Adverse effects of simulated hyper- and hypo-phosphatemia on endothelial cell function and viability

Effect of Lanthanum Carbonate on Serum Phosphate, Oxidative Stress, and Vascular Dysfunction in CKD: A Mechanistic Randomized Controlled Trial

Key Points

A key mechanism contributing to vascular dysfunction in CKD is increased oxidative stress. Lanthanum carbonate did not discernibly affect vascular endothelial function, arterial stiffness, or markers of endothelial oxidative stress.

Background

Vascular endothelial dysfunction and arterial stiffness are common in CKD and independently predict cardiovascular disease. Elevated serum phosphorus, even within the normal range, associates with cardiovascular disease and mortality in CKD. Excess phosphorus may increase oxidative stress leading to vascular dysfunction.

Methods

This is a randomized double-blind trial in which we compared lanthanum carbonate, a noncalcium phosphate binder, with placebo on vascular function and endothelial and circulating measures of oxidative stress and inflammation in 54 participants with CKD 3b–4 and normal phosphorus levels. Primary end points were change in brachial artery flow-mediated dilation (FMDBA) and carotid-to-femoral pulse-wave velocity (cfPWV) at 12 weeks. Mechanistic end points were changes from baseline in FMDBA after ascorbic acid infusion and circulating and endothelial markers of oxidative stress and inflammation.

Results

The age was 65±8 years and eGFR was 38±14 ml/min per 1.73 m2. At 12 weeks, serum phosphorus did not change with lanthanum (3.44±0.47 versus 3.44±0.52 mg/dl; P = 0.94) but tended to increase with placebo (3.42±0.80 versus 3.74±1.26 mg/dl; P = 0.09). FMDBA and cfPWV did not change from baseline in either group: FMDBA lanthanum 3.13%±2.87% to 2.73%±2.48% versus placebo 3.74%±2.86% to 3.09%±2.49% (P = 0.67); CfPWV lanthanum 1214±394 to 1216±322 cm/s versus placebo 993±289 to 977±254 cm/s (P = 0.77). Ascorbic acid infusion to inhibit oxidative stress did not differentially affect FMDBA. Circulating and endothelial markers of oxidative stress and inflammation did not differ between groups.

Conclusions

Lanthanum carbonate did not discernibly affect vascular endothelial function, arterial stiffness, or markers of endothelial oxidative stress among participants with CKD 3b–4 and normophosphatemia.

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

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

Calcium-Phosphorus Product Is Associated with Adverse Prognosis in Hospitalized Patients with Heart Failure and Chronic Kidney Disease

It has been reported that high levels of calcium-phosphorus (Ca-P) product are an indicator of coronary calcification and mortality risk in patients undergoing chronic hemodialysis. In the present study, we aimed to evaluate the significance of Ca-P product to predict the prognosis of patients with heart failure (HF) and chronic kidney disease (CKD). We conducted a prospective observational study of 793 patients with decompensated HF and CKD, and measured the value of Ca-P product. The cut-off value was obtained from the survival classification and regression tree (CART) analysis to predict post-discharge all-cause mortality and/or worsening HF, and the patients were divided into 2 groups: a high group (Ca-P product > 28, n = 594) and a low group (Ca-P product ≤ 28, n = 199). We compared the patient baseline characteristics and post-discharge prognosis between the 2 groups. The age as well as the prevalence of male sex, ischemic etiology, and anemia were significantly higher in the low group than in the high group. In contrast, there was no difference in echocardiographic parameters between the 2 groups. In the Kaplan-Meier analysis (mean follow-up 1089 days), all-cause mortality and/or worsening HF event rates were higher in the low group than in the high group (log-rank P = 0.001). In the multivariable Cox proportional hazard analysis, lower Ca-P product was found to be an independent predictor of all-cause mortality and/or worsening HF (hazard ratio 0.981, P = 0.031). Lower Ca-P product predicts adverse prognosis in patients with HF and CKD.

Impact of Uremic Toxins on Endothelial Dysfunction in Chronic Kidney Disease: A Systematic Review

Patients with chronic kidney disease (CKD) are at a highly increased risk of cardiovascular complications, with increased vascular inflammation, accelerated atherogenesis and enhanced thrombotic risk. Considering the central role of the endothelium in protecting from atherogenesis and thrombosis, as well as its cardioprotective role in regulating vasorelaxation, this study aimed to systematically integrate literature on CKD-associated endothelial dysfunction, including the underlying molecular mechanisms, into a comprehensive overview. Therefore, we conducted a systematic review of literature describing uremic serum or uremic toxin-induced vascular dysfunction with a special focus on the endothelium. This revealed 39 studies analyzing the effects of uremic serum or the uremic toxins indoxyl sulfate, cyanate, modified LDL, the advanced glycation end products N-carboxymethyl-lysine and N-carboxyethyl-lysine, p-cresol and p-cresyl sulfate, phosphate, uric acid and asymmetric dimethylarginine. Most studies described an increase in inflammation, oxidative stress, leukocyte migration and adhesion, cell death and a thrombotic phenotype upon uremic conditions or uremic toxin treatment of endothelial cells. Cellular signaling pathways that were frequently activated included the ROS, MAPK/NF-κB, the Aryl-Hydrocarbon-Receptor and RAGE pathways. Overall, this review provides detailed insights into pathophysiological and molecular mechanisms underlying endothelial dysfunction in CKD. Targeting these pathways may provide new therapeutic strategies reducing increased the cardiovascular risk in CKD.

Impact of different hemodiafiltration solutions on ionemia in long-term CRRT

Critical patients with Acute Kidney Injury (AKI) requiring renal replacement therapy are in most cases eligible only for continuous modalities where the electrolyte balance control is a critical issue. The standard solutions used for hemodiafiltration, containing potassium at 2 mmol/L and no phosphorus, determines during the extended renal replacement therapy hypokalemia and hypophosphatemia. Therefore, solutions containing potassium and phosphate in physiological concentrations were formulated to avoid electrolyte imbalances and reduce ion alterations in prolonged treatments, these solutions are not routinely used in the standard clinical practice. To avoid electrolyte imbalances, we have first introduced in our practice two different solutions and then we have retrospectively analyzed the electrolyte balance upon these two solutions in order to identity the impact of these solutions on potassium and phosphate according to our clinical practice. We retrospectively analyzed 96 patients treated with Continuous Renal Replacement Therapy (CRRT) in the intensive care units (ICU) at Padua's University Hospital to evaluate the role on electrolyte balance of Phoxilium^® and Prismasol 2^® that differ in their composition and the need for electrolytes infusions. In the Phoxilium group the frequency of hypokalemia, hypophosphatemia, and the need of potassium and phosphate replacement were significantly reduced resulting in a reduction in complications, workload, and clinical risk associated with infusions of electrolytes. Our data demonstrated that the use of these two different hemodiafiltration solutions can reduce the occurrence of hypokalemia and hypophosphatemia during CRRT performing personalized treatments without the use of potassium and phosphate infusions.

Hypoxia and chronic kidney disease: Possible mechanisms, therapeutic targets, and relevance to cats

There is mounting evidence that kidney ischaemia/hypoxia plays an important role in feline chronic kidney disease (CKD) development and progression, as well as in human disease and laboratory animal models. Ischaemic acute kidney injury is widely accepted as a cause of CKD in people and data from laboratory species has identified some of the pathways underlying this continuum. Experimental kidney ischaemia in cats results in morphological changes, namely chronic tubulointerstitial inflammation, tubulointerstitial fibrosis, and tubular atrophy, akin to those observed in naturally-occurring CKD. Multiple situations are envisaged that could result in acute or chronic episodes of kidney hypoxia in cats, while risk factors identified in epidemiological studies provide further support that kidney hypoxia contributes to spontaneously occurring feline CKD. This review evaluates the evidence for the role of kidney ischaemia/hypoxia in feline CKD and the proposed mechanisms and consequences of kidney hypoxia. As no effective treatments exist that substantially slow or prevent feline CKD progression, there is a need for novel therapeutic strategies. Targeting kidney hypoxia is one such promising approach, with therapies including those that attenuate the hypoxia-inducible factor (HIF) pathway already being utilised in human CKD.

Calciprotein Particles: Balancing Mineral Homeostasis and Vascular Pathology

[Figure: see text].

Uremic Toxins, Oxidative Stress, Atherosclerosis in Chronic Kidney Disease, and Kidney Transplantation

Patients with chronic kidney disease (CKD) are at a high risk for cardiovascular disease (CVD), and approximately half of all deaths among patients with CKD are a direct result of CVD. The premature cardiovascular disease extends from mild to moderate CKD stages, and the severity of CVD and the risk of death increase with a decline in kidney function. Successful kidney transplantation significantly decreases the risk of death relative to long-term dialysis treatment; nevertheless, the prevalence of CVD remains high and is responsible for approximately 20-35% of mortality in renal transplant recipients. The prevalence of traditional and nontraditional risk factors for CVD is higher in patients with CKD and transplant recipients compared with the general population; however, it can only partly explain the highly increased cardiovascular burden in CKD patients. Nontraditional risk factors, unique to CKD patients, include proteinuria, disturbed calcium, and phosphate metabolism, anemia, fluid overload, and accumulation of uremic toxins. This accumulation of uremic toxins is associated with systemic alterations including inflammation and oxidative stress which are considered crucial in CKD progression and CKD-related CVD. Kidney transplantation can mitigate the impact of some of these nontraditional factors, but they typically persist to some degree following transplantation. Taking into consideration the scarcity of data on uremic waste products, oxidative stress, and their relation to atherosclerosis in renal transplantation, in the review, we discussed the impact of uremic toxins on vascular dysfunction in CKD patients and kidney transplant recipients. Special attention was paid to the role of native and transplanted kidney function.

Phosphate as a Signaling Molecule

Phosphorus plays a vital role in diverse biological processes including intracellular signaling, membrane integrity, and skeletal biomineralization; therefore, the regulation of phosphorus homeostasis is essential to the well-being of the organism. Cells and whole organisms respond to changes in inorganic phosphorus (Pi) concentrations in their environment by adjusting Pi uptake and altering biochemical processes in cells (local effects) and distant organs (endocrine effects). Unicellular organisms, such as bacteria and yeast, express specific Pi-binding proteins on the plasma membrane that respond to changes in ambient Pi availability and transduce intracellular signals that regulate the expression of genes involved in cellular Pi uptake. Multicellular organisms, including humans, respond at a cellular level to adapt to changes in extracellular Pi concentrations and also have endocrine pathways which integrate signals from various organs (e.g., intestine, kidneys, parathyroid glands, bone) to regulate serum Pi concentrations and whole-body phosphorus balance. In mammals, alterations in the concentrations of extracellular Pi modulate type III sodium-phosphate cotransporter activity on the plasma membrane, and trigger changes in cellular function. In addition, elevated extracellular Pi induces activation of fibroblast growth factor receptor, Raf/mitogen-activated protein kinase/ERK kinase (MEK)/extracellular signal-regulated kinase (ERK) and Akt pathways, which modulate gene expression in various mammalian cell types. Excessive Pi exposure, especially in patients with chronic kidney disease, leads to endothelial dysfunction, accelerated vascular calcification, and impaired insulin secretion.

Hyperphosphatemia Drives Procoagulant Microvesicle Generation in the Rat Partial Nephrectomy Model of CKD

Hyperphosphatemia has been proposed as a cardiovascular risk factor, contributing to long-term vascular calcification in hyperphosphatemic Chronic Kidney Disease (CKD) patients. However, more recent studies have also demonstrated acute effects of inorganic phosphate (Pi) on endothelial cells in vitro, especially generation of pro-coagulant endothelial microvesicles (MV). Hitherto, such direct effects of hyperphosphatemia have not been reported in vivo. Thirty-six male Sprague-Dawley rats were randomly allocated to three experimental groups: (1) CKD induced by partial nephrectomy receiving high (1.2%) dietary phosphorus; (2) CKD receiving low (0.2%) dietary phosphorus; and (3) sham-operated controls receiving 1.2% phosphorus. After 14 days the animals were sacrificed and plasma MVs counted by nanoparticle tracking analysis. MVs isolated by centrifugation were assayed for pro-coagulant activity by calibrated automated thrombography, and relative content of endothelium-derived MVs was assessed by anti-CD144 immunoblotting. When compared with sham controls, high phosphorus CKD rats were shown to be hyperphosphatemic (4.11 ± 0.23 versus 2.41 ± 0.22 mM Pi, p < 0.0001) with elevated total plasma MVs (2.24 ± 0.37 versus 1.31 ± 0.24 × 10⁸ per ml, p < 0.01), showing increased CD144 expression (145 ± 25% of control value, p < 0.0001), and enhanced procoagulant activity (18.06 ± 1.75 versus 4.99 ± 1.77 nM peak thrombin, p < 0.0001). These effects were abolished in the low phosphorus CKD group. In this rat model, hyperphosphatemia (or a Pi-dependent hormonal response derived from it) is sufficient to induce a marked increase in circulating pro-coagulant MVs, demonstrating an important link between hyperphosphatemia and thrombotic risk in CKD.

Inorganic Phosphate (Pi) Signaling in Endothelial Cells: A Molecular Basis for Generation of Endothelial Microvesicles in Uraemic Cardiovascular Disease

Hyperphosphataemia increases cardiovascular mortality in patients with kidney disease. Direct effects of high inorganic phosphate (Pi) concentrations have previously been demonstrated on endothelial cells (ECs), including generation of procoagulant endothelial microvesicles (MVs). However, no mechanism directly sensing elevated intracellular Pi has ever been described in mammalian cells. Here, we investigated the hypothesis that direct inhibition by Pi of the phosphoprotein phosphatase PP2A fulfils this sensing role in ECs, culminating in cytoskeleton disruption and MV generation. ECs were treated with control (1 mM [Pi]) vs. high (2.5 mM [Pi]), a condition that drives actin stress fibre depletion and MV generation demonstrated by confocal microscopy of F-actin and NanoSight Nanoparticle tracking, respectively. Immuno-blotting demonstrated that high Pi increased p-Src, p-PP2A-C and p-DAPK-1 and decreased p-TPM-3. Pi at 100 μM directly inhibited PP2A catalytic activity. Inhibition of PP2A enhanced inhibitory phosphorylation of DAPK-1, leading to hypophosphorylation of Tropomyosin-3 at S284 and MV generation. p-Src is known to perform inhibitory phosphorylation on DAPK-1 but also on PP2A-C. However, PP2A-C can itself dephosphorylate (and therefore inhibit) p-Src. The direct inhibition of PP2A-C by Pi is, therefore, amplified by the feedback loop between PP2A-C and p-Src, resulting in further PP2A-C inhibition. These data demonstrated that PP2A/Src acts as a potent sensor and amplifier of Pi signals which can further signal through DAPK-1/Tropomyosin-3 to generate cytoskeleton disruption and generation of potentially pathological MVs.

DAXX mediates high phosphate-induced endothelial cell apoptosis in vitro through activating ERK signaling

BACKGROUD AND PURPOSE

Hyperphosphatemia, which is a high inorganic phosphate (Pi) level in the serum, promotes endothelial cells dysfunction and is associated with cardiovascular diseases in patients with chronic kidney diseases (CKD). However, the underlying mechanism of high Pi-induced endothelia cell apoptosis remains unclear.

METHODS

Human umbilical vein endothelial cells (HUVECs) were treated with normal Pi (1.0 mM) and high Pi (3.0 mM), and then cell apoptosis, abnormal gene expression and potential signaling pathway involvement in simulated hyperphosphatemia were examined using flow cytometry, quantitative PCR (qPCR) and western blot analysis. A two-step 5/6 nephrectomy was carried out to induce CKD and biochemical measurements were taken.

RESULTS

The rat model of CKD revealed that hyperphosphatemia is correlated with an increased death-domain associated protein (DAXX) expression in endothelial cells. In vitro, high Pi increased the mRNA and protein expression level of DAXX in HUVECs, effects that were reversed by additional phosphonoformic acid treatment. Functionally, high Pi resulted in a significantly increased apoptosis in HUVECs, whereas DAXX knockdown markedly repressed high Pi-induced cell apoptosis, indicating that DAXX mediated high Pi-induced endothelial cell apoptosis. High Pi treatment and DAXX overexpression induced the activation of extracellular regulated protein kinases (ERKs), while DAXX knockdown inhibited high Pi-induced ERKs activation. Finally, we demonstrated that DAXX overexpression induced HUVECs apoptosis in the presence of normal Pi, whereas additional treatment with U0126 (a specific ERK inhibitor) reversed that effect.

CONCLUSION

Upregulated DAXX promoted high Pi-induced HUVECs apoptosis by activating ERK signaling and indicated that the DAXX/ERK signaling axis may be served as a potential target for CKD therapy.

Uremic Toxins and Vascular Dysfunction

Vascular dysfunction is an essential element found in many cardiovascular pathologies and in pathologies that have a cardiovascular impact such as chronic kidney disease (CKD). Alteration of vasomotricity is due to an imbalance between the production of relaxing and contracting factors. In addition to becoming a determining factor in pathophysiological alterations, vascular dysfunction constitutes the first step in the development of atherosclerosis plaques or vascular calcifications. In patients with CKD, alteration of vasomotricity tends to emerge as being a new, less conventional, risk factor. CKD is characterized by the accumulation of uremic toxins (UTs) such as phosphate, para-cresyl sulfate, indoxyl sulfate, and FGF23 and, consequently, the deleterious role of UTs on vascular dysfunction has been explored. This accumulation of UTs is associated with systemic alterations including inflammation, oxidative stress, and the decrease of nitric oxide production. The present review proposes to summarize our current knowledge of the mechanisms by which UTs induce vascular dysfunction.

Should We Consider the Cardiovascular System While Evaluating CKD-MBD?

Cardiovascular (CV) disease is highly prevalent in the population with chronic kidney disease (CKD), where the risk of CV death in early stages far exceeds the risk of progression to dialysis. The presence of chronic kidney disease-mineral and bone disorder (CKD-MBD) has shown a strong correlation with CV events and mortality. As a non-atheromatous process, it could be partially explained why standard CV disease-modifying drugs do not provide such an impact on CV mortality in CKD as observed in the general population. We summarize the potential association of CV comorbidities with the older (parathyroid hormone, phosphate) and newer (FGF23, Klotho, sclerostin) CKD-MBD biomarkers.

Clinically-defined preoperative serum phosphorus abnormalities and outcomes of coronary artery bypass grafting: Retrospective analysis using inverse probability weighting adjustment

BACKGROUND

Serum phosphorus is a well-known marker of vascular calcification, but the effects of serum phosphorus abnormalities defined by clinical criteria on the outcomes of coronary artery bypass grafting (CABG) remain unclear. We aimed to evaluate whether preoperative serum phosphorus abnormalities defined based on clinical criteria are associated with outcomes of CABG using a relatively new statistical technique, inverse probability weighting (IPW) adjustment.

METHODS

From January 2001 to December 2014, 4,989 consecutive patients who underwent CABG were stratified into normal (2.5-4.5 mg/dl; n = 4,544), hypophosphatemia (<2.5 mg/dl; n = 238), or hyperphophatemia (>4.5 mg/dl; n = 207) groups depending on preoperative serum phosphorus level.

RESULTS

The primary outcome was all-cause death during a median follow-up of 48 months. Secondary outcomes were cardiovascular death, graft failure, myocardial infarction, repeat revascularization, and stroke. In multivariate Cox analysis, preoperative hypophosphatemia was significantly associated with all-cause death (hazard ratio [HR] 1.76; 95% confidence interval [CI] 1.13-2.76; P = 0.01). However, this association varied depending on chronic kidney disease and emergent operation (p for interaction = 0.05 and 0.03, respectively). In addition, analysis after IPW adjustment demonstrated that preoperative serum phosphorus abnormalities were not significantly associated with all-cause death (P = 0.08) or any secondary outcomes except graft failure. Graft failure was significantly associated with preoperative hypophosphatemia (HR 2.51; 95% CI 1.37-4.61; P = 0.003).

CONCLUSION

Our study showed that preoperative serum phosphorus abnormalities in clinical criteria were not associated with outcomes after CABG except for graft failure. And, the association of hypophosphatemia with graft failure remains to be evaluated.

Association between Serum Indoxyl Sulfate Levels and Endothelial Function in Non-Dialysis Chronic Kidney Disease

Indoxyl sulfate (IS), a product metabolized from tryptophan, is negatively correlated with renal function and cardiovascular diseases in patients with chronic kidney disease (CKD). We investigated the association between serum IS levels and endothelial function in patients with CKD. Fasting blood samples were obtained from 110 patients with stages 3–5 CKD. The endothelial function, represented by vascular reactivity index (VRI), was measured non-invasively using digital thermal monitoring. Serum IS levels were determined using liquid chromatography–mass spectrometry. Twenty-one (19.1%), 36 (32.7%), and 53 (48.2%) patients had poor (VRI < 1.0), intermediate (1.0 ≤ VRI < 2.0), and good (VRI ≥ 2.0) vascular reactivity. By univariate linear regression analysis, a higher prevalence of smoking, advanced age, higher systolic, and diastolic blood pressure (DBP), elevated levels of serum phosphorus, blood urea nitrogen, creatinine, and IS were negatively correlated with VRI values, but estimated glomerular filtration rate negatively associated with VRI values. After being adjusted by using multivariate stepwise linear regression analysis, DBP and IS levels were significantly negatively associated with VRI values in CKD patients. We concluded that IS level associated inversely with VRI values and had a modulating role in endothelial function in patients with stages 3–5 CKD.

Serum Phosphate and Microvascular Function in a Population-Based Cohort

BACKGROUND AND OBJECTIVES

Higher serum phosphate is associated with cardiovascular events and all-cause mortality. Explanations of this association have focused on large vessel calcification and stiffness. Studies suggest that a higher serum phosphate induces microvascular dysfunction, but relationships in humans with direct measures of microvascular function are lacking.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We performed a cross-sectional analysis of 3189 community-living participants that underwent skin capillaroscopy, laser-Doppler flowmetry, and flicker light-induced retinal vessel responses. We used linear regression to assess the association between serum phosphate and each microvascular outcome. The primary outcome was skin capillary recruitment during postocclusive peak reactive hyperemia by capillaroscopy. Secondary outcomes included capillary recruitment during venous congestion, heat-induced skin hyperemic response, flicker light-induced retinal arteriolar, and venular dilation.

RESULTS

The mean age of the cohort was 59±8 years, 48% were women, 7% had an eGFR <60 ml/min per 1.73 m², and the mean serum phosphate concentration was 3.2±0.5 mg/dl. A 1 mg/dl higher serum phosphate was independently associated with a 5.0% lower postocclusive capillary recruitment (95% CI, -10.0% to -0.1%). Results were similar for capillary recruitment with venous congestion (-4.5%; 95% CI, -9.8% to 0.7%). A 1 mg/dl higher serum phosphate was also independently associated with a 0.23% lower retinal venular dilation in response to flicker light (95% CI, -0.44% to -0.02%). A higher serum phosphate was not associated with change in flicker light-induced retinal arteriolar dilation or heat-induced skin hyperemic response, however a higher serum phosphate was associated with a lower heat-induced skin hyperemic response among men (-149% [95% CI, -260 to -38] per 1 mg/dl higher serum phosphate) but not women (P interaction, 0.01).

CONCLUSIONS

Higher serum phosphate concentrations, even within the normal range, are associated with microvascular dysfunction in community-living individuals.

PODCAST

This article contains a podcast at https://www.asn-online.org/media/podcast/CJASN/2019_09_20_CJN02610319.mp3.

Atherosclerosis in Chronic Kidney Disease: More, Less, or Just Different?

Patients with chronic kidney disease (CKD) are at an increased risk of premature mortality, mainly from cardiovascular causes. The association between CKD on hemodialysis and accelerated atherosclerosis was described >40 years ago. However, more recently, it has been suggested that the increase in atherosclerosis risk is actually observed in early CKD stages, remaining stable thereafter. In this regard, interventions targeting the pathogenesis of atherosclerosis, such as statins, successful in the general population, have failed to benefit patients with very advanced CKD. This raises the issue of the relative contribution of atherosclerosis versus other forms of cardiovascular injury such as arteriosclerosis or myocardial injury to the increased cardiovascular risk in CKD. In this review, the pathophysiogical contributors to atherosclerosis in CKD that are shared with the general population, or specific to CKD, are discussed. The NEFRONA study (Observatorio Nacional de Atherosclerosis en NEFrologia) prospectively assessed the prevalence and progression of subclinical atherosclerosis (plaque in vascular ultrasound), confirming an increased prevalence of atherosclerosis in patients with moderate CKD. However, the adjusted odds ratio for subclinical atherosclerosis increased with CKD stage, suggesting a contribution of CKD itself to subclinical atherosclerosis. Progression of atherosclerosis was closely related to CKD progression as well as to the baseline presence of atheroma plaque, and to higher phosphate, uric acid, and ferritin and lower 25(OH) vitamin D levels. These insights may help design future clinical trials of stratified personalized medicine targeting atherosclerosis in patients with CKD. Future primary prevention trials should enroll patients with evidence of subclinical atherosclerosis and should provide a comprehensive control of all known risk factors in addition to testing any additional intervention or placebo.

The Influence of Physicochemical Properties of Biomimetic Hydroxyapatite on the In Vitro Behavior of Endothelial Progenitor Cells and Their Interaction with Mesenchymal Stem Cells

Calcium phosphate (CaP) substrates are successfully used as bone grafts due to their osteogenic properties. However, the influence of the physicochemical features of CaPs in angiogenesis is frequently neglected despite it being a crucial process for bone regeneration. The present work focuses on analyzing the effects of textural parameters of biomimetic calcium deficient hydroxyapatite (CDHA) and sintered beta-tricalcium phosphate (β-TCP), such as specific surface area, surface roughness, and microstructure, on the behavior of rat endothelial progenitor cells (rEPCs) and their crosstalk with rat mesenchymal stem cells (rMSCs). The higher reactivity of CDHA results in low proliferation rates in monocultured and cocultured systems. This effect is especially pronounced for rMSCs alone, and for CDHA with a fine microstructure. In terms of angiogenic and osteogenic gene expressions, the upregulation of particular genes is especially enhanced for needle-like CDHA compared to plate-like CDHA and β-TCP, suggesting the importance not only of the chemistry of the substrate, but also of its textural features. Moreover, the coculture of rEPCs and rMSCs on needle-like CDHA results in early upregulation of osteogenic modulator, i.e., protein deglycase 1 might be a possible cause of overexpression of osteogenic-related genes on the same substrate.

Salvianolic acid B attenuates experimental pulmonary inflammation by protecting endothelial cells against oxidative stress injury

Endothelial cell injury and subsequent inflammation play pivotal roles in the pathogenesis of pulmonary fibrosis, a progressive and fatal disorder. We found previously that salvianolic acid B (SAB) attenuated experimental pulmonary fibrosis. Pulmonary fibrosis is driven by inflammation, but the anti-inflammatory role and mechanism of SAB on the treatment of pulmonary fibrosis is still unknown. Here, our in vivo studies showed that SAB had a strong anti-inflammatory effect on bleomycin-instilled mice by inhibiting inflammatory cell infiltration and inflammatory cytokine production. Moreover, SAB protected endothelial cells against oxidative stress injury and inhibited endothelial cell apoptosis in bleomycin-treated mice. The in vitro studies also showed that SAB decreased the H₂O₂-induced overproduction of reactive oxygen species to protect EA.hy926 endothelial cells from oxidative damage, and further inhibited H₂O₂-induced permeability and overexpression of pro-inflammatory molecules. The next studies revealed that SAB inhibited the H₂O₂-induced cell apoptosis and attenuated the decrease of tight junction-related gene expression, resulting in a decrease of the endothelial permeability in injured endothelial cells. Furthermore, Western blot analysis suggested that SAB decreased endothelial cell permeability and expression of pro-inflammatory cytokines by inhibiting MAPK and NF-κB signaling pathways. Taken together, these data indicate that SAB exerted anti-inflammatory roles in pulmonary fibrosis by protection of the endothelial cells against oxidative stress injury, mediated by inhibition of endothelial permeability and expression of pro-inflammatory cytokine via the MAPK and NF-κB signaling pathways.

Impaired intestinal immune barrier and physical barrier function by phosphorus deficiency: Regulation of TOR, NF-κB, MLCK, JNK and Nrf2 signalling in grass carp (Ctenopharyngodon idella) after infection with Aeromonas hydrophila

In aquaculture, the occurrence of enteritis has increased and dietary nutrition is considered as one of the major strategies to solve this problem. In the present study, we assume that dietary phosphorus might enhance intestinal immune barrier and physical barrier function to reduce the occurrence of enteritis in fish. To test this assumption, a total of 540 grass carp (Ctenopharyngodon idella) were investigated by feeding graded levels of available phosphorus (0.95-8.75 g/kg diet) and then infection with Aeromonas hydrophila. The results firstly showed that phosphorus deficiency decreased the ability to combat enteritis, which might be related to the impairment of intestinal immune barrier and physical barrier function. Compared with optimal phosphorus level, phosphorus deficiency decreased fish intestinal antimicrobial substances activities or contents and down-regulated antimicrobial peptides mRNA levels leading to the impairment of intestinal immune response. Phosphorus deficiency down-regulated fish intestinal anti-inflammatory cytokines mRNA levels and up-regulated the mRNA levels of pro-inflammatory cytokines [except IL-1β and IL-12p35 in distal intestine (DI) and IL-12p40] causing aggravated of intestinal inflammatory responses, which might be related to the signalling molecules target of rapamycin and nuclear factor kappa B. In addition, phosphorus deficiency disturbed fish intestinal tight junction function and induced cell apoptosis as well as oxidative damage leading to impaired of fish intestinal physical barrier function, which might be partially associated with the signalling molecules myosin light chain kinase, c-Jun N-terminal protein kinase and NF-E2-related factor 2, respectively. Finally, based on the ability to combat enteritis, dietary available phosphorus requirement for grass carp (254.56-898.23 g) was estimated to be 4.68 g/kg diet.

Deleterious effects of phosphate on vascular and endothelial function via disruption to the nitric oxide pathway

Background

Hyperphosphataemia is an independent risk factor for accelerated cardiovascular disease in chronic kidney disease (CKD), although the mechanism for this is poorly understood. We investigated the effects of sustained exposure to a high-phosphate environment on endothelial function in cellular and preclinical models, as well as in human subjects.

Methods

Resistance vessels from rats and humans (± CKD) were incubated in a normal (1.18 mM) or high (2.5 mM) phosphate concentration solution and cells were cultured in normal- (0.5 mM) or high-phosphate (3 mM) concentration media. A single-blind crossover study was performed in healthy volunteers, receiving phosphate supplements or a phosphate binder (lanthanum), and endothelial function measured was by flow-mediated dilatation.

Results

Endothelium-dependent vasodilatation was impaired when resistance vessels were exposed to high phosphate; this could be reversed in the presence of a phosphodiesterase-5-inhibitor. Vessels from patients with CKD relaxed normally when incubated in normal-phosphate conditions, suggesting that the detrimental effects of phosphate may be reversible. Exposure to high-phosphate disrupted the whole nitric oxide pathway with reduced nitric oxide and cyclic guanosine monophosphate production and total and phospho endothelial nitric oxide synthase expression. In humans, endothelial function was reduced by chronic phosphate loading independent of serum phosphate, but was associated with higher urinary phosphate excretion and serum fibroblast growth factor 23.

Conclusions

These directly detrimental effects of phosphate, independent of other factors in the uraemic environment, may explain the increased cardiovascular risk associated with phosphate in CKD.

Hematological, biochemical, and histopathological impacts of barium chloride and barium carbonate accumulation in soft tissues of male Sprague-Dawley rats

The present study was designed to investigate the hematotoxicity, sero-biochemical and histological changes due to the accumulation of BaCl₂ and BaCO₃, the most important barium salts in our daily lives, in different soft tissues including the liver, kidney, heart, and spleen of adult rats after an oral exposure for 30 consecutive days, and to explain the different mechanisms by which this metal can exert these impacts. For this purpose, adult male rats were divided into three main groups of 15 animals each: group I, serving as controls, group II, receiving BaCl₂ orally in a dose of 179 mg barium/kg b.wt, and group III, receiving BaCO₃ orally in a dose of 418 mg barium/kg b.wt. for 30 consecutive days. Obviously, normocytic normochromic anemia was evident in both barium groups. Serum biochemical analysis revealed significant declines in glutathione peroxidase, catalase, superoxide dismutase, and urea with significant elevations in malondialdehyde, lactate dehydrogenase, and creatine kinase levels. Hyperphosphatemia, hypokalemia, hypocalcemia, and hypochloremia were also evident in both barium groups. Besides, residual analysis of both barium salts in different body organs revealed significantly abundant barium residues in the liver, spleen, heart, and kidney, respectively in both barium salts groups. Moreover, splenic tissue showed hemosiderosis, peritubular congestion, and necrotic glomeruli with intratubular hemorrhage. Sever subepicardial congestion with intramuscular edema was evident in the heart. In conclusion, BaCl₂ and BaCO₃ were able to deliver mortalities, antioxidant enzymes exhaustion, and a sort of normocytic normochromic anemia, as well as marked disturbances in cardiac, hepatic, and renal functions due to the accumulation of these two salts in the soft tissues. Therefore, these results demonstrate the unrecognized toxicity of those two barium salts due to their accumulation in various soft tissues of the body and so, this needs to reconsider about barium exposure.

Hyperphosphatemia induces senescence in human endothelial cells by increasing endothelin-1 production

Hyperphosphatemia is related to some pathologies, affecting vascular cell behavior. This work analyzes whether high concentration of extracellular phosphate induces endothelial senescence through up‐regulation of endothelin‐1 (ET‐1), exploring the mechanisms involved. The phosphate donor β‐glycerophosphate (BGP) in human endothelial cells increased ET‐1 production, endothelin‐converting enzyme‐1 (ECE‐1) protein, and mRNA expression, which depend on the AP‐1 activation through ROS production. In parallel, BGP also induced endothelial senescence by increasing p16 expression and the senescence‐associated β‐galactosidase (SA‐ß‐GAL) activity. ET‐1 itself was able to induce endothelial senescence, increasing p16 expression and SA‐ß‐GAL activity. In addition, senescence induced by BGP was blocked when different ET‐1 system antagonists were used. BGP increased ROS production at short times, and the presence of antioxidants prevented the effect of BGP on AP1 activation, ECE‐1 expression, and endothelial senescence. These findings were confirmed in vivo with two animal models in which phosphate serum levels were increased: seven/eight nephrectomized rats as chronic kidney disease models fed on a high phosphate diet and aged mice. Both models showed hyperphosphatemia, higher levels of ET‐1, and up‐regulation in aortic ECE‐1, suggesting a direct relationship between hyperphosphatemia and ET‐1. Present results point to a new and relevant role of hyperphosphatemia on the regulation of ET‐1 system and senescence induction at endothelial level, both in endothelial cells and aorta from two animal models. The mechanism involved showed a higher ROS production, which probably activates AP‐1 transcription factor and, as a result, ECE‐1 expression, increasing ET‐1 synthesis, which in consequence induces endothelial senescence.

α-Klotho expression determines nitric oxide synthesis in response to FGF-23 in human aortic endothelial cells

Endothelial cells (ECs) express fibroblast growth factor (FGF) receptors and are metabolically active after treatment with FGF-23. It is not known if this effect is α-Klotho independent or mediated by humoral or endogenous endothelial α-Klotho. In the present study, we aimed to characterize EC α-Klotho expression within the human vascular tree and to investigate the potential role of α-Klotho in determining FGF-23 mediated EC regulation. Human tissue and ECs from various organs were used for immunohistochemistry and Western blot. Primary cultures of human aortic endothelial cells (HAECs) and human brain microvascular endothelial cells (HBMECs) were used to generate in vitro cell models. We found endogenous α-Klotho expression in ECs from various organs except in microvascular ECs from human brain. Furthermore, FGF-23 stimulated endothelial nitric oxide synthase (eNOS) expression, nitric oxide (NO) production, and cell proliferation in HAECs. Interestingly, these effects were not observed in our HBMEC model in vitro. High phosphate treatment and endothelial α-Klotho knockdown mitigated FGF-23 mediated eNOS induction, NO production, and cell proliferation in HAECs. Rescue treatment with soluble α-Klotho did not reverse endothelial FGF-23 resistance caused by reduced or absent α-Klotho expression in HAECs. These novel observations provide evidence for differential α-Klotho functional expression in the human endothelium and its presence may play a role in determining the response to FGF-23 in the vascular tree. α-Klotho was not detected in cerebral microvascular ECs and its absence may render these cells nonresponsive to FGF-23.

Effect of dietary phosphorus deficiency on the growth, immune function and structural integrity of head kidney, spleen and skin in young grass carp (Ctenopharyngodon idella)

This study evaluates the effects of dietary phosphorus on the growth, immune function and structural integrity (head kidney, spleen and skin) of young grass carp (Ctenopharyngodon idella) that were fed graded levels of available phosphorus (0.95-8.75 g/kg diet). Results indicated that phosphorus deficiency decreased the growth performance of young grass carp. In addition, the results first demonstrated that compared with the optimal phosphorus level, phosphorus deficiency depressed the lysozyme (LZ) and acid phosphatase (ACP) activities and the complement 3 (C3), C4 and immunoglobulin M (IgM) contents, and down-regulated the mRNA levels of antimicrobial peptides, anti-inflammatory cytokines, inhibitor of κBα (IκBα) and target of rapamycin (TOR), whereas it up-regulated pro-inflammatory cytokines, nuclear factor kappa B (NF-κB) p65 and NF-κB p52 mRNA levels to decrease fish head kidney and spleen immune functions. Moreover, phosphorus deficiency up-regulated the mRNA levels of Kelch-like-ECH-associated protein 1a (Keap1a), Fas ligand (FasL), apoptotic protease activating factor-1 (Apaf-1), Bcl-2 associated X protein (Bax), caspase -2, -3, -7, -8 and -9, p38 mitogen-activated protein kinase (MAPK) and myosin light chain kinase (MLCK), whereas it depressed the glutathione (GSH) contents and antioxidant enzymes activities, and down-regulated the mRNA levels of antioxidant enzymes, NF-E2-related factor 2 (Nrf2), B-cell lymphoma protein-2 (Bcl-2), myeloid cell leukemia-1 (Mcl-1) and tight junction complexes to attenuate fish head kidney and spleen structural integrity. In addition, phosphorus deficiency increased skin hemorrhage and lesions morbidity. Finally, based on the percent weight gain (PWG) and the ability to combat skin hemorrhage and lesions, the dietary available phosphorus requirements for young grass carp (254.56-898.23 g) were estimated to be 4.10 and 4.13 g/kg diet, respectively. In summary, phosphorus deficiency decreases the growth performance, and impairs immune function and structural integrity in the head kidney, spleen and skin of young grass carp.

Protein Arrays III: Reverse-Phase Protein Arrays

The reverse-phase protein array (RPPA) is to use highly specific antibodies to interrogate pan or posttranslationally modified protein targets, such as phosphorylated proteins, particularly the proteins involved in cell signaling pathways. In this protocol we will cover the preparation of cell (or tissue) lysates, sample printing, antibody validation, antibody interrogation, signal amplification steps, imaging and data analysis. In this protocol, colorimetric catalyzed signal amplification (CSA) chemistry, fluorescence and near-infrared (NIR) based detection methods will be described.

Systems biological understanding of the regulatory network and the possible therapeutic strategies for vascular calcification

Since there is no precise therapy for treating vascular calcification by directly targeting the vascular wall, we aim to unveil novel drug targets through mining the molecular effect of a high phosphate environment on vascular cells through computational methods. Here, we hypothesize that manipulation of the vascular pathogenic network by small molecule therapeutics predicted from prior knowledge might offer great promise. With this, we intend to understand the publicly available transcriptomic data of vascular smooth muscle cells and endothelial cells exposed to the high phosphate induced vascular calcification milieu and to re-examine the above published experiments for reasons different from those examined in the previous studies through multilevel systems biological understanding. Hence, in this study the differentially expressed genes were subjected to both upstream and downstream network analysis through multiple standalone software and web servers. To provide an insight into causal signaling, we simultaneously predicted upstream regulatory layers through transcription factor and kinome enrichment analysis. Moreover the possible systems pharmacological choices were presented in three ways as (1) drug induced expression modulation, (2) drugs that interact with upstream and downstream regulatory targets, (3) possible natural product therapeutics from target-compound relationship. Furthermore for validating the current study we have specifically evaluated the preventive effect of two predicted natural compounds in a bovine aortic calcification model. The overall observation predicts a few novel mechanisms that might be involved in vascular dysfunction and calcification in both cell types. Also, the systems pharmacological investigation provides clues for the possible therapeutic options along with validation. In conclusion, the current study indicates that reanalysis of transcriptomic data propels us to reposition the approved drugs and use natural compounds as novel therapeutic agents for vascular calcification.

Phosphate-a poison for humans?

Maintenance of phosphate balance is essential for life, and mammals have developed a sophisticated system to regulate phosphate homeostasis over the course of evolution. However, due to the dependence of phosphate elimination on the kidney, humans with decreased kidney function are likely to be in a positive phosphate balance. Phosphate excess has been well recognized as a critical factor in the pathogenesis of mineral and bone disorders associated with chronic kidney disease, but recent investigations have also uncovered toxic effects of phosphate on the cardiovascular system and the aging process. Compelling evidence also suggests that increased fibroblastic growth factor 23 and parathyroid hormone levels in response to a positive phosphate balance contribute to adverse clinical outcomes. These insights support the current practice of managing serum phosphate in patients with advanced chronic kidney disease, although definitive evidence of these effects is lacking. Given the potential toxicity of excess phosphate, the general population may also be viewed as a target for phosphate management. However, the widespread implementation of dietary phosphate intervention in the general population may not be warranted due to the limited impact of increased phosphate intake on mineral metabolism and clinical outcomes. Nonetheless, the increasing incidence of kidney disease or injury in our aging society emphasizes the potential importance of this issue. Further work is needed to more completely characterize phosphate toxicity and to establish the optimal therapeutic strategy for managing phosphate in patients with chronic kidney disease and in the general population.

Ornithine is a key mediator in hyperphosphatemia-mediated human umbilical vein endothelial cell apoptosis: Insights gained from metabolomics

AIMS

Hyperphosphatemia is associated with accelerated vascular endothelial dysfunction in patients with chronic kidney disease (CKD). The purpose of this study is to investigate the molecular mechanisms underlying hyperphosphatemia-caused endothelial dysfunction.

MAIN METHODS

The metabolic fingerprinting of human umbilical vein endothelial cells (HUVECs) subjected to hyperphosphatemia was characterized using an integrated metabolomics approach. HUVECs cultured in physiologically simulated hyperphosphatemia with or without phosphonoformic acid, a sodium-dependent phosphate transporter inhibitor (N=6) were collected for metabolomics analysis. Multivariate principle component analysis and partial least squares discriminant analysis were applied to analyze the metabolic data. The key metabolites were confirmed by quantitative analysis using liquid chromatography coupled with tandem mass spectrometer (LC-MS/MS).

KEY FINDINGS

36 metabolites were significantly altered in HUVECs following the challenges of hyperphosphatemia mimic, involving several metabolic pathways (all P<0.05). Among them, ornithine increased significantly in the HUVECs mediated by hyperphosphatemia mimic, and its levels positively correlated with cell apoptosis rate (r=0.674, P=0.002), and several additional metabolites in multiple metabolic pathways. The changes in the levels of ornithine and other several metabolites were supported by subsequent quantitative analyses using LC-MS/MS. Further study demonstrated that the increase in ornithine level may result from the increased expression of arginase 2 in HUVECs, which mediates the hydrolysis of arginine to form ornithine.

SIGNIFICANCE

This is the first study demonstrating ornithine a key molecule mediating hyperphosphatemia-induced apoptosis of ECs. Arginase 2 may be a therapeutic target for hyperphosphatemia-associated cardiovascular events.

Distinct Effects of Inorganic Phosphate on Cell Cycle and Apoptosis in Human Vascular Smooth Muscle Cells

Inorganic phosphate (Pi) is an essential nutrient to all living organisms. Nevertheless, hyperphosphatemia is now recognized as a risk factor for cardiovascular events and mortality in chronic kidney disease (CKD) patients. To our knowledge, the mechanisms by which elevated Pi alters smooth muscle cell proliferation have been poorly addressed. Therefore, in this study, we investigated the effects of Pi on cell cycle regulation and apoptosis in human aortic smooth muscle cells (HAoSMC). HAoSMC were treated with physiologic (1 mM) or high (2 and 3 mM) Pi concentrations. We showed that Pi not only decreased significantly cell viability (P < 0.001) but also induced apoptosis of HAoSMC. Moreover, Pi treatment blocked G1/S cell cycle progression by increasing cell number in G0/G1 phase up to 82.4 ± 3.4% for 3 mM vs 76.2 ± 3.1% for control (P < 0.01) while decreasing cell number in S phase. Accordingly, this was associated with a decrease protein expression of cyclin E and its associated CDK (CDK2), and phosphorylated retinoblastoma protein. Moreover, we observed an increase of protein expression of cell cycle inhibitors p15, p21, and p27. Interestingly, we also found that induction of cell cycle arrest was partially dependent on phosphate uptake. Our results demonstrated that Pi reduced HAoSMC proliferation by inducing apoptosis and cell cycle arrest. Indeed, we showed for the first time that Pi affected HAoSMC cell cycle by blocking G1/S progression. These findings would be useful for a better understanding of molecular mechanisms involved in vascular complications observed in CKD patients.

Extracellular regulated protein kinases play a key role via bone morphogenetic protein 4 in high phosphate-induced endothelial cell apoptosis

AIMS

Hyperphosphatemia is an independent risk factor of cardiovascular events in the patients with chronic kidney disease. High phosphate can induce endothelial cell apoptosis, but the exact mechanism is not clear. This study fills this knowledge gap.

MATERIALS AND METHODS

Microarray analysis was used to identify differentially expressed gene profiles in human umbilical vein endothelial cells (HUVECs) in high phosphate (3.0mM) and normal phosphate (1.0mM) medium. Microarray informatics analysis was used to explore key pathways and genes. High phosphate-induced apoptosis is marked by annexin V-FITC/PI staining and cleavage of caspase-3. Immunoblotting and quantitative real-time PCR were performed to identify the microarray analysis.

KEY FINDINGS

Our microarray informatics analysis reveals that the mitogen-activated protein kinase (MAPK) plays a key role. As suggested by gene coexpression network analysis, bone morphogenetic protein 4 (BMP4) gene is a potential key regulatory gene in high phosphate environment. Both the expressions of BMP4 protein and mRNA are decreased. Extracellular regulated protein kinases (ERKs) are activated, while the inhibition of ERK by U0126 increases the expression of BMP4. Both recombinant BMP4 protein pretreatment and U0126 pretreatment reduce the apoptosis of endothelial cells in simulated hyperphosphatemia. However, BMP4 protein pretreatment had no effect on the activation of ERK MAPK pathway.

SIGNIFICANCE

Our results indicate that the inhibition of ERK MAPK pathway protects endothelial cells from apoptosis by upregulating bone morphogenetic protein 4 in endothelial cells exposed to hyperphosphatemia. Our study provides potential molecular targets for developing new strategies to reduce the endothelial cell apoptosis induced by high phosphate.

Hyperphosphatemia, Phosphoprotein Phosphatases, and Microparticle Release in Vascular Endothelial Cells

Hyperphosphatemia in patients with advanced CKD is thought to be an important contributor to cardiovascular risk, in part because of endothelial cell (EC) dysfunction induced by inorganic phosphate (Pi). Such patients also have an elevated circulating concentration of procoagulant endothelial microparticles (MPs), leading to a prothrombotic state, which may contribute to acute occlusive events. We hypothesized that hyperphosphatemia leads to MP formation from ECs through an elevation of intracellular Pi concentration, which directly inhibits phosphoprotein phosphatases, triggering a global increase in phosphorylation and cytoskeletal changes. In cultured human ECs (EAhy926), incubation with elevated extracellular Pi (2.5 mM) led to a rise in intracellular Pi concentration within 90 minutes. This was mediated by PiT1/slc20a1 Pi transporters and led to global accumulation of tyrosine- and serine/threonine-phosphorylated proteins, a marked increase in cellular Tropomyosin-3, plasma membrane blebbing, and release of 0.1- to 1-μm-diameter MPs. The effect of Pi was independent of oxidative stress or apoptosis. Similarly, global inhibition of phosphoprotein phosphatases with orthovanadate or fluoride yielded a global protein phosphorylation response and rapid release of MPs. The Pi-induced MPs expressed VE-cadherin and superficial phosphatidylserine, and in a thrombin generation assay, they displayed significantly more procoagulant activity than particles derived from cells incubated in medium with a physiologic level of Pi (1 mM). These data show a mechanism of Pi-induced cellular stress and signaling, which may be widely applicable in mammalian cells, and in ECs, it provides a novel pathologic link between hyperphosphatemia, generation of MPs, and thrombotic risk.

Elevated cardiac markers in chronic kidney disease as a consequence of hyperphosphatemia-induced cardiac myocyte injury

Background

Elevated cardiac markers (CMs) and hyperphosphatemia are commonly encountered in patients with chronic kidney diseases (CKD), but the causal relationship between them has not been established.

Material/Methods

We enrolled 151 patients with different kidney functions in a cross-sectional study to explore the relationship of serum phosphorus with CMs, including cardiac troponin T (cTnT), myoglobin (MYO), creatine kinase-MB (CK-MB), and brain natriuretic peptide (BNP). Then, the effect of reducing phosphorus levels on CMs by taking phosphate binder for 3 months was prospectively observed in 64 hemodialysis patients. Finally, human cardiomyocytes were exposed to different concentrations of inorganic phosphorus to examine its underlying mechanism.

Results

1) Serum phosphorus and CMs gradually increased as the glomerular filtration rate declined in CKD patients (p<0.01). 2) Elevation of CMs was much greater and cardiac structure and function were worse in CKD patients who had higher serum phosphorus concentrations (p<0.05). 3) Serum phosphorus level positively correlated with cTnT, MYO, and BNP in CKD patients (p<0.001). 4) In hemodialysis patients, the reduction of cTnT, MYO, and CK-MB was synchronous with the pharmacologically-induced decline of serum phosphorus level. However, levels of serum Fibroblast growth factor 23 (FGF23) had no statistical decrease. 5) Simulated hyperphosphatemia inhibited proliferation of human cardiomyocytes in a time- and concentration-dependent manner.

Conclusions

Hyperphosphatemia may induce myocardial damage in CKD patients, possibly through triggering apoptosis of human cardiomyocytes, and this could account for the elevated cardiac markers in CKD patients.

Increased extracellular pressure stimulates tumor proliferation by a mechanosensitive calcium channel and PKC-β

Large tumors exhibit high interstitial pressure heightened by growth against the constraining stroma. Such pressures could stimulate tumor proliferation via a mechanosensitive ion channel. We studied the effects of 0-80 mmHg increased extracellular pressure for 24 h on proliferation of SW620, Caco-2, and CT-26 colon; MCF-7 breast; and MLL and PC3 prostate cancer cells, and delineated its mechanism in SW620 cells with specific inhibitors and siRNA. Finally, we compared NF-kB, phospho-IkB and cyclin D1 immunoreactivity in the high pressure centers and low pressure peripheries of human tumors. Pressure-stimulated proliferation in all cells. Pressure-driven SW620 proliferation required calcium influx via the T-type Ca(2+) channel Cav3.3, which stimulated PKC-β to invoke the IKK-IkB-NF-kB pathway to increase proliferation and S-phase fraction. The mitotic index and immunoreactivity of NF-kB, phospho-IkB, and cyclin D1 in the center of 28 large human colon, lung, and head and neck tumors exceeded that in tumor peripheries. Extracellular pressure increases [Ca(2+)]i via Cav3.3, driving a PKC-β- IKK- IkB-NF-kB pathway that stimulates cancer cell proliferation. Rapid proliferation in large stiff tumors may increase intratumoral pressure, activating this pathway to stimulate further proliferation in a feedback cycle that potentiates tumor growth. Targeting this pathway may inhibit proliferation in large unresectable tumors.

Vascular toxicity of phosphate in chronic kidney disease: beyond vascular calcification

Chronic kidney disease (CKD) is characterized by high cardiovascular morbidity/mortality, which is linked in part to vascular calcification (VC) and endothelial dysfunction (ED). Hyperphosphatemia, a feature of CKD, is a well-known inducer of VC in preclinical models and is associated with poor outcomes in epidemiological studies. However, it remains to be seen whether lowering phosphate levels in CKD patients reduces VC and the morbidity/mortality rate. Furthermore, it is now clear from preclinical and clinical studies that phosphate is involved in ED. The present article reviews the direct and indirect mechanisms (eg, via fibroblast growth factor 23 and/or parathyroid hormone) by which hyperphosphatemia influence the onset of VC and ED in CKD.

Cross-talk between endothelin-1 and mineral metabolism in hemodialysis patients: a cross-sectional study

Background:

Endotheline-1 (ET-1), an endothelial mediator, influences on mineral metabolism; especially vascular calcification in uremic patients.

Objectives:

The aim of the present study was to evaluate of ET-1, high-sensitivity C-reactive protein (hs-CRP) and mineral metabolites as the main factors for vascular calcification and inflammation in hemodialysis (HD) patients.

Patients and Methods:

In this cross-sectional study, 46 chronic stable HD patients were selected from nephrology departments of Tabriz University of Medical Sciences affiliated hospitals and classified based on phosphorus (P), Ca-P product (Ca × P) and intact Parathyroid Hormone (iPTH) levels. We evaluated fasting serum ET-1and hs-CRP levels by the standard methods and compared with 46 healthy control subjects.

Results:

The levels of serum hs-CRP and ET-1 were significantly higher in the patient’s group compared with controls (4.40 ± 1.26 vs. 1.38 ± 1.61, P < 0.0001, and 2.31 ± 0.87 vs. 0.75 ± 0.48, P < 0.0001, respectively) and with regard to Ca × P product cut-off point (3.99 ± 0.78 vs. 5.33 ± 1.64, P < 0.0001, and 2 ± 0.73 vs. 3.04 ± 0.73, P < 0.0001 respectively). ET-1 was correlated significantly with hs-CRP level (r = 0.776, P < 0.0001). Serum P, Ca × P and iPTH levels directly and Ca indirectly were correlated with serum ET-1 in HD patients (r = 0.932, P < 0.0001, r = 0.766, P < 0.0001, r = 0.514, P < 0.0001, r = -0.538, P < 0.0001 respectively). Multiple regression analysis demonstrated that serum P were independently associated with ET-1 levels (β = 0.932, P < 0.0001).

Conclusions:

Serum P and iPTH levels were independently associated with ET-1 and those may play a role in development of endothelial dysfunction in chronic kidney disease.

The role of inorganic pyrophosphate in aortic valve calcification

BACKGROUND AND AIM OF THE STUDY

Aortic valve (AV) calcification is a major cause of morbidity and mortality, yet the molecular mechanisms involved are poorly understood. Hence, an ex vivo model of calcification in intact AVs was developed in order to test the role of orthophosphate and pyrophosphate (PPi), both of which factors are known to influence vascular calcification.

METHODS

Porcine AV leaflets were cultured in serum-free medium under static conditions for eight days, over which time leaflet architecture and viability were preserved. Calcification was measured as the incorporation of 45Ca, with confirmation by Alizarin Red staining.

RESULTS

Calcification required both a high phosphate concentration (3.8 mM) and removal of PPi with alkaline phosphatase or inorganic pyrophosphatase. Calcification occurred predominantly on the fibrosa and was arrested by the bisphosphonate etidronate, a non-hydrolyzable analog of PPi. Leaflets released PPi into the medium, and this was enhanced by MLS38949, a specific inhibitor of tissue non-specific alkaline phosphatase (TNAP). Furthermore, leaflets synthesized PPi from extracellular ATP, which was reduced by β,γ-methylene-ATP, an inhibitor of ectonucleotide pyrophosphorylase phosphodiesterase (NPP1).

CONCLUSION

The ex vivo AV calcification model developed in the present study showed that extracellular PPi, produced by valvular tissue, is a potent inhibitor of valvular calcification. In addition to synthesis, hydrolysis by TNAP also controls PPi levels and calcification. The results suggest that a decreased synthesis or increased hydrolysis of pyrophosphate may contribute to valvular calcification, and that bisphosphonates or inhibitors of TNAP are potential preventive strategies of the process. TNAP are potential preventive strategies.

Hyperphosphatemia induces protective autophagy in endothelial cells through the inhibition of Akt/mTOR signaling

OBJECTIVE

Hyperphosphatemia-induced endothelial dysfunction has been shown to play a pathogenic role in the development of atherosclerosis in chronic kidney disease (CKD) through unclear mechanisms. Emerging evidence indicates that autophagy is involved in the maintenance of normal cardiovascular function. However, it is unclear whether autophagy participates in the molecular mechanism underlying high phosphate (Pi)-induced endothelial dysfunction.

METHODS

The autophagy activity was determined by the immunofluorescence staining of the expression of endothelial microtubule-associated protein 1 light chain 3 (LC3) in the 5/6 nephrectomy rat model of CKD and sham-operated control rats. The LC3-II/LC3-I ratio and the activation of the Akt/mammalian target of rapamycin (mTOR) signaling pathway were determined in cultured human microvascular endothelial cell (HMEC-1) endothelial cells that were exposed to a high concentration of Pi with or without the Pi influx blocker phosphonoformic acid, the autophagy inhibitor 3-methyladenine, and the autophagy inducer rapamycin. The impacts of autophagy on Pi-induced apoptotic damage were assessed by flow cytometry.

RESULTS

The in vivo rat model of CKD revealed that hyperphosphatemia is associated with increased endothelial LC3 staining. The exposure of HMEC-1 cells to high Pi induced both dose-dependent and time-dependent increases in the LC3-II/LC3-I expression ratio accompanied by the inhibition of the Akt/mTOR signaling pathway. In HMEC-1 cells, high Pi-induced autophagy and the inhibition of Akt/mTOR signaling were reversed by phosphonoformic acid through the blockage of Pi influx. Apoptosis, characterized by the levels of cleaved caspase 3 and poly(ADP-ribose) polymerase, along with autophagy was induced by high Pi, and the inhibition of autophagy by 3-methyladenine significantly aggravated high Pi-induced apoptosis. The flow cytometry results confirmed that the blockage of autophagy promoted the apoptosis of endothelial cells.

CONCLUSIONS

Hyperphosphatemia induces endothelial autophagy, possibly through the inhibition of the Akt/mTOR signaling pathway, which may play a protective role against high Pi-induced apoptosis.

Roles of phosphate and fibroblast growth factor 23 in cardiovascular disease

Disturbances in phosphate homeostasis are common in patients with chronic kidney disease. As kidney function declines, circulating concentrations of phosphate and the phosphate-regulatory hormone, fibroblast growth factor (FGF)-23, rise progressively. Higher serum levels of phosphate and FGF-23 are associated with an increased risk of adverse outcomes, including all-cause mortality and cardiovascular events. The associations between higher FGF-23 levels and adverse cardiovascular outcomes are generally independent of serum phosphate levels, and might be strongest for congestive heart failure. Higher serum phosphate levels are also modestly associated with an increased risk of cardiovascular events even after accounting for FGF-23 levels. This observation suggests that FGF-23 and phosphate might promote distinct mechanisms of cardiovascular toxicity. Indeed, animal models implicate high serum phosphate as a mechanism of vascular calcification and endothelial dysfunction, whereas high levels of FGF-23 are implicated in left ventricular hypertrophy. These seemingly distinct, but perhaps additive, adverse effects of phosphate on the vasculature and FGF-23 on the heart suggest that future population-level and individual-level interventions will need to simultaneously target these molecules to reduce the risk of associated cardiovascular events.

High-efficiency on-line haemodiafiltration improves conduit artery endothelial function compared with high-flux haemodialysis in end-stage renal disease patients

BACKGROUND

Middle molecular weight uraemic toxins are considered to play an important role in vascular dysfunction and cardiovascular outcomes in end-stage renal disease (ESRD) patients. Recent dialysis techniques based on convection, specifically high-efficiency on-line haemodiafiltration (HDF), enhance the removal of middle molecular weight toxins and reduce all-cause mortality in haemodialysis (HD) patients. However, the mechanisms of these improved outcomes remain to be established.

METHODS

This prospective study randomly assigned 42 ESRD patients to switch from high-flux HD to high-efficiency on-line HDF (n=22) or to continue HD (n=20). Brachial artery endothelium-dependent flow-mediated dilatation, central pulse pressure, carotid artery intima-media thickness (IMT), internal diastolic diameter and distensibility and circulating markers of uraemia, inflammation and oxidative stress were blindly assessed before and after a 4-month follow-up.

RESULTS

Brachial flow-mediated dilatation and carotid artery distensibility increased significantly in the HDF group compared with HD, while carotid IMT and diameter remained similar. HDF decreased predialysis levels of the uraemic toxins β2-microglobulin, phosphate and blood TNFα mRNA expression. Oxidative stress markers were not different between the HD and HDF groups. Blood mRNA expression of protein kinase C β2, an endothelial NO-synthase (eNOS) inhibitor, decreased significantly with HDF.

CONCLUSIONS

High-efficiency on-line HDF prevents the endothelial dysfunction and stiffening of the conduit arteries in ESRD patients compared with high-flux HD. HDF decreases uraemic toxins, vascular inflammation, and is associated with subsequent improvement in eNOS functionality. These results suggest that reduced endothelial dysfunction may be an intermediate mechanism explaining the beneficial outcomes associated with HDF.

High phosphate directly affects endothelial function by downregulating annexin II

Hyperphosphatemia is associated with increased cardiovascular risk in patients with renal disease and in healthy individuals. Here we tested whether high phosphate has a role in the pathophysiology of cardiovascular events by interfering with endothelial function, thereby impairing microvascular function and angiogenesis. Protein expression analysis found downregulation of annexin II in human coronary artery endothelial cells, an effect associated with exacerbated shedding of annexin II-positive microparticles by the cells exposed to high phosphate media. EAhy926 endothelial cells exposed to sera from hyperphosphatemic patients also display decreased annexin II, suggesting a negative correlation between serum phosphate and annexin II expression. By using endothelial cell-based assays in vitro and the chicken chorioallantoic membrane assay in vivo, we found that angiogenesis, vessel wall morphology, endothelial cell migration, capillary tube formation, and endothelial survival were impaired in a hyperphosphatemic milieu. Blockade of membrane-bound extracellular annexin II with a specific antibody mimicked the effects of high phosphate. In addition, high phosphate stiffened endothelial cells in vitro and in rats in vivo. Thus, our results link phosphate and adverse clinical outcomes involving the endothelium in both healthy individuals and patients with renal disease.