were no correlations recorded between log FGF-23 levels and LVMI (r = 0.2, P = 0.66). LVMI was significantly lower in HD patients on long nocturnal dialysis procedure (r = -0.31, P = 0.05). Patients treated with long nocturnal HD showed lower LV mass, lower P-values and higher 25-OH-D3 supply. Plasma FGF-23 concentration was comparable between the groups and was not associated with LVMI in our maintenance HD patients.

Osteoprotegerin and kidney disease

Vascular calcification in chronic kidney disease (CKD) patients is associated to increased mortality. Osteoprotegerin (OPG) is a soluble tumor necrosis factor (TNF) superfamily receptor that inhibits the actions of the cytokines receptor activator of nuclear factor kappa-B ligand (RANKL) and TNF-related apoptosis-inducing ligand (TRAIL) by preventing their binding to signaling receptors in the cell membrane. OPG-deficient mice display vascular calcification while OPG prevented calcification of cultured vascular smooth muscle cells and protected kidney cells from TRAIL-induced death. OPG may be a biomarker in patients with kidney disease. Circulating OPG is increased in predialysis, dialysis and transplant CKD patients and may predict vascular calcification progression and patient survival. By contrast, circulating OPG is decreased in nephrotic syndrome. In addition, free and exosome-bound urinary OPG is increased in human kidney disease. Increased urinary OPG has been associated with lupus nephritis activity. Despite the association of high OPG levels with disease, experimental functional information available suggests that OPG might be protective in kidney disease and in vascular injury in the context of uremia. Thus, tissue injury results in increased OPG, while OPG may protect from tissue injury. Recombinant OPG was safe in phase I randomized controlled trials. Further research is needed to fully define the therapeutic and biomarker potential of OPG in patients with kidney disease.

The Association between Fibroblast Growth Factor-23 and Vascular Calcification Is Mitigated by Inflammation Markers

BACKGROUND

Fibroblast growth factor-23 (FGF-23) has been linked to vascular calcification, ventricular hypertrophy and mortality in chronic kidney disease (CKD), although these links may not be direct and independent. Similar grave outcomes are associated with inflammation and oxidative stress in CKD. Recently, accumulating evidence has linked components of phosphate homeostasis to inflammation and oxidative stress. The interaction between the triad of inflammation, FGF-23 and cardiovascular outcomes is underinvestigated.

METHODS

We studied 65 patients with stage 5 CKD on hemodialysis. Serum levels of FGF-23, high-sensitivity C-reactive protein (hsCRP), endogenous soluble receptor of advanced glycation end products (esRAGE), advanced oxidation protein products (AOPP), parathormone, lipids, calcium and phosphorous were measured. The aortic calcification index (ACI) was determined using non-contrast CT scans of the abdominal aorta.

RESULTS

FGF-23 was elevated (mean: 4,681 pg/ml, SD: 3,906) and correlated with hsCRP, esRAGE, AOPP, dialysis vintage and phosphorus in univariate analysis. In multiple regression analysis, hsCRP, AOPP and phosphorus but not esRAGE were all significantly correlated to FGF-23 (R² = 0.7, p < 0.001). In univariate analysis, ACI correlated with hsCRP, esRAGE, FGF-23, dialysis vintage, systolic blood pressure (BP) and serum cholesterol. In multiple regression analysis not including inflammation markers, ACI was associated with FGF-23. However, inclusion of inflammation markers in another multiple regression analyses showed that ACI correlated with hsCRP, BP, dialysis vintage and esRAGE but not with FGF-23 (R² = 0.65, p < 0.001).

CONCLUSION

FGF-23 is strongly correlated to various markers of inflammation and oxidative stress in hemodialysis patients. The association between FGF-23 and vascular calcification was mitigated when corrected for inflammation markers.

Correction of hypocalcemia allows optimal recruitment of FGF-23-dependent phosphaturic mechanisms in acute hyperphosphatemia post-phosphate enema

Both parathyroid hormone (PTH) and fibroblast growth factor 23 (FGF23) are phosphaturic hormones. These hormones should increase in response to phosphate excess. However, they also regulate serum calcium; PTH increases serum calcium concentration and FGF23 suppresses renal production of calcitriol, favoring hypocalcemia. We report the case of an 83-year-old woman with hyperphosphatemia and hypocalcemia resulting from phosphate-containing enemas. PTH and calcitriol increased in response to hypocalcemia, and FGF23 increased in response to hyperphosphatemia. Unexpectedly, peak FGF23 did not coincide with peak serum phosphate. Rather, peak FG23 was observed only after severe hypocalcemia was partially corrected with exogenous calcium administration, even though serum phosphate had been already decreasing for 32 h. Correction of severe hypocalcemia was thus associated with peak FGF23 values and with a precipitous decrease in PTH. Peak FGF23 was followed by an accelerated decrease in serum phosphate and significant phosphaturia. This clinical report is consistent with experimental data in rats showing a blunted FGF23 response to high phosphate in the presence of severe hypocalcemia. Thus, complementary experimental and clinical data suggest that partial correction of severe hypocalcemia is required for optimal FGF23-mediated phosphaturia, which takes place despite correction of PTH levels. We believe this the first human report suggesting blunting of the FGF23 response to high phosphate by severe hypocalcemia.

Assay development of inducible human renal phosphate transporter Npt2A (SLC34A1) in Flp-In-Trex-HEK293 cells

Hyperphosphatemia is associated with severe decline of renal function in chronic kidney disease and elevates cardiovascular mortality. Type II sodium dependent phosphate transporter 2A (Npt2A) plays a major role in renal phosphate reabsorption and could be explored as a target for anti-hyperphosphatemia therapy. Human Npt2A transporter activity was examined upon transfection into CHO, MDCK, HEK293, Flp-In-CHO and Flp-In-HEK293 cells. Only kidney-derived cells expressed functional Npt2A. HEK293 and Flp-In-HEK293 cell lines stably transfected with hNpt2A could be selected, but these cells were inactive in phosphate transport. This suggests that high-level, constitutive Npt2A expression has deleterious effects on the cell. By using the conditional promoter in the Flp-In-Trex vector, functional expression of Npt2A was achieved by doxycycline induction in HEK293 cells. The EGFP tagged and non-tagged, inducible stable hNpt2A-HEK293 cell lines afforded development of a robust phosphate uptake assay mediated by hNpt2A, which can be used to screen hNpt2A inhibitors and inducers of hNpt2A expression. Using this assay, the small molecule LC-1 was identified as a potent inhibitor of hNpt2A, suggesting that it is feasible to develop potent specific hNpt2A inhibitors to control phosphate overloading for hyperphosphatemia therapy.

Serum phosphate as a risk factor for cardiovascular events in people with and without chronic kidney disease: a large community based cohort study

BACKGROUND

Serum phosphate is a known risk factor for cardiovascular events and mortality in people with chronic kidney disease (CKD), however data on the association of these outcomes with serum phosphate in the general population are scarce. We investigate this relationship in people with and without CKD in a large community-based population.

METHODS

Three groups from an adult cohort of the Quality Improvement in Chronic Kidney Disease (QICKD) cluster randomised trial (ISRCTN56023731) were followed over a period of 2.5 years: people with normal renal function (N = 24,184), people with CKD stages 1-2 (N = 20,356), and people with CKD stages 3-5 (N = 13,292). We used a multilevel logistic regression model to determine the association between serum phosphate, in these groups, and a composite outcome of all-cause mortality, cardiovascular events, and advanced coronary artery disease. We adjusted for known cardiovascular risk factors.

FINDINGS

Higher phosphate levels were found to correlate with increased cardiovascular risk. In people with normal renal function and CKD stages 1-2, Phosphate levels between 1.25 and 1.50 mmol/l were associated with increased cardiovascular events; odds ratio (OR) 1.36 (95% CI 1.06-1.74; p = 0.016) in people with normal renal function and OR 1.40 (95% CI 1.09-1.81; p = 0.010) in people with CKD stages 1-2. Hypophosphatemia (<0.75 mmol/l) was associated with fewer cardiovascular events in people with normal renal function; OR 0.59 (95% CI 0.36-0.97; p = 0.049). In people with CKD stages 3-5, hyperphosphatemia (>1.50 mmol/l) was associated with increased cardiovascular risk; OR 2.34 (95% CI 1.64-3.32; p<0.001). Other phosphate ranges were not found to have a significant impact on cardiovascular events in people with CKD stages 3-5.

CONCLUSIONS

Serum phosphate is associated with cardiovascular events in people with and without CKD. Further research is required to determine the mechanisms underlying these associations.

Postoperative hyperphosphatemia significantly associates with adverse survival in colorectal cancer patients

BACKGROUND AND AIM

Hyperphosphatemia has been implicated in the development and treatment of various cancers. However, whether it can be used as a direct prognostic marker of colorectal cancer (CRC) has remained unexplored. Given new insights into the importance of hyperphosphatemia in CRC, we sought to evaluate the association of hyperphosphatemia with the clinical outcomes of this disease.

METHODS

In a retrospective analysis of a well-characterized clinic-based cohort with 1241 CRC patients, we assessed the association of postoperative hyperphosphatemia with patient overall survival.

RESULTS

Postoperative hyperphosphatemia measured within the first month after surgery was significantly associated with CRC survival. Compared to patients with a normal phosphate level, those with hyperphosphatemia exhibited a significant unfavorable overall survival with a hazard ratio (HR) of 1.84 (95% confidence interval [CI] 1.49-2.29, P = 2.6 × 10(-8) (log-rank P = 1.2 × 10(-7) ). Stratified analyses indicated the association was more pronounced in patients with colon (HR = 2.00, 95% CI 1.57-2.56, P = 3.17 × 10(-8) ) but not rectal cancer (HR = 0.96, 95% CI 0.58-1.59, P = 0.889) (P interaction = 0.023), as well as in those not receiving chemotherapy (HR = 2.15, 95% CI 1.59-2.90, P = 6.2 × 10(-7) ) but not in those receiving chemotherapy (HR = 1.30, 95% CI 0.92-1.82, P = 0.136) (P interaction = 0.012). Flexible parametric survival model demonstrated that the increased risk for death conferred by postoperative hyperphosphatemia persisted over 150 months after surgery.

CONCLUSION

Our data indicated that postoperative hyperphosphatemia might be used as a prognostic marker of CRC patients after surgery. Since phosphate level is routinely tested in clinics, it may be incorporated into clinical models to predict CRC survival.

Alkaline Phosphatase, Serum Phosphate, and Incident Cardiovascular Disease and Total Mortality in Older Men

Objective—

We have examined the association between serum phosphate and alkaline phosphatase (ALP) with incident cardiovascular disease (CVD) outcomes and total mortality in older men.

Approach and Results—

A prospective study of 3381 men, aged 60 to 79 years, without a history of myocardial infarction or stroke followed up for an average 11 years during which there were 605 major CVD events (fatal coronary heart disease and nonfatal myocardial infarction, stroke, and CVD death) and 984 total deaths. ALP but not serum phosphate was associated with increased risk of coronary heart disease and overall CVD events which persisted after adjustment for CVD risk factors and markers of inflammation and after exclusion of men with chronic kidney disease (adjusted hazard ratio per SD, 1.19 [1.05, 1.34]; P =0.007 and 1.10 [1.01, 1.21]; P =0.04). In contrast, serum phosphate was only associated with increased CVD mortality owing to noncoronary heart disease or stroke causes (adjusted hazard ratio per SD, 1.35 [1.01, 1.83]; P =0.04). Both raised phosphate and ALP were associated with significantly increased total mortality after full adjustment and exclusion of men with chronic kidney disease.

Conclusions—

ALP but not serum phosphate is associated with coronary heart disease risk in elderly men. High levels of ALP and serum phosphate are both associated with increased total mortality.

Postprandial effects of calcium phosphate supplementation on plasma concentration-double-blind, placebo-controlled cross-over human study

Background

The aim of the present study was to examine the postprandial calcium and phosphate concentrations after supplementation with pentacalcium hydroxy-triphosphate (CaP).

Methods

Ten men participated in this double-blind, placebo-controlled, cross-over study. The participants were divided into two groups. One group consumed bread enriched with CaP (plus 1 g calcium/d) and the other group a placebo product for three weeks. After a two week wash-out, the intervention was switched between the groups for another three weeks. Blood samples were drawn at the beginning (single administration) and at the end (repeated administration) of the intervention periods at 0, 30, 60, 120, 180 and 240 min. Between 0 and 30 min, a test meal, with or without CaP was consumed. The plasma concentrations of calcium and phosphate were examined. One participant dropped out due to personal reasons.

Results

CaP supplementation resulted in a significantly higher plasma calcium concentration after 240 min compared to placebo. After repeated CaP administration, the AUC for the increment in plasma calcium concentration was significantly higher compared to placebo.

After single and repeated CaP supplementation, plasma phosphate concentration significantly decreased after 30, 60, 120 and 180 min compared to 0 min. The placebo administration resulted in significant decreases after 30, 60 and 120 min compared to 0 min.

Conclusion

Our results show that CaP contributes to an adequate calcium supply, but without increasing the plasma concentration of phosphate.

Trial registration

http://www.clinicaltrials.gov; NCT01296997

Management of hyperphosphataemia in chronic kidney disease-challenges and solutions

Hyperphosphataemia is a clinical consequence of the advanced stages of chronic kidney disease (CKD). Considerable evidence points to a role of hyperphosphataemia in the pathogenesis of CKD-associated cardiovascular (CV) complications, including vascular calcification, and with increased all-cause and CV mortality. These observations place management of hyperphosphataemia at the centre of CKD treatment. Although our increased understanding of the physiological role of FGF-23 may provide a long-term alternative biomarker of phosphate load and underlying disease progression, regular determination of serum phosphate is currently the most frequently used parameter to evaluate phosphate load in clinical practice. This review considers the challenges physicians and patients face in trying to control hyperphosphataemia. Amongst these are the limitations of dietary phosphate restriction, giving rise to the need for phosphate binder therapy to maintain serum phosphate control. Once the decision to use phosphate binders has been made, considerations include the relative efficacy, different potential side effects and pill burden associated with various phosphate binders. Although a number of phosphate binders are available, adherence poses a major obstacle to effective treatment. This emphasizes that further improvements to phosphate binder therapy can be made. Evaluation of novel agents and their potential role in the clinic should continue.